用改进的焦碳模型研究煤粉锅炉内的燃烧行为

FURTHER STUDIES ON THE COAL COMBUSTION BEHAVIOR IN THE TANGENTIALLY FIRED BOILER FURNACE

采用改进了的焦炭燃烧模型 ,数值研究了煤粉颗粒在四角切向燃烧锅炉炉膛内的燃烧行为。在计算中 ,将煤岩学对煤进行分类研究的思路引入燃烧学 ,对不同煤岩类别的煤分别进行研究 ,同时在焦碳燃烧模型中还考虑了煤焦在高温下石墨化对燃烧速率的影响。计算所得煤粉在锅炉内的未完全燃烧热损失与实际情况相符。结果表明 ,由于煤焦在高温下迅速石墨化 ,燃烧速率降低 ,使原来部分非难燃大颗粒煤粉在开始燃烧后变成难燃性煤焦 ,从而加重了煤粉在炉膛内的未燃烬率及出口处残余热量分布的非均匀性 ,进而将直接加重水平烟道处温度、热量分布的左右偏差 ,导致超温爆管。

The coal combustion behavior in a tangentially fired boiler furnace is numerically studied using a modified char combustion model. Coal particles with different lithologic characteristics are studied with the consideration of the graphitization effects during combustion process. Calculated result of unburning heat loss is in good agreement with the practical data. The numerical result also shows that the rapid grahitization of coal particles in high temperature results in continuously decreasing combustion rate. Thus, some of the coal particles which are originally easy to burn become difficult to burn out. Therefore the unburning out rate and the deviation of unburning heat between the right side and left side in the outlet of the furnace are apparently intensified. This unburning heat deviation will cause deviation of the gaseous temperature and heat distribution, and thus led to overheating and explosion of the reheaters and superheaters.