Method and device for burning mineral, carbonatic raw material and waste gas utilisation method and waste gas utilisation unit for same

Abstract

The invention relates to a waste gas utilisation unit (4) for the utilisation of CO2-containing waste gas, in particular a waste gas utilisation unit (4) for furnace waste gas from furnaces (2) for burning carbonatic raw material, preferably limestone and / or magnesite and / or dolomite and / or marl, comprising a methanation unit (26) for converting the CO2 contained in the waste gas into methane and water with the addition of hydrogen, a methane pyrolysis unit (27) for converting the methane generated in the methanation unit (26) into hydrogen and solid carbon, and means for conveying the hydrogen generated in the methane pyrolysis unit (27) into the methanation unit (26), as well as a corresponding waste gas utilisation method. The invention also relates to a device and a method for burning carbonatic, flowable raw material, preferably limestone and / or magnesite and / or dolomite and / or marl, with a waste gas utilisation unit of this type or a waste gas utilisation method of this type.

Description

[0001] Method and device for burning mineral, carbonate raw material as well as exhaust gas recycling method and exhaust gas recycling device therefor

[0002] The present invention relates to a method and a device for burning mineral, carbonate, granular, or bulk raw material or fuel, in particular rock, preferably for burning limestone and / or magnesite and / or dolomite to produce quicklime and / or caustic magnesia and / or sintered magnesia and / or doloma. Furthermore, the invention relates to an exhaust gas recycling method and an exhaust gas recycling device therefor.

[0003] Preferably, the invention relates to a lime burning process and a device with a lime kiln for producing quicklime.

[0004] The term firing refers to various thermal processes used in the production of materials and semi-finished products. The term firing is frequently used in the production of ceramic materials, powder metallurgy, and alcohol production. Firing involves the application of energy to achieve a chemical reaction or a transformation of the crystal structure of a material.

[0005] A granular material is known to be a bulk material. A bulk material is a dry mixture consisting of grains in a pourable form. If the grains are very fine, it is a powder or flour. In particular, flour has a grain size of < 400 pm. If the grains are also coarse, it is a lumpy (raw) material. In particular, a lumpy material also has grains with a grain size of > 5 mm.

[0006] Unless otherwise specified within the scope of the invention, the grain size is determined in particular according to DIN 66165-1:2016-08. For powdery material with a grain size < 400 pm, the grain size is determined by air jet sieve analysis. For lumpy raw material, the grain size can also be measured using a caliper for grain sizes > 50 mm.

[0007] In terms of its chemical composition, carbonate raw material consists predominantly (> 50 mass%), preferably > 70 mass%, particularly preferably > 80 mass%, and most preferably > 85 mass%, of the respective carbonate(s). A raw material that contains only carbonate impurities is not a carbonate raw material. The composition is determined in particular according to DIN EN 196-2:2013-10.

[0008] Quicklime, or burnt lime (calcined CaO), is produced by burning or calcining limestone (CaCO3) in a lime kiln. This process is known as lime burning. At temperatures above approximately 800 °C, calcium carbonate is deacidified, meaning carbon dioxide is expelled, and calcium oxide is formed:

[0009] CaCO3 CaO + CO2

[0010] In an analogous manner, doloma or caustic burnt dolomite or calcined dolomite (calcined CaO MgO) is produced by burning or calcining dolomite stone (CaMg(CO3)2).

[0011] Magnesia (caustic magnesia, caustic magnesia, caustic magnesia, and sintered magnesia) consists primarily of magnesium oxide (MgO). It is primarily produced by thermal decarbonation or deacidification of magnesite at temperatures of 600–800°C (caustic magnesia) or 1800–2200°C (sintered magnesia). Natural magnesium carbonate (MgCO3) is referred to as magnesite or raw magnesite. The deacidification process of magnesite begins at approximately 550–800°C, producing caustic magnesia. To obtain sintered magnesia, the caustic magnesia undergoes further thermal treatment in one or two phases at 1800–2200°C. Sintered magnesia can also be produced directly from raw magnesite in a single-stage firing process.

[0012] All of the combustion processes described above produce a large amount of CO2. The CO2 contained in the exhaust gas comes partly from the raw materials and partly from the combustion of fossil fuels. Thus, these combustion processes contribute significantly to global warming.

[0013] As a result, there are several approaches to utilizing and storing the CO2 contained in exhaust gases (see, for example, Dr. F. Ausfelder, Dr. A. Bazzanelle, DECHEMA eV, discussion paper "Utilization and Storage of CO2"). For example, the CO2 is separated from the exhaust gas. This is achieved, for example, by absorption or adsorption, Ca-based chemical looping using membranes, or by the oxyfuel process. In the oxyfuel process, in contrast to conventional combustion with air, the fuel is burned with pure oxygen (i.e., without nitrogen). In the ideal case of stoichiometric combustion of a pure hydrocarbon with oxygen, the only combustion products are CO2 and water. The CO2 content is around 80 vol.%. After condensation of the water, only pure CO2 remains. However, due to its high purity, this is only possible with the use of natural gas.

[0014] The EU-funded LEILAC 2 (Low Emissions Intensity Lime and Cement) project (https: / / cordis.europa.eu / project / id / 884170 / en) is testing a new technology that reengineers existing processes by directly heating limestone. This project builds on the successes of the Horizon 2020 LEILAC project (which succeeded in capturing 5% of the CO2 process emissions of an average cement factory) and plans to scale up its performance to approximately 20% of the CO2 process emissions of an average cement factory using a deployable and scalable module.

[0015] According to DE 10 2010 019 330 A1, when burning carbonates in the fuel mixture, technical oxygen or air enriched with technical oxygen is used as an oxidizing agent and the CO2-containing exhaust gas produced during combustion is at least partially returned to the fuel mixture as a diluent gas and / or introduced as a cooling gas into a cooling zone at the lower end of the calcining kiln.

[0016] EP 2 818 227 A1 discloses a method for operating a shaft kiln producing burnt lime, dolomite, magnesia or cement from carbonate-containing raw materials, in particular a method for operating a shaft kiln for producing burnt lime or cement, wherein the shaft kiln has at least one upper raw material inlet zone, at least one middle combustion zone and at least one lower combustion material outlet zone, characterized by the following measures: a) Combustion of a fuel mixture of a carbon-containing fuel, e.g. a fossil fuel, preferably methane or methanol, and industrially produced technical oxygen in the combustion zone of the shaft kiln and calcination of the carbonate-containing raw material in the combustion zone and above it, wherein carbon dioxide is additionally introduced into the combustion zone and / or the outlet zone of the shaft kiln, each as a substitute for the nitrogen-containing,atmospheric air, b) taking off an exhaust gas containing at least 60, in particular at least 80, preferably over 90 vol.% carbon dioxide, resulting from the combustion of the fuel, e.g. methane or methanol, with oxygen and the supplied carbon dioxide, at the inlet opening of the raw material inlet zone and introducing the exhaust gas into an exhaust gas storage device, wherein the carbon dioxide supplied according to feature a) was taken from the carbon dioxide-containing exhaust gas storage device, c) producing methane or methanol in a methanation or methanolation reactor from carbon dioxide supplied to the reactor from the exhaust gas storage device and hydrogen supplied to the reactor and introducing the methane or methanol into a methane or methanol storage device,d) Supplying a carbon-containing, e.g. fossil fuel and / or a known substitute fuel such as waste oil or animal meal to the combustion zone of the shaft furnace and / or preferably extracting methane or methanol from the methane or methanol storage facility and supplying the methane or methanol as fuel to the combustion zone of the shaft furnace, e) Optionally producing hydrogen and oxygen from water, preferably taken from the public water network, by electrolysis in an electrolysis plant powered by electricity taken from the public power grid and / or a plant's own power generation plant, and storing the hydrogen in a hydrogen storage facility and the oxygen in an oxygen storage facility,f) Supplying hydrogen to the methane or methanol reactor for carrying out the methanation or methanation, in particular by taking hydrogen from the hydrogen storage and / or using hydrogen obtained from third parties, g) Supplying oxygen to the combustion zone and / or the outlet zone of the shaft furnace, in particular by taking oxygen from the oxygen storage and / or using oxygen obtained from third parties.

