WO2015062956A1

WO2015062956A1 - Method for operating an electric arc furnace and electric arc furnace

Info

Publication number: WO2015062956A1
Application number: PCT/EP2014/072713
Authority: WO
Inventors: Manfred Baldauf; Martin Hergt; Thomas Matschullat
Original assignee: Siemens Aktiengesellschaft
Priority date: 2013-10-31
Filing date: 2014-10-23
Publication date: 2015-05-07
Also published as: DE102013222159A1

Abstract

The invention relates to a method for operating an electric arc furnace (10), which comprises at least one electrode (18), which is made of graphite and which has a passage opening (32), wherein in the method an arc (20) is generated between the at least one electrode (18) and a material to be melted (16) and a first additive is introduced into the passage opening (32) of the electrode (18), wherein a chemical reaction is caused by the introduction of the first additive into the passage opening (32), wherein carbon is formed in the chemical reaction, which carbon is deposited on the at least one electrode (18).

Description

description

A method of operating an electric arc furnace and Lichtbo ^¬ genofen

The present invention relates to a method for Operator Op ^¬ ben an electric arc furnace. Moreover, the present invention relates to an electric arc furnace for melting a melted material.

In an electric arc furnace, in particular an electric arc furnace, an electric arc leads electrical energy in the form of arcs via graphite electrodes to solid scrap and in a later phase of a melt. In the first phase, the solid scrap is heated directly by the arc and / or indirectly by the radiation of the arc on ^¬ and melted down. In later phases, the

Melt brought by the energy of the arc to the desired target temperature. A high energy input into the scrap or the melt is important in order to keep the melting time short to ensure high production capacities and to increase the energy efficiency of the process.

Usually, with a furnace transformer, a medium voltage is transformed into a low voltage and to the

Electrodes applied. The spacing of the electrodes to the scrap and to the melt can be varied in order to ignite the arc with a small distance and during operation by increasing the distance electrical operating parameters, such as the electrical voltage and / or current to stunning ^¬ influence.

During operation of the arc furnace, the graphite electrodes are subject to a high temperature gradient. At the upper end, the electrode temperature is in the vicinity of ambient. Hall temperature, while the lower end just above the melt is about 3000 K hot. These high temperatures combined with the arc lead to a reinforced Burning of the electrodes in the surrounding air. The burn-up of the graphite electrodes is attributed to approx. 50% of the side oxidation. Incidentally, the burnup is proportional to the square of the current. This means that when operating conventional arc furnaces, attempts are made to avoid the highest possible currents with small arcs at the same time in order to keep the graphite burn-up low.

Temperature gradients along the electrodes can further lead to mechanical stresses that can lead to the chipping of fragments or in extreme cases to the termination of the electrode. Electrode breakage would not only lead to increased electrode consumption but also to production stoppages and carburizing of the steel when the graphite electrode or fragments thereof fall into the melt. The energy input into the melt or into the scrap is influenced today exclusively by the electrical parameters and the mechanical distance from the electrode to the metal.

From WO 2013/064413 Al a method for operating an electric arc furnace is known, in which the arc can be influenced by mixing To ^¬ mixing of additives, so that in the individual operating phases of the arc furnace certain characteristics can be set advantageously. Depending on the type of additive added, the conductivity in the

Arc and radiation power can be increased or decreased. An increase in the conductivity in the arc or in the plasma leads to larger electrode distances and thus to a reduction in the current fluctuations and the so-called flicker. At the same time, the radiant power is increased and precipitates voluminous, so that the large-volume energy dissipation leads to a rapid Schrottaufheizprozess. In this way, the energy requirement can be reduced in this phase. To increase the conductivity in the arc, a metal or a metal salt can be introduced into the plasma. On the other hand, a reduction in the conductivity of the plasma leads to a smaller electrode spacing and lower radiation powers and thus also to lower radiation losses at the furnace walls. As a result, when operating with liquid phase very efficiently electrical energy in the

Melt entered. In order to reduce the conductivity of the arc gases like can be introduced into the plasma, such as argon, nitrogen, methane, Koh ^¬ dioxide or. To introduce the gases into the arc hollow electrodes made of graphite can be used, which have in their upper region corresponding nipples for the connection of gas supply lines. Via the nipples, the gas can be introduced into the interior of the hollow electrode and from there into the arc which is located at the lower end of the hollow electrode.

In the case of the conventional electric arc furnace for melting scrap, such a process is not yet in use. In some ladle furnaces, however, the principle of gas introduction via hollow electrodes is known. In this case, however, argon is primarily blown in order to avoid carburizing the melt.

The cooling of the electrodes is usually carried out on the outside by spraying or trickling down of water. This measure had an immense influence on the graphite consumption after its introduction about 30 years ago. However, as the trickling water evaporates, the lower part of the ^{electrode is} not cooled. In addition, the interior of the electrode undergoes no cooling effect at all. In this context, WO 2013/064413 AI further describes that the arc, an additive can be supplied, which acts a reaction ^¬ , which leads to a cooling of the electrode due to their energy consumption.

The object of the present invention is to operate an electric arc furnace of the type mentioned more efficiently. This object is achieved by a method having the features of patent claim 1 and by an electric arc furnace having the features of patent claim 11. Advantageous further ^¬ formations of the present invention are the subject of the dependent claims.

In the inventive method for operating a

Arc furnace, which comprises at least one electrode which is made of graphite and which has a passage opening, an arc between the at least one electrode and a melt is generated and a first additive is introduced into the through hole of the electrode, where ^¬ by the Introducing the first additive in the passage opening a chemical reaction is effected and wherein in the chemical reaction carbon is formed, which deposits on the at least one electrode.

The electric arc furnace can be designed in particular as an electric arc furnace. The electric arc furnace comprises at least one electrode made of graphite or carbon. An electrical voltage can be provided at the electrode with the aid of a furnace transformer, as a result of which an arc is formed between the electrode and the melt. In particular, steel scrap can be used as the melting material. The at least one electrode is designed as hollow ^¬ electrode. In the interior of the electrode, ie in the through-hole, a first additive can be introduced. As a first additive, a solid, an aerosol and / or a fluid can be introduced. In particular, a gas is introduced into the opening of the ^electrode as the first additive.

In the present case, the first additive is selected so as to effect a chemical reaction in which carbon is formed. The carbon formed in the reaction is deposited on the at least one electrode. This can counteract the erosion of the electrode during operation of the arc furnace entgegenge ^¬ acts. The first additive can be chosen in this way be that an endothermic chemical reaction is effected. Energy is needed in this chemical reaction. This energy can be taken from the heated electrode. This has the consequence that the electrode emits heat energy and is thus cooled. Thus, the area of the electrode which is heated in the operation of the arc furnace can be cooled.

Preferably, a hydrocarbon is introduced as the first additive in the passage opening. For example, methane, ethane and / or propane can be introduced into the passage opening. Such a gas can be stored in a SpeI ^¬ chereinrichtung and introduced via a corresponding connection device in the passage opening of the elec- rode. In addition, the gas can be metered by an ent ^¬ speaking control device, such as a controllable valve.

In one embodiment, the introduction of the first inflow is set substance is controlled so that the chemical reaction to the ^¬ ^¬ to one electrode is effected least least partially within the through hole. In addition, the Einbrin ^¬ gene can be controlled so that the chemical reaction takes place in a side facing the melting area of the electrode. Thus, a deposition of the carbon within the

Through hole, in particular in a melt-facing region of the electrode can be achieved.

In a further embodiment, upon introduction of the first additive, an amount of the first additive introduced into the passage opening is controlled as a function of time. By influencing the amount of the first additive, the deposition of the carbon at the electrode can be controlled as a result of the chemical reaction.

In a further embodiment, when introducing the first additive, a flow velocity of the first Additive controlled within the passage opening.

By controlling the flow rate of the first additive along the passage opening, it can be set at which position within the passage opening the carbon is deposited.

When introducing the first additive, it is preferable to change a position at which first additive is introduced into the passage opening. For this purpose, the electrode can have a plurality of openings through which the first additive can be introduced into the passage opening. Thus, the area at which the carbon deposits on the electrode can be influenced. In one embodiment, in addition, a second additive, which is designed to oxidize carbon, is introduced into the passage opening. In particular, an oxidizing gas such as Sau ^¬ erstoff, carbon dioxide and / or water vapor can be introduced into the through holes opening in addition to the first additive. By the admixture of the second additive, an unwanted deposition of the carbon ^¬ material in an upper region of the electrode, the

Fused material is prevented, be prevented. Preference is given to an amount of the first additive and / or an amount of the second additive to be introduced into the passage opening ^¬, ge ^¬ controlled as a function of time. By the proportions of the first and / or the second additive can be controlled in which region of the electrode, the carbon is deposited. Also can be influenced ^¬ enced the area in which the electrode is carried on an oxidation of the carbon formed. Furthermore, the amount of depositing carbon can be influenced. It is also advantageous if, in addition, a second additive for reducing and / or increasing a field strength of the arc is introduced into the passage opening. To reduce the field strength of the arc or of the plasma, a second additive can be introduced into the passage ^¬ opening, which reduces the ionization energy in the arc. For this purpose, for example, a metal or a metal salt can be introduced as a second additive. To increase the field strength, a second additive may be introduced which increases the ionization energy in the arc. Refer to as a second additive in ^¬ play, a gas, such as argon, nitrogen, methane, Kohlendi ^¬ oxide or the like, are introduced into the plasma. Thus, in addition to the cooling of the at least one electrode, the arc can be influenced.

In a further embodiment, an outer surface of the at least one electrode is cooled with water. For example, water can be sprayed onto the electrode from the outside. Preferably, the electrode can be cooled with water only in the lower region, which faces the melt. Thus ^¬ with the electrode may be cooled from the outside in addition to the chemical cooling in the interior of the electrode.

Furthermore, the invention provides an arc ^¬ furnace for melting a molten material having at least one electrode is formed of graphite and the one having through ^¬ hole, an electric power source for generating an arc between the at least one electrode and the melt, a memory means, in of a first additive is arranged, the first of which is to ^¬ record material in the through hole of the electrode can be introduced, wherein through the introduction of the first additive, a chemical reaction is effected in the passage opening and being formed during the chemical reaction of carbon, is located at the deposits at least one electrode.

The advantages and further developments described above in connection with the method according to the invention can be transferred analogously to the electric arc furnace according to the invention. The present invention will now be explained in more detail with reference to the accompanying drawings. Showing:

1 shows a representation of an arc furnace according to the

Prior art in a first phase of operation;

2 shows the electric arc furnace according to FIG. 1 in a second

operating phase; and

3 shows a schematic representation of an electrode

Arc furnace.

The embodiments described in more detail below represent preferred embodiments of the present invention.

1 shows an arc furnace 10 according to the prior art in a sectional side view. The electric arc furnace 10 is formed as an electric arc furnace. The electric arc furnace 10 comprises an upper housing part 12 and a lower housing part 14, which can be moved relative to each other. The electric arc furnace 10 serves to melt a melted material 16, in particular steel scrap. The melt 16 is located in the lower housing part 14th

Furthermore, the electric arc furnace 10 comprises at least one electrode 18. In the present exemplary embodiment, the electric arc furnace 10 comprises three electrodes 18. The electrodes 18 are connected to a furnace transformer, not shown here, with which an electrical voltage can be supplied to the electrodes 18. At the electrodes 18, the electrical voltage and / or the electric current are selected so that an arc 20 is formed between the electrodes 18 and the melt 16. The distance of the electrodes 18 to the melt 16 can be adjusted to ignite the arc 20 at a small distance and during operation by increasing the distance to influence electrical Be ^¬ operating parameters. In Figure 1, the electric arc furnace 10 is shown in a first phase of operation. Here, the melt 16 is present as a solid 22. The solid 22 or the scrap is supplied by the arcs 20 energy. This causes the solid 22 is melted and the melt 16 is thus present as a melt 24.

2 shows the electric arc furnace 10 according to FIG. 1 in a second operating phase. Here, the melt 16 is already completely before as melt 24. By the energy that is introduced into the melt 24 with ^¬ means of the arcs 20, a predetermined target temperature of the melt 24 is ^¬ represents may be. 3 shows a schematic representation of an electrode 18 of an arc furnace 10 in a sectional side view. During operation of the arc furnace 10, a temperature gradient forms along the electrode 18. This is due to the fact that the electrode 18 in a lower region 26 facing the molten metal 16 passes through the

Arc 20 and the melt 24 is heated to a temperature of up to 3000 K. At the lower region 26 of the ^electrode 18, the electric arc 20 is also formed. An upper portion 28 of the electrode 18, the overall genüberliegt the lower region 26 has approximately the temperature of the environment where the ambient temperature ^¬ playing in a hall on. The temperature gradient is presented by the arrow 30 veran ^¬ shows. As a result of the temperature gradient, mechanical stresses can arise within the electrode 18 which can result in damage to the electrode 18. In addition, the high temperatures in the lower region 26 of the electrode 18 can cause a burnup of the electrode 18.

In the present case, the electrode 18 is designed as a hollow electrode. The electrode 18 has substantially the shape of a

Hollow cylinder on. The electrode 18 has a passage ^opening 32, which extends from the upper region 28 to the lower region 26 of the electrode 18 along a longitudinal extension. ckungrichtung of the electrode 18 extends. In the passage ^¬ opening 32, a first additive can be introduced. This is illustrated here by the arrow 36. For this purpose, an appropriate check may be disposed final element of the electrode 18 which is connected to a spoke pure ^¬ direction or a reservoir, in which the first additive is disposed.

As a first additive, a hydrocarbon can be introduced into the passage opening 32 of the electrode 18.

For example, methane, ethane or propane can be introduced into the passage opening 32. By introducing the first additive in the passage opening 32, a chemical reaction is effected in which carbon is formed. This causes a carbon deposit inside the hollow electrode. Thus, the erosion of the electrode 18 in a lower hot region 34, which faces the melt 16, be counteracted by in-situ production of carbon. This reaction is exemplified for methane as the first additive in equation (1). The reaction can be carried out in an analogous manner with higher hydrocarbons, which are even subject to a greater extent of soot formation. CH ₄ "> C + 2 H ₂ ; ΔΗ _Κ = + 74.5.0 kJ / mol (1)

AH _{R describes} the amount of energy needed for the reaction. Since the reaction according to equation (1) is endothermic, ie under heat consumption, it can simultaneously serve to cool the hot region 34 of the electrode 18. The reaction according to equation (1) sets at temperatures above 200 ° C and the equilibrium position is shifted with stei ^¬ gender temperature more on the side of the products and H2 C. At the same time, the kinetics increase faster as a result of the temperature increase, so that more carbon is formed both thermodynamically and kinetically supported at the hot region 34 of the electrode 18 than in the remaining regions of the electrode 18. Moreover, the addition of methane to be made to the gas flow through the interior of the electrode 18 so that the main methane ^¬ factually in the bottom hot region 34 of the electrode 34 is advantageously located at the output, decomposed. Thus, the carbon formed is deposited at the point where the graphite electrode is consumed by electrode erosion. If the formation of carbon took place in an upper region 36 of the electrode 18, the deposits would narrow the flow cross-section and clog the gas feed, since no erosion takes place in this region by the arc 20.

To allow the deposition of the carbon to proceed in the desired range, so it can be provided a system by which the amount of the first additive and / or the flow rate of the first additive is so gesteu ^¬ ert that the first additive in the upper region 36 of the electrode 18 is only preheated and only in the lower region 34 and at the output of a large part of the additive is decomposed. Therefore, it is further proposed to suppress the undesired deposition of the carbon in the upper region 36 of the electrode 18 by the admixture of a second additive. The second additive may be an oxidizing effect founding gas such as oxygen, carbon dioxide and / or ^¬ What serdampf. Such gases can convert undesired carbon to prevent clogging of the flow area in low temperature regions. Examples of such reactions may be, for example:

C0 ₂ + C -> 2 CO; ΔΗ _Κ = +172.6 kJ / mol (2)

C + H ₂ O -> CO + H ₂ ; ΔΗ _Κ = +131.4 kJ / mol (3)

C + 2 H ₂ O -> C0 ₂ + 2 H ₂ ; ΔΗ _Κ = + 90.2 kJ / mol (4) C + 0 ₂ - »C0 ₂ ; ΔΗ _Κ = -393, 82 kJ / mol (5)

By controlling the amount of the first and second additives and their flow rate within the Through hole 32 creates a control and automation ^¬ tion concept for electric arc furnaces 10th

