1.1 INTRODUCTION
Process control is concerned with the control of unit operation and unit processes. Chemical
plant processes can be regulated to obtain the objectives and effectiveness by applying the
feed backward or feed forward principles using various computing devices like sensors,
transmitters, controllers etc. It requires sensors for measuring variables and valves for
implementing decisions. The piping and instrumentation (P&I) diagram is a pictorial
representation of a process plant having all the equipment along with the piping, valves,
insulation and instrumentation.
1.2 INSTRUMENTS
The different instruments used in the P&I diagram generally are
• Flow meters
• Level Meters
• Pressure gauge
• Thermometers and thermocouples
• Quality analysis devices
• Radiation measuring devices
The instruments are used for indicating, recording and controlling purposes. The
instruments are all identified by a code number. The first letter of the code refers to the
property measured.
✓ F - Flow rate
✓ T - Temperature
✓ P - Pressure
✓ L - Level
The second letter is either I, R or C which indicates to indicating, recording and
controlling respectively.
1
1.3 MODES OF CONTROLLER
PID-Controller
The PID controller is used as temperature controller and the basic modes of controller
are
• On-off control
• Integral control
• Proportional control
• Rate or derivative control
P-Controller
The most common application of the p-controller is level controller. There is an offset in
the p-controller. The maintaining of the level does not require any accurate measurements.
So, P-controller is used as level controller.
PI-Controller
The PI controller is used as flow rate controller. PI-controller does not have any offset. The
measurement of the flow rate must be accurate and does not have any offset. So, PIcontroller is most commonly used as a flow controllerpressure controller. In PID controller,
the response will be faster and accurate. the temperature and pressure must measure accurate
and faster for taking the control action. So, PID controller is most commonly used.
1.4 CONTROL OBJECTIVES
The main objective of process control and instrumentation on the chemical plants are as
follows:
• To suppress the external and internal disturbances on the process system.
• To ensure the stability of the process.
• To optimize the performance of the process there by making the process more
economical.
1.4.1 NECESSITY OF PROCESS CONTROL
2
• Safety - To look for hazardous situation and to mitigate those situations by providing
emergency alarms, control valves and automatic shutdown systems.
• Product Specification - To maintain the production composition according to its
quality standards.
• Environmental Regulation - To avoid environmental pollution by treating the waste
and vent gases and only an appreciable amount accepted by Pollution Control Board is
made to release into the atmosphere.
• Plant Economy - To operate the plant at very low production and operating cost in
order to increase the plant economy.
1.5 MEASURING ELEMENTS:
• Temperature Measurement - It is essential for the effective production of the product.
Thermocouples, Resistance thermometers, Pyrometers are used for the measurement of
temperature.
• Pressure Measurement - Mechanical and Electrical pressure sensors are used for
measuring pressure in the process plant.
• Level Measurement - Liquid head pressure devices, dielectric constant measuring
instruments, sonic resonance devices are used primarily for the measurement of level.
• Flow Measurement - Obstruction type, inferential, electromagnetic, ultrasonic, Mass
flow meters. These are the type of flow meters widely used.
CONTROL LOOPS: For instrumentation and control of different sections and equipment’s
of plants, following control loops are most often used.
1. Feedback control loop
2. Feedforward control loop
3. Cascade control loop
3
1.FEEDBACK CONTROL LOOP
A method of control in which a measured value of a process variable is compared with
the desired value of the process variable and any necessary action is taken. Feedback control
is considered as the basic control loops system. Its disadvantage lies in its operational
procedure.
For example if a certain quantity is entering in a process, then a monitor will be there at
the process to note its value. Any changes from the set point will be sent to the final control
element through the controller so that to adjust the incoming quantity according to desired
value (set point). But in fact changes have already occurred and only corrective action can
be taken while using feedback control system.
2.FEEDFORWARD CONTROL LOOP
A method of control in which the value of disturbance is measured than action is taken
to prevent the disturbance by changing the value of a process variable. This is a control
method designed to prevent errors from occurring in a process variable. This control system
is better than feedback control because it anticipates the change in the process variable before
it enters the process and takes the preventive action. While in feedback control system action
is taken after the change has occurred.
3.CASCADE CONTROL LOOP
This is a control in which two or more control loops are arranged so that the output of
one controlling element adjusts the set point of another controlling element. This control
loop is used where proper and quick control is difficult by simple feed forward or feed
backward control. Normally first loop is a feedback control loop.