[0017] The object of the present invention is to provide a method and a device for burning mineral, carbonate-containing or carbonate raw material or fuel, preferably for burning limestone and / or magnesite and / or dolomite for the sustainable production of quicklime and / or magnesia causter and / or sintered magnesia and / or doloma.

[0018] In addition, an efficient exhaust gas recycling process and an exhaust gas recycling device for CO2-containing exhaust gas are to be provided.

[0019] These objects are achieved by an exhaust gas utilization device according to claim 1, a use according to claim 9, an exhaust gas utilization method according to claim 10, a device according to claim 15 and a method according to claim 41. Advantageous developments of the invention are characterized in the subsequent subclaims.

[0020] The invention is explained in more detail below using a drawing as an example. The drawings show:

[0021] Figure 1: Schematic and highly simplified exhaust gas treatment according to the invention

[0022] Scoring facility

[0023] Figure 2: Schematic and highly simplified view of a kiln with exhaust gas recirculation

[0024] Figure 3: Schematic and highly simplified view of a kiln with exhaust gas recirculation according to another embodiment

[0025] Figure 4: Schematic and highly simplified view of a kiln with exhaust gas recirculation according to another embodiment

[0026] Figure 5: Schematic and highly simplified view of a kiln with exhaust gas recirculation according to another embodiment

[0027] Figure 6: Schematic and highly simplified view of a kiln according to a further embodiment. The device 1 according to the invention (Figures 1, 2) comprises a kiln 2, an exhaust gas recirculation device 3, an exhaust gas utilization device 4, a hot gas supply device 5 and a cooling gas supply device 6.

[0028] As already explained, the device 1 according to the invention is preferably used for producing quicklime and / or magnesia causter and / or sintered magnesia and / or doloma from mineral, carbonate raw material or firing material, preferably by firing limestone and / or magnesite and / or dolomite.

[0029] Preferably, the device 1 is used to produce quicklime. Consequently, the kiln 2 is preferably a lime kiln.

[0030] In addition, the kiln 2 according to a first embodiment of the invention (Fig. 2) is a single-chamber shaft kiln or normal shaft kiln 7 with a single vertical kiln shaft 7a.

[0031] The kiln 2, in particular the standard shaft kiln 7, has an upper kiln end 2a, at which the raw material to be fired is added, and a lower kiln end 2b, at which the fired, in particular calcined, material, preferably quicklime, is discharged from the kiln 2. The lower kiln end 2b is thus arranged downstream of the upper kiln end 2a in a vertical material transport direction 8.

[0032] The kiln 2, in particular the standard shaft kiln 7, also has, as seen in the material transport direction 8, a raw material lock 9, a preheating zone 10, a firing zone 11, a cooling zone 12, and a discharge lock 13 for removing the fired material, in particular the quicklime, from the kiln 2. The raw material lock 9 is thus arranged at the upper kiln end 2a, and the discharge lock 13 is arranged at the lower kiln end 2b.

[0033] In addition, the standard shaft furnace 7 has, in a conventional manner, a furnace interior or furnace combustion chamber 14 and a furnace shell 15 surrounding it. The furnace interior 14 is also sealed gas-tight in a conventional manner.

[0034] The raw material lock 9 serves, in a manner known per se, for the batchwise introduction of the raw material to be fired into the furnace shaft 7a. It is designed such that it can be sealed gas-tight, particularly after filling with the raw material.

[0035] The discharge lock 13 serves, in a conventional manner, for the batch-wise discharge of the fired material from the furnace shaft 7a. It is also designed to be gas-tight.

[0036] At the lower end of the furnace 2b, a relatively cool furnace process gas or cooling gas is also supplied. The cooling gas preferably has a temperature of -20 to 150°C, more preferably 5 to 80°C. In particular, the cooling gas is supplied at the lower end of the cooling zone 12.

[0037] And at the upper kiln end 2a, the kiln exhaust gas is discharged. The gas thus flows through the kiln 2 in a direction opposite to the material transport direction 8. The kiln 2 is thus operated according to the countercurrent principle.

[0038] Preferably, the kiln 2 is operated in a pure CO2 atmosphere. This means that the kiln process gas in the kiln interior 14 has a CO2 content of > 50 mass%, preferably > 75 mass%, more preferably > 80 mass%, particularly preferably > 90 mass%, and most preferably > 98 mass%.

[0039] Within the scope of the invention, the CO2 content of the gases is measured in a conventional manner using conventional measuring probes, preferably as part of a bypass measurement. This means that the measuring probe is arranged in a bypass.

[0040] Of course, the CO2 content in the furnace interior 14 does not have to be completely constant. However, it has the specified minimum CO2 content everywhere. This is ensured by ensuring that all furnace process gases introduced into the firing furnace 2 consist of > 50 mass%, preferably > 75 mass%, more preferably > 80 mass%, particularly preferably > 90 mass%, and most particularly preferably > 98 mass%, of CO2.

[0041] In particular, the introduced furnace process gases do not contain any oxygen.

[0042] Furthermore, it is preferably provided that no combustion of fuels takes place within the kiln 2 to generate the heat necessary for firing the raw material. During combustion, a substance reacts chemically with oxygen or (rarely) another gas.

[0043] No combustion within the kiln 2 or in the kiln interior 14 means that no combustion takes place in which the kiln process gases present in the kiln 2 or in the kiln interior 14 react or participate. In other words, no combustion takes place that influences the kiln atmosphere prevailing in the kiln interior 14. The kiln 2 therefore does not have a fuel heating system with a burner for directly heating the raw material.

[0044] However, combustion may optionally take place decoupled from the furnace atmosphere, e.g., in a chamber located within the furnace interior 14 but sealed gas-tight from the furnace interior 14. This results in indirect heating of the raw material.

[0045] For heat generation, electrical energy, preferably from green electricity, is used preferably, preferably exclusively.

[0046] According to a first embodiment of the invention (Fig. 2), the heat required for firing the raw material is introduced into the firing zone 11 by supplying hot gas. In particular, the hot gas is supplied at a hot gas inlet point 34 at the lower end of the firing zone 11. As already explained, the hot gas is furnace process gas with the previously stated high CO2 content. Furthermore, the hot gas preferably has a temperature of 800 to 1250°C, more preferably 900 to 1100°C. For this purpose, the hot gas is heated in a hot gas heating device 16 of the heating gas supply device 5, which will be discussed in more detail below.

[0047] Firing in kiln 2 is carried out as follows:

[0048] First, the pourable, lumpy raw material to be burned, preferably limestone, is filled into the raw material lock 9. The raw material preferably has a minimum grain size of >15 mm, preferably >30 mm, and / or a maximum grain size of <180 mm, preferably <120 mm.

[0049] Once the raw material lock 9 is filled, it is sealed gas-tight and purged with purge gas. As already explained, the purge gas is furnace process gas with the previously stated high CO2 content. Furthermore, the purge gas preferably has an overpressure of 200 to 1800 mbar, preferably 200 to 800 mbar. For this purpose, the device 1 preferably has a purge gas compression device 17. The purge gas compression device 17 is preferably a rotary piston blower or a screw compressor or a hybrid blower, i.e., a combination of the two aforementioned blowers.

[0050] In addition, the purge gas preferably comes from a process gas storage device 22 or from gas cylinders (not shown). However, it always has the previously stated high CO2 content.

