Method and system for carbon neutralization power generation

Abstract

A method and system for carbon neutralization power generation that integrates power generation through a gas turbine using hydrogen as fuel. Hydrogen is produced by a modular natural gas steam reforming unit. Carbon capture and heat recovery from turbine exhaust are also provided to heat natural gas and steam fed to the steam reforming step.

Description

Technical Field

[0001] The present disclosure relates to a method for carbon-neutral power generation and a related system for carbon-neutral power generation, which are based on the conversion of an existing natural gas pipeline installation for power generation using natural gas, by generating hydrogen in-situ and using pre-combustion technology and a gas turbine to capture carbon dioxide, burning hydrogen as fuel and air as oxidant.

[0002] The embodiments disclosed herein specifically relate to methods and systems for carbon-neutral power generation, including Background Art

[0003] Gas turbines are commonly used to generate electricity in power plants by burning fuel therein. In particular, the basic operation of a gas turbine is the Brayton cycle with air as the working fluid: atmospheric air flows through a compressor, which raises it to a higher pressure; then energy is added by injecting fuel into the air in the combustion chamber and igniting it, such that combustion generates a high-temperature stream; this high-temperature pressurized gas enters the turbine, during which shaft work output is generated, which is used to drive the compressor; the unused energy is released in the form of exhaust gas, which can be reused for external work, such as directly generating thrust in a turbojet engine, or rotating a second independent turbine (called a power turbine) that can be connected to a fan, propeller, or generator. The design of a gas turbine is determined by its purpose in order to achieve the most ideal energy distribution between thrust and shaft work. Since a gas turbine is an open system that does not reuse the same air, the fourth step of the Brayton cycle (cooling of the working fluid) is omitted.

[0004] Commonly used fuels include natural gas, propane, diesel, biogas, and biodiesel. One of the main problems associated with burning fuels such as these in a gas turbine is the ultimate production of carbon dioxide (CO2) gas. The increasing level of CO2 in the atmosphere is harmful to the environment and is a known cause of global warming. Therefore, it is necessary to prevent the CO2 produced by a gas turbine from entering the atmosphere, i.e., to reduce carbon emissions from gas turbine power generation.

[0005] Currently, there are two ways to reduce carbon emissions from gas turbine power generation:

[0006] - Using a carbon capture unit to capture CO2 from the exhaust gas of a gas turbine;

[0007] - Operating the gas turbine with the fluid switched from natural gas to hydrogen or a blended fuel.

[0008] However, both of these technologies are affected by important limitations. In fact, the exhaust gas of a gas turbine consists of a very small amount of CO2, namely only 3 mol%. Because of this, the size of the required carbon capture unit is huge and very expensive. On the other hand, operating a gas turbine with hydrogen instead of natural gas as fuel greatly reduces the carbon footprint, but in order to feed hydrogen to the gas turbine, a hydrogen infrastructure needs to be established, including pipelines, storage and conversion devices specifically designed for hydrogen.

[0009] Steam reforming is currently the most cost-effective technology for producing hydrogen, especially when natural gas or exhaust gas can be used as raw materials. Steam reforming of natural gas is the mainstay of this production and is a very efficient process with the highest H2 / CO ratio and the lowest cost of production (CoP). However, this process does not eliminate CO2 emissions.

[0010] When producing hydrogen by the steam reforming process, a part of CO2 (usually ~50 - 60% of the total) is generated in the steam reforming (CH4 + H2O = CO + 3H2) and water gas shift (CO + H2O = CO2 + H2) reactors and in the process syngas of the downstream stage, while another part (40 - 50%) is generated additionally in the steam reformer furnace, and the heat provided by external fuel combustion in the steam reformer furnace provides the necessary heat input for the endothermic reaction. It is estimated that about 0.9 kg of CO2 is generated per Nm 3 of H2.

[0011] In particular, according to the prior art, the process architecture of a conventional hydrogen production unit using steam reforming of natural gas raw materials includes the following conventional process steps:

[0012] i. Compression and preheating of natural gas,

[0013] ii. Pretreatment to remove harmful compounds,

[0014] iii. Reacting compressed natural gas with steam to obtain hydrogen and carbon monoxide together with residual steam,

[0015] iv. Heat recovery from both the process stream and the flue gas through steam generation and steam superheating,

[0016] v. Reacting carbon monoxide with steam to obtain hydrogen and carbon dioxide (water gas shift reaction),

[0017] vi. Purifying the hydrogen stream by pressure swing adsorption.

[0018] Reference Figure 1 , shows a block diagram of a conventional natural gas hydrogen production unit, where the natural gas stream 10 is fed under pressure to a pretreatment unit (not shown) to remove those compounds that are harmful to the downstream steam reforming catalyst.

