Coal-fired power stations for electricity generation are well known to suffer from chronic problems in coal handling and flow affecting the operation of pulverisation mills and combustors. The economic impact of coal handling facilities can be significant, resulting in total shutdown of the power generating plant in some extreme cases. In coal-fired power generation, optimal operation of the combustors requires the ash content of pulverised coal not exceed 20%. Excessive ash content would result in lower calorific value. Therefore, the overall profitability of the market coal tends to be strongly effected by the ash content of the raw coal. However, the flowability of coal tends to be strongly affected by the moisture content of the constituent particles, as well as the presence of high fines fraction. The experimental work described in this paper aims to illustrate how flowability can be enhanced by optimising particle size distribution and particle surface moisture in blends of raw and washed coals. The results of the flowability tests obtained with "microstructurally" blended samples indicate that to ensure flowability in process vessels, it is necessary to blend according to important microstructural criteria as well as minimising ash content. Microstructural blending is not included in current industrial practice, which only blends washed and raw coals to produce high calorific value and low ash content. The work presented here establishes methodology for microstructural blending to enhance bulk flowability. (C) 2000 Elsevier Science S.A. All rights reserved.
