RU2819943C1 - Production of steel from molten iron - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method involves production of sponge iron (10) from initial material (11) containing iron oxides by direct reduction with reducing gas (13). Reducing gas (13) consists of at least 20 vol.% hydrogen H₂. Molten iron with carbon content of 1–5 wt.% is obtained from sponge iron (10). At that, sponge iron is subjected to treatment, which includes supply of energy and introduction of additives to create melt and slag, control of carbon content in melt and reduction of at least part of iron oxides contained in sponge iron. Wherein the energy supply is essentially performed in the form of electrical energy, and power supply performed by electric energy is performed by means of electric arc and electric resistive heating. Slag (60) has basicity B2 less than 1.3. Slag is separated during and/or after treatment. Steel is obtained from molten iron formed in this way.

EFFECT: obtaining steel with reduced emission of CO₂.

12 cl, 1 dwg

Description

Field of technology to which the invention relates

The invention relates to a method for producing steel with the production of molten iron using sponge iron formed by direct reduction under the action of a reducing gas.

State of the art

Modern steel production is largely based on the use of a blast furnace process followed by a LD/BOF steelmaking plant. With this process approach, a wide range of iron ores can be processed, as the contained gangue can be removed in slag form with negligible iron loss in the blast furnace, and a subsequent BOF process can produce high quality, universally applicable unalloyed iron ores. steel.

A much smaller proportion of steel production is based on direct reduction by reducing gas to produce sponge iron, also called direct reduced iron (DRI), followed by electric arc furnace (EAF) steel production. In this case, compared to the blast furnace process, it is necessary to use higher-grade raw materials with a low gangue content in order to limit the amount of slag generated in traditional EAF, thereby limiting iron losses and energy and raw material costs. The traditional electric arc furnace also requires a high degree of metallization of the sponge iron. Process-wise, the quality of unalloyed steel also tends to be lower; therefore, in order to achieve comparable levels of steel quality, it is necessary to carry out expensive post-treatments on the unalloyed steel produced in the EAF.

To reduce industrial CO ₂ emissions, it is desirable to reduce the share of the blast furnace process in the volume of total steel production, since it is based on the use of coal, respectively, coke. Increasing the share of direct reduction in global steel production is in principle proposed as a trade-off since it could also be accommodated by a lower CO ₂ emitting approach - for example using reducing gas based on natural gas or hydrogen. However, the disadvantages associated with this approach in relation to the blast furnace process limit the potential for reorienting steel production towards direct reduction.

The essence of the invention

Technical challenge

The objective of the invention is to create a method and device by means of which these disadvantages are eliminated, accordingly, their scope can be at least reduced.

Technical solution

This problem is solved by means of a method for producing steel,

including

- producing sponge iron from a starting material containing iron oxides by direct reduction with a reducing gas, wherein the reducing gas consists of at least 20 vol.% hydrogen H ₂ ,

and

- producing molten iron with a carbon content of 1-5 wt.%, and at least part of the sponge iron obtained by direct reduction with a reducing gas from a starting material containing iron oxides is subjected to processing,

wherein the processing includes:

- supplying energy and introducing additives to create a melt and slag, wherein the energy supply is carried out essentially in the form of electrical energy, and wherein the slag has a B2 basicity of less than 1.3, preferably less than 1.25, especially preferably less than 1.2,

- regulation of carbon content in the melt,

- reduction of at least part of the iron oxides contained in sponge iron,

and wherein during and/or after the treatment the slag is separated,

and

- use of molten iron to produce steel.

The method involves direct reduction, which occurs through a reducing gas that is at least 20 vol.% hydrogen. Thus, steel production can be carried out with less CO ₂ emissions than when using a blast furnace process to reduce the starting material containing iron oxides, or performing direct reduction with a low amount of hydrogen. Direct reduction is carried out without the addition of solid carbon, or solid carbon-containing materials, as a reducing agent.

Direct reduction occurs in a direct reduction reactor, which, for example, can be configured as a fixed bed reactor or a fluidized bed reactor or a fluidized bed reactor.

The higher the hydrogen content of the direct reduction gas, the lower the carbon content of the sponge iron becomes.

