Slagging Characteristics of Zhundong Coal during Circulating Fluidized Bed Gasification
2016
Song, Guoliang | Qi, Xiaobin | Song, Weijian | Lu, Qinggang
Three types of Zhundong coal with different sodium contents—Shenhuazhundong coal (SHZD), Shaerhu coal (SEH), and Tianchimulei coal (TCML)—were investigated to understand their slagging behaviors during circulating fluidized bed gasification (CFBG). Generally, the operational stability of Zhundong coal decreases with the rise of sodium content. Zhundong coal with low sodium content is suitable as a gasification fuel of a circulating fluidized bed. For high-sodium-content coal, agglomeration, and even defluidization, should be the focus. Agglomeration or defluidization could be alleviated or avoided by controlling the bed temperature. There is a one-to-one correspondence between temperature fluctuation and sodium content in bottom slags. Slagging is affected by sodium occurrence modes and some ash components (e.g., SiO₂ and Fe₂O₃). Due to different contents of chemical components, especially chlorine, silicon, and sodium, the three types of Zhundong coal cause different problems. Chlorine and sodium in SEH, mainly existing as NaCl, play an important role in corroding metal walls. Microanalysis of agglomeration particles in the tests with TCML shows that the SiO₂-to-Na₂O ratio gradually increases from surfaces to the inner part, which confirms the effect of the Na₂O–SiO₂ reaction on the agglomeration. The SiO₂ content in high-alkali coal decisively impacts on the slagging morphology by the interaction between Na₂O and SiO₂ in coal itself for high-SiO₂ coals or additional SiO₂ from quartz sands for low-SiO₂ coals.
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