Comparison of pyrolysis test rigs for oxy-fuel conditions

In oxy-combustion, coal particles undergo devolatilization in CO2 enriched atmospheres. Besides the well-known influence of thermal conditions, the composition of the pyrolysis atmosphere may also have important effects on the formation and properties of pyrolysis products. In an international collaboration, researchers from three institutions from Aachen, Bochum and Naples carried out pyrolysis experiments with a medium rank coal in a fixed bed, fluidized bed and drop tube reactor, substituting N2 with CO2. The goal of the current study was to investigate the influence of increased CO2 concentrations on the pyrolysis products (tar, gas and solids) when different heating rates, temperature and residence times are applied. Pyrolysis products were analyzed by several techniques to highlight differences in structure and chemical composition. At low heating rates and temperature, the differences between N2 and CO2 pyrolysis products were marginal. A CO2 rich atmosphere, instead, impacted severely the properties of pyrolysis products under the fast heating-short residence time conditions typical of drop tube reactors. Upon prolonged exposure to severe treatment differences apparently leveled off.