In-situ analysis of the sintering behavior of coal ash and a phosphorus-rich biomass ash under gasification condition

The relatively high contents of some ash-forming elements (Na, K, Ca, Mg, P) in biomass ash can cause serious ash-related problems (deposition, slagging, corrosion, etc.) during the co-gasification of coal and biomass, influencing the stable operation of gasifier. The sintering behavior of Jincheng coal ash (JCA) and a phosphorus-rich Jatropha seed cake ash (JSCA) were investigated by in-situ heating stage microscopy, while the sintering mechanism was revealed by phase studies employing X-ray powder diffraction and thermodynamic modelling. Results indicated that the sintering temperature of blended ashes reached the minimum at the 20 wt% blending ratio of JSCA in the coal-biomass ash mixture. The high sintering temperatures of JCA and JSCA were due to the extensive mullite and quartz crystallization in the high acidic JCA system and the widespread formation of K–Ca phosphate and K–Mg phosphate in the high basic JSCA system, respectively. The transition of the phosphorus from fluxing effect to refractory effect on the sintering of ash mixture was identified at the 20 wt% blending ratio of JSCA. It was also found that the role of mullite and quartz decreased, while the role of anorthite, gehlenite, leucite, and calcium phosphate increased with increasing JSCA content, leading to the lowest sintering temperature. Finally, the variation trend of sintering temperatures against the JSCA additions was in accord with the change of the liquidus temperatures that was calculated by thermodynamic modelling. These observations can be used for the potential prediction of the ash sintering temperature in the coal-biomass gasifier.