孔隙结构对褐煤干燥动力学的影响
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摘要
研究了胜利和昭通褐煤在低温(60～140℃)干燥过程中孔隙结构的演变,计算了2种不同结构褐煤脱水过程的有效水分扩散系数(D_(eff)),讨论了褐煤孔隙结构参数和水分扩散特性参数的关系。结果表明,胜利褐煤的孔隙结构以开放的圆柱形孔隙、平行壁状狭缝孔和尖劈型毛细孔为主;而昭通褐煤以一端封闭的不透气性孔为主。随着干燥时间增加,2种褐煤比表面积均减小,平均孔径变化趋势与孔容变化相反。随着干燥温度升高,2种褐煤比表面积、孔容、平均孔径均增大,平均孔径变化趋势与孔容变化相同。关联动力学参数表明,煤样的孔容比及比表面积都与D_(eff)有较好关联度,2种褐煤的孔容比与比表面积呈正相关;水分扩散系数更是与比表面积呈线性关系。胜利褐煤在孔径小于7 nm时孔容比随温度的升高而增大;而孔径区间介于7～10 nm的孔容比随温度的升高而减小。昭通褐煤在孔径小于10 nm的孔容比随温度的升高而增大;而孔径区间介于10～20 nm的孔容比随温度的升高而减小。2种褐煤的D_(eff)均受微孔及较小孔径的中孔控制。同时,计算得出低温干燥过程胜利褐煤的活化能(16.95 kJ/mol)低于昭通褐煤(21.84 kJ/mol),这说明相同条件下胜利褐煤脱水所克服的能垒更低。
The pore structure variation of Shengli and Zhaotong lignite were investigated in the low temperature drying process(60-140 ℃).Meanwhile,the effective moisture diffusivities(D_(eff)) of the two types of lignite were calculated,from which the relationship between pore structure and effective moisture diffusivities was discussed.The results indicate that pore structure of Shengli lignite is dominated by open cylindrical pores and cracks pores,whilst,it is mainly dead end pores closed at one end for Zhaotong lignite.Furthermore,by increasing the drying time,the specific surface area of two lignite decreases and the variation trend of pore volume is opposite to that of average pore diameter.While the specific surface area,pore volume and average pore size increase with the improvement of drying temperature and the variation trend of average pore size is the same as that of pore volume.The correlation dynamics parameters demonstrate that the pore volume fraction and specific surface area of coal samples have good correlation with D_(eff).The pore volume fraction of lignite is positively related to the specific surface area,and the D_(eff) is linear with the specific surface area.With the increase of the temperature,the pore volume fraction of the Shengli lignite is increased when the pore diameter is less than 7 nm and decreased at 7-10 nm,but difference is that the pore volume fraction of Zhaotong lignite is increased when the pore diameter is less than 10 nm,and decreased at 10-20 nm.D_(eff) is controlled by micropores and mesoporous pores.Meanwhile,the data manifest that Shengli lignite(16.95 kJ/mol) possesses lower activation energy than Zhaotong lignite( 21.84 kJ/mol) in the low temperature drying process,implying that the actual energy required for the drying of Shengli lignite is relatively low.
The pore structure variation of Shengli and Zhaotong lignite were investigated in the low temperature drying process(60-140 ℃).Meanwhile,the effective moisture diffusivities(D_(eff)) of the two types of lignite were calculated,from which the relationship between pore structure and effective moisture diffusivities was discussed.The results indicate that pore structure of Shengli lignite is dominated by open cylindrical pores and cracks pores,whilst,it is mainly dead end pores closed at one end for Zhaotong lignite.Furthermore,by increasing the drying time,the specific surface area of two lignite decreases and the variation trend of pore volume is opposite to that of average pore diameter.While the specific surface area,pore volume and average pore size increase with the improvement of drying temperature and the variation trend of average pore size is the same as that of pore volume.The correlation dynamics parameters demonstrate that the pore volume fraction and specific surface area of coal samples have good correlation with D_(eff).The pore volume fraction of lignite is positively related to the specific surface area,and the D_(eff) is linear with the specific surface area.With the increase of the temperature,the pore volume fraction of the Shengli lignite is increased when the pore diameter is less than 7 nm and decreased at 7-10 nm,but difference is that the pore volume fraction of Zhaotong lignite is increased when the pore diameter is less than 10 nm,and decreased at 10-20 nm.D_(eff) is controlled by micropores and mesoporous pores.Meanwhile,the data manifest that Shengli lignite(16.95 kJ/mol) possesses lower activation energy than Zhaotong lignite( 21.84 kJ/mol) in the low temperature drying process,implying that the actual energy required for the drying of Shengli lignite is relatively low.
