CFD数值模拟在FCC烟气脱硝中的应用

Application of CFD numerical simulation in FCC flue gas denitrification for refinery

以某炼油厂FCC余热锅炉的脱硝反应器及喷氨格栅、导流板、整流格栅等内构件为研究对象,采用计算流体动力学(CFD)软件对选择性催化还原(SCR)脱硝反应系统的流场进行数值模拟,确定SCR脱硝反应系统的内构件尺寸,确保反应物氨能均匀地分散在烟气中,且烟气能均匀、垂直地通过催化剂床层,保证SCR脱硝反应系统的脱硝效果与氨逃逸值达标。CFD数值模拟结果表明,内构件经优化后,可保证反应器内催化剂床层的烟气流速偏差为9%,烟气流向偏差不大于5°,氨气浓度分布偏差小于5%,而系统压力降仅增加180 Pa,压力分布比较均匀。装置投产后,其脱硝效率大于75%,氨逃逸质量浓度小于0.4 mg/m3,满足使用要求,说明根据CFD数值模拟结果设计的SCR反应器内构件满足流场要求。

In a case study of the denitrification reactor and internal components including ammonia injection grids,guide plates,rectification grids for FCC heat recovery boiler of a refinery,the computational fluid dynamics（CFD）method was applied to simulate the flow field of the selected catalytic reduction（SCR）denitrification system.Sizes of the internal components were designed based on the numerical simulation to ensure that the reactant ammonia could disperse in the flue gas evenly and the flue gas could get through the catalyst bed uniformly and vertically so as to meet the specified denitrification rate of SCR system and ammonia escaping value.According to the CFD numerical simulation,after the optimization of the internal components,the deviations of flue gas flow rate,the flue gas flow direction and the concentration deviation of NH3 in the reactor catalyst bed were no more than 9%,5% and 5%,respectively.Whereas,the total pressure drop in the system rose by only 180 Pa and the pressure distribution is quite uniform.The performance tests after the plant was put into operation showed that the denitrification efficiency was more than 75%,while the ammonia escaping value was less than 0.4 mg / m3,meeting the operating requirements.The operating data prove that the SCR reactor and internals designed based on the CFD numerical simulation has satisfied the requirements of flow field.