A method for rapid start-up of a galvanizing unit under a fixed zinc pot

Abstract

This invention relates to the field of hot-dip galvanizing technology for strip steel, specifically to a method for rapid start-up of a galvanizing unit under a fixed zinc pot. By comprehensively controlling the production organization method before shutdown, the power of the annealing furnace burners, the power of the induction heating, and the cooling model of the annealing furnace after shutdown, the furnace temperature cooling rate is controlled in stages at different time periods, thereby achieving rapid and stable cooling and start-up. This significantly reduces the shutdown and start-up time, shortening it from more than 18 hours to less than 10 hours, improving the effective operating rate of the unit, and resulting in significant economic benefits.

Description

Technical Field

[0001] This invention relates to the field of hot-dip galvanizing technology for steel strips, and specifically to a method for rapidly starting up a galvanizing unit under a fixed zinc pot. Background Technology

[0002] With the rapid development of the automotive and home appliance industries, especially the opportunities brought by automotive lightweighting, the demand for hot-dip galvanized steel coils has increased significantly. However, under the constraints of existing production capacity, galvanizing units need to improve their operating rates to achieve greater efficiency. Typically, these units require regular maintenance, including periodic furnace start-ups for inspection and maintenance. However, steel coils produced by stationary zinc pot galvanizing units do not have the conditions for rework, therefore, they cannot be reused to lower the annealing temperature. The conventional furnace start-up process includes steps such as shutdown, burner extinguishing, electric heating shutdown, and high-nitrogen purging, allowing the annealing furnace to cool to below 100°C before starting. This process takes at least 18 hours, severely restricting the improvement of production efficiency.

[0003] CN 109990569 A discloses a drying method for an annealing furnace based on cooling and dehumidification, comprising the following steps: A) introducing a protective gas into the annealing furnace, followed by heating and holding; B) after holding, continuing to introduce the protective gas to cool the annealing furnace; repeating steps A) and B) until the dew point inside the annealing furnace remains stable and reaches the designed dew point range, at which point the drying process ends. This patent mainly achieves the drying effect by repeatedly raising and lowering the temperature, and provides a high-nitrogen purging cooling method in the drying process. This method is inefficient, has a long cooling time, and the overall drying time reaches 5-7 days. Summary of the Invention

[0004] To address the technical problem of long start-up and annealing time for galvanizing units, this invention provides a method for rapid start-up of galvanizing units under a fixed zinc pot, which significantly reduces the downtime for start-up of galvanizing units, shortening the start-up time to less than 10 hours, improving the effective operating rate of the unit, and having significant economic benefits.

[0005] This invention provides a method for rapidly starting up a galvanizing unit under a fixed zinc pot, comprising the following steps:

[0006] S1. Two coils of galvanized products are produced before the galvanizing pot is shut down. Before production, the annealing furnace temperature is T0, and the burner power in each zone is P0. Control the burner power P0 in each zone to decrease.

[0007] S2. Welding shutdown material: During the welding process, control the burner power of each zone of the annealing furnace to decrease from P0 to P1. When the shutdown material is put into the line, control the furnace temperature of the annealing furnace to decrease from T0 to T1.

[0008] S3. When the material to be shut down enters the annealing furnace inlet, control the burner power of each zone of the annealing furnace to P2. When the material to be shut down reaches the outlet flying shear, the furnace stops. At this time, the furnace temperature of the annealing furnace drops to T2.

[0009] S4. After shutdown, start the high-nitrogen purging of the annealing furnace, turn off all electric heating in the furnace area, start the cooling circulation fan in the pre-oxidation chamber, adjust the opening of the vent valve, and control the temperature drop of the annealing furnace.

[0010] S5. When the furnace temperature of the annealing furnace drops to T3, stop the hydrogen supply and inject cold air into the radiant tubes for rapid cooling.

[0011] S6. When the furnace temperature of the annealing furnace drops to T4, turn off the high nitrogen purging function, open the furnace top strip hole, and increase air convection to further accelerate the cooling rate of the annealing furnace while ensuring that the equipment in the furnace area is not damaged.

