Title of Invention	METHOD AND DEVICE FOR OPERATING AN ELECTRIC ARC FURNACE
Abstract	The invention relates to a method for operating an electric arc furnace (1 ) comprising at least one electrode (2), comprising a performing a tapping step in an operating cycle of the electric arc furnace (1) including a sequence of a power-on period (t'3), a power-off period (t'03) and a last power-on period (t'f1, t''f), with energy being supplied to the at least one electrode (2) during the power-on periods (t'3, t'f1,t"f) and no energy being supplied during the power-off period (t'03), characterized in that the tapping step is performed after the power-off period (t'03), and in that energy is supplied to the at least one electrode (2) at least for part of the time even during the tapping step.

Title of Invention

METHOD AND DEVICE FOR OPERATING AN ELECTRIC ARC FURNACE

Abstract

The invention relates to a method for operating an electric arc furnace (1 ) comprising at least one electrode (2), comprising a performing a tapping step in an operating cycle of the electric arc furnace (1) including a sequence of a power-on period (t'3), a power-off period (t'03) and a last power-on period (t'f1, t''f), with energy being supplied to the at least one electrode (2) during the power-on periods (t'3, t'f1,t"f) and no energy being supplied during the power-off period (t'03), characterized in that the tapping step is performed after the power-off period (t'03), and in that energy is supplied to the at least one electrode (2) at least for part of the time even during the tapping step.