4
1.6 CASCADE CONTROL LOOP ON REACTOR (R-1):
The reaction is exothermic and the heat generated is removed by coolant, which flows in
the jacket around the tank. The control objectives is to keep the temperature of the reacting
ammonia and nitric acid constant at 131℃. Possible disturbances to the reactor include feed
temperature Tf and the coolant temperature Tc. The only manipulated variable is coolant
flowrate Fc.
If we use feedback control, we will measure reactor outlet temperature and manipulate
coolant flowrate Fc. Therefore, the feedback control will be very effective for compensating
changes in temperature of outlet but less effective for changes in coolant temperature.
We can improve the response of feedback control to changes in the coolant temperature by
measuring Tc and taking control action before its effect has been felt by the reacting mixture.
Thus, if Tc goes up, increase the flowrate of the coolant to remove the same amount of heat.
Decrease the coolant flowrate when Tc decreases.
5
Therefore, we have two control loops using two different measurements, T and Tc, but
sharing a common manipulated variable, Fc.
1. The loop that measures T (controlled variable) is the dominant, or primary, or master
control loop and uses a set point supplied by the operator.
2. The loop that measures Tc, uses the output of the primary controller as its set point and
is called the secondary or slave loop.
1.7 PREHEATER:
CONTROL OBJECTIVE
To maintain the required temperature of feed
CONTROLLER USED
PID control is the satisfactory control for
temperature control.
MANIPULATED VARIABLE
Flow rate of steam
CONTROL VARIABLE
Temperature of product stream in preheater.
6
1.8 COOLER
CONTROL OBJECTIVE
To maintain the product steam at desired
temperature level
CONTROLLER USED
PID control is the satisfactory control for
temperature control
MANIPULATED VARIABLE
Flow rate of water.
CONTROL VARIABLE
Temperature of product stream.
7
1.9 STORAGE TANK
CONTROL OBJECTIVE
To maintain the desired level of feed in tank
and to ensure it does not overflow.
CONTROLLER USED
PI control is the satisfactory control for
flow.
MANIPULATED VARIABLE
Flowrate of input stream
CONTROL VARIABLE
Level of liquid in vessel.
8
1.10 EVAPORATOR
CONTROL OBJECTIVE
1.To maintain process stream at desired
temperature range.
2. To maintain the optimum ratio of
Nitric acid and ammonium nitrate.
3.To maintain desired inlet flow rate
CONTROLLER USED
PI control is the satisfactory control for
flow.
MANIPULATED VARIABLE
Flowrate of input stream
CONTROL VARIABLE
Level of liquid in vessel.
9
1.11 PRILLING TOWER
2.FAULT TREE ANALYSIS
FTA is a top-down process by which an undesirable event (failure in a project objective
or a critical failure that can affect the project), referred to as the top event, is logically
decomposed into possible causes in increasing detail to determine the causes or combinations
of causes of the top event. FTA can yield both qualitative and quantitative information about
the system understudy.
1. Qualitative information may include failure paths, root causes, and weak areas of the
system/project.
2. Quantitative analysis of a fault tree gives a probabilistic estimation of the top event
10
2.1 LIST OF SYMBOLS IN FAULT TREE ANALYSIS :
SYMBOL
NAME
DESCRIPTION
Top event; Secondary or Contributing events; A
Rectangle
System state requiring more investigation on lower levels
Circle
Basic fault event; no further development required
House
Not a fault event; an event that is expected to occur under
normal operation
Diamond
Undeveloped event; one that, by either choice or necessity,
will not be developed further
Oval
An event that places qualified conditions on the fault
sequence
AND GATE
Describes an operation where all input events must occur
for the operation to occur
OR GATE
Describes an operation where one or more of the input
events can occur in order for the output to occur
Used to show logic flow between two parts of the fault tree;
F
Transfer GATE
