Efficient use of renewable feeds and reduction of emissions in e-fuel plant

Abstract

A process for operation of an e-fuel plant is provided to maximize overall feed utilization. The process includes first operating mode (A) and second operating mode (B) of said plant. An e-fuel plant suitable for use in this process is also provided.

Description

[0001] EFFICIENT USE OF RENEWABLE FEEDS AND REDUCTION OF EMISSIONS IN E-FUEL PLANT

[0002] TECHNICAL FIELD

[0003] The present invention relates to a more efficient sustainable hydrocarbon production system and process, where sustainable feed utilization is maximized by minimizing emissions. Moreover, the present invention enables more economical and faster transition to normal operating mode from non-normal operating mode, such as transient mode of operation, including start-up.

[0004] BACKGROUND

[0005] The fossil-derived hydrocarbon products are responsible for a major part of global green-house gas (GHG) emission. A part of that is expected to be substituted by direct electrification or direct use of H2from electrolysis. However, still a significant part of fossil-derived products, such as - fuels for the aviation industry, heavy-duty transportation etc., is deemed challenging to replace via direct electrification or direct use of H2. Therefore, it is extremely important to substitute the root of the hydrocarbon products from fossil-sources to more sustainable sources. Such sustainable sources include but are not limited to, CO2from direct air capture or fermentation process or flue gas or other point sources; H2from electrolysis or other sustainable sources or processes; gases derived from biomass etc.

[0006] When hydrocarbon fuels derived from sustainable sources are also called eFuels. There exist various routes for eFuels production. One of them is conversion of sustainable feeds first to synthesis gas or syngas (a gas rich in CO and H2), which can be converted further to valuable products including eFuels such as jet-fuel, kerosene such as synthetic paraffinic kerosene (SPK) and / or diesel produced for example by the Fischer-Tropsch (F-T) process.

[0007] The primary feeds to such eFuels plants (such as H2 and CO2) are quite expensive. Thus, waste of these expensive feeds should be minimized to the extent possible both during normal operation and non-normal operating mode, such as start-up.

[0008] The eFuels plant comprises various sections and some of these sections interact with each other with recycle stream(s) during normal operation. Therefore, starting up these sections and integrating them to reach normal operating conditions may take up to several hours, if not days. Moreover, it is only reasonable to stop overall plant operation, including upstream syngas generation, when a long downtime is foreseen. Sometimes downstream synthesis stage operation is stopped only for a limited period. Such situations may occur due to spurious trips within a downstream synthesis stage or other unavoidable situations. Often, in such situations, the affected part of the plant (i.e., downstream synthesis stage) is taken back in operation as soon as possible, following recommended procedures to establish normal operation at full capacity, which may still take hours.

[0009] In another scenario, reduced power availability can potentially limit availability of one or more sustainable feed supply (e.g. H2from electrolysis, CO2from DAC etc.). This may happen due to the unpredictability and intermittency of a renewable energy supply. Therefore, it may not be prudent to stop the operation of entire plant and continue operation by consuming the lowest possible sustainable feeds, preferably continuing production at the lowest possible rate.

[0010] These conditions can be termed as 'non-normal' operating mode of the plant. The 'non-normal' operation may include steady-state operating mode but away from designed plant capacity and / or designed process conditions. The 'non-normal' operation may also include transient operations, such as start-up, shut down etc. During such 'non-normal' operating modes, flaring of effluent gases from one or more sections of the plant is common, while preferably operating at or close to the minimum operable capacity of the individual stages and / or the plant.

[0011] Flaring effluent gases in eFuels plants means wasting expensive sustainable feeds, which include H2, CO2, etc. The longer the time required to return to normal operation is, the more expensive and expansive the waste of sustainable feeds would be. Furthermore, such 'non- normal' operations may occur several times within plant's lifetime, with each start-up causing an accumulated loss of valuable feeds and impacting overall plant economy.

[0012] However, no substantial research has been carried out into efficient utilization of feeds during 'non-normal' operating modes, which may take several hours, even days. Therefore, it is necessary to provide a system and a process to address this problem and find a solution. The invention, disclosed herein, minimizes emissions and thereby, waste of expensive feeds during 'non-normal' operating modes, including start-up, of eFuels plant.

[0013] Publications in this field include: US2014165569, US2018093888, US2012159841, US2021340447, US2021246034, US2023069964 and US9108894. SUMMARY

[0014] It has been found by the present inventor(s) that sustainable feed utilization can be maximized, and emissions are minimized using selected process and plant layouts. The current invention provides layouts / methods of reducing waste of expensive sustainable feeds by recycling at least a part of the processed feeds. Processed feeds include syngas feed to synthesis section.