Full Text	Description Method and device for operating an electric-arc furnace The invention relates to a method for operating an electric-arc furnace comprising at least one electrode and one tapping method step. Furthermore the invention relates to a correspond- ing device. Charge materials containing in particular iron are melted and/ or treated in an electric-arc furnace. Electrical energy serves in the electric-arc furnace preferably to heat, melt and superheat and/or clean the charge materials. In electric-arc furnaces, heat is generated by electric arcs, i.e. by electric current flowing between electrodes or between one or more electrodes and furnace elements, with the electric arcs giving off their energy to the charge materials to be melted and to the melt in the electric-arc furnace. Steel production in the electric-arc furnace is described in "Stahlerzeugung im Lichtbogenofen" by Manfred Jellinghaus, 1994, Verlag Stahleisen mbH, Diisseldorf. Pages 100 and 101 of the above-mentioned publication, in particular, go into the operation of electric-arc furnaces in more detail. In order to achieve the highest possible productivity in an electric-arc furnace, attempts are made to melt the charge materials as quickly as possible, to supply the highest possible electrical energy during the entire melting time and to keep the power-off or non-productive times without energy supply as short as possible. It is proposed, for example, that in order to increase the productivity of electric-arc furnaces, more powerful furnace transformers are used, or that the material flow of all the raw materials to the electric-arc furnace is organized better. The object of the invention is to further improve the productivity of an electric- arc furnace. This object is achieved by a method for operating an electric arc furnace (1) comprising at least one electrode (2), comprising a performing a tapping step in an operating cycle of the electric arc furnace (1) including a sequence of a power-on period (t'3), a power-off period (t'03) and a last power- on period (t'f1, t"f), with energy being supplied to the at least one electrode (2) during the power-on periods (t'3, t'f1,t"f) and no energy being supplied during the power- off period (t'03), characterized in that the tapping step is performed after the power-off period (t'03), and in that energy is supplied to the at least one electrode (2) at least for part of the time even during the tapping step. By contrast with known methods of operation of an electric-arc furnace, according to the invention the energy supply to the at least one electrode is no longer switched off before the tapping method step. Instead energy continues to be supplied at least part of the time even during the tapping method step. In this way the tapping method step can start earlier than with the traditional method of operation. Compared with the traditional method of operation of an electric-arc furnace, this results in a significant saving in time. The productivity of an electric arc furnace is thus increased and the electrode consumptions are reduced due to the shorter operating times. The energy content of the melt in the electric-arc furnace is advantageously increased even during the tapping method step. This further increases the productivity of the electric arc furnace and a lower overall energy consumption is achieved. The energy supply is advantageously controlled by means of the inputs by an operator. The method can thus be implemented with extremely little advance investment cost. The energy supply is advantageously controlled by means of a meter. As a result, calculations and evaluations associated with the operation of the electric arc furnace in particular no longer have to be carried out by an operator. The energy supply is advantageously controlled by means of a model for the energy and mass balance implemented in a control device. An extremely fast-reacting and extensively automated control method for the operation of an electric-arc furnace is thus provided. The object of the invention is also achieved by a device for performing the method described above in its various forms, with an electric-arc furnace and a control device connected to the electric-arc furnace, with the control device comprising a model for the energy and mass balance and being configured in such a way that it controls the position and the energy supply of the at least one electrode of the electric-arc furnace even during the tapping method step. The advantages of the device according to the invention can be derived by analogy with the advantages of the method according to the invention. Details and further advantages of the invention are explained in further detail below by reference to exemplary embodiments in conjunction with the drawings, in which Figure 1 shows an exemplary schematic representation of an electric-arc furnace, Figure 2 shows an exemplary schematic representation of the energy distribution during the traditional operation of an electric-arc furnace, Figure 3 shows an exemplary schematic representation of the energy distribution during the operation of an electric-arc furnace according to the invention. Figure 1 shows an example of an electric-arc furnace 1 with a furnace vessel 11 and a vessel substructure 12 with furnace scales. In the example shown there is a cover 5 in the upper area of the furnace vessel. In the example shown the cover 5 is movable and can preferably be opened for admitting charge materials to the furnace vessel 11, for example. In the example, melt 4 is shown located in the furnace vessel 11. The designation "melt" 4 is used to refer to both charge materials in the electric-arc furnace 1 and to melted material. Melt 4 is also used to refer to a mixture of charge materials and melted material. Charge materials are, for example, scrap, i.e. ferrous wastes, crude iron and/or sponge iron. Additives such as slag forming agents, fluxes, refining agents, carbonizing agents, slag reduction agents and/or additions such as deoxidation and alloying agents are frequently added to the melt 4. In the example shown, the electric-arc furnace 1 has several electrodes 2 that are inserted through openings in the cover 5. By means of the electrodes 2 and by supplying energy, electric arcs 3 are created by means of which energy is supplied to the melt 4 in the form of heat. The electric-arc furnace 1 can be designed, for example, as a direct current (DC) electric-arc furnace or as an alternating current (AC) electric-arc furnace. A