US2929442A - Combustion system - Google Patents

Description

Filed March 26, 1957 United States Patent 6 COMBUSTION SYSTEM Gabriel Brola, Bourg la Reine, France, assignor to Genrale Thermique-Procedes Brola, Le Pre Saint-Gervais,

rance Application March 26, 1957, Serial No. 648,704

Claims priority, application France March 29, 1956 '6 Claims. (Cl. 158-77) In the steady-state operation of a burner, the flame propagation velocity must equal the rate of feed of the combustible mixture to the burner. Whenever it is desired to increase the combustion rate, therefore, it is necessary simultaneously to increase the flame velocity. The present invention provide a combustion system whereby such a result is conveniently accomplished. In the improved combustion system means are provided for creating within the ignited mixture of fuel and air, vortices that act to return said mixture rearwards, or in other words to recycle the flame.

Another object of the invention is to provide an improved burner for liquid or gaseous fuels based on the principle just set forth. The improved burner is principally characterized in that it includes means'for creating vortices within the burning mixture to recycle the flame.

In a preferred embodiment of the invention, the burner may comprise a rotary spray-nozzle consisting of a pair of concentric, axially-spaced rotary cup elements defin ing between them an annular space for the intake of primary air, the foremost or upstream cup element being formed with a central fuel intake aperture and the rearward or downstream cup element being formed or provided at its terminal end with fins arranged adjacent a fixed wall surface or shoulder so as to define a secondary air passage so arranged that the secondary air will, on contacting the mixture of fuel and primary air, generate an annular vortex generally coaxial with the cup elements and directed rearward.

' In cases where the burner is arranged within a furnace tube, the downstream cup element is preferably provided along its edge with bafiles adapted to channelize part of the secondary air into the furnace tube. The baffles are rotatable with the cup element and will impart a circular sweep movement to the deflected air stream so that it will sweep past the inner wall surface of the furnace tube thereby preventing formation of carbona- .iceous deposits.

In accordance with a further feature of this invention an electrical resistance for use on starting the burner is arranged in a groove formed around the combustion chamber and is cooled by an air stream which simultaneously serve to prevent formation of uncombusted deposits.

Further according to the invention the rate of supply of the liquid or gaseous fuel is controlled by a needle valve or the like associatedwith a rotary valve seat, an arrangement which will act to eliminate impurities tending to clog the fuel flow while at the same time providing for accurate and uniform flow regulation without requiring any preliminary fuel filtering step.

The above and further objects, features and advantages of the invention will appear clearly from the ensuing description made with reference to the accompanying drawing wherein:

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Fig. 1 is an axial sectional view of a preferred embodiment of a burner according to the invention;

Fig. 2 is a larger-scale sectional view of the spraynozzle used in the embodiment of Fig. 1; and

Fig. 3 is a side view of a detail.

Referring to Fig. 1, an electric motor 1 is shown as driving a shaft 2. The motor 1 is surrounded by a casing 3 having formed in it an aperture 4 which is adjustable by means of a valve 5. The shaft 2 directly drives a fan 6 operating within a casing shell 7 secured with screws to the motor casing 3. The air drawn in through the aperture 4 cools the motor windings then flows through the fan 6 and is discharged towards the outlet after flowing through a set of director vanes 8 secured within a casing shell 7a, screwed to the casing shell 7.

An air distributor 9 secured to the casing shell 7a supports vanes or baffles 10 for distributing the air supplied to it from the fan.

The drive shaft 2 inaddition to driving the fan simultaneously drives the rotor 23 of a vane type fuel feed pump. The fuel from the pump is discharged by way of a duct 24 past a flow controlling or regulating means 25. The body 27 of the fuel feed pump is secured to the casing 3.

The fuel is delivered (by means not appearing in the drawing) from the regulating means 25 into an annular space 28 surrounding the needle valve 29. The needle valve cooperates with a rotatable valve seat 30 formed at the end of, and rotatable with, the drive shaft 2. The fuel flow controlling assembly is likewise secured to the casing 3. Extending axially through the drive shaft 2 is a fuel feed duct 31.

Secured on motor shaft 2 by means of a screw 42 is a rotary spray nozzle which comprises a coaxial pair of cup members 43 and 44 assembled by means of e.g. three spider arms 45. A check-valve having a ball 40 applied against its seat by a spring 41 and positioned olfcenter from the burner axis controls the fuel feed from duct 31 into an obliquely extending duct 39 opening into cup member 43. 'The cup member 44 extends downstream from cup member 43 so that it operates in tandem or cascade relation with it. Formed in the inner wall surface of cup 44 is a groove 46 which communicates by way of a set of radially outwardly inclined ports 47 with the outer wall surface of the cup member. Pro- I jecting from the outer wall surface of the cup member 44 at the outlets of the ports is a flange 48.

Removably mounted within cup member 44 is a ring 49 which serves to determine the flow rate and angle of the primary airflow passing between cups 43 and 44.

