First principles dynamic modeling and multivariable control of a cryogenicdistillation process

In order to investigate the feasibility of constrained multivariable contro l of a heat-integrated cryogenic distillation process, a rigorous first pri nciples dynamic model was developed and tested against a limited number of experiments. It was found that the process variables showed a large amount of interaction, which is responsible for the difficulties with the presentl y used, PID-based, control scheme, especially in load-following situations, which are common in air separation plants such as for instance integrated coal gasification combined cycle plants. Contrary to what is suggested in t he literature, it was found that vapor hold-up in low-temperature, high-pre ssure columns does not play a significant role in the process dynamics. Des pite large throughput changes and non-linear process behavior, multivariabl e model predictive control using a linearized model for average operating c onditions, could work well provided all process flows have sufficient range . Due to the strong interactive nature of the process variables, process ch anges have to be made slowly, since otherwise manipulated variables easily saturate and process output targets cannot be maintained. (C) 2000 Elsevier Science Ltd. All rights reserved.