Method for producing pig iron in an electric smelting furnace and associated electric smelting furnace

Abstract

The present invention relates to a method for producing pig iron in an electric smelting furnace 13 comprising a vessel 20, the following consecutive steps: - loading the vessel 20 with a DRI product, - melting the DRI product to form a pig iron layer 14 covered by a slag layer 23, and - directly injecting a desulphurization reagent into the pig iron layer 14. The present invention also deals with the production of steel from said pig iron and the associated electric smelting furnace.

Description

Technical Field

[0001] The present invention relates to a method for producing pig iron, also called hot metal, and a method for producing steel from such pig iron.

Background Art

[0002] Currently, steel can be produced through two main manufacturing routes. Today, the most commonly used manufacturing route, called the "BF-BOF route", consists of producing hot metal in a blast furnace by reducing iron oxide using a reducing agent, mainly coke, and then converting the hot metal into steel in a converter process or a basic oxygen furnace (BOF). This route emits a significant amount of CO2 both in the production of coke from coal in a coke plant and in the production of hot metal.

[0003] The second main route includes the so-called "direct reduction method". Among them, there are methods such as those by brands MIDREX (registered trademark), FINMET (registered trademark), ENERGIRON (registered trademark) / HYL, COREX (registered trademark), FINEX (registered trademark), etc., where 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). Sponge iron in the form of HDRI, CDRI and HBI is further processed in an electric furnace to produce steel.

[0004] Therefore, one of the main options for steelmakers to reduce CO2 emissions is to switch from the BF-BOF route to the DRI route. However, there are some limitations to using DRI products in a classical electric furnace together with iron scrap. In fact, scrap contains many impurities and the resulting molten steel needs to be further processed to produce high-quality steel grades. Therefore, an investment in new molten steel treatment tools is required.

Summary of the Invention

Problems to be Solved by the Invention

[0005] Accordingly, an object of the present invention is to improve the drawbacks of the manufacturing routes of pig iron and steel by providing a new route that efficiently minimizes the impact on such manufacturing environments without incurring large investments.

Means for Solving the Problems

[0006] This problem is solved by a method for manufacturing pig iron as detailed in claim 1.

[0007] Such a method can also include the optional features of claims 2 to 8, considered separately or in any possible technical combination.

[0008] The present invention also addresses a method for manufacturing steel as described in claim 9.

[0009] Such a method can also include the optional feature of claim 10.

[0010] The present invention also addresses an electric smelting furnace as detailed in claim 11.

[0011] Other features and advantages of the present invention will become apparent from the following description of the invention, given by way of example and with reference to the accompanying drawings, which are in no way limiting.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0013] The elements in the figures are illustrative and may not be drawn to scale.

[0014] Figure 1 shows a steel manufacturing route via the DRI route from the reduction of iron to the casting of steel into semi-finished products such as slabs, billets, blooms or strips. Iron ore 10 is first reduced in a direct reduction plant 11. This direct reduction plant 11 can be designed to implement any type of direct reduction technology such as MIDREX (registered trademark) technology or Energiron (registered trademark). The direct reduction process may be, for example, a process based on traditional natural gas or biogas.

[0015] In a preferred embodiment, the DRI product used in the method according to the invention is produced using a reducing gas based on biogas resulting from the combustion of biomass.

[0016] Biomass is a renewable organic material derived from plants and animals. Biomass sources include, in particular, wood and wood processing waste such as sawdust, wood pellets and wood chips, sawdust and waste from sawmills and furniture factories, and black liquor from pulp and paper mills, crops and agricultural waste such as corn, soybeans, sugarcane, switchgrass, woody plants and algae, and crop and food processing residues, but also municipal solid waste such as paper, cotton and wool products, and food, yard and wood waste, animal excrement and biologically derived materials in domestic sewage. In the context of the present invention, biomass may also include plastic residues such as recycled waste plastics such as solid waste fuels or SRF.

[0017] Whenever natural gas or biogas is used as the reducing gas, the carbon content of the DRI product can be set to a maximum of 3 wt%, usually in the range of 2 - 3 wt%.

[0018] In another preferred embodiment, the DRI product used in the method according to the invention is produced by a so-called H2-DRI process in which the reducing gas contains more than 50% by volume, preferably more than 60, 70, 80 or 90% by volume of hydrogen, or consists entirely of hydrogen. H2-DRI products contain carbon at levels much lower than natural gas or biogas DRI, typically less than 1% by weight or even lower. In a preferred embodiment, the hydrogen used in the DRI reducing gas is derived from the electrolysis of water, which is preferably powered in part or in whole by CO2-neutral electricity. CO2-neutral electricity is defined in particular as electricity from renewable sources collected as energy from renewable resources that are naturally replenished on a human time scale, including sources such as sunlight, wind, rain, tides, waves and geothermal. In some embodiments, the use of electricity from nuclear sources can be used because it does not emit the CO2 being produced.

