Method and system for heating hot air in pre-oxidation furnace with coupled heat recovery

Abstract

This invention belongs to the field of carbon fiber pre-oxidation furnace heating technology, specifically relating to a method for burning waste or low-grade fuels, and particularly to a pre-oxidation furnace hot air heating method and system coupled with heat recovery. This method divides the fresh air entering the pre-oxidation furnace into two parts. One part of the fresh air undergoes multiple gradient heating stages, then mixes with the return air from the previous process flow of the pre-oxidation furnace for a third gradient heating stage, followed by a fourth gradient heating stage via a thermal oil heater. Then, another part of the fresh air, which has only undergone one heating stage and has not been mixed, is introduced. This fresh air is then mixed again with the mixed air heated to above the process temperature. Once the process temperature is reached, it is sent into the pre-oxidation furnace. By controlling the flow rate of the newly introduced fresh air, the temperature of the mixed air can be precisely controlled at the process temperature.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber pre-oxidation furnace heating technology, specifically relating to a method for burning waste or low-grade fuels, and particularly to a pre-oxidation furnace hot air heating method and system coupled with heat recovery. Background Technology

[0002] Currently, domestic pre-oxidation furnaces mainly use electric heating and direct natural gas heating, which have certain shortcomings: electric heating systems have extremely high energy consumption, the electricity consumption of pre-oxidation furnace groups accounts for too high a proportion of production costs, and there is a tendency to face insufficient power supply during peak electricity demand periods; although direct natural gas heating can reduce electricity consumption, the combustion heater is placed in the furnace air duct, which poses significant risks such as localized high temperature of the heater and flue gas leakage, and the temperature of the pre-oxidation hot air fluctuates greatly. When the temperature fluctuation is too large, it can easily affect the oxidation quality of carbon fiber, or even cause uncontrolled oxidation and ignition of the fiber.

[0003] On the other hand, although the exhaust air from the pre-oxidation furnace has a high temperature, it contains tar, making heat recovery difficult. Directly using fresh air and exhaust air for heat recovery can easily lead to tar components condensing and forming coking blockages on the inner wall of the air supply duct. Without heat recovery of the exhaust air, the exhaust duct network is difficult to insulate, and the indoor heat dissipation is large, affecting the workshop environment and causing energy waste. Currently, a safe, stable, and energy-efficient method and system for heating hot air in pre-oxidation furnaces is still lacking.

[0004] Patent CN103352273A discloses a temperature-adjustable pre-oxidation furnace head device. It utilizes a conical inner shell, a built-in U-shaped heat-conducting oil system, and a temperature-sensing layer to collaboratively control temperature, while a nano-insulating coating and outer shell insulation layer reduce heat loss. This patent solves the problem of low temperatures at both ends of the furnace body; however, this design relies on an external power source to heat the heat-conducting oil, resulting in high energy consumption during long-term operation.

[0005] Patent CN115707801B discloses a drying and densification process for polyacrylonitrile fibers. This process employs a circulating heat-conducting oil system to perform multi-stage drying and densification of nascent fibers, while strictly controlling the uniformity of the surface temperature of the hot rollers. This patent improves the drawability of polyacrylonitrile filaments during the pre-oxidation process, while effectively reducing fuzz and breakage rates. However, this patent uses heat-conducting oil for the drying and densification process and does not address waste heat recovery.

[0006] Therefore, there is an urgent need to provide a pre-oxidation furnace hot air heating method and system with coupled heat recovery to solve the technical problems of high requirements for hot air temperature fluctuation, high requirements for heating energy saving, and high requirements for heating stability and safety in the above-mentioned related technologies.

[0007] 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

[0008] This disclosure provides at least one method and system for heating hot air in a pre-oxidizing furnace with coupled heat recovery.

[0009] In a first aspect, embodiments of this disclosure provide a method for heating hot air in a pre-oxidation furnace with coupled heat recovery. The method involves dividing the fresh air to be introduced into the pre-oxidation furnace into two streams. One stream of fresh air undergoes multiple gradient heating processes before being mixed with the other stream of fresh air. Once the mixture reaches the process temperature, it is then fed into the pre-oxidation furnace. The specific steps include:

[0010] Step S1: Connect the first waste heat exchanger, the second waste heat exchanger, the thermal oil heater, and the pre-oxidation furnace in sequence, and connect the make-up air pipe to the air inlet of the pre-oxidation furnace. Connect the exhaust port of the pre-oxidation furnace to the exhaust pipe and the circulation pipe respectively. The circulation pipe is connected to the main pipe between the second waste heat exchanger and the thermal oil heater, and the exhaust pipe is connected to the second waste heat exchanger.

