Efficient preheater for rotary kiln

Abstract

The utility model relates to the technical field of preheaters, and provides an efficient preheater for a rotary kiln, which is characterized in that a distributor is arranged in a shell and is used for dividing the interior of the shell into an upper preheating bin and a lower preheating bin; the discharging chute tube is arranged in the shell and located on the periphery of the distributing device, the upper end of the discharging chute tube is communicated with the upper preheating bin, and the lower end of the discharging chute tube is communicated with the lower preheating bin; one end of the lower preheating pipeline is used for being communicated with a waste gas discharge pipe, and the other end of the lower preheating pipeline is used for extending into the lower preheating bin; one end of the upper preheating pipeline is used for being communicated with a waste gas discharging pipe, and the other end of the upper preheating pipeline is communicated with the upper preheating bin. One end of the lower waste gas recovery pipe is communicated with the lower preheating bin, and the other end of the lower waste gas recovery pipe is communicated with waste gas treatment equipment; one end of the upper waste gas recovery pipe is communicated with the upper preheating bin, and the other end of the upper waste gas recovery pipe is communicated with the lower waste gas recovery pipe. According to the technical scheme, the problem that the preheating effect of a preheater on materials needs to be improved in the prior art is solved.

Description

Technical Field

[0001] This utility model relates to the field of preheater technology, specifically to a high-efficiency preheater for rotary kilns. Background Technology

[0002] The rotary kiln preheater is one of the most important pieces of equipment in a rotary kiln system, directly affecting the kiln's thermal efficiency and production costs. The functions of the preheater are: ① To improve thermal efficiency: It utilizes the high-temperature exhaust gas from the rotary kiln to preheat the material entering the kiln, fully recovering the heat from the exhaust gas, reducing energy consumption, and improving the overall system's thermal efficiency; ② To improve material properties: The preheating process evaporates moisture from the material, reducing its water content, and causes physicochemical changes such as decomposition of some minerals, improving the material's calcinability and thus enhancing the calcination quality and output of the rotary kiln.

[0003] The preheater works as follows: material enters the top of the preheater from the raw material silo, and under gravity, it sequentially enters the preheating chamber through various discharge chutes. Inside the preheating chamber, it exchanges heat with the high-temperature exhaust gas from the rotary kiln, preheating the material. The material then enters the rotary kiln for calcination. After the high-temperature exhaust gas has completed heat exchange, it is treated by exhaust gas treatment equipment, and the exhaust gas meeting national emission standards is released into the atmosphere through a chimney. However, the preheating effect of this type of preheater needs improvement. Utility Model Content

[0004] This invention proposes a high-efficiency preheater for rotary kilns, which solves the problem that the preheating effect of preheaters on materials needs to be improved in related technologies.

[0005] The technical solution of this utility model is as follows: A high-efficiency preheater for a rotary kiln, used to connect to the exhaust pipe of the rotary kiln, the key feature being: comprising,

[0006] case,

[0007] A material distributor, which is disposed inside the housing, is used to divide the interior of the housing into an upper preheating chamber and a lower preheating chamber;

[0008] The material discharge chute is disposed inside the housing and located around the material distributor. The upper end of the material discharge chute is connected to the upper preheating chamber, and the lower end of the material discharge chute is connected to the lower preheating chamber.

[0009] A lower preheating pipe, one end of which is used to connect to the exhaust pipe, and the other end of which is used to extend into the lower preheating chamber;

[0010] An upper preheating pipe, one end of which is connected to the exhaust gas discharge pipe, and the other end of which is connected to the upper preheating chamber;

[0011] A lower exhaust gas recovery pipe, one end of which is connected to the lower preheating chamber, and the other end of which is used to connect to the exhaust gas treatment equipment;

[0012] An upper waste gas recovery pipe is provided, one end of which is connected to the upper preheating chamber, and the other end of which is connected to the lower waste gas recovery pipe.

[0013] The lower preheating pipe and the upper preheating pipe are located on one side of the shell, and the lower waste gas recovery pipe and the upper waste gas recovery pipe are located on the other side of the shell.

[0014] There are multiple lower preheating pipes and multiple upper preheating pipes, and their axes are arranged radially along the shell. All the lower preheating pipes and the upper preheating pipes are arranged circumferentially along the shell.

