Systems and methods for carbon-free generation of electric power and

Abstract

The invention includes power generation systems and methods. An oxyfuel combustor may be used to heat a CO2 gas, which in turn may be used to generate mechanical work in a first turbine, where first and second portions of the CO2 gas exiting the first turbine are respectively directed to (1) a second turbine to generate additional mechanical work, and (2) a gas heating steam methane reforming (SMR) reactor for use as a heating gas. A splitter may be disposed between the first turbine, the second turbine, and the SMR reactor and configured to vary the relative size of the first and second portions. The heat recovery stage may receive first and second portions of the CO2 gas from the second turbine and the SMR reactor and remove thermal energy from the CO2 gas; and a recompression stage may receive the CO2 gas from the heat recovery stage, and compress the CO2 gas. The preheating stage may receive the CO2 gas from the recompression stage, receive thermal energy from the heat recovery stage to heat the CO2 gas, and direct the preheated CO2 gas to a combustor; and an exhaust valve may be disposed between the recompression stage and the heating stage to divert a portion of the CO2 gas out of the system. In at least some examples, mechanical work may be used for power generation.

Description

Technical Field

[0001] This disclosure generally relates to power generation in methods for producing chemicals, and more specifically, but not limited to, systems and methods for generating electricity and producing hydrogen, said systems and methods allowing for the continuous utilization of assets by taking into account varying electricity demand through changes in the relative rates of power generation and hydrogen production. Background Technology

[0002] As chemical plants shift from burning fossil fuels to meet their daily electricity needs to using electricity from renewable energy sources, the availability and cost of electricity will change over time. For example, solar and wind power production varies with the time of day and weather conditions; for instance, nighttime and cloudy days reduce or interrupt the power generation of solar panels. Similarly, wind turbine power generation is reduced or interrupted during periods when wind is weak or absent. However, commercially, it is often important for chemical plants to maintain consistent production levels even when electricity from renewable energy sources is less available or unavailable. Summary of the Invention

[0003] Exclusive use of solar and wind energy requires storage to draw power from them when they are less or unavailable. Battery storage is one option for energy storage, drawing power from the low-power or no-power intervals inherent in green energy sources; however, battery storage may be too expensive and impractical in many cases.

[0004] Another option is to combine wind and / or solar power with a backup system that generates electricity by burning fossil fuels during periods of low or no power. However, such systems typically require expensive flue gas carbon capture systems to collect CO2 emissions, as well as the preparation and compression of such emissions for storage. Furthermore, because such backup systems are typically shut down or operate at far below maximum capacity during periods when solar or wind power is available, they are often underutilized and capital inefficient.

[0005] This system and method generate both electricity and hydrogen, with a dynamic rebalancing of the relative electricity and hydrogen production to accommodate periods of low and no electricity, while utilizing CO2 as the working fluid to significantly simplify the system required for recapture. The power for the driving system comes from an oxymethane burner, and when green electricity is unavailable or scarcely available, a relatively large proportion of the combustion energy can be diverted to the electricity cycle. When green energy is more readily available, a relatively large proportion of the combustion energy can be diverted to hydrogen production, which can be used as an energy carrier in a variety of other applications.

[0006] This system and method utilize the Allam cycle (an improved Brayton cycle using CO2 as the working fluid), and the net CO2 produced by combustion is discharged from the loop as a high-pressure pure CO2 stream, ready for sequestration, without requiring expensive carbon capture kits. The hydrogen cycle uses gas to heat a steam methane reforming (SMR) reactor, where the thermal energy for heating, provided by the hot CO2 loop, drives the SMR chemistry. Using a gas-heated SMR reactor avoids the additional flue gas emissions typically associated with combustion-driven SMR reactors, and tail gas from the PSA (unreacted CH4, CO, and CO2) can be sent as fuel to the combustor, thus avoiding the cost and complexity of recirculation and separation subsystems usually required in SMR processes. Because combustion energy is convertible between the power cycle and the hydrogen cycle, this system and method allow most assets to be used continuously, with only a small portion used intermittently, resulting in significantly improved capital efficiency compared to conventional fossil fuel backup power systems that could be simply shut down during periods when major electricity demand can be met by electricity from renewable energy sources such as solar and / or wind.

