A method for reducing converter lime consumption

Abstract

The invention discloses a method for reducing converter lime consumption, and belongs to the technical field of converter steelmaking. The test method of the invention controls the lime adding time and the amount thereof in batches through the linkage of basicity setting, bottom blowing intensity control, and top gun position control; in the design and development of the arrangement of the converter bottom blowing element, the bottom blowing intensity control mode, and the basicity setting coefficient, the symmetrical stirring bottom blowing mode is used to accelerate the steel slag flow renewal speed and promote the C-O reaction balance and the dephosphorization reaction balance, thereby solving the problem of excessive converter lime consumption and the converter terminal phosphorus content exceeding the standard under the same basicity setting with the same terminal phosphorus content requirement, reducing lime consumption, stabilizing the smelting process, and improving the metal recovery rate.

Description

Technical Field

[0001] The invention relates to the technical field of converter steelmaking, and more particularly to a method for reducing converter lime consumption. Background Art

[0002] Lime is the main slag-making material for converter steelmaking. Its function is to remove phosphorus and balance the acidic oxides of SiO2 in the desiliconization product in the slag to form alkaline slag to protect the converter lining. The current amount of lime added is mainly based on the target [P] content of the smelting steel grade to set the basicity R, and then according to the [Si] content of the molten iron according to W = R × 2.14 × w [Si] / w CaO Calculation is performed. In the formula, w [Si] is the silicon content of molten iron, weight percentage %; w CaO is the effective CaO content of lime, weight percentage. In order to meet the needs of dephosphorization, this method leaves a surplus for insurance when setting the alkalinity, which has two results: ① artificially increasing the amount of lime, resulting in excessive consumption of lime; ② this alkalinity setting is too broad, resulting in excessive phosphorus content due to different converter end temperatures under the same end phosphorus content requirements. Especially for high-temperature steel grades, due to the need to increase the temperature in the middle and late stages of smelting, the molten steel will return to phosphorus and peroxidation, and lime must be added, which not only increases lime consumption, but also affects the metal recovery rate.

[0003] At present, my country's steel industry is implementing the national "carbon peak and carbon neutrality" policy. Reducing converter lime consumption is also one of the ways to reduce carbon dioxide emissions from limestone mining and lime kiln firing. Reducing converter lime consumption has become an urgent problem to be solved in converter steelmaking.

[0004] After searching, Chinese invention patent CN110387447A discloses a method for reducing lime consumption in a converter, which uses KR molten iron pretreatment to preheat lime, thereby increasing the lime melting rate of the converter and reducing lime consumption, but significantly reducing the temperature of the molten iron entering the furnace. CN103468859 A discloses a method for calculating the amount of slag left in a converter to determine the amount of lime used. The method calculates the actual weight of the slag left in the converter according to the silicon content in the molten iron by using the slag left in the converter, and then accurately adds lime to reduce unit consumption. CN113362903B discloses a method for intelligently adding lime in the TSC stage of a large converter. The method uses a "mechanism model + artificial intelligence prediction" method to predict the amount of lime added in the TSC stage of a converter controlled by a secondary gun method according to the silicon content in the molten iron, thereby reducing the consumption of lime per ton of steel. CN103757173B, CN111719032A, CN 109762960 A, etc. use slag left, batch feeding to strengthen slagging, etc. to reduce the amount of lime used. The methods for reducing the lime consumption of the converter in the above patented technologies mainly include the converter slag left method, the method of replacing lime with limestone, dolomite or sludge balls, and the early slagging technology. These technologies are not necessarily suitable for the stable smelting of large converters, and the effect of reducing lime consumption is also unstable. Summary of the invention

[0005] 1. Technical problem to be solved by the invention

[0006] The purpose of the present invention is to overcome the problems in the prior art that the amount of lime used in converter steelmaking is large, which affects the metal recovery rate, and the effect of reducing lime consumption in the smelting of large converters is unstable. A method for reducing the lime consumption of the converter is provided. The timing and amount of lime addition are controlled in batches through the linkage of alkalinity setting, bottom blowing intensity control, and top gun position control. While reducing the lime consumption of converter steelmaking, the problem of excessive converter terminal phosphorus content under the same basicity setting with the same terminal phosphorus content requirement is solved, and the smelting process is stabilized.

