CPA EoS in NeqSim

The CPA-EoS

An example of using the the CPA-EoS from NeqSim is given in the following python script. The default CPA-EoS will be the version from Statoil.

import neqsim
from neqsim.thermo.thermoTools import fluid, TPflash
from neqsim.thermo import dataFrame

system = fluid('cpa')
system.addComponent('methane', 0.5, 'mol/sec')
system.addComponent('water', 0.5, 'mol/sec')
system.setMixingRule(10) # Composition dependent and temperature dependent mixing rule
system.setPressure(10.0, 'bara')
system.setTemperature(25.0, 'C')

TPflash(system)

dataFrame(system)

A dataframe with the results of the calculations will be displayed.

The sCPA-SRK-EoS

The cubic-plus-association (CPA) equation of state combines the Soave–Redlich–Kwong equation with the association term from SAFT based on Chapman's extensions and simplifications of a theory of associating molecules due to Michael Wertheim. The development of the equation began in 1995 as a research project that was funded by Shell, and in 1996 an article was published which presented the CPA equation of state.

$$ P = \frac{RT}{(V - b)} - \frac{a}{V (V + b)} + \frac{RT}{V} \rho \sum_{A} \left[ \frac{1}{X^\text{A}} - \frac{1}{2} \right] \frac{\partial X^\text{A}}{\partial \rho} $$

where V is the molar volume, XAi is the fraction of A-sites of molecule i that are not bonded with other active sites, and xi is the mole fraction of component i. The letters i and j are used to index the molecules, whereas the letters A and B indicate the bonding sites on a given molecule.

The term ΔAiBj, which is the association (binding) strength between site A on molecule i and site B on molecule j is given by

where εAiBj and βAiBj are the association energy and volume of interaction between site A of molecule i and site B of molecule j, respectively, and g(Vm)ref is the contact value of the radial distribution function for the reference fluid (i.e., a fluid of hard spheres, meaning that only repulsive forces are present).

The sCPA-SRK-EoS-statoil