[0015] The lower preheating pipe and the upper preheating pipe are arranged in a one-to-one correspondence along the vertical direction.

[0016] It also includes an intake regulating valve, the inlet of which is connected to the exhaust pipe, one outlet of which is connected to the lower preheating pipe, and the other outlet of which is connected to the upper preheating pipe.

[0017] The number of both the lower waste gas recovery pipe and the upper waste gas recovery pipe is at least two, and they are connected in a one-to-one correspondence.

[0018] It also includes an exhaust gas regulating valve, which is installed on the upper exhaust gas recovery pipe.

[0019] It also includes a preheating chamber, which is located inside the housing and around the material distributor. The lower end of the discharge chute is connected to the preheating chamber. The lower preheating pipe and the lower waste gas recovery pipe are both connected to the preheating chamber. A discharge port is provided at the bottom of the preheating chamber.

[0020] The lower end of the shell includes an upper buffer section and a lower discharge section. The diameters of both the upper buffer section and the lower discharge section gradually decrease from top to bottom, and the minimum diameter of the upper buffer section is equal to the maximum diameter of the lower discharge section. The preheating chamber is located above the upper buffer section. The preheater also includes...

[0021] A pusher plate, which is slidably disposed on the upper buffer section and located below the preheating chamber;

[0022] A push-pull rod, the inner end of which is hinged to the push plate, and the outer end of which passes through the housing and extends to the outside of the housing;

[0023] A positioning rod is located around the periphery of the housing. The upper end of the positioning rod is hinged to the housing, and the lower end of the positioning rod is inclined away from the housing. The outer end of the push-pull rod is hinged to the positioning rod.

[0024] A push-pull drive mechanism is located around the periphery of the housing and below the push-pull rod. The lower end of the push-pull drive mechanism is hinged to the housing, and the upper end of the push-pull drive mechanism is hinged to the positioning rod.

[0025] Both the lower and upper waste gas recovery pipes have filters at their inlet ends.

[0026] The working principle and beneficial effects of this utility model are as follows: The material distributor is installed inside the housing to divide the interior of the housing into an upper preheating chamber and a lower preheating chamber; the material discharge chute is installed inside the housing and located outside the material distributor, with its upper end connected to the upper preheating chamber and its lower end connected to the lower preheating chamber; one end of the lower preheating pipe is connected to the exhaust gas discharge pipe, and the other end of the lower preheating pipe extends into the lower preheating chamber; one end of the upper preheating pipe is connected to the exhaust gas discharge pipe, and the other end of the upper preheating pipe is connected to the upper preheating chamber; one end of the lower exhaust gas recovery pipe is connected to the lower preheating chamber, and the other end of the lower exhaust gas recovery pipe is connected to the exhaust gas treatment equipment; one end of the upper exhaust gas recovery pipe is connected to the upper preheating chamber, and the other end of the upper exhaust gas recovery pipe is connected to the lower exhaust gas recovery pipe.

[0027] After entering the top of the preheater from the raw material silo, the material first enters the upper preheating chamber, separated by a distributor within the shell. Then, under gravity, it flows through various discharge chutes into the lower preheating chamber. The high-temperature exhaust gas from the rotary kiln exits through the exhaust pipe. Part of the exhaust gas enters the upper preheating chamber through the upper preheating pipe, exchanging heat with the material there. The other part extends into the lower preheating chamber through the lower preheating pipe, exchanging heat with the material there as well. The heated material then enters the rotary kiln for calcination. After heat exchange, the high-temperature exhaust gas exits through the lower and upper exhaust gas recovery pipes and is then treated by the exhaust gas treatment equipment. In other words, the material undergoes initial preheating in the upper preheating chamber and then secondary preheating in the lower preheating chamber. This double preheating increases the contact area and time between the material and the exhaust gas, effectively improving the preheating effect. This allows the material to reach the required temperature more quickly and evenly, providing better conditions for calcination in the rotary kiln and contributing to improved product quality and production efficiency. Attached Figure Description

[0028] The preferred embodiments will be described below in a clear and easy-to-understand manner, in conjunction with the accompanying drawings, to further explain the above-mentioned characteristics, technical features, advantages and implementation methods of this utility model.

