DEVICE AND METHOD FOR CONTROLLING A FUEL-OXIDIZER MIXTURE FOR A PREMIX GAS BURNER

Abstract

A device for controlling a fuel-oxidizer mixture for a premix gas burner includes: an intake duct, including an inlet, a mixing zone, and a delivery outlet; an injection duct; a gas regulating valve, located along the injection duct; a fan, located in the intake duct to generate therein a flow of the oxidizer fluid or of the mixture; a control unit, configured for generating drive signals; a sensor unit, configured to detect a first differential pressure, between a first detecting section, located in the intake duct upstream of the mixing zone in the direction of inflow and a second detecting section, located in the intake duct downstream of the mixing zone in the direction of inflow, and configured to detect a second differential pressure, between the first detecting section and a third detecting section, located in the injection duct between the gas regulating valve and the mixing zone.

Claims

1. A device for controlling a fuel-oxidizer mixture for a premix gas burner, comprising: an intake duct, which defines a section for the admission of an oxidizer fluid into the duct and includes an inlet for receiving the oxidizer, a mixing zone for receiving the fuel and allowing it to be mixed with the oxidizer, and an outlet for delivering the mixture to the burner; an injection duct, which defines a section for the admission of the fuel and which is connected to the intake duct in the mixing zone to supply the fuel; a gas fuel regulating valve, located along the injection duct; a fan, located in the intake duct to generate therein a flow of the oxidizer fluid or of the fuel-oxidizer mixture in a direction of inflow oriented from the inlet to the delivery outlet; a control unit, configured for generating drive signals, for regulating the gas regulating valve and the rotation speed of the intake fan; a sensor unit, in communication with the control unit and configured for detecting a first differential pressure, between a first detecting section, located in the intake duct upstream of the mixing zone in the direction of inflow and a second detecting section, located in the intake duct downstream of the mixing zone in the direction of inflow, and a second differential pressure, between the first detecting section and a third detecting section, located in the injection duct between the gas regulating valve and the mixing zone.

2. The device according to claim 1, comprising a mixer, located along the intake duct, at the mixing zone, wherein the sensor unit is associated with the mixer, and wherein the mixing zone is positioned upstream or downstream of the fan.

3. The device according to claim 2, wherein the mixer comprises: a first through cavity, open onto the first detecting section; a second through cavity, open onto the second detecting section; and a third through cavity, open onto the third detecting section; wherein the sensor unit comprises a first pressure connection, a second pressure connection and a third pressure connection, which are located inside the first, second and third through cavities, respectively.

4. The device according to claim 1, wherein the sensor unit comprises: a first sensor, including a respective pressure connection for the first detecting section and a respective pressure connection for the second detecting section, and a second sensor, including a respective pressure connection for the first detecting section and a respective pressure connection for the third detecting section, or a single sensor, including a pressure connection for the first detecting section, a pressure connection for the second detecting section, and a pressure connection for the third detecting section.

5. The device according to claim 1, wherein the control unit is programmed for: commanding a predetermined flow rate variation by regulating the fan or the gas regulating valve; detecting a first variation, representing a variation in the first differential pressure due to the predetermined flow rate variation; detecting a second variation, representing a variation in the second differential pressure due to the predetermined flow rate variation; and performing a diagnosis of the sensor unit based on the first and the second variation.

6. The device according to claim 5, wherein the control unit is programmed for: comparing the first variation with a first predetermined variation; and comparing the second variation with a second predetermined variation, the first and the second predetermined variation being associated with the predetermined flow rate variation.

7. The device according to claim 5, wherein the control unit is programmed for: determining a first trend, representing the fact that the first variation is positive or negative; determining a second trend, representing the fact that the second variation is positive or negative; comparing the first trend with the second trend, to check that the first and the second variation are both positive or both negative; and generating a notification of possible fault if the first and the second variation have opposite signs.

8. The device according to claim 1, wherein the sensor unit comprises a first pressure connection, a second pressure connection and a third pressure connection, in fluid communication with the first detecting section, the second detecting section and the third detecting section, respectively, and wherein the first differential pressure is measured across the first pressure connection and the second pressure connection, and the second differential pressure is measured across the first pressure connection and the third pressure connection.

9. A method for controlling a fuel-oxidizer mixture in a premix gas burner, comprising the following steps: generating an air flow, by means of a fan, in an intake duct including an inlet for receiving the oxidizer, a mixing zone, and an outlet for delivering the mixture to the burner; feeding fuel to the mixing zone through an injection duct; mixing the oxidizer and the fuel in the mixing zone; regulating the fuel flow rate through a gas regulating valve; generating drive signals through a control unit and sending the drive signals to the gas regulating valve and to the fan; detecting a first differential pressure, between a first detecting section, located in the intake duct upstream of the mixing zone in the direction of inflow and a second detecting section, located in the intake duct downstream of the mixing zone in the direction of inflow; and detecting a second differential pressure, between the first detecting section and a third detecting section, located in the injection duct between the gas regulating valve and the mixing zone.

10. The method according to claim 9, comprising a step of diagnosing, including the following steps, performed by a processor of the control unit: commanding a predetermined flow rate variation by regulating the fan or the gas regulating valve; detecting a first variation, representing a variation in the first differential pressure due to the predetermined flow rate variation; detecting a second variation, representing a variation in the second differential pressure due to the predetermined flow rate variation; and performing a diagnosis of the sensor unit based on the first and the second variation.

11. The method according to claim 10, wherein the step of diagnosing comprises the following steps: comparing the first variation with a first predetermined variation; and comparing the second variation with a second predetermined variation, the first and the second predetermined variation being associated with the predetermined flow rate variation.

