TECHNICAL FIELD

A process and a plant are described for boosting the feedstock conversion in a reforming plant and to control the product quality, by using an electrical steam methane reformer (e- SMR) in a subsequent reforming step.

BACKGROUND

One challenge of convective reformers - in particular fired convective bayonet reformers - is that their maximum operating temperature is often confined due to the requirement for a driving force for energy transfer between the convective medium and the heated zone. Still, convective reformers are attractive as they offer a route for better energy utilization in chemical plants by utilizing hot flue gas as energy source for the reforming reaction.

This - in turn - constrains the operation of the equipment, as the ultimate control of the product quality (i.e. reforming temperature) must be done by controlling either the feed or fuel (hot gas for energy transfer).

The standard solution for a bayonet convective reformer includes a built-in product control mechanism on a feed line. The product quality is done on fuel feed to the burner chamber of the reformer.

SUMMARY

A plant is provided which comprises a reforming section (A), a gas separation section (B) and a hydrocarbon-containing feed, wherein said reforming section (A) is arranged to receive said hydrocarbon-containing feed and provide a synthesis gas stream, wherein said reforming section (A) comprises a fired reformer and an electrical steam methane reformer, e-SMR, arranged downstream of said fired reformer; said fired reformer comprising one or more reactor tubes housing a first catalyst, said fired reformer further comprising one or more burners arranged to provide heat to said one or more reactor tubes, said one or more reactor tubes being arranged to receive a first portion of the hydrocarbon-containing feed and convert said first portion of the hydrocarbon- containing feed to a first synthesis gas stream; said e-SMR housing a second catalyst and being arranged to receive at least a portion of the first synthesis gas stream from said fired reformer and convert it to a second synthesis gas stream; wherein the plant comprises a control system arranged to control the electrical power supply to ensure that the temperature of the gas exiting the e-SMR lies in a predetermined range; wherein the gas separation section (B) is arranged to receive a synthesis gas stream from said reforming section (A) and separate it into at least a condensate and a product gas.

Also provided is a process for providing a product gas from a hydrocarbon-containing feed in a plant according to the invention. Further details of the invention are provided in the following description, figures and dependent claims.

LEGENDS TO THE FIGURES

Fig. 1 shows a schematic plant layout, without an e-SMR

Fig. 2 shows a schematic plant layout, including an e-SMR

DETAILED DISCLOSURE

The present invention describes a process and a plant for boosting the feedstock conversion in a reforming plant and to control the product quality, by using an electrical steam methane reformer (e-SMR) in a subsequent reforming step.

Using a fired reformer together with an electrical reformer in series gives a synergy, because the process control of the product quality is moved from the fired reactor to the electrically heated reactor. The fired reformer technology works by providing the energy input by combustion externally to the catalytic reactor system. In practice, this means that the process must be controlled by balancing two chemical reactors against each other; on one side the combustion reactor and on the other side the catalytic reactor. At all time, these must be balanced, and especially the combustion side is not allowed a large offset from the catalyst side, otherwise overheating and thereby mechanical failure will occur. It only adds increased complexity that the catalytic reactor side is configured as several parallel tubes with one tube being able to process in the order of 100 Nm ³ /h gas in a typical configuration and added capacity is gained by multiplying the number of tubes. In practice, this means that fired reformer are tedious to operate and care must be taken to maintain the process in steady state where a degree of distribution between the individual tubes is accepted. The e- SMR is in contrast not a segregated system. As heating is not transferred across a pressure baring wall, risk of mechanical failure is not critical. From a catalyst point of view, temporary overheating is not a problem, it will just produce a very hot synthesis gas. This gives the ability for the e-SMR to adjust output temperature much faster, thereby giving a more constant outlet temperature and a consequential more stable reactant conversion.

Specifically, using a convective bayonet reformer together with an electrical reformer gives a synergy, because the convective reformer operates in a mode where a maximum increase in chemical energy is achieved while still operating at a relatively low outlet temperature, which makes it possible to combine directly with an e-SMR in which limitations are placed on e-SMR inlet temperatures due to electrical connections in this apparatus.

The configuration allows for better feedstock utilization, improved energy recovery, and not least a means of retrofitting existing plants. Potentially, the retrofitting can be done to change the operation of an existing reforming plant to a mode with lower CO2 emissions relative to the amount of synthesis gas produced.

The term product quality is meant to denote a quantitative process for determining the conversion of the reactant to the desired product in the chemical reactor. For the endothermic steam reforming reaction, a good way to follow this is by the equilibrium temperature. The equilibrium temperature of the steam reforming reaction is found by initially calculating the reaction quotient (Q) of the given gas as:

Here yj is the molar fraction of compound j, and P is the total pressure in bar. This is used to determine the equilibrium temperature (T _eq ) at which the given reaction quotient is equal to the equilibrium constant:

Q — ^SMIi (Tq) where K _S MR is the thermodynamic equilibrium constant of the steam methane reforming reaction. The approach to equilibrium of the steam methane reforming (AT _app ,sMR) reaction is then defined as: T _apP:SMR = T — T _eq

Where T is the bulk temperature of the gas surrounding the catalyst material used. Classically, large scale industrial SMRs have been designed to obtain an approach to equilibrium of 5-20°C at the outlet thereof.

