Coal pyrolysis under varied atmospheres and temperatures in a moving-bed pyrolyzer for blue-coke production

To solve the prevailing problems in industrial blue-coke production such as the low utilization of coal and the low calorific value of product gas, a novel blue-coke production technology using slack coal has been proposed. The coarse coal in the feed is pyrolyzed in a moving-bed pyrolyzer with the gasification gas (G-gas) from the fluidized gasification of the fine coal as the heat carrier, so that high-quality blue-coke, tar and gas are obtained. To elucidate the effect of G-gas on pyrolysis, the coarse coal pyrolyses in a moving-bed pyrolyzer were investigated under steam, CO2 and G-gas atmospheres in the temperature range of 500–800 °C. Compared to N2 atmosphere, the steam increased the tar yield below 700 °C due to the enhanced water-gas shift reaction. The CO2 increased the tar yield around 600–700 °C because of the restrained decomposition of calcite in the coal. Above 600 °C, the coke's partial gasification under the reactive atmospheres led to increased gas yield and decreased coke yield; meanwhile, the specific surface area of the coke increased and the electrical resistivity decreased. The contribution of the reactive atmospheres was in the same order of their reactivities, i.e. steam > G-gas > CO2. •A novel blue-coke production technology using slack coal has been proposed.•Coal was pyrolyzed under reactive atmosphere in moving-bed pyrolyzer at 500–800 °C.•Steam enhanced tar yield at 500–700 °C by intensified water-gas shift reaction.•Reaction of coke with reactive atmospheres above 600 °C reduced its resistivity.