A method for calculating a slab entry temperature of a heating furnace

Abstract

The application discloses a slab entry temperature calculation method of a heating furnace. Firstly, the slab temperatures of each slab reaching a hot rolling conveying roller are calculated according to the continuous casting initial temperatures of each point in the thickness direction of the slab and the continuous casting cutting time; then the slab temperatures of each slab leaving the hot rolling conveying roller are calculated according to the conveying time; secondly, the slab temperatures of each destination are calculated based on the different destinations of each slab after leaving the hot rolling conveying roller; finally, the temperature measurements of the upper surface and the lower surface of the slab are completed through the temperature measuring instrument arranged before entering the furnace, and then the determination of the slab entry temperature is completed according to the comparison between the measured values and the calculated values of the upper surface temperature and the lower surface temperature. The slab entry temperature calculation method of the heating furnace is accurate in tracking the temperature based on the different paths and time of the slab before entering the furnace since the continuous casting of the slab, and the correction of the entry temperature is established in combination with the upper surface temperature detection and the lower surface temperature detection, so that the determination of the entry temperature is more accurate.

Description

Technical Field

[0001] This invention belongs to the field of combustion control technology for metallurgical heating furnaces, and specifically relates to a method for calculating the temperature of a slab entering a heating furnace. Background Technology

[0002] The slab temperature entering the furnace varies greatly depending on the interval and path of continuous casting. Some slabs enter the furnace 20 minutes after continuous casting is completed; these are called direct-loading slabs, and their furnace temperature is often above 800℃. Other slabs are stored in a holding pit or holding furnace for several hours before entering the furnace, with a furnace temperature of around 400-600℃; these are called hot slabs. Still other slabs are stored in the slab warehouse for several days before entering the furnace, with a furnace temperature of only room temperature; these are called cold slabs.

[0003] Regarding the issue of accurately measuring the furnace entry temperature of slabs, the existing technology involves infrared thermography of the upper surface of each slab before it enters the furnace. If the measured temperature is greater than 100℃, then the measured temperature is the furnace entry temperature of the upper and lower surfaces of the slab. The other three points along the thickness direction are calculated using empirical functions to ensure the highest temperature at the center and symmetrical temperatures across the top and bottom. If the measured temperature is less than 100℃, then all five points along the thickness direction represent ambient temperature.

[0004] The main problems with this method are as follows: a) Except for cold billets with lower furnace entry temperatures, the temperatures of slabs entering the furnace cannot be symmetrical due to differences in stacking methods and convection coefficients; b) On-site production reports indicate that the calculation accuracy for slabs with higher furnace entry temperatures has certain issues. This is because while the surface temperatures of slabs from different paths, at different storage times, and in different storage locations may be similar, their core temperatures may differ. These problems directly affect the accuracy of subsequent temperature tracking of the slabs in the heating furnace, and to date, there is no good method to improve this issue.

[0005] The invention application with application number CN201910472522.4 discloses "a comprehensive control method for slabs entering a hot-rolled heating furnace". The method includes the following steps: S1, verifying the relevant data of slab weight; S2, verifying the measured temperature data of slab; S3, verifying the relevant data of slab length; S4, verifying the relevant data of slab width.

[0006] Invention application CN202211319895.6 discloses "a method, apparatus, equipment, and computer storage medium for predicting the temperature of a slab entering a furnace." The method involves obtaining measured temperature values ​​of multiple slabs in a stack; obtaining the position of each slab within the stack; and obtaining a prediction result based on the position of a first slab within the stack and its measured temperature value. The first slab can be any one of the multiple slabs. In this method, the measured temperature values ​​of each slab are obtained using a high-temperature furnace entry gauge. Then, based on the position of the first slab within the stack, the measured temperature values ​​are used as calculation data to predict the temperature of the first slab, thereby obtaining a more accurate prediction result. Summary of the Invention

[0007] To address the above problems, this invention provides a method for calculating the furnace entry temperature of a heating furnace slab, the specific technical solution of which is as follows:

[0008] A method for determining the furnace entry temperature of a slab in a heating furnace includes the following steps:

[0009] S1: Calculate the slab temperature at which each slab reaches the hot rolling conveyor roller table based on the initial continuous casting temperature and continuous casting cutting time at each point in the slab thickness direction.

