WO2014160104A1

WO2014160104A1 - Method and apparatus for generating oxygen and diluent

Info

Publication number: WO2014160104A1
Application number: PCT/US2014/025825
Authority: WO
Inventors: III William S. ROLLINS
Original assignee: Rollins Iii William S
Priority date: 2013-03-14
Filing date: 2014-03-13
Publication date: 2014-10-02
Also published as: WO2014160104A9

Abstract

A method and system for generating at least one of a desired supply of oxygen and a desired supply of a diluent from a source of heated compressed air. The method/system comprises a housing for receiving heated compressed air and discharging oxygen depleted air. The housing accommodates a first stage of and a second stage of membranes and the first stage is separated from the second stage by a first oxygen-depleted zone. A first interstage exhaust outlet communicates with the first oxygen-depleted zone for discharging a portion of the heated compressed air from the housing while a remaining portion of the heated compressed air, which flows though the second stage of the system, is further depleted of oxygen. The method/system generates at least one of a desired supply of oxygen and a desired supply of a diluent from the source of heated compressed air.

Description

[0001] METHOD AND APPARATUS FOR GENERATING OXYGEN AND DILUENT

[0002] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR

DEVELOPMENT

This invention was made with government support under Cooperative Agreement No, DE-FC28-98FT40343 between Air Products and Chemicals, inc. and the U.S. Department of Energy, The United States Government has certain rights in this invention.

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to a method and apparatus utilizing a specialized separation membrane system for efficiently and effectively obtaining (1 ) a desired quantity of oxygen and/or (2) a desired quantity of a substantially inert diluent.

[0005] BACKGROUND OF THE INVENTION

[0006] Oxygen is a basic element that has a multitude of uses, including industrial, commercial, and medical applications. Although several techniques exist for obtaining oxygen, including pressure swing absorption and molecular sieves; the predominant method for producing oxygen at higher purities and higher production rates is the cryogenic separation process. During the cryogenic separation process, air is typically compressed and cooled to the boiling point of nitrogen/oxygen (the two elements that comprise about 99% of the composition of dry air). Through a distillation process, the nitrogen condenses into a liquid and a stream of oxygen, which is 95+% pure, can be produced. With further refinement, higher purities of oxygen can be obtained. In addition, the liquid nitrogen can be utilized for other applications, and the oxygen can be liquefied by further refrigeration. Single train air separation units (ASU's) have been built that can produce over 4,000 tons of oxygen per day.

[0007] However, typical cryogenic separation processes are expensive, and require a great deal of power to operate. The Department of Energy (DOE) has examined these attributes and determined, for Integrated Gasification Combined Cycle (IGCC) power plants, the ASU represents about 12 to 15% of the overall capital cost of such a plant, and requires a significant amount of auxiliary power to operate. Therefore, the DOE has funded the development of specialized separation membranes (SSMs) that separate oxygen from air at high temperatures. Studies indicate that these membranes, when integrated into power production, can reduce the overall cost of oxygen production as well as the associated power consumption.

>08] These specialized separation membranes are "activated" at elevated temperatures, typically in excess of 700°C (1 , 1 12°F). Some specialized separation membranes are designed to operate in the range of 800 to 900°C (1 ,472°F to 1 ,652°F). Once at the active temperature range, the specialized separation membranes absorb oxygen and the differential pressure across the membrane induces the flow of oxygen through the membrane. Although these plants, incorporating specialized separation membranes, can produce gaseous oxygen, due to their high temperature operation, such plants are not well suited for the production of Iiquid products, such as iiquid oxygen or Iiquid nitrogen. In addition, due to their inherent properties, these membranes, which are ceramic in nature, are thus brittle and subject to failure from several causes:

1) Thermal shock;

2} Mechanical shock;

3) High differential pressures; and

4) Excessive oxygen removal rates.

09] Therefore, great care must be taken to ensure that these specialized separation membranes avoid mechanical shock, i.e., care must be exercised during startup and shutdown of the system to ensure that the specialized separation membranes are slowly heated/cooled in a gradual and even manner so as to avoid thermal shock.

10] In order to pass oxygen efficiently through the specialized separation membranes, a sufficient pressure differentia! must exist between the upstream side (sometimes referred to as "non-permeate side") and downstream side (sometimes referred to as the "permeate side") of the membrane. Although increasing the pressure differential across the specialized separation membranes will increase the oxygen flux, it also increases the stress on the membrane. This may call for increased membrane thickness in order to provide the required structurai integrity. However, increased thickness of the specialized separation membranes reduces the oxygen f!ux. Accordingly, there is a careful balance between the optimum pressure differential and the thickness of the membrane. Once a membrane thickness is chosen, the application must be designed to ensure that the design pressure differential is not exceeded.

[001 1 ] Another problem, which leads to failure of specialized separation membranes, is cracking of the specialized separation membranes due to an excessively high oxygen removal rate. Attempts to remove more than 80% of the oxygen contained within an air stream (e.g., reduce the oxygen content of air from its typical 21 % 0₂ content to an oxygen content of less than 5%, for example), tends to lead to failure of the membrane. Therefore, excessive flux rates must be avoided.

[0012] This inability of the specialized separation membranes to efficiently produce an inert gas stream, e.g. , generally containing less than 5% oxygen (with less than 2% being preferable), is an associated drawback, since such an inert stream of this composition is often required by many gas turbines as a diluent in order to suppress the formation of NOx (oxides of nitrogen) within its combustion system. Therefore, unlike the cryogenic ASU's which can readily supply a diluent steam (primarily nitrogen with less than 2% oxygen), the specialized separation membranes cannot. This usually means that the gas turbine(s), in a plant that utilize specialized separation membranes in lieu of a cryogenic ASU. will typically require water or steam in order to suppress NOx formation. Since this water or steam will eventually be vented up the exhaust stack, this wastes precious water resources.

[0013] Studies have been completed to determine the optimum system and method for integrating these specialized separation membranes with power cycles, particularly IGCC. One such study, initiated by Stein et al. and delivered at the 27^th International Technical Conference on Coal Utilization and Fuel Systems, on March 4-7, 2002, in Coolwater, FL, examined two basic integration methods for specialized separation membranes in an IGCC plant.

[0014] The first method involved direct firing of fuel (syngas in this example) in a pressurized air stream to create a "vitiated" air stream (i.e., one that contains air and the products of combustion). This direct firing step was necessary to raise the temperature of the pressurized air stream to the required temperature (800 to 900°C (1 ,472°F to 1 ,652°F)) for the specialized separation membranes. Some of this vitiated air was directed to the specialized separation membranes, while the remaining portion of this vitiated air was delivered to the combustion section of a gas turbine, which is part of a combined cycle power plant.

The second method employed indirect firing, where the pressurized air stream is indirectly heated in tubes, or some other conventional heat exchange device, it is to be appreciated that in this case, the fuel (e.g., the syngas) is supplied to duct burners in the heat recovery steam generator (HRSG) in order to achieve the necessary temperature in the heat recovery steam generator for heating the pressurized air stream. This heated air was directed to the specialized separation membranes.

Although both the direct and the indirect methods with specialized separation membranes provided a lower cost for oxygen production than the cryogenic process, only the direct-fired specialized separation membranes system was more efficient, while the indirect-fired specialized separation membranes system actually was calculated to have a lower efficiency than even the conventional cryogenic separation process. It is to be appreciated that Sower efficiency not only effects fuel consumption, but also has an impact on the associated capital cost, as the net result is either more and/or larger components (e.g., ASU's, gasifiers, gas cleaning systems, turbines, etc.) are required in order to provide an output which equals that of more efficient systems.

Thus, a prior art system typically includes an IGCC plant integrated with the direct-fired specialized separation membranes. A customized gas turbine (GT) with an oversized compressor section (for extracting excess pressurized air) was employed. A portion of the compressed air, from the gas turbine compressor section, is directed to specialized separation membranes system. The first step consumes fuel in the pressurized air stream in order to increase the temperature of the air stream to the required temperature level. If is to be appreciated that this process consumes some oxygen contained within the air stream, during the combustion process, thereby lowering the overaii oxygen concentration in the now vitiated air stream. In addition, this process has the potential to introduce possible contaminants which may eventually flow to the specia!ized separation membranes, if the fuel is a syngas, as in the case of the !GCC for example, and if a sulfur cleanup system, which is typically located after to the gasification process, were to malfunction for some reason, this could introduce high levels of sulfur into the fuel and ultimately into the specialized separation membranes. Such high levels of sulfur could seriously impact or damage the effectiveness of the specialized separation membranes and thus are to be avoided.

] After leaving the combustion zone, this stream of vitiated air (e.g., the air with combustion byproducts) is then directed to specialized separation membranes. Some oxygen in this vitiated air is able to permeate through the specialized separation membranes toward a zone at a lower pressure. Thereafter, the produced oxygen, still at high temperature, can be cooled and compressed for use in the gasification process or other desired processes at the facility. The non-permeate stream, which does not permeate through the specialized separation membranes, generally becomes an oxygen-depleted stream of vitiated air. This vitiated air stream can be reentered into the gas turbine combustion system and expanded, through the turbine section of the system, to extract energy contained therein,] Turning now to Fig. 1 , this drawing is a basic schematic of the prior art system 1 which integrates specialized separation membranes with a combined cycle power plant. As shown therein, the air 2 is drawn into the compressor section 3 of a gas turbine 4 and compressed in a conventional manner. This compressed air 20 is then directed to a combustor 5 where a suitable fuel 6 is added, mixed and combusted with the compressed air 20 in order to increase the temperature of the air to the required temperature level. This stream of vitiated air is then directed to the specialized separation membranes assembly 7, where some of the oxygen, is removed therefrom. A stream of the removed and produced oxygen 8 may be subsequently cooled, by a heat exchanger 9 for example, to remove and recover heat therefrom and then the oxygen is compressed by a compressor 10, for example, and sent to a desired area of the system 1 where the produced oxygen 8 may be utilized and/or consumed in a desired manner. As such utilization and/or consumption of the produced oxygen 8 is conventional and well known in the art, a further detail description concerning the same is not provided. It is to be appreciated that the energy obtained from cooling the oxygen, e.g., by the heat exchanger 9 for exampie, can be utilized to produce steam and enhance the power output of the steam turbine.

[0020] The remaining gas, which exits from the specialized separation membranes assembly 7, is a vitiated air stream 1 1 which is now depleted of some of its oxygen. This vitiated air stream 1 1 is then directed to the combustor section 12 of the gas turbine 4 where it is heated, by a conventional combustion process, and then expanded through the turbine section 13 of the gas turbine 4.

[0021] For combined cycle applications, the exhaust gases from the gas turbine 4 can be directed to a heat recovery device 14, such as a heat recovery steam generator. The steam, from the heat recovery device14, can then be utilized in a steam turbine (ST) or some other conventional apparatus or engine, for example, in order to produce additional power therefrom.

[0022] Drawbacks of the Prior Art

[0023] Although prior studies indicate that the direct-fired integration scheme for specialized separation membranes will provide lower capital cost and slightly improved efficiency for oxygen production versus a cryogenic system, it is to be appreciated that there are associated drawbacks with this method of integration. Such drawbacks include, for example:

1 ) The direct-firing method consumes oxygen contained within the vitiated air stream, which reduces the oxygen separation potential of the specialized separation membranes;

2) The vitiated air stream can be polluted by contaminants contained within the fuel, such as sulfur, and such contaminants may decrease or destroy the specialized separation membranes ability to separate oxygen;

3) Poor combustion could produce byproducts, such as particulate matter, that could eventually clog the specialized separation membranes;

4) The system is highly integrated with the gas turbine, and issues with the specialized separation membranes could affect the airflow needed in the gas turbine, i.e., the gas turbine may not achieve full power; 5) A separate flow stream (e.g., typically water or steam) must be used as a diluent within the gas turbine combustion system in order to reduce the formation of NOx;

6) Further cost reductions are desirable; and

7) Additional efficiency would not only reduce fuel consumption, but also reduce overall plant costs (and generally a lesser amount of and/or smaller equipment may be required).

[0024] One problem associated with the above discussed combined cycle technology is that by use of currently available technology, it is difficult to efficiently and effectively obtain a sufficient quantity of suitable diluent. That is, a substantially inert gas stream which comprises less than about 5%, more preferably less than about 4% and most preferably less than about 2% oxygen that is suitable for injection into the gas turbine so as to minimize the generation of nitrous oxides within the gas turbine during combustion of the fuel.