引文
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[12]杨云龙,刘晓,景晓霞,等.干燥时间对褐煤孔结构变化及其复吸行为的影响[J].太原理工大学学报,2013,44(4):417-421.YANG Yunlong,LIU Xiao,JING Xiaoxia,et al.Effect of Drying time on the change of pore structure and re-adsorption behavior of lignite[J].Journal of Taiyuan University of Technology,2013,44(4):417-421.
[13]NAKAGAWA T,KOMAKI I,SAKAWA M,et al.Small angle X-ray scattering study on change of fractal property of Witbank coal with heat treatment[J].Fuel,2000,79:1341-1346.
[14]武建军,李霞,周国莉,等.脱水褐煤的孔隙结构对复吸性能影响[J].中国矿业大学学报,2013,42(5):806-811.WU Jianjun,LI Xia,ZHOU Guoli,et al.Effect of pore structure on moisture readsorption of dewatered lignite[J].Journal of China University of Mining&Technology,2013,42(5):806-811.
[15]YU Jianglong,TAHMASEBI A,HAN Y,et al.A review on water in low rank coals:The existence,interaction with coal structure and effects on coal utilization[J].Fuel Processing Technology,2013,106:9-20.
[16]CLARKSON C R,BUSTIN R M.The effect of pore structure and gas pressure upon the transport properties of coal:A laboratory and modeling study.1.Isotherms and pore volume distributions[J].Fuel,1999,78(11):1333-1344.
[17]赵卫东,刘建忠,周俊虎,等.褐煤等温脱水热重分析[J].中国电机工程学报,2009,29(14):74-79.ZHAO Weidong,LIU Jianzhong,ZHOU Junhu,et al.Investigation on the isothermal dewatering of brown coal by thermobalance[J].Proceedings of the CSEE,2009,29(14):74-79.
[18]赵虹,郭飞,杨建国.印尼褐煤的吸附特性及脱水研究[J].煤炭学报,2008,33(7):799-802.ZHAO Hong,GUO Fei,YANG Jianguo.Adsorption characteristic of Indonesia lignite and dewater experiment[J].Journal of China Coal Society,2008,33(7):799-802.
[19]刘晓,景晓霞,李志强,等.褐煤的等温干燥特性及其脱水动力学分析[J].太原理工大学学报,2014,45(5):661-665.LIU Xiao,JING Xiaoxia,LI Zhiqiang,et al.Isothermal drying characteristics of lignite and kinetic analysis of dewatering[J].Journal of Taiyuan University of Technology,2014,45(5):661-665.
[20]周国莉.基于不同能量作用形式的胜利褐煤脱水机理及过程动力学研究[D].徐州:中国矿业大学,2014.ZHOU Guoli.Study on the dehydration mechanism and dynamics of shengli lignite dried by different energy forms[D].Xuzhou:China University of Mining&Technology,2014.
[21]熊程程.褐煤干燥过程的实验研究及动力学分析[D].北京:中国科学院研究生院(工程热物理研究所),2011.XIONG Chengcheng.Experimental study and kinetie analysis of lignite drying[D].Beijing:Graduate School of Chinese Academy of Sciences(Institute of Engineering Thermophysics),2011.
[2]WANG Qingsong,LIU Wei,YUAN Xueliang.Future of lignite resources:A life cycle analysis[J].Environ Sci Pollut Res,2016(23):24796-24807.
[3]熊程程,向飞,吕清刚.温度和相对湿度对褐煤干燥动力学特性的影响[J].化工学报,2011,62(10):2898-2904.XIONG Chengcheng,XIANG Fei,LQinggang.Effects of temperature and relative humidity on drying kinetics of lignite[J].CIESCJournal,2011,62(10):2898-2904.
[4]杨亚利,王志超,杨忠灿,等.褐煤等温干燥过程及动力学研究[J].洁净煤技术,2017,23(1):19-23.YANG Yali,WANG Zhichao,YANG Zhongcan,et al.Study on isothermal drying process and kinetics of lignite[J].Clean Coal Technology,2017,23(1):19-23.
[5]贺琼琼.褐煤干燥的孔隙水运移及其机制研究[D].徐州:中国矿业大学,2016.HE Qiongqiong.Mechanism of moisture transport in the pores of lignite during drying process[D].Xuzhou:China University of Mining&Technology,2016.
