GB2410789A

GB2410789A - Gas burner manifold arrangement

Info

Publication number: GB2410789A
Application number: GB0502137A
Authority: GB
Inventors: Edward D Hart; Dennis Lewis
Original assignee: Sit Bray Ltd
Current assignee: Sit Bray Ltd
Priority date: 2004-02-06
Filing date: 2005-02-02
Publication date: 2005-08-10
Anticipated expiration: 2025-02-02
Also published as: US20050181321A1; GB0502137D0; GB2410789B; DE102005004844A1

Abstract

A burner manifold (2 fig 3) for one or a series of burners (128 fig 5) has a first chamber 22, and pressurised air is introduced into this chamber from an inlet (28 fig 1G). The chamber also has at least one outlet 4 leading to the burner or burners, and gas is introduced to mix with the air. The air can be introduced from a second chamber 24, which is separated by a wall 30, but in fluid communication with the first chamber via a plurality of apertures (32 fig 2). The apertures may control the flow of air between the first and second chambers, and the gas may be supplied into the first chamber for mixing to occur. The gas may be supplied from a third chamber 26 via a duct 10 which acts as gas injection means. The manifold also includes a front plate 8 in which the outlet apertures 4 are formed. All the pressurised air may be supplied from a fan unit.

Description

1 2410789 Air/Gas Burner System The invention to which this application

relates is a system for allowing the controlled and efficient introduction of air and gas into a burner for the air and gas mixture to be burned to provide a heating effect.

Under traditional means gas flows through a tubular steel manifold to a controlled brass orifice to regulate the quantity of gas injected into a burner. Changes in gas pressure affect the volume of primary air being induced into the burner.

Therefore, any loss in gas pressure translates to a reduction in air entering the burner under atmospheric conditions.

Typically, atmospheric burners operate between 50-70% primary aeration with NOx emission of approximately 200-250 ppm.

The apparatus typically comprises a manifold into which air is introduced and, in relation to said manifold, there are provided one or a series of gas inlets for introducing gas into or through the manifold. Connected to the manifold, are one or a series of burners, the same located with respect to the manifold such that the gas and air is introduced into the burners as a mixture of desired gas/air quantities for ignition and burning through the burners. A preferred form of burner is described within the applicant's patent US-6461152.

Typically, a plurality of burners are provided, each with an open end connected to the manifold, at spaced locations along the manifold, which is typically in a linear form. The provision of manifolds of this type to provide a gas and air mixture which is subsequently burned on the burners is known.

One patent, namely US-6461152 describes a system for hypo stoichiometric burners whereby there is provided a manifold which is open to atmosphere so as to allow air to enter the manifold and a series of gas inlets are provided with respect to the manifold so that gas also enters the same. Further air is introduced with a volume of approximately 1-30% of additional air via a fan unit which introduces the additional air in a pressurised manner into the manifold in addition to the air which is able to enter the manifold from atmosphere. The gas and air are then allowed to leave the manifold in a direction towards the burners passing through a Venturi tube, which is a well known feature in burner assemblies. The mixing of the gas and air occurs within the Venturi tube prior to entering the burner. While it is claimed that this provides an efficient manger of providing an air and gas mixture, it has been found to be impractical in that in order to operate successfully, the pressure of the gas is required to be at a relatively high level and, furthermore, of a uniform flow rate so as to ensure that the required gas and air mixture ratio occurs every time. However, in certain areas such as, for example, certain States in the USA, it is found that the gas supply pressure is relatively low which can cause problems in the operation and, furthermore, that there can be relatively large fluctuations in the gas pressure over time which can also cause problems in the operation. These problems, in turn, mean that the burning efficiency is poor and emissions can be too high such that emission limit requirements can be exceeded therefore meaning that the burners cannot be used.

Global awareness of harmful emissions has lead to legislation to control and reduce emissions of gas appliances particularly in the European Community countries and USA. Pre-mix burners offer the benefits of low Co (carbon monoxide) and NOx (nitric oxide).

However the market direction calls for more compact heating units at lower production cost with an increased output yet with lower Co and NOx emission. These factors cause conflict for the appliance designer.

