CN113167468B

CN113167468B - Mixer for an exhaust gas recirculation burner

Info

Publication number: CN113167468B
Application number: CN201880099788.2A
Authority: CN
Inventors: 里卡尔多·潘科里尼
Original assignee: CIB Unigas SpA
Current assignee: CIB Unigas SpA
Priority date: 2018-09-27
Filing date: 2018-09-27
Publication date: 2023-10-24
Anticipated expiration: 2038-09-27
Also published as: WO2020065378A1; EP3857124B1; EP3857124A1; CN113167468A

Abstract

A mixer (1) for an exhaust gas recirculation burner defining a first inlet portion (12) for a combustion air flow, a second inlet portion (13) for a recirculation flue gas flow, a mixing chamber (11) for said air and recirculation flue gas and an outlet portion (14) for said mixture of air and recirculation flue gas, said mixer (1) further comprising: -first valve means (20) interposed between said first inlet portion (12) and said mixing chamber (11) for controlling the flow rate of said combustion air flow; -second valve means (30) interposed between said second inlet portion (13) and said mixing chamber (11) for controlling the flow rate of said recirculated flue gas flow; -actuation means (40) acting on said first valve means (20) and on said second valve means (30) for actuating both simultaneously; an adjustment member (50) interposed between said actuation means (40) and at least one respective valve means (20, 30) for defining a movement after actuation of said actuation means (40). The adjustment member (50) may be configured according to a plurality of different configurations such that the same actuation of the actuation means (40) corresponds to different movements of the respective valve means (30) and is associated with an adjustment tool (80) configured to set the configuration of the adjustment member (50).

Description

Mixer for an exhaust gas recirculation burner

Technical Field

The present invention relates to a mixer applicable to an exhaust gas recirculation burner, which can be installed in a boiler, a furnace, a dryer, etc.

The invention also relates to an exhaust gas recirculation burner comprising the above-mentioned mixer and to a heat unit comprising such a burner.

The burner may be powered by natural gas (G20/G25) or LPG (G30/G31) or other gases not explicitly indicated herein, or may be mixed (gas and diesel or fuel gas and naphtha or any other substances not explicitly indicated herein).

In particular, the invention is applicable to exhaust gas recirculation burners, i.e. burners commonly powered by natural gas, which are configured to reintroduce part of the combustion gases into the combustion chamber.

The combustion gases contain a low percentage of residual oxygen and have a relatively high temperature, mixing with the air taken in from the environment, so that the total volume of combustion improver required to complete the combustion process increases.

This results in an energy loss generated during combustion in a specific volume, which increases with a subsequent decrease in absolute flame temperature and a decrease in NOx formation due to thermal effects.

The burner head is an element of the burner which allows a correct mixing between the combustion improver and the fuel which produce the first flame source and correctly forms its holding area, so as to guarantee the operational stability with minimum pollutant emission values.

In particular, the mixer for a burner according to the invention is arranged upstream of the burner head and the ventilation section of the burner and is used to regulate the flow rates of the combustion air and of the recirculated flue gases.

In more detail, the ratio between the amounts of recirculated flue gas and combustion air required for obtaining such an optimal development varies within a percentage comprised between 0% and 20% and depends in a non-linear way on a number of parameters, such as the specific process conditions, the back pressure of the generator and the flame stability.

Background

In the prior art, the burner with flue gas recirculation comprises two regulating valves which control the inflow of combustion air and the inflow of recirculated flue gas to the combustion intake, respectively.

The known solution comprises a burner comprising two servomotors connected to a first valve and a second valve, respectively, for controlling them independently.

Such a burner also comprises a control system (BMS or PLC) connected to the two servomotors and configurable to determine a ratio profile that ensures correct adjustment according to the combustion values, while maintaining flame stability.

This solution, while technically effective, implies the drawback of having to add new expensive components and of making the installation of the burner itself more complex.

Disclosure of Invention

Under such circumstances, the object of the present invention is to achieve a mixer for an exhaust gas recirculation burner, an associated burner head and an associated burner, which overcome the above-mentioned drawbacks.

