A method of controlling ladle slagging

Abstract

The application discloses a method for controlling ladle slagging, which comprises the following steps: setting nozzles on the same height of the side wall of a ladle, triggering the blowing of cooling gas to liquid top slag through the nozzles by the rotation of molten steel, and completing the cooling of the top slag; and through the cooling of the liquid top slag, the liquid top slag is changed into semi-solid state, and the rotation of the molten steel is inhibited. The method for controlling ladle slagging comprises the following steps: setting nozzles on the side wall of the ladle in the height range in which the molten steel starts to rotate at the end of ladle pouring, directly blowing cooling gas into high-temperature liquid top slag through the nozzles, reducing the temperature of the top slag in contact with the molten steel, increasing the viscosity of the top slag, and preventing the top slag from being pulled into the molten steel when the molten steel rotates, so that the purpose of controlling the ladle slagging is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of continuous casting process, and particularly relates to a method for controlling ladle slag. BACKGROUND

[0002] In the steel production process, the ladle is used to carry molten steel, and the top slag is on the surface layer of the molten steel in the ladle. During pouring, the height of the molten steel in the ladle gradually decreases. When the height of the molten steel decreases to a certain height, the molten steel drives the top slag to rotate. With the increase of the rotation speed, the molten steel rotation surface is concave, and a vortex is formed, which points to the ladle nozzle. The shear force generated by the vortex pulls the top slag into the vortex, and then a large amount of top slag enters the tundish with the molten steel, causing the contamination of the molten steel. The above slagging process affects the purity of the molten steel, and cannot meet the quality requirements of high-grade steel. Therefore, how to solve the ladle slagging during pouring is an important problem in the production of pure steel.

[0003] The application number CN2013104494542 discloses a "ladle slag suppressing device". The device includes a first blocking arm, a second blocking arm and a third blocking arm. The central axes of the first blocking arm and the second blocking arm are perpendicular to each other and are fixedly crossed. The central axis of the third blocking arm is perpendicular to the plane formed by the first blocking arm and the second blocking arm, and the third blocking arm penetrates the intersection of the first blocking arm and the second blocking arm. The inside of the slag suppressing device formed by the first blocking arm, the second blocking arm and the third blocking arm is a cast iron block. The outside of the cast iron block is provided with a coating layer, which is composed of the following components with a mass percentage of 89-94% CaO, 3.7-4.3% MnO, 0-0.5% Al2O3, 0-3.5% SiO2, 0-0.05% FeO, 0-0.1% Fe2O3 and 2.3-3.5% ZrO2. The device can suppress the formation of vortex, thereby preventing slagging and preventing gas from entering the tundish, and can also adsorb inclusions in the molten steel, so that the inclusions in the molten steel are further removed while the slag is blocked.

[0004] The application number CN201410805369X discloses a "method for controlling ladle slagging by blowing argon through the ring-shaped argon brick at the bottom of the ladle". The ring-shaped argon brick with a gas permeation width of 50-300mm is arranged around the taphole at the bottom of the ladle. During the pouring process of the ladle, when the pouring liquid level of the molten steel in the ladle is 150-400mm, the argon is blown into the molten steel through the ring-shaped argon brick by controlling the argon blowing pressure to be 0.2-0.7MPa, so as to suppress the ladle slagging. SUMMARY

[0005] The present application aims to provide a method for suppressing the ladle slagging under the premise that the medium does not directly remove the molten steel.

[0006] To achieve the above technical purposes, the present application provides a method for controlling ladle slagging, and the technical scheme is as follows:

[0007] A method for controlling the slagging of a ladle, characterized in that:

[0008] The nozzles are arranged at the same height on the side wall of the ladle, and the cooling gas is blown through the nozzles to the liquid top slag when the liquid steel is rotating, so as to complete the cooling of the top slag.

[0009] The liquid top slag is cooled to change from liquid state to semi-solid state, so as to inhibit the slagging of the liquid steel.

[0010] In the steelmaking process, the liquid steel height in the ladle reaches the set liquid steel height to represent the moment when the liquid steel is rotating,

[0011] The nozzles are arranged according to the set liquid steel height.

