Conversion of H2 and CO2-containing off-gas to synthetic fuels

Abstract

Abstract A method for producing a hydrocarbon product stream in a hydrocarbon plant is provided, the hydrocarbon plant comprising a reverse water gas shift (RWGS) unit (I) and a second feed to the reverse water gas shift (RWGS) unit (I) comprising carbon dioxide, the second feed being process off-gas comprising less than 75% CO and being the only carbon dioxide-containing feed to the reverse water gas shift (RWGS) unit (I).

Description

[Technical Field]

[0001] Technical Field The present invention relates to a method for producing a hydrocarbon product stream in a hydrocarbon plant, the hydrocarbon plant comprising a reverse water gas shift (RWGS) unit (I) and a feed to the reverse water gas shift (RWGS) unit (I) comprising carbon dioxide. The feed is a process off-gas containing less than 75% CO2 and is the only carbon dioxide-containing feed to the reverse water gas shift (RWGS) unit (I). The method of the present invention provides an overall better utilization of carbon dioxide. [Background technology]

[0002] background Carbon capture and utilization (CCU) has become more important in light of the increase in atmospheric CO2 since the Industrial Revolution. One way to utilize CO2 is to convert CO2 and H2 into synthesis gas (a gas rich in CO2 and H2), which can be further converted into valuable products such as alcohols (including methanol), fuels (e.g., gasoline, jet fuel, kerosene, and diesel, produced by the Fischer-Tropsch (FT) process), and / or olefins.

[0003] Existing technologies primarily focus on stand-alone reverse water gas shift (RWGS) processes that convert CO2 and H2 into syngas, which is then converted into valuable products in downstream processes such as those mentioned above. The reverse water gas shift reaction proceeds according to the following reactions: [ka]

[0004] One or both of the methanation reactions may produce undesirable by-products, such as methane: [ka]

[0005] The RWGS reaction (1) is an endothermic process and requires a significant energy input to effect the desired conversion. High temperatures are required to sufficiently convert carbon dioxide to carbon monoxide to make the process economically viable. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] WO2021 / 110806 [Patent Document 2] PCT / EP2021 / 078304 Summary of the Invention [Problem to be solved by the invention]

[0007] Several patents have been filed in recent years for the construction of methods for converting H2 and CO2 into synthetic fuels. However, in some situations, CO2 feed streams containing high concentrations of CO2 are not always available, and alternative solutions need to be found.

[0008] Patent publication WO2021 / 110806 discloses an eRWGS reactor, and patent application PCT / EP2021 / 078304 discloses various process configurations with various feed stream configurations using RWGS.

[0009] In the following, "selective RWGS" means that only the reverse water gas shift reaction takes place on the catalyst or in the reactor, and "non-selective RWGS" means that in addition to the reverse water gas shift, other reactions take place, for example, one or more methanation reactions (including reverse methanation). [Means for solving the problem]

[0010] overview A method for producing a hydrocarbon product stream in a hydrocarbon plant is provided. wherein the hydrocarbon plant comprises: - Reverse Water Gas Shift (RWGS) Unit (I), - Syngas production unit (II), optionally, a first feed comprising hydrogen to said reverse water gas shift (RWGS) unit (I); a second feed to said reverse water gas shift (RWGS) unit (I) comprising carbon dioxide; a third feed to said synthesis gas production unit (II) comprising methane, - Fischer-Tropsch (FT) section (III), The method includes the following steps: a) optionally feeding said first feed comprising hydrogen to said reverse water gas shift (RWGS) unit (I); b) feeding said second feed to said reverse water gas shift (RWGS) unit (I); wherein the second feed is a process off-gas containing less than 75% CO2 and is the only carbon dioxide-containing feed to the reverse water gas shift (RWGS) unit (I); c) converting said second feed and—if present— said first feed into a first synthesis gas stream in said reverse water gas shift (RWGS) unit (I); d) feeding the third feed comprising methane to the synthesis gas production unit (II) and converting it into a second synthesis gas stream; and e) feeding at least a portion of the first synthesis gas stream and at least a portion of the second synthesis gas stream to the Fischer-Tropsch (FT) section (III) and converting said portions of the first and second synthesis gas streams into at least a hydrocarbon product stream and an FT off-gas stream.

[0011] Conventional RWGS-based processes typically use high-purity CO2-containing feedstocks, e.g., feedstocks containing at least 95% CO2, typically 99% CO2 or more. The present invention is based on the surprising experimental finding that it is possible to operate an RWGS reactor using a low-purity CO2-containing feedstock, e.g., a CO2 content of 20-35%. The present invention is further based on the recognition that this fact allows off-gas from the Fischer-Tropsch (FT) section to be used as the CO2-containing feed to the RWGS reactor or as a separate, low-purity CO2-containing feedstock. Furthermore, the present invention is based on the surprising finding that it is possible to operate an RWGS reactor using off-gas from the Fischer-Tropsch (FT) section as the only CO2-containing feed.

