Impact of Selective Oxygen Injection on NO, LOI, and Flame Luminosity in a Fine Particle, Swirl-Stabilized Wood Flame

摘要

Wood biomass is a renewable, carbon dioxide neutral fuel that has no sulfur and mercury emissions. Co-firing of wood biomass with coal allows the benefits of large scale high efficiency power plants to be obtained without the need for a continuous supply of fuel. One issue with wood as a fuel however, is that biomass particles are typically ground to a larger size than coal particles and can therefore produce poor burnout and elongated flames. Changes in flame shape and burnout alter the heat flux profile of a boiler making intermittent use of biomass more problematic. This paper investigates the use of strategic oxygen enrichment to reduce flame length and improve particle burnout. Measurements of exhaust NO, loss on ignition (LOI) and natural flame luminosity were obtained from a 150 kW, down-fired burner with oxygen enrichment. The fuel burned was a finely ground (224 μm) hardwood. Flame images were obtained with a calibrated RGB digital camera allowing a calculation of visible radiative heat flux. The results showed that oxygen can be both beneficial and detrimental to the flame length depending on the momentum of the oxygen jet. Generally, the addition of oxygen increased emissions of NO but had little impact on LOI. Flame images suggest a small amount of oxygen can be used to stabilize the flame and increase devolitilization rates from the biomass with only minor increases to NO.