煤粉燃烧产生的飞灰导致炉膛和烟道内出现结渣沾污现象，飞灰的黏附特性受煤中碱金属/碱土金属(Alkali and Alkaline Earth Metals,AAEM)的影响，为减少飞灰在换热面上的沉积，分析其燃烧过程中AAEM的赋存形态和迁移机理，论述了AAEM蒸汽冷凝对飞灰特性产生的影响，同时分析了飞灰在换热面上的沉积机理。结果表明，燃烧温度和AAEM赋存形态的差异导致其析出过程和析出量不同。温度升高会促进AAEM的释放，随着AAEM在萃取液中的溶解性降低，在燃烧时释放更困难；释放到气相中的AAEM在换热面或飞灰表面异相冷凝形成黏性层，增大了换热面对飞灰的捕集效率；在气相中均相冷凝形成气溶胶，气溶胶作为前驱体在后续聚并过程中形成亚微米飞灰；飞灰的沉积受分子扩散、布朗运动、涡流碰撞、热泳、重力沉降、惯性碰撞等多种因素影响，重力沉降、惯性碰撞主要影响大粒径飞灰颗粒的运动轨迹，其他因素则主要影响小颗粒的运动；在换热面上形成的沉积层会出现分层结构，沉积内层的生成主要由无机蒸汽冷凝和小粒径飞灰沉积造成，外层沉积层主要由大颗粒飞灰沉积形成。黏附在换热面上的飞灰影响锅炉热效率、高温下腐蚀金属壁面，对锅炉的安全稳定运行埋下隐患。因此部分学者提出煤粉的水洗、掺烧、吹灰、换热面涂层、结构改进等方案来减缓沉积层的形成。但由于煤中成分多变，难以准确预测对燃料结渣沾污行为，应加强不同赋存形态元素的研究、不同形态飞灰的沉积及飞灰形成过程中复杂的物理化学，为结渣沾污的防治提供理论支持。

The fly ash leads to slagging and fouling in the furnace and flue,and the ash particle sticking behavior will be affected by Alkali and Alkaline Earth Metals (AAEM) rich in coal. In order to reduce the threat of molten,sticky ash particles adhering to heat exchanging surfaces,the occurrence form and transformation characteristics of AAEM in the combustion process were analyzed,the influence of AAEM steam condensation on the characteristics of fly ash was discussed,and the deposition mechanism of fly ash sticking on the heat exchange surface was analyzed. The results show that the difference of combustion temperature and occurrence form of AAEM leads to different released processes and amount. The increase of temperature will promote the release of AAEM. With the decrease of the solubility of AAEM in the extract,it will be more difficult to release AAEM during combustion.The AAEM released into the gas phase then heterogeneous condenses on the heat exchange surface or ash particles surface to form a sticky layer,which increases the capture efficiency of fly ash on the heat exchange surface,homogeneous condenses in the gas phase to form aerosols,and aerosols as precursors form sub-micron particles in the subsequent coalescence process. The deposition of fly ash is affected by many factors,such as molecular diffusion,Brownian motion,eddy impaction,thermophoresis,gravity sedimentation,inertial impaction and so on. Gravity sedimentation and inertial impaction mainly affect the trajectories of large ash particles,while other factors mainly affect the trajectories of small particles.The deposition layer have a layered structure. The formation of the inner layer is mainly caused by inorganic steam condensation and small particle impaction,and the outer deposition layer is mainly formed by large particle impaction. The fly ash adhered to the heat exchange surface affects the thermal efficiency of the boiler,corrodes metal at high temperature,and buries hidden dangers for the safe and stable operation of the boiler. Therefore,many scholars have proposed pulverized coal washing or mixed combustion,soot-blowing,coating of heat exchange surface and structural improvement of furnace to slow down the deposit formation. However,due to the changeable components in coal,it is difficult to predict the slagging and fouling behavior perfectly. It is necessary to strengthen the research on the elements with different occurrence forms,deposition of different forms of fly ash and the complex physical-chemistry reactions in the formation process of fly ash,so as to provide theoretical support for the prevention and control of slagging and contamination.

0 引言

1 AAEM的赋存形态及迁移机理

   1.1 AAEM的测定方法及赋存形态

   1.2 AAEM的迁移机理

2 AAEM对灰颗粒形成的影响

3 飞灰沉积机理与积灰影响因素

   3.1 飞灰沉积的影响因素

   3.2 结渣沾污的影响因素

4 改善灰沉积的方法

5 研究展望

6 结语