FIELD OF THE INVENTION

The present invention concerns a delivery device, and a corresponding method of use, suitable for use in a combustion apparatus in which a mixture of combustible gas and air is used as fuel.

By way of a non-limiting example, the combustion apparatuses in question can comprise boilers, storage water heaters, stoves, ovens, fireplaces, or other similar or comparable apparatuses.

BACKGROUND OF THE INVENTION

It is known that combustion apparatuses fed by a mixture of air and gaseous fuel, or combustible gaseous mixture, are provided with a delivery device which allows to regulate the quantity of gaseous fuel to be sent to a mixing zone in order to mix it with comburent air.

The delivery device generally comprises an air feed duct and a gaseous fuel feed duct, which join together in a common duct in a mixing zone.

Feed means are generally provided along the gaseous fuel duct, generally a valve device comprising an aperture which is selectively opened and closed by means of a safety solenoid valve and a pressure regulator. In some cases, there may also be a flow rate regulator which varies the passage section of the gaseous fuel.

The gaseous fuel fed to the delivery device, and then to the burner, can contain one or more natural gases, such as methane, LPG (liquefied petroleum gas), or hydrogen.

The gaseous mixture which is sent to the burner when fully operational must normally comply with a specific air/fuel ratio, with respect to the stoichiometric air/fuel value defined by the lambda coefficient “ ”, in order to allow to achieve high efficiency of the system and at the same time guarantee complete gas combustion, limiting the generation of combustion residues.

In combustion apparatuses that use natural gas or LPG, in the combustion chamber there is usually a detector of the air/fuel ratio, or ionization electrode, which is able to supply a feedback signal which is used to regulate the flow rates of the gas and air.

However, when a gaseous fuel with a high percentage of hydrogen is used, in particular 100% hydrogen, it is not possible to use the ionization electrodes as above, and therefore to use a feedback control based on an ionization electrode, since the signal of the ionization current would be insufficient for a correct control.

When a gas with a high percentage of hydrogen is used, in particular 100% hydrogen, it is necessary to guarantee that, at the time of ignition, there is no excess hydrogen in the combustion chamber, which could lead to explosions or flashbacks. In this case, it is advisable for the lambda coefficient to be set, during the ignition phase, to higher values than those of the steady state phase, and it can then be subsequently modified.

US2019/376828A1 describes a control system of a traditional type burner, which comprises a sensor module suitable to detect characteristics of a flow of air and/or gas. The solution described in US2019/376828A1 is intended to show how to monitor and reduce condensation in the sensor module, but it does not allow precise real-time control of the air flow rate fed to the burner under all circumstances, nor does it allow to identify if there is an obstruction or blockage in the chimney or if a malfunction occurs in the ventilator.

US2014/080075A1 describes a system for controlling a burner which uses one or more differential pressure sensors or flow rate sensors connected on one side to the air passage channel and on the other side to a bypass channel which in turn connects the gas passage channel to the combustion chamber. The solution described in US2014/080075A1 does not allow to monitor the flow rate of the air fed to the burner in real-time and furthermore, since it only provides one or more sensors which in fact all monitor only a pressure difference between the air and the gas, in order to control that the air/gas ratio remains stable over time it is also necessary to have a sensor suitable to detect combustion residues, on the basis of which the controller regulates the pressure of the gas and air accordingly.

FR2921461A1 describes a device for regulating the flow rate of a gas fed to a burner, which provides to use only sensors suitable to detect a pressure difference along the air duct or between the air and gas ducts, and which therefore has the same disadvantages of the other known solutions described above.

There is therefore a need to perfect a delivery device which can overcome at least one of the disadvantages of the state of the art.

One purpose of the present invention is to provide a delivery device, and to perfect a corresponding method of use, which guarantees in every situation a correct feed of the gaseous mixture into combustion apparatuses both when traditional fuels such as natural gas, methane or LPG are used, and also when gases with a high percentage of hydrogen, and with 100% hydrogen, are used.

Another purpose of the present invention is to provide a delivery device whose operation is not affected by possible wear or damage to its parts or components.

Another purpose is to provide a delivery device which avoids, especially in the ignition phase, the risk of explosions or flashbacks.

Another purpose is to perfect a method to use a delivery device which allows effective and safe fuel delivery without needing to use combustion detectors or lambda sensors.

Another purpose of the invention is also to provide a delivery device which can possibly be converted, with minimal modifications, to be used with different types of gas.

