WO2025052088A1

WO2025052088A1 - A method and system for forming syngas

Info

Publication number: WO2025052088A1
Application number: PCT/GB2024/051755
Authority: WO
Inventors: Peter Edward James Abbott; Graham Charles Hinton
Original assignee: Johnson Matthey Davy Technologies Limited
Priority date: 2023-09-08
Filing date: 2024-07-04
Publication date: 2025-03-13

Abstract

A method of forming a syngas, the method comprising: supplying first feed gas comprising hydrogen and carbon dioxide to a reverse water-gas-shift reactor comprising a reverse water-gas shift catalyst, wherein the first feed gas to the reverse water-gas shift reactor has a combined mole fraction of hydrogen and carbon dioxide which is greater than 0.5; heating the first feed gas; passing the heated first feed gas comprising hydrogen and carbon dioxide over the reverse water-gas shift catalyst within the reverse water-gas shift reactor to form a reverse water-gas shifted gas stream by converting at least a portion of the carbon dioxide to carbon monoxide; passing the reverse water-gas shifted gas stream from the reverse water-gas shift reactor to a heat exchange post-reformer which comprises a steam methane reforming catalyst; supplying second feed gas comprising methane and steam to the heat exchange post-reformer, wherein the second feed gas to the heat exchange post-reformer has a combined mole fraction of methane and water which is greater than 0.5, wherein the reverse water-gas shifted gas stream heats the second feed gas within the heat exchange post-reformer to drive a steam methane reforming reaction as the heated second feed gas is passed over the steam methane reforming catalyst to produce a steam methane reformed gas stream comprising carbon monoxide and hydrogen, and wherein a syngas product stream comprising carbon monoxide and hydrogen exits the heat exchange post-reformer.

Description

A METHOD AND SYSTEM FOR FORMING SYNGAS

Field

The present specification relates to a method and system for forming a syngas which comprises a mixture of hydrogen and carbon monoxide (also known as synthesis gas). The present specification also relates to a method and system for producing hydrocarbons from the syngas.

Background

Gas streams comprising hydrogen and carbon monoxide (syngas) are used in processes for the synthesis of chemicals including hydrocarbons and oxygenated hydrocarbons such as alcohols. Typically, these syngas streams are optimally low in inert content (CO2, CH4, N2, etc) and are produced at a target ratio of H2/CO, typically in the range 1.8-2.2.

Syngas generation using a reverse water-gas shift (RWGS) reaction can be beneficial since it makes use of carbon dioxide that may have been destined to be released to the atmosphere. Furthermore, hydrogen for the reverse water-gas shift reaction can be produced by water electrolysis using renewably produced electricity (so called, green hydrogen). Following this route to producing syngas, and using the syngas to produce hydrocarbons, can thus provide a fully integrated process to synthesise green hydrocarbons from carbon dioxide and hydrogen from the electrolysis of water.

The reverse water-gas shift reaction may be depicted as follows:

H₂ + CO₂ ^ CO + H₂O

The reverse water-gas shift reaction is endothermic and thus a higher conversion of hydrogen and carbon dioxide to carbon monoxide and water is favoured by high temperatures. Various processes for carrying out RWGS are known in the art including:

(i) Combusting part of the CO2/H2 feed with oxygen in a burner and passing the hot gases over a bed of RWGS catalyst so that the RWGS reaction proceeds towards equilibrium adiabatically.

(ii) Passing the feed CO2/H2 through RWGS catalyst in tubes in a furnace and combusting a fuel in the furnace to provide the heat for the RWGS reaction.

(iii) Preheating the CO2/H2 feed upstream of the RWGS catalyst using electrical energy. For instance, this could be by using a static electric resistance heater or by heating the gas directly, such as by using Turbo Machinery Heating (TMH).

(iv) Providing electrical resistance heating within the RWGS catalyst.

(v) Passing the CO2/H2 feed through tubes containing catalyst in a heat exchanger, where the tubes are heated by a fluid in a secondary heating circuit (the secondary heating utilising, for example, electrical energy).

Since high equilibrium RWGS conversion is favoured by high temperatures, the gas leaving the RWGS catalyst will usually be at a high temperature, and it would be advantageous to recover high temperature heat from this stream to reduce the primary energy input used in any of the heating processes (i) to (v) listed above. Another known method for generating syngas is via a steam methane reforming reaction which his depicted below:

CH₄ + H₂O CO + 3H₂

This reaction is also endothermic and thus a higher conversion of methane and steam to carbon monoxide and hydrogen is favoured by high temperatures.

Syngas produced using methodologies as described above can be converted to liquid hydrocarbons using a Fischer-Tropsch process. Fischer-Tropsch reactions occur in the presence of metal catalysts, typically at temperatures of 150-300°C and pressures of one to several tens of atmospheres. The Fischer-Tropsch process involves a series of chemical reactions that produce a variety of hydrocarbons, ideally having the formula (CnF n+z). The more useful reactions produce alkanes as follows:

where n may be 1-100, or higher. The formation of methane (n = 1) is unwanted. In addition to alkane formation, competing reactions give small amounts of alkenes, as well as alcohols and other oxygenated hydrocarbons. The Fischer-Tropsch reaction is a highly exothermic reaction due to a standard reaction enthalpy (AH) of -165 kJ/mol CO combined.

W02022079408 describes a reverse water-gas shift process for producing a gas stream comprising carbon monoxide by feeding a gas mixture comprising carbon dioxide and hydrogen to a burner disposed in a reverse water-gas shift reactor and combusting it with a sub-stoichiometric amount of an oxygen gas stream to form a combusted gas mixture containing carbon monoxide, carbon dioxide, hydrogen and steam. The mixture is then passed through a reverse water-gas shift catalyst to form a crude product gas comprising carbon monoxide, carbon dioxide, hydrogen and steam. The gas is then cooled so that the water content condenses and can be separated and removed. The gas stream then passes to a carbon dioxide removal unit to remove carbon dioxide, which can be recycled to the feed gas mixture to the reverse water-gas shift reactor and produce a syngas comprising carbon monoxide and hydrogen.

