Method and device for hydrogen production with low carbon dioxide levels

Abstract

The invention relates to a method and a device for generating a hydrogen product (10), in which a carbon-containing feed (1) is reacted by reformation (R) and water-gas shift (S) to give a hydrogen- and carbon-dioxide-containing synthesis gas (5), from which, in a CO2 removal step (T), carbon dioxide (7) is removed to leave raw hydrogen (8), which is processed by way of at least one further method step to form the hydrogen product (10), wherein a fuel (12) is combusted to obtain process heat and the carbon dioxide (7) removed from the synthesis gas (5) is disposed of by sequestration or utilized materially. It is a characteristic feature here that a portion (9) of the synthesis gas (5), for the removal of carbon compounds (13), is passed through a membrane (M) to give a gas fraction which consists largely of hydrogen and which is employed as fuel (12).

Description

[0001] Description

[0002] Process and device for low-carbon hydrogen production

[0003] The invention relates to a process for producing a hydrogen product, in which a carbon-containing feed is converted by reforming and water gas shift in order to obtain a synthesis gas containing hydrogen and carbon dioxide, from which raw hydrogen is produced in a CO2 separation step by separating carbon dioxide, which is processed into the hydrogen product in at least one further process step, wherein a fuel is burned to obtain process heat and the carbon dioxide separated from the synthesis gas is disposed of by sequestration or used as a material.

[0004] Furthermore, the invention relates to a device for carrying out the method according to the invention.

[0005] Hydrogen products such as pure hydrogen, which consists of at least 99.5 mol% hydrogen, or ammonia synthesis gas, which contains a 3:1 ratio of hydrogen to nitrogen, are still predominantly produced from carbon-based feedstocks, resulting in the formation and release of large amounts of climate-damaging carbon dioxide. However, there are increasing efforts to dispose of the resulting carbon dioxide through sequestration or material utilization rather than releasing it into the atmosphere.

[0006] According to the state of the art, to produce a hydrogen product, a carbon-containing feedstock, such as natural gas, is desulfurized if necessary and then reformed, for example, by partial oxidation, autothermal reforming, steam reforming, or a combination of two or more of these processes, into a gas mixture known as synthesis gas. This gas mixture consists largely of hydrogen, carbon monoxide, and carbon dioxide and may also contain other substances such as methane or argon. The synthesis gas is then subjected to water-gas conversion to convert the contained carbon monoxide with water to hydrogen and carbon dioxide, yielding a synthesis gas consisting largely of hydrogen and carbon dioxide.In a CO2 separation step, typically carried out as acid gas scrubbing, carbon dioxide is separated from the synthesis gas, yielding a carbon dioxide fraction with a purity sufficient for its sequestration or material use and a hydrogen fraction referred to as raw hydrogen, which contains residues of carbon monoxide, carbon dioxide and methane and whose hydrogen content is usually around 98 mol%.

[0007] To form the hydrogen product, the raw hydrogen is treated, for example, by methanation, partial condensation, nitrogen scrubbing or pressure swing adsorption, whereby carbon monoxide and carbon dioxide are separated after conversion to methane and water or directly, and a largely carbon- and oxygen-free hydrogen fraction is produced, which forms the hydrogen product or from which, for example, by adding nitrogen, an ammonia synthesis gas is obtained as a hydrogen product.

[0008] Using the methods described, no more than approximately 90% of the carbon used to produce the hydrogen product can be captured in the form of carbon dioxide and disposed of through sequestration or used as a material. However, depending on the legal requirements and penalties levied on carbon dioxide emissions, it may be necessary to achieve higher carbon capture quotas.

[0009] The object of the present invention is therefore to provide a method of the generic type and a device for carrying it out, which allow carbon separation rates of more than 90% to be achieved.

[0010] According to the invention, this object is achieved in that part of the synthesis gas or part of the raw hydrogen is passed through a membrane to separate carbon dioxide in order to obtain a gas fraction consisting largely of hydrogen, which is used as fuel.

[0011] If raw hydrogen is used to obtain the fuel, the processing of the raw hydrogen to the hydrogen product also includes the division of the raw hydrogen into at least a first and a second part, whereby the hydrogen product is produced from the first part in at least one further process step and the second part is passed through the membrane to separate carbon-containing components such as carbon monoxide, carbon dioxide and methane.