[0015] So, in a first aspect the present invention relates to a process for operation of an eFuels plant, is provided, said eFuels plant comprising : a first feed comprising hydrogen; a second feed comprising CO2; optionally, a fourth feed comprising steam; a syngas stage comprising a reverse water gas shift (RWGS) section, said RWGS section being arranged to receive at least a part of the first feed, at least a part of the second feed, a third stream comprising hydrocarbons, and - where present - at least a part of the fourth feed, and to output a first syngas stream; a synthesis stage, said synthesis stage being arranged to receive at least a first portion of the first syngas stream and provide at least a hydrocarbon product stream and a hydrocarbon-containing off-gas stream; wherein - in a first operating mode (A) of said plant - the process comprises:

[0016] • feeding at least a first portion of the first syngas stream from the syngas stage to the synthesis stage and providing at least a hydrocarbon product stream and a hydrocarbon-containing off-gas stream;

[0017] • feeding at least a portion of the off-gas stream from the synthesis stage to syngas stage, as at least a portion of said third stream comprising hydrocarbons, upstream the RWGS section; and and wherein - in a second operating mode (B) of said plant - the process comprises:

[0018] • feeding at least a second portion of the first syngas stream from the RWGS section back to syngas stage, upstream the RWGS section.

[0019] An e-fuel plant is also provided, said e-fuel plant comprising : a first feed comprising hydrogen; a second feed comprising CO2; optionally, a fourth feed comprising steam; a syngas stage comprising a reverse water gas shift (RWGS) section, said RWGS section being arranged to receive at least a portion of the first feed, at least a part of the second feed, a third stream comprising hydrocarbons, and - where present - at least a portion of the fourth feed, and to output a first syngas stream; a synthesis stage, said synthesis stage being arranged to receive at least a first portion of the first syngas stream and provide at least a hydrocarbon product stream and a hydrocarbon-containing off-gas stream; said plant being arranged to provide at least a portion of the hydrocarbon-containing off-gas stream from the synthesis stage to the syngas stage, as at least a portion of said third stream comprising hydrocarbons, upstream the RWGS section said plant being further arranged to feed at least a second portion of the first syngas stream from the RWGS section to syngas stage, upstream the RWGS section.

[0020] Further details of the technology are provided in the enclosed dependent claims, figures and examples.

[0021] LEGENDS

[0022] The invention is illustrated by means of the following schematic illustrations, in which:

[0023] Figure 1 shows a simple layout of the system / process of the invention. Figure 1A shows the first operating mode A; Figure IB shows the second operating mode B.

[0024] Figure 2 shows another layout of the system / process of the invention. Figure 2A shows the first operating mode A; Figure 2B shows the second operating mode B.

[0025] DETAILED DISCLOSURE

[0026] Unless otherwise specified, any given percentages for gas content are % as dry volume. All feeds are preheated / cooled, compressed and purified from any impurities, as required.

[0027] The term "synthesis gas" (abbreviated to "syngas") is meant to denote a gas comprising hydrogen, carbon monoxide, carbon dioxide and small amounts of other gasses, such as argon, nitrogen, methane, steam, etc. A plant may comprise one or more stages; a stage may comprise one or more sections; a section may comprise one or more units. The unit operations are described as the units in this invention.

[0028] In this invention, the capacity of a plant or a stage or a section or a unit is defined by the throughput. For an example - 50% plant capacity indicates that amounts of product(s) out from the plant is at 50% of the product(s) amount, for what the plant is designed. If a plant comprises more than one stages with recycle of intermediate stream(s), in a certain operating mode individual stages may operate at higher capacity, say 50%, while the plant product capacity may become lower, say 30%, due to relatively higher recycle flow of intermediate stream(s).

[0029] Operational flexibility of a plant or a stage or a section or a unit, to large extent, is defined by the minimum operable capacity. The lower the minimum operable capacity is, more flexible the operation of the plant or stage or section or unit would be. Typically, the minimum operable capacity of the eFuels plant lies at or below 50% of design capacity, preferably at or below 30% of the design capacity, more preferably at or below 20% of design capacity. Minimum operable capacity of individual stages, however, may differ from overall plant capacity. For example - one or more stages in eFuels plant may have minimum operable capacity at 30% of design capacity, while the overall eFuels plant may produce 20% of designed product amount and consume less sustainable feeds.

[0030] 'Normal operation' of plant or stage or section or unit refers to a stable operating condition where the final product or effluent from the said plant or stage or section or unit is as per approved and / or designed specification. During 'normal operation', the said plant or stage or section or unit is operated at more than minimum operable capacity, preferably > 50%, more preferably > 75%, even more preferably at or more than 100% of its design capacity of the plant. All other operating conditions, including start-up and shutdown of the plant, fall within 'non-normal' operating mode.

[0031] In a first aspect, a process for operation of an e-fuel plant (X), is provided, said e-fuel plant (X) comprising the following feeds: a first feed comprising hydrogen; a second feed comprising CO2; and optionally, a fourth feed comprising steam.

[0032] Feeds A first feed comprising hydrogen is provided. The first feed of hydrogen is hydrogen-rich meaning that the major portion of this feed is hydrogen, i.e. over 75%, such as over 85%, preferably over 90%, more preferably over 95%, even more preferably over 99% of this feed is hydrogen. Suitably, the first feed consists essentially of hydrogen. One source of the first feed of hydrogen can be one or more electrolyser units. In addition to hydrogen the second feed may for example comprise steam, nitrogen, argon, carbon monoxide, carbon dioxide, and / or hydrocarbons. In some cases, a minor content of oxygen may be present in this feed, typically less than 100 ppm. At least a first portion of said hydrogen-rich feed is provided to the RWGS section.

