WO2025104292A1

WO2025104292A1 - Excess heat from co2 electrolysis to generate steam to steam electrolysis

Info

Publication number: WO2025104292A1
Application number: PCT/EP2024/082566
Authority: WO
Inventors: Sofie Holme BARTHOLDY
Original assignee: Haldor Topsoe AS
Current assignee: Topsoe AS
Priority date: 2023-11-15
Filing date: 2024-11-15
Publication date: 2025-05-22
Anticipated expiration: 2026-05-15

Abstract

The invention relates to a system and a method for producing a synthesis gas from a carbon dioxide-rich feed stream and a water feedstock via electrolysis, wherein excess heat from CO2 electrolysis is arranged to generate steam to steam electrolysis. More specifically, a system and a process are provided for production of a synthesis gas stream, said system comprising: a carbon dioxide-rich feed stream; a first H2O-rich feed stream; a first solid oxide electrolysis (SOEC) section; a second solid oxide electrolysis (SOEC) section; and a conversion section. Optimal use of heat energy is achieved by heat transfer from the output of the first SOEC section to the input of the second SOEC section.

Description

EXCESS HEAT FROM CO2 ELECTROLYSIS TO GENERATE STEAM TO STEAM ELECTROLYSIS

TECHNICAL FIELD

The invention relates to a system and a method for producing a synthesis gas from a carbon dioxide-rich stream and a water feedstock via electrolysis, wherein excess heat from CO₂ electrolysis is arranged to generate steam for steam electrolysis. The invention further relates to plant(s) comprising the system. In this way, the synthesis gas may be used for the production of synthetic alcohols such as methanol, or synthetic hydrocarbon(s) such as synthetic fuels (e.g. jet fuel and/or kerosene) by Fischer-Tropsch synthesis (FT) or such as substitute natural gas (SNG) (e.g. methane).

BACKGROUND

Consistent efforts are being made to replace fossil fuels and to move towards sustainable production and storage of energy and chemicals. An important contribution to drive such efforts is "Power-to-X" (PtX), which relates to systems and methods enabling electricity conversion, energy storage, and reconversion pathways to use electric power from wind and solar power generation to store energy in the form of chemicals such as synthetic alcohols, synthetic fuels or substitute natural gas.

One way to use electric power is to electrolyse water to produce H₂. It is known then to combine the H₂ and CO₂ into a mixed stream, and to convert the mixed stream to a CO- and H₂-rich synthesis gas, which can be further converted to valuable products like alcohols (including methanol), synthetic fuels (such jet-fuel kerosene and/or diesel) or substitute natural gas. However, at present, it is often ineffective and energy consuming to produce synthesis gas for synthetic alcohols and synthetic hydrocarbons from H₂ and CO₂.

Recently developments have disclosed the possibility of providing a synthesis gas by combining a H₂-rich stream from H₂O electrolysis with a CO-rich stream from CO₂ electrolysis, optionally where the electrolyses are conducted separately. Within such systems external heater units or alternatively downstream processes may be arranged to provide heat to drive the H₂O electrolysis. See e.g. WO 2022/136374 where two separate SOEC electrolyzers are used for producing H2 and CO respectively, which is combined into a synthesis gas where H2 :CO ratio may be easily controlled. However, there is a general need for further development of such systems to make these feasible for sustainable production and bring energy consumption down, hereby lowering the CO₂ footprint of such systems and methods. SUMMARY

It has been found by the present inventor(s) that the energy required for production of a synthesis gas stream may be reduced in a system and method using a first solid oxide electrolysis section for electrolysis of a carbon dioxide-rich feed stream to a carbon monoxide-rich stream and a second solid oxide electrolysis (SOEC) section for electrolysis of a SOEC steam feed stream to a hydrogen-rich stream, if thermal communication is allowed between a first H₂O-rich feed stream and at least one product stream provided from the first solid oxide electrolysis section.

More specifically, in a first aspect the present invention relates to a system for production of a synthesis gas stream, said system comprising: a carbon dioxide-rich feed stream; a first H₂O-rich feed stream; a first solid oxide electrolysis (SOEC) section; a second solid oxide electrolysis (SOEC) section; a conversion section; wherein the first SOEC section is arranged to receive the carbon dioxide-rich feed stream and electrolyse it to a carbon monoxide-rich stream and a first oxygen enriched stream; wherein the conversion section is arranged to receive the first H₂O-rich feed stream and at least one of: i) at least a portion of the carbon monoxide-rich stream, and ii) at least a portion of the first oxygen enriched stream, and to output an SOEC steam feed stream, and at least one of: iii) a cooled carbon monoxide-rich stream and iv) a cooled first oxygen enriched stream; wherein the second SOEC section is arranged to receive at least a portion of the SOEC steam feed stream and electrolyse it to a hydrogen-rich stream and a second oxygen- enriched stream; wherein at least a portion of the hydrogen-rich stream is arranged to be mixed with at least a portion of the cooled carbon monoxide-rich stream and/or at least a portion of the carbon monoxide-rich stream, to provide a synthesis gas stream. In a second aspect, the invention relates to a synthetic alcohol plant, comprising the system as disclosed herein, said synthetic alcohol plant further comprising an alcohol synthesis section, said alcohol synthesis section being arranged to receive the synthesis gas stream and output an alcohol-rich stream.

In a third aspect, the invention relates to a synthetic hydrocarbon plant, comprising the system as disclosed herein, said hydrocarbon plant further comprising a hydrocarbon synthesis section, said hydrocarbon synthesis section being arranged to receive the synthesis gas stream and output a hydrocarbon-rich stream.

In a fourth aspect, the invention relates to a process for production of a synthesis gas stream in the system as disclosed herein, said process comprising the steps of: providing a carbon dioxide-rich feed stream and a first H₂O-rich feed stream; feeding the carbon dioxide-rich stream feed to a first solid oxide electrolysis (SOEC) section and electrolysing it to provide a carbon monoxide-rich stream and a first oxygen enriched stream; providing the first H₂O-rich feed stream and at least one of: i) at least a portion of the carbon monoxide-rich stream, and ii) at least a portion of the first oxygen enriched stream, to the conversion section and outputting an SOEC steam feed stream, and at least one of: iii) a cooled carbon monoxide-rich stream and iv) a cooled first oxygen enriched stream; from said conversion section; feeding at least a portion of the SOEC steam feed stream to a second solid oxide electrolysis (SOEC) section and electrolysing it to provide a hydrogen-rich stream and a second oxygen-enriched stream; mixing at least a portion of the hydrogen-rich stream with at least a portion of the cooled carbon monoxide-rich stream and/or at least a portion of the carbon monoxide-rich stream, to provide a synthesis gas stream.

Using two separate second solid oxide electrolysis (SOEC) sections for converting carbon dioxide and water in separate systems and only combining the streams as desired after electrolysis provides advantages over conducting co-electrolysis of both carbon dioxide and water in a single electrolysis section. Having both H₂O and CO present at high temperatures increases the risk of carbonisation within a solid oxide electrolysis section, since there is a risk of creating a corrosive environment. Controlling the relative amounts of H₂O, H₂, CO₂ and CO is complicated and requires careful selection of operation parameters. Using remaining heat in a product gas (e.g. CO, CO₂, CO) to evaporate water rather than to use it to preheat a gas, e.g. CO2 feed, is advantageous because a better heat utilization is achieved, since the evaporation temperature is constant during evaporation.

Further details of the system and process for producing the synthesis gas stream, and the related plants, are specified in the following detailed description, figures and claims.

LEGENDS

Fig. 1 shows a first schematic system and method for production of the synthesis gas stream according to the invention.

Fig. 2 shows a schematic system and method for production of the synthesis gas stream according to an embodiment of the invention.

Fig. 3 shows a schematic system and method for production of the synthesis gas stream according to another embodiment of the invention.

Fig. 4 shows a schematic system and method for production of the synthesis gas stream according to another embodiment of the invention. Fig. 5 shows a schematic system and method for production of the synthesis gas stream according to another embodiment of the invention.

Fig. 6 shows a schematic system and method for production of the synthesis gas stream according to another embodiment of the invention.

