CN108424994B - Method for reducing slagging loss of molten iron - Google Patents
Method for reducing slagging loss of molten iron Download PDFInfo
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- CN108424994B CN108424994B CN201710075537.8A CN201710075537A CN108424994B CN 108424994 B CN108424994 B CN 108424994B CN 201710075537 A CN201710075537 A CN 201710075537A CN 108424994 B CN108424994 B CN 108424994B
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/064—Dephosphorising; Desulfurising
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C1/00—Refining of pig-iron; Cast iron
- C21C1/02—Dephosphorising or desulfurising
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Abstract
The invention relates to a method for reducing slagging-off loss of molten iron, which comprises the following steps: the method comprises the steps of firstly setting a risk reserve value according to the requirement of finished sulfur of a smelting steel type, secondly determining a target desulfurization grade of molten iron pretreatment, thirdly calculating the total mass of sulfur in slag after molten iron desulfurization and the mass of sulfur in the residual slag after slag skimming, further determining the proportion of slag remaining amount after slag skimming, fourthly determining a theoretical slag skimming weight interval, fifthly performing early-stage slag skimming, performing gas blowing and slag removal and later-stage slag skimming when the slag skimming amount reaches 50-70% of the lower limit of the theoretical slag skimming weight interval, monitoring by using a camera in the operation process, sixthly obtaining an actual slag area proportion, comparing the actual slag area proportion with the target slag remaining area proportion, and weighing to obtain an actual skimming weight and judging whether the actual skimming weight is within the theoretical slag skimming weight interval when the two are skimming are performed simultaneously. The invention has the advantage that the refining rate of the sulfur reaches 100 percent.
Description
Technical Field
The invention belongs to the technical field of metallurgy, and particularly relates to a method for reducing slagging loss of molten iron.
Background
For most steel grades, sulfur is a harmful element which reduces the workability of steel, deteriorates the weldability of steel, causes "hot shortness" and high temperature cracking of steel, and also significantly reduces the plasticity of steel, so that the lower the sulfur in molten steel, the better the steel is generally smelted. The pre-desulfurization before the smelting of the converter is an indispensable technical means for smelting low-sulfur clean steel. The desulfurization products generated by the pre-desulfurization of the molten iron can completely float into the molten iron slag, so that the sulfur content of the molten iron slag can be improved along with the increase of the sulfur content of the molten iron, and generally, the sulfur content of the blast furnace molten iron slag is about 20-50 times of the sulfur content of the blast furnace molten iron. Therefore, most of sulfur elements can be removed by a molten iron desulphurization and slag removal method before converter smelting. In the prior art, the residual quantity of molten iron after desulfurization and slagging-off of molten iron slag has a great influence on the end point sulfur content of the converter, and because a large amount of steel scraps and slagging auxiliary materials need to be added in the smelting process of the converter, the sulfur content of the steel scraps and slagging auxiliary materials also has a great influence on the end point sulfur content of the converter, and because the influences cannot be removed in the smelting process of the converter, the influence of the steel scraps, slagging auxiliary materials and the like on the end point sulfur of the converter must be reduced by a method of reducing the slag quantity of the molten iron entering the converter.
In the process of smelting low-sulfur steel, the conventional molten iron slagging-off method is mainly used for completely slagging off molten iron slag or simply determining the slagging-off grade according to the sulfur content of a finished product of the smelting steel, and the influence of the factors such as initial sulfur of molten iron, slag-carrying resulfurization of molten iron and the like on the terminal sulfur content of the converter cannot be comprehensively considered. In the molten iron slagging process, the slag removed usually carries about 50% molten iron, which causes high metal consumption and cost increase. Meanwhile, as the slag skimming operation is manually operated, the amount of iron in the slag skimming process is greatly different, and operators lack quantitative concepts on how much slag is skived off and can only operate the slag skimming operation by experience. If the slag skimming amount is insufficient, resulfurization can be caused during steelmaking, and the quality of molten steel is further influenced. A large number of investigations and analyses find that the resulfurization amount caused by the steel scrap and the slagging auxiliary materials in the smelting process of the converter is basically stable, and the main factor influencing the sulfur concentration of the desulfurized slag is the initial sulfur content of the molten iron, so that a method capable of determining a reasonable molten iron slagging weight interval and a molten iron slagging area according to the requirements of the initial sulfur content of the molten iron and the sulfur content of steel is urgently needed.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method can determine a reasonable slagging weight interval, compare the actual slagging weight with a theoretical slagging weight interval to control the slagging weight and reduce the iron-carrying loss in the slagging process, quantize the area proportion of the slag left after the molten iron slagging, and then control the slagging amount according to the quantized slag area proportion, thereby effectively controlling the influence of the slag left after the molten iron slagging on resulfurization.
The technical scheme for solving the technical problems of the invention is as follows:
a method for reducing slagging loss of molten iron comprises the following steps:
firstly, setting the end point sulfur content of a converter according to the requirement of smelting and tapping steel grade finished product sulfur, wherein the end point sulfur content of the steel grade finished product is greater than the end point sulfur content (in mass percentage) of the converter, setting the difference value between the end point sulfur content and the end point sulfur content as a risk reserve value and recording the risk reserve value as SRisk reservationPercent; turning to the second step;
second step, based on mass percent (the following% unless otherwise specified)All are mass percent), the sulfur content of the steel grade finished product is recorded as SSulfur content of steel grade finished productPercent, the resulfurization amount in the converter smelting process is recorded as SAmount of sulfur returned from converter% and the target desulfurization grade before converter smelting and in the molten iron pretreatment process is recorded as STarget desulfurization gradePercent, and then according to the sulfur content S of the finished steel productSulfur content of steel grade finished product% requirement and SAmount of sulfur returned from converter％、SRisk reservation% to determine a target desulfurization level of the molten iron pretreatment such that the target desulfurization level satisfies formula (1),
Starget desulfurization grade％≤SSulfur content of steel grade finished product％-SRisk reservation％-SAmount of sulfur returned from converter％ (1)
At the above-mentioned STarget desulfurization gradeTaking an integer in the calculation process of percent; turning to the third step;
thirdly, recording the weight of the slag with the slag in the desulfurized molten iron in the molten iron ladle as MSlag quantity of molten ironAnd calculating the weight of the slag in the ladle after the molten iron is desulfurized according to the formula (3),
Mslag quantity of molten iron＝SArea of ladle×hSlag thickness×ρDensity of molten iron slag(3)
Wherein SArea of ladleIs the surface area of the molten iron in the ladle, hSlag thicknessIs the slag layer thickness in the ladle, rhoDensity of molten iron slagThe density of the slag in the ladle is 1.9-3.5 t/m3(ii) a Go to step (32);
(32) setting the total mass of sulfur in the slag after molten iron desulphurization as MTotal mass of sulfur in slag after molten iron desulfurizationThe sulfur content in the slag before the molten iron desulfurization is SSulfur content of blast furnace slagPercent, the weight of the molten iron in the ladle is MWeight of molten ironThe initial sulfur content of the molten iron smelted by the converter is SInitial sulfur of molten ironPercent, and calculating the total mass of sulfur in the slag after the molten iron desulphurization according to a formula (4),
