WO2025120353A1

WO2025120353A1 - Method of producing steel including the addition of lime

Info

Publication number: WO2025120353A1
Application number: PCT/IB2023/062247
Authority: WO
Inventors: Guillaume STECHMANN; Mathieu Sanchez; Guillaume BROSSE; Jean Christophe HUBER; Humberto GAMA DE MAGALHAES; Lucille GERMAIN
Original assignee: ArcelorMittal SA
Current assignee: ArcelorMittal SA
Priority date: 2023-12-05
Filing date: 2023-12-05
Publication date: 2025-06-12
Anticipated expiration: 2026-06-05
Also published as: WO2025120558A1

Abstract

Method of producing steel including the addition of lime The method of producing steel comprises loading a load (L) in a steelmaking furnace (2) for converting the load (L) into steel and adding lime particles (10) to the load (L), the method comprising a step of preheating the lime particles (10) to 500°C or more and a step of coating the pre-heated lime particles (10) with a coating (12) before adding the lime particles (10) to the load (L).

Description

Method of producing steel including the addition of lime

The present invention relates to a method of producing steel comprising melting a load in a steelmaking furnace to obtain a melt with added lime for adjusting the final chemical composition of the melt.

Steel can be currently produced through two mains production routes, the first main production route, which is currently the most used production route, making use of a Basic Oxygen Furnace (BOF) and the second main production route making use of an Electrical Arc Furnace (EAF). The BOF and the EAF are referred to as steelmaking furnaces.

In some examples, the first main production route comprises producing iron in a Blast Furnace (BF), by use of a reducing agent, mainly coke, to reduce iron oxides and then transform the iron into steel into a BOF. This route releases significant quantities of CO2, both in the production of coke from coal in a coking plant and in the production of the iron. Such route is referred to as a “BF-BOF route”. The furnace used for producing iron, here the BF, is referred to as an ironmaking furnace.

In some examples, the second main route involves so-called “direct reduction methods” using Direct Reduced Iron (DRI). Among them are methods according to the brands MIDREX®, FINMET®, ENERGIRON®/HYL, COREX®, FINEX® etc., in which sponge iron is produced in the form of HDRI (hot direct reduced iron), CDRI (cold direct reduced iron), or HBI (hot briquetted iron) from the direct reduction of iron oxide carriers. Sponge iron in the form of HDRI, CDRI, and HBI undergoes further processing in an EAF to produce steel. Such route is also referred to as “DRI-EAF route”.

The addition of lime during the production of steel allows forming a slag that has affinity with phosphorus and allows therefore to reduce the phosphorus content of the produced steel. Moreover, lime allows also to reduce the viscosity of the slag and to protect the refractories which are present in the steelmaking vessels.

However, when stored before use, lime can deteriorate thus leading to loss of a fraction of the lime before use for producing steel and/or leading to a decrease of the reactivity of the lime, thus necessitating the use of a larger amount of lime and/or a longer duration of processing, thus increasing energy consumption, increasing production costs and reducing productivity. Moreover, production of lime emits carbon dioxide and it is thus important to reduce its consumption to reduce the global CO2 footprint of the steelmaking process.

One of the aims of the invention is to propose a method of producing steel with an improved productivity. To this end, the invention proposes a method of producing steel comprising loading a load in a steelmaking furnace for converting the load into steel, the method of producing steel comprising adding lime particles to the load, wherein the method comprises a step of preheating the lime particles to 500°C or more and a step of coating the pre-heated lime particles with a coating before adding the lime particles to the load.

During storage, lime reacts with water and carbon dioxide contained in the ambient air. Hydration and carbonation of lime lower the reactivity of lime and can even render lime improper to produce steel.

The hydration of lime is lower at a temperature equal or higher than 500°C than at ambient temperature. Pre-heating the lime particles to 500°C or more diminishes the water content in the lime particles and prevents hydration of the lime particles.

Coating the pre-heated lime particles prevents lime from hydrating or carbonating, even if the temperature of lime particles is lowered between the pre-heating step and the addition of the lime during the production of steel.

This avoids loss of a fraction of the lime before use for producing steel and/or maintains the reactivity of the lime, thus making the steel making process more efficient.

