Pre-oxidation furnace import and export hall

Abstract

The application provides a pre-oxidation furnace import and export hall, and relates to the technical field of carbon fibers, so as to solve one of the technical problems that the effective length of the constant temperature zone of the furnace cavity of the pre-oxidation furnace is short, the temperature of the carbon fiber tows changes suddenly when entering the furnace cavity from the outside, and the air seal stability is poor. The pre-oxidation furnace import and export hall is used for being arranged at the import end and / or the export end of the pre-oxidation furnace, and the hall comprises a body and a circulating air system arranged around the body. The body comprises a cavity for passing the carbon fibers, which is surrounded by a shell, and the cavity is used for preheating the carbon fibers. The pre-oxidation furnace import and export hall can effectively improve the effective length of the constant temperature zone of the furnace cavity of the pre-oxidation furnace.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber technology, and in particular to an inlet / outlet hall for a pre-oxidation furnace. Background Technology

[0002] The pre-oxidation furnace is a crucial piece of equipment in the production of PAN-based carbon fiber. In the pre-oxidation furnace, PAN precursor fibers combine with oxygen molecules in the air, transforming the linear molecular chains of the PAN precursor fibers into pre-oxidized fibers with a heat-resistant trapezoidal structure. These fibers are then carbonized at high temperatures to form carbon fibers with a disordered graphite structure. During the pre-oxidation process, some waste gas overflows from the furnace through the inlet and outlet, causing an increase in the temperature around the furnace and the generation of harmful gases. Summary of the Invention

[0003] The purpose of this invention is to provide an inlet and outlet hall for a pre-oxidation furnace to solve one of the technical problems of short effective length of constant temperature zone in the furnace cavity, sudden temperature change of carbon fiber bundles entering the furnace cavity from the outside, and poor gas seal stability.

[0004] To achieve the above objectives, the present invention provides the following technical solution: This invention provides an inlet and outlet hall for a pre-oxidation furnace, the hall being disposed at the inlet end and / or outlet end of the pre-oxidation furnace, the hall comprising a body and a circulating air system surrounding a portion of the body; The body includes a cavity enclosed by a shell for passing through carbon fibers, the cavity being used to preheat the carbon fibers.

[0005] According to at least one embodiment of the present invention, the housing includes a frame structure and a furnace plate disposed on the frame structure.

[0006] According to at least one embodiment of the present invention, the furnace plate is composed of an insulation plate and an aluminized plate covering the insulation plate.

[0007] According to at least one embodiment of the present invention, the thickness of the insulation board is 200 mm.

[0008] According to at least one embodiment of the present invention, the insulation board includes multiple sub-boards, each layer having multiple sub-boards, and the joints of the sub-boards in each layer are staggered.

[0009] According to at least one embodiment of the present invention, the temperature inside the cavity is less than or equal to the furnace cavity temperature of the pre-oxidation furnace.

[0010] According to at least one embodiment of the present invention, the temperature inside the cavity is 150°C to 200°C.

[0011] According to at least one embodiment of the present invention, the circulating air system includes a return air box, an inlet air box, and an air duct connecting the return air box and the inlet air box; The return air box is located at the top of the main body and communicates with the cavity; the air inlet box is located at the bottom of the main body and communicates with the cavity; the air duct is located on one side of the main body.

[0012] According to at least one embodiment of the present invention, the circulating air system further includes a filter, a fan, and a heater, wherein the filter, the fan, and the heater are sequentially arranged in the air duct along the direction from the return air box to the inlet air box.

[0013] According to at least one embodiment of the present invention, the circulating air system further includes an exhaust pipe, which is in communication with the cavity.

[0014] In one or more technical solutions provided in the exemplary embodiments of the present invention, at least one of the following beneficial effects can be achieved.

