RECOVERY AND UTILIZATION OF FINE CLEAN COAL IN A THERMAL DRYER SYSTEM

摘要

Two specific problems exist at a large number of coal preparation plants in the United States using thermal dryers for producing product coal, cyclones for first-stage recovery of coal fines, and second-stage wet scrubbers to remove coal carry-over from the dryer exhaust gas. The first problem involves a need for eliminating the common practice of sacrificing clean ultra-fine coal captured in the scrubbers. The second problem involves a need for mitigating over-dry fine coal dusting from in the dryer product.The second problem, controlling fine coal dusting, has been met by applying a solution of surfactants and process water to the over-dry coal fraction, de-dusting the product coal. To date, the problems associated wit the recovery and use of fine clean coal from dryer scrubber effluent have not been solved. The program, reported in this paper, demonstrates a simple process improvement, involving use of a belt press, will simultaneously solve both the de-dusting and the dryer scrubber effluent recovery issues.This program proposes to use a combination of a clean coal thickener with a squeeze belt press to recover the ultra-fine coal in dryer scrubber effluent before it is mixed in with the balance-of-plant tailings. As an additional essential part of this program, we propose to demonstrate that the coal-water mixture (CWM) produced from the scrubber sludge of a thermal dryer can be used as a dust suppressant. The net effect of these two coal circuit changes will be to Integrate the thickener underflow into the thermal dryer circuit. This will essentially close the loop and permit maximum efficiency from the system, by recycling a former waste stream (sludge) as an effective dust suppressant.