The presence of mineral matter in a pulverised coal particle may affect the behaviour of the particle during combustion, and could influence the level of unburnt carbon in ash experienced in power stations. This paper presents details of a computer-controlled scanning electron microscopy (CCSEM) method of characterising the mineral content of individual pulverised coal particles and describes the distribution of mineral matter in pulverised coal samples. The possible influences of the mineral matter distribution on levels of unburnt carbon are discussed in the light of burnout measurements for the same coal samples. Pulverised coal particles may be divided into three types on the basis of their mineral content: organic-rich particles, organic particles with included minerals, and excluded mineral particles. The relative proportions of these different particle types have been characterised for a suite of 18 power station coals from around the world. Organic-rich particles are the most abundant, and particles containing included minerals form a greater mass fraction of the coals than excluded mineral particles. The excluded mineral particles have a considerably finer size distribution than the particles containing organic material, and the organic-rich particles an generally slightly larger than the organic particles with included minerals. Ranking the coals by degree of mineral-organic association shows a strong separation of coals on a geographical basis. Australian and South African coals show higher levels of mineral-organic association than British and North American coals. Although there are a number of possible mechanisms by which included minerals might modify the combustion behaviour of pulverised coal particles, comparison between the mineral distribution and the combustion performance of these coals does not favour any particular mechanism for influencing levels of unburnt carbon. (C) 1997 Elsevier Science Ltd.