[0015] The exemplary embodiment of the present invention provides a hall with a hot air circulation system. The length of the constant temperature zone affected by heat exchange at the inlet and outlet of the furnace cavity is only about 0.3 meters, which increases the total length of the effective constant temperature zone in the furnace cavity. That is, while ensuring the full oxidation of the fiber bundle in the pre-oxidation furnace cavity, the running speed of the carbon fiber bundle can be increased by more than 10%.

[0016] Furthermore, since the air inlets of the upper and lower air-sealed boxes face each other, the two streams of air form an air curtain after they collide here, and then diffuse into and out of the hall. Part of it moves into the hall along the wire-laying channel, which just prevents the gas in the hall from escaping outward; the other part moves out of the hall along the wire-laying channel, mixes with the cold air entering from outside the hall, and then enters the return air chamber through the return air inlet, so that the mixed gas will not enter the hall.

[0017] Furthermore, the perforated plate of the return air inlet is a tracked perforated plate. It can be moved out of the wire feeding channel along the track groove by a stepper motor and guide rollers, and the broken wires attached to the surface can be cleaned by a cleaning brush. The area of ​​the perforated plate after cleaning is reintroduced into the wire feeding channel to continue working. The whole process does not require machine shutdown, ensuring the continuity of the air seal and significantly improving the operating efficiency of the equipment and the consistency of carbon fiber quality. Attached Figure Description

[0018] The accompanying drawings illustrate exemplary embodiments of the invention and, together with the description thereof, serve to explain the principles of the invention. These drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification.

[0019] Figure 1This is a partial cross-sectional structural schematic diagram of the entrance hall and oxidation furnace according to an embodiment of the present invention; Figure 2 This is a top view of the entrance hall and oxidation furnace according to an embodiment of the present invention; Figure 3 This is a cross-sectional structural schematic diagram of an air-sealing system according to an embodiment of the present invention; Figure 4 yes Figure 3 Enlarged view of part A; Figure 5 This is a front view structural diagram of the entrance hall according to an embodiment of the present invention.

[0020] Figure label: 100. Fiber bundle; 101. Fiber feeding channel; 10. Ontology; 20. Oxidation furnace; 31. Return air box; 32. Air duct; 321. Filter screen; 322. Fan; 323. Heater; 33. Air inlet box; 34. Exhaust pipe; 40. Air seal box; 41. Air inlet chamber; 411. Air inlet; 42. Return air chamber; 421. Return air outlet; 421a. Track groove; 43. Valve; 44. Main air inlet duct; 45. Main return air duct; 50. Perforated plate; 51. Guide roller; 52. Cleaning brush; 61. Laser module; 62. Regulating valve; 63. Airbag. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0022] When carbon fiber precursor undergoes pre-oxidation in the pre-oxidation furnace, some toxic waste gas overflows through the furnace inlet and outlet, causing an increase in ambient temperature and posing a risk of leakage of toxic gases such as HCN. While existing gas collection hoods installed at the furnace inlet and outlet can extract some waste gas, they also draw out high-temperature airflow from the furnace, disrupting the internal thermal balance and exacerbating temperature fluctuations.

[0023] Example 1 To address the issue of reduced constant temperature zone within the furnace cavity due to heat exchange between the furnace body and the external environment. Figure 1 This is a partial cross-sectional structural schematic diagram of the entrance hall and oxidation furnace according to an embodiment of the present invention; Figure 2 This is a top view of the entrance hall and oxidation furnace according to an embodiment of the present invention. Figure 1 and Figure 2As shown, an exemplary embodiment of the present invention provides a vestibule structure with a temperature buffer function, wherein the vestibule is located at the inlet end and / or outlet end of the pre-oxidation furnace 20, thereby reducing heat loss in the furnace cavity.

