GB2083183A - Metal refining apparatus - Google Patents

Abstract

Top blown steel refining apparatus includes two tuyeres projecting through the base of the vessel, said two tuyeres being located, in the normal upright operational position of the vessel, adjacent to a vertical plane passing through a vessel axis through trunnion pins thereof, and being disposed one on each side of the centre point of the base of the vessel at between one quarter and one half of the radius of the base of the vessel from the centre point, and each tuyere being inclined, at entry to the vessel, at a tilt angle to a plane parallel to said vertical plane of up to 45 DEG and at a skew angle to a plane at right angles to said vertical plane of up to 45 DEG . A radiation pyrometer may be mounted at the base of one of the tuyeres outside the vessel wall whereby the melt and/or reaction temperatures adjacent the tuyere outlet may be monitored. <IMAGE>

Description

SPECIFICATION Metal refining apparatus This invention relates to apparatus for refining metal and more particularly to steel refining apparatus of the kind (hereinafter referred to as "the kind described") comprising a melt containing vessel and including an overhead lance for the passage of refining gas, such as oxygen, on to the upper surface of the melt in the vessel and including at least one tuyere projecting through the wall of the vessel below the level of the melt therein for the injection of a stirring or processing gas, sometimes together with entrained solid reactants in powder or granular form, directly into the melt.

Such vessels are mounted for rotation about a horizontal axis for sampling andfortapping purposes on trunnion pins. Usually the vessel is arranged to turn in one direction to a sampling position and in the opposite direction for tapping.

According to the invention there is provided steel refining apparatus of the kind described including two tuyeres projecting through the base of the vessel, said two tuyeres being located, in the normal upright operational position of the vessel, adjacent to a vertical plane passing through the vessel axis through the trunnion pins, and being disposed one on each side of the centre point of the base of the vessel at between one quarter and one half of the radius of the base of the vessel from the centre point, and each tuyere being inclined, at entry to the vessel, at a tilt angle (as hereinafter defined) of up to 45" and at a skew angle (as hereinafter defined) of up to 45 .

By the expression "tilt angle" as used herein is meant an inclination of the or each tuyere with respect to the vertical in vertical plane parallel to the above-mentioned vertical plane through the axis of the trunnion pins. By the expression "skew angle" as used herein is meant an inclination with respect to the vertical of the or each tuyere in a plane at right angles to the aforementioned vertical plane through the axis of the trunnion pins.

The tuyeres may comprise double tuyeres formed of twin concentric tubes. The use of two tuyeres in many commercial instances provides perfectly adequate gas flow for processing and/or stirring of the metal in the refining vessel. However, in some instances, for example when using a particularly large vessel, one or more additional tuyeres may be located in the base of the vessel. Such additional tuyeres desirably conform to the above specification criteria with regard to their location and inclination.

We have found that the criteria defined herein with regard to the arrangement of tuyeres in relation to the vessel have a surprisingly beneficial and interrelated effect upon the operation of the steel refining apparatus.

Thus by way of example location ofthetuyeres adjacent to a vertical plane passing through the axis of the trunnion pins, amongst other things, ensures the minimum of danger to personnel from metal slag splashing or ejection when the vessel is horizontal in the sampling position, since by means of this location of the tuveres they will be clear of the metal/slag during sampling. Hence the necessity for complicated shielding around the vessel to protect operating personnel is greatly reduced. Similarly, when the vessel is turned for tapping, the tuyeres in the location indicated are, or very shortly become, clear of the metallslag thereby limiting metal or slag splashing.

Again, we have found that the disposition of the tuyeres in relation to the diameter of the vessel as defined essentially by the vertical plane passing through the axis of the trunnions is of considerable importance in establishing satisfactory and safe gas flow through the tuyeres into the vessel. Thus we have found that by disposition and inclination of the tuyeres within the ranges herein above specified, stability of the melt is surprisingly satisfactory. Thus precession (which comprises a moving surface wave formation) and wall washing problems can be particularly diminished and plume formation, which is caused by conjunction of streams from two tuyeres at the bath surface, can be avoided. In addition, highly satisfactory bath circulation for a given gas flow rate will be obtained.

The angle of tilt may be up to 20 and the angle of skew may be up to 10 .

The tuyeres may be disposed at between 0.4 and 0.5 of the radius of the base of the vessel from the centre point thereof.

The tuyeres may be spaced from said vertical plane by a distance between 0.1 and 0.2 of the radius of the base of the vessel.

In order that the invention may be more readily understood one embodiment thereof will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a schematic elevation of steel refining apparatus according to the invention.

Figure 2 is a schematic plan of the base of the vessel of Figure 1; Figure 3 is a schematic view of a double tuyere of concentric design; and Figure 4 is a schematic view of an alternative form of tuyere design.

Referring to the drawings it is to be seen that there is provided a steel refining vessel 1 having a refractory lining 2, a lance 3 is provided by means of which oxygen can be blown on to the surface of the melt 4 contained in the vessel for refining purposes.

As will be noted, the melt carries a slag layer 5. The vessel is mounted for rotation upon trunnion pins 6.

Passing through the base 7 of the vessel are two tuyeres 8. As is to be noted in particular from Figure 2, these tuyeres are located adjacent the vertical plane passing through the trunnion axis and are spaced from the centre of the base of the vessel by between one quarter and one half of the radius of the vessel. As can be seen from Figure 1, the tuyeres at their point of entry into the vessel are angled with respect to the vertical.

In operation the tuyeres are arranged to inject air sheathed by an inert gas into the melt for stirring and processing purposes.

In an experimental example, an LD refining vessel of nominal 110 tonne capacity was provided with two double concentric tuyeres located at a position from the centre point of the vessel base equal to approximately three eights of the radius of the vessel. The tuyeres were inclined such that the angle of tilt was 30 and the angle of skew was 45 . It was found that with this arrangement satisfactory bath circulation and processing occurred at a gas flow rate up to 1200 m3/h overall (using tuyeres having an outer nominal diameter of 25.4 mm). At the same time plume formation was avoided, as was precession and wall washing.

In two operational examples, LD refining vessels of 150 tonne and 100 tonne respectively were provided with 25 mm o.d. twinn double tuyeres.

These were located at positions 0.44 and 0.48 of the radii of the vessels from the centre points thereof respectively and 0.15 and 0.17 of the radii of the vessels from the vertical plane through the trunnions respectively. the tilt angles were 7" and 13 respectively and the skew angles 5 and 3 respectively.

Maximum total gas flows used were 1200 m3/h and 1000 m3/h respectively. In both cases bath circulation and metallurgical processing were very satisfactory, whilst plume formation precession and wall washing were avoided.

Figures 3 and 4 illustrate alternative designs of tuyere for use in the apparatus herein above described.

The tuyeres used consist of two concentric stainless steel pipes 9 and 10. The construction of the basic type is shown in Figure 3. The inner core pipe 9 is spaced from the outer pipe 10 by small weld blobs 11 on the outer surface along the length of the core pipe 9. By carefully machining the weld metal and annular gap betwee the pipes can be accurately maintained around its circumference which is very important from a tuyere wear viewpoint.

Tuyeres installed in converters can be up to 2 m in length and it is important that the annular spacing is maintained along the working length, i.e. the length of the tuyere within the refractory lining of the vessel which is usually between 455 and 610 mm. The actual spacing can be varied and it is advantageous to have the annular gap as small as possible which extends the range of operation of the tuyere and means that annular gas protection flow rates can be reduced and could be important from a cost aspect if argon were used for protection.

However, over a long length with a very small annular gap, the pressure drops can be very large and hence a stepped tuyere has been designed which has a narrow annular gap along its working length and a wider annular gap for the rest of its length. Typically, for a stepped tuyere, using a stepped inner pipe 12, the annular gaps can be 0.87 mm and 1.6 mm respectively. A stepped tuyere construction is shown in Figure 4.

In some embodiments of tuyere arrangements it is possible to incorporate a radiation pyrometer mounted at the base of the tuyere outside the vessel wall. Such a radiation pyrometerwould be chosen so that its focal length is matched to the optimum tuyere length, so that the pyrometer can be used for measuring the melt temperature andlor monitoring temperature fluctuations on reactions adjacent to the tuyere outlet within the vessel. For an even temperature measurement, an inert gas should be passed through the tuyere during the temperature measurement period.

Claims (10)

1. Steel refining apparatus of the kind described including two tuyeres projecting through the base of the vessel, said two tuyeres being located, in the normal upright operational position of the vessel, .

adjacent to a vertical plane passing through the vessel axis through the trunnion pins, and being disposed one on each side of the centre point of the base of the vessel at between one quarter and one half of the radius of the base of the vessel from the centre point, and each tuyere being inclined, at entry to the vessel, at a tilt angle (as hereinafter defined) of up to 450 and at a skew angle (as hereinafter defined) of up to 45 .

2. Apparatus according to Claim 1 wherein the tuyeres are double tuyeres formed of twin concentric tubes.

3. Steel refining apparatus according to Claim 2 wherein at least one ofthetuyeres has a narrow annular gap between the concentric tubes along its working length, and a wider annular gap for the rest of its length.

4. Apparatus according to Claim 1,2 or 3 wherein one or more additional tuyeres are located in the base of the vessel.

5. Apparatus according to Claim 4 wherein the location and inclination of said one or more additional tuyeres is determined in accordance with the same criteria determining the location and inclination of said two tuyeres.

6. Apparatus according to any one of the preceding claims wherein the angle of tilt is up to 200 and the angle of skew is up to 10 .

7. Apparatus according to any one of the preceding claims wherein the tuyeres are disposed at between 0.4 and 0.5 of the radius of the base of the vessel from the centre point thereof.

8. Apparatus according to any one of the preceding claims wherein the tuyeres are separated from said vertical plane by a distance between 0.1 and 0.2 of the radius of the base of the vessel.

9. Apparatus according to any one of the preceding claims wherein a radiation pyrometer is mounted at the base of one ofthetuyeres outside the vessel wall whereby the melt temperature and/or reaction temperatures adjacent the tuyere outlet can be monitored.

10. Steel refining apparatus substantially as shown in and as hereinbefore described with respect to the accompanying drawings.