[0033] A second feed comprising carbon dioxide is provided. The second feed of CO2 is CC -rich meaning that the major portion of this feed is CO2; i.e. over 75%, such as over 85%, preferably over 90%, more preferably over 95%, even more preferably over 99% of this feed is CO2. Suitably, the second feed consists essentially of CO2. One source of the second feed of carbon dioxide can be one or more exhaust stream(s) from one or more chemical plant(s). One source of the second feed of carbon dioxide can also be carbon dioxide captured from one or more process stream(s) or from atmospheric air. Another source of the second feed could be CO2 captured or recovered from the flue gas for example from fired heaters, steam reformers, power plants and / or cement plants. The second feed may in addition to CO2 comprise for example steam, oxygen, nitrogen, oxygenates, amines, ammonia, carbon monoxide, and / or hydrocarbons. At least a first portion of said CCh-rich feed is provided to the RWGS section.

[0034] If H2and / or CO2feeds contain O2, higher hydrocarbons and catalyst poisons (such as S), they are converted and / or removed within the syngas stage, in the presence of suitable catalysts, upfront the RWGS section.

[0035] The ratio of H2 / CO2 provided to the RWGS section inlet varies from 2.0 - 7.0. This ratio is defined as any H2 and CO2 in external streams (i.e. not including hydrogen and / or carbon dioxide via recycled off-gas streams). This ratio will depend upon the desired end-product in the synthesis stage. For example, the desired Fh / CO-ratio of the synthesis gas will typically be around 2.0, if it is to be used in a Fischer-Tropsch synthesis. For an F-T synthesis stage the H2 / CO2-ratio at the RWGS section inlet (i.e. not including hydrogen and / or carbon dioxide in any recycle streams) should be in the range of 2.0-7.0 or more preferably from 3.0-6.0 and most preferably 3.0-5.0.

[0036] RWGS section is arranged to receive a third stream comprising hydrocarbons. In first operating mode (A), the third stream may be at least partially constituted by the off-gas stream from the synthesis stage. Therefore, the third stream comprising hydrocarbons is a recycle stream from downstream in the plant. The third stream may be supplemented, as required, by an external hydrocarbon feed.

[0037] A fourth feed comprising steam is optionally provided. The fourth feed is steam-rich meaning that the major portion of this feed is steam; i.e. over 75%, such as over 85%, preferably over 90%, more preferably over 95%, even more preferably over 99% of this feed is steam. Suitably, the fourth feed consists essentially of steam.

[0038] Hvdrocarbon-containing off-gas stream

[0039] The hydrocarbon-containing off-gas stream is produced as side product from the synthesis stage. In one embodiment, where the synthesis stage is a Fischer-Tropsch (F-T) synthesis stage, the off-gas stream comprises carbon monoxide (5-40 vol. %), hydrogen (10-50 vol %), carbon dioxide (20-50 vol %), methane (10-40 vol %) and higher hydrocarbons (1-20 vol%). Additional components such as argon and nitrogen may also be present in smaller amounts. The higher hydrocarbons comprise olefins and paraffins with two or more carbon atoms.

[0040] The exact composition of the off-gas from synthesis stage (S2) may vary significantly depending on the process conditions and catalyst used in the synthesis stage. A key parameter for making the above utilization of CO2 sustainable is to recycle the off-gas such that the carbon therein may be reintroduced in the production of the synthesis gas, thereby improving the overall carbon efficiency of the process.

[0041] Syngas stage

[0042] The syngas stage comprises at least one reverse water gas shift (RWGS) section, said RWGS section being arranged to receive at least a part of the first feed, at least a part of the second feed, a third stream comprising hydrocarbons, and at least a part of the fourth feed comprising steam, and to output a first syngas stream.

[0043] The RWGS section

[0044] The RWGS section (I) may comprise non-electrical RWGS or electrical RWGS reactors. Nonelectrical RWGS reactors include but are not limited to one or more fired RWGS reactors and autothermal RWGS reactors. For fired RWGS, any sustainable fuel, including H2, can be combusted to provide heat to the endothermic reaction. Oxygen (in the form of fifth feed comprising oxygen) is required as an additional feed when autothermal RWGS is used.

[0045] The RWGS section (I) may comprise one or more electrically heated RWGS reactors, such as a resistance heated RWGS reactor or an induction heated RWGS reactor which may be arranged in series or parallel. Resistance heated RWGS reactors are described, inter alia, in WO2019228797A1.

[0046] The RWGS catalyst can be either selective or non-selective. Selective RWGS catalyst is only active in RWGS reaction (reaction 1). While non-selective RWGS catalyst can catalyse both RWGS (reaction 1) and methanation and steam reforming reactions (reaction 2). co2+ H2«-> CO + H2O (1)

[0047] CO2+ 4H2CH4+ 2H2O (2)

[0048] If selective RWGS catalyst is used in RWGS section, then third stream comprising hydrocarbons needs to be processed in the presence of a separate catalyst, having steam methane reforming (opposite of reaction (2)) activity.

[0049] In one aspect, electrical RWGS can comprise structured catalyst comprising a macroscopic structure of electrically conductive material capable of catalysing both a reverse water gas shift reaction and a methanation reaction. The RWGS reactors may comprise catalysts that are active in both RWGS and methanation reactions, and / or catalysts that are active in only RWGS reaction. The catalyst may also be active in steam reforming.

