DE102022118640A1 - Process for producing molten iron in an electric melter - Google Patents

Abstract

The invention relates to a method for producing an iron melt (1) in an electric melter (10).

Description

The invention relates to a method for producing iron melt in an electric melter.

Methods and devices for producing iron melts in electric melters are state of the art.

From the DE 600 04 062 T2 a method is known which discloses melting sponge iron in an electric melter. In the electric melter, molten iron and liquid slag are produced from the batch introduced, with additional carbon being blown into the vicinity of the electrodes of the electric melter immersed in the slag with the aim of foaming the liquid slag around the electrodes, thus producing CO and, associated with this, promotes the creation of a plasma arc and thus the productivity of the melter can be increased, and through further addition of oxygen promotes afterburning of CO into CO ₂ and thus more energy can be released in the form of heat. Therefore, the carbon should be blown into the lower third of the liquid slag layer, preferably into the melt-slag interface when blowing in carbon-containing solids. The injected carbon added to foam the slag near the electrodes must be added in addition to the carbon required for charge reduction and metal carburization.

Also the EP 1 025 267 B1 describes a process for melting sponge iron to form a molten iron and a liquid slag located on the molten iron in an electric melter, with additional carbon and oxygen being introduced separately via blowing lances in order to form a stable foamed slag. Furthermore, carbon-containing material in solid, liquid or gaseous form can be fed to the iron melt via the bottom nozzles of the melter.

The state of the art assumes that carbon can be supplied in any form in order to produce a targeted foam slag of the liquid slag through a chemical reaction.

It is also known from the iron carbon diagram that the carbon content in the solid to be melted has a significant influence on the melting temperature and thus also on the enthalpy of fusion of the material. The higher the carbon content (up to 4.7% by weight), the lower the melting temperature and thus also the amount of energy and electrode consumption required in the melter. Low temperatures also mean less wear on the refractory material in the melter. This also results in lower radiation losses and reduced energy consumption.

The object of the present invention is to further develop this method in such a way that no decarburization occurs when melting sponge iron in an electric melter and can therefore provide an iron melt containing sufficient carbon for further process steps.

This task is solved by a method with the features of claim 1. Further refinements are described in the subclaims.

A method for producing an iron melt in an electric melter, containing a vessel and at least one electrode, comprises the steps: - loading the melter with a defined amount of solids containing iron-containing substances and slag formers, the loading taking place locally via several loading points and the vessel of melter is filled, - applying energy to the at least one electrode to melt the solids, the melting being initiated in the area on and/or below the electrode and, in the course of the melting operation, a melting front spreading from the area radially to the wall of the vessel and at least 80 % of the charged solid is melted to form a molten iron and a liquid slag arranged at least partially on the molten iron, - tapping off the liquid slag and the molten iron, the melter being additionally charged with carbon-containing substances during the melting operation, in such a way that the additional carbon-containing substances The resulting carbon causes an enrichment of the carbon content in the iron melt and the iron melt, in particular after tapping, has a higher carbon content compared to the carbon content of the defined amount of charged solids considered in total.

The invention makes use of the fact that the additional carbon-containing substance introduced is specifically introduced in order to increase the carbon content in the iron melt. A high carbon content in the iron melt is necessary, among other things, in order to achieve the desired material properties of the (liquid) slag produced during melting with low levels, preferably in the melter Iron oxide content to be produced as a result of the reduced conditions and in order to preferentially refine the iron melt or pig iron produced in the further course of the process, in particular with regard to the sulfur content and/or phosphorus content, if viewed in the process direction, other existing aggregates, such as in the steelworks of the converter, in can continue to be used economically in a smelter network. Depending on the requirements for the pig iron quality to be produced or the downstream steel production, it makes sense to carburize the iron melt or the resulting pig iron in the electric melter.

The additionally introduced carbon-containing substance is specifically introduced during the melting operation, i.e. some of the solids have already been melted, so that the carbon of the additionally introduced carbon-containing substance diffuses largely into the iron melt and does not become gaseous due to the chemical reactions and does not or only insignificantly combines with oxygen to form CO ₂ and is removed, which would disadvantage the CO ₂ balance of the electric melter.

