WO2023100208A1

WO2023100208A1 - Gas delivery device and method

Info

Publication number: WO2023100208A1
Application number: PCT/IT2022/050309
Authority: WO
Inventors: Simon BOBBO; Massimo Giacomelli; Nicola Lollo; Luca MASTELLARI; Roberto Mottola
Original assignee: Sit S.P.A.
Priority date: 2021-11-30
Filing date: 2022-11-29
Publication date: 2023-06-08
Also published as: IT202100030365A1

Abstract

A valve delivery device (10) comprises feed means (11) for feeding a gaseous fuel containing hydrogen into a first channel (12) and a second air feed channel (15) which joins said first channel (12) in a mixing zone (16) in which the gaseous fuel and the air mix according to a predefined air/gas ratio before being sent to a burner (17).

Description

"GAS DELIVERY DEVICE AND METHOD"

FIELD OF APPLICATION

The present invention relates to a delivery device present in a combustion apparatus, for feeding a burner, in which a gas, particularly a mixture of air and combustible gas, is used as fuel.

By way of not limiting example, the combustion apparatuses discussed above may comprise boilers, storage water heaters, stoves, ovens, fireplaces, or other similar or comparable apparatuses.

BACKGROUND ART

Combustion apparatuses fed by an air-gas mixture are known to be provided with a delivery device that allows to adjust the quantity of gas to be sent to a mixing zone for mixing thereof with comburent air.

The delivery device generally comprises a gas feed channel and an air feed channel, which join in a common duct in a mixing zone.

Along the first channel there are generally provided gas feed means, generally a valve device, comprising an aperture that is selectively opened and closed by a safety solenoid valve and a pressure regulator. In some cases a flow regulator that varies the gas passage section toward the outlet may also be present. Flow regulators, however, generally entail an increase in the overall size of the valve device and an increase in costs.

The air/gas mixture that is sent to the burner at full operation must normally comply with a certain air/gas ratio, defined by the lambda coefficient " ", for example of 1.2- 1.5 to allow a high efficiency of the system to be achieved and at the same time guarantee a complete combustion of the gas by limiting the generation of combustion residues.

The gas fed into such a delivery device and thus to the apparatus that uses it as a fuel may be, for example, methane, but recently such apparatuses use mixtures of gases containing hydrogen.

When a gas with a high percentage of hydrogen is used, it must be ensured at the time of ignition that there is no excessive quantity of hydrogen in the combustion chamber, which might lead to explosions or flame returns.

In the case of delivery devices without flow regulators and/or variable type pressure regulators (e.g. motorized), it is not possible to properly adjust the ratio between air and gas flow rates under conditions of ignition of the system. Thus, when combustible gases having high flame propagation speeds such as hydrogen are used, this may entail a risk of explosion upon ignition of the flame, or a generation of toxic residues even under ignition conditions that are normally safe when methane gas is used (with lambda equal to about 1.3).

To allow the air/gas ratio in the mixture to be modified, solutions are also known that provide for acting on the calibration of the pressure regulator, in particular when it is of the servo-assisted type, keeping it very low, for example by about - 45Pa with respect to the normal value of -5Pa. In this way, when the system operates at low powers, there is a low gas pressure and therefore a low flow rate, allowing thereby to have air in excess during ignition; this gas pressure increases progressively as the regulator modulates towards the ignition point, resulting consequently in a progressive increase of the air/gas ratio automatically. Such known solutions, however, are strongly affected by the ageing of the pressure regulator and of the valve device in general, which is also called "drift" in the sector. In fact, such a drift results in an oscillation, albeit minimal, of its gas delivery capacity, and consequently in low powers and the gas at the mixing device may not be sufficient or may be fed irregularly. To partly compensate for the problems caused by the combination of drift of the system and very low calibration of the pressure regulator it would be necessary to increase the depression at the output, letting it pass from about -50Pa to -90Pa, but this would require a more powerful and hence more expensive fan.

Document US-A-2015/0354810 (US’810) describes a mixing apparatus suitable for mixing air and combustible gas together and supplying the mixture to a burner. The apparatus is provided with a throttle valve arranged along an air feed duct, which has the function of changing the resistance for the air flow and with a resistance switching valve for the gas, arranged along a gas feed duct, which is connected to the throttle valve and is actuated simultaneously therewith. The solution of US’810 provides for simultaneously increasing the resistance to which the air flow and the gas flow are subjected in order to keep the air/gas ratio constant even when the required flow rates are low and close to the operating limits of the fan or of the gas delivery valve. Document US-A-2015/0050608 (US’608) discloses a device for mixing air and gas to be supplied to a burner. The device of US’608 comprises an air feed channel comprising a first and a second part separated by a first partition, a gas feed channel comprising a first and a second part separated by a second partition and a valve associated with opening/closing means of the second part of the air feed channel and of the gas feed channel. In US’608, the actuation of the valve involves both a reduction of the air flow rate and a reduction of the gas flow rate, in order to keep the air/gas ratio constant even in operating conditions of the burner at low powers.