In particular, it is an object of the present invention to achieve a mixer for an exhaust gas recirculation burner, an associated burner head and an associated burner which are simpler, cheaper and easier to install in construction than prior art solutions with similar combustion efficiency.

It is another object of the present invention to achieve a mixer for an exhaust gas recirculation burner, an associated burner head and an associated burner which allow to reduce NOx emissions and to increase combustion efficiency with the same power generation.

The stated object is basically achieved by a mixer for an exhaust gas recirculation burner, a burner body comprising such a mixer and a burner head.

Drawings

Other features and advantages of the present invention will become more apparent from the detailed description of some preferred, but not exclusive, embodiments, which is set forth in the accompanying drawings, in which:

fig. 1 shows a perspective view of a mixer for an exhaust gas recirculation burner according to the invention;

fig. 2 shows a perspective view of the mixer according to fig. 1 from different angles;

fig. 3 shows a different perspective view of the mixer of fig. 1, with some elements removed in order to better highlight the other elements.

Fig. 4 shows a side view of a detail of the mixer of fig. 1;

fig. 5 shows a perspective view of an exhaust gas recirculation burner according to the invention;

fig. 6 shows a simplified view of a thermal unit according to the invention, with some elements removed to better highlight other elements.

Detailed Description

An exhaust gas recirculation burner is shown in fig. 5 and is generally designated by the reference numeral 100. Reference will be made below to the burner 100 by way of a simplified symbol.

Such a burner 100 comprises at least:

-a frame 110;

a burner head 120 mounted on the frame 110 and defining an end portion of the burner 100 on which a flame is generated;

a mixer 1 mounted on the frame 110 upstream of the burner head 120 and configured to mix at least the combustion air and the recirculated flue gases, as will be better explained below.

The frame 110 is configured for connecting the burner 100 with a combustion chamber, such as a boiler, such that the burner head 120 is arranged inside the combustion chamber itself.

As already mentioned, the burner 100 comprises a mixer 1 for an exhaust gas recirculation burner, which essentially forms the subject of the present invention and is shown in the figures, indicated with reference numeral 1. Reference will be made below to this by the simplified symbol "mixer 1".

In the embodiment shown, the mixer 1 comprises a box-shaped body 10 defining the geometry of the mixer and configured to be mounted on the frame of the burner 100.

In an embodiment not shown, the mixer 1 is integrated into the structure of the burner 1, the box-shaped body 10 being made in one piece with the frame 110 of the burner 100 itself.

More generally, the box-shaped body 10 defines: a mixing chamber 11; a first inlet portion 12 and a second inlet portion 13 leading to the mixing chamber 11; and an outlet portion 14 of the same mixing chamber 11.

The first inlet portion 12 is configured to convey the flow of combustion air towards the mixing chamber 11 and is preferably defined by an opening in the box-shaped body 10 directly facing the mixing chamber 11.

The second inlet portion 13 is configured to convey at least part of the flow of recirculated flue gas towards the mixing chamber 11 so as to mix it with the above-mentioned combustion air flow.

Preferably, the box-shaped body 10 defines a duct 15 converging into the mixing chamber 11 and in turn defines the second inlet portion 13.

Such duct 15 is configured to be connected to the exhaust emission of the burner 100 (for example on the chimney of the generator or on the flue gas circuit thereof) for receiving at the inlet a portion of the combustion fumes coming from the emission of the burner 100 itself.

The outlet portion 14 is configured to convey the mixture of combustion air and recirculated flue gas from the mixing chamber 11 towards the combustion head 120 of the burner 100, in which a fuel, preferably gaseous, in particular methane, is added and combustion of the mixture of combustion air, recirculated flue gas and fuel begins.

In the embodiment shown, the aforesaid flows are sucked by a fan mounted in the frame 110 of the burner 100, outside the mixer 1, which "re-sucks" the gases contained in the mixing chamber 11 through the outlet portion 14 and directs them towards the burner head 120.