[0010] S2: Calculate the slab temperature of each slab when it leaves the hot rolling conveyor roller table based on the conveying time;

[0011] S3: Monitor the destination of each slab after it leaves the hot rolling conveyor rollers;

[0012] When the monitoring indicates that the slab has left the hot rolling conveyor and entered the holding furnace, proceed to step S4;

[0013] When the monitoring shows that the slab has left the hot rolling conveyor and entered the heat preservation pit, proceed to step S5;

[0014] If the monitoring indicates that the slab is directly fed into the furnace after leaving the hot rolling conveyor rollers, proceed to step S6;

[0015] S4: Calculate the slab temperature when the slab leaves the holding furnace based on the time the slab spends in the holding furnace, and proceed to step S6;

[0016] S5: Calculate the slab temperature when the slab leaves the insulation pit based on the time the slab spends in the insulation pit, and proceed to step S6.

[0017] S6: The temperature of the upper and lower surfaces of the slab is measured by a temperature measuring instrument installed before entering the furnace. The furnace entry temperature of the slab is then determined by comparing the measured values ​​of the upper and lower surface temperatures with their respective calculated values.

[0018] Furthermore,

[0019] Step S2 involves calculating the slab temperature of each slab as it leaves the hot rolling conveyor rollers.

[0020] In step S4, the slab temperature is calculated when the slab leaves the holding furnace.

[0021] The calculation of the slab temperature when the slab leaves the insulation pit in step S5 is completed by combining the heat conduction equation with the convection temperature drop model.

[0022] The heat conduction equation is:

[0023]

[0024] The convective temperature drop model is as follows:

[0025]

[0026] In the above formula,

[0027] ρ: Slab density, unit: kg / m³ 3 ;

[0028] C: Specific heat of slab, unit: J / kg℃;

[0029] V: Mesh volume, unit: m 3 ;

[0030] λ: Thermal conductivity of slab, unit: W / m·℃;

[0031] Δy: The distance of a small grid segment in the thickness direction of the slab;

[0032] Δτ: Time step;

[0033] t 1 Current temperature, in °C;

[0034] t 2 Temperature at the next time step, in °C;

[0035] i: The coordinate position of a node in the thickness direction of the slab;

[0036] When i = 1, Q = Q1. When i = 5, Q = Q2. When i = 2, 3, 4, Q = 0;

[0037] Q1: Heat flow at the nodes on the upper surface of the slab, unit: W;

[0038] Q2: Heat flow at the node on the lower surface of the slab, unit: W;

[0039] A: Heated surface area of ​​the slab, unit: m² 2 ;

[0040] h 上 Convection coefficient of the upper surface of the slab, unit: W / km 2 ;

[0041] h 下 Convection coefficient of the lower surface of the slab, W / km 2 ;

[0042] T(1): Temperature of the upper surface of the slab, unit: °C;

[0043] T(5): Temperature of the lower surface of the slab, unit: °C;

[0044] Te: Ambient temperature, unit: °C.

[0045] Furthermore,

[0046] When calculating the real-time slab temperature from the time the slab arrives at the hot rolling conveyor rollers until it leaves the hot rolling conveyor rollers, the corresponding convection coefficient on the upper surface of the slab is taken as 40 W / km. 2 The convection coefficient of the lower surface is taken as 20 W / km. 2 The ambient temperature is set at 20℃.

[0047] When calculating the real-time slab temperature from its arrival at the holding furnace until its departure from the holding furnace section, the corresponding convection coefficient of the slab's upper surface is taken as 20 W / km. 2 The convection coefficient of the lower surface is taken as 10 W / km. 2 The ambient temperature is set at 500℃;

[0048] When calculating the real-time temperature of the slab from its arrival at the insulation pit until its departure from the insulation pit, the corresponding convection coefficient of the upper surface of the slab is taken as 20 W / km. 2 The convection coefficient of the lower surface is taken as 10 W / km. 2 The ambient temperature is set at 20℃.

[0049] Furthermore,

[0050] Because the slabs are stacked in a stacked manner when they enter the holding furnace or holding pit, they form slab stack blocks.

