Conversion of H2 and co2-containing tail gas to synthetic fuel

Abstract

A process for producing a hydrocarbon product stream in a hydrocarbon production plant is provided. The hydrocarbon production plant comprises a reverse water gas shift (RWGS) unit (I), and a second feed comprising carbon dioxide fed to said reverse water gas shift (RWGS) unit (I). The second feed is a process off-gas having a CO2 content of less than 75% and is the only carbon dioxide-containing feed supplied to the reverse water gas shift (RWGS) unit (I).

Description

Technical Field

[0001] The present invention relates to a method for producing a hydrocarbon product stream in a hydrocarbon production apparatus. The hydrocarbon production apparatus includes a reverse water gas shift (RWGS) unit (I), and a carbon dioxide-containing feedstock supplied to the reverse water gas shift (RWGS) unit (I). The feedstock is a process tail gas with a CO2 content of less than 75%, and is the only carbon dioxide-containing feedstock supplied to the reverse water gas shift (RWGS) unit (I). The method of the present invention can make better use of carbon dioxide. Background Art

[0002] Since the Industrial Revolution, the concentration of CO2 in the atmosphere has been continuously rising, and carbon capture and utilization (CCU) has been increasingly emphasized. One way to utilize CO2 is to convert CO2 and H2 into syngas (a gas rich in CO and H2), and the syngas can be further converted into valuable products such as alcohols (including methanol), fuels (such as gasoline, aviation fuel, kerosene, and / or diesel, for example, produced by the Fischer-Tropsch (F-T) process), and / or olefins, etc.

[0003] The prior art mainly focuses on the independent reverse water gas shift (RWGS) process to convert CO2 and H2 into syngas. Subsequently, the syngas can be converted into the above-mentioned valuable products in a downstream process. The reverse water gas shift reaction proceeds according to the following reaction formula:

[0004]

[0005] One or both of the following methanation reactions may produce unwanted by-products such as methane:

[0006]

[0007] The RWGS reaction (1) is an endothermic process and requires a large amount of energy input to achieve the required conversion. High temperatures are required to fully convert carbon dioxide into carbon monoxide to make the process economically viable.

[0008] In recent years, there have been many patent applications regarding the process configurations for converting H2 and CO2 into synthetic fuels. However, in some cases, a CO2 feed stream with a high concentration of CO2 may not always be available, so alternative solutions may need to be sought.

[0009] Patent Publication No. WO2021 / 110806 describes an eRWGS reactor, and Patent Application PCT / EP2021 / 078304 describes various process configurations with RWGS and various feed stream configurations.

[0010] As used hereinafter, "selective RWGS" shall mean that the reverse water-gas shift reaction occurs only on the catalyst or in the reactor, while "non-selective RWGS" shall mean that, in addition to the reverse water-gas shift reaction, other reactions occur, such as one or more methanation reactions (including also reverse methanation). Summary of the Invention

[0011] A method for producing a hydrocarbon product stream in a hydrocarbon production apparatus is provided, the hydrocarbon production apparatus comprising:

[0012] - a reverse water-gas shift (RWGS) unit (I),

[0013] - a syngas production unit (II),

[0014] - optionally, a first feed containing hydrogen, which is supplied to the reverse water-gas shift (RWGS) unit (I),

[0015] - a second feed containing carbon dioxide, which is supplied to the reverse water-gas shift (RWGS) unit (I),

[0016] - a third feed containing methane, which is supplied to the syngas production unit (II),

[0017] - a Fischer-Tropsch (F-T) section (III),

[0018] The method comprises the following steps:

[0019] a) optionally, supplying the first feed containing hydrogen to the reverse water-gas shift (RWGS) unit (I);

[0020] b) supplying the second feed to the reverse water-gas shift (RWGS) unit (I);

[0021] wherein the second feed is a process tail gas with a CO2 content of less than 75% and is the only carbon dioxide-containing feed supplied to the reverse water-gas shift (RWGS) unit (I);

[0022] c) in the reverse water-gas shift (RWGS) unit (I), converting the second feed and, if present, the first feed into a first syngas stream;

[0023] d) supplying the third feed containing methane to the syngas production unit (II) and converting it into a second syngas stream;

[0024] e) supplying at least a portion of the first syngas stream and at least a portion of the second syngas stream to the Fischer-Tropsch (F-T) section (III) and converting the portions of the first and second syngas streams into at least a hydrocarbon product stream and an F-T tail gas stream.

[0025] Typically, the RWGS-based process uses high-purity CO2-containing feedstocks, e.g., feedstocks with a CO2 content of at least above 95%, typically above 99%. The present invention is based on a surprising experimental finding that an RWGS reactor can be operated using a low-purity CO2-containing feedstock, where the CO2 content can be as low as, for example, 20 - 35%. The present invention is also based on the recognition that this fact enables the use of the tail gas from the Fischer-Tropsch (F-T) section as a CO2-containing feedstock for supplying the RWGS reactor, or other low-purity CO2-containing feedstocks. In addition, the present invention is based on a surprising finding that the tail gas from the Fischer-Tropsch (F-T) section can be used as the sole CO2-containing feedstock to operate the RWGS reactor.

