Method and system for carbon-neutral power generation

Abstract

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

Description

[Technical Field]

[0001] The present disclosure relates to a method and related system for carbon-neutral power generation based on the conversion of existing natural gas pipeline facilities to generate electricity using natural gas with local generation of hydrogen and CO capture using pre-combustion techniques and gas turbines to combust H as fuel and air as oxidant.

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

[0003] Gas turbines are commonly used to generate electricity in power plants by burning fuel. The basic operation of a gas turbine is the Brayton cycle, which uses air as the working fluid. Air flows through a compressor, which raises the pressure. Energy is then added to the air in a combustion chamber by spraying and igniting fuel, generating a hot stream through combustion. This hot, pressurized gas enters the turbine, generating shaft work in the process and used to drive the compressor. Unused energy exits the exhaust gases, which can be reused for external work, such as directly generating thrust in a turbojet engine or to spin a second, independent turbine (known as a power turbine) that can be connected to a fan, propeller, or generator. The gas turbine's objective determines its design to achieve the most desirable energy division between thrust and shaft work. The fourth step of the Brayton cycle (cooling the working fluid) is omitted because gas turbines are open systems that do not reuse the same air.

[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 gas turbines is the resulting production of carbon dioxide (CO2) gas. Increasing CO2 levels in the atmosphere are harmful to the environment and a known cause of global warming. Therefore, there is a need to prevent CO2 produced by gas turbines from entering the atmosphere, i.e., decarbonize gas turbine power generation.

[0005] Currently, there are two ways to decarbonize gas turbine power generation: -Capturing CO2 from the exhaust gas of a gas turbine using a carbon capture unit; -Operating gas turbine fluids that switch from natural gas to hydrogen or mixed fuels.

[0006] However, both technologies are affected by important limitations. Indeed, gas turbine exhaust gases consist of very small amounts of CO2, i.e., only 3 mole %. For this reason, the size of the required carbon capture units is enormous and very expensive. On the other hand, operating gas turbines with hydrogen as fuel instead of natural gas significantly reduces the carbon footprint, but it is necessary to establish a hydrogen infrastructure, including pipelines, storage and conversion plants specially designed for hydrogen, to supply the gas turbines with hydrogen.

[0007] Steam reforming is currently the most cost-effective technology for producing hydrogen, especially when natural gas or off-gas can be used as the feedstock. Steam reforming of natural gas is the mainstay for such production, being a highly efficient process with the highest H / CO ratio and lowest cost of production (CoP). However, such processes are subject to CO emissions.

[0008] In hydrogen production by the steam reforming process, a portion of the CO2 (typically about 50-60% of the total amount) is generated in the process syngas in the steam reforming reactor (CH4 + H2O = CO + 3H2) and the water gas shift reactor (CO + H2O = CO2 + H2) and downstream stages, while another portion (40-50%) is additionally generated in the steam reformer where heat provided by external fuel combustion supplies the heat input required for the endothermic reaction. 3 It is estimated that approximately 0.9 kg of CO2 is produced per

[0009] In particular, according to the prior art, the process architecture of a conventional hydrogen production unit involving steam reforming of a natural gas feedstock comprises the following conventional process steps: i. Compression and preheating of natural gas; ii. pretreatment to remove harmful compounds; iii. reacting the compressed natural gas with water vapor to obtain hydrogen and carbon monoxide, along with residual water vapor; iv. Heat recovery from both process streams and flue gases by steam generation and steam superheating; v. Reacting carbon monoxide with water vapor to obtain hydrogen and carbon dioxide (aqueous shift reaction); vi. Purification of the hydrogen stream by pressure swing adsorption.

[0010] Referring to FIG. 1 , a block diagram of a conventional natural gas hydrogen production unit is shown in which a natural gas stream 10 is fed under pressure to a pretreatment unit (not shown) to remove compounds that are harmful to the downstream steam reforming catalyst.

[0011] The treated natural gas stream 10 is then mixed with a controlled amount of steam 11 according to a selected value for the steam / carbon molar ratio (S / C=3 mol / mol, typical) and preheated to 550° C. (typical). Central to this process is the endothermic reaction of methane with steam over a Ni catalyst: CH4+H2O⇔CO+3H2ΔH0=+206kJ / mol (1)

[0012] Reaction (1) takes place in a tubular catalytic reactor 12 heated by combustion of an external fuel stream 13 in a furnace (not shown). Consecutive to the main methane reaction, a water-gas shift reaction converts some of the CO produced by the first reaction into additional H and CO, as follows: CO+H2O⇔CO2+H2ΔH0=-41kJ / mol (2)

[0013] The process steam added to the feed exceeds the stoichiometric amount to improve the hydrocarbon conversion and prevent any carbon deposition on the catalyst. The reforming temperature is selected in the high range (typically 850 / 920°C) to obtain a high hydrogen yield. The steam reforming operation generates excess heat Q, which is usually recovered in a heat exchanger 14 through the generation of high-pressure steam, which can be partially used as the steam feed stream 11. In addition to this, additional steam is generated by a process gas heat exchanger (not shown) employed to cool the process synthesis gas 15 at the outlet of the reactor 12.

