LU86804A1 - Temp. measurement in steel converter - using extrapolation from three measurements taken at intervals through thickness of container wall - Google Patents

Abstract

In a steel converter the steel is contained with a reservoir having a base (F) and an internal surface layer (C). The steel (B) lies above the internal surface layer (c). In order to determine the temperature in the bath, represented for example on the inner surface (o) the temperature is measured at thtree points (1-3) situated quarter, half, and three-quarters of the way through the inner surface. At a given instant the three temperature valves may be (t-dt), (t-2dt) and (t-3dt) where t represents the steel temperature. By monitoring the movement of temperature at the three points the steel temperature may be measured continuously.

Description

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BL-4009 / BM

Claim of the priority of a patent application filed in Belgium on March 10, 1987 under No 6 / 48.210 (904.460) C 2356/8603.

METALLURGICAL RESEARCH CENTER -CENTRUM V00R RESEARCH IN DE METALLURGIE,

Non-profit association -Vereniging zonder winstoogmerk in BRUXELLES, (Belgium).

Method for continuously determining the temperature of a metal bath.

The present invention relates to a method for continuously determining the temperature of a metal bath contained in a metallurgical vessel, in particular a bath of liquid steel in a steelworks converter.

In the description which follows, the reference to a steel bath in a converter is however only given for information, because the present invention can also be applied to any metal bath, ferrous or non-ferrous, contained in a metallurgical container.

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We know the importance of knowing the temperature of a steel bath, as well as the evolution of this temperature over time, to appreciate in particular the degree of completion of the decarburization reactions. Obtaining the desired steel grade involves monitoring these reactions and therefore the bath temperature as precisely and continuously as possible, in order to accurately determine the timing of the converter drawdown.

In the current technique, there are various means of measuring the temperature of a metal bath. As an example, we can cite the lost thermocouples, housed in bombs and launched into the bath where they are destroyed after the measurement, as well as the auxiliary lance called "sub-lance" which plunges into the bath through the layer slag.

These known means, however, do not fully meet the objective, because they only provide point and instantaneous measurements which do not necessarily reflect the actual thermal state of the bath and do not allow the evolution thereof to be determined. In addition, they are expensive because each measuring element can only be used once.

The present invention provides a continuous measurement method which makes it possible to remedy the aforementioned drawbacks.

The method of the present invention is based on the observation that the temperature of any point on the bottom of the container follows the evolution of the temperature of the bath; with a certain delay which depends on the position of the point in the background and the nature of the material constituting the

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3.- background. It goes without saying that the process of the invention is not limited to the bottom proper, but that it can also be applied in any part of the lining situated below the level of the bath. For this purpose, the process which makes the object of the present invention is essentially characterized in that the temperature is measured at at least two points located within a region of the wall of said container which is in contact with the metal bath, in that the 'the evolution of the temperature of said points is continuously recorded and that the evolution of the temperature of the bath over time is deduced therefrom, which makes it possible to determine the temperature of the bath at any time.

In the context of this process, it has proved advantageous to measure the temperature at a series of points, for example at three points, distributed according to the thickness of the inner layer of said wall along a straight line perpendicular to this wall. By inner layer is meant a layer of relatively small thickness, for example the wear layer, closest to the metal bath.

According to the invention, the temperature of the metal bath is determined at a given instant from the temperature values measured at said points, by means of a mathematical model which takes into account the position of the points in the wall and the nature of the material. constituting said wall, in particular of its thermal conductivity.

The method of the invention will be explained in detail below, with reference to the appended figures representing, by way of example:

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Fig.l: the position of three measurement points in the inner layer of a converter base;

Fig. 2: the short evolution of the temperature of these points as a function of time.

