Double-heat-source carbon fiber pre-oxidation system and operation method thereof

Abstract

The invention belongs to the technical field of pre-oxidation furnaces, and particularly relates to a dual-heat-source carbon fiber pre-oxidation system and an operation method thereof.The dual-heat-source carbon fiber pre-oxidation system comprises a pre-oxidation furnace, a fresh air preheater, a natural gas combustion furnace, a flue gas heat exchanger and an electric heating device, and the pre-oxidation furnace, the flue gas heat exchanger and the electric heating device are sequentially communicated and form a heating loop; the flue gas heat exchanger is suitable for providing 60%-90% of process heat load for the pre-oxidation furnace; the electric heating device is suitable for accurately adjusting the air supply temperature of the pre-oxidation furnace and supplying 10%-40% of process heat load to the pre-oxidation furnace; and the fresh air preheater is used for recycling flue gas waste heat generated by the natural gas combustion furnace. A double-heat-source mode is adopted, the operation cost of the pre-oxidation technology is reduced, the temperature control accuracy of the technological process is improved, meanwhile, heat in high-temperature flue gas is recycled, and the heat efficiency of the system is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of pre-oxidation furnaces, and particularly relates to a double-heat-source carbon fiber pre-oxidation system and a running method thereof. BACKGROUND

[0002] Carbon fibers have excellent mechanical properties and chemical stability, and the density is lower than that of aluminum and the strength is higher than that of steel. Carbon fibers are currently the most high-performance fibers with the highest specific strength and the highest specific modulus among high-performance fibers that have been mass-produced, and have the characteristics of low density, corrosion resistance, high temperature resistance, friction resistance, fatigue resistance, high vibration attenuation, high electrical and thermal conductivity, low thermal and moisture expansion coefficient, high X-ray penetration, non-magnetic but electromagnetic shielding effect, etc. Carbon fibers are important strategic materials for the development of national defense and military industry and national economy, and are applied to the fields of national defense industry and high-performance civilian fields, such as military industry, aerospace, marine engineering, sports goods, automobile industry, new energy equipment, medical devices, engineering machinery, transportation, building and structure reinforcement, etc.

[0003] The pre-oxidation process is a key core process link in the process of preparing large-tow high-performance carbon fibers, and is a bridge connecting the original yarn and carbon fibers. As the equipment of the pre-oxidation process, the guarantee of various performances is the basis for developing the pre-oxidation furnace.

[0004] At present, the pre-oxidation furnaces applied in the industry at home and abroad are mainly electric heating, and the installed power (power consumption in the running process) of the pre-oxidation furnace in most production lines has exceeded 50% of the total power of the whole line, which is a typical large energy consumer. Combined with the energy prices in various regions, the operation cost is relatively large. In recent years, natural gas heating type pre-oxidation furnaces have begun to rise, and compared with the electric heating type pre-oxidation furnace, the operation cost is significantly reduced, but there is a significant temperature control relaxation phenomenon.

[0005] Therefore, there is still a lack of a double-heat-source carbon fiber pre-oxidation system and a running method thereof which are high in efficiency and energy saving and accurate in temperature control. SUMMARY

[0006] The application aims to provide a double-heat-source carbon fiber pre-oxidation system to solve the above technical problems. The application provides a double-heat-source carbon fiber pre-oxidation system, which comprises a pre-oxidation furnace, a fresh air pre-heater, a natural gas combustion furnace, a flue gas heat exchanger, and an electric heating device. The natural gas combustion furnace is communicated with the flue gas heat exchanger, and is used for indirectly exchanging heat between the high-temperature flue gas and the mixed fresh air in the flue gas heat exchanger. The pre-oxidation furnace, the flue gas heat exchanger, and the electric heating device are sequentially communicated and form a heating loop. The flue gas heat exchanger is adapted to provide 60%-90% of the process heat load to the pre-oxidation furnace. The electric heating device is adapted to accurately adjust the air supply temperature of the pre-oxidation furnace and supply 10%-40% of the process heat load to the pre-oxidation furnace. The pre-oxidation furnace is adapted to deliver the return air to the cold air inlet of the flue gas heat exchanger.