[0011] Step S2: Fresh air is introduced into the first waste heat exchanger, and the fresh air exchanges heat with the first waste heat exchanger, and the temperature of the fresh air rises from the ambient temperature T0 to T1.

[0012] In step S3, the fresh air passes through the first waste heat exchanger, and the temperature of the fresh air is raised to above the critical point of tar condensation. It is then split into two paths: the main duct and the make-up air duct. The fresh air in the main duct enters the second waste heat exchanger for heat exchange, and the temperature of the fresh air rises from T1 to T2.

[0013] In step S4, the fresh air passes through the second waste heat exchanger, and the circulating air in the pre-oxidation furnace mixes with the fresh air passing through the second waste heat exchanger, thereby raising the temperature of the mixed air from T2 to T3.

[0014] In step S5, the mixed air enters the heat transfer oil heater to exchange heat with the oil, and the temperature of the mixed air rises from T3 to T4.

[0015] In step S6, the mixed air is mixed with the fresh air in the make-up air duct, the temperature drops from T4 to T5, and then enters the pre-oxidation furnace.

[0016] In one optional embodiment, the target temperature of the exhaust port of the thermal oil heater is set to T4, and the actual temperature of the exhaust port of the thermal oil heater is T. a4 ;

[0017] If T a4 If the temperature is less than T4, then increase the power of the thermal oil heater and raise the temperature T. a4 To T4;

[0018] If Ta4 If the temperature is greater than T4, then reduce the power of the thermal oil heater and lower the temperature T. a4 To T4.

[0019] In one optional implementation, the target temperature at the air inlet of the pre-oxidation furnace is set to T5, and the actual temperature is reduced to T5 after the mixing air from the thermal oil heater is mixed with the fresh air in the make-up air duct. a5 ;

[0020] If T a5 If T < T5, increase the circulating airflow and reduce the proportion of fresh air in the makeup air duct to improve T. a5 Up to T5;

[0021] If T a5 If the airflow is greater than T5, reduce the circulating airflow and increase the proportion of fresh air in the makeup air duct to reduce T. a5 To T5.

[0022] In one optional implementation, the target oxygen concentration inside the pre-oxidation furnace is set to C1, and the actual oxygen concentration inside the pre-oxidation furnace is C0.

[0023] If C0 < C1, then increase the fresh air volume Q1 to increase the oxygen concentration in the pre-oxidation furnace, and at the same time increase the exhaust air volume Q2 of the pre-oxidation furnace. The exhaust air volume Q2 is 1 to 1.2 times that of Q1 to maintain the pressure state inside the furnace as negative pressure, until the oxygen concentration inside the furnace C0 = C1.

[0024] If C0 > C1, reduce the exhaust air volume of the pre-oxidation furnace and simultaneously reduce the fresh air volume to lower the oxygen concentration in the pre-oxidation furnace until C0 = C1.

[0025] Secondly, this disclosure also provides a pre-oxidizing furnace hot air heating system with coupled heat recovery, applied to perform the pre-oxidizing furnace hot air heating method with coupled heat recovery as described above, the pre-oxidizing furnace hot air heating system with coupled heat recovery comprising:

[0026] The main pipeline, and the first waste heat exchanger, the second waste heat exchanger, the thermal oil heater and the pre-oxidation furnace connected in sequence through the main pipeline;

[0027] The exhaust port of the pre-oxidation furnace is connected between the second waste heat exchanger and the thermal oil heater;

[0028] Among them, there is also a makeup air pipe between the thermal oil heater and the pre-oxidation furnace, and the other end of the makeup air pipe is connected between the first waste heat exchanger and the second waste heat exchanger.

[0029] The exhaust vent of the pre-oxidation furnace is equipped with an exhaust pipe and a circulation pipe. The circulation pipe is connected between the second waste heat exchanger and the thermal oil heater, and the exhaust pipe is connected to the second waste heat exchanger.

[0030] Furthermore, the gas discharged from the pre-oxidation furnace enters the exhaust pipe and the circulation pipe respectively to form an exhaust gas flow and a circulation gas flow.

[0031] In one optional embodiment, a third solenoid valve and a fourth solenoid valve are respectively installed on the exhaust pipe and the circulation pipe to control the opening degree of the exhaust pipe and the circulation pipe.

[0032] In one optional embodiment, the thermal oil heater has a thermal oil furnace on one side, and both the thermal oil furnace and the thermal oil heater have circulating oil circuits inside.

