Characteristics of ammonia oxidation and NO_x emission in a bubbling fluidised bed: Part 1: Effect of operating conditions

This study investigates ammonia (NH₃) oxidation behaviour and NO _x emission in a laboratory-scale bubbling fluidised bed (BFB) reactor, focusing on the effect of operating conditions, namely, fluidisation number ( FN , 0.5–1.9), static bed depth ( BD , 0–63 mm), temperature (750–1050 °C) and equivalence ratio ( Φ , 0.65–1.15). NH₃ conversion was determined from the measured concentrations of N₂, O₂, NH₃(g) and H₂ in the flue gas, while NO _x and N₂O emissions were evaluated by measuring the NO, NO₂ and N₂O concentrations. The observed trends in NH₃ conversion underscore the strong influence of gas–solid contact and gas residence time. Compared to the empty bed, adding a BD of 21 mm quartz particles as bed materials enhanced NH₃ conversion by 2.96 %–4.95 % when FN = 1.0. A greater BD of 63 mm further promoted NH₃ conversion. In contrast, NH₃ conversion increased initially with increasing FN , reached to a plateau at the incipient fluidisation ( FN = 1.0), but decreased afterwards with a further increasing in FN to 1.9. Moreover, NH₃ conversion was found to be promoted significantly by increasing temperature and decreasing Φ , achieving a near-complete conversion at 1050°C and Φ = 0.65. As for NO _x emissions, while NO₂ was not found under all experimental conditions, NO dominated at 750 °C (510 ppm, empty bed), and was effectively eliminated via selective non-catalytic reduction at 850–950 °C, but rebounding at 1050 °C (273 ppm) due to thermal NO formation. With fluidised quartz, NO emissions reduced significantly to 10–20 ppm, which was 10 times lower than the empty bed conditions. While fuel-lean conditions promoted NO formation, fuel-rich conditions ( Φ = 1.15) enhanced NO reduction at the expense of increased NH₃ slip. N₂O, comparably, was only found at 750 °C under empty bed condition.