Carbon fiber pre-oxidation furnace main chamber boundary layer control method and boundary layer control system

Abstract

This invention belongs to the field of carbon fiber pre-oxidation technology, specifically relating to a boundary layer control method and control system for the main chamber of a carbon fiber pre-oxidation furnace. The method includes: obtaining the boundary layer thickness development formula for the pre-oxidation furnace wall; calculating the key node positions of the boundary layer control system; and, by arranging a negative pressure exhaust system, promptly removing stagnant gases with low oxygen content and high pollutant concentrations near the wall surface based on the oxygen concentration deviation information between the mainstream zone and the boundary layer within the furnace. This includes low-velocity gases in the laminar boundary layer and swirling gases in the turbulent boundary layer. This invention provides a theoretical basis for actual process operation; significantly improves the uniformity of the flow field within the furnace, and enhances the quality of carbon fiber products.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber pre-oxidation technology, specifically relating to a boundary layer control method and a boundary layer control system for the main chamber of a carbon fiber pre-oxidation furnace. Background Technology

[0002] Carbon fiber possesses excellent mechanical properties and chemical stability. It has a lower density than aluminum and a higher strength than steel. Among the high-performance fibers currently in mass production, it has the highest specific strength and the highest specific modulus. It also features low density, corrosion resistance, high temperature resistance, friction resistance, fatigue resistance, high vibration damping, high electrical and thermal conductivity, low thermal and moisture expansion coefficients, high X-ray penetration, and electromagnetic shielding effect despite being non-magnetic. It is an important strategic material for the development of national defense and the national economy, and is used in defense industries and high-performance civilian fields, including military, aerospace, marine engineering, sporting goods, automotive industry, new energy equipment, medical devices, engineering machinery, transportation, construction and structural reinforcement.

[0003] In the entire process of preparing high-performance carbon fibers, the pre-oxidation process is a key link affecting the quality of carbon fibers, serving as a bridge between the precursor fiber and the carbon fiber. The pre-oxidation process has high requirements for the uniformity of the airflow field and the oxygen content in the furnace. In traditional pre-oxidation equipment, the inlet air velocity of the furnace is uniform, but due to the presence of the velocity boundary layer, gas stagnation zones (laminar boundary layer) and swirling zones (turbulent boundary layer) with high pollutant concentration and low oxygen content appear on both sides of the wall. As the hot air advances, the boundary layer thickness increases and gradually invades the oxidation zone of the carbon fiber precursor fiber, restricting product quality.

[0004] Therefore, it is urgent to design a boundary layer control method and a boundary layer control system for the main chamber of a carbon fiber pre-oxidation furnace to solve the technical problem that gas stagnation zones (laminar boundary layer) and swirling zones (turbulent boundary layer) with high pollutant concentration and low oxygen content appear on both sides of the furnace wall. As the hot air moves forward, the boundary layer thickness increases and gradually invades the carbon fiber precursor oxidation zone, which restricts product quality.

[0005] It should be noted that the information disclosed in this background section is only for understanding the background technology of this application concept, and therefore may include information that does not constitute prior art. Summary of the Invention

[0006] This disclosure provides at least one method and control system for the boundary layer of the main chamber of a carbon fiber pre-oxidation furnace.

[0007] In a first aspect, this disclosure provides a method for controlling the boundary layer of the main chamber of a carbon fiber pre-oxidation furnace. This method involves obtaining a formula for the development of the boundary layer thickness on the furnace wall, calculating the key node positions of the boundary layer control system, and promptly removing stagnant gases with low oxygen content and high pollutant concentrations near the wall surface by arranging a negative pressure exhaust system. These gases include low-velocity gases in the laminar boundary layer and swirling gases in the turbulent boundary layer, thereby significantly improving the uniformity of the airflow field within the furnace. The specific steps include:

[0008] Step A: Trial run of the pre-oxidation furnace, and perform the following analysis and calculations:

[0009] A1. Measure the airflow velocity at characteristic locations within the oxidation furnace. Based on the above measurement data and combined with the theory of flat plate boundary layer thickness development, obtain the formula for the development of the boundary layer thickness of the pre-oxidation furnace wall:

