US2765621A

US2765621A - Combustion apparatus with toroidal eddy flame stabilizer

Info

Publication number: US2765621A
Application number: US404635A
Authority: US
Inventors: Poulston Bernard Vincent; Shepheard Edmund Richard
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1953-01-23
Filing date: 1954-01-18
Publication date: 1956-10-09
Anticipated expiration: 1973-10-09
Also published as: BE525924A; CH324031A; FR1095893A; GB743851A

Description

COMBUSTION APPARATUS WITH TOROIDAL EDDY FLAME STABILIZER Filed Jan. 18, 1954 B. V. POULSTON EI'AL Oct. 1956 2 Sheets-Sheet 1 I NVENTORS BERNARD VINCENT POULSTON EDMUND RICHARD SHEPHEARD BY MA m THEIR ATTORNEY Get. 9, 1956 B. v. POULSTON ETAL 2,765,621

COMBUSTION APPARATUS WITH TOROIDAL. EDDY FLAME STABILIZER Filed Jan. 18,1954

2 Sheets-Sheet 2 FIG. 3

INVENTORs BERNARD vmcENT POULSTON 2 ED uuo mcumzo SHEPHEARD BY- M Tuzuz ATTORNEY COMBUSTION APPARATUS WITH TOROIDAL EDDY FLAME STABILIZER Application January 18, 1954, Serial No. 404,635

Claims priority, application Great Britain January 23, 1953 15 Claims (Cl. 6ll39.72)

This invention relates to apparatus for the combustion of fluent fuel, e. g., gaseous, liquid or finely divided solid fuels, in which the fuel is injected into a stream of air (or other combustion-supporting gas hereinafter referred to as air for the sake of brevity) and is particularly but not exclusively suitable for gas turbine combustion chambers.

It is an object of the invention to provide a combustion apparatus wherein the flame is stabilized by producing turbulence effective for good mixing of the fuel with sufficient air without recourse to steady tangential or radial flow components, so as to obviate or significantly diminish the tendency of the flame to spread against the walls of the combustion chamber.

A further object is to provide an improved combustion apparatus wherein the life of the combustion chamber wall is extended and/or wherein a thinner refractory lining may be used for such wall or, in some cases, omitted, by reducing the tendency of the flame to spread out and play against the wall.

According to the present invention, apparatus for the combustion of gaseous, liquid or finely divided solid fuel comprises a combustion chamber (also known as a flame tube) having operatively associated therewith a burner or the like (also known as an atomizer in the case of liquid fuels) which delivers fuel into the combustion chamber in which air guide means are provided for causing two or more series of successive toroidal eddies to be formed in the main air stream substantially at the zone where this air stream meets the fuel issuing from the burner, and to travel longitudinally through the combustion chamber. Preferably more than two series of successive substantially concentric toroidal eddies are formed at a number of positions around the axis of the burner and each travels along the combustion chamber; again preferably, in the case of finely divided liquid or solid fuel, such toroidal eddies are generated along the surface of a cone similar to the cone containing the spray of atomized fuel and coaxial therewith.

The main air stream means the preponderant proportion, at least 80%, of the air supporting combustion and does not include the auxiliary air stream which is sometimes but not always present immediately surrounding the burner and has for its object the prevention of a deposit .of combustion products on the burner tip.

toroidal eddies in the main air stream surrounding the burner.

A plurality of concentric shrouds are preferably employed, each of which is provided with an outwardly projecting or external lip which restricts the air flow in the space between any two shrouds and thereby produces a series of successive toroidal eddies. As an alternative arrangement, the shrouds are also provided with inwardly projecting or internal lips; a preferred arrangement is that in which alternate shrouds only are provided with internal lips.

The arrangement is preferably such that the shroud of smallest radius terminates in a lipped edge only a short axial distance beyond the end of the burner, whereas the outermost shroud with the largest radius has its lipped edge in a plane at a greater axial distance from the end of the burner. Intermediate shrouds are arranged with their ends in planes at intermediate distances from the end of the burner.