Transfers everything under the event it is attached to;
Reference is made by an alphanumeric code
11
2.2 FAULT TREE ANALYSIS FOR STIRRED TANK REACTOR
FIG 2.2 FAULT TREE ANALYSIS FOR STIRRED TANK REACTOR
12
2.3 FAULT TREE ANALYSIS FOR SHELL AND TUBE HEAT EXCHANGER
FIG 2.3 FAULT TREE ANALYSIS FOR SHELL AND TUBE HEAT EXCHANGER
2.4 FAULT TREE ANALYSIS FOR CENTRIFUGAL PUMP
FIG 2.4 FAULT TREE ANALYSIS FOR CENTRIFUGAL PUMP
13
2.5 FAULT TREE ANALYSIS FOR STORAGE TANK
FIG 2.5 FAULT TREE ANALYSIS FOR STORAGE TANK
14
3.1 PARAMETERS FOR COST ESTIMATION
The various parameters to be considered in the cost estimation are:
• Process Equipment Cost
• Fixed Capital Investment
• Working Capital Investment
• Fixed & Direct Charges
• Total Manufacturing Cost
3.2 ESTIMATION OF PURCHASED EQUIPMENT COST
The equipment costs are calculated using the following formulas:
1. Ce = a + b*Sn
Where,
Ce – Cost of equipment in lakhs
S – Size
a, b, n – constants depending on the equipment
2. CE = CB (Q/QB) M FP FM FY
Where, CE – Equipment cost for carbon steel equipment at moderate temperature with
capacity Q
CB – Bare cost of equipment with capacity QB
M – Constant depending on material used
FP – Correction factor of design pressure
FM – Correction factor depending on material of construction
FY – Correction factor of design temperature
15
3.3 PURCHASED EQUIPMENT COST
EQUIPMENT
EQUIPMENT
QUANTITY
TOTAL COST(In
Lakhs INR)
CSTR 1
1
36.6
CSTR 2
1
43.6
PREHEATER 1
1
6.25
PREHEATER 2
1
7.13
EVAPORATOR
1
95.79
STORAGE TANK
4
45.22
PRILLING TOWER
1
97.16
CONDENSOR
1
11.84
PUMP
4
16.16
TOTAL PROCESS EQUIPMENT COST [PEC] = 359.86Lakhs INR
3.4 DIRECT COST (DC):
S.NO COST TYPE
INR(In Lakhs)
1
Purchased equipment installation [45% PEC]
161.94
2
Instrumentation (15% PEC)
53.98
3
Electrical (13% PEC)
46.78
4
Piping (13%PEC)
46.78
5
Building including services (30% PEC)
107.96
6
Yard Improvement (12% PEC)
43.18
7
Land
251.90
TOTAL DIRECT COST [DC] = 712.53 Lakhs INR
16
3.5 INDIRECT COST (IDC):
S.NO
COST TYPE
INR(In Lakhs)
1
Engineering & Supervision (34% PEC)
122.35
2
Construction Expenses (32% PEC)
115.15
3
Contractor fees (20% PEC)
71.97
4
Contingency (30% PEC)
107.96
TOTAL INDIRECT COST [IDC] = 417.44 Lakhs INR
FIXED CAPITAL INVESTMENT [FCI] = DC + IDC
FIXED CAPITAL INVESTMENT [FCI] = 712.53 + 417.44
= 1129.98 Lakhs INR
WORKING CAPITAL INVESTMENT [WCI] = 18% FCI
= 203.39 Lakhs INR
TOTAL CAPITAL INVESTMENT [TCI] = FCI + WCI
= 1129.98 + 203.39
= 1333.38 Lakhs INR
FIXED CHARGES [FC]:
Depreciation, D = (𝑉−𝑉𝑠)/𝑛
(By straight-line method )
Where,
V = FCI = 1129.98 Lakhs INR
VS = 5% FCI = 56.49 Lakhs INR
n = 20 years
∴ Depreciation = 53.67 Lakhs INR
17
TOTAL PRODUCT COST [TPC] = TCI – D
= 1333.38 - 53.67
= 1279.70 Lakhs INR
TOTAL FIXED CHARGES = 12% Total Product Cost
= 0.12*1279.70
= 153.56 Lakhs INR
3.6 DIRECT CHARGES [DC]:
Raw material Costs:
S.NO RAW MATERIAL
COST/kg
TOTAL COST/
DAY
(Lakhs INR)
TOTAL COST
(Lakhs INR)
1
Ammonia
68
1.191
393.14
2
Nitric Acid
48
3.169
1045.82
3
Water
12
0.253
83.66
TOTAL RAW MATERIAL COST=1522.63 Lakhs INR
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OPERATING LABOUR COST:
S.NO
POSTS
NO.OF
POSTS
ANNUAL
SALARY IN
Lakhs INR
TOTAL
SALARY IN
Lakhs INR
1
General manager
1
12
12
2
Production manager
2
10
20
3
Engineer
5
7.5
37.5
4
Skilled Workers
15
4
60
5
Clerks
8
2
16
6
Medical Staff
6
1.5
9
7
Unskilled labour
20
1.1
22
8
Administrative
10
2
20
9
Security
4
1.1
4.4
10
Fire Officier
2
1.5
3
TOTAL OPERATING LABOUR COST = 203.90 Lakhs INR
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S.NO COST TYPE
COST (Lakhs
INR)
1
Operating labour
203.90
2
Direct Supervisory & Electric
204.75
Labour (16%TPC)
3
Utilities (12% TPC)
153.56
4
Maintenance (4% TPC)
51.18
5
Operating Supplies (15% TPC)
191.95
6
Laboratory Charges (16% TPC)
204.75
7
Patent (4% TPC)
51.18
Operating Cost = OL + OS + M = 447.04 Lakhs INR
Plant Overhead Cost = 60% OC
PLANT OVERHEAD COST = 268.22 Lakhs INR
TOTAL DIRECT CHARGES [TDC] = 2583.94 Lakhs INR
GENERAL EXPENSES:
S.
