U.S. patent number 3,701,517 [Application Number 05/062,180] was granted by the patent office on 1972-10-31 for oxy-fuel burners in furnace tuyeres.
This patent grant is currently assigned to Airco. Invention is credited to Bronis G. Gray.
United States Patent |
3,701,517 |
|
October 31, 1972 |
OXY-FUEL BURNERS IN FURNACE TUYERES
Abstract
Industrial furnaces for processing metal bearing charge in which
a plurality of oxy-fuel burners are interposed through the walls of
the furnace to direct high velocity streams of oxygen and
hydrocarbon fuel into the hearth portion of the furnace. Each of
the burners comprising a plurality of separate channels for high
velocity streams of commercially pure oxygen and hydrocarbon fluid
fuel, said channels terminating in a nozzle constructed to emit a
plurality of high velocity jets of oxygen surrounding at least one
jet of hydrocarbon fuel.
Inventors: |
Bronis G. Gray (Orange,
NJ) |
Assignee: |
Airco (Inc., New York)
|
Family
ID: |
26741958 |
Appl.
No.: |
05/062,180 |
Filed: |
August 7, 1970 |
Current U.S.
Class: |
266/222; 266/186;
266/188; 266/189 |
Current CPC
Class: |
C21B
5/001 (20130101); F27B 1/28 (20130101); C22B
13/00 (20130101); F27B 1/08 (20130101); F27B
1/16 (20130101); C21B 5/003 (20130101); F23D
17/00 (20130101); Y02P 10/32 (20151101); Y02E
20/344 (20130101); Y02P 10/34 (20151101); Y02E
20/34 (20130101) |
Current International
Class: |
C21B
5/00 (20060101); F23D 17/00 (20060101); C22B
13/00 (20060101); F27B 1/08 (20060101); F27B
1/16 (20060101); F27B 1/28 (20060101); F27B
1/00 (20060101); F27d 023/00 () |
Field of
Search: |
;75/41-43 ;239/132.3
;266/29,30,41 ;263/44 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gerald A. Dost
Attorney, Agent or Firm: Edmund W. Bopp H. Hume Mathews
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This is a Division of copending application Ser. No. 602,381, filed
Dec. 16, 1966 for OXY-FUEL BURNERS IN FURNACE TUYERES and now U.S.
Pat. No. 3,547,624.
Claims
1. In a furnace for processing metal bearing charge, having a shaft
portion, a hearth portion, means for introducing a composite of
said charge and coke into the shaft of said furnace, means for
sustaining a process including combustion and chemical action in
the hearth portion of said furnace, and means for drawing the
molten metal product and slag formed as a result of said process,
the improvement comprising: a plurality of oxy-fuel burners
interposed through tuyeres of said furnace and directed toward the
hearth portion of said furnace, a source of commercially pure
oxygen and a source of hydrocarbon fluid fuel, each of said burners
comprising a plurality of separate channels for high velocity
streams respectively of the pure oxygen and fluid fuel, said
channels terminating in a nozzle constructed to emit a plurality of
high velocity jets of oxygen surrounding at least one jet of said
hydrocarbon fuel, means for post-mixing said jets to obtain a
turbulent mixture at the tips of said burners for producing a
single homogeneous, high velocity, high temperature flame in an
established combustion zone and which remains seated at each
nozzle, said flame having a temperature within the range of from
3,000.degree. to 5,000.degree. F and having a flame velocity of
from 500 to 3,500 feet per second at a flame temperature within
said aforementioned temperature range, a delivery system for
respectively connecting said oxygen and fuel sources to said
separate channels in each of said burners, and means for supplying
said tuyeres from a blast main with air to produce an air blast
velocity in the tuyeres in the range of from 150 to 1,000 feet per
second during the operation of said burners, the velocity of the
flame of each of said burners at least exceeding the velocity of
said blasts of air in said tuyeres, whereby the charge-to-coke
ratio is substantially increased in said furnace
2. A furnace in accordance with claim 1 wherein said burners are of
the form of self-atomizing tip mixers, each comprising an
axially-disposed oil channel terminating at the nozzle in a central
vent comprising a relatively narrow neck, and wherein said nozzle
includes in addition a plurality of oxygen vents disposed in a
circular array substantially
3. A furnace in accordance with claim 1 wherein said fuel comprises
a principal component of natural gas and said burners are of the
form of rocket burners each comprising a bundle of gas channels
terminating in a plurality of vents in circular array substantially
centered in said nozzle, said nozzle including a plurality of
oxygen vents adjacent to and
4. The combination in accordance with claim 3 wherein said burners
and said delivery system are constructed and arranged to sustain at
each of said nozzles flame velocities of between 1,000 and 3,500
feet per second at a
5. A furnace in accordance with claim 3 wherein said fuel comprises
principal components of both gas and oil, and said rocket burners
include a single axially disposed oil channel terminating in a
central oil vent at said nozzle, in addition to said gas and oxygen
vents which are
6. The combination in accordance with claim 1 wherein said furnace
is surrounded by a blast main, pumping means and a conduit
connected to said blast main for generating a high velocity stream
of air in said blast main, and a plurality of tuyeres are
interposed in the wall of said furnace adjacent said hearth portion
and connected to receive a portion of the high velocity air stream
from said blast main, said burners being interposed in at least a
portion of said tuyeres and surrounded by said high velocity air,
and wherein said tuyeres include water cooling means, and wherein
the nozzle of each of said burners is recessed in said respective
tuyeres to the exterior limit of said water cooling means in
7. The combination in accordance with claim 1 wherein said furnace
is a water-cooled iron-ore smelting blast furnace having a circular
wall of refractory material surrounding said hearth portion, said
tuyeres, including water cooling means therefor, being interposed
in said walls in circular array in a plane adjacent to and slightly
above said hearth portion, oxy-fuel burners extending into said
tuyeres and adapted to establish flame stability within respective
tuyeres at fuel and oxygen
8. The combination in accordance with claim 1 wherein said furnace
is a blast furnace of rectangular plan comprising substantially
plane metal walls for processing ore containing a principal
component of a metal selected from the group consisting of lead and
antimony, at least one pair of said walls including a plurality of
tuyeres disposed in a plane adjacent to and slightly above said
hearth portion, said tuyeres substantially aligned and facing each
other, said burners being interposed into at least a portion of
said tuyeres on opposite sides of said furnace and directed toward
said hearth portion.
Description
This invention relates in general to industrial melting and
smelting processes and apparatus, and more particularly to
techniques and arrangements for using tuyere burners in various
types of shaft furnaces for processing metals.
In melting iron and steel in cupolas, and smelting ore containing
iron and other metals in blast furnaces, the economics of the
processes and the quality of their products are functions of the
rates and temperatures of the melting and smelting operations.
The cupola, for example, is designed to melt pig iron and steel
scrap, using coke as fuel, to produce molten castings. Changes in
the melting rate, temperature, and composition of the product can
be made by proper manipulation of the charge, fuel, and air
blast.
In the prior art, various attempts have been made to reduce the
consumption of coke and to increase the proportion of steel scrap
used in place of more expensive pig iron in the charge by supplying
low cost units of heat directly to the combustion area of the
furnace, by the expedient of placing burners in the furnace
tuyeres. The use of burners in the prior art manner has been only
partially successful, inasmuch as these burners are designed to
operate with relatively low velocity flames sustained by air, or
slightly enriched air, containing insufficient oxygen to effect a
complete combustion of the burner fuel in an established combustion
zone in the burner tuyere. A particular disadvantage of such an
arrangement is that a substantial amount of nitrogen remains after
the combustion, in addition to certain undesired combustion
products, including water vapor, which cool the flame and carry
combustion heat up the stack. Another disadvantage of prior art
tuyere burner arrangements is that the combustion products are not
properly mixed before entering the furnace, thereby producing an
uneven, unpredictable effect on the melting or smelting processes.
A further disadvantage is that after shutdown or in starting up,
the temperature and melting rate in the furnace increases very
slowly. Another disadvantage in the prior art operation of melting
and smelting processes is that the temperature in the furnace is
often insufficient to prevent the formation of what are known in
the art as "bridges" and "skulls," the former arising when pieces
of scrap become fused in the cupola stack and the latter arising
when molten metallics solidify and form accretions within the
shaft.
Accordingly, it is a general object of the present invention to
improve the melting of iron, steel, and other metals or smelting
their ores in shaft furnaces by substantially increasing the rate
at which charge is consumed, and substantially increasing the metal
or ore-to-coke ratio.
A more particular object of the present invention is to increase
the melting or smelting rate and to increase the temperature in the
furnace.
Another object is to provide techniques and apparatus which require
the use of less expensive charge materials, such as steel scrap
instead of pig iron and silicon dioxide in place of higher priced
silicon alloys.
Another object of the invention is to improve the chemical
composition of the product, and render the same subject to more
exact control, by increasing the uniformity and predictability of
the process.
Other objects of the invention are to increase the slag fluidity
and decrease the tendency for the formation of bridges and skulls
in the furnace.
These and other objects are realized in improved techniques and
apparatus for melting and smelting iron and other metals in
accordance with the present invention in a shaft furnace having a
plurality of tuyeres adjacent the hearth portion which are equipped
with inwardly directed oxy-fuel burners. A salient feature of the
tuyere burners of the present invention is that combustion takes
place in an established combustion zone in the tuyeres, in the form
of a single, homogeneous, coherent, high velocity, high temperature
flame adjacent to or seated at the end of the burner which creates
a high degree of turbulence inside of the tuyeres mixing the
combustion products into a substantially homogeneous stream.
These burners are supplied with streams of fuel comprising
hydrocarbon fluid surrounded with high velocity streams of
commercially pure oxygen, the latter at a mass flow rate of from
one-quarter to twice the stoichiometric requirement for complete
combustion of the fuel. Together, these streams produce flames
having temperatures of from 3,000.degree. to 5,000.degree. F. and
flames velocities within the range 500 to 3,500 feet per second,
which flames are adapted to remain seated in the mouth of the
burner, conforming to an established combustion zone in the tuyere,
notwithstanding the presence of inwardly directed, surrounding air
blasts having velocities of between 150 and 1,000 feet per second
in the tuyere. In these cases where combustion is well established
within either the burner or the tuyere, flame velocity is defined
as the arithmetic mean of the oxygen and fuel free stream
velocities measured in the plane of the inner end of the
tuyere.
In one specific embodiment of the invention described hereinafter,
which relates to the making of molten iron in a cupola, a plurality
of furnace tuyeres were equipped with oxy-oil water-cooled burners
comprising self-atomizing tip mixers. These were supplied with
streams of fuel oil (A.S.T.M. grade 2) and high velocity streams of
commercially pure oxygen, the latter in an amount representing 65
percent or more of the stoichiometric requirement for complete
combustion of the oil. These arrangements produced a single
coherent homogeneous flame in each of the burner tuyeres having
flame velocities of between 500 and 1,500 feet per second, and
flame temperatures within the range 4,000.degree. to 5,000.degree.
F., which were stable in wind velocities up to 500 feet per second
flowing through the tuyeres. Under these arrangements the melting
rate of charge supplied to the cupola was increased 90 percent. The
burner tips were withdrawn from the ends of the tuyeres so that
complete combustion took place in an established combustion zone in
each of the tuyeres.
In another embodiment in accordance with the invention, water
cooled rocket burners were employed in the tuyeres of the iron
melting cupola. These latter burners were supplied with
commercially pure oxygen and natural gas, having a heating value of
approximately 1,000 British thermal units per cubic foot, at an
oxy-fuel ratio of 1.5:1, the oxygen being 75 percent of the
stoichiometric requirement for complete combustion of the natural
gas fuel. This embodiment is also characterized in each burner by a
homogeneous high velocity seated flame, notwithstanding high wind
velocities, and showed an increase over prior art techniques in the
melting rate of the charges supplied to the cupola, which was a
substantial improvement over the prior art, although less
pronounced than that achieved with oil fuel.
In accordance with additional modifications disclosed hereinafter,
the principals of the invention are also applied to the smelting of
ores comprising a principal component of iron and other metals,
such as copper, lead, and antimony, in blast furnaces wherein
burners, also of a high-velocity flame type, are installed for
these applications in the furnace tuyeres or at the level of the
combustion zone in the furnace. In each case, a single high
velocity, high temperature oxy-fuel flame is employed, total
combustion taking place in an established zone in the tuyere, or
furnace barrel.
The particular advantages to be derived from employing oxy-fuel
furnace burners with homogeneous high velocity coherent flames in
melting and smelting furnaces in the manner disclosed in detail in
the specification hereinafter and the attached drawings are: 1.
Higher metal temperatures are produced; and the melting rate is
increased. 2. The uniformity and predictability of the process is
increased. 3. The coke consumption in the furnace is decreased. 4.
More economical types of charge can be employed in the processes.
For example, in the 8" cupola, scrap steel can readily be
substituted for more expensive pig iron, and silicon dioxide
substituted for more expensive silicon alloys. 5. The product is
improved and the composition is more readily controlled. In the
iron melting cupola, for example, the carbon pick-up is increased,
whereas the sulfur pick-up is decreased, and silicon and manganese
losses are decreased. In the smelting process, the chemical
composition of the combustion products of the burner flame can be
carefully controlled to facilitate the reduction process. 6. The
actual functioning of the furnaces is improved by increased slag
fluidity and lessened tendency for the formation of "bridges" and
"skulls.