[0012] The number of the nozzles is determined according to the amount of the top slag to be cooled,

[0013] Or the nozzles are arranged at the same height on the side wall of the ladle, and the number of the nozzles is 12, and the actual number of the nozzles to be used is determined according to the amount of the top slag to be cooled.

[0014] The flow rate of the cooling gas of each nozzle is determined according to the following formula:

[0015]

[0016] In the formula,

[0017]

[0018] The initial temperature of the top slag to be cooled is determined according to the lower limit value of the liquid steel temperature.

[0019] The target temperature of the top slag to be cooled is determined by comprehensively considering the highest melting point of the top slag and the lower limit value of the liquid steel temperature.

[0020] The weight of the top slag to be cooled is determined according to 9%-11% of the total amount of the top slag in the ladle.

[0021] Further,

[0022] The cooling gas is nitrogen or argon.

[0023] Further,

[0024] The blowing of the cooling gas is triggered to be turned off when the ladle casting is completed.

[0025] Further,

[0026] The ladle weight is monitored in real time to represent whether the liquid steel height in the ladle reaches the set liquid steel height.

[0027] Further,

[0028] Specifically comprising the following steps:

[0029] S1: based on the current ladle tonnage, according to the current ladle top slag volume to be cooled and the volume of the sprayed gas, the number of nozzles is determined;

[0030] S2: Real-time monitoring of the state of the molten steel is established from the start time of the ladle pouring; when the molten steel is monitored to rotate, the cooling gas is blown to the liquid top slag through the nozzle according to the calculated flow and the set blowing duration.

[0031] Further,

[0032] The nozzles are opened at the same height of the ladle side wall, and according to the size of the ladle, one group, two groups or multiple groups are arranged in the height direction.

[0033] The method for controlling the ladle slag of the application is characterized in that: nozzles are arranged on the side wall of the ladle in the range of the height of the slag falling when the molten steel starts to rotate at the end of the ladle pouring, and cooling gas is directly blown into the high-temperature liquid top slag through the nozzles, so as to reduce the temperature of the top slag in contact with the molten steel, increase the viscosity of the top slag, and prevent the top slag from being easily pulled into the molten steel when the molten steel rotates, thereby achieving the purpose of controlling the ladle slag. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 It is a schematic diagram of the specific control steps of the application;

[0035] Figure 2 It is a schematic diagram of the side blowing cooling gas control process in the working principle part of the specific embodiment of the application;

[0036] Figure 3 It is a schematic diagram of the distribution of the top slag thickness direction in different states in the working principle part of the specific embodiment of the application;

[0037] Figure 4 It is a schematic diagram of the effect of side blowing cooling top slag in the specific embodiment of the application;

[0038] Figure 5 It is a schematic diagram of the ladle gas nozzle layout position in the embodiment of the application. DETAILED DESCRIPTION

[0039] Next, the method for controlling the ladle slag of the application will be further specifically described according to the drawings and the specific embodiment of the specification.

[0040] The understanding of the following working principle and process can be combined with Figure 1 、 2 , 3, 4, 5.

[0041] The composition system of the ladle top slag is:

[0042] CaO: 30~40%,

[0043] SiO2: 3%~10%,

[0044] Al2O3: 30~50%,

[0045] MgO: 3%~10%,

[0046] MnO: 2%~8%.

[0047] According to the slag melting point measurement of different slag components, it can be concluded that the melting point of the top slag of the component system can reach about 1530℃ at most, and the temperature of the liquid steel in the ladle is >=1570℃, so the top slag directly contacted with the liquid steel is in a completely liquid state, and there is a obvious temperature gradient in the thickness direction of the top slag from the liquid steel surface (as shown in Figure 3 , and the top slag above is in a semi-solid state), with the continuous decrease of the temperature, the amount of high melting point components precipitated in the top slag increases, and the corresponding viscosity increases, until the top slag at the air contact surface is in a completely solid state, which can be seen from Figure 3 . As can be seen from Figure 3 , the top slag contacted with the liquid steel surface is in a low viscosity liquid state because the temperature of the liquid steel is higher than the melting point of the top slag, so the shear force generated by the rotation of the liquid steel at the end of ladle pouring can pull the top slag into the vortex, thereby polluting the liquid steel; the top slag near the air surface is in a semi-solid or solid state with high viscosity because the air temperature is relatively low, so the shear force generated by the rotation of the liquid steel at the end of ladle pouring is not easy to pull the high viscosity top slag into the vortex. The technical solution can reduce the temperature of the top slag contacted with the liquid steel by setting nozzles on the side wall of the ladle and directly blowing cooling gas into the high temperature liquid top slag at the height range of the ladle slag at the end of ladle pouring, so that the viscosity of the top slag is increased, and the top slag is not easy to be pulled into the liquid steel when the liquid steel rotates, thereby achieving the purpose of controlling the ladle slag.