The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independent claims. The dependent claims describe other characteristics of the present invention or variants to the main inventive idea.

In accordance with the above purposes, and to resolve the technical problem disclosed above in a new and original way, also achieving considerable advantages compared to the state of the prior art, a device for delivering a combustible gaseous mixture according to the present invention comprises a first duct for feeding air and a second duct for feeding a gaseous fuel, which join in a mixing zone in which the gaseous fuel and air mix according to an air/fuel ratio before being sent to a burner, a ventilation device for feeding the air and simultaneously suctioning gaseous fuel along the ducts and means for regulating the flow of the gaseous fuel.

In accordance with one aspect of the present invention, the delivery device comprises a first sensor for measuring an air flow rate and at least one second sensor for measuring the gas flow, calculating it by means of an air/gas pressure ratio, and a control unit. In accordance with another aspect of the present invention, the delivery device comprises a speed sensor for measuring the actual rotation speed of the ventilation device.

The control unit is configured to process the data supplied by the first and second sensors and the speed sensor, and to control the ventilation device and the regulation means in order to keep the air /fuel ratio within predefined intervals and a ratio between the air flow rate and the rotation speed substantially constant around a certain initial value.

Doing so achieves at least the advantage of being able to detect possible anomalies in the pneumatic system of the combustion apparatus, which are not compatible with the correct operation of the combustion apparatus, such as partial blockages in the chimney or in the combustion fumes discharge paths, or the presence of wind that generates an air flow that is not controlled by the ventilation device, which could make the ignition of the combustion apparatus unsafe.

The presence of the first sensor for measuring the air flow rate together with the sensor for measuring the actual rotation speed of the ventilation device, in fact, allows to achieve a precise and punctual control of the power of the boiler, which directly depends on the mass of air introduced into the burner, and in particular a real-time control which therefore allows to immediately determine if there is an obstruction or blockage in a chimney of the combustion apparatus, or a possible malfunction of the ventilation device.

The simultaneous presence and the simultaneous operation of the first and second sensors and of the speed sensor allows to have a redundancy of the data detected, which allows to effectively and punctually control the ventilation device and the regulation means, and at the same time verify the correct operation of the combustion apparatus, including any malfunctions of one or more sensors, without needing to provide ionization electrodes or sensors to detect combustion residues which are instead necessary in traditional devices that are without a speed sensor associated with the ventilation device, in which it is not possible to verify that the ventilation device actually rotates at the set speed.

Advantageously, in this way it is also possible to replace the feedback control with ionization electrode with a safe and reliable open loop combustion control. In particular, this characteristic is relevant when the combustion apparatus is fed with 100% hydrogen, since in this case an ionization electrode to have feedback control over the flame is not possible.

Furthermore, the configuration with three sensors as above allows to vary the air/fuel ratio even during steady state operation of the combustion apparatus, in order to control the ignition and regulation of the combustion in the burner. In applications with a high percentage of hydrogen it is in fact important to be able to vary the air/fuel ratio according to predefined proportions even during the operation of the combustion apparatus.

DESCRIPTION OF THE DRAWINGS

These and other aspects, characteristics and advantages of the present invention will become apparent from the following description of some embodiments, given as a non-restrictive example with reference to the attached drawings wherein:

- fig. la is a schematic view of a first variant of a delivery device according to the present invention in a first configuration;

- fig. lb is a schematic view of a delivery device according to the present invention in a second configuration;

- figs, from 2 to 5 are flow diagrams of the method to use the delivery device according to the present invention.

We must clarify that in the present description the phraseology and terminology used, as well as the figures in the attached drawings also as described, have the sole function of better illustrating and explaining the present invention, their function being to provide a non-limiting example of the invention itself, since the scope of protection is defined by the claims.

To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings. It is understood that elements and characteristics of one embodiment can be conveniently combined or incorporated into other embodiments without further clarifications. DESCRIPTION OF SOME EMBODIMENTS OF THE PRESENT INVENTION

With reference to fig. la, a device 10 for delivering a combustible gaseous mixture M is configured to cooperate with a burner 50 of a combustion apparatus 53.

The combustible gaseous mixture M is a mixture of air A and gaseous fuel G. The gaseous fuel G used in the present device 10 can be a natural gas, such as methane, LPG (liquefied petroleum gas), a mixture of natural gases but also a gas mixture containing hydrogen.

