Release and Transformation Pathways of Various K Species during Thermal Conversion of Agricultural Straw. Part 1: Devolatilization Stage

The serious K-induced ash problems during biomass thermal conversion are closely related to release and transformation behavior of K. The aim of this work is to explore contribution of different occurrence forms of K on K-release and transformation pathway among various K-species during devolatilization of agricultural straw. Devolatilization experiments under different heat treatment conditions (i.e. temperature, heating rate and atmosphere) were carried out using a fixed-bed apparatus, and occurrence forms of K in virgin sample and residual chars were quantitatively determined by sequential chemical fraction analysis combined with ICP-OES (inductively coupled plasma optical emission spectrometry). The unstable water-soluble and ion-exchangeable K in wheat straw accounted for about 89.3% of total K, and were mainly responsible for the K-release. Part of the unstable K were directly decomposed into atomic K or sublimated, and a large fraction of them were first bound to char matrix to form char-K and then...