US3481680A - Direct fired burner - Google Patents

Description

Dec. 2, 1969 H. M. KOHN 3,481,680

DIRECT FIRED'BURNER Filed Nov. 20, 1967 INVENTOR.

f/aeaser M. Aa/m/ United States Patent 3,481,680 DIRECT FIRED BURNER Herbert M. Kohn, Toledo, Ohio, assignor to Midland- Ross Corporation, Toledo, Ohio, a corporation of Ohio Filed Nov. 20, 1967, Ser. No. 684,319 Int. Cl. F23m 1/00, 4/00; F23d 15/00 US. Cl. 431-182 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a direct fired burner that provides a flame capable of spreading across the surface of a furnace wall. The burner is attached to a wall about, and coaxially with, an opening within the wall that defines a combustion chamber. The burner has a first cylindrical member defining a passageway that is confluent with the combustion chamber and into which fuel is introduced axially. Air -is introduced into this passageway tangentially to impart a stable flame thereto. Disposed about the first cylindrical member is a second cylindrical member forming an annular plenum therebetween into which air is introduced tangentially. The plenum is in confluent relationship with the combustion chamber and air flows therefrom into the combustion chamber with a spinning act-ion. When air from the plenum meets the ignited fuel emerging from the passageway at the entrance of the combustion chamber, the airfuel mixture tends to hug the walls of the combustion chamber as they emerge therefrom due to the effect of the spinning gas flows.

In heat treating operations, it is often desirable to uniformly disperse flame from a burner so that heat may be extended over a large surface area. By so doing, a large quantity of heat may be applied without too great an amount of heat being concentrated in one area, thus tending to eliminate damaging high temperatures. An example of applications where a spreading flame is desirable is the heat treating of metal sheets in coil annealing furnaces. One way that heat has been provided over a large area in the past is to fire burners through the furnace end walls into radiant elements located along the length of the furnace. This method does not give the degree of flexibility in controlling or changing the heat pattern along the furnace length that is needed. Also,the radiant elements are expensive and have to be periodically replaced because of bum-out problems. This involves considerable maintenance and furnace down time. Consequently, it would be beneficial to have a small number of burners capable of providing relative uniform heat across a large expanse.

It is, therefore, an object of this invention to provide a burner capable of spreading a flame across a large area.

It is another object of this invention to provide a furnace with a burner having spinning gas streams that spread the flame issuing therefrom across a large surface of the furnace.

It is still another object of this invention to provide means for radiantly heating work using a combustion burner.

It is a further object of this invention to provide a burner that requires no premix pilot and yields a spreading flame at a lower air pressure drop.

In the drawings:

FIG. 1 shows a cross sectional, elevational view of a burner encompassing the features of the instant invention.

FIG. 2 is a view taken along the lines 22 of FIG. 1.

Referring now to the drawing, a burner is shown generally at and includes part of a furnace wall 12 having an opening 14 therein. Refractory material 16 is received within the opening 14 and defines a cylindrical combustion chamber 17. The refractory material 16 has a curved surface 18 formed at one end thereof adjacent the inner surface 19 of the furnace wall 12. An annular orifice plate 20 is secured to the refractory material 16, as by bolts 22, about the chamber 17. The bolts 22 are received by a collar 23 that is welded to the furnace wall 12. Secured to the orifice plate 20 is a first cylindrical member 24 that is disposed coaxially with the combustion chamber 17. Received within the cylindrical member 24 is a second cylindrical member 28 that forms a plenum 29 between the two cylinders. The second cylindrical member defines a passageway 31. The diameter of the first member 24 is larger than the diameter of the combustion chamber 17 and the diameter of the second member is smaller, thereby defining a shoulder 33. Between the second cylindrical member 28 and the shoulder 33 an orifice is formed that provides a confluent relationship between the plenum 29 and the combustion chamber 17.

Secured to the back end of the first and second cylindrical members 24 and 28 is an annular back plate 30 having a central opening 32 therein. The back plate 30 partially encloses the plenum 29 and passageway 31. A fuel pipe 34 is received within the central opening 32 and is coaxial with the passageway 31. A plate 36 having a central opening 38 is secured to the inside end of the fuel pipe 34.

The first cylindrical member 24 has an opening 40 therein that receives a generally radially extending air pipe 42. The air pipe 42 has a converging portion 44 that directs air tangentially into the plenum 29 at a slight positive pressure. The second cylindrical member 28 has a plurality of circumferentially disposed radial apertures 46 therein so that a portion of the air received within the plenum 29 flows radially into the passageway 31. At the upstream end of the annular member 28, a pair of tangential air inlets 50 is secured within the walls of the member to provide a supply of spinning air to the passageway 31, the air flowing through the inlet pipes 50 from the plenum 29.

The back plate 30 has a second opening 52 therein, which opening receives a spark plug 54. The spark plug 54 serves to ignite the fuel supplied from the pipe 34 and air coming from the tangential air inlet 50, only a small percentage of the total air required for combustion being provided by the tangential air inlet pipes. A spinning air stream is thus formed that circumposes the axially flowing fuel stream emitted into the passageway through the fuel pipe 34. The combustible mixture of fuel and air formed at the interface of the spinning air stream and the axially flowing fuel stream is ignited by the spark plug 54 to establish a spinning, slow mixing, stable flame. The air entering apertures 46 produces a back eddy current that promotes stable burning with maximum mixing.

