DESCRIPTION

Technical field

The present invention relates to a mixer applicable to exhaust fume recirculation burners that can be installed in boilers, furnaces, driers, etc. The present invention further relates to an exhaust fume recirculation burner comprising the aforesaid mixer and a thermal unit comprising such burner.

The burners may be powered by natural gas (G20/G25) or LPG (G30/G31 ) or other gases not expressly indicated herein or can be mixed (gas and diesel or gas and naphtha or anything else not expressly indicated herein). In particular, the present invention applies to exhaust fume recirculation burners, i.e. to burners, prevalently powered by natural gas, configured to re-introduce part of the combustion gases into the combustion chamber. The combustion gases, which contain a low percentage of residual oxygen and have a relatively high temperature, mixed with the air sucked from the environment, cause an increase in the total volumetric quantity of comburent necessary for completing the combustion process.

This causes a loss of the energy generated during combustion in a specific volume which is greater with the consequent reduction of the absolute flame temperature and decrease in formation of NOx due to the thermal effect.

The combustion head is an element of the burner that allows correct mixing between comburent and fuel generating the first source of flame and developing a retaining zone thereof so as to guarantee operating stability with minimal pollutant emission values.

The mixer for burners according to the present invention, in particular, is arranged upstream of the combustion head and the ventilating part of the burner and is used to regulate the flow rates of comburent air and recirculation fumes. In more detail, the ratio between the quantity of recirculation fumes and comburent air necessary for obtaining such optimal development varies within a percentage comprised between 0% and 20% and depends, in a non-linear way, on numerous parameters such as, for example, the specific process conditions, the back pressure of the generator and the flame stability.

Prior Art

Burners that, in the prior art, exploit the recirculation of fumes comprise two regulation valves, which control the inflow of comburent air and of recirculation fumes towards the comburent suction, respectively.

A known solution consists of burners comprising two servomotors connected to the first and to the second valve, respectively, for controlling them independently.

Such burners further comprise a control system (BMS or PLC) connected to both servomotors and configurable to determine the ratio curves that guarantee the correct regulation as a function of the combustion values while maintaining the flame stability.

This solution, although technically valid, implies the drawbacks of having to provide for the addition of new costly components and making the installation of the burner itself more complicated.

Object of the invention

In this situation, the object of the present invention is to realise a mixer for exhaust fume recirculation burners, a related combustion head and a related burner that overcome the mentioned drawbacks.

It is in particular an object of the present invention to realise a mixer for exhaust fume recirculation burners, a related combustion head and a related burner that are structurally simpler, less expensive and easier to install with respect to the solutions of the prior art having analogous combustion efficiency. It is yet another object of the present invention to realise a mixer for exhaust fume recirculation burners, a related combustion head and a related burner that allow the NOx emissions to be reduced with the same generated power and to improve the combustion efficiency.

The indicated objects are substantially reached by a mixer for exhaust fume recirculation burners, a burner body comprising such mixer and a combustion head.

Brief description of the drawings

Further characteristics and advantages of the present invention will become more apparent from the detailed description of some preferred, but not exclusive, embodiments, which are illustrated in the attached drawings, of which:

- figure 1 shows a perspective view of a mixer for exhaust fume recirculation burners according to the present invention;

- figure 2 shows a perspective view according to a different angle of the mixer of figure 1 ;

- figure 3 shows a different perspective view of the mixer of figure 1 with some elements which have been removed in order to better highlight others.

- figure 4 shows a side view of a detail of the mixer of figure 1 ;

- figure 5 shows a perspective view of an exhaust fume recirculation burner according to the present invention;

- figure 6 shows a simplified view of a thermal unit according to the present invention with some elements which have been removed for better highlighting others.

Detailed description of preferred embodiments of the invention

An exhaust fume recirculation burner is illustrated in figure 5 and indicated generally with reference number 100. Reference will be made thereto in the following by the simplified notation“burner 100”. Such burner 100 comprises at least:

- a frame 1 10;

- a combustion head 120 mounted on the frame 1 10 and defining the terminal part of the burner 100 on which the flame is created;

- a mixer 1 mounted on the frame 1 10 upstream of the combustion head 120 and configured to mix at least comburent air and recirculation fumes as will be better explained below.

The frame 1 10 is configured for the connection of the burner 100 with a combustion chamber, for example of a boiler, so that the combustion head 120 is arranged inside the combustion chamber itself.