In an embodiment, the desired product quality of e.g. the second synthesis gas stream would have a steam methane reforming equilibrium temperature of 850°C, more preferably 950°C, and even more preferably 1050°C, with an accompanied approach to equilibrium of below 50°C, more preferably below 25°C and even more preferably below 10°C.

In the following, all percentages are given as volume %, unless otherwise specified. The term "substantially pure" should be understood as meaning more than 80% pure, ideally more than 90%, such as more than 99% pure.

The term "steam reforming" or "steam methane reforming reaction" is meant to denote a reforming reaction according to one or more of the following reactions:

CH ₄ + H ₂ O CO + 3H ₂ (i)

CH ₄ + 2H ₂ O CO ₂ + 4H ₂ (ii)

CH ₄ + CO ₂ 2CO + 2H ₂ (iii)

Reactions (i) and (ii) are steam methane reforming reactions, whilst reaction (iii) is the dry methane reforming reaction.

For higher hydrocarbons, viz. C _n H _m , where n>2, m > 4, equation (i) is generalized as:

CnHm + n H ₂ O «-> nCO + (n + m/2)H ₂ (iv) where n>2, m > 4.

Typically, steam reforming is accompanied by the water gas shift reaction (v) :

CO + H ₂ O co ₂ + H ₂ (v) The terms "steam methane reforming" and "steam methane reforming reaction" are meant to cover the reactions (i) and (ii), the term "steam reforming" is meant to cover the reactions (i), (ii) and (iv), whilst the term "methanation" covers the reverse reaction of reaction (i). In most cases, all of these reactions (i)-(v) are at, or close to, equilibrium at the outlet from the reforming reactor.

The plant - illustrated schematically in the enclosed figures - comprises a reforming section (A), a gas separation section (B) and a hydrocarbon-containing feed.

The reforming section (A) is arranged to receive the hydrocarbon-containing feed and provide a synthesis gas stream. In general terms, the reforming section (A) comprises a fired reformer and an electrical steam methane reformer, (e-SMR) arranged downstream of the fired reformer. These components are described in more detail in the following.

Hydrocarbon-containing feed

A hydrocarbon-containing feed is supplied to the plant; at least to the reforming section (A) thereof. In this context, the term "hydrocarbon-containing feed" is meant to denote a gas with one or more hydrocarbons and possibly other constituents. Thus, a hydrocarbon- containing feed typically comprises a hydrocarbon gas, such as CH ₄ and optionally also higher hydrocarbons often in relatively small amounts, in addition to small amounts of other gasses. Higher hydrocarbons are components with two or more carbon atoms such as ethane and propane. Examples of "hydrocarbon-containing feed" may be natural gas, town gas, naphtha or a mixture of methane and higher hydrocarbons, biogas or LPG. Hydrocarbons may also be components with other atoms than carbon and hydrogen such as oxygen or sulphur.

The hydrocarbon-containing feed may additionally comprise - or be mixed with one more coreactant feeds - steam, hydrogen and possibly other constituents, such as carbon monoxide, carbon dioxide, nitrogen and argon. Typically, the hydrocarbon-containing feed has a predetermined ratio of hydrocarbon, steam and hydrogen, and potentially also carbon dioxide. The hydrocarbon feed will - in most practical applications - contain steam.

In one aspect, the hydrocarbon-containing feed comprises a gas mixture with a biogas feed. 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 (CH ₄ ) and carbon dioxide (CO2) and may have small amounts of hydrogen sulfide (H ₂ S), moisture, siloxanes, and possibly other components. Up to 30% or even 50% of the biogas may be carbon dioxide. The hydrocarbon-containing feed may have gone through at least steam addition (present as a co-reactant feed) and optionally also pretreatment (described in more detail in the following).

In an embodiment, the hydrocarbon-containing feed is a mixture of CH ₄ , CO, CO2, H ₂ , and, H2O, where the concentration of CH ₄ is 5-50 mole%, the concentration of CO is 0.01-5%, the concentration of CO2 is 0.1 to 50%, the concentration of H ₂ is 1-10%, and the concentration of H ₂ O is 30-70%.

Fired reformer

The reforming section (A) comprises a fired reformer. The term "fired reformer" is meant to denote a reforming reactor wherein a fuel is burned off in order to supply heat for the steam methane reforming reaction. The fired reformer is - in a preferred instance - a convective bayonet reformer.

The fired reformer comprises one or more reactor tubes, extending along the length of the fired reformer. The reactor tubes house a first catalyst.

The one or more reactor tubes are arranged to receive a first portion of the hydrocarbon- containing feed and convert said first portion of the hydrocarbon-containing feed to a first synthesis gas stream. Conversion takes place over the first catalyst.

The fired reformer further comprising one or more burners arranged to provide heat to (the outside of) the one or more reactor tubes. Reformer tubes and burners are arranged within a fired reformer housing.

