Heat treatment plant and method for operating a heat treatment plant

Abstract

The heat treatment plant according to the invention has a process chamber and at least one sealing arrangement to seal the process chamber against the environment to prevent the ingress of false air, wherein the sealing arrangement has at least one first seal facing the environment and at least one second seal facing the process chamber, and wherein an intermediate chamber is formed between the first and the second seal, which is connected to a vacuum source for extracting gas that has entered the intermediate chamber.

Description

[0001] The invention relates to a heat treatment plant and a method for operating a heat treatment plant with a process chamber and at least one sealing arrangement for sealing the process chamber against the environment to prevent false air from entering the process chamber from the environment.

[0002] Heat treatment plants are used, for example, in the cement industry. This industry generates high CO2 emissions because, in addition to the CO2 from the fuel, CO2 from the feedstock, such as lime, is also released during combustion. Therefore, the current aim is to separate the CO2 afterward and prevent it from entering the environment. To obtain exhaust gas with the highest possible CO2 content, the so-called oxyfuel process is used, which operates with the purest possible oxygen as the combustion gas. The oxygen is converted to carbon dioxide, ideally resulting in a gas mixture of water and carbon dioxide. In practice, achieving this level of purity is not feasible. However, any reduction in inert gas, especially nitrogen, ultimately reduces the effort required for separation. Therefore, any unwanted gas input, known as false air, into the process has a negative impact.

[0003] To operate the cement production process as efficiently as possible, it is therefore crucial that ideally no false air enters the overall process unless absolutely necessary for the process itself (for example, during combustion). The introduction of false air can lead to both energy losses and contamination of the process gas. Especially when the plant is operated with pure oxygen in the so-called oxyfuel process, contamination of the process gas is associated with significant additional costs. In this context, the rotary kiln inlet and outlet represent a particularly challenging point in cement production, as a seal must be created between the rotating kiln tube and the stationary inlet and outlet housing. It is important to note that the kiln tube can exhibit a wobbling motion at the inlet and outlet, which can result in unfavorable mechanical stress on the sealing components.In addition, high temperatures and a dust-laden atmosphere, for example with abrasive clinker dust, must be taken into account. In the case of an oxygen-rich atmosphere (such as that found in the oxyfuel process), further influences, such as oxidation of the materials used, must also be considered.

[0004] Common solutions for sealing rotary kilns (for example, in the cement industry) include lamellar gaskets, graphite block gaskets, and contact gaskets (DE 31 14 695 A1). However, these types of gaskets typically only offer limited gas tightness (> 1,000 Nm). 3 / h false air ingress) and are therefore not well suited for applications with high sealing requirements (such as the oxyfuel process).

[0005] DE 20 2022 104 257 U1 further discloses that the contact seal on the rotary furnace has an enclosure which is connected to one of the system elements, wherein the enclosure has a gas supply line for the supply of a barrier gas. The barrier gas is preferably carbon dioxide or recirculated exhaust gas or process gas.

[0006] Furthermore, EP 2 282 836 B1 discloses a roller mill which has a barrier gas seal to seal the mill interior in the area of ​​the grinding plate against the outside atmosphere. For this purpose, the barrier gas seal has a first sealing chamber and a second sealing chamber, wherein the first sealing chamber is pressurized with a first barrier gas and the second sealing chamber with a second barrier gas, the second barrier gas having a lower pressure than the first barrier gas. A vent is connected to the second sealing chamber to discharge the second barrier gas.

[0007] However, if CO2-containing barrier gas is used, its release into the environment can be penalized with additional costs, and the barrier gas must be provided in sufficient quantities.

[0008] The invention is therefore based on the objective of providing a heat treatment plant or a heat treatment process with an improved seal that enables the best possible sealing of the process chamber, in particular against the ingress of false air.

[0009] According to the invention, this problem is solved by a heat treatment system having the features of claim 1 and a heat treatment method according to claim 11. Advantageous embodiments are described in the dependent claims, the following description, and the drawings.

[0010] The heat treatment plant according to the invention has a process chamber and at least one sealing arrangement to seal the process chamber against the environment to prevent the ingress of false air, wherein the sealing arrangement has at least one first seal facing the environment and at least one second seal facing the process chamber, and wherein an intermediate chamber is formed between the first and the second seal, which is connected to a vacuum source for extracting gas that has entered the intermediate chamber.

