Combustion Characteristics of Single Particles from Bituminous Coal and Pine Sawdust in O2/N2, O2/CO2, and O2/H2O Atmospheres

Burning fuels in an O2/H2O atmosphere is regarded as the next generation of oxy-fuel combustion for CO2 capture and storage (CCS). By combining oxy-fuel combustion and biomass utilization technology, CO2 emissions could be further reduced. Therefore, this work focuses on investigating the combustion characteristics of single particles from bituminous coal (BC) and pine sawdust (PS) in O2/N2, O2/CO2 and O2/H2O atmospheres at different O2 mole fractions (21%, 30%, and 40%). The experiments were carried out in a drop tube furnace (DTF), and a high-speed camera was used to record the combustion processes of fuel particles. The combustion temperatures were measured by a two-color method. The results reveal that the particles from BC and PS all ignite homogeneously. Replacing N2 by CO2 results in a longer ignition delay time and lower combustion temperatures. After substituting H2O for N2, the ignition delay time is shortened, which is mainly caused by the steam gasification reaction (C + H2O→ CO + H2) and steam shift reaction (CO + H2O→ CO2 + H2). In addition, the combustion temperatures are first decreased at low O2 mole fractions, and then increased at high O2 mole fractions because the oxidation effect of H2O performs a more important role than its volumetric heat capacity and thermal radiation capacity. At the same condition, particles from PS ignite earlier because of their higher reactivity, but the combustion temperatures are lower than those of BC, which is owing to their lower calorific values.