[6]孟召平,刘珊珊,王保玉,等.不同煤体结构煤的吸附性能及其孔隙结构特征[J].煤炭学报,2015,40(8):1865-1870.MENG Zhaoping,LIU Shanshan,WANG Baoyu,et al.Adsorption capacity and its pore structure of coals with different coal body structure[J].Journal of China Coal Society,2015,40(8):1865-1870.
[7]冯磊,张世红,杨晴,等.焦煤微波干燥特性及动力学研究[J].煤炭学报,2015,40(10):2458-2464.FENG Lei,ZHANG Shihong,YANG Qing,et al.Study on microwave drying characteristics and kinetics of coking coal[J].Journal of China Coal Society,2015,40(10):2458-2464.
[8]XU Shenqi,ZHOU Zhijie,YU Guangsuo,et al.Effects of pyrolysis on the pore structure of four Chinese coals[J].Energy Fuel,2010,24(2):1114-1123.
[9]陈萍,唐修义.低温氮吸附法与煤中微孔隙特征的研究[J].煤炭学报,2001,26(5):552-556.CHEN Ping,TANG Xiuyi.The research on the adsorption of nitrogen in low temperature and micro-pore properties in coal[J].Journal of China Coal Society,2001,26(5):552-556.
[10]TANG Jiewu,FENG Li,LI Yajun,et al.Fractal and pore structure analysis of Shengli lignite during drying process[J].Powder Technology,2016(303):251-259.
[11]严继民,张培元.吸附与凝聚[M].北京:科学出版社,1979:111-121.
[12]杨云龙,刘晓,景晓霞,等.干燥时间对褐煤孔结构变化及其复吸行为的影响[J].太原理工大学学报,2013,44(4):417-421.YANG Yunlong,LIU Xiao,JING Xiaoxia,et al.Effect of Drying time on the change of pore structure and re-adsorption behavior of lignite[J].Journal of Taiyuan University of Technology,2013,44(4):417-421.
[13]NAKAGAWA T,KOMAKI I,SAKAWA M,et al.Small angle X-ray scattering study on change of fractal property of Witbank coal with heat treatment[J].Fuel,2000,79:1341-1346.
[14]武建军,李霞,周国莉,等.脱水褐煤的孔隙结构对复吸性能影响[J].中国矿业大学学报,2013,42(5):806-811.WU Jianjun,LI Xia,ZHOU Guoli,et al.Effect of pore structure on moisture readsorption of dewatered lignite[J].Journal of China University of Mining&Technology,2013,42(5):806-811.
[15]YU Jianglong,TAHMASEBI A,HAN Y,et al.A review on water in low rank coals:The existence,interaction with coal structure and effects on coal utilization[J].Fuel Processing Technology,2013,106:9-20.
[16]CLARKSON C R,BUSTIN R M.The effect of pore structure and gas pressure upon the transport properties of coal:A laboratory and modeling study.1.Isotherms and pore volume distributions[J].Fuel,1999,78(11):1333-1344.
[17]赵卫东,刘建忠,周俊虎,等.褐煤等温脱水热重分析[J].中国电机工程学报,2009,29(14):74-79.ZHAO Weidong,LIU Jianzhong,ZHOU Junhu,et al.Investigation on the isothermal dewatering of brown coal by thermobalance[J].Proceedings of the CSEE,2009,29(14):74-79.
[18]赵虹,郭飞,杨建国.印尼褐煤的吸附特性及脱水研究[J].煤炭学报,2008,33(7):799-802.ZHAO Hong,GUO Fei,YANG Jianguo.Adsorption characteristic of Indonesia lignite and dewater experiment[J].Journal of China Coal Society,2008,33(7):799-802.
[19]刘晓,景晓霞,李志强,等.褐煤的等温干燥特性及其脱水动力学分析[J].太原理工大学学报,2014,45(5):661-665.LIU Xiao,JING Xiaoxia,LI Zhiqiang,et al.Isothermal drying characteristics of lignite and kinetic analysis of dewatering[J].Journal of Taiyuan University of Technology,2014,45(5):661-665.
[20]周国莉.基于不同能量作用形式的胜利褐煤脱水机理及过程动力学研究[D].徐州:中国矿业大学,2014.ZHOU Guoli.Study on the dehydration mechanism and dynamics of shengli lignite dried by different energy forms[D].Xuzhou:China University of Mining&Technology,2014.
[21]熊程程.褐煤干燥过程的实验研究及动力学分析[D].北京:中国科学院研究生院(工程热物理研究所),2011.XIONG Chengcheng.Experimental study and kinetie analysis of lignite drying[D].Beijing:Graduate School of Chinese Academy of Sciences(Institute of Engineering Thermophysics),2011.
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