[0007] Some configurations of this power generation system include: an oxy-fuel burner, a first turbine, a second turbine, a gas-heated steam methane reforming (SMR) reactor, a splitter, a heat recovery stage, a recompression stage, a preheating stage, and an exhaust valve. In such a configuration, the oxy-fuel burner is configured to receive methane, oxygen, and carbon dioxide (CO2) gas, and to use oxygen to burn methane to heat the CO2 gas; the first turbine is configured to receive CO2 gas in a first state from the burner and to convert the thermal energy in the CO2 gas into mechanical work; and the second turbine is configured to receive a first portion of the CO2 gas from the first turbine and to convert the thermal energy in the first portion of the CO2 gas into mechanical work. The SMR reactor can be configured to receive a second portion of the CO2 gas from the first turbine, receive a mixture of methane (CH4) and steam (H2O), and transfer thermal energy from the second portion of the CO2 gas to the mixture without mixing the CO2 gas and the mixture. The splitter can be disposed between the first turbine, the second turbine, and the SMR reactor, and is configured to change the relative size of the first and second portions. The heat recovery stage can be configured to receive a first portion of CO2 gas from the second turbine and a second portion of CO2 gas from the SMR reactor, and remove heat energy from the CO2 gas. The recompression stage can be configured to receive CO2 gas from the heat recovery stage and compress the CO2 gas. The preheating stage can be configured to receive CO2 gas from the recompression stage, receive heat energy from the heat recovery stage to heat the CO2 gas, and guide the preheated CO2 gas to the burner. An exhaust valve can be located between the recompression stage and the heating stage, and is configured to divert a portion of the CO2 gas out of the system.

[0008] In some of the aforementioned configurations of this power generation system, a first turbine is connected to a generator to produce electricity.

[0009] In some of the aforementioned configurations of this power generation system, a second turbine is connected to a generator to produce electricity.

[0010] In some of the aforementioned configurations of this power generation system, the system further includes: one or more shift reactors coupled to an SMR reactor to receive a purified gas stream from the SMR reactor and generate a hydrogen stream; and a pressure swing adsorption (PSA) unit configured to receive the hydrogen stream from the one or more shift reactors and remove components other than hydrogen (H2), the PSA unit having a first outlet for the purified hydrogen stream and a second outlet for tail gas including components other than hydrogen. In some such configurations, the second outlet of the PSA unit is coupled to a combustor to return the tail gas from the PSA unit to the combustor. Some such configurations further include: a second recompression stage disposed between the second outlet of the PSA and the combustor to compress the tail gas.

[0011] In some of the aforementioned configurations of this power generation system, the heat recovery stage and the heating stage are both defined by a common heat exchanger.

[0012] In some of the aforementioned configurations of this power generation system, the first turbine, the second turbine, and the recompression stage share a common axis of rotation.

[0013] In some embodiments of this method for producing electricity and hydrogen, the method includes: burning methane in an oxy-fuel burner to heat carbon dioxide (CO2) gas; receiving CO2 gas from the burner at a first turbine and converting the thermal energy in the CO2 gas into mechanical work to generate electricity; receiving a first portion of CO2 gas from the first turbine at a second turbine and converting the thermal energy in the first portion of CO2 gas into mechanical work to generate electricity; receiving a second portion of CO2 gas from the first turbine at a gas-heated steam methane reforming (SMR) reactor and transferring thermal energy from the second portion of CO2 gas to a mixture of methane (CH4) and steam (H2O) without mixing the CO2 gas and the mixture to generate a reformed gas stream; recombining the first and second portions of CO2 gas; extracting thermal energy from the CO2 gas in a heat recovery stage; compressing the CO2 gas after extracting the thermal energy; removing a portion of the compressed CO2 gas for storage; reheating the remaining portion of the compressed CO2 gas in a heating stage; and returning the heated and compressed CO2 gas to the burner.

