WO2023119343A1

WO2023119343A1 - Device for the delivery of a combustible gaseous mixture and procedure

Info

Publication number: WO2023119343A1
Application number: PCT/IT2022/050341
Authority: WO
Inventors: Filiberto Rimondo; Massimo Giacomelli; Simone NACCI; Loris Barduca; Roberto Mottola; Pierluigi Tiberi
Original assignee: Sit S.P.A.
Priority date: 2021-12-23
Filing date: 2022-12-22
Publication date: 2023-06-29
Also published as: IT202100032567A1

Abstract

The present invention describes a device (10) for delivering a combustible gaseous mixture (M) comprising a first duct (11) for feeding air (A) and a second duct (12) for feeding a gaseous fuel (G), which join in a mixing zone (13), in which the gaseous fuel (G) and air (A) mix according to a lambda coefficient (X) before being sent to a burner (50), a ventilation device (14) for feeding the air (A) and at the same time suctioning gaseous fuel (G) along said ducts (11, 12), and means (16) for regulating the flow rate of gaseous fuel (G). The invention also concerns a method to use a device (10) for controlling the delivering of a combustible gaseous mixture (M).

Description

DEVICE FOR THE DELIVERY OF A COMBUSTIBLE GASEOUS MIXTURE AND PROCEDURE

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 and possibly 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.

Known solutions normally provide to measure an air/fuel ratio, with respect to the stoichiometric air/fuel value, defined by the lambda coefficient “ ”, and possibly to evaluate the percentage of one and the other downstream of a mixing zone in order to keep the air/fuel ratio constant when the combustion apparatus is operating.

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, since the signal of the ionization current would be insufficient for a correct control. Moreover, at the moment of ignition it is necessary to guarantee that there is no excess quantity of 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 sensor module can comprise one or more sensors for measuring a pressure difference respectively along the gas passage channel and the air passage channel, or respectively along the gas passage channel. 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 a precise and redundant detection of a pressure difference between the air passage channel and the gas passage channel, nor to verify that the sensors are suitably calibrated.

US2014/080075 Al 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.

JPS60213729A describes a device for controlling combustion for a combustion apparatus, in which the device comprises two differential pressure sensors, which are used to guarantee greater safety and to shut off the gas supply to the combustion apparatus in the event that some operating anomaly is detected. The solution described in JPS60213729A, however, requires the intervention of an operator to restart the combustion apparatus and does not provide any automatic procedure to recalibrate a sensor, returning it to a correct working point, in the event that an anomaly in its operation is found.

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 and safe 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.

One purpose of the present invention is also to reduce the downtimes of the combustion apparatus due to malfunctions and/or the intervention of a technician to reset the combustion apparatus.

Another purpose is to provide a delivery device which is able to automatically manage small modifications in the working conditions of one or more sensors, without requiring intervention by an operator.

Another purpose is to perfect a method of use for a delivery device which allows an effective and safe delivery of the fuel without needing to use ionization electrodes.

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 a lambda coefficient 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 rate of gaseous fuel.

In accordance with one aspect of the present invention, the delivery device comprises a first sensor for measuring an air flow rate in the first duct, at least two second sensors, each connected between the first and second duct, for measuring the flow of gas, calculating it by means of an air/fuel pressure ratio, and a control unit.

The control unit is configured to command a procedure for the automatic recalibration of the first and second sensors.

Advantageously, it is therefore possible to guarantee that the first and second sensors perform precise measurements of the air flow rate and of the air/fuel pressure ratio, guaranteeing a correct feed of the gaseous mixture. This allows to increase both the efficiency as well as the safety of use of the combustion apparatus. Furthermore, the presence of the first sensor for measuring the flow rate of air in the first duct allows to achieve a precise and punctual control of the power of the boiler, which depends directly on the mass of air introduced into the burner.

As an additional advantage, the combustion apparatus can, by means of said automatic procedure, restore the correct operation of the combustion apparatus without the intervention of a technician.

The first and second sensors are configured to supply data to a control unit at least in order to keep the lambda coefficient within predefined intervals of values, by controlling the ventilation device and the regulation means.

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.

Furthermore, the configuration disclosed above allows to vary the lambda coefficient 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 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 6 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 or 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 X, also called lambda coefficient X.

According to one aspect of the present invention, the lambda coefficient X 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.

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 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.

