Nozzle for refining lance

Nozzles for a refining lance are presented which are spaced upwardly from the head of the lance and supply post-combustion oxygen to the space above a molten metal bath undergoing refining. Each of the nozzles has a mouthpiece with two parallel sharp edges which are arranged in planes passing substantially through the axis of the lance and which are connected by slightly rounded edges. Above the mouthpiece of each nozzle is a converging part.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the field of metallurgical refining 
lances. More particularly, this invention relates to a nozzle of a 
refining lance for supplying post-combustion oxygen to the space above a 
molten metal bath undergoing refining. 
Refining lances are known in the prior art which have, apart from vertical 
nozzles supplying supersonic refining oxygen, several auxiliary nozzles. 
These auxiliary nozzles have angles of between 25.degree. and 60.degree. 
(see, for example, patents LU 78 906 and LU 83 814) in relation to the 
vertical axis. They deliver jets of oxygen for the purpose of 
post-combustion. Because these jets of oxygen are subsonic, the auxiliary 
nozzles are fed by an independent oxygen circuit which permits adjustment 
of delivery. 
A means of increasing the degree of turbulence of the jet is also known 
(see Patent LU No. 82 846) and is provided in the conduits of the nozzles 
which guide the post-combustion oxygen. Such turbulence increasing means 
may comprise plates arranged in the conduits of the secondary nozzles so 
as to form spirals. In another embodiment, the walls of the conduits are 
provided with grooves which may be circular and arranged in a plane 
perpendicular to the axis of the conduit or may be spiral. The angles of 
inclination of the post-combustion oxygen jets are dictated by those of 
the nozzles; once they have been determined by empirical tests or methods 
(taking into account the angles of the primary oxygen jets, their 
arrangement, the dimensions of the converter, the height of the head of 
the lance above the bath etc.), the angles remain constant. These prior 
art nozzles do not permit the space above the bath to be swept with jets 
of oxygen and they do not permit post-combustion oxygen to be sent to the 
converter at an angle which varies according to the refining stage in 
progress. Patent LU No. 86 329 (Corresponding to U.S. Pat. No. 4,730,814, 
which is assigned to the assignee hereof and fully incorporated herein by 
reference) describes a supersonic nozzle which supplies post-combustion 
oxygen at a variable angle to the space above a molten metal bath. This 
nozzle comprises a wall along which the gas passes in a straight line 
before ending at a pointed edge which forms part of the mouthpiece. The 
nozzle is level with the top of the pointed edge, and as a result, the jet 
expands and is deflected by the pointed edge. The angle of deflection 
varies according to the pressure of the gas at the edge, i.e. the higher 
the pressure of the gas is at this point, the greater the angle of 
deflection. Conversely, the deflection effect of the edge is practically 
nil when the gas has a subsonic speed at this point. By varying the 
pressure of the gas feeding the nozzle within predetermined limits, an 
angle close to 30.degree. can be swept. The resulting turbulences (from 
this pressure variance) in the converter favor the creation of an extended 
zone, permanently supplied with oxygen. Although this nozzle has a 
post-combustion rate superior to that of conventional nozzles, it may 
still be improved. Indeed, as a result of construction constraints (space 
available in the head of the lance) it is not possible to arrange these 
nozzles around the entire circumference of the head of the lance, but only 
in certain discrete places, so that the space is only fed in an imcomplete 
manner. 
SUMMARY OF THE INVENTION 
The above discussed problems and other disadvantages of the prior art are 
overcome or alleviated by the lance nozzle of the present invention. The 
present invention comprises a nozzle which allows the creation of a 
practically homogeneous layer of oxygen above the molten metal bath of the 
converter. The nozzle is spaced upwardly from the head of the refining 
lance and has a mouthpiece with two parallel sharp edges which are 
arranged in planes passing substantially through the axis of the lance and 
which are connected by slightly rounded edges. The above discussed and 
other features and advantages of the present invention will be apparent to 
and understood by those skilled in the art from the following detailed 
description and drawings.

DESCRIPTION OF THE PRESENT INVENTION 
Referring to FIG. 1, a lance is shown generally at 1. Three refining oxygen 
jets 2 emerge from the head of lance 1. Spaced upwardly from the head of 
lance 1, at a distance of about ten centimeters, are a plurality of 
mouthpieces 3 of several nozzles 4 which are arranged all around the body 
of lance 1 and which supply post-combustion oxygen. Nozzles 4 have above 
mouthpieces 3 an optional throat preceded by a converging part. The 
vertical sides of the mouthpieces 3 have sharp, preferably pointed edges 
and the horizontal sides are preferably rounded. The ratio of the lengths 
between the elongated, sharp edges and the rounded edges is at least 3:1. 
Also, the sharp edges are preferably at no less than 15 mm apart from each 
other. The sharp edges preferably form an angle of about 90.degree. 
Nozzles 4 can be fed in parallel from a single oxygen source and a single 
pressure-reducing valve (See U.S. Pat. No. 4,730,814). It is necessary to 
ensure that oxygen supply conduits are dimensioned in a way that pressure 
differences (differential head losses) are avoided between nozzles 4 and 
between different places in a mouthpiece 3. A pressure sensor (See item 9 
in U.S. Pat. No. 4,730,814) measures the actual pressure P at the entry of 
one of nozzles 4. This pressure P is compared with a reference pressure Po 
and in the event of difference, a regulation loop acts upon the degree of 
opening of the valve. 
