US3000435A - Furnace burner - Google Patents

Description

Sept 19, 1961 F. s. BLooM ETAL 3,000,435

FUNACE BURNER Filed April 28, 195o v 2 sheets-sheet 1 fig. 5'. 55,

INVENTORS Frede/fkk 5. 5/0 0 /77 anddames HOV/s United States Patent 3,000,435 FURNACE BURNER vFrederick S. Bloom and James E. Hovis, Allegheny County, Pa., assignors, by direct and mesne assignments, to Selas Corporation of America, Dresher, Pa.,

a corporation of Pennsylvania Filed Apr. 28, 1950, Ser. No. 158,904 3 Claims. (Cl. 158-11) This invention relates to furnace burner apparatus, and more particularly to high thermal release burners for high temperature heat-treating furnaces.

The furnace burner of our invention is particularly useful in furnaces for heat-treating a moving line of objects, such as metal pieces which must be raised to temperatures in the order of 2200 F. preparatory to subsequent working of the pieces. Such furnaces should be exible in their operation so that there Will be a high rate of thermal release from the furnace burners to heat the pieces quickly as they pass rapidly through the furnace and so that the rate of thermal release can be sharply reduced without becoming unlit in the event that movement through the furnace is temporarily slowed down or halted for any reason. In order to achieve such flexible operation it is desirable to use burners having the highest possible rate of thermal release per cubic foot of furnace volume and a furnace structure as small and compact as possible, so that heat can be rapidly applied to pieces moving rapidly through the furnace and so that when pieces are temporarily halted in the furnace and the burners are turned down the residual heat in the furnace will not be great enough to injure the halted pieces. It is further desirable to be able to use either gas or oil as the furnace fuel so that one can be used When the other is not available. Several interrelated factors must be considered. Whether using gas or oil the furnace burners should be capable of developing the greatest possible amount of heat release per cubic foot of furnace volume, should be easily regulated from high to low rate of thermal release over as Wide range as possible, should not backfire or go out at lowest turndown, should provide for mixing the combustion air and fuel at a point near the nozzle tip of each burner to minimize damage in case of backfire, should provide for thoroughly mixing the incoming fuel and air and heating the mixture to a temperature approaching the furnace temperature before it leaves the nozzle, and should be simple in construction and long-lasting in service. Among the many diiculties in meeting these conditions in the past has been the choice of burner materials. Conventional refractory materials are brittle, are rapidly destroyed when in contact with oil, and have such a low rate of thermal conductivity as to prevent the incoming fuel from being fully preheated before leaving the nozzle. Metals, on the other hand, cannot stand high furnace temperatures, even in the case of the best heatresistant alloys, unless the metals exposed to the furnace heat are adequately cooled, and in the past it has not been considered feasible to cool metal burner nozzles exposed to furnace temperature in the order of 2200 F., especially in the case of nozzles of the type having radially-extending outlets. Another diiculty is the relationship of the size of each burner unit to the problem of fuel regulation. Large numbers of small burners are desirable to obtain maximum heating Within the furnace, but fuel regulation becomes more difficult as the burner size decreases, particularly when using oil. One Way of overcoming this difficulty is to feed a pre-rnixed supply of air and fuel to a number of burners from a common mixing chamber, but such pre-mixing is complicated when using oil by the fact that the oil will not ice remain fully vaporized unless the mixture is kept at a temperature of at least 70D-800 F., and when using gas by the fact that the pre-mixture is liable to backfire and explode. In addition to all of the above considerations, it is important that the burner units be adapted to use gas and oil inerchangeably instead of using separate sets of burners for gas and oil respectively, not only to avoid duplication but also to obtain maximum heating in the smallest possible furnace space.

