Hydrogen production method linked to CO2 capture

Abstract

The invention relates to a method for producing hydrogen starting from a hydrocarbon feed, comprising the steps of reacting the hydrocarbon feed with steam to obtain a gas stream comprising hydrogen, carbon monoxide and carbon dioxide (synthesis gas), the step being provided with heat obtained by an electric power source, and removing carbon dioxide from the gas stream. The invention further relates to a plant for producing hydrogen starting from a hydrocarbon feed, comprising an electrically driven steam reformer and at least one CO2 capture system arranged downstream of the electrically driven steam reformer.

Description

[Technical Field]

[0001] The present invention relates to a hydrogen production method linked to CO2 capture, configured to achieve zero steam emissions. [Background technology]

[0002] As is well known, carbon dioxide is a by-product of many industrial processes and the final combustion product of carbon-containing fuels. Such carbon dioxide is generated in large quantities as gaseous emissions at industrial and energy production sites, and is released in small amounts and in dispersed manner during activities such as building heating and transportation.

[0003] In either case, since most of the process raw materials and fuels are fossil-derived, the CO2 emitted results in anthropogenic carbon emissions, causing an increase in atmospheric CO2 concentration and contributing to climate change.

[0004] CO2 is the leading greenhouse gas, and stationary CO2 emissions are estimated to account for approximately 60% of global CO2 emissions [https: / / www.ipcc.ch / pdf / special-reports / srccs / srccs_chapter2.pdf [Accessed April 2018]].

[0005] The main industrial sectors that contribute to CO2 sequestering emissions are power plants and energy-intensive industries. In particular, the refining industry accounts for approximately 6% of total CO2 sequestering emissions [Jiri van Straelen, Frank Geuzebroek, Nicholas Goodchild, Georgios Protopapas, Liam Mahony, CO2 capture for refineries, a practical approach, Energy Procedia 1(2009)179-185].

[0006] Meanwhile, hydrogen demand reached nearly 75 million tons in 2018, increasing at approximately 6% annually [IEA.org / reports / the-future-of-hydrogen, June 2019], with over 50% used for purification purposes as hydrotreatment and hydrocracking, and the remainder used primarily for ammonia and methanol production. According to the IEA, approximately 830 million tons of CO2 are currently associated with annual hydrogen production. This carbon flow is important because, in the coming years, the CO2 emissions associated with each single chemical process will be the first and most important parameter for evaluating technology choices, including hydrogen production.

[0007] Currently, steam reforming is the most cost-effective technology for hydrogen production, particularly in the refining industry which uses natural gas or off-gas as raw materials. Steam reforming of natural gas and light naphtha is the mainstay of such production because it is a highly efficient process with the highest H2 / CO ratio and the lowest cost of production (CoP). Such processes account for at least up to 20% of CO2 emissions in the refining industry [J. van Straelen, F. Geuzebroek, N. Goodchild, G. Protopapas, L. Mahony, International Journal of greenhouse control, 4(2010)316].

[0008] In the steam reforming process, some of the CO2 (typically about 50% to 60% of the total) is generated in the process synthesis gas during steam reforming (CH4 + H2O = CO + 3H2) and in the water-gas shift (CO + H2O = CO2 + H2) reactor and downstream stages, while the other portion (40% to 50%) is further generated in the steam reformer where the heat input necessary for the endothermic reaction is supplied by the heat provided by the combustion of an external fuel [G. Collodi, Chemical Engineering Transactions 19(2010)37]. Approximately 0.9 kg of CO2 is converted to Nm³ of H2. 3 It is estimated that it will be generated in that area.

[0009] Furthermore, furnaces with burners installed internally have a very complex steam reforming system configuration, resulting in a plant with a considerably large footprint.

[0010] In fact, a major challenge in achieving carbon-neutral energy and production systems is decarbonizing industries that are currently heavily reliant on fossil fuel resources such as oil and natural gas. The most promising option for the future decarbonization of end-user energy and raw materials used in the chemical industry is to convert the relatively abundant potential of wind and solar energy, which can be generated in the form of electricity, into heat, chemicals, and fuels. In fact, electrification has the potential to bring about significant progress in improving sustainability and reducing the use of fossil energy and raw materials. Electrifying conventional thermal chemical reactors has the potential to not only reduce CO2 emissions but also provide more flexible and compact heat generation solutions.

[0011] Assuming that electricity costs will decrease and renewable energy will become increasingly available in the future, it would be reasonable to replace the current combustion step that supplies reaction heat within the steam reformer with an electric device, thereby eliminating CO2 emissions from the furnace burner.

[0012] Furthermore, since it is possible to maximize the efficiency of heat exchange, it can help reduce raw material consumption and limit CO2 emissions from the process side. [Overview of the Initiative] [Problems that the invention aims to solve]

[0013] Based on these factors, a reconfiguration of the process architecture will be necessary.

