尿素制氨机理及影响因素分析
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摘要
电厂采用的制氨方法有尿素热解法和水解法,针对某电厂300 MW机组利用Aspen Plus软件对比分析了2种方案的优劣,从水解制氨系统的尿素进料质量分数、反应温度及压力3个方面,分析了不同反应条件对水解产物的影响。结果表明:水解方案反应温度低,可采用低品质蒸汽作为热源且能耗量仅为热解的20%～30%,从节能角度出发,水解制氨为最佳方案;随尿素进料质量分数的增加,产氨量增加,耗热量降低,但液相中尿素质量分数也随之升高,易发生设备腐蚀;随着温度的上升,尿素水解速率提高,但耗热量上升明显,经济性较差;增加压力能降低设备发生腐蚀的风险,但会对气体的析出产生抑制;综合考虑,尿素水解反应条件为尿素进料质量分数50%,温度150～160℃,压力0.6～0.8 MPa比较合适。
The ammonia production methods used in power plants include urea pyrolysis and hydrolysis.Numerical simulation was conducted by Aspen Plus for the two processes in a 300 MW coal-fired power plant.From the aspects of urea feed mass fraction, reaction temperature and pressure, the effects of reaction condition on hydrolysis products were investigated. The results show that, compared with pyrolysis, the hydrolysis scheme has a lower reaction temperature, its energy consumption is only about 20%～30% of that of pyrolysis. What's more,low-quality steam can be used as the heat source of the hydrolysis scheme. From the point of energy saving,hydrolysis to ammonia is the best method. The simulation result shows a same tendency with the experimental data, verifying the reliability of the hydrolysis model. When the urea feed mass fraction was increased, the ammonia concentration in the product gas increased, the heat consumption decreased, while the urea in the liquid also increased, which leads to a rise in the risk of corrosion. As the temperature increased, the urea hydrolysis rate increased, but the heat consumption rose rapidly, and the economy was poor. Increasing the pressure can reduce the risk of corrosion. However, excessive operating pressure will inhibit the release of gaseous products.Considering comprehensively, the condition with urea feed mass fraction of 50%, temperature of 150 °C～160°C and pressure of 0.6～0.8 MPa is suitable for the urea hydrolysis.
The ammonia production methods used in power plants include urea pyrolysis and hydrolysis.Numerical simulation was conducted by Aspen Plus for the two processes in a 300 MW coal-fired power plant.From the aspects of urea feed mass fraction, reaction temperature and pressure, the effects of reaction condition on hydrolysis products were investigated. The results show that, compared with pyrolysis, the hydrolysis scheme has a lower reaction temperature, its energy consumption is only about 20%～30% of that of pyrolysis. What's more,low-quality steam can be used as the heat source of the hydrolysis scheme. From the point of energy saving,hydrolysis to ammonia is the best method. The simulation result shows a same tendency with the experimental data, verifying the reliability of the hydrolysis model. When the urea feed mass fraction was increased, the ammonia concentration in the product gas increased, the heat consumption decreased, while the urea in the liquid also increased, which leads to a rise in the risk of corrosion. As the temperature increased, the urea hydrolysis rate increased, but the heat consumption rose rapidly, and the economy was poor. Increasing the pressure can reduce the risk of corrosion. However, excessive operating pressure will inhibit the release of gaseous products.Considering comprehensively, the condition with urea feed mass fraction of 50%, temperature of 150 °C～160°C and pressure of 0.6～0.8 MPa is suitable for the urea hydrolysis.
引文
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[13]KAUSHAL N,AMSINI S,JOHANNES J.Numerical investigation of adBlue droplet evaporation and thermal decomposition in the context of NOx-SCR using a multi-component evaporation model[J].Energies,2018,11(1):222-244.
[14]BERNHARD A M,PEITZ D,ELSENER M,et al.Hydrolysis and thermolysis of urea and its decomposition byproducts biuret,cyanuric acid and melamine over anatase TiO2[J].Applied Catalysis B:Environmental,2012,115/116(15):129-137.