control device not shown in further detail in the drawing is preferably provided for the electric-arc furnace 1. This control device has an electrode control device to allow the power conversion in the electric- arc furnace 1 to be set in the desired manner by adjusting the electrodes 2. The ignition of the electric arcs 3, the setting of the arc length and the compensation of the burn-off are achieved essentially by raising and lowering the electrodes 2. Particularly during melting of material in the electric-arc furnace 1, the electrodes 2 are mostly adjusted so quickly that the electric arcs 3 are not interrupted and short-circuits that can occur, for example, due to the collapse of scrap are compensated within a minimum of time by a rapid upward movement of the electrodes 2. The electric-arc furnace 1 preferably has a door 7 in order to discharge slag 6, for example by means of a slag ladle 10. At the end of a melt, referred to below also as operating cycle, the finished melt 4 is discharged from the electric-arc furnace 1 as raw steel 8. The discharge of the finished melt 4, i.e. the removal of raw steel 8 from the electric-arc furnace 1, is referred to as tapping method step. The raw steel 8 is transferred from the electric-arc furnace 1 into a ladle 9 via the tapping spout 13 that in the example shown is designed as a siphon tap. The furnace vessel 11 is preferably tilted during this process. After the tapping method step, the raw steel 8 can be transferred to a casting device, for example a continuous casting plant, by means of the ladle 9 that is also referred to as a pouring ladle. Figures 2 and 3 show diagrammatically and by way of example the energy distribution during the operation of an electric-arc furnace 1. Figure 2 refers to the traditional method of operation of an electric-arc furnace 1, while in contrast, Figure 3 illustrates the method of operation of an electric-arc furnace 1 according to the invention. In each of Figures 2 and 3, the effective power Pw is plotted against time t. Figures 2 and 3 both show the energy distri- bution during a complete operating cycle of the electric-arc furnace 1 and merely as an indication the start of a temporally following operating cycle. The temporally preceding operating cycle that is shown in full is referred to below as the first operating cycle; the temporally following operating cycle, the start of which is only indicated in Figures 2 and 3, is referred to below as the second operating cycle. During operation of an electric-arc furnace 1 there are generally several - often a large number of - consecutive operating cycles. Additional standstill, installation and/or maintenance periods can lie between two operating cycles, with great efforts being made to minimize these periods in the striving for the highest possible furnace utilization. Charge materials are charged into the electric-arc furnace 1 at the times TA1, TA2 and TA3 or T'A1, T'A2 and T'A3 during the first operating cycle. The charge materials are generally charged into the furnace vessel 11 by means of a basket or bucket with the cover 5 open. After charging of the charge materials into the electric-arc furnace 1, energy is supplied to the electrodes 2 during the power-on periods t1 t2 and t3 or t'1, t'2 and t'3. During the power-on periods t1, t2, t3 or t'1, t'2, t'3, melt 4 is melted and/or treated in some other way in the furnace vessel 11. The power-on periods t1, t2, t3 or t'1, t'2, t'3 are followed by power-off periods t01, t02, t03 or t'01, t'02, t'03 during which no energy is supplied. During a final power-on period t4 or t'4 it is necessary to ensure that the energy content of the raw steel 8 is high enough during tapping and correctly set for its further treat- ment. During the power-off periods t01, t02 or t'01, t'02, charge materials can be charged as already described, for example. At least during the power-off period t03 or t'03 that precedes the last power-on period t4 or t'4 of the first operating cycle, at least one sample is taken from the melt 4 at the moment TP or T'P. The time interval from moment T0 or T'0, the start of the first power-on period t1 or t'1 of the first operating cycle, up to the end of the last-but-one power-on period t3 or t'3 of an operating cycle, is referred to as the melting time te or t'e. The last power-on period t4 or t'4 is also referred to as the finishing time tf or t'f or t"f. It is important to set the energy content of the melt 4 or of the raw steel 8 correctly during the finishing time tf, t'f or t"f. Refining and/or purification of the melt 4 can also take place during the finishing time tf, t'f or t"f. The last power-on period t4 or t'4 of the first operating cycle, in other words the finishing time tf, t'f or t"f of the first operating cycle, is followed by a final power-off period t04, t'04 or t"04 that lasts until moment T1 or T'1, the start of the first power-on period of the second operating cycle. The time interval from moment T0 or T'0, the start of the first power-on period t1 or t'1 of the first operating cycle, up to the moment T1 or T'1, the start of the first power-on period of the second operating cycle, is referred to as the cycle time tx or t'x. In the traditional method of operation of an electric-arc furnace 1, no energy is supplied to the electrodes 2 during the tapping method step (cf. Fig. 2). In the traditional method of operation, the tapping time ta, i.e. the time from moment TT0, the start of the tapping method step, up to moment TT1, the end of the tapping method step, lies completely within the last power-off period t04. The finishing energy level Pf generally lies significantly below the average energy level during the power-on periods t1, t2 and t3 during the melting time te. According to the invention, energy is supplied to the electrodes 2 of the electric-arc furnace 1 for at least part of the time during the tapping method step, i.e. during the tapping time t'a, as indicated in Figure 3. By comparison with the traditional method of operation of an electric-arc furnace 1, the tapping process according to the invention begins significantly earlier, offering savings in time in operation of the electric-arc furnace 1. The cycle time t'x during operation of an electric-arc furnace 1 according to the invention is thus shortened by comparison with the cycle time tx for traditional operation. According to the invention, the energy content of the melt 4 in the electric-arc furnace 1 is also selectively increased even during the tapping method