Mtotal mass of sulfur in slag after molten iron desulfurization＝(SInitial sulfur of molten iron％-STarget desulfurization grade％)×MWeight of molten iron+SSulfur content of blast furnace slagMeasurement of％×MSlag quantity of molten iron(4) (ii) a Turning to step (33);
(33) setting the weight of the scrap steel added in the smelting process of the converter to be MWeight of scrapThe content of sulfur in the scrap steel is SSulfur content of scrapPercent, the mass of resulfurization after adding the scrap steel in the smelting process of the converter is MResulfurization quality of scrap steelAnd calculating the resulfurization quality of the scrap steel according to a formula (5),
Mresulfurization quality of scrap steel＝MWeight of scrap×SSulfur content of scrap％×(1-ADesulfurization efficiency of converter％) (5)
Then setting the weight of the slagging auxiliary material added in the smelting process of the converter as MWeight of auxiliary materialsThe content of sulfur in the auxiliary material is SSulfur content of auxiliary materialPercent, the mass of resulfurization after adding slagging auxiliary materials in the smelting process of the converter is MQuality of resulfurization of auxiliary materialsCalculating the resulfurization quality of the slagging auxiliary material according to a formula (6),
Mquality of resulfurization of auxiliary materials＝MWeight of auxiliary materials×SSulfur content of auxiliary material％×(1-ADesulfurization efficiency of converter％) (6)
Wherein A isDesulfurization efficiency of converter% of the total fatty acid is 20-30%; turning to step (34);
(34) setting the mass M of resulfurization in the residual slag after slagging-offThe quality of resulfurization of the slag amount left after slag skimming is allowedAnd calculating the mass of sulfur in the residual slag after the allowable slag skimming according to a formula (7),
Mthe quality of resulfurization of the slag amount left after slag skimming is allowed＝(SSulfur content of steel grade finished product％-STarget desulfurization grade％-SRisk reservation％)×(MWeight of molten iron+MWeight of scrap)×AYield of molten steel-MResulfurization quality of scrap steel-MQuality of resulfurization of auxiliary materials(7)
Wherein A isYield of molten steelThe mass of the molten steel produced in the smelting process of the converter accounts for the total mass of the molten iron and the scrap steel, and the value is generally 95 percent; turning to step (35);
(35) setting the mass of sulfur in the slag left after slagging-off to account for the total mass of sulfur in the slag before slagging-offThe mass percentage is ARatio of amount of slag remainingAnd calculating the slag remaining quantity proportion A after slag skimming according to a formula (8)Ratio of amount of slag remaining，
ARatio of amount of slag remaining＝MThe quality of resulfurization of the slag amount left after slag skimming is allowed/MTotal mass of sulfur in slag after molten iron desulfurization(8)
Turning to the fourth step;
fourthly, determining a theoretical slag skimming weight interval, dividing the slag skimming process into an early stage and a later stage according to the iron content in the skived slag, and setting the iron coefficient of a slag skimming zone as XCoefficient of band ironThen, the coefficient of iron in the early-stage slagging-off zone is 0.1-0.4, the coefficient of iron in the later-stage slagging-off zone is 0.4-0.6, and the weight of the slag removed in the slagging-off process is set to be MAmount of slag removedThe mass of the injected material is M when the current heat is desulfurizedMass of material to be blownThen, calculating the theoretical slag-raking weight interval according to a formula (9),
Mamount of slag removed＝[MSlag quantity of molten iron+MMass of material to be blown+MWeight of molten iron×(SInitial sulfur of molten iron％-STarget desulfurization grade％)]×(1-ARatio of amount of slag remaining)×(1+XCoefficient of band iron) (9)
Turning to the fifth step;
fifthly, carrying out early-stage slagging-off operation, when the slagging-off amount reaches 50-70% of the lower limit of the theoretical slagging-off weight interval obtained in the fourth step, carrying out gas blowing and slag removing and later-stage slagging-off operation by using a gas blowing and slag removing device, monitoring by using a camera in the slagging-off operation process, enabling a camera of the camera to face the surface of molten iron, and acquiring image information of the surface of the molten iron in the molten iron ladle in real time by using the camera and transmitting the image information to an image processing module of a control system; turning to the sixth step;
sixthly, calculating to obtain the actual slag area ratio of the molten iron surface in the ladle according to the image information of the molten iron surface by an image processing module of the control system, comparing the actual slag area ratio with the target slag remaining area ratio by the control system, and judging that the expected slag skimming effect is achieved when the actual slag area ratio is the same as the target slag remaining area ratio, and finishing slag skimming; turning to the seventh step;
and step seven, weighing the weight of the slag removed to obtain the actual slag removing weight, and judging whether the actual slag removing weight is in the theoretical slag removing weight interval obtained in the step four, wherein if yes, the iron coefficient in the slag removing process is in a set interval, the slag removing quality is excellent, the iron loss is reduced, and if not, the iron coefficient is not in the set interval, and the slag removing quality is poor.
The invention fully considers the factors influencing resulfurization in the slagging process, quantificationally determines the slagging amount of the slagging according to the influence of the slag coefficient of molten iron on the slagging amount in the slagging process, establishes a slagging weight interval, quantificationally determines the area proportion of the slagging of the molten iron after slagging according to the difference of the initial sulfur content and the finished product sulfur content of the molten iron, then weighs the actual slagging weight by a metering device, transmits the actual slagging weight of the early-stage slagging operation to a display in real time so as to be convenient for observation of slagging operators, standardizes the operation of the slagging operators, guides the slagging operators to control the slagging weight, uses an air blowing slag removal device to carry out the later-stage slagging operation when the actual slagging amount reaches 50-70% of the lower limit of the theoretical slagging weight interval, uses a high-resolution camera to monitor and calculate the actual slagging area proportion in the slagging process, and determines the slagging grade, and comparing the actual slag remaining area proportion with the quantitatively determined slag remaining area proportion, and finishing slag skimming when the actual slag remaining area proportion and the quantitatively determined slag remaining area proportion are the same, wherein the method not only can accurately control the slag skimming area and the slag skimming amount to achieve the aim of accurately controlling resulfurization and the terminal sulfur content of the converter, but also can ensure that the refining rate of sulfur reaches 100 percent and reduce the slag skimming iron loss per ton of about 2 kg/t.
The technical scheme of the invention is further perfected as follows:
preferably, in the first step, the converter end point sulfur content is recorded as SEnd point sulfur content of converterPercent, the sulfur content at the end point of the converter needs to satisfy the formula (10),
Srisk reservation％＝SSulfur content of steel grade finished product％-SEnd point sulfur content of converter％ (10)。
Preferably, in the first step, said SRisk reservation% is in the range of 0-0.005%. The invention is based on the initial sulfur content of the molten ironAnd controlling the resulfurization of the molten iron slag according to the molten iron slag remaining area under different initial sulfur conditions and different steel types, so that the risk between the final sulfur content of the converter and the sulfur content of the steel type finished product is 0-0.005%, and setting a risk reservation value aims to prevent the final sulfur content of the converter from being higher than the sulfur content of the finished product and finally making the sulfur content of the steel finished product difficult to reach the steel type standard.