These and other objects, features, and advantages will be apparent
to those skilled in the art from a study of the detailed
specifications hereinafter with reference to the attached drawings,
in which:
FIG. 1 shows, partly in sectioned front elevation and partly in
schematic, a system including an iron melting cupola modified to
include oxy-fuel burners in accordance with the present
invention;
FIG. 2 shows in enlarged longitudinal section the location of an
oxy-fuel burner in one of the tuyeres of the cupola of FIG. 1;
FIGS. 3A and 3B show, in longitudinal section and in cross section
respectively, a self-atomizing tip mixer type of oxy-oil burner for
use in accordance with the present invention;
FIG. 4 shows, in enlarged perspective, details of the oxy-fuel and
water supply lines in the system of FIG. 1;
FIG. 5 shows an oxygen-oil supply system for the oxy-oil tuyere
burner system of FIGS. 3A, 3B;
FIGS. 6A and 6B show an oxy-gas rocket burner insert for
modification of the burner combination shown in FIGS. 3A, 3B;
FIG. 7 shows an oxygen-gas supply system for use with a burner
employing an insert of the type shown in FIGS. 6A, 6B;
FIGS. 8A and 8B, combined along their lines x--x, show in
longitudinal section an oxygen-fuel rocket burner for alternative
employment in the arrangements of FIG. 1 of the present
invention;
FIG. 8C is a cross sectional showing of the burner of FIGS. 6A,
6B;
FIG. 9 shows the relation between observed wind heating by an
oxy-gas burner in a tuyere and calculated values;
FIG. 10 shows a plot of melting rate as measured by charges
consumed per hour versus wind rate for a cupola operating without
burners in accordance with prior art practice;
FIG. 11 shows a similar plot of melting rate versus wind rate for a
cupola operating with oxy-fuel burners in accordance with the
present invention, employing high gas flows;
FIG. 12 shows a similar plot of melting rate versus wind rate for a
cupola operating with oxy-oil burners in accordance with the
present invention;
FIGS. 13A and 13B are a comparison of the distributions of spout
temperatures for normal operation of a cupola and operation
including oxy-oil burners in accordance with the present
invention;
FIG. 14 shows, partly in front elevation and partly in schematic, a
system including an iron ore smelting blast furnace modified to
include oxy-fuel burners in accordance with the present
invention;
FIG. 15 shows in enlarged cross section a tuyere and surrounding
area in the blast furnace of FIG. 14, indicating the oxy-fuel
burner location in accordance with the present invention;
FIG. 16 shows, partly in longitudinal section and partly in
schematic, a rectangular blast furnace, suitable for the smelting
of ore containing lead or antimony, including oxy-fuel burners in
accordance with the present invention;
FIG. 17 shows in plan view the location of the tuyere burners in
the lead blast furnace of FIG. 16;
FIG. 18 shows, in enlarged longitudinal section, the location of an
oxy-fuel burner in one of the tuyeres of the lead blast furnace of
FIG. 16; and
FIGS. 19A, 19B show, in longitudinal section and cross-section,
respectively, typical rocket burners suitable for use in the
tuyeres of the lead blast furnace of FIG. 16.
Referring to FIG. 1 of the drawings, there is shown a conventional
hot blast iron melting cupola 1 (water jacket not shown) which is
one of the types of furnaces suitable for application of the
oxy-fuel tuyere burners in the manner of the present invention.
The specific cupola shown for purposes of the present illustration
comprises a cylindrical steel shell 2, which is 90 inches in outer
diameter. The shell 2 consists of heavy steel plates, rolled into
cylindrical sections, and riveted, bolted, or welded together with
downwardly lapping joints. The top of the stack 2 is reinforced
with an angle-iron ring 3, which is riveted on in such a manner as
to afford protection against rain seepage between the lining and
the shell. The top of the stack generally extends to a minimum of
10 feet above the roof of the foundry and is sometimes carried
further to provide for additional natural draft at the charging
opening, or to provide additional space to permit complete
combustion of the gases above the charged column. The angle-iron 3
supports a plurality of upwardly extending rods on which are
mounted a conventional slant-roofed, perforated spark arrestor 5,
which has an external annular opening 4a, a foot or so high, at the
bottom, and a smaller annular opening 4b in the upper portion, for
release of smoke and exhaust gases.
The lower, or body, section of the cupola is supported by four
columns 6, about 8 feet high, mounted on a concrete foundation 7.
The lower section is substantially constructed to give proper
support to the load of the upper sections, since the total weight
may be of the order of 136,000 pounds, or more, for a cupola, say,
45 feet high. Shelf segments are bolted to the inside of the shell
2 at regularly spaced intervals for supporting a lining 8, about
nine inches thick of fire-brick, in the illustrative "acid-lined"
embodiment.
The cast iron bottom of the cupola, which in the present embodiment
is 8 feet above the foundation level, is equipped with a pair of
hinged drop doors 9a, 9b, which are used for removing coke from the
cupola after the molten iron has been drained from it.
Fuel is supplied to the cupola 1 through a charging door 18,
covering a rectangular opening in the cupola wall 2, roughly 7 feet
by 10 feet, the bottom of which is located at a height of about 35
feet above the foundation level. Just below the level of charging
door 18, the cupola is surrounded by a platform 17 for facility in
charging the furnace.
Layers of fuel, such as coke, and iron bearing charge, such as
scrap steel or pig iron, are fed into the furnace through charging
door 18, forming alternate layers of coke and charge, the coke
layer being approximately half the thickness of the metallic
charges, to a level of about 27 feet above the foundation level of
the cupola.
The hot gases rising in the cupola from combustion of the coke tend
to melt the iron in the charge, which trickles down through the
cupola and is withdrawn through a downwardly inclined spout 19,
located about 10 feet above the foundation. Slag, which floats on
top of the molten iron, is drawn off through slag spout 21, located
at a level about 11 feet above the foundation of the cupola.
Surrounding the lower end of the cupola 1, at a level about 18 feet
above the foundation, is an annular pipe of rectangular cross
section known as the wind box 11, which in the present example is
180 inches in outer diameter, 120 inches in inner diameter, and 36
inches high. Wind box 11 is connected through an external conduit
12 to a conventional centrifugal blower 13, which is designed to
furnish a continuous blast of air. In the present illustration a
heating unit 13a is interconnected with conduit 13, for heating the
blast up to a temperature of about 1,200.degree. F., although it
will be apparent that in other examples, other arrangements are
contemplated, such as the use of blasts of lower temperatures, or
cold blasts, or in some cases, no blast at all.
The blast of air carried in wind box 11 is admitted to the lower or
body portion of the cupola through a plurality of tuyere openings
14, which may vary in size, shape and number from one iron melting
cupola to another. In the example under description, tuyeres 14 are
eight in number, and are symmetrically distributed around the
circumference of the cupola wall at a horizontal level which is
roughly 5 feet above the hearth level. Tuyeres 14 are cylindrical
in form, having an inner diameter of 6 inches, are 30 inches long,
and are downwardly inclined from the horizontal at an angle of
roughly 12.degree., as will be indicated in greater detail in the
enlarged cross-sectional showing of FIG. 2. Each tuyere opening 14
is lined with a tuyere water-jacket pipe 14a of copper, which is 30
inches long, 111/2 inches in outer diameter, and 1/2 inch thick.
The pipe 14a concentrically surrounds an inner pipe 14b of copper,
7 inches in outer diameter and 1/2 inch thick. The two pipes 14a,
14b are welded or sealed together at their inner ends, and have a
radial spacing between them of 2 inches, to accommodate water
cooling of the tuyere passing in through a conventional water
cooling system, entering and leaving the jacket through pipes 23a,
23b.
The end of the water jacket 14a, 14b of the tuyere pipe protrudes
an axial distance of 16 inches from the inner face of the cupola
wall into the interior of the cupola. The water jacket 14a, which
has an overall length of about 34 inches, protrudes axially 16
inches from the outer face of the cupola wall, and terminates in an
annular flange 15, to which is bolted the matching flange 21 at the
inner end of tuyere extension pipe 24.
Flange 21 is 19 inches in outer diameter, about 61/2 inches in
inner diameter and 1/2 inch thick. It is sealed to flange 15
against a small intervening gasket 15a, by means of a plurality of
bolts 22. Steel extension pipe 24, which has an inner diameter of 6
inches and an outer diameter of 61/2 inches, extends outwardly from
the junction of the flanges an overall distance of about 38 inches,
so that the total outward-extending length from the inner end of
the tuyere water jacket 14a, 14b to the outer end of pipe 24 is
about 6 feet. Pipe 24 protrudes about 52 inches from the outer wall
of the cupola. Centered about 21 inches inches from the outer end
of pipe 24 is a downcomer arm 24a, about 6 inches in inner diameter
and 6 1/2 inches in outer diameter which executes a half circle,
and passes up through a flexible expansion joint (not shown) to
make connection to wind box 11 overhead.
In accordance with the present invention, in order to expedite the
iron melting process in the cupola 1, and to supply more units of
heat directly to the combustion area in substitution for bulky
units of coke added through the charging door, oxy-fuel burners 10
are inserted into seven of the eight cupola tuyeres 14. These
burners are each designed to generate a single, homogeneous,
coherent, seated flame, having a flame velocity within the range of
500 to 3,500 feet per second, which produces flame temperatures
within the range 4,000.degree. to 5,000.degree. F., notwithstanding
the presence in the tuyere pipes 24 of inwardly directed air blasts
of between 150 and 500 feet per second.
FIG. 2 shows, in enlarged section, one of the cupola tuyeres 14,
including the tuyere extension pipe 24, and showing the position of
a typical oxy-fuel burner 10 in the specific embodiment under
description.
The tuyere extension pipe 24, which is disposed concentrically with
the tuyere pipes 14a, 14b, abutting the latter, is held in place by
a plurality of set screws 22 on the cover 21. Pipe 24 extends
outwardly about 48 inches from its inner end and 8 inches from the
downcomer 24a, and is closed at its outer end by an annular closure
25 of steel, which is 10 inches in outer diameter and 1 inch thick,
and which is fastened at its outer periphery to a lug bracket 26,
welded or brazed to the outer circumference of pipe 24 by a
plurality of lugs 27. The closure 25 has at its inner opening a
nipple 25a, about 2 1/2 inches in inner diameter, in which is
mounted concentrically the burner assembly 10, which will be
presently described in detail with reference to FIGS. 3A, 3B. The
inner end of burner assembly 10, including the water jacket 28,
which is held in place by a conventional spider arrangement 29, is
recessed, in the present example, a distance of about 2 inches from
the corresponding inner end of the inner tuyere pipe 14b. The
actual burner tip 31 may be further recessed so that its end is
withdrawn about 6 inches inside of the water-jacket 28. However, as
will be described in detail with reference to FIGS. 3A, 3B
hereinafter, the position of burner assembly 10, including the
water-jacket 28, is adjustable in the inner tuyere pipe 14b to any
one of a number of different longitudinal positions, depending on
the specific operation under description.
The outer end of burner assembly 10 terminates in burner body head
32, to which are connected the fuel feed line 33, the oxygen feed
line 34, and the cooling water pipes 35 and 36 to water pumping
system 96. The feed lines 33 and 34 are connected to the oxy-fuel
supply system 95, which system and connecting conduits will be
described in detail with reference to FIGS. 4 and 5,
hereinafter.
Let us refer, now, to FIGS. 3A, 3B which are detailed longitudinal
and cross-sectional showings of the self-atomizing tip mix burner,
which is a preferred type employed in the practice of the present
invention in a cupola for iron melting, such as shown in FIG. 1,
since it provides for the development of a stable, homogeneous,
high velocity oxy-oil flame, combustion being initiated in or
taking place in an established combustion zone immediately adjacent
the burner tip.
The outer pipe 30 of the burner assemblage 10, which includes the
enclosing water jacket 28, is a hard-drawn, seamless brass tube
0.109 inch in wall thickness and 65 3/8 inches long, having an
outer diameter of 2 1/2 inches, which is disposed concentrically in
the inner tuyere pipe 14b and the abutting extension pipe 24.
Concentrically disposed inside of pipe 30, and terminating one-half
inch from the inner end of the latter, is a second pipe 37, also of
seamless brass tubing 0.065 inch in wall thickness 66 3/8 inches
long, and 2 inches in outer diameter. A third pipe 38, also part of
the water jacket, is located concentrically inside of pipes 30 and
37, the inner end of the latter being flush with the pipe 30. Pipe
38 is also of seamless brass tubing 0.065 inch in wall thickness,
68 3/8 inches long, and 1 1/2 inches in inner diameter. An annular
brass plug 39, which is 2 5/16 inches in outer diameter, 1 1/2
inches in inner diameter, and one-quarter inch thick, is fitted
into the inner end of the water jacket assemblage 28, and brazed
with silver solder in the peripheral junctions. The three
concentric pipes 30, 37, and 38, constituting the water jacket 28,
which are held in position by conventional separators, are fitted
at their external ends into the terminal fitting or burner breech
assembly 32, which is a cylindrical brass element 5 1/2 inches in
axial length and 3 1/2 inches in diameter, having four openings,
each communicating with a different concentric channel. The water
intake pipe 35, which is about 1 inch in outer diameter, is tapped
into a cylindrical arm which protrudes laterally about
three-quarters of an inch from the burner breech assembly 32. The
cylindrical arm is 1 1/2 inches in outer diameter and 1 inch in
inner diameter, and leads at its inner end to the annular chamber
between the brass pipes 37 and 38 of the water jacket 28. An
oppositely directed lateral arm on burner breech assembly 32, which
is similarily dimensioned, screws onto the water outlet pipe 36 and
taps into the annular space between pipes 30 and 37, so that a
stream of water entering at 35 flows the length of the water jacket
28 through the outer annular passage, and returns through the inner
annular passage to 36, where it flows out.
