DE102020116425A1 - Process for the production of crude steel with a low N content - Google Patents

Abstract

The invention relates to a method for producing crude steel (11) using an electric arc furnace (9) with the following steps: - producing sponge iron (7) in a direct reduction system (5), - feeding the sponge iron (7) to the electric arc furnace (9) ) at least as a partial iron girder. In order to achieve low nitrogen contents in the crude steel, it is proposed that the direct reduction system (5) and / or the sponge iron (7) be supplied with a pre-selected amount of a carbon-containing medium (8, 13) in order to use the electric arc furnace (9) to produce crude steel ( 11) with an N content of <60 ppm, preferably <35 ppm.

Description

The invention relates to a method for producing crude steel using an electric arc furnace with the following steps: generating sponge iron in a direct reduction system and feeding the sponge iron to the electric arc furnace at least as a partial iron support.

There has recently been a great deal of interest in producing steel in the most resource-efficient way possible and with reduced CO _{2 emissions.} Not only are material cycles closed, in which residues and by-products are reused internally or across sectors, but new process routes are also developed. In addition to the classic steel production, which takes place via the production of pig iron from iron ore in the blast furnace and converter, the electric arc furnace process has also increasingly established itself in the course of increasing sustainability and environmental requirements, known in the English "Electric Arc Furnace (EAF)" process. In the EAF process, scrap steel or sponge iron as a product of a direct reduction process in the form of DRI (direct reduced iron), HDRI (hot direct reduced iron), CDRI (cold direct reduced iron) or HBI (hot briquette iron) is mostly used as input material .

From the published patent application WO 2014/040989 A2 a use of hydrogen from regenerative processes as a reaction gas for a direct reduction process is known with which sponge iron is produced. The reaction gas used can, depending on availability, consist of fossil sources or entirely of hydrogen from regenerative processes, or it can be partially or completely replaced by biogas and gas from pyrolysis of renewable raw materials. It is also pointed out that in order to adjust the carbon content of the sponge iron, a minimum of a carbon-containing gas will be required as the reaction gas. The sponge iron produced by the direct reduction process has carbon contents of 0.0005 to 6.3% by weight, preferably 1 to 3% by weight. For the production of crude steel, the sponge iron in the form of DRI, HDRI, CDRI or HBI is usually fed to an electric arc furnace together with steel scrap.

The patent specification U.S. 4,834,792 already describes such a direct reduction process for the production of sponge iron by means of a shaft furnace. In the shaft furnace, iron ore fed to the shaft furnace is reduced to sponge iron with a reaction gas in a reduction zone. The reaction gas consists essentially of carbon monoxide, hydrogen and unreformed methane. In order to be able to adjust the carbon content of the sponge iron in a range from 0.5 to 4% by weight, methane is also fed to the shaft furnace in a controlled manner as a carbon source.

The invention is based on the object of providing a method for producing crude steel using an electric arc furnace in which low nitrogen contents can be achieved in the crude steel.

This object is achieved by a method for producing steel in the electric arc furnace process with the features of claim 1. In the dependent claims 2 to 14, advantageous embodiments of the invention are specified.

According to the invention, in a method for producing crude steel using an electric arc furnace with the following steps: generating sponge iron in a direct reduction plant, supplying the sponge iron to the electric arc furnace at least as a partial iron carrier, low nitrogen contents in the crude steel are achieved by using the direct reduction plant and / or the sponge iron a carbon-containing medium is supplied in a preselected amount in order to use the electric arc furnace to produce crude steel with an N content of <60 ppm, preferably <35 ppm. Thus, in connection with the production of crude steel, a lower N content can be achieved and corresponding secondary metallurgical measures can be dispensed with. This crude steel with a low N content is particularly suitable for steels in deep drawing quality, which are used, for example, in the automotive industry. This also prevents higher nitrogen contents from leading to undesirable aging of the steel products made from them.

In connection with the invention and the exemplary embodiment, the term "sponge iron" used, sponge iron as a product of a direct reduction process in the form of DRI (direct reduced iron), HDRI (hot direct reduced iron), CDRI (cold direct reduced iron) or HBI ( hot briquette iron) understood.

For the sake of simplicity, only the term “sponge iron” is used.

As an alternative or in addition, provision can be made for the sponge iron to be carburized to a carbon content of 0.1 to 6% by weight with the carbon-containing medium after the direct reduction system and before the electric arc furnace. In this case, the sponge iron is preferably coated with the carbon-containing medium. The carbon-containing medium is, in turn, of biogenic or regenerative origin as far as possible, such as with biogenic, solid, liquid or gaseous carbon sources (biochar, biogas, etc.) or carbon-containing residues as a by-product from other processes. In connection with the invention, the term biogenic or regenerative origin as possible is understood to mean that the carbon-containing medium is preferably of biogenic or regenerative origin, but can also be of fossil origin. The carbon-containing medium is preferably predominantly and particularly preferably of completely biogenic or regenerative origin.

