Gas composition during thermochemical conversion of dry solid fuels and waste-derived slurries

Abstract

Coal has long remained a promising and widely used energy resource all over the world. Special emphasis is usually put on the research and development of environmentally friendly technologies for the use of coal and coal processing waste. The development of slurry fuels based on coal waste is one of the promising ways to use raw materials with energy potential, recover wastes, and reduce the environmental load. However, no combustion technology has yet been created for heterogeneous wastes as water-based slurries. The physical principles and parameters of the corresponding processes have not been studied adequately. In this research, the environmental combustion indicators (CO₂, CO, H₂, NO_x, and SO₂ concentrations) of slurries based on water and petrochemical, coal, and plant wastes were analyzed for the first time in a wide range of temperatures covering all the typical stages of thermochemical fuel conversion: pyrolysis (400-700 °C), gasification (700-900 °C), and combustion (700-1000 °C). We established the key patterns and aspects of changes in gas concentrations at all the main stages during the thermal decomposition of fuels. The use of water-based fuels at the pyrolysis stage was notable for up to 96% higher concentrations of the key combustible gases (CO, H₂). The temperature extrema were 50-100 °C lower than those of bituminous coal. In terms of the key anthropogenic emissions (CO₂, NO_x, and SO₂), the combustion of slurries also appeared to be 20-77% more environmentally friendly than that of coal depending on the temperature conditions and fuel composition. The maximum positive effect from adding biomass to coal-water slurries was achieved in the temperature range of 850 to 1000 °C. The research findings can be used for developing the technologies for thermal recovery of waste as water slurries, in particular, by intensifying the pyrolysis, gasification, and combustion.

Keywords: Anthropogenic emission; Coal-water slurry; Combustion; Flue gases; Gasification; Pyrolysis.