Method for calculating strip entry temperature into a pot of a continuous hot-dip high-aluminum zinc coating line based on heat balance equation

Abstract

The application discloses a continuous hot-dip high-aluminum zinc unit strip steel entering a pot temperature calculation method based on a heat balance equation, analyzes a production environment of a high-aluminum zinc pot of the hot-dip high-aluminum zinc unit, establishes and calculates each heat outflow item and heat inflow item of the high-aluminum zinc pot region, establishes a heat balance equation, and reversely deduces a suitable strip steel entering pot temperature, so that zinc slag generation in the hot-dip high-aluminum zinc process is reduced, and the coating quality of the strip steel surface is improved.

Description

Technical Field

[0001] This invention relates to the field of hot-dip galvanizing technology, and more specifically, to a method for calculating the strip temperature entering the hot-dip galvanizing unit for high-aluminum zinc based on the heat balance equation. Background Technology

[0002] The structure of a high-alumina zinc galvanizing unit differs from that of a hot-dip galvanizing unit. The high-alumina zinc galvanizing unit has a pre-melting pot and a high-alumina zinc pot, thus the thermal balance of the high-alumina zinc galvanizing unit differs from that of the pure zinc galvanizing unit. If the strip temperature entering the pot is much lower than the zinc bath temperature, the wetting performance of the zinc liquid on the steel plate decreases, which is very detrimental to the formation of the inhibition layer and affects the adhesion of the coating. If the strip temperature entering the high-alumina zinc pot is much higher than the zinc bath temperature, the zinc bath temperature will rise rapidly, the reaction rate will be accelerated, and the inhibition layer will become uneven. As the saying goes, "no iron, no slag," if the strip temperature entering the pot is too high, a large amount of zinc dross will be generated; if the strip temperature is too low, a large amount of zinc dross will also be generated. Therefore, a suitable strip temperature entering the pot plays a crucial role in maintaining a stable zinc bath temperature and improving the galvanizing quality. In actual production, the actual temperature of the strip steel is mainly determined by the plate thermometer. However, the plate thermometer is installed at a relatively far distance, and its accuracy in detecting the actual plate temperature is limited. Most units cannot reflect the actual temperature of the strip steel entering the pot. Therefore, the actual temperature of the strip steel entering the pot is in an "uncontrolled" state.

[0003] Combination Figure 1 As shown, in the hot-dip high-alumina zinc galvanizing unit, high-alumina zinc ingots 4 are melted in the pre-melting pot 1 under the action of the hoist 3. The molten high-alumina zinc liquid flows into the high-alumina zinc pot 2 through the chute 5, continuously replenishing the zinc liquid for the strip steel to be coated with high-alumina zinc. During the continuous hot-dip high-alumina zinc galvanizing process of the strip steel, due to the deviation between the temperature of the strip steel entering the pot and the temperature of the zinc liquid in the high-alumina zinc pot, slag will inevitably be generated. On the one hand, the slag directly adheres to the surface of the strip steel, affecting the surface quality of the coating; on the other hand, the slag will continuously accumulate on the submerged roller 7 and the stabilizing roller 8, forming dot-like indentations. Therefore, controlling the temperature of the strip steel entering the pot can suppress the generation of slag and improve the coating quality; however, due to environmental factors, the plate thermometer (the instrument for measuring the temperature of the strip steel) has a deviation, so this phenomenon has not been solved.

[0004] Therefore, it is necessary to study a method for calculating the temperature of strip steel entering the pot, which can provide compensation for the operation of the plate thermometer, solve the deviation in the temperature measurement of strip steel by the plate thermometer, thereby reducing the amount of zinc dross generated during the hot-dip high-alumina zinc galvanizing process and improving the coating quality of the strip steel surface. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for calculating the strip entry temperature of a continuous hot-dip high-alumina zinc galvanizing unit based on a heat balance equation. Starting from the energy balance perspective of the high-alumina zinc galvanizing pot area, a heat balance equation is established by defining and calculating various heat expenditure and heat input items in the high-alumina zinc galvanizing pot area, and the appropriate strip entry temperature is derived from this equation. This reduces the amount of zinc dross generated during the hot-dip high-alumina zinc galvanizing process and improves the coating quality of the strip surface.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a method for calculating the strip temperature entering the pot of a continuous hot-dip high-alumina zinc galvanizing unit based on a heat balance equation. The method analyzes the production environment of the high-alumina zinc galvanizing pot of the hot-dip high-alumina zinc galvanizing unit, determines and calculates the various heat expenditure and heat input items in the high-alumina zinc galvanizing pot area of ​​the hot-dip high-alumina zinc galvanizing unit, thereby establishing a heat balance equation, and calculating the strip temperature entering the pot based on the heat balance equation.

