Radiative intensity, no emissions, and burnout for oxygen enriched biomass combustion

As concern over global climate change continues, the use of biomass as a substitute for coal is one method of reducing CO2 emissions. One of the primary problems with utilizing biomass in boilers originally designed to burn coal is burnout. Biomass particles cannot be economically ground to the fine particle size typical of coal particles, creating a problem for particle burnout. The impact of oxygen injection in a swirl-stabilized burner on particle burnout and NO emissions was investigated by measuring NO and LOI, as well as flame characteristics, including flame imaging, flame intensity, and flame temperature. The results showed that when a low momentum flow of pure (>99%) oxygen is introduced into the center of a swirl stabilized biomass flame, an inverted diffusion flame is produced with oxygen in the center and volatiles on the outside of the flame. This high intensity center flame is surrounded by a lower intensity turbulent air/volatiles flame. This high temperature inner flame can heat incoming particles more rapidly than a conventional air flame improving burnout and flame stabilization without increasing effluent NO as long as the center flame does not extend into and disturb the fuel rich recirculation zone. Oxygen injection can therefore be used to improve burnout without increasing NO formation.