Method for using a white dolomite produced in a converter process

Abstract

The present application belongs to the technical field of converter steelmaking, and particularly relates to a method for using raw dolomite in a converter process. The method uses the residual heat of the slag left after tapping to decompose raw dolomite, replacing part of the lightly calcined dolomite; full mixing of the raw dolomite and the residual slag is achieved through slag splashing to prolong the service life of the splashed slag layer; raw dolomite is added before adding scrap steel to improve the utilization rate of the raw dolomite and reduce the incidence of slag splashing; the drying state and particle size range of the raw dolomite are strictly controlled to avoid quality defects. The method can improve the decarburization efficiency, inclusion removal rate and coal gas recovery, can inhibit the rapid heating of the molten steel at the initial blowing stage to improve the phosphorus removal qualification rate, thereby improving the process stability and product quality.

Description

Technical Field

[0001] This invention belongs to the field of converter steelmaking technology, specifically relating to a method for using raw dolomite in a converter process. Background Technology

[0002] Slag splashing for converter lining is a core auxiliary process in modern converter steelmaking. Its principle is to utilize the high-temperature slag remaining after tapping (typically 1400-1600℃) to splash onto the converter lining surface using bottom-blown argon or nitrogen gas, forming a dense, wear-resistant slag layer. This extends the lining's service life and reduces the frequency and cost of lining repairs. In traditional slag splashing processes, to ensure the slag has suitable viscosity and MgO content (typically a target MgO content of 8%-12%), lightly calcined dolomite is often used as a slag conditioner. Lightly calcined dolomite, after pre-calcination (at 800-1000℃), has undergone partial decomposition and can quickly participate in slag formation after being added to the converter. However, the calcination process of lightly calcined dolomite requires additional energy, resulting in higher production costs.

[0003] Dolomite (main component CaCO3) MgCO3 is a commonly used MgO-containing slag material in converter steelmaking. Based on its processing state, it can be divided into raw dolomite (uncalcined) and lightly calcined dolomite (partially calcined) used as a slag conditioner in traditional slag splashing furnace protection processes. However, the application of raw dolomite in current technologies still has many limitations, making it difficult to achieve large-scale, efficient utilization. (1) Decomposition of raw dolomite (CaCO3) The process of MgCO33 → CaO + MgO + 2CO2↑ requires the absorption of a large amount of heat, which can easily lead to a temperature drop of 30-50℃ in the molten steel. Additional heating is required (such as increasing the temperature of the molten iron or increasing the amount of coke added), which will increase energy consumption. (2) The mixing uniformity of raw dolomite and the slag left in the converter is poor. The decomposed CaO and MgO are difficult to be evenly dispersed in the slag, which affects the slag viscosity adjustment effect and thus reduces the quality of slag splashing and furnace protection. (3) The utilization rate of raw dolomite is low (usually <60%), which may also cause quality defects such as porosity and hydrogen embrittlement in molten steel; (4) The crude method of adding slag materials can easily cause the slag to "dry out" or splash, which affects the dephosphorization and desulfurization effects and prolongs the blowing cycle.

[0004] Furthermore, during the converter blowing process, the amount and timing of slag addition (lime, dolomite, fluorite, etc.) directly affect the slag formation rate, slag basicity, and smelting effect. In traditional processes, slag is often added in "one-time or two-batch" batches, leading to insufficient slag in the early stage (low dephosphorization efficiency) and excessive slag in the later stage (overly thin slag, poor slag splashing effect), and it is difficult to accurately control the MgO content in the slag.

[0005] Currently, the application of converter raw dolomite in the industry is still mainly "auxiliary and extensive," with the core pain points concentrated in: 1) High cost: The proportion of lightly calcined dolomite is too high, and calcination energy consumption accounts for 15%-20% of the converter's auxiliary energy consumption; 2) Low efficiency: The utilization rate of raw dolomite is less than 60%, failing to fully leverage its low-cost advantage; 3) Poor stability: Slag splashing occurs at a rate of 8%-12%; 4) Energy waste: The residual heat of the slag left after the converter tapping (about 200-300MJ / furnace) is not utilized and is directly lost with the slag cooling.

[0006] In summary, while existing converter dolomite application technologies can meet basic smelting requirements, they have significant shortcomings in terms of economy, process stability, product quality, environmental protection, and efficiency.