[0007] 2. Technical solution

[0008] In order to achieve the above object, the technical solution provided by the present invention is:

[0009] The invention discloses a method for reducing lime consumption in a converter. The method controls lime adding timing and adding amount in batches through linkage of basicity setting, bottom blowing intensity control and top gun position control. The arrangement of bottom blowing elements in the converter, bottom blowing intensity control mode and basicity setting coefficient are designed and developed to accelerate steel-slag flow renewal speed, promote a symmetrical stirring bottom blowing mode of CO reaction balance and dephosphorization reaction balance, solve the problems of excessive lime consumption in the converter and excessive phosphorus content in the converter at the same basicity setting under the same phosphorus content requirement at the same end point, reduce lime consumption, stabilize the smelting process and improve metal recovery rate.

[0010] Furthermore, the basicity R is set according to the target [P] content of the smelting steel grade and the target end temperature of the converter, where [P] refers to the mass fraction of P; the bottom blowing intensity is controlled to be distributed in a ring-shaped symmetrical manner with the center of the converter bottom as the center of the circle; the top gun position is controlled to first set the start-blowing gun position L0, and then adjust the process gun position based on the start-blowing gun position L0 according to the oxygen step, optimize the bottom blowing element layout and the bottom blowing intensity control mode, strengthen the stirring force of the molten pool, and program the converter smelting operation to achieve basicity-bottom blowing-gun position linkage control to reduce the converter lime consumption, and the oxygen step refers to the proportion of the total oxygen supply.

[0011] Furthermore, the oxygen step set by the converter L2 control system program is used to control and adjust the top gun position control, bottom blowing intensity control and batch control of lime addition timing and amount during the blowing process.

[0012] Furthermore, the bottom blowing intensity control includes the bottom blowing mode, and the bottom blowing mode and its corresponding basicity R correction coefficient X are selected according to the type of steel being smelted. i , and timely adjust the consumption of converter lime to further reduce its consumption.

[0013] Furthermore, the converter L2 control system automatically collects the [Si] and [P] contents of the molten iron, inputs the effective CaO content of the lime tested during the shift, and determines the amount of lime added for the furnace according to the relationship (1):

[0014] W = 1000 × R × X i ×(2.14×w [Si] +1.31×w [P] ) / w CaO有效 (1)

[0015] Where: W is the amount of lime added to the converter, kg / t metal material; w [Si] is the silicon content of molten iron, weight percentage %; w [P] is the phosphorus content of molten iron, weight percentage %; w CaO is the effective CaO content of lime, weight percentage %; X i is the basicity correction factor corresponding to the bottom blowing mode.

[0016] Furthermore, the converter L2 control automatically collects the [Si], [P], [C], and [Mn] contents of the molten iron and automatically calculates the total oxygen blowing amount required for this furnace based on the heat balance model, and allocates the time step and oxygen blowing amount of the oxygen step according to the smelting process to avoid wasting energy.

[0017] Furthermore, in the top gun position control, when the oxygen step process reaches 5% of the total oxygen blowing amount, the process gun position is reduced by 10-25% based on L0, and the first batch of lime is added, and the amount added is 40%-55% of the total lime. When the oxygen step process reaches 25% of the total oxygen blowing amount, the process gun position is reduced by 10% based on L0, and the amount of lime added is 30%-40%; when the oxygen step process reaches 40%-50% of the total oxygen blowing amount, all the remaining lime is added. When the oxygen blowing amount reaches 75%, the process gun position is reduced by 30% based on L0 until the blowing is completed; after clicking the start blowing button, the time step and oxygen blowing amount of the oxygen step can be allocated according to the smelting process.

[0018] Furthermore, five bottom blowing modes, A, B, C, D, and E, are set according to the type of steel being blown, and the bottom blowing air supply intensity is controlled at 0.02-0.16Nm 3 / (t·min), adjust the bottom blowing gas flow rate according to the oxygen step during the blowing process, and set the basicity correction coefficient X for the five bottom blowing modes A, B, C, D, and E respectively. i , the correction coefficient range is 0.75~1.15.

