Semi-closed cycle turbine power system to produce saleable CO2 product

Abstract

Disclosed is a semi-closed cycle turbine engine power system, operating with air, enriched air, or oxygen as the oxidizer, is made non-emissive via the semi-closed cycle, in a manner which produces saleable CO.sub.2 product at pressure. In an embodiment of the present disclosure, the system includes, among other elements, an oxidizer supply subsystem for producing an oxidizer and a turbine engine. The oxidizer supply subsystem provides at least a portion of the oxidizer produced by the oxidizer supply sub-system to a main compressor stage of the turbine engine. A fuel supply system is also included for providing fuel to turbine engine. Operation of the turbine engine produces power and an exhaust gas. At least a portion of the exhaust gas is recirculated via a recirculation subsystem to the main compressor stage of the turbine engine.

Claims

1. A semi-closed cycle turbine power system to produce saleable CO.sub.2 product, comprising: an oxidizer supply subsystem for producing an oxidizer; a turbine engine that includes at least one main compressor stage, a combustor and a main turbine, wherein the oxidizer supply subsystem provides at least a portion of the oxidizer produced by the oxidizer supply subsystem to the at least one main compressor stage; a fuel supply system for providing fuel to the combustor of the turbine engine and wherein operation of the turbine engine produces power and an exhaust gas; an exhaust gas recirculation subsystem for recirculating at least a portion of the exhaust gas created by operation of the turbine engine to the at least one main compressor stage of the turbine engine; a molecular sieve based CO.sub.2 capture and cleanup subsystem for producing pressurized CO.sub.2 from at least a portion of the exhaust gas, the molecular sieve based CO.sub.2 capture and cleanup subsystem having one or more adsorption beds; and a heat recovery unit which receives at least a portion of the exhaust gas produced by operation of the turbine, wherein the heat recovery unit is configured to generate additional power via a super critical Brayton CO.sub.2 cycle, and the heat recovery unit configured to produce dry CO.sub.2, and wherein the heat recovery unit is operatively connected to the one or more adsorption beds to provide the dry CO.sub.2 produced by the heat recovery unit to the one or more adsorption beds to regenerate the one or more adsorption beds used in the molecular sieve based CO.sub.2 capture and cleanup subsystem.

2. The system of claim 1, further comprising a non-condensable turbo expander for additional waste heat and power recovery.

3. The system of claim 1, wherein the exhaust gas recirculation subsystem includes a heat exchanger and a water cooling and separation subsystem.

4. The system as recited in claim 1, wherein the oxidizer from the oxidizer supply subsystem includes air.

5. The system as recited in claim 4, wherein the air and oxidizer mixture is enriched air greater than 21 percent but less than 100 percent oxygen by volume.

6. The system as recited in claim 5, wherein the oxidizer supply subsystem includes a compressor and a buffer tank.

7. The system as recited in claim 1, wherein the oxidizer supply subsystem provides high purity oxygen having an oxygen content of greater than 90% as an oxidizer to the turbine engine.

8. The system as recited in claim 7, wherein the oxidizer supply subsystem includes a pump and a vaporizer.

9. The system as recited in claim 1, further comprising a recuperator positioned between the at least one main compressor stage and combustor of the turbine engine.

10. The system as recited in claim 1, wherein a portion of the oxidizer produced by the oxidizer supply subsystem is provided to the combustor of the turbine engine.

11. The system as recited in claim 1, further comprising an adsorption chiller refrigeration system.

12. The system as recited in claim 1, wherein CO.sub.2 capture and cleanup subsystem includes at least two Thermal Swing Adsorption beds for purifying at least a portion of the exhaust gas.

13. The system as recited in claim 1, wherein CO.sub.2 capture and cleanup subsystem includes at least two Pressure Swing Adsorption or Vacuum Pressure Swing Adsorption (VPSA) beds for purifying at least a portion of the exhaust gas.

14. The system as recited in claim 1, wherein the one or more adsorption beds include a combination of Thermal Swing Adsorption beds and Pressure Swing Adsorption or Vacuum Pressure Swing Adsorption (VPSA) beds for purifying at least a portion of the exhaust gas.

15. The system as recited in claim 1, wherein CO2 produced by the CO.sub.2 capture and cleanup subsystem is adapted for use in enhanced oil recovery process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) So that those skilled in the art to which the subject invention appertains will readily understand how to make and use the systems and methods of the subject invention without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain FIGURES, wherein:

(2) FIG. 1 illustrates a representative embodiment of the present invention.

