DE102022118858A1 - Thermal cracking of methane or natural gas - Google Patents

Abstract

Process for producing hydrogen by thermal splitting of gaseous hydrocarbons at temperatures above 1000 ° C, at least one device for storing and / or releasing thermal energy being provided, characterized in that: - the hydrocarbon is brought to a predetermined temperature in the device (1 ) is preheated to store and/or release thermal energy, - the hydrocarbon or a product gas is heated in a high-temperature section, wherein - this further heating is brought about at least in part by supplying oxygen into the high-temperature section and a subsequent combustion of part of the hydrogen produced and/or the further heating is carried out at least partially by an electrically operated heating device, - the product gas is cooled, in particular in a second device (2) for storing and/or releasing thermal energy.

Description

The invention relates to a method and devices for thermal cracking of gaseous hydrocarbons and in particular of methane molecules in order to produce hydrogen as the main product and pure carbon as a by-product. In addition to methane from natural gas, bio-methane, for example from biogas, can also be used to transform in this way.

In thermal cracking, hydrocarbon fractions are heated under pressure to approximately 450 to 900 ° C (depending on the process). The long hydrocarbon molecules vibrate so strongly that the hydrocarbon chains break. Short-chain olefinic hydrocarbon molecules are formed.

The term “cracking” is used below

Methane cracking is a promising method under recent development and research. In this process, methane is broken down into its molecular components, namely hydrogen and pure carbon, at high temperatures. An important factor is that the reaction does not release any CO2 emissions because it takes place in the absence of oxygen.

The hydrogen produced serves as an energy source, while the carbon is available for commercial use, for example the production of carbon fibers. Alternatively, it can be readily stored for future use. It is known from current research that methane cracking is a viable process, and the applicant's new work results, which have not yet been published, show that this technology can be applied on an industrial scale.

In order to achieve thermal cracking, very high temperatures (e.g. 1500 ° C) and a long residence time (e.g. 1 second) are required, as explained in more detail below. At lower temperatures you have to extend the residence time, or at even higher temperatures you have to shorten it significantly.

The process according to the invention achieves a higher efficiency and a higher H ₂ yield than the previously known processes and at the same time leads to significantly lower investment costs by avoiding costly and technologically demanding components. Preferably, particularly depending on the type of heating or the type of heating, no climate-damaging CO2 is produced, or at least significantly less than, for example, with steam reforming processes.

State of the art

Hydrogen plays a crucial role in the energy transition, in Germany and worldwide. As a secondary energy source, hydrogen does not produce any climate-damaging gases when used. Unfortunately, however, the largest amount of hydrogen is currently produced through steam reforming of natural gas. This produces up to 13 kg of CO2 per kilogram of hydrogen produced. For this reason, this H ₂ is referred to as “gray” hydrogen.

Hydrogen from renewable energies is the right solution, but currently plays a very minor role, not least because of high costs. The best-known process is the electrolysis of water using electricity from renewable energy. There are various electrolysis processes with different efficiencies, so that 1 kg of H2 to over 60 kWh of electricity is required to produce it. Hydrogen produced in this way is called “green”. If the electricity comes from nuclear power, i.e. also CO2-neutral, the term “red” hydrogen is used.

Another option is to obtain hydrogen from biomass, usually via a gasification process. Other processes such as torrefaction, pyrolysis or fermentation are also possible, although with lower utilization of the input material. In principle, this is also “green” hydrogen, as no additional amounts of CO2 are produced. Unfortunately, also due to many mistakes in the recent past, biomass has a bad image, so that some authors describe the hydrogen obtained in this way as “orange”.

In order to produce larger quantities of hydrogen under acceptable cost conditions, attempts are being made to produce it again from fossil natural gas, but without CO2 emissions into the atmosphere. You can continue to use the well-known steam reforming processes, but with the CO2 being separated from the exhaust gases and deposited in underground caverns. This process is also controversial, especially since there is no long-term experience with so-called CCS (Carbon Capture and Storage) technologies. Hydrogen obtained in this way is called “blue”.

Another possibility is the splitting or cracking of the methane molecule, the main component of natural gas. This creates hydrogen and pure solid carbon, according to the equation: CH ₄ → 2H ₂ + C

The necessary heat of reaction for the endothermic reaction is 74.9 kJ/mol. The storage or use of solid carbon is much simpler and more attractive, which speaks in favor of such processes. Hydrogen produced in this way is called “turquoise”.

Processes with catalytic cleavage enable a significantly lower temperature (see Schneider et al., Overview of the process for producing hydrogen through natural gas pyrolysis, Chemie Ingenieur Technik, 92, No. 8, 2020 ).

The first development has been discontinued because the reactivation of the catalyst incurs high costs and carbon dioxide is released into the atmosphere.