[0033] Furthermore, the circulating oil circuit of the thermal oil furnace is connected to that of the thermal oil heater;

[0034] One side of the thermal oil furnace is connected to a natural gas source.

[0035] In one optional embodiment, one end of the thermal oil furnace is connected to a third waste heat exchanger, which contains circulating cooling water, and the flue gas from the thermal oil furnace exchanges heat with the circulating cooling water of the third waste heat exchanger.

[0036] The third waste heat exchanger is connected to the first waste heat exchanger.

[0037] In one optional embodiment, the pre-oxidation furnace hot air heating system with coupled heat recovery further includes a control module, a first solenoid valve is installed on the main pipeline, and a second solenoid valve is installed on the make-up air pipeline, the second solenoid valve being electrically connected to the control module.

[0038] The beneficial effects of this invention are that it uses multiple waste heat recovery units to perform gradient heating of fresh air, then mixes and heats the circulating air in the pre-oxidation furnace with the fresh air, then heats this part of the fresh air to above the process temperature through a thermal oil heater, and finally introduces preheated fresh air to mix again, cools the mixed airflow to the process temperature, and replenishes the oxygen content.

[0039] The beneficial effects of this invention are as follows: By introducing an innovative design of indirect heating using a thermal oil furnace, this solution fundamentally avoids the risk of direct heating of circulating air by traditional natural gas direct combustion methods. This technical approach completely isolates the natural gas combustion heat source from the circulating airflow, effectively eliminating the hidden danger of local overheating causing carbon fiber bundle combustion.

[0040] This solution employs an innovative design that efficiently exchanges high-temperature flue gas from the pre-oxidation furnace with fresh air within a waste heat recovery system. This achieves continuous maintenance of flue gas temperature. Specifically, circulating cooling water first exchanges heat with the flue gas from the thermal oil furnace. After its temperature is increased, the circulating cooling water is transported to the first waste heat exchanger for heat exchange with fresh air. The fresh air temperature is then raised above the tar condensation critical point before being transported to the second waste heat exchanger for heat exchange with the pre-oxidation furnace flue gas. This ensures that the pre-oxidation furnace flue gas itself remains at a stable high temperature throughout the entire transport process, thereby completely avoiding the phase change condensation phenomenon of tar components due to sudden temperature drops and effectively eliminating the risk of coking and blockage on the inner wall of the pipeline. Simultaneously, heat recovery from the high-temperature exhaust air is achieved, reducing heat loss and insulation requirements of the high-temperature exhaust duct.

[0041] 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.

[0042] 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

[0043] 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.

[0044] Figure 1 A flowchart of a pre-oxidation furnace hot air heating method coupled with heat recovery provided for embodiments of this disclosure;

[0045] Figure 2 A schematic diagram of a pre-oxidation furnace hot air heating system with coupled heat recovery provided in an embodiment of this disclosure;

[0046] Figure 3 This is a schematic diagram of the connection relationship of a main pipeline provided in an embodiment of the present disclosure;

[0047] Figure 4 This is a schematic diagram of the connection relationship of a waste heat recovery pipeline provided in an embodiment of this disclosure.

[0048] In the picture:

[0049] 1. First waste heat exchanger; 2. Second waste heat exchanger; 3. Thermal oil heater; 4. Thermal oil furnace; 5. Third waste heat exchanger; 6. Pre-oxidation furnace; 7. Natural gas source; 8. Control module;

[0050] 21. First fan; 22. Second fan; 23. Third fan; 24. Fourth fan; 25. Water pump;

[0051] 31. First solenoid valve; 32. Second solenoid valve; 33. Third solenoid valve; 34. Fourth solenoid valve; 35. Fifth solenoid valve; 36. Sixth solenoid valve; 37. Seventh solenoid valve;

[0052] 41. First temperature sensor; 42. Second temperature sensor;

[0053] 51. Oxygen content sensor. Detailed Implementation

[0054] 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.

[0055] Research has shown that the pre-oxidation stage in carbon fiber preparation plays a decisive role in carbon fiber performance. Currently, domestic pre-oxidation furnaces mainly use electric heating and direct natural gas heating, which have certain shortcomings: electric heating systems have extremely high energy consumption, the electricity consumption of pre-oxidation furnace groups accounts for a high proportion of production costs, and there is a tendency to face power shortages during peak electricity demand periods; although direct natural gas heating can reduce electricity consumption, the combustion heater is placed in the furnace air duct, which poses significant risks such as localized high temperatures in the heater and flue gas leakage. The pre-oxidation hot air temperature fluctuates greatly, and when the temperature fluctuation is too large, it can easily affect the oxidation quality of carbon fibers, or even cause uncontrolled oxidation and ignition of the fibers.