[0011] In the inventive method for operating a heat treatment plant with a process chamber, the process chamber is sealed against the environment by means of a sealing arrangement to prevent false air ingress, wherein at least one first seal facing the environment and at least one second seal facing the process chamber are used, wherein a gas which penetrates into an intermediate chamber formed between the first and the second seal via the first and / or second seal is extracted from the intermediate chamber.

[0012] While known solutions rely on the principle of a barrier gas supply, the invention takes the opposite approach by achieving the sealing effect through extraction from an intermediate chamber located between two seals. The (negative) pressure in the intermediate chamber can be regulated / maintained at the level of the adjacent process pressure in the process chamber to prevent the ingress of ambient air (typically ambient air) into the process chamber. The ambient air is thus extracted directly via the second seal facing the environment by means of extraction, without entering the process chamber. For the most efficient implementation of this sealing principle, the two seals (or their tightness) should be matched to the extraction capacity. Process- and / or ambient-related fluctuations in parameters such as temperature, gas composition, and / or pressure may require regulation of the extraction.

[0013] One advantage of this new sealing concept is that even a certain degree of leakage between the two seals can be tolerated while still preventing the ingress of false air into the process chamber. For example, with a seal diameter of 7,000 mm, a tilted gap of 1 mm to 5 mm can be tolerated in a pneumatic contact seal. In the area of ​​the furnace inlet, a slight fan negative pressure of -25 mbar would be sufficient if the process chamber is operated at a negative pressure of -5 mbar. The expected extraction volume would then be approximately 1,600 to 8,000 m³. 3 / h.

[0014] Regarding the pressure losses or pressure ratios of the two seals, essentially three designs are conceivable, each with its own advantages and disadvantages: According to one initial design, the second seal facing the process chamber can have a higher sealing effect and / or greater flow resistance compared to the first seal facing the environment. The advantage is that fewer furnace gases are extracted, and ideally, only the ambient air is "diverted." Consequently, the exhaust gas could also be discharged directly into the environment. However, should the first seal facing the environment suddenly become significantly leaky, the existing extraction volume may no longer be sufficient, and the ingress of false air will increase, especially since the extraction system draws in more ambient air when the sealing gap is large.

[0015] In a second design, the second seal facing the process chamber can have a lower sealing effect and / or lower flow resistance compared to the first seal facing the environment. While this directly reduces the potential for false air ingress, and can even prevent it with an extraction system, it also results in more gases being drawn out of the process chamber. This contributes to the fan exhaust being warmer and containing higher levels of emissions and dust. In this case, the exhaust duct can, for example, be supplied with an additional "fresh air" supply.

[0016] According to a third design, both seals could also be identical. This could be implemented, for example, in the raw meal feed area of ​​the cement clinker production process, where the raw meal is conveyed via two rotary valves, which form the first and second seals, and the ambient air drawn in from the outside is extracted between the two rotary valves. Currently, the ingress of ambient air is also prevented at this point using a barrier gas (e.g., CO2).

[0017] However, a combination of these designs is also conceivable: For example, in the second design, when combined with fan extraction, it must be ensured that the first seal facing the environment is always sufficiently tight so that the fan's negative pressure does not drop. Consequently, the first seal facing the environment can, for example, have a "tracking" function, so that initially the second seal facing the process chamber is tighter, but during operation the sealing effect of the first seal facing the environment increases relative to the second seal. This, of course, requires that the extraction pressure control is adjusted accordingly.

[0018] If the process chamber is operated according to the oxyfuel process, pure oxygen is used more extensively or exclusively as the combustion gas, resulting in an atmosphere in the process chamber with at least 70% to 90% CO2 or at most 10% to 30% N2.

[0019] The negative pressure source can be created, in particular, by an exhaust fan whose extraction capacity is preferably adjustable. The gas extracted from the intermediate chamber ideally contains primarily ambient air and is therefore fed to a section of the heat treatment system that has an atmosphere of less than 70% CO2 or more than 30% N2. Alternatively, the extracted gas can also be discharged directly or after processing (depending on the exhaust gas composition) into the environment.

[0020] Within the scope of the invention, it is also conceivable that the intermediate chamber is connected to a process gas line. In this case, the negative pressure in the intermediate chamber could, for example, be created by a throttle valve in the extraction line between the intermediate chamber and the process gas line.

