Control method for improving slag washing refining effect of steel ladle based on biomass carbonization

Abstract

The invention relates to a control method for improving slag washing and refining effects of a steel ladle based on biomass carbonization, which comprises the following steps: crushing a biomass raw material, flushing and mixing the crushed biomass raw material with refining circulating slag in the steel ladle, adding a proper amount of aluminum blocks according to the components of the refining circulating slag, and cracking, carbonizing and pre-melting in an anoxic state. The advantages of strong kinetic energy and potential energy of molten steel in the tapping process of a converter are utilized, so that steel slag is fully mixed, pre-melted mixed slag with high alkalinity and low melting point is melted in advance and mixed with the molten steel, and efficient slag washing and refining of tapping are realized due to the unique physical and chemical properties of the biomass charcoal and the components of the mixed slag, and the purity of the molten steel is improved. After the molten steel enters the refining process, due to the high alkalinity and low oxygen potential of the refining entering slag, oxygen and sulfur in the steel can be further removed through the interface reaction of the steel slag, the refining efficiency can be improved, the slag desulfurization and inclusion removal capacity is improved, the refining effect and efficiency are improved, and the process cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of comprehensive utilization of steel smelting resources. Specifically, the present invention relates to a control method for improving the slag washing and refining effect of molten steel in a ladle by utilizing biomass carbonization during the steel tapping process. Background Art

[0002] The slag washing process in steelmaking uses synthetic slag or pre-melted slag to treat molten steel (also known as steel) outside the furnace. It is the simplest refining method for obtaining clean steel. The slag washing process involves pouring slag of a specific composition, pre-melted in a slag melting furnace, into a ladle. This is then hoisted to the converter tapping point, where normal tapping is performed. The impact of the molten steel during tapping emulsifies the slag, creating optimal conditions for removing non-metallic inclusions and sulfur from the steel while also improving the morphology of the inclusions.

[0003] According to the steelmaking process, there are three main slag washing methods commonly used internationally, namely, same-furnace slag washing, different-furnace slag washing and mixed steelmaking.

[0004] 1) Same-furnace slag washing refining method: When the electric furnace smelting is about to reach the end, the slag washing material is added into the electric furnace for melting. After the slag washing material is completely melted, the slag washing material and molten steel are poured into the ladle at the same time to carry out a series of slag washing refining reactions.

[0005] 2) Different-furnace slag washing and refining: This is the most representative slag washing and refining method. A smaller electric furnace is converted into a slag melting furnace. The slag washing material is first completely melted and mixed in the slag melting furnace. The slag washing material is then poured out, cooled, and crushed into the required particle size. When the steelmaking furnace is tapped, the granular slag washing material is added to the ladle along with the molten steel for slag washing and refining. Different-furnace slag washing is commonly used in actual production, and slag washing in this field generally refers to different-furnace slag washing.

[0006] 3) Mixed steelmaking method: First, the smelting steel grade is smelted into semi-finished molten steel according to the standard of ordinary carbon steel in a large-capacity steelmaking furnace. Then, based on the demand for the target steel grade and the amount of molten steel in the steelmaking furnace, the required amount of ferroalloy and slag washing material is calculated. According to the calculated values, the required ferroalloy and slag washing material are added to another smaller capacity electric arc furnace for melting. After they are completely melted and mixed, they are poured into a ladle. Subsequently, the molten steel from the large-capacity steelmaking furnace is poured into the ladle containing the molten ferroalloy and slag washing material, so that the molten steel, ferroalloy and slag washing material completely collide, mix and react, and finally the target steel grade is obtained.

[0007] With the increasing demand for low-sulfur steel, ultra-low-sulfur steel, and HIC-resistant pipeline steel in recent years, metallurgists are increasingly focusing on how to produce steels with even lower sulfur contents. Using synthetic slag for slag washing in a tank, and particularly using solid slag for in-tank steel refining, has proven to be a widely applicable, simple, and cost-effective method. Synthetic slag typically consists of a base slag, a desulfurizer, a foaming agent, a reducing agent, and a flux.

