US 3561740 A
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United States Patent Inventors Appl. No. Filed Patented Assignee CROP DRYING OIL BURNER 12 Claims, 7 Drawing Figs.
u.s.c1 263/19, 431/11s,431/17s,431/1s3 1m.c1 F24h 3/02 FieldofSearch 431/115, 116, 158, 174, 175, 182, 183; 263/19 Primary ExaminerEdward G. Favors Att0rneysArthur G. Gilkes, William T. McClain and John J.
Connors ABSTRACT: This burner includes a cylindrical combustion chamber, and means which blow air through the chamber. A circular opening in the chambers front plate and a plurality of peripheral apertures and radial slits in the chambers rear plate allow air to pass through the chamber. Pitched blades adjacent the slits cause this moving air to form a vortex within the chamber, and when oil is injected into the vortex and ignited, a clean, smoke-free flame shoots out the circular opening. If a centrifugal fan is used as the air blowing means, the chamber is ideally located in the quiet zone opposite the fan s hub. In this instance, air intercepting and directing means collect some air from the peripheral air stream generated by the fan, and direct this intercepted air into the chamber.
I I I 16 'PATEN-TEDIFEB len 3.1561; 74
I sum 5 or 5 07 TOP V5) .7147 20 122 pmafia aw CROP DRYING OIL BURNER BACKGROUND OF THE INVENTION Crop drying is potentially one of the largest markets for fuel oil, yet it remains virtually untapped: the reason, incomplete, smoky oil combustion which impairs the taste, odor, and color of the grain being dried. Grain may be dried using either a direct-fired or indirect-fired burner. In the latter case, air coming into contact with the grain is heated indirectly so that it never intermingles with the flame of the burner. This is a very expensive system. The direct-fired burner is a much more economic system, but fuel combustion .must be complete so that taste, odor, and color contaminants are not fed into the grain. Most conventional crop dryers employ direct-fired burners fueled by clean burning liquid petroleum gas (LPG) or natural gas. Because fuel oil generally costs considerably less per B.t.u. than LPG, and because of the scarcity of LPG and natural gas in some areas, direct-fired crop drying oil burners would be highly desirable. But to date most, if not all, attempts to design an oil burner suitable for direct-fired crop drying have resulted in failure because smoky oil combustion could not be eliminated.
Three major factors govern smoke-free oil combustion: the oil-air ratio, the temperature inside the burners combustion chamber, particularly the temperature of the inner wall of the combustion chamber, and the manner in which the air flows through the chamber. Sufficient air must always be present to insure complete combustion of the oil. Insufficient air causes smoking. However if too much air is blown through the chamber, the inner wall of the chamber cools, and when the burner is shutdown, any oil remaining in the chamber vaporizes slowly, causing smoky afterbuming. Thus, the proper balance of air and oil must be maintained to guarantee smoke-free combustion and to avoid excessive cooling of the chamber. Moreover, even when the oil-air ratio and chamber temperature are optimized, smoky combustion products still form. We have found that by restricting the air flow at the front of the chamber, these combustion products can be recirculated within the chamber until they are completely consumed.
BRIEF DESCRIPTION OF THE INVENTION We have invented an oil burner which provides clean, smoke-free burning at startup, throughout prolonged operation, and at shutdown. This 'bumer has many excellent attributes. The most outstanding is,of course, that it provides a clean, smoke-free flame. But it is also easy to build, inexpensive to operate and maintain, provides reliable, trouble-free service, and can readily be designed to provide a heat output of from about one million to about ten million B.t.u.s per hour in a 30-60 m.p.h. blast of air. Such a high heat output burner is exceptionally well suited for use in most conventional crop dryers.
Our oil burner, in common with most oil burners, includes a combustion chamber having rear and front openings for allowing air to enter and exit, means adjacent the rear opening for moving air rapidly through the chamber, and means for feeding oil into the chamber and igniting the oil-air mixture. What characterizes our invention is the way in which air moves through our burner. We have designed our burner so that there are three principal air currents within the chamber: l a vortex of spinning air in the central portion of the chamber, (2) a laminar-like stream near the inner wall of the chamber which surrounds the vortex of the spinning air and flows out the front opening, and (3) a recirculating air stream flowing counter to the laminarlike air stream. The vortex of spinning air intimately mixes oil and air; the laminarlike air stream aids in confining this oil-air mixture to the central portion of the chamber and in keeping oil off the chambers inner wall; and the recirculating air stream aids in keeping the fuel oil particles within the chamber until they are completely vaporized.