[0007] Further, the natural gas burner inlet is respectively communicated with pipeline one and pipeline two, wherein, the pipeline one is provided with a gas regulating valve; the pipeline two is provided with a combustion air fan, wherein, the pipeline two and the combustion air fan are further provided with an air volume regulating valve; the electric heating device and the pre-oxidation furnace are further provided with a pressurizing fan.

[0008] Further, the pre-oxidation furnace and the flue gas heat exchanger are further provided with a fresh air preheater, the high-temperature inlet of the fresh air preheater is communicated with the flue gas outlet of the flue gas heat exchanger, for recycling waste heat in the flue gas; the fresh air outlet of the fresh air preheater is communicated with the cold air inlet of the flue gas heat exchanger, and the fresh air inlet of the fresh air preheater is communicated with a fresh air system, and the waste gas outlet of the fresh air preheater is communicated with the outside; the pre-oxidation furnace exhaust air duct is connected to the outside, and is provided with an exhaust air regulating valve.

[0009] Further, the pre-oxidation furnace is further communicated with a fire-fighting water tank, wherein, the pre-oxidation furnace and the fire-fighting water tank are further provided with a fire-fighting spray water pump.

[0010] In another aspect, the application further provides a running method using the pre-oxidation system, comprising S1: obtaining pre-oxidation process related parameters and equipment size, including pre-oxidation furnace design air supply wind speed v, design air supply temperature T0, allowable air supply temperature difference a, pre-oxidation furnace air supply cross-sectional area S, natural gas low heat value H L , unit gas theoretical air volume V0, combustion excess air coefficient α, flue gas heat exchanger heat exchange efficiency η, pre-oxidation process fresh air volume Q X ;

[0011] S2: running the pre-oxidation furnace equipment line, adjusting the pre-oxidation furnace exhaust air regulating valve, so that the flow is Q X , real-time collection of temperature data of each temperature sensor (Ti), and calculation:

[0012] Pre-oxidation furnace air supply flow Q=v S;

[0013] Pre-oxidation process total heat load: H g =c·Q·(T0-T1);

[0014] Natural gas combustion furnace heat load: H g1 =(0.6H g ~0.9H g ) / η;

[0015] Gas flow: Q g =3600H g1 / H L ;

[0016] Combustion air flow: Q a= aV0Q g ;

[0017] Heat load of electric heating device: H g2 = c·Q·(T0-T2).

[0018] Further, a temperature sensor T1 is arranged at the cold air inlet of the flue gas heat exchanger, a temperature sensor T2 is arranged at the outlet of the flue gas heat exchanger, a temperature sensor T3 is arranged at the outlet of the electric heating device, a temperature sensor T4 is arranged at the outlet of the pre-oxidation furnace, and a temperature sensor T5 is arranged at the flue gas discharge pipeline of the fresh air pre-heater. T1, T2, T3, T4 and T5 are continuously and real-timely measured and collected.

[0019] Further, the above-mentioned related parameters and formulas are programmed into the information processing host of the control center, which is calculated by the information processing host and sequentially controls as follows:

[0020] When the temperature T1 on the air inlet pipeline of the flue gas heat exchanger is less than T0, the required gas flow and combustion air flow are calculated by the program, a first signal is fed back to the output controller, and the opening degrees of the gas regulating valve and the air volume regulating valve of the natural gas combustion furnace are controlled to make them run at the set flow Q g , Q a The information processing host calculates the heat load of the electric heating device, feeds back a second signal to the output controller, adjusts the heating power of the electric heating device, and realizes precise temperature adjustment.

[0021] When T1>T0, a third signal is fed back to the output controller, the opening degrees of the gas regulating valve and the air volume regulating valve of the natural gas combustion furnace are adjusted to be reduced, and the power of the electric heating device is adjusted.

[0022] When |T3-T0|≤a, a fourth signal is fed back to the output controller, and the system keeps the current running parameters of the natural gas combustion furnace and the electric heating device to continue running.

