Pitt Logo LinkContact Us

Nanostructured Oxygen Carriers for Chemical Looping Combustion and Chemical Looping Hydrogen Production

Solunke, Rahul Dushyantrao (2011) Nanostructured Oxygen Carriers for Chemical Looping Combustion and Chemical Looping Hydrogen Production. Doctoral Dissertation, University of Pittsburgh.

[img] PDF - Primary Text
Restricted to University of Pittsburgh users only until 26 January 2016.

Download (2167Kb) | Request a copy

    Abstract

    Chemical looping combustion (CLC) is an emerging technology for clean energy-production. In CLC, an oxygen carrier is periodically oxidized with air and then reduced in contact with a fuel. CLC is thus a flame-less oxy-fuel combustion without an air separation unit, producing sequestration-ready CO2-streams without significant energy penalty. However, a major hurdle towards technical implementation of CLC is the development of robust oxygen carrier materials. In this thesis, we report on a combined study of theoretical and experimental investigations of oxygen carriers for CLC. A detailed thermodynamic screening of oxygen carriers based on several comparison criteria was carried out to come up with the best candidates for CLC and then effect of sulfur contamination in the fuel stream on the performance of these selected oxygen carriers was studied. In sulfur-free streams the carriers show stable and fast reduction and re-oxidation kinetics. Sulfur contamination results not only in sulfidation of the metal carrier component, but also in partial sulfidation of the support matrix which marginally alters the redox kinetics but does not affect carrier stability. Interestingly, the support sulfidation leads to a significant increase in the oxygen carrying capacity of the carriers. Further investigation of Cu-based carriers showed that efficient desulfurization of the fuel reactor exit stream is achievable with quantitative S-recovery in the air reactor effluent. Beyond combustion, chemical looping can be used to produce hydrogen by replacing air with steam as oxidant in a 'chemical looping steam reforming' process (CLSR). The effluent of the oxidizer is PEMFC-ready hydrogen without further purification steps, resulting in significant process intensification. Challenges in CLSR are slower steam vs air oxidation kinetics, high-temperature carrier stability, and attrition due to large solids transport in a two-bed process. In the final part of the thesis, we report on experimental investigations of Fe-based nanostructured carriers to study their oxidation kinetics and high-temperature stability. Effect of temperature and particle size on hydrogen production and carrier utilization was studied which further demonstrated the importance of nano-sizing of the carrier. Finally, a reactor model was developed demonstrating that a fixed-bed approach is feasible for CLSR.


    Share

    Citation/Export:
    Social Networking:

    Details

    Item Type: University of Pittsburgh ETD
    ETD Committee:
    ETD Committee TypeCommittee MemberEmail
    Committee ChairVeser, Goetzgveser@pitt.edu
    Committee MemberMcCarthy, Josephmccarthy@engr.pitt.edu
    Committee MemberEnick, Robertrme@pitt.edu
    Committee MemberJin, Rongchaorongchao@andrew.cmu.edu
    Title: Nanostructured Oxygen Carriers for Chemical Looping Combustion and Chemical Looping Hydrogen Production
    Status: Unpublished
    Abstract: Chemical looping combustion (CLC) is an emerging technology for clean energy-production. In CLC, an oxygen carrier is periodically oxidized with air and then reduced in contact with a fuel. CLC is thus a flame-less oxy-fuel combustion without an air separation unit, producing sequestration-ready CO2-streams without significant energy penalty. However, a major hurdle towards technical implementation of CLC is the development of robust oxygen carrier materials. In this thesis, we report on a combined study of theoretical and experimental investigations of oxygen carriers for CLC. A detailed thermodynamic screening of oxygen carriers based on several comparison criteria was carried out to come up with the best candidates for CLC and then effect of sulfur contamination in the fuel stream on the performance of these selected oxygen carriers was studied. In sulfur-free streams the carriers show stable and fast reduction and re-oxidation kinetics. Sulfur contamination results not only in sulfidation of the metal carrier component, but also in partial sulfidation of the support matrix which marginally alters the redox kinetics but does not affect carrier stability. Interestingly, the support sulfidation leads to a significant increase in the oxygen carrying capacity of the carriers. Further investigation of Cu-based carriers showed that efficient desulfurization of the fuel reactor exit stream is achievable with quantitative S-recovery in the air reactor effluent. Beyond combustion, chemical looping can be used to produce hydrogen by replacing air with steam as oxidant in a 'chemical looping steam reforming' process (CLSR). The effluent of the oxidizer is PEMFC-ready hydrogen without further purification steps, resulting in significant process intensification. Challenges in CLSR are slower steam vs air oxidation kinetics, high-temperature carrier stability, and attrition due to large solids transport in a two-bed process. In the final part of the thesis, we report on experimental investigations of Fe-based nanostructured carriers to study their oxidation kinetics and high-temperature stability. Effect of temperature and particle size on hydrogen production and carrier utilization was studied which further demonstrated the importance of nano-sizing of the carrier. Finally, a reactor model was developed demonstrating that a fixed-bed approach is feasible for CLSR.
    Date: 26 January 2011
    Date Type: Completion
    Defense Date: 28 September 2010
    Approval Date: 26 January 2011
    Submission Date: 28 September 2010
    Access Restriction: 5 year -- Restrict access to University of Pittsburgh for a period of 5 years.
    Patent pending: No
    Institution: University of Pittsburgh
    Thesis Type: Doctoral Dissertation
    Refereed: Yes
    Degree: PhD - Doctor of Philosophy
    URN: etd-09282010-220320
    Uncontrolled Keywords: Chemical looping combustion; hydrogen production; nanomaterial; sulfur capture
    Schools and Programs: Swanson School of Engineering > Chemical Engineering
    Date Deposited: 10 Nov 2011 15:02
    Last Modified: 07 May 2012 09:59
    Other ID: http://etd.library.pitt.edu/ETD/available/etd-09282010-220320/, etd-09282010-220320

    Actions (login required)

    View Item

    Document Downloads