[0008] Preferably, the heat input item for the high-alumina zinc bath area of ​​the hot-dip galvanizing unit includes the heating amount Q of the induction heater. IH , The steel strip is put into the pot to release heat Q Strip 1. Molten high-alumina zinc liquid is poured into a high-alumina zinc pot, releasing heat Q. zn ;

[0009] The heat expenditure item in the high-alumina zinc pot area of ​​the hot-dip high-alumina zinc galvanizing unit includes the free heat dissipation Q from the surface of the zinc liquid in the high-alumina zinc pot. Loss Air knife blowing heat dissipation Q Wipe .

[0010] Preferably, the heating amount Q of the induction heater IH The calculation formula is as follows:

[0011] Q IH =IH1_AVR×IH1_dur+IH2_AVR×IH2_dur

[0012] P IH =(IH1_AVR·IH1_dur+IH2_AVR·IH2_dur) / dur

[0013] Where IH1_AVR and IH2_AVR are the average power of induction heaters IH1 and IH2 during the strip steel production process, respectively, in kW;

[0014] IH1_dur and IH2_dur are the working times of induction heaters IH1 and IH2, respectively, in seconds.

[0015] dur represents the duration of strip steel production, measured in seconds (s).

[0016] P IHThis refers to the heating power of the induction heater, measured in kW.

[0017] Preferably, the heat released when the steel strip enters the pot is Q. Strip The calculation formula is as follows:

[0018] Q Strip =P st ×dur

[0019] P st =s×v×ρ t ×CS

[0020]

[0021] Among them, P st The heat release power of the strip steel entering the pot is expressed in kW.

[0022] dur represents the duration of strip steel production, measured in seconds (s).

[0023] s is the cross-sectional area of ​​the strip steel, in meters. 2 ;

[0024] v is the strip speed, in m / s;

[0025] ρ t The density of the strip steel is taken as 7.8 × 10⁻⁶. 3 kg / m 3

[0026] CS is the specific heat capacity of strip steel when the temperature changes rapidly, in J / kg·K;

[0027] T st The temperature at which the strip enters the pot is expressed in K.

[0028] T ba This refers to the zinc bath temperature, expressed in Kelvin (K).

[0029] a2, b2, c2, and d2 are the heating coefficients of the strip steel, which are 504.2 J / kg·K, -0.1309 J / kg·K, and -5.179 × 10⁻⁶ J / kg·K, respectively. -6 J / kg·K, 4.4797×10 -4 J / kg·K.

[0030] Preferably, the heat released Q when the molten high-aluminum zinc is poured into the high-aluminum zinc pot zn The calculation formula is:

[0031] Q zn =P zn ×dur

[0032] P zn=Wg×[a3×(Tba-Tme)] / (1000×dur1)

[0033] Among them, P zn The heat release power of molten high-alumina zinc entering a high-alumina zinc pot is expressed in kW.

[0034] dur represents the duration of strip steel production, measured in seconds (s).

[0035] Wg represents the mass of molten high-aluminum zinc added to the high-aluminum zinc pot, in kg.

[0036] Tba is the temperature at which the molten high-aluminum zinc is added to the high-aluminum zinc pot, in K;

[0037] Tme is the melting temperature of high-alumina zinc ingots, expressed in K.

[0038] a3 is the specific heat capacity of the zinc-aluminum mixture in the high-aluminum zinc pot;

[0039] dur1 is the time taken for the molten high-aluminum zinc to reach the zinc bath temperature, measured in seconds.

[0040] Preferably, the free heat dissipation Q from the surface of the high-alumina zinc pot molten zinc is... Loss The method for obtaining the data is as follows: The continuous hot-dip high-alumina zinc galvanizing unit is shut down, air knife purging is stopped, and molten high-alumina zinc is not added to the high-alumina zinc pot. The temperature change of the thermocouples inside the high-alumina zinc pot is monitored, and the free heat dissipation power P from the surface of the zinc liquid in the high-alumina zinc pot is calculated. Loss This allows for the acquisition of Q, the amount of free heat dissipation from the surface of the high-alumina zinc pot's molten zinc. Loss .

[0041] Preferably, the heat dissipation Q of the air knife purging Wipe The method for obtaining the data is as follows: The continuous hot-dip high-alumina zinc galvanizing unit is shut down, the air knife continues purging, and molten high-alumina zinc is not added to the high-alumina zinc pot. The temperature change of the thermocouple inside the high-alumina zinc pot is monitored, and the free heat dissipation power P from the surface of the zinc liquid in the high-alumina zinc pot is determined. Loss Calculate the heat dissipation power P of air knife purging wipe Thus, the heat dissipation Q from the air knife blowing is obtained. Wipe .