[0026] The method effectively utilizes various streams, especially process tail gases. The technical advantages of the present invention are at least reflected in the following two aspects:

[0027] 1) Process tail gases are typically used as fuel gas, which leads to the emission of CO2 into the atmosphere, which is not desirable. This includes the CO2 from the process tail gas itself, as well as the CO2 generated from burning hydrocarbons when using the tail gas as fuel. The present invention can reduce or completely avoid these emissions.

[0028] 2) The carbon efficiency of the method is improved because the carbon contained in the process tail gas is recycled and reused in the process, so that a higher proportion of the carbon supplied to the process is converted into the hydrocarbon product stream.

[0029] In addition, the method of the present invention provides the possibility of retrofitting (also known as modifying) existing synthetic fuel production processes / equipment, which includes a syngas production reactor and a Fischer-Tropsch unit (without an RWGS unit), simply by adding an RWGS unit to the process. Through this retrofit of the existing process, the modified process can achieve technical advantages 1) and 2).

[0030] For more details on this technology, please refer to the accompanying dependent claims, drawings, and examples.

[0031] Brief Description of the Drawings

[0032] This technology is illustrated by the following schematic diagrams, where:

[0033] Figure 1 The first layout of the hydrocarbon production equipment of the present invention is shown, which has various feeds.

[0034] Figure 2 Another layout of the hydrocarbon production equipment of the present invention is shown, which has various feeds, where the F-T tail gas stream from the F-T section is supplied as a second feed to the RWGS unit.

[0035] Figure 3shows Figure 2 a variant in which the syngas production unit (II) is an autothermal reforming (ATR) unit (IIa), and in which a portion of the FT tail gas stream from the F-T section is supplied as a second feed to the RWGS unit (I), and a portion of the FT tail gas stream is supplied to the ATR unit (IIa). DETAILED DESCRIPTION OF THE INVENTION

[0037] Unless otherwise stated, any given percentage of gas content is by volume. All feeds are preheated as required.

[0038] The present technology relates to a tail gas stream as a second feed stream, which preferably has a low to medium content of CO2 (i.e., less than 75% CO2), and optionally also contains hydrogen and / or hydrocarbons and / or CO.

[0039] Carbon capture and utilization has received increasing attention in recent years. Known plant layouts provide a solution for utilizing CO2 in the presence of H2 to produce syngas and subsequently converting the syngas into valuable products, such as syngas-derived liquid fuels, also known as synthetic fuels. To convert the CO2 and H2 feeds into syngas, an electrically heated RWGS (e-RWGS) unit is preferably used.

[0040] 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 gas typically contains hydrocarbon gases, such as CH4, and optionally contains higher hydrocarbons with relatively low normal contents, as well as various amounts of other gases. Higher hydrocarbons are components having two or more carbon atoms, such as ethane and propane. Examples of "hydrocarbon gases" can be natural gas, town gas, naphtha or a mixture of methane and higher hydrocarbons, biogas or LPG. Hydrocarbons may also be components containing other atoms in addition to carbon and hydrogen, such as oxygenates. The term "hydrocarbon-containing feed gas" refers to a feed gas containing a mixture of hydrocarbon gas (containing one or more hydrocarbons) with steam, hydrogen, and possibly other components (such as carbon monoxide, carbon dioxide, nitrogen, and argon).

[0041] The term "syngas" refers to a gas containing hydrogen, carbon monoxide, and also carbon dioxide and small amounts of other gases (such as argon, nitrogen, methane, etc.).

[0042] As described above, the method of the present invention is carried out in a hydrocarbon production plant, which includes:

[0043] - a reverse water gas shift (RWGS) unit (I),

[0044] - a syngas production unit (II),

[0045] - Optionally, a first feed containing hydrogen is supplied to the reverse water gas shift (RWGS) unit (I).

[0046] - A second feed containing carbon dioxide is supplied to the reverse water gas shift (RWGS) unit (I).

[0047] - A third feed containing methane is supplied to the syngas production unit (II).

[0048] - The Fischer-Tropsch (F-T) section (III).

[0049] The method comprises the following steps:

[0050] a) Optionally, supplying the first feed containing hydrogen to the reverse water gas shift (RWGS) unit (I);

[0051] b) Supplying the second feed to the reverse water gas shift (RWGS) unit (I);

[0052] wherein the second feed is a process tail gas with a CO2 content of less than 75% and is the only carbon dioxide-containing feed supplied to the reverse water gas shift (RWGS) unit (I);

[0053] c) In the reverse water gas shift (RWGS) unit (I), converting the second feed and, if present, the first feed into a first synthesis gas stream;

[0054] d) Supplying the third feed containing methane to the syngas production unit (II) and converting it into a second synthesis gas stream;

[0055] e) Supplying 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 (F-T) section (III) and converting the portions of the first and second synthesis gas streams into at least a hydrocarbon product stream and an F-T tail gas stream.

