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

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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

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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: 3 of 17

CHANGE LIST

SECTION CHANGE 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: 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.:

JI-195

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.:

JI-195

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.:

JI-195

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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Date: 03 Aug. 09

DYNAMIC SIMULATION STUDY Doc. No.: ELM-PUL-PR-XXX-034 Rev: R1FOR SCENARIO – PN02 Page: 8 of 17

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.:

JI-195

Date: 03 Aug. 09

DYNAMIC SIMULATION STUDY Doc. No.: ELM-PUL-PR-XXX-034 Rev: R1FOR SCENARIO – PN02 Page: 9 of 17

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.:

JI-195

Date: 03 Aug. 09

DYNAMIC SIMULATION STUDY Doc. No.: ELM-PUL-PR-XXX-034 Rev: R1FOR SCENARIO – PN02 Page: 10 of 17

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).

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: 11 of 17

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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Date: 03 Aug. 09

DYNAMIC SIMULATION STUDY Doc. No.: ELM-PUL-PR-XXX-034 Rev: R1FOR SCENARIO – PN02 Page: 12 of 17

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.:

JI-195

Date: 03 Aug. 09

DYNAMIC SIMULATION STUDY Doc. No.: ELM-PUL-PR-XXX-034 Rev: R1FOR SCENARIO – PN02 Page: 13 of 17

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.:

JI-195

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.:

JI-195

Date: 03 Aug. 09

DYNAMIC SIMULATION STUDY Doc. No.: ELM-PUL-PR-XXX-034 Rev: R1FOR SCENARIO – PN02 Page: 15 of 17

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.:

JI-195

Date: 03 Aug. 09

DYNAMIC SIMULATION STUDY Doc. No.: ELM-PUL-PR-XXX-034 Rev: R1FOR SCENARIO – PN02 Page: 16 of 17

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

SONATRACH / ANADARKO ASSOCIATIONEL MERK PROJECT

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DOCUMENT TITLE: Project No.:

JI-195

Date: 03 Aug. 09

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7.0 APPENDIX-MODEL SNAPSHOT