step, i.e. during the tapping time t'a- First of all, the energy state of the melt is determined before the moment T'T0, the start of the tapping method step, and the further change in the energy content of the melt 4 is pre-calculated by means of a melting controller that can be designed e.g. as a meter and/or using an online process tracking model for the energy and mass balance. The optimum moment T'T0, the start of the tapping method step, and the optimum moment T'T1, the end of the tapping method step, are also preferably pre-calculated by means of a melting controller and/or a model for the energy and mass balance. The model for the energy and mass balance can be implemented in a control device. The model for the energy and mass balance is preferably implemented in the control device that comprises the electrode controller for the electric-arc furnace 1. Alternatively there is a first control device that comprises a model for the energy and mass balance that is connected to a second control device that comprises the above-mentioned electrode controller. Alternatively or additionally, the method of operation of the electric-arc furnace 1 can be influenced by an operator. The model for the energy and mass balance is used to prevent any melting through of the furnace vessel 11 and/or of the vessel substructure 12 by a corresponding control of the energy supply to the electrodes 2. The energy level during the finishing time t'f or t"f can preferably be steadily reduced (cf. finishing energy level P"f) during the tapping time t'a. The finishing energy level P'f or P"f can also be reduced, for example, in steps and/or according to a prolonged, initially constant curve. The latter alternatives are not, however, shown in further detail in Figure 3. The energy level during the finishing time t'f or t"f can also be held more or less constant during the tapping time t'a (cf. finishing energy level P'f). Two examples of a curve of the energy level accord- ing to the invention during the tapping time t'a are shown diagrammatically, plotting the finishing times t'f and t"f against the finishing energy levels P'f and P"f. In both the method of operation according to the invention and the traditional method of operation of the electric-arc furnace 1, an operating cycle can comprise one or more power-on periods t1, t2, t3 or t'1, t'2, t'3 during its melting time te or t'e. It is fundamentally also possible that in an operating cycle the finishing time tf or t'f is not preceded by a melting time te or t'e. After the tapping time ta or t'a, charge materials are again charged into the electric-arc furnace 1 before the moment T1 or T'1 at a moment TB1 or T'B1. The fundamental concept for the invention can be essentially summarized as follows: The invention relates to a method for operating an electric-arc furnace comprising at least one electrode and one tapping method step. By not switching off the energy supply via the at least one electrode 2 of the electric-arc furnace 1 at the beginning of the tapping method step and continuing to supply energy to the at least one electrode 2 even during the tapping method step, the tapping method step can start earlier than with the traditional method of operation of an electric-arc furnace 1. This saves time, reduces the consumption of electrodes and energy, and also increases productivity. The desired energy content of the raw steel 8 is ensured by the pre-calculation of the alteration of the energy content of the melt 4 during the tapping step and the danger of over-heating is compensated. WE CLAIM 1. Method for operating an electric arc furnace (1) comprising at least one electrode (2), comprising a performing a tapping step in an operating cycle of the electric arc furnace (1) including a sequence of a power-on period (t'3), a power-off period (t'03) and a last power-on period (t'f1, t"f), with energy being supplied to the at least one electrode (2) during the power-on periods (t'3, t'f1,t"f) and no energy being supplied during the power-off period (t'03), characterized in that the tapping step is performed after the power-off period (t'03), and in that energy is supplied to the at least one electrode (2) at least for part of the time even during the tapping step. 2. Method as claimed in Claim 1, wherein the energy content of a melt (4) in the electric arc furnace (1) is selectively increased even during the tapping method step. 3. Method as claimed in Claim 1 or 2, wherein the energy supply is controlled by means of inputs by an operator. 4. Method as claimed in Claim 1 or 2, wherein the energy supply is controlled by means of a meter. 5. Method as claimed in Claim 1 or 2, wherein the energy supply is controlled by means of a model for the energy and mass balance implemented in a control device. 6. Method as claimed in one of the preceding claims, wherein the beginning of the tapping step (TTO) lies in the last power-on period (t'F1, t"F) and the end of the tapping step (TT1) lies in a final power-off period (t'04,t"04) following the last power on period (t'F1, t"F). 7. Method as claimed in Claim 6, wherein the energy supply in the last power-on period (t",) is steadily decreased during the tapping step. 8. Method as claimed in Claim 6, wherein the energy supply in the last power-on period (t'F1,t'F) is decreased in steps and/or according to a prolonged, initially constant curve. 9. Device for performing a method as claimed in one of Claims 5 to 8, with anelectric arc furnace (1 ) and a control device connected to the electric arc furnace (1), wherein the control device comprises a model for the energy and mass balance and is configured in such a way that it controls the position and the energy supply to the at least one electrode (2) even during the tapping step. ABSTRACT METHOD AND DEVICE FOR OPERATING AN ELECTRIC FURNACE" The invention relates to a method for operating an electric arc furnace (1 ) comprising at least one electrode (2), comprising a performing a tapping step in an operating cycle of the electric arc furnace (1) including a sequence of a power-on period (t'3), a power-off period (t'03) and a last power-on period (t'f1, t'f), with energy being supplied to the at least one electrode (2) during the power-on periods (t'3, t'f1,t"f) and no energy being supplied during the power-off period (t'03), characterized in that the tapping step is performed after the power-off period (t'03), and in that energy is supplied to the at least one electrode (2) at least for part of the time even during the tapping step.