[0025] It is to be appreciated that air has an approximate composition of 20.7% oxygen, 77.3% nitrogen, 0.9% argon and 1.1 % H₂O. Moreover, during some applications, it is desirable to produce approximately equal amounts of oxygen and diluent. However, is be appreciated that according to the prior art, it was generally not possible to produce a sufficiently quantity of a depleted oxygen stream, e.g., containing less than about 5%, more preferably less than about 4% and most preferably less than about 2% oxygen, which is suitable for use as a diluent. Further, if all of the oxygen depleted gas could eventually be formed into the diluent, this typically results in production of about 1.5 to 2 times as much diluent as is typically required for many applications.

[0026] Several of the drawbacks to the prior art include issues related to the combustion process. As fuel is directly combusted within an air stream, such fuel consumes oxygen, during combustion, as the fuel is burned and energy is released. This energy heats the air stream, however, the air stream now contains the byproducts of the combustion process. This heated air stream is now a vitiated air stream which includes combustion byproducts, such as H₂O and CO_2i but also typical components such as CO, SOx, NOx, and other byproducts of combustion such as volatile organic compounds (VOC's) and particulate matter. Some of these byproducts, such as the su!fur bearing compounds (SOx) or sulfur oxides and particulate matter, are of particular concern since they can destroy or harm the effectiveness of the specialized separation membranes, e.g., either contaminating, poisoning and/or clogging the specialized separation membranes.

in addition to these potential issues related to combustion, the combustion process consumes oxygen. Typically, ambient air contains approximately 20.7% oxygen by volume. In order to heat ambient air to the required working temperature of 800 to 900°C (1 ,472°F to 1 ,652°F) of the specialized separation membranes, the oxygen content of the vitiated air stream is typically reduced to a content of approximately 16 to 18% oxygen. This lower oxygen content, in turn, produces a lower potential driving force (i.e., the partial pressure of oxygen in the vitiated air stream is reduced), and thus equates to less oxygen that can be permeated and readily removed from the vitiated air at a given air flow. Thus, more air must be compressed in order to separate the desired amount of oxygen during this oxygen separation process. Such additional air compression, in turn, equates to greater power consumption by the system and is to be avoided if at all possible.

Accordingly, the use of an indirect-fired heater for heating an air stream that does not contain any combustion byproducts and has higher oxygen content (containing approximately 20.7% oxygen by volume), can be quite advantageous in generating oxygen and/or diluent.

In addition, the prior art gas turbine 4, diagrammatically illustrated in Fig. , is a customized machine which is designed for use with the specialized separation membrane assembly 7. This customized gas turbine 4 includes an oversized compressor section that provides the necessary air for both the specialized separation membrane assembly 7 as well as the necessary air for the gas turbine 4. Unfortunately, such gas turbine 4 does not currently exist, and a new gas turbine 4, of a similar design, must be developed for the various sized specialized separation membrane systems that require oxygen.

Also, the integrated system, illustrated in Fig. 1 , places a great deal of reliance on the gas turbine 4. Without the gas turbine 4, the oxygen system cannot work. Therefore, an integrated system that places less emphasis on the gas turbine 4, and especially one that utilizes a gas turbine that currently exists and is readily available is highly beneficial.

[0031 ] Another consideration for integration of specialized separation membranes, with power cycies, is the need for a diluent When burning lower rank fuels, such as syngas from an IGCC plant or off-gases from a petrochemical plant, the gas turbine combustion system utilizes a diffusion combustion arrangement, which necessitates an additional inert fluid in the combustion zone in order to dilute the flame temperatures. Studies have shown that the formation of NOx emissions increase exponentially when flame temperatures exceed about 3,000°F.

[0032] According to the prior art, the common practice has been to use water or steam, as a diluent, in order to reduce the formation of NOx within the combustors. However, with an increased emphasis on water conservation, it is preferred to utilize nitrogen (or some other inert gas), especially since nitrogen is a byproduct of oxygen production in the conventional cryogenic ASU. But when oxygen is produced by specialized separation membrane technology, the prior art is unable to produce a sufficient quantity of an inert gas stream-which contains less than about 5%, more preferably less than about 4% and most preferably less than about 2% oxygen-due to the membrane cracking issues noted above when high flux rates were required. Thus, the prior art systems conventionally relied upon use of water or steam, instead of nitrogen, as a diluent.

[0033] SUMMARY OF THE INVENTION

[0034] Wherefore, it is an object of the present invention to address and overcome a number of the above noted drawbacks of the prior art so as to provide a more complete and effective solution to the integration of specialized separation membranes with a variety of different power cycles.

[0035] One object of the present invention is to provide a method and an apparatus for efficiently and effectively obtaining a suitable quantity of diluent (e.g., a syngas diluent) which is a substantially inert gas stream containing less than about 5%, and most preferably less than about 2% oxygen, so that the diluent is thereby a substantially inert gas stream which minimizes the generation or production of any nitrous oxides, during combustion, within the gas turbine. [0036] A further object of the present invention is to provide a method and an apparatus, for use with combined cycle technology as well as other related technologies, for efficiently obtaining a sufficient quantity of the required oxygen..

[0037] The present invention employs a method and a system for integrating an indirect-fired process in combination with at least two separate stages of specialized separation membranes which addresses, solves and/or alleviates many, if not ail, of the above noted and associated drawbacks of the prior art.

[0038] The present invention is directed at a method and a system which is readily capable of producing the desired amount of oxygen and/or diluent/inert gas, by utilization of specialized separation membranes, for a desired power producing facility, e.g., a steel plant where production of oxygen is desired, some other oxygen consuming facility or virtually any other application where the production of either oxygen and/or a diluent is required at relatively low cost and high efficiency.

[0039] Another object of the present invention is to produce only the required amount of oxygen and/or only the required amount of the diluent so as to thereby preserve and conserve precious energy and resources as well as minimize the consumption of the energy input, e.g., coal, oil, natural gas, etc., consumed in order to produce the required oxygen and/or the diluent.

[0040] A still further object of the present invention is to produce the required amount of diluent but avoid producing excess diluent.

[0041 ] A further object of the present invention is to remove a significant portion of the oxygen contained within the compressed air, thus reducing airflow, power consumption and equipment cost.

[0042] Yet another object of the present invention is to utilize indirect firing, to heat the compressed air, so as to alleviate concerns of contamination of the compressed air which may occur by direct firing.

[0043] Another object of the present invention is to provide an oxygen system, such as that included with an IGCC plant, that is more efficient and thus has fewer components and/or smaller equipment which results in a lower overall cost.

[0044] A still further object of the present invention is to increase efficiency thereby extracting more oxygen from a given air flow stream. [0045] Still another object of the present invention is to provide a SS system that can operate independently of the gas turbine (GT) while also providing higher reliability.

[0046] Another object of the present invention is to extract, to the extent feasible, all available energy contained within each one of the flow streams, , or utilize, to the extent possible, ail available energy contained within each one of those flow streams so as to increase the overall efficiency of the system and the method according to the present invention.

[0047] A still further object of the present invention is to supply a stream of diluent that is produced in the SSM system.

[0048] Another object of the present invention is to facilitate extraction of the energy contained within the non-permeated stream and/or the oxygen stream by either converting the energy, contained within either or both of those streams into steam, in a conventional manner, for use in a gas turbine, or by use of a gas expander.

[0049] The present invention also relates to a system for generating at least one of a desired supply of oxygen and a desired supply of a diluent from a source of heated compressed air, the system comprising: a housing having an inlet for supplying the heated compressed air to an interior of the housing and an outlet for discharging oxygen depleted air from the housing; the housing accommodating at least a first stage of specialized separation membranes and a second stage of specialized separation membranes, each of the first and the second stages of specialized separation membranes facilitating contact with the heated compressed air, as the heated compressed air flows through the system and thereby permitting oxygen from the heated compressed air to permeate through the specialized separation membranes and flow into an oxygen supply duct exiting from the housing; the first stage being separated from the second stage by a first oxygen-depleted zone; and a first interstage exhaust outlet communicating with the first oxygen-depleted zone for discharging a portion of the oxygen-depleted air from the housing and thereby preventing the discharged portion, of the oxygen-depleted air exiting via the first interstage exhaust outlet, from flowing though the second stage and being further depleted of oxygen while a remaining portion of the oxygen-depleted air, which flows though the second stage of the system being, being further depleted of oxygen so as to generate at least one of the desired supply of oxygen and the desired supply of a diluent from the source of heated compressed air.

[0050] The present invention also relates to a method of generating at least a desired supply of a diluent from a source of heated compressed air, the method comprising the steps of: generating a stream of heated compressed air; removing oxygen from the stream of heated compressed air so as to form at least a diluent stream; supplying the diluent stream to a gas turbine at an elevated temperature; thus allowing the gas turbine to generate rated power without extracting compressed air from the compressor section of the gas turbine.

[0051] The term "diluent," as used within this patent application and the appended claims, means an inert gas stream which contains a quantify of oxygen which is equal to or less than about 5%, and most preferably less than about 2% oxygen, by volume, which is suitable for injection in a gas turbine combustion system so as to suppress the production of NOx.

[0052] The term "gaseous stream," as used herein and in the appended claims, is intended to mean an oxygen containing gas stream.

[0053] The term "air stream," as used herein and in the appended claims, is intended to mean a stream of gas which primarily comprises air and includes mostly nitrogen and oxygen.

[0054] BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate various embodiments of the invention and together with the general description of the invention given above and the detailed description of the drawings given beiow, serve to explain the principles of the invention. It is to be appreciated that the accompanying drawings are not necessarily to scale since the emphasis is instead placed on illustrating the principles of the invention. The invention will now be described, by way of example, with reference to the accompanying drawings in which:

[0056] Fig. 1 is a diagrammatic drawing of a system which integrates specialized separation membranes with a combined cycle power plant according to the prior art; [0057] Fig. 2 is a diagrammatic drawing showing the multi-stage SSM system and method integrated with a power plant, according to the present invention, for producing a desired quantity of oxygen and/or diluent;

[0058] Fig. 3 is a diagrammatic view showing the dual stage SSM system, according to the present invention, containing a plurality of permeable membranes for forming both the desired oxygen and the desired diluent;

[0059] Fig. 4 is a diagrammatic perspective view illustrating how the oxygen, from the compressed air, flows through the separation membrane, in a conventional manner, and collects downstream of the separation membranes to form a purified oxygen stream;

[0060] Fig. 5 is a diagrammatic view showing the triple stage SSM system, according to the present invention, containing a plurality of permeable membranes for forming both the desired oxygen and the desired diluent;

[0061] Fig. 6 is a diagrammatic view showing the quadruple stage SSfvl system, according to the present invention, containing a plurality of permeable membranes for forming both the desired oxygen and the desired diluent;

[0062] Fig. 7 is a diagrammatic drawing showing a modification of the first embodiment of the multi-stage SSM system, according to the present invention, which provides greater efficiency;

[0063] Fig. 8 is a diagrammatic drawing showing a simplest form of the multi-stage

SSM system, according to the present invention, for producing both a desired amount of oxygen and diluent;

[0064] Fig. 9 is a diagrammatic drawing showing an arrangement incorporating the multi-stage SSM system, according to the present invention, for use in a steel mill or other oxygen consuming facility, for example;

[0065] Fig. 10 is a diagrammatic drawing showing a simplest form of the multi-stage

SS system, according to the present invention, for producing a desired amount of diluent; and

[0066] Fig. 1 1 is a diagrammatic drawing showing the compressed airflow, out of the compressor section, and the gas flow into the turbine section of the gas turbine incorporating the present invention. [0067] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0068] The present invention will be understood by reference to the following detailed description, which should be read in conjunction with the appended drawings. It is to be appreciated that the following detailed description of various embodiments is by way of example only and is not meant to limit, in any way, the scope of the present invention.

[0089] Integrated System

[0070] With reference to Fig. 2, a first embodiment of the present invention will now be discussed. According to this embodiment, the present invention relates to a multi-stage SS system 20 that is able to produce a desired quantity of either, or both, oxygen 0₂ for a desired process and/or a low oxygen content inert gas or diluent for a desired process. This inert gas, for example, may be used as diluent D in a power plant or some other facility. In addition to the multi-stage SSM system 20, the present invention also relates to both a system and a method for integrating the multi-stage SSM system 20 into a desired power cycle, such as a combined cycle power plant.

[0071] According to this embodiment, an "off-the-shelf gas turbine 22 is employed.

