EP0981034B1 - Process to determine the melt level in an electric arc furnace - Google Patents

Abstract

The height of the bath mirror (8) is determined using calculated connection of the linear dimensions. The liner dimensions are measured in part directly, indirectly and preferably outside of the high temperature range of the electric arc oven (1). In the process of determining the height of the bath mirror of an electric arc oven (1), the electric arc oven (1) has an oven tank (2) with a slag door (13) and a height adjustable electrode support are (5) for at least a graphite electrode (4).

Description

The invention relates to a method for determining the height the bath level of an electric arc furnace, the one Oven vessel with a slag door and a height-adjustable one Electrode support arm for at least one graphite electrode having.

In the electric arc furnace, the melt is oxidic Slag covered. For the degree of purity of the steel and for the Casting quality, it is important that when tapping into the The ladle runs with as little slag as possible. The slag contains oxygen, aluminum additives to remove it are needed. The aluminum is oxidized to alumina, which the casting properties deteriorate and the clogging of the Diving spout, which promotes so-called "clogging". Moreover the oxygen from the iron oxide in the slag complicates the Desulphurization and degassing of the steel at the secondary metallurgical treatment.

Running slag is visually difficult to identify. Some Operators therefore use an electromagnetic process for slag detection. However, its warning signal is only given then, when the slag already through the tap hole in the Ladle is running. Only because of the negative casting properties you can see that the tapping was not low in slag.

It is known that due to the "bathtub effect" - one Vortex formation over the tap hole - the slag idler already begins before the slag layer reaches the tap hole reached. It is therefore important that the bathroom mirror over the Tap hole at the end of the tap a certain minimum height having.

This minimum height of the bath level cannot be measured because the furnace vessel is tilted when tapping. The permissible Tapping weight required to reach the minimum bath level depends on the height of the bath level before tapping. There is between this height and the permissible tapping weight a connection for which there are empirical values, so that at known bath level the permissible tapping weight is also known.

The tapping weight is determined using load cells under the Pouring ladle measured in the steel extraction trolley, the racking until the permissible tapping weight is reached is. The key point is knowledge of the Initial height of the bathroom mirror.

In a known method for determining the starting height of the bath level, this is derived from the bath weight is measured by load cells under the furnace vessel. The Bath weight is made up of the tapping weight and the residual steel weight remaining in the furnace vessel after tapping. However, the latter increases over time as the Fireproof lining of the furnace vessel, especially in the area of the floor profile and on the wall in the bathroom mirror area wears out as a result of high temperatures, temperature changes and pressure changes. Therefore, the bath weight is not a reliable indicator for the height of the bathroom mirror.

With the current state of the art, the height of the bath level is measured in order to a targeted lowering of the oxygen lance into the converter or into the furnace vessel to reach. For this purpose, a water-cooled measuring probe with two contact pins used on the measuring head. After passing through the slag layer changes electrical resistance when the probe is immersed in the steel bath between the contact pins and thus signals the position of the bathroom mirror. This However, the procedure is time-consuming, especially if you consider the additional measurement taking the racking into consideration.

The invention has for its object to provide a method that is accurate and inexpensive determination of the height of the bath level of an electric arc furnace leads shortly before its racking.

The task is solved in that the height of the bath level by difference preferably outside the high temperature range of the electric arc furnace directly measured lengths of the position value of the one in the working position Electrode support arm and the graphite electrode and the indirectly determined arc length corrected with a correction element is determined. The exact Measuring lengths outside the high temperature range in normal temperature The environment of the electric arc furnace is comparatively simple and inexpensive. This allows the measurement process to be accurate and inexpensive.

The length of the arc is advantageously determined using electrical parameters such as voltage, power factor (cosine Φ), resistance, reactance and others Measured variables determined during operation. These electrical readings drop without this in operation and require no additional equipment, time and Operating expenses.

It is advantageous that when determining the arc length an empirical determined correction element for the unevenness of the bath level is taken into account. This increases the accuracy of the bath level determination.

