ADAPTIVE THERMODYNAMIC MODELS FOR CHEMICAL PROCESS DESIGN -- A NEW COMPUTATIONAL APPROACH

Date of Completion

January 1982

Keywords

Engineering, Chemical

Degree

Ph.D.

Abstract

This study addresses several aspects of the problem posed by rigorous thermodynamic and physical property evaluation in computer-aided chemical process design computation. The evaluation of physical properties has a significant effect on the speed, accuracy and stability of algorithms used for design calculations. It is generally agreed that between 80-90% of the number of equations and computer time required to formulate and solve design problems concern thermodynamic evaluations. Here adaptive, local thermodynamic models are proposed as a means of overcoming these difficulties.^ The adaptive thermodynamic models are local approximations to the rigorous models. A number of new local models are proposed based upon the rigorous thermodynamic equations for equilibrium ratios in multicomponent vapor-liquid and liquid-liquid systems. Composition dependence is explicitly included in the local models to enable their use for highly nonideal systems. During the design calculations the validity of the local models is continually maintained by updating parameters imbedded in the models. Parameter updating requires rigorous physical property evaluations on which to base the updated estimate of the parameters. A number of updating strategies are presented and studied.^ These concepts have been tied together and a new class of algorithms proposed, based upon the use of local thermodynamic models. A wide range of design problems have been solved using these methods. Results indicate that the stability and accuracy of the new methods are comparable to conventional alternatives. However, use of the thermodynamic database can often be reduced by a factor of 10-100. ^

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