Effect of carrier gas on gasification performance of two-stage entrained-flow coal gasifier

doi:10.16085/j.issn.1000-6613.2017.01.018

Abstract

Abstract: Replacing the N₂ in carrier gas with CO₂ would lower N₂ level in the product gas which is good for CO₂ capture. However,the lower O₂ diffusivity in CO₂ would affect char reactivity,thus gasifier operation performance. To clarify the effect of carrier gas on gasification performance of a two-stage entrained-flow coal gasifier,a modified char reaction model is proposed by combining the shrinking core model with the Langmuir-Hinshelwood kinetic rate expression which considers the inhibitive effect of CO on char gasification reaction. The predictions of the flow,temperature,species distributions are provided and the results consiste with the operating data. In addition,at two coal feed rates of the 2nd stage(3817kg/h,11104kg/h),the effect of carrier gas(N₂,CO₂) on the gasifier operating performance is evaluated by comparing with the distributions of carbon conversion efficiency (CCE),gas temperature and species mole fractions in the gasifier. The results indicate that in the injection region of the 1st stage,the substitution of CO₂ for N₂ results in decreases in the gas temperature and CCE due to the lower O₂ diffusivity in CO₂. And the enhanced char-CO₂ reaction caused by the increased CO₂ has only a minor effect on CCE. Above the injection region of the 1st stage,the O₂ diffusion effect is weaken due to lower O₂ concentration,and the enhanced char-CO₂ reaction increases CCE. Meanwhile,the results also confirmed that replacing the N₂ in carrier gas with CO₂ results in an increase in CO formation and a decrease in H₂ formation.

Key words: gasification, simulation, coal combustion, carrier gas, two-stage entrained-flow gasifier

摘要： 相比于N₂，CO₂作为气化炉煤粉载气会降低合成气中N₂的含量而有利于后续CO₂捕集，但O₂在CO₂中较小的扩散系数会影响焦炭的反应特性，进而影响气化炉运行结果。为此，考虑到气化炉中较高的CO含量及其对煤气化反应的抑制作用，将Langmuir-Hinshelwood动力学模型与缩核模型相结合，提出一个改进的焦炭反应模型，并对两段式干煤粉气化炉内的流场、温度场和组分浓度场进行了模拟分析，结果与实炉实测数据一致。在此基础上，模拟分析了气化炉在不同煤粉载气（N₂、CO₂）、两种二段给煤量下的气化特性。结果表明，煤粉载气由N₂改为CO₂后，由于O₂在CO₂中较低的扩散速率，一段气化室喷嘴区域气体温度和碳转化率降低，该区域CO₂增多对焦炭-CO₂反应的促进作用对提高碳转化率的影响较小；在一段气化室喷嘴区域之上，O₂浓度较低导致O₂扩散性影响减弱，同时CO₂增多促进焦炭-CO₂反应进而提高碳转化率。研究结果还证实，煤粉载气由N₂改为CO₂会促进CO的生成，抑制H₂的生成。

关键词: 气化, 模拟, 煤燃烧, 载气, 两段式气化炉

CLC Number:

TQ54

FAN Qiang, LIU Yinhe, LI Guangyu, CHE Defu. Effect of carrier gas on gasification performance of two-stage entrained-flow coal gasifier[J]. Chemical Industry and Engineering Progree, 2017, 36(01): 136-145.

樊强, 刘银河, 李广宇, 车得福. 载气对两段式干煤粉加压气化炉气化特性的影响[J]. 化工进展, 2017, 36(01): 136-145.