[0014] Some of the aforementioned embodiments of this method further include increasing the relative size of the first portion of the CO2 gas to increase the rate at which power is generated in the second turbine.

[0015] Some of the aforementioned embodiments of this method further include increasing the relative size of the second portion of CO2 gas to increase the rate of hydrogen production.

[0016] In some of the aforementioned embodiments of this method, the heat removed from the CO2 gas in the extraction step is transferred to the CO2 gas in the reheating step.

[0017] Some of the foregoing embodiments of this method further include: directing a reformed gas stream from an SMR reactor through one or more shift reactors to produce a hydrogen stream. Some such embodiments further include: removing components other than hydrogen from the hydrogen stream to produce a tail gas stream and a purified hydrogen stream. Some such embodiments further include: redirecting the tail gas stream to an oxy-fuel combustor.

[0018] The term “connection” is defined as a link, although not necessarily directly or mechanically; the two items in a “connection” may be integral with each other. Unless otherwise expressly required by this disclosure, the terms “a” and “an” are defined as one or more. As will be understood by one of ordinary skill in the art, the term “substantially” is defined as most, but not necessarily all, of the specified contents (and includes the specified contents; for example, substantially 90 degrees includes 90 degrees, and substantially parallel includes parallel). In any embodiment of the device, kit, and method, the term “substantially” may be replaced by the specified “within [percentage] of”, where the percentage includes 0.1%, 1%, 5%, and / or 10%.

[0019] The terms “comprises” (and any form of inclusion, such as “comprises” and “comprising”), “has” (and any form of having, such as “has” and “having”), “includes” (and any form of inclusion, such as “includes” and “including”), and “contains” (and any form of containing, such as “contains” and “containing”) are open-ended connecting verbs. Therefore, an apparatus or kit that “comprises,” “has,” “includes,” or “contains” one or more elements possesses, but is not limited to, possessing only those elements. Similarly, a method that “comprises,” “has,” “includes,” or “contains” one or more steps possesses, but is not limited to, possessing only those steps.

[0020] In addition, a device, apparatus or system configured in a certain way is configured at least in this way, but may also be configured in other ways than those specifically described.

[0021] Any embodiment of this device and method may consist of or substantially consist of any of the described steps, elements and / or features, rather than including / comprises / contains / has any of the described steps, elements and / or features. Therefore, in any claim, the terms “consisting of” or “substantially consisting of” may replace any of the foregoing open-ended connecting verbs in order to change the scope of the given claim from the scope of otherwise used open-ended connecting verbs.

[0022] Details relating to the implementation schemes described above and other implementation schemes are presented below.

[0023] Some details relating to aspects of this disclosure have been described above, while other details are described below. Further embodiments, advantages, and features of this disclosure will become apparent upon review of the entire application, including the description of the drawings, detailed description, and claims. Attached Figure Description

[0024] The following figures are shown by way of example and not limitation. For the sake of brevity and clarity, each feature of a given structure is not always labeled in every figure in which the structure appears. The same reference numerals or figure labels do not necessarily indicate the same structure. Rather, the same figure labels may be used to indicate similar features or features with similar functions, and different figure labels may also be used.

[0025] Figure 1 A schematic diagram depicts a first instance of this system for the variable production of electricity and hydrogen.

[0026] Figure 2 A schematic diagram of a second example of the system for producing electricity and hydrogen is depicted, showing the flow rate and load of combustion energy distributed 50-50 between the secondary power generation cycle and the hydrogen production cycle.

[0027] Figure 3 Depicting Figure 2 A schematic diagram of the system, showing the flow rate and load of combustion energy allocated 90-10 between the secondary power generation cycle and the hydrogen production cycle.

[0028] Figure 4 Depicting Figure 2 A schematic diagram of the system, showing the flow rate and load of combustion energy allocated between the secondary power generation cycle and the hydrogen production cycle in a 10-90 ratio.