In particular, the device 10 is suitable for use of gaseous fuel G with high percentages of hydrogen, even higher than 30-40%, preferably higher than 50- 60%, and even more in particular containing only 100% hydrogen. In the present disclosure, we will also refer to the gaseous fuel G with the generic term “gas” G.

The gaseous mixture M is defined by a volume ratio of air A to gas G with respect to the stoichiometric volume ratio, defined as the air/gas ratio , also called lambda coefficient .

According to one aspect of the present invention, the lambda coefficient can be regulated so as to assume different values according to the phase of the combustion, such as the ignition lambda coefficient XI or the steady state or normal operation lambda coefficient X2.

For example, in the ignition phase the lambda coefficient XI can be comprised in a first interval II of values; during normal operation the lambda coefficient X2 can be comprised in a second interval 12 of values.

For example, in the case of hydrogen in very high volumetric percentages or at 100%, it is necessary for the lambda coefficient XI to be of a high value (high excess of air) in order to prevent dangerous flashback phenomena caused by the high propagation speed of the hydrogen-oxygen combustion, which in some cases could irreparably damage some components of the combustion apparatus 53 and create dangerous situations.

In particular, according to some embodiments of the invention, the lambda coefficient XI can be equal to at least 3 - 4 times the lambda coefficient X2. In the case of 100% hydrogen, the interval II can be substantially comprised between 2 and 5, preferably equal to about 4, and the interval 12 can be comprised between about 1.2 and 2, and preferably equal to about 1.3 - 1.5.

According to other embodiments, it can be provided that even with other types of gas G, the lambda coefficient XI in the ignition phase is different from the value of the lambda coefficient X2 during normal operation: in the case of ignitions with very low temperatures, for example, it could be convenient for there to be a higher quantity of gas G and therefore with a lower lambda coefficient XI.

According to some embodiments, the value of the lambda coefficient X can vary according to the type of gas G used.

For example, the lambda coefficient XI values typical during ignition for a gas G other than hydrogen could be comprised between 1 and 2.

As an additional example, in the case of natural gases, the interval II can be comprised between 1 and 4 and the interval 12 can be comprised between 1 and 2, preferably between 1.2 and 1.5.

The device 10 comprises a first duct 11 for feeding air A, a second duct 12 for feeding gas G, a mixing zone 13, a ventilation device 14 and means 16 for regulating the flow of gas G.

The first duct 11 can comprise a reduced cross section 18 for the passage of the air A, for example a choke, a nozzle or suchlike. The cross section 18 can be able to create a pressure difference between the areas upstream and downstream of the cross section 18.

The second duct 12 joins the first duct 11 in the mixing zone 13, and can comprise a reduced cross section 19 for the passage of the gas G, for example a choke, a nozzle or suchlike.

The cross sections 18, 19 can be able to create a pressure difference between the areas upstream and downstream of the cross sections 18, 19 which, in a known manner, can be sized to allow better control of the lambda coefficient X.

The gas G and the air A mix in the mixing zone 13, indicated in figs, la, lb with dotted lines, according to the lambda coefficient X, before being sent to the burner 50.

The ventilation device 14 is disposed inside the first duct 11 to feed the air A. For example, fig. la shows a ventilation device 14a disposed downstream of the mixing zone 13 and operating in suction mode, while in fig. lb the ventilation device 14b is disposed upstream of the mixing zone 13 and operates in thrust mode. In the present disclosure, the ventilation devices 14a and 14b can be indicated generically with reference 14.

The action of the ventilation device 14a, operating in suction mode, also contributes to suctioning the gas G present in the first duct 12. This effect, however, can also be achieved with the ventilation device 14b operating in thrust mode.

The delivery device 10 can comprise a valve device 15, comprising the regulation means 16 and safety means 17.

The safety means 17 can be able to perform a safety shut-off and can be one or several safety solenoid valves, able to be selectively commanded in order to allow or prevent the flow of gas G in the second duct 12. In particular, when the safety means 17 are in a closed condition, no gas G flows in the first duct 12.

The regulation means 16 can be configured to regulate the flow of gas G flowing in the duct 12.

For example, the regulation means 16 can comprise at least one of either a flow rate modulator or a pressure modulator.

The regulation means 16 can comprise a shutter 16a, a valve or suchlike and an actuation member 16b. The shutter 16a can be configured to selectively open or close an aperture in the second duct 12. The actuation member 16b can be a stepper motor, an electromagnet configured to move the shutter 16a toward and away from the aperture, or suchlike.