The burner of our invention overcomes these diculties and is capable of using both gas and oil alternatively as fuel With a turndown ratio as high as 10:1 When using either gas or oil and Without resorting to very high maximum feeding pressures to increase the turndown ratio. Moreover, the burner of our invention is capable of a very high rate of heat release per cubic foot of furnace volume with either gas or oil as the fuel, in the order of 750,000 B.t.u. per cubic foot. As a result of this combination of high turndown ratio and high rate of heat release the burner greatly improves flexibility of furnace operation. A further feature of the burner of our invention is that it is constructed of metals or the like having high thermal conductivity, including the burner nozzle which projects into the furnace.

The burner of our invention is of the type having a nozzle with radial outlets therefrom. These radial outlets all extend directly from a small pre-mixing chamber disposed vrthin the nozzle and closed at one end by the metal cap of the nozzle. All of the incoming fuel and combustion air is fed into the pre-mixing chamber and this relatively cool stream of fuel and air cools the metal cap suiciently to permit it to withstand high furnace temperatures in the order of 2200o F., and at the same time the heat absorbed by the incoming fuel and air preheats the mixture so that full combustion is achieved in the furnace close to the burner nozzle. For example, tests have shown that all of the fuel is burned Within 8 to l2 inches from the face of the refractory block surrounding the burner nozzle. With this construction We have found that backfire does not occur even when using gas as a fuel, contrary to the indication of the prior art. One factor in preventing backfire is the use of a large number of small nozzle outlets, not only to improve heat distribution but also to increase the rate of flow through each opening, even at lowest turndown, to an extent exceeding the rate of back-burning through each nozzle opening. Another factor preventing backfire is the cooling effect of the metal parts of the burner. The pre-mixing chamber in the nozzle is small and is preferably supplied With a spray of oil or jets of gas directed generally toward the nozzle cap, With radially-directed streams of air fed in transversely of the streams of fuel to give maximum turbulence Within the pre-mixing chamber for thorough mixing of fuel and combustion air. The fuel and air ducts leading to the nozzle are preferably concentric for greatest compactness and are preferably metallic in order to aid in cooling the part of the nozzle exposed to the furnace and to preheat the incoming fuel and air progressively as it approaches the mixing chamber.

We provide a refractory block closely fitted around the base of the nozzle with refractory surfaces radiating out- Wardly adjacent and substantially parallel to the respective nozzle outlet openings. These refractory surfaces are exposed to the flaming mixture as it emerges from the nozzle outlets but are not in the line of the central core of the stream from the respective outlets, as this would cool rather than heat the refractory surfaces. The heat absorbed `from the tiames makes these surfaces incandescent to aid in burning the mixture fed out from the nozzle and also to direct radiant heat toward the interior of the furnace so that the heat is not concentrated along the burner ames. Preferably a plurality of rows of radial outlets are provided in the nozzle with the outlets lin each row arranged in staggered relation so that there is almost a continuous ring of llame around the nozzle. The lower outlets re along channels in the surrounding refractory block and this has the further advantage of increasing the area of the refractory block exposed to the various flames so that the incandescent radiant heating effect is increased.

We further provide a fuel oil atomizer of increased efciency for injecting fuel oil into the pre-mixing chamber.

The atomizer is arranged to direct converging opposed jets of compressed air or steam at right angles to the incoming stream of fuel oil, with the result that the oil is broken up into a tine mist sprayed out in a wide cone. This cone is intersected by the combustion air so that the oil will be turbulently mixed with air and fully vaporized :in the pre-mixing chamber.

Other details, objects and advantages of the invention will become apparent from the following detailed description and in the accompanying drawings. We have shown in the drawings, for purposes of illustration only, the following present preferred embodiment of our invention, in which:

FIGURE l is a side sectional View of a burner incorporating my invention;

FIGURE 2 is a partial sectional View on the line II--II in FIGURE 1;

FIGURE 3 is an enlarged view of the fuel oil atomizer shown in FIGURE l, turned 45 from the position shown in FIGURE l;

FIGURE 4 -is a side elevational view of the upper part of the refractory block shown in FIGURE 1;

FIGURE 5 is a front view of one quarter of the refractory block shown in yFIGURE l;

