Formation of N-containing gas-phase species from char gasification in steam

The formation of N-containing products during char-steam gasification has been investigated in a laboratory scale fixed bed reactor. Experiments were conducted at 1000 °C, 0.1-1.0 MPa, and 6-46% of H₂O in He base flow. Two very different coal chars, which were prepared from the rapid heating of Australian bituminous and sub-bituminous coals, were studied. The nitrogen-containing products released during the gasification were measured using an FTIR spectrometer (NH₃, HCN and HNCO) and gas chromatography (N₂). The major N-containing products formed during char-steam gasification are NH₃, HCN and N₂. Reactions of HCN in the same reactor were also studied; these experiments were conducted with HCN alone, HCN/steam, and HCN/steam/char. The results are consistent with a mechanism in which HCN is the primary N-containing product of the char-steam reaction, and the additional products result from further reactions of HCN either in the gas phase or promoted by the surface of the reactor or the char. Increasing concentrations of steam significantly influence the distribution of char-N to N-containing gas-phase products, resulting in the increase of NH₃ at the expense of N₂. Some differences in char behaviour are also observed, particularly on the distribution of N-containing products at 0.1 MPa total pressure.