By means of the regulation means 16 it is possible to modify the flow of gas G in the duct 12, and therefore modify the value of the lambda coefficient during the operation of the burner 50.

In particular, in the step of igniting the burner 50, it is possible to obtain a lambda coefficient XI comprised in the first interval II of values and, in the steady state phase, a lambda coefficient X2 comprised in the second interval 12.

The device 10 comprises a first flow sensor 23 for measuring the air A flow rate, disposed in correspondence with the first duct 11 , and at least one second flow sensor 24 for measuring an air/gas pressure ratio and calculating a gas G flow rate along the second duct 12.

The first sensor 23 can be a flow sensor of the differential type or, preferably, of the thermomassic type.

In particular, the first sensor 23 can be located between two measurement points, or terminals, 25, 26. The two terminals 25, 26 can be disposed in correspondence with the first duct 11, before and after the cross section 18, respectively.

The air can enter through the terminal 25 and exit from the terminal 26. If it is of the differential type, the first sensor 23 can read the pressure differences between the terminals 25 and 26. If it is of the thermomassic type, the first sensor 23 can detect a flow which can then be converted into a pressure differential S1=P2-P1 between the points P 1 and P2 of the duct 11.

According to some embodiments, the at least one second sensor 24 can be a flow sensor of the thermomassic type. The at least one second sensor 24 can detect a flow of air A from the duct 11 to the duct 12, which is then converted into a pressure differential required to calculate what is the flow of gas G in the duct 12.

In particular, the flow of air has to always be directed from the duct 11 to the duct 12, in order to prevent the gas G from entering the second sensor 24, damaging it, or even from escaping into the duct 11 , potentially causing a flashback.

If the gas G used is known, the sensor 24 can also measure the mass of the gas.

In a similar way to the first sensor 23, the second sensor 24 can comprise two measurement points, or terminals 27, 28. The terminals 27, 28 can be located between the duct 11 and the duct 12, at the outlet of the regulation means 16, and allow the flow of air A from the duct 11 to the duct 12. In particular, one terminal 27 can be positioned in the first duct 11 upstream of the cross section 18, and the other terminal 28 just before the cross section 19 of the second duct 12.

The device 10 also comprises a speed sensor 29 for measuring the actual rotation speed of the ventilation device 14.

The speed sensor 29 can generally be suitable to detect the drive level of the ventilation device 14, that is, its actual operation. For example, the speed sensor 29 can be suitable to detect the number of revolutions of a fan of the ventilation device 14.

By way of example, the speed sensor 29 can be a Hall effect sensor, an encoder or suchlike, preferably it is a Hall effect sensor connected to the ventilation device 14 and sensitive to the variation of the magnetic field created by an object located on the rotating part of the fan.

The device 10 comprises a control unit 30 configured to regulate the operation of the device 10.

In particular, the control unit 30 is configured to receive data at least from the first and second sensors 23, 24 and process them to suitably regulate at least the regulation means 16 in order to keep the lambda coefficient A, within intervals II, 12 of predefined values.

The control unit 30 is also configured to process the data detected by the first sensor 23 and the speed sensor 29 in order to keep a parameter K, given by the ratio between the air A flow rate and the rotation speed, substantially constant around a certain initial value KO thereof, by suitably controlling the ventilation device 14.

The control unit 30 can comprise storage and processing devices able to store and execute control algorithms, in particular a software or firmware for managing the lambda coefficient .

The control unit 30 can calculate the value of the lambda coefficient X on the basis of the data detected by the sensors 23, 24, 29: in particular, the first sensor

23 and the speed sensor 29 give the measurement of the volume of air A, advantageously also during the operation of the burner 50, substantially in real time, the composition of the air A being essentially known, while the second sensor

24 gives the proportional and precise measurement of the volume of gas G.

The control unit 30 allows a precise volumetric control of the air A and of the gas G, and can calculate the mass flow rate of the air A, the composition of the air A being known.

Thanks to the first sensor 23, to the at least one second sensor 24 and to the speed sensor 29 it is therefore possible to know in a precise and punctual manner the quantity of gas and air mixed, without providing ionization electrodes or sensors that detect fuel residues, that is, without needing feedback on the combustion.