Such an "off-the-shelf gas turbine 22 includes, for example, current gas turbines produced by manufacturers that are designed to burn natural gas, fuel oil, or other fuels, including fuel gases. The gas turbine 22, for utilization with the present invention, does not require an oversized compressor section 24 or any other specialized design in order to be incorporated and utilized with the multi-stage SSM system 20 according to the present invention. However, the present invention does not preclude the use of such gas turbines.

[0072] The advantages of an "off-the-shelf gas turbine 22 include, for example:

1) More competitive pricing for the gas turbine;

2) It is proven and commercially available at the present time;

3) The multi-stage SSM system 20 is not dependent upon the gas turbine operation;

4) The supplemental compressor system 28 (discussed below) may be more efficient than the gas turbine compressor section 24; and 5) The gas turbine can obtain full power, even when the SS!vl system is inactive,

As is conventional in the art, a compressor section 24 of the gas turbine 22 typically ingests ambient air and compresses such ambient air to its designed discharge pressure. For a conventional gas turbine 22, such as a GE 7FA or 7FB manufactured by General Electric Company of Fairfield, Connecticut, the compressor discharge pressure is nominally at 225 psia. Depending upon the appiication and system parameters, some of the discharged airfrom this compressor can be directed to the multi-stage SSM system 20, but the amount of the discharged compressed air 23, from the compressor section 24 of the gas turbine 22, which is directed to the multi-stage SSM system 20 typically does not exceed more than 20% of the total compressor discharge flow from the "off-the-shelf gas turbine 22. The remaining 80% of the total compressor discharge flow, from the compressor section 24, is supplied to the gas turbine combustion system 54.

Since most oxygen systems (such as an IGCC plant) may require more oxygen than is contained within this 20% flow of the discharged compressed air 23 from the compressor 24 of the gas turbine 22, a supplemental compressor system 28 may also be employed to provide additional compressed air or possibly may be exclusively utilized. This supplemental compressed air supply system 28 also supplies compressed air 30 which mixes with the discharged compressed air 23 from the compressor section 24 of the gas turbine 22. As shown in Fig. 2, the supplemental compressor system 28 may supply the compressed air 30 at a pressure typically somewhat similar to the pressure of the discharged compressed air 23 from the compressor section 24 of the gas turbine 22. However, it is to be appreciated that this is not a requirement since the compressed air 30, supplied by the supplemental compressor system 28, may be supplied at any desired supply pressure. The compressed air 30, being supplied by the supplemental compressor system 28, typically contains about 20.7% oxygen, for example.

The compressed air 30, from the supplemental gas compression system 28 combines with the gas turbine compressor extraction air 23 and the total combined air flow 26 is the supplied to the inlet of a boost compressor 32 - which is optional and not required for all applications. The optional boost compressor 32, if utilized, is provided for increasing the supply pressure of the compressed air to the desired supply pressure for the multi-stage SSM system 20.

[0078] It is to be appreciated that the particular design of boost compressor 32 is not of particular importance to the present invention. For example, a centrifugal, axial flow, reciprocating, or virtually any other type of compressor may be utilized as the boost compressor. In addition, the boost compressor 32 may or may not include an intercooling feature. In the following discussion, it is assumed that the boost compressor 32 is employed to pressurize the compressed air 26 to the desired pressure. It is to be appreciated that for applications where a diluent D or an oxygen-depleted gas is not required, the boost compressor 32 may not be required or be feasible.

[0077] For example, if the multi-stage SSM system 20 is utilized in a steel mill application for producing oxygen 0₂, electrical power is typically required and the multi-stage SSM system 20 may also be integrated with a combined cycle power plant that is fueled by natural gas. For such application-especia!ly if the gas turbine 22 has a Dry Low NOx (DLN) combustion system-there is no need for diluent D in the gas turbine 22. Therefore, the only product required to be generated by the multi-stage SSM system 20 is oxygen 0₂, Although this plant may not require a multi-stage system, as described below in further detail, it still may be more efficient to utilize the present invention, since the multi-stage SSM system 20 extracts more oxygen 0₂ from the gas stream (i.e., has a lower oxygen content in the gas stream exiting the multi-stage SSM system 20). This reduces the inlet gas flow requirements for the multi-stage SSM system 20 and thus reduces the power required for gas compression. Therefore, another advantage of the present invention is a reduction in air/gas consumption as well as a reduction in parasitic load.

[0078] However, for applications where diluent D or a higher-pressure stream of oxygen-depleted gas is required, the boost compressor 32 may be beneficial or highly desirable. An example of this application would be for a coal-based IGCC plant. The GE 7FB gas turbine, for such a plant, burns syngas in its combustors, and utilizes a diffusion combustion system that requires a diluent D in order to control NOx production and/or emissions. The preferred diluent D is an inert gas containing iess than less than about 5%, and most preferably less than about 2% oxygen. For modern !GCC plants, this is a stream of gas comprising primarily, or mostly, nitrogen that is supplied by the cryogenic ASU. An example of such an "off- the-shelf gas turbine 22 and an !GCC arrangement is the Duke Edwardsport !GCC facility in Edwardsport, Indiana ("Duke Edwardsport !GGC").

The diluent D for the GE 7FB gas turbine, besides typically containing less than 2% oxygen, must be at a supply pressure of 460 psia or higher. The pressure of the discharged air, from the compressor of the GE 7FB gas turbine, is nominally 225 psia. Although the 225 psia air from the GE 7FB gas turbine could be heated to 800 to 900°C (1 ,472°F to 1 ,652⁰F), this would necessitate that the created diluent D (still at a temperature of typically between 800 to 900°C (1 ,472°F to 1 ,652°F)) be compressed to over 460 psia. This method is not advisable for the following major reasons:

1 ) Compressor materials may not be available for compressing gases at the elevated temperatures of 800 to 900°C (1 ,472°F to 1 _S652°F);

2) Compressor materials at elevated temperatures are expensive; and

3) It takes more energy to compress a hot gas than to compress a cold or cooler gas.

Therefore, the boost compressor 32 alleviates these issues by compressing the cooler gases (i.e., air) prior to such air being heated.

Another advantage to the boost compressor 32 is an improvement in the effectiveness of the multi-stage SSSV1 system 20. It is to be appreciated that as the pressure increases this, in turn, increases the partial pressure of the oxygen on the non-permeate side of the membrane which facilitates improved transfer of the oxygen 0₂ through the specialized separation membranes. This also increases oxygen flow rate per unit area of the specialized separation membrane and thus reduces the size as well as potential cost of the multi-stage SSM system 20. Accordingly, in some instances where a diluent D or an oxygen-depleted gas is not required, it still may be advantageous to utilize the boost compressor 32.

After the compressed air exits from the boost compressor 32 (if provided), the compressed air may flow into an inlet of a conventional heat exchanger 34 where the temperature of the compressed air is partially heated toward the desired supply temperature of typically between 800 to 900°C (1 ,472°F to 1 ,652°F), due to heat being transferred from the higher temperature gas stream exiting from the multistage SSM system 20, which is discussed below in further detail. The partially preheated compressed air then exhausts from an outlet of the conventional heat exchanger 34 and is supplied to an inlet of an indirect heater 36 for additional heating.

[0083] The indirect heater 38, in turn, heats the compressed air to the required supply temperature for the multi-stage SSM system 20, which is typically 800 to 900^CC (1472 to 1 ,652°F). It is to be appreciated that indirect heater 36 can comprise a variety of different heating devices including, for example, a fired heater, an electric resistance heater or heat exchanger with another fluid, etc. The important aspect of the indirect heater 38 is that the compressed air is sufficiently heated to the required supply temperature of typically about 800 to 900°C (1 ,472°F to 1 ,652°F) without depleting the oxygen content contained within the compressed air and also without adding any impurities or pollutants thereto.

[0084] In the event that a fired heater is employed, typically there will be some remaining heat that can be recovered from the exhaust stream, of the indirect heater 36, and recovered and utilized in a conventional manner somewhere within the system. For a system incorporating the GE 7FB gas turbine, the typically temperature of the compressed air, which discharges from the outlet of the boost compressor 32, is approximately 820°F. In such instance, the fired heater 36 would have an exhaust temperature at least at this temperature. This energy, e.g., heat, could be utilized to generate steam, in a conventional manner, that could be used in the steam turbine to supplement the power generation at the facility incorporating the multi-stage SSM system 20.

[0085] Once the compressed air has been sufficiently heated to the required supply temperature of between 800° to 900X (1 ,472° to 1 ,652°F), such heated compressed air 38 is then supplied to the inlet of the multi-stage SSM system 20. The multi-stage SSM system 20, as shown in further detail in Fig. 3, is a dual stage SSM system 20. As noted above in the background section, it is important, for efficiency reasons, to only produce: 1 ) the desired quantity of oxygen 0₂, 2) the desired quantity of diluent D (or the oxygen-depleted gas), and/or 3) the desired quantity of both oxygen 0₂ and diluent D (or the oxygen-depieted gas) with the multistage SSM system 20 according to the present invention. St is to be appreciated that generating an insufficient amount of either oxygen O, and/orthe diluent D decreases the capacity of the plant, while producing an excess amount of either the oxygen 0₂ and/or the diluent D generally increases the overall production costs and requires more energy. The present invention permits precise control of the amount of oxygen 0₂ and/or diluent D which is to be produced,

[0086] In the embodiment discussed below, it is assumed that the heated compressed air 38, supplied to the inlet of the multi-stage SSM system 20, is heated compressed air which typically has a composition of 20.7% oxygen. 77.3% nitrogen, 0.9% argon and 1.1 % H₂0. As is apparent from this assumption, the heated compressed air contains significantly more nitrogen than it does oxygen. For a typical IGCC application at 640 MW, the diluent D requirement for a pair of gas turbines would be approximately 1 ,000,000 Sb/hr total while the oxygen requirement would be approximately 420,000 Ib/hr, at 95% purity. To provide the required oxygen, the multi-stage SSM system 20 must be nominally supplied with 2,000,000 ib/hr of heated compressed air.

[0087] As diagrammatically shown in Fig. 3, the heated compressed air 38 enters the inlet of the multi-stage SSM system 20 and then passes through the first stage 40 of the multi-stage SSM system 20. The first stage 40 includes a first array of specialized membranes. As noted above, the oxygen contained within the heated compressed air flows over and contacts the exposed surfaces of the specialized separation membranes 42, located within the first stage 40, and permeates therethrough from the high pressure non-permeated side to the low pressure permeate side (such permeation of the oxygen through the specialized separation membranes 42 is discussed below with reference to Fig. 4). The remaining oxygen- depleted air, referred to herein as the first stage non-permeate stream 44, is an oxygen-depleted air stream and exits the first stage 40, as diagrammatically shown in Fig. 3.

[0088] After passing though the first stage 40, the multi-stage SSM system 20 only produces or extracts a desired portion of the required oxygen 0₂, but has essentially produced zero percent of the required diluent D, since the first stage non-permeate stream 44, exiting from the first stage 40, still contains too much oxygen, e.g., may still have an oxygen content ranging from about 5-12 %, for example.

[0089] If the entire first stage non-permeated stream 44 were directed toward and permitted to flow through the second stage 48 of the multi-stage SSM system 20, comprising a second array of specialized separation membranes 43, such volume of the first stage non-permeated stream 44 would most likely produce an excessive amount of diluent D and, as noted above, this is to be avoided. Therefore, according to the present invention, one solution for controlling production of the diluent D is to permit only a desired quantity of the first stage non-permeated stream 44 to flow through the second stage 46, while a remaining portion of the first stage non- permeated stream 44 is directly exhausted from the multi-stage SSM system 20 by way of a first interstage exhaust outlet 48. As such, the portion of the first stage non-permeated stream 44, which is exhausted by the interstage exhaust outlet 48, thereby avoids flowing thought the second stage 46 of the SSM system 20 and is not formed into a diluent D. However, the portion of the first stage non-permeated stream 44, which is permitted to flow through the second stage 46, is permitted to contact the exposed surfaces of the specialized separation membranes 43 of the second stage 46 and oxygen, contained within the first stage non-permeated stream 44, is permitted to permeate through the specialized separation membranes 43 of the second stage 46, from the high pressure non-permeated side to the low pressure permeate side, and generate additional oxygen 0₂. The remaining flow stream, referred to as a second stage non~permeate stream 52, is generally a diluent D, i.e., a sufficiently oxygen-depleted inert gas that typically contains less than 2% oxygen.

