TECHNICAL DOCUMENTATION FRONT SHEET
BP Angola Block 18
GREATER PLUTONIO PROJECT
S ONANGOL
Process Control System Narratives
C1
12/05/05
Approved for Construction
J. Kellett
L. D’Costa
M. Fidler
B. Nicholas
D1
22/12/04
Approved for Design
J. Kellett
K. Haiday
M. Fidler
B. Nicholas
A2
13/07/04
For IDC
J. Kellett
K. Haliday
A1
09/07/04
SDC
J. Kellett
K. Haliday
Rev
Date
Reason for Issue
Prepared
Checked
Approved
Approved
Disc. Eng.
Disc. Lead
Project
Client
KBR
Category Code
Greater Plutonio Project
Description
Area Identifier
System Number
Fluid ID
Life Cycle Code
This document is the property of BP Angola
(Block 18) BV and KBR. It is not to be copied
nor shown to a third party without prior
consent.
d:\40672286.doc
AFE No
Project
ID
Orig
Code
Disc
Code
Doc Type
Sequence
No
Revision
BLK18
GP
K
IN
SPE
0101
C1
CONTENTS
FRONT PAGE & DOCUMENT REVISION RECORD
CONTENTS
ABBREVIATIONS
HOLDS
1.0
INTRODUCTION
2.0
INTEGRATED CONTROL SYSTEM OVERVIEW
3.0
COMMON CONTROL FUNCTIONS
3.1
Vessel Motion – Effect On Level Measurements
3.2
Process Controller Shutdown Action
3.3
Control Valves
3.4
Dual Controller Pressure Control
3.5
Nucleonic Level Profile Instruments
3.6
Pump Controls
3.7
Sand Monitors – Acoustic
3.8
Sand Monitors - Erosive
3.9
Corrosion Monitors
3.10
Bursting Disc Rupture Monitors
3.11
PSS Interface
3.12
ESD Interface
3.13
F&G Interface
3.14
Foundation Fieldbus Interface
3.15
Alarm Suppression
3.16
ESD Valve Testing
3.17
Serial Interfaces
3.18
Minimum Flow Bypass Controller Set Point
3.19
Emerson Terminology
4.0
FLOWLINE PIG RECEIVERS / INLET PRODUCTION MANIFOLDS
5.0
SLUG CATCHERS
6.0
HP SEPARATION
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7.0
PRODUCTION HEATER
8.0
LP SEPARATION
9.0
LP SEPARATOR WATER RECYCLE PUMPS
10.0
CRUDE OIL TRANSFER PUMPS
11.0 ELECTROSTATIC COALESCER, WASH WATER HEATER AND ELECTROSTATIC
COALESCER WATER RECYCLE PUMP
12.0
CRUDE OIL RUNDOWN COOLER
13.0
CRUDE OIL METERING PACKAGE
14.0
OIL EXPORT BOOSTER PUMPS
15.0 FLOWLINE DISPLACEMENT SYSTEM AND NORTHERN SERVICES LINE PIG
LAUNCHER / RECEIVER
16.0
GAS COMPRESSORS
17.0
GLYCOL CONTACTOR AND REGENERATION PACKAGE
18.0
GAS INJECTION
19.0
RISER BASE GAS LIFT
20.0
HP FLARE KO DRUM AND PUMPS
21.0
LP FLARE KO DRUM AND PUMPS
21.1
Vapour recovery package
22.0
PRODUCED WATER TREATMENT SYSTEM
23.0
SEAWATER SYSTEM LIFT PUMPS & HYPOCHLORITE PACKAGE.
24.0
WATER INJECTION AND SULPHATE REMOVAL SYSTEMS
25.0
AIR COMPRESSOR AND DRYER PACKAGE
26.0
NITROGEN SYSTEM
27.0
HEATING MEDIUM SYSTEM
28.0
GENERATORS AND WASTE HEAT RECOVERY SYSTEMS
29.0
CHEMICAL INJECTION SYSTEM
30.0
METHANOL INJECTION SYSTEM
31.0
FUEL GAS SYSTEM
32.0
DRAIN WATER HYDROCYCLONE
33.0
HVAC SYSTEM
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ABBREVIATIONS
Ac
Alternating Current
API
American Petroleum Institute
BS
British Standards
CCC
Compressor Controls Corporation
CCR
Central Control Room
CENELEC
European Committee for Electrical Standardisation
Dc
Direct Current
DP
Differential Pressure
EFS
Emergency Shutdown and Fire & Gas System
ESD
Emergency Shutdown System
F&G
Fire & Gas
FF
Foundation Fieldbus
FOV
Fast Opening Valve
FPSO
Floating Production, Storage and Offloading
HP
High Pressure
HVAC
Heating Ventilation Air Conditioning
ICS
Integrated Control System
IEC
International Electro-Technical Committee
IL
Integrity Level
I/O
Input/Output
IP
Ingress Protection
IS
Intrinsically Safe
ISO
International Standards Organisation
HART
Highway Addressable Remote Transducer
LER
Local Equipment Room
KW
Kilowatt
LP
Low Pressure
MA
Milliamp
MAC
Marine Advisory and Control system
PA
Public Address
PC
Personal Computer
PCS
Process Control System
P&ID
Process and Instrument Diagram
PID
Proportional, Integral, Derivative (Controller)
PLC
Programmable Logic Controller
PSS
Process Safety System
RTD
Resistance Thermometer Detector
SCS
Subsea Control System
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SPCU
Subsea Power and Communications Unit
UCP
Unit Control Panel
UPS
Un-Interruptible Power Supply
V
Volt
VDU
Visual Display Unit
HOLDS
Inlet Production Manifold Valve Hydraulic Power Unit
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1.0
INTRODUCTION
The Greater Plutonio development, located in deepwater offshore Angola, has proven
resources in six fields (Cobalto, Cromio, Galio, Paladio, Platina and Plutonio) with an
anticipated field life of 25 years.
The Greater Plutonio project will initially develop the resources of five of these fields:
Cobalto, Cromio, Galio, Paladio and Plutonio. Platina (and other resources) will be
developed later.
An FPSO will be used as a hub processing the fluids produced from or injected into the
subsea production and injection wells.
The concept selected consists of a spread-moored FPSO, located south east of
Paladio at a water depth of approximately 1300 metres, with all production, gas and
water injection wells being subsea.
The production from the subsea manifolds will be configured to generate production
flows along a single flowline (with a service line for circulation) for the Northern (Galio,
Cromio and Paladio) system and a loop flowline for the Southern (Cobalto and
Plutonio) systems.
The manifolds will be off-line (connected to the production flowline at an in-line tee)
and be equipped with a multi-phase flowmeter for well testing.
Injection water will be transported by a single flowline for the Northern system and by
two flowlines in the Southern System.
Gas is injected in the Southern system only via a single flowline.
The topsides facilities will consist of three-stage gas-oil separation plus oil desalting
sized to produce 200mbd (annual average rate) of export quality oil.
Associated gas will be compressed and dehydrated to provide fuel gas and riser gas
lift as an aid to production. Surplus gas will be re-injected into the Plutonio reservoir.
When the regional gas solution becomes available, the gas handling system will be
capable of delivery to that solution.
Water injection of treated produced water supplemented by treated seawater will be
used to provide reservoir pressure maintenance.
The purpose of this document is to define the configuration details for the Process
Control System and the interfaces to the other control systems on the FPSO, in
particular the Process Safety System (PSS) and the Emergency Shutdown and Fire
and Gas System (EFS).
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2.0
INTEGRATED CONTROL SYSTEM OVERVIEW
The term Integrated Control System (ICS) has been selected to indicate the required
fully integrated functionality to be provided for the monitoring and control of all process,
marine and safety systems. “Integrated functionality” means that the primary operator
interface facilities shall be centralised, with consistent display formats and control
interface for all subsea, topsides and marine plant on the facility.
The component parts of the ICS are summarised as follows:

Process Control System (PCS): This system will be configured to the distributed
control principle, with control system cabinets located in LER’s within the process
and utility modules. The scope of the PCS includes the primary operator interface
for the overall facility.

Process Safety System (PSS): The PSS provides the independent process and
utility safety system for those shutdown loops that have been designated as IL 1 or
that are not IL rated. It will be implemented based on Delta V hardware, but shall
be segregated apart from the workstation display, from the Input/Output (I/O)
facilities and control logic of the PCS.

ESD and F&G Systems (EFS): These protection facilities shall operate in
functionally standalone modes, separate from the PCS and PSS. Full integration
of detection and protection shall be provided between the process and the marine
ESD/F&G facilities. The system cabinets will be located in the LER’s for the
topsides, marine and subsea facilities and will be configured using hard wired I/O
for system integrity.

Marine Advisory and Control System (MACS): This system will be configured from
separate sub-systems, typically comprising a control system, a protection system,
a tank and ballast control system, environmental monitoring systems, mooring
monitoring systems, etc. Post integration, marine systems will be fully integrated
with the ICS, with operator access via the ICS operator workstations.

Subsea Control System (SCS): The control point for the subsea equipment will be
the ICS operator workstations in the CCR.
The Subsea Power and
Communications Unit (SPCU) located topside, provides the interface between the
subsea control modules at the manifolds and wells and the ICS. Communication
between the SCS and the ICS will be via redundant OPC data links.