W02022079408 also describes a process for synthesising hydrocarbons where at least a portion of the H2/CO containing gas from the RWGS process as described above is fed to a Fischer-Tropsch (FT) unit to make hydrocarbons and FT water. At least a portion of this water can be recycled back to an electrolysis unit which makes the hydrogen feed to the RWGS reactor. It is also described that a gas mixture comprising methane and carbon dioxide formed by pre-reforming a Fischer-Tropsch tail gas (or "tailsgas"), and optionally non-condensable hydrocarbons recovered from a downstream Fischer- Tropsch process, can be recycled and fed to the reverse water-gas shift reactor.

W02022079098 describes a plant to synthesise hydrocarbons from hydrogen and carbon dioxide comprising an electrically heated water gas shift section (e-RWGS). This is exemplified by using a structured catalyst comprising a macroscopic structure of electrically conductive material capable of catalysing a reverse water gas shift reaction, a methanation reaction and a steam reforming reaction.

WO2022253965 describes a system comprising a RWGS reactor and a Heat Exchange Reactor (HER) where a feed comprising hydrogen and carbon dioxide is fed to each reactor. At least a portion of the RWGS shifted gas leaving the first reactor is fed to the heating side of the HER thereby allowing further RWGS to occur in this reactor producing a second product gas comprising CO. A small quantity of methane containing gas can also be fed to the first and/or second hydrogen/carbon dioxide feeds. WO2022253965 also discloses a method of conducting the RWGS in the process (tube) side of the HER, where the main reactions in the first part of the tubes (closest to the entry) are methanation of CO2 and CO to methane (and RWGS) and in the second part of the tubes are steam reforming of methane to CO/CO2 (and RWGS). The stated advantage of this approach is that the temperature rises quickly in the first part of the tubes so that carbon formation on the catalyst (by the CO reduction or Boudouard reactions) is not favoured. However, the disadvantage of conducting RWGS in the HER in this way is that it constrains the amount of heat recuperation that can be achieved in this reactor, so that more primary heating overall (from an external source) will be needed.

The present specification is concerned with providing an improved method and system for producing syngas and particularly one which is more efficient from a thermal management perspective.

Summary

The present specification provides a method of forming a syngas, the method comprising: supplying first feed gas comprising hydrogen and carbon dioxide to a reverse water-gas-shift reactor comprising a reverse water-gas shift catalyst, wherein the first feed gas to the reverse water- gas shift reactor has a combined mole fraction of hydrogen and carbon dioxide which is greater than 0.5 (optionally greater than 0.6, 0.7, 0.8, 0.9, or 0.95); heating the first feed gas; passing the heated first feed gas comprising hydrogen and carbon dioxide over the reverse water-gas shift catalyst within the reverse water-gas shift reactor to form a reverse water-gas shifted gas stream by converting at least a portion of the carbon dioxide to carbon monoxide; passing the reverse water-gas shifted gas stream from the reverse water-gas-shift reactor to a heat exchange post-reformer which comprises a steam methane reforming catalyst; supplying second feed gas comprising methane and steam to the heat exchange post-reformer, wherein the second feed gas to the heat exchange post-reformer has a combined mole fraction of methane and water which is greater than 0.5 (optionally greater than 0.6, 0.7, or 0.8), wherein the reverse water-gas shifted gas stream heats the second feed gas within the heat exchange post-reformer to drive a steam methane reforming reaction as the heated second feed gas is passed over the steam methane reforming catalyst to produce a steam methane reformed gas stream comprising carbon monoxide and hydrogen, and wherein a syngas product stream comprising carbon monoxide and hydrogen exits the heat exchange post-reformer.

The first feed gas to the reverse water-gas shift reaction consists, or at least primarily comprises, carbon dioxide and hydrogen but may have small quantities of other components such as methane, carbon monoxide, and nitrogen. To reflect the nature of the feed composition, the catalyst in the reverse water gas shift reactor is selected to at least primarily drive a reverse water gas-shift reaction. The second feed gas to the heat exchange post-reformer consists, or at least primarily comprises methane and steam (water) but may have small quantities of other components such as higher hydrocarbons, carbon dioxide, carbon monoxide, hydrogen and nitrogen. To reflect the nature of the feed composition, the catalyst in the heat exchange post-reformer is selected to at least primarily drive a steam methane reforming reaction. The second feed gas may have a mole fraction of methane which is higher than one or more of a mole fraction of carbon dioxide, a mole fraction of hydrogen, or a combined mole fraction of carbon dioxide and hydrogen within the second feed gas. The second feed gas comprising methane and steam can be at least partially formed from one or more of: a gas purged, and optionally deriched, from a downstream hydrocarbon synthesis step; a naphtha or LPG stream, optionally deriched, which is separated from a downstream hydrocarbon synthesis product stream; a biogenic feed source (biogas); and natural gas. While the second feed gas to the heat exchange post-reformer primarily comprises methane and steam (water), some carbon dioxide may be added to the second feed gas and this may have some advantages in reducing metal dusting. For example, the second feed gas to the heat exchange post-reformer may comprise a carbon dioxide content of: at least 10 mol%, 15 mol%, 20 mol %, or 25 mol%; no more than 40 mol%, 35 mol%, or 30 mol%; or within a range defined by any combination of the aforementioned lower and upper limits.

This differs from the approach disclosed in WO2022253965 in which both the feed gas to the reverse water-gas shift reactor and the feed gas to the heat exchange reformer (HER) are primarily composed of carbon dioxide and hydrogen, with a small quantity of methane in either or both of the feeds being optional. In WO2022253965 the catalyst in both the reverse water-gas shift reactor and the heat exchange reformer is selected to at least primarily drive a water gas-shift reaction to reflect the nature of the CO2/H2 feed gas to both reactors. This contrasts with the approach of the present specification in which a feed stream which is primarily methane/steam is provided to the heat exchange postreformer which comprises a steam-methane reforming catalyst to drive a steam methane reforming reaction and the hot gas stream from the RWGS reactor is utilized to drive the steam methane reforming reaction downstream of the RWGS reactor. It has been found that the present approach is more thermally efficient and enables more high temperature heat to be recuperated than heat exchange recovery in the prior configuration which utilises a co-feed of H2 and CO2 to both the RWGS reactor and the HER reactor with the need to suffer a methanation exotherm at the RWGS catalyst inlet of the HER to prevent carbon formation on the RWGS catalyst in the HER. The present approach gives more efficient utilisation of a primary heat source. A comparison of the two approaches is given in the detailed description indicating that the present approach allows the amount of heat recovered to be increased by >2x and the required heat input to be reduced by ~27%.

