Conversion of carbon-containing feed gas stream to syngas

Abstract

The invention relates to a process for producing a syngas comprising the steps of: a) providing a carbon-containing feed gas stream, wherein the composition of the carbon-containing feed gas stream is non-constant over time, b) feeding the carbon-containing feed gas stream to a syngas generating section comprising a steam reforming reactor, c) carrying out steam methane reforming of said carbon-containing feed gas stream in the syngas generating section to form a syngas, d) out-letting a syngas from the syngas generating section and providing at least part of the syngas to a downstream section for converting said syngas into a hydrocarbon product and / or a refined syngas and / or ammonia, wherein the composition of the carbon-containing feed gas stream before feeding it to the syngas generating section is subjected to an adjustment to maintain each of an H / C (mol / mol) ratio and an O / C (mol / mol) ratio of the carbon-containing feed gas stream within a range of a selected set point plus minus 10%, and wherein said adjustment is carried out by addition of one or two adjustment gasses.

Description

[0001] Conversion of carbon-containing feed gas stream to syngas

[0002] FIELD OF THE INVENTION

[0003] Embodiments of the invention generally relate to a process and a system for producing a syngas from a carbon-containing feed gas stream, said syngas is used for the production of a hydrocarbon product, in particular a synthetic fuel such as diesel by subsequent Fischer-Tropsch synthesis.

[0004] BACKGROUND

[0005] Biogas is a renewable energy source that can be used for heating, electricity, and many other operations. Biogas can be cleaned and upgraded to natural gas standards, when it becomes bio-methane. Biogas is considered to be a renewable resource because its production-and-use cycle is continuous, and it generates no net carbon dioxide. When the organic material has grown, it is converted and used. It then regrows in a continually repeating cycle. From a carbon perspective, as much carbon dioxide is absorbed from the atmosphere in the growth of the primary bio-resource as is released, when the material is ultimately converted to energy. Biogas is a mixture of gases produced by the breakdown of organic matter in the absence of oxygen. Biogas can be produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste or food waste. Biogas is primarily methane (CH4) and carbon dioxide (CO2), typically containing 60-70% vol. methane, and may have small amounts of hydrogen sulfide (H2S), moisture, siloxanes, and possibly other components. Up to 30% or even 40% of the biogas may be carbon dioxide. Typically, this carbon dioxide is removed from the biogas and vented in order to provide a methane rich gas for further processing or to provide it to a natural gas network.

[0006] Biogas is indicated as an essential platform to realize circular industrial economy, where it allows for integrating waste streams back into industry. Such an approach will allow moving away from the "Take, Make, Dispose" society established in the 20thcentury and into the "Make, Use, Return" society, which will be needed for achieving a truly sustainable future. This thought is gaining increased focus within Europe and large biogas plants are already installed. Within Denmark alone, a large capacity is already installed and is expected to increase to a capacity of 17 PJ / year by 2020, but the overall potential could be as high as 60 PJ / year for Denmark. Today, biogas plants are typically coupled to the natural gas grid, because this is the most feasible utilization. However, the nature of the biogas with roughly 40% CO2 and 60% CH4 does not allow for its direct mixing into the natural gas network, why CO2 must be removed from the gas, and this requires a gas separation plant.

[0007] The classical approach to the production of syngas (synthesis gas) involves steam reforming of a hydrocarbon feed gas, normally natural gas, and a major associated CO2 emission. As the highly endothermic steam reforming reaction is facilitated in conventional steam methane reformers (SMR), i.e. fired reformers using large furnaces operating at temperatures in the vicinity of 1000°C, the process economy is heavily favoured by economy of scale to enable high process efficiency and integrated waste heat management. Such plants are therefore difficult to scale down economically due to the integrated design and high upfront capital investment.

[0008] The conversion of the hydrocarbon feed gas to syngas by such conventional SMR results in a syngas, which does not have a composition optimal for some downstream production processes, e.g. production of synthetic fuels (synfuels) via a Fischer-Tropsch process.

[0009] SUMMARY OF THE INVENTION

[0010] The invention relates to a process for producing a syngas comprising the steps of: a) providing a carbon-containing feed gas stream, wherein the composition of the carbon-containing feed gas stream is non-constant over time, b) feeding the carbon-containing feed gas stream to a syngas generating section comprising a steam reforming reactor, c) carrying out steam methane reforming of said carbon-containing feed gas stream in the syngas generating section to form a syngas, d) out-letting a syngas from the syngas generating section and providing at least part of the syngas to a downstream section for converting said syngas into a hydrocarbon product and / or a refined syngas and / or ammonia, wherein the composition of the carbon-containing feed gas stream before feeding it to the syngas generating section is subjected to an adjustment to maintain each of an H / C (mol / mol) ratio and an O / C (mol / mol) ratio of the carbon-containing feed gas stream within a range of a selected set point plus minus 10%, and wherein said adjustment is carried out by addition of one or two adjustment gasses selected from the group consisting of hydrogen, steam, carbon dioxide, methane and combinations thereof, wherein the adjustment gas is a high-purity gas with a level of contaminants below 20 %.

[0011] The present invention is based on the general recognition that by subjecting a carbon- containing feed gas stream, such as biogas, natural gas, a carbon dioxide-rich gas and methane, to an adjustment of its chemical composition before being fed to a syngas generating section, a number of technical advantages can be obtained.

[0012] Thus, the present invention is based on a first recognition that it is possible to use as a feed for syngas generation carbon-containing feed gas streams, such as high-purity CO2 and methane, provided the composition of the feed gas stream is subjected to an adjustment of its composition before being fed to a syngas generating section to maintain the level of the H / C ratio and the O / C ratio within selected ranges.

[0013] Furthermore, the invention addresses the technical problem that the chemical composition of some carbon-containing feed gas streams, such as biogas and natural gas, in particular biogas, changes significantly in composition over time, and such a change in composition significantly reduces both the quality of the syngas and hence the hydro- carbon product. Also, such a change in composition reduces the efficiency of the process with respect to cost efficiency and utilization of the carbon content of the feed gas stream. In particular, the changes in composition of the feed gas stream may in periods lead to production of a syngas, which does not meet the requirement of the downstream process and hence must be discarded.

[0014] Accordingly, the invention is based on the second recognition that it is possible to avoid variations of the composition of the feed to a syngas generating section provided the composition of the feed gas stream is subjected to a continuous adjustment over time of its composition before being fed to a syngas generating section to maintain the level of the H / C ratio and the O / C ratio within selected ranges. In other words, the process of the invention is dynamic over time in the sense that when the composition of the carbon-containing feed gas stream changes, the amount of the one or two adjustment gasses added also changes in order to maintain the level of the H / C ratio and the O / C ratio within selected set point ranges.

[0015] Specifically, the invention enables production of a syngas product with a very stable specific composition applicable for a desired specific synthesis process of e.g. a hydrocarbon product. This is the result of the invention enabling continuous production of syngas which is in accordance with the stochiometric requirement of the specific synthesis process and thereby maximizing the yield of product from said synthesis to give high process efficiency. In particular, discarding syngas, which does not meet the stochiometric requirement of the specific synthesis process, is avoided.

[0016] Furthermore, the present invention is based on the third recognition that when using a biogas as a carbon-containing feed gas stream, it is possible to avoid a costly and technically complex step of removal of carbon dioxide from the biogas, which up to now has been required, provided the composition of the feed gas stream is subjected to an adjustment of its composition before being fed to a syngas generating section to maintain the level of the H / C ratio and the O / C ratio within selected ranges. Moreover, the present invention is based on the fourth recognition that the overall carbon utilization efficiency of a carbon-containing feed may be further optimised, when the optimal process control for improved carbon utilization provided by the present invention is used in combination with an electrically heated reformer, which provides a non-fuel combustion type of synthesis gas producing technology with no CO2 emissions. Furthermore, when an electrically heated reformer is used, it is essential to be able to produce a syngas product with a precise and stable composition, since any syngas produced, which is not within the specifications of composition, cannot be used as a fuel for heating a steam methane reformer as is common in processes using conventional fuel fired reformers.

[0017] Additionally, the present invention is based on the fifth recognition that in order to be able to control the adjustment of the composition of the feed gas stream to achieve a feed gas with an H / C ratio and an O / C ratio within a range of a selected set point plus minus 10%, it is required to use a high-purity adjustment gas, i.e. an adjustment gas with a high content of its mail component.

[0018] In conclusion, the invention has provided a possibility of utilizing sources of carbon- containing feed gas streams for producing a syngas, which it has not been possible previously to use for this purpose, as well as a possibility of utilizing carbon-containing feed gas streams more efficiently. This in turn has provided a possibility of reducing emission and sequestration of greenhouse gasses, such as carbon dioxide and methane. By means of the invention it becomes possible to have very high carbon utilization efficiency from sustainable carbon sources which will be a requirement when looking into future scenarios of decoupling the chemical industry from fossil resources and where carbon feedstocks will be a scarcer resource requiring optimal utilization.

[0019] The invention further relates to a plant for producing a syngas comprising a carbon-containing feed gas stream, wherein the composition of the carbon- containing feed gas stream is non-constant over time, a syngas generating section comprising a steam reforming reactor for carrying out steam methane reforming of said carbon-containing feed gas stream to form a syngas, a downstream section for converting said syngas into a hydrocarbon product and / or a refined syngas and / or ammonia, means for feeding the carbon-containing feed gas stream to the syngas generating section, means for out-letting a syngas from the syngas generating section and providing at least part of the syngas to the downstream section, means for adjusting the composition of the carbon-containing feed gas stream before feeding it to the syngas generating section to maintain each of an H / C (mol / mol) ratio and an O / C (mol / mol) ratio of the carbon-containing feed gas stream within a range of a selected set point plus minus 10%, and means for carrying out said adjustment by addition of one or two adjustment gasses selected from the group consisting of hydrogen, steam, carbon dioxide, methane and combinations thereof, wherein the adjustment gas is a high-pu- rity gas with a level of contaminants below 20 %.

[0020] DETAILED DESCRIPTION OF THE INVENTION

[0021] Adjustment of composition of carbon-containing feed gas stream

[0022] The H / C and O / C ratios are calculated on the basis of the content of hydrogen, carbon and oxygen in the carbon-containing feed gas stream as measured in mol.