[0014] The cooled process gas is then fed to a high temperature shift conversion stage at an inlet temperature of about 320° C. Shift reactor 16 is a fixed-bed adiabatic reactor that uses an iron / chromium / copper oxide catalyst to convert carbon monoxide and water vapor present in the synthesis gas into additional hydrogen and carbon dioxide according to the water gas shift reaction (reaction 2). Optionally, an additional stage of shift conversion (not shown) at a lower temperature is installed and operated downstream.

[0015] The process synthesis gas stream 17 at the outlet of the shift conversion reactor 16 is cooled to about 40° C. through a heat recovery section and an after-cooler (not shown). Downstream, a device for water condensate removal (not shown) is installed, from which the synthesis gas stream 17 is sent to a pressure swing adsorption unit 18 for feed hydrogen purification. The pressure swing adsorption unit 18 operates through short adsorption / desorption cycles carried out on selected adsorbent materials, operated in parallel vessels at different time stages.

[0016] Hydrogen stream 19 is discharged from pressure swing adsorption unit 18 at a set pressure (e.g., typically about 20 barg in refinery applications). Hydrogen recovery in pressure swing adsorption unit 18 can achieve values ​​up to 90%, while the balance of the hydrogen, along with impurities present in the feed hydrogen stream, is discharged in off-gas stream 20, which exits pressure swing adsorption unit 18 at a lower pressure (about 0.3 barg). Pressure swing adsorption unit 18 can reach hydrogen purities of up to 99.9999% by volume. A typical hydrogen purity specification in a refinery is >99.9%.

[0017] The off-gas stream 20 from the pressure swing adsorption unit 18, recovered at about atmospheric pressure and containing the produced CO and residual hydrogen (an exemplary composition of this stream is 18 mol% CH, 10.24 mol% CO, 45.10 mol% CO, 26 mol% H, 0.55 mol% HO), is recycled back to the reformer (not shown) (recycle stream, not shown) where the residual hydrogen and CO are combusted with supplemental fuel 13 and the resulting flue gas is sent to the stack.

[0018] Carbon capture and storage (CCS) is also known as the process of removing or reducing the CO2 content of streams that would normally be 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-scale point sources, such as process streams, heater and boiler exhausts, and vents from various 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: post-combustion, pre-combustion, and oxy-fuel combustion.

[0019] In post-combustion capture processes, CO2 removal is performed after combustion has occurred. Flue gases leaving a combustion plant are typically treated using chemical or physical adsorbents to selectively remove CO2 from the gas mixture. It is an end-of-pipe solution in which CO2 is removed from the flue gas before it is released into the atmosphere via the chimney. The advantage of post-combustion processes is that they are suitable for new installations as well as being able to be retrofitted to existing plants. The main challenge is that CO2 levels in combustion flue gases are typically very low, between 5% and 20% by volume, depending on the off-gas content in the fuel gas mixture.

[0020] In pre-combustion capture processes, fuel (usually coal or natural gas) is pretreated before combustion. Specifically, it is generally gasified or reformed to produce a syngas stream, which is then subjected to a water-gas shift reaction and subsequent gas cleaning to separate the produced hydrogen from CO2. The gas cleaning step is usually accomplished using similar methods employed as described for post-combustion processes, but with the advantage of removing CO2 from the syngas, which is primarily related to the pressure of the gas, reducing compression energy requirements. Hydrogen is used as the input fuel to the combustion process, while CO2 is available in a concentrated form for compression, transportation, and storage. The high concentration of CO2 (>20%) in the H2 / CO2 fuel gas mixture facilitates CO2 separation.

[0021] In oxy-combustion, oxygen is used for combustion instead of air. This reduces the amount of nitrogen present in the flue gas, which affects subsequent separation processes. The main components of flue gas are CO2, water, particulates, and SO2. After removal of particulates, SO2, and water, the remaining gas contains a high concentration of CO2, approximately 80-98% (depending on the fuel used).

[0022] Both pre- and post-combustion techniques for CO2 capture can be applied to hydrogen production plants by steam reforming of natural gas. Pre-combustion techniques are applied to the synthesis gas stream exiting the water-gas shift reactor, while post-combustion techniques are applied to the flue gas from the furnace.