[0019] Then, the treated natural gas stream 10 is mixed with a controlled amount of steam 11 and preheated at 550 °C (typical value) according to the selected value of the steam / carbon molar ratio (S / C = 3 mol / mol, a typical value). The core of the process is the endothermic reaction of methane with steam on a Ni catalyst, as follows:

[0020]

[0021] Reaction (1) takes place in a tubular catalytic reactor 12, which is heated by burning an external fuel stream 13 in a furnace (not shown). In series with the main methane reaction, the water-gas shift reaction converts some of the CO produced by the first reaction into additional H2 and CO2, as follows:

[0022]

[0023] The process steam added to the feed exceeds the stoichiometric amount to increase hydrocarbon conversion and prevent any carbon deposition on the catalyst. To obtain a high hydrogen yield, the reforming temperature is selected in a high range (usually 850÷920 °C). The operation of steam reforming results in the generation of excess heat Q, which is normally recovered in a heat exchanger 14 by generating high-pressure steam, and the high-pressure steam can be partially used as the steam feed stream 11. In addition, additional steam is generated by a process gas heat exchanger (not shown) used to cool the process syngas 15 at the outlet of the reactor 12.

[0024] Then, the cooled process gas is fed to a high-temperature shift stage at an inlet temperature of about 320 °C. The shift reactor 16 is a fixed-bed adiabatic reactor using an iron / chromium / copper oxide catalyst, which converts the carbon monoxide and steam present in the syngas into additional hydrogen and carbon dioxide according to the water-gas shift reaction (Reaction 2). In some cases, an additional lower-temperature shift stage (not shown) is installed and operated downstream.

[0025] The process syngas stream 17 at the outlet of the shift reactor 16 is cooled to about 40 °C by a heat recovery section and a final cooler (not shown). Downstream, a device for removing water condensate (not shown) is installed, and the syngas stream 17 is sent from this device to a pressure swing adsorption unit 18 for crude hydrogen purification. The pressure swing adsorption unit 18 operates by short adsorption / desorption cycles carried out on a selected adsorbent material and running in parallel vessels at different time stages.

[0026] The hydrogen stream 19 is released from the pressure swing adsorption unit 18 at a set pressure (e.g., typically about 20 barg for refinery applications). The hydrogen recovery factor of the pressure swing adsorption unit 18 can reach a value of up to 90%, and the remaining hydrogen, together with the impurities present in the crude hydrogen stream, is released in the form of an offgas stream 20 and leaves the pressure swing adsorption unit 18 at a low pressure (about 0.3 barg). The pressure swing adsorption unit 18 can achieve a hydrogen purity of up to 99.9999% by volume. The typical hydrogen purity specification in a refinery is >99.9%.

[0027] The tail gas stream 20, which is recovered from the pressure swing adsorption unit 18 at near atmospheric pressure and contains the produced CO2 and residual hydrogen (an exemplary composition of this stream is 18% mol CH4, 10.24% mol CO, 45.10% mol CO2, 26% mol H2, 0.55% mol H2O), is recycled back (recycle stream, not shown) to a reformer (not shown), where the residual hydrogen and CO are burned together with the make-up fuel 13 and the produced flue gas is sent to the stack.

[0028] It is also known that carbon capture and storage (CCS) is a process for removing or reducing the CO2 content of a stream that is normally released to the atmosphere and transporting the captured CO2 to a location for permanent storage. CCS can be applied to a wide range of large single point sources, such as process streams, heater and boiler exhausts, and vents of a range of high CO2 footprint industries, including power generation, refining, natural gas processing, chemicals, cement production, and steel production. There are three main CO2 capture systems associated with different combustion processes, namely, post-combustion, pre-combustion, and oxy-fuel combustion.

[0029] In the post-combustion capture process, the removal of CO2 is carried out after combustion has occurred. Chemical or physical sorbents are typically used to treat the flue gas leaving the combustion device to selectively remove CO2 from the gas mixture. This is an end-of-pipe solution, where CO2 is removed from the flue gas before it is discharged to the atmosphere via the stack. The advantage of the post-combustion process is that it is applicable not only to new facilities but also can be retrofitted to existing plants. The main challenge is that the CO2 level in the combustion flue gas is typically very low, at 5% to 20% by volume, depending on the offgas content in the mixed fuel gas.

[0030] In the pre-combustion capture process, the fuel (usually coal or natural gas) is pre-treated before combustion. In particular, it is typically gasified or reformed into a syngas stream, and then the syngas stream is subjected to a water-gas shift reaction and subsequent gas purification to separate the hydrogen produced from the CO2. Although the advantages of removing CO2 from syngas are mainly associated with the pressure of the gas (thus reducing the compression energy requirements), the gas purification step is typically achieved using methods similar to those described for post-combustion processes. The hydrogen is used as the input fuel for the combustion process, while the CO2 can be obtained in a concentrated form for compression, transportation, and sequestration. A high concentration (>20%) of CO2 in the H2 / CO2 fuel gas mixture is beneficial for CO2 separation.

[0031] In oxy-fuel combustion, oxygen rather than air is used for combustion. This reduces the amount of nitrogen present in the flue gas that affects the subsequent separation process. The main components of the flue gas are CO2, water, particulate matter, and SO2. After removing the particulate matter, SO2, and water, the remaining gas contains a high concentration of CO2, approximately 80 - 98% (depending on the fuel used).

[0032] Both pre-combustion and post-combustion technologies for CO2 capture can be applied to hydrogen production plants that steam reform natural gas. The pre-combustion technology will be applicable to the syngas stream leaving the water-gas shift reactor, while the post-combustion technology will be applicable to the flue gas from the furnace.

