Auxiliary cooling method for secondary flue gas of converter

Abstract

The invention provides an auxiliary cooling method for secondary flue gas of a converter, and belongs to the field of secondary dust removal of converter steelmaking. The method comprises the following steps: arranging a temperature sensor at a converter flue gas outlet to measure the temperature of the flue gas discharged by the converter; a plurality of spray guns for cooling are arranged in smoke boxes on the two sides of the converter and in a secondary pipeline for connecting the converter with a secondary dust remover; an air mixing valve is arranged on the secondary pipeline; each spray gun is provided with an electric valve for controlling start and stop; starting and stopping of the spray guns and the air mixing valves in the pipeline are regulated and controlled according to the temperature measured by the temperature sensor, and self-adaptive cooling is conducted on smoke in the pipeline. The device is simple in structure; the installation is easy; the plant does not need to be transformed; the problems that a secondary flue gas pipeline cannot be prolonged due to the fact that an old steel workshop is difficult to transform, a dust collector bag is burnt, and the production process is forced to stop are solved simply and effectively.

Description

Technical Field

[0001] The invention relates to the technical field of secondary dust removal in converter steelmaking, and in particular to a converter secondary flue gas auxiliary cooling method. Background Art

[0002] During the production process, the converter secondary dust removal equipment is an environmental protection measure taken to make up for the lack of primary dust removal. It mainly collects the flue gas emitted during iron addition, scrap steel addition and steel tapping operations. Under normal working conditions, the dust collector inlet temperature must be lower than 120℃ to avoid high-temperature flue gas burning the bags and causing production stoppage accidents.

[0003] According to the relevant requirements of ultra-low emission control in the steel industry, in the converter process, the operating parameters of the secondary dust removal equipment must be monitored on the same screen as the parameters of the converter smelting equipment, and the data must be saved for more than one year. In addition, the online monitoring data of the secondary dust removal is uploaded to the provincial environmental protection website for real-time monitoring. Therefore, it is very important to ensure the normal operation of the secondary dust removal equipment.

[0004] However, there are uncertainties in the actual smelting process. If too much powder is added to the steelmaking raw materials, a large area of ​​flame spraying may occur at the furnace mouth during the iron addition process, causing the smoke box inlet temperature to be too high, and even sparks to be directly sucked into the dust removal pipe; in the converter smelting process, the scrap steel added to the furnace cannot be 100% qualified. In special cases, large-scale slag spraying may occur in the converter. The flame and flue gas are mixed to form high-temperature flue gas. The temperature of the smoke box in front of the furnace can reach 600-800℃. At this time, once the high-temperature flue gas reaches the dust collector through the pipeline, a large area of ​​bag burnout will occur. This causes the converter to stop production. (In the steel industry, due to the limitations of bag cost and filter material, dust removal bags with a temperature resistance of 120-180℃ are generally used). Once this fault occurs, the functional accuracy of the secondary dust removal equipment will be reduced, the emission will not meet the standard, and the converter process will be shut down for a long time.

[0005] The existing solution is to have a certain distance between the secondary dust removal equipment and the converter body when planning the general plan, so that after the secondary high-temperature flue gas is sucked into the smoke hood, there is a natural cooling process through the dust removal pipeline. However, except for the reasonable layout of newly built and relocated steel enterprises in other places, most steel enterprises did not consider the problem of cooling the secondary dust removal flue gas when they were built. The reconstruction of the dust collector is limited by the site, and the distance between the secondary dust collector and the converter cannot reach an effective cooling distance. In the field of smelting, water can be used to cool the flue gas, such as patent CN100357458C "A method for cooling and dust removal of converter flue gas". However, its cooling method is to involve liquefied water in the flue gas circulation. Although this method can achieve a cooling effect, it will produce sewage during the cooling process. The sewage formed needs to be further treated, and a sewage treatment system is added. The sewage must be recycled and purified to meet the emission standards. The process is cumbersome, and liquid water is easy to freeze at low temperatures, which is not suitable for the low temperature weather that occurs in the north in winter.