Both solutions described in US’810 and US’608 have the purpose of allowing the air/gas ratio to be kept constant even under low load and therefore low power operating conditions, but they do not allow the air/gas ratio to be varied during the functioning of the burner.

Therefore, there is a need to improve a delivery device and method that can overcome at least one of the drawbacks of the prior art.

In particular, an object of the present invention is to realize a delivery device that allows to effectively and safely feed a gaseous fuel containing hydrogen, even in high percentages, or a gaseous fuel comprising 100% hydrogen, in gas-fired combustion apparatuses.

A further object of the present invention is to realize a delivery device that avoids, especially when ignited, the risk of explosions or flame returns.

Still an object of the present invention is to provide a delivery device which allows to change the air/gas ratio during the functioning steps of the combustion apparatus even with valve devices without flow regulators or motorized pressure regulators.

A further object of the present invention is to realize a delivery device by means of which it is possible, in a simple and effective way, to send to the burner an air/gas mixture whose ratio between the quantity of air and the quantity of gas, for example between the mass of air and the mass of gas, is significantly higher than the ratio expected in the normal fully operational functioning of the apparatus.

Another object is to realize a gas delivery device which is efficient and ensures in every situation a correct gas feed towards the mixing device without being affected by a possible wear or drift of its components.

A further object is to devise an effective and safe gas delivery method that allows to change the air/gas ratio in the mixture to be sent to the burner according to the needs and the operating state of the latter.

The Applicant has studied, tested and realized the present invention to overcome the drawbacks of the prior art, and to obtain the above as well as further objects and benefits.

DISCLOSURE OF THE INVENTION

The present invention is expressed and characterized in the independent claims. The dependent claims show other features of the present invention or variants of the main solution proposed.

In accordance with the aforementioned objects, a delivery device according to the present invention comprises a first channel provided with feed means for feeding a combustible gas with a desired pressure, and a second air feed channel, cooperating with air feed means, which joins said first channel in a mixing zone in which the combustible gas and the air mix according to a predefined air/gas ratio before being sent to a burner.

The gas adjustment means may comprise in a known manner a valve device comprising at least one pressure regulator and at least one safety solenoid valve, which is selectively openable and closable to allow the combustible gas supplied from a feed source to flow along the first channel.

According to a characteristic aspect of the invention, the delivery device comprises, along the first channel, a main aperture for the passage of the combustible gas which can be selectively closed and opened by means of a valve and at least one bypass aperture independent of the aforementioned valve, configured to allow the passage of a minimum quantity of gas towards the mixing zone when the main aperture is closed.

According to the present invention, the valve is configured to selectively open and close only said main aperture, without interfering with said second channel and with a quantity of air fed therethrough, in order to modify said air/gas ratio during the functioning of the burner.

In this way, even when such a main aperture is closed by such a valve, it is possible to allow a reduced quantity of combustible gas to be sent towards the mixing zone, such as to obtain, downstream of such a mixing zone, an air/gas ratio of the mixture greater than the air/gas ratio that is generally achieved when the main aperture is open.

This solution turns out to be simple and effective as it allows to change the air/gas ratio of the mixture without acting on the gas feed means or respectively the air feed means, the functioning of which can be adjusted on the basis of the quantity of heat required, or defined on the basis of other parameters.

The bypass aperture defines a minimum passage section for the gas, smaller than a maximum overall section Smax achievable when said main aperture is open.

This solution allows in particular to send a minimum quantity of gas in a step of igniting a combustion apparatus, in order to have air in excess and avoid the risks of flame return that might occur in case hydrogen is used as a combustible gas.

This bypass aperture, according to embodiments, can be made as a bypass hole separate and independent of the main aperture.

According to possible variants of embodiment, this bypass aperture is made in continuity with the main aperture, and can be defined by a portion of the latter on which the valve does not act. In such a case, opening and closing the valve results in a change in the area of the equivalent gas passage section.

In particular, the term "equivalent passage" can be intended to mean the passage given by the outlet of the valve device, passage valve, gas nozzle of a mixing device at the mixing zone.

In both cases, in the closing condition of the valve there is a minimum section for the passage of gas, while in the opening condition there is a maximum section. The area of the minimum section substantially coincides with the area of the bypass aperture, while the area of the maximum section may substantially correspond to the area of the main aperture or to the sum of the areas of the two apertures.

According to a further aspect of the invention, the area of the minimum section is equal to about 20-40% of the area of the maximum section that is achieved when said main aperture is in the opened condition.

The present device, thanks to the bypass aperture, allows to effectively and safely use a gaseous fuel containing hydrogen, for example hydrogen in high percentages, or even only 100% hydrogen.

In fact, this bypass aperture allows to achieve an air/gas ratio at ignition that is much greater than the air/gas ratio at fully operational functioning of the burner, thus avoiding the risk of explosions and flame return phenomena.

By way of example, the air/gas ratio at ignition may be at least 3-4 times the air/gas ratio during combustion at full operation.

According to a further aspect of the invention, said air/gas ratio at ignition, achievable through the passage of gaseous fuel only in said bypass aperture is comprised between about 2 and about 5 and preferably equal to about 4.