Depending on the configuration of the heat exchange post-reformer, the reverse water-gas shifted gas stream can be mixed with the steam methane reformed gas stream within the heat exchange postreformer such that the syngas product stream exiting the heat exchange post-reformer comprises a mixture of the reverse water-gas shifted gas stream and the steam methane reformed gas stream. Alternatively, the reverse water-gas shifted gas stream can remain separated from (but thermally coupled with) the steam methane reformed gas stream within the heat exchange post-reformer, in which case two separate syngas product streams exit the heat exchange post-reformer, one formed from the reverse water-gas shifted gas stream and one formed from the steam methane reformed gas stream. These separate syngas streams can be subsequently combined.

The first feed gas is heated prior to the first feed gas entering the reverse water gas-shift reactor and/or the first feed gas is heated within the reverse water gas-shift reactor. The first feed gas can be heated by one or more of: a turbo machinery heater which directly heats the first feed gas prior to entering the reverse water-gas shift reactor; a turbo machinery heater which heats a heat transfer fluid, the heat transfer fluid then heating the first feed gas either prior to entering the reverse water-gas shift reactor or within the reverse water-gas shift reactor; an electrical heating system either prior to entering the reverse water-gas shift reactor or within the reverse water-gas shift reactor; one or more heat exchangers prior to entering the reverse water-gas shift reactor; combustion of oxygen and hydrogen within the reverse water-gas shift reactor, the reverse water-gas shift reactor being an autothermal reformer.

In certain configurations, at least a portion of the syngas product stream from the heat exchange postreformer can be fed through an autothermal reformer to increase CO content. For example, when the heat exchange post-reformer is configured to produce two separate syngas product streams, one formed from the reverse water-gas shifted gas stream and one formed from the steam methane reformed gas stream, the syngas product stream formed from the steam methane reformed gas stream can be fed through the autothermal reformer prior to being mixed with the syngas product stream formed from the reverse water-gas shifted gas stream.

The present specification also provides a method of producing hydrocarbons, the method comprising: forming a syngas as described above; and passing the syngas through a Fischer-Tropsch reactor to produce the hydrocarbons. In this regard, the syngas produced by the reverse water gas shift reactor and heat exchange post-reformer can be utilized to produce hydrocarbon products via a Fischer- Tropsch process. In addition to producing desired hydrocarbon products, the Fischer-Tropsch process also produces a tail gas (or "tailsgas") which can be recycled and used, at least in part, as the input feed gas to the heat exchange post-reformer. Optionally downstream processing of hydrocarbon products can be practised, such as hydrotreating/hydrocracking. This improves the product value but also can produce a naphtha stream which is less valuable. Such a naphtha stream can also be recycled and used, at least in part, as the input feed gas to the heat exchange post-reformer. These recycle streams can be subjected to derichment in one or more derichment reactors to produce a methane containing stream for input to the heat exchange post-reformer. This differs from configurations disclosed in W02022079408 where a gas mixture comprising methane and carbon dioxide formed by pre-reforming a Fischer-Tropsch tail gas, and optionally non-condensable hydrocarbons recovered from a downstream Fischer-Tropsch process, is recycled and fed to the reverse water-gas shift reactor rather than a heat exchange post-reformer which is heated by a reverse water-gas shift reactor product stream.

The present specification also provides a system for performing the method as described herein, the system comprising: a first feed gas supply unit configured to supply a first feed gas comprising hydrogen and carbon dioxide to a reverse water-gas-shift reactor, wherein the first feed gas supply unit is configured to supply the first feed gas to the reverse water-gas shift reactor with a combined mole fraction of hydrogen and carbon dioxide which is greater than 0.5; a heating unit configured to heat the first feed gas; a reverse water-gas shift reactor comprising a reverse water-gas shift catalyst, the reverse water-gas shift reactor being configured to receive the first feed gas, pass the first feed gas over the reverse water-gas shift catalyst to form a reverse water-gas shifted gas stream, and to pass the reverse water-gas shifted gas stream from the reverse water-gas-shift reactor to a heat exchange postreformer; a second feed gas supply unit configured to supply a second feed gas comprising methane and steam to the heat exchange post-reformer with a combined mole fraction of methane and water which is greater than 0.5; and a heat exchange post-reformer comprising steam methane reforming catalyst, the heat exchange post-reformer being configured to receive the second feed gas and pass the second feed gas over the steam methane reforming catalyst, the heat exchange post-reformer being further configured to receive the reverse water-gas shifted gas stream and provide heat exchange from the reverse water- gas shifted gas stream to the second feed gas to heat the second feed gas and drive a steam methane reforming reaction as the heated second feed gas is passed over the steam methane reforming catalyst to produce a steam methane reformed gas stream comprising carbon monoxide and hydrogen, the heat exchange post-reformer thereby producing a syngas product stream comprising carbon monoxide and hydrogen.

The system may further comprise a Fischer-Tropsch unit comprising a Fischer-Tropsch catalyst, the Fischer-Tropsch unit being configured to receive the syngas product stream and pass the syngas product stream over the Fischer-Tropsch catalyst to produce a hydrocarbon product stream.

Several different examples of heating, reactor, and flow sheet configurations are set out in the figures and detailed description.

Brief Description of the Drawings

Figure 1 shows a flow sheet for a method of forming syngas using a reverse water-gas shift reactor followed by a heat exchange post-reformer.