[0029] Figure 1This is a schematic diagram of the structure of this utility model.

[0030] Figure 2 This is a top view of the arrangement of the preheating pipe and the waste gas recovery pipe in this utility model.

[0031] Figure 3 This is a schematic diagram of the connection structure between the pusher plate and the push-pull drive mechanism in this utility model.

[0032] In the diagram: 1. Shell, 2. Material distributor, 3. Feed chute, 4. Lower preheating pipe, 5. Upper preheating pipe, 6. Lower waste gas recovery pipe, 7. Upper waste gas recovery pipe, 8. Inlet regulating valve, 9. Outlet regulating valve, 10. Preheating chamber, 11. Push plate, 12. Push-pull rod, 13. Positioning rod, 14. Push-pull drive mechanism. Detailed Implementation

[0033] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the specific implementation methods of this utility model will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of this utility model. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0034] To keep the drawings concise, only the parts relevant to the utility model are shown schematically in each drawing; these do not represent the actual structure of the product. Furthermore, for ease of understanding, in some drawings, only one of the components with the same structure or function is schematically shown, or only one is labeled. In this document, "a" not only means "only one," but can also mean "more than one," and "several" includes "two" and "more than two."

[0035] In this document, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0036] Furthermore, in the description of this application, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0037] Example, refer to Figures 1-2As one embodiment of this utility model, a high-efficiency preheater for a rotary kiln is proposed, which is used to connect to the exhaust gas pipe of the rotary kiln. It includes a shell 1, a distributor 2, a discharge chute 3, a lower preheating pipe 4, an upper preheating pipe 5, a lower exhaust gas recovery pipe 6, and an upper exhaust gas recovery pipe 7. The distributor 2 is disposed inside the shell 1, dividing the interior of the shell 1 into an upper preheating chamber and a lower preheating chamber. The discharge chute 3 is disposed inside the shell 1 and located outside the distributor 2. The upper end of the discharge chute 3 communicates with the upper preheating chamber, and the lower end of the discharge chute 3 communicates with the lower preheating chamber. The preheating chamber is connected; one end of the lower preheating pipe 4 is used to connect to the exhaust gas discharge pipe, and the other end of the lower preheating pipe 4 is used to extend into the lower preheating chamber; one end of the upper preheating pipe 5 is used to connect to the exhaust gas discharge pipe, and the other end of the upper preheating pipe 5 is used to connect to the upper preheating chamber; one end of the lower exhaust gas recovery pipe 6 is used to connect to the lower preheating chamber, and the other end of the lower exhaust gas recovery pipe 6 is used to connect to the exhaust gas treatment equipment; one end of the upper exhaust gas recovery pipe 7 is used to connect to the upper preheating chamber, and the other end of the upper exhaust gas recovery pipe 7 is used to connect to the lower exhaust gas recovery pipe 6.

[0038] In this embodiment, the upper end of the material distributor 2 is conical. The cooperation between the material distributor 2 and the discharge chute 3 ensures the uniform distribution and orderly flow of materials within the preheater, preventing material blockage and accumulation, and improving the stability and reliability of the system operation. After the material enters the top of the preheater from the raw material silo, it first enters the upper preheating chamber separated by the material distributor 2 within the shell 1, and then enters the lower preheating chamber through the various discharge chutes 3 under gravity. After the high-temperature exhaust gas from the rotary kiln is discharged from the exhaust gas discharge pipe, part of the exhaust gas enters the upper preheating chamber through the upper preheating pipe 5 to exchange heat with the material in the upper preheating chamber, and the other part of the exhaust gas extends into the lower preheating chamber through the lower preheating pipe 4 to exchange heat with the material in the lower preheating chamber. The heated material enters the rotary kiln for calcination. After the high-temperature exhaust gas has completed heat exchange, it is discharged through the lower exhaust gas recovery pipe 6 and the upper exhaust gas recovery pipe 7, and then enters the exhaust gas treatment equipment for processing. In other words, the material is first preheated in the upper preheating chamber and then preheated a second time in the lower preheating chamber. This double preheating increases the contact area and time between the material and the exhaust gas, effectively improving the preheating effect. This allows the material to reach the required temperature more quickly and evenly, providing better conditions for calcination in the rotary kiln and helping to improve product quality and production efficiency.

