U.S. patent application number 11/060808 was filed with the patent office on 2005-07-07 for system for optically analyzing a molten metal bath.
Invention is credited to Cates, Larry E..
Application Number | 20050145071 11/060808 |
Document ID | / |
Family ID | 36927886 |
Filed Date | 2005-07-07 |
United States Patent
Application |
20050145071 |
Kind Code |
A1 |
Cates, Larry E. |
July 7, 2005 |
System for optically analyzing a molten metal bath
Abstract
A system for optically analyzing a molten metal bath wherein a
high velocity argon gas stream is passed from a lance to the bath
and is maintained coherent by a flame envelope to provide a clear
sight pathway through the argon gas stream for sighting the molten
metal bath longitudinally through the argon gas stream from a
remote or spaced sighting point.
Inventors: |
Cates, Larry E.;
(Brownsburg, IN) |
Correspondence
Address: |
PRAXAIR, INC.
LAW DEPARTMENT - M1 557
39 OLD RIDGEBURY ROAD
DANBURY
CT
06810-5113
US
|
Family ID: |
36927886 |
Appl. No.: |
11/060808 |
Filed: |
February 18, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11060808 |
Feb 18, 2005 |
|
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10387544 |
Mar 14, 2003 |
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Current U.S.
Class: |
75/382 ; 266/80;
75/384 |
Current CPC
Class: |
F27D 2003/166 20130101;
C21C 5/4673 20130101; F27D 2003/164 20130101; F27D 19/00 20130101;
F27D 21/00 20130101; F27D 2019/0003 20130101; F27D 21/02 20130101;
F27D 3/16 20130101; F27D 21/0014 20130101; F27D 2019/0006 20130101;
C21C 7/072 20130101; C21C 5/4606 20130101 |
Class at
Publication: |
075/382 ;
266/080; 075/384 |
International
Class: |
C21C 007/00; C21D
001/74 |
Claims
1. A method for optically analyzing a molten metal bath comprising:
(A) forming a coherent argon gas stream by passing an argon gas
stream out from a lance and surrounding the argon gas stream with a
flame envelope; (B) passing the coherent argon gas stream to a
molten metal bath; (C) sighting longitudinally through the coherent
argon gas stream to view the molten metal bath and obtain optical
data therefrom; and (D) passing the optical data to an
analyzer.
2. The method of claim 1 wherein the sighting through the coherent
argon gas stream comprises using a light source transmitting light
through the coherent, argon gas stream.
3. The method of claim 2 wherein the light source is a laser.
4. The method of claim 1 wherein the flame envelope extends from
the lance to the molten metal bath.
5. The method of claim 1 wherein the coherent argon gas stream has
a supersonic velocity when it contacts the molten metal bath.
6. The method of claim 1 wherein the optical data enables the
determination of the composition of the molten metal of the molten
metal bath.
7. The method of claim 1, wherein the optical data enables the
determination of the temperature of the molten metal of the molten
metal bath.
8. The method of claim 1 wherein the molten metal bath comprises
unmelted scrap and the optical data enables the determination of
melted versus unmelted scrap in the molten metal bath.
9. The method of claim 1 wherein the molten metal bath comprises
molten metal and a slag layer above the molten metal, and wherein
the coherent argon gas stream passes through the slag layer to the
molten metal.
10. Apparatus for optically analyzing a molten metal bath
comprising: (A) a molten metal furnace containing a molten metal
bath; (B) a lance having an ejection end for passing a coherent
argon gas stream to the molten metal bath; (C) a sight glass
mounted on the lance on the end opposite the ejection end to
provide a pressure seal to prevent leakage of argon gas from the
lance while providing an optically transparent view port and
aligned so as to view the molten metal bath longitudinally through
the coherent argon gas stream to obtain optical data; and (D) an
analyzer and means for passing the optical data to the
analyzer.
11. The apparatus of claim 10 further comprising a light source for
generating light for passage through the coherent argon gas
stream.
12. The apparatus of claim 11 wherein the light source is a
laser.
