Systems and processes for producing synthesis gas

Abstract

1. A system for producing a synthesis gas having a reduced hydrogen / CO ratio, the system comprising: a reforming reactor (5) configured to react a hydrocarbon feed (1) with an oxidant gas stream (4) to thereby produce a reformer effluent comprising a synthesis gas stream; and a reverse water gas shift reactor (17) configured to receive a CO2-rich stream, an H2-rich stream, and the reformer effluent and produce a synthesis gas having a reduced hydrogen / CO ratio, the reverse water gas shift reactor comprising: a vessel including: at least one catalyst tube configured to receive the H2-rich stream and the CO2-rich stream and produce a shift effluent enriched in CO and HO; a heat transfer zone configured to receive the reformer effluent and transfer heat of the pre-reformer effluent to the pre-catalyst tube; and means configured to mix the shift effluent with the reformer effluent to produce a synthesis gas having a reduced hydrogen / CO ratio.

Description

[Technical Field]

[0001] The present invention relates to a system and process aimed at producing synthesis gas having a hydrogen / CO ratio of 3.0 or less, preferably less than 2.0. [Background technology]

[0002] Syngas, a mixture of hydrogen and carbon monoxide, is an important building block for a wide range of chemicals and fuels produced in downstream synthesis units. Such products include, but are not limited to, synthetic fuels, waxes, alcohols (e.g., methanol and ethanol), and base chemicals for polymer production. Depending on the downstream synthesis, the H2 / CO ratio varies. For example, in Fischer-Tropsch synthesis, depending on the product and catalyst type, the optimal H2 / CO ratio can be as low as 0.6 for iron-based catalysts or 1.8-2.1 for cobalt-based catalysts.

[0003] Syngas is traditionally produced by reforming fossil hydrocarbons such as natural gas, LPG, or naphtha. The hydrocarbon feedstock is pretreated to remove impurities before steam is added to the feedstock. The steam / hydrocarbon mixture is further heated to the inlet temperature of the reforming section. In the reforming section, the hydrocarbon and steam mixture reacts to form a syngas mixture containing hydrogen, carbon monoxide, carbon dioxide, unreacted steam, and small amounts of unconverted methane, as well as some inerts, such as nitrogen, if present. Because the reaction is endothermic, the conversion of the hydrocarbons is facilitated by a high outlet temperature, preferably at least 800°C or higher. The process gas is cooled, and optionally, one or more shift reactors are present to convert CO with H2O to CO2 and H2 to increase the H2 / CO ratio of the syngas. Condensed water is removed from the process gas, and CO2 is captured to form a CO2-depleted process gas. Depending on the desired product quality and composition, further separation steps may be included.

[0004] Further details of various processes for producing synthesis gas with low H2 / CO ratios can be found in "Industrial scale experience on steam reforming of CO2-rich gas", P.M. Mortensen & I. Dybkjasr, Applied Catalysis A: General, 495 (2015), 141-151.

[0005] The terms "reforming" and "methane reforming" refer to the reaction: CH4 + H20 <CO+3H2(i) CH4+2H20 <C02+4H2(ii) CH4+C02<2CO+2H2(iii) The term "reformation reaction" is intended to refer to a reforming reaction by one or more of the following:

[0006] Reactions (i) and (ii) are steam methane reforming reactions, and reaction (iii) is a dry methane reforming reaction.

[0007] For higher hydrocarbons, i.e., CnHm (n≧2, m≧4), equation (i) is generalized to: CnHm+nH2O->nCO+(n+m / 2)H2(iv), In the formula, n≧2 and m≧4.

[0008] Typically, the reforming involves the water gas shift reaction (v) below: CO+H20 <C02+H2(V)

[0009] The term "steam methane reforming" is intended to encompass reactions (i) and (ii) (i.e., methane conversion) proceeding from the left to the right of the arrow, while the term "methanation" is intended to encompass reactions (i) and / or (ii) (i.e., methane formation) proceeding from the right to the left of the arrow. Thus, the term "steam methane reforming / methanation reaction" is intended to refer to reactions (i) and (ii) proceeding toward equilibrium. The term "reverse water gas shift" is intended to refer to reaction (v) proceeding from the right to the left of the arrow. In most cases, all of these reactions are at or near equilibrium at the outlet from the catalyst bed or catalyst zone of the associated reactor.

[0010] Processes based on autothermal reforming (ATR) are an alternative route for the production of synthesis gas, especially when low hydrogen-to-carbon monoxide ratios are required. The main elements of an ATR reactor are a burner, a combustion chamber, and a catalyst bed contained within a refractory-lined pressure shell. Within the ATR reactor, partial combustion of the hydrocarbon feed with less than stoichiometric amounts of oxygen is followed by steam reforming of the partially burned hydrocarbon feed stream over a fixed bed of steam reforming catalyst. Steam reforming also occurs to some extent within the combustion chamber due to the high temperatures. The steam reforming reaction is accompanied by a water-gas shift reaction. Typically, the gas is at or near equilibrium with the steam reforming and water-gas shift reactions at the reactor outlet. The temperature of the outlet gas is typically in the range of 850–1100°C. Further details and a complete description of ATR can be found in the art, such as in "Studies in Surface Science and Catalysis, Vol. 152," "Synthesis gas production for FT synthesis," Chapter 4, pp. 258-352, 2004.

