Cooling method for a horizontal annealing furnace

Abstract

The application discloses a cooling method of a horizontal annealing furnace, which comprises the following steps: when the temperature is higher than a preset temperature, keeping the pressure in the horizontal annealing furnace higher than the external pressure, only opening the end air inlet of the horizontal annealing furnace, and only sucking air at the front end air outlet of the horizontal annealing furnace to form a single gas flow from the end to the front end of the horizontal annealing furnace to realize push-pull cooling; when the temperature is lower than the preset temperature, opening the furnace doors one by one from the end to the front end of the horizontal annealing furnace to make the gas in the hearth of the horizontal annealing furnace flow smoothly from the end to the front end of the horizontal annealing furnace. The cooling method of the horizontal annealing furnace can shorten the cooling time, thereby shortening the shutdown time, improving the production capacity, reducing the energy consumption and the cost of equipment maintenance.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical equipment technology, and in particular relates to a cooling method for a horizontal annealing furnace. Background Technology

[0002] Hot-dip galvanizing (aluminum) is an effective method of metal corrosion protection. Hot-dip galvanized (aluminum) steel strip refers to steel strip that is immersed in preheated molten zinc (aluminum) to form a uniform and dense zinc (aluminum) layer on its surface. Before being immersed in the zinc (aluminum) pot, the steel strip needs to be annealed to ensure the quality of the subsequent coating.

[0003] In traditional hot-dip galvanizing (aluminum) processes, various annealing processes exist. Among them, the modified Sendzimir process is currently the mainstream annealing process. It involves heating the strip steel to 680°C to 750°C in a controlled atmosphere oxidation-free furnace, followed by a longer radiant tube heating furnace and a radiant tube soaking furnace. After soaking, the strip steel enters a cooling section, achieving the goals of evaporating rolling emulsion in the oxidation-free furnace, shortening the furnace length, and saving costs. The modified Sendzimir process flow is as follows: the strip steel is heated to 680°C to 750°C in a controlled atmosphere oxidation-free furnace, then further heated to 690°C to 880°C in a radiant tube heating furnace. After soaking in the radiant tube soaking furnace, the strip steel enters a cooling section and is rapidly cooled to 460°C to 480°C. The traditional modified Sendzimir horizontal annealing furnace consists of a preheating section (PH), a non-oxidizing heating section (NOF), a radiant tube heating section (RTF), a radiant tube soaking section (SF), a rapid cooling section (RJC), a low-temperature holding section (EQ), and a thermal expansion chamber (ES).

[0004] During production, the furnace temperature of the annealing furnace is usually as high as 680℃ to 1230℃. When the annealing furnace needs to be inspected or maintained, it must be cooled before maintenance can be carried out to ensure the safety of equipment and personnel. At present, the cooling method of the annealing furnace is mainly to open all furnace doors and rely on natural heat dissipation, combined with the exhaust fan of the NOF section to assist in suction heat dissipation. However, this method has the following problems: First, the airflow is turbulent and the cooling efficiency is low: the simultaneous intake of air through multiple furnace doors causes the airflow in the furnace to have no fixed direction, forming local vortices, which hinders the discharge of hot air and makes it impossible to form a through flow in the narrow furnace. The cooling time is more than 32 hours, which seriously affects the efficiency of maintenance and the production capacity of the unit. Second, the energy consumption is seriously wasted: the fan runs at full load during the cooling process, resulting in excessive power consumption. Third, the risk of equipment damage is high: the temperature drop in the furnace is uneven, and the local temperature difference is too large, which can easily generate thermal stress, leading to accelerated aging of the furnace lining, shortening the life of the radiant tube, increasing the equipment operation and maintenance costs and downtime risk. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a cooling method for a horizontal annealing furnace, which can shorten cooling time, thereby reducing downtime, increasing production capacity, reducing energy consumption, and lowering equipment maintenance costs.