[0006] Therefore, a method is needed to cool the converter secondary flue gas in a clean and environmentally friendly manner without rebuilding the factory building. Summary of the invention

[0007] Aiming at the industry problem that the temperature of the secondary flue gas of the converter is too high due to various reasons, a large number of bag burns, resulting in production suspension accidents and the inability to effectively control the problem, the present invention provides a method for auxiliary cooling of the secondary flue gas of the converter, which cools the secondary flue gas of the converter and ensures the normal operation of the secondary dust removal equipment.

[0008] To this end, the present invention provides the following technical solutions:

[0009] A secondary flue gas auxiliary cooling method for a converter, wherein a set of temperature sensors are respectively installed on the flue gas pipes inside the smoke boxes on both sides of the converter; a set of spray guns are respectively arranged behind the temperature sensors on the flue gas pipes inside the smoke boxes on both sides along the flue gas flow direction; a set of temperature sensors are installed on the straight pipe section of the secondary pipe, and a plurality of spray guns are arranged at intervals on the secondary pipe along the flue gas flow direction; the spray guns are inserted into the pipe from obliquely above, and the nozzle direction is installed along the flue gas flow direction; each spray gun is equipped with an electric valve for controlling the start and stop; the distance between the temperature sensor and the spray gun, as well as the distance between each spray gun are set according to the flue gas flow rate, the pipe length, and the action time of the electric valve, and an air mixing valve is arranged on the secondary pipe; the method comprises:

[0010] The multiple temperature sensors arranged at the converter flue gas outlet are used to measure the temperature of the converter flue gas in real time;

[0011] According to the temperature measured by the temperature sensor, the electric valve is used to control the linkage start and stop of each spray gun and the air mixing valve in the pipeline, and the flue gas temperature is always greater than 110°C when water mist is used for cooling; the spray gun is a dual-medium mixed spray gun, and its media include: water and compressed air; the nozzle at the front end of the spray gun, the sprayed water mist particles will instantly vaporize under the high-temperature flue gas and turn into water vapor, the water vapor with molecular structure can pass through the dust removal bag, and be directly discharged with the filtered flue gas, without forming sewage, and no mud will be formed to adhere to the surface of the bag.

[0012] Furthermore, the diameter of the water mist particles is within 121 μm.

[0013] Furthermore, the spray gun and the medium pipeline are connected by a metal hose.

[0014] Furthermore, there are 6 sets of dual-media spray guns, 2 sets are arranged inside the smoke boxes on both sides of the converter; and 4 sets are arranged in the straight pipe part of the secondary pipeline.

[0015] Furthermore, the start and stop of each spray gun and air mixing valve in the pipeline is controlled according to the temperature measured by the temperature sensor, including:

[0016] The opening of the air mixing valve and the spray gun is regulated according to the temperature detected by the temperature sensors inside the smoke boxes on both sides of the converter;

[0017] During the cooling process, the air mixing valve and the opened spray gun are regulated to be closed according to the temperature detected by the temperature sensor on the middle section of the secondary pipeline.

[0018] Furthermore, the opening of the air mixing valve and the spray gun is regulated according to the temperature detected by the temperature sensors inside the smoke boxes on both sides of the converter.

[0019] include:

[0020] When the temperature detected by the internal temperature sensors of the smoke boxes on both sides of the converter is between 150 and 250°C, the air mixing valve is opened to reduce the smoke temperature, and the dust collector inlet temperature is lower than 120°C;

[0021] When the temperature detected by the temperature sensors inside the smoke boxes on both sides of the converter is between 250-350°C, the air mixing valve is opened, and at the same time, a spray gun near the dust collector inlet is opened to cool down;

[0022] When the temperature detected by the temperature sensors inside the smoke boxes on both sides of the converter is between 350-450°C, the air mixing valve is opened and the two spray guns near the dust collector inlet are opened to cool down the temperature;

[0023] When the temperature detected by the temperature sensors inside the smoke boxes on both sides of the converter is 450-500°C, the air mixing valve is opened and the four spray guns in the secondary pipe are opened to cool down;

[0024] When the temperature detected by the temperature sensors inside the smoke boxes on both sides of the converter is greater than 500° C., the air mixing valve is opened and all 6 spray guns are opened at the same time to cool down.

