AU2023316006A1 - Method for producing an iron melt in an electric fuser - Google Patents

Abstract

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

Description

Method for producing an iron melt in an electric fuser

The invention relates to a process for producing an iron melt in an electrical smelter.

Processes and apparatuses for production of iron melts in electrical smelters are prior art.

DE 600 04 062 T2 discloses a process that discloses smelting of iron sponge in an electrical

smelter. In the electrical smelter, iron melt and liquid slag are produced from the charge in

troduced, with additional blowing of carbon into the vicinity of the electrodes of the electrical smelter immersed into the slag, with the aim of foaming the liquid slag around the electrodes,

hence enabling generation of CO, and the associated formation of a plasma light arc, and hence an increase in the productivity of the smelter, and promoting postcombustion of CO to

CO2 by further addition of oxygen and hence release of more energy 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 carbonaceous solids are blown in. The carbon blown in, which is added for foaming of the slag in the vicinity of the electrodes, has to be introduced

in addition to the carbon required for the reduction of the charge and carburization of the

metal.

EP 1025 267 B1 also describes a process for smelting iron sponge to form an iron melt and a liquid slag present on the iron melt in an electrical smelter, where carbon and oxygen are

additionally also introduced separately via blowing probes in order to form a stable foam slag. In addition, carbonaceous material in solid, liquid or gaseous form can be fed to the iron melt

via nozzles in the base of the smelter.

The starting point from the prior art is to feed in carbon in any form in order to create a con

trolled foam slag of the liquid slag by chemical reaction.

It is also known from the iron-carbon diagram that the carbon content in the solids to be

smelted has a significant effect on the melting temperature and hence 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 hence also the amount of energy required or else electrode con sumption in the smelter. Lower temperatures also mean lowerwearto the refractory material in the smelter. These additionally also result in lower radiation losses and reduced energy consumption.

It is an object of the present invention to further develop this process such that it does not bring about any decarburization in the melting of iron sponge in an electrical smelter and

hence can provide sufficient carbonaceous iron melt for further process steps.

Said object is achieved by a method having the features of claim 1. Further configurations are

described in the dependent claims.

A process for producing an iron melt in an electrical smelter, containing a vessel and at least one electrode, comprises the steps of: - charging a smelter with a defined amount of solids

comprising iron-containing materials and slag formers, where the charging is effected locally via one or more charge points and the vessel of the smelter is filled, - supplying the at least

one electrode with energy to melt the solids, where the melting is initiated in the region at

and/or below the electrode and a melting front spreads radially from the region to the wall of the vessel in the course of melting operation, and at least 80% of the charged solids is melted

to form an iron melt and a liquid slag disposed at least over some regions of the iron melt, tapping the liquid slag and the iron melt, wherein the smelter is additionally charged with

carbonaceous materials during melting operation in such a waythat the carbon resulting from the additional carbonaceous materials results in an increase in the carbon content in the iron

melt, and the iron melt, especially aftertapping, has a higher carbon content compared to the carbon content of the defined amount of charged solids considered overall.

The invention makes use of the fact of controlled introduction of the carbonaceous material additionally introduced in order to increase the carbon content in the iron melt. Reasons for

the need for a high carbon content in the iron melt are in order to preferably establish the

desired physical properties of the (liquid) slag produced on smelting with a low iron oxide content as a result of the reduced conditions in the smelter, and in order preferably to refine the iron melt or raw iron produced later on in the process, especially with regard to sulfur content and/or phosphorus content, when, considered in process direction, further existing aggregates, for example the converter in a steelworks, in an integrated smelter, are to con tinue to be utilized economically. It is thus advisable, depending on the requirement on the raw iron quality to be produced or downstream steel production, to carburize the iron melt or the raw iron resulting therefrom in the electrical smelter.

The additionally introduced carbonaceous material is introduced in a controlled manner dur

ing melting operation, meaning that some of the solids have already melted, such that the carbon in the carbonaceous material additionally introduced has very substantially diffused

into the iron melt and has not become gaseous as a result of the chemical reactions, and is bound only insignificantly, if at all, with oxygen to form CO 2 and removed, which would impair

the CO 2 balance of the electrical smelter.

In one configuration, the charging of the carbonaceous admixture results in an increase in the carbon content in the iron melt by at least 0.50% by weight. According to the carbon content

of the defined amount of solids considered overall, the increase may especially be at least

1.00% by weight, preferably at least 1.50% by weight, more preferably at least 2.00% by weight, as a result of the charging of the carbonaceous admixture.

In one configuration, the carbonaceous admixture is charged so as to establish a carbon con

tent in the iron melt of at least 3.50% by weight. The carbon content of the iron melt may especially be at least 3.60% by weight, 3.70% by weight, 3.80% by weight, preferably at least

3.90% byweight, 4.00% byweight, more preferably at least 4.10% byweight, 4.20% by weight.

In one configuration, the carbonaceous admixture is charged via at least one probe, wherein

the mouth of the probe is positioned in the solids comprising the iron sponge and optionally the iron-containing additives and/or slag formers. This has the advantage that the carbona

ceous admixture is introduced, for example, into the bed of solids such that the carbon in the

carbonaceous admixture can be transferred into the iron melt with the solids via heating and subsequent smelting. In addition, moreover, among other factors, the difference in density of the carbonaceous admixture by comparison with the iron melt or liquid slag and the reaction times between the tapping operations are taken into account. A further advantage is the mix ing caused by forced convection, and hence increased diffusion capacity of the carbon intro duced and homogenization of the iron melt.

According to whether the vessel of the electrical smelter is essentially completely emptied or tapped, or a small portion remains in the vessel, which especially has advantages in the melt

ing of the starting material owing to the energy present in the remaining melt and the im

provement in electrical contact via the liquid phase into the melt, the defined substances are charged again such that the solids are applied at least in regions above the liquid slag and/or

iron melt.

As already outlined, a melting front forms radially to the wall of the vessel in the course of melting operation from the region in which the electrode forces meltingto occurvia introduc

tion of energy, such that, in a preferred configuration, the mouth of the probe is positioned in the cohesive zone. The cohesive zone corresponds to the state between solid and liquid, which

corresponds essentially before or partly to the radially advancing melt front. The melt front or

cohesive zone is present only temporarily between charging and tapping during melting oper ation, such that the time of positioning of the probe with its mouth should be adjusted in a

controlled manner. The introduction of the carbonaceous admixture into the cohesive zone has the advantage, owing to a low flow rate within the cohesive zone, of promoting a longer

reaction time of the carbon introduced and hence a longer dwell time of the carbon for car burization of the iron melt. In addition, it is also possible for base nozzles, tangential nozzles

and/or sidewall nozzles to be disposed in the vessel of the electrical smelter for introduction of the carbonaceous admixture.

By means of the probe and the optional additional nozzles, it is possible to optimize the (pulsed) flow within the iron melt and hence to influence reaction- and diffusion-optimized

carburization.

The flow rates may be adjusted according to the mode of operation of the electrical smelter,

or according to the phase operation (flat bath phase, high bath phase).

In addition, a "slag spray" is also possible for increasing the service lives of the refractory ma

terial in the vessel of the electrical smelter.

In one configuration, wherein a solid or gaseous carbonaceous admixture is charged. This can

be effected via solid admixtures, for example biocoke, coke, charcoal and/or carbonaceous or

hydrocarbonaceous gases, including foundry gases, especially coking furnace gas, converter gas, top gas from electrical smelters.

The electric smelter is preferably a furnace of the OSBF (Open Slag Bath Furnace) type. This

includes electric reduction furnaces, especially SAFs (Submerged Electric Arc Furnaces), which are smelting furnaces with arc resistance heating which form arcs between the electrode and

the solid and/or the slag or which heat the solid and/or the slag by means of the Joule effect. In the SAF, the electrode is (or the electrodes are, if there are multiple) immersed in the charge

and/or slag. Depending on the principle of function/mode of operation, the electric reduction

furnaces can be configured as AC submerged arc furnaces (SAFac) or DC submerged arc fur naces (SAFdc). Alternatively, it is also possible to use smelting furnaces with direct arc action,

known as EAFs (Electric Arc Furnaces), which differ from the principle of function/mode of operation described above and form arcs between the electrode and the metal. This includes

the AC electric arc furnace (EAFac), the DC electric arc furnace (EAFdc) and the ladle furnace (LF).

The advantage of using electric reduction furnaces with arc resistance heating (SAFs) is that

they are operated with a reducing atmosphere, whereas smelting furnaces with direct arc ac

tion (EAFs) are operated with an oxidizing atmosphere.

The invention is elucidated in detail by the working examples that follow, in conjunction with

the drawing.

Figure 1 illustrates the invention using the example of an electrical smelter (10) in a schematic

sectional diagram at different operating times. The electrical smelter (10) comprises a vessel (15) which is charged with a defined amount of solids (3) comprising iron-containing materials

and slag formers. Depending on the size of the vessel (15) or of the electrical smelter (10), a central point may be provided, for example centrally, for charging. In order to fill the vessel

(15) of the electrical smelter (10) with solids, charging is effected locally via multiple charging points (12). The electrical smelter (10) may comprise a lid (18) that can close the vessel (15) at

the top and hence can be adjusted within a defined or controlled atmosphere. The lid (18) is

in an essentially vertically movable arrangement; see double-headed arrow. If a lid (18) is pre sent, the charge points (12) are openings in the lid (18) with corresponding feed conduits. The

required solids (3) can be fed in via means that are not shown. After the solids (3) have been charged, cones of loose material can arise in the vessel (15) beneath the charge points. The

upper diagram in figure 1 shows by way of example that tapping was incomplete and hence the base of the vessel (15) is covered with iron melt (1) and/or liquid slag (2). The iron melt (1)

to be generated results from the defined amount of the solids (3) introduced.

The solids (3) contain iron-containing substances, preferably iron sponge. In addition, it is also

possible to feed in further iron-containing substances, for example iron-containing scrap, in order to improve the recycling rate. The slag formers, for example lime, silicon dioxide, mag

nesium oxide and/or aluminum oxide, are mixed in, especially when the "matrix" of the iron sponge used with preference is insufficient, depending thereon, for establishing the desired

basicity of the liquid slag (2) to be tapped. This measure is familiar to the person skilled in the art.

Once the defined amount of solids (3) has been introduced, and at least one electrode, three

electrodes (11) in this working example, where the number of electrodes (11) is chosen es

sentially depending on the dimensions of the electrical smelter (10), is supplied with energy for melting of the solids (3). The positioning of the electrode (11) may be adjusted vertically

in order preferably not to allow a light arc to form between solids (3) and electrode (11), pref

erablywith provision at least of immersion of the electrode tip into the solids (11); see double headed arrow. The energy required for melting may preferably have been generated from renewable energy (solar, wind, water), in order to be able to lower the CO 2 balance of the electrical smelter (10).

The middle diagram of figure 1 shows that the melting is initiated in the region (X) at and/or

below the electrode (11) and a melting front spreads radially from the region (X) to the wall of the vessel (15) in the course of melting operation, and at least 80% of the charged solids (3) is melted to form an iron melt (1) and a liquid slag (2) disposed at least over some regions of

the iron melt (1).

The preferred input of iron sponge as iron-containing material, depending on its production

and depending on whether iron ore has been reduced to iron sponge in a direct reduction process by means of carbonaceous gas, for example CO, or hydrocarbonaceous gas, for exam

ple CH 4 or natural gas, or hydrogenous gas, for example H 2 , or mixtures thereof, has varying and low carbon contents. The person skilled in the art is aware of this fact and will generally

feed in carbonaceous substances prior to melting operation via the charging. According to the invention, the smelter (10) is additionally charged with carbonaceous materials during melting

operation in such a way that the carbon resulting from the additional carbonaceous materials

results in an increase in the carbon content in the iron melt (1), and the iron melt (1) has a higher carbon content compared to the carbon content of the defined amount of solids (3)

considered overall, especially prior to melting operation. The charging of the carbonaceous admixture is intended to result in an increase in the carbon content in the iron melt (1) by at

least 0.50% by weight. The carbonaceous admixture is charged so as to establish a carbon content in the iron melt (1) of at least 3.50% by weight.

The carbonaceous admixture can be charged via at least one probe (13, 13.1), where the

mouth of the probe (13, 13.1) is positioned in the solids (3). The probe (13, 13.1) may be in a

movable arrangement; see double-headed arrow. The probe (13) may, for example, be im mersed into the solids (3) via the charge point (12) or via an opening in the side wall of the

vessel (15). More preferably, the mouth of the probe (13, 13.1) is positioned in a cohesive

zone (4). The carbonaceous admixture may be charged in solid and/or gaseous form. If a solid form is chosen, a carrier gas preferably including a carbonaceous component may promote the charging.