[0011] ATR uses oxygen and steam, and optionally carbon dioxide, in a reaction with the hydrocarbon feed stream to form synthesis gas. The ratio of hydrogen to carbon monoxide in the outlet gas depends on the selected operating conditions, including the hydrocarbon feed stream and / or the amount of steam and carbon dioxide added to the ATR reactor. The reforming section can include a pre-reformer, a steam methane reformer, an autothermal reformer, or any combination thereof. For all reforming options, increasing the amount of carbon dioxide reduces the hydrogen to carbon monoxide ratio in the product gas, but increases the reactor size for higher flow rates, as well as increasing the risk of carbon formation (thus typically requiring increased steam to carbon flow rates).

[0012] It is an object of the present invention to provide a process and system for producing synthesis gas having a predetermined H / CO ratio. It is also an object of the present invention to provide a process and system for producing synthesis gas having a low H / CO ratio, preferably without generating excess heat, i.e., by maximizing the available amount to minimize energy input to the unit. In one object of the present invention, the reforming section includes a steam reforming unit, in which case the system and process require a reduced combustion load input. It is also an object of the present invention to provide a system and process for producing synthesis gas, in which the reforming reactor is an ATR reactor, and the system and process have lower oxygen consumption and the size of the ATR reactor is reduced. It is also an object of the present invention to provide a process and system that provides high CO production from a reforming plant. It is a further object of the present invention to provide a process and system that is useful as a retrofit of existing processes and systems when it is necessary to change the composition of the product gas stream to produce more carbon monoxide from the existing processes and systems, or to increase carbon monoxide production capacity.

[0013] It is an object of the present invention to provide a system for producing synthesis gas with higher CO content and greater flexibility in H2 / CO.

[0014] The solution of the present invention is a system for producing synthesis gas containing a reduced hydrogen / CO ratio, the system comprising: a reforming reactor 5 configured to react the hydrocarbon feed 1 with an oxidant gas stream 4, thereby producing a reformer effluent comprising a synthesis gas stream; a reverse water gas shift reactor 17 configured to receive the CO2-rich stream, the H2-rich stream and the reformer effluent and to produce a synthesis gas having a reduced hydrogen / CO ratio; The reverse water gas shift reactor is at least one catalyst tube configured to receive the H-rich stream and the CO-rich stream and to produce a shift effluent enriched in CO and HO; a heat transfer zone configured to receive the reformer effluent and transfer heat from the reformer effluent to the catalyst tubes; and means configured to mix the shift effluent with the reformer effluent to produce a synthesis gas having a reduced hydrogen / CO ratio.

[0015] The term "reforming reactor" is meant to refer to a synthesis gas production reactor, such as a steam methane reforming reactor, a pre-reforming reactor, a dry reforming reactor, an autothermal reforming reactor, or a combination thereof.

[0016] The term "synthesis gas" is meant to encompass a gas containing at least hydrogen and carbon monoxide, but may also include carbon dioxide, methane and water vapor, and possibly small amounts of other gases such as argon, nitrogen, etc.

[0017] In one embodiment, the reforming reactor is an ATR reactor. The ATR reactor includes a burner, a combustion chamber, and a bed of a first catalyst housed within a refractory-lined pressure shell. In another embodiment, the reforming reactor is a steam methane reforming reactor. The steam methane reforming reactor includes multiple tubes containing a first catalyst within a furnace having a burner.

[0018] The product gas stream is a synthesis gas having a reduced hydrogen / CO ratio. The term "reduced" is used relative to the synthesis gas contained in the reformer effluent. Preferably, the product gas stream is a synthesis gas containing an H2 / CO ratio of less than 3.0, preferably less than 2.0, more preferably less than 1.8, even more preferably less than 1.6, and most preferably less than 1.4.

[0019] The temperature of the reformer effluent is comprised between 500 and 1100°C, more preferably between 800 and 1100°C. The reformer effluent thus provides heat for the reverse water gas shift reaction and heats the gas to the required outlet temperature (preferably above 750°C). The CO2-rich gas and the hydrogen-rich gas are mixed upstream and preheated to the required inlet temperature (preferably above 400°C, more preferably between 600 and 700°C) before entering the catalyst tubes of the reverse water gas shift reactor. Preheating can be achieved by an external heat exchanger, an electric heater, or a combustion heater, or by applying a heat transfer-enhancing non-catalytic insert above the catalyst bed in the catalyst tubes inside the reverse water gas shift reactor. The preheated CO2-H2 mixture is fed through the catalyst bed in the catalyst tubes.

[0020] The catalyst is high temperature resistant and active at least for the reverse water gas shift reaction, and typically also for methanation, although this is preferably minimized. The catalyst is typically nickel-based for its thermal stability and availability. Alternatively, noble metal catalysts or iron and / or copper-based catalysts can be applied.