[0012] S7. When the furnace temperature of the annealing furnace drops to T5, open the furnace top cover and manhole to further increase the cooling rate of the annealing furnace.

[0013] S8. When the furnace temperature of the annealing furnace drops to T6, open the furnace bottom cover for further cooling until the furnace temperature cools down to T7.

[0014] Furthermore, in step S1, T0 ≥ 800℃, the burner power P0 in each zone is controlled to decrease from ≥ 50% to ≤ 30%.

[0015] Furthermore, in step S2, 15%≤P1≤20% ensures that the temperature of the material before shutdown meets the process requirements; 700℃≤T1≤720℃ significantly reduces the furnace temperature while ensuring the mechanical properties of the strip.

[0016] Furthermore, in step S3, P2=0, that is, all burners of the annealing furnace are shut down. According to the principle of energy conservation, a large amount of annealing furnace temperature is carried away by the cold strip steel; T2=T1-k1*L / V, k1 is the cooling rate, L is the length from the annealing furnace inlet to the stop position, and V is the unit speed; T2≤620℃.

[0017] Furthermore, in step S3, while controlling the burner power of each zone of the annealing furnace to P2, the induction heating power of the equalization section is controlled to be greater than 50% to ensure that the strip temperature when entering the zinc pot is >400℃, so as to avoid dezincification of cold strip due to low plate temperature when entering the zinc pot during the replacement furnace temperature.

[0018] Furthermore, in step S4, the furnace temperature is controlled by an energy medium, and the high-nitrogen purging injection flow rate is ≥3600 Nm³. 3 / h, vent valve opening ≥80%, furnace pressure control ≥0.1kPa.

[0019] Furthermore, in step S5, T3 ≤ 400℃, and the time for the annealing furnace temperature to drop from T2 to T3 is 5.5h.

[0020] Furthermore, in step S6, T4 ≤ 250℃, and the time for the annealing furnace temperature to drop from T3 to T4 is 2.0h.

[0021] Furthermore, in step S7, T5 ≤ 150℃, and the time for the annealing furnace temperature to drop from T4 to T5 is 1.0h.

[0022] Furthermore, in step S8, T6 ≤ 100℃, and the time for the annealing furnace temperature to drop from T5 to T6 is 19 minutes.

[0023] The beneficial effects of this invention are as follows:

[0024] (1) This invention comprehensively controls the production organization method before shutdown, the power of the annealing furnace burner, the power of the induction heating and the cooling model of the annealing furnace after shutdown, so as to control the furnace temperature cooling rate stepwise at different time periods, thereby achieving rapid and stable cooling and furnace opening, significantly reducing the shutdown and furnace opening time, shortening the furnace opening time from more than 18 hours to less than 10 hours, improving the effective operating rate of the unit, and having obvious economic benefits.

[0025] (2) The stepped cooling model of the annealing furnace provided by the present invention improves the adaptability of the equipment, protects the annealing furnace equipment, and extends its service life.

[0026] (3) The present invention can meet the product performance requirements while achieving rapid cooling and furnace opening, and reduces the re-judgment situation caused by furnace shutdown. Attached Figure Description

[0027] 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, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 These are the stepped cooling model curves of the annealing furnace at different stages in specific embodiments of the present invention. Detailed Implementation

[0029] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0030] Example 1

[0031] A method for rapidly starting up a galvanizing unit under a fixed zinc pot includes the following steps:

[0032] (1) Before the shutdown, it is planned to produce two rolls of galvanized products. The products are ordinary grade strip steel. Before production, the annealing temperature T0 is generally T0≥800℃. The burner power P0 of each zone of the annealing furnace is reduced from more than 50% to less than 30%, thereby reducing the furnace temperature of the annealing furnace.

[0033] (2) Welding shutdown material. During the welding process, control the burner power P1 of each zone of the annealing furnace to 15%≤P1≤20%, and stabilize the furnace temperature at T1 before shutdown to 700℃≤T1≤720℃, so as to ensure the performance of the strip steel in the furnace.