[0014] According to conventional technology, the process architecture of a conventional hydrogen production unit (HPU) with steam reforming of natural gas as a raw material includes the following conventional process steps: (i) Compression of natural gas (not shown) and preheating, (ii) Hydrogenation of olefins and removal of sulfur components (in pretreatment unit 1), (iii) Steam reforming (in combustion-heated steam reforming apparatus 2) (iv) Heat recovery from process stream and flue gas by steam generation and steam heating (not shown), (v) Conversion of carbon monoxide by shift reaction (in water-gas shift reactor 3), (vi) Purification of hydrogen by pressure swing adsorption (in a pressure swing adsorption apparatus or PSA4).

[0015] Between steps (ii) and (iii), a pre-reformation step may be added depending on the hydrocarbon feedstock used.

[0016] Referring to Figure 1, a block diagram of a conventional natural gas hydrogen production unit is shown. Although excess steam is not shown in Figure 1, it is present and will be described below. The natural gas feedstock is supplied under pressure to pretreatment unit 1 to remove compounds that would adversely affect the downstream steam reforming catalyst. Pretreatment unit 1 performs the first hydrogenation step and the second desulfurization step, optionally combined into a single step. Using a CoMox or NiMox catalyst, the first step is carried out in a fixed-bed catalytic reactor to hydrogenate organic sulfur to H2S and organic chlorine components to hydrogen chloride. Olefins present in the feedstock are also hydrogenated in this step.

[0017] The required hydrogen (approximately 3 mol%, a typical value for natural gas feedstocks) is reused from the H2 product stream and / or extracted from hydrogen sources available beyond the plant boundary. The resulting hydrogenated compounds are then sent to a desulfurization step, which typically involves a reaction with a zinc oxide bed equipped with an optional hydrogen chloride adsorbent material for H2S adsorption.

[0018] Next, the processed raw material is mixed with a controlled amount of steam according to a selected steam / carbon molar ratio (S / C = 3 mol / mol, standard value) and preheated to 550°C (standard value) in the convection section of reformer 2.

[0019] The core of this process is the endothermic reaction (Reaction 1) of steam and methane on a Ni catalyst. CH4 + H2O ⇔ CO + 3H2 ΔH0 = +206 kJ / mol (1) The reaction is carried out in a tubular catalytic reactor heated by external fuel combustion in the radiant section of the furnace. Following the main steam reforming reaction, the water gas shift reaction (Reaction 2) converts a portion of the CO produced by the first reaction into additional H2 and CO2. CO + H2O ⇔ CO2 + H2 ΔH0 = -41 kJ / mol (2) The process steam added to the feed exceeds the stoichiometric amount to improve the conversion of hydrocarbons and prevent carbon deposition on the catalyst. To obtain a high hydrogen yield, the reforming temperature is selected in a high range (typically 850 °C to 920 °C). Performing the steam reforming reaction in the heating heater causes the generation of excess heat associated with a decrease in the thermal efficiency of the radiant section. The excess heat is usually recovered in the convection section through high-pressure steam generation.

[0020] In addition to this, an additional steam is generated in the process gas boiler and the process synthesis gas is cooled at the outlet of the steam reformer. Since the total steam generated exceeds the amount required for the process itself, the excess steam amount becomes available at the plant boundary as a by-product. Then, the cooled process gas is fed to the high-temperature shift conversion stage (HTS) at an inlet temperature of about 320 °C.

[0021] The HTS shift reactor 3 is a fixed-bed adiabatic reactor using an iron / chromium / copper oxide catalyst that converts carbon monoxide and steam present in the synthesis gas into additional hydrogen and carbon dioxide according to the water gas shift reaction (Reaction 2). In some cases, an additional low-temperature shift conversion stage (LTS) is installed and carried out downstream.

[0022] The process synthesis gas at the outlet of the shift conversion stage is cooled to about 40 °C through a heat recovery section and a final cooler. Downstream, a device for removing condensed water is installed, from which the synthesis gas is sent to the PSA unit 4 for the purification of raw hydrogen.

[0023] The PSA unit operates through short adsorption / desorption cycles carried out on a selected adsorbent material and operates in parallel vessels at different time stages.

[0024] Hydrogen is released from the PSA unit 4 at a set pressure (e.g., typically about 20 bar g in purification applications). The hydrogen recovery factor of PSA can achieve a value of up to 90%, but the hydrogen balance is released into the off-gas stream along with the impurities present in the raw hydrogen stream and leaves the PSA unit 4 at a low pressure (about 0.3 bar g). The PSA unit 4 can reach a hydrogen purity of up to 99.9999% by volume. The typical hydrogen purity specification in the purification industry is above 99.9%.