[0025] Furthermore, during the cooling process, the closing of the air mixing valve and the spray gun is regulated according to the temperature sensor on the straight pipe in the middle section of the secondary pipe, including:

[0026] When the temperature detected by the temperature sensor on the middle section of the secondary pipeline drops to 250-350°C, the three spray guns in the secondary pipeline are closed;

[0027] When the temperature detected by the temperature sensor on the middle section of the secondary pipeline drops to 170-250°C, the four spray guns in the secondary pipeline are closed;

[0028] When the temperature detected by the temperature sensor on the middle section of the secondary pipeline drops to 110-170°C, all spray guns in the secondary pipeline are closed;

[0029] When the temperature detected by the temperature sensor on the middle section of the straight pipe of the secondary pipe is less than or equal to 110° C., all spray guns and air mixing valves in the secondary pipe are closed.

[0030] Advantages and positive effects of the present invention:

[0031] The present invention realizes the goal of autonomously detecting high-temperature flue gas and intercepting and cooling the flue gas in echelon groups through the interlocking control of the temperature sensor and the quick-opening valve of the spray gun. The medium of the spray gun of the present invention is water and compressed air, which is not only easy to obtain; the medium pipeline requirements are low; and it is safe. Moreover, the heat of the flue gas is taken away by water vapor, which meets the requirements of environmental protection and cooling, and can control the temperature of the secondary flue gas below 120°C; it is far lower than the ignition point of the dust bag, and effectively prevents the dust collector bag from being burned due to the high temperature of the flue gas; the water mist particle size of the spray gun of the present invention is less than 121μm, and after gasification, it is 0.0004μm, which can pass through the dust bag (gap 4μm), and will not form mud attached to the surface of the bag, and after cooling, the water vapor is discharged together with the filtered flue gas, and no waste that needs to be treated is generated; it meets the requirements of cooling, not affecting the dust removal effect of the flue gas, and being clean and environmentally friendly; thereby reducing the economic losses caused by production shutdowns due to the failure of the dust collector to work normally, and responding to the national call for environmental protection. The device of the present invention only needs a spray gun and a temperature sensor, with less additional equipment, low cost, and low installation difficulty; and no reconstruction of the factory building is required; the spray gun of the present invention is inserted into the pipeline from the upper side, which is convenient for removing water in the medium pipeline when the production is stopped in winter to prevent ice from forming in winter and damage to the equipment; the nozzle of the spray gun is installed in the direction of the flue gas flow, which can prevent particulate matter in the flue gas from entering the spray gun and causing blockage. The present invention enables the secondary dust removal process of the old steel smelting plant that cannot be rebuilt to run smoothly. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0033] Figure 1 The schematic diagram of a converter secondary flue gas assisted cooling method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0035] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0036] According to the guidance proposed in Section 6.4.6 of the General Technical Specifications for Bag Dust Removal Engineering HJ2020-2012, "When the flue gas temperature in the pipeline is greater than 350°C, the flue gas should be cooled." Taking into account the cost and the occurrence rate of secondary flue gas above 350°C, the most effective cooling medium, water, is selected in the present invention for cooling the secondary flue gas.

[0037] It is generally believed that spraying water in the secondary flue gas pipe of the converter will cause particles to combine with water droplets, and the combination will be deposited in the pipe, and even the dust and water will mix into "mud" and adhere to the bag surface, causing the bag to be blocked and unable to be used effectively. According to data query, water will vaporize above 100°C and turn into water vapor. The essence of water vapor is composed of countless water molecules. The diameter of water molecules is 0.0004μm. The filtration accuracy of common dust bag filter materials in the steel industry is about 5μm. In theory, when water is sprayed in a closed flue gas pipe above 350°C, the heated water medium will vaporize into water vapor in a short time and turn into a small molecule form. It will not stay in the pipe, let alone adhere to the surface of the dust bag. The above principle analysis shows that when the secondary flue gas temperature reaches a certain limit, spraying water in the secondary pipe to cool it down as an auxiliary means of the air mixing valve is feasible in principle.

