EP2683999A1

EP2683999A1 - Method for operating an alternating-current electric arc furnace, device for performing the method, and alternating-current electric arc furnace having such a device

Info

Publication number: EP2683999A1
Application number: EP12713904.6A
Authority: EP
Inventors: Thomas Matschullat; Detlef Rieger
Original assignee: Siemens AG
Current assignee: Primetals Technologies Germany GmbH
Priority date: 2011-04-13
Filing date: 2012-03-20
Publication date: 2014-01-15
Also published as: US20140112365A1; MX338597B; RU2605739C2; MX2013011878A; EP2511638A1; RU2013150350A; WO2012139859A1

Abstract

The invention relates to a method for operating an alternating-current electric arc furnace, to a device for performing the method, and tp an alternating-current electric arc furnace having such a device. During the operation of an alternating-current electric arc furnace (1), which comprises at least one electrode (3a, 3b, 3c) for producing a melt, vibrations are measured at a wall (2a) of a furnace vessel (2), whereby a slag height (H_rel) of the melt is determined. A rapid reaction to the change in the slag height is made possible by adjusting the arc length of the at least one electrode (3a, 3b, 3c) in the case of deviations of a measured actual value (A, B, C) of the slag height (H_rel) from a target value (S).

Description

description

Method for operating an AC electric arc furnace, apparatus for carrying out the method and an AC electric arc furnace with such a device

The invention relates to a method for operating an alternating current electric arc furnace, comprising at least one electrode for producing a melt in a furnace vessel, where vibrations are measured ^¬ on a wall of the furnace vessel, through which a slag height of the melt is determined. The invention further relates to a device for carrying out this method and an AC electric arc furnace with such a device.

In the production of steel in an electric arc furnace, particularly in an AC electric arc furnace, a foamed slag or slag is formed and blown by blowing in a mixture of media, e.g. a mixture of injection coal and oxygen, foamed to improve the energy input by means of an arc generated by the electrodes of the electric arc furnace or to reduce the losses by radiation. The state of the foam slag of the melt is a measure of the effectiveness of the energy input. The aim is therefore to achieve as far as possible the process requirements adapted level of foamed slag in the furnace interior.

From WO 2007/009924 it is known to determine the energy supply in an electric arc furnace with the aid of electrical sensors and to measure vibrations in the electric arc furnace. By evaluating the measured data of the electrical sensors and by evaluating the measured vibrations, the height of the foamed slag is determined.

From WO 2010/088972, is also known, for controlling a carbon monoxide emission of an electric arc furnace determine the height of the foamed slag, wherein the coal ^¬ entry and / or the oxygen supply are controlled so that the height of the foamed slag is kept below a maximum value ^¬ .

However, the control of the carbon input has the disadvantage that if no constant and uniform slag height is achieved for all areas of the electric arc furnace in a short time due to delay in the coal conveyance, too much radiant power is delivered to the walls. Hot spots are produced on the furnace walls, causing energy losses and increasing wear.

The object of the invention is to enable a rapid reaction to the change in slag height in the AC electric arc furnace.

The object is achieved by a method for operating an AC electric arc furnace, comprising at least one electrode for producing a melt in a furnace vessel, wherein vibrations are measured on a wall of the Ofenge ^¬ vessel, through which a slag height of the melt is determined and wherein given by a set value control and / or control signals in case of deviations of a he ^¬ mediated actual value of the slag height, through which an arc length which is adapted at least one electrode.

The object is further achieved according to the invention by a device comprising

at least one structure-borne sound sensor for detecting vibrations on a wall of a furnace vessel of an AC electric arc furnace, wherein the AC electric arc furnace has at least one electrode for producing a melt in the furnace vessel,

- a computing unit for calculating the actual value of the sleep ^¬ ckenhöhe in the furnace vessel, - And a control or Regelemheit for adjusting the arc length of the at least one electrode at Abwei ^¬ chungen the actual value of the slag height of the target value.

The object is also achieved according to the invention by a

AC electric arc furnace with such Vorrich device.

The advantages and preferred embodiments set forth below with respect to the method are to be transferred analogously to the device and the AC electric arc furnace.

In this case, the target value is not an absolute value, but an allowable range, which is characterized by a permissible maximum value and a permissible minimum value. Upon exceeding or falling below the target range of the allowable maximum value over ^¬ reached or the permissible minimum value is thus maintained.

The invention is based on the idea that, in response to a change in the height of the slag in the furnace vessel, the length of the arcs z generated in the AC electric arc furnace can be influenced. This is done by a corresponding control of the at least one electrode of the AC electric arc furnace, in particular via regulation of the impedance of the electrode. It is true that an increase in the impedance leads to an extension of the arc length and thus to a He increase the radiation power. A lower impedance in turn leads to the reduction of the arc length and thus the radiation power, but in this case the thermal convection of the arc is increased.