Convective bayonet reformers typically have a maximum reforming temperature of around 900°C. At the typical operating pressures, this means a relative high slip of methane. The current configuration allows to increase the reforming temperature by the electrical reformer, where the maximum energy utilization is extracted from the hot process gas (flue gas/synthesis gas), and as such operated in a self-balanced scheme, while the electrical reformer is used as controlling device to lift the reforming temperature to achieve higher feedstock conversion. In this way minimum overall energy to a reforming section is achieved.

When using the convective bayonet reformer, it is an advantage that the reforming equilibrium temperature of the first synthesis gas is higher than the outlet temperature from the fired reformer. This allows for maximum chemical energy in the first synthesis gas, while having a low temperature which is more easily applicable with the configuration of an electrically heated reformer because the electrically heated reformer in some configurations has temperature-sensitive parts which are more easily protected when the feed gas is colder.

The fired reformer has an outlet for waste gas from the combustion process which takes place in the burners.

Electrical steam methane reformer (e-SMR)

The other primary component of the reforming section A is an electrical steam methane reformer, e-SMR.

Electrical steam methane reformers are known e.g. from Wismann et al, Science 2019: Vol. 364, Issue 6442, pp. 756-759, WO2019/228798, and WO2019/228795, the contents of which are incorporated by reference.

The e-SMR houses a second catalyst and is arranged to receive at least a portion of the first synthesis gas stream from the fired reformer and convert it to a second synthesis gas stream.

Since the e-SMR is electrically heated, less overall energy consumption takes place compared to a fired steam methane reforming reactor, since a high temperature flue gas of the e-SMR is avoided. Moreover, if the electricity utilized for heating the electrically heated reforming reactor and possibly other units of the synthesis gas plant is provided from renewable energy resources, the overall consumption of hydrocarbons for the synthesis gas plant is minimized and CO ₂ emissions accordingly reduced.

The e-SMR reactor is arranged to be heated by a first electricity flow. In an embodiment, the e-SMR comprises:

- a pressure shell housing an electrical heating unit arranged to heat the first catalyst, where the first catalyst comprises a catalytically active material operable to catalyzing steam reforming of the first part of the feed gas, wherein the pressure shell has a design pressure of between 5 and 50 bar,

- a heat insulation layer adjacent to at least part of the inside of the pressure shell, and - at least two conductors electrically connected to the electrical heating unit and to an electrical power supply placed outside the pressure shell, wherein the electrical power supply is dimensioned to heat at least part of the first catalyst by passing an electrical current through the electrical heating unit.

An important feature of the e-SMR is that the energy is supplied inside the reforming reactor, instead of being supplied from an external heat source via heat conduction, convection and radiation, e.g. through catalyst tubes. In an e-SMR with an electrical heating unit connected to an electrical power supply via conductors, the heat for the reforming reaction is provided by resistance heating. The hottest part of the e-SMR will be within the pressure shell of the electrically heated reforming reactor. Preferably, the electrical power supply and the electrical heating unit within the pressure shell are dimensioned so that at least part of the electrical heating unit reaches a temperature of 900°C, more preferably 1000°C or even more preferably 1100°C.

In an embodiment, the e-SMR comprises a second catalyst as a bed of catalyst particles, e.g. pellets, typically in the form of catalytically active material supported on a high area support with electrically conductive structures embedded in the bed of catalyst particles.

Alternatively, the catalyst may be catalytically active material supported on a macroscopic structure, such as a monolith.

When the e-SMR comprises a heat insulation layer adjacent to at least part of the inside of the pressure shell, appropriate heat and electrical insulation between the electrical heating unit and the pressure shell is obtained. Typically, the heat insulation layer will be present at the majority of the inside of the pressure shell to provide thermal insulation between the pressure shell and the electrical heating unit/first catalyst; however, passages in the heat insulation layers are needed in order to provide for connection of conductors between the electrical heating unit and the electrical power supply and to provide for inlets/outlets for gasses into/out of the electrically heated reforming reactor.

The presence of heat insulating layer between the pressure shell and the electrical heating unit assists in avoiding excessive heating of the pressure shell and assists in reducing thermal losses to the surroundings of the electrically heated reforming reactor. The temperatures of the electrical heating unit may reach up to about 1300°C, at least at some parts thereof, but by using the heat insulation layer between the electrical heating unit and the pressure shell, the temperature of the pressure shell can be kept at significantly lower temperatures of e.g. 500°C or even 200°C. This is advantageous since typical construction steel materials are unsuitable for pressure bearing applications at high temperatures, such as above 1000°C. Moreover, a heat insulating layer between the pressure shell and the electrical heating unit assists in control of the electrical current within the e-SMR, since heat insulation layer is also electrically insulating. The heat insulation layer could be one or more layers of solid material, such as ceramics, inert material, refractory material or a gas barrier or a combination thereof. Thus, it is also conceivable that a purge gas or a confined gas constitutes or forms part of the heat insulation layer.

