CO2 POWER CYCLE WITH ADIABATIC COMPRESSION

Abstract

The present disclosure relates to systems and methods useful for power production. In particular, a power production cycle utilizing CO.sub.2 as a working fluid may be combined with a second cycle wherein a compressed CO.sub.2 stream from the power production cycle, which can be heated and expanded to produce additional power and to provide additional heating to the power production cycle.

Claims

1. A power production cycle comprising: combusting a hydrocarbon fuel stream with oxygen to produce combustion products; combining the combustion products with a preheated circulating pressurized CO.sub.2 stream to form a mixture; and feeding the mixture to a power turbine to create a discharge, the discharge then being fed into a recuperative heat exchanger to preheat the circulating pressurized CO.sub.2 stream; wherein an adiabatic compression system is used to adiabatically compress the circulating pressurized CO.sub.2 stream and the oxygen from a lesser pressure to a greater inlet pressure of the power turbine and to heat the circulating pressurized CO.sub.2 stream and the oxygen; wherein the circulating pressurized CO.sub.2 stream and the oxygen leaving the adiabatic compression system enter the recuperative heat exchanger where they are further heated against the discharge from the power turbine; and wherein the discharge from the power turbine leaving the recuperative heat exchanger enters a second heat exchanger that heats one or more fluid streams supplied from one or more external sources.

2. The power production cycle according to claim 1, wherein the one or more fluid streams heated in the second heat exchanger comprise one or both of boiler feed-water and process steam delivered from a steam-based power cycle.

3. The power production cycle according to claim 1, wherein the one or more fluid streams heated in the second heat exchanger comprises a pressurized water flow.

4. The power production cycle according to claim 1, wherein the adiabatic compression system comprises a CO.sub.2 compressor and a compressor for a mixture of the oxygen and CO.sub.2.

5. The power production cycle according to claim 4, wherein a separate stream of CO.sub.2 is taken from the discharge of the CO.sub.2 compressor and introduced into the power turbine as a cooling fluid.

6. The power production cycle according to claim 4, wherein the mixture comprises about 15% to about 60% molar oxygen.

7. The power production cycle according to claim 1, wherein the discharge from the power turbine leaving the second heat exchanger is cooled to near ambient temperature by ambient cooling means, and wherein net product water and CO.sub.2 are removed before entering the adiabatic compression system.

8. The power production cycle according to claim 1, further comprising preheating the hydrocarbon fuel stream in the second heat exchanger and then heating the hydrocarbon fuel stream in the recuperative heat exchanger before combusting the hydrocarbon fuel stream.

9. The power production cycle according to claim 1, wherein the hydrocarbon fuel stream comprises natural gas that has been compressed to the inlet pressure of the power turbine.

10. The power production cycle according to claim 1, wherein an inlet pressure of the adiabatic compression system is in a range of about 4 bar (0.4 MPa) to about 40 bar (4 MPa).

11. The power production cycle according to claim 1, wherein an inlet temperature of the power producing turbine is in a range of about 1000 C. to about 1600 C.

12. The power production cycle according to claim 1, wherein the inlet pressure of the power producing turbine is in a range of about 200 bar (20 MPa) to about 500 bar (50 MPa).

13. The power production cycle according to claim 1, wherein a pressure ratio of the power turbine is in a range of about 15 to about 40.

14. The power production cycle according to claim 1, wherein substantially all of the circulating pressurized CO.sub.2 stream is adiabatically compressed from the lesser pressure to the greater inlet pressure of the power turbine.

15. The power production cycle according to claim 1, wherein near 100% of carbon in the hydrocarbon fuel stream that is combusted is captured.

16. The power production cycle according to claim 1, wherein the mixture of the combustion products and the preheated circulating pressurized CO.sub.2 stream comprises about 0.1% to about 4.0% molar oxygen.

