热等离子体裂解甲烷制乙炔过程的数值模拟
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摘要
针对热等离子体甲烷裂解过程,建立了直流电弧反应器的数值模型,使用磁流体力学理论对反应器内的电弧和流场进行数值模拟,考察了电弧运动变化的规律和射流场特点,并分别耦合热力学平衡模型和宏观动力学模型探索了裂解反应的特点及其与电弧的相互影响关系。结果表明反应器内电弧做规律运动和形态变化,惰性无反应气氛下电弧形态变化不显著,运动平稳。放电区发生反应时,一方面气体的组成及热力学性质发生迅速变化,气体放电特性受到影响,等离子体的稳定性下降,化学反应是等离子体不稳定性的重要来源。另一方面,反应和扩散的特征时间小于电弧运动变化的特征时间,各物质在空间的分布较为均匀,受温度场非均匀性的影响较小,模拟的甲烷转化率和乙炔收率与实验结果相近。本工作尤其是等离子体物理模型与甲烷裂解化学反应模型的耦合,为理解热等离子体裂解相关过程提供了直接的帮助和指导。
A numerical model with respect to thermal plasma pyrolysis of methane was established and a numerical study of the plasma and the reaction via the theory of magnetohydrodynamics(MHD) was carried out. The arc motion pattern and the characteristics of the fluid field regarding to temperature and velocity distribution inside the reactor were concluded, and further reaction model respectively considering thermodynamic equilibrium and simplified macro-kinetics was individually coupled into the MHD model toshowtheinfluenceofpyrolysisreactiononplasmaarcandtheinteractionsbetweenthem.Generally,with pure argon as discharge media, the arc moved in a smooth and steady pattern, whereas the addition of methane would prolong the arc and accelerate the switch of arc-anode-spot. When reaction kinetics was considered, the gradient of temperature was elevated, yet the distribution of species was much more homogeneousduetotherapiddiffusionofgas.Theinstabilityofarcunderpre-mixingstrategywasattributed to the pyrolysis reaction and the differences of thermodynamic properties of individual component.
A numerical model with respect to thermal plasma pyrolysis of methane was established and a numerical study of the plasma and the reaction via the theory of magnetohydrodynamics(MHD) was carried out. The arc motion pattern and the characteristics of the fluid field regarding to temperature and velocity distribution inside the reactor were concluded, and further reaction model respectively considering thermodynamic equilibrium and simplified macro-kinetics was individually coupled into the MHD model toshowtheinfluenceofpyrolysisreactiononplasmaarcandtheinteractionsbetweenthem.Generally,with pure argon as discharge media, the arc moved in a smooth and steady pattern, whereas the addition of methane would prolong the arc and accelerate the switch of arc-anode-spot. When reaction kinetics was considered, the gradient of temperature was elevated, yet the distribution of species was much more homogeneousduetotherapiddiffusionofgas.Theinstabilityofarcunderpre-mixingstrategywasattributed to the pyrolysis reaction and the differences of thermodynamic properties of individual component.
引文
[1] FINCKE J R, ANDERSON R P, HYDE T, et al. Plasma thermal conversion of methane to acetylene[J]. Plasma Chemistry and Plasma Processing, 2002, 22(1):105-136.
[2] CHENG Yan, YAN Binhang, LI Tianyang, et al. Experimental study on coal tar pyrolysis in thermal plasma[J]. Plasma Chemistry and Plasma Processing, 2015, 35(2):401-413.
[3] AN Hang, CHENG Yan, LI Tianyang, et al. Numerical analysis of methane pyrolysis in thermal plasma for selective synthesis of acetylene[J]. Fuel Processing Technology, 2018, 172:195-199.
[4]程炎,李天阳,金涌,等.热等离子体超高温化学转化的过程研发和应用进展[J].化工进展, 2016, 35(6):1676-1686.CHENG Yi, LI Tianyang, JIN Yong, et al. State-of-the-art development of research and applications of chemical conversion processes at ultra-high temperature in thermal plasma reactors[J].Chemical Industry and Engineering Progress, 2016, 35(6):1676-1686.
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[6]王志斌,陈国旭,王哲,等.三电极非热电弧发生器放电模式的实验研究[J].清华大学学报(自然科学版), 2014(1):73-77.WANG Zhibin, CHEN Guoxu, WANG Zhe, et al. Experimental investigation of the discharge modes of a non-thermal arc plasma generator with three-electrode configuration[J]. Journal of Tsinghua University(Science and Technology), 2014(1):73-77.
[7]付友,王振,王宁会.用于高效冶炼氧化镁的双电极直流电弧炉的仿真与实验[J].电工技术学报, 2016,31(24):79-87.FU You, WANG Zhen, WANG Ninghui. Simulation and experiment investigation on a dual-electrode DC arc furnace with high smelting efficiency for MgO production[J]. Transactions of China Electrotechnical Society, 2016,31(24):79-87.
[8]董其鹏,张炯明,雷少武,等.直流等离子体电弧特性的模拟[J].焊接学报, 2014(12):27-30.DONG Qipeng, ZHANG Jiongming, LEI Shaowu, et al. Simulation of characteristics of DC plasma arc[J]. Transactions of the China Welding Institution, 2014(12):27-30.