As the hottest part of the e-SMR during operation is the electrical heating unit, which will be surrounded by heat insulation layer, the temperature of the pressure shell can be kept significantly lower than the maximum process temperature. This allows for having a relative low design temperature of the pressure shell of e.g. 700°C or 500°C or preferably 300°C or 200°C of the pressure shell whilst having maximum process temperatures of 900°C or even 1100°C or even up to 1300°C.

Another advantage is that the lower design temperature compared to a fired SMR means that in some cases the thickness of the pressure shell can be decreased, thereby saving costs.

It should be noted that the term "heat insulating material" is meant to denote materials having a thermal conductivity of about 10 W- r^K ^-1 or below. Examples of heat insulating materials are ceramics, refractory material, alumina-based materials, zirconia- based materials and similar.

In an embodiment, the synthesis gas plant further comprises a control system arranged to control the electrical power supply to ensure that the temperature of the gas exiting the electrically heated reforming reactor lies in a predetermined range and/or to ensure that the conversion of hydrocarbons in the first part of the feed gas lies in a predetermined range and/or to ensure the dry mole concentration of methane lies in a predetermined range and/or to ensure the approach to equilibrium of the steam reforming reaction lies in a predetermined range. Typically, the maximum temperature of the gas lies between 900°C and 1000°C, such as at about 950°C, but even higher temperatures are conceivable, e.g. up to 1300°C. The maximum temperature of the gas will be achieved close to the most downstream part of the first catalyst as seen in the flow direction of the feed gas.

In an embodiment, the synthesis gas plant further comprises a control system, which as a sole product quality control mechanism is arranged to control the electrical power supply to ensure that the temperature of the gas exiting the electrically heated reforming reactor lies in a predetermined range. Thus, in this embodiment the product quality is controlled by feedback control on the e-SMR alone, i.e. no control of e.g. the fired reformer is carried out. In one embodiment, the control system is not arranged to provide feedback control on the outlet temperature of said fired reformer. The control of the electrical power supply is the control of the electrical output from the power supply. The control of the electrical power supply may e.g. be carried out as a control of the voltage and/or current from the electrical power supply, as a control of whether the electrical power supply is turned on or off or as a combination hereof. The power supplied to the electrically heated reforming reactor can be in the form of alternating current or direct current.

Process control on the electrically heated SMR (e-SMR) gives a direct feedback loop on the operation, where a control change of the operating conditions is carried out by increasing or decreasing the electricity input to the reactor from an associated power supply unit. Such a power supply unit can be configured in different ways depending on the circumstances, where most common configurations are a thyristor controller and an autotransformer. Irrespective of chosen technology, the power supply unit can be configured to allow fast changes (less than seconds of response time) and very precise control. This means that an immediate feedback can be built around the e-SMR such that a given exit temperature from the reactor can be obtained by coupling the exit temperature to a control scheme, which actuates on the supplied electricity from the power supply unit. As a result, a very precise operating temperature in the e-SMR can be achieved. As the operating temperature is a key parameter for controlling the conversion of the endothermic steam methane reforming reaction, this translates directly into having a very stable and precisely defined product gas composition.

Due to the advantages and fast response of the control mechanism of the e-SMR reactor it is an advantage to direct control of a chemical plant towards the e-SMR reactor. In the present invention this is specifically utilized by combining the e-SMR reactor with a fired reformer. A typical fired reformer has a very slow control scheme to achieve a given outlet temperature and e.g. associated product quality, because this control mechanism involves a fuel mix system where both amount of fuel and amount of oxidant air must be controlled to provide a hot gas, which will transfer heat to the catalyst zone of the fired reformer. This transfer of heat to the catalyst zone has a relative slow response to changes, because a steady state needs to establish over the heat transfer mechanism across a tube wall, which means that some time (from minutes up to an hour) is needed to see the full response in a control action on the product quality. If the fired reformer is operated with a practically constant feed of fuel, or alternatively by letting the fuel be a non-controlled feedstock from e.g. an off-gas, the product gas will have a transient nature where the temperature and the degree of conversion in the product gas will not be constant. However, this can easily be compensated by the downstream e-SMR where the faster electrical feedback control compensates for any transients in the slower controlled operation of the fired reformer and consequently the combined operation of the fired reformer and the e-SMR gives a stable production of product irrespective of the settings of the fuel supply to the fired reformer. This also means that the configuration of the present invention will achieve an intended steady state production faster than e.g. a similar configuration where the e-SMR is replaced with a more traditional fired reformer.

In an embodiment, the electrical heating unit comprises a macroscopic structure of electrically conductive material, where the macroscopic structure supports a ceramic coating and the ceramic coating supports a catalytically active material. Thus, during operating of the synthesis gas plant, an electrical current is passed through the macroscopic structure and thereby heats the macroscopic structure and the catalytically active material supported thereon. The close proximity between the catalytically active material and the macroscopic structure enables efficient heating of the catalytically active material by solid material heat conduction from the resistance heated macroscopic structure. The amount and composition of the catalytically active material can be tailored to the steam reforming reaction at the given operating conditions. The surface area of the macroscopic structure, the fraction of the macroscopic structure coated with a ceramic coating, the type and structure of the ceramic coating, and the amount and composition of the catalytically active material may be tailored to the steam reforming reaction at the given operating conditions.