[0051] Therefore, the determination of the initial temperature of the slab when it enters the holding furnace or holding pit is based on treating the stacked slab blocks as a whole; specifically:

[0052] The temperature of the first slab entering the stack is taken as the initial lower surface temperature of the stack.

[0053] The contact surface between adjacent slabs is taken as a temperature point in the thickness direction, and the initial temperature of this temperature point is characterized by the average of the upper surface temperature of the lower slab and the lower surface temperature of the upper slab.

[0054] The temperature of the top surface of the last slab to enter the stack is taken as the initial top surface temperature of the stack.

[0055] The initial temperature of the remaining temperature points in the thickness direction of each slab in the stacked block is characterized by the corresponding temperature at which they entered.

[0056] Furthermore,

[0057] Step S6 is as follows:

[0058] When the absolute value of the difference between the measured value and the calculated value of the upper surface temperature of the slab exceeds the set threshold, and when the absolute value of the difference between the measured value and the calculated value of the lower surface temperature of the slab exceeds the set threshold, the calculated value temperature is used directly to characterize the slab temperature entering the furnace.

[0059] If the absolute value of the difference between the measured value and the calculated value of the upper surface temperature of the slab does not exceed the set threshold and the absolute value of the difference between the measured value and the calculated value of the lower surface temperature of the slab does not exceed the set threshold, the temperature of the slab entering the furnace is determined based on the set first correction operation.

[0060] When the absolute value of the difference between the measured value and the calculated value of the upper surface temperature of the slab exceeds the set threshold, or when the absolute value of the difference between the measured value and the calculated value of the lower surface temperature of the slab exceeds the set threshold, the temperature of the slab entering the furnace is determined based on the set second correction calculation.

[0061] Furthermore,

[0062] The threshold values ​​for the absolute difference between the measured and calculated values ​​of the temperature on the upper surface of the slab and the threshold values ​​for the absolute difference between the measured and calculated values ​​of the temperature on the lower surface of the slab are both taken from any value within the range (100-300℃).

[0063] Furthermore,

[0064] The first correction operation is specifically as follows:

[0065] T1=Ru

[0066]

[0067]

[0068]

[0069] T 5 = R d

[0070] In the above formula,

[0071] T1, T2, T3, T4, T5: Temperature points from top to bottom along the thickness direction of the slab;

[0072] Ru: Measured value of the upper surface temperature, unit: °C;

[0073] Rd: Measured value of the lower surface temperature, unit: °C;

[0074] t1, t2, t3, t4, t5: Calculated temperatures at various points along the thickness of the slab from top to bottom, in °C.

[0075] Furthermore,

[0076] When the absolute value of the difference between the measured and calculated values ​​of the upper surface temperature of the slab exceeds a set threshold, while the absolute value of the difference between the measured and calculated values ​​of the lower surface temperature of the slab does not exceed the set threshold, the corresponding second correction calculation is performed, specifically as follows:

[0077]

[0078]

[0079]

[0080]

[0081] T5 = Rd

[0082] In the above formula,

[0083] T1, T2, T3, T4, T5: Temperature points from top to bottom along the thickness direction of the slab;

[0084] Rd: Measured value of the lower surface temperature, unit: °C;

[0085] t1, t2, t3, t4, t5: Calculated temperatures at various points along the thickness of the slab from top to bottom, in °C.

[0086] Furthermore,

[0087] When the absolute value of the difference between the measured and calculated values ​​of the upper surface temperature of the slab does not exceed the set threshold, but the absolute value of the difference between the measured and calculated values ​​of the lower surface temperature of the slab exceeds the set threshold, the corresponding second correction calculation is performed, specifically as follows:

[0088] Specifically:

[0089] T1=Ru

[0090]

[0091]

[0092]

[0093]

[0094] In the above formula,

[0095] T1, T2, T3, T4, T5: Temperature points from top to bottom along the thickness direction of the slab;

[0096] Ru: Measured value of the upper surface temperature, unit: °C;

[0097] t1, t2, t3, t4, t5: Calculated temperatures at various points along the thickness of the slab from top to bottom, in °C.

