Patent Application
20250010260
The present invention relates to a plant and process for producing hydrogen, as well as a method of retrofitting an existing plant for producing hydrogen. The plant and process utilize a primary reforming unit, such as a steam methane reforming unit (SMR), which comprises a combustion section having arranged therein catalyst filled tubes and burners for providing heat to the steam methane reforming, thereby generating a flue gas and a synthesis gas. The primary reforming unit comprises also a convection section for cooling the flue gas by means of a first set of heat exchangers. The synthesis gas is converted to hydrogen by conducting the synthesis gas to a hydrogen purification unit, such as a pressure swing adsorption unit (PSA unit), for generating a hydrogen-rich gas and an off-gas. A first fuel gas being a portion of the hydrogen-rich gas, or a second fuel gas being a mixture of the first fuel gas and the off-gas, is used as fuel for the burners of the primary reforming unit. The fuel gas is free of sulfur, thereby enabling cooling the flue gas from the primary reforming to lower temperatures without risking sulfuric acid condensation and resulting corrosion problems, thereby also enabling to extract more heat duty which can be used for preheating of streams in the plant or process. The use of import fuel for the burners, such as natural gas, is also significantly reduced or eliminated, thereby improving the energy efficiency of the plant.
The present invention relates also to a method of retrofitting a plant for producing hydrogen.
In conventional plants for producing hydrogen, a hydrocarbon feed gas, typically natural gas is desulfurized and converted into a synthesis gas i.e. a gas containing carbon oxides (CO, CO2) and hydrogen by prereforming and subsequent steam methane reforming. The resulting synthesis gas is then enriched in hydrogen by water gas shift according to the exothermic reaction CO+H2 CO2+H2, followed by carbon dioxide removing step in a CO2-removal section such as an amine wash unit, and the synthesis gas is finally purified into a hydrogen-rich stream in a hydrogen purification unit such as a pressure swing adsorption unit (PSA unit). The PSA unit generates also a PSA off-gas stream which contains methane, hydrogen as well as carbon oxides. In a conventional steam methane reforming unit (SMR, also known as tubular reformer), steam methane reforming according to the endothermic reaction CH4+H2O
CO+3H2 is conducted at 700-1000° C. in a plurality of catalyst filled tubes provided in the combustion section of the SMR and where the heat needed is provided by several burners arranged therein. The fuel to the burners is typically provided by importing natural gas. Flue gas from the burning is generated at high temperatures, e.g. at around 1000° C., and is used typically to preheat the hydrocarbon feed, e.g. natural gas or prereformed natural gas, as well as to preheat the combustion air used in the burners.
Typically also, the flue gas after delivering heat needs to be at a temperature high enough to avoid reaching the dew point of sulfuric acid, which is 138° C. or higher depending on the sulfur, more specifically sulfur trioxide, content of the flue gas. If the temperature decreases below this level, condensation of sulfuric acid in any equipment in contact with this gas will suffer of highly undesirable corrosion problems.
EP 2103569 A2 discloses a process for generating hydrogen and/or synthesis gas by steam-hydrocarbon reforming along with generating steam using waste heat from the steam-hydrocarbon reforming process, in which the process generates little or no steam export.
EP 3573925 A1 (WO18140686 A1) discloses a system and method to mitigate the above-mentioned problem of condensation of sulfuric acid in any equipment in contact with the flue gas. The system includes an desulfurization unit for removing sulfur from a natural gas, a portion of which is then used as fuel gas, a pre-reformer for converting heavy hydrocarbons in the other portion of the desulfurized natural gas (process gas stream) to methane, a steam methane reformer for producing a synthesis gas and a flue gas, a PSA unit for producing a product hydrogen stream and a PSA off-gas stream, and an air preheater for cooling the flue gas against a combustion air and the PSA off-gas to a temperature below the dew point of sulfuric acid. Import of natural gas for use as fuel is required as so is the need of conducting a step for removing its sulfur content, thus conveying a penalty in terms of natural gas consumption and energy efficiency of the plant, as well as a larger desulfurization unit e.g. sulfur absorber and attendant sulfur adsorbing material, thereby resulting in higher capital and operating expenses.
It is an object of the present invention to provide an alternative and superior way, i.e. providing higher energy efficiency and less capital and operating expenses, of mitigating the issue of condensing sulfuric acid when wanting to extract duty from the flue gas of a primary reforming unit such as an SMR in a plant or process for producing hydrogen.
