Systems and processes for producing synthetic fuels

Abstract

1. A system for producing synthetic fuel, comprising: a reforming reactor (7) configured to react a light hydrocarbon feed (24) with an oxidant gas stream (20) to thereby produce a reformer effluent comprising a synthesis gas stream; a reverse water gas shift reactor (6) configured to receive a CO2-rich stream, an H2-rich stream, and the reformer effluent and to produce a synthesis gas having a reduced H2 / CO ratio; and a synthesis unit (17) configured to receive the synthesis gas having a reduced H2 / CO ratio and to produce a feed (18) comprising synthetic fuel, wherein the reverse water gas shift reactor (17) comprises: a vessel including at least one catalytic zone, preferably catalytic tubes, configured to receive the H2-rich stream and the CO2-rich stream and to produce a shift effluent enriched in CO and HO; and a heat transfer zone configured to receive the reformer effluent and transfer heat of the reformer effluent to the catalytic zone; and means configured to mix the shift effluent with the reformer effluent to produce a synthesis gas having a reduced H2 / CO ratio.

Description

[Technical Field]

[0001] The present invention relates to a system and process for producing synthetic fuels.

[0002] A synthesis fuel or synfuel is a liquid, or sometimes gaseous, fuel derived from syngas (synthesis gas), a mixture of carbon monoxide and hydrogen, obtained from the gasification of a solid feedstock such as coal or biomass, or by reforming natural gas.

[0003] Currently, it is crucial to develop processes that utilize alternative energy sources to provide fuels that can readily replace hydrocarbon fuels currently in use. Such fuels, compatible with today's combustion engines, would obviate the need for extensive, time-consuming technological development and infrastructure changes. Of particular interest is the production of sustainable aviation fuel (SAF), as this is a difficult industry to decarbonize.

[0004] One industrial-scale process for producing synthetic liquid hydrocarbon fuels is based on classical Fischer-Tropsch chemistry, converting syngas into a variety of hydrocarbons via Fischer-Tropsch synthesis.

[0005] Syngas is traditionally produced by reforming fossil hydrocarbons such as natural gas, LPG (liquefied petroleum gas), 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, hydrocarbon conversion is facilitated by a high outlet temperature, preferably at least 800°C or higher. The process gas is cooled, 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.

[0006] 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.

[0007] The terms "reforming" and "methane reforming" are meant to refer to reforming reactions according to one or more of the following reactions: CH4+H20 <CO+3H2(i) CH4+2H20 <C02+4H2(ii) CH4+C02<2CO+2H2(iii)

[0008] Reactions (i) and (ii) are steam methane reforming reactions, and reaction (iii) is a dry methane reforming reaction.

[0009] For higher hydrocarbons, i.e., CnHm (n≧2, m≧4), equation (i) is generalized to: CnHm+nH2O->nCO+(n+m / 2)H2(iv), where n≧2 and m≧4.

[0010] Typically, the reforming involves the water gas shift reaction (v) below: CO+H20 <C02+H2(V)

[0011] 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.

[0012] 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 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."

[0013] 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.

[0014] 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 in the feed reduces the hydrogen to carbon monoxide ratio in the product gas, but increases the reactor size due to higher flow rates, as well as increasing the risk of carbon formation (thus typically requiring increased steam to carbon flow rates, which in turn reduces overall energy efficiency).

[0015] Depending on the downstream synthesis, the H2 / CO ratio will vary; for example, in Fischer-Tropsch synthesis, depending on the product and catalyst type, the optimum H2 / CO ratio can be as low as 0.6 for iron-based catalysts or 1.8-2.1 for cobalt-based catalysts.

[0016] Several processes are known for producing synthetic fuels, including Fischer-Tropsch synthesis, but these processes are often characterized by high hydrogen utilization rates and high power consumption (especially associated with hydrogen production by electrolysis).

[0017] It is an object of the present invention to provide an improved process and an improved system for producing synthetic fuels.