[0023] Further, the set range of the air supply temperature difference a is 0℃

[0024] Further, when the information processing host identifies that the temperature T5 at the flue gas discharge pipeline of the fresh air pre-heater is less than 200℃, a fifth signal is fed back to the output controller, and the opening degree of the gas regulating valve is adjusted to be increased within the range of 95% total load, so as to prevent the phenomenon of flue corrosion caused by low flue gas temperature.

[0025] Further, when the information processing host identifies that the temperature difference T4-T0 between the return air temperature T4 and T0 is greater than 100 DEG C, it is judged that a fire occurs in the furnace, and the information processing host feeds back a seventh control signal to the output controller to forcibly cut off the power supply of the gas regulating valve, the electric heating device and the pressure fan, and to open the fire-fighting spray pump in linkage to ensure the safe operation of the pre-oxidation process.

[0026] The present application has the following advantages: 1. The double heat source type reduces the operation cost of the pre-oxidation process and greatly improves the temperature control accuracy of the process; 2. The heat in the high-temperature flue gas is recovered through the fresh air preheater to improve the thermal efficiency of the system; 3. The opening of the gas regulating valve and the air volume regulating valve is intelligently adjusted by the control system to meet the demand of process load regulation; 4. The power supply is cut off and the fire-fighting spray system is opened when a fire occurs in the pre-oxidation furnace to ensure the safe operation of the entire process; and 5. The intelligent level of the pre-oxidation process is improved.

[0027] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the application.

[0028] In order to make the above objectives, features and advantages of the present application more apparent, the following preferred embodiments are specifically described with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or the prior art description. Obviously, the drawings described below are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without any creative effort.

[0030] Figure 1 is a schematic view of the preferred embodiment of the present application.

[0031] In the drawings:

[0032] 1, pre-oxidation furnace; 2, pressure fan; 3, electric heating device; 4, flue gas heat exchanger; 5, fresh air preheater; 6, natural gas combustion furnace; 7, gas regulating valve; 8, combustion air fan; 9, air volume regulating valve; 10, fire-fighting spray pump; 11, pre-oxidation furnace exhaust regulating valve. DETAILED DESCRIPTION

[0033] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0034] Embodiment 1

[0035] As shown in the figure, the double-heat-source carbon fiber pre-oxidation system of the present embodiment comprises a pre-oxidation furnace 1, a fresh air pre-heater 5, a natural gas combustion furnace 6, a flue gas heat exchanger 4, and an electric heating device 3. The natural gas combustion furnace 1 is communicated with the flue gas heat exchanger 4, for indirectly exchanging heat between the high-temperature flue gas and the mixed air of fresh air and return air in the flue gas heat exchanger 4. The pre-oxidation furnace 1, the flue gas heat exchanger 4, and the electric heating device 3 are sequentially communicated and form a heating loop. The flue gas heat exchanger 4 is adapted to provide 60%-90% of the process heat load to the pre-oxidation furnace 1. The electric heating device 3 is adapted to accurately adjust the air supply temperature of the pre-oxidation furnace 1, and supply 10%-40% of the process heat load to the pre-oxidation furnace 1. The pre-oxidation furnace 1 is adapted to deliver return air to the cold air inlet of the flue gas heat exchanger 4.

[0036] The natural gas burner 6 inlet is respectively communicated with a pipeline one and a pipeline two. The pipeline one is provided with a gas regulating valve 7. The pipeline two is provided with a combustion air fan 8. A wind volume regulating valve 9 is further arranged between the pipeline two and the combustion air fan 8. By controlling the opening degrees of the gas regulating valve 7 and the wind volume regulating valve 9 of the natural gas combustion furnace 6, the requirement of equipment load adjustment can be realized.

[0037] A pressurized air fan 2 is further arranged between the electric heating device 3 and the pre-oxidation furnace 1. The pressurized air fan 2 can pressurize and deliver the heated mixed air into the pre-oxidation furnace 1.