[0056] The following are the detailed information on the components constituting the hydrocarbon production equipment:

[0057] Reverse water gas shift (RWGS) unit (I)

[0058] The carbon dioxide and, if present, the hydrogen feed are mainly processed in the reverse water gas shift (RWGS) unit, which is preferably an electrically heated reverse water gas shift (e-RWGS) unit.

[0059] The first feed containing hydrogen (if present) and the second feed containing carbon dioxide are arranged to be properly mixed to provide a combined feed supplied to the RWGS unit.

[0060] The RWGS unit (I) is arranged to convert at least a portion of the first feed (comprising hydrogen) and at least a portion of the second feed (comprising CO2) into a first synthesis gas stream.

[0061] The first synthesis gas stream produced in the RWGS unit typically has the following composition (by volume):

[0062] - 0.5 - 5% methane (dry basis)

[0063] - 40 - 70% H2 (dry basis)

[0064] - 10 - 40% CO (dry basis)

[0065] - 2 - 20% CO2 (dry basis)

[0066] The first synthesis gas stream may also contain other components, such as water vapor and / or nitrogen.

[0067] e-RWGS unit

[0068] Preferably, the RWGS unit is an electrically heated reverse water gas shift e - RWGS unit. The electrically heated reverse water gas shift e - RWGS enables a more efficient reverse water gas shift process through resistance heating of the reactor and significantly reduces or preferably avoids the use of fossil fuels as a heat source.

[0069] The e - RWGS reactor can be selective or non - selective: "selective" means that only the RWGS reaction (Reaction 1 above) occurs; "non - selective" means that both the RWGS reaction (1) and the methanation reaction (Reaction 2 above) occur. The non - selective process can also carry out other reactions, such as steam reforming of higher hydrocarbons (hydrocarbons containing two or more carbon atoms, such as ethane). For a detailed description of e - RWGS, reference can be made to documents such as "Angew.Chem.Int.Ed.2022,61,e202109696".

[0070] In the present invention, the e - RWGS unit is used to effect the reverse water gas shift reaction between CO2 and H2. The e - RWGS unit preferably comprises the following components:

[0071] - A structured catalyst for catalyzing the RWGS reaction, the structured catalyst comprising a macroscopic structure of a conductive material, the macroscopic structure being loaded with a ceramic coating, wherein the ceramic coating is loaded with a catalytically active material (for selective e - RWGS);

[0072] - A pressure-resistant shell that houses the structured catalyst; the pressure-resistant shell includes an inlet for introducing the feed and an outlet for discharging the syngas product; wherein the position of the inlet is such that the feed enters from the first end of the structured catalyst, and the syngas product is discharged from the second end of the structured catalyst;

[0073] - A heat-insulating layer between the structured catalyst and the pressure-resistant shell; and

[0074] - At least two conductors that are electrically connected to the structured catalyst and a power source located outside the pressure-resistant shell, wherein the power source is designed to heat at least a portion of the structured catalyst to a temperature of at least 500 °C by passing an electric current through the macroscopic structure of the conductive material; wherein the at least two conductors are connected to the structured catalyst at a position closer to the first end of the structured catalyst than to the second end of the structured catalyst, and wherein the structured catalyst is configured to direct the electric current from one conductor substantially towards the second end of the structured catalyst and then back to the second of the at least two conductors, and wherein the structured catalyst has electrically insulating components that are arranged to direct the electric current from one conductor closer to the first end than the second end of the structured catalyst towards the second end of the structured catalyst and then back to another conductor closer to the first end than the second end of the structured catalyst.

[0075] The design pressure of the pressure-resistant shell is typically between 25 and 45 bar. The design pressure of the pressure-resistant shell can also be between 30 and 200 bar. The at least two conductors are typically led out through joints on the pressure-resistant shell to electrically insulate the at least two conductors from the pressure-resistant shell. The pressure-resistant shell further includes one or more inlets near or in combination with at least one joint to enable a cooling gas to flow through, around, near, or into at least one of the conductors within the pressure-resistant shell. The outlet temperature of the e-RWGS unit (I) is preferably 900 °C or higher, more preferably 1000 °C or higher.

[0076] For non-selective e-RWGS, in addition to the RWGS reaction, methanation reactions according to reactions (2) and / or (3) also occur. The advantage of this is that the carbon monoxide concentration inside the reactor is lower than in the case where only the reverse water-gas shift reaction occurs. This is particularly important in the low to medium temperature range of approximately 600 - 800 °C. In this temperature range, compared with selective RWGS catalysts, when using non-selective catalysts, the possibility of carbon deposition or metal dusting exists, or this possibility is significantly greater.