[0025] The off-gas recovered from the PSA at approximately atmospheric pressure and containing the generated CO2 and residual hydrogen (an exemplary composition of this stream is 18 mol% CH4, 10.24 mol% CO, 45.10 mol% CO2, 26 mol% H2, 0.55 mol% H2O) is recycled back to the reformer 2 (recycle stream), where the residual hydrogen and CO are combusted with the make-up fuel and the generated flue gas is sent to the chimney.

[0026] Also, carbon dioxide capture and storage (CCS) is also known to be a process that typically removes or reduces the content of CO2 in the stream released to the atmosphere and transports the recovered CO2 to a place for permanent storage. CCS can be applied to a wide range of large-scale single-point sources, such as process streams, heater and boiler exhausts, and exhausts from high CO2 footprint industries including power generation, purification, natural gas processing, chemicals, cement production, and steel production.

[0027] There are three main CO2 capture systems associated with different combustion processes, namely post-combustion, pre-combustion, and oxy-fuel combustion.

[0028] In post-combustion recovery processes, CO2 removal is carried out after combustion has occurred. Flue gases exiting a combustion plant are typically treated with chemical or physical adsorbents to selectively remove CO2 from the gas mixture. This is an end-of-pipe solution where CO2 is removed from the flue gas before it is released into the atmosphere through the chimney.

[0029] The advantage of post-combustion processes is that they are not only suitable for new facilities but can also be used to modify existing plants [SUZANNE FERGUSON and MIKE STOCKLE, Carbon capture options for refiners, PTQ Q2 2012 77].

[0030] The main challenge is that the CO2 concentration in the combustion flue gas is typically quite low, ranging from 5% to 20% by volume, depending on the off-gas content in the mixed fuel gas.

[0031] In pre-combustion recovery processes, the fuel (typically coal or natural gas) is pre-treated before combustion. Specifically, it is generally gasified or reformed into a synthesis gas stream, followed by a water-gas shift reaction and subsequent gas purification to separate the hydrogen produced from CO2. Removing CO2 from the synthesis gas has the advantage of reducing compression energy requirements, primarily related to gas pressure, although the gas purification step is usually achieved using methods similar to those described in the post-combustion process. The hydrogen is used as fuel to be fed into the combustion process, while the CO2 is available in concentrated form for compression, transport, and storage. High concentrations (over 20%) of CO2 in H2 / CO2 fuel gas mixtures facilitate CO2 separation [ST Wismann, JS Engbaek, SB Vendelbo, FBB Endixen, WLE Riksen, K. Aasberg-Petersen, C. Frandsen, I. Chorkendorff, PMMortesen, Electrified methane reforming: A compact approach to greener industrial hydrogen production, Science, 2019, 364, 756-759].

[0032] In oxygen fuel combustion, oxygen is used for combustion instead of air. This reduces the amount of nitrogen present in the exhaust gas, which affects subsequent separation processes. The main components of flue gas are CO2, water, particulate matter, and SO2. After the removal of particulate matter, SO2, and water, the remaining gas contains a high concentration of CO2, approximately 80-98% (depending on the fuel used).

[0033] Both pre-combustion and post-combustion technologies for CO2 capture can be applied to steam reforming plants.

[0034] Pre-combustion technology is applied to the synthesis gas stream coming out of the water-gas shift reactor, while post-combustion technology is applied to the flue gas from the furnace.

[0035] However, in the first case, only the CO2 generated from the process is recovered, and in the second case, all CO2 can be recovered, but the cost of such an option is higher considering that the partial pressure of CO2 in flue gas is lower than that of CO2 in synthesis gas. Furthermore, since flue gas is available at near atmospheric pressure, a large-scale CO2 recovery system is required, further increasing the cost of such an option.

[0036] Electro-steam reforming has been extensively studied in recent years. In this regard, Haldor Topsoe recently published the results of a collaborative study conducted in cooperation with the Technical University of Denmark, which involves applying electricity to catalyst-coated tubes for steam reforming reactions [ST Wismann, JS Engbaek, SB Vendelbo, FBB Endixen, WLE Riksen, K. Aasberg-Petersen, C. Frandsen, I. Chorkendorff, PMMortesen, Electrified methane reforming: A compact approach to greener industrial hydrogen production, Science, 2019, 364, 756-759]. Experimental and model studies are underway to verify the performance of the proposed solution. Initial results indicate that close contact between the electric heat source and the reaction site can bring the reaction closer to thermal equilibrium, increase catalyst utilization, limit the formation of undesirable byproducts, and further reduce the size of current reformer platforms by an order of magnitude.