[0023] In the first case, only the CO2 coming from the process is captured. In the second case, all the CO2 can be captured, but the cost of such an option is higher considering the low CO2 partial pressure in the flue gas compared to the CO2 partial pressure in the synthesis gas. Additionally, since the flue gas is available at nearly atmospheric pressure, a large CO2 capture system is required, further increasing the cost of such an option.

[0024] Therefore, improved systems and methods for power generation that address the problem of CO2 emissions into the atmosphere of current technology systems would be beneficial and welcome in the art. More generally, it would be desirable to provide methods and systems adapted to more efficiently address the problems associated with current methods and systems for power generation using natural gas. Summary of the Invention

[0025] In one aspect, the presently disclosed subject matter is directed to a method for carbon-neutral power generation, the method comprising the steps of: - Producing hydrogen by steam reforming of natural gas from a natural gas pipeline to obtain hydrogen and tail gas; - combusting the hydrogen from the hydrogen generation step with air in a gas turbine coupled to an electric generator to produce electrical energy and a hot hydrogen flue gas; - capturing a CO2 fraction from the tail gas from said hydrogen production step to obtain a CO2-free tail gas; - exchanging heat of the hot exhaust gas from the hydrogen combustion step with natural gas used in the hydrogen production step by steam reforming to obtain hot natural gas and residual hot exhaust gas; - exchanging heat of the residual hot exhaust gas from the preceding step with water and / or steam used in the hydrogen production step by steam reforming to obtain hot compressed steam and residual exhaust gas.

[0026] The method may also include providing heat to the hydrogen production step by combusting CO2-free tail gas from the CO2 fraction capture step with air to produce flue gas. compressing the flue gas from the step of combusting the CO2-free tail gas and recycling it to the hydrogen production step, or - Capturing a CO2 fraction from flue gas from the step of combusting the CO2-free tail gas.

[0027] In one embodiment, the natural gas used to produce hydrogen by steam reforming is drawn from a natural gas pipeline, its pressure previously reduced to 8-10 bar, and its temperature increased to a maximum of 300-350°C. Using natural gas from a natural gas pipeline has the advantage that no pretreatment of the feed is required, since the natural gas has already been processed upstream to meet pipeline specifications. Additionally, the higher pressure of the natural gas from the pipeline than that required to power the hydrogen production process by steam reforming allows for the possibility of utilizing the higher pressure to provide additional power.

[0028] A further aspect of the present disclosure is a system for carbon-neutral power generation, comprising: - a natural gas supply line connected to a natural gas pipeline; - water vapor supply line, - a hydrogen generation unit by steam reforming of natural gas to obtain hydrogen and tail gas; a gas turbine connected upstream to a hydrogen outlet of the hydrogen generation unit, the gas turbine being configured to combust hydrogen with air to obtain exhaust gases, and coupled to a generator to generate electrical energy; a first heat exchanger configured to heat a natural gas feed upstream of the hydrogen production unit by exchanging heat with exhaust gas from the gas turbine; a second heat exchanger configured to heat a stream of water or steam flowing in the steam supply line upstream of the hydrogen production unit by exchanging heat with exhaust gas from the gas turbine downstream of the first heat exchanger; a carbon capture unit connected upstream to the tail gas outlet of the hydrogen generation unit.

[0029] Additionally, the system for carbon-neutral power generation can include a furnace for combusting tail gas downstream of the carbon capture unit to provide heat to the hydrogen production unit.

[0030] Alternatively, the system for carbon-neutral power generation can include a carbon capture unit to remove CO2 from the exhaust gas from the furnace, or a compressor to compress the exhaust gas from the furnace before it is recycled to the hydrogen production unit. [Brief explanation of the drawings]

