A Feasibility Study Evaluating the Efficiency of Fine Coal Washing Using Gravity Separation Methods

Abstract

Coal mining and washing activities in South Africa often lead to the generation of
 fine and ultra-fine coal which is in most cases discarded due to high handling and
 transportation costs. Studies conducted revealed that a large quantity of these fines
 have market acceptable calorific values and lower ash contents. In order to reduce
 fines discarded, processes have been developed to re-mine and process the fine coal
 discards with the aim of improving the calorific value, adding them to coarse washed
 coal to increase the yield as well as pelletizing the fines so as to meet the market
 specifications in terms of size.
 The goal of this study was to evaluate the efficiency of fine coal washing using
 gravity separation methods and comparing the products thereof to the market
 specifications with regards to the calorific value and the ash content. Coal fines from
 the No.4 lower seam of the Witbank coalfield in South Africa resulting from a dry
 coal sorting plant were subjected to a double-stage spiral test work, heavy liquid
 separation and reflux classifier test work respectively.
 The reflux classifier achieved products with low ash content and an increased
 calorific value, at high mass yields. At higher fluidization water flowrate, the reflux
 classifier performance was superior to that of the spirals with products of lower ash
 content and higher calorific value. At low cut point densities, heavy liquid separation
 yielded the cleanest products with very low ash content but at much lower mass
 yields. As the density increased, the mass yields increased with the ash content while
 the calorific value decreased. Most of the products from the different processes met
 most of the local industries’ specifications but none of them met the export market
 as well as the gold and uranium industry specifications due to the high ash content.

Demineralization of a Low-Rank Coal to Produce Clean Coal for Industrial Utilization

“…Consequently, the %age of fixed carbon (grade) of coal improved from 35.25% to 48.47% corresponding to 37.50% increase. The gravity separation was found an effective technique for rejecting of high-density ash bearing minerals and sulphur containing pyrite from raw coal at the coarsest possible size and recovering a relatively high-quality clean coal [18][19][20].…”