[0037] Considering all of the above, it is clear that there is a need to reduce or eliminate the CO2 emissions associated with producing hydrogen from hydrocarbons, particularly natural gas.

[0038] In connection with this, and considering that government regulations are increasingly pressuring the industry to reduce CO2 emissions, the present invention proposes a solution that, instead of the combustion step that supplies reaction heat in conventional steam reforming equipment, employs a step in which heat is supplied by an electrical device, thereby maximizing heat exchange efficiency and improving the conversion of natural gas to H2, reducing natural gas raw material consumption, and thus limiting CO2 emissions from the process side.

[0039] In this regard, as a solution according to the present invention, we propose to provide a hydrogen production method linked to CO2 capture, based on the combination of an electric steam reformer and CO2 capture technology, in order to simultaneously generate a CO2 stream and a hydrogen stream with minimal CO2 emissions.

[0040] Furthermore, according to the present invention, the generated CO2 stream can create value through downstream use.

[0041] In particular, the hydrogen production method linked to CO2 capture according to the present invention includes using an electric steam reformer instead of a combustion-heated steam reformer in order to maximize the efficiency of heat exchange, improve the conversion from natural gas to H2, and eliminate the generation of CO2 associated with fuel combustion.

[0042] The hydrogen production method linked to CO2 capture according to the present invention is based on an innovative proposal that allows the stream obtained after separation of hydrogen products to be reused as feed by replacing a conventional combustion-heated steam reformer with an electric-heated steam reformer. If the amount of feed does not match the required purity of the hydrogen produced, it is necessary to purge only a small amount to avoid the accumulation of inert components in the system.

[0043] Therefore, the present invention aims to provide a hydrogen production method linked to CO2 capture that overcomes the limitations of conventional solutions and enables the achievement of the aforementioned technical results.

[0044] A further objective of the present invention is to enable the hydrogen production method, which is linked to CO2 capture, to be realized at substantially limited costs.

[0045] Although not the ultimate goal of this invention, we propose a hydrogen production method linked to CO2 capture that is substantially simple and reliable, and in particular has a low risk of explosion associated with combustion. [Means for solving the problem]

[0046] Therefore, the first specific object of the present invention is a method for producing hydrogen, - A synthesis gas production system comprising an electric steam reformer, a water-gas shift reactor, and a hydrogen separation unit, preferably a pressure swing adsorption unit, is supplied with a raw hydrocarbon feed, such as natural gas or biogas or another raw hydrocarbon feed. - A step of reacting the hydrocarbon feed with steam in the electric steam reformer to produce synthesis gas containing hydrogen, CO, and CO2, - The steps of shifting the synthesis gas in the water-gas shift reactor to form a hydrogen-enriched synthesis gas containing hydrogen and CO2 (as well as unconverted methane and water), - In the pressure swing adsorption unit that provides a hydrogen product stream and a recirculation stream, the steps include separating the hydrogen from the synthesis gas, - The step of compressing the recirculation stream and supplying it to the electric steam reformer, A method for producing hydrogen, comprising the step of removing CO2 from the process.

[0047] In particular, according to the present invention, the synthesis gas production system includes a desulfurization unit upstream of the electric steam reformer, in which sulfur, chlorides, and olefins are removed from the hydrocarbon feed.

[0048] In particular, according to the present invention, at least part or all of the recirculation stream is supplied to the desulfurization unit.

[0049] Alternatively, according to the present invention, CO2 is removed from the hydrogen-enriched synthesis gas containing hydrogen and CO2, or from the compressed recirculation stream, or both.

[0050] Furthermore, according to the present invention, a portion of the recirculation stream is purged intermittently or continuously, and in particular, 7 volume% or less of the recirculation stream is purged, preferably 0.1 to 5 volume% of the recirculation stream is purged, and most preferably about 2 volume% of the recirculation stream is purged.

[0051] Furthermore, according to the present invention, in the step of reacting a hydrocarbon feed with steam after adding a compressed recirculation stream, the steam-to-carbon ratio is set to 2.8 to 3.

[0052] In particular, according to the present invention, the electricity supplied to the above-mentioned electro-steam reforming is obtained from renewable resources, such as solar, wind, or hydroelectric power.

[0053] Finally, a further specific object of the present invention is a plant for producing hydrogen from a hydrocarbon feed, comprising an electrically driven steam reformer and at least one CO2 recovery system located downstream of the electrically driven steam reformer. [Brief explanation of the drawing]

[0054] The present invention is disclosed below illustratively, particularly with reference to the drawings of the appended drawings, in accordance with preferred embodiments, but is not intended to limit the invention. [Figure 1] -Figure 1 shows a block diagram of a conventional natural gas hydrogen production unit. [Figure 2] -Figure 2 shows a block diagram of a hydrogen production plant linked to CO2 recovery according to the first embodiment of the method of the present invention. [Figure 3] -Figure 3 shows a block diagram of a hydrogen production plant linked to CO2 recovery according to a second embodiment of the method of the present invention. [Figure 4]-Figure 4 shows a block diagram of a hydrogen production plant linked to CO2 recovery according to a third embodiment of the method of the present invention. [Modes for carrying out the invention]

[0055] The hydrogen production method linked to CO2 capture proposed in this invention can be realized according to three different configurations.