[0090] As noted above and shown in Fig. 3, this diluent D, at an elevated temperature, is then supplied to the heat exchanger 34 where a portion of the heat is removed from the diluent D and transferred to the compressed air 26 to assist with partial heating the compressed air prior to supplying the same to the indirect heater 36 (see Fig. 2). Thereafter, the diluent D is conveyed to the gas turbine combustion system 54, briefly discussed above and shown in Fig. 2,

[0091 ] It is to be appreciated that the production rate of the diluent D can be adequately controlled by controlling the amount and/or flow rate of first stage non- permeated stream 44 that is vented or exhausted by the interstage exhaust outlet 48 of the multi-stage SSM system 20, and thereby avoid flowing through the second stage 46 of the multi-stage SSM system 20, versus the amount and/or flow rate of first stage non-permeated stream 44 thai is permitted to flow through the second stage 48 of the multi-stage SSM system 20. A first interstage exhaust outlet flow valve 80 is coupled to a control unit 62, which incorporates a processor, as well as various sensors (not shown in detail) which are installed at various locations throughout the multi-stage SSM system 20 for detecting and supplying various temperature, pressure and flow reading and measurements to the control unit 62. The first interstage exhaust outlet flow valve 80, possibly located adjacent the first interstage exhaust outlet 48, controls the flow rate of the first stage non-permeated stream 44 which is permitted to exhaust out through the interstage exhaust outlet 48 of the multi-stage SSM system 20 and thereby bypass the second stage 46 of the multi-stage SSM system 20. The control valve 80 may also be a control valve or set of control valves at the inlet of an expander turbine 64.

in view of the above arrangement, the portion stream of the first stage non- permeated stream 44 which is permitted to flow through the second stage 46 of the SSM system 20, and thereafter eventually exits from the multi-stage SSM system 20 as a second stage non-permeated stream 52, generally produces the desired quantity of the diluent D which has an oxygen content of typically less than about 5%, and most preferably less than about 2% oxygen. In addition, all of the oxygen 0₂ which is produced by first stage 40 of the multi-stage SSM system 20 may be combined with the oxygen 0₂ produced by the second stage 46 of the multi-stage SSM system 20 so as to produce the required amount of oxygen 0₂ which can, thereafter, be utilized or consumed within the plant or facility in a conventional manner.

Since the oxygen 0₂, which is generated by the multi-stage SSM system 20, is still essentially at the same temperature at which the compressed air was when such compressed air entered the multi-stage SSM system 20, the generated oxygen 0₂ may be subsequently cooled in order to remove the associated excess energy therefrom, if desired, before this oxygen 0₂ is eventually processed further, e.g., compressed for further use, combined with the fuel during the gasification process, etc. The energy removed/recovered from the produced oxygen 0₂ may be subsequently utilized to perform a number of desired functions, such as preheating air/gas supplied to the heater, producing steam for the plant, etc.

[0094] The portion of the first stage non-permeated stream 44, that exhausts from the multi-stage SSM system 20, via the interstage exhaust outlet 48 and thus avoids passing through the second stage 48, also typically exits the multi-stage SSM system 20 at a pressurize and at a temperature at or near the temperature and pressure at which the heated compressed air entered the multi-stage SSM system 20. The portion of the first stage non-permeated stream 44, that exhausts from the multi-stage SSM system 20, may be directed to an expander 64 (Fig. 2), for example, in order to produce power and, thereafter, subsequently sent to a conventional heat recovery device Alternatively, the energy contained within the exhausted first stage non-permeated stream 44 may be utilized for a variety of other conventional purposes.

[0095] The second stage non-permeate stream 52, which forms the diluent D, is also at high pressure and at a high temperature. Although the diluent D may be compressed, it is typically more advantageous to use the boost compressor 32 (Fig. 2) to provide the diluent D at the required pressure within the SSM system. That is, it is desirable to supply the diluent D to the gas turbine 22 at a temperature typically no greater than 1 ,000^CF. Therefore, this second stage non-permeate stream 52 or diluent D can be utilized to preheat the compressed air. via the heat exchanger 34, or used to generate steam for some other process, or utilized by some other conventional heat recovery process.

[0098] For a typical process, the heated compressed air 38, with 20.7% oxygen content by volume, is supplied to the inlet of the multi-stage SSM system 20. The oxygen content of the oxygen-depleted air stream 44, exiting the first stage 40, is typically between 5 and 16% oxygen by volume.

[0097] As noted above, the first stage non-permeated stream 44 exits from the specialized separation membranes 42 of the first stage 40 and a portion of that first stage non-permeated stream 44 is exhausted out through the first interstage exhaust outlet flow valve 60 and thus bypasses the second stage 46 of the multi-stage SSM system 20, while a remainder of the first stage non-permeated stream 44 flows through the second stage 46. Typically, between about 0% to about 90% of the first

" 2 - stage non-permeated stream 44 (mass basis) is discharged out through the first interstage exhaust outlet flow valve 80 while typically between about 100% to about 10% (mass basis) of the first stage non-permeated stream 44 flows through the second stage 46.

[0098] The second stage non-permeate stream 52, which forms the diluent D, exits from the second stage 48 of the multi-stage SSM system 20. Typically between about 0% to about 80% (mass basis) of the supplied heated compressed air 38 exits the final stage as a diluent.

[0099] With reference now to Fig. 4, a brief description concerning the conventional process of how the oxygen flows or permeates through the membrane 42 will now be briefly discussed. As diagrammatically shown in that drawing, the heated compressed air flows over and along the exposed surfaces of the membranes 42. As noted above, the heated compressed air is at a temperature of between 800 to 900°C (1 ,472°F to 1 ,652°F) and typically at a pressure of greater than or equal to 14 bar (200 psia). According to this example, the oxygen, contained within the heated compressed air, will permeate through the membrane 42 to the permeate side, due to a pressure differential.

[0100] With reference now to Fig. 5, a detailed description concerning the triple- stage SSM system 20', according to the present invention, will now be described. As this embodiment is similar to the dual stage SSM system 20 described above, only the differences between the triple-stage embodiment and the dual-stage embodiment will be discussed in detail.

[0101] As diagrammatically shown in Fig. 5, the heated compressed air 38 enters the inlet of the triple-stage SSM system 20' and then passes through the first stage 40 of the triple-stage SSM system 20'. As noted above, the oxygen contained within the heated compressed air flows permeates through the membranes from the high pressure non-permeated side to the low pressure permeate side. As noted above, the first stage non-permeate stream 44 is generally an oxygen-depleted air stream.

[0102] As with the dual-stage SSM system 20, only a desired quantity of the first stage non-permeated stream 44 is permitted to flow through the second stage 46, while a remaining portion of the first stage non-permeated stream 44 is directly exhausted from the triple-stage SSM system 20' by way of the first interstage exhaust outlet 48. As such, the remaining portion of the first stage non-permeated stream 44, which is permitted to flow through the second stage 46, contacts the exposed surfaces of the specialized separation membranes 43 of the second stage 46 and generates additional oxygen O. Due to utilization of either a lesser amount of and/or smaller sized specialized separation membranes 42, the second stage non-permeate stream 52, according to this embodiment, is generally an oxygen- depleted gas that still contains more than 2% oxygen.

[0103] As with the first embodiment, a first interstage exhaust outlet flow valve 60 is typically located adjacent the interstage exhaust outlet 48 and is coupled to the centra! control unit 62 for controlling the flow rate of the first stage non-permeated stream 44 which permitted to exhaust out through the first interstage exhaust outlet 48 of the triple-stage SSM system 20^! and thereby bypass the subsequent second and third stages 46, 68 of the triple-stage SSM system 20'.

[0104] If the entire second stage non-permeated stream 52 were directed toward and flow through the third stage 68 of the triple-stage SSM system 20', such volume of the second stage non-permeated stream 52 may, or possibly may not, produce an excess amount of the diluent D. Therefore, according to the present invention, only a desired quantity of the second stage non-permeated stream 52 is permitted to flow through the third stage 68, while a remaining portion of the second stage non-permeated stream 52 is directly exhausted from the triple-stage SSM system 20' by way of a second interstage exhaust outlet 70, As such, the exhausted portion of the second stage non-permeated stream 52 thereby avoids flowing through the third stage 68 of the triple-stage SSM system 20' and is not formed into the diluent D. However, the portion of the second stage non-permeated stream 52, which is permitted to flow through the third stage 68, is permitted to contact the exposed surfaces of the specialized separation membranes 45 of the third stage 68 and some of the remaining oxygen, contained within the second stage non-permeated stream 52, is permitted to permeate through the specialized separation membranes 45 of the third stage 68, from the high pressure non-permeated side to the low pressure permeate side, and generate additional oxygen O. The remaining flow stream, referred to as a third stage non-permeate stream 72, is generally the diluent D, i.e., a sufficiently oxygen-depleted inert gas that typically contains less than 2% oxygen. As noted above, this diluent D is then supplied to the heat exchanger 34 where a portion of the heat and/or energy is removed from the diiuent D prior to use,

Turning now to Fig. 6, a detailed description concerning the quadruple-stage SSM system 20", according to the present invention, will now be described. As this embodiment is similar to the triple stage SSM system 20' described above, only the differences between the quadruple-stage embodiment and the triple-stage embodiment will be discussed in detail.

As diagrammaticaily shown in Fig. 8, the heated compressed air 38 enters the inlet of the quadruple-stage SSM system 20" and then passes through the first stage 40 of the quadruple-stage SSM system 20". As noted above, the oxygen contained within the compressed air flows over and contacts the exposed surfaces of the specialized separation membranes 42 of the first stage 40 and permeates therethrough from the high pressure non-permeated side to the low pressure permeate side. As noted above, the first stage non~permeate stream 44 is generally a partially oxygen-depleted air stream.

As with both the dual-stage and triple-stage SSM systems 20, 20', only a desired quantity of the first stage non-permeated stream 44 is permitted to flow through the second stage 46, while a remaining portion of the first stage non- permeated stream 44 is directly exhausted from the quadruple-stage SSM system 20" by way of the first interstage exhaust outlet 48. As such, the remaining portion of the first stage non-permeated stream 44, which is permitted to flow through the second stage 46, and contact the exposed surfaces of the specialized separation membranes 43 of the second stage 46, generates additional oxygen O. Due to utilization of either a lesser amount of and/or smaller sized specialized separation membranes 43, the second stage non-permeate stream 52, is generally a partially oxygen-depleted gas which still contains more than 2% oxygen.

As with the first and second embodiments, the first interstage exhaust outlet flow valve 60 is typically located adjacent the first interstage exhaust outlet 48 and is coupled to the central control unit 62 for controlling the flow rate of the first stage non-permeated stream 44 which permitted to exhaust out through the first interstage exhaust outlet 48 of the quadruple-stage SSM system 20" and thereby bypass the subsequent second, third, and four stages 46, 68, 74 of the quadruple-stage SSM system 20".

[0109] !f the entire second stage non-permeated stream 52 were directed toward and permitted to fiow through the third stage 68 of the quadruple-stage SSM system 20", such volume of the second stage non-permeated stream 52 may, or possibly may not, produce excess di!uent D. Therefore, according to the present invention, only a desired quantity of the second stage non-permeated stream 52 is permitted to flow through the third stage 68, while a remaining portion of the second stage non-permeated stream 52 is directly exhausted from the quadruple-stage SSM system 20" by way of a second interstage exhaust outlet 70. A second interstage exhaust outlet flow valve 71 , also coupled to the control unit 62, is typically located adjacent the second interstage exhaust outlet 70 for controlling the flow rate of the second stage non-permeated stream 52 which permitted to exhaust out through the second interstage exhaust outlet 70 of the SSM system 20" and thereby bypass the third stage 68 of the multi-stage SSM system 20". As such, the exhausted portion of the second stage non-permeated stream 52 thereby avoids flowing thought the third stage 68 of the quadruple-stage SSM system 20" and is not formed into a diluent D. However, the portion of the second stage non-permeated stream 52, which is permitted to flow through the third stage 68, is permitted to contact the exposed surfaces of the specialized separation membranes 45 of the third stage 68 and a portion of the remaining oxygen, contained within the second stage non- permeated stream 52, is permitted to permeate through the third stage membranes 45, from the high pressure non-permeated side to the low pressure permeate side, and generate additional oxygen O. It is to be appreciated that the remaining fiow stream, referred to as a third stage non-permeate stream 72, still typically contains a quantity of oxygen greater than 2%.

