Difference control of parallel streams temperatures

This paper is concerned with controller design for a multi-stream, multi-burner furnace commonly seen in petroleum refineries. The process of the oil heating in the furnace is nonlinear, multivariable, time varying, has serious coupling between streams and burners, has frequent dynamic changes and a large time delay. In order to maintain the furnace running in a safe, stable and high efficiency state it is necessary to control the outlet temperatures of the multiple streams to be the same. Traditional control methods have trouble in maintaining these temperatures, and some advanced control methods including predictive control, adaptive control and robust control are usually too complex for convenient use. In this paper, a novel multivariable controller design based on a difference control technique (DCT) is explained and demonstrated. The application of the DCT to a real-life petroleum refinery furnace gave good results. The DCT design method has the following advantages: it does not need complicated design procedures, the controller structure is simple, it is easy to apply, and it eliminates the problem of coupling among multiple loops.