[0021] Depending on the embodiment, the system according to the invention may include one or more of the following features. the ends of the catalyst tubes are open in the heat transfer zone and mixing means configured to mix the shift effluent with the reformer effluent are arranged in the heat transfer zone of the vessel, this first configuration being referred to as "Option A". - the ends of the catalyst tubes are contained within a vessel and open into a zone fluidly isolated from the heat transfer zone, and the means for mixing the shift effluent with the reformer effluent is located at the reverse water gas shift reactor outlet; this second configuration is referred to as "Option B." the system comprises a CO2 capture unit 7 configured to receive a synthesis gas having a reduced hydrogen / CO ratio and to produce a CO2 stream and a synthesis gas that is CO2-depleted and has a reduced hydrogen / CO ratio, preferably the catalyst tubes are configured to receive a CO2 stream that comes at least in part from the CO2 capture unit 7. the system comprises a gas separator 9 configured to receive a synthesis gas stream having a reduced hydrogen / CO ratio and to produce an H2-rich stream and a synthesis gas or CO stream, the catalyst tubes of the reverse gas shift reactor being configured to receive at least a portion of this H2-rich stream coming from the gas separator 9. The system is equipped with an external hydrogen source, and the catalyst tubes of the reverse gas shift reactor receive the H2-rich stream coming from the gas separator and hydrogen coming from the external hydrogen source. The upper part of the catalyst tube is filled with a catalytically inactive heat transfer promoting component. The system includes a hydrocarbon feed purification section 3 upstream of the reforming reactor. The system includes means for mixing the hydrocarbon feed with the oxidant stream upstream of the reforming reactor, where "mixing means" means, for example, a mixing tee. The CO2 capture unit is selected from an amine adsorption unit, a carbonate solution adsorption unit, a cryogenic unit, a membrane unit, an electrochemical compression, a temperature swing adsorption or a pressure swing adsorption unit. The reforming reactor comprises one or a combination of the following reforming units: a pre-reformer, a steam methane reformer, a dry methane reformer, an autothermal reformer or a partial oxidation. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 shows schematic diagrams of two configurations of a reverse water gas shift reactor. [Figure 2] FIG. 1 illustrates a process according to the present invention, including optional features.

[0023] FIG. 1 shows two schematic configurations of a reverse water gas shift reactor (Option A and Option B). A preheated mixture of CO-rich and H-rich streams (M) enters the catalyst tubes at a minimum of 400°C, preferably above 600°C, and more preferably above 650°C to minimize the risk of methane and carbon formation. If the upper portion of the catalyst tube is utilized as a heat transfer enhancement zone without a catalytically active material (HZP), the inlet temperature may be a lower minimum ambient temperature, and the heat transfer enhancement zone is sized such that the catalyst bed inlet temperature is at least 400°C, preferably above 600°C, or more preferably above 650°C. The catalytic zone (CZP) contained within the catalyst tube reacts CO with H to form CO and HO following the reverse water gas shift reaction. As a by-product, some methane is formed by the methanation reaction. The catalyst bed (shift effluent) outlet temperature should be at least 500°C, more preferably above 750°C, and / or preferably above 850°C, or typically below 1000°C, to maximize CO2 conversion and minimize methane formation. In Option A, the ends of the catalyst tubes are open in the heat transfer zone, and a means for mixing the CO2- and HO-rich shift effluent with the reformer effluent is located in the heat transfer zone. By "means for mixing the C2 shift effluent with the reformer effluent," we mean a mixing volume within the reverse water gas shift reactor, below the catalyst tube outlet and at the reformer effluent inlet. Thus, a synthesis gas with a reduced hydrogen / CO2 ratio is formed in the heat transfer zone (HTZ). The temperature of the synthesis gas with a reduced hydrogen / CO2 ratio is 400-900°C at the outlet of the heat transfer zone. It then exits the reactor (S) after being collected in a collection tube. The collector can be located either directly at the outlet of the heat transfer zone (i.e., at the top below the catalyst tube sheet) or between the catalyst tubes in the reverse water gas shift reactor, opposite the catalyst tube outlet. The latter is the preferred solution in retrofit scenarios, as it is subject to less mechanical stress and is easier to route for connection to existing equipment. In Option A, the reverse water gas shift reactor therefore has two inlet streams and one outlet stream.The main advantage of this concept over the reverse water gas shift is the reduced potential for carburization by diluting the CO2-rich shift effluent with the less carbon-rich reformer effluent, thus reducing the partial pressure of CO compared to the shift effluent.

[0024] Alternatively, Option B can be applied. In this concept, the preheated CO2-H2 mixture (M) is reacted in the catalytic zone (CZP) of the catalyst tube under the same conditions as in Concept 1, but the ends of the catalyst tube are contained within a vessel and open into a zone fluidly separated from the heat transfer zone. The means for mixing the shift effluent with the reformer effluent (to provide a syngas with a reduced hydrogen / CO ratio (S)) is located at the outlet of the reverse water-gas-shift reactor rather than within the reactor. The shift effluent therefore exits the reactor in a separate stream. The advantage of this concept is a slightly higher temperature compared to Option A. In fact, the heating gas is the reformer effluent itself before mixing with the shift effluent. Therefore, a reverse water-gas-shift catalyst outlet temperature 10 to 50°C higher than in Option A is achievable. The additional synthesis gas produced with a reduced hydrogen / CO ratio can be further processed separately. That is, the shift effluent can be separated from the reformer. Alternatively, the two products can be combined. Because reverse water-gas-shift reactors have a high potential for carburization, the outlet system should be designed accordingly. Preferably, the reverse water-gas-shift catalyst tubes are coated to protect against carburization / metal dusting. Alternatively, materials with a low level of susceptibility to carburization can be selected.

[0025] In one particular scenario where the reverse water gas shift reactor inlet temperature is relatively low, i.e., below 400°C, or preferably below 600°C, and a higher catalyst bed inlet temperature is preferred, the upper part of the tubes can be packed with a catalytically inactive inert component to enhance heat transfer in order to initially raise the CO-H mixture temperature before entering the catalyst bed. Such an inert layer can be, for example, ceramic balls or metal inserts that promote turbulence. This is particularly beneficial when the reverse water gas shift reactor inlet temperature is below 400°C, especially below 300°C, or even down to ambient temperature.

