A method for controlling the timing of slag discharge in a converter double-slag smelting process

Abstract

This invention discloses a method for controlling the timing of slag discharge in a converter double-slag smelting process. It utilizes the tension changes on the converter oxygen lance wire rope to predict the slag state within the converter, thereby selecting the timing for the end of blowing before the first slag discharge. This maximizes the discharge of high-P2O5 content slag, significantly improving the dephosphorization rate. The method includes: installing a tension sensor on the wire rope suspending the oxygen lance; collecting the tension data of the wire rope via a computer system; processing the tension signal to obtain the oxygen lance tension change rate; and determining the slag state based on the change rate, thus determining the timing for the first slag discharge. This invention fully utilizes the changes in oxygen lance tension during converter blowing to accurately select the timing for the first slag discharge in the double-slag dephosphorization process. This avoids the problems of poor dephosphorization effect if the first slag discharge is performed too early, or the problem of excessive carbon-oxygen reaction and temperature rise in the converter, resulting in viscous slag that cannot be discharged, thus ensuring the dephosphorization effect of the converter.

Description

Technical Field

[0001] This invention belongs to the field of converter steelmaking technology in the metallurgical industry, specifically relating to a method for controlling the timing of slag discharge in the converter double-slag smelting process. Background Technology

[0002] In the production processes of low-phosphorus steel ([P] < 0.01%–0.02%) and ultra-low-phosphorus steel ([P] < 0.005%), controlling the phosphorus content of molten steel is a crucial step in converter steelmaking. In recent years, with the increasing demand for high-quality steel, more and more steel grades require lower phosphorus content. Therefore, achieving low-phosphorus steel production in converters at the lowest cost is a key research focus in the steelmaking field.

[0003] Currently, major Japanese steel companies widely adopt the converter "double-slag" operation process, but this process has high equipment requirements. There is also an operation mode that continuously performs dephosphorization and decarburization blowing of molten iron on the same converter, namely the converter double-slag process. This process is simple to operate, requires no additional equipment, and has been widely adopted both domestically and internationally, especially by steel mills with limited equipment. The double-slag process is a widely used method in converter smelting, particularly in the smelting of high-phosphorus iron and low-phosphorus steel. The efficient double-slag smelting process reduces slag consumption while significantly improving the dephosphorization rate.

[0004] The principle of dephosphorization by the dual-slag method: Phosphorus should be removed as much as possible during the converter smelting process. Converter dephosphorization mainly takes place at the steel-slag interface in the early stage of smelting at low temperature. Therefore, the composition and properties of the slag have a great influence on dephosphorization. The most important factors are slag basicity, oxidizing properties, molten pool temperature, and slag viscosity and melting characteristics related to kinetic conditions.

[0005] For the converter dual-slag process, based on the thermodynamic conditions of converter dephosphorization, a high-basicity, high-oxidizing, and low-temperature operating mode is adopted before the first slag dumping. In the early stages of converter smelting, while ensuring the slag is quickly smelted, as the smelting temperature rises, the dephosphorization stage blowing is terminated at an appropriate time before the large-scale, intense decarburization reaction occurs, and the high-P2O5 content dephosphorized slag is quickly dumped. Adjusting and optimizing the dephosphorization process parameters in the early stages of smelting, and dumping as much slag as possible after dephosphorization, is key to slag formation and dephosphorization in the converter dual-slag method. Therefore, rationally controlling the slag state during the first slag dumping, selecting an appropriate slag viscosity, and controlling the timing of ending the blowing before the first slag dumping are particularly crucial.

[0006] The traditional method for detecting the state of slag is for oxygen lance operators to judge the melting status of slag based on information such as the flame condition at the furnace opening and the sounds emitted from inside the furnace. Some converters use sound detection equipment installed at the furnace opening to detect the noise intensity of the oxygen flow and use this to judge the melting status of slag. However, this method has the problem that the noise cannot be accurately detected when the converter hood is lowered or when slag accumulates at the furnace opening. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, this invention provides a method for controlling the timing of slag discharge in the converter double-slag smelting process. This method utilizes the tension changes on the converter oxygen lance wire rope to predict the slag state inside the converter and selects the timing of the end of blowing before the first slag discharge. This achieves the goal of discharging as much high-P2O5 content slag as possible, thus achieving the best dephosphorization effect.

