Regulation of Ash-fusion Behaviors for High Ash-fusion-temperature Coals in the Huainan & Huaibei Mining Area by Flux Addition

To produce coal with a high ash fusion temperature (AFT) as the raw material for gasification, the addition of fluxes is often adopted. In this paper, the ash chemistry of coals from the Huainan–Huaibei mining area (Zhuji and Taoyuan) was analysed to investigate the mechanisms of the composition modulation and, subsequently, the ash melting behaviour of coals with high-ash melting points in relation to non-pure matter fluxes. The chemical composition of the mixed ash was studied via X-ray powder diffractometry using normalised reference intensity ratio software, with the mineral transformation behaviour obtained using a scanning electron microscope analyser equipped with an energy-dispersive X-ray spectrometer and summarised using FactSage8.1 software analysis. For coals from Taoyuan and Zhuji, which have high silica–aluminium oxide content, the AFTs were significantly reduced when flux additions of 6% were used to meet the requirements of the entrained flow gasifier. To balance the gasification requirements and the controlled addition, the optimum addition level for the two high-ash-melting-point coals is 5–6%. The increase in flux addition leads to the conversion of high-melting-point mullite, sillimanite and quartz to amorphous materials, which reduces the corresponding AFTs, with the amorphous materials subsequently producing a liquid phase with a content that reflects the change in AFT.