[0048] According to the above specific setting idea and setting process (the following description is made to the 12 equal arcs opened on the side wall of the ladle, the actual number of nozzles to be used is determined according to the amount of top slag to be cooled, the setting of 12 nozzles is to adapt to the equal arc distribution response of single nozzle or double nozzle; and the number of nozzles to be set can be determined according to the amount of top slag to be cooled, which can follow the same setting idea and process):

[0049] Referring to Figure 1 , first, based on the tonnage of the current ladle, the number of nozzles is determined according to the volume of the top slag to be cooled and the volume of the gas to be blown out;

[0050] Then, the cooling gas is blown through the nozzle by taking the liquid steel rotation as the trigger condition; in the steelmaking process, the liquid steel height in the ladle reaches the set liquid steel height to represent the rotation time of the liquid steel, the real-time monitoring of the ladle weight represents whether the liquid steel height in the ladle reaches the set liquid steel height; when the liquid steel height reaches the set target height, the cooling gas blowing valve is opened, the cooling gas is blown through the nozzle, and the blowing valve is closed until the ladle pouring is completed. In the technical solution, the set liquid steel height or the set target height is determined according to a large amount of historical data, which is about 400 mm in the technical solution, and the tonnage of the ladle only affects the radius of the ladle, but does not affect the height of the ladle. By setting the height as a constant value that does not change with the size of the ladle, the technical solution is convenient and unified.

[0051] The volume of the top slag in the current ladle that needs to be cooled is determined according to the weight of the top slag that needs to be cooled, and the weight of the top slag that needs to be cooled is determined according to the calculation of historical data as 9%-11% of the total top slag amount of the ladle, preferably 10%; the volume of the gas is calculated according to the shape of the specific nozzle, and the calculation and example of the specific numerical value are carried out in the technical solution taking the nozzle as a rectangle (the calculation of other shapes of nozzles is referred to) ;

[0052] In order to ensure the cooling effect of the top slag, the blowing amount of the cooling gas needs to be calculated, and the corresponding calculation is carried out according to the following formula:

[0053] Known conditions:

[0054] The average heat capacity of the top slag is 2.5 kJ / (kg·℃),

[0055] The weight of the top slag that needs to be cooled: 3500 kg*10% = 350 kg, that is, the total amount of the top slag is 3500 kg, and the weight of the top slag that needs to be cooled is determined according to the proportion of 10%;

[0056] The initial temperature of the top slag that needs to be cooled: 1570℃, that is, the initial temperature of the top slag that needs to be cooled is set according to the lower limit value of the liquid steel temperature; it needs to be reminded that the actual temperature will have a deviation, but the deviation degree is within the error allowable range, so this value can be set uniformly;

[0057] The target temperature of the top slag that needs to be cooled: 1550℃, that is, the target temperature of the top slag that needs to be cooled is determined by combining the highest melting point of the top slag and the lower limit value of the liquid steel temperature;

[0058] The blowing duration: 2-3 min,

[0059] The number of nozzle groups / single nozzle group: 1-3 / 4-6,

[0060] Nitrogen specific heat capacity at constant pressure: 1.038 J / (g*K),

[0061] Nitrogen initial temperature: 25℃,

[0062]