[0031] A more complete understanding of the disclosed embodiments of this invention and many of the attendant advantages thereof will be readily obtained as the same become better understood by reference to the following detailed description when considered in connection with the accompanying drawings. [Figure 1] 1 illustrates a block diagram of a prior art steam reforming system. [Figure 2] 1 illustrates a schematic diagram of a system for carbon-neutral power generation according to a first embodiment. [Figure 3] 1 illustrates a schematic diagram of a system for carbon-neutral power generation according to a second embodiment. [Figure 4] 1 illustrates a schematic diagram of a system for carbon-neutral power generation according to a third embodiment. [Figure 5] 10 illustrates a schematic diagram of a system for carbon-neutral power generation according to a fourth embodiment. [Figure 6] 1 illustrates a flowchart of a method for carbon-neutral power generation according to a first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0032] According to one aspect, the present subject matter is directed to a method and system for carbon-neutral power generation. Specifically, in some embodiments disclosed herein, a system for carbon-neutral power generation is provided, which includes integrating a gas turbine with a modular natural gas steam reforming unit that produces hydrogen for use as feed for the gas turbine. The system for carbon-neutral power generation additionally includes at least one carbon capture unit for removing CO2 from the tail gas of the hydrogen generation unit. Additionally, after CO2 removal, the tail gas of the hydrogen generation unit is combusted with air in a furnace to generate heat and exhaust gas. The carbon capture unit is provided for removing CO2 from the furnace exhaust gas. Because the CO2 content in the tail gas of the hydrogen generation unit is high (40-45 mol%) and the CO2 content in the furnace exhaust gas is also relatively high (15-35 mol%), both carbon capture units operate under favorable conditions. As a result, the size and cost of the carbon capture unit are lower than those of carbon capture units for steam reforming hydrogen generation units according to current technology. 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 that is fed to the steam reforming unit.

[0033] According to one embodiment, the hydrogen production step of the method for carbon-neutral power generation comprises the following substeps: - reacting hot natural gas with hot compressed steam over a catalyst by providing heat to obtain a first gas mixture comprising hydrogen and carbon monoxide together with residual natural gas and steam; - reacting carbon monoxide of the first gas mixture with water vapor to obtain a second gas mixture containing a high concentration of hydrogen together with carbon dioxide and residual natural gas, water vapor and carbon monoxide, i.e., water gas shift; separating hydrogen from the remaining components of the second gas mixture from the water-gas shift step by adsorbing the remaining components of the second gas mixture onto 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., hydrogen pressure swing adsorption.

[0034] 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 supply line, the reactor configured to react hot natural gas with hot compressed steam over 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 first gas mixture outlet of the steam reformer, the water-gas shift reactor configured to react carbon monoxide and steam from the steam reformer to obtain a second gas mixture having a higher concentration of hydrogen together with heat, carbon dioxide and residual natural gas, steam, and carbon monoxide; and a pressure swing adsorber, i.e., a plurality of vessels containing an adsorbent material and configured to separate hydrogen from the remaining components of the second gas mixture from the water-gas shift reactor by adsorbing the remaining components of the second gas mixture onto the adsorbent material and periodically and alternately desorbing the adsorbed components by reducing the pressure in each vessel to produce a tail gas.

[0035] According to yet another aspect, a method for carbon-neutral power generation enables converting an existing natural gas-based gas turbine to a hydrogen-based gas turbine.

[0036] According to yet another aspect, a method for carbon-neutral power generation enables favorable operating conditions for natural gas steam reforming, with temperatures ranging from 350 to 800°C and pressures of approximately 10 bar. In particular, the temperature of the feed to the steam reforming hydrogen production step is much lower than in the prior art as a result of the relatively low temperature of the flue gas from the hydrogen combustion step in the gas turbine, which is utilized first to exchange heat with natural gas upstream of the steam reforming hydrogen production step and second to exchange heat with water and / or steam upstream of the steam reforming hydrogen production step. The low temperature of the reactants in the steam reforming hydrogen production step is balanced with the greater availability of heat to operate the steam reforming hydrogen production step due to the greater availability of tail gas from the same hydrogen production step.

[0037] Reference will now be made in detail to the embodiments of the present disclosure, one or more examples of which are illustrated in the figures. Each example is provided by way of explanation of the disclosure, not as a limitation of the disclosure. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. References throughout this specification to "an embodiment" or "one embodiment" or "some embodiments" mean that a particular feature, structure, or characteristic described in connection with an 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 all referring to the same embodiment. Furthermore, particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0038] When presenting elements of various embodiments, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be non-exclusive and mean that there may be additional elements other than the listed elements.

[0039] Referring now to the drawings, Figure 2 shows a schematic diagram of an exemplary system for carbon-neutral power generation. The system consists of a hydrogen generation unit 100 including a natural gas steam reformer 101, in which natural gas from a natural gas stream supply line 102 reacts with steam from a steam supply line 103 to form hydrogen and carbon monoxide, i.e., synthesis gas, according to the following reaction: CH4+H2O⇔CO+3H2ΔH0=+206kJ / mol (1)

[0040] Heat Q' is provided to the steam reformer 101 to maintain a temperature comprised between 350 and 800° C. The pressure inside the steam reformer 101 is about 10 bar.

