燃煤机组SCR烟气脱硝系统流场均布一体化建模与性能优化

Integrated modeling and performance optimization of flow field homogenization in SCR denitrification system of coal-fired unit

选择性催化还原(SCR)烟气脱硝效率与其内部烟气和还原剂流动的均匀性密切相关。在建立SCR脱硝反应数学模型基础上,采用用户自定义子程序耦合了多组分烟气流动与反应过程;通过比较不同负荷下330 MW等级燃煤机组脱硝性能的实测与模拟数据验证了模型的可靠性和有效性,基于对反应器内烟气和还原剂流动及其反应特性的数值模拟分析,提出了喷氨格栅上游导流板结构优化方案,进而考察了操作条件对NO和NH3排放质量浓度的影响。结果表明:喷氨格栅来流烟气速度分布的非均匀性是导致烟气与还原剂混合效果较差的主要原因,进而通过调整喷氨格栅上游导流板结构并在烟道壁面增设挡板可将脱硝效率提高约3.37%;为满足NO_(x)质量浓度为50 mg/m^(3)及NH3质量浓度为2.5 mg/m^(3)的排放限值需选取适宜喷氨量,以所选取SCR脱硝装置为例,当烟气初始NO质量浓度为650 mg/m^(3),SCR脱硝系统适宜氨氮摩尔比应约为0.94。

The denitration efficiency is closely related to the uniformity of flue gas and reductant agent within SCR for the coal-fired unit.Based on the established mathematical model for SCR denitration reaction,a user-defined subroutine is coupled the multi-component flue gas flow with reaction process.The reliability and effectiveness of the CFD model are verified by comparing the measured and simulated data of the SCR performance of 330MW coal-fired units under different loads.According to the hydrodynamics of flue gas and reductant agent together with the chemical reaction process in SCR reactor,a new intensification scheme is proposed by optimizing the structure of deflectors before the ammonia injection grids.Furthermore,the performance of SCR system is evaluated depending on the operational conditions.The numerical results indicates that the maldistribution of incoming flue gas to ammonia injection grids leads to the poor mixing behavior of flue gas and reducing reagent.However,the denitration efficiency of SCR reactor could be improved about 3.37%by the optimized deflectors and baffles configurated around the wall.Taking the SCR denitration unit in this work as an example,the appropriate molar ratio of NH3 to NO is 0.94 for the initial NO concentration of 650 mg/m^(3),which could meet with the emission limit for air pollutions of 50 mg/m^(3) for NO_(x) and 2.5 mg/m^(3) for NH3,respectively.