[0098] Furthermore,

[0099] The measured values ​​of the upper and lower surface temperatures of the slab are both represented by the maximum values ​​along the length of the slab.

[0100] This invention discloses a method for calculating the slab entry temperature in a heating furnace. First, two infrared thermometers are installed on the furnace entry side, aimed at the upper and lower surfaces of the slab before it enters the furnace. This addresses the previous method using only one thermometer, which resulted in completely symmetrical slab temperatures. Simultaneously, the center temperature of each slab is optimized along its thickness direction based on the measured upper and lower surface temperatures, the slab's different paths and times in the slab storage, the initial continuous casting temperature, and its position in the storage. This makes the calculated slab entry temperature (initial value for slab heating furnace thermal tracking) more accurate and helps improve the accuracy of subsequent slab temperature calculations within the furnace, thereby improving the quality of slab production and reducing unnecessary energy consumption. Attached Figure Description

[0101] Figure 1 This is a schematic diagram illustrating the determination steps of the present invention;

[0102] Figure 2 This is a schematic diagram illustrating the determination process in an embodiment of the present invention;

[0103] Figure 3 This is a schematic diagram of the stacked blocks of slabs entering the heat preservation furnace or heat preservation pit in this invention. Detailed Implementation

[0104] The following is a further detailed description of a method for calculating the furnace entry temperature of a heating furnace slab according to the present invention, based on the accompanying drawings and specific embodiments.

[0105] The slab temperature mentioned in this technical solution refers to the temperature of five temperature points evenly distributed along the thickness direction of a conventional slab; this is a basic common sense point, and all slab temperatures mentioned in this technical solution are taken as the basis for understanding.

[0106] A method for determining the furnace entry temperature of a slab in a heating furnace, such as... Figure 1 As shown, it includes the following steps:

[0107] S1: Calculate the slab temperature at which each slab reaches the hot rolling conveyor roller table based on the initial continuous casting temperature and continuous casting cutting time at each point in the slab thickness direction.

[0108] S2: Calculate the slab temperature of each slab when it leaves the hot rolling conveyor roller table based on the conveying time;

[0109] S3: Monitor the destination of each slab after it leaves the hot rolling conveyor rollers;

[0110] When the monitoring indicates that the slab has left the hot rolling conveyor and entered the holding furnace, proceed to step S4;

[0111] When the monitoring shows that the slab has left the hot rolling conveyor and entered the heat preservation pit, proceed to step S5;

[0112] If the monitoring indicates that the slab is directly fed into the furnace after leaving the hot rolling conveyor rollers, proceed to step S6;

[0113] S4: Calculate the slab temperature when the slab leaves the holding furnace based on the time the slab spends in the holding furnace, and proceed to step S6;

[0114] S5: Calculate the slab temperature when the slab leaves the insulation pit based on the time the slab spends in the insulation pit, and proceed to step S6.

[0115] S6: The temperature of the upper and lower surfaces of the slab is measured by a temperature measuring instrument installed before entering the furnace. The furnace entry temperature of the slab is then determined by comparing the measured values ​​of the upper and lower surface temperatures with their respective calculated values.

[0116] The specific working process and principles of the above steps are as follows. The following understanding can be combined with... Figure 2 , 3 conduct:

[0117] Step 1: Install two infrared thermometers beside the roller conveyor before the slab enters the heating furnace. One thermometer is positioned over the upper surface of the slab along its length, while the other is used to lower the slab to the roller conveyor using a crane. While the slab is still in the air, the temperature measured is the lower surface along the length of the slab. Regardless of the upper or lower surface, the measured temperature will be the maximum value along the length of the slab.

[0118] Step Two: The computer control system can collect information such as the initial continuous casting temperature of the slab to be fed into the furnace, the continuous casting cutting time, the current furnace feeding time, and the time and path position of the slab in the slab storage. Based on the above information, a convection temperature drop model and an internal heat conduction model in the thickness direction of the slab are constructed. The temperature distribution at five points in the thickness direction of the slab before entering the furnace is calculated. The specific formulas are as follows:

[0119] Convection temperature drop models are constructed based on the slab in different paths:

[0120] Q1 = A × h 上 ×(T e -T(1))

[0121] Q2=A×h 下 ×(T e -T(5))

[0122] Where: Q1—heat flow at the node on the upper surface of the slab, W,

[0123] Q2—Heat flow rate at the node on the lower surface of the slab, in W.

