Reduction of co2 emissions in the production of cement clinker

Abstract

The present invention relates to a system for producing cement clinker, the system having a raw-material supply (10), a mill (50), a pre-heater (60), a calciner (70), a furnace (80) and a material cooler (90), the material flow from the raw-material supply (10) being guided via the mill (50), the pre-heater (60), the calciner (70), the furnace (80) and the material cooler (90), and the material cooler (90) having a product outlet, characterised in that the system has a screen device (30), the screen device (30) being connected to the raw-material supply (10) for the feeding of raw material, the screen device (30) being designed to separate a coarse particle flow and a fine particle flow, the system having a shaft furnace (40), the screen device (30) being connected to the shaft furnace (40) for transfer of the coarse particle flow, and the shaft furnace (40) being connected to the mill (50) for transfer of the thermally treated raw material.

Description

[0001] Reduction of CO2 emissions in the production of cement clinker

[0002] The invention relates to a device and a method for the simple partial separation of CO2 which is produced during the production of cement clinker

[0003] On the one hand, there is the possibility of scrubbing and separating CO2 from the exhaust gas of any plant. Such processes are universally applicable. However, due to the typically high nitrogen content, they are complex. Therefore, there are plants that operate with pure oxygen, for example, so that virtually pure CO2 is ultimately produced, thus eliminating the need for separation. However, this usually requires a redesign of the plant.

[0004] DE 10 2018 206 673 A1 and DE 10 2018 206 674 A1 disclose plants for the production of cement clinker in which the oxygen enriched as much as possible is used in the process, resulting in the exhaust gas containing as pure carbon dioxide as possible, making it relatively easy to separate it for use or storage. The disadvantage, however, is that an existing plant must be completely rebuilt or a new plant must be constructed.

[0005] There is therefore interest in simply modifying existing plants to reduce at least some of the CCH emissions without having to build a completely new plant. The focus is therefore on quick and easy implementation, but only partial capture.

[0006] A lime shaft kiln is known from DE 10 2021 204 175.

[0007] An annular shaft furnace is known from DE 10 2021 202 485.

[0008] DE 11 2010 004 030 B4 discloses a vertical kiln with three concentric cylinders. EP 2 018 353 B1 discloses a process and plant for producing cement clinker.

[0009] WO 2007 / 099 415 A1 discloses a process and a plant for drying and conveying moist mineral raw materials.

[0010] A plant for the production of cement clinker is known from DE 199 29 066 A1.

[0011] DE 198 45 495 A1 discloses a process for burning carbonate-containing rock while generating a waste gas stream with a high CO2 content, as well as a double-shaft furnace for carrying out the process.

[0012] From DE 10 2008 059 370 A1 a process and a plant for the production of cement are known.

[0013] The object of the invention is to provide a plant for the production of cement clinker which separates part of the CO2 in a simple manner starting from a conventional plant.

[0014] This object is achieved by the system having the features specified in claim 1 and the method having the features specified in claim 6. Advantageous further developments emerge from the subclaims, the following description and the drawing.

[0015] The plant according to the invention is used to produce cement clinker. The plant comprises a raw material supply, a mill, a preheater, a calciner, a kiln, and a material cooler. The raw material supply can be a stockpile, a delivery point, for example, an unloading station, a silo, or the like. The material flow is conducted from the raw material supply via the mill, the preheater, the calciner, the kiln, and the material cooler. The material cooler has a product outlet. This plant is a conventional plant for producing cement clinker. In particular, it can also be an existing plant for producing cement clinker that is modified according to the invention in order to simply reduce some of the CCh emissions. The plant for producing cement clinker according to the generic term is therefore known to the person skilled in the art.

[0016] A corresponding state-of-the-art plant is thus modified in accordance with the invention in order to separate a portion of the CO2 in a simple manner and thus to at least quickly reduce the climate impact within the framework of a simple measure.

[0017] The system has a screening device. The screening device is connected to the raw material supply for the supply of raw material. The screening device is designed to separate a coarse particle stream from a fine particle stream. The separation between coarse particles and fine particles preferably occurs between 5 mm and 50 mm, although an exact separation accuracy is of course not necessary and is not technically advisable. For example, even fine particles can unintentionally end up in the coarse fraction during a screening process. Thus, the separation between coarse particles and fine particles is between 5 mm and 50 mm. Purely as an example, a sieve with a hole size of 30 mm is used; theoretically, in the ideal case, this would result in a fine particle fraction with all particles smaller than 30 mm and a coarse particle fraction with particles larger than 30 mm. Thus, the fine particle fraction is found in the fine particle stream and the coarse particle fraction in the coarse particle stream.The plant comprises a shaft furnace. Shaft furnaces are well known; for example, and preferably, they can be a shaft furnace according to DE 10 2021 204 175 or DE 10 2021 202 485. The screening device is connected to the shaft furnace for transferring the coarse particle stream. Thermal treatment of only the coarse particle fraction then takes place in the shaft furnace. The shaft furnace is connected to the mill for transferring the thermally treated raw material.