The term "electrically conductive" is meant to denote materials with an electrical resistivity in the range from: 10 ^-4 to IO ^-8 Q m at 20°C. Thus, materials that are electrically conductive are e.g. metals like copper, silver, aluminum, chromium, iron, nickel, or alloys of metals. Moreover, the term "electrically insulating" is meant to denote materials with an electrical resistivity above 10 Q m at 20°C, e.g. in the range from 10 ⁹ to 10 ²⁵ Q-m at 20°C.

As used herein, the term "electrical heating unit comprises a macroscopic catalyst" is not meant to be limited to a reforming reactor with a single macroscopic structure. Instead, the term is meant to cover both a macroscopic structure with ceramic coating and catalytically active material as well as an array of such macroscopic structures with ceramic coating and catalytically active material.

The term "macroscopic structure supporting a ceramic coating" is meant to denote that the macroscopic structure is coated by the ceramic coating at, at least, a part of the surface of the macroscopic structure. Thus, the term does not imply that all the surface of the macroscopic structure is coated by the ceramic coating; in particular, at least the parts of the macroscopic structure which are electrically connected to the conductors and thus to the electrical power supply do not have a coating thereon. The coating is a ceramic material with pores in the structure which allows for supporting catalytically active material on and inside the coating and has the same function as a catalytic support. Advantageously, the catalytically active material comprises catalytically active particles having a size in the range from about 5 nm to about 250 nm.

As used herein, the term "macroscopic structure" is meant to denote a structure which is large enough to be visible with the naked eye, without magnifying devices. The dimensions of the macroscopic structure are typically in the range of centimeters or even meters. Dimensions of the macroscopic structure are advantageously made to correspond at least partly to the inner dimensions of the pressure shell, saving room for the heat insulation layer and conductors.

A ceramic coating, with or without catalytically active material, may be added directly to a metal surface by wash coating. The wash coating of a metal surface is a well-known process; a description is given in e.g. Cybulski, A., and Moulijn, J. A., Structured catalysts and reactors, Marcel Dekker, Inc, New York, 1998, Chapter 3, and references herein. The ceramic coating may be added to the surface of the macroscopic structure and subsequently the catalytically active material may be added; alternatively, the ceramic coat comprising the catalytically active material is added to the macroscopic structure.

Preferably, the macroscopic structure has been manufactured by 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. 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 macroscopic structure. Due to close proximity between the heat source and the catalytically active material, the heat transfer is effective, so that the macroscopic structure can be very efficiently heated. A compact reforming reactor in terms of gas processing per reforming reactor volume is thus possible, and therefore the reforming reactor housing the macroscopic structure may be compact. The reforming reactor of the invention does not need a furnace, and this reduces the size of the electrically heated reforming reactor considerably.

Preferably, the macroscopic structure comprises Fe, Ni, Cu, Co, Cr, Al, Si or an alloy thereof. Such an alloy may comprise further elements, such as Mn, Y, Zr, C, Co, Mo or combinations thereof. Preferably, the catalytically active material is particles having a size from 5 nm to 250 nm. The catalytically active material may e.g. comprise nickel, ruthenium, rhodium, iridium, platinum, cobalt, or a combination thereof. Thus, one possible catalytically active material is a combination of nickel and rhodium and another combination of nickel and iridium.

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, say 10-500 pm. In addition, a catalyst may be placed within the pressure shell and in channels within the macroscopic structure, around the macroscopic structure or upstream and/or downstream the macroscopic structure to support the catalytic function of the macroscopic structure.

The "catalysts" mentioned herein (e.g. the first and second catalysts) are catalysts suitable for the steam reforming reaction, the prereforming reaction, methanation and/or the water gas shift reaction. Examples of relevant such catalysts are Ni/MgAI ₂ O ₄ , Ni/CaAI ₂ O ₄ , Ni/AI ₂ O ₃ , Fe ₂ O ₃ /Cr ₂ O ₃ /MgO, and Cu/Zn/AI ₂ O ₃ . Examples of steam reforming catalysts are Ni/MgAI ₂ O ₄ , Ni/AI ₂ O ₃ , Ni/CaAI ₂ O ₄ , Ni/ZrO ₂ , Ru/MgAI ₂ O ₄ , Rh/MgAI ₂ O ₄ , Ir/MgAI ₂ O ₄ , Mo ₂ C, Wo ₂ C, CeO ₂ , a noble metal on an AI ₂ O ₃ carrier. Other catalysts suitable for reforming are also conceivable.

In one aspect, the e-SMR is arranged to receive a second portion of the hydrocarbon- containing feed. This allows for increasing the overall product gas production, which can be done without significantly changing on the operation of the fired reformer.

In an embodiment, the concept involves a reforming section and a gas separation section (preferably PSA or methanol synthesis), where the reforming section includes a fired convective reformer running with the separation section off-gas as only fuel source, while the eSMR controls the resulting reforming temperature to stabilize production.