[0042] Preferably, the sum of the heat input items of the high-alumina zinc pot in the hot-dip high-alumina zinc galvanizing unit equals the sum of the heat output items, thereby establishing the following heat balance equation:

[0043] Q IH +Q Strip +Q zn =Q Loss +Q Wipe

[0044] Among them, Q IH Q represents the heating amount of the induction heater.Strip The strip steel is added to the pot to release heat; Q zn The process involves releasing heat by pouring molten high-alumina zinc into a high-alumina zinc pot; Q Loss Q represents the free heat dissipation from the surface of the molten zinc in a high-alumina zinc pot. Wipe This is to dissipate heat through air knife blowing.

[0045] Preferably, the temperature at which the strip enters the pot is determined based on the heat balance equation and the heat released Q upon entering the pot. Strip The calculation formula is obtained.

[0046] This invention proposes for the first time a method for calculating the strip entry temperature of a continuous hot-dip high-alumina zinc galvanizing unit based on a heat balance equation. Starting from the energy balance perspective of the high-alumina zinc galvanizing bath area, it establishes a heat balance equation by defining and calculating various heat expenditure and input terms in the high-alumina zinc galvanizing bath area, and then derives the appropriate strip entry temperature. This reduces the amount of zinc dross generated during the hot-dip high-alumina zinc galvanizing process and improves the coating quality on the strip surface. This invention effectively solves the drawbacks of previous hot-dip galvanizing processes that relied solely on production experience and past production results to control the strip entry temperature, which contained fuzziness and lag. It plays a crucial role in maintaining stable zinc bath temperature and improving galvanizing quality. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the continuous hot-dip high-aluminum zinc galvanizing production line of the present invention;

[0048] In the diagram, 1. Pre-melting pot; 2. High-alumina zinc pot; 3. Hoist; 4. High-alumina zinc ingot; 5. Chute; 6. Tension roller; 7. Submerged roller; 8. Stabilizing roller; 9. Straightening roller; 10. Tower top roller. Detailed Implementation

[0049] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0050] This invention takes into account that the energy of the high-alumina zinc bath in a hot-dip high-alumina zinc galvanizing unit is balanced. From the perspective of energy balance, the contribution of the strip steel to the energy balance of the zinc bath is calculated. Based on this, the plate thermometer is calibrated, and then the temperature of the strip steel entering the bath is adjusted by the calibrated plate thermometer, so as to make the strip steel contribute "positive energy" to the high-alumina zinc bath as much as possible, or at least "minimize the negative energy", thereby reducing the amount of zinc dross generated to a certain extent.

[0051] This invention provides a method for calculating the strip temperature entering the pot of a continuous hot-dip galvanizing high-alumina zinc unit based on a heat balance equation. Taking the heat balance equation of the high-alumina zinc pot area as the starting point, the production environment of the high-alumina zinc pot in the hot-dip galvanizing unit is analyzed, and the various heat expenditure and heat input items of the high-alumina zinc pot area of ​​the hot-dip galvanizing unit are determined and calculated. Thus, a heat balance equation is established, and the strip temperature entering the pot is calculated based on the heat balance equation.

[0052] Combination Figure 1 As shown, the continuous hot-dip high-alumina zinc galvanizing unit is divided into a pre-melting pot 1 and a high-alumina zinc pot 2, which are connected by a chute 5. The high-alumina zinc ingot 4 is melted in the pre-melting pot 1 under the action of the hoist 3. The molten high-alumina zinc liquid flows into the high-alumina zinc pot 2 through the chute 5 to replenish the high-alumina zinc galvanizing liquid for the strip. During the hot-dip galvanizing process of the strip, the strip enters the zinc bath of the high-alumina zinc pot 2 under the action of the tension roller 6. After passing through the submerged roller 7, the stabilizing roller 8, and the straightening roller 9, it exits the high-alumina zinc pot 2 and then enters the next process along the top roller 10.

[0053] In the continuous production process of a hot-dip high-alumina zinc galvanizing machine, high-alumina zinc ingots are fed into the pre-melting pot of the machine by a hoist. Inside the pre-melting pot, the high-alumina zinc ingots are melted by an induction heater (typically 640℃). During this process, the high-alumina zinc absorbs heat and melts, lowering the temperature of the molten zinc in the pre-melting pot. The molten high-alumina zinc then flows through a chute into the high-alumina zinc galvanizing pot, continuously replenishing the zinc for the strip to be coated. During this process, the molten high-alumina zinc dissipates heat again. However, even after these two cooling processes, the temperature of the molten high-alumina zinc in the pre-melting pot is generally still higher than that in the high-alumina zinc galvanizing pot.