Usually, in the case of deviations of the measured height of the foamed slag from the predetermined desired value, the coal feed is increased or reduced for a specific time, as can be deduced from WO 2010/088972. Due to the delay in delivery elapses until the reaction to this measure egg ^¬ niger time, in the order of about 20 seconds lies. In comparison, the electrode control takes place to adapt the arc length with a significantly shorter reaction time of about one second. Thanks to the control of the Lichtbo ^¬ gene length lower radiation losses are present, which have a minimized radiation to the furnace walls result.

The targeted, demand-oriented performance optimization of the electrodes also achieves a uniform and rapid melting of the solids or scrap filling of the alternating current electric arc furnace. A further advantage of the optimized control of the arc length is the re ^¬ duzierung of Einblaskohlenstoffes, thus less CO ₂ ^¬ shock is achieved by lower energy and carbon consumption. The process is thus characterized by higher productivity, lower energy losses, lower operating time and by reducing wall wear.

The measurement of the height of the slag is based on that in the

WO 2007/009924 and WO 2010/088972 described methods.

The arithmetic unit, which determines the slag height in the furnace vessel on the basis of the measurement signals of the at least one structure-borne sound ^sensor , is in particular part of the control and / or regulating unit which, for the sake of simplicity, is further referred to as Regelein ^¬ unit. After the actual value of the slag height has been calculated, it is compared with the desired value or desired range. In case of deviations, the control unit generates the control and / or control signals for adjusting the arc length.

To ensure a highly dynamic and targeted control or re gelung arc length of the melting process is divided into at least two, in particular in three periods of the development of slag and regulates the arc length of the at least is one electrode in dependence of the Ent ^¬ development period. In particular, a distinction must be made between the following three development periods: a slag buildup or initial period in which the slag is formed; a slag period in which the height of the slag reaches a maximum level, and an end period in which the Height of the slag goes back again. The response to the slag change is thus taking into account the time elapsed since the start of the smelting process in the AC electric arc furnace, since this time is crucial for the development of slag.

If a very low slag condition is measured in the initial period, this indicates that the scrap has not completely melted. In this case, the optimum regulation of the arc length depends on which area of the furnace vessel scrap with the larger piece size is located. Under measure of the lumpiness of a solid each particular size is understood, which is geeig ^¬ net, show differences in the lumpiness of different lumpy solid. Under lumpiness of the solid substance ^¬ each physical size of the solid can be verstan the ^¬, which influences the burning behavior of the arc on the solid. In particular, this may be taken to mean the size of a contiguous solid part and / or its compactness, where compactness is to be understood in the sense of a measure of a given solids density distribution. A method of determining the measure of lumpiness for solid in an electric arc furnace is disclosed in US Pat

WO 2009/095293 A2.

If ^¬ det at an initial period of the at least one Elect ^¬ rode solid which befin with a large Stückigkeitsmaß, is preferably the arc length is at least reduced when it falls below the target value of the one electrode, WO by an increased convective near or below Electrode is achieved.

However, if solid with a large Stückigkeitsmaß located farther away from the electrode in the vicinity of the wall, then advantageously the arc length of the at least one electrode he ^¬ heights when falling below the target value. This increases the radiant power and this favors the melting of the scrap in the vicinity of the wall. If an increase in the radiation power and therefore the waste radiation should not be accepted to the furnace wall, is according to an alternative preferred embodiment in value fell below the target value in the initial period of the light ^¬ arc length at least maintaining the unchanged one electrode and the Operating time of the power supply is extended.

According to a preferred variant, the arc length of the at least one electrode is reduced both in the slag period and in the end period of the slag development when the value falls below the desired value. In order to avoid wear on the furnace walls, in this case the radiation power delivered to the furnace wall is reduced.

Exceeding the target value is treated equally in all development periods of the slag in particular. If the actual value exceeds the nominal value, preference ^¬, the arc length of höht at least one ER electrode.