As already mentioned, the burner 100 comprises the mixer 1 for exhaust fume recirculation burners that forms in itself the subject matter of the present invention and is illustrated in the appended figures and indicated with the numerical reference 1. Reference will be made thereto in the following by the simplified notation“mixer 1”.

In the illustrated embodiment, the mixer 1 comprises a box-shaped body 10 that defines the geometry thereof and is configured to be mounted on the frame of the burner 100.

In a not illustrated embodiment in which the mixer 1 is integrated into the structure of the burner 1 , the box-shaped body 10 is made in a single body with the frame 1 10 of the burner 100 itself.

More generally, the box-shaped body 10 defines a mixing chamber 1 1 , a first and a second inlet section 12 and 13 to the mixing chamber 1 1 and an outlet section 14 of the same mixing chamber 1 1.

The first inlet section 12 is configured to convey a flow of comburent air towards the mixing chamber 1 1 and is preferably defined by an opening in the box-shaped body 10 directly facing the mixing chamber 11.

The second inlet section 13 is configured to convey a flow of at least a part of the recirculation fumes towards the mixing chamber 11 for mixing it with the aforesaid flow of comburent air.

Preferably, the box-shaped body 10 defines a conduit 15 converging into the mixing chamber 1 1 and defining in turn the second inlet section 13. Such conduit 15 is configured to be connected to an exhaust gas discharge of the burner 100, for example on the chimney of the generator or on a fume circuit thereof, for receiving at the inlet a part of the combustion fumes coming from the discharge of the burner 100 itself.

The outlet section 14 is configured to convey the mixture of comburent air and recirculation fumes from the mixing chamber 1 1 towards the combustion head 120 of the burner 100, in which a fuel (preferably gaseous and in particular methane) is added and the combustion of the mixture of comburent air, recirculation fumes and fuel begins.

In the illustrated embodiment, the aforementioned flows are sucked by a fan installed in the frame 1 10 of the burner 100, outside the mixer 1 , which “re-sucks” the gases contained in the mixing chamber 11 through the outlet section 14 and directs them towards the combustion head 120.

The mixer 1 according to the present invention comprises a first valve device 20 interposed between the first inlet section 12 and the mixing chamber 1 1 for controlling the flow rate of the flow of comburent air through it.

Preferably, the first valve device 20 comprises one or more gates 21 parallel to each other and rotatably movable between a closed position and an open position so as to control the inflow of comburent air.

Furthermore, the mixer 1 comprises a second valve device 30 interposed between the second inlet section 13 and the mixing chamber 1 1 for controlling the flow rate of the flow of recirculation fumes.

Preferably, the second valve device 30 comprises a throttle valve 31 rotatably movable between a closed position and an open position so as to control the inflow of recirculation fumes.

According to the present invention, the mixer 1 comprises a single activation device 40 active on the first and on the second valve device 20 and 30 for activating them simultaneously and adjusting the position thereof between the closed position and the open position. Preferably, the activation device 40 comprises 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, preferably arranged outside the box-shaped body 10, interposed between the activation device 40 and the valve devices 20 and 30 for defining the movement of the latter following the actuation of the activation device 40.

In other words, the adjustment member 50 establishes a kinematic connection between the activation device 40 and at least one valve device 20 and 30 for defining the opening law of such device as a function of the action of the activation device 40.

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

In the preferred embodiment the activation device 40 comprises an activation shaft 41 connected directly to the servomotor and to the first valve device 20 for the actuation of the latter.

Furthermore, the first valve device 20 comprises a transmission mechanism 22 configured to transmit the rotary motion of the activation shaft 41 to the individual gates 21.

In this embodiment, the adjustment member 50 is rotationally solidly constrained to the activation shaft 41 for transmitting the movement thereof to the second valve device 30, defining a kinematic mechanism such as to control and vary the opening law thereof with respect to the first valve device 20.

The subject matter of the present invention is also an alternative embodiment in which the activation shaft 41 is connected to the second valve device 30 for actuating it while the adjustment member 50 is configured to transmit the movement thereof to the first valve device 20. Such alternative embodiment will not be described in detail below as it is technically equivalent to the first embodiment illustrated below. Preferably, the adjustment member 50 comprises a rotatable member 51 , preferably fan-shaped.