[0023] In a particular embodiment of the invention, each of the H / C ratio and the O / C ratio is maintained within a range of a selected set point plus minus 9%, preferably 8%, preferably 7%, preferably 6%, preferably 5%, preferably 4%, preferably 3%, preferably 2%, and most preferably 1%. The deviation of the set from the set point is calculated as a percentage in relation to an absolute value of the set point.

[0024] In a particular embodiment of the invention, the adjustment gas is a high-purity gas with a level of contaminants below 18 vol%, preferably below 16 vol%, preferably below 14 vol%, preferably below 12 vol%, preferably below 10 vol%, preferably below 8 vol%, preferably below 6 vol%, preferably below 4 vol%, preferably below 2 vol%, and most preferably below 1 vol%. The term "contaminant" means any component of the high-purity adjustment gas not being its main component.

[0025] In a particular embodiment of the invention, the carbon-containing feed gas stream is selected from the group consisting of biogas, natural gas, a carbon dioxide-rich gas, methane and a mixture thereof.

[0026] The steam methane reforming, which takes place in the steam reforming reactor of the syngas generating section, proceeds according to the following reactions:

[0027] CH4+ H2O CO + 3H2

[0028] CH4 + 2H2O CO2 + 4H2

[0029] CH4 + CO2 2CO + 2H2

[0030] In a particular embodiment of the invention, in addition to the steam methane reforming, a reverse water gas shift (RWGS) reaction takes place in the syngas generating section. The reverse water gas shift reaction proceeds according to the following reaction:

[0031] CO2+ H2O CO + H2O

[0032] In a particular embodiment of the invention, the one or two adjustment gasses is selected from the group consisting of hydrogen, steam and carbon dioxide. In a particu- lar embodiment of the invention, two adjustment gasses are used, and the two adjustment gases are added to the carbon-containing feed gas stream separately or as a mixture.

[0033] In a particular embodiment of the invention, the composition of the carbon-containing feed gas stream is non-constant over time, wherein non-constant means that the primary component of the carbon-containing feed gas stream with the highest concentration has a variation of more than plus minus 2 mole% points over a period of 1 hour. Here, the phrase "a variation of more than plus minus 2 mole% point" means that the level of the primary component of the carbon-containing feed gas stream as expressed in mole% increases or decreases more than 2 units of mole%, e.g. increases more than from 50 mole% to 52 mole%.

[0034] In a first specific embodiment of the invention, the carbon-containing feed gas stream is a biogas. In a particular embodiment of the first specific embodiment, the composition of the carbon-containing feed gas stream before feeding it to the syngas generating section is adjusted to maintain the levels of methane (CH4) and carbon dioxide (CO2) within the following ranges: 40%<CH4<75%, preferably 55%<CH4<65%, 25%<CO2<60%, preferably 35%<CH4<45%, or to maintain the CO2 / CH4 ratio within the following range:

[0035] 0<CO2 / CH4<9. In the first specific embodiment, the adjustment gasses are hydrogen and / or H2O.

[0036] In a particular embodiment of the invention, the carbon-containing feed gas stream containing 90% vol. or more biogas, the biogas containing 60-70% methane and 30- 40% carbon dioxide. In a particular embodiment, the carbon-containing feed gas stream comprises only biogas. In a second specific embodiment of the invention, the carbon-containing feed gas stream is natural gas. In a particular embodiment of the second specific embodiment the adjustment gasses are carbon dioxide and hydrogen and / or steam.

[0037] In a third specific embodiment of the present invention, the carbon-containing feed gas stream is a carbon dioxide-rich gas. The carbon dioxide-rich gas may contain 50- 100 % carbon dioxide, preferably 60-100 % carbon dioxide, more preferably 70-100 % carbon dioxide, more preferably 80-100 % carbon dioxide, more preferably 90-100 % carbon dioxide, and most preferably 95-100 % carbon dioxide. In a particular embodiment of the third specific embodiment, the adjustment gasses are steam and hydrogen and / or methane. In a particular embodiment of the third specific embodiment, the downstream section is a hydrocarbon synthesis section comprising a Fischer-Tropsch (FT) reactor for converting the syngas from step d) to a mixture of higher hydrocarbons and a carbon-containing off-gas, wherein carbon-containing off-gas from the Fischer- Tropsch reactor is subjected to pre-reforming and recycled to the carbon-containing feed gas stream or to the syngas generating section, and wherein the adjustment gasses are steam and hydrogen, or steam and methane.

[0038] In a fourth specific embodiment of the present invention, the carbon-containing feed gas stream is methane. In a particular embodiment of the fourth specific embodiment, the adjustment gasses are carbon dioxide and hydrogen and / or steam.

[0039] A particular embodiment of the process of the invention comprises the steps of operating the process in a first operation mode with a first carbon-containing feed gas stream, first set points for the H / C and O / C ratios and addition of one or two first adjustment gasses, and shifting the process to a second operation mode, wherein the process is operated with a second carbon-containing feed gas stream different from the first carbon-containing feed gas stream, second set points for the H / C and O / C ra- tios different or the same as the first set points, and addition of one or two second adjustment gasses different or the same as the one or two first adjustment gasses.

[0040] Such a process using two operation modes may e.g. be relevant in situations, where it is required to shift the process from the use of a first type of carbon-containing feed gas stream to a second type of carbon-containing feed gas stream, e.g. in the event of insufficient supply of the first type of carbon-containing feed gas stream. Likewise, such a process using two operation modes may e.g. be relevant in situations, where it is required to shift the process from the use of a first composition of the carbon-containing feed gas stream to a second composition of the carbon-containing feed gas stream, e.g. in the event of variations in the carbon-containing feed gas stream being supplied to the process from an external source. It is an advantage of the process of the present invention that it provides a possibility to keep the process in operation, even in situations, where the supply of carbon-containing feed gas stream is missing in periods or where the composition of the carbon-containing feed gas stream undergoes significant changes over time. Thus, the process of the present invention provides the advantage of avoiding or reducing downtime of the process.

[0041] In a particular embodiment of the invention, the composition of the syngas from the syngas generating section before providing at least part of the syngas to a downstream section is adjusted by addition of an addition gas. Preferably, the addition gas is carbon monoxide or hydrogen, more preferably hydrogen. In this embodiment the composition of the syngas is adjusted before being used in the downstream section in addition to the adjustment of the composition of the syngas obtained by the adjustment of the composition of the carbon-containing feed gas stream. Such an additional adjustment of the composition of the syngas might be relevant for some configurations of the syngas generating section and / or some types of carbon-containing feed gas streams. Also, such an additional adjustment of the composition of the syngas might be relevant as a transient measure in periods, where process conditions of the reforming section is changed and / or the composition of the carbon-containing feed gas stream is changed, in which case transient changes of the syngas produced in the syngas generating section may occur. By means of said additional adjustment of the composition of the syngas the control of the composition of the syngas is further enhanced to further reduce the variation of the composition of the syngas.

[0042] Downstream section

[0043] In a particular embodiment of the process of the invention, said downstream section comprises a syngas upgrading section arranged to generate a stream of purified CO2, H2, and / or CO from the syngas, thereby providing a refined syngas and optionally a carbon-containing offgas , and / or said downstream section comprises a hydrocarbon synthesis section for converting said syngas into a hydrocarbon product and a carbon-containing off-gas, and / or said downstream section comprises an ammonia synthesis section for converting said syngas into ammonia and a carbon-containing off-gas.

[0044] In a particular embodiment of the process of the invention, the selected set point for the level of the H / C ratio is in the range of 1.4-2.4, preferably 1.6-2.4, more preferably 1.8-2.4 and most preferably 1.9-2.3, and the selected set point for the level of the O / C ratio is in the range of 3.4-8.1, preferably 3.8-7.5, more preferably 4.0-7.0 and most preferably 4.2-6.6.

[0045] In a particular embodiment of the invention, the carbon-containing off-gas formed in the downstream section is recycled to the carbon-containing feed gas stream or to the syngas generating section. In a particular embodiment of the invention, the recycled carbon-containing off-gas formed in the downstream section is subjected to pre-re- forming and recycled to the carbon-containing feed gas stream or to the syngas generating section. In a particular embodiment of the invention, the carbon-containing off-gas from the downstream section is recycled to the carbon-containing feed gas stream or to the syngas generating section, and the levels of a H / C ratio and a O / C ratio are calculated based on the combined carbon-containing feed and recycled carbon-containing offgas.

[0046] The downstream section may be any downstream process layout comprising any unit and combination of units known for the downstream section in question, i.e. a downstream section for providing a refined syngas, a hydrocarbon synthesis section and an ammonia synthesis section.

[0047] Syngas upgrading section

[0048] In a particular embodiment of the invention, wherein the downstream section is a syngas upgrading section, the refined syngas is hydrogen. In a particular embodiment, the syngas upgrading section of the downstream section comprises a hydrogen separation unit and optionally a Water Gas Shift Unit upstream the hydrogen separation unit. In a particular embodiment of the invention, the hydrogen separation unit of the downstream section is selected from the group of a Pressure Swing Adsorption (PSA) unit, a membrane separation unit, an absorption separation unit, a cryogenic separation unit and combinations thereof.

[0049] The carbon-containing off-gas formed in the hydrogen separation unit of the syngas upgrading section contains unreacted methane and carbon dioxide and unreacted low- chain hydrocarbons, if present in the carbon-containing feed gas stream.

[0050] Hydrocarbon synthesis section

[0051] In a particular embodiment of invention, wherein the downstream section is a hydrocarbon synthesis section, the hydrocarbon synthesis section is selected from the group consisting of a methanol synthesis section, an oxyalcohol synthesis section, an acetic acid synthesis section, a Fischer-Tropsch (FT) section for producing a liquid hydrocarbon product, a synthetic fuel synthesis section, and combinations thereof.

[0052] In a particular embodiment of the invention, said downstream section comprises a hydrocarbon synthesis section for converting said syngas into a hydrocarbon product and a carbon-containing off-gas, wherein for production of methanol as hydrocarbon product, the selected set point for the O / C ratio is in the range of 1.4 - 2.4, and the selected set point for the H / C ratio is in the range of 4.5 - 8.1. In a particular embodiment thereof, the selected setpoint for the O / C ratio is in the range of 1.4 - 2.4, and the selected H / C ratio is in a range of plus minus 14 %, preferably 10%, more preferably 8% and most preferably 6%, of a H / C ratio calculated from a selected O / C ratio by the following Equation 3: 1.85 2.70 Equation 3

[0053] In this embodiment, the 0 / C ratio is preferably in the range of 1.6-2.4, more preferably 1.8-2.4, more preferably 2.0-2.4 and most preferably 2.1-2.3.