It is also advantageous that the length of the graphite electrode is determined as the difference the position value of the raised electrode support arm and the position value an optical position measuring device, with the help of which the tip of the raised graphite electrode is located through the open slag door. The Position values of the electrode arm and optical measuring device become easier Measured way and outside the high temperature zone. The contact to The tip of the graphite electrode is a purely optical one.

Since the optical position measurement of the tip of the graphite electrode according to its The length measurement is carried out after the overheating phase shortly before the Racking made. This will give the exact length of the Graphite electrode taking into account their current Condition of wear for the determination of the bath level used.

It has been shown to be advantageous that the Electrode consumption from that measured during the melting process Consumption of electrical and chemical energy determined becomes. This empirical procedure offers an indirect indication the current electrode length before tapping.

It is therefore advantageous that the bathroom mirror with a arithmetic linkage of the length dimensions determined and with the electrical and chemical energy calculated electrode consumption is checked. In this way the security of the Bath level measurement further increased.

Further details, features and advantages result from the following specific description and drawings, in which an embodiment of the invention schematically is shown.

Fig. 1

einen Schnitt durch einen Elektrolichtbogenofen mit Stahlentnahmewagen,

Fig. 2

einen Teil des geschnittenen ELektroLichtbogenofens mit offener Schlackentür und optischem Messgerät.

Show it:

Fig. 1

a section through an electric arc furnace with steel removal trolley,

Fig. 2

part of the cut electric arc furnace with open slag door and optical measuring device.

In the electric arc furnace (1) of Figure 1, electrical steel is made Scrap and possibly melted from sponge iron and pig iron. A furnace vessel (2) is tiltable as a fire-resistant liner Steel vessel, which has a pivotable furnace lid (3) having. In this way, the scrap in baskets from above be placed in the oven.

The supply of electrical energy for heating the Electric arc furnace (1) takes place in DC operation a graphite electrode (4). This is on one Electrode support arm (5) attached by means of a not shown lifting device through an opening in the furnace cover (3) can be lowered into the furnace space, being its Position by a position sensor, not shown is shown. An arc (6) transfers the energy the input materials.

The SchmeLze (7) has a bath level (8) in the right half of Fig. 1 the level before and in the left Half during racking. On the bathroom mirror (8) a layer of slag floats (9). The molten steel pours into a ladle (10) on a steel extraction trolley (11) with which the ladle (10) to the Pouring equipment or other processing facilities is transported. There are load cells under the ladle (10) (12) arranged to measure the steel weight tapped can.

Figure 2 shows a section of Fig. 1 with a raised slag door (13), which is the view of the top the graphite electrode (4) also pulled up for a optical position measuring device (14) releases.

The method according to the invention works as follows: after melting, the liquid steel (7) of the electric arc furnace (1) is overheated in order to achieve an optimal tapping temperature. Towards the end of overheating. the electrode support _arm (5) takes the position H _{arm, 1} . At this point, the bath level (8) is smooth and the arc (6) burns quietly under the slag (9). The arc length L _arc can be determined from the electrical measurement values of the electric _arc furnace (1).

As can be seen from FIG. 1, the height of the bath level (8) can be determined as follows: H bath = H poor 1 - L gr - (L arc - c)

H_arm,1= Position des Elektrodentragarms (5) gegen Ende der überhitzung,

L_gr = die Länge der Graphitelektrode (4) unter dem Elektrodentragarm (5),

L_arc = die Länge des Lichtbogens (6),

c = ein Korrekturglied zur Berücksichtigung der Unebenheit der BadoberfLäche.

Here are:

H _{arm, 1} = position of the electrode support _arm (5) towards the end of overheating,

L _gr = the length of the graphite electrode (4) under the electrode support arm (5),

L _arc = the length of the arc (6),

c = a correction element to take into account the unevenness of the bathroom surface.

The determination of the electrode length L _{gr is} shown schematically in FIG. L gr = H poor, 2 - H gr

H_arm,2 = die Position des Elektrodentragarms (5) nach Anheben der Graphitelektrode (4),

H_gr = Position der ELektrodenspitze (mittels optischem Positionsmessgerät (14) durch die offene SchLackentür (13) geortet).

Here are:

H _{arm, 2} = the position of the electrode support _arm (5) after lifting the graphite electrode (4),

H _gr = position of the electrode tip (located by means of an optical position measuring device (14) through the open slag door (13)).

