Process and apparatus for hydrogen production with low carbon dioxide levels

Abstract

The invention relates to a process and to an apparatus for producing a hydrogen product (14), in which a carbonaceous feed (1) is converted by reforming (R) and water gas conversion (S) in order to obtain a hydrogen- and carbon dioxide-containing gas mixture (5) referred to as synthesis gas, from which, in a first CO2 separation step (T1), the removal of carbon dioxide gives rise to crude hydrogen (8), and this is processed by at least one further process step (B) to give the hydrogen product (14), wherein process heat is obtained by combustion of a fuel (16) and carbon dioxide (13) separated from the synthesis gas (5) is disposed of by sequestration or sent to a physical use. The characteristic feature here is that the synthesis gas (5) is separated into a first (6) and a second synthesis gas substream (7), of which the first (6) is treated in the first CO2 separation step (T1) in order to obtain the crude hydrogen (8), while a combustion gas (16) consisting largely of hydrogen is formed from the second synthesis gas substream (7) by the removal of carbon dioxide in a second CO2 separation step (T2) and is combusted to obtain process heat.

Description

[0001] Description

[0002] Method 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 conversion in order to obtain a gas mixture containing hydrogen and carbon dioxide, referred to as synthesis gas, from which raw hydrogen is produced in a first CCh separation step by separating carbon dioxide, which is processed into the hydrogen product by at least one further process step, wherein process heat is obtained by combustion of a fuel and carbon dioxide separated from the synthesis gas is disposed of by sequestration or fed to a material use.

[0004] 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, producing and releasing 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.

[0005] According to the current state of the art, to produce a hydrogen product, a carbon-containing feedstock, such as natural gas, is desulfurized if necessary and then converted 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 hydrogen sulfide 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%.

[0006] To form the hydrogen product, the raw hydrogen is treated, for example, by methanation, nitrogen scrubbing or pressure swing adsorption, whereby carbon monoxide is converted or separated together with carbon dioxide in a residual gas and a largely carbon-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.

[0007] Acid gas scrubbing utilizes the ability of liquids to selectively absorb carbon dioxide and other acid gases from a gas mixture and retain them in solution. The higher the pressure at which the scrubbing is carried out, the better the acid gases are absorbed and separated from the gas mixture to be purified. Since the synthesis gas is produced at a pressure level typically between 25 and 45 bar, the volume flow to be treated is small, allowing the synthesis gas to be treated by acid gas scrubbing with comparatively low investment and operating costs.

[0008] Carbon dioxide is also present in flue gases produced during the production of hydrogen products in reformers and / or furnaces, which typically burn natural gas or carbon-containing residual gases for heating. Unlike syngas, these flue gases are pressureless. Because they can therefore only be treated with acid gas scrubbing, which is very costly and laborious, they are usually released into the atmosphere along with the carbon dioxide produced during combustion.

[0009] Therefore, with the methods described, only a maximum of 95% of the carbon used to produce the hydrogen product can be separated in the form of carbon dioxide and disposed of through sequestration or used as a material. Depending on the legal requirements and penalties for carbon dioxide emissions, it may be necessary to achieve higher carbon capture rates. The object of the invention is to provide a process of the generic type and a device for its implementation that enable the production of hydrogen products with significantly lower carbon dioxide emissions than in the prior art.

[0010] This object is achieved according to the invention in terms of the process in that the synthesis gas is separated into a first and a second synthesis gas partial stream, the first of which is treated in the first CO2 separation step in order to obtain the raw hydrogen, while from the second synthesis gas partial stream, by separating carbon dioxide in a second CO2 separation step, a fuel gas consisting largely of hydrogen is produced, which is burned to obtain process heat.

[0011] The fuel gas produced in the second CO2 separation step from the second synthesis gas stream contains only small amounts of carbon compounds such as carbon dioxide, carbon monoxide, or methane, so that its combustion produces a largely carbon dioxide-free flue gas. It is sensible to completely dispose of the carbon dioxide separated from the synthesis gas in both the first and second CO2 separation steps through sequestration or recycle it. Since the fuel gas replaces at least part of the carbon-containing fuels used in the process according to the state of the art, the amount of carbon dioxide released into the atmosphere during the production of the hydrogen product is reduced compared to the state of the art.