Full Text

Description
Method and device for operating an electric-arc furnace
The invention relates to a method for operating an electric-arc
furnace comprising at least one electrode and one tapping
method step. Furthermore the invention relates to a correspond-
ing device.
Charge materials containing in particular iron are melted and/
or treated in an electric-arc furnace. Electrical energy serves
in the electric-arc furnace preferably to heat, melt and
superheat and/or clean the charge materials. In electric-arc
furnaces, heat is generated by electric arcs, i.e. by electric
current flowing between electrodes or between one or more
electrodes and furnace elements, with the electric arcs giving
off their energy to the charge materials to be melted and to
the melt in the electric-arc furnace.
Steel production in the electric-arc furnace is described in
"Stahlerzeugung im Lichtbogenofen" by Manfred Jellinghaus,
1994, Verlag Stahleisen mbH, Diisseldorf. Pages 100 and 101 of
the above-mentioned publication, in particular, go into the
operation of electric-arc furnaces in more detail. In order to
achieve the highest possible productivity in an electric-arc
furnace, attempts are made to melt the charge materials as
quickly as possible, to supply the highest possible electrical
energy during the entire melting time and to keep the power-off
or non-productive times without energy supply as short as
possible. It is proposed, for example, that in order to
increase the productivity of electric-arc furnaces, more
powerful furnace transformers are used, or that the material
flow of all the raw materials to the electric-arc furnace is
organized better.

The object of the invention is to further improve the productivity of an electric-
arc furnace. This object is achieved by a method for operating an electric arc
furnace (1) comprising at least one electrode (2), comprising a performing a
tapping step in an operating cycle of the electric arc furnace (1) including a
sequence of a power-on period (t'3), a power-off period (t'03) and a last power-
on period (t'f1, t"f), with energy being supplied to the at least one electrode (2) during the
power-on periods (t'3, t'f1,t"f) and no energy being supplied during the power-
off period (t'03), characterized in that the tapping step is performed after the
power-off period (t'03), and in that energy is supplied to the at least one electrode
(2) at least for part of the time even during the tapping step.
By contrast with known methods of operation of an electric-arc furnace,
according to the invention the energy supply to the at least one electrode is no
longer switched off before the tapping method step. Instead energy continues to
be supplied at least part of the time even during the tapping method step. In this
way the tapping method step can start earlier than with the traditional method of
operation. Compared with the traditional method of operation of an electric-arc
furnace, this results in a significant saving in time. The productivity of an electric
arc furnace is thus increased and the electrode consumptions are reduced due to
the shorter operating times.
The energy content of the melt in the electric-arc furnace is advantageously
increased even during the tapping method step. This further increases the
productivity of the electric arc furnace and a lower overall energy consumption is
achieved.

The energy supply is advantageously controlled by means of the inputs by an
operator. The method can thus be implemented with extremely little advance
investment cost.
The energy supply is advantageously controlled by means of a meter. As a
result, calculations and evaluations associated with the operation of the electric
arc furnace in particular no longer have to be carried out by an operator.

The energy supply is advantageously controlled by means of a
model for the energy and mass balance implemented in a control
device. An extremely fast-reacting and extensively automated
control method for the operation of an electric-arc furnace is
thus provided.
The object of the invention is also achieved by a device for
performing the method described above in its various forms,
with an electric-arc furnace and a control device connected to
the electric-arc furnace, with the control device comprising a
model for the energy and mass balance and being configured in
such a way that it controls the position and the energy supply
of the at least one electrode of the electric-arc furnace even
during the tapping method step. The advantages of the device
according to the invention can be derived by analogy with the
advantages of the method according to the invention.
Details and further advantages of the invention are explained
in further detail below by reference to exemplary embodiments
in conjunction with the drawings, in which
Figure 1 shows an exemplary schematic representation of an
electric-arc furnace,
Figure 2 shows an exemplary schematic representation of the
energy distribution during the traditional operation of an
electric-arc furnace,
Figure 3 shows an exemplary schematic representation of the
energy distribution during the operation of an electric-arc
furnace according to the invention.
Figure 1 shows an example of an electric-arc furnace 1 with a
furnace vessel 11 and a vessel substructure 12 with furnace
scales. In the example shown there is a cover 5 in the upper
area of the furnace vessel. In the example shown the cover 5 is