[0018] The solution of the present invention is a system for producing synthetic fuels, comprising: a reforming reactor 7 configured to react a light hydrocarbon feed 24 with an oxidant gas stream 20, thereby producing a reformer effluent comprising a synthesis gas stream; a reverse water gas shift reactor 6 (rWGS) configured to receive the CO2-rich stream, the H2-rich stream and the reformer effluent and to produce a synthesis gas having a reduced H2 / CO ratio; a synthesis unit 17 configured to receive a synthesis gas having a reduced H2 / CO ratio and to produce a feed 18 comprising a synthetic fuel; Equipped with The reverse water gas shift reactor 17 comprises: at least one catalytic zone, preferably a catalytic tube, configured to receive the H-rich stream and the CO-rich stream and to produce a shift effluent enriched in CO and H2O; a heat transfer zone configured to receive the reformer effluent and transfer heat from the reformer effluent to the catalyst zone; a container, and The system includes means configured to mix the shift effluent with the reformer effluent to produce a synthesis gas having a reduced H2 / CO ratio.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] The product gas stream is a syngas having a reduced H2 / CO ratio. The term "reduced" is used relative to the syngas contained in the reformer effluent. Preferably, the product gas stream is a syngas 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.

[0023] 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.

[0024] 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.

[0025] Depending on the embodiment, the system according to the invention may include one or more of the following features. the synthesis unit 17 is any of a methanol synthesis unit, a methanol synthesis unit combined with a methanol-gasoline or methanol-jet fuel unit, a syngas-olefin synthesis unit, a syngas-ethylene oxide unit, and a Fischer-Tropsch FT unit, or any combination thereof. the system comprises at least a separation unit 19 configured to receive a feed 18 comprising synthetic fuel coming from a synthesis unit (17) and to produce a feed (22) comprising synthetic fuel 21, water 26 and light hydrocarbons, preferably the reforming reactor 7 being configured to receive the light hydrocarbons coming from the separation unit 19; the system comprises a first CO2 capture unit 23 configured to receive a feed comprising light hydrocarbons and to produce a CO2 stream 25 and light hydrocarbons 24, preferably the reforming reactor 7 is configured to receive the light hydrocarbons coming from the CO2 capture unit 23 and / or preferably the reverse water gas shift reactor 6 is configured to receive the CO2 stream 25 coming from the CO2 capture unit 23. The system comprises an electrolyzer unit 3 configured to receive water 1 and to produce an H2 stream 4 and an O2 stream 20, a reverse water gas shift reactor 6 configured to receive the H2 stream 4 coming from the electrolyzer unit 3, and preferably a reforming reactor 7 configured to receive the O2 stream coming from the electrolyzer unit 3 as oxidant gas stream 20. - the end of the catalyst zone is open in the heat transfer zone and mixing means configured to mix the shift effluent with the reformer effluent are located in the heat transfer zone of the vessel, this first configuration being referred to as "Option A". - the end of the catalytic zone opens into a zone contained within a vessel and fluidly separated from the heat transfer zone, and means for mixing the shift effluent with the reformer effluent is located at the reverse water gas shift reactor outlet, this second configuration being referred to as "Option B". the system comprises a second CO2 capture unit 12 configured to receive a synthesis gas having a reduced H2 / CO ratio and to produce a CO2 stream 13 and a CO2-depleted synthesis gas 16 having a reduced H2 / CO ratio, preferably wherein the catalytic zone is configured to receive the CO2 stream coming at least in part from the CO2 capture unit 12. The system was equipped with an external hydrogen source, and the catalytic zone of the reverse gas shift reactor received hydrogen partially 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 comprises means for mixing the hydrocarbon feed with the oxidant stream upstream of the reforming reactor, where "means for mixing" means, for example, a mixing tee. the first capture unit and / or 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]

[0026] [Figure 1] FIG. 1 is a schematic diagram showing two configurations (Option A and Option B) of a reverse water gas shift reactor. [Figure 2] FIG. 1 illustrates a process according to an aspect of the present invention, including optional features.

[0027] 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 catalytic zone at a minimum of 400°C, preferably above 600°C, or 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 CO 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 CO- and HO-rich shift effluent with the reformer effluent is located in the heat transfer zone. By "means for mixing the 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 H / CO ratio is formed in the heat transfer zone (HTZ). The temperature of the synthesis gas with a reduced H / CO ratio is between 400 and 900°C at the outlet of the heat transfer zone. It is then collected in a collection tube and exits the reactor (S). 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.

