US3208502A - Fuel burners having air control means - Google Patents

Description

p 8, 1965 w. B. CARLSON 3,208,502

FUEL BURNERS HAVING AIR CONTROL MEANS Filed March 7, 1962 .2 Sheets-Sheet 1 FIG.1

INVENTOR. Walrer B. Carlson Sept. 28, 1965 w. B. CARLSON FUEL BURNERS HAVING AIR CONTROL MEANS 2 Sheets-Sheet 2 Filed March 7, 1962 FIG.2

ATTORNEY United States Patent 3,208,502 FUEL BURNERS HAVING AIR CONTROL MEANS Walter Berndt Carlson, London, England, assignor t0 'Babcock & Wilcox Limited, London, England, a British company Filed Mar. 7, 1962, Ser. No. 178,044

Claims priority, application Great Britain, Mar. 8, 1961, 8,462/ 61 1 Claim. (Cl. 158-15) This invention relates to combustion apparatus of the kind in which fluent fuel is discharged from a nozzle into a combustion zone.

The efliciency with which apparatus of this kind operates depends partly upon the mixing of fuel and hot gases and it is an object of the present invention to provide improved combustion apparatus in the use of which fuel and hot gases become mixed.

According to the present invention, there is provided combustion apparatus including a nozzle for the discharge of fluent fuel into a combustion zone, means for supplying secondary air to the combustion zone including a baffle member movable relatively to a co-operating member for controlling the supply of secondary air to the combustion zone, and means for directing discrete jets of combustion air towards the axis along which fuel is discharged from the nozzle from separate locations distributed around the nozzle and in the downstream direction of the flow of fuel. I

By using a baflle member to control the supply of secondary air, it is possible to maintain the pressure of combustion air upstream of the baflle member substan tially constant so that the pumping energy that is wasted is less than the waste that occurs when the more normal dampers are used and result in turbulence occurring in the combustion air before it reaches the combustion zone.

In some embodiments :of the invention, the discrete jets of combustion .air may be provided by the secondary air while in other embodiments the discrete jets may be of primary air discharged within a shroud of secondary air.

By way of example, embodiments of the invention will now be described with reference to the accompanying somewhat diagrammatic drawings in which:

FIGURE 1 is an axial section through combustion apparatus; and

FIGURE 2 is an axial section through alternative combustion apparatus.

In FIGURE 1, a furnace wall is indicated at 1 and has a circular opening lined by the frustoconical ring 2 secured by theflange 3 to a front plate 4 lining the front face of the furnace wall 1. A register indicated at 5 is fixed to the plate 4 to extend forwardly of the ring 2 and is provided with large openings, not shown, through which secondary air may be admitted.

Thefront wall 5A of theregister 5 is provided centrally with a circular opening provided with an air-tight gland (not shown) in which a baflle tube 6 may be reciprocated axially. The inner end of the baflie tube 6 is provided with a frusto-conical annular member 7 diverging towards the furnace and the outer edge of the member 7 carries a baflle flange 8 of such a shape that its outer surface can mate against the inner surface of the ring 2.

Adistance tube 9 extends co-axially through baflle tube 6 and is supported from it by thespider 10. In this embodiment, thespider 10 is fixed relatively to the baffle tube 6 and thedistance tube 9 but in a modification it may be adjustably clamped to thedistance tube 9 so that the position of this tube is adjustable relatively to the baffle tube 6.

The end of thedistance tube 9 is provided with anannular orifice plate 11 having asleeve 12 that is fitted to the end of thedistance tube 9 so that there .are air "Ice passages between thesleeve 12 and thetube 9, leading to a somewhat dome-shaped chamber 13 containing the atomizinghead 14 of a liquidfuel burner barrel 15. Theorifice plate 11 is provided with fourpassageways 11A separated from each other and uniformly distributed around theplate 11 and so disposed that air flowing axially towards theplate 11 between thedistance tube 9 and the baflle tube 6 will be directed in four discrete jets towards the axis of the fuel discharged from thehead 14.

The surface of the annular member 7 that faces the furnace is protected from the heat of the furnace by refractoryinsulating material 16 lining the outer ring of the member 7 and anannular plate 17, which is itself protected by refractoryinsulating material 18, spaced from the plate 7 to provide a passage through which cooling air can flow over the plate 7. Theplate 17 is supported from the plate 7 bystubs 19. A snout 20, having the same inner diameter as the tube 6 extends towards the furnace from the inner periphery of theplate 17. The outer edge of theorifice plate 11 lies close to the inner surface of the snout 20, the gap being as small as will conveniently allow theorifice plate 11 to be adjusted axially within the snout 20 should that prove desirable. The snout 20 is provided withopenings 20A through which cooling air can flow over theinsulating material 18.

To support the outer edge of the baffle plate 8, it is provided withmembers 22 extending towards thefront plate 5A of theregister 5 and each having an outwardly extendingarm 22A that can slide along aguide rod 23 fixed at one end to theflange 3 and at the other end to thefront plate 5A.

In operation of the apparatus described, secondary air is supplied from thefan 24 to the windbox and is discharged to the combustion zone from theregister 5 in the form of a continuous convergent cone between the ring 2 and the baffle flange 8. The direction of flow is towards the axis of discharge of fuel from theburner head 14 and in the downstream direction of the flow of fuel. The flow of secondary air may be adjusted by moving the baffle flange 8 towards or away from the ring 2 so that thefan 24 supplying secondary air to the windbox may be operated continuously at constant speed without the need for vanes or dampers.