[0024] Figure 1 The diagram shows the foyer structure, with a partial sectional view of the left half and the right half showing the airtight structure at the foyer entrance. Combined with... Figure 1 and Figure 2 It can be seen that, in Figure 1 In the process, the pre-oxidation furnace 20 is located behind the portal hall, which is located at the inlet end of the oxidation furnace 20. That is, after the carbon fiber enters the portal hall through the gas seal structure at the inlet of the portal hall, it enters the furnace chamber of the oxidation furnace 20 through the gas seal structure between the portal hall and the furnace chamber for pre-oxidation reaction. After the oxidation reaction is completed, it enters the outlet portal hall through the gas seal structure between the furnace chamber and the outlet portal hall, and is finally led out by the gas seal structure at the outlet of the portal hall.

[0025] Figure 1 The carbon fiber bundle 100 shown is its cross-section. The carbon fiber bundle 100 enters the interior of the hall through a slit-like wire-feeding channel 101 formed between two upper and lower air-sealing boxes 40 of the air-sealed structure.

[0026] Continue as Figure 1 As shown, the hall provided in an exemplary embodiment of the present invention includes a body 10 and a circulating air system surrounding a portion of the body 10; the body 10 includes a cavity enclosed by a shell for passing through carbon fibers, the cavity being used to preheat the carbon fibers. The shell includes a frame structure and a furnace plate disposed on the frame structure.

[0027] For example, the circulating air system includes a return air box 31, an inlet air box 33, and an air duct 32 connecting the return air box 31 and the inlet air box 33; the return air box 31 is located at the top of the body 10 and communicates with the cavity, the inlet air box 33 is located at the bottom of the body 10 and communicates with the cavity; the air duct 32 is located on one side of the body 10. The circulating air system also includes a filter 321, a fan 322, and a heater 323, which are sequentially arranged in the air duct along the direction from the return air box to the inlet air box. In practical applications, the airflow driven by the fan 322 is heated by the heater 323 and then evenly sent into the cavity through the air inlet box 33. It is then collected by the return air box 31 and purified by the filter screen 321, forming a closed-loop hot air circulation.

[0028] The return air box 31 is located at the top of the cavity. Its return air perforation plate 50 adopts a long strip opening design and has built-in reinforcing ribs to ensure structural strength and airflow uniformity. The air inlet box 33 is installed at the bottom of the cavity. The air inlet box 33 is connected to the cavity through the air inlet perforation plate 50. The surface of the perforation plate 50 is evenly distributed with 8mm air inlet holes. After the air is distributed through the air inlet holes, the air volume of the fan 322 is controlled to control the air velocity of the air inlet perforation plate 50 at 3m / s. The uniformity of the air velocity is maintained at ±0.2m / s, thereby ensuring that the temperature difference at various points in the cavity of the hall is within ±2℃.

[0029] Specifically, the air in the lobby is drawn into the air duct 32 through the return air box 31, filtered by the filter screen 321, and then the circulating air is heated by the fan 322 and passed downward through the heater 323. Finally, it is sent into the lobby cavity from bottom to top through the air inlet box 33. The purpose of setting the circulating air in the lobby cavity to be bottom-in and top-out is to prevent the broken fibers from easily adhering to the perforated plate 50 of the return air box 31 after the fiber bundle 100 breaks. This would prevent a large number of broken fibers from entering the circulating air system during the operation of the fiber bundle 100. At the same time, the broken fiber ends adhering to the surface of the return air box 31 due to the breakage of the fiber bundle 100 would pull on the fiber bundle 100 and easily affect the operation of the surrounding fiber bundles 100 during operation. During operation, the temperature in the lobby cavity needs to be monitored by a temperature sensor and controlled at 150℃~200℃. At the same time, the impurities in the circulating air are filtered and cleaned regularly to avoid contamination of the carbon fiber fiber bundle 100.

