Devolatilization of a single fuel particle in a fluidized bed under oxy-combustion conditions. Part A: Experimental results

Artikel i vetenskaplig tidskrift, 2015

Devolatilization of a single fuel particle and the related flame combustion were studied in a two-dimensional fluidized bed with a quartz wall, allowing visual observation of the conversion process. The aim was to evaluate the devolatilization behavior (ignition, flame temperature, flame life-time, devolatilization time) of different fuels (4 ranks of coal from lignite to anthracite and wood) when replacing O2/N2 by O2/CO2 in O2 volume concentrations from 0% to 40%, at a fixed bed temperature of 1088 K using 6 mm spherical fuel particles. The volatiles’ flame was recorded by a color video camera to analyze ignition and extinction. The flame temperature was estimated by two-color pyrometry. Two thermocouples were inserted in the fuel particle to measure the temperature at the center and near the surface. Homogeneous and heterogeneous ignition modes, times of devolatilization, and flame duration (flame-life) under different gas atmospheres were analyzed. Results indicate that the mode of ignition of bituminous coal, lignite coal and wood changes when N2 is replaced by CO2. The ignition-delay time is much longer, and the flame temperature is lower in the O2/CO2 atmosphere than in an O2/N2 atmosphere for all the tested fuels. The devolatilization time of the anthracite particle is almost unaffected by the surrounding atmosphere, while for the other fuels this time is generally longer in O2/CO2 than in O2/N2 at the same O2 concentration. The presence of a flame during the volatiles combustion did not accelerate the particle heating, not even at the highest O2 concentration tested (40 vol%), however, after the extinction of the flame, the rate of particle heating is significantly affected by the oxygen concentration.