[0007] Existing technologies have optimized the use of raw dolomite, such as Chinese patent document CN113046513A, but they have not effectively solved the core technical problems of high energy consumption, low utilization rate, unstable process and increased carbon emissions in the application of dolomite in converters. Therefore, it is urgent to develop a new technology for the application of dolomite in converters to break through the existing technical bottlenecks and promote the development of converter steelmaking processes towards energy saving, high efficiency, low carbon and stability. Summary of the Invention

[0008] To address the technical problems of high cost, low utilization rate, unstable process, and energy waste in the use of raw dolomite in the converter process of existing technologies, this invention optimizes the application process of raw dolomite in the converter smelting process, providing a method for using raw dolomite in the converter process that can achieve efficient utilization of raw dolomite and reduce production costs. The method utilizes the residual heat of the slag remaining after steel tapping in the converter to decompose raw dolomite, replacing part of the lightly calcined dolomite, thus reducing the cost of slag per ton of steel and calcination energy consumption; slag splashing is used to ensure thorough mixing of raw dolomite and the remaining slag, extending the life of the splashed slag layer; adding raw dolomite before adding scrap steel improves the utilization rate of raw dolomite and reduces the incidence of slag splashing; and strictly controlling the drying state and particle size range of the raw dolomite avoids quality defects.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A method for using raw dolomite in a converter process includes the following steps: S1. After the steel is tapped from the converter, slag is left in the converter for splashing and furnace protection. S2. Add raw dolomite into the converter, the amount of raw dolomite being 0.05-0.15% of the slag mass; S3, slag splashing protection for the furnace; S4. Add scrap steel into the converter, the amount of scrap steel being added being 3-8 times the mass of the slag, and then add molten iron, the amount of molten iron being added being 18-32 times the mass of the slag. S5. Lower the oxygen lance and start blowing. Add the slag materials into the converter in sequence, with each slag material added at a rate of 2 / 3 to 3 / 4 of the total amount. The addition should be completed within 3 minutes of starting the blowing process. The slag materials should include at least lime and lightly calcined dolomite. S6. When the blowing process has been going on for 3-5 minutes, check the melting state of the slag. After the slag has melted, add the remaining slag material in small batches and multiple times evenly. All the slag material should be added 3 minutes before the end.

[0010] Preferably, in step S1, the mass of slag retained in the converter for slag splashing and furnace protection is 4-6 tons, and the capacity of the converter is 120 tons.

[0011] Preferably, the raw dolomite in step S2 needs to be dried, and the moisture content of the dried raw dolomite is ≤0.5%, and the proportion of raw dolomite with a particle size of 5-30mm is >90%.

[0012] Preferably, the raw dolomite composition in step S2, by mass fraction, includes: CaO 30-40%, SiO2 2.5-4%, MgO 17-25%, P≤0.01%, S≤0.01%, and the remainder being impurity elements.

[0013] Preferably, the amount of raw dolomite added in step S2 accounts for 0.07-0.13% of the slag mass.

[0014] Preferably, the amount of raw dolomite added in step S2 is calculated according to formula (1): (1) Where: n is the substitution coefficient, t1 is the amount of molten iron added, t, t2 are the amount of scrap steel added, t, , where is the slag coefficient, %; (MgO) 目标 The target MgO content in converter slag is expressed as %, (MgO). 铁水 The content of MgO in molten iron is expressed in tons (t), where (MgO) is present. 废钢 The MgO content of scrap steel, %, m 轻白 The effective utilization efficiency of lightly calcined dolomite is %, (MgO). 轻白 The MgO content of lightly calcined dolomite is given in %, (MgO). 生白 The MgO content (CaO) of raw dolomite is given in percentage. 轻白 The CaO content of lightly calcined dolomite is given in percentages (CaO). 生白 The CaO content of raw dolomite is %.

[0015] Preferably, the amount of scrap steel added in step S4 is 3.3-7.8 times the mass of slag, and the amount of molten iron added is 19.9-31 times the mass of slag.

[0016] Preferably, the amount of scrap steel added in step S4 accounts for 12%-20% of the total mass percentage of scrap steel and molten iron added.

[0017] Preferably, the slag material in step S5 further includes any one or more of sintered ore, red mud pellets, iron oxide pellets, and dust removal ash pellets.