[0038] A fresh air pre-heater 5 is further arranged between the pre-oxidation furnace 1 and the flue gas heat exchanger 6. The high-temperature inlet of the fresh air pre-heater 5 is communicated with the flue gas outlet of the flue gas heat exchanger 4, for recovering the waste heat in the flue gas. The fresh air outlet of the fresh air pre-heater 5 is communicated with the cold air inlet of the flue gas heat exchanger 4. The fresh air inlet of the fresh air pre-heater 5 is communicated with a fresh air system. The waste gas outlet of the fresh air pre-heater 5 is communicated with the outside. The pre-oxidation furnace exhaust air duct is connected to the outside, and an exhaust air regulating valve 11 is arranged.

[0039] The pre-oxidation furnace 1 is further communicated with a fire-fighting water tank. A fire-fighting spray water pump 10 is further arranged between the pre-oxidation furnace 1 and the fire-fighting water tank.

[0040] The cold air inlet of the flue gas heat exchanger 4 is provided with a temperature sensor T1, and the outlet of the flue gas heat exchanger 4 is provided with a temperature sensor T2; the outlet of the electric heating device 3 is provided with a temperature sensor T3; the outlet of the pre-oxidation furnace 1 is provided with a temperature sensor T4; and the exhaust flue of the fresh air preheater 5 is provided with a temperature sensor T5.

[0041] Further comprising a control system, including an information processing host, which is connected with the temperature sensor T1, the temperature sensor T2, the temperature sensor T3, the temperature sensor T4, the temperature sensor T5, the gas regulating valve 7, the combustion air fan 8, the air volume regulating valve 9, the electric heating device 3, the pressurizing fan 2, the spray water pump 10, the pre-oxidation furnace exhaust regulating valve 11, etc. through a temperature acquisition module and an output controller.

[0042] A running method of a double-heat-source carbon fiber pre-oxidation system is as follows:

[0043] S1: Obtain pre-oxidation process related parameters and equipment sizes, including the pre-oxidation furnace 1 design air supply speed v, the design air supply temperature T0, the allowable air supply temperature difference a, the pre-oxidation furnace 1 air supply cross-sectional area S, the natural gas low heat value H L , the unit gas theoretical air quantity V0, the combustion excess air coefficient α, the flue gas heat exchanger 4 heat exchange efficiency η, and the pre-oxidation process fresh air quantity Q X ;

[0044] S2: Run the pre-oxidation furnace equipment line, adjust the pre-oxidation furnace exhaust regulating valve 11 so that its flow is Q X , and collect the temperature data of each temperature sensor (Ti) in real time, and calculate:

[0045] The pre-oxidation furnace air supply flow Q=v S;

[0046] The pre-oxidation process total heat load: H g =c·Q·(T0-T1);

[0047] The natural gas combustion furnace heat load: H g1 =(0.6H g ~0.9H g ) / η;

[0048] The gas flow: Q g =3600H g1 / H L ;

[0049] The combustion air flow: Q a =αV0Q g ;

[0050] The electric heating device heat load: H g2 =c·Q·(T0-T2).

[0051] The above-mentioned related parameters and formula are programmed into the information processing host of the control center, and the information processing host calculates and controls as follows:

[0052] When the temperature T1 on the air inlet pipeline of the flue gas heat exchanger 4 is less than T0, the required gas flow and combustion air flow are calculated by the program, a first signal is fed back to the output controller, and the opening degrees of the gas regulating valve 7 and the air volume regulating valve 9 of the natural gas combustion furnace 6 are controlled to make them run at the set flow Q g , Q a The information processing host calculates the heat load of the electric heating device 3, feeds back a second signal to the output controller, adjusts the heating power of the electric heating device 3, and realizes accurate temperature regulation.

[0053] When T1>T0, a third signal is fed back to the output controller, the opening degrees of the gas regulating valve 7 and the air volume regulating valve 9 of the natural gas combustion furnace 6 are adjusted to be reduced, and the power of the electric heating device 3 is adjusted.

[0054] When |T3-T0|≤a, a fourth signal is fed back to the output controller, and the system keeps the running parameters of the natural gas combustion furnace 6 and the electric heating device 3 to continue running. In this embodiment, the set range of the allowable air supply temperature difference a is 0℃<a≤2℃, and preferably 0℃<a≤1℃.