NO
COST TYPE
COST (Lakhs INR)
1
Administration cost (25% OL)
50.975
2
Distribution & Selling Price (15% TPC)
191.95
3
Research & Development (5% TPC)
63.98
4
Finance (5% TPC)
63.98
20
TOTAL GENERAL EXPENSES = 370.90 Lakhs INR
Total Manufacturing Cost = FC + DC + Overhead Cost + General Expense
TOTAL MANUFACTURING COST [TMC] = 3376.63 Lakhs INR
PROFITABILITY INDEX
S.NO PRODUCT
COST/kg
kg/DAY
(Lakhs INR)
TOTAL COST (Lakhs
INR)
1
Ammoium Nitrate
150
12.24
4088.16
2
Water
12
0.0049
1.641
TOTAL INCOME = 4089.802 Lakhs INR
GROSS INCOME = Total Income – TMC = 713.16 Lakhs INR
TAX = 28% of GROSS INCOME = 199.68 Lakhs INR
NET PROFIT = GROSS INCOME – TAX = 513.47 Lakhs INR
RATE OF RETURN = (Net Profit / Total Capital Investment) *100
= (513.47 / 1333.38) * 100 = 38.50 %
PAY BACK PERIOD = FCI / (Net Profit + Depreciation)
= 1.99 years
= 2 years
21
4.1 HAZOP ANALYSIS
A Hazard is something which may cause harm and is an undesired event. The word HAZOP
refers to the detail study regarding operability and hazards. It’s a formal procedure to identify
hazards in a chemical process facility. This systematic study is used to find out operability
problems and equipment hazards or all plant hazards. The method for doing HAZOPS study
involves detail examination of each equipment (instruments, piece of equipment, pipeline)
and the finding out all possible deviation from normal operating conditions. Before the
HAZOP study is started, detailed information on the process must be available. This includes
up-to-date process flow diagrams (PFDs), process and instrumentation diagrams (P&IDs),
detailed equipment specifications, materials of construction, and mass and energy balances.
A HAZOP study is conducted in the following steps :
Specify the purpose, objective, and scope of the study. The purpose may be the analysis of
a yet to be built plant or a review of the risk of unexisting unit. The scope of the study is the
boundaries of the physical unit, and also the range of events and variables considered. The
initial establishment of purpose, objectives, and scope is very important and should be
precisely set down so that it will be clear, now and in the future, what was and was not
included in the study. These decisions need to be made by an appropriate level of responsible
management.
• HAZOP team is selected.
• For the collection of data following materials are needed:
• Process description
• Process flow sheets
• Data on the chemical, physical and toxicological properties of all raw materials,
intermediates, and products.
• Piping and instrument diagrams (P&IDs)
• Equipment, piping, and instrument specifications
22
• Process control logic diagrams
• Layout drawings
• Operating procedures
• Maintenance procedures
• Emergency response procedures
• Safety and training manuals
4.1.1 Objectives of HAZOP study:
• To find out those areas in design which can have significant hazard potential.
• To study and find out those aspect of design that effects the occurrences of hazardous
incidence.
• To make study team familiar with design information.
• To make sure that systematic study of areas involving hazard potential is made.
• To provide a mechanism for feedback to the client of the study team's detailed comments
4.2 Key Elements:
Key elements of a HAZOP are:
✓ HAZOP team.
✓ Full description of process.
