铁基载氧体的污泥化学链气化过程中氮迁移热力学模拟与实验研究
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摘要
基于吉布斯自由能最小化原理,采用HSC Chemistry 6.0软件,对污泥化学链气化过程中NO_x前驱物(NH3和HCN)与Fe_2O_3载氧体的氧化还原行为迚行了热力学模拟。基于污泥热解实验中NO_x前驱物的含量,计算载氧体与污泥的摩尔比(OC/SS)对NH3、HCN以及NH3和HCN混合气氧化过程的影响。热力学模拟结果表明:Fe_2O_3能显著促迚NO_x前驱物的氧化和裂解,主要生成N2,几乎无NO_x生成;当NH3、HCN以及混合气(NH3和HCN)分别作为还原剂时,其最优OC/SS分别为0.02、0.04和0.05;由于HCN还原性强于NH3,其氧化速率较快。基于Fe_2O_3/Al2O3混合物(FeAl)载氧体,实验对比了污泥化学链气化与污泥热解过程中NO_x前驱物的释放特性,发现Fe_2O_3能显著降低烟气中NO_x前驱物的产率,NH3和HCN产率分别下降32%和62%。实验结果与热力学模拟结果一致。
Based on the Gibbs free energy minimization principle, thermodynamic analysis and process simulation of the redox reactions between the NO_x precursors(NH_3 and HCN) and Fe_2O_3(oxygen carrier) during the sludge chemical looping gasification were performed using the software of HSC Chemistry 6.0. According to the content of NO_x precursors during the sludge pyrolysis, the effect of the molar ratio of oxygen carrier to the sludge(OC/SS) on the oxidation of NH_3,HCN, and the mixed gas of NH_3 and HCN were investigated. The simulation results showed that the oxidation of NO_x precursors was effectively promoted by Fe_2O_3, the N element was mainly converted to N2 and almost no NO_x was formed.The OC/SS ratio of 0.02, 0.04, and 0.05 were determined to achieve the complete conversion of NO_x precursors as well as minimize the amount of oxygen carrier when the NH_3, HCN, and the mixed gas of NH_3 and HCN were used as the reductants, respectively. Additionally, the oxidation rate of HCN was higher than that of NH_3 due to the stronger reducibility of HCN. Furthermore, the yields of NO_x precursors during the sludge pyrolysis and the sludge chemical looping gasification were compared in a fixed bed. It was found that the yields of NO_x precursors in the flue gas were significantly reduced by Fe_2O_3, and the yields of HCN and NH_3 decreased by 62% and 32%, respectively. The thermodynamic analysis was validated by the experiment results, and the chemical looping gasification of sludge was beneficial to inhibit the generation of the NO_x.
Based on the Gibbs free energy minimization principle, thermodynamic analysis and process simulation of the redox reactions between the NO_x precursors(NH_3 and HCN) and Fe_2O_3(oxygen carrier) during the sludge chemical looping gasification were performed using the software of HSC Chemistry 6.0. According to the content of NO_x precursors during the sludge pyrolysis, the effect of the molar ratio of oxygen carrier to the sludge(OC/SS) on the oxidation of NH_3,HCN, and the mixed gas of NH_3 and HCN were investigated. The simulation results showed that the oxidation of NO_x precursors was effectively promoted by Fe_2O_3, the N element was mainly converted to N2 and almost no NO_x was formed.The OC/SS ratio of 0.02, 0.04, and 0.05 were determined to achieve the complete conversion of NO_x precursors as well as minimize the amount of oxygen carrier when the NH_3, HCN, and the mixed gas of NH_3 and HCN were used as the reductants, respectively. Additionally, the oxidation rate of HCN was higher than that of NH_3 due to the stronger reducibility of HCN. Furthermore, the yields of NO_x precursors during the sludge pyrolysis and the sludge chemical looping gasification were compared in a fixed bed. It was found that the yields of NO_x precursors in the flue gas were significantly reduced by Fe_2O_3, and the yields of HCN and NH_3 decreased by 62% and 32%, respectively. The thermodynamic analysis was validated by the experiment results, and the chemical looping gasification of sludge was beneficial to inhibit the generation of the NO_x.
引文
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[2]WERLE S,WILK R K.A review of methods for the thermal utilization of sewage sludge:the Polish perspective[J].Renewable energy,2010,35(9):1914-1919.DOI:10.1016/j.renene.2010.01.019.
[3]ADANEZ J,ABAD A,GARCIA-LABIANO F,et al.Progress in chemical-looping combustion and reforming technologies[J].Progress in energy and combustion science,2012,38(2):215-282.DOI:10.1016/j.pecs.2011.09.001.
[4]LI F X,KIM H R,SRIDHAR D,et al.Syngas chemical looping gasification process:oxygen carrier particle selection and performance[J].Energy&fuels,2009,23(8):4182-4189.DOI:10.1021/ef900236x.
[5]CAO J J,SHEN Z X,CHOW J C,et al.Winter and summer PM2.5 chemical compositions in fourteen chinese cities[J].Journal of the air&waste management association,2012,62(10):1214-1214.DOI:10.1080/10962247.2012.701193.
[6]SONG T,SHEN L H,XIAO J,et al.Nitrogen transfer of fuel-N in chemical looping combustion[J].Combustion and flame,2012,159(3):1286-1295.DOI:10.1016/j.combustflame.2011.10.024.
[7]SONG T,SHEN T X,SHEN L H,et al.Evaluation of hematite oxygen carrier in chemical-looping combustion of coal[J].Fuel,2013,104:244-252.DOI:10.1016/j.fuel.2012.09.030.
[8]GU H M,SHEN L H,ZHONG Z P,et al.NO release during chemical looping combustion with iron ore as an oxygen carrier[J].Chemical engineering journal,2015,264:211-220.DOI:10.1016/j.cej.2014.11.083.
[9]MENDIARA T,IZQUIERDO M T,ABAD A,et al.Release of pollutant components in CLC of lignite[J].International journal of greenhouse gas control,2014,22:15-24.DOI:10.1016/j.ijggc.2013.12.013.
[10]牛欣,肖军.污泥化学链燃烧过程中氮迁移转化特性研究[J].燃料化学学报,2017,45(4):505-512.DOI:10.3969/j.issn.0253-2409.2017.04.016.
[11]TAN L L,LI C Z.Formation of NOx and SOx precursors during the pyrolysis of coal and biomass.Part I.Effects of reactor configuration on the determined yields of HCNand NH3 during pyrolysis[J].Fuel,2000,79(15):1883-1889.DOI:10.1016/S0016-2361(00)00078-8.
[12]VARISLI D,KORKUSUZ C,DOGU T.Microwaveassisted ammonia decomposition reaction over iron incorporated mesoporous carbon catalysts[J].Applied catalysis B:environmental,2017,201:370-380.DOI:10.1016/j.apcatb.2016.08.032.
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