含K成分形成初始沉积层的数学模型及烟气条件影响分析

Model for the formation of initial deposited layer by K-containing species and influence analysis of flue gas conditions

针对积灰初始沉积层形成的两种主要机理即凝结和热泳机理,建立了含K成分形成初始沉积层的数学模型,采用文献中的实验结果检验了模型,表明考虑沉积层厚度、表面温度随位置和时间的变化对模型预测有合理的改善。应用该模型研究含K气体成分和气溶胶颗粒在受热面上的沉积过程,并考察烟气中含K成分组成、烟温和烟速等因素的影响。研究表明,由于烟气中含K气体成分和气溶胶颗粒相对浓度的差异,凝结和热泳在沉积过程开始时都可能对初始沉积层的形成起主要作用,而在沉积过程后期热泳沉积则占据主导地位;烟温和烟速对含K成分沉积过程的影响相似,即较高的烟气温度和速度,其初期沉积速率高,而后期沉积速率相对低,形成的沉积层厚度较低。

Aiming at the two main mechanisms of initial deposition layer of ash deposition,namely,condensation and thermophoresis mechanism,a mathematical model for the formation of initial deposition layer by K-containing species was established.The rationality of the model was validated by the experimental results in the literature which indicates that considering the changes of the thickness of the deposition layer and the surface temperature have a reasonable improvement.The model was used to study the deposition process of K-containing gas and aerosol particles on the heating surface,and to investigate the effects of K-containing species composition,flue gas temperature and velocity.The results show that,because of the difference in the relative concentrations of Kcontaining gas and aerosol particles,both condensation and thermophoresis deposition may play a major role in the formation of the initial deposition layer at the beginning of the deposition process,while thermophoretic deposition dominates the later stage.The effects of flue gas temperature and velocity on the deposition process is similar,that is,the higher flue gas temperature and velocity,the higher the initial deposition rate,the lower the later deposition rate,and the lower the thickness of the deposited layer.