Oxygen blowing lance capable of being used in an electric furnace

An oxygen blowing lance capable of directing oxygen jet streams onto a molten metal in an electric furnace, the lance being insertable into an electric furnace through a sidewall working port, the lance being positionable above the molten metal in the electric furnace. The lance includes a horizontal segment and an angled segment, the angled segment being positioned on the distal portion of the horizontal segment and being inclined relative to the horizontal segment. The lance also includes a tip, the tip being positioned on the distal portion of the angled segment, with the distal portion of the tip being directed toward the molten metal. The horizontal segment, the angled segment and the tip define an oxygen flow channel and a cooling water flow channel. The oxygen flow channel extends substantially the length of the lance, and the cooling water flow channel surrounds the oxygen flow channel. The lance also includes a plurality of nozzles, each having a throat portion having a throat diameter and an outlet portion having an outlet diameter, the throat portions of the nozzles being positioned on the distal portion of the tip. The nozzles are operatively engaged with the oxygen flow channel, and at least one of the nozzles is positioned nearer the molten metal than the other nozzles.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a lance for blowing oxygen and, in 
particular, to a lance for blowing oxygen capable of being used in an 
electric furnace containing molten iron. 
2. Description of the Related Art 
Electric furnaces for the melting of metals, the refining of molten metals, 
and like processes, are well known in the art. Direct current electric 
furnaces melt metals and/or refine molten metals using an electric arc 
generated between an upper electrode disposed above the metal material and 
a lower electrode disposed on the bottom section, sidewall or a similar 
location on the furnace. In contrast, alternating current electric 
furnaces utilize an electric arc generated by conducting a current between 
three electrode disposed above the metal material. In both types of 
furnaces, however, the melting of a metal material, refining of a molten 
metal and like processes are accelerated by blowing oxygen or powder into 
the molten metal using a lance. 
An example of a conventional lance is disclosed in Japanese Utility Model 
Application Laid-Open No. 2-38457 and is shown in FIG. 8 herein. Lance 31, 
having a linear shape, is inserted into electric furnace, disposing an 
upper electrode 36, 33 through a sidewall by self-propelled cart 32. A 
single oxygen blowing nozzle 34 is formed at the extreme end of the lance 
31. 
A small diameter (about 40 mm) pipe usually comprises lance 31. Therefore, 
if the back pressure in the interior of the oxygen blowing nozzle 34 
(i.e., gas pressure on the nozzle outlet side) is to be maintained at a 
critical pressure (nozzle inside pressure/atmospheric pressure &gt;1.89), 
oxygen flow through the pipe must be increased to impractical levels. 
Thus, the back pressure in the interior of the nozzle is set at or below 
the critical pressure, that is, the velocity of oxygen ejected from nozzle 
34 is at sonic velocity or less. Since the oxygen ejection velocity is 
equal to or less than sonic velocity, and the oxygen is fed through just 
one nozzle 34 as described above, oxygen is directly introduced into the 
molten metal to ensure a sufficient supply by dipping the extreme end of 
the lance 31 into molten metal 35. 
However, when the extreme end of lance 31 is dipped into the molten metal 
35 as described above, lance 31 is gradually consumed by the heat of 
molten metal 35. Consequently, replacement lances must be supplied to the 
self-propelled cart 32, which is troublesome and expensive. In addition, 
the extreme end of lance 31 can be bent by heat so that oxygen is ejected 
upward, which can damage a furnace wall to the extent that the furnace 
cannot be operated. 
To address these problems, a water-cooled type lance has been disclosed in 
Japanese Patent Application Laid-Open No. 6-192718. 
As shown in FIG. 9 herein, water-cooled and linearly-shaped lance 37 is 
inserted into electric furnace 33 and disposed above the surface of molten 
metal 35 through working port 39 in the sidewall of electric furnace 33. 
Further, a Laval type nozzle 38 having a slightly broadened end is used at 
the distal end of lance 37 to eject an oxygen jet stream to the surface of 
the molten metal 35. Since the Laval type nozzle 38 slightly broadens 
toward the end as seen in cross section and shown in FIG. 10, nozzle 38 
can eject an oxygen jet stream at an ultrasonic velocity unlike ordinary 
straight nozzles and abruptly expanding nozzles (as seen in cross 
section). 
