U.S. patent application number 12/169861 was filed with the patent office on 2008-11-06 for metallurgical lance with annular gas flow control.
Invention is credited to John Kelvin Batham, Andrew Miller Cameron, Andrew Peter Richardson, Michael Strelbisky, Mark Alan Wilkinson.
Application Number | 20080272524 12/169861 |
Document ID | / |
Family ID | 37854283 |
Filed Date | 2008-11-06 |
United States Patent
Application |
20080272524 |
Kind Code |
A1 |
Strelbisky; Michael ; et
al. |
November 6, 2008 |
Metallurgical Lance with Annular Gas Flow Control
Abstract
A method of controlling total jet pressure from the head of a
metallurgical lance for introducing gas into a volume of metal in a
vessel. The lance head has at least one ejector, which has a nozzle
located in a bore of the lance head and has an annular gas passage
between at least one nozzle and the wall of the bore. The method
proceeds by adjusting the annular gas velocity from a first Mach
number to a second mach number to effect change of the total jet
pressure.
Inventors: |
Strelbisky; Michael;
(Burlington, CA) ; Richardson; Andrew Peter;
(Clinton, NJ) ; Wilkinson; Mark Alan; (Lincoln,
MA) ; Cameron; Andrew Miller; (Matlock, GB) ;
Batham; John Kelvin; (Cherry Burton, GB) |
Correspondence
Address: |
The BOC Group, Inc.
575 MOUNTAIN AVENUE
MURRAY HILL
NJ
07974-2082
US
|
Family ID: |
37854283 |
Appl. No.: |
12/169861 |
Filed: |
July 9, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11222567 |
Sep 9, 2005 |
|
|
|
12169861 |
|
|
|
|
Current U.S.
Class: |
266/44 |
Current CPC
Class: |
C21C 5/32 20130101; C21C
5/4606 20130101 |
Class at
Publication: |
266/44 |
International
Class: |
C21C 5/00 20060101
C21C005/00 |
Claims
1. A method of controlling total jet pressure from a head of a
metallurgical lance for introducing gas into a volume of metal in a
vessel, the lance head having at least one ejector comprising a
nozzle located in a bore of the lance head and having an annular
gas passage between the nozzle and a wall of the bore, the method
comprising adjusting the annular gas velocity from a first Mach
number to a second Mach number to effect change of the total jet
pressure.
2. The method according to claim 1, wherein the at least one
ejector comprises primary gas outlets and a plurality of secondary
gas outlets adjacent each of the primary gas outlets, and supplies
shrouding gas to the secondary gas outlets.
3. The method according to claim 1, wherein the annular gas
velocity is changed from a value of about Mach 1.
4. The method according to claim 1, wherein the annular gas
velocity is changed to a value of about Mach 1.
5. The method according to claim 1, wherein the gas is selected
from the group consisting of oxygen, argon, nitrogen and mixtures
thereof.
6. The method according to claim 1, wherein the gas supplied to the
at least one ejector and the annular gas passage is independently
selected from the group consisting of oxygen, argon, nitrogen and
mixtures thereof.
7. The method according to claim 2, wherein the gas is selected
from the group consisting of oxygen, argon, nitrogen and mixtures
thereof.
8. The method according to claim 2, wherein the gas supplied to the
at least one ejector, the annular gas passage and the plurality of
secondary gas outlets is independently selected from the group
consisting of oxygen, argon, nitrogen and mixtures thereof.
9. The method according to claim 2, wherein the shrouding gas
protects critical dimensions of the nozzle from damage.
10-20. (canceled)
Description
FIELD OF THE INVENTION
[0001] This invention relates to metallurgical lances with annular
gas flow control.
BACKGROUND OF THE INVENTION
[0002] In steel making, it is known to provide a metallurgical
lance above a volume of molten metal in a vessel for the supply of
a jet of oxygen thereto. In the early stages of a steel making
process, it may be desirable to have a softer blow so as to produce
a relatively large contact area to aid in formation of slag. A blow
refers to the nature of the oxygen jets in steelmaking or the
period of time in which the oxygen is flowing during the conversion
process. Once a slag has been formed, applying a harder blow may
reduce the jet impact area, provide better jet penetration and
better and more complete oxygen reaction with the metal bath.