[01 10] If the entire third stage non-permeated stream 72 were directed toward and through the fourth stage 74 of the quadruple-stage SSM system 20", such volume of the third stage non-permeated stream 72 may, or possibly may not, produce excess diluent D. Therefore, according to the present invention, only a desired quantity of the third stage non-permeated stream 72 is permitted to flow through the fourth stage 74, while a remaining portion of the third stage non-permeated stream 72 is directly exhausted from the quadruple-stage SSM system 20" by way of a third interstage exhaust outlet 76. A third interstage exhaust outlet flow valve 77, also coupled to the control unit 82, is typically located adjacent the third interstage exhaust outlet 76 for controlling the flow rate of the third stage non-permeated stream 72 which permitted to exhaust out through the third interstage exhaust outlet 76 of the SSM system 20" and thereby bypass the fourth stage 74 of the multi-stage SSM system 20". As such, the exhausted portion of the third stage non-permeated stream 72 thereby avoids flowing thought the fourth stage 74 of the quadruple-stage SSM system 20", which comprises a fourth array of specialized separation membranes 47, and is not formed into a diluent D. However, the portion of the third stage non-permeated stream 72, which is permitted to fiow through the fourth stage 74, is permitted to contact the exposed surfaces of the specialized separation membranes 47 of the fourth stage 74 and some of the remaining oxygen, contained within the third stage non-permeated stream 72, is permitted to permeate through the specialized separation membranes 47 of the fourth stage 74, from the high pressure non-permeated side to the low pressure permeate side, and generate additional oxygen O. The remaining fiow stream, referred to as a fourth stage non- permeate stream 78, is generally the diluent D, i.e., a sufficiently oxygen-depleted inert gas that typically contains less than 2% oxygen. As noted above, this diluent D is then supplied to the heat exchanger 34 where a portion of the heat/energy is removed from the diluent D, as noted above, prior to utilization thereof.

[01 1 1 ] Turning now to Fig. 7, a detailed description concerning a modification of the embodiment shown in Fig. 2 will now be described. As this embodiment is similar to the first embodiment described above with reference to Fig. 2, only the differences between this embodiment and the first embodiment will be discussed in detail.

[01 12] The major difference between this second embodiment and the first embodiment is location of the indirect heater 36. According this embodiment, the indirect heater 36 is located directly within the heat recovery steam generator which facilitates initial heating of the compressed air 28. The most important benefit of locating the indirect heater 38 within the heat recovery steam generator is that the exhaust gases, from the gas turbine 22, which are typically near 1 , 100°F, can be further heated by energy now supplied to the duct burners in the HRSG, the compressed air can be heated to its desired temperature of between 800 to 900°C (1 ,472°F to 1 ,652°F). As a resuit of locating the indirect heater 36 within the heat recovery steam generator, the amount of heat that is required to the heat compressed air 26 to its desired temperature of between 800 to 900°C (1 ,472°F to 1 ,652"F) is significantly reduced thereby resulting in an overall cost savings. In addition, the energy exiting the indirect heater is utilized in the HRSG to produce additional steam and more energetic steam and increase the power generation. Other than the above noted modification, the second embodiment is substantially identical to the first embodiment in all other respects.

] It is to be appreciated that the feature of the present invention are consistent with the combined cycle technology set forth in United States Patent No. 6,230,480 and related patents, integration with the technology of the present invention in GCC applications not only provides for heat recovery within the heat recovery steam generator, but also maximizes efficiency by using this energy to enhance the overall efficiency of the bottoming cycle (steam cycle in most instances).

] The following example, of an IGCC plant, similarto Duke Edwardsporf IGCC, with 2 gas turbines. 2 heat recovery steam generators, and one steam turbine, generally is in accordance with Fig. 7 of the drawings except that the air compressor 28 is a standalone compressor which compresses 2.8 million Ib/hr of air. Since there generally is not any need to extract air from the compressor section of the GT, the air compressor 28 compresses the air to a pressure of about 520 psia, either with or without a separate boost compressor. This compressed air is then preheated, in the heat exchanger 34, and then divided into two equal streams and supplied to the heating sections in each of two heat recovery steam generators, where it is heated to a nominal temperature of 1 ,600°F, This combined pressurized, heated air stream is then directed to the SSM system.

] The SSM system comprises a dual stage SSM system 20. The heated air contacts the membranes, in the first stage, and the oxygen permeates through the membranes and is delivered to the non-permeate side of the membranes, which is typically maintained at a pressure of about 5 psia. About 510,000 Ib/hr of the oxygen permeates through the membranes, while the remaining flow of air passes through the first stage to the interstage area. The oxygen content of the interstage flow is typically about 5.3%.

[01 18] For proper control, typically about 1 ,300,000 !b/hr of this interstage flow is vented, or directed out, of the dual stage SSM system 20 to the expander 64, where this vented stream may be used to produce shaft power and/or electrical power. The exhaust conditions of the expander 64 are nominally at atmospheric pressure and a temperature of about 560°F. This stream may be supplied to an economizer, for example, to preheat feed water for use in the steam cycle.

[01 17] With the utilization of a highly fired HRSG, there is a generally need for a great deal of feed water. Some of this feed water may be heated in the economizer section of the HRSG, however, there is generally insufficient energy to preheat all the system feed water within the HRSG. Thus, additional feed water can be preheated by recouping heat or energy from other energy streams, such as the exhaust gas from the expander 64. Again, this represents another advantage of the present invention,

[01 18] The remaining interstage flow, of approximately 990,000 Ib/hr, is directed to the second stage 46 of the dual stage SSM system 20. This oxygen depleted air stream 44 is typically at a nominal pressure of 490 psia and a temperature of 1 ,60G°F. An additional 40,000 !b/hr of oxygen, from this stream, typically permeates through the membranes of the second stage 46 and combines with the permeated oxygen from the first stage oxygen stream. Total oxygen 0₂ flow is 550,000 Ib/hr which is typically the required flow of oxygen for the plant. The flow of the second stage non-permeated stream 52 is reduced to 950,000 Ib/hr at an oxygen content of approximately 1.7%, e.g., a suitable diluent. This stream of diluent D is then supplied to the heat exchanger 34, for preheating air, prior to being supplied to the HRSG. This diluent stream is then typically divided into two equal diluent D streams which are each at a pressure of about 460 psia and a temperature of about 1 ,000°F + 200-500°F and supplied, as diluent, to each one of the two (2) gas turbines 22.

[01 19] The combined permeated oxygen, now at a pressure of about 5 psia and a temperature of about 1 ,600^QF, may be directed, for example, to a heat recovery device that boils feed water into high-pressure saturated steam. This steam may be subsequently supplied to each HRSG, where it is superheated and reheated in the steam cycle. Again, the highly fired HRSG provides the needed energy to improve the steam cycle efficiency.

[0120] The cooled oxygen, which exits the heat recovery device (e.g., an oxygen cooler), is then compressed for use in the gasification plant. In this example, the oxygen is compressed to a pressure of about 1 ,000 psia for use in the high-pressure gasifiers.

[0121] Any additional syngas produced by the gasification plant, beyond that required by either or both of the gas turbine combustion system 54 and/or any other associated IGCC plant equipment, is supplied to the duct burners in the HRSG. The heat, not consumed by the air heaters 36, in the HRSG, is typically utilized to superheat, reheat, and produce steam. This improves the efficiency of the steam cycle, and thus overall IGCC plant efficiency.

[0122] Although similar in physical size to the Duke Edwardsport IGCC, a facility which incorporates the features of the present invention produces a net power output of 980 MW, e.g., about a 54% increase over the Duke Edwardsport IGCC plant. With the SSIV1 system and the low cost added capacity in the steam cycle, the incremental cost for building this facility is only about 20% more. Thus, the specific capital costs are reduced by about 28% from $500Q7kW to $3,900/kW. Further, the plant heat rate, for a plant incorporating the features of the present invention, calculates to about 8,665 BTU/kWh.

[0123] Thus, this example of the present invention - when compared to a conventional IGCC plant - produces about 54% more power, costs about 28% less to construct on a $/kW basis and consumes about 2.5% less fuel per MWh. Since the present invention, according to this example, still only has two GTs, two HRSG's, and one ST, the operating and maintenance costs are projected to be about 30% less. Overall, the present invention has a much lower cost of electricity production than a conventional IGCC plant.

[0124] The following example will compare an optimized IGCC plant, incorporating the present invention, versus the Duke Edwardsport IGCC plant. The Duke Edwardsport IGCC plant has two GT's (GE 7FB's) and a nominal 300 MW steam turbine. The gasifiers produce the syngas using oxygen from a cryogenic ASU. Net plant output is nominally 630 MW, with a heat rate of approximately 8,890 BTU/kwh. Total plant cost is in excess of $3 billion, with an estimated specific cost of about $5,000 per kW.

[0125] A similar plant, employing both SSM oxygen separation and duct firing in the HRSG, as disclosed and discussed above, can provide the following important functions, namely, 1 ) heat the compressed air for the SSM system, 2) increase the plant capacity (in the steam cycle) at only an incremental cost, and 3) allow for improved heat recovery in the plant.

[0128] This new integrated approach, according to the present invention, still utilizes only two GT's - similar to the Duke Edwardsport IGCC- and two HRSG's, however, the steam turbine ("ST") is increased from about 300 MW to about 675 MVV. The gasifier capacity is increased, and the oxygen capacity is also increased. However, there is no need for any additional diluent, as there are still only two gas turbines 22. This factor serves to increase plant efficiency and less overall air needs to be compressed by the system according to the present invention.

[0127] Another important factor, in overall plant efficiency, is the optimization of the gas turbines 22. A GE 7FB gas turbine can produce up to 232 MVV (if is to be appreciated that the shaft torque is the limiting factor). However, as more diluent and/or more fuel is supplied to the turbine section of the gas turbine, the mass flow through the turbine section increases, and the power output increases. To offset these factors, generally compressed air is extracted from the discharge of the compressor section of the gas turbines. This practice reduces the gas turbine output to acceptable levels.

[0128] The extracted air from the compressor section of the gas turbine can be supplied to the SSM system. However, this can add additional cost and complication, and the extracted airflow is relatively small (typically only 2 to 20%) compared to the total air required by the SSM system. In this example, it is to be appreciated that it is more efficient and cost effective to operate the compressor section of the gas turbine without any air extraction.

[0129] Turning now to and examining the gas turbine for this application, the syngas has a nominal energy content of 4,823 BTU/lb. This is considerably less than natural gas which is 21 ,5 5 BTU/lb. Therefore, if the gas turbine 22 is burning syngas, instead of natural gas, the gas turbine 22 requires a greater mass flow of fuel. This added fuel flow (supplied at the required fuel pressure of about 400 psi) increases the mass flow through the turbine section of the gas turbine 22. This, in turn, increases the power output. A diluent must be provided to control the formation of NOx during combustion.

] The gas turbine combustion system is supplied with air, from the compressor, fuel and diluent, and then heats this entire combined flow to the required turbine firing temperature, nominally about 2,350°F for a turbine of this type. This combined flow is then directed to the turbine section of the gas turbine 22 and produces much more power than in the case of a gas turbine which is fired by natural gas. In many instances, the power increase is so large that the generated power is too great for the shaft to transmit safely to the generator, i.e., the gas turbine reaches its torque limit. To alleviate this high power output issue, for most !GCC applications the gas turbines are designed to extract a desired amount of air from the discharge of the compressor section. This practice, in turn, reduces the airflow through the turbine section of the gas turbine 22 and thus reduces the generated power to, or below, the torque limit for the gas turbine (typically about 232 MW for the GE 7FB).

] However, extraction of air from the compressor section of the gas turbine 22 is not always desirable. Since such extracted air only represents about 2-20% of the total ASU air supply requirements, a second air compression system is still required. If may be more efficient and less costly to provide this additional 2-20% of compressed air from a single, separate air compressor system as briefly noted above. However, power plant operators typically want to operate their gas turbines at their full load and at their most efficient operating parameters. This may necessitate the use of air extraction from the compressor section of the gas turbine. Moreover, since it requires a significant amount of energy in order to compress the air in the compressor section of the gas turbine, it is desirable to use such compressed air somewhere within the IGCC plant rather than to discard and waste such compressed air, which is inefficient.