[0054] During continuous production, an air knife continuously blows near the zinc bath to control the thickness of the zinc liquid, which causes heat loss from the high-alumina zinc bath. The high-alumina zinc pot is equipped with induction heaters IH1 and IH2, both with roughly the same operating power and duration, to heat the high-alumina zinc liquid and maintain a stable temperature. Under the action of the two induction heaters, the temperature of the zinc bath in the high-alumina zinc pot is controlled within the range of 590℃±5℃ (this temperature may vary depending on actual production conditions).

[0055] An analysis of the aforementioned production environment factors reveals the main factors affecting the heat balance of the high-alumina zinc boiler area, involving heat input and heat output items. Specifically, the heat input item for the high-alumina zinc boiler area of ​​the hot-dip galvanizing unit includes the heating amount Q from the induction heater. IH , The steel strip is put into the pot to release heat Q Strip 1. Molten high-alumina zinc is poured into a high-alumina zinc pot, releasing heat Q. zn The heat expenditure item for the high-alumina zinc bath area of ​​the hot-dip galvanizing unit includes the free heat dissipation Q from the surface of the molten zinc in the high-alumina zinc bath. Loss Air knife blowing heat dissipation Q Wipe .

[0056] Ideally, the temperature of the molten zinc remains constant throughout the production process, i.e., controlled within a set range (590℃ ± 5℃). In this case, the heat input item includes the heating amount Q from the induction heater. IH , The steel strip is put into the pot to release heat Q Strip 1. Molten high-alumina zinc is poured into a high-alumina zinc pot, releasing heat Q. znHowever, in actual production, the temperature of the zinc bath cannot be maintained within the set range (590℃±5℃). Due to the heating of the induction heater and the addition of molten high-alumina zinc, the temperature of the zinc bath varies within a certain range before and after the production of a strip. Since the zinc bath has a huge volume, even a small temperature change will bring a large difference in heat. Therefore, in the actual production process, we need to set a suitable strip entry temperature for each specification of strip in advance to achieve the purpose of maintaining a stable zinc bath temperature.

[0057] I. To determine and accurately calculate the various energy levels in the high-alumina zinc pot region, the specific process is as follows:

[0058] (1) Heating calculation of induction heater

[0059] In the high-alumina zinc bath, two induction heaters operate simultaneously at low settings to ensure the zinc bath temperature remains within a set range (e.g., 590℃, which can be considered a constant). The induction heaters are a crucial factor in the heat gain of the zinc bath. When performing heat balance calculations for the high-alumina zinc bath area, the power of the induction heaters is based on real-time data, and the heating time is taken as the duration of strip steel production.

[0060] Induction heater heating quantity Q IH The calculation formula is as follows:

[0061] Q IH =IH1_AVR×IH1_dur+IH2_AVR×IH2_dur (1)

[0062] P IH =(IH1_AVR·IH1_dur+IH2_AVR·IH2_dur) / dur (2)

[0063] Where IH1_AVR and IH2_AVR are the average power of induction heaters IH1 and IH2 during the strip steel production process, respectively, in kW;

[0064] IH1_dur and IH2_dur are the working times of induction heaters IH1 and IH2, respectively, in seconds.

[0065] dur represents the duration of strip production (the time it takes for each coil to pass through the strip), measured in seconds.

[0066] P IH This refers to the heating power of the induction heater, measured in kW.

[0067] (2) Calculation of heat release when steel strip enters high-aluminum zinc pot

[0068] Before the strip steel enters the high-alumina zinc bath for galvanizing from the furnace nose outlet, its own temperature is higher than the zinc bath temperature. Therefore, the strip steel will transfer heat to the zinc bath during galvanizing. From a physical point of view, the heat released by the strip steel entering the bath is Q. Strip The calculation formula is as follows:

[0069] Q Strip =P st ×dur (3)

[0070] P st =s×v×ρ t ×CS (4)

[0071] Among them, P st The heat release power of the strip steel entering the pot is expressed in kW.

[0072] dur represents the duration of strip steel production, measured in seconds (s).

[0073] s is the cross-sectional area of ​​the strip steel, in meters. 2 ;

[0074] v is the strip speed, in m / s;

[0075] ρ t The density of the strip steel is taken as 7.8 × 10⁻⁶. 3 kg / m 3 ;

[0076] CS is the specific heat capacity of strip steel under rapid temperature change, measured in J / kg·K; the formula for calculating CS is as follows:

[0077]

[0078] T st The temperature at which the strip enters the pot is expressed in K.

