Effects of Typical Inorganics on the Emission Behavior of PM₁₀ during Combustion of Ash-Removed Coals Loaded with Sodium and Quartz

To examine the real effects of typical inorganics on the emission behavior of PM10 during coal combustion and explore the interactions between the typical vaporized and refractory inorganics, Na-, Si-, and (Na+Si)-loaded coals prepared from the ash-removed PDS bituminous coal and ZD subbituminous coal were combusted in a high temperature drop-tube furnace (DTF) at 1500 °C in air. The produced inorganic PM10 and PM2.5 were collected and characterized. The experimentally measured PM emission results from the combustion of the (Na+Si)-loaded coals were compared with the calculated results that are the sum of PM emitted from the combustion of the Na- and Si-loaded coals. The calculated yields of PM0.3 of two studied coals are higher than the experimental ones, while the calculated yields of PM0.3-2.5 are lower. The experimental yield of PM0.3-2.5 is mainly enhanced by the sodium condensing heterogeneously on fine quartz particles, while the sodium would contribute to PM0.3 homogeneously, leading to the higher calculated result derived from the Na-loaded coal. Na is prevalent in only submicron particles for both the Na- and the (Na+Si)-loaded coals. The homogeneous partitioning ratio of Na is unaffected by the loading of quartz, but the heterogeneous partitioning ratio is affected by the quartz particles on which vaporized Na can condense into particles larger than 0.2 μm. Si presents similar distribution characteristics of trimodal for both the Si- and the (Na+Si)-loaded coal. The partitioning of Si in PM0.3 appears to be affected by Na due to the higher partitioning ratio of the (Na+Si)-loaded coal. The apparent catalytic effects of Na species on the combustion reactivity should beneficiate the local reducing atmosphere, and thereby promote the reduction of SiO2 to SiO, which is easily vaporized to contribute to PM0.3 for the (Na+Si)-loaded coal.