WO1991005206A1

WO1991005206A1 - Gas burners

Info

Publication number: WO1991005206A1
Application number: PCT/GB1990/001485
Authority: WO
Inventors: Michael Cafferty
Original assignee: Bray Burners Limited
Priority date: 1989-09-30
Filing date: 1990-09-28
Publication date: 1991-04-18
Also published as: DE69020901T2; EP0494888A1; ATE125028T1; EP0494888B1; DE69020901D1; GB8922086D0

Abstract

The invention provides that a gas burner body having a row of outlet apertures (10) for the gas air mixture is provided with a wall (14) adjacent the said row of apertures so that the curtain of mixture (13) issuing from said apertures lie adjacent the wall and the flame (F) will be established on the top edge of the wall. The other side of the curtain is sufficiently open to the atmosphere to allow additional air (15) to be drawn into the curtain for combustion in order to effect a higher degree of combustion and therefore a reduction in the amount of toxic emission caused by the combustion of the mixture. Various embodiments comprising different configurations of burner as possible.

Description

Gas Burners

This invention relates to gas burners and has as an object to reduce the levels of toxic emissions which are produced as a result of the combustion in conventional gas burners.

The by-products of gas combustion include a number of toxic compounds such as nitrogen oxides and carbon monoxide. An increase in our understanding of the harmful effects of these compounds on the environment, coupled with an increase in environmental awareness, has prompted investigations to determine a way of eliminating, or reducing, the toxic by¬ products associated with combustion.

It is known that conventional, atmospheric, gas burners used, for example, in cookers, boilers snd central heating systems, generally emit in excess of 100 ppm of nitrogen oxides when functioning under normal operational conditions.

This value can be reduced by increasing the amount of air intimately mixed with the fuel gas before ignition. This air, normally called primary air, is usually expressed as a volume percentage of that amount known as the Theoretical Air Requirement or T.A.R. required for complete combustion for the particular fuel. Thus, for example, it is possible to reduce emissons of nitrogen oxides down to a level below 40 ppm by including extra air to a level of 40% in excess of the (T.A.R) in the primary gas fuel mixture.

Furthermore, it is also known that the reduction in emitted nitrogen oxides is related to the amount of excess air in the gas fuel mixture.

However, a prerequisite to increasing the amount of air in the primary gas fuel mixture to these levels involves redesign of the burner such that it can sustain the excess air and function efficiently. Such redesigned burners are normally equipped with a fan and control means and are known as premix burners. ,

Alterations of this nature are costly and moreover conflict with recent developments in the gas appliance industry, as atmospheric gas burners are today designed with emphasis on reducing the weight, volume and complexity of the burner.

Alternative ways of incorporating additional primary air into the system comprise automatically entraining air into the system as a result of the fuel being injected into the burner. This is known as primary aeration and conventional burners operating in this way can achieve primary aeration levels of between 40 and 80% of T.A.R. The balance of air required to complete the combustion reaction diffuses into the flame after ignition and is called secondary air.

It is known that emission of nitrogen oxides peaks at a primary aeration level of approximately 50% and so it therefore follows that maximum amounts of nitrogen oxides are being produced during routine operation of an atmospheric gas burner. A reduction in primary aeration leads to an increase in other toxic products such as carbon monoxide. On the other hand, because of the design constraints of a conventional atmospheric gas burner, it is not possible to increase primary aeration levels beyond 60 - 70%.

The process of primary aeration can conveniently be sub¬ divided into first and second stages, the first stage representing the aeration which takes place prior to the gas fuel mixture leaving one or more primary outlet ports and the second stage representing the aeration that occurs following emissions of the gas fuel mixture from the outlets prior to ignition .

By the present invention it has been established that it is possible to provide an increase in primary aeration at the aforementioned second stage and thus the present invention provides a means' of increasing the amount of air entering the gas fuel mixture before ignition such that perceived or total primary aeration levels up to and greater than 100% can be achieved.

According to one aspect of the invention there is provided an apparatus comprising a gas burner having aerial outlet means in the form of a row of fuel outlets, or a single elongated outlet slit or slot, adjacent the base of and extending parallel to a wall so that a side of a fuel air curtain issuing from said outlets or said slit/slot passes up the wall and the other side of said curtain is sufficiently open to the atmosphere for air (extra air) to be drawn into said curtain.

Preferably, the fuel means comprises at least a single row on at least one side of the wall.

The provision of a wall facilitates laminar flow of the gas air mixture and the intake of the extra air. The burner m?y be such that the flame is established along the top edge of said wall; the provision of said wall in fact stabilizes the flame burning on the upper edge thereof. The extra air is induced into the gas fuel mixture progressively as the gas fuel mix passes up the wall. The invention creates conditions at the flame front such that substantive reduction in the levels of nitrogen oxides are evident in the combustion products.