In some examples, the method of producing steel comprises on or several of the following optional features, taken individually or according to any technically feasible combination:

- the coating is hydrophobic;

- the coating comprises or consists in paraffin;

- the lime particles are preheated to 700°C or more;

- the preheating is performed using steelmaking gases;

- the lime particles are preheated in a pre-heating furnace;

- the pre-heated and coated lime particles are stored before adding the lime particles to the load;

- the method of producing steel comprises injecting oxygen in the steelmaking furnace;

- the lime particles are added before injecting oxygen in the steelmaking furnace;

- the method of producing steel comprises removing a slag generated by the lime particles from the steelmaking furnace before injecting the oxygen in the steelmaking furnace;

- the steelmaking furnace is an electric arc furnace;

- the load comprises at least 40% by weight of steel scrap;

- the load comprises from 40% to 60% by weight of direct reduced iron; - the load comprises from 40% to 60% by weight of steel scrap, up to 30% by weight of pig iron and from 10% to 60% by weight of direct reduced iron;

- the steelmaking furnace is a basic oxygen furnace;

- the method of producing steel loading the load in an ironmaking furnace for transforming the load into a melt made of iron and transferring the melt from the ironmaking furnace to the steelmaking furnace for converting the melt into steel;

- the ironmaking furnace is an electrical smelting furnace;

- the load loaded in the electrical smelting furnace comprises from 80% to 98% by weight of direct reduced iron and/or from 1% to 20% by weight of steel scrap;

- the ironmaking furnace is a blast furnace;

- the load comprises ore and/or coal.

The invention and its advantages will be better understood upon reading the following description, which is given solely by way of non-limiting example, and which is made with reference to the appended drawings, in which:

- Figure 1 illustrates first examples of methods of producing steel using an Electrical Arc Furnace (EAF); and

- Figure 2 illustrates second examples of methods of producing steel using a blast Furnace (BF) and a Basic Oxygen Furnace (BOF);

- Figure 3 illustrates third examples of methods of producing steel using an Electric Smelting furnace (ESF) and a Basic Oxygen Furnace (BOF).

The method of producing steel illustrated on Figure 1 comprises a step E1 of loading a load L in a steelmaking furnace 2.

The steelmaking furnace 2 is able to melt the load L to produce molten metal M, to convert the load L into steel or to maintain the temperature or refine the composition of the molten metal M.

In the following, “load” designates the load L during the different transformation steps performed for transforming the load L into steel, before and after melting, and “molten metal” or “melt” designates the molten metal resulting from melting the load L, in particular in the steelmaking furnace 2.

The steelmaking furnace 2 is for example an Electrical Arc Furnace (EAF) configured for melting the load L by generating electrical arcs. The melted load L forms a melt M.

The load L contains metal materials, in particular steel scrap SC and, optionally, iron in addition to the steel scrap SC, in particular direct reduced iron DRI and/or pig iron PI.

In some examples, the load L comprises at least 40% by weight of steel scrap SC.

In some examples, load L comprises at least 40% by weight of direct reduced iron DRI, preferably from 40 to 60% by weight of direct reduced iron DRI. In some examples, the load L comprises from 40 to 60% by weight of steel scrap SC, up to 30% by weight of pig iron PI and from 10% to 60% by weight of direct reduced iron DRI.

For instance, the steel scrap SC that can be used is referred to, in the EU-21 Steel Scrap specification, as old scraps (category E1 or E3), new scraps (category E8), shredded scraps (category E40) or fragmentized scraps (category E46).

When adding direct reduced iron DRI, the direct reduced iron DRI is loaded initially with the metal scrap SC or after partial melting of the metal scrap SC or after complete melting of the metal scrap SC.

When adding pig iron PI to the metal scrap SC, the pig iron PI is loaded initially with the metal scrap SC or after partial melting of the metal scrap SC or after complete melting of the metal scrap SC. Pig Iron PI may be loaded in solid or in liquid form.

The percentage of DRI and/or of pig iron PI in the load L is highly dependent on the quality of the steel scrap SC which is used and of the steel grade to be produced. If the level of impurities, such as copper, chromium, molybdenum, nickel, tin, antimony, zinc and/or arsenic in the scrap SC is low then the quantity of scrap SC to be charged may be increased and thus the quantity of DRI and/or pig iron PI decreased.