Figure 2 shows a flow sheet for a method of forming a hydrocarbon product stream by combining the syngas forming method of Figure 1 with a Fischer-Tropsch unit.

Figure 3 shows a more detailed flow sheet for a method of forming a hydrocarbon product stream.

Figures 4(a) to 4(c) show examples of heat exchange post-reformer configurations.

Figure 5 shows a flow sheet for a method of forming a hydrocarbon product stream using a turbo machinery heater to heat the feed gas to the reverse water-gas shift reactor.

Figure 6 shows a flow sheet for a method of forming a hydrocarbon product stream using micro- resistive heating for the reverse water gas shift reactor (e-RWGS).

Figure 7 shows a flow sheet for a method of forming a hydrocarbon product stream using a turbo machinery heater to heat a thermal transfer gas which is used to heat the reverse water-gas shift reactor.

Figure 8 shows a flow sheet for a method of forming a hydrocarbon product stream using an autothermal reactor (ATR) as the reverse water-gas shift reactor.

Figure 9 shows a flow sheet for a method of forming a hydrocarbon product stream using an autothermal reactor (ATR) downstream of the heat exchange post-reformer.

Figure 10 shows a flow sheet (not according to the present specification) in which a gas mixture comprising F , CO2, tailsgas, and steam are fed to a reverse water-gas shift reactor and to a heat exchange reactor which is heated by reverse water-gas shifted gas.

Figure 11 shows temperature profiles for the heat exchange reactor using the configuration illustrated in Figure 10.

Figure 12 shows a flow sheet according to the present specification in which a gas mixture comprising H2 and CO2 are fed to a reverse water-gas shift reactor and a gas mixture comprising tailsgas and steam are fed to a heat exchange reactor which is heated by reverse water-gas shifted gas. Figure 13 shows temperature profiles for the heat exchange reactor using the configuration illustrated in Figure 12 noting that the shell-side gas can be cooled down much further compared to the configuration of Figures 10 and 11 and this allows the amount of heat recovered to be increased by >2x and the required heat input to be reduced by ~27%.

Figure 14 shows a flow sheet in which an additional feedstock of crude biogas is fed to the heat exchange post-reformer together with tailsgas and steam.

Figure 15 shows a flow sheet in which both naphtha and tailsgas are fed to the heat exchange postreformer via two separate derichment reactors.

A summary of the reference numerals used in the figures is set out in the table below.

Detailed Description

Figure 1 illustrates the basic steps in the method of forming a syngas according to the present specification. The method comprises supplying first feed gas 2 comprising hydrogen and carbon dioxide to a reverse water-gas shift reactor 4 comprising a reverse water-gas shift catalyst. The first feed gas 2 can be provided as a gas mixture of hydrogen and carbon dioxide or as separate hydrogen and carbon dioxide feed streams.

The first feed gas 2 is heated. This heating of the feed gas 2 can be done prior to the feed gas entering the reverse water gas-shift reactor 4 and/or within the reverse water gas-shift reactor 4.

The heated first feed gas 2 comprising hydrogen and carbon dioxide is passed over the reverse water- gas shift catalyst within the reverse water-gas shift reactor 4 to form a reverse water-gas shifted gas stream 6 by converting at least a portion of the carbon dioxide to carbon monoxide. This reverse water-gas shifted gas stream 6 is then passed from the reverse water-gas shift reactor 4 to a heat exchange post-reformer 10 which comprises a steam methane reforming catalyst.

A second feed gas 8 comprising methane and steam is fed to the heat exchange post-reformer 10. The second feed gas 8 has a mole fraction of methane which is higher than one or more of a mole fraction of carbon dioxide, a mole fraction of hydrogen, and a combined mole fraction of carbon dioxide and hydrogen. That is, the second feed gas 8 is primarily a methane/steam feed gas in contrast to the first feed gas 2 which is primarily a carbon dioxide/hydrogen feed gas. The reverse water-gas shifted gas stream 6 heats the second feed gas 8 within the heat exchange postreformer 10 to drive a steam methane reforming reaction as the heated second feed gas 8 is passed over the steam methane reforming catalyst to produce a steam methane reformed gas stream comprising carbon monoxide and hydrogen.

Finally, a syngas product stream 12 comprising carbon monoxide and hydrogen exits the heat exchange post-reformer 10. The syngas product stream 12 may be formed by a mixture of the reverse water-gas shifted gas stream and the steam methane reformed gas stream. Alternatively, two syngas product streams 12 may exit the heat exchange post-reformer 10, one corresponding to the reverse water-gas shifted gas stream and one corresponding to the steam methane reformed gas stream. This will depend on the internal configuration of the heat exchange post-reformer 10 and whether the two streams are mixed within the heat exchange post-reformer 10 or kept as separate (but thermally coupled) streams. Examples of different heat exchange post-reformer configurations for these options are given later.

The syngas produced by the reverse water gas shift reactor and heat exchange post-reformer can be utilized to produce hydrocarbon products via a Fischer-Tropsch process. Figure 2 shows a flow sheet for a method of forming a hydrocarbon product stream by combining the syngas forming method of Figure 1 with a Fischer-Tropsch unit. The syngas generation parts are as described in relation to Figure 1 and so will not be repeated (like reference numerals have been used for like parts). The syngas product stream 12 is passed to a Fischer-Tropsch reactor 14 comprising a Fischer-Tropsch catalyst to produce a hydrocarbon product stream 16. Typically, the syngas from the heat exchange post-reformer will be passed through a water removal unit and a carbon dioxide removal unit, and optionally further purification steps to remove other impurities which could poison the Fischer-Tropsch catalyst, prior to passing into the Fischer-Tropsch reactor 14.

In addition to producing desired hydrocarbon products, the Fischer-Tropsch process also produces a tail gas 18 which can be recycled, mixed with steam 19, and used, at least in part, as the input feed gas to the heat exchange post-reformer 10. Optionally, Fischer-Tropsch products may be further reacted / upgraded. Other less desirable fractions of the hydrocarbon product stream from downstream upgrading, such as naphtha, can also be recycled and used, at least in part, as the input feed gas to the heat exchange post-reformer 10. These recycle streams can be subjected to derichment in one or more derichment reactors 20 to produce a methane containing stream 22 for input to the heat exchange post-reformer 10.