The size and shape of the chamber, especially the size and shape of the front and rear openings, are also important. By regulating the shape and dimensions of the chamber and openings, we can balance the oil-air ratio and control, at least partially, the chambers temperature. The chamber must have a large enough volume to accommodate the oil being fed into it, and the openings must be sufficiently expansive to permit entry of enough air, and thereby guarantee smoke-free oil combustion, and sufficiently restrictive to prohibit entry of excess air, and thereby guarantee against undue cooling of the chamber with attendant smoky shutdown.
For a particular set of parameters, the proper chamber size and proper opening dimensions can be determined empiri cally. For example, most moist grains can be dried if the burner is fired at a rate between 1 and 45 gallons per hour. Using a conventional centrifugal fan which generates a pressure between about 2 and about 4 inches of water, air is blown through the chamber of the burner at a rate of from about 20 to 900 c.f.m. The grain ordinarily presents a back pressure of between I and 3 inches of water, and the air temperature generally ranges between 0 and F. Under these conditions, the dimensions of the front and rear chamber openings are adjusted so that temperature of the chambers inner wall remains above about l400 F., preferably in the range of from about 1600* F. to about 2000 F. If the chamber is insulated, this temperature is more easily maintained. If oil particles strike this hot inner wall, they evaporate immediately and burn completely with a minimum of coke and smoke formation.
In accordance with a more detailed feature of our invention, the combustion chamber is a hollow cylinder having a front and rear plate. Preferably the chamber is made of a heat resistant metal alloy or cast iron wrapped in an insulating material or a nonporous ceramic or like heat resistant-insulating material. In the chambers front plate, there is a centrally located, circular outlet which has a diameter equal to from about one-third to about two-thirds, preferably about onehalf, the diameter of the chamber. The ratio of chamber diameter to chamber length to outlet diameter is about 2:23:l, preferably about 212.521. Although these ratios can vary somewhat, if they vary too greatly, smoky burning results.
In the chambers rear plate, there are a plurality of apertures adjacent the plates periphery, and a plurality of radially extending slits between the plates periphery and center. As the air enters the chamber, pitched blades, mounted adjacent the slits, swirl the air about to form a vortex within the chamber. Oil feeding and igniting means, centrally mounted within the rear plate, inject oil into this vortex and set the oilair mixture afire, so that the forward two-thirds of the chamber is filled with flame that shoots out the outlet inthe front plate. The apertures direct air entering the chamber along a course adjacent the chambers inner wall so that the swirling mass of oil and air tends to be confined to the central portion of the chamber. Some air strikes the inside of the front plate and recirculates, carrying unvaporized oil and combustion products with it back into the vortex.
Preferably the oil feeding and igniting means includes a shield and, a plurality of nozzles. The shield is a frustoconical element which surrounds the oil feeding and igniting means and prevents overheating of these means and buildup thereon of carbon or the like. The spray from the noules is aimed at the center of the chamber. This reduces the amount of oil thrown against the inner walls of the chamber, and consequently, also reduces the possibility of smoking. The feeding of oil into one or more of the nozzles may be controlled by a thermostat located in the crop dryer.
In designing an oil burner for crop drying, we also encountered another problem. Conventional crop dryers employ large radial or backward pitched centrifugal fans which push air away from the fans but towards the fan's housing. The combustion chamber of a burner is ideally located in the quiet zone opposite the hub, but since there is little or no air flow through this zone, smoky oil combustion will occur unless measures are taken to introduce more air into the chamber. We overcome this problem by mounting, between the fan and chamber, means which intercept air coming from the peripheral edge of the fan and which direct this intercepted air into the chamber.
In accordance with this feature of our invention, we employ a revolving fan having a plurality of vanes extending radially from the fan's hub. The spinning vanes force air away from the hub, towards the periphery of the fan, and generate a high velocity air stream which flows away from the fan along a course that intersects the plane through which the fan revolves. A combustion chamber, including oil feeding and igniting means and having an air passageway, is aligned opposite the hub on the same side of the fan as the air stream, but out of said air stream. A plurality of conduits positioned between the chamber and fan collect some air from the stream and feed this air into the passageway. Thus, the chamber receives an adequate supply of air.
DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a conventional crop dryer employing the oil burner of our invention.
FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1.
FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2
FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 2.
FIG. 5 is a cross-sectional view taken along line 5-5 of FIG. 2.
FIG. 6 is a cross-sectional view taken along line 6-6 of FIGv 2.
