(583f) Experimental and Model Comparison of Chemical Looping H2 Production Using Ferrites in a Packed Bed Reactor
The chemical looping hydrogen (CLH) production process is an alternative method to water-gas shift to generate pure H2, as well as a separate stream of pure and easily-sequestered CO2, from any synthesis gas without complicated and expensive separations equipment. Synthesis gas is used to reduce a metal oxide material at moderate to high temperatures as it leaves a gasifier (500°C to 1000°C), producing a stream of CO2 and H2O. The resulting reduced metal is then oxidized with H2O to produce H2 and regenerate the metal oxide. This process requires use of a metal oxide material that achieves high H2 and CO conversions to H2O and CO2 during the reduction step. Complete regeneration of the metal oxide using only H2O as an oxidant is also desirable. In this study, the mixed metal ferrites CoFe2O4 and NiFe2O4 were investigated experimentally and shown to meet the criteria for CLH metal oxides. A comparison was made with Fe2O3, which is the current state of the art CLH metal oxide. At low solid conversions the mixed metal ferrites allowed the recovery of nearly three times more H2 during H2O oxidation than was recovered using Fe2O3 under the same conditions. This H2 recovery required additional steam generation due to the low H2O to H2 conversion during the oxidation of near-stoichiometric CoFe2O4 and NiFe2O4. A system model developed based on the mixed metal ferrite equilibrium with the H2/H2O and CO/CO2 systems was used to investigate the effects of syngas composition, temperature and a supplementary O2 oxidation on the steam production required for complete oxide regeneration and the overall efficiency of the system. The CoFe2O4 and NiFe2O4 materials offer significant benefit over conventional Fe2O3 at lower reduction temperatures and for a lower quality feed syngas.