A method to improve the dephosphorization rate of converter

Abstract

This invention discloses a method for improving the dephosphorization rate of a converter steelmaking process, belonging to the field of converter steelmaking technology. The method includes the following steps: During the converter smelting process from the start to time t1, bottom-blown oxygen is used for stirring; t1 is the moment when the mass fraction of Si in the molten steel in the converter reaches 0.08-0.12%; During the converter smelting process from t1 to t2, bottom-blown lime is used as the carrier gas for the first dephosphorization, t2 is the moment when the mass fraction of C in the molten steel in the converter reaches 2.8-3.2%; During the converter smelting process from t2 to the end, a mixture of oxygen and carbon dioxide is used as the carrier gas for the second dephosphorization, bottom-blown lime. The method provided by this invention improves the dephosphorization effect per unit of lime.

Description

Technical Field

[0001] This invention belongs to the field of converter smelting technology, specifically relating to a method for improving the dephosphorization rate of converters. Background Technology

[0002] Bottom blowing powder injection in converters is a widely used technique for efficient converter smelting. This technology injects lime powder into the converter through a bottom blowing system, providing favorable thermodynamic and kinetic conditions for dephosphorization of molten iron at the bottom of the converter.

[0003] In existing technologies, the flow rate of lime powder blown from the bottom of the converter remains constant throughout the process, approximately 23.0 kg / t of steel, resulting in low dephosphorization efficiency.

[0004] The conventional technique involves using a fixed powder-to-air ratio throughout the entire injection process, with the O2 / CaO ratio remaining constant.

[0005] However, in the actual converter smelting process, Si, P, C and other elements are oxidized sequentially from front to back. Therefore, the main chemical reactions in the converter also change with the process. If the intensity of bottom blowing powder injection gas supply is controlled, it can better match the reaction rhythm of the entire smelting process, improve the utilization rate of bottom blowing lime powder, and achieve better dephosphorization effect under the same powder injection amount. Summary of the Invention

[0006] To solve the above-mentioned technical problems, the present invention provides a method for improving the dephosphorization rate of converters, thereby increasing the dephosphorization rate per unit of lime.

[0007] The technical solution of the present invention is as follows: a method for improving the dephosphorization rate of a converter is provided, comprising the following steps:

[0008] During the converter smelting process from the start to time t1, bottom-blown oxygen is used for stirring; t1 is the moment when the mass fraction of Si in the molten steel in the converter reaches 0.08-0.12%.

[0009] During the converter smelting process from time t1 to t2, oxygen is used as the carrier gas for bottom-blown lime dephosphorization, and the mass-to-volume ratio of lime to oxygen is 4-7 kg / Nm³. 3 t2 is the moment when the mass fraction of carbon in the molten steel in the converter reaches 2.8-3.2%;

[0010] During the converter smelting process from time t2 to the end, a mixture of oxygen and carbon dioxide is used as the carrier gas for bottom-blown lime for secondary dephosphorization. Specifically, from time t2 to t3, the mass-to-volume ratio of lime to the mixed gas is 0.7-2 kg / Nm³, and from time t3 to the end, the mass-to-volume ratio is 2.5-4.5 kg / Nm³. 3t3 is the moment when the mass fraction of carbon in the molten steel in the converter reaches 0.4-0.8%.

[0011] In some embodiments, during the first dephosphorization process, the bottom blowing flow rate of lime is 4.0-6.0 kg / min / t steel.

[0012] In some embodiments, during the time interval from t2 to t3, the bottom blowing flow rate of the lime is 0.5-2.0 kg / min / t steel.

[0013] In some embodiments, during the process from time t3 to the end, the bottom blowing flow rate of the lime is 3.0-4.0 kg / min / t steel.

[0014] In some embodiments, the oxygen flow rate is 0.6-1 Nm³ during the period from start to time t1. 3 / min / t steel.

[0015] In some embodiments, the oxygen flow rate is 0.6-1.0 Nm³ during the time period from t1 to t2. 3 / min / t steel.

[0016] In some embodiments, during the period from time t2 to time t3, the volume ratio of oxygen to carbon dioxide in the mixed gas is 1.8~2.2:0.8~1.2; and during the period from time t3 to the end, the volume ratio of oxygen to carbon dioxide in the mixed gas is 0.8~1.2:0.8~1.2.

[0017] In some embodiments, the flow rate of the mixed gas is 0.6-1.0 Nm³ during the time interval from t2 to t3. 3 / min / t steel; during the process from time t3 to the end, the flow rate of the mixed gas is 0.8-2.0 Nm³. 3 / min / t steel.