[0054] In a particular embodiment, a methanol module of the carbon-containing feed gas stream is in the range of from 1.9 to 2.2, preferably 1.93 to 2.1, more preferably 1.95 to 2.05, wherein the methanol module is (H2-CO2) / (CO + CO2).

[0055] In a particular embodiment of the invention, said downstream section comprises a hydrocarbon synthesis section for converting said syngas into a hydrocarbon product and a carbon-containing off-gas, wherein for production of a synthetic fuel via a Fischer- Tropsch process as hydrocarbon product, the selected set point for the O / C ratio is in the range of 1.6 - 2.4 and the selected set point for the level of the H / C ratio is in the range of 3.4 - 5.3. In a particular embodiment thereof, the selected setpoint for the 0 / C ratio is in the range of 1.6 - 2.4, and the selected H / C ratio is in a range of plus minus 18 %, preferably 14%, more preferably 10% and most preferably 8%, of a H / C ratio calculated from a selected O / C ratio by the following Equation 4: 0.3313 3.67 Equation 4

[0056] In this embodiment, the O / C ratio is preferably in the range of 1.7-2.3, more preferably 1.8-2.2 and most preferably 1.9-2.1.

[0057] In a particular embodiment, a H2 / CO ratio of the carbon-containing feed gas stream is in the range of from 1.9 to 2.1, preferably 1.93 to 2.07, more preferably 1.95 to 2.05.

[0058] The Fischer-Tropsch section comprises a Fischer-Tropsch unit for producing a primary Fischer-Tropsch product mixture containing vax, hydrocarbon condensate, a carbon- containing off-gas (FT tail gas) and reaction water. In a particular embodiment of the invention, the Fischer-Tropsch section comprises a Water Gas Shift unit upstream the Fischer-Tropsch unit. In a particular embodiment of the invention, the Fischer-Tropsch section comprises one or more upgrading units, such as hydrorefining unit(s), e.g. for hydrocracking of waxes contained in the primary Fischer-Tropsch product mixture. In a particular embodiment of the invention, the primary Fischer-Tropsch product mixture, and the cracked vaxes, if present, is subjected to fractionation to produce a final Fischer-Tropsch product, which may be in the form of diesel, naphtha, gasoline, jet fuel, kerosane, LPG (Liquid Petroleum Gas) or mixtures thereof.

[0059] The carbon-containing off-gas (FT tail gas) formed in the FT unit of the downstream section contains methane, hydrogen and carbon dioxide, carbon monoxide, nitrogen, and low-chain hydrocarbons, if present in the carbon-containing feed gas stream. In a particular embodiment of the invention, the synthetic fuel synthesis section is a methanol synthesis section for carrying out a process comprising the steps of subjecting the syngas from the syngas generating section to a cooling step to condense and remove water in the syngas to produce a dewatered syngas stream, optionally mixing the dewatered syngas stream with a first hydrogen-rich stream to produce a mixed syngas stream with an adjusted methanol module M = (H2-CO2) / (CO+CO2), feeding the mixed syngas stream to a methanol synthesis section to produce a raw methanol stream and a purge gas, feeding the raw methanol stream to a purification section to produce a purified final methanol product, feeding the purge to a hydrogen recovery section to produce a second hydrogen-rich stream and an offgas, wherein a part of the second hydrogen-rich stream is optionally used as the first hydrogen-rich stream, and optionally using the offgas as fuel in the process.

[0060] In the cooling step heat is generated, which can be used to produce steam, superheat steam, as re-boiling duty for distillation and water preheating.

[0061] Most of the water in the gas in the cooling step is condensed and separated before the dewatered syngas stream, if required, is mixed with a hydrogen-rich stream and sent to the methanol synthesis section. The dewatered syngas stream is adjusted , if required, to ensure a methanol module M above 1.8 in the mixed syngas stream.

[0062] The methanol synthesis section can be arranged to perform any methanol synthesis known in the art, so as to convert a portion of the mixed syngas stream to a raw methanol stream and a purge gas. This conversion can for example be achieved by compressing the mixed syngas stream and sending it through a boiling water reactor where a portion of the CO, CO2 and H2 is converted to methanol followed by a condensation section separating the methanol in a liquid phase. A portion of the purge gas can be recycled to a boiling water reactor. The raw methanol stream is sent to a purification section where methanol of any desired quality in the final methanol product stream can be made. The purge gas 9 sent to a hydrogen recovery section. The hydrogen recovery section converts the purge gas to a second hydrogen-rich stream and an off-gas stream. The conversion may be achieved either by using a PSA or a membrane. The second hydro- gen-rich stream is used to adjust the methanol module M, if required, of the dewatered syngas stream. The off-gas stream may be used as fuel in the process.

[0063] If the methanol module M in the dewatered syngas stream is above 2 then addition of a hydrogen-rich stream is not required. In this case the methanol synthesis section does not include a hydrogen recovery section and the purge gas be directly used as fuel in the process.

[0064] In a particular embodiment of the invention, the synthetic fuel synthesis section is a methanol-to-gasoline synthesis section. The methanol-to-gasoline synthesis section may be any conventional methanol-to-gasoline synthesis section. The methanol used as feed for the methanol-to-gasoline synthesis section may be obtained by the methanol synthesis section of the present invention.

[0065] In a particular embodiment of the invention, the synthetic fuel synthesis section is a syngas-to-gasoline synthesis section. The syngas-to-gasoline synthesis section may be any conventional syngas-to-gasoline synthesis section.

[0066] In a particular embodiment of the invention, the synthetic fuel synthesis section is an methanol-to-jet fuel synthesis section. The methanol-to-jet fuel synthesis section may be any conventional methanol-to-jet fuel synthesis section.

[0067] Ammonia synthesis section In a particular embodiment of the invention, the synthetic fuel synthesis section is an ammonia synthesis section for carrying out a process comprising the steps of subjecting the syngas from the syngas generating section to a Water Gas Shift step to produce a shifted syngas, optionally subjecting the shifted syngas to a wash with water to reduce the methanol content to obtain a washed syngas, optionally subjecting the shifted or the washed syngas to a carbon dioxide removal step to obtain a carbon diox- ide-rich stream and a carbon dioxide-depleted stream, optionally subjecting the shifted, the washed or the carbon dioxide-depleted syngas to a nitrogen wash step or a hydrogen separation step to obtain an hydrogen-rich, nitrogen-containing stream and an offgas, subjecting the hydrogen-rich, nitrogen-containing to an ammonia synthesis step to produce an ammonia product, optionally recycling the offgas to the syngas generating section and optionally recycling part of the hydrogen-rich, nitrogen-con- taining for use as fuel in the process. section

[0068] In a particular embodiment of the invention, the syngas generating section comprises one or more reformer units selected from the group consisting of, a steam methane reformer (SMR), an electrically heated steam methane reformer (e-SMR), a heat exchange reformer, a reverse water gas shift (RWGS) reformer, an electrically heated reverse water gas shift reactor (e-RWGS) and combinations thereof arranged in series and / or in parallel, preferably an electrically heated steam methane reformer (e-SMR). In a particular embodiment of the invention, the syngas generating section comprises a steam methane reformer (SMR) or an electrically heated steam methane reformer (e- SMR) containing a catalyst active for both steam methane reforming and the reverse water gas shift reaction. In a particular embodiment of the invention, the syngas generating section comprises both a steam methane reformer (SMR) or an electrically heated steam methane reformer (e-SMR), which contains a catalyst active for steam methane reforming, and a reverse water gas shift (RWGS) reformer or an electrically heated reverse water gas shift reactor (e-RWGS), which contains a catalyst active for the reverse water gas shift reaction.

[0069] When an electrically heated reformer is used, the invention has a particular advantage. Thus, when an electrically heated reformer is used it is essential to be able to produce a syngas product with a precise and stable composition, since any syngas produced, which is not within the specifications of composition, cannot be used as a fuel for heating a steam methane reformer as is common in processes using conventional fuel fired reformers.

[0070] In an embodiment of the invention, the method further comprises:

[0071] - prereforming of the carbon-containing feed gas stream together with a steam feedstock in a prereforming unit prior to said steam reforming, and / or

[0072] -purifying the carbon-containing feed gas stream in a gas purification unit prior to said steam reforming, and / or prior to said prereforming.

[0073] Hence, an optional step of pre-reforming may be provided prior to the electrically heated steam methane reforming. In the pre-reforming unit(s) all higher hydrocarbons can be converted to carbon oxides and methane, but the pre-reforming unit(s) are also advantageous for light hydrocarbons. Providing the pre-reforming unit(s), hence prereforming step(s), may have several advantages including the provision of an efficient sulphur guard resulting in a practically sulphur free feed gas entering the downstream units. The pre-reforming step(s) may be carried out at temperatures between 300 - 650°C, preferably 390-500°C, such as 390-480°C. Preferably, the pre-reforming is conducted in one or more adiabatic pre-reforming stages with inter-stage preheating, i.e. with heating in between pre-reforming stages. The steam feedstock added to the prereforming may also stem from the superheated steam is used as steam feedstock in said step of carrying out said steam methane reforming. Optionally, where a pre-re- forming step is used, the steam is only added to the pre-reforming, i.e. no steam is added to the reforming reactor, as the necessary steam has already been incorporated during the prereforming.

[0074] Also, an optional step of purifying the carbon-containing feed gas stream in a gas purification unit may be provided prior to said steam reforming, and / or prior to said prereforming. In the gas purification unit, the carbon-containing feed gas stream, impurities such as sulfur, chlorine and heavy metals are removed by use of several catalytic reactors, as is well known for the skilled person. Prior to entering the gas purification unit, a small amount of hydrogen may be added to the carbon-containing feed gas stream; the carbon-containing feed gas stream may also be compressed and preheated to the required temperature of the purification unit.

[0075] The carbon-containing feed gas stream to the reformer is provided as a purified carbon-containing feed gas stream, as a pre-reformed carbon-containing feed gas stream gas, as a carbon-containing feed gas stream with added steam. All constituents of the carbon-containing feed gas stream are pressurized, either separately or jointly, upstream the reformer. Steam is preferably pressurized separately; whilst the other constituents of the carbon-containing feed gas stream may be pressurized jointly. The pressure(s) of the constituents of the carbon-containing feed gas stream is / are chosen so that the pressure within the reformer lies between 5 to 100 bar, preferably between 20 and 50 bar.