Packaged Plant Control Systems: Major packaged plant, typically gas compressors
or main power generators, fiscal metering skids, etc, will be provided with integral
control systems. It is intended that Supplier standard control systems are
provided, with an interface into the PCS/PSS/EFS for operator interface and
protection integration.
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3.0
COMMON CONTROL FUNCTIONS
As would be expected, most control and monitoring functions on the FPSO are normal
industry standard functions consisting of indications, alarms and PID controls. It is not
intended that this document will detail these standard functions on an individual basis.
The required definition for the standard loops will be by the combined use of the P&IDs
and the ICS I/O schedule. The purpose of this document therefore is to explain and
define the requirements of the non-standard control and monitoring functions and
these will be documented on a process system basis.
Certain functions, such as pump motor controls occur repeatedly throughout the
process system. The general requirements for these functions will be defined in this
section and will be referenced as necessary within the process system description that
follow, together with any special requirements that are specific to the particular
application.
Where possible the PCS configuration shall be based on standard function blocks that
have a proven operational history or modifications to standard function blocks where
particular functionality is required.
Within this document a hierarchy of access to the PCS functionality is described based
on three levels of seniority, operator, supervisor and engineer. The operator will be
given access to all the PCS functionality necessary for normal operation. Certain
functions that will generally only require occasional access will be restricted to the
supervisor level, typically reset of totalisers would fall into this category and is primarily
provided to avoid operator error. Finally there is the engineer level, where all aspects
of the system are accessible, including modifications to the configuration. Where
appropriate, the limitations of access considered necessary are noted.
3.1
Vessel Motion – Effect On Level Measurements
Because the FPSO will be affected by wave motion, liquid within the vessels and tanks
will be subject to constant movement which will effect level measurements. In order to
provide a stable level signal that avoids hunting of control loops, false alarms and trips,
a suitable input filter shall be provided by the PCS / PSS which shall act on the
measured variable before it is used for it’s PCS or PSS function.
The frequency and amplitude of the waves within the FPSO vessels will vary
considerably, so the filter should provide a wide range of adjustment. It is intended
that each application will be tuned during on-station commissioning to determine the
appropriate optimum filter settings. These settings will only be adjustable at the
engineer level of access. There may be occasions when it is appropriate to switch off
the filtering function and this will be made available at the operator level of access.
For controller loops, it will be necessary to tune the controller with the filter operating.
Additionally a check shall be made that the loop remains stable if the filter function is
switched off.
All level applications shall be provided with the filtering function unless noted
otherwise.
3.2
Process Controller Shutdown Action
In many cases, to guard against failure of the main control loop, an independent
process transmitter and shutdown valve will be installed in series with the control
valve. The logic to monitor the shutdown transmitter is provided by the PSS or ESD
systems to ensure its independence from the main process control function. If the
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process control loop fails to maintain the measured variable within the normal control
range and the process condition reaches the trip setting of the shutdown transmitter,
the shutdown logic will trip the shutdown valve to the safe condition.
When the problem that caused the loss of control has been rectified, the shutdown
loop will be reset, moving the shutdown valve to its healthy condition. To ensure that a
controlled restart is achieved following the shutdown reset, the associated process
controller shall be automatically changed to manual mode and the controller output set
to move the control valve to its closed condition. This action shall be carried out as
soon as the shutdown occurs, with the necessary shutdown signal being internally
interfaced to the PCS PID control logic from the PSS or ESD as appropriate. The
signal shall be originated from the shutdown logic that controls the digital output used
for the applicable shutdown valve.
For each process description section in the main text, a table will be included to detail
the appropriate shutdown valves, controller and associated control valves where this
requirement is applicable. Generally shutdown valves close on shutdown and the
required action for the control valve is to the closed position, any exceptions to this
requirement will be noted in the tables.
3.3
Control Valves
Most of the control valves are provided with a Foundation Fieldbus positioner. This will
provide a feedback signal of the control valves actual position. For a control loop, the
output value from the controller will normally be displayed on the VDU. The operators
screen display shall provide a standard faceplate selectable on demand that will
display both the controller output and actual valve position side by side. For valves
that are not supplied with a FF positioner, this feature will not be operable.
3.4
Dual Controller Pressure Control
In some applications, the gas pressure control for a vessel is implemented using two
independent pressure controllers (controller “A” and controller “B”) each with their own
control valves, but acting from one common pressure transmitter. Control loop “A” is
used for normal control, passing gas from the vessel to the next process stage, thus
maintaining the vessel pressure at the set point for controller “A”.
If a process upset occurs, such as a compressor trip, control loop “A” may not be able
to maintain control, even with its control valve fully open, causing the pressure in the
vessel to rise. Control loop “B”, which passes excess gas to the flare system, is
designed to provide control in these circumstances. This is achieved by having the set
point for controller “B” a little higher than controller “A”, so under normal conditions the
pressure in the vessel is controlled below its set point and it keeps control valve “B”
closed.
To ensure that the operator does not accidentally change this relationship, the set
point of “B” shall be linked so that it is 1.05 times the set point for “A”. Either
controller’s set point shall be adjustable by the operator and the other shall be
automatically adjusted to maintain the defined ratio. The multiplier setting of 1.05 may
be modified at the engineering level of access, either during commissioning or more
likely, if found to be necessary when the facility is in operation.
If the vessel pressure rises until it reaches the set point for controller “B”, then it begins
to open control valve “B”, dumping the excess gas to the flare and maintaining control
at the set point for controller “B”. Dumping of gas to the flare is not a desirable
situation and shall be alarmed to the operator. To produce the alarm, the output to
control valve “B” shall be monitored by the PCS so that the operator is alarmed if the
valve is not in the fully closed position.
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For these applications, this method of control gives more flexibility than the traditional
split range approach, allowing the set point to be adjusted to suit the specific operating
scenarios. Adjustment of the set points, although allowing greater operating flexibility,
is also open to operator error and set point adjustment for these loops shall only be
possible at the supervisor level.
3.5
Nucleonic Level Profile Instruments
It is anticipated that certain of the process vessels will accumulate sand carried
forward with the well fluids. These vessels are being equipped with nucleonic based
level monitoring facilities which can provide a level profile of the fluids within the
vessel, including the sand.
The field mounted equipment consists of three vertical tubes covering the whole
working level within the vessel. One tube contains the nuclear source and the other
two contain a vertical array of gamma ray detectors, the detectors in each tube being
vertically offset to improve level detection resolution. The detectors are interfaced via
a fibre optic bus to a vendor supplied PLC complete with PC and VDU. The PLC
carries out the raw data processing and provides the output signals to the PCS, whilst
the PC and VDU act as a local readout device complete with diagnostics. The PLC
and PC / VDU are housed in a vendor supplied cabinet located in local equipment
room 116 (Port Process LER).
In the three phase HP and LP Separators the process fluids will separate into a
number of layers, from the bottom up these will consist, sand, produced water, oil /
water emulsion, oil and foam, with hydrocarbon vapour above. The Nucleonic level
profile instrument will provide a linear 4-20mA signal for each layer, 5 analogue inputs
to the PCS in total, each representing the top of each of its layers. The range for each
signal will be 0 – 100% of the full detector length. Since each signal represents the top
level of each band of fluid type, it can be seen that the sand level signal should never
be more than a few percent of its 0-100% range. Similarly for each of the other
defined layers, each being a measured percentage of the same 0-100% range.
For the HP and LP separators, these signals are required to be represented as a
dynamic vertical bar with a different colour for each of the fluid layers.
For the Slug Catchers, which are two phase separators, there will be one fewer fluid
layers than in the separators and therefore one fewer input to the PCS. The layers will
consist, sand, produced water, oil / water mixture and foam, with hydrocarbon vapour
above.
Although the Slug Catchers do not have separate water take offs, a small produced
water layer will form as a result of the internally elevated oil / water take off nozzles.
The separated water layer that is deliberately allowed to form is to minimise the
likelihood of oil contamination during sand washing operations. For the slug catchers
there will therefore be 4 analogue, 4-20 mA, linear signals representing the top of each
layer of sand, produced water, oil / water mixture and foam and again, each will
represent its measured percentage of the whole 0 -100% range. As with the
separators, these levels will also be required to be represented as a vertical bar with
different colours for the different fluid types.
The nucleonic level monitoring equipment incorporates automatic system diagnostics
and will provide an alarm signal to warn the operator of a fault. The fault alarm signal
from the “level transmitter” to the PCS will be provided as an analogue signal, which
has the added advantage that it will be monitored by the PCS with an alarm initiated if
the signal falls outside the normal 4-20mA analogue signal range. The 4-20 mA, linear
fault alarm signal shall be treated as follows by the PCS:
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An “in range”, 16mA or more signal will represent a healthy, no fault condition.
An “out of range”, 10mA or below signal will represent a fault and will alarm the
operator.
Certain of the 4-20mA signals from the level profiler are required to provide non IL
rated shutdown functions, these will require to be directly connected to the PSS and
repeated by system bus to the PCS, this will described where applicable in the process
system descriptions that follow.
3.6
3.6.1
Pump Controls
General Pump Requirements
Controls for pump drives are interfaced from the PCS and PSS to the electrical
switchboard. The PCS provides the control and monitoring functions and the PSS,
where indicated on the PSS cause and effects diagrams, provides a shutdown signal
to trip the pump.
The Block 18 project uses intelligent switchboards that connect to the PCS via dual
modbus serial links. Unless defined otherwise, each drive will have the following
signals:
Start : Output signal from PCS to start the pump, this will normally be a “zero” bit, with
a 5 second pulse change to logic 1 to start the pump.
Stop : Output signal from the PCS to stop the pump, this will normally be a “zero” bit,
with a 5 second pulse change to logic 1 to stop the pump .
Running / Stopped : Input signal from the switchboard to signal that the pump is
running or stopped, logic “zero” signifies the pump is stopped, logic 1 signifies the
pump is running.
Available / Not available : Input signal from the switchboard defining the drive status,
logic 1 signifies available, logic “zero” signifies not available.
Available indicates that the drive is available to start if required by the PCS logic or
manually by the PCS operator.
Not available indicates that the drive is not available to be started from the PCS.
There can be many reasons for this, for example, it can mean that one or more of the
electrical protection relays has tripped, that the pump has been disconnected from the
board, that it has been set at the switchboard to local manual start only. Not available
in this case is therefore a generic term to cover all the reasons why the operator does
not have the drive available for PCS start.
Many of the pumps will be subject to a shutdown requirement from the PSS, these will
be identified from the ICS I/O schedule and the PSS cause and effects diagrams. To
provide a higher integrity and a fail safe design, the shutdown signals are hard wired
directly from the PSS to the electrical switchboard. The digital output will be connected
to an interposing relay located within the switchboard. This 24 V dc relay will isolate
the contactor voltage level used in the motor control circuit from the PSS panel. The
output will be normally energised, de-energise to trip and will be powered from the
PSS.
In many applications pumps will be provided with a minimum flow bypass and a low
low flow shutdown. Generally shutdowns are initiated from a separate transmitter to
that used for normal control, so that failure of the control transmitter does not also
cause failure of the shutdown loop. An exception has been made for some of the
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minimum flow bypass loops because in most cases, under normal operation, the
minimum flow bypass control is not required to operate and to have simultaneous
failure of the transmitter and a block in the pump discharge that requires a pump
shutdown is an unlikely double jeopardy event.
Additionally since the transmitters in most applications are Foundation Fieldbus type,
they have automatic diagnostics that can detect a fault in the transmitter and send an
alarm to advise the PCS of the problem. The operator can then decide if he should
swap the pumps over whilst the transmitter fault is repaired.
As is the case for alarm settings, the minimum flow set point for a pump’s minimum
flow controller is a function of the process and pump design and is generally fixed.
Thus as with alarms, the pump minimum flow controller set point shall be fixed such
that it can only be modified at the engineering access level.
To ensure a safe start up of the pumps following a shutdown, when the PSS shuts
down a pump, it shall also set the pump controls in the PCS to manual and off.
The operator will be provided with a standard faceplate presentation for each pump.
This will in each case allow individual pumps to be started and stopped in manual if
available for start.
In general, duty pumps will be started in manual and then switched to auto. Standby
and duty assist pumps will be switched to auto ready for automatic start if called to do
so.
For the block 18 project there are many different process applications, some are a
single pump, others consist of two or more pumps operating in groups; the standard
operating requirements for these groups are described below.
The appropriate group type, together with any specific requirements will be detailed in
process system descriptions which follow.
3.6.2
Single 100% Duty Pump (Plus Multiple Pumps To Achieve 100% - Without Spare)
Most of these pump applications require remote start and stop from the PCS in the
CCR. Since they are single 100% duty pumps, there is no requirement for auto start of
a spare pump. Generally these pumps will be manually started and stopped, however
if auto start and stop of the pump is required, it will be defined in the process systems
section.
The same requirements are applicable to two or more duty pumps that operate without
a spare, normally with all pumps in the group running to meet the 100% process flow
requirement. Since these do not have a spare, there is no requirement for auto start of
a standby. However there may be a requirement for automatic start and stop based
on process signals, if this functionality is required, then it will be defined in the
applicable process system section.
3.6.3
Duty / Standby Pumps
For applications with two 100% pumps that are required to operate on a duty / standby
basis, the PCS pump logic shall treat the first pump to be started as the duty pump.
The second pump will then be selected as the standby, but only if it has an available
signal from the motor switchboard and is switched to auto.
3.6.4
Duty / Duty / Standby Pumps
For applications with three 50% pumps that are required to operate on a duty, duty,
standby basis, the logic shall be similar to the two pump case. The operator starts the
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first and second pumps and switches each to auto, the remaining pump is then
selected as the standby by switching it to auto, as long as it has an available signal
from the switchboard. If process conditions are such that a single duty pump is able to
meet the process demand, the logic shall allow the selection of a first standby and
second standby pump if required, or the second standby may not be set, leaving it in
manual and off.
3.6.5
Duty / Assist Pumps
Some pumps are required to operate on a duty / assist basis. In these applications,
the duty pump will normally provide sufficient capacity to meet the process pumping
duty alone. However it is anticipated that under certain process conditions, the second
pump will also be required to operate. The first duty pump will be nominated by the
operator and the second pump will then become the assist pump, assuming it is
available and set to auto.
The basis for starting the assist pump will be explained in the process system
description as required.
3.6.6
Standby Auto-Start Pumps
Auto start of a standby pump is required to be initiated if the duty pump stops for
abnormal reasons, the standby shall not start if the operator manually stops the
running duty pump. Similarly (with the exception of 3 below) a PSS shutdown of a
pump will not try to start the standby because the shutdown signal will simultaneously
be sent to each pump in the group and the logic is required to switch each pump to
manual and off.
If auto start of a standby pump is initiated, the duty pump shall be forced to manual
and off and the PCS shall provide an alarm to signal the auto start event to the
operator.
Auto start standby should be initiated under any of the following conditions:
1. The stopped signal is received from the motor starter for the previously running
duty pump and the operator has not initiated the stop (or if automatic PCS stop
/ start logic has not initiated the stop)
2. The not available signal is received from the motor starter and the motor was
previously running
3. A pump specific shutdown signal is received for a running duty pump, eg Low
Low discharge flow or Low Low suction pressure is received and the operator
has not stopped the duty pump
To implement some of these logic functions it will be necessary to include suitable time
delays on the signals.
Where a process initiated auto start as noted above is required, it will be detailed in the
process section descriptions that follow.
In addition to its auto start function, the not available signal shall also act as a
permissive, if “not available” is present; the pump shall be forced to manual and off and
hence the start signal cannot be initiated.
If the not available signal is received for a pump set as standby, an alarm shall be
initiated to warn the operator.
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3.6.7
Automatic Alarm and Shutdown Overrides
Many of the pumps are provided with low discharge flow alarms and low low flow trips.
It is necessary to automatically override these functions when the pump is not running
to avoid unnecessary alarms and to provide start up overrides to allow the pumps to be
started.
The low flow alarm and low low flow trip shall be immediately inhibited when the
operator stops a pump, this should disable the alarm and PSS shutdown trip before the
pump flow drops below the trip points. The alarms and trips shall remain overridden
until the “start up” override defined below is removed.
Start up override for a pump shall automatically override the low flow alarm and low
low flow shutdown for a timed period, the override duration shall be long enough for
the pump flow to increase above the trip points. When the pump flow exceeds the trip
points and after a short delay (typically 3 seconds) the start up override shall be
automatically removed and the trip and alarm will be active. If the discharge flow fails
to exceed the trip flows, the timer will automatically remove the inhibit and the pump
shall be shutdown via the hard wired PSS shutdown contact and the pump forced to
manual and off. The initiation of the start up override timer shall be taken from the
pump start command.
The above description is generally applicable to pumps with low pressure alarms and
low low pressure trips on the pump discharge (or suction if noted in the process
description section) and unless noted otherwise shall be applied in the same manner
as for the flow alarms and trips.
3.6.8
Pump Seals
Many of the process pumps are provided with mechanical seals fed with a seal barrier
fluid at a higher pressure than the pumped fluid. The seal fluid is generally
pressurised by nitrogen and the fluid is circulated by the main pumps rotation. The
seal fluid is part of a closed loop that includes a cooler and a fluid reservoir. The level
in the seal fluid reservoir is monitored by a level transmitter and the seal system /
reservoir pressure is monitored by a pressure transmitter. The transmitter signals are
repeated to the PCS to provide a level indicator and low level alarm and a pressure
indicator and low pressure alarm. Special cases and the pump specific tag numbers
will be noted within the process descriptions.
3.7
Sand Monitors – Acoustic
The acoustic sand monitors measure sand entrainment in the flowing fluid by detecting
the ultra-sonic acoustic characteristic sound produced when sand particles impact the
inner surface of the piping. The sensor is attached to the outside of the pipe just
downstream of a pipe elbow; the change of flow direction causes the sand particles to
impact the pipe allowing any entrained sand to be detected.
The acoustic sand detectors are supplied with the local equipment room interfacing
devices mounted in a system cabinet. This includes a personal computer running
custom software that calculates the sand production rate for each of the detectors and
outputs the analogue signal to the PCS. The repeated linear analogue signals are 420mA, non IS, and the PCS powers the loop.
The software requires the process flow velocity at each detector as one of the
parameters for its calculation. It is therefore necessary to provide an analogue repeat
output of the appropriate flow rates for connection to the suppliers personal computer
interface. The signals that require repeating will be defined in the appropriate process
description sections that follow. The repeat analogue outputs shall be 4-20mA, non IS
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and shall also be powered by the PCS. The PC will calculate the flow velocity from the
PCS volumetric flowrate and the pipe inside diameter.
3.8
Sand Monitors - Erosive
The erosive sand monitors are based on measuring extremely small changes in
resistance of a probe that is located inside the pipe and exposed to fluid that may
contain sand. As sand impacts the probe it erodes minute quantities of metal from the
surface thus changing its overall resistance. The measuring principle is based on an
extension of the Wheatstone bridge principle, but claimed to give an increase in
sensitivity by a factor of 100:1 over the standard circuit. An interface unit provides
temperature compensation using a reference probe not exposed to the erosion and
converts the measured signal to a 4-20mA input to the PCS. This will use a standard
non FF analogue input which provides real time sand production rates.
3.9
Corrosion Monitors
The corrosion monitor is basically the same as the erosive sand monitor, except the
probe is now monitored for changes of resistance as a result of corrosion. It includes a
similar temperature compensating interface unit that provides a real time linear signal
for the rate of corrosion from the probe. The interface unit provides a 4-20mA input to
the PCS using a standard non FF analogue input to display corrosion rates.
3.10
Bursting Disc Rupture Monitors
The bursting discs used on the project are provided with a break wire burst detection
facility. This consists of a fine wire attached to the bursting disc that normally provides
the equivalent to a closed switch contact. If the bursting disc is ruptured, the wire is
broken and this is the equivalent to the switch contact opening. The break wire unit is
tagged “ZE” and the PCS alarm that is to be initiated when the disc breaks is tagged
“ZA”. The break wire unit should be treated as a switch for hazardous area purposes
and the ICS I/O schedule will define which detectors require intrinsically safe barrier
devices.
3.11
PSS Interface
The PCS workstations will provide the operator interface for the PSS system using the
normal process displays and appropriately designed graphic displays to show the
status (healthy, tripped, overridden, etc) of the shutdown inputs and outputs.
All PSS inputs and outputs shall therefore be interfaced to the PCS for presentation on
the workstations. In some cases, signals are required for joint use by the PSS and
PCS. Generally these will be directly connected to the PSS for the shutdown duty and
the repeated signal internally routed via the system bus to the PCS. The process
description sections that follow will define these cases. Where used for control duty,
due regard shall be taken to the effect on control loop stability if any substantial delay
is caused by the signal transfer between systems.
The PSS design requirements will be defined by the ICS I/O schedule and the PSS
cause and effects diagrams. Any special interaction between the PSS and the PCS
will be described in the appropriate section.
Shutdown overrides are required for the PSS inputs so that maintenance and testing
operations can be carried out without initiating process shutdowns. The PSS input
overrides shall be applied from the operator workstation. When in place, the override
shall stop the shutdown action from occurring, but will not stop the shutdown alarm.
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It is necessary to provide a means of controlling the application of the input overrides
and this will be implemented by installing an input override enable key switch located
on the matrix panel. The use of the override key will be controlled by the supervisor
following a defined procedure. When the key is operated it will initiate a timed pulse
signal which enables the operator to set the override at the PCS workstation. The
pulse duration shall provide sufficient time to set the override, but shall not extend for
an excessive period to minimise misuse.
The key shall be turned against a spring to the override enable position, returning to
the null position when released. The key is removed when the override has been set
and a red LED below the key switch is lit when any override in the PSS is active. All
overrides shall be logged in the PCS and an override report shall be printed on
demand by the system; this will generally be at shift changeovers.
The PCS configuration shall allow the operator to remove a PSS shutdown override
via the workstation without operation of the key switch. The removal process shall
require two separate actions to avoid accidental removal of an override.
There is no requirement for output overrides, all real and spurious shutdowns shall be
logged and time stamped by the PCS and it is anticipated these will supplement any
shutdown testing required. Testing of the shutdown outputs will actually initiate the
shutdown, since there are no output overrides.
3.12
ESD Interface
The PCS workstations will also provide the operator interface for the ESD system
using both the normal process displays where applicable and appropriately designed
graphic displays to provide the status of the shutdown inputs and outputs.
Unlike the PSS, input overrides will not be initiated from the PCS workstations, these
will be directly initiated from the matrix panel. As for the PSS, there will be no output
overrides and all shutdowns shall be logged and time stamped by the PCS.
3.13
F&G Interface
The PCS workstations will also provide the operator interface for the F&G system
utilising graphic displays based on geographic layout.
An overview display similar to that shown on the matrix panel will provide summary
F&G status for the whole facility. From the overview display, the operator may select
individual fire zone displays which will geographically display each F&G device within
the fire zone together with its status. In addition, within the fire zone display, a
standardised block will indicate confirmed fire, confirmed high level gas and Manual
Alarm Callpoint initiated.
Individual detectors will be provided with appropriate faceplates selected from the fire
zone display. The faceplates will provide the detailed information appropriate to the
type of detector, eg 20% LEL, 60% LEL, window obscured, fault, etc.
The F&G detectors shall be provided with input inhibit facilities to allow testing and
maintenance as provided for the PSS input inhibits. A matching key switch and LED
will be provide on the Matrix panel and the override facilities, display, logging, etc will
be the same as that defined in the PSS section.
3.14
Foundation Fieldbus Interface
Most of the process transmitters, control valve positioners and certain specific items,
are Foundation Fieldbus type that in addition to the normal signal provides many
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additional functions including diagnostics, maintenance monitoring features and fault
alarms. It is not intended that the control room operator will be presented with all of
this functionality except where it is of direct use for operating the plant.
3.15
Alarm Suppression
It is required that standing alarms on non active equipment shall be automatically
suppressed when they will be present under normal operation, but are not valid as a
live warning to the operator. A typical example is a low pressure alarm on a pump or
compressor discharge that is not running. If the machine is not running then the
pressure may be expected to be low and although the alarm will be tripped, it should
be suppressed from the display. In this case the suppression should be based on the
pump motor running signal.
A similar situation applies to low flow on a pump discharge and the same philosophy
applies, in particular for low low flow trips and automatic start up override, the
requirements for this are described more fully in section 3.6.7.
3.16
ESD Valve Testing
It is a requirement that all air fail closed ESD valves will be partially stroke tested at
regular intervals. The testing is an automatic process utilising the Neles ValvGuard
System and each of the valves to be tested is listed below:
VALVE TAG No
AUTO TEST INITIATION
ALARM
FAILED TEST ALARM
XXV 340011
XA 340011A
XA 340011B
XXV 340013
XA 340013A
XA 340013B
XXV 340027
XA 340027A
XA 340027B
XXV 340028
XA 340028A
XA 340028B
XXV 340029
XA 340029A
XA 340029B
XXV 850080
XA 850080A
XA 850080B
XXV 850081
XA 850081A
XA 850081B
XXV 200015
XA 200015A
XA 200015B
XXV 202015
XA 202015A
XA 202015B
XXV 203015
XA 203015A
XA 203015B
XXV 220009
XA 220009A
XA 220009B
XXV 273018
XA 273018A
XA 273018B
XXV 220013
XA 220013A
XA 220013B
Each ESD valve will have two hard wired digital input signals from the test equipment
to the PCS. The first is a short duration signal that advises that the valve is about to
be tested, this signal shall be logged, but since the testing occurs as a background
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automatic function, the operator does not need to be advised that it is occurring. The
actual test event takes only a short time and assuming that the ESD valve passes the
test, then the second signal, which is a test failure alarm, will remain in the healthy
condition. If however the ESD valve fails its test, then the digital alarm input shall
initiate an ESD valve test failure alarm. The alarm contacts will be normally closed
open for alarm, 24 Vdc, powered from the PCS.
Because of the design of the test circuit, both alarms will be initiated if an actual ESD
occurs that closes the ESD valve. Since these are not valid alarms in this context, it
will be necessary to inhibit them and the ESD system shall therefore provide a signal
for each valve to inhibit both alarms when an ESD valve is tripped.
Similarly when the valve is tested, the valve will partially close and the open limit
switch signal will be lost causing the PCS to generate an out of position alarm. Again
this is not a valid alarm in this context and will also require to be inhibited.
In this case the inhibit shall be applied when the auto test initiation alarm is received,
this shall inhibit the out of position alarm for a timed period and then automatically
removed. The timer shall initially be set at 1 minute, but this may be modified during
commissioning to suit the actual pre-test warning time and valve test stoke time.
3.17
Serial Interfaces
Within the process section descriptions, reference is made to various serial link
derived signals. As with the hardwired signals, only where the serial link control loop is
non standard and needs further description will it be included in this Control System
Narrative. Excluding the signals for motor drives, serial link signals are generally
repeats of status and analogue signals from package control systems and will be
displayed on custom screen displays typically based on the vendors PLC screen
display.
3.18
Minimum Flow Bypass Controller Set Point
If a pump is operated at very low flow rates, the temperature of the fluid in the pump
may increase to the point where vaporisation can occur and possibly cause cavitation
which can damage the pump. To avoid the possibility of this condition occurring and
thus to avoid possible damage to the pump, the manufacturer defines the minimum
continuous flow that is required to pass through the pump. This flow shall be used as
the minimum set point that the operator can select for each of the minimum flow
bypass controllers.
3.19
Emerson Terminology
The Emerson Delta V system has an extensive library of standard function blocks
which are described in Emerson’s standard published documentation. Unfortunately
the terminology used is sometimes not consistent with that generally used outside of
the Emerson environment. A particular example that may cause confusion is
associated with the functional block for pumps.
It is normal practice to use the term “manual” meaning that the pump has been put into
a condition where the pump start or stop is manually controlled by the operator from
the PCS workstation and where any external logic or remote control is disconnected.
Emerson use the term “auto” in place of manual.
Similarly the normal meaning of the word “auto” in the context of a pump is that if a
pump is switched to “auto” it is automatically controlled by external logic and cannot be
started and stopped by the operator until switched back to manual. Emerson use the
term “cascade” for this function in an analogy to a controller being put into cascade.
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In order to avoid confusion, this write up is based on normal terminology, so that
anyone reading the text will understand what is being described without knowledge of
the special definitions that Emerson impose.
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4.0
FLOWLINE PIG RECEIVERS / INLET PRODUCTION MANIFOLDS
Reference P&IDs: BLK18-GP-K-PR-PID-200001, 202001, 203001, 209000.
The following sections of this document will address specific process and utility
systems and will describe any special features or requirements that are not clearly
defined by the P&ID and ICS I/O schedule.
The flowline pig receivers and manifolds are fairly typical in that the systems are based
on standard instrument loops that generally will require little further explanation.
Erosive sand detecting transmitters are installed for each flowline, AT 200016, AT
202016, AT 203016, are standard units as described in section 3.8 and require a
normal analogue indicator display.
Similarly, corrosion monitoring transmitters CT 200024, CT 202024, CT 203024, are
also installed for each flowline; these are standard units as described in section 3.9
and also require a normal analogue indicator display.
MOV 200010, MOV 202010, MOV 203010 are motor operated on / off valves with local
operation only and fitted with key interlock devices, for use during pigging operations.
They are not operated from the control room via PCS, but the open and closed status
is required to be displayed. The electric motor actuators are Foundation Fieldbus type
and the position feedback, as well as diagnostic features will be an input to the PCS.
Similarly for MOV 200001, MOV 202001, MOV 203001, these valves are the same as
the MOV’s above, except they are inching design, rather than on / off type and will also
require the percentage open position feedback to be displayed on the PCS operator
station.
For each of the three flowlines, a pressure control loop is provided to maintain
sufficient backpressure to limit the flow velocity in the risers (PIC 200002, 202002,
203002). The control valves for these loops are typical number 48 which includes a
solenoid valve in the air supply to the actuator. The solenoid valve is controlled by the
PSS logic, which vents the air supply to the actuator, causing the control valve to close
under the shutdown conditions defined in the PSS cause and effect diagrams. The
PSS shall also provide a signal to the controller to automatically switch it to manual
and close the valve.
The MOV’s on the Inlet Production Manifold (MOV 200007, 202007, 203007,273046,
200019, 202019, 203019, 273016) are all On/Off type with remote control from the
PCS workstation. The PCS will provide a pulse signal to open and a pulse signal to
close the valve. The PCS shall monitor the valve travel and initiate an alarm if it does
not receive confirmation of reaching the end of travel and stopping within the allowed
time; the time duration shall be set during commissioning.
Valves XV 200023, XV 202023, XV 203023, XV 200021, XV 202021 and XV203019
are all hydraulically actuated, typical type 47 valves. They are controlled by the PSS as
defined by the cause and effects and can be opened and closed by the operator. As
with all shutdown valves, the shutdown requirement always takes precedence if the
operator requirement conflicts with a tripped shutdown state.
Inlet Production Manifold Valve Hydraulic Power Unit
(ON HOLD UNTIL VENDOR DESIGN IS COMPLETED)
Reference P&ID:- Breda Energia CB-C-S-00059.
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The hydraulic fluid is provided by the Hydraulic Power Unit, HPU 20901. This is a
package unit supplied by the valve actuator vendor, complete with instrumentation but
without a control panel; instead the control is provided by the PCS with shutdown by
the PSS.
The Hydraulic fluid is stored in a supply tank, the outlet of which is connected to the
suction of the hydraulic pumps. There are two hydraulic pumps, P-2901A and P2901B which shall be configured as typical type 26, which operate on a duty / assist
basis with the normal signals as defined in section 3.6. The first pump set to auto will
be the first duty pump, the second pump when put to auto will be the assist pump.
The starting and stopping of the pumps is controlled by the signal from PIT 209503
which measures the hydraulic system pressure and has a number of set points
described below:

P1: Low pressure alarm

P2: Start assist pump

P3: Start duty

P4: Stop running pump (pumps)