[0018] Preferably, the amount of lightly calcined dolomite added in step S5 is calculated according to formula (2).

[0019] (2) Where: w 生白 Dolomite addition amount, t, m 生白 To improve the effective utilization efficiency of dolomite.

[0020] Preferably, the total amount of lime added in step S5 is 0.45-1.1 times the mass of slag.

[0021] More preferably, the total amount of lime added in step S5 is 0.48-1.02 times the mass of slag.

[0022] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a method for using raw dolomite, which utilizes the heat of the slag left after the converter tapping to decompose the raw dolomite into CaO and MgO that can be used in steelmaking, thereby reducing production costs and saving energy. Adding raw dolomite before adding scrap steel to the converter allows for full contact with the molten iron when it is added to the steel, improving the utilization effect of the raw dolomite. The generated CO2 can fully react with C in the molten iron, which can not only improve the decarburization efficiency, but also increase the CO concentration in the furnace gas at the beginning of smelting. Starting the gas recovery in advance can increase the amount of gas recovered. Adding raw dolomite during the blowing process can reduce the problem of slag splashing. The method can improve the decarburization efficiency, inclusion removal rate and gas recovery rate, and can suppress the rapid temperature rise of the molten steel at the beginning of blowing to improve the dephosphorization qualification rate.

[0023] (2) The slag splashing protection of the converter can fully mix the raw dolomite with the slag, which is beneficial to increase the viscosity of the slag and improve the effect of slag splashing protection.

[0024] (3) The method of the present invention absorbs heat through the endothermic reaction of carbon dioxide and carbon, which can suppress the rapid temperature rise of molten steel in the early stage of blowing and contribute to improving the dephosphorization effect.

[0025] (4) Optimizing the timing of adding raw dolomite, and making the raw dolomite into a suitable particle size and drying it can improve the material recovery rate, improve the reaction effect, avoid the huge fluctuation of molten steel caused by the sudden increase of CO2 production, or even the problem of splashing, thereby improving the process stability and improving product quality.

[0026] (5) Drying raw dolomite can reduce the moisture content of the material, which can not only improve the safety of converter production, but also reduce the problem of high H content in molten steel caused by excessive moisture.

[0027] (6) The method of the present invention reduces the amount of light-burned dolomite used, which reduces the problem of a large amount of carbon dioxide gas generated during the production of light-burned dolomite, thereby effectively reducing carbon emissions in the steel industry; at the same time, the present invention improves the utilization rate of raw dolomite and improves the stability of the process, thus having both environmental and economic benefits. Detailed Implementation

[0028] Table 1. Component content of raw dolomite and lightly calcined dolomite

[0029] Table 2. Relevant data from the embodiments.

[0030] Example 1 A method for using raw dolomite in a converter process includes the following steps: S1. 4 tons of slag are left in a converter with a nominal capacity of 120t for slag splashing and furnace protection. S2. Add raw dolomite into the converter. The raw dolomite, according to the weight percentage, the content of each component is shown in Table 1. The raw dolomite is dried, with a moisture content of 0.2%, and the proportion of raw dolomite with a particle size of 5-30mm is 95%. The amount of raw dolomite added is calculated according to formula (1), and the specific amount added is shown in Table 2. (1) Where: n is the substitution coefficient, t1 is the amount of molten iron added, t, t2 are the amount of scrap steel added, t, , where is the slag coefficient, %; (MgO) 目标 The target MgO content in converter slag is expressed as %, (MgO). 铁水 The content of MgO in molten iron is expressed in tons (t), where (MgO) is present. 废钢 The MgO content of scrap steel, %, m 轻白 The effective utilization efficiency of lightly calcined dolomite is %, (MgO). 轻白 The MgO content of lightly calcined dolomite is given in %, (MgO). 生白 The MgO content (CaO) of raw dolomite is given in percentage. 轻白The CaO content of lightly calcined dolomite is given in percentages (CaO). 生白 The CaO content of raw dolomite is %.