It is another object of the present invention to provide a plant or process for producing hydrogen which is capable of capturing about 90% of the carbon dioxide generated in the plant, while at the same time providing for high plant or process integration.
It is another object of the present invention to provide a simple method of retrofitting an existing plant for producing hydrogen which uses a primary reforming unit for generating synthesis gas, whereby the energy efficiency of the plant is significantly increased.
These and other objects are solved by the present invention.
Accordingly, in a first aspect the invention provides a plant for producing hydrogen, comprising:
In an embodiment, the plant is arranged to receive only said first fuel gas stream or second fuel gas stream as fuel to said one or more burners. Accordingly, the plant is absent of means, such as a conduit, for providing a separate fuel gas stream, such as natural gas stream or desulfurized natural gas stream, to said one or more burners.
Thereby it is now possible to stop or significantly reduce the use of import fuel (natural gas) for the burners, and instead, using hydrogen produced in the plant as supplementary fuel, suitably together with off-gas from the hydrogen purification unit. The new fuel gas, for instance the second fuel gas stream which combines the off-gas and hydrogen (hydrogen-rich stream), does not contain any sulfur, so it is now possible to cool the flue gas in the primary reforming unit to a lower temperature without risking condensation of sulfuric acid. Furthermore, by reducing or eliminating the use of import fuel for the burners, such as natural gas, improved energy efficiency of the plant and process is achieved. The plant being absent of a means, such as a conduit, for providing a separate fuel gas stream such as natural gas stream or desulfurized natural gas stream to said one or more burners, further enables less piping requirements and attendant costs: there is no need of increasing costs for providing additional natural gas and thereby inducing higher energy consumption. Furthermore, the desulfurization unit upstream the primary reforming can be made smaller, as the natural gas fed to this unit is only the natural gas used as process gas in the primary reforming unit, not a larger natural gas stream also envisaging its use as fuel gas for the burners.
For the purposes of the present application, the term “comprising” includes also “comprising only” i.e. “consisting of”.
The term “first aspect of the invention” or simply “first aspect” relates to the process of the invention; the term “second aspect of the invention” refers to the plant for carrying out the process, and the term “third aspect of the invention” refers to the method of retrofitting a plant for producing hydrogen, i.e. method of retrofitting an existing hydrogen plant.
The term “present invention” or simply “invention” may be used interchangeably with the term “present application” or simply “application”.
The term “suitably” may be used interchangeably with the term “optionally”, i.e. an optional embodiment.
The term “catalyst suitable for steam methane reforming” means “steam reforming catalyst”.
The term “juncture” and “junction” are used interchangeably.
Other definitions are provided in connection with one or more embodiments of the invention.
In an embodiment according to the first aspect of the invention, said primary reforming unit is a fired steam methane reformer (SMR), said combustion section being arranged to accommodate a plurality of catalyst filled tubes suitable for the steam methane reforming, thereby generating said first synthesis gas stream and said flue gas stream; said convection section being arranged downstream said combustion section and arranged to receive said flue gas stream and to accommodate said first set of heat exchangers, suitably a plurality of heat exchangers arranged in series such as heating coils arranged in series, thereby generating said cooled flue gas stream; said primary reforming unit being provided with an outlet for withdrawing said first synthesis gas stream and an outlet for withdrawing said cooled flue gas stream.
It would be understood that the term, “convection section being arranged downstream said combustion section” is with respect to the flow direction of the flue gas generated in the combustion section of the SMR.
In an embodiment according to the first aspect of the invention, the first set of heat exchangers comprises:
Suitably, the heat exchanger is provided as a coil arranged in the convection section, through which the combustion air, or the fuel gas stream i.e. first or second fuel gas stream, passes. The additional duty (heat duty) resulting from incorporating the first or second fuel gas streams enables preheating of these, or any other feed streams to the e.g. primary reforming unit.
Suitably, the first set of heat exchangers also comprises additional heat exchangers, for instance a boiler for producing steam against the flue gas.
Suitably, said preheated combustion air is generated in a heat exchanger of said first set of heat exchangers, such as in the heat exchanger arranged upstream the most downstream heat exchanger thereof.
In an embodiment according to the first aspect of the invention, the plant further comprises:
Thereby it is possible to enrich the synthesis gas in hydrogen and remove its carbon dioxide content prior to the shifted, i.e. third synthesis gas stream, entering the hydrogen purification unit. The CO2-rich stream may then e.g. be safely stored, thereby reducing the carbon footprint of the plant and process.
