US2965167A - Low velocity gas burner - Google Patents

Description

- "in. ad I Dec. 20, 1960 Filed Dec. 2, 1958 D. A. CAMPBELL LOW VELOCITY GAS BURNER 2 Sheets-Sheet 1 INvaN-roa DONALD A.CAMPBELL Dec. 20, 1960 D. A. CAMPBELL LOW VELOCITY GAS BURNER 2 Sheets-Sheet 2 Filed Dec. 2, 1958 INvEN'roR DONALD A.CAMPBELL L'OW VELOCITY GAS BURNER Donald A. Campbell, Rockford, Ill., assignor to llclipse Fuel Engineering (30., Rockford, 111., a corporation of Illinois Filed Dec. 2, 1958, Ser. No. 777,704

8 Claims. (Cl. 158-113) The present invention relates to gas burners and has particular reference to a gas burner of novel design capable of producing a low velocity flame of wide expanse wherein the flame is developed within a comparatively short combustion zone.

There are many industrial applications in which it is desirable to develop a large expanse of radiant surface which may be directed toward an item to be heated and from which surface the flow of combustion gases are at a low velocity. For example, in glass annealing furnaces it is necessary to uniformly heat a large area of glass with no localized heating or hot spots resulting from flame impingement. The burner requirements for such furnaces therefore are the production of a flame of large expanse which may be directed against the work in close proximity thereto, uniformity of flame temperature throughout the entire flame area, minimum turbulence within the flame structure, and low forward velocity of the products of combustion. Large flame expanse is obviously necessary in a single burner furnace. Uniformity of temperatuer must be maintained to prevent localized heating of the work. Minimum turbulence is desirable since any form of flame turbulence, once initiated within a flame structure cannot be controlled and the presence of turbulence is apt to creat uncontrollable eddy currents and localized heating by convection. Low forward velocity is a requirement for substantially the same reason and for the additional reason that with a high forward velocity flame length is increased at the expense of accurate heat control in the vicinity of the work.

Burners constructed in conformity with the above requirements may find wide industrial application other than for the annealing of glass, as for example in the heating of galvanizing kettles, for firing melting furnaces, flat roof rotary heat treatment furnaces, billet heaters, cover fired ladles, process tubing heaters and a wide variety of other installations too numerous to mention. For an all purpose low velocity, flat flame combustion type burner of the type set forth above, vertical firing in either direction, horizontal firing, or firing at any inbetween angle is a further consideration that must be borne in mind.

The above industrial requirements for large area surface heating are readily and conveniently met by the use of radiant electric heaters and, where electric power is available at moderate cost, many such heaters are employed. The use of electrically generated radiant heat naturally suggests the use of radiant heat in connection with combustion heating for the same purpose, since the uniformity of heat which is generated by radiant energy is too well known to need discussion. By constructing a combustion burner which depends to a large extent upon the generation of radiant heat by a radiant element after absorption of heat by that element from combustion gases by a process of convection, the work undergoing treatment may be spared the consequences of contates Patent ice vection heating, for example localized heating and poor heat control and, in some instances, undue oxidation.

There are on the market and in current use burners which meet the above outlined large area, low velocity flame requirements and which furthermore depend for their efficiency upon a large measure of radiant heat being generated. Many of these burners consist of concave refractory shapes of cup-shape configuration through which premixed gas and air is deliveerd for combustion purposes and then deflected along the inside walls of the refractory cup. Such burners require some method of premixing the gas and air, as for example the use of a fuel proportioning apparatus, and they are subject to fre quent backfiring.

The present invention is designed to overcome the above-noted limitations that are attendant upon the use of such burners which use premixed gaseous constitutents for combustion purposes and, toward this end, briefly, it contemplates the provision of a burner assembly in cluding a relatively simple burner casting of novel design capable of developing a highly radiant surface by means of gas combustion and incorporating the advantages of a nozzle burner in that it has a wider range of heating capacity, is not subject to backfiring, and is extremely simple to control. The provision of a burner construction of this type is an important object of the present invention and, in carrying out this object, the invention contemplates the provision of a burner casting having separate gas and air passages and arranged to deliver the gas and air at the outside circumference of a generally circular refractory or other radiant eement. Small streams or jets of the gas and air are delivered to each of a series of circumferentially arranged spaced localized combustion regions and provision is made for causing the gas and air to interrnix at or near the periphery of the radiant element with the products of combustion sweeping across the front face of the radiant element so that the latter will absorb heat therefrom for subsequent radiation forwardly against the work. Mixing and com bustion takes place at or close to the surface of the refractory or other radiant element and provision is made whereby the combustion gases, during and after combustion, assume a circular motion which is conducive toward intimate mixing and substantially complete dissipation of heat with an extremely small component of forward motion. Stated in other words, the necessary turbulence for intimate mixing of the gas and air and consequent complete combustion is directed in a circular path rather than in an axial path so that an extremely short flame characteristic is attained.