There are also several developments that use plasma splitting. The Kvaerner company has tested such a process (see above, as well as the patent specification DE 692 08 686.2 ) and development stopped in 2003 due to inadequate quality of the thermal soot. There are several other developments using plasma processes, some up to TRL 8, which have significantly lower electrical energy requirements compared to electrolysis. However, all of these processes require significantly higher amounts of energy than the theoretical heat of reaction for methane splitting.

There are several processes for the thermal cracking of methane, or hydrocarbons in general. Some use the externally or internally obtained carbon as a catalyst to accelerate the fission reaction or to reduce the reaction temperature somewhat, such as in the patent specification US 6,670,058 B2 described. There, a lot of the inlet gas is burned with air and this energy is used to preheat the carbon particles to high temperatures. The carbon particles preheated in this way are fed to a reactor to enable the endothermic reaction.

In the patent specification WO 2013/004398 A2 A process is described in which the splitting takes place in a reaction space in the presence of carbon-containing granules. The necessary heat is obtained again by burning a tail gas in an external combustion chamber and introduced into the reaction chamber by overheating part of the product gas (hydrogen) in an external heat exchanger.

An advantageous overheating temperature in the range 1100°C to 1400°C has been mentioned, but without explaining the means by which such overheating can be implemented. According to the state of the art, the maximum temperatures for certain heat exchangers such as recuperative heat exchangers are in a range slightly above 900°C, which means that anything above 1000°C is currently not possible, which affects the degree of implementation and the quality of the product (hydrogen and /or carbon) has a significant negative impact.

The patent specification EP 3 521 241 A1 describes a process for the thermal/catalytic cracking of methane in a metal bath made of tin. The bath is thermally heated to 900°C-1200°C and the methane enters through a structure with nozzles under the bath. Bubbles of methane form which split into H2 and C due to high temperatures and long residence times. A layer of carbon forms on the upper surface of the bath, which constantly grows over time and therefore has to be removed periodically. According to the information in the patent, the electricity consumption is 7.5 kWh/kg H ₂ and is therefore significantly lower than with water electrolysis, but still 30% above the theoretical energy requirement for the endothermic reaction. It is also stated that the conversion rate of methane is only 58.6%, which is due to the too low temperature of 1100 ° C. It is not shown or discussed how the construction and material selection of the thermal heaters are made. Furthermore, it is not described how the waste heat should be handled at temperatures above 1100°C and how this influences the energy balance or the efficiency of the system.

In another article about these procedures ( Geißler T. et al., Hydrogen production via methane pyrolysis in a liquid metal bubble column reactor with a packed bed, Chemical Engineering Journal 299 (2016) 192-200 ) an H ₂ yield of up to 78% is reported at a bath temperature of 1175°C. It is shown there that the electrical energy is used to maintain the temperature of the tin bath. There are also no better values for the H ₂ yield in the current web presentation of the project (https://www.kit.edu/kit/pi_2019_wasserstoff-aus-erdgas-ohne-co2-missions.php).

Aim of the invention

The present invention is therefore based on the object of providing a device and a method which enable cracking of gaseous hydrocarbons and in particular methane. In addition, the efficiency of the production of hydrogen should be increased.

The present invention also has the task of providing a method and a device for the splitting of gaseous hydrocarbons, such as methane, in which the investment costs are lower and the efficiency is higher than in the prior art. The hydrogen produced in this way is significantly cheaper, when you also take into account the costs for landfilling or storing carbon dioxide.

Another task is to use significantly less energy for fission than competing processes. At the same time, the investment costs should be significantly reduced by avoiding technically sophisticated and expensive components, such as plasma torches and recuperative high-temperature heat exchangers, as well as by using more compact and cost-effective components.

This task is described with a method and a device according to the independent patent claims. Further design variants that provide advantages and improvements to the basic design are specified in the corresponding subclaims.

The process described here is particularly suitable for the use of methane or natural gas as an input material, but any gaseous hydrocarbons can also be used.

In a method according to the invention for producing hydrogen by thermally splitting gaseous hydrocarbons at temperatures above 1000 ° C, at least one heating device is provided for storing or releasing thermal energy.

According to the invention, the hydrocarbon is first heated and in particular preheated and in particular preheated to a predetermined reaction temperature in the said heating device.

In a further process step, the preheated hydrocarbon and/or in particular a product gas resulting from the hydrocarbon (in particular through cracking) is heated further or the hydrocarbon and/or the product gas resulting from the hydrocarbon is heated further and/or the product gas is heated again in particular in a reaction space and/or high-temperature section of the device.

This heating takes place at least partially by supplying (and in particular by injecting) oxygen into the high-temperature zone and preferably a subsequent combustion of part of the hydrogen produced and/or the further heating is effected by an electrically operated heating device.

The cracking process, which is an endothermic reaction, causes the product gases to cool down. These are preferably warmed up again, preferably after the deposition of carbon.

This reheating is particularly preferably carried out in order to be able to release heat again in the second device for storing heat, so that continuous operation can be guaranteed in this way.