[0012] Preferably, sufficient synthesis gas is fed to the second CO2 separation step via the second synthesis gas substream to obtain a fuel gas quantity sufficient to fully cover the fuel demand for hydrogen production. Particularly preferably, no more fuel gas is produced than is needed to fully cover the fuel demand for the production of the hydrogen product. However, it is also possible to produce a larger quantity of fuel gas and export fuel gas not usable in the process for credit.

[0013] Various separation methods are known in the art for separating carbon dioxide from synthesis gas, each of which can be used in both the first and second CO2 separation steps. In particular, combination processes involving membrane separation, pressure swing adsorption (PSA), and cryogenic gas separation can be used in a CO2 separation step. However, at least one of the two CO2 separation steps is preferably carried out as acid gas scrubbing, using, for example, an alkaline aqueous amine solution as the scrubbing agent.

[0014] Particularly preferably, the first and second CO2 separation steps are carried out as acid gas scrubbing, with the same scrubbing agent being used in both acid gas scrubbing steps. In this case, the two acid gas scrubbing steps can be operated in such a way that the scrubbing agent loaded with carbon dioxide in the first acid gas scrubbing step is regenerated together with the scrubbing agent loaded with carbon dioxide in the second acid gas scrubbing step. Apart from the potentially shared scrubbing agent regeneration, the two

[0015] Acid gas scrubbers are conveniently operated independently of each other, allowing the carbon dioxide contents of raw hydrogen and fuel gas to be individually optimized. For example, it may be economically viable to operate the second acid gas scrubber at a lower carbon dioxide removal rate than the first acid gas scrubber.

[0016] The generated fuel gas is preferably burned to generate steam required for the process or to preheat a feedstock for reforming. However, it is also possible to heat a steam reformer or a pre-reformer used for reforming with the fuel gas.

[0017] The process according to the invention is particularly suitable for use in ammonia synthesis, wherein the raw hydrogen is processed into an ammonia synthesis gas by methanation or nitrogen scrubbing or nitrogen addition.

[0018] The conversion of the carbonaceous 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 may be preceded by pre-reforming. The process according to the invention can be used with particular advantage when the carbonaceous feedstock is converted by autothermal reforming or partial oxidation. Unlike the use of a steam reformer, in these cases only small furnaces are heated, for example, those used to heat feedstocks or generate steam, releasing comparatively small amounts of flue gas into the atmosphere.In order to cover the fuel requirements of these furnaces with a fuel gas consisting largely of hydrogen, only a small portion of the synthesis gas needs to be treated in the second CO2 separation step, so that the second CO2 separation step can be realized with low investment costs.

[0019] Furthermore, the invention relates to a device for producing a hydrogen product, with a reforming device and a water gas converter 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 conversion, a first CO2 separation device with which carbon dioxide can be separated from the synthesis gas in order to obtain raw hydrogen, which can be processed into the hydrogen product in at least one processing device connected to the first CO2 separation device, and a combustion device in which a fuel can be combusted to generate process heat, wherein carbon dioxide separated from the synthesis gas can be disposed of by sequestration or can be used for material purposes.

[0020] The stated object is achieved by the device according to the invention in that it comprises a second CO2 separation device which is connected to the first CO2 separation device via a flow divider, via which the synthesis gas can be divided into a first synthesis gas partial stream for introduction into the first CO2 separation device and a second synthesis gas partial stream for introduction into the second CO2 separation device, wherein the raw hydrogen can be obtained from the first synthesis gas partial stream in the first CO2 separation device and carbon dioxide can be separated from the second synthesis gas partial stream in the second CO2 separation device in order to obtain a fuel gas consisting largely of hydrogen for use in the combustion device. Preferably, both the carbon dioxide that can be separated in the first and also that in the second CO2 separation device can be disposed of entirely by sequestration or used for material purposes.