[0056] On the other hand, although the exhaust air from the pre-oxidation furnace has a high temperature, it contains tar, making heat recovery difficult. Directly using fresh air and exhaust air for heat recovery can easily lead to tar components condensing and forming coking blockages on the inner wall of the air supply duct. Without heat recovery of the exhaust air, the exhaust duct network is difficult to insulate, and the indoor heat dissipation is large, affecting the workshop environment and causing energy waste. Currently, a safe, stable, and energy-efficient method and system for heating hot air in pre-oxidation furnaces is still lacking.

[0057] There is an urgent need to provide a pre-oxidation furnace hot air heating method and system with coupled heat recovery to solve the technical problem in the above-mentioned related technologies that the carbon fiber pre-oxidation furnace has high requirements for temperature fluctuations, and conventional heaters cannot cope with the technical problem of local high temperature in the furnace duct causing thermal runaway of carbon fiber raw materials.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] Based on the above research, this disclosure provides a method for heating hot air in a pre-oxidation furnace with coupled heat recovery. The method involves dividing the fresh air to be introduced into the pre-oxidation furnace 6 into two streams. One stream is heated through multiple gradients before being mixed with the other stream. Once the mixture reaches the process temperature, it is then sent into the pre-oxidation furnace 6. The specific steps include:

[0062] Step S1: Connect the first waste heat exchanger 1, the second waste heat exchanger 2, the thermal oil heater 3, and the pre-oxidation furnace 6 in sequence, and connect the make-up air pipe to the air inlet of the pre-oxidation furnace 6, and connect the exhaust port of the pre-oxidation furnace 6 to the second waste heat exchanger 2 and the thermal oil heater 3.

[0063] Step S2: Fresh air is introduced into the first waste heat exchanger 1, and the fresh air exchanges heat with the first waste heat exchanger 1, and the temperature of the fresh air rises from the ambient temperature T0 to T1.

[0064] In step S3, the fresh air passes through the first waste heat exchanger 1 and is split into the main duct and the makeup air duct. The fresh air in the main duct enters the second waste heat exchanger 2 for heat exchange, and the fresh air temperature rises from T1 to T2.

[0065] In step S4, the fresh air passes through the second waste heat exchanger 2, and the circulating air in the pre-oxidation furnace 6 mixes with the fresh air passing through the second waste heat exchanger 2, thereby raising the temperature of the mixed air from T2 to T3.

[0066] In step S5, the mixed air enters the heat transfer oil heater 3 to exchange heat with the oil, and the temperature of the mixed air rises from T3 to T4.

[0067] In step S6, the mixed air is mixed with the fresh air in the make-up air duct, the temperature drops from T4 to T5, and then enters the pre-oxidation furnace 6.

[0068] In the above steps, T0 is the ambient temperature, T1 is preferably 30℃~70℃, T2 is preferably 50℃~100℃, T3 is preferably 120℃~170℃, T4 is preferably 260℃~280℃, and T5 is preferably 200℃~250℃. That is, the fresh air passes through the first waste heat exchanger 1, and its temperature rises from the ambient temperature T0 (20℃-30℃) to T1 (30℃~70℃). The fresh air passes through the second waste heat exchanger 2, and its temperature rises from T1 (30℃~70℃) to T2 (50℃~100℃). After the fresh air mixes with the circulating air, its temperature rises from T2 (50℃~100℃) to T3 (120℃~170℃). The mixed air enters the thermal oil heater 3 to exchange heat with the oil, and its temperature rises from T3 (120℃~170℃) to T4 (260℃~280℃). The mixed air mixes with the fresh air in the makeup air duct, and its temperature drops from T4 (260℃~280℃) to T5 (200℃~250℃).

[0069] According to the above steps, after being heated twice, the fresh air is mixed with the circulating air and return air from the previous process in the pre-oxidation furnace 6 for a third gradient heating. At this time, the temperature of the mixed air formed by the fresh air and the circulating air has reached a relatively high level. Then, it is heated a fourth time through the thermal oil heater 3, so that the temperature of the mixed air can be heated to a level higher than the process temperature in a short time. Then, another fresh air that has only been heated once and has not been mixed is introduced, so that this fresh air is mixed with the mixed air heated to a level higher than the process temperature again. By controlling the flow rate of the newly introduced fresh air, the temperature of the mixed air can be accurately controlled at the process temperature.