Oxygen is preferably injected under a pressure that is between 2 bar and 200 bar.

In a further process step, the product gas is cooled, in particular in a second device for storing and/or releasing thermal energy.

Preferably, the heating device for storing and/or releasing thermal energy in the broadest sense is a heat exchanger, which interacts in particular with a fluid flowing through it, in particular a gas or steam, depending on the temperatures of this fluid and the heating device either thermal energy is released from the fluid to the heating device or, conversely, the heating device heats this fluid.

This heating device preferably has a supply device for supplying a fluid and also a discharge device for discharging the fluid, which here is in particular gaseous hydrocarbon or hydrogen mixtures.

A method is proposed in which two heating devices are provided, which in particular are operated alternately. One of the two heating devices is preferably used to preheat the gaseous hydrocarbons and the other heating device is used to cool the process gas, i.e. H. of hydrogen.

These two heating devices are preferably operated alternately, which means that when one of the heating devices heats the hydrocarbons, the second heating device simultaneously cools the resulting process gas. The advantage of this approach is that the corresponding heating The device itself is reheated to a certain extent by the process gas. In this way, a continuous process is possible by appropriately connecting valves.

The gaseous hydrocarbons are particularly preferably preheated to a temperature that is greater than 1000 ° C, preferably greater than 1500 ° C. The gaseous hydrocarbons are preferably preheated to a temperature that is less than 1800 ° C, preferably less than 1600 ° C.

The further heating and/or reheating of the process gas preferably takes place as mentioned above, either by an electrical heating device or by supplying oxygen and burning part of the hydrogen that has already been produced. It is also possible for this further heating to be achieved through several processes, for example both electrical heating and the supply of oxygen. It may be possible, for example, that at the beginning of a process the heating is primarily carried out electrically and in a further stage of the process the heating is continued predominantly by partial combustion of hydrogen.

Particular preference is therefore given to partly electrical heating and partly to heating by combustion, whereby these proportions can change during operation.

Particularly preferably, the carbon-containing gases in the high-temperature section are heated to a temperature that is greater than 1000° C., preferably greater than 1100° C., preferably greater than 1200° C., preferably greater than 1300° C., preferably greater than 1400° C. and preferably greater than 1500° C.

In a further preferred method, a residence time of the carbon-containing gases in the high-temperature section is greater than 0.1 s, preferably greater than 0.2 s, preferably greater than 0.3 s, preferably greater than 0.4 s and particularly preferably greater than 0 .5s.

In a further advantageous embodiment, a residence time of the gases in the high-temperature section is less than 40 s, preferably less than 30 s. preferably less than 20 s, preferably less than 15 s and particularly preferably less than 10 s and preferably less than 5 s and preferred less than 3 s.

These precisely defined residence times enable a particularly efficient splitting of the hydrocarbons to be achieved.

A residence time of the hydrocarbons in the high-temperature section is preferably controlled and in particular controlled as a function of at least one further process parameter. For example, you can control the flow (through the valves), but you can also design the system accordingly (e.g. by appropriately dimensioning the pipes) in order to achieve the desired residence time).

This control is preferably carried out by valve devices that are controlled accordingly. The further process parameter is preferably a temperature and in particular a temperature of the hydrocarbon gases in the high-temperature section and/or a temperature of the high-temperature section itself.

In a further preferred method, at least two devices for storing and/or releasing thermal energy are operated alternately.

Particularly preferably, at least one of these devices for storing and/or releasing thermal energy is so-called bulk material generators. These have a bulk material which is used for heat exchange with another medium, here the respective gases.

In a further preferred process, methane (CH ₄ ) is used as the gaseous hydrocarbon. It has been shown that methane is particularly well suited for the fission processes described here.

The gaseous hydrocarbons are particularly preferably heated to temperatures of over 1500 ° C and particularly preferably split at this temperature.

In a preferred process, the preheated gaseous hydrocarbons are conveyed to the high temperature section. This is preferably done with the help of pipelines and by appropriately controlling valves.

In a further preferred method, carbon is deposited and in particular carbon is deposited in the form of a fine powder. Carbon is particularly preferably deposited in a separation device which is arranged after and/or between the high-temperature tongues.

In a further preferred method, oxygen is supplied to the heated product, in particular after carbon has been removed, in particular in order to heat the product gas further and/or again, as mentioned above. This supply of oxygen particularly preferably takes place after the separation device described above.

In a further preferred method, a gas mixture, in particular a resulting gas mixture, is cooled and this cooling preferably takes place in order to separate water formed by the combustion from hydrogen. This cooling particularly preferably takes place in a condenser.

Cooling is particularly preferably carried out to a temperature that is less than 50°C, particularly advantageously less than 20°C. In particular, the gas mixture to be cooled is a mixture of hydrogen and water, more precisely of hydrogen and water vapor.

