Method and system for improving carbon efficiency in production of syngas and synthetic fuels

Abstract

The invention relates to a method and system for enhancing carbon efficiency in syngas and synthetic fuel production. This is achieved by utilizing a syngas unit designed to use at least syngas from gasification and Fischer-Tropsch (FT) tail gas as feedstock and integrating one or more reverse water gas shift (RWGS) reactor(s) within the syngas section to recover carbon from the FT-tail gas. The syngas section can be configured to boost syngas production by processing the FT-tail gas. The RWGS reactor(s) are adapted to reduce CO2 emissions by converting CO2 in the FT-tail gas and in raw syngas back into CO and by converting CH4 in the FT-tail gas back into CO and H2. One or more gasifiers produce raw syngas (2) from a carbon-source feed, such as waste or biomass. The syngas section operates without significant amounts of renewable hydrogen from electrolysis.

Description

[0001] Method and System for improving carbon efficiency in production of syngas and synthetic fuels

[0002] TECHNICAL FIELD

[0003] The invention relates to a method and system for enhancing carbon efficiency in syngas and synthetic fuel production. This is achieved by utilizing a syngas unit or section designed to use at least syngas from gasification and FT-tail gas as feedstock and integrating a reverse water gas shift (RWGS) reactor within the syngas unit or section to recover carbon from the FT-tail gas.

[0004] BACKGROUND

[0005] The field of renewable energy, specifically the production of fuels from renewable feedstocks, has seen significant advancements over the years. One such method is the gasification-to-fuels process, which involves converting various feedstocks, such as biomass or waste, into a gas mixture known as syngas, primarily composed of hydrogen (H2) and carbon monoxide (CO). This syngas is then cleaned, conditioned, and used to produce fuels through processes such as Fischer-Tropsch Synthesis (FTS) or Methanation. Despite its potential, the gasification-to-fuels process is not very carbon efficient. A large amount of CO2 produced in the gasification process is removed in CO2 removal steps and either ends up as CO2 emission or is captured in a concentrated stream in the CO2 removal unit and sequestered or stored. In the present invention, it is understood that CO2 removal step in current renewable solutions are preferably part of the gasification section. A large amount of CH4 is also produced. This results in a significant portion of the carbon-containing material not being used to make final fuel products. Additionally, there are other carbon-rich gases that are available as off-gas in the fuel process, which result in CO2 emissions if burnt as fuel, such as refinery off-gas or LPG, or captured by additional CO2 removal steps and sequestered or stored. This inefficiency in carbon utilization and the associated CO2 emissions present a significant challenge in the field of renewable fuel production.

[0006] In standard gasification to fuels process layouts renewable carbon-containing feed is gasified to produce CO and hydrogen, but a large part of the carbon from the primary feedstock is converted to CO2 during the gasification process and also during an additional shift process to adjust the syngas module (H2 / CO ratio) to produce hydrogen to make the syngas suitable for FT-synthesis. In previous layouts we have experienced that the CO2 is mostly captured and sequestered without further use of the CO2 within the process. Additionally, the FT-synthesis unit and in Product upgrading and fractionation unit, off gases are produced, like a FT tail gas and off-gas from the upgrading unit (carbon rich streams), and these carbon-rich streams are used as fuel in the facility, and CO2 is produced and emitted. This is represented in Figure 1. This layout is not very carbon efficient due to the loss of carbon to CO2.

[0007] As an alternative to adjust the module by shifting the gas from gasification, is the option to add hydrogen to obtain the required syngas ratio (Figure 2). In this case, also a previous layout to the present invention, the CO2 removal is still necessary in order to limit the CO2 content in the syngas to FT (inert gas).

[0008] SUMMARY

[0009] A method and system are provided for enhancing carbon efficiency in a synthetic fuel system. The method involves utilizing a syngas section (A) designed to use FT-tail gas as feedstock and integrating a reverse water gas shift (RWGS) reactor within the syngas section to recover carbon from the FT-tail gas. The syngas section can be configured to boost syngas production by processing the FT-tail gas. The RWGS reactor is adapted to reduce CO2 emissions by converting CO2 in the FT-tail gas back into CO and by converting CH4 in the FT-tail gas back into CO and H2. The syngas section operates without significant amounts of renewable hydrogen from electrolysis, distinguishing it from conventional renewable fuel plants. One or more gasifiers produce raw syngas (2) from a carbon-source feed, such as waste or biomass.

