Characteristics of fine particle formation during combustion of Xinjiang high-chlorine-sodium coal

Shaerhu (SEH) coal in Xinjiang province of China, with a reserve of 90 billion tons, is one of the most representative high-chlorine-alkaline coal. However, the chlorine content in coal exceeding 1% easily leads to severe problems of ash deposition and hot corrosion on tubes, which are closely related to the evolution of fine particles. In this study, the formation of fine particle from the combustion of two types of SEH coal (#1 and #2) are investigated in the temperature range of 900–1300 °C. Their results are compared with Xinjiang Tianchi (TC) coal (high-sodium but low-chlorine). In order to demonstrate the formation mechanism of fine particles, the particle size distribution, elemental composition and morphology of fine particles, as well as chlorine- and sulfur-containing gas products, are characterized. The results show that the particle size distribution of PM₁₀ present a bimodal distribution. Fine-mode particles (PM_0.4) from SEH#1 coal combustion mainly consist of NaCl since the molar ratio of Na/Cl is about 1.0, while fine-mode particles from TC coal combustion could be Na₂SO₄ and CaSO₄. Coarse-mode particles (PM_0.4-10) mainly consist of silicon, aluminum, calcium and magnesium, whose compositions are not significantly affected by combustion temperature, and calcium accounts for the largest proportion in coarse-mode particles. As the temperature increased to 1150 °C, the chlorine and sulfur in SEH coal were fundamentally associated to solid ashes, while for TC coal extra sulfur existed as the gaseous form of SO₂.