US 3676048 A
Description (OCR text may contain errors)
July 11, 1972 SELLORS, JR" ETAL 3,676,048
EXCESS AIR BURNER Filed March 13, 1970 2 Sheets-Sheet 1 INVENTORS.
JOHN ELLORS,JR. H RD E. SHULAR Wyn, 5%
United States Patent 3,676,048 EXCESS AIR BURNER John Sellors, Jr., and Howard E. Shular, Cleveland, Ohio,
assignors to Pyronics Inc., Cleveland, Ohio Filed Mar. 13, 1970, Ser. No. 19,305 Int. Cl. F23d /02 US. Cl. 431-353 1 Claim ABSTRACT OF THE DISCLOSURE A gas burner particularly adapted for operation with exceptionally large quantities of excess air. The preferred embodiment of the burner comprises a generally cylindrical, ceramic burner block having a central bore which increases in diameter non-uniformly from the inlet to the outlet. The gas inlet comprises a tube member positioned axially of the bore and terminating closely adjacent the inlet end. A circular flange extends outwardly about the end of the tube into close proximity with the bore to define a narrow annular gap or space. Air is supplied annularly of the tube and flows through the narrow gap with substantial velocity. This causes a vacuum across the face of the flange and gas supply tube to produce good mixing and efficient combustion. By properly relating the size of the flange, the annular opening and the bore, the burner gives excellent combustion characteristics throughout substantial variations in gas-air ratios.
The present invention is directed toward the fuel burner art and, more particularly, to an improved gas burner.
The invention will be described with particular reference to a burner of the type generally referred to as an air preheater or excess air burner and will be described with particular reference thereto; however, it will be appreciated the invention is capable of broader application and could be used in a variety of different burner types.
One of the commonly used gas burners comprises a a ceramic burner block which is cemented into a cast iron holder. A cage extends rearwardly from the holder and a blast burner nozzle is positioned therein. A gas-air mixture is supplied to the nozzle and burned with additional air induced through the cage.
The general type of burner described is manufactured with variety of specific internal structures and configurations. Various blast nozzles have been used and air has been supplied to the units at atmospheric pressure, as well as, at substantial positive pressure. With all of the prior structures, there have been problems. For example, there have been difliculties in obtaining high turn down ratios. Likewise, there have been problems in providing burners which could operate efliciently in high velocity air streams. Problems with the burners requiring extensive warm-up time have also been prevalent.
In general, attempts to overcome these problems have resulted in increasingly complex and costly burners. Additionally, the burners have required increasingly complex controls and have not been particularly suitable for use in a variety of environments.
The present invention provides a gas burner which overcomes the above problems and is extremely simple in construction. Additionally, burners formed in accordance with the invention are capable of operation throughout a high turn-down range and with either constant or variable airflow.
In accordance with the invention there is provided a gas burner especially suited for operation with substantial amounts of excess air. According to the invention the burner comprises a burner block member having a central bore extending therethrough and increasing in cross-sec- 3,676,048 Patented July 11, 1972 tion from an inlet end to an outlet end. A tubular gas supply member extends axially into the inlet end. Air supply means are connected to the inlet end for supplying air to the bore annularly of the tubular gas supply member. Extending generally radially outwardly of the end of the tubular member is an imperforate flange member which has its outermost peripheral edge closely spaced from the innerwall of the inlet end of the bore. The air is thus caused to exit at substantially velocity about the end of the tubular gas supply member in a manner which produces a low pressure or vacuum across the face of the flange. The relationship of the disc to the bore and the tubular member is such as to provide extremely good gasair mixing and stable combustion throughout a wide range of firing rates and gas-air ratios.
In accordance with a more limited aspect of the invention, the bore has a non-uniform or stepped cross-section which further enhances mixing and combustion.
Accordingly, a primary object of the invention is the provision of a highly simplified gas burner which can operate throughout a high turndown range.
Another object is the provision of a gas burner which can operate throughout a wide range with air supplied at constant velocity.
Yet another object is the provision of a gas burner which requires substantially no warm-up time.
A still further object of the invention is the provision of a burner which can operate efficiently with up to as much as 3000 percent excess air.
Still another object is the provision of an excess air burner which can produce flue gas temperatures from 2500 F. and higher to as low as 250 F.
Yet a further object is the provision of a burner which can produce a wide range of precisely controllable temperatures with a substantial constant volume of hot gas output.
A further object is the provision of a gas burner which has the above mentioned operational characteristics with an extremely simple internal structure.