[0051] The raw material lock 9 is purged with the purge gas until it is completely filled. The purge gas flow is then shut off, and the raw material lock 9 is opened to the furnace interior 14, allowing raw material to fall into the furnace interior 14, particularly into the preheating zone 10. The connection between the raw material lock 9 and the furnace interior 14 is, of course, gas-tight. Because the raw material lock 9 is filled with the purge gas, no ambient air enters the furnace interior 14. In the preheating zone 10, the raw material is preheated in a conventional manner by the gas coming from the firing zone 11, which flows through the preheating zone 10 in the opposite direction to the material transport direction 8. This gas contains, on the one hand, the supplied furnace process gases and, on the other hand, the gases produced during the firing of the raw material.

[0052] The raw material travels in countercurrent, namely in the material transport direction 8, through the preheating zone 10 and reaches the combustion zone 11.

[0053] In the combustion zone 11, the raw material is heated by the hot gas which flows through the raw material against the material transport direction 8 in such a way that it is burned, in particular deacidified.

[0054] When limestone, magnesite, and dolomite are burned, CO2 is the primary gas produced, as is well known. However, due to impurities in the raw material, other gases, particularly water vapor, can also be produced during burning.

[0055] The material travels in countercurrent, namely in the material transport direction 8, through the combustion zone 11 and reaches the cooling zone 12.

[0056] In the cooling zone 12, the fired material is cooled by the cooling gas, which flows through the fired material against the material transport direction 8.

[0057] From the cooling zone 12, the cooled, fired material finally reaches the discharge lock 13, which discharges the material from the kiln 2. Before the discharge lock 13 is opened, it is sealed gas-tight from the kiln interior 14 located above it to prevent ambient air from penetrating it.

[0058] After the fired material has been discharged, the discharge lock 13 is purged with purge gas, similar to the raw material lock 9, until it is completely filled. The purge gas flow is then shut off, and the discharge lock 13 is opened to the furnace interior 14. The connection between the discharge lock 13 and the furnace interior 14 is, of course, gas-tight.

[0059] As already explained, the kiln exhaust gas is also discharged from the kiln 2 at the upper kiln end 2a into the exhaust gas utilization device 4. The kiln exhaust gas preferably has a temperature of 20 to 250°C, more preferably 50 to 100°C. Furthermore, the kiln exhaust gas is discharged continuously or in batches, for example, when a certain overpressure, e.g., 600 mbar, is exceeded in the kiln interior 14. This is regulated in particular via a pressure sensor and a valve controlled based on the pressure sensor measurements.

[0060] Furthermore, the furnace exhaust gas preferably has a CO2 content of > 50 wt.%, preferably > 75 wt.%, preferably > 80 wt.%, particularly preferably > 90 wt.%, most particularly preferably > 98 wt.%.

[0061] The exhaust gas recirculation device 3 has, arranged downstream of one another, preferably a first dedusting device 18, preferably a dehumidifying device 19, preferably a second dedusting device 20, preferably an exhaust gas compression device 21 and the process gas storage device or exhaust gas storage device 22.

[0062] The first and second dust removal devices 18; 20 each serve to separate dust from the furnace exhaust gas.

[0063] Preferably, the first dust removal device 18 comprises one or more cyclones. Cyclones are also called centrifugal separators.

[0064] The second dust removal device 20 preferably has one or more filters, preferably filter bags. The dehumidification device 19 serves to separate water and other moist components from the furnace exhaust gas. It is preferably a condensate drain, preferably with a refrigeration dryer.

[0065] The exhaust gas compression device 21 serves to compress the furnace exhaust gas. Compression serves to compensate for pressure losses. Preferably, the exhaust gas compression device 21 comprises a screw compressor, a rotary piston blower, a hybrid blower, or a pneumatic dynamic pressure compressor.

[0066] The exhaust gas storage device 22 serves, in a conventional manner, to temporarily store the exhaust gas. The exhaust gas storage device 22 serves, in particular, as a system buffer. The exhaust gas is preferably stored at approximately 1 bar.

[0067] From the exhaust gas storage device 22, an exhaust gas flow is discharged into the hot gas supply device 5, an exhaust gas flow into the cooling gas supply device 6 and an exhaust gas flow into the exhaust gas utilization device 4.

[0068] The hot gas supply device 5 has a hot gas compression device 23 and the adjoining hot gas heating device 16.

[0069] The hot gas compression device 23 serves to compress the gas discharged from the exhaust gas storage device 22 to, in particular, 200 to 1800 mbar, preferably 200 to 800 mbar. The compression serves to convey the hot gas through the furnace interior 14 with sufficient pressure. The hot gas compression device 23 is preferably a screw compressor, a rotary piston blower, a hybrid blower, or a pneumatic dynamic pressure compressor.

[0070] Preferably, the kiln 2 is operated at overpressure. This also serves to maintain the CO2 atmosphere in the kiln interior 14. This prevents gases from outside from penetrating the kiln interior 14. The overpressure in the kiln interior 14 is preferably 50 to 1200 mbar, more preferably 200 to 800 mbar.

[0071] From the hot gas compression device 23, the gas then flows to the hot gas heating device 16.

[0072] The hot gas heating device 16 preferably has at least one electrically operated heater, preferably a resistance heater. In a resistance heater, heat is generated by passing current through a heating resistance element made of electrically conductive material, which heats it up due to Joule heating. The resistance heater therefore has at least one heating resistance element around which the gas to be heated flows, thereby heating it.

[0073] However, the hot gas heating device 16 can also alternatively or additionally comprise at least one heat exchanger. The heat exchanger comprises, in a conventional manner, one or more heat exchanger tubes through which a hot medium flows and around which the gas to be heated flows. According to one embodiment of the invention, combustion, preferably of natural gas or a fossil fuel, can take place in the heat exchanger tubes.

[0074] As already explained, the hot gas heating device 16 serves to heat the gas to a temperature high enough to fire the raw material or to the required firing temperature. The hot gas heating device 16 thus generates the hot gas, which is then introduced into the firing furnace 2 at the lower end of the firing zone 11.

[0075] The cooling gas supply device 6 has a cooling gas compression device 24 and a cooling gas cooling device 25 connected thereto.

[0076] The cooling gas compression device 24 serves to compress the gas discharged from the exhaust gas storage device 22 to, in particular, 200 to 1800 mbar, preferably 200 to 800 mbar. The compression serves to compensate for pressure losses. The cooling gas compression device 24 is preferably a screw compressor, a rotary piston blower, a hybrid blower, or a pneumatic dynamic pressure compressor.

[0077] From the cooling gas compression device 24, the gas then flows to the cooling gas cooling device 25. The cooling gas cooling device 25 serves to cool the compressed gas, in particular to between -20 and 150°C. For this purpose, the cooling gas cooling device 25 preferably has at least one heat exchanger. The cooling gas is thus provided by the cooling gas cooling device 25, which is then introduced into the kiln 2 at the lower end of the cooling zone 12.

[0078] The exhaust gas utilization device 4 according to the invention (Fig. 1) has a methanation device 26, a methane pyrolysis device 27 and optionally an electrolysis device 28 and optionally a gas cleaning device 29.

[0079] In addition, the exhaust gas utilization device 4 preferably has a high-pressure compressor 46, a high-pressure accumulator 47, and a pressure reducer 48 upstream of the methanation device 26. The pressure reducer serves to reduce the pressure precisely to the pressure required for the methanation device 26.

[0080] The gas purification device 29, which is arranged upstream of the methanation device 26, serves to purify the exhaust gas and, in particular, ensures that no oxygen enters the methanation device 26. It separates, in particular, the CO2 from the remaining components, in particular the oxygen, of the furnace exhaust gas. For this purpose, the gas purification device 29 preferably comprises at least one membrane filter in a conventional manner.

[0081] The methanation device 26 serves to convert CO2 into methane (CH4). Specifically, methane is produced from hydrogen and carbon dioxide according to the following equation: CO2 + 4H2 = CH4 + 2H2O

[0082] The methanation device 26 preferably comprises means for methanogenesis, or microbial methane formation, or biological methane formation. In methanogenesis, methane is formed through the metabolism of living organisms referred to as methanogens or methane producers. The methane producers are preferably archaea. Methanogenesis is carried out in a bioreactor using the methane producers, preferably archaea.