[0041] The synthesis gas from the steam reformer 101, which also contains unreacted steam, is conducted through a first synthesis gas stream line 104 to a heat exchanger 105 to reduce the temperature of the synthesis gas to 320°C, and then through a second synthesis gas stream line 106 to a water-gas shift conversion reactor 107 where a portion of the CO of the synthesis gas is converted to CO by reacting with the steam in the reaction: CO+H2O⇔CO2+H2ΔH0=-41kJ / mol (2) is converted to additional H2 and CO2 by

[0042] The water gas shift reactor 107 contains a fixed bed iron / chromium / copper oxide catalyst.

[0043] The process syngas at the outlet of the water-gas shift reactor 107 is sent through a third syngas stream line 108 to a heat exchanger 109 where it is cooled to approximately 40°C. A water condensate stream is removed from the process syngas stream through a water condensate stream line 110, and the cooled process syngas is then sent through a cooled process syngas stream line 111 to a pressure swing adsorption unit 112 for feed hydrogen purification. In some embodiments, the pressure swing adsorption unit 112 comprises multiple vessels, each vessel containing a bed of a selected adsorbent material, such as zeolite or activated carbon. The pressure swing adsorption unit 112 operates through short adsorption / desorption cycles performed on the selected adsorbent material, operated in parallel vessels (not shown) at different time stages. In particular, at a first operating pressure, hydrogen in the gas stream from the water-gas shift reactor 107 permeates the adsorbent material, while the remaining components of the gas stream are adsorbed onto the adsorbent material. Each vessel is cyclically and alternately operated at a lower pressure to facilitate desorption of the adsorbed gas. A hydrogen stream is discharged from pressure swing adsorption unit 112 through hydrogen stream line 113 at a pressure of about 9 bar. Tail gas from pressure swing adsorption unit 112 is collected through tail gas line 114 at a pressure of about 1 bar and a temperature of about 40°C.

[0044] Hydrogen from pressure swing adsorption unit 112 is compressed in compressor 115, which is provided with electrical power via power line 116. The compressed hydrogen is sent through hydrogen flow line 117 to gas turbine 118, where it is combusted with air from air supply line 119. Gas turbine 118 is coupled to generator 120, which converts the kinetic energy of gas turbine 118 into electrical power 121.

[0045] The flue gas from the gas turbine 118 has a temperature of approximately 490°C and is utilized to heat the reactant streams to the hydrogen generation unit 100, namely the steam reformer 101. In particular, the flue gas from the gas turbine 118 is first routed through a first flue gas flow line 122 to a natural gas heat exchanger 123 to heat the natural gas that is routed through the natural gas flow line 102 to the steam reformer 101 to a temperature of up to approximately 340°C. Downstream of the natural gas heat exchanger 123, the flue gas stream is routed through a second flue gas flow line 124 to a water / steam heat exchanger 125 to heat and vaporize the water / steam that is routed through the steam flow line 103 to the steam reformer 101 to a temperature of up to approximately 340°C. The flue gas stream, at a residual temperature of approximately 330-335°C, is then discharged to the atmosphere through a third flue gas flow line 126.

[0046] The natural gas heated in the natural gas heat exchanger 123 is withdrawn from a natural gas pipeline (not shown) through natural gas flow line 127. Because 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 expanded in expander 128 to provide additional power 129 and then directed to the heat exchanger 123 through expanded natural gas flow line 130.

[0047] Tail gas from pressure swing adsorption unit 112 is recovered at near atmospheric pressure through tail gas stream line 114. Because the CO content in the tail gas from pressure swing adsorption unit 112 is high (40-45 mol%), the tail gas is directed to carbon capture unit 131 to separate the CO, which can be recovered through CO line 132, from a CO-free tail gas stream. The carbon capture unit uses pre-combustion carbon capture technologies, such as KCO adsorbent or a mixed salt process (e.g., a mixture of KCO and (NH)CO). In some embodiments, the carbon capture absorption unit comprises a large packed-bed absorber with a circulating chemical solvent, such as an amine-based solvent, fluidly connected to a regeneration column. A CO-containing gas mixture enters the bottom of the absorber. The downward-flowing solvent selectively captures the CO flowing upward through the column, resulting in CO-free gas exiting the top of the absorber. The CO2-rich solvent is recycled to a regeneration column, where CO2 is desorbed from the solvent by providing steam. The lean solvent is then recycled back to the absorber after heat removal. In some alternative embodiments, a multiple packed-bed absorber is used. In some embodiments, other means of dissociation energy are used instead of steam. The CO2-free tail gas stream is sent through CO2-free tail gas stream line 133 and mixed with air from air supply line 134. Air is recovered from the atmosphere at atmospheric pressure via low-pressure air line 135 and compressed by compressor 136, which is provided with power via power line 137. The gas mixture consisting of the tail gas and air is conducted through first gas mixture line 138 to heat exchanger 105, heated by synthesis gas from steam reformer 101, and then conducted through second gas mixture line 139 to furnace 140, where the air and tail gas are combusted to generate exhaust gas and heat Q', which are provided to steam reformer 101. Exhaust gas from furnace 140, at a temperature of about 130°C, is passed through first furnace exhaust gas stream line 141 to heat exchanger 142 to preheat a water stream from water stream line 143, which includes recycle water and make-up water.The preheated water is sent through preheated water stream line 144 to heat exchanger 125 where it is further heated and also partially vaporized by exchanging heat with the flue gas stream from gas turbine 118. Downstream of heat exchanger 142, the flue gas from the furnace, which has a relatively high CO2 content (15-35 mol%), is conducted through second furnace flue gas stream line 145 to a second carbon capture unit 146, together with a stream of steam at a temperature of 133°C and a pressure of 3 bar, which steam comes from heat exchanger 109 through steam stream line 147.