[0056] Referring to Figure 2, a block diagram of a hydrogen production plant linked to CO2 recovery according to the first embodiment of the method of the present invention, based on electro-steam reforming and CO2 recovery, is shown.

[0057] In particular, the hydrogen production method linked to CO2 recovery according to this embodiment consists of the steps of mixing a natural gas (NG) feedstock with a recirculation stream generated from a pressure swing adsorption (PSA) unit 14, heating it to 380°C, and transporting it to a pretreatment unit 10 where sulfur, chloride, and olefins are removed. The purified process stream is then mixed with steam at a preferred steam-to-carbon ratio of 2.8 to 3. The ratio of 2.8 is optimized to achieve zero steam emissions. The steam-to-carbon ratio can be further reduced depending on whether a catalyst capable of working at a lower steam-to-carbon ratio without losing activity is available.

[0058] Next, the stream is preheated to 550°C through a heat exchanger (not shown). The heat exchanger preferably uses a reforming stream, with a temperature of 850°C to 900°C, as the heat exchange fluid to heat the process stream. The heat from the reforming stream can also be used in a different heat exchanger to generate the steam required for the reforming reaction. Alternatively, a standalone heater, such as an electric heater or a gas heater, can be used. In particular, it is preferable to use an electric heater to remove CO2 emissions associated with fuel combustion. Alternatively, to reduce power consumption, an electric heater can be used instead of a gas heating step carried out by burning air and some natural gas. The resulting flue gas is sent to a chimney. This solution is not compact. However, although it has a greater impact in terms of CO2 emissions, it offers greater system independence from the possibility of utilizing electricity generated from renewable raw materials.

[0059] Next, the preheated stream is sent to the steam reformer 11 at a temperature that protects the catalyst in the steam reformer 11 and allows it to enter the catalyst bed of the steam reformer 11, which has already exceeded the threshold catalyst temperature.

[0060] Along the catalyst bed, a temperature profile is established that depends on both the endothermic nature of the reaction and the heat provided by the electric heat source, achieving a temperature in the range of 850°C to 900°C at the outlet of the catalyst bed.

[0061] In some plant configurations, when heavy raw materials are primarily used, a pre-reforming step can be provided upstream of the steam reformer 11. In this additional step, preliminary reforming occurs at a lower temperature.

[0062] Next, the reforming stream is cooled, and the heat from the reforming stream is preferably at least partially recovered as described above to generate steam or preheat the process stream upstream of the reformer 11. The outlet stream is then sent to the water-gas shift reactor 12 at high or medium temperature, preferably 340°C, depending on the available heat, where a certain conversion from CO to CO2 is achieved.

[0063] The water-gas shift conversion can be performed at high temperatures (water-gas shift inlet temperature of approximately 320°C to 350°C) or medium temperatures (water-gas shift inlet temperature of approximately 250°C to 280°C), depending on the heat recovery in the overall process.

[0064] The process stream generated from the water-gas shift reactor 12, which is rich in H2 and CO2, is cooled by a series of heat exchangers (not shown) to recover heat. It is then sent to a CO2 recovery unit 13 (i.e., amines, membrane separation, cryogenics, adsorption systems, and combinations thereof) where the CO2 is separated and a pure CO2 stream is collected, ultimately generating value.

[0065] Finally, the H2-rich gas is sent to the PSA system 14 for purification, while the off-gas or recirculation stream is compressed in the compressor 15 and reused at the front of the plant. The purge gas is split (in order of total 2-3%) to separate it from the main recirculation stream and control the amount of N2 or other inert substances present in the natural gas to prevent accumulation in the recirculation stream.

[0066] Referring to Figure 3, in the alternative hydrogen production plant linked to CO2 recovery according to the second embodiment of the method of the present invention, the CO2 recovery step is provided in the recovery and compression recirculation stream from the PSA.

[0067] In this alternative configuration, the process stream generated from the water-gas shift reactor 12 is sent to the PSA system 14 for purification after heat recovery, while the off-gas or recirculation stream is compressed by the compressor 15 and then sent to the CO2 recovery unit 13' where CO2 is separated (compression and CO2 separation can also be integrated into a single unit), a pure CO2 stream is collected, and the remaining stream is reused at the front of the plant after an optional purge of approximately 2-3% by weight.