[0050] In another alternative, the RWGS section may comprise a methanation section followed by autothermal reforming section. The methanation section may comprise one or more methanation units arranged in series or parallel. Methanation units may be heated reactors or adiabatic reactors.

[0051] Off-gas conversion section

[0052] In one embodiment, the syngas stage (SI) may additionally comprise an off-gas conversion section (II), wherein the off-gas is processed before feeding it to RWGS section (I).

[0053] The off-gas conversion section (II) may comprise one or more water-gas shift (WGS) units, arranged in series or parallel. WGS units may be adiabatic or isothermal or heated / cooled WGS units. The inlet temperature to the WGS reactors may vary from 150°C - 400°C, preferably 180°C - 350°C, more preferably 200°C - 320°C; outlet temperature from WGS reactors may vary from 250°C- 550°C, preferably 280°C-500°C, more preferably 300°C - 480°C. The off-gas conversion section (II) may also comprise a hydrogenation unit, arranged in series or parallel, upstream of the WGS unit. The hydrogenation unit may include one or more adiabatic or isothermal or heated / cooled hydrogenation reactors. The outlet temperature from the hydrogenator reactor may vary from 100°C - 250°C, preferably 120°C - 220°C, more preferably 150°C - 200°C.

[0054] The off-gas conversion section (II) may also comprise a higher hydrocarbon conversion unit, arranged in series or parallel downstream of the WGS unit. The higher hydrocarbon conversion unit may include one or more adiabatic or isothermal or heated / cooled higher hydrocarbon conversion reactors. The inlet temperature to the higher hydrocarbon conversion reactors may vary from preferably 250°C - 400°C, more preferably 280°C - 320°C; the outlet temperature from higher hydrocarbon conversion reactor may vary from 350°C - 650°C, preferably 400°C

[0055] - 550°C, more preferably 450°C - 500°C. The HHC conversion unit is also active for WGS / RWGS and methanation / steam reforming of methane.

[0056] Recycled syngas treating section

[0057] In other embodiment, the syngas stage (SI) may additionally comprise a syngas treating section (not shown in the figures). The syngas treating section comprises one or more WGS reactors arranged in series or parallel, wherein, - in the second operating mode (B) of the plant

[0058] - said process comprises: feeding at least a part of the second portion of the first syngas stream from the syngas stage and at least a part of the fourth feed comprising steam to the syngas treating section and outputting a treated syngas stream; and feeding at least a portion of the treated syngas stream to the RWGS section in the syngas stage.

[0059] The second portion of first syngas stream may be recycled to the syngas treating section, which may comprise at least one reactor active in the WGS reaction and / or the methanation reaction. In one embodiment, such dedicated syngas treating section may be kept idle under inert atmosphere at required process conditions during normal operation but may be taken into operation when the second portion of first syngas is recycled in operating mode B.

[0060] The syngas treating section may comprise one or more water-gas shift (WGS) units, arranged in series or parallel. The WGS unit includes adiabatic or isothermal or heated / cooled WGS reactors. The inlet temperature to the WGS reactors may vary from 150°C - 400°C, preferably 180°C - 350°C, more preferably 200°C - 320°C; outlet temperature from WGS reactors may vary from 250°C- 550°C, preferably 280°C-500°C, more preferably 300°C - 480°C.

[0061] In one embodiment, the syngas treating section may further comprise at least one hydrogenation unit, a water gas shift (WGS) unit, and at least one higher hydrocarbon conversion unit, wherein the hydrogenation unit(s), are arranged upstream of the WGS unit, and the higher hydrocarbon conversion unit(s) are arranged downstream of the WGS unit.

[0062] In a preferred embodiment, syngas treatment is performed in the off-gas conversion section (II) in operation mode B and only the hydrogenation unit upstream the WGS unit is completely or partially bypassed.

[0063] In another preferred embodiment, syngas treatment is performed in the off-gas conversion section (II) in operation mode B, and both hydrogenation unit upstream the WGS unit and higher hydrocarbon conversion unit downstream WGS unit are completely or partially bypassed.

[0064] In another preferred embodiment, wherein syngas treatment is performed in the off-gas conversion section (II) in operation mode B, at least a part of the treated syngas is recycled back to inlet of syngas treatment. In such preferred embodiment, any hydrogenation unit upstream the WGS unit may be completely or partially bypassed,

[0065] In one embodiment, at least a part of the recycled syngas is first taken through one or more hydrogen separation units arranged to separate at least a portion of the hydrogen and output a recovered hydrogen rich stream before syngas treatment, or before being fed to the synthesis stage. The hydrogen separation unit(s) could be a pressure swing adsorption unit(s) (PSA) or a selective membrane unit(s). The recovered H2rich stream may be sent to the RWGS section after necessary compression and / or heating. In another embodiment, at least a part of the first feed comprising CO2is added to the recycled syngas B before syngas treatment in operating mode.

[0066] In one embodiment, more than one of the above-mentioned embodiments for recycled syngas treatment are combined. The syngas stage may comprise external heating equipment, including electric heaters, which may, optionally, be used only second operating mode (B) but with reduced or no use in first operating mode (A). synthesis stage is arranged to receive at least a first portion of the first syngas stream (from the syngas stage), and provide at least a hydrocarbon product stream and a hydrocarbon- containing off-gas stream. The synthesis stage is suitably a Fischer Tropsch (FT) stage.

