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JIHAR Stage 3 Project
HPC Contract No.: HPC/08-06
Petrofac Job No.: JI-191
TRAINING COURSE MATERIAL MODULE M10
GAS TREATMENT PLANT
Gas Dehydration and LPG Recovery
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TABLE OF CONTENTS
1.
1.1
1.2
1.3
1.4
GAS DEHYDRATION ...................................................................... 3
Brief process Description .............................................................. 3
Control System ........................................................................... 6
Salient features .......................................................................... 7
Sketch of PFD / P&IDs ................................................................... 7
2.
2.1
2.2
2.3
2.4
TURBO EXPANDER – DE-METHANISER SYSTEM .................................... 21
Brief process Description ............................................................ 21
Control System ......................................................................... 22
Salient features ........................................................................ 24
Sketch of PFD / P&IDs ................................................................. 25
3.
3.1
3.2
3.3
3.4
DE-ETHANISER SYSTEM ............................................................... 42
Brief process Description ............................................................ 42
Control System ......................................................................... 42
Salient features ........................................................................ 44
Sketch of PFD / P&IDs ................................................................. 45
4.
4.1
4.2
4.3
4.4
DE-BUTANISER SYSTEM ............................................................... 53
Brief process Description ............................................................ 53
Control System ......................................................................... 53
Salient features ........................................................................ 55
Sketch of PFD ........................................................................... 55
5.
5.1
5.2
5.3
5.4
SALES GAS COMPRESSOR ............................................................. 62
Brief process Description ............................................................ 62
Control System ......................................................................... 62
Salient features ........................................................................ 62
Sketch of PFD ........................................................................... 63
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1. GAS DEHYDRATION
1.1
•
Brief process Description
The function of the Dehydration unit is to lower the water content of the
incoming feed gas, using molecular sieve bed, to an acceptable level for
the downstream LPG recovery system that operates at low temperature (60ºC). The expected water content at the outlet of dehydration unit is 0.1
ppm.
•
The high pressure gas from HP separator V-2101 is cooled & cooled
recovered gas from 2nd stage recycle compressor C-2302 are mixed
together and sent to a De-methaniser reboiler E-2501 to be cooled to 48°C
& then through feed gas cooler E-2401 ( indirect cooling with propane
refrigeration) to be cooled to 27°C .
•
By cooling the feed gas to 27°C the water loading to mol sieve is greatly
reduced.
•
The cold feed gas from E-2401 flows to Molecular Sieve Inlet Separator V2401 & Coalescer F-2401 to remove the entrained liquid.
•
Wet gas from filter coalescer F-2401 flows to Molecular sieve dryers
through RO-2402-01 designed for 98% of the design flow rate and a slip
stream is fed to Dehydration inlet heater E-2402 so that the total gas is
preheated by 2°C using hot oil. This is done to avoid any retrograde
condensation in the molecular sieve beds.
The figure below explains the retrograde region in a typical phase envelope
diagram.
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Gas is dried in mol sieve adsorbers. The configuration of three molecular
sieve beds, two in parallel adsorption and one in regeneration, has been
installed. The feed gas flows from top to bottom through the molecular
sieve dryer.
•
The hot regeneration gas from Heater E-2403A/B enters Dryer bottom
through sequence valve and leaves the dryer at the top.
•
A dryer is in absorption cycle for approximately 16 hrs and in regeneration
for 8 hrs. The adsorption sequence structure as follows.
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Control System
The following standard control loop is implemented to control the dehydration
system.
•
Gas Cooler E-2401 Outlet Temperature TIC-2401-05 is controlled
by
adjusting the control valve TV-2401-05 ( propane compressor suction line)
•
The Level Controller LIC-2401-01 controls the propane liquid level by
controlling propane flow through the Level Control Valve LV-2401-01 on the
liquid propane inlet line to the shell side of E-2401.
•
Mole sieve Inlet Separator Level V-2401 level is controlled by LIC-2401-02,
which operates LV-2401-02.
•
Mole sieve Inlet Filter Coalescer bridle and filter Level is controlled by LIC2401-12 & LIC-2401-08 (ON/OFF), which operates LV-2401-12 and LV-240108.
•
The temp differential rise across inlet heater E-2402 is controlled by Hot
oil outlet temp via TIC-2402-04, which operates TV-2402-04.
