空气分级技术对焙烧炉内煤气燃烧生成的影响

煤气化后的煤气常用于氢氧化铝焙烧过程。煤气中一般含有一定量的氨气,造成焙烧过程的氮氧化物生成量较高。针对一种燃用煤气的氢氧化铝气态悬浮焙烧炉,采用空气分级的方案,开展了煤气低氮燃烧过程的研究,探究空气分级技术对焙烧炉内煤气燃烧氮氧化物生成的影响规律,从而指导实际焙烧炉内的燃烧组织设计及优化。利用BarracudaTM气固两相流动计算软件,分析了一台3 000 t/h的氧化铝焙烧炉的炉内气固流动及燃烧过程。结果表明,悬浮焙烧炉炉膛底部存在明显的高温区,局部高温负荷点较集中,最高温度达1 700 K。随着炉膛高度的增加,炉膛温度逐渐降低。同时由于气流回流的作用,炉膛内部在炉膛底部以及上部气流转向处存在明显的颗粒堆积造成的颗粒高浓度区域。基于气固流动计算得到炉内的温度场,耦合详细化学反应机理来考虑详细的化学反应过程,利用Chemkin Pro软件建立了反应器网络,通过数值计算探究空气分级技术对含氨煤气在焙烧炉内燃烧过程中NOx生成的影响。结果表明,燃用煤气的焙烧炉内生成的氮氧化物主要为燃料型氮氧化物。空气分级为20%时,空气分级对煤气燃烧氮氧化物生成的抑制效果有限。当空气比例为40%时,主燃烧区呈还原性气氛,焙烧炉内煤气燃烧生成NOx减排率达70. 3%。 Abstract:Coal gas produced from coal gasification,is frequently used as a fuel in the aluminium hydroxide calcination process.Normally,coal gas generally contains a certain amount of ammonia,resulting in a high amount of nitrogen oxides in the roasting process.In this paper,the low-nitrogen combustion process of gas was studied by air classification method in a gas-fired aluminum hydroxide suspended calciner,and the influence of air classification technology on the formation of nitrogen oxides in gas combustion in the calciner was investigated,so as to guide the actual combustion structure design and optimization in the calciner.BarracudaTM software was utilized to simulate the gas-solid two-phase flow and the combustion process in a 3 000 t/h Al2O3 calciner.The results show that there is an obvious high temperature zone at the bottom of the suspension calciner.The local high temperature load point is concentrated,and the maximum temperature is up to 1 700 K.With the increase of furnace height,the mean temperature decreases gradually.Additionally,due to the effect of airflow reflux,there is a high concentration area of particles in the bottom of the furnace and the upper airflow diversion.Based on the temperature field in the furnace calculated by gas-solid flow,and the detail chemical reaction process was considered by coupling the detailed chemical reaction mechanism.The reactor network was established by using Chemkin Pro software,and the influence of air classification technology on the formation of NOx in the combustion process of ammonia-containing gas in the calciner was investigated by numerical calculation.The results show that the main nitrogen oxides produced in the calciner burning gas are fuel nitrogen oxides.In addition,the inhibition effect of air classification on the formation of NOx in gas combustion is limited when the staged-air ratio is 20%.However,the NOx emission generated by gas combustion in calciner reduced up to 70.3% when the staged-air ratio is 40%,and the reducing atmosphere appears in the main