[0083] Consequently, the methanation device 26 preferably comprises at least one bioreactor containing archaea. The bioreactor is also preferably operated at overpressure, preferably at a pressure of 1 to 100 bar, particularly preferably 10 to 35 bar, and most particularly preferably 10 to 20 bar.

[0084] The methanation device 26 may also alternatively or additionally comprise means for technical or chemical methanation. In particular, the methanation device 26 comprises at least one membrane reactor for this purpose.

[0085] However, methanogenesis is preferred.

[0086] According to the invention, the hydrogen used for methanation comes at least partially from the methane pyrolysis unit 27. The methane pyrolysis unit 27 serves to convert the methane produced in the methanation unit 26 into hydrogen and solid carbon. In this case, it is referred to as "turquoise hydrogen." Methane pyrolysis requires heat energy, which can be generated with electricity. The power consumption is significantly lower than with electrolysis.

[0087] In particular, the methane is converted according to the following equation:

[0088] CH4= 2H2+ C Preferably, the methane pyrolysis device 27 comprises at least one liquid metal bubble column reactor filled with molten metal, preferably with molten tin.

[0089] In the liquid metal bubble column reactor, the methane gas is introduced at the bottom of the reactor and released there in the form of bubbles. Due to the density difference, the bubbles rise upwards and form a kind of micro-reactor chamber for the decomposition during pyrolysis. Due to the hot metal, the methane quickly reaches the required reaction temperature, so that decomposition occurs while the bubbles are still rising. The released carbon is deposited on the surface of the bubbles. When the bubbles reach the top of the liquid metal reactor, they burst and release a mixture of hydrogen, carbon, and possibly residual methane. The solid carbon is then separated from the gas mixture. The produced hydrogen is separated using a gas separation process, ultimately resulting in two separate reaction products. The residual methane is added back to the pyrolysis circuit of the liquid metal bubble column reactor.

[0090] However, the methane pyrolysis device 27 can also comprise means for carrying out methane pyrolysis using the Kvaerner process. In the Kvaerner process, the hydrocarbons are separated into pure carbon and hydrogen in a plasma torch at approximately 1600 °C.

[0091] If necessary, natural gas, in particular from a pipeline or a natural gas storage facility, can also be supplied to the methane pyrolysis device 27 in addition to the methane originating from the methanation device 26.

[0092] As already explained, the exhaust gas utilization system 4 can also additionally comprise the electrolysis system 28. This serves to additionally provide hydrogen for methanation. Using the electrolysis system 28, hydrogen is generated from water according to the following equation:

[0093] 2H2O = 2H2+ 02 Water from a pipeline or a water reservoir is preferably used for the electrolysis.

[0094] Furthermore, the additional hydrogen for methanation can also be provided from a hydrogen storage facility and / or a hydrogen network.

[0095] In addition, the additional hydrogen can also be provided using the LOHC (liquid organic hydrogen carrier) process. Hydrogenation involves chemically bonding H2 to a liquid, which can then be transported by tanker or pipeline and dehydrated again on-site.

[0096] The advantage of the method according to the invention and the device 1 according to the invention with the exhaust gas utilization device 4 according to the invention is that the CO2 produced during combustion does not enter the atmosphere, but is first converted into methane in the methanation device 26, which is then converted into solid carbon by methane pyrolysis. However, solid carbon, unlike carbon dioxide, is not harmful to the climate and can be used, for example, as fertilizer.

[0097] Another advantage of methane pyrolysis is that it requires 80% less energy than electrolysis, which in turn also reduces costs.

[0098] Half of the hydrogen consumed in the methanation plant 26 is also recovered by methane pyrolysis.

[0099] By operating kiln 2 with a pure CO2 atmosphere and burning the fuel without fuel combustion, the kiln exhaust gas is much cleaner and contains hardly any contaminants, eliminating the need for exhaust gas purification. If necessary, exhaust gas purification is only necessary if the contaminants have accumulated in the kiln exhaust gas. Especially for the bioreactor, it is important that the kiln exhaust gas to be methanized contains few contaminants, as the archaea are sensitive to these contaminants. The potential elimination of exhaust gas purification also saves energy and costs.

[0100] Another advantage of archaea is that they are sensitive to oxygen in the exhaust gas, but insensitive to high sulfur content in the exhaust gas.

[0101] Since preferably all of the energy required to operate the device 1, in particular the kiln 2 and the exhaust gas utilization device 4, is electrical energy, preferably from green electricity, the entire device 1 is almost climate-neutral.

[0102] Furthermore, the efficiency of Kiln 2 can be increased by operating it exclusively in a CO2 atmosphere, as the dew point temperature can be lowered, which in turn saves energy. This is because the combustion of natural gas and other fuels produces water vapor. Furthermore, these fuels often contain sulfur, which reacts with the water to form sulfurous acid, causing kiln corrosion. Without the combustion of fuels in the kiln interior, these problems do not occur.

[0103] The above-described operation of kiln 2 naturally refers to normal operation of kiln 2. During an initial phase, the CO2 concentration in the kiln interior 14 and the gases may not yet correspond to the specified concentration. In this case, kiln 2 is operated as described above until the desired CO2 concentration is reached through concentration. Only when this concentration is reached is the exhaust gas utilization system 4 activated. Before this, the excess exhaust gas is released into the atmosphere.

[0104] Alternatively, the kiln interior 14 can be purged with purge gas having the desired CO2 concentration before start-up. The purge gas originates, for example, from the exhaust gas storage device 22 or gas cylinders. According to a further embodiment of the invention (Fig. 3), the kiln 2 has a firing material heating device 30, preferably arranged in the kiln interior 14, for heating the raw material or firing material in the firing zone 11 to the temperature required for firing. The firing material heating device 30 generates the heat without burning any fuel in the kiln interior 14.

[0105] The firing material heating device 30 does not have a fuel heater with a burner for directly heating the raw material.

[0106] In addition, the firing material heating device 30 is preferably arranged at the upper end of the firing zone 11.

[0107] Preferably, the firing material heating device 30 is electrically operated. It therefore has at least one electrically operated heater.

[0108] The firing material heating device 30 preferably has at least one resistance heater. The resistance heater preferably has at least one, preferably several, electrical heating resistance element(s) 31, preferably heating rods or heating coils. The heating resistance element(s) 31 are arranged in the furnace interior 14 or protrude into it. In particular, the heating resistance element(s) 31 protrude into the raw material bed located in the furnace interior 14. Therefore, baffle plates 32 or similar mechanical protective elements are preferably also present to mechanically protect the heating resistance elements 31 from the raw material flow. In addition, several heating resistance elements 31 can be arranged next to one another and / or one above the other. In addition, the heating resistance elements 31 can also be distributed over the entire firing zone 11.

[0109] Alternatively or in addition to the electric heater, the firing material heating device 30 can also have at least one heat exchanger (not shown). In particular, several heat exchangers can be arranged side by side and / or one above the other. Furthermore, the heat exchangers can also be distributed throughout the entire firing zone 11. The heat exchangers are also preferably mechanically protected from the raw material flow.

[0110] A heat exchanger comprises, in a conventional manner, one or more heat exchanger tubes through which a hot medium flows and around which the raw material to be heated and the furnace process gas flow. According to one embodiment of the invention, combustion, e.g., of natural gas or a fossil fuel, can take place in the heat exchanger tubes (indirect heating of the raw material). Or at least one solid oxide fuel cell (SOFC) can be arranged in the heat exchanger tubes.

[0111] Furthermore, the electrically operated firing material heating device 30 can also have at least one microwave heater, which has means for heating the raw material by means of microwaves, and / or at least one arc heater with an anode and cathode arranged in the furnace interior 14.

[0112] Since no combustion of fuels takes place directly in the furnace interior 14 of the kiln 2 even in the embodiment with the kiln heating device 30, the kiln exhaust gas is not contaminated by gases and unburned oxygen produced during combustion.