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 A,, 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, while in fig. lb the ventilation device 14b is disposed upstream of the mixing zone 13. In the present disclosure, the ventilation devices 14a and 14b can be indicated generically with reference 14.

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 X 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 1 comprised in the first interval II of values and, in the steady state step, 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 two second flow sensors 24a, 24b 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 Pl and P2 of the duct 11.

According to some embodiments, the at least two second sensors 24a, 24b can be flow sensors of the thermomassic type. The at least two second sensors 24a, 24b 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 A has to always be directed from the duct 11 to the duct 12, in order to prevent the gas G from entering the second sensors 24a, 24b, damaging them, or even from escaping into the duct 11 , potentially causing a flashback.

If the gas G used is known, the second sensors 24a, 24b can also measure the mass of the gas.

In a similar way to the first sensor 23, the second sensors 24a, 24b can comprise two pairs of measurement points, or terminals, 27a, 27b, and 28a, 28b, respectively. The pairs of terminals 27a, 27b, and 28a, 28b can be disposed in correspondence with the first and second duct 11, 12, respectively, and allow the flow of air A from the duct 11 to the 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 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.

Thanks to the presence of both the first sensor 23 and also of the speed sensor 29, it is possible to monitor and control the air flow rate in real time, whereby the device 10 is immediately able to warn if there is an obstruction or blockage in a chimney 54 of the combustion apparatus 53, or a malfunction of the ventilation device 14.

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 command a procedure 1000 for the automatic recalibration of the first and second sensors 23, 24a, 24b.

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

The control unit 30 can be configured to command the procedure for recalibrating the sensors 23, 24a, 24b automatically, in a step of preparing to ignite a flame F in the burner 50.

The control unit 30 can be configured to command a verification of the coherence of the second sensors 24a, 24b and, if the difference between the values detected by the sensors 24a, 24b is greater than a predetermined percentage difference D2, to command the valve device 15 to close the passage of the gas G. It can then activate a procedure 1000 for recalibrating the sensors.

The control unit 30 can be configured to command the verification of the coherence of the sensors 23, 24a, 24b in a step of igniting the flame F and/or, periodically or continuously, in an operating step of the burner 50.

The control unit 30 can also be configured to process 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.

Doing so achieves at least the advantage of being able to detect possible anomalies in the pneumatic system of the combustion apparatus 53, which are not compatible with the correct operation of the combustion apparatus 53, such as partial blockages in the chimney 54 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 14, which could make the ignition of the combustion apparatus 53 unsafe.

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 be connected to the ventilation device 14 and command the latter to regulate the air A flow rate.

The control unit 30 can also be connected to the regulation means 16, and command the latter to regulate the flow of gas G.

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 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.

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 two second sensors 24a, 24b.

The method 100 provides a procedure 1000 for the automatic recalibration of the first and second sensors 23, 24a, 24b. It also provides to detect data by means of the first and second sensors 23, 24a, 24b and to process it in order to control the ventilation device 14 and the regulation means 16 at least in order to keep the lambda coefficient A, within intervals II, 12 of predefined values.

According to some embodiments, the method according to the invention provides to start the procedure for recalibrating the sensors 23, 24a, 24b automatically, in a step of preparing to ignite a flame F in the burner 50, so as to guarantee a correct control of the combustion during the operation of the combustion apparatus 53.

In particular, the recalibration procedure 1000 can provide to carry out, keeping a valve device 15 closed in order to stop the flow of gas G, a measurement of the air A flow rate, substantially simultaneously, with all the first and second sensors 23, 24a, 24b. In particular, the calibration occurs through the measurement of the flow of air that passes through the first and second sensors 23, 24a, 24b.

In particular, and as shown in fig. 2, the recalibration 1000 provides to verify whether at least one of either the first or the at least two second sensors 23, 24a, 24b returns a measurement that differs by more than a predefined percentage difference DI with respect to the other two.

The predefined percentage difference DI is comprised between 2% and 10%, preferably 5%.

The percentage difference between the measurements made between two of the sensors 23, 24a, 24b can be calculated by comparing the absolute value of the difference between the measurements and one of the respective measurements, for example the one with the highest value or the lowest value, or the average value between the measurements.

In the event A that the calculated percentage differences are lower than the predefined percentage difference DI, the method provides to exit the recalibration procedure and resume, possibly after other steps not indicated in the drawings, the subsequent step of the method 100.

