Conversion of fuel-N into HCN and NH3 during the pyrolysis and gasification in steam:: A comparative study of coal and biomass

Conversion of fuel-N into HCN and NH3 during the pyrolysis and gasification of coal and biomass in steam were compared using fluidized-bed/fixed-bed and two-stage fluidized-bed/tubular reactors. During the pyrolysis and gasification of coal and biomass in steam, the thermal cracking of volatile-N was the main route for the formation of HCN while a small amount of HCN was formed from the breakdown of relatively unstable N-containing structures in char. Our results indicate that once the fuel-N in both biomass and coal is condensed/polymerized into the solid-phase char-N during the gasification in steam, the main nitrogen-containing gaseous product from char-N would be NH3. However, the thermal-cracking/reforming of volatile-N constitutes an additional important route of NH3 formation during the gasification of biomass (e.g., cane trash) in steam while this route is negligible for the gasification of coal. The selectivity of char-N toward HCN and NH3 is largely controlled by char-N stability and/or the availability of H and/or other radicals during the gasification of coal and biomass.