presentation on line pack calculation

5/20/2018 Presentation on Line Pack Calculation

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COMPARISON OF LINE PACK CALCULATION USING

ASPEN PLUS DYNAMICS AND BY USING MANUAL

CALCULATIONSPREPARED BY:

MUHAMMAD WAQAS MANZOOR

PROCESS ENGINEER

Contact: [email protected]


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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.


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CALCULATION USING ASPEN PLUS DYNAMICS

First of all, build a steady state

simulation of the pipe line

segment, in Aspen PLUS


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SPECIFICATIONS OF PIPE SEGMENT IN ASPEN PLUS


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SPECIFICATIONS OF PIPE SEGMENT IN ASPEN PLUS


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SPECIFICATIONS OF VALVE BV-1 IN ASPEN PLUS


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SPECIFICATIONS OF INLET STREAM NG-1 IN ASPEN PLUS


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EXPORTING SIMULATION TO ASPEN PLUS

DYNAMICS

After that, set Input mode to

dynamic from steady state.


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DYNAMICS

After that, click on File Menu, and

select Pressure Driven from

Update Aspen PLUS Dynamics

Menu.


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DYNAMICS

These 03 files and a folder are

created in the same folder where

Aspen PLUS .bkp file was

previously stored.


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SNAPSHOT OF ASPEN PLUS DYNAMICS WINDOW


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INITIAL BOUNDARY CONDITIONS IN ASPEN PLUS

DYNAMICS


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FINAL BOUNDARY CONDITIONS IN ASPEN PLUS

DYNAMICS


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CONFIGURATION OF PIPE SEGMENT IN ASPEN PLUS

DYNAMICS


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CALCULATION USING ASPEN PLUSDYNAMICS


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CALCULATION OF LINE PACK FROM SIMULATIONRESULTS 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


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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


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CALCULATION OF COMPRESSIBILITY FACTOR



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CALCULATION OF AVERAGE PRESSURE AND

AVERAGE TEMPERATURE

Here P1 and P2 are in absolute

pressure units.

Average Temperature is

typically calculated by taking

arithmetic mean of inlet and

out temperatures (in absolute

units) of the pipe segment.



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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


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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

.

.

.. 14.314 100

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

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