US2952307A - Burner apparatus - Google Patents

Description

Sept' 13 1960 l H. w. scHRAMM ETALA 2,952,307

BURNER APEARATUS Filed oct. 26,1955

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nited States Patent() BURNER APPARATUS Henry W. Schramm and Chester Cipriani, Toledo, Ohio, assignors, by mesne assignments, to Midland-Ross Corporation, Cleveland, Ohio, a corporation of Ohio Filed oct. 26, 195s, ser. No. 542,9 2s -2 claims. (cl. rss- 7) This invention pertains to burning of combustible fuel and has particular application to apparatus for'burning fuel with which a large temperature variation may be attained.

There are a large number of applications for such apparatus. A typical example of this is a batch type furnace in which Work is to be hardened and then drawn. The first operation may require a furnace temperature of l700 F. and the latter, a temperature of' 700 F. Unless the single furnace has burner'equipment capable of properly operating at and maintaining both of. these temperatures, two separate furnaces must be employed.

A large temperature Variation has been previously attempted with a variety of apparatus. For instance, two or more separately controllable sets of burners have been employed. All sets of burners would be used when high temperatures were desired and one or more setswould then be turned off when lower temperatures were to be maintained. This system, although relatively inexible, worked reasonably well but resulted in a higher first cost for such furnace installations due to the extra number of burners necessary. Theextra burners also resultin extra controls, extra fuel, additional piping, and additional space. Also, these burners did not create comparatively large temperature ranges in the furnace chamber even when several sets of burners were employed.

As an alternate to this system, a single set of larger combustible air-gas mixture would be fed directly into the furnace chamber with an explosion hazard resulting. This is not a danger at higher temperatures, labove 1400" F., since the tunnel walls of the burner will be maintained, Idue to heat from the furnace chamber, at temperatures that will ignite the air-gas mixture on contact if the pilot is extinguished.

A third means of attaining a large temperature range in a furnace chamber was by variation of the firing rate of the burners in place of operating them in an on-oif manner. However, such burners must have a very large range of turndown to fire properly at the Very low tiring rates required for low furnace temperatures. Burners are designed to tire at certain capacities, however, and will only operate properly within certain variations from this capacity, most burners having a turndown range of less than 4 to l. To produce a temperature range in a furnace of, for example 700 F. to 1700" F., a much larger range of turndown is required.

In such cases, at the required very low rates of firing, the volume of air and gas passing through the burner nozzle is reduced and the velocity thereof is likewise decreased. However, the rate of flame propagation will be constant with the result that, as the velocity of the air-gas mixture is decreased, the flame moves back through the nozzle. The velocity of flowback of the nozzle is, of course, less than that through the nozzle burners has been used in place of the above and are operated at their full firing rate at higher temperatures and in an on-ol manner at lower temperatures. Howeverg such burners are incapable of maintaining a steady temperature particularly below 1000 F. when controlled by a thermocouple and temperature control instrument. v

With this system, the burners `are turned oi when the temperature of the chamber slightly exceeds the control tempera-ture and are likewise turned on when the temperature falls slightly below this control temperature. However, the heating elect from the burners continues, at these lower temperatures, to raise the temperature of the chamber even after the burners are shut olf with the result that the control temperature is overridden and large temperature variations occur-the lower the temperature desired to be maintained, the larger the variation in temperature actually attained. During the period the burners are not firing temperature differences within the chamber also result due to lack of circulation. -This will be more fully discussed subsequently. Furthermore,

with the result that the ilame, once having penetrated back through the nozzle, spreads quickly through the remaining air-gas mixture up to the point where the air and gas are combined. This explosion, or backring, may damage the apparatus, particularly if there is a large volume of the air-gas` mixture. Even without damage occurring, there is danger involved since the explosion generally extinguishes the ame with the result that the subsequent unignited mixture is emitted intothe furnace chamber.

