EP0981034A1 - 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 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.

Slag that has run along 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 through 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 crucial point is knowledge of the Initial height of the bathroom mirror.

In a known method for determining the initial height of the bath level, this is derived from the bath weight, which is measured by measuring 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. The latter, however, increases over time, since the refractory lining of the furnace vessel wears particularly as a result of the high temperatures in the area of the floor profile and on the wall in the area of the bathroom mirror,
Temperature change and pressure change stresses. Therefore, the bath weight is not a reliable indicator of the level of the bath.

With today's state of the art, the height of the bathroom mirror measured in order to lower the oxygen lance in a targeted manner To reach converter or in the furnace vessel water-cooled measuring probe with two contact pins on the measuring head used. After passing through the slag layer changes itself when the probe is immersed in the steel bath electrical resistance between the contact pins and signals the position of the bathroom mirror. This procedure is however, especially if you take the additional measurement before taking the racking into consideration.

The invention has for its object a method specify that for the exact and cost-effective determination of the Height of the bath level of an electric arc furnace just before whose racking leads.

The task is solved in that the height of the bathroom mirror determined by mathematical linking of length dimensions that is partly direct and partly indirect as well preferably outside the high temperature range of Electric arc furnace can be measured. The exact measurement of Lengths are comparative in a normal temperature environment simple and inexpensive. This allows the measurement process to be accurate and be inexpensive.

In a development of the invention, the height of the bath level from the difference of the position value of the in working position located electrode support arm and the length of the Graphite electrode and the corrected length of their Arc determined. The position values of the Electrode support arm and the length of the graphite electrode directly measured, the length of the arc indirectly.

The length of the arc is advantageously determined using electrical parameters such as voltage, power factor, (cosine ) Resistance, reactance and other parameters during the Operating determined. These electrical measured values drop without this in operation and do not require any additional Apparatus, time and operating expenses.

It is advantageous that when determining the Arc length is an empirically determined correction element for the unevenness of the bathroom mirror is taken into account. Thereby the accuracy of the determination of the bath level increases.

It is also advantageous that the length of the graphite electrode is determined as the difference in the position value of the raised electrode support arm and the position value of one optical position measuring device, with whose help the tip the raised graphite electrode through the open one Slag door is located. The position values of Electrode support 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 pure more optical.

Because the optical position measurement of the top of the Graphite electrode after raising it following the overheating phase, the length measurement is made shortly before 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 height used.

It has been shown to be advantageous that the Electrode consumption from the 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 from the electrical used in melting 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, electric steel is made Scrap and possibly melted from sponge iron and pig iron. A furnace vessel (2) is tiltable as a refractory lined 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, taking its Position by a position sensor, not shown is shown. An arc (6) transfers the energy the input materials.

The melt (7) has a bath level (8) which 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 tapped steel weight 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 molten 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) assumes the position H _{arm, 1} . At this point, the bathroom mirror (8) is smooth and the arc (6) burns quietly under the slag (9). The arc length L _arc can be determined from the existing electrical measured 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 bath surface.

The determination of the electrode length L _{gr is} shown schematically in FIG. L gr = H poor, 2nd - 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 bath = H bad, is - H bad, should . The weight difference can be derived from this ▴G bath = ▴H bath · A deduce, where A is the bath surface.

In case of a weight deficit - if available - additional iron supports such as directly reduced iron or Iron sponge (DRI) and / or hot briquetted iron or Iron sponge briquettes (HBI) continuously over one 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 have 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, depending 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 it 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 (8)

Method for determining the height of the bath level of an electric arc furnace (1), which has a furnace vessel (2) with a slag door (13) and a height-adjustable electrode support arm (5) for at least one graphite electrode (4), characterized in that the height of the bath level ( 8) is determined by arithmetic linking of length dimensions, which are measured partly directly and partly indirectly, and preferably outside the high temperature range of the electric arc furnace (1). A method according to claim 1, characterized in that the height (H _bad ) of the bath level (8) from the difference in the position value (H _{arm, 1} ) of the electrode support _arm (5) in the working position and the length (L _gr ) of the graphite electrode (4 ) and the corrected length (L _arc - c) of the arc (6) is determined. Method according to claim 1 or 2, characterized in that the length (L _arc ) of the arc (6) is determined with the aid of electrical parameters such as voltage, power factor (cos ), resistance, reactance and other measured variables during operation. Method according to one or more of claims 1 to 3, characterized in that an empirically determined correction element (c) for the unevenness of the bath level (8) and the electrode tip is taken into account when determining the arc length (L _arc ). Method according to one or more of claims 1 to 4, characterized in that the length (L _gr ) of the graphite electrode (4) is determined as the difference between the position values (H _{arm, 2} ) of the raised electrode support _arm (5) and the position value (H _gr ) an optical position measuring device (14), by means of which the tip of the raised graphite electrode (4) is located through the opened slag door (13). Method according to claim 5, characterized in that the optical position measurement (14) of the tip of the graphite electrode (4) takes place after the latter has been raised following the overheating phase. Method according to one or more of claims 1 to 6, characterized in that the electrode consumption (▴L _gr ) is determined from the consumption of electrical and chemical energy measured during the melting process. Method according to one or more of claims 1 to 7, characterized in that the bath level (8) is determined from a computational combination of the length dimensions (H _{arm, 1} , H _{arm, 2} , H _gr , L _arc - c) and with that the electrical and chemical energy used during melting is checked.

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