[0008] Synthetic slag is a new generation of auxiliary steelmaking materials. It's suitable for use as a refining purifier during ladle refining. Due to its strong deoxidation and desulfurization properties, synthetic slag can reduce gas and inclusions in steel. Synthetic slag is a mineral composed primarily of 12CaO and 7Al2O3, produced by melting various refined materials. The high concentration of calcium components, exceeding 90%, reacts with oxygen and sulfur in molten steel to form a low-melting-point, buoyant product, thereby purifying the molten steel. Feedback from manufacturers currently using synthetic slag indicates that, with a low initial sulfur content of 0.027%, it can achieve desulfurization down to 0.0052%, achieving a desulfurization rate exceeding 80%, achieving the desired effect.

[0009] Adding synthetic slag during the tapping process leverages the powerful kinetic and potential energy of the tapping process to fully mix the slag. This not only melts the synthetic slag early, but also allows the high-basicity, low-melting-point synthetic slag to be mixed with the molten steel, performing a slag washing and refining process, improving the purity of the molten steel. The high basicity and low oxygen potential of the refined incoming slag facilitate the removal of oxygen and sulfur from the steel through interfacial reactions within the slag.

[0010] With the continuous optimization of product structure and the steady improvement of molten steel quality, the load of steelmaking and refining process has increased. Adding refined synthetic slag to the bottom of the ladle in advance can achieve the purpose of early slag making, which is conducive to the optimization of production organization and functional distribution of each process. However, due to cost pressure, the current synthetic slag is only a simple ratio of lime (containing CaO) and fluorite (containing CaF2) and a small amount of other materials. Therefore, there are some problems as follows:

[0011] 1) Unreasonable proportions and backward production technology can easily cause segregation of the components of the synthetic slag, resulting in unstable use effects;

[0012] 2) It is easy to absorb water and pulverize, which reduces the reactivity of the components in the synthetic slag;

[0013] 3) Manual addition is required, which results in high labor intensity and a harsh working environment;

[0014] 4) Some synthetic slags are difficult to melt, the refining time is long, and the power consumption is high.

[0015] Refined slag recycling involves pouring the slag from the continuous casting ladle directly into an empty ladle before tapping (or into a ladle after tapping) rather than pouring it into the slag basin. This allows for the recovery and reuse of both the ladle casting residue and the refined slag. Refined slag processed in the LF (Ladle Furnace) refining furnace has high basicity, low oxidizing properties, and a low melting point. Furthermore, due to its unique composition, it is particularly susceptible to pulverization.

[0016] Biomass refers to substances produced during life processes. Biomass from plants, such as herbaceous and woody plants, is primarily composed of cellulose, hemicellulose, and lignin. Biomass carbonization involves carbonizing biomass, such as plants, plant waste, municipal waste, animal manure, and urban and industrial waste, to produce a carbon-rich product, biochar (also known as biochar). Similar to charcoal produced through thermal cracking, biochar is primarily composed of carbon molecules. Currently, biochar is primarily produced through hydrothermal conversion and pyrolysis carbonization. The pyrolysis temperature of biochar generally ranges from 200 to 800°C, occasionally reaching temperatures as high as 1000°C. Studies have shown that increasing the pyrolysis temperature increases the porosity and specific surface area of ​​biochar, which in turn increases its carbon and ash content. By using the "pyrolysis" method, biomass such as wood, grass, rice straw, rape straw, corn straw, waste wood, garden trimmings, etc. is placed in an oxygen-deficient state and decomposed in a controlled manner at high temperature to obtain biochar with extremely rich carbon content. Summary of the Invention

[0017] The purpose of the present invention is to provide a control method for improving the slag washing and refining effect of the ladle based on biomass carbonization, which can solve the problems existing in the aforementioned prior art. During the steel tapping process, biomass carbonization is used to improve the slag washing and refining effect of the molten steel in the ladle and increase the desulfurization rate of the molten steel.