DETAILED DISCLOSURE

Unless otherwise specified, any given percentages for gas content are % by volume. The terms "synthesis gas" and "syngas" are used interchangeably in this text.

A "carbon dioxide-rich feed stream" is to be understood as a feed rich in carbon dioxide. In the context of the system for production of a synthesis gas section, the carbon dioxide-rich feed stream is to be understood as a carbon dioxide-rich feed inlet.

A "H₂O-rich feed stream" is to be understood as a feed rich in H₂o. In the context of the system for production of a synthesis gas section, the H₂O-rich feed stream is to be understood as a carbon dioxide-rich feed inlet.

In the context of the system for production of a synthesis gas section, all references to streams are intended to be understood as referring to inlets, outlets and conduits for conveying the streams.

Production of the carbon monoxide-rich stream

In the first aspect, the system for production of a synthesis gas stream comprises a carbon dioxide-rich feed stream and a first solid oxide electrolysis (SOEC) section.

The carbon dioxide-rich feed stream is specified as being rich in carbon dioxide such as comprising more than 50 vol.% carbon dioxide , such as more than 70, 80, 90 or 97 vol.% carbon dioxide, preferably more than 98 vol.% or more than 99%. In embodiments the remainder of the carbon dioxide-rich feed stream is carbon monoxide and impurities. Carbon dioxide-rich feed stream comprises carbon dioxide from external sources such as from biogas upgrading or fossil fuel-based syngas (synthesis gas) plants or biomass and/or fossil fuel based powerplant or from cement production or from fermentation processes like ethanol production. Preferably, the carbon dioxide-rich feed stream is a high purity stream where apart from carbon dioxide and carbon monoxide, impurities make up less than 1%, more preferred less than 0.5% or even less than 0.1%. The first solid oxide electrolysis (SOEC) section comprises a solid oxide electrolysis cell (SOEC) such as one or more SOECs arranged in an SOEC stack. The solid oxide electrolysis cell is a solid oxide fuel cell (SOFC) run in reverse mode, which uses a solid oxide or ceramic electrolyte to produce a carbon monoxide-rich stream. In this way, the first SOEC section is arranged to receive the carbon dioxide-rich feed stream and electrolyse it to a carbon monoxide-rich stream and a first oxygen enriched stream.

Specifically for the first SOEC section, CO₂ is led to the fuel side of the cell with an applied current and excess oxygen is transported to the oxygen side of the cell (e.g. anode side), so as to electrolyse CO₂ to CO. Thus, the first SOEC section provides a carbon monoxide-rich stream from the fuel side of the cell and a first oxygen-enriched stream from the oxygen side of the cell. The carbon monoxide-rich stream provided by the first SOEC comprises a mixture of CO and CO₂, wherein the content of CO is preferably 20-80%.

Optionally, a flushing gas stream such as air or nitrogen is led to the oxygen side to flush the oxygen side. Flushing the oxygen side of the SOEC has two advantages, i) reducing the oxygen concentration and related corrosive effects within the cell and ii) providing means for feeding energy into the first SOEC as the operation is endothermic.

In embodiments, the carbon monoxide-rich stream comprising a mixture of CO and CO₂, is arranged to be led to a separation unit such as to a pressure swing adsorption (PSA) unit, temperature swing adsorption (TSA) membrane separation unit, cryogenic separation unit, or liquid scrubber technology unit, such as a wash with N-methyl-dietyanolamine (MDEA). The purpose of the separation unit is to produce a further enriched carbon monoxide-rich stream and a balance stream enriched in carbon dioxide. In embodiments, the balance stream may be either recycled to the carbon monoxide-rich stream arranged to be fed to one or more separation units and/or to the inlet of the first SOEC section for further conversion, optionally admixed with the carbon dioxide-rich feed stream. In this way, the exact composition of the carbon monoxide-rich stream may vary. In all embodiments the carbon monoxide-rich stream may be a further enriched carbon monoxide stream.

In alternative preferred embodiments, the electrolysis of CO₂ is conducted as a once-through operation, i.e. the SOEC section is a once-through electrolysis unit. The term "once-through" means that there is no need for recycling of CO₂. Compared to traditional systems for conducting CO₂ electrolysis, this enables that the need for a recycle compressor is eliminated, and thereby also the need for valves, pipes, and control system. Attendant operating expenses such as electric power needed for the compressor as well as maintenance of the recycle compressor and the other equipment (such as valves and pipes), are thereby saved. Moreover, the need for a pressure swing adsorption (PSA) unit is also eliminated, thereby significantly simplifying the system, process and plant for producing the synthesis gas for further conversion. Additionally, the once-through SOEC for CO₂ electrolysis may be operated with partial conversion. In alternative embodiments, a portion of the carbon monoxide rich stream may be recycled to the inlet of the first SOEC section for further conversion, optionally admixed with the carbon dioxide-rich feed stream.

In embodiments, the system further comprises one or more heating unit(s) arranged to heat the carbon dioxide-rich feed stream and/or optionally the flush gas stream. Preferably, the operation temperature of the one or more heating unit(s) is at least the operation temperature of the first SOEC section plus 50°C, preferably at least the operation temperature of the first SOEC section. In this way, heat may be supplied to the SOEC.

In preferred embodiments, the first solid oxide electrolysis (SOEC) section operates in the temperature range of 500-900 °C, preferably 700-800 °C. Operating at these temperatures provides advantages of higher conversion efficiencies than low-temperature electrolysis because of favourable thermodynamics and kinetics at higher operating temperatures. In addition, high temperature operation results in lower operation expenses due to lower cell voltage as well as lower capital expenses to higher current densities.

Independent of embodiments, the first SOEC section is arranged to receive the carbon dioxide-rich feed stream and provide a carbon monoxide-rich stream and a first oxygen enriched stream.

Production of the first steam stream

In all aspects of the invention, the system for production of a synthesis gas stream comprises a first H₂O-rich feed stream. The first H₂O-rich feed stream may comprise a first portion of water. In embodiments the first H₂O-rich feed stream is water-rich, such as comprising more than 50 vol.% liquid water, preferably more than 60, 70, 80, 90, 95 or 99vol. % liquid water. Additionally, or alternatively, the first H₂O-rich feed stream may comprise a first portion of steam, such as comprising more than 50 vol.% steam, preferably more than 60, 70, 80, 90, 95 or 99vol. % steam. For the avoidance of doubt, it is to be understood that the total amount of H₂O in the first H₂O-rich feed stream is 100 vol.%. Preferably, the first H₂O-rich feed stream has a high purity, such as 99 vol% H₂O, such as 99.5, 99.8 or 99.9 vol%. In an embodiment, the first H₂O-rich feed stream may be provided from a water treatment unit. The stream may be exemplified by the following composition: DMW purity(quality) pH value at 25°C pH 6-7,

Specific conductivity at 25°C (pS/cm) < 0.2,

Oxygen (O₂) (mg/kg) saturated or from 7 ppb by weight (0.0005 cm³/L) or less,

Metals and salts (mg/kg) < 5,

Oil, grease (mg/kg) < 1.

Specifically, a conversion section is arranged to receive the first H₂O-rich feed stream and at least one of: i) at least a portion of the carbon monoxide-rich stream, and ii) at least a portion of the first oxygen enriched stream, and to output an SOEC steam feed stream, and at least one of: iii) a cooled carbon monoxide-rich stream and iv) a cooled first oxygen enriched stream.

In this way, the conversion section is arranged to transfer heat, such as a portion of the excess energy in the carbon dioxide electrolysis, to at least a portion of the first H₂O-rich feed stream. Herein the term "transfer heat" should be understood as transfer of energy, and it may be direct or indirect. Precise layouts for the conversion section are set out in the following.

