Development and application of a digital control system for chemical engineering education

The purpose of this study was to develop a digital control system for a shell and tube heat exchanger in order to provide a laboratory for students in chemical engineering. An existing heat exchanger was modified to include analog transmitters and connected to a Texas Instruments PM550 programmable controller. The following control strategies were applied to the heat exchanger: temperature feedback, temperature-flow cascade, temperature-pressure cascade, feedforward with temperature feedback, and feedforward with lead lag. Each of these strategies was programmed into the controller, tuned by Ziegler-Nichols, Cohen-Coon, and trial and error methods, and evaluated by response to both set point and load changes. Each strategy was found to be approximately equally efficient in controlling the outlet water temperature for the load applied; however, the feedforward control method was the most effective for the load change used.