Systems and methods for carbon-free generation of power and hydrogen in variable combinations

Abstract

This disclosure includes power-generation systems and methods. An oxyfuel combustor can be used to heat CO2 gas which, in turn, can be utilized to generate mechanical work in a first turbine, with first and second portions of the CO2 gas exiting the first turbine being directed, respectively, to (1) a second turbine to generate additional mechanical work, and (2) a gas-heated steam methane reforming (SMR) reactor for use a heating gas. A diverter can be disposed between the first turbine, the second turbine, and the SMR reactor, and configured to vary the relative sizes of the first and second portions. A heat-recovery stage can receive the 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 can receive the CO2 gas from the heat recovery stage, and compress the CO2 gas. A preheating stage can receive the CO2 gas from the recompression stage, receive thermal energy from the heat-recovery stage to heat the CO2 gas, and direct the pre-heated CO2 gas to the combustor; and an offtake valve can be disposed between the recompression stage and the heating state, to divert a portion of the CO2 gas out of the system. In at least some examples, the mechanical work can be used to generate electricity.

Description

SYSTEMS AND METHODS FOR CARBON-FREE GENERATION OF POWER AND HYDROGEN IN VARIABLE COMBINATIONSFIELD OF DISCLOSURE

[0001] The present disclosure is generally related to generation of electricity in processes for producing chemicals and, more particularly but not by way of limitation, to systems and methods for generating electricity and producing hydrogen that allows for continuous asset utilization by varying the relative rates of electricity generation and hydrogen production to account for varying electricity needs.BACKGROUND

[0002] As chemical plants move from burning fossil fuels to meet daily power needs to using electricity from renewable sources, the availability and cost of electricity will vary over time.For example, production of solar and wind energy varies with time of day and weather conditions — e.g., night hours and overcast time periods reduce or interrupt the generation of electricity by solar panels. Likewise, during periods when wind is slower or non-existent, generation of electricity by wind turbines is reduced or interrupted. Commercially, however, it is typically important for a chemical plant to maintain consistent throughput, even when electricity is less available or unavailable from renewable sources.SUMMARY

[0003] Exclusive usage of solar and wind requires storage from which power can be drawn when wind and solar are less available or unavailable. Battery storage is one option for power storage from which electricity can be drawn during the low- or no-power intervals inherent with green energy, but battery storage may in many circumstances be too expensive to be practical.

[0004] Another option is to combine wind and / or solar with a back-up system that combusts fossil fuels to generate electricity during low- or no-power intervals, but such systems typically require expensive flue gas carbon capture systems to collect CO2 emissions, and prepare and compress such emissions for sequestration. Additionally, with such a backup system typically being turned off or operated far below maximum capacity during periods in which solar or wind power is available, the backup system is typically very underutilized and capital inefficient.

[0005] The present systems and methods generate both electricity and hydrogen, with dynamic rebalancing of relative power and hydrogen generation to adapt to low- and no-power intervals, while utilizing CO2 as a working fluid to greatly simplify the systems needed for recapture. Energy to drive the system comes from an oxy-methane combustor, and a relatively larger proportion of the combustion energy can be directed to a power cycle when green power is not or less available. When green energy is more available, a relatively larger proportion of the combustion energy can be directed to production of hydrogen, which can be used as an energy vector in a variety of other applications.

[0006] The present systems and methods utilize an Allam cycle (a modified Brayton cycle using CO2 as the working fluid) and the net CO2 made by combustion is bled out of the loop as a high pressure pure CO2 stream ready for sequestration, without requiring an expensive carbon capture kit. The hydrogen cycle uses a gas heated steam methane reforming (SMR) reactor, with thermal energy for heating provided by the hot CO2 loop to drive the SMR chemistry. The use of a gas-heated SMR reactor avoids the additional flue gas emissions typically associated with a combustion-driven SMR reactor, while the tail gas from the PSA (unreacted CEE, CO, and CO2) can be sent to the combustor as fuel, and so avoids the cost and complexity of a recycle and separation subsystem usually required in an SMR process. With combustion energy shiftable between the power cycle and the hydrogen cycle, the present systems and methods allow for most of the assets to be utilized full time and only a fraction of the assets used intermittently, so the capital efficiency is much improved relative to a conventional fossil fuel backup power systems that may be simply turned off during periods when primary power requirements can be met with power from renewable sources such as solar and / or wind.