[0010] By integration of a reverse water gas shift step in a synthetic fuels system and plant, the CO2 emission problem is minimized and the carbon efficiency from renewable carbon containing feed to final fuel product is much improved.

[0011] The advantage of the integrated layout in e.g. Figure 4 is also a reduced consumption of hydrogen.

[0012] DRAWINGS

[0013] FIG. 1 (prior art) shows a conventional Gasification-to-fuels layout with module adjustment by shift process.

[0014] FIG. 2 (prior art) shows a conventional Gasification-to-fuels layout with module adjustment by H2 addition. FIG. 3 shows an improved carbon efficiency layout with Recycle of FT-tail gas. The CO2 and CH4 content in the gasification syngas are high and these components are inerts in the FT-synthesis and they are passed unconverted to the FT-tail gas, therefore filling up gas volume in the FT-section, which increases the size of required equipment and also cost.

[0015] FIG. 4 shows an improved carbon efficiency layout with combined syngas unit coprocessing Syngas from Gasification step and FT-tail gas. An alternative lay-out is to pass the syngas from gasification to the syngas section and co-process the syngas together with the FT-tail gas instead of passing the syngas to the FT-section. When the gasification syngas is passed through the RWGS step the content of CO2 and CH4 in syngas to FT is reduced, producing additional H2 and CO.

[0016] FIG. 5 shows an improved carbon efficiency layout with combined syngas unit coprocessing Syngas from Gasification step and FT-tailgas and Refinery off-gas and LPG. The carbon efficiency can be thereby further increased by recycling the refinery off gas and LPG-type streams.

[0017] FIG. 6 shows an improved carbon efficiency layout with combined syngas unit coprocessing Syngas from Gasification step and FT-tailgas and Refinery off-gas and LPG and Naphtha. In a situation where only one final product - e.g. kerosene for SAF is beneficial, a recycle of Naphtha product stream to the syngas unit can be used, either alone or together with off-gas and / or LPG stream(s).

[0018] FIG. 7A, 7B and 7C show a syngas section in detail with different preferred layouts. In particular, figure 7B shows a preferred embodiment where the one or more tail gas shift reactor(s) and the one or more syngas shift reactor(s) are combined into a single shift section. Figure 7C shows another preferred embodiment where the one or more tail gas shift reactor(s) are separated from the one or more syngas shift reactor(s) in the shift section.

[0019] FIG. 8 shows a layout comprising one or more reactor(s) having a RWGS integrated in the syngas section, which can be arranged in parallel or in series. In particular, it is shown a first reactor having an RWGS integrated is an electrical RWGS and a second reactor having a RWGS integrated is an autothermal reactor. DETAILED DESCRIPTION

[0020] The present invention refers to a method and system for improving carbon efficiency in production of syngas and synthetic fuels. Preferred embodiments are the following:

[0021] 1. A method for increasing carbon efficiency in synthetic fuel production, comprising: a) Feeding a mixture comprising syngas (1), raw syngas (2) and hydrogen (3), to a FT section (B) to produce:

[0022] - a FT-tail gas stream (4) comprising light hydrocarbons, a small, insignificant amount of water, unreacted syngas, CPU and CO2 and

[0023] - higher hydrocarbons for production of synthetic fuels; b) Feeding one or more feedstocks to the syngas section (A), wherein at least one of said feedstocks is FT-tail gas stream (4); c) Feeding said FT-tail gas stream (4) into a compressor section; d) hydrogenation of the resulting olefins into paraffins; e) Feeding said FT-tail gas with paraffins into a shift section, together with steam; f) pre-conversion of higher hydrocarbons in FT-tailgas into CPU-rich gas; g) cooling and condensing a mixture comprising CPU, steam and raw syngas with H2, CO2 and CO, h) separation of a liquid fraction, wherein said liquid fraction comprises mostly water; the remaining gas fraction being optionally mixed with steam and / or hydrogen before going through a reverse water gas shift step which converts the CO2 in the FT-tail gas stream (4) back into CO, to produce syngas to be used in the FT section and converts CPU in the FT-tail gas back into CO and H2.