FIGURE 6 is an enlarged partial view of the nozzle shown in FIGURE l;

FIGURE 7 is a front view of the nozzle shown in FIG- URE V6, with one row of nozzle openings shown in dotted lines;

FIGURE 8 is a sectional view of the casing of the fuel oil atomizer shown in FIGURE 3, with the interior plug removed;

FIGURE 9 is a front View of the atomizer casing shown in FIGURE 8;

FIGURE l() is an enlarged front View of the plug for the fuel oil atomizer shown in FIGURE 3;

FIGURE l1 is a sectional View on the line XI-XI shown in FIGURE l0; and

FIGURE l2 is a sectional View on the line XLI-XII in FIGURE l0.

Referring now more particularly to the drawings and considering rst the structure shown in FIGURE l, the illustrated burner comprises a tubular heat-conductive body including a nozzle 29 surrounded by a rectangular refractory block 21 which is set among other refractory blocks 22 and 23 forming a furnace wall. The nozzle 20 has a cylindrical wall 24 which iits closely against the surrounding refractory block 21 at its base and which projects into the lfurnace to form the free or working end of the nozzle. The free end of the nozzle 20 is sealed by a tip 25 which is integral with the wall 24. The outer surface of the tip 25 is flat and the inner surface is slightly conical with the point extending away from the furnace chamber. A row of outlet openings 26 extend radially through the cylindrical wall 24 immediately adjacent the tip 25 and a second row of outlet openings 27 extend radially through the wall 24 immediately adjacent and in staggered relation to the lirst Vrow of openings 26. A tubular element 28 is secured to the base of the cylindrical wall 24 and the wall 24 and element 28 form a hollow cylindrical enclosure 29 which serves as an enlongated pre-mixing chamber for air and fuel supplied to the openings 26 and 27. Four radial air-inlet openings 30 (FIGURE 2) extend through the tubular element 28 adjacent the cylindrical wall 24, and an integral wall 31 extends transversely across the tubular element 28 adjacent the openings 30 to define the inner end of the premixing chamber 29. The outer casing 32 of a liquid fuel sprayer or fuel oil ato-mizer 33 (FIGURE 3) projects through a central opening in the wall 31 into the preimixing chamber 29, and gaseous fuel is admitted into the pre-mixing chamber 29 through gaseous-fuel inlet openings 34 in the wall 31 extending parallel to the nozzle axis from the gaseous-fuel duct means defined by the space between the atomizer casing 32 and the tubular element 28.

Concentric ducts are connected to the pre-mixing chamber 29 to supply it with fuel and air (FIGURE l). The innermost duct is a fuel oil line 35 connected at one end to the atomizer 33 and at the other end through a tting 36 to a fuel oil supply line 37. Around the line 35 is a tube 38 connected at one end to the atomizer 33 and at the other end through a fitting 39 to a supply line 40 for compressed air (or steam). The compressed air from the line 4G is fed between the fuel oil line 35 and the tube 38 to the atomizer 33 to convert the fuel oil from the line 40 into a line conical spray as it enters the pre-mixing chamber 29. A gaseous supply line 41 is connected through a tting 42 to the space between the tubular elements 28 and 38 in order to supply gaseous fuel through the openings 34 into the pre-mixing chamber 29. A rear extension 43 of the nozzle 20 surrounds the tubular element 28 with a space therebetween and a conduit 44 secured to the base of the extension 43 serves as a closed duct means to transmit combustion air from a supply line 45 into the space between the extension 43 and the tubular element 28, and thence the combustion air passes through the openings 30 into the pre-mixing chamber 29, Valves 46, 47, 48' and 49 are illustrated diagrammatically in FIGURE 1 for controlling the rate of ow through the fuel oil supply line 37, the compressed air supply line 40, the gas supply line `41 and the combustion air supply line 45, respectively. These valves may be controlled manually but are preferably subject to automatic controls (not shown) responsive to furnace conditions and operations so that the burner will be turned down promptly when furnace temperatures rise above predetermined limits or when the movement of pieces through the furnace is interrupted. The valve 49 controlling the combustion air flow is regulated in conjunction with the gas valve 41 or the oil valve 46 in order to maintain a proper balance of fuel and combustion air, preferably by automatic controls (not shown) such as those disclosed in theL copending application Serial No. 694,734 of Frederick S. Bloom, led September 4, 1946 for Controlling Fuel Supply to Multi-Zone Heating Furnaces, now U.S. Patent Number 2,523,644.