[0012] The method of the present invention makes efficient use of various streams, particularly process off-gas. The technical advantages of the present invention are at least twofold: Process off-gas is typically used as fuel gas, which results in unwanted CO2 emissions into the atmosphere. This includes CO2 from the process off-gas itself and CO2 from the combustion of hydrocarbons when the off-gas is used as fuel. The present invention can reduce or completely avoid these emissions. Carbon contained in the process off-gas is recycled and reused in the process, improving the carbon efficiency of the process and converting a higher proportion of the carbon fed to the process into hydrocarbon products.

[0013] Furthermore, the method of the present invention provides the possibility of upgrading (also called retrofitting) an existing synthetic fuel production method / plant that includes a synthesis gas production reactor and a Fischer-Tropsch unit but does not have a RWGS unit by adding a RWGS unit to the process. By retrofitting an existing method in this way, the technical advantages 1) and 2) of the retrofitted method can be achieved.

[0014] Further details of the technology are set out in the accompanying dependent claims, figures and examples.

[0015] Figure legend This technique is illustrated by the following schematic diagram: [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 shows a first layout of a hydrocarbon plant of the invention with various feeds. [Figure 2] FIG. 2 shows a further layout of a hydrocarbon plant of the present invention with various feeds, where the FT off-gas stream from the FT section is fed as a second feed to the RWGS unit. [Figure 3] FIG. 3 shows a variation of FIG. 2 in which the synthesis gas production unit (II) is an autothermal reforming (ATR) unit (IIa), and a portion of the FT off-gas stream from the FT section is fed as a second feed to the RWGS unit (I), and a portion of the FT off-gas stream is fed to the ATR unit (IIa). DETAILED DESCRIPTION OF THE INVENTION

[0017] Detailed Disclosure Gas content percentages are by volume unless otherwise specified. All feeds are preheated as needed.

[0018] The technology relates to a second feed stream which is an off-gas stream, preferably having a low to moderate CO content (i.e., less than 75% CO), and optionally also containing hydrogen and / or hydrocarbons and / or CO.

[0019] Carbon capture and utilization has been of interest for many years. Plant layouts are known that provide solutions for utilizing CO2 in the presence of H2 to produce synthesis gas, which is then converted into valuable products such as synthesis gas-derived liquid fuels (also known as synthetic fuels). Electrically heated RWGS (e-RWGS) units are preferably used to convert CO2 and H2 feeds into synthesis gas.

[0020] In this context, the term "hydrocarbon-containing feed" refers to a gas containing one or more hydrocarbons and possibly other components. Thus, a hydrocarbon-containing feed typically contains hydrocarbon gases such as CH4, in addition to varying amounts of other gases, and optionally, often relatively small amounts of higher hydrocarbons. Higher hydrocarbons are components with two or more carbon atoms, such as ethane and propane. Examples of "hydrocarbon gases" include natural gas, city gas, naphtha, or mixtures of methane and higher hydrocarbons, biogas, and LPG. Hydrocarbons may also be components with atoms other than carbon and hydrogen, such as oxygenates. The term "hydrocarbon-containing feed gas" refers to a feed gas containing one or more hydrocarbons mixed with steam, hydrogen, and possibly other components, such as carbon monoxide, carbon dioxide, nitrogen, and argon.

[0021] The term "synthesis gas" means a gas that contains hydrogen, carbon monoxide, carbon dioxide, and small amounts of other gases, such as argon, nitrogen, methane, and the like.

[0022] As mentioned above, the process of the present invention is carried out in a hydrocarbon plant, said hydrocarbon plant comprising: - Reverse Water Gas Shift (RWGS) Unit (I), - Syngas production unit (II), optionally a first feed (1) comprising hydrogen to said reverse water gas shift (RWGS) unit (I), a second feed (2) to said reverse water gas shift (RWGS) unit (I) comprising carbon dioxide, a third feed (3) to said synthesis gas production unit (II) comprising methane, - Fischer-Tropsch (FT) section (III).

[0023] The method comprises the steps of: a) optionally feeding said first feed (1) comprising hydrogen to said reverse water gas shift (RWGS) unit (I); b) feeding said second feed (2) to said reverse water gas shift (RWGS) unit (I); provided that said second feed (2) is a process off-gas containing less than 75% CO2 and is the only carbon dioxide-containing feed to said reverse water gas shift (RWGS) unit (I); c) converting said second feed (2) and—if present— said first feed (1) into a first synthesis gas stream (11) in said reverse water gas shift (RWGS) unit (I); d) feeding said third feed (3) comprising methane to said synthesis gas production unit (II) and converting it into a second synthesis gas stream (21); e) feeding at least a portion of the first synthesis gas stream (11) and at least a portion of the second synthesis gas stream (21) to the Fischer-Tropsch (FT) section (III) and converting said portions of the first and second synthesis gas streams into at least a hydrocarbon product stream (31) and an FT off-gas stream (32).