[0008] The double-slag method in converter smelting is widely used in the production of high-phosphorus iron and low-phosphorus steel. However, there is no mature technology for selecting the timing of the first slag dumping in the double-slag method. The state of the converter slag at the time of dumping is particularly important. If the dumping is done too early, the dephosphorization effect will not be achieved; if the dumping is done too late, a violent decarburization reaction will occur, resulting in low FeO content, high viscosity, and severe dryness in the slag, making it impossible to dump the slag. The oxygen lance is one of the important pieces of equipment in converter production. The oxygen lance is raised and lowered by a winch that directly lifts the oxygen lance carriage. The oxygen lance carriage is raised and lowered by two steel wire ropes on the drum that pass around the movable pulley of the carriage. Each steel wire rope has one end (free end) connected to the drum, and the other fixed end connected to a tension sensor. The tension on each steel wire rope is detected by the tension sensor and displayed on the operation screen. The purpose of this invention is to use the tension value changes detected by the two tension sensors connected to the two steel wire ropes on the oxygen lance carriage drum to determine the viscosity state of the slag in the converter and to determine the timing of the first slag dumping in the double-slag method.

[0009] A method for controlling the timing of slag discharge in a converter double-slag smelting process, the method comprising: installing a tension sensor on the steel wire rope suspending the oxygen lance, collecting the stress on the steel wire rope by a computer system, processing the tension signal by the computer system to obtain the oxygen lance tension change rate, determining the slag condition based on the change rate, and then determining the timing of slag discharge.

[0010] During the converter smelting process, oxygen is blown into the molten steel pool by an oxygen lance. The surface of the converter molten pool is covered by a slag layer. Due to variations in the content of components such as FeO in the slag, the viscosity of the slag layer changes significantly, resulting in variations in thickness. During the blowing process, the oxygen lance is subjected to the reaction force of the oxygen flow, the buoyancy of the molten slag, and the impact force of the molten slag, which results in different tension values ​​on the tension sensor. The forces acting on the oxygen lance vary depending on the molten slag's melting state. When the molten slag has a lower viscosity, the buoyancy and impact force on the oxygen lance are greater as the slag rises, and the tension on the oxygen lance rope decreases accordingly.

[0011] In the above technical solution, when the [P] content of the molten iron smelted by the converter is ≥0.09% or the finished steel grade requires the [P] content to be ≤0.0050%, it is necessary to use the double slag method to operate dephosphorization and to determine the timing of the furnace dumping and slag dumping by following the oxygen lance tension value change rule.

[0012] Furthermore, the tension value A of the oxygen lance wire rope is collected before the blowing of this converter heat and is processed as a reference value for the change of oxygen lance tension value in this heat.

[0013] Furthermore, the oxygen lance tension value B during the blowing process is acquired and processed by computer, and compared with the oxygen lance wire rope tension value A before the converter blowing process to obtain the change in oxygen lance tension value (AB) and the rate of change (AB) / A×100%.

[0014] Furthermore, the judgment is made based on the rate of change of the oxygen lance tension value: if the rate of change of the oxygen lance tension value is -20% to 0, the slag condition is unmelted or dry, the slag viscosity is high, and it is impossible to pour out the slag; if the rate of change is 0% to 10%, the slag condition is molten, the slag viscosity is normal, and a small amount of slag can be poured out; if the rate of change is 10% to 30%, the slag condition is that the oxygen lance is submerged in slag, the viscosity is low, and a large amount of slag can be poured out.