If the composition of the gas G is known, the control unit 30 can also allow to calculate the mass flow rate of the gas G. In particular, by controlling the regulation means 16, the control unit 30 can allow to modify the gas G flow rate in the duct 12 and therefore modify the value of the lambda coefficient X during the operation of the burner 50.

The control unit 30 can be connected to the ventilation device 14 to regulate the air A flow rate.

The control unit 30 can also be associated with the regulation means 16 to regulate the gas G flow rate. In particular, the control unit 30 can be configured to regulate the regulation means 16 whenever it is necessary to vary the lambda coefficient A of the mixture M.

The control unit 30 can also be configured to receive data from a flame F presence sensor 51, for example an optical sensor, a thermocouple, a UV sensor (in the ultraviolet), or suchlike. The flame F presence sensor 51 can be positioned in correspondence with the combustion chamber 52 of the burner 50, for example outside an optical window in the case of an optical sensor, or inside the chamber 52 in the case of a thermocouple.

If 100% hydrogen is used, an optical sensor is used as sensor 51 for verifying the presence of the flame F.

The operation of the delivery device 10 described heretofore, which corresponds to the method 100 of use according to the present invention, comprises feeding air A into a first duct 11 and feeding a gas G into a second duct 12 which joins the first duct 11 in a mixing zone 13, in which the gas G and air A mix according to a predefined lambda coefficient A, before being sent to a burner 50, by means of a ventilation device 14 and regulation means 16, respectively.

The method 100 provides to measure the air A flow rate, along the first duct 11 , by means of a first sensor 23.

The method 100 provides to measure an air/gas pressure ratio between the first duct 11 and the second duct 12, by means of at least one second sensor 24.

The method 100 provides to measure a rotation speed of a ventilation device 14, by means of a speed sensor 29.

The method 100 then provides to process the data detected, in particular for the air A flow rate and the air/gas pressure ratio, in order to keep the lambda coefficient A, within intervals II, 12 of predefined values.

The method 100 also provides to process the data for the air A flow rate and the rotation speed in order to keep a parameter K, given by the ratio between the air A flow rate and the rotation speed, around a certain initial value K0 thereof.

In particular, and as shown in fig. 2, the method 100 can provide an initial step 101 of detecting a request for ignition of the combustion apparatus 53 by a user.

The method 100 can then provide the following steps:

- preparing 200 to ignite the flame F;

- ignition;

- activation of normal operation 600.

In the step of preparing 200 (fig. 3) to ignite the flame F, the method 100 can provide to receive 201, as input datum, a value of quantity of heat QC required, indicative of the temperature desired by the user. The method 100 can then provide to determine, for example on the basis of memorized and predefined tables, an air A flow rate necessary to obtain the required quantity of heat and the regulation of the rotation speed of the ventilation device 14 to supply the air A flow rate determined.

In this step, it is provided to keep a valve device 15 closed in order to prevent the flow of gas G along the second duct 12.

The regulation of the rotation speed can provide:

- switching on 202 the ventilation device 14; and

- calculating and regulating the air A flow rate required for ignition.

To calculate the air A flow rate, the method 100 can provide to:

- detect 203 a difference between the necessary air A flow rate and the real air A flow rate - the latter being zero in the initial instant and then greater than zero starting from the immediately subsequent instants;

- regulate 204 the air A flow rate and measure it, by means of an indirect measurement based on the signal detected by the first sensor 23.

The measurement of the air A flow rate can be determined as a function of a pressure difference S1=P2-P1 between the points Pl and P2 of the duct 11 for feeding air A (figs, la, lb). The first sensor 23 measures this difference SI and transduces it into an equivalent air A flow rate value.

According to some embodiments, substantially simultaneously, given that the pressure in point P of the duct 12 for feeding fuel, in the absence of a flow of gas G, is equal to the pressure in point P2, the second sensor 24 (figs, la, lb) can measure the same pressure difference that the first sensor 23 measures. Advantageously, it is therefore possible to have a redundant measurement of the air A flow rate with at least the two sensors 23 and 24.

The correct ignition of the device 10 depends on the appropriate air A flow rate, as well as on the respective gas G flow rate. It is therefore necessary for the ventilation device 14 to have a rotation speed such as to reach a certain air A flow rate which depends on the combustion apparatus 53 and on the type of gas G used.

