(135g) Chemical Looping Partial Oxidation of Solid Fuels for High Purity Syngas Production

The Ohio State University is developing the chemical looping partial oxidation (CLPO) processes for the production of high-purity syngas from solid carbonaceous fuels including biomass and coal. Compared to conventional coal and biomass gasification processes, the CLPO processes eliminate the need for molecular oxygen from an air separation unit (ASU), and deliver increased cold gas efficiencies and decreased fuel consumptions. The CLPO processes utilize the unique co-current moving bed gas-solid reducer reactors for the partial oxidation of solid fuels to syngas with metal oxide oxygen carriers. The co-current moving bed reactor design provides a desirable gas-solid contacting while minimizing gas bypassing and solid back mixing, which result in high fuel conversion and close-to-equilibrium gas composition. In this study, active iron-titanium composite metal oxide (ITCMO) materials are used as the oxygen carrier in the CLPO processes. Theoretical analysis aided by a modified Ellingham Diagram illustrates that syngas production is thermodynamically favored in presence of ITCMO oxygen carrier. Fundamental reaction mechanism studies are performed using density functional theory (DFT) simulation to unveil the role of oxygen vacancy in partial oxidation reactions by metal oxide oxygen carrier. The experimental results from a bench-scale moving bed reactor have successfully shown the production of high purity syngas from coal and biomass with the combination of moving bed reducer and ITCMO oxygen carrier. Adjustable syngas compositions were achieved by the co-injection of steam or CO₂. A fully integrated sub-pilot scale test unit with non-mechanical gas sealing and solid circulation devices was designed, constructed, and tested for continuous syngas production. The bench and sub-pilot demonstrations confirmed the syngas produced from the CLPO processes are consistent with the prediction from thermodynamic equilibrium models.