In a preferred embodiment, the rotatable member 51 has a coupling portion 51 a at which it is fitted onto the activation shaft 41 so as to rotate solidly constrained thereto, defining an axis of rotation“R” of the rotatable member 51.

In the illustrated embodiment, the rotatable member 51 is fitted onto the activation shaft 41 by means of a clamping jaw.

In a possible alternative embodiment which is not illustrated, according to the present invention, the coupling portion 51 a is hinged to a fixed point of the mixer 1 so as to allow the rotation of the rotatable member 51 about the axis of rotation“R”. In this embodiment the rotatable member 51 is kinematically connected to the activation shaft 41 , for example through meshing.

Preferably, the adjustment member 50 comprises a cam mechanism 52 with a variable geometry, in turn comprising a cam or curved guide 53, rotationally solidly constrained to the activation shaft 41 and in particular connected to the rotatable member 51.

Preferably, the guide 53 has a spiral-shaped curved extension about the axis of rotation“R” (and therefore the coupling portion 51 a) and is fixed at a side of the rotatable member 51 , in particular so as to rotate about a longitudinal axis of the activation shaft 41.

In more detail, the guide 53 comprises a plate 54 preferably made of metal extending along a prevalent spiral-shaped curved extension line preferably centred at the axis of rotation“R” (and, in the illustrated embodiment, at the activation shaft 41 ).

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

Furthermore, the plate 54 has an angular extension preferably comprised between 0° and 120° with respect to the centre of its own prevalently spiral-shaped extension line (and, in the illustrated embodiment, at the activation shaft 41 ).

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

In the preferred embodiment, the 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 engaged on the guide 53 and connected to the second valve device 30 so that a rotation of the activation shaft 41 causes the sliding of the cam follower 55 on the guide 53 and a consequent movement of the valve device 30, in particular a rotation of the throttle valve 31.

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

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

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

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

Furthermore, the rocker 60 has a second movable portion 62 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 activated.

Preferably, the fulcrum 60a is arranged 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 rod 65 constrained to the second movable portion 62 and connected to the second valve device 30 for activating it and adjusting the opening thereof following a rotation of the guide 53.

Advantageously, according to an aspect of the present invention the adjustment member 50 can be configured according to a plurality of different configurations so that a same actuation of the activation 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 means 80 configured to set such configurations.

In the preferred embodiment, the cam mechanism 52 has a variable geometry and the adjustment means 80 is active thereon, and in particular on the guide 53, for varying the geometry thereof.

In more detail, the adjustment means 80 is configured to continuously vary the distance of the guide 53 from the axis of rotation“R” of the rotatable device 51 so as to change the profile thereof and therefore the path of the cam follower 55 following a rotation of the activation shaft 41.

In other words, the adjustment means 80 is configured to set the opening law of the second valve device 30 as a function of a movement of the activation device 40 and, more generally, change the mutual opening law of the first and second valve devices 20 and 30 so as to adjust the fraction of recirculation fumes mixed with the comburent air corresponding to each comburent air flow rate.

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

In more detail, the adjustment means 80 comprises a succession of adjustable support members 81 active on the plate 54 at the support points thereof described above.

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

Advantageously, following such adjustment, the flexibility of the plate 54 determines a connection between the support points making the path of the guide 53 regular and, therefore, the opening function defined thereby. To allow the correct adjustment of the position and shape of the plate 54, in the preferred solution only one of the support members 81 is configured to translationally constrain the plate 54 to the rotatable member 51.

Preferably, the other support members 81 constrain the plate 54 to the rotatable member 51 so as to allow the sliding thereof along its extension direction during an adjustment of the support points.

In other words, the other support members 81 allow an adjustment in the position of the plate 54 along its longitudinal extension as a result of variations in the position of the support points and constrain the movement of the plate itself 54 with respect to the remaining degrees of freedom. Preferably, a support member 81 arranged substantially centrally with respect to the plate 54 constrains the plate 54 itself at the respective support point so as to let it slide at the ends during adjustment.

Preferably, the support members 81 have a longitudinal extension oriented in the radial direction with respect to the activation shaft 41 (and therefore with respect to the axis of rotation“R”).

