Comparison of Cu-, Fe- and Ni- Based Oxygen Carriers for Chemical-Looping Combustion

Chemical-looping combustion (CLC) is the indirect combustion of fossil fuels for power generation taking place in two reactors (a Reducer and an Oxidizer) with inherent CO₂ separation, which is accomplished in the Reducer reactor using an oxygen carrier (metal oxide) instead of air. Oxygen carriers in a CLC power plant are expected to be carbon-resistant, exhibit high reaction rates and conversions, and be regenerative over successive cycles. Different metal oxides have been proposed and tested as promising candidates for the CLC process, for instance, CuO, NiO, Fe₂O₃ and Mn₂O₃. In this study, Cu-, Fe-, and Ni- oxygen carriers, prepared via the incipient wetness impregnation on Al₂O₃-SiO₂ supports are compared in terms of their reactivity, selectivity and stability. A fixed-bed reactor (Figure 1) is used to test the oxygen carrier reactivity and CO₂ separation efficiency. A sample of the experiments of this work and the model prediction for Ni-based CLC is presented in Figure 2. Physical and chemical properties of the fresh and used samples, such as active metal oxide loading, available phases, surface structure, surface area and pore volume are characterized by TGA, XRD, SEM and BET, respectively.

Kinetic networks and parameters are presented for all three oxygen carriers. A summary of the fixed-bed experimental data analyzed and utilized to validate the proposed kinetic network, including all the relevant published data for CLC with CH₄ and Fe₂O₃ and CuO as the oxygen carrier, is presented in Table 1 (for the kinetics of Ni-based oxygen carriers, see [1]).

Table 1:  CLC fixed-bed units

In this presentation, operating conditions, design values and OC characterization is presented for the three most common metal oxides and natural gas. Implementation of the kinetic network in different fixed-bed units of the various CLC laboratories will be shown.

 

Figure 1: Fixed-bed chemical-looping setup used in this work.	Figure 2: Chemical-looping reduction selectivity using Ni/NiO and CH4 in fixed-bed reactors; experimental data from UConn fixed-bed reactor at 800蚓.

Acknowledgement: This material is based upon work supported by the National Science Foundation under Grant No. 1054718.

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