FIG. 7 is an enlarged perspective view of one of the slits in the rear plate shown in FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 depicts burner 10 of our invention mounted in rear wall 12 of portable crop dryer 14. A high velocity hot air stream coming from burner I0 dries moist grain 16 being continually fed into hopper 24 at the top of drycr l4. Simultaneously, dry grain 18 is withdrawn from the bottom of dryer l4. Auger 20 uniformly distributes grain 16 over the top of dryer 14, and under the guidance of inclined walls 26 and 28, and under the influence of gravity, this grain l6 flows over pcrforated roof 30 of internal housing 32, between perforated sidewalls 34 of internal housing 32 and perforated sidewalls 36 of external housing 40, sidewalls then into passageways 42 (only one shown) on opposite sides of dryer 14. Partition 46 divides internal housing 32 into upper section 48 and lower section 50. Burner 10 blows hot air through the upper section 48 and out roof 30 and sidewalls 34. This hot air, moving countercurrent to the flow of grain 16, dries the grain and then leaves dryer 14. At the same time, cool air fan 52 blows cool air through lower section 50 and then out perforated sidewalls 34. Consequently, when grain 16 arrives at passageways 42, it is both dry and cool. Augers 54 (only one shown) within passageways 42, feed dried grain 18 out ports 58 and 60 and into a suitable storage bin (not shown).
Burner 10, best shown in FIG. 2, has three major components: air moving assembly 62, combustion chamber 64 positioned in front of the air. rnoving assembly, and fuel injecting and igniting assembly 66 attached to the chamber. Assembly 62 blows air into chamber 64, and assembly 66 simultaneously sprays oil into chamber 64 and ignites the oil-air mixture.
Air moving assembly 62 includes conventional centrifugal fan 68 and spiderlike subassembly 70 (FIGS. 2-4) which serves as air intercepting and directing means. As the fans power shaft 72 turns, vanes 74, bristling forth from the fan s hub 76 and almost touching the fan's housing 78, bite into the air and throw air against housing 78. Housing 78 trains this speeding air along a course indicated by arrows a. Because of the manner in which fan 68 operates, there is little or no movement of air outwardly from hub 76v As mentioned, this poses a problem, Namely, chamber 64, ideally located opposite hub 76, will not receive enough air to guarantee smokefree combustion unless corrective measures are adopted. Subassembly 70 provides the necessary corrective measures.
More specifically, subassembly 70 catches a portion of the air coming from the periphery of fan 68 and feeds it into chamber 64. This subassembly 70 includes compartment 80 and radial air ducts 82 which merge in the compartment. Each duct 82 has an open ended elbow 84 twisted so that its opening 86 lines up with the direction of flow of the high velocity air stream indicated by arrows a. Each duct 82 also has an open ended arm 88 coupled to compartment 80 so that its opening 90 (FIG. 2) allows air to enter the compartment. Air flows through ducts 82 into compartment 80 and then out the compartments exit 92 into chamber 64, which is attached to the compartment.
Chamber 64 is preferably a hollow, cylinder 96 made, for example, of a nonporous ceramic or other suitable heat resistant, insulating material. Front plate 98, integral with chamber 64, has circular opening 100 therein which has its center coincident with the longitudinal axis of chamber 64. Circular opening 100 has a diameter (11,) equal to about onehalf the chambers diameter (11,). The Chamber's length (1,) is slightly greater than the chambers diameter ((1,).
As best illustrated in FIGS. 5-7, the chambers rear plate 102 has a plurality of apertures 106 adjacent the plates periphery and a plurality of radial slits 108 between the plates periphery and center; Each slit 108 has a length (1,) equal to about one-sixth the diameter (11,) of chamber 64, and near each slit 108 is a blade I10 also having a length (I,,)-equal to about one-sixth the diameter ((1,) of chamber 64. Blades 110 are pitched at an angle of about 45 relative to the back 112 (FIG. 7) of rear plate 102, and they cover about one-half of the slit's opening. Apertures 106 and slits 108 are designed so that the ratio of air entering chamber 64 through the apertures to air entering chamber 64 through slits 108 is about l:l.Air from subassembly 70 rushes into chamber 64 via apertures I06 and slits 108, and blades I10 chop into this blast of air, causing it to swirl about violently and form a vortex within chamber 64. Air passing through apertures 106 confines this vortex within the central portion of chamber 64, and aids in keeping oil off inner wall 104 of chamber 64. Most of the air entering chamber 64 gushes from opening 100, but some strikes the inside of front plate 98 and recirculates. This recirculating air aids in keeping oil particles within chamber 64 until they are completely vaporized. We prefer to have plate 98 at a right angle relative wall 104 in order to maximize recirculation.