P5: High pressure alarm
The application of these defined trip points is explained in context below:
1. The normal operating condition is that the hydraulic pressure is between the
duty pump start and stop pressures with both pumps stopped. The pressure
slowly decays by the inevitable leaks in the system, or a demand made on the
hydraulic system to actuate one or more valves. This causes the pressure to
drop as the accumulators supplies the required high pressure fluid. When the
pressure reaches P3, the duty pump will start. The pressure increases until P4
is reached when the pump is stopped – no alarms since this is normal
operation.
2. From a starting point where the hydraulic system has been out of service, the
pressure in the accumulators is effectively atmospheric and hence below P1.
Duty pump if switched to auto will start, assist pump when switched to auto will
also start to assist pressurisation of the accumulators. Pressure rises (after an
extended period because of the relatively large accumulator volume). When
pressure P4 is reached both pumps will stop. Because this condition is not
normal, it is not considered necessary to inhibit the low pressure alarm. When
the pressure rises above P1 it can be reset and should not occur again unless
the pumps fail to start from a previously “normal” condition, as described in (1).
3. Starting from the situation in (1) above, but assuming a number of valve
operations are ongoing. Pressure drops below P3, duty pump starts. However
because the demand is higher than a single pump can supply the pressure
continues to drop until it reaches P2 when the assist pump starts. This should
cause the pressure to rise until it reaches, when both pumps stop. – again no
alarm because this also can be considered normal operation.
4. The high pressure alarm operates at P5 which could occur if the pumps fail to
stop for any reason at the pump stop pressure P4.
5. The low pressure alarm operates at P1 which could occur if both pumps fail to
start for any reason at P3 and P2.
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For these pumps it is not necessary to provide automatic override of the pre alarms
and shutdown alarm.
In addition to the control pressure transmitter, an independent pressure transmitter PIT
HOLD is installed to provide a high high pressure shutdown to protect the hydraulic
system from over pressurisation. This is defined in the PSS cause and effects
diagrams and the shutdown alarm and analogue signals shall be repeated to the PCS
for display on the operator workstation as normal.
The tank is provided with a level transmitter LIT 209501. This shall be connected to
the PSS where it will provide a low low level shutdown to protect the hydraulic pumps,
as defined on the PSS cause and effects diagrams. The signal and trip alarm shall be
repeated from the PSS to the PCS to provide a level indication as well as a low level
pre alarm.
When a shutdown occurs that closes a shutdown valve, it is a requirement to put any
PID control loops in the same process line into manual and close its control valves
(see section 3.2). The table below lists the control loops and valves that are applicable
to this requirement for the Flowline Pig Receivers and Inlet Production Manifolds.
Controller Shutdown Action – Flowline Pig Receivers and Inlet Production
Manifolds.
SHUTDOWN
VALVE
CONTROLLER
CONTROL
VALVE
XXV 200015
PIC 200002
PV 200002
XXV 202015
PIC 202002
PV 202002
XXV 203015
PIC 203002
PV 203002
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5.0
SLUG CATCHERS
Reference P&IDs: BLK18-GP-K-PR-PID-210000, 210100.
There are two slug catchers which are the initial reception vessels for the production
fluids from the wells. These provide a substantial volume to cope with the large slug
flows that might occur during unusual production operations. They provide the initial
two phase separation of process gas from the combined oil and produced water. For
this section, only Slug Catcher 1 (V-21001) will be described, but the control systems
are identical and the same description is equally valid for Slug Catcher 2 (V-21002)
with the appropriate tag numbers substituted.
The gas flow from slug catcher V-21001 is measured by an orifice plate; the flow
differential pressure transmitter FIT 210025 will provide the required square root
extraction, providing a linear signal to the PCS. The flow shall be corrected to
standard conditions (15 degrees centigrade and 1.01325 bara pressure) using
pressure and temperature inputs from PIT 210008, and TIT 210026.
It should be noted that the pressure transmitter PIT 210008 is not an absolute
pressure device, but absolute pressure is required for the pressure correction
calculation. In this application, because the normal pressure is approximately 27 barg,
the addition by the PCS algorithm of 1.013 bar to the measured value to approximate
to a real absolute pressure measurement is an acceptable approach which will cause
a small but acceptable error.
The PCS shall use the standardised flow for FQI 210025 to provide a rate of flow
indicator plus a digital flow totaliser. The number of totalised digits shall be set to allow
continued accumulation without rollover for approximately 3 months operation. Manual
reset to zero of the totalised figure shall be provided from the operator station, but only
at the supervisor level.
As well as providing a pressure signal for the flow compensation, PIT 210008 also
provides the input to PIC 210008 that controls the slug catcher pressure. If a process
upset causes the pressure to rise, the controller releases excess gas to the HP wet
flare header to maintain pressure control. The requirement for this pressure release is
most likely to occur if the MP compressor is tripped by a shut down condition.
Although the slug catchers are large vessels providing considerable buffering capacity,
the pressure rise can be expected to be quite rapid, requiring suitably aggressive
tuning for the pressure controller and with operating experience, it may be necessary
to apply a more advanced control algorithm.
The Slug Catcher acts as a two phase separator with mixed oil and produced water
flowing from the vessel. However elevated internal liquid take off nozzles will cause
some produced water to separate out on top of the anticipated sand layer. The vessel
is equipped with a nucleonic level profile system, LT 210003, as described in section
3.5.
The vessel can be expected to have several fluid layers consisting, sand, produced
water, oil / produced water mixture, foam and vapour space. The level of the oil /
produced water mixture is controlled by LIC 210003, with its process variable being the
level profiler’s oil / produced water mixture liquid level signal.
The interface signal that is derived from the level profiler’s produced water liquid level
signal is used for a non IL rated LL level shutdown. This signal shall therefore be
connected to the PSS and the signal repeated to the PCS for display on the level
profiler’s PCS indicator.
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The level profiler provides four separate level signals which are required to be
displayed as a vertical bar, with each level representing the separate liquid layer; this
requirement is explained in more detail in section 3.5.
An independent radar type level transmitter, LIT 210061 will be used as the HH and LL
oil / produced water mixture level shutdown transmitter. This will be connected to the
PSS and its signal repeated to the PCS for display.
The mixed oil and produced water flow from the Slug Catcher liquid outlet is measured
with a standard venturi flow meter FIT 210049. This provides a 4-20 mA analogue
signal that has had the required square root linearization carried out in the transmitter.
The PCS shall use this signal for FQI 210049 to provide a normal rate of flow indicator
plus a digital flow totaliser. The number of totalised digits shall be set to allow
continued accumulation without rollover for approximately 3 months operation. Manual
reset to zero of the totalised figure shall be provided from the operator station, but only
at the supervisor level.
The mixed oil and produced water flow from the Slug Catcher liquid outlet is monitored
with a corrosion probe, CT 210047, see section 3.9 for details and an acoustic sand
detector, AT 210017, see section 3.7 for details.
As noted in section 3.7, it is necessary to repeat the process flowrate at the sand
detector to the sand detector’s PC from which it will calculate the real time flow velocity
necessary for use in its calculations. For AT 210017 the required flow signal is FI
210049. (For Slug Catcher 2, V-21002, the sand detector is AT 210038 and the
required repeated flow signal is FI 210055).
When a shutdown occurs that closes a shutdown valve, it is a requirement to put any
PID control loops in the same process line into manual and close its control valves
(see section 3.2). The table below lists the control loops and valves that are applicable
to this requirement for the Slug Catcher.
Controller Shutdown Action – Slug Catcher.
SHUTDOWN
VALVE
CONTROLLER
CONTROL
VALVE
XV 210009
LIC 210003
LV 210003
Slug Catcher 1
XV 210040
LIC 210032
LV 210032
Slug Catcher 2
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6.0
HP SEPARATION
Reference P&IDs: BLK18-GP-K-PR-PID-220000, 220100, 400001 and Petreco HP
Separator Hydrocyclone Package Z41001 P&ID L295-K-001.
The HP Separator is a three phase vessel and is equipped with a nucleonic level
profile system, LT 220002; see section 3.5 for details.
The level profiler provides five separate level signals which are required to be
displayed as a vertical bar, with each level representing the separate liquid layers
measured by the level profiler; this requirement is explained in more detail in section
3.5.
The oil level within the HP Separator is controlled by LIC 220012 with its process
variable measured by a radar type level transmitter, LIT 220012. An independent
radar transmitter LT 220065 is provided for the HH and LL oil level shutdown function.
This will be connected to the PSS and its signal repeated to the PCS for display.
Because there is only one HP separation train, it is considered appropriate to provide
redundancy for the oil level control valves and a piping installation that allows
maintenance of the standby valve without the necessity to shutdown the HP separator.
Thus LIC 220012 has two control valve outputs, one to LV 220012A and the other to
LV 220012B.
Under normal operation one valve will be operating whilst the other is on standby. A
software selector switch, HS 220012 will be provided to allow the operator to select the
duty valve. The standby valve shall be provided with a “low” signal to keep the valve
closed and the duty valve will receive the normal control signal output.
The level of the oil / produced water interface is controlled by LIC 220002, with its
process variable being the level profiler’s produced water liquid level signal. The same
signal is used to initiate a non IL rated shutdown in the PSS. The signal is therefore
connected to the PSS and repeated to the PCS for control and display purposes.
The oil / produced water interface level control is provided with two control valves LV
220002A and LV 220002B, installed to allow duty and standby configuration. A
software selector switch, HS 220002 will be provided to allow the operator to select the
duty valve. The standby valve shall be provided with a “low” signal to keep the valve
closed and the duty valve will receive the normal control signal output. The control
valves are located in the Produced Water Treatment Package Z-40001.
In the early years of the fields operation, the production fluids will have only a small
amount of associated produced water, this being insufficient for continuous throttling
operation of the control valve. The level controller LIC 220002 shall therefore initially
be configured as a differential gap controller with a 4-20mA output signal that opens
and closes the control valve as required to maintain level control. The controller output
shall not fully open the valve, but shall provide an output that causes a flow of 160
m3/hr; this requires a controller output of 5.9 mA to give 12% of valve travel. Because
valve sizing is not precise, the flow rate shall be checked when the plant is operational
utilising FI 220055 and if necessary, the output of the controller adjusted to give the
required 160 m3/hr.
As field life continues and the amount of produced water increases, it will be necessary
to convert LIC 220002 to a normal PID controller; the configuration should allow this
change to be achieved by a simple software update.
BLK18-GP-K-IN-SPE-0101
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The pressure in the HP separator is controlled by PIC 220008A and PIC 220008B
which are configured as a standard dual controller pressure control loop as defined in
section 3.4.
The oil outlet from the HP Separator includes an acoustic sand detector, AT 220026
see section 3.7 for details.
As noted in section 3.7, it is necessary to repeat the process flowrate at the sand
detector to the sand detector’s PC from which it will calculate the real time flow velocity
necessary for use in its calculations.
Unfortunately we do not have a specific flow measurement for AT 220026 and the
computer will have to derive the flow from the following three separate signals that
require to be repeated. These are FI 230026 on the discharge of the crude oil transfer
pumps, FI 230020 on the discharge of the LP separator water recycle pumps and FI
240019 which is the water phase flow rate from the coalescer. The PC calculates the
required flow rate as FI 230026 + FI 230020 – FI 240019.
When a shutdown occurs that closes a shutdown valve, it is a requirement to put any
PID control loops in the same process line into manual and close its control valves
(see section 3.2). The table below lists the control loops and valves that are applicable
to this requirement for the HP Separator System.
Controller Shutdown Action – HP Separator
SHUTDOWN
VALVE
CONTROLLER
CONTROL
VALVE
XXV 220009
LIC 220012
LV 220012A
Two control valves – duty &
standby
XXV 220009
LIC 220012
LV 220012B
Two control valves – duty &
standby
XV 220010
LIC 220002
LV 220002A
Two control valves – duty &
standby
XV 220010
LIC 220002
LV 220002B
Two control valves – duty &
standby
XXV 220013
PIC 220008A
PV 220008A
PIC 22008B remains in auto
allowing gas to vent to flare
BLK18-GP-K-IN-SPE-0101
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7.0
PRODUCTION HEATER
Reference P&IDs: BLK18-GP-K-PR-PID-220100
The Production Heater consists of two heat exchangers operating in parallel and
utilising heating medium to heat the process fluids prior to the inlet to the LP
Separator. Each heater is rated to produce more than 50% of the heating duty and
under normal process conditions, both heaters are in operation.
Temperature controller TIC 220017 controls the process fluid inlet temperature to the
LP Separator. The controller has two control valve outputs TV 220017A and TV
220017B that control the heating medium flow to each heat exchanger, the control
valve signals shall be the same to both control valves.
BLK18-GP-K-IN-SPE-0101
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8.0
LP SEPARATION
Reference P&IDs: BLK18-GP-K-PR-PID-230000, 240400
The LP Separator is a three phase vessel and is equipped with a nucleonic level
profile system, LT 230002. It provides five separate level signals which are required to
be displayed as a vertical bar, with each level representing the separate liquid layers
measured by the level profiler; this requirement is explained in more detail in section
3.5.
The level of the oil / produced water interface is controlled by LIC 230002, with its
process variable being the level profiler’s produced water level signal. The same
signal is used to initiate a non IL rated shutdown in the PSS. The signal is therefore
connected to the PSS and repeated to the PCS for control and display purposes.
The oil level within the LP Separator is controlled by LIC 230013 with its process
variable measured by a radar type level transmitter, LIT 230013 and its control valves
located downstream of the Crude Oil Rundown Coolers. The oil is pumped from the
LP Separator by the Crude Oil Transfer Pumps, through the Electrostatic Coalescer
and on to the Crude Oil Rundown Coolers.
Like HP Separation, there is only one LP Separation train and it is considered
appropriate to provide redundancy for the oil level control valves. Thus LIC 230013
has two control valve outputs, one to LV 230013A and the other to LV 230013B.
Under normal operation one valve will be operating whilst the other is on standby. A
software selector switch, HS 230013 will be provided to allow the operator to select the
duty valve. The standby valve shall be provided with a “low” signal to keep the valve
closed and the duty valve will receive the normal control signal output.
An independent radar transmitter LT 230052 is provided for the HH and LL oil level
shutdown function. This will be connected to the PSS and its signal repeated to the
PCS for display.
The pressure in the LP separator is controlled by PIC 230007A and PIC 230007B
which are configured as a standard dual controller pressure control as defined in
section 3.4
When a shutdown occurs that closes a shutdown valve, it is a requirement to put any
PID control loops in the same process line into manual and close its control valves
(see section 3.2). The table below lists the control loops and valves that are applicable
to this requirement for the LP Separator System.
Controller Shutdown Action – LP Separator
SHUTDOWN
VALVE
CONTROLLER
CONTROL
VALVE
XV 230010
LIC 230013
LV 230013A
Two control valves – duty &
standby – see also section 12
XV 230010
LIC 230013
LV 230013B
Two control valves – duty &
standby – see also section 12
BLK18-GP-K-IN-SPE-0101
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XV 230011
LIC 230002
LV 230002
XV 230009
PIC 230007A
PV 230007A
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PIC 230007B remains in auto
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9.0
LP SEPARATOR WATER RECYCLE PUMPS
Reference P&IDs: BLK18-GP-K-PR-PID-230100, Vendor Drawing BPAA-BL18PME11A-C0101 (V 14993)
The LP Separator Water Recycle Pumps, P-23002A and P-23002B are 2 x 100%
pumps configured as duty and standby, with auto start of the standby. Section 3.6
provides further details of pump requirements including auto start, start up overrides
and alarm suppression.
Each of the pumps is provided with its own minimum flow bypass controller based on
orifice plate flow measurements with square root linearisation carried out in the
transmitter. Pump P-23002A has flow controller FIC 230016 and P-23002B has flow
controller FIC 230029.
Under normal conditions flow from the pump exceeds the minimum flow and the
controller maintains the bypass control valve closed. If a fault occurs in the process
system causing the flow to drop below the bypass controller’s set point, then it opens
the control valve, returning the flow to the LP Separator and maintaining flow through
the pump at its minimum safe flowrate. If the process fault condition is such that it
cannot meet the minimum flow requirement of the pump, then a low flow alarm shall be
initiated to warn the operator.
If the pump discharge flow drops below the low low flow trip point, this will initiate a
PSS shutdown for the pump to protect it against damage. The low low flow shutdown
of the duty pump shall also initiate auto start of the standby pump and the PSS shall
provide the necessary signal to initiate the action, see section 3.6 for further details.
Since the flow transmitters are used for shutdown, they will be connected to the PSS
and the signal repeated to the PCS for control purposes.
The combined produced water discharge from the pumps is measured with an orifice
plate based flowmeter, FIT 230020, which provides a 4-20 mA analogue signal that
has had the required square root linearisation carried out in the transmitter. The PCS
shall use this signal for FQI 230020 to provide a normal rate of flow indicator plus a
digital flow totaliser. The number of totalised digits shall be set to allow continued
accumulation without rollover for approximately 3 months operation. Manual reset to
zero of the totalised figure shall be provided from the operator station, but only at the
supervisor level.
The pumps are provided with pressurised seals as described in section 3.6.8, the
instrument tag numbers are detailed below:
For Pump P 23002A : PI 230530 and LI 230533.
For Pump P 23002B : PI 230540 and LI 230543.
BLK18-GP-K-IN-SPE-0101
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10.0
CRUDE OIL TRANSFER PUMPS
Reference P&IDs: BLK18-GP-K-PR-PID-230200, Vendor Drawing BPAA-BL18PME11A-C0401 (V 14992)
The Crude Oil Transfer Pumps P-23001A and P-23001B and P-23001C are 3 x 50%
pumps configured as duty, duty and standby, with auto start of the standby pump
required. Section 3.6 provides further details of pump requirements including auto
start, start up overrides and alarm suppression.
Each of the pumps is provided with its own minimum flow bypass controller based on
orifice plate flow measurements with square root linearisation carried out in the
transmitter. Pump P-23001A has flow controller FIC 230022, P-23002B has flow
controller FIC 230024 and P-23002C has flow controller FIC 230037.
Under normal conditions flow from the pump exceeds the minimum flow and the
controller maintains the bypass control valve closed. If a fault occurs in the process
system causing the flow to drop below the bypass controller’s set point, then it opens
the control valve, returning the flow to the LP Separator and maintaining flow through
the pump at its minimum safe flowrate. If the process fault condition is such that it
cannot meet the minimum flow requirement of the pump, then a low flow alarm shall be
initiated to warn the operator.
If the pump discharge flow drops below the low low flow trip point, this will initiate a
PSS shutdown for the pump to protect it against damage. The low low flow shutdown
of the duty pump shall also initiate auto start of the standby pump and the PSS shall
provide the necessary signal to initiate the action, see section 3.6 for further details.
Since the flow transmitters are used for shutdown, they will be connected to the PSS
and the signal repeated to the PCS for control purposes.
The crude oil discharge from the pumps is measured with an orifice plate based
flowmeter, FIT 230026, which provides a 4-20 mA analogue signal that has had the
required square root linearisation carried out in the transmitter. The PCS shall use this
signal for FQI 230026 to provide a normal rate of flow indicator plus a digital flow
totaliser. The number of totalised digits shall be set to allow continued accumulation
without rollover for approximately 3 months operation. Manual reset to zero of the
totalised figure shall be provided from the operator station, but only at the supervisor
level.
The pumps are provided with pressurised seals as described in section 3.6.8 except
that for these pumps there are two separate seal units, one for the pump driven end
and one for the pump non driven end, the instrument tag numbers are detailed below:
For Pump P 23001A driven end, PI 230500 and LI 230503.
For Pump P 23001A non driven end, PI 230550 and LI 230553.
For Pump P 23001B driven end, PI 230510 and LI 230513.
For Pump P 23001B non driven end, PI 230560 and LI 230563.
For Pump P 23001C driven end, PI 230520 and LI 230523.
For Pump P 230011C non driven end, PI 230570 and LI 230573.
BLK18-GP-K-IN-SPE-0101
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11.0
ELECTROSTATIC COALESCER, WASH WATER HEATER AND
ELECTROSTATIC COALESCER WATER RECYCLE PUMP
Reference P&IDs: BLK18-GP-K-PR-PID-240000, 240500, 240600, Vendor Drawing
BPAA-BL18-PME11A-C0401 (V 14992)
Oil and approximately 5% entrained produced water from the LP Separator are mixed
with wash water to dilute the salt content of the water phase prior to entering the
Coalescer. Intimate mixing is achieved during flow through valve PDV 240028 under
differential pressure control from PDIC 240028. This produces an oil / water emulsion
in the Coalescer which normally operates as a liquid full vessel. The vessel contains
three electrode banks maintained with a high electrostatic voltage that breaks down
the emulsion to form an oil / water interface.
Although the vessel is normally completely full, it is possible for vapour to accumulate
at the top of the vessel. To monitor for this condition, a radar type level transmitter,
LIT 240083, is installed and provides the process measurement for a standard PCS
indicator, LI 240083. Because the vessel is designed to operate completely full, the
linear, 0–100%, 4-20mA signal will normally provide a 100% signal. If a vapour space
is formed and the signal drops below the LL trip setting, LIT 240083 initiates a
shutdown, as defined in the PSS cause and effect diagram. The signal is therefore
connected to the PSS and repeated to the PCS to provide the monitoring and prealarm function.
The three transformers that power the electrode banks within the Coalescer each
provide a common fault alarm to the PCS and the PSS provides a shutdown signal to
each transformer as defined in the PSS cause and effect diagrams. The fault alarms
from each transformer XA 240007, XA 240086, XA 240082 are provided by the
transformer switchgear status contact at the electrical switchboard and are connected
to the PCS via the dual serial link.
The water/emulsion interface is detected using a nucleonic level system. This system
is different to that described in section 3.5, this being a more conventional type. The
nuclear source is located inside the vessel, with two independent level transmitter
detectors located outside and in the path of the gamma ray emissions. LT 240002
provides the signal for LIC 240002 to control the interface level and LT 240080
provides an independent level interface signal to the PSS for HH and LL shutdown.
Both transmitters have the same 0–100% range and provide a linear, 4-20mA,
analogue signal.
The water phase flow rate from the Coalescer is measured with an orifice plate based
flowmeter, FIT 240019, which provides a 4-20 mA analogue signal that has had the
required square root linearisation carried out in the transmitter. The PCS shall use this
signal for FQI 240019 to provide a normal rate of flow indicator plus a digital flow
totaliser. The number of totalised digits shall be set to allow continued accumulation
without rollover for approximately 3 months operation. Manual reset to zero of the
totalised figure shall be provided from the operator station, but only at the supervisor
level or above.
The wash water is heated before being mixed with the oil by the Wash Water Heater
under temperature control from TIC 240054 which regulates the heating medium flow
through the heat exchanger. The wash water flowrate to the Coalescer is controlled by
FIC 240053, acting on FV 240053.
It is required that the water flow into and out of the Coalescer is monitored and
compared to ensure that the flow out, measured by FQI 240019 is always higher than
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the flow in, measured by FIC 240053; if this condition is not met, an alarm shall be
raised to the operator.
The Electrostatic Coalescer Water Recycle Pump P-24003 is a single 100% duty
pump. This is manually stopped and started by the operator and is as described in
section 3.6.
The pump discharge flowrate is measured with an orifice plate based flowmeter, FIT
240094, which provides a 4-20 mA analogue signal that has had the required square
root linearisation carried out in the transmitter. This is connected directly to the PSS to
provide the LL flow shutdown of the pump as defined in the PSS cause and effects.
The signal shall be repeated to the PCS as the measured variable for FIC 240094,
which controls the pump discharge flowrate via FV 240094. There is no minimum flow
bypass for P-24003.
The pump is provided with a pressurised seal as described in section 3.6.8, the
instrument tag numbers are detailed below:
For Pump P 24003 : PI 240500 and LI 240503.
When a shutdown occurs that closes a shutdown valve, it is a requirement to put any
PID control loops in the same process line into manual and close its control valves
(see section 3.2). The table below lists the control loops and valves that are applicable
to this requirement for the Electrostatic Coalescer.
Controller Shutdown Action – Electrostatic Coalescer
SHUTDOWN
VALVE
CONTROLLER
CONTROL
VALVE
XV 240008
LIC 240002
LV 240002
XV 240052
FIC 240053
FV 240053
BLK18-GP-K-IN-SPE-0101
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12.0
CRUDE OIL RUNDOWN COOLER
Reference P&IDs: BLK18-GP-K-PR-PID-240400
The Crude Oil Rundown Cooler consists of two heat exchangers operating in parallel
and utilising seawater to cool the oil prior to entering the crude oil import header. Each
cooler is rated to produce more than 50% of the cooling duty and under normal
process conditions, both coolers are in operation.
Temperature controller TIC 240040 controls the oil outlet temperature and has two
control valve outputs, TV 240040A and TV 240040B that control the seawater flow to
each heat exchanger.
Under normal operating conditions the control valve signals shall be the same to both
control valves.
However there is a possibility of wax depositing within the cooler. If this is detected, it
will be necessary to decrease the cooling to the partially blocked exchanger by
decreasing the output to its seawater control valve. This should allow the exchanger
temperature to increase sufficiently to re-melt the wax, when control can be returned to
the normal balanced state if required.
In order to achieve this effect, a software signal multiplying function shall be
incorporated into the controller output for TV 240040A. The multiplication factor shall
be adjustable by the operator over a range of 0.5 to 1.5. A faceplate, selectable on
demand, will provide the operator interface for adjusting the multiplying factor.
By setting the multiplier to less than or greater than 1, the operator can decrease or
increase the signal to control valve TV 240040A relative to the output to TV 240040B.
Since the control valve outputs are from a common controller, the different signals will
result in different valve positions and reduced cooling as required. Although this will
result in the individual exchanger oil outlet flow temperatures being different, the
combined flow temperature is maintained at the required temperature set point. Thus
a reduction in the cooling flow for “A” will result in an increase in cooling flow for “B” to
achieve set point and visa versa.
The multiplier will affect the loop gain and hence the controller tuning, however it is not
expected that the defined multiplier range of 0.5 to 1.5 will result in any unacceptable
loop instability, although, to lessen the chance of instability, it is desirable to reduce the
selectable range of the multiplier to the minimum necessary. To allow this to be
modified, based on operating experience, the multiplier range shall be adjustable at
the engineer access level, thus reducing the multiplier range that the operator can
select from. It should be noted that under normal operation, the multiplier will be set at
x 1.0.
The oil flow to the marine cargo tanks is measured with an ultrasonic flowmeter FIT
240075 which provides a linear 4-20 mA analogue signal. The PCS shall use this
signal for FQI 240075 to provide a normal rate of flow indicator and a digital flow
totaliser. The number of totalised digits shall be set to allow continued accumulation
without rollover for approximately 3 months operation. Manual reset to zero of the
totalised figure shall be provided from the operator station, but only at the supervisor
level.
The oil flow from the cooler to the crude oil import header can be routed fore or aft by
the manual on / off valves XV 240078 and 240081 operated from the PCS workstation.
These valves are TYP 35, of failed locked design and each has two solenoid valves,
each therefore requires two digital outputs. They shall be arranged so that when the
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valve is to be opened, the open solenoid valve output is energised and remains
energised and the closed solenoid valve output is de-energised and remains deenergised. The requirement for closing the main valve is the exact opposite.
When a shutdown occurs that closes a shutdown valve, it is a requirement to put any
PID control loops in the same process line into manual and close its control valves
(see section 3.2). The table below lists the control loops and valves that are applicable
to this requirement for the Crude Oil Rundown Cooler.
Controller Shutdown Action – Crude Oil Rundown Cooler
SHUTDOWN
VALVE
CONTROLLER
CONTROL
VALVE
XV 240049
LIC 230013
LV 230013A
Two control valves – duty &
standby – see also section 8
XV 240049
LIC 230013
LV 230013B
Two control valves – duty &
standby - see also section 8
BLK18-GP-K-IN-SPE-0101
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13.0
CRUDE OIL METERING PACKAGE
Reference P&IDs: BLK18-GP-K-PR-PID-270000 + Vendor P&ID’s BPAA-BL18PIC06A-C0001, C0002.
The Crude Oil Metering Package, Z 27001, is a turbine meter based, self contained
system, complete with its own package control panel. This controls all metering, meter
proving and automatic analysis operations. The package has two supervisory
computers arranged in duty and hot standby configuration. Each provides a dual
modbus serial link to the PCS and this shall be configured to provide automatic change
over to the standby link if the duty fails; this action shall be alarmed.
The metering package has its own VDU located in the Starboard Process LER from
which all metering operations can be conducted. The serial links interface the
metering signals to the PCS where they are presented on workstation graphics
displays that mimic those of the metering computers. These allow the control room
operator to carry out normal metering operations as required. Additionally the PCS will
be required to produce custom metering reports from the serial data that will be
developed before the facility starts to produce oil.
If more detailed metering information is required or if changes to the vendors metering
configuration software are necessary, these will only be accessible at the LER
workstation and then only to personnel with the correct security access.
There are no shutdown signals to or from the metering system.
BLK18-GP-K-IN-SPE-0101
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14.0
OIL EXPORT BOOSTER PUMPS
Reference P&IDs: BLK18-GP-K-PR-PID-271000, Vendor Drawing BPAA-BL18PME11B-C0001 (DDM403599)
The Oil Export Booster Pumps P-27101A and P-27101B and P-27101C are designed
as 3 x 33⅓ pumps, thus all three pumps are normally running and there is therefore no
spare or auto start required.
These are large pumps and each has its own PLC based control system to provide the
logic to control the pump and the auxiliary systems such as lube oil, mechanical seal
sealant systems, etc.
The pump PLC’s have hard wired connections to the motor switchboard for start and
stop of the main and auxiliary lube oil pump motors.
The pump PLC’s have dual modbus serial links which route all required package
signals to and from the PCS for display and interaction by the control room operator.
For these pumps there are no hard wired PCS signals to the pump PLC’s.
The only hard wired signals to the pumps PLC’s are PSS shutdown signals as defined
in the PSS cause and effect diagrams.
Unlike pumps without package control panels, the operator does not directly send a
serial link start or stop signal to the motor switchboard from the PCS. Instead a pump
start or stop is sent to the pumps PLC that will initiate the start or stop logic. If all the
pump systems are operating correctly, the pump logic will subsequently send the hard
wired start or stop signals to the motor switchboard.
Thus the standard serial link signals defined in section 3.6 will not be provided from the
MCC and the graphic screens developed to display the pump serial link signals shall
incorporate the pump start and stop, running, fault, etc to and from the pump PLC’s.
The pressure of the oil export booster pump suction manifold is indicated by PI
271023. This has a low pressure alarm that has to be inhibited unless loading
operations are in progress. The criteria for removing the inhibit shall be taken from the
metering package total rate of flow signal, FI 270468A. The inhibit shall be removed
when the flowrate is greater than 2000M3/hr. It is estimated that at this flowrate the
backpressure in the tanker loading pipe will be above the low pressure alarm trip point
for PI 271023; this shall be confirmed during loading initial loading operations and if
necessary a suitable adjustment of the 2000M3/hr criteria shall be made.
There is no minimum flow bypass provided for the pumps since the oil is metered prior
to the pump suction and therefore cannot be returned to the storage tanks. Also the oil
cannot be routed to the pump suction since it will rapidly overheat, potentially causing
damage to the pump and will exceed the system design temperature.
Protection for the pumps is therefore provided by monitoring the discharge flow using
orifice plate flow measurements with square root linearisation carried out in the flow
transmitters. Pump P-27101A has flow indicator FI 271024, P-27101B has flow
indicator FI 271025 and P-27101C has flow indicator FI 271026. Unlike other
applications, these do not provide a pump shutdown function, only a rate of flow
indication and a low flow pre alarm, they are therefore directly connected to the PCS.
Utilising the same orifice plate, a second transmitter is provided for the protective
shutdown of the pumps. These provide a rate of flow indication as well as a low low
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flow shutdown as defined in the PSS cause and effects diagrams. As before the
square root linearisation is carried out in the flow transmitters which are connected to
the PSS. These transmitters are FT 271005 for P-27101A, FT 271010 for P-27101B
and FT 271015 for P-27101C
Starting of the pumps is a manual function that requires the operator to follow a
specific start up sequence, parts of which are outlined below.
Since there is no minimum flow bypass, the pressure controller on the pump discharge
is set to manual with the control valve set to 6% open. With the pump suction and
discharge valves opened, the pump is started. After allowing sufficient time for the
pump to run up to speed, the pressure controller is switched to auto causing the
control valve to open until the pressure is reduced to the controller’s set point.
Because of the specific start up requirements, local start of the pump from the PLC
control panel is not allowed without the operator’s interaction. To ensure this cannot
occur, the operator is required to send an “ICS permissive to start signal” to the PLC
logic, again via the serial link. Without this signal, the pump PLC logic ensures that the
pump cannot be started locally or by the operator from the PCS workstation.
When the operator initiates the “ICS permissive to start signal” the serial link bit shall
be set to a continuous logic 1. It shall remain at logic 1 until the pump running signal is
received, when the PCS shall automatically reset the signal to zero. If the running
signal is not received with 15 minutes, the PCS shall also set the bit to zero.
The off loading of oil is not a continuous process function and thus a number of alarms
and PSS trips will require to be automatically overridden when loading operations are
not functioning. For each pump these will be:

Low suction pressure alarm (for P-27101A - PI 271004)

Low Low suction pressure shutdown (for P-27101A - PI 271004)

Low discharge pressure alarm (for P-27101A - PIC 271007)

Low discharge flow alarm (for P-27101A - FI 271024)

Low Low discharge flow trip (for P-27101A - FI 271005)
The equivalent signals and tag numbers as defined on the P&ID are similarly
applicable to the B & C pumps.
The removal of the inhibits and the start up overrides will be initiated for each
individual pump when the pump start is initiated as described in section 3.6.7.
The pumps are provided with pressurised seals as described in section 3.6.8 except
that for these pumps there are two separate seal units, one for the pump driven end
and one for the pump non-driven end, the instrument tag numbers are detailed below:

For Pump P 27101A driven end, PI 271518 and LI 271536.