The burner proper, whose tip 31 is designed to be moved to
different positions within the inner sleeve 38, and in the present
illustration is disposed at a position about 12 inches from the
inside or furnace end of the tuyere pipe 14a, is housed in brass
tube 38. Fitted inside of brass tube 38 is a cylindrical block
burner element 41. This is a copper cylinder 1 inch long and 1 3/8
inches in outer diameter. A bore 41a, which is nine-sixteenths inch
in diameter, extends through the length of the element in an axial
position. Extending parallel to and surrounding the bore 41a are a
plurality of smaller bores 41b which are 16 in number and
one-eighth inch in diameter in the present embodiment and serve to
transmit streams of oxygen. These are symmetrically disposed with
their centers on a circle 1 1/16 of an inch in diameter and
concentric with bore 41a.
Terminating in and fitted into the bore 41a of block burner element
41, and silver brazed in place, is a stainless steel tube 42,
three-fourths of an inch in outer diameter, one-sixteenth of an
inch in wall thickness, and 79 3/4 inches long, which serves as a
conduit for fuel oil. At the inner terminal in the block burner
element 41, the stainless steel tube 42 is screw threaded to a
depth of about 3/8 of an inch, designed to receive a matching
screw-in fitting on the burner orifice element 43, which is a brass
cylindrical element 1/2 inch deep and about three-quarters of an
inch in diameter. The central opening 43a, 43b of orifice element
43 is axially disposed having a larger cylindrical portion 43a
about 1/4 inch in inner diameter, which communicates with the
conduit 42, and extends axially to about 1/8 inch from the end
toward the furnace, where it abruptly narrows to a much smaller
opening 43b, about 1/16 inch in diameter in the present
embodiment.
The stainless steel conduit 42 extends axially through the burner
breech assembly 32 and terminates at its outer end in a brass
bushing 33a which is 3/4 inch in outer diameter and 1/2 inch in
inner diameter and internally screw threaded for coupling to the
oil feed line 33.
A lateral inlet arm 34a, which is 1 1/2 inches in outer diameter
and 1 inch in inner diameter leads out of the burner body assembly
32 and is coupled in a gas-tight seal with the oxygen hose 34, for
introducing oxygen into the annular space between the stainless
steel oil conduit 42 and the inner brass tube 38.
Referring to FIG. 4, there is shown in perspective an example of
the configuration of the oxygen, fuel, and cooling water pipes
connected between a typical pair of tuyere burners and the
respective supply systems for oxygen, fuel, and cooling water in
accordance with the present invention.
In preferred arrangement, water for cooling the tuyere burner
system is brought into the burner breech assembly 32 at a pressure
of 50 pounds per square inch absolute, flow rate of 10 to 15
gallons per minute, and ambient temperature, from any ordinary
water tap under control of the 3/4 inch globe valve 35a, passing
through a 3/4 inch inner diameter flexible hose 35 of neoprene
rubber or the like. The water passes through the concentric
channels in the water jacket 28 of burner 10 and passes through the
3/4 inch inner-diameter outlet pipe 36 to the outlet 36a, from
which it drains away. A bimetallic thermometer 36b measures the
temperature of the emerging water as one check on the temperature
generated in the tuyere burners.
Oxygen for the tuyere burners is derived from the two inch inner
diameter oxygen manifold 62 of steel pipe. Manifold 62 is connected
into each of the tee connections 49 through the respective branch
line 63, of 1 1/2 inches inner diameter, to a second tee connection
65, where it separates out into two equal branches, each of which
is under control of a pair of valves in series, the nearest to the
tee being a 1 inch inner diameter Airco station valve 66a, and the
second, a 3/4 inch inner diameter ball valve 66b. Following the
valves 66a, 66b is a conventional pressure gauge 64, which is
scaled to read branch line pressures within the range zero to 100
pounds per square inch. Leading out from each of the latter is a
3/4 inch inner diameter hose 34 formed of neoprene, one-quarter
inch thick and 80 inches long in the present embodiment. The latter
is coupled in gas-tight connection to the orifice coupling element
34a of the burner breech assembly 32 through a 3/4 inch inner
diameter connecting union. In each case, the length of the oxygen
hose 34 and of water hoses 35 and 36 is sufficient to permit the
removal of the burner 10 from the tuyere pipe 14a without altering
the connections or disconnecting the pipe systems.
Oil is piped to each of the burner locations from a distribution
system including control rack 80 which will be presently described
in detail with reference to FIG. 5. Four branches 81a, 81b, 81c,
and 81d, each of copper tubing 3/8 inch in outer diameter and 0.035
inch wall thickness, lead out in parallel from the control rack 80
to a respective one of the three-eighths inch inner diameter tee
junctions 51, each of which services a pair of tuyere burners, with
the exception of the tuyere adjacent the spout 19 which services
only one. Just ahead of the respective tee junctions 51, the 3/8
inch inner diameter copper branches 81a, 81b, 81c, and 81d,
respectively pass through couplings which are fitted into steel
pipes in which the inner diameters are reduced to one-quarter inch,
and which are welded to supporting brackets, not shown.
From the tee junctions 51, two equal branches 33, each of annealed
copper tubing 3/8 inch in outer diameter, are oppositely directed,
the flow in each branch under control of a 3/8 inch inner diameter
ball valve 53. In the present illustrative embodiment, the copper
tubes 33 are each 60 inches long and looped to allow the burners to
be removed from the tuyeres or to be operated in various withdrawal
positions. Each of copper tubes 33 at its end feeds into a second
tee junction 52 (see FIG. 4) in which the internal diameter is
reduced to one-quarter inch. At each of the tee junctions 52 is
located a small pressure gauge 33b, designed to accommodate a range
from zero to 50 pounds per square inch. The opposite arm of each of
tee junctions 52 is connected through a coupling 33a to the burner
breech assembly 32.
FIG. 5 of the drawings shows schematically the entire oxy-fuel oil
system, of which the pipe system was described with reference to
the perspective showing of FIG. 4.
A conventional 3,000 gallon tank 70 provides oil storage for a
maximum fuel consumption of 300 gallons per hour for 8 hours at
ambient temperature and pressure. Tank 70 is connected to the inlet
side of a conventional 5 horsepower centrifugal pump 73 under
control of the valve 72. Motor 73 is preferably a 200 or 440 volt
three-phase type. The outlet side of pump 73 is connected through a
11/2 inch inner diameter copper pipe to one leg of a tee junction
74, a second leg of which is connected through a 1 inch inner
diameter bypass line 71 under control of normally closed valve 72a,
returning to the tank 70, or alternatively, to an outlet vent 72b.
The third leg of tee 74 is connected to a 1 inch inner diameter
steel pipe which passes under control of solenoid-actuated valve 78
to a fuel oil control rack 80 through a pressure regulator 76 and a
positive displacement flowmeter 77. Solenoid actuated valve 78 may
be of a manual reset type, such as part No. 082251, described in
Bulletins of the Automatic Switch Company of Florham Park, New
Jersey, and referred to on page 52 of their catalog No. 203. The
pressure regulator 76 may be of a conventional type. Flowmeter 77
is also of any type well-known in the art. In the present example,
means is also provided for filtering the oil flow entering rack 80.
The flow entering rack 80 is regulated to a pressure of 90 pounds
per square inch absolute and a flow rate of 180 to 300 gallons per
hour at ambient temperature. The control rack 80 comprises a
manifold steel pipe, 1 inch in inner diameter, from which the oil
is fed out through a plurality of substantially identical pipes of
soft copper tubing, each 3/8 inch in inner diameter.
The four branches employed for oil distribution to the
tuyere-burner system of cupola 1 are 81a, 81b, 81c, and 81d, the
flow in each branch being controlled by a respective one of the
dual valves 82a, 82b, 82c, and 82d, which preferably include
conventional needle valves. The positive displacement meters 84a,
84b, 84c, and 84d in the individual branches respectively measure
the flow in each branch.
An additional conduit 89 is connected under control of the solenoid
operated valve 87, which may be of the type previously described,
and the manual valve 86 to a storage tank 89a of nitrogen, for
purging the oil from the burner oil delivery system through a
series of branch lines 88a, 88b, 88c, and 88d, which are
respectively connected to branch oil lines 81a, 81b, 81c, and 81d,
of the fuel oil control rack 80 under control of individual cut-off
valves in each line. The latter branches respectively lead into the
tee junctions 51, which separate into the branches leading to pairs
of individual burners 10, as previously described with reference to
the perspective showing of the oil delivery system of FIG. 4.
The electrical control panel 83, which is powered by the 110 volt
alternating current source 92, provides a push button electrical
control for the manual-reset solenoid operated valve 78 at the
inlet to fuel rack 80, and relays and timers for controlling the
solenoid operated valve 87 to the nitrogen purge system. Control
panel 83 provides power to energize the normally operated relays 93
and 94, which react to changes in pressure in the wind box 11 or
failure in the oil pressure to cut-off the oil supply to the fuel
rack 80. The foregoing relationship is indicated schematically in
FIG. 5. The fuel rack 80 in one embodiment embraced electrical
control panel 83, and was devised for experimental purposes
enabling individual control and purge of each burner. Subsequently,
an improvement and simplification of controls has been devised
using commercially available ratio controllers such as shown, for
example, on page 43 of Catalogue No. 2, Publication 13316, printed
July 1959 by Fischer and Porter Company of Warminster, Pa.
Additionally, a purge system is used in conjunction with the ratio
controller to bleed nitrogen or steam into the oil lines, using
commercially available valves and timers.
Oxygen for the burners 10 is furnished from a liquid oxygen station
56. In the present illustration this is a stainless steel vessel of
the type shown, for example, on page 11 of Catalogue No. 450,
issued November 1960, by Air Reduction Company, Incorporated, 150
East 42nd Street, New York, New York. The liquid oxygen in station
56 is maintained at a temperature of -240.degree. F., under a
pressure of 165 pounds per square inch absolute.
In the present example, a copper tube 57 having an outer diameter
of 2 1/8 inches and 0.083 inch in wall thickness, connects station
56 to a vaporizer 58. The latter is a conventional electrically
energized unit capable of converting liquid oxygen at a temperature
of -240.degree. F. and pressure of 165 absolute, at the rate of
40,000 standard cubic feet per hour to vapor at 40.degree. F. at
the same pressure. The newly generated vapor passes through a
pressure regulator 61, where its pressure is regulated to a
pressure of approximately 145 pounds per square inch absolute.
Regulator 61 may be a conventional type of pressure-reducing
regulator capable of operating in the range of 315 pounds per
square inch absolute inlet pressure to 165 pounds per square inch
absolute outlet pressure. This regulator preferably handles a
volume of 40,000 standard cubic feet per hour, minimum, at the
foregoing pressures.
Regulator 61 is connected at its output to a steel conduit 59 which
is 2 inches in inner diameter and 0.218 inch in wall thickness,
into which is interposed an orifice flange 55a from which a conduit
system 55b comprising a 3/8 inch outer diameter copper tube 0.035
inch in wall thickness leads off to the main line flowmeter 67 is
of a conventional type, under control of an appropriate system of
valves.
The conduit 59 is connected to a similar conduit 68 through
solenoid operated valve 69, which is remotely energized from the
control panel 83. Valve 69 is also connected to be actuated through
control panel 83 to relays 93 and 94 which are responsive to
changes in the pressure in the wind box or failure in the oil
pressure, to cut-off the flow of oil to the oil rack 80, followed
by cut-off of oxygen in conduit 68 about 2 minutes later.
The steel conduit 68, which is 2 3/8 inches in outer diameter and
0.218 inch in wall thickness, leads from the valve 69, normally
open during operation of the system, to the tee junction 68a which
leads into the oxygen manifold 62, under control of a 2 inch ball
valve 68b. The manifold 62 is a pipe formed of steel, 2 3/8 inches
in outer diameter and 0.218 inch in wall thickness, which forms a
horseshoe, partly surrounding and adjacent to the wind box 11 of
the cupola 1, having an outer diameter of 16 feet, and an inner
diameter of 15 1/2 feet. Oxygen manifold 62 has four outlets 49 at
symmetrically spaced positions on its inner perimeter, which are
located adjacent the corresponding tee junctions 51 which lead out
from the oil rack 80. As previously described with reference to the
perspective showing of FIG. 3, the tee junctions 49 each supply
oxygen to the tuyere burners 10 through four branch lines 63, which
are each divided into two branch lines 34, with the exception of
the junction nearest the spout 19, which services only one branch
line.
The four oxygen branch lines 63 are each equipped with orifice
flanges 63a into which a branch line flowmeter 97, similar in form,
but of smaller capacity than the previously described main line
flowmeter 67, can be plugged into the branch line through the
conduit system 98.
In accordance with prior art practice, a cupola of the type shown
in FIG. 1, without tuyere burners arranged in accordance with the
teachings of the present invention, conventionally operated in the
following manner to produce molten iron.
The 5,000 pound metal charge, which was introduced into the furnace
through the charging door 18 by means of a bottom-drop bucket,
contained approximately 20 percent steel scrap, the balance being
iron scrap. An identical bucket was used to introduce coke and
fluxes, such as limestone, into the furnace between the metal
charges. The coke rate was normally 240 pounds per ton of metal
charge, corresponding to a metal-to-coke ratio of 8.35:1.