In an embodiment according to the first aspect of the invention,
The provision of the plant incorporating the new fuel gas stream, e.g. the second fuel gas combining the off-gas and hydrogen i.e. hydrogen-rich stream from the hydrogen purification unit, makes it possible to add an additional heat exchanger, suitably a preheating coil, in the convection section of the primary reforming unit to extract more duty, thereby enhancing the efficiency of the plant. This duty can be used for i.a. preheating a fuel gas stream, preheating of the solvent solution e.g. amine solution from the amine wash unit, preheating DMW/BFW, or preheating the hydrocarbon feed stream.
It would be understood that the term “DMW/BFW” means demineralized water and/or boiling feed water.
It would also be understood that for the purposes of the present application, the term “and/or” means one of the options or a combination of the options. For instance, DMW and/or BFW means DMW, BFW or a combination thereof.
The duty can also be used in a CO2-reboiler of a CO2-removal section arranged downstream said convection section of the primary reforming unit as a flue gas-CO2-removal section. The thus captured CO2 from the flue gas may then be safely stored. This removal section is also referred to as “post carbon capture removal unit”.
The CO2-stripper of a CO2-removal section, either when the latter is arranged for capturing CO2 in the process gas, more specifically the synthesis gas downstream the primary reforming unit, or when arranged for capturing CO2 in the flue gas from said primary reforming unit (post carbon capture removal unit), is normally provided with a reboiler and a feed/effluent heat exchanger for pre-heating the solvent solution e.g. the amine solution. The additional duty provided by the invention may be further utilized by arranging a preheater coil e.g. an amine preheater coil, downstream said feed/effluent heat exchanger, or as an additional reboiler in the CO2-stripper. Hence, the invention enables i.a. preheating of e.g. the amine solution in a CO2-removal section of the plant, and providing duty for driving e.g. the post carbon capture removal unit. This further enables reduced energy waste and thus results in increased energy efficiency of the plant.
In a particular embodiment, said second set of heat exchangers comprises one or more heat exchangers, suitably one heat exchanger, arranged downstream said first set of heat exchangers. The heat exchanger is suitably provided as a coil, as is also the case in connection with the first set of heat exchangers.
Hence, a second heat exchanger set is suitably provided in the convection section, also referred to as flue-gas section, of the primary reforming unit to extract more duty enabling thereby, along with the stop of the use of natural gas as external fuel source, a higher energy efficiency of the plant—and process. The low temperature of the cooled flue gas at, e.g. 110-120° C., is advantageously utilized.
For instance, in connection with i) a portion of the first or second fuel gas stream, instead of its entirety being preheated in a heat exchanger of the first set of heat exchangers, it is suitably fed to a heat exchanger of the second set of heat exchangers. The preheated fuel gas stream from the latter, which suitably is arranged downstream the heat exchanger of the first set, is also sent to a heat exchanger of the first set before feeding it as preheated fuel gas stream to the burners.
In connection with ii), in an e.g. amine-wash unit, as is well known in the art, the CO2-stripper (also referred to as desorber) comprises a so-called CO2-reboiler at the bottom, where a stream derived from the bottom of the CO2-stripper and comprising amine is heated for thereby removing CO2 from the amine. Normally, an amine solution (lean amine-solution) is withdrawn as a bottom product of the CO2-stripper. The bottom product then delivers heat in an amine preheater (feed/effluent heat exchanger) to an amine solution (rich amine-solution) withdrawn from the bottom of upstream CO2-absorber and which after being preheated is fed to the CO2-stripper, normally to the top of the CO2-stripper. After delivering heat in the amine preheater, the amine solution (lean amine-solution) withdrawn from the bottom of the CO2-stripper is fed to the top of the CO2-absorber. By an embodiment of the invention, said second set of heat exchangers, suitably a heat exchanger arranged downstream the first set, functions instead as an ammine preheater suitably arranged downstream the feed/effluent heat exchanger, which thereby extracts additional duty from the flue gas, thus also enabling less duty in the CO2-reboiler of the CO2-stripper. The provision of a CO2-reboiler smaller in size is thereby also possible. Further, the need of using e.g. steam, more specifically low-pressure steam, for driving the CO2-reboiler, as is often the case, is also reduced. Moreover, higher integration in the plant or process is achieved by directly fluid-communicating the amine wash unit with the convection section of the primary reforming unit, as the amine-solution (rich amine-solution) runs through the heat exchanger arranged therein, e.g. through a coil, against cooled flue gas travelling through the convection section. The cooled flue gas from the first set of heat exchangers, being for instance at 120° C., delivers heat to the amine-solution (rich amine-solution) so it is preheated to e.g. 150-110° C., suitably after the feed/effluent heat exchanger, prior to entering the top of the CO2-stripper.
