Precise control method for harmful elements in molten iron

Abstract

The invention belongs to the technical field of steel smelting, and particularly relates to a precision control method for harmful elements in molten iron. Comprising the following steps: S1, online detection: carrying out real-time component analysis on molten iron in a molten iron tank by utilizing an online detection device to obtain real-time contents of sulfur, phosphorus and arsenic elements; s2, model calculation: the multi-element cooperative control model calculates the total amount of required additives according to the real-time content and based on an inter-element interaction compensation algorithm; and S3, additive injection, wherein the additive is injected into the molten iron through a staged gradient temperature control injection process. According to the method, cooperative control of S, P and As elements is established through a multi-element cooperative control model by virtue of an LIBS (laser-induced breakdown spectroscopy) online detection device, and the dosage of the additive is actively adjusted in real time, so that the influence of excessive or insufficient additives on removal of harmful elements is avoided, and the control precision of the harmful elements is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel smelting, and particularly relates to a precise control method for harmful elements in molten iron. BACKGROUND

[0002] In the process flow of blast furnace ironmaking-converter steelmaking, the pretreatment of molten iron (desulfurization, dephosphorization and dearsenization) is a key link to ensure the quality of final steel. At present, steel plants generally use spectral analysis to analyze harmful components in molten iron, which needs manual sampling and sample preparation, and the analysis results are seriously lagging, so that real-time feedback control cannot be realized, resulting in the pretreatment process being in a "blind adjustment" state. At the same time, the control of harmful elements is based on the empirical formula of mixing uniformity, and the principle is to assume that the average content of harmful elements in the mixed material is equal to the weighted average of the content of the element in various charging raw materials. The essence of this technology is preventive control. This method has a large mixing amount, and the control of harmful elements is not accurate, and is greatly affected by raw material fluctuations and experience. Moreover, once the mixed material pile is built, the composition cannot be adjusted. Therefore, in order to ensure the pretreatment effect, an excessive amount of additives is generally used, resulting in low utilization efficiency of additives and high production cost. SUMMARY

[0003] The application aims to provide a precise control method for harmful elements in molten iron to solve the problems in the prior art.

[0004] The technical scheme adopted by the application to solve the technical problems is as follows:

[0005] A precise control method for harmful elements in molten iron, comprising the following steps:

[0006] S1, online detection: using an online detection device to perform real-time component analysis on the molten iron in the molten iron tank to obtain the real-time content of sulfur, phosphorus and arsenic elements;

[0007] S2, model calculation: a multi-element collaborative control model calculates the total amount of required additives based on the real-time content and an element interaction compensation algorithm;

[0008] S3, additive injection: injecting the additives into the molten iron through a staged gradient temperature control injection process.

[0009] Further, the online monitoring device in step S1 is a LIBS laser-induced breakdown spectroscopy online detection device, with a wavelength range of 200-900 nm and a detection frequency of ≥5 times / min.

[0010] Further, the formula of the element interaction compensation algorithm in step S2 is:

[0011]

[0012] wherein ΔC is the element compensation amount, e-βt is an element decay function, reflecting the degree of decay of the element chemical reaction rate over time t, and a and β are element decay weight coefficients, determined by historical process data fitting and experiments, is the oxygen partial pressure in the furnace, which is a key thermodynamic parameter determining the direction and limit of the oxidation-reduction reaction, and γ is the oxygen partial pressure weight coefficient, representing the influence degree of oxygen partial pressure on the element reaction, determined by historical process data fitting and experiments;

[0013] After calculating the element compensation amount ΔC of each element through the formula of the element interaction compensation algorithm, the element compensation amount ΔC of each element is added to obtain ΣΔC.

[0014] Further, the formula of the multi-element collaborative control model in step S2 is:

[0015] Q0=K1·[S] 1.2 +K2·[P] 0.8 +K3·[As] 1.5

[0016] Wherein: Q0 is the basic amount of additives per 1 t of molten iron, K1, K2, and K3 are empirical coefficients, [S], [P], and [As] are the initial contents of sulfur, phosphorus, and arsenic elements, respectively, and 1.2, 0.8, and 1.5 are the removal indexes of S, P, and As elements, respectively;

[0017] The total amount of additives Q is calculated through the formula Q=(Q0+ΣΔC)W, wherein W is the total weight of molten iron.

