Experimental study of the NOX reduction through the staged oxygen supply in the oxy-fuel combustion in a 30 kWth bubbling fluidized bed

Abstract

This paper presents a comprehensive experimental study of the NOX reduction through the staged injection of oxygen in the oxy-fuel combustion of lignite and wooden pellets in a 30kWth bubbling fluidized bed experimental facility. A number of experiments was performed examining the impact of relevant operational parameters on the efficiency of NOX reduction. Various secondary to primary oxygen ratios were selected while keeping the overall concentration of oxygen in dry flue gas the same for constant ratio of O2/CO2 concentration in fluidizing gas and for constant fluidized bed temperature. Besides that, the impact of the overall oxygen stoichiometry was studied.The results showed that oxygen staging can be used successfully to reduce NOX emissions. Within the experiments, the NOX reduction efficiency as high as 50% was achieved (compared to the operation without oxygen staging) for the ratio of secondary and primary oxygen 0.5 in case of lignite and 1 in case of wood combustion. The extensive staged injection of oxygen also caused a significant raise of the freeboard temperature. There, it was measured about 900 °C for the lignite combustion and 880 °C in the fluidized bed, and about 950 °C for the combustion of wood and 880 °C in the fluidized bed. Oxygen staging is a promising path to reduce NOX in the oxy-fuel combustion in bubbling fluidized beds or to provide convenient conditions for the application of non-selective catalytic reduction in the freeboard section of the fluidized bed facility.