According to a further aspect of the invention, said bypass hole is made in proximity to said main aperture.

According to a further aspect of the invention, said bypass hole is made substantially on the same plane where said main aperture is made.

According to a further aspect of the invention, the delivery device comprises a control unit associated with at least said valve and configured to automatically actuate said valve when a change in the air/gas ratio in the mixture is required.

In particular, when a change in the air/gas ratio is required, the control unit is configured to change only the quantity of gas fed to the mixing zone by actuating the valve, without changing the quantity of air and keeping the functioning of the gas and air feed means unchanged.

The quantities of gas and air that are fed to the mixing zone are actually correlated to the respective flow rates of the flows along the respective ducts.

In particular, the control unit may be configured to open the valve when the ignition of the burner is completed.

According to preferred embodiments, the valve may be of the normally closed type when in an inactive state. In this way it is possible to ensure greater safety of the delivery device, since even in the event of a malfunction the main aperture remains closed and only a negligible quantity of combustible gas could pass through the bypass aperture.

According to a further aspect of the invention, the delivery device comprises adjustment means configured to partly open or close said bypass aperture in order to partialise the passage section for the gas.

In embodiments, such adjustment means comprise at least one screw translatable in one sense or the other in a given direction in order to at least partly open and close said bypass aperture.

According to a further aspect of the invention, said direction of translation can be substantially transverse to the direction along which said bypass hole is made.

According to a further aspect of the invention, the valve may comprise partialisation means suitable for modifying the passage section of the main aperture. This would allow to obtain an intermediate passage section area for the passage of gas, smaller than the maximum section area, and thus an additional level of adjustment of the air/gas ratio.

A further object of the invention is a method for delivering a mixture of air and gas, comprising feeding a combustible gas containing hydrogen by means of feed means into a first channel, feeding air into a second channel which joins said first channel in a mixing zone in which the combustible gas and the air mix according to a predefined air/gas ratio before being sent to a burner.

The delivery method according to the invention provides, at least in a functioning step, to keep closed, or to close, a main aperture of the first channel by means of at least one valve and to make the combustible gas transit towards said mixing zone through at least one bypass aperture independent of said valve, in such a way as to send into said mixing zone a quantity of combustible gas such as to obtain, downstream of said mixing zone, a mixture with an air/gas ratio, when said main aperture is closed, greater than an air/gas ratio that is achieved when said main aperture is open.

The method may further provide, at least in another functioning step, to actuate said valve in order to open said main aperture, without interfering with said second channel and with a quantity of air fed therethrough, and to make said combustible gas transit both through said bypass aperture and through said main aperture.

Preferably, the delivery method provides to keep the main aperture closed during a step of igniting the burner, and to open said main aperture after the ignition has been completed.

According to a further aspect of the present invention, during the ignition step the method provides to activate a ventilation device in order to feed a desired quantity of air along the second duct and simultaneously draw combustible gas passing through the bypass aperture in order to obtain a first value of the air/gas ratio comprised between about 2-5 and trigger the combustion of the mixture of air and gas obtaining a flame.

According to embodiments, the method provides to verify the presence of the flame within a determinate time interval before activating the valve in order to open the main aperture in such a way as to increase the quantity of combustible gas fed to the mixing zone by substantially keeping said quantity of fed air constant and obtaining a second value of the air/gas ratio in a range of 1.2-1.5.

The method according to the invention provides to activate the valve while keeping unchanged the functioning of the gas and air feed means, whereby only the quantity, i.e. the flow rate of the gas is modified while the quantity, or flow rate of the air remains substantially constant.

According to embodiments, before feeding said combustible gas into the first channel, the method provides to verify the closed state of an electromagnet of the at least one valve on the basis of a variation of an inductance of the electromagnet.

According to further embodiments, in order to verify the closed state of the electromagnet, the method provides to supply a test electric voltage with a defined intensity and/or frequency to a coil of said electromagnet and to detect a voltage signal respectively at the ends of said coil or of a resistor connected in series to said coil and compare it with a respective threshold value.

ILLUSTRATION OF THE DRAWINGS

These and other aspects, features and advantages of the present invention will become clear from the following embodiment disclosure, given by way of example only, with reference to the accompanying drawings in which:

- Fig. 1 is a schematic view of a first variant of a delivery device according to the present document in a first functioning mode;

- Fig. 2 is a schematic view of the delivery device of Fig. 1 in a second functioning mode;

- Fig. 3 is a schematic sectional and axonometric view of part of a delivery device according to the invention in the functioning mode of Fig. 1 ;

- Fig. 4 is a schematic sectional and axonometric view of part of the delivery device of Fig. 3 in the functioning mode of Fig. 2;

- Fig. 5 is a schematic view of another variant of delivery device according to the present document in a first functioning mode;

- Fig. 5a is a schematic view of a detail of Fig. 5 in a second functioning mode;

- Figs. 6-7 are schematic views of a delivery device in accordance with a further variant of the invention, respectively in a first and a second functioning mode; - Fig. 8 shows a control circuit of a solenoid valve of a delivery device according to the present invention in accordance with a first embodiment;

- Fig. 9 shows a block diagram of a method for controlling a solenoid valve with the circuit in Fig. 8;

- Fig. 10 shows a block diagram of a variant of a method for controlling a solenoid valve with the circuit of Fig. 8;

- Fig. 11 shows a control circuit of a solenoid valve in accordance with a second embodiment;

- Fig. 12 shows a control circuit of a solenoid valve in accordance with a third embodiment;

- Fig. 13 shows a graph of the functioning of the control circuit of Fig. 12 in the case of a solenoid valve in the closed state or in the open state.

