Improvement of ash flow properties of low-rank coal for entrained flow gasifier

Abstract

In order to meet the demand of slagging for entrained flow gasifier, addition of refractory agent kaolinite and coal with high SiO2 and Al2O3 contents was applied to improve ash flow properties of low-rank coal including fusion temperature and viscosity. The FACTsage software package was used to predict proportion of solid phase and minerals as a function of temperature. X-ray diffraction (XRD) analysis was carried out to identify the major crystalline phases in ash. The results show that the variation of ash fusion temperatures (AFTs) with addition of kaolinite is similar to that with addition of coal with high SiO2 and Al2O3 contents. It first decreases with increasing amount of kaolinite addition and coal with high SiO2 and Al2O3 contents, and then decreases and reaches a minimum value before increasing again. The location of ash composition in pseudoternary phase diagram and mineral changes in ash can be used to explain the variation of ash fusion temperatures of low-rank coal with addition of kaolinite or coal with high SiO2 and Al2O3 contents. Viscosity of slag also increases with increasing additions of kaolinite and coal with high SiO2 and Al2O3 contents. The sensitivity of slag viscosity to temperature excursion decreases with increasing of kaolinite addition and coal with high SiO2 and Al2O3 contents, because the sensitivity of the SiO2–Al2O3–‘FeO’–CaO–MgO system to temperature excursions decreases with increasing kaolinite addition and coal with high SiO2 and Al2O3 contents. Meanwhile, coal blending method has a larger tapping temperature range and shows a better effect on improving ash flow properties for entrained flow gasifier.