Power plants – Combustion products used as motive fluid
Reexamination Certificate
2000-05-04
2001-09-25
Kim, Ted (Department: 3746)
Power plants
Combustion products used as motive fluid
C060S039010, C060S039170, C096S008000, C096S010000
Reexamination Certificate
active
06293084
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an oxygen separator and method of separating oxygen that uses oxygen-selective, ion conducting ceramic membranes. More particularly, the present invention relates to such an oxygen separator in which such oxygen-selective ceramic membranes are located within a duct that is either directly connected to an exhaust of a gas turbine or connected to a burner of the gas turbine to receive air heated by combustion of a fuel.
BACKGROUND ART
Separation of oxygen from heated, elevated pressure air streams produced by gas turbines can readily be accomplished by oxygen-selective, ion conducting ceramic membranes because gas turbines produce more high temperature air than is required to support combustion within the turbine. In fact, there is a sufficient excess of high temperature air to allow for significant quantities of oxygen to be extracted as a by-product.
There are a number of references in the prior art that disclose integrations of gas turbines with oxygen separators that employ oxygen-selective, ion conducing ceramic membranes (hereinafter referred to in the specification and claims as “oxygen-selective ceramic membranes”). For instance, J. D. Wright (et al., “Advanced Oxygen Separation Membranes”, pp 33-61 (1990) discloses an integration in which compressed air is indirectly heated to the requisite membrane operating temperature by a fired heater. The air is then passed through the retentate side of the separator where a portion of the contained oxygen is transferred to the permeate side by a pressure driven ion conducting ceramic membrane. The oxygen depleted retentate is heated in a fired heater to turbine inlet temperature and is then expanded in a turbine to produce power. The fired heater contains a heat exchange coil for heating the separator feed. A similar integration is shown in U.S. Pat. No. 5,516,359. In this patent, air is compressed to an elevated pressure and is heated to a membrane operating temperature by a burner or by indirect heat exchange. The heated compressed air is then introduced to the retentate side of a membrane separator that extracts oxygen from the air. The oxygen depleted retentate is further heated to a turbine inlet temperature by direct combustion before being expanded in a turbine to generate power. U.S. Pat. No. 5,562,754 discloses the introduction of steam into the oxygen depleted retentate stream as a replacement for the separated oxygen and also deploys steam as a sweep gas for the permeate side of the membrane to improve the driving force for oxygen transfer.
U.S. Pat. No. 5,852,925 describes different process options that are especially suited for retrofitting existing installations. In one option, only a portion of the compressed air stream is processed by the membrane separator. The resultant oxygen depleted retentate is combined with a stream that has bypassed the separator prior to turbine expansion. Another option provides a separate air compressor to supply the membrane separator. The oxygen depleted retentate is heated in a second stage combustor and is then expanded in a turbine.
U.S. Pat. No. 5,865,878 introduces various concepts of integrating an oxygen-selective ceramic membrane with a gas turbine in which such reactants as steam and natural gas are introduced into the permeate side of the membrane separator to react with the permeated oxygen to form desired products such as syngas.
U.S. Pat. No. 5,820,654 discloses a process and apparatus in which oxygen is extracted from a heated oxygen containing stream by an oxygen-selective ceramic membrane in which the oxygen product is cooled through indirect heat transfer with a portion of the incoming air stream. The gas separation and cooling are integrated within a single apparatus to maximize the use of conventional materials of construction.
All of the foregoing references disclose separator-gas turbine integrations that require the use of ancillary equipment such as heat exchangers and long piping systems for extracting air and re-injecting oxygen depleted air. As may be appreciated, such equipment and piping adds to the complexity and expense of the integration of membrane separator and gas turbine. Additionally, long piping runs produce pressure drops and difficulties in providing the separator with a uniform flow distribution.
As will be discussed, the present invention provides oxygen separators and methods, employing oxygen-selective ceramic membranes, that are designed for integration with a gas turbine without the use of long piping runs. As a result, the pressure drop involved in handling the large air flow between the components of the system is minimized and flow distribution problems are reduced.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides an oxygen separator for separating oxygen from a heated oxygen containing gas discharged from an expander of a gas turbine hot gas generator used to drive a power turbine. It is to be noted that a hot gas generator consists of an air compressor, a combustor and an expander which drives the compressor. The expander exhaust is at both elevated pressure and temperature and can be used to drive the power turbine which normally is on a separate shaft from the compressor-expander shaft. Usually the hot gas generator-power turbine combination is an aircraft derivative design.
The oxygen separator utilizes a duct open at opposite ends and configured to be directly mounted between the expander of the hot gas generator and the power turbine in an in-line relationship to receive the heated oxygen containing gas from the expander and to discharge an oxygen depleted gas to the power turbine. A plurality of oxygen-selective ceramic membranes are provided for extracting oxygen from the heated gas. Such membranes are mounted within the duct so that the oxygen separates from the heated oxygen containing gas. The separated oxygen collects within the oxygen-selective ceramic membranes and an external flow of the oxygen depleted gas forms within the duct. A means is provided for recovering the oxygen from said oxygen-selective ceramic membranes.
Since a duct containing the oxygen-selective ceramic membranes directly connects the exhaust of the expander with the power turbine, the integration is simply accomplished and with the avoidance of a significant pressure drop in extraction of the heated oxygen containing gas from the expander and the reintroduction of the oxygen depleted gas to the power turbine. Further, where oxygen separators are not integrated in the manner set forth above, pressure drops as high as between about 3.45 bar and about an 5.52 bar are often required at the reintroduction point to achieve adequate distribution. This is inefficient in that it requires a greater degree of compression in the first instance.
Another integration is with the burners of a gas turbine of an industrial type. The turboexpander of these units drives both the air compressor and other connected load such as generators or process compressors. The exhaust from the tuboexpander is typically at near atmospheric pressure. This aspect of the present invention provides an oxygen separator for separating oxygen from compressed air flowing to a burner of a gas turbine. An elongated duct, open at opposite ends, is configured to be connected to the burner of the gas turbine to receive a heated oxygen containing gas formed from the compressed air after having been heated and to discharge an oxygen depleted gas. A plurality of oxygen-selective ceramic membranes are provided for extracting oxygen from the heated gas. Such membranes are mounted within the duct so that the oxygen separates from the heated oxygen containing gas. The separated oxygen collects within the oxygen-selective ceramic membranes and an external flow of the oxygen depleted gas forms within the duct. A means is provided for recovering the oxygen from the oxygen-selective ceramic membranes.
The duct can be mounted between the burner and the gas turbine. Alternatively, a pre-burner can be provided to heat the compressed air and t
Drnevich Raymond Francis
Gottzmann Christian Friedrich
Shah Minish Mahendra
Kim Ted
Praxair Technology Inc.
Rosenblum David M.
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