This affects the temperature range of the melting process during processing. This also affects the amount of carbon emissions generated by the respective steelmaking process, and this can also affect the carbon content of the resulting steel.

The processing according to the invention is a bath process and not a fixed bed process. It is designed to use sponge iron from the direct reduction method to obtain a product similar to the blast furnace product - liquid cast iron. This liquid product must have a carbon content of between 1-5% by weight, both extremes of this range being included. The percentage by weight - wt.% - denotes the mass fraction. To do this, energy is supplied to the sponge iron and additives are introduced, which leads to the formation of slag based on the gangue contained in the sponge iron from the original ore. The additives are, for example, limestone and/or dolomite, both of which can be unfired or, preferably, burnt quartz. The slag has a B2 basicity of less than 1.3, preferably less than 1.25, particularly preferably less than 1.2. This kind of slag is similar to blast furnace slag, and can accordingly be used, for example, in the cement industry. The lower the basicity, the smaller the amount of slag produced, whereby the implementation of the method according to the invention also becomes energetically more favorable.

Basicity B2 means the ratio of calcium oxide to silicon dioxide CaO/SiO ₂ in mass percent.

When obtaining molten iron, sponge iron is processed.

Sponge iron may be used as the source of iron in the molten iron in combination with other iron sources such as scrap or cast iron, or sponge iron alone may be used as the source of iron in the molten iron.

The carbon content in the melt is adjusted to the desired level - the molten iron obtained according to the method should have a carbon content of 1-5 wt.%, and adjustment is carried out accordingly;

for example, by introducing carbon sources into the melt and/or by introducing means to reduce the carbon content of the melt, such as oxygen.

The treatment also includes reducing at least a portion of the iron oxides contained in the sponge iron to metallic iron such that the amount of metallic iron in the melt becomes greater than that in the original sponge iron; this occurs during and/or after the application of energy.

The energy supply is essentially in the form of electrical energy. In this case, it is generally understood that at least more than 50% of the input energy, preferably more than 65% of the input energy, especially preferably more than 80% of the input energy are supplied.

More specifically, with an increase in the proportion of electrical energy in the generation of current using renewable energy sources, the CO ₂ balance of the process, respectively, of the steel produced from the liquid iron product, is thereby improved.

In the blast furnace process, the formed slag is separated from the pig iron, for example, for which the pig iron and slag are tapped, and separated by gravity, taking advantage of their mutual insolubility in each other and different densities. According to the claims, the slag is separated during and/or after processing. The melt is obtained as a liquid cast iron product with a carbon content of 1 wt.% to 5 wt.%. Slag removal is carried out, for example, by draining while tilting. By separating the slag, which is formed from the gangue and additives contained in the sponge iron, the gangue present in the iron oxide-containing raw material is removed.

The molten iron obtained according to the invention with a carbon content of 1.0 wt.% to 5 wt.% consists mainly of iron - it is a liquid cast iron product; The expression "liquid iron product" in the present application is used synonymously with the name "molten iron" for the molten iron formed according to the invention. Liquid cast iron product with carbon content from 1 wt.% to 5 wt.%. from the point of view of the method of steel production - for example, LD/BOF - is similar to blast furnace cast iron, that is, it can, in principle, be processed in the same way as blast furnace cast iron, that is, with the subsequent production of steel without the blast furnace process. The higher the carbon content, the more cold scrap can be used in subsequent processing into steel; the increased amount of cold scrap reduces CO ₂ emissions per unit amount of steel formed from the liquid iron product obtained according to the invention.

The carbon content of the liquid iron product is preferably at least 1.25% by weight, particularly preferably at least 1.5% by weight. The carbon content of the liquid iron product is preferably up to 4 wt%, particularly preferably up to 3.5 wt%, most preferably up to 3 wt%.

When performing the method according to the invention, it may be preferable to load the sponge iron into a ladle in which there is already a small amount of sponge iron as a slurry (residue); for example, this residue when emptying the ladle remains after the previous implementation of the method according to the invention, but it can also come from another source, for example cast iron, which, for example, is obtained in a blast furnace.