Full production in this furnace required an air blast of 8,000
standard cubic feet per minute into the eight tuyeres and consumed
between six and eight charges per hour. A blast of air, accelerated
by the blower 13 and heated up to 1,200.degree. F. in the stove
13a, was circulated in the wind box 11 from which it was delivered
to the interior of the furnace through the tuyeres 14 at a volume
flow rate of between 4,000 and 10,000 standard cubic feet per
minute. Metal was tapped continuously to a tilting fore-hearth for
distribution to transfer ladles which supplied metal to centrifugal
pipe casting machines and to a conveyor line for the casting of
pipe fittings. The neutral-to-slightly-basic slag was broken up by
a water stream and removed by a bucket conveyor. Charge chemistry
was maintained during the operation to allow production of iron at
the spout containing approximately 3.70 percent carbon and 2.10
percent silicon, according to half-hourly measurements. The metal
temperature at the spout was usually maintained in excess of
2,900.degree. F., during operation.
In accordance with the present invention the auxiliary oxy-oil
burner system 10, described with reference to FIGS. 1 through 5, is
operated in the following manner, in conjunction with cupola
operation substantially as described in the foregoing
paragraphs.
Buttons are initially pushed on panel 83 to close the solenoid
operated valve 78 to the oil line 75 and the solenoid operated
valve 69 to the oxygen line 59, and to open the normally-closed
solenoid operated valve 87 to the nitrogen (or steam) purge system,
thereby admitting nitrogen (or steam) from the nitrogen source 89
(or alternate steam source) to the system of branch purge conduits
88a, 88b, 88c, and 88d connected to respective oil conduits 81a,
81b, 81c, and 81d. For the purposes of the present purging
operation, nitrogen is fed into each of the aforesaid branch lines
of oil rack 80 at a volume flow rate of 20 standard cubic feet per
minute, at a pressure of 75 pounds per square inch absolute, at
ambient temperature. This flow is continued for a period of 3
minutes until each of the oil lines is purged of fuel and gases
remaining from a previous operation. After this purge operation has
been completed, valve 87 is closed and the system is made ready for
operation of the burners. Referring to FIG. 4, the water, which is
constantly flowing in the burner cooling system, passes through the
intake hose 35, under control of valve 35a, entering the burner
jacket through the burner body head assembly 32 at a pressure of
about 50 pounds per square inch absolute, at ambient temperature,
and a volume flow rate of 10 to 15 gallons per minute. The water is
each of the burner jackets flows out through the return hose 36 and
vent pipe 36a, the temperature being measured by the thermometer
36b.
The centrifugal blower 13 is operated to force a blast of air
through pipe 12 to the wind box 11 where it enters at a pressure of
15.0 to 16.2 pounds per square inch absolute, a temperature of
1,200.degree. F., and circulates in the wind box at a volume flow
rate of 8,000 cubic feet per minute, or a velocity of 5,700 feet
per minute.
Prior to the lighting of the burners 10, the wind is spilled
through a vent pipe (not shown) in the wind box 11 and is not
released into the tuyeres 14.
The technique for lighting the burners is to first turn on the fuel
supply alone, without the oxygen. Thus, oil valve 78 is reopened to
permit oil to flow through the oil rack 80 at an initial rate of 20
gallons per hour, at a pressure of 17 pounds per square inch
absolute, at ambient temperature. The flow passes into each of the
branches 81a, 81b, 81c, and 81d, which transmit the separate
streams of oil under control of the branch line valves 84a, 84b,
84c, and 84d, through the tee junctions 51 and the individual lines
33 to the fittings 33a in the burner body head assembly 32 in each
of the tuyere-burners 10. Assuming the furnace is in operation, the
oil is immediately ignited by the heat of the furnace. Otherwise,
conventional auxiliary means of lighting are employed, such as an
electrical igniter, or an oxy-acetylene torch, which would be
interposed into the tuyere through a separate opening (not
shown).
For optimum operation in the embodiment under description, the end
of each of the burners 10 may be withdrawn from the inner end of
the tuyere 14a a distance of 2 feet. In fact, to provide a greater
length of the burner barrel in which combustion may take place, the
burner may be withdrawn to the limit of the water cooling in the
tuyere, which in the present embodiment would be at the
cross-sectional plane of the butt junction between the outer end of
tuyere pipe 14b and extension pipe 24. Moreover, the burners 10 are
concentrically disposed in the tuyeres 14 by means of the spider
arrangement 29. After the burners have been lighted, the rate of
oil flow is increased so that, in the present example, each
separate oil stream enters the burner body head assembly 32 at a
volume flow rate of 25 to 30 gallons per hours, a pressure of 35 to
65 pounds per square inch absolute, and ambient temperature.
Immediately after the oil is lighted, a stream of oxygen is caused
to flow into the conduit 68 at a volume flow rate of 500 to 600
standard cubic feet per minute. The stream flows through the tee
junction 68a into the oxygen main 62, from which it is delivered
through the auxiliary branches 63 and the individual lines 34 to
the burner breech assembly 32. In the present illustration, the
oxygen flows into each of the latter at a volume flow rate of
one-seventh of the flow rate through the conduit 68, at a pressure
of 45 to 65 pounds per square inch absolute, and ambient
temperature.
Assuming the parameters given, an oxy-burner flame is produced in
the burners which extends approximately 36 inches from the burner
tip 31, and which is characterized by a flame velocity of about 800
feet per second and a flame temperature of between 4,000.degree.
and 5,000.degree. F. Once the high velocity flame is seated in the
burner, the blast from wind box 11 is restored to the tuyeres 14 at
a volume flow rate of between 8,000 and 9,000 standard cubic feet
per minute, or a wind velocity in each of the individual tuyeres of
5,700 feet per minute.
During continuous operation for a week, in the example under
description, the self-atomizing tip mix burner 10, of the form
shown in FIGS. 3A, 3B, used an average of 189 gallons per hour of
oil and 39,550 standard cubic feet per hour of oxygen, or 210
standard cubic feet of oxygen to a gallon of oil. This amounts to
75 percent of the oxygen stoichiometrically required for complete
combustion of the fuel oil. Oxygen preferred for the purposes of
the present invention is a commercial grade, 99.5 percent pure,
which is manufactured by the Air Reduction Company, Inc. to the
following specifications:------------------
---------------------------------------------------------Typical
Analysis Impurity Content: Argon 0.15-0.3 percent (by volume)
Carbon Dioxide 0.0005 percent (by volume) Hydrocarbon (C.sub.2
H.sub.2) 0.00002 percent (by volume) Nitrogen 0.1-0.25 percent (by
volume) Maximum Due Point 80 degrees fahrenheit Water Vapor 7.8
parts per million
_________________________________________________________________________
_
An oil suitable for the purposes of the present invention is
identified as No. 2 industrial fuel oil, according to the standard
of the American Society for Testing Materials. Another oil suitable
for the purposes of the present invention is identified as No. 6
heavy industrial fuel oil (Federal Specification Board, Bunker Oil
"C") identified in the United States Bureau of Standards Commercial
Standard CS 12-29.
Table I which follows gives analysis of the principal components of
No. 2 fuel oil and "Bunker C," derived from page 66, Babcox &
Wilcox, Useful Tables, 8th Edition, 1963:
TABLE I
Oil Analysis
(Percentages by Weight) No. 2 Bunker C
_________________________________________________________________________
_ Sulphur 0 .01-0.5 0.7-3.5 Hydrogen 11 .8-13.9 9.5-12.0 Carbon 85
.9-86.7 86.5-90.2 Ash Nil 0.01-0.50 Heating Value 19,170-19,750
17,410-18,990 per lb (British Thermal Units)
_________________________________________________________________________
_
Alternative types of the oxy-oil self-atomizing tip mix burners 10
disclosed and described in detail with reference to FIGS. 3A, 3B of
the drawings, which may also be used successfully in the tuyeres 14
in accordance with the present invention, are rocket burners 100 of
the design shown in detail in longitudinal section in FIG. 6A, and
in cross section in FIG. 6B. These include the same water jacket 28
as shown with reference to the burners of FIGS. 3A, 3B, including
concentric tubes 30, 37 and 38, only the internal burner portions
being modified as shown in accordance with the burner insert
indicated in FIGS. 6A, 6B.
Referring to the latter figures, there is shown an axially disposed
fuel gas tube 138 of stainless steel, which is three-quarters inch
in outer diameter, 0.035 inch in wall thickness, and 60 21/32
inches long, which terminates at its outer end in a male connector
133a, for connection to the branch gas line 133 in the gas supply
system to be described presently. At the inner end tube 138 is
fitted into and fastened with silver braze in the cup-shaped
opening of a cylindrical brass adapter 139, which is three-quarter
inch in inner diameter, 1 inch in outer diameter, and 1 inch in
axial length. The adapter 139, which terminates 2 1/2 inches from
the terminal end of the burner block 141, accommodates a bundle of
five stainless steel tubes 140, each one-quarter inch in outer
diameter, 0.020 inch in wall thickness, and 6 1/4 inches long,
which are nearly parallel to the principal axis of the burner and
disposed in symmetrical array about the burner axis. The terminal
ends of tubes 140 pass through the burner block 141, so that the
centers of their orifices in a cross sectional plane lie in a
circle forty-one sixty-fourths of an inch in diameter. The burner
block 141, which replaces burner block 41 of burner 10, is a copper
cylinder 1 3/8 inches in outer diameter, which is slidably fitted
inside of the inner pipe 38 of the water jacket 28 of FIGS. 3A, 3B.
In addition to fuel gas tubes 140, burner block 141 includes a
plurality of parallel bores for oxygen vents 142a and 142b, each
one-eighth inch in diameter, which are symmetrically arranged with
their centers in two concentric circles, the outer one comprising
vents 142a being 1 1/8 inch in diameter, and the inner one
comprising vents 142b, being 1 7/64 inch in diameter.
As in burner 10 previously described, oxygen flows through coupling
134a into burner body head 32. The annular space between the inner
water jacket pipe 38 and the gas tube 138 serves to conduct oxygen
to the burner block 141 where it passes through orifices 142a and
142b. Gas passes in through the connector 133a and pipe 138 to
adapter 139, where it is fed into the five gas tubes 140 in the
burner block.
Referring again to FIG. 4 of the drawings which shows in
perspective the connecting hoses between the fuel supply system and
the burners in the tuyeres 14, the arrangement for employing the
rocket burners 100 in place of the self-atomizing tip mix burners
10, described in the earlier part of the specification, is
substantially similar except that for the purposes of the
embodiment to be presently described, a gas supply system such as
shown in FIG. 7 will replace the oil supply system previously
described with reference to FIG. 5.
It will be apparent that in both the systems disclosed in FIG. 5
and FIG. 7, the oxygen supply system is substantially similar, the
latter being designated with numbers which have the same tens and
digit termination to avoid a duplication of description. Thus, in
the system of FIG. 5 the elements of the oxygen supply system are
designated by numerals ranging from 49 through 69; and, in the
supply system of FIG. 7, the elements of the oxygen supply system
are designated by numerals 149 through 169.
Referring now to the gas supply system shown in FIG. 7 of the
drawings, the natural gas is derived from a conventional gas pipe
line 170 under control of a conventional ball-type valve 172, the
outlet of which is connected to the inlet of a conventional gas
pressure regulator 173.
The outlet of the pressure regulator 173 passes through a steel
pipe 175, which is 2 3/8 inches in outer diameter and 0.218 inches
in wall thickness, to an orifice flange 145a which serves for the
connection through conduit 145, comprising a pair of three-eighths
inch outer diameter flexible copper lines, to the flowmeter 167.
The latter may be of any conventional type capable of measuring up
to 20,000 standard cubic feet per hour natural gas at an inlet
pressure of 65 pounds per square inch absolute.
The gas line 181 passes through the manual reset solenoid-operated
valve 182 which is energized through the electrical control panel
183, by the 115 volts, 10 amperes alternating current source 192.
Valve 182 may be of any of the types well-known in the art.
From the valve 182 the gas line 181 passes into a tee connection
148 which leads to the gas manifold 147. The latter which is a pipe
formed of steel, 0.218 inch in wall thickness, has an outer cross
sectional diameter of 2 3/8 inches, and surrounds the cupola in a
plane above the wind box 11 of FIG. 1, forming a circle having an
outer diameter of 192 inches and an inner diameter of 187 inches.
The gas main 147 four symmetrically spaced outlets 144, each of
which leads into a branch line 150. On each of the lines 150 is an
orifice flange 150a to which may be connected a branch line
flowmeter of a type similar to the main line flowmeter 167 except
that its capacity is more limited, and the reading more accurate.
Each of the branch lines 150 leads into a tee junction 151, each of
the arms of which separate into a pair of branches 133, except for
the one nearest the cupola spout 19 which has only a single branch.
Tee junctions 151 are formed of steel pipe, and have inner
diameters of 1 inch. The connecting branches 133 are each of 3/4
inch inner diameter flexible rubber hose, 108 inches long, and are
controlled at the tee junction 151 by a pair of ball valves 153.
The branch pipes 133 are made long enough and flexible enough to
permit the position of burners 100 to be adjusted in the tuyeres
114 or removed altogether without rupturing the hose. Each of the
branches 133 is tapped into the fitting 133a on burners 100,
leading to the gas pipes 140 therein (See FIG. 6B). Each of the
individual lines 133 has a meter for measuring pressure and flow
rate into the burner 100.
Whereas in preferred form for use in the cupola, oxy-gas burners
may assume the form of the rocket burner insert indicated in FIGS.