[0113] In addition, only electrical energy, preferably from green electricity, is used for heat generation by means of the electrically operated fuel heating device 30.

[0114] It may also be sufficient to provide only the firing material heating device 30 for heating the firing material and to dispense with the introduction of the hot gas into the firing zone 11.

[0115] According to a further embodiment of the invention, the kiln 2 is an inclined shaft kiln 33 (Fig. 4). The inclined shaft kiln 33 is also operated in a manner known per se using the countercurrent principle. The inclined shaft kiln 33 has, in a manner known per se, a firing zone 11 with several firing zone regions 11a-d arranged one above the other. The firing zone regions are also designed such that the firing material passes through the firing zone 11 in a meandering path. The kiln shaft 33a is thus designed in a meandering shape in the region of the firing zone 11. In addition, each firing zone region 11a-d preferably has a hot gas inlet point 34 for introducing hot gas. This ensures optimal heating of the firing material.

[0116] Preferably, the hot gas inlet points 34 of the combustion zone regions 11 ad arranged directly above one another are located opposite one another. This means that there are always two hot gas inlet points 34 located one above the other. This is particularly due to space constraints.

[0117] Preferably, the hot gas supply device 5 also has a hot gas compression device 23 and two hot gas heating devices 16, each connected to the hot gas compression device 23. Two hot gas streams are discharged from each of the hot gas heating devices 16 and introduced into one of the combustion zone regions 11 ad.

[0118] It is, of course, also within the scope of the invention that the combustion zone regions 11a-d may have a combustion material heating device 30 (not shown) in addition to or as an alternative to the hot gas inlet points 34. For example, some of the combustion zone regions 11a-d may have a combustion material heating device 30 and some may have a hot gas inlet point 34.

[0119] If the kiln heating device 30 is electrically operated and uses resistance heating or arc heating, the resistance heating elements, or anode and cathode, are preferably arranged so that they are located within the kiln interior 14 but outside the raw material bed. This also applies to the heat exchanger tubes. This significantly reduces mechanical wear on the respective heating elements. The advantage of the inclined shaft kiln 33 is a more even heat and energy distribution. This provides greater control over the quality of the fired material.

[0120] According to a further embodiment of the invention, the kiln 2 is a floating shaft kiln 35 (Fig. 5). The floating shaft kiln 35 also has a single vertical kiln shaft 35a.

[0121] In contrast to the other mentioned kilns 2; 7; 33, the floating shaft kiln 35 is operated according to the cocurrent principle. This means that the material transport direction 8 corresponds to the flow direction of the kiln process gas. Furthermore, the material transport direction 8 runs from bottom to top. The material outlet is thus at the upper kiln end 2a.

[0122] Furthermore, the floating shaft kiln 35 is not used for firing lumpy raw material, but rather powdered raw material, preferably limestone powder. The powdered raw material has a grain size of < 400 pm, preferably < 200 pm, and more preferably < 90 pm.

[0123] For this reason, the firing material in the floating shaft furnace 35 is dispersed in the furnace process gas or floats in the floating shaft furnace 35. The firing material is thus transported through the floating shaft furnace 35 by means of the furnace process gas. An aerosol of the furnace process gas and firing material and / or fired material is present.

[0124] The device 1 according to the further embodiment (Fig. 5) also has an exhaust gas recirculation device 3, an exhaust gas utilization device 4 and a hot gas supply device 5.

[0125] The floating shaft furnace 35 comprises, from bottom to top, a hot gas distribution device 36, a combustion zone 37, and a recuperation zone 38. Furthermore, the floating shaft furnace 35 comprises a raw material lock 39 and a raw material inlet point 49, which is arranged above the hot gas distribution device 36 and below the combustion zone 37 and adjacent to the furnace shaft 35a.

[0126] The firing zone 37 also has one or more, preferably up to 30, firing zone regions 42 arranged one behind the other in the material transport direction 8. The firing zone regions 42 each have a firing material heating device 43.

[0127] The firing material heating device 43 preferably has at least one electrically operated heater, preferably an arc heater, a resistance heater, or a microwave heater, and / or at least one heat exchanger. Analogous to the other firing furnaces 2; 7; 33, the heating resistance elements 31 of the resistance heater, or the anode and cathode, or the heat exchanger tubes, are arranged in the furnace interior 14.

[0128] Firing in the floating shaft kiln 35 now takes place as follows:

[0129] By means of the hot gas supply device 5, hot gas is conveyed into the hot gas distribution device 36 at the lower furnace end 2b at the hot gas inlet point 34 into the furnace shaft 35a. The hot gas is previously heated in the hot gas heating device 16, preferably to 300 to 800°C, preferably 550 to 750°C. Preferably, the hot gas supply device 5 also has a conveying fan 50 arranged upstream of the hot gas heating device 16.

[0130] It is distributed over the entire furnace cross-section by the hot gas distribution device 36 and flows upwards through the furnace shaft 35a in the material transport direction 8.

[0131] The loose, powder-like raw material to be burned, preferably limestone powder, is filled into the raw material lock 39.

[0132] Once the raw material lock 39 is filled, it is sealed gas-tight and purged with purge gas (not shown). The purge gas is also furnace process gas with the specified high CO2 content. Furthermore, the purge gas preferably has an overpressure of 200 to 1800 mbar. For this purpose, the device 1 preferably has a purge gas compression device 17 (not shown in Figure 5). The purge gas compression device 17 is preferably a rotary piston blower, a screw compressor, a hybrid blower, or a pneumatic dynamic pressure compressor.

[0133] The raw material lock 39 is purged with the purge gas until it is completely filled. Then, the purge gas flow is shut off, and the raw material lock 39 is opened to the furnace interior 14, allowing raw material to be conveyed into the furnace interior 14.

[0134] Preferably, a preheating device 41 is arranged between the raw material lock 39 and the furnace interior 14, which serves to preheat the raw material before it is introduced into the furnace interior 14. The raw material is preferably preheated to 300 to 800°C.

[0135] The preheating device 41 is preferably electrically operated and preferably has at least one electric heater, preferably a resistance heater. However, it can also alternatively or additionally have a heat exchanger.

[0136] Furthermore, the preheating device 41 can also have at least one microwave heater.

[0137] As soon as the raw material enters the furnace interior 14, it is held in suspension by the hot gas stream and carried along in the material transport direction 8.

[0138] The raw material then enters the firing zone 37, is transported through it, and is fired during this process. After the firing zone 37, the fired material enters the recuperation zone 38, where it cools by transferring its thermal energy to a heat exchanger or a heat storage unit, which in turn is used to preheat the raw material.

[0139] From the recuperation zone 38, the fired material is discharged into the exhaust gas recirculation device 3 together with the furnace exhaust gas in which it is dispersed.

[0140] In the first dedusting device 18, the furnace exhaust gas is separated from the fired, dust-like material.

[0141] The furnace exhaust gas is then conveyed into the exhaust gas storage device 22 as described above and from there into the hot gas supply device 5 and the exhaust gas utilization device 4 according to the invention.

[0142] The fired material separated in the first dedusting device 18 is preferably classified in a classifying device 44. In particular, fully fired, in particular fully calcined, material is separated from incompletely fired, in particular incompletely calcined, material. The classifying device 44 preferably has an air classifier that separates heavy unfired material from lighter fired material by forcing light fired material outward, for example, with air, and allowing heavy fired material to fall downward without being deflected.

[0143] The incompletely fired material is then fed together with the raw material to the raw material lock 39.

[0144] And the fully fired material is preferably conveyed into a storage device 45.

[0145] The advantage of the 35-gauge kiln is the use of extremely fine material, with virtually no undersize particles. Furthermore, the kiln can be started up and shut down much faster than conventional kilns.

[0146] According to a further embodiment of the invention, the kiln 2 is also a normal shaft kiln 7 (Fig. 6).

