EP0451923A2

EP0451923A2 - Burner

Info

Publication number: EP0451923A2
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: 1991-10-16
Anticipated expiration: 2011-04-11
Also published as: ES2064881T3; HUT60027A; SI9110667A; FI911764A0; EP0451923A3; YU66791A; NL9000883A; PL165631B1; ATE115260T1; DK0451923T3; DE69105588D1; JPH04225709A; NO911413D0; LTIP1567A; RU2042883C1; DE69105588T2; FI911764A; NO911413L; EP0451923B1; CS104091A2

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, 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).

Description

The invention relates to a burner comprising a primary conduit for supplying a mixture of combustible gas and air; and at least one primary mixture chamber, having at least one inflow opening connected with the primary mixture supply conduit, the diameter of which opening is of the same order as that of the primary mixture supply conduit, and at least one primary discharge opening, which discharges into the space surrounding the burner, and the diameter of which is small relative to the diameter of the primary mixture supply conduit.
Such burners are already frequently being used for heating purposes. However, known burners have the drawback, that at high burner loads (when a large amount of mixture is burnt per unit of time) high combustion temperatures occur in the burning mixture. At these high combustion temperatures, large quantities of nitrogen oxide (NOx) are formed.
Furthermore, these known burners have the drawback of only being adjustable over a limited range of loads. Therefore, when used in a heating installation, known burners have to be turned on and off regularly in order to maintain a temperature within a given range. This not only leads to a reduced convenience to the user, but also results in accelerated wear of the heating installation. Furthermore, substances which are damaging to humans and to the environment are emitted every time the burner is turned on or off.
The limited adjustability of the known burners is due to the fact that as burner power is increased by increasing mixture supply, at a certain point the velocity at which the mixture to be burnt discharges from the primary discharge openings exceeds its combustion velocity. Thereby, the flame is "blown away" as it were, and the burner extinguishes.
The present invention therefore has for its object to provide a burner having an improved adjustability vis-à-vis the burners described above, and in which a relatively low combustion temperature is maintained throughout the entire range of loads. This is accomplished according to the invention by flame stabilizing means arranged near the primary discharge opening.
By using flame stabilizing means near the discharge opening of the primary mixture chamber a stable combustion, which may also occur outside the burner, can be maintained over a large range of loads. As a result of the diameter of the primary discharge opening being small relative to the diameter of the primary 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. The flame stabilizing means function to keep the combustion velocity in at least one point of the flame front substantially equal to the discharge velocity of the mixture to be burnt, whereby the flame "rests" in that point. This point stabilizes the combustion in the remainder of the flame front.
When the primary mixture chamber has a plurality of discharge areas with primary discharge openings arranged therein in a regular pattern, and the flame stabilizing means have the shape of vortex strips mutually separating the discharge areas, a sturdy burner having an improved adjustability is provided in an easy manner.
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 a number of examples, 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 first embodiment of the burner according to the invention;
fig. 2 illustrates the combustion at a low load in a detailed view along the arrow II;
figs. 3 and 4 illustrate the combustion at increasing loads in a view corresponding to fig. 2;
fig. 5 shows a burner according to the first embodiment of the invention with a large heating capacity assembled from modules;
fig. 6 shows a second embodiment of the burner according to the invention;
fig. 7 shows a partially cut away perspective view of a third embodiment of the 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. 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 a ceramic burner according to the invention 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.
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.
An alternative embodiment of the ceramic burner according to the invention uses flame stabilizing means in the form of so called vortex strips 14 (fig. 7). In this embodiment the primary mixture chamber 6 is covered on its upper side by a burner plate 15, in which a large number of primary discharge openings 7 is arranged. The primary 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 primary 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 primary discharge openings 7. Furthermore, the use of combinations of the flame stabilizing means discussed here may be envisaged.

Claims

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

- at least one primary mixture chamber (6), having at least one inflow opening connected with the primary mixture supply conduit (2), the diameter of which opening is of the same order as that of the primary mixture supply conduit (2), and at least one primary discharge opening (7), which discharges into the space surrounding the burner (1), and the diameter of which is small relative to the diameter of the primary mixture supply conduit (2);
characterized by flame stabilizing means arranged near the primary discharge opening (7).
The burner according to claim 1, characterized in that the primary mixture chamber (6) has a plurality of discharge areas with primary discharge openings (7) arranged therein in a regular pattern, and in that the flame stabilizing means have the shape of vortex strips mutually separating the discharge areas.
The burner according to claim 2, characterized in that the vortex strips (14) form an irregular pattern on a burner plate (15) covering the primary mixture chamber (6).
The burner according to any one of the preceding claims, characterized in that the burner (1) is made of a ceramic material.
The burner according to claim 4, characterized in that the flame stabilizing means are formed by at least one secondary mixture chamber (3), which is connected to at least one secondary mixture supply conduit (4) and which is connected to the space surrounding the burner (1) through at least one secondary discharge opening (5) discharging near the primary discharge opening (7), the diameters of the secondary mixture supply conduit (4) and the secondary discharge opening (5) being small relative to the diameter of the primary mixture supply conduit (2).
The burner according to claim 5, characterized in that the secondary mixture supply conduit (4) is connected with the primary mixture supply conduit (2).
The burner according to claim 6, characterized in that the secondary mixture chamber (3) is annular, arranged around the primary mixture supply conduit (2) and having several circumferential spaced radial secondary mixture supply conduits (4), and in that the primary mixture chamber (6) is placed downstream of the secondary mixture supply conduits (4), has the shape of a cylinder concentric with the primary mixture supply conduit (2), and has several circumferentially spaced radial primary discharge openings (7).
The burner according to claim 7, characterized by a plurality of primary and secondary mixture chambers (6,3) placed in series, each primary mixture chamber (6) located in the direction of flow between successive secondary mixture chambers (3) having a throughflow opening arranged opposite its inflow opening.
The burner according to claim 5, characterized in that the primary mixture supply conduit (2) is slit-shaped, an elongate secondary mixture chamber (3) having several mutually spaced secondary mixture supply conduits (4) is arranged on at least one side of the supply conduit (2), and in that the primary mixture chamber (6) is located downstream of the secondary mixture supply conduit (4), as an elongate shape and has several mutually spaced primary discharge openings (7).