Mathematical Modeling and Control of a Multiboiler Steam Generation System

This paper explores the development of a dynamic mathematical model of a three-boiler steam generation process, experimental verification of the model, and the development of an effective control structure to improve dynamic robustness. The process is highly interacting because of a common feedwater system and a common steam header. Serious operating problems in the form of “cascading trips” had been experienced (the sudden shutdown of one boiler causes the other boilers to shutdown). The process has hard constraints: a high or low steam drum level causes the boiler to interlock down. A trip of one boiler causes a drop in the steam header pressure, which produces “boiler swell” (steam drum level increases) in the untripped boilers and can trip these boilers. Openloop plant tests were conducted, and a model “swell” parameter was adjusted to produce good dynamic model fidelity. The model was then used to test alternative control structures. The recommended control structure was installed in the plant and was very successful in preventing cascading trips.