movable and can preferably be opened for admitting charge
materials to the furnace vessel 11, for example.
In the example, melt 4 is shown located in the furnace vessel
11. The designation "melt" 4 is used to refer to both charge
materials in the electric-arc furnace 1 and to melted material.
Melt 4 is also used to refer to a mixture of charge materials
and melted material. Charge materials are, for example, scrap,
i.e. ferrous wastes, crude iron and/or sponge iron. Additives
such as slag forming agents, fluxes, refining agents,
carbonizing agents, slag reduction agents and/or additions such
as deoxidation and alloying agents are frequently added to the
melt 4.
In the example shown, the electric-arc furnace 1 has several
electrodes 2 that are inserted through openings in the cover 5.
By means of the electrodes 2 and by supplying energy, electric
arcs 3 are created by means of which energy is supplied to the
melt 4 in the form of heat.
The electric-arc furnace 1 can be designed, for example, as a
direct current (DC) electric-arc furnace or as an alternating
current (AC) electric-arc furnace. A control device not shown
in further detail in the drawing is preferably provided for the
electric-arc furnace 1. This control device has an electrode
control device to allow the power conversion in the electric-
arc furnace 1 to be set in the desired manner by adjusting the
electrodes 2. The ignition of the electric arcs 3, the setting
of the arc length and the compensation of the burn-off are
achieved essentially by raising and lowering the electrodes 2.
Particularly during melting of material in the electric-arc
furnace 1, the electrodes 2 are mostly adjusted so quickly that
the electric arcs 3 are not interrupted and short-circuits that
can occur, for example, due to the collapse of scrap are

compensated within a minimum of time by a rapid upward movement
of the electrodes 2.
The electric-arc furnace 1 preferably has a door 7 in order to
discharge slag 6, for example by means of a slag ladle 10.
At the end of a melt, referred to below also as operating
cycle, the finished melt 4 is discharged from the electric-arc
furnace 1 as raw steel 8. The discharge of the finished melt 4,
i.e. the removal of raw steel 8 from the electric-arc furnace
1, is referred to as tapping method step. The raw steel 8 is
transferred from the electric-arc furnace 1 into a ladle 9 via
the tapping spout 13 that in the example shown is designed as a
siphon tap. The furnace vessel 11 is preferably tilted during
this process. After the tapping method step, the raw steel 8
can be transferred to a casting device, for example a
continuous casting plant, by means of the ladle 9 that is also
referred to as a pouring ladle.
Figures 2 and 3 show diagrammatically and by way of example the
energy distribution during the operation of an electric-arc
furnace 1. Figure 2 refers to the traditional method of
operation of an electric-arc furnace 1, while in contrast,
Figure 3 illustrates the method of operation of an electric-arc
furnace 1 according to the invention.
In each of Figures 2 and 3, the effective power Pw is plotted
against time t. Figures 2 and 3 both show the energy distri-
bution during a complete operating cycle of the electric-arc
furnace 1 and merely as an indication the start of a temporally
following operating cycle. The temporally preceding operating
cycle that is shown in full is referred to below as the first
operating cycle; the temporally following operating cycle, the
start of which is only indicated in Figures 2 and 3, is

referred to below as the second operating cycle. During
operation of an electric-arc furnace 1 there are generally
several - often a large number of - consecutive operating
cycles. Additional standstill, installation and/or maintenance
periods can lie between two operating cycles, with great
efforts being made to minimize these periods in the striving
for the highest possible furnace utilization.
Charge materials are charged into the electric-arc furnace 1 at
the times TA1, TA2 and TA3 or T'A1, T'A2 and T'A3 during the first
operating cycle. The charge materials are generally charged
into the furnace vessel 11 by means of a basket or bucket with
the cover 5 open.
After charging of the charge materials into the electric-arc
furnace 1, energy is supplied to the electrodes 2 during the
power-on periods t1 t2 and t3 or t'1, t'2 and t'3. During the
power-on periods t1, t2, t3 or t'1, t'2, t'3, melt 4 is melted
and/or treated in some other way in the furnace vessel 11. The
power-on periods t1, t2, t3 or t'1, t'2, t'3 are followed by
power-off periods t01, t02, t03 or t'01, t'02, t'03 during which no
energy is supplied.
During a final power-on period t4 or t'4 it is necessary to
ensure that the energy content of the raw steel 8 is high
enough during tapping and correctly set for its further treat-
ment.
During the power-off periods t01, t02 or t'01, t'02, charge
materials can be charged as already described, for example. At
least during the power-off period t03 or t'03 that precedes the
last power-on period t4 or t'4 of the first operating cycle, at
least one sample is taken from the melt 4 at the moment TP or
T'P. The time interval from moment T0 or T'0, the start of the