In the amine wash unit, the CO2-absorber operates suitably in the temperature range 30-50° C., and pressure range 1-200 atm abs., while the CO2-stripper operates suitably in the temperature range 110-130° C. and 1.2-2 atm abs. at the bottom of the CO2-stripper.
As mentioned, a post carbon capture-removal unit may be provided. Accordingly, an additional solvent wash unit, suitably an amine wash unit for removing CO2 from the flue gas, also comprising a CO2-absorber and CO2-stripper with attendant CO2-reboiler, may be provided. For instance, in connection with the above recited embodiment ii), an amine preheater is also suitably used for preheating an amine solution from this additional amine wash unit. Thus, in embodiment ii) said second set of heat exchangers may also be arranged to receive a solvent solution, e.g. an amine-solution, from: from an additional CO2-removal section which is arranged downstream said convection section of the primary reforming unit, suitably an additional solvent wash unit, e.g. an additional amine wash unit; thereby generating a further cooled flue gas stream and a preheated solvent-solution, e.g. a preheated amine-solution.
Suitably also, another heat exchanger, e.g. a coil, may be arranged in parallel in the convection section, and used as amine preheater for said additional amine wash unit.
Now, more specifically, in an embodiment according to the first aspect of the invention, the plant further comprises an additional CO2-removal section arranged to receive said cooled flue gas stream or said further cooled flue gas stream, thereby generating a second CO2-rich stream and a CO2-depleted flue gas stream, and in which said additional CO2-removal section also comprises a CO2-absorber under the addition of a solvent solution and a CO2-stripper for regenerating the solvent solution.
Thereby, CO2 emissions from the hydrogen plant can be reduced by 90% or more, thus drastically further reducing the carbon-footprint of the plant. Heretofore, there have not been developed standard solutions for capturing CO2 from the flue gas of a primary reforming unit, particularly an SMR, in a plant for producing hydrogen.
By combining this additional CO2-removal/capture section (post-CO2-capture) with the CO2-removal/capture section downstream the water gas shift section (pre-CO2-capture), the above mentioned percentage reduction in CO2 emissions is achieved, while at the same time further integrating the additional duty (heat duty) available in the flue gas with the additional CO2-removal/capture section by means of said preheating of the amine solution used therein, i.e. amine-rich solution, by the cooled flue gas of the primary reforming unit. The post-CO2-capture acts thereby also synergistically with the rest of the plant for producing hydrogen. The CO2 from pre-CO2-capture and post-CO2 capture is then suitably transported for e.g. sequestration in geological structures.
In connection with the above-recited embodiment iii), it would be understood that BFW as well as DMW are imported streams in the plant. Normally, the BFW will go to a steam drum and from there, a stream is withdrawn which is used for cooling a synthesis gas stream. Normally also, DMW for use in the plant is preheated by cooling a synthesis gas stream, suitably the synthesis gas stream generated after water gas shift yet prior to a process gas (here synthesis gas) air cooler, where the temperature of the synthesis gas is around 120-130° C. Additional duty is extracted from the cooled flue gas instead, as its temperature is also around this range.
As recited above, the heat exchanger of the second set of heat exchangers is suitably provided as a coil. Accordingly, in an embodiment, the portion the fuel gas in i), or the solvent solution in ii), or the BFW or DMW in iii), runs inside the coil against the flue gas stream, more specifically the cooled flue gas stream.
In an embodiment according to the first aspect, said shift section comprises a high temperature shift (HTS). In another embodiment, the shift section comprises one or more additional high temperature shift units in series. In yet another embodiment, said shift section further comprises one or more additional shift units downstream the HTS unit, wherein the one or more additional shift units are one or more medium temperature shift (MTS) units and/or one or more low temperature shift (LTS) units. As is well-known in the art, in the shift section, the syngas is enriched in hydrogen by conducting the water gas shift reaction CO+H2=CO2+H2, as already recited farther above.
In an embodiment according to the first aspect of the invention, the plant further comprises one or more prereforming units (prereformers) arranged upstream said primary reforming unit and arranged to receive said hydrocarbon feed, such as natural gas e.g. desulfurized natural gas.
Hence, it would be understood that said hydrocarbon feed may also be a pre-reformed hydrocarbon feed. As is well-known in the art, in a pre-reformer all higher hydrocarbons can be converted to carbon oxides and methane, thus resulting in a higher methane content of the gas being fed to the primary reforming unit.
