Laboratory and numerical experiments of coal pyrolysis in air and oxy-fuel combustion conditions

摘要

Laboratory experiments of the coal pyrolysis process were conducted in electrically heated drop-tube furnace. It enables to perform tests in conditions comparable to full-scale pulverised fuel combustion systems, i.e. at the temperatures, particle heating rates and residence times up to 1300°C, 10~4 K/s and 0.5 s, respectively. Behaviour of the two bituminous coals, during devolatilisation in air (100% N_2) and oxy-fuel (100% CO_2) atmosphere, temperature range 900-1300°C, particle size 63-90 μm and residence time 25-300 ms was investigated in laboratory and numerical experiments. An influence of the gaseous atmosphere on pyrolysis behaviour changes with the reaction temperature. The volatile matter loss in similar both in air and oxy-fuel atmosphere at 900°C, while at higher temperatures (1100-1300°C) yield is higher in CO_2 than N_2 by 5-20%_(wt). It is evident that the operating conditions (such as particle size, heating rate, final temperature and residence time) have a great impact on the coal behavior during pyrolysis in N_2 and CO_2 atmospheres. Analysis on the laboratory data were supported by CFD modelling of research stand. The coal devolatilisation in drop-tube furnace was in details modelled, and particle thermal histories and trajectories along the furnace were obtained. Advanced, hybrid analytical and CFD method provided kinetic constants, which allow for good predictions of the coal pyrolysis in N_2 and CO_2 atmospheres. The modification of the single first order rate devolatilisation model was proposed to improve the numerical predictions.