elm pul pr xxx 034 agc final
TRANSCRIPT
EL MERK PROJECT
ELM-PUL-PR-XXX-034
TRANSIENT STUDY REPORT -TRIP ASSOCIATED GAS COMPRESSOR (PA01)
R1 03/08/2009 JSK SGW - - - Issued for Information
REV DATE BY CHKD ENGAPPV
CLIENTAPPV
PAGENO.
DESCRIPTION
SONATRACH / ANADARKO ASSOCIATIONEL MERK PROJECT
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DOCUMENT TITLE: Project No.:
JI-195
Date: 03 Aug. 09
DYNAMIC SIMULATION STUDY Doc. No.: ELM-PUL-PR-XXX-034 Rev: R1FOR SCENARIO – PN02 Page: 2 of 17
TABLE OF CONTENTS
1.0 OBJECTIVE.....................................................................................................................4
2.0 STEADY STATE STARTTING POINT & ACTION...............................................4
3.0 OBSERVATIONS........................................................................................................6
4.0 HOLDS.........................................................................................................................7
5.0 CONCLUSION.............................................................................................................8
6.0 TRENDS.......................................................................................................................9
7.0 APPENDIX-MODEL SNAPSHOT.........................................................................15
SONATRACH / ANADARKO ASSOCIATIONEL MERK PROJECT
PETROFAC
DOCUMENT TITLE: Project No.:
JI-195
Date: 03 Aug. 09
DYNAMIC SIMULATION STUDY Doc. No.: ELM-PUL-PR-XXX-034 Rev: R1FOR SCENARIO – PN02 Page: 3 of 17
CHANGE LIST
SECTION CHANGE DESCRIPTION
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DOCUMENT TITLE: Project No.:
JI-195
Date: 03 Aug. 09
DYNAMIC SIMULATION STUDY Doc. No.: ELM-PUL-PR-XXX-034 Rev: R1FOR SCENARIO – PN02 Page: 4 of 17
1.0 OBJECTIVE
A dynamic process model has been built of the Associated Gas Compressor to confirm
whether additional surge protection is required on shutdown such as hot or cold gas
bypass valves, and come up with a preliminary sizing.
2.0 STEADY STATE STARTTING POINT & ACTION
The model is built in a modular fashion. Initially one train of each compression system is
built based on preliminary piping data and vendor compressor curves. The model starts
from Vapor outlet of C01-2001 and ends at second stage associated gas compressor
outlet. Tripping of the compressors is intituled from a steady state. Peak Oil Winter is the
governing case for the compressor and the same has been used as basis for this study.
The simulation model is built in UniSim Design Dynamics version R380.1 which contains
the following key features:
All associated pipework is modelled in order to correctly account for
pressure drops in pipework and its associated volume based on preliminary
Isometrics
All process equipment volumes are modelled to simulate variations of
pressure with flow
Compressor performance curves along with the compressor motor
performance are simulated by the use of vendor preliminary data
Compressor inertia characteristic is estimated based on similar systems and
modelled to represent spin-down characteristics upon tripping or shutdown.
All valve CVs are assumed based on industry practice.
The flare back pressure is considered as a fixed pressure boundary at 2.5
Bara.
The outlet of the model downstream of the discharge of the compressor was
a fixed pressure boundary set at 39.72 bara.
Basis of input data:
Antisurge-valve: In absence of data for ASVs, Cv has been calculated based on the outlet
pressure @ surge conditions and compressor inlet pressure. This Cv has been doubled
and used in this study. A stroke time for ESD trip is assumed at 1 second.
SONATRACH / ANADARKO ASSOCIATIONEL MERK PROJECT
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DOCUMENT TITLE: Project No.:
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Date: 03 Aug. 09
DYNAMIC SIMULATION STUDY Doc. No.: ELM-PUL-PR-XXX-034 Rev: R1FOR SCENARIO – PN02 Page: 5 of 17
Aircooler: Aircooler with design parameters is modelled outside the main process model,
the k value and UA value with margin becomes the basis for the aircooler in main process
model. Variable speed fan control from the corresponding TIC is assumed to be between
100% and 40% of the maximum fan air flow. 10% natural draft is considered per fan
when shut down (variable as well as fixed speed).
Aircooler Inlet / outlet distribution sub- headers have been accounted for in the isometric
analysis for calculation of equivalent length on a pro-rated basis. (Refer Isometric Analysis
Spreadsheet)
Compressor: Minimum and maximum molecular weight case have been selected for
performance curve input. 2.5% head rise is considered over surge point and the curves
have been extrapolated.
Set point for anti-surge control is based on the surge flow with varying molecular weight
with a 10% margin considered over calculated surge flow for the surge control line.
Inertia: The string rotational inertia is estimated based on driver power and speed from
experience on similar motor driven compressor systems.
