Static model of coal pyrolysis in a circulating fluidised-bed reactor

Four different coals were investigated: two sub-bituminous, one bituminous and lignite, which were processed in the temperature range 750-950 °C. The heat for pyrolysis was generated by partial gasification of the char produced. Air was used as the gasifying medium with amounts of 0.6-1.5 m3/kg of coal, depending on the required gasification-temperature. Two sequential phenomena were taken into account: char gasification and coal devolatilisation in respect of temperature. The experimental data on carbon dioxide and monoxide concentrations in a LCV gas produced were used for the correlation of Boudouard's equilibrium and the data on carbon burn-off and final volatile matter content in char were used for the solid-products yield. The equations for the quasi-equilibrium state were developed and calculated values were compared with the measurements. The model takes into account the equations developed and the total energy-balance assuming the heat losses of the experimental system. The investigated coal throughput amounted to 200-300 kg/h depending on the coal properties. Process characteristics were discussed, namely: the effect of air/coal ratio on the pyrolysis temperature; char and gas yield, volatile matter and ash content in a char; as well as the gas calorific value.