13. The apparatus of claim 10 wherein the lance is positioned so as
to provide the coherent argon gas stream to the molten metal bath
in a direction perpendicular to the surface of the molten metal
bath.
14. The apparatus of claim 10 wherein the means for passing optical
data to the analyzer comprises a light guide assembly comprising
optical fiber passing from the sight glass to the analyzer.
15. The apparatus of claim 10 wherein the means for passing optical
data to the analyzer comprises a light guide assembly comprising a
system of lenses and mirrors.
16. The apparatus of claim 10 wherein the analyzer comprises an
optical spectrometer.
17. The apparatus of claim 10 wherein the analyzer comprises a
pyrometer.
Description
RELATED APPLICATIONS
[0001] This application is a continuation-in-part of prior U.S.
Ser. No. 10/387,544, filed Mar. 14, 2003.
TECHNICAL FIELD
[0002] This invention relates generally to refining molten metal,
e.g. steel, and, more particularly, to analyzing the molten metal
bath during the refining.
BACKGROUND ART
[0003] Metals such as steel are typically produced and refined in a
refractory lined vessel by heating charge materials such as metal
bearing scrap, pig iron, ore, limestone, dolomite, etc. to a molten
state and blowing oxygen into the resulting molten metal bath in
order to oxidize impurities. It is not always possible to know the
precise chemical composition of the charge materials prior to the
start of processing. Therefore, the composition must be determined
after the charge materials have become molten and thoroughly mixed.
Moreover, the changing composition of the molten metal bath must be
at least periodically determined so as to know the timing and
quantity of additives made to the refining vessel contents. The
standard method for determining the composition of a molten metal
bath is to stop the production process, withdrawn a small sample of
material, and analyze this sample using a mass spectrometer.
[0004] Continuous on-line measurement is more desirable but the
high temperature and the presence of dust, fume, and slag do not
permit locating measuring devices inside the molten metal bath.
Those skilled in the art have attempted to deal with these problems
by using optical fibers close to the surface of the molten metal
bath or using such aids as lenses, mirrors and prisms in order to
pass data from the molten metal bath to an analyzer. However such
arrangements are unsatisfactory because they are complicated to set
up and difficult to maintain during the refining process, thus
compromising the accuracy of the data gathered and compromising the
integrity of the analysis based on such data.
SUMMARY OF THE INVENTION
[0005] One aspect of the invention is:
[0006] A method for optically analyzing a molten metal bath
comprising:
[0007] (A) forming a coherent argon gas stream by passing an argon
gas stream out from a lance and surrounding the argon gas stream
with a flame envelope;
[0008] (B) passing the coherent argon gas stream to a molten metal
bath;
[0009] (C) sighting longitudinally through the coherent argon gas
stream to view the molten metal bath and obtain optical data
therefrom; and
[0010] (D) passing the optical data to an analyzer.
[0011] Another aspect of the invention is:
[0012] Apparatus for optically analyzing a molten metal bath
comprising:
[0013] (A) a molten metal furnace containing a molten metal
bath;
[0014] (B) a lance having an ejection end for passing a coherent
argon gas stream to the molten metal bath;
[0015] (C) a sight glass mounted on the lance on the end opposite
the ejection end to provide a pressure seal to prevent leakage of
argon gas from the lance while providing an optically transparent
view port and aligned so as to view the molten metal bath
longitudinally through the coherent argon gas stream to obtain
optical data; and
[0016] (D) an analyzer and means for passing the optical data to
the analyzer.
[0017] As used herein, the term "flame envelope" means a combusting
stream around at least one other non-combusting gas stream.
[0018] As used herein, the term "coherent gas stream" means a gas
stream whose diameter remains substantially constant.
[0019] As used herein, the term "molten metal bath" means the
contents of a metal refining furnace comprising molten metal and
which also may comprise slag.
[0020] As used herein, the term "optical data" means a value
describing a characteristic of a molten metal bath which can be
sensed by a receiver spaced from the molten metal bath.
[0021] As used herein, the term "longitudinally" means in line with
the major axis.
