Method for producing steel including the addition of lime

Abstract

Method of producing steel including the addition of lime, the method of producing steel including charging a charge (L) into a steelmaking furnace (2) to transform the charge (L) into steel and adding particles of lime (10) into the charge (L), the method including the step of preheating the particles of lime (10) to 500°C or more and the step of coating the preheated particles of lime (10) with a coating (12) before adding the particles of lime (10) into the charge (L).

Description

Technical Field

[0001] The present invention relates to a method for producing steel, the method comprising melting furnace charge in a steelmaking furnace to obtain a melt, and adding lime to adjust the final chemical composition of the melt. Background Technology

[0002] Currently, steel can be produced via two main production routes. The first main production route (which is the most commonly used route) uses a basic oxygen converter (BOF), and the second main production route uses an electric arc furnace (EAF). BOF and EAF are collectively referred to as steelmaking furnaces.

[0003] In some examples, the primary production route involves producing iron in a blast furnace (BF) by reducing iron oxides using a reducing agent (primarily coke), and then converting the iron into steel in a BOF. This route releases significant amounts of CO2 in both the coking plant's coke production from coal and the iron production process. Such a route is referred to as the "BF-BOF route." The furnace used to produce iron (here, the BF) is called a blast furnace.

[0004] In some examples, the second main route involves the so-called "direct reduction method" using direct reduced iron (DRI). This includes methods from brands such as MIDREX®, FINMET®, ENERGIRON® / HYL, COREX®, and FINEX®, in which sponge iron is produced from the direct reduction of an iron oxide carrier in the form of HDRI (hot direct reduced iron), CDRI (cold direct reduced iron), or HBI (hot briquetted iron). The sponge iron in HDRI, CDRI, and HBI forms is then further processed in EAF (exchange-embedded iron) to produce steel. Such a route is also known as the "DRI-EAF route."

[0005] Adding lime during steel production allows for the formation of slag with an affinity for phosphorus, thus allowing for a reduction in the phosphorus content of the produced steel. Furthermore, lime also reduces the viscosity of the slag and protects the refractory materials present in the steelmaking vessel.

[0006] However, lime can deteriorate when stored before use, resulting in the loss of some lime before it is used in steel production, and / or reduced reactivity, requiring larger quantities of lime and / or longer processing times, thus increasing energy consumption, production costs, and reducing productivity. Furthermore, lime production emits carbon dioxide, so it is important to reduce its consumption to decrease the overall CO2 footprint of the steelmaking process. Summary of the Invention

[0007] One of the objectives of this invention is to provide a method for producing steel with improved productivity.

[0008] Therefore, the present invention proposes a method for producing steel, the method comprising charging a furnace charge into a steelmaking furnace to convert the furnace charge into steel, the method comprising adding lime particles to the furnace charge, wherein the method comprises the steps of preheating the lime particles to 500°C or higher, and the steps of coating the preheated lime particles with a coating before adding the lime particles to the furnace charge.

[0009] During storage, lime reacts with water and carbon dioxide contained in the ambient air. The hydration and carbonization of lime reduce its reactivity and may even render it unsuitable for steel production.

[0010] Lime hydrates to a lesser degree at temperatures equal to or above 500°C than at ambient temperature. Preheating lime granules to 500°C or higher reduces the water content in the lime granules and prevents hydration.

[0011] Coating preheated lime granules prevents lime hydration or carbonization, even as the temperature of the lime granules decreases between the preheating step and the addition of lime during steel production.

[0012] This avoids the loss of some lime before it is used in steel production and / or preserves the reactivity of the lime, thus making the steelmaking process more efficient.

[0013] In some examples, the method of producing steel includes one or more of the following optional features, either alone or in any technically feasible combination:

[0014] - The coating is hydrophobic;

[0015] - The coating contains or is composed of paraffin wax;

[0016] - The lime granules are preheated to 700°C or higher;

[0017] - The preheating is performed using steelmaking gases;

[0018] - The lime particles are preheated in a preheating furnace;

[0019] - Preheated and coated lime granules are stored before being added to the furnace charge;

[0020] - The method of producing steel includes injecting oxygen into the steelmaking furnace;

[0021] - The lime granules are added before oxygen is injected into the steelmaking furnace;

[0022] - The method of producing steel includes removing slag produced by the lime particles from the steelmaking furnace before injecting oxygen into the steelmaking furnace;

[0023] - The steelmaking furnace is an electric arc furnace;