[0147] The normal shaft furnace 7 has a raw material feed device 51, the raw material lock 9, optionally the preheating zone 10, the firing zone 11, the cooling zone 12 and the discharge lock 13.

[0148] In addition, the device 1 according to the further embodiment has the exhaust gas evaluation device 4 and the hot gas supply device 5, but preferably no cooling gas supply device 6.

[0149] The raw material feed device 51 serves to feed the raw material to the raw material lock 9. It preferably has a feed screw 51a, preferably a trough screw, with a heat exchanger. This preheats the raw material in the feed screw 51a. The heat exchanger of the feed screw 51a preferably has heat exchanger tubes (not shown) arranged externally around a screw wall of the feed screw 51a, through which a heat exchange medium, preferably thermal oil, flows. However, the feed screw 51a can also have an electric heater with at least one heating coil arranged around the screw wall of the feed screw 51a.

[0150] The raw material lock 9 has an upper and a lower pendulum flap 52a; 52b. The two pendulum flaps 52a; 52b have an open and a closed position. In the closed position, they close the raw material lock 9. If the upper pendulum flap 52a is open, the raw material lock 9 can be filled with raw material from above using the raw material feed device 51. If the lower pendulum flap 52c is open, the raw material falls from the raw material lock 9 into the furnace interior 14, in particular the preheating zone 10. For opening and closing the two pendulum flaps 52a; 52b, the standard shaft furnace 7 has corresponding drive means, preferably hydraulic and / or pneumatic drive means and / or an electric motor and / or a servomotor.

[0151] The normal shaft kiln 7 also has an electrically operated firing material heating device 53 for heating the raw material or firing material in the firing zone 11 to the temperature required for firing.

[0152] The firing material heating device 53 has two resistance heaters in the form of heating sleeves 54 for each firing zone 11a-d, which are arranged outside the furnace shell 15, which is preferably made of steel.

[0153] The heating sleeves 54 each have an inner heating shell 55, an insulating shell 56 arranged outside around the heating shell 55 and preferably a sleeve outer shell 57 arranged outside around the insulating shell 56.

[0154] The heating shells 55 each have at least one electrical heating resistance element, preferably at least one heating coil, preferably several heating coils (not shown).

[0155] The furnace shell 15 is thus heated by means of the heating sleeves 54 and the heat generated by the heating sleeves 54 is transferred through the furnace shell 15 into the furnace interior 14 by means of heat conduction.

[0156] The hot gas supply device 5 preferably has a hot gas circulation device or furnace exhaust gas circulation device 58, the first dedusting device 18, a heat exchanger 59 for cooling the exhaust gas, a throttle 60, the exhaust gas compression device 21, the exhaust gas storage device 22, and a further throttle 61. The hot gas circulation device or furnace exhaust gas circulation device 58 serves to circulate a portion of the hot furnace exhaust gas exiting the combustion zone 11 at the upper end. In particular, the hot gas circulation device 58 serves to discharge the hot furnace exhaust gas at the upper end of the combustion zone 11 and to recirculate the hot furnace exhaust gas at the lower end of the combustion zone 11. For this purpose, the hot gas circulation device 58 has corresponding hot gas lines and at least one hot gas drive device or furnace exhaust gas drive device 62 for accelerating the hot gas or furnace exhaust gas.Preferably, the hot gas drive device 62 is a Coanda nozzle 63 or a high-temperature blower (not shown).

[0157] Heat exchanger 59 serves to cool the exhaust gas and uses, for example, thermal oil as the heat exchange medium. The heated thermal oil from heat exchanger 59 can be used, for example, for the feed screw 51a.

[0158] The cooling zone 12 preferably has a cooling screw 64, which is preferably designed as a trough screw and has a closed, circumferential screw wall 64a. Furthermore, the cooling screw 64 has a heat exchanger and thus means for dissipating the heat of the fired, in particular calcined, material. The heat exchanger of the cooling screw 64 preferably has heat exchanger tubes (not shown) arranged externally around a screw wall of the cooling screw 64, through which a heat exchange medium, preferably thermal oil, flows. The heated thermal oil can be used, for example, for the feed screw 51a. In contrast to the previously described embodiments, no cooling gas is introduced into the cooling zone 12.

[0159] The cooling screw 64 has a cooling screw drive motor 65 in a conventional manner. As already explained, the discharge lock 13 adjoins the cooling zone 12. Analogous to the raw material lock 9, the discharge lock 13 also has two swing flaps 66a;b for opening and closing the discharge lock 13.

[0160] In the normal shaft kiln 7 according to the further embodiment, the firing process now proceeds as follows:

[0161] The raw material to be fired is first weighed and fed in batches into the raw material feed device 51, in particular the screw conveyor 51a, until it is full. Then, the screw conveyor 51a is started, and the raw material is fed into the raw material lock 9. The upper swing flap 52a of the raw material lock 9 is open, while the lower swing flap 52b of the raw material lock 9 is closed.

[0162] As usual, the entire firing process is a discontinuous process.

[0163] As soon as the raw material lock 9 is completely filled, the upper pendulum flap 52a is closed and the raw material lock 9 is purged with purge gas as described above. The raw material lock 9 is purged with the purge gas, as also explained, until it is completely filled. Then, the purge gas flow is shut off, and the raw material lock 9 is opened to the furnace interior 14 by opening the lower pendulum flap 52b of the raw material lock 9. As a result, the raw material falls into the furnace interior 14, in particular into the preheating zone 10.

[0164] The raw material travels in countercurrent, namely in the material transport direction 8, through the furnace interior 14 and reaches the firing zone 11.

[0165] In the firing zone 11, the raw material is heated by the hot gas flowing through it in the opposite direction to the material transport direction 8, as described above, so that it is fired, in particular deacidified. The material migrates countercurrently, namely in the direction of material transport 8, through the firing zone 11 and reaches the cooling zone 12. In contrast to the method described above, however, the hot gas is not heated in a hot gas heating device 16 outside the furnace interior 14, but rather it is heated within the furnace interior 14 while flowing through the firing zone 11 in the opposite direction to the material transport direction 8. The hot gas is heated by means of the firing material heating device 53.

[0166] As described above, the heating sleeves 54 heat the furnace shell 15 and the hot gas flowing along it. This embodiment is particularly advantageous because no heating elements are arranged in the furnace interior 14 to impede the material flow.

[0167] However, it is within the scope of the invention that a hot gas heating device is present if necessary.

[0168] As already explained above, the hot gas or the furnace exhaust gas is also circulated by means of the hot gas circulation device 58:

[0169] For this purpose, the furnace exhaust gas is discharged from the furnace interior 14 at the upper end of the combustion zone 11. A first exhaust gas stream is fed, as described above, to the exhaust gas storage device 22 via the dedusting device 18, the heat exchanger 59, the throttle 60, and the exhaust gas compression device 21.

[0170] Another exhaust gas stream of the furnace exhaust gas, the recirculating hot gas, is fed to the hot gas drive device 62, preferably the Coanda nozzle 63. In particular, the ratio of the first exhaust gas stream to the recirculating hot gas is 1:5 to 1:10. The recirculating hot gas is preferably not dedusted, but fed directly to the hot gas drive device 62, preferably the Coanda nozzle 63. In particular, it is not temporarily stored in the exhaust gas reservoir 22.

[0171] In the hot gas drive device 62, preferably the Coanda nozzle 63, the circulating hot gas is accelerated and then returned to the furnace interior 14 below the combustion zone 11. The acceleration of the circulating hot gas in the Coanda nozzle 63 takes place in a conventional manner by means of a drive gas, which is also supplied to the Coanda nozzle 63. The drive gas is also furnace exhaust gas, which is discharged from the exhaust gas storage device 22 and supplied to the Coanda nozzle.

[0172] The drive gas and the circulating hot gas mix in the Coanda nozzle in a manner known per se and are then returned below the combustion zone 11 into the furnace interior 14 and flow through the combustion zone 11 from bottom to top as described above.

