还原区当量比对煤粉预热燃烧特性的影响

Influence of equivalence ratio of reduction zone on preheating combustion characteristics of pulverized coal

预热燃烧是煤粉先高温预热改性、预热燃料再燃烧的新型技术,基于30 kW煤粉预热燃烧试验平台,保持循环流化床当量比、预热温度、过量空气系数等运行参数不变,研究了还原区当量比对煤粉预热燃烧特性的影响规律。结果表明,当还原区当量比增加时,下行燃烧室的主燃区向顶部喷口方向移动,喷口附近区域温度升高,下行燃烧室沿程温度随与喷口距离的增加而降低。下行燃烧室喷口至三次风给入的还原性区域内,发现含氮气体主要以NO_(2)形式存在,在给入三次风后的下行燃烧室氧化性区域内,含氮气体主要以NO形式存在。还原区当量比的增加会使下行燃烧室还原区内的CO质量浓度降低,即还原性气氛减弱,较低质量浓度的CO对NO_(2)的还原抑制作用减弱,从而导致还原区内NO_(2)被还原成N_(2)的比例增加,NO_(2)质量浓度降低,氧化性气氛下的NO质量浓度也随着还原区空气当量比的增加而下降。说明预热燃料燃烧中含氮气体的形态与燃烧室气氛密切相关。当还原区当量比为0.96时,生成的尾部NO和CO排放质量浓度均较低。

Preheating combustion is a new technology of high temperature preheating modification of pulverized coal and re-combustion of preheated fuel.Based on the 30 kW pulverized coal preheating combustion test apparatus,the influence of the change of the equivalence ratio in the reduction zone on the preheating combustion characteristics of the pulverized coal was researched by basically keeping the operating parameters of the circulating fluidized bed equivalence ratio,preheating temperature,and excess air coefficient unchanged.The results show that the main combustion zone of the downward combustion chamber moves toward the top nozzle,the temperature near the nozzle increases,and the temperature along the downward combustion chamber decreases with the increase of the distance from the nozzle when the equivalence ratio of the reduction zone increases.From the nozzle of the downward combustion chamber to the reducing zone where the tertiary air is fed,it is found that the nitrogen-containing gas mainly exists in the form of NO_(2).In the oxidizing zone of the downward combustion chamber after the tertiary air being fed,the nitrogen-containing gas mainly exists in the form of NO.The increase of the equivalence ratio of the reduction zone reduces the CO concentration in the reduction zone of the downward combustion chamber,that is,the reducing atmosphere is weakened.The inhibition effect of low concentration of CO content on NO_(2) reduction is weakened,resulting in proportion increase of NO_(2) reduced to N_(2).The NO_(2) concentration in the reduction zone is reduced.The ratio of NO_(2) being reduced to N_(2) increases.The NO concentration in the oxidizing atmosphere also decreases with the increase of the air equivalence ratio in the reduction zone.It indicates that the form of nitrogen-containing gas in the preheated fuel combustion is closely related to the combustion chamber atmosphere.The generated NO and CO concentrations are both low when the reduction zone equivalence ratio is 0.96.