[0024] - The furnace charge contains at least 40% scrap steel by weight;

[0025] - The furnace charge contains 40% to 60% direct reduced iron by weight;

[0026] - The furnace charge comprises 40% to 60% by weight scrap steel, up to 30% by weight pig iron, and 10% to 60% by weight direct reduced iron;

[0027] - The steelmaking furnace is an alkaline oxygen converter;

[0028] - The method of producing steel involves charging the furnace charge into an ironmaking furnace to convert the furnace charge into a molten metal made of iron, and transferring the molten metal from the ironmaking furnace to the steelmaking furnace to convert the molten metal into steel;

[0029] - The blast furnace is an electric melting furnace;

[0030] - The charge fed into the electric melting furnace comprises 80% to 98% direct reduced iron and / or 1% to 20% scrap steel by weight;

[0031] - The iron-making furnace is a blast furnace;

[0032] - The furnace charge comprises ore and / or coal. Attached Figure Description

[0033] The invention and its advantages will be better understood after reading the following description, which is given only as a non-limiting example and with reference to the accompanying drawings, in which:

[0034] - Figure 1 This illustrates a first example of a method for producing steel using an electric arc furnace (EAF); and

[0035] - Figure 2 A second example of a method for producing steel using a blast furnace (BF) and a basic oxygen converter (BOF) is shown;

[0036] - Figure 3 A third example of a method for producing steel using an electric melting furnace (ESF) and a basic oxygen converter (BOF) is shown. Detailed Implementation

[0037] Figure 1 The method for producing steel shown includes step E1, which involves charging the furnace charge L into the steelmaking furnace 2.

[0038] Steelmaking furnace 2 can melt furnace charge L to produce molten metal M, thereby converting furnace charge L into steel, or maintaining the temperature of molten metal M or refining the composition of molten metal M.

[0039] In the following text, “charge” refers to the charge L during the various conversion steps performed to convert charge L into steel (before and after melting), and “molten metal” or “melt” refers to the molten metal produced by melting charge L, particularly in steelmaking furnace 2.

[0040] The steelmaking furnace 2 is, for example, an electric arc furnace (EAF) configured to melt the furnace charge L by generating an electric arc. The molten furnace charge L forms a melt M.

[0041] The charge L contains metallic materials, particularly scrap steel SC, and optionally, in addition to scrap steel SC, it also contains iron, particularly direct reduced iron (DRI) and / or pig iron (PI).

[0042] In some examples, the charge L contains at least 40% scrap steel SC by weight.

[0043] In some examples, the charge L contains at least 40% direct reduced iron (DRI) by weight, preferably 40% to 60% DRI by weight.

[0044] In some examples, the charge L contains 40% to 60% by weight scrap steel SC, up to 30% by weight pig iron PI, and 10% to 60% by weight direct reduced iron DRI.

[0045] For example, the scrap steel that can be used is referred to as old scrap (Category E1 or E3), new scrap (Category E8), shredded scrap (Category E40) or fragmented scrap (Category E46) in the EU-21 scrap steel specification.

[0046] When adding direct reduced iron (DRI), DRI is initially loaded together with the scrap metal (SC), or after the scrap metal (SC) has partially melted, or after the scrap metal (SC) has completely melted.

[0047] When adding pig iron PI to scrap metal SC, the pig iron PI is initially added together with the scrap metal SC, or added after the scrap metal SC has partially melted, or added after the scrap metal SC has completely melted. The pig iron PI can be added in solid or liquid form.

[0048] The percentage of DRI and / or PI in the charge L is highly dependent on the quality of the scrap steel SC used and the type of steel to be produced. If the levels of impurities (e.g., copper, chromium, molybdenum, nickel, tin, antimony, zinc, and / or arsenic) in the scrap SC are low, the amount of scrap SC to be charged can be increased, thereby reducing the amount of DRI and / or PI.

[0049] The steelmaking furnace 2 provided as an electric arc furnace (EAF) includes a container 4 for receiving charge L and two or more electrodes 6 configured to generate an electric arc between the electrodes 6 and the charge L received in the container 4.

[0050] Each electrode 6 is made of graphite, for example.

[0051] Each electrode 6 is connected, for example, to a power source 8. The power source 8 includes, for example, a power grid and / or a power plant that preferably uses one or more renewable energy sources.

