PSV SIMULATION
FOR
GAS-WATER SEPARATION SYSTEM

Description

This example shows the simulation of 4 pressure safety devices to be design for an off-shore gas-condensate treatment plant.

It also presents how the SETSTR (stream creation) function can be used for preparing input streams of pressure safety devices.

A Gas/Water Separation System, to be installed on an offshore platform, is designed to separate from hydrocarbon gas and condensate as much as possible the produced and condensed free water. Separation of the sour water is necessary for sealine corrosion protection.

This system includes also a facilities for testing individual wells that are gathered at the inlet of this plant.

The system operates at very high pressure: gas condensate feed stream is received at 241 bar.

The inlet fluid is treated in two parallel free water KO-drums (FWKO). Separated water will be sent to sour water treatment system.

FWKO drums operate at about 125 bar with a design pressure of 140 bar

Pressure safety devices are to be design to protect equipments from various contingencies (fire, equipment failures, etc.).

Feed stream

The feed composition is defined using 23 chemical components and a hypothetical components. Its status as generated by the simulation is as follows.

* STREAM 'FEED '

- Temperature 90.000 CENT - Pressure 241.0000 BAR

Phase TOTAL VAPOUR LIQUID H LIQUID W

Molar Flow Rate KMOL /HR 60862.000 59171.896 1000.998 689.106

Weight Flow Rate KG /HR 1316665.937 1234900.224 69348.029 12417.685

Molar Fraction 0.972231 0.016447 0.011322

Weight Fraction 0.937899 0.052669 0.009431

Molecular Weight 21.6336 20.8697 69.2789 18.0200

Std Vap Vol Rate N-CUMT /HR 1399110.2132

Std Liq Vol Rate CUMT /HR 112.5573 100.1524 12.4049

Act Volume Rate CUMT /HR 6725.2869 6607.8690 104.6977 12.7202

Enthalpy M-KJ /HR -62242.3146 -24650.8843 -10862.0757 -26729.3545

Spec. Enthalpy KJ/KG -47.281 -19.965 -156.660 -2152.914

KJ/KMOL -1022.865 -416.674 -10853.214 -38795.522

Spec. Heat Cap. KJ/KG-C 3.058130 3.084924 2.384704 4.154357

KJ/KML-C 66.158446 64.381464 165.209567 74.861527

Spec. Entropy KJ/KG-C 7.2934 7.6017 2.5359 3.2065

KJ/KML-C 157.7835 158.6452 175.6861 57.7816

Compressibility 0.891208

Density KG/CUMT 195.7784 186.8833 662.3641 976.2215

Gravity at 60/60 0.692407 1.001004

Isentr. Exponent 1.240206

Viscosity CP 0.2332E-01 0.2296 0.3129

Thermal Conduct. W/MC 0.069149 0.135337 0.663746

Surface Tension DYCM 7.4670 60.8376

Reference Gas Status - Temperature 15°C - Pressure 1 atm

----- TOTAL PHASE -----

No Components Mol. Rate Mol. Fr Wt. Rate Wt. Fr.

KMOL/HR KG /HR

1 NITROGEN 1811.525 0.029764 50740.795 0.038537

2 CARBON DIOXIDE 1076.219 0.017683 47364.411 0.035973

3 HYDROGEN SULPHIDE 486.152 0.007988 16568.068 0.012583

4 METHANE 49989.814 0.821363 801836.267 0.608990

5 ETHANE 3158.166 0.051891 94966.078 0.072126

6 PROPANE 1052.519 0.017294 46416.116 0.035253

7 ISOBUTANE 227.276 0.003734 13209.289 0.010032

8 BUTANE 382.845 0.006290 22250.941 0.016899

9 ISOPENTANE 155.569 0.002556 11224.281 0.008525

10 PENTANE 155.569 0.002556 11224.281 0.008525

11 HEXANE 179.269 0.002945 15449.368 0.011734

12 CYCLOHEXANE 23.700 0.000389 1994.609 0.001515

13 METHYLCYCLOPENTANE 18.231 0.000300 1534.314 0.001165

14 BENZENE 12.154 0.000200 949.334 0.000721

15 HEPTANE 185.346 0.003045 18573.477 0.014106

16 METHYLCYCLOHEXANE 48.008 0.000789 4713.763 0.003580

17 METHYLBENZENE 18.231 0.000300 1679.777 0.001276

18 OCTANE 197.499 0.003245 22560.348 0.017134

19 ETHYLBENZENE 77.784 0.001278 8258.364 0.006272

20 NONANE 167.115 0.002746 21434.144 0.016279

21 1-METH-3-ETH-BENZENE 23.700 0.000389 2848.588 0.002163

22 DECANE 131.261 0.002157 18677.139 0.014185

23 C11 PLUS FRAC 305.060 0.005012 64550.801 0.049026

24 WATER 978.989 0.016085 17641.385 0.013399

*** TOTAL *** 60862.000 1.000000 1316665.937 1.000000

Thermodynamic methods

The Soave-Redlich-Kwong (SRK) or Peng-Robinson (PR) equations of state can be used to simulate this problem. In this particular case the SRK-KD, Kabadi-Danner modification of the SRK equation, is selected to get a better results of the water-hydrocarbon interactions.

Results

The SETSTR operations copy necessary stream compositions to be used for the simulation of safety valves and reset the flow-rate to a nominal 1000 kmol/hr for easy scaling of the results.

One of the simulated pressure safety devices is presented hereunder.