[0024] The Fischer-Tropsch (FT) process is a series of chemical reactions that convert a mixture of carbon monoxide (CO) and hydrogen (H2) into liquid hydrocarbons. These reactions occur in the presence of a metal catalyst, typically iron or cobalt.

[0025] The process is used to produce synthetic petroleum substitutes, e.g. natural gas, waste or biomass. The resulting products are in the form of long chain hydrocarbons, e.g. mainly paraffinic hydrocarbons, which can be processed further to produce a range of products, including synthetic diesel, jet fuel, and chemical feedstocks. The light hydrocarbons obtained in step a) are of both olefinic and paraffinic nature.

[0026] The basic reaction in the Fischer-Tropsch process can be represented as: where n is the number of repetitions of the process, and (-CH2-)n represents a hydrocarbon chain with n carbon atoms.

[0027] By adding a syngas unit, or section comprising one or more syngas units, with one or more reverse water gas shift reactor(s), it is possible to recover the carbon in the FT tail gas from the fuel system and boost the syngas production, while reducing the CO2emission. The syngas unit(s) can use the FT-tail gas as the sole feedstock in contrast to other renewable fuels plant where the Syngas Unit with RWGS operate on captured CO2 and renewable hydrogen and recycle of FT tailgas. It is remarkable noted that the syngas unit is operating without large amounts of renewable hydrogen from electrolysis.

[0028] The RWGS reaction runs in the opposite direction from the water-gas shift (WGS) reaction. It is exothermic, meaning it releases heat and combines carbon dioxide (CO2) and hydrogen (H2) to produce carbon monoxide (CO) and water (H2O):

[0029] CO2+ H2-> CO + H2O

[0030] The RWGS reactor can be an electrical heated RWGS reactor or it can be heated by an external flue gas from combustion of a carbon-rich or a hydrogen-rich fuel. The RWGS reactor can also be internally heated by internal combustion of hydrocarbons, CH4, CO or Hydrogen by an oxygen-rich oxidant. The one or more RWGS reactor(s) can be a thermal, catalytic, electrically heated, etc. are integrated with the syngas section. It is designed to recover carbon from the FT-tail gas, which is a significant step towards enhancing carbon efficiency in the fuel system.

[0031] Steam Methane Reforming (SMR) is a process used to produce hydrogen and carbon monoxide from methane (the main component of natural gas) and steam. The overall reaction for steam methane reforming can be broken down into two steps: 1. Steam Reforming Reaction: In the first step, methane reacts with steam to produce carbon monoxide and hydrogen:

[0032] CH4+ H2O -> CO + 3H2

[0033] 2. Water-Gas Shift Reaction: In the second step, the carbon monoxide produced in the first step reacts with more steam to produce carbon dioxide and additional hydrogen:

[0034] CO + H2O -> CO2+ H2

[0035] So, the overall reaction for steam methane reforming is:

[0036] CH4+ 2H2O -> CO2+ 4H2

[0037] This reaction is endothermic, meaning it absorbs heat, and it typically occurs at high temperatures (700-1000°C) and pressures (1-25 bar) in the presence of a nickel- based catalyst.

[0038] The resulting synthesis gas, or syngas (a mixture of hydrogen and carbon monoxide), can be used to produce hydrogen, ammonia, methanol, or other chemicals.

[0039] The reverse methanation reaction involves the reaction of methane and water to produce carbon monoxide or carbon dioxide and hydrogen:

[0040] These reverse reactions are similar to the steam reforming reactions used to produce synthesis gas (syngas) from natural gas. They are endothermic, meaning they require heat to proceed, and typically occur at high temperatures and pressures in the presence of a catalyst.

[0041] 2. Method according to embodiment 1, further comprising a gasification step before production of syngas and synthetic fuel, for producing raw syngas (2) from a carbon-source feed, such as waste or biomass. Raw syngas is preferably obtained from waste gasification, which is a thermal process that converts organic materials or waste into a synthetic gas, also known as syngas. This process is used in the production of synthesis gas and fuels. In such a process, the pre-treated waste is subjected to high temperatures (above 700°C) in a controlled environment with a limited supply of oxygen. This process, called partial oxidation, breaks down the waste into syngas, which is primarily a mixture of hydrogen (H2) and carbon monoxide (CO).

