This presentation demonstrates comparison of Line Pack calculation, using Aspen PLUS Dynamics and using Manual Calculations. The calculation results match closely. For the example problem discussed in the presentation. the line pack calculated by Aspen PLUS Dynamics is 35.988 MMSCF and the line pack calculated by using manual calculations is 34.969 MMSCF. The slight difference between the two may be attributed to the difference in computational method in Aspen PLUS Dynamics software.

1. COMPARISON OF LINE PACK CALCULATION USING
ASPEN PLUS DYNAMICS AND BY USING MANUAL
CALCULATIONS
PREPARED BY:
MUHAMMAD WAQAS MANZOOR
PROCESS ENGINEER
Contact: engr.waqasmanzoor@gmail.com

2. 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.

3. CALCULATION USING ASPEN PLUS DYNAMICS
• First of all, build a steady state
simulation of the pipe line
segment, in Aspen PLUS

4. SPECIFICATIONS OF PIPE SEGMENT IN ASPEN PLUS

5. SPECIFICATIONS OF PIPE SEGMENT IN ASPEN PLUS

6. SPECIFICATIONS OF VALVE ‘BV-1’ IN ASPEN PLUS

7. SPECIFICATIONS OF VALVE ‘BV-1’ IN ASPEN PLUS

8. SPECIFICATIONS OF VALVE ‘BV-2’ IN ASPEN PLUS

9. SPECIFICATIONS OF VALVE ‘BV-2’ IN ASPEN PLUS

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

11. EXPORTING SIMULATION TO ASPEN PLUS
DYNAMICS
• After that, set ‘Input mode’ to
‘dynamic’ from ‘steady state’.

12. EXPORTING SIMULATION TO ASPEN PLUS
DYNAMICS
• After that, click on ‘File Menu’, and
select ‘Pressure Driven’ from
‘Update Aspen PLUS Dynamics
Menu’.

13. EXPORTING SIMULATION TO ASPEN PLUS
DYNAMICS
• These 03 files and a folder are
created in the same folder where
Aspen PLUS ‘.bkp‘ file was
previously stored.

14. SNAPSHOT OF ASPEN PLUS DYNAMICS WINDOW

15. INITIAL BOUNDARY CONDITIONS IN ASPEN PLUS
DYNAMICS

16. FINAL BOUNDARY CONDITIONS IN ASPEN PLUS
DYNAMICS

17. CONFIGURATION OF PIPE SEGMENT IN ASPEN PLUS
DYNAMICS

18. CALCULATION USING ASPEN PLUS
DYNAMICS

19. 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

20. EQUATIONS USED FOR MANUAL CALCULATION OF
LINE PACK
• Here Vb represents Line Pack,
calculated for a pipe segment
having an internal diameter D,
length L, and containing natural
gas at an average pressure and
temperature of Pavg, and Tavg,
respectively.
• Tb, and Pb represent thr base
temperature and base pressure,
respectively.
Ref: ‘Gas Pipeline Hydraulics’ by E. Shashi Menon

21. CALCULATION OF COMPRESSIBILITY FACTOR
Ref: ‘Gas Pipeline Hydraulics’ by E. Shashi Menon

22. 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.
Ref: ‘Gas Pipeline Hydraulics’ by E. Shashi Menon

23. 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

24. 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 calculation
methods and computational methods in Aspen PLUS Dynamics. However, results of Aspen PLUS Dynamics
are more accurate.
* California Natural Gas Association