The mixer 1 according to the invention comprises first valve means 20 interposed between the first inlet portion 12 and the mixing chamber 11 for controlling the flow rate of the combustion air flow through it.

Preferably, the first valve means 20 comprise one or more doors 21 parallel to each other and rotatably movable between a closed position and an open position, so as to control the inflow of combustion air.

Furthermore, the mixer 1 comprises a second valve means 30, arranged between the second inlet portion 13 and the mixing chamber 11, for controlling the flow rate of the recirculated flue gas flow.

Preferably, the second valve means 30 comprises a throttle valve 31 rotatably movable between a closed position and an open position in order to control the inflow of recirculated flue gas.

According to the invention, the mixer 1 comprises a single actuation device 40 acting on the first valve device 20 and on the second valve device 30 for simultaneously actuating them and adjusting their position between a closed position and an open position.

Preferably, the actuation means 40 comprise a single, preferably electric, rotary servomotor fixed to the outside of the box-shaped body 10.

Advantageously, the mixer 1 comprises a mechanical adjustment member 50, which mechanical adjustment member 50 is preferably arranged outside the box-shaped body 10 and between the actuation means 40 and the valve means 20 and 30 for defining the movement of the valve means 20 and 30 after actuation of the actuation means 40.

In other words, the regulating member 50 establishes a kinematic connection between the actuating device 40 and the at least one valve device 20 and 30 for defining the opening law of such devices according to the action of the actuating device 40.

Preferably, this opening law is non-linear and determines an asynchronous opening of the first valve device 20 with respect to the second valve device 30 and vice versa.

In a preferred embodiment, the actuation means 40 comprise an actuation shaft 41 directly connected to the servo motor and to the first valve means 20 for actuating the first valve means 20.

Furthermore, the first valve device 20 comprises a transmission mechanism 22, which transmission mechanism 22 is configured to transmit the rotational movement of the actuation shaft 41 to the individual door 21.

In this embodiment, the regulating member 50 is rotationally solidly constrained to the actuation shaft 41 for transmitting its movement to the second valve device 30, defining a kinematic mechanism for controlling and varying its law of opening with respect to the first valve device 20.

The subject of the invention is also an alternative embodiment, in which the actuation shaft 41 is connected to the second valve device 30 for actuation thereof, while the adjustment member 50 is configured to transmit its movement to the first valve device 20. Such an alternative embodiment will not be described in detail hereinafter, as it is technically equivalent to the first embodiment shown hereinafter.

Preferably, the adjustment member 50 comprises a rotatable member 51, preferably in the shape of a fan.

In a preferred embodiment, the rotatable member 51 has a coupling portion 51a where the rotatable member 51 is fitted to the actuation shaft 41 so as to be securely restrained from rotation on the actuation shaft, defining a rotational axis "R" of the rotatable member 51.

In the embodiment shown, the rotatable member 51 is fitted to the actuating shaft 41 by means of clamping jaws.

In a possible alternative embodiment, not shown, the coupling portion 51a is hinged to a fixed point of the mixer 1, according to the invention, so as to allow the rotatable member 51 to rotate about the rotation axis "R". In this embodiment, the rotatable member 51 is kinematically connected to the actuation shaft 41, for example by meshing.

Preferably, the adjustment member 50 comprises a cam mechanism 52 having a variable geometry, which cam mechanism 52 in turn comprises a cam or curved guide 53 which is rotatably solidly constrained to the actuation shaft 41 and in particular connected to the rotatable member 51.

Preferably, the guide 53 has a helical curvature extending around the rotation axis "R" (and thus around the coupling portion 51 a) and is fixed to one side of the rotatable member 51, in particular, so as to rotate around the longitudinal axis of the actuation shaft 41.

In more detail, the guide 53 comprises a plate 54, preferably made of metal, which plate 54 extends along a generally helically curved extension line, preferably centred on the rotation axis "R" (and in the illustrated embodiment at the actuation shaft 41).

Preferably, the plate 54 is supported on a plurality of support points, to which the rotatable member 51 is connected.

