Chemistry of inorganic compounds – Carbon or compound thereof – Oxygen containing
Reexamination Certificate
1999-10-26
2003-03-25
Hendrickson, Stuart L. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Oxygen containing
Reexamination Certificate
active
06537514
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the use of solid electrolyte ionic conductor systems, and in particular to oxygen-selective ion transport membranes (OTM's) in gas separation systems and most particularly to the use of OTM's in gas purification systems.
BACKGROUND OF THE INVENTION
Non-cryogenic bulk oxygen separation systems, for example, organic polymer membrane systems, have been used to separate selected gases from air and other gas mixtures. Air is a mixture of gases which may contain varying amounts of water vapor and, at sea level, has the following approximate composition by volume: oxygen (20.9%), nitrogen (78%), argon (0.94%), with the balance consisting of other trace gases. An entirely different type of membrane, however, can be made from certain inorganic oxides. These solid electrolyte membranes are made from inorganic oxides typified by calcium- or yttrium-stabilized zirconium and analogous oxides having a fluorite or perovskite structure.
Although the potential for these oxide ceramic materials as gas separation membranes is great, there are certain problems in their use. The most obvious difficulty is that all of the known oxide ceramic materials exhibit appreciable oxygen ion conductivity only at elevated temperatures. They usually must be operated well above 500° C., generally in the 900° C. to 1100° C. range. This limitation remains despite much research to find materials that work well at lower temperatures. Solid electrolyte ionic conductor technology is described in more detail in Prasad et al., U.S. Pat. No. 5,547,494, entitled Staged Electrolyte Membrane, which is incorporated by reference in its entirety herein to more fully describe the state of the art. The elevated temperatures of operation, however, make ion transport processes intrinsically well suited for integration with high temperature processes such as vapor-based, gas-based, or combined power cycles.
Recent developments have produced solid oxides which have the ability to conduct oxygen ions at elevated temperatures if a chemical driving potential is applied. The chemical driving potential is established by maintaining an oxygen partial pressure difference across the material. These pressure-driven ionic conductor materials may be used as membranes for the extraction of oxygen from oxygen-containing gas streams if a sufficiently high ratio of oxygen partial pressures is applied to provide the chemical driving potential. Namely, the oxygen partial pressure is maintained at a higher value on the cathode side of the membrane, that is exposed to the oxygen-containing gas, than on the anode-side, where oxygen transported through the material is recovered.
The membranes have “oxygen selectivity”. Oxygen selectivity is the tendency of the membrane to transport oxygen ions in preference to other elements and ions thereof. Since the selectivity of these materials for oxygen is infinite (a total preference for transporting oxygen ions to the exclusion of other ions), and oxygen fluxes several orders of magnitude higher than that for polymeric membranes can be obtained, attractive opportunities are created for the production of oxygen as well as for oxygen-requiring oxidation processes, especially with applications that involve elevated temperatures. A prominent example is gas turbine cycles which typically process a significant amount of excess air to keep the turbine inlet temperature within the capabilities of available materials and therefore make available excess oxygen for recovery as a co-product.
Some of the key problems that have to be addressed in the design of ion transport membrane systems and their integration into a high temperature cycle such as a gas turbine involve maximizing driving forces for ion transport, minimizing gaseous diffusion resistance, avoiding excessive stresses from thermal and compositional expansion and contraction and sealing the ion transport elements within the ion transport apparatus. The latter problem is aggravated by ion transport membrane operating temperatures being in the range from 800° C. to 1100° C.
Advances in the state of the art of air separation using solid electrolyte ionic conductors have been presented in the technical literature. For example, Mazanec et al., U.S. Pat. No. 5,306,411, entitled Solid Multi-Component Membranes, Electrochemical Reactor Components, Electrochemical Reactors and Use of Membranes, Reactor Components, and Reactor for Oxidation Reactions, relates to electrochemical reactors for reacting an oxygen-containing gas with an oxygen-consuming gas and describes a shell and tube reactor with the oxygen-consuming gas flowing on one side of the solid electrolytic membrane and the oxygen consuming gas on the other. Mazanec et al., however, does not address issues related to integrating such systems with oxygen production from gas turbine cycles, heat management to maintain membrane surfaces at the desired uniform temperatures, flow dynamics to achieve effective mass transfer, or the need for balancing reaction kinetics with oxygen ion conductivity to maintain the appropriate oxygen partial pressure for materials stability.
Gottzmann et al., U.S. Pat. No. 5,820,655, entitled Solid Electrolyte Ionic Conductor Reactor Design, describes an ion transport reactor and process using an ion transport membrane for extracting oxygen from a feed gas stream flowing along its retentate side. A reactant gas flows along the permeate side to react with the oxygen permeated through the membrane. Provisions are included to transfer the heat of the anode side reaction to a fluid stream flowing through the reactor in a fashion which maintains the membrane operating temperature within its operating range. The patent is silent on the recovery of carbon dioxide from the reacted permeate stream.
Prasad et al., U.S. Pat. No. 5,837,125, entitled Reactive Purge for Solid Electrolyte Membrane Gas Separation, describes a system and process for obtaining high purity oxygen-free products from an oxygen containing feed stream by permeating the contained oxygen to the permeate side of an oxygen ion transport membrane where the permeated oxygen reacts with a reactant purge stream to establish a low partial oxygen pressure at the anode. This permits removal of oxygen down to very low concentrations. The patent is silent on production and recovery of carbon dioxide.
Kang et al., U.S. Pat. No. 5,565,017, entitled High Temperature Oxygen Production with Steam and Power Generation, relates to a system integrating an ion transport membrane with a gas turbine to recover energy from the retentate gas stream after it is heated and steam is added. The retentate gas stream is the stream on the cathode side of the membrane following contact with the membrane wherein a portion of the elemental oxygen is transported through the membrane, while a permeate gas stream is on the anode side and receives such transported oxygen. Oxygen transported across the membrane from the cathode side to the anode side is designated as permeate oxygen or a permeate oxygen portion of the oxygen initially contained on the cathode side. The injection of steam or water into the ion transport retentate stream compensates for the loss of the oxygen mass from the turbine feed gas stream.
Kang et al., U.S. Pat. No. 5,562,754, entitled Production of Oxygen By Ion Transport Membranes with Steam Utilization, discloses a system integrating an ion transport membrane with a gas turbine to recover energy from the retentate gas stream after it is heated. Steam is added as a sweep gas on the anode side to enhance oxygen recovery. A stream containing a mixture of oxygen and steam is produced on the anode side which can be withdrawn as a product.
Kang et al., U.S. Pat. No. 5,516,359, entitled Integrated High Temperature Method for Oxygen Production, describes heating a compressed air feed gas stream to the appropriate ion transport operating temperature by a first combustor which, in one embodiment, is inserted between the compressor discharge and the ion transport separator. Subsequently, the r
Gottzmann Christian Friedrich
Keskar Nitin Ramesh
Prasad Ravi
Schwartz Joseph Michael
Hendrickson Stuart L.
Praxair Technology Inc.
Rosenblum David M.
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