[0079] T ba This refers to the zinc bath temperature, expressed in Kelvin (K).

[0080] a2, b2, c2, and d2 are the heating coefficients of the strip steel, which are 504.2 J / kg·K, -0.1309 J / kg·K, and -5.179 × 10⁻⁶ J / kg·K, respectively. -6 J / kg·K, 4.4797×10 -4 J / kg·K.

[0081] For steel strips of different specifications and at different temperatures when entering the pot, the amount of heat released and the heat output power of the steel strips when entering the high-alumina zinc pot will also be different.

[0082] (3) Calculation of heat release when molten high-aluminum zinc is poured into the high-aluminum zinc pot

[0083] Molten zinc is added from a chute to a high-alumina zinc bath and heated until its own temperature reaches the zinc bath temperature. The molten zinc releases heat (Q) into the high-alumina zinc bath. zn The calculation formula is:

[0084] Q zn =P zn ×dur (6)

[0085] P zn =Wg×[a3×(Tba-Tme)] / (1000×dur1) (7)

[0086] Among them, P zn The heat release power of molten high-alumina zinc entering a high-alumina zinc pot is expressed in kW.

[0087] dur represents the duration of strip steel production, measured in seconds (s).

[0088] Wg represents the mass of molten high-aluminum zinc added to the high-aluminum zinc pot, in kg.

[0089] Tba is the temperature at which the molten high-aluminum zinc is added to the high-aluminum zinc pot, in K;

[0090] Tme is the zinc bath temperature in the high-alumina zinc pot, in K;

[0091] a3 is the specific heat capacity of the zinc-aluminum mixture in the high-aluminum zinc pot, which is 668 J / kg·K;

[0092] 1000 is the power conversion factor;

[0093] dur1 is the time taken for the molten high-aluminum zinc to reach the zinc bath temperature, measured in seconds.

[0094] (4) Calculation of free heat dissipation from the surface of the zinc liquid in the high-alumina zinc pot

[0095] Since the ambient temperature in the workshop is much lower than the temperature of the zinc bath, the surface of the zinc bath will continuously radiate heat to the outside during production. This invention is the first to accurately obtain the free heat dissipation power of the zinc liquid surface in the high-alumina zinc pot by observing the temperature change inside the high-alumina zinc pot when the machine is stopped.

[0096] During normal production, the weight of the zinc bath in the high-alumina zinc pot is calculated in Wg (e.g., 270t). The specific heat capacity of the zinc-aluminum mixture in the high-alumina zinc pot can be calculated based on the aluminum-zinc ratio. For example, when the aluminum content in the zinc bath is approximately 55%, the specific heat capacity of the zinc liquid is 388 J / kg·K; the specific heat capacity of the aluminum liquid is 897 J / kg·K. The specific heat capacity of the zinc-aluminum mixture, a3, is calculated as a3 = 388 * 0.45 + 897 * 0.55 = 668 J / kg·K. Therefore, the heat released when the zinc bath temperature drops by 1°C is calculated as Wg * a3 (e.g., 270 * 668 = 1.8 × 10⁻⁶). 5 kJ).

[0097] In specific operation, the free heat dissipation Q from the surface of the high-alumina zinc pot molten zinc is... Loss The method for obtaining the value is as follows: The continuous hot-dip high-alumina zinc galvanizing unit is shut down, strip steel production is stopped, air knife purging is stopped, and molten high-alumina zinc is not added to the high-alumina zinc bath. At this time, the only factor affecting the zinc bath temperature is the free heat dissipation from the zinc bath surface. The temperature change of the thermocouple inside the high-alumina zinc bath is observed and measured (for example, the time required for the zinc bath temperature to drop by 1℃ is 570s). Based on this, the free heat dissipation power P from the zinc liquid surface of the high-alumina zinc bath is calculated. Loss (Based on the data mentioned above, P) Loss It can be 1.8×10 5 / 570=316kW), thus obtaining the free heat dissipation Q from the surface of the high-alumina zinc pot zinc liquid. Loss .

[0098] (6) Calculation of heat dissipation by air knife blowing

[0099] An air knife is positioned above the high-alumina zinc bath, continuously purging the surface of the zinc bath during production, thus accelerating the heat transfer process from the liquid to the outside. This invention innovatively calculates the heat dissipation and power of the air knife purging process by observing temperature changes inside the high-alumina zinc bath during shutdown.