It has been demonstrated that conventional burners operating at normal fuel injection pressures produce emissions of nitrogen oxides in excess of 100 ppm. In contrast, a conventional burner adapted according to the invention when operating under the same conditions produces emissions of nitrogen oxides below 50 ppm. These results illustrate considerable reductions in the levels of emission of nitrogen oxide, such levels having hitherto been unobtainable when operating a conventional gas burner, and the invention has considerable environmental advantage.

It is envisaged that a whole range gas burner designs may be produced in accordance with the invention. Thus, bar burners may be provided with walls on at least one side of the outlet ports and ring burners may be provided with concentric walls on at least one side of the outlet ports.

The invention therefore also has advantages economically in that it provides a means of adapting existing burners with the minimum amount of modification such that they can function within the same apparatus more effectively and desirably.

Embodiments according to the invention will now be described by way of example and with reference to the accompanying drawings of which:-

Fig. 1 is a perspective view of a known burner;

Fig. 2 is a perspective view of a burner constructed in accordance with the invention;

Fig. 3 is a sectional view of the burner shown in Fig. 2;

Fig. 4 is a perspective view of a bar burner in accordance with another embodiment of the invention; Fig. 5 is a perspective view of a burner in accordance with another embodiment of the invention;

Fig. 6 is a plan view of a body burner in accordance with another embodiment of the invention;

Fig. 7 is a perspective view of a the burner of Fig. 6;

Fig. 8 is a perspective view of a burner in accordance with another embodiment of the invention; and

Fig. 9 is a perspective view of a burner adapted in accordance with another embodiment of the the invention.

Referring to the drawings. Fig. 1 shows a burner which comprises two symmetrical metal plates, one of which is shown in Fig. 1 and illustrated by reference numeral 2. The said plates are spaced in opposed relationship and sealed about their adjoining perimeters 4 along sides 1A, IB and IC by overlapping the edges relating thereto. Each of the plates is pressed in like manner hence it will be apparent that the features illustrated in Fig. 1 on side 2 of the burner are also present on the opposing plate (not shown) .

Plate 2 is fashioned such that a fuel injection port 6 is located towards the lower front edge of the burner and is of a generally circular section. Injection port 6 leads to a U shaped path 6 which leads to the upper surface of the burner.

The upper surface of the burner is sealed by means of a plate 12 which contains a plurality of outlet ports 10 arranged in a plurality of longitudinal rows wherein the spacing between individual ports is fixed within but not between rows which provides a means of effectively combusting the fuel supply.

In use, a supply of fuel mixture is injected through the fuel injection port 6 and travels in a sinusoidal direction along injection path 6A ultimately issuing through the outlet ports 10 provided in plate 12 where combustion occurs. The first stage of primary aeration occurs during the injection of the fuel mixture into injection port 6 as air is induced into the mixture at port 6.

Referring now to Fig. 2 which shows the burner illustrated in Fig. 1 which has been adapted in accordance with the invention. It can be seen that plate 12 is provided with an elongate central wall 14. Moreover, the outlet ports 10 are arranged in two parallel rows located on either side of wall 14.

Wall 14 is preferably between 6-15mm in height and ports 10 are located preferably no more than 2.5 mm away from the base of wall 14. These parameters represent optimum construction conditions for the efficient functioning of the burner having regard to the typical sizes of the burners to which the invention mainly relates. The ports 10 must be sufficiently close to wall 14 to enable the fuel mixture issuing therefrom to travel up the wall. Furthermore, the velocity of the fuel mixture issuing from ports 10 must be greater than the burning velocity of the flame as desireably the flame, as shown at F in Fig. 3 should be established on the top edge of the wall 14. If this is not achieved the fuel mixture will ignite on the ports 10 and so augmentation at the second stage as the fuel travels up the wall, prior to ignition will not be possible. On the other hand, those skilled in the art will appreciate that, if the velocity of the fuel mixture significantly exceeds that of the burning velocity of the flame the fuel mixture will not ignite. In addition, the spacing between individual ports will be determined by the size of same, for example, in Fig. 2 and indeed in any embodiment the ports 10 are preferably 1 mm in diameter and the spacing between adjacent port centres is 2.5mm.

Port size and spacing are important parameters to consider when adapting a burner to function in accordance with the invention as if the ports are too widely spaced the flame will be unstable and if the ports are too closely spaced mutual stability will enable the fuel mixture to burn on the ports and so again augmentation of the primary air fuel mixture at the second stage will not be possible.

Consequently, under normal operating conditions it is necessary to design the burner substantially in a manner as hereinbefore if it is to function effectively.

In use, a supply of fuel mixture is injected through the fuel injection port 6 and travels in a sinusoidal direction in the burner body, ultimately issuing through the primary outlet ports 10 provided in plate 12 and upwardly along wall 14. The first stage of primary aeration occurs during the injection of the fuel mixture into port 6 in that air is drawn in the mixture at port 6 and the second stage of primary aeration occurs after the gas fuel mixture issues from the ports 10 as it travels up wall 14.

