Combustion Characteristics of Leached Biomass

Abstract

The simple leaching of straw, grass (e.g. switchgrass) and other types of biomass with water is shown to result in substantial improvements to the combustion behavior. Although the economic feasibility of leaching is case specific, leaching does extract large amounts of alkali metals and chlorine which improve the fouling, slagging, and burning characteristics of biomass fuels, especially grasses and straws. Increases in the fusion temperature of ash arise from extraction of alkali elements by leaching, and decreases are, in general, observed in the amount of volatile ash. Pilot combustion tests showed lower rates of fouling when burning leached rice straw compared to unleached fresh material. Pyrolysis rates obtained via dynamic thermogravimetric analysis are slower for leached materials, probably as a result of a reduction in catalytic effects due to alkali metal salts, although volatile matter emission is observed to terminate earlier under isothermal heating for leached compared to unleached fuel. For the highly refractory fuel--rice straw--improvements in the ignition and burning characteristics of single straws have been observed to accompany leaching, possibly as a result of lower chlorine activity in terminating free radical chain reactions.