[0018] Further, the staged gradient temperature control injection process in step S3 is to divide the reaction process into three stages:

[0019] The first stage is a low-temperature reaction stage, the temperature is controlled at 1320-1350℃, the injection rate of additives for a 100 t molten iron system is 0.8-1.0 Nm 3 / min, the phosphorus content in the molten iron is reduced to below 0.015%, and the arsenic content is reduced to below 0.010%;

[0020] The second stage is a medium-temperature optimization stage, the temperature is controlled at 1350-1420℃, the injection rate of additives for a 100 t molten iron system is 0.9-1.1 Nm 3 / min, so that the slag generated in the first stage is fully melted, aggregated, and floated, and separated from the molten iron by slagging;

[0021] The third stage is a high-temperature reaction stage, the temperature is controlled at 1420-1450℃, the injection rate of additives for a 100 t molten iron system is 1.0-1.2 Nm 3 / min, to stably and deeply remove the sulfur content in the molten iron to below 0.008%.

[0022] Further, the additive is a CaO-Al2O3-based composite additive with a particle size of less than or equal to 1 mm, wherein the particles with a size of 0.5-1 mm account for 80%, and the additive is composed of a matrix and a functional agent, wherein the matrix accounts for 94-100% by weight, and the functional agent accounts for 0-6% by weight.

[0023] Further, the component ratio of the matrix is as follows: lime: 70-74% by weight, bauxite: 19-23% by weight, cerium-rich rare earth: 1.5-2.5% by weight, and fluorite: 4.5-5.5% by weight.

[0024] When the additive is used for the first stage of injection, the functional agent is iron oxide scale;

[0025] When the additive is used for the second stage of injection, the functional agent accounts for 0% by weight in the additive;

[0026] When the additive is used for the third stage of injection, the functional agent is a mixture of graphite powder and carbide, wherein the mass ratio of graphite powder to carbide is 4:1.

[0027] The present application has the following beneficial effects:

[0028] 1. The present application relies on the LIBS laser-induced breakdown spectroscopy online detection device, and the synergistic control of S, P and As elements is established through a multi-element synergistic control model, so that the amount of additive is adjusted in real time and actively, thereby avoiding the influence of excessive or insufficient additive on the removal of harmful elements and improving the control accuracy of harmful elements.

[0029] 2. The element interaction compensation algorithm solves the quantification problem of multi-element competitive reaction and compensates for the amount of additive, thereby further improving the control accuracy of harmful elements.

[0030] 3. Through the staged gradient temperature control injection process, the reaction process is divided into three stages according to the characteristics of S, P and As element removal, and the temperature control and injection rate control are performed respectively, so that the pretreatment process is more controllable.

[0031] 4. Through the optimized additive ratio and in combination with the characteristics of the three stages, the components of the additive in each stage are adjusted accordingly, so that the additive can fully play its role, thereby achieving the effect of saving the amount of additive. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with specific examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0033] Example 1:

[0034] A precise control method of harmful elements in molten iron, comprising the following steps:

[0035] S1, online detection: taking 100 t of molten iron system as an example, using LIBS laser-induced breakdown spectroscopy online detection device (wavelength range 200-900 nm, detection frequency 5 times / min) to perform real-time component analysis on the molten iron in the molten iron tank, and obtain the real-time content of sulfur, phosphorus and arsenic elements, [S] 0.035%, [P] 0.025%, [As] 0.012%.

[0036] S2, model calculation: a multi-element collaborative control model calculates the total amount of additives required according to the real-time content and based on an element interaction compensation algorithm.

[0037] According to the formula of the element interaction compensation algorithm:

[0038]

[0039] Wherein: ΔC is the element compensation amount of 1 t of molten iron, e -βt is an element attenuation function, reflecting the degree of attenuation of the chemical reaction rate of the element with time t, α and β are element attenuation weight coefficients, which are determined by historical process data fitting and experiments, is the oxygen partial pressure in the furnace, which is a key thermodynamic parameter determining the direction and limit of oxidation-reduction reaction, and γ is the oxygen partial pressure weight coefficient, representing the influence degree of oxygen partial pressure on the reaction of the element, which is determined by historical process data fitting and experiments. At t=0 moment, the oxygen partial pressure is 0.1 atm, and the weight coefficient values of each element and the element compensation amount ΔC calculation results are shown in the following table 1:

[0040] Table 1: Calculation results of element interaction compensation algorithm

[0041] α β γ ΔC S 0.08 0.3 -0.015 0.1145 P 0.05 0.24 0.025 -0.0076 As 0.03 0.18 0.018 -0.0114

[0042] After adding the element compensation amount ΔC of each element, ΣΔC is calculated to be 0.0955 kg / t of molten iron.