[0019] 3. Beneficial effects

[0020] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0021] (1) The method of reducing converter lime consumption of the present invention first designs and develops an optimized layout of converter bottom blowing elements, a bottom blowing intensity control mode and an alkalinity setting coefficient, and solves the problem of excessive converter lime consumption and excessive converter endpoint phosphorus content under the same endpoint phosphorus content requirement and the same alkalinity setting through a smelting method of "alkalinity setting-bottom blowing intensity-gun position linkage control", thereby reducing lime consumption, stabilizing the smelting process and improving metal recovery rate;

[0022] (2) The method of reducing the lime consumption of the converter of the present invention can accelerate the steel-slag flow renewal speed, promote the CO reaction balance and the dephosphorization reaction balance, and achieve stable smelting with low alkalinity under the smelting mode of "alkalinity setting-bottom blowing intensity-gun position linkage control". The lime consumption is reduced by 8-15%, and the dephosphorization rate is increased by 2-5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The schematic diagram of the bottom blowing nozzle arrangement of the converter of the present invention;

[0024] Figure 2 The gun position changes during the smelting process of Examples 1-3 and Comparative Examples 1-3.

[0025] In the figure: 1. converter; 3. auxiliary gun; 5. bottom blowing nozzle. DETAILED DESCRIPTION

[0026] In order to further understand the content of the present invention, the present invention is described in detail in conjunction with the accompanying drawings.

[0027] The present invention will be further described below in conjunction with the embodiments.

[0028] Implementation

[0029] The method of reducing the consumption of converter lime in this embodiment takes the single slag method smelting of ultra-low carbon steel by a 300-ton top and bottom double-blown converter in a certain factory as an example. The converter is equipped with a static model + a dynamic model for one-button steelmaking, and is equipped with an auxiliary gun and a sonar slag monitoring system. The main slag-making materials are lime and dolomite, among which the effective CaO content of lime is ≥80%. The smelting process is to splash slag to protect the furnace after the previous furnace is tapped, add scrap steel and molten iron, ignite and start blowing, and perform blowing according to the one-button steelmaking procedure. The scrap steel loading amount is 20t~60t, the molten iron loading amount is ≥280t, and the total loading amount is 320t~340t. The blowing gun position is 2600mm~3000mm, and the gun position drops by no more than 200mm each time. The specific steps are:

[0030] (1) The 16 bottom blowing nozzles of the top and bottom combined blowing converter are arranged on the circumferences of 0.45D and 0.5D with the center of the converter 1 as the center (D is the inner diameter of the furnace), and 8 bottom blowing nozzles 5 are arranged on each circumference. Figure 1 As shown, this arrangement stirs the molten pool symmetrically, speeds up the steel-slag flow renewal speed, promotes the CO reaction balance and the dephosphorization reaction balance, and gives full play to the dephosphorization effect in the early and middle stages of blowing. When the pressure and flow rate of the 16 bottom blowing nozzles 5 are distributed by the converter L2 control system program in steps according to the flow field, asymmetric stirring can also be achieved; both forms of bottom blowing arrangements can make the converter molten pool more evenly stirred, the slag surface renewal speed is faster, and the reaction kinetic conditions are improved to avoid the risk that the dephosphorization rate cannot meet the needs of the steel grade when the lime is reduced.

[0031] (2) Five bottom blowing modes, A, B, C, D, and E, are set according to the type of steel being blown. The bottom blowing gas supply intensity is controlled at 0.02-0.16 Nm3 / (t·min). During the blowing process, the bottom blowing gas flow rate is automatically adjusted by the secondary system according to the oxygen step, and the basicity correction coefficient Xi is set for the five bottom blowing modes A, B, C, D, and E respectively, and the correction coefficient range is 0.75-1.15.

[0032] Mode A: Target carbon content of smelting steel group ≤ 0.1%;

[0033] Mode B: Target carbon content of smelting steel group (0.1% to 0.15%);

[0034] C mode: Target carbon content of smelting steel grade group (0.15% to 0.25%);

[0035] D mode: target carbon content of smelting steel group (0.25% to 0.35%);

[0036] E mode: The target carbon content of the smelting steel group is ≥ 0.35%.

