U.S. patent application number 09/987323 was filed with the patent office on 2003-05-15 for method and apparatus for melting metal in a shaft furnace.
Invention is credited to Li, Xueping.
Application Number | 20030090044 09/987323 |
Document ID | / |
Family ID | 25533185 |
Filed Date | 2003-05-15 |
United States Patent
Application |
20030090044 |
Kind Code |
A1 |
Li, Xueping |
May 15, 2003 |
Method and apparatus for melting metal in a shaft furnace
Abstract
A system wherein oxygen is provided to a shaft furnace in
addition to the blast air, and a flame shroud is formed around the
oxygen stream enabling deep penetration of the oxygen into the
furnace for not only combusting carbonaceous material for
generating heat but also for cutting and oxidizing metal within the
furnace.
Inventors: |
Li, Xueping; (Somers,
NY) |
Correspondence
Address: |
PRAXAIR, INC.
LAW DEPARTMENT - M1 557
39 OLD RIDGEBURY ROAD
DANBURY
CT
06810-5113
US
|
Family ID: |
25533185 |
Appl. No.: |
09/987323 |
Filed: |
November 14, 2001 |
Current U.S.
Class: |
266/218 ;
266/225; 75/499 |
Current CPC
Class: |
C21C 5/4606 20130101;
F27D 2003/164 20130101; F27D 2003/0083 20130101; C21C 1/08
20130101; F27B 1/16 20130101 |
Class at
Publication: |
266/218 ;
266/225; 75/499 |
International
Class: |
C21B 013/02 |
Claims
1. A method for melting metal in a shaft furnace comprising: (A)
passing blast air into a shaft furnace containing a charge
comprising metal, carbonaceous material, and flux material; (B)
providing a stream of oxygen from a lance, and surrounding the
stream of oxygen with combusting fuel and oxidant forming a flame
shroud around the stream of oxygen; (C) passing the stream of
oxygen into the shaft furnace; and (D) combusting carbonaceous
material and cutting and oxidizing metal with the stream of oxygen
within the shaft furnace and generating heat for melting metal
within the shaft furnace.
2. The method of claim 1 wherein the stream of oxygen is passed
into the cupola furnace with the blast air.
3. The method of claim 1 wherein the stream of oxygen has a
supersonic velocity.
4. The method of claim 1 wherein the carbonaceous material
comprises coke.
5. A shaft furnace for melting metal comprising a refractory lined
furnace wall, a blast air tuyere positioned in the furnace wall for
passing blast air into the cupola furnace, and an oxygen lance
positioned within the blast air tuyere, said oxygen lance having a
tip which is recessed from the end of the blast air tuyere, having
means for passing oxygen in an oxygen stream out from the lance at
the tip, and having means for providing fuel and oxidant out from
the lance to form a flame shroud around the oxygen stream.
6. The shaft furnace of claim 5 wherein the means for passing
oxygen from the lance includes a central passage which communicates
with an opening at the lance tip.
7. The shaft furnace of claim 6 further comprising a
converging/diverging nozzle positioned in the central passage.
8. The shaft furnace of claim 5 wherein the means for providing
fuel out from the lance includes an inner ring of holes at the
lance tip and the means for providing oxidant out from the lance
includes an outer ring of holes at the lance tip.
9. The shaft furnace of claim 5 wherein the oxygen lance tip is
recessed from 2 to 6 inches from the end of the blast air
tuyere.
10. The shaft furnace of claim 5 having a plurality of blast air
tuyeres with at least two of said tuyeres having an oxygen lance
positioned therein, said oxygen lance having a tip which is
recessed from the end of the blast air tuyere, having means for
passing oxygen in an oxygen stream out from the lance at the tip,
and having means for providing fuel and oxidant out from the lance
to form a flame shroud around the oxygen stream.
Description
TECHNICAL FIELD
[0001] This invention relates generally to the operation of a shaft
furnace and, more particularly, to the operation of a shaft furnace
using oxygen enrichment.
BACKGROUND ART
[0002] A shaft furnace, such as a cupola or blast furnace, is a
vertical, generally cylindrical furnace wherein metal is melted.
The furnace is typically charged with alternating layers of coke
and metal along with limestone or other fluxing material. During
operation metal is heated and then melted as it descends downward
through the shaft and collects in the hearth or crucible at the
bottom of the furnace as a molten metal pool. The fluxing material
is also heated and melted, and the resultant lighter molten slag
accumulates as a layer on top of the molten metal. The molten metal
and slag is tapped from the furnace into a runner through a tapping
spout located at the base of the furnace and the molten slag is
subsequently removed by skimming in the runner system.
[0003] The coke combusts with incoming air to form carbon dioxide
in an exothermic reaction which generates heat which is employed to
melt the metal. The carbon dioxide rising within the furnace also
reacts with coke to form carbon monoxide. While this is a heat
consuming reaction, it is important as the produced carbon monoxide
and the partial reduction of carbon dioxide serve to hold down the
rate of metallic oxidation within the furnace.