[0070] By using gradient heating, the temperature in each local area of ​​the pipeline is relatively controllable, and there is no problem of sudden temperature rise or fall. In the final heating stage, namely the heating stage of the heat transfer oil heater 3, the mixed air has already reached a high temperature level, and there will be no local overheating or excessive temperature fluctuations, thus avoiding the problem of uncontrolled oxidation or even combustion of carbon fiber materials.

[0071] On the other hand, setting the heat transfer oil heater 3 to heat the mixed air to above the process temperature and introduce unheated fresh air for secondary mixing can ensure that the temperature is precisely controlled uniformly before the mixed air enters the pre-oxidation furnace 6. At the same time, the introduced fresh air can also supplement the oxygen content of the mixed air.

[0072] In at least one embodiment, to monitor and precisely control the temperature of the mixed air discharged from the thermal oil heater 3, a temperature sensor is installed at the exhaust port of the thermal oil heater 3. The target temperature of the exhaust port is set to T4 (260℃~280℃), and the actual temperature of the exhaust port is T. a4 If T a4 If T<4, then increase the power of the thermal oil heater 3 and increase the temperature T. a4 Up to T4; if T a4 If the temperature is greater than T4, then reduce the power of the thermal oil heater 3 and lower the temperature T. a4 Up to T4. With the above settings, when the system experiences temperature fluctuations due to a certain factor, the temperature sensor can continuously monitor and control the power of the thermal oil heater 3, ensuring that the actual temperature at the exhaust port of the thermal oil heater 3 can be adjusted in time to recover and maintain at T4 (260℃~280℃).

[0073] In at least one embodiment, to monitor the temperature of the mixed air at the inlet of the pre-oxidation furnace 6 and ensure that the temperature of the mixed air entering the pre-oxidation furnace 6 is maintained at the process temperature, a temperature sensor can be installed at the inlet of the pre-oxidation furnace 6, and the target temperature of the inlet of the pre-oxidation furnace 6 can be set to T5 (200℃~250℃). After the mixed air is mixed with the fresh air in the make-up air duct by the heat transfer oil heater 3, the actual temperature is reduced to T5. a5 If T a5 If T < T5, increase the flow rate of the mixed air and decrease the flow rate of the fresh air in the makeup air duct to increase T. a5 Up to T5; if T a5 If the airflow is greater than T5, reduce the flow rate of the mixed air and increase the flow rate of fresh air in the makeup air duct to reduce T. a5 Up to T5. With the above settings, when the temperature of the mixed air entering the pre-oxidation furnace 6 changes, the flow rate of the mixed air and the flow rate of the unheated fresh air can be adjusted simultaneously to precisely regulate the temperature of the mixed air entering the pre-oxidation furnace 6.

[0074] It should be noted that although adjusting the flow rate of the mixed air or the flow rate of the unheated fresh air can regulate the temperature of the mixed air entering the pre-oxidation furnace 6, the unheated fresh air will also affect the oxygen content of the mixed air that finally enters the pre-oxidation furnace 6. Therefore, adjusting a single factor will directly lead to changes in the oxygen content of the mixed air. Thus, it is necessary to adjust both factors simultaneously to ensure that the oxygen content is maintained within the range required by the process while maintaining the temperature.

[0075] Specifically, in at least one embodiment, an oxygen content sensor 51 can be installed at the air inlet of the pre-oxidation furnace 6, and the target oxygen concentration inside the pre-oxidation furnace 6 is set as C1, while the actual oxygen concentration inside the pre-oxidation furnace 6 is C0. If C0 < C1, the fresh air volume Q1 is increased to increase the oxygen concentration in the pre-oxidation furnace 6, and the exhaust air volume Q2 of the pre-oxidation furnace 6 is increased at the same time. The exhaust air volume Q2 is 1 to 1.2 times that of Q1 to maintain the pressure state inside the furnace as negative pressure, with a vacuum degree of -30Pa to 0Pa, until the oxygen concentration inside the furnace C0 = C1. If C0 > C1, the exhaust air volume of the pre-oxidation furnace 6 is reduced, and the fresh air volume is reduced at the same time to reduce the oxygen concentration in the pre-oxidation furnace 6 until C0 = C1.

[0076] In addition, refer to Figure 2 This disclosure also provides a pre-oxidation furnace hot air heating system with coupled heat recovery, which is applied to perform the pre-oxidation furnace hot air heating method with coupled heat recovery as described above. The pre-oxidation furnace hot air heating system with coupled heat recovery includes: a main pipeline, and a first waste heat exchanger 1, a second waste heat exchanger 2, a thermal oil heater 3 and a pre-oxidation furnace 6 connected in sequence through the main pipeline.