Attached to the downstream edge of cup 44 are a plurality of deflector vanes 50. Moreover, a set of radial fins 51 are formed around the periphery of the edge of the cup member 44 and project at an angle both to the axis of rotation and to a transverse plane. The fins or vanes 51 are positioned opposite to a shoulder 52a projecting from a divergent section of a combustion chamber 52. Centrally arranged is the rotary spray nozzle. Between the chamber 52 and cup member 44 an annular space 53 is defined for the flow of both secondary and tertiary air.

The combustion chamber is formed at its downstream end with a circumferential groove 17 in which a shielded ignition resistor 18 is positioned. The groove 17 connects with the annular space 53 by way of a plurality of ducts 20 for the tertiary airflow which serves to cool the resistor. The igniting resistor 18 is retained in its groove 17 and protected by means of a conical member 54 made from refractory metal sheeting formed with a plurality of holes 55 for discharging the tertiary air into the flame.

The furnace tube 22 made of refractory material extends from the outlet of the combustion chamber 52 and is removably connected therewith by means of a hinge connection 21. i v

The burner just described operates in the following manner. With the motor stationary the 'ign'iter resistor 18 is energized and, when a suitable temperature has been attained by it the motor 1 is started and the resistor deenergized. The fan 6 now draws in the necessary combustion air in an amount controlled byradjustment of valve 5. This air cools the motor 1, flows through the fan and is discharged into distributor 9. 1

This primary air flows past vanes 10 which impart to y it a certain, rotational velocity, then passes around the foremost cup member 43 to atomize the film of fuel which is supplied in the manner hereinafter described in detail and which emerges tangentially from the edges of that cup member and has a helical movement, including both an axial and a tangential component, imparted thereto by the primary air. The secondary air flowing through annular space 53 is directed towards the fins 51 of the rearward cup member 44. The secondary air flows past these fins in a direction which includes a tangential component into the combustion chamber where it encounters the com bustible mixture of primary air and fuel. The secondary air flowing past fins 51'has a higher velocity than that of the combustible mixture because in addition to the axial movement .of the air there is a tangential component of motion .due to the rotation of cup 44. As a result, the secondary air on striking the combustible mixture deflects the mixture towards the axis and tends to direct it back towards the cup member 43. The fins 51 are so positioned and oriented and the intervening space between the shoulder 52a and cup 44 is so dimensioned, with regard to the rates of flow of the air and fuel, that an annular vortex is generated coaxially with the burner axis, as shown by the arrows 56. The effect of this vortex is to increase the combustion rate and to stabilize the flame front. The combustion thus proceeds in the combustion chamber; the flame then has tertiary air fed to it. This tertiary airflow is discharged from the annular space 53 through the openings 20 into the circular groove 17 and finally issues through ports 55 formed in the conical securing member 54. This tertiary air has a further function in that it likewise serves to cool the igniting resistor 18 when the fan is operating. This prevents the temperature of the resistor from exceeding a predetermined limit when subiected to radiation from the flame. The combustion continues within the furnace tube 22 and terminates finally at the outlet of the tube.

To prevent carbonaceous deposits within the furnace tube 22, part of the secondary air is introduced tangentially into the chamber and is directed towards the inner wall surface of the furnace tube by the action ofdefiector baffies secured to the cup member 44. The rotational movement of the deflectors causes the air to swirl around the wall of the furnace tube thereby to burn up progres sively any deposits which may tend to settle thereon; while simultaneously protecting the refractory material by a film of cool air. The number and length of the deflectors and the rotational velocity are so predetermined as toprovide a desired percentage ratio of this scavenging air to secondary air.

The fuel feed pump driven by motor 1 delivers the fuel into annular space 28 by way of regulating means 25, and then past needle valve 29 into axial duct 31. Since seat 30 of valve 29 is rotated, there is no danger of clogging, and it is possible to eliminate the usual preliminary filtering of the fuel. The olfcenter location of check valve ball 40 subjects the latter :to celltrifugal force which lifts the ball off its seat and thereby permits the fuel to flow into duct 39 only when the shaft 2 is being rotated. Under centrifugal force the fuel supplied through duct 39 is forced to spread over the inner surface of cup 43 into a thin film and is tangentially projected to impinge on the primary air which is delivered around that cup. When the motor is stopped the thin residual fuel .film remaining on the wall of cup 43 flows downwardly under gravity on to the outer Wall surface of the cup member from which it drops into the groove 46, in cup member '44. The fuel then flows by way of ports 47 on .to the inner wall surface of combustion chamber 52 whence it is discharged by way 7 Burners according to the invention possess a very high combustion efficiency and produce ashort; compact, dense and stable flame. This makes them particularly well suited for use in combustion apparatus-having limited furnace capacity. 1