[0010] δ(x)=k1x / Re x 1 / 2 Re x ≤Re cr Laminar boundary layer;

[0011] δ(x)=k2x / Re x 1 / 5 Re x >Re cr turbulent boundary layer;

[0012] Where δ(x) is the plate velocity boundary layer thickness, and Reynolds number Re is... x =ux / v is the ratio of fluid inertial force to viscous force, v is the kinematic viscosity of air, u is the set air velocity of the pre-oxidation furnace, and Re is the fluid velocity. cr is the critical Reynolds number for the transition between laminar and turbulent flow, k1 and k2 are correction coefficients, and x is the position of the leading edge of the plate;

[0013] A2, obtain the minimum distance d between the carbon fiber bundle and the wall during the actual process, calculate the position x0 where the velocity boundary layer invades the bundle running area, let δ(x)=d, and solve for x=x0;

[0014] A3, let Re x =ux / v=Re cr Find x = x1, and calculate the system target exhaust volume Q and the target negative pressure setpoint P at the exhaust outlet;

[0015] When x0 < x1

[0016]

[0017] When x0≥x1

[0018]

[0019] Where L is the length of the pre-oxidation furnace, W is the width of the pre-oxidation furnace, H is the height of the pre-oxidation furnace, x1 is the position where the laminar boundary layer transitions to the turbulent boundary layer, τ is the set exhaust time, P0 is the measured pressure value of the boundary layer gas, u1 is the exhaust velocity, and ρ is the air density.

[0020] Step B: Based on the above analysis data, deploy the boundary layer control system and run the pre-oxidation furnace. When the deviation between the measured oxygen concentration F0 and the target oxygen concentration F is a1 = |F-F0| / F > a0, a first signal is fed back to the control system. The control system sends a signal to the fresh air fan to adjust the fresh air volume. When a1 ≤ a0, the fresh air fan continues to operate at the current air volume, where a0 is the allowable deviation of the oxygen concentration in the pre-oxidation furnace.

[0021] Step C: The detector collects the measured oxygen concentration values ​​F1 and F2 of the wall boundary layer and the mainstream zone at position x = x0 in the pre-oxidation furnace and sends them to the control system. The control system calculates the relative deviation a2 = |F1-F2| / F.

[0022] When a2 > a0, it is determined that the oxygen concentration in the boundary layer is too low, the flow field non-uniformity increases, and the process requirements cannot be met. The second signal is fed back to the control system, which controls the negative pressure exhaust system to start the negative pressure exhaust. At the same time, the control system controls the circulating fan to adjust the return air volume so that the supply air flow rate is maintained at Q0.

[0023] When a2≤a0, it is determined that the oxygen concentration in the furnace is uniform, and a third signal is fed back to the control system. The control system then controls the negative pressure exhaust system to stop exhausting.

[0024] In one optional implementation, in step B, the target oxygen concentration F ranges from 5% to 20%, and the allowable deviation of oxygen concentration a0 ranges from 1% to 2%.

[0025] In one alternative implementation, in step A, the critical Reynolds number Re cr The value range is: 3.5 × 10 5 ≤Re cr ≤5×10 5 .

[0026] In step A, the target exhaust volume Q does not exceed 30% of the target supply volume Q0 of the pre-oxidation furnace.

[0027] In one alternative implementation, the arrangement of the negative pressure system ranges from x2 to L, where 0.85x0 ≤ x2 ≤ x0.

[0028] In one optional implementation, the deviation ΔT = |T0-T1| between the actual supply air temperature T1 and the target supply air temperature T0 is monitored, and ΔT ≤ 1℃ is maintained.

[0029] In one optional implementation, the exhaust velocity u1 ranges from 1 m / s to 3 m / s.

[0030] Secondly, embodiments of this disclosure also provide a pre-oxidation furnace boundary layer control system, applied to execute the boundary layer control method as described above, the pre-oxidation furnace boundary layer control system comprising:

[0031] The main chamber has at least one negative pressure exhaust mechanism, which includes a negative pressure generator and an exhaust chamber. The negative pressure generator is connected to the exhaust chamber and is used to provide the power required for exhaust.

[0032] An exhaust flow meter is installed at the outlet of the exhaust chamber, and the exhaust flow meter is used to provide feedback on the actual exhaust volume.