Topovercome this, a burner may be supplied mixture through separate air and gas conduits whose outlets lie behind, and adjacent to, the nozzle. Any backring occurring here, then, merely extends to this point of mixing with very little ignitable volume involved. A small backiring occurring here, however, is still suicient to extinguish the flame which again results in the mixture being fed, unignited, into the furnace chamber. If backring will not extinguish the flame, an unstable llame front may nevertheless occur thatcauses ineiiicient combustion and generally unsatisfactory operation of the burner. i Furthermore, particularly in burners of this nozzle mixing type, the air-gas mixture is very diicult to proportion at very low tiring rates. Thus the correct stoichiometric mixture to give complete combustionjfor these burners generally rely on pilots for ignition when turned on, and should the pilots be extinguished, the

In View of the aforementioned difliculties and manyl others, a burner` and method ofnoperation have beendeveloped that will operate effectively at full rates and Very low rates of liring with none of these problems. Furthermore, this burner is capable of producing a temperattire range in a furnace chamber of 400 to 2400 F. c I

For further consideration of what is novel and our in,-

Patented Sept. 13, 1960,

Vention, reference is made to the accompanying drawing, subsequent specification, and claims.

In the drawing:

Figure 1 is a partially sectional end view of apparatus embodying our invention, and

Figure 2 is a side View shown partially in section as taken on line 2-2 of Figure l.

The burner of Figure 2 comprises a tunnel block 11 and a holder 12 attached to burner body 13. Tunnel block 11 is of refractory composition and square configuration with a cylindrical tunnel chamber 14 extending longitudinally therethrough. The portion nearer the holder 12 is offset to accommodate the holder which is generally made of cast steel and is adapted to be installed in a furnace wall and fastened to the outer casing thereof by means of bolts through bolt holes 15. Burner body 13 is attached to holder 12 by means of bolts 16 extending through bolt holes 17 land 18, located in body 13 and holder 12 respectively, and so positioned that the body is properly aligned with respect to cylindrical chamber 14.

Burner body 13 has cast portions 20` and 21 united by bolts 22 extending through bolt holes 23 and into tapped holes 24. This forms a cylindrical chamber 25 and a sharply tapered chamber 26 that tapers toward tunnel chamber 14. It also forms a smaller cylindrical chamber 27 that extends slightly into tunnel chamber 14 and an air inlet passage 28 which tapers outwardly from chamber 25. Air volume to this inlet is controlled by oriiice plate 29.

Cast portion, or rear wall, 20` has -a fuel port 30` drilled through it in `axial alignment with chamber 25, tapered chamber 26, small chamber 27, and tunnel chamber 14. A fuel nozzle 31 is axially aligned with this port 30 and threaded thereinto 4by means of fitting 32. A frustoconical chamber 33 is formed around nozzle 31 by wall 34 which is integrally connected with portion 20. Wall 34 has four equally spaced yair ports 39 drilled therein. In addition, it is suitably lthreaded yat its outer portion to receive tube 35 which is axially aligned with nozzle 31 and extends into tunnel chamber 14 past small chamber 27.

Fuel port 30 is supplied fuel through pipe nipple 36, T 37, and pipe 38 which lead to a source of fuel (not shown). A Valve 40 is disposed in pipe 38 to control fuel flow therethrough; it is an electrically-operated, motor-driven valve in the preferred form of application. T 37 contains a plug 41 at its unused outlet which is periodically removed and a brush or other suitable cleaning means is extended thereinto to clean port 30 and nozzle 31 in which carbon and impurities in the fuel may gradually -be deposited.

Three tapped holes 42, 42a, and 42h are provided in portion 20. The axes of these holes intersect the superimposed axes of port 30, nozzle 31, tube 35, and the various chambers at some point within tube 35. A commercially available flame rod safety device may be placed in one of these holes to shut olf a valve upstream of valve 40 should the flame in tube 35 become extinguished. A sight glass may be installed in the second hole to permit limited observation of the internal operation. In the third hole, an ignition means may be placed to initially light the fuel-air mixture.

