US2823628A - Multi-fuel burner - Google Patents

Description

A. J. POOLE ETAL Feb. 18, 1958 MULTI-FUEL. BURNER 2 Sheets-Sheet 1 n ww, mw N VER. -atzz w mmm TeA m5 ,WJJ -...,PFN ,af mm 4W New MN MN n M\\\ 111,1- ,i i al. .......H @n o l o O C o o MN o o A7 T TONE Y A. J. POOLE ET AL MULTI-FUEL BURNER Feb. 18, 1958 2 Sheets-Sheet 2 Filed Jan. 21, 1953 United States Patent 2,823,628 MULTI-FUEL BURNER Arthur J. Poole, Belleville, and Warren S. Blundin, North Plainfield, N. J., assignors to The Babcock & Wilcox I(Iompany, New York, N. Y., a corporation of New ersey Application January 21, 1953, Serial No. 332,418

Claims'. (Cl. 110-28) This invention relates to fuel burners of the type comprising coaxially arranged cylindrical fuel conduits or burner nozzles of varying diameter. More particularly, the invention is directed to means for preventing an accumulation of fuel deposits on the inner surface of a relatively large diameter tube or housing, adapted to form a burner, due to the static pressure existing therein when a much smaller diameter cylindrical fuel nozzle coaxial therewith is discharging a combustible vmixture under pressure.

When firing a combustible mixture under pressure into a furnace, the velocity of the discharged stream of coinbustibles results in a decrease in the static pressure of the space immediately surrounding the stream of the combustible, causing the discharged combustible mixture to eddy or circulate back into this zone of reduced static pressure. This is noticeable in any furnace fired by gaseous or fluent fuel streams under pressure. In a fuel burner comprising a relatively small diameter cylindrical nozzle arranged coaxially within a relatively large diameter tube or housing adapted to form a burner to deliver furnace or flue gas for combustion, this tube must be made of relatively large diameter because of the 'relatively low caloric value of the furnace gas, which necessitates a relatively larger quantity of such gas being delivered to the furnace to obtain the same heating effect as would be attained when using higher caloric fuels discharged through one or more inner and much smaller diameter nozzles; For example, the inner and smaller diameter nozzles may be arranged to deliver oil or coal as the fuel. Y

In a particular instance, the diameter of the tube or housing may be substantially three times the diameter of the cylindrical nozzle coaxial therewith and, in any event, is usually yover twice that of -the inner nozzle.

The furnace fuel is supplied -to the large diameter tube through valved means which may be closed when the furnace is burning fuel other than the furnace gas. However, when the supply of furnace gas to the tube is shut off, there is a space therewithin having a relatively large volume and open at its exit or discharge end. If the furnace is now fired with high velocity streams of fuel and air from the inner smaller diameter nozzle, the static pressure withinthe large diameter outer tube is decreased by virtue of the high velocity mixture discharged from the inner nozzle. Accordingly, there is a tendency for the discharge combustible mixture to eddy or re-circulate back intothe outer tube andfin so doing, to deposit solids out of 'the combustible mixture onto the inner surface thereof. If these deposits are allowed to build up, they offer `serious obstruction to the flow of furnace gas when it is desired to re the furnace withsuch gas.

In Vaccordance with the Vpresent invention, this static pressure is relieved, and any accumulated deposits are swept from the inner surface of the outer tube, by virtue of openings through the discharge end of such tube located within lan air register. This air register, which receives air under pressure from a windbox, directs a "ice stream of air circumferentially around the discharge end of the outer tube and, through a deflector forming part of the air register, into the furnace. Ports or scoops are provided at the discharge end of the outer tube so that the .air moving circumferentially around this discharge end is diverted or deflected to flow inwardly through the Wall of the Vouter tube and sweep the inner surface thereof. This air relieves the decreased static pressure in the outer tube, thus alleviating any tendency for the fuel mixture from the inner nozzle to eddy into the outer tube, and at the same time sweeps circumferentially over the inner surface of the discharge end of the outer tube to sweepany accumulated deposits therefrom and discharge these deposits through the burner port.

The various features of novelty which characterize our invention are pointed out with particularity in the claims annexed to and forming a part of this specification. `For a better understanding of the invention, its operating advantages and Yspecific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which we have illustrated and described a preferred embodiment of our invention.

Of the drawings:

Fig. l is a side elevation of a burner assembly, partly in section, illustrating an embodiment of the invention;

Fig. 2 is a combination end and side View of the burner assembly, partly broken away;

Figs. 3 and 4 are fragmentary end and side views, respectively, showing a modified form of gas nozzle;

Fig. 5 is a fragmentary sectional view of Fig. 4, taken along line 5 5;

Figs. 6 and 7 are fragmentary end and side views, respectively, showing a second modied form of gas nozzle; and

Fig. 8 is a fragmentary sectional view of Fig. 7, taken along line 8-8.