[0028] 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 (S) with a reduced H2 / CO ratio) 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 product syngas with a reduced H2 / 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.

[0029] 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.

[0030] Another object of the invention is a process for producing synthetic fuels, said process implementing a system according to the invention and comprising: a) reforming (7) a hydrocarbon feed (24) with an oxidant gas stream (20) to produce a reformer effluent comprising a synthesis gas stream; b) heating the catalytic zone of the reverse water gas shift reactor by heat exchange with the reformer effluent; c) a reverse water gas shift reaction step (6) of the CO2-rich stream and the H2-rich stream (5) in a catalytic zone 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 (9) having a reduced H2 / CO ratio; e) a step (17) of synthesizing a feed (18) containing synthetic fuel from a synthesis gas (9) having a reduced H2 / CO ratio; Includes.

[0031] Depending on the embodiment, the process according to the invention may include one or more of the following features. The synthesis process is a Fischer-Tropsch synthesis process. The process comprises the steps of separating a synthetic fuel-containing feed 18 to produce a synthetic fuel 21, water 26 and a feed 22 comprising light hydrocarbons, and preferably recycling the light hydrocarbons 24 in the reforming reactor 7. The process comprises a first step of capturing CO2 contained in a feed 22 comprising light hydrocarbons to produce a CO2 stream 25 and light hydrocarbons 24, preferably recycling the light hydrocarbons 24 in a reforming reactor 7, and preferably recycling the CO2 stream 25 in a reverse water gas shift reactor 6. The H2-rich stream 5 comes at least partly from an external hydrogen source. The process comprises an electrolysis step of water 1 to produce an H2 stream 4 and an O2 stream 20, the O2 stream produced in the electrolysis step being preferably used as an oxidant gas stream 20 in a reforming step 7, and the H2 stream produced in the electrolysis step being introduced into a reverse water gas shift reactor 6. The process comprises a step of cooling the synthesis gas 9 coming from step d). The process comprises a second step of capturing the CO2 contained in the synthesis gas 9 with a reduced H2 / CO ratio, and recycling the CO2 stream 13 in the reverse water gas shift reactor 6, to produce a CO2 stream 13 and a CO2-depleted synthesis gas 16 with a reduced H2 / CO ratio. An alternative option of the process does not include the second CO2 capture step, when the CO2 concentration in the synthesis gas with a reduced H2 / CO ratio is already below an acceptable limit. - A cooling step, preferably at temperatures between 900 and 300°C, typically to 30-50°C to knock out water and to the operating temperature of the next process step, e.g. e) or separation. Cooling is achieved by heat exchangers, e.g. feed preheat, steam generation and superheat, and BFW preheat. Heat recovery is typically maximized to minimize external energy demand for synthesis gas production. The process includes, before the reforming step 7, a mixture step of light hydrocarbons 24 with an oxidant stream 20. - In step c), the CO2-rich and H2-rich streams are introduced into the catalytic zone 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 catalytic operating temperature. - The reformer effluent is at a temperature comprised between 700 and 1100°C.

[0032] The present invention describes the integration of a reverse water gas shift (rWGS) reaction step with a downstream synthesis unit, particularly a Fischer-Tropsch synthesis unit, that produces feeds containing synthetic fuels, in order to close the carbon loop and minimize the required imported hydrogen.

[0033] FIG. 2 illustrates a process according to the present invention, including optional features.

[0034] The process is an efficient route to utilize CO2 while minimizing the hydrogen input (and therefore the power input) required to produce the product.

[0035] The process utilizes carbon dioxide and hydrogen to first produce synthesis gas and then chemicals, particularly synthetic fuels, such as sustainable aviation fuel (SAF). A CO2-rich stream (2) is mixed with an H2-rich stream (4) and fed to a reverse water gas shift reactor (6).

[0036] The CO2-rich stream can be from any source with a high CO2 concentration, preferably >75% CO2, more particularly >90% CO2, and more particularly >95% CO2. Lower CO2 concentrations are possible if the major other component in the stream is hydrogen; in this scenario, less hydrogen should be mixed with the CO2-rich stream. The source is preferably a biological CO2 source, e.g., from a fermentation process or direct air capture (DAC), although industrial point sources can also be treated without impact.