By means of the combustion apparatus of the present invention, it is possible to secure flame stabilization, that is to say mixing of the fuel with sufficient air for its combustion, by producing turbulence without steady tangential or radial flow components in the turbulent air. By this means it is possible to obviate or substantially diminish the tendency of the flame to spread outwards to the walls of the combustion chamber or flame tube. This tendency to spread outwards is always marked in combustion apparatus where the combustion air has a tangential or radial component of flow. With the com bustion apparatus of the present invent-ion, therefore, the walls of the flame tube or combustion chamber are, to a large extent, protected from overheating and hence have a longer life. The protective lining of refractory material used in many combustion chambers may be omitted when using the apparatus of the present invention.

A further advantage of combustion apparatus according to the present invention is that the air pressure drop involved in feed-ing the air to the combustion chamber or flame tube is substantially reduced in comparison with known types of combustion apparatus in which turbulence is imparted to the air by a swirling motion or by air streams injected into the combustion chamber at an angle to the longitudinal axis thereof.

The invention is further illustrated by reference to the accompanying drawings in which:

Figure 1 is a diagrammatic longitudinal section of a preferred type of combustion apparatus according to the present invention, which is suitable for use with a gas turbine;

Figure '2 is a similar section of a modified arrangement, and

Figure 3 is cross section on the line 3'3 of Figure 2.

The combustion chamber or flame tube C shown in Figure l is of circular cross ssction and is of a known type of construction having an air inlet opening G for the admission of a primary air stream for supporting combustion of the fuel, said primary air being supplied, for example, from a blower (not shown) and flows longitu dinally through the combustion chamber. A secondary air stream flows through an annular space between the chamber and an air casing D and is admitted into the combustion chamber through openings E to dilute the resulting combustion products. The subsequent descriptron is concerned with the primary air stream.

Mounted concentrically within the com-bustion chamber C and arranged to inject atomized liquid fuel in the axial direction thereof is a burner B. The function and construction of this burner does not form any part of the present invention; hence, any known burner may be employed. For liquid fuels the burner is advantageously an atomizer that emits atomized fuel as a spray cone S.

Closely surrounding this burner B is a concentric atomizer shroud A of known type, i. e., tubular-in form, open at front and back and having an inward flange F at the front. The clearance between the outer wall of the burner B and the inner wall of this atomizer shroud A is about equal to the radius of the burner body. The function of this atomizer shroud A is to define the auxiliary combustion air stream referred to above.

Concentric shrouds 4, 5, 6, 7 and 8 are disposed around the burner B outside the atomizer shroud A, each one of which is spaced from its neighbours by an equal distance (a distance which is advantageously between the radius and diameter of the burner body).

As the radii of these concentric shrouds are progressively greater so the shrouds terminate in planes which are disposed downstream from the end of the burner by progressively increasing axial distances. The number of shrouds is such as substantially to fill the cross-sectional area of the combustion chamber and need not be five as shown, but may be varied accord-Eng to the distance between neighbouring shrouds and the diameter of the combustion chamber.

The main air stream as defined above flows into the combustion chamber through the annular spaces between the shrouds.

The shrouds 4 to 8, inclusive, are provided at their forward or downstream parts with external lips 45:, 5a, 6a, 7a and 8a, respectively, which project partly across the space between each shroud and its neighbor, or in the case of the largest shroud 8, between that shroud and the wall of the combustion chamber C. In addition, shrouds 6 and 8 have

internal lips

6b and 8b, respectively. Each external lip extends substantially halfway across the corresponding space; however, a wider lip may be used as shown for example for the lip 7a, whereby the air emerging between this lip and the shroud 8 is directed wholly against the lip 8b for inward deflection. The internal lips 6b and 812 project inwardly to about the same extent that the lips 6a and 8a project outwardly. These lips, together with the shrouds, constitute air guides for forming the stabilizing toroidal eddies. The lips are situated substantially at, e. g., slightly in back of, the zone where the air stream picks up the atomized fuel.

The shrouds 5 to 8 are supported in any known manner, for example by means of a cruciform bracing 9 placed across the combustion chamber C behind the shrouds. Since it is desirable to reduce the size of such supporting means to the minimum, in order to reduce interference with the air flow, it is desirable to reduce the axial length of the shrouds as much as possible, so that there is the minimum load on the supporting means.