6A and 6B, just described; alternatively, oxy-gas burners may be of
the form shown in FIGS. 8A, 8B, 8C which is a variant type of
rocket burner designed for use with either gas or oil, or both, as
fuel, using oxygen as a combustant.
Referring to FIGS. 8A, 8B, 8C, the burners 200 are designed to be
placed in the tuyeres 14 in substantially the same manner as
burners 10, as indicated in FIG. 2 of the drawings. Each of burners
200 is 44 1/2 inches long and equipped with a water jacket. The
latter comprises an outer brass tube 202 which is 4 1/2 inches in
outer diameter, 0.125 inch in wall thickness, and 24 3/8 inches
long; a second concentric brass tube 203, which is 4 inches in
outer diameter, 0.065 inch in wall thickness, and 25 5/8 inches
long; and an inner concentric brass tube 204 which is 3 and 1/4
inches in outer diameter, 0.135 inch in wall thickness, and 28
inches long. The three concentric tubes 202, 203, and 204 forming
the water jacket are mounted so that tubes 202 and 204 are flush at
their inner ends, and tube 203 is recessed from the inner end by
one-half inch. The ends of tubes 202 and 204 are spaced apart by an
annular brass ring plug which is 4 1/4 inches in outer diameter and
3 1/2 inches in inner diameter and 1/4 inch in axial extent and is
fastened into place with a silver solder braze.
The three concentric tubes 202, 203, and 204 terminate at their
outer ends away from the furnace in a burner breech assembly 205.
This is a brass cylindrical fitting 7 and 1/2 inches long, and 5
1/2 inches in outer diameter, which at its inner end has a collar
fitting over the end of the brass tube 203, overlapping it for 1/4
inch, the two surfaces being brazed together by means of a 1/16
inch silver solder wire. Axially disposed in tubes 202, 203, and
204 is an additional tube 206, which is formed of type 304
stainless steel 3/4 inch in outer diameter, 0.035 inch in wall
thickness, and 39 inches long. The inner end of the center tube 206
terminates in a cylindrical brass block burner fitting 211 which is
3.23 inches in outer diameter at the peripheral end of the burner
and 2 inches in axial extent, terminating at its end away from the
orifice in a slight flange 3/16 inch deep, over which is fitted a
stainless steel tube 212 3 inches in outer diameter, 0.065 inch in
wall thickness, and 6 inches long, which is held in position on the
flange by means of silver solder braze. The block burner fitting
211 has an axial opening, at its inner or burner end, 3/4 inch deep
which accommodates the terminal end of the central tube 206,
centered on a connecting opening 207 which is 1/2 inch in inner
diameter and one-half inch long. The connecting opening 207 flares
slightly three-eighths inch from its burner end, terminating in a
female screw fitting 207a five-eighths inch deep and three-quarters
inch in diameter, into which may be fitted any one of a plurality
of orifice male fittings 208, the size of whose orifice depends on
the type of fuel contemplated for use.
In the present embodiment the orifice fitting 208 is a brass
screw-in fitting, at the connecting end of which, away from the
orifice, there is a cylindrical opening 208a one-half inch in
diameter extending one-quarter inch toward the end. The diameter of
the opening then sharply narrows to a centered mouth 208b
one-quarter inch in diameter. Adjacent the mouth 208b, are a pair
of blind holes 209, one-eighth inch deep and one-eighth inch
across, at diametrically opposite positions for screwing the
orifice fitting 208 in place. Surrounding the center pipe 206 and
located with their centers on a circle one inch in diameter are
eight symmetrically spaced tubes 210. Each of the latter is of
stainless steel one-half inch in outer diameter, 0.02 inch in wall
thickness and 8 inches long, terminating in the block burner
fitting 211 with the ends flush with the end of the orifice
208b.
Looking at the cross-sectional view of FIG. 8C, it is apparent that
between the central orifice 208b and the circle of larger openings
210, are concentrically arranged eight smaller 1/4 inch diameter
openings 213, the centers of which lie on a circle 1 1/8 inches in
diameter, and which are symmetrically spaced and midway between
each of the adjacent openings 210. On an outer concentric circle 2
3/8 inches in diameter, are an additional series of symmetrically
disposed openings 214, also eight in number, which are each
five-sixteenths inch in diameter. The central orifice 208b and the
connecting central pipe 206 may serve for the transmission of fuel
oil in the burner, whereas the surrounding openings 210 may serve
for the transmission of fuel gas, the interspersed smaller openings
213 and 214 serving for the transmission of oxygen.
Between 7 and 7 1/2 inches from the inner end of burner orifice
208b is an adapter tube 215, one-half inch in axial extent, which
serves to hold the bundle of tubes 210 in position within the
enclosing concentric tubes 202, 203, and 204, and which also
retains the center tube 206 in its axial position. The adapter 215
is also flanged to accommodate a stainless steel tube 216 which is
one-half inch in outer diameter, 0.065 inch thick, and 27 inches
long, and which fits concentrically around tube 106.
The burner breech assembly 205 is machined of brass to accommodate
the center tube 206 and the surrounding concentric tube 216, in
addition to the outer tubes 202, 203, and 204. The burner breech
assembly 205 includes a pair of oppositely directed lateral brass
bushings 217 and 218, each having an outer diameter of 1 3/4 inches
and protruding outwardly three-quarters inch from the edge of the
fitting 205. The connecting pipe to bushing 218 is tapped into the
annular spacing between tubes 203 and 204, serving as a water
inlet; whereas the connecting pipe to bushing 217 is tapped into
the annular spacing between the tubes 202 and 203, serving as a
water outlet.
An additional brass bushing 219, which is 2 1/2 inches in outer
diameter and 1 3/4 inches in inner diameter, serves as a connecting
inlet for fuel gas into the annular space between the tubes 104 and
216. The inner tube 206 and the concentrically enclosing tube 216
are extended through a conventional connecting element 226 to arm
227 of a tee fitting 220 having a lateral inlet 223 2 1/2 inches in
outer diameter, 2 inches in inner diameter, and protruding about
three-quarters inch from the outer pipe periphery. The latter
serves as an oxygen inlet to the annular spacing between the
central pipe 206 and the concentric pipe 216. The central pipe 206
passes through arm 221 of the tee connection 220 and terminates in
a coupling 222 about three-quarters inch in inner diameter and 1
1/2 inches in outer diameter for feeding fuel oil into the center
pipe 206.
Burners of the form shown in FIGS. 3A, 3B, modified according to
FIGS. 6A, 6B, designated burners 100, were employed for performing
the series of oxy-gas tuyere burner tests about to be described,
instead of the self-atomizing tip-mix burners described with
reference to FIGS. 3A, 3B which were employed in the oxy-oil tests
previously described. However, it will be understood that the
burners 200, just described, which are designed to be alternatively
employed as oxy-gas or oxy-oil burners, or to burn a combination of
oil and gas fuels, could alternatively be employed for this
purpose, assuming the cupola tuyeres are properly dimensioned to
accommodate the larger cross-sectional burners.
The oxygen used in the operation about to be described is of a
commercial grade of purity meeting the specifications set forth in
the previous description with reference to the operation of the
oxy-oil burners of FIGS. 3A, 3B.
Gas to be used as fuel in the burners 100 is preferably natural
gas, of which the following Table II shows an analysis of the
principal components.
TABLE II
Natural Gas
(Percentages by Volume) Source Pittsburgh Kansas City Los Angeles
_________________________________________________________________________
_ Methane, CH.sub.4 83.4 84.1 77.5 Ethane, C.sub.2 H.sub.6 15.8 6.7
16.0 Carbon Dioxide, CO.sub.2 -- 0.80 6.5 Nitrogen, N.sub.2 .80 8.4
-- Heating Value, BTU/Ft..sup.3 1124 974 1073
_________________________________________________________________________
_ Furthermore, any of the following hydrocarbon oils or gases may
be employed as fuels for the rocket burners of the present
invention, such as, for example, methane CH.sub.4, ethane C.sub.2
H.sub.6, propylene C.sub.3 H.sub.6, propane C.sub.3 H.sub.8, or
fuel oils Grades No. 1 to No. 6 as enumerated on page 66 of Babcock
& Wilcox, Useful Tables, 8th Edition, 1963, either singly or in
various mixtures.
The general operation of the 90-inch cupola of FIG. 1 is
substantially as previously described. During the lighting of the
burners, the air blast, which has been heated to a temperature of
1,200.degree. F. and is circulating in the wind box 11, as
indicated in FIG. 1, is spilled out through a vent pipe (not shown)
so that it does not pass through tuyeres 14.
To start up operation of the system, a button on a control panel
183 is depressed to open the solenoid controlled valve 182. This
permits gas from connecting line 175 to flow into the line 181 and
from there into the circular main 147, through the tee junction 148
and through tee junctions 144 and branches 150 into the individual
branches 133. From each of the branches 133 a stream of gas flows
into the connecting gas inlet 133a of each of the burners 100.
During the initial stages, the gas flow rate into the individual
burners is 800 standard cubic feet per hour, at a pressure of 10
pounds per square inch absolute, and ambient temperature.
As in the case of the self-atomizing tip mix burners, assuming the
furnace to be operating, the burners would be immediately ignited
as soon as gas flows into them. If the furnace were cold, auxiliary
lighting means would be employed, of a type previously described.
As soon as the flame is lighted in the burners 100, the oxygen is
turned on by depressing a button on panel 183 and manually lifting
the manual reset solenoid operated valve 169. A stream of oxygen
then flows into main 162, and into burners 100 through a conduit
system similar to that described with reference to FIG. 5 of the
drawings, in the oxy-oil system.
In the present example, oxygen flow control and measurement was
made at each of the burner branch lines 134, so that oxygen flow
into the individual couplings 134a of the burners 100 was
maintained at 70 to 150 standard cubic feet per minute, at ambient
temperature, and a pressure of 40 to 65 pounds per square inch
absolute.
As son as the flames were properly lighted and seated in burners
100, the vent of the wind box 11 was closed, and the blast again
directed through tuyeres 14 at a rate of 4,000 to 8,000 standard
cubic feet per minute.
As in the case of the oxy-oil system, pressure switches 193 and
194, which are normally operated, are designed to be actuated in
the event of gas pressure loss or wind spillage to shut off the
supply of gas and oxygen by closing manual reset valves 182 and
169.
During the initial tests to be described, the burners 100 were
water cooled, using individual water jackets 28 in the manner
previously described; and, only four of the seven burners 100 were
used, these being symmetrically spaced in alternate tuyeres 14
around the cupola. The burners 100 were designed to be long enough
to allow them to be inserted to within 2 inches of the coke bed in
the cupola, the position of the burners 100 being slidably
adjustable in the water jacket 28, the concentric and lateral
position of each of the burners in tuyeres 14, being controlled by
a support spider 29.
The original criterion used in testing the effectiveness of tuyere
burners 100 was their effect in increasing the preheat of the
blast. While this criterion was used to determine firing rates of
tuyere burners, it was realized that it would not be entirely
accurate, inasmuch as the tuyere burners introduce combustion
products into the furnace which produce either an oxidizing or
reducing effect on the product, depending on the oxy-fuel ratio
selected. Moreover, it was also realized that the combustion of
natural gas in the burners released large quantities of water vapor
into the furnace which extracts considerable heat when striking the
hot coke.
As a starting point, the gas fuel in the burners was regulated to
provide 200.degree. F. increments of air preheat, assuming 100
percent efficiency in combustion and heat transfer from the burners
to the air blast in the tuyeres. Tuyere burner firing rates during
the tests described were substantially matched to the wind rates,
firing rates of the burners being left unchanged for minor
variations in the wind rates. Air blast temperatures were measured
with a thermocouple (not shown) inserted into the tuyere through a
sight port in the cover 25 (see FIG. 2), with the burner fired in
maximum withdrawn position, as previously specified, to determine
the efficiency of the heat transfer.
FIG. 9 of the drawings is a plot showing the relationship between
observed wind heating by an oxy-gas burner 100 in one of tuyeres 14
and calculated values, with the total wind rate directed into all
of the eight tuyeres at an average of 5,000 standard cubic feet per
minute. The abscissa shows wind temperature measured in degrees
Fahrenheit times 100; while the ordinate shows natural gas flow per
tuyere measured in standard cubic feet per hour times 100. The
calculated values indicated by points X are derived by assuming 100
percent efficiency for the combustion of fuel and heat transfer, as
described in the foregoing paragraph.
It will be seen from the Figure that efficiencies of 33.4 to 49.6
percent in heating up blast air in the tuyeres were obtained with a
2:1 oxy-gas ratio, with the higher firing rates being more
efficient. It is also apparent from the Figure that the 1.5:1
oxy-gas volume ratio was less efficient than the 2:1 volume ratio
at the higher firing rates. During these tests, the cooling water
flow through the burner jackets 28 varied from 10 to 15 gallons per
minute with a temperature pick-up of approximately 25.degree.
F.
The independent variables under study during the tests described
were charge composition, wind rate, burner firing rate, and
gas-oxygen ratio. Dependent variables included melting rate, iron
temperature, iron composition, iron chill depth, flue gas
temperature, and burner cooling water losses. Melting rate was
measured on the basis of the number of 5,000-pound metal charges
consumed by the cupola over an hour period. Iron temperature was
measured by optical pyrometer readings taken every half hour.