References

[1] 王辅臣,于广锁,龚欣,等. 大型煤气化技术的研究与发展[J]. 化工进展,2009,28(2):173-180. WANG F C,YU G S,GONG X,et al. Research and development of large-scale coal gasification technology[J]. Chemical Industry and Engineering Progress,2009,28(2):173-180.
[2] 许世森,王保民. 两段式干煤粉加压气化技术及工程应用[J]. 化工进展,2010,29(s1):290-294. XU S S,WANG B M. Engineering application and technology of two-stage dry feed entrained flow gasifier[J]. Chemical Industry and Engineering Progress,2010,29(s1):290-294.
[3] XU S,REN Y,WANG B,et al. Development of a novel 2-stage entrained flow coal dry powder gasifier[J]. Applied Energy,2014,113(0306/2619):318-323.
[4] REN Y,XU S,LI G. Experimental study on the operational performance of an advanced two-stage entrained-flow coal gasifier[J]. Energy & Fuels,2014,28(8):4911-4917.
[5] LI X,LI G,CAO Z,et al. Research on flow characteristics of slag film in a slag tapping gasifier[J]. Energy & Fuels,2010,24(9):5109-5115.
[6] WANG B,LI X,XU S,et al. Performance of chinese coals under conditions simulating entrained-flow gasification[J]. Energy & Fuels,2005,19(5):2006-2013.
[7] PERALTA D,PATERSON N,DUGWELL D,et al. Pyrolysis and CO₂ gasification of Chinese coals in a high-pressure wire-mesh reactor under conditions relevant to entrained-flow gasification[J]. Energy & Fuels,2005,19(2):532-537.
[8] WU X,ZHANG Z,PIAO G,et al. Behavior of mineral matters in Chinese coal ash melting during char-CO₂/H₂O gasification reaction[J]. Energy & Fuels,2009,23(5):2420-2428.
[9] SUN Z,DAI Z,ZHOU Z,et al. Numerical simulation of industrial opposed multiburner coal-water slurry entrained flow gasifier[J]. Industrial & Engineering Chemistry Research,2012,51(6):2560-2569.
[10] 陈超. CO₂和H₂O混合气氛条件下煤焦气化机理及数值模拟研究[D]. 武汉:华中科技大学,2013. Mechanism and numerical simulation of char gasification in Mixtures of CO₂ and H₂O[D]. Wuhan:Huazhong University of Science and Technology,2013.
[11] 周俊虎,匡建平,周志军,等. 粉煤气化炉冷态和热态流场分布特性的数值模拟[J]. 中国电机工程学报,2007,27(20):30-35. ZHOU J H,KUANG J P,ZHOU Z J,et al. Numerical simulation for pulverized coal gasifier's fluid flow characteristic on cold and hot condition[J]. Proceedings of the CSEE,2007,27(20):30-35.
[12] 吴玉新,张建胜,王明敏,等. 简化PDF模型对Texaco气化炉的三维数值模拟[J]. 化工学报,2007,58(9):2369-2374. WU Y X,ZHANG J S,WANG M M,et al. 3D numerical simulation of Texaco gasifier using assumed PDF model[J]. CIESC Journal,2007,58(9):2369-2374.
[13] 赵庆,王晓亮,陶舒畅. 基于常压TGA的煤焦-CO₂加压反应动力学数据求解[J]. 东方电气评论,2012,26(4):1-6. ZHAO Q,WANG X L,TAO S C. Solution of coal char-CO₂ pressurized kinetic parameters besed on atmospheric pressure TGA[J]. Dongfang Electric Review,2012,26(4):1-6.
[14] 王明敏,张建胜,岳光溪,等. 煤焦与水蒸气的气化实验及表观反应动力学分析[J]. 中国电机工程学报,2008,28(5):34-38. WANG M M,ZHANG J S,YUAN G X,et al. Experimental study and apparent reaction kinetics analysis on the char-steam gasification[J]. Proceedings of the CSEE,2008,28(5):34-38.
[15] HUANG Z,ZHANG J,ZHAO Y,et al. Kinetic studies of char gasification by steam and CO₂ in the presence of H₂ and CO[J]. Fuel Processing Technology,2010,91(8):843-847.
[16] 李伟伟,李克忠,康守国,等. 煤催化气化中非均相反应动力学的研究[J]. 燃料化学学报,2014,42(3):290-296. LI W W,LI K Z,KANG S G,et al. Heterogeneous reaction kinetics of catalytic coal gasification[J]. Journal of Fuel Chemistry and Technology,2014,42(3):290-296.
[17] 李超,代正华,孙钟华,等. 气流床气化炉综合模型及颗粒粒径对气化结果的影响研究[J]. 高校化学工程学报,2013,27(4):597-603. LI C,DAI Z H,SUN Z H,et al. Development of a comprehensive model of entrained flow coal gasifier and study of effects of particle diameter on gasification results[J]. Journal of Chemical Engineering of Chinese Universities,2013,27(4):597-603.
[18] 张健,章明川,于娟,等. 考虑颗粒边界层气相反应的炭粒气化过程模型预报[J]. 燃烧科学与技术,2011,17(1):49-55. ZHANG J,ZHANG M C,YU J,et al. Modeling of char gasification process taking into account homogeneous reactions in particle boundary layer[J]. Journal of Combustion Science and Technology,2011,17(1):49-55.
