Effect of potassium-containing sulfates on high-temperature mineral transformation and coal ash fusibility

Abstract

ABSTRACT Potassium-containing sulfates are important species that aggravates fouling and slagging in coal and biomass co-combustion plants. K2SO4, K2S2O7, and K3Fe(SO4)3 were added to coal ash to study the effects of potassium-containing sulfates on coal ash fusibility and mineral transformation at high temperature. Ash Fusion Temperatures (AFTs) of ash samples were tested. Mineral transformation was analyzed by X-Ray Diffraction (XRD) spectra and was simulated by thermodynamic equilibrium calculation. AFTs test results showed that when potassium-containing sulfate content increased by 5%, AFTs dropped by 10°C approximately. XRD analyses illustrated that at 1000°C-1200°C, potassium-containing sulfates reacted with quartz, corundum to form aluminosilicate. K was firstly present in microcline and transformed into leucite kalsilite as K content increased. Thermodynamic simulations showed that when K2SO4 content increased, microcline and leucite content increased rapidly while quartz, corundum, and kyanite content gradually decreased. The low melting temperature and eutectic effect of potassium-containing minerals lead to a significant decrease in AFTs. This work can provide guidance for coal and biomass co-combustion plants to regulate blended ratio of biomass so as to prevent fouling and slagging resulted from potassium-containing sulfates.