[0018] In order to achieve the above-mentioned purpose of the present invention, the present invention adopts the following technical solutions:

[0019] The present invention provides a control method for improving the slag washing and refining effect of a ladle based on biomass carbonization, comprising the following steps:

[0020] (1) Preliminary crushing of the biomass raw materials until the length of the crushed biomass raw materials is ≤50 mm to improve the carbonization effect and efficiency;

[0021] (2) Adding the preliminarily crushed biomass raw materials, aluminum blocks or aluminum particles into the ladle in sequence; opening the bottom blowing argon of the ladle, pouring the refined circulating slag at 1520°C-1600°C after continuous casting into the ladle, and using the kinetic energy and potential energy of the circulating slag during pouring to mix the refined circulating slag and the biomass raw materials, so that the refined circulating slag and the biomass raw materials are fully mixed and the aluminum blocks or aluminum particles are melted, and closing the bottom blowing argon after 2 minutes;

[0022] The weight ratio of the refined cycle slag to the biomass raw material is 2 to 3:1;

[0023] The amount of the aluminum blocks or aluminum particles added is 5%-13% based on the total weight of the refined recycled slag and the biomass raw material;

[0024] (3) Covering the ladle, and performing cracking and carbonization of the biomass raw material in an oxygen-deficient environment at 600° C. to 900° C. to obtain a pre-melted mixed slag;

[0025] (4) After the converter blowing is completed, the cover of the ladle is removed and the bottom blowing of the ladle is opened;

[0026] Small-grained limestone is added as top slag, and the molten steel from the converter is tapped and flows into the ladle for slag washing and refining;

[0027] (5) After steel tapping is completed, the bottom argon blowing is turned off to complete the slag washing and refining and desulfurization of the molten steel.

[0028] In a specific embodiment, the biomass raw material includes one or more of wood, grass, rice straw, rape straw, corn straw, waste wood, and garden trimmings.

[0029] In one embodiment, the primary crushing is performed using a crusher.

[0030] In one embodiment, the ladle is a normally used turnover hot ladle, and the bottom blowing air bricks are in good condition;

[0031] In one specific embodiment, in step (2), the flow rate of argon is controlled at 30-50 L / min, and the pressure of argon is controlled at 0.35-0.45 MPa.

[0032] In a specific embodiment, in step (2), the refined circulating slag comes from the ladle after the continuous casting machine is finished casting, and the refined circulating slag includes: SiO2 2-12wt%, Al2O3 22-37wt%, CaO 35-56wt%, and MgO 1-10wt%.

[0033] In one embodiment, the composition of the mixed slag of refined recycled slag and biomass raw materials can reach:

[0034] CaO, % <![CDATA[Al2O3,%]]> MgO, % SiO2, % Al，％ 40-65 15-28 4-12 2-5 5-13

[0035] In one specific embodiment, the dead weight of the molten steel and the height difference generate strong kinetic energy and potential energy, so that the molten steel and the pre-melted mixed slag in the ladle are fully stirred and mixed. Since the pre-melted mixed slag with high basicity and low melting point has been melted in advance, it plays a good role in slag washing and refining.

[0036] In one embodiment, in step (4), the pressure of argon is controlled at 0.5 MPa, and the flow rate of argon is controlled as follows: Figure 1 The argon flow rate is relatively high in the early stage of tapping to ensure sufficient mixing of molten steel and mixed slag and improve the slag washing effect; the argon flow rate is reduced in the later stage of tapping to facilitate the judgment of the end of tapping and the slag blocking requirement.

[0037] The control method for improving the slag washing and refining effect of the ladle based on biomass carbonization of the present invention comprises crushing the biomass raw material and then mixing it with the refining cycle slag in the ladle, adding an appropriate amount of aluminum blocks (or aluminum particles) according to the composition of the refining cycle slag, and performing cracking, carbonization, and pre-melting under an oxygen-deficient state. By taking advantage of the strong kinetic energy and potential energy of the molten steel in the converter tapping process, the steel slag is fully mixed, the pre-melted mixed slag with high alkalinity and low melting point is melted in advance and mixed with the molten steel, and the unique physical and chemical properties of the biomass carbon and the composition of the mixed slag achieve efficient slag washing and refining during tapping, thereby improving the purity of the molten steel. After the molten steel enters the refining process, due to the high alkalinity and low oxygen potential of the refining station slag, it is beneficial to further utilize the interfacial reaction of the steel slag to remove oxygen and sulfur from the steel, and is also beneficial to improving the refining efficiency, improving the slag desulfurization and inclusion removal capabilities, improving the refining effect and efficiency, and reducing the process cost. It has significant economic benefits and broad promotion prospects.

