A Comprehensive Review of Ash Issues in Oxyfuel Combustion of Coal and Biomass: Mineral Matter Transformation, Ash Formation, and Deposition

To alleviate the global warming issue, various CO2 abatement technologies have been proposed. As one of the leading options for CO2 capture in power plants mostly firing coal and biomass, the oxyfuel combustion technology has been actively developed for decades. Progress at different stages of the development has been continuously updated in several reviews. However, they usually cover a wide range of topics, which vary significantly in detail. The ash issues are very critical to the design and operation of oxyfuel boilers, but may be one of the most controversial topics. The knowledge is widely scattered in different research articles, and a relatively comprehensive description is not available in the published reviews. Therefore, it is difficult for one to have a clearer picture of this important topic. The present review attempts to provide a more complete understanding. It pays particular attention to experimental data, because they are the basis for model development and full-scale simulation. Different from previous reviews that presented limited information on mineral matter transformation under oxyfuel conditions, this Review summarizes most of the related results reported in the open literature. Data on ash formation and deposition in oxyfuel combustion are also updated. They are organized according to different combustion technologies, i.e., oxyfuel pulverized fuel combustion (oxy-PFC) and oxyfuel fluidized bed combustion (oxy-FBC). By correlating between the three aspects, an in-depth understanding of ash issues in oxyfuel combustion may be achieved. At the end of this Review, key messages regarding mineral matter transformation, ash formation and deposition in oxyfuel combustion, and future research needs are presented.