To investigate the release and transformation of fuel K during air gasification of biomass, wheat straw, corn stalk and rice straw are gasified in a fixed-bed reactor system from 400 to 1000 Â°C. Weight measurement, elemental composition analysis, and chemical fractionation analysis are performed. The influences of release of Cl, fuel type and gasification temperature on the release of K are discussed. The results show that for all biomass fuels, the release ratio of K and Cl increases with gasification temperature. In the 400-600 Â°C interval, the release of K and Cl increases gently and sharply respectively, and the trend from 600 to 1000 Â°C is the opposite. From the release ratio of K and Cl together with the distribution ratio of water-soluble K, it can be concluded that part of water-soluble K transforms to gas phase in the form of KCl in the 600-1000 Â°C interval.