In an embodiment, the plant further comprises a gas purification unit and/or a prereforming unit upstream the reforming section (A). The gas purification unit may be e.g. a desulfurization unit, such as a hydrodesulfurization unit. In the prereformer, the hydrocarbon gas will, together with steam, and potentially also hydrogen and/or other components such as carbon dioxide, undergo prereforming (according to reaction (iv) above) in a temperature range of ca. 350-550°C to convert higher hydrocarbons as an initial step in the process. Prereforming usually takes place downstream any desulfurization step. This removes the risk of carbon formation from higher hydrocarbons on catalyst in the subsequent process steps. Optionally, carbon dioxide or other components may also be mixed with the gas leaving the prereforming step to form the "hydrocarbon-containing feed" for the reforming section (A).

Gas separation section (B)

The gas separation section (B) is arranged to receive a synthesis gas stream from said reforming section (A) and separate it into at least a condensate and a product gas.

The synthesis gas stream provided to the gas separation section (B) from the reforming section (A) is typically the second synthesis gas stream from the e-SMR. Alternatively, the synthesis gas stream provided to the gas separation section (B) from the reforming section (A) may be a mixture of first and second synthesis gas streams. If post-processing is included, the synthesis gas stream provided to the gas separation section (B) from the reforming section (A) may be the post processed synthesis gas stream.

The gas separation section (B) comprises one or more of the following units: a flash separation unit, a CO ₂ removal unit, a pressure swing adsorption unit (PSA unit), a membrane, and/or a cryogenic separation unit.

By flash separation is meant a phase separation unit, where a stream is divided into a liquid and gas phase close to or at the thermodynamic phase equilibrium at a given temperature.

By CO ₂ removal is meant a unit utilizing a process, such as chemical absorption, for removing CO ₂ from the process gas. In chemical absorption, the CO ₂ containing gas is passed over a solvent which reacts with CO2 and in this way binds it. The majority of the chemical solvents are amines, classified as primary amines as monoethanolamine (MEA) and digylcolamine (DGA), secondary amines as diethanolamine (DEA) and diisopropanolamine (DIPA), or tertiary amines as triethanolamine (TEA) and methyldiethanolamine (MDEA), but also ammonia and liquid alkali carbonates as K ₂ CO ₃ and NaCO ₃ can be used.

By swing adsorption, a unit for adsorbing selected compounds is meant. In this type of equipment, a dynamic equilibrium between adsorption and desorption of gas molecules over an adsorption material is established. The adsorption of the gas molecules can be caused by steric, kinetic, or equilibrium effects. The exact mechanism will be determined by the used adsorbent and the equilibrium saturation will be dependent on temperature and pressure. Typically, the adsorbent material is treated in the mixed gas until near saturation of the heaviest compounds and will subsequently need regeneration. The regeneration can be done by changing pressure or temperature. In practice, this means that a process with at least two units is used, saturating the adsorbent at high pressure or low temperature initially in one unit, and then switching unit, now desorbing the adsorbed molecules from the same unit by decreasing the pressure or increasing the temperature. When the unit operates with changing pressures, it is called a pressure swing adsorption unit, and when the unit operates with changing temperature, it is called a temperature swing adsorption unit. Pressure swing adsorption can generate a hydrogen purity of 99.9% or above.

By membrane is meant separation over an at least partly solid barrier, such as a polymer, where the transport of individual gas species takes place at different rates defined by their permeability. This allows for up-concentration, or dilution, of a component in the retentate of the membrane.

By cryogenic separation is meant a process utilizing the phase change of different species in the gas to separate individual components from a gas mixture by controlling the temperature, typically taking place below -150°C.

In a specific embodiment, the gas separation unit comprises a flash separation unit in series with a pressure swing adsorption unit. A condensate comprising mostly water is thereby firstly separated in the flash separation unit, and then a hydrogen product is purified in the pressure swing adsorption unit. The pressure swing adsorption unit will in this embodiment also produce an off-gas comprising CO ₂ , CO, CH ₄ , and H ₂ .

In another specific embodiment, the gas separation unit has a flash separation unit in series with a carbon removal unit, in series with a CO cold box. A condensate comprising mostly water is thereby firstly separated in the flash separation unit, and then CO2 is removed in the CO2 removal unit. Finally, the product gas is separated into a product gas of substantially pure CO, a product gas of substantially pure H2, and an off-gas. The off-gas will in this case comprise CO, CH ₄ , and H ₂ .

By the configuration of the synthesis gas plant, maximum utilization of all streams is achieved by returning the fuel rich off-gases generated from different embodiments of gas separation units to the one or more burners of the fired reformer. In an aspect, gas separation section (B) is arranged to also provide an off-gas. In a preferred aspect, at least part of the off-gas from the gas separation section (B) is arranged to be provided as fuel for said one or more burners of the fired reformer. Even more preferably the off-gas from the gas separation section (B) is arranged to be provided as the only fuel for said one or more burners of the fired reformer.