[0015] Furthermore, during the converter blowing process, the oxygen lance operator should pay attention to the double-slag method lance lifting reminder signal in the intelligent steelmaking system. When the change rate of the oxygen lance wire rope tension value is between 10% and 30%, the blowing should be stopped. The furnace shaker operator should shake the furnace to pour out as much high-P2O5 content slag as possible to create conditions for dephosphorization.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] This invention fully utilizes the changes in oxygen lance tension during converter blowing to accurately select the timing of slag discharge during the double-slag dephosphorization process. This avoids the problems of poor dephosphorization effect when the lance is discharged too early or too late, resulting in violent carbon-oxygen reaction, increased temperature, and viscous slag that cannot be discharged, thus ensuring the dephosphorization effect of the converter. Detailed Implementation

[0018] The present invention will be further described below with reference to specific embodiments, but this does not limit the invention in any way. To avoid redundancy, unless otherwise specified, the raw materials used in the following embodiments are all commercially available products, and the methods used are all conventional methods unless otherwise specified.

[0019] Example 1

[0020] A method for controlling the timing of slag discharge in a converter double-slag smelting process, the method comprising: installing a tension sensor on the steel wire rope suspending the oxygen lance, collecting the stress on the steel wire rope by a computer system, processing the tension signal by the computer system to obtain the oxygen lance tension change rate, determining the slag condition based on the change rate, and then determining the timing of slag discharge.

[0021] ① When the [P] content of molten iron smelted in a converter is ≥0.09% or the finished steel grade requires a [P] content ≤0.0050%, the double-slag method must be used for dephosphorization. The timing of slag removal should be determined by the oxygen lance tension value change rule. When the [P] content of molten iron is 0.12%, the double-slag method should be used for dephosphorization.

[0022] ② Before the current blowing cycle in the converter, the tension value A of the oxygen lance wire rope is collected and processed as a reference value for the change in oxygen lance tension value in this cycle. Before ferroalloying, the tension value of the converter oxygen lance wire rope is 10t.

[0023] ③ The oxygen lance tension value B during the blowing process is acquired and processed by computer, and compared with the oxygen lance wire rope tension value A before converter blowing to obtain the change in oxygen lance tension value (AB) and the rate of change (AB) / A×100%. After 4 minutes and 30 seconds of converter blowing, the converter oxygen lance wire rope tension value is 8.3t;

[0024] The rate of change of the wire rope tension value of the converter oxygen lance is (10-8.3) / 10*100%=17%.

[0025] ④ Based on the rate of change of oxygen lance tension, if the value is -20% to 0, the slag condition is unmelted or dry, the slag viscosity is high, and it is impossible to pour out the slag; if the value is 0% to 10%, the slag condition is molten, the slag viscosity is normal, and a small amount of slag can be poured out; if the value is 10% to 30%, the slag condition is that the oxygen lance is submerged, the viscosity is low, and a large amount of slag can be poured out.

[0026] ⑤ During the converter blowing process, when the oxygen lance wire rope tension change rate is between 10% and 30%, the intelligent steelmaking system displays a double-slag method lance lifting reminder signal, indicating the end of blowing and the start of slag dumping. Based on the calculations in step ③, the oxygen lance wire rope tension change rate is 17%, allowing for the dumping of a large amount of slag. The oxygen lance operator lifts the lance, ending the blowing process and performing a first slag dump; the first slag dump is approximately 60% of the converter's total slag; the converter endpoint [P] content is 0.0097%.

[0027] Example 2

[0028] A method for controlling the timing of slag discharge in a converter double-slag smelting process, the method comprising:

[0029] ① Dephosphorization was performed using a dual-slag method, with a [P] content of 0.088% in the molten iron;

[0030] ②The tension value A of the oxygen lance wire rope was collected before the current blowing in the converter. Before the iron was added, the tension value of the oxygen lance wire rope in the converter was 11t.

[0031] ③ The oxygen lance tension value B during the blowing process is collected and processed by computer. After 4 minutes and 50 seconds of converter blowing, the tension value of the converter oxygen lance wire rope is 9.2t; the change rate of the converter oxygen lance wire rope tension value is (11-9.2) / 11*100%=16%.