The lower diagram in figure 1 shows the end of the melting operation, such that the solids (3)

have been essentially completely melted to iron melt (1) and liquid slag (2) disposed thereon. The process gas generated during melting operation is removed via at least one opening (14). The liquid slag (2) is tapped via at least one taphole (16) and the iron melt (1) via at least one

taphole (17), and the vessel (15) can be recharged with solids (3); see upper diagram in figure 1.

Figure 2 shows a schematic top view of the electrical smelter (10) and lid (18) according to the design in figure 1. The three electrodes (11) are arranged in the relative middle, and the charge

points (12) are distributed locally at a radial distance from the electrodes (11). The four charge points (12) shown by way of example are in a circular arrangement in 90° steps. Four openings

(14) for removal of the process gas are provided in a circular arrangement in further 90° steps and between the charge points (12).

Nozzles (not shown) for influencing the movement of the iron melt (1) may be disposed in the vessel (15). The electrical smelter (10) may be mounted pivotably in order to enable tilting and

hence tapping of liquid slag (2) in one direction and iron melt (1) in the other direction. The operating of electrical smelters (10) is likewise familiar to the person skilled in the art.

Likewise not shown is how the iron melt (1) is withdrawn and fed to a further processing step.

The iron melt (1) is preferably sent to a treatment in order to reduce the carbon in the iron melt to a desired level. This is effected, for example, by means of oxygen in what is called an

oxygen blowing process, more preferably in a converter. The tapped liquid slag (2) is also pref

erably sent to a pelletization in order to produce slag for the building industry in particular.

In one working example, 100 kg of iron sponge from a direct reduction which used 100% hy

drogen as reducing gas was used in an SAF on a laboratory scale. The total carbon content introduced via the solids was thus less than 0.30% by weight. No slag formers were added.

The melt front was detected by metrology, and 4 kg of charcoal particles having a grain size

< 0.30 mm was charged in a controlled manner with N 2 as carrier gas, using a blowing probe preferably with refractory protection, the mouth of which has been positioned in the cohesive

zone. After melting operation, a carbon content of 4.45% by weight was ascertained in the iron melt. Determination of carbon content is known to the person skilled in the art.

Claims (6)

Claims

1. A process for producing an iron melt (1) in an electrical smelter (10), containing a vessel (15) and at least one electrode (11), comprising the steps of:

- charging the smelter (10) with a defined amount of solids (3) comprising iron-con taining materials and slag formers, where the charging is effected locally via one or more charge points (12) and the vessel (15) of the smelter (10) is filled,

- supplying the at least one electrode (11) with energy to melt the solids (3), where the melting is initiated in the region (X) at and/or below the electrode (11) and a melting front spreads radially from the region (X) to the wall of the vessel (15) in the course of melting operation, and at least 80% of the charged solids (3) is melted to form an iron melt (1) and a liquid slag (2) disposed at least over some regions of the iron melt (1),

- tapping the liquid slag (2) and the iron melt (1),

characterized in that the smelter (10) is additionally charged with carbonaceous ma terials during melting operation in such a way that the carbon resulting from the addi tional carbonaceous materials results in an increase in the carbon content in the iron melt (1), and the iron melt (1), especially after tapping, has a higher carbon content compared to the carbon content of the defined amount of charged solids (3) consid ered overall.

2. The process as claimed in claim 1, wherein the charging of the carbonaceous admixture results in an increase in the carbon content in the iron melt (1) by at least 0.50% by weight.

3. The process as claimed in either of the preceding claims, wherein the carbonaceous

admixture is charged so as to establish a carbon content in the iron melt of at least 3.50% by weight.

4. The process as claimed in any of the preceding claims, wherein the carbonaceous ad mixture is charged via at least one probe (13, 13.1), wherein the mouth of the probe

(13, 13.1) is positioned in the solids (3) comprising the iron sponge and optionally the

iron-containing additives and/or slag formers.

5. The process as claimed in claim 4, wherein the mouth of the probe (13, 13.1) is posi

tioned in a cohesive zone (4).

6. The process as claimed in any of the preceding claims, wherein a solid and/or gaseous

carbonaceous admixture is charged.