High-Purity Syngas Generation via Moving Bed Chemical Looping Gasification of Versatile Biomass Feedstocks for Liquid Fuel Generation

The chemical looping gasification of waste biomass feedstocks is a green alternative to conventional gasification systems, such as indirect gasification with lower energy requirements. Moving bed biomass to syngas (CL-BTS) Chemical looping system developed at The Ohio State University enables high-purity syngas generation due to deeper reduction of iron–titanium composite metal oxide (ITCMO) particles. The ITCMO particles, having a composition of Fe2TiO5, are reduced into FeTiO3 and the Fe phase at the reactor outlet. The presence of FeTiO3 and Fe phase at the reactor outlet facilitates a stable syngas purity plateau region, which enables the gasification of different biomass feedstock at a fixed OC flow rate with high-purity syngas at isothermal conditions. 2.5 kWth Bench-scale experiments demonstrate ∼90% syngas purity for pine wood, hazelnut shells, rice hulls, and Allegheny hardwood at 1 kmol/h carbon input. The addition of steam as a char gasifying agent decreases the syngas operating plateau region due to an excess supply of molecular oxygen in the system. A comparison between the biomass indirect gasifier (BIG) and the CL-BTS system shows that the CL-BTS unit performs better than the BIG unit in terms of cold gas efficiency (CGE) and effective thermal efficiency (ETE). Further, the syngas produced from the chemical looping unit and the indirect gasifier is used in the downstream Fischer–Tropsch process to produce diesel and gasoline liquid fuels. The liquid fuel yield and carbon efficiency for gasoline and diesel formation show superior results for the CL-BTS unit compared to the BIG unit. Overall, the flexibility of the moving bed chemical looping system to handle versatile biomass feedstock could be a significant step toward the commercialization of the CL-BTS system.