These and other objects and advantages will become apparent from the following description when read in conjunction with the accompanying drawings wherein:
FIG. 1 is a cross-sectional view through a preferred embodiment of the present invention;
FIG. 2 is a cross-section taken on line 2-2 of FIG. 1;
FIG. 3 is an enlarged cross-sectional view showing the air and gas inlet portion or throat of the FIG. 1 embodimerit;
FIG. 4 is a longitudinal cross-section through a modified burner formed in accordance with the invention; and
FIG. 5 is a cross-sectional view taken on line 5-5 of FIG. 4.
Referring more particularly to FIG. 1, it will be seen that the preferred form of the invention comprises a burner including a burner block or combustion chamber forming section A and an air-fuel inlet section B. In the embodiment under consideration, the burner block or combustion chamber portion A comprises a generally cylindrical body formed from a high temperature refractory ceramic. A bore 12 extends longitudinally through member 10. As can be seen, the bore 12 has a circular outlet opening 14 which connects with a uniformly tapering portion 16 extending a substantial distance into the block 10. A smaller diameter tapered portion 18 is joined through a truncated chronical transition 20 with the inner end of the portion 16. The inlet end of the burner block 10 is defined by a circular opening 22 of uniform diameter which connects with the portion 18 by a tapered transition 24. As can be seen, the described arrangement gives the bore 12 a stepped configuration. A desirability of this relationship will be described more fully hereafter.
The burner block 10 is mounted in a block holder member 28 which includes a cylindrical sleeve or wall 30 which is received in a recess 32 formed on the external surface of the block 10. A rear wall 34 connects to the cylindrical sleeve 30 and has an outwardly extending annular flange portion 36 which serves to mount the burner structure. It will be noted that the flange 36 is provided with circumferentially spaced mounting holes 40.
The block holder 28 is preferably formed from cast iron and joined to the block by a cement or adhesive 42 although obviously other types of materials and joining methods could be used.
The fuel air inlet portion of the burner comprises an air manifold section 50 which is comprised of a generally cylindrical portion 52 terminating in a radially extending flange 54. The flange 54 is connected to the end wall 34 of the block holder 28 by a plurality of machine screws 56. A gasket 58 is positioned within flange 54 and the endwall 34. Extending laterally from the portion 52 is the air inlet section 60 which is provided with a suitable flange 62 for connection to an air supply line 64.
Gas is supplied to the burner from any convenient source. In the embodiment under consideration, the gas is supplied through a manifold 68 having an outlet opening 70 connected to the rear of the air manifold 52.
Of particular importance to the invention it is the arrangement of the air and gas supply. The combination of the gas-air supply arrangement together with the stepped burner block provides a burner which can function over a wide range of gas and air ratio, and which does not require any warm-up time.
The preferred form of air-gas supply arrangement can best be seen from FIGS. 1 and 3. As shown therein, the gas is supplied from manifold 68 through a circular tubular member or pipe 80 which terminates inwardly a short distance from the outer end of opening 22. The air is supplied through the chamber 52 annularly about the pipe 80. At the outlet end of pipe 80 a disc member or outwardly extending flange portion 82 is positioned such that it is closely spaced from the inner wall of the bore thereby causing the air to flow through a narrow annular slit or opening 84. The relationship between the gas outlet opening diameter (i.e., the diameter of the opening 86) and the annular opening 84 is such that a substantial air velocity is produced annularly about the opening 86. This produces a suction or vacuum across the face of the disc or flange member 82 and causes mixing of the fuel and air while simultaneously shielding the mixture from the incoming air so as to permit it to begin combustion. The shielding effect of the disc allows combustion to proceed a substantial amount with a full flame being produced across the interior of the disc.
The stepped burner bore arrangement with its somewhat sudden increase of diameter up to the wall 16 causes the flame to be somewhat short. Additionally the sharp diameter increase of the steps causes small eddy flames to be produced Within the steps. This eliminates the need for the block to be heated-up prior to full or maximum operation of the burner.
The stepped design in combination with the air-gas inlet arrangement produces extremely good flame stability throughout a Wide range of firing rates. Additionally, it is possible to operate the burner at up to 3.000% excess air.
Also of importance to one aspect of the invention is the pilot burner arrangement. As seen in FIG. 1, a pilot or ignition opening for the burner is shown as a circular opening 88 which extends into the first step of the bore 12. Note that the opening 88 comes in at approximately the juncture between the wall 24 and the wall 18. An ordinary gas pilot burner (not shown) extends into the opening for igniting the gas-air mixture supplied to the bore. Proper lighting of the mixture at all flow rates is assured by a short tab 90 which extends radially of the annular opening between pipe 80 and bore 22. As shown in FIG. 2, the tab 90 is approximately the width of the pilot opening 88. This tab shields the pilot flame and produces a negative air pressure which, in combination with the stepped bore, assures proper pilot operation without regard to the velocity within the bore 12.