[0033] In the first case, only the CO2 from the process will be captured. In the second case, all of the CO2 can be captured; however, considering the low CO2 partial pressure in the flue gas compared to the CO2 partial pressure in the syngas, the cost of this option will be higher. Additionally, since the flue gas is available at approximately atmospheric pressure, a large-sized CO2 capture system will be required, making the cost of this option even higher.

[0034] Accordingly, an improved system and method for power generation to address the problem of existing systems releasing CO2 into the atmosphere would be beneficial and would be readily accepted in the technical community. More generally, it would be desirable to provide methods and systems suitable for more effectively addressing the problems posed by current methods and systems for generating electricity using natural gas. Summary of the Invention

[0035] In one aspect, the subject matter disclosed herein relates to a method for carbon-neutral power generation, the method comprising the steps of:

[0036] - generating hydrogen by steam reforming natural gas from a natural gas pipeline to obtain hydrogen and a tail gas;

[0037] - Combust the hydrogen from the hydrogen generation step together with air in a gas turbine connected to a generator to generate electric power and hot hydrogen combustion exhaust gas;

[0038] - Capture the CO2 fraction from the tail gas from the hydrogen generation step to obtain a CO2-free tail gas;

[0039] - Exchange the heat of the hot exhaust gas from the hydrogen combustion step with the natural gas to be used in steam reforming in the hydrogen generation step to obtain hot natural gas and residual hot exhaust gas;

[0040] - Exchange the heat of the residual hot exhaust gas from the foregoing step with water and / or steam to be used in steam reforming in the hydrogen generation step to obtain hot compressed steam and residual exhaust gas.

[0041] The method may include a step of providing heat to the hydrogen generation step by combusting the CO2-free tail gas from the CO2 fraction capture step together with air, wherein flue gas is generated. Alternatively, the method may further include:

[0042] - A step of compressing and recycling the flue gas to the hydrogen generation step, the flue gas being from the step of combusting the CO2-free tail gas, or

[0043] - A step of capturing the CO2 fraction from the flue gas, the flue gas being from the step of combusting the CO2-free tail gas.

[0044] In one aspect, the natural gas used to generate hydrogen by steam reforming is obtained from a natural gas pipeline, the pressure of which is pre-reduced to 8 bar to 10 bar and the temperature of which is raised to 300 °C to 350 °C. Since the natural gas from the natural gas pipeline has been processed upstream of the pipeline to meet pipeline specifications, using the natural gas from the natural gas pipeline has the advantage of not requiring pretreatment of the feed. In addition, the pressure of the natural gas from the natural gas pipeline is higher than the pressure required to provide for the hydrogen generation process by steam reforming, which makes it possible to utilize the higher pressure to provide additional electric power.

[0045] Another aspect of the present invention relates to a system for carbon-neutral power generation, the system comprising:

[0046] - A natural gas feed line connected to a natural gas pipeline;

[0047] - A steam feed line;

[0048] - A hydrogen generation unit that obtains hydrogen and tail gas by steam reforming natural gas;

[0049] - A gas turbine connected to the hydrogen outlet of the hydrogen generation unit upstream, the gas turbine being configured to burn hydrogen together with air to obtain exhaust gas, and the gas turbine being coupled to a generator to generate electrical energy;

[0050] - A first heat exchanger configured to heat the feed of natural gas upstream of the hydrogen generation unit by exchanging heat with the exhaust gas from the gas turbine;

[0051] - A second heat exchanger configured to heat a stream of water or steam flowing in the steam feed line upstream of the hydrogen generation unit by exchanging heat with the exhaust gas from the gas turbine downstream of the first heat exchanger;

[0052] - A carbon capture unit connected upstream to the tail gas outlet of the hydrogen generation unit.

[0053] In addition, the system for carbon-neutral power generation may include a furnace to burn the tail gas downstream of the carbon capture unit and provide heat to the hydrogen generation unit.

[0054] Alternatively, the system for carbon-neutral power generation may include a carbon capture unit to remove CO2 from the exhaust gas of the furnace; or a compressor to compress the exhaust gas of the furnace before it is recycled to the hydrogen generation unit. Description of the Drawings

[0055] When considered in conjunction with the accompanying drawings, the disclosed embodiments of the present invention and many of their attendant advantages become better understood, and thus a more comprehensive understanding of them will be readily obtained, wherein:

[0056] Figure 1 A block diagram of a steam reforming system according to the prior art is illustrated;

[0057] Figure 2 A schematic diagram of a system for carbon-neutral power generation according to a first embodiment is illustrated;

[0058] Figure 3 A schematic diagram of a system for carbon-neutral power generation according to a second embodiment is illustrated;

[0059] Figure 4 A schematic diagram of a system for carbon-neutral power generation according to a third embodiment is illustrated;

[0060] Figure 5 A schematic diagram of a system for carbon-neutral power generation according to a fourth embodiment is illustrated; and

[0061] Figure 6The figure shows a schematic diagram of a method for carbon-neutral power generation according to a first embodiment. Detailed implementation