As described above, water-cooled lance 37 increases the amount of oxygen 
supplied to the molten metal 35 by ejecting an oxygen jet stream at 
ultrasonic velocity using the Laval type nozzle 38. In other words, the 
above-described lance-degradation problems are solved by ejecting oxygen 
at ultrasonic velocity from a position above the molten metal 35, thereby 
increasing oxygen unitizing efficiency without having to introduce the 
extreme end of the lance 37 into the molten metal 35. 
For molten metal refining in a converter, the water-cooled lance is 
inserted through an upper furnace port of the converter and ejects an 
oxygen jet stream to the molten metal through the Laval type nozzle at an 
ultrasonic velocity of 500 m/s or higher. The distance from the surface of 
the molten metal to the nozzle (hereinafter referred to as "lance height") 
is set between 2 to 4 m so that the velocity of the oxygen jet stream 
reaching the molten metal surface is 50 m/s or slower. Thus, scattered 
molten metal and slag generated when the oxygen jet stream collides 
against the surface of the molten metal is suppressed by limiting the 
stream velocity to 50 m/s or less. 
However, when water-cooled lance 37 is inserted through working port 39 of 
the sidewall of said electric furnace 33, the lance height of lance 37 is 
limited by the size of the working port 39. Thus, the lance height range 
in electric furnace 33 is greatly limited as compared with the converter 
described above. Contemplated solutions to this problem include insertion 
of lance 37 through the upper portion of the electric furnace 33 as in the 
case of the converter, or increasing the lance height by tilting lance 37 
upward as a whole as shown by a two-dot-and-dash-line in FIG. 9. However, 
since the height of the electric furnace 33 is about one half that of the 
converter, a lance height similar to that of the converter cannot be 
obtained. It is also difficult to insert lance 37 through the upper 
portion of the electric furnace 33 because the electrode 36 is disposed on 
the upper portion. Moreover, tilting lance 37 upward reduces the angle at 
which the oxygen jet stream strikes molten metal 35, thereby increasing 
the amount of slag and/or molten metal scattered to the sidewall of the 
furnace. 
Since lance height is greatly limited when linear lance 37 is used with 
electric furnace 33, the velocity of the oxygen stream at the molten metal 
surface becomes 100 m/s or higher. Consequently, the impact energy of the 
oxygen jet stream on the surface of the molten metal 35 is increased 
greatly as compared with the case of the converter. As a result, the 
impact energy disadvantageously acts on the molten metal and slag as a 
stirring force and a shearing force, thereby causing a large amount of the 
molten metal and particulate slag to be scattered. 
When scattered molten metal and slag are deposited on the wall or other 
components of the electric furnace, electrodes are often short-circuited 
through the furnace lid which can result in fire damage to the furnace 
lid. Water-cooled boxes, which typically cover the sidewall of the 
furnace, can also be damaged by scattering, whereby water leaks occur. 
Further, scatter-deposited metal falling from the furnace lid into the 
molten metal causes a temperature drop in the molten metal, 
decarbonization and other potential problems. Damage to electrodes caused 
by scattering can shorten electrode life. 
Additionally, deposition of scattered molten metal on the furnace lid 
increases the weight of the furnace lid, thereby inhibiting movement of 
the furnace lid upward and downward. The deposition of scattered molten 
metal on the water-cooled lance melts and damages the lance. Also, the 
yield of iron is lowered when a large quantity of molten metal is 
scattered. 
It is clear that there is a strong need in the art for an oxygen blowing 
lance which can avoid these problems. 
OBJECT OF THE INVENTION 
An object of the invention is to provide a durable oxygen blowing lance 
which limits the scattering of molten metal and slag when oxygen is blown 
through the lance into molten metal in a furnace. 
Other objects of the invention will become apparent from the description 
provided below. 
