Automatic Control of Coal Flotation and Dewatering Processes

Abstract

Coal preparation plant operators often do not optimize the flotation and dewatering processes. In order for these processes to operate efficiently, the equipment should be adjusted after every change in feed rate or quality. Unfortunately, neglect of the final coal processes causes processing additives and coal to be wasted and in some cases, unnecessary outages of the entire cleaning plant. Consequently, revenues decrease.

A control system for the froth flotation and dewatering processes was developed and is now operational in four bituminous coal preparation plants owned by Consolidation Coal Company (CONSOL Inc.). The system controls 1) the flotation tailings ash content via flotation reagent adjustment. 2) the froth cell level by adjusting the tailings dart valve positioning, and 3) the vacuum disc filter level via filter rotational speed and flocculant feed rate adjustments. Central to the system operation is a newly developed sensor. This innovative optoelectronic sensor is used to estimate the amount of fine coal in the solids fraction of the tailings slurry. The instrument uses a collimated illumination source and a photosensor which measures the reflection of light from within the slurry. The instrument's signal is used as the feedback signal in a control loop. In addition to the optoelectronic sensor, combinations of pressure transmitters and dual bubble-tube assemblies measure the froth cell and filter tank liquid levels for the above mentioned control capabilities. All of the important process parameters are always available to the operator in the control room. The operator is now more aware of the status of the final coal recovery system.

After the control systems were installed, the coal recovery from the fine coal processes increased as much as 60%.

Key words:

• coal flotation
• automatic control
• dewatering