[0062] According to one aspect, the subject matter of the present invention relates to methods and systems for carbon-neutral power generation. Specifically, in several embodiments disclosed herein, a system for carbon-neutral power generation is provided that includes integrating a gas turbine with a modular natural gas steam reforming unit that produces hydrogen to be used as feed for the gas turbine. The system for carbon-neutral power generation further includes at least one carbon capture unit to remove CO2 from the tail gas of the hydrogen production unit. Additionally, after removing CO2, the tail gas of the hydrogen production unit is burned with air in a furnace to produce heat and flue gas. A carbon capture unit is provided to remove CO2 from the flue gas of the furnace. Both carbon capture units operate under favorable conditions because the CO2 content in the tail gas of the hydrogen production unit is relatively high (40 mol% to 45 mol%), and the CO2 content in the flue gas of the furnace is also relatively high (15 mol% to 35 mol%). Therefore, the size and cost of the carbon capture units are lower than those of the carbon capture units for hydrogen production units by steam reforming according to the prior art. To meet the energy requirements of the natural gas steam reforming unit of the hydrogen production unit, the turbine exhaust gas is used to heat the natural gas and steam fed to the steam reforming unit.

[0063] According to one aspect, the hydrogen production step of the method for carbon-neutral power generation includes the following sub-steps:

[0064] - Reacting hot natural gas together with hot compressed steam on a catalyst by providing heat to obtain a first gas mixture including hydrogen and carbon monoxide together with residual natural gas and steam;

[0065] - Reacting the carbon monoxide and steam of the first gas mixture to obtain a second gas mixture that includes a higher concentration of hydrogen together with carbon dioxide and residual natural gas, steam, and carbon monoxide; i.e., water gas shift;

[0066] - Separating hydrogen from the remaining components of the second gas mixture by adsorbing the remaining components of the second gas mixture from the water gas shift step on an adsorbent material and periodically desorbing the adsorbed remaining components of the second gas mixture by reducing the pressure to produce a tail gas (i.e., pressure swing adsorption of hydrogen).

[0067] According to another aspect, a system for carbon-neutral power generation includes a steam reformer, i.e., a reactor connected upstream to a natural gas pipeline and a steam feed line, the reactor being configured to react hot natural gas together with hot compressed steam on a catalyst by providing heat to obtain a first gas mixture of hydrogen and carbon monoxide together with residual natural gas and steam; a water-gas shift reactor, i.e., a reactor connected upstream to the outlet of the first gas mixture of the steam reformer, the water-gas shift reactor being configured to react carbon monoxide and steam from the steam reformer to obtain heat and a second gas mixture having a higher concentration of hydrogen together with carbon dioxide and residual natural gas, steam, and carbon monoxide; and a pressure swing adsorber, i.e., a plurality of containers containing an adsorbent material and configured to separate hydrogen from the residual components of the second gas mixture from the water-gas shift reactor by adsorbing the remaining components of the second gas mixture on the adsorbent material and by periodically and alternately desorbing the adsorbed components by reducing the pressure in each container to produce a tail gas.

[0068] According to still another aspect, a method for carbon-neutral power generation allows an existing natural gas-based gas turbine to be converted into a hydrogen-based gas turbine.

[0069] According to yet another aspect, a method for carbon-neutral power generation allows favorable operating conditions for natural gas steam reforming, with a temperature between 350 °C and 800 °C and a pressure of about 10 bar. In particular, the temperature of the feed for the hydrogen production step by steam reforming is much lower than in the prior art, due to the relatively low temperature of the flue gas from the hydrogen combustion step in the gas turbine, which is first used to exchange heat with the natural gas upstream of the hydrogen production step by steam reforming and secondly used to exchange heat with water and / or steam upstream of the hydrogen production step by steam reforming. The low temperature of the reactants in the hydrogen production step by steam reforming is used to operate a large heat availability balance for the hydrogen production step by steam reforming, due to the large tail gas availability from the same hydrogen production step.

[0070] Reference will now be made in detail to embodiments of the present disclosure, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the present disclosure and not limitation thereof. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the present disclosure without departing from the scope or spirit of the present disclosure. References throughout this specification to "one embodiment" or "an embodiment" or "some embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosed subject matter. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" or "in some embodiments" in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, in one or more embodiments, the particular features, structures, or characteristics may be combined in any suitable manner.

[0071] When introducing elements of various embodiments, the articles "a", "an", "the", and "said" are intended to mean that there is one or more of the elements. The terms "comprising", "including", and "having" are intended to be inclusive and mean that additional elements may exist in addition to the listed elements.

[0072] Referring now to the drawings, Figure 2 a schematic diagram of an exemplary system for carbon-neutral power generation is shown. The system consists of a hydrogen generation unit 100 including a natural gas steam reformer 101, in which natural gas from a natural gas feed stream pipeline 102 reacts with steam from a steam feed pipeline 103 to form hydrogen and carbon monoxide, i.e., syngas, according to the following reaction:

[0073]

[0074] Heat Q' is supplied to the steam reformer 101 to maintain a temperature in the range of 350°C to 800°C. The pressure inside the steam reformer 101 is about 10 bar.

[0075] The syngas (also including unreacted steam) from the steam reformer 101 is directed through a first syngas stream pipeline 104 to a heat exchanger 105 to reduce the temperature of the syngas to 320°C, and then through a second syngas stream pipeline 106 to a water-gas shift conversion reactor 107, in which part of the CO in the syngas is converted into additional H2 and CO2 by reacting with steam according to the following reaction:

[0076]

[0077] The water-gas shift reactor 107 includes a fixed bed iron / chromium / copper oxide catalyst.