Samples for chemical analysis of carbon and silicon were taken from
the forehearth every half hour. Slag was judged mainly by the
appearance of water cooled granules. Flue gas samples were analyzed
for carbon dioxide (CO.sub.2), carbon monoxide (CO), and oxygen
(O.sub.2), using a standard orsat apparatus flue-gas temperatures
were measured with a thermocouple placed in the stack 2 at the
level of the charging door 18 (see FIG. 1).
During the first of the oxy-gas cupola trials, four symmetrically
disposed burners 100 were operated firing natural gas at rates up
to 9,300 standard cubic feet per hour, using oxy-gas ratios ranging
from 1.2:1 to 2.0:1. The burners 200 were operated with their
muzzles a foot from the inner end of the tuyeres 14. Burners were
lighted with the wind off, in the manner previously described, to
insure seating of the flame.
Observation of the slag, chill depth, and metal chemistry indicated
that improper operation of the burners, without adjustment of
certain parameters in accordance with the present invention in the
manner set forth hereinafter, could influence the furnace operation
adversely by lowering metal temperatures, lowering the silicon and
carbon content of the product, increasing the chill, and obtaining
slag samples which indicated improper fluxing. It was discovered in
accordance with the present invention that optimum results were
obtained using an oxygen-to-fuel gas ratio of at least about 1.5:1,
which is 75 percent of the stoichiometric oxygen required for
complete combustion of the fuel gas. The colling water flow through
these burners, which varied from 10 to 15 gallons per minute,
showed a temperature pick-up of approximately 25.degree.F.
In accordance with another alternative method of operation of the
present invention, seven oxy-gas burners 100, instead of four as
previously described, were disposed in seven of the eight tuyeres
in the cupola of FIG. 1, the tuyeres nearest the spout 19 not being
used, as in the case of the oxy-oil burners, because of the high
temperature in that location. The oxy-gas ratio was maintained at
1.5 to 1, but the burners 100 were operated in withdrawn position
(23 inches from the coke bed).
Total firing rates of 19,120 standard cubic feet per hour of gas
fuel burned were used. The volume of wind flow in the wind box 11
was reduced to 5,000 standard cubic feet per minute, to compensate
for the increased production resulting from the burner.
The outstanding effect of the oxy-gas burners 100, as used in the
manner of the present invention, was an increase in melting rate.
Although this was not as great as that achieved with the oxy-oil
self-atomizing tip mix burners 10 (described with reference to
FIGS. 3A, 3B), it was nevertheless very significant.
The increase in the melting rate achieved will be better understood
with reference to FIGS. 10, 11 and 12. These figures respectively
show the melting rate in the cupola of FIG. 1, as indicated by the
number of 5,000 pound charges melted per hour plotted against the
volume flow rate of wind into the collective tuyeres, in standard
cubic feet per minute multiplied by 1,000; in each of three cases:
FIG. 10 using no burners, FIG. 11 using oxy-gas burners at high
firing rates, and FIG. 12 using oxy-oil burners at high firing
rates. In each of the figures the points represent full hour
periods without spills or wind changes; and the method of average
points was used to construct the line.
In FIG. 11 relating to the use of oxy-gas burners in the cupola,
the maximum flow was 19,170 standard cubic feet per hour of natural
gas and 28,410 standard cubic feet per hour of oxygen. These flows
are equally divided among seven tuyere gas burners 100,
substantially of the form indicated in FIGS. 6A, 6B, 6C. It was
estimated that melting rate increases of approximately 25 percent
were obtained using oxy-gas burners during periods of high burner
firing rates.
In the plot of FIG. 12, which relates to the use of oxy-oil burners
10 of the type described with reference to FIGS. 3A, 3B in the
tuyeres, the superiority of oil fuel over gas is immediately
apparent. During the first trial the burners were fired using 189
gallons per hour of oil and 39,550 standard cubic feet per hour of
oxygen. (This represents 75 percent of the stoichiometric
requirement of oxygen for complete combustion of the fuel oil.) The
melting rate increased so drastically that the wind flow rate of
8,000 to 9,000 standard cubic feet per minute flowing from wind box
11 into tuyeres 14, which is normally required to melt seven
charges per hour with no burners, as shown in FIG. 10, had to be
reduced to between 4,000 and 5,000 standard feet per minute to melt
at the same rate, using oxy-oil burners 10 of the type described
with reference to FIGS. 3A, 3B. This showed an increase of 90
percent or greater of the melting rate. Moreover, during periods of
low metal requirements, it was found that the burners were
effective in minimizing the adverse effects of wind spills, such as
low metal temperatures and low carbon and silicon contents. After a
temporary halt and wind spill, the furnace temperatures were
rapidly returned to levels above 2.900.degree. F., using oxy-oil
burners 10; and the average metal temperature during burner use was
higher than that obtained without burners, even though the
frequency and duration of the periods of wind spill were much
greater.
In two additional tests, which were run at the beginning of a
period of maximum casting production with a low level in the cupola
or hearth, the cupola 1 was converted to a double charging practice
which consisted of adding two splits of coke, limerock, spar and
silicon to one bucket, followed by two buckets each with a 5,000
pound metallic charge. This procedure increased the capacity of the
charging system and increased the packing in the shaft to reduce
stack gas velocity.
The first of these tests employed a wind rate of 8,000 standard
cubic feet per minute into the collective tuyeres 14. Oil flow was
maintained at 210 gallons per hour, and oxygen was varied between
29,750 and 36,750 (51 percent and 62.5 percent, respectively, of
the stoichiometric requirement for complete combustion). Whereas
without burners, this wind rate would normally melt about 7 1/2
charges per hour, during a measured hour in the instant test the
furnace melted seven double charges, equivalent to 14 single
charges.
In the second of these tests, the wind rate was decreased from
8,000 to 7,000 standard cubic feet per minute. Oil flow was 210
gallons per hour and oxygen was introduced at the rate of 40,250
standard cubic feet per hour (68.4 percent of the stoichiometric
requirement). The number of charges melted over a measured hour of
burner use was six double charges, equivalent to 12 single charges.
From these tests, it was evident that the productivity increase, at
a wind rate of 8,000 standard cubic feet per minute into the
collective tuyeres, was approximately 90 percent. Points
representing each of these tests are indicated in FIG. 12 of the
drawings. It is apparent from the figure that using the oxy-fuel
burners in the manner described herein, with oxygen of about 75
percent of the requirement for complete combustion, the performance
of the cupola greatly exceeds that of the condition in which the
wind blast is used without the auxiliary burners.
Another advantage shown by the tests just described was a decrease
of about 10 percent in the coke required; but, during these tests
it did not appear that a very large reduction in coke would be
advisable since a pick-up in the carbon content had been attempted.
Moreover, charge changes had also been made during part of the
period of the oxy-oil burner tests, which tended to restrict the
amount of coke reduction possible.
Another advantage of the oxy-fuel burner techniques of the present
invention is indicated in FIGS. 13A and 13B of the drawings, which
plot frequencies of distribution against spout temperatures, for
normal operation of the cupola without oxy-fuel burners, and for a
similar period, using oxy-oil burners 10. The burners 10, operated
in the manner previously described, used on an average 189 gallons
per hour of oil and 39,550 standard cubic feet per hour of oxygen
(75 percent of the stoichiometric requirement). In the burner
operation, wind rates were reduced from between 8,000 and 9,000
standard cubic feet per minute, as in the normal operation, to
between 4,000 and 5,000 standard cubic feet per minute. Spout
samples indicated the presence of saturated iron in the product of
the oxy-oil burner operation. Furthermore, silicon production from
reduction of core sand in the charge was increased to above 3.0
percent in the product.
Further tests were made to determine whether the burners could be
operated effectively with less than 100 percent oxygen. When the
burner was started in the tuyere using only air, together with a
cupola wind rate of 5,000 standard cubic feet per minute, the
tuyere darkened and no flame was visible. When oxygen was then used
to enrich the air until some burning became visible, it was found
that the combination of 3,550 standard cubic feet per hour of air
and 3,550 standard cubic feet per hour of oxygen (about 60 percent
of the oxygen total required for stoichiometric combustion) would
support combustion. It is apparent from these findings that it is
more economical and generally satisfactory to operate the burner
with 100 percent commercially pure oxygen at lower flow rates, than
to introduce primary air into the combustion.
Another test was run in which straight oil injection without oxygen
was also tried for a one hour period on all burners, using 210
gallons of oil per hour. During this test, the tuyeres darkened at
once and the metal temperature dropped from 2,930.degree. to
2,770.degree. F. Carbon content, in the product dropped from 3.45
percent to 3.33 percent; and silicon content in the product dropped
from 2.10 percent to 1.90 percent. This test tends to substantiate
the conclusion that straight oxygen, or a higher blast temperature,
is needed to offset the chilling effect to the furnace of straight
fuel injection and that increased amounts of fuel injection require
combustion through an oxy-fuel burner of the aforementioned
design.
A further test using oxy-oil burners 10 in accordance with the
present invention, as applied to molten iron making in a cupola of
the general form indicated in FIG. 1, may be summarized as follows,
with reference to Table III. The furnace, which has a water jacket
(not shown), is fitted with water cooled copper tuyeres and is
operated with a 1,200.degree. F. wind blast. The burners 10, which
were located in seven of the eight tuyeres, were self-atomizing tip
mixers of the general form indicated in FIGS. 3A, 3B of the
drawings. The fuel used was No. 2 fuel oil which was burned with
commercially pure oxygen, according to the standards previously set
forth.
TABLE III Normal Oxy-Oil Tuyere Operation Burners
_________________________________________________________________________
_ Melting Rate (tons per hour) 18.75 30.0 Wind (Standard cubic feet
per minute) 8,000 8,000 Coke (pounds per ton) 240 216 Oil Flow
(gallons per hour) -- 210 Oxygen Flow (Standard cubic feet per
hour) -- 40,250 Oxygen (Stoichiometric percent of requirement for
complete combustion) -- 66.0
_________________________________________________________________________
_
At an individual burner head, typical parameters are as follows:
with the oxygen flow rate indicated in Table III, the pressure was
42 pounds per square inch absolute, temperature was 80.degree. F.,
with the oil flow as indicated, the pressure was 25 pounds per
square inch absolute, temperature was 80.degree. F. The range of
burner flame temperatures was 4,000.degree. to 5,000.degree. F.
Table IV summarized a series of tests in an automotive factory,
conducted on a water cooled cupola substantially of the form
indicated in FIG. 1, in which normal operation is compared with
operation in accordance with the present invention using oxy-oil
burners 10, substantially as shown in FIGS. 3A, 3B, in seven of the
seven symmetrically spaced water cooled tuyeres of the cupola. As
in the prior tests the oil was No. 2 fuel oil (according to the
standard of the American Society of Testing Materials); and oxygen
was commercially pure grade.
TABLE IV Normal Oxy-Oil Burner Operation Use
_________________________________________________________________________
_ Melting Rate (tons per hour) 28-30 44 Wind Rate (Standard cubic
feet per minute) 14,500 11,800 Coke (pounds per ton) 300 233
Comparison of steel to iron scrap employed, indicated by ratio of
carbon to oxygen in the charge 45 52 Oil Flow (gallons per hour) --
170 Oxygen Flow (Standard cubic feet per hour) -- 59,000 Oxygen
(Stoichiometric percent of oxygen required for complete combustion)
-- 120
_________________________________________________________________________
_
As indicated in the previous example, typical parameters at the
burner head at the flow rates indicated are: oxygen absolute
pressure was 70 pounds per square inch, at 80.degree. F; oil
absolute pressure was 40 pounds per square inch at 80.degree. F.
Flame temperatures were within the range 4,000.degree. to
5,000.degree. F.
In general, the type of furnace operation dealt with in the
preceding discussion, involving the melting of pig iron and steel
scrap to form molten iron in a cupola, contemplates the ore or less
complete combustion of the hydrocarbon fuel to form carbon dioxide,
and water, according to the equation:
CH.sub.4 + 20.sub.2 = CO.sub.2 + 2H.sub.2 O. (1)
In this situation, optimum results are achieved by the use of an
amount of oxygen as a combustant which is between 60 and 150
percent, or in preferred operation between 60 and 100 percent, by
weight, of the stoichiometric quantity of oxygen required for
complete combustion in the burner.
However, in other types of furnace operations the incomplete
combustion or pyrolysis of the hydrocarbon fuel may be desired in a
hypothetical reaction approximating the following:
CH.sub.4 + 1/2 O.sub.2 = 2H.sub.2 + CO. (2) This reaction
contemplates the use of about 25 percent by weight of the
stoichiometric quantity of oxygen required for complete combustion
in the burner.
The following are analyses of gas samples taken at the combustion
chambers of various rocket burners, operating to produce pyrolysis
of hydrocarbon fuels consumed.
Of significance in these tests was the capability of the rocket
burner to effect almost complete transformation of methane CH.sub.4
to carbon monoxide CO and hydrogen H.sub.2, as evidenced in test
No. 3 of Series No. 1.
The lower yields in Series No. 2 are explainable by the lower
combustion chamber length-to-area ratio and possibly by higher
rates of flow of oxygen and fuel.
TABLE V H.sub.2 CO CO.sub.2 CH.sub.4 O.sub.2 N.sub.2 A Total
_________________________________________________________________________
_ Series No. 1 1" dia. .times. 8"" Comb. Chamber 1. 1500 scfh gas
750 scfh O.sub.2 = (25% stoichio- metric) 39.2 28.0 5.7 17.4 90.3
2. 1500 scfh gas 900 scfh O.sub.2 = (30% stoichio- metric) 43.0
33.6 7.4 8.0 92.0 3. 1500 scfh gas 1050 scfh O.sub.2 = (35%
stoichio- metric) 41.4 39.9 8.0 2.1 91.4 Series No. 2 11/2 dia.