[0031] S3, slag splashing protection for the furnace; S4. Add scrap steel to the converter. The amount of scrap steel added, the MgO content and the proportion of scrap steel are shown in Table 2. Add molten iron. The amount of molten iron added, the MgO content of molten iron are shown in Table 2. The composition of molten iron is shown in Table 2. S5. Lower the oxygen lance to start blowing. Add lime and lightly calcined dolomite into the converter in sequence. Add each material according to 2 / 3 of the total amount added. The addition should be completed within 3 minutes of starting the blowing process. The total amount of lime added is 3.39t. The total amount of lightly calcined dolomite added is calculated according to formula (2). (2) Where: w 生白 Dolomite addition amount, t, m 生白 To improve the effective utilization efficiency of dolomite.

[0032] The calculation results are shown in Table 2.

[0033] S6. When the blowing process has been carried out for 3-5 minutes, check the melting state of the slag. After the slag has melted, add the remaining slag material in two batches evenly. All the slag material should be added 3 minutes before the end.

[0034] The endpoint refers to the smelting endpoint determined by the system when both the carbon content and temperature meet the process requirements. The specific determination method is not part of the technical solution claimed by this invention.

[0035] Example 2 Everything else is the same as in Example 1, except that: S1. The mass of slag retained in the converter for slag splashing and furnace protection is 6t; S2. The weight percentage of each component of the raw dolomite and lightly calcined dolomite is shown in Table 1; the raw dolomite with a particle size of 5-30mm accounts for 96%; S4. Add scrap steel to the converter. The amount of scrap steel added, the MgO content and the proportion of scrap steel are shown in Table 2. Add molten iron. The amount of molten iron added, the MgO content of molten iron are shown in Table 2. The composition of molten iron is shown in Table 2. S5. The total amount of lime added is 4.023t. The total amount of lightly calcined dolomite added is calculated according to formula (2). The results are shown in Table 2.

[0036] Example 3 Everything else is the same as in Example 1, except that: S1. 5 tons of slag are left in the converter for slag splashing and furnace protection. S2. The content of each component of the raw dolomite and lightly calcined dolomite by weight percentage is shown in Table 1; the proportion of raw dolomite with a particle size of 5-30mm is 92%. S4. Add scrap steel to the converter. The amount of scrap steel added, the MgO content and the proportion of scrap steel are shown in Table 2. Add molten iron. The amount of molten iron added, the MgO content of molten iron are shown in Table 2. The composition of molten iron is shown in Table 2. S5. The total amount of lime added is 4.001t. The total amount of lightly calcined dolomite added is calculated according to formula (2). The results are shown in Table 2.

[0037] Example 4 Everything else is the same as in Example 1, except that: S1. The mass of slag retained in the converter for slag splashing and furnace protection is 6t; S2. The content of each component of the raw dolomite and lightly calcined dolomite, by weight percentage, is shown in Table 1. Raw dolomite with a particle size of 5-30 mm accounts for 95%. S4. Add scrap steel to the converter. The amount of scrap steel added, the MgO content and proportion of scrap steel are shown in Table 2. Add molten iron. The amount of molten iron added, the MgO content of molten iron are shown in Table 2. The composition of molten iron is shown in Table 2.

[0038] S5. The total amount of lime added is 2.926t. The total amount of lightly calcined dolomite added is calculated according to formula (2). The results are shown in Table 2.

[0039] Example 5 Everything else is the same as in Example 1, except that: S1. The mass of slag retained in the converter for slag splashing and furnace protection is 4t; S2. The content of each component of the raw dolomite and lightly calcined dolomite, by weight percentage, is shown in Table 1. Raw dolomite with a particle size of 5-30 mm accounts for 94%. S4. Add scrap steel to the converter. The amount of scrap steel added, the MgO content and proportion of scrap steel are shown in Table 2. Add molten iron. The amount of molten iron added, the MgO content of molten iron are shown in Table 2. The composition of molten iron is shown in Table 2.

[0040] S5. The total amount of lime added is 4.077t. The total amount of lightly calcined dolomite added is calculated according to formula (2). The results are shown in Table 2.

[0041] Comparative Example 1 The converter process uses lightly calcined dolomite as slag, and includes the following steps: S1. 4 tons of slag are left in a converter with a nominal capacity of 120t for slag splashing and furnace protection. S2, slag splashing protection of the furnace; S3. Add scrap steel to the converter. The amount of scrap steel added, the MgO content and the proportion of scrap steel are shown in Table 3. Add molten iron. The amount of molten iron added, the MgO content of molten iron are shown in Table 3, and the composition of molten iron is shown in Table 3. S4. Lower the oxygen lance and begin blowing. Add lightly calcined dolomite into the converter at a rate of 2 / 3 of the total amount, completing the addition within 3 minutes of starting the blowing process. The weight percentage of each component in the lightly calcined dolomite is shown in Table 4. The amount of lightly calcined dolomite added is shown in Table 3.

