350054 Reactivity Analysis of Ni, Cu, Fe Oxygen Carriers in Fixed Bed Chemical Looping Combustion

Monday, November 4, 2013
Grand Ballroom B (Hilton)
Oscar Nordness, Department of Chemical & Biomolecular Engineering, University of Connecticut, Storrs, CT, Zhiquan Zhou, Department of Chemical, Materials & Biomolecular Engineering, University of Connecticut, Storrs, CT and George Bollas, University of Connecticut

Reactivity Analysis of Ni, Cu, Fe Oxygen Carriers in Fixed Bed Chemical Looping Combustion.  

Oscar Nordness, Zhiquan Zhou, George M. Bollas

                Chemical Looping Combustion (CLC) is an indirect method of fuel combustion through the use of an oxygen carrying material that separates oxygen from air via self-oxidation, and oxidizes fuels while it is being reduced and regenerated. This process takes places in two separate reactors. In the first reactor, the oxidized oxygen carrier is reduced with a carbon based fuel source producing CO2 and H2O. In the second reactor, the reduced oxygen carrier is re-oxidized; producing oxygen depleted air. This cycle allows for the separation of CO2, while the overall reaction and heat of reaction are equivalent to those of direct fuel oxidation. Oxygen carriers in a CLC power plant are expected to be carbon-resistant, exhibit high reaction rates and conversion, and be regenerative over successive cycles. There are currently several proposed oxygen carriers for use in CLC; CuO, NiO, Mn2O3, and Fe2O3. In this presentation a comprehensive study of the structural stability and reactivity of Iron, Copper, and Nickel oxygen carriers tested in a fixed bed reactor will be discussed. The Nickel proved to be the most reactive; however, this was accompanied by high levels of carbon deposition. Furthermore Nickel is very toxic and is not a good environmental option. Copper based oxygen carriers also showed good reactivity; however, due to the highly exothermic naturea of its oxidation; the copper based oxygen carriers were subject to agglomeration, thus, decreasing their ability to regenerate.  Iron based oxygen carriers showed poor reactivity in comparison with the Nickel and Copper and were also subject to agglomeration. Figure 1 demonstrates the fixed bed experimental set up in which the flow of Argon, Methane, and Air can be controlled via 3 separate mass flow controllers. The oxygen carrier is held in the center of a quartz tube reactor. The products of the oxidation and reduction steps flow to a mass selective detector to be analyzed.    

Figure 1:

Figure 2 is a graphic representation of the product gas after 5 successive cycles of chemical looping combustion with a Copper oxygen carrier. Note that the initial peak represents the reduction of the oxygen carrier as displayed by the spike in CO2. The subsequent presence of CH4 in the product gas indicates the complete reduction of the oxygen carrier. The reduction period for this experiment was 2 minutes; where 15% CH4 mixed with inert Argon entered the reactor bed at a flow rate of 100 sccm. The reactor was then purged for 5 minutes. This was followed by a 4 minute oxidation period during which 100 sccm of air entered the reactor re-oxidizing and effectively regenerating the oxygen carrier. It is important to note the stability of this oxygen carrier over successive cycles as indicated by the levels of the product gases remaining constant.  This proves the regenerability of Copper as a potential oxygen carrier.

Figure 2:

SEM images were taken of the samples both before and after testing in order to observe structural changes to the oxygen carriers. Figure 3 represents an SEM image of the Copper carrying catalyst before use in chemical looping combustion.

Figure 3

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