The adjustment of the arc length is in particular comple ^¬ zend to a regulation of carbon and oxygen injection in response to the change of the slag level. Against this background, advantageously the coals ^¬ material supply in the AC electric arc furnace at variations in the slag height from the nominal value is also regu ^¬ lines. If, for example, the slag height is above the desired value or setpoint range, the coal ion is reduced. Since the reaction time to this operation is several Se ^¬ customer, the arc length of the electrode is adjusted in parallel. Conversely, when falling below the target value for the slag height, the carbon supply he ^¬ increases and at the same time the arc length is also adjusted. Analog is conveniently the oxygen supply to the AC electric arc furnace at the slag height deviations from the nominal value corresponding to gesteu ^¬ ert or regulated. The oscillations of the AC electric arc furnace are preferably measured with the aid of at least one structure-borne sound ^sensor , in particular an acceleration sensor. The structure-borne sound of the arc is passed through the melt and / or through the foam slag to the furnace vessel and can be measured there in the form of vibrations. The structure-borne sound sensors are in particular indirectly and / or directly connected to the furnace vessel or to the wall of the furnace vessel. The structure-borne sound sensors, for example, are arranged at regular intervals around the furnace vessel. In order to increase the accuracy of the structure-borne sound measurements, a structure-borne sound sensor is provided in particular per electrode.

The alternating current electric arc furnace expediently has three electrodes and one structure-borne sound sensor is provided for each electrode. Each electrode is assigned to a zone of the furnace vessel and the height of the slag is determined for each zone. The control or regulation of each of the three electrodes takes place in particular independently of the other two electrodes. The foam slag height is measured separately in all three zones of the furnace vessel and the arc length of each of the three electrodes is adjusted individually to the spatial slag height distribution in the furnace vessel on the basis of the measurement data of the corresponding zone.

Preferably, at least one fuzzy controller is used to control the electrode. Fuzzy controllers are systems that belong to the class of characteristic controllers that correspond to the theory of fuzzy logic. In each control step, three sub-steps are performed: a fuzzyfication, an inference and finally a defuzzification. The individual inputs and outputs are called linguistic variables, which each include fuzzy sets. Such a fuzzy controller can, for example, fall back on a reaction model stored in the arithmetic unit. An embodiment of the invention will be described with reference to a

Drawing explained in more detail. Herein show:

1 shows schematically an AC electric arc furnace, and

2 shows the time course of the slag height in one

AC electric arc furnace.

Like reference numerals have the same meaning in the various figures.

1 shows an AC electric arc furnace 1 with a furnace vessel 2, into which a plurality of electrodes 3a, 3b, 3c, which are coupled via power supply lines to a power supply device 12, are guided. The power supply ^device 12 preferably has a furnace transformer. By means of the three electrodes 3 a, 3 b, 3 c, feed materials such as scrap are melted in the alternating current electric arc furnace 1. In the production of steel in the AC electric arc furnace 1, a slag or foam slag not shown here is formed.

On a wall 2a of the furnace vessel 2, ie at the outer boundary of the furnace vessel 2, structure-borne noise sensors 4a, 4b, 4c for measuring vibrations are arranged. The structure-borne sound ^¬ sensors 4a, 4b, 4c may be connected to the furnace vessel 2 indirectly and / or directly. The acoustic emission sensors 4a, 4b, 4c are in particular to the electrodes 3a, 3b, 3c arranged gegenü ^¬ berliegenden sides of the wall 2a. The structure-borne sound sensors 4a, 4b, 4c are in this case preferably designed as Accelerati ^¬ supply sensors and positioned above the foaming slag in the furnace vessel. 2 Each structure-borne sound sensor 4a, 4b, 4c is an electrode 3a, 3b, associated 3c can thus cavities ^¬ Lich resolved information about the slag height in three zones of the furnace vessel 2 which are formed around each of the electrodes 3a, 3b, 3c, can be obtained. The measured values or signals of the structure-borne sound sensors 4a, 4b, 4c are performed via protected lines 5a, 5b, 5c in a ^¬ opti cal device 6 and passed from there via an optical fiber 7 in the direction of a computing unit. 8 The signal lines 5a, 5b, 5c are preferably protected from heat, electromagnetic fields, mechanical stress and / or other loads.

In the exemplary embodiment shown in FIG. 1, sensor and control devices 13a, 13b, 13c are provided on the power supply lines of the electrodes 3a, 3b, 3c, with the aid of which current and / or voltage or the energy supplied to the electrodes 3a, 3b, 3c is measured and can be regulated. The sensor and control devices 13a, 13b, 13c are formed with a control unit 8, for example via a cable

Signal lines 14a, 14b, 14c coupled. More Signallei ^¬ obligations 14d, 14e, 14f serve to connect the sensor and control devices 13a, 13b, 13c with a control or regulating device 9, which receives the control requirements of the computing unit. 8 The control and / or regulating device 9 is further referred to simply as a control device 9. Alternatively to the embodiment according to FIG 1, the integrated Regelein ^¬ 8 may be an integral part of the control and / or regulating device. 9

The structure-borne noise sensors 4a, 4b, 4c, the sensor and control devices 13a, 13b, 13c, the arithmetic unit 8 and the control device 9 are part of a device 10, which is indicated in FIG 1 by dashed lines.

