EP2167876B1

EP2167876B1 - Modulating burner

Info

Publication number: EP2167876B1
Application number: EP08750991.5A
Authority: EP
Inventors: Luca Barozzi; Sandro Lugli
Original assignee: Worgas Bruciatori SRL
Current assignee: Beckett Thermal Solutions SRL
Priority date: 2007-05-21
Filing date: 2008-05-21
Publication date: 2013-07-10
Anticipated expiration: 2028-05-21
Also published as: EP2167876A2; US20100227285A1; WO2008142531A2; WO2008142531A3; ITMO20070167A1

Description

The present invention relates to a modulating burner Such as described by US2006/0154191 , in particular to a modulating burner with which an ionization sensor is associated for monitoring the combustion of a mixture of air and fuel delivered to the burner.
The ionization sensors are in general associated with burners for controlling the presence of the flame and the quality of combustion.
It is known that the flame produced by the combustion of the mixture delivered to a burner causes ionisation of the burnt mixture in the zone immediately surrounding the flame.
The ionization sensor is arranged near the surface of the diffuser of the burner, so as to be located in the zone affected by the ionisation produced by the flame and to generate a signal that is proportional to the ionization in said zone.
In the diagramming set out below, the typical pattern of the signal S₀ produced by the ionization sensor in a prior-art burner is shown.
If the signal S₀ produced by the ionization sensor falls below a preset first value S_min or exceeds a preset second value S_x, or becomes unstable, this indicates that combustion is absent or irregular and that it is necessary to intervene to restore normal combustion conditions.
In modulating burners, as the power is decreased at which the burner is run, the ionisation produced by the flame remains almost constant, or decreases only slightly, until the operating power of the burner reaches a minimum value P_min, which, in known prior-art burners, is equal to approximately 17-20% of the nominal power of the burner, after which the intensity of ionisation decreases suddenly until it falls below the limit value S_lim of sensor sensibility, when the operating power falls below a value P₀<P_min. The signal So generated by the ionization sensor is also maintained substantially constant or decreases slightly, nevertheless remaining between the values S_min and S_max until the operating power becomes less than P_min, after which it falls sharply below the value S_min until it is completely cancelled when ionization intensity falls below the sensibility limit of the sensor, when the operating power becomes less than P₀.
It would be theoretically possible to define, for each operating power value between P_min and P₀, the value S_min and S_max within which the signal of the sensor has to be maintained if combustion is regular, but this is complex and difficult to manage.
In known prior-art burners it is not therefore possible to use the ionization sensor to monitor combustion for operating power below P_min.
The present invention aims to provide a burner that enables the field of use of an ionization sensor to be extended that is associated with a premixed burner, in operating conditions with a power output below 17-20% of the nominal power of the burner down to operating conditions with power output approximately 10% of the nominal power of the burner. According to the present invention a burner is provided according to the object of claim 1
The flow of mixture that exits the openings made on the diffuser in the zone near which the ionization sensor is arranged creates combustion conditions that cause ionisation to be kept substantially constant when the operating power of the burner is varied up to approximately 10% of nominal power, so as to enable correct operation of the ionization sensor until said operating power value. In this way it is possible to extend the adjusting range of the burner beyond the currently possible limits, which entails greater flexibility in the operation of the burner and savings in operating costs.
According to the invention, the diffuser, in the zone adjacent to the ionization sensor has a double row of openings in the shape of slits, that are separated by a surface portion of diffuser devoid of slits, said ionisation probe being arranged parallel to said portion of diffuser devoid of slits.
The arrangement of the slits in the zone of the diffuser near which the ionization sensor is arranged contributes to stabilising ionisation in the zone surrounding the flame.
The invention will now be disclosed, by way of non-limiting example, with reference to the attached tables of drawings, in which:

Figure 1 is a schematic perspective view of a first embodiment of a burner according to the invention;
Figure 2 is a raised view of the burner in Figure 1;
Figure 3 is section III-III in Figure 2;
Figure 4 is an elevation view of a distributing element associated with the burner in Figure 1;
Figure 5 is a top view of a second embodiment of a burner according to the invention;
Figure 6 is section VI-VI of Figure 5;
Figure 7 a bottom view of the burner in Figure 5.

