Method for producing pig iron in electric smelting furnace and associated smelting furnace
By using direct reducing iron (DRI) products in the steel manufacturing process to reduce in the melting furnace and adding silicon-containing materials, the CO2 emissions and impurities problems in the existing routes are solved, and more environmentally friendly and efficient steel production is achieved.
Patent Information
- Application Number
- CN202280097272.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2022-07-29
- Publication Date
- 2025-02-07
AI Technical Summary
The existing steel manufacturing routes, especially the BF-BOF route, have resulted in a large amount of CO2 emissions. The DRI products used in direct reduction method have impurities when combined with iron-containing waste in classic electric furnaces, which require further processing, which increases environmental impact and production. cost.
Using a new manufacturing route, the reduction of direct reduction iron (DRI) products in a smelting furnace is used to generate pig iron, and silicon-containing materials are added in the process to improve deoxygenation capacity and reduce environmental footprints.
It effectively reduces CO2 emissions in the steel manufacturing process, reduces the carbon and sulfur content of pig iron, improves the quality of molten steel, reduces the demand for new molten steel treatment tools, and reduces production costs and environmental impact.
Smart Images
Figure CN119403942A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a method of making pig iron (also called hot metal) and to a method of producing steel from such pig iron. Background Art
[0002] Steel can currently be produced by two main manufacturing routes. Today, the most commonly used production route, known as the "BF-BOF route", involves producing hot iron in a blast furnace by using a reducing agent (mainly coke) to reduce iron oxides, which is then converted into steel in a converter process or Basic Oxygen Furnace (BOF). This route releases large amounts of CO2 both in the production of coke from coal in the coking plant and in the production of hot iron.
[0003] The second major route involves the so-called "direct reduction process". In these processes, sponge iron is produced in the form of HDRI (hot direct reduced iron), CDRI (cold direct reduced iron) or HBI (hot briquetted iron) by direct reduction of an iron oxide carrier. The sponge iron in the form of HDRI, CDRI and HBI undergoes further processing in an electric furnace to produce steel.
[0004] Therefore, one of the main options chosen by steelmakers to reduce CO2 emissions is to switch from the BF-BOF route to the DRI route. However, the use of DRI products with ferrous scrap in a classic electric furnace has some limitations. In fact, the scrap contains a lot of impurities and the resulting steel will need to be further processed to produce high-quality steel grades. Therefore, investments in new steel treatment tools will be necessary. Summary of the invention
[0005] It is therefore an object of the present invention to remedy the disadvantages of pig iron and steelmaking manufacturing routes by providing a new route that effectively minimizes the environmental impact of such manufacturing routes.
[0006] This problem is solved by a method for producing pig iron as specified in claim 1 .
[0007] Such a method may also comprise the optional features of claims 2 to 7 considered alone or in any possible technical combination.
[0008] The invention also relates to a method for producing steel according to claim 8 .
[0009] Such a method may also comprise the optional features of claim 9 or 10 considered alone or in any possible technical combination.
[0010] The invention also relates to a smelting furnace according to claim 11 . BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Other characteristics and advantages of the invention will emerge clearly from the description of the invention, which is given below by way of indication and which is in no way limiting, with reference to the accompanying drawings, in which:
[0012] - Figure 1 shows the pig iron and steel making process according to the smelting / BOF route,
[0013] - Figure 2 A smelting furnace is shown.
[0014] Elements in the drawings are illustrative and may not be drawn to scale. DETAILED DESCRIPTION
[0015] Figure 1 The steel production route according to the DRI route is shown, 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. The direct reduction plant 11 can be designed to implement any kind of direct reduction technology, such as Technology or The direct reduction process may be, for example, a conventional natural gas-based or biogas-based process.
[0016] In a preferred embodiment, the DRI product used in the process according to the invention is produced using a reducing gas based on biogas from the combustion of biomass.