[0007] Some configurations of the present power-generation systems comprise: an oxyfuel combustor, a first turbine, a second turbine, a gas-heated steam methane reforming (SMR) reactor, a diverter, a heat-recovery stage, a recompression stage, a pre-heating stage, and an offtake valve. In such configurations, the oxyfuel combustor is configured to receive methane, oxygen, and carbon dioxide (CO2) gas, and to burn the methane with the oxygen to heat the CO2 gas; the first turbine is configured to receive from the combustor the CO2 gas in the first state, and convert 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 convert thermal energy in the first portion of the CO2 gas into mechanical work. The SMR reactor can beconfigured 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 diverter can be disposed between the first turbine, the second turbine, and the SMR reactor, and configured to vary the relative sizes of the first and second portions. The heat-recovery stage can be configured to receive the first portion of the CO2 gas from the second turbine and the second portion of the CO2 gas from the SMR reactor, and to remove thermal energy from the CO2 gas. The recompression stage can be configured to receive the CO2 gas from the heat recovery stage, and to compress the CO2 gas. The pre-heating stage can be configured to receive the CO2 gas from the recompression stage, to receive thermal energy from the heat-recovery stage to heat the CO2 gas, and direct the pre-heated CO2 gas to the combustor. The offtake valve can be disposed between the recompression stage and the heating state, and configured to divert a portion of the CO2 gas out of the system.

[0008] In some of the foregoing configurations of the present power-generation systems, the first turbine is coupled to a generator to generate electrical power.

[0009] In some of the foregoing configurations of the present power-generation systems, the second turbine is coupled to a generator to generate electrical power.

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

[0011] In some of the foregoing configurations of the present power-generation systems, the heat-recovery stage and the heating stage are both defined by a common heat exchanger.

[0012] In some of the foregoing configurations of the present power-generation systems, the first turbine, the second turbine, and the recompression stage share a common rotational axis.

[0013] In some implementations of the present methods for producing electrical power and hydrogen, the method comprises: burning methane in an oxyfuel combustor to heat carbon dioxide (CO2) gas; receiving at a first turbine the CO2 gas from the combustor, and converting thermal energy in the CO2 gas into mechanical work to generate electrical power; receiving at a second turbine a first portion of the CO2 gas from the first turbine, and converting thermal energy in the first portion of the CO2 gas into mechanical work to generate electrical power; receiving at a gas-heated steam methane reforming (SMR) reactor a second portion of CO2 gas from the first turbine, and transferring thermal energy from the second portion of the CO2 gas to a mixture of methane (CH4) and steam (H2O) without mixing the CO2 gas and the mixture to produce a reformed gas stream; recombining the first and second portions of the 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 sequestration; reheating the remainder of the compressed CO2 gas in a heating stage; and returning the heated, compressed CO2 gas to the combustor.

[0014] Some of the foregoing implementations of the present methods further comprise: increasing the relative size of the first portion of the CO2 gas relative to increase the rate at which power is generated in the second turbine.

[0015] Some of the foregoing implementations of the present methods further comprise: increasing the relative size of the second portion of the CO2 gas to increase the rate at which hydrogen is produced.

[0016] In some of the foregoing implementations of the present methods, the thermal energy removed from the CO2 gas in the extracting step is transferred to the CO2 gas in the reheating step.

[0017] Some of the foregoing implementations of the present methods further comprise: directing the reformed gas stream from the SMR reactor through one or more shift reactors to produce a hydrogen stream. Some such implementations further comprise: removing components other than hydrogen from the hydrogen stream to produce a tail gas stream and apurified hydrogen stream. Some such implementations further comprise: redirecting the tail gas stream to the oxyfuel combustor.

[0018] The term “coupled” is defined as connected, although not necessarily directly, and not necessarily mechanically; two items that are “coupled” may be unitary with each other. The terms “a” and “an” are defined as one or more unless this disclosure explicitly requires otherwise. The term “substantially” is defined as largely but not necessarily wholly what is specified (and includes what is specified; e.g., substantially 90 degrees includes 90 degrees and substantially parallel includes parallel), as understood by a person of ordinary skill in the art. In any embodiment of the present apparatuses, kits, and methods, the term “substantially” may be substituted with “within [a percentage] of’ what is specified, where the percentage includes 0.1, 1, 5, and / or 10 percent.

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

[0020] Further, an apparatus, device or system that is configured in a certain way is configured in at least that way, but it can also be configured in other ways than those specifically described.