[0033] The negative pressure exhaust mechanism also includes an exhaust port, which is located on the side wall of the main chamber of the pre-oxidation furnace and connected to the exhaust chamber.

[0034] An exhaust solenoid valve is also provided between the negative pressure generator and the exhaust chamber.

[0035] In one optional embodiment, an exhaust outlet pressure sensor is installed at the outlet of the exhaust chamber to provide feedback on the exhaust pressure P.

[0036] A boundary layer pressure sensor is installed on the side wall of the main chamber to provide feedback on the airflow pressure P0 within the boundary layer.

[0037] In one optional embodiment, a first oxygen concentration sensor and a second oxygen concentration sensor are respectively arranged on the wall boundary layer and the main flow zone at the x=x0 position of the main chamber.

[0038] In one optional embodiment, the boundary layer control system further includes a fresh air fan, a circulating air fan, and an electric heater. The fresh air fan and the circulating air fan are respectively connected to the inlet of the electric heater. The outlet of the electric heater is connected to the inlet of the main chamber through an air supply pipe. The outlet of the main chamber is connected to the inlet of the circulating air fan through a circulation pipe.

[0039] The fresh air fan is used to provide the oxygen required for the pre-oxidation process, the circulating air fan is used to provide the power for the return air circulation, and the electric heater is used to provide the heat required for the pre-oxidation process;

[0040] The air supply duct is also equipped with an air supply temperature sensor, an air supply flow meter, and an intake oxygen concentration sensor to provide feedback on the air supply temperature, air supply flow, and oxygen concentration within the air supply duct.

[0041] The beneficial effects of this invention are: 1. This invention obtains the velocity boundary layer development parameters of the pre-oxidation furnace wall and calculates the target exhaust volume and pressure of the boundary layer, providing a theoretical basis for the actual process operation; 2. Based on the deviation information between the mainstream zone and the boundary layer oxygen concentration in the furnace, this invention uses the exhaust system to promptly remove stagnant gas and swirling gas with high pollutant concentration and low oxygen concentration in the boundary layer, thereby significantly improving the uniformity of the flow field in the furnace.

[0042] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained in accordance with the structures particularly pointed out in the description, claims and drawings.

[0043] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0044] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0045] Figure 1 A schematic flowchart illustrating a method for controlling the boundary layer of the main chamber of a carbon fiber pre-oxidation furnace, provided in an embodiment of this disclosure;

[0046] Figure 2 This is a schematic diagram of the structure of a pre-oxidation furnace boundary layer control system provided in an embodiment of the present disclosure;

[0047] Figure 3 This is a schematic diagram of the distribution of laminar and turbulent boundary layers inside a main chamber, provided as an embodiment of this disclosure.

[0048] In the picture:

[0049] 1. Main chamber; 11. Exhaust vent; 12. Exhaust chamber; 2. Exhaust solenoid valve; 3. Exhaust flow meter; 4. Negative pressure generator; 50. Exhaust outlet pressure sensor; 51. Boundary layer pressure sensor; 60. Inlet oxygen concentration sensor; 61. First oxygen concentration sensor; 62. Second oxygen concentration sensor; 7. Supply air temperature sensor; 8. Supply air flow meter; 9. Electric heater; 10. Fresh air fan; 13. Circulating air fan;

[0050] C1, First Control Center; C2, Second Control Center. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] Research has shown that the pre-oxidation process has high requirements for the uniformity of the airflow field and the oxygen content in the furnace. In traditional pre-oxidation equipment, the inlet air velocity of the furnace is uniform, but due to the presence of the velocity boundary layer, gas stagnation zones (laminar boundary layer) and swirling zones (turbulent boundary layer) with high pollutant concentration and low oxygen content will appear on both sides of the wall. As the hot air moves forward, the boundary layer thickness increases and gradually invades the oxidation zone of the carbon fiber precursor, which restricts product quality.

[0053] The shortcomings of the above solutions are the result of the inventor's practical experience and careful research. Therefore, the discovery process of the above problems and the solutions proposed in this disclosure below should be considered as the inventor's contribution to this disclosure.

