US3701517A

US3701517A - Oxy-fuel burners in furnace tuyeres

Info

Publication number: US3701517A
Application number: US62180A
Authority: US
Inventors: Bronis G Gray
Original assignee: Airco Inc
Current assignee: Airco Inc
Priority date: 1966-12-16
Filing date: 1970-08-07
Publication date: 1972-10-31
Anticipated expiration: 1989-10-31

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.

Description

United States Patent Gray [54] OXY-FUEL BURNERS IN FURNACE TUYERES [72] Inventor: Bronh G. Gray, Orange, NJ.

[73] Assignce: Airco, Inc., New York, NY.

[22] Filed: Aug. 7, 1970 [21] Appl. No; 62,180

Related US. Application Data [62] Division of Ser. No. 602,381, Dec. 16, 1966,

Pat. No. 3,547,624.

1 Oct.3l, 1972 3,089,766 5/1963 DeWald ..75/43 3,213,918 10/1965 Rudzki et al............239/l32.3 3,224,679 12/1965 Kear et a1. ..239/ 1 32.3 3,236,281 2/1966 Bain et a1 ..239/ 132.3 3,266,552 8/1966 Denis ..239l132.3 3,317,309 5/ 1967 Rinesch ..75/43 3,366,469 1/ 1968 Kedama et a1 ..266/29 Primary ExaminerGera1d A. Dost Attorney-Edmund W. Bopp and H. Hume Mathews 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.

8 Claim, 25 Drawing Figures OXVGEN -FUEL SUPPLV SYSTEM WATER PUMPING SYSTEM PATENTED B 2 3 701 517

sum

01 or 16 FIG.

OXYGEN -FUEL SUPPLY SYSTEM WATER PUMPING SYSTEM PKTENTED B I973 3,701,517

sum new 16 BURNER COOLING WATER INLETS 35 PATENTEU nm a 1 m2 SHEET DBBF 16 PAIENTEDucI 31 1912 3.701 51 T sum near 16 PATENTED um 31 m2 sum DSUF 16 FIG. 9

32 OXY-GAS BURNERS 3o CALCULATED III-OBSERVED I.51IOXY-FUEL RATIO (BY VOLUME) 28 OBSERVED 2:!

OXY'FUEL RATIO O 7 M24 d g LL 22 CALCULATED 0, g EFFECTIVE 0 520 O E 43.6% I6 GFEUWE E 3 as M EFFECTIVE OllilllllllllllL NATURAL GAS FLOW PER TUYERE- SCFH I00 PATENTEDBBT 31 m2 MELTING RATE N0.0F 5000 LB.CHARGES MELTED PER HOUR SHEET llUF 16 X-CALCULATED O-OBSERVED LSII zOXY-FUEL RATIO OXY- GAS BURNERS AVERAGE LINE NO BURNERS l l l 1 l l l WIND RATE-SCFM I000 P'ATENIED um 31 I972 FREQUENCY- PER CENT A G) FREQUENCY -PER. CENT a m SIIEEI' 120T 16 DISTRIBUTION OF SPOUT TEMPERATURES NORMAL OPERATION I44 OBSERVATIONS MEAN2903F.

SPOUT TEMP. DE

FIG. /.3B

DISTRIBUTION OF SPOUT TEMPERATURES OXYGEN-OIL BURNER USE I00 OBSERVATIONS MEAN|2920E 4% I 4| 8 I3 Z5I I SPOUT TEMP DEGF.

PATENTEDncm 1912 3.701 517 sum 13 0F 16 OXYGEN-FUEL SUPPLY SYSTEM WATER PUMPING SYSTEM FIG. /5

OXYGEN FUEL PNENTEDum 31 m2 SHEET lSUF 16 FIG. /7

FIG. [8

OXY-FUEL BURNERS IN FURNACE 'I'UYERES CROSS REFERENCE TO RELATED APPLICATION This is a Division of copending application Ser. No. 602,381, filed Dec. 16, 1966 for OXY-FUEL BUR- NERS IN FURNACE TUYERES and now US. Pat. No. 3,547,624.

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.

ln 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 shafl furnaces by substantially increasing the rate at which charge is consumed, and substantially increasing the metal or ore-tocoke 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 to 5,000 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-atornizing 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 to 5,000 E, 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 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 butners were supplied with commercially pure oxygen and natural gas, having a heating value of approximately L000 British thermal units per cubic foot, at an my 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 em ploying 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.

. 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, 38;

FIGS. 6A and 6B show an oxy-gas rocket burner insert for modification of the burner combination shown in FIGS. 3A, 38;

FIG. 7 shows an oxygen-gas supply system for use with a burner employing an insert of the type shown in FIGS. 6A, 68;

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. I of the present invention;

FIG. 8C is a cross sectional showing of the burner of FIGS. 6A, 68;

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 eupols 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 oxyfuel 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. [3A 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 long'tudinal section, the location of an oxy-fuel burner in one of the tuyeres of the lead blast furnace of FIG. 16; and

FIGS. 19A, 198 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. I of the drawings, there is shown a conventional hot blast iron melting cupola I (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 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 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 40, 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 sub stantially 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 1 1 feet above the foundation of the cupola.

Surrounding the lower end of the cupola l, 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, I20 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 130 is interconnected with conduit 13, for heating the blast up to a temperature of about l,200 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, 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 waterjacket pipe of copper, which is 30 inches long, 1 1 inches in outer diameter, and inch thick. The pipe 14a concentrically surrounds an inner pipe 14b of copper, 7 inches in outer diameter and A 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 140, 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 l9 inches in outer diameter, about 6% inches in inner diameter and is 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 6% 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 2i inches inches from the outer end of pipe 24 is a downcomer arm 240, about 6 inches in inner diameter and 6 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 l, 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 to 5,000 F., notwithstanding the presence in the tuyere pipes 24 of inwardly directed air blasts of between 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.

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* to 5,000* 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 during said process.

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 concentric with said central oil vent.

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 symmetrically spaced with reference to said gas vents.

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 flame temperature within the range 3,200* to 5,000* F.

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 symmetrically disposed relative to said oil vent.

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 said tuyeres.

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 velocities ranging from 10 feet per second to supersonic velocities.

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.