[0021] Any embodiment of any of the present apparatuses and methods can consist of or consist essentially of - rather than comprise / include / contain / have - any of the described steps, elements, and / or features. Thus, in any of the claims, the term “consisting of’ or “consisting essentially of’ can be substituted for any of the open-ended linking verbs recited above, in order to change the scope of a given claim from what it would otherwise be using the open-ended linking verb.

[0022] Details associated with the embodiments described above and others are presented below.

[0023] Some details associated with the aspects of the present disclosure are described above, and others are described below. Other implementations, advantages, and features of the present disclosure will become apparent after review of the entire application, including the Brief Description of the Drawings, Detailed Description, and the Claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The following drawings illustrate by way of example and not limitation. For the sake of brevity and clarity, every feature of a given structure is not always labeled in every figure in which that structure appears. Identical labels or reference numbers do not necessarily indicate an identical structure. Rather, the same reference number may be used to indicate a similar feature or a feature with similar functionality, as may non-identical reference numbers.

[0025] FIG. 1 depicts a schematic diagram of a first example of the present systems for variable generation of power and hydrogen.

[0026] FIG. 2 depicts a schematic diagram of a second example of the present systems for generation of power and hydrogen, with flowrates and duties for a 50-50 split of combustion energy between a secondary power generation cycle and a hydrogen-production cycle.

[0027] FIG. 3 depicts a schematic diagram of the system of FIG. 2, with flowrates and duties for a 90-10 split of combustion energy between a secondary power generation cycle and a hydrogen-production cycle.

[0028] FIG. 4 depicts a schematic diagram of the system of FIG. 2, with flowrates and duties for a 10-90 split of combustion energy between a secondary power generation cycle and a hydrogen-production cycle.

[0029] FIG. 5 depicts a chart of changes in certain system variables as the split between 10-90 (FIG. 4) and 90-10 (FIG. 3) for a given combustion fuel input.

[0030] FIG. 6 depicts a chart of changes in certain system variables as combustion fuel input increases for a given split between a secondary power generation cycle and a hydrogenproduction cycle.DETAILED DESCRIPTION

[0031] Referring now to the drawings, and more particularly to FIG. 1, shown there and designed by the reference numeral 10 is a first example of the present systems for variable generation of power and hydrogen. In the depicted example, system 10 comprises: an oxyfuel combustor 14, a first turbine 18, a diverter 22, a secondary power cycle 26, and a hydrogenproduction 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 pre-heating stage 42. In the example shown, secondary power cycle 26 comprises a second turbine 46; and hydrogenproduction cycle 30 comprises a gas-heated steam methane reforming (SMR) reactor 50, one or more shift reactors 54, and a pressure swing adsorption (PSA) unit 58. Diverter 22 is configured to be actuated to vary the relative proportions of working fluid (first and second portions of the CO2 gases) directed from turbine 18 to the secondary power cycle (26) and the hydrogenproduction cycle (30).

[0032] Oxy fuel combustor 14 is configured to receive methane (CH4), oxygen (O2), and carbon dioxide (CO2) gas, and to bum the methane with the oxygen to generate additional CO2 and H2O and to heat the combined CO2 gas to a first state with a first temperature and a first pressure.

[0033] First turbine 18 is configured to receive from the combustor the CO2 gas in the first state, convert thermal energy in the CO2 gas into mechanical work, for example driving an electrical generator to generate electrical power at Pl. First turbine 18 may be referred to as a high-temperature turbine because it is configured to operate with the working fluid (CO2 gas) at the first temperature and pressure coming from the combustor. In operation, after conversion of a certain amount of thermal energy to mechanical work, first turbine 18 outputs the CO2 gas in a second state at a second temperature and 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, first turbine 18 runs continuously to remove energy from the CO2 gas and thereby reduce the temperature of the CO2 gas to a level at which the CO2 gas is suitable for use in either of SMR reactor 50 or second turbine 46. In other configurations of the present systems, an alternate thermal load (e.g., a heat exchanger) may be included in place ofthe first turbine to reduce the temperature and / or pressure of the CO2 gas to a level at which the CO2 gas is suitable for use in either of the SMR reactor or the second turbine.

[0034] Second turbine 46 is configured to receive a first portion of the CO2 gas in the second state, convert thermal energy in the CO2 gas into mechanical work, for example driving an electrical generator to generate electrical power at P2. Second turbine 46 may be referred to as a low-temperature turbine because it is configured to operate with the working fluid (CO2 gas) at the second temperature and pressure coming from the first turbine. In operation, after converting a certain amount of thermal energy to mechanical work, the second turbine outputs the CO2 gas in a third state at a third temperature and third pressure.