•
Regeneration gas flow is maintained by FIC-2401-01A/B at compressor A &
B outlet, which controls the respective compressor recycle flow control
valves (FV-2401-01 A/B)
•
Regeneration gas temperature is controlled by TIC-2403-04, which operates
both main (TV-2403-04B) and Bypass valve (TV-2403-04A) in gas line.
However, a direct temperature control on hot oil return line also is
provided (TIC-2403-03), which operates the TV-2403-03 to maintain the hot
oil return temperature
•
Regenerated gas is further cooled to 55oC in Regeneration Gas Cooler (A2401). The temperature of the cooler outlet is controlled (TIC-2401-08) by
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adjusting fan blade pitch automatically by use of pneumatic actuator for
50% fans and remaining 50% of the blade pitch control shall be controlled
by sequence logic in on-off mode.
•
The condensate from Regen Gas KO Drum (V-2403) is recycled to MP
separator under level control. Level is controlled with the help of gap type
(on/off) level controller (LIC-2403-01), which controls
1.3 Salient features
The molesieve is provided with following salient features.
•
Molecular Sieve Inlet Filter Coalescer F-2401 is protected by PSV-2401-22,
•
The gas outlet line and oil outlet line from E-2402 are protected by PSV2402-09 and PSV-2402-07 respectively.
•
Molesive bed is protected by PSV-2402-11
•
The filters F-2402A & B are protected by PSV-2402-24 and PSV-2402-25,
respectively.
•
The differential pressure across the filters is indicated in PDI-2402-23 and a
high alarm is provided.
•
The regeneration gas compressor is a constant volume, reciprocating
machine.
•
Compressor Capacity control is achieved by Recycle valves (FV-2401-01
A/B).
•
The Compressor is manually loaded / unloaded (from 0% to 100% in steps of
25%) from compressor package PLC
1.4
•
Sketch of PFD / P&IDs
See below the system PFD and P&ID
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2. TURBO EXPANDER – DE-METHANISER SYSTEM
2.1
•
Brief process Description
Dry gas coming from the outlet of dehydration unit is sent to a Gas/Gas
exchanger E 2502 for cooling the gas and then sent to the low temperature
separator V 2501.
•
The condensate from LT Separator (V-2501) is routed to De-methanizer
Column
•
The dry gas from LT separator is fed to the turbo expander (EXP-2501) and
then to the De-methanizer Column
•
The De-methanizer column is provided with 12 trays and a chimney tray.
The top of the column has a higher diameter due to higher vapour load.
•
The De-methanizer column is designed for 110% design capacity and a
turndown of 40%.
•
The De-methanizer overhead vapour cool the demethaniser reflux via E2504 exchanger and is sent to the gas/gas exchangers as cooling medium
for the incoming dry gas. Further this dry gas is sent to the gas
recompressor suction drum V-2502 and then to the C-2501 recompressor
(driven by turbo-expander).
•
Recompressor discharge gas is sent to the sales gas compressor C-2502
A/B/C.
•
The reboiler uses the inlet dry gas as heating medium. However, a hot oil
kettle reboiler is provided for start up or in case the gas from wells is too
cold to reach the desired column bottom temperature
•
Liquids from the De-methanizer bottom is sent to the De-ethanizer
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Control System
Low Temperature Separator
Pressure Control
•
The pressure of LT Separator (V-2501) is maintained by inlet pressure
controller (PIC-2501-36) located at Turbo-expander inlet.
Level Control
•
The condensate level is maintained by LIC-2501-01, which operates level
control valve LV-2501-01 at the liquid outlet line.
Gas Turbo-expander
•
The dry gas from LT separator is fed to the turbo expander (EXP-2501).
During normal operation the pressure controller PIC-2501-36 regulates the
inlet guide vanes (IGV). The IGV controls both gas throughput and
efficiency of the machine.
•
During start-up of turbo expander, the controller PIC-2501-36 shall be in
auto mode and the pressure shall be maintained via J-T valve (PV-250136).
•
Turbo-expander speed ramping procedure shall be started via expander
unit control panel (UCP). Turbo-expander IGV shall progressively open by
the package controller to achieve the minimum operating speed. During
speed ramping procedure, turbo expander inlet pressure will gradually
drop (as IGV is opening). To compensate this drop in inlet pressure, J-T
valve shall progressively close automatically by PIC-2501-36.
