Characteristics of high temperature C-CO2 gasification reactivity of Victorian brown coal char and its blends with high ash fusion temperature bituminous coal

Abstract

This research paper explores the high temperature gasification reactivity of brown coal char and its potential for promoting the gasification of high-ash-fusion temperature bituminous coal under entrained-flow gasification conditions. Using thermogravimetric analysis (TGA), the C-CO2 gasification reactivity for a brown coal char and two bituminous coals with low/high ash contents and high ash fusion temperatures, as well as their blends were investigated over a temperature range of 900–1300°C and atmospheric pressure. The nth order reaction rate equations were fitted based on a random pore model of the gasification reaction. The results show that the brown coal char has a high reactivity compared to the two bituminous coals, which mainly due to its more porous physical structure, whereas the catalytic effect of its ash-forming elements is insignificant above 1100°C. The intrinsic activation energy was determined to be 154.5kJ/mol for the brown coal char, which is lower than the higher activation energy of the two bituminous coals of 189.61kJ/mol and 196.02kJ/mol. Upon increasing the bituminous coal fraction, the activation energy increases stably due to the increased ash amount and increased molten ash that inhibit the gas diffusion. For the low-ash bituminous coal blended with 20–40% brown coal char, its C-CO2 reactivity is maximised at 1200°C when the ash turns soft. Upon further increase of the temperature, its reactivity decreases due to the enhanced melting of the ash. Instead, for the high-ash bituminous coal, its addition of 20% to brown coal char is beneficial in decreasing the overall ash melting temperature. The C-CO2 gasification reactivity of 20% high-ash bituminous coal blended with brown coal char is maximised at 1100°C when the ash turns soft and is minimised at 1200°C when the ash is fully molten.