It is also possible to supply a carbon-containing medium to the electric arc furnace. This is usually done by blowing in powder form or by adding in lump form. Here, too, the carbon-containing medium is, if possible, of biogenic or regenerative origin, as described above.

It is particularly advantageous that after the raw steel has been tapped from the electric arc furnace, the carbon-containing medium is fed to a raw steel remaining in the electric arc furnace and then becomes effective in the subsequent melt.

Particularly advantageous embodiments of the invention provide that the carbon-containing medium is at least partially fed to the direct reduction system as a carbon-containing solid and / or that the carbon-containing solid is at least partially blown into the direct reduction system as a powder. The powder here preferably has a particle size smaller than 5 mm, preferably smaller than 2 mm. In this way, a uniform distribution of the carbon on the sponge iron is achieved in each case.

It is advantageously provided that the carbon-containing solid, in particular with more than 30% by weight of carbon, is blown into a lower part of the direct reduction plant at around 600 to 750.degree. This creates finely distributed cementite and carbon deposits on the sponge iron.

In addition or as an alternative, it is provided that, in addition to the carbon-containing solid, a carbon-containing gas is also fed to the direct reduction plant as the carbon-containing medium. With regard to a reduction in the CO ₂ footprint, it is also advantageous that the carbon-containing gas is supplied at least partially as a biogenic gas and / or at least partially as a CO or CO ₂ -containing exhaust gas from other production processes.

In order to achieve the desired reduction in nitrogen in the crude steel, it is provided that the electric arc furnace is supplied with carbon in a preselected amount of 0 via the iron support, which consists at least partially of sponge iron that has already been carburized with the carbon-containing medium, and optionally via a carbon-containing medium , 1 to 6% by weight based on the melt in the electric arc furnace is fed. The subsequent formation of carbon monoxide bubbles in the melt results in a breakdown or reduced absorption of nitrogen in the melt.

In one embodiment of the invention it is provided that the direct reduction system is supplied as a reaction gas with a hydrogen-containing gas which contains more than 50% hydrogen. This high hydrogen content makes it necessary to use an alternative carbon source for the sponge iron, since less carbon is available from the H ₂ -rich reducing gas.

The so-called CO ₂ footprint of crude steel production can advantageously be further reduced if the hydrogen-containing gas is generated from renewable sources.

If the iron support in the electric arc furnace consists predominantly of carburized sponge iron, a uniform distribution of the carbon in the melt of the electric arc furnace can be achieved. In this context, “predominantly” means more than 50% by weight. Preferably more than 70% by weight can be used.

• 1 ein schematisches Verfahrensschaubild zur Herstellung von Rohstahl.

An exemplary embodiment of the invention is explained in greater detail on the basis of the following description. It shows:

• 1 a schematic process diagram for the production of crude steel.

the 1 shows a schematic process diagram for the production of so-called green crude steel via the direct reduction electric arc furnace route. The crude steel produced has a reduced N content of <60 ppm, preferably <35 ppm. This crude steel production goes hand in hand with reduced CO ₂ emissions compared to the blast furnace-converter route through the use of regenerative energy. The starting point is an energy generation plant 1 , in which regenerative energy in the form of electrical power 2 is generated from solar and / or wind and / or water and / or bioenergy. According to a so-called “Power to Gas” principle, the electricity is generated by means of water electrolysis 2 in an electrolyzer 3 in hydrogen 14th and converted to oxygen. The hydrogen 14th is using a carbonaceous gas 13th from a gas storage tank 15th to a hydrogen-containing gas 4th mixed. Here, the hydrogen-containing gas 4th a volume fraction of more than 50% hydrogen 14th on. Also a hydrogen containing gas 4th without a portion of carbonaceous gas 13th is called a hydrogen-containing gas in this context 4th Roger that. The carbonaceous gas 13th consists at least partially of biogenic gas and / or at least partially of a CO or CO ₂ -containing exhaust gas from production processes. Here, biogenic gas is taken to mean digester gases such as landfill gases, biogases or sewage gases, biomethane and, if necessary, synthetic natural gas (SNG). SNG is synthetically produced natural gas that is produced on the basis of biomass and possibly coal or lignite. The carbonaceous gas 13th can also be a gas of fossil origin, such as natural gas. Preferably the carbon-containing gas is made 13th more than 50% from biogenic gas. The CO or CO ₂ -containing exhaust gases from crude steel production processes are, for example, those that arise in the smelter network, such as converter gas, blast furnace gas or coke oven gas.