[0021] The two CO2 separation devices are devices known from the prior art for separating carbon dioxide from synthesis gas. In particular, at least one of the two CO2 separation devices can be designed as a combination of membrane separation, pressure swing adsorber, and cryogenic gas separation. Preferably, however, at least one of the two CO2 separation devices is a sour gas scrubber, which can be operated, for example, with an alkaline aqueous amine solution as the scrubbing agent.

[0022] The first and second CO2 separation devices are expediently designed as acid gas scrubbers. This variant of the device according to the invention allows for a reduction in investment costs and footprint by providing a scrubbing agent regeneration system that can be used simultaneously by the first and second CO2 separation devices and connects the two acid gas scrubbers.

[0023] The combustion device could, for example, be a burner-fired furnace used to heat a feedstock to be fed into 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 that can be heated via a burner.

[0024] One embodiment of the device according to the invention provides a treatment device comprising a pressure swing adsorber that allows pure hydrogen with a hydrogen content of more than 99.5 mol% to be obtained from the raw hydrogen. The pure hydrogen can be discharged as a hydrogen product or further processed to produce the hydrogen product.

[0025] 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 producing 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 mechanized or partial condensation or nitrogen scrubber.

[0026] 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 burner-fired steam or pre-reformer.

[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, which is preferably methane, is fed to the burner-fired furnace O for heating. Together with oxygen 3, the heated feed 2 is converted 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 obtained in the water gas converter S. Via the flow divider L, the synthesis gas 5 is separated into a first 6 and a second synthesis gas partial stream 7, of which the first 6 is fed into the first CO2 separation device T1, designed as an acid gas scrubber, and the second (7) is fed into the second CO2 separation device T2, also designed as an acid gas scrubber.

[0030] In the first CO2 separation device T1, an amine scrubbing agent is preferably used to separate carbon dioxide from the first synthesis gas partial stream 6 and to obtain a hydrogen-rich gas fraction 8 comprising carbon monoxide, methane, and carbon dioxide residues, referred to as raw hydrogen. To separate carbon dioxide, the scrubbing agent 9 loaded during the scrubbing is fed to the scrubbing agent regeneration W, which supplies the first CO2 separation device T1 with regenerated scrubbing agent 10. The second CO2 separation device T2 is operated with the same scrubbing agent as the first CO2 separation device T1, so that the scrubbing agent regeneration W can also be used to regenerate the scrubbing agent 11 loaded with carbon dioxide during the scrubbing of the second synthesis gas partial stream 7, from which the second CO2 separation device T2 is also supplied with regenerated scrubbing agent 12.In the detergent regeneration W, the separated carbon dioxide 13 is produced with a purity that allows its disposal by sequestration or material utilization (both not shown).

[0031] The raw hydrogen 8 is processed in the processing facility B, for example, by a combination of methanation, partial condensation, nitrogen scrubbing, and nitrogen admixture, to produce an ammonia synthesis gas 14 that is, in particular, free of 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 15 obtained in the ammonia synthesis A is stored, for example, in liquid form (not shown).

[0032] The gas phase 16 obtained from the second synthesis gas partial stream 7 in the second CO2 separation device T2 consists predominantly of hydrogen and contains only small amounts of carbon in the form of carbon monoxide, carbon dioxide, and methane. The gas phase 16 is used as fuel gas in the burner-fired furnace O, the combustion of which produces a flue gas 17 containing only a very small amount of carbon dioxide. The size of the second synthesis gas partial stream 7 is adjusted via the flow divider L such that the amount of fuel gas 16 is sufficient to fully provide the heat required for heating the feed 1, thus eliminating the need to burn a carbon-containing fuel.