[0077] Reference Figure 3 The exhaust port of the pre-oxidation furnace 6 is equipped with a three-way pipe. One end of the three-way pipe is connected to the pre-oxidation furnace 6, and the other two ends are connected to the exhaust pipe and the circulation pipe, respectively. The circulation pipe is connected to the main pipe between the second waste heat exchanger 2 and the thermal oil heater 3, and the exhaust pipe is connected to the second waste heat exchanger 2. The gas discharged from the pre-oxidation furnace 6 is divided into two streams after passing through the three-way pipe. One stream enters the circulation pipe to form a circulating airflow, and the other stream enters the exhaust pipe to form a discharge airflow.

[0078] Specifically, refer to Figure 3 fresh air along f1 After passing through the first waste heat exchanger 1, the air direction splits into two paths. One path, containing fresh air, continues along the main duct, i.e., continues along... f1 In the direction, after passing through the second waste heat exchanger 2, it is along the... f12 The circulating airflow in the direction of the flow mixes, and the mixed air continues along... f1 One direction of fresh air passes through the thermal oil heater 3; another direction of fresh air enters the makeup air duct, which is located between the first waste heat exchanger 1 and the second waste heat exchanger 2, and extends to the outlet of the thermal oil heater 3 at the other end. The fresh air in the makeup air duct flows along... f2 The direction bypasses the second waste heat exchanger 2 and the thermal oil heater 3, and is mixed a second time with the mixing air in the main pipeline. After mixing, it continues along... f1 The gas enters the pre-oxidation furnace 6 in the following direction. The gas discharged from the pre-oxidation furnace 6 is divided into two streams through a three-way pipe. f11 Directional flow of exhaust air and along f12 A circulating airflow with directional flow.

[0079] Reference Figure 3 The exhaust airflow passes through the second waste heat exchanger 2, where it exchanges heat with the fresh air passing through the first waste heat exchanger 1, thus subjecting the fresh air to a second gradient heating. The recirculated airflow enters the main duct and mixes with the fresh air passing through the second waste heat exchanger 2, thereby subjecting the fresh air to a third gradient heating.

[0080] Reference Figure 3 In at least one embodiment, a third solenoid valve 33 and a fourth solenoid valve 34 are respectively installed on the exhaust pipe and the circulation pipe to control the opening of the exhaust pipe and the circulation pipe, so as to adjust the ratio of the exhaust gas flow and the circulation gas flow discharged from the pre-oxidation furnace 6 into the exhaust pipe or the circulation pipe.

[0081] Reference Figure 4 In at least one embodiment, a thermal oil heater 3 has a thermal oil furnace 4 on one side, and both the thermal oil furnace 4 and the thermal oil heater 3 have circulating oil circuits. The circulating oil circuits of the thermal oil furnace 4 and the thermal oil heater 3 are connected. One side of the thermal oil furnace 4 is connected to a natural gas source 7. With the above arrangement, the natural gas source 7 continuously supplies natural gas into the interior of the thermal oil furnace 4 and burns it to heat the oil inside the thermal oil furnace 4. A hot oil pump is provided between the circulating oil circuit of the thermal oil furnace 4 and the circulating oil circuit of the thermal oil heater 3, thereby sending the oil in the thermal oil furnace 4 into the thermal oil heater 3 and returning it to the thermal oil furnace 4 through the other end, thereby continuously heating the thermal oil heater 3 so that the thermal oil heater 3 performs a fourth gradient heating on the hot mixed air.

[0082] Reference Figure 4 In at least one embodiment, one end of the thermal oil furnace 4 is connected to a third waste heat exchanger 5, which contains circulating cooling water. The flue gas from the thermal oil furnace 4 exchanges heat with the circulating cooling water in the third waste heat exchanger 5. Furthermore, the third waste heat exchanger 5 is connected to the first waste heat exchanger 1 via two waste heat recovery pipes. The circulating cooling water, after being heated, flows through one of the waste heat recovery pipes along… f3 The air is transported in the direction of the first waste heat exchanger 1 to exchange heat with fresh air, and then transported through another waste heat recovery pipe along... f 3 The waste heat is then returned to the third waste heat exchanger 5. At least one waste heat recovery pipe is equipped with a water pump 25 to achieve circulating cooling water flow. That is, after natural gas heats the thermal oil heater 4, the flue gas further enters the third waste heat exchanger 5 and heats it. Then, the third waste heat exchanger 5 heats the first waste heat exchanger 1 through circulating cooling water. This fully utilizes the residual temperature of the flue gas after the natural gas heats the thermal oil heater 3.