[0042] The advantage of waste gasification is that it reduces the need for landfill space and can convert waste into useful energy or products. It also has the potential to lower greenhouse gas emissions compared to traditional waste disposal methods. The raw syngas from gasification, comprising H2, CO2 and CO, is very rich in CO, and the CO / CO2-ratio is high, and can trigger challenges in the RWGS section through high exotherm reactions from CO conversion to methanation and CO-induced metal dusting.

[0043] 3. Method according to embodiment 2 wherein raw syngas (2) is fed to the syngas section (A).

[0044] 4. Method according to embodiment 2 wherein raw syngas (2) is mixed with syngas (1) and hydrogen (3) before being fed to the FT section (B).

[0045] 5. Method according to any one of the previous embodiments wherein a further processing step in a PWU section, upgrades higher hydrocarbons to fuel fractions comprising (i) an off-gas, (ii) an LPG stream, (iii) a naphtha product stream, (iv) a kerosene stream and / or (v) diesel.

[0046] A PWU section comprises one or more PWU units.

[0047] A PWU refers to a Product Work-Up unit. This is an important part of the Fischer- Tropsch (FT) process where the raw product stream from the FT reactor, which includes light gases, water, unreacted syngas, and heavier hydrocarbons (like wax), is processed:

[0048] Wax Hydrocracking: The long-chain hydrocarbons in the wax are broken down into shorter chains, which are more suitable for use as liquid fuels (like diesel and jet fuel). Separation: The raw product stream is first separated into different components. Light gases (e.g., methane, ethane) and water are typically removed and can be recycled back into the process.

[0049] Product Upgrading: Depending on the desired end-product, the separated fractions may undergo further processing or upgrading to meet specific fuel standards.

[0050] Distillation or fractionation: The hydrocracked product is distilled to separate it into different fractions based on boiling point. This results in different types of fuel products.

[0051] The PWU upgrades the long chain hydrocarbons to fuel fractions with well-defined boiling point range, i.e. Kerosene and / or Diesel and / or Naphtha.

[0052] The specifics of the PWU process can vary depending on the design of the FT plant and the desired end products.

[0053] The terms "heavy hydrocarbons", "higher hydrocarbons" and "long-chain hydrocarbons" are used interchangeably in the present invention. They all refer to hydrocarbon compounds that have a large number of carbon atoms in their molecular structure. Typically, hydrocarbons with more than 12 carbon atoms are often referred to as higher or heavy or long-chain hydrocarbons. These hydrocarbons tend to be less reactive and have higher boiling points than smaller, lighter hydrocarbons. They are often found in heavier fractions of crude oil and are important in the production of diesel fuel, lubricating oils, and waxes.

[0054] 6. Method according to embodiment 5 wherein at least one of streams (i) an off-gas, (ii) an LPG stream and (iii) a naphtha product stream is fed into the syngas section (A).

[0055] 7. Method according to any one of the previous embodiments wherein at least one of the streams (i) off-gas and / or (ii) LPG and / or iii) naphta are recycled from a PWU and desulphurized before going through steps f) to i).

[0056] 8. Method according to any one of the previous embodiments wherein the reverse water gas shift step is used to adjust the H2 / CO ratio in the syngas and fuel produced. 9. Method according to any one of the previous embodiments wherein the raw syngas before being mixed has a H2 / CO ratio between 0.5 and 2.0.

[0057] 10. Method according to any one of the previous embodiments wherein syngas fed into the FT section has a H2 / CO ratio between 1.9 and 2.1, preferably 2.0.

[0058] The hydrogen used for module adjustment can be renewable hydrogen from electrolysis or from a Blue Hydrogen unit where natural gas is used as feed and carbon is removed and sequestered. The hydrogen added for adjusting the syngas composition and the H2 / CO-ratio module before sending the syngas to FT-synthesis can be added at the backend of the syngas section or hydrogen can be added through the syngas unit as part of the total feed to the RWGS reactor in integrated way or as a combination of the two.