The proper relationship between the gas outlet area of opening 86 and the arrangement of the air outlet opening 84 can be found experimentally. One example of a burner size which is especially advantageous is adapted to handle from between 50 to 1500 standard cubic feet per hour of gas with a constant air flow of 15,000 standard cubic feet per hour. A burner adapted for this type of operation has the opening 22 of 4% inches in diameter and the disc 82 with a diameter of 3% inches. The velocity of air flow through the gap 84 is in a range of about 416 feet per second. The burner will operate with a variety of air flow rates of, for example, from as low as approximately 40 ft. per second to as high as in the range of 800 ft. per second through the gap 84.
The relationship of the stepped burner block is substantially less critical and the inlet air gas arrangement can be used in many types of blocks; however, the relationship shown in FIG. 1 is approximately to scale and is extremely advantageous. An important feature of the stepped burner block being the creation of small eddy flames which prevent quenching of the main flame on start-up and which, additionally, produce excellent flame stability at all firing rates.
Although the embodiment shown in FIGS. 1-3 is preferred, the same general type of arrangement can be used in burners having other cross-sections. FIGS. 4 and 5 show an embodiment which has a rectangular cross-section and produces a Wide flat flame. As shown, the burners in FIGS. 4 and 5 have generally the same air gas inlet arrangement and includes a first cast housing or manifold member which has an air inlet opening 102 and a gas supply inlet 104. Openings 102 and 104 are connected to suitable supply manifolds not shown. The member 100 extends across the back width of the burner and is connected to a burner block holder 106 in any suitable manner such as by a plurality of machine screws 108. A seal member 110 is positioned between the member 100 and the burner block holder 106.
The burner block holder 106 has a generally rectangular cross-section and has an outwardly extending mounting flange 112 provided with a plurality of holds 114 for receiving bolts to mount the burner.
The burner block in the FIGS. 4 and 5 embodiment has generally the same longitudinal cross-sectional configuration as the 1-3 embodiment but is rectangular as best seen in FIG. 5. The block 116 is received in the member 106 and held therein by ceramic cement 117. As can be seen, the center bore of the burner block 116 is unifromly tapered from the outlet end 118 to a short distance forward of the air-gas inlet end. The air-gas inlet end includes a rectangular opening 120 having a width which is substantially greater than its height.
The air-gas inlet arrangement is generally the same in function and arrangement as that described with reference to the FIGS. l-3 embodiments. Note that a plurality of gas supply tubes 122 extend into the inlet end of the bore along its transverse axis. A flange member 124 extends outwardly of the terminal end of tubes 122 to form a narrow, generally annular gap 126 which extends about the inner face of the inlet end. The gap is sized to produce high air velocity therethrough and a vacuum across the face of the member 124.
The pilot for the burner is arranged in the same manner as described with reference to FIGS. 1-3. Note that there is a pilot burner opening 128 which opens into the bore just forwardly of the inlet 120. Additionally, a tab portion 130 extends outwardly immediately behind the opening 128 to shield the pilot burner (not shown) from the incoming air.
The invention has been described in great detail sufficient to enable one of ordinary skill in the burner art to make and use the same. Obviously, modifications and alterations of the preferred embodiments will occur to others upon a reading and understanding of the specification and it is our intention to include all such modifications and alterations as part of our invention insofar as they come within the scope of the appended claim.
Having thus described our invention, we claim:
1. A gas burner especially suited for operation with substantial amounts of excess air comprising:
a burner block member having a central bore extending therethrough and increasing in cross-section from an inlet end to an outlet end;
a tubular gas supply member extending axially into the inlet end of the bore, air supply means connected to the inlet end of the bore for supplying air to the bore annularly of the tubular gas supply member;
an imperforate flange extending generally radially outwardly of the end of the tubular member, said flange member having its outermost peripheral edge closely spaced from the innerwall of the inlet end of the bore whereby the air is caused to exit at substantial velocity about the end of the flange member in a man- 6 her which produces a low pressure area across the face of the flange and the outlet end of said gas supply member;
a pilot burner port formed through said burner block and opening into said bore adjacent said flange member in a direction toward said outlet; and
a bafile member aligned with said port and extending between said flange and the wall of the inlet end of said bore.
References Cited UNITED STATES PATENTS 2,368,370 1/1945 Maxon 431-353 X 2,375,625 5/1945 Conway 431-187 X 3,368,605 2/1968 Reed 431-353 3,529,917 9/1970 Hindenlang 431351 CARROLL B. DORITY, IR., Primary Examiner US. Cl. X.R.