[0100] In specific operation, the air knife blows out heat Q. Wipe The method for obtaining the temperature is as follows: The continuous hot-dip high-alumina zinc galvanizing unit is shut down, strip steel production ceases, and air knife purging continues. Simultaneously, molten high-alumina zinc is not added to the high-alumina zinc bath. At this point, the only factors affecting the zinc bath temperature are free heat dissipation from the zinc bath surface and heat dissipation from air knife purging. The temperature change of the thermocouple inside the high-alumina zinc bath is observed and measured (e.g., the time required for the zinc bath temperature to drop by 1°C is 420 seconds). The free heat dissipation power P from the zinc molten surface of the high-alumina zinc bath is then used as the basis for this measurement. Loss Calculate the heat dissipation power P of air knife purging wipe (Based on the data mentioned above, P) wipe It can be 1.8×10 5 / 420-316=113kW), thus obtaining the heat dissipation Q from the air knife purging. Wipe .

[0101] II. Since the total heat input of the high-alumina zinc pot in the hot-dip high-alumina zinc galvanizing unit equals the total heat output, the following heat balance equation is established:

[0102] Q IH +Q Strip +Q zn =Q Loss +Q Wipe (8)

[0103] Among them, Q IH Q represents the heating amount of the induction heater.Strip The strip steel is added to the pot to release heat; Q zn The process involves releasing heat by pouring molten high-alumina zinc into a high-alumina zinc pot; Q Loss Q represents the free heat dissipation from the surface of the molten zinc in a high-alumina zinc pot. Wipe This is to dissipate heat through air knife blowing.

[0104] Therefore, the temperature of the strip entering the pot is based on the heat balance equation and the heat released by the strip entering the pot, Q. Strip The calculation formula is obtained, and the heat release Q of the strip entering the pot can be calculated from the remaining four parts of thermal energy. Strip ;

[0105] Q Strip =Q Loss +Q Wipe -Q zn -Q IH (9)

[0106] Q Loss Q Wipe Q zn Q IH All calculations show that, in actual calculations, since each heat energy is directly proportional to the duration of strip steel production (dur), the heat balance equation can eliminate the time and directly calculate based on the power of each heat energy. Then, based on the heat power of the remaining five components of the heat balance, the heat release power of the strip steel entering the pot can be deduced. Finally, based on the other strip steel parameters, the temperature T of the strip steel entering the pot can be solved. st This allows for temperature compensation of the plate thermometer.

[0107] Example

[0108] Based on Table 1, this embodiment uses the production performance of a hot-dip high-aluminum zinc galvanizing unit in Zhanjiang as data to calculate the calculated value of the strip steel entering the pot temperature and compare it with the measured value of the plate thermometer.

[0109] Table 1 Production Performance Table

[0110]

[0111] When the hot-dip high-alumina zinc galvanizing unit is shut down, strip steel production stops, air knife purging is stopped, and molten high-alumina zinc is not added to the high-alumina zinc bath. Temperature changes inside the high-alumina zinc bath are observed. The results show that it takes 570 seconds for the zinc bath temperature to drop by 1°C. Based on the zinc-aluminum content ratio in the zinc bath and the specific heat capacities of pure zinc and pure aluminum, the specific heat capacity of the high-alumina zinc solution is calculated to be 668 J / kg·K. Furthermore, considering the weight of the zinc bath in the high-alumina zinc bath during normal production (Wg = 270t), the heat released when the zinc bath temperature drops by 1°C is calculated to be 270 * 668 = 1.8 × 10⁻⁶. 5 kJ, from which P can be calculated Loss =1.8×10 / 570=316kW.

[0112] When the hot-dip high-alumina zinc galvanizing unit is shut down, strip steel production stops, air knife purging continues, and molten high-alumina zinc is not added to the high-alumina zinc bath. Temperature changes inside the high-alumina zinc bath are observed. The results show that the time required for the zinc bath temperature to drop by 1℃ is 420s. This, combined with the zinc bath weight Wg = 270t during normal production, the zinc bath's heat capacity of 668J / kg·K, and P... Loss =316kW, from which P can be calculated wipe =270*668 / 420-316=113kW.

[0113] According to the heat balance formula (8), the free heat dissipation power P on the zinc bath surface is known. Loss Air knife blowing heat dissipation power P Loss Given the duration of strip production (i.e., the plate-passing time), the corresponding heat can be calculated.

[0114] According to the heat balance formula (8), all heat energy is proportional to the duration of strip production, so the heat balance equation can eliminate the time and directly calculate based on the power of each heat energy.

[0115] As shown in Table 1, the heating power P of the induction heater IH Since the two induction heaters IH1 and IH2 operate for the same time, therefore P IH =Power of High-Aluminum Zinc Boiler 1#IH1 + Power of High-Aluminum Zinc Boiler 2#IH2 = 171.17 + 167.18 = 338.35kW.