Preferably, in the second step, the target desulfurization grade should also satisfy formula (2),
(Ssulfur content of steel grade finished product％-SRisk reservation％-SAmount of sulfur returned from converter％)-STarget desulfurization grade％≥0.001％ (2)。
Further preferably, in the second step, the target desulfurization grade further satisfies formula (11),
0.002％≤(Ssulfur content of steel grade finished product％-SRisk reservation％-SAmount of sulfur returned from converter％)-STarget desulfurization grade％≤0.003％ (11)
Wherein S isAmount of sulfur returned from converterThe% value range is 0.003-0.006%.
Therefore, the method is favorable for obtaining proper desulfurization depth and controlling the stability of resulfurization of the molten iron slag.
Preferably, the resulfurization amount S of the converter smelting process is calculatedAmount of sulfur returned from converter%, wherein SAmount of sulfur returned from converter% of the sulfur recovery amount of the scrap steel and the sulfur recovery amount of the auxiliary materials, calculating the converter sulfur recovery according to a formula (12),
Samount of sulfur returned from converter％＝(MResulfurization quality of scrap steel+MQuality of resulfurization of auxiliary materials)÷(MWeight of molten iron×AYield of molten steel+MWeight of scrap×AYield of molten steel) (12)。
In addition, the desulfurization coefficient (i.e., A) in the converter smelting processDesulfurization efficiency of converterPercent) is calculated according to 20-30 percent, the converter desulfurization coefficient can be selected according to the converter smelting mode, and when the converter smelting adopts the slag remaining mode for smelting, the converter desulfurization coefficient is 20 percent; when the converter smelting adopts a slag-free mode for smelting, the desulfurization coefficient of the converter is 30 percent.
Preferably, between the fifth step and the sixth step, the following steps are further included: a. calculating the area proportion of the target slag, and recording the initial sulfur content of the molten iron smelted by the converter as S under the condition that the target desulfurization grade of the molten iron pretreatment is the sameInitial sulphur 1 of molten iron％，SInitial sulphur 2 of molten iron％，SInitial sulphur 3 of molten iron％，…SInitial sulfur X of molten ironPercent, acquiring the corresponding target slag remaining area proportion in the ladle according to the initial sulfur content of the molten iron, and recording the corresponding target slag remaining area proportion as A1％，A2％，A3％，…AXPercent, then calculating the initial sulfur content of the molten iron to be S under the same desulfurization grade condition according to the formula (13)Initial sulfur X of molten iron% time target slag remaining area ratio AXThe value of the percentage (c) is,
AX％＝(A2％-A1％)×(Sinitial sulphur 2 of molten iron％-SInitial sulfur X of molten iron％)÷(SInitial sulphur 2 of molten iron％-SInitial sulphur 1 of molten iron％)+A2％ (13)
Wherein S isInitial sulphur 2 of molten iron％＞SInitial sulphur 1 of molten iron％。
Preferably, in step a, SInitial sulphur 2 of molten iron％、SInitial sulphur 1 of molten iron% also needs to satisfy equation (14),
20≤(Sinitial sulphur 2 of molten iron％-SInitial sulphur 1 of molten iron％)×1000≤50 (14)。
Preferably, the following steps are further provided between the step a and the step six:
b. setting the maximum slag remaining area ratio in the ladle to AmaxPercent and the maximum slag remaining area proportion meets the formula (15),
Amaxthe percentage is less than or equal to 80 percent (15); turning to step c;
c. setting the minimum slag remaining area ratio in the ladle to AminPercent and the minimum slag remaining area proportion meets the formula (16),
Aminpercent is more than or equal to 5 percent (16); and turning to the sixth step.
The maximum slag remaining area is set to ensure that a certain exposed surface exists in the ladle so as to effectively control the thickness of the molten iron residues and further control the resulfurization of the converter; the minimum slag remaining area is set to control the molten iron loss in the slag removing process and prevent the increase of the slag removing iron loss caused by the over-small proportion of the slag remaining area.
Preferably, in the fifth step, the desulfurization before the converter smelting is carried out according to the target desulfurization grade obtained in the second step, and the early-stage slagging-off operation is carried out after the desulfurization is finished.
Preferably, in the sixth step, the specific image processing method of the control system is as follows: and the image processing module adopts an otsu algorithm to process and calculate to obtain the area proportion of the molten iron slag in the image.
The beneficial effect of the invention is that the measures of camera monitoring, weighing by a weighing system and the like are adopted to replace manual judgment, so that the refining rate of sulfur reaches 100%.
Drawings
FIG. 1 is a picture of the surface of a ladle shot by a camera after slagging-off is finished.
Fig. 2 is a schematic diagram of one embodiment of the present invention.
Detailed Description
The invention is described in further detail below with reference to embodiments and with reference to the drawings. The invention is not limited to the examples given.
As shown in fig. 2, the method of the present invention comprises the following steps:
firstly, according to the requirement of smelting and tapping steel grade finished product sulfur, setting the converter end point sulfur content (namely the mass percentage of sulfur element in the total molten steel amount at the converter end point), setting the smelting and tapping steel grade finished product sulfur content (namely the mass percentage of sulfur element in the finished product steel) to be greater than the converter end point sulfur content, setting the difference value between the two as a risk reserve value and recording as SRisk reservation％(SRisk reservationThe percentage value range is 0-0.005%), and the sulfur content at the end point of the converter is recorded as SEnd point sulfur content of converterPercent, the sulfur content of the finished steel product is recorded as SSulfur content of steel grade finished productPercent, the sulfur content at the end point of the converter needs to satisfy the formula (10),
Srisk reservation％＝SSulfur content of steel grade finished product％-SEnd point sulfur content of converter％ (10)。
Secondly, recording the sulfur return amount in the converter smelting process (namely the mass percentage of the sulfur element returned to the molten steel in the converter smelting process in the total amount of the molten steel) as SAmount of sulfur returned from converter% and the target desulfurization grade before converter smelting and in the molten iron pretreatment process is recorded as STarget desulfurization gradePercent (namely the mass percent of the sulfur element which is expected to be removed by desulfurization treatment and accounts for the total amount of the molten iron) and then according to the sulfur content S of the finished steel productSulfur content of steel grade finished product% requirement and SAmount of sulfur returned from converter％、SRisk reservation% to determine a target desulfurization level of the molten iron pretreatment such that the target desulfurization level satisfies formula (1),
Starget desulfurization grade％≤SSulfur content of steel grade finished product％-SRisk reservation％-SAmount of sulfur returned from converter％ (1)
At the above-mentioned STarget desulfurization grade% is an integer. Wherein, the target desulfurization grade also needs to satisfy the formula (2),
(Ssulfur content of steel grade finished product％-SRisk reservation％-SAmount of sulfur returned from converter％)-STarget desulfurization grade％≥0.001％ (2)，
The target desulfurization grade preferably satisfies formula (11),
0.002％≤(Ssulfur content of steel grade finished product％-SRisk reservation％-SAmount of sulfur returned from converter％)-STarget desulfurization grade％≤0.003％ (11)
Wherein S isAmount of sulfur returned from converterThe% value range is 0.003-0.006%.