[0067] In particular, the product stream may be a hydrocarbon product stream. Fischer-Tropsch Synthesis stage

[0068] The Fischer-Tropsch (F-T) synthesis stage receives said at least a portion of the first synthesis gas stream and provides a raw hydrocarbon stream and a hydrocarbon-containing off-gas stream.

[0069] At the inlet of said F-T synthesis stage, the synthesis gas stream suitably has a H2 / CO ratio in the range 1.00 - 4.00; preferably in the range 1.50-2.10. In another aspect, the synthesis gas stream at the inlet of said F-T synthesis stage suitably has a (H2 - CC>2) / (CO + CO2) ratio in the range 1.50 - 2.50; preferably 1.80 - 2.30, more preferably 1.90 - 2.20.

[0070] The product stream provided by the F-T synthesis stage is a raw hydrocarbon stream comprising higher hydrocarbons such as long chain hydrocarbons and olefins. The ratio between long chain hydrocarbons and olefins in the raw product from the F-T synthesis stage depends on the type of catalyst, reaction temperature etc. used in the process.

[0071] Operating Modes

[0072] In a first operating mode (A) of said plant - the process comprises:

[0073] • feeding at least a first portion of the first syngas stream from the syngas stage to the synthesis stage and providing at least a hydrocarbon product stream and a hydrocarbon-containing off-gas stream;

[0074] • feeding at least a portion of the off-gas stream from the synthesis stage to syngas stage, as at least a portion of said third stream comprising hydrocarbons, upstream the RWGS section.

[0075] Optionally, in this operating mode (A), a second part of the first syngas stream may also be fed to the syngas stage.

[0076] In a specific operating scenario within operating mode A, syngas stage (SI) and synthesis stage (S2) may operate at higher capacity than eFuels plant capacity. For example - syngas stage (SI) and synthesis stage (S2) operate higher than respective minimum operable capacities, while eFuels plant production is close to or at minimum operable capacity, ensuring minimum consumption of expensive sustainable feeds.

[0077] 1. Such a situation may occur when renewable power supply is limited due to seasonal impact and / or intermittent supply or other reasons, necessitating either 'non-normal' operation of the plant or complete stop of operation. Often complete stop of operation may not be the most economical proposition, because such situation is temporary and start from complete stop requires overall longer unproductive time. Therefore, continuing operation of a part of plant or entire plant is preferable, though with limited power consumption. This is possible by restricting consumption of expensive sustainable feeds. Therefore, it may be economical to operate the plant with inefficient feed utilization to increase unconverted reactants and recycle them back to the process to reduce consumption of fresh sustainable feed. Thereby, it may be possible to keep on operating and producing with lowest possible power consumption during period of limited power supply. Operating mode A may therefore be implemented in response to, or in anticipation of, reduced power supply to the e-fuel plant.

[0078] In a second operating mode (B) of said plant - the process comprises:

[0079] • feeding at least a second portion of the first syngas stream from the RWGS section back to syngas stage, upstream the RWGS section (I).

[0080] Preferably, in this operating mode, no off-gas stream from synthesis stage is fed to syngas stage (SI).

[0081] Therefore, only a set of 'non-normal' operations, including but not limited to start-up and shut down, fall within boundaries of operating mode B. Moreover, in operation mode B syngas stage (SI) preferably operates at < 50%, more preferably < 30%, even more preferably < 20% of design capacity.

[0082] Primarily operating mode A covers normal operation scenarios. However, during change over between operating modes, operating mode A also covers some of the 'non-normal' operating scenarios. For example - a period of the eFuels plant start-up, when syngas stage (SI) and / or synthesis stage (S2) capacities are at or below minimum operable capacity, is covered with operation mode B. Without operating mode B, it would result in increased flaring of effluent gases. As the eFuels plant capacity increases and process conditions resemble more normal operating conditions, operating mode is changed from B to A. During this change over, operation mode A also covers 'non-normal' operating scenarios. Once change over is complete, operation continues in mode A, which also includes normal operation.

[0083] Similarly, situation may occur during planned reduction of capacities, when a part of 'non- normal' operation is covered in operating mode A.

[0084] The proposed solution will ensure recycle of at least a part of produced syngas to the inlet of RWGS section (I). During syngas recycle it may be advantageous to modify the process conditions in syngas stage (SI), particularly in RWGS section, as the inefficient conversion, relative to normal operation, of sustainable feeds is preferable during syngas recycle primarily for two reasons -

[0085] 1. To reduce energy consumption in syngas stage which fits better during reduced availability of power.

[0086] 2. To reduce consumption of sustainable feeds by inefficient conversion

[0087] In one embodiment, the RWGS section outlet temperature is kept lower than that during normal operation. It will ensure lower conversion of sustainable feeds to syngas comprising H2and CO. For example - during normal operation, RWGS unit(s) within RWGS section (I) is operated at high temperatures, such as > 800°C, preferably > 900°C, more preferably > 950°C, even more preferably > 1000°C. However, it may be advantageous to operate RWGS unit(s) within RWGS section (I) at lower than normal operating temperature, such as < 950°C, preferably < 850°C, more preferably < 800°C, when operating in 'non-normal' operating mode within operating mode A and operating mode B.