Fuel injecting and igniting subassembly 66, located securely within rear plate 102 at the plates center, includes support block 114 which carries nozzles 116, 118, and 120, and electrodes I22 and 124. Fuel line 126, which has three branches 128, I30, and 132, leading respectively into nozzles 116, 118, and 120, feeds oil into these nozzles. Nozzles 116, 118, and then spray oil into the vortex. Desirably, nozzles 116, I18, and 120 are tilted slightly inwardly so that a line passing through their respective orifices intersects the center of chamber 64. Aiming nozzles 116, 118, and 120 in this manner reduces the amount of oil spewed against inside wall 104 (FIG. 2) of chamber 64, and consequently, reduces the likelihood of smoking. A high voltage established between electrodes 122 and 124 causes a spark to flash across the gap between them. This spark ignites the whirlpool of oil and air in chamber 64, filling forward end of chamber 64 with flame 142 that shoots out opening 100.
We have found that in some instances recirculating air carries with it carbon that is deposited on porcelain holders 143 for electrodes I22 and 124. This shorts out electrodes 122 and 124. By providing shield means which surround fuel injecting and igniting assembly 66, this problem is avoided. The preferred form of shield means is a frustoconical member 144 welded to rear plate 102. The size of this memhers mouth 146 is carefully adjusted so that member 144 does not interfere with the oil spray, but will still protect assembly 66 against carbon deposits. Member 144 also helps maintain assembly 66 at a reasonably low temperature, so that this assembly is not damaged by overheating.
In operation. oil is fed into nozzle 120 continuously at a predetermined rate, whereas oil is fed to nozzles 116 and 118 intermittently under the control of thermostats 148 and 150 (FIG. I) located in crop dryer l4. Thermostats 148 and 150 control the operation of valves 152 and 154 (FIG. 4), which are respectively located in branch lines 128 and 130. When the temperature of grain l6 in contact with thermostats 148 and 150 falls below a predetermined level, the thermostats activated solenoids (not shown) which open valve 152 or valve 154 or both.
We have built three different size burners generally in accordance with the above disclosed design. Each burner provides smoke-free combustion; each burner employs a conventional, high velocity fan which generates a forward air pressure against the rear plate of about 3 inches of water; and each burner is used to dry crops which present a back pressure of about 2 inches of water (the back pressure normally encountered in drying crops). These burners meet the following specifications:
Burner 1 Burner 2 Burner 3 Chamber length, 1 inches- 8 10. 5 15. 5 Chamber diameter, dc, inches 6 8 12 Opening diameter, d, inches 3. 25 4. 3 6. 5 Total aperture opening, square 2 2. 9 4. 8 Total slit opening, square inches 2 2. 9 4. 8 Total open area in rear plate, square inches 4 5. 8 9. 6 Air velocity through chamber, cubic feet per minute -100 -23O -500 Temperature of chambers inner wall,
-1, 600 -1, 600 -1, 600 Firing rate, gallons per hour 3-9 7-21 15-45 Heat output, B.t.u. per hour (MM)... 0. 4-1. 3 1. -2. 9 2. 1-6. 3
Note, in all instances, the diameter of the opening in the front plate is about one-half the diameter of the cylinder. This appears to be one of the more important characteristics of our invention. If the front opening is too large, smoking occurs, and if it is too small, puffing or noisy sputtering occurs.
1. An oil burner comprising:
a cylindrical combustion chamber having an internal cylindrical surface defining a passageway through said chamber, said passageway terminating at one end as an air inlet and at the other end as an air outlet in the form of a restrictive circular opening;
said chamber having predetermined dimensions such that the ratio of chamber diameter to chamber length to opening diameter is about 222-321, preferably about 2:2.5: 1;
means for moving air through the passageway, including:
a. means for directing some of the moving air towards the air outlet opening along the center of the passageway and for swirling this air to establish within the passageway a vortex,
b. means for directing some of the moving air towards the air outlet opening along the internal surface of the chamber to establish within the passageway a barrier stream which aids in keeping oil off said surface, and
c. means "fBFHireEtin'g smae 'artie'anemia t3 the direction of movement of the barrier stream to establish within the passageway a recirculating air stream;
means for feeding oil into the vortex, whereby the vortex intimately mixes the oil and air, and the barrier air stream aids in confining this oil-air mixture to the central portion of the passageway; and
means for igniting the oil-air mixture, whereby the recirculating air stream aids in keeping combustion products within the passageway.
2. The burner defined in claim 1 including insulating means for maintaining the internal surface of said chamber at a temperature in excess of about 1400 F., preferably within the range of from about l600 F. to about 2000 F.
