EP3126737B1

EP3126737B1 - Pre-mixed gas burner cooled by an air-gas mixture

Info

Publication number: EP3126737B1
Application number: EP15718080.3A
Authority: EP
Inventors: Alessandro MAROCCOLO
Original assignee: Ferroli SpA
Current assignee: Ferroli SpA
Priority date: 2014-04-04
Filing date: 2015-03-31
Publication date: 2019-11-13
Anticipated expiration: 2035-03-31
Also published as: ES2769814T3; PL3126737T3; RU2664267C2; RU2016135504A3; RU2016135504A; EP3126737A1; WO2015150902A1

Description

BACKGROUND OF THE INVENTION

The present invention relates to a pre-mixed gas burner cooled by an air-gas mixture.
As is known, a pre-mixed gas burner operates to produce a flame for generating heat by a controlled burning of a comburent air-fuel gas mixture.
A typical use application of a pre-mixed gas burner is a use in thermal generators for producing heat.
Such a burner is arranged in a combustion chamber upstream of a heat exchanger or directly in a heat exchanger.
High temperature fumes generated by the burner head flame are caused to flow through the heat exchanger and their heat is transferred to a heat conveyor fluid circulating in the exchanger.
The pre-mixed gas burners conventionally comprise a gaseous fuel and comburent air mixture feeding and mixing system, an air-gas mixture conveying system and a flame generating head having an outer surface thereon a flame is generated.
During its operation, the burner head is heavily heated by the generated flame, in particular in a minimum power mode of operation, as the outlet speed of the air-gas mixture from the burner head is low and the flame is formed nearer to the burner surface.
In prior use applications, the high temperature of the burner head, besides limiting the burner head lifetime, requires to adopt insulating and/or refractory materials to protect the outer parts of the burner, not affected by the burner flame, and of the conveying system therethrough said air-gas mixture flows.
Such an application of insulating materials, however, is comparatively difficult because of the involved temperatures, and, moreover, the lifetime of said insulating materials is very small because of a continuous exposition to the flame, thereby they represent one of the parts which are quickly deteriorated in existing burners.
Moreover, the heat transmitted to the burner parts near the burner head, for example the conveyor, represents a dispersed heat.
The document US 2010/316967 discloses substantially the preamble of claim 1.
In particular US 2010/316967 A1 discloses a burner for gas fuels with premixing, comprising a burner body designed to be housed in a combustion chamber of a heating apparatus, the burner body being provided with a burner head on which an air and gas mixture supplied to the combustion chamber is burnt. The burner head has a surface profile in the form of a dome-shaped spherical segment, the height of the dome being less than half of the diameter of the sphere to which the segment belongs.
CH 371 237 A discloses a gas burner comprising a radiator and a chamber which is connected to the supply source for the gas and in which the air-gas mixture is formed and which is terminated on the outlet side by a gas-permeable wall. An intermediate wall is provided in the chamber for the passage of the mixture flow. The gas-permeable wall consists of a plate provided with small holes which is combined with at least one net which rests against one of the surfaces of the gas-permeable wall, so that its meshes form with the holes of the wall passages, through which the combustion mixture arriving in the region of the network is guided.
US 5 355 841 A discloses a water heater comprising: a tank adapted to contain a body of water, in which the tank has a water inlet, a water outlet and a bottom; a combustion chamber defined by the tank bottom, a side wall substantially gas tightly sealed to the tank bottom and a bottom pan substantially gas tightly sealed to the side wall; a flue passing through the tank having an inlet in the tank bottom: a burner substantially gas tightly sealed along and to the side wall and adapted to contain combustion above the burner; a fuel and air proportioner adapted to admit air and fuel to the combustion chamber; and the combustion chamber being substantially gas tight except for the proportioner and the flue.