According to one embodiment, the charging of the carbon-containing aggregate causes an enrichment of the carbon content in the iron melt by at least 0.50% by weight. Depending on the carbon content of the defined amount of solids considered in total, the enrichment can in particular be at least 1.00% by weight, preferably at least 1.50% by weight, preferably at least 2.00% by weight by charging the carbon-containing additive be.

According to one embodiment, the charging of the carbon-containing aggregate is calculated in such a way that a carbon content of at least 3.50% by weight is achieved in the iron melt. The carbon content of the iron melt can in particular be at least 3.60% by weight, 3.70% by weight, 3.80% by weight, preferably at least 3.90% by weight, 4.00% by weight, preferably at least 4.10% by weight, 4.20% by weight.

According to one embodiment, the carbon-containing aggregate is charged via at least one lance, the mouth of the lance being positioned in the solid comprising the sponge iron and optionally the iron-containing additives and/or slag formers. This has the advantage that the carbon-containing aggregate is introduced, for example, into the bed of the solid, so that the carbon of the carbon-containing aggregate can be transferred with the solid into the iron melt by heating and subsequent melting. Furthermore, among other things, the difference in density of the carbon-containing aggregate compared to the iron melt or liquid slag and the reaction times between tappings are taken into account. Another advantage is the mixing caused by forced convection and thus increased diffusivity of the introduced carbon and homogenization of the iron melt.

Depending on whether the vessel of the electric melter is essentially completely emptied or tapped off, or a small part, which has particular advantages when melting the feed material due to the energy contained in the remaining melt and the improved electrical contact via the liquid phase into the melted material remains in the vessel, the defined substances are re-charged so that the solids are applied at least in some areas above the liquid slag and/or molten iron.

As already described, a melting front spreads in the course of the melting operation from the area in which the electrode forces melting through energy input, radially to the wall of the vessel, so that according to a preferred embodiment, the mouth of the lance is positioned in the cohesive zone. The cohesive zone corresponds to the state between solid and liquid, which corresponds essentially in front of or partially to the radially advancing melting front. The melting front or cohesive zone is only temporarily present between charging and tapping during the melting operation, so the time at which the lance is positioned with its mouth should be carefully adjusted. Introducing the carbon-containing aggregate into the cohesive zone has the advantage of promoting a longer reaction time of the introduced carbon and thus a longer residence time of the carbon for carburizing the iron melt due to low flow velocities within the cohesive zone. In addition, floor nozzles, tangential nozzles and/or side wall nozzles can also be arranged for introducing the carbon-containing aggregate into the vessel of the electric melter.

The lance and the optional additional nozzles can be used to optimally adjust (impulse) the flow within the iron melt and thus influence the reaction and diffusion-optimized carburization.

Depending on the operating style of the electric melter or depending on the operating phase (flat bath phase, high bath phase), the flow velocities can be adjusted.

Furthermore, a so-called “SlagSpray” is also possible to increase the service life of the refractory material in the vessel of the electric melter.

According to one embodiment, a solid and/or gaseous carbon-containing aggregate is charged. This can be done via solid additives such as biocoke, coke, coal and/or carbon-containing or hydrocarbon-containing gases, among others. Metallurgical gases, in particular coke oven gas, converter gas, blast furnace gas from electric melters.

The electric melter is preferably an OSBF (Open Slag Bath Furnace) furnace. These include electric reduction furnaces, especially SAF (Submerged Electric Arc Furnace), which are melting furnaces with arc resistance heating that form arcs between the electrode and the solid and/or the slag or which heat the solid and/or the slag using the Joule effect . In SAF, the electrode (or electrodes if there are several) is immersed in the charge and/or slag. Depending on the functional principle/mode of operation, the electric reduction furnaces can be designed as alternating current arc reduction furnaces (SAFac) or direct current arc reduction furnaces (SAFdc). Alternatively, melting furnaces with direct arc action, which deviate from the functional principle/mode of operation described above, so-called EAF (Electric Arc Furnace) can also be used, which form arcs between the electrode and the metal. This includes the AC Arc Melting Furnace (EAFac), the DC Arc Melting Furnace (EAFdc) and the LF (Ladle Furnace).