Useful results of the invention

The invention opens up the possibility, starting from sponge iron, to produce steel efficiently and economically without using the traditional EAF process (electric arc process) on an industrial scale. In this case, steel production technologies known for cast iron can be used.

The traditional EAF process for steel production is carried out under oxidizing conditions to reduce carbon content at high temperature and high basicity. In sponge iron, a higher degree of metallization and a lower gangue content are required to keep the loss of iron to iron oxides in the slag low. Therefore, the use of high-quality iron sources is required when producing sponge iron fed into the traditional EAF process - with "high-quality" meaning that the iron sources contain a small amount of gangue; The less waste rock is added to the EAF by sponge iron, the less slag is added to the EAF. The smaller the amount of slag, the less iron can be lost as iron oxide. The higher the degree of metallization, the less iron oxides are contained in the sponge iron, accordingly, the risk of loss of iron oxides with the slag is correspondingly reduced.

In the process mode according to the invention, carbon is present; In this way, at least part of the iron oxides contained in the sponge iron can be reduced with carbon, with the result that the sponge iron used can also be used at a lower degree of metallization compared to the conventional EAF process. Thanks to iron oxide reduction, iron losses due to iron oxides contained in the slag are reduced compared to the processing of sponge iron in traditional EAF.

As a result of the presence of carbon in the melt, the temperature range of the smelting process, that is, the temperature range in which the iron product changes from a solid to a liquid state of aggregation, can also be reduced, thereby requiring less energy input for melting. This means that the production of steel starting from sponge iron using the process according to the invention requires comparatively less energy consumption than in the case of the traditional EAF process.

To create a cast iron product, it is not necessary to adjust the slag basicity to such a high value as for the traditional EAF process, since the main purpose of the process, unlike the traditional EAF process, is not to produce steel. Accordingly, in sponge iron-based steel production using the process according to the invention, less slag is generated than in the traditional EAF process - accordingly, sponge iron can be processed with a higher gangue content from lower quality raw materials at a comparable rate to traditional EAF - process amount of slag. That is, the smaller amount of slag compared to the traditional EAF process is facilitated by the fact that the approach according to the invention is carried out with a lower slag basicity and thus with fewer additives, since, compared to the EAF process, the focus is more on waste rock removal, rather than improving the quality of steel. Less slag also means less energy required for heating and therefore melting, since less material needs to be heated. The method according to the invention is preferably carried out with a B2 basicity below 1.3, particularly preferably with a B2 basicity below 1.25, most preferably with a B2 basicity of 1.2.

When using the method according to the invention, a wide range of iron ores can be processed, since part of the waste rock is removed in the form of slag with less iron loss already upon obtaining a liquid iron product with a carbon content of 1.0% - 5%. Thus, the processing stages of the liquid cast iron product when producing steel are not burdened by the already removed slag. In contrast, the traditional EAF process for recycling sponge iron is burdened with clearly large quantities of slag.

Since the liquid iron product with a carbon content of 1.0 wt.% to 5 wt.% in the subsequent steelmaking process - for example, LD/BOF - can basically be processed in the same way as blast furnace iron, steel with appropriate quality characteristics and universal application possibilities; In this way, the related limitations caused by the use of the traditional EAF process can be overcome and costly additional treatments can therefore be avoided.

According to one preferred embodiment of the method, direct reduction is carried out with a reducing gas consisting of more than 45 vol.% hydrogen H ₂ . The higher the hydrogen content, the lower the CO ₂ balance of the method according to the invention becomes, respectively, of the steel obtained from the liquid cast iron product.

According to one preferred embodiment, the direct reduction is carried out in a direct reduction reactor, and the processing in a processing reactor, the direct reduction reactor and the processing reactor being spatially separated from each other. The sponge iron can be transferred from the direct reduction reactor to the treatment reactor by means of a conveyor.

It is also possible to place the direct reduction reactor and the processing reactor in a common device, that is, directly adjacent, without spatial separation from each other.

According to one preferred embodiment, the energy is supplied via an electric arc.

According to one preferred embodiment, the energy supply is via electrical resistance heating. In this case, for example, we can talk about carrying out electrolysis.

According to one preferred embodiment, the energy is supplied via an electrically generated hydrogen plasma.