[0083] Reference Figure 2 In at least one embodiment, to control the opening and closing of each pipe and its degree of opening, and to monitor the temperature and oxygen content in the main pipe, the pre-oxidation furnace hot air heating system with coupled heat recovery also includes a control module 8. Simultaneously, a first solenoid valve 31 is installed between the second waste heat exchanger 2 and the thermal oil heater 3 in the main pipe; a second solenoid valve 32 is installed on the make-up air pipe; a fifth solenoid valve 35 is installed at the exhaust port of the pre-oxidation furnace 6; a third solenoid valve 33 is installed on the exhaust pipe; a fourth solenoid valve 34 is installed on the circulation pipe; a sixth solenoid valve 36 is installed between the natural gas source 7 and the thermal oil furnace 4; and a seventh solenoid valve 37 is installed on the waste heat recovery pipe. A first temperature sensor 41 is installed at the exhaust port of the thermal oil heater 3, and a second temperature sensor 42 is installed at the air inlet of the pre-oxidation furnace 6. An oxygen content sensor 51 is also installed at the air inlet of the pre-oxidation furnace 6. All of the above components are electrically connected to the control module 8. The control module 8 can receive feedback from the first temperature sensor 41 to control the opening of the sixth solenoid valve 36, thereby regulating the flow rate of the natural gas source 7 and thus adjusting the heating power of the thermal oil furnace 4. The control module 8 can also receive feedback from the second temperature sensor 42 to adjust the opening of the fourth solenoid valve 34 and the second solenoid valve 32, thereby adjusting the proportion of circulating air and the proportion of fresh air entering the make-up air duct. Furthermore, the control module 8 can receive feedback from the oxygen content sensor 51 to adjust the opening of the third solenoid valve 33 and the fourth solenoid valve 34, thereby adjusting the proportion of circulating airflow entering the circulation duct. In addition, the operator can set corresponding control logic according to the actual situation to control other components and achieve related functions; these details will not be elaborated here.

[0084] Reference Figure 2 In at least one embodiment, in order to control the airflow to flow continuously and stably in each pipe, a first fan 21 is installed at the beginning of the main pipe, a second fan 22 is installed at the air inlet of the pre-oxidation furnace 6, a third fan 23 is installed at the end of the main pipe, and a fourth fan 24 is installed at the air inlet of the thermal oil furnace 4.

[0085] 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 heating hot air in a pre-oxidizing furnace with coupled heat recovery, characterized in that, The fresh air to be introduced into the pre-oxidation furnace is divided into two streams. One stream of fresh air is heated through multiple gradients before being mixed with the other stream. Once the process temperature is reached, the mixture is sent into the pre-oxidation furnace. The specific steps include the following: Step S1: Connect the first waste heat exchanger (1), the second waste heat exchanger (2), the thermal oil heater (3), and the pre-oxidation furnace (6) in sequence, and connect the make-up air pipe to the air inlet of the pre-oxidation furnace (6). Connect the exhaust port of the pre-oxidation furnace (6) to the exhaust pipe and the circulation pipe respectively. The circulation pipe is connected to the main pipe between the second waste heat exchanger (2) and the thermal oil heater (3), and the exhaust pipe is connected to the second waste heat exchanger (2). Step S2: Fresh air is introduced into the first waste heat exchanger (1), and the fresh air exchanges heat with the first waste heat exchanger (1), and the temperature of the fresh air rises from the ambient temperature T0 to T1. In step S3, the fresh air passes through the first waste heat exchanger (1), and the temperature of the fresh air is raised to above the critical point of tar condensation. It is then split into two paths: the main pipeline and the make-up air pipeline. The fresh air in the main pipeline enters the second waste heat exchanger (2) for heat exchange, and the temperature of the fresh air rises from T1 to T2. In step S4, the fresh air passes through the second waste heat exchanger (2), and the circulating air in the pre-oxidation furnace (6) mixes with the fresh air passing through the second waste heat exchanger (2), thereby raising the temperature of the mixed air from T2 to T3. In step S5, the mixed air enters the heat transfer oil heater (3) and exchanges heat with the oil, and the temperature of the mixed air rises from T3 to T4; In step S6, the mixed air is mixed with the fresh air in the make-up air duct, the temperature drops from T4 to T5, and then enters the pre-oxidation furnace (6).