In Figures 1 to 4 a first embodiment of a burner 1 according to the invention is illustrated. The burner 1 has a cylindrical shape with a diffuser 2 mounted between an upper base 3 and a lower base 4.
The upper base 3 has a central ridge 5 facing inside the burner. Similarly, the lower base 4 has a central ridge 6, facing inside the burner, in which a central opening 4a is made for delivering a mixture of air and fuel inside the burner 1.
Between the two ridges 5 and 6 there is mounted and centred a distributing element 7, which is also cylinder-shaped, having a dimension that is less than the diameter of the del diffuser 2, so that a space 8 remains between the external surface of the distributing element 7 and the internal surface of the diffuser 2.
The diffuser 2 is provided with first openings 9 and with second openings 9a, to enable the mixture to pass from the space 8 to the outside of the burner 1, where combustion of the mixture is brought about.
The first openings 9 take the shape of holes, whilst the second openings 9a take the shape of slits.
Groups of rows of holes 9, arranged parallel to a longitudinal axis of the burner 1 alternate with rows of slits 9a, which are also arranged parallel to the axis of the burner 1.
Over the entire surface of the diffuser 2 the groups of rows of holes 9 alternate with single rows of slits 9a, except in a zone A of diffuser in which there are two facing rows 9b of slits 10a that are separated by a surface portion B of diffuser devoid of openings.
The distributing element 7 is provided with further first openings 10 and with further second openings 10a, distributed over the entire surface of the distributing element 7, to enable the passage of the mixture delivered to the burner 1 in said space 8.
The second further openings 10a of the distributing element 7 are arranged at said zone A of the surface of the diffuser 2, so that the mixture that passes through the second further openings 10a exits the diffuser 2 through the rows 9b of slits 9a.
The second further openings 10a have a different distribution from the distribution of the further first openings 10 and/or greater dimensions than the dimensions of the further first openings 10. Advantageously, the further second openings 10a may have a greater distribution density than the distribution density of the further first openings 10. Distribution density is defined as the number of openings per surface unit of the distributing element 7.
At the portion B of diffuser there is arranged, in a direction that is substantially parallel to the surface of the diffuser 2 an ionization sensor 11, represented schematically, in Figure 2, by a rectilinear segment. The ionization sensor 11 has a first free end and is fixed at a second end to a supporting element 11a that can be mounted on the burner 1 or also on a wall of a combustion chamber in which the burner 1 is installed.
The number and/or density of the holes 10a is greater near said second end, whilst it decreases towards said first end. During operation of the burner 1, at the two adjacent rows 9b of slits a combustion zone is formed in which ionisation is maintained substantially constant when the operating power of the burner varies, up to operating power of approximately 10% of the nominal power of the burner.
This ensures that the ionisation sensor 11 can operate correctly even when the burner operates at very reduced power, down to even approximately 10% the nominal power of the burner, whilst in known prior-art burners the sensor becomes ineffective when power falls below approximately 17-20% of the nominal power of the burner.
In the diagram set out below the signal So generated by the ionization sensor in a prior-art burner and the signal S'₀ generated by the ionization sensor in a burner according to the invention are compared.
As can be easily seen the signal S'₀ is maintained substantially constant or decreases only slightly up to an operating power value P'_lim that is noticeably less than the value P_lim of a prior-art burner.
Owing to the invention, it is thus possible to obtain a burner modulation range that is wider than that of prior-art burners, which permits greater flexibility in the adjustment of the burner and savings in operating costs.
In Figures 5, 6 and 7 there is shown a second embodiment of a burner 1a according to the invention, in which the diffuser 2a has a substantially flat surface and consists of a series of diffuser elements 12 that are alongside one another.
With the diffuser 2a a distributing element 7a is associated, which also has a substantially flat surface. The distributing element 7a consists of a series of distributing elements 13 that are alongside one another, each arranged inside a corresponding diffuser element 12. Between each distributing element 13 and the surface of the corresponding diffuser element 12 a space 8a is defined, in which a mixture of fuel and air is distributed that is delivered to the burner before exiting from the diffuser 2a.
On the surface of each diffuser element 12 first openings are made consisting of two groups of rows of holes 9, interrupted by a row of second slit-shaped openings 9a.
In a diffuser element 12a, on the other hand, two rows of adjacent slits 9b are made that are separated by a diffuser zone that is devoid of openings.
At said diffuser zone devoid of openings, in a direction substantially parallel to the surface of the diffuser 2a, an ionization sensor 11 is arranged that is represented schematically in Figure 5, with a rectilinear segment. The ionization sensor 11 has a first free end and is fixed at second end to a supporting element 11a that can be mounted on the burner 1a or also to a wall of a combustion chamber in which the burner 1a is installed.
Each distributing element 13 is provided with first further openings 10, in the shape of holes, distributed in a substantially uniform manner on the surface of the distributing element 13. A distributing element 13a, associated with the diffuser element 12a, is provided with further second openings 10a having a different distribution and/or dimensions greater than the first further openings 10. Advantageously, the further second openings 10a may have a greater distribution density than the distribution density of the further first openings 10.
The second further openings 10a are distributed in a substantially similar way to the second further openings 10a of the distributing element 7 of the burner shown in Figures 1 to 4 and perform the same function already disclosed previously.
The slits 9a made in the diffuser 2 of the burner 1 and in the diffuser 2a of the burner 1a have, for example, a length comprised between 4mm and 8 mm and a width comprised between 0.4 mm and 0.8 mm, the length of' the slits 9a is 6 mm, with a width of 0.6 mm.
The holes 9 made in the diffuser 2 of the burner 1 and in the diffuser 2a of the burner 1a have a diameter of at least 0.7 mm.
The dimensions of the holes 10 and 10a made in the diffuser 7 of the burner 1 and in the distributing elements 13a of the burner 1a have a diameter comprised between approximately 2.5 mm and 5 mm.
In the practical embodiment, the materials, the dimensions and the constructional details may be different from those indicated without thereby leaving the scope of the invention as defined by the claims.

