PROCESS CONTROL OF HEAVY MEDIA SYSTEMS FOR COAL PREPARATION PLANTS.

The concurrent demand for both lower-sulfur coal and lower-priced coal has resulted in an increased interest in control of unit operations within the coal preparation plant. While equipment control is widely used, process control of liquid/solid mixtures is seldom used and is fraught with problems. The control of the medium's specific gravity in a heavy-media cyclone-separation process exemplifies many of the issues which must be addressed. These include sensor and sensing problems, control scheme selection, and process modeling constraints. These issues are examined, as is a pilot circuit which was constructed to acquire a better understanding of the problems.