The advantage of using electric arc resistance heating (SAF) reduction furnaces is that they operate with a reducing atmosphere, whereas direct arc melting furnaces (EAF) operate with an oxidizing atmosphere.

The invention is explained in more detail using the following exemplary embodiments in conjunction with the drawing.

In 1 The invention is explained using the example of an electric melter (10) in a schematic sectional view at different operating times. The electric melter (10) comprises a vessel (15) into which a defined amount of solids (3) containing iron-containing substances and slag formers is charged. Depending on the size of the vessel (15) or the electric melter (10), a central point, for example in the middle, can be provided for loading. In order to fill the vessel (15) of the electric melter (10) with solids, the loading takes place locally via several loading points (12). The electric melter (10) can comprise a lid (18), which can close the vessel (15) at the top and can thus be set within a defined or targeted atmosphere. The cover (18) is arranged to be essentially vertically movable, see double arrow. If a lid (18) is present, the loading points (12) are openings in the lid (18) with corresponding supply lines. The required solids (3) can be supplied via means not shown. After the solids (3) have been charged, so-called bulk cones can form in the vessel (15) below the charging points. In the illustration above 1 is shown by way of example that tapping has not been completed and the bottom of the vessel (15) is therefore covered with molten iron (1) and/or liquid slag (2). The iron melt (1) to be produced results from the defined amount of solids (3) introduced.

The solids (3) contain iron-containing substances, preferably sponge iron. In addition, other iron-containing materials, such as iron-containing scrap, can also be added to improve the recycling rate. The slag formers, for example lime, silicon dioxide, magnesium oxide and/or aluminum oxide, are mixed in, particularly if the so-called gangue of the sponge iron preferably used is not sufficient to set the desired basicity of the liquid slag (2) to be tapped off. This measure is familiar to those skilled in the art.

If the defined amount of solids (3) has been introduced and at least one, in this exemplary embodiment there are three, electrodes (11), the number of electrodes (11) being selected essentially depending on the dimension of the electrical melter (10), supplied with energy to melt the solids (3). The positioning of the electrode (11) can be adjusted vertically, preferably in order not to allow an arc to arise between the solid (3) and the electrode (11), with at least one immersion of the electrode tip in the solid (11) being preferably provided, see double arrow . The energy required for melting can preferably have been generated from renewable energy (sun, wind, water) in order to be able to reduce the CO ₂ balance of the electrical melter (10).

In the middle representation of the 1 it is shown that the melting is initiated in the area (X) at and/or below the electrode (11). and in the course of the melting operation, a melting front spreads radially from the area (X) to the wall of the vessel (15) and at least 80% of the charged solid (3) forms a molten iron (1) and at least partially arranged on the molten iron (1). Liquid slag (2) is melted.

The preferred use of sponge iron as an iron-containing substance, depending on its production and depending on whether iron ore is produced using carbon-containing gas, for example CO, or hydrocarbon-containing gas, for example CH ₄ or natural gas, or hydrogen-containing gas, for example H ₂ , or mixtures thereof in one Direct reduction process to sponge iron has been reduced, varying and low carbon contents. The person skilled in the art is aware of this fact and usually supplies carbon-containing substances via the feed before the melting operation. The invention provides for the melter (10) to be additionally charged with carbon-containing substances during the melting operation, such that the carbon resulting from the additional carbon-containing substances causes an enrichment of the carbon content in the iron melt (1) and the iron melt (1) has a higher one Carbon content in comparison to the carbon content of the defined amount of solids (3) considered in total, in particular before the melting operation. The charging of the carbon-containing aggregate should result in an enrichment of the carbon content in the iron melt (1) by at least 0.50% by weight. The charging of the carbon-containing aggregate is calculated in such a way that a carbon content in the iron melt (1) of at least 3.50% by weight is achieved.

The carbon-containing aggregate can be charged using at least one lance (13, 13.1), the mouth of the lance (13, 13.1) being positioned in the solid (3). The lance (13, 13.1) can be arranged to be movable, see double arrow. The lance (13) can, for example, be immersed in the solid (3) via the loading point (12) or via an opening in the side wall of the vessel (15). The mouth of the lance (13, 13.1) is particularly preferably positioned in a cohesive zone (4). The carbon-containing aggregate can be charged in solid and/or gaseous form. If a solid form is chosen, a carrier gas, which preferably has a carbon-containing component, can promote charging.

