Equation 6 is called the Rachford-Rice equation and it may be solved using a solver like Excel by using known values of ki's and zi's and solving for the equilibrium vapor fraction (v) at 65 degrees F and 500 psia. Once v is known, V, L, xi, and yi can be found using the above equations.

Another method that may be used is a program called Distill which uses the Redlich-Kwong equation to find the vapor fraction by determining the vapor phase fugacity. Then once the vapor fraction (v) is determined, the program Distill determines the V, L, xi, and yi using the above equations. Click here to see the composition of the vapor and liquid streams from the isothermal flash of the volatile oil at 65 degrees F and 500 psia.

After the isothermal flash of the volatile oil, there is still some residual light hydrocarbons in the liquid stream as can be seen from the composition of the liquid stream. In order to recover this residual amount of light hydrocarbons, the liquid is isothermally flashed at a temperature of 70 degrees F and a pressure of 14.7 psia. The compositions of the vapor and liquid stream of the second isothermal flash are analytically solved in the same way as was described above. Click here to see the resulting composition of the vapor and liquid streams from the second isothermal flash of the liquid at 70 degrees F and 14.7 psia.