[0054] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the embodiments and features described below can be combined with each other. Furthermore, in the accompanying drawings, the thickness of components may be exaggerated or reduced for the purpose of effectively describing the technical content.

[0055] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0056] Based on the above research, and referring to Figure 1 This disclosure provides a method for controlling the boundary layer in the main chamber of a carbon fiber pre-oxidation furnace. The method involves obtaining a formula for the development of the boundary layer thickness on the furnace wall, calculating the locations of key nodes in the boundary layer control system, and using a negative pressure exhaust system to promptly remove stagnant gases with low oxygen content and high pollutant concentrations near the wall surface. These gases include low-velocity gases in the laminar boundary layer and swirling gases in the turbulent boundary layer, thereby significantly improving the uniformity of the airflow field within the furnace. The specific steps include:

[0057] Step A: Trial run of the pre-oxidation furnace, and perform the following analysis and calculations:

[0058] A1. Measure the airflow velocity at characteristic locations within the oxidation furnace. Based on the above measurement data and combined with the theory of flat plate boundary layer thickness development, obtain the formula for the development of the boundary layer thickness of the pre-oxidation furnace wall:

[0059] δ(x)=k1x / Re x 1 / 2 Re x ≤Re cr Laminar boundary layer;

[0060] δ(x)=k2x / Re x 1 / 5 Re x >Re cr turbulent boundary layer;

[0061] Where δ(x) is the plate velocity boundary layer thickness, and Reynolds number Re is... x =ux / v is the ratio of fluid inertial force to viscous force, v is the kinematic viscosity of air, u is the set air velocity of the pre-oxidation furnace, and Re is the fluid velocity. cr is the critical Reynolds number for the transition between laminar and turbulent flow, k1 and k2 are correction coefficients, and x is the position of the leading edge of the plate;

[0062] A2, obtain the minimum distance d between the carbon fiber bundle and the wall during the actual process, calculate the position x0 where the velocity boundary layer invades the bundle running area, let δ(x)=d, and solve for x=x0;

[0063] A3, let Re x =ux / v=Re cr Find x = x1, and calculate the system target exhaust volume Q and the target negative pressure setpoint P at the exhaust outlet;

[0064] When x0 < x1

[0065]

[0066] When x0≥x1

[0067]

[0068] Where L is the length of the pre-oxidation furnace, W is the width of the pre-oxidation furnace, H is the height of the pre-oxidation furnace, x1 is the position where the laminar boundary layer transitions to the turbulent boundary layer, τ is the set exhaust time, P0 is the measured pressure value of the boundary layer gas, u1 is the exhaust velocity, and ρ is the air density.

[0069] Step B: Based on the above analysis data, deploy the boundary layer control system and run the pre-oxidation furnace. When the deviation between the measured oxygen concentration F0 and the target oxygen concentration F is a1 = |F-F0| / F > a0, a first signal is fed back to the control system. The control system sends a signal to the fresh air fan to adjust the fresh air volume. When a1 ≤ a0, the fresh air fan continues to operate at the current air volume, where a0 is the allowable deviation of the oxygen concentration in the pre-oxidation furnace.

[0070] Step C: The detector collects the measured oxygen concentration values ​​F1 and F2 of the wall boundary layer and the mainstream zone at position x = x0 in the pre-oxidation furnace and sends them to the control system. The control system calculates the relative deviation a2 = |F1-F2| / F.

[0071] When a2 > a0, it is determined that the oxygen concentration in the boundary layer is too low, the flow field non-uniformity increases, and the process requirements cannot be met. The second signal is fed back to the control system, which controls the negative pressure exhaust system to start the negative pressure exhaust. At the same time, the control system controls the circulating fan to adjust the return air volume so that the supply air flow rate is maintained at Q0.

[0072] When a2≤a0, it is determined that the oxygen concentration in the furnace is uniform, and a third signal is fed back to the control system. The control system then controls the negative pressure exhaust system to stop exhausting.

[0073] In at least one embodiment, in step B, the target oxygen concentration F ranges from 5% to 20%, and the allowable deviation of oxygen concentration a0 ranges from 1% to 2%.

[0074] In at least one embodiment, in step A, the critical Reynolds number Re cr The range of values ​​is:

[0075] 3.5×10 5 ≤Re cr ≤5×10 5 .

