Ash transformation and slagging behaviour during combustion of sorghum residues

To unlock the potentials of biomass as a renewable energy source, one of the biggest challenges to be overcome is associated with ash fusion. In this study, the ash transformation and slagging characteristics of treated and untreated sorghum residues (straw), in two particle sizes, were investigated through experiments, fuel and ash analysis methods, as well as thermodynamic equilibrium and viscosity calculations. Except calcium for which its fuel ash content increased by more than 70% by water-leaching, contents of other ash-forming elements reduced to varying percentages by leaching, with concentration of potassium being reduced to 89 and 83%, in leached fractions of size 5 mm and size 2 mm, respectively. Aluminum, magnesium, potassium and phosphorus contents varied from 41.60 to 175.00; 554.00 to 2040.00, 640.00 to 7270.00 ad 451.00 to 1900.00 mg/kg TS, respectively, with higher proportion obtained in the unleached fractions (SR5 and SR2). At all temperature ranges, the viscosities of unleached fractions were lower than the leached fraction. The results also indicated that 2 mm fractions produced higher predicted quartz phases (more silica enriched phase) than 5 mm fractions. The findings of this study showed that leaching and sieving pretreatment of the sorghum waste can contribute to the improvement of the ash-melting behavior of the biomass, and thus reduce slag formation especially at higher conversion temperatures.