(3) These and other aspects of the subject invention will become more readily apparent to those having ordinary skill in the art from the following detailed description of the invention taken in conjunction with the drawings.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

(4) The present invention is now described more fully with reference to the accompanying drawing, in which an illustrated embodiment of the present invention is shown. The present invention is not limited in any way to the illustrated embodiment as the illustrated embodiment described below is merely exemplary of the invention, which can be embodied in various forms, as appreciated by one skilled in the art. Therefore, it is to be understood that any structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative for teaching one skilled in the art to variously employ the present invention. Furthermore, the terms and phrases used herein are not intended to be limiting but rather to provide an understandable description of the invention.

(5) Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, exemplary methods and materials are now described. All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited.

(6) It must be noted that as used herein and in the appended claims, the singular forms a, an, and the include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a stimulus includes a plurality of such stimuli and reference to the signal includes reference to one or more signals and equivalents thereof known to those skilled in the art, and so forth.

(7) The present disclosure generally relates to a system of operating a gas turbine (Brayton cycle) engine in a semi-closed cycle, at pressure and in a manner which is non-emissive, and which produces saleable products, in particular CO.sub.2 at pressure. The power system is fed with high pressure gaseous or liquid air, enriched air, or oxygen and with hydrocarbon fuel. Exhaust gas, which is mostly CO.sub.2 when pure oxygen is used, and mostly N.sub.2 when air is used, is recirculated to provide a combustion diluent and working fluid. System high grade waste heat can be used to generate additional power via a sub/super critical CO.sub.2 Brayton cycle. System high grade waste heat can also be used to warm any non-condensable gas (such as N.sub.2, when the diluent is air), prior to expansion and exhaust. Product CO.sub.2 can also be generated at pressure, purified, and provided at pressure for the user, and also as a working fluid in the heat recovery system. The heat recovery system can additionally provide dry hot CO.sub.2 for use in regenerating the gas purification thermal swing adsorption molecular sieves. Optionally, low grade waste heat is used via the adsorption chiller process to provide refrigeration for CO.sub.2 liquefaction.

(8) It is to be appreciated this system of the present invention is of particular use wherein both power and CO.sub.2 at pressure are required for a process. Enhanced Oil Recovery is an example of such a process. It is further to be appreciated that the ability to operate on air vs. oxygen, although at much lower cycle efficiency, is beneficial when the duration of the operation is brief, high purity oxygen is unavailable, or when the deployment of an oxygen plant would not be practical (for example in offshore oil production platforms).

(9) It is noted that while the below described system has many components for the embodiment with the highest efficiency, portions of the system are optional, for example, the waste heat recovery system or the adsorption chiller refrigeration system. Several alternative embodiments with various combinations of the aforementioned building blocks are also claimed.

(10) Turning now to the drawings, FIG. 1 depicts a semi-closed cycle gas turbine engine power system, with separate high pressure oxidizer supply, heat recovery system, gas clean up system, and turbo expander system. Generally, in a closed cycle Brayton power generator, speed is a constant, and therefor pressure ratio is nominally constant, with power level changed by adding or removing mass from the cycle. In a semi-closed cycle, the same is true, but now it is the difference in added mass (fuel/oxidizer) and removed mass (product water, CO.sub.2, and non-condensable gases) which are controlled to maintain a desired pressure/operating power level.

(11) Accordingly, oxidizer, which is either air, or enriched air (predominantly oxygen/nitrogen, but with greater than 21% oxygen by volume), or high purity oxygen is provided via compressor/pump 1 to a buffer tank/pressure vessel 2, which in the case of cryogenic oxidizer supply would include a vaporizer. The oxidizer can be supplied in a range of pressures, up to a value in excess of the full combustion pressure of the system at full load, but generally at about 700-1,500 psia, greater than the inlet pressure of the main compressor. The oxidizer is supplied via control valve 3 to the inlet of the main compressor stages 4, and optionally via control valve 5 to the combustor 6. Valve 5 would be used for starting, for low pressure operation of the system, and by design at any time when the oxidizer supply pressure exceeds the combustion pressure. High pressure fuel is introduced to the combustor 6 via interface 7. The mixture of fuel, oxidizer, and compressed working fluid, heated via recuperator 8 generates the design point temperature for the main turbine 9, which is coupled to the main generator 10 or other driven load. The very high pressure (supercritical at design point, generally 1,000 to 6,000+ psia) nature of the cycle makes the recuperator much smaller than would be typical, and also reduces the relative to system pressure level pressure drop in the recuperator. Typically, at 1700+ F. turbine inlet temperature a pressure ratio of nominally 5 would be used (6000/1200 psia), generating turbine exhaust temperature of 1300-1400 F and combustor inlet temperatures of 1000-1200 F., depending on recuperator effectiveness and other factors. Higher temperatures are possible, and will result in higher cycle efficiencies, though the temperatures and material selection of the recuperator must be very well managed at these high temperatures and pressures.