] With reference now to Fig. 8, a brief description concerning a broader form of the present invention, shown in this Figure, will now be briefly described. As this embodiment is similar to the first embodiment described above, only the differences between this embodiment and the first embodiment will be discussed in detail. [0133] As shown in Fig. 8, the basic components of the multi-stage SSM system 20, according to the present invention for producing a desired quantity of either a diluent D and/or for producing a desired quantity of oxygen 0₂, are shown. That is, as will be appreciated from this Figure, the multi-stage SSM system 20 may be utilized with virtually any desired source of energy and/or at virtually any facility for producing a desired quantity of either a desired quantity of oxygen 0₂ and/or a diluent D.

[0134] Turning now to Fig. 9, a brief description concerning another embodiment of the invention will now be discussed. As this embodiment is similar to the first embodiment described above with reference to Fig. 2, only the differences between this embodiment and the first embodiment will be discussed in detail.

[0135] The primary difference between this embodiment in the previous embodiment is that the production of a diluent D is not required by this embodiment. That is, this embodiment is only primarily interested in producing an adequate supply of oxygen 0₂ but is not particularly interested in producing any diluent D. As indicated in Fig. 7, the fired heater may be incorporated into the HRSG, and the fuel for the gas turbines and duct burners may be natural gas, oil, or other fuel besides syngas.

[0136] Now turning now to Fig. 10, a brief description concerning a still further embodiment of the present invention will now be discussed. As this embodiment is similar to the embodiment of Fig. 9, only the differences between the this embodiment and the first embodiment will be discussed in detail.

[0137] The primary difference between this embodiment and the previous embodiment is that the production of either a desired diluent D and/or oxygen 0₂ may be obtained. As indicated in Fig. 7, the fired heater may be incorporated into the HRSG, and the fuel for the gas turbines and duct burners may be natural gas, oil, or other fuel besides syngas.

[0138] With reference now to Fig. 1 1 , a brief description concerning the major components of a gas turbine, for an IGCC plant, will now be discussed. Ambient air 1 10 is drawn into the compressor section 1 2 of the gas turbine and compressed in a conventional manner. The generated compressed air 1 14, discharged from the compressor section 1 12, is split into first and second airstreams. The first stream comprises a majority of the generated compressed air 1 18 which is directed to the combustion system 120 of the turbine section of the gas turbine, while the second stream comprises an air extraction 1 18, e.g., a small fraction or portion of the compressed air, which is extracted, via a control valve 140, and available for use within the IGCC plant. The extracted air 1 16 may only comprise about 2 to 5% of the compressed air 1 14. For a GE 7FB, this would typically equate to about 60,000 to 150,000 Ib/hr of air.

[0139] The first stream of compressed air 1 18 flows to the combustion system 120 for the gas turbine where that generated compressed air 1 18, and the syngas (fuel) 122 are combusted. The diluent is also supplied to the combustion system. The combusted gases (including the diluent) 126 (e.g., at a nominal temperature of 2,350°F for a GE 7FB application), are then directed into an in!et of the turbine section 128 of the gas GT where the heated and combusted gases 126 expand within the turbine section of the gas turbine and produce power in a conventional manner. The heated and combusted gases 126 eventually exit the turbine section 128 of the gas turbine as exhaust gases 130. The power, created by expansion of the heated and combusted gases 126 within the turbine section 128 of the gas turbine, in turn, drives the shaft which drivingly interconnects, with one another, the compressor section 1 12, which generates the compressed air, the turbine section 128 and the generator 150, which generates electricity.

[0140] To achieve optimum combustion, it is desirable to maintain the heating value of the combustion reactants (the fuel 122 and the diluent 124) between 125 and 150 BTU/SCF (BTU per standard cubic foot). It is to be appreciated that this value may change depending upon the fuel composition, the hydrogen content of the fuel and other fuel and system related factors and parameters.

[0141] In a cryogenic oxygen separation plant, the diluent (e.g., mostly nitrogen) generally exits the ASU at a low pressure and at a temperature that is slightly less than ambient. This diluent must first be compressed to about 460 psia in order to be utilized within the turbine section 120 of the GT. As a result of typically conventional compression and intercooling, the supply temperature for the diluent is typically between 200°F and 400°F. This diluent is generally sufficient to suppress the formation of NOx to acceptable levels.

[0142] According to the present invention, the pressurized diluent D typically exits the SSM system at a nominal temperature of 1 ,600°F and at a pressure typically above 350 psi, for example. By supplying this higher temperature diluent D to the combustion system 120 for the gas turbine, more initial energy is delivered to the combustion system, and less fuel is typically required to heat the compressed air 1 18, the syngas (fuel) 122 and the diluent 124 to the firing temperature (e.g., 2,350°F in this example) of the GT. Thus, even if the temperature of the diluent D is reduced to about 1 ,000°F (e.g., by transferring some of its heat to the compressed air via use of the heat exchange 34, for example), still less fuel and thus less diluent D is required by the combustion system 120.

For this GE 7FB application, with about 4,823 BTU/lb in the fuel, the diluent flow calculates to about 474,000 Ib/hr. With the reduced fuel flow and reduced diluent flow, the power produced in the turbine section of the gas turbine is thus reduced, and so the gas turbine can achieve full power (232 MW in this example) without the need for any air extraction 1 16. This increases the efficiency of the gas turbine while, at the same time, eliminates the need for any associated air extraction piping, valves, controls, and other related equipment. This, in turn, simplifies and reduces the overall cost of the IGCC plant.

Since the SSM process, according to the present invention, produces high temperature diluent - in this example the diluent D is supplied to the gas turbines at a temperature of about 1 ,000°F - such higher temperature diluent D provides additional energy to the combustion system 120 and thus, reduces the required input flow of fuel. This provides several benefits, namely, 1) the gas turbine is more efficient, 2) the fuel/diluent mix is typically within the design specification of the GT, 3) the gas turbine does not need to extract air from the compressor in order to maintain the central shaft of the gas turbine within its recommended torque limit.

As is apparent from the above discussion, the multi-stage SSM system 20 utilizes a multi-stage approach for removing oxygen 0₂ from the supplied heated compressed air. Although a dual stage system is shown in Figs. 2 and 3 by way of example, it is to be appreciated, however, that the muiti-stage SSM system 20 may comprise a three stage system and the associated method (see Fig. 5), a four stage system and the associated method (see Fig. 8), or possibly five or more stages (not shown in detail but included as part of the present invention) depending upon the overall production/consumption requirements of the facilitate. ] Each one of the primary oxygen supply conduits eventually combine with one another into a common primary oxygen supply duct. It is to be appreciated, however, that one or more of the oxygen supply conduits do not have to be combined with one another into a common primary oxygen supply duct but couid be separately utilize within the process, if so desired. The oxygen 0₂, flowing through the common primary oxygen supply duct, is then fed to the oxygen consumption area of the facility, e.g., a gasification process.

] The heated compressed air which eventually passes through and exits from the second stage 46 of the specialized separation membranes 43 typically has an oxygen content of equal to or less than about 5%, and most preferably less than about 2% oxygen, for example, depending upon the amount of the specialized separation membranes 43, the size of the specialized separation membranes 43 in the second stage, the length or depth of the second stage 48, the flow rate of the heated compressed airthrough the second stage, etc. This compressed air, with the reduced oxygen content, then flows out through the housing outlet and forms the diluent D for the desired use, e.g., for supply to the gas turbine 22, for example. As noted above, the diluent D is substantially an inert gas which is effective in reducing nitrous oxide production within the gas turbine 22. Prior to being supplied to the gas turbine 22, this syngas diluent D typically passes through the heat exchanger 34 which is utilized for preheating the compressed air to be supplied to the housing,] The heated compressed air typically enters the multi-stage SSM system 20 at a pressure P1 and at a required temperature, which typically is between 800 to 900°C (1 ,472°F to 1 ,652°F), for example. It is to be appreciated that for this system, the gaseous stream could include ambient air, vitiated air from a combustion process, or some other oxygen containing gas stream. A portion of the oxygen 0₂ is removed by the first stage 40, as the gaseous stream permeates through the specialized separation membranes 42 to the lower pressure side of the membrane 42. Between the first and the second stages 40, 46, some of the interstage oxygen- depleted air may be removed from the multi-stage SSM system 20. Some interstage oxygen-depleted air continues to the second stage 48 where more oxygen 0₂ is removed. The gas stream exhausting from the second stage 46 may contain less than about 5%, and most preferably less than about 2% oxygen. This is achieved, however, without exceeding a nominal 80% oxygen extraction rate since an excessive flux rate can, as noted above, lead to membrane failure.

[0149] As the heated compressed air, with the reduced oxygen content, flows through the second array of membrane modules, additional oxygen is removed from the heated compressed air, with the reduced oxygen content, before this heated compressed air can eventually exit from the second opposite side of the second array of membrane modules. For example, the heated compressed air, with the reduced oxygen content, will typically have an oxygen content of approximately 16.0- 5.0%, as this heated compressed air enters and commences flowing through the second array of membrane modules. As described above, the second array of membrane modules are designed to further reduce the oxygen content of the heated compressed air, with the reduced oxygen content, as this air passes through and exiting from the second array of membrane modules, to an oxygen content of equal to or less than about 5%, and most preferably less than about 2% oxygen.

[0150] By way of example, the dual stage SSM system 20 of Fig. 3 may utilize pressurized ambient air at required temperature as its input gaseous stream. Ambient air contains 20.7% oxygen and as this air passes over and aiong the membrane surfaces, 70% of the air is permitted to permeate through the membrane surface to the iow-pressure side of the membrane. This leaves 6.2% oxygen in the interstage area of the SSM system 20. This interstage gas, as noted above, is then directed toward the second stage 46 of the SSM system 20 where again 70% of the oxygen content of the air is permitted to permeate through the surface of the membrane 42 to the low-pressure side of the membrane 42, This results in a gas stream, which exits from the SSM system 20, after passing through both stages, that typically contains 1.86% oxygen. Since this stream contains mostly nitrogen and argon, with possibly trace amounts of other gases, and generally less than 2% oxygen, it can be utilized as diluent D in the gas turbine(s), thereby eiiminating the need for utilizing water or steam in the gas turbine(s) 22 for NOx suppression.

[0151] The process for calculating the performance of specialized separation membranes is well known in the art and briefly discussed below. The flow across the membrane 42 is a function of several parameters, including the oxygen partial pressure on the supply side, the oxygen partial pressure on the permeate side, the surface area of the specialized separation membrane 42, the effectiveness of the specialized separation membrane 42, and a few other factors.

[0152] The flow of oxygen through a specialized separation membrane depends upon a pressure differential between the partial pressure of the oxygen in the supply gas stream versus the partial pressure of the oxygen in the permeate stream located within the common oxygen supply duct, As this partial pressure differential is reduced, there is less flux through the membrane. Once the non-permeate and permeate partial pressures become substantialiy equal, there is very little oxygen flow through the specialized separation membrane.

[0153] For specialized separation membranes, the oxygen recovery rate, R, is defined as a fraction of the oxygen removed from the supply stream as a proportion of that available.

[0154] For a given gas stream supplied to a specialized separation membrane with pressure P, temperature T, and oxygen composition X_{SU P(y}, only oxygen permeates through the membrane to a Sower pressure P_perrn. The temperature of the permeated stream remains substantially unchanged and the permeated composition is 100% oxygen.

[0155] The portion of the gas stream that does not permeate through the membrane - referred to as non-permeated stream - remains at pressure P and temperature T. However, it has now been depleted of some of its oxygen content and given the symbol X_np. The maximum theoretical oxygen recovery rate, R_T, for a specialized separation membrane is given as:

Π - Y \ p

_D rp " supply perm

_ χ ( p _ p )

supply perm )

[0156] Actual oxygen recovery rate R is theoretical oxygen recovery rate R_T times an effectiveness coefficient E. A typical effectiveness coefficient might be, for example, 85%. Therefore,

R = R_T * E.

[0157] The resultant oxygen ^ con ce ntration in the n on- permeate stream X._in is given by X _t„. - _^{<ilp /i'}- — the equation:

n" (I - RX_supply ) [0158] The following examines the prior art IGCC of Fig. 1 and assumes a commercially available gas turbine, like the GE 7FB for instance. Although the GE 7FB can only provide a portion of the airflow needed by the SSM system in an IGCC, the following will examine such system with the assumption that the arrangement wi!f have an insufficient airflow.

[0159] The compressor discharge pressure of the GE 7FB is nominally 225 psia.