Pressure Po is determined by routine testing so as to have a deflection 
which provides a uniform supply of oxygen to the space in the area of 
mouthpiece 3. When nozzle 4 is supplied under a pressure which is rising 
from a zero pressure, a gaseous jet emerges at an increased speed. 
Starting at a predetermined pressure, which is dependent upon details of 
construction of the nozzle, the speed of the emerging gas becomes sonic. 
At this predetermined pressure, further increases in the supply pressure 
no longer have any effect on the speed of the emerging gas which remains 
sonic. However, further pressure increases will raise the internal 
pressure of the system. At the level of mouthpiece 3, the emerging gas or 
jet expands while forming the center of a multitude of shock waves which 
are the basis of an increase in speed of the jet and of its bilateral 
deflection. The angle of deflection varies according to the pressure of 
the gas at the mouthpiece (i.e. the greater the pressure of the gas at 
this point, the greater the deflection--and the quantity of gas 
deflected). Consequently, the ratio of the quantities of gas which emerge 
in a straight line from nozzle 4 and those which are deflected from the 
two lateral sides of nozzle 4 decreases upon an increase of internal 
pressure. A pressure range exists within which the most uniform supply of 
oxygen is obtained in the space opposite nozzle 4. There is also a 
deflection of the jet around the upper and lower sides of mouthpiece 3. 
However, these sides are not very wide and are slightly rounded, thus the 
effect is not very pronounced. While it is reasonable to expect that the 
refractory lining at which the emerging oxygen jet is aimed, would wear 
quickly; this was not observed. The oxygen jet reaches the refractory 
lining as a result of a braking action due to an interaction of the 
pressure reduction of the jet with the shock waves. The turbulence which 
results from the above interaction favors the combustion of carbon 
monoxide. This is a surprising and unexpected feature of the present 
invention. 
Preferably, pressurized gas at the mouthpiece is at least equal to 200,000 
Pascal. In many cases, the arrangement of post-combustion nozzle 4 as 
shown in FIG. 1 is not feasible as a result of construction constraints. 
However, now referring to FIG. 2, it is possible to modify a standard 
lance head 20 with round post combustion holes 21 (intended for subsonic 
blowing) to create a layer of oxygen as proposed by the present invention. 
To achieve this end, insertion pieces 31 are introduced into holes 21 from 
the outside. This forms a converging area 32 and a throat and also 
modifies mouthpiece 3 so that it has sharp edges 33 which are vertical and 
parallel. These edges (For example, about one centimeter apart), are 
connected at top and bottom by curved pieces which fit the profile of the 
original holes. Although the cross sectional area of blowing hole 21 is 
greatly reduced by the fitting of pieces 31, the quantity of gas blown 
into the space is nevertheless increased. This is a result of the 
supersonic speed at which the blowing is carried out. 
Prior art post-combustion nozzles, when supplied under a pressure such that 
the oxygen jet becomes supersonic upon emerging, also deflect around 
mouthpiece 3. Mouthpiece deflection is not preferred because the jet only 
diverges around the blowing axis (with an angle of divergence proportional 
to the pressure) without providing, in conjunction with the neighboring 
jets, a continuous or homogeneous gaseous layer. 
It will be appreciated that it is not inconvenient for post-combustion 
nozzles 4 to have an angle of several tens of degrees in relation to the 
vertical axis. Nozzle 4 may also be arranged in a circle surrounding the 
refining nozzles, on the front of the lance. The oxygen layer, instead of 
being horizontal as is the case in FIG. 1, will be angled towards the 
surface of the molten metal bath, having roughly the shape of an umbrella 
three quarters open. In the arrangement of nozzle 4 described with regard 
to FIG. 1, all the carbon monoxide emerging from the bath must cross the 
continuous layer of oxygen before it reaches the chimney. In this 
alternative embodiment, as the jets are aimed at the bath, an amount of CO 
emerging from the bath outside the surface area delimited by the angled 
layer of oxygen, will not be burnt. However, this amount of CO represents 
only a small proportion of the total quantity. The essential fact is that 
combustion takes place in this case at a shorter distance from the bath, 
which gives better thermal efficiency. 
When post-combustion nozzles are not distributed uniformly on the 
circumference of the head of lance 1, but grouped in pairs, it is 
recommended that the blowing axis of the nozzles be modified so as to 
obtain a better distribution of oxygen in the 
space between two pairs of nozzles. Preferably, the axis of the nozzle is 
angled at up to 50.degree. in relation to the axis of the lance. In FIG. 
4a and 4b such a pair of nozzles 43 has been represented. The insertion 
pieces 41 have only one converging part (without a throat) and they modify 
blowing axis 42 of nozzle 43 in the direction of the neighboring pairs of 
nozzles 43. Thus, in each nozzle, one of the sharp edges is rounded and 
one of the sharp edges is pointed. In addition to this expedient, there is 
also the possibility of moving back the edges from the side of the 
mouthpiece neighboring the other pairs of nozzles 43 towards the inside of 
the body (see item 44) in such a way as to cause with these sides a 
deflection of the jet before it emerges from the head of lance 1. Thus, 
one of the sharp edge in a nozzle will be spaced back in relation to the 
other sharp edge. 
While preferred embodiments have been shown and described, various 
modifications and substitutions may be made thereto without departing from 
the spirit and scope of the invention. Accordingly, it is to be understood 
that the present invention has been described by way of illustrations and 
not limitation.