[0017] Biomass is a renewable organic material from plants and animals. Biomass sources include wood and wood processing waste (e.g., firewood, wood particles and wood chips, wood and furniture factory sawdust and waste), and black liquor from pulp and paper mills, agricultural crops and waste materials (e.g., corn, soybeans, sugar cane, switchgrass, woody plants and algae), and crop and food processing residues, and also include biogenic materials in municipal solid waste (e.g., paper, cotton and wool products), and food, yard and wood waste, animal manure and human filth. In the sense of the present invention, biomass can also include plastic residues, such as recycled waste plastics, such as solid refuse fuel (Solid Refuse Fuel) or SRF.
[0018] 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 %, and is typically set in the range of 2 wt % to 3 wt %.
[0019] In another preferred embodiment, the DRI product used in the method according to the present invention is manufactured by the so-called H2-DRI process, wherein the reducing gas contains more than 50% by volume, and preferably more than 60%, 70%, 80% or 90% hydrogen, or even completely composed of hydrogen. The H2-DRI product will contain carbon at a level far lower than that of natural gas or biogas DRI, and is therefore typically less than 1% by weight, or even lower. In a preferred embodiment, the hydrogen used in the DRI reducing gas comes from the electrolysis of water, and the electrolysis is preferably partially or entirely powered by CO2-neutral electricity. CO2-neutral electricity particularly includes electricity from renewable sources, which is defined as energy collected from renewable resources (including resources like sunlight, wind, rain, tides, waves and geothermal) that are naturally replenished on a human time scale. In some embodiments, the use of electricity from nuclear sources can be used because it does not produce CO2 emissions.
[0020] Regardless of the DRI process used, the resulting Direct Reduced Iron (DRI) product 12 is then charged to a smelting furnace 13 where reduction of the iron oxides is completed and the product is melted to produce pig iron.
[0021] The DRI product may be transferred to the smelting furnace in various forms. Preferably, the direct reduced iron product (DRI product) is fed to the smelting furnace in hot form as a HDRI product (so-called hot DRI), or in cold form as a CDRI product (so-called cold DRI), or in hot briquetted form as a HBI product (so-called hot briquetted iron) and / or in pelletized form (preferably having an average particle size of at most 10.0 mm, more preferably having an average particle size of at most 5.0 mm).
[0022] The DRI product is preferably loaded directly at the outlet of the direct reduction unit 11 as a hot product at a temperature of 500° C. to 700° C. This allows reducing the amount of energy required to melt it. When hot loading is not possible, for example if the direct reduction unit 11 and the smelting furnace 13 are not co-located, or if the smelting furnace 13 is stopped for maintenance and the DRI product must therefore be stored, the DRI product can be cold loaded, or a preheating step can be carried out.
[0023] The smelting furnace 13 utilizes electrical energy provided by several electrodes to melt the DRI product 12 and produce pig iron 14. In a preferred embodiment, part or all of the required electricity comes from CO2 neutral electricity. Figure 2A further detailed description of the smelting furnace is given.
[0024] The pig iron 14 is then transferred to a pig iron ladle through at least one tap hole 25 provided with at least one launder 26. Such tap holes 25 are located in the lower part of the container 20. They can be located in the side walls of the container or in its bottom wall. There are usually as many auxiliary launders as tap holes, which then intersect to form a main launder, thereby directing the extracted pig iron to the pig iron ladle.
[0025] The cast iron ladle may be a simple ladle, but may also be a torpedo ladle.
[0026] The pig iron 14 can optionally be sent to a desulfurization station 15 for a desulfurization step. The desulfurization step can be carried out in a dedicated container, or preferably directly in the pig iron pot to avoid molten metal transfer and related heat losses. The desulfurization step is necessary for the production of steel grades requiring low sulfur content (which is, for example, set to a maximum of 0.03 weight percent sulfur). Desulfurization under oxidizing conditions is ineffective, and therefore the pig iron is preferably desulfurized before oxygen refining, or desulfurized in a ladle after the steel is deoxidized. For very low sulfur contents (e.g., less than 0.004 weight percent sulfur), deoxidation and desulfurization are combined to obtain higher overall performance. Therefore, low sulfur grades benefit from desulfurization of the pig iron before the conversion step.