The hydrogen-containing gas 4th is used as a reaction gas in a direct reduction plant 5 fed, in which iron ore is used as an iron carrier 6th in the form of pellets, compacted iron-containing residues or lump ore at around 950 ° C to form sponge iron 7th as a starting product is reduced. The sponge iron 7th contains between 60% and 95% iron, which should then be more than 90% metallic. The reaction gas used can consist entirely of hydrogen, depending on availability 14th consist of regenerative processes or are partially or completely replaced by natural gas, biogas and gas from pyrolysis of renewable or fossil raw materials. With an increasing proportion of hydrogen 14th the carbon content in the sponge iron decreases in the reaction gas 7th .

Then the sponge iron 7th an electric arc furnace 9 together with steel scrap 10 and / or supplied to solid or liquid pig iron. In principle, it is also possible to use the electric arc furnace 9 exclusively sponge iron 7th to feed. The proportion is preferably sponge iron 7th as iron girders greater than 50% by weight.

In connection with the production of crude steel in the electric arc furnace 9 using sponge iron 7th that with hydrogen-containing gas 4th as a reaction gas in a direct reduction plant 5 is for a setting of a low nitrogen content of <60 ppm, preferably <35 ppm, in the crude steel 11 In the course of raw steel production, a carbon-containing medium that is as evenly distributed as possible in the furnace vessel 8th necessary. For certain fields of application, for example in the automotive industry, it is important that the steel produced has a low nitrogen content in order to achieve a deep-drawing quality. It is also generally known that higher nitrogen contents in crude steel lead to undesirable aging of the steel products made from it.

The addition of the carbonaceous medium 8th promotes as is known in the production of crude steel in the electric arc furnace 9 the creation and maintenance of a foaming slag layer. The foaming takes place on the one hand by blowing in oxygen and the subsequent reaction with carbon from the carbon-containing medium 8th and on the other hand by a reduction of the metal oxides in the melt by the carbon-containing medium 8th and the resulting gas bubbles in the melt and rising into the slag. The advantages associated with this are known and essentially consist of reduced heat losses from the arc to the side walls of the electric arc furnace 9 , to be seen in an improved heat transfer from the arc to the melt and reduced noise emissions by encasing the arc. Also is in the sponge iron 7th there is always a lower proportion of iron oxide, as it is in the direct reduction plant 5 For economic reasons, no 100% metallization or reduction of the iron ore 6th takes place or the sponge iron after the direct reduction plant 5 oxidized again in the ambient air, at least close to the surface. This proportion of iron oxide in combination with carbon on the sponge iron also favors a uniform foam slag formation. With regard to the reduction in the nitrogen content in crude steel aimed at in the context of the present invention 11 causes the carbonaceous medium 8th together with the foaming and in particular a dense layer of slag, that less contact is achieved between the electrodes or the arc with the nitrogen from the ambient air. This results in an additional nitrogen uptake by the melt in the electric arc furnace 9 reduced. In addition, the rising gas bubbles, in particular carbon monoxide, cause nitrogen and other gaseous impurities such as hydrogen to be driven out of the melt. Among other things, this results in a breakdown of nitrogen in the melt. In this context, an early formation of the foamed slag layer is also aimed for, ideally before the arc has ignited.

In connection with, for example, pneumatic conveying of the sponge iron 7th to the electric arc furnace 9 can the sponge iron 7th Contain nitrogen from the conveying air. This nitrogen can be passed through an argon curtain or flushing the sponge iron 7th with CO or CO2-containing exhaust gas from the electric arc furnace 9 be reduced.

The carbonaceous medium 8th can be fed in at different locations in the course of crude steel production. A feed to the direct reduction plant 5 and / or to the sponge iron 7th and in addition to the electric arc furnace 9 come into question here. The aim here is that the electric arc furnace 9 with respect to the entire sponge iron support 7th and / or steel scrap 10 and / or solid or liquid pig iron and / or the carbon-containing medium 8th a total carbon content of 1 to 6% by weight is supplied. As carbonaceous media 8th Individuals or combinations of the following media are possible: biogenic coal, biogenic mass, biogenic gases, biogenic liquid, synthetic natural gas based on coal, lignite or biomass, carbon from renewable sources and / or carbon from fossil sources (pyrolysis). With a view to reducing the CO ₂ footprint of the crude steel production according to the invention, biogenic or regeneratively produced carbon-containing media are used 8th to prefer. Also, the carbonaceous media 8th selected in such a way that these are already as low in nitrogen as possible (<2%) in order to be able to more easily achieve the inventive goal of reducing nitrogen in the crude steel.