According to one preferred embodiment, the energy supply is produced in part by introducing oxygen to gasify carbon introduced into the melt in a solid or liquid state, or carbon dissolved in the melt. In practice, this is done, for example, by means of a burner or with the help of oxygen supply lances.

Preferably, oxygen is introduced which is at least commercially pure.

According to one preferred embodiment, the carbon content of the melt is controlled by means of input carbon sources.

In this case, we can talk about solid carbon sources and/or liquid carbon sources and/or gaseous carbon sources. Carbon sources may include, for example, coal dust, breeze coke, pulverized graphite, or natural gas. Carbon sources may also be partly or wholly derived from fixed carbon sources (carbon neutral), for example from biomass, such as charcoal; this improves the CO ₂ balance of the process. For example, carbon sources can be introduced through supply tubes or nozzles in the bottom of the bath.

According to one preferred embodiment, the carbon content in the melt is controlled by introducing oxygen. If the carbon content is to be higher than the desired value for the molten iron, an oxidative reduction in the carbon content can be achieved by introducing oxygen, for example, the carbon in the melt can react to form CO and escape from the melt in a gaseous state.

According to one preferred embodiment, the reduction of at least part of the iron oxides contained in the sponge iron is carried out by introducing carbon sources.

These may be solid carbon sources and/or liquid carbon sources and/or gaseous carbon sources. For example, carbon sources may include coal dust, breeze coke, pulverized graphite, or natural gas. Carbon sources may also be partly or wholly derived from carbon-neutral sources, such as biomass, such as charcoal; this improves the CO ₂ balance of the process.

According to one preferred embodiment, the reduction of at least part of the iron oxides contained in the sponge iron occurs via the carbon present in the sponge iron.

Carbon may be present in sponge iron, for example in the form of cementite (Fe ₃ C), bound and/or dissolved, and/or as elemental carbon.

According to one preferred embodiment, the reduction of at least part of the iron oxides contained in the sponge iron is carried out, at least in part, by means of an electric current. This can be done, for example, under electrolysis conditions, or using hydrogen plasma.

According to one preferred embodiment, the treatment reduces the melting region by introducing solid carbon sources and/or liquid carbon sources and/or gaseous carbon sources. We are talking, for example, about coal dust, coke breeze, pulverized graphite, and natural gas. Carbon sources may also be partly or wholly derived from carbon-neutral sources, such as biomass, such as charcoal; this improves the CO ₂ balance of the process. The reduction should be understood in comparison with the melting point of iron. The method according to the invention is preferably carried out at a temperature below 1550ºC, preferably below a temperature of 1500ºC, especially preferably at a temperature below 1450ºC.

According to one preferred embodiment, the LD/BOF process is used to produce steel. This is preferably carried out with the addition of scrap in an amount of at least 10% by weight, preferably at least 15% by weight, particularly preferably at least 20% by weight.

An additional object of the present application is a signal processing device with machine-readable program code, which has control instructions for executing the method according to the invention. A further aspect of the present application is computer readable program code for such a signal processing device, wherein the program code has control instructions that cause the signal processing device to execute the method of the invention. An additional object of the method according to the invention is a storage medium with such machine-readable program code stored therein.

Brief description of drawings

The invention will now be explained in more detail using examples of execution. The drawing is exemplary and is intended to represent exactly the essence of the invention, but in no way limit or depict it as final. As shown:

Fig. 1 is a schematic representation of the method according to the invention.

Brief Description of Embodiments of the Invention

Examples

Fig. 1 schematically shows the process for producing molten iron according to the invention. The sponge iron 10 is produced from the iron oxide-containing starting material 11 by direct reduction in a direct reduction reactor 12 by means of a reducing gas 13. The reducing gas 13 consists of at least 20 vol.% hydrogen H ₂ . The sponge iron 10 is introduced into the treatment reactor 20. It is processed in the treatment reactor 20. The processing involves the supply of energy, which is represented by arrow 30. The supply of energy is substantially in the form of electrical energy.

The processing includes the introduction of additives 40. During processing, a melt 50 and slag 60 are formed. The slag has a basicity B2 of less than 1.3.

The processing includes adjusting the carbon content in the melt 50; for example, this is represented by the addition of 70 carbon sources.