[0019] Regardless of the DRI process used, the resulting direct reduced iron (DRI) product 12 is then charged into a smelting furnace 13 where the reduction of the iron oxide is completed and the product is melted to produce pig iron.

[0020] The DRI product can be transferred to the smelting furnace in various forms. Preferably, the directly reduced iron product (DRI product) is in a hot form as an HDRI product (so-called Hot DRI), or in a room temperature form as a CDRI product (so-called Cold DRI), or in a hot formed form as an HBI product (so-called hot briquette iron), and / or preferably in a particulate form having an average particle size of up to 10.0 mm, more preferably up to 5.0 mm, and is supplied to the smelting furnace.

[0021] This is preferably charged directly as a hot product having a temperature of 500°C to 700°C at the outlet of the direct reduction plant 11. Thereby, the amount of energy required for melting can be reduced. If hot charging is not possible, for example, when the direct reduction plant 11 and the steelmaking furnace 13 are not in the same location, or when the steelmaking furnace 13 is stopped for maintenance and thus the DRI product has to be stored, the DRI product may be charged at room temperature or a preheating step may be carried out.

[0022] The steelmaking furnace 13 uses electrical energy provided by several electrodes to melt the DRI product 12 and produce hot metal 14. In a preferred embodiment, some or all of the required electric power is derived from CO2-neutral power. A more detailed description of the steelmaking furnace will be given later with reference to FIG. 2.

[0023] The hot metal 14 can then be transferred into the converter 17. The converter basically converts the molten metal into molten steel by blowing oxygen into the molten bath for decarburization. This is generally called a basic oxygen furnace (BOF). Iron scrap 18 resulting from the recycling of steel may also be charged into the converter 17 to take advantage of the heat released by the exothermic reaction resulting from the oxygen injection into the hot metal.

[0024] The molten steel 19 thus formed can then be transferred at any time as required to one or more secondary metallurgy tools 20A, 20B, for example, ladle furnace, RH (Ruhrstahl-Heareus) vacuum vessel, vacuum tank degassing device, alloying and stirring station, etc., and can be processed to reach the steel composition required according to the steel grade to be produced. The molten steel having the required composition 21 can then be transferred to the casting plant 22, where it can be converted into solid products such as slabs, billets, blooms or strips.

[0025] As shown in Figure 2, the smelting furnace 13 consists of a vessel 20 capable of containing molten iron. The vessel 20 may be, for example, circular or rectangular. This vessel 20 is closed by a roof provided with several openings for receiving electrodes 22 to be inserted into the vessel 20 and other openings for allowing the charging of raw materials into the vessel 20.

[0026] The electrodes 22 provide the electrical energy necessary to melt the charged raw materials to form pig iron. They are preferably Soederberg type electrodes.

[0027] During melting of the raw materials, two layers are formed: a layer of pig iron 14, which is the densest and therefore located at the bottom of the vessel 20, and a layer of slag 23, which is located above the pig iron 14. The slag layer 23 may be partially covered by a pile of raw materials 24 waiting to be melted.

[0028] The vessel 20 also includes openings called tap holes 25 located at its bottom and allowing the discharge of the pig iron 14 while retaining most of the slag within the vessel 20. They may be located in the side walls of the vessel or in its bottom wall.

[0029] The smelting furnace 13 may be an SAF (Submerged-Arc Furnace) where the electrode is immersed in the slag layer 23 or an OSBF (Open Slag Bath Furnace) where the electrode 22 is located above the slag layer 23. It is preferably an OSBF as shown in the figure.

[0030] In the mechanism of the present invention, the desulfurization reagent is added directly into the pig iron layer 14 in the smelting furnace 13. This addition can be done though an injection device.

[0031] In fact, the inventors have observed that the reducing conditions of the smelting furnace 13 favor efficient removal of sulfur.

[0032] By performing desulfurization in the smelting furnace, the necessity for desulfurization treatment between the smelting furnace 13 and the converter 17 can be suppressed, or such treatment can be at least reduced.

[0033] The final sulfur content of the pig iron is preferably set to a maximum value of 0.03 wt%, preferably a maximum value of 0.004 wt%.

[0034] In a preferred embodiment, the injection device is the tuyere 26 inserted at the bottom of the container 20. Such a bottom tuyere opens into the pig iron layer 14 to enable direct addition.

[0035] The use of this bottom tuyere 26 avoids the injection of desulfurization reagents from the upper part of the smelting furnace 13 where the available space may be insufficient due to the presence of electrodes and charging devices for DRI products.