17. The power production cycle according to claim 1, wherein the hydrocarbon fuel stream comprises natural gas.

18. The power production cycle according to claim 1, wherein the hydrocarbon fuel stream comprises syngas.

19. A power production cycle comprising: combusting a hydrocarbon fuel stream with oxygen to produce combustion products; combining the combustion products with a preheated circulating pressurized CO.sub.2 stream to form a mixture; and feeding the mixture to a power turbine to create a discharge, the discharge then being fed into a recuperative heat exchanger to preheat the circulating pressurized CO.sub.2 stream; wherein an adiabatic compression system is used to adiabatically compress substantially all of the circulating pressurized CO.sub.2 stream and the oxygen from a lesser pressure to a greater inlet pressure of the power turbine and to heat substantially all of the circulating pressurized CO.sub.2 stream and the oxygen, the adiabatic compression system comprising a CO.sub.2 compressor and a compressor for a mixture of the oxygen and CO.sub.2, and the inlet pressure of the power turbine being in a range of about 200 bar (20 MPa) to about 500 bar (50 MPa); wherein the circulating pressurized CO.sub.2 stream and the oxygen leaving the adiabatic compression system enter the recuperative heat exchanger where they are further heated against the discharge from the power turbine; and wherein the discharge from the power turbine leaving the recuperative heat exchanger enters a second heat exchanger that heats one or more fluid streams supplied from one or more external sources.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Having thus described the disclosure in the foregoing general terms, reference will now be made to the accompanying drawing, which is not necessarily drawn to scale, and wherein:

[0015] FIG. 1 is a flow diagram of an example system and method of power production according to the present disclosure.

DETAILED DESCRIPTION

[0016] The present subject matter will now be described more fully hereinafter with reference to example embodiments thereof. These example embodiments are described so that this disclosure will be thorough and complete, and will fully convey the scope of the subject matter to those skilled in the art. Indeed, the subject matter can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. As used in the specification, and in the appended claims, the singular forms a, an, the, include plural referents unless the context clearly dictates otherwise.

[0017] In various embodiments, the present disclosure describes a power production cycle that provides additional heating for one or more secondary processes. For example, in one embodiment, a power production cycle is described that comprises combusting a carbonaceous or hydrocarbon fuel stream with an oxidant stream to produce combustion products, combining the combustion products with a preheated circulating pressurized CO.sub.2 stream to form a mixture, and feeding the mixture to a power turbine to create a discharge, the discharge then being fed into a recuperative heat exchanger to preheat the circulating pressurized CO.sub.2 stream, wherein an adiabatic compression system is used to compress the circulating CO.sub.2 and oxidant from a turbine discharge pressure region to a turbine inlet pressure region, wherein the CO.sub.2 and oxygen streams leaving the adiabatic compression system enter the recuperative heat exchanger where they are heated against a cooling turbine exhaust flow, and wherein turbine exhaust leaving the recuperative heat exchanger enters a second heat exchanger that heats one or more fluid streams supplied from external sources.

[0018] A CO.sub.2 stream recycled in the combustor can have a pressure of about 100 bar (10 MPa) to about 600 bar (60 MPa) or 200 bar (20 MPa) to about 400 bar (40 MPa) and a temperature of about 400 C. to about 800 C. or about 500 C. to about 700 C. The fuel can be a carbonaceous fuel or a hydrocarbon fuel, but other fuels, such as hydrogen, may also be used. The oxidant can comprise about 15% to about 60% or about 20% to about 40% molar oxygen with the remaining portion formed of a diluent, such as substantially pure CO.sub.2. Fuel and oxidant entering the combustor are preferably preheated to a temperature of about 400 C. to about 800 C. or about 550 C. to about 700 C. The combustion product leaving the combustor is at a pressure substantially close to the CO.sub.2 recycle inlet pressure and a temperature of about 900 C. to about 1600 C. or about 1100 C. to about 1500 C. and comprises predominately CO.sub.2 and H.sub.2O with a small amount of residual oxygen of about 0.1% to about 4.0% molar. The turbine is operated to provide an expanded stream at about 8 bar (0.8 MPa) to about 30 bar (3 MPa) or about 10 bar (1 MPa) to about 20 bar (2 MPa). The expanded stream is cooled in the recuperative heat exchanger to a temperature of about 200 C. to about 600 C. or about 300 C. to about 500 C., and the heat released is transferred to the circulating high pressure CO.sub.2 inlet stream. Heat is also provided to the fuel gas inlet stream and the oxidant inlet stream.