[0068] Finally, in a third embodiment of the method of the present invention, a hydrogen production plant linked to CO2 capture is shown in Figure 4, in which two CO2 capture units are provided both downstream of the water-gas shift reactor 12 and on the recirculation stream of the PSA unit 14.

[0069] The hydrogen production method linked to CO2 capture according to the present invention overcomes the disadvantages of conventional technologies based on the linkage of conventional combustion-type heating reformers and CO2 capture, in the following respects. - Because the amount of CO2 produced is inherently low, this parameter can be reduced by up to 45%. - CO2 capture is performed on a process stream where higher concentrations of CO2 are present, resulting in high CO2 capture efficiency. - High CO2 capture efficiency reduces the total amount of CO2 released into the atmosphere (the amount that is not captured).

[0070] The hydrogen production method linked to CO2 capture according to the present invention avoids CO2 generation by generating the electricity required to operate the electric steam reformer from renewable resources. However, in short-term scenarios of energy transitions, the availability of renewable energy may not fully satisfy the hydrogen market based on such technology. To enable the reduction of CO2 emissions, the break-even point for the hydrogen production method linked to CO2 capture according to the present invention was calculated based on the premise that up to 30-40% of the electricity is supplied from fossil / coal, with the remainder supplied from renewable energy, in order to equalize the CO2 emissions of the combustion-type and electric-type thermal reformers. Example 1 Using the hydrogen production method linked to CO2 capture according to the present invention, natural gas feedstocks were processed with the compositions shown in Table 1. [Table 1]

[0071] The main technical results achieved by the hydrogen production method linked to CO2 capture according to the present invention are shown in Table 2, evaluated by treating natural gas according to the embodiment disclosed with reference to Figure 2, assuming two different levels of CO2 removal efficiency, compared with a conventional combustion-heated steam reforming apparatus. [Table 2]

[0072] SR stands for steam reformer.

[0073] WGS stands for Water-Gas Shift Reactor.

[0074] BL represents the plant boundary. (*) Any consumption utility of the CO2 removal step is not considered (if electricity or natural gas consumption is required to perform the CO2 capture step). (**) Remaining portion in purge gas (***) Because CO2 is reused at the front of the plant, the percentage of CO2 recovered is higher than the stated recovery efficiency (70%).

[0075] The efficiency of hydrogen production is calculated as: Feed (LHV) + Fuel (LHV) / Hydrogen Products (Nm³) 3 It is calculated as follows, and LHV represents the low heating value. Example 2 The technical results achieved by the hydrogen production method linked to CO2 capture according to the present invention were evaluated by processing the same natural gas as in the above-mentioned examples, using the embodiment disclosed with reference to Figure 3, compared with a conventional combustion-heated steam reformer. These results are shown in Table 3, assuming two different levels of CO2 removal efficiency, as in the above-mentioned examples. (See Table 3) [Table 3]

[0076] SR stands for steam reformer.

[0077] WGS stands for Water-Gas Shift Reactor.

[0078] BL represents the plant boundary. (*) Any consumption utility of the CO2 removal step is not considered (if electricity or natural gas consumption is required to perform the CO2 capture step). (***) Because CO2 is reused at the front of the plant, the percentage of CO2 recovered is higher than the stated recovery efficiency (70%).

[0079] The efficiency of hydrogen production is calculated as: Feed (LHV) + Fuel (LHV) / Hydrogen Products (Nm³) 3 It is calculated as follows, and LHV represents the low heating value. Example 3 The technical results achieved by the hydrogen production method linked to CO2 recovery according to the present invention were evaluated by processing the same natural gas as in the above-mentioned examples, according to the embodiment disclosed with reference to Figure 4, compared with a conventional combustion-heated steam reformer. These results are shown in Table 4, assuming that the CO2 removal efficiency in the CO2 recovery unit 13 located downstream of the water-gas shift reactor is 70% and the CO2 removal efficiency in the CO2 recovery unit 13' located in the purge gas stream is 80%. [Table 4]

[0080] SR represents a steam reformer.

[0081] WGS represents a water gas shift reactor.

[0082] B.L. represents the plant boundary line. (*) Do not consider any consumption utility of the CO2 removal step (if power or natural gas consumption is required for the execution of the CO2 recovery step) (***) Since CO2 is reused at the front end of the plant, the recovered CO2 (%) is higher than the indicated recovery efficiency (70%).

[0083] The efficiency to hydrogen is calculated as Feed (LHV) + Fuel (LHV) / Hydrogen Product (Nm 3 ), and LHV represents the lower heating value.

[0084] Regardless of the installation type of the CO2 recovery unit, the hydrogen production method in cooperation with CO2 recovery according to the present invention enables a reduction of CO2 emissions up to 45%.