For Pump P 27101A non driven end, PI 271516 and LI 271533.

For Pump P 27101B driven end, PI 271618 and LI 271635.

For Pump P 27101B non driven end, PI 271616 and LI 271633.

For Pump P 27101C driven end, PI 271718 and LI 271736.
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
For Pump P 27101C non driven end, PI 271716 and LI 271733.

These signals will be included on the serial link from each pump’s PLC.
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15.0
FLOWLINE DISPLACEMENT SYSTEM AND NORTHERN SERVICES
LINE PIG LAUNCHER / RECEIVER
Reference P&IDs: BLK18-GP-K-PR-PID-273000, 273001, 273100, 273200 Vendor
Drawing BPAA-BL18-PME11A-C0301 (V14991)
Flowline Displacement Pumps
If a production shutdown occurs that is expected to be in operation for an extended
period, then the oil in the flowlines will cool and will potentially cause
hydrate/wax/gelling problems. To avoid this situation the production oil has to be
replaced by pumping diesel or dead oil down the flowlines to displace the production
oil and if necessary by heating the fluid to raise the temperature of the subsea system.
The Flowline Displacement Pumps P-27301A, P-27301B and P-27301C are provided
to pump the displacing fluid. The pumps may be operated in different configurations to
suit the specific operational needs. Any two of the pumps may be selected for series
operation with the first pumps discharge becoming the suction of the second pump.
The remaining pump may then be used for pumping displacement fluids to a different
flowline.
Each pump has a shutdown valve on the discharge line and it is a requirement that if
the pump stops, its respective shutdown valve is closed. This requirement is not a
shutdown, but may be considered as a process interlock. It shall utilise the
appropriate motor stopped signal from the motor switchboard serial link to initiate valve
closure:

For P 27301A the valve is XV 273004

For P 27301B the valve is XV 273008

For P 27301C the valve is XV 273028
There is no spare for the pumps and thus in circumstances that require flowline
displacement operations, all three pumps will normally be running and there is
therefore no requirement for standby auto start.
Flowline displacement is not a normal operation and thus a number of alarms and PSS
trips will require to be automatically overridden when fluid displacement is not
operational. For each pump these will be:

Low suction pressure alarm (for P-27301A - PI 273001)

Low Low suction pressure shutdown (for P-27301A - PI 273001)

Low discharge flow alarm (for P-27301A - FI 273003)

Low Low discharge flow trip (for P-27301A - FI 27003)
The equivalent signals and tag numbers as defined on the P&ID are similarly
applicable to the B & C pumps.
The removal of the inhibits and the start up overrides will be initiated for each
individual pump when the pump start is initiated as described in section 3.6.7.
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The discharge from the pumps can be routed to any of the subsea flowlines with the
flow being measured by either FI 273041 or FI 273042. Each has a low flow alarm
which also requires to be overridden when the displacement system is not running.
The criteria to be used to remove the overrides are:
FI 273041: remove low flow alarm inhibit if either XXV 200015 OR XXV 273018 is
open AND P 27301 A OR B OR C is running.
FI 273042: remove low flow alarm inhibit if either XXV 203015 OR XXV 202015 is
open AND P 27301 A OR B OR C is running.
The Flowline Displacement Pumps are located in enclosures that potentially could
contain flammable hydrocarbons. Although the hazardous area certification for the
pumps is suitable for its location, as an added precaution it is required to air purge the
pump enclosure before the pump is started. Thus when the operator initiates the
pump start pushbutton on the workstation, it will not immediately start the pump, but
shall initially de-energise the digital output that will open the air purge solenoid valve to
initiate the purge cycle.
The start pushbutton additionally starts a timer that maintains the purge valve output in
the de-energised state for the required 6 minutes purge time. It will then close the
purge solenoid valve by re-energising the digital output and automatically initiate the
start signal to the motor switchboard via the normal serial link. To avoid the timer
interfering with the normal alarm and shutdown inhibits described in section 3.6.7, the
separate timer that removes the inhibits shall be linked to the actual starting signal to
the pump, rather than the initiation of the start pushbutton from the workstation that is
normally used.

For P-27301A the purge solenoid valve output is PV 804027

For P-27301B the purge solenoid valve output is PV 804038

For P-27301C the purge solenoid valve output is PV 804023
The digital outputs are 24Vdc signals powered by the PCS.
Each of the pumps is provided with its own minimum flow bypass controller based on
orifice plate flow measurements with square root linearisation carried out in the
transmitter. Pump P-27301A has flow controller FIC 273003, P-27301B has flow
controller FIC 273007 and P-27301C has flow controller FIC 273036.
Under normal operating conditions, flow from the pump exceeds the minimum flow and
the controller maintains the bypass control valve closed. If a fault occurs in the
process system causing the flow to drop below the bypass controller’s set point, then it
opens the control valve, returning the flow to either the Diesel Displacement Tank or
the Cargo Tanks and thus maintains flow through the pump at its minimum safe flow
rate. If the process fault condition is such that it cannot meet the minimum flow
requirement of the pump, then a low flow alarm shall be initiated to warn the operator.
If the pump discharge flow drops below the low low flow trip point, this will initiate a
PSS shutdown for the pump as defined in the PSS cause and effects diagrams, to
protect it against damage.
Since the flow transmitters are used for shutdown, they will be connected to the PSS
and the signal repeated to the PCS for control purposes
The pumps are provided with pressurised seals as described in section 3.6.8 except
that for these pumps there are two separate seal units, with some shared facilities, one
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for the pump driven end and one for the pump non driven end. Additionally these seal
systems are pressurised by air driven pumps and hydraulic accumulators rather than
nitrogen gas. The air pumps operate automatically pumping the seal fluid and
pressurising the accumulator until the air pump stalls, restart of the air pumps is
automatic when the seal fluid pressure drops below the stall pressure. The instrument
tag numbers are detailed below:
For Pump P 27301A driven end accumulator pressure PI 273500
For Pump P 27301A non driven end accumulator pressure PI 273501
For Pump P 27301A common seal fluid header pressure PI 273504
For Pump P 27301A common seal fluid tank level LI 273508
For Pump P 27301B driven end accumulator pressure PI 273520
For Pump P 27301B non driven end accumulator pressure PI 273521
For Pump P 27301B common seal fluid header pressure PI 273524
For Pump P 27301B common seal fluid tank level LI 273528
For Pump P 27301C driven end accumulator PI 273540
For Pump P 27301C non driven end accumulator PI 273541
For Pump P 27301C common seal fluid header pressure PI 273544
For Pump P 27301C common seal fluid tank level LI 273548
The flowline displacement flow is controlled by FIC 273041 or FIC 273042 as required
operationally. The flow measurements are based on orifice plates and the differential
pressure transmitters provide the required square root linearization. In order to
monitor the volume of displacement fluid pumped down the flowlines, flow totalisers
are required for each of the two flow loops. The totalisers shall be scaled to display in
cubic meters and shall have 5 digits. The reset for these two specific applications shall
be accessible by the operator.
Flowline Displacement Fluid Heater / Cooler and Fluid Separator
When the liquids from the 2nd Stage LP Compressor Suction Scrubber are to be used
for top up of the diesel displacement tank, either all or part of the liquids from the
scrubber are diverted from their normal route, which is to the LP Separator, instead
they are routed to the Displacement Fluid Maker Equipment. The selection of diverting
all or part of the liquids is determined by whether the crude oil rundown temperature is
40°C or 60°C.
If the crude oil rundown temperature is 40°C, then the Displacement Fluid Maker
Equipment consisting of the Displacement Fluid Heater X-27401, the Displacement
Fluid Separator V-27401 and Displacement Fluid Cooler X-27403 has sufficient
capacity to take all the fluids produced. In this situation the level controller for the
suction scrubber, LIC 300003, which normally controls LV 300003, will be set as a
cascade master for the flow controller FIC 274027 which acts on FV 274027. This flow
control valve, located at the inlet to the Displacement Fluid Maker Equipment then
takes over control of the level in the suction scrubber. The facility to set the level
controller to its cascade mode is via selector switch HS 300003. When selected for
operation in cascade mode, with the cascade controller output for LIC 300003 set as
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cascade master for FIC 274027, the normal controller output to LV 300003 shall be set
at 4mA to close the valve.
The control will remain in this mode until the operator switches HS 300003 back to
normal mode or a PSS shutdown automatically switches HS 300003 back to the
normal mode. The circumstances when the shutdown system initiates this shutdown
action will be defined in the PSS cause and effect diagrams.
Under normal operating conditions, with no displacement fluid being produced, the
flow controller FIC 274027 will be in manual, with no cascade master connected and
with its output set to 4mA to keep the valve closed.
If the crude oil rundown temperature is 60°C, then the Displacement Fluid Maker
Equipment does not have sufficient capacity to handle the full amount of the fluid
produced.
Thus for operation with a crude oil rundown temperature of 60°C, the operator will
switch the controller FIC 274027 to auto and adjust the set point to divert as much flow
from 2nd Stage LP Compressor Suction Scrubber as is required, up to the maximum
that the equipment can process. The flow controller is not set to cascade and the level
controller on the 2nd Stage LP Compressor Suction Scrubber, LIC 300003 will allow the
surplus liquids from the Scrubber to flow to the LP separator as usual and thus
maintain level control.
Pig Receiver / Launcher
As with the pig receivers described in section 4.0, the Northern services pig launcher /
receiver is provided with motor operated on / off valves which have local operation
only, but with open and closed status displayed in the control room. MOV 273022 is
open / close operation only and MOV 273021 has inching facility. They are foundation
fieldbus type providing positive feedback and diagnostics to the PCS. The inching
valve will also require percentage open display.
When a shutdown occurs that closes a shutdown valve, it is a requirement to put any
PID control loops in the same process line into manual and close its control valves
(see section 3.2). The table below lists the control loops and valves that are applicable
to this requirement for the Flowline Displacement System and Northern Services Line
Pig Launcher / Receiver.
Controller Shutdown Action – Flowline Displacement System and Northern
Services Line Pig Launcher / Receiver
SHUTDOWN
VALVE
CONTROLLER
CONTROL
VALVE
XV 273035
TIC 230033
TV 273033
XV 274015
FIC 274027
FV 274027
XV 274025
LIC 274021
LV 274021
XV 274026
LIC 274023
LV 274023
BLK18-GP-K-IN-SPE-0101
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16.0
GAS COMPRESSORS
Reference P&IDs: BLK18-GP-K-PR-PID-300000, 300100, 300200, 300301, 300302,
300400, 311000, 311100, 311200, 311300, 311400, 311500, 312000, 312100,
312200, 312300, 312400, 312500, 331000, 331100, 331200, 331300, 331400,
332000, 332100, 332200, 332300, 332400.
There are three separate compressor pressure levels, LP, MP and HP with the glycol
dehydration facility located between the MP and HP levels. Each compression level
consists of two stage machines, each driven by a common motor driver. The LP level
is a single train, fixed speed machine with its common motor driver, whilst the MP and
HP levels are variable speed, each consisting of two stages, again with their common
motor drivers and arranged as two parallel trains. In normal operation both parallel
trains are operational; they are listed for clarity:

1st Stage LP compressor C-30001 – fixed speed

2nd Stage LP compressor C-30002 – fixed speed

1st Stage MP compressor Train 1 C-31101 - variable speed

2nd Stage MP compressor Train 1 C-31102 - variable speed

1st Stage MP compressor Train 2 C-31201 - variable speed

2nd Stage MP compressor Train 2 C-31202 - variable speed

1st Stage HP compressor Train 1 C-33101 - variable speed

2nd Stage HP compressor Train 1 C-33102 - variable speed

1st Stage HP compressor Train 2 C-33201 - variable speed

2nd Stage HP compressor Train 2 C-33202 - variable speed
The compressors are provided as packaged units, consisting of the common motor
drive, the 1st and 2nd stage compressors and where appropriate, a variable speed
gearbox between the motor and the compressors. There is only one variable speed
gearbox per package, so the 1st and 2nd stage compressors both run at the same
speed. Basic control of the compressors is based on suction pressure and the speed
is adjusted to maintain the compressors at the required suction pressure set point.
Each compressor package is supplied with its own control panel which includes a PLC
based control system, CCC anti-surge controller and Bently Nevada temperature and
vibration monitoring system, all located in the appropriate LER. For the MP and HP
compressors which have two parallel trains, the CCC controller additionally acts to
share the load between the two trains.
The CCC anti-surge control system will receive the suction pressure, temperature and
flow rate and the discharge pressure and temperature. With these signals it will
control the recycle valve to avoid compressor surge and if necessary for reduced
throughput conditions, will control the compressor with an appropriate degree of
recycle. The anti-surge controllers utilises algorithms that are insensitive to changes in
gas molecular weight.
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The CCC system has its own serial link (not dual) to the PCS which is used to provide
repeats of the main process parameters noted above for display on the PCS
workstations as well as selected data derived by the CCC controller.
The Bently Nevada machine monitoring system measures bearing vibration and thrust
as well as the various shaft speeds, key phasor information and bearing temperatures.
This data is connected to the PLC and is used for monitoring, pre-alarms and where
appropriate, shutdown, as well as more detailed diagnostic information for predictive
maintenance, post fault diagnostics, etc.
The PLC will normally control the complete start up sequence including purging and
pressurisation of the system, this includes the opening of the main inventory isolation
valves and the blowdown valves. The PLC monitors the differential pressure across
these isolation valves to ensure that the main valve is only opened when the
differential pressure across the valve is at an acceptable level.
Each compressor package will be provided with workstations to allow complete control
of the compressor package from the LER, although control shall also be possible from
the PCS in the control room.
The PCS will provide suitable graphic displays for the compressor packages based on
those implemented on the package vendor’s workstations. It is intended that only
those inputs and outputs that the operator needs for normal operation and monitoring
will be interfaced to the PCS. Inputs and outputs that are only used for fault
diagnostics, maintenance, etc, will not be included and will only be available on the
vendor’s workstation in the LER.
The compressor automatic start up sequences are similar for each package, in
particular for the control room operator interfaces and these will be described as a
sequence that can be considered to be applicable for each machine.
It may become necessary as the project develops to expand and modified this general
sequence to suit specific requirements for individual machines; this will be covered by
subsequent revisions of this document if appropriate.
The complete start up (as well as stop and shutdown) sequences are fully detailed in
the compressor vendors logic and will not be duplicated here. After initiation of the
sequence, the PLC steps through the logic until it reaches various stop points which
require manual intervention via the control room operator. The sequence of stop
points that is detailed below represents the current compressor design.
Control Room Operator Start Up Sequence Interface:
Before starting a compressor start up sequence the operator will set the appropriate
valves to the correct position, switch them to cascade to allow the PLC to take control,
carry out a number pre-defined checks to ensure that all process, utility and systems
are ready to start. When all is confirmed ready the operator will send a start
permissive:

START PERMISSIVE TO PLC
The compressor PLC steps through the logic carrying out its own system checks which
when completed sends a return signal to the PCS and to its own screen:

"UNIT START PERMISSIVE ACHIEVED" FROM PLC
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The compressor is then ready to start, either from the local compressor control panel
or remotely from the PCS (if the mode selector switch is set to "remote"). The operator
can now start the compressor start up sequence from the PCS:

"START COMPRESSOR" SIGNAL TO PLC
The compressor logic runs through it start up sequence. It checks for a pressurised or
de-pressurised start, carries out the purge and pressurising sequences if required,
starts and confirms correct operation of its auxiliary systems and moves valves to the
correct position in a predefined and timed sequence. For some start up cases the PLC
logic will require the opening of a defined manual blowdown bypass valve. It initiates
this by sending a signal to the PCS operator and holds the logic sequence until
confirmation that it has been opened is received:

"OPEN MANUAL BLOWDOWN BYPASS VALVE" FROM PLC
The operator advises the field operator to carry out the function and when confirmed
open, sends the confirming signal:

"MANUAL BLOWDOWN BYPASS VALVE OPEN" TO THE PLC
The sequence proceeds until the PLC will requires the same valve to be closed again.
Again this is requested by sending the signal and holding the logic:

"CLOSE MANUAL BLOWDOWN BYPASS VALVE" FROM PLC
The operator advises the field operator to close the valve again and when confirmed
closed, sends the confirming signal:

"MANUAL BLOWDOWN BYPASS VALVE CLOSED" TO THE PLC
The PLC continues its sequence until it reaches a stage that requires the compressor
case to be drained when it will hold the logic and send the signal:

"DRAIN COMPRESSOR CASE" FROM PLC
The operator advises the field operator to drain the compressor case and when
confirmed closed, sends the confirming signal:

"COMPRESSOR CASE DRAINED" TO PLC
This completes the control room operator’s manual interventions and the compressor
continues its start up sequence to bring the compressor on line.
For configuration of the PCS it will be necessary to produce a start up screen for each
compressor that mirrors the PLC's screen display, but simplified commensurate with
the reduced amount of data transmitted to the PCS.
In addition to the normal operating data, shutdown signals will also be required to
interface between the PLC and the PSS and ESD systems. These signals will be
defined by the PSS and ESD cause and effects diagrams and the signals will be hard
wired. The signals will be 24V dc powered by the PSS / ESD and will be fail safe,
energised in the healthy condition.
The compressor’s PLC provides automatic monitoring, control and shutdown for the
package and auxiliary systems together with automatic sequencing for start up,
stopping and shutdown of the compressor systems.
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The compressor on/off isolation valves will normally be controlled by the package PLC,
with the sequence controlled by the compressor logic. However as with all on/off
isolation/shutdown valves, the operator in the control room can switch these valves to
manual (“auto” in Emerson terminology) and directly control them as required. These
valves are also required to be operated by the PSS shutdown system and for the
blowdown valves, by the ESD system. If a shutdown is initiated that conflicts with the
PLC or operator requirements, the shutdown system will take priority and the valves
will move to the shutdown position.
The interconnection for these valves is somewhat complicated and is described here
for clarity. The PLC has hard wired valve open/close outputs to the PCS where the
valve logic functionality is located. These PLC valve command outputs to the PCS are
connected to the “cascade” input of the “valve logic block”; the operator workstation
connects to the “valve logic block” through the normal PCS internal network. Control
by the operator is by selection of manual from the valve faceplate and control by the
PLC is by selection of cascade.
These valves are used for start up, in particular for the purging and pressurisation
stage. However they are also shutdown valves and the outputs are therefore
hardwired from the PSS, where the shutdown logic resides (ESD for the blowdown
valves) to the valve’s solenoid valve.
If there is no shutdown in operation that affects the valve, then the position required by
the PLC or the operator from the workstation (depending on which is set for control, ie
valve set to cascade or manual) is interfaced to the PSS (or ESD for blowdown valves)
and the valve is moved to the required position.
If a shutdown is initiated that affects the valve, then the valve is moved to the
shutdown position if this conflicts with the PLC/PCS requirement. In addition a signal
is interfaced back to the PCS “valve logic block” which is connected to the “interlock”
input. This has the effect of putting the valve logic into “local override” which overrides
the other input signals, “greys out” the open and close and cascade / auto screen
buttons indicating that they are not operable, switches the valve to manual (auto) and
its PCS output to the shutdown position. This avoids a spurious out of position alarm
and ensures that when the shutdown is subsequently reset, the valve remains in the
shutdown condition until the operator decides to move it back to the normal operating
position.
The limit switches for the valve are connected to the “valve logic block” in the PCS
which provides the necessary monitoring facility for the valve logic. The limit switch
status is also transmitted to the Compressor PLC via the dual serial link.
The PLC provides normal control and sequencing as well as machine protective
shutdowns for the compressor and its auxiliary systems. The compressor shutdowns
and the associated external process PSS (and ESD) shutdowns interact with each
other and these interfaces and associated logic are defined in the cause and effect
diagrams. In particular, if the compressor’s mechanical seal fails, the compressor is
shutdown, the inventory isolation valves closed and the PLC initiates blowdown via the
ESD logic to mitigate uncontrolled gas leakage from the seals. All other shutdowns
associated with the compressor are PSS shutdowns.
The level control valve for V-30001 is LV 300018 and is required to close if the
compressor is tripped to the depressurised state. This is achieved by incorporating a
solenoid valve into the pneumatic signal to the actuator. If an appropriate shutdown is
initiated by the PSS, it will vent the actuator to its fail safe closed position. The PSS
shall additionally provide a signal to automatically switch LIC 300018 to manual and
close the controller valve output. It shall remain in manual after the shutdown has
been reset waiting for the operator to put the valve back into operation and auto.
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The process design requires that the liquids that accumulate in the 1st stage LP
compressor suction scrubber V-30001 require pumps to route the fluids back into the
process stream, the remaining scrubber vessels for the compressor systems do not
require pumps.
The 1st Stage LP Compressor Suction Scrubber Recycle Pumps P-30001A and P30001B are 2 x 100% duty and standby pumps without auto start and configured as
defined in section 3.6. The minimum flow bypass is provided by automatic mechanical
valves without any control or monitoring facility required from the PCS. The pumps are
shutdown by the PSS in accordance with the PSS cause and effects diagrams.
The pumps are provided with pressurised seals as described in section 3.6.8, the
instrument tag numbers are detailed below:
For Pump P-30001A : PI 300500 and LI 300503.
For Pump P-30001B : PI 300510 and LI 300513.
CT 300058 on the inlet to the 2nd stage LP compressor suction scrubber, V-30002 and
CT 300059 on the liquid outlet of the 1st stage LP compressor suction scrubber, V30001, are standard corrosion transmitters as described in section 3.9.
Displacement fluid maker
Under normal operation, fluids that are collected in the 2nd Stage LP Compressor
Suction Scrubber have sufficient pressure to be directly returned to the main process
stream in the LP Separator without any pumping. This is the normal mode of
operation and the level in the vessel is controlled by LIC 300003
This same fluid can be stabilised and then utilised for flowline displacement (see
section 15) by topping up the displacement diesel tank. The fluid produced from this
source is stabilised by heating in the Displacement Fluid Heater X-27401, removing
gas and water in the displacement fluid separator V-27401 and subsequent cooling in
the Displacement Fluid Cooler X-27403. The stabilised displacement fluid is then used
to top up the Diesel Displacement Tank ready for operational use.
This section of the process narrative is primarily concerned with the compressors with
the 2nd Stage LP Compressor Suction Scrubber operating in its normal mode as a
simple PID controller, LIC 30003, acting on LV 300003. As noted above it will
occasionally be used for the alternative process duty where it acts as a cascade
master.
Because this is not directly concerned with the compressor’s PCS
configuration, this operational mode is described in detail in section 15.0.
Marine tank gas blanketing supply
The following is a specific requirement for the suction header of the 1st stage MP
compressors (Reference P&IDs: BLK18-GP-K-PR-PID-311000)
Gas is taken for marine tank blanketing duty from the 1st stage MP compressor suction
header under pressure control from PIC 311089. Because of the low pressure
capabilities of the marine tanks, the set point range for the controller shall be limited.
The range of operator adjustment shall be from 0.095 to 0.105 barg, with the normal
set point being 0.1 barg.
The pressure transmitter for this loop is PIT 911010 which is located on the inlet gas /
fuel gas header in the marine facilities and will be connected to the marine PCS, it is a
conventional 4-20mA signal.
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Because of the very low pressure rating of the tanks and the need to avoid pressure
relief from excess gas feeding to the tanks, it is a requirement to monitor the actual
position of control valve PV 311089 relative to the required controller output.
Thus the PCS shall compare the actual valve position and the required valve position
and raise an alarm to the operator if the difference in either positive or negative
direction exceeds a set percentage. This will be set during system commissioning to
the lowest practical difference that avoids nuisance alarms, but should initially be set at
+/- 2%. To ensure that transient differences that might occur if a fast acting process
upset occurs, a time delay shall be incorporated so that the alarm is not initiated whilst
the valve positioner is “catching up”. The timer shall inhibit the alarm unless it has
been continuously present for more than 5 seconds, this time may be adjusted if
appropriate during commissioning.
When a shutdown occurs that closes a shutdown valve, it is a requirement to put any
PID control loops in the same process line into manual and close its control valves
(see section 3.2). The table below lists the control loops and valves that are applicable
to this requirement for the compressors.
Controller Shutdown Action - Compressors
SHUTDOWN
VALVE
CONTROLLER
CONTROL
VALVE
XV 510041
PIC 510040
PV 510040
XV 300049
LIC 300018
LV 300018
XV 300008
LIC 300003
LV 300003
XV311091
PIC 311089
PV 311089
XV 311004
LIC 311003
LV 311003
XV311065
TIC 311016
TV 311016
XV 311054
TIC 311031
TV 311031
XV 311008
LIC 311009
LV 311009
XV 311058
TIC 311047
TV 311047
XV 312065
TIC 312016
TV 312016
XV 312004
LIC 312003
LV 312003
XV 312054
TIC 312031
TV 312031
XV 312008
LIC 312009
LV 312009
XV 312058
TIC 312047
TV 312047
BLK18-GP-K-IN-SPE-0101
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XV 331003
LIC 331004
LV 331004
XV 331044
TIC 331015
TV 331015
XV 331021
LIC 331022
LV 331022
XV 331048
TIC 331037
TV 331037
XV 332003
LIC 332004
LV 332004
XV 332044
TIC 332015
TV 332015
XV 332021
LIC 332022
LV 332022
XV 332048
TIC 332037
TV 332037
BLK18-GP-K-IN-SPE-0101
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17.0
GLYCOL CONTACTOR AND REGENERATION PACKAGE
Reference P&IDs: BLK18-GP-K-PR-PID-320000, 320100 + VENDOR P&ID’S BPAABL18-C-0001, 0002, 0003, 0004, 0005, 0006, 0007.
The Glycol dehydration equipment is located between the MP and HP compression
trains and its function is to remove any water carried forward with the gas stream prior
to HP compression. The glycol contactor mixes lean glycol with the gas stream in a
counter-current packed column where the glycol absorbs the water. The dry gas exits
to the HP compressor and the rich glycol is routed to the regeneration package where
the water is removed, ready for re-use. The regeneration package is supplied as
process hardware complete with instrumentation wired to skid edge junction boxes.
Although this is a package, it will be controlled by the PCS and PSS as if the
equipment was part of the normal topsides process equipment.
As with most of the process systems, the control is very straightforward with most
loops being standard indicators and PID control loops. The requirements for the PSS
logic for the glycol system are defined in the PSS cause and effects diagrams.
The Glycol Contactor Suction Scrubber has two vertical sections, each with level
control, LIC 320007 for the upper section and LIC 320008 for the lower section. Both
controllers are differential gap type providing on/off control to their control valves. The
high and low control points shall be set 5% below and 5% above the high and low
alarm settings, although this figure may require to be adjusted during commissioning.
Because there is only one Glycol Contactor System, it is considered appropriate to
provide an installed spare for level control valves LV 320007A and LV 320007B and a
piping installation that allows maintenance of the standby valve without the necessity
to shutdown the system.
Thus LIC 320007 has two control valve outputs, one to LV 320007A and the other to
LV 320007B, both are 100% capacity valves. Under normal operation one valve will
be operating whilst the other is on standby. A software selector switch, HS 320007 will
be provided to allow the operator to select the duty valve. The standby valve shall be
provided with a “low” signal to keep the valve closed and the duty valve will receive the
normal control signal output.
The same arrangement is required for LIC 320008 and its two control valves,
LV320008A and LV 32008B; the software selector switch is HS 320008.
Similarly for LIC 320022, controlling the level of the Glycol Contactor V-32002 and its
two control valves, LV 320022A and LV 320022B; the software selector switch is HS
320022. LIC 320022 is however a normal PID controller, not a differential gap type as
for the previous controllers.
Finally the same arrangement is required for LIC 320522, controlling the Glycol Flash
Drum V-32006 within the package vendors supplied equipment and its two control
valves, LV 320522A and LV 320522B; the software selector switch is HS 320522. LIC
320522 is also a normal PID controller, not a differential gap type.
The gas inlet to the Glycol Contactor V-32002 has an on / off motor operated valve,
MOV 320050. This is a standard foundation fieldbus type with remote open and close
facilities from the PCS workstation with position feedback and diagnostics provided as
inputs to the PCS.
The Glycol Contactor V 32002 has temperature indicators for the main process gas
inlet, TI 320012 and the glycol stream from the regeneration package, TI 320023. In
BLK18-GP-K-IN-SPE-0101
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addition, TDI 320055 calculates and displays the differential temperature between
these signals. This allows the operator to adjust process parameters to achieve the
optimum differential temperatures for process operation. TDI 320055 is calculated as
TI 320023 minus TI 320012 = TDI 320055.
The gas outlet from the Glycol Contactor has a corrosion monitor CI 320048 which is a
standard type as described in section 3.9.
Within the Glycol Regeneration Package, LIC 320522 is a normal PID controller but
also requires two identical outputs to control valves LV 320522A and LV 320522B as
previously described. The software switch in this application is HS 320522.
The Glycol Reboiler V-32003 is supplied with three installed electrical heating bundles
EEH 32001 A/B/C, each rated at 400 kW. Two of the heaters are normally operating
and the third is spare.
The heat output from each of the on-line heaters is regulated by TIC 320581, this
provides 3 separate, but identical controller output, 4-20mA signals to the thyristor
control panel, one for each heater bank.
The following additional interfaces to the thyristor control panel are required for heater
banks EEH 32001 A, B & C respectively:

HS 320676 A, B, C – PCS Digital Output, Heater Start / Heater Stop. 24 V dc,
powered from PCS. Output energised = start heater, Output de-energised =
Stop Heater

XI 320685 A, B, C – PCS Digital Input, Heater Running / Stopped. 24 V dc,
powered from PCS. Contact maintained open = Heater Stopped, Contact
maintained closed = Heater Running

XI 320687 A, B, C – PCS Digital Input, Local Control / Remote (PCS) Control.
24 V dc, powered from PCS. Contact maintained open = Local Control,
Contact maintained closed = Remote Control

XA 320684 A, B, C - PCS Digital Input, Healthy / Fault. 24 V dc, powered from
PCS. Contact maintained closed = Healthy, Contact maintained open = Fault

XI 320686 A, B, C - PCS Digital Input, Heater Duty, On / Standby. 24 V dc,
powered from PCS. Contact maintained closed = Heater On Duty, Contact
maintained open = Heater On Standby

XA 320683 A, B, C - PCS Digital Input, Heater Element High Temperature
Alarm. 24 V dc, powered from PCS. Contact maintained closed = Healthy,
Contact maintained open = Heater Element Temperature High
The Glycol Recirculation Pumps P-32001 A and P-32001 B are 2 x 100% positive
displacement type configured as duty and standby, however they do not require auto
start and will be started manually by the operator. If the duty pump stops without being
requested, the alarm generated will prompt the operator to start the standby pump.
Each pump is physically located in an individual acoustic enclosure and requires the
associated cooling fan to run whenever the pump is running.
The cooling fans will have the same serial interface signals to the motor switchboard
as is depicted for pump typical number 24. This will be start / stop, running / stopped,
available / not-available as well as a hard wired shutdown trip from the PSS.
BLK18-GP-K-IN-SPE-0101
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To avoid operator errors the pump shall be inhibited from starting until its associated
cooling fan “motor running” signal is received from the motor switchboard via the serial
link.

for pump P-32001A, the running signal from K-32001 shall remove the start
inhibit.

for pump P-32001B, the running signal from K-32002 shall remove the start
inhibit.
Stopping the pump shall not be inhibited since it does not matter if the fan continues to
run with the pump stopped. The fan will be stopped when required by the operator.
If a pump is required to be shutdown then the associated fan shall also be shutdown,
this will be reflected in the PSS cause and effects charts.
The Vent Condenser KO Drum Water Pumps P-32006 A and P-32006 B are 2 x 100%
units configured as duty and standby.
The pumps are controlled by level controller LIC 320525 on the Vent Condenser KO
Drum. This shall be configured for On / Off differential gap control. It shall start the
pump on high level (set 5% below the high alarm setting) and stop the pump on low
level (set 5% above the low alarm setting). Thus normal start and stop of the pumps
shall not initiate alarms, this will only occur if the pump fails to start or stop.
The duty pump is selected by the operator via software switch HS 320577; this routes
the serial link on / off control signals to the selected motor at the switchboard. If the
duty pump stops without being requested or a level alarm trip point is reached, the
alarm generated will prompt the operator to change to the standby pump if appropriate.
The Glycol Transfer Pump P32002, the Glycol Sump Pump P-32003, the pH Chemical
Injection Pump P-32004 and the Antifoam Chemical Injection Pump P-32005 are all
100% duty, single pumps with manual start / stop as described in section 3.6.
When a shutdown occurs that closes a shutdown valve, it is a requirement to put any
PID control loops in the same process line into manual and close its control valves
(see section 3.2). The table below lists the control loops and valves that are applicable
to this requirement for the Glycol System.
Controller Shutdown Action – Glycol System
SHUTDOWN
VALVE
CONTROLLER
CONTROL
VALVE
XV 320009
LIC 320007
LV 320007A
Two control valves – duty &
standby
XV 320009
LIC 320007
LV 320007B
Two control valves – duty &
standby
XV 320010
LIC 320008
LV 320008A
Two control valves – duty &
standby
XV 320010
LIC 320008
LV 320008B
Two control valves – duty &
standby
XV 320019
LIC 320022
LV 320022A
Two control valves – duty &
standby
BLK18-GP-K-IN-SPE-0101
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XV 320019
LIC 320022
LV 320022B
Two control valves – duty &
standby
XV 320026
PIC 850001A
PV 850001A
Two control valves – duty &
standby (see section 31)
XV 320026
PIC 850001B
PV 850001B
Two control valves – duty &
standby (see section 31)
BLK18-GP-K-IN-SPE-0101
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18.0
GAS INJECTION
Reference P&IDs: BLK18-GP-K-PR-PID-340000
The instrument loops for this system are generally standard types that need no further
explanation other than the P&ID and ICS I/O schedule.
The water in oil transmitter AT 340069 provides a 4-20mA linear signal to the PCS.
The associated high moisture content alarm provides the operator with a warning to
avoid any significant water carry over that could lead to hydrate formation and possible
blocking in the downstream subsea pipework.
The gas flow is measured by an orifice plate; the flow differential pressure transmitter
FIT 340009 will provide the required square root extraction, providing a linear signal to
the PCS. The PCS shall display rate of flow indication plus a digital flow totaliser. The
number of totalised digits shall be set to allow continued accumulation without rollover
for approximately 3 months operation. Manual reset to zero of the totalised figure shall
be provided from the operator station, but only at the supervisor level.
The temperature transmitter TIT 340071 initiates an ESD shutdown and shall therefore
be directly connected to the ESD system with the analogue indicator signal and the
high high trip alarm repeated to the PCS.
BLK18-GP-K-IN-SPE-0101
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19.0
RISER BASE GAS LIFT
Reference P&IDs: BLK18-GP-K-PR-PID-340100
As for the Gas Injection System, the instrument loops for this system are generally
standard types that need no further explanation other than the P&ID and ICS I/O
schedule.
The gas flow to the three risers are measured and controlled utilising ultrasonic flow
transmitters, FT 331064, FT 331065 and FT 340066 that provide linear signals to the
PCS. In addition to the flow controllers, the PCS shall provide digital flow totalisers for
each of the flow control loops. The number of totalised digits shall be set to allow
continued accumulation without rollover for approximately 3 months operation. Manual
reset to zero of the totalised figure shall be provided from the operator station, but only
at the supervisor level.
Temperature transmitters TIT 331069, TIT 331070 and TIT 340026 initiate ESD
shutdown and shall therefore be directly connected to the ESD system with the
analogue indicator signals and the high high trip alarms repeated to the PCS.
Temperature indicator TI 340070 utilises a Foundation Fieldbus, surface mounted
temperature transmitter and provides a low low temperature shutdown as defined in
the PSS cause and effect diagrams. The transmitter will be connected to the PSS and
the indicator and alarm signals repeated to the PCS as usual.
When a shutdown occurs that closes a shutdown valve, it is a requirement to put any
PID control loops in the same process line into manual and close its control valves
(see section 3.2). The table below lists the control loops and valves that are applicable
to this requirement for the Riser Base Gas Lift system.
Controller Shutdown Action – Riser Base Gas Lift System
SHUTDOWN
VALVE
CONTROLLER
CONTROL
VALVE
XV 340027
FIC 331064
FV 331064
XV 340028
FIC 341065
LV 331065
XV 340029
FIC 340066
LV 340066
BLK18-GP-K-IN-SPE-0101
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20.0
HP FLARE KO DRUM AND PUMPS
Reference P&IDs: BLK18-GP-K-PR-PID-510100, 520100, Vendor Drawing BPAABL18-PME11A-C0401 (V 14992)
The HP Flare system collects gas and liquids from the HP flare wet and dry flare
headers which flow into HP Flare KO Drum V 51001. This has a large capacity
allowing liquids to accumulate and separate from the hydrocarbon vapours. The
liquids are pumped from the drum to the LP Separator or the marine off-spec header /
diesel oil displacement tank T-93500, with the vapours routed to the HP flare.
Under normal operational conditions, the vapour is not actually routed to the flare stack
and burnt, but is instead routed to the suction of the 1st Stage LP Compressor.
In order to stop the vapour from entering the flare stack, a fast opening valve (FOV)
closes off the pipe. This valve and a similar valve on the LP Flare, together with the
Vapour Recovery Compressors are part of a package from ABB. The fast opening
valve is controlled by a PLC included with the package and is opened in less than 2
seconds if the pressure in the flare line exceeds the high pressure trip point of PI
510030. This transmitter is directly connected to the PLC and is repeated via serial
link to the PCS for operator display, together with the high pressure trip alarm.
If the flow rate to the HP flare header exceeds the capacity of the 1st Stage LP
Compressor or if the compressor shuts down, it is critical that the FOV opens as
required to allow the gas an open path to the HP flare. To provide additional integrity
for opening the FOV when required, a second, independent pressure transmitter is
provided for PI 510031, which is an input to the ESD system. With a slightly higher trip
pressure, it will also open the FOV if the PLC trip fails to open the valve. The FOV is
supplied with two solenoid valves, one driven by the PLC, the other by the ESD
system.
Under flaring conditions it is necessary to monitor the rate of flow and the total flow
that is released to the HP flare stack. This is measured with a special ultrasonic flare
flow meter complete with flow computer, FI 510002. The flow computer carries out
pressure correction from PIT 510001 and temperature correction from TIT 510003 and
transmits the standardised flow rate to the PCS.
Although nitrogen is purged into the flare under normal operation to avoid air back
flowing down the stack, the injection point is downstream of the flow meter, thus under
normal operation there is no flow registered by the flare meter.
The flow rate indicator FI 510002 requires a high flow alarm, although this will be set at
1% of the flow indicator range and its primary function is to monitor for a small leakage
past the bursting disc, without full failure of the disc. In addition however it will provide
a secondary function, which will advise the operator that flaring has been initiated.
The PCS shall use the standardised flow rate for FQI 510002 to provide a rate of flow
indicator plus a digital flow totaliser. The number of totalised digits shall be set to allow
continued accumulation without rollover for in excess of 12 months operation. Manual
reset to zero of the totalised figure shall be provided from the operator station, but only
at the supervisor level.
The HP Flare KO Drum Pumps, P-51001A and P-51001B take suction from the flare
drum and re-inject the liquids to the LP Separator. The pumps shall be configured as
typical type 26, which operate on a duty / assist basis with the normal signals as
defined in section 3.6.
BLK18-GP-K-IN-SPE-0101
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The pumps will normally be in the auto state with starting and stopping controlled by
level controller LIC 510028. The first pump set to auto will be the first duty pump, the
second pump when put to auto will be the assist pump. LIC 510028 does not act as a
normal PID controller but provides a number of trip points which will not be adjustable
by the operator. In order to define the requirements, a number of typical operating
scenarios will be described.
1. Initial situation, both pumps stopped, liquid level normal and rising. Level rises
until level H1 is reached; this starts the duty pump, no alarm. Level begins to
fall until it reaches L1, this stops the duty pump, no alarm
2. From the same starting point as (1), but with a liquid flow into the flare drum
that exceeds the capacity of a single pump. Level rises until H1 is reached,
this starts the duty pump, no alarm. Level continues to rise, although at a
slower rate. Level reaches H2, duty assist pump is started, no alarm, level
starts to fall. Level reaches L1, both pumps stop, no alarm.
3. Again from the same starting point, level rising, at H1 duty pump starts, level
continues to rise, at H2 duty assist starts but level still continues to rise. This
may be because one or both pumps fail to start, which result in fail to start
alarms as normal. Or it may be because of a physical problem such as a
blockage, or flow rate into the drum exceeds the capacity of two pumps.
Whatever the cause, the level continues to rise reaching a 3rd high trip point H3
that initiates a high level alarm, H3 is therefore the high alarm level.
4. With a different starting condition, level dropping one or both pumps running.
At L1 running pump(s) should stop, but actually continue to run. Level
continues to fall until a lower trip point is reached L2, which initiates a low level
alarm, L2 is therefore the low level alarm
The above description is for normal level control in the HP Flare Drum, however if an
extended production shutdown occurs on the facility, it is necessary to displace the
production oil because it will cool and may deposit wax and become excessively
viscous. In this situation, known as “flowline displacement mode” the HP Flare Drum
will be utilised in an alternative process role and the level control will be changed from
the normal system described above.
When the alternative functionally is required, the level control function is switched to
LIC 510035 which instead of acting on the pumps, will act upon control valve LV
510035; this controller will have normal PID control algorithms. The level control is
switched by software switch HS 510035 on the operator workstation. Under flowline
displacement mode, pumps P 51001A and P 51001B are switched to manual and off
by the operator. Only the duty controllers, alarms and trips shall be active, the non
duty controller’s alarms and trips shall be inhibited; this shall be based on the selector
switch status.
When in normal operation each of the pumps is provided with its own low low flow trip
based on orifice plate flow measurements with square root linearisation carried out in
the transmitter. The flow transmitter will be connected to the PSS and the shutdown
requirements will be as defined in the PSS cause and effects diagrams. The flow rate
signal and the low low trip alarm shall be repeated to PCS which will use the signal to
display a flow indicator together with a low flow pre alarm. For Pump P 51001A the
flow indicator is FI 510014 and for Pump P 51001B the flow indicator is FI 510013.
The pumps will both be in auto, but not running for part of the time under normal
operation. To avoid repeated low and low low flow alarms and shutdowns, the
automatic overrides described in section 3.6 shall be applied to both FI 510013 and FI
510014.
BLK18-GP-K-IN-SPE-0101
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The pumps are provided with pressurised seals as described in section 3.6.8, the
instrument tag numbers are detailed below:
For Pump P 51001A : PI 510500 and LI 510503.
For Pump P 51001B : PI 510510 and LI 510513.
The HP Flare Drum has additional level transmitters that provide shutdowns as defined
in the PSS cause and effect diagrams.
Level indicator LI 510043 provides a low low level trip to protect the pumps and is
therefore connected to the PSS. The level indicator and low low trip alarm shall be
repeated to the PCS as normal.
High high level in the HP Flare KO Drum is a significant shutdown action that causes a
production shutdown. To avoid this action occurring from a spurious condition, three
independent level transmitters, LI 51017, LI 510018, LI 510024, are installed and
connected to the PSS. As defined in the PSS cause and effect diagrams, the high
high level trips derived from these transmitter signals are voted on a two out of three
(2oo3) basis. Each transmitter signal and the alarms are repeated as normal to the
PCS with each transmitter providing a separate indicator.
The HP Flare KO drum is provided with two heaters, EEH 51001A and EEH 51001B
that are controlled by TIC 510022 and which is configured to provide differential gap
control (it does not have an analogue output). At the defined high temperature control
point both heaters are switched off and at the low temperature control point both
heaters are switched on; these actions do not cause alarms. Each heater has the
same set of serial link signals to the switchboard as for a pump, i.e. start, stop,
running/stopped, available/not-available, for clarity the tag numbers are listed below
(see section 3.6 for further explanation).
EEH-51001A:

Start – HST 510022A

Stop – HSP 51022A

Running / Stopped – XI 510022A

Available / Stopped – XA 510022A
EEH-51001B:

Start – HST 510022B

Stop – HSP 51022B

Running / Stopped – XI 510022B

Available / Stopped – XA 510022B
If the heater fails to switch off or switch on, the high or low temperature alarms may be
initiated, although because of the high ambient temperature expected off the coast of
Africa, the low temperature alarm is unlikely to be initiated under normal operating
conditions.
A high high and low low temperature shutdown is provided by TI 510020 as defined by
the PSS cause and effects diagrams. The shutdown signal is connected to the PSS
BLK18-GP-K-IN-SPE-0101
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and the indicator and High high and low low shutdown alarms are repeated to the PCS
as normal.
When a shutdown occurs that closes a shutdown valve, it is a requirement to put any
PID control loops in the same process line into manual and close its control valves
(see section 3.2). The table below lists the control loops and valves that are applicable
to this requirement for the HP Flare KO Drum and Pumps system.
Controller Shutdown Action – HP Flare KO Drum and Pumps system
SHUTDOWN
VALVE
CONTROLLER
CONTROL
VALVE
XV 510034
LIC 510035
LV 510035
BLK18-GP-K-IN-SPE-0101
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21.0
LP FLARE KO DRUM AND PUMPS
Reference P&IDs: BLK18-GP-K-PR-PID-520100, 510200, Vendor Drawing BPAABL18-PME11A-C0401 (V 14992)
The LP Flare system collects gas and liquids from the closed drains and the LP flare
header which flow into LP Flare KO Drum V 52001. This has a large capacity allowing
liquids to accumulate and separate from the hydrocarbon vapours. The liquids are
pumped from the drum to the LP Separator and the vapours are routed to the LP flare.
Under normal operational conditions, the vapour is not actually routed to the flare stack
and burnt, but is instead connected to the suction of the Vapour Recovery
Compressors C 55001A & B which raises the pressure until it can form part of the
suction flow to the 1st Stage LP Compressor.
In order to stop the vapour from entering the flare stack, a fast opening valve closes off
the pipe. This valve and the vapour recovery compressors are part of a package from
ABB. The fast opening valve is controlled by a PLC included with the package and is
opened in less than 2 seconds if the pressure in the flare line exceeds the high
pressure trip point of PI 510020. This transmitter is directly connected to the PLC and
is repeated via serial link to the PCS for operator display, together with the high
pressure trip alarm.
If the flow rate to the LP flare header exceeds the capacity of the Vapour Recovery
Compressor or if the compressor shuts down, it is critical that the fast opening valve
(FOV) opens as required to allow the gas an open path to the LP flare. To provide
additional integrity for opening the FOV when required, a second, independent
pressure transmitter, PI 520021 is provided, which is an input to the ESD system.
With a slightly higher trip pressure, it will also open the FOV if the PLC trip fails to open
the valve. The FOV is supplied with two solenoid valves, one controlled by the PLC,
the other by the ESD system.
Under flaring conditions it is necessary to monitor the rate of flow and the total flow
that is released to the LP flare stack. This is measured with a special ultrasonic flare
flow meter complete with flow computer, FI 520001. The flow computer carries out
pressure correction from PIT 520029 and temperature correction from TIT 520030 and
transmits the standardised flow rate to the PCS.
Although nitrogen is purged into the flare under normal operation to avoid air back
flowing down the stack, the injection point is downstream of the flow meter, thus under
normal operation there is no flow registered by the flare meter.
The flow rate indicator FI 520001 requires a high flow alarm, although this will be set at
1% of the flow indicator range and its primary function is to monitor for a small leakage
past the bursting disc, without full failure of the disc. In addition however it will provide
a secondary function, which will advise the operator that flaring has been initiated.
The LP Flare KO Drum Pumps, P-52001A and P-52001B take suction from the flare
drum and re-inject the liquids to the LP Separator. The pumps shall be configured as
typical type 26, which operate on a duty / assist basis with the normal signals defined
in section 3.6.
The pumps will normally be in the auto state with starting and stopping controlled by
level controller LIC 520026. The first pump set to auto will be the first duty pump, the
second pump when put to auto will be the assist pump. LIC 520026 does not act as a
normal PID controller but provides a number of trip points which will not be adjustable
by the operator. In order to define the requirements, a number of typical operating
scenarios will be described.
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1. Initial situation, both pumps stopped, liquid level normal and rising. Level rises
until level H1 is reached; this starts the duty pump, no alarm. Level begins to
fall until it reaches L1, this stops the duty pump, no alarm
2. From the same starting point as (1), but with a liquid flow into the flare drum
that exceeds the capacity of a single pump. Level rises until H1 is reached,
this starts the duty pump, no alarm. Level continues to rise, although at a
slower rate. Level reaches H2, duty assist pump is started, no alarm, level
starts to fall. Level reaches L1, both pumps stop, no alarm.
3. Again from the same starting point, level rising, at H1 duty pump starts, level
continues to rise, at H2 duty assist starts but level still continues to rise. This
may be because one or both pumps fail to start, which result in fail to start
alarms as normal. Or it may be because of a physical problem such as a
blockage, or flow rate into the drum exceeds the capacity of two pumps.
Whatever the cause, the level continues to rise reaching a 3rd high trip point H3
that initiates a high level alarm, H3 is therefore the high alarm level.
4. With a different starting condition, level dropping one or both pumps running.
At L1 running pump(s) should stop, but actually continue to run. Level
continues to fall until a lower trip point is reached L2, which initiates a low level
alarm, L2 is therefore the low alarm level.
The LP Flare Drum has additional level transmitters that provide level shutdowns as
defined in the PSS cause and effect diagrams.
Level indicator LI 520032 provides a low low level trip to protect the pumps and is
therefore connected to the PSS. The level indicator and low low trip alarm shall be
repeated to the PCS as normal.
High high level in the LP Flare KO Drum is a significant shutdown action that causes a
production shutdown. To avoid this action occurring from a spurious condition, three
independent level transmitters, LI 520010, LI 520016, LI 520018, are installed and
connected to the PSS. As defined in the PSS cause and effect diagrams, the high
high level trips derived from these transmitter signals are voted on a two out of three
(2oo3) basis. Each transmitter signal and the alarms are repeated as normal to the
PCS with each transmitter providing a separate indicator.
Each of the pumps is provided with its own low low flow trip based on orifice plate flow
measurements with square root linearisation carried out in the transmitter. The flow
transmitter will be connected to the PSS and the shutdown requirements will be as
defined in the PSS cause and effects diagrams. The flow rate signal and the low low
flow trip alarm shall be repeated to PCS which will use the signal to display a flow
indicator together with a low flow pre alarm. For Pump P 52001A the flow indicator is
FI 520003 and for Pump P 52001B the flow indicator is FI 520011.
The pumps will both be in auto, but not running for part of the time under normal
operation. To avoid repeated low and low low alarms and shutdowns, the automatic
overrides described in section 3.6 shall be applied to both FI 520003 and FI 520011.
The pumps are provided with pressurised seals as described in section 3.6.8, the
instrument tag numbers are detailed below:
For Pump P 52001A : PI 520500 and LI 520503.
For Pump P 52001B : PI 520510 and LI 520513.
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21.1
Vapour recovery package
Reference P&IDs: BLK18-GP-K-PR-PID-550000
As noted above, the vapour recovery package, which also includes control of the fast
opening flare line blocking valves and the flare ignition system, are all controlled by a
PLC located in the vendors control panel.
The control panel provides hard wired shutdown signals to the PSS and ESD systems
that interact with the shutdown logic as defined in the cause and effect diagrams. In
addition it provides a dual serial link to the PCS for the display of the package status
signals, together with a number of operator remote controls:

A software switch on the PCS workstation that allows the operator to manually
initiate flare ignition: HST 550407
The vapour recovery compressors can operate in different modes depending on the
suction gas source, each with their own dedicated package logic start and stop. The
vapour recovery package logic responds to these inputs to automatically start or stop
the machines and open or close the appropriate valves to suit the mode selected:

Start with gas suction from flare recovery: HST 550404

Stop with gas suction from flare recovery: HSP 550404

Start with gas suction from marine tank blanketing: HST 550405

Stop with gas suction from marine tank blanketing: HSP 550405

Start with gas suction from both flare recovery and marine tank blanketing:
HST 550406

Stop with gas suction from both flare recovery and marine tank blanketing:
HSP 550406
The custom graphics that will be developed to provide the operator interface will
include the required VDU software switches to enable these limited package
operations to be initiated from the control room.
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22.0
PRODUCED WATER TREATMENT SYSTEM
Reference P&IDs: BLK18-GP-K-PR-PID-400001, 400002, 400003, 400004 + Package
Vendors Operating Manual BPAA-BL18-PME22A R-0002 (L295-H-001)
The produced water system consists of normal process equipment with
instrumentation controlled by the ICS and package unit equipment, complete with
instrumentation that is wired to skid mounted junction boxes. For these packages, the
instrumentation is also controlled by the ICS, there are no package control panels.
The following valves that are included in the vendors package are required to be
shutdown by the PSS, the outputs to the solenoid valves for these valves will therefore
be from the PSS: XV 280527, XV 280528, XV 280529, XV 280530 XV 280533.
The remaining package on / off valves are not required to be shutdown by the PSS
and will therefore have the solenoid valve output from the PCS.
Package Vendors HP Separator Hydrocyclone
Reference Vendors P&IDs: BPAA-BL18-PME22A C-0001 (L295-K-001) & Cause and
Effect Diagram BPAA-BL18-PME22A C-0062 (L295-J-752)
This P&ID includes control valves LV 220002A and LV 220002B which are configured
as a duty and installed spare to allow maintenance or removal without requiring a
shutdown of the equipment. These valves are controlled by LIC 220002 on the HP
Separator. See the HP Separator section for more details.
The reject valve XV 410508 and the backwash valve XV 410509 are Type 30 on / off
valves. Although these can be opened and closed by the operator, there is a
requirement for a timed automatic opening and closing of the valves to facilitate
backwashing of the process equipment. Under normal operation, XV 410508 is open
and XV 410509 is closed. Every 12 hours this is required to be reversed so that XV
410509 is opened and then XV 410508 is closed. This produces the required
backwash and after one minute the valves shall be returned to the previous normal
state.
Additionally there is also a requirement that:

If XV 410508 is opened, then XV 410509 is closed and

If XV 410509 is opened, then XV 410508 is closed
The sequence of opening and closing should be such that both valves cannot be
closed at the same time, so a closed valve shall be opened before the other is closed.
The operator shall not be able to override this requirement.
Control for the hydrocyclone is achieved by a ratio controller PDIC 410052 that adjusts
control valve PDV 410502 to control the ratio of differential pressures between the inlet
and outlet and the inlet and reject streams from the hydrocyclone. PDI 410501 and
PDI 410502 provide indication and high and low alarms for monitoring the individual
differential pressures. The package vendors operating manual provides further details.
Package Vendors Sand Removal Hydrocyclone
Reference Vendors P&IDs: BPAA-BL18-PME22A C-0002 (L295-K-002) & Cause and
Effect Diagram BPAA-BL18-PME22A C-0063 (L295-J-753)
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The Sand removal Hydrocyclone needs little explanation, although it should be noted
that the sand level alarm in the hydrocyclone is measured by a level switch LSH
412502 for V-41202A and LSH 412503 for V-41202B, they will therefore require digital
inputs.
XV 412513 is a type 30 manual on / off valve controlled by the operator and as noted
above, is not shutdown by the PSS, so the output to its solenoid valve will be from the
PCS. A further requirement for this valve is that if it is opened it is required to inhibit
the opening of valve XV 280528 (see sandwash hydrocyclone description following).
Package Vendors Sandwash Hydrocyclone
Reference Vendors P&IDs: BPAA-BL18-PME22A C-0031 (L295-K-003) & Cause and
Effect Diagram BPAA-BL18-PME22A C-0061 (L295-J-751)
This system requires more explanation than the other parts of the package and
includes a number of valves that require shutdown by the PSS. As normal, if the PSS
logic requires a shutdown for a valve, the “valve logic” in the PCS will be locked into
“local override”, the faceplate set to manual, the output set to close and the open /
close push buttons “greyed out” and made inoperable. The requirements for these
shutdowns are detailed in the PSS cause and effects diagrams and are supplemented
in the vendors cause and effects.
It should be noted that a number of inputs from this part of the package are derived
from process switches and will therefore require digital inputs.
The Sand Jetting Pump P 28001 is a manual start only pump with the normal group of
interfaces with the switchboard, HS 280546, as described in section 3.6. The pump is
shutdown in accordance with the PSS cause and effects diagrams.
The pump discharge valve XV 280527 is shutdown as required by the PSS cause and
effects and shall also be closed by the PCS if P 28001 is stopped. This will not be a
shutdown, but the signal shall be internally interfaced from the PCS to the PSS.
Valve XV 280527 shall additionally be inhibited from opening if XV 280528, or XV
280531 or XV 280532 are open.
Valve XV 280528 is shutdown as required by the PSS cause and effects and shall also
be closed by the PCS if P 28001 is stopped. This will also not be a shutdown, but the
signal shall be internally interfaced from the PCS to the PSS.
Valve XV 280528 shall additionally be inhibited from opening if XV 280527, or XV
280529 or XV 280530 or XV 412513 are open.
Valve XV 280529 is shutdown as required by the PSS cause and effects.
Valve XV 280529 shall additionally be inhibited from opening if XV 280528, or XV
280530 or XV 280531 or XV 280532 are open.
Valve XV 280530 is shutdown as required by the PSS cause and effects.
Valve XV 280530 shall additionally be inhibited from opening if XV 280528, or XV
280529 or XV 280531 or XV 280532 are open.
Valve XV 280531 is not shutdown by the PSS, but shall be closed if XV 280528 is
closed. Additionally it shall be inhibited from opening if XV 280529, or XV 280530 or
XV 280532 are open.
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Valve XV 280532 is not shutdown by the PSS, but shall be closed if XV 280528 is
closed. Additionally it shall be inhibited from opening if XV 280529, or XV 280530 or
XV 280531 are open.
Valve XV 280533 is shutdown by the PSS but is otherwise not inhibited in its operation
by the operator.
Valve XV 280534 is not shutdown by the PSS, however when it is opened controller
PDIC 280505 shall be set to manual and the control valve output to PDV 280505 shall
be closed.
Control for the Water / Oil Separator Hydrocyclone V-28003 is achieved by a ratio
controller PDIC 280505 that adjusts control valve PDV 280505 to control the ratio of
differential pressures between the inlet and water outlet and the inlet and oil outlet
streams from the hydrocyclone. Although not shown on the vendors P&ID, to be
consistent with similar control loops for these packages, separate indicators shall also
be provided on the operator display for the actual differential pressures as well as the
ratio that will be displayed on the PDIC display. The tag numbers for these indicators
shall be PDI 280504 and PDI 280505. The package vendors operating manual
provides further details.
The remaining part of this section describes the equipment that is not part of the
vendor package.
The software switch HS 220002 is already described in the HP Separator section and
is used to select which of the control valves LV 220002A or LV 220002B is in service
and which is closed.
Flow transmitter FIT 220055 is a Foundation Fieldbus electromagnetic type that
provides a linear signal to FQI 220055. This provides the rate of flow indicator plus a
digital flow totaliser. The number of totalised digits shall be set to allow continued
accumulation without rollover for approximately 3 months operation. Manual reset to
zero of the totalised figure shall be provided from the operator station, but only at the
supervisor level.
The produced water is cooled by the Produced Water Coolers X-41201A and X41201B under the control of TIC 412001 which regulates the flow of cooling seawater
through the heat exchangers. Both of the coolers are normally operational, so the
controller requires two control outputs, each with the same control signal for the two
control valves TV 412001A and TV 412001B. In addition there is a requirement that
these two valves shall never be completely closed in operation and a limit shall be set
on the controller output to each valve so that each may not be fully closed.
The valves have actuators that fail open on loss of air, the controller outputs shall
therefore have a limit set so that it cannot be increased above 18mA under automatic
or manual control. The value of this limit will be checked and modified to the exact
requirement during commissioning.
Flow transmitter FIT 412014 is a ultrasonic type that provides a linear signal to FQI
412014. This provides the rate of flow indicator plus a digital flow totaliser. The
number of totalised digits shall be set to allow continued accumulation without rollover
for approximately 3 months operation. Manual reset to zero of the totalised figure shall
be provided from the operator station, but only at the supervisor level.
The quality of the produced water is monitored by AI 412015 which measures the
residual oil in the produced water stream. If the oil level is below the permitted level,
the water may be dumped overboard via PV 412016B. If the oil contamination
exceeds the permitted level then the operator is warned by the analyser alarm and the
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flow of produced water can be diverted to the Off-Spec Produced Water Tank via PV
412016A. The pressure controller PIC 412016 has two outputs, one for each valve.
To allow the operator to choose which route the water will follow, a software selector
switch HS 412016 shall be provided. The selected route will receive the normal control
signal to the selected valve and the valve for the non selected route will receive a 4mA
signal from the controller to close it.
It should be noted that under normal operation, with the water injection equipment
operating, all produced water is passed to the suction of the Water Injection Pumps. In
this scenario, the pressure is maintained below the set point of PIC 412016 by the
combined action of the suction of the injection pumps and PIC 442030. The output of
PIC 412016 will therefore be such that both PV 412016 A & B will be closed.
The level in the Produced Water Degasser V-41201 is controlled by LIC 412012 which
has two control outputs to control valves LV 412012A and LV 412012B. Under normal
operation one valve will be operating whilst the other is on standby. A software
selector switch, HS 412012 will be provided to allow the operator to select the duty
valve. The standby valve shall be provided with a 4mA signal to keep the valve closed
and the duty valve will receive the normal control signal output.
Produced water from the Produced Water Degasser Drum is Pumped by the Produced
Water Transfer Pumps to the Produced Water Sand Removal Package. The
Produced Water Transfer Pumps P-41201A, P-41201B and P-41201C are 3 x 50%
pumps configured as duty, duty and standby, with auto start of the standby pump
required. Section 3.6 provides further details of pump requirements including auto
start, start up overrides and alarm suppression.
The Produced Water Transfer Pump motor enclosures potentially could contain
flammable hydrocarbons. Although the hazardous area certification for the pump
motors is suitable for their location, as an added precaution it is required to air purge
the enclosure before the pump is started.
However because of the short process vessel hold up time available, it is not possible
to delay the start of the standby pump for the 6 minutes purge period, as is the case
for the Flowline Displacement Pumps previously described.
To overcome this problem, it is intended to provide each pump with a continuous small
volume air purge with the rate set by a restriction orifice. This should ensure that the
enclosure will be slightly pressurised and therefore stop any flammable gas from
entering. If the pumps have been out of service for some time however, with the air
purge shut off, e.g. for maintenance, it is possible that gas may have entered the
enclosure. In this situation it will be necessary to carry out the 6 minute higher volume
purge prior to starting any of the pumps.
It is required that this 6 minute purge be carried out automatically when appropriate.
The criteria to be used by the PCS to initiate this requirement shall be that all three
pump not running signals have been present for more than 30 minutes. When this
occurs AND the operator tries to start any of the three pumps, the PCS will not
immediately start the pump, but shall initially de-energise the three digital outputs that
will open the air purge shutoff solenoid valves to initiate the purge cycle. At the same
time it will inhibit the start of all three pumps, this shall “grey out” the start pushbutton
on the three pump faceplates to indicate to the operator that the pump cannot be
started.
The initiation of any of the pumps start pushbuttons shall additionally starts a timer that
maintains the three purge valve outputs in the de-energised state for the required 6
minutes purge time. It will then close the purge valves by re-energising the digital
outputs and automatically initiate the start signal for the originally selected pump via
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the motor switchboard serial link. To avoid the purge timer delay interfering with the
normal alarm and shutdown inhibits described in section 3.6.7, the separate timer that
removes the alarm and shutdown inhibits shall be linked to the actual starting signal to
the pump switchboard, rather than the initiation of the start pushbutton from the
workstation that is normally used.
At the end of the purge period, the first pump is automatically started and the other two
are both fully purged and ready to be started or be put to standby by the operator.
The digital outputs to the purge solenoid valves are:

For P-41201A the purge solenoid valve output is PV 804029

For P-41201B the purge solenoid valve output is PV 804032

For P-41201C the purge solenoid valve output is PV 804035
The digital outputs are 24Vdc signals powered by the PCS.
Each of the pumps is provided with its own minimum flow bypass controller based on
orifice plate flow measurements with square root linearisation carried out in the
transmitter. Pump P-41201A has flow controller FIC 412005, P-41201B has flow
controller FIC 412007 and P-41201C has flow controller FIC 412009.
Under normal conditions flow from the pump exceeds the minimum flow and the
controller maintains the bypass control valve closed. If a fault occurs in the process
system causing the flow to drop below the bypass controller’s set point, then it opens
the control valve, returning the flow to the Produced Water Degasser and maintaining
flow through the pump at its minimum safe flowrate. If the process fault condition is
such that it cannot meet the minimum flow requirement of the pump, then a low flow
alarm shall be initiated to warn the operator.
If the pump discharge flow drops below the low low flow trip point, this will initiate a
PSS shutdown for the pump to protect it against damage. The low low flow shutdown
of the duty pump shall also initiate auto start of the standby pump and the PSS shall
provide the necessary signal to initiate the action, see section 3.6 for further details.
Since the flow transmitters are used for shutdown, they will be connected to the PSS
and the signal repeated to the PCS for control purposes.
The pumps are provided with pressurised seals as described in section 3.6.8 except
that for these pumps there are two separate seal units, one for the pump driven end
and one for the pump non driven end, the instrument tag numbers for each pump are
detailed below:
For Pump P 41201A driven end, PI 412500 and LI 412503.
For Pump P 41201A non driven end, PI 412530 and LI 412533.
For Pump P 41201B driven end, PI 412510 and LI 412513.
For Pump P 41201B non driven end, PI 412540 and LI 412543.
For Pump P 41201C driven end, PI 412520 and LI 412523.
For Pump P 41201C non driven end, PI 412550 and LI 412553.
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23.0
SEAWATER SYSTEM LIFT PUMPS & HYPOCHLORITE PACKAGE.
Reference P&IDs: BLK18-GP-K-PR-PID-854000, 854100, 854200 441000, 442000,
442100, 442200. Seawater Lift pump Cooling Oil System, Vendors P&IDs: BPAABL18-PME04-C-0005 (1623-009-1), Vendors Logic Drawing: BPAA-BL18-PME04B-C0008 (1623-016-3), Instructions for operation: BPAA-BL18-PME04B-C-0009 (1623016-3)
The seawater lift pumps P-85401 A, B, C, D are manually started and stopped by the
operator, there is no auto start facility required. Normally three pumps will be
operating with one available to be started if required.
Each of the seawater lift pumps have their own dedicated cooling oil system which is
supplied as a package of equipment complete with instrumentation but without a
control panel, control is provided by the PCS and shutdown requirements by the PSS.
The required configuration will be described for P-85401A, but shall be applied
similarly for each of the four seawater lift pumps with the appropriate tag numbers
substituted; the tag numbers are listed on the referenced vendors P&ID.
The cooling oil package consists of a cooling oil tank, filters, pressurising and
circulation pumps, oil pressure accumulator and oil cooler.
The cooling oil system for each seawater lift pump has to be pressurised and
circulating as a precondition before the main lift pump is stated.
Since at least one of the main lift pumps and its associated pressurising and circulation
pumps will be not be running under normal operation of the facility, all low pressure
and low flow alarms and low low flow shutdowns shall be inhibited when the
appropriate pumps are not running as described in the general pump description in
section 3.6.
The starting and stopping sequence of the pressuring pump P-85404A and the
circulation pump P-85403A are initiated by manual start of the pumps by the operator.
First the pressurising pump, which takes cooling oil from the oil tank and automatically
starts if the system pressure is below the start pressure of 16 barg. It continues to run
until it has pressurised the accumulators to the switch off point of 17 barg, when it is
automatically stopped. The pump start and stop are controlled by PIC 854609 acting
in differential gap mode. If the pump fails to stop or fails to start, then the high
pressure pre-alarm set at 24 barg or the low pressure pre-alarm set at 14 barg shall be
initiated, but no alarms are required for the pump if it starts and stops normally. The
pump start and stop points shall not be adjustable at the operator or supervisor level of
access.
It should be noted that the pressure high and low pre-alarms are shown on the
vendors P&ID, being derived from PI 854607, this is incorrect. PI 854607 is configured
in the PSS to provide the high high and low low pressure shutdowns as defined in the
PSS cause and effect diagrams.
The bladder type pressure accumulator compensates for the inevitable small leakage
of oil throughout the system with an accompanying reduction of pressure. When the
pressure eventually decays to the low pressure set point, the pressurising pump is
automatically started and continues to run until the high set point is reached when it is
automatically stopped and the cycle repeats.
The circulation pump circulates the pressurised cooling oil first through the filter and
then through the main lift pump system. The returning oil is cooled in the circulating oil
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heat exchanger under the control of a self acting 3 way diverting valve that maintains
the correct operating temperature.
The detailed logic for the main seawater lift pumps and the pressuring and circulation
pumps is defined in the package vendor’s logic drawing referenced above. This logic,
including the requirement to continue to run the circulation pump for 10 minutes after
the main lift pump is stopped to allow for safe cool down, shall be implemented in the
PCS and PSS. The 10 minute delay shall grey out the circulating oil pump stop button
on the faceplate (and the start pushbutton if they are unavoidably linked) and it shall
not be possible for the operator to override this function to stop the pump. The PCS
configuration shall specifically exclude any shutdown logic that is also shown in the
vendors logic diagram since this is controlled by the PSS and incorporated in the PSS
cause and effects diagrams.
The PSS shutdowns shall have the indicators and shutdown alarms repeated to the
PCS as usual. If a shutdown signal requires the circulation pump to be shutdown
during the 10 minute timed period, then the inhibit shall be removed, the pump
shutdown by the PSS hardwired signal to the MCC and the pump set to manual and
off as usual for a pump shutdown.
For each seawater lift pump, the motor operated valve on the pump discharge shall be
closed when the pump is not running; for P-85401A, this is MOV 854014. The valve
closure shall be automatic and initiated by the not running signal. After the pump is
stopped, to allow the pump flow rate to slow before closure of the valve is initiated, a
short time delay shall be incorporated; this shall be set at 10 seconds, but accurately
established during commissioning based on the rundown time of the pump.
The seawater lift pump shall have its start inhibited unless the discharge valve closed
signal is present. Following start up, the discharge valve shall remain closed for a
timed period after the pump running signal is received, the setting for the time delay
shall be 30 seconds. The time delay is to avoid surge by ensuring that the air in the
vertical pump discharge pipe is exhausted from the vent valve before the forward path
is opened; the exact time delay required will be accurately set during commissioning.
Each pump has its own minimum flow bypass, which will be open when the lift pump
starts and dumps the diverted seawater overboard. When the MOV opens the pump
discharge, the forward flow into the seawater system should increase above the set
point of the minimum flow controller causing it to close the dump valve. For lift pump
P-85401A, the minimum flow bypass controller is FIC 854049.
The minimum flow bypass controller is based on orifice plate flow measurement with
square root linearisation carried out in the transmitter.
Under normal operating conditions flow from the pump exceeds the minimum flow and
the controller maintains the dump control valve closed. If a fault occurs in the process
system causing the flow to drop below the bypass controller’s set point, then it opens
the control valve, diverting the flow to the Seawater Disposal Caisson and maintaining
flow through the pump at its minimum safe flow rate. If the process fault condition is
such that it cannot meet the minimum flow requirement of the pump, then a low flow
alarm shall be initiated to warn the operator.
If the pump discharge flow drops below the low low flow trip point, this will initiate a
PSS shutdown for the pump to protect it against damage, see section 3.6 for further
details.
For Pump P-85401A, the minimum flow bypass transmitter is FT 854049 and will be
connected to the PSS with the shutdown requirements defined in the PSS cause and
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effects diagrams. The flow rate signal and the low low trip alarm shall be repeated to
PCS which will use the signal for FIC 854049 and the low flow pre alarm.
Hypochlorite solution is dosed into the lift pump caissons to sterilise the seawater.
The hypochlorite is produced by an electrolysis process in the Hypochlorite Package.
This has its own control system and the only interfaces to the PCS are the following
status signals:

Hypochlorite Package Running : Tag Number XI 854036

Hypochlorite Package Common Alarm Tag Number XA 854037

Hypochlorite Package Tripped Alarm Tag Number XA 854038
In addition the package is shutdown from the PSS as defined in the PSS cause and
effects diagrams.
The hypochlorite flow rate is measured by a transmitting variable area flowmeter; for
P-85401A, this is FIT 854054 which provides a linear 4-20 mA signal.
As defined in the PSS cause and effects diagrams, the shutdown valve XV 854056
closes off the flow of hypochlorite to the pump caisson if the pump is shutdown by the
PSS. This is to avoid overdosing the seawater in the caisson causing potential
damage of the downstream sulphate removal package membranes. Since this can
also occur if the pump is stopped (but not shutdown) it is necessary to send a signal
through the ICS network to the PSS to request that the valve is closed whenever the
seawater lift pump is stopped. The associated hypochlorite low flow alarm (FI 854054
for pump P-85401A) shall be overridden when the seawater lift pump is not running.
The seawater flow from the seawater lift pump manifold is measured by FIT 854025.
This is an ultrasonic type flowmeter providing a linear 4-20 mA analogue signal to the
PCS which shall be configured to display a flow rate indication and a flow totaliser.
The number of totalised digits shall be set to allow continued accumulation without
rollover for approximately 3 months operation. Manual reset to zero of the totalised
figure shall be provided from the operator station, but only at the supervisor level.
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24.0
WATER INJECTION AND SULPHATE REMOVAL SYSTEMS
Reference P&IDs: BLK18-GP-K-PR-PID-441000, 442000, 442100, 442200, 442300,
443000, 450000, 450100, 450200
Vendor Drawings: Sulphate Removal Package: BPAA-BL18-PME08A (04015W-PD00-000-0003 sheets 1 - 31)
Vendor Drawing: Water Injection Pumps: BPAA-BL18-PME11A (E-1-104.429.815
sheets 1 – 2)
The water supply for injection to the subsea wells consists of all the produced water
from the production wells after it has been suitably cleaned to remove the oil, plus
sufficient make up water to meet the total water injection requirements for all of the
injection wells. The make up water is seawater that has had sulphate and other
minerals reduced to an acceptable level to avoid scaling in the water injection system.
The removal of the sulphates and other minerals is achieved in a reverse osmosis
process that forms the basis for the Seawater Sulphate Removal Package (SRP).
This is a large package that is controlled by its own PLC. It has its own operator
workstation located in the equipment room (LER 124) with the control panel. The
workstation provides complete control and engineering access to the package control
system. However normal operation of the package is from the PCS workstation in the
control room. The package PLC interfaces the control signals to and from the PCS via
dual serial links and they are displayed on a number of PCS graphics screens
developed in conjunction with the package vendor.
The seawater from the seawater lift pump header is initially filtered in the Seawater
Coarse Filter Package, Z-85401. This is a self contained package and the only
interface to the PCS is a common fault alarm XA 854047.
Part of the seawater flow is then routed to the SRP package for treatment prior to
being combined with the treated produced water ready for water injection. The treating
process includes further filtration, chemical dosing and pressurisation prior to being
demineralised by the reverse osmosis membranes. Following the sulphate reduction
process, the air is removed from the seawater in the two vacuum Seawater Deaeration
Columns V-44201 and V-44202. After deaeration, the pressure of the seawater has to
be increased before it can be combined with the produced water and this is carried out
by the Water Injection Booster Pumps P 44202 A, B, C. All of this equipment is part of
the SRP package and is controlled by the package PLC.
The SRP is made up of a number of RO banks with the number of banks in operation
set to most nearly match the process flowrate demand. Since each bank corresponds
to a fixed specific flowrate, the number of banks set into operation normally exceeds
the process requirement. Any surplus is dumped overboard downstream of the
deaerators, the dumping rate being controlled by level controllers on the deaerators.
When the level is controlled on set point, the process demand plus the dump flow
exactly matches the supply from the SRP.
If however the process demand (determined by the injection water flow rate) exceeds
the capacity of the number of banks operating in the SRP, then the dump valve will be
automatically closed. But since there is insufficient supply from the SRP, the level in
the deaerators will fall. In this case, independent secondary level controllers with a
lower level set point will take over control. The control action will be to switch the
water injection flow controllers FIC 450019, 450017 and 450018 to cascade and
reduce the injection rate set point until supply again matches demand and the level in
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the deaerators is controlled at the secondary controller’s set point. The water injection
flow controllers and the detailed operation of the cascade loops are described later in
this section.
After the deaerated water is discharged from the Booster Pumps it is available to act
as make-up water as required to supplement the produced water so that it meets the
required total seawater injection flow rate. The make up quantity is controlled by PIC
442030 using the water injection manifold pressure as the criteria to control the makeup flow rate. If the pressure drops, then more make up water is required and the valve
PV 442030 has to be opened further. This is a fail closed valve, so PIC 442030 will be
set as a reverse acting controller.
The Water Injection Pumps P-45001A and P-45001B and P-45001C are designed as 3
x 33⅓ pumps, thus all three pumps are normally running and there is therefore no
spare or auto start required.
These are large pumps with 10,000 kW motors and can provide a discharge pressure
that exceeds the PSV set pressure of 275 barg. Each pump is provided with its own
PLC based control system for the pump logic and auxiliary systems such as lube oil
and to provide automatic control of the suction and discharge valves during start, stop
and shutdown operations.
The pump PLC’s have hard wired connections to the motor switchboard for start and
stop of the main and auxiliary lube oil pump motors.
The pump PLC’s have dual modbus serial links which route all required package
signals to and from the PCS for display and interaction by the control room operator.
Unlike pumps without package control panels, the operator does not directly send a
serial link start or stop signal to the motor switchboard from the PCS. Instead a pump
start or stop signal is sent to the pumps PLC that will initiate the start or stop logic. If
all the pump systems are operating correctly, the pump logic will subsequently send
the hard wired start or stop signals to the motor switchboard.
Thus the standard serial link signals defined in section 3.6 will not be provided from the
MCC and the graphic screens developed to display the pump serial link signals and
the hard wired signals listed below shall incorporate the pump start and stop, running,
fault, etc, to / from the pump PLC’s.
In addition to the serial link signals, the pump logic requires a number of hardwired
signals between the PCS and the pump control panels, these are detailed below:
For Pump P-45001A – PCS Digital Outputs - From PCS to Package Panel
Start Pump : HST 450807 (signal to Package logic – initiates the start up sequence)
Stop Pump : HSP 450807 (signal to Package logic – initiates the stop sequence)
Suction Valve Available : XL 450003 - closed when available
Suction Valve Open : ZSH 450003A - closed when open
Suction Valve Closed : ZSL 450003A - closed when closed
Discharge Valve Available : XL 450014 - closed when available
Discharge Valve Open : ZSH 450014A - closed when open
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Discharge Valve Closed : ZSL 450014A - closed when closed
The valve signals shall be taken from the suction valve MOV 450003 and discharge
valve MOV 450014. These are Foundation Fieldbus electric motor operated valves
which will provide the required signals.
The start signal will be normally open and will pulse closed for 5 sec and then return to
open.
The stop signal will be normally closed and will pulse open for 5 seconds and then
return to closed.
The PCS digital output signals shall be 24Vdc powered from the PCS.
For Pump P-45001A – PCS Digital Inputs - From Package Panel to PCS
Open Suction Valve : HSO 450003A - closed to open valve
Close Suction Valve : HSC 450003A - closed to close valve
Open Discharge Valve : HSO 450014A - closed to open valve
Close Discharge Valve : HSC 450014A - closed to close valve
Common Package Fault Alarm : XA 450803 – closed in the healthy condition, open to
alarm
Available for ICS Control : XL 450804 - closed when available
The PCS digital input signals shall be 24Vdc powered from the PCS.
For Pump P-45001B - PCS Digital Outputs - From PCS to Package Panel
Start Pump : HST 450837 (signal to Package logic – initiates the start up sequence)
Stop Pump : HSP 450837 (signal to Package logic – initiates the stop sequence)
Suction Valve Available : XL 450004 - closed when available
Suction Valve Open : ZSH 450004A - closed when open
Suction Valve Closed : ZSL 450004A - closed when closed
Discharge Valve Available : XL 450015 - closed when available
Discharge Valve Open : ZSH 450015A - closed when open
Discharge Valve Closed : ZSL 450015A - closed when closed
The valve signals shall be taken from the suction valve MOV 450004 and discharge
valve MOV 450015. These are Foundation Fieldbus electric motor operated valves
which will provide the required signals.
The start signal will be normally open and will pulse closed for 5 sec and then return to
open.
The stop signal will be normally closed and will pulse open for 5 seconds and then
return to closed.
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The PCS digital output signals shall be 24Vdc powered from the PCS.
For Pump P-45001B - PCS Digital Inputs - From Package Panel to PCS
Open Suction Valve : HSO 450004A - closed to open valve
Close Suction Valve : HSC 450004A - closed to close valve
Open Discharge Valve : HSO 450015A - closed to open valve
Close Discharge Valve : HSC 450015A - closed to close valve
Common Package Fault Alarm : XA 450833 – closed in the healthy condition, open to
alarm
Available for ICS Control : XL 450834 – closed when available
The PCS digital input signals shall be 24Vdc powered from the PCS.
For Pump P-45001C - PCS Digital Outputs - From PCS to Package Panel
Start Pump : HST 450867 (signal to Package logic – initiates the start up sequence)
Stop Pump : HSP 450867 (signal to Package logic – initiates the stop sequence)
Suction Valve Available : XL 450005 – closed when available
Suction Valve Open : ZSH 450005A – closed when open
Suction Valve Closed : ZSL 450005A – closed when closed
Discharge Valve Available : XL 450016 – closed when available
Discharge Valve Open : ZSH 450016A – closed when open
Discharge Valve Closed : ZSL 450016A – closed when closed
The valve signals shall be taken from the suction valve MOV 450002 and discharge
valve MOV 450016. These are Foundation Fieldbus electric motor operated valves
which will provide the required signals.
The start signal will be normally open and will pulse closed for 5 sec and then return to
open.
The stop signal will be normally closed and will pulse open for 5 seconds and then
return to closed.
The PCS digital output signals shall be 24Vdc powered from the PCS.
For Pump P-45001C - PCS Digital Inputs - From Package Panel to PCS
Open Suction Valve : HSO 450005A - closed to open valve
Close Suction Valve : HSC 450005A - closed to close valve
Open Discharge Valve : HSO 450016A - closed to open valve
Close Discharge Valve : HSC 450016A - closed to close valve
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Common Package Fault Alarm : XA 450863 – closed in the healthy condition, open to
alarm
Available for ICS Control : XL 450864 – closed when available
The PCS digital input signals shall be 24Vdc powered from the PCS.
Although all three pumps will normally be running, it is likely that extended periods may
occur when one or more of the pumps are not operational. A number of alarms and
trips will therefore require to be overridden on the non running pumps. The application
and removal of these inhibits shall in general be as described in section 3.6.7, but
incorporating any adaptations that may be necessary, since these pumps do not have
the normal serial links.
The low pressure and low flow alarms and trips to be inhibited for each pump are listed
below:

Low Low suction pressure shutdown (for P-45001A – PI 450006)

Low discharge pressure alarm (for P-45001A – PI 450009)

Low discharge flow alarm (for P-45001A – FI 450012)

Low Low discharge flow shutdown (for P-45001A – FI 450012)
The equivalent signals and tag numbers as defined on the referenced P&IDs are
similarly applicable to the B & C pumps.
The pumps are provided with minimum flow bypass protection which ensures that the
pump’s minimum safe flow is always flowing through the pump when the pump is
running. The PCS controls the minimum flow bypass for each pump which is dumped
overboard via the produced water disposal caisson.
The minimum flow controllers are FIC 450012 for P-45001A, FIC 450013 for P-45001B
and FIC 450011 for P-45001C. The flow transmitters for these duties are ultrasonic
type that provides a linear 4-20mA signal. The flow transmitters are used to provide a
low low and high high flow shutdown as defined in the PSS cause and effects
diagrams. The high high shutdown is required since the drive motor is not rated for
end of pump curve operation. Since the flow transmitters are used for shutdown, they
will be connected to the PSS and the signal repeated to the PCS for the minimum flow
controllers and the high and low flow pre alarms.
Water Injection Manifold
The three Water Injection Pumps discharge into a manifold that supplies high pressure
injection water to the South Eastern, South Western and Northern water injection
risers. Under normal operation the operator will set the required injection flow rate for
each of the subsea injection flow lines using FIC 450019 for the South Eastern system,
FIC 450017 for the South Western system and FIC 450018 for the Northern system.
As the operator increases the flow set point and hence increases the opening of the
flow control valve, the back pressure in the flowline will also increases. The increase
in pressure will depend on the permittivity of each of the wells and the position of the
subsea chokes, these parameters will change over time. The Seawater Injection
Pumps are capable of exceeding the discharge relief valve set pressure and it is
therefore not possible to define a specific maximum flow rate limit that will avoid
exceeding the pressure limit. It is therefore necessary to have a pressure controller for
each of the flowlines that can take over control from the flow controller if the flow set
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point causes the pressure to exceed an upper limit set by the pressure controller set
point.
This is achieved by a signal selector that routes the flow or pressure signal to the valve
as appropriate to the process conditions.
For the South Eastern Water Injection flowline, the flow controller FIC 450019 and the
pressure controller PIC 450022 will both be set as reverse acting and the signal
selector FY 450019 will be a low select function. Thus with lower flow rates, the
flowline back pressure will be below the set point of PIC 450022 and its control output
will be “high” in comparison to the flow controller output; the flow controller output will
therefore be routed out to the control valve by the low signal selector.
If the flow controller set point is increased, the flow rate and hence the flowline back
pressure will rise. As the flow set point is further increased, the pressure will increase
above the set point of PIC 450022 and because it is reverse acting, will cause the
pressure controller output to reduce. At the point where the pressure controller output
drops below the output of the flow controller, the low selector will automatically switch
the control valve to the pressure controller, thus limiting any further opening of the
control valve FV 450019 and limiting the pressure to the pressure controller’s set point.
The controller’s set point shall therefore be set at a pressure below the maximum
pressure limit and shall only be adjustable at the engineer’s level of access.
The same description is applicable to the equivalent controls for the South Western
and Northern water injection risers with the appropriate tag numbers substituted.
As previously noted, the flow controllers FIC 450017, 450018, 450019 will require to
be operated as cascade slaves in the situation when the SRP flow is insufficient to
meet demand. The change to cascade control is required to be automatic and not
normally an operator action. To achieve this, the SRP package provides a digital
signal to the PCS as well as the analogue cascade master signal.
The digital signal “LIC 442015B_MODE” is one of the serial link signals from the
package PLC, which when received by the PCS sets all three flow controllers to
cascade operation. The analogue master cascade signal, LIC 442015B, which is also
a serial link signal, shall then be set to act as the cascade master for all three flow
controllers so that it drives all three set points up or down together.
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25.0
AIR COMPRESSOR AND DRYER PACKAGE
Reference P&IDs: BLK18-GP-K-PR-PID-804000, 804100, 804200
The Air Compression System consists of three vendor controlled packages Z-80401,
80402 and 80403. These packages include the three 50 % air compressors, the air
dryers, coolers, pumps, etc; all controlled from the package vendors control systems.
The air systems are treated as a utility that requires very little operator interaction
under normal operation of the facility. The operator interfaces to the PCS are
therefore simple with no direct control. The package provides a common alarm XA
804010 and a common shutdown alarm XA 804013 for the Compressor Package and
similarly a common alarm XA 804020 and common shutdown alarm XA 804021 for the
Dryer Package. If a fault or shutdown is alarmed in the control room or it is necessary
to access the detailed controls, these are available on the package skid.
In addition to the common fault and shutdown alarms, the air compressor package
monitors the air dryness with a dew point analyser AI 804782 which will be hard wired
to an indicator in the PCS complete with a high dew point alarm.
The differential pressure between the inlet and outlet of the air dryer package is
measured by a differential pressure transmitter which monitors for blocking of the
filters or desiccant packing. This is also hard wired to a PCS indicator PDI 804783 and
has a high differential alarm.
All other controls for the air systems are standard loops or shutdowns with the
necessary repeat from the PSS or ESD systems to provide the operator workstation
displays.
When a shutdown occurs that closes a shutdown valve, it is a requirement to put any
PID control loops in the same process line into manual and close its control valves
(see section 3.2). The table below lists the control loops and valves that are applicable
to this requirement for the Air Compressor and Dryer Package.
Controller Shutdown Action – Air Compressor and Dryer Package
SHUTDOWN
VALVE
CONTROLLER
CONTROL
VALVE
XV 805002
PIC 805003
PV 805003
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26.0
NITROGEN SYSTEM
Reference P&IDs: BLK18-GP-K-PR-PID-806000, 806100, Vendor Drawing BPAABL18-PME33A-C0001 (130716-100-01)
The Nitrogen Generation package uses membrane technology to preferentially
separate an oxygen rich stream from its instrument air supply. This stream is vented
to a safe location leaving the nitrogen as the product stream discharging into the
Nitrogen Receiver.
The instrument air is first filtered and then passes to a thyristor controlled heater EEH80601 to bring the air to the optimum temperature for membrane separation.
The nitrogen package is provided with process hardware and instrumentation but is
directly controlled by the PCS and the required shutdowns are configured in the PSS.
The air heater however is provided with a thyristor control panel.
The air temperature after passing through the heater is measured by TT 806512 which
provides the input to PCS controller TIC 806512. Its output is connected as a 4-20mA
signal to the heater control panel to regulate the heater. A high temperature alarm
shall be provided from the controller.
The heater control panel (ICP-80601) provides a hard wired common alarm contact XA
806019 and a heater (package) tripped alarm contact XA 806021 for connection to the
PCS.
The oxygen content of the nitrogen gas is monitored by three independent oxygen
analysers AT 806509A, AT 806509B, AT 806509C. These are used as two out of
three (2oo3) voted inputs to the PSS, and as defined in the PSS cause and effect
diagrams, if two or three detectors reach the high high oxygen trip point, all the flow
from the package is diverted to the vent via valves XV 806504 and XV 806505. The
high and high high alarms shall be repeated to the PCS.
The heater has a high temperature safety trip TIT 806511, which monitors the heating
element temperature and shuts down the heater if the temperature exceeds the trip
point. This device acts directly on the heater circuit and is not connected to the PCS
or PSS; if a trip is initiated, the operator is advised via the trip alarm.
The process controls for the Nitrogen system outside the package are standard loops
which need no explanation. The only unusual loop is the 2oo3 voted low low pressure
shutdown to the PSS and as described for the oxygen analysers above, each alarm is
repeated to the PCS.
When a shutdown occurs that closes a shutdown valve, it is a requirement to put any
PID control loops in the same process line into manual and close its control valves
(see section 3.2). The table below lists the control loops and valves that are applicable
to this requirement for the Air Compressor and Dryer Package.
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Controller Shutdown Action – Nitrogen System
SHUTDOWN
VALVE
CONTROLLER
CONTROL
VALVE
XV 806023
PIC 806026
PV 806026
XV 806006
PIC 806007
PV 806007
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27.0
HEATING MEDIUM SYSTEM
Reference P&IDs: BLK18-GP-K-PR-PID-816000, 816001, 816100, 816200
Level transmitter LIT 816013 located on the Heating Medium Expansion Tank provides
level indication and high and low level pre-alarms as well as high high and low low
PSS shutdowns. The signal shall therefore be connected directly to the PSS system
and will be internally routed to the PCS for the pre-alarm and indication functions.
The Heating Medium Circulation Pumps P-81601A,B,C are 3 x 50% pumps configured
as duty, duty, standby, with auto start of the standby. Section 3.6 provides further
details of pump requirements including auto start and alarm suppression, there is no
low low flow shutdown for these pumps, so start up shutdown override is not
applicable and the flow transmitters are directly connected to the PCS rather than the
PSS, as is generally required.
Each of the pumps is provided with its own minimum flow bypass controller based on
orifice plate flow measurements with square root linearisation carried out in the
transmitter. Pump P-81601A has flow controller FIC 816028, P-81601B has flow
controller FIC 816029 and P-81601C has flow controller FIC 816031.
The Heating Medium Start-Up / Shutdown Pump P-81602 is a single 100% pump with
manual start and stop from the operator workstation only, section 3.6 provides further
details of pump requirements.
The temperature of the heating medium return header is to be controlled by TIC
816048 which has two control actions, each controlled with its own output and each
with the same control mA value:

to regulate PDV 816006 which when opened increases the flow of hot water
from the feed supply header to raise the temperature of the return header.

to open TV 816037 causing water from the supply header to flow through the
Heating Medium Dump Cooler X-81601 and reduce the temperature of the
return header.
Under normal operating conditions, the process design will dictate that the differential
control valve will be partially open and the cooler valve closed.
The required control actions shall be achieved by split ranging the two outputs of TIC
816048. In the case of control of PDV 816006, it will be necessary for the TIC 816048
control output to act a cascade master to PDIC 816006.
For split range loops it is necessary for the control action required for both outputs to
be the same, in this case reverse action.
The split range functionality shall be set as follows:

TIC 816037 output to TV 816037 shall be: 4mA, valve will be fully open, 12mA,
valve fully closed (12 to 20mA, valve remains fully closed).