The following are preferred locations for exposure to the carbonaceous media 8th in the course of crude steel production and the preferred carbonaceous media 8th described. Each of the options described can be used on its own or combinations thereof. In addition, the supply of a carbon-containing gas as described above 13th to the direct reduction plant 5 the target total carbon content in the melt is also increased.

The carbon-containing medium is particularly preferred 8th the direct reduction plant 5 at least partially, preferably completely, supplied as a carbonaceous solid, in particular with more than 30% by weight of carbon. Here, the carbon-containing solid is fed into the direct reduction plant, which is usually designed as a shaft furnace 5 in a lower part 5a the direct reduction plant 5 blown in at about 600 to 750 ° C. This creates finely distributed cementite and carbon deposits on the sponge iron 7th .

Alternatively or additionally it can be provided that the sponge iron 7th after the direct reduction plant 5 and in front of the electric arc furnace 9 with the carbonaceous medium 8th is carburized to a carbon content of 0.1 to 6% by weight. The sponge iron is preferred here 7th with the carbonaceous medium 8th coated. The carbonaceous medium 8th is in turn of biogenic or regenerative origin such as biogenic, solid, liquid or gaseous carbon sources (biochar, biogas, etc.) or carbon-containing residues as a by-product from other processes. If necessary, these can be supplemented by carbonaceous media 8th from fossil carbon sources.

In both cases, a sponge iron is created 7th , in which the carbon is evenly distributed in the iron carrier, ie within a batch the fluctuation range of the C content should be below 2 percentage points. As a result, there are no strong fluctuations in the concentration of carbon in the melt, which in turn means that there is no electrical arc furnace 9 a uniform formation of the foamed slag layer and an expulsion of the nitrogen evenly promoted over the entire melt. In addition, the even distribution of carbon in the melt means that there is always enough carbon on the surface of the melt for slag formation. Carbon monoxide is thus advantageously formed just below the slag or on the melt in order to protect the melt from the atmosphere quickly and as completely as possible via the foamed slag. As described above, this happens, if possible, before the arc is formed. Sufficient and evenly distributed carbon ensures that the foam slag layer is continuously maintained after the arc has been formed. Here the sponge iron points 7th advantageously also has a lower density than the melt and therefore does not sink deep into the melt.

In addition, a so-called nitrogen avoidance coefficient (SVK), which is a ratio of the carbon content in sponge iron 7th in% by weight to the density of the sponge iron 7th in g / cm ³ , be as large as possible. At a density of sponge iron 7th from 2 to 4 g / cm ³ and a carbon content of the sponge iron 7th from 0.1 to 6% by weight SVK is 0.025 to 3% cm ³ / g. It is particularly advantageous if the coefficient is related to the biogenic carbon content in the sponge iron 7th is between 0.3 and 1.0.

According to the invention, by binding the carbon-containing medium 8th to the sponge iron 7th before the electric arc furnace 9 is supplied, achieved in an advantageous manner that despite the use of a hydrogen-containing gas 4th in the direct reduction plant 5 a desired increase in the carbon content of the sponge iron 7th is achieved and thus an even distribution of the carbon over the sponge iron 7th in the melt of the electric arc furnace 9 .

The one caused by the addition of the carbonaceous medium 8th to the sponge iron 7th increased carbon content in sponge iron 7th prevents or reduces nitrogen absorption in the sponge iron 7th for example during the transport of the sponge iron 7th between the direct reduction plant 5 and the electric arc furnace 9 , which usually happens in the ambient air and thus under a nitrogenous atmosphere.

The binding of the carbonaceous medium 8th to the sponge iron 7th has the further advantage that with continuous charging of the electric arc furnace 9 with sponge iron 7th the electric arc furnace 9 continually replenishing carbon. This can be done with the lid of the electric arc furnace closed 9 take place, whereby a further protection against ingress of atmosphere is given and a constant short arc results.

The electric arc furnace is also conceivable 9 additionally a carbonaceous medium 8th to feed. This is usually done by blowing in a carbon-containing medium 8th in powder form or is added in lump form. The powder here preferably has a particle size smaller than 5 mm, preferably smaller than 2 mm. Experience has shown that this can only be evenly distributed in the melt with the help of equipment such as rinsing devices. Alternatively or additionally contain the other possible metallic input materials for the electric arc furnace 9 such as scrap steel 10 or solid or liquid pig iron already carbon. It is also possible, as before with the sponge iron 7th also explains a carbonaceous medium 8th to the steel scrap 10 to apply.