[0076] In a particular embodiment of the invention, the syngas generating section does not comprise an autothermal reformer (ATR).

[0077] In a particular embodiment of the invention, the syngas generating section in addition to the steam reforming reactor comprises an autothermal reformer (ATR) in parallel to the steam reforming reactor, wherein a hydrocarbon feed gas stream separate from the carbon-containing feed gas stream is fed to the ATR. Preferably, the composition of the hydrocarbon feed gas stream is not subjected to any adjustment before feeding it to the syngas generating section.

[0078] In a particular embodiment of the invention, the syngas generating section in addition to the steam reforming reactor comprises an autothermal reformer (ATR) in series to and downstream the steam reforming reactor.

[0079] Electrically heated steam methane reformer and biogas as carbon-containing feed gas stream

[0080] In this section the invention for illustrative purposes is described in further detail with respect to an embodiment using an electrically heated steam methane reformer as steam methane reforming reactor and biogas as carbon-containing feed gas stream. However, part of the text is general and apply equally to other steam methane reforming reactors and other carbon-containing feed gas stream as will be apparent to a person skilled in the art.

[0081] In a conventional SMR, the outlet temperature is often 850-900°C due to mechanical limitations. In the electrical reforming reactor according to the invention, the exit gas temperature can be above 900°C, such as above 950°C, above 1000°C, and even above 1050°C. This increases the methane conversion and the higher temperature in itself also decreases the H2 / CO-ratio. Any of these factors contributes improving the economics of a Gas-to-Liquids (GTL) plant, which in the present context means a plant for converting a hydrocarbon feed gas stream, preferably biogas, into a syngas and then converting the syngas into a hydrocarbon product, particularly a synthetic fuel.

[0082] The electrical reforming reactor also avoids the need for combustion of a carbon rich gas to provide heat for the endothermic steam reforming reaction as in a convention SMR. This reduces the emissions of CO2 from the plant and also reduces other emissions associated with combustion such as NOXand particles. Furthermore, when the electricity needed for the electrical reforming reactor comes from renewable sources the overall emissions of CO2 compared to a conventional SMR and substantially reduced.

[0083] The electrical reforming reactor is also significantly more compact than the conventional steam reformer. This has the potential to reduce the overall cost of the plant and thereby also improve economics.

[0084] Use of an electrically heated reformer offers also an opportunity for an easily regulated chemical plant as the reactor operation is controlled by the feedstock flow, i.e. flow of hydrocarbon stream comprising biogas, and the applied power alone. Thereby, production can easily be adjusted to the availability of electricity. Accordingly, in an embodiment according to the invention, the production of hydrocarbon product is regulated according to availability of renewable energy.

[0085] Use of an electrically heated reformer enables producing syngas and converting the syngas to hydrocarbon products in periods, where sustainable electricity such as electricity from wind power is available in excess, while the process or plant can be down- regulated in periods where it is not. For instance, this enables installation of a larger fraction of sustainable electricity in the Danish grid. Such processes or plants for production of hydrocarbons can be installed either directly on a biogas site, or the biogas can be collected and potentially upgraded for conversion at a centrally placed site. The plants may also be coupled to the district heating system for increased process and / or thermal efficiency.

[0086] Use of an electrically heated reformer in the process of the invention solves a longstanding need of using biogas as the carbon source in sustainable society models. Biogas is a completely different hydrocarbon feed than natural gas, the latter being the typical hydrocarbon feed used for syngas production and subsequently conversion into hydrocarbon products. Further, the central element of biogas production is the anaerobic digestion of biomass such as sludge from wastewater treatment, by micro-organisms to turn it into biogas. Today, the biogas industry is heavily dependent on subsidies because biogas has difficulties competing on price when used for electricity of biomethane production, both cases having higher production costs than relative sales prices of the fossil based equivalents. In this context, it must be realized that a biogas plant never is a standalone unit and always will be combined with a downstream unit to convert the biogas into an end-product, the downstream unit in its simplest form normally being a gas motor. When the target product is biomethane, the added gas cleaning step comes with an added production cost of 15-20% relative to the energy output, due to cost for energy use in the separation unit and plant depreciation. By the present invention, the biogas can instead be converted into syngas and then a hydrocarbon product having a significantly higher commercial value than biomethane.

[0087] The traditional hydrocarbon production involves steam reforming of natural gas in an autothermal reformer, followed by a FT synthesis unit. This provides for a major associated CO2 emission. Due to the high content of CO2 in biogas, i.e. 30-40% vol., at least part of the CO2 may require removal, viz. from the hydrocarbon feed gas stream, in a gas separation unit prior to feeding the remaining feed gas stream, together with steam, into the autothermal reformer. When using an electrically heated reformer in the present invention, instead of building a separation plant to remove / upgrade the CO2 of the biogas, the inherent mixture of CO2 and CH4 in the biogas makes it a good feedstock for hydrocarbon production by eSMR ("eSMR-GTL (Gas-To-Liquid)"), whereby essentially all carbon atoms can be converted into hydrocarbon products.

[0088] It may in some instances still be necessary to remove some carbon dioxide. Accordingly, in an embodiment, a separation unit is provided for removing a part of the CO2 in the biogas of the hydrocarbon feed gas stream. If a prereforming unit is present, as explained farther below, the removal of CO2 preferably takes place upstream the prereforming unit. If a purification unit is present, as also explained farther below, the removal of CO2 preferably takes place upstream the purification unit. The separation unit is e.g. a membrane unit.

[0089] In an embodiment according to the invention, the electrical power supplied is generated at least partly by means of renewable energy sources. The method and plant of the invention uses renewable electricity to increase the energy value of hydrocarbon feed comprising biogas into hydrocarbon products. The electrically heated steam methane reformer (eSMR) is a very compact steam reforming reactor, resulting in a lower capital investment than classical (conventional) steam reforming equipment. The hydrocarbons in the hydrocarbon feed gas stream comprising biogas are mainly from methane; however, the hydrocarbon feed gas stream may also comprise small amounts of higher hydrocarbons. Because heating is facilitated by electricity, it will be an improvement at least over instances where existing or conventional fired reformers are used together with autothermal reforming, by saving the direct CO2 emissions.

[0090] The use of autothermal reforming brings some advantages, particularly when the tail gas produced is recycled to the front-end, i.e. to the reforming section including the reforming reactor and in this case also an autothermal reforming unit. Accordingly, in an embodiment according to the invention, the process further comprises autothermal reforming in an autothermal reforming unit (ATR) after conducting said steam methane reforming for producing said syngas.

[0091] In one embodiment, said reformer i.e. eSMR produces an exit gas, said exit gas has a temperature of 500°C or higher, such as above 550°C, above 600°C, or about or above 650°C. The exit gas from the eSMR may then directed to the ATR for producing said syngas. Compared to the traditional design using a fired heater for conducting preheating, the new approach according to the present invention may save oxygen. The normal approach in the art to reduce the oxygen consumption in an ATR plant is to include a heat exchange reformer either in-series or in parallel to the ATR. However, the use of heat exchange reforming involves the risk of metal dusting and high alloy and expensive materials may be needed. The risk of metal dusting is avoided when using an electrical reformer.

[0092] Furthermore, the reduction of oxygen consumption in the ATR is obtained without compromising the quality of the syngas in terms of the H2 / CO molar ratio, i.e. H2 / CO molar ratio of 1.8-2.2, preferably 1.9 - 2.1, in the syngas is maintained.

[0093] In an embodiment according to the invention, the electrical power supplied is generated at least partly by means of renewable energy sources. Suitable renewable sources are for instance wind i.e. wind power from windmills and / or solar energy from e.g. solar panels, and water e.g. hydropower. The reformer according to the invention, i.e. the electrically heated steam methane reformer (eSMR), is a very compact steam reforming reactor, resulting in a lower capital investment than classical (conventional) steam reforming equipment.

[0094] In an embodiment according to the invention, the process is conducted without autothermal reforming of the syngas, i.e. syngas from the reforming reactor.

[0095] In an embodiment according to the invention, a hydrogen rich stream is added to the syngas to further balance the module of said syngas to be in said range of 1.9 to 2.2, preferably 1.9 - 2.1, said hydrogen rich stream preferably being generated from using a water feedstock in an electrolysis unit. This embodiment is particularly suitably where there is no autothermal reforming of the syngas from the reforming reactor. In a particular embodiment, the electrolysis unit is a solid oxide electrolysis cell unit and said water feedstock is in the form of steam produced from other processes of the method. In an embodiment according to the invention, a combination of steam superheating and steam generation is integrated in waste heat recovery of said syngas from the reforming reactor and / or the ATR, and wherein the superheated steam is used as steam feedstock in said step of carrying out said steam methane reforming. Waste heat recovery will be from the ATR, if this is included downstream the eSMR. The combination of steam superheating and steam generation may also be used to generate power.

[0096] Part or all of this power may be used in the eSMR.

[0097] In an embodiment according to the invention, the pressure of the gas inside said reformer is between 20 and 100 bar, preferably between 40 and 90 bar, and the temperature of the exit gas from said reformer is between 850 and 1150°C, preferably between 900 and 1150°C. These exit gas temperatures are preferably used in an embodiment without the use of autothermal reforming. Where an ATR is used, as described above, the exit gas has a temperature of 500°C or higher, such as above 550°C, above 600°C, or about or above 650°C, preferably up to 700°C. The exit gas from the eSMR is then directed to the ATR for producing said syngas.

[0098] In an embodiment according to the invention, the space velocity evaluated as flow of gas relative to the geometric surface area of the structured catalyst is between 0.6 and 60 Nm3 / m2 / h and / or the flow of gas relative to the occupied volume of the structured catalyst is between 700 Nm3 / m3 / h and 70000 Nm3 / m3 / h. Preferably, the flow of gas relative to the occupied volume of the structured catalyst is between 7000 Nm3 / m3 / h and 10000 Nm3 / m3 / h.

[0099] In an embodiment according to the invention, the plot area of the reformer is between 0.4 m2and 4 m2. Preferably, the plot area is between 0.5 and 1 m2. Here the term "plot area" is meant to be equivalent to "ground area", viz. the area of land that the reformer will take up when installed. In an embodiment according to the invention, the process further comprises providing a plurality of reforming reactors arranged in parallel to each other.