(12) The gas mixture at this point, the recuperator exit, will be the same as the combustion gas mixture, and will always include a small amount of water (steam), a greater amount of CO.sub.2, and depending on the oxidizer choice, an amount of nitrogen. At 1750 F. combustion temperature, with 100% oxygen oxidizer, the working fluid at this point is 97% CO.sub.2, 3% Water (by mass); with air as the oxidizer, the working fluid becomes about 17% CO.sub.2, 3% Water, and 80% Nitrogen/Inert (Argon). This CO.sub.2, N.sub.2, and steam mixture flows to the super/sub-critical CO.sub.2 Brayton cycle heat recovery generator, or (optionally) the Organic Rankine Cycle heat recovery generator, which cools it via the hot-side heat exchanger 11.

(13) The heat recovery generator in general consists of a compressor/pump 12, a turbine 13, generator 14, and a low side heat exchanger 15. The heat recovery generator sub-system uses pure CO.sub.2 (R744) as the working fluid, in the variant with the CO.sub.2 Brayton Cycle, or for lower temperature heat recovery R134A, or R245FA. In the case of the Organic Rankine Cycle (ORC) heat recovery unit, the system inventory/pressure will not change radically with power level. The heat recovery system or generator, whether it is a SC CO2 (supercritical carbon dioxide) system or Rankine cycle system, such as R134A, or R245FA, can include a recuperator.

(14) The closed supercritical CO.sub.2 Brayton cycle heat recovery system is controlled via management of the load at generator 14 (runs at constant speed, hence constant pressure ratio) and by varying the total mass in the cycle. While 1200 psia inlet, 6000 psia outlet might be the compressor design point at full power, at 1/10.sup.th power one would expect nominally 120 psia, and 600 psia at the same pointsand cycle efficiency would in theory be unchanged (in fact it degrades slightly, since the cycle is closer to optimum at supercritical pressures). Other choices in pressure ratio and heat exchanger design pressure are of course possible, and one may choose to recuperate the heat recovery/waste heat to power sub-system. The pressure ratio of 5 is not optimum for the Brayton cycle alone, but gives reasonably low compressor exit temperatures, enabling good use of the available engine exhaust waste heat.

(15) Note that additional engine high grade waste heat is recovered via the system final turbo expander 16 and control valve 16A (to be discussed later). In air breathing applications, the power at this generator will exceed and essentially replace the heat recovery unitthis is as a result of non-condensable gas flow being high (dominated by Nitrogen). With pure oxygen delivered to the cycle, and perfect combustion yielding CO.sub.2 and water, there would not be a non-condensable flowrequiring a larger portion of the waste heat to be recovered with the closed supercritical CO.sub.2 system or ORC. The cooled gas from high side heat exchanger 11, typically at 150-300 F, flows to the system cooler 17, and to the water separator column 18. Additional cooling is provided, which results in the majority of water from the combustion process condensing. Liquid water collects in the bottom of the water separator, with the amount of water withdrawal controlled via liquid level control, and via thermal management (cooling) of the water separator. The amount of cooling at this point determines the saturation level (partial pressure) of the water vapor in the recirculated exhaust stream at 19. At 140 deg F., the partial pressure of water vapor will be about 3 psia at point 19.

(16) If the system pressure is 400 psia, then the recirculated exhaust will be 0.75% ( 3/400.sup.th) water vapor by volume. Water vapor concentration can be increased to double that by cooling to only 170 F, or half of that by cooling to 110 F. Materials on the low pressure side of the system, from the recuperator 8 through the heat exchanger 11 to cooler 17 and separator 18 must be corrosion resistant. Condensation of the water in the exhaust will in most circumstances occur within heat exchanger 11. What liquid water droplets are produced will quickly saturate with CO.sub.2, forming carbonic acid. Fortunately the overall water concentration is low, and hence the overall level of corrosion from the mixture is manageable.