[0034] (3) When the material to be shut down enters the annealing furnace inlet, control the burner power P3 of each zone of the annealing furnace at this time, P3=0, and carry away a large amount of annealing furnace temperature through the cold strip steel. Before shutdown, the furnace temperature T2=T1-k1*L / V, where k1 is the cooling rate (℃ / min), which is generally 2.4℃ / min, L is the length from the annealing furnace inlet to the shutdown position (m), and V is the unit speed (m / min). At the same time, control the induction heating power of the equalization section to be >50% to ensure that the temperature of the strip steel when entering the zinc pot is greater than 400℃, and avoid zinc stripping on the surface of the material to be shut down.

[0035] (4) When the material reaches the outlet flying shear, the machine is stopped at this time, and the furnace temperature is T2, which is generally T2≤690℃. At the same time, the high nitrogen purging function of the annealing furnace is turned on, and its injection flow rate is ≥3600Nm. 3 / h, shut down all electric heating in the furnace area, turn on the cooling circulation fan in the pre-oxidation chamber, adjust the vent valve opening to ≥80%, and ensure the furnace pressure ≥0.1Kpa to achieve rapid reduction of furnace temperature. Furnace temperature T3 = T2 - k2 * t2, where k2 is the cooling rate (°C / min) from T2 to T3, which is generally 0.86°C / min, and t2 is the time (min) from T2 to T3.

[0036] (5) After 5.5 hours of shutdown, when the furnace temperature T3 ≤ 400℃, stop the hydrogen supply and inject cold air into the radiant tubes, with an air flow rate ≥ 100 Nm³ / h in each tube. 3 / h, rapidly cool the radiant tube to further improve the cooling rate. Furnace temperature T4 = T3 - k3 * t3, where k3 is the cooling rate (°C / min) from T3 to T4, which is generally 1.33°C / min, and t3 is the time (min) from T3 to T4.

[0037] (6) After the radiant tube has cooled for 2 hours, the furnace temperature T4 ≤ 250℃. The high nitrogen purging function is turned off and the furnace top piercing hole is opened to further accelerate the cooling rate of the annealing furnace. The furnace temperature T5 = T4 - k4 * t4, where k4 is the cooling rate (℃ / min) from T4 to T5, which is generally 1.68℃ / min, and t4 is the time (min) from T4 to T5.

[0038] (7) After the threading hole is opened for 1 hour, the furnace temperature T5 ≤ 150℃. Open the furnace top cover and manhole to further improve the cooling rate of the annealing furnace. The furnace temperature T6 = T5 - k5 * t5, where k5 is the cooling rate (℃ / min) from T5 to T6, which is generally 2.1℃ / min, and t5 is the time (min) from T5 to T6.

[0039] (8) After opening the furnace top cover and manhole for 19 minutes, the furnace temperature T6 ≤ 100℃. Open the furnace bottom cover and increase the cooling rate to the maximum extent until it reaches T7. The furnace temperature T7 = T6 - k6 * t6, where k6 is the cooling rate (℃ / min) from T6 to T7, which is generally 2.7℃ / min. t6 is the time (min) from T6 to T7. The above annealing furnace cooling and opening is completed.

[0040] Figure 1 The step cooling model curves of the annealing furnace at different stages are shown.

[0041] This invention provides a specific production example:

[0042] The machine is scheduled to shut down at 2:00 AM on a certain day. The production plan before the shutdown and the burner power control and furnace temperature at each stage are shown in Table 1.

[0043] Table 1 Production plan before shutdown and burner power control and furnace temperature data at each stage

[0044]

[0045] The actual furnace temperature and control method at each time point after shutdown are shown in Table 2.

[0046] Table 2 Actual furnace temperature and control method at different times after shutdown

[0047]

[0048] As shown in Table 2, the furnace start-up work was completed in 9 hours on the same day, and the furnace area operation was completed in 9.5 hours, shortening the maintenance period by 9 hours.