[0078] The process syngas at the outlet of the water gas shift reactor 107 is directed through a third syngas stream line 108 to a heat exchanger 109 where it is cooled to about 40 °C. A stream of water condensate is removed from the process syngas stream through a water condensate stream line 110 and then the cooled process syngas is directed through a cooled process syngas stream line 111 to a pressure swing adsorption unit 112 for crude hydrogen purification. In some embodiments, the pressure swing adsorption unit 112 includes a plurality of vessels, each containing a bed of a selected adsorbent material such as zeolite or activated carbon. The pressure swing adsorption unit 112 operates by short adsorption / desorption cycles that occur on the selected adsorbent material and are run in parallel vessels (not shown) at different time phases. In particular, at a first operating pressure, hydrogen in the gas stream from the water gas shift reactor 107 permeates through the adsorbent material while the remaining components in the gas stream are adsorbed on the adsorbent material. Each vessel is cycled and alternately operated at a low pressure to promote desorption of the adsorbed gas. The hydrogen stream is released from the pressure swing adsorption unit 112 through a hydrogen stream line 113 at a pressure of about 9 bar. The tail gas from the pressure swing adsorption unit 112 is collected through a tail gas line 114 at a pressure of about 1 bar and a temperature of about 40 °C.

[0079] The hydrogen from the pressure swing adsorption unit 112 is compressed in a compressor 115, and electricity is supplied to the compressor through an electricity line 116. The compressed hydrogen is directed through a hydrogen stream line 117 to a gas turbine 118 where it is combusted with air from an air feed line 119. The gas turbine 118 is coupled to a generator 120 to convert the kinetic energy of the gas turbine 118 into electricity 121.

[0080] The flue gas from the gas turbine 118 has a temperature of about 490 °C and is used to heat the stream of reactants to the hydrogen production unit 100 (i.e., to the steam reformer 101). In particular, the flue gas from the gas turbine 118 is first directed through a first flue gas stream line 122 to a natural gas heat exchanger 123 to heat the natural gas directed through a natural gas stream line 102 to the steam reformer 101 to a temperature of about 340 °C. Downstream of the natural gas heat exchanger 123, the flue gas stream is directed through a second flue gas stream line 124 to a water / steam heat exchanger 125 to heat and evaporate the water / steam directed through a steam stream line 103 to the steam reformer 101 to a temperature of about 340 °C. Then the flue gas stream with a residual temperature of about 330 °C to 335 °C is released to the atmosphere through a third flue gas stream line 126.

[0081] The natural gas heated within the natural gas heat exchanger 123 is obtained from a natural gas pipeline (not shown) via the natural gas feed stream line 127. Since the pressure of the natural gas from the natural gas pipeline is higher than the pressure required to supply the steam reformer 101, it is then expanded in the expander 128 to provide additional electricity 129 and subsequently directed to the heat exchanger 123 via the expanded natural gas feed stream line 130.

[0082] The tail gas from the pressure swing adsorption unit 112 is recovered at near atmospheric pressure through the tail gas stream pipeline 114. Since the CO2 content in the tail gas of the pressure swing adsorption unit 112 is relatively high (40 mol% to 45 mol%), the tail gas is then directed to the carbon capture unit 131 to separate the CO2 that can be recovered through the CO2 pipeline 132 and the CO2-free tail gas stream. The carbon capture unit uses pre-combustion carbon capture technology, such as K2CO3 adsorbent or mixed salt process (such as a mixture of K2CO3 and (NH4)2CO3). In some embodiments, the carbon capture absorption unit includes a large packed bed absorption tower that has a circulating chemical solvent, such as an amine-based solvent, fluidly connected to a regeneration tower. A mixture of gases containing CO2 enters the bottom of the absorption tower. The downward flowing solvent selectively captures the CO2 flowing upward through the tower, such that the CO2-free gas exits from the top of the absorption tower. The CO2-rich solvent is recycled to the regeneration tower, where the CO2 is desorbed from the solvent by providing steam. The lean solvent is then recycled back to the absorption tower after removing heat. In some alternative embodiments, multiple packed bed absorption towers are used. In some embodiments, other means of dissociation energy are used instead of steam. The CO2-free tail gas stream is directed through the CO2-free tail gas stream pipeline 133 to mix with the air from the air feed pipeline 134. The air is recovered from the atmosphere at ambient pressure through the low-pressure air pipeline 135 and compressed by the compressor 136, and power is supplied to the compressor through the power pipeline 137. The gas mixture composed of the tail gas and the air is directed through the first gas mixture pipeline 138 to the heat exchanger 105 to be heated by the syngas from the steam reformer 101, and then through the second gas mixture pipeline 139 to the furnace 140, where the air and the tail gas are burned in the furnace to generate flue gas and the heat Q' to be provided to the steam reformer 101. The flue gas at a temperature of about 130 °C from the furnace 140 is directed through the first furnace flue gas stream pipeline 141 to the heat exchanger 142 to preheat the water stream from the water stream pipeline 143, which includes recycled water and makeup water. The preheated water is sent through the preheated water stream pipeline 144 to the heat exchanger 125 to be further heated and even partially vaporized by exchanging heat with the flue gas stream from the gas turbine 118. Downstream of the heat exchanger 142, the flue gas from the furnace with a relatively high CO2 content (15 mol% to 35 mol%) together with a stream of steam at a temperature of 133 °C and a pressure of 3 bar is directed through the second furnace flue gas stream pipeline 145 to the second carbon capture unit 146, and the steam exits from the heat exchanger 109 through the steam stream pipeline 147.