[0088] In other embodiment, syngas stage (SI) pressure is kept lower such that syngas feed to synthesis stage (S2) is supplied at lower than that during normal operation. This will ensure lower conversion of syngas feed to hydrocarbon product and increase the recycle flow. For example - during normal operation, RWGS section (I) is operated at high pressures, such as > 20 bar g, preferably > 25 bar g, more preferably > 30 bar g, even more preferably > 35 bar g. However, it may be advantageous to operate RWGS section (I) at lower than normal operating pressure, such as < 30 bar g, preferably < 25 bar g, more preferably < 20 bar g, when operating in 'non-normal' operating mode A and operating mode B. This will ensure lower syngas feed pressure to synthesis stage (S2) causing lower conversion to hydrocarbon product.

[0089] Within operating mode B, all or part of the first syngas may be recycled instead of flaring, when the synthesis stage (S2) is not ready to receive syngas feed but syngas stage (SI), specifically the RWGS section (I), requires continued operation. This situation could be 'non-normal' operations. As described above, such 'non-normal' operation includes regaining production after trip of the synthesis stage (S2), or start-up or shut down of the plant or operation of plant at reduced power availability. Recycle of all or a part of the syngas as feed, in said situations, keeps consumption of expensive renewable feeds (such as - H2 from electrolysis; CO2 from direct air capture) to its minimum and ensures lowest possible emission from such plant.

[0090] By means of the process and plant of the present invention, syngas flaring may be reduced by at least 20-40%, preferably 40% - 75%; more preferably 75 - 100%. In one particular aspect, illustrated in Figure 2A and 2B, the syngas stage additionally comprises an off-gas conversion section. The off-gas conversion section is arranged to receive at least a portion of the off-gas stream from the synthesis stage, and / or at least a second portion of the first syngas stream from the syngas stage; and at least a portion of the fourth feed comprising steam, and to output a third stream comprising hydrocarbons; a part of which is arranged to be sent to the RWGS section in the syngas stage.

[0091] Therefore, in a first operating mode (A) of the plant, the process comprises: feeding at least a portion of the off-gas stream from the synthesis stage (S2) and optionally, at least a part of fourth feed comprising steam to the off-gas conversion section, so as to output said third stream comprising hydrocarbons; and feeding at least a portion of third stream comprising hydrocarbons to the RWGS section; and wherein - in a second operating mode (B) of said plant - the process comprises: feeding at least a second portion of the first syngas stream from the RWGS section (I) and optionally, at least a part of fourth feed comprising steam to the off-gas conversion section, so as to output said third stream comprising hydrocarbons; and feeding at least a portion of the third stream to the RWGS section (I).

[0092] In one embodiment, the third stream from the off-gas conversion section to the RWGS section comprises less hydrocarbons (in mol%) in operating mode B compared to that in operating mode A.

[0093] Particular preferred aspects of the process of the invention are as follows: in the first operating mode (A) - none of the first syngas stream from the syngas stage is fed from the RWGS section back to syngas stage; in the second operating mode (B) - none of the first syngas stream from the RWGS section is fed to the synthesis stage; in the second operating mode (B), all or a part of the optional fourth feed comprising steam, is fed to the RWGS section; the flow of the fourth stream in the second operating mode (B) could be higher than in the first operating mode (A).

[0094] In an embodiment, an e-fuel plant is provided, suitable for carrying out the above process. The e-fuel plant comprises: a first feed comprising hydrogen; a second feed comprising CO2; optionally, a fourth feed comprising steam; a syngas stage comprising a reverse water gas shift (RWGS) section, said RWGS section being arranged to receive at least a portion of the first feed, at least a part of the second feed, a third stream comprising hydrocarbons, and - where present - at least a portion of the fourth feed, and to output a first syngas stream; a synthesis stage said synthesis stage being arranged to receive at least a first portion of the first syngas stream and provide at least a hydrocarbon product stream and a hydrocarbon-containing off-gas stream; said plant being arranged to provide at least a portion of the hydrocarbon-containing off-gas stream from the synthesis stage to the syngas stage as at least a portion of said third stream comprising hydrocarbons, upstream the RWGS section; said plant being further arranged to feed at least a second portion of the first syngas stream from the RWGS section to syngas stage, upstream the RWGS section.

[0095] In one aspect, the syngas stage additionally comprises an off-gas conversion section, said offgas conversion section being arranged to receive: at least a portion of the off-gas stream from the synthesis stage, and / or at least a second portion of the first syngas stream from the syngas stage; and optionally, at least a portion of the fourth feed comprising steam, and to output a third stream comprising hydrocarbons; a part of which is arranged to be sent to the RWGS section in the syngas stage.

[0096] All details of the process described above are relevant to the e-fuel plant. In particular, the synthesis stage suitably comprises a Fischer Tropsch (FT) stage.

