Correlation of Sub-micrometer Ash Formation from Pulverized Biomass Combustion with Ash Composition

The present work investigated the relationship of sub-micrometer ash (inorganic particulate matter with an aerodynamic diameter of <1 mu m, PM1) formation from pulverized biomass combustion with fuel ash composition. PM, 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 PM, 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 PM, 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.