[0024] The details of the components that make up the hydrocarbon plant are as follows:

[0025] Reverse Water Gas Shift (RWGS) Unit (I) The carbon dioxide and - if present - hydrogen feed is primarily processed in a reverse water gas shift (RWGS) unit, which is preferably an electrically heated reverse water gas shift (e-RWGS) unit.

[0026] Suitably, the first feed comprising hydrogen to the RWGS unit (if present) and the second feed comprising carbon dioxide to the RWGS unit are arranged to be mixed to provide a combined feed that is supplied to the RWGS unit.

[0027] The RWGS unit (I) is arranged to convert at least a portion of said first feed (comprising hydrogen) and at least a portion of said second feed (comprising CO2) into a first synthesis gas stream.

[0028] The first synthesis gas stream produced in the RWGS unit preferably has the following composition (by volume): 0.5-5% methane (dry) · 40-70%H2 (dry) · 10-40%CO (dry) · 2-20%CO2 (dry)

[0029] The first synthesis gas stream may further comprise other components, such as steam and / or nitrogen.

[0030] e-RWGS unit Preferably, the RWGS unit is an electrically heated reverse water gas shift (e-RWGS) unit. An electrically heated reverse water gas shift (e-RWGS) unit uses an electrically resistively heated reactor to perform a more efficient reverse water gas shift process, substantially reducing or preferably avoiding the use of fossil fuels as a heat source.

[0031] An e-RWGS reactor can be selective or non-selective. "Selective" means that only the RWGS reaction (reaction 1 above) takes place. "Non-selective" means that both the RWGS reaction (reaction 1 above) and the methanation reaction (reaction 2 above) take place. Non-selective processes can also carry out other reactions, such as steam reforming of higher hydrocarbons (hydrocarbons with two or more carbon atoms, such as ethane). e-RWGS is described in more detail in Angew. Chem. Int. Ed. 2022, 61, e202109696, among others.

[0032] The e-RWGS unit is used in the present invention to carry out the reverse water-gas shift reaction between CO and H. The e-RWGS unit preferably comprises: a structured catalyst configured to catalyze the RWGS reaction, the structured catalyst comprising a macrostructure of an electrically conductive material, the macrostructure supporting a ceramic coating, the ceramic coating supporting a catalytically active material (for selective e-RGWS); a pressure shell containing the structured catalyst; the pressure shell including an inlet for receiving the feed and an outlet for receiving the syngas product; the inlets positioned such that the feed enters the structured catalyst at a first end thereof and the syngas product exits the structured catalyst at a second end thereof; an insulating layer between the structured catalyst and the pressure shell; and at least two conductors electrically connected to the structured catalyst and a power source located external to the pressure shell, the power source being dimensioned to pass an electrical current through the macrostructure of electrically conductive material, thereby heating at least a portion of the structured catalyst to a temperature of at least 500°C; and at least two conductors connected to the structured catalyst at a location on the structured catalyst closer to the first end of the structured catalyst than to the second end of the structured catalyst, the structured catalyst being configured to pass an electrical current from one conductor substantially to the second end of the structured catalyst and return to a second conductor of the at least two conductors, the structured catalyst having an electrically insulating portion positioned to conduct an electrical current from one conductor closer to the first end of the structured catalyst than to the second end of the structured catalyst and return to a second conductor closer to the first end of the structured catalyst than to the second end.

[0033] The pressure shell preferably has a design pressure of 25 to 45 bar. The pressure shell may also have a design pressure of 30 to 200 bar. At least two conductors are typically routed through the pressure shell in fittings such that the at least two conductors are electrically insulated from the pressure shell. The pressure shell further comprises one or more inlets near or in combination with at least one fitting for allowing a cooling gas to flow over, around, near, or within at least one conductor within the pressure shell. The outlet temperature of the e-RWGS unit (I) is preferably 900°C or higher, preferably 1000°C or higher.

[0034] In non-selective e-RWGS, methanation via reactions (2) and / or (3) is carried out in addition to the RWGS reaction. This has the advantage that the carbon monoxide concentration inside the reactor is lower than when reverse water gas shift is used alone. This is particularly important in the low- to medium-temperature range, up to about 600-800 °C. In this temperature range, the potential for carbon formation and metal dusting is present or significantly greater when using selective RWGS catalysts than when using non-selective catalysts.