[0030] Furthermore, the main body 10 of the entrance hall adopts a modular furnace plate splicing structure, supported by an external frame structure. The furnace plate can be an insulation board. The insulation board is filled with high-temperature resistant ceramic fiber cotton with a thickness of 200mm and covered with an aluminized plate. The insulation board can include multiple sub-boards, with multiple sub-boards per layer. The joints of the sub-boards are staggered, and the staggered installation of multiple sub-boards can reduce the thermal bridging effect. This can prevent heat in the entrance hall from escaping along the gaps in the insulation material. The furnace plates are spliced ​​together and welded to the frame structure to form the main body 10 of the entrance hall. This can keep the surface temperature of the entrance hall below 40°C, reducing the risk of burns to personnel and minimizing the impact on the surrounding ambient temperature.

[0031] Because the vestibule cavity has hot air circulation, it provides a low-temperature buffer zone with a similar or smaller temperature difference to the furnace cavity of the oxidation furnace 20 when the pre-oxidized fibers enter and exit the furnace 20, which is more conducive to the conversion of the precursor fiber molecular chains. At the same time, when the air in the furnace cavity of the pre-oxidation furnace 20 exchanges heat with the air in the vestibule, the small temperature difference between the two has a smaller impact on the constant temperature zone in the furnace cavity. In the prior art, pre-oxidation furnaces using a gas collection hood structure have a gas temperature lower than the set temperature of the furnace cavity for at least 1 meter at both ends of the constant temperature zone; while the pre-oxidation furnace 20 with the vestibule cavity of this invention, which has a hot air circulation system, has a constant temperature zone affected by heat exchange at both ends of the furnace cavity that is only about 0.3 meters long. Based on this, since the carbon fiber tow 100 usually travels back and forth in the furnace cavity of the pre-oxidation furnace 20 dozens of times, the hall with the hot air circulation system can increase the total length of the effective constant temperature zone in the furnace cavity by at least 10 meters. That is, while ensuring that the tow 100 is fully oxidized in the furnace cavity of the pre-oxidation furnace 20, the running speed of the carbon fiber tow 100 can be increased by more than 10%.

[0032] Continue to combine Figure 1 and Figure 2 As shown, the circulating air system provided in the exemplary embodiment of the present invention further includes an exhaust pipe 34, which is connected to the cavity.

[0033] In practical applications, an exhaust fan is also installed on the exhaust pipe 34. The air volume of the exhaust fan is controlled by a concentration sensor, temperature sensor, pressure sensor and other sensors installed on the top of the hall body 10. The frequency of the exhaust fan can be automatically adjusted according to the changes in temperature, pressure and exhaust gas concentration in the hall cavity, thereby controlling the exhaust volume of the exhaust pipe 34, so as to ensure the constant temperature field in the furnace cavity of the oxidation furnace 20 as much as possible, and to promptly remove the small amount of exhaust gas overflowing from the furnace cavity and generated in the hall.

[0034] Example 2 To address the issue of heat exchange between the furnace cavity and the vestibule of the oxidizer 20, and between the vestibule's cavity and the outside air, and to prevent exhaust gas from escaping from the furnace, this exemplary embodiment further optimizes the air seal structure of the vestibule based on Embodiment 1, thereby lengthening the constant temperature zone within the furnace cavity of the oxidizer 20.

[0035] Figure 3 This is a cross-sectional structural schematic diagram of an air-sealing system according to an embodiment of the present invention. (Combined with...) Figure 1 and Figure 3 As shown, air seal structures are installed at the entrance of the hall and between the hall and the furnace chamber. The following text will take the air seal structure at the entrance of the hall as an example.

[0036] Carbon fiber enters the hall (the cavity of the hall) from outside through the wire feeding channel 101.