[0085] Referring to the fact that inert components (such as nitrogen) may be contained in natural gas, it is necessary to describe the important technical highlights.

[0086] One of the specific aspects of the hydrogen production method in cooperation with CO2 recovery according to the present invention is that, regardless of the embodiment, when a compression step is applied, the off-gas generated from PSA can be directly reused in the supply section, thereby reducing the amount of necessary makeup water. In a conventional combustion type heat reformer, this solution is not applied. The reason is that in the latter case, due to the presence of at least one burner, from a technical perspective, it is more convenient to return the off-gas from PSA to the fuel section for reuse, thereby reducing the amount of necessary makeup fuel and avoiding the recompression step of the off-gas generated from PSA.

[0087] The main advantages of the hydrogen production method linked to CO2 capture according to the present invention are highlighted below. - Compared to a combustion-heated steam reforming system, the amount of CO2 produced is reduced. -When biogas is used as a feedstock, the entire system will have a completely negative carbon load because biogas is a renewable raw material. - Reduce raw material consumption. - Eliminate fuel consumption. - A chimney is not needed. - Higher efficiency (LHV basis). - Reduce noise. - Reduce the size of the steam reforming reactor. - The feed from the PSA can be fully recovered and, instead of being burned in the furnace, reused and mixed with makeup water. - No steam is emitted as long as the steam-to-carbon ratio is maintained within the preferred range of 2.8 to 3.

[0088] Furthermore, as electricity is inexpensive and increasingly supplied from renewable resources, the advantages of the hydrogen production method linked to CO2 capture according to the present invention will increase over time.

[0089] Furthermore, according to the first embodiment described above, the process stream upstream of the reformer 11 is also preheated by an electric heater, and the hydrogen production method linked to CO2 recovery according to the present invention also includes the following advantages. - The fact that there is no need for a convection section to recover heat from the flue gas basically means that a chimney gas duct is not needed. - No combustion air supply system is required.

[0090] Referring to the embodiments shown in Figures 2 and 4, CO2 recovery during pre-combustion allows for an increase in the hydrogen partial pressure upstream of the PSA. Therefore, the PSA can be smaller in size.

[0091] Another advantage of the hydrogen production method linked to CO2 capture according to the present invention is that it avoids the need to reuse and return a portion of the hydrogen from the plant boundary to carry out the desulfurization step. In fact, the amount of hydrogen required for such a step is already contained in the recirculation stream generated from the PSA. However, according to the proposed solution, it can also work with a recirculation stream routed directly from the PSA to the electro-steam reformer. In this last case, hydrogen from the plant boundary is required to enable the hydrodesulfurization of the hydrocarbon feedstock.

[0092] Another advantage of the hydrogen production method linked to CO2 capture according to the present invention is that it may not release pollutants into the atmosphere. This last advantage depends on the end use of the segmented purge gas generated from the recirculation stream (PSA off-gas). If it is sent to a flare, it will cause the emission of pollutants. On the other hand, if it can be used to create value, the environmental impact can be reduced.

[0093] Even if purge gas is sent to the flare, the overall CO2 emissions are significantly lower (approximately 90%) than those of conventional combustion-type heat reformers that integrate CO2 capture.

[0094] Another advantage is that, depending on the plant capacity and the type of shift reactor used, all the heat required to perform additional services such as steam generation and feedstock preheating can be generated by heat recovery from the process stream.

[0095] The present invention is disclosed for illustrative and non-limiting purposes in its preferred embodiments, but it should be understood that any modifications and / or alterations may be made by those skilled in the art without escaping from the claims set forth herein.

Claims

1. The steps include: reacting a hydrocarbon feedstock added to a compressed recirculation stream with steam in an electrically driven steam reformer to obtain a gas stream containing hydrogen, carbon monoxide, and carbon dioxide (synthesis gas); The steps include: reacting the carbon monoxide from the gas stream obtained from the above step with vapor in a water-gas shift reactor to obtain a gas stream enriched with hydrogen and carbon dioxide; In a pressure swing adsorption apparatus, the steps include separating hydrogen from the enriched gas stream to obtain a hydrogen product stream and a recirculation stream, The steps include compressing the recirculation stream in a compressor to obtain a compressed recirculation stream, Upstream of the electrically driven steam reformer, the step of mixing the compressed recirculation stream and the hydrocarbon feed is performed. A method for producing hydrogen starting from a hydrocarbon feed, including, In the step of reacting the hydrocarbon feed with water vapor, heat obtained from a power source is provided. And any of the following a) to c): a) Before separating hydrogen, in the CO2 recovery system, ２ To remove hydrogen and carbon dioxide from the gas stream enriched with these, b) Before mixing with the hydrocarbon feed, the CO2 recovery system removes CO2 from the compressed recirculation stream. ２ To remove, c) Before separating hydrogen, in the CO2 recovery system, hydrogen and carbon dioxide are extracted from the gas stream enriched with CO2. ２ Before removing and mixing with the hydrocarbon feed, the CO2 recovery system removes CO2 from the compressed recirculation stream. ２ To remove, Includes, A method for producing hydrogen, comprising purging a portion of a recirculation stream intermittently or continuously to form a purge gas stream, and removing at least some inert components from the recirculation stream.

