GB2066445A

GB2066445A - Radiant Tube Heating Devices

Info

Publication number: GB2066445A
Application number: GB8031915A
Authority: GB
Original assignee: BRITISH FURNACES Ltd
Current assignee: BRITISH FURNACES Ltd
Priority date: 1979-10-10
Filing date: 1980-10-03
Publication date: 1981-07-08

Abstract

So as to promote adequate mixing of the fuel and air in a radiant tube to give complete combustion, a burner head (28) is of frusto-conical shape, widening out in the direction in which flame is to be projected into the tube, a fluid fuel nozzle (30) is arranged to produce a fan-like spray of fuel within the burner head and the latter is provided with a plurality of apertures (36) for the flow of air into the space within the burner head, said apertures (36) being inwardly inclined to mix with the fluid fuel. <IMAGE>

Description

SPECIFICATION Radiant Tube Heating Devices The invention relates to radiant tube heating devices of the kind in which heat produced by the combustion of fuel in a closed tube is radiated outwards from the external surface of the tube, the tube, in use, being inserted into or through the furnace or other space to be heated.

Radiant tube heating devices are well known and commonly comprise, in combination, a burner, at least one tube which when the device is in use will extend into or through a furnace or other space to be heated, an outlet for waste gases and separate inlets for fluid fuel and air.

Heating devices of this kind are of two separate types, that is to say as follows:- 1. A first type consisting of a single continuous tube which when the device is in use is sealed at each end to a furnace casing, and in this case the burner is arranged to fire into one end of the tube whilst the products of combustion are extracted from the other end. The tube may be a straight tube or, alternatively, it may be of U or W configuration.

2. A second type consisting of two concentric tubes, the outer end of the tubes when the device is in use being sealed to a furnace casing at one end and being blanked off at the other end, and the inner one of the tubes extending along the outer one of the tubes to within a short distance of its blanked off end. In this case, the burner is arranged to fire into one end of the inner tube and the products of combustion pass down the inner tube and return to the outlet for waste gases along the annular space formed between the two tubes.

It is also well known for the burner to be of the so-called nozzle mixing type, that is to say where a burner head extends into the tube into which the burner is to fire and is provided with separate sets of outlet openings for the fluid fuel and air respectIvely, the openings being disposed so as to cause intermixing of the fuel and air and to produce a diffusion flame.

Heating devices of the kind described generally work quite well but it is sometimes found that the fuel and air is not adequately mixed to give complete combustion. It is also found that good heat transfer through the walls of the tubes is not always achieved. In these circumstances high thermal efficiency cannot be obtained. It is the object of the invention to provide a heating device of the kind described which will at least alleviate these problems to enable a high thermal efficiency to be achieved.

According to the invention, there is provided a radiant tube heating device including a burner head extending into a tube along which it is arranged to fire, the burner head being of frustoconical shape which widens out in the direction in which flame is to be projected into the tube, the narrower end of the burner head being connected to a fluid fuel nozzle carried at the outer end of a fluid fuel inlet pipe, said nozzle being provided with a plurality of jets which each extend at an angle to the axis of the burner head so that they can project the fluid fuel as a fan-like spray within the internal configuration of the burner head, and the frusto-conical wall of the burner head being provided with a plurality of apertures for the flow of air from the annular space surrounding the fluid inlet pipe into the space within the burner head, the arrangement being such that the fluid fuel and air are caused to intermix in the frusto-conical space within the burner head and to produce diffusion flame. Preferably, the plurality of apertures which extend through the wall of the burner head for the flow of air will be inwardly inclined towards the axis of the burner head so that the streams of air flowing through them into the space within the burner head each have a radial velocity and a tangential velocity which impart a swirling motion to promote effective mixing of the fuel and air streams as well as an axial velocity which gives the gaseous mixture a forward movement. The larger end of the burner head may fill the cross sectional area of the flow passage of the tube in which it is fitted so that the entire flow of air is through the apertures in the wall of the burner head.Alternatively, the larger end of the burner head may be somewhat smaller than the flow passage of the tube in which it is fitted so that a proportion of the air can flow around the outside of the burner head, and in this case the latter will preferably be provided with a plurality of external fins inclined at an angle to create a turbulent flow of air around the outside of the burner head.

In order that the invention may be fully understood and readily carried into effect, the same will now be described, by way of example only, with reference to the accompanying drawings, of which: Fig. 1 is a diagrammatic part-sectional view of a radiant tube heating device embodying the invention, and Fig. 2 is a sectional view, drawn to a much larger scale than Fig. 1, of a burner head forming part of the heating device.

Referring now to Fig. 1, the radiant tube heating device there illustrated includes two concentric tubes 10 and 12, the tube 10 being sealed to a furnace casing at one end 14 and being blanked off at the other end 16, and the tube 12 extending along the tube 10 to within a short distance of its blanked off end. A burner, generally indicated 18, is arranged to fire into one end of the tube 12 and the products of combustion pass down the inner tube and return to an outlet 20 for waste gases along an annular space 22 formed between the two tubes.