[0012] The hydrogen present in the gas fractions to be separated by the membrane represents the "fast" gas component, which can pass through the membrane much more easily than the carbon compounds carbon dioxide, carbon monoxide, and methane also present in the gas fraction. The resulting permeate stream, which represents the gas fraction consisting largely of hydrogen, is therefore at a significantly lower pressure level than the retentate stream, which is obtainable without any significant pressure loss and comprises the majority of the carbon compounds present in the gas fraction to be separated. It makes sense to recycle the retentate stream and feed it into the reforming process together with the carbon-containing feed. This is possible with little effort due to the small pressure difference between the two material streams.

[0013] Preferably, enough synthesis gas or raw hydrogen is separated through the membrane to obtain a gas fraction consisting largely of hydrogen in a quantity sufficient to fully cover the heating energy requirements for hydrogen production. It makes sense to produce the gas fraction consisting largely of hydrogen in a quantity that precisely covers the heating energy requirements. However, it is also possible to produce a larger quantity of the gas fraction consisting largely of hydrogen and export the portion not usable in the process for credit.

[0014] It should not be ruled out that the gas fraction, which consists largely of hydrogen, could be extracted in a quantity sufficient to cover only part of the heating energy requirements for hydrogen production, and that the remaining gap could be sensibly closed by heating energy generated without carbon dioxide emissions, for example using “green” electricity.

[0015] Preferably, the gas fraction, which consists largely of hydrogen, is combusted to generate the steam required for the process or to preheat a feedstock for reforming. However, it is also possible to heat a steam or pre-reformer used for reforming with the fuel. The process according to the invention is particularly suitable for use in ammonia synthesis, wherein the raw hydrogen not passed through the membrane is processed into a feed gas for ammonia synthesis by methanation and / or nitrogen scrubbing and / or nitrogen addition.

[0016] The conversion of the carbon-containing feedstock can be carried out within the scope of the process according to the invention by partial oxidation, autothermal reforming, steam reforming, or a combination of two or more of these processes, which can be preceded by pre-reforming. The process according to the invention can be used with particular advantage when the carbon-containing feedstock is converted by autothermal reforming or partial oxidation. Unlike when a steam reformer is used, in these cases only small furnaces are heated, for example those used to heat feedstocks or to generate steam, releasing comparatively small amounts of flue gas into the atmosphere. In order to cover the heating energy requirements of these furnaces with the gas fraction consisting largely of hydrogen, only a small proportion of the synthesis gas or raw hydrogen needs to be separated via the membrane.

[0017] Various separation methods are known in the art for separating carbon dioxide from synthesis gas. In particular, a combination of membrane separation, pressure swing adsorption, and cryogenic gas separation can be used in a CO2 separation step. The CO2 separation step is preferably carried out as acid gas scrubbing, using, for example, an alkaline aqueous amine solution as the scrubbing agent.

[0018] Furthermore, the invention relates to a device for producing a hydrogen product, with a reforming device and a water gas shift connected to the reforming device, via which a carbon-containing feed can be converted into a synthesis gas containing hydrogen and carbon dioxide by reforming and water gas shift, as well as a CO2 separation for separating carbon dioxide from the synthesis gas and for obtaining raw hydrogen, which can be processed into the hydrogen product in a processing device connected to the gas scrubber, as well as a combustion device in which a fuel can be combusted to obtain process heat, wherein the CO2 separation is connected or connectable to a device for sequestration or material use of the carbon dioxide separated from the synthesis gas.

[0019] The stated object is achieved according to the invention in that the device comprises a membrane unit connected to the combustion device and a flow divider arranged upstream or downstream of the CO2 separation, via which flow divider a part of the synthesis gas or a part of the raw hydrogen can be introduced into the membrane separation unit in order to obtain a gas fraction consisting largely of hydrogen by separating carbon compounds, which gas fraction can be fed to the combustion device as fuel.

[0020] The membrane unit is expediently designed so that the gas fraction consisting largely of hydrogen is available as a permeate stream.

[0021] In a preferred embodiment of the device according to the invention, the membrane unit is connected to the reforming unit in such a way that at least a portion of the carbon compounds separated from the raw hydrogen, such as in particular carbon dioxide, carbon monoxide and methane, can be recycled as feed into the reforming unit.