In the illustrative embodiment, a multifuel burner B is shown in assembled relation to a refractory furnace wall 2 having an inwardly diverging burner opening or throat 3 therein through which the burner discharges into a furnace combustion chamber 4. Fluid heating tubes 5 are arranged along the inner face of the wall and are suitably bent as indicated so as to embrace the burner opening 3. Suitably, the furnace chamber 4 may be associated with a boiler or other form of heat exchanger having provision for maintaining a flow of cooling lfluid through tubes 5.

The burner assembly is of generally cylindrical forma.- tion about a central axis which, in the form shown, is horizontally arranged, at substantially righ't angles to the upright furnace wall 2. An inner tube or nozzle 6 of circular cross section provides an interior flow passage for aruent fuel mixture comprising, for example, a stream of primary air and solid fu'el particles, such as coal, in suspension, the outer end of tube 6 being connected through'an elbow 7 to conduit 8 and thereby to a suitable source of supply, not shown. Exteriorly of nozzle 6, and concentric therewith, is a tubular nozzle 9 for a gaseous fuel, such as coke oven gas, which is admitted through an inlet supply conduit 1li. The gas is discharged from the annular intertube space llthrou'gh a frusto-conical nozzle tip section 12, the latter being formed as a casting having its outer circumferential wall portion welded as at v13 yto the adjoining end of tube 9. The inner circumferential wall portion of tip section 12 engages the outer Wall of nozzle 6 so as to provide a slip joint 14 permitting relative movement of the contacting elements while maintaining a nid tight joint at the normal operating pressures. The nozzle tip 12 is formed with circumferentially spaceddischarge passages or ports 15 which extend longitudinally therethrough, the ports 15"suitably being of quadrangular cross section throughout and terminating at the conical end surface in discharge openings 16 of similar formation. The outer end of space 11, between tubes 6 and 9, is closed by means including an annular plate 17 formed with a lance port 1S for which a suitable closure v19 is provided, other ports and closures, not shown, beingsimilarly arranged at circumferentially spaced locations.

Exteriorly of tube 9 and concentric therewith is a tube or nozzle 20 of circular cross section which with tube 9 defines an annular passage 21 to which a gaseous fuel such as blast furnace gas is supplied through a known form of scroll housing 23 at the outer end whereby a whirling movement is imparted to the gas passing through and discharging from the nozzle. The gas under pressure is admitted tangentially to housing 23 through gas inlet conduit 24. Doors 25 of suitable form or forms are installed over openings in the housing to afford cleaning access to interior surfaces. A spacer bar 26, and similar bars not shown, extend outwardly from nozzle 9 to the inner wall of nozzle 20 to maintain the nozzles in concentric relationship while permitting the withdrawal of one from within the other. As indicated in Fig. 1, the gas nozzle 20 terminates forwardly of nozzles 6 and 9 at a plane spaced from the outer face of furnace wall 2.

An air register 27 of known form is positioned adjacent the outer face of wall 2 so as to admit air for combustion circumferentially of the fuel nozzle assembly, the register 27 having curved doors or shutter plates 28 pivotally supported on and between end plates 29, 31 and simultaneously operable by means including a shaft 32 and crank handle 34. As indicated in Fig. 2, the air register doors 28 are arranged to effect a counter-clockwise rotational movement of the incoming air as viewed from the outer end of the burner assembly, and thus corresponding to the rotational movement of blast furnace gas flowing through nozzle 20, as indicated by the arrow in Fig. 2. Air is supplied to the register from a windbox compartment which is defined in part by a casing wall 3S spaced from furnace wall 2, the air from the register being directed into throat 3 by means of a frusto-conical extension 36 of end plate 31.

In addition to the burner means hereinbefore described, a pilot burner 37 is provided centrally of the assembly and, in the form shown, comprises a fuel supply tube 3S extending longitudinally within nozzle 6 and terminating at its inner furnace end in a perforated tip or sprayer head 39 by which a fluent fuel such as coke oven gas, for example, is discharged so as to provide a flame in the vicinity of fuel discharge from one or more of the other nozzles. The burner tube 38 is supported within a pipe 40 which also serves as a support for a fuel dispersing device or impeller 41 by which the fuel-air mixture discharging from nozzle 6 is dispersed into intimate mingling relation with secondary air admitted through register 27 and entering the combustion zone 4 through burner wall opening 3.. Pipe 40 is supported centrally of nozzle 6 by means of a strut 42, and others not shown, which slidably engage the inner wall of the nozzle. The impeller 41 is substantially of the form shown in U. S. Patent 2,380,463, A. J. Poole, and thus comprises an assembly of spaced frusto-conical vanes 43 of progressively decreasing inner and outer diameters, toward the furnace.

