新型低氮燃气分级燃烧器燃烧特性和NOx排放的CFD研究

应用CFD软件Fluent数值模拟了某二甲苯塔再沸炉在役油气联合燃烧器燃烧和NOx排放特性，分析了其NOx排放浓度较高的原因，提出了新型低NOx燃气分级燃烧器的改造方案，并数值模拟了新型燃烧器空气预热温度Tair、过剩空气系数α和主辅喷枪燃气质量分率Rp对辐射室壁面热通量、出口温度、火焰高度和炉膛出口NOx排放浓度的影响。针对在役燃烧器的模拟结果与现场运行数据吻合良好，说明所选模型能够正确模拟炉膛内部的流动、辐射、燃烧和NOx生成过程。新型燃烧器模拟结果表明，增加Tair会增加辐射壁面热通量，同时也会增加NO的排放；辐射壁面热通量随α增加而降低，NOx排放浓度随α增加而增加；Rp对炉内传热和NOx排放的影响并不明显。当Tair = 220℃、α = 1.05及Rp= 0.24时，新型燃烧器在模拟范围内达到最佳运行工况，辐射壁热通量为37.45kW/m2，NOx排放浓度为12.1μL/L。

CFD study on combustion properties and NOx emission of reboiling furnace for xylene tower

By using CFD software Fluent，a numerical simulation was carried out to study the combustion behavior and NOx emission of a xylene tower in gas-oil burner. The problem of high NOx emission was analyzed and a novel low NOx staged-fuel burner structure was brought up. Based on the new burner structure，orthogonal simulations were conducted to study the influences of operating parameters (including air preheated temperature Tair, excess air factor α, and primary fuel gas mass ratio Rp) on the radiation surface heat flux （RSHF），radiation section outlet temperature （RSOT），flame height and volume fraction of NOx. Simulation results of the in-service burners showed good agreement with site running data，suggesting good prediction of the chosen models for the internal flow，radiation，combustion and NOx formation. Simulation results of the new burner showed that higher air preheated temperature could increase the radiative heat flux while also aggravating the NOx emission；excess air factor could enlarge the radiative heat flux and reduce NOx emission；varied primary fuel gas mass ratio made no obvious differences on both radiative heat flux and NOx emission. It was concluded that air preheated temperature of 220℃，excess air ratio of 1.05 and primary gas ratio of 0.24 were the optimal operating conditions，under which radiative heat flux was 37.45kW/m2 while NOx emission simulated to be 12.1μL/L.