[0022] As used herein, the term "sight glass" means an optically
transparent material, such as sapphire or quartz, capable of
providing a seal between a pressurized stream of argon gas in a
lance and the fiber optic cable or other optical components. A
light source, such as a laser, may be fitted to the sight glass to
increase the energy of the molten metal bath observed through the
coherent argon gas jet so as to improve the effectiveness of the
analysis.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The sole FIGURE is a simplified cross sectional
representation of one preferred arrangement which may be used in
the practice of the invention.
DETAILED DESCRIPTION
[0024] The invention will be described in detail with reference to
the Drawing. Referring now to the FIGURE, there is shown molten
metal furnace 10 which contains a molten metal bath comprising
molten metal 4 and a slag layer 5, which may be molten and/or
solid, above the pool of molten metal. Typically the molten metal
will comprise iron or steel. The slag layer generally comprises one
or more of calcium oxide, silicon dioxide, magnesium oxide,
aluminum oxide and iron oxide.
[0025] Lance 1 is positioned so as to provide argon gas to the
molten metal bath. The embodiment illustrated in the FIGURE is a
preferred embodiment wherein the lance is positioned so as to
provide the argon gas to the molten metal bath in a direction
perpendicular to the surface of the molten metal bath.
Alternatively, the lance could be positioned through a sidewall of
furnace 10 so as to provide the argon gas angularly to the surface
of the bath.
[0026] In the practice of this invention, argon is used as the gas
through which an optical sighting is made. Unlike conventional
sensing systems which employ oxygen or another reactive gas, argon,
due to its inertness relative to the molten metal, provides for a
much clearer optical view of the molten metal from the remote sight
position. In addition, the heaviness of the argon gas makes for a
better defined impact site at the molten metal than the
conventional more lighter gases employed with conventional systems.
The combination of reduced splashing and other visual impediments
at the gas-metal impact site due to the non-reactivity of the argon
gas, coupled with the better defined impact site due to the density
of the argon gas, enables a much clearer optical view than is
possible with conventional systems. This clearer optical view
enables better data acquisition and improved data analysis.
[0027] The argon gas is provided from the lance at a high velocity,
preferably at sonic or supersonic velocity. Generally the velocity
of the argon gas stream 3 provided from the lance has a velocity of
at least 1000 feet per second (fps) and preferably at least 1500
fps. Most preferably the argon gas stream has a supersonic velocity
upon ejection from the lance and also has a supersonic velocity
when it contacts the bath surface.
[0028] Fuel and oxidant are provided out from the lance around the
argon gas stream and combust to form a flame envelope 2 around the
argon gas stream 3. Preferably, as shown in the FIGURE, the flame
envelope extends for the entire length of the argon gas stream
within the furnace from the lance ejection end to the bath. The
fuel used to form flame envelope 2 is preferably gaseous and may be
any fuel such as methane or natural gas. The oxidant used to form
flame envelope 2 may be air, oxygen-enriched air having an oxygen
concentration exceeding that of air, or commercial oxygen having an
oxygen concentration of at least 90 mole percent.
[0029] Flame envelope 2 serves to keep ambient gas, e.g. furnace
gases, from being drawn into or entrained into argon gas stream 3,
thereby keeping the velocity of argon gas stream 3 from
significantly decreasing and keeping the diameter of argon gas
stream 3 from significantly increasing, generally for a distance of
at least 20 d where d is the diameter of the nozzle at the lance
ejection end from which gas stream 3 is ejected. That is, flame
envelope 2 serves to establish and maintain argon gas stream 3 as a
coherent gas stream generally for a distance of at least 20 d.
Preferably, as shown in the FIGURE, argon gas stream 3 is a
coherent gas stream from the lance to the bath.
[0030] The use of a coherent jet of argon gas to penetrate through
the slag layer and fume above the bath is not envisioned by
conventional practice. The gas stream issuing from a standard lance
does not penetrate the slag layer from a long distance and does not
provide a clear view of a molten metal bath to accurately measure
its properties. The use of a shroud fuel gas is required to produce
the concentrated or coherent stream of argon gas. The shroud gas
also generates light signals at specific wavelengths due to the
combustion of elements and molecules such as sodium, potassium,
CaO, and MnO, which can be used to determine whether the slag is
being completely penetrated.