[0037] The air-sealing structure comprises multiple air-sealing boxes 40 arranged sequentially from top to bottom at intervals. The interval between two adjacent air-sealing boxes 40 forms a yarn-feeding channel 101 through which the yarn bundle 100 passes. Each air-sealing box 40 includes an air inlet chamber 41 and a return air chamber 42. The air inlet chamber 41 is divided into a first chamber and a second chamber with a slit-type air inlet 411 by an air distribution plate. The air inlet 411 is vertically arranged facing the yarn-feeding channel 101. The air inlets 41 on the upper and lower sides of the yarn-feeding channel 101 are arranged in a mirror symmetrical manner, that is, the two airflows from the upper and lower sides meet at the air inlet 411 and form a stable air curtain. This air curtain can effectively block the exchange of gases between the inside and outside of the room.

[0038] It should be noted that the air distribution plate not only plays a role in equalizing the flow, but also ensures that the pressure drop of the airflow between the first and second chambers is controllable through the precise opening design, thereby ensuring the stability of the wind speed at the slit-type air inlet 411.

[0039] For example, the slit-type air inlet 411 is 3mm wide and extends laterally through the entire length of the air seal box 40.

[0040] Figure 5 This is a front view structural diagram of the entrance hall according to an embodiment of the present invention. (Combined with...) Figure 3 and Figure 5 As shown, hot air enters the first chamber through the main air inlet duct 44, and then flows evenly into the second chamber after being distributed by the air distribution plate. Finally, it is ejected from the slit-type air inlet 411. The airflow converges symmetrically on both sides of the wire-feeding channel 101 to form a dense air curtain barrier. This air curtain barrier effectively blocks the overflow of high-temperature gas in the hall and the intrusion of cold air from outside the hall.

[0041] Meanwhile, a return air inlet 421 is provided on the side of the return air chamber 42 facing the yarn feeding channel 101. The return air inlets 421 on the upper and lower sides of the yarn feeding channel 101 are arranged in a mirror symmetrical manner, and each return air chamber 42 is connected to the return air main duct 45. The negative pressure of the return air main duct 45 forms a negative pressure cavity in the yarn feeding channel 101.

[0042] In actual operation, in the same wire feeding channel 101, the air inlet chamber 41 is close to the inside of the hall, and the return air chamber 42 is close to the outside of the hall, forming a pressure gradient of "positive inside and negative outside". This pressure gradient not only enhances the air curtain sealing, but also makes the trace amount of escaping waste gas actively captured to the return air system, and then discharged in compliance with standards after purification treatment.

[0043] Since the air inlets 411 of the two air-sealing boxes 40 face each other, the two streams of air form an air curtain after they collide here, and then diffuse into and out of the hall. Part of it moves into the hall along the wire-feeding channel 101, which just prevents the gas in the hall from escaping outward; the other part moves out of the hall along the wire-feeding channel 101, mixes with the cold air entering from outside the hall, and then enters the return air chamber 42 through the return air inlet 421, so that the mixed gas will not enter the hall.

[0044] After the return air main duct 45 collects the air from the return air chambers 42 of all the air seal boxes 40, it is drawn in by the air seal fan 322 and delivered to the heater 323. After being heated to the set temperature of 150°C, it is sent back into the inlet air main duct 44 for the next cycle. The entire air seal cycle forms a loop.

[0045] Each air seal box 40 has a valve 43 between its return air chamber 42 and return air main duct 45, and between its inlet air chamber 41 and inlet air main duct 44, so that the air intake and return air volume of each air seal box 40 can be adjusted.

[0046] For example, the return air inlet 421 can be an orifice plate type return air inlet 421, which can make the transverse air intake of the entire air seal more uniform.

[0047] To address the problem of the return air inlet 421 of the return air chamber 42 becoming clogged with broken fibers from the carbon fiber due to negative pressure, thus rendering the entire airtight structure ineffective, the following steps were taken: Figure 3 As shown, the return air inlet 421 is the bottom of a groove formed on the surface of the return air chamber 42 facing the wire feeding channel 101, that is, the perforated plate 50 is the bottom of the groove. Thus, the broken wires adsorbed at this groove can accumulate in the groove without blocking the wire feeding channel 101, thereby not affecting the passage of the wire bundle 100 and its tension stability, and improving the production quality of the wire bundle 100.