A further problem which is experienced is that the gas and air mixture is not efficiently supplied to each of the burners such that, for example, one burner may receive a higher proportion of gas in the gas and air mixture than other burners connected to the manifold at different locations with respect to the manifold.

Indeed, what typically happens is that the burner which is at the furthest end of the manifold from the additional air inlet, receives a larger percentage of air in the gas and air mixture compared to the other burners. Similarly this problem can be attributed to other burner arrangements wherein varying amounts of the mixture with differing proportions of air and gas are supplied to different areas of one or more burner plates, resulting in inconsistent temperature distributions during use.

The aim of the present invention is to provide a burner manifold system which allows a uniform supply of the gas and air mixture, particularly for super stoichiometric combustion and also to provide a more predictable operation of the same such that the required emission levels can be met.

In a first aspect of the invention, there is provided a burner manifold for one or a series of burners, said manifold including a first chamber having at least one outlet leading to said one or more burners and into which air is introduced from a second chamber, an inlet for the supply of air under pressure into the second chamber, and gas supply means arranged to introduce gas to mix with the air, wherein said first and second chambers are arranged to be in fluid communication via a plurality of apertures.

According to a preferred embodiment, the gas supply means introduces gas downstream of the second chamber. Typically, in the vicinity of the outlet or outlets from the manifold, mixing of the air and gas occurs such that an air/gas mixture is supplied to the burner.

Typically, the shape of the outlet is selected so as to control the air/gas mixture which is supplied to the burner. In one embodiment, the burner may be connected directly to the manifold or each can be connected via a tube which links the burner to the manifold and along which the air/gas mixture passes to the burner.

In one embodiment, the air is introduced into the second chamber of the manifold via a fan unit with the air inlet located at one end of the said manifold. The manifold is not open to atmosphere and therefore all, or substantially all, of the air which is utilised in the manifold is supplied under pressure from the fan unit. Thus the fan unit is provided to supply required air, typically 120%-135% of the required air. This therefore ensures that efficient supply of air is provided and the manifold is not required to induce air from the atmosphere or by any other means. As a result, lower NOx emissions are achievable with the capability to increase loading to the burner hence resulting in lower cost combustion.

Typically, the manifold first and second chambers are separated by a plate which passes along the length of the manifold and defines one of the walls of the said first and second chambers.

The plate has apertures provided therein to allow the passage of air from the second chamber into the first chamber. The plate may be perforated and the size, shape and pattern of the apertures on the plate can be selected to suit particular manifold design requirements. The provision of the plate with the apertures, ensures that air is supplied more uniformly along the length of the manifold such that each of the burners receive, at their location, the required quantity of air which mixes with the gas which is introduced at that location. Typically, a gas supply means is provided for each of the burners which are connected to the manifold.

In one embodiment, one of the burners may be supplied with an air/gas mixture which is richer in gas than the other burners so as to ensure that that burner will ignite more readily when attempting to ignite the burners.

To assist a homogeneous gas/air mixture, more than one radial outlet may be used and, furthermore the arrangement which will be described herein, allows gas to be injected tangentially to the air flow.

Typically the system as herein described, is for use with premix burners being supplied with air at approximately 120% to 135% of the required air for operation i.e including excess air, to allow super stoichiometric combustion.

In a second aspect of the invention there is provided a burner manifold system, said manifold system incorporating a manifold to which is connected one or a series of burners, said manifold incorporating gas supply means, for introducing gas to a burner via an outlet in the manifold, a first chamber into which air is introduced from a second chamber wherein substantially all of the air supplied to said one or more burners is introduced from externally of the manifold under pressure into the second chamber via at least one air inlet.

In one embodiment some gas may be present in the first chamber so as to allow mixing to occur, as the gas and air leave the outlet apertures in the manifold towards the burner. The provision of the apertures provide control for the gas and air as the mixture enters the burner and also offer a means to assist timely, smooth, ignition.

Typically, the system can operate at low gas pressure such as below 7.5 mbars and is not reliant upon high gas pressure, above 7.5 mbars to induce aeration atmospherically.