[0063] In the technical solution, since the gas blowing mode is adopted, no anti-rotation component is added in the ladle, so the molten steel pollution caused by the melting loss of the anti-rotation component will not occur; since the mode of directly blowing the cooling gas into the top slag through the nozzle on the side of the ladle wall is adopted, the problem of pollution of the molten steel caused by the gas stirring the molten steel to cause the slag entrainment is avoided; since the mode of directly blowing the cooling gas into the top slag is adopted, the temperature of the gas entering the top slag is also at the lowest, so that the cooling efficiency of the top slag is improved (see Figure 4 ); in order to ensure that the cooling gas can affect all the top slag in the circumferential range of the ladle, on the one hand, the nozzle is arranged in the range of 0~400mm in height at the bottom of the ladle, and on the other hand, according to the size of the ladle capacity, 1~3 groups of nozzles can be arranged, and each group of nozzles is arranged along the wall of the ladle according to the size of the diameter of the ladle (that is, the number of groups is arranged in the height direction, and the number of each group is arranged in the circumferential direction, see Figure 5 ). Since only the top slag in direct contact with the molten steel needs to be controlled to have a high viscosity to avoid the influence of the shear force of the molten steel on the vortex of the slag entrainment, the weight of the top slag to be cooled accounts for 10% of the total amount of the top slag in the ladle; in order to ensure that the cooling gas blowing has the best effect, the timing of the gas blowing cooling needs to be accurately controlled, that is, the gas valve needs to be started immediately after the high-temperature part of the top slag enters the nozzle range to perform the slag cooling operation. Therefore, an on-line weighing device of the ladle needs to be configured, and the weight signal of the molten steel is converted into the height signal of the molten steel in real time to trigger the opening of the cooling gas blowing valve (see Figure 2 ).

[0064] The specific determination process of the number of nozzles is as follows:

[0065] The volume of the top slag to be cooled in the ladle = π*r 2 *h; the volume of the top slag to be cooled in a 300-ton ladle is: 3.14*1.8m 2 *0.01m=0.1m 3 Generally, if 70% of the weight of the top slag reaches the target temperature, it is considered that the top slag can be effectively prevented from being pulled into the molten steel when the molten steel rotates, and then the volume of the top slag to be cooled is: 0.1*0.7=0.07m 3 .

[0066] Assuming that the gas blown out of the nozzle is rectangular, the volume of the gas blown out is 1.2m*0.7m*0.01m=0.0084m 3 , and 0.07m 3 of the top slag needs the number of nozzles to be: 0.07m 3 / 0.0084m3 ≈8.

[0067] As for the selection of cooling gas, according to whether the steel grade composition has strict requirements for nitrogen, when there is no strict requirement for N, nitrogen is selected as the cooling gas; when the steel grade composition has strict requirements for N, argon is selected as the cooling gas.

[0068] Considering the different nominal capacities of the ladles, the number of nozzle groups and single nozzle groups on the ladle wall is different, then:

[0069] The design gas flow of a single nozzle is 100L / min~300L / min; the corresponding nozzle outlet design pressure is 150~1000kpa.

[0070] Embodiment

[0071] In a certain steelmaking production process, a 100-ton ladle carries molten steel for casting. According to the size of the ladle, a group of four side-blown nozzles is symmetrically installed along the circumference of the ladle wall. Since the steel grade composition has no strict requirement for N, nitrogen is selected as the blowing gas. During the casting process, the ladle weighing system continuously weighs the ladle, and at the same time, the molten steel weight data is converted into molten steel height data and compared with the target 400mm. When the molten steel height decreases to 400mm, the nitrogen valve is opened, and the single nozzle outlet blows nitrogen at a flow rate of 110L / min and a parameter of 600kpa, with a duration of 2 minutes. The top slag in contact with the molten steel surface is cooled by room temperature nitrogen, and a large amount of high melting point components is precipitated. The viscosity of this part of the top slag rises, and the molten steel rotational shear force cannot pull it into the molten steel, thereby controlling the ladle slag. When the ladle casting is completed, the gas valve is closed, and the whole process is ended.