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

Furthermore, each support member 81 comprises a constraining element 81 c, arranged between the first and the second end 81 a and 81 b and engaged with the plate 54 so as to support it at a respective support point. In the preferred embodiment the constraining elements 81 c have a gripper conformation and engage both faces of the plate 54. In alternative not illustrated embodiments at least some constraining elements 81 c support a single face of the plate 54 so as to adjust the shape thereof. The support members 81 allow the adjustment of the position of the constraining elements 81 c and of the respective support points along the longitudinal extension thereof.

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

Furthermore, each constraining element 81 c is engaged in a relevant radial guide (with respect to the axis of rotation “R”) presented by the rotatable member 51 so as to slide in the radial direction with respect to the axis of rotation“R” as a result of a rotation of the threaded stem.

Preferably, the threaded rods are constrained at the first end 81 a by a locking nut solidly constrained thereto to allow the rotation thereof about its longitudinal axis.

Furthermore, the adjustment members 81 preferably comprise the respective adjustment heads, in particular solidly constrained with the aforesaid threaded rods and arranged at the second end 81 b and defining respective adjustment screws.

Preferably such adjustment heads are accessible in the radial direction with respect to the activation shaft 41 (and therefore with respect to the axis of rotation“R”) for adjusting the position of the support points.

Preferably, the plate 54 has a width, transversally to its own prevalent extension direction, such as to have a first longitudinal strip provided for coupling with the support members 81 , in particular with the constraining elements 81 c, and a second longitudinal strip, adjacent to the first, designed for slidable engagement with the cam follower 55, so that the constraining elements 81 c do not disturb the sliding thereof.

Preferably, the plate 54 comprises two overlapping laminar layers to prevent any bending of the plate 54 itself and promote its resistance. In that case, the thickness of the plate 54 previously described is doubled as there are two overlapping layers.

Advantageously, in the described configuration, the thickness, the material and the structure of the plate 54 determine the bending strength thereof in the transverse direction to its extension line and allow it to withstand the shear stress caused thereon by the cam follower 55 with respect to its support points.

Further subject matter of the present invention is the burner 100 described above, comprising the mixer 1 reversibly or irreversibly connected to the frame 1 10 thereof.

The burner 100 comprises a first tubular body internally defining a first conduit connected or connectable to the box-shaped body 10 of the mixer 1 so as to receive therein the mixture of comburent air and recirculation fumes from the outlet section 14.

The burner 100 further comprises a motorised fan, preferably electric, arranged downstream of the mixing chamber 1 1 for conveying the mixture of comburent air and recirculation fumes towards the first conduit.

The burner 100 further comprises a second tubular body internally defining a second conduit connectable to a source of preferably gaseous fuel, e.g. a public methane gas grid.

The first and the second tubular body define respective end portions of the first and the second conduit configured to uniformly mix the mixture of comburent air and recirculation fumes and the fuel at the combustion head 120.

The burner 100 further comprises an ignition device arranged at the respective end portions of the first and the second conduit and configured to light the burning of the mixture of fuel, comburent air and recirculation fumes.

Further subject matter of the present invention is a thermal unit 200, illustrated in figure 6, comprising a burner 100 analogous to the one described above and a combustion chamber 210 associated with the burner 100, so that the combustion head 120 of the burner 100 is arranged inside the combustion chamber 210 itself for directing the flame inside it. For simplicity purposes, with reference to the mixer 1 of the thermal unit 200, in the embodiment illustrated in figure 6, the mechanical movement members of the first and of the second valve devices 20 and 30, the activation device 40, the adjustment member 50 and the adjustment means 80 have not been shown.

The thermal unit 200 has a recirculation conduit 220, in one of its possible embodiments, arranged downstream of the combustion chamber 210 so as to establish a flow connection between the combustion chamber 210 itself and the mixing chamber 1 1 of the mixer 1 through the second inlet section 13 described above.

The present invention achieves the proposed object, overcoming the aforementioned drawbacks in the prior art.

Advantageously, the configuration and arrangement of the described adjustment member allows two different opening laws to be mechanically determined for the two valve devices of the mixer so as to adjust the flow rate of recirculation fumes as a function of the inflow of comburent air. Furthermore, the adjustment means active on the cam mechanism of the adjustment member allows the profile of the guide to be modified while setting the burner, which can be performed during the installation step, so as to adjust such function based on the environmental parameters and other variables necessarily manageable on the system.

Advantageously, such modifications require a simple mechanical adjustment operation by the installers on the described support members, which is easy to perform based on the operating conditions of the machine.