SUMMARY OF THE INVENTION

Accordingly, the aim of the present invention is to provide such a pre-mixed gas burner specifically designed for overcoming the above mentioned drawbacks of prior art burners.
Within the scope of the above mentioned aim, a main object of the invention is to provide such a burner which is very simple construction wise and which, moreover, has a construction cost much lower than that of corresponding prior burners.
Another object of the present invention is to provide such a burner adapted to operate in a broad power modulating range, with a minimum power-maximum power ratio higher than 1:10.
Yet another object of the present invention is to provide such a burner which does not require a use of insulating and refractory materials.
Yet another object of the present invention is to provide such a burner which, owing to its specifically designed structural features, is very reliable and safe in operation.
According to one aspect of the present invention, the above mentioned aim and objects, as well as yet other objects, which will become more apparent hereinafter, are achieved by a pre-mixed gas burner according to claim 1.
During the operation of the subject burner, an air and fuel or combustible gas mixture flows through the conveyor element and, as it arrives, through the distributing element, at the head of the burner, a burner flame is accordingly formed on an outer surface thereof.
The distributing element comprises a plurality of different throughgoing holes allowing an increased air-gas mixture amount to flow to the burner head regions devoid of holes and flame, thereby allowing said regions to be cooled; said conveyor element being furthermore thermally protected by the distributing element and the air-gas mixture flow.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention will become more apparent hereinafter from the following detailed disclosure of a preferred, though not exclusive, embodiment of the invention, which is illustrated, by way of an indicative but not limitative example, in the accompanying drawings, where:

Figure 1 is a cross-sectioned side elevation view of the burner according to the present invention;
Figure 2 is a top plan view of the distributing element; and
Figure 3 is a top plan view of the conveyor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the number references of the above mentioned figures, the pre-mixed gas burner according to the present invention, which has been generally indicated by the reference number 1, comprises a conveyor element 2, a burner head 3 and a distributing element 4.
Through said conveyor element 2 is conveyed an air-gas flow coming from upstream elements, that is a fan assembly, a gas valve and mixing assembly, which have not been shown in the figures.
The conveyor element 2 operates as a support and holder for the distributing element 4 and the burner head 3.
According to the present invention, the conveyor element 2 is thermally protected by the distributing element 4 and the air-gas mixture flow, thereby preventing said conveyor element 2 from being overheated.
The burner head 3 has a convex shape and such a size as to fully close the combustion chamber 5 therewithin said burner head 3 is arranged.
Moreover, said burner head 3 comprises a throughgoing hole pattern through the central region 6, whereas its outer crown is devoid of throughgoing holes.
In the operation of the inventive pre-mixed burner, an air-gas mixture 8 is ejected from the burner head holes, which mixture, directed on the outer surface of said burner head 3, provides a combustion reaction with a corresponding formation of a burning flame 7.
The mentioned convex configuration helps to properly mechanically stabilize the burner, while preventing individual flame fronts from overlapping one another, thereby providing a "cleaner" combustion mode of operation.
As shown, the geometry or pattern of said burner head 3 is, in the embodiment herein shown, a circular one, but said head may have any other desired configurations or patterns such as a square, rectangular, polygonal, elliptical configuration or pattern and so on.
The throughgoing hole pattern 6 of said head 3 has been specifically designed to provide a homogeneous flame and an optimum combustion.
More specifically, throughgoing holes of different diameters are herein provided to drive the flame 7 on the burner surface.
The burner head 3 hole pattern 6 is, in the embodiment herein illustrated, a circular one, but it would also be possible to provide holes or openings of any other desired geometrical patterns, such as elongated slot, elliptical and rectangular hole patterns.
The hole size may be either a constant or an uneven one, and said holes may have an even or uneven geometry, thereby providing spaced regions of larger and smaller hole density and with either a constant or uneven hole pitch pattern.
The outermost portion of the head 3, that is the outer crown for a circular burner or a region near an outer perimeter for a polygonal burner, is devoid of holes and accordingly of flames.
At a given spacing from the burner head 3, and preferably with a like size, is arranged the distributing element 4, coupled to the burner head 3 by a clamping connection 9 along the head perimeter.
The distributing element 4 has a convex shape and comprises a perforated distributing element surface, with uneven dimensions between the outer circular crown 10 and inner region 11, to allow the air-gas mixture to circulate between the distributing element and the burner head and to be evenly distributed through the outlet holes.
More specifically, the enlarged hole cross-section along said crown or outer perimeter 10 is designed to facilitate an enhanced air-gas mixture conveying and feeding to the peripheral unperforated region of the burner head 3.
The above technical solution, which represents a main feature of the present invention, allows a portion of the air-gas mixture to circulate between the distributing element 4 and the burner head 3, at said unperforated region.
Thus, the circulating air-gas mixture before being ejected from said holes and generating the flame, will touch the burner head 3 surface at the region of said head 3 devoid of holes and flame, thereby removing heat therefrom and reducing its temperature.
The distributing element 4 further provides a thermal screening function of the underlying conveyor element 2 to protect the latter from the burner head 3 high temperature thereby preventing said conveyor from being overheated.
Moreover, the specifically designed distributing element 4 hole pattern allows said element 4 to be properly cooled, by the same circulating air-gas mixture.
It has been found that the invention fully achieves the intended aim and objects.
In fact, the invention has provided a pre-mixed gas burner overcoming the above prior art problems by a very simple safely operating and inexpensive structure, including a cooling system driven by the same air-gas mixture flowing through the burner, thereby greatly reducing the burner head flameless region temperature.
This enhanced cooling, in combination with a burner head so designed as to tightly close the head combustion chamber, achieves in particular the object of avoiding any insulating refractory materials.
Moreover, owing to the conveyor thermal screening provided by the distributing element, the burner according to the present invention can also operate with an air-gas mixture low outlet speed, and a flame very close to the burner head surface, thereby reducing the operating burner minimum power, while enhancing the power modulation range to a ratio higher than 1:10.
In addition, the different diameter burner head holes provide an optimum and homogeneous combustion through an "extended" power range of the inventive burner.
Furthermore, the convex shape and the clamping of burner head and distributing element provide the burner with an improved mechanical stability and lifetime, and a very simple burner construction.
In practicing the invention, the used materials, as well as the contingent size and shapes, can be any, depending on requirements.