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

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

[0037] Recompression stage 38 is configured to receive the CO2 gas from heat recovery stage 34, and to compress the CO2 gas. The recompression stage will typically include a compressor which may, for example, share a common rotational axis with (e.g., may be driven by) the second turbine (46), which itself may also share a common rotational axis with the first turbine (18). Recompression stage 38 may also be configured to condense the H2O made in the combustor from the CO2 gas to purify the working fluid stream such that a portion of the CO2 gas can be removed via offtake valve 70 for sequestration. By using CO2 gas as the working fluid, and positioning offtake valve 70 downstream of recompression stage 38, pure CO2 gas canbe removed from the system for sequestration without requiring additional equipment for isolation or compression of CO2 gases prior to sequestration.

[0038] Working fluid (CO2 gases) that is not removed via offtake valve 70 is routed to preheating stage 42, where thermal energy is added to the CO2 gases to increase the temperature of the CO2 gases, which are then routed to the combustor (14) to be further heated for circulation through the system. In the depicted example, pre-heating stage 42 and heat-recovery stage 34 are defined by opposing “sides” of a common heat exchanger in which thermal energy is transferred from a first portion of the CO2 gases in the heat-recovery stage (34) to a second portion of the CO2 gases in the pre-heating stage (42).

[0039] In the hydrogen -product! on cycle 30, the reformed gas stream exits the SMR reactor from outlet 74 and is directed to the shift reactor(s) 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 content of hydrogen and thereby produce a hydrogen stream. The hydrogen stream is then directed to the pressure swing adsorption (PSA) unit which is configured to remove components other than hydrogen (H2). Generally, a PSA unit is configured to trap non-hydrogen gas species onto solid surfaces under high pressures to effectively purify hydrogen gas. 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 and a second outlet 82 for tail gases that contain the components other than hydrogen - CO, CO2, and CPU - and a third outlet for the condensed water. As shown, the tail gases from the PSA can be returned to the combustor, avoiding the need for additional equipment to isolate and / or otherwise process the tail gases.

[0040] System 10 utilizes a modified Allam-Fetvedt Cycle that operates as a recuperated, high-pressure, Brayton cycle employing a transcritical CO2 working fluid with an oxy-fuel combustor. The cycle begins by burning a gaseous fuel (CPU) with oxygen (O2) and a hot, high- pressure, recycled supercritical CO2 working fluid from pre-heating stage 42. The recycled CO2 stream serves the dual purpose of lowering the combustion flame temperature to a manageable level, and diluting the combustion products such that the cycle working fluid is predominantly CO2. The pressure in the combustor (14) can be as high as approximately 30 MPa and the combustion feedstock includes approximately 95% recycled CO2 by mass. The combustor (14)provides a high-pressure exhaust that is supplied to first turbine 18 (and second turbine 46 in power cycle 26) with a combined pressure ratio of from 6 and 12. The discharge reaches heatrecovery stage 34 as a subcritical CO2 mixture predominantly comingled with combustion derived water. Heat -recovery stage 34 (e.g., an economizer heat exchanger) cools this discharge down to below 65°C against the stream of CO2 being pre-heated in pre-heating stage 42 on its way to back the combustor (14). In some variations, heat-recovery stage 34 may also include further cooling of the discharge 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 of nearly pure CO2 is then directed to the recompression stage (38). The compression system can include a conventional inter-cooled centrifugal compressor with an inlet pressure below the CO2 critical pressure. In some implementations, the CO2 working fluid can then be compressed and cooled to near ambient temperature in a compressor after-cooler, for example, to achieve a density in excess of 500 kg / m3, such that, in the resulting condition, the CO2 stream can be pumped to the high combustion pressure required using a multi-stage centrifugal pump. The repressurized working fluid can then be sent back through the pre-heating stage (42) (e.g., an economizer heat exchanger) to be reheated and returned to the combustor. To maintain mass balance, the net CO2 product derived from the addition of fuel and oxygen in the combustor can be removed from the high-pressure stream via offtake valve 70. As noted above, with offtake valve 70 at this point in the system, the CO2 product is high pressure and high purity, ready for sequestration or utilization without requiring further compression.