In FIG. 1, a portion of the inner layer C of a bottom F of the converter is shown schematically, in contact with a steel bath B. Let 0 be a point on the bottom surface which is directly exposed to the bath B. The temperature Tq at point 0 therefore represents the temperature of the steel bath, assumed to be homogeneous. Vertical to point 0 are located three measurement points 1, 2, 3 which, for simplicity, are regularly distributed according to the thickness of the inner layer C; they are positioned respectively at quarter, half and three-quarters of the thickness of this layer, counted from point 0.

The method of the invention consists in measuring the three temperatures T ^, T2 and T3 at points 1, 2, 3 at any time t, and in deducing therefrom the temperature TQ of point 0 at this same time t.

If the temperature Tq of point 0 undergoes a variation AT at an instant t, this variation does not manifest itself instantaneously at points 1, 2 and 3, because of the time required to allow thermal diffusion from point 0 to the other points 1, 2 , 3. The distances between these points 0, 1, 2, 3 being equal, the variation in temperature AT is manifested at points 1, 2 and 3 only at the following instants; point 1: t + At point 2: t + 2 At point 3: t + 3 At.

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As already indicated above, the time At depends on the distance separating two neighboring measurement points and on the thermal diffusivity of the material. As an example, for measurement points 5 cm apart from each other, the time At is worth approximately 6 minutes for a background in magnesia-carbon and only 10 seconds for copper.

Figure 2 shows the temperature evolution curves as a function of time, up to time t, for the three measurement points 1, 2 and 3. The curve corresponding to point 0, that is to say on the surface of the refractory and therefore at the temperature of the bath, is known only until the instant t "'= t - 3 At, following the previous operating cycles. On these curves, the temperatures measured at points 1, 2, 3 at times t; t '= t - At; t "= t - 2 At; t '"= t - 3 At.

The temperature T ^, measured at point 3 at time t, is the result of the change in temperature at point 3 from time t '= t - At to time t, under the effect of the heat received from point 2 and of the heat transferred to a deeper point 4, not shown, during the time interval At. The temperature therefore depends on the temperatures T ^, and T ^, as well as on the nature of the refractory and the distance between the measurement points.

Likewise, the temperature depends on T £, and and T ^, and the temperature depends on T ”'/ T J" and T ^' '.

Knowing the temperatures measured from points 1, 2 and 3 at times t, t ', t ", t’ "as well as the thermal profile, which prevails in the thickness of the bottom of the converter at 6.- *"

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time t '", we give ourselves a temperature from which we can calculate the temperatures TL1 *, T' * and = jj r 2 T ^. We then determine the differences between these temperatures and the actual measured temperatures T £, and at the same points, then these differences are minimized in order to obtain the effective temperature T ”'.

By imposing itself, a rate of variation of the surface temperature of the refractory, that is to say a desired evolution of the temperature of the steel bath, the temperature Tq at time t is calculated by extrapolating on l time interval 3 At. This interval can be made sufficiently small by a judicious choice of the materials used and by an appropriate positioning of the measurement points.

All these calculation operations are carried out by a computer, under the supervision of an appropriate mathematical model, in order to give almost instantaneously the value of the temperature Tq at point 0 at time t.

The “extrapolation” method which is the subject of the invention therefore has, in addition to a very high speed, an accuracy which is largely sufficient for industrial needs.

Claims (3)

7.- Λ K Claims. 1. A method for continuously determining the temperature of a metal bath contained in a metallurgical container, characterized in that the temperature of at least two points located within a region of the wall of said container which is measured is measured is in contact with the metal bath, in that the change in temperature of said points is continuously recorded and in that the change in temperature of the bath over time is deduced therefrom. 2. Method according to claim 1, characterized in that the temperature is measured at a series of points distributed along the thickness.de the inner layer of said wall, along a straight line perpendicular to this wall. 3. Method according to one of claims 1 and 2, characterized in that the temperature of the metal bath is determined at a given instant from the temperature values measured at said points, by means of a mathematical model which takes account the position of the points in the wall and the nature of the material constituting said wall, in particular its thermal conductivity.