Effects of CO2 and CO on the reduction of NO over calcined limestone or char in oxy-fuel fluidised bed combustion

To reveal the effects of CO2 and CO on the reduction of NO in oxy-fuel fluidised bed combustion, NO-CO reduction catalysed by calcined limestone and NO-char reduction were studied in a suspension-bed reactor under CO2 or N-2 atmosphere with the CO concentration varied from 0.28 to 1.88%. Results showed that the calcined limestone is an effective catalyst for NO-CO reduction. The activation energy of NO-CO reduction over calcined limestone was 157-164 kJ/mol at low temperature (600-800 degrees C) and decreased to 58.7-102.1 kJ/mol at high temperature (800-100 degrees C). In CO2 atmosphere, the NO conversion ratio was nearly zero during the NO-CO reduction process, and for NO-char reduction, the NO conversion ratio in CO2 was lower than that in N-2. However, CO showed promotion effect on NO reduction. In NO-CO reduction process, as the CO concentration increased from 0.28% to 1.88%, the NO reduction ratio increased from 0.40 to 0.75. For NO-char reduction in N-2, the NO conversion ratio was obviously higher when 1% CO was introduced, and the promotion effect of CO became weaker as the temperature increased. Moreover, the promoting effect of CO was inhibited in CO2 atmosphere.