Process control of heavy-media systems for coal-preparation plants

The concurrent demands for lower-sulfur coal and lower-priced coal have resulted in an increased interest in control of unit operations within the coal-preparation plant. While equipment control is vvidely used, process control of liquid/solid mixtures is seldom used and is fraught with problems. The control of medium specific gravity in a heav-media cyclone-separation process exemplifies many of the issues (hat must be addressed. These include sensor and sensing problems, control-scheme selection, and process modeling constraints. This paper examines these issues and describes a pilot circuit that was constructed to facilitate a better understanding of the problems.