In addition, the resulfurization amount S in the converter smelting processAmount of sulfur returned from converter% of the sulfur recovery amount of the scrap steel and the sulfur recovery amount of the auxiliary materials, calculating the converter sulfur recovery according to a formula (12),
Samount of sulfur returned from converter％＝(MResulfurization quality of scrap steel+MQuality of resulfurization of auxiliary materials)÷(MWeight of molten iron×AYield of molten steel+MWeight of scrap×AMolten steelYield of the product)(12)。
Thirdly, considering the influence of the slag quantity of the molten iron on the sulfur concentration in the slag after the molten iron is desulfurized, and recording the weight of the slag of the desulfurized molten iron in the molten iron as MSlag quantity of molten ironAnd the weight of the slag in the ladle after the molten iron is desulfurized is calculated according to the formula (3) after the thickness of the slag layer is measured,
Mslag quantity of molten iron＝SArea of ladle×hSlag thickness×ρDensity of molten iron slag(3)
Wherein SArea of ladleIs the surface area of the molten iron in the ladle, hSlag thicknessIs the slag layer thickness in the ladle, rhoDensity of molten iron slagThe density of the slag in the ladle is 1.9-3.5 t/m3(ii) a Go to step (32);
(32) setting the total mass of sulfur in the slag after molten iron desulphurization as MTotal mass of sulfur in slag after molten iron desulfurizationThe sulfur content in the slag before the molten iron desulfurization is SSulfur content of blast furnace slagPercent, the weight of the molten iron in the ladle is MWeight of molten ironThe initial sulfur content of the molten iron smelted by the converter is SInitial sulfur of molten ironPercent, and calculating the total mass of sulfur in the slag after the molten iron desulphurization according to a formula (4),
Mtotal mass of sulfur in slag after molten iron desulfurization＝(SInitial sulfur of molten iron％-STarget desulfurization grade％)×MWeight of molten iron+SSulfur content of blast furnace slag％×MSlag quantity of molten iron(4) (ii) a Turning to step (33);
(33) setting the weight of the scrap steel added in the smelting process of the converter to be MWeight of scrapThe content of sulfur in the scrap steel is SSulfur content of scrapPercent, the mass of resulfurization after adding the scrap steel in the smelting process of the converter is MResulfurization quality of scrap steelAnd calculating the resulfurization quality of the scrap steel according to a formula (5),
Mresulfurization quality of scrap steel＝MWeight of scrap×SSulfur content of scrap％×(1-ADesulfurization efficiency of converter％) (5)
Then setting the weight of the slagging auxiliary material added in the smelting process of the converter as MWeight of auxiliary materialsIn the auxiliary materialsThe content of sulfur being SSulfur content of auxiliary materialPercent, the mass of resulfurization after adding slagging auxiliary materials in the smelting process of the converter is MQuality of resulfurization of auxiliary materialsCalculating the resulfurization quality of the slagging auxiliary material according to a formula (6),
Mquality of resulfurization of auxiliary materials＝MWeight of auxiliary materials×SSulfur content of auxiliary material％×(1-ADesulfurization efficiency of converter％) (6)
Wherein A isDesulfurization efficiency of converter% of the total sulfur content is 20-30%, and the desulfurization coefficient (namely A) in the smelting process of the converterDesulfurization efficiency of converterPercent) is calculated according to 20-30 percent, the converter desulfurization coefficient can be selected according to the converter smelting mode, and when the converter smelting adopts the slag remaining mode for smelting, the converter desulfurization coefficient is 20 percent; when the converter smelting adopts a slag-free mode for smelting, the desulfurization coefficient of the converter is 30 percent; turning to step (34);
(34) setting the mass M of resulfurization in the residual slag after slagging-offThe quality of resulfurization of the slag amount left after slag skimming is allowedAnd calculating the mass of sulfur in the residual slag after the allowable slag skimming according to a formula (7),
Mthe quality of resulfurization of the slag amount left after slag skimming is allowed＝(SSulfur content of steel grade finished product％-STarget desulfurization grade％-SRisk reservation％)×(MWeight of molten iron+MWeight of scrap)×AYield of molten steel-MResulfurization quality of scrap steel-MQuality of resulfurization of auxiliary materials(7)
Wherein A isYield of molten steelThe mass of the molten steel produced in the smelting process of the converter accounts for the total mass of the molten iron and the scrap steel, and the value is generally 95 percent; turning to step (35);
(35) the mass percentage of the mass of the sulfur in the residual slag after the slag skimming to the total mass of the sulfur in the slag before the slag skimming is set as ARatio of amount of slag remainingAnd calculating the slag remaining quantity proportion A after slag skimming according to a formula (8)Ratio of amount of slag remaining，
ARatio of amount of slag remaining＝MThe quality of resulfurization of the slag amount left after slag skimming is allowed/MTotal mass of sulfur in slag after molten iron desulfurization(8)。
Thus, a slag amount proportion formula after slagging-off is determined according to the initial sulfur content of molten iron, the slag amount of molten iron before desulfurization, the sulfur content of molten iron slag, the slag amount of molten iron after desulfurization, the resulfurization amount in the smelting process of the converter and the requirement of the sulfur of a steel product, and the proportion of the residual slag allowed to remain when the set end-point sulfur content of the converter is reached is calculated.
Fourthly, determining a theoretical slag skimming weight interval, dividing the slag skimming process into an early stage and a later stage according to the iron content in the skived slag, and setting the iron coefficient of a slag skimming zone as XCoefficient of band ironThen, the coefficient of iron in the early-stage slagging-off zone is 0.1-0.4, the coefficient of iron in the later-stage slagging-off zone is 0.4-0.6, and the weight of the slag removed in the slagging-off process is set to be MAmount of slag removedThe mass of the injected material is M when the current heat is desulfurizedMass of material to be blownThen, calculating the theoretical slag-raking weight interval according to a formula (9),
Mamount of slag removed＝[MSlag quantity of molten iron+MMass of material to be blown+MWeight of molten iron×(SInitial sulfur of molten iron％-STarget desulfurization grade％)]×(1-ARatio of amount of slag remaining)×(1+XCoefficient of band iron) (9)。
The iron content of the slag-off product is determined to be 0.1-0.4 because the slag amount in the early slag-off process is large and the iron content in the slag is small, and the iron content of a large amount of molten iron slag is high when the molten iron slag is removed for fine slag-off, so the iron content of the slag-off product in the later period is 0.4-0.6, and the slag-off weight interval during slag-off can be obtained according to the proportion of the slag amount and the iron content coefficient during slag-off.