[0036] Furthermore, this bottom injection enables high efficiency of desulfurization because the reagent passes through the entire height of the pig iron layer 14.

[0037] In a preferred embodiment, to avoid clogging of the injection device, the desulfurization reagent is injected together with a carrier gas. This gas is preferably inert and can be made of nitrogen, argon, helium or carbon monoxide, or any mixture of such gases.

[0038] In a preferred embodiment, the silicon-containing material may be injected into the pig iron layer 14 together with the desulfurization reagent. Silicon has a strong deoxidizing ability at high temperatures, particularly at about 1600 °C which is the temperature of the molten steel in the converter. Silicon reacts with oxygen and then contributes to the formation of slag. This reaction is exothermic and thus provides additional energy to improve the performance of the desulfurization operation.

[0039] Such silicon can be added in different forms. The silicon may be metallic silicon Si, silicon carbide SiC, silicomanganese SiMn, calcium silicate SiCa, or ferrosilicon alloy FeSi such as FeSi75 or FeSi65.

[0040] When using DRI products in the smelting furnace 13, a natural amount of silicon of usually less than 0.2% by weight, and further less than 0.1% by weight is brought about. The final silicon content of the pig iron is preferably set to a value of 0.1 - 0.4% by weight, preferably 0.2 - 0.4% by weight. If necessary, further addition of silicon can be carried out in the converter 17.

[0041] In a preferred embodiment, the carbon-containing material can also be injected together with the desulfurization reagent, regardless of the presence or absence of silicon addition.

[0042] The carbon content of the pig iron 14 produced via the DRI route is generally less than 3% by weight. However, in order to meet the requirements of the subsequent steelmaking process in the converter, the pig iron should preferably have a carbon content as close as possible to the saturation level of 4.5% by weight. In a preferred embodiment, by adding the carbon-containing material, the pig iron carbon content is set in the range of 4.0 - 4.5% by weight.

[0043] The carbon-containing material can be derived from different sources. This can be selected, for example, from coke, anthracite, silicon carbide, calcium carbide or a mixture of any of these sources, but can also advantageously be obtained from renewable sources such as biomass for part or all of the carbon load. In particular, biochar can be used. Adding calcium carbide is particularly advantageous because calcium atoms can provide a desulfurization effect. Adding silicon carbide is particularly advantageous because it enables an increase in the silicon content of the pig iron.

[0044] The carbon-containing material injected through the injection device preferably has a particle size of less than 3 mm. In a preferred embodiment, the material has a particle size of 75 μm or less, and the remaining particles have a particle size of 2 mm or less.

[0045] In another embodiment, the carbon-containing material may also be made of a composite briquette in which an iron source is mixed with one or several of the aforementioned carbon sources.

[0046] In a preferred embodiment, the iron source can be selected from sludge from an electric furnace, a converter or a smelter, slag from an electric furnace or a converter, or any iron-rich waste material from the steel manufacturing route.

[0047] It should be noted that the addition of calcium carbide is particularly advantageous because the carbide addition provides carbon addition to the pig iron while also desulfurizing it. The addition of a mixture of calcium carbide and silicon carbide is even more advantageous because it provides carbon and silicon addition while ensuring desulfurization.

Claims

1. A method for producing pig iron in an electric smelting furnace (13) comprising a container (20), the following continuous steps: - Loading a DRI product into said container (20); - Melting said DRI product to form a pig iron layer (14) covered with a slag layer (23); and - Directly injecting a desulfurizing reagent material into said pig iron layer (14). A method comprising the above.

2. The method according to claim 1, wherein said smelting furnace (13) comprises at least one bottom tuyere (27) provided in such a container (20) through which said desulfurizing reagent is directly injected into said pig iron layer (14).

3. The method according to claim 1 or 2, wherein said desulfurizing reagent is injected in an amount sufficient to reach a final sulfur content of less than 0.02% by weight in the pig iron layer (14).

4. The method according to any one of claims 1 to 3, wherein said desulfurizing reagent is injected together with a carrier gas.

5. The method according to any one of claims 1 to 4, wherein said desulfurizing reagent is selected from sodium carbonate, lime, calcium carbide, magnesium or any mixture of these materials.

6. The method according to any one of claims 1 to 5, wherein the injected desulfurizing reagent has particles with a particle size of less than 3 mm.

7. The method according to any one of claims 1 to 6, wherein said DRI product is produced using a reducing gas containing at least 50% by volume of hydrogen before being loaded into said smelting furnace (13).

8. The method according to any one of claims 1 to 7, wherein a silicon-containing material and / or a carbon-containing material is added to the desulfurizing reagent and injected into the pig iron layer (14).

9. [[ID= ​ ​ ​ ​

Images