[0018] In some embodiments, the lime has a particle size of 0.01-0.1 mm, wherein the mass fraction of particles with a particle size within ±0.01 mm is not less than 80%.

[0019] In some embodiments, the converter has a capacity of 30-300t.

[0020] The beneficial effects of the present invention include at least the following:

[0021] The present invention provides a method for improving the dephosphorization rate of a converter, comprising the following steps: During the converter smelting process from the start to time t1, bottom-blown oxygen is used for stirring; t1 is the moment when the mass fraction of Si in the molten steel in the converter reaches 0.08-0.12%; During the converter smelting process from time t1 to t2, bottom-blown lime is used as the carrier gas for the first dephosphorization, wherein the mass-to-volume ratio of the lime to the oxygen is 4-7 kg / Nm³. 3 t2 is the moment when the mass fraction of carbon in the molten steel in the converter reaches 2.8-3.2%. During the converter smelting process from t2 to the end, a mixture of oxygen and carbon dioxide is used as the carrier gas for bottom-blown lime dephosphorization. Specifically, during the time interval from t2 to t3, the mass-to-volume ratio of the lime to the mixed gas is 0.7-2 kg / Nm³. 3 During the period from time t3 to the end, the mass-to-volume ratio of the lime to the mixed gas is 2.5-4.5 kg / Nm³. 3 t3 is the moment when the mass fraction of carbon in the molten steel in the converter reaches 0.4-0.8%.

[0022] In the initial stage of converter smelting, from the start to time t1, silicon and manganese oxidize before phosphorus. Therefore, only oxygen is blown into the bottom, not lime, to accelerate the desiliconization and demanganese removal processes. From t1 to t2, the molten iron temperature is relatively low, providing favorable dephosphorization conditions. A higher lime bottom-blowing flow rate is controlled to improve the dephosphorization effect. From t2 to t3, dephosphorization conditions deteriorate, and the lime bottom-blowing flow rate is reduced. From t3 to the end of the process, dephosphorization conditions improve, and a higher lime bottom-blowing flow rate is controlled. By controlling each stage of converter smelting, the lime bottom-blowing flow rate is matched with the dephosphorization conditions, thus improving the dephosphorization effect. Attached Figure Description

[0023] Figure 1 A process flow diagram illustrating a method for improving the dephosphorization rate of a converter according to an embodiment of this application is shown. Detailed Implementation

[0024] To enable those skilled in the art to better understand this application, the technical solution of this application will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] In existing smelting technologies, the bottom-blown lime dephosphorization process uses a fixed gas-to-lime ratio throughout, meaning the mass ratio of carrier gas to lime remains constant. This results in low lime utilization and a low dephosphorization rate per unit of lime.

[0026] The present application provides a method for improving the dephosphorization rate of a converter, applicable to converters with a capacity of 30-300t, and at least to a certain extent improves the dephosphorization rate per unit of lime.

[0027] Please combine Figure 1The method for improving the dephosphorization rate of a converter provided in this application includes the following steps:

[0028] S1, during the process of converter smelting from the start to time t1, bottom-blown oxygen is used for stirring; t1 is the moment when the mass fraction of Si in the molten steel in the converter reaches 0.08-0.12%;

[0029] From the start to time t1, the molten iron in the converter has a high Si and Mn content. Si and Mn oxidize before P, and P participates in the reaction to a very small extent. Therefore, lime is not injected during this stage. Instead, only bottom-blown oxygen is used for stirring, which, together with top-blown oxygen, ensures the stirring effect of the molten iron and promotes the desiliconization and demanganese reactions.

[0030] In some embodiments, the oxygen flow rate is 0.6-1 Nm³ during the period from start to time t1. 3 / min / t steel. Controlling a larger bottom-blowing oxygen flow rate can, on the one hand, improve the stirring effect and shorten the time of the desilication reaction (Si+O2=SiO2) and demanganese reaction (2Mn+O2=2MnO), thereby improving production efficiency. On the other hand, it can also ensure that more FeO is generated near the outlet of the bottom-blowing device, forming a high-oxygen-content area, which reacts with the P element in the molten iron to form P2O5, with the chemical reaction equation: 2[P]+5FeO=5[Fe]+P2O5, which reacts with the lime blown in the next stage, improving dephosphorization efficiency. If the bottom-blowing oxygen flow rate is too small, the stirring force will be insufficient to a certain extent, which will prolong the time of this stage and affect production efficiency. If the bottom-blowing oxygen force is too large, the stirring effect will not be significantly improved to a certain extent, resulting in waste.