SUMMARY OF THE INVENTION 
To achieve the objects of the invention, there is provided an oxygen 
blowing lance for an electric furnace which may be inserted into the 
electric furnace from a working port on the sidewall of the electric 
furnace and is disposed above molten metal in the electric furnace. The 
lance has nozzles positioned on the distal portion thereof for ejecting 
oxygen to the surface of the molten metal. The lance includes an oxygen 
flow channel extending substantially the length of the lance, and a 
cooling water channel surrounding the oxygen flow channel. The lance has a 
horizontal segment adjacent to an angled segment, the angled segment being 
inclined and positioned distally relative to the horizontal segment. A 
lance tip is positioned on the distal portion of the angled segment, with 
at least the distal portion of the tip itself facing the surface of the 
molten metal. The tip is also provided with a plurality of nozzles on its 
distal portion. 
Since the angled segment of the lance is inclined, the distal end of the 
lance is higher than the working port through which it is inserted. As a 
result, lance height is increased without decreasing the angle at which 
the oxygen jet stream strikes the molten metal, as is required in the case 
of a conventional lance. 
An embodiment of the invention utilizes straight nozzles, i.e., nozzles 
having a substantially uniform diameter. Straight nozzles limit the 
maximum ejection velocity to sonic velocity. Thus, even if the back 
pressure in the interior of the nozzle is higher than the critical 
pressure, the oxygen jet stream velocity at the molten metal surface is 
slowed, thereby reducing the impact energy imparted to the molten metal by 
the oxygen stream. The same is true of an abruptly expanding nozzle, i.e., 
a nozzle having an increasing diameter from throat to outlet, which can 
likewise be used in the invention. Ejection velocity can be set to any 
selected velocity equal to or less than sonic velocity by adjusting the 
ratio of the small diameter portion (throat diameter) thereof to the large 
diameter portion (outlet diameter) thereof, and the back pressure in the 
interior of the nozzle. 
The invention also promotes effective oxygen/molten metal reaction by 
compensating for the potential shortage of oxygen supplied to the molten 
metal caused by setting the oxygen ejection velocity to sonic velocity or 
less. This is accomplished by utilizing a plurality of nozzles. 
The invention also enables a plurality of nozzles to direct a broad oxygen 
jet stream onto a large area of the molten metal surface, thereby lowering 
the impact energy per unit area, which in turn reduces molten metal 
scattering. This is accomplished by adjusting nozzle dimensions and/or 
lance height. Specifically, in an embodiment of the invention where a 
plurality of nozzles are positioned on the distal portion of the lance and 
some of the nozzles are close enough to the surface of the molten metal to 
potentially cause scattering, the oxygen jet stream ejection velocities 
from the respective nozzles are controlled by increasing the outlet 
diameters of nozzles nearer to the surface of the molten metal relative to 
the outlet diameters of more distant nozzles, so that the ejection 
velocity of the nearer nozzles is slowed relative to the more distant 
nozzles. 
In an embodiment of the invention where a plurality of the nozzles of the 
straight and abruptly expanding type are positioned on the distal portion 
of the lance, and where some of the nozzles are close enough to the 
surface of the molten metal to potentially cause scattering, the diameters 
of the abruptly expanding nozzles, which can be varied to produce any 
oxygen ejection velocity up to sonic velocity, are adjusted so that the 
oxygen ejection velocity of the abruptly expanding nozzles is slowed 
relative to the oxygen ejection velocity of the straight nozzles. This is 
typically accomplished by increasing the outlet diameter relative to the 
throat diameter. 
Other embodiments of the present invention will become apparent to those of 
ordinary skill in the art from the following detailed description.

DESCRIPTION OF THE INVENTION 
The invention will now be described in reference to FIGS. 1-7. The 
description and figures are illustrative of the invention and are not 
intended to limit the scope of the invention defined in the appended 
claims. 
Referring to FIG. 1, direct current furnace 1 (hereinafter simply referred 
to as electric furnace 1) includes a furnace body 2 composed of a 
refractory material, a water-cooled box 3 covering a sidewall 4 of furnace 
body 2, furnace lid 5 positioned on the upper portion of furnace body 2, 
and an upper electrode 6 which is vertically and movably inserted into 
electric furnace 1 through a small ceiling portion 7 at the center of 
furnace lid 5. Electric arc is generated at upper electrode 6 by 
conducting a direct current between upper electrode 6 and a lower 
electrode (not shown) mounted on or near bottom section 8 of furnace body 
2. Heat generated by the electric arc is used to melt scraps charged into 
electric furnace 1, refine a molten metal 9, increase the temperature of a 
molten iron, or the like. 