Fifthly, carrying out desulfurization before converter smelting according to the target desulfurization grade obtained in the second step, carrying out early-stage slagging operation after desulfurization is finished, weighing the weight of the slag removed in the early-stage slagging operation process, when the actual slagging amount reaches 50-70% of the lower limit of the theoretical slagging weight interval obtained in the fourth step, using an air blowing slag removing device to continuously carry out air blowing slag removing and later-stage slagging operation, controlling the insertion depth of a slagging head to be 150-250 mm during the air blowing slag removing and later-stage slagging operation, carrying out slagging in the sequence of the middle and the two sides, stopping the slagging head at a tank opening for 2-3 seconds every time the slagging head removes slag, thus being beneficial to reducing slagging iron loss, adopting a camera to monitor in the later-stage slagging operation process, enabling the camera of the camera to face the surface of molten iron, acquiring image information of the surface of the molten iron in the molten iron ladle in real time and transmitting the image information (namely the change condition of the area of the molten iron in the molten iron ladle) to an image processing module of a control system And (4) keeping the tilting angles of the ladle before and after slag skimming unchanged.
a. Calculating the target slag area proportion, and recording the initial sulfur content of the molten iron smelted by the converter (namely the mass percentage of sulfur element in the molten iron before smelting by the converter to the total amount of the molten iron) as S under the condition that the target desulfurization grade of the molten iron pretreatment is the sameInitial sulphur 1 of molten iron％，SInitial sulphur 2 of molten iron％，SInitial sulphur 3 of molten iron％，…SInitial sulfur X of molten ironPercent, acquiring the corresponding target slag remaining area ratio (area percentage, namely the percentage of the slag area after slag skimming to the surface area of the molten iron) before and after the molten iron is skimmed in the molten iron ladle according to the initial sulfur content of the molten iron, and recording the corresponding target slag remaining area ratio as A1％，A2％，A3％，…AX% to obtain A1％、A2% and value of initial sulfur content of molten iron (e.g. S)Initial sulphur 1 of molten iron％，SInitial sulphur 2 of molten iron％，SInitial sulphur 3 of molten iron％,…SInitial sulfur X of molten iron%) and then calculating the initial sulfur content of the molten iron to be S according to the formula (13) under the same desulfurization grade conditionInitial sulfur X of molten iron% time target slag remaining area ratio AXThe value of the percentage (c) is,
AX％＝(A2％-A1％)×(Sinitial sulphur 2 of molten iron％-SInitial sulfur X of molten iron％)÷(SInitial sulphur 2 of molten iron％-SInitial sulphur 1 of molten iron％)+A2％(13)
Wherein S isInitial sulphur 2 of molten iron％＞SInitial sulphur 1 of molten iron％，SInitial sulphur 2 of molten iron％、SInitial sulphur 1 of molten iron% also needs to satisfy equation (14),
20≤(Sinitial sulphur 2 of molten iron％-SInitial sulphur 1 of molten iron％)×1000≤50 (14)。
b. Setting the maximum slag remaining area ratio in the ladle to AmaxPercent and the maximum slag remaining area proportion meets the formula (15),
Amaxthe percentage is less than or equal to 80 percent (15); turning to step c;
c. setting the minimum slag remaining area ratio in the ladle to AminPercent and the minimum slag remaining area proportion meets the formula (16),
Amin％≥5％ (16)。
sixthly, calculating to obtain the actual slag area ratio of the molten iron surface in the ladle according to the image information of the molten iron surface by an image processing module of the control system, wherein the specific image processing method of the control system is as follows: the image processing module or software adopts otsu algorithm (also called maximum inter-class variance method, Dajin algorithm, which is considered as the optimal algorithm for image threshold segmentation, and the calculation is simple, is not affected by image brightness and contrast and has the lowest error rate), and the area proportion of the molten iron slag in the image is obtained after the calculation. And then the control system compares the actual slag area proportion with the target slag remaining area proportion, and when the actual slag area proportion is the same as the target slag remaining area proportion, the control system judges that the expected slag skimming effect is achieved, and skimming is finished.
And step seven, weighing the weight of the slag removed to obtain the actual slag removing weight, and judging whether the actual slag removing weight is in the theoretical slag removing weight interval obtained in the step four, wherein if yes, the iron coefficient in the slag removing process is in a set interval, the slag removing quality is excellent, the iron loss is reduced, and if not, the iron coefficient is not in the set interval, and the slag removing quality is poor.
Examples
Producing a steel grade which requires S for sulfurSulfur content of steel grade finished product% is 0.0125%, and sulfur requirement of converter end point is SEnd point sulfur content of converter% is 0.0095%, SAmount of sulfur returned from converter% is 0.003-0.006%. Current heat SInitial sulfur of molten iron% of 0.025%, sulfur content (S) in scrapSulfur content of scrap% of the steel scrap was 0.025% by weight (M)Weight of scrap) 38 tons of ironWeight of water (M)Weight of molten iron) 252 tons, mass percent of sulfur in the molten iron slag (S)Sulfur content of blast furnace slag% is 0.9% and the ladle area, i.e., the internal molten iron surface area (S) of the ladleArea of ladle) Is 15.2m2Measuring the thickness (h) of the molten iron slag of the current heatSlag thickness) 0.06m, density (. rho.) of molten iron slagDensity of molten iron slag) Is 2.0t/m3，AYield of molten steelTaking 95% of ADesulfurization efficiency of converter% of 20%, XCoefficient of band ironThe value range is 0.2-0.5.
1. Determining the proportion of the amount of the slag left under different initial sulfur conditions: firstly, determining S according to the sulfur content of the steel grade finished product and the end point sulfur content of the converterRisk reservationPercent is 0.003 percent. Thirdly, calculating the resulfurization amount S of the converter smelting process according to the resulfurization amount of the scrap steel and the resulfurization amount of the auxiliary materialsAmount of sulfur returned from converter％＝(MResulfurization quality of scrap steel+MQuality of resulfurization of auxiliary materials)÷(MWeight of molten iron×AYield of molten steel+MWeight of scrap×AYield of molten steel) (0.0076t +0.00264t) ÷ (252t × 95% +38t × 95%) -0.0037%, then SAmount of sulfur returned from converter% in the range of 0.003% to 0.006%. In addition, SAmount of sulfur returned from converter% maximum value according to desulfurization grade STarget desulfurization grade％≤SSulfur content of steel grade finished product％-SRisk reservation％-SAmount of sulfur returned from converter% of the principle, STarget desulfurization grade％≤0.0035％。SAmount of sulfur returned from converter% is 0.0037%, SSulfur content of steel grade finished product％-SRisk reservation％-SAmount of sulfur returned from converter0.0125% -0.003% -0.0037% -0.0058%, and satisfies (S)Sulfur content of steel grade finished product％-SRisk reservation％-SAmount of sulfur returned from converter％)-STarget desulfurization gradeMore than or equal to 0.001 percent, preferably less than or equal to 0.002 percent (S)Sulfur content of steel grade finished product％-SRisk reservation％-SAmount of sulfur returned from converter％)-STarget desulfurization grade％≤0.003％，0.0058％-0.003≤STarget desulfurization grade0.0058-0.002%, i.e. 0.0028-0.002STarget desulfurization grade0.0038 percent, wherein S isTarget removerSulphur grade% is an integer of 0.003%, thus STarget desulfurization gradeThe% value is 0.003% reasonably.
Secondly, the influence of the slag quantity of the molten iron on the sulfur concentration in the slag after the molten iron is desulfurized is considered, and the weight M of the slag in the ladle after the molten iron is desulfurized is calculated and obtainedSlag quantity of molten iron＝SArea of ladle×hSlag thickness×ρDensity of molten iron slag＝15.2㎡×0.06m×2.0t/m31.824t, the total mass M of sulfur in the slag after hot metal desulfurizationTotal mass of sulfur in slag after molten iron desulfurization＝(SInitial sulfur of molten iron％-STarget desulfurization grade％)×MWeight of molten iron+SSulfur content of blast furnace slag％×MSlag quantity of molten ironAfter the weight M of the resulfurized scrap steel is calculated, wherein the weight M is equal to (0.025% -0.003%) × 252t + 0.9% × 1.824.824 t equal to 0.071856tResulfurization quality of scrap steel＝MWeight of scrap×SSulfur content of scrap％×(1-ADesulfurization efficiency of converter38t × 0.025.025 percent × (1-20 percent) 0.0076t, and calculating the mass M of the resulfurization of the slagging auxiliary materialQuality of resulfurization of auxiliary materials＝MWeight of auxiliary materials×SSulfur content of auxiliary material％×(1-ADesulfurization efficiency of converter5t × 0.035.035% × (1-20%) +3t × 0.035.035% × (1-20%) +2t × 0.02.02% × (1-20%) -0.00264t, and auxiliary material (M) is addedWeight of auxiliary materials) The lime-light burned dolomite production line is 10 tons and comprises lime, light burned dolomite and ore, wherein the sulfur content of the lime is 0.035%, the using amount of the lime is 5 tons, the sulfur content of the light burned dolomite is 0.035%, the using amount of the light burned dolomite is 3 tons, the sulfur content of the ore is 0.02%, and the using amount of the ore is 2 tons. The allowable mass M of sulfur in the slag remaining after slag skimmingThe quality of resulfurization of the slag amount left after slag skimming is allowed＝(SSulfur content of steel grade finished product％-STarget desulfurization grade％-SRisk reservation％)×(MWeight of molten iron+MWeight of scrap)×AYield of molten steel-MResulfurization quality of scrap steel-MQuality of resulfurization of auxiliary materials(0.0125% -0.003% -0.003%) × (252t +38t) × 95% -0.0076t-0.00264t ═ 0.0076675t, and finally, calculating the ratio A of the slag quantity left after slag skimmingRatio of amount of slag remaining＝MThe quality of resulfurization of the slag amount left after slag skimming is allowed/MMolten iron desulphurization after-furnaceTotal mass of sulfur in slag＝10.67％。
2. Determining a theoretical slag skimming weight interval: calculating theoretical slag skimming weight interval MAmount of slag removed＝[MSlag quantity of molten iron+MMass of material to be blown+MWeight of molten iron×(SInitial sulfur of molten iron％-STarget desulfurization grade％)]×(1-ARatio of amount of slag remaining)×(1+XCoefficient of band iron)＝[1.824t+0.4t+252t×(0.025％-0.003％)]× (1-10.67%) × (1+ 0.2-0.5) ═ 2.443 t-3.054 t, where MMass of material to be blownThe method is determined according to an actual model, and different models have different values.
3. The method comprises the steps of carrying out desulfurization before converter smelting according to a target desulfurization grade, carrying out early-stage slagging-off operation after desulfurization is finished, weighing the weight of the slag to be removed in the early-stage slagging-off operation process, when the actual slagging-off amount reaches 50% (namely 1.2215t) of the lower limit of a theoretical slagging-off weight interval, using an air blowing slag removing device to continuously carry out air blowing slag removing and later-stage slagging-off operation, controlling the insertion depth of a slag removing head to be 150-250 mm during the air blowing slag removing and later-stage slagging-off operation, carrying out slagging-off in the sequence of the first middle part and the second side part, and stopping the slag removing head at a tank mouth for 2-3 seconds when the slag removing head is used for removing slag and iron.
4. Adopt the camera to monitor among the later stage slagging-off operation process, the camera of camera is towards the molten iron surface, and the image information of molten iron surface in the ladle is acquireed in real time to the camera and transmits image information for control system's image processing module and carries out image processing, confirms the area proportion of remaining slag under the different initial sulphur conditions simultaneously: when the initial sulfur content S of the molten iron smelted by the converterInitial sulphur 2 of molten ironWhen% > is 0.05%, the compound is STarget amount of flowPerforming desulfurization control on percent of S to be 0.003 percent, and selecting S in the smelting process of a converterAmount of sulfur returned from converter% of the heat is between 0.003 and 0.006 percent, and the initial sulfur content S of the molten iron is obtained through a cameraInitial sulphur 2 of molten ironThe ratio of the area of the slag left in the molten iron is 0.05 percent2Percent is 30 percent; when the initial sulfur content S of the molten ironInitial sulphur 1 of molten ironWhen% > is 0.010%, the compound is STarget desulfurization gradePerforming desulfurization control on percent of S to be 0.003 percent, and selecting S in the smelting process of a converterAmount of sulfur returned from converterThe furnace number with the% level between 0.003 and 0.006 percent is obtained through a camera, and the initial sulfur content S of the molten iron is obtainedInitial sulphur 1 of molten ironThe area ratio A of the slag left in the molten iron under the level of 0.010%170% by weight, the final sulfur content obtained was S at the initial sulfur contentInitial sulfur X of molten iron% of the area ratio A of the target slagX％＝(A2％-A1％)×(SInitial sulphur 2 of molten iron％-SInitial sulfur X of molten iron％)÷(SInitial sulphur 2 of molten iron％-SInitial sulphur 1 of molten iron％)+A2％＝(70％-30％)×(0.05％-Sx%) + 30% and/or (0.05% -0.01%). Then, when the initial sulfur content S of the molten ironInitial sulfur x of molten ironWhen the percentage is 0.02%, the corresponding target slag remaining area ratio is AXFrom the above equation, the initial sulfur content S of molten iron can be obtained by dividing% by (70% -30%) × (0.05% -0.02%) + by (0.05% -0.01%) + 30% + 60%Initial sulfur x of molten iron% target area proportion of slag at various levels, results are shown in Table 1.
TABLE 1 area ratio of slag left in different initial sulfur conditions of molten iron
5. Firstly, dividing the gray degree of an image into two parts according to the gray level by adopting a clustering idea so that the difference between the two parts is maximum, the difference inside the two parts is minimum (the suitable gray level division level is found through the calculation of variance), supposing that T is a set threshold and is the suitable gray level division level, W0 is the proportion of the pixel points of the divided molten iron to the image, U0 is the average gray level of the divided molten iron, W1 is the proportion of the pixel points of the divided molten iron to the image, U1 is the average gray level of the divided molten iron, wherein W0, U1, U1, the pixel points of the divided molten iron occupy the image, W L is obtained through a preset threshold, the variance of the pixel points of the divided molten iron occupies the image, U1 is the average gray level of the divided molten iron, wherein the value of the T is the value of a traversal formula of 35255, the maximum value of the T26 is obtained through the preset threshold, and the value of the traversal formula T is an integral value of the molten iron, wherein the value of the T is obtained through the formula, and the following steps:
g＝W0×W1×(U0-U1)2
and carrying out T value calculation on a large number of images shot on site through an otsu algorithm to obtain the molten iron and the iron slag which can be effectively segmented when the segmentation threshold value of the molten iron and the iron slag is 25-70. And when the T value is used, the shot image is segmented and dyed, the molten iron is used when the actual value is greater than 70, the molten iron is used when the actual value is 25-70, the molten iron is reflected in the red area of the image, and the iron slag is reflected in the green area of the image. When the pixel number of the molten iron is represented by COUNT (f is red) and the pixel number of the iron slag is represented by COUNT (f is green), the area ratio of the iron slag can be calculated as follows:
and then, the control system compares the actual slag area proportion with the target slag remaining area proportion, and when the actual slag area proportion is the same as the target slag remaining area proportion, the control system judges that the expected slag skimming effect is achieved, and skimming is finished. For example, when the initial sulfur content of the molten iron is 0.022%, the corresponding slag remaining area proportion is 58%, the molten iron slag area proportion in the ladle is calculated in real time through image processing software, and slagging off is finished when the slag area proportion reaches 58%.
6. Weighing the weight of the slag removed to obtain the actual slag removing weight, and judging whether the actual slag removing weight is within the theoretical slag removing weight interval, if so, indicating that the iron content coefficient is within a set interval in the slag removing process, the slag removing quality is excellent, and the iron loss is favorably reduced, otherwise, indicating that the iron content coefficient is not within the set interval, and the slag removing quality is poor.
In a word, according to the initial sulfur content of molten iron and the influence of scrap steel and auxiliary materials on resulfurization in the smelting process of a converter, the mass proportion of the allowable residual sulfur when the set end-point sulfur content of the converter is reached is calculated, after the mass proportion of the allowable residual sulfur is obtained, further determining a reasonable slagging weight interval by determining the iron content coefficient of the slagging product, then carrying out desulfurization, carrying out early-stage slagging-off operation after desulfurization, transmitting the slagging-off weight in real time through a weighing system on a molten iron car, when the slag removing weight reaches 50-70% of the lower limit of the theoretical slag removing weight interval, the air blowing slag removing device is used for carrying out air blowing slag removing and later-stage slag removing operation, the camera is used for acquiring the molten iron slag area in the ladle during the slag removing operation, meanwhile, the molten iron slag area is calculated in real time, determining different target slag remaining area proportions according to the difference of the initial sulfur content of the molten iron and the sulfur content of the steel type finished product, and finishing slagging when the actual molten iron slag area reaches the target slag remaining area.
In addition to the above embodiments, the present invention may have other embodiments. All technical solutions formed by adopting equivalent substitutions or equivalent transformations fall within the protection scope of the claims of the present invention.
Claims (8)
1. A method for reducing slagging loss of molten iron is characterized by comprising the following steps:
firstly, according to the requirement of smelting and tapping steel grade finished product sulfur, the sulfur content of the steel grade finished product is greater than the end point sulfur content of a converter, the difference value between the two is set as a risk reserve value and is recorded as SRisk reservationPercent; turning to the second step;
secondly, recording the sulfur content of the steel product as S in percentage by massSulfur content of steel grade finished productPercent, the resulfurization amount in the converter smelting process is recorded as SAmount of sulfur returned from converter% and the target desulfurization grade in the pretreatment of molten iron is recorded as STarget desulfurization gradePercent, and then according to the sulfur content S of the finished steel productSulfur content of steel grade finished product% requirement and SAmount of sulfur returned from converter%、SRisk reservation% to determine a target desulfurization level of the molten iron pretreatment such that the target desulfurization level satisfies formula (1),
Starget desulfurization grade%≤SSulfur content of steel grade finished product%- SRisk reservation%- SAmount of sulfur returned from converter% （1）
Turning to the third step;
third step, (31) adding ironThe weight of the slag in the desulfurized molten iron in the water drum is recorded as MSlag quantity of molten ironAnd calculating the weight of the slag in the ladle after the molten iron is desulfurized according to the formula (3),
Mslag quantity of molten iron=SArea of ladle×hSlag thickness×ρDensity of molten iron slag（3）
Wherein SArea of ladleIs the surface area of the molten iron in the ladle, hSlag thicknessIs the slag layer thickness in the ladle, rhoDensity of molten iron slagIs the density of the slag in the ladle; go to step (32);
(32) setting the total mass of sulfur in the slag after molten iron desulphurization as MTotal mass of sulfur in slag after molten iron desulfurizationThe sulfur content in the slag before the molten iron desulfurization is SSulfur content of blast furnace slagPercent, the weight of the molten iron in the ladle is MWeight of molten ironThe initial sulfur content of the molten iron smelted by the converter is SInitial sulfur of molten ironPercent, and calculating the total mass of sulfur in the slag after the molten iron desulphurization according to a formula (4),
Mtotal mass of sulfur in slag after molten iron desulfurization=（SInitial sulfur of molten iron%- STarget desulfurization grade%）×MWeight of molten iron+ SSulfur content of blast furnace slag%×MSlag quantity of molten iron(4) (ii) a Turning to step (33);
(33) setting the weight of the scrap steel added in the smelting process of the converter to be MWeight of scrapThe content of sulfur in the scrap steel is SSulfur content of scrapPercent, the mass of resulfurization after adding the scrap steel in the smelting process of the converter is MResulfurization quality of scrap steelAnd calculating the resulfurization quality of the scrap steel according to a formula (5),
Mresulfurization quality of scrap steel=MWeight of scrap×SSulfur content of scrap%×（1-ADesulfurization efficiency of converter%） （5）
Then setting the weight of the slagging auxiliary material added in the smelting process of the converter as MWeight of auxiliary materialsThe content of sulfur in the auxiliary material is SSulfur content of auxiliary materialPercent, the mass of resulfurization after adding slagging auxiliary materials in the smelting process of the converter is MQuality of resulfurization of auxiliary materialsCalculating the resulfurization quality of the slagging auxiliary material according to a formula (6),
