The present work investigated the correlations of the particulate matter with an aerodynamic diameter of <1 μm (PM1) yield from pulverized coal combustion with coal and ash composition. PM1 yields from burning pulverized coals under similar conditions in laboratory reactors, together with analytical contents and ash composition of the parent coals, were collected from the literature to form a large database containing results of 75 coals. On this basis, linear regression analysis was employed to examine the correlations between the PM1 yield and the coal and particularly ash composition, using the Pearson correlation coefficient to denote the degree of correlation. The indexes evaluated include the volatile matter, ash, and sulfur contents of the coal, the contents and summed contents of oxides, and the ratios of the content or summed content of basic oxides to the summed content of acidic oxides of coal ash. PM1 yields were observed to have positive correlations with the contents and summed contents of basic oxides, except K2O, and all of the ratio indexes and negative correlations with the contents and summed contents of acidic oxides. The correlations and their degrees are strongly rank-dependent, with significant differences between lower rank (lignite and sub-bituminous) and higher rank (bituminous and anthracite) coals. Fairly good correlations exist with some combined indexes of ash composition, including Na2O + MgO, (Na2O + MgO)/(SiO2 + Al2O3) ratio, content ratio of all basic oxides to all acidic oxides (B/A ratio), and the linear combination of oxide contents. They are potentially applicable for estimating PM1 formation from pulverized coal combustion for practical purposes.

The present work investigated the relationship of sub-micrometer ash (inorganic particulate matter with an aerodynamic diameter of <1 μm, PM1) formation from pulverized biomass combustion with fuel ash composition. PM1 yields from burning pulverized biomasses under similar experimental conditions, together with ash composition of the parent fuels, were gathered from the literature. The correlations between the PM1 yield and the indexes related to ash composition were evaluated using linear regression analysis. Pulverized biomass combustion generates PM1 over a wide range from 0.2 up to 37% of the total ash mass, mostly comparable to burning lower rank coals. The yields from herbaceous biomasses are almost all <4%, with half of the samples <1%, significantly different from those of woody biomasses with all >1% and nearly half >5%. The PM1 yield was found to have rough linear trends of increasing with K2O, MgO, and CaO contents and decreasing with SiO2 content, similar to those for lower rank coals but with lower degrees of correlation. These correlations for herbaceous biomasses are much better, even better than those for lower rank coals, while those for woody biomasses are very poor. The difference is mainly attributed to the effects of ash-forming interactions between SiO2 and K2O, MgO, and CaO on sub-micrometer ash formation, which is dependent upon their contents in biomass ash. Using the sums of some acidic or basic oxide contents as indexes to correlate with the PM1 yield achieved slight improvements on the correlation quality over individual oxide contents. Much better correlations were obtained using multiple linear regression analysis to relate the PM1 yield with the linear combination of ash composition. The best correlations were achieved by separate regression for woody and herbaceous biomasses, which have potential for application to estimate the PM1 yield from pulverized biomass combustion based on ash composition.

The present work aims to model ash vaporization from a burning char particle during pulverized coal combustion in an oxygen-enriched O 2 /CO 2 atmosphere. The modeling development was to apply the classic ash vaporization model of Quann and Sarofim to cover oxy-coal combustion over a wide range of O 2 concentrations by coupling it with the double-film char burning submodel to properly describe the burning process of a single char particle. The model was extensively validated with literature data on the vaporization of SiO 2 , MgO, and CaO in both O 2 /N 2 and O 2 /CO 2 atmospheres. The model was proved to be able to predict the vaporization behavior of SiO 2 during char conversion stages in both atmospheres, covering the effects of coal type, particle size, and O 2 concentration. The model predicts the vaporization of MgO and CaO during char combustion of bituminous coal, but improvement is required to describe the vaporization of MgO and CaO during char combustion of lower-rank coals by considering the occurrence of Mg and Ca in the coals and their interactions with other included minerals at high temperatures. The model validations demonstrated the importance of considering CO homogeneous oxidation in the boundary layer to reasonably predict the char particle burning process and ash vaporization in both O 2 -enriched O 2 /N 2 and O 2 /CO 2 atmospheres.