Method for recycling KR desulfurization slag in converter

Abstract

The invention discloses a method for recycling KR desulfurization slag in a converter, and belongs to the technical field of comprehensive utilization of slag. The method comprises the following steps that S1, waste steel is added into a furnace, molten iron is added, and then an oxygen lance is put down for oxygen blowing operation; s2, after oxygen blowing is started, a composite oxidizing agent is added into the converter, the basicity and oxidability of early-stage slag of the converter are controlled, and KR desulfurization slag is added into the converter after oxygen blowing is carried out for 1 min; wherein the composite oxidizing agent is prepared from the following components in percentage by mass: 80 to 90 percent of 2Fe2O3. SiO2 and 10 to 20 percent of MnCO3; or the composite oxidizing agent is prepared from the following components in percentage by mass: 80 to 90 percent of 2Fe2O3. SiO2 and 10 to 20 percent of MnCO3. According to the method, by optimizing the technological parameters of converter early-stage smelting, the KR desulfurization slag can be used for converter smelting, CaO and iron resources in the KR desulfurization slag are utilized to the maximum extent, and therefore the purposes of simplifying the working procedure and reducing the cost are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of comprehensive utilization of slag, and more specifically to a method for recycling KR desulfurization slag in a converter. Background Art

[0002] The KR desulfurization process is widely adopted by domestic and foreign steel enterprises because of its simple operation and high desulfurization efficiency. At present, the KR desulfurizer is mainly lime-based. The chemical composition and mineral phase composition of the desulfurization slag formed after KR desulfurization are CaO, Fe (in the form of oxides or other iron compounds), CaF2 and CaS, etc. In the KR desulfurization of molten iron, the desulfurization product CaS will be wrapped on the surface of the lime, hindering the internal lime from continuing to play a desulfurization role, making the utilization efficiency of the lime less than 20%, resulting in a large amount of resource waste. In addition, after KR desulfurization, slag treatment is required. Due to the poor separation effect of slag and iron, the iron content in the KR desulfurization slag exceeds 50%, resulting in a waste of iron resources and an increase in smelting costs.

[0003] The resource utilization of KR desulfurization slag has always been one of the hot topics in the research field of smelting. After searching, the Chinese patent application with publication number CN111250518A discloses a method for efficient resource utilization of KR desulfurization slag. The method first crushes the desulfurization slag to a specified particle size, then uses magnetic separation to obtain slag iron and tailings, and further grinds the tailings for sintering. Although this application can achieve the cascade use of metallic iron and tailings in KR desulfurization slag to a certain extent, its process is complicated and the processing cost is high.

[0004] For another example, the Chinese patent application with publication number CN1730674A discloses a method for using hot metal desulfurization slag for hot metal desulfurization. The application mainly uses the desulfurization slag and lime to reuse for hot metal desulfurization, but it can only reduce the discharge of KR desulfurization slag, and the number of cycles is generally only 1. In addition, the desulfurization efficiency of this desulfurization method is average.

[0005] A Chinese patent application with publication number CN116855667A discloses a method for recycling solid waste from molten iron pretreatment. The method mainly applies KR desulfurization slag to the smelting of sulfur-containing free-cutting steel. KR desulfurization slag is added during the LF refining process, and the slag-metal reaction is used to increase the sulfur content of the molten steel. However, the application scope of this application is limited.

[0006] A Chinese patent application with publication number CN117965837A discloses a method for hot recycling of KR hot metal pretreatment slag. The application mainly involves adding Fe2O3 and bauxite during the slag removal process of hot metal pretreatment. However, it has the following problems: (1) the melting point of the directly added Fe2O3 is above 1500°C, and the melting speed is slow, which limits the reaction rate of Fe2O3 with the KR desulfurization slag, thereby resulting in low desulfurization efficiency; (2) SO2 formed after desulfurization easily reacts with Ca in the KR desulfurization slag to form CaSO4. The decomposition of CaSO4 under high temperature conditions will cause backsulfurization, affecting the desulfurization effect.