WhatI claim is: v

1. In a combustion device; the combination of means defining an elongated combustion chamber having opposed ends with an inlet section at one of said ends, a rotatable burner nozzle mounted withinsaid inlet ,section with the axis of rotation of said nozzle aligned with the longitudinal axis of said chamber, means rotating said burner nozzle said nozzle including a relatively small diameter cup-like member and a concentric relatively large diameter cup-like member each having a free edge at which. the cup-like member opens axially in the direction toward the other of said ends .of the combustion chamber, said large diameter cup-like member extend: ing axially beyond said smalldiameter cup-like member in said direction toward the other end of the chamber and said nozzle further having an annular space defined between said large diameter and small diameter cuplike members, means supplying fuel into the interior of said small diameter cup-like member so that thefuel is spread into a thin film over the inner surface thereof by said nozzle, means producing a flow of primary air through said annular space to atomize said free fuel of said film at the edge of said small diameter cup-like member and thereby to form a combustible mixture .of the atomized fuel and primary air, means for igniting said combustible mixture to produce a flame, said means defining the combustion chamber including a member having an annular shoulder adjacent said free edgeof said large diameter cup-like member and defining an annular space therebetween which opens generally towards the longitudinal axis of the combustion cham ber to form an'inlet for secondary air, and deflector means in said inlet for secondary air directing the latter with a tangential component of motion so that the secondary air issuing from'said inlet forms spiral vortices which heat back said flame and thereby create a stable vortical combustion zone adjacent said nozzle.

2. In a combustion device; the combination as in claim 1, wherein said deflector means are fins projecting from said free edge of the large diameter cup-like-memher and, thus, rotating with said nozzle.

3. In a combustion device; the combination as in claim 2, wherein said fins are each at an angle with respect to a radial plane passing through the axis of rotation of the nozzle.

4. In a combustion device; the combination as in claim 1, wherein said annular space between the large diameter and small diameter cup-like members has frusto-conical inner and outer wall surfaces decreasing in diameter in the direction toward said free edge of the small diameter cup-like member so that the flow tgf primary air has a radially inwardly directed component to cause increased impact between the primary and the fuel which is thrown centrifugally from said free edge of the small diameter cup-like member.

5. In a combustion device; the combination as in claim 1, further comprising defiector vanes extending from said free edge of the large diameter cup-like member for rotation with the latter, said vanes projecting across said inlet for the secondary air and being directed generally toward said other end of the combustion chamber beyond said annular shoulder of the member included in the means defining the combustion chamber so that said vanes axially deflect a portion of the secondary air entering the chamber at said inlet therefor along the inner wall surface of the chamber extending away from said inlet section and cause swirling fiow of the deflected portion of the secondary air to form a cooling, scavenging layer of air against said innerwall surface.

6. In a combustion device; the combination of means defining an elongated combustion chamber having opposed ends with an inlet section at one of said ends, a rotatable burner nozzle mounted within said inlet section with the axis of rotation of said nozzle aligned with the longitudinal axis of said chamber, means rotating said burner nozzle, said nozzle including a relatively small diameter cup-like member and a concentric relatively large diameter cup-like member each having a free edge at which the cup-like member opens axially in the direction to ward the other of said ends of the combustion chamber, said large diameter cup-like member extending axially beyond said small diameter cup-like member in said direction toward the other end of the chamber and said nozzle further having an annular space defined between said large diameter and small diameter cup-like members, means supplying fuel into the interior of said small diameter cup-like member so that the fuel is spread into a thin film over the inner surface thereof by centrifugal force upon rotation of said nozzle, means producing a flow of primary air through said annular space to atomize the fuel of said film at said free edge of said small diameter cup-like member and thereby to form a combustible mixture of the atomized fuel and primary air, said means defining the combustion chamber including a member having an annular shoulder adjacent said free edge of said relatively large diameter cup-like member and defining an annular space therebetween forming an inlet for secondary air, said means defining the combustion chamber further having an annular groove opening into said chamber at a location beyond said inlet for secondary air in the direction toward said other end of the chamber, electrical resistance means in said annular groove for igniting said combustible mixture to produce a flamedefiector means in said inlet for directing secondary air flowing through the latter so that the secondary air beats back said fiame and creates a stable vortical combustion zone adjacent said nozzle, duct means opening into said annular groove for supplying a flow of tertiary air through the latter to said chamber so that said tertiary air cools said resistance means during normal operation of the combustion device, said large diameter cup-like member having radial openings therethrough communicating with said duct means for the tertiary air flow so that, when rotation of the nozzle is halted, fuel remaining in said small diameter cup-like member can drip into said large diameter cup-like memher to pass through the lowermost of said radial openings into said duct means for collection in said annular groove, whereby said resistance means can ignite the fuel collected in said annular groove upon subsequent starting of the combustion device.

References Qited in the file of this patent UNITED STATES PATENTS 1,697,279 Klemm Jan. 1, 1929 1,699,488 Klemm Jan. 15, 1929 1,726,640 Benniger Sept. 3, 1929 1,935,318 Hawxhurst Nov. 14, 1933 2,005,832 Vidalie June 25, 1935 2,200,826 Johnson May 14, 1940 2,680,951 Winter June 15, 1954

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