.times. 8" Comb. Chamber 1. 7480 scfh gas 6150 scfh O.sub.2 = (41%
stoichio- metric) 25.7 17.13 4.11 48.5 0.11 .65 .05 96.25 21/2"
dia. .times. 12" Comb. Chamber 2. 7480 scfh gas 6150 scfh O.sub.2 =
41% stoichio- metric) 29.6 18.59 3.93 44.3 0.13 .51 .05 97.11
_________________________________________________________________________
_ In Series No. 2, O.sub.2 and H.sub.2 determinations were by mass
spectrometer, balance by chromatograph.
A modification of the invention will now be described in which the
oxy-fuel tuyere burners are incorporated into an iron smelting
blast furnace in accordance with the teachings of the present
invention.
In the iron ore smelting blast furnace shown in FIGS. 14 and 15,
the tuyere burners 200 are disposed in tuyeres 14 substantially in
the manner shown with reference to FIG. 2 of the drawings. In
preferred form they may utilize natural gas fuel in the water
cooled rocket burner 200 described in detail with reference to
FIGS. 8A, 8B, 8C of the drawings and serviced by means of a piping
system and an oxy-gas supply system substantially of the form shown
and described with reference to FIG. 7. It will be understood,
however, that both gas and oil can be simultaneously employed as
fuels in a rocket burner in accordance with the design of FIGS. 8A,
8B, 8C, in which case the burner would be connected to an
appropriate supply system which would combine the oil and gas
supply systems of FIGS. 4 and 7. As other alternatives, the oxy-oil
self-atomizing tip mix burner 10 of FIGS. 3A, 3B can be employed in
the tuyeres 14 of the iron blast furnace of FIGS. 14 and 15, or the
oxy-gas rocket insert 100 of FIGS. 6A, 6B, using the water jacket
of FIGS. 3A, 3B. In each case an appropriate supply system
according to FIGS. 4 or 7 would be employed.
Referring now to FIG. 14 of the drawings, there is shown an iron
blast furnace of a conventional type suitable for use of oxy-fuel
burners in accordance with the techniques of the present
invention.
This comprises a foundation 302, which is 60 feet in diameter and
11 feet high, of concrete or the like, on which is supported a base
or bottom portion 303, which comprises layers of firebrick built up
to a level of 2 feet above the top of the foundation, and having an
inner diameter of 24 feet. Surrounding the base or bottom portion
is a substantially cylindrical wall 304 of firebrick, 36 inches
thick, having an outer diameter of 30 feet, this portion rising to
a height of 10 feet above the base portion and embracing what is
known as the hearth. Notch 306, which opens off from the lower part
of the hearth portion, is adapted to drain off the molten iron,
whereas notch 307, at a slightly higher level, is designed to drain
off the slag floating on top of the molten iron.
In the top of the hearth portion 305, symmetrically arranged in a
horizontal plane about 9 feet above the base of the hearth 305, are
a plurality of tuyere openings 314. In the present embodiment these
number 20, and comprise, in each case, a frustro-conical opening in
the brick wall 304 having a diameter 16 inches at the outer end and
10 inches at the inner end, at the inner end of which is mounted a
metal tuyere 314a which is 10 inches in outer diameter, water
cooled, and has 1/2 inch thick walls. Each of the blow-pipes 324
mounted inside of the tuyeres is 60 inches long and terminates a
distance of 8 inches from the inner face of the brickwork tuyere
opening 314. The blow pipes 324, which are formed of refractory
lined steel, are downwardly inclined, each making an angle of about
10.degree. with the horizontal. These house oxy-fuel burners 200
which are located concentrically in the blow-pipes 324, in the
manner described generally with reference to the cupola embodiment
shown in FIGS. 1 and 2 hereinbefore, and which will be described in
greater detail hereinafter.
Referring to FIG. 15, which is an enlarged sectional showing of the
tuyere and wind pipe area in the furnace of FIG. 14, the tuyere
blow-pipes 324 are connected through a downcomer pipe 324a of steel
sections which increases in inner diameter from about 10 inches at
the inner connection to the tuyere blow-pipe 324, to 16 inches at
the outer connection, where they each feed into a blast main or
bustle pipe 311. The latter, which comprises a steel shell lined
with firebrick to a thickness of about 18 inches, has an inner
diameter of 4 feet and is supported in a frame so that it surrounds
concentrically what is known as the "bosh" 309 of the blast
furnace. The brick walls 308 of the bosh 309 taper outwardly from
an inner diameter of 24 feet in a plane just above the plane of
tuyeres 314, to an inner diameter of 28 feet in the plane of the
main or bustle pipe 311, a vertical height of 10 feet.
The bustle pipe 311 is connected through a system of conduits 312
including a brick or iron stove 313a for heating the blast by means
of exhaust gases from the furnace, or in any other conventional
manner. The blast originates in a conventional type reciprocating
or turbine blower 313 designed to generate an air blast of the
desired volume, velocity, and pressure.
Also surrounding the upper portion of bosh 309 is a concentric
water pipe system 316 which cools the bosh and hearth areas. A
plurality of vertical pipes 316a, which are connected to the
concentric pipe system 316, deliver cooling water streams down past
the bosh 309 and heater portions 305, which pass out onto the
foundation.
At the top of bosh 309 is an annular iron frame 317, called the
mantle, built into the brickwork which supports the stack 315 about
56 feet high and tapering from a maximum inner diameter of 28 feet
at the junction with the bosh 309, to an inner diameter of 19 feet
at the throat 317. As in the lower portion, the stack 315 comprises
a steel shell lined with firebrick to a thickness of about 27
inches. The throat 320 has an inner diameter of 19 feet and is
closed with a bell or cone 318 which serves to prevent the escape
of gases from the stack. Above the bell 318 is the charging hopper
321, in which charge is placed for the purpose of dumping it into
the furnace. In general the charge is conveyed up to the charging
hopper by some type of a skip car, running on a track and operated
by a system of pulleys, all of which is conventional, and not
shown.
The steel pipes 322 which are 6 feet in inner diameter, serve as
gas uptakes to carry off the exhaust gases which may be cleansed
and passed through the stove 313a (in an arrangement not shown) to
heat up the ingoing air blast in conduit 312.
In accordance with the present invention, oxy-gas tuyere burners
200 of the form shown in FIGS. 8A, 8B, 8C, are employed in an iron
ore smelting blast furnace, substantially of the type shown in
FIGS. 14 and 15.
The tuyere burners 200 are mounted in all of the tuyeres 314a in
the blast furnace of FIG. 14. In the present example, these number
20, and each water cooled with a stream of water flowing in through
the water jacket at a minimum pressure of 65 pounds per square inch
absolute and a flow rate of 25 gallons per minute.
The burners 200 (FIGS. 8A, 8B, 8C), after being lighted in the
manner described with reference to the cupola operation of FIG. 1,
are operated in the example under description with commercially
pure oxygen flowing into each of burner body heads 205 through
coupling 223 at a flow rate of 5,000 standard cubic feet per
minute, an absolute pressure of 30 pounds per square inch, and
ambient temperature. Simultaneously, natural gas flows into the
coupling 219 at a flow rate of 3,500 standard cubic feet per
minute, an absolute pressure of 20 pounds per square inch, and
ambient temperature.
The following table details the operation in the preferred
mode:
TABLE VII Control Period Burner Period
_________________________________________________________________________
_ Wind (to all burners, standard cubic feet per min.) 72000 68,000
Smelting Rate (tons of hot metal per day) 1200 1,800 Coke Rate
(tons for above number of tons of hot metal) 1150 950 Burner Oxygen
(to all burners, standard cubic feet per hour) 0 100,000 Burner Gas
(to all burners, standard cubic feet per hour) 0 70,000 Burner Oil
if used (to all burners gallons per hour) 0 450
_________________________________________________________________________
_
In the iron-smelting blast furnace, typical burner flame
temperatures lie within the range 3,000.degree. to 5,000.degree.
F.; and, rocket burner flame velocities lie within the range 3,000
to 3,500 feet per second.
It will be apparent that the principles of the present invention
are applicable to other types of furnaces than those described in
the foregoing pages of the specification, including furnaces for
smelting ores containing copper, lead, and antimony.
A typical rectangular lead blast furnace applicable to modification
in accordance with the present invention is shown in FIG. 16 of the
drawings, in front elevation.
The lead blast furnace of FIG. 16 comprises a foundation of
firebrick, or the like, in which is formed a well or crucible 401,
which narrows from a width of about 4 1/2 feet at its surface to 4
feet at the bottom, is 6 feet long, 20 to 36 inches deep, and
serves to channel the molten lead derived from the smelting
process. An outlet 403b serves to tap off molten lead from crucible
401; whereas the slag floating on top is drawn off through the
outlet 407.
Rising above the crucible 401 is the hearth portion 405 of the
furnace, in the form of a rectangular iron box, having an inner
dimension of say 5 1/2 feed wide by 15 feet long. The vertical cast
iron walls, three-eights inch thick, rise to a height of about 5
feet above the foundation 402. At the upper end of hearth 405, the
cast iron walls 408 continue to extend upwardly to form the bosh
409, which has an inner dimension of roughly the same as the hearth
portion, or slightly larger. The walls of the bosh 409 rise,
substantially vertically, for about 3 1/2 feet. A framework of
supporting bars support the upper combustion section 416 which
broadens out from a width of about 5 1/2 and length of 15 feet, at
its lower end, to a slightly greater width in a rise of about 7
feet. This entire lower section of the furnace is water jacketed in
a casing of cast iron one-half inch thick, forming the inner walls
of the furnace. The upper combustion section 416 terminates in a
brick stack 415 which rises to a substantial height above the
foundation and is supported by a framework including columns
420.
The furnace may be equipped with two separate sets of tuyere pipes
414a, 414b, each 3 inches in inner diameter, which pass
horizontally, or with slight declination, through the furnace
walls. The lower set of tuyeres 414b is located in the hearth area,
about one foot above the crucible. The tuyeres in this set number
16, spaced approximately 12 inches apart in the east and west walls
of the hearth area. There may also be tuyeres on the north and
south walls (not shown). There may also be a second set of tuyeres,
414a, similarly spaced to the lower set, entering the furnace in
the bosh area, several feet above the lower set. These latter
tuyeres may also number 16 each in the east and west walls; and
there may also be tuyeres at this level in the north and south
walls (not shown).
The tuyeres 414a and 414b, at both levels, each have connecting
downcomer pipes 424a and 424b, which are respectively connected to
an upper bustle pipe 411a, and a lower bustle pipe 411b surrounding
the furnace. Each of the bustle pipes 411a and 411b is connected
through respective conduits to an air compressor (not shown) as
described with reference to the previous figures.
In accordance with the present invention, burners of any of the
types previously described may be placed in the furnace at the
level of tuyeres 414b with highly beneficial results to the
production of lead, preferably, within alternate tuyeres 414b. In
certain modifications, the burners may alternatively be interposed
directly into the walls of the furnace, or in the front or back
tuyeres, or in the tuyeres 414a, also with beneficial results to
the process.
In the preferred embodiment which will be described, the
orientation of the burners in the furnace is substantially as
indicated schematically in FIG. 17, which is a plan view of the
lead blast furnace of FIG. 16, including burners in alternate
tuyeres 414b, in the east and west walls. As indicated in FIG. 17,
the separation between adjacent burners of each side of the furnace
is approximately 2 feet. In the preferred arrangement, the burners
of the two sides of the furnace are placed in staggered relation,
so that in each case the burner on one side faces an empty tuyere
on the side across the furnace.
FIG. 18 shows a section of the furnace wall of FIG. 16, indicating
the location of the burners 428 in the tuyeres 414b. The inner and
outer walls of the lead blast furnace of FIG. 16 are spaced apart 6
inches. The tuyere pipes 414b, which penetrate through the
thickness of the double wall are 3 1/2 inches in outer diameter,
one-quarter of an inch thick, and 16 1/2 inches long, including the
tuyere pipe extension 424. The may be tilted slightly downward at
an angle of, say, 5.degree.. If the tuyere pipe is horizontal, the
tuyere burner is positioned at a slight declination (about
5.degree.) to the longitudinal axis of the tuyere. On the other
hand, if the tuyere pipe has a downward inclination, the burner is
placed concentric with the longitudinal axis. The center of the
tuyere pipe may protrude into the interior of the furnace a slight
distance. At its outer end, the tuyere pipe 414b terminates in a
flange, to which is attached the matching flange of a tuyere
extension pipe 424 of 3 inches inner diameter, which extends
outwardly a distance of 12 inches. Connected to tuyere extension
pipe 424 is the downcomer pipe 424b leading to the air main 411b.
The outer end of the tuyere extension pipe 424 is closed by a cover
plate 425, in substantially the manner of extension pipe 24 of FIG.
2, described with reference to the iron melting cupola.
Fitted concentrically into the 3 inch inner diameter tuyere pipe
414b and extension pipe 424, is a rocket burner 428 of the form
indicated in FIGS. 19A, 19B of the drawings. The inner end of the
burner 428 is preferably recessed a distance of about 6 inches from
the inner end of tuyere pipe 414b, to the outer limit of the water
jacketing in the tuyere.