Furthermore, the plate 54 has a centre (and in the embodiment shown at the actuation shaft 41) with respect to its own generally helical extension line, preferably including an angular extension between 0 ° and 120 °.

The above-mentioned support points are preferably distributed along such an extension line at regular intervals comprised between 15mm and 20 mm.

In a preferred embodiment, plate 54 is made of 20MnB5 steel and has a thickness comprised between 0.3 and 0.8 mm.

The cam mechanism 52 further comprises a cam follower 55 which is engaged on the guide 53 and connected to the second valve device 30 such that rotation of the actuating shaft 41 causes sliding of the cam follower 55 on the guide 53 and subsequent movement of the valve device 30, in particular rotation of the throttle valve 31.

Preferably, the cam follower 55 comprises a pair of bearings 55a and 55b opposite each other and arranged to abut on opposite sides of the plate 54 so as to follow the profile thereof.

To support the cam follower 55, in a preferred embodiment, the mixer 1 comprises a rocker 60, which rocker 60 is hinged to a fixed part of the same mixer 1 at a fulcrum 60a, connected to the box-shaped body 10.

The rocker 60 has a first movable portion 61, and the cam follower 55 is connected to the first movable portion 61. Such a first movable portion 61 is kinematically constrained by the structure of the rocker 60 itself to move along a circular trajectory about its fulcrum 60 a.

In more detail, the cam follower 55 comprises a connecting portion supporting the bearings 55a and 55b and hinged to the first movable portion 61 so as to follow the shape of the plate 54.

In addition, the rocker 60 has a second movable portion 62, which is kinematically constrained by the structure of the rocker 60, to move along a circular trajectory about its fulcrum 60a and through which the second valve device 30 is actuated.

Preferably, the fulcrum 60a is provided at an end of the rocker 60, and the first movable portion 61 is interposed between the fulcrum 60a and the second movable portion 62.

Preferably, the mixer 1 further comprises a lever 65, which lever 65 is constrained to the second movable portion 62 and is connected to the second valve device 30 for activating the latter and regulating its opening after rotation of the guide 53.

Advantageously, according to one aspect of the present invention, the adjustment member 50 may be configured according to a plurality of different configurations such that the same actuation of the starting device 40 corresponds to different movements of the respective first and/or second valve devices 20 and 30.

More particularly, the adjustment member 50 is associated with an adjustment device 80 configured to set such a configuration.

In a preferred embodiment, the cam mechanism 52 has a variable geometry and the adjusting means 80 act on it, in particular on the guide 53, for changing its geometry.

In more detail, the adjustment tool 80 is configured to continuously vary the distance of the guide 53 from the rotation axis "R" of the rotatable device 51, so as to vary its profile and thus the path of the cam follower 55 after rotation of the actuation shaft 41.

In other words, the adjusting means 80 are configured to set the law of opening of the second valve device 30 according to the movement of the starting device 40, and more generally to vary the law of reciprocal opening of the first and second valve devices 20 and 30, so as to adjust the ratio of the recirculated flue gas mixed with the combustion air corresponding to each combustion air flow rate.

In a preferred embodiment, the plate 54 is flexible and the shape of the plate 54 can be changed by changing the position of the support points at which the plate 54 is fixed to the rotatable member 51.

In more detail, the adjustment tool 80 comprises a series of adjustable support members 81, which act on the plate 54 at the above-mentioned support points of the plate 54.

Such support members 81 constrain the plate 54 to the rotatable member 51 and allow for adjustment of the distance between discrete points of the plate 54 and the axis of rotation "R" of the rotatable member 51.

Advantageously, after such adjustment, the flexibility of the plate 54 determines the connection between the support points that makes the path of the guides 53 regular and thus the opening function defined thereby.

To allow for proper adjustment of the position and shape of the plate 54, in a preferred embodiment, only one support member 81 is configured to translationally constrain the plate 54 to the rotatable member 51.

