Emission of suspended PM10 from laboratory-scale coal combustion and its correlation with coal mineral properties

Four pulverized coals were subjected to combustion in a laboratory-scale drop tube furnace to investigate the emission of suspended particulate matter smaller than 10 μm (PM10) and to study the correlation of PM10 emission with mineral properties of the coals. Combustion conditions of 1200 °C, 2.4 s and 20% atmospheric oxygen content were used and all the carbon was consumed under given conditions. The properties of PM10 were studied including its concentration, particle size distribution and elemental composition. Two typical sizes were also subjected to Computer controlled scanning electron microscopy (CCSEM) analysis for determination of chemical species within them. To investigate the influence of coal mineral properties, the metallic elements in the raw coals were divided into three parts: organically bound, included inorganic particles and excluded ones. The results indicated that during coal combustion, about 0.5–2.5 wt% of inherent minerals changed into the suspended PM10. With an increase in the coal ash content, the concentration of PM10 increased proportionally. The resulting PM10 had a bimodal size distribution with two peaks around 2.5 and 0.06 μm, respectively. SiO2 and Al2O3 dominated the large mode around 2.5 μm, which is formed by the direct transformation of inherent minerals. On the other hand, SO3 and P2O5 were prevalent in the small mode around 0.06 μm, which is formed by vaporization of these two elements. For other metals found in PM10, the refractory metals were enriched in the large mode, with concentrations proportional to their content in the excluded minerals in the raw coal. Volatile metals were however enriched in the small mode since, they react with gaseous SO2 and P2O5 to form sulfates and phosphates in the solid phase. The study showed that experimental observations agree with thermodynamic equilibrium considerations.