[0072] In a certain steelmaking production process, a 200-ton ladle carries molten steel for casting. According to the size of the ladle, a group of eight side-blown nozzles is symmetrically installed along the circumference of the ladle wall. Since the steel grade composition has strict requirements for N, argon is selected as the blowing gas. During the casting process, the ladle weighing system continuously weighs the ladle, and at the same time, the molten steel weight data is converted into molten steel height data and compared with the target 400mm. When the molten steel height decreases to 400mm, the nitrogen valve is opened, and the single nozzle outlet blows nitrogen at a flow rate of 160L / min and a parameter of 500kpa, with a duration of 2.5 minutes. The top slag in contact with the molten steel surface is cooled by room temperature argon, and a large amount of high melting point components is precipitated. The viscosity of this part of the top slag rises, and the molten steel rotational shear force cannot pull it into the molten steel, thereby controlling the ladle slag. When the ladle casting is completed, the gas valve is closed, and the whole process is ended.

[0073] In a steel production process, 300 tons of ladle carries liquid steel for casting. According to the size of the ladle, 2 groups of 8 side blowing nozzles are symmetrically installed along the circumference of the ladle wall. Since the composition of the steel has strict requirements for N, the gas selected for blowing is argon. During the casting process, the ladle weighing system continuously weighs the ladle, and at the same time converts the liquid steel weight data into liquid steel height data and compares it with the target 400mm. When the liquid steel height is reduced to 400mm, the nitrogen valve is opened, the single nozzle outlet sprays nitrogen at a flow rate of 220L / min and a parameter of 850kpa, and the duration is 3.0 minutes. The top slag in contact with the liquid steel surface is cooled by contacting with room temperature argon, and a large amount of high melting point components is precipitated. The viscosity of this part of the top slag increases, and the liquid steel rotating shear force cannot pull it into the liquid steel, thereby controlling the ladle slag. When the ladle casting is completed, the gas valve is closed and the whole process is completed.

[0074] The method for controlling the ladle slag has the characteristics of high efficiency and no secondary pollution, and achieves the purpose of controlling the ladle slag under pollution-free conditions.

Claims

1. A method for controlling slag discharge from a steel ladle, characterized in that: By opening nozzles at the same height and with equal arc on the side wall of the ladle, and using the swirling of molten steel as the trigger condition, cooling gas is blown into the liquid top slag through the nozzles to cool the top slag. By cooling the liquid top slag to reduce its temperature, it is transformed from a liquid to a semi-solid state, thereby suppressing the slag from rotating in the molten steel. The moment when the molten steel in the ladle reaches a predetermined height during the steelmaking process is used to characterize the moment when the molten steel begins to swirl. The nozzles are deployed according to the set molten steel height; The number of nozzles is determined based on the amount of top slag that needs to be cooled. Alternatively, the nozzles may be 12 nozzles arranged at the same height and arc on the side wall of the ladle, and the actual number of nozzles used may be determined based on the amount of top slag that needs to be cooled. The cooling gas flow rate of each nozzle is determined according to the following formula: In the formula, The initial temperature of the top slag requiring cooling is determined based on the lower limit of the molten steel temperature; The target temperature for cooling the top slag is determined by combining the highest melting point of the top slag and the lower limit of the molten steel temperature. The weight of the top slag requiring cooling is determined based on 9%-11% of the total top slag amount in the ladle.

2. The method for controlling slag discharge from a steel ladle according to claim 1, characterized in that: The cooling gas is either nitrogen or argon.

3. The method for controlling slag discharge from a steel ladle according to claim 1, characterized in that: The cooling gas supply is shut off when the ladle pouring is completed.

4. The method for controlling slag discharge from a steel ladle according to claim 1, characterized in that: Real-time monitoring of the ladle weight is used to monitor whether the molten steel level in the ladle has reached the set molten steel level.

5. The method for controlling slag discharge from a steel ladle according to claim 1, characterized in that: Specifically, the steps include the following: S1: Based on the current ladle tonnage, determine the number of nozzles according to the current ladle top slag volume to be cooled and the volume of ejected gas; S2: Real-time monitoring of the molten steel state is established from the moment the ladle pouring begins; when the molten steel is detected to start swirling, cooling gas is blown into the liquid top slag through the nozzle according to the calculated flow rate and the set blowing duration.

6. The method for controlling slag discharge from a steel ladle according to claim 1, characterized in that: The nozzles are set at the same height and arc on the side wall of the ladle, and depending on the size of the ladle, there may be one, two or more sets in the height direction.

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