[0031] S2. During the converter smelting process from t1 to t2, oxygen is used as the carrier gas for bottom-blown lime dephosphorization, and the mass-to-volume ratio of lime to oxygen is 4-7 kg / Nm³. 3 t2 is the moment when the mass fraction of carbon in the molten steel in the converter reaches 2.8-3.2%;

[0032] After the desilication and demanganese reactions from start to time t1, the dephosphorization reaction begins. At this time, the molten iron temperature is still relatively low, not exceeding 1450℃. Dephosphorization is extremely sensitive to temperature; the lower the molten iron temperature, the easier it is to dephosphorize. Therefore, during the time period from t1 to t2, a good dephosphorization environment should be provided as much as possible. Oxygen carrying lime is blown in from the bottom of the converter. After the oxygen enters the molten iron, it forms bubbles. On the one hand, the lime powder carried by the bubbles rises with the bubbles, and the oxygen in the bubbles oxidizes the phosphorus element in the molten iron near the lime particles to P2O5. This P2O5 and the P2O5 formed near the outlet of the bottom blowing device in the first stage react with the lime powder carried by the oxygen to produce C3P (CaO·3(P2O5)). The chemical reaction formula is: CaO + P2O5 = CaO·3(P2O5); During the low-temperature, high-speed dephosphorization period from t1 to t2, some of the Si in the molten iron is oxidized to form SiO2. This SiO2 will further combine with C3P, the product of bottom-blown oxygen dephosphorization, to generate a relatively stable dephosphorization phase C2SC3P (CaO·2(SiO2)·CaO·3(P2O5)) in the molten steel. The chemical reaction equation is as follows:

[0033] CaO + 2SiO₂ = CaO·2(SiO₂)

[0034] CaO·2(SiO2)+3 P2O5=CaO·2(SiO2) ·CaO·3(P2O5)

[0035] C2SC3P will rise to the steel-slag interface under the dynamic conditions of molten steel, completing the dephosphorization process and avoiding the decomposition of unstable C3P in the molten steel, which would affect the dephosphorization efficiency. Then, it will move upwards into the slag phase to complete efficient dephosphorization. A larger lime-to-oxygen mass ratio is used in this stage to meet the dephosphorization requirements and improve the dephosphorization rate.

[0036] In some embodiments, the oxygen flow rate is 0.6-1.0 Nm³ during the time period from t1 to t2. 3 / min / t steel. Oxygen, as the carrier gas for lime, not only stirs the molten iron in the converter, but also reacts with the phosphorus element in the molten iron. The resulting P2O5 then combines with the lime. If the oxygen flow rate is too high, it will waste energy to some extent; if the oxygen flow rate is too low, it will weaken the dephosphorization effect to some extent.

[0037] In some embodiments, during the first dephosphorization process, the bottom-blowing flow rate of lime is 4.0-6.0 kg / min / t steel. Using a larger bottom-blowing flow rate of lime in conjunction with the current favorable low dephosphorization temperature improves the dephosphorization effect. Too small a bottom-blowing flow rate of lime will reduce the dephosphorization effect to some extent; too large a bottom-blowing flow rate of lime will lead to energy waste to some extent.

[0038] S3. During the converter smelting process from t2 to the end, a mixture of oxygen and carbon dioxide is used as the carrier gas for bottom-blown lime for the second dephosphorization. During the time interval from t2 to t3, the mass-to-volume ratio of the lime to the mixed gas is 0.7-2 kg / Nm³. 3 During the period from time t3 to the end, the mass-to-volume ratio of the lime to the mixed gas is 2.5-4.5 kg / Nm³. 3 t3 is the moment when the mass fraction of carbon in the molten steel in the converter reaches 0.4-0.8%.