[0035] In one embodiment, when a non-selective catalyst is used in the e-RWGS reactor, the methanation reaction also occurs at and near the reactor inlet. However, at a given temperature (which depends on the feed gas composition, pressure, catalyst activity, degree of heat input, and other factors), the reverse reaction of the methanation reaction is thermodynamically favored. In other words, methane is produced in the first section of the RWGS reactor, and consumed in the second section downstream of the first section according to the reverse of reactions (2) and / or (3).

[0036] The combined activity of reverse water gas shift and methanation in the eRWGS reactor of the present invention involves the reaction scheme within the reactor starting exothermically in the initial part of the reactor system but finishing endothermically towards the outlet of the reactor system. This is in accordance with the general heat balance of the plug flow reactor system, with the heat of reaction (Q) added or removed during the reaction. r ) related to:

[0037] FC pm -dT / dV=Q (add) +Q r =Q add +Σ(-Δ r H i )-(-r (i )) where F is the flow rate of the process gas, C pm is the heat capacity, V is the volume of the reaction zone, T is the temperature, and Q add is the energy supply / removal from the surroundings, Q ris the energy supply / removal associated with a chemical reaction, given as the sum of all chemical reactions catalyzed within a volume, and calculated as the product of the reaction enthalpy and the reaction rate of a given reaction.

[0038] Low concentrations of methane can be achieved by using high temperatures in the e-RWGS reactor. High temperatures have the added benefit of increasing the conversion of CO to CO. In one embodiment, the outlet temperature of the gas from the e-RWGS reactor is greater than 900°C, e.g., greater than 1000°C, or greater than 1050°C. An advantage of the proposed reactor is that it can achieve higher temperatures than are typically possible in externally fired reactors.

[0039] By using an e-RWGS unit (compared to a conventional RWGS unit), it is possible to produce a syngas product stream with a low CO2 content (e.g., 20% or less), due to the high temperature operation of the e-RWGS. 2の Since a high conversion rate to CO is ensured, it is desirable for multiple applications, such as FT synthesis and methanol synthesis.

[0040] Downstream of the RWGS unit there may be one or more component removal units (such as to remove H2 or CO2 as needed) to provide an upgraded first synthesis gas stream.

[0041] Syngas Production Unit (II) The synthesis gas production unit (II) is arranged to convert at least a portion of the third feed (comprising methane) into a second synthesis gas stream. Additional feeds to the synthesis gas production unit II (comprising, for example, oxygen and / or steam) may be required.

[0042] The synthesis gas production unit (II) may be selected from the group consisting of an autothermal reformer (ATR) unit (IIa), a steam methane reforming (SMR) unit (IIb) and an electrically heated steam methane reforming (e-SMR) unit (IIc), preferably an electrically heated steam methane reforming (e-SMR) unit (IIc).

[0043] The second synthesis gas stream may have the following composition (by volume): · 40-70%H2 (dry) · 10-30%CO (dry) · 2-20%CO2 (dry) 0.5-5% CH4 (dry)

[0044] In one embodiment, the synthesis gas production unit (II) may be an autothermal reforming (ATR) unit (IIa). The autothermal reforming (ATR) unit converts a third feed containing methane into a second synthesis gas stream. In one embodiment, at least a portion of the FT off-gas stream from the FT section (III) is supplied to the synthesis gas production unit (II). In this way, the amount of the third feed supplied to the synthesis gas production unit (II) can be reduced.

[0045] ATR units typically include a combustor (burner), combustion chamber, and catalyst bed housed within a flame-retardant-lined pressure shell. In an ATR unit, partial combustion of a hydrocarbon-containing feed with substoichiometric oxygen is followed by steam reforming of the partially combusted 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 exits the reactor at or near equilibrium with respect to the steam reforming and water-gas shift reactions.

[0046] Typically, the (second) synthesis gas stream from the ATR unit has a temperature of 900-1100°C. The (second) synthesis gas stream usually contains H2, CO, CO2, and water vapor. Trace amounts of other components such as methane, nitrogen, and argon may also be present. The operating pressure of the ATR unit is 5-100 bar, more preferably 15-60 bar.

[0047] The second syngas stream from the ATR unit is typically cooled in a cooling train containing a waste heat boiler (WHB) and one or more additional heat exchangers. The cooling medium in the WHB is boiler feed water, which is evaporated to steam. The second syngas stream is further cooled below its dew point, for example, by utility preheating and / or partial preheating of one or more feed streams and cooling in air and / or water coolers. The condensed HO is removed as process condensate in a separator, providing a low-HO syngas stream that can be sent to the Fischer-Tropsch (FT) section (III). Further details and a complete description of the ATR can be found in the technical literature, e.g., "Studies in Surface Science and Catalysis, Vol. 152, 'Synthesis gas production for FT synthesis'; Chapter 4, pp. 258-352, 2004."