Attempts have been made to effect soft and hard blows, but there is
still a need for a more satisfactory arrangement in this
respect.
SUMMARY OF THE INVENTION
[0003] The invention is based on the discovery that the performance
of a metallurgical lance may be improved to provide satisfactory
soft and hard blows by providing an annular gas flow around a main
(central) jet of oxygen and varying the annular gas velocity.
[0004] The invention provides a metallurgical lance with which soft
and hard blows can be more satisfactorily effected.
[0005] The invention also provides a method of controlling the
total pressure exerted by the jet from the head of a metallurgical
lance for introducing gas into a volume of molten metal in a
vessel, the lance head having at least one ejector comprising a
nozzle located in a bore in the lance head and having an annular
gas passage between the nozzle and the wall of the bore, the method
including changing the annular gas velocity from a first Mach
number to a second Mach number so as to change the total pressure
exerted by the jet.
[0006] In another embodiment, this invention provides a
metallurgical lance head for introducing gas into a volume of metal
in a vessel. The head has at least one ejector comprising a nozzle
located in a bore of the head and having an annular gas passageway
between the ejector and a wall of the bore. The wall curves inwards
at an intermediate region before a discharge end of the ejector.
The wall near the intermediate region provides a convergent distal
end portion of a secondary gas passageway.
[0007] In yet another embodiment, this invention provides a
metallurgical lance head for introducing gas into a volume of metal
in a vessel. The head has at least one ejector comprising a nozzle
located in a bore of the head and having an annular gas passageway
between the ejector and a wall of the bore. The wall curves inwards
at an intermediate region before a discharge end of the ejector.
The wall near the intermediate region provides a convergent distal
end portion of a secondary gas passageway. Further, the head has a
plurality of secondary gas outlets separated from and surrounding a
primary gas outlet. The secondary gas outlet is directed at an
angle away from the annular gas outlet effective to form a gaseous
layer around a gas discharged from the primary gas outlet.
[0008] The annular gas flow advantageously protects the
convergent-divergent internal profile of the ejector from damage
due to exposure to the harsh converter atmosphere. Conventional
lances have carefully designed and machined convergent-divergent
nozzle profiles for specific oxygen flowrates and supply pressure.
The nozzles are designed such that the flow issuing from the
convergent-divergent nozzle is expanded to the ambient pressure in
the converter proximate to the nozzle exit. A lower volume of gas
flowing through the nozzle results in a lower pressure at the
nozzle exit, known as an `underblown` condition, and leads to the
recirulation of material from the converter atmosphere into the
nozzle and exacerbated nozzle wear. The flow of annular gas around
the ejector ensures that not only is clean gas passed continuously
around the ejector exit, but that any material recirculated into
the ejector is also clean. This serves to protect the critical
dimensions of the convergent nozzle from damage through normal and
underblown conditions and extends nozzle life.
[0009] Ejector outlets may constitute primary gas outlets, with the
method also including providing a plurality of secondary gas
outlets adjacent each primary gas outlet and supplying the
shrouding gas also to the secondary gas outlets. The gas supplied
to the ejector and the annular passage are independently selected
from the group consisting of oxygen, argon, nitrogen or mixtures
thereof. The primary gas is selected from the group consisting of
oxygen, argon, nitrogen or mixtures thereof. The secondary gas is a
shrouding gas, and is selected from the group consisting of oxygen,
argon, nitrogen or mixtures thereof.
[0010] In this invention, the annular gas velocity is changed from
or to about mach 1, at which velocity the total jet pressure is at
a minimum. In one embodiment, the annular gas velocity is changed
from about 1 mach at which velocity the total pressure is at a
minimum. In another embodiment, the annular gas velocity is changed
to about 1 mach at which velocity the total pressure is at a
minimum.