[0042] S5. Start blowing for 3-5 minutes. After the slag has been properly oxidized, add the remaining slag material in two batches evenly. Add all the slag material 3 minutes before the end.

[0043] Comparative Example 2 The differences from Comparative Example 1 are as follows: S1. 6 tons of slag are left in a converter with a nominal capacity of 120t for slag splashing and furnace protection. S3. Add scrap steel to the converter. The amount of scrap steel added, the MgO content and the proportion of scrap steel are shown in Table 3. Add molten iron. The amount of molten iron added, the MgO content of molten iron are shown in Table 3, and the composition of molten iron is shown in Table 3. S4. The content of each component of lightly calcined dolomite by weight percentage is shown in Table 4. The amount of lightly calcined dolomite added is shown in Table 2.

[0044] Comparative Example 3 The differences from Comparative Example 1 are as follows: S1. 5 tons of slag are left in a converter with a nominal capacity of 120t for slag splashing and furnace protection. S3. Add scrap steel to the converter. The amount of scrap steel added, the MgO content and the proportion of scrap steel are shown in Table 3. Add molten iron. The amount of molten iron added, the MgO content of molten iron are shown in Table 3, and the composition of molten iron is shown in Table 3. S4. The content of each component of lightly calcined dolomite by weight percentage is shown in Table 4. The amount of lightly calcined dolomite added is shown in Table 3.

[0045] Comparative Example 4 The rest is the same as in Example 1, except that in step S2, raw dolomite is not added, and slag splashing is performed directly to protect the furnace; the raw dolomite is added all at once before adding lime during the blowing process. The amount of raw dolomite and lime added is the same as in Example 1, and the amount of lightly calcined dolomite added is 3.64t; the amount of scrap steel added, the MgO content of scrap steel, the amount of molten iron added, and the MgO content of molten iron are shown in Table 3; During the production process, the addition of slag materials (lime, dolomite, etc.) during the blowing process can easily cause the slag to "dry out" or splash, affecting the dephosphorization and desulfurization effects and prolonging the blowing cycle.

[0046] Comparative Example 5 The rest is the same as in Example 1, except that the moisture content of the raw dolomite used in step S2 is 1.0%, the amount of raw dolomite and lime added is the same as in Example 1, and the amount of lightly calcined dolomite added is 2.97t; the amount of scrap steel added, the MgO content of scrap steel, the amount of molten iron added, and the MgO content of molten iron are shown in Table 3. When the moisture content is 1.0%, adding high-temperature molten steel can easily cause splashing and increase the hydrogen content of the molten steel, resulting in low utilization of raw dolomite (usually <60%), and may also cause quality defects such as porosity and hydrogen embrittlement in the molten steel. Comparative Example 6 The rest is the same as in Example 1, except that the proportion of raw dolomite with a particle size of 5-30mm used in step S2 is 85%; the amount of raw dolomite and lime added is the same as in Example 1, and the amount of lightly calcined dolomite added is 3.13t; the amount of scrap steel added, the MgO content of scrap steel, the amount of molten iron added, and the MgO content of molten iron are shown in Table 3. Particles smaller than 5mm are easily carried away by airflow, while those larger than 30mm are not fully decomposed, resulting in low utilization of raw dolomite (usually <60%), and may also cause quality defects such as porosity and hydrogen embrittlement in molten steel.

[0047] Table 3 Comparative data

[0048] Table 4. Content of various components in lightly calcined dolomite

[0049] The production results and costs of Examples 1-5 are shown in Table 5.

[0050] Table 5 Production Results and Costs of the Example

[0051] The production results and costs of comparative examples 1-6 are shown in Table 6.

