Soot Volume Fractions in Volatile Matter Envelope Flames of Bituminous Coal Particles in Air and Oxy-Fuel Combustion

This work calculated volume fractions of soot in volatile matter envelope flames which form around burning single particles of bituminous coal. Both conventional combustion in air and simulated oxy-fuel combustion, with oxygen mole fractions in the range of 20–40% in CO₂, were studied. Particles of 75–90 μm were injected in a bench-scale, transparent drop-tube furnace (DTF), at wall temperatures of 1400K. Upon ignition, optical pyrometry and high-speed photography were implemented to optically diagnose the burning particles. The method of Timothy et al[1] was applied to determine the instantaneous spatially-average soot volume fraction in these envelop flames. Results showed that soot shell forming around the particle was thicker and more luminous in air than the shell forming at the same O₂ concentration in CO₂. The soot volume fraction was decreased when N₂ in air was replaced by CO₂. Average soot volume fraction in the envelope flames in air was in the order of 7×10⁻⁵, whereas it was in the range 3.5×10⁻⁵ – 5.0×10⁻⁵ in oxy-fuel atmospheres.