SLAGGING CHARACTERISTICS OF AUSTRALIAN BROWN COAL ASHES

摘要

The behaviour of coal mineral matter must be considered when matching coals to the most appropriate gasification technology. While non-slagging gasifiers require coal processing at temperatures below ash melting or ash softening, slagging gasifiers require the mineral matter to melt and flow with a viscosity suitable for steady slag tapping. Some entrained-flow gasifiers also require the slag to form a protective layer in the water-cooled wall of the gasification chamber, which sets a minimum ash content for the feed coal.rnThe mineral matter composition of Australian brown coals is highly variable and covers a wide range of compositions in the Si-Al-Fe-Ca-Mg-O system. In this work, we investigate the slagging characteristics (e.g. phase compositions and viscosity) of typical brown coal ashes from Latrobe Valley in Victoria, Australia.rnSlag compositions were calculated using thermodynamic modelling tools and confirmed experimentally by analysis of quenched slags. Experimental slag viscosity data were obtained from 1200–1650℃. The liquid phase appearance in the low-temperature slagging region (900–1100℃) strongly depends on the slag’s chemical composition and the primary phase field, but is not directly related to ash fusion temperatures. High-silica slags typically have Newtonian slag flow behaviour and high viscosity, which may require fluxing to reduce viscosity and make them suitable for use in entrained-flow gasification (5–25 Pa·s). High iron–magnesium and high aluminium slags have low viscosities at high temperatures (above 1500℃), although the slag flow has non-Newtonian behaviour over the entire investigated temperature range. These slags need to be blended with other coals for use in entrained-flow installations.