[0052] Table 6 Comparative Production Results and Costs

[0053] As shown in Tables 5 and 6, the method described in this invention can meet the requirements of converters, reduce the average H content by 0.2 ppm, increase the average slag cost per ton of steel by 0.85 yuan / ton, improve the dephosphorization rate by 1.48%, and increase the gas recovery per ton of steel by 2.636 m³. 3 Based on converter gas at 4.2 yuan / m³ 3Calculations show that the benefit from gas recovery is 11.08 yuan / ton of steel. Although the slag cost increases slightly, it has the effect of reducing H content and improving dephosphorization rate, which can improve the purity of molten steel. Furthermore, the gas recovery benefit still results in cost reduction and improved steel quality. This indicates that the method described in this invention has good effects in reducing converter production costs and improving dephosphorization efficiency, and has good economic benefits.

Claims

1. A method for using raw dolomite in a converter process, characterized in that, Includes the following steps: S1. After the steel is tapped from the converter, slag is left in the converter for splashing and furnace protection. S2. Add raw dolomite into the converter, the amount of raw dolomite being 0.05-0.15% of the slag mass; S3, slag splashing protection for the furnace; S4. Add scrap steel into the converter, the amount of scrap steel being added being 3-8 times the mass of the slag, and then add molten iron, the amount of molten iron being added being 18-32 times the mass of the slag. S5. Lower the oxygen lance and start blowing. Add the slag materials into the converter in sequence, with each slag material added at a rate of 2 / 3 to 3 / 4 of the total amount. The addition should be completed within 3 minutes of starting the blowing process. The slag materials should include at least lime and lightly calcined dolomite. S6. When the blowing process has been going on for 3-5 minutes, check the melting state of the slag. After the slag has melted, add the remaining slag material in small batches and multiple times evenly. All the slag material should be added 3 minutes before the end.

2. The method for using raw dolomite in the converter process according to claim 1, characterized in that, The raw dolomite mentioned in step S2 needs to be dried, and the moisture content of the dried raw dolomite is ≤0.5%.

3. The method for using raw dolomite in the converter process according to claim 1, characterized in that, In step S2, the proportion of raw dolomite with a particle size of 5-30mm is >90%; the composition of raw dolomite by mass fraction includes: CaO 30-40%, SiO2 2.5-4%, MgO 17-25%, P≤0.01%, S≤0.01%, and the remainder are impurity elements.

4. The method for using raw dolomite in the converter process according to claim 1, characterized in that, The amount of raw dolomite added in step S2 accounts for 0.07-0.13% of the slag mass.

5. The method for using raw dolomite in the converter process according to claim 1, characterized in that, The amount of raw dolomite added in step S2 is calculated according to formula (1): （1） Where: n is the substitution coefficient, t1 is the amount of molten iron added, t, t2 are the amount of scrap steel added, t, , where is the slag coefficient, %; (MgO) 目标 The target MgO content in converter slag is expressed as %, (MgO). 铁水 The content of MgO in molten iron is expressed in tons (t), where (MgO) is present. 废钢 The MgO content of scrap steel, %, m 轻白 The effective utilization efficiency of lightly calcined dolomite is %, (MgO). 轻白 The MgO content of lightly calcined dolomite is given in %, (MgO). 生白 The MgO content (CaO) of raw dolomite is given in percentage. 轻白 The CaO content of lightly calcined dolomite is given in percentages (CaO). 生白 The CaO content of raw dolomite is %.

6. The method for using raw dolomite in the converter process according to claim 2, characterized in that, In step S4, the amount of scrap steel added is 3.3-7.8 times the mass of slag, and the amount of molten iron added is 19.9-31 times the mass of slag.

7. The method of using raw dolomite in the converter process according to claim 6, characterized in that, The amount of scrap steel added in step S4 accounts for 12%-20% of the total mass of scrap steel and molten iron.

8. The method for using raw dolomite in the converter process according to claim 1, characterized in that, The slag material mentioned in step S5 also includes any one or more of sintered ore, red mud pellets, iron oxide pellets, and dust removal ash pellets.

9. The method for using raw dolomite in the converter process according to claim 8, characterized in that, The amount of lightly calcined dolomite added in step S5 is calculated according to formula (2): （2） Where: w 生白 Dolomite addition amount, t, m 生白 To improve the effective utilization efficiency of dolomite.

10. The method of using raw dolomite in the converter process according to claim 9, characterized in that, The total amount of lime added in step S5 is 0.45-1.1 times the mass of slag; preferably, the total amount of lime added in step S5 is 0.48-1.02 times the mass of slag.

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