[0076] In step A, the target exhaust volume Q does not exceed 30% of the target supply volume Q0 of the pre-oxidation furnace.

[0077] Reference Figure 3 In at least one embodiment, the arrangement of the negative pressure system ranges from x2 to L, where 0.85x0≤x2≤x0.

[0078] In at least one embodiment, the deviation ΔT = |T0-T1| between the actual supply air temperature T1 and the target supply air temperature T0 is monitored, and ΔT ≤ 1℃ is maintained.

[0079] In at least one embodiment, the exhaust velocity u1 ranges from 1 m / s to 3 m / s.

[0080] Furthermore, this disclosure also provides a pre-oxidation furnace boundary layer control system, applied to the boundary layer control method described above, with reference to... Figure 2 The pre-oxidation furnace boundary layer control system includes: a main chamber 1, which is a square cavity with process parameters of length L, width W, and height H based on its square structure. The interior of the main chamber 1 is suitable for carbon fiber pre-oxidation. At least one negative pressure exhaust mechanism is installed on the side wall of the main chamber 1. The negative pressure exhaust mechanism includes a negative pressure generator 4 and an exhaust chamber 12. The outlet of the exhaust chamber 12 is connected to the negative pressure generator 4 via an exhaust pipe. The negative pressure generator 4 provides the power required for exhaust. The negative pressure exhaust mechanism also includes exhaust ports 11. Several exhaust ports 11 are evenly arranged on the side wall of the main chamber 1 of the pre-oxidation furnace, and the exhaust ports 11 are connected to the exhaust chamber 12. The exhaust ports 11 guide the gas in the main chamber 1 to be discharged. The exhaust chamber 12 collects the gas discharged from each exhaust port 11 and transmits it to the negative pressure generator 4.

[0081] Reference Figure 1 In at least one embodiment, an exhaust flow meter 3 is provided at the outlet of the exhaust chamber 12, and the exhaust flow meter 3 is used to provide feedback on the actual exhaust volume.

[0082] Reference Figure 1 In at least one embodiment, an exhaust solenoid valve 2 is also provided between the negative pressure generator 4 and the exhaust chamber 12. The exhaust solenoid valve 2 is used to adjust the opening of the exhaust pipe, wherein the minimum opening is when the exhaust pipe is closed, and the maximum opening is when the exhaust pipe is fully open.

[0083] Reference Figure 1 In at least one embodiment, an exhaust outlet pressure sensor 50 is installed at the outlet of the exhaust chamber 12 to provide feedback on the exhaust pressure P. A boundary layer pressure sensor 51 is installed on the side wall of the main chamber 1 to provide feedback on the airflow pressure P0 within the boundary layer.

[0084] Reference Figure 1 In at least one embodiment, two negative pressure exhaust mechanisms are provided, and the two negative pressure exhaust mechanisms are respectively located on both sides of the main chamber 1, so that the two negative pressure exhaust mechanisms can uniformly exhaust the gas in the main chamber 1 from both sides.

[0085] Reference Figure 1 In at least one embodiment, a first oxygen concentration sensor 61 and a second oxygen concentration sensor 62 are respectively arranged on the wall boundary layer and the main flow zone at position x = x0 in the main chamber 1 to monitor the oxygen concentration in the main chamber 1. Preferably, the first oxygen concentration sensor 61 and the second oxygen concentration sensor 62 are ZrO2 sensors.

[0086] Reference Figure 1In at least one embodiment, the boundary layer control system further includes a fresh air fan 10, a circulating air fan 13, and an electric heater 9. The fresh air fan 10 and the circulating air fan 13 are respectively connected to the inlet of the electric heater 9. The outlet of the electric heater 9 is connected to the inlet of the main chamber 1 through an air supply duct, and the outlet of the main chamber 1 is connected to the inlet of the circulating air fan 13 through a circulation duct. The fresh air fan 10 is used to provide oxygen required for the pre-oxidation process, the circulating air fan 13 is used to provide return air circulation power, and the electric heater 9 is used to provide heat required for the pre-oxidation process. The air supply duct is also equipped with an air supply temperature sensor 7, an air supply flow meter 8, and an intake oxygen concentration sensor 60 to provide feedback on the air supply temperature, air supply flow rate, and oxygen concentration within the air supply duct.

