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The Modification Of SRK Equation Of State And Phase Equilibrium Calculation

Posted on:2007-05-30Degree:MasterType:Thesis
Country:ChinaCandidate:M J LuoFull Text:PDF
GTID:2121360212480344Subject:Chemical processes
Abstract/Summary:PDF Full Text Request
Cubic equations of state are the frequently used method for modeling phase behavior. Activity coefficient is also the generally used method for modeling phase equilibrium. The recently developed GE mixing rules have bridged the cubic equations of state and activity method. The new mixing rules have increased the accuracy and range of applicability of the cubic equations of state. For more accuracy results, equations themselves should be modified.In this thesis, the errors of SRK equation of state when calculating saturated pressure for pure substance was analyzed, the newα(T ,ω) was deduced as . Comparison of saturated pressure prediction errors for alkanes, organics containing chlorine, organics containing florine, organics containing oxygen, inorganics and water were presented. For 37 substance 1447 points calculated, the average error of original SRK equation of state is 2.521%, and the modified one 1.673%.Further examinations were carried out for mixture phase equilibria modeling. The SRK equation of state was combined with MHV1 mixing rule and UNIFAC method for mixture phase equilibria modeling. Binary vapor-liquid of alkanes, alcohols containing mixtures and water containing mixtures were studied. For 1165 isothermal data, the prediction pressure error of original SRK equation of state is 5.905% in average and the modified one 4.339%; for 801 isobar data, the prediction temperature error of original SRK equation of state is 1.202℃in average and the modified one 0.896℃; for 1808 points with vapor phase composition, the prediction vapor phase mole fraction of original SRK equation of state is 0.02785 in average and the modified one 0.02202.Binary gas-liquid eqilibria of methane, ethane, nitrogen in nonpolarity, polarity solvent was calculated. For 899 data points of methane/alkanes system, the pressure error of original SRK equation of state is 4.939% in average and the modified one 3.740%, the mole fraction errors are 0.1536 and 0.1352, respectively. For 190 data points of etane/alkanes system are 2.386%, 2.235%, 0.01013 and 0.01062. The characteristic of the original and modifiedαalso analyzed for explain why the results of modified one are better.All kind of phase equilibrium calculation results indicated the modified SRK equation of state is more accurate than the original one.
Keywords/Search Tags:equation of state, activity coefficient, phase equilibria, mixing rule, saturate pressure, G~E/EOS method
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