Ash Fusion Properties and Mineral Transformation Behavior of Gasified Semichar at High Temperature under Oxidizing Atmosphere

Abstract

The carbon conversion of fluidized bed gasification has been restricted by the entrainment of semichars with high carbon content. Recently, the disposal of the semichar has become an intractable problem. In this study, the ash fusion properties and mineral transformation behavior at high temperature of the semichar from an industrial circulating fluidized bed (CFB) gasifier were investigated under oxidizing condition. In comparison to the raw coal, the total base content increases from 27.92 to 29.45 after partial gasification, which results in a decrease in the ash fusion temperatures (AFTs) of the semichar. Kaolinite decomposed into quartz, alumina, and water via dihydroxylation reaction and anhydrite was transformed into oldhamite in the CFB gasifier. As the particle size increases, the AFTs of the semichar decrease first and then remain almost unchanged, which coincides with the variations in acid-to-base ratio; however, the disparity is relatively small, which favors its melting utilization. Quartz, anorthite, pyroxene, and hematite are the main crystalline phases of the semichar ash at high temperature, and the major molten phase turns out to be anorthite. The liquidus temperature (1325 °C) predicted by FactSage is slightly higher than the flow temperature (1310 °C) of the semichar ash due to kinetic limits and mass transfer. In situ observation of the semichar ash melting process indicates that low-melting-point minerals first fuse and flow between the adjacent particles; as the temperature increases, high-melting-point minerals then start to melt, the molten-phase content increases, and the flow behavior accelerates.

Transformation of alkali and alkaline earth metals during the preparation of activated carbon from Zhundong high-alkali coal

“…The thermodynamic equilibrium calculations, based on the principle of minimisation of the Gibbs free energy, were performed using FactSage (version 7.3) soware. 18,19 FactSage with FToxide and FactPS was used to simulate the evolutionary behaviours of the AAEM species during the preparation of AC under different conditions as described in this paper. The calculated system was elaborately dened based on the XRF analyses of ash, and the required data for the thermodynamic equilibrium calculations included: Al, C, Ca, Cl, H, K, Mg, N, Na, O, S, and Si.…”

Study on Char-Ash-Slag-Liquid Transition and Its Effect on Char Reactivity

“…Currently, the research on the influence of ash on gasification mainly focuses on the ash fusibility − and mineral matter transformation. − In order to investigate the effect of ash melting on the reactivity of gasification, most literatures have treated raw coal by acid-washing. Sharma et al adopted the method with a solid–liquid ratio of 1:15 to conduct acid-washing, and the content of demineralized ash was 0.1 wt %.…”

Synergistic effect of CaO and MgO addition on coal ash fusibility in a reducing atmosphere

“…Therefore, alkali earth metals, such as Ca‐ or Mg‐bearing compounds (oxide or carbonate), are usually selected as additives in commercial gasifiers because of their low cost and abundance. Many researchers have investigated the effect of Ca‐ or Mg‐bearing compound addition on the ash fusibility at high temperature and built a relationship between the content of the Ca‐ or Mg‐bearing compounds added and the ash FT . An increase in the content of CaO causes an initial decrease in the ash FT and a subsequent increase .…”