The burner 1 8 is of the so-called nozzle mixing type, that is to say where a burner head extends into the tube 12. The construction of the burner is not here illustrated. Suffice to say that a supply of fluid fuel is admitted at 24, a supply of air is admitted at 26, and at the burner head, which will presently be described, there are provided separate sets of outlet openings for the fluid fuel and air respectively, the openings being disposed so as to cause intermixing of the fuel and air and to produce a diffusion flame within the tube 12.

Referring now to Fig. 2, it can be seen that the burner head 28 which is located in one end of the tube 12 is of frusto-conical shape and widens out in the direction in which flame is to be projected into the tube. The wider end of the burner head is somewhat smaller than the flow passage of the tube 12. The narrower end of the burner head is connected to a fluid fuel nozzle 30 carried at the outer end of a fluid fuel inlet pipe 32, the latter being in communication with the fluid fuel inlet 24. The nozzle 30 is provided with a plurality of jets 34 which each extend as shown, at an angle to the axis of the burner head so that the jets can project the fluid as a fan-like spray within the internal configuration of the burner head.

The frusto-conical wall of the burner head is provided with a plurality of apertures 36 for the flow of air from the annular space surrounding the fluid fuel inlet pipe 32 (and which communicate with the air supply 26) into the space within the burner head.

The arrangement is such that when the heating device is in operation the fluid fuel and air are caused to intermix in the frusto-conical space within the burner head and thus produce a diffusion flame. It will be seen that the plurality of apertures which extend through the wall of the burner head for the flow of air are inwardly inclined towards the axis of the burner head.

Consequently, the streams of air flowing through said apertures into the space within the burner head each have a radial velocity (indicated Vr in Fig. 2) and a tangential velocity (indicated Vt in Fig. 2), which impart a swirling motion to promote effective mixing of the fuel and air streams, in addition to an axial velocity which gives the gaseous mixture a forward movement. A proportion of the total volume of air flowing along the annular space surrounding the inlet pipe 32 is allowed to flow around the outside of the burner head, and although it is not apparent from the drawings, the burner head is provided with a plurality of external fins which are inclined at an angle to create a turbulent flow of air around the outside of the burner head. This turbulence not only assists the mixing of the fluid fuel and air but also promotes good heat transfer through the walls of the tubes.

Thus there is provided a radiant tube heating device which by virtue of the excellent mixing of the fluid fuel and air resulting from the design of the burner head has been found to be very efficient in operation.

Various modifications may be made without departing from the scope of the invention. For example, it will be understood that instead of the larger end of the burner head being somewhat smaller than the flow passage of the tube in which it is fitted, it may be of the same size so that all the air passing along the annular space surrounding the fluid fuel inlet pipe is caused to flow through the plurality of apertures in the frusto-conical wall of the burner head. On the other hand, where a slower rate of combustion is required and is brought about by a proportion of the air being allowed to flow around the outside of the burner head, the ratio of the primary air passing through the plurality of apertures in the frusto-conical wall of the burner head to the amount to secondary air passing around the outside of the burner head may be determined by experiments to give the required rate of combustion for different operating characteristics.

Although the invention has been described as applied to a heating device of the type consisting of two concentric tubes, it will be understood that it could with equal advantage be applied to a heating device of the type consisting of a single continuous tube.

Claims

1. A radiant tube heating device including a burner head extending into a tube along which it is arranged to fire, the burner head being of frusto-conical shape which widens out in the direction in which flame is to be projected into the tube, the narrower end of the burner head being connected to a fluid fuel nozzle carried at the outer end of a fluid fuel inlet pipe, said nozzle being provided with a plurality of jets which each extend at an angle to the axis of the burner head so that they can project the fluid fuel as a fan-like spray within the internal configuration of the burner head, and the frusto-conical wall of the burner head being provided with a plurality of apertures for the flow of air from the annular space surrounding the fluid inlet pipe into the space within the burner head, the arrangement being such that the fluid fuel and air are caused to intermix in the frusto-conical space within the burner head and to produce a diffusion flame.

2. A radiant tube heating device according to claim 1, in which the plurality of apertures which extend through the wall of the burner head for the flow of air are inwardly inclined towards the axis of the burner head so that the streams of air flowing through them into the space within the burner head each have a radial velocity and a tangential velocity which impart a swirling motion to promote effective mixing of the fuel and air streams as well as an axial velocity which gives the gaseous mixture a forward movement.

3. A radiant tube heating device according to either one of the preceding claims, in which the larger end of the burner head fills the cross sectional area of the flow passage of the tube in which it is fitted so that the entire flow of air is through the apertures in the wall of the burner head.

4. A radiant tube heating device according to either one of claims 1 and 2, in which the larger end of the burner head is somewhat smaller than the flow passage of the tube in which it is fitted so that a proportion of the air can flow around the outside of the burner head.

5. A radiant tube heating device according to claim 4, in which the outside of the burner head is provided with a plurality of external fins inclined at an angle to create a turbulent flow of air around the outside of the burner head.

6. A radiant tube heating device constructed, arranged and adapted to operate substantially as hereinbefore described, with reference to and as illustrated by the accompanying drawings.