In the event B that at least two calculated percentage differences are greater than the predefined percentage difference DI, the method provides to activate a safety shut-off mode 1010.

In the event C that only one of the calculated percentage differences is greater than the predefined percentage difference DI, the method provides to continue with the recalibration procedure 1000.

The method 100 can provide to verify whether the automatic recalibration procedure 1000 has been performed previously. If it has, the method 100 provides to activate a safety shut-off mode 1010.

If it hasn’t, the rotation speed of the ventilation device 14 can be set 1003 to a first value, for example to an average value between the maximum and minimum values provided.

The method 100 can provide to perform, substantially simultaneously, additional measurements by means of all the first and second sensors 23, 24a, 24b.

The method 100 can provide to recalibrate, amongst the sensors 23, 24a, 24b, the one that supplies a calculated percentage difference greater than the predefined percentage difference DI compared to the other two sensors 23, 24a, 24b, changing the scale factor thereof in such a way that it returns an intermediate value between the other two, preferably the average value between the other two.

The rotation speed of the ventilation device 14 can be set to a second value, for example to its minimum value provided.

The method 100 can provide to carry out additional measurements with all the sensors 23, 24a, 24b and verify 1004 that they do not differ from each other by more than the predefined percentage difference DI .

The rotation speed of the ventilation device 14 can be set to a third value, for example to its maximum value provided.

The method 100 can provide to carry out additional measurements with all the sensors 23, 24a, 24b and once again verify 1005 that they do not differ from each other by more than the predefined percentage difference DI.

If any of the verifications 1004 or 1005 give a negative result, indicating that the measurements differ from each other by more than the predefined percentage difference DI, the method provides to activate a safety shut-off mode 1010.

Otherwise, the recalibration procedure 1000 is successfully completed and the method 100 provides to pass to the next step.

The method 100 can also provide to measure the rotation speed of a ventilation device 14. The data of the air A flow rate and of the rotation speed can be processed 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 KO thereof.

In particular, and as shown in fig. 3, the method 100 can provide an initial step 101 of detecting a request for ignition of the combustion apparatus 53 by a user.

According to an embodiment not shown, the method 100 can provide to command a procedure 1000 for the automatic recalibration of the first and second sensors 23, 24a, 24b upon detection 101 of a request for ignition.

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. 4) 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 quantity of heat QC required and the regulation of the rotation speed of the ventilation device 14 in order 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 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.

The method 100 can provide to perform the automatic recalibration 1000 of the first and second sensors 23, 24a, 24b in order to verify they are operating correctly, in particular that the first sensor 23 is operating correctly.

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. Advantageously, the sensors 23, 24a and/or 24b guarantee that the air A flow rate is reached safely, the device 10 being suitable to detect the malfunctioning of the sensors 23, 24a and/or 24b and stop the continuation of the ignition of the combustion apparatus 53.

If there are deviations in the value of the air A flow rate required with respect to the air A flow rate measured, the method 100 can provide to retry the ignition procedure in a subsequent moment, or provide a finite number of ignition preparation attempts.

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.

If the time Ttimeout has not elapsed, the calculation of the air A flow rate 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 the ignition; - a sub-step 500 of detecting the flame F.

In the regulation sub-step 400, the gas flow rate suitable for the ignition can be defined as a function of a first value XI 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 24a and/or 24b, 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.

According to some embodiments, both sensors 24a, 24b can detect the difference Pl-P, in a redundant manner.

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

Qg=Qair/(X*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:

Sl-S2=(Qair/(X*R))^A2/Kg^A2 (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 then provide to command the regulation means 16 so that the relationship (4) is satisfied in relation to the respective value XI set for the lambda coefficient.

In particular, and as shown in fig. 5, the regulation sub-step 400 can provide to read 401, as input datum, a predefined value of the lambda coefficient XI. The value of the lambda coefficient XI can, for example, 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 at least one of the second sensors 24a, 24b.

In particular, in the steps other than the calibration step 1000, the method can provide to detect signals S2 only with one of the second sensors 24a, 24b or with both second sensors 24a, 24b.

In a preferred embodiment, in which the measurement is performed with both second sensors 24a, 24b, the method can provide to verify 405 whether the percentage difference between the data detected by the second sensors 24a, 24b is lower than a predetermined percentage difference D2. Advantageously, in this case, it is possible to verify that the second sensors 24a, 24b are operating correctly.

