EP0451923B1

EP0451923B1 - Burner

Info

Publication number: EP0451923B1
Application number: EP91200856A
Authority: EP
Inventors: Willem Meijer
Original assignee: Dru BV
Current assignee: Dru BV
Priority date: 1990-04-12
Filing date: 1991-04-11
Publication date: 1994-12-07
Anticipated expiration: 2011-04-11
Also published as: DE69105588D1; NO911413D0; LTIP1567A; HUT60027A; EP0451923A2; FI911764A0; EP0451923A3; ATE115260T1; SI9110667A; YU66791A; HU911220D0; JPH04225709A; PL165631B1; BG94249A; NL9000883A; DK0451923T3; RU2042883C1; NO911413L; CS104091A2; FI911764A

Abstract

A burner (1) is provided, comprising a primary mixture supply conduit (2) and a primary mixture chamber (6) connected with the supply conduit (2), the primary mixture chamber (6) having primary discharge openings (7) for discharging burning mixture into the space surrounding the burner (1). The burner (1), which may be made of a ceramic material, which may be made of a ceramic material, further comprises flame stabilizing means arranged near the primary discharge openings (7). The flame stabilizing means may be vortex strips (14) separating areas (16) of discharge openings (7), or they may be secondary discharge openings (5), discharging burning mixture from a secondary mixture chamber (3) near the primary discharge openings (7). <IMAGE>

Description

The invention relates to a burner comprising conduit for supplying a mixture of combustible gas and air; and at least one mixture chamber, having at least one inflow opening connected with the mixture supply conduit, the cross-section of which opening is of the same order as that of the mixture supply conduit, and at a plurality of discharge openings, which discharge into the space surrounding the burner, and the diameter of which is small relative to the diameter of the mixture supply conduit; and flame stabilizing means arranged near the discharge opening.
Such a burner is known from DE-A-2035563. This known burner comprises an annular main mixture chamber located at the end of the mixture supply conduit, and having radially spaced main discharge openings arranged in the sidewall of the mixture chamber. The burner is further provided with flame stabilizing means, which comprise an annular auxiliary mixture chamber arranged concentriccally around the mixture supply conduit, and in communication therewith through radially spaced openings. The auxiliary mixture chamber is further in communication with the space surrounding the burner through a plurality of radially spaced auxiliary discharge openings, which are arranged adjacent the main discharge openings.
In use, part of the mixture supplied by the supply conduit is led through the auxiliary mixture chamber and the auxiliary discharge openings, while the greater part of the mixture to be burnt is led through the main mixture chamber and main discharge openings. The velocity at which the mixture is discharged from the auxiliary discharge openings is much lower than the discharge velocity from the main discharge openings. Therefore, at high burner loads, when the discharge velocity of the mixture from the mean discharge openings exceeds its combustion velocity and therefore the flame risks being "blown away", the combustion is stabilized by the mixture that is discharged through the auxiliary discharge openings at a velocity that is lower than its combustion velocity, and therefore stably burns in a so called auxiliary flame, the heat of which increases the combustion velocity of the mixture flowing through the main discharge openings, thus leading to a stable combustion of the mixture.
The adjustability of a burner having flame stabilizing means over an extended range of loads is very advantageous when such burners are used in a heating installation. Because of the extended adjustability burners with flame stabilizing means do not have to be turned on and off frequently in order to maintain a temperature within a given range, as is necessary for burners without stabilizing means. A burner having flame stabilizing means therefore is more user friendly and less susceptible to wear. Furthermore, the emission of substances which are damaging to humans and to the environment every time the burner is turned on and off, is reduced with burners having flame stabilizing means.
The present invention seeks to provide a burner having flame stabilizing means as described in the preamble of claim 1, which is further improved vis-à-vis the known burner. This is accomplished according to the invention, in that the mixture chamber has a plurality of discharge areas with the discharge openings arranged therein in a regular pattern, and in that the flame stabilizing means have the shape of vortex strips mutually separating the discharge areas and forming zones of reduced flow velocities between the discharge areas, the width of the vortex strips being such at the distance between adjacent discharge areas is greater than the distance between adjacent discharge opening in said discharge areas. Thus, flame stabilization is achieved through a local reduction of the discharge velocity, rather than through a local increase of the combustion velocity. The result is a sturdy burner, which may be easily manufactured.
By using the flame stabilizing means of the present invention a stable combustion, which may also occur outside the burner, can be maintained over a wide range of loads. As a result of the diameter of the discharge opening being small relative to the diameter of the mixture supply conduit, at high loads a high flow velocity of the mixture to be burnt develops therein. Thus a fan shaped flame front having a large surface develops, whereby the combustion temperature is kept relatively low (in the order of 1000-1100°C), and the combustion thus clean.
Preferably, the burner is made of a ceramic material. Ceramic burners have a very clean combustion relative to conventional steel burners. Especially the emission of nitrogen oxide is strongly reduced when using a ceramic burner. This is due to the isolating action of the ceramic material, whereby a relatively low combustion temperature is maintained. The isolating action of the ceramic material further prevents the gas-air mixture in the supply line of the burner from being preheated. This is important, since with preheating dissociation of the mixture, and thence forming of nitrogen oxide already occurs in the supply line.
Further, by providing ceramic burners with flame stabilizing means according to the invention, the drawback that ceramic burners are only adjustable within a small range of loads is obviated.
Mentioned and other features of the burner according to the invention are further elucidated with regard to an example, with reference being made to the accompanying drawing, in which like parts are designated by like reference numerals, and in which:

