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

Co-combustion experiments of rice straw with K, Si-riched rice straw and coal were conducted in a horizontal tube furnace at 600-1000 degrees 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. Kin the rice straw mainly formed KCl, K2SiO3, while in both coal combustion and co-combustion" was in the form of aluminosilicate. At 1000 degrees 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. (C) 2017 Elsevier Ltd. All rights reserved.