Effect of Carbon Deposition on the Oxidation Rate of Copper/Bentonite in the Chemical Looping Process
The presented work is part of the Industrial Carbon Management Initiative (ICMI) on the development of metal oxide oxygen carriers for use in the chemical looping combustion process. An oxygen carrier, CuO/bentonite (60:40%), was reacted with methane gas and then oxidized in air. The change in weight and reaction gas concentrations were measured using a thermogravimetric analyzer (TGA) equipped with a real-time gas analyzer. The reduction–oxidation cycle was conducted within the temperature range of 750–900 °C for 10 cycles, using 20, 50, and100% CH{sub 4} concentrations in N{sub 2} for the reduction segment and dry air for the oxidation segment. Several analysis methods were evaluated to fit the oxidation of reduced CuO (i.e., Cu) data over the complete conversion range with suitable rate expressions derived from existing models for oxidation, including the shrinking core model (diffusion and reaction control), first- and second-order reaction rates, parallel and series reaction mechanisms, and Johnson–Mehl–Avrami (JMA) rate. The best agreement between the experimental data and the models of the Cu oxidation was accomplished using the JMA model. The reactivity of the oxygen carrier during the oxidation reactions was affected by the CH{sub 4} concentration as well as the temperature. The rate of fractional uptake of oxygen onto the carrier decreased as the temperature increased, contrary to expectations and indicative that the mechanism is changing during the test. Analysis of the exit gas provided evidence of carbon deposition on the reduced sorbent particle and resulted in the CO{sub 2} product upon oxidation. The oxidation of this carbon releases significant heat that is capable of changing the particle morphology (Zhu, Y.; Mimura, K.; Isshiki, M. Oxid. Met. 2004, 62, 207-222). On the basis of experimental results, the overall reaction process in the fuel reactor may be considered to consist of the decomposition of CH{sub 4} into C and H{sub 2} and reduction of CuO/bentonite by the resulting H{sub 2} and the parallel reaction of CH{sub 4} with CuO/bentonite. The extent of carbon deposition in the carrier particle increased with an increasing temperature and CH{sub 4} concentration. This deposited carbon not only leads to CO{sub 2} release from the oxidation reactor but, more importantly, causes degredation of the carrier capacity and its reactivity.
- Research Organization:
- National Energy Technology Lab. (NETL), Pittsburgh, PA, and Morgantown, WV (United States). In-house Research
- Sponsoring Organization:
- USDOE Office of Fossil Energy (FE)
- DOE Contract Number:
- DE-FE0004000
- OSTI ID:
- 1129885
- Report Number(s):
- A-CONTR-PUB-018
- Journal Information:
- Energy and Fuels, Vol. 26, Issue 11; ISSN 0887-0624
- Publisher:
- American Chemical Society (ACS)
- Country of Publication:
- United States
- Language:
- English
Similar Records
Chemical-looping combustion of coal-derived synthesis gas over copper oxide oxygen carriers
Chemical-looping combustion of coal-derived synthesis gas over copper oxide oxygen carriers