[0029] Figure 5 It describes the relationship between 10⁻⁹ ( ) and 90 ( ) for a given combustion fuel input. Figure 4 ) and 90-10 ( Figure 3 A graph showing the changes in certain system variables allocated between )

[0030] Figure 6 A graph depicts how certain system variables change as the input of combustion fuel increases for a given allocation between the secondary power generation cycle and the hydrogen production cycle. Detailed Implementation

[0031] Now refer to the attached diagram, and more specifically to... Figure 1 The figure shown, and designed by reference numeral 10, is a first example of the system for the variable generation of electricity and hydrogen. In the depicted example, system 10 includes: an oxy-fuel burner 14, a first turbine 18, a splitter 22, a secondary power cycle 26, and a hydrogen production cycle 30. Downstream of these two cycles, the depicted example of system 10 also includes a heat recovery stage 34, a recompression stage 38, and a preheating stage 42. In the illustrated example, the secondary power cycle 26 includes a second turbine 46; the hydrogen production cycle 30 includes a gas-heated steam methane reforming (SMR) reactor 50, one or more shift reactors 54, and a pressure swing adsorption (PSA) unit 58. The splitter 22 is configured to be actuated to change the relative proportions of the working fluids (a first and a second portion of CO2 gas) directed from turbine 18 to the secondary power cycle (26) and the hydrogen production cycle (30).

[0032] The oxy-fuel burner 14 is configured to receive methane (CH4), oxygen (O2) and carbon dioxide (CO2) gas, and to use oxygen to burn methane to produce additional CO2 and H2O, and to heat the combined CO2 gas to a first state having a first temperature and a first pressure.

[0033] The first turbine 18 is configured to receive CO2 gas in a first state from a combustor, convert the thermal energy in the CO2 gas into mechanical work, such as driving a generator to produce electricity at P1. The first turbine 18 may be referred to as a high-temperature turbine because it is configured to operate with a working fluid (CO2 gas) from the combustor at a first temperature and pressure. In operation, after converting a certain amount of thermal energy into mechanical work, the first turbine 18 outputs CO2 gas in a second state at a second temperature and a second pressure. The second temperature is typically lower than the first temperature, and the second pressure may also be lower than the first pressure. In the depicted configuration, the first turbine 18 operates continuously to remove energy from the CO2 gas, thereby reducing the temperature of the CO2 gas to a level suitable for use in either the SMR reactor 50 or the second turbine 46. In other configurations of this system, an alternative heat load (e.g., a heat exchanger) may be included instead of the first turbine to reduce the temperature and / or pressure of the CO2 gas to a level suitable for use in either the SMR reactor or the second turbine.

[0034] The second turbine 46 is configured to receive a first portion of CO2 gas in a second state, converting the thermal energy in the CO2 gas into mechanical work, such as driving a generator to produce electricity at P2. The second turbine 46 can be referred to as a cryogenic turbine because it is configured to operate with a working fluid (CO2 gas) from the first turbine at a second temperature and pressure. In operation, after converting a certain amount of thermal energy into mechanical work, the second turbine outputs CO2 gas in a third state at a third temperature and pressure.

[0035] The gas-heated SMR reactor 50 is configured to receive a second portion of CO2 gas in a second state, and a mixture of methane (CH4) and vapor (H2O) at inlet 62. In use, the gas-heated SMR reactor transfers heat from the CO2 gas to the mixture (CH4 and H2O) without mixing the CO2 gas and the mixture, outputting a reformed gas stream containing hydrogen, CO2, CO, H2O and unreacted methane, and separately outputting CO2 gas in a fourth state at a fourth temperature and a fourth pressure.

[0036] The heat recovery stage 34 is configured to receive a first portion of CO2 gas in a third state from the second turbine and a second portion of CO2 gas in a fourth state from the SMR reactor. For example, in the depicted instance, the first portion of CO2 gas from the second turbine 46 and the second portion of CO2 gas from the SMR reactor 50 are recombined at point 66 and directed to the heat recovery stage 34. In use, the heat recovery stage 34 removes heat energy from the CO2 gas and outputs the combined CO2 gas in a fifth state at a fifth temperature and a fifth pressure.