[0059] 11. Method according to any one of the previous embodiments wherein raw syngas (2) is mixed with steam and submitted to one or more shift step(s) before going through steps g) to i).

[0060] 12. Method according to the previous embodiment wherein raw syngas (2) is polished or cleaned before being mixed with steam and submitted to one or more shift step(s).

[0061] Syngas polishing or cleaning is a process used to clean or purify synthesis gas (syngas) after it has been produced. The goal is to remove contaminants and impurities that could harm downstream equipment or affect the efficiency of subsequent processes.

[0062] Syngas is polished or cleaned to remove impurities, such as sulphur, chlorine, and heavy metals, which can be harmful if released into the environment or could damage downstream equipment. The clean syngas can then be used to produce electricity, heat, or transportation fuels. It can also be used as a building block for chemicals such as ammonia and other.

[0063] In a preferred embodiment of the present invention, the syngas polishing step comprises at least sulphur removal of e.g. COS or carbonyl sulfide, which is ideally removed because it can be harmful to catalysts used at a later stage, H2S or hydrogen sulfide, which is a significant impurity in many gas streams, such as natural gas, biogas and synthesis gas and can be corrosive to many metals and harmful to catalysts used in refining and chemical processes, and also HCN or hydrogen cyanide which can be an undesirable and toxic component of syngas produced by gasification of e.g. biomass.

[0064] 13. Method according to any one of the previous embodiments wherein the one or more shift step(s) comprise one or more tailgas shift step(s) and one or more syngas shift step(s).

[0065] In a preferred embodiment of the present invention, in particular the syngas section, is to arrange a pre-treatment of the gasification syngas prior to feeding the stream to the RWGS reactor where the CO is shifted in a catalytic shift reactor to reduce the CO-content of the raw syngas. It is counter-intuitive to reduce the CO-content as CO is the final product in order to get a more efficient process. The CO2 and CH4 content in the gasification syngas are high and these components are inerts in the FT-synthesis and they are passed unconverted to the FT-tail gas and is therefore filling up gas volume in the FT-section and that increases size of equipment and cost.

[0066] The advantage of waste gasification is that it reduces the need for landfill space and can convert waste into useful energy or products. It also has the potential to lower greenhouse gas emissions compared to traditional waste disposal methods. The raw syngas from gasification, comprising H2, CO2 and CO, is very rich in CO, and the CO / CO2-ratio is high, and can trigger challenges in the RWGS section through high exotherm reactions from CO conversion to methanation and CO-induced metal dusting.

[0067] This is why we want to send the Gasification Syngas to RWGS section to convert CO2 to CO by RWGS reaction and Convert CH4 to CO and H2 by steam reforming.

[0068] Another preferred embodiment of the syngas section in the present invention is to arrange the pre-treatment of the gasification syngas in a separate high temperature shift catalytic reactor before the syngas is mixed with the tail gas, after its pretreatment through olefin saturation, steam addition, water gas shift medium and / or low temperature shift and hydrocarbon pre-conversion.

[0069] Figure 7A shows a detailed view where said reactors are combined (Figure 7B) and separated (7C). 14. Method according to any one of the previous embodiments wherein hydrogen is mixed before and / or after the RWGS step (Figure 7 A).

[0070] 15. A system for enhancing carbon efficiency in synthetic fuel production, comprising:

[0071] - A syngas section (A) for producing syngas comprising: a) a tail gas compressing section; b) an olefine hydrogenation section; c) a shift section; d) a pre-conversion section; e) a cooling and condensation section; and f) one or more reactors having a reverse water gas shift (RWGS) section; and

[0072] - A FT section (B) for producing a FT-tail gas, wherein the syngas section is arranged to use FT-tail gas as a feedstock, with the one or more reactor(s) having a RWGS integrated in said syngas section to recover carbon from the FT-tail gas according to embodiments 1 to 14.

[0073] 16. System according to embodiment 15 wherein a gasification section comprising one or more gasifiers and a hydrogen gas stream source are located upstream to both syngas section and FT section.

[0074] 17. System according to any one of embodiments 15 or 16 wherein the FT section is arranged such that it is fed with a mixed stream comprising syngas (1), raw syngas

[0075] (2) and hydrogen (3), as shown in figure 3.