[0083] The carbon capture unit 146 separates water and CO2 from the furnace exhaust gas stream. The carbon capture unit 146 implements post-combustion carbon capture technology. In some embodiments, the carbon capture unit 146 includes a rotating packed bed absorber. The rotating packed bed contains rotating packing disks enclosed in a container. The concentrated solvent (such as an amine-based solvent) flows radially from the inner edge towards the outer edge of the rotating packed bed. When the gas mixture mainly composed of CO2 flows inside the absorber tower, the solvent absorbs CO2. The CO2-rich solvent removes CO2 in the rotating regenerator packed bed by providing heat input (such as by introducing steam). In some embodiments, multiple rotating packed bed absorber towers are used. Then, the furnace exhaust gas stream without water and CO2 is guided through the exhaust gas stream pipeline 148 to be mixed with the gas turbine exhaust gas stream of the exhaust gas stream pipeline 126 and then released into the atmosphere.

[0084] The water and CO2 from the carbon capture unit 146 are collected through the water collection pipeline 149 and the CO2 collection pipeline 150 respectively.

[0085] In some embodiments, there is an additional heat exchanger 151 configured to transfer the heat Q” from the water gas shift reactor 107 to the water stream in the thermodynamic cycle, and the thermodynamic cycle includes a steam turbine 152 configured to generate electricity 153. In particular, the steam with a temperature of 250 °C and a pressure of 15 bar from the heat exchanger 151 is guided through the high-pressure pipeline 154 to the steam turbine 152, and the stream at the outlet of the steam turbine 152 returns to the heat exchanger 151 through the low-pressure pipeline 155.

[0086] Continuing to refer Figure 2 , Figure 3 illustrates a second embodiment of the system for carbon-neutral power generation. The same reference numerals indicate the same or corresponding parts, elements or components that have been shown and described above, and these parts, elements or components will not be described again. Figure 2 In

[0087] According to this embodiment, the exhaust gas from the furnace 140 is not released into the atmosphere but recycled to the hydrogen generation unit 101. In particular, the compressor 156 is connected to the exhaust gas outlet of the furnace 140 through the exhaust gas stream pipeline 141 upstream and to the hydrogen generation unit 100 through the compressor outlet pipeline 158 downstream. The tail gas of the pressure swing adsorption unit 112 is guided to the carbon capture unit 159 to separate CO2, and the carbon capture unit 159 is additionally connected to the steam stream with a temperature of 133 °C and a pressure of 3 bar coming out of the heat exchanger 109 through the steam stream pipeline 160 upstream. CO2 is collected from the carbon capture unit 159 through the CO2 pipeline 132, and water is collected from the carbon capture unit 159 through the water stream pipeline 161.

[0088] Continuing reference Figure 2 and Figure 3 in Figure 4 shows another embodiment of a system for carbon-neutral power generation. The same reference numerals indicate the same or corresponding parts, elements or components shown in Figure 2 and Figure 3 above, and these parts, elements or components will not be described again. The system differs from the system shown in Figure 2 in that an adsorbent technology is used in the carbon capture unit 162. In some embodiments, the carbon capture unit 162 includes a packed bed vertical vessel filled with an adsorbent material (such as mesoporous silica or zeolite). A mixture of gases containing CO2 enters the vessel at the bottom and flows upward, and the adsorbent selectively adsorbs CO2 from the gas mixture, allowing other gases to exit from the top. After a certain time, the gas mixture is transported through a second vessel while the first bed is regenerated by heating to desorb the CO2 leaving the bed. In some embodiments, a fluidized bed of the adsorbent material is used. In some embodiments, multiple vessels arranged in parallel are used. In some embodiments, a reduced pressure is used to desorb CO2 from the bed. Hot potassium carbonate is fed to the carbon capture unit 162. The adsorbent technology reduces the steam requirement for carbon capture. Thus, the steam exiting from the heat exchanger 109 through the steam stream line 147 can be split and directed to the carbon capture unit 146 through the steam sub-stream line 147' and to the carbon capture unit 162 through the steam sub-stream line 147'' respectively.