[0037] The recompression stage 38 is configured to receive CO2 gas and compressed CO2 gas from the heat recovery stage 34. The recompression stage will typically include a compressor, which may, for example, share a common axis of rotation with (e.g., be driven by) a second turbine (46), which itself may also share a common axis of rotation with the first turbine (18). The recompression stage 38 may also be configured to purify the working fluid stream by condensing H2O from the CO2 gas in the combustor, such that a portion of the CO2 gas can be removed via exhaust valve 70 for storage. By using CO2 gas as the working fluid and positioning exhaust valve 70 downstream of the recompression stage 38, pure CO2 gas can be removed from the system for storage without the need for additional equipment for isolating or compressing the CO2 gas prior to storage.

[0038] The working fluid (CO2 gas) that has not been removed by the exhaust valve 70 is sent to the preheating stage 42, where heat energy is added to the CO2 gas to raise its temperature. The CO2 gas is then sent to the burner (14) for further heating and circulates through the system. In the depicted example, the preheating stage 42 and the heat recovery stage 34 are defined by opposite "sides" of a common heat exchanger, in which heat energy is transferred from a first portion of the CO2 gas in the heat recovery stage (34) to a second portion of the CO2 gas in the preheating stage (42).

[0039] In hydrogen production cycle 30, the reformed gas stream exits the SMR reactor from outlet 74 and is directed to one or more shift reactors 54. The one or more shift reactors 54 are configured to convert carbon monoxide (CO) and H2O in the reformed gas stream into carbon dioxide (CO2) and additional H2 to increase the hydrogen content, thereby producing a hydrogen stream. The hydrogen stream is then directed to a pressure swing adsorption (PSA) unit, which is configured to remove components other than hydrogen (H2). Typically, the PSA unit is configured to trap non-hydrogen gaseous substances onto a solid surface under high pressure to efficiently purify the hydrogen. Before entering the PSA bed, the gas is cooled and water is condensed and removed. The PSA unit has a first outlet 78 for the purified hydrogen stream, a second outlet 82 for the tail gas containing components other than hydrogen (CO, CO2, and CH4), and a third outlet for condensate. As shown, exhaust gas from the PSA can be returned to the combustor, thus avoiding the need for additional equipment to isolate and / or otherwise process the exhaust gas.

[0040] System 10 utilizes a modified Allam-Fetvedt cycle, which operates as a high-pressure Brayton cycle with reheating, employing a transcritical CO2 working fluid and an oxygen-fuel combustor. The cycle begins by burning gaseous fuel (CH4) with oxygen (O2) and hot, high-pressure, recirculated supercritical CO2 working fluid from preheating stage 42. The recirculated CO2 stream serves the dual purpose of reducing the combustion flame temperature to a manageable level and diluting the combustion products so that the circulating working fluid is primarily CO2. The pressure in the combustor (14) can reach up to approximately 30 MPa, and the combustion feedstock comprises approximately 95% recirculated CO2 by mass. The combustor (14) provides high-pressure exhaust gas, which is supplied to the first turbine 18 (and the second turbine 46 in the electric cycle 26) at a combined pressure ratio of 6 to 12. The exhaust gas arrives at the heat recovery stage 34 as a subcritical CO2 mixture primarily mixed with combustion-derived water. Heat recovery stage 34 (e.g., an economizer heat exchanger) utilizes the CO2 stream preheated in preheating stage 42 and returning to the burner (14) to cool the emissions to below 65°C. In some variations, heat recovery stage 34 may also include further cooling the emissions stream to near ambient temperature to condense H2O into liquid water for removal from the working fluid and recycling for other uses. The remaining working fluid, now almost pure CO2, is then directed to recompression stage (38). The compression system may include a conventional intercooled centrifugal compressor with an inlet pressure below the CO2 critical pressure. In some embodiments, the CO2 working fluid may then be compressed and cooled to near ambient temperature in a compressor aftercooler, for example, to achieve a pressure exceeding 500 kg / m³. 3 The density is such that, under the resulting conditions, the CO2 stream can be pumped to the required high combustion pressure using a multi-stage centrifugal pump. The repressurized working fluid can then be returned via a preheating stage (42) (e.g., an economizer heat exchanger) to be reheated and returned to the burner. To maintain mass balance, the net CO2 products originating from the addition of fuel and oxygen in the burner can be removed from the high-pressure stream via exhaust valve 70. As described above, with exhaust valve 70 at this point in the system, the CO2 products are high-pressure and high-purity, ready for sequestration or utilization without further compression.