(17) Valve 20 and positive blower/compressor 21, driven by variable speed motor 22, combined with valve 23 (when system pressure is high), combine to balance the overall inventory in the system. Produced/excess gases are captured in pressure vessel 24. Excess recirculation gases are withdrawn from line 19 via positive displacement compressor 21 and variable speed motor 22. The speed of motor 22 is varied to maintain the desired pressure in the recirculation line, and indirectly at the main compressor inlet 4. As discussed, the gas withdrawn is mostly CO.sub.2, if the system is running with oxygen as the oxidizer (preferred), but will be dominated by N.sub.2 if air is the oxidizer and will also include some portion of O.sub.2, Ar, and even some products of incomplete combustion, such as HC or CO.

(18) In addition, the gas is saturated in water vapor, at probably 0.7% or so by volume. The full feature compressor 21, removes most of the water vapor by the combination of compression, cooling and coalescing filter moisture separation, but dew points can be expected to remain at 45-50 deg F. of so, which is a partial pressure of 0.1-0.2 psia of water. Thermal Swing Adsorber (TSA) beds 28 or 29 are used, controlled via three way valves 26 and 27, to complete the drying process, and adsorb a portion of other undesirable gases. The TSA is functionally similar to PSA (the use of a PSA or VPSA or a combination of TSA and PSA or VPSA is an alternative if two stage contaminant removal is required), a molecular sieve approach which adsorbs certain molecule sizes (with a 3A adsorbent or alumina, focused mostly on water removal, and with small amounts of other adsorbents to be tuned based on expected contaminants), but the regeneration is thermalwith hot dry gas used via ports/valves 30-33 to renew the beds (methodology to follow later). The amount of material (water) being removed is already very low, and cycle times for these beds will be many hours. Drying to dew points of 80 F. or lower is possible with this technology, though is not required for this application. The goal is only to remove water vapor, and a portion of the other non-CO.sub.2 contaminants, to the level where frosting will not occur in later semi-cryogenic portions of the process, and as necessary to meet customer requirements. It is expected that dew points of 40 deg F. or better will be achieved at point 27, but that some non-condensable gases will remain. Large amounts of N.sub.2 or Ar may be present, and depending on the operating conditions of the system, O.sub.2 may exist. The latter is a problem for pipeline specification CO.sub.2 (desired O.sub.2 level 10 ppm).

(19) Elimination of the O.sub.2 is by physical separation of the liquid CO.sub.2 from gaseous (non-condensable) contaminants. To that end, a counterflow heat exchanger 34, using the heat of vaporization of the previously liquefied CO.sub.2, 38, provides initial cooling of the CO.sub.2 rich mixture, which then flows to a low temperature chiller 35. CO.sub.2 liquid is separated physically from other gases via separator 36, pumped as a liquid to 2000+ psig via pump 39, and vaporized back to the gaseous state in the heat exchanger. Non-condensable gases are vented at point 37, reheated in heat exchanger 11, and expanded via the turbo expander generator and control valve 16, and 16A to maintain the desired backpressure in the separation column 36.

(20) When the oxidizer is oxygen, in theory if perfectly pure, the amount of non-condensable gases would be low (would still include some Argon) and the power level at the turbo expander would be insignificant. On the other hand, a 24 MW net main turbine system, if running on air, could require upwards of 15,000 hp of air compression at 1, but makes more than 9,000 hp at turbine 16. This difference in power, 7,000 hp is a parasitic load on the system, which is about twice the load of an appropriately sized cryogenic air separation unit. Hence, the air separation unit, and the ability to run on nearly pure oxygen are preferred, but are not required. In all cases, substantial net power is produced, at reasonable cycle efficiency, and the product gaseous, dry, and relatively pure CO.sub.2 is provided at point 40.

(21) At the more detailed level, an additional integration of this TSA drying system, the SC CO.sub.2 Brayton Cycle Heat Recovery Unit, and the Turbo Expander 16 is not shown, but is discussed herein. Periodically, as discussed, the beds will require regeneration. Normally, product (dry CO.sub.2) is electrically heated to 600 F. or more, and is blown counterflow back through the beds for drying. This wastes product and power, and also requires additional components.