Preferably, the other support members 81 limit the plate 54 to the rotatable member 51 so as to allow the plate 54 to slide in its extending direction during adjustment of the support point.

In other words, the other support members 81 allow the position of the adjustment plate 54 to be extended longitudinally along the plate 54 due to the variation in the position of the support points, and limit the movement of the plate 54 itself with respect to the remaining degrees of freedom.

Preferably, the support member 81, which is substantially centrally disposed with respect to the plate 54, constrains the plate 54 itself to the corresponding support point so as to allow it to slide at the end during adjustment.

Preferably, the support member 81 has a longitudinal extension oriented radially with respect to the actuation shaft 41 (and therefore with respect to the rotation axis "R").

In particular, each support member 81 has a first end 81a facing the coupling portion 51a and a second end 81b facing in the opposite direction, and is preferably configured for manual adjustment of the position of the support point.

Further, each support member 81 includes a limiting element 81c, which limiting element 81c is arranged between the first end 81a and the second end 81b and engages with the plate 54 so as to support it at the respective support point.

In the preferred embodiment, the limiting element 81c has a clamp configuration and engages both sides of the plate 54. In an alternative embodiment, not shown, at least some of the limiting elements 81c support a single face of the plate 54 in order to adjust the shape of the plate 54.

The support member 81 allows adjustment of the position of the limiting element 81c and the position of the corresponding support point extending longitudinally thereof.

In more detail, each support member 81 comprises a rotatable threaded rod, and the respective limiting element 81c has a threaded coupling with the threaded rod.

Furthermore, each limiting element 81c is engaged in the relative radial guide (with respect to the rotation axis "R") presented by the rotatable member 51 so as to slide in a radial direction with respect to the rotation axis "R" as a result of the rotation of the threaded rod.

Preferably, the threaded rod is restrained at the first end 81a by a locking nut securely restrained thereto to permit rotation thereof about the longitudinal axis of the threaded rod.

Furthermore, the adjustment member 81 preferably comprises a respective adjustment head, in particular firmly constrained with the aforementioned threaded rod, and is arranged at the second end 81b and defines a respective adjustment screw.

Preferably, such an adjustment head is radially accessible with respect to the actuation shaft 41 (and therefore with respect to the rotation axis "R") to adjust the position of the support point.

Preferably, the plate 54 has a width transverse to its own general extension, so as to have a first longitudinal band provided for coupling with the support member 81, in particular with the limiting element 81c, and a second longitudinal band adjacent to the first longitudinal band and designed for slidable engagement with the cam follower 55, so that the limiting element 81c does not interfere with its sliding.

Preferably, the plate 54 comprises two superimposed laminar layers to prevent any bending of the plate 54 itself and to promote its resistance. In this case, the thickness of the aforementioned plate 54 is doubled, since there are two overlapping layers.

Advantageously, in this configuration, the thickness, material and structure of the plate 54 determine the bending strength of the plate 54 in the transverse direction of its extension line and allow it to withstand the shear stresses induced on the plate by the cam follower 55 with respect to its support point.

A further subject of the invention is the burner 100 described above, comprising a mixer 1 connected reversibly or irreversibly to its frame 110.

The burner 100 comprises a first tubular body defining internally a first duct connected or connectable to the box-shaped body 10 of the mixer 1 so as to receive therein a mixture of combustion air and recirculated flue gases from the outlet portion 14.

The burner 100 further comprises a motorized fan, preferably electric, arranged downstream of the mixing chamber 11, for conveying the mixture of combustion air and recirculated flue gases towards the first duct.

The burner 100 further comprises a second tubular body defining internally a second conduit connectable to a source of preferably gaseous fuel (for example a public methane gas network).

The first and second tubular bodies define respective ends of the first and second conduits configured to uniformly mix the mixture of combustion air and recirculated flue gas and fuel at the combustion head 120.

The burner 100 further includes an ignition device disposed at respective ends of the first and second conduits and configured to ignite combustion of the mixture of fuel, combustion air, and recirculated flue gas.