In a preferred embodiment, at least a portion of the carbon monoxide-rich stream is arranged to be in thermal communication with at least a portion of the first H₂O-rich feed stream to provide an SOEC steam feed stream and at least a cooled carbon monoxide-rich stream. In another preferred embodiment, at least a portion of the carbon monoxide-rich stream, and at least a portion of the first oxygen enriched stream, is arranged to be in thermal communication with at least a portion of the first H₂O-rich feed stream so as to provide an SOEC steam feed stream and a cooled carbon monoxide-rich stream and a cooled first oxygen enriched stream. Allowing thermal communication between at least a portion of the carbon monoxide-rich stream and the at least a portion of the first H₂O-rich feed stream has the advantage of further cooling the carbon monoxide-rich stream, which is desirable when forming the synthesis gas from the cooled carbon monoxide-rich stream. In this way, providing a cooled carbon monoxide-rich stream may eliminate or reduce the need of separate cooling systems or allow the capacity of such cooling systems to be reduced.

In embodiments, the system further comprises a first heat exchanger arranged to transfer heat from at least a portion of the carbon monoxide-rich stream to at least a portion of the first H₂O-rich feed stream, so as to output a first steam stream and a cooled carbon monoxide-rich stream; and/or the system comprises a second heat exchanger arranged to transfer heat from at least a portion of the first oxygen enriched stream to at least a portion of the first H₂O-rich feed stream so as to output a second steam stream and a cooled first oxygen enriched stream. Preferably, both first and second heat exchangers are present. Suitably, the first H₂O-rich feed stream is sent to both first and second heat exchangers in parallel. However, a series arrangement may be possible, in which the first H₂O-rich feed stream is sent to one of the heat exchangers before being sent to the other. The first steam stream and/or the second steam stream and may optionally be combined to output one or more SOEC steam feed streams, which are suitable for H₂O electrolysis.

The first and/or second heat exchangers provide a way to transfer heat i.e. excess energy, to at least a portion of the first H₂O-rich feed stream from the carbon monoxide-rich stream and/or at least a portion of the first oxygen enriched stream. Excess energy is transferred to at least a portion of the first H₂O-rich feed stream either by direct heat transfer or indirect heat transfer. Direct heat transfer should be understood as not involving intermediate heat media (i.e. additional streams) being present in the heat transfer, i.e. the stream delivering said excess energy is only separated from the first H₂O-rich feed stream by a heat exchange surface, whereas indirect heat transfer should be understood as involving one or more intermediate heat media stream(s), such as a boiler water feed, in the heat transfer for providing an SOEC steam feed stream. Direct heat transfer is specifically advantageous as it allows for transfer and storage of energy in a phase transition, such that the energy is deposited in the water to provide steam. In this way, exploiting the phase transition allows for more energy/per feed to be transferred to the receiving feed or stream.

In preferred embodiments, the heat transfer involves direct heat transfer. Transferring heat, i.e. excess energy, directly to the first H₂O-rich feed stream or directly to the second H₂O-rich stream may result in maximum transfer of energy, wherein a minimum of energy is lost e,g. as heat transfer to the surroundings.

The heat exchangers may be independently selected from double pipe heat exchanger, shell- and-tube heat exchanger, plate heat exchanger or cross flow exchanger. Preferably, in embodiments, said first and said second heat exchangers are shell-and-tube heat exchangers. The first and second heat exchangers may be cross flow exchangers.

The flow of streams within the heat exchangers may be arranged as parallel-flow, counterflow or cross-flow. In preferred embodiments, the flow of streams is arranged as counter-flow of streams. Counter-flow of streams is advantageous in embodiments, wherein the heat transfer results primarily in an increase in temperature such as providing a heated or evaporated H₂O-rich stream. The counter-flow of streams allows for optimised heat transfer efficiency (heat transfer per unit mass) because the average temperature difference along any unit length is higher compared to alternative flow arrangements. In more preferred embodiments, the flow of streams is arranged as cross-flow of streams. Cross flow of streams is particularly advantageous in embodiments wherein the heat transfer results primarily in a phase transition such as a transition from water to steam.

In most preferred embodiments, the system is arranged such that the heat transfer results in at least a portion of the first H₂O-rich feed stream, the second H₂O-rich stream or the intermediate heat media stream undergoing phase transition so as to provide a stream comprising at least a portion of steam or, alternatively, in the case the system comprises an intermediate heat media, to provide a stream comprising gaseous heat media. Exploiting phase transition allows for more energy/pr feed stream to be transferred to the receiving stream. In this way, it may be advantageous to preheat the stream receiving excess energy prior to this stream being fed to the first or second heat exchangers. Using remaining heat in a product gas (e.g. CO, CO₂, CO) to evaporate water rather than to use it to preheat a gas, e.g. CO2 feed, is advantageous because a better heat utilization is achieved, since the evaporation temperature is constant during evaporation.

In embodiments, where both of i) at least a portion of the carbon monoxide-rich stream and ii) at least a portion of the first oxygen enriched stream are arranged to transfer heat, it is preferred that said portions i) and ii) are arranged with the same flow arrangement.

In specific embodiments, the first and second heat exchangers are arranged to provide an SOEC steam feed stream suitable for H₂O electrolysis. In this way, embodiments are provided where the system allows for the first heat exchange to constitute the only necessary unit/section for providing thermal communication and for providing the SOEC steam feed stream suitable for H₂O electrolysis. Within this embodiment said first H₂O-rich feed stream is preferably a water-rich stream. Additionally, it may be advantageous to preheat the first H₂O-rich feed stream such as preheating said stream to preferably around 10 °C below boiling temperature. The pressure of the first H₂O-rich feed stream may be 0-19 bar g preferably between 1-4 bar g. Accordingly, in embodiments according to the present invention, the preheating may be obtained by receiving heat from external sources.

In alternative embodiments, said system further comprises a steam drum wherein said steam drum is arranged to provide an SOEC steam feed stream to the second SOEC section. Thus, the provided SOEC steam feed stream is suitable for H₂O electrolysis. The steam drum functions as a reservoir of water and steam and further as a phase-separator for the water and steam mixture. The steam drum may also provide a buffer for pressure and temperature to reduce pressure and temperature fluctuations downstream of the steam drum. In a specific embodiment, said conversion section comprises a first heat exchanger and/or a second heat exchanger, and further comprises a steam drum, wherein the steam drum is arranged to receive at least a portion of the first H₂O-rich feed stream, and provide a second H₂O-rich stream and a steam stream; wherein the first heat exchanger is arranged to transfer heat from at least a portion of the carbon monoxide-rich stream to at least a portion of the first H₂O-rich feed stream, so as to output a first steam stream and a cooled carbon monoxide-rich stream; and/or wherein the second heat exchanger is arranged to transfer heat from at least a portion of the first oxygen enriched stream to at least a portion of the first H₂O-rich feed stream so as to output a second steam stream and a cooled first oxygen enriched stream.

Preferably, at least a portion of said first steam stream and/or at least a portion of said second steam stream may be arranged into a combined third steam stream and are arranged to be fed to the steam drum.

Within said embodiments, the steam drum comprises a combined vessel such that the combined vessel receives at least a portion of the first H₂O-rich feed stream, where said portion is in fluid communication with at least a portion of the second H₂O-rich stream, and at least a portion of the third steam stream. In this way, at least a portion of the heat present in excess after electrolysis of CO₂ to CO is transferred to the liquid phase (i.e. the water phase) of the combined vessel which enables the steam drum to provide an SOEC steam feed stream.

More specifically, in embodiments, at least a portion of the first H₂O-rich feed stream is arranged to be provided to the combined vessel. The first H₂O-rich feed stream may have a temperature of between 0 to 200 °C, preferably the first H₂O-rich is a water-rich feed and with a temperature between 30 and 130 °C. The pressure of the first H₂O-rich feed stream may be 1-20 bar g preferably 2-5 bar g. The combined vessel provides a second H₂O-rich stream, which is fed to the heat exchangers. In embodiments, the second H₂O-rich stream may be water-rich and have a temperature of between 30 to 200 °C, preferably between 30 and 130 °C, most preferably 10 °C below boiling point. The pressure of the second H₂O-rich stream may be 1-20 bar g preferably between 2-5 bar g. The heat exchangers allow for heat transfer to provide first and second steam streams which may be combined into the third steam stream. In embodiments, the third steam stream may be steam-rich, hence comprise more than 90% steam such as more than 99% steam, and have a temperature of between 100 to 210 °C, preferably between 130 - 160 °C. The pressure of the third steam stream may be 0-19 bar g preferably between 1-4 bar g. Preferably, the third steam stream may have close to the same temperature as second H₂O-rich stream, such as a temperature difference of no more than 10 °C. The third steam stream may have a lower pressure than the second H₂O-rich stream. In this way, the energy transfer to the second H₂O-rich stream preferably results in a phase transition of water to steam. The third steam stream is fed to the liquid phase (i.e., the water phase) of combined vessel. In this way, the steam may travel through the liquid phase of the steam drum and any water drops remaining within the first/second/third steam streams maybe trapped in the liquid phase. Embodiments are also provided where the system arrangement allows for the steam drum and the heat exchanger to be arranged as two different units such as in different sections (i.e., physical locations) within the system.