[0007] Therefore, it is of great significance to develop a new method for resource utilization of KR desulfurization slag. Summary of the invention

[0008] In view of the problem that the resource utilization process of KR desulfurization slag in the prior art is relatively complicated or the resource utilization effect is not good, the present invention provides a method for recycling KR desulfurization slag in a converter. The method optimizes the process parameters of the early smelting of the converter so that KR desulfurization slag can be used for converter smelting, and the CaO and iron resources therein are utilized to the maximum extent, thereby achieving the purpose of simplifying the process and reducing costs.

[0009] The present invention provides a method for reducing the amount of smoke and dust in the early stage of blowing in a converter double-slag smelting process, comprising:

[0010] S1: Add scrap steel and molten iron into the furnace, and then lower the oxygen lance to perform oxygen blowing operation; S2: After the oxygen blowing starts, add a composite oxidant into the converter to control the basicity and oxidizability of the early slag of the converter, add KR desulfurization slag into the converter after blowing oxygen for 1 minute, and continue blowing; wherein, the composite oxidant includes the following components in mass percentage: 80-90% 2Fe2O3·SiO2, 10-20% MnCO3; or the composite oxidant is composed of the following components in mass percentage: 80-90% 2Fe2O3·SiO2, 10-20% MnCO3.

[0011] The CaO in the existing KR desulfurization slag is mainly wrapped by CaS, and the CaO inside it cannot be used directly as a slag-making agent. In the traditional converter smelting process, the slag is mainly composed of highly oxidizing FeO due to oxygen blowing, and the distribution ratio of sulfur between slag and metal is very low. Sulfur will spontaneously transfer to the molten iron, causing the sulfur content of the molten iron to increase. Therefore, if the KR desulfurization slag is directly reused as a slag-making agent in the converter using the existing smelting process, the sulfur element in the KR desulfurization slag will flow back into the molten iron of the converter, resulting in an increase in the sulfur content of the molten iron. In addition, since the converter smelting process requires the control of alkalinity to dephosphorize, the gasification desulfurization capacity in the early stage of smelting is limited.

[0012] The present invention controls the process parameters in the early stage of converter smelting, especially controls the basicity and oxidizability of the slag in the early stage of the converter, so that the KR desulfurization slag can be directly recycled and utilized in the converter. It should be noted that the selection of the composite oxidant in the present invention is particularly important. The composite oxidant is added to the converter. On the one hand, 2Fe2O3·SiO2 in the composite oxidant is a pre-melted slag with a melting point of about 1200°C, which is lower than the temperature of the molten iron, so that the pre-melted slag can be melted quickly, thereby increasing the desulfurization reaction rate of the KR desulfurization slag. On the other hand, the traditional converter slag is mainly FeO, which cannot be used for gasification of S. The composite oxidant can provide Fe2O3 required for the sulfur oxidation reaction. Moreover, in the gasification desulfurization process, compared with SO2, SiO2 in the composite deoxidizer reacts preferentially with the Ca element to form silicate, which can avoid the reaction of SO2 and Ca to form CaSO4, thereby facilitating the escape of SO2 generated by oxidation. In addition, MnCO3 in the composite oxidant will decompose to generate CO2 and MnO. The decomposed MnO can lower the melting point of the slag and promote the dissolution of lime in the KR desulfurization slag. At the same time, CO2 is an oxidizing atmosphere, which is conducive to promoting the desulfurization reaction.

[0013] Furthermore, when the oxygen lance in S1 performs oxygen blowing operation, the oxygen blowing conditions include: the oxygen supply intensity of the oxygen lance is controlled to be 2.2-3.0 m 3 / t / min, the oxygen lance position is controlled to be 2-3m above the molten iron surface, and the oxygen partial pressure is controlled to be 10 -5 -10 -3 Mpa. It should be noted that the parameter limitation of oxygen blowing conditions is particularly important. The oxygen supply intensity, gun position and oxygen partial pressure of the oxygen gun are controlled. The low oxygen supply intensity and high gun position operation are used in blowing to improve the oxidizability of the slag, that is, to increase the Fe2O3 / FeO content in the slag, and provide favorable conditions for subsequent gasification and dephosphorization; the purpose of controlling the oxygen partial pressure is to prevent C in the molten steel or CO in the furnace gas from reducing Fe2O3 in the slag, so that the Fe2O3 content in the slag is high. Further, the specific conditions for adding molten iron to the S1 are that the temperature of the molten iron is 1300-1500°C, and the sulfur content is 0.02-0.045%. The temperature of the molten iron entering the furnace is limited. When the temperature of the molten iron entering the furnace is too low, the distribution ratio of sulfur between the slag and the metal is reduced, so that the sulfur element in the KR desulfurization slag migrates to the molten iron, which is not conducive to the gasification and removal of sulfur in the slag. On the contrary, when the temperature is too high, CO will react in advance, reduce the oxidizability of the slag, and is also not conducive to the gasification and removal of sulfur. In addition, since elemental sulfur can only be oxidized into SO2 in the slag, the sulfur content in the molten iron is controlled. Under a certain sulfur distribution ratio, the sulfur element in the KR desulfurization slag is maximized to be present in the slag layer, thereby preparing for the subsequent oxidation and removal of the sulfur element.