[9] TANG K M, YAN J D, CHAPMAN C, et al. Three-dimensional modelling of a DC arc plasma in a twin-torch system[J]. Journal of Physics D:Applied Physics, 2010, 43(34):345201.
[10] HUR M, HONG S H. Comparative analysis of turbulent effects on thermal plasma characteristics inside the plasma torches with rod-and well-type cathodes[J]. Journal of Physics D:Applied Physics, 2002, 35(16):1946-1954.
[11]余徽,印永祥,戴晓雁.等离子体射流裂解甲烷制乙炔的数值模拟[J].化工学报, 2006, 57(10):2319-2326.YU Hui, YIN Yongxiang, DAI Xiaoyan. Numerical simulation of methane conversion to acetylene in plasma jet reactor[J]. Journal of Chemical Industry and Engineering(China), 2006, 57(10):2319-2326.
[12]周前红.直流电弧等离子体炬的数值模拟[D].上海:复旦大学,2009.ZHOU Qianhong. Numerical simulation of a DC arc plasma torch[D].Shanghai:Fudan University, 2009.
[13]李和平,陈熙.等离子体反应器中传热与流动的三维数值模拟[J].工程热物理学报, 2001(3):324-327.LI Heping, CHEN Xi. Three-dimensional simulation of heat transfer and fluid flow in a thermal plasma reactor[J]. Journal of Engineering Thermophysics, 2001(3):324-327.
[14] WU Changning, CHEN Jiaqi, CHENG Yi. Thermodynamic analysis of coal pyrolysis to acetylene in hydrogen plasma reactor[J]. Fuel Processing Technology, 2010, 91:823-830.
[15] National Aeronautics and Space Administration Glenn Research Center. Chemical equilibrium with applications[CP/OL].[2019-01-17]. https://cearun.grc.nasa.gov.
[16]罗义文,漆继红,印永祥,等.热等离子体裂解甲烷的热力学与动力学分析[J].四川大学学报(工程科学版), 2003(4):33-37.LUO Yiwen, QI Jihong, YIN Yongxiang, et al. Kinetic and thermodynamic analysis of the thermal plasma decomposition system of methane[J]. Journal of Sichuan University(Engineering Science Edition), 2003(4):33-37.
[17] HOLMEN A, ROKSTAD O A, SOLBAKKEN A. High-temperature pyrolysis of hydrocarbons. I. Methane to acetylene[J]. Industrial&Engineering Chemistry Research, 1976, 15(3):439-444.
[18] HOLMEN A, OLSVIK O, ROKSTAD O A. Pyrolysis of natural gas:chemistry and process concepts[J]. Fuel Processing Technology, 1995,42(2):249-267.
[19]郭平,涂汉敏,汪周华,等.多组分气-气扩散系数的计算[J].天然气工业, 2015, 35(8):39-43.GUO Ping, TU Hanmin, WANG Zhouhua, et al. Calculation of multicomponent gas-gas diffusion coefficient[J]. Natural Gas Industry,2015, 35(8):39-43.
[20] LI Tianyang, REHMET C, CHENG Yan, et al. Experimental comparison of methane pyrolysis in thermal plasma[J]. Plasma Chemistry and Plasma Processing, 2017, 37(4):1033-1049.
[21]李和平,吴贵清,李鹏,等.阴极边界条件对双射流电弧等离子体特性影响的二维数值模拟[J].高电压技术, 2013(7):1549-1556.LI Heping, WU Guiqing, LI Peng, et al. Two-dimensional modeling concerning the effects of the boundary conditions along the cathode sheath-arc column interface on the characteristics of the dual-jet arc plasmas[J]. High Voltage Engineering, 2013(7):1549-1556.
[22] MORROW R, LOWKE J J. A one-dimensional theory for the electrode sheaths of electric arcs[J]. J. Phys. D:Appl. Phys., 1993, 26:634.
[2] CHENG Yan, YAN Binhang, LI Tianyang, et al. Experimental study on coal tar pyrolysis in thermal plasma[J]. Plasma Chemistry and Plasma Processing, 2015, 35(2):401-413.
[3] AN Hang, CHENG Yan, LI Tianyang, et al. Numerical analysis of methane pyrolysis in thermal plasma for selective synthesis of acetylene[J]. Fuel Processing Technology, 2018, 172:195-199.
[4]程炎,李天阳,金涌,等.热等离子体超高温化学转化的过程研发和应用进展[J].化工进展, 2016, 35(6):1676-1686.CHENG Yi, LI Tianyang, JIN Yong, et al. State-of-the-art development of research and applications of chemical conversion processes at ultra-high temperature in thermal plasma reactors[J].Chemical Industry and Engineering Progress, 2016, 35(6):1676-1686.
[5]张祥富,曾达权.天然气等离子体法制乙炔[J].天然气化工, 1998(4):39-43.ZHANG Xiangfu, ZENG Daquan. The plasma method for acetylene production from natural gas[J]. Natural Gas Chemical Industry, 1998(4):39-43.
