This title appears in the Scientific Report :
2009
Please use the identifier:
http://hdl.handle.net/2128/3729 in citations.
Oxygen Permeation and Thermochemical Stability of MIEC Membrane materials for the Oxyfuel Process
Oxygen Permeation and Thermochemical Stability of MIEC Membrane materials for the Oxyfuel Process
The reduction of CO$^{2}$ emissions, generally held to be one of the most significant contributors to global warming, is a major technological issue. CO$^{2}$ Capture and Storage (CCS) techniques applied to large stationary sources such as coal-fired power plants could efficiently contribute to the...
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Personal Name(s): | Ellett, Anna Judith (Corresponding author) |
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Contributing Institute: |
Werkstoffstruktur und Eigenschaften; IEF-2 |
Imprint: |
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
2009
|
Dissertation Note: |
RWTH Aachen, Diss., 2009 |
ISBN: |
978-3-89336-581-4 |
Document Type: |
Book Dissertation / PhD Thesis |
Research Program: |
Rationelle Energieumwandlung |
Series Title: |
Schriften des Forschungszentrums Jülich : Energie & Umwelt / Energy & Environment
43 |
Subject (ZB): | |
Link: |
OpenAccess |
Publikationsportal JuSER |
The reduction of CO$^{2}$ emissions, generally held to be one of the most significant contributors to global warming, is a major technological issue. CO$^{2}$ Capture and Storage (CCS) techniques applied to large stationary sources such as coal-fired power plants could efficiently contribute to the global carbon mitigation effort. The oxyfuel process, which consists in the burning of coal in an oxygen-rich atmosphere to produce a flue gas highly concentrated in CO$^{2}$, is a technology considered for zero CO$^{2}$ emission coal-fired power plants. The production of this O$_{2}$-rich combustion gas from air can be carried out using high purity oxygen separation membranes. Some of the most promising materials for this application are mixed ionic-electronic conducting (MIEC) materials with perovskite and K$_{2}$NiF$_{4}$ perovskite-related structures. The present work examines the selection of La$_{0.58}$Sr$_{0.4}$Co$_{0.2}$Fe$_{0.8}$O$_{3-\delta}$ (LSCF58), La$_{2}$NiO$_{4+\delta}$, Pr$_{0.58}$Sr$_{0.4}$Co$_{0.2}$Fe$_{0.8}$O$_{3-\delta}$ (PSCF58) and Ba$_{0.5}$Sr$_{0.5}$Co$_{0.8}$Fe$_{0.2}$O$_{3-\delta}$ (BSCF50) as membrane materials for the separation of O$_{2}$ and N$_{2}$ in the framework of the oxyfuel process with flue gas recycling. Annealing experiments were carried out on pellets exposed to CO$_{2}$, water vapour, O$_{2}$ and Cr$_{2}$O$_{3}$ in order to determine the thermo-chemical resistance to the atmospheres and the high temperature conditions present during membrane operation in a coal-fired power plant. The degradation of their microstructure was investigated using Scanning Electron Microscopy (SEM) in combination with electron dispersive spectroscopy (EDS) as well as X-Ray Diffraction (XRD). Also, the oxygen permeation fluxes of selected membranes were investigated as a function of temperature. The membrane materials selected were characterised using thermo-analytical techniques such as precision thermogravimetric analysis (TGA) and thermo mechanical analysis (TMA). An increase in thermal expansion and oxygen permeation associated with an increase in oxygen vacancy concentration, observed also in the TGA curves, occurs during heating. BSCF50 exhibits permeation fluxes well above those of LSCF58, PSCF58 and La$_{2}$NiO$_{4+\delta}$, which are quite similar to each other. After exposure, no degradation of LSCF58, La$_{2}$NiO$_{4+\delta}$ and PSCF58 occurs. On the other hand BSCF50 is found to be unstable in CO$_{2}$- and/or H$_{2}$O-containing atmospheres and also to exhibit a chemical demixing. The thermo-chemical stability and the oxygen permeation performances are both crucial factors in the selection of high purity oxygen separation membranes for the oxyfuel process, thus making LSCF58, PSCF58 and La$_{2}$NiO$_{4+\delta}$ in this study the most suitable materials for this application. Serious issues arise, however, from the fact that secondary non-ion conducting oxide phases are formed in the bulk of every material, forming obstacles for oxygen ion migration, and also that a reaction with chromia occurs, preventing their use without protection. |