[0014] Furthermore, the amount of the composite oxidant added to S2 is 22-40 kg / t steel.

[0015] Furthermore, the amount of KR desulfurization slag added to S2 is 5 to 30 kg / t steel.

[0016] Furthermore, the amount of the composite oxidant added to S2 is 22-40 kg / t steel and the amount of the KR desulfurization slag added is 5-30 kg / t steel.

[0017] Furthermore, after the oxygen blowing in S2 starts, lime is added together with the composite oxidant, and the amount of lime added is controlled to be 0-3 kg / t steel.

[0018] Furthermore, the basicity of the slag in the early stage of the converter is controlled to be 1.0-1.3, the sum of the mass of FeO and Fe2O3 accounts for 20-45%, and the mass ratio of Fe2O3 to FeO is ≥4. Too low basicity in the early stage of the converter will cause the sulfur element in the slag to flow back into the molten iron. On the contrary, too high basicity is not conducive to the oxidation of sulfur in the slag. The main purpose of controlling the high Fe2O3 content in the slag is that the oxidation reaction of sulfur mainly relies on Fe2O3. The slag in the traditional converter is mainly FeO, and FeO cannot gasify sulfur.

[0019] Furthermore, after blowing for 3 to 4 minutes, lime and dolomite are continuously added to the converter in batches, wherein the amount of lime added is controlled to be 25 to 35 kg / t steel, and the amount of dolomite added is controlled to be 10 to 20 kg / t steel.

[0020] Furthermore, the basicity of the converter final slag is controlled to be 4-5, and the temperature is 1630-1680°C.

[0021] Furthermore, a converter slag splashing operation is performed before adding scrap steel and molten iron into the furnace.

[0022] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0023] (1) The present invention selects a composite oxidant containing 2Fe2O3·SiO2 and MnCO3. On the one hand, the composite oxidant oxidizes the sulfur element contained in the KR desulfurization slag to generate SO2, and the generated SO2 escapes from the slag layer; on the other hand, it generates MnO that can reduce the melting point of the slag and CO2 that is beneficial to the desulfurization reaction, thereby preventing the sulfur element contained in the KR desulfurization slag from flowing back into the molten iron, saving the processing steps of crushing, magnetic separation and oxidative desulfurization, realizing the direct resource utilization of the KR desulfurization slag in the converter, simplifying the process and reducing costs.

[0024] (2) The present invention further optimizes the oxygen supply conditions, controls the oxygen supply intensity of a small flow rate, the high gun position and the oxygen partial pressure, thereby increasing the oxygen level in the furnace gas, controlling the Fe2O3 / FeO in the slag, and further promoting the oxidation reaction of sulfur in the KR desulfurization slag. In addition, by controlling the basicity of the converter in the early stage, the sulfur element in the slag is prevented from flowing back into the molten iron, which is beneficial to further promote the oxidation reaction of the sulfur element in the slag.

[0025] (3) The present invention optimizes the design of composite oxidant, alkalinity and oxygen supply conditions to better achieve the oxidation and removal of sulfur in KR desulfurization slag, and realizes the resource utilization of KR desulfurization slag in the converter, thereby making full use of the unreacted CaO and iron resources in the KR desulfurization slag, reducing the consumption of converter steelmaking lime and steel materials, and saving production costs. In addition, the application of KR desulfurization slag in converter smelting can also appropriately improve the converter desulfurization capacity. DETAILED DESCRIPTION

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

[0027] The early stage of the converter refers to the period from the addition of the composite oxidant to the addition of lime and dolomite again, that is, from the start of blowing to 3 to 4 minutes after the start of blowing.