A movable air vane 43, which is somewhat similar to one in a Patent Number 1,943,590 to Carroll Cone, may be placed at the entrance of air inlet passage 28 into chamber 25, and directs the air in a tangential or radial direction into chamber 25. The vane consists of a metal sheet 44 rotatably attached to `a pin 45 which is horizontally disposed in chamber 25, parallel to the axis thereof, yand secured -at its ends to portions 20 and 21. A threaded shank 46, having a knurled head 47, extends through a tapped hole 48 in portion 21 and is rotatably secured to Vane 44.

When an electrically-operated, motordriven valve 40 is employed in fuel pipe 38, it is controlled by a temperature controller 50` through line 51. This controller 50 is responsive to temperature in furnace chamber 52 by a thermocouple or temperature bulb 53 which extends through the furnace wall as represented by dotted line 54.

In operation, air is supplied through inlet 28 with the majority flowing through tapered chamber 26, small chamber 27, and into tunnel chamber 14. A smaller portion of this air enters air ports 39 to subsequently mix with a portion of the fuel emitting from nozzle 31. The Iair entering ports 39 is sucient to create a combustible mixture with a portion of the aforementioned fuel when ignited. This burning mixture, along with the raw fuel, passes out of tube 35 where the unignited fuel mixes with the additional air, forms a combustible mixture, and is ignited by the former burning mixture. When the burner is firing at its full capacity, orifice plate 29 is sized to allow entry of sufficient air .to form -a stoichiometric mixture with the fuel that permits complete combustion with no residual air resulting. This is the preferred method of operation with air being turned on and olf by a valve upstream of the orice. The burner will thus oper-ate at stoichiometric proportions of fuel and air as long as it is operating at capacity which will be maintained until the temperature of the furnace chamber reaches that desired. At this point, temperature controller 50 will tend to close valve 40. An excessive `amount of air will then be supplied to the burner for the amount of fuel input and this excess will increase for lower furnace temperatures where the fuel input is further decreased. However, the burner will still operate efficiently and with a positive, stable ame for any air-fuel ratio that may be created. This is achieved for two principal reasons: The llame emitting from tube 35 forms Ia constant point for ignition of the air and unburned fuel that initially mix at this point; this helps assure a stable flame front. Secondly, the air and fuel emerging from separate points tend to mix slowly enough to prevent excesive dilution of the fuel in the air before ignition can occur and thus form an unignitable mixture. This is true regardless of the amount of excess air encountered since, upon emission from tube 35, the combination fuel and burning mixture immediately begin to m-ix With the air, with additional combustion occurring constantly. Such mixing prohibits excessive dilution since this additional burning constantly occurs as soon as a portion of the unburned fuel mixes with sucient air to support combustion. Furthermore, .the raw fuel in tube 35 is heated by the ignited portion of fuel and air therein. This heated fuel then tends to expand as it emits from the relatively conned volume defined by tube 35. The expansion hastens mixing of the fuel and air suiciently to prevent the possibility of excessive air from lowering the tempera-ture of the air-fuel mixture to the point where the llame will be extinguished.

When very low temperatures of approximately 400 to 600 F. are desired in `the furnace, the fuel supplied will be decreased to a point where all the fuel is burned with the air entering ports 39 and no burning occurs in tunnel chamber 14. Again, there is a stable flame produced with efcient burning. This occurs because the air entering ports 39 is directed toward the rear of chamber 33 `to prevent -any possibility of its velocity blowing off the flame. The -air will thus properly support cornbustion for even the smallest amount of fuel emitting from nozzle 31, and, of course, for higher rates of fuel ow the uucombusted fuel is combusted with the air emitting from small chamber 27. Therefore, it may be seen that eicient combustion and a stable, positive flame occurs for any rate of fuel flow.

