内/外烟气再循环对天然气燃烧NO_x生成的影响
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摘要
烟气再循环作为一种有效抑制NO_x生成的技术,广泛应用于化工、制药和酿酒等行业的天然气低氮燃烧过程,其作用机理是学术界和工业界关注的热点。本文根据内/外烟气再循环的作用不同,设计了弱/强内烟气再循环两种扩散式燃烧器,结合外烟气再循环技术,在0.8MW中试实验台上研究了内/外烟气再循环对天然气燃烧过程NO_x生成的影响规律,同时开展了Fluent数值模拟。结果表明:内烟气再循环能够有效抑制NO_x的生成,同时保证燃烧稳定。相同工况下,带内烟气再循环燃烧器初始排放远低于传统低氮燃烧器。同时结合外烟气再循环技术,可使NO_x排放量维持在30mg/m~3以下。Fluent模拟结果显示了外烟气再循环能够显著地降低天然气燃烧火焰区的温度和O2浓度。其中温度的降低对于NO_x生成的抑制起到了决定性的作用。当NO_x降低到约30mg/m~3时,快速型NO_x对整体NO_x生成的贡献超过热力型NO_x,此情况下必须考虑对快速型NO_x进行抑制。
Flue gas recirculation, an effective way to inhabit NO_x formation, is widely used in the natural gas low-NO_x combustion process in chemical engineering, pharmaceutical and brewing industries. Its working mechanism attracts attentions from both academia and industry. Considering the effects of the internal/external flue gas recirculation(i-/e-FGR), two types of diffusion-combustion burners with weak/strong i-FGR were designed in this study. Combined with the e-FGR technology, pilot-scale(0.8 MW) experiments were conducted to reveal the i-/e-FGR effect on the NO_x emission of the natural gas combustion. Additionally, Fluent simulation was also conducted. Results showed that i-FGR significantly restrained the NO_x formation while guaranteed a stable combustion. The initial emission of the burner with i-/e-FGR was far below that of the traditional burner. Combined with e-FGR, NO_x emission was maintained below 30 mg/m~3. Fluent simulation indicated that e-FGR dramatically decreased the flame temperature and O_2 concentration. The decrease of temperature played a decisive role in the suppression of the NO_x formation. When the NO_x emission was around 30 mg/m~3, the prompt NO_x mechanism dominated the overall NO_x formation, which drove a need to depress the prompt NO_x formation to further decrease the overall NO_x formation.
Flue gas recirculation, an effective way to inhabit NO_x formation, is widely used in the natural gas low-NO_x combustion process in chemical engineering, pharmaceutical and brewing industries. Its working mechanism attracts attentions from both academia and industry. Considering the effects of the internal/external flue gas recirculation(i-/e-FGR), two types of diffusion-combustion burners with weak/strong i-FGR were designed in this study. Combined with the e-FGR technology, pilot-scale(0.8 MW) experiments were conducted to reveal the i-/e-FGR effect on the NO_x emission of the natural gas combustion. Additionally, Fluent simulation was also conducted. Results showed that i-FGR significantly restrained the NO_x formation while guaranteed a stable combustion. The initial emission of the burner with i-/e-FGR was far below that of the traditional burner. Combined with e-FGR, NO_x emission was maintained below 30 mg/m~3. Fluent simulation indicated that e-FGR dramatically decreased the flame temperature and O_2 concentration. The decrease of temperature played a decisive role in the suppression of the NO_x formation. When the NO_x emission was around 30 mg/m~3, the prompt NO_x mechanism dominated the overall NO_x formation, which drove a need to depress the prompt NO_x formation to further decrease the overall NO_x formation.
引文
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[7]刘慧,张林,杨晓晰,等.缝式低NOx燃烧器结构的优化模拟[J].化工学报,2018,69(4):1723-1730.LIU Hui,ZHANG Lin,YANG Xiaoxi,et al.Structure optimization simulation of slit burner with low NOx[J].CIESC Journal,2018,69(4):1723-1730.
[8]岑可法,姚强.高等燃烧学[M].杭州:浙江大学出版社,2002:603-610.CEN Kefa,YAO Qiang.Advanced combustion[M].Hangzhou:Zhejiang University Press,2002:603-610.
[9]吴晓磊,刘波,任政,等.新型低氮燃气分级燃烧器燃烧特性和NOx排放的CFD研究[J].化工进展,2014,33(9):2298-2303.WU Xiaolei,LIU Bo,REN Zheng,et al.CFD study on combustion properties and NOx emission of reboiling furnace for xylene tower[J].Chemical Industry and Engineering Progress,2014,33(9):2298-2303.