[0076] 18. System according to any one of embodiments 15 to 17 wherein the FT section is arranged such that it is fed with a mixed stream comprising syngas (1) and hydrogen

[0077] (3), as shown in figures 4, 5 and 6.

[0078] 19. System according to any one of embodiments 15 to 18 wherein a PWU section is located downstream to both syngas section and FT section and said PWU section is arranged to process FT products, e.g. paraffinic hydrocarbons such as wax.

[0079] 20. System according to any one of embodiments 15 to 19 wherein said one or more reactor(s) having a RWGS integrated in said syngas section can be arranged in parallel or in series. 20. 1 System according to the previous embodiment wherein the first reactor having an RWGS integrated is an electrical RWGS and the second reactor having a RWGS integrated is an autothermal reactor.

[0080] 21. System according to any one of embodiments 15 to 20 wherein said shift section comprises one or more tail gas shift reactor(s) and one or more syngas shift reactor(s), as shown in figures 7 A, 7B and 7C.

[0081] 22. System according to the previous embodiment wherein the one or more tail gas shift reactor(s) and the one or more syngas shift reactor(s) are combined into a single shift section, as shown in figure 7B.

[0082] 23. System according to embodiment 21 wherein the one or more tail gas shift reactor(s) are separated from the one or more syngas shift reactor(s) in the shift section, as shown in figure 7C.

[0083] The shift section in the system of the present invention comprises one or more tail gas shift reactor(s) (LTS or Low Temperature Shift) and one or more syngas shift reactor(s), e.g. a first syngas shift reactor (HTS or High Temperature Shift) and a second syngas shift reactor (MTS or Medium Temperature Shift). In different layouts of the invention these reactors can be combined into one reactor (Figure 7B) or separated (Figure 7C).

[0084] Typical temperature ranges (inlet / outlet temperatures) for shift reactors can be described as High temperature shift, typically in the range of 330 to 450°C with a more typical inlet temperature in the range 330 to 380°C. As Medium temperature shift, typically in the range 190 to 330°C, with a more typical inlet temperature in the range 190 to 210°C. As Low temperature shift, typically in the range 190 to 250°C, with a more typical inlet temperature in the range 190 to 205°C. An optimal catalyst can be selected for each of the temperature ranges. And the CO-conversion is affected by the catalyst type and the operating temperature and feed composition.

[0085] 24. System according to any one of embodiments 15 to 23 wherein a desulphurization section is any which is suitable for the purpose of desulphurizing off gas or LPG streams recycled from the PWU section in the present invention and is located upstream to the pre-conversion section for desulphurize recycle stream(s) off gas, LPG and / or naphtha from the PWU. In a preferred embodiment the desulphurizing section comprises a hydrogenation reactor and a sulphur absorption reactor.

[0086] 25. System according to any one of embodiments 15 to 24 wherein a syngas polishing section to clean the raw syngas (2) is located upstream to the shift section.

Claims

CLAIMS1. A method for increasing carbon efficiency in synthetic fuel production, comprising: a) Feeding a mixture comprising syngas (1), raw syngas (2) and hydrogen (3), to a FT section (B) to produce:- a FT-tail gas stream (4) comprising light hydrocarbons, unreacted syngas, CF and CO2 and- higher hydrocarbons for production of synthetic fuel; b) Feeding one or more feedstocks to the syngas section (A), wherein at least one of said feedstocks is FT-tail gas stream (4); c) Feeding said FT-tail gas stream (4) into a compressor; d) hydrogenation of the resulting olefins into paraffins; e) Feeding said FT-tail gas with paraffins into a shift section, together with steam; f) pre-conversion of higher hydrocarbons in FT-tailgas into CF -rich gas; g) cooling and condensing a mixture comprising CH4, steam and raw syngas with H2, CO2 and CO, h) separation of a liquid fraction; the remaining gas fraction being optionally mixed with steam and / or hydrogen before going through a reverse water gas shift step which converts the CO2 in the FT-tail gas stream (4) back into CO, to produce syngas to be used in the FT section and converts CH4 in the FT-tail gas back into CO and H2.

