Rate-based column simulation in the complex domain

Abstract

Several organizations provide both equilibrium stage and rate-based column models in commercially available process simulation software. Many years of troubleshooting rate-based simulations tells us that they are more likely to suffer convergence issues than is an equivalent equilibrium stage model. The increased difficulty of converging rate-based simulations has to do with ties to actual equipment size that does not exist in the classic equilibrium stage model. Some years ago, Lucia and coworkers proposed solving chemical process models using computations in the complex-domain. They found that some hard-to-converge equilibrium stage column simulations were much easier to solve when carried out in the complex domain. We wondered if Lucia’s approach could help converge very challenging rate-based simulations. To answer that question, we have built a rate-based complex-domain code. Our most important result is that the complex-domain code can easily solve-rate based column simulations that are too difficult for the real-domain code.