✓ Relevant guide words.
✓ Conditions conducive to brainstorming.
✓ Recording of meeting.
✓ Follow up plan
23
4.3 HAZOP Team:
HAZOP studies are carried out using a `brainstorming' approach by a team, chaired and
coordinated by a qualified person experienced in Team leadership Following are the
members of HAZOP team:
• Team Secretary
• Process Engineer
• Mechanical Engineer
• Commissioning/Operations
• Engineer/Manager
• Instrument Engineer
4.3.1 Strength of HAZOP:
• HAZOP is a systematic, reasonably comprehensive and flexible.
• It gives good identification of cause and excellent identification of critical deviations.
• The use of keywords is effective and the whole group is able to participate.
• HAZOP is an excellent well-proven method for studying large plant in a specific
manner.
4.3.2 Weakness of HAZOP:
• HAZOP is very time consuming and can be laborious with a tendency for boredom for
analysts.
• It tends to be hardware-oriented and process-oriented, although the technique should be
amenable to human error application.
• HAZOP does not identify all causes of deviations and therefore omits many scenarios.
24
4.3.3 Responsibility of HAZOP Team Members:
• Plan sessions and timetable
• Control discussion
• Limit discussion
• Encourage team to draw conclusion
• Ensure secretary has time for taking note
• Keep team in focus
• Encourage imagination of team members
• Motivate members
• Discourage recriminations
• Judge importance issues
25
4.4 GUIDE WORDS:
Guide Words
Meaning
Comments
No, Not, None
The complete negation of No part of the design intention is
the intention
achieved, but nothing else happens.
More, Higher, Greater
Quantitative increase
Less, Lower
Quantitative decrease
As well as
Qualitative increase
Part of
Qualitative decrease
Reverse
The logical opposite of
the intention
Other Than
Complete substitution
26
Applies to quantities such as flow
rate and temperature and to
activities such as heating and
reaction
Applies to quantities such as flow
rate and temperature and to
activities such as heating and
reaction.
All the design and operating
intentions are achieved along with
some additional activity, such as
contamination of process streams.
Only some of the design
intentions are achieved, some are
not.
Most applicable to activities such
as flow or chemical reaction.
Also applicable to substances, for
example, poison instead of
antidote.
No part of the original intention is
achieved. The original intention is
replaced by something else.
4.5 HAZOP ANALYSIS OF REACTOR:
Title: HAZOP Analysis
Study Node: Reactor (CSTR)
Operating conditions: 131oC
GUIDE
WORD
DEVIATION
CAUSES
CONSEQUENCES
Flow rate
i.No Feed in storage
i.Decrease in
tank
production or
ii.Feed pump rupture no production
iii.Supply pipe rupture
iv.Valve is closed
v.Pump is off
i.Cleaning of line
ii.Level control system
iii.Maintenance of pipes
iv.Automatic valve
v.Automatic pump
Level
i.Blockage in line
ii.Valve is closed
i.Decrease in
production or
no production
i.Maintenance of pipes
ii.Automatic valve
Temperature
i.Fault in Preheater
ii.Steam pipe
rupture
i.Decrease in
production or
no production
i.Maintenance of pipes
Pressure
i.Fault in Preheater
i.Decrease in
production or
no production
i.Maintenance of
Preheater
Flow rate
i.More valve
opening
i.Explosion
i.Automatic valve
ii.Less conversion ii.Check reactor
conditions
Level
i.More valve
opening
i.Overflow
No
More
27
ACTION REQUIRED
i.Check valve
Temperature
i.Fault in Preheater
i.Explosion
i.Maintenance
Pressure
i.Fault in Preheater
i.Less
production
i.Check valve
Flow rate
i.Less of opening of i.Decrease in
valves
production or
no production
i.Automatic valve
ii.Temperature control
at reactor feed
preparation
Level
i.Less of opening of i.Decrease in
valves
production
i.Check valve
Temperature
i.Fault in Preheater i.Less conversion i.Temperature control
Pressure
i.Fault in Preheater i.Less Production i.Maintenance
Impurities in
feed stream
i.Problem in raw
material
ii.Fouling in pipes
i.Low Conversion i.Quality control of
rate
raw material and
ii.Decrease in
product
product quality
ii. Maintenance
Higher or
Lower
percentage of
Nitric Acid
i.High quality of
feed
ii.Less quality of
feed
i.More or less
pure production
than intended
Less
All
well
as
Part of
28
i.Quality control of
raw material and
product
Other
than
Replacement
of Raw
Material
i.Wrong connection i.Explosion
during plant
modification
Corrosion of
Equipment
i.No proper cleaning and
i.Scale
i.Regular checks
maintenance
formation
ii.Proper cleaning and
ii.Leads to cracks maintenance
and crevices
iii.Reactor
Explosion
Corrosion of
Cooling
water coils
i.No proper
cleaning and
maintenance
Corrosion
Conta
mination
i.Better management
of changing procedure
i.Scale
i.Regular checks
formation
ii. Proper cleaning and
ii.Leads to cracks maintenance
and revises
iii.process
disruption
Contamination i.leakage
i.Disruption in the i.Regular checks
of process
ii.Catalyst getting mixed
process
ii.Proper cleaning and
fluid line
with process fluid ii.Damage in the maintenance
internal and
external parts of
the equipment’s
due to long term
exposure if the
chemical has
harmful properties .
