Emissions of nitrogen oxides in pulverized peat combustion between 730 and 900 °C

Five Finnish peats were burned in an entrained flow reactor at temperatures between 730 and 900 °C to study the conversion of peat nitrogen to nitrogen oxides (N₂O, NO and NO₂) in conditions simulating low-temperature, unstaged pulverized fuel combustion. Oxygen content was varied between 1 and 18 %. The major product was NO (conversion of fuel-N to NO varied between 10 and 43%), but the concentration of N₂O was high at low temperatures and at 730 °C the degree of conversion of fuel-N to N₂O sometimes exceeded that of fuel-N to NO. Unlike NO, the formation of N₂O was not sensitive to oxygen content of the reaction environment, and it decreased with increasing ratio in the peat. This led to marked differences in the molar concentrations of N₂O in the flue gas from different peats between 730 and 800 °C. Particle sizes in the range 16–205 μm and moisture contents of 5–20% had no observed effect on fuel nitrogen conversions. Conversion of fuel-N to NO₂ was < 1%.