[0077] In one embodiment, when a non-selective catalyst is used in the e-RWGS reactor, the methanation reaction also occurs at and near the inlet of the reactor. However, at a given temperature (depending on the composition of the feed gas, pressure, catalyst activity, degree of heat supply, and other factors), the reverse reaction of the methanation reaction will be thermodynamically dominant. In other words, methane is generated in the first part of the RWGS reactor, while in the second part downstream of the first part, methane will be consumed according to the reverse reactions of reactions (2) and / or (3).

[0078] The combined reaction of reverse water-gas shift and methanation in the eRWGS reactor of the present invention means that the reaction mechanism inside the reactor starts with an exothermic reaction in the first part of the reactor system and ends with an endothermic reaction at the outlet of the reactor system. This is related to the reaction heat (Qr) added or removed during the reaction. According to the overall heat balance of the plug flow reactor system:

[0079] F·C pm ·dT / dV = Q add +Q r =Q add +∑(-Δ r H i )·(-r i )

[0080] 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, Q add is the energy supply / removal from the environment, Q r is the energy supply / removal related to the chemical reaction, and the latter refers to the sum of all chemical reactions facilitated within this volume and is calculated as the product of the reaction enthalpy and reaction rate of a given reaction.

[0081] The high temperature exiting the e-RWGS reactor enables a low concentration of methane. Another advantage of the high temperature is that it can convert more CO2 into CO. In one embodiment, the gas temperature discharged from the e-RWGS reactor is higher than 900 °C, such as higher than 1000 °C, or even higher than 1050 °C. The advantage of the proposed reactor is that it can achieve a higher temperature than that typically achievable by conventional external flame reactors.

[0082] By using an e-RWGS unit (compared to a conventional flame RWGS unit), a syngas product gas stream with a lower CO2 content (e.g., less than 20%) can be produced. This is ideal for certain applications, such as Fischer-Tropsch synthesis or methanol synthesis, because the high-temperature operation of e-RWGS ensures a high conversion rate of CO2 to CO.

[0083] One or more component removal units (e.g., removing H2 or CO2 as needed) can be provided downstream of the RWGS unit to provide a upgraded first syngas stream.

[0084] Syngas production unit (II)

[0085] The syngas production unit (II) is configured to convert at least a portion of the third feed (comprising methane) into a second syngas stream. The syngas production unit II may require additional feeds (e.g., comprising oxygen and / or steam).

[0086] The syngas production unit (II) can be selected from the following: an autothermal reforming (ATR) unit (IIa), a steam methane reforming (SMR) unit (IIb), and an electrically heated steam methane reforming (e-SMR) unit (IIc), and is preferably an electrically heated steam methane reforming (e-SMR) unit (IIc).

[0087] The second syngas stream can have the following composition (by volume):

[0088] - 40 - 70% H2 (dry basis)

[0089] - 10 - 30% CO (dry basis)

[0090] - 2 - 20% CO2 (dry basis)

[0091] - 0.5 - 5% CH4 (dry basis)

[0092] In one aspect, the syngas production unit (II) can be an autothermal reforming (ATR) unit (IIa). The autothermal reforming (ATR) unit converts the third feedstock comprising methane into a second syngas stream. In one aspect, at least a portion of the F-T tail gas stream from the F-T section (III) is supplied to the syngas production unit (II). In this way, the amount of the third feed supplied to the syngas production unit (II) can be reduced.

[0093] The ATR unit generally includes a burner, a combustion chamber, and a catalyst bed contained within a pressure-resistant shell lined with refractory material. In the ATR unit, the hydrocarbon feed is first partially combusted with sub-stoichiometric oxygen, and then the partially combusted hydrocarbon feed stream is steam reformed by a steam reforming catalyst in a fixed bed. Due to the high temperature, steam reforming also occurs to some extent in the combustion chamber. The steam reforming reaction is accompanied by a water-gas shift reaction. Generally, at the reactor outlet, the gas is at or near equilibrium with respect to the steam reforming and water-gas shift reactions.

[0094] Typically, the temperature of the (second) syngas stream from the ATR unit is 900 - 1100 °C. This (second) syngas stream typically contains H2, CO, CO2, and water vapor. Other components such as methane, nitrogen, and argon may also be present, but usually in smaller amounts. The operating pressure of the ATR unit is typically between 5 and 100 bar, more preferably between 15 and 60 bar.