In other specific embodiments, said conversion section comprises a first heat exchanger and/or a second heat exchanger, and further comprises a steam drum, said first heat exchanger and/or said second heat exchanger being arranged within said steam drum, and wherein: the steam drum is arranged to receive at least a portion of the first H₂O-rich feed stream, and provide an SOEC steam feed stream; wherein said first heat exchanger and/or said second heat exchanger are arranged to vaporize liquid water in said steam drum to steam by means of heat from at least one of the carbon monoxide-rich stream and of the first oxygen enriched stream.

Within said embodiments, the steam drum comprises a combined vessel such that the combined vessel receives at least a portion of the first H₂O-rich feed stream, where said portion is in thermal communication with at least a portion of at least one of i) the carbon monoxide-rich stream and of ii) the first oxygen enriched stream. More specifically, the combined vessel may comprise at a first and/or a second heat exchanger such as a heating coil, wherein said heat exchangers are arranged within the liquid phase (i.e., the water phase) of the combined vessel. At least one of the carbon monoxide-rich stream and of the first oxygen enriched stream from the first SOEC section is/are arranged to pass through the heat exchangers such that heat i.e. excess energy may be transferred from the at least one of the carbon monoxide-rich stream and of the first oxygen enriched stream to said liquid phase. It follows that, at least a portion of the heat present in excess after electrolysis of CO₂ to CO is transferred to the liquid phase (i.e., the water phase) of the combined vessels leading to vaporization of water, which enables the combined vessel to provide an SOEC steam feed stream. In one preferred embodiment, the first H₂O-rich feed stream may have a temperature of between 0 to 210 °C, such as a temperature between 30 and 130 °C. In this way, the first H₂O-rich feed stream may be a water-rich feed. The pressure of the first H₂O- rich feed stream may be 1-20 bar g, preferably 2-5 bar g. In other specific embodiments, said conversion section comprises a first heat exchanger and/or a second heat exchanger, and further comprises a steam drum wherein the steam drum comprises a third heat exchanger, and wherein the steam drum is arranged to receive at least a portion of the first H₂O-rich feed stream, and provide an SOEC steam feed stream; said first heat exchanger being arranged to receive heat from the carbon monoxiderich stream and provide heat to said third heat exchanger; said second heat exchanger being arranged to receive heat from the first oxygen enriched stream and provide heat to said third heat exchanger; wherein the third heat exchanger is arranged to vaporize liquid water in said steam drum to steam, by means of the heat provided by the first heat exchanger and/or said second heat exchanger.

The first H₂O-rich feed stream may have a temperature of between 0 to 200 °C, preferably the first H₂O-rich feed stream is a water-rich feed stream and with a temperature between 30 and 130 °C. The pressure of the first H₂O-rich feed stream may be 1-20 bar g preferably 2-5 bar g. In this embodiment, the steam drum further comprises a third heat exchanger. An intermediate heat media stream is arranged as a closed loop connecting the first and/or second heat exchanger with the third heat exchanger. In embodiments, the intermediate heat media stream comprises a boiler feed water loop. Specifically, the first and/or second heat exchanger is arranged to receive a first intermediate heat media stream from the steam drum, wherein said first intermediate stream is rich in liquid heat media such as comprises more than 50% liquid heat media. The heat exchangers are arranged to receive heat from at least one of the carbon monoxide-rich stream and of the first oxygen enriched stream and provide a second intermediate heat media steam, preferably wherein said second intermediate stream is a heated heat media steam. The third heat exchanger is arranged to receive the second intermediate heat media steam. The third heat exchanger is arranged within the liquid phase (i.e., the water phase) of the combined vessel and is thus arranged to vaporize liquid water in said steam drum to steam such that the steam drum is arranged to provide an SOEC steam feed stream. In this way, at least a portion of the heat present in excess after electrolysis of CO₂ to CO is transferred to the liquid phase (i.e. the water phase) of the combined vessels leading to vaporization of water. Hence, embodiments are provided where the system arrangement allows for the steam drum and the first and/or second heat exchanger to be arranged as two different units such as in different sections (i.e. physical locations) within the system, however being in thermal communication through the intermediate heat media loop. Within all embodiments, the provided SOEC steam feed stream is suitable for H₂O electrolysis. In a specifically preferred embodiment, the temperature of the SOEC steam feed stream is between 100 - 210 °C, preferably 130 - 160 °C and the pressure of the SOEC steam feed stream is between 1-4 bar g. The SOEC steam feed stream is of very high purity steam, such as 99% H₂O, 99.5% H₂O, 99.9% H₂O or 99.95% H₂O. In this way, the SOEC steam feed stream is suitable for being used as a steam stream for electrolytic production of a hydrogen stream.

Within all embodiments, said system may further comprise a fourth heat exchanger being located within said stream drum, wherein said fourth heat exchanger is arranged to vaporize liquid water in said steam drum to steam by means of heat from at least one of the hydrogen-rich stream and of the second oxygen-enriched stream.

In this way, embodiments are provided wherein the system further comprises a fourth heat exchanger arranged within said steam drum. The fourth heat exchanger is arranged to receive at least one of the hydrogen-rich stream and a second oxygen-enriched stream from the second SEOC section and provide at least one of a cooled hydrogen-rich stream and a cooled second oxygen-enriched stream. Providing a cooled carbon monoxide-rich stream and a cooled hydrogen-rich stream may eliminate or reduce the need of a separate cooling systems or allow the capacity of such cooling systems to be reduced.

Production of a hydrogen (H₂) stream

The system comprises a second solid oxide electrolysis (SOEC) section. The second SOEC section is arranged to receive at least a portion of the SOEC steam feed stream and electrolyse it to a hydrogen-rich stream and a second oxygen-enriched stream.

The second SOEC section comprises a solid oxide electrolysis cell (SOEC) such as a SOEC stack. This SOEC uses the solid oxide or ceramic electrolyte to produce the hydrogen-rich stream. More specifically, the SOEC steam feed stream is led to the fuel side of the cell with an applied current and excess oxygen is transported to the oxygen side of the cell (e.g. anode side), such to electrolyse H₂O to hydrogen. Optionally, a flushing gas stream such as air or nitrogen is led to the oxygen side to flush the oxygen side. This leads to the second SOEC section providing a hydrogen-rich stream from the fuel side of the cell and a second oxygen-enriched stream from the oxygen side of the cell. The hydrogen-rich stream provided by the second SOEC comprises H₂ and steam, wherein the content of H₂ is between 20- 100%, preferably 40-80%. In embodiments, the system further comprises an external steam feed arranged to be fed to the second solid oxide electrolysis (SOEC) section. The external steam feed may be provided from a water treatment system such being of high purity such as 99.99% H₂O. The external steam feed may have a temperature of 100-210 °C, preferably 130-160 °C and a pressure of 1-19 bar g, preferably 1-4 bar g at the inlet of the SOEC. Alternatively, the external steam feed may be mixed with the SOEC steam feed stream before being fed as a feed to the second SOEC section.

In embodiments, the system further comprises one or more heating unit(s) arranged to heat the external steam feed and/or optionally the flush gas stream. Preferably, the operation temperature of the one or more heating unit(s) is/are at least the operation temperature of the second SOEC section plus 50 °C, preferably at least the operation temperature of the second SOEC section. In this way, heat may be supplied to the SOEC.

In embodiments, the external steam feed may be arranged to be heated by means of excess heat from downstream processes. In this way, the system may further comprise or alternatively to one or more heating unit(s) comprise means for thermal communication between the external steam feed and streams from downstream processes. The downstream processes may provide excess heat to the external steam feed through both indirect and direct fluid communication.