The air directed into the plenum 29 from the air pipe 42 spins within the plenum as a result of the converging portion 44. The spin imparts a centrifugal force to the air, which force causes the bulk of the air to flow in close proximity to the cylindrical member 24, which is the outer wall of the plenum 29. As the air thus spins, it tends to form a helix, while traveling along the plenum 29. If the air were to enter the combustion chamber 17 with a helical pattern, it would create a condition of fluctuating temperature resulting from non-uniform combustion. To eliminate this problem, a restriction, in the form of the shoulder 33, is provided that causes a pressure drop as the air flows through the orifice 35.

It has been found advantageous to have the restricting member, shoulder 33, adjacent the outside wall of the plenum 29 so that the air flows into the chamber 17 along the second cylindrical member 28, or inside wall of the plenum 29. It has been found that a much higher pressure drop is required to disrupt the helical pattern when the orifice 35 is located adjacent the outside wall of the plenum 29. The reason for this is believed to be that the shoulder 33 causes the spinning air that is traveling along the outside wall of plenum 29, due to the centrifugal force, to turn at a right angle before it enters the chamber 17 when the shoulder 33 is adjacent the outside wall of the plenum. This abrupt turn tends to break up, or distort, the helical pattern, and thus requires a reduced pressure drop than if the orifice 35 were located adjacent the outside wall of plenum 29.

As the air spins along the length of the plenum 29, it enters the combustion chamber 17 through the orifice 35 located between the second cylindrical member 28 and the shoulder 33. This combination forms a vena contracta that will tend to cause the resulting mixture of fuel and air to expanded as it enters the combustion chamber 17. This expansion and the effect of the spinning gases tend to keep the flame close to the wall of the combustion chamber 17. As the air and fuel mixture passes through the combustion chamber 17 and across the curved portion 18, the tendency to keep on the wall continues beyond the curved portion so that the exiting flame tends to cling to the furnace wall inner surface 19.

The burner shown and described has two distinct advantages over prior burners in that no premix pilots are required and the spreading flame is obtained at a lower air pressure drop. The need for a premix pilot is obviated by the presence of the spinning air stream that is provided by the tangential air inlets 50. This air stream yields a stable flame after initial ignition by the spark plug 54.

In the prior practice, spinning air is achieved by a pressure drop across specifically shaped orifice plates, for example, half moon shaped openings. The need for such specifically shaped orifices is eliminated in the burner of this invention because the air is introduced tangentially by the conveying portion 44 of the air pipe 42. This spinning air, along with the location of the orifice 35 as previously described, reduces the air pressure requirements.

Thus, a burner having high capacity can be provided to yield a large quantity of heat over a substantial area so that a large quantity of heat may be provided to the work being heat treated without raising the temperature of the work to a point where damage would result therefrom. The heat supplied to the work is in the form of radiant heat for the flame heats the refractory wall, which in turn radiantly heats the Work. With the burner 10, there is no direct impingement of the flame upon the work; consequently, no discoloration or other damaging effects are imparted to the work.

Although only a single embodiment of this invention has been shown and described, it is understood that changes and modifications can be made therein, and this description is illustrative only and not for the purpose of rendering this invention limited to the details illustrated or described except insofar as they are limited by the terms of the following claims.

I claim:

1. In an industrial gas burner, a wall member defining a combustion chamber having spaced, open ends, a housing having a first right cylindrical member, means for securing said first cylindrical member substantially normally to one end of said wall member in coaxial alignment with said chamber, a second cylindrical member coaxially disposed within said first member to define a plenum therebetween, said plenum being confluent with said combustion chamber, said first cylindrical member having a larger diameter than said combustion chamber and said second cylindrical member having a smaller diameter than said combustion chamber, thereby defining a restriction means where said plenum and said combustion chamber are confluent, means for supplying fuel axially to said second member, means for supplying air tangentially to said second member, and means for supplying air tangentially to said plenum.

2. The burner of claim 1 wherein the end of the combustion chamber opposed to the housing has outwardly curved surfaces.

3. In an industrial burner, the combination comprising: a furnace wall having a cylindrical opening therein, a right cylindrical housing, means for securing said housing substantially normally to a first side of said furnace wall coaxially with the opening, said housing having a larger diameter than the opening, thereby defining a shoulder about the opening, a cylindrical sleeve received within said housing and having a diameter smaller than the opening to form an orifice in cooperation with the shoulder, said housing and said sleeve defining a plenum therebetween, means for supplying air tangentially to said plenum, means for supplying a combustible fuel to said sleeve, means for introducing air tangentially to said sleeve, and means for igniting the air-fuel mixture in said sleeve.

References Cited UNITED STATES PATENTS 2,952,307 9/1960 Schramm et al 43 l18 3,187,799 6/1965 Nesbitt 431-9 3,267,984 8/1966 Reed et al 431 EDWARD G. FAVORS, Primary Examiner

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