3. An oil burner comprising: a hollow, cylindrical chamber having front and rear plates; said front plate having therein a centrally located, circular opening which has a diameter equal to from about one-third to about two-thirds the diameter of the chamber;
said rear plate having therein aperture means adjacent the periphery of said rear plate, and radially extending slit means between the periphery of the rear plate and the center of the rear plate;
fuel injecting means mounted centrally within said rear plate for spraying oil into said chamber;
means adjacent said rear plate for rapidly moving air through said aperture means and slit means, into said chamber, and out said opening;
pitched blade means mounted on said rear plate adjacent said slit means for causing the air being moved through said chamber to swirl about and mix with the oil being sprayed into said chamber; and
means in said chamber for igniting the oil-air mixture.
4. The burner defined in claim 3 wherein the ratio of chamber diameter to chamber length to opening diameter is about 222-3: 1 preferably about 212.5:1.
5. The burner defined in claim 4 wherein the ratio of air entering said chamber through said aperture means to air entering said chamber through said slit means is about 1:1.
6. The burner defined in claim 5 wherein said chamber is insulated.
7. The burner defined in claim 5 wherein a frustoconical shield, attached to the inside of said rear plate, surrounds said fuel injecting means and said igniting means and prevents overheating said fuel injecting means and igniting means and buildup of carbon and the like on said igniting means.
8. The combination comprising:
a revolving fan having a hub and a plurality of vanes extending radially from said hub;
said vanes forcing air away from the hub and towards the periphery of the fan and generating a high velocity air stream which moves away from the fan along a line that intersects the plane through which the fan revolves;
a burner aligned opposite the hub on the same side of the fan as the air stream but out of said air stream, said burner having an air passageway therein through which air can pass; and
a plurality of tubular conduits between said burner and fan, each of said conduits having an open end terminating in the air stream and facing said fan so that air is intercepted and flows into said conduit, and another open end terminating near the air passageway in the burner so that intercepted air flows through each of said conduits and said burner.
9. Burner defined in claim 1 wherein the means for feeding oil into the vortex include a plurality of nozzles aligned to direct oil toward the center of the chamber, one of said nozzles injecting oil continuously and another of said nozzles injecting oil intermittently in response to thermostat control means.
10. Burner defined in claim 9 including means which surrounds said oil feeding and igniting means and prevents over; heating of said oil feeding and igniting means and buildup of carbon and the like on said igniting means.
11. The combination comprising:
a revolving fan having a hub and a plurality of vanes extending radially from said hub, said vanes forcing air away from the hub toward the periphery of the fan and generating a high velocity air stream which moves away from the fan along a line that intersects the plane through which the fan revolves;
an oil burner aligned opposite the hub on the same side of the fan as the air stream but out of said air stream, said burner including:
a. a cylindrical combustion chamber having an internal cylindrical surface defining an air passageway through b. means coupled to said chamber for directing some air which moves through the passageway toward the air outlet opening along the center of the passageway and for swirling this air to establish within the passageway a vortex,
c. means coupled to said chamber for directing some of the air which moves through the passageway toward the air outlet opening along the internal surface of the chamber to establish within said passageway a barrier stream which aids in keeping oil off said surface,
d. means coupled to said chamber for directing some of the air which moves through the passageway counter to the direction of movement of the barrier stream to establish within the passageway a recirculating air stream,
e. means for feeding oil into the vortex, whereby the vortex intimately mixes the oil and air, and the barrier stream aids in confining this o ii-air mixture through the central portion of the passageway, and
means for igniting the oil-air mixture, whereby the recirculating air stream aids in keeping combustion products within the passageway; and
a plurality of conduits between said burner and fan, each of said conduits having an open end terminating in the air stream and facing said fan so that air is interceptedand flows into each of said conduits, and another open end terminating near the air inlet end of said passageway so that intercepted air flows through each of said conduits and into said burner to supply air combustion.
12. A combination comprising: fan means for generating a high velocity air stream; oil burner means located at a position outside said air stream, said oil burner comprising:
a. a hollow, cylindrical chamber having front and rear plates,
b. said front plate having therein a centrally located, circular opening which has a diameter equal to from about one-third and two-thirds the diameter of the chamber,
c. said rear plate having therein aperture means adjacent the periphery of said rear plate, and radially extending slit means between the periphery of the rear plate and the center of the rear plate,
. fuel injecting means mounted centrally within said rear plate for spraying oil into said chamber,
. pitched blade means mounted on said rear plate adjacent said slit means for causing the air being moved through said chamber to swirl about and mix with the oil being sprayed into said chamber, and
. means in said chamber for igniting the oil-air mixture; and means which intercept a portion of the air stream and direct this air stream toward the rear plate of the burner so that the intercepted air is blown through the burner to provide the air of combustion.