CO_2含量对污泥燃烧Fuel-N析出特性的影响
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摘要
在模拟水泥分解炉气氛条件下,考察了CO_2浓度对污泥燃料N(Fuel-N)析出特性的影响,结果表明污泥Fuel-N的析出形式主要为NH_3、HCN及NO_x.在研究的CO_2浓度范围(体积分数0～35%)内,CO_2浓度的升高将消耗更多的含氮位点和H自由基,导致NH_3的析出受到抑制;而CO_2能直接氧化HCN或—CN官能团,导致HCN的析出随着CO_2浓度的升高逐渐降低.NO_x的析出量随CO_2含量的升高先减小后升高,在25%时达到最小值.NO_x的生成和还原反应是同步发生的,在燃烧温度和O_2含量一定的情况下,NO_x的析出主要受NO_x还原反应的影响,研究表明燃烧过程中同时存在NO_x的气相均相还原反应和气固异相还原反应.当CO_2浓度从0上升至25%时,CO_2分子与污泥焦反应生成的CO相对增加,在污泥焦表面的催化作用下,NO_x被CO还原的量增多,此时污泥焦对NO_x的气固异相还原占据主导地位;继续增加CO_2浓度至35%时,还原性气体HCN生成幅度下降较大,此时HCN、NH_3对NO_x的气气均相还原占据主导地位,导致NO_x的析出逐渐升高.
The effect of CO_2 content on the fuel-N release characteristics from sewage sludge combustion was investigated in simulated flue gas of cement precalciner. The experimental results showed that the emission forms of Fuel-N were mainly NH_3、HCN and NO_x. The increasing of CO_2 content consumed more nitrogen containing sites or H free radicals, resulting in the inhibition of NH_3 release. As CO_2 directly oxidized HCN or —CN functional groups, the amount of HCN release gradually decreased with the increasing of CO_2 content. The amount of NO_x decreased first and then increased as the CO_2 contents increased, with a minimum value at 25%. NO_x generation and reduction reactions occured synchronously, while the emission of NO_x was mainly affected by NO_x reduction under the condition of certain combustion temperature and O_2 content, the results showed that the homogeneous and heterogeneous reduction reaction of NO_x were both concurrence during combustion. With the increasing of CO_2 content from 0 to 25%, the CO generated by the reaction between CO_2 molecules and sludge char increased relatively, the amount of NO_x reduction by CO increased under the catalytic of sludge char surface, thus the sludge char played a leading role in the gas-solid heterogeneous reduction of NO_x. The generation of reducing gas HCN decreased significantly as continue increasing CO_2 concentration to 35%, and the gas-gas homogeneous reduction of NO_x by HCN and NH_3 was dominated, leading to the gradual increasement of NO_x emission.
The effect of CO_2 content on the fuel-N release characteristics from sewage sludge combustion was investigated in simulated flue gas of cement precalciner. The experimental results showed that the emission forms of Fuel-N were mainly NH_3、HCN and NO_x. The increasing of CO_2 content consumed more nitrogen containing sites or H free radicals, resulting in the inhibition of NH_3 release. As CO_2 directly oxidized HCN or —CN functional groups, the amount of HCN release gradually decreased with the increasing of CO_2 content. The amount of NO_x decreased first and then increased as the CO_2 contents increased, with a minimum value at 25%. NO_x generation and reduction reactions occured synchronously, while the emission of NO_x was mainly affected by NO_x reduction under the condition of certain combustion temperature and O_2 content, the results showed that the homogeneous and heterogeneous reduction reaction of NO_x were both concurrence during combustion. With the increasing of CO_2 content from 0 to 25%, the CO generated by the reaction between CO_2 molecules and sludge char increased relatively, the amount of NO_x reduction by CO increased under the catalytic of sludge char surface, thus the sludge char played a leading role in the gas-solid heterogeneous reduction of NO_x. The generation of reducing gas HCN decreased significantly as continue increasing CO_2 concentration to 35%, and the gas-gas homogeneous reduction of NO_x by HCN and NH_3 was dominated, leading to the gradual increasement of NO_x emission.