[0004] In order to improve the operation of a shaft furnace, there
has long been practiced the provision of oxygen to the furnace in
addition to the primary air. One of the most successful commercial
oxygen enrichment cupola practices is the supersonic direct
injection process disclosed in U.S. Pat. No. 4,324,583 wherein
oxygen is provided to a cupola at a supersonic velocity.
[0005] The operation of shaft furnaces such as cupola furnaces for
melting metal has significant economic importance and thus any
improvement would be highly desirable.
[0006] Accordingly, it is an object of this invention to provide a
system for melting metal in a shaft furnace which enables an
improvement in operation over heretofore available systems for
melting metal in a shaft furnace.
SUMMARY OF THE INVENTION
[0007] The above and other objects, which will become apparent to
those skilled in the art upon a reading of this disclosure, are
attained by the present invention one aspect of which is:
[0008] A method for melting metal in a shaft furnace
comprising:
[0009] (A) passing blast air into a shaft furnace containing a
charge comprising metal, carbonaceous material, and flux
material;
[0010] (B) providing a stream of oxygen from a lance, and
surrounding the stream of oxygen with combusting fuel and oxidant
forming a flame shroud around the stream of oxygen;
[0011] (C) passing the stream of oxygen into the shaft furnace;
and
[0012] (D) combusting carbonaceous material and cutting and
oxidizing metal with the stream of oxygen within the shaft furnace
and generating heat for melting metal within the shaft furnace.
[0013] Another aspect of the invention is:
[0014] A shaft furnace for melting metal comprising a refractory
lined furnace wall, a blast air tuyere positioned in the furnace
wall for passing blast air into the shaft furnace, and an oxygen
lance positioned within the blast air tuyere, said oxygen lance
having a tip which is recessed from the end of the blast air
tuyere, having means for passing oxygen in an oxygen stream out
from the lance at the tip, and having means for providing fuel and
oxidant out from the lance to form a flame shroud around the oxygen
stream.
[0015] As used herein the term "oxygen" means a fluid having a
molecular oxygen concentration of at least 70 mole percent.
[0016] As used herein the term "blast air" means a fluid comprising
primarily molecular oxygen and molecular nitrogen, such as ambient
air.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a cross-sectional view of a lance positioned for
providing an oxygen stream into a shaft furnace which, in this
embodiment, is a cupola furnace.
[0018] FIG. 2 is a head on view of one embodiment of a lance tip
which may be employed for providing an oxygen stream in the
practice of this invention.
[0019] FIG. 3 is a cross-sectional view of the lance shown in FIG.
2 in operation showing the oxygen stream and the flame shroud.
[0020] FIG. 4 is a cross-sectional plan view of a cupola furnace
showing an arrangement which was used to test the method of this
invention.
DETAILED DESCRIPTION
[0021] The invention will be described in detail with reference to
the Drawings and in reference to the operation of a cupola furnace.
In the Drawings common or similar elements have the same
numeral.
[0022] Referring now to FIG. 1, tuyere 50 is positioned in sidewall
51 of a cupola furnace for providing blast air from blast air
source 52 into the cupola furnace. Typically a shaft furnace such
as a cupola furnace will have from 4 to 10 blast air tuyeres
positioned around its perimeter so as to provide blast air in a
relatively even distribution pattern into the shaft furnace.
[0023] The cupola furnace contains carbonaceous material such as
coke and also contains solid metal to be melted. Typically the
metal is ferrous metal such as pig iron, scrap iron or scrap steel.
The solid metal and carbonaceous material charge in the cupola
furnace is in alternating layers of metal and carbonaceous
material. The charge also typically contains flux material to
facilitate the refining of the molten metal resulting from the
operation of the cupola furnace and to protect the refractory
lining from excessive wear.
[0024] Oxygen lance 1 is used to provide oxygen to the cupola
furnace. The embodiment of the invention illustrated in FIG. 1 is a
preferred embodiment wherein the oxygen lance is positioned within
the blast air tuyere. The oxygen lance may also be positioned
outside the blast air tuyere so as to provide the oxygen to the
cupola furnace separately from the blast air. Oxygen is provided to
oxygen lance 1 as shown by input arrow 53. Preferably the oxygen is
commercially pure oxygen having an oxygen concentration of at least
90 mole percent. Fuel, such as methane, propane, natural gas and
the like, is provided to oxygen lance 1 as shown by flow arrow 54,
and oxidant, which is preferably commercially pure oxygen, is
provided to oxygen lance 1 as shown by flow arrow 55. The oxygen,
fuel and oxidant flow through oxygen lance 1 and are ejected from
the tip or face 5 of oxygen lance 1. Preferably, as shown in FIG.
1, tip 5 of oxygen lance 1 is recessed, typically from 2 to 6
inches, from the tip or end 56 of blast air tuyere 50.