For a better understanding of the invention, its advantages, and specific objects attained with its use, reference may be had to the accompanying two sheets of drawings and the following descriptive matter wherein a preferred embodiment of the present burner has been shown and described.

in these drawings:

Fig. l is a front elevational view of a burner assembly constructed in accordance with the principles of the present invention;

Fig. 2 is a sectional view taken substantially along the line 2-2. of Fig. l and schematically illustrating certain flame and radiant heat characteristics which are associated with the use of the present burner; and

Fig. 3 is a fragmentary rear elevationalview of a limited portion or sector of the burner assembly. 7 7

Referring now to the drawings in detail, the burner assembly of the form of the invention selected for illustration herein involves in its general organization a main burner casting N9 of generally cylindrical design and or dished or cup-shaped external configuration. The can: ing is provided with a flat circular rear wall'1'2,'a'stepped,

dished cup-shaped front wall 14 and an interconnecting generally cylindrical outer wall 16 having a special shapecharacteristic which will be described presently. The three walls 12, 14 and 16 define an internal space or chamber which is divided into an air chamber 18 and a gas chamber 20 by means of a cup-shaped intermediate partition wall 22, the circular rim of which is joined to the front wall 16. A circular web or boss 24 connects the rear and intermediate walls 22 at the central regions thereof and communicates with a threaded inlet opening 24 designed for threaded reception therein of one end of a gas supply pipe 26 whereby gas may be admitted to the interior of the chamber 20. The rear wall 12 is formed with an opening 28 in the peripheral regions thereof having a thickened boss portion 30 which may be tapped as at 32 (Fig. 2) for reception of the clamping screws 34 by means of which a bolting flange 36 associated with a suitable pipe fitting 38 may be secured in position over the opening 28. The fitting 38 is designed for connection to a suitable air supply pipe (not shown) whereby air may be introduced into the interior of the chamber 18.

The front wall 14 is of circular stepped, dished configuration and includes an extreme forward annular Wall section 40, an intermediate annular wall section 42, and a rear inside or bottom section 44. A cylindrical wall section 46 connects the sections 40 and 42, while a similar cylindrical wall section 48 connects the wall sections 42 and 44. The steps of the front wall 12 thus provide a shallow circular depression, of which the wall portion 42 and the wall portion 44 constitute the bottom wall.

The cylindrical outer wall 16 is formed with a radial flange 50 intermediate its ends. The flange 50 has secured thereto by means of bolts 52 a ring member 54 by means of which the burner as a whole may be operatively secured to a furnace wall, such as the wall shown at 56 with the burner projecting through a furnace opening 58 provided in the wall, clamping bolt 60 being employed for securing purposes.

Suitably secured, as 'by cementing, within the dished, cup-shaped front wall 14 of the burner casting is a radiant element 62. This element may, according to the present invention be formed of various materials capable of heat absorption and radiation, as for example a refractory or ceramic material, asbestos block, metal alloy, etc. In the illustrated form of the invention the element 62 is formed of a refractory material and is generally of mushroom configuration and is formed with a short stem portion 64 and a crown portion 66 preferably, but not necessarily, presenting a convex forward or outer face 68. The stem portion 64 of the radiant element 62 seats within the bottom region of the front wall 14 and the rim region of the crown portion 66 seats on the annular wall 42. The crown apex may project a slight distance forwardly of the plane of the forward annular wall or face 40 of the burner casting. The crown portion 66 of the radiant element 62 is provided with a short cylindrical outer face 70 which is spaced inwardly a slight distance from the cylindrical wall section 46, thus defining an annular pocket 72 in the forward face of the burner structure, considered as a whole. The pocket immediately surrounds the convex face 68 of the element 62.