引文
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熊思江,章北平,玉东科,等.2011.干燥污泥与含水污泥的热解动力学研究[J].华中科技大学学报,39(2):124-128
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信晶.2015.煤焦-NO反应过程中氮转化机理与试验研究[C].北京:华北电力大学
Zhang Y C,Zhang J,Sheng C D,et al.2011.X-ray photoelectron spectroscopy(XPS)investigation of nitrogen functionalities during coal char combustion in O2/CO2and O2/Ar atmospheres[J].Energy fuels,25(1):240-245
张辉,胡勤海,吴祖成,等.2013.城市污泥能源化利用研究进展[J].化工进展,32(5):1145-1151
蔡吕清,陆继东,吕刚.2010.分解炉内CO2含量对燃煤NO释放特性的影响[J].硅酸盐学报,38(7):1209-1214
Duan L B,Zhao C S,Ren Q Q,et al.2011.NOxprecursors evolution during coal heating process in CO2atmosphere[J].Fuel,90(4):1668-1673
邓飞飞,毛志伟,程群,等.2016.水泥窑协同处置污泥降低NOx排放工程实例分析[J].中国水泥,(7):80-83
Fang P,Tang Z J,Huang J H,et al.2015.Using sewage sludge as a denitration agent and secondary fuel in a cement plant:A case study[J].Fuel Processing Technology,137:1-7
Gimenez-Lopez J,Millera A,Bilbao R,et al.2010.HCN oxidation in an O2/CO2atmosphere:An experimental and kinetic modeling study[J].Combustion and Flame,157(2):267-276
Jin R,Zhan J Y,Liu G R,et al.2017.Profiles of polychlorinated biphenyls(PCBs)in cement kilns co-processing solid waste[J].Chemosphere,174:165-172
Kim J,Yi C K,Zi G.2015.Waste glass sludge as a partial cement replacement in mortar[J].Construction and Building Materials,75(30):242-246
Li C Z,Tan L L.2000.Formation of NOxand SOxprecursors during the pyrolysis of coal and biomass.Part III.Further discussion on the formation of HCN and NH3during pyrolysis[J].Fuel,79(15):1899-1906
Liu F S,Guo H S,Smallwood G J.2003.The chemical effect of CO2replacement of N2in air on the burning velocity of CH4and H2premixed flames[J].Combustion and Flame,133(4):495-497
Liu H,Okazaki K.2003.Simultaneous easy CO2recovery and drastic reduction of SOxand NOxin O2/CO2coal combustion with heat recirculation[J].Fuel,82(11):1427-1436
Liu H,Zailani R,Gibbs B M.2005.Pulverized coal combustion in air and in O2/CO2mixtures with NOxrecycle[J].Fuel,84(16):2109-2115
李庆钊,赵长遂,武卫芳,等.2009.O2/CO2气氛下燃煤NO排放特性的实验研究[J].中国电机工程学报,29(33):33-39
刘定平,黄群亮.2015.水泥分解炉掺烧干污泥对NOx排放的影响[J].环境工程学报,9(4):1911-1915
Liu H,Zhang Q,Hu H Y,et al.2015.Catalytic role of conditioner CaOin nitrogen transformation during sewage sludge pyrolysis[J].Proceedings of the Combustion Institute,35(3):2759-2766
刘敬勇,傅杰文,孙水裕,等.2016.不同来源污泥混燃特性及其综合燃烧性能评价[J].环境科学学报,36(3):940-952
Tian F J,Li B Q,Chen Y,et al.2002.Formation of NOxprecursors during the pyrolysis of coal and biomass.Part V.Pyrolysis of a sewage sludge[J].Fuel,81(17):2203-2208
Tian Y,Zhang J,Zuo W,et al.2013.Nitrogen conversion in relation to NH3and HCN during microwave pyrolysis of sewage sludge[J].Environmental Science&Technology,47(7):3498-3505
熊思江,章北平,玉东科,等.2011.干燥污泥与含水污泥的热解动力学研究[J].华中科技大学学报,39(2):124-128
Xu W,Xu J C,Liu J,et al.2014.The utilization of lime-dried sludge as resource for producing cement[J].Journal of Cleaner Production,83(15):286-293
信晶.2015.煤焦-NO反应过程中氮转化机理与试验研究[C].北京:华北电力大学
Zhang Y C,Zhang J,Sheng C D,et al.2011.X-ray photoelectron spectroscopy(XPS)investigation of nitrogen functionalities during coal char combustion in O2/CO2and O2/Ar atmospheres[J].Energy fuels,25(1):240-245
张辉,胡勤海,吴祖成,等.2013.城市污泥能源化利用研究进展[J].化工进展,32(5):1145-1151
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