[0037] The hydrogen-rich stream 4 imported for the process is typically produced in an electrolyzer unit 3 where water 1 is electrolytically dissociated into H and O. Alternatively, hydrogen can be produced in other processes such as steam reforming, pyrolysis, partial oxidation, or by separation from another hydrogen-containing stream.

[0038] The reverse water gas shift reactor unit 6 converts CO and H over a catalyst to CO and water by-products. Prior to entering the reverse water gas shift reactor 6, the combined CO and H feed 5 is preferably preheated; additionally, if beneficial, some steam may be blended with the feed. Because the reaction is endothermic, CO conversion is higher at higher temperatures, with catalyst bed outlet temperatures preferably between 600 and 1000°C, more preferably above 750°C, and more preferably above 800°C. Heat for the reverse water gas shift reactor is provided by hot reformer effluent 8 from the reforming section 7.

[0039] The outlet temperature of the combined gas 9 from the reverse water-gas shift reactor 6, which is a synthesis gas with a reduced H2 / CO ratio, is typically 600-800°C and is fed to the cooling, condensation, and separation section 10. The hot gas from the reverse water-gas shift reactor (6) is cooled and used, for example, for steam generation, steam superheat, BFW (boiler feedwater) preheat, demineralized water preparation and preheat, and feed preheat. The water condensed in the cooled raw synthesis gas stream is separated from the gas phase. The condensate 13 can be utilized internally within the integrated rWGS / reforming unit for process steam generation, recycled to the electrolyzer (3), or treated in a wastewater treatment plant. Note that the condensate may contain some contaminants for the electrolyzer and may require additional pretreatment steps to remove these impurities. Purification steps are not shown.

[0040] The cooled syngas 11 contains primarily CO, H, unconverted CO and CH, as well as some nitrogen and / or other inerts, and is saturated with water. This syngas stream is further processed in purification and conditioning unit 12. This conditioning may include CO capture, hydrogen removal, methane removal, or other purification processes to clean the syngas for downstream synthesis units. As a result of the thermodynamic equilibrium of the WGS reaction, a significant portion of CO is still present in this stream. If this is not acceptable for downstream units (e.g., if CO is a poison or an inert), CO can be captured in a CO capture unit, which may be, for example, a membrane, vacuum swing adsorption (VSA), pressure swing adsorption (PSA), cryogenic, amine adsorption process, or any conventional CO capture process for extracting CO from syngas. CO from capture unit 13 is recycled back to the rWGS reactor as feedstock; for this reason, hydrogen in the CO stream is also acceptable. If there is excess hydrogen in the conditioned syngas to the synthesis unit, the hydrogen can be extracted, for example by a membrane unit, and recycled to the rWGS unit as well. 14 If there is a shortage of hydrogen in the syngas, additional hydrogen make-up 15 can be added to the syngas.

[0041] The purified and conditioned synthesis gas 16 is fed to a downstream synthesis unit 17. In the synthesis unit, the synthesis gas is reacted over a catalyst to produce synthetic hydrocarbons. In a preferred embodiment, the synthesis unit is a Fischer-Tropsch (FT) unit, producing synthetic fuels, including, but not limited to, LPG, gasoline, diesel, wax, and, particularly preferred, jet fuel. Alternatively, the synthesis unit can be methanol, methanol-gasoline / jet fuel, higher alcohols, syngas-olefins, syngas-ethylene oxide, or hybrid synthesis. In the case of low single-pass conversions, internal recirculation of unconverted synthesis gas is included in the synthesis unit. For example, excess energy from the exothermic FT reaction that cannot be utilized internally is recovered as steam. FT typically produces medium-pressure steam. This steam can be utilized in upstream and downstream reboilers to minimize exergy losses within the system.