The steelmaking furnace 2 provided as an Electrical Arc Furnace (EAF) comprises a vessel 4 for receiving the load L and two or more electrodes 6 configured for generating electrical arcs between the electrodes 6 and the load L received in the vessel 4.

Each electrode 6 is for example made of graphite.

Each electrode 6 is for example connected to an electrical source 8. The electrical source 8 comprises for example an electrical network and/or an electrical power plant using preferably one or several renewable energy sources.

The electrical power plant is preferably operated using CO2 neutral electricity which includes notably electricity from renewable sources which is defined as energy that is produced from renewable resources, which are naturally replenished on a human timescale, including sources like sunlight, wind, rain, tides, waves, geothermal heat and biogas.

In some embodiments, the use of electricity coming from nuclear sources can be used as it is not emitting CO2 to be produced.

A biogas is a renewable energy source that can be obtained by the breakdown of organic matter in the absence of oxygen inside a closed system called 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 materials.

The method of producing steel comprises a step E2 of adding lime particles 10.

The addition of lime particles 10 allows dephosphorization of the melt M. Lime is a slagging material that has affinity with phosphorus. The addition of lime will generate a slag S with phosphorus affinity on top of the melt M, thus allowing the transfer of the phosphorus contained in the melt M towards the slag, then reducing the phosphorus content of the melt M.

The lime particles 10 are added to the load L, before melting and/or after melting. The lime particles 10 are preferably added to the load L after melting, i.e. in the melt M.

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

The method of producing steel comprises a step E3 of pre-heating the lime particles 10 to 500°C or more and then a step E4 of coating the pre-heated lime particles 10 with a coating 12 before adding the lime particles 10 to the load L, preferably after melting.

The level of hydration of lime is diminished at a temperature of 500°C or more. Preheating the lime particles 10 to 500°C or more thus limits the hydration of the lime particles 10.

The lime particles 10 are preferably pre-heated such that the water content of the lime particles L is 1.4 % by weight or lower, preferably 1.2 % by weight or lower, more preferably 1 .0 % by weight or lower.

Coating the pre-heated lime particles 10 with a coating 12 prevents the reaction of lime with water and carbon dioxide contained in the ambient air, even if the lime particles 10 are stored with cooling down before addition into the load L.

The coating 12 is preferably a hydrophobic coating. The hydrophobic coating 12 has no affinity with water and is thus efficient to prevent hydration of the lime.

In some examples, the coating 12 comprises or consists of paraffin. Paraffin is hydrophobic and can form a barrier preventing exchanges between the lime particles 10 and the ambient air, thus limiting hydration and carbonation of the lime particles 10.

Lime particles 10 are pre-heated in a pre-heating furnace 14 and then coated in a coating device 16 before adding the lime particles 10 to the load L.

The preheating of the lime particles 10 is advantageously performed using steelmaking gases. Steelmaking gases contain heat that can be used for heating the lime particles 10, at least in part. Steelmaking gases encompass all gases generated by the different production units in a steelmaking plant. It may be for example blast furnace gas, coke oven gas, sintering gas, direct reduction top gas, BOF gas or EAF gas. These gases may be used as fuel for burners or may be used for heat transfer, e.g. in a heat exchanger.

In some examples, the method of producing steel comprises storing the lime particles 10 at ambient air before adding the lime particles 10 to the load L. The duration of storage is for example 5 hours or more.

The addition of lime particles 10 to the load L is operated before melting the load L and/or after partial melting of the metal load L and/or after complete melting of the load L. The addition of lime particles 10 is preferably operated after partial melting of the load L and/or after complete melting of the load L, i.e. in to the melt M.

The method of producing steel comprises preferably separating the slag S generated by the lime particles 10 from the melt M, e.g. by removing the slag S from the steelmaking furnace 2, for example via a slag outlet provided on a sidewall of the vessel 4 of the steelmaking furnace 2 when the latter is provided as an EAF.

The method of producing steel comprises a step E5 of injecting oxygen in the steelmaking furnace 2. The steelmaking furnace 2 comprises for example an oxygen injection system 20 configured for injecting oxygen in the vessel 4 during operation of the steelmaking furnace 2.

