Transformation of AAEM and ash deposition characteristics during combustion of Zhundong coal

Zhundong coal is characterized by low ash content,low ignition temperature and excellent burnout perform- ance which make it a great power coal. However,sever slagging and fouling problems occur due to the high alkali / al- kaline earth metal content in Zhundong coal ash. The volatile AAEM may release and condense on the heating surfaces during combustion so as to promote slagging and fouling progress. In order to achieve safe,efficient and clean utiliza- tion of Zhundong coal,it is necessary to study the transformation characteristics of minerals (especially alkali / alkaline earth metal,AAEM) as well as melting characteristics of coal ash during the combustion of Zhundong coal. In this pa- per,the occurrence form and the migration of AAEM during the thermal conversion process of Zhundong coal were in- troduced. The melting characteristics of coal ash and the mechanism of slagging and fouling were also introduced. The key influencing factors of boiler slagging and pollution,and the commonly applied prevention and control methods were summarized. Due to the differences in experimental samples and conditions,there is no consensus on the release and transformation characteristics of AAEM during coal combustion and its effect on ash melting characteristics. Thermody- namic equilibrium calculations were often applied for the investigation of release of AAEM,but the corresponding dy- namic model lacks in-depth research. Whether the slagging and ash deposition characteristics obtained by the bench /pilot scale apparatus can reflect that in real boiler remains to be verified. The ash deposits collected from real boiler may have different morphologies due to the different operation conditions. Boiler design,co-firing,combustion adjust- ment can only reduce the slagging and deposition. For the safe,efficient and clean utilization of Zhundong coal,an in- depth study of the actual slagging and ash deposition mechanisms is required. A systematic study should be conducted on the effects of ashing temperature and atmosphere on the release and transformation characteristics of AAEM during coal thermal conversion. The release and mineral conversion kinetics model of AAEM in coal thermal conversion process should be established. The effects of temperature,atmosphere,coal composition,etc. on the slagging and fouling mechanism should be investigated to provide a basis for slagging and fouling prevention and control.