[0042] The synthesis product gas 18 contains a wide range of components and is further processed in a separation and conditioning unit 19, which includes gas cooling, condensation of water, further reactions (e.g., hydrogenation, hydrocracking, isomerization, and aromatization), and separation / purification of the final product. Reactor units as part of the conditioning may require additional feed gases, such as hydrogen for hydrogenation and hydrocracking. These units are typically included to increase product yield and / or quality. The water condensed in the conditioning unit is separated into a condensate stream (26). This stream can be utilized internally within the integrated rWGS / reforming unit for process steam generation, recycled to the electrolyzer, or treated in a wastewater treatment plant. Note that the condensate may contain some contaminants for the electrolyzer and may require additional pretreatment steps to remove these impurities. Purification steps are not shown. A light off-gas of the process, which contains some unconverted synthesis gas, light hydrocarbons (typically C1-C5), CO2 and other impurities, is separated from the product stream. Light off-gas stream 22 is recycled back to reforming section 7. Product stream 21 contains the desired products of the synthesis unit. In the example of FT synthesis, the desired products include LPG, gasoline, diesel, jet fuel and wax.

[0043] Light off-gas 22 can optionally be further purified in purification section 23 before being fed to reforming section 7. This section can include a CO2 capture unit, typically comprising membrane, vacuum swing adsorption (VSA), pressure swing adsorption (PSA), cryogenic, amine adsorption process, or any conventional CO2 capture process to extract CO2. In the case of CO2 capture, CO2 stream 25 is combined with other CO2 streams and recycled as feed for the rWGS option. This can be particularly beneficial for streams with high CO2 partial pressures (>10% CO2 by volume), as it reduces the risk of carbon formation in the reforming section as well as the steam requirements in the reforming section. If the hydrocarbon off-gas is very rich in hydrogen, it is possible to first apply a hydrogen separation step (e.g., membrane) before feeding the hydrocarbon off-gas to the reforming section.

[0044] In the reforming section, the off-gas stream 24 is preheated and mixed with the steam produced in the integrated reforming and rWGS section before being fed to the reforming reaction unit. The reforming reaction unit can be one or a combination of the following units: a pre-reformer, a steam methane reformer (SMR), an autothermal reformer (ATR), or a partial oxidation (POX). In the reforming reaction unit, the hydrocarbons in the off-gas are converted to a mixture of CO, H, CO, HO, and any residual methane. The outlet temperature of the reformer section is preferably above 700°C, more preferably above 900°C, to maximize hydrocarbon conversion and a high driving force for the rWGS reaction. The hot effluent from the reforming section 8, i.e., the reformer effluent, is directly mixed with the shift effluent in the rWGS reactor, as described above.

[0045] If the reforming reactor includes an SMR, the heat required for the reaction can be provided by either a combustion heater, an oxy-fuel heater, and / or an electric heater. In the case of a combustion heater / oxy-fuel heater, at least a portion of the oxygen from the electrolyzer can be utilized in the combustion system. The fuel for this system can be light off-gas, but is preferably hydrogen. If H2 fuel is used, the carbon loop of the entire process is completely closed. If the reforming reactor includes an ATR or POX, at least a portion of the oxygen from the electrolyzer 20 can be utilized in the reactor. This avoids the need for an air separation unit.

[0046] The integrated system is designed so that off-gas reforming provides enough heat to drive the rWGS reaction, and no additional systems are required. If the light hydrocarbons in the off-gas are insufficient to power the entire rWGS section, the rWGS can be partially charged or an additional hydrocarbon input stream (not shown) can be utilized. This input hydrocarbon is preferably from a biological source, such as off-gas from an adjacent biofuel plant or synthetic natural gas (e.g., produced by methanation of CO with hydrogen).

[0047] An essential part of the present invention is that the rWGS heat exchanger reactor is integrated with the reforming section. This minimizes the total (external) energy demand of the system. At the same time, it also allows for closing both the hydrogen and carbon balances of the complete process. Since part of the required syngas is generated from the off-gas of the downstream synthesis unit, the amount of syngas produced in the rWGS reaction can then be reduced, thus requiring less carbon dioxide and hydrogen import for the same amount of product. Reduced CO2 import means that more product can be produced from the same CO2 source. This is particularly beneficial in energy consumption when CO2 is captured using a DAC, where significant energy input is required to capture the carbon dioxide.