(22) In this system, turbine inlet bleed CO.sub.2 from 13 is ported to points 31 or 32, and vented with valves 30 or 33, to regenerate the bed. Turbo expander exhaust, 41, can also be used to cool down the dry beds after regeneration if this flow is significant. Also periodically, additional working fluid mass may be required in the SC CO.sub.2 Brayton Cycle Heat Recovery Unit. Dry CO.sub.2 is provided at pressure from point 40, to compressor inlet, 12 to increase mass in the SC CO.sub.2 Heat Recovery Unit. Finally, periodically, the mass in the SC CO.sub.2 Heat Recovery Unit must be reduced, the same line as for regeneration is used, but without opening valves 30 or 33.

(23) Other accessories, familiar to those with engine emissions control experience, can be integrated to this system to meet local emissions requirements. Obviously, the emission of CO.sub.2 is all but eliminated with this system, but HC or CO may exist at point 41, or 30/33. A catalytic or piloted reactor can be inserted as required to either burn off hydrocarbons/CO with additional oxygen injection, or consume/get excess oxygen via fuel injection. The use of excess O.sub.2, with certain catalysts, can also convert SO.sub.2 to SO.sub.3 at the temperatures that exist within recuperator 8this conversion would enable sulfur capture (as H.sub.2SO.sub.4) via water separator 18. Alternatively the bed molecular sieves in 28 and 29 may be adjusted to optimize for SO.sub.2 capture, and also for NOx, if the air breathing mode, combined with high combustion temperatures produces that product.

(24) Additional heat recovery/heat utilization techniques familiar to those in the industry can also be applied, over and above the ones discussed herein. Adsorption Chillers can be also be integrated with cooler 17 and/or low side heat exchanger 15 to produce refrigeration in lieu of 35, or for other processes.

(25) It is to be appreciated all the pressures and temperatures discussed herein can be varied quite a bit via the flexibility of the system. Turbine 9 inlet temperatures of 1000 F. to over 2500 F. have been studied and are effective. Compressor 4 inlet pressure should be near the critical point for CO.sub.2 if CO.sub.2 is the dominant working fluid to minimize compressor power1200 psia is a typical design point. A pressure ratio of 5 (6000 psia pressure at combustor 6) will give good performance, and higher pressures are actually optimum at higher temperatures, but at some point material considerations and capital cost become a greater concern than the last few points of cycle efficiency. There is no minimum pressure in the recirculating loop (point 19), and pressure will be reduced as power level is reduced. The pressure at 24, and throughout the gas capture/cleanup portion of the system, through point 37, needs to be consistent with liquefaction of CO.sub.2 and customer purity requirements (lower temperature at 35 will generally lower soluble gas contamination of the CO.sub.2 stream). In all cases one must stay above the triple point of CO.sub.2 (75 psia is probably a lower limit). All the pressures and other state variables discussed herein are nominal at this time (provisional filing), and will be narrowed/perfected in the coming year. The use of a conventional PSA/TSA/VPSA (or combinations thereof) mole sieve process for capture of CO.sub.2 to the phase separation approach of item 36 is of course an optionthe high system pressures of the overall Semi-Closed Cycle would make the beds of molesieve (13) physically much smaller than at lower pressures, due to the greater adsorption capability of mole sieves a high pressure.

(26) Optional embodiments of the present invention may also be said to broadly consist in the parts, elements and features referred to or indicated herein, individually or collectively, in any or all combinations of two or more of the parts, elements or features, and wherein specific integers are mentioned herein which have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

(27) The above presents a description of a best mode contemplated for carrying out the present invention and of the manner and process of making and using it in such full, clear, concise, and exact terms as to enable any person skilled in the art to which it pertains to make and use these devices and methods. The present invention is, however, susceptible to modifications and alternative method steps from those discussed above that are fully equivalent. Consequently, the present invention is not limited to the particular embodiments disclosed. On the contrary, the present invention encompasses all modifications and alternative constructions and methods coming within the spirit and scope of the present invention.

(28) The descriptions above and the accompanying drawing should be interpreted in the illustrative and not the limited sense. While the invention has been disclosed in connection with the preferred embodiment or embodiments thereof, it should be understood that there may be other embodiments which fall within the scope of the invention as defined by the following claims. Where a claim, if any, is expressed as a means or step for performing a specified function, it is intended that such claim be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof, including both structural equivalents and equivalent structures, material-based equivalents and equivalent materials, and act-based equivalents and equivalent acts.