The present invention is further directed to a device for producing hydrogen by thermal splitting of gaseous hydrocarbons, which has at least two devices for storing and/or releasing thermal energy. Each of these two devices is suitable and intended both for preheating the gaseous hydrocarbons and for cooling a product gas resulting from the splitting, in particular hydrogen.

The two devices for storing and/or releasing thermal energy are preferably separated from one another and in particular spaced apart from one another.

Particularly preferably, the device has at least one high-temperature section, which can be brought into flow connection with each of the devices for storing and / or releasing thermal energy in such a way that a gaseous hydrocarbon preheated by this device is further heated and / or can be heated in this high-temperature section and /or a product gas entering this high-temperature section is reheated or can be reheated, the device having a heating device which causes the gaseous hydrocarbons to be heated in the high-temperature section.

As mentioned above, the storage devices can be so-called bulk material regenerators. The storage device preferably has a receiving space which is suitable and intended for receiving bulk material.

This high-temperature section is preferably arranged downstream of the heating device in a flow direction of the gaseous hydrocarbons. In a preferred embodiment, the device has at least two high-temperature sections. In a further preferred embodiment, the device has a high-temperature section which can be brought into flow connection with both heating devices.

Particularly preferably, the high-temperature section is suitable and intended for heating a gas and in particular the gaseous hydrocarbons to a temperature that is greater than 1000 ° C, preferably greater than 1100 ° C, preferably greater than 1200 ° C, preferably greater than 1300 ° C , preferably greater than 1400 ° C and particularly preferably greater than 1500 ° C.

The device particularly preferably has a separation device for separating carbon from the heated hydrocarbons or the carbon-hydrogen mixture, this separation device preferably being able to be brought into flow connection with a high-temperature section and preferably with two high-temperature sections.

In a preferred embodiment, it is possible for the separation device to be arranged downstream of at least one high-temperature section and preferably both high-temperature sections (in the flow direction of the gaseous hydrocarbons and/or the product gas). It is therefore possible for this separation device to be located essentially in the middle of a high-temperature section viewed in its entirety or of the two high-temperature sections.

The high-temperature section is preferably a section in which gaseous hydrocarbons are heated further, in particular after they have already been preheated and enter the high-temperature section.

In a further advantageous embodiment, the heating device has an electrically operated heating unit and/or the heating device has a supply line for supplying oxygen into the high-temperature section. In the second embodiment, part of the hydrogen can be burned with the help of this oxygen.

As described above, two approaches are proposed in this way to further heat the hydrocarbons and/or to reheat the product gas, namely on the one hand an electrical heating means and on the other hand the supply of oxygen, in particular in order to burn the hydrogen-oxygen mixture and in this way to generate further thermal energy or heat. Particularly preferably, the device has a control device which controls the operation of the device and which in particular causes the above-mentioned heating devices to be operated alternately.

This means that in a certain period of time one of the two heating devices preheats the gaseous hydrocarbons and then the product gas resulting from the cracking process is further heated and during this period the second device cools the resulting process gas, in particular hydrogen. Continuous operation can also be achieved in this way.

In a further period of time, the other of the two heating devices preheats the gaseous hydrocarbons and then these preheated hydrocarbons are heated further and/or the resulting product gas is heated again and in this further period of time the second device cools the resulting process gas, in particular hydrogen. Continuous operation can also be achieved in this way.

In a preferred embodiment, the high-temperature section is designed such that a residence time of the gaseous hydrocarbons in this section is greater than 0.1 s, preferably greater than 0.2 s, preferably greater than 0.3 s, preferably greater than 0.4 s and preferably greater than 0.5 seconds.

Particularly preferably, said section is designed such that a residence time of the gaseous hydrocarbons in this section is less than 60 s, preferably less than 50 s, preferably less than 40 s, preferably less than 30 s, preferably less than 20 s, preferably less than 10 s, preferably less than 8 s, preferably less than 6 s, preferably less than 5 s, preferably less than 4 s and preferably less than 3 s.

In a further advantageous embodiment, at least one high-temperature section is designed as a line and in particular a pipeline.

The pipeline is preferably made of a material which is selected from a group of materials which contains mulite, or even better, pure alumina.

In a further advantageous embodiment, the separating device has a receiving space filled with a bulk material and in particular with a ceramic bulk material. In this way, the separation device can also work in such a way that the gas to be cleaned flows through this separation device and in this way carbon is separated or separated.

In a further advantageous embodiment, the separating device has deflection means which cause incoming gas to change its flow direction at least once and preferably several times as it flows through the bulk material.

These deflection means can be formed by the bulk material itself.

Carbon is also created through the thermal splitting of methane or other gaseous hydrocarbons. Hydrogen obtained in this way is significantly cheaper than obtaining it through electrolysis. If the carbon is not used as fuel, this hydrogen is just as environmentally friendly and climate-neutral as the H ₂ produced through the use of renewable energies. It is also suggested that instead of splitting fossil hydrocarbons, carbon from biomass should be used in order to achieve negative CO ₂ emissions.

