MULTIPLICITY IN NUMERICAL-SOLUTION OF NONLINEAR MODELS - SEPARATION PROCESSES

This paper analyzes the solutions from equilibrium based simulation mo dels for separation processes with respect to multiplicity of solution s. The causes of multiplicity are investigated and it is shown for dis tillation columns, when and how multiplicity can be obtained and how i t is conncted to design and operation of the separation process. Some of the causes of multiplicity are traced to over-design of staged sepa ration processes and to values of specified variables. It is shown tha t the number of multiple solutions may be related to the number of sta ges while the number of acceptable solutions depend on the set of spec ified variables. Numerical examples covering simple distillation colum n models and heterogeneous azeotropic distillation operations are pres ented.