In preferred embodiments, the second solid oxide electrolysis (SOEC) section operates in the temperature range of 500-900 °C, preferably 700-800 °C. In embodiments, the system further comprises one or more heating unit(s) arranged to provide additional heat to the second SOEC during operation. The one or more heating unit(s) may comprise feed effluent exchangers and/or electrical heaters.

Production of the synthesis gas stream

At least a portion of the hydrogen-rich stream and/or at least a portion of a cooled hydrogenrich stream is arranged to be mixed with at least a portion of the cooled carbon monoxiderich stream and/or at least a portion of the carbon monoxide-rich stream, to provide a synthesis gas stream.

In preferred embodiments, the system is arranged to provide a synthesis gas stream comprising at least a portion of the cooled hydrogen-rich stream and a least a portion of the cooled carbon monoxide-rich stream. In embodiments, said system further comprises a cooling system arranged to further cool at least one of iii) the cooled carbon monoxide-rich stream and/or iv) the hydrogen-rich stream, preferably prior to said streams being mixed to provide a synthesis gas stream.

The synthesis gas stream may have a temperature of 0-100 °C, preferably 20-50 °C. In embodiments, the cooling system may comprise cooling water, hence the temperature of the synthesis gas stream may depend on the temperature of the cooling water temperature, wherein a low temperature of the cooling water is preferred.

The preferred pressure of the synthesis gas stream may depend on the synthesis gas stream application e.g. whether it is used for production of alcohols such as methanol, or for production of hydrocarbons such as synthetic fuels, or alternatively for production of substitute natural gas (SNG) such as of methane. Suitably, the pressure of the synthesis gas stream may range between 10-90 bar. Typically, for methanol synthesis the pressure is 80- 90 bar g, for Fischer Tropsch the pressure is 20-45 bar g and for methanation the pressure is 10-50 bar g. The system may further comprise a compressor stage, such comprising at least one compressor system for compressing the synthesis gas stream to reach the preferred pressure of said synthesis gas. In systems where the synthesis gas is arranged to be compressed, the temperature of the compressed synthesis gas at the outlet of the last compression stage is typically 120-150°C.The preferred composition i.e. ratio of CO, H₂ and CO₂ of the synthesis gas stream also depends on the synthesis gas stream application. Compositions may be defined by the molar ratio H₂/CO₂ within the synthesis gas, by the module(M) defined as M = (H₂-CO₂)/(CO+CO₂) or by H₂/CO molar ratio. The preferred modules of the synthesis gas stream for specific applications are known in the art.

Production plant

A further aspect of the invention relates to chemical plants comprising the system described herein such as to i) a synthetic alcohol plant such as a methanol plant or ii) a synthetic hydrocarbon plant. In this way, the synthesis gas may be further converted to synthetic alcohols such as methanol or higher alcohol(s), or to synthetic hydrocarbons such as synthetic fuels (e.g., jet fuel and/or kerosene and/or gasoline), or to substitute natural gas (SNG) such as methane.

A synthetic alcohol plant, comprising the system as described herein is therefore provided, said synthetic alcohol plant further comprising an alcohol synthesis section, said alcohol synthesis section being arranged to receive the synthesis gas stream and output an alcohol- rich stream. In a preferred embodiment, the synthetic alcohol plant is a methanol plant, thus, the synthetic alcohol synthesis section may be a methanol synthesis section. The methanol synthesis section may be arranged to receive the synthesis gas stream and output a raw methanol-rich stream. The raw methanol-rich stream may optionally be arranged to be fed to one or more purification sections, where the raw methanol-rich stream is purified to a product methanol stream. Typically, the raw methanol-rich stream comprises 90% methanol whereas the product (i.e. purified) methanol stream may comprise above 99% methanol, such as above 99.9% methanol.

In alternative preferred embodiments, the synthetic alcohol plant is a higher alcohol production plant, thus, the synthetic alcohols synthesis section may be a higher alcohol synthesis section. The higher alcohol synthesis section may be arranged to receive the synthesis gas stream and output a raw higher alcohol-rich stream. The raw alcohol stream may optionally be arranged to be fed to one or more purification sections, where the raw alcohol stream is purified to a higher alcohol product stream.

A synthetic hydrocarbon plant, comprising the system as described herein is also provided, said hydrocarbon plant further comprising a hydrocarbon synthesis section, said hydrocarbon synthesis section being arranged to receive the synthesis gas stream and output a hydrocarbon-rich stream.

In a preferred embodiment, the hydrocarbon synthesis section comprises a Fischer-Tropsch synthesis section. Hence, the Fischer-Tropsch synthesis section may be arranged to receive the synthesis gas stream and output a hydrocarbon-rich stream. In embodiments, Fischer- Tropsch synthesis section may provide a hydrocarbon-rich steam wherein the major product is jet fuel and/or kerosene (e.g. comprising primarily C12-C15 hydrocarbons) and/or diesel (e.g. comprising primarily C15-C20 hydrocarbons). In this way the hydrocarbon plant may provide a synthetic fuel product stream. In embodiments, naphta (e.g. comprising primarily C₅- C12 hydrocarbons) and liquified petroleum gas (e.g. comprising primarily C₃-C₄ hydrocarbons) are also produced.

In another preferred embodiment, the hydrocarbon synthesis section comprises a natural gas synthesis section. In this way, natural gas synthesis section may be arranged to receive the synthesis gas stream and output a renewable natural gas stream. In embodiments, the renewable natural gas stream is a methane-rich stream such comprising more than 80% methane, such as more than 90% methane, such as more than 97% methane. Process for production of a synthesis gas stream

In a fourth aspect, a process is provided for production of a synthesis gas stream in the system described herein, said process comprising the steps of: providing a carbon dioxide-rich feed stream and a first H₂O-rich feed stream; feeding the carbon dioxide-rich feed stream to a first solid oxide electrolysis (SOEC) section and electrolysing it to provide a carbon monoxide-rich stream and a first oxygen enriched stream; providing the first H₂O-rich feed stream and at least one of: i) at least a portion of the carbon monoxide-rich stream, and ii) at least a portion of the first oxygen enriched stream, to the conversion section and outputting an SOEC steam feed stream, and at least one of: iii) a cooled carbon monoxide-rich stream and iv) a cooled first oxygen enriched stream; from said conversion section; via heat transfer; feeding at least a portion of the SOEC steam feed stream to a second solid oxide electrolysis (SOEC) section and electrolysing it to provide a hydrogen-rich stream and a second oxygen-enriched stream; mixing at least a portion of the hydrogen-rich stream with at least a portion of the cooled carbon monoxide-rich stream and/or at least a portion of the carbon monoxide-rich stream, to provide a synthesis gas stream.

In embodiments, wherein the conversion section comprises a first heat exchanger and/or a second heat exchanger, said process further comprises: transferring heat from at least a portion of the carbon monoxide-rich stream to at least a portion of the first H₂O-rich feed stream in said first heat exchanger so as to output a first steam stream and a cooled carbon monoxide-rich stream; and/or transferring heat from at least a portion of the first oxygen enriched stream to at least a portion of the first H₂O-rich feed stream in said second heat exchanger so as to output a second steam stream and a cooled first oxygen enriched stream;

Optionally combining first and second steam streams into a third steam stream; and

In preferred embodiments, said conversion section further comprises a steam drum and said process further comprises providing an SOEC steam stream from said steam drum. In one preferred embodiment, the conversion section further comprises a first heat exchanger and/or a second heat exchanger, and further comprises a steam drum, and said process further comprises, feeding at least a portion of the first H₂O-rich feed stream to the steam drum so as to provide a second H₂O-rich stream and an SOEC steam feed stream from the steam drum; feeding at least a portion of the second H₂O-rich stream to the first heat exchanger and transferring heat from at least a portion of the carbon monoxide-rich stream to at least a portion of the second H₂O-rich stream in said first heat exchanger, so as to output a first steam stream and a cooled carbon monoxide-rich stream; and/or feeding at least a portion of the second H₂O-rich stream to the second heat exchanger and transferring heat from at least a portion of the first oxygen enriched stream to at least a portion of the second H₂O-rich stream in said second heat exchanger, so as to output a second steam stream and a cooled first oxygen enriched stream, followed by; feeding at least a portion of the first steam stream and/or at least a portion of said second steam stream to the steam drum, optionally as a combined third steam stream.

