380 / 2018-12-17 10:48:52

Experimental exploration of the effect of oxy-fuel combustion on ash deposition behavior of Zhundong high-alkali coal

high-alkali coal, oxy-fuel combustion, ash deposit, micro-morphology

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Zhundong coalfield has a super-large reserve of coal resources. However, its high-alkali feature deteriorates the phenomenon of ash deposition and slagging in coal-fired boilers. Oxy-fuel combustion is a clean and efficient combustion technology, which not only benefits the large-scale capture of CO2 but also reduces NOx emission, and then promotes the efficient and clean utilization of high-alkali coals. While previous studies on Zhundong coal mainly focused on the deposition process and the migrations of alkali metals under air condition, the ash deposition behaviors of high-alkali coals in oxy-fuel case are still unclear. This study compared the differences in morphology and element distribution of ash deposits between air and oxy-fuel conditions to reveal the ash deposition characteristics and mineral migration during oxy-fuel combustion of high-alkali coals using a high temperature drop tube furnace and a specially designed sample probe. Experimental results show that the ash deposits of Zhundong coal were more compact with porous structure under air condition than those under oxy-fuel condition. The contents of sulphur, chloride, and calcium were higher but the contents of aluminum and silicon were lower in the ash deposits in air combustion compared with oxy-fuel combustion. The ash deposits of Zhundong coal had high contents of CaSO4 and mullite with the larger average particle size during air combustion. The proportion and diameter of spherical particle were declined in the ash deposits but the deposition propensity of Zhundong coal was increased as the increasing oxygen content. The main elements of ash deposits were sodium, aluminum, silicon, sulfur, calcium and iron at various oxygen contents. The contents of aluminum and silicon were raised and the content of calcium was reduced with the increase in oxygen content. More mullite was present in the ash deposits as the oxygen content increased.