The process is modeled on an industrial high temperature short time (HTST) pasteurisation process. In this process the product stream has to be kept at a predetermined temperature for a minimum time, usually for bacteriological purposes. This is effected by the use of a holding tube, which delays the product stream, thus posing particular process control problems and introducing the concept of dead time.
Other reasons why the HTST process is a particularly suitable basis for teaching process control are the use of a three stage heat exchanger (recycle, heating and cooling) and the use of a divert valve to reject inadequately treated product. Again these important industrial principles pose real process control problems and help maintain the students interest. Further process control problems are illustrated by the use of two feed tanks, with different level sensor types. Solenoid driven valves control the filling and emptying of these tanks. These enable different level control strategies to be developed and provide start up and shut down operational sequencing capability. The unit includes a wide range of instrumentation for temperature and flow measurement. It also includes a conductivity sensor,enabling simple process concentration experiments to be performed.
The unit comprises: