GB1591585A

GB1591585A - Metal refining lance head

Info

Publication number: GB1591585A
Application number: GB11443/78A
Authority: GB
Original assignee: SALZGITTER PEINE STAHLWERKE
Current assignee: SALZGITTER PEINE STAHLWERKE
Priority date: 1977-03-23
Filing date: 1978-03-22
Publication date: 1981-06-24
Also published as: AT372706B; IT1093897B; NL188232B; FR2384850B1; LU79277A1; SE7803333L; FR2384850A1; BE865235A; CA1099919A; BR7801849A; PT67808A; SE438870B; ZA781725B; ATA164878A; PL205521A1; DE2712745C2; DE2712745B1; IT7821417A0; NL7803193A; PL125025B1

Description

(54) A METAL REFINING LANCE HEAD (71) We, STAHLWERKE PEINE SALZGITTER AG., a German Body Corporate, of Postfach 1740, 3150 Peine, German Federal Republic, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an oxygen blow refining lance head for use in metal refining comprising a plurality of expansion nozzles extending outwardly from the longitudinal axis of the lance, which in use is directed towards the surface of a molten metal bath, and at least one supply and one return duct for a coolant, each duct being concentric with the longitudinal axis, a flow guide means for cooling the lance head and guiding the flow of coolant being disposed between the two ducts.

Oxygen blow lance heads of the kind being discussed have given excellent practical results in various metallurgical processes, e.g., LD, DLAC, LDS, SM and the electricfurnace process. In the foregoing sentence, the initials LD connote a top-blowing process, originally known as the Linz-Donawitz process; the initials LDAC connote the topblowing process using oxygen and lime, the initials AC connoting the firms A rbed and CRM of Belgium; the initials LDS the topblowing process, the initial S standing for Stahlwerke-Peine-Salzgitter; and the initials SM connote the Siemens-Martin process.

However, one problem relating to the refining operation is the relatively short life of the lance heads, which results in considerable expenditure in buying and installing replacements. No satisfactory method has hitherto been found of adequately increasing the service life of existing types of lance head.

Nearly all lance heads are destroyed by burning away of the centre of the lance end between the nozzles, after a short period of operation. These central defects are dangerous since the cooling water, which is under pressure, may spray through the resulting fractures into the bath of molten steel, resulting in an explosion of oxyhydrogen gas.

It is known that, during the refining process, the temperature in the neighbourhood of the lance head may be up to 2273 K (2000 C). The melting point of copper, on the other hand, is 1356 K (1083"C).

The heat energy applied to the outer surface of the lance head has to be conveyed inwardly and removed by a coolant, e.g.

water. A number of patents and patent applications disclose proposed industrial solutions of the difficult problem of efficiently conveying the coolant through the lance head in order to obtain optimum cooling.

In practice, in steelworks, however, it has been found that the resulting prior art is inadequate and none of the known solutions has produced lance heads having an adequate service life. It has also been found that, in the case of known refining lances of the aforementioned kind, the devices for conveying the coolant in the lance head do not meet the flow requirements sufficiently well to ensure adequate cooling of the most severelyheated parts of the lance head.

Although, theoretically, coolant is supplied to the centre of the lance head, the desired cooling action has not been obtained, inter alia because of turbulence and the formation of stagnant water spaces, since the water-conveying means are not constructed to meet all the requirements. For example, it has been proposed to insert coolant conveying rings in the lance head, but even when the rings surround the nozzles, they do not allow for the change in cross-sectional area between pairs of adjacent nozzles, to satisfy the hydrodynamic requirements.

In other known lance heads, the guide rings end in front of the outer cirle surrounding the nozzles, or variously-shaped circular segments or the like are disposed inside the lance head. These actually accentuate undesired harmful turbulence instead of eliminating it.