•
On completion of turbo-expander start-up sequence, the UCP shall provide
a status signal to DCS (PIC-2501-36) for switching the J-T valve (PV-250136) to full closure and transferring the IGV control to pressure controller
PIC-2501-36.
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J-T valve (PV-2501-36) shall be on line when Turbo-expander trips. During
J-T mode of operation, Pressure controller PIC-2501-36 will regulate the JT
valve. This JT valve shall remain closed while Turbo-expander unit is in
operation.
Whenever Turbo-expander trips, the package PLC shall give
signal to PIC-2501-36 to control the JT valve.
De-methanizer
Pressure Control
•
De-methanizer column pressure is not directly controlled. Column pressure
floats on the turbo-expander outlet pressure. Turbo-expander outlet
pressure depends on turbo-expander Recompressor performance which in
turn depends on the sales gas compressor suction pressure .
Temperature Control
•
The De-methanizer pump around i.e., part of gas/gas exchanger (E-2502)
return temperature is controlled by by-passing cold gas from Demethanizer top with the help of HV-2502-01 and by-pass valve HV-2502-02(
only 10% flow).
•
De-methanizer bottom temperature is controlled in reboiler. A DCS
selector switch YS-2501-17 is provided to select the reboiler for Mode-A:
De-methaniser Reboiler in line or Mode-B: De-methanizer Auxiliary Reboiler
in line.
Auxiliary Reboiler Temperature Control
•
A temperature sensor is located at Reboiler vapour return line, which
provides the process value input (PV) to temperature controller (TIC-250117), which is cascaded with the hot oil flow controller FIC-2505-01 , that
controls the valve FV-2505-01 in hot oil line and thus controls the column
bottom temperature.
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Demethaniser Reflux Pump Flow Control
•
Two separate flow controllers (FIC-2501-03A/B) are configured with the
same flow transmitter (FT-2501-03) to control main reflux flow and
minimum pump circulation flow
•
The flow controller (FIC-2501-03B) controls the main reflux flow by
operating FV-2501-03B. FIC-2501-03B is cascaded with the level control of
Deethanizer Overhead Receiver (V-2511) LIC-2511-05 and hence, it controls
the Deethanizer Overhead Receiver level.
•
The minimum flow control for Demethanizer reflux pump is maintained by
flow controller FIC-2501-03A, which operates FV-2501-03A to enable flow
back to Demethanizer reflux pump suction.
Level Control
•
The liquid level of the Demethanizer Sump is maintained by level
controller LIC-2501-07. The LIC-2501-07 is cascaded with flow controller
FIC-2501-01, which controls flow to Deethanizer column (T-2511) by
controlling FV-2501-01.
Recompressor
•
Recompressor discharge pressure floats on sales gas compressor suction
pressure. In case of high Recompressor discharge pressure, PIC-2502-08
provided on gas outlet of Recompressor suction drum will open PV-2502-08
and relieve gas to flare.
2.3
Salient features
Low Temperature Separator
•
The separator is protected against high pressure through PSV-2501-09A/B.
•
The separator is provided with a High-High and Low-Low Level trips
through LI-2501-03.
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Gas Turbo-expander
•
The Gas Turbo-Expander is protected against high pressure through PIC2501-36B reliving excess pressure to the Cold Flare. PSV-2501-30 is also
provided.
De-methanizer
•
De-methanizer column is protected against over pressure via PAHH-250116. PSV-2501-17A/B is also provided.
•
The column is provided with a High-High and Low-Low Level trips through
LI-2501-05.
•
The column is provided with a High-High Temperature trip through TI-250504
Recompressor
•
The Recompressor (C-2501) has a antisurge valve (FV-2501-101), which
provides machine protection. The antisurge controller maintains the
required flow through the recompressor above the surge limit by regulating
control valve FV-2501-101.
2.4
•
Sketch of PFD / P&IDs
See below the system PFDs / P&IDs
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Figure : Head vs Vol.Flow chart for recompressor
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Figure :Power Vs Flow for turboexpander
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TURBO EXPANDER – RECOMPRESSOR CONTROL SCHEME
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3. DE-ETHANISER SYSTEM
3.1
•
Brief process Description
Liquids from the de-methanizer bottom are sent to the de-ethanizer
column.
•
The De-ethanizer column is provided with 29 trays and a chimney tray.
•
The De-ethanizer column is designed for 110% design capacity and a
turndown of 40%.