[0043] According to the formula of the multi-element collaborative control model:

[0044] Q0=K1·[S] 1.2 +K2·[P] 0.8 +K3·[As] 1.5

[0045] Wherein: Q0 is the additive base amount of 1 t molten iron, K1, K2, K3 are empirical coefficients respectively taking values 9.5, 7.0, 12.0, [S], [P], [As] are the initial contents of sulfur, phosphorus, arsenic elements respectively, 1.2, 0.8, 1.5 are the removal indexes of S, P, As elements respectively. The removal index is 1, which means that the reaction rate is proportional to the concentration of the element in a linear relationship, and the concentration is halved, and the reaction rate is also halved; the index > 1 means that the reaction rate is highly sensitive to the concentration of the element, and the concentration is slightly reduced, and the reaction rate will decrease sharply, which shows that the removal of the element is very difficult, especially in the low concentration area; the index < 1 means that the reaction rate is not sensitive to the concentration of the element. Even at a lower concentration, a faster reaction rate can still be maintained, which shows that the element is relatively easy to remove.

[0046] The calculated Q0 is 0.482 kg / t of molten iron, and Q = (0.482 + 0.0955) x 100 = 57.75 kg. Thus, the calculation of Q at t = 0 is completed, since the detection is performed 5 times per minute, the next detection time point is t = 12 seconds, i.e. 0.2 min, the LIBS laser-induced breakdown spectroscopy online detection device detects the real-time content of sulfur, phosphorus and arsenic elements at t = 0.2 min and calculates Q0, according to the real-time oxygen partial pressure, the ΣΔC at this time is calculated, and finally the Q value at t = 0.2 min is calculated. Thus, the process is repeated until the additive injection is completed, and in this process, the Q value is adjusted in real time according to the real-time content of sulfur, phosphorus and arsenic elements, as well as the real-time oxygen partial pressure and the change of the element decay function.

[0047] S3, additive injection: the additive is injected into the molten iron through a staged gradient temperature control injection process. The additive is a CaO-Al2O3-based composite additive with a particle size ≤1 mm, of which 0.5-1 mm particles account for 80%, and the additive is composed of a matrix and a functional agent, wherein the matrix accounts for 95wt%, and the functional agent accounts for 5wt%. The composition ratio of the matrix is: lime: 72wt%, bauxite: 21wt%, cerium-rich rare earth: 2wt%, and fluorite: 5wt%.

[0048] The three stages of the staged gradient temperature control injection process are:

[0049] The first stage: low temperature reaction stage, the temperature is controlled at 1320-1350℃, and the additive injection rate of 100 t of molten iron system is 0.8-1.0 Nm 3 / min. The additive is a composite of a matrix and a functional agent, and the functional agent is iron oxide scale.

[0050] The main goal of the first stage is to remove phosphorus and arsenic, because the removal of P and As is a strong exothermic oxidation reaction with iron oxide, which does not require high temperature, but the activity of FeO is higher at low temperature, and the oxidation capacity is stronger, thereby more efficient removal of P and As. Excessive heating will also cause the reverse dephosphorization reaction, resulting in "phosphorus return", so the temperature control in the first stage is very critical, and the temperature should be in the range of 1320-1350°C. If the temperature exceeds the standard, appropriate cooling measures should be taken. In addition, the first stage also needs to form a high-alkalinity, high-oxidizing and good-flowing slag, so as to effectively adsorb the generated P2O5 and As2O5. Therefore, the functional agent in the additive sprayed in the first stage is iron oxide scale, which participates in the reaction as an oxidizing agent. Since the first stage is an exothermic reaction, a higher injection rate will bring stronger stirring energy, which will accelerate the reaction and cause the molten iron to heat up, which is not conducive to the core thermodynamic conditions of this stage. When the P and As content decreases, the heat release gradually decreases, and the temperature of the injected gas itself is low, so a higher injection rate will cool the molten iron and lower its temperature, so the temperature in the first stage will fluctuate. By adjusting the injection rate of the additive in the range of 0.8-1.0 Nm 3 / min, the temperature can be stabilized as an auxiliary means. But it cannot exceed the limit, otherwise the reaction will fluctuate violently, the reaction process will be more difficult to control, and the slag will be too dispersed or cause splashing; a slow injection rate prolongs the pretreatment time, the reaction is insufficient, the chemical heat release is less, and the molten iron temperature drops too much, which needs to be further heated, resulting in higher costs. When the phosphorus content in the molten iron is detected to be below 0.015%, and the arsenic content is below 0.010%, the first stage is completed.