[0173] The use of the Coanda nozzle 63 is particularly advantageous because it is wear-free.

[0174] As already explained above, the firing zone 11 is followed by the cooling zone 12 with the cooling screw 64. The cooling screw 64 is preferably also operated discontinuously. The fired material is thus transported through the cooling screw 64 and cooled, particularly by means of the thermal oil.

[0175] After the cooling screw 64, the fired material enters the discharge lock 13. For this purpose, the upper pendulum flap 66a of the discharge lock 13 is open, and the lower pendulum flap 66b of the discharge lock 13 is closed. As soon as the discharge lock 13 is completely filled, the upper pendulum flap 66a of the discharge lock 13 is closed, followed by the lower pendulum flap 66b of the discharge lock 13 being opened, and the fired material is discharged from the kiln 2.

[0176] After the fired material has been discharged, the discharge lock 13 is flushed with purge gas in the same way as the raw material lock 9, as also described above, until it is completely filled with it.

[0177] It is, of course, also within the scope of the invention to remove kiln exhaust gas from the firing kiln 2 at different locations. For example, the kiln exhaust gas supplied to the exhaust gas storage device 22 can be removed at a different location, for example, further up, than the kiln exhaust gas for the hot gas circulation device. A circulation device for circulating the exhaust gas can also be provided above the firing zone 11, for example. This circulation gas then serves to preheat the raw material.

[0178] It is also within the scope of the invention to use the exhaust gas utilization device 4 according to the invention for the utilization of the exhaust gas of a kiln 2 conventionally operated with the combustion of fuels in the kiln interior 14. Furthermore, the combustion can also be carried out according to the oxyfuel process.

[0179] In addition, the exhaust gas utilization device 4 can be used for other industrial kiln types, e.g. for a rotary kiln or a tunnel kiln or other shaft kilns, preferably a PGR kiln (cocurrent countercurrent regenerative kiln) or an annular shaft kiln, or a push-table kiln.

[0180] The industrial kilns are used for industrial burning / deacidification in contrast to small-volume laboratory kilns, which are used for experimental purposes.

[0181] The exhaust gas utilization device 4 can also be used for the exhaust gas utilization of other combustion processes in which CO2 is produced as a process emission gas or in which deacidification of the carbonatic raw material (= expulsion of CO2) takes place. The exhaust gas utilization device 4 can preferably be part of a device for the production of cement clinker. This is because carbonatic raw material, in particular limestone and / or marl, is also calcined or deacidified in the production of cement. For this purpose, such a device either has an upstream kiln (calcining kiln) or the calcination or deacidification takes place in the same kiln in which the sintering to cement clinker takes place. Furthermore, it is within the scope of the invention that, in addition to the methanation device, another conversion device for converting CO2 and preferably hydrogen into other hydrocarbons or alcohol can be present.This can also be achieved by converting CO2 into CO. Preferably, the conversion is carried out into propane and / or butane and / or propene and / or butene and / or methanol (methanation device) and / or synthetic fuels and / or synthetic engine oils. The conversion into synthetic fuels and / or engine oils is preferably carried out using Fischer-Tropsch synthesis.

Claims

Claims 1. Exhaust gas utilization device (4) for the utilization of CO2-containing exhaust gas, in particular exhaust gas utilization device (4) for furnace exhaust gas from kilns (2) for burning carbonate raw material, preferably limestone and / or magnesite and / or dolomite and / or marl, comprising: a) a methanization device (26) for converting the CO2 contained in the exhaust gas into methane and water with the addition of hydrogen, b) a methane pyrolysis device (27) for converting the methane produced in the methanization device (26) into hydrogen and solid carbon, and c) means for conveying the hydrogen produced in the methane pyrolysis device (27) into the methanization device (26).

2. Exhaust gas utilization device (4) according to claim 1 , characterized in that the methanization device (26) comprises means for methanogenesis, preferably at least one bioreactor with archaea as methanogens, wherein the bioreactor is preferably operable with an overpressure of 1 to 100 bar, preferably with 10 to 35 bar, particularly preferably with 10 to 20 bar.

3. Exhaust gas utilization device (4) according to claim 1 or 2, characterized in that the methanization device (26) comprises means for chemical methanization, preferably at least one membrane reactor.

4. Exhaust gas utilization device (4) according to one of the preceding claims, characterized in that the methane pyrolysis device (27) comprises at least one liquid metal bubble column reactor filled with molten metal, preferably with molten tin, and / or means for carrying out the methane pyrolysis by means of the Kvaerner process.

5. Exhaust gas utilization device (4) according to one of the preceding claims, characterized in that the exhaust gas utilization device (4) has an exhaust gas purification device (29) for purifying the furnace exhaust gas from components other than CO2 before methanization in the methanization device (26).

6. Exhaust gas utilization device (4) according to one of the preceding claims, characterized in that the exhaust gas utilization device (4) has an electrolysis device (28) for additional provision of hydrogen for the methanization device (26).

7. Exhaust gas utilization device (4) according to one of the preceding claims, characterized in that the exhaust gas utilization device (4) has a high-pressure compressor (46), a high-pressure storage tank (47) and a pressure reducer (48) upstream of the methanization device (26).

8. Exhaust gas recovery device (4) according to one of the preceding claims, characterized in that the exhaust gas utilization device (4) comprises means for additionally supplying natural gas to the methane pyrolysis device (27), preferably from a pipeline or a natural gas storage facility. Use of an exhaust gas utilization device (4) according to one of the preceding claims for the utilization of CO2-containing furnace exhaust gas from a kiln (2) for the deacidification of carbonate raw material, preferably limestone and / or magnesite and / or doloma and / or marl.Exhaust gas utilization process for utilizing CO2-containing furnace exhaust gas from kilns (2) for burning carbonate raw materials, preferably limestone and / or magnesite and / or dolomite and / or marl, in particular using an exhaust gas utilization device (4) according to any one of claims 1 to 8, comprising the following process steps: a) conversion of the CO2 contained in the exhaust gas into methane and water by methanation, and b) conversion of the produced methane into hydrogen and solid carbon by methane pyrolysis, and c) use of the hydrogen produced during methane pyrolysis for methanation. Exhaust gas utilization process according to claim 10, characterized in that. The methanization of at least part of the exhaust gas, preferably of the entire exhaust gas, is carried out by methanogenesis.

12. Exhaust gas utilization process according to claim 10 or 11, characterized in that the furnace exhaust gas has a CO2 content of > 50 wt.%, preferably > 75 wt.%, preferably > 80 wt.%, particularly preferably > 90 wt.%, most preferably > 98 wt.%, and is preferably purified of components other than CO2 before methanization.

13. Exhaust gas utilization process according to one of claims 10 to 12, characterized in that additionally supplied natural gas is used for the methane pyrolysis.

14. Exhaust gas utilization process according to one of claims 10 to 13, characterized in that hydrogen produced by electrolysis is additionally used for methanization.

15. Device (1) comprising a) a kiln (2) for burning carbonate, bulkable raw material, preferably limestone and / or magnesite and / or dolomite and / or marl, b) an exhaust gas utilization device (4) for utilizing the CO2-containing kiln exhaust gas exiting the kiln (2), characterized in that the exhaust gas utilization device (4) is designed according to one of claims 1 to 8.

16. Device (1) according to claim 15, characterized in that the kiln (2) has means for operating the kiln with a CO2 atmosphere, wherein CO2 atmosphere preferably means that the kiln process gas located in the kiln interior (14) of the kiln (2) has a CO2 content of > 80 wt.%, preferably > 90 wt.%, particularly preferably > 98 wt.%.

17. Device (1) according to claim 15 or 16, characterized in that the kiln (2) does not have means for burning fuels in the kiln interior (14) of the kiln (2) to generate the heat energy necessary for burning the raw material.

18. Device (1) according to one of claims 15 to 17, characterized in that the kiln (2) is operated with overpressure, wherein the overpressure in the kiln interior (14) is preferably 50 to 1200 mbar, preferably 200 to 800 mbar.

