Analysis of steam drum level control schemes for an 80,000 pph industrialized boiler model

Over the past 28 years, the chemical process defined in this paper has traditionally used a thermostatic regulator for steam drum level control. The plant steam load is cyclic in nature which has caused level variations of ±4 inches, as determined by high and low alarm positions.

To resolve the poor control performance of the mechanical device, three types of improved control schemes were investigated, namely, feedback, feedforward-feedback, and Smith-Predictor model designs. The problem solving technique involved model development from field data, controller design, and computer simulation of the controllers. A comparison of the simulated controller performance was used to determine the design appropriate for field application.

The feedforward-feedback design was chosen to replace the mechanical system. The controller demonstrated fast response and tight control. The level variation improved to ±1 inch during load upsets.