[0041] Unlike a conventional Allam cycle, the present systems allow a portion of the thermal energy added by the combustor to the working fluid to be utilized to heat SMR reactor 50 to produce hydrogen instead of for turbine operation. Thus, more of the thermal energy can be directed to the power cycle (26) to generate relatively more electrical power for use during periods of low- or no-power availability from solar and / or wind power sources, while using more of that thermal energy to generate hydrogen during times at which renewable power sources are online or more available.EXAMPLESExamples 1-3: Power and Hydrogen Production Systems

[0042] Another example of the present systems 10a was modeled for three different splits (50:50, 90: 10, and 10:90) of power generation in the secondary power cycle (26) versus hydrogen generation in the hydrogen-production cycle (30). FIG. 2 depicts Example 1 with a 50:50 split in which working fluid from first turbine 18 is divided evenly between the second power cycle (26) and the hydrogen-production cycle (30); FIG. 3 depicts Example 2 with a 90: 10 split in which working fluid from first turbine 18 is divided 90% to the secondary power cycle (26) and 10% to the hydrogen-production cycle (30); and FIG. 4 depicts Example 3 with a 10:90 split in which working fluid from the first turbine 18 is divided 10% to the secondary power cycle (26) and 90% to the hydrogen-production cycle (30). There are generally two ways of adjusting the output of the present systems. First, the amount of fuel (CH4) to the combustor can be adjusted to vary the amount of thermal energy added to the working fluid at the combustor. Second, the split between the secondary power cycle (26) and the hydrogen-production cycle (30) can be adjusted to vary the power and hydrogen outputs of the system.

[0043] System 10a is similar to system 10, with the primary exception that system 10a separately includes a cooling stage 36 between heat-recovery stage 34 and recompression stage 38, and also includes a second recompression stage 86 configured to compress tail gases from the PSA unit as those tail gases are returned to the combustor (18). Cooling stage 36 is configured to receive the working fluid discharge 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 recompression stage 38) to be recycled for other uses.

[0044] In each of Examples 1, 2, and 3 the rate of fuel to the combustor is held constant at 32,600 kilograms per hour (kg / hr), which also holds constant the rate of 529 megawatts (MW) at which energy is input at the combustor. FIGs. 2, 3, and 4 include various flowrates (e.g., CO2 recycled to combustor 14) in kilograms per hour (kg / hr), and various component duties (e.g., of second turbine 46) in megawatts (MW). Table 1 below lists values for various parameters at 10% intervals from 90% secondary power cycle (26) / l 0% hydrogen-production cycle (30) to 10% secondary power cycle (26) / 90% hydrogen-production cycle (30).TABLE 1. System Variables At Hydrogen-Production Fractions of 0.1 to 0.9

[0045] FIG. 5 charts certain of the variables in TABLE 1 for various hydrogen-production fractions (left to right from 0.1 to 0.9 on the X axis), and corresponding power fractions (right to left from 0.9 to 0.1 on the X axis). In particular, FIG. 5 charts combustor duty 100, net power 104, and SMR duty 108 in megawatts (MW), the scale of which is shown on the left Y axis; and charts recycle CO2 112 and hydrogen make 116 in kilotons per annum (KT A), the scale of which is shown on the right Y axis. As can be seen in TABLE 1 and FIG. 5, as the secondary power fraction decreases from 0.9 (90%) to 0.1 (10%), the SMR Duty and hydrogen production increases, net power generation declines by nearly 50%, the combustor duty increases due to the increase in tail gas returned from the PSA unit, and recycle CO2 returned to the combustor decreases. As such, when the system is used as a backup power supply to supplement periods during which solar and / or wind power is less available or not available, the secondary power generation cycle (26) can be maximized to nearly double the net power production by the system. 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 the asset for hydrogen production in lieu of a significant portion of power generation.

[0046] Additionally, system 10a was also modeled for various fuel feed rates to the combustor (14) at a fixed split of 50:50 between secondary power cycle 26 and hydrogenproduction cycle 30. TABLE 2 includes various parameters for operation of system 10a at a constant secondary power fraction of 0.5, and fuel flow rates of 400 KT A, 700 KT A, 1000 KT A, 1300 KTA, 1450 KTA, and 1573 KTA.TABLE 2. System Variables At Different Fuel Levels Secondary Power Fraction of 0.5