In a third aspect of the present invention there is provided a method of premixing air and gas prior to combustion comprising the steps of, providing a manifold including two or more chambers, introducing air into one chamber under pressure from externally of the manifold, introducing air into a further chamber from said one chamber via a plurality of apertures, introducing gas into the air flow downstream of said one chamber via gas supply means, passing said air and gas through one or more outlets in the manifold.

Typically the gas and air passes through the outlets in the manifold to a burner or burners which are connected directly to the manifold.

Specific embodiments of the invention will now be described with reference to the accompanying drawings, wherein: Figures la to lg illustrate a first embodiment of the invention in various views; Figure 2 illustrates a more detailed view of the gas manifold with a front plate removed; and Figure 3 illustrates the air/gas system in accordance with one embodiment of the invention.

Figure 4 shows a plan view of a manifold according to a second embodiment of the present invention.

Figure 5 shows a cross section of the manifold of figure 4 taken through the plane B-B.

Figure 6 shows a cross-section of the manifold of figure 4, taken through the plane A-A.

Figure 7 shows a part cut away perspective view of the manifold of figure 4.

Figure 8 shows a perspective view of the manifold of figure 4 with the burner removed.

Figure 9 shows a perspective view of the manifold of figure 4 with the burner attached.

Each of the embodiments described below provide for a manifold with two or more chambers disposed so as to allow control of the pressurised air flow in order to achieve the required distribution of the air/gas mixture for supply to one or more burners.

Referring firstly to Figures la to la, there are illustrated various views of the gas/air manifold in accordance with the invention.

In this embodiment, the manifold 2 is linear and elongate in shape and has a series of air/gas supply outlet apertures 4 and, although not shown, at each outlet aperture 4 there is provided a burner such that the air and gas leave each outlet 4 as indicated in the general direction of arrow 6 in Figure 1 a to enter the burners. The manifold has a front plate in which the outlet apertures 4 are formed and protruding through the outlet apertures 4 are the ends of the gas supply means in the form of ducts 10, which act as gas injection means 10. However it should be appreciated that the injection means need not protrude through the apertures 4 and may instead be provided with openings for the injection of gas which are substantially flush with the outlet apertures 4 or else retracted from the outlet apertures 4.

The manifold also has a top plate 12, end plates 14 and 16, a base plate 18 and rear wall 20 so as to form an elongate box with an air 28 and gas 36 inlet disposed at one end.

Figure le illustrates a cross sectional view along line A-A and shows the interior of the manifold. Figure lg shows part of the interior of the manifold with the front plate 8 having been removed.

The interior of the manifold comprises a first chamber 22, a second chamber 24 and a third chamber 26. Each of the first, second and third chambers run along the length of the manifold.

The first and second chambers 22, 24 are provided to receive air which is introduced into the second chamber 24 via the inlet 28 through which the air is blown under pressure by a fan unit, not shown. The air then passes along the chamber 24 and as it does so, it comes up against the plate 30 which separates the first and second chambers. Reference should also be made at this point to Figure 2 which illustrates the view of Figure lg in greater detail and shows how the plate 30 has a series of apertures provided along the length thereof, said apertures provided to allow air to pass from the second chamber 24 into the first chamber 22.

The apertures 32 are provided in a pattern to suit particular usage requirements and in this case, there are provided a plurality of clusters of apertures 34 spaced as shown in more detail in Figure 2. Air passes through these apertures into the second chamber 24 and it is found that, by altering the shape, size and numbers of apertures 32, a uniform airflow can be achieved into the chamber 22 along the entire length of the manifold. This allows for a substantially equal distribution of air to each of the outlet apertures 4 disposed along the length of the manifold 2.

The third chamber 26 is connected to receive a gas supply at pressure via the gas supply inlet 36. The chamber 26 is isolated from chamber 24 such that chamber 26 contains substantially no air and the chamber 24 contains substantially no gas. The gas passes through the in jection means 10 and, although, in this embodiment, the injection means are shown to pass through the chamber 22, it is possible that in certain arrangements, the injection means may stop at the wall of the chamber 22. 'the gas injection means 10 passes through the outlet apertures 4 in the front plate 8. A certain amount of the gas may pass into the chamber 22 which is mostly filled with air; however this is found not to be a problem. The air passes through the outlet apertures 4 around the space left between the outer wall of the front plate 8 and the gas injectors 10.

