W火焰锅炉脱硝系统流场CFD优化

CFD optimization of flow field in denitrification system of W flame boiler

由于W火焰锅炉炉膛设计热负荷与火焰中心温度较高,热力型NO_(x)生成增加,炉膛出口NO_(x)质量浓度远高于其他煤粉锅炉,对锅炉后部的选择性催化还原(SCR)脱硝装置要求很高。为探究流场和组分浓度分布对SCR装置脱硝效率和氨逃逸的影响,提升装置脱硝性能,采用计算流体力学(CFD)仿真手段建立某电厂660 MW机组W火焰锅炉脱硝系统的三维计算流体力学模型,并进行数值模拟;为使计算结果更贴近实际工况,按照锅炉满负荷下摸底试验数据设定入口NO_(x)浓度边界条件。通过详细分析SCR系统烟气速度分布、组分浓度分布、氨逃逸等流动特性,针对流场优化、分区喷氨和新型静态混合器对脱硝性能的影响进行模拟与优化,从而提高SCR系统流场及浓度场均匀性。优化前后模拟结果表明,通过增加顶部导流板数量,可提升催化剂入口速度分布均匀性,消除催化剂入口速度较高的条状区域,优化后催化剂入口烟气速度分布相对标准偏差由20.86%降至3.80%;通过增加三角翼型静态混合器可消除入口NO_(x)浓度分布不均的影响,提升浓度场均匀性,分区最大氨氮物质的量比相对标准偏差由10.72%降至1.78%;改造方案明显优于原始设计,对工程设计具有重要的借鉴意义。

Because of higher thermal load and flame center temperature of the flame center,the generation of thermal NO_(x)is increased.The down-fired boiler has higher NO_(x)mass concentration than other coal boilers,and the selective catalytic reduction(SCR)denitrification device at the rear of the boiler has high requirements.To investigate the influences of flow field and species concentration profile on deNO_(x)efficiency and ammonia slip in an industrial SCR reactor,a 3 D computational fluid dynamics(CFD)model of SCR device was established based on ANSYS FLUENT software,so as to improve the denitrification performance of device,and numerical simulation was carried out.In order to make the calculation results closer to the actual conditions,the actual NO_(x)concentration of the boiler under full load was used as the SCR inlet boundary conditions in the numerical simulation.Through detailed analysis of flow characteristics of SCR system such as flue gas velocity distribution,component concentration distribution,ammonia escape,etc.,simulation and optimization were carried out for the influence of flow field optimization,zoned ammonia injection and new static mixer on denitration performance,so as to improve the flow field and concentration field uniformity of SCR system.The simulation results show that by increasing the number of deflectors in the top chimney flue,the uniformity of catalyst inlet velocity distribution is improved,and the strip area with high velocity can be eliminated.After optimization,the relative standard deviation of catalyst inlet velocity distribution is reduced from 20.86%to 3.80%.The influence of uneven NO_(x)concentration distribution at the inlet can be eliminated by adding a static mixer with triangular airfoil,and SCR uniformity of the concentration field can be improved.The relative standard deviation of the maximum ammonia nitrogen molar ratio is reduced from 10.72%to 1.78%.The reconstruction scheme is obviously superior to the original design,which has important guiding significance for engineering design.