• - durch Sauerstoff-Eindüsung und Nachverbrennung von einer kleinen Menge Wasserstoffs und/oder anderer Spaltungsprodukte, und/oder
• - durch die elektrische Heizung, mit Hochtemperatur-Heizelemente die bevorzugt direkt im Hochtemperaturzone platziert sind.

In a further process according to the invention, the energy necessary to reach the reaction temperature (eg 1500 ° C) is already stored inside a reactor and further used to superheat the gas. The heat of reaction is also generated inside the reactor, in particular directly in a high-temperature zone. There are two main ways to generate this heat:

• - by oxygen injection and afterburning of a small amount of hydrogen and/or other fission products, and/or
• - through the electric heating, with high-temperature heating elements which are preferably placed directly in the high-temperature zone.

In this way, energy consumption is only reduced to a physically necessary amount, despite the very high temperatures in the reaction zone.

Preferably, one storage device is used to store the high-temperature heat and preferably at least two storage devices are used to superheat the inlet gas and to cool the product gas. This is preferably a regenerator and particularly preferably a bulk material regenerator.

This bulk material regenerator particularly preferably has a heat storage mass made of bulk material, which is arranged within a container and which is particularly preferably arranged within two mutually coaxial cylindrical grates, as in the patent specification DE 42 36 619 C2 and EP 0 620 909 B1 is described. The disclosure content of these two patent specifications is hereby incorporated in its entirety by reference into the present disclosure.

The inner of these two grates preferably surrounds a hot collecting space for the hot gases. A circumferential wall is preferably arranged around the outer cylindrical grate and particularly preferably a collecting space for cold gases is provided between the outer cylindrical grate and this wall.

In a further preferred embodiment, axially and/or vertically flowing beds are provided, which are particularly advantageous for smaller systems.

The heat storage mass particularly preferably has a spherical bed, which can exist even at very high temperatures. Various ceramic or natural materials are preferred; the balls made of aluminum are particularly advantageous, as they can be used up to 1700°C and still have a very good price/performance ratio.

In a further preferred method, the grain size of the bulk material is smaller than 30mm, preferably smaller than 25mm, preferably smaller than 20mm and particularly preferably smaller than 15mm. The grain size of the bulk material is preferably larger than 0.5 mm, preferably larger than 2 mm.

The reaction temperatures in the connecting pipe between two devices for storing and releasing thermal energy are preferably above 1000 ° C, particularly advantageously above 1500 ° C. The length and diameter of the connecting tube is selected so that the reaction volume ensures a predetermined residence time corresponding to the reaction temperature. For a temperature of 1500°C, the residence time should be at least 1 second. For even higher temperatures a shorter residence time is possible and vice versa; for lower temperatures the residence time should be significantly longer. This allows sufficient time for the methane to be completely split. In a test system for 2 to 4 m ³ _N /h CH4, an H2 yield of more than 94% was already achieved.

Between the two devices for storing and releasing thermal energy, a connecting pipe - in a further preferred method, a device for carbon separation - is particularly preferably arranged approximately in the middle. It is particularly advantageous to fill this device with ceramic bulk material, e.g. alumina.

Hydrogen-containing gas, which contains soot particles, will change its flow direction, preferably several times, and in the process most of the carbon will be separated. This preferably forms a filter cake, which then filters the carbon even more effectively. This device is preferably emptied continuously or periodically after a certain time.

Replacing this bed with deposited carbon dust preferably prevents a large accumulation from occurring and thus avoids excessive pressure loss.

The process can lead to a deposition of carbon, which cannot be removed 100%. A smaller amount of carbon can collect in the higher areas of the beds in the devices for storing and releasing thermal energy. In a preferred method, this bed is also periodically circulated and/or recirculated in order to remove the deposited soot, so that a large accumulation of carbon is prevented.

These accumulations of carbon on beds and in the carbon separation device preferably simultaneously serve as a catalyst for the fission reactions. Therefore, in a preferred process, this carbon removal should not be too intensive. It is advantageous to always leave a small amount of soot in the system.

In a further preferred embodiment, the device for separating carbon has a partition wall which divides at least part of an interior space of the device into two subspaces. The partition wall is preferably designed in such a way, or ends inside the device, in such a way that the two subspaces below the partition wall are connected to one another.

The device preferably has a first feed device in order to feed bulk material to the device for separating carbon. The device preferably has a second feed device in order to feed bulk material to the device for removing carbon.

Preferably, the first feed device and the second feed device can be operated separately from one another. The first feed device and the second feed device are preferably separated from one another.

Preferably, the first feed device opens into a first subspace of the device for deposition of carbon and the second feed device opens into a first subspace of the device for deposition of carbon.

The device preferably has a first removal device in order to remove bulk material from the device for separating carbon. The device preferably has a second removal device in order to remove bulk material from the device for separating carbon.