[0026] Another object of the invention is a process for producing synthesis gas containing a reduced hydrogen / CO ratio, said process implementing a system according to the invention and comprising: a) reforming 5 a hydrocarbon feed 1 with an oxidant gas stream 4 to produce a reformer effluent comprising a synthesis gas stream; b) heating the catalyst tubes of the reverse water gas shift reactor by exchange with the reformer effluent; c) a reverse water gas shift reaction of the CO-rich stream and the H-rich stream in the catalyst tubes of a reverse water gas shift reactor to produce a shift effluent enriched in CO and HO; d) mixing the shift effluent with the reformer effluent to produce a synthesis gas having a reduced hydrogen / CO ratio.

[0027] Depending on the embodiment, the process according to the invention may include one or more of the following features. the process comprises, after step d), a step e) of capturing the CO2 contained in the synthesis gas coming from step d) to produce a CO2 stream and a synthesis gas depleted in CO2 and comprising a reduced hydrogen / CO ratio, wherein in step c) the CO2-rich stream comes at least partly from step e). - After step e), the process comprises a separation step f), preferably a cryogenic separation step, for separating an H2-rich stream and a synthesis gas or CO2 stream from step d) or from the synthesis gas stream coming from step e), wherein in step c) the H2 stream comes at least partly from step f). The off-gas 12 of the separation step is typically rich in methane and can be recycled to step a) or burned in a combustion heater. If the synthesis gas is too hydrogen-rich, a hydrogen-permeable membrane can also be included to reduce the H2 / CO ratio in the synthesis gas to the desired ratio. the process comprises a purification step 3 of the hydrocarbon feed 1 before the reforming step 5, preferably comprising the following steps: The process is selected from a hydrogenation process, a dehalogenation process, a desulfurization process, or a metallization process. The process includes a mixture step of the hydrocarbon feed 1 with an oxidant stream 4 before the reforming step 5. The process includes a cooling step of the synthesis gas coming from step d), preferably at a temperature of 900-300°C, typically to 30-50°C to knock out the water and to the operating temperature of the next process step, e) or separation. Cooling is achieved, for example, by heat exchangers for feed preheating, steam generation and superheating, and BFW preheating. Heat recovery is typically maximized to minimize the external energy demand for synthesis gas production. - In step c), the CO2-rich and H2-rich streams are introduced into the catalyst tubes at a temperature higher than 400°C, preferably higher than 600°C, in case of lower temperatures a heat transfer non-catalytically active layer is included on top of the catalyst to ensure the desired catalyst operating temperature. - The reformer effluent is contained at temperatures between 700 and 1100°C.

[0028] FIG. 2 illustrates a process according to the present invention, including optional features.

[0029] Similar to a conventional synthesis gas production plant (HyCO), a hydrocarbon feedstock 1, typically natural gas, LPG, light naphtha, or off-gas, is pretreated in a purification section 3. The purification section may consist of, for example, hydrogenation, dehalogenation, desulfurization, or metal protection steps. To perform these steps multiple times, some (recycle) hydrogen 2 can be added to the feed upstream of the purification section. The purified hydrocarbon stream is then mixed with an oxidant stream 4. Typically, the preferred oxidant is steam, but CO2 can also be applied, depending on the selected reforming application. The mixed feedstock is fed to a reforming reactor 5.

[0030] The reforming reactor (5) may consist of any of the following components or combinations thereof: a pre-reformer, a steam reformer, an autothermal reformer, or a partial oxidation reactor. In a pre-reformer, the hydrocarbon feedstock reacts with steam to form a methane-rich reformate stream, typically at temperatures between 450 and 700°C. In a steam reformer, the hydrocarbon reacts with steam according to the steam reforming reaction. This is typically applied in a (multi-)tubular reactor, where heat is either provided by a firebox, a hot effluent (so-called gas-heated reformer), or electrically, with outlet temperatures typically between 750 and 1000°C. In autothermal reforming (ATR), the hydrocarbon reacts with O2 from air, enriched air, or purified oxygen combined with an oxidant such as CO2 or HO, followed by reaction with an active catalyst bed for the reforming reaction. Typical outlet temperatures are between 900 and 1100°C. Partial oxidation involves reacting with oxygen in the absence of an oxidizing agent, typically achieving an exit temperature of up to 1300°C.

[0031] The reformer effluent is then fed to the reverse water gas shift reactor 17, which includes a heat exchanger reactor, to provide the necessary load for the reverse water gas shift reaction. The CO-rich stream 13 and the hydrogen-rich stream 19 are mixed and preferably first preheated before being fed to the reverse water gas shift reactor. Preheating the CO-H mixture is essential to reach the required operating conditions in the reverse water gas shift catalyst unit, which are at least 400°C, preferably above 600°C, or more preferably above 650°C, to minimize methane formation and minimize the risk of carbon formation. To achieve preheating, this can be done in several processes, including a feed / effluent exchanger with the reformer effluent (syngas stream) or crude syngas, a combustion heater (or heat integration in the convection section, for example, in a steam reforming process), or an electric heater. Alternatively, (part of) the preheating can be done within the reverse water gas shift reactor tube in a dedicated, non-catalytically active preheat zone before entering the reverse water gas shift catalyst bed within the same tube. The preheat zone is then sized to achieve a catalyst bed inlet temperature of at least 400°C, preferably above 600°C, or more preferably above 650°C. Depending on the required product syngas ratio, as well as the availability of imported hydrogen and CO2 feedstock, the CO2 to H2 ratio in the fed reverse water gas shift reactor is between 1:0.5 and 1:4, with CO2:H2 ratios of 1:1 to 1:2 being of particular interest. Lower concentrations of hydrogen limit the conversion of CO2, while higher concentrations of hydrogen increase the amount of methane formed.