[10]BAI Wengang,LI Hao,DENG Lei,et al.Air-staged combustion characteristics of pulverized coal under high temperature and strong reducing atmosphere conditions[J].Energy&Fuels,2014,28(3):1820-1828.
[11]宋少鹏,卓建坤,李娜,等.燃料分级与烟气再循环对天然气低氮燃烧特性影响机理[J].中国电机工程学报,2016,36(24):6849-6858.SONG Shaopeng,ZHUO Jiankun,LI Na,et al.Low NOx combustion mechanism of a natural gas burner with fuel-staged and flue gas recirculation[J].Journal of Chinese Electrical Engineering Science,2016,36(24):6849-6858.
[12]刘皓,任瑞琪,黄永俊,等.富氧燃烧系统中NO的还原及其排放[J].化工学报,2011,62(2):495-501.LIU Hao,REN Ruiqi,HUANG Yongjun,et al.Reduction and emission of NO in oxy-fuel system[J].CIESC Journal,2011,62(2):495-501.
[13]LEE C Y,BAEK S W.Effects of hybrid reburning/SNCR strategy on NOx/CO reduction and thermal characteristics in oxygen-enriched LPG flame[J].Combustion Science and Technology,2007,179(8):1649-1666.
[14]AUDAI H A,JAMAL N,DAVID D.CFD modelling of air-fired and oxy-fuel combustion in a large-scale furnace at Loy Yang A brown coal power station[J].Fuel,2012,102:646-665.
[15]曾强,刘汉周,阎良.烟气再循环对天然气非预混燃烧NOx排放特性的影响[J].燃烧科学与技术,2018,24(4):369-375.ZENG Qiang,LIU Hanzhou,YAN Liang.Effect of flue gas recirculation on NOx emission characteristics of natural gas nonpremixed combustion[J].Journal of Combustion Science and Technology,2018,24(4):369-375.
[16]江子箫,陈晓平,蒋志坚,等.城市污泥流化床燃烧过程中气态污染物排放特性[J].化工进展,2018,37(1):368-374.JIANG Zixiao,CHEN Xiaoping,JIANG Zhijian,et al.Gaseous pollutants emissions from fluidized bed combustion of municipal sewage sludge[J].Chemical Industry and Engineering Progress,2018,37(1):368-374.
[17]张利琴,宋蔷,吴宁,等.煤烟气再循环富氧燃烧污染物排放特性研究[J].中国电机工程学报,2009,29(29):35-40.ZHANG Liqin,SONG Qiang,WU Ning,et al.Study on pollutant emission characteristics from oxy-fuel combustion of coal with recycled flue gas[J].Proceedings of the CSEE,2009,29(29):35-40
[18]HO E S,CHUNG S H.Numerical evaluation of NOx,mechanisms in methane-air counter flow premixed flames[J].Journal of Mechanical Science&Technology,2009,23(3):659-666.
[19]BALTASAR J,CARVALHO M G,COELHO P,et al.Flue gas recirculation in a gas-fired laboratory furnace:measurements and modelling[J].Fuel,1997,76(10):919-929.
[20]CHO E S,CHUNG S H.Characteristics of NOx emission with flue gas dilution in air and fuel sides[J].KSME International Journal,2004,18(12):2303-2309.
[21]徐旭常,吕俊复,张海.燃烧理论与燃烧设备[M].北京:机械工业出版社,1990.XU Xuchang,LüJunfu,ZHANG Hai.Combustion theory and combustion equipment[M].Beijing:China Machine Press,1990.
[22]MILLER J A,BOWMAN C T.Erratum:mechanism and modeling of nitrogen chemistry in combustion[J].Progress in Energy&Combustion Science,1990,16(4):287-338.
[23]王海峰,陈义良.湍流扩散火焰中氮氧化物排放的数值研究[J].化工学报,2005,56(2):209-214.WANG Haifeng,CHEN Yiliang.Numerical investigation of nitrogen oxides emission from turbulent non-premixed flames[J].Journal of Chemical Engineering and Industry(China),2005,56(2):209-214.
[24]谢正武,梁海杰.烟气再循环的作用及其对锅炉热力计算的影响[J].能源研究与信息,1999,15(3):42-48.XIE Zhengwu,LIANG Haijie.The function of the gas recirculation of boilers and its effect on thermal calculation[J].Energy Research and Information,1999,15(3):42-48.
[25]胡满银,乔欢,杜欣,等.烟气再循环对炉内氮氧化物生成影响的数值模拟[J].华北电力大学学报(自然科学版),2007,34(6):77-82.HU Manyin,QIAO Huan,DU Xin,et al.Numerical simulations of the influence of flue gas recycle on nitrogen oxide formation in boiler[J].Journal of North China Electric Power University,2007,34(6):77-82.
