多层二次风配风对玉米秸秆颗粒燃烧降低NOx产率及结渣的影响

秸秆类生物质具有碱金属及灰分含量高的特性，燃烧时灰分容易团聚结块而影响燃烧室内的配风及燃料的燃烧。该研究设计了一种具有多层二次风配风的生物质燃烧试验装置，以玉米秸秆颗粒为燃料，研究了不同一二次风分级配比、多层二次风配比对烟气中CO、NOx等污染物浓度、燃烧效率及灰分结渣率的影响规律。结果表明：当采用一二次风分级配风时，能够显著降低烟气中NOx的浓度，烟气中CO和NOx的浓度变化趋势相反，呈现一种竞争关系。二次风位置较高或下层二次风量的减少，都易导致玉米秸秆颗粒燃烧不完全，CO浓度显著提升。与对照组相比，二次风多层配风下，燃烧室内各测点的温度和烟气中NOx浓度均有所降低，最低NOx浓度排放放生在W1工况（空气系数为1.2，一、二次风配比为60%∶40%时，下、中、上二次风按（1/2，0，1/2）），约150 mg/m3。当采用二次风多层配风时，结渣率大幅度下降，最低为4.5%。W1工况的NOx浓度和结渣率均较低，综合评价为最优工况。常用的硅比指数G、碱酸比、Na含量指数、碱性指数Alc等4种结渣指数，均不能正确预测因燃料燃烧区温度T1变化而造成的结渣倾向变化，为此在硅比指数G中引入燃料燃烧区温度T1作为变量，修正后的硅比指数Gt可以很好地对玉米秸秆颗粒因燃料燃烧区温度T1引起的结渣倾向变化进行预测。

Influences of multi-layer secondary air distribution on NOx reduction rate and slagging tendency of maize stover particle combustion

Biomass refers to the material derived directly from plants, thereby serving as a renewable, low-carbon emission, and environment-friendly energy source. Straw biomass is characterized by high alkali metal and ash content, where the ash caking easily occurs during combustion. This feature has become one of the most important factors limiting the use of industrial boiler fuel, particularly affecting the air distribution and complete combustion in the reaction chamber. In this study, a biomass combustion test device was designed with multi-layer secondary air, thereby explorg the influence on the NOx reduction rate and slagging in corn straw particle combustion. Two types of parameters were set firstly, including different primary and secondary air grading ratios, and the multi-layer ratios of secondary air. An evaluation was also made on the concentration of pollutants, such as CO and NOx in flue gas, combustion efficiency, and ash slagging rate. The results show that the concentration of NOx in flue gas significantly reduced, when the primary and secondary air were distributed in stages, whereas, the concentration of CO and NOx in flue gas changed in opposite directions, showing a competitive relationship. Specifically, a higher secondary air position or lower secondary air volume led to incomplete combustion of corn straw particles, and a significant increase in CO concentration. The temperature at each measuring point and the NOx concentration in the flue gas in the combustion chamber was reduced significantly, compared with the control group, under different secondary air distribution modes. Moreover, the emission of the lowest NOx concentration was released in W1 working condition, about 150 mg/m3. The NOx concentration was also significantly reduced, whereas, the slagging rate decreased greatly, with the lowest of 4.5%, when the secondary air was equipped with multi-layer air. The slagging rate of corn stalk increased significantly, with the increase of temperature T1, indicating that the temperature T1 was an important factor affecting the slagging of corn stalk particles during combustion. Correspondingly, the best working condition was achieved, where there was a relatively low NOx concentration and slagging rate under W1 working conditions. Furthermore, the incomplete combustion of corn stalk particles was attributed to the higher secondary air position or the lower secondary air volume, whereas, the CO concentration was attributed to the higher carbon content in ash. Additionally, the combustion efficiency decreased at the low temperature on the bottom of the combustion chamber. Consequently, four slagging indexes cannot correctly predict the change of slagging tendency under various fuel zone at temperature T1, such as acid-base ratio, alkalinity index Alc, Na content index, and silicon ratio index G. More importantly, when the temperature T1 was introduced into the silicon ratio index g, the modified Gt can be expected to well predict the slagging tendency of corn straw particles in the combustion zone.