[0048] The "ATR unit" may also be a partial oxidation "POX" section. A POX section is similar to an ATR section, except that the ATR unit is replaced with a POX reactor. A POX reactor generally consists of a combustor (burner) and combustion chamber housed in a flame-retardant-lined pressure shell.

[0049] The ATR unit can also be a catalytic partial oxidation (cPOX) section.

[0050] The oxidant for an autothermal reformer can be oxygen, air, a mixture of air and oxygen, or an oxidant containing more than 80% oxygen, e.g., more than 90% oxygen. The oxidant can contain other components, such as steam, nitrogen, or argon. Typically, the oxidant in this case contains 5-20% steam.

[0051] In this embodiment, the method further comprises feeding a fourth feed comprising steam and, optionally, a fifth feed comprising oxygen to an autothermal reforming (ATR) unit (IIa). A sixth feed, which is part of the FT off-gas stream from the FT section (III), can also be fed to the synthesis gas production unit (II).

[0052] If the reforming unit is an SMR or e-SMR, a fourth feed containing steam is required.

[0053] In another embodiment, the synthesis gas production unit (II) is an electrically heated steam methane reforming (e-SMR) section (IIc). In this embodiment, the plant does not include an oxygen-containing feed to the electrically heated steam methane reforming (e-SMR) section (IIc). In this embodiment, the overall CO2 emissions from the plant can be further reduced.

[0054] First Supply The RWGS unit is supplied with a first feed, which optionally contains hydrogen. Preferably, the first feed consists essentially of hydrogen. The first feed of hydrogen is preferably "hydrogen-rich," meaning that the major component of the feed is hydrogen; that is, more than 75%, for example more than 85%, preferably more than 90%, more preferably more than 95%, and even more preferably more than 99% of the feed is hydrogen. One of the sources of the first feed of hydrogen can be one or more electrolysis units. In addition to hydrogen, the first feed can contain, for example, water vapor, nitrogen, argon, carbon monoxide, carbon dioxide, and / or hydrocarbons. In some cases, traces of oxygen may be present in the feed, typically less than 1000 ppm.

[0055] In one embodiment, the first feed is absent, and the process off-gas as the second feed is the only carbon dioxide-containing feed to the reverse water gas shift (RWGS) unit (I); and is the only hydrogen-containing feed to the reverse water gas shift (RWGS) unit (I). In other words, the process off-gas can essentially provide all the CO and all the H required for the process.

[0056] Secondary Supply A second feed containing carbon dioxide is fed to the RWGS unit. The second feed is a process off-gas containing less than 75% CO and is the only carbon dioxide-containing feed to the reverse water gas shift (RWGS) unit (I). This means that in the method of the present invention, CO recovery and purification steps can be avoided.

[0057] The second feed may include, in addition to CO2, for example, hydrogen, water vapor, nitrogen, oxygenates, amines, ammonia, carbon monoxide, and / or hydrocarbons.

[0058] If the first feed is not present, the second feed preferably comprises H2.

[0059] The second feed suitably contains only a low amount of higher hydrocarbons (ie excluding methane), for example less than 5% higher hydrocarbons, less than 3% higher hydrocarbons, less than 1% higher hydrocarbons.

[0060] The second feed may be process off-gas from a Fischer-Tropsch (FT) unit, process off-gas from a methanol loop unit, or a combination of two or more off-gases from two or more such units.

[0061] In a particular embodiment, at least a portion (6) of said FT off-gas stream (32) from FT section (III) is fed as at least a portion of the second feed (2) to the RWGS unit (I). In another embodiment, the process off-gas is a process off-gas from an FT unit external to the process of the present invention.

[0062] The methanol loop, from which process off-gas from the methanol loop unit is generated, is external to the process of the present invention. The methanol loop, i.e., the methanol synthesis section, includes one or more methanol synthesis reactors. A synthesis gas stream enters the methanol synthesis reactor, where it is converted into a feed product stream containing methanol in the presence of a catalyst. The feed product stream containing methanol may be cooled in one or more heat exchangers before being fed to a vapor-liquid separator, typically a high-pressure (HP) separator. The vapor-liquid separator unit provides a product stream containing methanol and a recycle stream containing H, CO, and CO, a portion of which is purged from the vapor-liquid separator unit as an off-gas stream. The methanol synthesis section can further include a hydrogen recovery unit configured to separate the methanol off-gas stream into an H-rich stream containing limited amounts of CO and CO and a hydrogen recovery off-gas. In certain embodiments, the process off-gas from the methanol loop unit is off-gas from a separator unit of the methanol loop unit or off-gas from a hydrogen recovery unit of the methanol unit.

[0063] In a particular embodiment of the process of the present invention, at least a portion (6) of said FT off-gas stream (32) from the FT section (III) is fed to a synthesis gas production unit (II).