[0038] Compared with the prior art, the method of the present invention utilizes a unique biomass carbonization method to improve the slag washing and refining effect of molten steel in the ladle during the steel tapping process. The advantages of the control method for improving the slag washing and refining effect of the ladle based on biomass carbonization are:

[0039] 1. The oxidation reaction of the biochar in the mixture can increase the heat of the converter molten pool. Since the biochar obtained by high-temperature cracking in the mixed slag has a rich microporous structure and high surface activity, it has good deoxidation and desulfurization capabilities for molten steel, and effectively reduces the surface tension of the slag, which is beneficial to the foaming of the slag. In addition, since the alkaline oxides (such as K2O and CaO) contained in the biochar can react with the acidic oxides (such as SiO2) in the molten steel, it can lower the melting point and effectively improve the fluidity of the molten steel, which is beneficial to metallurgical reactions such as dephosphorization and desulfurization. In addition, the porous structure of the biochar can capture gas during the ladle mixing process, promote the stability of bubbles, and form a stable foam slag, thereby increasing the contact area of ​​the reaction interface and improving the molten steel slag washing effect.

[0040] 2. Utilizing the temperature of the refining cycle slag in the ladle, biomass carbonization is performed in a covered, oxygen-deficient environment, saving costs and achieving efficient utilization of both the refining cycle slag and the biochar. Furthermore, the carbonization environment facilitates the removal of moisture introduced by the biomass raw materials, ensuring dryness of the mixed material and preventing moisture from entering the converter and affecting molten steel quality. Furthermore, the initial crushing of the biomass raw materials improves the effectiveness and efficiency of carbonization.

[0041] 3. Add an appropriate amount of aluminum blocks (or aluminum granules) based on the composition of the refining cycle slag to increase the Al2O3 content in the pre-melted mixed slag. On the one hand, this reduces the slag viscosity, promotes the slag-steel reaction, and is beneficial for desulfurization. On the other hand, Al2O3 is a surfactant that helps maintain the foamy slag, which also helps improve the deoxidation and desulfurization capabilities of the slag and enhances the slag washing effect.

[0042] 4. The present invention utilizes biomass carbon and refined circulating slag with high basicity, low oxidation and low melting point characteristics to improve the fluidity of molten steel. Therefore, only small-particle limestone needs to be added during the steel-making process to replace the small-particle fluorite commonly added in the prior art to improve the fluidity of molten steel, thereby avoiding the pollution of the environment by fluoride ions in fluorite (CaF2), which is beneficial to environmental protection and reduces the cost of auxiliary materials.

[0043] 5. After LF refining, the reducing agents such as Al and biochar added to the pre-melted mixed slag improve the reducing ability of the slag, reduce the oxidizing property of the slag, and reduce the (FeO) + (MnO) content in the slag. The slag after the LF refining process is basically yellow-white slag, which reduces the pollution of the highly oxidizing slag to the molten steel, shortens the refining time, and improves the refining efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A schematic diagram showing a control curve of the argon flow rate of the ladle bottom blowing;

[0045] Figure 2The flowchart of the control method for improving the slag washing and refining effect of the ladle based on biomass carbonization of the present invention is shown. DETAILED DESCRIPTION

[0046] Example 1:

[0047] The biomass raw materials (waste wood collected from a timber factory) were initially crushed by a crusher to a length of ≤50 mm.

[0048] A certain heat 1, 210t converter, 210t ladle (normally used turnover hot ladle, and bottom blowing air bricks are in good condition).