Oxygen injected in the steelmaking furnace 2 reacts with the carbon contained in the melt M thus reducing the carbon content of the melt M.

The oxygen injection system 20 is configured for injecting oxygen into the steelmaking furnace 2 during melting of the load L and/or, preferably, after melting of the load L.

The oxygen injection system 20 comprises one or several oxygen lances 22, each oxygen lance 22 opening inside the steelmaking furnace 2, and an oxygen source fluidly connected to each gas lance 22 for feeding said gas lance 22 with an oxygen flow 24.

Each oxygen lance 22 is for example oriented obliquely downwardly to inject a flux of oxygen 24 towards the surface of the melt M and/or into the melt M present in the steelmaking furnace 2, in particular if the latter is an EAF.

The addition of lime particles 10 and the removal of the slag S are preferably performed before the injection of oxygen in the steelmaking furnace 2 in particular if the latter is an EAF.

The slag S generated by the addition of lime particles 10 is preferably removed from the steelmaking furnace 2, in particular before tapping the metal melt M from the steelmaking furnace 2.

The method of producing steel optionally comprises addition of additional slagging materials different from lime in the steelmaking furnace 2 and removing a slag that is generated before performing a next slagging operation.

Each slagging material addition allows adjusting the composition of the metal melt M by lowering a content of the melt M in one or several elements with which the additional slagging material has affinity.

As illustrated on Figure 2 and 3, in some examples, methods of producing steel differ from that of Figure 1 in that these methods of producing steel comprise a step E6 of converting the load L into a melt M made of iron in an ironmaking furnace 30 and then transferring the melt M from the ironmaking furnace 30 to the steelmaking furnace 2, the steelmaking furnace 2 being configured for converting the melt M into steel.

As illustrated on Figure 2, in some examples, the ironmaking furnace 30 is a Blast Furnace (BF).

The steelmaking furnace 2 is for example a Basic Oxygen Furnace (BOF), in which case the method of producing steel implements a so-called “BF-BOF route”.

The load L comprises for example iron ore O and/or coal C.

The lime particles 10 are added to the load L in the steelmaking furnace 2.

As in the method of producing steel of Figure 1 , the lime particles 10 are pre-heated and coated before being added to the load L. The lime particles 10 are pre-heated in a preheating furnace 14 and then coated in a coating device 16 before adding the lime to the load L.

The lime particles 10 generate a slag S in the steelmaking furnace 2. The method of producing steel preferably comprises separating the slag S from the melt M, e.g. by tapping the melt M from the steelmaking furnace 2.

The method of producing steel preferably comprises a step of injecting oxygen in the melt M in the steelmaking furnace 2. The steelmaking furnace 2 is equipped with an oxygen injection system 20 similar of that of the steelmaking furnace 2 provided as EAF of Figure 1 .

The oxygen injection system 20 of Figure 2 differs from that of Figure 1 in that it comprises an oxygen lance 22 oriented vertically downwardly to inject a flux of oxygen 24 towards the surface of the melt M contained in the steelmaking furnace 2.

As illustrated on Figure 3, in some examples, the ironmaking furnace 30 is an Electrical Smelting Furnace (ESF), such as a Submerged Arc furnace (SAF) or an Open Slag Bath Furnace (OSBF).

The steelmaking furnace 2 is for example a Basic Oxygen Furnace (BOF) in which case the method of producing steel implements a so-called “ESF-BOF route”.

The load L comprises for example scrap SC, direct reduced iron DRI and/or pig iron PI. In some examples, the load L charged in the ESF comprises at least 60% by weight of direct reduced iron DRI, preferably from 80 to 98% by weight of direct reduced iron DRI and/or from 1 to 20% by weight of steel scrap (SC).

Lime particles 10 are added to the load L in the steelmaking furnace 2 and/or in the ironmaking furnace 30. Preferably, lime particles 10 are added to the load L in the steelmaking furnace 2.

As in the method of producing steel of Figure 1 , the lime particles 10 are pre-heated and coated before being added to the load L in the steelmaking furnace 2 and/or in the ironmaking furnace 30. The lime particles 10 are pre-heated in a pre-heating furnace 14 and then coated in a coating device 16 before adding the lime to the load L.

