Experimental investigation of physicochemical and slagging characteristics of inorganic constituents in ash residues from gasification of different herbaceous biomass

The physicochemical and slagging characteristics of inorganic constituents in ash residues from biomass gasification in a 25 kg/h lab-scale fixed-bed gasifier were experimentally investigated. The results indicated that among the studied ashes, the wheat straw ash (WSA) had the highest alkali and alkaline earth contents, followed by corn straw ash (CSA) and rice straw ash (RSA). Whilst, the chlorine content in the CSA (5.38 wt%) was higher than that of WSA (3.67 wt%) or RSA (3.26 wt%). Besides, the CSA presented the highest specific surface area of 86.98 m2/g, with the average pore size of 9.29 Å and pore volume of 0.162 cm3/g. But the WSA showed the lowest deformation temperature (938 °C) and could be completely melted at 1256 °C. These results indicated that ash melting and slagging behaviours were determined by alkali/alkaline earth content. The coexistence of arcanite and sylvite played important roles in promoting slag formation. The RSA particles were agglomerated with no obvious melting while an evident molten appearance with smooth surfaces on large aggregates of WSA was observed, coating with sylvite and potassium silicates. The formation and transformation of potassium containing minerals was regarded as the dominant reason for the slagging of herbaceous biomass ash.