[0049] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for rapid start-up of a galvanizing unit under a fixed zinc pot, characterized in that, Includes the following steps: S1. Before the galvanizing pot is shut down, two coils of galvanized products are produced. Before production, the annealing furnace temperature is T0, and the burner power in each zone is P0. The burner power P0 in each zone is controlled to decrease; the burner power P0 in each zone is controlled to decrease from ≥50% to ≤30%. S2. Welding shutdown material: During welding, control the burner power in each zone of the annealing furnace to decrease from P0 to P1. When the shutdown material is brought online, control the furnace temperature of the annealing furnace to decrease from T0 to T1; 15%≤P1≤20%; S3. When the material to be shut down enters the annealing furnace inlet, control the burner power of each zone of the annealing furnace to P2. When the material to be shut down reaches the outlet flying shear, the furnace stops. At this time, the furnace temperature drops to T2. P2=0. While controlling the burner power of each zone of the annealing furnace to P2, control the induction heating power of the equalization section to be greater than 50%. T2=T1-k1*L / V, k1 is the cooling rate, L is the length from the annealing furnace inlet to the shutdown position, and V is the unit speed. S4. After shutdown, start the high-nitrogen purging of the annealing furnace, turn off all electric heating in the furnace area, start the cooling circulation fan in the pre-oxidation chamber, adjust the opening of the vent valve, and control the temperature drop of the annealing furnace. S5. When the furnace temperature of the annealing furnace drops to T3, stop the hydrogen supply and inject cold air into the radiant tube for rapid cooling; furnace temperature T3 = T2 - k2 * t2, where k2 is the cooling rate from T2 to T3 and t2 is the time from T2 to T3. S6. When the annealing furnace temperature drops to T4, turn off the high-nitrogen purging function and open the furnace top strip hole for further cooling; furnace temperature T4 = T3 - k3 * t3, where k3 is the cooling rate from T3 to T4 and t3 is the time from T3 to T4. S7. When the annealing furnace temperature drops to T5, open the furnace top cover and manhole for further cooling; furnace temperature T5 = T4 - k4 * t4, where k4 is the cooling rate from T4 to T5 and t4 is the time from T4 to T5. S8. When the furnace temperature of the annealing furnace drops to T6, open the furnace bottom cover for further cooling until the furnace temperature drops to T7; furnace temperature T6 = T5 - k5 * t5, where k5 is the cooling rate from T5 to T6 and t5 is the time from T5 to T6; furnace temperature T7 = T6 - k6 * t6, where k6 is the cooling rate from T6 to T7 and t6 is the time from T6 to T7.

2. The method for rapid start-up of a galvanizing unit under a fixed zinc pot as described in claim 1, characterized in that, In step S1, T0 ≥ 800℃.

3. The method for rapid start-up of a galvanizing unit under a fixed zinc pot as described in claim 1, characterized in that, In step S2, 700℃≤T1≤720℃.

4. The method for rapid start-up of a galvanizing unit under a fixed zinc pot as described in claim 1, characterized in that, In step S3, T2 ≤ 620℃.

5. The method for rapid start-up of a galvanizing unit under a fixed zinc pot as described in claim 1, characterized in that, In step S4, the high nitrogen purge injection flow rate ≥ 3600 Nm 3 / h, the bleed valve opening degree ≥ 80%, and the furnace pressure control is ≥ 0.1 kPa.

6. The method for rapid start-up of a galvanizing unit under a fixed zinc pot as described in claim 1, characterized in that, In step S5, T3 ≤ 400℃, and the time for the annealing furnace temperature to drop from T2 to T3 is 5.5h.

7. The method for rapid start-up of a galvanizing unit under a fixed zinc pot as described in claim 1, characterized in that, In step S6, T4 ≤ 250℃, and the time for the annealing furnace temperature to drop from T3 to T4 is 2.0h.

8. The method for rapid start-up of a galvanizing unit under a fixed zinc pot as described in claim 1, characterized in that, In step S7, T5 ≤ 150℃, and the time for the annealing furnace temperature to drop from T4 to T5 is 1.0h.

9. The method for rapid start-up of a galvanizing unit under a fixed zinc pot as described in claim 1, characterized in that, In step S8, T6 ≤ 100℃, and the time for the annealing furnace temperature to drop from T5 to T6 is 19 minutes.

Images