[0100] As the plot area is reduced, it is now also possible to significantly reduce the capital expenses (CAPEX) of the plant, while at the same time being able to reduce CO2 emissions. In addition, multiple eSMRs i.e. a plurality of eSMRs is possible to arrange in a combined plot area, while still occupying a significantly smaller area than that of a single conventional SMR.

[0101] The invention may also enable increasing the carbon utilization, so that between 50% and 100%, preferably more than 60% i.e. between above 70 and 100%, such as between 70% and 90%, of the carbon in the carbon-containing feed gas stream is converted into synthetic fuel. This means than between 50% and 100% of the carbon atoms in the carbon-containing feed gas stream, e.g. natural gas, can be converted into carbon bounded in hydrocarbon product, e.g. diesel, molecules.

[0102] Hence, as mentioned above, by the invention it is now possible to build more compact plants for production of syngas and then hydrocarbon products with a higher carbon utilization. It has been namely found that an excellent synergy exists with biogas as the main or sole hydrocarbon feedstock that allows for practically full conversion of all carbon in the biogas to synthetic fuel, i.e. diesel. This can serve the following purposes: an energy vector which can be used for balancing the electricity grid a green transportation fuel

[0103] In an embodiment according to the invention, the biogas of the carbon-containing feed gas stream amounts to 500 Nm3 / h to 8000 Nm3 / h.

[0104] Electrically heated steam methane reformer and biogas as carbon-containing feed gas stream and Fischer-Tropsch section as downstream section In an embodiment according to the invention, the method comprises recycling at least part of the FT tail gas from the Fischer-Tropsch section to upstream said reformer i.e. electrically heated SMR (eSMR) and / or upstream said ATR, if present. This enables further flexibility in the adjustment of the module of said syngas so it is maintained at the desired value - this value typically being in the range 1.8 - 2.2, preferably 1.9 - 2.1.

[0105] By "tail gas" or "FT tail gas" is meant off-gas from a Fischer-Tropsch synthesis unit, the tail gas comprising: 5-35% vol. CO, 5-35% vol. H2, 5-35% vol. CO2, more than 2% vol. CH4. The tail gas may also comprise higher hydrocarbons such as ethane and propane and including olefins, as well as argon and nitrogen .

[0106] By the term "at least part of said tail gas" is meant that all the tail gas or part of it is recycled upstream the reformer or upstream the ATR, or a portion of the tail gas may be recycled to the reforming reactor and another portion to the ATR.

[0107] It would also be understood that the term "upstream said reformer", e.g. "upstream the ATR" also includes adding the stream directly to the reformer.

[0108] When using an electrically heated reformer, the fired heater is partly or completely replaced by an electrical steam reformer, i.e. the eSMR. The eSMR does not need fuel and will thereby not emit CO2 or other environmentally undesirable components such as CO, methane, particles, and NOX. If the power for the electrical reformer is produced in part or mainly / exclusively from renewable sources such as wind and / or solar sources, this will also reduce the overall CO2-emissions.

[0109] This means that the invention enables a larger part of the produced FT tail gas can be recycled to the reforming section. Less FT tail gas is needed to cover the fuel requirements as these are smaller. Recycle of the larger amount of tail gas to the reforming section would in principle lead to an undesirable reduction of the Fh / CO-ratio in the syngas. However, this can be countered by adjusting the power supplied to the electrically heated reformer. This will typically mean that the duty of the electrical reforming reactor will be higher in comparison with the fired heater in a stand-alone ATR reference case. The increase in duty will at the same time mean that the oxygen consumption in the ATR is reduced compared to the reference case, thereby also reducing capital expenses in connection with the Air Separation Unit (ASU).

[0110] In another particular embodiment according to the process without autothermal reforming of the syngas, the method further comprises: providing a reforming unit, preferably an ATR, for separate reforming of the FT tail gas.

[0111] Structure of electrically heated reformer

[0112] In a particular embodiment, the electrically heated reformer comprisesa pressure shell housing a structured catalyst arranged to catalyze steam reforming of a carbon-containing feed gas stream comprising biogas, said structured catalyst comprising a macroscopic structure of an electrically conductive material, said macroscopic structure supporting a ceramic coating, where said ceramic coating supports a catalytically active material; wherein the reforming reactor moreover comprises an electrical power supply placed outside said pressure shell and electrical conductors connecting said electrical power supply to said structured catalyst, allowing an electrical current to run through said macroscopic structure material to thereby heat at least part of the structured catalyst to a temperature of at least 500°C.

[0113] The structured catalyst of the reformer is configured for steam reforming. This reaction takes place according to the following reactions:

[0114] CH4+ H2O CO + 3H2

[0115] CH4 + 2H2O CO2 + 4H2

[0116] CH4 + CO2 2CO + 2H2 The structured catalyst is composed a metallic structure, a ceramic phase, and an active phase. The metallic structure may be FeCrAlloy, AINiCo, or similar alloys. The ceramic phase may comprise AI2O3, MgA Ch, CaA Os, ZrC , or a combination thereof. The catalytically active material may comprise Ni, Ru, Rh, Ir, or a combination thereof.

[0117] In an embodiment according to the invention, catalyst pellets are loaded on top of, around, inside, or below the structured catalyst of the reformer (reforming reactor). The catalyst material for the reaction may comprise Ni / AbOs, Ni / MgAbOs, Ni / CaAbCh, Ru / MgA C , or Rh / MgAbC . The catalytically active material may comprise Ni, Ru, Rh, Ir, or a combination thereof. This can improve the overall gas conversion inside the reforming reactor.

[0118] In an embodiment, the macroscopic structure(s) has / have a plurality of parallel channels, a plurality of non-parallel channels and / or a plurality of labyrinthic channels. The channels have walls defining the channels. Several different forms and shapes of the macroscopic structure can be used as long as the surface area of the structured catalyst exposed to the gas is as large as possible. In a preferred embodiment, the macroscopic structure has parallel channels, since such parallel channels render a structured catalyst with a very small pressure drop. In a preferred embodiment, parallel longitudinal channels are skewed in the longitudinal direction of the macroscopic structure. In this way, molecules of the gas flowing through the macroscopic structure will mostly tend to hit a wall inside the channels instead of just flowing straight through a channel without necessarily getting into contact with a wall. The dimension of the channels should be appropriate in order to provide a macroscopic structure with a sufficient resistivity. For example, the channels could be quadratic (as seen in cross section perpendicular to the channels) and have a side length of the squares of between 1 and 3 mm; however, channels having a maximum extent in the cross section of up to about 4 cm are conceivable. Moreover, the thickness of the walls should be small enough to provide a relatively large electrical resistance and large enough to provide sufficient mechanical strength. The walls may e.g. have a thickness of between 0.2 and 2 mm, such as about 0.5 mm, and the ceramic coating supported by the walls has a thickness of between 10 pm and 500 pm, such as between 50 pm and 200 pm, such as 100 pm. In another embodiment, the macroscopic structure of the structured catalyst is cross-corrugated. In general, when the macroscopic structure has parallel channels, the pressure drop from the inlet to the outlet of the reforming reactor system may be reduced considerably compared to a reactor where the catalyst material is in the form of pellets such as a standard SMR.

[0119] In an embodiment, the macroscopic structure(s) is / are extruded and sintered structures. Alternatively, the macroscopic structure(s) is / are 3D printed structure(s). A 3D printed structure can be provided with or without subsequent sintering. Extruding or 3D printing a macroscopic structure, and optional subsequent sintering thereof results in a uniformly and coherently shaped macroscopic structure, which can afterwards be coated with the ceramic coating.

[0120] Preferably, the macroscopic structure has been manufactured by 3D printing or extrusion of a mixture of powdered metallic particles and a binder to an extruded structure and subsequent sintering of the extruded structure, thereby providing a material with a high geometric surface area per volume. Preferably, the 3D printed extruded structure is sintered in a reducing atmosphere to provide the macroscopic structure. Alternatively, the macroscopic structure is 3D printed a metal additive manufacturing melting process, viz. a 3D printing processes, which do not require subsequent sintering, such as powder bed fusion or direct energy deposition processes. Examples of such powder bed fusion or direct energy deposition processes are laser beam, electron beam or plasma 3D printing processes. As another alternative, the macroscopic structure may have been manufactured as a 3D metal structure by means of a binder-based metal additive manufacturing process, and subsequent sintered in a non-oxidizing atmosphere at a first temperature Ti, where Ti > 1000°C, in order to provide the macroscopic structure. A ceramic coating, which may contain the catalytically active material, is provided onto the macroscopic structure before a second sintering in an oxidizing atmosphere, in order to form chemical bonds between the ceramic coating and the macroscopic structure. Alternatively, the catalytically active material may be impregnated onto the ceramic coating after the second sintering. When chemical bonds are formed between the ceramic coating and the macroscopic structure, an especially high heat conductivity between the electrically heated macroscopic structure and the catalytically active material supported by the ceramic coating is possible, offering close and nearly direct contact between the heat source and the catalytically active material of the structured catalyst. Due to close proximity between the heat source and the catalytically active material, the heat transfer is effective, so that the structured catalyst can be very efficiently heated. A compact reforming reactor system in terms of gas processing per reforming reactor system volume is thus possible, and therefore the reforming reactor system housing the structured catalyst may be compact. The reforming reactor system of the invention does not need a furnace and this reduces the overall reactor size considerably. Moreover, it is an advantage that the amount of syngas produced in a single pressure shell is increased considerably compared to known tubular steam reformers. In a standard tubular steam reformer, the amount of syngas produced in a single tube of the tubular steam reformer is up to 500 Nm3 / h. In comparison, the reforming reactor of the invention is arranged to produce up to or more than 2000 Nm3 / h, e.g. even up to or more than 10000 Nm3 / h, within a single pressure shell. This can be done without the presence of O2 in the feed gas and with less than 10% methane in the syngas produced. When a single pressure shell houses catalyst for producing up to 10000 Nm3 / h syngas, it is no longer necessary to provide a plurality of pressure shells or means for distributing feed gas to a plurality of such separate pressure shells.

[0121] As used herein, the terms "3D print" and "3D printing" is meant to denote a metal additive manufacturing process. Such metal additive manufacturing processes cover 3D printing processes in which material is joined to a structure under computer control to create a three-dimensional object, where the structure is to be solidified, e.g. by sintering, to provide the macroscopic structure. Moreover, such metal additive manufacturing processes cover 3D printing processes, which do not require subsequent sintering, such as powder bed fusion or direct energy deposition processes. Examples of such powder bed fusion or direct energy deposition processes are laser beam, electron beam or plasma 3D printing processes.