[0048] Similarly, reducing the input hydrogen reduces the size and energy required for the electrolyzer. The conversion of water to hydrogen (and oxygen) is electrically intensive, requiring approximately eight times more energy input than hydrogen produced from off-gas. Thus, the overall energy intensity is reduced. An additional benefit is that with reduced hydrogen demand, the input water required for the plant is also reduced, thereby reducing the size of the water purification system and scarce water resources. An additional benefit of water reduction can be achieved by recycling condensate from the syngas and synthesis products to the electrolyzer. Utilizing the off-gas to produce a portion of the syngas also allows the system to avoid direct CO2 emissions, while reducing scope 2 carbon emissions (primarily from power generation) and, in the case of DAC, resulting in negative CO2 emissions.

[0049] Table 1 shows an example of the present invention using a non-integrated rWGS scheme combined with Fischer-Tropsch synthesis. Fischer-Tropsch synthesis is based on conventional FT synthesis targeting higher hydrocarbons (mostly wax) followed by hydrocracking to produce primarily synthetic gasoline and jet fuel. For this reason, the Fischer-Tropsch unit is not comparable to conventional processes, including CTL and GTL, as both of these processes require fossil fuels as inputs. This example is based on a product flow rate of 1000 barrels per day.

[0050] 1) Base case: This includes an electrolyzer to produce hydrogen that is combined with the incoming CO2 fed into the rWGS reactor, followed by a FT synthesis and separation unit. The off-gas is utilized in a combined gas turbine cycle to generate electricity.

[0051] 2) The present invention includes an SMR-based reformer unit integrated with a parallel rWGS heat exchanger reactor. 3) A second embodiment of the invention comprising a pre-reformer and an ATR-based reformer integrated with a parallel rWGS heat exchanger reactor, where the ATR utilizes a portion of the oxygen from the electrolyzer.

[0052] [Table 1] Table 1 KTPA = Kilotons per Year 1) It is expected that approximately 90% of the electricity consumption will be consumed by the electrolyzer. 2) Based on Scope 1 and 2 emissions with an electrical carbon intensity of 20gCO2 / kWh 3) Including condensate recirculation

[0053] Because light hydrocarbons are not recycled to the rWGS process, the base case does not close the complete carbon loop. Therefore, the total carbon import required is approximately 50% lower for the present invention. In other words, for the same CO2 feedstock, the present invention allows for approximately twice the product flow rate. The light off-gas hydrocarbons are utilized in a combined-cycle gas turbine to generate power, and the generated CO2 is exhausted through the flue gas. Note that it is possible to capture a significant portion of the CO2 from the flue gas and then recycle it back to the rWGS feed, reducing the CO2 import to approach that of the present invention, at the expense of additional energy input for the carbon capture unit. Because flue gas exhaust is also a direct release of CO2 to the atmosphere, CO2 emissions are also reduced by approximately 110 kTPA.

[0054] The main advantage of the present invention over the base case is the reduction in hydrogen required. Because the recycled light hydrocarbons also contain hydrogen, the reformer section converts the hydrocarbons to hydrogen and CO, and then a reduction of up to about 25% of the hydrogen from the electrolyzer is required in Case 1. In the case of a reformer section including an autothermal reformer, this can be reduced even further by about 30% compared to the base case. This is possible due to the utilization of oxygen from the electrolyzer and the higher outlet temperature from the ATR. This also allows for lower methane slip and higher conversion (in both the reformer and rWGS sections), and subsequently, lower hydrogen requirements.

[0055] Typically, the majority of electricity consumption is associated with hydrogen production in the electrolyzer, which is reflected in the total power consumption. Current electrolyzer technology has a power intensity of approximately 50-60 kW / kg H, which generates 70-95% of the total power consumption, depending on the detailed layout of the system and the source of CO. Thus, saving hydrogen from an integrated system saves a significant portion of electricity. Furthermore, because the rWGS is fully integrated with the reformer, no external heat input (in the form of electrical power or combustion heaters) is required for the rWGS reactor. This saves electricity and, therefore, an additional 3-5% of the total energy input and global CO footprint.

[0056] A particular advantage of the proposed system compared to other previous publications is that, in addition to the reduced power and energy footprint, an additional benefit lies in the operational benefits of rWGS integration. The parallel reactions in the reformer and rWGS maximize CO conversion and minimize H2 transfer, since the equilibrium reactions are in more favorable conditions (for methane conversion and CO2 conversion) than when the two streams are combined prior to the reformer or rWGS catalyst. An additional benefit of this system is that the mixing of the rWGS effluent with the reformer effluent in the rWGS heat exchanger reactor reduces the risk of carburization and corrosion compared to separate rWGS effluents, especially in the temperature range of 600-800 °C.