[0025] FIG. 2 illustrates one embodiment of an arrangement of the
apertures on the lance face which may be used in the practice of
this invention, and FIG. 3 illustrates that embodiment of the lance
in cross-section. Referring now to FIGS. 2 and 3, oxygen passes
through central passage 2 of lance 1 and is ejected from opening 11
on lance face 5 to form oxygen stream 20. Preferably, as shown in
FIG. 3, central passage 2 communicates with converging/diverging
nozzle 57 which serves to deliver the oxygen from central passage 2
to opening 11 on face 5 and then out of lance 1 in stream 20. The
converging/diverging nozzle imparts a supersonic velocity to oxygen
stream 20. Preferably the velocity of oxygen stream 20 is within
the range of from 700 to 2100 feet per second.
[0026] Gaseous fuel is passed through inner annular passage 3 of
oxygen lance 1. Near the tip of oxygen lance 1 inner annular
passage 3 communicates with a plurality of individual passages 7
which come out on lance face 5 as inner ring of holes 9. The
gaseous fuel, e.g. natural gas, passes out from the tip of lance 1
through these inner holes 9. Oxidant is passed through outer
annular passage 4 of oxygen lance 1. Near the tip of oxygen lance 1
outer annular passage 4 communicates with a plurality of individual
passages 8 which come out on lance face 5 as outer ring of holes
10. The oxidant, e.g. commercially pure oxygen, passes out from the
tip of lance 1 through these outer rings of holes 10.
[0027] The gaseous fuel ejected from lance 1 through inner holes 9
and the oxidant ejected from lance 1 through outer holes 10 mix and
combust to form flame shroud 23 around and along the length of
oxygen stream 20. Flame shroud 23 serves to shield oxygen stream 20
from ambient gases which would otherwise aspirate into a high
velocity gas stream such as a supersonic gas jet. This flow or
aspiration of ambient gas into a gas stream expands the gas stream
and reduces its velocity. In contrast, with the use of the flame
shroud of this invention, the diameter of the oxygen stream remains
essentially constant for a distance of at least 20 d or until the
oxygen stream impacts the furnace contents, whichever event occurs
sooner, where d is the exit diameter of opening 11, and, in
addition, the velocity of the oxygen stream remains essentially
constant for the same distance, after the oxygen stream is ejected
from the tip 5 of oxygen lance 1. This has the effect of
maintaining the momentum of the oxygen stream concentrated within
the relatively small resulting cross-sectional area of the oxygen
stream 20 and not dissipated such as is the case with conventional
supersonic injection practice in shaft furnaces. That is, the flame
shroud serves to maintain the oxygen stream coherent from its
ejection from the lance to impact with the cupola charge. Thus the
oxygen stream ejected from oxygen lance 1 impacts the charge within
the cupola furnace with greater force than is possible with
conventional practice and this enables the oxygen to penetrate
deeper into the charge within the cupola furnace than would
otherwise be possible. This deeper penetration enhances the
evenness of the combustion of the carbonaceous material within the
cupola furnace which in turn improves the efficiency and thus the
productivity and raw material consumption of the cupola furnace
operation. In addition, the deeper penetration enables cutting and
oxidizing metal within the furnace. In pilot scale testing of the
invention in a box filled with foundry coke, the coherent oxygen
jet of this invention was able to penetrate into the coke bed for
distances of from 25 to 48 inches. In contrast, using the same
conditions but employing conventional supersonic injection of
oxygen, the oxygen jet was able to penetrate into the coke bed for
distances of only from 12 to 16 inches.
[0028] In some situations it may be preferred to provide the fuel
and oxidant for the flame shroud around the stream of oxygen from
one ring of holes rather than the two rings of holes of the
embodiment illustrated in FIG. 2. In yet another variation which
may be preferred in some situations, the oxidant for the flame
shroud is the same fluid as the oxygen for the oxygen stream and,
most preferably, that oxidant is taken from the main or central
oxygen passage using a bleed line to provide the oxidant fluid to
the flame shroud oxidant provision means.
[0029] FIG. 4 illustrates in top cross-sectional view a commercial
cupola furnace which was altered to test the invention. The cupola
furnace 60 had an inside diameter of 102 inches and was refractory
lined and water cooled. The cupola was normally operated with 10
blast air tuyeres 50 arranged as shown in FIG. 4 which supplied
blast air at a rate of about 15000 cubic feet per minute. Oxygen
was also supplied through each of tuyeres 50 using the conventional
supersonic direct injection practice disclosed in U.S. Pat. No.
4,324,583.
[0030] To demonstrate the advantages attainable with the practice
of this invention two of the tuyeres 50 were altered by inserting
therein oxygen lance 1 of the invention, as is shown in FIG. 4, and
the cupola furnace operation was carried out. In these
demonstration tests, the oxygen flow was 16000 standard cubic feet
per minute (Scfh), the gaseous fuel flow was 2700 Scfh and the
oxidant flow was 2025 Scfh. The productivity improvement for the
cupola furnace achieved in these tests with only two of the 10
tuyeres converted to use the invention ranged from 1.61 to 2.13
percent wherein productivity is defined as the maximum tons of iron
and steel scrap per hour that can be consumed and melted by the
cupola furnace.
[0031] These examples and comparative examples serve to demonstrate
the significant advantages attainable with the practice of this
invention over the heretofore most advanced commercial cupola
furnace practice.
[0032] Although the invention has been described in detail with
reference to a certain 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.
* * * * *