[0028] Example 1

[0029] This embodiment is carried out on a 180t converter and includes the following steps:

[0030] (1) After the converter slag splashing is completed, scrap steel and molten iron are added into the furnace. The composition and temperature of the molten iron are shown in Table 1. After the iron addition is completed, an oxygen lance is lowered to blow oxygen;

[0031] (2) Control the oxygen supply intensity to 2.5m 3 / t / min, the gun position is controlled at 2.3m, and the oxygen partial pressure is controlled at 10 -4.5 Mpa, after the oxygen blowing starts, 2kg / t steel lime and 22kg / t steel composite oxidant are added into the converter, and after the oxygen blowing for 1 minute, 12kg / t steel KR desulfurized slag is added into the converter; the mass proportion of 2Fe2O3.SiO2 in the composite oxidant used is 90%, and the mass proportion of MnCO3 is 10%;

[0032] (3) After blowing for 3.5 min, 31.4 kg / t steel of lime and 16.7 kg / t steel of dolomite were added in batches to control the final slag basicity to 4.2 and the molten steel temperature to 1656°C. The slag control conditions and converter smelting indicators are shown in Table 2.

[0033] In this embodiment, the sulfur content of the molten iron at the converter end point is 0.028%. Compared with the sulfur content of the molten iron entering the furnace, no resulfurization occurs at the converter end point. The total lime consumption is 33.4 kg / t steel, and the steel material consumption is 1071 kg / t.

[0034] Comparative Example 1

[0035] The composition and temperature of the molten iron in this comparative example are shown in Table 1. The difference between this comparative example and Example 1 is that no composite oxidant is used, and iron oxide is used instead of the composite oxidant. The amount of iron oxide added is 22 kg / t steel. After the start of oxygen blowing, 2 kg / t steel of lime is added to the converter. After 3.5 minutes of blowing, 32.8 g / t steel of lime and 16.7 kg / t steel of dolomite are added in batches. The rest of the operations are basically the same as in Example 1.

[0036] In this comparative example, the sulfur content of the molten iron at the converter end point is 0.049%. Compared with the sulfur content of the molten iron entering the furnace, resulfurization occurs at the converter end point, the total lime consumption is 34.8 kg / t steel, and the steel material consumption is 1069 kg / t steel.

[0037] Comparative Example 2

[0038] The composition and temperature of the molten iron in this comparative example are shown in Table 1. The difference between this comparative example and Example 1 is that the oxygen blowing conditions are different. The oxygen blowing conditions are as follows: the oxygen supply intensity of the oxygen lance is controlled to be 3.1m 3 / t / min, the oxygen lance position is controlled to be 1.2m above the molten iron level, and the oxygen partial pressure is controlled to be 10 -6 Mpa, after oxygen blowing started, 2kg / t steel of lime was added into the converter, and after blowing for 3.5min, 33.2kg / t steel of lime and 16.7kg / t steel of dolomite were added in batches, and the rest of the operation was basically the same as in Example 1.

[0039] In this comparative example, the sulfur content of the molten iron at the converter end point is 0.050%. Compared with the sulfur content of the molten iron entering the furnace, resulfurization occurs at the converter end point, the total lime consumption is 35.2 kg / t steel, and the steel material consumption is 1072 kg / t steel.

[0040] Comparative Example 3

[0041] The composition and temperature of the molten iron in this comparative example are shown in Table 1. The difference between this comparative example and Example 1 is that the temperature of the molten iron in the furnace is 1260°C, 2kg / t steel of lime is added to the converter after the oxygen blowing starts, and after 3.5 minutes of blowing, 32.7kg / t steel of lime and 16.7kg / t steel of dolomite are added in batches, and the remaining operations are basically the same as in Example 1.

[0042] In this comparative example, the sulfur content of the molten iron at the converter end point is 0.046%. Compared with the sulfur content of the molten iron entering the furnace, resulfurization occurs at the converter end point, the total lime consumption is 34.7 kg / t steel, and the steel material consumption is 1068 kg / t steel.