[2]夏怀祥,段传和.选择性催化还原法(SCR)烟气脱硝[M].北京:中国电力出版社,2012:12-23.XIA Huaixiang,DUAN Chuanhe.Selective catalytic reduction flue gas denitration[M].Beijing:China Electric Power Press,2012:12-23.
[3]戚春萍,武文粉,王晨晔,等.燃煤电厂废旧SCR脱硝催化剂中TiO2载体的回收与再利用[J].化工学报,2017,68(11):4239-4248.QI Chunping,WU Wenfen,WANG Chenye,et al.Recycling and reuse of TiO2 carrier from waste SCRcatalysts used in coal-fired power plants[J].CIESCJournal,2017,68(11):4239-4248.
[4]陈镇超,杨卫娟,周俊虎,等.尿素催化水解特性实验研究[J].中国电机工程学报,2011,31(35):41-46.CHEN Zhenchao,YANG Weijuan,ZHOU Junhu,et al.Experimental Investigation on the properties of urea thermohydrolysis with catalysts[J].Proceedings of the CSEE,2011,31(35):41-46.
[5]惠润堂,韦飞,闫世平,等.国产首套尿素水解装置在大型火电厂的工业应用及技术优化[J].中国电力,2014,47(7):150-155.HUI Runtang,WEI Fei,YAN Shiping,et al.The industrial application and technical optimization of first domes-tically-made urea hydrolysis unit in large power plants[J].Electric Power,2014,47(7):150-155.
[6]SAHU J N,PATWARDHAN A V,MEIKAP B C,et al.Equilibrium and kinetic studies of in situ generation of ammonia from urea in a batch reactor for flue gas conditioning of thermal power plants[J].Industrial&Engineering Chemistry,2009,48(5):2705-2712.
[7]SAHU J N,GANGADHARAN P,PATWARDHAN A V,et a1.Catalytic hydrolysis of urea with fly ash for gene-ration of ammonia in a batch reactor for flue gas condi-tioning and NOx reduction[J].Industrial&Engineering Chemistry Research,2009,48(3):727-734.
[8]SAHU J N,RAMA V S,HUSSAIN S,et a1.Optimization of ammonia production from urea in continuous process using ASPEN Plus and computational fluid dynamics study of the reactor used for hydrolysis process[J].Industrial&Engineering Chemistry,2010,16(4):577-586.
[9]姚宣,沈滨,郑鹏,等.烟气脱硝用尿素水解装置性能分析[J].中国电机工程学报,2013,33(14):38-43.YAO Xuan,SHEN Bin,ZHENG Peng,et al.Characteristics of urea hydrolysis equipment for flue gas denitration[J].Proceedings of the CSEE,2013,33(14):38-43.
[10]张向宇,高宁,张波,等.高浓度尿素水解制氨试验研究[J].热力发电,2016,45(6):57-62.ZHANG Xiangyu,GAO Ning,ZHANG Bo,et al.Experimental study on ammonia preparation by high concentration urea hydrolysis[J].Thermal Power Generation,2016,45(6):57-62.
[11]杨双桥,马丽君,谢裕忠,等.尿素水解和热解SCR脱硝系统的模拟[J].舰船防化,2016(2):56-59.YANG Shuangqiao,MA Lijun,XIE Yuzhong,et al.Simulation of SCR denitration system with ammonia prepared by technology of urea pyrolysis and hydrolysis[J].Chemical Defence on Ships,2016(2):56-59.
[12]江辉,吴凤玲,刘民,等.SCR脱硝工艺计算实例分析[J].环境与发展,2014,26(7):65-67.JIANG Hui,WU Fengling,LIU Min,et al.Instance analysis on calculation of SCR denitration process[J].Environment and Development,2014,26(7):65-67.
[13]KAUSHAL N,AMSINI S,JOHANNES J.Numerical investigation of adBlue droplet evaporation and thermal decomposition in the context of NOx-SCR using a multi-component evaporation model[J].Energies,2018,11(1):222-244.
[14]BERNHARD A M,PEITZ D,ELSENER M,et al.Hydrolysis and thermolysis of urea and its decomposition byproducts biuret,cyanuric acid and melamine over anatase TiO2[J].Applied Catalysis B:Environmental,2012,115/116(15):129-137.
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