[0031] The use of a spectrometer or other instrument capable of
measuring light intensity at several wavelengths is employed. Two
separate wavelengths are used for measuring temperature. Other
wavelengths are used for measuring the quantity of various
elements, such as carbon, silicon, copper, chromium, etc. Yet other
wavelengths indicate the presence of oxides such as CaO, MnO, and
MgO in the field of view, and can be used to determine whether the
slag containing these oxides is being completely penetrated. A
further indicator of penetration of the slag layer is the
conversion of light signals from the combustion of sodium and
potassium by the shroud fuel, from emission spectra to absorption
spectra. This has been shown to occur when the inert argon gas
penetrates completely through the slag layer.
[0032] The argon gas passed to the bath in gas stream 3 serves to
help refine the molten metal by mixing the bath. Preferably, as
shown in the FIGURE, the high velocity and coherent nature of argon
gas stream 3 serves to drive gas stream 3 through slag layer 5 and
deep into molten metal 4 so as to enhance the mixing action of the
gas delivered to the bath in argon gas stream 3.
[0033] As has been discussed above, it is desirable at least
periodically, and preferably continuously, to monitor the condition
of the molten metal to determine, for example, its composition,
temperature and/or the proportion of scrap that has been melted. In
the practice of this invention these parameters are monitored by
sighting through sight glass 9. As shown in the FIGURE, sight glass
9 is mounted on lance 1 on the end opposite the ejection end to
provide a pressure seal to prevent leakage of argon gas from the
lance while providing an optically transparent view port. This
leakage prevention serves not only to reduce gas losses but also
serves to reduce the chance of pressure imbalances which could
negatively impact the formation and maintenance of the coherency of
the argon gas stream. The formation and the maintenance of a
coherent gas stream is not attainable with conventional sensing
systems.
[0034] The coherent nature of argon gas stream 3, which keeps
furnace gases, fumes, particles, etc. from being entrained into
argon gas stream 3, enables a clear line of sight to form from
sight glass 9 to the molten metal bath. This enables viewing the
molten metal bath by sighting longitudinally through the
unobstructed pathway provided by coherent argon gas stream 3. This
viewing enables the gathering of optical data from the bath. Data
that can be gathered by viewing the molten metal through the
coherent argon jet include temperature by way of optical pyrometry,
measurement of the quantities of various elements contained in the
molten metal bath and slag by way of spectroscopic analysis, and
conditions of the process such as the proportion of melted scrap by
analysis of the temperature trends.
[0035] The optical data is passed to an analyzer 7, such as by
light guide assembly 8 which may comprise fiber optic cable or a
system of lenses and mirrors. Analyzer 7 may be, for example, an
optical spectrometer optical pyrometer, or a combination of these
instruments. Analyzer 7 employs the data to provide measurements of
temperature and composition of the molten metal bath, thereby
enabling the operator to make adjustments to the amounts and timing
of additional charge materials, fluxing agents, alloys, electrical
energy, and reactive agents such as oxygen, to facilitate arriving
at the desired endpoint of the refining process.
[0036] By observing the current temperature of the molten bath and
the quantity of carbon, chromium, manganese or other elements
remaining in the molten metal bath, the operator can determine when
the processing of the metal has reached the conditions specified
for the type of metal being produced. Further, if the quantity of
certain trace elements such as copper are observed to be outside
the quality limitations for the metal being produced, the operator
will be able to make adjustments to bring the product into
specification before the completion of processing. By knowing the
proportion of scrap melted, the operator will know the appropriate
time to add additional scrap to the furnace.
[0037] By the use of the invention one can obtain continuous and
on-line measurement of molten metal bath properties without need
for using optical fibers close to the surface of the molten metal
bath or using such aids as lenses, mirrors and prisms. Although the
invention has been described in detail with reference to a
preferred embodiment, those skilled in the art will recognize that
there are other embodiments of the invention within the spirit and
the scope of the claims.
* * * * *