[0051] The second stage is the medium-temperature optimization stage, with a controlled temperature of 1350-1420°C, and the injection rate of the additive for a 100t molten iron system is 0.9-1.1 Nm 3 / min, so that the slag generated in the first stage is fully melted, aggregated and floated, and separated from the molten iron by slagging. The additive is a base, that is, the functional agent in the additive accounts for 0wt%.

[0052] The second stage is a transition period, the early stage of the second stage is a continuation of P and As removal, and the later stage is a preparation for desulfurization, and also for slagging, so the temperature is increased to make the molten slag more fluid. Since the oxidizing functional agent has been added in the first stage, it is not necessary to add functional agents, and the second stage provides sufficient reaction time for the remaining unreacted oxidizing agent, so that it is almost completely reacted, and then switches to a reducing functional agent. Since the oxidation reaction is almost over, the reaction heat is less, and the temperature can be gradually increased to 1350-1420°C, and the injection rate can be increased to 0.9-1.1 Nm 3 / min to strengthen the stirring to separate the phosphorus slag that has been formed, prevent "back phosphorus", and make the composition and temperature of the molten iron more uniform to prepare for the next stage of desulfurization reaction. With the same increase in injection rate, the cooling effect is enhanced, and the contact between the functional agent and P and As elements is promoted, making the reaction more complete, but it also causes fluctuations in temperature. Therefore, the injection rate should be adjusted within the range of 0.9-1.1 Nm 3 / min, and attention should be paid not to exceed the limit. Too fast injection rate will cause the cooling effect to be too large, resulting in a large temperature drop of the molten iron; too slow injection rate will not have the effect of strengthening the stirring, and the slag melting effect will be poor. After slagging, the next stage is entered.

[0053] The third stage is a high-temperature reaction stage, the temperature is controlled at 1420-1450°C, and the injection rate of the additive for a 100 t molten iron system is 1.0-1.2 Nm 3 / min. The additive is a composite of the base and the functional agent, and the functional agent is a mixture of graphite powder and carbide, in which the mass ratio of graphite powder to carbide is 4:1.

[0054] The main task of the third stage is desulfurization, and the desulfurization reaction is a reduction endothermic reaction, which requires a higher temperature. High temperature can improve the thermodynamic conditions, but the reaction rate depends on the mass transfer process. S must diffuse from the inside of the molten iron to the reaction interface (such as the surface of the lime particles). A very high injection rate can produce strong stirring, greatly increase the reaction interface and reduce the thickness of the diffusion layer, thereby significantly accelerating the desulfurization reaction and achieving deep desulfurization. Although high temperature reduces the viscosity of the molten iron, a large amount of solid additive added will make the molten metal sticky, and strong stirring is the key to overcoming the stickiness of the molten metal, ensuring effective dispersion of the additive, and avoiding clumping. Molten iron treatment is a link in continuous production, which must be completed within a limited time. Using a high injection rate at high temperature can shorten the time required to reach the ultra-low sulfur level and improve production efficiency. Similarly, a high injection rate also enhances the cooling effect, and combined with the endothermic nature of the reaction itself, a large temperature fluctuation can occur. The injection rate can be adjusted within the range of 1.0-1.2 Nm 3 / min to assist in temperature control. For example, if the temperature drop of the molten iron is too large, the injection rate can be appropriately reduced to 1.0 Nm 3 / min, and in the later stage of the reaction, it can be increased to 1.2 Nm 3 / min, but not exceeding the limit. Too large injection rate will cause the temperature to be out of control due to a large temperature drop, and too small injection rate will affect the mass transfer effect, prolong the pretreatment time, and result in an increase in cost. The third stage ends when the sulfur content in the molten iron is stably and deeply removed to below 0.008%.

[0055] Embodiment 2: The embodiment provides a molten iron harmful element precision control method, method steps are basically same with embodiment 1, the difference is that: additive is composed of matrix and functional agent, wherein the matrix accounts for 94wt%, and the functional agent accounts for 6wt%. The component ratio of the matrix is: lime: 70wt%, bauxite: 23wt%, cerium-rich rare earth: 1.5wt%, and fluorite: 5.5wt%.

[0056] Embodiment 3: The embodiment provides a molten iron harmful element precision control method, method steps are basically same with embodiment 1, the difference is that: additive is composed of matrix and functional agent, wherein the matrix accounts for 95wt%, and the functional agent accounts for 5wt%. The component ratio of the matrix is: lime: 74wt%, bauxite: 19wt%, cerium-rich rare earth: 2.5wt%, and fluorite: 4.5wt%.