Atomised fuel from thehead 14 is discharged into the combustion zone as a divergent cone towards the secondary air, the fuel flow being controlled byvalve 15A according to the heat requirements of the furnace.

Primary air is directed to the combustion zone axially between the baflle tube 6 and thedistance tube 9. Some is splayed outwardly to cool the refractoryinsulating material 16 and 18; the remainder flows through the spaces between thesleeve 12 and thetube 9, and through thepassageways 11A while a little will flow through the gap between theorifice plate 11 and the snout 20. The air flowing through thepassageways 11A emerges in the form of discrete, convergent jets discharged in the downstream direction of the fuel.

The embodiment illustrated in FIGURE 2 is such that the secondary air is itself supplied in the form of discrete jets.

A conical ring 31 is provided as a lining for a circular opening in afurnace wall 32, the ring 31 having aflange 33 that is fixed to afront plate 34 lining the front face of thewall 32. A register indicated diagrammatically at 35 extends from thefront plate 34 in a direction away from the furnace.

Aflange 31A at the inner periphery of the ring 31 lies in a recess formed at the opening in thewall 32 and theflange 36A extending outwardly from adrum 36 is fastened by thebolts 37 to theflange 31A. The heads of thebolts 37 lie in indentations provided for them in thewall 32.

The end of thedrum 36 remote from theflange 36A is provided with an inwardly directedflange 36B provided at its inner periphery with across-web 36C co-axial with the opening in the wall. Atube 38 through which a mixture of pulverized fuel and primary air may be directed to the furnace is fixed within thecross-web 36C and extends rearwardly through an opening in the front wall of theregister 35.

Thedrum 36 is provided with fourpassages 40 of substantially rectangular cross-section uniformly distributed around its curved surface. Each passage has its maximum dimension in the circumferential direction and the sides of the passage are inclined, the shorter sides lying in planes that meet on the axis of thetube 38 while the longer sides lie on cones that are similar to that containing the outer surface of the ring 31.

Although thepassages 40 are of fixed cross-section, their effective area is determined by the position of thebaffle member 41 which is movable axially to provide a frusto-conical passageway between thebafiie member 41 and the ring 31 of uniform thickness which can be varied by moving thebaffle member 41 axially. Thebaflle member 41 is thickened at its inner periphery to provide a surface that slides in close contact with the outer surface of thedrum 36. The position of thebaffle member 41 is controlled by the threerods 44 that are secured into its thickened portion and pass through glands (not shown) in the front wall of theregister 35.

In the operation of the apparatus shown in FIGURE 2, a mixture of pulverized fuel and primary air is discharged directly into the combustion zone whilst the secondary air is introduced from thefan 45 into the windbox and is discharged towards the stream of the mixture in discrete and separate jets.

Both the embodiments described permit a high turndown ratio whilst maintaining the stability of the flame. The number of jets of combustion air shown in both the accompanying figures is four but in other embodiments other numbers of jets may be used. The passages shown in FIGURE 2 may also be replaced by passages of other configurations having their center lines converging towards the axis of the fuel discharge.

I claim:

In combination with a wall of a furnace, said wall having a circular port formed therein, a fuel burner comprising a frusto-conical throat member converging forwardly toward said furnace and having its smallest diameter at said port, a baffle member including a baflie tube disposed coaxially with said port, an outwardly extending imperforate support member attached to the forwardmost end of said baflle tube, and an annular flange portion having an outer frusto-conical surface in concentric parallelism with the inner surface of said throat member to form an annular passage therebetween, an axially extending fuel burner barrel having a fuel atomizing head at its end, an annular air directing member spaced from and connected with said fuel burner barrel and forming a dome-shaped chamber around said head, said air directing member including means forming a plurality of orifices to direct discrete jets of combustion air towards the axis along which fuel is discharged from said head from separate locations distributed around said head and in the downstream direction of the flow of fuel, source of supply of combustion air at substantially constant pressure, means for introducing primary combustion air through said baflle tube and directing said primary air so that a first portion passes through the space between the fuel burner barrel and the air directing member into the dome-shaped chamber, a second portion passes through the orifices in said air directing member, and a third portion flows radially over the forward surface of said support member to effect cooling thereof, means for supplying secondary combustion air at a constant pressure to the annular passage formed between the inner surface of said throat member and the outer surface of said flange portion and passing said secondary combustion air through the annular passage and into said furnace in the form of a continuous convergent cone directly impinging with the fuel flowing from said head, and means for axially positioning said bafile member to adjust the extent of the annular passage so that the velocity of said secondary combustion air through said passage remains substantially constant throughout the load range of said burner.

References Cited by the Examiner UNITED STATES PATENTS 1,055,715 3/13 Dahl 158-1175 1,172,755 2/16 Wilson 158-1.5 1,412,023 4/22 Erickson 158-15 1,966,524 7/34 Schenck 158-15 2,334,314 11/43 Campbell 158-15 2,472,720 6/49 Nagel 158-1175 FOREIGN PATENTS 238,108 3/26 Italy.

JAMES W. WESTHAVER, Primary Examiner.

PERCY L. PATRICK, FREDERICK L. MATTESON,

JR., Examiners.

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