[6]王志斌,陈国旭,王哲,等.三电极非热电弧发生器放电模式的实验研究[J].清华大学学报(自然科学版), 2014(1):73-77.WANG Zhibin, CHEN Guoxu, WANG Zhe, et al. Experimental investigation of the discharge modes of a non-thermal arc plasma generator with three-electrode configuration[J]. Journal of Tsinghua University(Science and Technology), 2014(1):73-77.
[7]付友,王振,王宁会.用于高效冶炼氧化镁的双电极直流电弧炉的仿真与实验[J].电工技术学报, 2016,31(24):79-87.FU You, WANG Zhen, WANG Ninghui. Simulation and experiment investigation on a dual-electrode DC arc furnace with high smelting efficiency for MgO production[J]. Transactions of China Electrotechnical Society, 2016,31(24):79-87.
[8]董其鹏,张炯明,雷少武,等.直流等离子体电弧特性的模拟[J].焊接学报, 2014(12):27-30.DONG Qipeng, ZHANG Jiongming, LEI Shaowu, et al. Simulation of characteristics of DC plasma arc[J]. Transactions of the China Welding Institution, 2014(12):27-30.
[9] TANG K M, YAN J D, CHAPMAN C, et al. Three-dimensional modelling of a DC arc plasma in a twin-torch system[J]. Journal of Physics D:Applied Physics, 2010, 43(34):345201.
[10] HUR M, HONG S H. Comparative analysis of turbulent effects on thermal plasma characteristics inside the plasma torches with rod-and well-type cathodes[J]. Journal of Physics D:Applied Physics, 2002, 35(16):1946-1954.
[11]余徽,印永祥,戴晓雁.等离子体射流裂解甲烷制乙炔的数值模拟[J].化工学报, 2006, 57(10):2319-2326.YU Hui, YIN Yongxiang, DAI Xiaoyan. Numerical simulation of methane conversion to acetylene in plasma jet reactor[J]. Journal of Chemical Industry and Engineering(China), 2006, 57(10):2319-2326.
[12]周前红.直流电弧等离子体炬的数值模拟[D].上海:复旦大学,2009.ZHOU Qianhong. Numerical simulation of a DC arc plasma torch[D].Shanghai:Fudan University, 2009.
[13]李和平,陈熙.等离子体反应器中传热与流动的三维数值模拟[J].工程热物理学报, 2001(3):324-327.LI Heping, CHEN Xi. Three-dimensional simulation of heat transfer and fluid flow in a thermal plasma reactor[J]. Journal of Engineering Thermophysics, 2001(3):324-327.
[14] WU Changning, CHEN Jiaqi, CHENG Yi. Thermodynamic analysis of coal pyrolysis to acetylene in hydrogen plasma reactor[J]. Fuel Processing Technology, 2010, 91:823-830.
[15] National Aeronautics and Space Administration Glenn Research Center. Chemical equilibrium with applications[CP/OL].[2019-01-17]. https://cearun.grc.nasa.gov.
[16]罗义文,漆继红,印永祥,等.热等离子体裂解甲烷的热力学与动力学分析[J].四川大学学报(工程科学版), 2003(4):33-37.LUO Yiwen, QI Jihong, YIN Yongxiang, et al. Kinetic and thermodynamic analysis of the thermal plasma decomposition system of methane[J]. Journal of Sichuan University(Engineering Science Edition), 2003(4):33-37.
[17] HOLMEN A, ROKSTAD O A, SOLBAKKEN A. High-temperature pyrolysis of hydrocarbons. I. Methane to acetylene[J]. Industrial&Engineering Chemistry Research, 1976, 15(3):439-444.
[18] HOLMEN A, OLSVIK O, ROKSTAD O A. Pyrolysis of natural gas:chemistry and process concepts[J]. Fuel Processing Technology, 1995,42(2):249-267.
[19]郭平,涂汉敏,汪周华,等.多组分气-气扩散系数的计算[J].天然气工业, 2015, 35(8):39-43.GUO Ping, TU Hanmin, WANG Zhouhua, et al. Calculation of multicomponent gas-gas diffusion coefficient[J]. Natural Gas Industry,2015, 35(8):39-43.
[20] LI Tianyang, REHMET C, CHENG Yan, et al. Experimental comparison of methane pyrolysis in thermal plasma[J]. Plasma Chemistry and Plasma Processing, 2017, 37(4):1033-1049.
[21]李和平,吴贵清,李鹏,等.阴极边界条件对双射流电弧等离子体特性影响的二维数值模拟[J].高电压技术, 2013(7):1549-1556.LI Heping, WU Guiqing, LI Peng, et al. Two-dimensional modeling concerning the effects of the boundary conditions along the cathode sheath-arc column interface on the characteristics of the dual-jet arc plasmas[J]. High Voltage Engineering, 2013(7):1549-1556.
[22] MORROW R, LOWKE J J. A one-dimensional theory for the electrode sheaths of electric arcs[J]. J. Phys. D:Appl. Phys., 1993, 26:634.