The AC electric arc furnace 1 further includes carbon blowing devices 15a, 15b, 15c and oxygen blowing devices 16a, 16b, 16c. In the arithmetic unit 8, the measured values or signals of the structure-borne sound sensors 4a, 4b, 4c and of the sensor and control devices 13a, 13b, 13c are detected and evaluated in order to determine the height of the foamed slag in the furnace vessel 2. The of the Structure-borne noise sensors 4a, 4b, 4c detected measured values or signals are correlated with the height of the slag, with a temporal resolution in the range of about one to two seconds is possible. The arithmetic unit 8 transmits at least one control signal or a regulation input based on the currently calculated height of the foamed slag per zone in the furnace vessel 2 or averaged over the zones to the control device 9.

The control device 9 regulates the specification of the computing unit 8 both the supply of carbon and oxygen and the arc lengths of the electrodes 3a, 3b, 3c on the impedance of the electrodes 3a, 3b, 3c. Decisive for this scheme is a temporal differentiation between the different development periods of the foamed slag, so that the arc is regulated differently depending on the different stages of slag formation. The control device 9 preferably comprises a fuzzy controller 11.

The procedure for controlling the arc of the

Electrodes 3a, 3b and 3c will be explained with reference to the diagram in FIG. 2, in which the relative slag height H _re i is shown in FIG

Time t is applied. The X-axis represents time in seconding ^¬ the beginning of the melting operation in the AC electric-arc furnace 1. The measurement signal of the three-borne sensors 4a, 4b, 4c, ie the course of the sleep ^¬ ckenhöhe for the three zones determined in the Oven vessel 2 is indicated by three os ^¬ zillierende lines A, B, C. During the development of the slag, essentially three different stages can be recognized. An initial or slag build-up period I, in which the slag height increases, lasts, according to FIG. 2, to approximately 2450 seconds after the start of the melting process. It is followed by a slag period in which the

Slag height averaged over time remains essentially con ^¬ stant. From about 3150 seconds after the start of the melting process in the AC electric arc furnace 1 begins a final period of slag formation, in which the fluctuations of the slag height H _re i. are particularly strong and the average te relative slag height is slightly lower than in the slag period.

The reference symbol S in FIG. 2 denotes a desired value for the relative slag height H _re i. The target value S is different in the three development periods of the slag. The setpoint value S may alternatively represent a setpoint range between a permissible minimum value and a permissible maximum value.

In the initial period I can be a strong foaming occurring defects ^¬ th, but the foaming may in some areas that are not heated enough, be greatly delayed. With regard to the initial period I, four cases can be distinguished:

1) In a zone such as e.g. that of the measured value C, is the

Slag level greatly exaggerated, while in the other two zones the slag level is normal. In this case, the arc is extended at the electrode 3c.

2) When an excessive slag condition is measured in all three zones, the arc of all three electrodes 3a, 3b, 3c extended, resulting in increased radiation ^¬ performance.

3) If the slag height too low, the control of the arc length depends on whether the larger scrap chunks in the vicinity of the electrodes or the wall of the AC electric arc furnace befin ^¬ the. When you are below the electrode, the arc is shortened; if you are closer to the wall, the arc lengthens.

4) If the slag height in all zones A, B, C is too low, this means that the melt takes longer to Aufhei ^¬ tion, it is thus made no change in the arc length.

In the slag period II and in the final period III, the same four cases are to be distinguished, but some require a different approach: 1) If at least one zone of the slag condition is interpreting ^¬ Lich higher than in the other zones, is treated with respect to the initial period I as in the case. 1

2) If all three zones have an excessive slag Stand up, is treated as in the case 2 with respect to the Anfangsperio ^¬ en I.

3) If at least one zone, the target value setting S un ^¬ is undershot, then the arc lengths of the respective electrode 3a, 3b, 3c, which is ordered to-this zone is reduced. Thus, the radiation power is correspondingly corrected ^¬ down to conserve the wall 2a in operation.

4) And finally, when all the actual measured values A, B, C fall for the slag height H _re i in all zones of the AC electric arc furnace 1 below the target value S, the arc lengths at all three electrodes 3a, 3b, 3c reduced and thus reduces the radiant power to the intermediate reaction of the slag on the introduced carbon.