[0124] A – Heated surface area of ​​the slab, m 2 ,

[0125] htop — Convection coefficient of the upper surface of the slab, W / km- 2 Different values ​​are used depending on the path of the slab. For example, 40 is used in an outdoor environment, while 20 is used in an insulation pit or furnace.

[0126] h_lower—Convection coefficient of the lower surface of the slab, W / km 2 Because the lower surface of the slab has less contact with the outside environment, 20 is used whether it is in the outdoor environment or in the heat preservation pit and heat preservation furnace.

[0127] T(1) — Temperature of the upper surface of the slab, °C

[0128] T(5) — Temperature of the lower surface of the slab, °C

[0129] Te – Ambient temperature, which varies depending on the path taken by the slab. For example, it is taken as room temperature in an outdoor environment, 20℃ in an insulation pit, and 500℃ in an insulation furnace.

[0130] The heat conduction equations for each node of the slab are constructed based on the convection temperature drop model as follows:

[0131]

[0132] Where: ρ—slab density, kg / m³ 3

[0133] c—Specific heat of slab, J / kg℃

[0134] λ—thermal conductivity of the slab, W / m·℃

[0135] Δy—the distance of a small section of the grid in the thickness direction of the slab.

[0136] Δτ — time step

[0137] t—slab temperature, t 1 Let t be the temperature at the current moment. 2 Temperature at the next time step

[0138] i—Coordinate position of a node along the thickness direction of the slab

[0139] When i = 1, Q = Q1. When i = 5, Q = Q2. When i = 2, 3, 4, Q = 0.

[0140] It's important to note that when slabs are stacked in the insulation pit or furnace of the slab warehouse, it's not a single slab in one stack, but rather multiple slabs stacked together. Therefore, when calculating the slab temperature, the boundary conditions of just one slab cannot be considered. Instead, all slabs above and below the stack must be treated as a single unit for temperature drop calculation. If a stack has N slabs (typically N = 10), there are 5 × N - (N - 1) temperature calculation points along the thickness direction, with one calculation point for the vertical distance between adjacent slabs. The boundary condition for the upper surface of the top slab in the stack is Q1, and the boundary condition for the lower surface of the bottom slab is Q2. The temperature values ​​of other adjacent slabs are calculated by averaging. For example, if the lower surface of the second slab and the upper surface of the third slab come into contact, the temperature will be the average of the two.

[0141] The specific values ​​for the convection coefficient are shown in the table below:

[0142] <![CDATA[Convection coefficient of the upper surface W / Km 2 > <![CDATA[Lower surface convection coefficient W / Km 2 > Ambient temperature ℃ On the roller conveyor from continuous casting to hot rolling 40 20 20 Insulation furnace 20 10 500 Slab storage insulation pit 20 10 20

[0143] Step 3: If the difference between the infrared temperature measurement of the upper and lower surface temperatures of the slab and the temperature calculated by the slab temperature drop model is greater than 200℃ (in principle, any value within the range (100, 300) can be used, but 200℃ is preferred here), then the infrared temperature measurement is considered to have a significant deviation. The slab entry temperature at 5 points along the thickness direction is equal to the value calculated by the slab temperature drop model.

[0144] Step 4: Assume that the temperatures in the thickness direction of the slab calculated by the slab temperature drop model are t1, t2, t3, t4, t5 from top to bottom; the upper surface temperature of the slab detected by infrared is Ru, and the lower surface temperature is Rd; the optimized and fitted slab furnace entry temperatures in the thickness direction are T1, T2, T3, T4, T5 from top to bottom.