[0037] Since current on-site production is basically aimed at orders with a carbon content of ≤0.1%, the A mode smelting is used, unless a very small number of tests are carried out before the smelting mode is changed.

[0038] The staged bottom blowing intensity and alkalinity correction coefficients of the five bottom blowing modes are shown in Table 1.

[0039] (3) The characteristics of the blowing process for reducing the lime consumption in the converter based on the arrangement of the bottom blowing elements and the bottom blowing mode are that the timing and amount of lime addition are controlled by linkage of "basicity setting - bottom blowing intensity - top gun position". The main steps are as follows:

[0040] S1: The basicity R is set according to the target [P] content of the smelting steel grade and the target converter endpoint temperature.

[0041] S2: Select the bottom blowing mode and its corresponding basicity correction factor X according to the type of steel being smelted i . As shown in Table 1.

[0042] S3: The converter L2 system automatically collects the [Si] and [P] contents of the molten iron, manually inputs the effective CaO content of the lime tested during the shift, and determines the amount of lime added for the furnace according to the relationship (1):

[0043] W = 1000 × R × X i ×(2.14×w [Si] +1.31×w [P] ) / w CaO有效 (1)

[0044] Where: W is the amount of lime added to the converter, kg / t metal material; w [Si] is the silicon content of molten iron, weight percentage %; w [P] is the phosphorus content of molten iron, weight percentage %; w CaO is the effective CaO content of lime, weight percentage %; X iis the basicity correction coefficient corresponding to the bottom blowing mode. Among them, the coefficient 2.14 is the ratio of the relative molecular mass of SiO2 to the relative atomic mass of Si; the coefficient 1.31 is the ratio of the relative molecular mass of P2O5 to the relative atomic mass of P, assuming that 90% of the phosphorus content of the metal material is oxidized into the slag. (0.634×142 / 62×90%, 0.634 is the assumption that the slag contains two compounds 2CaO·SiO2 and 3CaO·P2O5. According to the ability to combine with CaO, 1 gram of P2O5 is equivalent to 1.5 grams of SiO2, and 0.634 is the equivalent ratio of their combination with CaO, 1.5×60 / 142=0.634); mathematically modularizing the amount of converter lime added can realize the programming of converter smelting operations, realize the linkage control of basicity-bottom blowing-gun position, and thus reduce the consumption of converter lime.

[0045] S4: The converter L2 system automatically collects the [Si], [P], [C], and [Mn] contents of the molten iron and automatically calculates the total oxygen blowing amount required for this furnace based on the heat balance model, and allocates the time step and oxygen blowing amount of the oxygen step according to the smelting process.

[0046] S5: Click the Start Blowing button to control and adjust the oxygen gun position, bottom blowing intensity, lime addition timing and amount of the blowing process according to the oxygen step set by the program. Among them, the control of the gun position is to first set the opening gun position L0, and then adjust the process gun position based on the opening gun position L0 according to the oxygen step. When the oxygen step process reaches 5% of the total oxygen blowing volume, the process gun position drops by 10-25% on the basis of L0, and the first batch of lime is added, and the amount added is 40%-55% of the total lime. When the oxygen step process reaches 25% of the total oxygen blowing volume, the process gun position drops by 10% on the basis of L0, and the lime addition amount is 30%-40%; when the oxygen step process reaches 40%~50% of the total oxygen blowing volume, all the remaining lime is added. When the oxygen blowing volume reaches 75%, the process gun position drops by 30% on the basis of L0 until the end of blowing. The linkage control of lime addition and gun position is shown in Table 1.

[0047] In this embodiment, the smelted steels of Examples 1-3 and Comparative Examples 1-3 are all ultra-low carbon steels, and the converter endpoint control requirements are [P] ≤ 0.015%, [C] 0.020% to 0.060%, and active oxygen 0.030% to 0.060%, where the above % are all weight percentages, and [] are the weight percentages of the corresponding elements.

[0048] The bottom blowing mode of the embodiment is mode A, and the lime adding timing and amount, bottom blowing intensity and top blowing gun position are controlled according to Table 1.

[0049] Table 1 Bottom blowing mode of the present invention and lime addition and linkage gun position control under each oxygen step

[0050]

[0051] And as Figure 2 As shown, the gun position changes in the smelting process of Examples 1-3 and Comparative Examples 1-3 were adjusted.