Another subject of the invention is a thermal unit 200, shown in fig. 6, comprising a burner 100 similar to the burner described above and a combustion chamber 210 associated with the burner 100, such that the burner head 120 of the burner 100 is arranged inside the combustion chamber 210 itself for guiding the flame inside it.

For the sake of simplicity, referring to the mixer 1 of the thermal unit 200, in the embodiment shown in fig. 6, the mechanical moving members of the first and second valve devices 20 and 30, the actuating device 40, the adjusting member 50 and the adjusting tool 80 are not shown.

In one of the possible embodiments, the heat unit 200 has a recirculation duct 220 arranged downstream of the combustion chamber 210, so as to establish a flow connection between the combustion chamber 210 itself and the mixing chamber 11 of the mixer 1 through the second inlet portion 13 described above.

The present invention achieves the proposed object and overcomes the above-mentioned drawbacks of the prior art.

Advantageously, the construction and arrangement of the regulating member allow to mechanically determine two different opening laws for the two valve devices of the mixer, so as to regulate the flow rate of the recirculated flue gas according to the inflow of combustion air.

Furthermore, the adjustment tool acting on the cam mechanism of the adjustment member allows to modify the profile of the guide while setting up the burner, which can be performed during the installation step, in order to adjust this function based on environmental parameters and other variables that must be manageable on the system.

Advantageously, such modifications require a simple mechanical adjustment operation by the installer on the support member, which is easy to perform, depending on the operating conditions of the machine.

Claims

1. A mixer (1) for an exhaust gas recirculation burner defining a first inlet portion (12) for a combustion air flow, a second inlet portion (13) for a recirculation flue gas flow, a mixing chamber (11) for said air and recirculation flue gas and an outlet portion (14) for said mixture of air and recirculation flue gas, said mixer (1) comprising:

-first valve means (20) interposed between said first inlet portion (12) and said mixing chamber (11) for controlling the flow rate of said combustion air flow;

-second valve means (30) interposed between said second inlet portion (13) and said mixing chamber (11) for controlling the flow rate of said recirculated flue gas flow;

-actuation means (40) acting on said first valve means (20) and said second valve means (30) for simultaneously actuating said first valve means (20) and said second valve means (30);

-an adjustment member (50) interposed between the actuation means (40) and at least a respective one of the valve means (20, 30) for defining a movement of the respective valve means (30, 20) after actuation of the actuation means (40), and wherein the adjustment member (50) is configurable according to a plurality of different configurations such that a same actuation of the actuation means (40) corresponds to a different movement of the respective valve means (30, 20), the adjustment member (50) being associated with an adjustment tool (80), the adjustment tool (80) being configured to set the configuration of the adjustment member (50); the adjustment member (50) comprises a cam mechanism (52) having a variable geometry, the adjustment tool (80) acting on the cam mechanism (52) for changing the geometry of the cam mechanism (52);

characterized in that the actuation means (40) comprise an actuation shaft (41), and in that the cam mechanism (52) with variable geometry comprises:

-a curved guide (53) rotationally solidly constrained to said actuation shaft (41);

-a cam follower (55) engaged on said guide (53) and connected to said respective valve device (30) such that rotation of said actuation shaft (41) determines a corresponding movement of said respective valve device (30).

2. Mixer (1) according to claim 1, wherein the adjustment member (50) comprises a sector-shaped rotatable member (51) and the guide (53) comprises a deformable plate (54), the deformable plate (54) being supported on a plurality of support points and the cam follower (55) being movable on the deformable plate (54), the adjustment tool (80) comprising a series of adjustable support members (81), the series of adjustable support members (81) being connected to the rotatable member (51) and acting on the plate (54) at the plurality of support points.

3. The mixer (1) according to claim 2, wherein the support member (81) is oriented radially with respect to the start-up shaft (41) and comprises a respective linear actuator.

4. A mixer (1) according to claim 2 or 3, wherein the support member (81) is manually adjustable.

5. Mixer (1) according to claim 2, wherein the support member (81) comprises a respective limiting element (81 c) having a gripper configuration and engaging with the plate (54), and a respective threaded rod engaging with the limiting element (81 c) for adjusting the position of the limiting element (81 c) in a radial direction with respect to the actuation shaft (41).