[0095] The second syngas stream from the ATR unit is typically cooled in a cooling system that includes one or more waste heat boilers (WHB) and one or more additional heat exchangers. The cooling medium in the WHB is (boiler feed) water, which is vaporized into steam. The second syngas stream is further cooled below the dew point, for example, by preheating devices and / or partially preheating one or more feed streams, and cooled in an air cooler and / or a water cooler. The condensed H2O is removed as process condensate in a separator, thereby providing a syngas stream with a low H2O content, which can be sent to the Fischer - Tropsch (F - T) section (III). More detailed information and a complete description of ATR can be found in the prior art, such as "Studies in Surface Science and Catalysis, Vol. 152", "Synthesis gas production for FT synthesis"; Chapter 4, p. 258 - 352, 2004".

[0096] The "ATR unit" can be a partial oxidation "POX" section. The POX section is similar to the ATR section, except that the ATR unit is replaced by a POX reactor. The POX reactor typically includes a burner and a combustion chamber, which are contained in a pressure - resistant shell lined with refractory materials.

[0097] The ATR unit can also be a catalytic partial oxidation (cPOX) section.

[0098] The oxidant for the 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 also contain other components, such as steam, nitrogen, and / or argon. Typically, in this case, the oxidant will contain 5 - 20% steam.

[0099] In this regard, the process further includes supplying a fourth feed (containing steam) and optionally a fifth feed (containing oxygen) to the autothermal reforming (ATR) unit (IIa). A sixth feed, which is part of the F - T tail gas stream from the F - T section (III), can also be supplied to the syngas production unit (II).

[0100] If the reforming unit is SMR or e - SMR, a fourth feed containing steam is required.

[0101] On the other hand, the syngas production unit (II) is an electrically heated steam methane reforming (e-SMR) section (IIc). In this regard, the apparatus does not include a feed containing oxygen being supplied to the electrically heated steam methane reforming (e-SMR) section (IIc). By this aspect, the overall CO2 emissions of the apparatus can be further reduced.

[0102] First feed

[0103] Optionally, a first feed containing hydrogen is provided to the RWGS unit. Suitably, the first feed consists mainly of hydrogen. The first feed hydrogen is suitably "hydrogen-rich", which means that the main part 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. The source of the first feed hydrogen can be a single or multiple electrolyzer units. In addition to hydrogen, the first feed may also contain, for example, steam, nitrogen, argon, carbon monoxide, carbon dioxide, and / or hydrocarbons. In some cases, a small amount of oxygen may be present in the feed, usually less than 1000 ppm.

[0104] On the other hand, the first feed is absent, and the process tail gas as the second feed is the only carbon dioxide-containing feed supplied to the reverse water gas shift (RWGS) unit (I); it is also the only hydrogen-containing feed supplied to the reverse water gas shift (RWGS) unit (I). In other words, the process tail gas can substantially provide all the CO2 and all the H2 required for the process.

[0105] Second feed

[0106] A second feed containing carbon dioxide is supplied to the RWGS unit. The second feed is a process tail gas with a CO2 content of less than 75%, and it is the only carbon dioxide-containing feed supplied to the reverse water gas shift (RWGS) unit (I). This means that the CO2 capture and purification steps can be avoided in the process of the present invention.

[0107] In addition to CO2, the second feed may also contain, for example, hydrogen, steam, nitrogen, oxygenates, amines, ammonia, carbon monoxide, and / or hydrocarbons.

[0108] If the first feed is absent, the second feed preferably contains H2.

[0109] The second feed suitably contains only a small amount of higher hydrocarbons (i.e., excluding methane), such as less than 5% of higher hydrocarbons, or less than 3% of higher hydrocarbons, or less than 1% of higher hydrocarbons.

[0110] The second feed is the process off-gas of a Fischer-Tropsch (F-T) unit, the process off-gas of a methanol loop unit, or a combination of two or more such off-gases from two or more such units.

[0111] In a particular embodiment, at least a portion (6) of the F-T off-gas stream (32) from the F-T section (III) is supplied as at least a portion of the second feed (2) to the RWGS unit (I). In another embodiment, the process off-gas is the process off-gas of an F-T unit external to the process of the present invention.

[0112] The methanol loop, i.e., the methanol loop unit that generates the process off-gas, is located outside the method of the present invention. The methanol loop, i.e., the methanol synthesis section, includes one or more methanol synthesis reactors. The synthesis gas stream enters the methanol synthesis reactor and is converted in the presence of a catalyst into a crude product stream containing methanol. The crude product stream containing methanol can be cooled in one or more heat exchangers and then fed into a gas-liquid separator unit, which is typically a high-pressure (HP) separator. The gas-liquid separator unit provides a product stream containing methanol and a recycle stream containing H2, CO, and CO2, a portion of which is discharged as an off-gas stream from the gas-liquid separator unit. The methanol synthesis section may further include a hydrogen recovery unit for separating the methanol off-gas stream into a hydrogen-rich gas stream rich in H2 and containing a small amount of CO and CO2 and a hydrogen recovery off-gas. In a particular embodiment, the process off-gas from the methanol loop unit is the off-gas from the separator unit of the methanol loop unit or the off-gas from the hydrogen recovery unit of the methanol unit.