[0032] The operating pressure of the reverse water-gas shift reactor unit is determined by the downstream operating pressure and is typically 2 to 100 bar, particularly 20 to 40 bar. At higher pressures, the methane concentration in the product increases slightly, according to Le Chattelier's principle. In addition to the hydrogen and CO2 in the feed, some co-feeding of steam can be applied to compromise carbon and methane formation. However, because this also adversely affects CO2 conversion, the addition of steam is typically limited to a maximum of 40% of the feed flow rate, but preferably less than 20%, more preferably less than 5%. Also, the amount of methane can be tolerated up to a maximum of 20% of the feed flow rate, more preferably less than 5%. However, because methane in the feed increases the risk of carbon formation and subsequent catalyst failure, the actual limit depends on the operating conditions. It is also noted that since the catalyst is active for methanation, it is also active for steam methane reforming, and therefore methane can also be converted with steam to form CO and H, although this will have a negative impact on the conversion of CO as per le Chatellier's principle.

[0033] The CO2-rich stream contains at least 70% CO2, preferably greater than 95%, and even more preferably greater than 99%. The CO2-rich stream can be captured (16), and another portion can come from a CO2 capture unit (7). The captured CO2 can be from any CO2 source; for example, a point source for carbon capture from an industrial process is CO2 from a biological source. The CO2 source should be essentially free of poisons (e.g., amines, sulfur, or heavy hydrocarbons) for the catalyst of the reverse water gas shift reactor. If these poisons are present in the CO2-rich feed, some additional pretreatment steps for the CO2 may be required. Because CO2 is formed in the reforming section (5) and the residual CO2 from the reverse water gas shift reaction step is formed due to only partial conversion (equilibrium-limited reactions), a significant amount of CO2 is still present in the synthesis gas with a reduced hydrogen / CO ratio, typically containing 1 to 20% by volume on a dry basis, preferably with a hydrogen / CO ratio of 3 or less, or more preferably 2 or less (referred to as "crude synthesis gas"). Thus, the crude syngas is cooled in cooling train section 6 and then optionally processed in CO2 capture unit 7. The captured CO2 13 is typically compressed and applied as a feedstock for reverse water gas shift reactor 17, although a portion 18 of the captured CO2 can also be applied as a partial oxidant in reforming reactor 5. The CO2 capture unit, e.g., an amine adsorption unit, a carbonate solution adsorption unit, a cryogenic unit, a membrane unit, electrochemical compression, temperature swing adsorption, or a pressure swing adsorption unit, can be any available technology for capturing CO2 from syngas.

[0034] The hydrogen required for the reverse water-gas shift step can be either generated internally in the gas separator 9 or imported (22). The imported hydrogen-rich gas can originate from another process unit, but is preferably "green" hydrogen, for example, produced from the electrolysis of water using renewable electricity. The internally produced hydrogen is produced in the reforming section (5), which also results from the partial conversion of hydrogen in the reverse water-gas shift reactor. Some hydrogen remains in the crude syngas. After cooling, the crude syngas can optionally be fed to a crude hydrogen separation unit 20, which is particularly beneficial when the H / CO ratio of the syngas is higher than the desired product ratio. In the crude hydrogen separation unit, a hydrogen-rich stream is separated from the crude syngas stream, for example, by a hydrogen-permeable membrane. In particularly advantageous cases, a portion of the CO from the crude syngas is separated along with the hydrogen. It is preferable to minimize carbon monoxide and water in the recycle stream and limit methane and water in the feedstock to acceptable limits. If a crude hydrogen separation unit is present, the CO2-rich product stream is optionally fed to a CO2 capture unit. A further advantage of this crude separation unit is that the gas flow rate through the CO2 capture unit and downstream synthesis gas purification units is reduced, thus allowing for smaller sizing and energy consumption.

[0035] The CO2-depleted synthesis gas (referred to as "CO2-depleted synthesis gas"), having a hydrogen / CO ratio of 3 or less, preferably 2 or less, is fed to a gas separator 9 to remove residual impurities to meet product specifications if the purity is not within the acceptable product specifications. These impurities typically include argon, nitrogen, methane, residual water, or CO2, if present. Furthermore, the purification unit can also, if necessary, separate the synthesis gas into a high-purity CO2 stream 10 (preferably greater than 80% by volume pure, more preferably greater than 95% by volume pure, even more preferably greater than 99% pure) and a high-purity hydrogen stream 11 (preferably greater than 80% by volume pure, more preferably greater than 95% by volume pure, even more preferably greater than 99% pure). The removed impurities form an off-gas stream 12. This off-gas stream can either be sent to the fuel gas network used internally for the combustion heater (e.g., the radiant section of a steam reformer) or recycled upstream to the feed purification or reforming section. The last option is particularly beneficial when the amount of methane is significant, as the reformer produces additional hydrogen from the methane and closes the carbon loop of the system. A small purge stream is then required to prevent the accumulation of inerts such as nitrogen or argon. The high-purity hydrogen stream 23 can also be recycled to the reverse water-gas shift reactor 17 instead of or in combination with the hydrogen from the crude hydrogen separation unit or the captured hydrogen.

[0036] The gas separator 9 can be of any available technology. Typically, a dryer followed by a cryogenic cold box is preferred, but electrochemical compression units, pressure swing adsorption units, vacuum swing adsorption units, membrane separation units, or combinations thereof, for example, have also been applied for such separation.