During certain periods of operation, particularly when pulverized solid fuel is the only fuel being burned, there may be a tendency for some of the finer solid fuel particles to collect in the large diameter gas nozzle 20. Moreover, when coke oven gas is being fired, there may also be a tendency for this fuel to burn back into the ,larger nozzle 20. It has been found however that both of these tendencies may be successfully counteracted by suitable introduction of combustion air into the annular gas discharge passage 21.

Accordingly, Figs. 3 to 5 show a modiiied construction of gas nozzle 20a wherein slots or openings 44 are formed in the nozzle at a relatively short distance from its inner discharge end 45. The slots 44.extend circumferentially of the nozzle in a common plane and are circumferentially spaced, with one continuous slot provided in each quadrant, as illustrated in Fig. 3 for one such quadrant. Each slot is formed with parallel sides 46 which extend circumferentially of the conduit, and with end margins 47 at an inclination of 45 to the sides so as to conform in general to the helical path of gas flow interiorly of the nozzle. At the outer circumference of the nozzle, each slot is covered by a hood or scoop 48 having an outer circumferential wall or roof 49 inclined outwardly and forwardly toward the gas inlet end of the nozzle, and having triangular end walls 51, thereby defining an arcuately extending air inlet 52 into the scoop. At the inner circumference of the nozzle, each slot is covered by a similar hood or scoop 48a having an inner inclined wall or roof 49a and end walls 51a so as to define an arcuately extending air outlet 52a into fuel passage 21. The inclined scoop wall 49 at the outer side of the nozzle is arranged at 45 to the length of the nozzle whereas the inclined scoop wall 49a at the inner side is arranged at 30 to the nozzle length.

Figs. 6 to 8 show a modified air-slot arrangement wherein a gas nozzle 20h is formed with circumferentially spaced slots or openings 54 of smaller arcuate extent than slots 44 hereinbefore described, and equally spaced throughout the circumference of the nozzle. In this form, each slot 54 is defined by parallel sides 55, and parallel ends 56, all arranged at angles of 45 to the length of the nozzle. A hood 57, having an inclined main wall 58, is positioned over each slot at the outer side of the nozzle to form an air inlet 59 into the slot, and a hood 57a, having an inclined main wall 58a, at the inner side, to form an air outlet 59a into the fuel passage 21. The inclinations of outer and inner scoop walls 58 and 58a, relative to the length of the nozzle, are suitably the same as described for similar scoops in Figs. 3 to 5.

While in accordance with the provisions of the statutes we have illustrated and described herein the best form of the invention now known to us, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by our claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

l. In a fuel burner, a substantially cylindrical fuel nozzle; a substantially cylindrical relatively large diameter tube, adapted to form a burner, in sustantially coaxial surrounding relation with said nozzle, the diameter of said tube being at least twice that of said nozzle; means for supplying fluent fuel under pressure to said nozzle for discharge from the discharge end thereof; the discharge from said nozzle creating a static low pressure in said tube, when the latter is inactive as a burner, resulting in a tendency for the uent fuel discharged from said nozzle to build up deposits on the inner surface of the discharge end of said tube; an air registersurrounding said tube at the discharge end thereof for directing'air circumferentially therearound; deflector means operatively associated with said air register to direct such air toward the axis of said tube and nozzle to intersect such axis downstream of the discharge ends of the tube and nozzle; and means, including said, air register and including openings through the wall of said tube within sald air register upstream of said deflector means, for effect-` ing a ow of such air into said tube to relieve such static low pressure therein, and helically over the inner surface of its discharge end to dislodge any deposits of the fluent fuel therefrom for discharge axially of said tube and nozzle. Y

,2.- In a multi-fuel burner, the structure defined 1n claim 5 1 in which the fuel supplied to said nozzle is pulverulent fuel in suspension in air under pressure.

3. In a fuel burner, the structure dened in claim 1 wherein said openings are formed as slots having opposite margins inclined in a direction corresponding to the helical movement of uid through said tube, and means positioned over each of said openings for directing the air inwardly therethrough.

4. In a fuel burner, the structure as dened in claim 3 wherein the air directing means associated with individual openings are formed as scoops having main wall portions inclined outwardly and upstream relative to air flow through said surrounding region.

5. In a fuel burner, the structure as dened in claim 4 wherein scoops having inclined main wall portions are positioned over individual openings at the inner side of 6 the tube, said Ilast named scoops opening downstream of uid ow through the housing.

References Cited in the le of this patent UNITED STATES PATENTS 1,647,675 Vedder Nov. 1, 1927 1,702,298 Hetsch Feb. 19, 1929 1,938,335 Hubbard et a1. Dec. 5, 1933 1,949,277 Jackson Feb. 27, 1934 2,044,296 Hardgrove June 16, 1936 2,275,394 Hardgrove Mar. 3, 1942 2,475,911 Nathan July 12, 1949 FOREIGN PATENTS 312,254 Great Britain May 23, 1929 312,380 Great Britain May 27, 1929

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