[0055] S3: When the information processing host identifies that the temperature T5 of the exhaust gas pipeline of the fresh air preheater is less than 200℃, a fifth signal is fed back to the output controller, and the opening degree of the gas regulating valve 7 is adjusted to be increased within the range of 95% total load, so as to prevent the phenomenon of flue corrosion caused by low exhaust gas temperature.

[0056] S4: When the information processing host identifies that the temperature difference T4-T0 between the return air temperature T4 and T0 is greater than 100℃, it is judged that the fire phenomenon occurs in the furnace, the information processing host feeds back a seventh control signal to the output controller, forcibly cuts off the power supply of the gas regulating valve 7, the electric heating device 3 and the pressure fan 2, and opens the fire-fighting water spray pump 10 in linkage, so as to ensure the safe operation of the pre-oxidation process.

[0057] In summary,

[0058] Each device (parts without specific structure) selected in the present application is a general standard part or a part known to those skilled in the art, and its structure and principle can be known by technical personnel through a technical manual or through a conventional experimental method. Moreover, the software programs involved in the present application are prior art, and the present application does not involve any improvement on the software programs.

[0059] In the description of the embodiments of the present application, unless specifically defined and limited otherwise, the terms "mount", "connected", "connection" should be interpreted broadly, for example, can be fixed connection, can also be detachable connection, or integrally connected; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0060] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0061] In several embodiments provided in the present application, it should be understood that the disclosed system, device and method can be implemented in other ways. The device embodiments described above are only schematic, for example, the division of the units is only a logical function division, and actual implementation can have another division manner, and for example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the coupling or direct coupling or communication connection between the units shown or discussed can be indirect coupling or communication connection through some communication interface, device or unit, which can be electrical, mechanical or other forms.

[0062] The units described as separate components can or can not be physically separated, and the components shown as units can or can not be physical units, i.e. they can be located in one place, or can be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the present embodiment.

[0063] In addition, each functional unit in each embodiment of the present application can be integrated into a processing unit, or each unit can exist physically, or two or more units can be integrated into one unit.

[0064] With the above ideal embodiments according to the present application as the inspiration, through the above description, relevant staff can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the content of the specification, and must be determined according to the scope of the claims.

Claims

1. A dual heat source carbon fiber pre-oxidation system, characterized by, It comprises: a pre-oxidation furnace, a fresh air pre-heater, a natural gas combustion furnace, a flue gas heat exchanger, and an electric heating device, the natural gas combustion furnace is communicated with the flue gas heat exchanger, and is used for conveying high-temperature flue gas into the flue gas heat exchanger to exchange heat with the mixed fresh air indirectly; the pre-oxidation furnace, the flue gas heat exchanger, and the electric heating device are sequentially communicated and form a heating loop, wherein the flue gas heat exchanger is suitable for providing 60%-90% of the process heat load for the pre-oxidation furnace; the electric heating device is suitable for accurately adjusting the air supply temperature of the pre-oxidation furnace, and supplying 10%-40% of the process heat load for the pre-oxidation furnace; the pre-oxidation furnace is suitable for conveying the return air to the cold air inlet of the flue gas heat exchanger.

2. The dual-heat-source carbon fiber pre-oxidation system according to claim 1, wherein the natural gas combustion furnace inlet is respectively communicated with pipeline one and pipeline two, wherein the pipeline one is provided with a gas regulating valve; the pipeline two is provided with a combustion air fan, and a wind volume regulating valve is further arranged between the pipeline two and the combustion air fan; a pressurized air fan is further arranged between the electric heating device and the pre-oxidation furnace.

3. The dual-heat-source carbon fiber pre-oxidation system according to claim 1, wherein a fresh air pre-heater is further arranged between the pre-oxidation furnace and the flue gas heat exchanger, the high-temperature inlet of the fresh air pre-heater is communicated with the flue gas outlet of the flue gas heat exchanger, and is used for recovering the waste heat in the flue gas; the fresh air outlet of the fresh air pre-heater is communicated with the cold air inlet of the flue gas heat exchanger; the fresh air inlet of the fresh air pre-heater is communicated with a fresh air system, and the exhaust gas outlet of the fresh air pre-heater is communicated with the outside; the pre-oxidation furnace exhaust air duct is connected to the outside, and is provided with an exhaust air regulating valve.