The treatment involves reducing at least a portion of the 10 iron oxides contained in the sponge iron.

During and/or after processing, slag 60 is removed, which is not more specifically shown. Melt 50 is a desired molten iron with a carbon content of 1-5 wt.%. For example, as represented by the dotted arrow, it may be sent to the converter 80 to produce steel using the LD process using a blow lance 90.

The sponge iron 10 is produced from the iron oxide-containing raw material by direct reduction through a reducing gas; wherein the reducing gas consists, for example, of at least 20 vol.% hydrogen.

The direct reduction is carried out in a direct reduction reactor, and the processing is carried out in a treatment reactor 20. The direct reduction reactor and the treatment reactor 20 can be spatially separated from each other, and the sponge iron can be transferred from the direct reduction reactor to the treatment reactor via a conveyor.

It is also possible to place the direct reduction reactor and the processing reactor 20 in a common device, that is, directly adjacent, without spatial separation from each other.

List of reference items

10 sponge iron

11 iron oxide containing raw material

12 direct reduction reactor

13 reducing gas

20 processing reactor

30 power supply

40 supplements

50 melt

60 slag

70 carbon source

80 converter

90 blow lance

Claims (27)

1. Method of producing steel, including - producing sponge iron (10) from a starting material (11) containing iron oxides by direct reduction with a reducing gas (13), wherein the reducing gas (13) consists of at least 20 vol.% hydrogen H ₂ , and - producing molten iron with a carbon content of 1-5 wt.%, and at least part of the sponge iron (10), obtained by direct reduction with a reducing gas (13) from a starting material (11) containing iron oxides, is subjected to processing, wherein the processing includes: - supply of energy and introduction of additives to create a melt (50) and slag (60), wherein the energy supply is essentially performed in the form of electrical energy, and the energy supply performed essentially by electrical energy is produced by means of an electric arc and electric resistance heating, and wherein the slag (60) has a ratio of calcium oxide to silica CaO/SiO ₂ in percent by weight, designated as basicity B2, less than 1.3, preferably less than 1.25, especially preferably less than 1.2, - regulation of carbon content in the melt (50), - reduction of at least part of the iron oxides contained in the sponge iron (10), and wherein during and/or after the treatment the slag (60) is separated, and - use of molten iron to produce steel. 2. Method according to claim 1, characterized in that direct reduction is carried out with a reducing gas (13) consisting of more than 45 vol.% hydrogen H ₂ . 3. Method according to claim 1 or 2, characterized in that the direct reduction is carried out in a direct reduction reactor (12), the processing is carried out in a treatment reactor (20), and the direct reduction reactor (12 and the treatment reactor (20) are spatially separated from each other from friend. 4. Method according to any one of paragraphs. 1-3, characterized in that the energy is supplied through hydrogen plasma created by an electric current. 5. Method according to any one of paragraphs. 1-4, characterized in that the energy supply is partially produced by introducing oxygen for gasification of carbon introduced into the melt (50) in a solid or liquid state, or carbon dissolved in the melt. 6. Method according to any one of paragraphs. 1-5, characterized in that regulation of the carbon content in the melt (50) is carried out by means of input carbon sources (70). 7. Method according to any one of paragraphs. 1-6, characterized in that regulation of the carbon content in the melt (50) is carried out by means of introduced oxygen. 8. Method according to any one of paragraphs. 1-7, characterized in that the reduction of at least part of the iron oxides contained in sponge iron (10) is carried out by means of introduced carbon sources (70). 9. Method according to any one of paragraphs. 1-8, characterized in that the reduction of at least part of the iron oxides contained in the sponge iron (10) occurs through the carbon contained in the sponge iron (10). 10. Method according to any one of paragraphs. 1-9, characterized in that the reduction of at least part of the iron oxides contained in the sponge iron (10) is carried out, at least in part, using an electric current. 11. Method according to any one of paragraphs. 1-10, characterized in that during processing the melting area is reduced by introducing solid carbon sources (70), and/or liquid carbon sources (70), and/or gaseous carbon sources (70). 12. Method according to any one of paragraphs. 1-11, and when producing steel, the LD/BOF method is used.