29
4.6 HAZOP ANALYSIS OF PREHEATER:
Title: HAZOP Analysis
Study Node: Preheater
Operating conditions: 25oC
PARAMETER
GUIDE
WORD
DEVIATION
Less
CAUSES
CONSEQUENCES
ACTIONS REQUIRED
Less
i.Fouled
temperature heat
tubes
ii.Flow
leakage
i.Impact on
efficiency
ii.Excessive
pressure drop
Incorporate Nickel to
the MOC to improve
corrosion resistance and
prevent fouling
More
More
High
temperature feed
flow
rate
i.Increase in
pressure
ii.Reboiler duty
will fail
Use plug valves to
control feed flow rate
No
No flow
Control
valve
fails/
closed
No further
operability
Regular maintanance
More
More flow
Plug
control
valve
failure
Coking
Shutdown in
case of either
pump failure
Control system is
employed to control the
amount of steam that
passes through the
turbine
Temperature
Flow
30
4.7 HAZOP ANALYSIS OF CONDENSOR:
Title: HAZOP Analysis
Study Node: Condensor
Operating conditions: 66oC
PARAMETER
GUIDE
WORD
DEVIATION
CAUSES
Condenser
Cooling Water
System
Temperature High
High
Tube’s heat
Temperature up, then cool
Excursion
and with
possible
breakage
from thermal
induced stress
Tube’s heat
up, then cool
and with
possible
breakage
from thermal
induced
stress
Condenser
Suction
System
Flow
regimes
Phases
Flow
Condensate
dropping out
in the steam
supply line
Slugging
leading to
piping system
damage
Provide
condensate
upstream of
isolation
valve and a
warm up line
Condenser
Ejector
Supply
Flow
High
Loss of
condensate
flow to the
ejector
condenser
Full steam
the exhaust
line to the
vent. Potential
for increased
friction losses
in the vent
piping.
Check the
pressure
drop
in
exhaust line
to vent at full
steam flow
conditions to
determine if
overpressure
of the ejector
31
CONSEQUENCES
ACTIONS
REQUIRED
Condenser
Vessel
System
Flow
Low
Running the
condensate
system while
shutdown
Lose the
steam
condensate
supply
Add a line
and valve
from
downstream
to the
condenser
fill nozzle
4.8 HAZOP ANALYSIS OF PUMP:
Title: HAZOP Analysis
Study Node: Centrifugal pump
Operating conditions: 25oC
PARAMETER
GUIDE
WORD
CAUSES
CONSEQUENCES
ACTIONS
REQUIRED
More
i.Failure/leak/improper
cooling system
connections
ii.Very low flow
iii.High pressure
iv.Pump not
submerged
Vaporization of
liquid increase in
Pressure causing
destruction of pump
internal explosion
and fire
i.Check cooling
system
ii.Check
pressure/vent/
valve
iii.Increasing
cooling
Temperature Low
i.More open of cooling i.Lubricant
system
Character
ii.Low flow rates
changes and
viscosity
ii.Damage of
bearings
32
i.Check cooling
system
ii.Check no of
engine rounds
More
i.Blockage in outlet
valve
ii.Faulty pressure
sensor Vaporizing
liquid
i.Deterioration
of bearings
ii.Stop production
explosion
Check drain
pipes replace
the gasket and
damage check
i.Close suction valve
ii.Faulty sensor
iii.Air leaks in suction
Line
Cavitation Vibration
damaging internal
pump
i.Loss in
fittings
ii.Ensure
NPSHa>NPSHr
Pressure
Low
4.9 HAZOP ANALYSIS OF STORAGE TANK:
Title: HAZOP Analysis
Study Node: Storage Tank
Operating conditions: 25oC
PARAMETER
GUIDE
WORD
DEVIATION
CAUSES
CONSEQUENCES
No
No flow
Delay in
Install and
dispatch
maintain interlock
Material
system
evaporation
from storage tan
More
More flow
Master valve
failed to open
Manifold valve
failed to open
Blockage in
manifold valve
There is no
logical
sequence
Flow
33
There is no
consequences
ACTIONS
REQUIRED
No actions
required
4.10 HAZOP ANALYSIS OF EVAPORATOR:
Title: HAZOP Analysis
Study Node: Evaporator
Operating conditions: 131oC
PARAMETER
GUIDE
WORD
CAUSES
CONSEQUENCES
Less
Valve fails
open
Difficult to control
heating process
More
Pump failure,
pipe partially
blocked
No
Pipe blockage
or valve fails
open
Waste energy and
Install flow detector
increase production and alarm Regular