Figure 3 shows a more detailed flow sheet for the combined process of forming syngas and using the syngas to produce a hydrocarbon product stream.

A stream of pressurised hydrogen 30 (e.g., renewable hydrogen from a pressurised electrolysis unit) is imported into the process. A stream of carbon dioxide 32 is also introduced, compressed if required, (and optionally purified to remove compounds that poison catalysts like sulphur compounds). A part of the CO2 stream is imported into the plant. Another part of the CO2 stream 34 may be separated from the cooled, dewatered downstream syngas and recycled back to the RWGS unit.

The CO2 and hydrogen streams 30, 32, 34 are mixed together and then fed to a reactor 40 containing RWGS catalyst to give a RWGS shifted product. The RWGS equilibrium temperature of the gas at the outlet of the catalyst is at least 750°C, preferably at least 800°C, more preferably at least 850°C, even more preferably at least 900°C, and still even more preferably 950°C. Heat can be provided only to the reactor feeds (H2 and CO2 separately or together), in which case the RWGS reactor is adiabatic, or only to the gases and catalyst in the RWGS reactor, or partly to each. In the flow sheet illustrated in Figure 3, the feed gas is heated by a feed interchanger 36 and a pre-heater 38 prior to passing into the RWGS reactor 40. Further heating may be provided within the RWGS reactor via combustion with oxygen or via electrical heating within the reactor as described in the background section.

Separately a stream of methane containing gas is mixed with steam and fed to the tube (process) side of a heat exchange post-reformer (HEPR 42), typically at a temperature of 350-500°C. The methane/steam gas feed can be generated by mixing a tailsgas and/or naphtha gas stream 44 from the downstream FT synthesis unit with HP steam 46, heating the mixture in an interchanger 48, and passing the gas mixture through a derichment reactor 50. In certain arrangements which recycle both a tailsgas stream and a naphtha stream, two separate derichment reactors can be provided and the resultant methane containing streams combined and fed into the HEPR 42.

The methane/steam containing gas passes through tubes in the HEPR 42 in a counter-current direction to hot RWGS shifted product stream gas from the RWGS reactor 40 flowing on the heating side, the methane/steam gas absorbing heat as the endothermic steam reforming reaction proceeds to produce a steam methane reformed gas comprising carbon monoxide and hydrogen. The tubes can be open- ended at the outlet so that the heated, reformed gas passes into the heating side of the HEPR 42. The RWGS shifted product stream is fed to the heating (shell) side of the Heat Exchange Post Reformer 42, where it provides heat for the steam methane reforming reaction and mixes with the heated, reformed gas and cools as it flows through the shell, transferring heat to the process side, leaving at the shell outlet as a CO rich product.

The CO rich product is cooled in stages. This cooling can be used to raise steam 52 (as used in the process and optionally exported) and to preheat feed streams via interchangers 53. Further cooling is needed to condense and separate water content from the gas 55. The gas is then fed to a CO2 removal unit 54, where unreacted CO2 is separated 56 and can be recycled upstream 34 of the RWGS unit so that the remaining syngas is substantially a H2/CO syngas.

The H2/CO syngas can be purified (to remove FT catalyst poisons) and optionally compressed before passing to a Fischer-Tropsch (FT) or other liquid hydrocarbon synthesis unit 58. As well as producing FT liquids 60, this also produces a hydrocarbon rich tailsgas stream 64 and FT water. The latter water stream may be (optionally purified and) recycled and provided as feed to an electrolysis unit if one is being used locally to provide renewable hydrogen feed. The tailsgas 64 can be recycled to upstream 44 of the heat exchange post-reformer to produce or contribute to the methane containing feed to the heat exchange post-reformer. The liquid hydrocarbon production may also produce a naphtha stream 62 surplus to requirements as a product, and this can also be recycled to upstream 44 of the heat exchange post-reformer to produce or contribute to the methane containing feed to the heat exchange post-reformer.

Several process designs of HEPR are possible, which all use a RWGS shifted stream to provide the heat for endothermic steam reforming and are shown in Figures 4(a) to 4(c).

The configuration illustrated in Figure 4(a) is the same as that shown in Figure 3. The H2/CO2 feed gas is heated in a pre-heater 72 and passed to a reverse water-gas shift reactor 74. The resultant reverse water-gas shifted gas 76 is fed to the heat exchange post-reformer 78. The heat exchange postreformer 78 comprises a shell and a plurality of open-ended tubes comprising steam methane reforming catalyst. A methane/steam feed gas 80 is fed through the tubes while the reverse water-gas shifted gas 76 is fed to the shell-side of the heat exchange post-reformer 78 and heats the methane/steam feed gas 80 as it passes over the catalyst material in the tubes and undergoes a steam methane reforming reaction. The steam methane reformed gas exits the tubes at the open end thereof and mixes with the reverse water-gas shifted gas in the shell-side of the HEPR. The mixed CO rich syngas product stream 82 then exits the shell side of the HEPR. As such, this configuration of HEPR produces a single syngas product stream formed of a mixture of the reverse water-gas shifted gas and the steam methane reformed gas.

Figure 4(b) shows an alternative HEPR configuration in which the reverse water-gas shifted gas and the steam methane reformed gas are not mixed within the HEPR but instead exit the HEPR as separate CO rich product streams. This configuration of HEPR comprises a plurality of tubes comprising steam methane reforming catalyst material and a surrounding shell side. However, the flow path through the tubes is kept separate from the flow path through the shell side of the HEPR. The illustrated design has two tube sheets which serve to keep the two flow paths separated. Reverse water-gas shifted gas 76 is passed through the shell side of the HEPR 78. The methane/steam feed gas 80 is fed through the plurality of tubes comprising steam methane reforming catalyst. Heating for endothermic reforming within the tubes is provided by the cooling RWGS shifted stream surrounding the outer surface of the tubes. Two CO rich products are made, the first being the heated reformed gas 82(i) and the second being the cooled RWGS shifted stream 82(ii). The first CO rich product 82(i) may optionally be added to the feed to the RWGS in order to enable further conversion of residual methane and CO2 in this stream.