Claims

Patent claims 1. A process for producing a hydrogen product (14), in which a carbon-containing feedstock (1) is converted by reforming (R) and water-gas conversion (S) to obtain a gas mixture (5) containing hydrogen and carbon dioxide, referred to as synthesis gas, from which raw hydrogen (8) is produced in a first CO2 separation step (T1) by separating carbon dioxide, which raw hydrogen is processed into the hydrogen product (14) by at least one further process step (B), wherein process heat is obtained by combustion of a fuel (16) and carbon dioxide (13) separated from the synthesis gas (5) is disposed of by sequestration or fed to a material utilization, characterized in that the synthesis gas (5) is separated into a first (6) and a second synthesis gas partial stream (7), of which the first (6) is treated in the first CO2 separation step (T1) to obtain the raw hydrogen (8),while from the second synthesis gas partial stream (7) a fuel gas (16) consisting largely of hydrogen is produced by the separation of carbon dioxide in a second CO2 separation step (T2), which fuel gas is burned to obtain process heat.

2. Process according to claim 1, characterized in that the two CO2 separation steps (T1, T2) are carried out as acid gas scrubbing, the same scrubbing agent being used in each of the two acid gas scrubbing steps.

3. Process according to claim 2, characterized in that the washing agent (9) loaded with carbon dioxide in the first CO2 separation step (T1) is regenerated (W) together with the washing agent (11) loaded with carbon dioxide in the second CO2 separation step (T2).

4. Process according to one of claims 1 to 3, characterized in that the fuel gas (16) consisting largely of hydrogen is burned to generate steam or to preheat (O) a charge (1) for reforming (R) or to heat a steam or pre-reformer.

5. Process according to one of claims 1 to 4, characterized in that the raw hydrogen (8) is processed into an ammonia synthesis gas (14) by methanation or nitrogen scrubbing or nitrogen addition.

6. Process according to one of claims 1 to 5, characterized in that the reforming (R) comprises an autothermal reforming or a partial oxidation or a steam reforming or a pre-reforming.

7. A device for producing a hydrogen product (14), comprising a reforming device (R) and a water-gas converter (S) connected to the reforming device (R), via which a carbon-containing feedstock (1) can be converted by reforming and water-gas conversion into a synthesis gas (5) containing hydrogen and carbon dioxide, a first CO2 separation device (T1) with which carbon dioxide can be separated from the synthesis gas (5) to obtain raw hydrogen (8), which can be processed into the hydrogen product (14) in at least one processing device (B) connected to the first CO2 separation device (T1), and a combustion device (O) in which a fuel (16) can be combusted to generate process heat, wherein carbon dioxide (13) separated from the synthesis gas (5) can be disposed of by sequestration or used for material purposes, characterized in that it comprises a second CO2 separation device (T2),which is connected to the first CO2 separation device (T1) via a flow divider (L), via which the synthesis gas (5) can be divided into a first synthesis gas partial stream (6) for introduction into the first CO2 separation device (T1) and a second synthesis gas partial stream (7) for introduction into the second CO2 separation device (T2), wherein the raw hydrogen (8) can be obtained from the first synthesis gas partial stream (6) in the first CO2 separation device (T1) and carbon dioxide can be separated from the second synthesis gas partial stream (7) in the second CO2 separation device (T2) in order to obtain a fuel gas (16) consisting largely of hydrogen for use in the combustion device (O).

8. Device according to claim 7, characterized in that the first (T 1) and the second CO2 separation device (T2) are designed as acid gas scrubbers which can be operated with the same scrubbing agent.

9. Device according to claim 8, characterized in that the first (T1) and the second CO2 separation device (T2) are connected to one another via a jointly usable detergent regeneration (W).

10. Device according to one of claims 7 to 9, characterized in that the combustion device is a burner-fired furnace (O) or a steam generator or a steam or pre-reformer.

11. Device according to one of claims 7 to 10, characterized in that the processing device (B) is connected to an ammonia synthesis (A) and is designed to process the raw hydrogen (8) into an ammonia synthesis gas (14) which can be fed to the ammonia synthesis (A) as feed gas.

12. Device according to claim 11, characterized in that the treatment device (B) comprises a methanation or a partial condensation or a nitrogen wash or a nitrogen supply.

13. Device according to one of claims 7 to 12, characterized in that the reforming device (R) is designed with an autothermal reformer or a partial oxidation reactor or a steam reformer or a pre-reformer.

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