[26]FEESE J J,TURNS S R.Nitric oxide emissions from laminar diffusion flames:effects of air-side versus fuel-side diluent addition[J].Combustion&Flame,1998,113(1/2):66-78.
[27]LIPARDI A C A,BERGTHORSON J M,BOURQUE G.NOx emissions modeling and uncertainty from exhaust-gas-diluted flames[J].Journal of Engineering for Gas Turbines&Power,2015,138(5):051506.
[28]DRISCOLL J F,CHEN R H,YOON Y.Nitric oxide levels of turbulent jet diffusion flames:effects of residence time and Damk?hler number[J].Combustion&Flame,1992,88(1):37-49.
[29]李新宇.天然气非催化部分氧化转化炉内燃烧特性研究[D].上海:华东理工大学,2017.LI Xinyu.Study of the combustion characteristics in natural gas noncatalytic partial oxidation reformer[D].Shanghai:East China University of Science and Technology,2017.
[2]北京市环境保护局.锅炉大气污染物排放标准:DB11/139-2015[S].北京:北京市环境保护局,2015.Beijing Environmental Protection Bureau.Emission standard of air pollutants for boilers:DB11/139-2015[S].Beijing:Beijing Environmental Protection Bureau,2015.
[3]宋少鹏,卓建坤,李娜,等.天然气供热锅炉低氮燃烧技术研究现状[J].供热制冷,2016(2):18-21.SONG Shaopeng,ZHUO Jiankun,LI Na,et al.Research status of low nitrogen combustion technology for natural gas heating boiler[J].Heating and Cooling,2016(2):18-21
[4]胡元,罗永浩,周力行,等.外二次旋流风对旋流煤粉燃烧及NO生成的影响[J].化工学报,2010,61(9):2437-2441.HU Yuan,LUO Yonghao,ZHOU Lixing,et al.Effect of outer secondary air on swirling pulverized-coal combustion and NOformation[J].CIESC Journal,2010,61(9):2437-2441.
[5]SURJOSATYO A,PRIAMBODHO Y D,KWOK C K.Investigation of gas swirl burner characteristic on biomass gasification system using combustion unit equipment(CUE)[J].Journal Mekanikal,2011,33(12):15-31.
[6]HOU S S,LEE C Y,LIN T H.Efficiency and emissions of a new domestic gas burner with a swirling flame[J].Energy Conversion and Management,2007,48(5):1401-1410.
[7]刘慧,张林,杨晓晰,等.缝式低NOx燃烧器结构的优化模拟[J].化工学报,2018,69(4):1723-1730.LIU Hui,ZHANG Lin,YANG Xiaoxi,et al.Structure optimization simulation of slit burner with low NOx[J].CIESC Journal,2018,69(4):1723-1730.
[8]岑可法,姚强.高等燃烧学[M].杭州:浙江大学出版社,2002:603-610.CEN Kefa,YAO Qiang.Advanced combustion[M].Hangzhou:Zhejiang University Press,2002:603-610.
[9]吴晓磊,刘波,任政,等.新型低氮燃气分级燃烧器燃烧特性和NOx排放的CFD研究[J].化工进展,2014,33(9):2298-2303.WU Xiaolei,LIU Bo,REN Zheng,et al.CFD study on combustion properties and NOx emission of reboiling furnace for xylene tower[J].Chemical Industry and Engineering Progress,2014,33(9):2298-2303.
[10]BAI Wengang,LI Hao,DENG Lei,et al.Air-staged combustion characteristics of pulverized coal under high temperature and strong reducing atmosphere conditions[J].Energy&Fuels,2014,28(3):1820-1828.
[11]宋少鹏,卓建坤,李娜,等.燃料分级与烟气再循环对天然气低氮燃烧特性影响机理[J].中国电机工程学报,2016,36(24):6849-6858.SONG Shaopeng,ZHUO Jiankun,LI Na,et al.Low NOx combustion mechanism of a natural gas burner with fuel-staged and flue gas recirculation[J].Journal of Chinese Electrical Engineering Science,2016,36(24):6849-6858.
[12]刘皓,任瑞琪,黄永俊,等.富氧燃烧系统中NO的还原及其排放[J].化工学报,2011,62(2):495-501.LIU Hao,REN Ruiqi,HUANG Yongjun,et al.Reduction and emission of NO in oxy-fuel system[J].CIESC Journal,2011,62(2):495-501.