[0006] The present invention provides a cooling method for a horizontal annealing furnace, comprising:

[0007] When the temperature is higher than the preset temperature, the pressure inside the furnace is kept greater than the external pressure. Only the end air inlet of the horizontal annealing furnace is opened, and only the exhaust port at the front end of the horizontal annealing furnace is drawn in, forming a single flow of gas from the end to the front end of the horizontal annealing furnace to achieve push-pull cooling.

[0008] When the temperature reaches below the preset temperature, the furnace doors are opened one by one from the end to the front of the horizontal annealing furnace, so that the gas in the furnace chamber flows smoothly from the end to the front of the horizontal annealing furnace.

[0009] Preferably, in the cooling method of the horizontal annealing furnace described above, the preset temperature is 400°C to 450°C.

[0010] Preferably, in the cooling method of the above-mentioned horizontal annealing furnace, maintaining the pressure inside the furnace higher than the external pressure when the temperature is above the preset level further includes:

[0011] Close the inlet gate, emergency nitrogen inlet valve, and No. 2 mixing station inlet valve.

[0012] Preferably, in the cooling method of the horizontal annealing furnace described above, opening only the end air inlet of the horizontal annealing furnace includes:

[0013] Only open the valve at the mixed gas inlet of the ES hot tension chamber of the horizontal annealing furnace.

[0014] Preferably, in the cooling method for the horizontal annealing furnace described above, opening only the end air inlet of the horizontal annealing furnace further includes:

[0015] Nitrogen gas is introduced into the furnace of the horizontal annealing furnace through the mixed gas inlet of the ES hot tension chamber to maintain the pressure in the furnace at 30 Pa to 50 Pa.

[0016] Preferably, in the cooling method of the above-mentioned horizontal annealing furnace, when the temperature is higher than the preset temperature, the method further includes:

[0017] The fan in the RJC rapid cooling section is started to blow nitrogen into the furnace, where it exchanges heat with the hot gas inside the furnace.

[0018] Preferably, in the cooling method of the above-mentioned horizontal annealing furnace, when the temperature is below the preset temperature, the method further includes:

[0019] Close the valve at the mixed gas inlet of the ES hot expansion chamber and the fan of the RJC rapid cooling section, open the furnace door of the ES hot expansion chamber, and start the exhaust fan at the front end of the horizontal annealing furnace at high power to maintain the pressure in the furnace chamber within the range of -250Pa to -350Pa, thereby creating negative pressure cooling in the furnace chamber and drawing fresh air from outside the furnace into the furnace chamber.

[0020] Preferably, in the cooling method of the above-mentioned horizontal annealing furnace, opening the furnace doors one by one from the end to the front of the horizontal annealing furnace includes:

[0021] According to the furnace temperature, open the furnace doors of the ES hot expansion chamber, EQ soaking section, RJC rapid cooling section, SF supplementary heating section, RTF radiant tube heating section, NOF open flame heating section and PH preheating section one by one.

[0022] Preferably, in the cooling method of the above-mentioned horizontal annealing furnace, when the temperature of the preset area is lower than 60°C, the furnace door of the adjacent section of the preset area is opened.

[0023] Preferably, in the cooling method of the above-mentioned horizontal annealing furnace, the horizontal annealing furnace is a modified Sendzimir process horizontal annealing furnace.

[0024] As described above, the cooling method for the horizontal annealing furnace provided by this invention, by maintaining the furnace pressure higher than the external pressure when the temperature is above a preset level, prevents outside air from entering and causing oxidation of the strip at high temperatures. It only opens the end air inlet of the horizontal annealing furnace and only draws air from the front exhaust outlet, forming a single gas flow from the end to the front of the furnace to achieve push-pull cooling. Therefore, it achieves directional gas flow, quickly removing heat from the furnace and eliminating the turbulent airflow seen in existing technologies. Furthermore, when the temperature drops below the preset level, the reducing gas in the furnace is inertized. Once the gas is diluted to below a safe level and the strip surface is no longer in a highly reactive state, outside air can be used as the cooling gas. The furnace doors are then opened sequentially from the end to the front of the horizontal annealing furnace, allowing the gas inside the furnace to flow smoothly from the end to the front. The exhaust fan at the furnace inlet draws outside air into the furnace and discharges it through the exhaust fan. Because the pressure inside the furnace is lower than outside, it is a negative pressure ventilation state, allowing outside air to enter the furnace through the opened doors. This method shortens cooling time, reduces downtime, increases production capacity, reduces energy consumption, and lowers equipment maintenance costs. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0026] Figure 1 A schematic diagram illustrating an embodiment of a cooling method for a horizontal annealing furnace provided by the present invention;