[0052] The power plant preferably operates using CO2-neutral electricity, which specifically includes electricity from renewable energy sources. Renewable energy is defined as energy generated from renewable resources that are naturally replenished over human timescales, including sources such as sunlight, wind, rain, tides, waves, geothermal energy, and biogas.

[0053] In some embodiments, electricity from a nuclear source can be used because it does not emit the CO2 to be produced.

[0054] Biogas is a renewable energy source that can be obtained by breaking down organic matter under anaerobic conditions in a closed system called a bioreactor. Biogas can be produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, food waste, or any biodegradable material.

[0055] The method for producing steel includes step E2, which involves adding lime particles 10.

[0056] The addition of lime particles 10 allows for dephosphorization of melt M. Lime is a slag-forming material with an affinity for phosphorus. The addition of lime will generate phosphorus-affinity slag S on top of melt M, thereby allowing the transfer of phosphorus contained in melt M to the slag, thus reducing the phosphorus content of melt M.

[0057] Lime particles 10 are added to the furnace charge L before and / or after melting. Preferably, lime particles 10 are added to the furnace charge L, i.e., to the melt M, after melting.

[0058] Lime reacts with water (H2O) and carbon dioxide (CO2) in the ambient air.

[0059] Lime can be highly reactive, moderately reactive, or lowly reactive. They are also referred to as light-burned lime, medium-burned lime, and hard-burned lime, respectively. These different types are determined by the lime-making process. Lime is produced by calcining limestone, and the production of light-burned, medium-burned, and hard-burned lime depends on the calcination conditions, particularly temperature and residence time.

[0060] The method of producing steel includes step E3 of preheating lime particles 10 to 500°C or higher, and step E4 of coating the preheated lime particles 10 with coating 12 before adding the lime particles 10 to the furnace charge L, preferably after melting.

[0061] The hydration level of lime decreases at temperatures of 500°C or higher. Therefore, preheating lime particles 10 to 500°C or higher limits the hydration of lime particles 10.

[0062] Preferably, the lime particles 10 are preheated so that the water content of the lime particles L is 1.4% or less by weight, preferably 1.2% or less by weight, and more preferably 1.0% or less by weight.

[0063] Coating 12 with preheated lime granules 10 prevents the lime from reacting with water and carbon dioxide contained in the ambient air, even if the lime granules 10 are stored under cooling before being added to the furnace charge L.

[0064] The coating 12 is preferably a hydrophobic coating. The hydrophobic coating 12 has no affinity for water, thus effectively preventing lime hydration.

[0065] In some examples, coating 12 comprises or is composed of paraffin wax. Paraffin wax is hydrophobic and can form a barrier that prevents the exchange between lime particles 10 and ambient air, thereby limiting the hydration and carbonization of lime particles 10.

[0066] Before adding lime granules 10 to the furnace charge L, the lime granules 10 are preheated in the preheating furnace 14 and then coated in the coating device 16.

[0067] Preheating of lime particles 10 is advantageously carried out using steelmaking gases. Steelmaking gases contain heat that can be used to at least partially heat the lime particles 10. Steelmaking gases encompass all gases produced by different production units in a steel plant. These can be, for example, blast furnace gas, coke oven gas, sintering exhaust gas, direct reduction furnace top gas, BOF gas, or EAF gas. These gases can be used as fuel for burners or for heat transfer, such as in heat exchangers.

[0068] In some examples, the method of producing steel includes storing lime granules 10 in ambient air before adding them to the furnace charge L. The storage duration is, for example, 5 hours or longer.

[0069] The addition of lime particles 10 to the charge L is performed before the charge L is melted and / or after the charge L is partially melted and / or after the charge L is completely melted. Preferably, the addition of lime particles 10 is performed after the charge L is partially melted and / or after the charge L is completely melted, i.e., into the melt M.

[0070] The preferred method of producing steel includes separating the slag S produced by the lime particles 10 from the melt M, for example by removing the slag S from the steelmaking furnace 2, for example, when the steelmaking furnace 2 is provided as an EAF, via a slag discharge port provided on the side wall of the vessel 4 of the steelmaking furnace 2.

[0071] The method of producing steel includes step E5, which involves injecting oxygen into a steelmaking furnace 2. The steelmaking furnace 2 includes, for example, an oxygen injection system 20 configured to inject oxygen into a container 4 during operation of the steelmaking furnace 2.

[0072] The oxygen injected into the steelmaking furnace 2 reacts with the carbon contained in the melt M, thereby reducing the carbon content of the melt M.