[0022] The combustion device could, for example, be a burner-fired furnace used to heat a feedstock to be fed to the reforming device. However, the combustion device could also be a burner-fired steam generator used to generate process steam, or a steam or pre-reformer of the reforming device, which can be heated via a burner.

[0023] A further embodiment of the device according to the invention provides a treatment device comprising a pressure swing adsorber, which allows pure hydrogen with a hydrogen content of more than 99.5 mol% to be obtained from raw hydrogen. The pure hydrogen can be released as a hydrogen product or further processed to form the hydrogen product.

[0024] Preferably, the treatment facility is connected to an ammonia synthesis plant and configured to process the raw hydrogen into an ammonia synthesis gas, which can be fed to the ammonia synthesis plant as feed gas. The treatment facility may, for example, comprise a pressure swing adsorber for generating pure hydrogen and a nitrogen supply through which the pure hydrogen can be mixed with the ammonia synthesis gas. However, it is also possible for the treatment facility to comprise a methanizer, a partial condensation plant, or a nitrogen scrubber.

[0025] A reforming device particularly suitable for the device according to the invention is designed with an autothermal reformer or a partial oxidation reactor, which only require fuel for burner-fired auxiliary units, such as furnaces used to heat feedstocks. Therefore, only a small amount of synthesis gas needs to be diverted to obtain the fuel gas, which consists largely of hydrogen, in order to produce the hydrogen product with no or only very little release of carbon dioxide into the atmosphere. However, this should not preclude the reforming device from being designed with a steam or pre-reformer.

[0026] CO2 separation can be implemented as a combination of membrane separation, pressure swing adsorption, and cryogenic gas separation. However, CO2 separation is preferably carried out by acid gas scrubbing, in which, for example, an alkaline aqueous amine solution serves as the scrubbing agent.

[0027] In the following, the invention will be explained in more detail using an embodiment shown schematically in Figure 1.

[0028] The embodiment of Figure 1 shows a preferred embodiment of the process according to the invention, in which an ammonia synthesis gas is produced as the hydrogen product using an autothermal reformer.

[0029] A carbon-containing feed 1, which is preferably methane, is fed to the burner-fired furnace O for heating. The heated feed 3 is converted together with oxygen 2 in the autothermal reformer R into a raw synthesis gas 4 comprising hydrogen, carbon monoxide and water, from which a synthesis gas 5 consisting largely of hydrogen and carbon dioxide is produced in the water gas converter S. This synthesis gas 5 is separated via the flow divider L into a first synthesis gas sub-stream 6 and a second synthesis gas sub-stream 9. In the CO2 separation T, an amine scrubbing agent is preferably used to separate carbon dioxide from the first synthesis gas sub-stream 6 and to obtain a hydrogen-rich gas fraction 8 comprising carbon monoxide, methane and residues of carbon dioxide, referred to as raw hydrogen, as well as a carbon dioxide fraction 7, which is disposed of by sequestration or used as a material (neither shown).

[0030] The second synthesis gas substream 9 is separated in the membrane unit M into a hydrogen-rich, largely carbon-free permeate stream 12 and a retentate stream 13. Since the retentate stream 13, which contains the majority of the carbon compounds present in the raw hydrogen substream 9, is essentially obtained at the pressure of the raw hydrogen substream 9, it can be recycled with little compression effort (not shown) and used in the autothermal reformer R. The permeate stream 12, which consists largely of hydrogen and contains only small amounts of carbon in the form of carbon monoxide, carbon dioxide, and methane, is used as fuel gas in the burner-fired furnace O, the combustion of which produces a flue gas 14 that contains only a very small amount of carbon dioxide.The size of the second raw hydrogen partial flow 9 is adjusted via the flow divider L so that the amount of fuel gas 12 is sufficient to completely provide the heat required for heating the feed 1, so that the combustion of a carbon-containing fuel can be dispensed with.

[0031] The raw hydrogen 8 is processed, for example, by a combination of methanation, partial condensation, nitrogen scrubbing, and nitrogen admixture to produce an ammonia synthesis gas 10 that is largely free of oxygen-containing components, in particular carbon monoxide, and in which hydrogen and nitrogen are present in the stoichiometric ratio of 3:1 for the subsequent ammonia synthesis A. The ammonia 11 obtained in the ammonia synthesis A can be stored in liquid form (not shown).