Extending around the forward end of the burner casting is a refractory or radiant ring or combustion block 80 which may be formed of the same material as that of the element 62, and which seats within the space existing between the cylindrical wall 16 and a forwardly extending circular flange 82 provided on the ring member 54. The radiant or refractory ring overhangs the front annular wall 40 of the burner casting 10 and is formed with a forwardly and outwardly flared frusto-conical surface 84, the slant angle of which may be in the neighborhood of 45? although the specific angle selected is not critical,

and the slant height of which is relatively short. The

the longitudinal axis of the burner casting it). The small base of the cone frustum defining the surface 84 lies close to the outer burner rim, i.e. the circular juncture between the wall sections 40 and 46, while the large base of the cone frustum is of a diameter slightly greater than the overall diameter of the burner casting 10.

The annular pocket or recess 72 communicates with the gas chamber 20 by means of a series of small gas passages 92 which extend through the wall section 42 at the bottom of the pocket. A similar series of small air passages 90 extend through the wall section 46 near the forward rim thereof and establish communication be tween the pocket 72 and the air chamber 18. The passages 90 and 92 are arranged in pairs, which is to say that each port 90 in the wall section 46 is in close proximity to a port 92 in the wall section 42 with the port locations being aligned in the same radial plane. The ports 92 extend in a longitudinal direction while the ports 90 converge or are inclined forwardly and inwardly at an angle of approximately 85" with respect to the longitudinal axis of the casing. This angle is not critical and it is selected preferably so that the stream or jet of air issuing therefrom within the combustion ring or block 80 will be directed tangentially inwardly across the peripheral regions of the convex surface 68 of the refractory element 62. The pairs of passages and 92 are circumferentially and equally spaced around the periphery of the element 62 and, while in the illustrated embodiment of the invention twenty-four such pairs of passages have been illustrated, it will be understood that a lesser or greater humber thereof may be supplied if desired. Generally speaking, the diameter of the burner will control the number of pairs of passages employed.

As best illustrated in Fig. l, the air passages 90 do not extend in truly radial planes. In addition to their slight forward inclination, as previously described, these passages have their axes extending along lines which are tangent to a small circle which is concentric with the burner axis as indicated by the dotted lines a, a, etc. and the dotted circle b.

In the operation of the burner assembly, the pressure of air maintained within the chamber 18 is usually appreciably greater than the pressure of gas within the chamber 20. As a consequence, small jets or streams of gas will issue from the various passages 92 and be picked up so to speak, by the more forceful jets of air issuing from the passages 90 and admixture and combustion will take place as the two comingling streams move inwardly across the convex face 68 of the radiant element 62. At the central region of the convex face 68 there will be impingement between the comingling streams issuing from all of the various pairs of passages 90 and 92 and, due to the tangential impact which takes place at this region, a swirling or circular motion will be set up. Due to the distance between the central axis of the burner casting, and also due to gas expansion upon combustion thereof, the impacting streams at the central region of the burner structure will have considerably larger volume than the combined volume of the streams as they emerge from the passages 90 and 92. As a con' sequence, considerable turbulence will be. set up within the combustion block or ring 80 but this turbulence will be of a controlled nature in that its resultant vectorial component of motion will be in various tangential directions extending around the burner rather than in axial direction. In other words, the rotary motion which is developed within the combustion ring 80 will appreciably dampen or restrict the forward velocity of the products of combustion so that an extremely short flame will result.

During such travel of the products of combustion as described above, much heat will be generated at or near the front convex face 68 of the radiant element 72. The pressures maintained in the air and gas chambers 18 and 20 respectively are preferably such that stoichiometric gasair ratios exist Within the combustion block or ring 80, thus leading to substantially complete combustion of the gas and air with neither excess air nor excess gas remaining which would exert a cooling effect within the combustion space. Thus maximum temperatures will be attained in this region. Due to the fact that heat is generated at or near the face of the radiant member 62, much of this heat will be absorbed by the member and subsequently radiated forwardly therefrom. This radiant heat will be of a uniform nature as is characteristic of radiated heat when issuing from a surface of large expanse.

The essential and operative elements of the improved burner assembly of the present invention have been described above and certain alternative or auxiliary instrumentalities such as peep-sight, piloting and electrode devices 160, I02 and N4 respectively (Fig. 3) are believed to require no detailed description. It is deemed sufficient to state that provision is made for these devices by affording a thickened region 106 (Fig. 2) in the casting body in the upper region thereof and providing tapped holes therein for removable reception thereof.