The fuel oil atomizer 33 comprises a hollow cylindrical outer casing 32 (FIGURES 3, 8 and 9) and a plug 50 therein (FIGURES 3, l0, l1 and l2). The rear end of the casing 32 is threaded to receive the correspondingly threaded end of the tube 38 and an intermediate portion of the casing 32 is threaded to receive corresponding broken threads 51 along four edges of the plug 50. The plug 50 is in the form of a generally rectangular block with an axial opening 51' therethrough. One end of the opening 51 is threaded to receive the correspondingly threaded end of the oil line 35 and the other end is narrowed to a small axial orilice 52. The end of the casing 32 adjacent the pre-mixingk chamber 29 is closed except for a relatively small axial opening 53. 'Ihe plug 50 is screwed into the casing 32 until it abuts the closed end of the casing 32. The opening 52 of the plug and the opening 53 of the casing are separated by a small space resulting from milling small intersecting notches 54 in the plug 5 perpendicular to the common control axis through the openings 52 and 53. Four larger notches 55 in the plug 50 extend at 45 angles between WAL... -nn..

the outer ends of the notches 54 and the four flat sides 56 of the plug 50. As a result of this construction a channel for compressed air is formed between the plug 50 and casing 32 whereby compressed air is fed in four separate streams along the at sides 56 of the plug 50, along the notches 55 and along the notches 54 until the streams come together again in two pairs of oppositely moving streams converging at right angles to the ow of fuel oil out of the plug opening 52. The compressed air thus fed into the oil causes a ne mist of fuel oil to be sprayed out of the opening 53 into the premixing chamber 29 in the form of a cone having a flat apex angle in the order of 75. The cone of sprayed oil is directed toward the combustion air openings 30 where it it caught by the incoming combustion air and thoroughly mixed and vaporized in the pre-mixing chamber 29. When gas and oil are used together as fuel the arrangement of the openings 31 for conducting the gas simultaneously into the pre-mixing chamber 29 provides a satisfactory mixture of the sprayed oil and gas with the combustion arr.

As the mixed air and fuel approaches the nozzle tip 25 the high temperature of the nozzle, which is in an exposed portion in the furnace, completely vaporizes the fuel so that it bursts into ame as it passes out through the nozzle openings 26 and 27. The nozzle tip 25, the nozzle Walls 24, and the various elements 28, 33, 35, 38, 43 and 44, and the fittings and supply lines leading thereto, are all made of materials, preferably metal, which rapidly transfer heat from the relatively hot nozzle tip 25 and Walls 24 toward the cooler elements within and behind the surrounding refractory block 21. This rearwardly flowing heat is progressively absorbed by the incoming fuel and combustion air so that the advantages of preheating of the fuel and air are obtained without any additional pre-heating equipment. The result is to hold the temperatures around the outside of the nozzle tip 25 and Walls 24 below temperatures harmful to heatresistant alloy steels, and to hold the temperatures of the nozzle tip 25 and walls 24 within the pre-mixing chamber 29 low enough to prevent backiiring the combustible mixture therein but high enough for complete vaporization of fuel oil before it reaches the furnace combustion chamber. Although the control of nozzle temperatures depends in part on the cooling effect of incoming fuel and air, flashback does not occur in the pre-mixing chamber 29 when the nozzle flame is reduced in a fully-heated furnace, whether gas or oil or a mixture of both is used as fuel.

