Gasification of wood char by ultra-superheated steam in an entrained flow reactor

Slow pyrolysis is one of the process options for energy from waste and biomass by producing storable char along with other products. Pinewood cubes were pyrolysed in a fixed-bed reactor under nitrogen at a final temperature of 350-700 °C with a heating rate of 10 °C min ^-1 and the resulting char was gasified in ultra superheated steam (USS), which is a very high-temperature mixture of steam and CO₂. The mass yield of the char from pyrolysis was 21 to 33%, while the energy yield was 34 to 49% with decreasing temperatures. The char has a calorific Value of more than 30 MJ kg ^-1 for the tested range of temperature and showed a linear relationship in the decrease of H/C and O/C ratios. The char powder produced from a final temperature of 500 °C was gasified under two different conditions of the USS in a laboratory-scale entrained-flow reactor, and its performance was compared with an anthracite sample by analysing the syngas composition, the solid residue and the conversion efficiency. The carbon conversion of the char was estimated to be 46-53%, which was very satisfactory for the laboratory-scale unit. Full carbon conversion can be achieved in industrial-scale reactors by increasing the particle residence time and/or by recycling unconverted char.