Experimental study of SO2 and NOx emissions in fluidized bed oxy-fuel combustion

This paper studies the SO2 and NOx emissions from coal oxy-firing in bubbling fluidized bed combustors. The influence of bed temperature and excess oxygen is measured and discussed. The results are also compared with conventional air combustion, in order to determine whether oxy-firing contributes to increase emission levels. Two completely different coals, Central Europe bituminous and domestic Spanish high-sulfur lignite, have been tested in the CIRCE 90 kW fluidized bed combustor. Although literature data are scarce, a comparison with the findings of the research is fair. Good SO2 capture efficiencies have been reached, even for the lignite tests, pointing towards the direct sulphation of added sorbent-limestone as the dominant mechanism. As for the NOx emissions, significant coupled influences of oxygen and carbon monoxide concentrations are reported. Notwithstanding this, no relevant differences are observed between air- and oxy-firing if NOx emissions are normalized by energy unit. The paper provides clear insights into the effect of operating conditions of oxy-fuel fluidized beds upon SO2 and NOx emissions.