[0116] In the hot-dip high-alumina zinc galvanizing unit, the molten high-alumina zinc liquid in the pre-melting pot flows into the high-alumina zinc pot through a chute. The relevant data is shown in Table 1. The temperature of the high-alumina zinc liquid in the pre-melting pot is higher than that in the high-alumina zinc pot. This process actually releases heat from the molten high-alumina zinc liquid. In this embodiment, the aluminum content in the molten high-alumina zinc liquid from the pre-melting pot is 55%, the specific heat capacity of the zinc liquid is 388 J / kg·K, and the specific heat capacity of the aluminum liquid is 897 J / kg·K. The specific heat capacity of the zinc-aluminum mixture is a3 = 388 * 0.45 + 897 * 0.55 = 668 J / kg·K. The weight of the added zinc ingot is 683.02 kg. Under normal circumstances, when the zinc ingot is completely dissolved, the weight of the added zinc ingot is equal to the weight of the molten high-alumina zinc. Therefore, the weight of the molten high-alumina zinc is Wg = 683.02 kg. The temperature of the molten zinc added to the high-alumina zinc pot is Tba = 890.99 K, and the temperature of the zinc bath in the high-alumina zinc pot is Tme = 865.24 K.

[0117] Therefore, the heat release power P of molten high-alumina zinc entering the high-alumina zinc pot zn=Wg×(a3×(Tba-Tme)) / dur=683.02*[668*(890.99-865.24)] / 1800=6.53kW.

[0118] Calculate P based on the heat balance formulas (8) and (9). strip =316+113-6.53-338.35=84.12kW; strip speed v=4849 / 1800=2.69m / s, combined with the heat released by the strip entering the high-alumina zinc pot (4) and (5), the temperature of the strip entering the pot is 600.25℃. At this time, the temperature measured by the plate thermometer is 598.39℃, with a deviation of 1.86℃. The temperature of the strip entering the pot obtained by the heat balance equation is close to the temperature of the strip entering the pot measured by the plate thermometer over the years, which is in line with the general law of strip production and the production experience over the years. Therefore, it can meet the needs of the site.

[0119] In summary, this invention calculates the strip steel entry temperature based on the heat balance equation, which can compensate for the operation of the plate thermometer, solve the deviation in the plate thermometer's measurement of strip steel temperature, thereby reducing the amount of zinc dross generated during hot-dip high-aluminum zinc galvanizing and improving the coating quality of the strip steel surface.

[0120] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A method for calculating the strip temperature entering the boiler in a continuous hot-dip galvanizing high-aluminum zinc unit based on the heat balance equation, characterized in that: The production environment of the high-alumina zinc pot in the hot-dip high-alumina zinc galvanizing unit was analyzed. The various heat expenditure and heat input items in the high-alumina zinc pot area of ​​the hot-dip high-alumina zinc galvanizing unit were determined and calculated. Based on this, a heat balance equation was established, and the temperature of the strip entering the pot was calculated according to the heat balance equation.

2. The method for calculating the strip temperature entering the boiler in a continuous hot-dip galvanizing high-aluminum zinc unit based on the heat balance equation as described in claim 1, characterized in that... The heat input item for the high-alumina zinc bath area of ​​the hot-dip galvanizing unit includes the heating amount Q of the induction heater. IH , The steel strip is put into the pot to release heat Q Strip 1. Molten high-alumina zinc is poured into a high-alumina zinc pot, releasing heat Q. zn ; The heat expenditure item in the high-alumina zinc pot area of ​​the hot-dip high-alumina zinc galvanizing unit includes the free heat dissipation Q from the surface of the zinc liquid in the high-alumina zinc pot. Loss Air knife blowing heat dissipation Q Wipe .

3. The method for calculating the strip temperature entering the boiler in a continuous hot-dip galvanizing high-aluminum zinc unit based on the heat balance equation as described in claim 2, characterized in that: The heating amount Q of the induction heater IH The calculation formula is as follows: Q IH =IH1_AVR×IH1_dur+IH2_AVR×IH2_dur P IH (IH1_AVR·IH1_hard+IH2_AVR·IH2_hard) / hard Where IH1_AVR and IH2_AVR are the average power of induction heaters IH1 and IH2 during the strip steel production process, respectively, in kW; IH1_dur and IH2_dur are the working times of induction heaters IH1 and IH2, respectively, in seconds. dur represents the duration of strip steel production, measured in seconds. P IH This refers to the heating power of the induction heater, measured in kW.