[0038] The inventive concept of the present invention is: by spraying water mist into the secondary flue gas duct, the high temperature of the secondary flue gas causes the water mist to instantly turn into water vapor and evaporate, taking away part of the heat, and assisting the air mixing valve to cool the secondary flue gas; through the linkage control of multiple sets of temperature sensors, the flue gas temperature is maintained within an appropriate range.

[0039] For ease of understanding, first explain the relevant equipment:

[0040] In order to achieve auxiliary cooling of the secondary flue gas of the converter, the present invention is equipped with 3 sets of temperature sensors, 6 sets of dual-media spray guns, 6 electric valves and other parts. Specifically, T101, T102, and T103 are three temperature sensors, 2 sets (T101, T102) are arranged inside the smoke boxes on both sides of the converter, and 1 set (T103) is arranged on the straight pipe in the middle section of the secondary pipeline, about 100 meters away from the converter. V-ZLP1, V-ZLP2, V-ZLP3, V-ZLP4, V-ZLP5, and V-ZLP6 are six sets of dual-media spray guns, which are made of stainless steel, and the internal media are water and compressed air. The water supply pressure of a single pipe is 0.3-0.4Mpa, and the flow rate is 3-5m 3 / h. The pressure of low-pressure compressed air is 0.6Mpa, and the flow rate of a single spray gun is 4500Nm3 / h. The nozzle at the front end of the spray gun has a spray particle size of D90<121μm. Two sets of spray guns are arranged inside the smoke boxes on both sides of the converter, and the remaining four sets are arranged in batches at a distance of about 30 meters in the straight section of the secondary pipeline, taking into account that the filtration wind speed of the straight pipe section of the dust collector is higher than that of the vertical section. In this embodiment, the distance between the converter body and the entrance of the secondary dust collector is about 150 meters. During the production process, the high-temperature flue gas is pulled by the suction force of the fan and moves forward at a flow rate of 18 meters per second. Before the high-temperature flue gas reaches the entrance of the dust collector, the flue gas temperature is reduced to below the safe value. The dual-media spray gun is arranged in sections, and the step-by-step start-up method is linked to the temperature sensor. In the event of a high-temperature flue gas failure, the spray cooling is started first with the spray gun V-ZLP6 at the end of the pipeline to avoid the situation where the high-temperature flue gas has passed through other spray guns and cannot be effectively cooled. If the flue gas temperature exceeds a certain range, the spray gun is started from the back to the front to overcome the contradictory relationship between the flue gas flow rate and temperature reduction.

[0041] like Figure 1 As shown, the embodiment of the present invention provides a converter secondary flue gas auxiliary cooling method. During the production process, when T101 and T102 detect that the secondary flue gas temperature is higher than 120°C, the following specific steps are performed:

[0042] S1. When the detection temperature of T101 and T102 is between 150-250℃, open the air mixing valve to reduce the flue gas temperature and the dust collector inlet temperature is lower than 120℃;

[0043] S2. When the detection temperature of T101 and T102 is between 250-350℃, open the air mixing valve and V-ZLP6 spray gun to cool down;

[0044] S3. When the detection temperature of T101 and T102 is between 350-450℃, open the air mixing valve and open the V-ZLP6 and V-ZLP5 spray guns to cool down;

[0045] S4, when the detection temperature of T101 and T102 is between 450-500℃, open the air mixing valve and open the spray guns of V-ZLP3, V-ZLP4, V-ZLP5 and V-ZLP6 to cool down;

[0046] S5. When the detection temperature of T101 and T102 is above 500℃, open the air mixing valve and all V-ZLP1, V-ZLP2, V-ZLP3, V-ZLP4, V-ZLP5 and V-ZLP6 spray guns to cool down.