[0089] Continuing reference Figure 2 、 Figure 3 and Figure 4 , Figure 5 illustrates a further embodiment of a system for carbon-neutral power generation. The same reference numerals indicate the same or corresponding parts, elements or components shown in Figure 2 、 Figure 3 and Figure 4the same or corresponding parts, elements, or components shown therein, and these parts, elements, or components will not be described again. This embodiment is envisioned to recover the waste heat of the flue gas from the gas turbine 118 downstream of the heat exchangers 123 and 125 by generating additional electricity. In particular, the thermodynamic system 200 is connected upstream through the flue gas stream pipeline 126 to the flue gas outlet of the second heat exchanger 125. The thermodynamic system 200 includes a heat exchanger 201, which is connected upstream to the flue gas stream pipeline 126 and is configured to transfer the waste heat of the flue gas to the working fluid in the thermodynamic cycle, and the thermodynamic cycle is configured to generate additional electricity. In particular, the working fluid can be water, and the thermodynamic cycle is a steam Rankine cycle. The heat exchanger 201 heats and evaporates the water into steam at a temperature of 330 °C and a pressure of 15 bar. The steam is guided through the high-pressure steam pipeline 204 to the steam turbine 202, which is configured to generate electricity 203. The water stream at the outlet of the steam turbine 202 returns to the heat exchanger 201 through the low-pressure water pipeline 205.

[0090] Figures 2 to 5 The various arrangements illustrated therein can be combined with each other in various ways. For example, in Figure 2 , Figure 3 and Figure 4 the embodiment of, a thermodynamic system 200 can also be provided, which is envisioned to recover the waste heat of the flue gas from the gas turbine 118 downstream of the heat exchangers 123 and 125 by generating additional electricity.

[0091] Figure 6 FIG. illustrates a schematic diagram of a method for carbon-neutral power generation according to a first embodiment. The method includes the following steps:

[0092] - Generating (30) hydrogen by steam reforming natural gas from a natural gas pipeline to obtain hydrogen and tail gas; this step preferably consists of: reacting hot natural gas together with hot compressed steam on a catalyst by providing heat to obtain a first gas mixture containing hydrogen and carbon monoxide, and then performing water-gas shift and hydrogen pressure swing adsorption;

[0093] - Burning (40) the hydrogen from the hydrogen generation step (30) together with air in a gas turbine coupled to a generator to generate electrical energy and exhaust gas;

[0094] - Capturing (50) the CO2 fraction from the tail gas from the hydrogen generation step to obtain a CO2-free tail gas;

[0095] - Exchanging (60) the heat of the hot exhaust gas from the hydrogen combustion step with the natural gas to be used for steam reforming in the hydrogen generation step to obtain hot natural gas and residual hot exhaust gas;

[0096] - Exchange the heat of the residual hot exhaust gas from the foregoing step with water and / or steam to be used in steam reforming in the hydrogen generation step (70) to obtain thermally compressed steam and residual exhaust gas.

[0097] Although aspects of the invention have been described in accordance with various specific embodiments, it will be apparent to those of ordinary skill in the art that various modifications, variations, and omissions are possible without departing from the spirit and scope of the claims. Additionally, unless otherwise specified herein, the order or sequence of any process or method steps may be altered or re-ordered according to alternative embodiments.

Claims

1. A method for carbon-neutral power generation, the method comprising the following steps: - Generating (30) hydrogen by steam reforming of natural gas from a natural gas pipeline to obtain hydrogen and tail gas; - Burning (40) the hydrogen from the hydrogen generation step together with air in a gas turbine coupled to a generator to generate electrical energy and hot hydrogen combustion exhaust gas; - Capturing (50) the CO2 fraction from the tail gas from the hydrogen generation step to obtain CO2-free tail gas; - Exchanging (60) the heat of the hot exhaust gas from the hydrogen combustion step with the natural gas to be used in the hydrogen generation step by steam reforming to obtain hot natural gas and residual hot exhaust gas; - Exchanging (70) the heat of the residual hot exhaust gas from the foregoing step with water and / or steam to be used in the hydrogen generation step by steam reforming to obtain hot compressed steam and residual exhaust gas.

2. The method according to claim 1, the method comprising the step of providing heat to the hydrogen generation step by burning the CO2-free tail gas from the CO2 fraction capture step together with air, wherein flue gas is generated.

3. The method according to claim 2, the method comprising the step of compressing and recycling the flue gas from the step of burning the CO2-free tail gas to the hydrogen generation step.

4. The method according to claim 2, the method comprising the step of capturing the CO2 fraction from the flue gas from the step of burning the CO2-free tail gas.

5. The method according to any one of the foregoing claims, the method comprising the following steps before the hydrogen generation step: - Obtaining natural gas from a natural gas pipeline; - Reducing the pressure of the natural gas to 8 bar to 10 bar; - Heating the natural gas to obtain hot natural gas; - Feeding the hot natural gas to the hydrogen generation step.

6. The method according to any one of the foregoing claims, the method comprising the step of compressing the hydrogen from the hydrogen generation step before feeding it to the hydrogen combustion step.

7. The method according to claim 3, the method comprising the step of exchanging the heat of the flue gas from the step of burning the CO2-free tail gas with water before the step of exchanging heat with the residual hot exhaust gas.

8. The method according to any one of the foregoing claims, the method comprising the step of exchanging the heat of the residual exhaust gas with a working fluid in a thermodynamic cycle such as an organic Rankine cycle, a steam Rankine cycle or a CO2 cycle.