[0145] When the difference between the infrared temperature measurement of the upper and lower surface temperatures of the slab and the calculated upper and lower surface temperatures of the slab is within 200℃, the infrared temperature measurement is considered normal. The upper surface temperature of the slab entering the furnace is equal to the upper surface temperature measured by infrared radiation, and the lower surface temperature of the slab entering the furnace is equal to the lower surface temperature measured by infrared radiation. Other point temperatures are adjusted proportionally to the slab temperature drop model and the infrared measurement temperatures, i.e.:

[0146] T1=Ru

[0147]

[0148]

[0149]

[0150] T5 = Rd

[0151] If the difference between the infrared temperature measurement of the upper and lower surfaces of the slab and the calculated upper and lower surface temperatures of the slab exceeds 200℃, the infrared temperature measurement at that point is considered to be biased. The fitted temperature at that point is adjusted proportionally to the slab temperature drop model and the bias-free infrared measurement temperature. If the slab is directly fed into the furnace from continuous casting and the lower surface cannot be directly measured, the lower surface temperature is also calculated using the above method. For example, if the upper surface temperature is normal but the lower surface temperature is biased:

[0152] T 1 = R u

[0153]

[0154]

[0155]

[0156]

[0157] If the lower surface test is normal but the upper surface test is abnormal, the furnace entry temperature should be adjusted according to the following determination:

[0158]

[0159]

[0160]

[0161]

[0162] T5 = Rd

[0163] Finally, the calculated furnace entry temperature values ​​at 5 points along the slab thickness direction are input into the heating furnace thermal tracking calculation model as the initial values ​​for the slab heating model.

[0164] The above method involves installing two infrared thermometers on the furnace feed side, pointing them at the upper and lower surfaces of the slab before it enters the furnace. This addresses the previous method, which used only one thermometer and resulted in perfectly symmetrical slab temperatures. Simultaneously, the temperature along the thickness of each slab is optimized and fitted based on the measured upper and lower surface temperatures, the slab's different paths and times in the slab storage, the initial continuous casting temperature, and its position in the storage. This makes the calculated slab feed temperature (the initial value for slab heating furnace thermal tracking) more accurate and helps improve the accuracy of subsequent slab temperature calculations within the furnace, thereby improving the quality of slab production and reducing unnecessary energy consumption.

[0165] Example 1:

[0166] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0167] Taking a hot rolling production line as an example, the temperature of each point in the thickness direction of a slab before it enters the walking beam furnace can be determined by the method described in this invention.

[0168] After the continuous casting and cutting process of a slab, the temperatures at five points along the thickness direction, from top to bottom, are 1100℃, 1250℃, 1350℃, 1250℃, and 1100℃. It arrives at the holding furnace of the hot rolling mill after 20 minutes. On the roller conveyor of the hot rolling mill, the ambient temperature is 20℃, and the convection coefficients of the upper and lower surfaces of the slab are taken as 40 W / km. 2 and 20W / Km 2 The temperatures at five points along the thickness direction decrease from top to bottom to 1098℃, 1165℃, 1196℃, 1191℃, and 1158℃. Ten slabs at different temperatures were stacked in one position within the holding furnace. This particular slab was the fifth one from the top in the stack. After being stored in the holding furnace for 240 minutes, it entered the pre-furnace roller conveyor of the heating furnace for temperature measurement of its upper and lower surfaces. The temperature in the holding furnace was 500℃, and the convection coefficient of the uppermost slab surface in the holding furnace was taken as 20 W / km. 2 The convection coefficient of the lower surface of the bottommost slab is taken as 10 W / km. 2 Treating the 10 slabs on the stack in the heat-insulating furnace as a whole, the temperatures at five points along the thickness direction of each slab decrease from top to bottom to 628℃, 656℃, 671℃, 672℃, and 660℃. Afterwards, the slabs are subjected to temperature measurements on the upper and lower surfaces on the roller conveyor before entering the furnace. The measured temperature on the upper surface is 591℃, and the measured temperature on the lower surface is 645℃. The fitted temperature based on the calculated and measured temperatures at each point along the thickness direction of the slab is:

[0169] T1 = 591℃

[0170]

[0171]

[0172]

[0173] T5 = 645℃

[0174] Finally, points T1 to T5 are used as the initial values ​​for the heating furnace thermal tracking model for subsequent calculations.