Figure 4(c) shows another HEPR design 78 with one tube sheet and utilising bayonet tubes. Methane containing gas and steam 80 passes down a catalyst-filled annular space absorbing heat from the shellside reverse water-gas shifted gas 76 and a central bayonet tube. The heated reformed gas leaves then passes back up the central tube, giving up heat to the process gas in the annular tube. Heating for endothermic reforming is provided by the cooling RWGS shifted stream. Two CO rich products are made, the first being the cooled RWGS shifted stream 82(i) and the second being the cooled reformed gas 82(ii). The two products can be mixed together downstream to form a single H2/CO syngas stream to send to hydrocarbon synthesis.

It is to be noted that within the HEPR, the methane/steam feed is passed over the steam methane reforming catalyst while the reverse water-gas shifted gas stream from the reverse water-gas-shift reactor is not passed over the steam methane reforming catalyst.

Various options are available to provide heat for the RWGS reaction. Figures 5 to 9 show flow sheet configurations similar to the one shown in Figure 3 but with different options for providing the heat for the RWGS reaction. Like parts are indicated by like reference numerals and a repeated description of the complete flow sheet is not repeated for reasons of conciseness.

Alternative ways of electrically heating are static electric heating or "turbo-machinery heating" (TMH) of the H2 and CO2 feed to the RWGS reactor.

For instance, static electric heating can be accomplished by passing the feed gas through tubes inside an electrical furnace equipped with electrically heated radiative panels. Alternatively, the feed gas can be heated in a heat exchanger, which contains one or more resistive heating elements (enclosed in insulated sheathes).

The term "turbo-machinery heating" means utilising apparatus that imparts kinetic energy to a gas, thereby heating the gas, by means of a rotatable shaft assembly - this is shown schematically in Figure 5 in which the H2 and CO2 feed passes through a turbo-machinery heater 90 to heat the feed gas prior to entering the RWGS reactor 40. In this configuration, the H2 and CO2 feed gas is directly heated by the turbo-machinery heater. Alternatively, micro-resistive in-situ heating of catalyst and flowing gas inside the RWGS reactor can be utilised. Electrical energy is directly converted into heat within the RWGS catalyst. This is shown in Figure 6 which comprises an electrically heated reverse water-gas shift reactor (e-RWGS 92) and which provides heat for RWGS by in situ resistive heating of RWGS catalyst.

Combustion of a hydrocarbon containing gas /fossil fuel with an oxygen containing gas is another heating method. In one embodiment heating can be accomplished by passing the feed gas through tubes inside an atmospheric combustion furnace. Any fuel could be used, but it will be evident that fuels that have a low greenhouse gas (GHG) warming potential will be preferential if the carbon intensity of downstream products is to be minimised. One such fuel is biogas.

Figure 7 shows yet another alternative for heating the reverse water-gas shift reaction (and subsequent provision of heat into the heat exchange post-reformer). This configuration uses turbo-machinery heating 100 or static electrical heating of a heat transfer fluid, whereby this fluid can be used to indirectly provide heat for the RWGS reactor 40. The heat transfer fluid flows on the heating side of a RWGS heat exchange reactor with the RWGS taking place on the process side (i.e., tubes in which RWGS catalyst is disposed). In the illustrated embodiment, the heat transfer fluid is provided by a CO2 gas 96 which is passed to a buffer 98 prior to being heated in a turbo-machinery heater 100. The heated gas then flows through the shell side of the heat exchange RWGS reactor 40 exchanging heat with CO2/H2 process gas within the tube-side of the RWGS reactor. The heat transfer gas then passes back to the buffer 98 and is recirculated through the turbo-machinery heater 100. As such, Figure 7 shows an option to use turbo-machinery heating of a heat transfer fluid, which indirectly provides heat to the RWGS reaction.

Figure 8 shows another option to provide heat for the reverse water-gas shift reaction by internal combustion of oxygen 104 (substoichiometrically) with hydrogen in the H2/CO2 stream and then passing the high temperature gas over an adiabatic RWGS bed. This is known as autothermal reforming (ATR) and thus the reverse water-gas shift reactor is an ATR RWGS reactor 102. As such, Figure 8 shows an option to use ATR to provide for RWGS by internal combustion.

Another possible embodiment, particularly applicable to the HEPR designs shown in figures 4(b) and 4(c), is to feed the second CO rich gas to an autothermal reformer (ATR 106) as shown in Figure 9. This ATR consists of an oxygen-fired burner upstream of an adiabatic steam reforming catalyst bed. The ATR 106 thus boosts the temperature at which the second CO rich gas is at RWGS equilibrium and hence the conversion to CO at the expense of a partial loss of hydrogen in the gas. As such, Figure 9 shows an option to feed one of the CO rich gas streams (i.e., the steam methane reformed gas stream) from the HEPR to an oxygen-fired autothermal reformer (ATR). The resultant gas stream having increased CO content can then be combined with the other CO rich gas stream from the HEPR (i.e., the reverse water-gas shifted gas stream).

There are many possible sources of methane containing gas. Examples include the following:

(i) Gas purged from downstream hydrocarbon synthesis steps such as FT synthesis ("tail gas" or "tailsgas") contains methane and light hydrocarbons. It can be recycled back to enable it to be steam reformed to produce CO and H2. Depending on the composition it could be beneficial to derich (pre-reform) this gas first to form a methane containing gas to feed to the HEPR.

(ii) A light naphtha or LPG stream can be separated from the hydrocarbon synthesis product in a downstream upgrading step. This product can be recycled back for de-richment and steam reforming. It can be beneficial to treat this light naphtha or LPG stream in a separate derichment vessel to the tailsgas in order to optimize derichment conditions for the different recycle streams and produce methane containing gas for the HEPR.