[0048] It should be noted that the gas seal structure between the vestibule and the furnace cavity is largely the same as the gas seal structure at the vestibule inlet. The difference is that the gas seal structure between the vestibule and the furnace cavity only has an inlet chamber 41 and no return air chamber 42. That is, only a positive pressure air curtain barrier is formed in the wire-feeding channel 101. Its function is to unidirectionally block the diffusion of high-temperature gas from the furnace cavity into the vestibule, avoiding heat loss and temperature field disturbance. This positive pressure air curtain is also formed by the ejection and counter-ejection of air from the slit-type air outlet. The wind speed and temperature are precisely controlled according to the process requirements inside the furnace, so that the airflow stability and sealing integrity are maintained even without negative pressure adsorption. Based on this, the temperature difference between the furnace cavity and the vestibule is not large. The use of a positive pressure air curtain can effectively prevent the high-temperature gas in the furnace cavity from escaping. It is lower in cost and simpler in structure, and can also reduce the risk of wire bundle 100 disturbance caused by negative pressure.

[0049] Example 3 To address the difficulty in cleaning the perforated plate 50 of the return air inlet 421 after it becomes clogged, the structure of the return air inlet 421 is further optimized based on Embodiment 2.

[0050] Figure 4 yes Figure 3 A magnified view of part A. Combined with... Figures 3-5As shown, the perforated plate 50 of the return air inlet 421 is a tracked perforated plate, such as a porous thin metal plate. Guide rollers 51 are respectively provided on both sides of the air seal box 40 and located on both sides of the corresponding wire feeding channel 101. The tracked perforated plate 50 passes around the two guide rollers 51 to form a closed loop. A part of the tracked perforated plate 50 is located in the groove of the return air chamber 42 to form the bottom of the groove, and a part is located in the groove of the return air chamber 42 on the other side of the same wire feeding channel 101 to form the bottom of the groove.

[0051] For example, such as Figure 4 As shown, low-friction ceramic slide rails are embedded in the track grooves 421a on the two side walls of the groove for the sliding of the tracked perforated plate 50, so that the tracked perforated plate 50 can move back and forth without jamming.

[0052] A cleaning brush 52 is provided above the tracked perforated plate 50, and a dust collection box is provided below the tracked perforated plate 50 at a position corresponding to the cleaning brush 52. The dust collection box can be set below the tracked perforated plate 50 above the guide roller 51 by a bracket, that is, set in the annular space of the tracked perforated plate 50.

[0053] For example, one of the guide rollers 51 located on both sides of the same wire feeding channel 101 is driven by a stepper motor. A pressure sensor is also installed in the return air chamber 42. The pressure sensor, the stepper motor and the controller are connected in communication. When the pressure sensor detects that the negative pressure value exceeds a certain set value, the controller controls the stepper motor to start and drive the tracked perforated plate 50 to move out of the wire feeding channel 101 along the track groove 421a. The broken wires attached to the surface are cleaned by the cleaning brush 52. Then the tracked perforated plate 50 is reversed by the guide roller 51 and the cleaned area is reintroduced into the wire feeding channel 101 to continue working. The whole process does not require machine shutdown, which ensures the continuity of the air seal, maintains the temperature stability in the hall, avoids production interruption caused by manual intervention, and significantly improves the equipment operating efficiency and carbon fiber quality consistency.

[0054] Example 4 To address the issue of fiber filament breakage due to tension variations in the carbon fiber bundle 100 causing friction with the air-sealed box 40, the structure of the entrance hall was further optimized based on Embodiment 2 or Embodiment 3.