The combustion air stream enters the combustion chamher through the inlet G substantially without rotation about the longitudinal axis of the combustion chamber. In installations wherein the air ducts from the air fan are such that such a rotation would occur, straightening vanes may be provided either in the approach ducts or even within the combustion chamber, e. g., as radial vanes on the shrouds; such straightening vanes being well known, per se, they are not further described herein.

As a result of the construction described above, the air flowing through the spaces between the shrouds has its direction of flow changed by the lips of the various shrouds and each lip produces in the combustion chamber a series of successive toroidal eddies which are arranged, when generated, substantially along the surface of a cone similar to, and coaxial with, the fuel spray cone S, which eddies subsequently travel forwardly, longitudinally through the combustion chamber. These eddies resemble smoke rings in general way and travel as entities. Within each. torus the fluids travel with ring-like movements in directions that are influenced by the direction of the lip. Thus, in the eddies emerging from the

lips

4a, 6a and 8a the matter on the downstream faces thereof moves toward the central axis of the combustion chamber and away from the combustion chamber wall, while in the eddies emerging from the

lips

6b and 8b the rotation in the opposite direction is encountered. "It is desirable that the outermost eddies rotate in such a way that matter on their downstream faces moves toward their axis. This movement assists in keeping fuel away from the combustion chamber walls and is achieved by the described arrangement of the lips.

The flame is thereby stabilized without, however, recourse to centrifugal or radial movements that would impinge the flame against the combustion chamber wall. The combustion products, after dilution by secondary air admitted through the openings E, continue through the part C of the combustion chamber, which has the usual outlet (not shown) which may be connected to a gas turbine or other device.

It has been found that a combustion chamber as shown in the accompanying drawing and which had an internal diameter of 13 inches enabled a maximum combustion intensity of l.1 10' B. t. u./(hour) (cubic foot of combustion chamber)/ (atmosphere of combustion chamber pressure) to be reached satisfactorily with a pressure drop across the combustion chamber of 0.8% of the air supply pressure when this supply pressure was 2 atmospheres.

*It has also been found that combustion of a lean overall fuel/ air mixture may proceed satisfactorily in the combustion chamber of the invention, apparently due to the formation of relatively stagnant or less turbulent air zones near the double lipped shrouds which act as zones of local fuel enrichment and thus maintain even combustion.

In a modified apparatus, the concentric shrouds may be arranged so that they can be axially displaced in relation to one another and can thus provide toroidal eddies along the surface of fuel spray cones having different cone angles.

In a further modification, the concentric shrouds may be given a slightly frusto-conical, forwardly divergent form so that relative axial movement of the shrouds in relation to each other provides a means for controlling the amount of air supplied to the combustion chamber as well as providing the succession of toroidal eddies.

It will be understood that the concentric shrouds need not be arranged to produce toroidal eddies over substantially the entire cross-section of the combustion chamber as indicated above, but only a part thereof, for example two or more series of successive toroidal eddies near the combustion chamber wall, or again, closely adjacent to the burner.

It will be appreciated that several other modifications may be made. Thus the planes in which the concentric shrouds terminate, downstream from the burner, may be regularly or irregularly spaced from each other to conform to the characteristics of the fuel spray. For similar reasons, radial distance between the shrouds may be varied, and the projection of the external and/or internal lips into the intershroud space may also be varied from that stated. The clearance between the burner and the atomizer shroud may also be varied to produce the most suitable air velocity for controlling the spray.

Again, the alternation of double-lipped and single-lipped shrouds is not essential; there may be, for example, pairs of double-lipped shrouds alternating with single-lipped shrouds.

Furthermore, the burner and shrouds need not be coaxial with the combustion chamber; thus one or more burners may be located between the shrouds, with or without the central burner. This arrangement is particularly suitable for gas fuel and is shown in Figures 2 and 3.