DESCRIPTION OF THE DRAWINGS
[0011] Embodiments of the invention will now be described, by way
of example, with reference to the accompanying drawings, of
which:
[0012] FIG. 1 is a sectional side view of a lance head in
accordance with one embodiment of the invention,
[0013] FIG. 2 is a front view of the lance head of FIG. 1,
[0014] FIG. 3 is a sectional side view of a lance head in
accordance with another embodiment of the invention,
[0015] FIG. 4 is a front view of the lance head of FIG. 3, and
[0016] FIG. 5 is a graph showing the relationship of the total
pressure of a gas jet emitted from the lance head relative to the
velocity of the shroud gas.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0017] Referring to FIGS. 1 and 2, a head 12 of a metallurgical
lance has a central gas chamber 14 which supplies gas to a
plurality of spaced and preferably inclined ejectors 16 or nozzles.
Each of the ejectors 16 are preferably disposed radially outwardly
with respect to horizontal axis "A" of the head 12. Preferably, but
only by way of example, there is a plurality of ejectors 16 per
head 12, such as four (4) ejectors 16 per head 12, although such
number can be varied depending upon the application required. Each
ejector 16 comprises a passageway 18 and is mounted in a bore 20 at
a tip 22 of the lance head 12. The passageways 18 are of
convergent-divergent kind, and which are able to eject oxygen at
supersonic velocity. The oxygen is supplied at an elevated pressure
to the central gas chamber 14. Each ejector 16 is recessed from the
tip 22 within its respective bore 20.
[0018] An annular gas passage 24 is provided between each ejector
16 and a wall 25 of the bore 20. The wall 25 of the bore 20 curves
inwards at an intermediate region 27 before a discharge end 29 of
the ejector 16. The wall 25 at the region 27 in combination with
the ejector 16 provides a generally convergent distal end portion
31 of the annular shrouding gas passage 24. Spacers 23 are disposed
in the passage 24 to provide support for the ejectors 16 arranged
in the bore 20. The spacers 23 are designed to only minimally
restrict the gas flow.
[0019] Downstream from the distal end of the ejector 16, the wall
25 of the bore 20 no longer converges, but rather retains an
approximately constant diameter at right angles to a longitudinal
axis B of the bore 20 (which is coaxial with the passageway 18).
Shroud gas fed by an annular feed passage 26 surrounds the central
gas chamber 14 and is independent therefrom. Annular passages are
also provided for cooling fluid, such as an inner cooling passage
28 and an outer cooling passage 30 in communication by a connecting
passage 32.
[0020] It has been found in the invention that manipulating the
velocity of the shroud gas at the convergent distal end portion 31
can affect the force (or total pressure) exerted downstream of the
ejectors 16 along an axis of the combined jet exhausted from
passage 18. This force or total pressure of the combined jet is
important in that it affects jet penetration into the bath of
molten metal and is an indicator of jet velocity decay and
cross-sectional growth. The total pressure exerted by the jet is
that exerted when the gas is brought to rest or stagnation, in
which stagnation pressure is defined as the pressure that a fluid
exerts when it is motionless.
[0021] FIG. 5 shows the effect of shroud Mach number on the total
pressure as measured by a stagnation probe positioned 15.5 inches
from the distal end of the bore 20 along the axis of the combined
jet. As the Mach number of the annular gas flow at portion 31 is
increased towards unity (or Mach 1) while the primary jet velocity
at passage 18 remains constant at Mach 2.1, there is a rapid drop
in the total pressure of the combined jet. This is unexpected
because the thrust of the combined annular jet and central jet has
increased and a corresponding increase in the total pressure might
have been expected. Because there is an actual reduction in jet
centre-line stagnation pressure, the combined jet spread at a
greater rate. A further increase in Mach number of the annular jet
has the effect of increasing the combined jet pressure. Thus, it is
possible to control the performance of the jet in terms of total
pressure by variation of the shroud Mach number.
