Study On The Calculation Of Chemical And Phase Equilibrium In Complex System

Calculation of chemical and phase equilbrium in multiphase and multi-component complex system is not only the basic problem of thermodynamic research,but also the important tache of chemical engineering design, process simulation and optimization. The method of minimization of Gibbs free engegy is an improtant approach for computing chemical and phase calculation,its principle is that thermodynamical problem is transformed into mathematical optimization problem,and then,by solving this optimization problem,the equilibrium compositions can be obtained. Many mathematical programming methods based on derivative are used to calculate the minimization of Gibbs free engegy,but they have a lot of limitations,therefore,random optimization technique ---- Genetic Algorithm(GA) is used to calculate chemical and phase equilibrium in complex system,and a set of mathematic models of chemical and phase calculation are established as to different systems,besides,the solution strategies are proposed by using GA. The following research works have been performed in this paper.(1) As to the complex system in which the number and states of phase are known,the applied scope of the method based on minimization of Gibbs free energy is extended into the complex systems including organic reaction system,volatile weak electrolyte system and inorganic salts-azeotropic organics/water system. The mahematic model and solution strategy by using GA for all kinds of systems is established. It is found that the calculated results agree well with those reported in the literatures,in addition,the method is easy and general to implement,at the same time,the proposed method can calculate the contents of trace components accurately.(2) As to the calculation of phase equilibrium in complex system in which the number and states of phase are unknown , Mixed-Integer Non Linear Programming(MINLP) is proposed to describe the problem. 0-1 binary variable denotes the existence or not of the phase and the concept of the matrix of phase code is presented,then,MINLP model and solution strategy by using GA are established. Finally,organic solution system and mixed aqueous electrolyte solution system are taken as examples,which show that the proposed method can compute equilibrium problems in complex system in which the number and states of phase are unknown,and phase stability judgment is not needed.(3) Theτ-method used to compute multiple phase equilibrium is extended into calculating simultaneous chemical and phase equilibrium. Based on modifying the mole fraction summation,atom conservation and material conservation in phase equilibrium replace the matter conservation used in the model of literature,besides,the constrains of chemical equilibrium balance equations are also introduced into the improved model,accordingly,an improvedτ-method and solution strategy by using GA are established. Finally,two systems are taken as examples to validate the feasibility and validity of the proposed method.The research shows that the methods proposed in this paper as to different systems have many advantages,such as good stablity,high convergence,easy to implement,and so on,which indicates that the methods can be used to calculate simultaneous chemical and phase equilibrium in complex system.