first power-on period t1 or t'1 of the first operating cycle,
up to the end of the last-but-one power-on period t3 or t'3 of
an operating cycle, is referred to as the melting time te or
t'e. The last power-on period t4 or t'4 is also referred to as
the finishing time tf or t'f or t"f.
It is important to set the energy content of the melt 4 or of
the raw steel 8 correctly during the finishing time tf, t'f or
t"f. Refining and/or purification of the melt 4 can also take
place during the finishing time tf, t'f or t"f.
The last power-on period t4 or t'4 of the first operating cycle,
in other words the finishing time tf, t'f or t"f of the first
operating cycle, is followed by a final power-off period t04,
t'04 or t"04 that lasts until moment T1 or T'1, the start of the
first power-on period of the second operating cycle. The time
interval from moment T0 or T'0, the start of the first power-on
period t1 or t'1 of the first operating cycle, up to the moment
T1 or T'1, the start of the first power-on period of the second
operating cycle, is referred to as the cycle time tx or t'x.
In the traditional method of operation of an electric-arc
furnace 1, no energy is supplied to the electrodes 2 during the
tapping method step (cf. Fig. 2). In the traditional method of
operation, the tapping time ta, i.e. the time from moment TT0,
the start of the tapping method step, up to moment TT1, the end
of the tapping method step, lies completely within the last
power-off period t04. The finishing energy level Pf generally
lies significantly below the average energy level during the
power-on periods t1, t2 and t3 during the melting time te.
According to the invention, energy is supplied to the
electrodes 2 of the electric-arc furnace 1 for at least part of
the time during the tapping method step, i.e. during the

tapping time t'a, as indicated in Figure 3. By comparison with
the traditional method of operation of an electric-arc furnace
1, the tapping process according to the invention begins
significantly earlier, offering savings in time in operation of
the electric-arc furnace 1. The cycle time t'x during operation
of an electric-arc furnace 1 according to the invention is thus
shortened by comparison with the cycle time tx for traditional
operation.
According to the invention, the energy content of the melt 4 in
the electric-arc furnace 1 is also selectively increased even
during the tapping method step, i.e. during the tapping time
t'a- First of all, the energy state of the melt is determined
before the moment T'T0, the start of the tapping method step,
and the further change in the energy content of the melt 4 is
pre-calculated by means of a melting controller that can be
designed e.g. as a meter and/or using an online process
tracking model for the energy and mass balance. The optimum
moment T'T0, the start of the tapping method step, and the
optimum moment T'T1, the end of the tapping method step, are
also preferably pre-calculated by means of a melting controller
and/or a model for the energy and mass balance. The model for
the energy and mass balance can be implemented in a control
device. The model for the energy and mass balance is preferably
implemented in the control device that comprises the electrode
controller for the electric-arc furnace 1. Alternatively there
is a first control device that comprises a model for the energy
and mass balance that is connected to a second control device
that comprises the above-mentioned electrode controller.
Alternatively or additionally, the method of operation of the
electric-arc furnace 1 can be influenced by an operator.
The model for the energy and mass balance is used to prevent
any melting through of the furnace vessel 11 and/or of the