(iii) A light naphtha or LPG stream or tailsgas, which is a byproduct of another process to convert vegetable oils into renewable diesel (RND) or sustainable aircraft fuel (SAF) can be be fed to a derichment reactor to produce a renewable source of methane containing gas.

(iv) Another potential biogenic feed stream is biogas, such as is produced in landfill gas facilities or anaerobic digestion (AD) plants. After purification, the composition is typically 40-60% CO2 and 40-60% CH4. It can be added as a feedstock to the HEPR. This can be advantageous in order produce extra hydrogen from a biogenic feed source, at the same time as providing biogenic CO2 feed, which will enable less hydrogen (from a renewable source) to be used.

Another embodiment is to feed part of the CO2 feedstock, up to 10%, together with the methane containing gas feed, directly to the HEPR, in which case there would need to be less CO2 in the combined H2/CO2 feed to the RWGS reactor in order to achieve a required target overall syngas H2/CO ratio. This may be advantageous in order to increase the amount of high-level heat recuperated in the HEPR and further reduce the external heating duty.

It will also be realised that a small amount of hydrogen may be advantageously added together with the methane containing gas feed, directly to the HEPR. The purpose of this addition may be to chemically assist with feedstock purification or to condition a catalyst (such as the derichment catalyst) and will normally be present at a level of <5% of any methane containing gas, rather than to promote the RWGS reaction in the HEPR.

Another option is to add a methane containing stream along with the H2/CO2 to the RWGS reactor. The circumstances of this approach may be if it is desired to feed a large quantity of the methane containing stream through the system (compared to the H2/CO2 stream). In this case the amount of methane may be higher than that which can be usefully steam reformed in a HEPR heated by the RWGS shifted gas. As such, in this case the methane can be split with a portion being passed through the RWGS reactor with the H2/CO2 feed stream and the rest of the methane being fed through the HEPR.

Calculated examples are provided below. All examples are computed to give a combined gas containing ~3200 kgmols/hr of H2/CO at a ratio of 2.14 in a syngas containing the same quantity of methane and utilise the same amount and composition of tailsgas being recycled from a downstream Fischer- Tropsch process.

Figure 10 shows a schematic not according to the present specification, where H2 and CO2, tailsgas, and steam are fed to both an RWGS reactor and an HER heated by the RWGS shifted gas. The external heating for the RWGS may be provided either upstream or within the RWGS. This corresponds to the approach described in WO2022253965 which is discussed in the background section of this specification. That is, rather than providing a primarily methane containing stream to the heat exchange post-reformer in order to essentially perform steam methane reforming in the heat exchange post-reformer, both the feed to the RWGS reactor and the heat exchange reformer are mainly H2 and CO2 with only minor amounts of methane and steam. The mixed ^/CCh/tailsgas/steam is split with 78% going to RWGS and 22% passing to the process side of the HER with the mass balance for this Counter-Example 1 shown in the table below.

In this process the gas feeding the HER undergoes an exothermic methanation reaction in the first part of the process side heating up to >700°C. This limits the amount of recuperative heat that can be recovered, only allowing the shell-side gas to cool down to ~750°C, as shown in Figure 11 which illustrates temperature profiles in the HER.

In contrast to the above, Figure 12 shows a schematic according to the present specification, where H2 and CO2 are fed to an RWGS reactor and tailsgas/steam to an HEPR heated by the RWGS shifted gas. The external heating for the RWGS may be provided either upstream or within the RWGS. In this example, the same amount of feed H2 is used as in the previously discussed counter-example. The mass balance for this Example 2 is shown in the table below where the feed to the RWGS reactor is primarily CO2/H2 and the feed to the HEPR is primarily methane/steam (H2O).

In this example, the shell-side gas can be cooled down much further, to ~590°C, as shown in Figure 13. This allows the amount of heat recovered to be increased by more than twice (>2x) compared to the previously discussed counter-example and the required heat input to be reduced by ~27%.

Figure 14 shows a schematic of Example 3 where there is an additional feedstock of crude biogas 108, containing ~50% methane and ~50% CO2, which is fed, together with tailsgas and steam to the HEPR 42. As in the previous example, all the H2/CO2 feed is fed to the RWGS reactor. The mass balance for this example is shown in the table below where the feed to the RWGS reactor is primarily CO2/H2 and the feed to the HEPR is still primarily methane/steam (H2O) although with an increased level of CO2 compared to the previous example.

In this example, with the mass balance shown above, the addition of ~3tes/hr of biogas allows the feed hydrogen to be reduced by ~7%. The shell-side gas can be cooled down even further than in the previous example, to ~525°C. This allows the amount of heat recovered to be further increased and the required heat input to be reduced by ~4%, compared to the previous example.

Another example (Example 4) is shown in Figure 15. There is an additional feedstock of naphtha 110, as might be formed as a byproduct in FT product upgrading and which is not useful as a fuel product. The naphtha feedstock contains mostly alkanes in the C4-C7 range. In this arrangement the naphtha is heated in a naphtha interchanger 112 and deriched in a naphtha derichment reactor 114 prior to being fed to the HEPR 42. In this example the tailsgas 44 is separately heated in a tailsgas interchanger 118 and deriched in a tailsgas derichment reactor 120 prior to being fed to the HEPR 42.

As in the previous example, all the H2/CO2 feed is fed to the RWGS reactor. The mass balance is shown in the table below for Example 4.

In this example, with the mass balance shown, the addition of ~1.65tes/hr of naphtha allows the feed hydrogen to be reduced by 13-14% (compared to Example 2). The shell-side gas can be cooled down even further than in Example 2, to ~490°C. This allows the amount of heat recovered to be further increased and the required heat input to be reduced by ~2%, compared to Example 2.