To facilitate understanding, identical reference numbers have been used, where possible, to identify identical common elements in the figures. It should be noted that elements and features of an embodiment can be conveniently combined or incorporated into other embodiments without further clarification.

DESCRIPTION OF EMBODIMENTS

Detailed reference will now be made to the possible embodiments of the invention, one or more instances of which are illustrated in the accompanying figures by way of example only. The phraseology and terminology used herein is also exclusively for illustrative purposes.

With reference, for example, to Figs. 1 and 2, a delivery device 10 according to the invention comprises a first channel 12 provided with feed means 11 for feeding a combustible gas G containing hydrogen and a second channel 15, cooperating with feed means 19 for feeding air A, which joins said first channel 12 in a mixing zone 16 in which the combustible gas and the air mix to obtain a mixture M according to a predefined air/gas ratio before being sent to a burner 17.

The combustible gas G used in this device 10 contains in particular high percentages of hydrogen, even greater than 30-40%, preferably greater than 50- 60%, and even more in particular it contains only hydrogen.

The feed means 11 may comprise in a known manner a valve device 31 having a pressure regulator 24 configured to adjust the pressure of the combustible gas G exiting from the feed means 11 and stabilize it around a predefined value, and at least one solenoid valve 25 having a safety function, which can be selectively commanded to allow or prevent the flow of combustible gas G in the first channel 12.

In particular, when the solenoid valve 25 is in a closed condition, no combustible gas G flows in the first channel 12.

Along the second channel 15, upstream or downstream of the mixing zone 16, there is arranged a ventilation device 19, 119 in order to feed air within said second channel 15.

For example, in Figures 1 and 2 there is illustrated a ventilation device 19 functioning to draw, which is arranged downstream of the mixing zone 16, while in Figure 5 there is shown a ventilation device 119 arranged upstream of the mixing zone 16 and functioning with thrust.

The action of the ventilation device 19, preferably in case it is located downstream of the mixing zone 16, contributes to drawing also the combustible gas G present in the first channel 12.

Such an effect, however, can also be achieved with a ventilation device 119 functioning with thrust.

The mixing zone 16 may comprise a narrowing 26 so as to create a Venturi effect that allows drawing the combustible gas G from the first channel 12 through a suitable passage aperture 48.

The passage aperture 48 may be realized at or in proximity to the narrowing 26.

According to one aspect of the invention, said first channel 12 comprises a main aperture 13 for the passage of combustible gas G to which at least one valve 14 is associated which is selectively actuatable so as to open or close said aperture 13.

Said device 10 further comprises at least one bypass aperture 18 independent of the main aperture 13 and the valve 14, which puts the first channel 12 and the mixing zone 16 in communication.

This bypass aperture 18 is configured to allow, when said main aperture 13 is closed by said valve 14, the passage therein of a quantity of combustible gas G such as to achieve, downstream of said mixing zone 16, an air/gas ratio of the mixture M greater than the air/gas ratio that is achieved when the main aperture 13 is open.

The valve 14, in particular, is configured to selectively open and close only the main aperture 13, without interfering in any way with the second channel 15 and with the quantity, i.e. the flow rate of air A fed into it.

In this way, it is possible to change the air/gas ratio with the same quantity of air A fed by the ventilation device 19 along the second duct 15.

In particular, by keeping the valve 14 closed in a step of igniting the burner 17, it is possible to achieve an air/gas ratio of the mixture M which is greater than the one occurring in the combustion at full operation with the valve 14 open.

Substantially, therefore, during an ignition step, in which the valve 14 closes the main aperture 13, a minimum quantity of gas is sent towards the mixing zone 16.

By means of the bypass aperture 18 and by actuating the valve 14 in order to close or open the main aperture 13, it is therefore possible to change the value of the air/gas ratio during the functioning of the burner 17, with no need to act on the ventilation device 19 or on the feed means 11.

In particular, when the main aperture 13 is closed like in the situation of Fig. 1 or Fig. 3, for example during the step of igniting the burner 17, it is possible to obtain a first value XI of the air/gas ratio in the mixing zone 16 greater than a second value X2 of the ratio occurring during normal combustion during the fully operational functioning.

According to embodiments, the first value XI of the air/gas ratio at ignition may be comprised between about 2 and about 5 and preferably equal to about 4.

In this way, at the time of triggering the mixture M, it is possible to have, with the same quantity of air A, a quantity of combustible gas G much lower than the one that would occur in a traditional apparatus without the valve 14 and the bypass aperture 18.