[0064] The process off-gas contains less than 75%, less than 60%, preferably 5-50%, more preferably 10-40%, and most preferably 20-35% CO2.

[0065] The process off-gas contains less than 60% H2, more preferably 10-50%, and most preferably 20-40%.

[0066] The process off-gas contains less than 30% hydrocarbons, preferably 1-25%, more preferably 5-25%, and most preferably 10-20%.

[0067] In a particularly preferred embodiment, at least a portion of the FT off-gas stream from FT section (III) is fed as at least a portion of the second feed to RWGS unit (I). By recycling this off-gas stream as the second feed, a more self-contained process is provided, reducing the number of external feeds / units required.

[0068] Combination Supplies Instead of separating the first and second feeds, the plant can provide a combined feed comprising hydrogen and carbon dioxide to the e-RWGS unit (I). Typically, the hydrogen content of this combined feed is 40-80%, preferably 50-70%.

[0069] Typically, the carbon dioxide content of the combined feed is between 15 and 50%, preferably between 20 and 40%. Typically, the carbon monoxide content of the combined feed is between 0 and 10%. Typically, the ratio of hydrogen to carbon dioxide in the combined feed is between 1 and 5, preferably between 2 and 4.

[0070] In addition to hydrogen and carbon dioxide, the combined feed may include, for example, steam, nitrogen, argon, carbon monoxide, and / or hydrocarbons. The combined feed suitably includes a low trace amount of hydrocarbons, for example, less than 5% hydrocarbons, less than 3% hydrocarbons, or less than 1% hydrocarbons.

[0071] Third Supply The third feed containing methane is fed to the synthesis gas production unit (II). The third feed may further contain other components, such as CO2 and / or CO and / or H2 and / or steam and / or nitrogen and / or argon. Preferably, the third feed is essentially hydrocarbon or a mixture of hydrocarbon and steam. The hydrocarbon third feed is preferably "hydrocarbon-rich," meaning that the major component of the feed is hydrocarbon; i.e., 50% or more, such as 75% or more, for example 85% or more, preferably 90% or more, more preferably 95% or more, and even more preferably 99% or more of the feed is hydrocarbon. The hydrocarbon concentration in this third feed is determined before the addition of steam (i.e., determined as the "dry concentration").

[0072] An example of such a third feed may include a natural gas stream external to the plant. In one embodiment, the third feed comprises one or more hydrocarbons selected from methane, ethane, propane, or butane.

[0073] In certain embodiments, the third feed comprising methane comprises at least 20%, preferably at least 30%, preferably at least 40%, preferably at least 50%, preferably at least 60%, preferably at least 70%, preferably at least 80%, and most preferably at least 90% methane.

[0074] The source of the third hydrocarbon-containing stream is preferably external to the plant. By "external to the plant" we mean that the stream does not originate from a recycle stream (or a recycle stream that has been further processed or converted) from any synthesis stage within the plant. The third hydrocarbon-containing source can be natural gas, LPG, refinery off-gas, naphtha, renewable energy, or other options.

[0075] Fischer-Tropsch (FT) Section (III) At least a portion of the first synthesis gas stream and at least a portion of the second synthesis gas stream are fed to a Fischer-Tropsch (FT) section (III) for conversion into at least a hydrocarbon product stream and an FT off-gas stream. Preferably, at least a portion of the first synthesis gas stream is combined with at least a portion of the second synthesis gas stream and the resulting combined synthesis gas stream is fed to the Fischer-Tropsch (FT) section (III).

[0076] The Fischer-Tropsch technology is well established and typically provides a hydrocarbon product stream in the form of fuel (such as gasoline, jet fuel, kerosene, and / or diesel). The output of the FT section (III) is long-chain hydrocarbons such as wax. These hydrocarbons are converted to fuels such as kerosene, naphtha, and / or diesel in a hydrocracking unit downstream of the FT section (III).

[0077] Suitably, the combined synthesis gas stream at the inlet of the Fischer-Tropsch (FT) section (III) has a hydrogen / carbon monoxide ratio in the range of from 1.00 to 4.00, preferably from 1.50 to 3.00, more preferably from 1.90 to 2.10.

[0078] The FT off-gas stream suitably has a composition corresponding to that given in the second feed above.

[0079] Specific embodiment examples 1 shows a first layout of a plant for use in the method of the present invention. The plant 100 comprises: - Reverse Water Gas Shift (RWGS) Unit (I), - Syngas production unit (II), - Fischer-Tropsch (FT) section (III), The feeds for the plant in Figure 1 are: a first feed 1 (optional) comprising hydrogen to said reverse water gas shift (RWGS) unit (I), a second feed 2 to said reverse water gas shift (RWGS) unit (I) comprising carbon dioxide, said second feed 2 being process off-gas containing less than 75% CO as specified and being the only carbon dioxide-containing feed to said reverse water gas shift (RWGS) unit (I); a third feed 3 to said synthesis gas production unit (II) comprising methane.

