A pyrometric method was used for simultaneous in situ measurement of the temperature and size of individual coal particles in a pressurized entrained flow reactor. Several series of measurements were made in the gas temperature range 1150−1270 K to study the effects of pressure (0.2−1.0 MPa) and oxygen volume fraction (3−30 vol %) on the particle temperature and size distributions and on the mean degree of burnoff at well-defined residence times. The fuels used in the experiments varied strongly in their reactivity: lignite from France (Gardanne), high-volatile bituminous (hvb) coals from Germany (Westerholt, Göttelborn) and Poland (mixture), and anthracite from Germany (Niederberg). Milled fuel was sieved into nominal-size fractions in the range from 75 to 180 μm. The strongest increase in combustion rate at increased pressure occurred for anthracite, which was the least reactive among the fuels studied. This is shown by increasing the mass-loss rate and increasing particle temperatures. Pressure had no effect on the combustion of the lignite sample, the most reactive fuel studied. Some evidence of swelling of hvb coal particles was observed during the early stages of combustion. The particle size remained roughly unchanged until the degree of burnoff exceeded 90%, whereafter the particle size started to decrease due to fragmentation. Experimental results from particle temperature measurements at various oxygen concentrations are compared with literature data. Results from in situ particle measurements including size and temperature recording have not been presented previously at elevated pressures for such a wide range of coals. Measurements on combustion rates, particle temperatures and particle sizes were analyzed with a single-particle combustion model. The effect of pressure on the surface reaction kinetics for an anthracite was found to be small compared to the oxygen content and temperature.
- solid fuels