[0047] During the cooling process, in order to prevent the flue gas temperature from being too low, causing the particles to combine with water droplets, the combination to settle in the pipe, or even the dust and water to mix into "mud" and adhere to the bag surface, causing the bag to be blocked and unable to be used effectively. The specific steps for controlling the spray gun and closing the air mixing valve through the temperature measured by T103 are as follows:

[0048] S1. When the T103 detection temperature is between 250-350℃, turn off the V-ZLP5, V-ZLP4 and V-ZLP3 spray guns;

[0049] S2. When T103 detects a temperature of 170-250°C, close the V-ZLP3, V-ZLP4, V-ZLP5, and V-ZLP6 spray guns;

[0050] S3. When T103 detects a temperature of 110-170°C, close all V-ZLP1, V-ZLP2, V-ZLP3, V-ZLP4, V-ZLP5, and V-ZLP6 spray guns;

[0051] S4. When T103 detects temperature ≤110℃, close all V-ZLP1, V-ZLP2, V-ZLP3, V-ZLP4, V-ZLP5, V-ZLP6 spray guns and air mixing valves.

[0052] For ease of understanding, a converter secondary flue gas auxiliary cooling method in the above embodiment is described below with an application example.

[0053] The secondary dust removal monitoring system of the D furnace fan in the steelmaking plant gave an alarm, and the computer records showed that the temperature of the smoke boxes on both sides of the converter was as high as 583.6℃ at the T101 measuring point and 643.4℃ at the T102 measuring point.

[0054] The PLC control system starts the auxiliary cooling system according to the program settings; while opening the air mixing valve, all V-ZLP1, V-ZLP2, V-ZLP3, V-ZLP4, V-ZLP5, and V-ZLP6 spray guns are opened for cooling; during the cooling process, when the temperature measured by T103 is lower than 350°C, the spray guns V-ZLP4, V-ZLP5, and V-ZLP6 are closed; when the temperature measured by T103 is lower than 250°C, the spray gun V-ZLP3 is also closed; when the temperature measured by T103 is lower than 170°C, all spray guns are closed; when the temperature measured by T103 is lower than 110°C, the air mixing valve is also closed. At this time, the dust collector inlet temperature is only 52°C. After cooling using the method of the present invention, none of the dust collector bags were burned, successfully avoiding an equipment shutdown accident.

[0055] The secondary dust removal monitoring system of the C furnace of the steelmaking plant gave an alarm, and the computer records showed that the temperature of the smoke boxes on both sides of the converter was as high as 414°C at the T101 measuring point and 365.5°C at the T102 measuring point.

[0056] The PLC control system started the auxiliary cooling system according to the program settings. The computer records showed that the dust collector inlet temperature was only 62°C at this time. None of the dust collector bags were burned, successfully avoiding a production equipment shutdown accident.

[0057] The flue gas temperature exceeded 350℃ twice in a short period of time, which verified that this system is indeed effective. According to previous experience, when the flue gas temperature is higher than 350℃-500℃, most of the dust bags of the dust collector body are likely to burn through. According to the 4080 bags for secondary dust removal in the fourth branch, each bag costs 180 yuan. The two failures directly reduced the failure losses by more than 1.5 million yuan. The accident stopped production and replaced 4080 bags, which is expected to take more than 24 hours. Reducing the accident time created economic benefits of more than 2 million. The industry problem of the converter secondary flue gas temperature exceeding 350℃ was successfully solved; the flue gas cooling requirements mentioned in the national "General Technical Specifications for Bag Dust Removal Projects" were successfully achieved; at this stage, this system is the "only" successful example of the converter secondary flue gas temperature being too high.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A converter secondary flue gas assisted cooling method, characterized in that: A set of temperature sensors are installed on the flue gas ducts inside the smoke boxes on both sides of the converter; a set of spray guns are respectively arranged behind the temperature sensors on the flue gas ducts inside the smoke boxes on both sides along the direction of flue gas flow; a set of temperature sensors are installed on the straight pipe section of the secondary pipe, and several sets of spray guns are arranged at intervals on the secondary pipe along the direction of flue gas flow; the spray guns are inserted into the pipe from obliquely above, and the nozzle direction is installed along the direction of flue gas flow; each spray gun is equipped with an electric valve for controlling the start and stop; the distance between the temperature sensor and the spray gun, as well as the distance between each spray gun are set according to the flue gas flow rate, the pipe length, and the action time of the electric valve, and a mixing valve is arranged on the secondary pipe; including: The multiple temperature sensors arranged at the converter flue gas outlet are used to measure the temperature of the converter flue gas in real time; According to the temperature measured by the temperature sensor, the electric valve is used to control the linkage start and stop of each spray gun and the air mixing valve in the pipeline, and the flue gas temperature is always greater than 110°C when water mist is used for cooling; the spray gun is a dual-medium mixed spray gun, and its media include: water and compressed air; the nozzle at the front end of the spray gun, the sprayed water mist particles will instantly vaporize under the high-temperature flue gas and turn into water vapor, the water vapor with molecular structure can pass through the dust removal bag, and be directly discharged with the filtered flue gas, without forming sewage, and no mud will be formed to adhere to the surface of the bag.