[0087] Reference Figure 1 In at least one embodiment, the boundary layer control system further includes a control module, which in turn includes a first control center C1 and a second control center C2. The negative pressure generator 4, exhaust flow meter 3, exhaust solenoid valve 2, first oxygen concentration sensor 61, second oxygen concentration sensor 62, exhaust outlet pressure sensor 50, and boundary layer pressure sensor 51 are all electrically connected to the first control center C1. The first control center C1 can control the opening and closing of the negative pressure generator 4 and the opening degree of the exhaust solenoid valve 2. Data collected by the inlet pressure sensor 50 and the boundary layer pressure sensor 51 are fed back to the first control center C1; the intake oxygen concentration sensor 60, the supply air temperature sensor 7, the supply air flow meter 8, the electric heater 9, the fresh air fan 10, and the circulating air fan 13 are all electrically connected to the second control center C2. The second control center C2 can control the opening and closing of the electric heater 9, the fresh air fan 10, and the circulating air fan 13. Data collected by the intake oxygen concentration sensor 60, the supply air temperature sensor 7, and the supply air flow meter 8 are fed back to the first control center C2.

[0088] Reference Figure 1 In at least one embodiment, the specific process by which the pre-oxidation furnace boundary layer control system executes the boundary layer control method for the main chamber of the carbon fiber pre-oxidation furnace as described above is as follows:

[0089] Step S1: Trial run of the pre-oxidation furnace;

[0090] Step S11: Measure the airflow velocity at characteristic locations inside the oxidation furnace. Based on the above measurement data and combined with the theory of flat plate boundary layer thickness development, obtain the formula for the development of the boundary layer thickness of the pre-oxidation furnace wall:

[0091] δ(x)=k1x / Re x 1 / 2 Re x ≤Re cr Laminar boundary layer;

[0092] δ(x)=k2x / Re x 1 / 5 Re x >Re cr turbulent boundary layer;

[0093] Where δ(x) is the plate velocity boundary layer thickness, and Reynolds number Re is... x =ux / v is the ratio of fluid inertial force to viscous force, v is the kinematic viscosity of air, u is the set air velocity of the pre-oxidation furnace, and Re is the fluid velocity. cr is the critical Reynolds number for the transition between laminar and turbulent flow, k1 and k2 are correction coefficients, and x is the position of the leading edge of the plate;

[0094] Step S12: Obtain the minimum distance d between the carbon fiber bundle and the wall during the actual process, calculate the position x0 where the velocity boundary layer invades the bundle running area, let δ(x)=d, and solve for x=x0;

[0095] Step S13, let Re x =ux / v=Re cr Find x = x1, and calculate the system target exhaust volume Q and the target negative pressure setpoint P at the exhaust outlet;

[0096] When x0 < x1

[0097]

[0098] When x0≥x1

[0099]

[0100] Where L is the length of the pre-oxidation furnace, W is the width of the pre-oxidation furnace, H is the height of the pre-oxidation furnace, x1 is the position where the laminar boundary layer transitions to the turbulent boundary layer, τ is the set exhaust time, P0 is the measured pressure value of the boundary layer gas, u1 is the exhaust velocity, and ρ is the air density.

[0101] Step S2: Based on the above analysis data, deploy the boundary layer control system, operate the pre-oxidation furnace, monitor the measured oxygen concentration F0 through the inlet oxygen concentration sensor 60 and feed it back to the second control center C2. The second control center C2 feeds back the signal to the control module. The control module calculates the deviation a1 between F0 and the target oxygen concentration F. When F > a0, the control module feeds back the first signal to the second control center C2. The second control center C2 sends a signal to the fresh air fan 13 to adjust the fresh air volume. When a1 ≤ a0, the fresh air fan 13 continues to operate at the current air volume, where a0 is the allowable deviation of the oxygen concentration in the pre-oxidation furnace.

[0102] In step S3, the first oxygen concentration sensor 61 and the second oxygen concentration sensor 62 respectively collect the measured oxygen concentration values ​​F1 and F2 of the wall boundary layer and the mainstream zone at position x = x0 in the pre-oxidation furnace, and feed them back to the first control center C1. The first control center C1 feeds back the signal to the control module, and the control module calculates the relative deviation a2 = |F1-F2| / F.