[0049] The composition of the refining circulating slag in the ladle (the ladle to be processed) after the casting of the converter continuous casting machine is detected and analyzed after the refining treatment is completed. The results are: SiO2 10wt%, Al2O3 25wt%, CaO 39wt%, MgO 8wt%.

[0050] One ton of crushed biomass feedstock is first loaded into a ladle, followed by 280 kg of aluminum blocks, representing 7% of the total weight of the refined recycled slag and biomass feedstock, to meet the Al% content in the mixed slag. Subsequently, the ladle's bottom argon blowing is turned on at a flow rate of 45 L / min and a pressure controlled at 0.40 MPa, and 3 tonnes of refined recycled slag at 1550°C is poured in. The kinetic and potential energy of the recycled slag during pouring is utilized for mixing, ensuring thorough mixing of the refined recycled slag and biomass feedstock and melting of the aluminum blocks. The bottom argon blowing is then turned off after 2 minutes.

[0051] The ladle is covered to keep it warm, and the biomass raw materials are cracked and carbonized in an oxygen-deficient environment at 900℃ to obtain a pre-melted mixed slag. After testing, the composition of the mixed slag of the refined recycled slag and the biomass raw materials is: CaO 45%, Al2O3 18%, MgO11%, SiO 2: 4.2%, Al 7%.

[0052] After the converter blowing is completed, remove the ladle cover, open the bottom of the ladle to blow argon, and follow the Figure 1 The flow control curve shown is for blowing argon. The argon flow rate is high in the early stage of tapping to ensure sufficient mixing of molten steel and mixed slag and improve the slag washing effect; the argon flow rate is reduced in the later stage of tapping to facilitate the judgment of the end of tapping and meet the slag blocking requirements.

[0053] After tapping, 380 kg of small size limestone was added as top slag. The amount of small size limestone M was calculated based on the CaO content: according to the average tapping slag amount of 1.2 t, the CaO % content of small size limestone was 65 %, and combined with the CaO 45 % in the mixed slag of 4 t of refining circulating slag and biomass raw material, and the CaO 39 wt % in the refining circulating slag, according to 4 x 45 % + M x 65 % = (4 + 1.2) x 39 %, M was calculated as about 0.38 t.

[0054] The molten steel of the converter was tapped and flowed into the ladle for slag washing refining. The self-weight and height difference of the molten steel formed strong kinetic and potential energy, so that the molten steel and the premelted mixed slag in the ladle were fully stirred and mixed, and the premelted mixed slag with high basicity and low melting point was melted in advance, thus playing a good role in slag washing refining.

[0055] After tapping, the bottom argon blowing was closed, and the next process was waited to be entered.

[0056] After the slag washing refining, the sulfur content in the molten steel was reduced from 0.036 % at the end of blowing to 0.011 %, and the desulfurization rate was 69.44 %, which was reduced by 14.22 % compared with the average desulfurization rate of 55.32 % of the same condition without the slag washing refining of the present application (i.e. the sulfur content in the molten steel at the end of blowing was also 0.036 % in the furnace). This shows that the method of the present application has obvious improvement on the effect of slag washing (desulfurization).

[0057] Example 2:

[0058] The biomass raw material (garden trimmings collected in a park) was preliminarily crushed to a length of ≤ 50 mm by a crusher.