[0019] The turbine exhaust stream 23 is passed through a heat recovery heat exchanger where it cools to a temperature of about 40 C. to about 80 C., such as about 60 C. in some embodiments, and provides heat to the fuel gas inlet stream and a secondary stream. The secondary stream can be, for example, a boiler feed-water stream at a temperature of about 25 C. to about 80 C. or about 30 C. to about 60 C. and a pressure of about 40 bar (4 MPa) to about 100 bar (10 MPa) or about 60 bar (6 MPa) to about 80 bar (8 MPa), which is heated to produce a superheated steam stream at about 200 C. to about 500 C. or about 300 C. to about 450 C., such as about 360 C. The fuel gas stream is compressed adiabatically to a pressure of about 150 bar (15 MPa) to about 500 bar (50 MPa) or about 250 bar (25 MPa) to about 400 bar (40 MPa). The turbine exhaust leaves the recuperative heat exchanger at a pressure of about 8 bar (0.8 MPa) to about 20 bar (2 MPa) or about 9 bar (0.9 MPa) to about 15 bar (1.5 MPa) and enters a direct contact water cooler. The cooled turbine exhaust stream leaving the top of the water direct contact cooler can be divided in two streams. A first stream can enter the adiabatic compressor where it is compressed to a pressure of about 100 bar (10 MPa) to about 600 bar (60 MPa) or 200 bar (20 MPa) to about 400 bar (40 MPa) and leaves at a temperature of about 250 C. to about 500 C. or about 300 C. to about 450 C. A second stream at about 8 bar (0.8 MPa) to about 15 bar (1.5 MPa), such as about 10.5 bar (1.05 MPa), and a temperature of about 15 C. to about 35 C., such as about 21 C., comprises CO.sub.2 derived from combustion of carbon fuel gas. A portion of this stream can be removed from the system for sequestration or other use, and the remaining portion can be mixed with oxygen to for the oxidant for the combustor. The oxidant stream enters an adiabatic compressor where it is compressed to a pressure of about 150 bar (15 MPa) to about 500 bar (50 MPa) or about 250 bar (25 MPa) to about 400 bar (40 MPa).

[0020] In some embodiments, the fluid streams heated in the second heat exchanger comprise boiler feed-water and process steam delivered from a steam-based power cycle. In some embodiments, the fluid stream heated in the second heat exchanger comprises a pressurized water flow. In some embodiments, the adiabatic compression system comprises a CO.sub.2 compressor and a compressor for an oxidant fluid stream comprising a mixture of oxygen and CO.sub.2. In some embodiments, a separate stream of CO.sub.2 is taken from the discharge of the CO.sub.2 adiabatic compressor and introduced into the power turbine as a cooling fluid.

[0021] In some embodiments, the turbine exhaust leaving the second heat exchanger is cooled to near ambient temperature by ambient cooling means, and net product water and CO.sub.2 are removed before entering the adiabatic compressors. In some embodiments, the carbonaceous or hydrocarbon fuel stream is preheated in the second heat exchanger and is then heated in the recuperative heat exchanger before it enters the combustor. In some embodiments, the carbonaceous or hydrocarbon stream comprises natural gas, syngas, and/or carbon monoxide that has been compressed to a turbine inlet region pressure. In some embodiments, an inlet pressure of the adiabatic compressor is in the range of about 2 bar (0.2 MPa) to about 60 bar (6 MPa) or about 4 bar (0.4 MPa) to about 40 bar (4 MPa). In some embodiments, a turbine inlet temperature is in the range of about 500 C. to about 1800 C., about 700 C. to about 1700 C., or about 1000 C. to about 1600 C. In some embodiments, a turbine inlet pressure is in the range of about 80 bar (8 MPa) to about 800 bar (80 MPa), about 150 bar (15 MPa) to about 600 bar (60 MPa), or about 200 bar (20 MPa) to about 500 bar (50 MPa). In some embodiments, a pressure ratio of the power turbine is in the range of about 10 to about 60, about 12 to about 50, or about 15 to about 40.

EXAMPLE

[0022] Embodiments of the present disclosure are further illustrated by the following example, which is set forth to illustrate the presently disclosed subject matter and is not to be construed as limiting. The following describes an example embodiment of a power production system and method with adiabatic compression, as illustrated in FIG. 1.