[0039] Furthermore, such as Figure 1 and Figure 2As shown, the lower preheating pipe 4 and the upper preheating pipe 5 are located on one side of the shell 1, while the lower waste gas recovery pipe 6 and the upper waste gas recovery pipe 7 are located on the other side of the shell 1. Taking the example where the lower preheating pipe 4 and the upper preheating pipe 5 are both located on the right side of the shell 1, and the lower waste gas recovery pipe 6 and the upper waste gas recovery pipe 7 are both located on the left side of the shell 1, the waste gas enters from the right side of the shell 1, exchanges heat with the material, and then exits from the left side of the shell 1. This ensures that the waste gas and the material are in full contact, allowing the material to absorb the heat from the waste gas more comprehensively and evenly, thereby reaching the preheating temperature more quickly and evenly, and improving the utilization rate of the waste gas heat. Moreover, the centralized arrangement of the pipes makes the structure more compact.

[0040] Furthermore, such as Figure 1 and Figure 2 As shown, there are multiple lower preheating pipes 4 and upper preheating pipes 5, and their axes are arranged radially along the shell 1. All lower preheating pipes 4 and upper preheating pipes 5 are arranged circumferentially along the shell 1. The number of lower preheating pipes 4 and upper preheating pipes 5 is 4-10. Taking eight as an example, the eight upper preheating pipes 5 are evenly arranged on the right side of the shell 1. Correspondingly, the eight lower preheating pipes 4 are also evenly arranged on the right side of the shell. This allows the high-temperature exhaust gas to be more evenly dispersed to various positions on the right side of the shell 1 after entering from the exhaust pipe. The radial arrangement facilitates the diffusion of exhaust gas in all directions and allows for more thorough contact with the materials.

[0041] Furthermore, such as Figure 1 and Figure 2 As shown, the lower preheating pipe 4 and the upper preheating pipe 5 are arranged in a one-to-one correspondence along the vertical direction, that is, each lower preheating pipe 4 is located directly below an upper preheating pipe 5, so that the materials in the upper and lower preheating chambers can be heated by the exhaust gas relatively evenly, ensuring the uniformity of preheating, and making the overall shape more neat and beautiful.

[0042] Furthermore, such as Figure 1 As shown, it also includes an intake regulating valve 8. The inlet end of the intake regulating valve 8 is connected to the exhaust gas discharge pipe, one outlet end of the intake regulating valve 8 is connected to the lower preheating pipe 4, and the other outlet end of the intake regulating valve 8 is connected to the upper preheating pipe 5. According to the actual production situation, by adjusting the intake regulating valve 8, the amount of exhaust gas entering the lower preheating pipe 4 and the upper preheating pipe 5 can be adjusted to achieve a better preheating effect and improve energy utilization.

[0043] Furthermore, such as Figure 1 and Figure 2As shown, there are at least two lower waste gas recovery pipes 6 and two upper waste gas recovery pipes 7, and they are connected in a one-to-one correspondence. The two lower waste gas recovery pipes 6 are symmetrically arranged on the left side of the shell 1, and the two upper waste gas recovery pipes 7 are also symmetrically arranged on the left side of the shell 1. Each lower waste gas recovery pipe 6 is located directly below one of the upper waste gas recovery pipes 7. This layout facilitates the separate collection of waste gas from the upper and lower preheating chambers after complete heat exchange, allowing the waste gas to be discharged quickly and orderly. The multiple pipes improve the efficiency of waste gas recovery, prevent waste gas accumulation in the chambers, ensure stable pressure in the preheating chambers, and promote normal preheating and flow of materials. This prevents waste gas from interfering with material preheating due to poor discharge, thus improving the stability of the system operation. The one-to-one correspondence between the lower waste gas recovery pipes 6 and the upper waste gas recovery pipes 7 makes the overall appearance neater and more aesthetically pleasing.

