Observations of Heterogeneity in Large Pulverized Coal Particles

The heterogeneity of the 125−212 μm size cuts from four pulverized coal samples from the United Kingdom, United States, and South Africa has been examined in detail by means of density separation and optical and scanning electron microscopy. While average properties of the overall size cut samples are similar to those of the parent coals, a high degree of heterogeneity exists between average compositions for the different density cuts within each sample, between different particles within the same density cuts, and, in many cases, within the particles themselves. Conventional analyses are unsuited for describing this heterogeneity and an alternative descriptive method based on maceral associations has been used, together with illustrative micrographs. The implications of coal heterogeneity for particle behavior during grinding, pulverized coal combustion and coal characterization for modeling purposes are discussed.