[0122] Preferably, the catalytically active material is particles having a size from 5 nm to 250 nm. The ceramic coating may for example be an oxide comprising Al, Zr, Mg, Ce and / or Ca. Exemplary coatings are calcium aluminate or a magnesium aluminum spinel. Such a ceramic coating may comprise further elements, such as La, Y, Ti, K or combinations thereof. Preferably, the conductors are made of different materials than the macroscopic structure. The conductors may for example be of iron, nickel, aluminum, copper, silver or an alloy thereof. The ceramic coating is an electrically insulating material and will typically have a thickness in the range of around 100 pm, e.g. about 10-500 pm.

[0123] The macroscopic structure is advantageously a coherent or consistently intra-con- nected material in order to achieve electrical conductivity throughout the macroscopic structure, and thereby achieve thermal conductivity throughout the structured catalyst and in particular providing heating of the a catalytically active material supported by the macroscopic structure. By using the coherent or consistently intra-connected material, it is possible to ensure uniform distribution of current within the macroscopic structure and thus uniform distribution of heat within the structured catalyst. Throughout this text, the term "coherent" is meant to be synonymous to cohesive and thus refer to a material that is consistently intra-connected or consistently coupled. The effect of the structured catalyst being a coherent or consistently intra-connected material is that a control over the connectivity within the material of the structured catalyst and thus the conductivity of the macroscopic structure is obtained. It is to be noted that even if further modifications of the macroscopic structure are carried out, such as provision of slits within parts of the macroscopic structure or the implementation of insulating material within the macroscopic structure, the macroscopic structure is still denoted a coherent or consistently intra-connected material.

[0124] In an embodiment, the structured catalyst has electrically insulating parts arranged to increase the current path between the conductors to a length larger than the largest dimension of the structured catalyst. The provision of a current path between the conductors larger than the largest dimension of the structured catalyst may be by provision of electrically insulating parts positioned between the conductors and preventing the current running through some part of the structured catalyst. Such electrically insulating parts are arranged to increase the current path and thus increase the resistance through the structured catalyst. In an embodiment, the at least one electrically insulating part has a length arranged to ensure that the minimum current path between the conductors is larger than the largest dimension of the macroscopic structure.

[0125] Non-limiting examples of such insulating parts are cuts, slits, or holes in the structure. Optionally, a solid insulating material such as ceramics in cuts or slits in the structure can be used. In a case where the solid insulating material is a porous ceramic material, the catalytically active material may advantageously be incorporated in the pores, by e.g. impregnation. A solid insulating material within a cut or slit assists in keeping the parts of the structured catalyst on the sides of the cut or slit from each other. As used herein, the term "largest dimension of the structured catalyst" is meant to denote the largest inner dimension of the geometrical form taken up by the structured catalyst. If the structured catalyst is box-formed, the largest dimension would be the diagonal from one corner to the farthest corner, also denoted the space diagonal.

[0126] It should be noted that even though the current through the structured catalyst may be arranged to twist or wind its way through the structured catalyst due to the electrically insulating parts arranged to increase the current path, the gas passing through the reforming reactor system is inlet at one end of the reforming reactor system, passes through the structured catalyst once before being outlet from the reforming reactor system. Inert material is advantageously present in relevant gaps between the structured catalyst and the rest of the reforming reactor system to ensure that the gas within the reforming reactor system passes through the structured catalyst and the catalytically active material supported thereby.

[0127] In an embodiment according to the invention, the length of the gas passage through the structured catalyst is less than the length of the passage of current from one conductor through the structured catalyst and to the next conductor. The ratio of the length of the gas passage to the length of the current passage may be less than 0.6, or 0.3, 0.1, or even down to 0.002.

[0128] In an embodiment, the structured catalyst has electrically insulating parts arranged to make the current path through the structured catalyst a zigzag path. Here, the terms "zigzag path" and "zigzag route" is meant to denote a path that has corners at variable angles tracing a path from one conductor to another. A zigzag path is for example a path going upwards, turning, and subsequently going downwards. A zigzag path may have many turns, going upwards and subsequently downwards many times through the structured catalyst, even though one turn is enough to make the path a zigzag path.

[0129] In an embodiment according to the invention, the reforming reactor comprises at least two conductors electrically connected to said structured catalyst and to an electrical power supply placed outside said pressure shell, wherein said electrical power supply is dimensioned to heat at least part of said structured catalyst to a temperature of at least 500°C by passing an electrical current through said macroscopic structure, wherein said at least two conductors are connected to the structured catalyst at a position on the structured catalyst closer to said first end of said structured catalyst than to said second end of said structured catalyst, and wherein the structured catalyst is constructed to direct an electrical current to run from one conductor substantially to the second end of the structured catalyst and return to a second of said at least two conductors. Thereby it is possible to better protect the connections between the conductor and catalyst, as well as better control of the temperature of the syngas.

[0130] SPECIFIC EMBODIMENTS OF THE INVENTION AND COMBINATIONS THEREOF

[0131] 1. A process for producing a syngas comprising the steps of: a) providing a carbon-containing feed gas stream, wherein the composition of the carbon-containing feed gas stream is non-constant over time, b) feeding the carbon-containing feed gas stream to a syngas generating section comprising a steam reforming reactor, c) carrying out steam methane reforming of said carbon-containing feed gas stream in the syngas generating section to form a syngas, d) out-letting a syngas from the syngas generating section and providing at least part of the syngas to a downstream section for converting said syngas into a hydrocarbon product and / or a refined syngas and / or ammonia, wherein the composition of the carbon-containing feed gas stream before feeding it to the syngas generating section is subjected to an adjustment to maintain each of an H / C (mol / mol) ratio and an O / C (mol / mol) ratio of the carbon-containing feed gas stream within a range of a selected set point plus minus 10%, and wherein said adjustment is carried out by addition of one or two adjustment gasses selected from the group consisting of hydrogen, steam, carbon dioxide, methane and combinations thereof, wherein the adjustment gas is a high-purity gas with a level of contaminants below 20 %.

[0132] 2. A process according to embodiment 1, wherein each of the H / C ratio and the O / C ratio is maintained within a range of a selected set point plus minus 9%, preferably 8%, preferably 7%, preferably 6%, preferably 5%, preferably 4%, preferably 3%, preferably 2%, and most preferably 1%. 3. A process according to any preceding embodiment, wherein the adjustment gas is a high-purity gas with a level of contaminants below 18 %, preferably below 16%, preferably below 14%, preferably below 12%, preferably below 10%, preferably below 8%, preferably below 6%, preferably below 4%, preferably below 2%, and most preferably below 1%.

[0133] 4. A process according to any preceding embodiment, wherein the carbon-containing feed gas stream is selected from the group consisting of biogas, natural gas, a carbon dioxide-rich gas, methane and a mixture thereof.

[0134] 5. A process according to any preceding embodiment, wherein the one or two adjustment gasses is selected from the group consisting of hydrogen, steam and carbon dioxide, wherein the one or two adjustment gasses is not carbon dioxide, when the carbon-containing feed gas stream is a carbon dioxide-rich gas.

[0135] 6. A process according to any preceding embodiment, wherein two adjustment gasses are used, and wherein the two adjustment gases are added to the carbon-containing feed gas stream separately or as a mixture.

[0136] 7. A process according to any preceding embodiment, wherein non-constant means that the primary component of the carbon-containing feed gas stream with the highest concentration has a variation of more than ±2 mole% points over a period of 1 hour.

[0137] 8. A process according to any preceding embodiment comprising the steps of operating the process in a first operation mode with a first carbon-containing feed gas stream, first set points for the H / C and O / C ratios and addition of one or two first adjustment gasses, and shifting the process to a second operation mode, wherein the process is operated with a second carbon-containing feed gas stream different from the first carbon-containing feed gas stream, second set points for the H / C and O / C ratios different or the same as the first set points, and addition of one or two second adjustment gasses different or the same as the one or two first adjustment gasses.

[0138] 9. A process according to any preceding embodiment, wherein said downstream section comprises a syngas upgrading section arranged to generate a stream of puried CO2, H2, and / or CO from the syngas, thereby providing a refined syngas and optionally a carbon-containing offgas , and / or wherein said downstream section comprises a hydrocarbon synthesis section for converting said syngas into a hydrocarbon product and a carbon-containing off-gas, and / or wherein said downstream section comprises an ammonia synthesis section for converting said syngas into ammonia and a carbon-containing off-gas.

[0139] 10. A process according to embodiment 9, wherein the downstream section is a hydrocarbon synthesis section, and wherein the hydrocarbon synthesis section is selected from the group consisting of a methanol synthesis section, an oxyalcohol synthesis section, an acetic acid synthesis section, a Fischer-Tropsch (FT) section for producing a liquid hydrocarbon product, a synthetic fuel synthesis section, and combinations thereof.

[0140] 11. A process according to embodiment 9 or 10, wherein the carbon-containing off-gas from the downstream sections is recycled to the carbon-containing feed gas stream or to the syngas generating section, and wherein the levels of a H / C ratio and a O / C ratio are calculated based on the combined carbon-containing feed and recycled carbon- containing off-gas.

[0141] 12. A process according to any of embodiments 9-11, wherein said downstream section comprises a hydrocarbon synthesis section for converting said syngas into a hydrocarbon product and a carbon-containing off-gas, wherein for production of methanol as hydrocarbon product, the selected set point for the O / C ratio is in the range of 1.4 - 2.4, and the selected set point for the H / C ratio is in the range of 4.5 - 8.1. In a particular embodiment thereof, the selected setpoint for the O / C ratio is in the range of 1.4 - 2.4, and the selected H / C ratio is in a range of plus minus 14 %, preferably 10%, more preferably 8% and most preferably 6%, of a H / C ratio calculated from a selected O / C ratio by the following Equation 3: . . . 1.85 2.70 Equation s.

[0142] 13. A process according to embodiment 12, wherein the O / C ratio is in the range of

[0143] 1.6-2.4, more preferably 1.8-2.4, more preferably 2.0-2.4 and most preferably 2.1-2.3.

[0144] 14. A process according to embodiment 12 or 13, wherein a methanol module of the carbon-containing feed gas stream is in the range of from 1.9 to 2.2, preferably 1.93 to 2.1, more preferably 1.95 to 2.05, wherein the methanol module is (H2-CO2) / (CO + CO2).