The first removal device and the second removal device can preferably be operated separately from one another. The first removal device and the second removal device are preferably separated from one another.

Preferably, at least one feed device and/or at least one discharge device and preferably several and preferably all feed devices and discharge devices have a valve device which controls a flow of bulk material.

In a further preferred method, oxygen is first blown in after the device for the carbon particles to generate the used reaction heat, so that the afterburning preferably takes place almost exclusively with part of the hydrogen produced, or so that no CO or CO2 is produced.

In a further preferred method it is provided that the necessary reaction heat is generated by electrical energy instead of with the oxygen or in addition to the oxygen. The corresponding high-temperature heating elements are preferably arranged in the reaction space from at least one side and preferably from both sides of the device for carbon deposition.

In a further advantageous process, a condenser is used to remove the water vapor contained in the product gas, which contains a lot of hydrogen. This water vapor is created by the oxidation of hydrogen, especially if oxygen is used to generate the heat of the reaction. The condensate from the condenser also contains a small amount of soot particles and can preferably be used to pelletize the soot from the system. If you don't need this water after filtering, it can be drained away.

The hydrogen produced can contain other very fine carbon particles. For this reason, a fine particle filter is advantageously provided after the system. If you need a very pure hydrogen, e.g. B. for use in fuel cells or carbon fibers, a PSA or membrane technology system can also be provided to completely remove any gases that may be present, such as methane, CO, CO2 or H2O.

• 1 eine schematische Darstellung des Verfahrens mit Erzeugung der notwendigen Reaktionswärme im Inneren des Reaktionsraums durch Sauerstoff-Eindüsung, gemäß der Erfindung.
• 2 ein Verfahrensschema gemäß der Erfindung, wobei die notwendige Reaktionswärme durch elektrische Heizung in Inneren des Reaktionsraum erzeugt wird.
• 3 zeigt eine vorteilhafte Ausführung der Vorrichtung für die Abscheidung von Kohlenstoff.

The patent application is described in detail with reference to the description and the 1 until 3 described. Show in it:

• 1 a schematic representation of the process with generation of the necessary reaction heat inside the reaction space by oxygen injection, according to the invention.
• 2 a process scheme according to the invention, wherein the necessary reaction heat is generated by electrical heating inside the reaction space.
• 3 shows an advantageous embodiment of the device for the separation of carbon.

According to the in the 1 and 2 In the illustrations shown in the present invention to split the methane into hydrogen and carbon, at least two devices 1, 2 are used alternately for storing and releasing thermal energy, with the gaseous hydrocarbons and in particular the methane flowing through one device and the hydrogen obtained flowing through the second device.

The switching elements that cause the flow direction to change through the system are also shown. These are valves 12, 11, 21 and 22. In 1 The closed valves are shown in black and the open valves are shown without black filling. This means that the in 1 In the situation shown, the device 1 is used to heat or preheat methane and the device 2 is used to cool the resulting product gas, in particular a mixture of hydrogen and water.

The reference numbers 31, 32, 33 and 34 identify measuring devices which measure the states of the hydrocarbons. The measuring devices 31 and 32 can be temperature measuring devices which measure a temperature of the hydrocarbons in the device 1 and the device 2, and the measuring devices 33 and 34 can be pressure measuring devices.

The reference number 36 and the reference number 35 each identify a temperature measuring device for determining a temperature of the hydrocarbons in a high-temperature section 4.

1 shows a process diagram and the arrangement of the devices, with the methane (or another gaseous hydrocarbon) passing through the opened valve 11 into the first device 1 as an example. There the methane heats from the inlet temperature (e.g. 20°C) to the reaction temperature (e.g. 1500°C) by the heat that was stored in the previous cycle.

The preheated methane enters a high-temperature connecting pipe 4 between devices 1 and 2.

A very intensive methane splitting occurs there and there is a corresponding drop in temperature. In the high-temperature connecting pipe 4 after the carbon separator 5 in the flow direction, the temperature rises again because of the oxygen injection and the oxidation of part of the previously formed hydrogen.

Because of the very high temperatures, intensive fission begins immediately and hydrogen and carbon are formed. In the middle of line 4, between devices 1 and 2, there is an additional device 5 for removing the resulting carbon. intended.

Gas flowing after the device 5 in the direction of the device 2 contains practically no carbon, only the fine soot particles. Because of the endothermic cracking reaction, the temperature of the gas drops significantly. In order to compensate for these temperature losses, the oxygen is injected through line 7. This oxygen usually reacts with hydrogen since the splitting of methane is practically complete, and the temperature of the gas rises again.

The control valve 71 is used to ensure that the same reaction temperature prevails again at the entry into the device 2. The mass flow of the gas mixture H2+H2O is lower than that of methane at the plant inlet due to the separation of carbon. The outlet temperature at valve 22 and through line 8 is approx. 5 to 200K higher.