[0048] The carbon capture unit 146 separates water and CO 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 comprises a rotating packed-bed absorber. The rotating packed bed includes a rotating packed disk enclosed within a vessel. A rich solvent (e.g., an amine-based solvent) flows radially from the inner edge to the outer edge of the rotating packed bed. As a gas mixture consisting primarily of CO flows through the interior of the absorber, the solvent absorbs the CO. The CO-rich solvent is stripped of CO in a rotating regenerator packed bed by providing heat input, for example, by passing steam through it. In some embodiments, multiple rotating packed-bed absorbers are used. The water- and CO2-free furnace exhaust gas stream is then sent through exhaust gas stream line 148 to be mixed with the gas turbine exhaust gas stream in exhaust gas stream line 126 and then released to the atmosphere.

[0049] Water and CO2 from carbon capture unit 146 are collected through water collection line 149 and CO2 collection line 150, respectively.

[0050] In some embodiments, there is an additional heat exchanger 151 configured to transfer heat Q" from the water-gas shift reactor 107 to a water stream in a thermodynamic cycle that includes a steam turbine 152 configured to produce electricity 153. In particular, water vapor from the heat exchanger 151 is passed through high-pressure line 154 to the steam turbine 152 at a temperature of 250°C and a pressure of 15 bar, and the flow at the outlet of the steam turbine 152 is returned to the heat exchanger 151 through low-pressure line 155.

[0051] Continuing with reference to Figure 2, Figure 3 illustrates a second embodiment of a system for carbon-neutral power generation. Like reference numerals represent the same or corresponding parts, elements, or components already illustrated in Figure 2 and described above, and will not be described again here.

[0052] According to this embodiment, the exhaust gas from furnace 140 is recycled to hydrogen generation unit 101 rather than being released to the atmosphere. In particular, compressor 156 is connected upstream to the exhaust gas outlet of furnace 140 through exhaust gas flow line 141 and downstream to hydrogen generation unit 100 through compressor outlet line 158. The tail gas of pressure swing adsorption unit 112 is led to carbon capture unit 159 for CO2 separation, and carbon capture unit 159 is additionally connected upstream to a stream of steam at a temperature of 133°C and a pressure of 3 bar coming from heat exchanger 109 through steam flow line 160. CO2 is collected from carbon capture unit 159 through CO2 line 132, and water is collected from carbon capture unit 159 through water flow line 161.

[0053] Continuing with reference to FIGS. 2 and 3, a further embodiment of a system for carbon-neutral power generation is shown in FIG. 4. Like reference numerals represent the same or corresponding parts, elements, or components already illustrated in FIGS. 2 and 3 and described above, and will not be described again here. The system differs from the system shown in FIG. 2 in that sorbent technology is used in the carbon capture unit 162. In some embodiments, the carbon capture unit 162 comprises a packed-bed vertical vessel filled with a sorbent material, such as mesoporous silica or zeolite. A CO2-containing gas mixture enters the bottom of the vessel and flows upward, with the sorbent selectively adsorbing CO2 from the gas mixture and other gases exiting the top. After a period of time, the gas mixture is passed through a second vessel, while the first bed is regenerated by heating to desorb the CO2 exiting the bed. In some embodiments, a fluidized bed of sorbent material is used. In some embodiments, multiple vessels arranged in parallel are used. In some embodiments, pressure reduction is used to desorb CO2 from the bed. The hot potassium carbonate is fed to carbon capture unit 162. Sorbent technology reduces the steam requirements for carbon capture. As a result, steam coming from heat exchanger 109 through steam stream line 147 can be split to be directed to carbon capture unit 146 through steam substream line 147′ and to carbon capture unit 162 through steam substream line 147″, respectively.