[0027] Desulfurization of pig iron can be accomplished by adding reagents, in particular reagents based on calcium or magnesium compounds, such as sodium carbonate, lime, calcium carbide and / or magnesium, to the pig iron. For example, it can be accomplished by injecting those reagents into a pig iron tank. The sulfur content of the desulfurized pig iron 16 is preferably less than 0.03% by weight, and preferably less than 0.004% by weight.
[0028] The desulfurized pig iron 16 can then be transferred to a converter 17. The converter essentially transforms molten metal into molten steel by blowing oxygen through the molten metal to decarburize it. It is commonly referred to as a basic oxygen furnace (BOF). Iron-containing scrap 18 from steel recovery can also be charged to the converter 17 to utilize the heat released by the exothermic reaction created by injecting oxygen into the pig iron.
[0029] The molten steel 19 thus formed can then be transferred to one or more secondary metallurgical tools 20A, 20B, such as a ladle furnace, a RH (Ruhrstahl-Heareus) vacuum vessel, a vacuum tank degasser, an alloying and stirring station, etc., if necessary, to be processed according to the type of steel to be produced so as to achieve the desired steel composition. The molten steel 21 with the desired composition can then be transferred to a casting device 22, where it can be transformed into a solid product, such as a slab, a billet, a bloom or a strip.
[0030] like Figure 2 As shown, the smelting furnace 13 is composed of a container 20 capable of containing hot molten iron. For example, the container 20 can have a circular or rectangular shape. The container 20 is closed by a top, which is provided with some holes to receive electrodes 22 to be inserted into the container 20, and is provided with other holes to allow raw materials to be loaded into the container 20.
[0031] Electrodes 22 provide the electrical energy required to melt the loaded raw materials and form pig iron. They are preferably During the melting of the raw material, two layers are formed, a layer of pig iron 14 which is the densest and therefore located at the bottom of the container 20, and a slag layer 23 located above the pig iron 14. The slag layer 23 may be partially covered by a pile of raw material 24 waiting to be melted.
[0032] The smelting furnace 13 may be a SAF (Submerged-Arc Furnace) in which the electrodes are immersed in a slag layer 23, or an OSBF (open-slag bath furnace) in which the electrodes 22 are located above the slag layer 23. It is preferably an OSBF as shown in the accompanying drawings.
[0033] In the framework of the present invention, silicon-containing material is added to the pig iron in at least one launder 26 of the tap hole 25 of the smelting furnace. Silicon has a strong deoxidizing ability at high temperatures and in particular about 1600° C., which is the temperature of the molten steel in the converter. It reacts with oxygen and then contributes to the formation of slag in the converter. The reaction is exothermic and therefore provides additional energy for the melting of the waste. The more waste is used, the smaller the environmental footprint of the process.
[0034] This addition can be done by top feed addition for low cost operation or by injection means such as submerged lances which provide high yields up to 90% and above.
[0035] By adding silicon to the pig iron at this stage, the inventors have observed that it allows good mixing with the pig iron during tapping as a gradual addition and benefits from intensive natural mixing when the pig iron is subsequently tapped in the ladle.
[0036] Such silicon can be added in different forms, such as metallic silicon Si, silicon carbide SiC, silicon manganese SiMn, calcium silicate SiCa or iron silicon alloy FeSi, such as FeSi75 or FeSi65.
[0037] The use of DRI products in the smelting furnace 13 will result in a natural amount of silicon generally below 0.2 wt.-% or even below 0.1 wt.-%. The final silicon content of the pig iron is preferably set to a value of 0.1 wt.-% to 0.4 wt.-%, preferably 0.2 wt.-% to 0.4 wt.-%. If necessary, further addition of silicon can be carried out in the converter 17.
