CO火焰对碳粒燃烧影响的理论分析和实验研究

Theoretical Analysis and Experimental Study of Influence of CO Flame on the Combustion of a Char Particle

建立了球坐标系下传热、传质和化学反应全耦合的碳粒燃烧数值模拟程序.在详细理论计算的配合下,通过精密设计的实验研究,用FTIR透射-发射实验测温方法成功捕捉了持续时间极短的“CO在颗粒表面被点燃而引起的颗粒高温”现象.连续膜模型的计算结果和FTIR测温实验结果表明,CO的空间反应与碳粒表面反应的相互作用及其对碳粒表面温度、总体反应速率的影响是极其复杂的.而CO能否在颗粒表面附近被点燃及其所引起的颗粒表面温度差可高达数百度.在实际煤粉火焰条件下,单膜模型和严格的连续膜模型的预报结果相差比较大,特别是对着火点及着火后某段区间内的颗粒温度的预报,是仅考虑表面氧化反应C+1/2O_2→CO的单膜模型所无法完成的,这说明单膜模型存在较大的应用局限性.

The programs for simulating carbon particle combustion, which take chemical reactions, heat and mass transfer into account, are established in a spherical coordinate system. With the support of detailed calculations, the phenomenon of elevated temperature of a particle caused by the ignition of CO at the particle surface, whose duration is very short, is captured successfully by using the FTIR Emission-Transmission technique. The results of the FTIR experiments and the calculations by continuous-film model for carbon combustion show that the effects of the volumetric reaction, CO ＋ 1/2O2→CO2 , on the surface temperature and the combustion rate of a carbon particle are extremely complicated. The theoretical calculations show that the surface temperature difference of particle caused by whether CO is ignited in the vicinity of particle or not, can be up to several hundred degrees Kelvin. Under conditions of pulverized coal flame, the differences between the predictions of the single-film model and those of the rigid continuous-film model are great. Specially, the ignition temperature and the particle temperature after ignition can not be predicted by the single-film model which only considers the surface oxidation reaction C ＋ 1/2O2→CO. It shows that the single-film model has remarkable limitation in the practical application.