The use of excess air at all but full firing rates has several advantages, particularly for lower furnace temperatures. This air, upon leaving chamber 27, mixes with the products of combustion and thus decreases their temperature which permits an even lower furnace tempei-rature to be attained. Of more importance, however,

is the fact that this air circulates the heat through the furnace chamber and thus aifords greater heat distribution than otherwise possible. If the burner, at low rates of firing, Were to operate with no excess air, this heat, due to lack of volume for circulation, would tend to be limited to -a relatively hot area adjacent the burner. At full rates of tiring, the volume of products of combustion are large enough to supply the necessary circulation -but for lesser firing rates the excess air must provide this. Furthermore, vthe-use of excess air permits the furnace pressure to be maintained above ambient whereas normally with low ring rates, the volume of combusted products is insufficient to effectively provide such pressure. Without this positive furnace pressure, relatively cool, ambient air tends to enter through various furnace openings such las at charge and .discharge ports. This, of course, develops areas of cooler temperatures which further vary temperature distribution.

Additional versatility is provided in our invention due to vane 43. Sheet 44 of the vane may be moved from the position shown in Figure 1 to a middle position in inlet passage 28. In the former position, all the air enters chamber 26 tangentially and is thereby spun around tube 35 and Wall 34. 'I'his air, still spinning, is pushed out through tapered chamber 26 and small chamber 27 into tunnel chamber 14 where it mixes with unburned fuel from tube 35. The total mixture of fuel, air, and combusted products is thereby spun and, as it emits from the contines of tunnel chamber 14, expands both forward and radially, the exact direction depending on the degree of spin imparted to the mixture. This flame emitting from tunnel chamber 14 thus appears as a cone, the apex `angle of which varies With the spin as heretofore mentioned. Such `a flame conliguration is useful in a variety of applications las, for instance, where work being heat treated is situated `in front of the burner and it is desirable for the burner flame not to impinge this work.

For lower firing rates, of course, the flame will not extend beyond the chamber 14, but the hot mixture of combusted products and air will do so and spinning in this case helps create greater heat distribution.

In the latter position of sheet 44, `air enters chamber 25 substantially equally on 4both sides of tube 35. Tendency to spin iis thus counter-acted and the air moves through tapered chamber 26, small chamber 27, and tunnel chamber 14 in substantially straight flow. This air mixes more slowly with the fuel and products of combustion from tube 35 and results in a somewhat longer llame. Furthermore, this flame tends to emit straight outward from tunnel chamber 14 in an axial direction which results in a long, directional flame that likewise has various applications, as where the burners are placed below or above the work being heat treated.

Vane 43 is adjusted by screwing threaded shank 46 in or out by turning knurled knob 47. Once this vane is adjusted, it is seldom necessary to move it unless the physical conditions under which the burner is operated vary.

Typical data showing the range of turndown and the variation in flame length when using oil for fuel are presented below:

Air Input, OilInEut, Air Pres- Oil Pres- Flame c.f.h. g.p. sure, Oz. sure,p.s.i. Air Direction Length,

S.I. Feet 10. 60 9. 8 75. 0 Straight.-." 9 10. 60 9. 8 75. O Spinning 6 8. 48 9. 8 48. 0 Straight 9 8.48 9.8 48. 4 6. 35 9. 8 27. 5 8 6. 35 9. 8 27. 5 3 4. 24 9. 8 13.0 4 4. 24 9. 8 13. 0 2 2. 12 9. 8 3. 4 Straight 1 2.12 9.8 3. 4 Spinning--- 0. 8 0. 706 9. 8 0. 42 Straight.- (l) 0. 706 9. 8 0. 42 Spinning-.- (1) 1 Flame within tunnel.

