氮氧化物(NOx)是燃烧产生的一种有害气体。为了满足低氮排放标准,烟气循环是减少NOx生成的有效方式。虽然烟气内循环较烟气外循环的热损失更少、降氮效果更好,但由于其需要在设备设计阶段进行优化,因此当前针对烟气内循环降氮的研究较少,对于实际降氮过程暂无系统性的分析研究。以带有烟气内循环的5kW甲烷扩散燃烧器为研究对象,采用CFD三维燃烧过程数值模拟来研究烟气内循环卷吸率对NOx生成过程的影响。在常规采用零维或一维的理论模型研究基础上,以模拟结果中的燃烧速率来表征燃烧强度,可以更为准确地预测实际燃烧过程。结果表明:改变空气渐缩段出口直径可以有效控制烟气卷吸率。烟气卷吸率最大可以增加到50%,NOx排放值相比无烟气内循环工况下的NOx排放值降低了94%。烟气内循环对不同的NOx生成路径都有一定的抑制作用,尤其是热力型NOx。增加卷吸率后快速型NOx替代热力型NOx成为主导路径,热力型NOx在整体NOx中的占比从52%降低到16%。快速型NOx也会影响最终降氮效果,因此在实际低氮燃烧器设计中,要综合考虑这几种路径的抑制。

Nitrogen oxides (NOx ) is a harmful pollutant produced during combustion. Flue gas recirculation (FGR) is an effective technical measure to reduce NOx generation. Al-though internal flue gas recirculation (IFGR) is preferred for less heat loss and better denitrifica-tion performance, there is currently less research on it because it needs to be optimized in the pre-design process. Few studies have been conducted on IFGR and there is limited systematic analysis of the actual combustion and denitrification process. In this paper, a 5 kW methane non-premixed combustor using IFGR was designed to discover the effects of the flue gas recirculation rate on the NOx generation process by using three-dimensional numerical simulation method. Based on conventional theoretical models such as zero-dimensional or one-dimensional computation, the combustion rate was set as the representative of combustion intensity for higher accuracy. The results show that changing the outlet diameter of the air contraction section can effectively manip-ulate the flue gas recirculation behaviors. The IFGR rate can peak at 50%, leading to a removal of 94% NOx generation. IFGR has a certain inhibitory effect on each NOx generation pathway, especially thermal NOx. When increasing the recirculation rate, prompt NOx replaces thermal NOx as the dominant pathway, and the proportion of thermal NOx to the total NOx generation decreases from 52% to 16%. Since prompt NOx contributes much in the non-premixed combus-tion, these pathways should be considered comprehensively when designing de-NOx techniques in practice.