[0054] Continuing with reference to FIGS. 2, 3, and 4, FIG. 5 illustrates a further embodiment of a system for carbon-neutral power generation. Like reference numerals denote the same or corresponding parts, elements, or components already illustrated and described in FIGS. 2, 3, and 4 and will not be described again here. This embodiment is designed to recover residual heat of the flue gas from the gas turbine 118 downstream of the heat exchangers 123 and 125 by generating additional power. In particular, a thermodynamic system 200 is connected upstream to the flue gas outlet of the second heat exchanger 125 through the flue gas flow line 126. The thermodynamic system 200 includes a heat exchanger 201 connected upstream to the flue gas flow line 126 and configured to transfer the residual heat of the flue gas to a working fluid in a thermodynamic cycle configured to generate additional power. In particular, the working fluid can be water, and the thermodynamic cycle is a steam Rankine cycle. Heat exchanger 201 heats and vaporizes water to steam at a temperature of 330° C. and a pressure of 15 bar. The steam is sent through high-pressure steam line 204 to steam turbine 202 configured to generate electricity 203. The water flow at the outlet of steam turbine 202 is returned to heat exchanger 201 through low-pressure water line 205.

[0055] The various arrangements illustrated in Figures 2-5 can be combined with one another in various ways. For example, a thermodynamic system 200 designed to recover residual heat in the flue gases from the gas turbine 118 by generating additional power downstream of the heat exchangers 123 and 125 can also be provided in the embodiments of Figures 2, 3 and 4.

[0056] 6 illustrates a flow chart of a method for carbon-neutral power generation according to a first embodiment. The method comprises the following steps: - producing hydrogen by steam reforming of natural gas from a natural gas pipeline to obtain hydrogen and a tail gas (30), preferably comprising providing heat to react hot natural gas with hot compressed steam over a catalyst to obtain a first gas mixture comprising hydrogen and carbon monoxide, followed by water-gas shift and hydrogen pressure swing adsorption; - a step (40) of burning the hydrogen from the hydrogen generation step (30) with air in a gas turbine coupled to a generator to produce electrical energy and exhaust gases; - capturing a CO fraction from the tail gas from said hydrogen production step to obtain a CO2-free tail gas (50); - exchanging heat of the hot exhaust gas from the hydrogen combustion step with natural gas used in the hydrogen production step by steam reforming (60) to obtain hot natural gas and residual hot exhaust gas; - exchanging heat of the residual hot exhaust gas from the preceding step with water and / or steam to be used in the hydrogen production step by steam reforming (70) to obtain hot compressed steam and residual exhaust gas.

[0057] While aspects of the present invention have been described in terms of various specific embodiments, it will be apparent to those skilled in the art that many modifications, changes, 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 varied or rearranged according to alternative embodiments.

Claims

1. 1. A method for carbon-neutral power generation, comprising the steps of: - Producing hydrogen by steam reforming of natural gas from a natural gas pipeline to obtain hydrogen and tail gas (30); - Combusting the hydrogen from the hydrogen production step with air in a gas turbine coupled to a generator to produce electrical energy and hot hydrogen flue gas (40); - CO from the tail gas from the hydrogen production step ２ The fraction is captured and CO ２ obtaining free tail gas (50); - exchanging heat of the hot exhaust gas from the hydrogen combustion step with the natural gas used in the hydrogen production step by steam reforming to obtain hot natural gas and residual hot exhaust gas (60); - exchanging heat of the residual hot exhaust gas from the preceding step with water and / or steam used in the hydrogen production step by steam reforming (70) to obtain hot compressed steam and residual exhaust gas.

2. The CO ２ The CO from the fraction capture step ２ 10. The method of claim 1, including providing heat to said hydrogen production step by combusting free tail gas with air to produce flue gas.

3. The CO ２ 3. The method of claim 2, including compressing and recycling the flue gas from the step of combusting free tail gas to the step of producing hydrogen.

4. The CO ２ and extracting CO from the flue gas from the step of burning the free tail gas. ２ The method of claim 2 including the step of capturing the fraction.

5. before the hydrogen generation step, - withdrawing natural gas from a natural gas pipeline; - reducing the pressure of the natural gas to 8-10 bar; - heating said natural gas to obtain hot natural gas; - feeding said hot natural gas to said hydrogen production step.

6. 6. The method of any one of claims 1 to 5, comprising compressing the hydrogen from the hydrogen generation step before feeding it to the hydrogen combustion step.

7. Before the step of exchanging heat with the residual hot exhaust gas, ２ 4. The method of claim 3, including the step of exchanging heat of the flue gas from the step of combusting free tail gas with water.