•
The overhead vapours from the de-ethanizer top are partially condensed
by a de-ethanizer overhead condenser (by propane refrigeration). The
condensed fraction is separated in the V-2511 overhead receiver and sent
as reflux both to the de-ethanizer column top and to the demethanizer
column top. The reflux to de-ethanizer is pumped under flow control by
the pumps P-2511 A/B. The reflux to de-methanizer is subcooled in the E2504 and pumped by the P-2501 A/B pumps under level control.
•
The vapours from the de-ethanizer overhead receiver are compressed by a
reciprocating compressor (C-2503) and sent to the sales gas compressor.
•
Heat input to de-ethanizer column is provided by means of kettle reboiler
which is supplied with hot oil as heating medium.
•
3.2
Liquids from the De-ethanizer bottom is sent to the De-butanizer
Control System
Pressure Control
•
De-ethanizer overhead pressure is maintained by PIC-2511-15 located at
De-ethanizer Overhead Receiver (V-2511) which also maintains the Deethanizer overhead compressor suction pressure.
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Temperature Control
•
The temperature profile of the column is established to ensure that the
product quality is achieved. The control system for both top and bottom
tray temperatures are described below:
Top Temperature Control:
•
Column top temperature is maintained by reflux flow. Accordingly, column
temperature controller TIC-2511-02 is cascaded with FIC-2511-05A, which
operates the valve FV-2511-05A downstream of Deethanizer Reflux Pump
(P-2511 A/B) to maintain reflux flow to deethanizer column.
Bottom temperature control:
•
Product quality is achieved by generating adequate boil-up in the reboiler.
A temperature sensor is located at reboiler vapour return line, which
provides the process value input (PV) to temperature controller TIC-251115, which is cascaded with the hot oil flow controller FIC-2511-03, that
controls the valve hot oil flow control valve FV-2511-03 and thus controls
the column bottom temperature.
Deethanizer Reflux Pump Flow Control
•
The Liquid from Deethanizer overhead receiver is pumped as reflux for
Deethanizer column via Deethanizer reflux pump (P-2511 A/B). Two
separate flow controllers (FIC-2511-05A/B) are configured with the same
flow transmitter (FT-2511-05) to control main reflux flow and minimum
pump circulation flow
•
The minimum flow control for Deethanizer reflux pump is maintained by
flow controller FIC-2511-05B, which operates FV-2511-03B to enable flow
back to Deethanizer overhead receiver.
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Deethanizer Condenser Control
•
Deethanizer Overhead Receiver temperature is controlled by TIC-2511-19
which simultaneously controls the valves on main line as well as bypass line
i.e., TV-2511-19A and TV-2511-19B respectively.
•
The Propane flow through the Chiller (Condenser) is independently
controlled by the condenser level. LIC-2507-01 operates the LV-2507-01 to
control Propane flow to E-2507.
•
The dethanizer overhead condenser E 2507 pressure is controlled by the
pressure control valve PV 2820-101 located on the propane gas line to
propane compressor.
Deethanizer Level Control
•
The liquid level of the Deethanizer Sump is maintained by level controller
LIC-2511-03. The LIC-2511-03 is cascaded with flow controller FIC-2511-01,
which controls flow to Debutanizer column (T-2521) by controlling FV-251101.
•
Dethaniser Overhead compressor
The dethaniser compressor is a constant volume, reciprocating machine.
Capacity control is achieved in steps 0,25,50,75,100 % by loading/unloading
cylinders. Dethaniser compressor is manually loaded/unloaded (from 0% to
100% in steps of 25%) from compressor package PLC. In addition, the
capacity control shall be automatically performed (in DCS) by the suction
pressure controller PIC-2511-15 controlling the recycle valve PV -2511-15.
3.3
•
Salient features
De-ethanizer column is provided with high high pressure trip PAHH-2511-08
and PSV-2511-06A/B for overpressure protection.
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The column is provided with a High-High and Low-Low Level trips through
LI-2511-01.
•
3.4
•
The column is provided with a High-High Temperature trips TAHH-2511-14.
Sketch of PFD / P&IDs
See below the system PFD / P&IDs
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4. DE-BUTANISER SYSTEM
4.1
•
Brief process Description
The liquids from the De-ethanizer column bottom are sent to the
debutanizer
•
The De-butanizer column is provided with 29 trays and a chimney tray.