[0145] 15. A process according to any of embodiments 9-11, wherein said downstream section comprises a hydrocarbon synthesis section for converting said syngas into a hydrocarbon product and a carbon-containing off-gas, wherein for production of a synthetic fuel via a Fischer-Tropsch process as hydrocarbon product, the selected set point for the O / C ratio is in the range of 1.6 - 2.4 and the selected set point for the level of the H / C ratio is in the range of 3.4 - 5.3. In a particular embodiment thereof, the selected setpoint for the O / C ratio is in the range of 1.6 - 2.4, and the selected H / C ratio is in a range of plus minus 18 %, preferably 14%, more preferably 10% and most preferably 8%, of a H / C ratio calculated from a selected O / C ratio by the following Equation 4:

[0146] H O _ . .

[0147] — = 0.3313 * - + 3.67 Equation 4. 16. A process according to embodiment 15, wherein the O / C ratio is preferably in the range of 1.7-2.3, more preferably 1.8-2.2 and most preferably 1.9-2.1.

[0148] 17. A process according to embodiment 15 or 16, wherein a H2 / CO ratio of the carbon- containing feed gas stream is in the range of from 1.9 to 2.1, preferably 1.93 to 2.07, more preferably 1.95 to 2.05.

[0149] 18. A process according to any preceding embodiment, wherein the syngas generating section comprises one or more reformer units selected from the group consisting of, a steam methane reformer (SMR), an electrically heated steam methane reformer (e- SMR), a heat exchange reformer, a reverse water gas shift (RWGS) reformer, an electrically heated reverse water gas shift reactor (e-RWGS) and combinations thereof arranged in series and / or in parallel, preferably an electrically heated steam methane reformer (e-SMR).

[0150] 19. A process according to any preceding claim, wherein the syngas generating section does not comprise an ATR.

[0151] 20. A process according to any preceding embodiment, wherein the carbon-containing feed is a biogas.

[0152] 21. A process according to embodiment 20, wherein the composition of the carbon- containing feed gas stream before feeding it to the syngas generating section is adjusted to maintain the levels of methane (CH4) and carbon dioxide (CO2) within the following ranges:

[0153] 40%<CH4<75%

[0154] 25%<CO2<60%, or to maintain the CH4 / CO2 ratio within the following range: 0<CO2 / CH4<9. 22. A process according to any of embodiments 20-21, wherein the adjustment gasses are hydrogen and / or steam.

[0155] 23. A process according to any of embodiments 1-19, wherein the carbon-containing feed is natural gas.

[0156] 24. A process according to embodiment 23, wherein the adjustment gasses are carbon dioxide and hydrogen and / or steam.

[0157] 25. A process according to any of embodiments 1-19, wherein the carbon-containing feed is a carbon dioxide-rich gas.

[0158] 26. A process according to embodiment 25, wherein the adjustment gasses are steam and hydrogen and / or methane.

[0159] 27. A process according to any of embodiments 25-26, wherein the downstream section is a hydrocarbon synthesis section comprising a Fischer-Tropsch reactor for converting the syngas from step d) to a mixture of higher hydrocarbons and a carbon-containing off-gas, wherein carbon-containing off-gas from the Fischer-Tropsch reactor is subjected to pre-reforming and recycled to the carbon-containing feed gas stream or to the syngas generating section, and wherein the adjustment gasses are steam and hydrogen, or steam and methane.

[0160] 28. A process according to any of embodiments 1-19, wherein the carbon-containing feed is methane.

[0161] 29. A process according to embodiment 28, wherein the adjustment gasses are carbon dioxide and hydrogen and / or steam. 30. A process according to any preceding embodiment, wherein the composition of the syngas from the syngas generating section before providing at least part of the syngas to a downstream section is adjusted by addition of an addition gas.

[0162] 31. A process according to embodiment 30, wherein the addition gas is carbon monoxide or hydrogen, preferably hydrogen.

[0163] 32. A plant for producing a syngas comprising a carbon-containing feed gas stream, wherein the composition of the carbon- containing feed gas stream is non-constant over time, a syngas generating section comprising a steam reforming reactor for carrying out steam methane reforming of said carbon-containing feed gas stream to form a syngas, a downstream section for converting said syngas into a hydrocarbon product and / or a refined syngas and / or ammonia, means for feeding the carbon-containing feed gas stream to the syngas generating section, means for out-letting a syngas from the syngas generating section and providing at least part of the syngas to the downstream section, means for adjusting the composition of the carbon-containing feed gas stream before feeding it to the syngas generating section to maintain each of an H / C (mol / mol) ratio and an O / C (mol / mol) ratio of the carbon-containing feed gas stream within a range of a selected set point plus minus 10%, and means for carrying out said adjustment by addition of one or two adjustment gasses selected from the group consisting of hydrogen, steam, carbon dioxide, methane and combinations thereof, wherein the adjustment gas is a high-pu- rity gas with a level of contaminants below 20 %.

[0164] EXAMPLES Thermodynamics of steam methane reforming

[0165] The steam methane reforming process is governed by the thermodynamically independent steam methane reforming (SMR) (Reaction 1) and water gas shift (WGS) (Reaction 2). The overall reaction scheme is highly endothermic and dependent on temperature and pressure.

[0166] Reaction 1

[0167] Reaction 2

[0168] For any steam methane reforming process, the principle of synthesis gas (syngas) production of any gas mixture in thermodynamic equilibrium in Reaction 1 and 2, can be calculated mathematically by realizing that any relevant gas mixture can be expressed in terms of the molar H / C (Eq. 1) and O / C (Eq. 2) ratio in the gas.

[0169] Equation 1

[0170] Equation 2

[0171] Evaluating Eq. 1 and Eq. 2, a normalized gas mixture of (yj), can be defined, which is the hypothetical gas composition for a given O / C and H / C ratio, where all gas molecules are normalized to a composition of CH4, H2O and CO2. Using this approach, any gas composition can be defined by translating a combination of O / C and H / C ratio into a normalized composition of CO2, H2O and CH4, and subsequently solving reaction 1 and 2 at thermodynamic equilibrium at selected pressure and temperature. Moreover, a specific process can now be targeting solving for a O / C and H / C ratio combination with respect to temperature and pressure at thermodynamic equilibrium, resulting in a specific syngas composition. Herein, two different processes were demonstrated targeting methanol (MeOH) and Fischer-Tropsch (FT) syngas production with a specific syngas composition of (H2- CO2) / (CO+CO2) ratio of 2 (MeOH module) and H2 / CO ratio of 2, respectively.

[0172] Thermodynamic model

[0173] In Fig. 1A, a methanol (MeOH) and Fischer-Tropsch (FT) model are shown based on thermodynamic equilibrium of a synthesis gas targeting a MeOH module ratio of 1.9- 2.2 and H2 / CO ratio of 1.9-2.1, respectively. The MeOH and FT models covering various process combination ranging from 800-1050 °C and 5-30 barg and O / C ratio from 1.4 to 2.4 for methanol production and 1.6 to 2.4 for FT production.

[0174] Fig. 1A shows a thermodynamic model for synthesis gas production suitable for methanol and Fischer-Tropsch processes. Synthesis gas production for methanol targets a (H2-CO2) / (CO2+CO) ratio in the synthesis gas of 1.9-2.2. Synthesis gas production for Fischer-Tropsch targets an H2 / CO ratio in the synthesis gas of 1.9-2.1. The thermodynamic model of methanol and Fischer-Tropsch is based on different O / C and H / C ratios. The thermodynamic models cover pressure and temperatures from 5-30 barg and 800-1050 °C, respectively, at different O / C ratios.

[0175] The carbon limit curve is at 25.5 bar for graphite and a typical industrial nickel catalyst. The left-hand sides of the carbon limit curve are the areas where carbon formation is expected for temperatures between 400 and 1050 °C. 70 Equation s

[0176] The MeOH function shown in Eq. 3 covers synthesis gas production of (H2- CO2) / (CO+CO2) ratio of 2.

[0177] The FT model can be expressed by Eq. 4: 0.3313 3.67 Equation 4

[0178] The FT function shown in Eq. 4 covers synthesis gas production of H2 / CO ratio of 2.

[0179] Fig. 1A further shows a range of H / C ratios calculated from a specific value of an O / C ratio by means of Eq. 3 and 4 by plus minus 14% and 18% for MeOH and FT, respectively.

[0180] Fig. IB shows the same as Fig. 1A for a specific MeOH module of 2.0 for methanol production and a H2 / CO ratio of 2.0 for FT production. Fig. IB further shows a range of H / C ratios calculated from a specific value of an O / C ratio by means of Eq. 3 and 4 by plus minus 10% and 14% for MeOH and FT, respectively.

[0181] EXAMPLE 1

[0182] Control of steam methane reforming of biogas for producing syngas with a stable composition for downstream methanol production

[0183] This example is a computer simulation of the following process: Biogas was used as carbon-containing feed gas stream for producing syngas with a stable composition for use for downstream production of methanol. Biogas is known to have a fluctuating composition, e.g. expressed as a CH4 / CO2 ratio, over time and hence adjustment of the composition of the biogas feed gas stream is required to obtain a syngas with a stable composition.

[0184] Steam methane reforming was carried out in an electrically heated steam methane re former with a biogas feed of 6 Nm3 / h, a pressure of 6 barg and a product exit temperature of 900°C. Steam and hydrogen were used as adjustment gases for adjusting the composition of the feed gas stream supplied to the steam reforming reactor. The target composition of the syngas is that the syngas has a MeOH module of 2, wherein

[0185] MeOH module = (H2-CO2) / CO + CO2).

[0186] The simulation is carried out in a test period of 80 hours. Steam and hydrogen addition is used to stabilize the H / C and O / C ratio setpoints based on Eq. 1 and Eq. 2. Fig. 2 shows the response of a feed forward control system as a function of time. Fig. 2A shows the adjustments in steam and hydrogen supply to the steam reforming reactor, Fig. 2B shows the controlled H / C and O / C ratios, and Fig. 2C shows the measured MeOH module of the produced syngas and the CH4 / CO2 ratio of the biogas feed.