[0103] When a2 > a0, it is determined that the oxygen concentration in the boundary layer is too low, the flow field non-uniformity is increased, and the process requirements cannot be met. The control module feeds back a second signal to the first control center C1. The control system controls the negative pressure generator to adjust the negative pressure value P of the exhaust port 11 and increases the opening of the exhaust solenoid valve 2 to start the negative pressure exhaust. At the same time, the second control center C2 controls the circulating fan 13 to adjust the return air volume so that the value of the gas flow meter 8 still maintains the set air supply flow rate Q0.

[0104] When a2≤a0, it is determined that the oxygen concentration in the furnace is uniform. The control module feeds back a third signal to the first control center C1. The first control center C1 controls the exhaust solenoid valve 2 to open to the minimum and stops the exhaust.

[0105] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. The apparatus embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. Furthermore, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Based on the above-described ideal embodiments of the present invention, and through the above description, those skilled in the art can make various changes and modifications without departing from the technical spirit of the disclosed embodiments. The technical scope of the embodiments of this disclosure is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for controlling the boundary layer of the main chamber of a carbon fiber pre-oxidation furnace, characterized in that, The formula for the development of the boundary layer thickness of the pre-oxidation furnace wall is obtained, the key node positions of the boundary layer control system are calculated, and a negative pressure exhaust system is arranged to promptly remove stagnant gases with low oxygen content and high pollutant concentration near the wall, including low-velocity gases in the laminar boundary layer and swirling gases in the turbulent boundary layer, thereby significantly improving the uniformity of the airflow field inside the furnace. The specific steps include the following: Step A: Trial run of the pre-oxidation furnace, and perform the following analysis and calculations: A1. Measure the airflow velocity at characteristic locations within the oxidation furnace. Based on the above measurement data and combined with the theory of flat plate boundary layer thickness development, obtain the formula for the development of the boundary layer thickness of the pre-oxidation furnace wall: δ(x) = k1x / Rex1 / 2, Rex≤Recr, laminar boundary layer; δ(x) = k2x / Rex1 / 5, Rex > Recr, turbulent boundary layer; Where δ(x) is the plate velocity boundary layer thickness, and Reynolds number Re is... x =ux / v is the ratio of fluid inertial force to viscous force, v is the kinematic viscosity of air, u is the set air velocity of the pre-oxidation furnace, and Re is the fluid velocity. cr is the critical Reynolds number for the transition between laminar and turbulent flow, k1 and k2 are correction coefficients, and x is the position of the leading edge of the plate; A2, obtain the minimum distance d between the carbon fiber bundle and the wall during the actual process, calculate the position x0 where the velocity boundary layer invades the bundle running area, let δ(x)=d, and solve for x=x0; A3, let Re x = ux / v = Re cr , find x = x1, calculate the system target exhaust air volume Q and the exhaust air outlet target negative pressure set value P; When x0 < x1 When x0≥x1 Where L is the length of the pre-oxidation furnace, W is the width of the pre-oxidation furnace, H is the height of the pre-oxidation furnace, x1 is the position where the laminar boundary layer transitions to the turbulent boundary layer, τ is the set exhaust time, P0 is the measured pressure value of the boundary layer gas, u1 is the exhaust velocity, and ρ is the air density. Step B: Based on the above analysis data, deploy the boundary layer control system and run the pre-oxidation furnace. When the deviation between the measured oxygen concentration F0 and the target oxygen concentration F is a1 = |F-F0| / F > a0, a first signal is fed back to the control system. The control system sends a signal to the fresh air fan to adjust the fresh air volume. When a1 ≤ a0, the fresh air fan continues to operate at the current air volume, where a0 is the allowable deviation of the oxygen concentration in the pre-oxidation furnace. Step C: The detector collects the measured oxygen concentration values ​​F1 and F2 of the wall boundary layer and the mainstream zone at position x = x0 in the pre-oxidation furnace and sends them to the control system. The control system calculates the relative deviation a2 = |F1-F2| / F. When a2 > a0, it is determined that the oxygen concentration in the boundary layer is too low, the flow field non-uniformity increases, and the process requirements cannot be met. The second signal is fed back to the control system, which controls the negative pressure exhaust system to start the negative pressure exhaust. At the same time, the control system controls the circulating fan to adjust the return air volume so that the supply air flow rate is maintained at Q0. When a2≤a0, it is determined that the oxygen concentration in the furnace is uniform, and a third signal is fed back to the control system. The control system then controls the negative pressure exhaust system to stop exhausting.