Then, a powder blowing lance 11 and two water-cooled oxygen blowing lances 
12a and 12b (shown in FIG. 3) are inserted into electric furnace 1 through 
a working port 10 located on sidewall 4 of furnace body 2 to facilitate 
the heating of the molten metal 9. Lances 11, 12a and 12b can be 
positionally adjusted relative to each other as well as advanced into and 
retracted from electric furnace 1 by a drive unit (not shown). 
Water-cooled oxygen blowing lances 12a will now be described in reference 
to FIGS. 2-5. As lances 12a and 12b are identical and are disposed 
symmetrically to each other in a horizontal direction as shown in FIG. 3, 
it is understood that the following description of lance 12a also applies 
to lance 12b. 
As shown in FIGS. 2 and 3, oxygen blowing lance 12a includes a body 13 
inserted into electric furnace 1 through working port 10. Body 13 includes 
a horizontal segment 15 and angled segment 16 inserted into electric 
furnace 1 substantially in a horizontal direction through working port 10. 
Angled segment 16 is adjacent to and inclines from the distal portion of 
horizontal segment 15. 
As shown in FIG. 4, an oxygen flow channel 17 is positioned in body 13 and 
is surrounded by a cooling water channel 18. Lance tip 14 is connected to 
the distal portion of angled segment 16. 
As shown in FIGS. 2 and 4, lance tip 14 is bent downward from the distal 
portion of angled segment 16, and extends therefrom so that the distal end 
surface of lance tip 14 faces to the surface of the molten metal 9 between 
the sidewall 4 and the upper electrode 6 (refer to FIG. 3). Lance tip 14 
includes an oxygen flow channel 19 and a cooling water channel 20 in 
operative engagement with oxygen flow channel 17 and cooling water channel 
18, respectively, of body 13. As shown in FIG. 2, the distal end of the 
lance tip 14 is positioned above the axial line X.sub.1 of the horizontal 
segment 15 (a line extending in the lance insertion direction), and can be 
moved vertically over a wide range without rendering the collision angle 
of the oxygen jet stream 25 against molten metal 9 disadvantageously 
small. 
As shown in FIG. 5, lance tip 14 has four nozzles 21 formed on the distal 
end surface thereof. As shown in FIG. 4, the nozzles 21 are of the 
abruptly expanding type. Each nozzle 21 has a small throat diameter 
portion 22 and a large outlet diameter portion 23. The oxygen jet stream 
25 ejection velocity can be set to any value up to and including sonic 
velocity by adjusting the ratio of throat diameter portion 22 to the 
outlet diameter portion 23, and the back pressure in the nozzle. 
As shown in FIG. 5, a pair of the four nozzles 21 is positioned on the 
lower portion of the distal end surface of lance tip 4, that is, nearer to 
the surface of the molten metal 9, while the other pair of nozzles is 
positioned on the upper portion on the distal end surface of lance tip 4, 
that is, farther from the surface of the molten metal 9 relative to the 
first pair. The individual nozzles of each nozzle pair described above are 
spaced laterally from each other, also shown in FIG. 5. Further, the pair 
of nozzles 21 positioned nearer to the surface of the molten metal 9 have 
an outlet diameter larger than the pair of nozzles 21 positioned farther 
from the molten metal surface. With this arrangement, the ejection 
velocity of oxygen jet streams 25 from the nearer pair of nozzles 21 is 
slowed relative to the ejection velocity of oxygen jet streams 25 from the 
farther pair of nozzles 21 to substantially balance the velocities of the 
oxygen jet streams 25 at the molten metal 9. 
As shown in FIG. 3, lances 12a and 12b are positioned to direct oxygen jet 
streams 25 toward the surface of molten metal 9 between sidewall 4 and 
upper electrode 6. Thus, the oxygen jet streams 25 ejected from nozzle 21 
do not directly strike upper electrode 6. 
Straight nozzles of various diameters may be used at the distal end of 
lance tip 14 in place of the aforesaid abruptly expanding nozzle 21. An 
example of a straight nozzle 24 is shown in FIG. 6. Since straight nozzles 
24 have a uniform cross-sectional shape, i.e., the throat diameter is 
substantially the same as the outlet diameter, the ejection velocity can 
be no greater than sonic velocity even if the back pressure in the nozzle 
is greater than a critical pressure. 