Referring now to Figures 2 and 3, there is shown a combustion chamber that may be provided with an air casing as shown in Figure 1, having four gas burners 11 supported by a support ring 12 and arranged symmetrically about the longitudinal axis of the chamber. An igniting device 13 is arranged substantially centrally of these burners, and concentric with this device 13 are arranged

shrouds

14, 15, 16, 17, 18, 19, 20, 21 and 22 having radial lips at their forward or downstream ends;

of these, shrouds 14, 16 and 17 have internal lips only, shrouds 18, 19 and 21 have external lips only, while

shrouds

15, 20, and 22 have both internal and external lips. It is thus seen that all shrouds have lips extending away from the burners while the last three enumerated shrouds additionally have lips toward the burners. Moreover. the shrouds 17 and i8 terminate in a plane nearest the burners and the other shrouds, situated progressively farther from the burners, terminate in planes that are axially progressively farther forward. The several shrouds, plate 12 and and the igniter 13 are mounted on a cruciform support including radial members 12a.

Air holes 23 are provided in the ring 12 in order to admit as much air as possible to the combustion chamber.

Another alternative is to have two or more burners, each with associated concentric shrouds arranged in one combustion chamber.

A certain deviation from concentricity of the shrouds can be tolerated according to the air flow and fuel spray characteristics.

For constructional convenience it is generally preferred to have all the shrouds 58 and 14-22 terminating in one plane at their ends remote from their lips; this means that the outermost shrouds 8 and 22 are the longest ones in the axial direction; such shrouds can conveniently be supported by a single frame or spider situated behind the burner as indicated above.

It is however possible to reduce the shroud length very considerably; in fact the shroud length may be reduced to such an extent that the axially overlapping shroud portions are only about five or less times as long as the radial distance across the gap between a given shroud and the associated lip of the next innermost shroud. When the length of the shroud is reduced greatly, e. g., so that the axial overlap vanishes, the lips become less effective. Such extremely short shrouds, as well as the omission of the tubular shrouds and the use of merely a series of rings, while included in the broadest aspect of the invention, are not preferred.

Finally it will be appreciated that the toroidal eddyproducing means of the present invention may be constructed as a separate assembly for fitting to existing combustion chambers.

We claim as our invention:

1. Apparatus for combustion of fluent fuel comprising a combustion chamber having an air inlet at one end thereof for the admission of a combustion air stream, a fuel burner which delivers fuel into said air stream within the combustion chamber, and a plurality of generally annular air deflectors of progressively different diameters situated in the path of at least the preponderant part of said air stream in the vicinity of and at different distances from the said burner so as to provide a plurality of intervening, annular openings for the passage of said air stream as a corresponding plurality of annular fractional air streams, said deflectors having deflecting surfaces disposed transversely to the direction of said air stream for imparting transverse velocity components to said fractional streams and thereby forming at least two series of successive toroidal eddies in said preponderant part of the air stream substantially at the zone wherein this part of the air stream meets the fuel issuing from the burner, whereby the toroidal eddies contain air and fuel and travel in succession through the combustion chamber in the said direction of the air stream.

2. Apparatus according to claim 1 wherein said chamber has an elongate enclosing combustion chamber wall and said deflectors are situated at progressively different distances from said enclosing wall, said deflecting surfaces being oriented in substantially transverse relation to said chamber wall so as to impart to said annular fractional air streams velocity components that are radial with respect to the said chamber wall, said combustion chamber and deflectors being free from any air guide means that imparts to the air a movement of rotation about the axis of the combustion chamber, whereby spreading of the flame which results from the ignition of the said fuel and air against the said chamber wall is minimized.

3. Apparatus according to claim 2 including a generally annular air shroud extending longitudinally with respect to said direction of air flow in spaced relation to said chamber wall for dividing said air stream into fractional air streams flowing respectively within and without the shroud, at least one of said air deflectors being an annular lip extending laterally from the downstream portion of said shroud.

4. Apparatus according to claim 3 wherein at least that one of said air deflectors nearest the combustion chamber wall is a lip directed laterally outwardly from a shroud, whereby matter in the toroidal eddies nearest the wall will rotate in such a way that matter on the downstream faces thereof moves away from the combustion chamber wall.