[0113] In a specific embodiment of the method of the present invention, at least a portion (6) of the F-T off-gas stream (32) from the F-T section (III) is supplied to the syngas production unit (II).

[0114] The process off-gas contains less than 75%, less than 60%, preferably 5 - 50%, more preferably 10 - 40% and most preferably 20 - 35% CO2.

[0115] The process off-gas contains less than 60%, more preferably 10 - 50% and most preferably 20 - 40% H2.

[0116] The process off-gas contains less than 30%, preferably 1 - 25%, more preferably 5 - 25% and most preferably 10 - 20% hydrocarbons.

[0117] In a particularly preferred aspect, at least a portion of the F-T off-gas stream from the F-T section (III) is supplied to the RWGS unit (I) as at least a portion of the second feed. Recycling the off-gas stream as the second feed provides a more self-consistent process and reduces the number of required external feeds / units.

[0118] Combined feed

[0119] As an alternative to feeding hydrogen and carbon dioxide separately, the apparatus can be fed with a combined feed comprising hydrogen and carbon dioxide to the e-RWGS unit (I). Generally, the hydrogen content in the combined feed is from 40% to 80%, preferably from 50% to 70%.

[0120] The carbon dioxide content in the combined feed is generally from 15% to 50%, preferably from 20% to 40%. The carbon monoxide content is generally from 0% to 10% of the combined feed. The ratio of hydrogen to carbon dioxide in the combined feed is generally from 1 to 5, preferably from 2 to 4.

[0121] In addition to hydrogen and carbon dioxide, the combined feed may also contain, for example, water vapor, nitrogen, argon, carbon monoxide and / or hydrocarbons. The combined feed suitably contains only a small amount of hydrocarbons, such as less than 5% hydrocarbons, or less than 3% hydrocarbons, or less than 1% hydrocarbons.

[0122] Third feed

[0123] A third feed comprising methane is provided to the syngas production unit (II). The third feed may also contain other components, such as CO2 and / or CO and / or H2 and / or steam and / or other components, such as nitrogen and / or argon. Suitably, the third feed consists mainly of hydrocarbons or a mixture of hydrocarbons and steam. Suitably, the third feed of hydrocarbons is "hydrocarbon-rich", which means that the main part of the feed is hydrocarbons; that is, more than 50%, such as more than 75%, such as more than 85%, preferably more than 90%, more preferably more than 95%, even more preferably more than 99% of the feed is hydrocarbons. The concentration of hydrocarbons in the third feed is determined before the addition of steam (i.e., determined as the "dry concentration").

[0124] An example of such a third feed can also be a natural gas stream outside the apparatus. In one aspect, the third feed comprises one or more hydrocarbons selected from methane, ethane, propane or butane.

[0125] In one aspect, the third feed comprising methane contains at least 20% methane, 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.

[0126] The source of the third feed comprising hydrocarbons is preferably outside the apparatus. The meaning of "outside the apparatus" stream means that the stream is not a recycle stream (or a recycle stream that has been further processed or converted) from any synthesis stage within the apparatus. Possible sources of the third feed comprising hydrocarbons include natural gas, LPG, refinery off-gas, naphtha and renewable energy, but other options can also be considered.

[0127] Fischer-Tropsch (F-T) section (III)

[0128] At least a portion of a first synthesis gas stream and at least a portion of a second synthesis gas stream are fed to a Fischer-Tropsch (F-T) section (III) and converted into at least a hydrocarbon product stream and an F-T tail gas stream. Suitably, at least a portion of said first synthesis gas stream is combined with at least a portion of said second synthesis gas stream, and the resulting combined synthesis gas stream is fed to said Fischer-Tropsch (F-T) section (III).

[0129] The Fischer-Tropsch technology is well established and typically provides a hydrocarbon product stream in the form of fuels (such as gasoline, aviation fuel, kerosene and / or diesel). The output of the (F-T) section (III) is long-chain hydrocarbons such as waxes. These hydrocarbons are converted into fuels such as kerosene, naphtha and / or diesel in a hydrocracking unit downstream of the FT section (III).

[0130] Suitably, the hydrogen / carbon monoxide ratio of the combined synthesis gas stream at the inlet of the Fischer-Tropsch (F-T) section (III) is in the range of 1.00 - 4.00; preferably 1.50 - 3.00; more preferably 1.90 - 2.10.