Operation of the electric arc furnace is preferred here 9 with a sufficiently large amount of after tapping the raw steel 11 from the electric arc furnace 9 in the electric arc furnace 9 remaining crude steel 11 (Residual steel). The amount of steel left after tapping in the electric arc furnace 9 remains (hot heel practice), is around 20 to 50% of the amount of raw steel tapped 11 . Before charging for the next melt in the electric arc furnace 9 begins, the residual steel becomes the carbonaceous medium 8th supplied as a solid. The raw steel 11 is made in the electric arc furnace 9 Alloyed up to 6% by weight of carbon. The carbonaceous medium 8th is ideally of biogenic origin. The melting point of the residual steel advantageously falls due to the higher carbon content. This means that oxygen can be blown in immediately and the formation of foamed slag starts before the electric arc of the electric arc furnace 9 is ignited. The sponge iron 7th , made with hydrogen containing gas 4th and carburized with the carbonaceous medium 8th , is then charged continuously in this case. An additional separate addition of carbonaceous medium 8th , e.g. B. in the form of injected coal or natural gas, in the electric arc furnace 9 , can then be minimized accordingly or omitted. It has proven to be advantageous to choose the amount of carbon added to the residual steel so that sufficient carbon, preferably more than 1% by weight, for a continuous foam slag in the electric arc furnace 9 is available throughout the entire process.

List of reference symbols

1

Power generation plant

2

electrical current

3

Electrolyzer

4th

hydrogen containing gas

5

Direct reduction plant

5a

lower part

6th

Iron ore

7th

Sponge iron

8th

carbonaceous medium

9

Electric arc furnace

10

Steel scrap

11th

Crude steel

12th

Secondary metallurgy plant

13th

carbonaceous gas

14th

hydrogen

15th

Gas storage

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• WO 2014/040989 A2 [0003]
• US 4834792 [0004]

Claims (14)

Method for producing crude steel (11) using an electric arc furnace (9) with the following steps: - producing sponge iron (7) in a direct reduction plant (5), - feeding the sponge iron (7) to the electric arc furnace (9) at least partially Iron carrier, characterized in that the direct reduction system (5) and / or the sponge iron (7) is supplied with a carbon-containing medium (8, 13) in a preselected amount in order to use the electric arc furnace (9) to produce crude steel (11) with an N- Content of <60 ppm, preferably <35 ppm, to be produced. Procedure according to Claim 1 , characterized in that the sponge iron (7) is coated with the carbon-containing medium (8, 13) after the direct reduction system (5) and before the electric arc furnace (9). Procedure according to Claim 1 or 2 , characterized in that the electric arc furnace (9) is additionally supplied with a carbon-containing medium (8, 13). Procedure according to Claim 3 , characterized in that after the raw steel (11) has been tapped from the electric arc furnace (9), the carbon-containing medium (8, 13) is fed to a raw steel (11) remaining in the electric arc furnace (9). Method according to one or more of the Claims 1 until 4th , characterized in that the carbon-containing medium (8, 13) is supplied from biogenic and / or renewable sources. Method according to one or more of the Claims 2 until 5 , characterized in that the direct reduction system (5) the carbon-containing medium (8) is at least partially fed as a carbon-containing solid. Procedure according to Claim 6 , characterized in that the carbon-containing solid is at least partially blown into the direct reduction system (5) as a powder. Procedure according to Claim 6 , characterized in that the carbon-containing solid is blown into a lower part of the direct reduction plant (5) at about 600 to 750 ° C. Method according to one or more of the Claims 6 until 8th , characterized in that, in addition to the carbon-containing solid, a carbon-containing gas (13) is also fed to the direct reduction system (5) as the carbon-containing medium. Procedure according to Claim 9 , characterized in that the carbon-containing gas (13) is supplied at least partially as a biogenic gas and / or at least partially as a CO or CO ₂ -containing exhaust gas from crude steel production processes. Method according to one or more of the Claims 1 until 10 , characterized in that the electric arc furnace (9) is fed to the electric arc furnace (9) via the iron support and optionally via a carbon-containing medium (8) in a preselected amount of 0.1 to 6% by weight based on the melt. Method according to one or more of the Claims 1 until 11 , characterized in that a hydrogen-containing gas (4) which contains more than 50% hydrogen is fed to the direct reduction system (5) as the reaction gas. Procedure according to Claim 12 , characterized in that the hydrogen-containing gas (4) is generated regeneratively. Method according to one or more of the Claims 1 until 13th , characterized in that the iron support consists predominantly of sponge iron (7).

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