This will serve as the supply gas stream. By utilizing a direct-fired system (fuel is combusted within the air stream to raise its temperature), the vitiated air stream oxygen content X_supp is approximately 16.5%.

[0160] Since lower permeate pressures provide higher yields, it is desired to create low pressures downstream of the specialized separation membranes. However, due to limitations of the oxygen compressor, valves, controls and system pressure drops, a practical limit for the permeate pressure is approximately 5 psia (absolute pressure),

[0161] Therefore, theoretical oxygen recovery rate R_T, for this example, is 0.885.

With an effectiveness of 0.85, if is to be appreciated that the actual oxygen recovery rate is 0.752.

[0162] The non-permeate oxygen content is calculated to be 0.0467. This 4.67% oxygen content represents the minimum oxygen content that can be practically realized in the prior art. As this oxygen content is greater than 2%, this non- permeate stream may not generally meet the requirements for diluent imposed by the gas turbine manufacturer and is thus not suitable for as a diluent.

[0163] In addition, the non-permeate is produced at a pressure of about 225 psia.

This pressure is far less than the 450 psia pressure required by the gas turbine. Although compression of non-permeate is possible, it is difficult to accomplish at higher temperatures, as discussed previously.

[0164] Thus, referring to the prior art, not only was the removal of more than 80% of the oxygen in a SSM probiematic (potential cracking issues for membranes), there was essentially insufficient system parameters to facilitate the production of the diluent, that is, an inert gas with iess than about 5%, and most preferably iess than about 2% oxygen.

[0165] As is weil known in the art, the specialized separation membrane 42 can be extremely selective and very fast in transporting or conveying the oxygen 0₂ from the heated compressed air through the dense specialized separation membrane 42 and collecting the same as a high purity oxygen gas stream for eventual consumption or use.

[0186] A suitable source for specialized separation membranes 42, for use with the present invention, are ceramic Ion Transport Membranes (IT ) produced by Air Products and Chemicals, Inc. An alternative source of specialized separation membranes 42, for use with the present invention, are Oxygen Transport Membranes (OT ) produced by Praxair, Inc.

[0167] The present invention may be suitable, for example, for an application where a steel mill consumes 2,520 tons per day (TPD) of oxygen during its manufacturing process, and also wishes to generate their own electricity, and sell the excess power to the grid, in this example, natural gas is selected as the fuel, and the optimum plant using SSM technology is also selected

[0188] The 2,520 TPD of oxygen equates to 210,000 Ib/hr of oxygen. For power, it is assumed that the steel mill requires 30 MW, and can sell the remaining power at favorable rates to a utility company, for example. In this example, a 54.2 MW combined cycle power plant, with a heat rate of 6,497 Btu/kwh LHV, is deemed optimum for this application.

[0169] As noted above in the prior art discussion, a direct-fired SSM system could be designed as generally indicated in Fig. 1. However, calculation for a single stage system indicates that this plant can only produce 2, 188 TPD of oxygen. In order to compensate for this inadequate quantity, the airflow to the air compressor must be increased. In addition, since the goal is to maximize power production, the heat recovery equipment can be used downstream of the expander to recover exhausted energy.

[0170] With this, the inlet air compressor flow is increased to 1 ,442,000 Ib/hr to provide the required oxygen flow of 210,000 Ib/hr. [0171] From the SSM performance data, this system can produce 10.4 MW and requires 305 M Btu LHV of natural gas. With an LM6000PD combined cycle power plant, the total power output for this plant is 84.6 MW and the total natural gas consumption is 657 MMBtu.

[0172] Thus, the combined plant from the prior art produces a net 64.8 MW, 2,520 TPD of oxygen and consumes 857 MMBtu of natural gas.

[0173] However, there are inefficiencies in every process. The air compression is less than 100% efficient (e.g., 84% in this example) and the expander efficiency is 80% in this example. In addition, there are heat losses and pressure drops for any system. Therefore, minimizing the airflow to achieve a given tonnage of oxygen leads to improved efficiency.

[0174] To integrate the SSM process with a combined cycle, as diagrammatically generally illustrate in Fig. 8, for example, an LM6000PD gas turbine may be fired with natural gas. The overall combined cycle utilizes NovelEdge Technology, described in United States Patent No. 6,230,480, and other related patents. A generous amount of supplemental firing is utilized in the HRSG to achieve high temperatures at the exit of the duct burner. The air heating section, downstream of the duct burners, heats the compressed air to the required temperature, 1 ,610°F in this example.

[0175] Thus, this new combined cycle plant, according to the present invention, produces a net 1 1 1 MW and 2,520 TPD of contained oxygen and consumes 929 MMBtu. Although this new integrated combined cycle plant consumes more fuel than plant from the prior art, it also produces substantially more power. The incremental fuel consumption is 929-657 or 272 MMBtu of natural gas. The incremental power production is 1 1 1-65 or 46 MW. Thus the incremental heat rate is 5913 Btu/kwh or better than the base combined cycle plant at 6,497 Btu/kwh. Thus, this integrated concept demonstrates improved efficiency over the prior art.

[0176] The following description will examine and provide comparisons between several IGCC options. The first option is to construct a plant similar to a plant in currently in operation, such as the Duke Edwardsport IGCC plant. This plant has a two (2) GE 7FB GT and utilizes single stage slurry-fed gasifiers. It produces approximately 630 MW of net power. [0177] The oxygen system for this plant typically produces about 395,000 Ib/hr of oxygen and 1 ,035,000 Ib/hr of diluent (mostly nitrogen) with an inlet airflow, to the ASU, of approximately 1 ,825,210 Ib/hr.

[0178] Since ambient air contains about 20.8% oxygen on a volume basis, and 23.0% on a mass basis, the total contained oxygen in the inlet airflow is about 419,800 Ib/hr. Thus, this cryogenic air system removes and captures approximately 94.1 % of the oxygen from the ambient air and supplies this to the IGCC plant. See Table 1 for a comparison of this oxygen removai technology versus other SSM options.

[0179] In addition, the cryogenic ASU from the prior art can supply large quantities of diluent, as it is adept at creating streams of oxygen and nitrogen with only small amounts of impurities contained within each stream. Thus, once oxygen is sufficiently separated, almost all remaining gases can be utilized as diluent. However, as previously discussed, a cryogenic plant, according to the prior art, is relatively large, expensive and generally consumes a great deal of energy.

[0180] A SSM system, according to the prior art, typically utilizes a direct-fired process, as generally illustrated in Fig. 1. The compressed air, discharged from the compressor section of a gas turbine, is typically directed to a fired heater which heats the air via a direct combustion process. This, in turn, typically reduces the oxygen content of the direct fired air to an oxygen content of about 18%. With heated air at a pressure of about 200 psia, for example, the practical maximum oxygen extraction rate would reduce the oxygen content of the vitiated air stream to about 5%. With an inlet airflow of 2,750,000 Ib/hr, this equates to a nominal oxygen recovery of about 382,000 ib/hr. Since the inlet airflow contains about 632,500 Ib/hr of oxygen, the oxygen recovery rate for this prior art system is approximately 60.4% of the total inlet airflow. It is to be appreciated, however, that this prior art system is incapable of creating a low-oxygen content diluent stream, e.g., a diluent stream containing less than 5% oxygen.

[0181] One embodiment of the present invention, as generally shown in Fig. 2, utilizes a boost compressor in order to increase the pressure of the air which is supplied the multi-stage SSM system. Although almost any pressure may be utilized, one reason for pressurization of the air supplied to inlet of the multi-stage SSM system is to create a diluent flow for the gas turbine(s) that wi!l arrive at the diluent connection, for the gas turbine(s), at the required pressure so that a subsequent compression of the diluent, flowing from the multi-stage SSM system, is generally not required prior to suppling the same to the gas turbine(s).

In addition, a fired heated is used to indirectly heat the compressed air. Thus, this compressed and heated air stream does not contain any combustion byproducts and still contains approximately 20.8% oxygen (by volume). This heated air stream is then directed to the multi-stage SSM system, according to the present invention, so as to maximize the amount of oxygen that can be readily separated, removed and recovered from this heated air stream.

The multi-stage SSM system, according to the present invention, generally requires airflow of 2,369,850 !b/hr. Such airflow, supplied to the inlet of the multistage SSM system, has a total oxygen content of about 545,060 Ib/hr of which about 378,970 Ib/hr of oxygen is typically removed by the multi-stage SSM system. This results in an oxygen removal rate of 69.5% of the total oxygen which is contained within the heated airflow supplied to the multi-stage SSM system. In addition, the multi-stage SSM system creates about 1 ,101 ,260 Ib/hr of a diluent stream which contains less than 2% oxygen. This diluent stream is cooled and subsequently supplied to the gas turbine(s), as described above. In this example, briefly discussed above and generally shown in Fig. 2, the diluent stream, which typically has an oxygen content of less than 2%, nominally comprises 46.5% of the inlet airflow which was supplied to the inlet of the multi-stage SSM system.

Another example of the present invention is illustrated in Fig. 7. Similar to Fig. 2, compressed air is boosted to a suitable pressure such that the diluent, created within the multi-stage SSM system, is supplied to and arrives as the gas turbine(s) at the required pressure for utilization. After passing through the boost compressor, the compressed air is directed to a heating section imbedded within the HRSG. Typically, this heating section is located downstream of duct burners within the HRSG, which are needed to create the necessary temperatures for heating the air. The exhaust gases, from the duct burners, provide the required heat to the compressed air, and these exhaust gases exit the compressed air heating section and subsequently supply heat within the HRSG for the production of steam. [0185] This compressed heated air is then directed to the inlet of the multi-stage SSM system as described above,

[0186] One example of the multi-stage SSM system, as generally shown in Fig. 7, typically requires an inlet airflow of 2,480,000 !b/hr to the system. This inlet airflow has a total oxygen content of about 570,400 Ib/hr and approximately 481 ,540 Ib/hr of oxygen is removed by the multi-stage SSM system from this inlet airflow. This results in an oxygen removal rate of about 84.4% of the total oxygen contained within the inlet airflow to the multi-stage SSM system. In addition, this multi-stage SSM system creates approximately 857.000 Ib/hr of a diluent stream which contains less than 2% oxygen. This diluent stream is then cooled and subsequently supplied to the gas turbine(s). in this example as generally shown in Fig. 7, the flow of diluent, containing less than 2% oxygen, nominally comprises about 26.5% of the inlet airflow which is supplied to the multi-stage SSM system.

[0187] Another example of the present invention is an integrated system for the production of either oxygen or diluent, or both. In this system, as generally shown in Fig. 8, the compressed air is supplied to the heating section, which can be either a fired heater, as generally shown in Fig. 2, or a heating section typically located within the HRSG, as generally illustrated in Fig. 7. The compressed and heated air stream is then subsequently supplied to the inlet of the multi-stage SSM system, however, the flow of non-permeated oxygen depleted air, which exhausts out through any of the interstage exhaust outlet(s), is reduced to zero. According to this system, high separation of oxygen and diluent is possible.

[0188] The multi-stage SSM system, as generally shown in Fig. 8, typically requires an inlet airflow of approximately 2,480,000 Ib/hr into the system. This inlet airflow has a total oxygen content of about 570,400 Ib/hr and approximately 530,000 Ib/hr of oxygen is removed by the multi-stage SSM system from this inlet airflow. This results in an oxygen removal rate of about 92.9% of the total oxygen contained within the inlet airflow supplied to the multi-stage SSM system. It is to be appreciated that this oxygen removal rate is very close to the removal rate for the cryogenic system. In addition, this multi-stage SSM system creates approximately 1 ,950,000 Ib/hr of a diluent stream which contains less than 2% oxygen. In this example as generally shown in Fig, 8, the flow of diluent, containing less than 2% oxygen, nominally comprises about 78.6% of the inlet airflow supplied to the multistage SSM system. It is to be appreciated the oxygen and/or diluent streams may be utilized at desired or required location within the process, or vented to atmosphere, depending upon the particular needs of the facility accommodating the system.

[0189] In view of the above discussion, it is to be appreciated that the present invention has the capability to remove a high percentage of oxygen from the airflow supplied to the inlet of the multi-stage SSM system, similar to that of cryogenic systems. In addition, the present invention has the ability of creating or generating a diluent stream that also represents a high percentage of the inlet airflow supplied to the system.