4. The method for calculating the strip temperature entering the boiler in a continuous hot-dip galvanizing high-aluminum zinc unit based on the heat balance equation as described in claim 2, characterized in that: The heat Q released when the strip steel is put into the pot Strip The calculation formula is as follows: Q Strip =P st ×dur P st =s×v×ρ t ×CS Among them, P st The heat release power of the strip steel entering the pot is expressed in kW. dur represents the duration of strip steel production, measured in seconds (s). s is the cross-sectional area of ​​the strip steel, in meters. 2 ; v is the strip speed, in m / s; ρ t The density of the strip steel is taken as 7.8 × 10⁻⁶. 3 kg / m 3 ; CS is the specific heat capacity of strip steel when the temperature changes rapidly, in J / kg·K; T st The temperature at which the strip enters the pot is expressed in K. T ba This refers to the zinc bath temperature, expressed in Kelvin (K). a2, b2, c2, and d2 are the heating coefficients of the strip steel, which are 504.2 J / kg·K, -0.1309 J / kg·K, and -5.179 × 10⁻⁶ J / kg·K, respectively. - 6 J / kg·K, 4.4797×10 -4 J / kg·K.

5. The method for calculating the strip temperature entering the boiler in a continuous hot-dip galvanizing high-aluminum zinc unit based on the heat balance equation as described in claim 2, characterized in that: The molten high-alumina zinc is added to the high-alumina zinc pot, releasing heat Q. zn The calculation formula is: Q zn =P zn ×dur P zn =Wg×[a3×(Tba-Tme)] / (1000×dur1) Among them, P zn The heat release power of molten high-alumina zinc entering a high-alumina zinc pot is expressed in kW. dur represents the duration of strip steel production, measured in seconds (s). Wg represents the mass of molten high-aluminum zinc added to the high-aluminum zinc pot, in kg. Tba is the temperature at which the molten high-aluminum zinc is added to the high-aluminum zinc pot, in K; Tme is the zinc bath temperature in the high-alumina zinc pot, in K; a3 is the specific heat capacity of the zinc-aluminum mixture in the high-aluminum zinc pot; dur1 is the time taken for the molten high-aluminum zinc to reach the zinc bath temperature, measured in seconds.

6. The method for calculating the strip temperature entering the boiler in a continuous hot-dip galvanizing high-aluminum zinc unit based on the heat balance equation according to claim 2, characterized in that: The free heat dissipation Q from the surface of the high-alumina zinc pot zinc liquid Loss The method for obtaining the data is as follows: The continuous hot-dip high-alumina zinc galvanizing unit is shut down, air knife purging is stopped, and molten high-alumina zinc is not added to the high-alumina zinc pot. The temperature change of the thermocouples inside the high-alumina zinc pot is monitored, and the free heat dissipation power P from the surface of the zinc liquid in the high-alumina zinc pot is calculated. Loss This allows for the acquisition of Q, the amount of free heat dissipation from the surface of the high-alumina zinc pot's molten zinc. Loss .

7. The method for calculating the strip temperature entering the boiler in a continuous hot-dip galvanizing high-aluminum zinc unit based on the heat balance equation as described in claim 6, characterized in that: The heat dissipation Q of the air knife blowing Wipe The method for obtaining the data is as follows: The continuous hot-dip high-alumina zinc galvanizing unit is shut down, the air knife continues purging, and molten high-alumina zinc is not added to the high-alumina zinc pot. The temperature change of the thermocouple inside the high-alumina zinc pot is monitored, and the free heat dissipation power P from the surface of the zinc liquid in the high-alumina zinc pot is determined. Loss Calculate the heat dissipation power P of air knife purging wipe Thus, the heat dissipation Q from the air knife blowing is obtained. Wipe .

8. The method for calculating the strip temperature entering the boiler in a continuous hot-dip galvanizing high-aluminum zinc unit based on the heat balance equation according to claim 2, characterized in that: The total heat input of the high-aluminum-zinc galvanizing unit's high-aluminum-zinc pot is equal to the total heat output, thus establishing the following heat balance equation: Q IH +Q Strip +Q zn =Q Loss +Q Wipe Among them, Q IH Q represents the heating amount of the induction heater. Strip The strip steel is added to the pot to release heat; Q zn The process involves releasing heat by pouring molten high-alumina zinc into a high-alumina zinc pot; Q Loss Q represents the free heat dissipation from the surface of the molten zinc in a high-alumina zinc pot. Wipe This is to dissipate heat through air knife blowing.

9. The method for calculating the strip temperature entering the boiler in a continuous hot-dip galvanizing high-aluminum zinc unit based on the heat balance equation according to claim 2, characterized in that: The temperature at which the strip enters the pot is determined based on the heat balance equation and the heat released Q upon entering the pot. Strip The calculation formula is obtained.

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