19. Device (1) according to one of claims 15 to 18, characterized in that the kiln (2) has at least one material heating device (30;43;53) for heating the raw material to the temperature required for firing in a firing zone (11;37) of the kiln (2), wherein the material heating device (30;43;53) exclusively comprises means for generating the heat energy required for heating without burning fuels in the kiln interior (14).

20. Device (1) according to claim 19, characterized in that the fuel heating device (30;43;53) has at least one electrically operated heater, preferably a resistance heater or a microwave heater or an arc heater, and / or at least one heat exchanger.

21. Device (1) according to claim 20, characterized in that the resistance heating has at least one heating resistance element (31) arranged in an interior space (14) of an oven.

22. Device (1 ) according to claim 20 or 21 , characterized in that the heat exchanger is arranged in the interior of the furnace (14).

23. Device (1) according to claim 20, characterized in that the fuel heating device (53) has at least one resistance heater in the form of a heating sleeve (54) for heating the furnace jacket (15), wherein the heating sleeve (54) is arranged outside around the furnace jacket (15), wherein the fuel heating device (53) preferably has several heating sleeves (54).

24. Device (1) according to claim 23, characterized in that the heating sleeves (54) have an inner heating shell (55), an insulating shell (56) arranged outside around the heating shell (55) and preferably an outer sleeve shell (57) arranged outside around the insulating shell (56).

25. Device (1) according to claim 24, characterized in that the heating shell (55) has at least one electrical heating resistance element, preferably at least one heating coil, preferably several heating coils.

26. Device (1) according to one of claims 15 to 25, characterized in that the device (1) has a hot gas supply device (5) for supplying hot gas into or below a combustion zone (11; 37) of the furnace (2) at one or more hot gas inlet points (34), wherein the hot gas supply device (5) has at least one hot gas heating device (16) for heating the gas and / or preferably at least one hot gas compression device (23).

27. Device (1) according to claim 26, characterized in that the hot gas heating device (16) has at least one electrically operated heater, preferably a resistance heater, and / or at least one heat exchanger for heating the gas.

28. Device (1) according to one of claims 15 to 27, characterized in that the device (1) has a furnace exhaust gas recirculation device (58) for removing at least a part of the furnace exhaust gas as recirculation gas at the upper end of the combustion zone (11) and for returning the recirculation gas at the lower end of the combustion zone (11).

29. Device (1) according to claim 28, characterized in that the furnace exhaust gas recirculation device (58) includes at least one furnace exhaust gas drive device (62), preferably a Coanda nozzle (63) or a It features a high-temperature blower for accelerating the circulating gas.

30. Device (1) according to claim 28 or 29, characterized in that the circulating gas from the furnace interior (14) is supplied to the furnace exhaust gas circulating device (58) without intermediate storage, in particular directly.

31. Device (1) according to one of claims 15 to 30, characterized in that the device (1) has a cooling gas supply device (6) for supplying cooling gas into a cooling zone (12) of the kiln (2).

32. Device (1) according to one of claims 15 to 30, characterized in that the cooling zone (12) has a cooling screw (64) which is designed as a heat exchanger and has means for removing the heat from the fired, in particular calcined, material, wherein the device (1) preferably does not have a cooling gas supply device (6) for supplying cooling gas to the cooling zone (12) of the kiln (2).

33. Device (1) according to one of claims 15 to 32, characterized in that the device (1) is a device (1) for the production of quicklime and / or magnesia and / or dolomite or cement clinker.

34. Device (1) according to one of claims 15 to 33, characterized in that the kiln (2) is a shaft kiln, preferably a vertical normal shaft kiln (7) or an inclined shaft kiln (33) or a floating shaft kiln (35) or a co-current counter-current regenerative kiln or an annular shaft kiln, or a rotary tube kiln or a pusher table kiln.

35. Device (1) according to one of claims 15 to 34, characterized in that the kiln (2) has a gas-tight sealable raw material lock (9;39) for batch-wise introduction of the raw material into a kiln interior (14) and means for purging the raw material lock (9;39) with purge gas.

36. Device (1) according to one of claims 15 to 35, characterized in that the kiln (2) has a gas-tight sealable discharge sluice (13) for batch discharge of the fired material from the kiln interior (14) and means for purging the discharge sluice (13) with purge gas.

37. Device (1) according to claim 36, characterized in that the kiln (2) is used for burning lumpy raw material, in particular raw material with grains with a grain size of > 5 mm, and, viewed in a material transport direction (8), has the raw material sluice (9), preferably a preheating zone (10), a firing zone (11), a cooling zone (12) and the discharge sluice (13) arranged one after the other.

38. Device (1) according to claim 34 or 35, characterized in that the kiln (2) is a floating shaft kiln (35) that can be operated on the direct current principle for burning flour-like raw material dispersed in the kiln process gas.

39. Device (1) according to claim 38, characterized in that the floating shaft furnace (35) has, viewed from bottom to top, a hot gas distribution device (36), a combustion zone (37) and a recuperation zone (38) as well as a raw material inlet point (49) arranged above the hot gas distribution device (36) and below the combustion zone (37).

40. Device (1) according to claim 39, characterized in that the combustion zone (37) has one or more combustion zone areas (42) arranged one behind the other in a material transport direction (8), wherein the combustion zone areas (42) each have a material heating device (43), wherein the material heating device (43) preferably has at least one electrically operated heater, preferably an arc heater or a microwave heater or a resistance heater or a microwave heater, and / or at least one heat exchanger.

41. Method for deacidifying carbonate, bulkable raw material, preferably limestone and / or magnesite and / or dolomite and / or marl, wherein the raw material is deacidified in a kiln (2), characterized in that the kiln exhaust gas exiting the kiln (2) is utilized according to the exhaust gas utilization method according to one of claims 10 to 14. A method according to claim 41, characterized in that the kiln (2) is operated with a CO2 atmosphere, wherein the kiln process gas located in the kiln interior (14) preferably has a CO2 content of > 50 wt.%, preferably > 75 wt.%, preferably > 80 wt.%, particularly preferably > 90 wt.%, and most preferably > 98 wt.%. A method according to claim 41 or 42, characterized in that no combustion of fuels takes place in the kiln interior (14) of the kiln (2) to generate the heat energy necessary for burning the raw material. A method according to any one of claims 41 to 43, characterized in that electrical energy, preferably from green electricity, is used at least partially, preferably exclusively, to generate the heat energy necessary for burning the raw material. A method according to any one of claims 41 to 44, characterized in that all kiln process gases introduced into the kiln (2) have a CO2 content of > 50 wt.%.-%, preferably > 75 wt.%, preferably > 80 wt.%, particularly preferably > 90 wt.%, most preferably > 98 wt.% consist of CO2 and / or contain no oxygen. A process according to any one of claims 41 to 45, characterized in that hot gas is present in or below a combustion zone (1 1 ;37) of the furnace (2). the process is initiated at a temperature sufficient to deacidify the raw material, preferably at a temperature of 800 to 1250°C, preferably 900 to 1100°C.

47. Method according to one of claims 41 to 46, characterized in that the raw material in a combustion zone (11; 37) of the kiln (2) is heated by means of a material heating device (30; 43), wherein the material heating device (30; 43) comprises at least one electrically operated heater, preferably a resistance heater or a microwave heater or an arc heater, and / or at least one heat exchanger.

48. Method according to claim 41, characterized in that combustion takes place in the interior (14) of the kiln (2) to generate the heat energy necessary for burning the raw material, wherein the combustion preferably takes place according to the oxyfuel process.

49. A method according to any one of claims 41 to 48, characterized in that the method is a method for producing quicklime, magnesia or doloma.

50. Method according to one of claims 41 to 48, characterized in that the method is part of a manufacturing process for the production of cement clinker.

51. Method according to any one of claims 41 to 50, characterized in that a device (1) according to one of claims 15 to 40 is used to carry out the method.

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