Supervisory Computer Control of a Methanol Refining Column Using a Digital Control System with a New Type of Instrument/Computer Interface

Summary

This paper describes an application of supervisory control on a refining column of a large methanol plant and introduces the concept of a small dedicated mini-computer controlling a section of a large plant which cannot easily be tightly controlled by conventional instrumentation. The initial financial case for the application is considerably eased by the introduction of a new type of instrument/computer interface which is cheaper and more easily installed and inherently more reliable than the more conventional multiplexed scanning system.

The application uses a systems approach to control and combines feed forward and feedback techniques with the objective of achieving and maintaining steady conditions within the column. The digital control equipment used on this application is new and uses a digital highway connection to the mini-computer which enables the computer to read inputs from the plant using the same instructions it would use to get data from its own core store.

Performance and reliability have been proved during the first year of the plant’s operation and the anticipated benefits are being fully achieved.