Abstract
Volatilization of alkali and alkaline earth metallic (AAEM) species during pyrolysis of pulverized biomass was investigated. Pine sawdust and sugarcane bagasse were pyrolyzed in a wire-mesh reactor, in which the secondary reactions of nascent volatiles were successfully minimized in the gas phase and over the surface of nascent char by forcing flow of He to pass through the monolayer of biomass particles being heated at a rate of 1 or 1000 K s-1 up to peak temperature of 573-1173 K. Upon heating the sawdust, AAEM species were released from the nascent char after completion of Cl release and evolution of tar and lighter volatiles. While heated at 1000 K s-1 from 823 up to 1173 K, the nascent char released Ca and Mg as extensively as K and Na with their losses of 20-25%. Release of AAEM species continued during further heating at 1173 K, which caused total losses of K and Na over 99% while those of Ca and Mg as high as 40-60% within a period of 100 s. In contrast to these results, no significant release of AAEM species were allowed during the pyrolysis in a fixed-bed reactor, in which no forced flow of the carrier gas was available through the fixed-bed of char particles. Repeated release of AAEM species and their readsorption onto the char surface thus suppressed or even inhibited the net volatilization. Based on the combined effects of the heating rate, peak temperature and holding time at the peak temperature, it was concluded that AAEM species were released from the char mainly as elemental species rather than hydroxides and chlorides.
