Investigation on Ash Fusion and Slagging Properties of Coal under Reducing Atmosphere

ABSTRACT

Liquid slag tapping at low operation temperature is a major challenge for the application of entrained-flow slagging gasifier. To obtain and elucidate a regulation on stable liquid slag tapping, the SiO₂-Al₂O₃-(CaO+MgO+Na₂O+K₂O)-Fe₂O₃ phase diagrams of ash fusion temperatures as well as the ash viscosity and components were studied with ash fusibility apparatus, high-temperature viscometer, SEM-EDS and FactSage software. Meanwhile, the potential slagging properties were analyzed by the difference between soften temperature and deformation temperature (DSI), base/acid ratio (B/A) and slag viscosity index G. Results indicated that the contours of fluid temperature (FT) in the SiO₂-Al₂O₃-(CaO+MgO+Na₂O+K₂O) pseudo-ternary diagrams presented inverted V-shaped distribution. Attributing to the positive effect of Al₂O₃ and the downward parabola effect of SiO₂, the FT first decreased and then increased with the increased SiO₂/Al₂O₃ at the minimum value of around 3.25. Also, with the increase of (SiO₂+ Al₂O₃+ CaO+MgO+Na₂O+K₂O)/Fe₂O_3, the FT showed a V-type distribution with a minimum value at 94:6, yet the effect of Fe₂O₃ was slight. Besides, high content of CaO+MgO+Na₂O+K₂O effectively reduced the FT, which favored the formation of molten slag and operation economy; but it shortened the DSI, disadvantaging the formation of long slag and the operation stability. Moreover, decreased ratio of (CaO+MgO)/(Na₂O+K₂O) not only reduced the FT, but also enlarged the DSI. Finally, a regulation method concerning stable liquid slag tapping at low operation temperature based on ash fusion and slagging properties was proposed: adjusting SiO₂/Al₂O₃ to 3.25 and the mass ratio of Fe₂O₃ nearby 6.0 wt.%, and doping CaO+MgO+Na₂O+K₂O with low (CaO+MgO)/(Na₂O+K₂O) ratio could effectively reduce the FT and viscosity and enlarge the DSI simultaneously, and vice versa.

KEYWORDS:

• Coal ash
• fluid temperature (FT)
• viscosity
• slag
• phase diagrams

Additional information

Funding

This work was supported by National Natural Science Foundation of China (Grant No. 51776161).