[0027] Figure 2 This is a schematic diagram of a horizontal annealing furnace. Detailed Implementation

[0028] The core of this invention is to provide a cooling method for a horizontal annealing furnace, which can shorten the cooling time, thereby shorten downtime, increase production capacity, reduce energy consumption, and reduce equipment maintenance costs.

[0029] The technical solutions of the embodiments of the present invention 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.

[0030] An example of an implementation of the cooling method for a horizontal annealing furnace provided by the present invention. Figure 1 As shown, Figure 1 This is a schematic diagram of an embodiment of a cooling method for a horizontal annealing furnace provided by the present invention. The method may include the following steps:

[0031] S1: When the temperature is higher than the preset temperature, the pressure inside the furnace is kept greater than the external pressure. Only the end air inlet of the horizontal annealing furnace is opened, and only the exhaust port at the front end of the horizontal annealing furnace is drawn in, forming a single flow of gas from the end to the front end of the horizontal annealing furnace to achieve push-pull cooling.

[0032] It should be noted that the preset temperature can be between 400℃ and 450℃, which can be selected according to actual needs. When 400℃ is selected, step S1 is used when the temperature is above 400℃, because the furnace atmosphere is reducing, and the strip steel inside is easily oxidized. If air enters, it will destroy the annealing effect, and the mixture of oxygen and reducing gas (hydrogen) in the furnace may form an explosive mixture. Therefore, it is necessary to maintain positive pressure in the furnace to reduce this explosion risk and ensure safety. When cooled to below 400℃, the reducing gas in the furnace has been diluted to a safe level (usually below 0.5%) by inert gas, and the surface of the strip steel in the furnace is no longer in a highly active state. The strip steel in the furnace will no longer be oxidized, and step S2 is then used, using air from outside the furnace as the cooling gas. Under the premise of ensuring safety and product quality, the consumption of inert gas can be saved, thus achieving both oxidation prevention and cooling effect. This approach combines the advantages of both efficiency and performance, ensuring a uniform temperature drop within the furnace, reducing equipment damage and aging risks, saving on equipment maintenance costs, and decreasing the operating power of the NOF and RJC fans, thereby reducing energy consumption. In this step, the furnace throat gate is opened first, and the inlet gate is closed. A directional air intake method is used here to ensure that the cooling gas flows smoothly from back to front within the furnace, forming a through flow inside the furnace to achieve through cooling, accelerating gas flow, and driving hot gas to be quickly discharged. This is different from the existing technology where multiple air intakes are used, which causes airflow turbulence and obstructs the discharge of hot gas, affecting cooling efficiency. Moreover, this step is a positive pressure cooling method, using the end air intake as the only air intake, and closing the inlet gate, emergency nitrogen intake valve, and No. 2 mixing station intake valve to ensure that the cooling gas in the furnace has a single flow direction from back to front. It should also be noted that, in one example, opening only the end inlet of the horizontal annealing furnace may include: opening only the valve of the mixed gas inlet of the ES hot tension chamber of the horizontal annealing furnace.

[0033] S2: When the temperature is below the preset temperature, open the furnace doors one by one from the end to the front of the horizontal annealing furnace so that the gas in the furnace chamber flows smoothly from the end to the front of the horizontal annealing furnace.