[0041] Unlike the conventional Allam cycle, this system allows a portion of the heat energy added to the working fluid via the burner to be used to heat the SMR reactor 50 to produce hydrogen, rather than for turbine operation. Therefore, more heat energy can be diverted to the electricity cycle (26) to generate relatively more electricity for use during periods when the availability of electricity from solar and / or wind sources is low or nonexistent, while using more heat energy to produce hydrogen when renewable energy sources are online or more readily available.

[0042] Example

[0043] Examples 1-3: Electricity and Hydrogen Production Systems

[0044] Another instance of this system 10a models three different allocations (50:50, 90:10, and 10:90) of power generation in the secondary power cycle (26) and hydrogen production in the hydrogen production cycle (30). Figure 2 Example 1 with a 50:50 distribution is described, wherein the working fluid from the first turbine 18 is uniformly distributed between the secondary power cycle (26) and the hydrogen production cycle (30); Figure 3 Example 2 is described with a 90:10 allocation, wherein 90% of the working fluid from the first turbine 18 is allocated to the secondary power cycle (26) and 10% is allocated to the hydrogen production cycle (30); and Figure 4 Example 3, with a 10:90 allocation, is described, where 10% of the working fluid from the first turbine 18 is allocated to the secondary power cycle (26) and 90% to the hydrogen production cycle (30). There are generally two ways to regulate the output of this system. First, the amount of fuel (CH4) supplied to the combustor can be adjusted to change the amount of heat energy added to the working fluid at the combustor. Second, the allocation between the secondary power cycle (26) and the hydrogen production cycle (30) can be adjusted to change the system's power and hydrogen output.

[0045] System 10a is similar to System 10, the main difference being that System 10a separately includes a cooling stage 36 between the heat recovery stage 34 and the recompression stage 38, and also includes a second recompression stage 86 configured to compress the exhaust gases from the PSA unit as they return to the combustor (18). Cooling stage 36 is configured to receive the working fluid exhaust stream from the heat recovery stage (34) and further cool that stream to near ambient temperature to condense H2O into liquid water for removal from the working fluid (e.g., at the recompression stage 38) for recycling to other uses.

[0046] In each of Examples 1, 2 and 3, the fuel-to-burner rate is kept constant at 32,600 kg / hr, which also keeps the energy input to the burner at a constant rate of 529 MW. Figure 2 , 34 includes various flow rates in kilograms per hour (kg / hr) (e.g., CO2 recirculated to burner 14) and various component loads in megawatts (MW) (e.g., the load of the second turbine 46). Table 1 below lists the values ​​of various parameters in 10% intervals from 90% secondary power cycle (26) / 10% hydrogen production cycle (30) to 10% secondary power cycle (26) / 90% hydrogen production cycle (30).