The particular shape of the apertures 4 with respect to the provision of the gas injection means can be designed so as to provide an optimum mixture of the gas and air. The gas and air then passes as indicated by arrow 6 in Figure la away from the manifold either directly into the burners or via tubes which connects the apertures 4 to the burner. In each case, the mixing of the gas and air occurs efficiently and uniformly along the length of the manifold.

It will be appreciated that by providing a manifold system as shown which is sealed from the surrounding atmosphere, the fan can control the amount of air being supplied for combustion.

Thus one or more burners can be attached directly to the manifold without the need to entrain air from the surrounding environment. In addition burners can be oriented as required by provision of tubing (not shown) connecting the burners to the manifold.

Figure 3 illustrates the manifold with burners connected thereto and illustrates, via the arrows 38, the air supply direction and arrows 40 which show the gas supply, and the mixing of the air/gas which occurs.

Turning now to Figures 4 to 9 which relate to a second embodiment of the present invention, there is illustrated a burner manifold arrangement which differs from the first embodiment in the arrangement of the gas injectors and the alignment of the burner.

The assembly of Figure 4 is similar to the first embodiment in that it includes an inlet 104 through which gas enters under pressure into the chamber 106 which passes along the length of the assembly. At spaced intervals along the chamber 106 are provided orifices in the form of injector ducts 108 which project forwardly as shown in Figures 2 and 3. There is also provided an inlet 114 which allows the entry of air under pressure into chamber 116 which passes along the length of the assembly.

Connecting this chamber 116 to the chamber 118 is a plate 120 which has a series of apertures which allows the air to pass from the chamber 116 into the chamber 118.

However in this embodiment, the injectors 108 stop short of the front plate 122 and the outlet apertures 124 arc offset from the in jectors 108 in order to promote mixing within the chamber 118. The air inside the chamber 118 and gas from the injectors 108 mix and pass through the plate 122 into the housing 130 via the series of apertures 124 at spaced intervals along the length thereof. In this example, the apertures 124 arc shown as having a relatively large size and large pitch. However it should be appreciated that in other embodimcuts of the invention a larger number of smaller holes with a smaller pitch can be provided to allow the passage of the gas air mixture. The gas and air therefore are introduced into the housing 130 which passes along the length of the assembly.

The housing 130 includes a side wall 128 which is formed as a flame strip and in which are provided a series of apertures in a particular configuration and designed to suit particular burning requirements. The flamestrip can be formed of any suitable materials such as, for example, Stainless Steel, woven ceramic, sintered metal. Figure 4 shows a portion 131, of the flame strip, with the remainder of the flame strip omitted for ease of reference. The air and gas mixture then passes through the flame strip and is ignited to allow flames to be generated from the flame strip.

The arrangement of this embodiment promotes mixing of the air/gas prior to passing through the outlets 124 and is thus particularly suited to an arrangement whereby a single burner is provided along the length of the manifold since it provides for even distribution of a substantially homogeneous mixture onto the length of the flamestrip 128. It will be noted that this arrangement provides a flamcstrip 128 that is substantially lateral to the flow entering the housing 130 through outlets 124, when compared to the longitudinal arrangement of the burners in the previous embodiment. That is to say that the burner in this embodiment runs along the length of the manifold, whereas the previous burners extended away from the manifold.

This second embodiment is beneficial in that a manifold and burner can be provided as a complete module and so any number of burners can be provided for a given application without the need to provide a predefined number of burners as with the arrangement of the first embodiment.

Figures 7 to 9 illustrate the separate components of the second embodiment. Figure 7 illustrates the rear of the assembly and shows the chamber 118 with plate 120 with apertures (not shown) and the in jectors 108 from the gas chamber passing thereinto. It should however be appreciated that the injectors 108 may not be required and in certain embodiments, the gas can simply be allowed to leave the chamber 106 to mix with the air in the chamber 118 prior to passing through the apertures 124 in the plate 122 as shown in Figure 8. The air and gas mixture therefore passes through these apertures 124 and into the housing 130 defined by the component added to the same as shown in Figure 9 with the flame strip 128 allowing the passage of air and gas mixture therethrough to be ignited 132 as indicated.