In one embodiment, the conversion section further comprises a first heat exchanger and/or a second heat exchanger, and further comprises a steam drum, wherein first heat exchanger and/or said second heat exchanger, is/are arranged within said steam drum and wherein said process further comprises: feeding at least a portion of the first H₂O-rich feed stream to the steam drum and providing an SOEC steam stream from the steam drum; vaporizing liquid water in the first heat exchanger and/or said second heat exchanger within said steam drum, to steam by means of heat from at least one of the carbon monoxide-rich stream and of the first oxygen enriched stream.

In embodiments, the step of vaporizing liquid water to steam by means of heat from at least one of the carbon monoxide-rich stream and of the first oxygen enriched stream, may alternatively be allowed through indirect thermal communication via a closed intermediate heat media loop. In this way, embodiments are provided, wherein the conversion section further comprises a first heat exchanger and/or a second heat exchanger, and further comprises a steam drum, wherein said steam drum comprises a third heat exchanger, wherein said process further comprises: feeding at least a portion of the first H₂O-rich feed stream to the steam drum and providing an SOEC steam feed stream from the steam drum; transferring heat from the carbon monoxide-rich stream in the first heat exchanger, and providing said heat to the third heat exchanger; and/or transferring heat from the first oxygen enriched stream to the second heat exchanger, and providing said heat to the third heat exchanger; vaporizing liquid water in said steam drum to steam in said third heat exchanger by means of the heat provided by the first heat exchanger and/or said second heat exchanger.

Independent of the specific arrangement of the first/second heat exchanger and the steam drum, said system may further comprise a fourth heat exchanger being located within the steam drum, and said process further comprises vaporizing liquid water in said steam drum to steam by means of heat supplied to the fourth heat exchanger from at least one of the hydrogen-rich stream and of the second oxygen-enriched stream.

To achieve optimal hydrogen production in the second solid oxide electrolysis (SOEC) section, the system may further comprise an external steam feed, and said process may further comprise feeding the external steam feed to the second solid oxide electrolysis (SOEC) section.

In embodiments, the process further comprises that the temperature of at least one of i) at least a portion of the carbon monoxide-rich stream and/or ii) at least a portion of the first oxygen enriched stream is/are in the range of 500-200 °C and the pressure of at least one of i) at least a portion of the carbon monoxide-rich stream and/or ii) at least a portion of the first oxygen enriched stream is/are in the range of 0-3 bar g.

In embodiments, the process further comprises that the first solid oxide electrolysis (SOEC) section operates in the temperature range of 500-900 °C, preferably 700-800 °C.

In embodiments, the process further comprises that the second solid oxide electrolysis (SOEC) section operates in the temperature range of 500-900 °C, preferably 700-800 °C.

In some embodiments, the process further comprises heating the carbon dioxide-rich feed stream by means of a heating unit and/or additionally/alternatively by means of heat from downstream processes, so as to supply heat to the SOEC, wherein the operation temperature of said heating unit is at least the operation temperature of the first SOEC section plus 50 °C, preferably at least the operation temperature of the first SOEC section. Additionally or alternatively, the process further comprises heating the optional flushing gas stream by means of a heating unit and/or additionally/alternatively by means of heat from downstream processes, so as to supply heat to the SOEC section, wherein the operation temperature of said heating unit is at least the operation temperature of the first SOEC section plus 50 °C, preferably at least the operation temperature of the first SOEC section.

In some embodiment, the process further comprises heating the optional external steam feed and/or the optional flushing gas stream provided to the second SOEC section by means of a heating unit or additionally/alternatively by means of heat from downstream processes so as to supply heat to the second SOEC section, wherein the operation temperature of said heating unit is at least the operation temperature of the second SOEC section plus 50 °C, preferably at least the operation temperature of the second SOEC section.

The process may further comprise heating the first SOEC section and/or the second SOEC section during operation by means of one or more heating unit(s).

In embodiments, the process further comprises that the temperature of the SOEC steam feed stream is between 100 - 210 °C, preferably 130 - 160 °C and wherein the pressure of the SOEC steam feed stream is between 1-4 bar g.

In embodiments, wherein the system further comprises a cooling system, said process further comprises a step of cooling at least one of the cooled carbon monoxide-rich stream and/or the hydrogen-rich stream, preferably prior to said streams are arranged to be mixed to provide a synthesis gas stream.

In embodiments, wherein the system further comprises a compressor system, said process further comprises a step of compressing the synthesis gas stream to provide a compressed synthesis gas stream.

Specific embodiments

In a first specific embodiment, illustrated in Figure 1, the system (100) provides for production of a synthesis gas stream (101). A first solid oxide electrolysis (SOEC) section (10) receives a carbon dioxide-rich feed stream (1) and electrolyses it to a carbon monoxiderich stream (11) and a first oxygen enriched stream (12). At least one of i) at least a portion of the carbon monoxide-rich stream (11), and ii) at least a portion of the first oxygen enriched stream (12), is in thermal communication in conversion section (30) with at least a portion of a first H₂O-rich feed stream (2) so as to provide an SOEC steam stream (52) and at least one of iii) a cooled carbon monoxide-rich stream (31) and iv) a cooled first oxygen enriched stream (32). A second SOEC section (20) receives at least a portion of the SOEC steam feed stream (52) and electrolyses it to a hydrogen-rich stream (21) and a second oxygen-enriched stream (22). A portion of the hydrogen-rich stream (21) is mixed with at least a portion of the cooled carbon monoxide-rich stream (31) and/or at least a portion of the carbon monoxide-rich stream (11a), to provide a synthesis gas stream (101). The system of this specific embodiment further comprises an optional external steam feed (3) arranged to be fed to the second solid oxide electrolysis (SOEC) section (20). In this way, the external steam feed (3) constitutes an additional steam feed in addition to the SOEC steam feed stream (52). This external steam feed may be used in connection with any of the enclosed embodiments.

In a second embodiment, illustrated in Figure 2, the conversion section (30) comprises: a first heat exchanger (40) arranged to transfer heat from at least a portion of the carbon monoxide-rich stream (11) to at least a portion of the first H₂O-rich feed stream (2), so as to output a first steam stream (40A) and a cooled carbon monoxide-rich stream (31); and a second heat exchanger (45) arranged to transfer heat from at least a portion of the first oxygen enriched stream (12) to at least a portion of the first H₂O-rich feed stream (2) so as to output a second steam stream (45A) and a cooled first oxygen enriched stream (32). In Figure 2, the first steam stream (40A) and the second steam stream (45A) are arranged to be output from the conversion section (30) as said SOEC steam feed stream (52).

In a third embodiment, illustrated in Figure 3, the first H₂O-rich feed stream (2) is provided to the steam drum (50). The first H₂O-rich feed stream (2) may have a temperature of between 0 to 200 °C, preferably between 30 and 130 °C and a pressure of 1-20 bar g, preferably between 2-5 bar g. The steam drum (50) provides a second H₂O-rich stream (51), which is fed to the first heat exchangers(s) (40). The second H₂O-rich stream (51) may be water-rich and may have a temperature of between 0 to 200 °C, preferably between 30 and 130 °C, more preferably at or near its boiling point and at a pressure of 1-20 bar g, preferably 2-5 bar g. The first and/or second heat exchanger(s) (40, 45) allows for heat transfer from at least one of the carbon monoxide-rich stream (11)/ first oxygen enriched stream (12) to the second H₂O-rich stream (51) thus to provide the third steam stream (42). In embodiments, the third steam stream (42) may be rich in steam and have a temperature of between 100 to 210 °C, preferably between 130 - 160 °C and a pressure of between 0-19 bar g, preferably between 1-4 bar g. Preferably the temperature difference between the second H₂O-rich stream (51) and the third steam stream (42) is no more than 10 °C, preferably less than 2 °C. The third steam stream (42) is fed to the steam drum (50) and the steam drum (50) provides the SOEC steam feed stream (52) to the second SOEC section (20). In a fourth specific embodiment, illustrated in Figure 4, the first H₂O-rich feed stream (2) is provided to the steam drum (50) which makes up the conversion unit (30) in this embodiment. The first heat exchanger (40) and the second heat exchanger (45) are arranged within said steam drum (50). The steam drum (50) is arranged to receive at least a portion of the first H₂O-rich feed stream (2) and to provide an SOEC steam feed stream (52). The first heat exchanger (40) and the second heat exchanger (45) are arranged to vaporize liquid water in said steam drum (50) to steam by means of heat from at least one of the carbon monoxide-rich stream (11) and of the first oxygen enriched stream (12).

