燃瓦斯气蓄热式加热炉再燃低氮改造数值模拟

Mathematical modeling on low nitrogen reconstruction by reburning in regenerative heating furnace fired refining gas

摘要:

为实现燃瓦斯气加热炉氮氧化物(NO_x)排放低于200 mg/m³ (O₂体积分数3.5%)的要求, 提出高效的再燃低氮改造方案.通过数值计算和工业试验相结合的方法对其进行验证.采用FLUENT软件计算不同再燃瓦斯气比例和当量比下，不同截面温度及NO_x质量浓度分布，NO_x生成还原特性和瓦斯气未燃尽率等.根据优化的数值计算结果对加热炉进行改造，进行连续一周的工业试验.结果表明：增加再燃比，燃烧空间高温区域比例降低，热力型NO_x生成量减少且减幅增大，再燃作用对NO_x的还原率先升高后降低.当再燃比为0.20时，再燃作用还原NO_x的效率最高.增加再燃比或降低主燃区当量比将降低NO_x浓度，但瓦斯气未燃尽率升高.通过与工业试验对比，验证了计算的可靠性.当再燃比为0.15~0.20，主燃区当量比为1.15~1.20时，NO_x质量浓度最高值约160 mg/m³，均值约130 mg/m³ (O₂体积分数3.5%)，且瓦斯气未燃尽率较低.

Abstract:

To realize nitric oxides(NO_x) emission regulation below 200mg/m³ (O₂ volume fraction at 3.5%) in heating furnace fired refining gas, a high efficiency low nitrogen reconstruction scheme by reburning technology was proposed, and it was confirmed by numerical calculation and industrial test. The software of FLUENT was applied to investigate the effects of reburn refining gas ratio and primary area stoichiometric ratio on the distribution of temperature and NO_x mass concentration at different sections, generation, reduction characteristics of NO_x and unburned rate of refining gas. According to the optimized numerical calculations, the reconstruction was implemented and industrial test was carried out for one week. The results showed that, with the reburn fuel ratio increasing, the proportion of high temperature space decreased, the amount of thermal NO_x reduced and reduction increased, the NO_x reduction efficiency by reburning impact firstly increased and then decreased. The highest NO_x reduction efficiency by reburning impact when the reburn fuel ratio was 0.20. Increasing the reburn fuel ratio and decreasing the primary area stoichiometric ratio could increase the NO_x reduction efficiency, but the unburned fuel ratio increased meanwhile. When the reburn fuel ratio between 0.15~0.20 and the primary area stoichiometric ratio between 1.15~0.20, the greatest and average values of NOx mass concentration were 160mg/m³ and 130mg/m³ (O₂ volume fraction at 3.5%) respectively.