In an embodiment according to the first aspect of the invention, the hydrogen purification unit is a Pressure Swing Adsorption unit (PSA unit).
As is well-known in the art, PSA is a noncryogenic air separation process that is commonly used in commercial practice, and which involves the adsorption of the synthesis gas by adsorbents such as zeolite and silica in a high-pressure gas column, thereby generating a hydrogen-rich gas of high purity, e.g. 99.9 wt % or more H2. From the PSA unit, the off-gas stream is for instance delivered at about 30-40° C., while the hydrogen-rich gas stream is for instance delivered at about 40-50° C.
It is also envisaged the use of additional hydrogen purification units, suitably also a second PSA unit, which may be provided to receive a portion of the off-gas from the first PSA unit, for thereby generating a second off-gas stream and a second hydrogen-rich gas stream. The off-gas streams from both PSA-units may be combined into a single off-gas stream, and the hydrogen-rich streams may also be combined into a single hydrogen-rich stream.
In a second aspect, the invention provides a process for producing hydrogen, the process comprising:
In an embodiment according to the second aspect of the invention, the process further comprises only supplying said first fuel gas stream or second fuel gas stream as fuel to said one or more burners. Accordingly, the process does not comprise supplying a separate fuel gas stream such as natural gas stream or desulfurized natural gas stream to said one or more burners.
In an embodiment according to the second aspect of the invention,
In an embodiment according to the second aspect of the invention, the flue gas is cooled to below 100° C., for instance about 70° C. Normally the flue gas is cooled down to 120-130° C., yet with much less or no sulfur in the flue gas, it is possible to cool it below 100° C., for instance about 70° C. which is the saturation point for water. Hence, in a particular embodiment, the flue gas is cooled to a temperature in the range 70-99° C., such as 75, 80, 85 or 95° C.
In an embodiment according to the second aspect of the invention, the process further comprises providing said convection section with a second set of heat exchangers, suitably a heat exchanger downstream said first set of heat exchangers, and:
It would be understood that said additional CO2-removal section, suitably an additional solvent wash unit, arranged downstream said convection section of the primary reforming unit, refers to a post carbon capture-removal unit, for thereby removing and capturing CO2 from the cooled flue gas or from the further cooled flue gas.
In an embodiment according to the second aspect of the invention, the process further comprises prereforming of said hydrocarbon feed in one or more prereforming units (prereformers) arranged upstream said primary reforming unit.
As in connection with the first aspect of the invention (plant), the process of the invention in accordance with the second aspect, enables the incorporation of a new fuel gas stream i.e. other than the hydrocarbon feed, e.g. natural gas, to the hydrogen plant. The new fuel gas stream, suitably being a mixture of PSA off-gas and hydrogen from the PSA, does not contain any sulfur, so that it is now possible to cool the flue gas to a lower temperature without risking condensation of sulfuric acid and resulting corrosion problems. This makes it possible to add an additional preheating coil in the flue gas section (convection section of the primary reforming unit) to extract more duty, thus enhancing the energy efficiency of the plant.
This duty can be used for i.a. preheating of DMW/BFW but also for preheating an amine solution entering the CO2-stripper of the CO2-removal section, such as the post carbon capture removal unit (i.e. the additional CO2-removal section arranged for receiving said further cooled or further cooled flue gas stream). Suitably also, the duty is used in a CO2 reboiler of the CO2-stripper of e.g. the post carbon capture removal unit. Thereby, it is now also possible to provide duty for driving the post carbon capture removal unit or for driving the CO2-removal section arranged between the primary reforming unit and hydrogen purification unit, instead of resorting to the use of low process steam (LP steam) generated in the plant/process or provided as import steam. LP steam is normally used for the CO2-reboiler. Hence, the invention enables also preheating of e.g. the amine solution in the CO2-removal section. At least reduced energy consumption and reduced steam consumption is thereby achieved.
Any of the embodiments and associated benefits of the first aspect of the invention (plant) may be used in connection with the second aspect of the invention (process), or vice versa.
In a third aspect, the invention provides a method of retrofitting an existing plant for producing hydrogen which uses a conventional primary reforming unit for generating a synthesis gas.
