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.