8. Organic Rankine cycle, steam Rankine cycle, or CO ２ A method according to any preceding claim, comprising exchanging heat from the residual exhaust gas with a working fluid in a thermodynamic cycle, such as a combustion cycle.

9. 1. A system for carbon-neutral power generation, comprising: a natural gas supply line (102) connected to a natural gas pipeline; - a water vapor supply line (103), a hydrogen production unit (100) by steam reforming of natural gas to obtain hydrogen and a tail gas stream, the hydrogen production unit (100) being connected upstream to said natural gas supply line (102) and said steam supply line (103) and downstream to a hydrogen stream line (117) and a tail gas stream line (114); a gas turbine (118) connected upstream to said hydrogen flow line (117), the gas turbine (118) being configured to combust hydrogen with air from an air supply line (119) to obtain exhaust gases, and coupled to a generator (120) to generate electrical energy (121); The system additionally comprises: a first heat exchanger (123) 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 supply line (102), the first heat exchanger (123) being configured to exchange heat with the exhaust gas from the gas turbine (118) to heat the natural gas feed upstream of the unit for producing hydrogen by steam reforming of natural gas (100); a second heat exchanger (125) 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 a steam supply line (144), the second heat exchanger (125) being configured to exchange heat with the exhaust gas from the gas turbine (118) downstream of the first heat exchanger (123) to heat a water or steam stream flowing in the steam supply line (144) upstream of the hydrogen generation unit (100) to obtain a hot compressed steam stream; a system for carbon-neutral power generation, characterized in that it comprises a first carbon capture unit (131, 159, 162) connected upstream to said tail gas flow line (114).

10. CO of the first carbon capture unit (131, 159, 162) through a furnace supply line (139). ２ a free tail gas outlet and an air inlet connected upstream thereof, and ２ 10. The system of claim 9, comprising a furnace (140) configured to combust free tail gas with air to generate heat and flue gases that are provided to the hydrogen production unit (100).

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

12. a second carbon capture unit (146) connected upstream to the flue gas outlet of said furnace (140) through a second carbon capture unit supply line (145), said second carbon capture unit (146) comprising: ２ The system of claim 10, further comprising a second carbon capture unit (146) configured to obtain free flue gas.

13. 13. The system of claim 9, wherein a gas turbine is arranged along a natural gas supply line upstream of the first heat exchanger, the gas turbine being configured to generate electricity by reducing the pressure of the natural gas to 8-10 bar.

14. 14. The system of claim 9, further comprising a compressor (115) connected upstream to a hydrogen outlet of the hydrogen generation unit (100) through a hydrogen outlet flow line (113) and connected downstream to the gas turbine (118) through the hydrogen supply flow line (117).

15. 11. The system of claim 10, further comprising a heat exchanger (142) connected upstream to an exhaust gas outlet of the furnace (140) through an exhaust gas flow line (141) and to a water inlet through a water inlet flow line (143), the heat exchanger being configured to heat water upstream of the second heat exchanger (125).

16. a second heat exchanger (125) connected upstream to the flue gas outlet thereof and configured to operate in an organic Rankine cycle, a steam Rankine cycle, or a CO ２ The system of any one of claims 9 to 15, comprising a thermodynamic system (200) configured to exchange residual heat of the flue gas with a working fluid in a thermodynamic cycle, such as a heat exchanger.

17. The hydrogen generation unit (100) comprises the following subunits: a steam reformer (101) configured to react hot natural gas from said natural gas supply line (102) with hot compressed steam from said steam supply line (103) over 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 upstream to said steam reformer (101) and configured to react carbon monoxide and steam of said first gas mixture from said 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 hydrogen pressure swing adsorption unit (109) connected upstream to the water-gas shift reactor (107) and 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 onto an adsorbent material and periodically desorbing the adsorbed components by reducing the pressure to produce a tail gas, 17. The system of claim 9, further comprising a heat exchanger (109) configured to exchange heat of the second gas mixture from the water-gas shift reactor (107) with water to obtain steam for use in the first carbon capture unit (131, 159, 162) and / or the second carbon capture unit (146).

18. upstream of the furnace (140) by exchanging heat with the first synthesis gas from the steam reformer (101); ２ 20. The system of claim 17, comprising a heat exchanger (105) connected upstream to the first gas mixture stream line (138) and the first syngas stream line (104), configured to heat the first gas mixture stream comprising free tail gas and air.

19. 19. The system of claim 17 or 18, comprising a heat exchanger (151) configured to transfer heat (Q") from the water-gas shift reactor (107) to a water flow to generate high temperature steam to supply an additional steam turbine (152) configured to generate electrical power.

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