Role of CO2and H2O on NO Formation during Biomass Char Oxidation

Abstract

We have investigated how CO2 and H2O influence NO release rates during char oxidation of biomass. In addition, the role of catalytic elements in these processes has been studied. NO release rates were determined from single-particle experiments of softwood and straw at 900 °C, in CO2/O2 (34/3%) and H2O/O2 (17/3%), with N2 as the balance gas. The NO release profiles differed in CO2/O2 and H2O/O2. In CO2/O2, the NO release increased as the char conversion proceeded. On the other hand, in H2O/O2, the NO release decreased as the char conversion proceeded. In neither of these cases, the conversion rates of char-N to NO were proportional to the conversion rates of char-C. To investigate how the ash-forming matter influenced the NO release rates, the biomasses were demineralized and the experiments were repeated. For the chars of the demineralized biomasses, the NO release profiles were almost identical in CO2/O2 and H2O/O2. In addition, for the demineralized chars, the conversion rates of char-N to NO were proportional to the conversion rates of char-C. The conversions of char-N to NO were significantly higher for the demineralized chars. For softwood, the total conversion of char-N to NO was as high as 85%. These results show that (i) CO2 and H2O influence the formation of char-N to NO in different ways and (ii) the ash-forming matter contributes to the differences in the NO release rates.