Investigation on Inorganic Constituents in Indian Coal and Emission Characteristics of the Particulates (PM2.5 and PM10)

Abstract

The micro-analysis of the inorganic constituents was performed on a tertiary Indian coal sample using computer-controlled scanning electron microscopy (CCSEM). A laboratory combustion experiment of the coal was also carried out to reveal the emission characteristics of particulate matters (PM2.5 and PM10). The results show the presence of major minerals like clay minerals, quartz, pyrite, and pyrrhotite forming the bulk of the mineral matter including some minor minerals, such as calcite, dolomite, ankerite, barite, oxidised pyrrhotite, and gypsum in the sample. The particle size distribution (PSD) of the included minerals is generally observed to be finer than that of the excluded ones in the coal. As a consequence, the coals rich in included minerals have smaller particles, which may affect its reactivity. The ratio of included to excluded minerals is found to be higher in majority of cases. It is found that Si mostly occurs as quartz and clay minerals, while Al mostly occurs as silicate minerals. Fe is primarily present as iron sulfides, iron oxide, and Fe-Al-silicate. S is partitioned into iron sulfides and gypsum. Most Ca occurs as carbonates and gypsum, with a minor fraction associated with clay minerals. Mg is mainly present as dolomite and clay minerals, with a very minor fraction present as ankerite. The majority of alkali elements are associated with aluminosilicates. P is mostly associated with kaolinite and/or present as more complex compounds containing Al, Si, and other elements as apatite is found to be absent in the coal studied. Ti is mainly present as rutile and kaolinite. The PSD of the individual elements were also determined in the coal by CCSEM data and 73.81 % of sulphur was found to be present as included indicating the high organically bound sulphur in the coal. During combustion, concentration of PM10 was found to be higher than PM2.5. The PMs are observed to contain of many potentially hazardous toxic elements viz. Si, Pb, S, Br, As, Cd, F and Cl.