Microstructural blending of coal to enhance flowability

Coal-fired power stations for electricity generation are well known to suff er 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 ge nerating plant in some extreme cases. In coal-fired power generation, optim al 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 stron gly effected by the ash content of the raw coal. However, the flowability o f coal tends to be strongly affected by the moisture content of the constit uent particles, as well as the presence of high fines fraction. The experim ental work described in this paper aims to illustrate how flowability can b e enhanced by optimising particle size distribution and particle surface mo isture in blends of raw and washed coals. The results of the flowability te sts obtained with "microstructurally" blended samples indicate that to ensu re flowability in process vessels, it is necessary to blend according to im portant microstructural criteria as well as minimising ash content. Microst ructural blending is not included in current industrial practice, which onl y blends washed and raw coals to produce high calorific value and low ash c ontent. The work presented here establishes methodology for microstructural blending to enhance bulk flowability. (C) 2000 Elsevier Science S.A. All r ights reserved.