A COMBINED SOAVE-REDLICH-KWONG AND NRTL EQUATION FOR CALCULATING THE DISTRIBUTION OF METHANOL BETWEEN WATER AND HYDROCARBON PHASES

With the purpose of achieving a thermodynamic capable of calculating t he distribution of methanol between oil, gas and water phases when met hanol is being used as a hydrate inhibitor in offshore multi phase flo w pipelines, parameters for methanol-hydrocarbon and methanol-water in teractions have been estimated in a model suggested by Huron and Vidal . The applied model takes the general' form of the Soave-Redlich-Kwong (SRK) equation but uses an NRTL type mixing rule for the a-parameter. For hydrocarbons the mixing rule reduces to the ordinary SRK mixing r ule. This is advantageous because it makes the obtained calculation re sults consistent with those obtained for methanol free mixtures using SRK and because an already existing C-7+ characterization procedure fo r use with the SRK equation does not have to be modified. Experimental data for the methanol distribution between water and the oil and gas phases of a North Sea reservoir fluid have been used to test the model and it is found that the predicted results agree very well with the e xperimental ones.