[0021] According to a preferred option, a pressure distribution chamber is connected to the intermediate chamber in the direction of extraction. The purpose of the pressure distribution chamber is to distribute the negative pressure generated by the fan as evenly as possible over its entire circumference. This effect is achieved in particular because the flow resistance within the pressure distribution chamber is significantly lower than that of the connection to the intermediate chamber. The gas contained in the intermediate chamber can then be extracted, for example, through circumferentially arranged bores.

[0022] According to a further embodiment of the invention, at least one sensor is arranged in the intermediate chamber, the adjoining pressure distribution chamber, or the extraction line to measure one or more of the following parameters: the pressure established in the intermediate chamber, the volume of the extracted gas, the temperature of the extracted gas, the gas composition of the extracted gas, and the CO2, N2, or O2 content of the extracted gas. The sensor is operatively connected to a control device for regulating the extraction rate.

[0023] The following rule algorithms can be used as examples: • If the temperature in the exhaust gas rises, the suction power is reduced to extract less process gas from the process chamber; • The pressure in the intermediate chamber is regulated via the extraction volume or extraction pressure so that it corresponds approximately to the pressure in the process chamber. • If the CO2 level in the intermediate chamber / extraction line rises (e.g. in the area of ​​the furnace inlet seal), the extraction power is reduced to draw less process gas out of the process chamber. • If the O2 value in the intermediate chamber / extraction line increases (e.g. in the area of ​​the furnace outlet seal), the extraction power is reduced to draw less process gas out of the process chamber.

[0024] Optionally, a barrier gas supply can be installed in the area of ​​the second seal facing the process chamber, for example to supply CO2 or the recirculated process gas as a barrier gas. However, the quantity required for this is significantly lower compared to known barrier gas solutions.

[0025] According to a preferred application, the process chamber is formed by a rotary furnace system, wherein a first sealing arrangement is provided in the area of ​​an inlet and / or a second sealing arrangement is provided in the area of ​​an outlet.

[0026] The two seals in the sealing assembly are designed, for example, as contact seals and / or labyrinth seals. The sealing surfaces of the two seals can be arranged in any configuration, for example, one above the other, perpendicular, offset, or parallel.

[0027] In another application, the sealing arrangement can form part of a material feed into the process chamber, with the first seal facing the environment and the second seal facing the process chamber each being formed by air shut-off devices (such as a rotary valve or flap).

[0028] The inventive method can be used particularly advantageously when the process chamber is operated in the so-called oxyfuel process, so that an atmosphere with at least 70% - 90% CO2 or at most 10% to 30% N2 is established in the process chamber and the gas extracted from the intermediate chamber is fed to a section of the heat treatment plant with less than 70% CO2 or more than 30% N2 and / or to the environment.

[0029] Further embodiments of the invention are explained in more detail with reference to the following description and the drawing.

[0030] The drawing shows Fig. 1 a schematic representation of the sealing arrangement according to the invention, Fig. 2 a schematic representation of a first embodiment of the sealing arrangement according to the invention in the area of ​​the outlet of a rotary kiln and Fig. 3 a schematic representation of a second embodiment of the sealing arrangement according to the invention, in which the sealing arrangement forms part of a material feed into a process chamber.

[0031] Fig. Figure 1 shows a heat treatment plant 1 with a process chamber 2 and at least one sealing arrangement 3 for sealing the process chamber 2 against the environment to prevent the ingress of false air F. The sealing arrangement 3 comprises a first seal 30 facing the environment and a second seal 31 facing the process chamber 2, both of which are, for example, designed as contact seals. An intermediate chamber 32 is formed between the first and second seals 30, 31. This intermediate chamber is connected via a pressure distribution chamber 36 to a vacuum source for extracting gas that has entered the intermediate chamber 32. In the illustrated embodiment, the vacuum source is formed by a fan 33. The extracted gas is discharged via an exhaust line 34, which is, for example, connected to a process line 35.Instead of the fan 33, a simple throttle valve could also be provided if the negative pressure created by the process line 35 is utilized. The fan 33 or the throttle valve is preferably designed to be controllable and is selectively controlled by a control device 4 to set a specific extraction pressure in the intermediate chamber 32.