[0052] Table 2 Comparison of main parameters of ultra-low carbon steel of Examples 1-3 and Comparative Examples 1-3

[0053]

[0054] It can be concluded from Table 2 that the method for reducing converter lime consumption provided by the present invention can accelerate the steel-slag flow renewal speed, promote the CO reaction balance and the dephosphorization reaction balance, and achieve stable smelting with lower alkalinity under the smelting mode of "alkalinity R setting-bottom blowing intensity control-gun position linkage control". The lime consumption is reduced by 8-15%, and the dephosphorization rate is increased by 2-5%, achieving unexpected technical effects.

[0055] The present invention and its embodiments are described schematically above, and the description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by it and designs a structural method and an embodiment similar to the technical solution without creativity without departing from the purpose of the invention, they shall all fall within the protection scope of the present invention.

Claims

1. A method for reducing converter lime consumption, characterized in that: The timing and amount of lime addition can be controlled in batches through the linkage of alkalinity setting, bottom blowing intensity control and top gun position control. The basicity R setting is set according to the target [P] content of the smelting steel grade and the target temperature of the converter end point; the bottom blowing intensity control is a ring-shaped symmetrical distribution with the center of the converter bottom as the center of the circle; the top gun position control is to first set the start-blowing gun position L0, and then adjust the process gun position based on the start-blowing gun position L0 according to the oxygen step; The oxygen step set by the converter L2 control system program is used to control the top gun position control, bottom blowing intensity control and batch control of lime addition timing and amount during the blowing process; The bottom blowing intensity control includes a bottom blowing mode, and the bottom blowing mode and its corresponding basicity R correction coefficient Xi are selected according to the type of steel being smelted; The converter L2 control system automatically collects the [Si] and [P] contents of molten iron, inputs the effective CaO content of lime tested during the shift, and determines the amount of lime added for the furnace according to the relationship (1): W=1000×R×Xi×(2.14×w[Si]+1.31×w[P]) / wCaO effective(1) Where: W is the amount of lime added to the converter, kg / t metal material; w[Si] is the silicon content of molten iron, weight percentage; w[P] is the phosphorus content of molten iron, weight percentage; wCaO is the effective CaO content of lime, weight percentage; Xi is the basicity correction coefficient corresponding to the bottom blowing mode; The converter L2 control automatically collects the [Si], [P], [C], and [Mn] contents of the molten iron and automatically calculates the total oxygen blowing amount required for this furnace according to the heat balance model, and allocates the time step and oxygen blowing amount of the oxygen step according to the smelting process.

2. The method for reducing converter lime consumption according to claim 1, characterized in that: In the top gun position control, when the oxygen step reaches 5% of the total oxygen blowing amount, the process gun position is reduced by 10-25% based on L0, and the first batch of lime is added, and the added amount is 40%-55% of the total lime amount; When the oxygen step reaches 25% of the total oxygen blowing volume, the process gun position is lowered by 10% based on L0, and 30%-40% of lime is added; when the oxygen step reaches 40%~50% of the total oxygen blowing volume, all the remaining lime is added; when the oxygen blowing volume reaches 75%, the process gun position is lowered by 30% based on L0 until the blowing is completed.

3. The method for reducing converter lime consumption according to claim 1 or 2, characterized in that: Five bottom blowing modes A, B, C, D and E are set according to the type of steel being blown. The bottom blowing gas supply intensity is controlled at 0.02-0.16Nm3 / (t·min). During the blowing process, the bottom blowing gas flow rate is automatically adjusted by the secondary system according to the oxygen step, and the basicity correction coefficient Xi is set for the five bottom blowing modes A, B, C, D and E respectively, and the correction coefficient range is 0.75~1.

15.

4. The method for reducing converter lime consumption according to claim 1, characterized in that: The bottom blowing nozzles of the converter are arranged on circles with the center of the converter as the center and 0.45 and 0.5 of the inner diameter of the furnace respectively.

5. The method for reducing converter lime consumption according to claim 1, characterized in that: The pressure and flow rate of the bottom blowing nozzle of the converter are allocated by the converter L2 control system program according to the flow field distribution.

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