[0037] Table 1 shows the results of an exemplary case of the present invention compared with other existing alternatives. All examples are based on a steam reforming process with a reforming catalyst outlet temperature of 930°C. The feedstock is natural gas, and the overall steam-to-carbon ratio is 2.0 mol / mol at the reforming reactor inlet. The reformer effluent (base case and case 1) or the reverse water-gas shift reactor effluent (cases 2 and 3) is cooled, and greater than 99.9% of the CO2 is captured before being fed to a cryogenic separation unit to produce high-purity hydrogen and CO2. All off-gas from the cryogenic unit is fed to the burners in the radiant section of the steam reformer, with additional supplemental fuel being natural gas. In this example, the air fed to the reformer combustion in the radiant section is kept at a constant preheat temperature of 500°C, and the excess steam generated is exported outside the device boundary. Further heat integration is possible to optimize combustion as well as steam export. The following table includes the following examples:

[0038] Base case: Conventional steam reforming without CO2 recycle

[0039] Case 1: A typical conventional synthesis gas production plant using steam reforming with CO2 recycle applied to the reformer feed. Additionally, a parallel heat exchanger reformer is applied in parallel with the fired heater to process a portion of the reformer feed to reduce the combustion required in the radiant section. In this case, there is no CO2-H2 mixture. The parallel heat exchanger reformer literally performs a portion of the reforming in parallel with the main steam reformer. In this case, there is no external CO2 intake.

[0040] Case 2: Steam reforming according to the base case with an adiabatic post-converter applying both recycled CO2 as well as CO2 taken from outside the system, as described in WO 2019 / 110267. The taken-up CO2 is preheated to 600°C in the convection section of the reforming unit.

[0041] Case 3: The present invention with a reverse water gas shift reactor having a catalyst outlet temperature of 900°C and applying both recycled CO2 according to the present invention and CO2 taken from outside the system. Hydrogen for the reverse water gas shift reactor is generated internally and recycled. The feed to the reverse water gas shift reactor (a mixture of H2-rich and CO2-rich streams) is preheated to 500°C and a CO2:H2 ratio of 1.0 is applied.

[0042] [Table 1]

[0043] The described base case clearly shows that for a conventional steam reforming plant, the H2 / CO ratio is high, exceeding 4.0 mol / mol. For many processes, a lower stoichiometric ratio of approximately 2.0 mol / mol is required, thus resulting in additional hydrogen that is often not needed. In the base case, the NG consumption per CO produced is also very high because all the carbon in the CO product comes from the natural gas feed. In Case 1, the CO2 produced in the process is captured, compressed, and recycled upstream of the reformer feed. This is often applied in syngas plants to shift the water-gas shift equilibrium toward more CO in the reforming reactor. In this example, a parallel heat exchanger reformer is also applied to convert a portion of the reformer feed while it is heated by the reformer effluent, thereby reducing combustion in the steam reformer. This represents a typical high-efficiency syngas production plant. Compared to the base case, the H2 / CO ratio in the crude syngas is reduced to approximately 3.0 mol / mol. Furthermore, the NG consumption per CO produced is reduced by 24%. Note that the CO2-to-carbon ratio at the reformer inlet is 0.34 mol / mol. As the amount of CO2 in the reformer increases, the risk of carbon formation increases. As a result, capturing CO2 in these cases is often not possible without significantly increasing the steam-to-carbon ratio (resulting in increased NG consumption and CO2 recirculation, resulting in increased energy consumption within the unit). In Case 2, this problem related to carbon formation in the reformer is overcome by applying an adiabatic post-converter, as described in known technology. Captured CO2 is still recycled, but additional captured CO2 can be applied because the upstream methane reforming reactor has already converted methane and steam to hydrogen and CO, thereby being outside the carbon formation boundary. This example shows a clear reduction in the H2 / CO ratio, which is 1.8 in the crude syngas. However, because the CO2 is mixed directly with the reformer effluent before entering the post-converter catalyst bed, the added CO2 is only partially converted to CO via the reverse water-gas shift reaction resulting from the water-gas shift equilibrium.This is evident from the significantly increased CO2 recirculation, which requires nearly twice the flow rate of Case 1. Furthermore, CO2 supply also results in partial methanation, with more methane being formed as more CO2 is supplied to the unit and the temperature decreases. Case 3 demonstrates the benefits of the present invention. As in Case 2, the risk of carbon formation in the reformer is avoided by supplying CO2 to a separate reactor, thus operating the reformer outside the carbon formation zone. Also, as in Case 2, the same H2 / CO ratio is achieved with equal CO2 uptake. Compared to Case 1, NG consumption is reduced by 25% because some of the CO is generated from CO2 uptake. There is also a 5% reduction in NG consumption compared to Case 2, which is due to the higher CO2 conversion and therefore less combustion required in the reformer. This is also observed in the amount of recirculated CO2, which is 25% lower compared to Case 2 and 37% higher compared to Case 1. Because an increase in CO2 recycle is proportional to an increase in CO2 uptake, we also emphasize that it is more attractive to convert CO2 in a separate reverse water-gas shift catalyst bed instead when mixed with the reforming effluent. The disadvantage is that some methane is formed from the captured CO2 in the reverse water-gas shift reactor, as indicated by an increase in methane slip, but the increase is relatively modest. This can be further reduced with the recycle of methane-rich off-gas. In the crude syngas purification unit, methane is separated from the syngas and utilized internally as fuel in the reformer, thereby reducing natural gas demand. Overall CO2 emissions are significantly lower than in the base case and similar in magnitude to Case 1. If the CO2 is of biogenic origin, the associated CO2 emissions may even be eliminated.