Since the reactions according to equations (1) to (4) are endothermic, if they run off in the upper region 36 of the ^electrodes 18, they also lead to a further decrease in temperature there, as a result of which the kinetics are slowed down. With a favorable choice of quantity and

Flow conditions can be prevented by reacting unwanted carbon deposits on the temperature reduction replication of new carbon. When metering in the second additive or the oxidizing gas, it is preferable to introduce only so much of the second additive that the oxidizing gas in the upper region 36 of the electrode 18 is consumed by one of the reactions according to Equations (2) to (5). At the output of the electrode 18 in the region 34, the deposition of carbon is wanted. There should be no additional chemical consumption by the reactions according to equations (2) to (5). At the end of the electrode removal takes place anyway by the Lichtbo ^¬ gene 20th

In addition, a third additive can be introduced into the passage ^opening 32 of the electrode 18, by means of which the properties of the arc 20 can be influenced. For example, the field strength of the arc 20 can be influenced by the third additive. Thus, a combination of the arc influencing and the chemical cooling of the electrodes 18 can be provided with a common apparatus design. To control the introduction of the first, the second and / or the third additive, the electrical voltage and / or the current strength of the arc can be monitored.

By the introduction of gases such as carbon monoxide, Kohlendio ^¬ dioxide, hydrogen, steam and / or methane, in addition to the OH gases such as argon, nitrogen, oxygen and / or compressed air Nehin used for influencing the arc plasma who can ^¬ a chemical repair can additionally be provided, and be compensated 18 of the erosion of the electrode by the decomposition of a hydrocarbon in the interior and / or at the output of the electrode 18th

This offers the possibility to develop a control and automation ^¬ approximately concept in which in a multidimensional parameter space both the energy input into the melt 16 through the arc 20 and the cooling of the electrodes 18 and the erosion of the electrodes 18 in a favorable manner by the choice of the gas combinations whose mixing ratios, the location of the feed of the gases into the passage opening 32, the flow velocity and / or the volume flow of the gases can be influenced.

Claims

claims

A method of operating an electric arc furnace (10) comprising at least one electrode (18) made of graphite and having a through-hole (32), the method comprising an arc (20) between the at least one electrode (18) and a melt (16) is produced and a first additive in the through hole (32) of the electrode (18) is introduced, wherein the introduction of the first additive in the through hole (32) causes a chemical reaction,

characterized in that

carbon is formed in the chemical reaction, which deposits on the at least one electrode (18).

2. The method according to claim 1, characterized in that a hydrocarbon is introduced as the first additive in the through ^¬ opening (32).

3. The method according to claim 1 or 2, characterized in that the introduction of the first additive is controlled such that the chemical reaction at least partially in ^¬ within the passage opening (32) of the at least one electrode (18) is effected.

4. The method according to any one of the preceding claims, characterized in that upon introduction of the first additive, an amount of the first additive, which is introduced into the passage ^¬ opening (32) is controlled as a function of time.

5. The method according to any one of the preceding claims, characterized in that upon introduction of the first additive, a flow rate of the first additive within the passage opening (32) is controlled.

6. The method according to any one of the preceding claims, characterized in that upon introduction of the first additive a position at which first additive is introduced into the passage ^¬ opening (32) is changed.

7. The method according to any one of the preceding claims, characterized in that in addition a second additive which is adapted to oxidize carbon, in the through ^¬ opening (32) is introduced.

8. The method according to claim 7, characterized in that an amount of the first additive and / or an amount of the second additive, which are introduced into the passage opening (32), is controlled as a function of time.

9. The method according to any one of the preceding claims, characterized in that additionally a third additive for

Reducing and / or increasing a field strength of the

Arc (20) is introduced into the through hole (32).

10. The method according to any one of the preceding claims, characterized in that an outer surface of the at least ei ^¬ nen electrode (18) is cooled with water.

11. An arc furnace (10) for melting a melt (16) having at least one electrode (18) made of graphite and having a through hole (32), an electrical energy source for generating an arc (20) between the at least one electrode (18) and the melt (16), a storage device in which a first additive is arranged, wherein the first additive in the through hole (32) of the electrode (18) can be introduced and by the introduction of the first additive in the through hole (32 ) a chemical reaction is effected, characterized in that