Claims

A pre-mixed gas burner (1), comprising a conveyor element (2), a burner head (3) with outlet holes and a distributing element (4), arranged between said burner head (3) and conveyor element (2), said distributing element (4) providing a thermal shielding of the underlying conveyor element (2) thereby protecting said underlying conveyor element (2) from a high temperature of the burner head (3) and preventing said underlying conveyor element (2) from being overheated; the hole pattern of the distributing element (4) allowing it to be cooled by an air-gas mixture (8) circulation, and the burner head (3) having a peripheral region that is free of outlet holes, characterized in that said distributing element (4) comprises a plurality of holes along its crown (10) or outer perimeter having an enlarged cross section, thereby facilitating a feeding of the air-gas mixture (8) to said peripheral region, thereby causing a portion of said air-gas mixture (8) to circulate between the distributing element (4) and burner head (3); said air-gas mixture (8), in such a circulation, before exiting the outlet holes of the burner head (3) and generating a flame (7), touching a burner head surface at said peripheral region free of flame, thereby removing heat and limiting a temperature.
A burner (1), according to claim 1, characterized in that said distributing element (4) comprises a plurality of different holes allowing an enlarged air-gas mixture (8) amount to flow therethrough, at the burner head peripheral region free of outlet holes and flame, thereby providing a cooling of said burner head region.
A burner (1), according to claim 1, characterized in that said conveyor element (2) supports and houses said distributing element (4) and burner head (3).
A burner (1), according to claim 1, characterized in that said burner head (3) has a convex shape and such a size as to fully close a combustion chamber (5) in which said burner head (3) is arranged.
A burner (1), according to one or more of the preceding claims, characterized in that said burner head (3) comprises a perforation in a central area thereof.
A burner (1), according to one or more of the preceding claims, characterized in that said burner head (3) has a convex shape that mechanically stabilizes said burner (1) while preventing burner individual flame fronts from overlapping onto one another, to provide operation conditions for a cleaner combustion.
A burner (1), according to one or more of the preceding claims, characterized in that said burner head (3) comprises different diameter holes to drive the burner flame (7) on the burner surface.
A burner (1), according to one or more of the preceding claims, characterized in that said distributing element (4) has a size equal to a size of the burner head (3) and being coupled to said burner head (3) by clamping along a whole burner head perimeter.
A burner (1), according to one or more of the preceding claims, characterized in that said distributing element (4) has a convex shape and comprises a distributing element (4) perforated surface having a different size between an outer circular crown (10) and an inner region (11) thereof, thereby allowing the air-gas mixture (8) to circulate between the distributing element (4) and the burner head (3) to be evenly distributed or delivered to outlet holes.