[0175] The heating furnace has completed a new batch of controlled production. Using this method to calculate the charging temperature, the new average calculated charging temperature is 634℃, the charging temperature is 1180℃, the furnace time is 181 minutes, and the rolling mill temperature is 1023℃. The average rolling mill temperature drop is 157℃. This helps reduce the rolling mill temperature drop by 7℃, indirectly reducing the heating furnace's energy consumption. Meanwhile, production quality has not been affected.

Claims

1. A method for determining the furnace entry temperature of a slab in a heating furnace, characterized in that... Includes the following steps: S1: Calculate the slab temperature at which each slab reaches the hot rolling conveyor roller based on the initial continuous casting temperature and continuous casting cutting time at each point in the slab thickness direction. S2: Calculate the slab temperature of each slab when it leaves the hot rolling conveyor roller table based on the conveying time; S3: Monitor the destination of each slab after it leaves the hot rolling conveyor rollers; When the monitoring indicates that the slab has left the hot rolling conveyor and entered the holding furnace, proceed to step S4; When the monitoring shows that the slab has left the hot rolling conveyor and entered the heat preservation pit, proceed to step S5; If the monitoring indicates that the slab is directly fed into the furnace after leaving the hot rolling conveyor rollers, proceed to step S6; S4: Calculate the slab temperature when the slab leaves the holding furnace based on the time the slab spends in the holding furnace, and proceed to step S6; S5: Calculate the slab temperature when the slab leaves the insulation pit based on the time the slab spends in the insulation pit, and proceed to step S6. S6: The temperature of the upper and lower surfaces of the slab is measured by a temperature measuring instrument installed before entering the furnace. The furnace entry temperature of the slab is then determined by comparing the measured values ​​of the upper and lower surface temperatures with their respective calculated values. Step S6 is as follows: When the absolute value of the difference between the measured value and the calculated value of the upper surface temperature of the slab exceeds the set threshold, and when the absolute value of the difference between the measured value and the calculated value of the lower surface temperature of the slab exceeds the set threshold, the calculated value temperature is used directly to characterize the slab temperature entering the furnace. If the absolute value of the difference between the measured value and the calculated value of the upper surface temperature of the slab does not exceed the set threshold and the absolute value of the difference between the measured value and the calculated value of the lower surface temperature of the slab does not exceed the set threshold, the temperature of the slab entering the furnace is determined based on the set first correction operation. When the absolute value of the difference between the measured value and the calculated value of the upper surface temperature of the slab exceeds the set threshold, or when the absolute value of the difference between the measured value and the calculated value of the lower surface temperature of the slab exceeds the set threshold, the temperature of the slab entering the furnace is determined based on the set second correction calculation.

2. The method for determining the furnace entry temperature of a slab in a heating furnace according to claim 1, characterized in that: Step S2 involves calculating the slab temperature of each slab as it leaves the hot rolling conveyor rollers. In step S4, the slab temperature is calculated when the slab leaves the holding furnace. The calculation of the slab temperature when the slab leaves the insulation pit in step S5 is completed by combining the heat conduction equation with the convection temperature drop model. The heat conduction equation is: ， The convective temperature drop model is as follows: In the above formula, : Slab density, unit: ; C: Specific heat of slab, unit: ; V: Mesh volume, unit: m 3 ; Thermal conductivity of slab, unit: ; The distance of a small section of grid in the thickness direction of the slab; Time step; t 1 Current temperature, in °C; t 2 Temperature at the next time step, in °C; i: The coordinate position of a node in the thickness direction of the slab; When i=1, Q=Q1, ; When i=5, Q=Q2. When i=2,3,4, Q=0; Q1: Heat flow at the nodes on the upper surface of the slab, unit: W; Q2: Heat flow at the node on the lower surface of the slab, unit: W; A: Heated surface area of ​​the slab, unit: m²; h 上 Convection coefficient of the upper surface of the slab, unit: W / km 2 ; h 下 Convection coefficient of the lower surface of the slab, W / km 2 ; T(1): Temperature of the upper surface of the slab, unit: °C; T(5): Temperature of the lower surface of the slab, unit: °C; Te: Ambient temperature, unit: °C.