Mquality of resulfurization of auxiliary materials=MWeight of auxiliary materials×SSulfur content of auxiliary material%×（1-ADesulfurization efficiency of converter%） （6）
Wherein A isDesulfurization efficiency of converter% of the total fatty acid is 20-30%; turning to step (34);
(34) setting the mass M of resulfurization in the residual slag after slagging-offThe quality of resulfurization of the slag amount left after slag skimming is allowedAnd calculating the mass of sulfur in the residual slag after the allowable slag skimming according to a formula (7),
Mthe quality of resulfurization of the slag amount left after slag skimming is allowed=（SSulfur content of steel grade finished product%-STarget desulfurization grade%- SRisk reservation%）×（MWeight of molten iron+MWeight of scrap）×AYield of molten steel-MResulfurization quality of scrap steel-MQuality of resulfurization of auxiliary materials（7）
Wherein A isYield of molten steelThe mass of the molten steel produced in the smelting process of the converter accounts for the total mass of the molten iron and the scrap steel; turning to step (35);
(35) the mass percentage of the mass of the sulfur in the residual slag after the slag skimming to the total mass of the sulfur in the slag before the slag skimming is set as ARatio of amount of slag remainingAnd calculating the slag remaining quantity proportion A after slag skimming according to a formula (8)Ratio of amount of slag remaining，
ARatio of amount of slag remaining=MThe quality of resulfurization of the slag amount left after slag skimming is allowed/MTotal mass of sulfur in slag after molten iron desulfurization（8）
Turning to the fourth step;
fourthly, determining a theoretical slag skimming weight interval, dividing the slag skimming process into an early stage and a later stage according to the iron content in the skived slag, and setting the iron coefficient of a slag skimming zone as XCoefficient of band ironThen, the coefficient of iron in the early-stage slagging-off zone is 0.1-0.4, the coefficient of iron in the later-stage slagging-off zone is 0.4-0.6, and the weight of the slag removed in the slagging-off process is set to be MAmount of slag removedThe mass of the injected material is M when the current heat is desulfurizedMass of material to be blownThen, calculating the theoretical slag-raking weight interval according to a formula (9),
Mamount of slag removed=［MSlag quantity of molten iron+MMass of material to be blown+MWeight of molten iron×（SInitial sulfur of molten iron%- STarget desulfurization grade%）］×（1-ARatio of amount of slag remaining）×（1+XCoefficient of band iron） （9）
Turning to the fifth step;
fifthly, carrying out early-stage slagging-off operation, when the slagging-off amount reaches 50-70% of the lower limit of the theoretical slagging-off weight interval obtained in the fourth step, carrying out gas blowing and slag removing and later-stage slagging-off operation by using a gas blowing and slag removing device, monitoring by using a camera in the slagging-off operation process, enabling a camera of the camera to face the surface of molten iron, and acquiring image information of the surface of the molten iron in the molten iron ladle in real time by using the camera and transmitting the image information to an image processing module of a control system;
a. calculating the area proportion of the target slag, and recording the initial sulfur content of the molten iron smelted by the converter as S under the condition that the target desulfurization grade of the molten iron pretreatment is the sameInitial sulphur 1 of molten iron%，SInitial sulphur 2 of molten iron%，SInitial sulphur 3 of molten iron%，…SInitial sulfur X of molten ironPercent, acquiring the corresponding target slag remaining area proportion in the ladle according to the initial sulfur content of the molten iron, and recording the corresponding target slag remaining area proportion as A1%，A2%，A3%，…AXPercent, then calculating the initial sulfur content of the molten iron as S according to a formula (13)Initial sulfur X of molten iron% time target slag remaining area ratio AXThe value of the percentage (c) is,
AX%=（A2%-A1%）×（Sinitial sulphur 2 of molten iron%-SInitial sulfur X of molten iron%）÷（SInitial sulphur 2 of molten iron%-SInitial sulphur 1 of molten iron%）+A2% （13）
Wherein S isInitial sulphur 2 of molten iron%＞SInitial sulphur 1 of molten iron%；
b. Setting the maximum slag remaining area ratio in the ladle to AmaxPercent and the maximum slag remaining area proportion meets the formula (15),
Amaxthe percentage is less than or equal to 80 percent (15); turning to step c;
c. setting the minimum slag remaining area ratio in the ladle to AminPercent and the minimum slag remaining area proportion meets the formula (16),
Aminpercent is more than or equal to 5 percent (16); turning to the sixth step;
sixthly, calculating to obtain the actual slag area ratio of the molten iron surface in the ladle according to the image information of the molten iron surface by an image processing module of the control system, comparing the actual slag area ratio with the target slag remaining area ratio by the control system, and judging that the expected slag skimming effect is achieved when the actual slag area ratio is the same as the target slag remaining area ratio, and finishing slag skimming; turning to the seventh step;
and step seven, weighing the weight of the slag removed to obtain the actual slag removing weight, and judging whether the actual slag removing weight is in the theoretical slag removing weight interval obtained in the step four, wherein if yes, the iron coefficient in the slag removing process is in a set interval, the slag removing quality is excellent, the iron loss is reduced, and if not, the iron coefficient is not in the set interval, and the slag removing quality is poor.
2. The method for reducing the slagging loss of the molten iron according to claim 1, which is characterized in that: in the first step, the converter end point sulfur content is recorded as SEnd point sulfur content of converterPercent, the sulfur content at the end point of the converter needs to satisfy the formula (10),
Srisk reservation%=SSulfur content of steel grade finished product%- SEnd point sulfur content of converter% （10）。
3. The method for reducing the slagging loss of the molten iron according to claim 2, which is characterized in that: in the first step, SRisk reservation% is in the range of 0-0.005%.
4. The method for reducing the slagging loss of the molten iron according to claim 1, which is characterized in that: in the second step, the target desulfurization grade also needs to satisfy the formula (2),
（Ssulfur content of steel grade finished product%- SRisk reservation%- SAmount of sulfur returned from converter%）- STarget desulfurization grade%≥0.001% （2）。
5. The method for reducing the slagging loss of molten iron according to claim 4, wherein in the second step, the target desulfurization grade further satisfies equation (11),
0.002%≤（Ssulfur content of steel grade finished product%- SRisk reservation%- SAmount of sulfur returned from converter%）- STarget desulfurization grade%≤0.003% （11）。
6. The method for reducing the slagging loss of the molten iron according to claim 1, which is characterized in that: calculating the resulfurization quantity S of the converter smelting processAmount of sulfur returned from converter%, wherein SAmount of sulfur returned from converter% of the sulfur recovery amount of the scrap steel and the sulfur recovery amount of the auxiliary materials, calculating the converter sulfur recovery according to a formula (12),
Samount of sulfur returned from converter%=（MResulfurization quality of scrap steel+ MQuality of resulfurization of auxiliary materials）÷（MWeight of molten iron×AYield of molten steel+ MWeight of scrap×AYield of molten steel） （12）。
7. The method for reducing the slagging loss of the molten iron according to claim 1, which is characterized in that: in step a, SInitial sulphur 2 of molten iron%、SInitial sulphur 1 of molten iron% also needs to satisfy equation (14),
20≤（Sinitial sulphur 2 of molten iron%- SInitial sulphur 1 of molten iron%）×1000≤50 （14）。
8. The method for reducing the slagging loss of the molten iron according to claim 1, which is characterized in that: in the fifth step, the desulfurization before the smelting of the converter is carried out according to the target desulfurization grade obtained in the second step, and the early-stage slag skimming operation is carried out after the desulfurization is finished; in the sixth step, the specific image processing method of the control system is as follows: and the image processing module adopts an otsu algorithm to process and calculate to obtain the area proportion of the molten iron slag in the image.
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