Primary Release of Alkali and Alkaline Earth Metallic Species during the Pyrolysis of Pulverized Biomass

Abstract

Release of alkali and alkaline earth metallic (AAEM) species was examined during pyrolysis of pulverized pine and sugarcane bagasse. The use of a wire-mesh reactor enabled the investigation of the primary release of AAEM species from pyrolyzing particles suppressing secondary interaction between them. Upon heating the pine at 1000 °C s-1 up to 800 °C, 15−20% of each AAEM species was released during the tar evolution and afterward. Further isothermal heating caused nearly complete release of alkalis within 150 s, while the release of alkaline earths terminated at levels of 20−40%. Heating the pine at 1 °C s-1 up to 800 °C brought about the release of AAEM species mainly after the tar evolution. Chlorides of AAEM species were found to be very minor volatiles over the range of conditions. Variations in K release with operating variables were reasonably explained by considering that elemental K volatilized from the char-bonded AAEM species was a major volatile K species. None of AAEM species were significantly released when a fixed bed of the pine was heated at 1 °C s-1 up to 900 °C without forced gas flow through the bed. It was suggested that repeated desorption from and adsorption onto the char surface within the fixed bed inhibited the release of AAEM species from the fixed bed and resultantly allowed them to transform into thermally stable char-bonded ones and/or nonvolatiles such as silicates.