cost
pipe cleaning and
checking leakage
No heating
Less
Steam Valve
partially
blocked
Feed Flow
ACTIONS REQUIRED
Outlet temperature
of feed varies
Installing Temperature
controller and alarm
Feed
More
Temperature
Steam Valve
fails Close
Possibility of
explosion. Waste
of energy and
increase cost
Less
Valve failure
or partially
blocked
Increases time to
heat
Frequent maintenance
and cleaning
More
Valve fails
Close
Increases pressure
Feed Overheated
Installing Flow
monitor
Steam flow
34
5.1 PLANT LOCATION AND SITE SELECTION
The location of the plant can have a crucial effect on the profitability of a project and the
scope for future expansion. Many factors must be considered when selecting a suitable site,
and only a brief review of the principal factors will be given in this section. Site selection for
chemical process plants is discussed in more detail by Merims (1966) and Mecklenburgh
(1985); see also AIChE (2003).
The principal factors to consider are
1. Location, with respect to the marketing area;
2. Raw material supply;
3. Transport facilities;
4. Availability of labor;
5. Availability of utilities: water, fuel, power;
6. Availability of suitable land;
7. Environmental impact, including effluent disposal;
8. Local community considerations;
9. Climate;
10.Political and strategic considerations.
5.2 SITE LAYOUT
The process units and ancillary buildings should be laid out to give the most economical
flow of materials and personnel around the site. Hazardous processes must be located at a safe
distance from other buildings. Consideration must also be given to the future expansion of the
site.
The ancillary buildings and services required on a site, in addition to the main processing units
(buildings), include
1. Storage for raw materials and products: tank farms and warehouses;
2. Maintenance workshops;
3. Stores, for maintenance and operating supplies;
35
4. Laboratories for process quality control;
5. Fire stations and other emergency services;
6. Utilities: steam boilers, compressed air, power generation, refrigeration,
transformer stations;
7. Effluent disposal plant: waste water treatment, solid and or liquid waste
collection;
8. Offices for general administration;
9. Canteens and other amenity buildings, such as medical centers;
10. Parking lots.
➢ When the preliminary site layout is roughed out, the process units are normally sited
first and arranged to give a smooth flow of materials through the various processing
steps, from raw material to final product storage. Process units are normally spaced at
least 30m apart; greater spacing may be needed for hazardous processes.
➢ The location of the principal ancillary buildings should then be decided. They should
be arranged so as to minimize the time spent by personnel in traveling between
buildings.
➢ Administration offices and laboratories, in which a relatively large number of people
will be working, should be located well away from potentially hazardous processes.
➢ Control rooms are normally located adjacent to the processing units, but those with
potentially hazardous processes may have to be sited at a safer distance.
➢ The siting of the main process units determines the layout of the plant roads, pipe alleys,
and drains. Access roads to each building are needed for construction and for operation
and maintenance.
➢ Utility buildings should be sited to give the most economical run of pipes to and from
the process units.
36
➢ The main storage areas should be placed between the loading and unloading facilities
and the process units they serve. Storage tanks containing hazardous materials should
be sited at least 70m (200 ft) from the site boundary.