Initial Condition : Mass flow: 5.103e+4 kg/hr
Pressure: 6 bar
Temperature: 68.26 C
Configuration : Compressor running at steady state
Comp speed = 8103 rpm
1st Stage Suction Pressure = 1.934 bara
1st Stage Discharge Pressure = 14.81 bara
2nd Stage Suction Pressure = 14.01 bara
2nd Stage Discharge Pressure = 40.57 bara
Action : After 60 seconds, the ESD signal is activated to trip the unit:
- the motor driver is tripped
- the ASV’s are tripped open (1 second opening time)
- the shutdown valves are tripped close.
Duration : 120 seconds (data points are collected for 60sec after the
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DOCUMENT TITLE: Project No.:
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Date: 03 Aug. 09
DYNAMIC SIMULATION STUDY Doc. No.: ELM-PUL-PR-XXX-034 Rev: R1FOR SCENARIO – PN02 Page: 6 of 17
trip).
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DOCUMENT TITLE: Project No.:
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Date: 03 Aug. 09
DYNAMIC SIMULATION STUDY Doc. No.: ELM-PUL-PR-XXX-034 Rev: R1FOR SCENARIO – PN02 Page: 7 of 17
3.0 OBSERVATIONS
It is of note that the 1st stage inlet cooler is not able to control to the desired inlet
temperature of 60C at the start of the scenario due to the design of this unit being for hot
recycle flow. When the trip occurs the cooler is unable to respond quickly enough to the
rapid change in inlet temperature +30C in <5 seconds, and the outlet temperature
increases by 20C to ~ 75C transiently. It may be beneficial on a trip (or opening of the
recycle valve) to increase the fan speed to allow for the sudden increase in inlet
temperature.
Based on the assumed inertia value of 1200 kg-m2, the rotational speed drops from
design (8103 rpm) to below 20% (1500 rpm) 20 seconds after the trip occurs (and
continues to decelerate beyond this). After 60 seconds the speed has dropped to ~5%.
1ST Stage Associated Gas Compressor
The opening of the anti-surge valve takes 1 second to complete. In this time the
compressor motor speed is decreasing at a faster rate than the discharge pressure is
declining (due to the valve opening). The compressor transiently surges, however the
assumed sizing of the anti-surge valve is such that the compressor runs down to the left
of the surge limit line (as assumed by the fan laws from the surge point of the design
speed curve).
There are a number of factors that would prevent this rundown trajectory:
A higher string inertia (this is assumed) and if it increases, will result in an
improved rundown trajectory
Having a large anti-surge valve size (this is currently assumed although is sized
based on standard methods) would produce a better rate of depressurisation.
However, having an oversized ASV is not desirable.
Increasing the rate of depressurisation of the discharge. This can be achieved by
employing a parallel valve with the ASV (with a CV of ~150). With such a
modification the compressor will only briefly enter surge for less than 1 second.
Typically from past experience this would not be considered to have any impact on
the machine (and is unlikely to be observable on the actual system).
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DOCUMENT TITLE: Project No.:
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Suction and discharge isolation valves close (at an assumed rate of 1 second per inch
valve size). Suction pressure rises to around 5 bara (after about 10 seconds), which is to
be expected due to the vent pressure on the upstream oil stabilizer column (with only 1
string modelled) being set at 6 bara and the closing time of the inlet isolation valve. The
pressure continues to rise (due to the leakage flow into the 1st stage loop from the second
stage discharge), and after 1 minute is at 5.34 bar. By the end of the 120 seconds (60
seconds after the trip) the discharge pressure to the 1st stage is also at this level.
It is not expected that the system will be able to restart from this pressure and some
blowdown is likely to be required before a restart. Also if parallel strings are in operation
then it is expected that their motor power limit controls would be active, limiting the
respective suction throttle valve positions.
Note that on the 1st stage discharge the leakage from the second stage discharge
continues to flow.
2nd Stage Associated Gas Compressor.
The opening of the anti-surge valve takes 1 second to complete. In this time the
compressor motor speed is decreasing at a faster rate than the discharge pressure is
declining (due to the valve opening). The compressor transiently surges, however this is
of duration of around 0.5 seconds and as such additional anti-surge protection is not
deemed a requirement.
Suction and discharge isolation valves close (at am assumed rate of 1 second per inch
valve size). Suction pressure rises transiently to 15.5 bara and then starts to fall as the 2nd
stage is slowly depressured via the 2nd stage discharge leakage (to the 1st stage loop). By
the end of 120 seconds, the 2nd stage loop pressure is only marginally above the original
2nd stage suction pressure (and continuing to fall).
The system should be retested at a later date once the data currently assumed becomes
available.