[0080] In FIG. 1, a first feed 1 comprising hydrogen and a second feed (2) comprising carbon dioxide are fed to a RWGS unit (I), which converts them into a first synthesis gas stream 11, which is fed to a FT section III.

[0081] In parallel, a third feed 3 comprising methane is fed to a synthesis gas production unit (II) and converted into a second synthesis gas stream 21 .

[0082] FT section III receives at least a portion of the first syngas stream 11 and at least a portion of the second syngas stream 21 and converts them to at least a hydrocarbon product stream 31 and an FT off-gas stream 32 .

[0083] Figure 2 shows another layout used in the process of the present invention. The components and flows in Figure 2 correspond to those in Figure 1. As shown, the FT off-gas stream 32 from the FT section (III) in Figure 2 is fed as the second feed 2 to the RWGS unit (I).

[0084] Figure 3 shows a variation of Figure 2 in which the synthesis gas production unit (II) is an autothermal reforming (ATR) unit (IIa) to which a fourth feed 4 comprising steam and a fifth feed 5 comprising oxygen are fed. In this layout, at least a portion 6 of the FT off-gas stream 32 from the FT section (III) is fed to the ATR unit (IIa).

[0085] The present invention has been described with reference to numerous embodiments and figures. However, those skilled in the art will be able to select and combine various embodiments within the scope of the present invention as defined by the appended claims. All documents referenced herein are incorporated by reference. [Example]

[0086] example This example provides process parameters for three process examples C1-C3, including a RWGS unit, a syngas production unit, and syngas production using an FT unit. Table 1 shows the process parameters, including flow rates and compositions of various feeds to the process for C1-C3 and the syngas product.

[0087] [Table 1]

[0088] The composition of the off-gas recycled from the FT is shown in Table 2.

[0089] [Table 2]

[0090] C1 C1 relates to the layout of an existing gas-to-hydrocarbon liquids plant, based on a third feed (3) containing methane that is processed in a syngas production unit (II) with autothermal reforming (s) to produce syngas of a quality suitable for downstream Fischer-Tropsch (FT) synthesis (III). The off-gas generated in the FT section (III) is partially utilized in the syngas production unit (II) to produce syngas of the desired quality (i.e., H2 / CO ratio). However, the amount of off-gas is often greater than the amount available in the syngas production unit (e.g., approximately 13% of the off-stream is not utilized as feed). This excess off-gas from the FT unit is utilized elsewhere in the plant, often as heating fuel or fuel for power generation. However, this leads to additional CO2 emissions within the hydrocarbon plant, which could be avoided by utilizing part of this off-gas as feed.

[0091] C2 C2 relates to a plant modification of C1, in which an additional amount of off-gas from the FT synthesis is used as feed to a synthesis gas production unit (II) including autothermal reforming(s). In this example, the recycled off-gas flow rate from the FT unit is increased by 34%. The synthesis gas production is increased to 105% of that in C1, improving the carbon mass balance of the process.

[0092] However, introducing an additional off-gas stream from the FT as a feed to the syngas production unit (II) poses certain challenges in existing plants. One of them is the increased O2 consumption in the syngas production unit, i.e., autothermal reforming, which increases the power consumption of the air separation unit (ASU) to generate O2. Another challenge is the quality of the product syngas. The H2 / CO ratio of the syngas product drops sharply when an additional off-gas stream is introduced. Therefore, to counteract the effect of the additional off-gas feed and maintain the required syngas quality, it is necessary to add an H2-rich stream to the syngas production unit (downstream of the autothermal reformer(s)). In this case, a feed containing H2 from electrolysis is used.

[0093] A further challenge is the retrofit of existing autothermal reformers. C2 shows an increase in off-gas flow of approximately 34%, which would require significant modifications to existing units.

[0094] C3 C3 relates to a process according to the present invention and represents an alternative and more suitable approach to retrofitting the plant cited in C1 by employing a parallel RWGS unit (I) using the off-gas stream from the FT-synthesis section (III) as the only second feed containing CO2 to the RWGS unit (I). The RWGS unit (I) can include electrically heated RWG reactor(s). The synthesis gas production is increased to 105% of that in C1, i.e., an improved carbon mass balance is obtained in this process. Also, this process does not generate excess CO2, which is utilized as fuel for heating, thereby reducing CO2 emissions.