[0047] Table 1. System variables when the hydrogen production ratio is 0.1 to 0.9

[0048]

[0049] Figure 5 Table 1 shows some variables for various hydrogen production ratios (0.1 to 0.9 on the X-axis from left to right) and corresponding electricity ratios (0.9 to 0.1 on the X-axis from right to left). Specifically, Figure 5 Combustion load 100, net power 104, and SMR load 108 in megawatts (MW) are plotted, with scale bars shown on the left Y-axis; and recycle CO2 112 and hydrogen production 116 in kiloton-per-year (KTA) are plotted, with scale bars shown on the right Y-axis. See Table 1 and... Figure 5 As can be seen, as the secondary power ratio decreases from 0.9 (90%) to 0.1 (10%), SMR load and hydrogen production increase, resulting in a nearly 50% decrease in net power generation. Burner load increases due to increased exhaust gas returned from the PSA unit, and recycle CO2 returned to the burner decreases. Therefore, when the system is used as a backup energy supply to supplement periods when solar and / or wind power is less available or unavailable, the secondary power generation cycle (26) can be maximized to nearly double the system's net power generation. Conversely, when less power is needed during periods when solar and / or wind power is more available, the hydrogen production cycle (30) can be maximized to utilize assets for hydrogen production, thereby replacing most of the power generation.

[0050] In addition, system 10a also models various fuel feed rates to the burner (14) under a fixed 50:50 distribution between the secondary power cycle 26 and the hydrogen production cycle 30. Table 2 includes various parameters for operating system 10a under a constant secondary power ratio of 0.5 and fuel flow rates of 400 KTA, 700 KTA, 1000 KTA, 1300 KTA, 1450 KTA and 1573 KTA.

[0051] Table 2. System variables at different fuel levels with a secondary power ratio of 0.5

[0052]

[0053] Figure 6 Table 2 shows some variables for various fuel feed rates (from 400 to 1573 KTA on the X-axis, from left to right). Specifically, Figure 6 The burner load 100, net power 104, and SMR load 108 in megawatts (MW) are plotted, with scale bars shown on the left Y-axis; and the recycle CO2 112 and hydrogen production 116 in kiloton-per-year (KTA) are plotted, with scale bars shown on the right Y-axis. See Table 2 and... Figure 6 As can be seen, as the fuel flow rate decreases, all other outputs decrease roughly proportionally. Therefore, the fuel flow rate to the burner can also be altered to regulate overall power generation and hydrogen production to accommodate varying levels of availability (or unavailability) of electricity from renewable energy sources. Furthermore, the proportion of secondary power and the fuel flow rate can be varied together to achieve a wide range of combinations of electricity and hydrogen production.

[0054] The foregoing specification and embodiments provide a complete description of the structure and use of exemplary embodiments. While certain embodiments have been described above with a degree of specificity or by reference to one or more individual embodiments, those skilled in the art can make many changes to the disclosed embodiments without departing from the scope of the invention. Therefore, the various illustrative embodiments of this device are not intended to be limited to the specific forms disclosed. Rather, they include all modifications and alternatives falling within the scope of the claims, and embodiments other than those shown may include some or all of the features of the depicted embodiments. For example, components may be combined into a unified structure, and / or connections may be replaced. Furthermore, where appropriate, aspects of any instance described above may be combined with aspects of any other instance described to form additional instances having comparable or different properties and solving the same or different problems. Similarly, it will be understood that the benefits and advantages described above may apply to one embodiment or to several embodiments.

[0055] The claims are not intended to include, nor should they be construed as including means plus function or steps plus function limitation, unless such limitation is expressly stated in the given claim by the phrases “means for…” or “steps for…” respectively.