9. A system for carbon-neutral power generation, the system comprising: - A natural gas feed line (102) connected to a natural gas pipeline; - A steam feed line (103); - A hydrogen generation unit (100) for steam reforming natural gas to obtain a hydrogen stream and a tail gas stream, the hydrogen generation unit (100) being connected upstream to the natural gas feed line (102) and the steam feed line (103), and the hydrogen generation unit (100) being connected downstream to a hydrogen stream line (117) and a tail gas stream line (114): - A gas turbine (118) connected upstream to the hydrogen stream line (117), the gas turbine (118) being configured to combust hydrogen together with air from an air feed line (119) to obtain exhaust gas, and the gas turbine (118) being coupled to a generator (120) to generate electrical energy (121); wherein the system is characterized in that it further comprises: - A first heat exchanger (123), the first heat exchanger having a first inlet connected to the exhaust gas outlet of the gas turbine (118) through a gas turbine exhaust line (122) and a second inlet connected to the natural gas feed line (102), the first heat exchanger (123) being configured to heat the feed of natural gas upstream of the hydrogen generation unit (100) by steam reforming natural gas by exchanging heat with the exhaust gas from the gas turbine (118); - A second heat exchanger (125), the second heat exchanger having a first inlet connected to the exhaust gas outlet of the first heat exchanger (123) through a first heat exchanger exhaust line (124) and a second inlet connected to the steam feed line (144), the second heat exchanger (125) being configured to heat a stream of water or steam flowing in the steam feed line (144) upstream of the hydrogen generation unit (100) by exchanging heat with the exhaust gas from the gas turbine (118) downstream of the first heat exchanger (123) to obtain a hot compressed steam stream; - A first carbon capture unit (131, 159, 162) connected upstream to the tail gas stream line (114).

10. The system according to claim 9, the system comprising a furnace (140), the furnace being connected upstream to the CO2-free tail gas outlet of the first carbon capture unit (131; 159; 162) and connected to an air inlet through a furnace feed line (139), and being configured to combust the CO2-free tail gas together with air to generate heat and flue gas to be supplied to the hydrogen generation unit (100).

11. The system according to claim 10, the system comprising a compressor (156), the compressor being connected upstream through an exhaust gas stream line (141) to the exhaust gas outlet of the furnace (140) and connected downstream through a compressor outlet line (158) to the hydrogen generation unit (100).

12. The system according to claim 10, wherein the system includes a second carbon capture unit (146) connected to the flue gas outlet of the furnace (140) through a second carbon capture unit feed line (145) upstream, and the second carbon capture unit (146) is configured to obtain flue gas free of CO2.

13. The system according to any one of claims 9 to 12, wherein a gas turbine (128) is arranged along the natural gas feed line (127) upstream of the first heat exchanger (123), and the gas turbine (128) is configured to generate electricity by reducing the pressure of the natural gas to 8 bar to 10 bar.

14. The system according to any one of claims 9 to 13, wherein the system includes a compressor (115) connected to the hydrogen outlet of the hydrogen generation unit (100) through a hydrogen outlet stream line (113) upstream and connected to the gas turbine (118) through the hydrogen feed stream line (117) downstream.

15. The system according to claim 10, wherein the system includes a heat exchanger (142) connected to the exhaust gas outlet of the furnace (140) through an exhaust gas stream line (141) upstream, connected to a water inlet through a water inlet stream line (143), and configured to heat the water upstream of the second heat exchanger (125).

16. The system according to any one of claims 9 to 15, wherein the system includes a thermodynamic system (200) connected to the flue gas outlet of the second heat exchanger (125) upstream and configured to exchange the waste heat of the flue gas with a working fluid in a thermodynamic cycle such as an organic Rankine cycle, a steam Rankine cycle or a CO2 cycle.

17. The system according to any one of claims 9 to 16, wherein the hydrogen generation unit (100) includes the following sub-units: - A steam reformer (101) configured to react hot natural gas from the natural gas feed line (102) together with hot compressed steam from the steam feed line (103) on a catalyst by providing heat (Q′) to obtain a first gas mixture of hydrogen and carbon monoxide together with residual natural gas and steam. - A water gas shift reactor (107) connected to the steam reformer (101) upstream and configured to react carbon monoxide and steam in the first gas mixture from the steam reformer (101) to obtain heat and a second gas mixture having a higher concentration of hydrogen together with carbon dioxide and residual natural gas, steam and carbon monoxide. - A pressure swing adsorption unit for hydrogen (109), which is connected upstream to the water gas shift reactor (107) and is configured to separate hydrogen from the remaining components of the second gas mixture from the water gas shift reactor (107) by adsorbing the remaining components of the second gas mixture on an adsorbent material and periodically desorbing the adsorbed components by reducing the pressure to produce a tail gas. And includes a heat exchanger (109), which is configured to exchange the heat of the second gas mixture from the water gas shift reactor (107) with water to obtain steam to be used in the first carbon capture unit (131, 159, 162) and / or the second carbon capture unit (146).

18. The system according to claim 17, the system includes a heat exchanger (105), which is connected upstream to the first gas mixture stream pipeline (138) and the first syngas stream pipeline (104), and is configured to heat the first gas mixture stream, which includes a tail gas without CO2 and air, by exchanging heat with the first syngas from the steam reformer (101) upstream of the furnace (140).

19. The system according to claim 17 or 18, the system includes a heat exchanger (151), which is configured to transfer heat (O”) from the water gas shift reactor (107) to the water stream and generate high-temperature steam to feed an additional steam turbine (152) configured to generate electricity.

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