Potassium transfer characteristics during co-combustion of rice straw and coal

Abstract

Co-combustion experiments of rice straw with K, Si-riched rice straw and coal were conducted in a horizontal tube furnace at 600–1000°C. Potassium migration and transformation during co-combustion was investigated via analysis of combustion products by Inductively Coupled Plasma (ICP), X-ray powder diffraction (XRD), Scanning Electron Microscope (SEM) and thermodynamic calculation software respectively. Results indicated that high temperature improved the release of K to the gaseous phase and promoted the generation of insoluble K compounds in the bottom ash. K in the rice straw mainly formed KCl, K2SiO3, while in both coal combustion and co-combustion was in the form of aluminosilicate. At 1000°C, a serious melting phenomenon was observed in ash of rice straw, bringing a decrease of K release while co-combustion could relieve this condition via increasing the melting temperature of ash effectively. The primary chemistry reaction during the co-combustion was Al migrated from coal ash to rice straw ash, forming relatively steady and high-melting point potassium aluminosilicate rather than potassium sulfate reported before. Furthermore, KCl(g) and K2CO3 were important predecessors to form K2SO4 and K2SiO3 in combustion by theory analysis.