[0034] It should be noted that this step involves increasing the power of the front exhaust to expel gas with greater force, creating a negative pressure environment inside the furnace. Since the temperature is relatively low at this point, there is no oxidation problem. Therefore, this negative pressure cooling method can be used to fully introduce outside air for cooling, avoiding the use of expensive inert gases. As cooling progresses, the temperature from the end to the front gradually decreases to the target temperature. Therefore, the furnace door can be opened gradually from back to front. This ensures that the gas inside the furnace flows smoothly from back to front. This directional air intake ensures that the airflow direction does not deviate from the back to front, solving the problem of airflow turbulence and slow hot gas flow caused by narrow furnace throats affecting gas flow velocity in traditional cooling methods.

[0035] It can be seen that by adopting the above method, through "air intake in the hot tension chamber + differential pressure drive + temperature-segmented furnace door control + fan-assisted cooling", the furnace gas flow rate can be increased by 3-5 times, achieving full airflow throughout the furnace, reducing the temperature difference to within 15℃, and shortening the cooling cycle by more than 50%, thus solving the problems of slow cooling in horizontal annealing furnaces and slow cooling when entering the furnace for maintenance.

[0036] As described above, in the embodiments of the cooling method for the horizontal annealing furnace provided by the present invention, the furnace pressure is maintained higher than the external pressure when the temperature is above the preset temperature. This prevents outside air from entering and causing oxidation of the strip at high temperatures. Only the end air inlet of the horizontal annealing furnace is opened, and air is drawn in only at the front exhaust port, forming a single gas flow from the end to the front of the furnace to achieve push-pull cooling. Therefore, directional gas flow can be achieved, quickly removing heat from the furnace and eliminating the turbulent airflow seen in existing technologies. Furthermore, when the temperature reaches below the preset temperature, the reducing gas in the furnace has already... Diluted to below a safe level by inert gas, the strip surface is no longer in a highly reactive state. At this point, outside air can be used as the cooling gas. The furnace doors are opened one by one from the end to the front of the horizontal annealing furnace, allowing the gas in the furnace chamber to flow smoothly from the end to the front. The exhaust fan at the furnace inlet draws outside air into the furnace and discharges it through the furnace. Since the air pressure inside the furnace chamber is lower than outside, it is a negative pressure ventilation state, allowing outside air to enter the furnace through the opened furnace doors. This method can shorten the cooling time, thereby reducing downtime, increasing production capacity, reducing energy consumption, and lowering equipment maintenance costs.

[0037] In a specific embodiment of the cooling method for the horizontal annealing furnace described above, opening only the end air inlet of the horizontal annealing furnace may further include:

[0038] Nitrogen gas is introduced into the furnace of the horizontal annealing furnace through the mixed gas inlet of the ES hot tension chamber, maintaining the pressure inside the furnace at 30 Pa to 50 Pa. It should be noted that this mixed gas inlet of the ES hot tension chamber is also the NH gas interface of the No. 1 mixing station in the hot tension chamber. This pressure of 30 Pa to 50 Pa better ensures that outside air cannot enter the furnace, thus preventing oxidation. Of course, other pressure values ​​can be maintained as needed; there are no restrictions here, as long as outside air cannot enter the furnace.

[0039] In another specific embodiment of the cooling method for the above-mentioned horizontal annealing furnace, when the temperature is higher than the preset temperature, the following steps may also be included: starting the fan of the RJC rapid cooling section to blow nitrogen into the furnace to exchange heat with the hot gas in the furnace. This provides more inert gas, thereby maintaining the positive pressure state inside the furnace more efficiently, and further improving the heat exchange efficiency.

[0040] In another specific embodiment of the cooling method for the above-mentioned horizontal annealing furnace, when the temperature reaches below the preset temperature, the following steps may also be included:

[0041] Close the valve at the mixed gas inlet of the ES hot expansion chamber and the blower of the RJC rapid cooling section, and open the furnace door of the ES hot expansion chamber, that is... Figure 2 The furnace doors #11 to #15 are on display. Figure 2 This is a schematic diagram of a horizontal annealing furnace. The exhaust fan at the front end of the horizontal annealing furnace is started with high power to maintain the pressure in the furnace chamber within the range of -250Pa to -350Pa, forming a negative pressure cooling in the furnace chamber and drawing fresh air from outside the furnace into the furnace chamber.

