Experimental study on transformation of alkali and alkaline earth metals during biomass gasification

To gain an in-depth understanding of AAEMs (alkali and alkaline earth metals) transformation during biomass gasification, a fixed-bed reactor is built to simulate the CO2 gasification at 500–900 °C. The influences of biomass species, gasification temperature, and particle size are examined. The results show that the AAEMs release follow a sequence of candlenut wood > wheat straw > corn stalk. The alkali metals mainly appear as water-soluble inorganic salts and the contents are more than 80%. K mainly occurs as KCl and KClO4. At higher temperatures, K could combine with Al and Si to form K(AlSi3)O8. For candlenut wood, a bigger particle size is beneficial to the transformation of water-soluble K to organic K. For candlenut wood with centimeter-scale, K mainly occurs as organic K in the biochar during 600–700 °C. When the gasification is carried out at 700 °C, K concentrates at the center and its content is even higher than that on the outer surface. While for biochar samples obtained from gasification at 600 and 900 °C, the K content at the center is lower than that on the outer surface due to the continuous outward transformation of K from the central biochar.