[0073] The oxygen injection system 20 is configured to inject oxygen into the steelmaking furnace 2 during and / or preferably after the melting of the charge L.

[0074] The oxygen injection system 20 includes one or more oxygen lances 22, each oxygen lance 22 having an opening inside the steelmaking furnace 2; and an oxygen source fluidly connected to each gas lance 22 for feeding an oxygen stream 24 into the gas lance 22.

[0075] Each oxygen lance 22 is tilted downwards, for example, to inject an oxygen stream 24 toward the surface of the melt M and / or into the melt M present in the steelmaking furnace 2, especially if the steelmaking furnace 2 is an EAF.

[0076] The addition of lime particles 10 and the removal of slag S are preferably carried out before oxygen is injected into the steelmaking furnace 2, especially if the steelmaking furnace 2 is an EAF.

[0077] The slag S produced by adding lime particles 10 is preferably removed from the steelmaking furnace 2, especially before the molten metal M is discharged from the steelmaking furnace 2.

[0078] The method of producing steel may optionally include adding an additional slag-forming material different from lime to the steelmaking furnace 2 and removing the resulting slag before performing the next slag-forming operation.

[0079] Each addition of slag-forming material allows for adjustment of the composition of molten metal M by reducing the content of one or more elements in the molten metal M, wherein the additional slag-forming material has an affinity for the one or more elements.

[0080] like Figure 2 and Figure 3 As shown, in some examples, the method of producing steel is similar to... Figure 1The difference between these methods is that they involve step E6, in which the charge L is converted into a molten iron M in a blast furnace 30, and then the molten iron M is transferred from the blast furnace 30 to a steelmaking furnace 2, which is configured to convert the molten iron M into steel.

[0081] like Figure 2 As shown, in some examples, the blast furnace 30 is a blast furnace (BF).

[0082] Steelmaking furnace 2 is, for example, a basic oxygen converter (BOF), in which case the method of producing steel implements the so-called "BF-BOF route".

[0083] The furnace charge L may contain, for example, iron ore O and / or coal C.

[0084] Add lime granules 10 to the furnace charge L in steelmaking furnace 2.

[0085] as Figure 1 Similar to the steel production method, lime particles 10 are preheated and coated before being added to the furnace charge L. Before being added to the furnace charge L, the lime particles 10 are preheated in a preheating furnace 14 and then coated in a coating apparatus 16.

[0086] Lime particles 10 produce slag S in steelmaking furnace 2. The preferred method for producing steel includes separating the slag S from the molten material M, for example by discharging the molten material M from steelmaking furnace 2.

[0087] The preferred method for producing steel includes the step of injecting oxygen into the molten metal M in a steelmaking furnace 2. The steelmaking furnace 2 is equipped with an oxygen injection system 20, which is similar to... Figure 1 The oxygen injection system for steelmaking furnace 2 provided by EAF is used in the middle.

[0088] Figure 2 oxygen injection system 20 and Figure 1 The difference in the oxygen injection system is that it includes a vertically downward oriented oxygen lance 22 to inject an oxygen stream 24 toward the surface of the melt M contained in the steelmaking furnace 2.

[0089] like Figure 3 As shown, in some examples, the blast furnace 30 is an electrical smelting furnace (ESF), such as a submerged arc furnace (SAF) or an open slag bath furnace (OSBF).

[0090] Steelmaking furnace 2 is, for example, a basic oxygen converter (BOF), in which case the method of producing steel implements the so-called "ESF-BOF route".

[0091] The charge L may include, for example, scrap SC, direct reduced iron (DRI), and / or pig iron (PI). In some examples, the charge L charged into the ESF contains at least 60% by weight direct reduced iron (DRI), preferably 80% to 98% by weight direct reduced iron (DRI), and / or 1% to 20% by weight scrap (SC).

[0092] Lime particles 10 are added to the furnace charge L in the steelmaking furnace 2 and / or the blast furnace 30. Preferably, lime particles 10 are added to the furnace charge L in the steelmaking furnace 2.

[0093] as Figure 1 Similar to the steel production method, lime particles 10 are preheated and coated before being added to the charge L in the steelmaking furnace 2 and / or blast furnace 30. The lime particles 10 are preheated in a preheating furnace 14 before being added to the charge L, and then coated in a coating apparatus 16.

[0094] The lime particles 10 added to the blast furnace 30 produce primary slag S1 in the blast furnace 30. The method of producing steel preferably includes separating the primary slag S1 from the melt M before or during the transfer of the melt M to the steelmaking furnace 2 to convert the melt M into steel.