4.0 HOLDS
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DOCUMENT TITLE: Project No.:
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The following parameters used in the study need to updated with compressor vendor final
inputs:
Anti-surge valve Cv and confirmed stroke time
Final piping / isometric data
String inertia (motor, couplings, gearbox, and rotors)
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DOCUMENT TITLE: Project No.:
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5.0 CONCLUSION
The model predicts that surge entry for the second stage occurs for a very brief period, and as such a hot gas bypass valve is not considered necessary.
On the first stage rundown occurs to the left of the (assumed) surge limit line. As such the compressor vendor should be consulted. If additional surge protection is required, then an additional small valve (installed in parallel to the ASV, possibly 4 inch) can provide the necessary surge protection on rundown.
System settleout pressure for the 1st stage will be such that some blowdown will be required before a restart can be attempted.
This analysis will should be revisited based on vendor data on compressor design and performance (and inertias).
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DOCUMENT TITLE: Project No.:
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6.0 TRENDS
Hot/cold bypass is required for first stage and for second stage as the time for which the compressor goes is 0.7 secs, bypass may not be required. However this will be again revisited based on vendor data on compressor design and performance. Trends are listed below for illustration purpose.
Ist Stage Associated Gas Compressor X-Y plot of performance map
El Merk: Compressor Trip - K01-2502-1 Operating Map
0
2000
4000
6000
8000
10000
12000
14000
16000
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
Suction Flow (ACT_m3/h)
Operating Point
Static Curve
Start
End
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DOCUMENT TITLE: Project No.:
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1st Stage Polytropic Head (m)
El Merk: Compressor Trip - K01-2502-1
12321
1980
2000
4000
6000
8000
10000
12000
14000
16000
0.0 20.0 40.0 60.0 80.0 100.0 120.0Time (Secs)
K01-2502-1
Max
Min
1st Stage Suction Volumetric Flow (m3/hr)
El Merk: Compressor Trip - K01-2502-1
16825
00
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
0.0 20.0 40.0 60.0 80.0 100.0 120.0Time (Secs)
K01-2502-1
Max
Min
1st Stage ASV flow (kg/hr)
El Merk: Compressor Trip
01FV-25205 - Mass Flow
78610
0
0
15000
30000
45000
60000
75000
90000
0.0 20.0 40.0 60.0 80.0 100.0 120.0Time (Secs)
Trendline
Max
Min
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DOCUMENT TITLE: Project No.:
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Date: 03 Aug. 09
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1st Stage Suction / Discharge Pressures
El Merk: Compressor Trip
5
2
15
5
0
2
4
6
8
10
12
14
16
0.0 20.0 40.0 60.0 80.0 100.0 120.0
Time (Secs)
K01-2502-1 - Feed P ressure K01-2502-1 - P roduct P ressure
1st stage suction cooler outlet temperature (C)
El Merk: Compressor Trip
A01-2501 - Tube Outlet Temperature
74.2
46.4
0
20
40
60
80
0.0 20.0 40.0 60.0 80.0 100.0 120.0Time (Secs)
Trendline
Max
Min
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DOCUMENT TITLE: Project No.:
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Date: 03 Aug. 09
DYNAMIC SIMULATION STUDY Doc. No.: ELM-PUL-PR-XXX-034 Rev: R1FOR SCENARIO – PN02 Page: 14 of 17
2nd Stage Associated Gas Compressor X-Y plot of performance map
El Merk: Compressor Trip - K01-2502-2 Operating Map
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
0 500 1000 1500 2000 2500 3000 3500 4000 4500
Suction Flow (ACT_m3/h)
Operating Point
Static Curve
Start
End
2nd Stage Polytrophic Head (m)
El Merk: Compressor Trip - K01-2502-2
7716
640
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
0.0 20.0 40.0 60.0 80.0 100.0 120.0Time (Secs)
K01-2502-2
Max
Min
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DOCUMENT TITLE: Project No.:
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Date: 03 Aug. 09
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2nd Stage Suction Volumetric Flow (m3/hr)
El Merk: Compressor Trip - K01-2502-2
3645
3010
500
1000
1500
2000
2500
3000
3500
4000
4500
0.0 20.0 40.0 60.0 80.0 100.0 120.0Time (Secs)
K01-2502-2
Max
Min
2nd Stage ASV mass flow (kg/hr)
El Merk: Compressor Trip
01FV25206 - Mass Flow
108962
0
0
20000
40000
60000
80000
100000
120000
0.0 20.0 40.0 60.0 80.0 100.0 120.0Time (Secs)
Trendline
Max
Min
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DOCUMENT TITLE: Project No.:
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Date: 03 Aug. 09
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2nd Stage Suction / Discharge Pressures
El Merk: Compressor Trip
1614
41
14
0
5
10
15
20
25
30
35
40
45
0.0 20.0 40.0 60.0 80.0 100.0 120.0
Time (Secs)
K01-2502-2 - Feed P ressure K01-2502-2 - P roduct P ressure
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DOCUMENT TITLE: Project No.:
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7.0 APPENDIX-MODEL SNAPSHOT