All this inevitably results in inadequate cooling, more particularly of the central, most severely-heated part of the lance head, so that the copper melts and the lance head is destroyed after a relatively short time. Consequently, the lance head becomes prema turely unserviceable, which means that operation has to be frequently interrupted and there is a delay in production. In addition, as previously mentioned, there is an additional safety risk from the possible formation of oxyhydrogen gas (through decomposition of water).

The main aim of the present invention is substantially to eliminate the aforementioned disadvantages of known lance heads and obtain more efficient cooling of the most severely-heated parts of the lance head and also increase the service life and reliability, by constructing the cooling region in an optimum manner in accordance with the hydrodynamic requirements for cooling lance heads.

To achieve this aim, the invention is directed to an oxygen blow refining lance head for use in metal refining comprising a plurality of expansion nozzles inside the lance head extending outwardly from the longitudinal axis of the lance head, at least one supply and one return duct inside the lance head for a coolant, a tube coaxial with the lance head axis separating the supply and return ducts, and an annular flow guide member inside the lance head integral with the end of the tube and axially spaced from the inner end of the lance head, the flow guide member closing the tube except for a central opening adjacent the centre of the inner end of the lance head, all the expansion nozzles passing through the flow guide member, the surface of the portion of the flow guide member facing the inner end of the lance head and through which the expansion nozzles pass being concave.

In the lance head according to the invention the surface of the flow guide member is concave so that when the flow cross-section is increasingly constricted between any pair of adjacent expansion nozzles in the horizontal plane, the constriction is proportionately compensated in the vertical plane by the concavity of the flow guide member so as to maintain a constant flow cross-section. The concave curvature can thus be exactly calculated.

In the lance head according to thd invention, therefore, the coolant flows at a uniform speed over the entire free internal surface of the end of the lance head, thus largely obviating film evaporation or reduction in the heat transfer from solid to liquid which, as is found, is causally related to premature melting of the copper in the central region of the end of the lance head.

The aforementioned function is particularly assisted if the central opening in the flow guide member lies inside a circle inwardly bounding the expansion nozzles, and the adjacent concave surface of the flow guide member is placed direct coolant to the central end face of the lance head. By this means the flow of coolant is intensively guided towards the central and most severely-heated region of the end of the lance head.

Advantageous operation of the lance head according to the invention is closely related to the return of the coolant, which must not encounter avoidable resistance, and is also important for optimum cooling. To this end, the upper surface of the flow guide member remote from the end of the lance head is convex, and the convex surface has substantially the same curvature as a concave surface of a distribution member spaced from and facing the flow guide member.

According to another optional feature of the invention, the flow-cross-section bounded by the convex surface of the flow guide member and the concave surface of the distribution member is at least equal to the flow cross-section bounded by the concave surface of the flow guide member and the inner end of the lance head. It has been found that if the teaching according to the invention is exactly adhered to, the coolant spaces can be constructed in such ideal manner that the coolant can be supplied and returned in opposite directions and still have a full cooling effect.

The inner surface of the end of the lance may be formed with ribs or the like to increase its surface area.

A lance head according to the invention will now be described in detail, by way of example, with reference to the accompanying drawings, which is a cross-section through a refining lance head according to the invention comprising four expansion nozzles 9 extending away from the longitudinal axis 7.

An annular flow guide member 1 is connected to a tube or tubular portion 5 separating a coolant inlet duct 3 from a coolant return duct 4. The flow guide member 1 can be secured to tube 5 by known means, e.g.

welding, soldering, clamping, adhesion or the like or by resilient connecting elements.

Member 1 is concave at the lower side, facing the baseplate 6, in the radial region 8 of the expansion nozzles 9, in accordance with the reduction in cross-section between nozzles 9 in region 8, in order to maintain a constant cross-sectional area at region 8 as previously described.

The edge portion 10 bounding the central opening in the flow guide member 1 extends inwardly of the circle 11 inwardly bounding the nozzles 9 and guides the coolant tdwards the central area 12 of end 6 of the lance head.