[0044] Furthermore, such as Figure 1 As shown, it also includes an exhaust gas regulating valve 9, which is installed on the upper exhaust gas recovery pipe 7 and can regulate the discharge flow rate and pressure of the exhaust gas in the upper preheating chamber. By adjusting the opening of the exhaust gas regulating valve, the gas pressure in the upper preheating chamber can be controlled to match the pressure of the lower preheating chamber and the entire system, ensuring smooth discharge of exhaust gas and helping to maintain stable operating conditions in the preheating chamber.

[0045] Furthermore, such as Figure 1 As shown, it also includes a preheating chamber 10, which is located inside the shell 1 and around the material distributor 2. The lower end of the discharge chute is connected to the preheating chamber 10. The lower preheating pipe 4 and the lower waste gas recovery pipe 6 are also connected to the preheating chamber 10. A discharge port is provided at the bottom of the preheating chamber 10. After the material enters the preheating chamber 10 through the discharge chute 3, it can fully exchange heat with the high-temperature waste gas entering through the lower preheating pipe 4 in this relatively concentrated space, which helps to uniformly increase the material temperature and further improve the preheating efficiency and the quality of material preheating. The discharge port ensures smooth material discharge, avoids material accumulation in the preheating chamber 10, and ensures the continuity and stability of production.

[0046] Furthermore, such as Figure 1 and Figure 3As shown, the lower end of the housing 1 includes an upper buffer section and a lower discharge section. The diameters of both the upper buffer section and the lower discharge section gradually decrease from top to bottom, and the minimum diameter of the upper buffer section is equal to the maximum diameter of the lower discharge section. The preheating chamber 10 is located above the upper buffer section. The preheater also includes a pusher plate 11, a push-pull rod 12, a positioning rod 13, and a push-pull drive mechanism 14. The pusher plate 11 is slidably disposed on the upper buffer section and located below the preheating chamber 10; the inner end of the push-pull rod 12 is connected to... The push plate 11 is hinged, and the outer end of the push-pull rod 12 extends through the housing 1 and to the outside of the housing 1. The positioning rod 13 is located on the periphery of the housing 1, with the upper end of the positioning rod 13 hinged to the housing 1 and the lower end of the positioning rod 13 inclined away from the housing 1. The outer end of the push-pull rod 12 is hinged to the positioning rod 13. The push-pull drive mechanism 14 is located on the periphery of the housing 1 and below the push-pull rod 12. The lower end of the push-pull drive mechanism 14 is hinged to the housing 1, and the upper end of the push-pull drive mechanism 14 is hinged to the positioning rod 13.

[0047] The diameters of the upper buffer section and the lower discharge section at the lower end of the housing 1 gradually decrease. The pusher plate 11 is slidably disposed in the upper buffer section and located below the preheating chamber 10. This structural design provides a transition buffer zone for the material during its downward flow, where the pusher plate 11 can play a better role. The push-pull drive mechanism 14 provides power for the movement of the pusher plate 11. Through the extension and retraction of the push-pull drive mechanism 14, the positioning rod 13 can be driven to rotate around its hinge point with the housing 1. The positioning rod 13 drives the pusher plate 11 to slide on the upper buffer section through the push-pull rod 12. The pusher plate 11 pushes the material smoothly through the upper buffer section into the lower discharge section. This effectively avoids material blockage in the upper buffer section, ensuring that the material can smoothly enter the next process from the preheating chamber 10, thus improving production efficiency.

[0048] Furthermore, both the lower waste gas recovery pipe 6 and the upper waste gas recovery pipe 7 have filter screens at their inlet ends. These filter screens prevent materials from entering subsequent waste gas treatment equipment, avoiding equipment blockage or damage, reducing equipment maintenance costs and failure rates, and ensuring the normal operation of the waste gas treatment system.

[0049] It should be noted that the above embodiments are only used to illustrate the technical solution of this utility model and are not intended to limit it. Although this utility model has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solution of this utility model without departing from the spirit and scope of the technical solution of this utility model, and all such modifications or substitutions should be covered within the scope of the claims of this utility model.