[0018] The burning of carbonate rock in a GGR shaft kiln has been known for around 60 years. Such a GGR shaft kiln, known for example from WO 2011 / 072894 A1, has two vertical, parallel shafts that operate cyclically, with burning taking place only in one shaft, the respective combustion shaft, while the other shaft operates as a regenerative shaft. Oxidation gas is fed to the combustion shaft in cocurrent with the material and fuel. The resulting hot exhaust gases, together with the heated cooling air supplied from below, are channeled via the overflow duct into the exhaust gas shaft, where the exhaust gases are discharged upward in countercurrent to the material, preheating the material. The material is usually fed into the shaft from above together with the oxidation gas, with fuels being injected into the combustion zone.In each shaft, the material to be burned usually passes through a preheating zone to preheat the material, a subsequent burning zone in which the material is burned and a subsequent cooling zone in which cooling air is supplied to the hot material.

[0019] It has been shown that the large lime particles in the coarse fraction in particular allow for easy separation of the CO2, especially from the starting material. A second advantage is that the grindability of the material, and therefore especially of the large particles, is improved by thermal treatment. Complete decarbonization does not have to be achieved in the shaft kiln. Rather, for the most efficient use of the overall system, it is advantageous to only decarbonize the coarse particle fraction by 80 to 90%, for example. The material thermally treated in the shaft kiln is fed via the mill to the usual process in the preheater, calciner and kiln, so that complete thermal treatment takes place here, especially in the kiln. The shaft kiln, however, reduces the fuel requirement in the calciner and also reduces the release of CO2 from the starting material.This means that the existing plant can remain unchanged; the CO2 separation is simply carried out for the CO2 emissions of the shaft furnace.

[0020] For example, a lime kiln system with at least one shaft kiln for burning and cooling material, such as carbonate rock, wherein the lime kiln system comprises two shafts and a channel extending between the two shafts. The shaft kiln comprises exactly one of the shafts of the lime kiln system, wherein the shaft has a material inlet for admitting material to be burned into the shaft and, in the direction of flow of the material, a preheating zone for preheating the material, a burning zone for burning the material, a cooling zone for cooling the material, and a material outlet for discharging the material from the shaft. The channel has a closure device for gas-technically closing the channel, such that a gas flow between the two shafts through the channel is prevented by means of the closure device.The material to be burned is preferably limestone or dolomite stone with a grain size of 10 to 200 mm, preferably 15 to 120 mm, most preferably 30 to 100 mm. The cooling gas is, for example, air. The lime kiln system is preferably a shaft kiln that can be operated as a co-current / countercurrent regenerative shaft kiln, wherein the channel connecting the shafts, in particular the firing zones of the shafts, has been closed. The lime kiln system has at least one shaft kiln. For example, the shaft kiln system has two shaft kilns, each of which comprises exactly one of the shafts of the lime kiln system. The shaft kilns are preferably separated from one another in terms of gas technology and, in particular, can be operated separately from one another for firing material.The shaft of the at least one shaft kiln of the lime kiln system preferably has a material inlet for admitting material to be fired into the shaft, wherein the material inlet is located in particular at the upper end of the shaft so that the material falls into the shaft due to gravity. The material inlet and / or the material outlet is / are designed in particular as a lock for admitting and / or discharging material into the shaft kiln. A material inlet designed as a lock is preferably configured such that only the raw material to be fired enters the shaft, but not the ambient air. The lock is preferably designed such that it seals the shaft airtight against the environment and allows solids, such as the material to be fired, to enter the shaft.In the direction of flow of the material, the material flows through a preheating zone following the material inlet for preheating the material to a temperature of, for example, approximately 600 °C to 800 °C. The firing zone is preferably directly adjacent to the preheating zone and serves to fire the material, which is preferably heated to a temperature of approximately 900 °C to 1600 °C. The cooling zone is preferably directly adjacent to the firing zone and serves to cool the fired material to a temperature of, for example, 100 °C. The material outlet is arranged, for example, in an outlet hopper adjoining the cooling zone, wherein the material outlet has, for example, a turntable or pushing tables for discharging material from the cooling zone into the outlet hopper. The cooling gas is preferably blown into the cooling zone of the shaft furnace via a cooling gas inlet.The cooling gas inlet is preferably arranged in the cooling zone, in particular below the turntable. A plurality of burners, in particular burner lances, are preferably arranged in the combustion zone of the shaft. It is also conceivable for the shaft to have a plurality of side burners extending through the shaft wall into the combustion zone. The side burners are preferably designed as burner lances and are in particular tubular. They serve to conduct fuel and preferably an oxidizing agent, which is introduced into the combustion zone together with exhaust gas. The closure device preferably extends over the entire cross-section of the channel. The gas-technical closure of the channel by means of a closure device enables the separate operation of the two shafts of the lime kiln system. For further embodiments, reference is made to DE 10 2021 204 175.