fig. 1 shows a partially cut away perspective view of a burner not forming part of the present invention;
fig. 2 illustrates the combustion at a low load in a detailed view along the arrow II in fig. 1;
figs. 3 and 4 illustrate the combustion at increasing loads in a view corresponding to fig. 2;
fig. 5 shows a modification of the burner of fig. 1 with a large heating capacity assembled from modules;
fig. 6 shows a further burner which does not form part of the invention;
fig. 7 shows a partially cut away perspective view of a burner according to the invention;
fig. 8 shows a cross-sectional detail of the burner of fig. 7 at a high combustion load; and
fig. 9 is a cross-sectional view corresponding to fig. 8 at a low combustion load.

A ceramic burner 1 (fig. 1) comprises a primary mixture supply conduit 2, around which an annular secondary mixture chamber 3 is arranged in order to stabilize the flame of the burner 1, said chamber being connected with the primary mixture supply conduit 2 over circumferentially spaced, radial secondary mixture supply conduits 4. It should be noted that this burner does not contain all features of the independent claim, and therefore does not form part of the present invention. The secondary mixture chamber 3 is connected to the space surrounding the burner over a secondary discharge opening 5. The primary mixture supply conduit 2 discharges into a cylindrical primary mixture chamber 6, which is connected to the space surrounding the burner 1 over a plurality of circumferentially spaced, radial primary discharge openings 7.
The primary and secondary mixture chambers 6,3 are formed by two stackable, concentric annular elements 9,10. By stacking several of these elements 9,10 in the manner indicated in the figure, a burner having the required heating capacity may easily be assembled.
A gas-air mixture that is supplied through the primary mixture supply conduit 2 (fig. 2,3 and 4) divides over the secondary mixture chamber 3 (as indicated by the arrows S) and the primary mixture chamber 6 (indicated by the arrows P). At low loads (fig. 2) the flow velocity of the mixture is relatively low, and combustion of the primary mixture flow P takes place in the primary discharge openings 7. The flame front 11 in this case is arc-shaped. The ceramic burner functions as a source of heat radiation, since the ceramic material surrounding the primary discharge openings 7 glows.
When the load is increased (fig. 3), the flow velocity of the mixture increases, and since the combustion velocity of the mixture does not change, the combustion moves outside the burner 1. The flame fronts 11 now rest on the outer edge of the burner 1 and are still arc-shaped.
With further increasing load (fig. 4) the flow velocity of the mixture increases still further, and exceeds the combustion velocity of the mixture by such an amount, that the flame would be blown out. However, the primary mixture flow P is preheated by the presence of the secondary mixture flow S flowing from the secondary mixture chamber 3, whereby the combustion velocity of the primary mixture flow P increases and in at least one point of the flame front becomes substantially equal to the discharge velocity thereof, so that a stable flame develops. Due to the high flow velocity of the primary mixture flow P in the primary discharge openings 7, the flame fronts 11 assume a fan shape. Since such a fan shaped flame front 11 has a larger surface than a comparable arc shaped flame front, and the combustion is thus spread over a larger area, the combustion temperature is lower than in a comparable arc-shaped flame front, whereby the formation of nitrogen oxide is strongly reduced.
The heating capacity of the ceramic burner as shown in fig. 1 may be further increased by connecting several stacks of annular elements 9,10 with a common main supply conduit 12 (fig. 5). The main supply conduit 12 is provided with a gas-air mixture by an injector 13, through which the gas G is spouted into the main supply conduit 12 with such high velocity, that air A is sucked in therewith.
When the heating capacity need not be varied, and a modular assembly of the heating system is thus not required, a ceramic burner as illustrated in fig. 6 will suffice. The wedge shaped configuration of the main supply conduit 12 warrants an even distribution of the gas-air mixture over the slit shaped primary mixture supply conduit 2 in this burner 1. This burner too falls outside the scope of the claimed invention.
Although in the illustrated examples the secondary mixture supply conduits 4 are each connected with a primary supply conduit 2, it may of course be envisaged to connect the secondary supply conduit 4 with a source of combustible mixture independent from the primary supply conduit 2. Thus, a well burning stabilizing flame is ensured under all circumstances.