2. A converter secondary flue gas assisted cooling method according to claim 1, characterized in that: The diameter of the water mist particles is within 121 μm.

3. The converter secondary flue gas assisted cooling method according to claim 1, characterized in that: The spray gun and the medium pipeline are connected by a metal hose.

4. A converter secondary flue gas assisted cooling method according to any one of claims 1 to 3, characterized in that: There are 6 sets of dual-media spray guns in total, 2 sets are arranged inside the smoke boxes on both sides of the converter; and 4 sets are arranged in the straight pipe part of the secondary pipeline.

5. A converter secondary flue gas assisted cooling method according to claim 4, characterized in that: The method of controlling the start and stop of each spray gun and air mixing valve in the pipeline according to the temperature measured by the temperature sensor includes: The opening of the air mixing valve and the spray gun is regulated according to the temperature detected by the temperature sensors inside the smoke boxes on both sides of the converter; During the cooling process, the air mixing valve and the opened spray gun are regulated to be closed according to the temperature detected by the temperature sensor on the middle section of the secondary pipeline.

6. A converter secondary flue gas assisted cooling method according to claim 5, characterized in that: The opening of the air mixing valve and the spray gun is regulated according to the temperature detected by the temperature sensors inside the smoke boxes on both sides of the converter, including: When the temperature detected by the internal temperature sensors of the smoke boxes on both sides of the converter is between 150 and 250°C, the air mixing valve is opened to reduce the smoke temperature, and the dust collector inlet temperature is lower than 120°C; When the temperature detected by the temperature sensors inside the smoke boxes on both sides of the converter is between 250-350°C, the air mixing valve is opened, and at the same time, a spray gun near the dust collector inlet is opened to cool down; When the temperature detected by the temperature sensors inside the smoke boxes on both sides of the converter is between 350-450°C, the air mixing valve is opened and the two spray guns near the dust collector inlet are opened to cool down the temperature; When the temperature detected by the temperature sensors inside the smoke boxes on both sides of the converter is 450-500°C, the air mixing valve is opened and the four spray guns in the secondary pipe are opened to cool down; When the temperature detected by the temperature sensors inside the smoke boxes on both sides of the converter is greater than 500° C., the air mixing valve is opened and all 6 spray guns are opened at the same time to cool down.

7. A converter secondary flue gas assisted cooling method according to claim 6, characterized in that: During the cooling process, the air mixing valve and the spray gun are closed according to the temperature sensor on the middle straight pipe of the secondary pipe, including: When the temperature detected by the temperature sensor on the middle section of the secondary pipeline drops to 250-350°C, the three spray guns in the secondary pipeline are closed; When the temperature detected by the temperature sensor on the middle section of the secondary pipeline drops to 170-250°C, the four spray guns in the secondary pipeline are closed; When the temperature detected by the temperature sensor on the middle section of the secondary pipeline drops to 110-170°C, all spray guns in the secondary pipeline are closed; When the temperature detected by the temperature sensor on the middle section of the straight pipe of the secondary pipe is less than or equal to 110° C., all spray guns and air mixing valves in the secondary pipe are closed.

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