[0021] According to the invention, the shaft furnace is designed for operation with a gas containing at least 50% oxygen.

[0022] In a further embodiment of the invention, the screening device is designed for a separation between 5 mm and 50 mm. The screening device is therefore selected so that the screen hole size is between 5 mm and 50 mm. This ensures that the fine fraction is below the selected value, while the coarse fraction is above the selected value.

[0023] In a further embodiment of the invention, the shaft kiln is designed for operation with a gas containing at least 90% oxygen. With pure oxygen (and no other gases arising from the raw material), the exhaust gas stream from combustion and the CO2 escaping from the lime (after water separation) would be pure carbon dioxide, which can then be easily reused or stored. Since, especially when retrofitting an existing cement plant, only one additional shaft kiln needs to be installed, it can be designed to operate with highly enriched oxygen without the existing components such as the preheater, calciner, and kiln having to be converted. The use of enriched oxygen therefore significantly simplifies CO2 separation.

[0024] In a further embodiment of the invention, a CO2 separation device is installed downstream of the shaft furnace. This can be implemented particularly simply if the shaft furnace is designed for operation with a gas containing at least 50% oxygen, preferably at least 90% oxygen. Water removal is usually always necessary. A dust collector or other conventional pretreatment processes can be installed upstream of the CO2 separation device.

[0025] In a further embodiment of the invention, the plant comprises two shaft kilns. In particular, the shaft kilns are designed according to DE 10 2021 204 175 and are operated alternately. Such an arrangement is referred to as a direct-current regenerative lime shaft kiln.

[0026] In a further aspect, the invention relates to a process for producing cement clinker. Preferably, a plant according to the invention is used for the process according to the invention. The process comprises the following steps: a) screening the raw material into a coarse fraction and a fine fraction, b) thermally treating the coarse fraction in a shaft furnace with a gas containing at least 50% oxygen, c) mixing the fine fraction and the thermally treated coarse fraction and then grinding, or grinding the fine fraction and grinding the thermally treated coarse fraction and then mixing, d) preheating the material, e) calcining the material, f) firing the material in a kiln, g) cooling the product.

[0027] In step a), the coarse fraction is separated. Optionally, an oversized fraction, for example, for particles larger than 100 to 200 mm, can also be separated. For example, before step a), the starting material is crushed in a crusher; in this case, the oversized fraction is preferentially returned to the crusher. This prevents excessively large particles from being included in the coarse fraction.

[0028] Thermal treatment in a shaft furnace b) allows a significantly coarser fraction to be thermally treated. Furthermore, the coarser fraction contains a particularly high amount of calcium carbonate. This allows for simple thermal treatment and thus the separation of the CO2 generated during this step, while the rest of the plant can be operated unchanged according to state-of-the-art technology. In addition to the comparatively simple separation of CO2, the grindability of the material also increases, which in turn reduces energy consumption, especially for the largest particles, thus further increasing the overall efficiency of the process.

[0029] In step c), there are two options. In the first step, the fine fraction and the thermally treated coarse fraction are first mixed and then ground together. In the second step, the two fractions are ground separately and then mixed. It is important that the two fractions are finally mixed again and fed into the cement clinker process in steps d) to g).

[0030] A key point here is that less energy is required during calcination in step e), since a portion (the coarse fraction) has already been decarbonized. Therefore, less energy and thus less fuel are required in the calciner, and thus less CO2 is produced, which is then released into the environment according to the state of the art. Thus, a portion of the CO2 originating from the fuel is also generated in the shaft furnace by the process according to the invention and thus separated.

[0031] In a further embodiment of the invention, the screening in step a) is carried out to a size of 5 to 50 mm, for example to 30 mm. This results in a good size distribution of the starting material for the shaft kiln for conventional raw materials. At the same time, this creates the possibility of transferring 20 to 40% of the CO2 produced into the shaft kiln, so that this CO2 can be easily separated without having to adapt the rest of the plant, in particular the kiln and calciner. It is therefore comparatively easy and quick to avoid a relevant proportion of CO2 emissions. In a further embodiment of the invention, the raw material is crushed before screening in step a).