6. Mixer (1) according to claim 5, wherein each support member (81) has an adjustment head solidly constrained to the respective threaded rod and is accessible in a radial direction with respect to the actuation shaft (41).

7. The mixer (1) according to claim 2, wherein the plate (54) has an angular extension comprised between 0 ° and 120 ° with respect to the actuation shaft (41).

8. The mixer (1) according to claim 2, wherein the support points are distributed at regular intervals along the general extension direction of the plate (54), the size of the intervals being comprised between 15mm and 20 mm.

9. Mixer (1) according to claim 2, wherein the plate (54) has a width transverse to its general extension, so as to have a first longitudinal band arranged for coupling with the support member (81) and a second longitudinal band adjacent to the first longitudinal band, designed for slidable engagement with the cam follower (55).

10. Mixer (1) according to claim 2, wherein the cam follower (55) comprises a pair of bearings (55 a, 55 b), the pair of bearings (55 a, 55 b) being arranged to abut on opposite sides of the plate (54).

11. Mixer (1) according to claim 2, wherein at least one of the support members (81) is configured to translationally constrain the plate (54) to the rotatable member (51), the other support members (81) constraining the plate (54) to the rotatable member (51) so as to allow sliding of the plate (54) with respect to the rotatable member (51) along a prevalent extension direction of the plate (54).

12. Mixer (1) according to claim 1, comprising:

-a rocker (60) having a fulcrum (60 a) hinged to a fixed portion of the mixer (1), and a first movable portion (61) and a second movable portion (62) rotatable about the fulcrum (60 a), the cam follower (55) being hinged to the first movable portion (61);

-a lever (65) hinged to the second movable portion (62) and configured to actuate the respective valve device (30).

13. Mixer (1) according to claim 1, wherein the first valve device (20) is actuated directly by the actuation shaft (41) and the second valve device (30) is actuated by the cam follower (55).

14. The mixer (1) according to claim 1, wherein the first valve arrangement (20) comprises one or more doors (21), the one or more doors (21) being rotatably movable between a closed position and an open position.

15. Mixer (1) according to claim 1, wherein the second valve arrangement (30) comprises a throttle valve (31), the throttle valve (31) being rotatably movable between a closed position and an open position.

16. The mixer (1) according to claim 1, comprising a box-shaped body (10) defining the mixing chamber (11), the first (12) and second inlet portions (13) and the outlet portion (14); the adjustment member (50) is arranged outside the box-shaped body (10).

17. Mixer (1) according to claim 1, wherein said starting means (40) comprise a single electric rotary servomotor.

18. An exhaust gas recirculation burner (100), comprising:

-a mixer (1) for an exhaust gas recirculation burner according to claim 1;

-a first tubular body defining internally a first duct connected or connectable to the outlet portion (14) of the mixer (1) for receiving a mixture of air and recirculated flue gas;

-a second tubular body defining internally a second conduit connected or connectable to a gaseous fuel source;

-an ignition device provided or applied to respective ends of the first and second ducts and configured to ignite combustion of the mixture of fuel, air and recirculated flue gas.

19. Burner (100) according to claim 18, comprising a motorized fan arranged downstream of the mixing chamber (11) of the mixer (1) for moving the mixture of air and recirculated flue gas through the outlet portion (14).

20. A heat unit (200) comprising a burner (100) according to claim 18, the heat unit (200) comprising:

-a combustion chamber (210) arranged downstream of the ignition means of the burner (100) to house a flame determined by igniting the mixture of fuel, air and recirculated flue gas; and

-a recirculation conduit (220) arranged downstream of the combustion chamber (210) for establishing a flow connection between the combustion chamber (210) and the mixing chamber (11) of the mixer (1) through the second inlet portion (13), the recirculation conduit (220) being configured to recirculate at least part of the exhaust gases from the combustion chamber (210).