高浓度水蒸气对煤粉富氧燃烧中NO生成及转化机理研究

Oxy-fuel combustion technology can realize the control of CO2, and NO release rate is just 1/5 to 1/3 that of traditional air combustion, which is one of the most promising technologies having the coal combustion emissions close to zero. The steam concentration in the circulating flue gas of oxy-fuel combustion is 8%～35%, and previous studies indicated that steam can reduce the NO formation in oxy-fuel combustion. Under high temperature (1473K～1773K) and rapid heating conditions in this study, we will use a 0.5MW vertical and hot-state swirl pulverized coal combustion experimental facility, a high-temperature drop furnace and so on, to study the effect of high-concentration steam atmosphere on the pyrolysis and combustion reaction of the typical power coal in China, the change rule of char structure and reactivity in the process of char formation under O2/CO2/H2O atmosphere in the real combustion situation, the law of fuel-N converted to NO under O2/CO2/H2O atmosphere, the mechanism of homogeneous reaction of volatile with reducing and recycling NO under O2/CO2/H2O atmosphere and the mechanism of heterogeneous reaction of char with reducing and recycling NO under O2/CO2/H2O atmosphere. We will study and obtain the main factors of NO formation, conversion path and reducing the systematic NO emission of the typical power coal in China under conditions of circulating wet flue gas oxy-fuel combustion through this program, and providing the theoretical support for the development of circulating wet flue gas oxy-fuel combustion.

富氧煤粉燃烧技术可实现控制CO2排放，其NO释放率仅为传统空气燃烧时的1/5～1/3，是现有较为有希望的燃煤近零排放技术之一。富氧燃烧循环烟气中水蒸气浓度为8%～35%，已有研究表明水蒸气可降低煤粉富氧燃烧NO的生成。本研究将在高温（1473～1773K）、快速加热条件下，利用0.5MW旋流煤粉立式热态燃烧试验台和高温沉降炉等试验系统，研究高浓度水蒸气对我国典型动力用煤的热解和燃烧反应过程的影响；O2/CO2/H2O气氛下真实燃烧情况时煤焦生成过程中煤焦结构及反应性的变化规律；燃料N在O2/CO2/H2O气氛下生成NO的规律；在O2/CO2/H2O气氛下挥发份还原烟气中循环型NO的同相反应机理，焦炭还原循环型NO的异相反应机理。通过本项目研究确定我国典型动力用煤湿烟气富氧循环燃烧条件下NO生成、转化路径和降低系统NO排放的主要因素。本项目可为发展湿烟气循环富氧燃烧技术提供理论支撑。

富氧燃烧技术能提高烟气中的CO2浓度，便于捕集和封存，同时能够降低NOx排放量。为了得到更接近于真实富氧锅炉下煤粉的燃烧特性，本文研究O2/CO2/H2O气氛对煤热解、燃烧的影响及NO的生成、还原特性。为煤粉富氧循环燃烧技术在实际锅炉的应用提供理论依据。. 我国四种典型动力用煤在O2/CO2/H2O气氛（40%O2，0~50%H2O）下燃烧特性。主要结果表明：（1）水蒸气浓度增大，神木烟煤的着火和燃尽提前了66.2℃和26.12℃，兴义无烟煤、晋城贫煤、海拉尔褐煤着火则延迟了15.4℃、15.53℃、44.79℃。水蒸气浓度增大，四种煤的失重速率和综合燃烧指数增大，高挥发分煤的综合燃烧指数受水蒸气的影响更大；（2）动力学求解表明，四种煤的燃烧均可认为是一级反应，且活化能E与煤的着火温度相关，着火温度越高，活化能越高。.制备了O2/CO2/H2O气氛（5%O2，10%~30%H2O）下的煤焦。主要结果表明：（1）神木烟煤在裂解生成煤焦的过程中，孔隙结构变得丰富，生成的孔径分布较广，水蒸气浓度的增加促进了1~10nm的微孔和中孔生成。（2）原煤在生成煤焦的过程中，不稳定的含碳官能团发生缩聚，sp2C含量增大，含氧官能团在高温下受热分解成小分子气体而脱除。随着水蒸气浓度由10%升高至30%，由于C(s)-H2O气化反应的进行，神木烟煤和兴义无烟煤焦表面的sp2C含量减少了19.7%和20.35%，兴义无烟煤煤焦表面的含氧官能团则由于气化反应的进行脱除量略有减小。. 以多反应控制段携带流（EFCM）反应器为研究对象，研究了水蒸气及挥发分浓度对生成NO的影响规律，再循环NO对挥发分燃烧时NO还原的影响情况，水蒸气和NO浓度对煤焦还原NO的影响规律，以及气氛，过量氧气系数，壁面温度和平均煤粉粒径对温度场，组分浓度，C(s)消耗类型以及NO排放的影响。主要结果表明：（1）水蒸气、O2浓度升高均会提高反应器内的温度，降低NO排放。在N2气氛下，增大O2浓度会显著提高热力型NO的量，水蒸气浓度提高则会降低热力型NO的产生；（2）C(s)异向反应竞争机制主要是扩散竞争，提高煤焦表面对应气体浓度均会增大对应异向反应所消耗的C(s)的占比。