- aresasoi For gas fuel, the burner is evenrmore eifective as evident in the 'following representative data:

. Gas Pres- .Air Input, Gas Air Pressure, Flame c.i.h. Input, sure Oz. Inches of Air Direction Length,

c fn si. Water Feet 1500 11. 0 0. 6 Straight... 8. 5 1500 11. 0 0. 6 Spinning--.. 3 1200 11. 0 0. 4 Straight-.-" 8 1200 11.0 0. 4 Spinning 2 900 11. 0 0. 3 Straight. 4 900 11. 0 0. 3 2 600 11.0 0.15 3 600 11. 0 0. 15 Spinning 1. 5 300 1l. 0 0. 08 Straight 2 300 11. 0 0. 08 Spinnjng 1 11. 0 0.05 Straight---. (4)

25 11. 0 (l) Spinning- (3) Inches of Water 3000.- 300 5. 0 (4) Straight.-. 3 300 5. 0 (4) Spinning- 8 250 5. 0 (4) Straight-.." 2. 5 250 5.0 (4) Spinning 7" 200 5.0 (4) Straight 2. 5 200 5. 0 (4) Spinning 6 5.0 (4) Straight--." 2 150 5. O (4) Spinning 6" 100 6. 0 (4) Straight. l. 5 100 5.0 (4) Spinning 6 50 5. O (4) Straight- 6 50 5. 0 (4) Spinning 4" 5 5. 0 (4) Straight (2) 5 5. 0 (4) Spinning.- (2) 1 Not measurable.

2 Flame within tunnel.

a Flame within inner tube. 4 Not measured.

It may be seen then, that the versatility of our burner is extended not only over a large range ofy temperatures, but also over a variety of ilame lengths and flame shapes, the latter ranging from linear to conical.

It may be noted here that whether air enters chamber 25 radially or tangentially, the volume of air entering ports 39 is not substantially varied. This is true since, regardless of the :mode of air entry, pressure in chamber 25 remains relatively constant due to the restriction afforded by tapered chamber 26 and small chamber 27, and thus forces a relatively constant volume through ports 39.

The foregoing disclosure is the best mode known to the inventors of carrying out this invention, the scope of which is limited only by the appended claims.

We claim:

1. Burner apparatus for burning fuel at a wide range of inputs in a furnace chamber comprising: a refractory lblock containing a cylindrical tunnel chamber extending longitudinally therethrough; a holder lfor attaching said block to a wall of said furnace; iirst Wall means attached to said holder and forming a small cylindrical chamber extending into said tunnel chamber, a tapered chamber With the smaller end thereof meeting the end of the smaller cylindrical chamber away from said tunnel chamber, and a larger cylindrical chamber with one end thereof meeting the larger end of said tapered chamber, the three chambers being substantially axially aligned with said tunnel chamber; rear wall means forming a closed end for said large cylindrical chamber at the other end thereof; an air inlet to said large cylindrical chamber located at one side thereof; nozzle means extending into said large cylindrical chamber, in substantially axial alignment with, and directed toward, said tunnel chamber; pipe means connecting a source of fuel to said nozzle means; and second wall means forming a cylindrical combustion chamber extending from said rear wall means, around said nozzle means, and into said tunnel chamber, said combustion chamber being in substantially axial alignment with said tunnel chamber and forming a series of equally spaced air ports for emitting air from said large cylindrical chamber substantially radially to said combustion chamber at a point upstream of the outlet of said nozzle means, and said small cylindrical chamber forming a restricted annular passage with said second wall means for the passage of air therethrough from said air inlet and said large cylindrical combustion chamber.

2. Apparatus according to claim 1 characterized by an electrically operated valve in said pipe means, and control means responsive to the temperature of the furnace chamber for operating said valve to vary the rate of gas ow therethrough, said air inlet containing a constant re- 10 striction whereby the ow of air therethrough will remain unchanged.

References Cited in the le of this patent UNITED STATES PATENTS Kemp Oct. 13, 1903 Cone Apr. 3, 1934 Bloom May 17, 1938 Naab et al. July 25, 1939 Maienshein Jan. 10, 1950 FOREIGN PATENTS Great Britain Nov. 24, 1937

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