[0131] The suitable composition of the F-T tail gas stream corresponds to the composition of the second feedstock described above. Specific embodiments

[0132] Figure 1 Shows a first layout of the equipment for the process of the present invention. The equipment 100 includes:

[0133] - A reverse water gas shift (RWGS) unit (I),

[0134] - A syngas production unit (II),

[0135] - A Fischer-Tropsch (F-T) section (III),

[0136] Figure 1 The feeds to the equipment are as follows:

[0137] - A first feed 1 (optional), which contains hydrogen and is fed to the reverse water gas shift (RWGS) unit (I),

[0138] - A second feed 2, which contains carbon dioxide and is fed to the reverse water gas shift (RWGS) unit (I), this feed is a process tail gas with a CO2 content of less than 75% (as described above), and is the only carbon dioxide-containing feed fed to the reverse water gas shift (RWGS) unit (I);

[0139] - A third feed 3, which contains methane and is fed to the syngas production unit (II).

[0140] InFigure 1 In Figure 1 , a first feed 1 containing hydrogen and a second feed (2) containing carbon dioxide are supplied to the RWGS unit (I), where they are converted into a first synthesis gas stream 11, and the first synthesis gas stream 11 is supplied to the F-T section III.

[0141] Meanwhile, a third feed 3 containing methane is supplied to the syngas production unit (II) and converted into a second synthesis gas stream 21.

[0142] The F-T section III receives at least a portion of the first synthesis gas stream 11 and at least a portion of the second synthesis gas stream 21 and converts them into at least a hydrocarbon product stream 31 and an F-T tail gas stream 32.

[0143] Figure 2 Another layout used in the method of the present invention is shown. Figure 2 The components and streams in Figure 2 correspond to the components and streams in Figure 1 As shown, the F-T tail gas stream 32 from the F-T section (III) in Figure 2 is supplied as the second feed 2 to the RWGS unit (I).

[0144] Figure 3 A variant of Figure 2 is shown, in which the syngas production unit (II) is an autothermal reforming (ATR) unit (IIa), and a fourth feed 4 containing steam and a fifth feed 5 containing oxygen are supplied to the autothermal reforming (ATR) unit (IIa). In this layout, at least a portion 6 of the F-T tail gas stream 32 from the F-T section (III) is supplied to the ATR unit (IIa).

[0145] The present invention has been described above with reference to multiple embodiments and drawings. However, those skilled in the art can select and combine various embodiments within the scope of the invention defined by the appended claims. All documents cited herein are incorporated herein by reference.

[0146] Example

[0147] This example provides the process parameters for three examples of C1-C3, which includes syngas production using an RWGS unit, a syngas production unit, and an FT unit. Table 1 shows the process parameters for processes C1-C3, including the flow rates and compositions of various feed streams, as well as the process parameters of the syngas product.

[0148] Table 1

[0149]

[0150] The composition of the recycle tail gas from F-T is shown in Table 2.

[0151] Table 2

[0152] Component UoM Value Hydrogen mol% 18.0-25.0 Carbon monoxide mol% 15.0-20.0 Carbon dioxide mol% 35.0-45.0 Methane mol% 10.0-18.0 Water mol% <1.0 HHC mol% <2.0 Inert gas mol% 2.0-5.0

[0153] C1

[0154] C1 relates to an existing equipment layout for gas-to-liquid hydrocarbons, which is based on a third feed (3) that contains methane processed in a syngas production unit (II). The syngas production unit includes an autothermal reformer to produce syngas of suitable quality for downstream Fischer-Tropsch (F-T) synthesis (III). A portion of the tail gas generated by the FT-section (III) is used in the syngas production unit (II) to produce syngas of the required quality (i.e., H2 / CO ratio). However, the amount of tail gas is typically higher than the amount that can be utilized by the syngas production unit (in this example, approximately 13% of the tail gas is not used as feed). The excess tail gas from the F-T unit is used elsewhere in the equipment, typically as fuel for heating or power generation. However, this results in additional CO2 emissions within the hydrocarbon production equipment, which can be avoided if this portion of the tail gas is used as feed.

[0155] C2

[0156] C2 relates to the modification of the C1 equipment, where an additional portion of the tail gas from the FT synthesis is used as feed to the syngas production unit (II) (including the autothermal reformer). In this example, the recycled tail gas flow from the F-T unit is increased by 34%. The syngas production is increased to 105% of the C1 production, i.e., the process achieves an improved carbon mass balance.

[0157] However, in existing equipment, introducing additional tail gas from the F-T as feed to the syngas production unit (II) poses some challenges. One challenge is the increased O2 consumption in the syngas production unit (i.e., the autothermal reformer), which requires the air separation unit (ASU) to consume more electricity to produce O2. Another challenge is the quality of the syngas product. Introducing an additional tail gas stream causes a significant decrease in the H2 / CO ratio of the syngas product. Therefore, it is necessary to add a H2-rich stream to the syngas production unit (downstream of the autothermal reformer) to offset the effect of the additional tail gas feed and maintain the required syngas quality. In this case, a feed containing H2 from electrolysis can be used.

[0158] Another challenge is the modification of the existing autothermal reformer. It can be seen that in C2, the tail gas flow is increased by approximately 34%. This may require significant modifications to the existing unit.