[0057] It should be noted that in certain cases, C3-C5 hydrocarbons are recovered as LPG product, thus reducing the recycle of light hydrocarbons. It should be noted that the CO2 imports will be closer to each other, but the advantages of the present invention remain.

[0058] The main advantages of the present invention can be summarized as follows: The main advantage over the base case is the reduction in hydrogen required. Because the recycled light hydrocarbons also contain hydrogen, the reformer converts the hydrocarbons to hydrogen and CO, and then a reduction of up to about 25% of the hydrogen from the electrolyzer is required in Case 1. In the case of a reformer including an autothermal reformer, this can be reduced even further by about 30% compared to the base case. This is possible due to the utilization of oxygen from the electrolyzer and the higher outlet temperature from the ATR. This also allows for lower methane slip and higher conversion (in both the reformer and rWGS sections), and subsequently, lower hydrogen requirements. Typically, the majority of electricity consumption is associated with hydrogen production in the electrolyzer, so this is reflected in the total power consumption. Current electrolyzer technology has a power intensity of approximately 50-60 kW / kg H, which generates 70-95% of the total power consumption, depending on the detailed layout of the system and the source of CO. Thus, saving hydrogen from an integrated system saves a significant portion of electricity. Furthermore, because the rWGS is fully integrated with the reformer, no additional external heat input (in the form of electricity or combustion heaters) is required for the rWGS reactor. This saves electricity and, therefore, an additional 3-5% of the total energy input and global CO footprint. A particular advantage of the proposed system compared to other previous publications is that, in addition to the reduced power and energy footprint, an additional benefit lies in the operational benefits of rWGS integration. The parallel reactions in the reformer and rWGS maximize CO conversion and minimize H2 transfer, since the equilibrium reactions are in more favorable conditions (for methane conversion and CO2 conversion) than when the two streams are combined prior to the reforming or rWGS catalyst. An additional benefit of this system is that the mixing of the rWGS effluent with the reformer effluent in the rWGS heat exchanger reactor reduces the risk of carburization and corrosion compared to separate rWGS effluents, especially in the temperature range of 600-800°C. - Carbon neutral or even negative CO2 footprint compared to processes starting with fossil fuel sources (e.g. gas, coal), especially when DAC is applied. -If the recycled hydrocarbon off-gas is not sufficient to provide all the heat, it is possible to co-feed some of the CO2 to the reforming feed, requiring a slight increase in the S / C ratio in the reformer. Alternatively, other hydrocarbon feedstocks can be used as feed to the unit.

[0059] An additional advantage of the present invention is that the reformer section can handle a very wide range of feedstocks, from light hydrogen-rich off-gas through LPG to light naphtha, thus also allowing the plant to utilize any undesired products as feedstock for the reformer section, keeping the carbon loop closed.

Claims

1. 1. A system for producing synthetic fuels, comprising: a reforming reactor (7) configured to react a light hydrocarbon feed (24) with an oxidant gas stream (20) thereby producing a reformer effluent comprising a synthesis gas stream; a reverse water gas shift reactor (6) configured to receive a CO2-rich stream, an H2-rich stream and the reformer effluent and to produce a synthesis gas having a reduced H2 / CO ratio; a synthesis unit (17) configured to receive said synthesis gas having a reduced H2 / CO ratio and to produce a feed (18) comprising synthetic fuel; Equipped with The reverse water gas shift reactor (17) at least one catalytic zone, preferably a catalytic tube, configured to receive said H-rich stream and said CO-rich stream and to produce a shift effluent enriched in CO and H2O; a heat transfer zone configured to receive the reformer effluent and transfer heat from the reformer effluent to the catalytic zone; a container, and means configured to mix the shift effluent with the reformer effluent to produce the synthesis gas having the reduced H2 / CO ratio.

2. 2. The system of claim 1, wherein the synthesis unit (17) is any one of a methanol synthesis unit, a methanol synthesis unit combined with a methanol-to-gasoline or methanol-to-jet fuel unit, a syngas-to-olefins synthesis unit, a syngas-to-ethylene oxide unit, and a Fischer-Tropsch (FT) unit, or any combination thereof.