In a fifth specific embodiment, illustrated in Figure 5, the conversion section (30) comprises a third heat exchanger (55) arranged within the steam drum and an intermediate closed heat media loop (53, 43), wherein the loop comprises an intermediate heat media stream (53) circulating from first and second heat exchangers (40, 45) to the third heat exchanger (55) and a second intermediate heat media stream (43) circulating from the third heat exchanger (55) to the first and second heat exchangers (40, 45). The intermediate closed heat media loop (53,43) is arranged to connect the first (40) and second (45) heat exchangers with the third (55) heat exchanger(s). Hence, the closed loop (53, 43) provides indirect thermal communication with both at least a portion of the first H₂O-rich feed stream (2) and with at least one of i) the carbon monoxide-rich stream (11) and ii) the first oxygen enriched stream (12) from the first SOEC section (10). Specifically, the first heat exchanger (40) is arranged to receive heat from the carbon monoxide-rich stream (11) and provide heat to said third heat exchanger (55) and the second heat exchanger (45) is arranged to receive heat from the first oxygen enriched stream (12) and provide heat to said third heat exchanger (55). The third heat exchanger (55) is arranged to vaporize liquid water in said steam drum to steam, by means of the heat provided by the first heat exchanger (40) and/or said second heat exchanger (45). The first intermediate heat media stream (53) may be a boiler feed water stream rich in water and have a temperature of between 0 to 200 °C, and a pressure of 1-20 bar g such as preferably of 2-5 bar g. The heat exchangers (40, 45) allow for heat transfer such to provide a heated second intermediate heat media stream (43) and at least one of iii) a cooled carbon monoxide-rich stream (31) and iv) a cooled first oxygen enriched stream (32). The heated second intermediate heat media stream (43) may have a temperature of above 30 to 130 °C and a pressure of 1-4 bar g. Alternatively, the first intermediate heat media stream (53) may be a boiler feed steam stream rich in steam and have a temperature of between 100 to 210 °C, and a pressure of 0-19 bar g such as preferably of 1-4 bar g and the second intermediate heat media stream (43) may be a boiler feed steam stream rich in steam and have a temperature of above 100 to 210 °C, and a pressure of 0-19 bar g such as preferably of 1-4 bar g. The steam drum (50) comprising the third heat exchanger (55) receives the heated second intermediate heat media stream (43) and the first H₂O-rich feed stream (2). The intermediate heat media (43) is arranged to circulate between the third heat exchanger (55), such as a heating coil, and the first and/or second heat exchangers (40, 43)where the third heat exchanger (55) is arranged within the liquid phase (i.e. water phase) within said steam drum (50). The third heat exchanger (55) allows for heat transfer from the heated second boiler feed stream (43) to at least a portion of the first H₂O-rich feed stream (2) such to provide the SOEC steam feed stream (52) to the second SEOC section (20).

In a further embodiment, illustrated in Figure 6, in addition to any one of the described specific embodiments comprising a steam drum, the conversion section (30) comprises a fourth heat exchanger (56), being located within said stream drum (50). The fourth heat exchanger (56) is arranged to vaporize liquid water in said steam drum (50) to steam by means of heat from at least one of the hydrogen-rich stream (21) and the second oxygen- enriched stream (22).

EXAMPLE 1

Case of producing low pressure steam for steam electrolysis.

In the set-up where CO₂ electrolysis is run as a parallel line to steam electrolysis for producing a syngas product, excess heat from the CO₂ rich stream and the oxygen rich stream leaving the CO₂ electrolysis is utilised for low pressure (0-5 barg) steam production. If the temperature of the CO rich stream is 210°C and the temperature of the enriched oxygen stream is 400°C, the temperature can be brought down to 155°C by producing low pressure steam at 2.5barg. In this case 0.1kWh/Nm3 CO product can be harvested, which can be used as steam input to the steam electrolysis line.

In addition, harvesting the excess heat for steam production reduces cooling water circulation needed for the CO₂ electrolysis unit by 33%.

Claims

1. A system (100) for production of a synthesis gas stream (101), said system (100) comprising : a carbon dioxide-rich feed stream (1); a first H₂O-rich feed stream (2); a first solid oxide electrolysis (SOEC) section (10); a second solid oxide electrolysis (SOEC) section (20); a conversion section (30); wherein the first SOEC section (10) is arranged to receive the carbon dioxide-rich feed stream (1) and electrolyse it to a carbon monoxide-rich stream (11) and a first oxygen enriched stream (12); wherein the conversion section (30) is arranged to receive the first H₂O-rich feed stream (2) and at least one of: i) at least a portion of the carbon monoxide-rich stream (11), and ii) at least a portion of the first oxygen enriched stream (12), and to output an SOEC steam feed stream (52), and at least one of: iii) a cooled carbon monoxide-rich stream (31) and iv) a cooled first oxygen enriched stream (32); wherein the second SOEC section (20) is arranged to receive at least a portion of the SOEC steam feed stream (52) from the conversion section (30) and electrolyse it to a hydrogen-rich stream (21) and a second oxygen-enriched stream (22); and wherein at least a portion of the hydrogen-rich stream (21) is arranged to be mixed with at least a portion of the cooled carbon monoxide-rich stream (31) and/or at least a portion of the carbon monoxide-rich stream (11a), to provide a synthesis gas stream (101).

2. The system according to any one of the preceding claims, wherein said conversion section (30) comprises: a first heat exchanger (40) arranged to transfer heat from at least a portion of the carbon monoxide-rich stream (11) to at least a portion of the first H₂O-rich feed stream (2), so as to output a first steam stream (40A) and a cooled carbon monoxide-rich stream (31); and/or a second heat exchanger (45) arranged to transfer heat from at least a portion of the first oxygen enriched stream (12) to at least a portion of the first H₂O-rich feed stream (2) so as to output a second steam stream (45A) and a cooled first oxygen enriched stream (32), preferably, wherein at least a portion of said first steam stream (40A) and/or at least a portion of said second steam stream (45A) are arranged to be output from the conversion section (30) as said SOEC steam feed stream (52).

3. The system according to any one of the preceding claims, wherein said conversion section (30) comprises a first heat exchanger (40) and/or a second heat exchanger (45), and further comprises a steam drum (50), wherein the steam drum (50) is arranged to receive at least a portion of the first H₂O-rich feed stream (2), and provide a second H₂O-rich stream (51) and an SOEC steam feed stream (52); wherein the first heat exchanger (40) is arranged to transfer heat from at least a portion of the carbon monoxide-rich stream (11) to at least a portion of the second H₂O-rich stream (51), so as to output a first steam stream (40A) and a cooled carbon monoxide-rich stream (31); and/or wherein the second heat exchanger (45) is arranged to transfer heat from at least a portion of the first oxygen enriched stream (12) to at least a portion of the second H₂O-rich stream (51) so as to output a second steam stream (45A) and a cooled first oxygen enriched stream (32), wherein at least a portion of said first steam stream (40A) and/or at least a portion of said second steam stream (45A) are arranged to be fed to the steam drum (50).

4. The system according to any one of claims 1-2, wherein said conversion section (30) comprises a first heat exchanger (40) and/or a second heat exchanger (45), and further comprises a steam drum (50), said first heat exchanger (40) and/or said second heat exchanger (45) being arranged within said steam drum (50), and wherein the steam drum (50) is arranged to receive at least a portion of the first H₂O-rich feed stream (2), and provide an SOEC steam feed stream (52); wherein said first heat exchanger (40) and/or said second heat exchanger (45) are arranged to vaporize liquid water in said steam drum (50) to steam by means of heat from at least one of the carbon monoxide-rich stream (11) and of the first oxygen enriched stream (12).