While this invention has been particularly shown and described with reference to certain examples, it will be understood to those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method of forming a syngas, the method comprising: supplying first feed gas comprising hydrogen and carbon dioxide to a reverse water-gas shift reactor comprising a reverse water-gas shift catalyst, wherein the first feed gas to the reverse water- gas shift reactor has a combined mole fraction of hydrogen and carbon dioxide which is greater than 0.5; heating the first feed gas; passing the heated first feed gas comprising hydrogen and carbon dioxide over the reverse water-gas shift catalyst within the reverse water-gas shift reactor to form a reverse water-gas shifted gas stream by converting at least a portion of the carbon dioxide to carbon monoxide; passing the reverse water-gas shifted gas stream from the reverse water-gas-shift reactor to a heat exchange post-reformer which comprises a steam methane reforming catalyst; supplying second feed gas comprising methane and steam to the heat exchange post-reformer, wherein the second feed gas to the heat exchange post-reformer has a combined mole fraction of methane and water which is greater than 0.5, wherein the reverse water-gas shifted gas stream heats the second feed gas within the heat exchange post-reformer to drive a steam methane reforming reaction as the heated second feed gas is passed over the steam methane reforming catalyst to produce a steam methane reformed gas stream comprising carbon monoxide and hydrogen, and wherein a syngas product stream comprising carbon monoxide and hydrogen exits the heat exchange post-reformer.

2. A method according to claim 1, wherein the first feed gas to the reverse water-gas shift reactor has a combined mole fraction of hydrogen and carbon dioxide which is greater than 0.6, 0.7, 0.8, 0.9, or 0.95.

3. A method according to claim 1 or 2, wherein the second feed gas to the heat exchange post-reformer has a combined mole fraction of methane and water which is greater than 0.6, 0.7, or 0.8.

4. A method according to any preceding claim, wherein the second feed gas has mole fraction of methane which is higher than one or more of a mole fraction of carbon dioxide, a mole fraction of hydrogen, or a combined mole fraction of carbon dioxide and hydrogen within the second feed gas.

5. A method according to any preceding claim, wherein the reverse water-gas shifted gas stream is mixed with the steam methane reformed gas stream within the heat exchange post-reformer such that the syngas product stream exiting the heat exchange post-reformer comprises a mixture of the reverse water-gas shifted gas stream and the steam methane reformed gas stream.

6. A method according to any one of claims 1 to 4, wherein the reverse water-gas shifted gas stream remains separated from, but thermally coupled with, the steam methane reformed gas stream within the heat exchange post-reformer, and two separate syngas product streams exit the heat exchange post-reformer, one formed from the reverse water-gas shifted gas stream and one formed from the steam methane reformed gas stream.

7. A method according to any preceding claim, wherein the first feed gas is heated prior to the first feed gas entering the reverse water gasshift reactor and/or the first feed gas is heated within the reverse water gas-shift reactor.

8. A method according to claim 7, wherein the first feed gas is heated by one or more of: a turbo machinery heater which directly heats the first feed gas prior to entering the reverse water-gas shift reactor; a turbo machinery heater which heats a heat transfer fluid, the heat transfer fluid then heating the first feed gas either prior to entering the reverse water-gas shift reactor or within the reverse water- gas shift reactor; an electrical heating system either prior to entering the reverse water-gas shift reactor or within the reverse water-gas shift reactor; one or more heat exchangers prior to entering the reverse water-gas shift reactor; combustion of oxygen and hydrogen within the reverse water-gas shift reactor, the reverse water-gas shift reactor being an autothermal reformer.

9. A method according to any preceding claim, wherein at least a portion of the syngas product stream from the heat exchange post-reformer is fed through an autothermal reformer.

10. A method according to claim 6 and 9, wherein the heat exchange post-reformer is configured to produce two separate syngas product streams, one formed from the reverse water-gas shifted gas stream and one formed from the steam methane reformed gas stream, and wherein the syngas product stream formed from the steam methane reformed gas stream is fed through the autothermal reformer prior to being mixed with the syngas product stream formed from the reverse water-gas shifted gas stream.

11. A method according to any preceding claim, wherein the second feed gas comprising methane and steam is at least partially formed from one or more of: a gas purged, optionally deriched, from a downstream hydrocarbon synthesis step; a naphtha or LPG stream, optionally deriched, which is separated from a downstream process to synthesise and upgrade hydrocarbons; and a biogenic feed source.

12. A method of producing hydrocarbons, the method comprising: forming a syngas according to any preceding claim; and passing the syngas through a Fischer-Tropsch reactor to produce the hydrocarbons.

13. A system for performing the method according to any preceding claim, the system comprising: a first feed gas supply unit configured to supply a first feed gas comprising hydrogen and carbon dioxide to a reverse water-gas-shift reactor, wherein the first feed gas supply unit is configured to supply the first feed gas to the reverse water-gas shift reactor with a combined mole fraction of hydrogen and carbon dioxide which is greater than 0.5; a heating unit configured to heat the first feed gas; a reverse water-gas shift reactor comprising a reverse water-gas shift catalyst, the reverse water-gas shift reactor being configured to receive the first feed gas, pass the first feed gas over the reverse water-gas shift catalyst to form a reverse water-gas shifted gas stream, and to pass the reverse water-gas shifted gas stream from the reverse water-gas-shift reactor to a heat exchange postreformer; a second feed gas supply unit configured to supply a second feed gas comprising methane and steam to the heat exchange post-reformer with a combined mole fraction of methane and water which is greater than 0.5; and a heat exchange post-reformer comprising steam methane reforming catalyst, the heat exchange post-reformer being configured to receive the second feed gas and pass the second feed gas over the steam methane reforming catalyst, the heat exchange post-reformer being further configured to receive the reverse water-gas shifted gas stream and provide heat exchange from the reverse water- gas shifted gas stream to the second feed gas to heat the second feed gas and drive a steam methane reforming reaction as the heated second feed gas is passed over the steam methane reforming catalyst to produce a steam methane reformed gas stream comprising carbon monoxide and hydrogen, the heat exchange post-reformer thereby producing a syngas product stream comprising carbon monoxide and hydrogen.

14. A system according to claim 13, further comprising a Fischer-Tropsch unit comprising a Fischer-Tropsch catalyst, the Fischer- Tropsch unit being configured to receive the syngas product stream and pass the syngas product stream over the Fischer-Tropsch catalyst to produce a hydrocarbon product stream.