[0044] It should be noted that when the reformer section consists of an autothermal reformer, the selected S / C ratio upstream of the reformer section for a synthesis gas production plant is typically lower than for a steam reforming plant (typically down to 1.2 mol / mol), and therefore CO recycle is even more limited, demonstrating a more significant benefit of alternatives such as those described in Cases 2 and 3. Also advantageous for the present invention is the higher outlet temperature of the ATR, which also allows for higher tube outlet temperatures for the reverse water gas shift reactor. The higher outlet temperature further increases the conversion of CO and significantly reduces the methane formed in the reverse water gas shift reactor.

[0045] This second example (Table 2) illustrates the application of reverse water gas shift in a bio-based refinery where some of the processes have hydrocarbon-containing off-gas. Case 1 is based on a stand-alone reverse water gas shift unit utilizing CO and hydrogen as feedstocks, with the hydrocarbon-containing off-gas being utilized for power generation in a combined cycle gas turbine. Case 2 represents the present invention where the off-gas is utilized as a feedstock for the reforming section of the reverse water gas shift unit. In both cases, the feed to the reverse water gas shift reactor is optimized to ensure a H:CO ratio of 2.0 in the product syngas.

[0046] [Table 2] * The off-gas is used to generate electricity in a combined cycle at 50% efficiency. The electricity is subtracted from the overall power requirement. Direct emissions also relate to the off-gas being combusted to generate electricity.

[0047] This example clearly demonstrates that for the same off-gas consumption and syngas production (at 2:1 H / CO), both the required CO uptake and the required H uptake are significantly lower in the present invention, reduced by approximately 80% and approximately 33%, respectively, compared to a stand-alone reverse water-gas shift process. Because hydrogen production is typically assumed to be performed by electrolysis using renewable electricity (so-called green hydrogen), hydrogen is a major contributor to overall power consumption, even when considering power generated by combustion of hydrocarbon-rich off-gas. The overall power consumption reduction is still approximately 10% from a comparison of a standalone reverse water-gas shift reactor with the present invention. Without power generation, power consumption would be reduced by more than 25%. Because the exhaust of the power generation unit is typically vented to the atmosphere, this also represents a direct CO emission that is not present in the present invention. Overall, the total energy input and carbon dioxide emissions of the present invention are significantly lower than a stand-alone reverse water-gas shift reactor when hydrocarbons (such as hydrocarbon-rich off-gas) are available.

[0048] Briefly, the present invention is an efficient CO2 utilization route that offers significant advantages over alternative routes and can be easily applied to existing as well as new units. The process avoids the risk of carbon formation and effectively utilizes the high levels of heat from the reforming process to convert CO2 to CO. The process can achieve H2 / CO ratios of less than 2.0, and even pure CO2 if necessary. Direct carbon dioxide emissions are comparable to current state-of-the-art processes, but significantly less fossil fuel is required to achieve the same syngas product flow rate, thus resulting in a lower overall carbon dioxide emission. The process allows for a high degree of flexibility in design. The process can be tailored depending on the required product composition as well as the availability of feedstock. One key variable is the feedstock to the reverse water gas shift reactor. Increasing the CO2-rich feed flow rate to the reverse water gas shift reactor allows for more CO2 conversion and therefore a lower H2 / CO ratio. An increased hydrogen-to-CO2 ratio allows for some additional CO2 conversion and therefore less CO2 in the product, which typically also results in an increased H2 / CO ratio. Therefore, this process can be applied to control the product H2 / CO ratio to the optimum conditions of downstream units or to match other processes, if necessary. This is particularly beneficial when the feedstock for the reforming section is inherently variable. For example, a plant may have multiple feedstocks, such as naphtha and natural gas, and the feedstock is selected based on availability. Because naphtha feed has a significantly lower C / H ratio than natural gas, the resulting syngas has a lower H2 / CO ratio than the NG feed. By adjusting the feed flow rate of the reverse water-gas shift reactor, the products can be maintained at a constant ratio. Also, with biobased feedstocks or off-gas, the concentration range of each component is typically higher than with conventional fossil feedstocks, and therefore, greater fluctuations in conditions are expected. The product syngas can be maintained within a constant range by adjusting the composition and flow rate of the reverse water-gas shift feed.This allows for continuous optimization of downstream units, thus improving overall efficiency in producing the final product. The same flexibility in operating conditions also allows for greater flexibility in operating over a larger range of capacities.

[0049] In summary, in the present invention, the presence of the reverse water gas shift reactor allows high flexibility in the H / CO ratio in the product. By adding some CO and recycled hydrogen, the product synthesis gas purity can be adjusted over a wide range.

[0050] This has two main advantages. -Downstream processes can be optimized depending on process parameters, or syngas can be applied to multiple downstream applications. For example, when syngas is applied to Fischer-Tropsch synthesis, the product composition depends on the operating conditions and syngas ratio. Therefore, the syngas ratio can be optimized to produce the most favorable product distribution. The present process significantly reduces the uptake of hydrogen and therefore the electricity demand for electrolysis compared to a stand-alone reverse water gas shift process, which is particularly beneficial when hydrocarbon-rich off-gas is available from a downstream unit. The process allows for easy maintenance of a constant H2 / CO ratio for different feedstocks. For example, a light naphtha feed is much more carbon-rich than an off-gas or natural gas feed. Thus, while conventional syngas generation units produce large differences in syngas ratios, the disclosed concept allows for the application of more CO2 uptake to the feed to increase the carbon content.

[0051] Furthermore, the present invention allows for operation at lower S / C ratios and therefore higher overall efficiency of the unit without risking carbon formation in the reforming section. This is not a limitation as there is no additional CO2 fed to the reforming section, the reverse water gas shift reactor is in parallel with the reforming section and has no / limited methane in the feed, therefore there is no risk of carbon formation over the catalyst bed.

