Switching Difference Control of Parallel Streams Temperatures

An industrial furnace with multiple parallel passes and multiple burners is commonly used in petroleum refineries to heat the preprocessed crude oil to a specific temperature. Due to that maintaining multiple outlet temperatures of such parallel passes equal is significant for improving product quality, plant safety, and economic efficiency, etc., great efforts have been taken to control such temperatures. In this paper, a control technique based on switching control schemes, called switching difference control technique (SDCT), is proposed to distribute the inlet oil flowrates such that the outlet temperatures are as identical as possible. The principle of the proposed technique is explained, and several switching policies are introduced. Simulation examples are provided to demonstrate the effectiveness of the proposed strategy. The SDCT technique has the following advantages: it avoids the flow valves too frequently being regulated; it solves the problem of the flow coupling among multiple passes conveniently, etc.