In particular, the predetermined percentage difference D2 can be comprised between 2% and 10%, preferably 5%.

If the outcome of the verification is negative, the method can provide to close 410 the valve device 15 in order to stop the flow of gas G and possibly to switch off the ventilation device 14. It can then provide to perform a recalibration 1000 of the first and second sensors 23, 24a, 24b, in order to verify that they are operating correctly, in particular that the second sensors 24a, 24b are operating correctly.

If the percentage difference D2 is lower than a predefined threshold, the method 100 can provide to verify 406 that the gas G flow rate corresponds to the one desired according to formula (1).

If it does correspond, the method 100 can provide to wait 407 for a pre- established time Tsafe for the regulation step 400 to elapse, and to pass to the substep 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 420 has not elapsed, the cycle can be restarted from substep 403, once again verifying a difference between the measured and the desired gas G flow rate, until the time Tsafe has elapsed, and then to pass to the sub-step 500 of detecting 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.

The transition to normal operation 600 (fig. 6) 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.

In the step of normal operation 600, a second value 12 of the predefined lambda coefficient can be detected 602 as input datum, stored in the control unit 30, for example.

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 12.

For the calculation 603, a value of the rotation speed can be set in order to obtain a value of the air A flow rate required based on the value of 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, regulate the flow of gas G to be supplied, by means of the regulation means 16, and measure the real gas G flow rate, by means of one or both the second sensor 24a, 24b, and the real value of the rotation speed RPM of the ventilation device 14, by means of the speed sensor 29.

If the measurement is carried out with both second sensors 24a, 24b, the method can provide to verify 605 whether the percentage difference D2 between the data detected by the second sensors 24a, 24b is lower than a predetermined percentage difference D2.

If it is not, the method can provide to close 610 the valve device 15 in order to stop the flow of gas G and possibly to switch off the ventilation device 14. It can then provide to perform a recalibration 1000 of the first and second sensors 23, 24a, 24b in order to verify that they are operating correctly, in particular that the second sensors 24a, 24b are operating correctly.

If the percentage difference is lower than the percentage difference D2, the method 100 can provide 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, activation of normal operation can provide to start the shutdown procedure 608 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 2, according to the power requirements of the combustion apparatus 53. In fact, the coefficient 2 can assume different values according to the preferences in the work location of the specific combustion apparatus 53. 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 M 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.

Claims

1. Device (10) for delivering a combustible gaseous mixture (M) comprising a first and a second duct (11, 12) for feeding air (A) and a gaseous fuel (G) respectively, which join in a mixing zone (13), mixing said gaseous fuel (G) and air (A) according to a predefined lambda coefficient (X) before they are sent to a burner (50), a ventilation device (14) for feeding the air (A) and the gaseous fuel (G) and means (16) for regulating the gaseous fuel (G) flow rate, characterized in that it comprises a first sensor (23) for measuring the air (A) flow rate along said first duct (11), at least two second sensors (24a, 24b) for measuring an air/fuel pressure ratio, which are connected between said first and second duct (11, 12), and a control unit (30) configured to command a procedure for the automatic recalibration of said sensors (23, 24a, 24b) and to process the data supplied by said first and second sensors (23, 24a, 24b) and control said ventilation device (14) and said regulation means (16) at least in order to keep said lambda coefficient (X) within predefined intervals (II, 12).

2. Device (10) as in claim 1, characterized in that said first sensor (23) is a flow sensor selected from a differential pressure sensor and a thermomassic sensor, located between two terminals (25, 26) disposed in correspondence with said first duct (11) respectively before and after a reduced cross section (18) thereof, and in that said at least two second sensors (24a, 24b) are flow sensors of the thermomassic type each comprising two terminals (27a, 27b, 28a, 28b) disposed respectively in correspondence with the first and second ducts (11, 12).

3. Device (10) as in any claim hereinbefore, characterized in that it comprises a speed sensor (29) for measuring the actual rotation speed of said ventilation device (14), and said control unit (30) is configured to process the data supplied at least by said first sensor (23) and said speed sensor (29) in order to control the quantity of air fed to the burner (50) in real time and keep a parameter (K), given by the ratio between said air (A) flow rate and said rotation speed, around a certain initial value (K0).