[0057] The above embodiments only describe the preferred embodiments of the present application, and do not limit the concept and scope of the present application. Without departing from the design concept of the present application, various modifications and improvements of the technical solutions of the present application made by those skilled in the art shall fall within the protection scope of the present application.

[0058] The technical, shape and structure parts not described in detail in the present application are well-known technologies.

Claims

1. A method for precisely controlling harmful elements in molten iron, characterized by, It comprises the following steps: S1, online detection: using online detection device to analyze the real-time composition of molten iron in the ladle, and obtaining the real-time content of sulfur, phosphorus and arsenic elements; S2, model calculation: a multi-element collaborative control model calculates the total amount of the required additive based on the real-time content and an element interaction compensation algorithm; S3, additive injection: the additive is injected into the molten iron through a staged gradient temperature control injection process.

2. The method of claim 1, wherein the harmful elements in molten iron are controlled in a precise amount. The online monitoring device in step S1 is a LIBS laser-induced breakdown spectroscopy online detection device with a wavelength range of 200-900 nm and a detection frequency of ≥5 times / min.

3. The method of claim 2, wherein the harmful element in molten iron is controlled in a precise amount. The formula of the element interaction compensation algorithm in step S2 is: wherein: AC is the element compensation amount, e -βt is the element decay function, reflecting the degree of decay of the element chemical reaction rate over time t, and a, b are element decay weight coefficients determined by historical process data fitting and experiments, is the oxygen partial pressure in the furnace, which is a key thermodynamic parameter determining the direction and limit of the oxidation-reduction reaction, and g is the oxygen partial pressure weight coefficient, representing the influence degree of the oxygen partial pressure on the element reaction, which is determined by historical process data fitting and experiments; After calculating the element compensation amount ΔC of each element by the formula of the element interaction compensation algorithm, the element compensation amounts ΔC of each element are added to obtain ΣΔC.

4. The method of claim 3, wherein the harmful elements in molten iron are controlled in a precise amount. The formula of the multi-element collaborative control model in step S2 is: Q0 = K1 - [S] 1.2 + K2 - [P] 0.8 + K3 - [As] 1.5 Wherein: Q0 is the basic amount of additive per ton of molten iron, K1, K2 and K3 are empirical coefficients, [S], [P] and [As] are the initial contents of sulfur, phosphorus and arsenic elements, respectively, and 1.2, 0.8 and 1.5 are the removal indexes of S, P and As elements, respectively; The total amount of additive Q is calculated by the formula Q=(Q0+ΣΔC)W, wherein W is the total weight of molten iron.

5. The method of claim 4, wherein the harmful elements in molten iron are controlled in a precise amount. The staged gradient temperature control injection process in step S3 divides the reaction process into three stages: The first stage is a low temperature reaction stage, the temperature is controlled at 1320-1350℃, the additive injection rate of 100t hot metal system is 0.8-1.0Nm / min, the phosphorus content in the hot metal is reduced to below 0.015%, and the arsenic content is reduced to below 0.010%; 3 / min, the phosphorus content in the hot metal is reduced to below 0.015%, and the arsenic content is reduced to below 0.010%; The second stage: the medium-temperature optimization stage, with the temperature controlled at 1350-1420℃, and the additive injection rate for a 100t molten iron system at 0.9-1.1 Nm. 3 / min, so that the slag generated in the first stage can be fully melted, aggregated and floated, and separated from the molten iron by slag skimming; The third stage is high temperature reaction stage, the temperature is controlled at 1420-1450℃, the blowing rate of the additive in 100t hot metal system is 1.0-1.2Nm / min, the sulfur content in the hot metal is steadily and deeply removed to below 0.008%. 3 % 6. The method of claim 5, wherein the harmful elements in molten iron are controlled in a precise amount. The additive is a CaO-Al2O3-based composite additive with a particle size of ≤1 mm, of which 0.5-1 mm particles account for 80%, and the additive is composed of a matrix and a functional agent, wherein the matrix accounts for 94-100wt%, and the functional agent accounts for 0-6wt%.

7. The method of claim 6, wherein the harmful elements in molten iron are controlled in a precise amount. The composition ratio of the matrix is: lime: 70-74wt%, bauxite: 19-23wt%, cerium-rich rare earth: 1.5-2.5wt%, and fluorite: 4.5-5.5wt%; When the additive is used for the first stage injection, the functional agent is iron oxide scale; When the additive is used for the second stage injection, the functional agent accounts for 0wt% in the additive; When the additive is used for the third stage injection, the functional agent is a mixture of graphite powder and calcium carbide, and the mass ratio of graphite powder to calcium carbide is 4:1.

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