According to embodiments, in the case of a bypass hole 32 separate from the main aperture 13, it may be made in proximity to said main aperture 13, so that the gas and air flows immediately join downstream of said bypass hole 18 and said main aperture 13 and so that they uniformly reach the mixing zone 16.

The bypass hole 32 can also be made substantially on the same plane P where this main aperture 13 is made.

Preferably the bypass aperture 18, the main aperture 13 and the valve 14 are made outside a housing 27 of the feed means 11, i.e. outside the valve device 31. For example, the bypass aperture 18 and the main aperture 13 can be associated with a housing 28 defining the mixing zone 16.

This allows to keep the already existing feed means 11 and/or valve devices 31 unchanged, which would require greater modifications and adjustments, making the modifications downstream of them.

The bypass aperture 18 can define a minimum passage section Smin equal to about 20-40% of the maximum passage section Smax that is achieved when the main aperture 13 is open.

In particular, the minimum passage section Smin may substantially coincide with the area S2 of the bypass aperture 18, while the maximum passage section Smax may substantially correspond to the sum of the area S 1 of the main aperture 13 and of the area S2 of the bypass aperture 18. The delivery device 10 comprises a control unit 20 configured to adjust the functioning of the delivery device 10 by commanding one or more among the feed means 11 , the ventilation device 19 and the valve 14.

The control unit 20 is associated with at least said valve 14 and configured to open it automatically when the ignition of the burner 17 is completed. This control unit 20 therefore allows said main aperture 13 to deliver the combustible gas G to said mixing zone 16 at the same time to deliver said combustible gas G through said by-pass aperture 18, lowering the air/gas ratio to a predetermined value, suitable for the combustion at full operation of the burner 17.

The control unit 20 may be configured to open and close the valve 14 whenever it is necessary to vary the air/gas ratio in the mixing zone 16.

In particular, when a variation of the air/gas ratio is required, the control unit 20 is configured to change only the flow rate of the combustible gas G by actuating the valve 14, without changing the quantity, i.e. the flow rate of the air A and by keeping the functioning of the feed means for feeding gas 11 and air 19 unchanged.

The second value X2 of the air/gas ratio at full operation is preferably comprised between about 1.2 and about 1.5 and preferably equal to about 1.3.

The valve 14 can be in particular a solenoid valve commanded by means of said control unit 20 and can comprise a shutter 21 configured to selectively open or close said main aperture 13 and an actuating member 22, in particular an electromagnet 33 provided with a coil 34, configured to move said shutter 21 towards and away from said main aperture 13.

The electromagnet 33 comprises in particular a static ferromagnetic part on which the coil 34 is wound and a movable core 33 integral with the shutter 21.

According to embodiments, for example described with reference to Figures 3 and 4, the shutter 21 can be associated with return elastic means 23 which, for safety reasons, keep the shutter 21 in the normally closed position. In this way, a possible absence of electrical signal results in the closure of the main aperture 13 by means of the shutter 21 pushed by these elastic means 23.

According to embodiments, in order to verify the correct closure of the valve 14 it is possible to read the electrical current absorbed by the coil, or the electric voltage at the ends thereof, when it is fed with a very low alternating voltage and therefore not sufficient to open the valve 14, as will be better explained below: the two open-closed positions are easily determinable because the current read in the two cases shows a net difference due to the different reluctance of the circuit.

In normal functioning, i.e. after the step of igniting the burner 17, when the control unit 20 commands the valve 14 to allow the passage of gas through the main aperture 13, the thrust force of these elastic means 23 is overcome and therefore the shutter 21 is recalled by the energized coils of the solenoid valve and moves away from this main aperture 13 allowing the passage of the gas G, like in Fig. 2 or Fig. 4.

The control unit 20 can be associated with the feed means 11 for feeding combustible gas G, and be configured to command the safety solenoid valve 25 allowing access to a containment vessel of said combustible gas G and possibly also to command the pressure regulator 24, at least in the case they are provided with electric actuating members, to change the operating pressure.

The control unit 20 is also associated with the ventilation device 19 and with the burner 17 and may be associated with sensors that detect the presence of a flame at the burner 17, or also the air/gas ratio that is sent to the burner 17 thus allowing the exact value to be established. On the basis of the received data, the control unit 20 can perform a feedback control of one or more components.

The device 10 may provide adjustment means 29 adapted to at least partly open or close the passage section of said bypass aperture 18, in the case of the example of the bypass hole 32. In embodiments, said means 29 comprise at least one screw 30 translatable in one sense or the other in a given direction X to at least partly open and close said bypass hole 32.

Such direction X of translation of the screw is substantially transverse to the direction Y along which such bypass hole 32 is obtained. Thus, said direction X may be substantially orthogonal or slightly inclined with respect to said direction

In embodiments, the screw 30 may have one end whose shape is at least in part conical or truncated conical to allow a progressive adjustment of the passage section of the bypass hole 32.

This makes it possible not to have a fixed air/gas ratio during the ignition step but to be able to vary it within a determinate interval in order to be able to adapt the delivery device 10 to burners 17 of a different type.