2. A method for producing hydrogen according to claim 1, comprising the step of removing sulfur, chloride, and olefin from the hydrocarbon feed to which a compressed recirculation stream has been added before reacting with steam.

3. The hydrogen production method according to claim 1, wherein in the step of reacting the hydrocarbon feed to which the compressed recirculation stream has been added with the vapor, the vapor-to-carbon molar ratio is 2.8 to 3.

4. The hydrogen production method according to claim 1, wherein the electricity supplied to the electro-steam reforming is obtained from renewable resources.

5. The hydrogen production method according to claim 4, wherein the renewable resource includes at least one of solar, wind, or hydropower.

6. The hydrogen production method according to claim 1, wherein 7 volume percent or less of the recirculation stream is purged.

7. The hydrogen production method according to claim 6, wherein 0.1 to 5 volume percent of the recirculation stream is purged.

8. The hydrogen production method according to claim 7, wherein 2 volume percent of the recirculation stream is purged.

9. CO ２ A hydrogen production method according to claim 1, which removes [the substance].

10. The hydrogen production method according to claim 9, wherein 7 volume percent or less of the recirculation stream is purged.

11. The hydrogen production method according to claim 10, wherein 0.1 to 5 volume percent of the recirculation stream is purged.

12. The hydrogen production method according to claim 10, wherein 2 volume percent of the recirculation stream is purged.

13. A method for producing hydrogen according to any one of claims 1 to 12, Before separating the hydrogen, the gas stream enriched with hydrogen and carbon dioxide is used to remove CO ２ When removing the hydrocarbon feed, the composition of the recirculation stream before mixing with the hydrocarbon feed is CH ４ : 14.5–15.5% by volume CO ２ : 0.5 to 1.0 volume% N ２ : 34.5 to 35.5% by volume CO: 15.5–16.5% by volume H ２ : 31.5–32.5% by volume H ２ O: 1.0 to 1.5 volume percent. Methods for producing hydrogen.

14. A method for producing hydrogen according to any one of claims 1 to 12, Before mixing with the hydrocarbon feed, CO from the compressed recirculation stream ２ When removing the hydrocarbon feed, the composition of the recirculation stream before mixing with the hydrocarbon feed is CH ４ : 11.5–12.5% ​​by volume CO ２ : 13.0–14.0% by volume N ２ : 29.0–30.5% by volume CO: 16.0–17.0% by volume H ２ : 26.5–27.5% by volume H ２ O: 1.0 to 1.5 volume percent. Methods for producing hydrogen.

15. The hydrogen production method according to claim 14, wherein the composition of the recirculation stream before mixing with the hydrocarbon feed is as follows: CH4 12.04 vol%, CO2 13.64 vol%, N2 29.56 vol%, CO 16.54 vol%, H2 27.06 vol%, H2O 1.15 vol%.

16. A method for producing hydrogen according to any one of claims 1 to 12, Before separating the hydrogen, the gas stream enriched with hydrogen and carbon dioxide is used to remove CO ２ Remove CO from the compressed recirculation stream before mixing it with the hydrocarbon feed. ２ When removing the hydrocarbon feed, the composition of the recirculation stream before mixing with the hydrocarbon feed is CH ４ : 12.0–13.0% by volume CO ２ : 0.5 to 1.5% by volume N ２ : 31.0–32.0% by volume CO: 14.5–15.0% by volume H ２ : 38.5–39.5% by volume H ２ O: 1.0–1.5% by volume That is, Methods for producing hydrogen.

17. A plant for producing hydrogen starting from hydrocarbon feed, Electrically driven steam reforming unit, A water-gas shift reactor downstream of the aforementioned electrically driven steam reforming apparatus, A pressure swing adsorption unit downstream of the aforementioned water-gas shift reactor, A hydrogen product streamline and an off-gas streamline downstream of the pressure swing adsorption unit, A recirculation streamline connecting the off-gas streamline to the hydrocarbon feed, Recirculation stream compressor and At least one CO2 located downstream of the electrically driven steam reformer ２ Collection system and Splitting of purge gas separated from the recirculation streamline, A hydrogen production plant equipped with [the necessary components].

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