[0055] Combination Figure 3 and Figure 5As shown, the portal frame is installed on the furnace body end face of the oxidation furnace 20 via a sliding groove, and its height can be adjusted by sliding up and down along the groove. A laser module 61 is installed in the wire feeding channel 101. The laser module 61 consists of a light curtain laser emitter and a laser receiver, which are respectively set on both sides of the wire feeding channel 101. The laser module 61 monitors the vertical position deviation of the wire bundle 100 in the wire feeding channel 101 in real time and transmits the data to the PLC in real time. The PLC compares and analyzes the data according to the preset height range of the wire bundle 100 and generates lifting and lowering adjustment commands.

[0056] Continue as Figure 3 As shown, multiple airbag-type lifting devices are installed at the bottom of the hall. Each airbag-type lifting device includes multiple airbags 63, and each airbag 63 is connected to the same automatic regulating valve 62 through parallel pipelines. After receiving commands from the PLC, the automatic regulating valve 62 precisely adjusts the inflation volume of each airbag 63 to dynamically adjust the height of the hall, ensuring that the running trajectory of the yarn feeding channel 101 and the yarn bundle 100 always maintains optimal matching, reducing the risk of friction caused by changes in the sag of the yarn bundle 100. At the same time, the airbag-type lifting device has a built-in pressure feedback unit to verify the linear relationship between the inflation pressure and the actual displacement of the hall in real time, ensuring that the height adjustment accuracy reaches ±0.1mm. The PLC also synchronously collects the current stroke data of the height adjustment mechanism, and through dual closed-loop collaborative control, ensures that the lifting of the hall and the vertical displacement of the air seal box 40 are strictly synchronized.

[0057] It should be noted that the parallel connection of multiple airbags 63 ensures that the pressure in all airbags 63 is consistent, and the entire hall rises and falls synchronously without tilting. Furthermore, the elastic deformation of the airbags 63 provides a good buffering effect, effectively suppressing overshoot and oscillation during the rising and falling process, making the adjustment process smooth, reducing the instantaneous impact force between the fiber and the air seal box 40 during the adjustment process, and further reducing the risk of fiber breakage.

[0058] Those skilled in the art should understand that the above embodiments are merely for illustrating the present invention and are not intended to limit the scope of the invention. Those skilled in the art can make other changes or modifications based on the above disclosure, and these changes or modifications still fall within the scope of the present invention.

Claims

1. An inlet / outlet hall for a pre-oxidation furnace, characterized in that, The entrance hall is used to be located at the inlet end and / or outlet end of the pre-oxidation furnace, and the entrance hall includes a body and a circulating air system surrounding a portion of the periphery of the body; The body includes a cavity enclosed by a shell for passing through carbon fibers, the cavity being used to preheat the carbon fibers.

2. The lobby according to claim 1, characterized in that, The shell includes a frame structure and a furnace plate disposed on the frame structure.

3. The lobby according to claim 2, characterized in that, The furnace plate consists of an insulation board and an aluminized plate covering the insulation board.

4. The lobby according to claim 3, characterized in that, The insulation board is 200mm thick.

5. The lobby according to claim 3, characterized in that, The insulation board includes multiple sub-boards, with multiple sub-boards in each layer, and the joints of the sub-boards in each layer are staggered.

6. The lobby according to claim 3, characterized in that, The temperature inside the cavity is less than or equal to the furnace temperature of the pre-oxidation furnace.

7. The lobby according to claim 3, characterized in that, The temperature inside the cavity is 150℃~200℃.

8. The lobby according to any one of claims 1-7, characterized in that, The circulating air system includes a return air box, an inlet air box, and an air duct connecting the return air box and the inlet air box; The return air box is located at the top of the main body and communicates with the cavity; the air inlet box is located at the bottom of the main body and communicates with the cavity; the air duct is located on one side of the main body.

9. The lobby according to claim 8, characterized in that, The circulating air system also includes a filter, a fan, and a heater, which are arranged sequentially in the air duct along the direction from the return air box to the inlet air box.

10. The lobby according to claim 8, characterized in that, The circulating air system also includes an exhaust pipe, which is connected to the cavity.

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