Claims

Burner (1) comprising a diffuser (2; 2a) in which first openings (9) and second openings (9a; 9b) are made for the passage of a mixture of fuel and air delivered to the burner, a distributing element (7; 13; 13a) arranged inside the burner (1) near said diffuser (2, 2a), said distributing element being provided with further first openings (10) and further second openings (10a) for the passage of said mixture, an ionization sensor (11) arranged near a zone (A) of the surface of said diffuser (2; 2a) in a direction substantially parallel to the surface of the diffuser (2; 2a), said first openings (9) having the shape of holes and said second openings (9a; 9b) having the shape of slits, in said zone (A) two rows of slits (9b) being made that are separated by a surface portion (B) of diffuser devoid of openings, characterised in that said ionization sensor (11) is arranged above said surface portion (B) of diffuser between said two rows of slits (9b), and in that said further second openings (10a) are arranged at said zone (A) of said diffuser (2, 2a), said further second openings (10a) have a distribution other than the distribution of said further first openings (10) and/or dimensions greater than the dimensions of said further openings (10).
Burner according to claim 1, wherein said further second openings (10a) have a distribution density that is greater than the distribution density of said further first openings (10).
Burner according to any preceding claim, wherein said diffuser (2) and said distributing element (7) have a substantially cylindrical shape.
Burner according to claim 1 or 2, wherein said diffuser (2a) and said distributing element (7a) have a substantially flat shape.
Burner according to claim 4, wherein said diffuser (2a) comprises a plurality of diffuser elements (12) that are arranged alongside one another.
Burner according to claim 5, wherein said distributing element (7a) comprises a plurality of distributing elements (13) each of which is associated with a respective diffuser element (12).
Burner according to claim 5, or 6, wherein said zone (A) comprises one of said diffuser elements (12a).
Burner according to claims 6 or 7, wherein each of said distributing elements (13) is provided with said first further openings (10).
Burner according to claim 8, wherein one of said distributing elements (13a) associated with said diffuser element (12a), is provided with said further second openings (10a).
Burner according to any preceding claim, wherein said first hole-shaped openings (9) have a diameter of at least 0.7 mm approximately.
Burner according to any preceding claim, wherein said second slit-shaped openings (9a) have a length comprised between 4mm and 8 mm and a width comprised between 0.4 mm and 0.8 mm.
Burner according to claim 11, wherein said second slit-shaped openings (9a) are 6 mm long and 0.6 mm wide.
Burner according to any preceding claim, wherein said first further openings (10) and said second further openings (10a) have a diameter comprised between approximately 2.5 mm and approximately 5 mm.