Effects of CO ₂ and CO on the reduction of NO over calcined limestone or char in oxy‐fuel fluidised bed combustion

Abstract

To reveal the effects of CO 2 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 CO 2 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°C) and decreased to 58.7-102.1 kJ/mol at high temperature (800-100°C). In CO 2 atmosphere, the NO conversion ratio was nearly zero during the NO-CO reduction process, and for NO-char reduction, the NO conversion ratio in CO 2 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 CO 2 atmosphere.

Research on the Influence of Combustion Methods on NOx Emissions from Co-combustion of Various Tannery Wastes

“…The NO x concentration approached its peak level in a longer time when the tertiary gas volume flow increased from 0.2 to 0.8 L/min due to the increase of flue gas being obstructed . It took more time for the reduction of NO x with the char layer until the great mass of NO x was converted into N 2 Based on Figure b, the increase of NO x conversion was exaggerated inversely with increasing tertiary gas volume flow.…”

“…It took more time for the reduction of NO x with the char layer until the great mass of NO x was converted into N 2 Based on Figure b, the increase of NO x conversion was exaggerated inversely with increasing tertiary gas volume flow. On the one hand, the increase of air volume flow promoted the oxidation reaction; on the other hand, the increase of tertiary gas volume flow promoted the reduction of char.…”

“…In addition, during the decoupling combustion process, pyrolysis gas such as CO, H 2 , and CH 4 might be produced. With the reductive effect of char, NO x could also be reduced by CO, H 2 , and CH 4 as described in the reactions. , On the other hand, HCN was considered the dominant product during the decoupling combustion for CTBD and CS . It was estimated that the NO x reduction was undertaken from HCN, which, once formed, followed the reaction pathway as HCN + O → NCO + H → H 2 + N .…”

“…With the reductive effect of char, NO x could also be reduced by CO, H 2 , and CH 4 as described in the reactions. 34,35 CO NO CO N 2 2…”