Bhavsar, Saurabh
(2014)
Reducible Oxide Based Oxygen Carriers for Chemical Looping Combustion and Partial Oxidation of Methane.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
Chemical looping combustion (CLC) is a novel combustion technology that offers a highly efficient route towards clean combustion of fuel with inherent CO2 capture. In CLC, a fuel is combusted in reducer reactor in contact with an oxygen carrier (typically a metal oxide) and subsequently re-oxidized by air in oxidizer. Condensation of steam from reducer effluent results in high purity sequestration ready CO2 streams. Thus CLC results in a NOx-lean, flame-less oxyfuel combustion process eliminating the need for air separation. Splitting the combustion into two half processes provides a high degree of flexibility in CLC for process intensification, e.g. a wide range of oxygen carriers, fuels and oxidant gases can be used, albeit use of various fuels/oxidants have their own challenges.
Typically in CLC, a metal is supported on a high temperature stable matrix to provide the required thermal stability in harsh redox conditions. However these non-reducible supports do not contribute any oxygen in the combustion process or facilitate the reduction of supported metal. Therefore in the present work, we test the applicability of reducible oxides like ceria as supports in CLC. It was found that, compared to non-reducible supports, the redox properties of ceria strongly facilitate efficient utilization of metal oxides in the process, thus resulting in improved redox kinetics and higher carrier conversion. The broad applicability of the concept was tested with various transition metals typically used in CLC. Furthermore, the reactivity of carriers was enhanced by employing systematically engineered mixed-oxides of iron, nickel and/or manganese.
Beyond combustion, tailoring the metal phase and reactor operation was used for partial oxidation of methane to produce syngas – a valuable feedstock in chemical industry. Utilization of the looping concept for partial oxidation results in a safe oxidation process eliminating the need for expensive air separation or noble metal catalysts. Steam, CO2 or mixtures of both can be used as oxidants for ultra-pure H2 or syngas generation and CO2 activation. Current work underscores the fact that reactor operation in chemical looping allows targeting clean combustion, partial oxidation or various reforming processes, but rational design of oxygen carriers makes these processes viable.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
|
| Date: |
16 June 2014 |
| Date Type: |
Publication |
| Defense Date: |
26 March 2014 |
| Approval Date: |
16 June 2014 |
| Submission Date: |
26 March 2014 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
200 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Chemical Engineering |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Chemical looping, carbon dioxide capture, partial oxidation, ceria, mixed oxides, nanomaterials |
| Date Deposited: |
16 Jun 2014 18:56 |
| Last Modified: |
15 Nov 2016 14:18 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/20777 |
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