TIC 816037 cascade master output to PDIC 816006 shall be: 20mA, set point
0% of controller measured variable range, 12mA, set point 100% of range
(12mA to 4 mA, set point remains at 100% of range.
It is common practice to incorporate a dead band in a split range control loop within
which the controlled process variable is allowed to move without any corresponding
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change to the two controller outputs. However in this case, the process design will
normally require an output in the range 12 to 20mA causing PDV 816006 to be
partially open and TV 816048 to be closed, a dead band is therefore not appropriate.
To avoid the possibility of condensation in the waste heat recovery equipment that will
lead to corrosion, it is necessary to impose a minimum set point limit of 105°C for TIC
816048; this limit may only be changed at the engineer level of access.
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28.0
GENERATORS AND WASTE HEAT RECOVERY SYSTEMS
Reference P&IDs: BLK18-GP-K-PR-PID-817000, 818000, 819000, 820000, 830100,
830200, 830300, 830400.
The installation is powered under normal conditions by four gas turbine powered
generators Z-83101, 83201, 83301, 83401, all four of which are normally operating. In
a production shutdown condition, when fuel gas will not be available, the generators
will automatically switch over to diesel as the fuel. In addition to the main generators,
there are two essential services generators and an emergency generator that are
located in the hull and are diesel powered. These only run under abnormal or
emergency conditions.
The main generators are supplied by Rolls Royce and each is individually controlled by
its own PLC which is located in a control cabin that forms part of the main package
skid.
The PCS control requirements for the generators is very limited since all individual
generator controls are provided by the generator’s PLC. Any control requirements for
the generators is carried out at the skid using the PLC’s VDU in the control cabin.
Since the process control operator is not generally required to make day to day control
changes to the generators and since all generator parameters that require monitoring
in the control room are repeated from the PLC’s via serial link, this control basis will
not be detrimental to normal operation. The repeated generator data will initiate
alarms and be displayed on suitable graphic displays on the PCS.
In addition a power management computer supervises the whole electrical system
including monitoring in real time the power being used on the facility, the operating
state of each of the generators and if necessary carrying out very fast load shedding in
case of an unplanned loss of generation capacity. Like the generators, the important
parameters that are monitored and controlled by the power management computer are
repeated to the PCS, again via serial link, with the data presented on custom graphic
displays.
Outside of the generator packages, there is very little associated instrumentation for
the PCS. Each generator has a shutdown valve for its diesel and fuel gas supplies
and a blowdown valve which depressurise the shut in fuel gas inventory. The required
PSS and ESD logic for these signals is defined in the cause and effect diagrams, the
status and out of position alarms for these valves shall be displayed by the PCS as
normal.
Each generator is provided with its own waste heat recovery unit X-81701, 81801,
81901, 82001, which are also controlled by the associated generator’s PLC. The
description below will be for X-81701, but the same description is applicable to the
other units with the tag numbers show on the referenced P&IDs substituted.
The hot exhaust gases are used to heat the heating medium which is used as a utility
within the process systems. The temperature of the heating medium at the discharge
of the heating coils is measured by an RTD detector, TE 817512, that is directly
connected to the PLC (without a transmitter). The PLC uses this as the measured
variable for TIC 817512 and the controller output adjusts the position of the hot gas
dampers to bypass more or less of the hot gases to complete the control loop. The
controller is part of the PLC configuration, but a serial link signal to the PCS is
provided for each generator/waste heat recovery unit and this includes the signal for
TE 81751. The PCS shall be configured to provide a temperature indicator for this
signal complete with high and low alarms, this is tagged TI 817512. The set point of
the TIC can only be modified at the PLC interface in the generator cabin, but since this
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temperature is used as the design basis for heating medium users, it will normally not
be changed.
The rate of flow of the heating medium on the discharge of the waste heat recovery
unit is measured by an orifice plate; the flow differential pressure transmitter FIT
817003 will provide the required square root extraction, providing a linear output
signal. The transmitter provides a PSS shutdown and the signal is therefore
connected to the PSS. The shutdown requirement is defined by the PSS cause and
effect diagram and the low low flow alarm shall be repeated to the PCS. The same
signal is also used to provide a rate of flow indicator and a low flow pre alarm, the
analogue signal shall therefore also be repeated from the PSS to the PCS.
To avoid permanent alarm if a generator is not operating, the generator running signal
from the serial link signals shall be used to enable the low temperature alarm for TI
817512.
The alarm shall be enabled 5 minutes after the generator running signal is received to
allow the temperature to reach its normal operating level. The duration of this timer
will require to be confirmed during commissioning to ensure it is appropriate.
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29.0
CHEMICAL INJECTION SYSTEM
Reference P&IDs: BLK18-GP-K-PR-PID-870000, 870100
Chemical Injection Pumps
Vendors P&IDs BPAA-BL18-PME13A (551258/1 to 15)
The chemical injection system is provided as a utility to the main process for the
injection of various chemicals into the process streams. In general individual
chemicals are stored in tanks that are gravity filled from transportable tote tanks that
are delivered to the facility by boat. The filling of the storage tanks is a manual
operation utilising flexible hoses connected to appropriate valve manifolds local to the
tanks.
Each of the chemical tanks is provided with two level transmitters, one acts as the
normal level indicator and has high and low level alarms. During manual filling
operations, the high alarm warns the operator that the tank is nearly full and that filling
has to be stopped. The control room operator is in radio contact with the operator in
the field who will be advised to close off the appropriate valves.
The tanks provide the supply to the chemical injection pumps described below. The
low level alarm acts as a pre-alarm prior to the low low level trip that protects the
pumps. The second transmitter provides the low low shutdown signal and is
connected to the PSS with the shutdown requirements defined in the PSS cause and
effects. These signals together with its low low level trip alarm are repeated to the
PCS in the normal manner.
The chemicals in the tanks are pumped to their injection points by a series of
diaphragm type positive displacement pumps. The design is based on the use of multi
headed pumps being driven by a common motor drive. Each individual chemical has
two or more associated pump drive motors each with one or more pump heads to suit
the number of chemical users.
Each pump drive is a manual start type with no requirement for auto start; the standard
pump motor drive signals defined in section 3.6 are required for each pump drive.
Each pump head has a double diaphragm for mechanical integrity with a vacuum
established between the two diaphragms; if the diaphragm ruptures, the second
diaphragm ensures that there is no leakage out of the pump. To monitor for
diaphragm rupture, the space between the two diaphragms is provided with a pressure
transmitter. The transmitter has a pressure indicator in the PCS that is normally
reading a vacuum, together with a high pressure alarm that detects that the diaphragm
has failed.
The discharge line from each pump head has a pressure transmitter with an
associated pressure indicator on the PCS operator display. The transmitter also has a
high pressure alarm which detects that the injection path for that particular pump head
is blocked and warns the operator that the relief valve is likely to have lifted. It also
has a low pressure alarm to advise the operator that the pump is not delivering
sufficient flow. This may be caused by the flow rate adjustment being set to zero flow
in error, a leak in the system or insufficient liquid being supplied to the pump suction.
Chemical Injection Water Dilution System:
Vendors P&ID BPAA-BL18-PME13A (551258/16)
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Because in some applications, the injection pump’s discharge flow rate is very small,
the chemical flow is “bulked out” by the addition of dilution water.
The dilution water tank T-88301 is provided with three level transmitters; LI 883505 is
the normal level indicator and is connected to the PCS, it also provides a low level prealarm to warn the operator prior to the low low level shutdown being tripped.
LI 883506 is a low low level trip as defined in the PSS cause and effects diagrams; it
provides protection for the pumps. The signal is connected to the PSS and the
indicator and low low trip alarm are repeated as usual to the PCS.
LI 883504 is connected to the PCS where it provides a second indication of level and a
high level alarm to warn the operator that filling operations should be stopped.
The dilution water is pumped to the users by the 2x100% Dilution Water Pumps P88301A and P-88301B. Each pump drive is a manual start type with no requirement
for auto start; the standard pump motor drive signals defined in section 3.6 are
required for each pump drive.
A minimum flow recycle is provided by flow control loop FIC 883500, which if the
bypass valve is operated, returns the pump discharge to the dilution tank.
It is required to control the supply pressure to the dilution water users and this is
achieved by PIC 883502.
As with other similar applications previously described, two control valves are
provided, a duty and standby, with a piping installation that allows the standby valve to
be maintained or replaced without impacting normal operation. A software selector
switch, HS 883502 is required to allow the operator to select the duty valve. The
standby valve shall be provided with a “low” signal to keep the valve closed and the
duty valve will receive the normal control signal output.
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30.0
METHANOL INJECTION SYSTEM
Reference P&IDs: BLK18-GP-K-PR-PID-825000, 825100, 825200, 825300, 825400
Vendors P&IDs are referenced below for clarity.
The methanol injection system, like the chemical injection system consists of a number
of packaged units with the process equipment and instruments supplied by the
package supplier, but controlled by the PCS and PSS.
High volume methanol injection pumps P-82501 A, B, C, D
Vendors P&ID BPAA-BL18-PME37B (0545910171/0D)
High volume methanol injection pumps & P-82502 A, B, C, D, E, F, G, H
Vendors P&ID BPAA-BL18-PME37B (0545910172/0D & 0545910173/0D)
Low volume methanol injection pumps P-82506 A, B
Vendors P&ID BPAA-BL18-PME37B (0527240165/1D)
Methanol inlet filters F-82501 A, B
P&ID BPAA-BL18-PME37B (1514691000/3P)
The package instrumentation for the above equipment is very limited; each pump has
a discharge pressure indicator and high pressure alarm. The pumps are all manual
start and therefore have no auto start requirements and shall be provided with the
standard pump signals described in section 3.6.
Pump shutdowns are detailed in the PSS cause and effects.
The filter package differential pressure is monitored by DPI 825797 which has a high
differential alarm.
Low volume methanol subsea barrier pumps P-82504 A, B & P-82505 A, B
Vendors P&ID BPAA-BL18-PME37B (1514961000/3P)
The level in the methanol storage tank T-82504 is monitored by 3 level transmitters; LI
825832 provides a high high shutdown as defined in the PSS cause and effect
diagrams and is connected to the PSS with a repeat of the indicator and alarm to the
PCS. Similarly LI 825830 provides a low low shutdown in the PSS and is also
repeated to the PCS. The third transmitter is the normal level indicator connected to
the PCS where it also provides high and low level pre-alarms.
The methanol is pumped by two sets of 2x100% pumps P82504 A & B and P82505 A
& B. Only one set is operational under normal conditions, the other set is not used.
Also only one of the pumps is running in normal operation, the other is a manually
started standby. The standard pump motor signals as defined in section 3.6 are
required for each of the pumps.
The selected duty pump does not operate continuously, but operates in a similar
manner to a hydraulic pump in that it pressurises sections of subsea pipework
between blocked off valves. It is not normally flowing methanol to the users, but
instead operates to pressurise the accumulators and then is automatically switched off.
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Any leakage in the whole system is compensated by the accumulators with the
accompanying drop in accumulator pressure. The automatic start and stop of the
pumps is achieved by PI 825784 for P-82504 A & B and PI 825804 for P-82505 A & B.
The two transmitter signals each have 4 trip points as follows:

pressure low, start pump – no alarm

pressure low low (pump failed to start) – low pressure alarm

pressure high, stop pump – no alarm

pressure high high (pump failed to stop) – high pressure alarm
An independent pressure transmitter on the pump discharge is installed for each of the
two groups of pumps, PI 825787 for P-82504 A, B and PI 825807 for P-82505 A, B.
They shall be connected to the PSS and as defined in the cause and effect diagrams,
will shutdown the pumps on high high pressure with the pressure indicator and alarms
repeated to the PCS. In addition to the High High trip, these pressure indicators shall
provide an independent low pressure alarm which will have a lower trip pressure than
the low pressure alarms defined above.
Because one set of “A / B” pumps will not be operating and may be isolated from the
common discharge header, the low pressure alarms may be present under normal
operation of the facility. Thus these alarms shall be inhibited as described in section
4.6. In these cases however, since either of the two pumps in the group can
pressurise the group’s common discharge, the criteria for inhibiting the trips is that:

If both “A” and “B” are stopped, then the inhibit shall be applied (since stopped
is a transient signal, it will be necessary to provide a latch in the logic to hold
the first pump’s stopped signal)

When “A” or “B” are subsequently started, then the start up override timer shall
be initiated.
The pumps are diaphragm type and each is fitted with a diaphragm failure alarm in the
form of a high pressure trip, for Pump P82504A this function is provided by PI 825782,
the tag numbers for the other pumps are shown on the referenced vendors P&ID.
Outside of the vendors packages the instrumentation consists of standard loops which
do not require further explanation.
There are however two P&IDs for spill back to the suction side from pump discharges,
which although are straightforward in implication are worth noting for the necessary
operator actions required.
The methanol pumps are high pressure positive displacement type that will very
rapidly reach full flow rate after the pump starts. Since it is an operational requirement
to start the pump and reach operating pressure before any methanol utility user opens
its block valve and starts to take flow, it is necessary to spillback the flow from the
discharge to the suction side of the pump to avoid lifting the relief valves. Because the
pressure build up will be very rapid following pump start up, the pressure loop will be
unable to open the spillback valve quickly enough. Prior to start up therefore, it is
necessary to put the appropriate pressure controller into manual and fully open the
spill back valve. After the pump has been started, the spill back valve will be slowly
closed in by the operator causing the discharge pressure to rise. When the pressure is
approximately at the controller set point, the operator switches the controller into auto
and it takes over control of pressure, adjusting the spillback valve to maintain pressure
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in the blocked in condition. When one of the methanol utility users is opened, the
spillback valve should fully close under the control of the spill back controller.
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31.0
FUEL GAS SYSTEM
Reference P&IDs: BLK18-GP-K-PR-PID-850100, 850200, 850300, Vendor Drawing
BPAA-BL18-PME32A C0001 (D-F-297)
The Fuel gas system consists of the normal topside process equipment and the fuel
gas treatment package which heats the fuel gas to provide the required level of
superheat to meet specification and subsequently filters the gas to ensure any liquid or
solid particulate matter is removed prior to use as fuel.
The fuel gas supply is taken downstream of the Glycol Contactor but requires
significant pressure reduction. This is controlled by PIC 850001A acting on PV
850001A and PIC 850001B acting on PV 850001B. The control arrangement for these
loops is unique to this and its look alike application (see PIC 850035A and PIC
850035B - described later in this section) and is dictated by the requirement to provide
two installed valves, one operating and the other an installed spare, but with the
changeover to the spare in case of a failure of the operating valve to the closed
position carried out quickly and without the need for operator intervention.
To achieve this controller PIC 85001B has a set point fixed one bar below the set point
of PIC 85001A, thus under normal operation, the pressure is above the set point of
controller PIC 85001B and control valve PV 850001B is closed. If PV 850001A fails to
the closed position, the pressure drops to the set point of PIC 850001B and PV
850001B takes over control.
High and low pressure alarms are required for the control loop PIC 850001, these will
be set on controller “A” only. However the changeover to PV 850001B shall be
alarmed and this shall be achieved by monitoring the controller output to PV 850001B
which if it is above 5mA for more than 30 seconds shall initiate the alarm.
The set point for controller PIC 85001B shall be linked to the set point of controller PIC
850001A so that it is always 1 bar less than that set for PIC 850001A; this relationship
shall not be adjustable at the operator or supervisor level. The set point of either
controller may be adjusted by the operator, but the other controllers set point shall
automatically be similarly adjusted to maintain the 1 bar difference.
After pressure letdown the gas is passed to the Fuel Gas Scrubber V-85001 where
any condensate and glycol carry over are removed prior to superheating in the Fuel
Gas Treatment Package.
The temperature of the gas prior to heating is measured by TI 850559.
The package has two heaters; a thyristor controlled Fuel Gas Electric Heater, X-85002
and a shell and tube heat exchanger, Fuel Gas Heater X-85001, which utilises heating
medium to superheat the fuel gas. The temperature of the fuel gas is measured by TT
850502 and is routed by the operator to the appropriate temperature controller via
selector switch HS 850558.
The electric heater is used infrequently, primarily for start up, and is controlled by TIC
850560 which regulates the electrical power via the thyristor to control the heat
addition to the gas.
After start up and when fuel gas is available to run the generators, waste heat recovery
will become operational and heating medium can be used for superheating the fuel
gas. The fuel gas heating function will then be changed over to X-85001 and the
operator changes control to TIC 850024. This controller regulates the gas temperature
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by bypassing a portion of the fuel gas around the heater as necessary to control the
heat addition and hence gas temperature.
The configuration shall be implemented so that TT 850502 is connected to both TIC
850560 and TIC 850024 (both controllers shall be reverse acting type), the selector
switch HS 850558 determines which controller is actively in control and the output of
the controller that is not active, shall be set to provide a 4mA output.
The low temperature alarm on the controller that is not operating shall be inhibited to
ensure that an alarm is not always present. The status of HS 850558 shall be used as
the criteria for inhibiting the appropriate low temperature alarm.
The thyristor panel provides a number interfaces to the PCS, including heater running /
stopped XI 320685, common fault XA 320684 and a number of high high temperature
trips that are connected to the thyristor panel and are repeated to the PCS. These are
TT 850518, 850519, 850520, 850521, 850522. and directly trip the heater on over
temperature.
The gas in the tubes of the heat exchanger X-85001, operates at considerably higher
pressure than the heating medium, such that a tube failure would be likely to cause a
rapid pressure rise that requires two bursting discs PSE 850517A and PSE 850517B
for pressure protection. The bursting discs are provided with burst failure detectors
that are effectively a loop of wire that is broken if the rupture disc is burst. These shall
be treated as a switch contact requiring a digital input. The detector shall be
considered as a made contact in the healthy condition with the bursting disc intact and
an open contact if the disc bursts to produce a PCS alarm.
After the gas is superheated it is passed to the operational Fuel Gas Filter, either F85001A or F-85001B. Each filter is fitted with a differential pressure indicator and high
differential pressure alarm, PDI850511 for filter F-85001A and PDI850512 for filter F85001B. This monitors for filter blockage and provides data to determine when filter
maintenance is necessary,
The fuel gas flow out of the treatment package is measured by an orifice plate; the flow
differential pressure transmitter FIT 850515 will provide the required square root
extraction, providing a linear signal to the PCS. The flow shall be corrected to
standard conditions (15 degrees centigrade and 1.01325 bara pressure) using
pressure and temperature inputs from PIT 850514, and TIT 850504 (note that the
computational element in the PCS is designated as FY 850515 on the P&ID, but in
practice this tag number is not appropriate as no additional hardware is necessary).
It should be noted that the pressure transmitter PIT 850514 is not an absolute
pressure device, but absolute pressure is required for the pressure correction
calculation. In this application, because the normal pressure is approximately 40 barg,
the addition by the PCS algorithm of 1.013 bar to the measured value to approximate
to a real absolute pressure measurement is an acceptable approach which will cause
a small but acceptable error.
The PCS shall use the standardised flow for FQI 850515 to provide a rate of flow
indicator plus a digital flow totaliser. The number of totalised digits shall be set to allow
continued accumulation without rollover for approximately 3 months operation. Manual
reset to zero of the totalised figure shall be provided from the operator station, but only
at the supervisor level.
The fuel gas from the treatment package is at the correct condition for use by the gas
turbine generators, but has to be further reduced in pressure for use in the glycol
regenerator package and for the flare tips.
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The required pressure reduction is controlled by PIC 850035A and PIC 850035B
acting on PV 850035A and PV 850035B respectively. For the same reasons
described for PIC 850001A & B above, these pressure control valves are configured
with PV 850035A normally operational and PV 850035B held closed by its controller
and ready to take over duty automatically if the duty valve fails closed. As before,
controller PIC 850035B has its set point linked to that for PIC 850035A, but set at 1
barg less. All other aspects of the configuration description are as described above,
including alarming the opening of PV 850035B.
The pressure indicators PI 850045, PI 850047, PI 850048 are low low pressure
shutdowns connected to the PSS. The PSS logic votes the shutdown on a two out of
three basis to avoid a spurious shutdown that will stop main generation and cause a
production shutdown. The pressure indications and the low low shutdown alarms shall
be repeated to the PCS for display on the operator workstation.
When a shutdown occurs that closes a shutdown valve, it is a requirement to put any
PID control loops in the same process line into manual and close its control valves
(see section 3.2). The table below lists the control loops and valves that are applicable
to this requirement for the Fuel Gas System.
Controller Shutdown Action – Fuel Gas System
SHUTDOWN
VALVE
CONTROLLER
CONTROL
VALVE
XV 850003
LIC 850057
LV 850057
XV 850049
PIC 850035A
PV 850035A
XV 850049
PIC 850035B
PV 850035B
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32.0
DRAIN WATER HYDROCYCLONE
Reference P&IDs: BLK18-GP-K-PR-PID-867000
The drain water hydrocyclone is used to remove hydrocarbon contaminants from the
oily water stream pumped from the marine slops tank, allowing the clean water to be
dumped overboard.
The instrumentation generally needs little description but includes an ultrasonic flow
meter, FIT 867001, to measure the rate of flow of the overboard water dump. This
produces a linear 4-20mA signal to FQI 867001 to provide the rate of flow indicator
plus a digital flow totaliser. The number of totalised digits shall be set to allow
continued accumulation without rollover for approximately 3 months operation. Manual
reset to zero of the totalised figure shall be provided from the operator station, but only
at the supervisor level.
An oil in water analyser monitors the water quality to ensure that the residual oil left in
the water after separation is below the acceptable level of 15 PPM. The analyser AT
867002 provides an input to the PSS which switches over the flow via XV 867003 and
XV 867004 if the oil level exceeds the allowable limit, the specific shutdown
requirements are defined in the PSS cause and effects diagrams. The analyser signal
and the high high trip alarm shall be repeated to the PCS as usual to provide the water
in oil indication as well as a high oil in water pre alarm.
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33.0
HVAC SYSTEM
The HVAC system is controlled and monitored by a number of dedicated PLC’s
located in the HVAC panels distributed around the facility in local equipment rooms.
The PLC’s interface with the F&G system for shutdown of fans and fire dampers as
defined in the F&G cause and effects diagrams. In addition, the PLC’s are interfaced
to the PCS via dual serial links that provide the operator with the important HVAC
status signals and alarms.
It is considered necessary to provide the operator with the facility to stop each of the
HVAC systems from the Control Room. Starting of the HVAC systems will only be
possible at the HVAC panel. The stop signals to the HVAC PLC’s will be included on
the serial links and the software switches will be located on the appropriate F&G
graphic display on the operator’s workstation.
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