[0052] Additionally, mixing the reverse water gas shift reactor effluent with the reformer effluent helps reduce the likelihood of carburization.

[0053] The process can also be applied to any reforming technology, which can include a pre-reformer, a steam methane reformer, a dry reformer, an autothermal reformer, or partial oxidation, or any combination of these technologies.

[0054] The process according to the present invention allows for the utilization of CO2 without the need for captured hydrogen and can be applied to both new and retrofit applications of hydrogen / syngas plants.

[0055] H2 / CO ratios in the crude syngas of less than 3 are readily achievable, which is highly beneficial since many downstream processes require H2 / CO ratios of 2.0 or less, thus reducing hydrocarbon consumption. H2 / CO ratios of 1.0, or even CO alone, are achievable with sufficient captured CO2 available.

[0056] The CO2 conversion rate in the reverse water gas shift reactor is higher compared to alternatives, thus minimizing the CO2 capture unit and recycle size.

Claims

1. 1. A system for producing a synthesis gas containing a reduced hydrogen / CO ratio, comprising: a reforming reactor (5) configured to react a hydrocarbon feed (1) with an oxidant gas stream (4) thereby producing a reformer effluent comprising a synthesis gas stream; a reverse water gas shift reactor (17) configured to receive a CO2-rich stream, an H2-rich stream and said reformer effluent and to produce a synthesis gas having a reduced hydrogen / CO ratio; The reverse water gas shift reactor (17) at least one catalyst tube configured to receive the H-rich stream and the CO-rich stream and produce a shift effluent enriched in CO and HO; a heat transfer zone configured to receive the reformer effluent and transfer heat from the reformer effluent to the catalyst tubes; and means configured to mix the shift effluent with the reformer effluent to produce the synthesis gas having the reduced hydrogen / CO ratio.

2. 2. The system of claim 1, wherein the ends of the catalyst tubes are open within the heat transfer zone, and a mixing means configured to mix the shift effluent with the reformer effluent is disposed within the heat transfer zone of the vessel.

3. 2. The system of claim 1, wherein the ends of the catalyst tubes are contained within the vessel and open within a zone fluidly separated from the heat transfer zone, and wherein means for mixing the shift effluent with the reformer effluent is located at the reverse water gas shift reactor outlet.

4. the system comprises a CO2 capture unit (7) configured to receive the synthesis gas having the reduced hydrogen / CO ratio and to produce a CO2 stream and a synthesis gas depleted in CO2 and having the reduced hydrogen / CO ratio, - A system according to any one of claims 1 to 3, wherein the catalyst tubes are preferably adapted to receive a CO2 stream coming at least partly from the CO2 capture unit (7).

5. the system comprises a gas separator (9) configured to receive the synthesis gas stream having the reduced hydrogen / CO ratio and to produce a H2-rich stream and a synthesis gas or CO stream; and A system according to any one of claims 1 to 4, wherein the catalyst tubes of the reverse gas shift reactor are configured to receive at least a portion of this H2-rich stream coming from the gas separator (9).

6. 6. The system of claim 5, wherein the system comprises an external hydrogen source, and the catalyst tubes of the reverse gas shift reactor receive the H2-rich stream from the gas separator and hydrogen from the external hydrogen source.

7. 7. The system of claim 1, wherein the upper portions of the catalyst tubes are filled with a catalytically inactive heat transfer enhancing component.

8. The system according to any one of the preceding claims, wherein the system comprises a hydrocarbon feed purification section (3) upstream of the reforming reactor.

9. A system according to any one of claims 1 to 8, wherein the system comprises means for mixing the hydrocarbon feed with an oxidant stream upstream of the reforming reactor.

10. 11. A process for producing synthesis gas containing a reduced hydrogen / CO ratio, the process implementing a system according to any one of claims 1 to 10, and a) reforming (5) a hydrocarbon feed (1) with an oxidant gas stream (4) to produce a reformer effluent comprising a synthesis gas stream; b) heating the catalyst tubes of the reverse water gas shift reactor by exchange with the reformer effluent; c) reverse water gas shift reaction of the CO2-rich stream and the H2-rich stream in the catalyst tubes of the reverse water gas shift reactor to produce a shift effluent enriched in CO and HO; d) mixing said shift effluent with said reformer effluent to produce a synthesis gas having said reduced hydrogen / CO ratio.

11. after step d), a step e) of capturing CO2 contained in the synthesis gas coming from step d) to produce a CO2 stream and a synthesis gas depleted in CO2 and having a reduced hydrogen / CO ratio, 11. The process according to claim 10, wherein in step c), the CO2-rich stream comes at least partly from step e).

12. after step e), a separation step f) for separating an H2-rich stream and a synthesis gas or CO stream from step d) or from said synthesis gas stream coming from step e), 12. The process according to claim 10 or 11, wherein in step c), the H2 stream comes at least partly from step f).

13. A process according to any one of claims 10 to 12, comprising a purification step (3) of the hydrocarbon feed (1) prior to the reforming step (5).

14. A process according to any one of claims 10 to 13, comprising a step of mixing the hydrocarbon feed (1) with an oxidant stream (4) before the reforming step (5).

15. The process according to any one of claims 10 to 14, comprising a step of cooling the synthesis gas coming from step d).

16. 16. The process according to any one of claims 10 to 15, wherein in step c) the CO2-rich stream and the H2-rich stream are introduced into the catalyst tubes at a temperature above 400°C.

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