[0023] The features of the proposed CO.sub.2 power cycle with adiabatic compression of the whole recycle CO.sub.2 flow, shown in FIG. 1, will be described with an example using methane as the fuel gas, although other fuel sources, such as syngas and/or carbon monoxide, are possible. In some embodiments, the fuel may be supplemented or even replace with hydrogen as reliable sources of hydrogen become available. A CO.sub.2 stream 21 at about 305 bar (30.5 MPa) and about 660 C. enters the mixing section of an oxy-fuel combustor 3 where it mixes with the combustion products from a methane stream 18 at about 305 bar (30.5 MPa) and about 550 C. burning in an oxidant stream 20 comprising about 25% molar oxygen mixed with about 75% molar CO.sub.2 at about 305 bar (30.5 MPa), which has been heated to about 660 C. Mixing the O2 with CO.sub.2 reduces the adiabatic flame temperature in the combustor to a level comparable to that demonstrated using air as the combustion oxidant. Stream 19 at about 300 bar (30 MPa) and about 1300 C. is a mixture of stream 21 and the combustion products, CO.sub.2 and H.sub.2O, from the oxy-fuel combustor/mixer 3. Stream 19 has about 0.5% to about 2.0% oxygen content to promote complete combustion of the hydrocarbon in the combustor 3. Stream 19 enters a power turbine 2 driving an electrical generator 47 where it expands from about 300 bar (30 MPa) to about 11.2 bar (1.112 MPa) pressure leaving the turbine as stream 22 at a temperature of about 670 C. Stream 22 enters the hot end of a recuperative heat exchanger 4 where it cools to about 379.4 C. leaving as stream 23. The heat released as the turbine discharge flow cools is transferred to the circulating high pressure CO.sub.2 inlet stream 24 leaving as stream 21, the oxidant inlet stream 25 leaving as stream 20 and the CH.sub.4 fuel gas inlet stream 44 which leaves as stream 18. All three of streams 24, 25, and 44 enter the recuperative heat exchanger 4 at about 357.8 C. The recuperative heat exchanger 4 can be a multichannel compact diffusion bonded heat exchanger such as those manufactured by the Heatric division of Meggitt Ltd. These units use grades of stainless steel and high nickel alloys such Specialty Metals grade 617 alloy depending on the temperature and pressure combination in the heat exchanger.

[0024] The turbine exhaust stream 23 is passed through the heat recovery heat exchanger 5 where it cools to about 60 C. leaving as stream 28. The heat released from the cooling turbine exhaust stream in heat exchanger 5 is used to heat the CH.sub.4 fuel gas stream 43 at about 305 bar (30.5 MPa) and about 221 C. and an externally supplied stream 26 which leaves as stream 27 at a temperature of about 370 C. The CH.sub.4 fuel gas stream 17 enters the power plant from a pipeline at about 15 C. and about 40 bar (4 MPa) pressure. It is compressed adiabatically to about 305 bar (30.5 MPa) in the compressor 1 driven by the motor 9 before entering heat exchanger 5 at an intermediate point. In one embodiment the stream 26 can be a boiler feed-water stream at about 40 C. and typically about 70 bar (7 MPa), which is heated to produce a superheated steam stream at about 360 C. Optionally there can be an additional reheated steam stream heated to about 360 C. (not shown in FIG. 1), which serves to increase the power output and efficiency of the steam power cycle. The heat transferred to the steam power cycle at this temperature level can be converted to power at a thermal efficiency of about 36%.