The fuzzy-based control system outputs the correction factors for the individual arc lengths, which are processed and adjusted in an electrode control. The wesentli ^¬ che advantage of controlling the arc length is the short reaction time of about one second. Thus it can be alternates to the ruling in the furnace vessel 2 conditions rea ^¬ particularly fast. The adaptation of the arc length is in particular ^¬ special in combination with a regulation of Kohlenstoffbzw. Operated oxygen supply and serves to optimize the power input and thus to lower radiation losses to the wall of the AC electric arc furnace.

Claims

claims

1. A method for operating an AC electric arc furnace (1), comprising at least one electrode (3a, 3b, 3c) for generating a melt in a furnace vessel (2), wherein vibrations on a wall (2a) of the furnace vessel (2) are measured by which a slag height (H _re i) of the melt is determined, characterized in that in case of deviations of a determined actual value (A, B, C) of the slag height (H _re i) of a target value (S) Control and / or control signals (14d, 14e, 14f) are given, by which an arc length of the at least one electrode (3a, 3b, 3c) is adjusted.

2. The method according to claim 1,

wherein the melting process is subdivided into at least two, in particular into three periods (I, II, III) of the development of the slag and the arc length of the at least one electrode (3a, 3b, 3c) ^depends on the development period (I, II, III ) is regulated.

3. The method according to claim 2,

characterized in that in an initial period (I) of the slag development falls below the desired value (S), the arc length of the at least one electrode (3a, 3b, 3c) is reduced, if under the at least one electrode (3a, 3b, 3c) Solid is located with a large Stückigkeitsmaß.

4. The method according to claim 2,

characterized in that in an initial period (I) of the slag development when falling below the desired value (S), the arc length of the at least one electrode (3a, 3b, 3c) is increased when solid with a large Stü ^¬ ckigkeitsmaß in the vicinity of Wall (2a) is located.

5. The method according to claim 2,

characterized in that in an initial period (I) of the slag development when falling below the desired value (S) the arc length of the at least one electrode (3a, 3b, 3c) is kept unchanged and the operating time of the at least ^¬ one electrode (3a, 3b, 3c) is extended.

6. The method according to any one of claims 2 to 5,

characterized in that in a slag period (II) and in an end period (III) of the slag development when falling below the desired value (S), the arc ^{length of ¬ at} least one electrode (3a, 3b, 3c) is reduced.

7. The method according to any one of the preceding claims, characterized in that when the set value (S) is exceeded, the arc length of the at least one electrode (3a, 3b, 3c) is increased.

8. The method according to any one of the preceding claims, characterized in that in case of deviations of the slag height (H _re i) from the desired value (S), a carbon supply in the AC electric arc furnace (1) is regulated.

9. The method according to any one of the preceding claims, characterized in that in deviations of the slag height from the desired value (S) an oxygen supply in the AC electric arc furnace (1) is regulated.

10. The method according to any one of the preceding claims, characterized in that the oscillations of the AC electric arc furnace (1) by means of at least one structure-borne sound sensor (4a, 4b, 4c), in particular a acceleration sensor, are measured.

11. The method according to any one of the preceding claims, characterized in that the AC electric arc furnace (1) has three electrodes (3a, 3b, 3c) and the height (H _re i) of the foamed slag in one of the respective electrode ^¬ ( 3a, 3b, 3c) associated zone of the Ofenge ^¬ vessel (2) is determined.

12. The method according to any one of the preceding claims, characterized in that a fuzzy controller (11) for Rege ^¬ ment of the arc length of the at least one electrode (3a, 3b, 3c) is used.

13. Device (10) for carrying out the method according to one of claims 1 to 12, comprising

- At least one structure-borne sound sensor (4a, 4b, 4c) for detecting vibrations on a wall (2a) of a furnace vessel

(2) an AC electric-arc furnace (1), wherein the alternating-current electric arc furnace (1) has at least one electrode (3a, 3b, 3c) for producing a melt in the furnace ^¬ vessel (2),

a calculation unit (8) for calculating the actual value (A, B, C) of a slag height (H _re i) in the furnace vessel (2),

- And a control or regulating unit (9) for adjusting the arc length of the at least one electrode (3a, 3b, 3c) in case of deviations of the actual value (A, B, C) of the slag height (H _re i) from the target value ( S).

14. Device (10) according to claim 13,

characterized in that the structure-borne sound sensor (4a, 4b, 4c) is an acceleration sensor.

15. Device (10) according to claim 13 or 14,

characterized by a fuzzy controller (11).

16. AC electric arc furnace (1) with a device (10) according to one of claims 13 to 15.

17, alternating current electric arc furnace (1) according to claim 16, characterized by three electrodes (3a, 3b, 3c), wherein for each electrode (3a, 3b, 3c), a respective structure-borne sound sensor (4a, 4b, 4c) is provided.