Claims

1. A high-efficiency preheater for a rotary kiln, used for connection to the exhaust pipe of the rotary kiln, characterized in that: include, Shell (1) Fabric feeder (2), the fabric feeder (2) is disposed inside the housing (1) and is used to divide the interior of the housing (1) into an upper preheating chamber and a lower preheating chamber; The material discharge chute (3) is located inside the housing (1) and outside the material distributor (2). The upper end of the material discharge chute (3) is connected to the upper preheating chamber, and the lower end of the material discharge chute (3) is connected to the lower preheating chamber. The lower preheating pipe (4) has one end connected to the exhaust pipe and the other end extended into the lower preheating chamber. Upper preheating pipe (5), one end of which is connected to the exhaust pipe, and the other end of which is connected to the upper preheating chamber; The lower waste gas recovery pipe (6) is connected at one end to the lower preheating chamber and at the other end to the waste gas treatment equipment. The upper waste gas recovery pipe (7) is connected at one end to the upper preheating chamber and at the other end to the lower waste gas recovery pipe (6).

2. The high-efficiency preheater for a rotary kiln according to claim 1, characterized in that: The lower preheating pipe (4) and the upper preheating pipe (5) are located on one side of the shell (1), and the lower waste gas recovery pipe (6) and the upper waste gas recovery pipe (7) are located on the other side of the shell (1).

3. The high-efficiency preheater for a rotary kiln according to claim 1, characterized in that: There are multiple lower preheating pipes (4) and upper preheating pipes (5), and their axes are arranged radially along the shell (1). All the lower preheating pipes (4) and upper preheating pipes (5) are arranged circumferentially along the shell (1).

4. A high-efficiency preheater for a rotary kiln according to claim 1, characterized in that: The lower preheating pipe (4) and the upper preheating pipe (5) are arranged in a one-to-one correspondence along the vertical direction.

5. A high-efficiency preheater for a rotary kiln according to claim 1, characterized in that: It also includes an intake regulating valve (8), the inlet end of which is connected to the exhaust pipe, one outlet end of which is connected to the lower preheating pipe (4), and the other outlet end of which is connected to the upper preheating pipe (5).

6. A high-efficiency preheater for a rotary kiln according to claim 1, characterized in that: The number of the lower waste gas recovery pipe (6) and the upper waste gas recovery pipe (7) are both at least two, and they are connected in a one-to-one correspondence.

7. A high-efficiency preheater for a rotary kiln according to claim 6, characterized in that: It also includes an exhaust regulating valve (9), which is installed on the upper exhaust gas recovery pipe (7).

8. A high-efficiency preheater for a rotary kiln according to claim 1, characterized in that: It also includes a preheating chamber (10), which is located inside the housing (1) and outside the material distributor (2). The lower end of the discharge chute (3) is connected to the preheating chamber (10). The lower preheating pipe (4) and the lower waste gas recovery pipe (6) are both connected to the preheating chamber (10). The bottom of the preheating chamber (10) is provided with a discharge port.

9. A high-efficiency preheater for a rotary kiln according to claim 8, characterized in that: The lower end of the shell (1) includes an upper buffer section and a lower discharge section. The diameters of the upper buffer section and the lower discharge section gradually decrease from top to bottom, and the minimum diameter of the upper buffer section is equal to the maximum diameter of the lower discharge section. The preheating chamber (10) is located above the upper buffer section. The preheater also includes... Pusher plate (11), which is slidably disposed on the upper buffer section and located below the preheating chamber (10); Push-pull rod (12), the inner end of which is hinged to the push plate (11), and the outer end of which passes through the housing (1) and extends to the outside of the housing (1); Positioning rod (13), the positioning rod (13) is located on the periphery of the housing (1), the upper end of the positioning rod (13) is hinged to the housing (1), the lower end of the positioning rod (13) is inclined away from the housing (1), and the outer end of the push-pull rod (12) is hinged to the positioning rod (13); Push-pull drive mechanism (14) is located around the housing (1) and below the push-pull rod (12). The lower end of the push-pull drive mechanism (14) is hinged to the housing (1), and the upper end of the push-pull drive mechanism (14) is hinged to the positioning rod (13).

10. A high-efficiency preheater for a rotary kiln according to claim 1, characterized in that: Both the lower waste gas recovery pipe (6) and the upper waste gas recovery pipe (7) have filters at their inlet ends.

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