Effect of Coal Gangue Addition on the Migration and Transformation Pattern of K and Cl During Rice Straw Combustion

The addition of coal gangue (CG) helps to reduce pollutant emissions and slagging during biomass combustion. Potassium (K) and chlorine (Cl) are the key elements responsible for biomass slagging; however, the effect of CG addition on their conversion mechanism is unclear. To effectively reduce biomass combustion slagging problems, in this work, the effect of adding 10%, 20% and 30% CG on the migration and transformation patterns of K and Cl elements during rice straw combustion was investigated by tube furnace combustion tests and thermodynamic simulations. The results showed that with the increase of 30% CG addition ratio, the release of K from the ash was inhibited by 11.24%, the release of Cl was promoted by 24.8%. The increase in CG addition ratio enhanced the conversion of water-soluble K and ammonium acetate-soluble K to hydrochloric acid-soluble K, KCl to HCl, fixed the alkali metal K in the ash and promoted the release of Cl. When the CG addition ratio was increased to 20%, the gas-phase K release rate decreased significantly, and the components of CG, such as Al2O3 and SiO2, reacted with KCl and KOH to form stable alumino-silicate compounds through the process of silicification-alumino-silicification. With the addition of CG, K was fixed in ash as a high melting point of silica-aluminates KAlSi3O8. After 800 degrees C, a large amount of K entered the gas phase as KCl (g), which was mitigated by increasing the CG addition ratio. A CG addition rate of 20%-30% can maximize the utilization benefit of CG, which was important for reducing slagging in biomass combustion.