Mineral conversion regularity and release behavior of Na, Ca during zhundong coal's combustion

Tianchi Energy coal was selected as the research object, and phase changes in high and low temperature ashes were comparatively analyzed. Mineral conversion in heating process was thoroughly and meticulously studied through thermogravimetric experiment of low-temperature ash. Contents of Na and Ca in coal ashes made at different temperatures were measured respectively to observe their release regularities, and precipitating types of Na, Ca were simulated by Factsage. Results show that the original minerals of Zhundong coal mainly include calcium sulfate hydrate, calcite, quartz, kaolinite and pyrite. During the process of combustion, complex chemical reactions occur among these minerals, and they transform to brownmillerite, calcium silicate, et al. Experiment results show that Na in coal begins to precipitate during 400-600℃, Ca partially precipitates before 600℃ and precipitates fastest after 1 000℃. Combining with simulation results, it's speculated that Na precipitates in the form of NaCl(g) before 1 000℃. After 1 000℃, Na precipitates in the form of NaOH(g) and Na2SO4(g). Eutectics are formed when Ca interacts with iron and silicon containing minerals after 1 000℃. The eutectics precipitate at molten state, which leads to sharp decrease of Ca. ©2015 Chin.Soc.for Elec.Eng.