[0042] Furthermore, in a preferred embodiment of the cooling method for the horizontal annealing furnace described above, opening the furnace doors one by one from the end to the front of the horizontal annealing furnace may include the following:

[0043] The furnace doors of the ES hot expansion chamber, EQ soaking section, RJC rapid cooling section, SF supplementary heating section, RTF radiant tube heating section, NOF open flame heating section, and PH preheating section are opened sequentially according to the furnace temperature. It should be noted that this means opening the remaining furnace doors in the order of the furnace gas flow direction. Furthermore, it can be further optimized that when the temperature of a preset area is below 60℃, the furnace door of the adjacent section of that preset area is opened. That is, when the temperature of a certain area is below 60℃, the furnace door adjacent to that area is opened. For example, when the temperature of the hot expansion chamber is below 60℃, furnace door #10 of the equalization section is opened; when the temperature of the equalization section is below 60℃, furnace door #9 is opened; when the temperature in the area between furnace doors #8 and #9 decreases, furnace door #8 is opened, and so on. This ensures that each location receives sufficient cooling.

[0044] In any embodiment of the cooling method of the above-mentioned horizontal annealing furnace, the horizontal annealing furnace used can be a modified Sendzimir process horizontal annealing furnace. This type of horizontal annealing furnace is the core equipment in the hot-dip galvanizing production line and is mainly used for continuous annealing heat treatment of strip steel. This technology is an improvement on the traditional Sendzimir process, which connects the originally separate oxidation furnace and reduction furnace into a whole and changes the oxidizing atmosphere in the oxidation furnace to a non-oxidizing atmosphere. Of course, the above method can also be applied to other similar annealing furnaces, and there are no restrictions here.

[0045] Applying the above method to the actual start-up cooling of a 1500mm horizontal annealing furnace in a galvanizing (aluminum) unit has the following advantages: First, it is easy to implement with low equipment dependence. No new dedicated cooling equipment is required; only the existing hot expansion chamber air inlet, NOF exhaust fan, 15 furnace doors, cooling fan, furnace throat gate and inlet sealing roller, and one axial flow fan are utilized. No additional equipment procurement or installation is needed. Second, operation is simple. Using 400℃ as the temperature node, the "fan start-up and shutdown, gate..." are specified in stages. The operating steps are clear: "plate / sealing roller switch, furnace door opening sequence, axial flow fan auxiliary position," such as prioritizing opening furnace doors 11-15, opening them section by section in the direction of "hot tension chamber → preheating section," and opening the next furnace door after the area cools to <60℃. This method is highly compatible and can be adapted to horizontal annealing furnaces of different specifications of galvanizing (aluminum) units, with a wide range of applications. Furthermore, it is more economical because it can shorten downtime and increase production capacity. The traditional horizontal annealing furnace has a maintenance and cooling time of >3 hours. In 2 hours, this solution can increase the furnace gas flow rate by 3 to 5 times, shorten the cooling cycle to less than 18 hours, and reduce downtime by more than 14 hours per furnace start-up. Calculated based on 6 furnace start-ups per year, the annual increase in effective operating time is more than 84 hours. With an hourly capacity of 50 tons per unit, this translates to an additional annual output of 4,200 tons, resulting in a significant increase in revenue. Finally, it can reduce energy consumption costs. By precisely controlling the operation of the blowers, such as only starting the RJC cooling blower and NOF exhaust blower above 400°C to ensure positive pressure cooling inside the furnace, and shutting down the RJC cooling blower below 400°C, energy saving is achieved. Only axial flow fans are needed for auxiliary cooling, avoiding the energy waste of running the blowers at full load in traditional cooling. Calculations show that energy consumption during the furnace start-up and cooling phase can be reduced by 25% to 30%. It can also reduce equipment operation and maintenance costs. Due to the uniform decrease in furnace temperature, thermal stress damage to the furnace body is reduced, the service life of the furnace lining is extended by 12 to 24 months, the replacement frequency of radiant tubes is reduced by 30%, and the annual reduction in equipment maintenance costs is 50,000 to 80,000 yuan.