According to further embodiments, it can also be provided that also the valve 14 is provided with partialisation means, not illustrated, configured to adjust the passage section of the combustible gas G through the main aperture 13.

For example, the shutter 21 and the main aperture 13 may have a shape that is at least in part conical or truncated conical, whereby a relative movement between them may vary the passage section for the combustible gas G.

This solution makes it possible to progressively adapt the quantity of combustible gas G fed into the mixing zone 16, so as to simultaneously vary the air/gas ratio, for example to allow a gradual passage of the air/gas ratio from the first value

to the second value 2.

A valve delivery method according to the present invention comprises feeding a combustible gas G containing hydrogen from a feed source into the first channel 12 and feeding air into the second channel 15 which joins said first channel 12 in the mixing zone 16 in which the gaseous fuel and the air mix according to a predefined air/gas ratio before being sent to a burner 17.

The method also provides, at least in a step of igniting the burner 17, to keep closed, or to close, the main aperture 13 by means of at least the valve 14, and to make the combustible gas G transit only through the bypass aperture 18, in such a way as to send into said mixing zone 16 a quantity of combustible gas G such as to obtain, downstream of said mixing zone 16, an air/gas ratio of the mixture greater than the air/gas ratio that is achieved in the combustion at full operation in said burner 17, i.e. when the main aperture 13 is open.

Preferably, the method according to the invention provides for obtaining in a step of igniting the burner 17 an air/gas ratio having a first value XI of about 2-5 and in a step of combustion of the burner 17 an air/gas ratio having a second value X2 of about 1.2- 1.5.

According to a further aspect of the present invention, during the ignition step the method provides to activate the ventilation device 19 in order to feed air A along the second duct 15 simultaneously drawing the combustible gas G passing through the bypass aperture 18 and to trigger the combustion of the mixture M of air and gas to obtain a flame when the air/gas ratio has the first value XI .

According to embodiments, the method provides to verify the presence of the flame in the burner 17 within a determinate time interval from an ignition instant before activating the valve 14 in order to open the main aperture 13 and to increase the quantity of combustible gas G fed to the mixing zone 16 in order to obtain said second value X2 of the air/gas ratio.

In particular, the ignition instant can be considered as the time in which the control unit 20 activates the feed means 11, and in particular commands the opening of the safety solenoid valve 25.

When the valve 14 is activated to open the main aperture 13, the method according to the invention provides to keep substantially constant the quantity of air fed in the mixing zone 16, i.e. to keep the functioning of the ventilation device 19 and also of the feed means 11 unchanged.

According to further embodiments, the method provides to verify the closed state of the valve 14 at the ignition instant, or in general at any moment when it is necessary to ensure air in excess in the mixing zone 16.

This verification can be carried out, for example, before starting the ventilation device 19, 119 and/or opening the safety solenoid valve 25.

According to further embodiments, the method may also provide for a verification of the closed state of the safety solenoid valve 25.

Embodiments disclosed herein refer to a control circuit 40 for a direct current powered electromagnet 33, in particular the electromagnet 33 of the valve 14 and/or of the safety solenoid valve 25, to verify a respective open or closed state thereof.

The coil 34 is normally connected via a switch device 36 to a power supply circuit 36 of a direct current power voltage Vcc suitable to bring and keep the respective valve 14 (or safety solenoid valve 25) in the open state.

The switch device 36 is selectively opened and closed by a command member 38 in order to supply electric voltage to the coil 34. The command member 38 may be the same control unit 20 or may be a separate device communicating with it.

The circuit 40 and the control method of the present invention exploit the properties of the electromagnet 33 to vary its inductance depending on the reciprocal position between the movable core 35 connected to the shutter 21 and the static ferromagnetic part of which the coil 34 is part.

Thanks to this property of the electromagnet 33, it is possible to measure a different inductance between an open electromagnet state and a closed electromagnet state by applying a variable waveform signal to the ends of the coil 34 of the electromagnet 33.

The inductance of the electromagnet 33 can be measured by directly processing the signal at the ends of the terminals 41 , 42 of the coil 34 or at the ends of a resistor 43 placed in the control circuit 40.

Fig. 8 illustrates a first embodiment of a control circuit 40 according to the present invention, which comprises an alternating voltage power supply circuit 44 configured to supply a test alternating electric voltage VA and connected via an impedance 45 with value ZA to a first terminal 41 of the coil 34 and a resistor 43 having resistance Rs, connected between the second terminal 42 and a ground connection 46.

The alternating voltage power supply circuit 41 can comprise a dedicated voltage generator, or can be defined by the outputs of a microprocessor, or still can be derived from a mains connection having a frequency of 50 Hz or 60 Hz.