[0043] Comparative Example 4

[0044] The composition and temperature of the molten iron in this comparative example are shown in Table 1. This comparative example adopts the existing converter smelting process, including the following steps:

[0045] (1) After the converter slag splashing is completed, scrap steel and molten iron are added into the furnace. The composition and temperature of the molten iron are shown in Table 1. After the iron addition is completed, an oxygen lance is lowered to blow oxygen;

[0046] (2) Control the oxygen supply intensity to 3.0m 3 / t / min, the oxygen lance position is controlled at 1.3m, and the oxygen partial pressure is controlled at 10 - 7 Mpa, 6kg / t steel lime is added into the converter immediately after oxygen blowing begins;

[0047] (3) Blowing for 0.5 min, adding 32.6 kg / t steel of lime and 21.2 kg / t steel of dolomite in batches, controlling the final slag basicity to 3.6 and the molten steel temperature to 1658°C; the slag control situation and converter smelting indicators are shown in Table 2.

[0048] In this comparative example, the sulfur content of the converter final molten iron is 0.024%, which is not reduced compared with the sulfur content of the molten iron entering the furnace. The total lime consumption is 38.6 kg / t steel, and the steel material consumption is 1076 kg / t steel.

[0049] Example 2

[0050] This embodiment is carried out on a 180t converter and includes the following steps:

[0051] (1) After the converter slag splashing is completed, scrap steel and molten iron are added into the furnace. The composition and temperature of the molten iron are shown in Table 1. After the iron addition is completed, an oxygen lance is lowered to blow oxygen;

[0052] (2) Control the oxygen supply intensity to 2.2m 3 / t / min, the oxygen lance position is controlled at 2m, and the oxygen partial pressure is controlled at 10 -5 Mpa, after the oxygen blowing starts, 3kg / t steel of lime and 40kg / t steel of composite oxidant are added into the converter, and after the oxygen blowing for 1 minute, 25kg / t steel of KR desulfurized slag is added into the converter; the mass proportion of 2Fe2O3.SiO2 in the composite oxidant used is 80%, and the mass proportion of MnCO3 is 20%;

[0053] (3) After blowing for 3.7 min, 27.9 kg / t of lime and 13.4 kg / t of dolomite were added in batches to control the final slag basicity to 5.0 and the molten steel temperature to 1632°C. The slag control conditions and converter smelting indicators are shown in Table 2.

[0054] The sulfur content of the molten iron at the converter end point of this embodiment is 0.023%. Compared with the sulfur content of the molten iron entering the furnace, no sulfur reversion occurs at the converter end point. The total lime consumption is 30.9 kg / t, and the steel material consumption is 1063 kg / t.

[0055] Example 3

[0056] This embodiment is carried out on a 180t converter and includes the following steps:

[0057] (1) After the converter slag splashing is completed, scrap steel and molten iron are added into the furnace. The composition and temperature of the molten iron are shown in Table 1. After the iron addition is completed, an oxygen lance is lowered to blow oxygen;

[0058] (2) Control the oxygen supply intensity to 3.0m 3 / t / min, the oxygen lance position is controlled at 3m, and the oxygen partial pressure is controlled at 10 -3 Mpa, after the oxygen blowing starts, add 34kg / t steel composite oxidant into the converter, after blowing oxygen for 1 minute, add 20kg / t steel KR desulfurized slag into the converter, wherein the mass proportion of 2Fe2O3.SiO2 in the composite oxidant is 86%, and the mass proportion of MnCO3 is 14%;

[0059] (3) After blowing for 4 min, 32.6 kg / t steel of lime and 18.1 kg / t steel of dolomite were added in batches to control the final slag basicity to 4.3 and the molten steel temperature to 1675°C; the slag control conditions and converter smelting indicators are shown in Table 2.

[0060] In this embodiment, the sulfur content of the molten iron at the converter end point is 0.017%. Compared with the sulfur content of the molten iron entering the furnace, no sulfur reversion occurs at the converter end point. The total lime consumption is 32.6 kg / t, and the steel material consumption is 1064 kg / t.