Claims

1. A power generation system, comprising: An oxy-fuel burner configured to receive methane, oxygen, and carbon dioxide gas, the burner being configured to use the oxygen to burn the methane to heat the carbon dioxide gas; A first turbine is configured to receive carbon dioxide gas in a first state from the burner and convert the thermal energy in the carbon dioxide gas into mechanical work. A second turbine is configured to receive a first portion of the carbon dioxide gas from the first turbine and convert the thermal energy in the first portion of the carbon dioxide gas into mechanical work. A gas-heated steam methane reforming (SMR) reactor is configured to receive a second portion of the carbon dioxide gas from a first turbine, receive a mixture of methane and steam, and transfer thermal energy from the second portion of the carbon dioxide gas to the mixture without mixing the carbon dioxide gas and the mixture to produce a reformed gas stream. A splitter is disposed between the first turbine, the second turbine, and the SMR reactor, and is configured to change the relative sizes of the first and second portions of the carbon dioxide gas. A heat recovery stage is configured to receive a first portion of the carbon dioxide gas from the second turbine and a second portion of the carbon dioxide gas from the SMR reactor, and to remove thermal energy from the carbon dioxide gas; A recompression stage is configured to receive the carbon dioxide gas from the heat recovery stage and compress the carbon dioxide gas. A preheating stage is configured to receive the carbon dioxide gas from the recompression stage, receive thermal energy from the heat recovery stage to heat the carbon dioxide gas, and guide the preheated carbon dioxide gas to the burner. and An exhaust valve, located between the recompression stage and the heating stage, is configured to divert a portion of the carbon dioxide gas out of the system.

2. The system of claim 1, wherein the first turbine is coupled to a generator to generate electricity.

3. The system according to any one of claims 1-2, wherein the second turbine is coupled to a generator to generate electricity.

4. The system according to any one of claims 1-3, further comprising: One or more shift reactors are coupled to the SMR reactor to receive the reformed gas stream and the produced hydrogen stream from the SMR reactor. and A pressure swing adsorption (PSA) unit is configured to receive the hydrogen stream from one or more of the shift reactors and remove components other than hydrogen. The PSA unit has a first outlet for the purified hydrogen stream and a second outlet for the tail gas including the components other than hydrogen.

5. The system of claim 4, wherein the second outlet of the PSA unit is coupled to the burner to return the exhaust gas from the PSA unit to the burner.

6. The system according to claim 5, further comprising: A second recompression stage is disposed between the second outlet of the PSA and the burner to compress the exhaust gas.

7. The system according to any one of claims 1-6, wherein the heat recovery stage and the heating stage are both defined by a common heat exchanger.

8. The system according to any one of claims 1-7, wherein the first turbine, the second turbine, and the recompression stage share a common axis of rotation.

9. A method for producing electricity and hydrogen, the method comprising: Methane is burned in an oxygen fuel burner to heat carbon dioxide gas; The carbon dioxide gas is received from the burner at the first turbine, and the thermal energy in the carbon dioxide gas is converted into mechanical work to generate electricity; The second turbine receives a first portion of the carbon dioxide gas from the first turbine and converts the thermal energy in the first portion of the carbon dioxide gas into mechanical work to generate electricity. A second portion of the carbon dioxide gas from the first turbine is received at the gas-heated steam methane reforming (SMR) reactor, and thermal energy is transferred from the second portion of the carbon dioxide gas to a mixture of methane and steam without mixing the carbon dioxide gas and the mixture to produce a reformed gas stream. The first and second portions of the carbon dioxide gas are recombined. Thermal energy is extracted from the carbon dioxide gas in the heat recovery stage; The carbon dioxide gas is compressed after the thermal energy is extracted; A portion of the compressed carbon dioxide gas is removed for storage; The remaining portion of the compressed carbon dioxide gas is reheated in the heating stage; and The heated and compressed carbon dioxide gas is returned to the burner.

10. The method of claim 9, further comprising: Increasing the relative size of the first portion of the carbon dioxide gas increases the rate at which power is generated in the second turbine.

11. The method of claim 9, further comprising: Increasing the relative size of the second portion of the CO2 gas increases the rate of hydrogen production.

12. The method according to any one of claims 9-11, wherein the heat removed from the carbon dioxide gas in the extraction step is transferred to the carbon dioxide gas in the reheating step.

13. The method according to any one of claims 9-12, further comprising: The reformed gas stream from the SMR reactor is guided through one or more shift reactors to produce a hydrogen stream.

14. The method of claim 13, further comprising: Components other than hydrogen are removed from the hydrogen stream to produce a tail gas stream and a purified hydrogen stream.

15. The method of claim 14, further comprising: The exhaust gas stream is redirected to the oxygen fuel burner.

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