Experimental investigation of nitrogen species distribution in wood combustion and their influence on NOx reduction by combining air staging and ammonia injection

The formation of the nitrogen species HCN, NH3 (N-intermediates), and NO out of fuel-bound nitrogen has a major influence on NO chemistry. Experiments have been carried out on an entrained flow reactor with pulverized wood as fuel. Staged combustion establishes a fuel-rich primary zone, where both N-intermediates and NO exist. The introduction of NRP as the ratio of the N-intermediates to NO offers a parameter that describes the nitrogen distribution in the primary zone, whereas TFN describes the overall amount of nitrogen. Air staging is an effective method for NOx reduction; the main controlling parameter is the primary air ratio, which defines both NRP and TFN. In fuel-rich conditions, NRP exceeds 1; with increased oxygen availability and temperature, the N-intermediates are depleted and NO is formed (NRP < 1). Thus, the NRP can be increased by adding NH3. Conventional SNCR is strongly temperature-dependent; hence, with increased temperatures, the best operation point shifts to lower air ratios. A comb...