Because of the small size of the tuyeres 414b of the lead blast
furnace, the burners are much smaller in diameter than those
previously described. The water jacket in the present burner
embodiment comprises two concentric copper pipes, the outer pipe
430 being 1 5/8 inches in outer diameter, 0.072 inch in wall
thickness, and 20 3/8 inches long; and, the inner pipe 438 being 1
1/8 inches in outer diameter, 0.065 inch in wall thickness, and 24
3/4 inches long. The foregoing concentric pipes 430 and 438 are
flush at their inner ends, which are sealed together internally
with a conventional annular plug 438 which fits between the inner
periphery of pipe 430 and the outer periphery of pipe 438, and
extends one-quarter inch inward in an axial direction.
Pipes 430 and 438 are maintained in concentric array by means of
two pairs of copper rods 447a, 447b, each three-sixteenths of an
inch in diameter, and disposed lengthwise in the annular space
between the two pipes at 90.degree. separations in the
cross-sectional plane and brazed to the outer surface of pipe 438.
The longer pair 447b is 20 3/4 inches long, and terminates
five-eighths of an inch from the inner end of the water jacket. The
shorter pair is three-fourths of an inch long, and terminates 2
inches from the inner end of the water jacket.
Concentric pipes 430 and 438 are fitted at their outer ends into a
cylindrical burner breech assembly 432, which is 2 1/2 inches in
outer diameter and 4 inches long. Burner breech assembly 432 has
water inlet and outlet connections 435 and 436, respectively, which
tap into the channel between copper tubes 430 and 438. Water inlet
and outlet connections 435 and 436 are connected to a conventional
water manifold (not shown).
Inside of the burner barrel, 6 inches from inner end 431, is
centered a cylindrical gas tube adapter 440. Concentrically fitted
into one end of adapter 440 is an axial gas conduit 442 of
stainless steel, one-half inch in outer diameter, 0.35 inch in wall
thickness, and 19 inches long, which is axially disposed in the
burner barrel and fits at its outer end into a central opening of
the burner breech assembly 432, where it communicates with the
connector 450 leading to a gas supply system of the type shown in
FIG. 7. Oxygen connection 434, which taps into the annular space
between inner tube 438 and central gas conduit 442, is connected to
an oxygen supply system, substantially of the type shown in FIG.
7.
The inner end of adaptor 440 accommodates a bundle of five
stainless steel tubes 437, symmetrically arranged with reference to
the longitudinal axis of the burner barrel, each three-sixteenths
inch in outer diameter, 0.02 inch in wall thickness, and 5 3/8
inches long. These fit into accommodating bores 441a in the
cylindrical stainless steel burner block element 441, which fits
into inner tube 438 with its inner end about 3 inches from the
inner end of the tube. Bores 441a containing the gas orifices lie
on a circle one-half inch in diameter.
In addition, burner block element 441 contains an inner circle
one-quarter inch in diameter of five oxygen orifices 441b, each
three-thirty-seconds inch in diameter, located between adjacent gas
orifices 441a; and, an outer circle thirteen-sixteenths of an inch
in diameter of 10 oxygen orifices 441c, also three-thirty-seconds
of an inch in diameter.
It will be appreciated that although in the specific example of the
lead blast furnace described, an oxy-gas rocket burner has been
employed, in accordance with the present invention, other types of
burners, such as self-atomizing tip mixers employing oil as a fuel,
with oxygen as a combustant, or rocket burners employing a
combination of gas and oil as a fuel, with oxygen as a combustant,
could be substituted for use in the lead blast furnace.
It is contemplated that the furnace of FIG. 16 will be operated for
lead smelting, using as charge a sinter of the general composition
indicated in Table VIII below.
TABLE VIII
Sinter (PerCent by Weight) Pb Cu Ao Sb S 34.5 2.1 1.0 1.4 1.7
an example of operation of the lead blast furnace of FIG. 16, in
accordance with the present invention, employing only five burners
interposed into the furnace walls, including front and back, at the
lower tuyere level, instead of 16 tuyere burners, disposed in the
manner disclosed in the preferred embodiment, was as follows:
TABLE IX Control Period Burner Period
_________________________________________________________________________
_ Wind (standard Cubic Feet per Minute) 6780 6780 Smelting Rate
(Sinter Tons per Day) 580 695 Coke Charges (Tons per Day) 56 42
Burner Oxygen (Per Burner) (Standard Cubic Feet per Hour) -- 6000
Burner Natural Gas (Per Burner) (Standard Cubic Feet per hour) --
5250
_________________________________________________________________________
_
The aforesaid data indicate an average increase in product of 20
percent (although at times as much as 100 percent increase is
obtained) with a concurrent coke saving of 25 percent, using a
burner arrangement which was less adequate than the preferred
arrangement disclosed with reference to FIGS. 16, 17, 18, and
19.
In operating the burner system described with reference to the
foregoing FIGS. 16, 17, 18, and 19, the following parameters are
suggested for preferred
operation:------------------------------------------------------
---------------------TABLE X Wind (Standard Cubic Feet per Minute)
7000 Burner Oxygen (Per Burner) (Standard Cubic Feet per Hour) 525
Velocity, in feet per second, of oxygen flow at the burner heads
(at absolute pressure of 35 pounds per square inch and temperature
of 70 degrees Fahrenheit) 600 Burner Natural Gas (Per Burner)
(Standard Cubic Feet per Hour) 750 Velocity, in feet per second, of
gas flow at the burner heads at absolute pressure of 30 pounds per
square inch and temperature of 70 degrees Fahrenheit 300 Average
Flame Velocity in Burners (Feet per Second at flame temperatures
within the range 3200 to 4000 degrees Fahrenheit. 2500-3 0 00
_________________________________________________________________________
_
A further example of the application of the oxy-fuel burner system
of the present invention is to the antimony blast furnace.
In general, the configuration of the antimony blast furnace is
substantially similar to that of the lead blast furnace shown in
FIG. 16, although there may be variations in scale and minor
variations in shape.
The antimony furnace in one operating example is 40 inches by 72
inches in the plane of the tuyeres, which plane is located 8 inches
above the base of the hearth. There are 16 tuyeres, each 2 1/2
inches in inner diameter, symmetrically disposed on each of the two
opposing 72-inch sides. The burner arrangement is substantially
similar to that shown in FIG. 17, with burners located in alternate
tuyeres on opposite 72-inch sides of the furnace, in staggered
arrangement, so that each burner faces an empty tuyere.
The burners employed in the antimony furnace may be rocket burners
substantially of the form and dimensions described with reference
to FIGS. 19A, 19B of the drawings, except that they are preferably
formed of stainless steel instead of copper, as disclosed with
reference of the lead blast furnace. Moreover, it may be necessary
to reduce the dimensions of the burners slightly in view of the
slightly smaller tuyeres. Furthermore, it will be understood that
as in the case of the lead blast furnace, self-atomizing tip-mixer
oxy-oil burners may be substituted for the rocket burner shown in
FIGS. 19A, 19B; and, rocket burners using a combination of gas and
oil for fuel may be substituted for those exclusively employing
gas, as shown.
The antimony smelting operation using oxy-fuel burners in
accordance with the present invention is practiced using charge of
the typical composition shown in Table XI.
TABLE
XI------------------------------------------------------------------
---------Charge Composition (PerCent by Weight) Rough Ore
comprising 30% Antimony; remainder: Silicon Dioxide (SiO.sub.2),
Aluminum Oxide (Al.sub.2 O.sub.3), and Calcium Oxide (CaO).
Briquettes comprising 35% Antimony; remainder: Silicon Dioxide
(SiO.sub.2), Aluminum Oxide (Al.sub.2 O.sub.3), and Calcium Oxide
(CaO). Slag and Dross comprising 40%-45% Antimony (Sb); remainder:
fused material comprising substantially the composition of the
rough ore and briquettes.
_________________________________________________________________________
_
TABLE XII
Requirements for processing a charge of antimony in accordance with
the present invention: Coke 600 Pounds Ore 1500 Pounds Briquettes
1500 Pounds Refinery Dross (includes return slag) 700 Pounds Iron
Ore 400 Pounds Limestone and Siliceous Ore 60 Pounds Air (Unheated)
2500 Standard Cubic Feet Per Minute (total for 16 tuyeres) *(Oxygen
2000 Standard Cubic Feet Per Hour *(Natural Gas 2000 Standard Cubic
Feet Per Hour *This provides 50% of the stoichiometric quantities
required for complete combustion of fuel.
Typical flame temperatures using rocket burners in the
above-described antimony smelting operation, are within the range
of 3,200.degree. to 4,000.degree. F.; and the flame velocities
within the range, 1,000 to 2,000 feet per second, at these
temperatures.
The principal products of the aforesaid combustion are hydrogen
(H.sub.2) and carbon monoxide (CO), at smelting temperatures of
3,500.degree. F. and metal and slag temperatures of 2,300.degree.
F.
Using oxy-fuel burners to carry out an antimony smelting operation
in accordance with the present invention, as aforesaid, a 20
percent coke reduction was realized with a 45 percent ore
through-put rate increase.
To recapitulate, a salient feature of each of the disclosed
embodiments of the present invention is that oxy-fuel burners,
which are introduced into a metal processing furnace of the shaft
type of the tuyere level, are operated with high velocity streams
of a hydrocarbon fuel and oxygen, the latter in pure rather than in
mixed form. In every case, combustion takes place in the tuyere or
burner barrel, in a single, homogeneous, high-velocity coherent
flame having an established combustion zone which originates at and
is seated in the burner. In the case of rocket burners, the flame
velocity is within the range 1,000 to 3,500 feet per second, and
flame temperature within the range 3,000.degree. to 5,000.degree.
F. Self-atomizing tip mixers have flame velocities ranging from 500
to 1,500 feet per second within this range of temperatures. The
successful tuyere burner design for the purposes of the present
invention is a post-mix type with a configuration of oxygen and
fuel ports such as to give flame stability within the tuyeres at
fuel and oxygen velocities ranging from 10 feet per second to
supersonic velocities. The high velocity flame provides turbulence
which completely mixes the combustion products before they enter
the furnace in a hot, homogeneous, high-velocity stream. In
accordance with actual practice, the oxygen used in the burners
varies from 27 to 300 percent by weight of the stoichiometric
requirement for complete combustion of the burner fuel. The heat
output of each of the burners in British Thermal Units varies from
600,000 to 10,000,000. When the burners are mounted in water cooled
tuyeres, the end of the burner is preferably withdrawn from the end
of the tuyere to the maximum distance of water cooling in the
tuyere. In installations in which the burner is not water cooled,
the tip is preferably withdrawn from 1 to 6 inches from the hot
inner face of the furnace lining.
In the iron melting cupola, for preferred operation oxy-oil burners
of the self-atomizing tip mix type are employed in the tuyeres.
Using this type of burner, flame velocities are preferably of from
500 to 1,500 feet per second at flame temperatures within the range
4,000.degree. to 5,000.degree. F. The cupola burners use
commercially pure oxygen in an amount within the range 60 to 150
percent by weight of the stoichiometric requirement for complete
combustion, and preferably within the range 60 to 100 percent. In
cupola operation, it is preferred that complete combustion take
place in the tuyeres or burners, giving rise to carbon dioxide and
water as the principal burner combustion products.
In the iron-ore smelting blast furnaces, either gas or oil, or a
combination of the two are preferably employed in a rocket type
burner, using oxygen as a combustant in an amount within the range
25 to 100 percent by weight of the stoichiometric requirement for
complete combustion, and preferably, within the range 25 to 50
percent. Flame velocities, employing the rocket burners are within
the range 1,500 to 3,500 feet per second, at flame temperatures
within the range 3,000.degree. to 5,000.degree. F. The principal
object of burner operation in the iron blast furnace is pyrolysis
of the fuel, creating hydrogen and carbon monoxide as burner
combustion products, thereby providing a reducing environment
within the furnace. One of the specific features of the present
invention is the adjustability of the burners to fit the burner
combustion products to the specific requirements of the furnace
operation.
In both the iron cupola and iron blast furnace, the tuyeres are
preferably of the downwardly inclined water cooled type. Moreover,
wind from the blast or bustle pipe surrounding the furnace may be
passed around the peripheries of those tuyeres in which burners are
mounted. Preferably, the flame velocity in each of the burners at
least exceeds the wind velocity in the surrounding tuyeres, in
order to provide a stable seated flame. However, alternatively, the
water cooled burners can be operated without wind.
In the lead and antimony furnaces, in which reduction of the ore is
the principal object, oxy-gas burners of the rocket type are
preferred, with commercially pure oxygen being supplied to the
burners preferably in an amount between 35 and 50 percent of the
stoichiometric requirement for complete combustion. The flame
temperatures in both lead and antimony furnace burners are within
the range 3,200.degree. to 4,000.degree. F. Flame velocities at
these temperatures in the lead furnace burners are within the range
2,500 to 3,000 feet per second; and in the antimony furnace
burners, flame velocities are the same using rocket burners and are
within the range 1,000 to 2,000 feet per second, using burners of
the self-atomizing tip-mixer type.
It will be understood, however, that either oxy-oil or oxy-gas
burners of the self-atomizing-tip-mix type, or of the rocket burner
types, such as disclosed herein, or such as disclosed, for example,
in T. L. Shepherd U.S. Pat. No. 3,092,166 issued June 4, 1963, or
in W. B. Moen et al. U.S. Pat. No. 3,135,626, issued June 2, 1964,
can be employed beneficially in any of the many types of shaft
melting or smelting furnaces, including those which may differ from
the furnaces specifically disclosed herein by way of illustration.
Moreover, the present invention is not limited to the specific
forms disclosed herein by way of illustration, but is defined in
the scope of the appended claims.
* * * * *