In this step, the sensors 23, 24 guarantee that this air A flow rate is reached safely, given that the device 10 can be suitable to detect the malfunction of a sensor 23, 24 and prevent the continuation of the ignition operations of the combustion apparatus 53. Advantageously, the measurement of the air A flow rate and of the rotation speed of the ventilation device 14, and the analysis of their ratio can allow to detect possible anomalies of the pneumatic system or of the chimney 54 of the combustion apparatus 53 during its operation.

In fact, partial blockages in the chimney 54 or in the combustion fumes discharge paths, or the presence of wind with a flow opposite to the forced ventilation, could make igniting the combustion apparatus 53 unsafe.

If there are deviations in the value of the air A flow rate required with respect to the air A flow rate measured by the sensors 23 and 24, exceeding a predefined threshold level, the method 100 can provide to retry the ignition procedure in a subsequent moment, or provide a finite number of ignition preparation attempts.

To calculate the air A flow rate, the method 100 can then provide to verify 205 that the air A flow rate measured corresponds to the air A flow rate required. In particular, the air A flow rate required is a stored value, for example a table value, necessary for ignition, while the air A flow rate measured is given by the sensor 23.

In the event that the air A flow rate measured does not correspond to the air A flow rate required, the method 100 provides to verify 210 whether a pre-established time Ttimeout for the step of preparing for the ignition 200 has already elapsed. In the event that it has not elapsed, the number of revolutions of the ventilation device 14 is readjusted, that is, a new number of revolutions is set (in increments or reductions) and the calculation of the air A flow rate required can be repeated. If the time Ttimeout has elapsed, the method 100 can provide to switch off 220 the ventilation device 14 and return to receiving 201 a value of quantity of heat QC required.

According to an embodiment not shown in the drawings, the method 100 can provide to repeat the verification of the time Ttimeout at most a pre-established number of times, after which the combustion apparatus 53 can lock down.

If the air A flow rate measured corresponds to the air A flow rate required, the method 100 provides to proceed with the ignition step.

According to some embodiments, the ignition step can provide:

- a sub-step 300 of activating a scintillator above the burner 50 and opening the valve device 15; - a sub-step 400 of regulating a gas flow rate suitable for ignition by means of the regulation means 16;

- a sub-step 500 of detecting the flame F.

In the regulation sub-step 400 (fig. 4), the gas flow rate suitable for ignition can be defined as a function of a first value Al of the lambda coefficient.

In general, the gas flow rate, indicated in the following formulas by Qg, can be determined by the formula:

Qg=Kg*sqrt(P-P2) (1)

When the valve device 15 is open allowing the flow of gas G, it is possible to know the value of the pressure difference P-P2 between the points P and P2 as the difference between the value SI detected by the first sensor 23 and a value S2 detected by the second sensor 24, according to the formula:

P-P2=S1-S2=(P1-P2)-(P1-P)= (2) where the value S2=P1-P is the pressure difference between points Pl and P.

The gas flow rate is also linked to the lambda coefficient A according to the formula:

Qg=Qair/(A*R) (3) where Qair is the air A flow rate and R is the stoichiometric ratio relating to the gas used for combustion;

From the formulas (1), (2), (3), the following relationship can therefore be obtained:

S l-S2=(Qair/(A*R)) ^A 2/Kg ^A 2 (4) where Kg is a constant depending on the sizes and shape of the passage area of the cross section 19.

The regulation sub-step 400 can the provide to command the regulation means 16 so that the relationship (4) is satisfied in relation to the respective value Al set for the lambda coefficient.

In particular, the regulation sub-step 400 can provide to read 401, as input datum, a predefined value of the lambda coefficient Al - for example, the value of the lambda coefficient l can be read by a control unit 30, where it can have been stored during the steps of construction, installation and overhaul of the combustion apparatus 53, or suchlike;

The regulation sub-step 400 can also comprise: - measuring 402 the air A flow rate and calculating the desired gas G flow rate on the basis of relationship (4) disclosed above;

- calculating 403 the difference between the desired gas flow rate and the actual gas flow rate - the latter being zero in the initial instant and then greater than zero starting from the immediately subsequent instants;

- regulating 404 the flow of gas G by means of the regulation means 16 in the second duct 12 and measuring the gas flow rate indirectly by calculating it on the basis of the signal S2 detected by the second sensor 24;

- verifying 405 whether the gas flow rate corresponds to the desired gas G flow rate according to formula (1).

If the measured gas G flow rate corresponds to the desired gas flow rate, the method 100 can provide to wait for a pre-established time Tsafe for the regulation step 400 to elapse, and pass to the sub-step 500 of detecting the flame F.