In order to condense water vapor and remove the condensate, a condenser 9 and/or a drainage 101 is preferably provided. The almost pure hydrogen emerges through line 100. If a level of purity as required for the fuel cell is desired, the remaining soot particles are preferably removed in an optional downstream particle filter.

In addition, an optional separation system (PSA or membrane technology) is provided to remove any gases such as CH ₄ , CO, CO ₂ or H ₂ O that may still be present.

After a predetermined time interval, the switching elements 11, 12, 21 and 22 change their position and the gas flows from device 2 towards device 1. The control valve 71 closes and the oxygen is injected through line 6 and the control valve 61.

2 shows an alternative in which the used reaction heat is introduced into the system not through hydrogen combustion with the injected oxygen, but through electrical energy. As in the previous case, the methane (or another gaseous hydrocarbon) enters the first device 1 through the opened valve 11.

There the methane heats up from the inlet temperature (e.g. 20°C) to the reaction temperature (e.g. 1500°C) by the heat that was stored in the previous cycle. The preheated methane enters a high-temperature connecting pipe 4 between devices 1 and 2. Because of very high temperatures, intensive fission begins immediately and hydrogen and carbon are formed.

In the middle of line 4, between devices 1 and 2, there is again an additional device 5 for removing the resulting carbon. Gas that flows into the device 2 after the device 5 contains practically no carbon anymore, only the fine soot particles. Because of the endothermic cracking reaction, the temperature of the gas is significantly reduced. In order to compensate for these temperature losses, the gas is heated with an electric heater 81 after device 1 and further with an electric heater 82 before device 2.

The performance of these heaters is controlled by the corresponding temperature measurements, so that a practically constant reaction temperature (eg 1500 ° C) is obtained throughout the entire tube 4. The stokers 81 and 82 are preferably integrated directly into the gas pipe.

No water vapor or carbon oxides are produced, which is very beneficial for the further process. The disadvantage is that the mass flow of the gas (in this case only H2), due to the deposition of carbon, is even lower than that of methane at the plant.

The outlet temperature at valve 22 and through line 8 increases by more than approx. 5 to 200K. Here, the steam condenser and drainage are preferably omitted. The pure hydrogen exits through line 100.

If the level of purity required for the fuel cell is desired, the remaining soot particles can be removed in a downstream particle filter. After a specified time interval, the switching elements 11, 12, 21 and 22 change their position and the gas flows from device 2 into device 1.

Instead of just using two bulk material regenerators 1 and 2, you can use 3 or more bulk material regenerators to achieve particularly uniform operation and to integrate a flushing phase during the switchover.

3 shows a device 5 for the separation of the carbon particles that arrive through the high-temperature line 4, mixed with the hydrogen. The device 5 is filled with a - preferably ceramic - bulk material 55.

The reference numeral 50 denotes a receiving space formed inside the device for receiving the bulk material. The reference number 57 refers to a partition which divides the receiving space of the device into two sub-spaces in an upper area.

The fill protrudes slightly beyond the lower end of the partition 57. In this way, the incoming gas is forced to flow through the two halves of the bulk material space.

The carbon particles settle, most of them immediately on the surface of the rubble, where they form a so-called filter cake 56. The filter cake 56 intensifies further deposition of the carbon particles and preferably acts catalytically for the further splitting of any methane molecules that may still be present.

The carbon particles form a very porous and permeable structure that creates little pressure loss. That's why even with the reverse flow direction, from bottom to top, the filter cake is not destroyed and most of the particles remain there.

If the layer of carbon particles 56 becomes very high, the separators 5 must be taught. To do this, it is preferable to open the bulk material valve (or lock) 52 until the entire left part becomes empty. Then the valve 52 is closed again and the upper valve 51 opens to let in the new amount of bulk material and to refill the left part.

This can be done while the system is operating, as the right half is still there and can act alone for separation for a short time. Slightly offset in time, the same procedures are also carried out with the right part of the separator by actuating valves 54 and 53.

The applicant reserves the right to claim all features disclosed in the application documents as essential to the invention, provided that they, individually or in combination, are new compared to the prior art. It should also be noted that the individual figures also describe features that can be advantageous in themselves. The person skilled in the art immediately recognizes that a specific feature described in a figure can be advantageous even without adopting further features from this figure. Furthermore, the person skilled in the art will recognize that advantages can also arise from a combination of several features shown in individual or different figures.