The convex surface 13 of member 1 has substantially the same curvature as the concave surface 14 of distribution member 2, thus ensuring that the coolant returns without interference or resistance.

In order to ensure that the coolant flows efficiently, member 1 must be carefully sealed from nozzles 9, e.g. non-releasably by welding, soldering or the like, or by releasable seals, e.g. made of a permanently resilient material such as thermoplastic or duroplastic elastomers.

Practical tests on lance heads according to the invention have shown that refining lance heads manufactured according to the invention can last considerably longer than known lance heads. This improves efficiency and also substantially reduces the risk of accidents due to failure of the centre of the end of the lance head.

The inner surface of the end of the lance may be formed with ribs to increase its surface area.

WHAT WE CLAIM IS: 1. An oxygen blow refining lance for use in metal refining comprising a plurality of expansion nozzles inside the lance head extending outwardly from the longitudinal axis of the lance head, at least one supply and one return duct inside the lance head for a coolant, a tube coaxial with the lance head axis separating the supply and return ducts, and an annular flow guide member inside the lance head integral with the end of the tube and axially spaced from the inner end of the lance head, the flow guide member closing the tube except for a central opening adjacent the centre of the inner end of the lance head, all the expansion nozzles passing through the flow guide member, the surface of the portion of the flow guide member facing the inner end of the lance head and through which the expansion nozzles pass being concave.

2. A lance head according to claim 1, in which an edge portion of the flow guide member bounding the central opening therein extends inwardly of a circle inwardly bounding the expansion nozzles, and the adjacent concave surface of the flow guide member is placed to direct coolant to the central end face of the lance head.

3. A lance head according to claim I or claim 2, in which the surface of the flow guide member remote from the end of the lance head is convex, and the convex surface has substantially the same curvature as a concave surface of a distribution member spaced from and facing the flow guide member.

4. A lance according to claim 3, in which the flow cross-section bounded by the convex surface of the flow guide member and the concave surface of the distribution member is at least equal to the flow cross-section bounded by the concave surface of the flow guide member and the inner end of the lance head.

5. A lance head according to any preceding claim, in which the coolant flow in the supply and return ducts is in opposite directions.

6. A lance head according to any preceding claim, in which the flow guide member is secured to the tube by welding, soldering, clamping, adhesion or by resilient connecting elements.

7. A lance head according to any preceding claim, in which the inner surface of the end of the lance head is formed with ribs or the like to increase its surface area.

8. A lance head according to any preceding claim, in which the seals between the flow guide member and the expansion nozzles are made of a permanently resilient material.

9. A lance head according to any preceding claim, in which the seals between the flow guide,member and the expansion nozzles are permanent.

10. An oxygen blow refining lance for use in metal refining, constructed and arranged substantially as herein described, with reference to and as illustrated in the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. sealed from nozzles 9, e.g. non-releasably by welding, soldering or the like, or by releasable seals, e.g. made of a permanently resilient material such as thermoplastic or duroplastic elastomers. Practical tests on lance heads according to the invention have shown that refining lance heads manufactured according to the invention can last considerably longer than known lance heads. This improves efficiency and also substantially reduces the risk of accidents due to failure of the centre of the end of the lance head. The inner surface of the end of the lance may be formed with ribs to increase its surface area. WHAT WE CLAIM IS:

1. An oxygen blow refining lance for use in metal refining comprising a plurality of expansion nozzles inside the lance head extending outwardly from the longitudinal axis of the lance head, at least one supply and one return duct inside the lance head for a coolant, a tube coaxial with the lance head axis separating the supply and return ducts, and an annular flow guide member inside the lance head integral with the end of the tube and axially spaced from the inner end of the lance head, the flow guide member closing the tube except for a central opening adjacent the centre of the inner end of the lance head, all the expansion nozzles passing through the flow guide member, the surface of the portion of the flow guide member facing the inner end of the lance head and through which the expansion nozzles pass being concave.