[0039] During the period from time t2 to t3, due to the oxidation of exothermic elements such as carbon and silicon, the temperature of the molten iron rises above 1500℃ during this stage, which to some extent worsens the dephosphorization conditions. During this stage, the carrier gas becomes a mixture of oxygen and carbon dioxide. The carbon dioxide can undergo an endothermic reaction with the carbon in the molten iron, reducing the temperature of the contact area between the bubble jet and the molten steel, thus promoting dephosphorization as much as possible and inhibiting phosphorus reversion. Furthermore, the carbon dioxide can also protect the bottom-blowing device of the converter through its cooling effect. From time t3 to the end of the process, except for Fe and P, other elements in the molten steel have been consumed to a minimum. The combined effect of top and bottom blowing oxygen results in a sufficiently high oxygen content, allowing the bottom-blown CaO to react rapidly, creating a favorable period for dephosphorization. At this time, the proportion of lime is increased again to reduce phosphorus levels. The chemical reactions during this process are as follows:

[0040] 2[Fe] + O₂ = 2FeO

[0041] 5FeO + 2[P] = 5[Fe] + P₂O₅

[0042] CaO + 3P₂O₅ = CaO·3(P₂O₅)

[0043] In some embodiments, the flow rate of the mixed gas is 0.6-1.0 Nm³ during the time interval from t2 to t3. 3 / min / t steel.

[0044] In some embodiments, during the time interval from t2 to t3, the volume ratio of oxygen to carbon dioxide in the mixed gas is 1.8~2.2:0.8~1.2, with the volume of oxygen being greater than that of carbon dioxide. The mid-term mixing of CO2, the reaction between CO2 and molten steel (C) is an endothermic reaction that can extend the life of the bottom blowing gun, but the CO2 content should not be too high. The reaction between CO2 and C is a volume-increasing reaction, and an excessively high mixing ratio will lead to splashing.

[0045] Specifically, during the time interval from t2 to t3, the bottom-blowing flow rate of the lime is 0.5-2.0 kg / min / t steel. Controlling the bottom-blowing flow rate to a smaller extent is suitable for the deteriorating dephosphorization conditions and reduces lime consumption. If the bottom-blowing flow rate of the lime is too large, it will lead to lime waste to some extent; if the bottom-blowing flow rate of the lime is too small, it will further increase phosphorus reversion to some extent and affect the dephosphorization effect.

[0046] In some embodiments, during the process from time t3 to the end, the volume ratio of oxygen to carbon dioxide in the mixed gas is 0.8~1.2:0.8~1.2, and the volume of oxygen is close to that of carbon dioxide. The proportion of CO2 mixed in is increased at the end because the carbon content is lower at the end, which greatly reduces the probability of splashing. In addition, the reaction between CO2 and molten steel C cools down the powder spray jet, which is beneficial to the dephosphorization reaction and extends the life of the bottom blowing gun.

[0047] In some embodiments, during the period from time t3 to the end, the flow rate of the mixed gas is 0.8-2.0 Nm³. 3 / min / t steel.

[0048] In some embodiments, during the process from time t3 to the end, the bottom-blowing flow rate of lime is 3.0-4.0 kg / min / t steel. Maintaining a relatively high lime flow rate is compatible with a favorable dephosphorization environment and improves the dephosphorization effect. Too low a lime bottom-blowing flow rate will reduce the dephosphorization effect to some extent; too high a flow rate will result in some waste.

[0049] The aforementioned lime can be passivated lime, granular, with a particle size of 0.01-0.1 mm, and the mass fraction of particles with a particle size within ±0.01 mm is not less than 80%.

[0050] The method for improving the dephosphorization rate of converters provided in this application will be further explained below with reference to specific embodiments.

[0051] Examples 1 to 5

[0052] Examples 1 to 5 provide a method for improving the dephosphorization rate of a converter, comprising the following steps:

[0053] Step 1: The converter is loaded with scrap steel and molten iron for top and bottom blowing smelting. During the time from the beginning to t1, bottom blowing oxygen is used for stirring. When the time reaches t1, the state of the molten iron is shown in Table 1.

[0054] Step 2: During the time intervals t1 to t2, dephosphorization is performed by bottom blowing oxygen and lime. The flow rates of oxygen and lime are shown in Table 1. At time t2, the state of the molten iron is shown in Table 1.

[0055] Step 3: During the time interval t2 to t3, a mixture of oxygen, carbon dioxide and lime is blown into the converter. The flow rates of oxygen, lime and carbon dioxide are shown in Table 2. At time t3, the state of the molten iron is shown in Table 2.

[0056] Step 4: From t3 to the end, continue bottom blowing a mixture of oxygen, carbon dioxide and lime into the converter. The flow rates of oxygen, lime and carbon dioxide are shown in Table 2.