2. The pre-oxidation furnace hot air heating method with coupled heat recovery as described in claim 1, characterized in that, The target temperature of the exhaust port of the thermal oil heater (3) is set to T4, and the actual temperature of the exhaust port of the thermal oil heater (3) is T. a4 ; If T a4 If T < T4, then increase the power of the thermal oil heater (3) and raise the temperature T. a4 To T4; If T a4 If the temperature is greater than T4, then reduce the power of the thermal oil heater (3) and reduce the temperature T. a4 To T4.

3. The pre-oxidation furnace hot air heating method with coupled heat recovery as described in claim 1, characterized in that, The target temperature of the air inlet of the pre-oxidation furnace (6) is set to T5. After the mixed air from the heat transfer oil heater (3) is mixed with the fresh air in the make-up air duct, the actual temperature is reduced to T. a5 ; If T a5 If T < T5, increase the circulating airflow and reduce the proportion of fresh air in the makeup air duct to improve T. a5 Up to T5; If T a5 If the airflow is greater than T5, reduce the circulating airflow and increase the proportion of fresh air in the makeup air duct to reduce T. a5 To T5.

4. The pre-oxidation furnace hot air heating method with coupled heat recovery as described in claim 1, characterized in that, The target oxygen concentration in the pre-oxidation furnace (6) is set to C1, and the actual oxygen concentration in the pre-oxidation furnace (6) is C0. If C0 < C1, then increase the fresh air volume Q1 to increase the oxygen concentration in the pre-oxidation furnace (6), and at the same time increase the exhaust air volume Q2 of the pre-oxidation furnace (6). The exhaust air volume Q2 is 1 to 1.2 times that of Q1 to maintain the pressure state inside the furnace as negative pressure, until the oxygen concentration inside the furnace C0 = C1. If C0 > C1, reduce the exhaust air volume of the pre-oxidation furnace (6) and reduce the fresh air volume at the same time to reduce the oxygen concentration of the pre-oxidation furnace (6) until C0 = C1.

5. A pre-oxidation furnace hot air heating system with coupled heat recovery, characterized in that, The pre-oxidizing furnace hot air heating system, which is applied to the coupled heat recovery method for performing any one of claims 1-4, comprises: The main pipeline, and the first waste heat exchanger (1), the second waste heat exchanger (2), the thermal oil heater (3) and the pre-oxidation furnace (6) connected in sequence through the main pipeline. The exhaust port of the pre-oxidation furnace (6) is connected between the second waste heat exchanger (2) and the thermal oil heater (3); Among them, there is also a make-up air pipe between the heat transfer oil heater (3) and the pre-oxidation furnace (6), and the other end of the make-up air pipe is connected between the first waste heat exchanger (1) and the second waste heat exchanger (2); The exhaust vent of the pre-oxidation furnace (6) is equipped with an exhaust pipe and a circulation pipe. The circulation pipe is connected between the second waste heat exchanger (2) and the thermal oil heater (3), and the exhaust pipe is connected to the second waste heat exchanger (2). In addition, the gas discharged from the pre-oxidation furnace (6) enters the exhaust pipe and the circulation pipe respectively to form an exhaust gas flow and a circulation gas flow.

6. The pre-oxidation furnace hot air heating system with coupled heat recovery as described in claim 5, characterized in that, The exhaust pipe and the circulation pipe are respectively equipped with a third solenoid valve (33) and a fourth solenoid valve (34) to control the opening degree of the exhaust pipe and the circulation pipe.

7. The pre-oxidation furnace hot air heating system with coupled heat recovery as described in claim 5, characterized in that, The thermal oil heater (3) has a thermal oil furnace (4) on one side, and both the thermal oil furnace (4) and the thermal oil heater (3) have circulating oil circuits inside. Furthermore, the circulating oil circuit of the thermal oil furnace (4) is connected to that of the thermal oil heater (3); One side of the thermal oil furnace (4) is connected to the natural gas source (7).

8. The pre-oxidation furnace hot air heating system with coupled heat recovery as described in claim 7, characterized in that, One end of the thermal oil furnace (4) is connected to the third waste heat exchanger (5), which has circulating cooling water inside. The flue gas of the thermal oil furnace (4) exchanges heat with the circulating cooling water of the third waste heat exchanger (5). The third waste heat exchanger (5) is connected to the first waste heat exchanger (1).

9. The pre-oxidation furnace hot air heating system with coupled heat recovery as described in claim 5, characterized in that, The pre-oxidation furnace hot air heating system with coupled heat recovery also includes a control module (8), a first solenoid valve (31) is installed on the main pipeline, and a second solenoid valve (32) is installed on the make-up air pipeline. The second solenoid valve (32) is electrically connected to the control module (8).

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