Emission Control

The N in NOx can come from both the N containing fuel compounds (e.g. coal, biomass, animal waste) and from the N in the air. The NOx generated from fuel N is called fuel NOx, and NOx formed from the air is called thermal NOx. Typically, 75 % of NOx in boiler burners is from fuel N. The current technologies developed for reducing NOx include: combustion controls (e.g. staged combustion or low NOx burners LNB, reburn) and post combustion controls (e.g. Selective Non-Catalytic Reduction, SNCR using urea, etc.). In reburning, additional fuel (coal or natural or gas) is injected down stream from the primary combustion zone to create a fuel rich zone where NOx is reduced through reactions with hydrocarbons. The nitrogen in the reburn fuel then recombines with oxygen to form NOx, or combines with N to form N2. After the reburn zone, additional air is injected in the burnout zone to complete the combustion process.

The current reburning experiments use a premixed propane burner along with a small amounts of NH3 to simulate coal combustion gases, and to test coal and feedlot biomass as reburn fuels in order to determine their NOx reducing capability. The reburn fuel is fed from a dry solids feeder. The reburn injection ports are located below the tip of the premixed propane flame, after all of the NO has been formed in the primary zone. An Enerac 3000E gas analyzer is then used to measure the concentration of oxygen and NO in the final sampling port.