[0032] ④ Based on the rate of change of oxygen lance tension, a large amount of slag can be poured out.

[0033] ⑤ The oxygen lance operator lifts the lance, ends the blowing process, and performs a slag dumping.

[0034] ⑥ The slag discharge rate of the rotary kiln is approximately 50%;

[0035] ⑦ The [P] content at the converter endpoint was 0.0037%.

[0036] Comparative Example 1

[0037] 1) Iron content [P] in molten iron is 0.12%;

[0038] 2) Before adding iron, the tension of the converter oxygen lance wire rope is 10t;

[0039] 3) The converter blowing process lasts for 4 minutes and 30 seconds, and the tension of the converter oxygen lance wire rope is 10.8t.

[0040] 4) The change rate of the tension value of the converter oxygen lance wire rope is (10-10.8) / 10*100%=-8%;

[0041] 5) The oxygen lance operator lifts the lance, ends the blowing process, and performs a slag dumping.

[0042] 6) The slag in the first rotary kiln was severely dried out, and the slag was not poured out;

[0043] 7) The [P] content at the converter endpoint was 0.019%.

[0044] Comparative Example 2

[0045] 1) Iron content [P] in molten iron is 0.088%;

[0046] 2) Before adding iron, the tension of the converter oxygen lance wire rope is 11t;

[0047] 3) The converter blowing process lasts for 4 minutes and 50 seconds, and the tension of the converter oxygen lance wire rope is 12.6t.

[0048] 4) The change rate of the tension value of the converter oxygen lance wire rope is (11-12.6) / 11*100%=-14%;

[0049] 5) The oxygen lance operator lifts the lance, ends the blowing process, and performs a slag dumping.

[0050] 6) The slag in the first rotary kiln was severely dried out, and the slag was not poured out;

[0051] 7) The [P] content at the converter endpoint was 0.0037%.

[0052] For anyone skilled in the art, many possible variations and modifications can be made to the technical solutions of this invention, or equivalent embodiments can be modified based on the disclosed technical content, without departing from the scope of the technical solutions of this invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this invention without departing from the content of the technical solutions of this invention should still fall within the protection scope of the technical solutions of this invention.

Claims

1. A method for controlling the timing of slag discharge in a converter double-slag smelting process, characterized in that, The method includes: installing a tension sensor on the wire rope suspending the oxygen lance, collecting the stress on the wire rope through a computer system, processing the tension signal through the computer system to obtain the oxygen lance tension change rate, and determining the slag condition based on the change rate, thereby determining the timing of slag dumping. When the [P] content of molten iron produced by converter smelting is ≥0.09% or the finished steel grade requires the [P] content to be ≤0.0050%, the dephosphorization is carried out by the double slag method, and the timing of the first slag dumping is determined by the oxygen lance tension value change rule. Before the converter blows this heat, the tension value A of the oxygen lance wire rope is collected and benchmarked to serve as a reference value for the change of oxygen lance tension value in this heat. The oxygen lance tension value B during the blowing process is acquired and processed by computer, and compared with the oxygen lance wire rope tension value A before the converter blowing process to obtain the change in oxygen lance tension value (AB) and the rate of change (AB) / A×100%. The following criteria are used to determine the slag condition based on the rate of change of oxygen lance tension: When the rate of change is -20% to less than or equal to 0, the slag is unmelted or dry, with high viscosity, and cannot be poured out easily; when the rate of change is greater than 0 to less than or equal to 10%, the slag is molten, with normal viscosity, and a small amount of slag can be poured out; when the rate of change is greater than 10% to 30%, the slag submerges the oxygen lance, has low viscosity, and a large amount of slag can be poured out. During the converter blowing process, when the change rate of the oxygen lance wire rope tension value is between 10% and 30%, the intelligent steelmaking system displays a double slag method lance lifting reminder signal, indicating that the blowing process should be terminated and the furnace shaker should be started to remove slag.