[0095] In C3, no additional O2 is required because no additional off-gas from the FT is recycled to the synthesis gas production unit (II). Furthermore, the required amount of H2-containing feed is reduced to half of that in C2. The lower consumption of the O2-containing fifth feed (5) and the H2-containing first feed (1) (compared to C2) reduces the power consumption for the air separation unit (ASU) and electrolysis, respectively. Considering alkaline electrolysis and a typical ASU, approximately 8% less power consumption can be achieved relative to the product compared to C2.

Claims

1. A process for producing a hydrocarbon product stream (31) in a hydrocarbon plant (100), comprising: The hydrocarbon plant (100) comprises: - Reverse Water Gas Shift (RWGS) unit (I), - a synthesis gas production unit (II), - optionally a first feed (1) comprising hydrogen to said reverse water gas shift (RWGS) unit (I), a second feed (2) to said reverse water gas shift (RWGS) unit (I) comprising carbon dioxide, a third feed (3) comprising hydrocarbons to said synthesis gas production unit (II), - Fischer-Tropsch (FT) section (III), The method includes the following steps: a) optionally feeding said first feed (1) comprising hydrogen to said reverse water gas shift (RWGS) unit (I); b) feeding said second feed (2) to said reverse water gas shift (RWGS) unit (I); However, the second feed (2) contains less than 75% CO ２ and is the only carbon dioxide-containing feed to the reverse water gas shift (RWGS) unit (I); and The process off-gas is a process off-gas from a Fischer-Tropsch (FT) unit, a process off-gas from a methanol loop unit, or a combination of two or more off-gases from two or more such units; c) converting said second feed (2) and—if present— said first feed (1) into a first synthesis gas stream (11) in said reverse water gas shift (RWGS) unit (I); d) feeding said third feed (3) comprising methane to said synthesis gas production unit (II) and converting it into a second synthesis gas stream (21); e) feeding at least a portion of said first synthesis gas stream (11) and at least a portion of said second synthesis gas stream (21) to said Fischer-Tropsch (FT) section (III) and converting said portions of each of said first and second synthesis gas streams into at least a hydrocarbon product stream (31) and an FT off-gas stream (32).

2. 2. The method of claim 1, wherein at least a portion of the FT off-gas stream (32) from the FT section (III) is fed to the RWGS unit (I) as at least a portion of the second feed (2).

3. The method according to any one of claims 1 to 2, wherein at least a portion (6) of the FT off-gas stream (32) from the FT section (III) is fed to a synthesis gas production unit (II).

4. The method according to any one of claims 1 to 3, wherein the process off-gas from the methanol loop unit is an off-gas from a separator unit of the methanol loop unit or an off-gas from a hydrogen recovery unit of the methanol unit.

5. The process off-gas is less than 60%, preferably 5-50%, more preferably 10-40%, and most preferably 20-35% CO ２ The method according to any one of claims 1 to 4, comprising:

6. 6. The method according to any one of claims 1 to 5, wherein the first feed (1) is absent and the process off-gas is the only hydrogen-containing feed to the reverse water gas shift (RWGS) unit (I).

7. 7. The process according to any one of claims 1 to 6, wherein the third feed (3) comprising methane comprises at least 20%, preferably at least 30%, preferably at least 40%, preferably at least 50%, preferably at least 60%, preferably at least 70%, preferably at least 80%, most preferably at least 90% methane.

8. 8. The method of any one of claims 1 to 7, further comprising combining at least a portion of the first synthesis gas stream (11) with at least a portion of the second synthesis gas stream (21) and feeding the resulting combined synthesis gas stream to the Fischer-Tropsch (FT) section (III).

9. The method according to any one of claims 1 to 8, wherein the RWGS unit (I) is an electrically heated reverse water gas shift (e-RWGS) unit.

10. 10. The method according to any one of claims 1 to 9, wherein the synthesis gas production unit (II) is selected from the group consisting of an autothermal reforming (ATR) unit (IIa), a partial oxidation (POX) unit, a steam methane reforming (SMR) unit (IIb) and an electrically heated steam methane reforming (e-SMR) unit (IIc).

11. 11. The method of claim 10, wherein the synthesis gas production unit (II) is an autothermal reforming (ATR) unit (IIa), and the method further comprises supplying at least a portion (6) of the F-T off-gas stream (32) from the F-T section (III), a fourth feed (4) comprising steam, and a fifth feed (5) comprising oxygen to the autothermal reforming (ATR) unit (IIa).

12. 12. The method of any one of claims 1 to 11, further comprising the step of mixing said first feed (1) comprising hydrogen with said second feed (2) comprising carbon dioxide to provide a combined feed that is fed to an e-RWGS unit (I).

13. 13. The process of any one of claims 1 to 12, wherein the synthesis gas stream(s) at the inlet of the Fischer-Tropsch (FT) section (III) have a hydrogen / carbon monoxide ratio in the range of from 1.00 to 4.00, preferably from 1.50 to 3.00, more preferably from 1.90 to 2.10.

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