[19] GUO X,DAI Z,GONG X,et al. Performance of an entrained-flow gasification technology of pulverized coal in pilot-scale plant[J]. Fuel Processing Technology,2007,88(5):451-459.
[20] PATANKAR S. Numerical heat transfer and fluid flow[M]. Washington D C:Hemisphere Publishing Corp.,1980.
[21] SHUEN J S,CHEN L D,FAETH G M. Evaluation of a stochastic model of particle dispersion in a turbulent round jet[J]. AIChE Journal,1983,29(1):167-170.
[22] ÖZıŞıK M N. Radiative transfer and interactions with conduction and convection[M]. Werbel & Peck,1973.
[23] SHIH T-H,LIOU W W,SHABBIR A,et al. A new k-ε eddy viscosity model for high reynolds number turbulent flows[J]. Computers & Fluids,1995,24(3):227-238.
[24] 毕大鹏,管清亮,玄伟伟,等. 基于双组分PDF模型的GSP气化炉数值模拟[J]. 化工学报,2014,65(10):3753-3759. BI D P,GUAN Q L,XUAN W W,et al. Numerical simulation of GSP gasifier based on double-mixture fractions PDF model[J]. CIESC Journal,2014,65(10):3753-3759.
[25] WATANABE H,OTAKA M. Numerical simulation of coal gasification in entrained flow coal gasifier[J]. Fuel,2006,85(12/13):1935-1943.
[26] BADZIOCH S,HAWKSLEY P G W. Kinetics of thermal decomposition of pulverized coal particles[J]. Industrial & Engineering Chemistry Process Design and Development,1970,9(4):521-530.
[27] BENFELL K E. Assessment of char morphology in high pressure pyrolysis and combustion[M]. University of Newcastle,2001.
[28] WEN C Y,CHAUNG T Z. Entrainment coal gasification modeling[J]. Industrial & Engineering Chemistry Process Design and Development,1979,18(4):684-695.
[29] LIU G-S,TATE A G,BRYANT G W,et al. Mathematical modeling of coal char reactivity with CO₂ at high pressures and temperatures[J]. Fuel,2000,79(10):1145-1154.
[30] 任轶舟,王亦飞,朱龙雏,等. 高温煤焦气化反应的Langmuir-Hinshelwood动力学模型[J]. 化工学报,2014,65(10):3906-3915. REN Y Z,WANG Y F,ZHU L C,et al. Langmuir-Hinshelwood kinetic model of high temperature coal char gasification reaction[J]. CIESC Journal,2014,65(10):3906-3915.
[31] MA J,ZITNEY S E. Computational fluid dynamic modeling of entrained-flow gasifiers with improved physical and chemical submodels[J]. Energy & Fuels,2012,26(12):7195-7219.
[32] CHEN Z. Experimental and numerical study on two-stage dry feed entrained flow gasification[D]. Xi'an:Xi'an Thermal Power Research Institute,2013.
[33] BEJARANO P A,LEVENDIS Y A. Single-coal-particle combustion in O₂/N₂ and O₂/CO₂ environments[J]. Combustion and Flame,2008,153(1/2):270-287.
[34] LI Q,ZHAO C,CHEN X,et al. Comparison of pulverized coal combustion in air and in O₂/CO₂ mixtures by thermo-gravimetric analysis[J]. Journal of Analytical and Applied Pyrolysis,2009,85(1/2):521-528.
[35] CHEN L,YONG S Z,GHONIEM A F. Oxy-fuel combustion of pulverized coal:characterization,fundamentals,stabilization and CFD modeling[J]. Progress in Energy and Combustion Science,2012,38(2):156-214.
[36] SHADDIX C R,MOLINA A. Particle imaging of ignition and devolatilization of pulverized coal during oxy-fuel combustion[J]. Proceedings of the Combustion Institute,2009,32(2):2091-2098.
[37] GUO X,LU W,DAI Z,et al. Experimental investigation into a pilot-scale entrained-flow gasification of pulverized coal using CO₂ as carrier gas[J]. Energy & Fuels,2011,26(2):1063-1069.
[38] BRIX J,JENSEN P A,JENSEN A D. Modeling char conversion under suspension fired conditions in O₂/N₂ and O₂/CO₂ atmospheres[J]. Fuel,2011,90(6):2224-2239.
[39] HARRIS D J,SMITH I W. Twenty-Third Symposium (International) on Combustion Intrinsic reactivity of petroleum coke and brown coal char to carbon dioxide,steam and oxygen[J]. Symposium(International)on Combustion,1991,23(1):1185-1190.
[40] TOLVANEN H,RAIKO R. An experimental study and numerical modeling of combusting two coal chars in a drop-tube reactor:a comparison between N₂/O₂,CO₂/O₂,and N₂/CO₂/O₂ atmospheres[J]. Fuel,2014,124:190-201.
[41] HECHT E S,SHADDIX C R,MOLINA A,et al. Effect of CO₂ gasification reaction on oxy-combustion of pulverized coal char[J]. Proceedings of the Combustion Institute,2011,33(2):1699-1706.