2. Method according to claim 1, further comprising a gasification step before production of syngas and synthetic fuel, for producing raw syngas (2) from a carbon-source feed, such as waste or biomass.

3. Method according to claim 2 wherein raw syngas (2) is fed to the syngas section (A).

4. Method according to claim 2 wherein raw syngas (2) is mixed with syngas (1) and hydrogen (3) before being fed to the FT section (B).

5. Method according to any one of the previous claims wherein a further processing step in a PWU, upgrades higher hydrocarbons to fuel fractionscomprising (i) an off-gas, (ii) an LPG stream, (iii) a naphtha product stream, (iv) a kerosene stream and / or (v) diesel.

6. Method according to any one of the previous claims wherein the reverse water gas shift step is used to adjust the H2 / CO ratio in the syngas and fuel produced.

7. Method according to any one of the previous claims wherein the raw syngas before being mixed has a H2 / CO ratio between 0.5 and 2.0.

8. Method according to any one of the previous claims wherein syngas fed into the FT section has a H2 / CO ratio between 1.9 and 2.1, preferably 2.0.

9. Method according to claim 5 wherein at least one of streams (i) an off-gas, (ii) an LPG stream and (iii) a naphtha product stream is fed into the syngas section (A).

10. Method according to any one of the previous claims wherein at least one of the streams (i) off-gas and / or (ii) LPG and / or iii) naphta are recycled from a PWU and desulphurized before going through steps f) to i).

11. Method according to any one of the previous claims wherein raw syngas (2) is mixed with steam and submitted to one or more shift step(s) before going through steps g) to i).

12. Method according to the previous claim wherein raw syngas (2) is polished before being mixed with steam and submitted to one or more shift step(s).

13. Method according to any one of the previous claims wherein the one or more shift step(s) comprise one or more tailgas shift step(s) and one or more syngas shift step(s).

14. Method according to any one of the previous claims wherein hydrogen is mixed before and / or after the RWGS step.

15. A system for enhancing carbon efficiency in synthetic fuel production, comprising:- A syngas section (A) for producing syngas comprising:a) a tail gas compressing section; b) an olefine hydrogenation section; c) a shift section; d) a pre-conversion section; e) a cooling and condensation section; and f) one or more reactors having a reverse water gas shift (RWGS) section; and- A FT section (B) for producing a FT-tail gas, wherein the syngas section is arranged to use FT-tail gas as a feedstock, with the one or more reactor(s) having a RWGS integrated in said syngas section to recover carbon from the FT-tail gas according to claims 1 to 14.

16. System according to claim 15 wherein a gasification section comprising one or more gasifiers and a hydrogen gas stream source are located upstream to both syngas section and FT section.

17. System according to any one of claims 15 or 16 wherein the FT section is arranged such that it is fed with a mixed stream comprising syngas (1), raw syngas (2) and hydrogen (3).

18. System according to any one of claims 15 to 17 wherein the FT section is arranged such that it is fed with a mixed stream comprising syngas (1) and hydrogen (3).

19. System according to any one of claims 15 to 18 wherein a PWU section is located downstream to both syngas section and FT section.

20. System according to any one of claims 15 to 19 wherein said one or more reactor(s) having a RWGS integrated in said syngas section can be arranged in parallel or in series.

21. System according to claim 20, wherein the first reactor having an RWGS integrated is an electrical RWGS and the second reactor having a RWGS integrated is an autothermal reactor.

22. System according to any one of claims 15 to 21 wherein said shift section comprises one or more tailgas shift reactor(s) and one or more syngas shift reactor(s).

23. System according to the previous claim wherein the one or more tailgas shift reactor(s) and the one or more syngas shift reactor(s) are combined into a single shift section.

24. System according to claim 22 wherein the one or more tailgas shift reactor(s) are separated from the one or more syngas shift reactor(s) in the shift section.

25. System according to any one of claims 15 to 24 wherein a desulphurization section comprises / is... and is located upstream to the pre-conversion section for desulphurize recycle stream(s) offgas, LPG and / or naphta from the PWU.

26. System according to any one of claims 15 to 25 wherein a syngas polishing section to clean the raw syngas (2) is located upstream to the shift section.

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