The synergy of CaO/MgO flux on ash fusion behaviors for high-silicon-aluminum coal

The ash fusion behaviors are widely used for coal gasifier selection and operation condition setting. In this work, the synergy effect caused by CaO/MgO (C/M) ratio on ash fusion behaviors was investigated. The results showed that the ash fusion temperature (AFT) exhibited a "V" shape with increasing C/M ratio for high-silicon-aluminum coal. Meanwhile, the ash with the lowest FT (1278 degrees C) and a higher polymerization degree was obtained when C/M ratio was 6/9, which suggested that the synergy between CaO and MgO was closely related to their ratio. The most of Ca element existed in anorthite, while Mg tended to occur in magnesium cordierite. The low-melting eutectic between cordierite and anorthite occurred when the M-(Cordierites)/M-(Anorthite) was 1.12 and resulted in a synergy effect on AFT, which was supported by the mineral composition and liquid mass fraction diagram. In addition, the calculated R-value (R = (Q(0) + Q(1))/(Q(2) + Q(3))) presented an opposite relationship with the AFT curve. This indicated that the synergy effect was related to the aluminosilicate structure, resulting in the change from Si-O-Si bonds to weak Si-O-N (N: Ca2+ or Mg2+). Meanwhile, the synergy was believed to accelerate the fusion process due to the reduction in the fusion range.