A ceramic burner comprising all features of the independent claim and therefore embodying the invention is shown in fig. 7 and uses flame stabilizing means in the form of so called vortex strips 14. In this burner the mixture chamber 6 is covered on its upper side by a burner plate 15, in which a large number of discharge openings 7 is arranged. The discharge openings 7 are arranged in regular patterns in a number of separate discharge areas 16, which are separated by the vortex strips 14.
The vortex strips 14 form zones of reduced flow velocities between the discharge areas 16, in which the warm mixture swirls around, igniting the mixture that is discharging at a high velocity. Therefore, even at high burner loads (fig. 8) there are points in the flame front 11 where the combustion velocity is substantially equal to the discharge velocity of the mixture. Thus the flame "rests" on those points and the complete flame front is stabilized.
The optimum pattern of the vortex strips 14 on the burner plate 15 and the relationship between the widths of the vortex strips 14, the dimensions of the discharge areas 16 and the diameters of the separate discharge openings 7 may be easily determined by someone skilled in the art on the basis of his experience and insight. It is recommended to choose an irregular pattern for the vortex strips 14, in order to prevent as much as possible the occurence of resonances.
In the example shown the mixture chamber 6 is rectangular. Possible variations in the flow velocity of the gas-air mixture due to this form hardly influence the performance of the burner 1, since the presence of the vortex strips 14 ensures the stability of the combustion over an extended range of loads, and thus over a large variety of mixture flow velocities.
The illustrated burner 1 is further provided with an aligning ring 17 arranged around the burner plate 15, for maintaining the burning mixture flow discharging along the edge of the plate 15 within the circumference of the burner plate 15. Under the inwardly extending part of the aligning ring 17 is arranged an outer row of discharge openings 7, from which the mixture flows against the aligning ring 17, again generating a vortex for stabilizing the flame. Between the aligning ring 17 and the burner plate 15 a cord-shaped gasket 18 of ceramic material is provided.
It will be appreciated that other means for stabilizing the combustion of mixture discharging at high velocities may be employed besides the flame stabilizing means disclosed above. For instance, strips of cooled material on which the combustion may stabilize might be arranged at some distance from the discharge openings 7. Furthermore, the use of combinations of the flame stabilizing means discussed here may be envisaged.

Claims

A burner (1) comprising:
- a conduit (2) for supplying a mixture of combustible gas and air;

- at least one mixture chamber (6), having at least one inflow opening connected with the mixture supply conduit (2), the cross-section of which opening is of the same order as that of the mixture supply conduit (2), and a plurality of discharge openings (7), which discharge into the space surrounding the burner (1), and the cross-section of which is small relative to the diameter of the mixture supply conduit (2); and

- flame stabilizing means arranged near the discharge openings (7);
characterized in that the mixture chamber (6) has a plurality of discharge areas (16) with the discharge openings (7) arranged therein in a regular pattern, and in that the flame stabilizing means have the shape of vortex strips (14) mutually separating the discharge areas (16) and forming zones of reduced flow velocities between the discharge areas (16), the width of the vortex strips (14) being such that the distance between adjacent discharge areas (16) is greater than the distance between adjacent discharge openings (7) in said discharge areas (16).
The burner according to claim 1, characterized in that each said discharge opening (7) has a dimension in the direction of flow that is substantially larger than its cross-sectional dimension perpendicular to the direction of flow.
The burner according to claim 1 or 2, characterized in that the discharge openings (7) are arranged in a burner plate (15) covering the mixture chamber (6), and the vortex strips (14) form an irregular pattern on said burner plate (15).
The burner according to any one of the preceding claims, characterized in that the burner (1) is made of a ceramic material.