[0032] The extraction pressure established in the intermediate chamber 32 must be adjusted to the pressure prevailing in the process chamber 2 to prevent gas from entering the intermediate chamber 2 from the intermediate chamber 32 or from excessive gas entering the intermediate chamber from the process chamber 2. For this purpose, a first pressure sensor M1 is provided in the process chamber 2 and a second pressure sensor M2 in the intermediate chamber 32, which measure the process pressure and the pressure in the intermediate chamber 32, respectively, and transmit this information to the control unit 4. Since the pressure measurement in the intermediate chamber 32 can be easily distorted by the introduction of false air, it can be advantageous to provide an additional sensor in the pressure distribution chamber 36, which adjoins the intermediate chamber 32 in the extraction direction.

[0033] With a process vacuum of, for example, -5 mbar in process chamber 2, a vacuum of -25 mbar can be set in the intermediate chamber 32 via the fan 33. Alternatively, one or more additional sensors can be provided, located in the intermediate chamber 32, the adjoining pressure distribution chamber 36, or the extraction line 34. In the illustrated embodiment, a third sensor M3 is provided in the extraction line 34, which measures, for example, the volume, temperature, or gas composition of the extracted gas, or its CO2, N2, or O2 content, and is connected to the control unit 4. Thus, for example, a high temperature, an increased volume, a high CO2 content, or a specific gas composition may indicate that the extraction pressure is set too high and that too much process gas is being extracted from process chamber 2.

[0034] Fig. Figure 2 shows an application of a sealing arrangement 3' in the area of ​​a rotary kiln system 5, specifically in the transition area between a stationary outlet housing 6 (hatched area) and a rotating rotary kiln 7.

[0035] A co-rotating flange ring 8 extending perpendicular to the axis of rotation 7a is provided on the rotary kiln 7, which interacts with a movable sealing element 9 mounted on the outlet housing 6.

[0036] A ring 10 is fixedly attached to the outlet housing 6. This ring is arranged coaxially with the rotary kiln 7 and has an annular channel 11 at its end, oriented towards the rotary kiln 7. A ring seal 12 (e.g., a sealing cord or the like) extending around its entire circumference is inserted into this channel and interacts with a ring 9a of the movable sealing element 9, which extends parallel to the axis of rotation 7a. The stationary ring 10 and the ring 9a of the movable sealing element 9, in conjunction with the sealing ring 12, can compensate for axial movement along the double arrow 13 and also for a certain degree of tilting.

[0037] The movable sealing element 9 is pressed against the flange ring 8, which rotates with the rotary kiln 7, by a plurality of force cylinders 9b distributed around its circumference. Between the movable sealing element 9 and the flange ring 8, a first seal 30' facing the environment and a second seal 31' facing the rotary kiln 7 are provided. An intermediate chamber 32' is formed between the first and second seals 30', 31', which is connected to a vacuum source for extracting gas that has entered the intermediate chamber 32'. In the illustrated embodiment, the vacuum source is again formed by a fan 33', with the extracted gas being discharged via an exhaust line 34' and fed to a process line 35'. However, a simple throttle valve could also be provided instead of the fan 33' if the vacuum generated by the process line 35' can be utilized.

[0038] Due to the large length and diameter of the rotary kiln 7, wobbling movements occur in the inlet and outlet areas, with movement components in the direction of the double arrow 13, which are largely compensated for by the movable sealing element 9. The "vertical" height compensation is achieved via the sealing surfaces of the first and second seals 30' and 31' – since these are not rigidly connected to each other.

[0039] Naturally, corresponding sensors M1, M2, M3 are also provided for this application, which interact with a control device not shown in detail.

[0040] Fig.Figure 3 shows a material feed 15 with which bulk material 16 can be metered into a process chamber 2''. To prevent ambient air from entering the process chamber 2'' along with the bulk material 16, a sealing arrangement 3'' is provided, which in turn has a first seal 30'' facing the environment and a second seal 31'' facing the process chamber 2'', both seals being designed as air shut-off devices (here as rotary valves). An intermediate chamber 32'' is provided between the two seals, which is connected to a vacuum source for extracting gas that has entered the intermediate chamber 32'' along with the bulk material. In the illustrated embodiment, the vacuum source is formed by a fan 33'', with the extracted gas being discharged via an exhaust line and, for example, introduced into a process line 35''.

[0041] Similarly, sensors M1 and M2 can be provided to measure the pressure in process chamber 2'' and intermediate chamber 32'', respectively, and transmit this data to a control device (not shown here). Furthermore, another sensor M3 can also be provided in the exhaust pipe 34''.