*** UNIT 10 - 'PSD1 ' - ' PRESSURE SAFETY DEVICE ' ***

--- Feed Streams --- - Product Streams -

'S1PSV ' 'S1O '

1) * OPERATING CONDITIONS *

Relief pressure 241.000 bar

Relief temperature 90.00 °C

Relief status - Molar fractions

Vap 0.969561 - Liq 1/H 0.015812 - Liq 2/W 0.014626

Flow is critical

Critical flow pressure 129.924 bar Ratio 0.5391

Critical flow temperature 51.47 °C

Status - Molar fractions

Vap 0.945761 - Liq 1/H 0.038487 - Liq 2/W 0.015752

Fluid velocity 367.531 MT/s

Sonic velocity 367.816 MT/s

Mach no 0.9992

Final pressure 1.000 bar

Final temperature 24.27 °C

2) * SIZE DATA *

Calculation method ' Isentr max flow '

Calculated discharge area 0.196 in2

1.262 CM2

KB value 1.000

KC value 1.000

KD value 1.000

2) * FEEDS *

Stream S1PSV

Temperature, °C 90.00

Pressure, bar 241.000

Total rate, kmol/h 1000.0

Vapor, kmol/h 969.56

Liquid 1/H, kmol/h 15.812

Liquid 2/W, kmol/h 14.6

3) * PRODUCTS *

Stream S1O

Temperature, °C 24.27

Pressure, bar 1.000

Total rate, kmol/h 1000.0

Vapor, kmol/h 978.06

Liquid 1/H, kmol/h 12.144

Liquid 2/W, kmol/h 9.80

Generated Keyword Input File

The generated key-word input file is listed hereunder.

<XPSIM> ...generated by XpsimWin v.1.06 ...

RUN ID=OFFSHORE CUSTOMER=A-CLIENT PROJECT='XYZ GAS FIELD'

DESC XYZ GAS FIELD PRODUCTION - PHASES 1&2

DIMENSION INPUT SI PRES=BAR

Petroleum Data

HYPO ID=C11+ NAME='C11 PLUS FRAC' SPGR=0.853 MW=211.6

System Data

CHEMCOMP N2 / CO2 / H2S / C1 / C2 / C3 / IC4 / NC4 / IC5 / NC5 / NC6 +

/ CH / MCP / BNZN / NC7 / MCH / TOLU / NC8 / EBZN / NC9 / M3EZ / +

NC10 / C11+ / H2O

THERMSET UID=M1

METHODS K=SRK-KD HS=LK CP=LK D=LK IV=LK TRAN=ELYHAN SURT=IDEAL

WOPT K=2

Flowsheet Data

EQUI 3PHASE LLSM=L1L2 KEY1=H2O

STREAM=FEED TEMP=90 PRES=241 RATE=60862 XBASIS=M

COMP N2:2.981 / CO2:1.771 / H2S:0.800 / C1:82.262 / C2:5.197 / +

C3:1.732 / IC4:0.374 / NC4:0.630 / IC5:0.256 / NC5:0.256 / NC6:0.295 +

/ CH:0.039 / MCP:0.030 / BNZN:0.020 / NC7:0.305 / MCH:0.079 / +

TOLU:0.030 / NC8:0.325 / EBZN:0.128 / NC9:0.275 / M3EZ:0.039 / +

NC10:0.216 / C11+:0.502 / H2O:1.611

SPLITTER IN FEED OUT S1T S1 UID=SPL1

SPEC STR=S1T RATE=5370.6

VALVE IN S1T OUT S2T UID=V1

CALC PRES=126

FLASH IN S2T OUT S3T(V) S5T(LW) S4T(LH) UID=VP-001 +

DESC='TEST SEPARATOR'

VALVE IN S1 OUT S2 UID=V2

CALC PRES=125

SPLITTER IN S2 OUT S3 S3A UID=SPL2

SPEC STR=S3 RATE=0.5 RATIO

FLASH IN S3 OUT S4(V) S6(LW) S5(LH) UID=VS-001

CALC ADIA DP=0

ENTRAIN PHASE=LW IN=LH RATIO(V)=0.08

VALVE IN S4 OUT S9 UID=V3

CALC DP=-2

MIXER IN S3T S9 OUT S9M UID=MX1

COMPSEP IN S5 OUT S7 S8 UID=SEP1

OVHD STR=S7

BTMS STR=S8

OVHFLOW COMP=N2,C11+ RATIO=1

OVHFLOW COMP=H2O RATIO=0.20

SETSTR UID=SS1 STR=S1PSV

COPY STR=S1

REDEF RATE(M)=1000

PSD IN S1PSV OUT S1O UID=PSD1

PARA CALC=1 METHOD=MXFLOW PSET=241 PBACK=1

SIZE DEVICE=VALVE KB=1 KC=1 KD=1

SETSTR UID=SS2 STR=S4PSV

COPY STR=S4

REDEF RATE(M)=1000

PSD IN S4PSV OUT S11 UID=PSD2

PARA CALC=1 METHOD=MXFLOW PSET=139 PBACK=1

SIZE DEVICE=VALVE KB=1 KC=1 KD=1

SETSTR UID=SS3 STR=S2PSV

COPY STR=S2

REDEF RATE(M)=1000

PSD IN S2PSV OUT S13 UID=PSD3

PARA CALC=1 METHOD=MXFLOW PSET=139 PBACK=1

SIZE DEVICE=VALVE KB=1 KC=1 KD=1

SETSTR UID=SS4 STR=S5PSV

COPY STR=S5

REDEF RATE(M)=1000

PSD IN S5PSV OUT S15 UID=PSD4

PARA CALC=1 METHOD=OMEGA PSET=139 PBACK=1

SIZE DEVICE=VALVE KB=1 KC=1 KD=1

Output Data

PRINT FORMAT=2

END