A generalized framework for computing bifurcation diagrams using process simulation programs

Interest in discovering multiple steady-state solutions for reaction and se paration processes grew exponentially in the 1990s. Process simulators like ASPEN PLUS, CHEMCAD, HYSYS, and PRO/II ale designed to obtain at best one solution. Simulation programs can find multiple solutions only by the expen diture of much effort. Here, a bifurcation technique using arclength contin uation is presented that can be incorporated as an add-in subroutine to a s imulation program to automatically trace a solution path, including turning points, to obtain multiple solutions with respect to a user-selected param eter. The technique is illustrated with applications to the ASPEN PLUS proc ess simulator. The algorithms are based on a predictor-corrector implementa tion where the predictors reside in add-in FORTRAN routines and the existin g nonlinear equation solvers in ASPEN PLUS equipment models serve as the co rrectors. Furthermore, the existing physical property packages in ASPEN PLU S are also utilized. The method was tested successfully on an adiabatic CST R example using the ASPEN RCSTR model, and homogeneous azeotropic, heteroge neous azeotropic, and reactive distillation examples using the ASPEN RADFRA C model. Two of these examples are presented hen. In all four examples, the range of the selected bifurcation parameter covers a region that produces three multiple solutions. (C) 2001 Elsevier Science Ltd. All rights reserve d.