[0097] The following reference numerals are used in the Figures:

[0098] 51 : syngas stage

[0099] 52 : synthesis stage

[0100] (I) : RWGS section

[0101] (II) : off-gas conversion section

[0102] 100 : first syngas stream from stage SI 100a: first part of first syngas stream to stage S2

[0103] 100b: second part of first syngas stream to stage SI, upstream RWGS section (I)

[0104] 100c: a part of first syngas stream to flare

[0105] 500 : hydrocarbon product 1 : first feed, comprising H2

[0106] 2 : second feed, comprising CO2

[0107] 3 : third stream, comprising hydrocarbons

[0108] 3' : off-gas stream (3') from synthesis stage (S2)

[0109] 4 : fourth feed, comprising steam 5 : fifth feed comprising oxygen (relevant if Autothermal RWGS)

[0110] 6 : sixth stream, comprising H2

[0111] EXAMPLE 1

[0112] In Table 1, various operation modes of an eFuels plant, fed with primarily first feed (1) comprising H2 and second feed (2) comprising CO2, are shown. Optional use of fourth feed (4) comprising hydrocarbons is also possible. All consumption numbers, except flaring, are reported relative to Cl, representing normal operation of the plant under operation mode A. Effluent flaring is reported relative to C2.

[0113] Table 1

[0114] As mentioned already, Cl corresponds to eFuels plant under normal operation at 100% of its capacity. In this example, a first portion (100a) of the first syngas (100) from syngas stage

[0115] (51), comprising RWGS section (I) and off-gas conversion section (II), is sent to synthesis stage (S2). No second portion (100b) syngas is recycled to off-gas conversion section (II) within syngas stage (SI). No flaring is needed, and all off-gas (3') from synthesis stage (S2) is routed to off-gas conversion section (II), comprising at least one WGS unit. In addition to WGS units, there are at least one hydrogenation unit and at least one higher hydrocarbon conversion unit upstream and downstream of WGS units, respectively.

[0116] The disadvantages of 'non-normal' mode operation according to existing prior art is shown in C2. In C2, the 'non-normal' operating condition is simulated where only syngas stage (SI) is under operation at lower capacity - 30% of design capacity, and synthesis stage (S2) is not in operation. Therefore, no first portion (100a) of first syngas (100) is sent to synthesis stage

[0117] (52), and there is no off-gas (3') available from synthesis stage (S2). All syngas effluent (100c) must be flared in such situation, resulting in about 30-40% consumption of first feed (1) and ca. 50 -60% consumption of second feed (2) relative to that in Cl. In other words, 30-40% of first feed (1) and 50-60% of second feed (2) are wasted (hourly basis). The longer the period of 'non-normal' operation is, higher the waste would be.

[0118] The solution in accordance with current invention is reported under C3, where the eFuels plant is also simulated for syngas stage (SI) with 30% of design capacity. The synthesis stage (S2) is not considered in operation. Thus, no first portion (100a) of first syngas (100) is sent to synthesis stage (S2), and there is no off-gas (3') available from synthesis stage (S2). However, a major part of the first syngas (100) is recycled as the second syngas (100b) to off-gas conversion section (II), comprising at least one WGS unit. The hydrogenation unit, upstream the WGS unit, and the high hydrocarbon conversion unit, downstream WGS unit, are bypassed.

[0119] As a result, effluent flaring is reduced to ca. 10% of that in C2. More importantly, the consumption of first and second feed is reduced significantly to <10% of that in normal operation. With many possible 'non-normal' operations, such solution would result in better utilization of expensive sustainable feedstocks and make the eFuels plant economically more feasible.

Claims

CLAIMS1. A process for operation of an e-fuel plant (X), said e-fuel plant (X) comprising : a first feed (1) comprising hydrogen; a second feed (2) comprising CO2; optionally, a fourth feed (4) comprising steam; a syngas stage (SI) comprising a reverse water gas shift (RWGS) section (I), said RWGS section (I) being arranged to receive at least a part of the first feed (1), at least a part of the second feed (2), a third stream (3) comprising hydrocarbons, and - where present - at least a part of the fourth feed (4), and to output a first syngas stream (100); a synthesis stage (S2), said synthesis stage (S2) being arranged to receive at least a first portion (100a) of the first syngas stream (100) and provide at least a hydrocarbon product stream (500) and a hydrocarbon-containing off-gas stream (3'); wherein - in a first operating mode (A) of the plant - the process comprises:• feeding at least a first portion (100a) of the first syngas stream (100) from the syngas stage (SI) to the synthesis stage (S2) and providing at least a hydrocarbon product stream (500) and a hydrocarbon-containing off-gas stream (3');• feeding at least a portion of the off-gas stream (3') from the synthesis stage (S2) to syngas stage (SI), and at least a portion of said third stream (3) comprising hydrocarbons, upstream the RWGS section (I); and wherein - in a second operating mode (B) of said plant - the process comprises:• feeding at least a second portion (100b) of the first syngas stream (100) from the RWGS section (I) to syngas stage (SI), upstream the RWGS section (I).