[0095] The lime particles 10 added to the steelmaking furnace 2 produce slag S in the steelmaking furnace 2. The method of producing steel preferably includes separating the slag S from the molten material M, for example, when the molten material M is discharged from the steelmaking furnace 2.

[0096] The preferred method for producing steel includes the step of injecting oxygen into the molten metal M in a steelmaking furnace 2. The steelmaking furnace 2 is equipped with... Figure 2 The oxygen injection system is similar to the oxygen injection system 20.

[0097] Thanks to this invention, high-quality and more reactive lime can be added to the furnace charge L during the steelmaking process, thereby limiting the required amount of lime and / or limiting the processing time of the furnace charge, especially in each furnace.

[0098] Shorter processing times mean less energy consumption, especially in each furnace (iron furnace 30 or steel furnace 2) used to process charge L. Therefore, steel production is more energy-efficient.

[0099] The method of the present invention also allows for the avoidance of hydrogen absorption in the melt M due to lime. In fact, in methods according to the prior art, the water contained in the lime generates hydrogen in the melt M. Even a few parts per million of hydrogen dissolved in steel can cause hairline cracks (white spots), hydrogen embrittlement, hydrogen blistering, and loss of tensile ductility, particularly in large steel castings, billets, and slabs.

Claims

1. A method for producing steel, comprising charging a furnace charge (L) into a steelmaking furnace (2) to convert the furnace charge (L) into steel, the method comprising adding lime particles (10) to the furnace charge (L), wherein, The method includes the steps of preheating the lime particles (10) to 500°C or higher, and coating the preheated lime particles (10) with a coating (12) before adding the lime particles (10) to the charge (L).

2. The method for producing steel according to claim 1, wherein, The coating (12) is hydrophobic.

3. The method for producing steel according to claim 1 or 2, wherein, The coating (12) contains or is composed of paraffin.

4. A method for producing steel according to any one of the preceding claims, wherein, The lime particles (10) are preheated to 700°C or higher.

5. A method for producing steel according to any one of the preceding claims, wherein, The preheating is performed using steelmaking gases.

6. A method for producing steel according to any one of the preceding claims, wherein, The lime particles (10) are preheated in a preheating furnace (14).

7. A method for producing steel according to any one of the preceding claims, wherein, The lime granules (10) are stored preheated and coated before being added to the furnace charge (L).

8. A method for producing steel according to any one of the preceding claims, comprising injecting oxygen into the steelmaking furnace (2).

9. The method for producing steel according to claim 8, wherein, The lime granules (10) are added before oxygen is injected into the steelmaking furnace (2).

10. The method of producing steel according to claim 9, comprising removing slag (S) generated by the lime particles (10) from the steelmaking furnace (2) before injecting the oxygen into the steelmaking furnace (2).

11. A method for producing steel according to any one of the preceding claims, wherein, The steelmaking furnace (2) is an electric arc furnace (EAF).

12. The method for producing steel according to claim 11, wherein, The furnace charge (L) contains at least 40% scrap steel (SC) by weight.

13. The method for producing steel according to claim 11 or 12, wherein, The charge (L) contains 40% to 60% direct reduced iron (DRI) by weight.

14. The method for producing steel according to claim 11 or 12, wherein, The furnace charge (L) comprises 40% to 60% by weight scrap steel (SC), up to 30% by weight pig iron (PI), and 10% to 60% by weight direct reduced iron (DRI).

15. A method for producing steel according to any one of the preceding claims, wherein, The steelmaking furnace (2) is a basic oxygen converter (BOF).

16. The method of producing steel according to claim 15, comprising charging the charge (L) into a blast furnace (30) to convert the charge (L) into a melt (M) made of iron, and transferring the melt (M) from the blast furnace (30) to the steelmaking furnace (2) to convert the melt (M) into steel.

17. The method for producing steel according to claim 16, wherein, The blast furnace (30) is an electric smelting furnace (ESF).

18. The method for producing steel according to claim 17, wherein, The charge (L) fed into the electric melting furnace comprises 80% to 98% by weight direct reduced iron (DRI) and / or 1% to 20% by weight scrap steel (SC).

19. The method for producing steel according to claim 16, wherein, The iron-making furnace is a blast furnace (BF).

20. The method for producing steel according to claim 19, wherein, The furnace charge (L) comprises ore (O) and / or coal (C).

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