| In recent years, huge coal field was discovered in succession in Xingjiang province. Among the coal field, Zhundong coal field is the largest coal field in china, even in the world. Zhundong coal mainly has properties of low content of ash and sulfur, high content of moisture, medium to high calorific value and high content of volatiles. The high sodium content property is one of the key factors restricting its extensive application. Existing research concerned mainly about slow pyrolysis, few focuses on fast pyrolysis of Zhundong coal.Sodium in Zhundong coal can be classified into 4 forms: water soluble, water insoluble but ammonium acetate soluble, ammonium acetate insoluble but acid soluble, acid insoluble. Among the 4 forms, water soluble and water insoluble but ammonium acetate soluble are the main existent form in the coal. This article focuses on the effects of pretreatment and the sodium transformation during fast pyrolysis of the coal. Firstly, several different kinds of solvents were selected to explore the effects of pretreatment on the characteristics of coal. Then, the appropriate solvent was selected for the subsequent sample preparation process of pyrolysis experiment. Secondly, the pyrolysis experiments were conducted on the sedimentation furnace, while most scholars use horizontal tube furnace. The experimental environment of sedimentation furnace is closer to the real condition of pulverized coal combustion, compared with horizontal tube furnace. Pyrolysis experiments chose samples including raw Zhundong coal, water washed coal, Na Cl?Na2SO4 loaded coal.In the process of pretreatment of Zhundong coal, deionized water, inorganic acid(HNO3?H2SO4?HCl)and organic acid(acetic acid?citric acid)were chosen for the experiments. The research found that, desodium rate of the deionized water was the lowest, and the effects of water on other characteristics of coal was the weakest. Sodium removal effect of inorganic acids was remarkable, among which hydrochloric acid was the best, but at the same time, hydrochloric acid would bring element Cl, which could affect the volatilization of sodium. Sodium removal efficiency of sulfuric acid and nitric acid was next only to hydrochloric acid. Nitric acid caused great damage to the surface of the coal. Compared with deionized water, organic acids had higher desodium rate and higher ash removal rate, and caused less damage to the surface of the coal. What's more, acetic acid could improve the pyrolysis performance. Citric acid increased the pore size of the sample. Therefore, suitable organic acid could be selected for sodium removal process of high sodium coal or related research. But as organic acids have not yet been widely used, this research would choose sulfuric acid for the pretreatment of pyrolysis coal sample, which would not bring element Cl.The transformation of sodium in Zhundong coal was studied through pyrolysis experiment. During raw coal pyrolysis, at 400?,water insoluble but ammonium acetate soluble sodium transform to water soluble sodium. At 600~800?, water soluble sodium convert to acid insoluble sodium. At 1000~1200?,higher temperature made the pores on the coal surface larger, which might cause the transformation from acid insoluble sodium to water soluble sodium. During water washed coal pyrolysis, at 400?, water insoluble but ammonium acetate soluble sodium might transform to water soluble sodium or acid insoluble sodium. At 1000 ?, acid insoluble sodium decreased, and might probably transform into volatile sodium. The char yield of Na Cl loaded coal was lower than Na2SO4 loaded coal, which showed better catalytic effect of Na Cl when pyrolysis. During Na2SO4 loaded coal pyrolysis, at 400?, the transformation from water soluble sodium to water insoluble but ammonium acetate soluble sodium was observed from the obtained data. During Na Cl loaded coal pyrolysis, water insoluble but ammonium acetate soluble content increased at 600~800?, as analyzed was conversed from acid insoluble sodium. |
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