The melting potential of various ash components generated from coal combustion: Indicated by the circularity of individual particles using CCSEM technology

•Melting potential of various ash components formed by coal combustion was studied.•Three coals with different ranks were burned in a drop tube furnace to form ashes.•Circularity tested by CCSEM was used to calculate the ratio of spherical particles.•Origins, spherical particle ratio and thermal behaviors of ashes were correlated.•Several types of Al-silicates, unclassified, quartz, iron oxide, etc., were focused.

This work aims to investigate the melting potential of various inorganic ash components by CCSEM (computer-controlled scanning electron microscopy). Three pulverized coals (anthracite YQ, bituminous coal DT and lignite CF) were burned in a drop tube furnace (DTF) at 1300 °C in simulated air atmosphere to generate ashes. The contents, chemical compositions and particle circularity of each mineral species in coals and ashes were identified by CCSEM. On the basis of that, the spherical particle number ratio and the thermal behaviors of ash components and their original minerals were correlated to illustrate the melting potential of ash components. Typical results are presented as below: The slight increase of content of basic elements in mullite-like phase is the major reason for its partial melting. K Al-silicate in anthracite and lignite ashes is generated from illite and tends to be melted as the low melting point of illite, but K Al-silicate in bituminous ash is mainly formed from thermally stable quartz and is unable to be melted. Iron oxide derived from mainly excluded siderite in lignite CF is difficult to be melted but that from excluded pyrite in bituminous coal DT is melted moderately, that is because of the different melting behaviors of decomposition products of siderite and pyrite (FeO or FeO–FeS, respectively).