[0025] Alternatively, the excess heat available from the cooling turbine exhaust flow in heat exchanger 5 can be transferred to a circulating pressurized water system used for heating domestic dwellings, hospitals, commercial buildings and for industrial heating applications replacing natural gas and heating oil currently used and avoiding CO.sub.2 emissions. A typical system can heat a circulating pressurized water flow from about 50 C. to about 140 C. The turbine exhaust leaves heat exchanger 5 at about 10.7 bar (1.07 MPa) and about 60 C. and enters the direct contact water cooler 13 where it contacts a downward flowing cold water stream 34 in a packed column section 14. The hot water stream 30 leaving the base of the tower divides in to two streams. A product water stream 32, derived from combustion of hydrogen from the CH.sub.4 fuel is removed from the system. The remaining bulk of the water stream 31 is pumped in a circulating pump 16 and the discharge stream 33 is then cooled in heat exchanger 15 against cooling water stream 35 at about 19 C. to stream 36 at about 28 C. before entering the top of the packing section 14 as stream 34. The cooled turbine exhaust stream 29 leaving the top of the water direct contact cooler 13 at about 21 C. divides in two streams. Stream 37 enters the adiabatic compressor 11 where it is compressed to about 305 bar (30.5 MPa) leaving as stream 46 at about 357.8 C. Stream 46 divides into stream 45, which enters the power turbine 2 as the internal cooling flow for turbine blades and inner casing and stream 24 which enters the recuperative heat exchanger 4. The adiabatic compressor 11 can, optionally, be directly coupled to the turbine electric generator 47. Stream 38 at about 10.5 bar (1.05 MPa) and about 21 C. divides into two stream. Stream 42 is the net CO.sub.2 product derived from combustion of carbon in the CH.sub.4 fuel gas. Substantially 100% of the carbon in the total CH.sub.4 feed stream 17 is captured in stream 42. The product CO.sub.2 stream 42 can be compressed to a convenient pressure in the range of about 100 bar (10 MPa) to about 200 bar (20 MPa) for delivery to a CO.sub.2 pipeline for sequestration or alternatively it can be liquefied and delivered as a saturated liquid at about 6 bar (0.6 MPa) to about 7 bar (0.7 MPa) pressure. The remaining CO.sub.2 stream 48 is mixed with a 99.5% molar purity O2 stream 39 at about 10.5 bar (1.05 MPa) pressure and about 20 C. from a cryogenic air separation plant 6 to produce an oxidant stream 40 having a molar composition about 25% O2 plus about 75% CO.sub.2. Stream 40 enters the adiabatic compressor 10 driven by motor 12 where it is compressed to about 305 bar (30.5 MPa) leaving as stream 25. The cryogenic pumped oxygen air separation plant 6 has an air feed stream 41 compressed to about 5.7 bar (0.57 MPa) pressure in the intercooled compressor 7 driven by motor 8. The compressed air stream 49 enters the air separation area 6 which comprises any of the components necessary for separation of oxygen from air, such as, for example, an air cooler, a dual-bed adsorptive air purifier, a booster air compressor, a cryogenic air separation unit, liquid oxygen pumps, cryogenic refrigeration turbines, and a liquid oxygen storage and back-up system.

[0026] A performance summary of example embodiments are shown in Tables 1-3 below (wherein all calculations are based on using pure methane (CH.sub.4) as the fuel gas).

TABLE-US-00001 TABLE 1 Parameter Value Natural Gas Input (40 bar at 15 C.) 755.6 MW Oxygen Input (99.5 mol % at 20 C. 5258.4 MT/day and 10.5 bar (1.05 MPa)) CO.sub.2 Output (98 mol % at 30 C. 3580.2 MT/day and 10.5 bar (1.05 MPa)) Turbine Inlet 1300 C. at 300 bar (30 MPa) Turbine Outlet 11.2 bar (1.12 MPa)

TABLE-US-00002 TABLE 2 Case 1 Power Parameter Production Net Power Output 463.2 Thermal efficiency (LHV basis) 61.3%

TABLE-US-00003 TABLE 3 Case 2 Plus District Parameter Heating Net Power Output 350.6 MW Hot water at 140 C. 312.6 MW

[0027] The terms about or substantially as used herein can indicate that certain recited values or conditions are intended to be read as encompassing the expressly recited value or condition and also values that are relatively close thereto or conditions that are recognized as being relatively close thereto. For example, unless otherwise indicated herein, a value of about a certain number or substantially a certain value can indicate the specific number or value as well as numbers or values that vary therefrom (+ or ) by 5% or less, 4% or less, 3% or less, 2% or less, or 1% or less. Similarly, unless otherwise indicated herein, a condition that substantially exists can indicate the condition is met exactly as described or claimed or is within typical manufacturing tolerances or would appear to meet the required condition upon casual observation even if not perfectly meeting the required condition. In some embodiments, the values or conditions may be defined as being express and, as such, the term about or substantially (and thus the noted variances) may be excluded from the express value.

[0028] Many modifications and other embodiments of the presently disclosed subject matter will come to mind to one skilled in the art to which this subject matter pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the present disclosure is not to be limited to the specific embodiments described herein and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.