[0046] In summary, the solution provided in this application solves the problems of "slow cooling, high energy consumption, and easy equipment damage" of traditional cooling methods by using the technology of "remote air intake + near-end suction + temperature-segmented through-cooling". It can be directly applied to the cooling process of horizontal annealing furnaces in various aluminized zinc units for furnace start-up and maintenance operations, thereby increasing production capacity and reducing costs. Moreover, the directional airflow improves the heat exchange efficiency of nitrogen, increasing nitrogen utilization by 35%, which can reduce resource waste and is more environmentally friendly.

[0047] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A cooling method for a horizontal annealing furnace, characterized in that, include: When the temperature is higher than the preset temperature, the pressure inside the furnace is kept greater than the external pressure. Only the end air inlet of the horizontal annealing furnace is opened, and only the exhaust port at the front end of the horizontal annealing furnace is drawn in, forming a single flow of gas from the end to the front end of the horizontal annealing furnace to achieve push-pull cooling. When the temperature reaches below the preset temperature, the furnace doors are opened one by one from the end to the front of the horizontal annealing furnace, so that the gas in the furnace chamber flows smoothly from the end to the front of the horizontal annealing furnace.

2. The cooling method for the horizontal annealing furnace according to claim 1, characterized in that, The preset temperature is 400℃ to 450℃.

3. The cooling method for the horizontal annealing furnace according to claim 1, characterized in that, Maintaining the furnace pressure higher than the external pressure at a temperature higher than the preset temperature also includes: Close the inlet gate, emergency nitrogen inlet valve, and No. 2 mixing station inlet valve.

4. The cooling method for the horizontal annealing furnace according to claim 3, characterized in that, The method of opening only the end air inlet of the horizontal annealing furnace includes: Only open the valve at the mixed gas inlet of the ES hot tension chamber of the horizontal annealing furnace.

5. The cooling method for the horizontal annealing furnace according to claim 4, characterized in that, The method of opening only the end air inlet of the horizontal annealing furnace also includes: Nitrogen gas is introduced into the furnace of the horizontal annealing furnace through the mixed gas inlet of the ES hot tension chamber to maintain the pressure in the furnace at 30 Pa to 50 Pa.

6. The cooling method for the horizontal annealing furnace according to claim 5, characterized in that, In cases where the temperature is higher than the preset temperature, the following is also included: The fan in the RJC rapid cooling section is started to blow nitrogen into the furnace, where it exchanges heat with the hot gas inside the furnace.

7. The cooling method for the horizontal annealing furnace according to claim 6, characterized in that, When the temperature reaches below the preset temperature, the following is also included: Close the valve at the mixed gas inlet of the ES hot expansion chamber and the fan of the RJC rapid cooling section, open the furnace door of the ES hot expansion chamber, and start the exhaust fan at the front end of the horizontal annealing furnace at high power to maintain the pressure in the furnace chamber within the range of -250Pa to -350Pa, thereby creating negative pressure cooling in the furnace chamber and drawing fresh air from outside the furnace into the furnace chamber.

8. The cooling method for the horizontal annealing furnace according to claim 7, characterized in that, The step of opening the furnace doors one by one from the end to the front of the horizontal annealing furnace includes: According to the furnace temperature, open the furnace doors of the ES hot expansion chamber, EQ soaking section, RJC rapid cooling section, SF supplementary heating section, RTF radiant tube heating section, NOF open flame heating section and PH preheating section one by one.

9. The cooling method for the horizontal annealing furnace according to claim 8, characterized in that, When the temperature of the preset area is below 60°C, the furnace door of the adjacent section of the preset area is opened.

10. The cooling method for the horizontal annealing furnace according to any one of claims 1-9, characterized in that, The horizontal annealing furnace is a modified Sendzimir process horizontal annealing furnace.

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