[13]LEE C Y,BAEK S W.Effects of hybrid reburning/SNCR strategy on NOx/CO reduction and thermal characteristics in oxygen-enriched LPG flame[J].Combustion Science and Technology,2007,179(8):1649-1666.
[14]AUDAI H A,JAMAL N,DAVID D.CFD modelling of air-fired and oxy-fuel combustion in a large-scale furnace at Loy Yang A brown coal power station[J].Fuel,2012,102:646-665.
[15]曾强,刘汉周,阎良.烟气再循环对天然气非预混燃烧NOx排放特性的影响[J].燃烧科学与技术,2018,24(4):369-375.ZENG Qiang,LIU Hanzhou,YAN Liang.Effect of flue gas recirculation on NOx emission characteristics of natural gas nonpremixed combustion[J].Journal of Combustion Science and Technology,2018,24(4):369-375.
[16]江子箫,陈晓平,蒋志坚,等.城市污泥流化床燃烧过程中气态污染物排放特性[J].化工进展,2018,37(1):368-374.JIANG Zixiao,CHEN Xiaoping,JIANG Zhijian,et al.Gaseous pollutants emissions from fluidized bed combustion of municipal sewage sludge[J].Chemical Industry and Engineering Progress,2018,37(1):368-374.
[17]张利琴,宋蔷,吴宁,等.煤烟气再循环富氧燃烧污染物排放特性研究[J].中国电机工程学报,2009,29(29):35-40.ZHANG Liqin,SONG Qiang,WU Ning,et al.Study on pollutant emission characteristics from oxy-fuel combustion of coal with recycled flue gas[J].Proceedings of the CSEE,2009,29(29):35-40
[18]HO E S,CHUNG S H.Numerical evaluation of NOx,mechanisms in methane-air counter flow premixed flames[J].Journal of Mechanical Science&Technology,2009,23(3):659-666.
[19]BALTASAR J,CARVALHO M G,COELHO P,et al.Flue gas recirculation in a gas-fired laboratory furnace:measurements and modelling[J].Fuel,1997,76(10):919-929.
[20]CHO E S,CHUNG S H.Characteristics of NOx emission with flue gas dilution in air and fuel sides[J].KSME International Journal,2004,18(12):2303-2309.
[21]徐旭常,吕俊复,张海.燃烧理论与燃烧设备[M].北京:机械工业出版社,1990.XU Xuchang,LüJunfu,ZHANG Hai.Combustion theory and combustion equipment[M].Beijing:China Machine Press,1990.
[22]MILLER J A,BOWMAN C T.Erratum:mechanism and modeling of nitrogen chemistry in combustion[J].Progress in Energy&Combustion Science,1990,16(4):287-338.
[23]王海峰,陈义良.湍流扩散火焰中氮氧化物排放的数值研究[J].化工学报,2005,56(2):209-214.WANG Haifeng,CHEN Yiliang.Numerical investigation of nitrogen oxides emission from turbulent non-premixed flames[J].Journal of Chemical Engineering and Industry(China),2005,56(2):209-214.
[24]谢正武,梁海杰.烟气再循环的作用及其对锅炉热力计算的影响[J].能源研究与信息,1999,15(3):42-48.XIE Zhengwu,LIANG Haijie.The function of the gas recirculation of boilers and its effect on thermal calculation[J].Energy Research and Information,1999,15(3):42-48.
[25]胡满银,乔欢,杜欣,等.烟气再循环对炉内氮氧化物生成影响的数值模拟[J].华北电力大学学报(自然科学版),2007,34(6):77-82.HU Manyin,QIAO Huan,DU Xin,et al.Numerical simulations of the influence of flue gas recycle on nitrogen oxide formation in boiler[J].Journal of North China Electric Power University,2007,34(6):77-82.
[26]FEESE J J,TURNS S R.Nitric oxide emissions from laminar diffusion flames:effects of air-side versus fuel-side diluent addition[J].Combustion&Flame,1998,113(1/2):66-78.
[27]LIPARDI A C A,BERGTHORSON J M,BOURQUE G.NOx emissions modeling and uncertainty from exhaust-gas-diluted flames[J].Journal of Engineering for Gas Turbines&Power,2015,138(5):051506.
[28]DRISCOLL J F,CHEN R H,YOON Y.Nitric oxide levels of turbulent jet diffusion flames:effects of residence time and Damk?hler number[J].Combustion&Flame,1992,88(1):37-49.
[29]李新宇.天然气非催化部分氧化转化炉内燃烧特性研究[D].上海:华东理工大学,2017.LI Xinyu.Study of the combustion characteristics in natural gas noncatalytic partial oxidation reformer[D].Shanghai:East China University of Science and Technology,2017.
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