If the measured gas G flow rate does not correspond to the desired gas G flow rate and the time Tsafe has not elapsed, the method 100 can provide to restart the cycle from sub-step 403, once again verifying a difference between the measured and the desired gas flow rate, until the time Tsafe has elapsed, and then to pass to the sub- step 500 of detecting the flame F.

The sub-step 500 of detecting the flame F can provide to verify the presence of the flame F by means of a sensor 51.

If the flame F is not correctly detected, the method 100 can provide to close 510 the valve device 15 in order to stop the flow of gas G, switch off 520 the ventilation device 14 and return to the detection 101 of an ignition request.

If the flame F is correctly detected, the method 100 can provide to activate normal operation 600 (fig. 5).

The transition to normal operation 600 can provide to measure 601, by means of the sensor 23, an initial value of the flow rate QairO of air A and an initial value of the rotation speed RPM0 of the ventilation device 14, and to calculate the initial parameter K0 given by the ratio:

K0=Qair0/RPM0 (5)

The parameter K0 can be stored in the control unit 30.

The step of normal operation 600 can also provide to detect 602, as input datum, a second value of the predefined lambda coefficient X.2. For example, the second value I of the lambda coefficient can be read by the control unit 30, where it can have been stored during the steps of construction, installation and overhaul of the combustion apparatus 53, or suchlike.

Normal operation 600 can provide to calculate 603 the gas G flow rate, on the basis of the relationship (4) disclosed previously, in which the lambda coefficient assumes the value A.2.

For the calculation 603 it can be provided to set a value of the rotation speed in order to obtain a value of the air A flow rate required based on the quantity of heat QC required.

Normal operation 600 can then provide to calculate 604 the difference between the gas G flow rate calculated as required, and the real gas flow rate.

Normal operation 600 can also provide to regulate 605 the flow of gas G to be supplied, by means of the regulation means 16, and to measure the real gas G flow rate, by means of the second sensor 24, and the real value of the rotation speed RPM of the ventilation device 14, by means of the speed sensor 29.

The method 100 then provides to verify 606 that the steady state parameter K given by the following formula:

K=Q1/RPM (6) deviates from the parameter K0 by a quantity smaller than a pre-established limit L. In formula (6), the value QI is the value of the measured air flow rate.

If |K0-K|<L, it can be provided to verify 607 that the demand for heat has been satisfied.

If the outcome of the verification is negative, it is possible to go back to substep 603 in order to once again calculate the gas G flow rate, based on the relationship (4).

According to another embodiment not shown in the drawings, if the outcome is negative, it is possible to go back to sub-step 605 in order to once again regulate the gas G flow rate.

If the outcome is positive, a shutdown procedure 608 can be started which provides to close the valve device 15 in order to stop the flow of gas G and possibly to clean the combustion chamber 52, for example by letting the ventilation device 14 operate at a certain speed, which preferably is about half the maximum speed.

If |K0-K|>L, the shutdown procedure 608 can be started directly. The combustion apparatus 53 can then be switched off due to malfunction, for example a clogged hood, or because the demand for heat has been satisfied. The method 100 can then provide to return to the initial step 101 of detecting a request for ignition of the combustion apparatus 53.

In the event that the shutdown occurred due to a malfunction, the combustion apparatus 53 will not be able to restart, since the verification 205 that the measured air A flow rate corresponds to the required air A flow rate cannot be satisfied.

According to an embodiment not shown in the drawings, normal operation 600 can provide to vary the rotation speed of the ventilation device 14, and therefore the flow of air A, and the lambda coefficient A.2, according to the power requirements of the combustion apparatus. In fact, the coefficient 2 can assume different values according to the preferences in the work location of the specific combustion apparatus.

In this case, the method 100 can possibly once again detect 602 the value of the lambda coefficient 2 and once again calculate 603 the gas G flow rate on the basis of relationship (4).

It is clear that modifications and/or additions of parts may be made to the delivery device 10 and to the method 100 as described heretofore, without departing from the field and 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 of skill in the art shall certainly be able to achieve many other equivalent forms of device 10 for delivering a combustible gaseous mixture and corresponding method 100 of use, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

In the following claims, the sole purpose of the references in brackets is to facilitate their reading and they must not be considered as restrictive factors with regard to the field of protection defined by the claims.