Effect Of Synergy Between Calcium Oxide And Magnesium Oxide On Coal Ash Melting Characteristics

Three typical Chinese coals were selected to study that whether the CaO&MgO has the synergistic effect on improving the coal ash fusion characteristics (i.e., coal ash temperature, ash slag flowability) or not. Coal ash temperature determinator and ash slag detector were, respectively, used to test the ash fusion temperatures and ash slag flowability of samples which were added to different ratios of CaO, MgO, and CaO-mixed-MgO. X-ray diffraction (XRD) combined with FactSage software was used to study the calcium-magnesium synergist mechanism. To sum up, the following conclusions were obtained:1) There is calcium-magnesium synergistic effect exiting between CaO&MgO at the level of descending the ash fusion temperatures and different ratios for different coals. The fluxing effect of CaO-MgO flux is better than that single CaO or MgO flux when the additive is the same and CaO-MgO flux can cut down the fusion temperature by about50℃than that of single flux.2) When the synergistic effect does exit in the CaO-MgO flux, the experiments on improving ash slag flowability were carried out. The results showed that CaO-MgO flux can reduce the initiative flow temperature by about50℃than that of single flux when the additive is the same, meanwhile, the flow temperature range became narrower.3) The high-temperature ash mineral compositions were analyzed. Anorthite was generated to reduce the ash fusion temperatures when adding CaO flux; cordierite, forsterite were generated to reduce the ash fusion temperatures when adding MgO flux; a mount of forsterite, spinel, monticellite, merwinite, anorthite and other minerals reduced obviously the ash fusion temperatures when adding CaO-MgO flux which exited synergistic effect. The results showed consistency with the results of SiO2-Al2O3-CaO-MgO phase diagram. The phase diagram results showed that coal ash compositions lied by the binary or ternary eutectic point, which meaned that the coal ash fusion temperatures were lower than that of the temperatures of around areas’ after adding CaO-MgO flux.