The configuration of the presented layouts allows for utilizing waste energy in a chemical process efficiently, while still operating the process at set conditions. Where process control typically has been done by import of fossil energy, the current configuration transfers this to electrical energy. In the case of a fired convective reformer, where the typical configuration is to import fossil fuel to the burner side to achieved the desired synthesis gas quality, where process control is achieved by this fuel import. The current configuration allows for only operating the fired convective reformer on waste energy in an off-gas, from e.g. a PSA, and then during the actual process gas reforming temperature control in the electrical reformer downstream the fired convective reformer. Also, using the electrical reforming step after a bayonet type convective reformer, higher reforming temperature can be achieved to allow better feedstock utilization.

In one embodiment, separation section (B) comprises a hydrogen separation section, wherein said hydrogen separation section is arranged to receive a synthesis gas stream from said reforming section (A) and provide product gas being a hydrogen-rich stream, and an off-gas, being an off-gas stream from the hydrogen separation section.

In another embodiment, separation section (B) comprises a flash separation unit and a pressure swing adsorption (PSA) unit, wherein said flash separation unit is arranged to receive a synthesis gas stream from said reforming section (A) and separate it into at least a condensate and a third synthesis gas stream, and wherein said PSA unit is arranged to receive said third synthesis gas stream from said flash separation unit and provide a product gas and an off-gas.

In another embodiment, separation section (B) comprises a methanol synthesis section, wherein said methanol synthesis section is arranged to receive a synthesis gas stream from said reforming section (A) and provide product gas being a methanol-rich stream, and an offgas being an off-gas stream from the methanol synthesis section.

In another embodiment, separation section (B) comprises a CO cold box, wherein said CO cold box is arranged to receive a synthesis gas stream from said reforming section (A) and provide product gas being a substantially pure CO stream, a second product stream, being a substantially pure H ₂ stream, and an off-gas being an off-gas stream from the CO cold box. In another embodiment, separation section (B) comprises an ammonia loop, wherein said ammonia loop is arranged to receive a synthesis gas stream from said reforming section (A) and provide product gas being a substantially pure ammonia stream, and an off-gas being an off-gas stream from the ammonia loop.

In another embodiment, separation section (B) comprises a Fischer-Tropsch section, wherein said Fischer-Tropsch section is arranged to receive a synthesis gas stream from said reforming section (A) and provide product gas being a stream of higher hydrocarbons, and an off-gas stream from the Fischer-Tropsch section.

In another embodiment, separation section (B) comprises a flash separation unit and a hydrogen separation section, wherein said flash separation unit is arranged to receive a synthesis gas stream from said reforming section (A) and separate it into at least a condensate and a third synthesis gas stream, and wherein said hydrogen separation section is arranged to receive said third synthesis gas stream from said flash separation unit and provide a product gas being a hydrogen-rich stream and an off-gas being an off-gas stream from the hydrogen separation section.

A post processing unit may be arranged between the reforming section (A) and the gas separation section (B), said post processing unit being arranged to receive the second synthesis gas stream from the e-SMR and provide a post processed synthesis gas stream, and wherein the gas separation section (B) is arranged to receive the post processed synthesis gas stream and separate it into at least a condensate, a product gas and an offgas.

Process

Also provided is a process for providing a product gas from a hydrocarbon-containing feed in a plant according to the invention, said process comprising the steps of: a. providing a plant as described herein, b. converting a first portion of the hydrocarbon-containing feed to a first synthesis gas stream in said fired reformer, c. converting at least a portion of the first synthesis gas stream from said fired reformer to a second synthesis gas stream in said e-SMR; d. controlling the product quality by feedback control on the e-SMR to ensure that the temperature of the gas exiting the e-SMR lies in a predetermined range, and e. supplying a synthesis gas stream from said reforming section (A) to said gas separation section (B) and separating it into at least a condensate and a product gas.

In an embodiment, the product quality is controlled solely by feedback control on the e-SMR to ensure that the temperature of the gas exiting the e-SMR lies in a predetermined range.

In an embodiment, step d also provides an off-gas.

In one preferred instance, the process further comprises the step of (e). arranging at least part of the off-gas from the gas separation section (B) to be provided as fuel for said one or more burners of the fired reformer. In one instance, the off-gas from the gas separation section (B) provides substantially the entirety of the fuel required for said burners of the fired reformer.

For stable production of said product gas, the fired reformer may be operated without feedback control on the outlet temperature of said fired reformer. "Stable production" is used to mean that the plant is in steady state.

In one aspect of the process defined herein, product quality (as defined above, and - in particular the product quality from the reforming section) is controlled by feedback control on the e-SMR alone.

Suitably, the fuel provided to the one or more burners of the fired reformer has a substantially constant set point value. By constant set point value is understood that the flow of fuel to the one or more burners is roughly constant, only varying as a consequence of process control equipment regulation mechanisms and electronics.

Advantages of the process and embodiments thereof correspond to the advantages of the plant and embodiments thereof and will therefore not be described in further detail here.

