准东煤中钠的赋存形态及蒸发冷凝特性
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摘要
针对新疆准东高碱煤由于高钠特性而在燃烧过程中出现严重结渣沾污等问题,通过三步萃取实验研究了准东煤中钠的赋存形态;通过钠的蒸发实验测量了不同燃烧温度下准东煤灰中钠的含量并分析其释放规律;通过钠的冷凝实验确定了钠的最佳冷凝温度区间并分析其冷凝形态;通过化学热力学平衡计算模拟了钠的析出及其化学反应.结果表明:准东煤中的钠大部分以水溶钠形式存在;在400～700℃,钠的蒸发最快,主要为水溶钠的释放过程,其析出活化能较低;钠的最佳冷凝温度区间为(670±20)℃,而冷凝区域具有分散、成块、呈流动性的特点;煤中钠的主要化学反应是NaCl、Na_2O·SiO_2、Na_2SO_4和NaOH等的固相、液相和气相之间的转化.
Due to the high content of sodium in Zhundong coal from Xinjiang,serious slagging and fouling problems may be encountered during the combustion process.The occurrence form of sodium in Zhundong coal was investigated via a three-step extraction experiment.The sodium content of Zhundong coal ash under different combustion temperatures was studied by an evaporation experiment,and the release characteristics of sodium were analyzed.The optimal condensation temperature range of sodium was measured by a condensation experiment,and the condensate morphology was analyzed.Finally,the chemical reactions of sodium were simulated by chemical thermodynamic equilibrium calculations.The results showed that sodium in Zhundong coal mainly presented in the form of water-soluble sodium.At 400—700 ℃,sodium evaporated fastest,which was mainly in the release process of water-soluble sodium.The optimum sodium condensation temperature range was(670±20)℃,and the condensation zone showed the characteristics of lump and fluid with disperse distribution.The main chemical reactions of sodium in coal involved the transformations of NaCl,Na_2O·SiO2,Na_2SO_4 and NaOH between the solid,liquid and gas phases.
Due to the high content of sodium in Zhundong coal from Xinjiang,serious slagging and fouling problems may be encountered during the combustion process.The occurrence form of sodium in Zhundong coal was investigated via a three-step extraction experiment.The sodium content of Zhundong coal ash under different combustion temperatures was studied by an evaporation experiment,and the release characteristics of sodium were analyzed.The optimal condensation temperature range of sodium was measured by a condensation experiment,and the condensate morphology was analyzed.Finally,the chemical reactions of sodium were simulated by chemical thermodynamic equilibrium calculations.The results showed that sodium in Zhundong coal mainly presented in the form of water-soluble sodium.At 400—700 ℃,sodium evaporated fastest,which was mainly in the release process of water-soluble sodium.The optimum sodium condensation temperature range was(670±20)℃,and the condensation zone showed the characteristics of lump and fluid with disperse distribution.The main chemical reactions of sodium in coal involved the transformations of NaCl,Na_2O·SiO2,Na_2SO_4 and NaOH between the solid,liquid and gas phases.
引文
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[4]He Y,Zhu J,Li B,et al.In-situ measurement of sodium and potassium release during oxy-fuel combustion of lignite using laser-induced breakdown spectroscopy:Effects of O2 and CO2 concentration[J].Energy Fuels,2013,27:1123-1130.
[5]Gao Qi,Li Shuiqing,Yuan Ye,et al.Ultrafine particulate matter formation in the early stage of pulverized coal combustion of high-sodium lignite[J].Fuel,2015,158:224-231.
[6]Van Alphen C.Automated mineralogical analysis of coal and ash products-Challenges and requirements[J].Minerals Engineering,2007,20(5):496-505.
[7]Quyn D M,Wu H,Li C Z.Volatilisation and catalytic effects of alkali and alkaline earth metallic species during the pyrolysis and gasification of Victorian brown coal(Ⅰ):Volatilisation of Na and Cl from a set of NaClloaded samples[J].Fuel,2002,81(2):143-149.
[8]Wang X B,Xu Z Y,Wei B,et al.The ash deposition mechanism in boilers burning Zhundong coal with high contents of sodium and calcium:A study from ash evaporating to condensing[J].Applied Thermal Engineering,2015,80(5):150-159.
[9]Bryers R W.Fireside slagging,fouling and hightemperature corrosion of heat-transfer surface due to impurities in steam-raising fuels[J].Progress in Energy and Combustion Science,1996,22(1):29-40.
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[12]刘扬,张成,王澜,等.高碱煤中钠基化合物对灰熔融特性的影响[J].燃烧科学与技术,2017,23(3):268-273.Liu Yang,Zhang Cheng,Wang Lan,et al.Influence of sodium-based compound on ash melting characteristics of high alkali coal[J].Journal of Combustion Science and Technology,,2017,23(3):268-273(in Chinese).
[13]齐晓宾,宋国良,宋维健,等.准东煤循环流化床气化过程中的矿物质转化行为特性[J].燃烧科学与技术,2017,23(1):29-35.Qi Xiaobin,Song Guoliang,Song Weijian,et al.Mineral transformation behavior of Zhundong coal during circulating fludized bed gasification[J].Journal of Combustion Science and Technology,2017,23(1):29-35(in Chinese).