5.3 PLANT LAYOUT
The economic construction and efficient operation of a process unit will depend on how
well the plant and equipment specified on the process flowsheet is laid out. A detailed account
of plant layout techniques cannot be given in this short section. A fuller discussion can be
found in the book edited by Mecklenburgh (1985) and in articles by Kern (1977, 1978),
Meissner and Shelton (1992), Brandt et al. (1992), and Russo and Tortorella (1992).
The principal factors to be considered are
1. Economic considerations: construction and operating costs;
2. The process requirements;
3. Convenience of operation;
4. Convenience of maintenance;
5. Safety;
6. Future expansion;
7. Modular construction.
5.3.1 COSTS
The cost of construction can be minimized by adopting a layout that gives the shortest run
of connecting pipe between equipment and the least amount of structural steel work; however,
this will not necessarily be the best arrangement for operation and maintenance.
5.3.2 OPERATION
Equipment that needs to have frequent operator attention should be located convenient to
the control room. Valves, sample points, and instruments should be located at convenient
positions and heights. Sufficient working space and headroom must be provided to allow easy
access to equipment. If it is anticipated that equipment will need replacement, then sufficient
space must be allowed to permit access for lifting equipment.
37
5.3.3 MAINTENANCE
Heat exchangers need to be sited so that the tube bundles can be easily withdrawn for
cleaning and tube replacement. Vessels that require frequent replacement of catalyst or
packing should be located on the outside of buildings. Equipment that requires dismantling
for maintenance, such as compressors and large pumps, should be placed under cover.
5.3.4 SAFETY
Blast walls may be needed to isolate potentially hazardous equipment and confine the
effects of an explosion. At least two escape routes for operators must be provided from each
level in process buildings.
5.3.5 PLANT EXPANSION
✓ Equipment should be located so that it can be conveniently tied in with any future
expansion of the process.
✓ Space should be left on pipe racks for future needs, and service pipes should be
oversized to allow for future requirements.
5.3.6 MODULAR CONSTRUCTION
In recent years there has been a move to assemble sections of a plant at the plantplant
manufacturer’s site. These modules include the equipment, structural steel, piping, and
instrumentation. The modules are then transported to the plant site, by road or sea.
The advantages of modular construction are
1. Improved quality control;
2. Reduced construction cost;
3. Less need for skilled labor on site;
4. Less need for skilled personnel on overseas sites.
Some of the disadvantages are
1. Higher design costs;
2. More structural steel work;
3. More flanged connections;
38
4. Possible problems with assembly, on site;
A fuller discussion of techniques and applications of modular construction is given by Shelley
(1990), Hesler (1990), and Whittaker (1984).
5.4 UTILITIES
The word utilities is used for the ancillary services needed in the operation of any
production process. These services are normally supplied from a central site facility and
include
1. Electricity;
2. Steam, for process heating;
3. Water for general use;
5.4.1 ELECTRICITY
The power required for electrochemical processes, motor drives, lighting, and general use
may be generated on site, but will more usually be purchased from the local supply
company.The voltage at which the supply is taken or generated will depend on the demand.
In the United States, power is usually transmitted over long distances at 135, 220, 550, or 750
kV. Local substations step the power down to 35 to 69 kV for medium voltage transmission
and then to 4 to 15 kV local distribution lines. Transformers at the plant are used to step down
the power to the supply voltages used on site. Most motors and other process equipment run
on 208V 3-phase power, while 120/240V single phase power is used for offices, labs, and
control rooms.
5.4.2 STEAM
The steam for process heating is usually generated in water tube boilers, using the most
economical fuel available.
5.4.3 WATER FOR GENERAL USE
The water required for general purposes on a site will usually be taken from the local
mains supply, unless a cheaper source of suitable quality water is available from a river,
lake, or well.
39
40
COOLER
REACTOR
AMMONIA
STORAGE
FIRE STATION
GARDEN AREA
PARKING AREA
PRILLING
TOWER
REACTOR
PREHEATER
AMMONIUM
NITRATE STORAGE
PACKAGING
UNIT
PLANT EXPANSION
CONTROL ROOM
PREHEATER
NITRIC ACID
STORAGE
PLANT EXPANSION
RESEARCH AND
DEVELOPMENT
ADMINISTRATION
BLOCK
HEALTH CENTRE
CANTEEN
ELECTRIC
SUBSTATION
SECURITY
DISPATCHING
UNIT
QUALITY
CONTROL
EVAPORATOR
PLANT UTILITIES
AMMONIUM
NITRATE PRILLS
STORAGE