[0057] Table 1

[0058]

[0059] Table 2

[0060]

[0061] Table 3

[0062]

[0063] As can be seen from the data in Table 3, the dephosphorization amount per unit of lime provided by the methods of Examples 1 to 5 of the present invention is 0.0069-0.0075%, which is high; while the dephosphorization amount per unit of lime provided by Comparative Examples 1 to 2 is 0.0032-0.0050%, which is not as high as that of Examples 1 to 5 of the present invention.

[0064] This invention provides a method for improving the dephosphorization rate in a converter. In the initial stage of converter smelting, from the start to time t1, silicon and manganese oxidize before phosphorus; therefore, only oxygen is blown into the bottom, not lime, to accelerate the desiliconization and demanganese removal processes. From t1 to t2, the molten iron temperature is relatively low, providing favorable dephosphorization conditions; controlling a higher lime bottom-blowing flow rate improves the dephosphorization effect. From t2 to t3, dephosphorization conditions worsen, and the lime bottom-blowing flow rate decreases. From t3 to the end of the process, dephosphorization conditions improve, and a higher lime bottom-blowing flow rate is maintained. By controlling each stage of converter smelting, the lime bottom-blowing flow rate is ensured to be compatible with the dephosphorization conditions, thus improving the dephosphorization effect. The method provided by this invention achieves a dephosphorization rate of 0.0069-0.0075% per unit of lime, demonstrating a high dephosphorization rate.

[0065] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0066] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for improving the dephosphorization rate of a converter, characterized in that, Includes the following steps: During the converter smelting process from the start to time t1, bottom-blown oxygen is used for stirring; t1 is the moment when the mass fraction of Si in the molten steel in the converter reaches 0.08-0.12%. During the converter smelting process from time t1 to t2, oxygen is used as the carrier gas for bottom-blown lime dephosphorization, and the mass-to-volume ratio of lime to oxygen is 4-7 kg / Nm³. 3 t2 is the moment when the mass fraction of carbon in the molten steel in the converter reaches 2.8-3.2%; During the converter smelting process from time t2 to the end, a mixture of oxygen and carbon dioxide is used as the carrier gas for bottom-blown lime dephosphorization. Specifically, during the time interval from t2 to t3, the mass-to-volume ratio of the lime to the mixed gas is 0.7-2 kg / Nm³. 3 During the period from time t3 to the end, the mass-to-volume ratio of the lime to the mixed gas is 2.5-4.5 kg / Nm³. 3 t3 is the moment when the mass fraction of carbon in the molten steel in the converter reaches 0.4-0.8%.

2. The method for improving the dephosphorization rate of a converter according to claim 1, characterized in that, In the first dephosphorization process, the bottom blowing flow rate of lime is 4.0-6.0 kg / min / t steel.

3. The method for improving the dephosphorization rate of a converter according to claim 2, characterized in that, During the time interval from t2 to t3, the bottom blowing flow rate of the lime is 0.5-2.0 kg / min / t steel.

4. The method for improving the dephosphorization rate of a converter according to claim 2, characterized in that, During the process from time t3 to the end, the bottom blowing flow rate of the lime is 3.0-4.0 kg / min / t steel.

5. The method for improving the dephosphorization rate of a converter according to any one of claims 2-4, characterized in that, During the period from the start to time t1, the oxygen flow rate is 0.6-1 Nm³. 3 / min / t steel.

6. The method for improving the dephosphorization rate of a converter according to any one of claims 2-4, characterized in that, During the time interval from t1 to t2, the oxygen flow rate is 0.6-1.0 Nm³. 3 / min / t steel.

7. The method for improving the dephosphorization rate of a converter according to any one of claims 2-4, characterized in that, During the period from time t2 to time t3, the volume ratio of oxygen to carbon dioxide in the mixed gas is 1.8~2.2:0.8~1.2; during the period from time t3 to the end, the volume ratio of oxygen to carbon dioxide in the mixed gas is 0.8~1.2:0.8~1.

2.

8. The method for improving the dephosphorization rate of a converter according to claim 7, characterized in that, During the time interval from t2 to t3, the flow rate of the mixed gas is 0.6-1.0 Nm³. 3 / min / t steel; during the process from time t3 to the end, the flow rate of the mixed gas is 0.8-2.0 Nm³. 3 / min / t steel.

9. The method for improving the dephosphorization rate of a converter according to any one of claims 2-4, characterized in that, The lime has a particle size of 0.01-0.1 mm, wherein the mass fraction of particles with a particle size within ±0.01 mm is not less than 80%.

10. The method for improving the dephosphorization rate of a converter according to any one of claims 2-4, characterized in that, The capacity of the converter is 30-300t.

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