[0061] Example 4

[0062] This embodiment is carried out on a 180t converter and includes the following steps:

[0063] (1) After the converter slag splashing is completed, scrap steel and molten iron are added into the furnace. The composition and temperature of the molten iron are shown in Table 1. After the iron addition is completed, an oxygen lance is lowered to blow oxygen;

[0064] (2) Control the oxygen supply intensity to 2.6m 3 / t / min, the oxygen lance position is controlled at 2.7m, and the oxygen partial pressure is controlled at 10 - 3.5Mpa after oxygen blowing starts, 2kg / t steel lime and 32kg / t steel composite oxidant are added into the converter, and 30kg / t steel KR desulfurized slag is added into the converter after oxygen blowing for 1 minute, wherein the mass proportion of 2Fe2O3.SiO2 in the composite oxidant is 87%, and the mass proportion of MnCO3 is 13%;

[0065] (3) After blowing for 3.8 min, 27.5 kg / t steel of lime and 15.6 kg / t steel of dolomite were added in batches to control the final slag basicity to 4.6 and the molten steel temperature to 1667°C; the slag control conditions and converter smelting indicators are shown in Table 2.

[0066] In this embodiment, the sulfur content of the molten iron at the converter end point is 0.032%. Compared with the sulfur content of the molten iron entering the furnace, no resulfurization occurs at the converter end point. The total lime consumption is 29.5 kg / t steel, and the steel material consumption is 1060 kg / t steel.

[0067] Table 1 Hot metal conditions and charging conditions

[0068]

[0069]

[0070] Table 2 Slag control and converter smelting indicators

[0071]

Claims

1. A method for recycling KR desulfurization slag in a converter, characterized in that: include: S1: Add scrap steel and molten iron into the furnace, then use an oxygen lance to blow oxygen; S2: After the oxygen blowing starts, a composite oxidant is added into the converter to control the basicity and oxidizability of the slag in the early stage of the converter. After the oxygen blowing for 1 minute, KR desulfurization slag is added into the converter to continue blowing; Wherein, the composite oxidant comprises the following components in mass percentage: 80-90% 2Fe2O3·SiO2, 10-20% MnCO3; or the composite oxidant comprises the following components in mass percentage: Composition: 80-90% 2Fe2O3·SiO2, 10-20% MnCO3.

2. The method for recycling KR desulfurization slag in a converter according to claim 1, characterized in that: When the oxygen lance in S1 is blowing oxygen, the oxygen blowing conditions include: the oxygen supply intensity of the oxygen lance is controlled to be 2.2-3.0 m 3 / t / min, the oxygen lance position is controlled to be 2-3m above the molten iron surface, and the oxygen partial pressure is controlled to be 10 -5 -10 -3 Mpa.

3. The method for recycling KR desulfurization slag in a converter according to claim 1, characterized in that: The specific conditions for adding molten iron into S1 are that the temperature of the molten iron is 1300-1500° C. and the sulfur content is 0.02-0.045%.

4. The method for recycling KR desulfurization slag in a converter according to claim 1, characterized in that: The amount of the composite oxidant added to S2 is 22-40 kg / t steel; and / or the amount of the KR desulfurization slag added is 5-30 kg / t steel.

5. The method for recycling KR desulfurization slag in a converter according to claim 1, characterized in that: After the oxygen blowing in S2 starts, lime is added together with the composite oxidant, and the amount of lime added is controlled to be 0-3 kg / t steel.

6. The method for recycling KR desulfurization slag in a converter according to any one of claims 1 to 5, characterized in that: The basicity of the slag in the early stage of the converter is controlled to be 1.0-1.3, the sum of the masses of FeO and Fe2O3 accounts for 20-45%, and the mass ratio of Fe2O3 to FeO is ≥4.

7. The method for recycling KR desulfurization slag in a converter according to claim 6, characterized in that: After blowing for 3 to 4 minutes, continue to add lime and dolomite into the converter in batches, with the amount of lime added being controlled at 25 to 35 kg / t steel and the amount of dolomite added being controlled at 10 to 20 kg / t steel.

8. The method for recycling KR desulfurization slag in a converter according to claim 7, characterized in that: The basicity of the converter final slag is controlled at 4-5 and the temperature is 1630-1680℃.

9. The method for recycling KR desulfurization slag in a converter according to any one of claims 1 to 5, characterized in that: The converter slag splashing operation is carried out before adding scrap steel and molten iron into the furnace.

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