[0190] SSM systems, according to the prior art, are typically only capable of removing and capturing up to 60% of the oxygen contained within from the inlet airflow, and such oxygen removal rate is generally not adequate to result in a stream which is sufficient to be utilized as a diluent stream. The multi-stage SSM system, according to the present invention, is able to remove and capture over 60% of the oxygen contained within the inlet airflow supplied to the system, and can thus create a diluent stream that is from approximately 0% to approximately 80% of the inlet airflow supplied to the multi-stage SSM system.

[0191] Of particular importance, the multi-stage SSM system, according to the present invention, has the flexibility of providing both the desired or required amount of oxygen and/or the desired or required amount of diluent for virtually any application, such as an IGCC plant, with an oxygen removal or recovery rate typically ranging from about 60 to approximately 100%, while having the capability of generating a diluent stream that ranges from about 0 to about 80% of the inlet ambient airflow which is supplied to the multi-stage SSfvl system. Table 1

] In the above description and appended drawings, it is to be appreciated that only the terms "consisting of and "consisting only of are to be construed in the limitative sense while of all other terms are to be construed as being open-ended and given the broadest possible meaning.

] While various embodiments of the present invention have been described in detail, it is apparent that various modifications and alterations of those embodiments will occur to and be readily apparent those skilled in the art. However, it is to be expressly understood that such modifications and alterations are within the scope and spirit of the present invention, as set forth in the appended claims. Further, the invention(s) described herein is capable of other embodiments and of being practiced or of being carried out in various other related ways, in addition, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

Claims

Wherefore, I claim:

1. A system for generating at least one of a desired supply of oxygen and a desired supply of a diluent from a source of heated compressed air, the system comprising:

a housing having an inlet for supplying the heated compressed air to an interior of the housing and a housing outlet for discharging non-permeated oxygen depleted air from the housing;

the housing accommodating at least a first stage of specialized separation membranes and a second stage of specialized separation membranes, each of the first and the second stages of spedaiized separation membranes facilitating contact with the heated compressed air, as the heated compressed air flows through the system and thereby permitting oxygen from the heated compressed air to permeate through the specialized separation membranes and flow into an oxygen supply duct which exits from the housing;

the first stage being separated from the second stage by a first oxygen-depleted zone; and

a first interstage exhaust outlet communicating with the first oxygen- depleted zone for discharging a portion of the non-permeated oxygen depleted air from the housing and controlling a flow of the non-permeated oxygen depleted air supplied to the second stage of the system for further depletion of oxygen therefrom so as to generate at least one of the desired supply of oxygen and the desired supply of a diluent from the source of heated compressed air.

2. The system according to claim 1 , wherein the heated compressed air, supplied to the inlet of the housing, is indirectly heated via a heater so as to avoid reducing any oxygen content of the heated compressed air suppiied to the inlet of the housing and also avoid introducing any contaminants into the heated compressed air.

3. The system according to claim 2, wherein the heater indirectly heats the compressed air to a temperature of between about 800 to 900°C (1 ,472°F to 1 ,652°F) without depleting the oxygen content contained therein.

4. The system according to claim 2, wherein a first compressor compresses air to an elevated pressure for supply to the heater.

5. The system according to claim 1 , wherein the diluent, which is discharged from the housing outlet of the housing, is supplied to a heat exchanger where heat is removed from the diluent and utilized to heat the compressed air being supplied to the inlet of the housing.

6. The system according to claim 4, wherein a supplemental compressor, in addition to the first compressor, supplies compressed air to a boost

compressor, and the boost compressor further increases a supply pressure of the compressed air being supplied to the inlet of the housing.

7. The system according to claim 1 , wherein the discharged portion of the oxygen depleted air, which exits from the housing via the first interstage exhaust outlet, is supplied to a heat recovery device where heat is recovered therefrom.

8. The system according to claim 1 , wherein the housing accommodates third stage of specialized separation membranes;

the second stage is separated from the third stage and the housing outlet by a second oxygen-depleted zone; and

a second interstage exhaust outlet communicates with the second oxygen-depleted zone for discharging a portion of the oxygen depleted air from the housing and preventing the discharged portion of the oxygen depleted air, exiting via the second interstage exhaust outlet, from flowing though the third stage of the system and being further depleted of oxygen.

9. The system according to claim 8, wherein the housing accommodates fourth stage of specialized separation membranes;

the third stage is separated from the fourth stage and the housing outlet by a third oxygen-depleted zone; and

a third interstage exhaust outlet communicates with the third oxygen-depleted zone for discharging a portion of the oxygen depleted air from the housing and preventing the discharged portion of the oxygen depleted air, exiting via the third exhaust outlet, from flowing though the fourth stage of the system and being further depleted of oxygen.

10. The system according to claim 1 , wherein the heated compressed air, which exits from the housing outlet is sufficiently depleted of oxygen and thus forms the diluent which has an oxygen content of about 5% or less of oxygen, and more preferably 2% or less of oxygen,

1 1. The system according to claim 1 , wherein the system minimizes the flow of air through the system and thus minimizes a power required for gas compression by removing a greater percentage of oxygen from the heated compressed air.

12. The system according to claim 1 , wherein the diluent, exhausting from the housing outlet of the housing has an oxygen content of about 5% or less, and an oxygen extraction rate, from the heated compressed air, is prevented from exceeding 80% in any membrane so as to avoid failure of the specialized separation membranes.

13. The system according to claim 1 , wherein in the second stage, the oxygen from the oxygen depleted air is permitted to permeate through the surface of the specialized separation membranes to a low-pressure side of the membrane which communicates with an oxygen supply duct.

14. The system according to claim 1 , wherein the system is integrated into a plant to facilitate production of at least one of the desired supply of the oxygen and the desired supply of the diluent from the heated compressed air.

15. A method of generating at least a supply of oxygen from heated compressed air, the method comprising the steps of:

supplying heated compressed air into an interior of a housing, via a housing inlet, and discharging oxygen depleted air from a housing outlet of the housing;

accommodating, within the housing, at least first and second stages of specialized separation membranes, and supplying oxygen which permeates through the specialized separation membranes to one or more oxygen supply ducts;

separating the first stage from the second stage by a first oxygen- depleted zone; and

connecting a first interstage exhaust outlet with the first oxygen- depleted zone for discharging a portion of the oxygen depleted air from the housing and preventing the discharged portion of the oxygen depleted air from flowing though the second stage of the system and being further depleted of oxygen while a remainder of the oxygen depleted air, which flows though the second stage of the system, is further depleted of oxygen.

18. The method of generating at least a supply of oxygen from heated compressed air according to claim 15, further comprising the step removing additionai oxygen, from the oxygen depleted air which flows though the second stage of the system, so as to form a diluent which has an oxygen content of 5% or less.

17. The method of generating at least a supply of oxygen from heated compressed air according to claim 15, further comprising the step of indirectly heating the compressed air, supplied to the inlet of the housing, via a heater so as to avoid reducing oxygen content of the heat compressed air and introducing any contaminants into the heated compressed air.

18. The method of generating at least a supply of oxygen from heated compressed air according to claim 15, further comprising the step of indirectly heating the compressed air to a temperature of between about 800 to 900°C (1 ,472°F to 1 ,652°F); and

compressing the air, via a first compressor, and supplying the compressed air to a boost compressor for increasing a supply pressure of the compressed air to a pressure greater than 300 psia.

19. The method of generating at least a supply of oxygen from heated compressed air according to claim 18, further comprising the step

accommodating a third stage of specialized separation membranes within the housing;

separating the second stage from the third stage and the housing outlet by a second oxygen-depleted zone; and

connecting a second interstage exhaust outlet with the second oxygen-depleted zone for discharging a portion of the oxygen depleted air from the housing and preventing the discharged portion of the oxygen depleted air, exiting via the second interstage exhaust outlet, from flowing though the third stage of the system and being further depleted of oxygen.

20. The method of generating at least a supply of oxygen from heated compressed air according to claim 19, further comprising the step of

accommodating a fourth stage of specialized separation membranes within the housing;

separating the third stage from the fourth stage and the housing outlet by a third oxygen-depleted zone; and

connecting a third interstage exhaust outlet with the third oxygen- depleted zone for discharging a portion of the oxygen depleted air from the housing to prevent that discharged portion of the oxygen depleted air, exiting via the third exhaust outlet, from flowing though the fourth stage of the system and being further depleted of oxygen.

21. A method of generating at least a desired supply of a diluent from a source of heated compressed air, the method comprising the steps of:

generating a stream of heated compressed air;

removing oxygen from the stream of heated compressed air so as to form at least a diluent stream;

supplying the diluent stream to a gas turbine at an elevated temperature;

utilizing the diluent stream to reduce nitrous oxide formation in a gas turbine combustion system; and

supplying sufficient energy to allow the gas turbine to generate rated power without extracting compressed air from a compressor section of the gas turbine.

22. The method of generating at least the desired supply of the diluent from the source of heated compressed air according to claim 21 , further comprising the step removing oxygen, from the stream of the heated compressed air, so that the diluent stream has an oxygen content of less than 5% of oxygen.

23. The method of generating at least the desired supply of the diluent from the source of heated compressed air according to claim 21 , further comprising the step of supplying the diluent stream, to the gas turbine, at a temperature between 500^UF and 1 ,200°F and a pressure of at least 350 psi.

24. The method of generating at least the desired supply of the diluent from the source of heated compressed air according to claim 21 , further comprising the step of minimizing a fuel flow and a diluent stream flow so that the gas turbine can achieve full power without any air extraction from the gas turbine thereby increasing efficiency of the gas turbine white, at the same time, eliminating the need for any associated air extraction piping, valves, controls, and other related equipment.

25. A multistage SSM system for removing oxygen contained within a supply gas, the multistage SSM system comprising:

an inlet for supplying the supplying gas and an outlet for

discharging a non-permeated oxygen depleted air; and

a plurality of specialized separation membranes which facilitate contact with the heated supply gas, as the heated supply gas flows through the multistage SSM system and thereby permitting oxygen, from the heated supply gas to permeate through the specialized separation membranes and flow into one or more oxygen supply ducts;

wherein the specialized separation membranes are arranged in stages which permit greater than 80% of a mass of the oxygen, contained within the supply gas, to be removed by the multistage SSM system.

26. The multistage system according to claim 25, wherein the specialized separation membranes are arranged in stages which permit generation of a diluent stream which ranges from 0% to 80% of the mass of a total of the supply gas supplied to the inlet.

27. The multistage system according to claim 25, wherein a flow of oxygen depleted air, which is permitted to flow out through at least one interstage exhaust outlet, is minimized so that both oxygen recovery, from the supply gas, and production of a diluent stream, from the supply gas, are both maximized.

28. The multistage system according to claim 25, wherein the multistage system produces sufficient diluent to meet requirements of the plant and/or the gas turbine.

29. A power plant incorporating a muitistage SSM system for at least one of removing oxygen contained within a heated supply gas and generating a diluent from the heated supply gas, the multistage SSM system comprising:

an inlet for supplying the heated supplying gas and an outlet for discharging a non-permeated oxygen depleted air;

a plurality of specialized separation membranes which facilitate contact with the heated supply gas, as the heated supply gas flows through the multistage SSM system and thereby permitting oxygen, from the heated supply gas, to permeate through the specialized separation membranes and flow into one or more oxygen supply ducts;

wherein a heater for heating the supply gas. which is supplied to the muitistage SSM system, is located within a heat recovery steam generator.

30. The power plant incorporating the multistage SSM system according to ciaim 29, wherein the heater for heating the supply gas comprises a heating section of the heat recovery steam generator.

31. The power plant incorporating the multistage SSM system according to claim 30, wherein the heat exchanger is located downstream of duct burners in the heat recovery steam generator.

32. The power plant incorporating the muitistage SSM system according to claim 29, wherein the heating section, located within the heat recovery steam generator, heats the supply gas, for the multistage SSM system, to a temperature of at least 800°C.

33. The power plant incorporating the multistage SSM system according to claim 29, wherein gases which exit the heating section, in the heat recovery steam generator, provide energy to the heat recovery steam generator for enhancing at least one of steam production and steam cycle efficiency.

34. The power plant incorporating the multistage SSM system according to claim 29, wherein gases which exit the heating section, in the heat recovery steam generator, are utilized for superheating or reheating an external steam flow that is supplied to the heat recovery steam generator.

35. The power plant incorporating the multistage SSM system according to claim 29, wherein a rate of duct firing sufficiently increases exhaust gas temperatures in the heat recovery steam generator, so as to create a heated air supply at or above required temperatures for the multistage SSM system while providing low-cost capacity for the power plant.