5. The system according any one of claims 1-3, wherein said conversion section (30) comprises a first heat exchanger (40) and/or a second heat exchanger (45), and further comprises a steam drum (50), wherein the steam drum (50) comprises a third heat exchanger (55), and wherein the steam drum (50) is arranged to receive at least a portion of the first H₂O-rich feed stream (2), and provide an SOEC steam feed stream (52); said first heat exchanger (40) being arranged to receive heat from the carbon monoxide-rich stream (11) and provide heat to said third heat exchanger (55); said second heat exchanger (45) being arranged to receive heat from the first oxygen enriched stream (12) and provide heat to said third heat exchanger (55); wherein the third heat exchanger (55) is arranged to vaporize liquid water in said steam drum to steam, by means of the heat provided by the first heat exchanger (40) and/or said second heat exchanger (45).

6. The system according to any one of claims 3-5, wherein said conversion section (30) comprises a fourth heat exchanger (56), being located within said stream drum (50), said fourth heat exchanger (56) being arranged to vaporize liquid water in said steam drum (50) to steam by means of heat from at least one of the hydrogen-rich stream (21) and the second oxygen-enriched stream (22).

7. The system according to any one of the preceding claims, wherein the system further comprises an external steam feed (3) arranged to be fed to the second solid oxide electrolysis (SOEC) section (20).

8. A synthetic alcohol plant, comprising the system according to any one of claims 1-7, said synthetic alcohol plant further comprising an alcohol synthesis section, said alcohol synthesis section being arranged to receive the synthesis gas stream (101) and output an alcohol-rich stream.

9. A synthetic hydrocarbon plant, comprising the system according to any one of claims 1-7, said hydrocarbon plant further comprising a hydrocarbon synthesis section, said hydrocarbon synthesis section being arranged to receive the synthesis gas stream (101) and output a hydrocarbon-rich stream.

10. A process for production of a synthesis gas stream (101) in the system (100) according to any one of claims 1-7, said process comprising the steps of: providing a carbon dioxide-rich feed stream (1) and a first H₂O-rich feed stream (2); feeding the carbon dioxide-rich feed stream (1) to a first solid oxide electrolysis (SOEC) section (10) and electrolysing it to provide a carbon monoxide-rich stream (11) and a first oxygen enriched stream (12); providing the first H₂O-rich feed stream (2) and at least one of: i) at least a portion of the carbon monoxide-rich stream (11), and ii) at least a portion of the first oxygen enriched stream (12), to the conversion section (30) and outputting an SOEC steam feed stream (52), and at least one of: iii) a cooled carbon monoxide-rich stream (31) and iv) iv) a cooled first oxygen enriched stream (32); from said conversion section (30); feeding at least a portion of the SOEC steam feed stream (52) to a second solid oxide electrolysis (SOEC) section (20) and electrolysing it to provide a hydrogen-rich stream (21) and a second oxygen-enriched stream (22); mixing at least a portion of the hydrogen-rich stream (21) with at least a portion of the cooled carbon monoxide-rich stream (31) and/or at least a portion of the carbon monoxide-rich stream (11), to provide a synthesis gas stream (101).

11. The process according to claim 10, wherein the conversion section (30) comprises a first heat exchanger (40) and/or a second heat exchanger (45), wherein said process further comprises: transferring heat from at least a portion of the carbon monoxide-rich stream (11) to at least a portion of the first H₂O-rich feed stream (2) in said first heat exchanger (40) so as to output a first steam stream (40A) and a cooled carbon monoxide-rich stream (31); and/or transferring heat from at least a portion of the first oxygen enriched stream (12) to at least a portion of the first H₂O-rich feed stream (2) in said second heat exchanger (40) so as to output a second steam stream (45A) and a cooled first oxygen enriched stream (32).

12. The process according to any one of claims 10-11, wherein the conversion section

(30) further comprises a first heat exchanger (40) and/or a second heat exchanger (45), and further comprises a steam drum (50), wherein said process further comprises: feeding at least a portion of the first H₂O-rich feed stream (2) to the steam drum (50) so as to provide a second H₂O-rich stream (51) and an SOEC steam feed stream (52) from the steam drum (50); feeding at least a portion of the second H₂O-rich stream (51) to the first heat exchanger (40) and transferring heat from at least a portion of the carbon monoxiderich stream (11) to at least a portion of the first H₂O-rich stream (51) in said first heat exchanger (40), so as to output a first steam stream (40A) and a cooled carbon monoxide-rich stream (31); and/or feeding at least another portion of the second H₂O-rich stream (51) to the second heat exchanger (45) and transferring heat from at least a portion of the first oxygen enriched stream (12) to at least a portion of the first H₂O-rich stream (51) in said second heat exchanger (45), so as to output a second steam stream (45A) and a cooled first oxygen enriched stream (32), followed by; feeding at least a portion of the first steam stream (40A) and/or at least a portion of said second steam stream (45A) to the steam drum (50).

13. The process according to any one of claims 10-12, wherein the conversion section (30) further comprises a first heat exchanger (40) and/or a second heat exchanger (45), and further comprises a steam drum (50), wherein first heat exchanger (40) and/or said second heat exchanger (45), is/are arranged within said steam drum (50) and wherein said process further comprises: feeding at least a portion of the first H₂O-rich feed stream (2) to the steam drum (50) and providing an SOEC steam feed stream (52) from the steam drum (50); vaporizing liquid water in the first heat exchanger (40) and/or said second heat exchanger (45) within said steam drum (50), to steam by means of heat from at least one of the carbon monoxide-rich stream (11) and of the first oxygen enriched stream (12).

14. The process according to any one of claims 10-12, wherein the conversion section (30) further comprises a first heat exchanger (40) and/or a second heat exchanger (45), and further comprises a steam drum (50), wherein said steam drum (50) comprises a third heat exchanger (55), wherein said process further comprises: feeding at least a portion of the first H₂O-rich feed stream (2) to the steam drum (50) and providing an SOEC steam feed stream (52) from the steam drum (50); transferring heat from the carbon monoxide-rich stream (11) in the first heat exchanger (40), and providing said heat to the third heat exchanger (55); and/or transferring heat from the first oxygen enriched stream (12) to the second heat exchanger (45), and providing said heat to the third heat exchanger (55); vaporizing liquid water in said steam drum (50) to steam in said third heat exchanger (55) by means of the heat provided by the first heat exchanger (40) and/or said second heat exchanger (45).

15. The process according to any one of claims 13-14, wherein said system further comprises a fourth heat exchanger (56) being located within said stream drum (50), wherein said process further comprises vaporizing liquid water in said steam drum (50) to steam by means of heat supplied to the fourth heat exchanger (56) from at least one of the hydrogenrich stream (21) and of the second oxygen-enriched stream (22).

16. The process according to any one of claim 10-15, wherein the system further comprises an external steam feed (3) and wherein said process further comprises feeding the external steam feed (3) to the second solid oxide electrolysis (SOEC) section (20).

17. The process according to any one of claims 10-16, wherein the temperature of at least one of i) at least a portion of the carbon monoxide-rich stream (11) and/or ii) at least a portion of the first oxygen enriched stream (12) is/are in the range of 500-200 °C and the pressure of at least one of i) at least a portion of the carbon monoxide-rich stream (11) and/or ii) at least a portion of the first oxygen enriched stream (12) is/are in the range of 0 - 3 bar g.

18. The process according to any one of claims 10-17, wherein the first solid oxide electrolysis (SOEC) section operates in the temperature range of 500-900 °C, preferably 700-800 °C.

19. The process according to any one of claims 10-18, wherein the second solid oxide electrolysis (SOEC) section operates in the temperature range of 500-900 °C, preferably 700-800 °C.

20. The process according to any one of claims 10-19, wherein the temperature of the SOEC steam feed stream (52) is between 100 - 210 °C, preferably 130 - 160 °C and wherein the pressure of the SOEC steam feed stream (52) is between 1-4 bar g.