COAL PARTICLE FLOW PATTERNS FOR O2 ENRICHED, LOW NOx BURNERS

The year-end report summarizes the results of the series of experiments conducted to evaluate the effects of oxygen partial pressure on coal combustion. Specifically, the effects of oxygen partial pressure in the transport air stream on flame stability, flame standoff distance and overall NO{sub x} emissions were examined. A series of experiments were conducted to determine the effect of oxygen partial pressure in the transport air on flame stability and resultant NO{sub x} emissions. In summary, the oxygen partial pressure experiments revealed that: (1) Increasing oxygen partial pressure in the transport air stream produced stable attached flames that were otherwise detached, reducing NO{sub x} emissions due to formation of fuel-rich central core which favors reduction of fuel nitrogen to N{sub 2}. Flame attachment also prevents premixing of fuel and air. (2) The degree of oxygen enrichment necessary to produce attached flames decreased with increasing wall temperature. (3) Increasing oxygen partial pressure in the transport air stream had little effect on emissions for always-attached and always-detached flames. The lack of an effect for always-detached flames is attributed to the extensive pre-mixing that occurs prior to ignition and the limited impact oxygen enrichment of the small transport air stream has on the oxygen concentration of the premixed transport and combustion air streams. (4) Reducing the oxygen partial pressure through nitrogen dilution destabilizes flames leading to flame detachment or blowout. These destabilizing effects increase with decreasing furnace temperature. These results are consistent with published literature. (5) The temperature dependence of NO{sub x,i} for detached flames is approximately 3 times greater than for attached flames