2. The boundary layer control method for the main chamber of the carbon fiber pre-oxidation furnace as described in claim 1, characterized in that, In step B, the target oxygen concentration F ranges from 5% to 20%, and the allowable deviation of oxygen concentration a0 ranges from 1% to 2%.

3. The boundary layer control method for the main chamber of the carbon fiber pre-oxidation furnace as described in claim 1, characterized in that, In step A, the critical Reynolds number Re cr The value range is: 3.5 × 10 5 ≤Re cr ≤5×10 5 ; In step A, the target exhaust volume Q does not exceed 30% of the target supply volume Q0 of the pre-oxidation furnace.

4. The boundary layer control method for the main chamber of the carbon fiber pre-oxidation furnace as described in claim 1, characterized in that, The negative pressure system is arranged in the range of x2 to L, where 0.85x0≤x2≤x0.

5. The boundary layer control method for the main chamber of the carbon fiber pre-oxidation furnace as described in claim 1, characterized in that, Monitor the deviation ΔT = |T0-T1| between the actual supply air temperature T1 and the target supply air temperature T0, and keep ΔT ≤ 1℃.

6. The boundary layer control method for the main chamber of the carbon fiber pre-oxidation furnace as described in claim 1, characterized in that, The exhaust velocity u1 ranges from 1 m / s to 3 m / s.

7. A pre-oxidation furnace boundary layer control system characterized by, The pre-oxidation furnace boundary layer control system, applied to the boundary layer control method as described in any one of claims 1-6, comprises: The main chamber (1) has at least one negative pressure exhaust mechanism, which includes a negative pressure generator (4) and an exhaust chamber (12). The negative pressure generator (4) is connected to the exhaust chamber (12) and is used to provide the power required for exhaust. An exhaust flow meter (3) is installed at the outlet of the exhaust chamber (12), and the exhaust flow meter (3) is used to provide feedback on the actual exhaust volume; The negative pressure exhaust mechanism also includes an exhaust port (11), which is located on the side wall of the main chamber (1) of the pre-oxidation furnace and is connected to the exhaust chamber (12). An exhaust solenoid valve (2) is also provided between the negative pressure generator (4) and the exhaust chamber (12).

8. The pre-oxidation furnace boundary layer control system as described in claim 7, characterized in that, An exhaust outlet pressure sensor (50) is installed at the outlet of the exhaust chamber (12) to provide feedback on the exhaust pressure P; A boundary layer pressure sensor (51) is installed on the side wall of the main chamber (1) to provide feedback on the airflow pressure P0 within the boundary layer.

9. The pre-oxidation furnace boundary layer control system as described in claim 7, characterized in that, The first oxygen concentration sensor (61) and the second oxygen concentration sensor (62) are respectively arranged on the wall boundary layer and the main flow zone at the position x=x0 in the main chamber (1).

10. The pre-oxidation furnace boundary layer control system as described in claim 7, characterized in that, The boundary layer control system also includes a fresh air fan (10), a circulating air fan (13), and an electric heater (9). The fresh air fan (10) and the circulating air fan (13) are respectively connected to the inlet of the electric heater (9). The outlet of the electric heater (9) is connected to the inlet of the main chamber (1) through an air supply pipe. The outlet of the main chamber (1) is connected to the inlet of the circulating air fan (13) through a circulation pipe. The fresh air fan (10) is used to provide the oxygen required for the pre-oxidation process, the circulating air fan (13) is used to provide the return air circulation power, and the electric heater (9) is used to provide the heat required for the pre-oxidation process; The air supply duct is also equipped with an air supply temperature sensor (7), an air supply flow meter (8), and an intake oxygen concentration sensor (60) to provide feedback on the air supply temperature, air supply flow, and oxygen concentration in the air supply duct.

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