Reference symbol list

1

First facility for storing and releasing thermal energy

2

Second device for storing and releasing thermal energy

3

Possible third device for storing and releasing thermal energy

4

High temperature line

5

Carbon capture device

6

first pipe for the injection of oxygen

7

second pipe for the injection of oxygen

8th

Exit line

9

capacitor

11

Switching element at the entrance to the first device for storing and releasing thermal energy

12

Switching element at the outlet of the first device for storing and releasing thermal energy

21

Switching element at the entrance to the second device for storing and releasing thermal energy

22

Switching element at the outlet of the second device for storing and releasing thermal energy

51-54

Bulk material valve / lock

55

Bulk material in the carbon separator

56

deposited carbon particles

57

partition wall

61

first control valve for oxygen

62

second control valve for oxygen

81

first electric heater

82

second electric heater

83

first electrical control unit

84

second electrical control unit

100

Hydrogen outlet line

101

Condensate drainage

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 69208686 [0015]
• US 6670058 B2 [0016]
• WO 2013/004398 A2 [0017]
• EP 3521241 A1 [0019]
• DE 4236619 C2 [0080]
• EP 0620909 B1 [0080]

Non-patent literature cited

• Schneider et al., Overview of the process for producing hydrogen through natural gas pyrolysis, Chemie Ingenieur Technik, 92, No. 8, 2020 [0013]
• Geißler T. et al., Hydrogen production via methane pyrolysis in a liquid metal bubble column reactor with a packed bed, Chemical Engineering Journal 299 (2016) 192-200 [0020]

Claims (15)

Process for producing hydrogen by thermally splitting gaseous hydrocarbons at temperatures above 1000 ° C, at least one device for storing and / or releasing thermal energy being provided, characterized in that: - the hydrocarbon is brought to a predetermined temperature in the device (1 ) is heated and/or preheated to store and/or release thermal energy, in particular to a reaction temperature, - the hydrocarbon and/or the product gas resulting from the carbon is heated in a high-temperature section, wherein - this further heating is at least partially achieved by supplying Oxygen is brought about in the high-temperature section and a subsequent combustion of part of the hydrogen produced and/or the further heating is carried out at least partially by an electrically operated heating device, - the product gas is cooled, in particular in a second device (2) for storage and/or delivery of thermal energy. Procedure according to Claim 1 , characterized in that a residence time of the gases and/or the gaseous hydrocarbons in the high-temperature section (4) is greater than 0.1s, preferably greater than 0.2s, preferably greater than 0.3s, preferably greater than 0.4s and especially preferably greater than 0.5s and/or a residence time of the gases in the high-temperature section (4) is less than 40s, preferably less than 30s, preferably less than 20s, preferably less than 15s and particularly preferably less than 10s. Method according to at least one of the preceding claims, characterized in that at least two devices for storing and/or releasing thermal energy are provided, which are preferably operated alternately. Method according to at least one of the preceding claims, characterized in that methane is used as the gaseous hydrocarbon. Method according to at least one of the preceding claims, characterized in that the gaseous hydrocarbons are split at temperatures above 1500°C. Method according to at least one of the preceding claims, characterized in that carbon is deposited. Procedure according to Claim 1 , characterized in that the oxygen is supplied and/or the product gas is heated after the carbon has been removed, in particular in a separator (5). Procedure according to Claim 1 , characterized in that a gas mixture, in particular a resulting gas mixture, is cooled in order to separate the water formed by the combustion from hydrogen, this cooling preferably taking place in a condenser (9). Device for producing hydrogen by, in particular, thermal splitting of gaseous hydrocarbons with at least two devices (1, 2) for storing and/or releasing thermal energy, each of the two devices (1, 2) being used both for preheating the gaseous hydrocarbons is suitable and intended for cooling a product gas formed during the splitting, characterized in that the device has at least one high-temperature section (4) which is in flow connection with each of the devices (1, 2) for storing and/or releasing thermal energy It can be brought about that a gaseous hydrocarbon and/or a product gas preheated by this device (1, 2) is heated in this high-temperature section (4), the device having a heating device which causes the gaseous hydrocarbon to be heated in the high-temperature section (4). . Device according to Claim 9 , characterized in that the device has a separation device for separating carbon from the heated hydrocarbons, this separation device preferably being able to be brought into flow connection with the high-temperature section Device according to at least one of the preceding claims, characterized in that the device has at least two separate high-temperature sections, which preferably alternately further heat the gaseous hydrocarbons and/or the product gas. Device according to at least one of the preceding claims, characterized in that the heating device has an electrically operated heating unit and/or the heating device has a supply line for supplying oxygen into the high-temperature section. Device (1) according to at least one of the preceding claims, characterized in that the high-temperature section is designed such that a residence time of the gaseous hydrocarbons in this section is greater than 0.1s, preferably greater than 0.2s, preferably greater than 0.3s , preferably greater than 0.4s and particularly preferably greater than 0.5s and/or a residence time of the gases in the high temperature zone (4) is less than 40s, preferably less than 30s, preferably less than 20s, preferably less than 15s and particularly preferred less than 10s. Device (1) according to at least one of the preceding claims, characterized in that at least one high-temperature section is designed as a line and in particular as a pipeline. Device according to at least one of the preceding claims, characterized in that the separating device has a receiving space filled with a bulk material and in particular with a ceramic bulk material (55) and / or the separating device has deflection means which cause the inflowing gas to change its flow direction at least once and preferably several times changes when the bulk material flows through.

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