[0042] Any air introduced into the intermediate chamber 32'' with the bulk material 16 via the first seal 30'' (rotary valve) can be extracted by the fan 33'', so that the entry of false air into the process chamber 2'' is prevented or at least greatly reduced. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 31 14 695 A1

[0004] DE 20 2022 104 257 U1

[0005] EP 2 282 836 B1

[0006]

Claims

[1] Heat treatment plant (1) with a process chamber (2) and at least one sealing arrangement (3) for sealing the process chamber (2) from the environment to prevent the ingress of false air, wherein the sealing arrangement (3) has at least one first seal (30) facing the environment and at least one second seal (31) facing the process chamber (2), and wherein an intermediate chamber (32) is formed between the first and the second seal (30, 31), which is connected to a vacuum source for extracting gas that has entered the intermediate chamber (32). [2] Heat treatment plant (1) according to claim 1, characterized by , that the second seal (31) facing the process chamber (2) has a higher sealing effect and / or a greater flow resistance compared to the first seal (30) facing the environment. [3] Heat treatment plant (1) according to claim 1, characterized by, that the second seal (31) facing the process chamber (2) has a lower sealing effect and / or a lower flow resistance compared to the first seal (30) facing the environment. [4] Heat treatment plant (1) according to claim 1, characterized by that the negative pressure source is formed by an exhaust fan (34) or that the intermediate chamber (32) is connected to a process gas line (35). [5] Heat treatment plant (1) according to claim 3, characterized by, that at least one sensor (M1, M2, M3) is arranged in the intermediate chamber (32) or in an adjoining extraction line (34) to measure one or more of the following parameters: the pressure established in the intermediate chamber (32), the volume of the extracted gas, the temperature of the extracted gas, the gas composition of the extracted gas, the CO2 and / or N2 and / or O2 content of the extracted gas; and the sensor (M1, M2, M3) is operatively connected to a control device (4) for controlling the extraction rate from the intermediate chamber (32). [6] Heat treatment plant (1) according to claim 1, characterized by , that a barrier gas supply opens in the area of ​​the second seal (31) facing the process chamber (2). [7] Heat treatment plant according to claim 1, characterized by, that the process chamber is formed by a rotary furnace system (5), wherein a first sealing system is provided in the area of ​​an inlet and / or a second sealing system is provided in the area of ​​an outlet. [8] Heat treatment plant (1) according to claim 1, characterized by , that the sealing arrangement (3'') forms part of a material feed into the process chamber (2''), wherein the first seal (30'') facing the environment and the second seal (31'') facing the process chamber (2'') are each formed by air sealing devices. [9] Heat treatment plant (1) according to claim 1, characterized by , that the first and second seals (30, 31) are designed as contact seals and / or labyrinth seals. [10] Heat treatment plant (1) according to claim 1, characterized by , that a pressure distribution chamber (36) is connected to the intermediate chamber (32) in the direction of extraction. [11] Method for operating a heat treatment plant (1) with a process chamber (2), wherein the process chamber (2) is sealed against the environment by means of a sealing arrangement (3) to prevent the ingress of false air, wherein at least one first seal (30) facing the environment and at least one second seal (31) facing the process chamber (2) are used, wherein a gas which enters an intermediate chamber (32) formed between the first and the second seal (30, 31) via the first and / or second seal (30, 31) is extracted from the intermediate chamber (32). [12] Method according to claim 11 characterized by , that for the second seal (32) a seal is used which has a higher sealing effect and / or a greater flow resistance compared to the first seal (31). [13] Method according to claim 11 characterized by, that for the second seal (31) a seal is used which has a lower sealing effect and / or a lower flow resistance compared to the first seal (31). [14] Method according to claim 11 characterized by , that at least one sensor (M1, M2, M3) is used in the intermediate chamber (32) or in an adjoining extraction line (34), to measure one or more of the following parameters: the pressure established in intermediate chamber (32), the volume of the extracted gas, the temperature of the extracted gas, the gas composition of the extracted gas, the CO2 and / or N2 and / or O2 content of the extracted gas; the measured parameter is used to control the suction pressure from the intermediate chamber (32). [15] Method according to claim 11 characterized by, that the process chamber (2) is operated in such a way that an atmosphere with at least 70% CO2 or at most 30% N2 is established in the process chamber (2) and the gas extracted from the intermediate chamber (32) is supplied to a section of the heat treatment plant (1) with less than 70% CO2 or more than 30% N2 and / or to the environment.

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