(587k) High-Purity Syngas Generation Via Moving Bed Chemical Looping Gasification of Versatile Biomass Feedstocks for Liquid Fuel Generation

Biomass gasification for synthesis gas (syn gas) generation is a promising route for converting biomass into value-added products. However, low syngas purity and high tar formation using steam/ air as a gasifying agent render the biomass gasification process inefficient. Further, the variability in biomass feedstocks hinder their utilization as a green renewable energy resource, negating their positive benefits. Hence, the syngas purity from biomass gasification is subject to biomass composition, posing operational challenges for gasification systems.

Chemical looping gasification is one of the promising technologies for high-purity syngas generation, removing the need for air separators, tar reformers and acid gas removers. The air/steam is replaced by iron-based oxygen carriers, which gasify the biomass feedstock by releasing lattice oxygen. The biomass feedstock is introduced into the first reactor, a co-current moving bed reducer where the iron-based oxygen carriers move down cocurrently. High-purity syngas is produced at the outlet, and the oxygen carrier particles are reduced to a lower oxidized form. The second reactor, a fluidized bed combustor, regenerates the oxygen carriers using air and recirculates them back into the reducer.

This work employs Fe₂TiO₅ oxygen carrier particles to generate high purity syngas using a moving bed reactor from different types of biomass. The biomass is fed cocurrently into a moving bed reactor with Fe₂TiO₅ oxygen carriers, producing syngas at the outlet and reduced particles comprising FeTiO_3. The reduced particles are regenerated using a fluidized bed combustor and recirculated back. The syngas produced is integrated into the Fisher Tropsch process to produce liquid fuels.

Process simulation studies using the Fe₂TiO₅ particles and moving bed reactor show a constant syngas purity of around 95 % for pine wood, hazelnut shells and Allegheny hardwood. The simulated results are validated experimentally using a 2.5 kW thermal setup, closely matching the thermodynamic limits (91% - 94%). The presence of the perovskite phase (FeTiO₃) in the reduced form at the gas outlet renders the catalytic effect on the oxygen carrier particles, ensuring that the syngas produced is of similar purity irrespective of the biomass type. The moving bed reactor and the presence of FeTiO₃ at the gas outlet supplement the production of high syngas purity. Moving bed chemical looping system could be a promising technology to solve variability in biomass for syngas generation.