[0038] In a preferred embodiment, the carbonaceous material may be injected into the pig iron together with the silicon-containing material.
[0039] As explained above, the carbon content of the pig iron 14 produced by the DRI route will generally be less than 3 wt%. However, in order to meet the requirements of the subsequent steelmaking process at the converter, the carbon content of the pig iron should preferably be as close to 4.5 wt%, which is the saturation level, as possible. In a preferred embodiment, the pig iron carbon content is in the range of 4.0 wt% to 4.5 wt%.
[0040] In fact, carbon is essential for the steelmaking process performed by oxygen blowing in the converter 17. This is because the reaction of carbon with oxygen produces carbon monoxide gas, which provides an intense and efficient stirring of the molten metal and thus improves the removal of impurities from the steel. The reaction is exothermic and thus provides additional energy for melting the iron-containing waste, allowing the incorporation of higher amounts of such iron-containing waste from steel recycling. The more iron-containing waste is used, the smaller the environmental footprint of the steelmaking process.
[0041] The carbonaceous material can come from different sources. It can be selected from, for example, coke, anthracite, silicon carbide, calcium carbide or a mixture of any of those sources, but can also advantageously come 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 the calcium atoms can provide a desulfurization effect.
[0042] The addition of silicon carbide is particularly advantageous, as it allows the carbon content of the pig iron to be increased on the basis of the addition of silicon. The addition of a mixture of calcium carbide and silicon carbide is even more advantageous, as it provides the addition of carbon and silicon while ensuring desulfurization.
Claims
1. A method for producing pig iron in an electric smelting furnace (13), the electric smelting furnace (13) comprising a container (20) provided with a tap hole (25), the method comprising the following steps: - loading the container (20) with a DRI product, - melting the DRI product to form a pig iron layer (14) topped by a slag layer (23), - tapping the pig iron (14) into a ladle, and - Adding silicon-containing material directly to the pig iron (14) in the launder of at least one of the smelting furnace tapholes (25).
2. The method according to claim 1, wherein the silicon-containing material is injected in an amount sufficient to achieve a final silicon content of 0.1% to 0.4% by weight in the pig iron layer (14).
3. The method according to claim 1 or 2, wherein the silicon-containing material is injected by an immersion lance.
4. The method according to any one of claims 1 to 3, wherein the silicon-containing material is selected from metallic silicon Si, silicon carbide SiC, silicon manganese SiMn, calcium silicate SiCa, iron silicon alloy FeSi or a mixture of any of those materials.
5. The method according to any one of claims 1 to 4, wherein the silicon-containing material added has particles with a particle size below 3 mm.
6. The method according to any one of claims 1 to 5, wherein the DRI product is produced using a reducing gas comprising at least 50% by volume of hydrogen before the DRI product is charged into the smelting furnace (13).
7. The method according to any one of claims 1 to 6, wherein a carbon-containing material is added to the silicon-containing material to be injected into the pig iron (14).
8. A method for producing steel, wherein the pig iron produced according to any one of claims 1 to 7 is transferred from the smelting furnace (13) to a converter (17), and then the carbon content of the pig iron is reduced to a value below 2.1 weight percent by oxygen blowing in the converter to obtain molten steel.
9. The method for manufacturing steel according to claim 8, wherein iron-containing scrap is added to the pig iron in the converter (17) and melted.
10. A method according to claim 8 or 9, wherein the pig iron is transferred from the smelting furnace (13) to a desulphurisation station (15) before being transferred to the converter (17).
11. An electric smelting furnace for producing pig iron (14), comprising a container (20) provided with tapping holes (25), the tapping holes (25) being associated with chutes (26) allowing the produced pig iron to be tapped into a pig iron pot, the furnace (13) also comprising injection means allowing the injection of silicon-containing material directly into the pig iron (14) in the chutes of at least one of the tapping holes (25) of the smelting furnace.