The second stage of primary aeration can be well understood and is illustrated diagrammatically in Fig. 3, wherein it can be seen that a gas fuel mixture issues out of ports 10 located on either side of the wall 14 and forms a fuel curtain 13 which passes upwardly along wall 14 prior to ignition on the uppermost surface edge of same. During upward passage of the fuel air curtain, additional air as illustrated by arrows 15, is drawn into the fuel mixture thus augmenting the degree of primary aeration at what is hereindescribed as the second_^stage.

When the gas fuel mixture issues from outlets 10 it travels vertically up wall 14 and during this process there is a progressive augmentation in the amount of air oxygen contained in the gas fuel mixture.

Ignition of the gas fuel mixture results in the provision of a stable flame F that is combusted on the uppermost edge of the wall 14.

It is thought that the provision of wall 14, which in turn provides for an increase in the degree of fuel aeration, optimises the combustion conditions and so reduces the level of toxic emissions.

It can be seen by reference to Figs. 4 to 9 that it is possible to provide a number of different burners in accordance with the invention. Specifically Fig. 4 shows a single bar burner which is provided on its uppermost surfaces 12 with a wall 14 and outlet ports 10 arranged on either side of same and parallel thereto.

Similarly, Fig. 5 shows a burner arranged to provide a horizontal curtain of fuel air mixture when provided with a wall 14 and ports 10. Figs. 6 and 2 illustrate a body burner having rows of circumferential ports 10 located on either side of rows of circumferential walls 14. When viewed in perspective, as seen in Fig. 7, it can be seen that ports 10 and walls 14 extend about only the upper fraction of the circumference of the burner and so combustion is confined to the upper surfaces of same. Fig. 8 shows a conventional ring burner which has been adapted in accordance with the invention such that a wall 14 is provided adjacent outlet ports 10.

Finally, Fig. 9 shows a bar burner which has been adapted in accordance with the invention and which has also been provided with a second wall 14A which is located opposite and parallel to wall 14. In addition, between walls 14 and 14A there is provided supplementary outlet ports 10A which augment the fuel supply at the site of combustion. The number of supplementary ports 10A is far less than the number of outlet ports 10. The provision of ports 10A enables the fuel, air mixture to be controlled and thus the total amount of primary aeration, as a result of augmentation at the fi_tst and second stage, may be adjusted by the supply of supplementary fuel in order to enhance flame stability. This arrangement may be used in any embodiment of the invention.

Existing designs of burners may be adapted in accordance with the invention or may be used in existing apparatus as the head space provided for combustion in existing apparatus is sufficient to accommodate the flame enhancing wall 14. This is an important feature of the preferred form of the invention as it enables operational burners to be adapted to function at lower nitrogen oxide emissions by making only minor modifications to the overall structure. The invention is not however to be considered as being limited to the adaptation of existing burners, it may be embodied in any and all suitable new and existing burner designs.

From the foregoing description it will be apparent that the advantages conferred by the utilisation of the invention represent a significant contribution to the art of combustion by burners.

Claims

1. A gas burner comprising a burner body for containing a combustible gas air mixture^ apperture means in the body enabling the issuence from the body of a curtain of the said gas air mixture, wall means adjacent the apperture means arranged so as to lie substantially parallel thereto and adjacent one side thereof, and providing a means on which a flame of the burner can be established, a burner being arranged so that the other side of the said curtain is sufficiently open to the atmosphere to arrange for the induction of extra air into the curtain and before the flame by virtue of the juxtar position of the curtain and said wall.

2. A burner according to claim 1, wherein said wall at a height in the range 6 - 15mm and the burner is designed so that the flame is established on the top edge of the wall.

3. The burner according to claim 2, wherein the aperture means is arranged so that the curtain will be displaid from the wall by a distance in the order of no more than 2.5mm.

4. The burner according to any preceding claim, wherein said aperture means comprises of a row of apertures in the burner body.

5. The burner according to any preceding claim, wherein said body is elongate and said wall and curtain are straight.

6. The burner according to any preceding claim, wherein the walls is divided by a plate, and there is aperture means to each side thereof so that two of said curtains to opposite sides of the wall are formed.

7. A Burner according to claim 6, wherein the said wall comprises spaced plate sections, and between the plate sections are augmentation outlet ports for the supply of extra fuel air mixture to tje flame and for the control of the flame, which is capable of being established on the top edge of the wall.

8. A burner according to any preceding claim, wherein the burner body is a tube, and the aperture mean comprises rows of apertures extending circumferentially of the tube, each row of apertures being adjacent a said wall.

9. A burner according to any preceding claim, wherein the burner body is circular, and is adapted for use so that the aperture means in the form of a ring of apertures is arranged to create a horizontally extended curtain of fuel air mixture, and said wall means comprises of flange which in use is adapted to lie horizontally.

10. A burner according to any preceding claim wherein the burner body has an inlet for the fuel and/or a mixture of fuel and air, and said inlet is adapted to effect the inducement of atmospheric air to provide the said fuel air mixture inside the body and which issues as said curtain.

11. A gas burner substantially has herein before described with reference to any of the embodiments disclosed in Figs. 2 -9 in the accompanying drawings.