[0159] C3

[0160] C3 relates to a method according to the present invention, which represents an alternative and superior solution for improving the device described in C1. The method of C3 employs parallel RWGS units (I), which utilize the tail gas from the FT synthesis section (III) as the only second feed containing CO2 delivered to the RWGS units (I). The RWGS units (I) may include electrically heated RWGS reactors. The syngas production is increased to 105% of the C1 production, i.e., the carbon mass balance of the method is improved. In addition, the method does not generate any excess CO2 that needs to be used as heating fuel, thereby reducing CO2 emissions.

[0161] In C3, since no additional tail gas from F-T is recycled to the syngas production unit (II), no additional O2 is required. In addition, the demand for the feed containing H2 is also reduced to half of that in C2. The consumption of the fifth feed (5) containing O2 and the first feed (1) containing H2 is lower (compared with C2), thereby reducing the power consumption of the air separation unit (ASU) and electrolysis respectively. Considering alkaline electrolysis and a typical ASU, the power consumption / product of this embodiment is reduced by approximately 8% compared with C2.

Claims

1. A method for producing a hydrocarbon product stream (31) in a hydrocarbon production apparatus (100), the hydrocarbon production apparatus (100) comprising: - a reverse water gas shift (RWGS) unit (I), - a syngas production unit (II), - optionally, a first feed (1) containing hydrogen, which is supplied to the reverse water gas shift (RWGS) unit (I), - a second feed (2) containing carbon dioxide, which is supplied to the reverse water gas shift (RWGS) unit (I), - a third feed (3) containing hydrocarbons, which is supplied to the syngas production unit (II), - a Fischer-Tropsch (F-T) section (III), The method comprises the following steps: a) Optionally, supply the first feed containing hydrogen to the reverse water gas shift (RWGS) unit (I); b) Supply the second feed to the reverse water gas shift (RWGS) unit (I); wherein the second feed (2) is a process tail gas with a CO2 content of less than 75%, and is the only carbon dioxide-containing feed supplied to the reverse water gas shift (RWGS) unit (I), and wherein the process tail gas is a process tail gas from a Fischer-Tropsch (F-T) unit or a process tail gas from a methanol loop unit, or a combination of two or more tail gases from two or more such units; c) In the reverse water gas shift (RWGS) unit (I), convert the second feed (2) and, if present, the first feed (1) into a first synthesis gas stream (11); d) Supply the third feed (3) containing methane to the syngas production unit (II) and convert it into a second synthesis gas stream (21); e) Supply 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 (F-T) section (III) and convert the portions of the first and second synthesis gas streams into at least a hydrocarbon product stream (31) and an F-T tail gas stream (32).

2. The method according to claim 1, wherein at least a portion of the F-T tail gas stream (32) from the F-T section (III) is supplied as at least a portion of the second feed (2) to the RWGS unit (I).

3. The method according to any one of the preceding claims, wherein at least a portion (6) of the F-T tail gas stream (32) from the F-T section (III) is supplied to the syngas production unit (II).

4. The method according to any one of the preceding claims, wherein the process tail gas from the methanol loop unit is a tail gas from a separator unit of the methanol loop unit or a tail gas from a hydrogen recovery unit of the methanol unit.

5. The method according to any one of the preceding claims, wherein the process tail gas contains less than 60%, preferably 5 - 50%, more preferably 10 - 40%, and most preferably 20 - 35% of CO2.

6. The method according to any one of the preceding claims, wherein there is no first feed (1), and wherein the process off-gas is the only hydrogen-containing feed supplied to the reverse water gas shift (RWGS) unit (I).

7. The method according to any one of the preceding claims, wherein the third feed (3) containing 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.

8. The method according to any one of the preceding claims, further comprising combining at least a portion of the first synthesis gas stream (11) and at least a portion of the second synthesis gas stream (21), and supplying the resulting combined synthesis gas stream to the Fischer-Tropsch (F-T) section (III).

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

10. The method according to any one of the preceding claims, wherein the syngas production unit (II) is selected from 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. The method according to claim 10, wherein the syngas production unit (II) is an autothermal reforming (ATR) unit (IIa), and wherein the method further comprises supplying at least a portion (6) of the F-T tail gas stream (32) from the F-T section (III), a fourth feed (4) containing steam and a fifth feed (5) containing oxygen to the autothermal reforming (ATR) unit (IIa).

12. The method according to any one of the preceding claims, further comprising the step of mixing a first feed (1) containing hydrogen with a second feed (2) containing carbon dioxide to provide a combined feed supplied to the e-RWGS unit (I).

13. The method according to any one of the preceding claims, wherein the synthesis gas stream at the inlet of the Fischer-Tropsch (F-T) section (III) has a hydrogen / carbon monoxide ratio of 1.00 - 4.00; preferably 1.50 - 3.00; more preferably 1.90 - 2.10.

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