[0059] A furnace 2, 210 t converter, 210 t ladle. The crushed biomass raw material 1.2 t was first loaded into the ladle, aluminum blocks 220 kg (5.5 % based on the total weight of the refining circulating slag and biomass raw material) were added, the bottom argon blowing of the ladle was opened, the argon flow was 45 L / min, 3 t of refining circulating slag was poured, and the composition of the circulating slag of this furnace was SiO2: 8 wt %, Al2O3: 28 wt %, CaO: 45 wt %, MgO: 7 wt %. The ladle was covered and kept warm, the biomass raw material was cracked and carbonized in the oxygen-deficient environment, and the tapping was waited. After the converter blowing was finished, the ladle cover was removed, the bottom argon blowing of the ladle was opened, and the flow control curve was controlled according to Figure 1 After tapping, 450 kg of small size limestone was added, and the bottom argon blowing was closed at the end of tapping, and the next process was waited to be entered. The composition detection results of the mixed slag of refining circulating slag and biomass raw material were as follows: CaO: 50 %, Al2O3: 20 %, MgO: 10 %, SiO 2:: 3.2%, Al: 7.7%. The sulfur content in the molten steel dropped from 0.032% at the end of blowing to 0.010%, resulting in a desulfurization rate of 68.75%, a 13.43% decrease from the average desulfurization rate of 55.32% for heats under the same conditions. This significantly improved slag washing (desulfurization) effectiveness. After the LF refining process, the slag was essentially yellowish-white, improving LF refining slag-making efficiency, shortening refining time, and increasing refining efficiency. After LF refining, the sulfur content was 0.001%, demonstrating excellent desulfurization results.

Claims

1. A control method for improving the slag washing and refining effect of a ladle based on biomass carbonization, comprising the following steps: (1) Preliminary crushing of the biomass raw material until the length of the crushed biomass raw material is ≤50 mm; (2) adding the preliminarily crushed biomass raw materials, aluminum blocks or aluminum pellets into the ladle in sequence; opening the bottom blowing argon of the ladle, pouring the refined circulating slag after continuous casting into the ladle, and using the kinetic energy and potential energy of the circulating slag during pouring to mix the refined circulating slag and the biomass raw materials, so that the refined circulating slag and the biomass raw materials are fully mixed and the aluminum blocks or aluminum pellets are melted, and then closing the bottom blowing argon; The weight ratio of the refined cycle slag to the biomass raw material is 2 to 3:1; The amount of the aluminum blocks or aluminum particles added is 5%-13% based on the total weight of the refined recycled slag and the biomass raw material; (3) Covering the ladle, and performing cracking and carbonization of the biomass raw material in an oxygen-deficient environment at 600° C. to 900° C. to obtain a pre-melted mixed slag; (4) After the converter blowing is completed, the cover of the ladle is removed and the bottom blowing of the ladle is opened; Small-grained limestone is added as top slag, and the molten steel from the converter is tapped and flows into the ladle for slag washing and refining; (5) After steel tapping is completed, the bottom argon blowing is turned off to complete the slag washing and refining and desulfurization of the molten steel.

2. The control method for improving the slag washing and refining effect of the ladle based on biomass carbonization according to claim 1, wherein the biomass raw material comprises one or more of wood, grass, rice straw, rape straw, corn straw, waste wood, and garden prunings.

3. The control method for improving the slag washing and refining effect of a ladle based on biomass carbonization according to claim 1, wherein the preliminary crushing is performed using a crusher.

4. The control method for improving the slag washing and refining effect of a steel ladle based on biomass carbonization according to claim 1, wherein the steel ladle is a normally used turnover hot ladle with good bottom blowing air bricks.

5. The control method for improving the slag washing and refining effect of a ladle based on biomass carbonization according to claim 1, wherein: In step (2), the flow rate of the argon gas is controlled at 30 to 50 L / min, and the pressure of the argon gas is controlled at 0.35 to 0.45 MPa.

6. The control method for improving the slag washing and refining effect of a ladle based on biomass carbonization according to claim 1, wherein: In step (2), the refined circulating slag comprises: SiO2 2-12wt%, Al2O3 22-37wt%, CaO 35-56wt%, and MgO 1-10wt%.

7. The control method for improving the slag washing and refining effect of a ladle based on biomass carbonization according to claim 1, wherein: In step (2), the temperature of the refined circulating slag is 1520°C-1600°C.

8. The control method for improving the slag washing and refining effect of a ladle based on biomass carbonization according to claim 1, wherein the components of the pre-melted mixed slag include: CaO 40-65%; Al2O3 15-28%; MgO4-12%; SiO2 2-5%; Al 5-13%.

9. The control method for improving the slag washing and refining effect of a ladle based on biomass carbonization according to claim 1, wherein: In step (4), the pressure of the argon gas is controlled at 0.5 MPa.

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