3. The method for determining the furnace entry temperature of a slab in a heating furnace according to claim 2, characterized in that: When calculating the real-time slab temperature from the time the slab arrives at the hot rolling conveyor rollers until it leaves the hot rolling conveyor rollers, the corresponding convection coefficient on the upper surface of the slab is taken as 40 W / Km. 2 The convection coefficient of the lower surface is taken as 20 W / km. 2 The ambient temperature is set at 20℃. When calculating the real-time slab temperature from its arrival at the holding furnace until its departure from the holding furnace section, the corresponding convection coefficient of the slab's upper surface is taken as 20 W / km. 2 The convection coefficient of the lower surface is taken as 10 W / km. 2 The ambient temperature is set at 500℃; When calculating the real-time temperature of the slab from its arrival at the insulation pit until its departure from the insulation pit, the corresponding convection coefficient of the upper surface of the slab is taken as 20 W / Km. 2 The convection coefficient of the lower surface is taken as 10 W / km. 2 The ambient temperature is set at 20℃.

4. The method for determining the furnace entry temperature of a slab in a heating furnace according to claim 1, characterized in that: Because the slabs are stacked in a stacked manner when they enter the holding furnace or holding pit, they form slab stack blocks. Therefore, the determination of the initial temperature of the slab when it enters the holding furnace or holding pit is based on treating the stacked slab blocks as a whole; specifically: The temperature of the first slab entering the stack is taken as the initial lower surface temperature of the stack. The contact surface between adjacent slabs is taken as a temperature point in the thickness direction, and the initial temperature of this temperature point is characterized by the average of the upper surface temperature of the lower slab and the lower surface temperature of the upper slab. The temperature of the top surface of the last slab to enter the stack is taken as the initial top surface temperature of the stack. The initial temperature of the remaining temperature points in the thickness direction of each slab in the stacked block is characterized by the corresponding temperature at which they entered.

5. The method for determining the furnace entry temperature of a slab in a heating furnace according to claim 1, characterized in that: The threshold values ​​for the absolute difference between the measured and calculated values ​​of the temperature on the upper surface of the slab and the threshold values ​​for the absolute difference between the measured and calculated values ​​of the temperature on the lower surface of the slab are taken from any value within the range of (100-300)℃.

6. The method for determining the furnace entry temperature of a slab in a heating furnace according to claim 1, characterized in that: The first correction operation is specifically as follows: In the above formula, T1, T2, T3, T4, T5: Temperature points from top to bottom along the thickness direction of the slab; Ru: Measured value of the upper surface temperature, unit: °C; Rd: Measured value of the lower surface temperature, unit: °C; t1, t2, t3, t4, t5: Calculated temperatures at various points along the thickness of the slab from top to bottom, in °C.

7. The method for determining the furnace entry temperature of a slab in a heating furnace according to claim 1, characterized in that: When the absolute value of the difference between the measured and calculated values ​​of the upper surface temperature of the slab exceeds a set threshold, while the absolute value of the difference between the measured and calculated values ​​of the lower surface temperature of the slab does not exceed the set threshold, the corresponding second correction calculation is performed, specifically as follows: In the above formula, T1, T2, T3, T4, T5: Temperature points from top to bottom along the thickness direction of the slab; Rd: Measured value of the lower surface temperature, unit: °C; t1, t2, t3, t4, t5: Calculated temperatures at various points along the thickness of the slab from top to bottom, in °C.

8. The method for determining the furnace entry temperature of a slab in a heating furnace according to claim 1, characterized in that: When the absolute value of the difference between the measured and calculated values ​​of the upper surface temperature of the slab does not exceed the set threshold, but the absolute value of the difference between the measured and calculated values ​​of the lower surface temperature of the slab exceeds the set threshold, the corresponding second correction calculation is performed, specifically as follows: In the above formula, T1, T2, T3, T4, T5: Temperature points from top to bottom along the thickness direction of the slab; Ru: Measured value of the upper surface temperature, unit: °C; t1, t2, t3, t4, t5: Calculated temperatures at various points along the thickness of the slab from top to bottom, in °C.

9. The method for determining the furnace entry temperature of a slab in a heating furnace according to claim 1, characterized in that: The measured values ​​of the upper and lower surface temperatures of the slab are both represented by the maximum values ​​along the length of the slab.

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