Specific embodiments

Figure 2 shows a plant 100 according to the invention comprising a reforming section (A) - in this case a convective bayonet reformer 10A - a gas separation section (B) and a hydrocarbon-containing feed 1. Reforming section (A) is arranged to receive the hydrocarbon-containing feed 1 and provide a synthesis gas stream 11. The reforming section (A) comprises a fired reformer 10 and an electrical steam methane reformer, e-SMR 20, arranged downstream of said fired reformer 10.

The fired reformer 10 comprises one or more reactor tubes 12, each of which houses a first catalyst. Only one reactor tube 12 is shown in Figure 1. The fired reformer 10 further comprises one or more burners 14 arranged to provide heat to said one or more reactor tubes 12. The one or more reactor tubes 12 are arranged to receive a first portion of the hydrocarbon-containing feed 1 and convert said first portion of the hydrocarbon-containing feed 1 to a first synthesis gas stream 11.

The e-SMR 20 housing a second catalyst is arranged to receive at least a portion of the first synthesis gas stream 11 from the fired reformer 10 and convert it to a second synthesis gas stream 21. The gas separation section (B) is arranged to receive a synthesis gas stream from said reforming section (A) and separate it into at least a condensate 41 and a product gas

42.

Figure 2 shows a post processing unit 30 arranged between the reforming section (A) and the gas separation section (B). The post processing unit 30 is arranged to receive the second synthesis gas stream 21 from the e-SMR 20 and provide a post processed synthesis gas stream 31, as shown. In an embodiment, this post processing unit 30 is a water gas shift reactor. The gas separation section (B) is arranged to receive the post processed synthesis gas stream 31 and separate it into at least a condensate 41, a product gas 42 and an off-gas

43.

Also in Figure 2, the off-gas 43 from the gas separation section (B) is arranged to be provided as fuel for said one or more burners 14 of the fired reformer 10.

Figure 2 shows the optional feature that the e-SMR 20 is arranged to receive a second portion 1' of the hydrocarbon-containing feed together with the first synthesis gas stream 11.

In the plant of Figure 2, separation section (B) comprises a flash separation unit 50 and a pressure swing adsorption (PSA) unit 60. The flash separation unit 50 is arranged to receive a synthesis gas stream from the reforming section (A) and separate it into at least a condensate 41 and a third synthesis gas stream 51. The PSA unit 60 is arranged to receive the third synthesis gas stream 51 from the flash separation unit 50 and provide a product gas 42 and an off-gas 43.

Other components of the plant 100 in Figure 2 are: heat exchangers 55 exhaust stream 56 from fired reformer 10

Figure 1 shows a plant analogous to that of Figure 2. However, the plant of Figure 1 is not according to the invention, as it does not comprise an e-SMR.

EXAMPLE 1

Table 1 and Table 2 summarize an embodiment of the invention. In this case a convective bayonet reformer is placed in series with an e-SMR, a WGS reactor, a flash separation unit, and a PSA. The hydrocarbon-containing feed is fed to the bayonet reformer and reformed to a maximum temperature of 820°C in the bottom of the reactor tubes (12). At this point the gas enters the bayonet of the reactor tubes (12) and heat exchanges with the catalyst bed in the reactor tubes (12), effectively reducing the temperature of the first synthesis gas stream to 600°C before leaving the fired reformer (10). The effluent is transferred directly to an e- SMR, where the temperature is elevated to 1050°C to achieve even further conversion of methane in the feed, as the methane mole fraction decreases from 8.8 outlet the fired reformer (10) to 0.5 outlet the e-SMR. The second synthesis gas is cooled and then shifted towards a more H2 rich product in a downstream WGS reactor. It is then cooled further to allow condensation of water in the stream. Finally, the stream is separated to a product gas of hydrogen in a PSA. The hydrogen product is in the given embodiment 31673 Nm ³ /h. The off-gas from the PSA is used as the only fuel source to the fired reformer (10), where the outlet temperature of this does not have any feedback control at all.

Table 1 Table 2

EXAMPLE 2

Table 3 and Table 4 summarize a comparative example to Example 1. In this case a convective bayonet reformer is placed in series with a WGS reactor, a flash separation unit, and a PSA. The hydrocarbon-containing feed is fed to the bayonet reformer and reformed to a maximum temperature of 900°C in the bottom of the reactor tubes (12). At this point the gas enters the bayonet of the reactor tubes (12) and heat exchanges with the catalyst bed in the reactor tubes (12), effectively reducing the temperature of the first synthesis gas stream to 600°C before leaving the fired reformer (10). The resulting synthesis gas is cooled and then shifted towards a more H ₂ rich product in a downstream WGS reactor. It is then cooled further to allow condensation of water in the stream. Finally, the stream is separated to a product gas of hydrogen in a PSA. The hydrogen product is in the given case 26128 Nm ³ /h. The off-gas from the PSA is used as the only fuel source to the fired reformer (10). Notice that Example 1 and 2 uses the exact same amount of hydrocarbon-containing feed (1), but by utilizing the e-SMR to increase the product quality out of the reforming section (A), the overall hydrogen yield is markedly increased by 17%.

Table 1

Table 2