Chemical Engineering Software

MixProps:  Natural Gas Transport Example

Natural gas flows from a well at 1425 psia and 60 F at a flowrate of 27 MMSCFD.  The gas is to be heated to 110 F before being directed to a transfer pipeline.  Calculate the duty of the heater and the dew point temperature of the gas.
Component Composition (mol %) Component Composition (mol %)
Methane 76.5588 n-Hexane 0.0774
Ethane 6.4501  n-Heptane 0.0253
Propane 4.2073  n-Octane 0.0155
i-Butane 1.0702 n-Nonane 0.0051
n-Butane 1.1903 CO2 4.3475
i-Pentane 0.3688 N2 2.2670
n-Pentane 0.2429 H2S 3.1739
Total: 100.0000
(NoteEngVert can easily convert mol/mass percentages and fractions of streams.)

NOTE:  To ease data entry, this flash calculation file is stored in the directory where MixProps is installed...

Step 1:  On the Mixprops "Settings" tab, perform a temperature-pressure flash at T = 60 F and P = 1425 psia.  Select the PR-78 EOS  model.

Step 2:  On the Mixprops "Composition" tab, enter the above natural gas analysis.

Step 3:  Click on the "Interaction Coefficients"tab.  Since the T/P conditions are well above the Tc/Pc conditions of typical natural gases, accurate BIPs will need to be entered to model the system.  Click on the Table button and drag/drop or copy/paste BIPs from the table to the MixProps interaction coefficients table.

Step 3:  Click on the MixProps "Properties" tab.  Mixprops performs the T-P Flash calculation and computes all the thermodynamic and transport properties of the natural gas.  Note the following:

T = 60 F .....  Vapor Enthalpy = -39,607.8 Btu/lbmol

Step 4:  Click on the MixProps "Settings" tab.  Perform another T-P but this time at T = 110 F and P = 1425 psia.

Step 5:  Click on the MixProps "Properties" tab again.  Note the following:

T = 110 F .....  Vapor Enthalpy = -38,833.6 Btu/lbmol

Step 6:  Compute the heater duty:

Duty = m * delH

(27 x 10^6 scf/d) ( 1/24 d/hr) ( 1/379.5 lbmol/scf) = 2,964.4 lbmol/hr

Duty = ( 2,964.4 lbmol/hr) [ -38,833.6 - ( - 39,607.8 ) Btu/lbmol] = 2.3 MMBtu/hr

Step 5:  Click on the MixProps "Settings" tab again.  Select a "Dew Point Temperature" calculation.  Click on the "Properties" tab.  Wait for the calculation to complete and then click on the "Summary" tab:

Dew Point Temperature = -9.62 F

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Last Modified:  Sept 30, 2005