The lower representation of the 1 shows the end of the melting operation, so that the solid (3) has been essentially completely melted into iron melt (1) and liquid slag (2) arranged thereon. The process gas generated during melting operation is discharged via at least one opening (14). The liquid slag (2) is tapped via at least one tap hole (16) and the iron melt (1) via at least one tap hole (17) and the vessel (15) can be charged again with solids (3), see the illustration above 1 .

2 shows a schematic top view of the electric melter (10) or cover (18) according to the version in 1 . The three electrodes (11) are arranged relatively centrally and the loading points (12) are distributed locally at a radial distance from the electrodes (11). The four loading points (12) shown as examples are arranged in a circle in 90° steps. Arranged in a circle in further 90° increments and, for example, four openings (14) are provided between the loading points (12) for discharging the process gas.

Not shown, nozzles can be arranged in the vessel (15) to influence the movement of the iron melt (1). The electric melter (10) can be pivoted to enable tilting and thus tapping of liquid slag (2) in one direction and molten iron (1) in the other direction. The person skilled in the art is also familiar with the operation of electrical melters (10).

It is also not shown how the molten iron (1) is removed and fed to a further processing step. The iron melt (1) is preferably treated in order to reduce the carbon in the iron melt to a desired level. This is done, for example, using oxygen in a so-called oxygen blowing process, particularly preferably in a converter. The tapped liquid slag (2) is also preferably fed to granulation in order to produce slag, particularly for the construction industry.

In one exemplary embodiment, 100 kg of sponge iron from a direct reduction using 100% hydrogen as the reducing gas were used in a laboratory-scale SAF. The total carbon content introduced via the solids was therefore less than 0.30% by weight. Slag formers were not added. The melting front was recorded using measurements and 4 kg of coal particles with a grain size < 0.30 mm and with N ₂ as carrier gas were specifically charged, using an injection lance that was preferably protected from fire, the mouth of which was positioned in the cohesive zone. After the smelting operation, a carbon content of 4.45% by weight was determined in the iron melt. The determination of the carbon content is known to those skilled in the art.

QUOTES INCLUDED IN THE DESCRIPTION

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Cited patent literature

• DE 60004062 T2 [0003]
• EP 1025267 B1 [0004]

Claims (6)

Method for producing an iron melt (1) in an electric melter (10), containing a vessel (15) and at least one electrode (11), comprising the steps: - feeding the melter (10) with a defined amount of solids (3) containing iron-containing substances and slag formers, the charging taking place locally via several charging points (12) and the vessel (15) of the melter (10) being filled, - applying energy to the at least one electrode (11) to melt the solids (3), wherein the melting is initiated in the area (X) on and/or below the electrode (11) and in the course of the melting operation a melting front spreads radially from the area (X) to the wall of the vessel (15) and at least 80% of the charged solid ( 3) is melted to form a molten iron (1) and a liquid slag (2) arranged at least partially on the molten iron (1), - tapping off the liquid slag (2) and the molten iron (1), characterized in that the melter (10) is additionally charged with carbon-containing substances during the melting operation, such that the carbon resulting from the additional carbon-containing substances causes an enrichment of the carbon content in the iron melt (1) and the iron melt (1), in particular after tapping, has a higher carbon content compared to the carbon content of the defined amount of charged solids (3) considered in total. Procedure according to Claim 1 , whereby the charging of the carbon-containing aggregate causes an enrichment of the carbon content in the iron melt (1) by at least 0.50% by weight. Method according to one of the preceding claims, wherein the charging of the carbon-containing aggregate is dimensioned such that a carbon content in the iron melt of at least 3.50% by weight is achieved. Method according to one of the preceding claims, wherein the carbon-containing aggregate is charged via at least one lance (13, 13.1), the mouth of the lance (13, 13.1) being in the solid (3) comprising the sponge iron and optionally the iron-containing additives and/or or slag former is positioned. Procedure according to Claim 4 , whereby the mouth of the lance (13, 13.1) is positioned in a cohesive zone (4). Method according to one of the preceding claims, wherein a solid and/or gaseous carbon-containing aggregate is charged.