【作者】 刘晓东；

【导师】 邹春；

【作者基本信息】 华中科技大学 ， 热能工程， 2011， 硕士

【摘要】 MILD燃烧技术具有高效率，低NOx、CO、SO_x等污染物排放等优点，被国际燃烧界誉为21世纪最具发展前景的新型燃烧技术之一。本文针对MILD燃烧需要预热空气的缺点，设计并建立规模为20kW的MILD燃烧中试实验台架。采用实验研究和CFD数值模拟的手段，以佳能气为燃料，实现了常温空气的MILD燃烧，并进行相关的实验研究。实验发现，常温空气下通过调整燃烧器钝体高度，可以实现常规燃烧到MILD燃烧的转化。实验测量结果表明：炉内温度分布均匀，温差在200K左右，没有明显火焰锋面，燃烧反应速率降低且发生在整个炉膛容积内，辐射换热增强；炉膛内处在低氧的水平，平均氧浓度为4.2%，NO的生成量很低，平均值仅为29ppm。在炉膛中心存在高浓度的CO分布，但在炉膛的其它区域内，几乎检测不到CO的存在。采样尾部烟气发现，O2和CO的浓度分别为11.0%和0，NO仅为17ppm，证明常温空气下MILD燃烧具有较高的减排水平。使用FLUENT软件，采用三种不同的湍流模型—standard k-ε模型、realizable k-ε模型、Reynolds Stress模型，结合层流火焰面燃烧模型和DO辐射模型对常温空气下C3H8的MILD燃烧进行模拟。结果显示Reynolds Stress模型结合Flamelet模型的温度和CO分布预报结果要明显地优于其他两个模型，而在O2浓度分布预报上三种组合模拟的结果相当；采用FLUENT自带NO反应模型可以对NO的趋势较为准确地预报；尾部烟气中CO和NO的预报值很低，与实验一致。研究表明，强烈的烟气内循环和高速燃气/空气射流的湍流混合对实现常温空气MILD燃烧起到非常重要的作用，常温空气MILD燃烧的数值模拟还需要流动和燃烧模型的进一步研究。更多还原

【Abstract】 MILD combustion is known as one of the most promising new combustiontechnologies in21st century, which has high efficiency and low NOx, CO, SO_xemissions.This paper has discussed the characteristics of MILD combustion using normaltemperature air with the method of experimental study and CFD simulation. A pilot scalefurnace of20kW has been designed and built. The experiment has been carried out bytaking LPG(>96%C3H8) as fuel with normal temperature air. The temperature field ismeasured and flue gas component is sampled and analyzed.Experimental results present that MILD combustion can also been realized without airpreheating. Temperature distribution in the furnace is uniform and there is no visual flame.It is indicated that the combustion reaction has lower rate and occurs in the wholechamber.Also the levels of oxygen and NO are very low in the furnace (average4.2%and29ppm separately). There is high level of CO distribution in the center part of furnace,besides of which CO is undetectable. It is also found that no CO and low NO (only17ppm)is detected in the exits which proves that MILD combustion has high ability of emissionreduction.Numerical simulation is also taken to predicted MILD combustion of C3H8without airpreheating by the software of FLUENT. Three kinds of turbulence model-standard k-εmodel, realizable k-ε model, Reynolds Stress model are chosen combined with the LaminarFlamelet model and DO radiation model. The results show that the prediction oftemperature field and the trend of CO concentration using Reynolds Stress model combinedwith Flamelet model are better than the other two groups, but the simulation of O2distribution on three kinds of combination has the similar results. The trend of NO can bemore accurately predicted by using FLUENT NO model. The modeling results of CO andNO in the exit are in accordance with experiment.Research shows that intense flue gas recirculation and high-speed gas/air jet play avery important role of MILD combustion under normal temperature air, and models onflow and combustion still need development. It is also considered that the characteristics of this technology-no air preheating, uniform temperature distribution and low NO emissionswill be very beneficial to its application and promotion.更多还原