Liquid heaters and vaporizers – Separators – Boiler circulation
Reexamination Certificate
2000-12-19
2002-05-28
Wilson, Gregory (Department: 3749)
Liquid heaters and vaporizers
Separators
Boiler circulation
C122S005000, C122S031100, C096S008000, C095S054000
Reexamination Certificate
active
06394043
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a oxygen separation and combustion apparatus and method that can be applied to such devices as a boiler or a nitrogen generator in which oxygen separated from an oxygen containing gas by oxygen transport membranes supports combustion of a fuel within a combustion chamber and temperature of the oxygen transport membranes is controlled by fluid circulating within fluid passages passing through the combustion chamber.
BACKGROUND OF THE INVENTION
Growing concerns about environmental issues, such as global warming and pollutant emissions, are driving industries to explore new ways to increase efficiency and reduce emissions of pollutants. This is particularly true for fossil fuel fired combustion systems, which represent one of the largest sources of carbon dioxide and air pollution emissions. One effective way to reduce emissions and to increase efficiency is to use oxygen, or oxygen enriched air, in the combustion process. The use of oxygen or oxygen enriched air reduces stack heat losses, which increases the system efficiency, while at the same time reducing NOx emissions. Further, the concentration of carbon dioxide in the flue gas is higher since there is little or no nitrogen to act as a diluent. The higher carbon dioxide concentration enhances carbon dioxide recovery options. Oxygen use in the prior art has been limited to those processes with high exhaust temperatures, such as glass furnaces. In such applications, the fuel savings and the benefits achieved are greater than the cost of the oxygen. In low exhaust temperature systems, such as boilers, the reverse is true. In these systems, the cost of oxygen produced with current technologies is more expensive than the available fuel savings. This makes oxygen use in such systems economically unattractive. Moreover, when the energy required to produce the oxygen is taken into consideration, the overall thermal efficiency decreases.
Oxygen transport membranes have been advantageously utilized in the prior art to produce oxygen for heat consuming oxygen separation and combustion apparatus and processes in a manner that results in a savings of energy that would otherwise have to be expended in the separation of oxygen. Oxygen transport membranes are fabricated from oxygen-selective, ion transport ceramics in the form of tubes or plates that are in themselves impervious to the flow of oxygen and other gases. Such ceramics, however, exhibit infinite oxygen selectivity at high temperatures by transporting oxygen ions through the membrane. In oxygen transport membranes, the oxygen is ionized on one surface of the membrane to form oxygen ions that are transported through the membrane. The oxygen ions on the opposite side of the membrane recombine to form oxygen with the production of electrons. Depending upon the type of ceramic, oxygen ions either flow through the membrane to ionize the oxygen or along separate electrical pathways within the membrane, or by an applied electric potential. Such solid electrolyte membranes are made from inorganic oxides, typified by calcium- or yttrium-stabilized zirconium and analogous oxides having fluoride or perovskite structures.
In U.S. Pat. No. 5,888,272 oxygen transport membranes are integrated into a combustion process itself, with all the oxygen produced going directly into the combustor. The heated flue gases can then be routed to a process wherein the thermal energy can be used to heat a fluid or perform useful work. In one embodiment, flue gases are recycled through a bank of oxygen transport membrane tubes and enriched with oxygen. Typically the flue gas enters the bank containing anywhere from 1 to about 3 percent oxygen and leaves the bank containing from about 10 to about 30 percent oxygen by volume. The enriched flue gas is then sent to a combustion space where it is used to burn fuel. In another embodiment, called reactive purge, the oxygen transport membrane tubes are placed directly in the combustion space. A fuel diluted with flue gas is passed through the tubes and combust with the oxygen as it passes through the tubes. Thus oxygen production and combustion take place simultaneously.
As will be discussed, the present invention utilizes oxygen transport membranes to produce oxygen to support combustion within a oxygen separation and combustion apparatus such as a boiler in a manner that inherently reduces the energy expenditures involved in compressing an incoming oxygen containing feed to the membranes. The advantages of the present invention will become apparent from the following discussion.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides an oxygen separation and combustion apparatus comprising a plurality of parallel oxygen transport membranes located within a combustion chamber. The plurality of parallel oxygen transport membranes serve to separate oxygen from an oxygen containing gas, thereby to provide the oxygen within the combustion chamber to support combustion of a fuel and generate heat. A plurality of fluid passages pass through the combustion chamber and are positioned so that a portion of the heat of combustion is transferred from the combustion to the oxygen transport membranes to heat the oxygen transport membranes to an operational temperature and a further portion of the heat is transferred from the combustion to the fluid passages to provide heat to heat the fluid and to promote stabilization of the operational temperature of the oxygen transport membranes. At least one inlet is provided for introducing at least the fuel into the combustion chamber and an exhaust from the combustion chamber discharges combustion products arising from combustion of the fuel. The exhaust and the at least one inlet are spaced apart from one another so that the combustion products flow in a direction predominantly parallel to the oxygen transport membranes.
The oxygen transport membranes and the fluid passages can be of tubular configuration. The direction of flow of the combustion products can either be countercurrent or co-current to gas flow of the oxygen containing gas within the oxygen transport membranes. Preferably, the oxygen transport membranes are closed at one end and open at the end to discharge an oxygen-depleted retentate and a plurality of coaxial lance tubes project into open ends of the oxygen transport membranes to supply the oxygen containing gas thereto. The at least one inlet can comprise an inlet to the combustion chamber for introducing a mixture of the fuel and a flue gas, if flue gas is required, into the combustion chamber. Alternatively, in case of open ended, tubular oxygen transport membrane units, the at least one inlet can comprise fuel nozzles located adjacent to the open ends of the oxygen transport membranes.
The fluid can be water and thus, the fluid heater can be a boiler. In such case, the fluid passages are interspersed between the oxygen transport membranes and the fluid passages and the oxygen transport membranes are parallel to one another. Preferably, the fluid passages communicate between fluid inlet and outlet manifolds to supply the fluid to the fluid passages and to discharge steam therefrom, respectively. In such case, the oxygen transport membranes project, from the open end thereof, from a retentate outlet manifold to discharge oxygen depleted air and the lance tubes project from an air inlet manifold.
In another aspect, the present invention provides an oxygen separation and combustion method in which an oxygen containing gas is introduced into a plurality of parallel oxygen transport membranes located within a combustion chamber. Oxygen is separated from the oxygen containing gas within the plurality of parallel oxygen transport membranes, thereby to provide oxygen within the combustion chamber. A fuel is introduced into the combustion chamber and the fuel is combusted within the combustion chamber in the presence of the oxygen to generate heat. The fluid is passed through a plurality of fluid passages also located within the combustion chamber and combu
Bool, III Lawrence E.
Kobayashi Hisashi
Praxair Technology Inc.
Rosenblum David M.
Wilson Gregory
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