In accordance with a first embodiment, for example described with reference to Fig. 9, in order to determine if the electromagnet 33 is closed, the method according to the invention provides to keep the switch device 36 open, to measure the voltage Vcoil at the ends of the contacts 41, 42 of the coil 34 and to verify if this value is less than a predefined threshold value Vcoil_0, wherein the threshold value Vcoil O is calculated on the basis of the values of VA, ZA, Zcoil and Rs. In the case where the measured voltage signal Vcoil is greater than the threshold value Vcoil O, then an open state of the electromagnet 33 is determined; in this case it may be provided to turn off the delivery device 10. Conversely, if the measured voltage signal Vcoil is less than the threshold value Vcoil O, a closed state of the electromagnet 33 is determined and the gas can be fed towards the burner 17.

In accordance with a second embodiment, for example described with reference to Fig. 10, in order to determine if the electromagnet 33 is closed, the method according to the invention provides to keep the switch device 36 open, to measure the voltage signal Vs at the ends of the resistor 43 and to verify if this value is greater than a predefined threshold value Vs_0, wherein also the threshold value Vs_0 is calculated on the basis of the values of VA, ZA, Zcoil and Rs.

In the case where the measured voltage signal Vs is lower than the threshold value Vs_0, then an open state of the electromagnet 33 is determined and the delivery device 10 is switched off. Conversely, if the measured voltage signal Vs is greater than the threshold value Vs_0, a closed state of the electromagnet 33 is determined and the gas may be fed towards the burner 17.

Fig. 11 illustrates a possible variant of a control circuit 140 to verify the state of correct closure of an electromagnet 33. The elements in common with the embodiment of Fig. 8 have been denoted with the same reference numerals, while different components have been denoted with numbers increased by 100.

According to the embodiment of Fig. 11, the command member 138 which actuates the switch device 36 is depicted as a relay although it could be realized in a different way, for example as a solid state device which serves to power the electromagnet 33 for the normal opening and closing operations.

Unlike the embodiment of Fig. 8, instead of the impedance 43 there is provided a capacitor 145 having a capacitance C. This solution, in fact, provides to exploit the resonance that occurs between the capacitance C of the capacitor 145 and an inductance Lc of the electromagnet 33 when the latter is in the closed state.

The verification method according to this embodiment provides to keep the switch device 36 open and to apply to the coil 34 a test alternating electric voltage having a value equal to VAsin(27ifs) where the frequency fs is calculated with the following formula:

In this way, the series impedance formed by the capacitance C and by the inductance Lc of the electromagnet 33 is close to zero and therefore the current passing through the resistor 43 will be maximized. Consequently, the voltage signal Vs measured at the ends of the resistor 43 will also have a maximum value and can therefore be efficiently compared with the threshold value Vs_0 as provided in the block diagram of Fig. 10.

According to further embodiments, described with reference to Fig. 12, the command member 238 can be a solid state device, e.g. a transistor, a MOSFET (metal-oxide-semiconductor field-effect transistor) or the like. In this case, the command member and the switch device are integrated into a single component. In accordance with the embodiment variant of Fig. 12, the alternating voltage power supply circuit 244 can be defined by a PWM (pulse-width modulation) modulator that supplies a square wave signal to the command member 238 having an appropriate frequency so as to supply the coil 34 with a test electric voltage with a desired duty cycle and exploit the variations in current due to the charge and discharge of the inductance L of the electromagnet 33.

Such variations in current cause consistent voltage variations at the ends of the resistor 43, which are suitably filtered by means of a filter 247, e.g., an R-C filter, so as to obtain a voltage signal Vs that can be measured.

This voltage signal Vs is subsequently compared with a threshold value Vs_0 as described above and, in the case where the measured voltage signal Vs is greater than the threshold value Vs_0, then an open state of the electromagnet 33 is identified (see Fig. 13) and the method according to the invention provides to open the safety solenoid valve 25 in order to feed the gas to the burner 17.

Conversely, if the measured voltage value Vs is less than, or equal to, the threshold value Vs_0, then a closed state of the electromagnet 33 is identified (see Fig. 13) and the delivery device 10 is switched off.

The square wave signal must have an appropriate duty cycle such that the voltage at the ends of the coil 34 remains in any case below an ignition threshold value VTR SO as not to allow in any case an undesired opening of the electromagnet 33.

At the end of the verification step, in the case where the correct closed state of the electromagnet 33 has been identified, when it must be brought into the open state, by means of the solid state command member 238 it can be commanded with a constant signal in such a way as to allow the correct opening of the electromagnet 33. In the case of the electromagnet 33 of the valve 14, the signal can be kept constant throughout the fully operational functioning downstream of the step of igniting the flame of the burner 17.

It is clear that modifications and/or additions of parts or steps can be made to the device 10 and/or to the delivery method described so far, without thereby departing from the scope of the present invention as defined by the claims.

It is also clear that, although the present invention has been described with reference to some specific examples, a person skilled in the art will be able to realize many other equivalent forms of device 10 and delivery method having the features expressed in the claims and therefore all of which falling within the scope of protection defined thereby.

In the following claims, the references in parentheses have the sole purpose of facilitating reading and must not be considered as limiting factors as regards the scope of protection underlying the specific claims.