Further, the nozzles 24 positioned nearer to the surface of the molten 
metal 9 have an outlet diameter larger than the nozzles 24 positioned 
farther from the molten metal surface. 
As shown in FIG. 7, both abruptly expanding nozzles 21 and straight nozzles 
24 may be used at the distal portion of a lance tip. Abruptly expanding 
nozzle 21 is disposed on the lower side of the distal end surface of the 
lance tip, that is, nearer to the surface of the molten metal. Nozzle 24 
is farther from the surface of the molten metal than abruptly expanding 
nozzle 21. 
A test was carried out using the oxygen blowing lance in accordance with 
the invention much as described above in reference to FIGS. 1-5. When the 
oxygen blowing lances were at a lance height of 300-1250 mm and contained 
an amount of oxygen equal to 60 m.sup.3 -norm/min per a lance, the 
velocity of the oxygen jet stream at the molten metal surface was 
controlled to 50 m/s or lower by adjusting the ejection velocity from a 
plurality of abruptly expanding nozzles to 150 m/s. 
A method of blowing oxygen through oxygen blowing lances in accordance with 
the invention will now be described in conjunction with an operational 
procedure involving an electric furnace. 
Scraps of a steel making material are charged into direct current electric 
furnace, and then are partially melted by electric arc generated from an 
upper electrode. Molten iron is charged into the direct current electric 
furnace, oxygen blowing lances are introduced into the electric furnace 
through a sidewall working port, then an oxygen jet stream is directed 
through abruptly expanding nozzles of the oxygen blowing lances onto the 
molten iron/scraps mixture in the vicinity of the working port so that 
scrap melting is accelerated. This procedure is known as a cutting 
operation. 
When the scraps in the vicinity of the working port are melted, the oxygen 
blowing lances are advanced into the inner portion of the electric furnace 
to thereby successively melt the scraps from the vicinity of the working 
port to the inner portion of the electric furnace. 
When the melting of the scraps is complete or substantially complete, the 
oxygen blowing lances are lifted (as shown by a two-dot-and-dash line in 
FIG. 2) to increase the lance height, and a temperature elevation and/or 
refining of the molten metal is carried out by directing an oxygen jet 
stream to the surface of the molten metal from the abruptly expanding 
nozzles of the oxygen blowing lances. 
The velocity of the oxygen jet stream at the molten metal surface is 
controlled to about 50 m/s or less, which is no more than one-half of the 
conventional velocity, by directing the oxygen jet stream to the molten 
metal surface from an elevated position without reducing the striking 
angle of the oxygen jet stream against the molten metal. Velocity of the 
oxygen jet stream at the molten metal surface is also controlled by 
limiting the ejection velocities of the oxygen jet streams from the 
abruptly expanding nozzles to sonic velocity or less as described above. 
As a result, impact energy applied to the surface of the molten metal can 
be greatly reduced. 
Even with ejection velocities limited to sonic velocity, sufficient oxygen 
for reaction is supplied because of the plurality of abruptly expanding 
nozzles feeding oxygen from the lance tip. Further, the oxygen jet stream 
can cover a large percentage of the surface area of the molten metal due 
to the increased lance height and plurality of nozzles, thereby increasing 
the surface area of molten metal impacted by the oxygen jet stream. 
Consequently, the impact energy per unit area of molten metal can be 
reduced and, as a result, the problematic scattering of molten metal and 
slag is greatly reduced as compared with processes involving conventional 
lances. 
The degradation of the upper electrode is also reduced by the oxygen 
blowing lances of the invention because the oxygen jet stream ejected from 
the nozzles is directed to the surface of the molten metal between the 
sidewall and the upper electrode. Thus, the potentially damaging oxygen 
jet stream does not directly strike the upper electrode. Further, since 
the oxygen blowing lances are disposed above the surface of the molten 
metal, the lances are not consumed by the heat of the molten metal as in 
the case of conventional lances. 
Although this invention has been described with reference to specific forms 
of apparatus and method steps, it is understood that many equivalent forms 
and steps may be substituted without departing from the spirit and scope 
of the invention defined in the appended claims.