Fine Coal Cleaning by Gravity Methods: A Review of Current Practice

Abstract

Effective beneficiation of fine coal; i.e., coal sized below 1 mm, either by means of deashing or dewatering, or a combination of both, is mainly dependent upon the following factors:

(a) favourable coal selling price and a growth situation in coal demand;

(b) improved performance and favourable cost of fine coal preparation equipment;

(c) degree of optimized beneficiation possible with respect to the coarser coal and the required product quality.

Further motivation has emerged as a result of a substantial increase in fines generation caused by expansion in mine mechanization coupled with sharply rising mining and transportation costs. With such incentives, research and development and progressive commercialization of new treatment devices has gathered momentum during the past ten years. The result has been that the demand for new treatment equipment, especially in the dewatering field, has tended to speed up development from the prototype machines to commercial application.

Almost all techniques for cleaning and dewatering fine coal have undergone some form of development, and new equipment for controlling or monitoring performance has emerged to create significant improvement in the performance of the more traditional, original methods.

In fine coal cleaning by means of jigs, tables, spirals, dense medium and autogenous (water) cyclones, collectively known as the gravity methods, all such methods have received attention as have froth flotation, oil agglomeration and certain magnetic and electrical separation and chemical techniques. In fine coal dewatering, vacuum and pressure filters, centrifuges of numerous types and thermal drying techniques have become widely used.

This paper reviews developments that have occurred in fine coal cleaning by gravity methods, concentrating on the past ten-year period. It also includes a brief glimpse into the immediate future in an attempt to try and forecast what may occur as a result of current research and development efforts.