4. The dual-heat-source carbon fiber pre-oxidation system according to claim 1, wherein the pre-oxidation furnace is further communicated with a fire-fighting water tank, and a fire-fighting spray water pump is further arranged between the pre-oxidation furnace and the fire-fighting water tank.

5. An operation method of the pre-oxidation system according to any one of claims 1-4, wherein S1: Obtain pre-oxidation process related parameters and equipment size, including pre-oxidation furnace design air supply speed v, design air supply temperature T0, allowable air supply temperature difference a, pre-oxidation furnace air supply cross-sectional area S, natural gas low heat value H L , unit gas theoretical air quantity V0, combustion excess air coefficient a, flue gas heat exchanger heat exchange efficiency Pre-oxidation process fresh air quantity Q X ; S2: Run the pre-oxidation furnace equipment line, adjust the pre-oxidation furnace exhaust regulating valve to make its flow rate Q X , real-time acquisition of temperature data of each temperature sensor (Ti), calculation: the pre-oxidation furnace air supply flow Q=v S; Pre-oxidation process total heat duty: H g = c Q (T0-T1); Natural gas fired furnace heat load: H g1 = (0.6H g ~ 0.9H g ) / η; Gas flow rate: Q g = 3600H g1 / H L ; Combustion air flow: Q a = aV0Q g ; Electrical heating device thermal load: H g2 = c Q (T0-T2).

6. The operation method according to claim 5, wherein a temperature sensor T1 is arranged at the cold air inlet of the flue gas heat exchanger, a temperature sensor T2 is arranged at the outlet of the flue gas heat exchanger, a temperature sensor T3 is arranged at the outlet of the electric heating device, a temperature sensor T4 is arranged at the outlet of the pre-oxidation furnace, and a temperature sensor T5 is arranged at the flue gas pipeline of the fresh air pre-heater; T1, T2, T3, T4, and T5 are continuously and real-timely measured and collected.

7. The operation method according to claim 6, wherein the above-mentioned related parameters and formulas are programmed into the information processing host of the control center, and the information processing host is used for self-computing and sequentially performing the following controls: When the temperature T1 on the air inlet pipeline of the flue gas heat exchanger is less than T0, the required gas flow and combustion air flow are calculated by the program, a first signal is fed back to the output controller, and the opening of the gas regulating valve and the air volume regulating valve of the natural gas combustion furnace is controlled to make them run at the set flow Q g , Q a The information processing host calculates the thermal load of the electric heating device, feeds back a second signal to the output controller, adjusts the heating power of the electric heating device, and realizes accurate temperature regulation. when T1>T0, a third signal is fed back to the output controller, the opening degrees of the gas regulating valve and the wind volume regulating valve of the natural gas combustion furnace are adjusted to be reduced, and the power of the electric heating device is adjusted; when |T3-T0|≤a, a fourth signal is fed back to the output controller, and the system keeps the operation parameters of the natural gas combustion furnace and the electric heating device to continue running.

8. The method of operating of claim 7, wherein, The setting range of the air supply temperature difference a is 0℃≤a≤2℃.

9. The method of operating of claim 8, wherein, When the information processing host recognizes that the temperature T5 at the exhaust flue of the fresh air preheater is less than 200℃, the fifth signal is fed back to the output controller, and the opening of the gas regulating valve is adjusted to increase within the range of 95% total load, so as to prevent the exhaust flue temperature from being too low and the flue corrosion from occurring.

10. The method of operating of claim 9, wherein, When the information processing host recognizes that the temperature difference T4-T0 between the return air temperature T4 and the temperature T0 is greater than 100℃, it is judged that a fire occurs in the furnace, the information processing host feeds back the seventh control signal to the output controller, forcibly cuts off the power supply of the gas regulating valve, the electric heating device and the pressure fan, and opens the fire-fighting water spray pump in linkage, so as to ensure the safe operation of the pre-oxidation process.

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