presentation on calculation of line pack of natural gas pipe using aspen plus dynamics and using...

COMPARISON OF LINE PACK CALCULATION USING ASPEN PLUS DYNAMICS AND BY USING MANUAL

CALCULATIONSPREPARED BY:

MUHAMMAD WAQAS MANZOOR

PROCESS ENGINEER

Contact: [email protected]

LINE PACK

• The quantity of natural gas contained in a certain segment of a pipeline is known as line pack.

• It is typically measured in MMSCF.

CALCULATION USING ASPEN PLUS DYNAMICS

• First of all, build a steady statesimulation of the pipe linesegment, in Aspen PLUS

SPECIFICATIONS OF PIPE SEGMENT IN ASPEN PLUS

SPECIFICATIONS OF VALVE ‘BV-1’ IN ASPEN PLUS

SPECIFICATIONS OF VALVE ‘BV-2’ IN ASPEN PLUS

SPECIFICATIONS OF INLET STREAM ‘NG-1’ IN ASPEN PLUS

EXPORTING SIMULATION TO ASPEN PLUS DYNAMICS

• After that, set ‘Input mode’ to ‘dynamic’ from ‘steady state’.


• After that, click on ‘File Menu’, and select ‘Pressure Driven’ from ‘Update Aspen PLUS Dynamics Menu’.


• These 03 files and a folder are created in the same folder where Aspen PLUS ‘.bkp‘ file was previously stored.

SNAPSHOT OF ASPEN PLUS DYNAMICS WINDOW

INITIAL BOUNDARY CONDITIONS IN ASPEN PLUS DYNAMICS

FINAL BOUNDARY CONDITIONS IN ASPEN PLUS DYNAMICS

CONFIGURATION OF PIPE SEGMENT IN ASPEN PLUS DYNAMICS

CALCULATION USING ASPEN PLUS DYNAMICS

CALCULATION OF LINE PACK FROM SIMULATION RESULTS OF ASPEN PLUS DYNAMICS• Molar concentration of gas within the pipe segment = 0.160589 lbmol/cf

• Actual volume of pipe segment = 3.14 x {(14.314/12)^2} /4 x 528000 ft = 590042.558 cf

• Number of Moles of gas contained in the pipe segment = 0.160589 lbmol/cf x 590042.558 cf = 94754.344 lbmol

Calculation of Molar Volume at Standard Conditions:• Molar Volume (Vmn) of any gas at normal conditions i.e. 0 C & 1 atm, is given by,

• Vmn = 22.414 Nm3 / kgmole = 22.414 Nm3 x (1 ft /0.3048 m)^3 x 0.454 kgmol/lbmol

• Vmn = 359.360 Ncf/lbmol

• Molar volume (Vms) at standard conditions i.e. 60 F (15.55 C) and 14.7 psia (1 atm), is given by

• 359.360 cf x 14.7 psi / 492 F = Vms x 14.7 / 520 F

• Or, Vms = 379.811 Scf/lbmol

Calculated Line Pack = 94754.344 lbmol x 379.811 Scf/lbmol = 35.988 MMSCF

EQUATIONS USED FOR MANUAL CALCULATION OF LINE PACK

• Here Vb represents Line Pack,calculated for a pipe segmenthaving an internal diameter D,length L, and containing naturalgas at an average pressure andtemperature of Pavg, and Tavg,respectively.

• Tb, and Pb represent thr basetemperature and base pressure,respectively.

Ref: ‘Gas Pipeline Hydraulics’ by E. Shashi Menon

CALCULATION OF COMPRESSIBILITY FACTOR


CALCULATION OF AVERAGE PRESSURE AND AVERAGE TEMPERATURE

• Here P1 and P2 are in absolutepressure units.

• Average Temperature istypically calculated by takingarithmetic mean of inlet andout temperatures (in absoluteunits) of the pipe segment.


MANUAL CALCULATION OF LINE PACK• Molecular Mass of gas used in Aspen PLUS simulation = 16.0427 lb/lbmol

• Specific gravity of gas = 16.0427 / 29 = 0.5531

• Pressure of gas at Inlet of pipe segment = 898.093 psia

• Pressure of gas at Outlet of pipe segment = 702.895 psia

• Average Pressure of gas across the pipe segment = 898.093 + 702.895 − . × .. .

= 804.460 psia = 789.76 psig (1 atm = 14.7 psia)

• Temperature of gas at Inlet of pipe segment = 74.1135 F = 534.1135 R

• Temperature of gas at Outlet of pipe segment = 63.44 F = 523.44 R

• Average Temperature of gas across the pipe segment = . . = 528.776 R

• Average compressibility of gas across the pipe segment = . × × . × .

. .

= 0.90807

MANUAL CALCULATION OF LINE PACK• Base Temperature = 60 F = 520 R

• Base Pressure = 14.7 psia

• Internal Diameter of pipe segment = 14.314 inches

• Total Length of pipe segment = 100 miles = 528000 ft

• Line Pack (Vb) calculated using CNGA* method is given by,

• Vb = 28.798 × .

× . . × .

× 14.314 × 100푚푖푙푒푠

• Vb = 34.969 MMSCF

• Line pack calculated using Aspen PLUS Dynamics = 35.988 MMSCF

• The calculated Line Pack ‘Vb’ closely matches with the line pack calculated using Aspen PLUS Dynamics.

• The difference between the two, may be attributed to the difference in physical properties calculationmethods and computational methods in Aspen PLUS Dynamics. However, results of Aspen PLUS Dynamicsare more accurate.

* California Natural Gas Association

presentation on calculation of line pack of natural gas pipe using aspen plus dynamics and using...

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