458454 Optimization of Reverse Water-Gas Shift Chemical Looping for Continuous Production of Syngas from CO2
One possible way to shift towards a more sustainable future is to use CO2 as the main carbon source instead of fossil fuels. In the context of sustainable syngas production, the reverse water-gas shift (RWGS) reaction is of high importance, as it converts CO2 to CO with the help of process heat and hydrogen. The traditional RWGS reaction can be improved by introducing a metal oxide as an oxygen carrier, splitting the original reaction in a reduction and oxidation reaction on the metal oxide. This cyclic two-step process is referred to as reverse water-gas shift chemical looping (RWGS-CL). It has been shown that by using this approach, efficiency improvements can be obtained because the two-step operation yields partially separated gas streams and thus simplifies downstream gas separation . This is especially true for syngas production with low H2/CO-ratio. Furthermore, unwanted side reactions can be eliminated by separating the reactants spatially or temporally and favorable thermodynamics can be obtained by choosing suitable oxygen carrier materials. Due to the cyclic switching between two process steps, RWGS-CL is more complex than the traditional RWGS process. A steady state operation in the traditional sense is not possible. However, a cyclic steady state (CSS) is achievable after prolonged cycling. Therefore, simulation and optimization techniques are used to understand the dynamic behavior and to improve the process.
Different reactor designs and configurations for the RWGS-CL process are examined and evaluated. For a fixed bed configuration, a 1D model for the two-step RWGS-CL process is derived based on  with kinetic information from . Process simulation is used to compute the cyclic steady state of the process for different flow regimes. On top of the simulation, a multi-objective optimization problem is formulated and solved to maximize the gas conversion and the utilization of the oxygen carrier material. Since both objectives are conflicting they lead to Pareto optimal solutions. The trade-off between gas conversion and the utilization of oxygen carrier material is investigated. The influence of the decision variables and the flow regime on the optimal solution is analyzed and discussed. Constraints on the decision variables are formulated such that continuous production of CO can be achieved with the RWGS-CL process. The simulation and optimization results are compared to those of the traditional RWGS process.
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