3. 3. The system of claim 1, further comprising at least a separation unit (19) configured to receive the feed (18) comprising synthetic fuel coming from the synthesis unit (17) and to produce a feed (22) comprising synthetic fuel (21), water (26), and light hydrocarbons.

4. a first CO2 capture unit (23) configured to receive said feed comprising light hydrocarbons and to produce a CO2 stream (25) and light hydrocarbons (24); and Preferably, said reforming reactor (7) is adapted to receive said light hydrocarbons coming from said CO2 capture unit (23), and / or Preferably, said reverse water gas shift reactor (6) is configured to receive said CO2 stream (25) coming from said CO2 capture unit (23), The system of claim 3 .

5. an electrolyzer unit (3) configured to receive water (1) and to produce a H2 stream (4) and an O2 stream (20), - said reverse water gas shift reactor (6) is configured to receive said H2 stream (4) coming from said electrolyser unit (3); A system according to any one of claims 1 to 4, wherein the reforming reactor (7) is preferably configured to receive the O2 stream coming from the electrolyzer unit (3) as oxidant gas stream (20).

6. 6. The system of claim 1, wherein an end of the catalytic zone is open within the heat transfer zone, and mixing means configured to mix the shift effluent with the reformer effluent is disposed within the heat transfer zone of the vessel.

7. 6. The system of claim 1, wherein an end of the catalytic zone opens into a zone contained within the vessel and fluidly separated from the heat transfer zone, and means for mixing the shift effluent with the reformer effluent is disposed at the reverse water gas shift reactor outlet.

8. the system comprises a second CO2 capture unit (12) configured to receive the synthesis gas having the reduced H2 / CO ratio and to produce a CO2 stream (13) and a CO2-depleted synthesis gas (16) having the reduced H2 / CO ratio; - A system according to any one of claims 1 to 7, wherein the catalytic zone is preferably configured to receive a CO2 stream coming at least partly from the CO2 capture unit (12).

9. A process for producing synthetic fuels, said process implementing a system according to any one of claims 1 to 8, and a) reforming (7) a hydrocarbon feed (24) with an oxidant gas stream (20) to produce a reformer effluent comprising a synthesis gas stream; b) heating the catalytic zone of the reverse water gas shift reactor by exchange with the reformer effluent; c) a reverse water gas shift reaction step (6) of the CO2-rich stream and the H2-rich stream (5) in the catalytic zone of the 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 (9) having the reduced H2 / CO ratio; e) synthesis (17) of a feed (18) comprising synthetic fuel from said synthesis gas (9) having a reduced H2 / CO ratio; The process includes:

10. 10. The process of claim 9, wherein the synthesis step is a Fischer-Tropsch synthesis step.

11. 11. The process of claim 9 or 10, comprising a step of separating said feed (18) comprising synthetic fuel to produce a feed (22) comprising synthetic fuel (21), water (26), and light hydrocarbons.

12. a first step of capturing the CO2 contained in said feed (22) comprising light hydrocarbons in order to produce a CO2 stream (25) and light hydrocarbons (24); - preferably recycling the light hydrocarbons (24) in said reforming reactor (7); - preferably recycling said CO2 stream (25) in said reverse water gas shift reactor (6); The process according to any one of claims 9 to 11, comprising:

13. - a step of electrolysis of water (1) to produce a stream of H2 (4) and a stream of O2 (20), Preferably, the O2 stream produced in the electrolysis step is used as oxidant gas stream (20) in the reforming step (7), - A process according to any one of claims 9 to 11, wherein the H2 stream produced in the electrolysis step is introduced into the reverse water gas shift reactor (6).

14. The process according to any one of claims 9 to 13, comprising a step of cooling the synthesis gas (9) coming from step d).

15. a second step of capturing the CO2 contained in said synthesis gas (9) with a reduced H2 / CO ratio to produce a CO2 stream (13) and a synthesis gas (16) depleted in CO2 and with said reduced H2 / CO ratio; - recycling said CO2 stream (13) in said reverse water gas shift reactor (6); The process according to any one of claims 9 to 14, comprising:

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