[0187] The fluctuating composition of the biogas feed in terms of the CH4 / CO2 ratio continuously changes the hydrogen and oxygen balance as function of the CH4 / CO2 ratio in the biogas. However, by adjusting steam and hydrogen flow to the system, the O / C and H / C is kept stable at their set points of 6.46±0.02 and 2.22±0.01, respectively, cf. Fig. 2B. This results in a stable synthesis gas production, which is shown in Table 1 of the average gas composition over the test period with standard deviation from equilibrium. The O / C and H / C control over time results in a stable MeOH module of 1.99 ± 0.01, cf. Fig. 2C, over the test period despite fluctuation in the biogas feedstock.

[0188] Table 1. Experimental and equilibrium concentration of the synthesis gas composition at 900 °C, 6 barg, 6.46 O / C and 2.22 H / C. Experimental values are based on an average over the experimental period of 80 hours shown in Fig. 2 with a standard deviation from equilibrium.

[0189] Components Experimental [mol / mol %] Equilibrium [mol / mol%]

[0190] F 53 . 0 ± 0 . 2 52 '~9

[0191] H2O 23 . 0 ± 0 . 4 23 . 3

[0192] CO 17 . 3 ± 0 . 2 17 . 5 CO26 . 2 ± 0 . 2 5 . 9

[0193] CH40 . 24 ± 0 . 03 0 . 27

[0194] MeOH Module 1 . 99 ± 0 . 01 2 . 00

[0195] EXAMPLE 2

[0196] Control of steam methane reforming of biogas for producing syngas with a stable composition for downstream Fischer-Tropsch processing

[0197] This example is a computer simulation of the following process: Biogas was used as carbon-containing feed gas stream for producing syngas with a stable composition for use for downstream processing in a Fischer-Tropsch (FT) unit. Biogas is known to have a fluctuating composition, e.g. expressed as a CH4 / CO2 ratio, over time and hence adjustment of the composition of the biogas feed gas stream is required to obtain a syngas with a stable composition.

[0198] Steam methane reforming was carried out in a electrically heated steam methane reformer with a biogas feed of 7 Nm3 / h, a pressure of 10 barg and a product exit temperature of 900°C. Steam and hydrogen were used as adjustment gases for adjusting the composition of the feed gas stream supplied to the steam reforming reactor. The target composition of the syngas is that the syngas has a H2 / CO ratio of 2.

[0199] The simulation is carried out in a test period of 60 hours. Steam and hydrogen addition is used to stabilize the H / C and O / C ratio setpoints based on Eq. 1 and Eq. 2. Fig. 3 shoes the response of a feed forward control system as a function of time. Fig. 3A shows the adjustments in steam and hydrogen supply to the steam reforming reactor, Fig. 3B shows the controlled H / C and O / C ratios, and Fig. 3C shows the measured H2 / CO ratio of the produced syngas and the CH4 / CO2 ratio of the biogas feed. The fluctuating composition of the biogas feed in terms of the CH4 / CO2 ratio continuously changes the hydrogen and oxygen balance as function of the CH4 / CO2 ratio in the biogas. However, by adjusting steam and hydrogen flow to the system, the O / C and H / C is kept stable at their set points of 4.34±0.02 and 1.97±0.01, respectively, cf. Fig. 3B. This results in a stable synthesis gas production, which is shown in Table 2 of the average gas composition over the test period with standard deviation from equilibrium. The O / C and H / C control over time results in a stable H2 / CO ratio of 2.00 ± 0.01, cf. Fig. 3C, over the test period despite fluctuation in the biogas feedstock.

[0200] Table 2. Experimental and equilibrium concentration of the synthesis gas composition at 900 °C, 10 barg, 4.340 / C and 1.97 H / C. Experimental values are based on an average over the experimental period of 60 hours shown in Fig.3 with a standard deviation from equilibrium.

[0201] Components Experimental [mol / mol%] Equilibrium [mol / mol%]

[0202] H245.5 ± 0.3 45.4

[0203] H2O 22.4 ± 0.4 22.7

[0204] CO 22.7 ± 0.2 22.6

[0205] CO28.8 ± 0.1 8.7

[0206] CH40.43 ± 0.20 0.62

[0207] H2 / CO 2.00 ± 0.01 2.00

Claims

49CLAIMS1. A process for producing a syngas comprising the steps of: e) providing a carbon-containing feed gas stream, wherein the composition of the carbon-containing feed gas stream is non-constant over time, f) feeding the carbon-containing feed gas stream to a syngas generating section comprising a steam reforming reactor, g) carrying out steam methane reforming of said carbon-containing feed gas stream in the syngas generating section to form a syngas, h) out-letting a syngas from the syngas generating section and providing at least part of the syngas to a downstream section for converting said syngas into a hydrocarbon product and / or a refined syngas and / or ammonia, wherein the composition of the carbon-containing feed gas stream before feeding it to the syngas generating section is subjected to an adjustment to maintain each of an H / C (mol / mol) ratio and an O / C (mol / mol) ratio of the carbon-containing feed gas stream within a range of a selected set point plus minus 10%, and wherein said adjustment is carried out by addition of one or two adjustment gasses selected from the group consisting of hydrogen, steam, carbon dioxide, methane and combinations thereof, wherein the adjustment gas is a high-purity gas with a level of contaminants below 20 vol%.

2. A process according to claim 1, wherein each of the H / C ratio and the O / C ratio is maintained within a range of a selected set point plus minus 9%, preferably 8%, preferably 7%, preferably 6%, preferably 5%, preferably 4%, preferably 3%, preferably 2%, and most preferably 1%.

3. A process according to any preceding claim, wherein the adjustment gas is a high- purity gas with a level of contaminants below 18 vol%, preferably below 16 vol%, preferably below 14 vol%, preferably below 12 vol%, preferably below 10 vol%, preferably50 below 8 vol%, preferably below 6 vol%, preferably below 4 vol%, preferably below 2 vol%, and most preferably below 1 vol%.

4. A process according to any preceding claim, wherein the carbon-containing feed gas stream is selected from the group consisting of biogas, natural gas, a carbon dioxiderich gas, methane and a mixture thereof.

5. A process according to any preceding claim, wherein the one or two adjustment gasses is selected from the group consisting of hydrogen, steam and carbon dioxide, wherein the one or two adjustment gasses is not carbon dioxide, when the carbon- containing feed gas stream is a carbon dioxide-rich gas.

6. A process according to any preceding claim, wherein two adjustment gasses are used, and wherein the two adjustment gases are added to the carbon-containing feed gas stream separately or as a mixture.

7. A process according to any preceding claim comprising the steps of operating the process in a first operation mode with a first carbon-containing feed gas stream, first set points for the H / C and O / C ratios and addition of one or two first adjustment gasses, and shifting the process to a second operation mode, wherein the process is operated with a second carbon-containing feed gas stream different from the first carbon-containing feed gas stream, second set points for the H / C and O / C ratios different or the same as the first set points, and addition of one or two second adjustment gasses different or the same as the one or two first adjustment gasses.

8. A process according to any preceding claim, wherein said downstream section comprises a syngas upgrading section arranged to generate a stream of purified CO2, H2,51 and / or CO from the syngas, thereby providing a refined syngas and optionally a carbon-containing offgas, and / or wherein said downstream section comprises a hydrocarbon synthesis section for converting said syngas into a hydrocarbon product and a carbon-containing off-gas, and / or wherein said downstream section comprises an ammonia synthesis section for converting said syngas into ammonia and a carbon-containing off-gas.

9. A process according to claim 8, wherein the downstream section is a hydrocarbon synthesis section, and wherein the hydrocarbon synthesis section is selected from the group consisting of a methanol synthesis section, an oxyalcohol synthesis section, an acetic acid synthesis section, a Fischer-Tropsch (FT) section for producing a liquid hydrocarbon product, a synthetic fuel synthesis section, and combinations thereof.

10. A process according to claim 8 or 9, wherein the carbon-containing off-gas from the downstream sections is recycled to the carbon-containing feed gas stream or to the syngas generating section, and wherein the levels of a H / C ratio and a O / C ratio are calculated based on the combined carbon-containing feed and recycled carbon-containing off-gas.

11. A process according to any preceding claim, where the syngas generating section comprises one or more reformer units selected from the group consisting of, a steam methane reformer (SMR), an electrically heated steam methane reformer (e-SMR), a heat exchange reformer, a reverse water gas shift (RWGS) reformer, an electrically heated reverse water gas shift reactor (e-RWGS) and combinations thereof arranged in series and / or in parallel, preferably an electrically heated steam methane reformer (e- SMR).

12. A process according to any preceding claim, wherein the syngas generating section does not comprise an ATR.5213. A process according to any preceding claim, wherein the carbon-containing feed is a biogas.

14. A process according to claim 13, wherein the composition of the carbon-containing feed gas stream before feeding it to the syngas generating section is adjusted to maintain the levels of methane (CH4) and carbon dioxide (CO2) within the following ranges: 40 vol%<CH4<75 vol%, preferably 55 vol%<CH4<65 vol%,25 vol%<CO2<60 vol%, preferably 35 vol%<CH4<45 vol%, or to maintain the CO2 / CH4 ratio within the following range:0<CO2 / CH4<9.

15. A process according to any of claims 13-14, wherein the adjustment gasses are hydrogen and / or steam.

16. A process according to any preceding claim, wherein the composition of the syngas from the syngas generating section before providing at least part of the syngas to a downstream section is adjusted by addition of an addition gas.

17. A process according to claim 16, wherein the addition gas is carbon monoxide or hydrogen, preferably hydrogen.

18. A plant for producing a syngas comprising a carbon-containing feed gas stream, wherein the composition of the carbon- containing feed gas stream is non-constant over time, a syngas generating section comprising a steam reforming reactor for carrying out steam methane reforming of said carbon-containing feed gas stream to form a syngas, a downstream section for converting said syngas into a hydrocarbon product and / or a refined syngas and / or ammonia,means for feeding the carbon-containing feed gas stream to the syngas generating section, means for out-letting a syngas from the syngas generating section and providing at least part of the syngas to the downstream section, - means for adjusting the composition of the carbon-containing feed gas stream before feeding it to the syngas generating section to maintain each of an H / C (mol / mol) ratio and an O / C (mol / mol) ratio of the carbon-containing feed gas stream within a range of a selected set point plus minus 10%, and means for carrying out said adjustment by addition of one or two adjustment gasses selected from the group consisting of hydrogen, steam, carbon dioxide, methane and combinations thereof, wherein the adjustment gas is a high-pu- rity gas with a level of contaminants below 20 %.

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