The manifold and burner assemblies as herein described provide an efficient gas air mixture which allows excess air (approximately 120-135%) for the super stoichiometric combustion and lower NOx emissions.

Claims

(,laims: 1. A burner manifold for one or a series of burners, said

manifold apparatus including a first chamber having at least one outlet leading to said one or more burners and into which air is introduced from a second chamber, an inlet for the supply of air under pressure into the second chamber, gas supply means arranged to introduce gas to mix with the air, wherein said first and second chambers are arranged to be in fluid communication via a plurality of apertures.
2. A burner manifold according to claim 1, wherein the first and second chambers are separated by a plate with the apertures provided therein so as to control the flow of air from the second chamber into the first chamber.
3. A burner manifold according to claim 2, wherein the plate is perforated.
4. A burner manifold according to claim 2, wherein the plate forms a wall of each of the first and second chambers.
5. A burner manifold according to claim 1, wherein the gas supply means supplies gas into the first chamber such that mixing of the air and gas occurs in said hrst chamber and the air/gas mixture is supplied to the one or more burners.
G. A burner manifold according to claim 1, wherein the gas supply means supplies gas into the vicinity of the one or more outlets from the first chamber such that the gas mixes with the air upon exit of the air from the first chamber so as to provide an air/gas mixture to the one or more burners.
7. A burner manifold according to claim 6, wherein the first chamber primarily contains air.
8. A burner manifold according to claim 1, including a third chamber primarily containing gas as part of the gas supply means.
9. A burner manifold according to claim 1, wherein the gas supply means includes one or a series of ducts having an opening through which gas is supplied.
10. A burner manifold according to claim 9, wherein one duct is provided for each of the burners which are connected to the manifold.
11. A burner manifold according to claim 1, wherein the gas supply means injects gas tangentially to the air flow.
12. A burner manifold according to claim 1, wherein the air is introduced into the second chamber via a fan unit.
13. A burner manifold according to claim 1, wherein substantially all of the air passing through the burner is supplied by the fan unit.
14. A burner manifold according to claim 1, wherein the one or more outlets include a main aperture and one or more radial apertures.
15. A burner manifold according to claim 1, wherein the manifold is substantially sealed from the atmosphere.
16. A burner manifold according to claim 1, wherein the manifold forms an elongate member and the first and second chambers extend along the length of the manifold.
17. A burner manifold according to claim 1, wherein the burner comprises a flamestrip which extends substantially along a side of the manifold.
18. A burner manifold according to claim 1, wherein the one or more burners comprise a flamestrip which extends from a side of the manifold.
19. A burner system, said system incorporating a manifold to which is connected one or a series of burners, said manifold incorporating gas supply means for introducing gas to each burner via one or more outlets in the manifold, and at least one chamber into which air is introduced via at least one air inlet, wherein substantially all of the air supplied to said one or more burners is introduced from externally of the manifold under pressure into said chamber.
20. A burner system according to claim 19, including a first chamber into which air is introduced from a second chamber.
21. A burner system according to claim 20, wherein air is introduced into the first chamber from the second chamber via a plurality of apertures.
22. A burner system according to claim 20, wherein the gas supply means introduces gas downstream of the second chamber.
23. A burner system according to claim 19, wherein the air is supplied under pressure to the manifold by a fan unit.
24. A burner system according to claim 19, wherein between 120-135% of the air required for combustion is supplied to the manifold.
25. A method of premixing air and gas prior to combustion comprising the steps of: providing a manifold including two or more chambers; introducing air into one chamber under pressure from externally of the manifold; introducing air into a further chamber from said one chamber via a plurality of apertures; introducing gas into the air flow downstream of said one chamber via one or more gas supply means; passing said air and gas through one or more outlets in the manifold.
26. A burner manifold apparatus substantially as hereinbefore described with reference to the accompanying drawings.
27. A burner manifold system substantially as hereinbefore described with reference to the accompanying drawings.
28. A method of premixing air and gas substantially as hereinbefore described with reference to the accompanying drawings.