Accordingly, there is also provided a method of retrofitting a plant for producing hydrogen
Thereby, there is no import of natural gas as external fuel source for the burners. The hydrogen-rich gas stream, or suitably the fuel gas mixture of hydrogen-rich gas and PSA-off gas, is free of sulfur, so it is possible to cool the flue gas to a lower temperature than in the existing primary reforming unit e.g. steam reforming unit without risking condensation of sulfuric acid and resulting corrosion problems. An additional set of heat exchangers, suitably an additional heat exchanger, such as a coil, is installed in the convection section of the reforming unit i.e. flue gas section, preferably downstream the first set of heat exchangers of the existing plant. This enables to extract more duty thereby further enhancing the energy efficiency of the plant.
In an embodiment according to the third aspect of the invention, the plant further comprises a shift section and a CO2-removal section arranged between the primary reforming unit and hydrogen purification unit, the CO2-removal section being a chemical absorption unit where a solvent solution needs regeneration by heating, suitably a solvent wash unit, such as an amine wash unit,
In a particular embodiment, the additional CO2-removal section is an additional chemical absorption unit where a solvent solution needs regeneration by heating, suitably a solvent wash unit, such as an amine wash unit;
Thereby it is possible to capture about 90% of the carbon dioxide generated in the plant, while at the same time providing for high plant or process integration.
As in connection with the first or second aspect of the invention, the method of retrofitting enables the incorporation of a new fuel gas stream i.e. other than the hydrocarbon feed, e.g. natural gas, to the existing hydrogen plant. The new fuel gas stream, suitably being a mixture of PSA off-gas and hydrogen (hydrogen-rich gas) from the PSA, does not contain any sulfur, so that it is now possible to cool the flue gas to a lower temperature without risking condensation of sulfuric acid and resulting corrosion problems. This makes it possible to add an additional preheating coil in the flue gas section (convection section of the primary reforming unit) to extract more duty, thus enhancing the energy efficiency of the plant.
This duty can be used for i.a. preheating of DMW/BFW but also for preheating an amine solution entering the CO2-stripper of the CO2-removal section, such as the post carbon capture removal unit, i.e. the additional CO2-removal section arranged for receiving said further cooled or further cooled flue gas stream. Suitably also, the duty is used in a CO2 reboiler of the CO2-stripper of e.g. the post carbon capture removal unit. Thereby, it is now also possible to provide duty for driving the post carbon capture removal unit or for driving the CO2-removal section arranged between the primary reforming unit and hydrogen purification unit, instead of resorting to the use of low process steam (LP steam) generated in the plant/process or provided as import steam. LP steam is normally used for the CO2-reboiler. Hence, the invention enables also preheating of e.g. the amine solution in the CO2 removal section. At least reduced energy consumption and reduced steam consumption is thereby achieved.
Any of the embodiments according to the first aspect of the invention (plant) or second aspect of the invention (process) and associated benefits, may be used in connection with the third aspect of the invention (method of retrofitting an existing hydrogen plant), or vice versa.
With reference to
From the SMR 4 a first synthesis gas stream, here first synthesis gas stream 5 is withdrawn and supplied to water gas shift section 12 comprising a high temperature shift reactor (not shown) and optionally a low or medium temperature shift reactor (not shown), thereby generating a second synthesis gas stream 7 which is enriched in hydrogen. This second synthesis gas stream 7 is then supplied to a CO2-removal/capture section 14, from which a CO2-rich gas 17 is withdrawn and a third synthesis gas stream 9 depleted from CO2 is generated. This third synthesis gas stream 9 is finally supplied to a hydrogen purification unit, suitably a PSA unit 16, thereby generating a hydrogen-rich stream 11 as final product and a PSA off-gas stream 13. The PSA off-gas stream 13 contains some methane and is therefore preheated in coil 10 of the first set of heat exchangers of the convection section 4iv of the SMR 4, or the PSA off-gas 13 is first combined with desulfurized natural gas 1′ before being preheated. The desulfurized natural gas 1′ is suitably a stream which is diverted from desulfurized natural gas stream 1 fed to the prereforming unit 2. The desulfurized natural gas may be also added directly to the burners 4′″. Cold air 19 is provided by an air blower (not shown) and preheated in coil 8 of the first set of heat exchangers, thereby sending a preheated air 19′ together with the preheated PSA off-gas and desulfurized natural gas mixture 13′, 13″, which is free of sulfur, to the burners 4′″.
With reference to
Similarly, increased energy efficiency is achieved by providing the additional duty of the convection section for driving a post CO2 capture, i.e. by providing e.g. an additional amine wash unit for removing CO2 from the further cooled flue gas stream 15.
| Number | Date | Country | Kind |
|---|---|---|---|
| PA 2021 01126 | Nov 2021 | DK | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/082733 | 11/22/2022 | WO |
