LABORATORY STUDY OF N2O FORMATION FROM BURNING - CHAR PARTICLES AT FBC CONDITIONS

Coal combustion in fluidized bed combuster is a cause of nitrous oxide emissions to the atmosphere. The formation of N2O seems to be related both to homogeneous and heterogeneous reactions taking place in the c ombustion process. The purpose of this investigation was to study the formation of N2O from burning char particles under different combustio n conditions. The experiments were carried out in a fixed bed reactor containing quartz sand (SiO2) to support the coal particles. A monolay er of bituminous coal particles between two layers of quartz sand was devolatilized prior to the actual combustion in an argon flow. The coa l particle sizes were varied between 0.090 and 2.80 mm. The inlet gas mixture contained NO, O-2, and Ar or just O-2 and Ar; The oxygen conce ntration was varied between 0.5 and 20% O-2 and the NO concentration w as varied between 0 and 1000 ppm NO. The inlet gas flow was varied bet ween 590 and 1581 mL/ min NTP (273 K, 1 atm) and the bed temperature w as varied between 1023 and 1123 K. The off-gases were analyzed for N2O , NO, CO, and CO2. Addition of NO to the flue gas increased the N2O yi eld. A low combustion temperature also favors high yields of N2O. A gr eat influence of the oxygen concentration was found (high oxygen conce ntrations give low N2O yields), which indicates that the combustion co nditions are very important for the N2O yield. A particle size of 1 mm gives the highest N2O yields.