[0047] FIG. 6 charts certain of the variables in TABLE 2 for various fuel feed rates (left to right from 400 to 1573 KTA on the X axis). In particular, FIG. 6 charts combustor duty 100, net power 104, and SMR duty 108 in megawatts (MW), the scale of which is shown on the left Y axis; and charts recycle CO2 112 and hydrogen make 116 in kilotons per annum (KTA), the scale of which is shown on the right Y axis. As can be seen in TABLE 2 and FIG. 6, as fuel flow rate declines, all other outputs decline roughly proportionally. As such, fuel flow rates to the combustor can also be varied to adjust the overall power generation and hydrogen generation to adapt to various levels of availability (or unavailability) of power from renewable power sources. Moreover, the secondary power fraction and fuel flow rate can be varied together to achieve a wide range of combinations of power and hydrogen production.* * *

[0048] The above specification and examples provide a complete description of the structure and use of exemplary embodiments. Although certain embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the scope of this invention. As such, the various illustrative embodiments of the present devices are not intended to be limited to the particular forms disclosed. Rather, they include all modifications and alternatives falling within the scope of the claims, and embodiments other than the one shown may include some or all of the features of the depicted embodiment. For example, components may be combined as a unitary structure, and / or connections may be substituted. Further, where appropriate, aspects of any of the examples described above may be combined with aspects of any of the other examples described to form further examples having comparable or different properties and addressing the same or different problems. Similarly, it will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments.

[0049] The claims are not intended to include, and should not be interpreted to include, means-plus- or step-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) “means for” or “step for,” respectively.

Claims

CLAIMS1. A power-generation system comprising: an oxyfuel combustor configured to receive methane, oxygen, and carbon dioxide gas, the combustor configured to bum the methane with the oxygen to heat the carbon dioxide gas; a first turbine configured to receive from the combustor the carbon dioxide gas in the first state, convert thermal energy in the carbon dioxide gas into mechanical work; a second turbine configured to receive a first portion of the carbon dioxide gas from the first turbine, and convert thermal energy in the first portion of the carbon dioxide gas into mechanical work; a gas-heated steam methane reforming (SMR) reactor configured to receive a second portion of the carbon dioxide gas from the 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 diverter disposed between the first turbine, the second turbine, and the SMR reactor, and configured to vary the relative sizes of the first portion and the second portion of the carbon dioxide gas; a heat-recovery stage configured to receive the first portion of the carbon dioxide gas from the second turbine and the second portion of the carbon dioxide gas from the SMR reactor, and remove thermal energy from the carbon dioxide gas; a recompression stage configured to receive the carbon dioxide gas from the heat recovery stage, and to compress the carbon dioxide gas; a pre-heating stage configured to receive the carbon dioxide gas from the recompression stage, to receive thermal energy from the heat-recovery stage to heat the carbon dioxide gas, and direct the pre-heated carbon dioxide gas to the combustor; and an offtake valve between the recompression stage and the heating state, the offtake 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 electrical power.

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

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

5. The system of claim 4, wherein the second outlet of the PSA unit is coupled to the combustor to return the tail gases from the PSA unit to the combustor.

6. The system of claim 5, further comprising: a second recompression stage disposed between the second outlet of the PSA and the combustor to compress the tail gases.

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

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

9. A method for producing electrical power and hydrogen, the method comprising: burning methane in an oxyfuel combustor to heat carbon dioxide gas; receiving at a first turbine the carbon dioxide gas from the combustor, and converting thermal energy in the carbon dioxide gas into mechanical work to generate electrical power; receiving at a second turbine a first portion of the carbon dioxide gas from the first turbine, and converting thermal energy in the first portion of the carbon dioxide gas into mechanical work to generate electrical power; receiving at a gas-heated steam methane reforming (SMR) reactor a second portion of carbon dioxide gas from the first turbine, and transferring thermal energy 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; recombining the first portion and the second portion of the carbon dioxide gas; extracting thermal energy from the carbon dioxide gas in a heat-recovery stage; compressing the carbon dioxide gas after extracting the thermal energy; removing a portion of the compressed carbon dioxide gas for sequestration; reheating the remainder of the compressed carbon dioxide gas in a heating stage; and returning the heated, compressed carbon dioxide gas to the combustor.

10. The method of claim 9, further comprising: increasing the relative size of the first portion of the carbon dioxide gas to increase 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 to increase the rate at which hydrogen is produced.

12. The method of any of claims 9-11, where the thermal energy removed from the carbon dioxide gas in the extracting step is transferred to the carbon dioxide gas in the reheating step.

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

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

15. The method of claim 14, further comprising: redirecting the tail gas stream to the oxyfuel combustor.

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