4. Device (10) as in any claim hereinbefore, characterized in that said speed sensor (29) is a Hall effect sensor connected to said ventilation device (14).

5. Method to use a device (10) for delivering a combustible gaseous mixture (M), comprising feeding air (A) in a first duct (11) and feeding a gaseous fuel (G) in a second duct (12) which joins said first duct (11) in a mixing zone (13), which is able to mix the gaseous fuel (G) and air (A) according to a predefined lambda coefficient ( ) before they are sent to a burner (50), by means of a ventilation device (14) and regulation means (16) respectively, characterized in that it provides to measure at least the air (A) flow rate along said first duct (11) by means of a first sensor (23) and the air/fuel pressure ratio between said first and second duct (11, 12) by means of at least two second sensors (24a, 24b) connected between said first and second duct (11, 12), the method providing a procedure for the automatic recalibration of said sensors (23, 24a, 24b) and to detect data by means of said first and second sensors (23, 24a, 24b) and to process such data in order to control said ventilation device (14) and regulation means (16) at least in order to keep said lambda coefficient (X) within predefined intervals (II, 12).

6. Method as in claim 5, characterized in that said calibration is performed on the basis of the measurement of the flow of air that passes through said first and second sensors (23, 24a, 24b).

7. Method as in either claim 5 or 6, characterized in that said recalibration procedure provides to keep a valve device (15) closed in order to stop the flow of gas (G), and to:

- measure the air (A) flow rate, substantially simultaneously, with all said first and second sensors (23, 24a, 24b), verifying whether at least one of either said first or at least two second sensors (23, 24a, 24b) return a measurement that differs, as a percentage difference, by more than a predefined percentage difference (DI) with respect to the other two;

- if only one of the calculated percentage differences is greater than said predefined percentage difference (DI), set the rotation speed of the ventilation device (14) to a first value and repeat, substantially simultaneously, the measurements by means of all said first and second sensors (23, 24a, 24b);

- recalibrate, amongst said sensors (23, 24a, 24b), the one that supplies said calculated percentage difference greater than said predefined percentage difference (DI) compared to the other two sensors (23, 24a, 24b), changing its scale factor in such a way that it returns an intermediate value between the other two.

8. Method as in claim 7, characterized in that said recalibration procedure also provides to: - set the rotation speed of the ventilation device (14) to a second value and verify that the measurements of all said sensors (23, 24a, 24b) do not differ from each other by more than said predefined percentage difference (DI).

9. Method as in claim 8, characterized in that said recalibration procedure also provides to:

- set the rotation speed of the ventilation device (14) to a third value and verify that the measurements of all the sensors (23, 24a, 24b) do not differ from each other by more than said predefined percentage difference (DI).

10. Method as in any claim from 8 to 9, characterized in that if any one of the verifications indicates that at least one of said measurements, as a percentage difference, differs from the other measurements by more than said predefined percentage difference (DI), the method provides to activate a safety shut-off mode, otherwise, it provides to conclude the recalibration procedure with a positive outcome.

11. Method as in any claim from 8 to 10, characterized in that if said percentage differences calculated for the measurements of said sensors (23, 24a, 24b) are all lower than said predefined percentage difference (DI), the method provides to exit said recalibration procedure, while if at least two of said calculated percentage differences are greater than said predefined percentage difference (D 1 ), the method provides to activate a safety shut-off mode.

12. Method as in any previous claim from 5 to 11, characterized in that it provides that said predefined percentage difference (DI ) is comprised between 4% and 6%, preferably 5%.

13. Method as in any claim hereinbefore, characterized in that it provides to activate said procedure for recalibrating said sensors (23, 24a, 24b) automatically, in a step of preparing to ignite a flame (F) in said burner (50).

14. Method as in any claim hereinbefore, characterized in that it provides a verification of the coherence of the data detected by said second sensors (24a, 24b), verifying whether the difference between the values detected by said second sensors (24a, 24b) is lower than a predetermined percentage difference (D2) and, if the outcome is negative, it provides to command said valve device (15) to close the passage of said gaseous fuel (G) and activate said procedure for recalibrating said sensors (23, 24a, 24b). - 22 -

15. Method as in claim 14, characterized in that it provides to carry out said verification of the coherence and possibly said recalibration of said sensors (23, 24a, 24b) in a step of igniting said flame (F) and/or, periodically or continuously, in an operating step of said burner (50).