Claims

Patent claims 1 . A process for producing a hydrogen product (10), in which a carbon-containing feedstock (1) is converted by reforming (R) and water gas shift (S) to obtain a synthesis gas (5) containing hydrogen and carbon dioxide, from which synthesis gas (5) is produced in a CO2 separation step (T) by separating carbon dioxide (7) to form raw hydrogen (8), which is processed into the hydrogen product (10) by at least one further process step, wherein a fuel (12) is burned to generate process heat and the carbon dioxide (7) separated from the synthesis gas (5) is disposed of by sequestration or used as a material, characterized in that a portion (9) of the synthesis gas (5) is passed over a membrane (M) to separate carbon compounds (13) in order to obtain a gas fraction consisting largely of hydrogen, which is used as fuel (12).

2. Process according to claim 1, characterized in that the gas fraction (12) consisting largely of hydrogen is obtained as permeate during the membrane separation (M).

3. Process according to one of claims 1 or 2, characterized in that the carbon compounds (13) separated via the membrane are recycled before the reforming (R).

4. Method according to one of claims 1 to 3, characterized in that the gas fraction (12) consisting largely of hydrogen is produced in an amount sufficient to completely cover the heating energy requirement of the hydrogen production.

5. Process according to one of claims 1 to 4, characterized in that the gas fraction (12) consisting largely of hydrogen is burned in order to obtain steam required for the process or to preheat a feedstock (1) for the reforming (R) or to heat a steam reformer or a pre-reformer used for the reforming (R).

6. Method according to one of claims 1 to 5, characterized in that the raw hydrogen (8) is produced by methanation and / or nitrogen scrubbing and / or pressure swing adsorption and / or partial condensation and / or Nitrogen addition to a feed gas for ammonia synthesis (10).

7. Process according to one of claims 1 to 6, characterized in that the CO2 separation step (T) is carried out as acid gas scrubbing.

8. Process according to one of claims 1 to 7, characterized in that the reforming (R) is carried out by autothermal reforming or partial oxidation or steam reforming or a combination of two or more of these methods.

9. A device for producing a hydrogen product (10), comprising a reforming device (R) and a water-gas shift (S) connected to the reforming device, via which a carbon-containing feedstock (1) can be converted by reforming and water-gas shift into a synthesis gas (5) containing hydrogen and carbon dioxide, as well as a CO2 separation (T) for separating carbon dioxide (7) from the synthesis gas (5) and for obtaining raw hydrogen (6), which can be processed into the hydrogen product (10) in a processing device (B) connected to the gas scrubber, as well as a combustion device (O) in which a fuel (12) can be combusted to obtain process heat, wherein the carbon dioxide separation device (T) is connected or connectable to a device for sequestering or materially utilizing the carbon dioxide separated from the synthesis gas, characterized in thatthat it comprises a membrane unit (M) connected to the combustion device (O) and a flow divider (L) arranged upstream of the CO2 separation (T), via which flow divider a portion (9) of the synthesis gas (5) can be introduced into the membrane separation unit (M) in order to obtain, by separating carbon compounds, a gas fraction (12) consisting largely of hydrogen, which can be fed to the combustion device (O) as fuel.

10. Device according to claim 9, characterized in that the gas fraction (12) consisting largely of hydrogen is obtained as a permeate stream. 1 1. Device according to one of claims 9 or 10, characterized in that carbon compounds (13) separated from the synthesis gas partial stream (9) are the membrane unit (M) before the reforming device (R).

12. Device according to one of claims 9 to 11, characterized in that the combustion device (O) is designed as a burner-fired furnace for heating the insert (1) or as a burner-fired steam generator for generating process steam or as a steam or pre-reformer which can be heated via a burner.

13. Device according to one of claims 9 to 12, characterized in that the processing device (B) comprises a methanizer and / or a nitrogen scrubber and / or a pressure swing adsorber and / or a partial condensation and / or nitrogen supply, via which the raw hydrogen (8) can be processed into a feed gas (10) for an ammonia synthesis (A).

14. Device according to one of claims 9 to 13, characterized in that the reforming device (R) is designed as an autothermal reformer or as a partial oxidation reactor or as a steam reformer or as a combination of two or more of these devices.

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