[0032] In a further embodiment of the invention, the thermal treatment in step b) is carried out in two shafts of a PFR shaft furnace in alternating sequence. For the implementation with two shaft furnaces, reference is made, for example, and in particular, to DE 10 2021 204 175.

[0033] In a further embodiment of the invention, the coarse fraction after treatment in the shaft furnace has a carbon dioxide content of between one and eight percent by mass, preferably between three and five percent by mass. The carbon dioxide is in the form of carbonate, i.e., chemically bound. This means that the coarse fraction releases this carbon dioxide from the carbonate during further treatment in the calciner and furnace. This range enables the greatest possible CO2 separation, and the residual content leads to an improved product after the actual treatment.

[0034] The system according to the invention is explained in more detail below using an embodiment shown in the drawing.

[0035] Fig. 1 Scheme of a system

[0036] Fig. 1 shows a schematic representation of a plant. In a raw material supply 10, the starting raw material for the production of cement clinker is provided. This contains, for example, calcium carbonate. The raw material is crushed in an optional crusher 20 and screened in a screening device 30. The coarse fraction, for example, everything over 20 mm, is fed to a shaft kiln 40 and thermally treated. The fine fraction from the screening device 30 and the thermally treated material from the shaft kiln 40 are fed together to a mill 50 and ground together, thereby intimately mixing them. The product ground in the mill 50 is preheated in a preheater 60, deacidified in the calciner 70, and finally fired in a kiln 80, in particular a rotary kiln. The fully fired cement clinker is cooled in the material cooler 90.

[0037] What's important is that, compared to a conventional plant, only the screening device 30 and, above all, the shaft furnace 40 are added. This allows for very easy retrofitting, allowing existing plants to be converted quickly and easily, thus saving at least some of the CO2 emissions.

[0038] Reference number 10 Raw material provision

[0039] 20 crushers

[0040] 30 screening device

[0041] 40 shaft furnace

[0042] 50 Mill 60 Preheater

[0043] 70 Calciner

[0044] 80 oven

[0045] 90 material coolers

Claims

Patent claims 1. A plant for producing cement clinker, the plant comprising a raw material supply (10), a mill (50), a preheater (60), a calciner (70), a kiln (80), and a material cooler (90), the material flow being guided from the raw material supply (10) via the mill (50), the preheater (60), the calciner (70), the kiln (80), and the material cooler (90), the material cooler (90) having a product outlet, characterized in that the plant comprises a screening device (30), the screening device (30) being connected to the raw material supply (10) for supplying raw material, the screening device (30) being designed to separate a coarse particle flow and a fine particle flow, the plant comprising a shaft furnace (40), the screening device (30) being connected to the shaft furnace (40) for transferring the coarse particle flow,wherein the shaft furnace (40) is connected to the mill (50) for transferring the thermally treated raw material, wherein the shaft furnace (40) is designed for operation with a gas of at least 50% oxygen., 2. Plant according to claim 1, characterized in that the shaft furnace (40) is designed for operation with a gas of at least 90% oxygen.

3. Plant according to one of the preceding claims, characterized in that the screening device (30) is designed for a separation between 5 mm and 50 mm.

4. Plant according to one of the preceding claims, characterized in that a CO2 separation device is connected downstream of the shaft furnace (40).

5. Plant according to one of the preceding claims, characterized in that the plant has two shafts of a GGR shaft furnace (40).

6. A process for producing cement clinker, the process comprising the following steps: a) screening the raw material into a coarse fraction and a fine fraction, b) thermally treating the coarse fraction in a shaft furnace (40) with a gas containing at least 50% oxygen, c) mixing the fine fraction and the thermally treated coarse fraction and then grinding them, or grinding the fine fraction and grinding the thermally treated coarse fraction and then mixing them, d) preheating the material, e) calcining the material, f) firing the material in a furnace, g) cooling the product. The method according to claim 6, characterized in that the screening in step a) is carried out to a size of 5 to 50 mm. The method according to any one of claims 6 to 7, characterized in that the raw material is crushed before the screening in step a). The method according to any one of claims 6 to 8, characterized in that the thermal treatment in step b) takes place in two shafts of a PGR shaft furnace (40) in alternating sequence.Process according to one of claims 6 to 9, characterized in that the coarse fraction after treatment in the shaft furnace has a carbon dioxide content of between one and eight percent by mass, preferably between three and five percent by mass.

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