The measured value L _gr is compared with that calculated on the electrode consumption ▴L _gr . The electrode consumption ▴L _gr can be determined empirically via the electrical and chemical energy consumed during the melting process and via electrical parameters.

When evaluating the data mentioned above, the difference ▴H _bad between the height of the actual bath level H _{bad, ist} and the target bath level H _{bad, soll occurs} . ▴H _bad = H _{bad, is} - H _{bad, should} . From this the weight difference ▴G _bad = ▴H _bad . Derive A, where A is the bath surface

In the event of a weight deficit - if available - additional iron carriers such as directly reduced iron or Iron sponge (DRI) and / or hot briquetted iron or Iron sponge briquettes (HBI) continuously over a Bunker system can be charged in the electric arc furnace (1) or the batch is tapped to less weight too much lowering of the bath level (8) and thus the To prevent slag tracking. For the next one or the next but one batch will be correspondingly more scrap in the Scrap basket loaded and charged. In the case of one Excess weight is for the next or the next Batch correspondingly less scrap loaded into the scrap basket and charged.

The method according to the invention is characterized by the following Benefits from:

- High measuring accuracy

Compared to measuring with pressure load cells under the Oven vessel (2), the method according to the invention is more precise, because the bath height is more crucial than for slag-free tapping the bath weight, which depends on the same bath height The state of wear of the furnace vessel (2) varies.

- Lower cost

The well-known method of bath level measurement in the furnace vessel (2) over oxygen lance and probe is more expensive than that measurement method according to the invention. This already uses the existing data and only requires an additional conventional optical measuring device (14).

- Early detection of an insufficient amount of bath

The method according to the invention offers the possibility of a rapid measurement of the bath level (8) even before tapping and gives information about the permitted tapping amount for a slag-free racking, which is necessary for the adjustment of the desired degree of purity is crucial. Also offers there decision support for scrap loading and re-charging for the timely correction of the bath quantity.

- No additional idle times

Because the measurements are taken during normal operational process steps are no additional idle times required, which lead to loss of production.

Claims (7)

1. A process for determining the height (H_bad) of the melt level in an electric arc furnace (1) that comprises a furnace vessel (2) with a slag door (13) and a height-adjustable electrode carrying arm (5) for at least one graphite electrode (4),
   characterized in that
   the height (H_bad) of the melt level (8) is determined by forming the difference between the lengths of the position value (H_arm,1) of the electrode carrying arm (5) in the operating position which are directly measured preferably outside the high-temperature region of the electric arc furnace (1) and the length (L_gr) of the graphite electrode (4) and the indirectly determined arc length (L_arc-c) that is corrected with a correction factor (c).
2. The process according to Claim 1,
   characterized in that
   the length (L_arc) of the arc (6) is determined during the operation with the aid of electrical parameters, e.g. voltage, power factor (cos Φ), resistance, reactance and other measuring variables.
3. The process according to Claim 1 or 2,
   characterized in that
   an empirically determined correction factor (c) for the unevenness of the melt level (8) and the electrode point is taken into account in determining the arc length (L_arc).
4. The process according to at least one of Claims 1-3,
   characterized in that
   the length (L_gr) of the graphite electrode (4) is determined in the form of the difference between the position values (H_arm,2) of the raised electrode carrying arm (5) and the position value (H_gr) of an optical position measuring device (14) that serves for determining the position of the point of the raised graphite electrode (4) through the opened slag door (13).
5. The process according to Claim 4,
   characterized in that
   the position of the point of the graphite electrode (4) is optically measured (14) once it is situated in the raised position after the superheating phase.
6. The process according to at least one of Claims 1-5,
   characterized in that
   the electrode consumption (ΔL_gr) is determined from the measured consumption of electrical and chemical energy during the melting process.
7. The process according to at least one of Claims 1-6,
   characterized in that
   the melt level (8) is determined from a mathematical combination of the length dimensions (H_arm,1, H_arm,2, Hgr, L_arc-c) and controlled with the electrode consumption that is calculated from the electrical and chemical energy consumed during the melting process.

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