Lime particles 10 added in the ironmaking furnace 30 generate a primary slag S1 in the ironmaking furnace 30. The method or producing steel preferably comprises separating the primary slag S1 from the melt M before or upon transferring the melt M into the steelmaking furnace 2 for converting the melt M into steel.

Lime particles 10 added in the steelmaking furnace 2 generated a slag S in the steelmaking furnace 2. The method of producing steel preferably comprises separating the slag S from the melt M, e.g. upon tapping the melt M from the steelmaking furnace 2.

The method of producing steel preferably comprises a step of injecting oxygen in the melt M in the steelmaking furnace 2. The steelmaking furnace 2 is equipped with an oxygen injection system 20 similar to that of Figure 2.

Owing to the invention, lime of good quality and better reactivity can be added to the load L in the steelmaking process, thus limiting the amount of lime that is necessary and/or limiting the duration of processing of the load, in particular in each furnace.

The shorter duration of processing implies that less energy is consumed, in particular in each furnace (ironmaking furnace 30 or steelmaking furnace 2) used for processing the load L. The production of steel is thus more energy-efficient.

The method of the invention allows also to avoid hydrogen pick-up of the melt M due to the lime. Indeed, with methods according to prior art, water contained into the lime generates hydrogen into the melt M. Just a few parts per million of hydrogen dissolved in steel can cause hairline cracks (flakes), hydrogen embrittlement, hydrogen blistering and loss of tensile ductility, particularly in large steel castings ingots, blooms and slabs.

Claims

1. A method of producing steel comprising loading a load (L) in a steelmaking furnace (2) for converting the load (L) into steel, the method of producing steel comprising adding lime particles (10) to the load (L), wherein the method comprises a step of preheating the lime particles (10) to 500°C or more and a step of coating the pre-heated lime particles (10) with a coating (12) before adding the lime particles (10) to the load (L).

2. The method of producing steel as in claim 1 , wherein the coating (12) is hydrophobic.

3. The method of producing steel as in claim 1 or 2, wherein the coating (12) comprises or consists in paraffin.

4. The method of producing steel as in any one of the preceding claims, wherein the lime particles (10) are preheated to 700°C or more.

5. The method of producing steel as in any one of the preceding claims, wherein the preheating is performed using steelmaking gases.

6. The method of producing steel as in any one of the preceding claims, wherein the lime particles (10) are preheated in a pre-heating furnace (14).

7. The method of producing steel as in any one of the preceding claims, wherein the pre-heated and coated lime particles (10) are stored before adding the lime particles (10) to the load (L).

8. The method of producing steel of any one of the preceding claims, comprising injecting oxygen in the steelmaking furnace (2).

9. The method of producing steel as in claim 8, wherein the lime particles (10) are added before injecting oxygen in the steelmaking furnace (2).

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

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

12. The method of producing steel of claim 11 , wherein the load (L) comprises at least 40% by weight of steel scrap (SC).

13. The method of producing steel as in claim 1 1 or 12, wherein the load (L) comprises from 40% to 60% by weight of direct reduced iron (DRI).

14. The method of producing steel as in claim 1 1 or 12, wherein the load (L) comprises from 40% to 60% by weight of steel scrap (SC), up to 30% by weight of pig iron (PI) and from 10% to 60% by weight of direct reduced iron (DRI).

15. The method of producing steel as in any one of the preceding claims, wherein the steelmaking furnace (2) is a basic oxygen furnace (BOF).

16. The method of producing steel as in claim 15, comprising loading the load (L) in an ironmaking furnace (30) for transforming the load (L) into a melt (M) made of iron and transferring the melt (M) from the ironmaking furnace (30) to the steelmaking furnace (2) for converting the melt (M) into steel.

17. The method of producing steel as in claim 16, wherein the ironmaking furnace (30) is an electrical smelting furnace (ESF).

18. The method of producing steel as in claim 17, wherein the load (L) loaded in the electrical smelting furnace comprises from 80 to 98% by weight of direct reduced iron (DRI) and/or from 1% to 20% by weight of steel scrap (SC).

19. The method of producing steel as in claim 16, wherein the ironmaking furnace is a blast furnace (BF).

20. The method of producing steel as in claim 19, wherein the load (L) comprises ore (O) and/or coal (C).