•
The De-butanizer column is designed for 110% design capacity and a
turndown of 40%.
•
The overhead vapours are totally condensed in the A-2521 air cooler.
Product LPG from the air cooler are sent to storage tanks, part of the
condensed liquids are recycled to the top of the column as reflux, by
means the pumps P-2521A/B.
•
Heat input to the debutanizer column is provided by a kettle reboiler
which is supplied with hot oil as heating medium.
•
4.2
Debutanizer bottom stream is sent to the Stabilizer Column.
Control System
Pressure Control
•
The debutaniser column pressure is controlled by PIC 2521-14 and PDIC 2521-15 controlling the control valves PV 2521-14 and PDV 2521-15.
•
A hot gas bypass is provided around the condenser to provide constant
differential pressure control between the debutanizer column and the
reflux drum. PDV-2521-15 is regulated by the controller PDIC-2521-15,
which maintains the desired differential pressure between the column &
reflux drum.
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Temperature Control
•
A temperature sensor is located at reboiler vapour return line, which
provides the process value input (PV) to temperature controller TIC-252114, which is cascaded with the hot oil flow controller FIC-2521-03, that
controls the hot oil flow control valve FV-2521-03 in hot oil line and thus
controlling the column bottom temperature.
Reflux Pump Flow Control
•
Two separate flow controllers (FIC-2521-05A/B) are configured with the
same flow transmitter (FT-2521-05) to control main reflux flow and
minimum pump circulation flow .
Level Control
•
The liquid level of the Debutanizer is maintained by level controller LIC2521-01. The LIC is cascaded with flow controller FIC-2521-01 and control
flow of heavies to Stabilizer column (T-2201) by controlling FV-2521-01.
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Receiver Level Control
•
The liquid level of Debutanizer Receiver is maintained by level controller
LIC-2521-05, which operates LV-2521-05 at Debutanizer Overhead Pump
discharge by controlling LPG flow to Storage Bullets.
Overhead Condenser Temperature Control
•
Temperature at the outlet of Debutanizer Overhead Condenser is
controlled by temperature controller TIC-2521-17 by adjusting fan blade
pitch automatically by use of pneumatic actuator for 50% fans and
remaining 50% of the blade pitch control manually. Moreover, louvers
(manual) are also provided for further control.
4.3
•
Salient features
De-butanizer column is provided with high high pressure trip PAHH-2521-05
and PSV-2521-06A/B for overpressure protection.
•
The column is provided with a High-High and Low-Low Level trips through
LI-2521-03.
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4.4
•
The column is provided with a High-High Temperature trips TAHH-2521-18.
Sketch of PFD
See below the system PFD
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5. SALES GAS COMPRESSOR
5.1
•
Brief process Description
Sales gas must be sent to the battery limit at a pressure of 80 barg. The
final pressure of 80 barg is achieved by means of C-2502 A/B sales gas
compressors (2 x 50%).
•
Compressor will be provided with suction valve unloader system and
recycle line for pressure regulation.
•
Sales gas will be cooled at 55°C by means of the Sales Gas Cooler (A-2501
A/B/C) and export.
•
5.2
A gas metering skid has been provided for gas metering in sales gas export.
Control System
Sales Gas Compressor Suction Pressure Control
•
The suction pressure of Sales Gas Compressor is maintained by recycle of
sales gas compressor discharge gas through recycle valve PV-2501-37A/B
operates in split range. The pressure controller (PIC-2501-37) at the
suction of Sales Gas Compressor shall provide the capacity control through
recycle valve (PV-2501-37A/B). Loading / unloading of the compressor are
done manually from the compressor package UCP.
Sales Gas Temperature Control
•
Temperature of sales gas is controlled by temperature controller TIC-250128 by adjusting fan blade pitch automatically by use of pneumatic actuator
for 50% fans and remaining 50% of the blade pitch control manually.
Moreover, louvers (manual) are also provided for further control.
5.3
•
Salient features
The Sales gas compressor is a constant volume, reciprocating machine.
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Compressor Capacity control is achieved by Recycle valves (PV-2501037A/B).
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Each recycle valve is sized for rated capacity of 1 compressor.
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The Compressor is manually loaded / unloaded (from 0% to 100% in steps of
25%) from compressor package PLC
5.4
•
Sketch of PFD
See below the system PFD
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