Claims

1. Valve delivery device (10) comprising a first channel (12) provided with gas feed means (11) and a second channel (15), cooperating with air feed means (19), which joins said first channel (12) in a mixing zone (16) in which the gas and the air are mixed forming a mixture having a predefined air/gas ratio before being sent to a burner (17), wherein said delivery device (10) comprises, along said first channel (12), a main aperture (13) which can be selectively opened or closed by an associated valve (14) and at least one bypass aperture (18, 32), independent of said valve (14), configured to allow the passage of gas to said mixing zone (16) when said main aperture (13) is closed, characterized in that said valve (14) is configured to selectively open and close only said main aperture (13) without interfering with said second channel (15) and with a quantity of air fed therethrough, in order to modify said air/gas ratio so that, when said main aperture (13) is closed, downstream of said mixing zone (16) it is possible to obtain a mixture with an air/gas ratio greater than the air/gas ratio that is achieved when said main aperture (13) is open.

2. Device (10) as in claim 1, characterized in that said air/gas ratio obtainable with the passage of combustible gas only through said bypass aperture (18, 32) has a first value ( I ) which is comprised between about 2 and about 5 and preferably equal to about 4.

3. Device (10) as in claim 1 or 2, characterized in that said bypass aperture (18) is defined by a bypass hole (32) separate and independent from said main aperture (13), preferably made in proximity to said main aperture (13), preferably on a same plane (P) where said main aperture (13) is made.

4. Device (10) as in claim 1 or 2, characterized in that said bypass aperture (18) is made in continuity with said main aperture (13).

5. Device (10) as in any preceding claim, characterized in that said bypass aperture (18) defines a minimum passage section (Smin) having an area equal to about 20-40% of the area of a maximum passage section (Smax) that is achieved when said main aperture (13) is open.

6. Device (10) as in any preceding claim, characterized in that it comprises a control unit (20) associated at least with said valve (14) and configured to automatically open said valve (14) when the ignition of the burner (17) is completed.

7. Device (10) as in any preceding claim, characterized in that it comprises adjustment means (29) configured to at least partly open or close said bypass aperture (18, 32).

8. Device (10) as in claim 7, characterized in that said adjustment means (29) comprise at least one screw (30) translatable in one sense or the other in a given direction (X) transverse to a direction (Y) in which said bypass aperture (18, 32) is made, in order to at least partly open or close said bypass aperture (18, 32).

9. Valve delivery method, comprising feeding a combustible gas containing hydrogen by means of gas feed means (11) into a first channel (12), feeding air by means of air feed means (19) into a second channel (15) which joins said first channel (12) in a mixing zone (16) in which the combustible gas and air are mixed forming a mixture having a predefined air/gas ratio before being sent to a burner (17), characterized in that it provides, at least in a functioning step, to keep closed, or to close, a main aperture (13) of the first channel (12) by means of at least one valve (14), and to make the combustible gas transit through at least one bypass aperture (18, 32), independent of said valve (14), in such a way as to send into said mixing zone (16) a quantity of combustible gas such as to obtain, downstream of said mixing zone (16), a mixture with an air/gas ratio greater than the air/gas ratio that is achieved when said main aperture (13) is open.

10. Method as in claim 9, characterized in that, in a step of igniting said burner (17), said method provides to activate a ventilation device (19; 119) in order to feed the air along said second duct (15) and at the same time draw combustible gas passing through said bypass aperture (18, 32) in order to obtain an air/gas ratio having a first value (X.1) comprised between 2 and 5 and trigger the combustion of the mixture of air and gas obtaining a flame.

11. Method as in claim 9 or 10, characterized in that it provides to verify the presence of a flame in said burner (17) within a determinate time interval before activating said valve (14) in order to open the main aperture (13) in such a way as to increase the quantity of combustible gas fed to said mixing zone (16) and obtain a second value ( 2) of the air/gas ratio comprised between 1.2-1.5.

12. Method as in any claim from 9 to 11, characterized in that before feeding said combustible gas into said first channel (12) it provides to verify the closed state of an electromagnet (33) of said at least one valve (14) on the basis of a variation of an inductance (L) of said electromagnet (33).

13. Method as in claim 12, characterized in that in order to verify said closed state of the electromagnet (33) it provides to supply a test electric voltage with a defined intensity and/or frequency to a coil (34) of said electromagnet (33) and to detect a voltage signal (Vcoil; Vs) respectively at the ends of said coil (34) or a resistor (43) connected in series to said coil (34), and to compare it with a respective threshold value (Vcoil O; Vs_0).

14. Method as in claim 13, characterized in that it provides to use a control circuit (140) comprising a capacitor (145) connected in series to said coil (34) and to supply a test electric voltage having a frequency such that a series impedance formed by the inductance (L) of said electromagnet (33) and by a capacitance (C) of said capacitor (145) is close to zero, so as to maximize a voltage signal (Vs) at the ends of said resistor (43).

15. Method as in claim 13, characterized in that it provides to supply a square wave command signal to a solid state command member (238) in order to supply a test electric voltage with a desired duty cycle to said coil (34) so as to obtain a current and voltage variation on said resistor (43) due to the charge and discharge of the inductance (L) of said electromagnet (33) and measure a voltage signal (Vs) corresponding to said voltage variation.