Iron Transformation and Ash Fusibility during Coal Combustion in Air and O2/CO2 Medium

Abstract

Little work has been performed on the transformation of iron and ash fusibility during oxy-coal combustion, which is of great significance to assessing ash deposition propensity. A high-iron bituminous coal was burnt at 1300 °C in a laboratory drop-tube furnace under four conditions: (1) 21 vol % O2/79 vol % N2 (air-firing), (2) 21 vol % O2/79 vol % CO2 (oxy-firing), (3) 27 vol % O2/73 vol % CO2 (oxy-firing), and (4) 32 vol % O2/68 vol % CO2 (oxy-firing). The bulk ash samples were subjected to X-ray fluorescence and Mossbauer spectroscopic analyses. The effects of changing from air combustion to O2/CO2 combustion and the effects of varying the O2 level in O2/CO2 combustion on iron transformation and ash fusibility were investigated. The results show that varying the combustion condition has insignificant effects on the elemental composition of coal ashes but has appreciable effects on the relative proportions of iron combustion products that were identified as hematite, magnetite, and Fe–glass phases. Thi...