[0022] A series of experiments were performed using a set of
central nozzles and shroud pieces to investigate the effect of
shroud mach on jet force. For each combined nozzle configuration
the same central nozzle Mach number (2.1) and flow (652 scfm dry
air) were used, and shrouds of constant flow (196 scfm dry air) and
differing Mach number (0.5-2.1) were used. Thus, for all
experiments discussed here a constant mass flow of 844 scfm was
used. Furthermore, for each case shown, the ejector tip 16 was
aligned to flush with the front face of the lance 22, although the
effect is not limited to this case. In addition, a constant nozzle
tip thickness was maintained leading to constant initial central
jet and shroud separation. Jet performance was determined by
measuring the jet total pressure using a stagnation probe mounted
on a 3-axis positioning device downstream of the jet so as to
facilitate accurate traverses of the probe across the jet
cross-section and location of the probe on the jet axis.
[0023] As discussed above, the Mach number of the shroud may have a
direct effect on the total pressure or force exerted by the jet. As
can be seen in FIG. (5), which shows the stagnation probe pressure
at 15.5 inches, as the Mach number of the shroud is increased
towards unity, a rapid drop in pressure is seen. This is surprising
given that the thrust of the combined shroud and central jet has
increased. A reduction in jet centerline stagnation pressure leads
one to conclude that the combined jet has spread at a greater rate
when considering the conservation of mass. Further increases in
shroud Mach number have the effect of increasing combined jet
pressure as the initial combined jet thrust is further increased.
Thus, it is possible to control the performance of the jet in terms
of total pressure by varying the shroud Mach number or flow
rate.
[0024] Thus, in a basic oxygen furnace (BOF) application, it is
possible to supply additional flow through the shroud and create a
softer blow by causing the Mach number of the shroud gas to rise to
near unity from a lower flow rate and Mach number, or supply
additional flow through the shroud and create a harder blow by
causing the Mach number to rise from near unity at a lower flow
rate to a higher Mach number at a higher flow rate. Thus, it is
also possible to reduce the flow through the shroud from a high
Mach number hard blowing value to a Mach number near unity to
create a softer blow. It is also possible increase the flow through
the shroud from a low Mach number soft blowing value higher than
unity to create a harder blow.
[0025] Another embodiment of a lance head according to the
invention is shown in FIGS. 3 and 4. The same reference numerals
will be used to illustrate elements which are the same or similar
to corresponding elements in the lance head shown in FIGS. 1 and 2,
unless otherwise indicated.
[0026] It will be seen that the lance head shown in FIGS. 3 and 4
differs from the lance head shown in FIGS. 1 and 2 in that the
lance head shown in FIGS. 3 and 4 has a plurality of secondary
oxygen port passageways 220 in communication with shroud gas
passages 26. Each of the passageways 220 is provided with a port
221 at passages 26 and a port 222 at the tip 22 of the head 12. The
gas flow at passage 26 is split to introduce into the passage 24
and the passageway 220. The discharge of the gas at the port 222
coacts with the gas jet at the end of the bore 20 downstream from
the ejector 16. As shown in FIG. 4, the passageways 220 are
arranged in the head 12 such that the ports 222 are in an arch or
semi-circular arrangement partially surrounding a respective one of
the bores 20 and located between bore 20 and a periphery 226 of the
lance head 12. Effectively, the plurality of secondary oxygen port
passageway 220 is arranged circumferentially or on a circle that is
concentric within the primary oxygen port passageway 18. Each
secondary oxygen port 220 is fed from the port 221 communicating
with the shroud gas supply passage 26. The angle of the secondary
oxygen port passageway 220 diverges from the primary oxygen port
passageway 18 (based on the longitudinal axis of each passageway
near the distal end of the lance head) in the range of up to about
45.degree.. Preferably, the range is from about 5.degree. to about
25.degree.. More preferably, the range is from about 10.degree. to
about 20.degree.. The embodiment shown in FIGS. 3 and 4 can be
operated in accordance with the invention in a manner similar to
that described in connection with the embodiments shown in FIGS. 1
and 2. The ejectors 16 may be demountable as described in
co-pending application U.S. Ser. No. 10/881,489, filed 30 Jun.
2004.
[0027] It will be understood that the embodiments described herein
are merely exemplary and that a person skilled in the art may make
many variations and modifications without departing from the spirit
and scope of the invention. All such modifications and variations
are intended to be included within the scope of the invention as
described herein. It should be understood that embodiments
described above are not only in the alternative, but combined.
* * * * *