While one specific and preferred form of the apparatus by means of which the principles of the invention may be carried out has been illustrated and described herein, it will be understood that this form of apparatus does not by any means indicate the only form contemplated. The form illustrated herein is only one which has been developed for commercial application of the process.

The invention is not to be understood as limited to the details described since these may be modified within the scope of the appended claims without departing from the spirit and scope of the invention.

Having thus described the invention what I claim as new and desire to secure by Letters Patent is:

1. In a gas burner assembly of the character described, in combination, a burner casing in the form of a hollow body of generally cylindrical design including a front wall, a rear wall and an interconnecting outer wall, a partition wall dividing the interior of the easing into a gas chamber and an air chamber, a supply pipe for gas in communication with said gas chamber, a supply pipe for air in communication with said air chamber, said front wall being dished to provide a shallow circular depression therein which is bounded, at least in part, by a short cylindrical section of the dished front wall, and a radiant element nested within said depression and having a peripheral surface spaced inwardly a slight distance from said cylindrical section of the front wall, said peripheral surface, in combination with said cylindrical section of the front wall and the bottom wall of the depression, defining an annular trough-like pocket surrounding the radiant element, there being a series of circumferentially spaced small air passages extending through the cylindrical section of the front wall and establishing communication between the pocket and the air chamber, said air passages being disposed substantially in a common transverse plane of the burner casing which is slightly forward of the front peripheral edge of the radiant element, said air passages having their longitudinal axes extending in directions which are approximately radial, said longitudinal axes of the air passages being substantially tangent to a circle of relatively small radius and which is coaxial with the burner casing and which lies slightly forwardly of the front face of said radiant element, there being an annular series of spaced small gas passages in said bottom wall of the depression establishing communication between said poeket and the gas chamber.

2. In a gas burner assembly of the character described, the combination set forth in claim 1 wherein said longi- 5 tudinal axes of the air passages are inclined forwardly and inwardly of the casing at a slight angle to said radial plane.

3. In a gas burner assembly of the character described, the combination set forth in claim 1 wherein said radiant element presents a curved forward surface and wherein said longitudinal axes of the air passages extend substantially tangential to said curved forward surface.

4. In a gas burner assembly of the character described, the combination set forth in claim 3 wherein said radiant element presents a substantially frusto-spherical forward surface.

5. In a gas burner assembly of the character described, the combination set forth in claim 3 wherein said radiant element presents a substantially frusto-spherical forward surface of convex configuration.

6. In a gas burner assembly of the character described, in combination, a burner casing in the form of a hollow body of generally cylindrical design including a front wall, a rear wall and an interconnecting outer wall, a partition wall dividing the interior of the easing into a gas chamber and an air chamber, a supply pipe for gas in communication with said gas chamber, a supply pipe for air in communication with said air chamber, said front wall being dished to provide a shallow circular depression therein which is bounded, at least in part, by a short cylindrical section of the dished front wall, and a radiant element nested within said depression and having a peripheral surface spaced inwardly a slight distance from said cylindrical section of the front wall, said peripheral surface, in combination with said cylindrical section of the front wall and the bottom wall of the depression, defining an annular trough-like pocket surrounding the radiant element, there being an annular series of circumferentially spaced small gas passages extending through the bottom wall of the depression and establishing communication between the pocket and the gas chamber, there being a series of circumferentially spaced small air passages extending through the cylindrical section of the front wall and establishing communication between the pocket and the air chamber, said air passages being disposed substantially in a common transverse plane of the burner casing which is slightly forward of the front peripheral edge of the radiant element, said gas and air passages being arranged in pairs with the air passage of each pair being disposed in close proximity to and forwardly of the gas passage of said pair and in the same longitudinal transverse plane, the longitudinal axes of the air passages being substantially tangent to a circle of relatively small radius and which is coaxial with the burner casing and which lies slightly forwardly of the front face of said radiant element.

7. In a gas burner assembly of the character described, the combination set forth in claim 6 wherein said longitudinal axes of the air passages are inclined forwardly 81nd inwardly of the casing at a slight angle to said radial p ane.

8. In a gas burner assembly of the character described, the combination set forth in claim 6 wherein said radiant element presents a curved forward surface and wherein said longitudinal axes of the air passages extend substantially tangential to said curved forward surface.

References Cited in the file of this patent FOREIGN PATENTS

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