The refractory block 21 around the nozzle 20 has a series of radiating surfaces 57 extending outwardly parallel to and adjacent the axes of the respective nozzle openings 27 (FIGURES l, 4 and 5), and a similar series of slightly raised surfaces 58 extending outwardly parallel to and adjacent the axes of the nozzle openings 56 (FIG- URES l, 4 and 5). These refractory surfaces become incandescent so that complete combustion is effected and radiant heat is directed into the furnace to improve the distribution of the heat of the burner llames. The axes of the nozzle openings 26 and 27 are arranged in the form of iiat cones and the corresponding surfaces 57 and 58 of the refractory block 21 form a generally conical indentation in the block 21. The lengths of the various surfaces 57 and 58 correspond to the maximum length of the nozzle flames. Ihe refractory surfaces 57 and 58 are spaced suiiiciently from the axes of the nozzle openings 27 and 28 so that the hot outer part of the ames will brush against these refractory surfaces but the cores of the flames, which are relatively cool, will be kept away from the refractory surfaces. The refractory block 21 is formed of conventional refractory materials with high heat resistance and low heat conductivity. The latter characteristic is desirable to prevent excessive transfer of heat away from the furnace chamber. While the metallic nozzle and associated elements within the refractory block 21 have high heat conductivity and cause some heat loss, these elements are relatively small and their heat loss is oifset by the return of heat absorbed by incoming air and fuel.

While we have illustrated and described a present preferred embodiment of the invention, it will be recognized that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the appended claims.

We claim:

1. A furnace burner comprising a tubular heat-conductive body adapted to project at one end into a furnace to be heated thereby, said body having an interior tubular wall and at each end thereof a transverse wall to deiine therebetween an elongated mixing chamber, radial outlet openings in said tubular wall adjacent the transverse wall at said one end constituting outlet openings from said chamber to said furnace, a liquid fuel sprayer mounted in said body and having a restricted discharge opening positioned centrally in the opposite end wall disposed to spray atomized fuel oil into said chamber at said opposite end in a cone extending axially toward said one end, radial air-inlet openings in said tubular wall adjoining the end wall at said opposite end, closed duct means spaced from and connected to said air-inlet openings to supply fresh combustion air to said mixing chamber at said opposite end in radial paths intersecting said cone whereby the combustion air is turbulently mixed with said sprayed atomized oil adjacent said opposite end of the chamber and the mixture passes through said chamber and out of said outlet openings while being heated by said heated conductive body, gaseous-fuel inlet openings in said opposite end wall surrounding said sprayer discharge opening, and duct means to introduce gaseous fuel in said inlet openings axially toward said one end of the chamber to intersect said combustion air entering through said radial air-inlet openings.

2. A burner according to claim 1 including separate valve means positively controlling the flow through the liquid fuel sprayer, the air-inlet openings, and the gaseous-fuel inlet openings.

3. A burner according to claim 2 including a refractory block fitting closely around said tubular heat-conductive body intermediate said radial outlet openings and said radial air-inlet openings and having a conical indentation receiving said body with the radial openings at its apex, said radial outlets being directed so that the mixture passing therefrom brushes against the conical surface, causing all of the fuel to burn close to said block to effect heating thereof.

References Cited in the tile of this patent UNITED STATES PATENTS 191,546 Parson June 5, 1877 1,334,747 Geyer Mar. 23, 1920 1,501,838 Cook July 15, 1924 1,539,249 Fesler May 26, 1925 1,542,491 Clasen June 16, 1925 1,587,249 Starr June 1, 1926 1,629,288 Morse May 17, 1927 1,841,169 Butz Jan. 12, 1932 1,860,942 Morse May 31, 1932 2,215,079 Hess Sept. 17, 1940 2,356,865 Mason Aug. 29, 1944 2,425,709 Bucknam et al. Aug. 19, 1947 2,452,543 Breault Nov. 2, 1948 FOREIGN PATENTS 14,935/28 Australia Aug. 7, 1928 820,672 France Aug. 2, 1933 418,299 Great Britain Oct. 16, 1934

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