2. The process according to claim 1, wherein syngas stage (SI) additionally comprises an off-gas conversion section (II), said off-gas conversion section (II) being arranged to receive at least a portion of the off-gas stream (3') from the synthesis stage (S2), and / or at least a second portion (100b) of the first syngas stream (100) from the syngas stage (Si); and optionally, at least a portion of the fourth feed (4) comprising steam, and to output a third stream (3) comprising hydrocarbons; a part of which is arranged to be sent to the RWGS section (I) in the syngas stage (SI);wherein - in a first operating mode (A) of the plant (X) - the process comprises: feeding at least a portion of the off-gas stream (3') from the synthesis stage (S2) to the off-gas conversion section (II), so as to output said third stream (3) comprising hydrocarbons; and feeding at least a portion of third stream (3) comprising hydrocarbons to the RWGS section (I); and wherein - in a second operating mode (B) of said plant - the process comprises: feeding at least a second portion (100b) of the first syngas stream (100) from the RWGS section (I) to the off-gas conversion section (II), so as to output said third stream (3) comprising hydrocarbons; and feeding at least a portion of the third stream (3) to the RWGS section (I).

3. The process according to claim 2, wherein the third stream (3) from off-gas conversion section (II) to the RWGS section (I) comprises less hydrocarbons (in mol%) in operating mode B compared to that in operating mode A.

4. The process according to any one of the preceding claims, wherein - in the first operating mode (A) - none of the first syngas stream (100) from the syngas stage (SI) is fed back to syngas stage (SI).

5. The process according to any one of the preceding claims, wherein - in the second operating mode (B) - none of the first syngas stream (100) from the syngas stage (SI) is fed to the synthesis stage (S2).

6. The process according to any one of claims 2 to 6, wherein the off-gas conversion section (II) comprises one or more water-gas shift (WGS) reactors, such as an adiabatic WGS reactor, a heated WGS reactor or a cooled WGS reactor.

7. The process according to any one of the proceeding claims, wherein the RWGS section (I) comprises one or more electrically heated RWGS reactors, such as a resistance heated RWGS reactor or an induction heated RWGS reactor.

8. The process according to any one of the preceding claims, wherein the RWGS section (I) comprises one or more non-electrical RWGS reactors, such as an autothermal RWGS reactor, said process further comprising feeding a fifth feed (5) comprising oxygen to said autothermal RWGS reactor.

9. The process according to any of claims 6-9, wherein the RWGS reactors comprise catalysts that are active in both RWGS and methanation reactions, and / or catalysts that are active in only RWGS reaction.

10. The process according to any one of claims 2-10, wherein the off-gas conversion section (II) further comprises at least one hydrogenation unit, a water gas shift (WGS) unit, and at least one higher hydrocarbon conversion unit, wherein the hydrogenation unit(s), are arranged upstream of the WGS unit, and the higher hydrocarbon conversion unit(s) are arranged downstream of the WGS unit.

11. The process according to claim 11, wherein the hydrogenation unit(s) is / are partially or completely bypassed in second operating mode (B).

12. The process according to claim 11 or claim 12, wherein, the higher hydrocarbon conversion unit(s) is / are partially or completely bypassed in second operating mode (B).

13. The process according to any one of the preceding claims, wherein syngas stage (SI) additionally comprises a syngas treating section, said syngas treating section comprising one or more WGS reactors arranged in series or parallel, wherein, - in the second operating mode (B) of the plant - said process comprises: feeding at least a part of the second portion (100b) of the first syngas stream (100) from the syngas stage (SI) and at least a part of the fourth feed (4) comprising steam to the syngas treating section and outputting a treated syngas stream; and feeding at least a portion of the treated syngas stream to the RWGS section (I) in the syngas stage (SI).

14. The process according to any one of the proceeding claims, wherein the synthesis stage (S2) is a Fischer Tropsch (FT) stage.

15. The process according to any one of the preceding claims, wherein the operating mode A is implemented in response to, or in anticipation of, reduced power supply to the e- fuel plant.

16. An e-fuel plant (X), said e-fuel plant (X) comprising : a first feed (1) comprising hydrogen; a second feed (2) comprising CO2; optionally, a fourth feed (4) comprising steam; a syngas stage (SI) comprising a reverse water gas shift (RWGS) section (I), said RWGS section (I) being arranged to receive at least a portion of the first feed (1), atleast a part of the second feed (2), a third stream (3) comprising hydrocarbons, and - where present - at least a portion of the fourth feed (4), and to output a first syngas stream (100); a synthesis stage (S2), said synthesis stage (S2) being arranged to receive at least a first portion (100a) of the first syngas stream (100) and provide at least a hydrocarbon product stream (500) and a hydrocarbon-containing off-gas stream (3'); said plant (X) being arranged to provide at least a portion of the hydrocarbon- containing off-gas stream (3') from the synthesis stage (S2) to the syngas stage (SI), as at least a portion of said third stream (3) comprising hydrocarbons, upstream the RWGS section (I) said plant (X) being further arranged to feed at least a second portion (100b) of the first syngas stream (100) from the RWGS section (I) to syngas stage (SI), upstream the RWGS section (I).

17. The e-fuel plant (X) according to claim 17, wherein the syngas stage (SI) additionally comprises an off-gas conversion section (II), said off-gas conversion section (II) being arranged to receive at least a portion of the off-gas stream (3') from the synthesis stage (S2), and / or at least a second portion (100b) of the first syngas stream (100) from the syngas stage (Si); and optionally, at least a portion of the fourth feed (4) comprising steam, and to output a third stream (3) comprising hydrocarbons; a part of which is arranged to be sent to the RWGS section (I) in the syngas stage (SI).

Images