vessel substructure 12 by a corresponding control of the energy
supply to the electrodes 2. The energy level during the
finishing time t'f or t"f can preferably be steadily reduced
(cf. finishing energy level P"f) during the tapping time t'a.
The finishing energy level P'f or P"f can also be reduced, for
example, in steps and/or according to a prolonged, initially
constant curve. The latter alternatives are not, however, shown
in further detail in Figure 3. The energy level during the
finishing time t'f or t"f can also be held more or less
constant during the tapping time t'a (cf. finishing energy
level P'f). Two examples of a curve of the energy level accord-
ing to the invention during the tapping time t'a are shown
diagrammatically, plotting the finishing times t'f and t"f
against the finishing energy levels P'f and P"f.
In both the method of operation according to the invention and
the traditional method of operation of the electric-arc furnace
1, an operating cycle can comprise one or more power-on periods
t1, t2, t3 or t'1, t'2, t'3 during its melting time te or t'e. It
is fundamentally also possible that in an operating cycle the
finishing time tf or t'f is not preceded by a melting time te or
t'e. After the tapping time ta or t'a, charge materials are
again charged into the electric-arc furnace 1 before the moment
T1 or T'1 at a moment TB1 or T'B1.
The fundamental concept for the invention can be essentially
summarized as follows:
The invention relates to a method for operating an electric-arc
furnace comprising at least one electrode and one tapping
method step. By not switching off the energy supply via the at
least one electrode 2 of the electric-arc furnace 1 at the
beginning of the tapping method step and continuing to supply
energy to the at least one electrode 2 even during the tapping

method step, the tapping method step can start earlier than
with the traditional method of operation of an electric-arc
furnace 1.
This saves time, reduces the consumption of electrodes and
energy, and also increases productivity. The desired energy
content of the raw steel 8 is ensured by the pre-calculation of
the alteration of the energy content of the melt 4 during the
tapping step and the danger of over-heating is compensated.

WE CLAIM
1. Method for operating an electric arc furnace (1) comprising at least one
electrode (2), comprising a performing a tapping step in an operating
cycle of the electric arc furnace (1) including a sequence of a power-on
period (t'3), a power-off period (t'03) and a last power-on period (t'f1, t"f), with
energy being supplied to the at least one electrode (2) during the power-on
periods (t'3, t'f1,t"f) and no energy being supplied during the power-off
period (t'03), characterized in that the tapping step is performed after the
power-off period (t'03), and in that energy is supplied to the at least one
electrode (2) at least for part of the time even during the tapping step.
2. Method as claimed in Claim 1, wherein the energy content of a melt
(4) in the electric arc furnace (1) is selectively increased even during the
tapping method step.
3. Method as claimed in Claim 1 or 2, wherein the energy supply is controlled
by means of inputs by an operator.
4. Method as claimed in Claim 1 or 2, wherein the energy supply is controlled
by means of a meter.
5. Method as claimed in Claim 1 or 2, wherein the energy supply is controlled
by means of a model for the energy and mass balance implemented in a
control device.

6. Method as claimed in one of the preceding claims, wherein the
beginning of the tapping step (TTO) lies in the last power-on period (t'F1, t"F)
and the end of the tapping step (TT1) lies in a final power-off period (t'04,t"04)
following the last power on period (t'F1, t"F).
7. Method as claimed in Claim 6, wherein the energy supply in the last
power-on period (t",) is steadily decreased during the tapping step.
8. Method as claimed in Claim 6, wherein the energy supply in the last
power-on period (t'F1,t'F) is decreased in steps and/or according to a
prolonged, initially constant curve.
9. Device for performing a method as claimed in one of Claims 5 to 8, with
anelectric arc furnace (1 ) and a control device connected to the electric
arc furnace (1), wherein the control device comprises a model for the
energy and mass balance and is configured in such a way that it
controls the position and the energy supply to the at least one electrode
(2) even during the tapping step.

ABSTRACT

METHOD AND DEVICE FOR OPERATING AN ELECTRIC FURNACE"
The invention relates to a method for operating an electric arc furnace (1 )
comprising at least one electrode (2), comprising a performing a tapping step
in an operating cycle of the electric arc furnace (1) including a sequence of a
power-on period (t'3), a power-off period (t'03) and a last power-on period (t'f1, t'f),
with energy being supplied to the at least one electrode (2) during the power-on periods
(t'3, t'f1,t"f) and no energy being supplied during the power-off period (t'03),
characterized in that the tapping step is performed after the power-off period
(t'03), and in that energy is supplied to the at least one electrode (2) at least
for part of the time even during the tapping step.

METHOD AND DEVICE FOR OPERATING AN ELECTRIC ARC FURNACE

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