5. Apparatus according to claim 1 wherein said air deflectors are situated at progressively different distances from the wall of said combustion chamber and are axially displaced from one another along said direction of air flow in such a way that the air deflector nearest the combustion chamber wall is farther downstream than an air deflector near the burner.

6. Apparatus for combustion of fluent fuel comprising an elongate combustion chamber having an air inlet at one end thereof for the admission 'of a combustion air stream and adapted for the passage of said air stream through the chamber substantially without rotation of the air about the longitudinal axis of the chamber, a fuel burner which delivers fuel into said air stream within the combustion chamber, said burner being spaced from the Wall of said combustion chamber, a plurality of radially spaced annular shrouds disposed in the path of at least the preponderant part of said air stream in advance of the zone whereat this part of the air stream meets the fuel issuing from the burner so as to divide the said air stream into a plurality of annular fractional streams, at least some of said shrouds being situated between the burner andthe said wall, and annular lips on the downstream parts of said shrouds extending laterally therefrom and situated in the vicinity of the said zone whereat the said part of the air stream meets the fuel for deflecting the said fractional air streams and forming a series of toroidal eddies in each one of said fractional streams, whereby the toroidal eddies contain air and fuel and travel in succession through the combustion chamber in the said direction of the air stream.

7. Apparatus according to claim 6 wherein the said shrouds have lips directed laterally in directions away from the burner.

8. Apparatus according to claim 7 wherein at least one but not all of said shrouds also has a lip directed laterally in a direction toward the burner.

9. Apparatus according to claim 6 wherein the lip on the shroud nearest the burner is situated in a transverse plane that lies at a shorter axial distance beyond the burner in the said direction of the air stream than the transverse plane containing the lip on the shroud farthest from the burner.

10. Apparatus according to claim 9 wherein the axial lengths of the shrouds are such that at least each pair of adjacent shrouds overlap.

11. Apparatus according to claim 10 wherein the extent of said overlap is at least five times the radial distance between the shroud and the lip on the neighboring shroud.

12. Apparatus according to claim 9 wherein said burner is situated substantially at the central axis of the combustion chamber and the lip on the shroud of greatest radius is directed outwardly from the shroud toward the wall of the combustion chamber.

13. Apparatus according to claim 6 including a plurality of burners situated between the central axis of the combustion chamber and the combustion chamber wall, a plurality of said shrouds being inner shrouds situated between the said central axis and the burners for dividing the central part of the air stream into annular fractional streams, the lip on the inner shroud nearest the burners being situated in a transverse plane that lies at a shorter axial distance beyond the burner in the said direction of the air stream than the transverse plane containing the lip on the shroud nearest the said central axis.

14. Apparatus according to claim 13 wherein the lip on the shroud nearest the burner and between the burners and the combustion chamber wall is situated in a transverse plane that lies a shorter axial distance beyond the burners in the said direction of the air stream than the transverse plane containing the lip on the shroud nearest the combustion chamber wall, the latter lip being directed outwardly from the shroud toward the combustion chamber Wall.

15. Apparatus for combustion of fluent fuel comprising an elongate combustion chamber having an air inlet at one end thereof for the admission of a combustion air stream, a fuel burner which delivers fuel into said air stream as a forwardly diverging cone Within the combustion chamber, said burner being spaced from the wall of said combustion chamber, a plurality of tubular, axially overlapping, radially spaced shrouds substantially coaxial with the longitudinal axis of the combustion chamber situated in the path of at least the preponderant part of the air stream so as to divide the said air stream into a plurality of annular fractional streams, said shrouds terminating at their downstream ends in lipped edges that project laterally across the paths of said fractional streams, said lips being situated at different axial distances forwardly from the burner so as to lie close to but in rear of said cone for deflection of said fractional streams and forming a series of toroidal eddies in each of said streams, whereby the toroidal eddies contain air and fuel and travel in succession through the combustion chamber in the said direction of the air stream.

References Cited in the file of this patent UNITED STATES PATENTS 1,344,029 Fischer June 22, 1920 1,474,867 Walker Nov. 20, 1923 2,560,207 Berggren et a1. July 10, 1951 FOREIGN PATENTS 229,158 Switzerland Dec. 16, 1943