12. The method according to claim 9, wherein the step of diagnosing comprises a step of diagnosing with the burner off, comprising the following steps: generating drive signals, representing a predetermined rotation speed of the fan, corresponding to a predetermined flow rate and/or pressure; detecting, through the sensor unit, a value of the first differential pressure and of the second differential pressure, responsive to the predetermined flow rate; sending the value of the first differential pressure and of the second differential pressure to the control unit; comparing, in the control unit, the first differential pressure and the second differential pressure with respective reference data representing reference values of the first predetermined differential pressure and of the second predetermined differential pressure for the specific flow rate set by the control unit; and diagnosing the operation of the first and the second sensor based on the comparison of the first differential pressure and the second differential pressure, detected by the sensor unit, with the reference data.

13. The method according to claim 10, wherein the step of diagnosing comprises the following steps: determining a first trend, representing the fact that the first variation is positive or negative; determining a second trend, representing the fact that the second variation is positive or negative; comparing the first trend with the second trend, to verify that the first and the second variation are both positive or both negative; and generating a notification of possible fault if the first and the second variation have opposite signs.

14. The method according to claim 9, wherein the method comprises a step of providing a mixer, mounted along the intake duct at the mixing zone and a step of connecting the sensor unit to the mixer.

15. The method according to claim 14, wherein the method comprises the following steps: providing a first pressure connection, a second pressure connection and a third pressure connection; and inserting the first pressure connection, the second pressure connection and the third pressure connection into a first, a second and a third through cavity of the mixer, respectively; wherein the first, the second and the third through cavity are open onto the first detecting section, the second detecting section and the third detecting section, respectively.

16. The method according to claim 9, wherein the method comprises a step of providing a first pressure connection, a second pressure connection and a third pressure connection, in fluid communication with the first detecting section, the second detecting section and the third detecting section, respectively, and wherein the first differential pressure is measured across the first pressure connection and the second pressure connection, and the second differential pressure is measured across the first pressure connection and the third pressure connection.

17. The method according to claim 9, comprising the following steps: receiving a flame signal representing the presence of a flame deriving from the combustion of a fuel belonging to a first predetermined type or a second predetermined type inside a combustion cell of the burner; and accessing fuel data, representing the fact that the gas fuel belongs to the first type or the second type; wherein the processor has access to a memory unit containing first regulation data and second regulation data, different from the first regulation data and is programmed to generate the drive signals based on the first regulation data or, alternatively, on the second regulation data, depending on the fuel data.

18. The method according to claim 9, comprising an additional step of diagnosing, including the following steps, performed by a processor of the control unit: detecting a temperature in the combustion cell; comparing the detected temperature value with one or more limit values; and compensating a reading of the sensor unit based on the preceding step of comparing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0078] These and other features will become more apparent from the following description of a preferred embodiment, illustrated by way of non-limiting example in the accompanying drawings, in which:

[0079] FIGS. 1A and 1B schematically illustrate a first and a second embodiment of a control device of this disclosure;

[0080] FIGS. 2A and 2B show, respectively, a perspective view and a schematic cross sectional view of a mixer of the device of FIG. 1;

[0081] FIGS. 3A and 3B show, respectively, a first perspective section and a second perspective section of an embodiment of a mixer of this disclosure;

[0082] FIGS. 4A and 4B show, respectively, a first perspective section and a second perspective section of the mixer of FIG. 2A;

[0083] FIG. 5 shows a perspective section of an embodiment of a mixer according to this disclosure.

DETAILED DESCRIPTION

[0084] With reference to the accompanying drawings, the numeral 1 denotes a device for controlling the fuel-oxidizer mixture in premix gas burners 100.

[0085] The device comprises an intake duct 2 which defines a section S through which a fluid is admitted into the duct. The intake duct 2 may be circular or rectangular in section. The intake duct 2 extends from (includes) an inlet 201, configured to receive the oxidizer, to (and) a delivery outlet 203, configured to supply the mixture to the burner 100. The intake duct 2 comprises a mixing zone 202 for receiving the fuel and allowing it to be mixed with the oxidizer.

[0086] The device 1 comprises an injection duct 3. The injection duct 3 is connected, at a first end of it, to the intake duct 2 in the mixing zone 202, to supply the fuel. The injection duct 3 is connected, at a second end of it, to a gas supply such as, for example, a gas cylinder or the national gas grid.

[0087] The device 1 comprises a gas regulating valve 7. The gas regulating valve 7 is located along the injection duct 3. In an embodiment, the gas regulating valve 7 is electronically controlled. The gas regulating valve 7 comprises a solenoid valve. The gas regulating valve 7 is configured to vary a section of the injection duct 3 as a function of drive signals 501 sent by a control unit 5.

[0088] The device 1 comprises a fan 9. The fan 9 rotates at a variable rotation speed v. The fan 9 is located in the intake duct 2 to generate therein a flow of oxidizer in a direction of inflow V oriented from the inlet 201 to the delivery outlet 203.

[0089] In an embodiment, the device 1 comprises a regulator 8. In an embodiment, the regulator 8 is configured to vary the flow rate of oxidizer flowing through the intake duct 2. In an embodiment, the regulator 8 is configured to prevent fluid from flowing in a return direction, opposite of the direction of inflow V.

[0090] In an embodiment, the regulator comprises at least one partializing valve (and/or a non-return valve) 8. By partializing valve is meant a valve capable of varying its operating configuration as a function of the rotation speed of the fan 9, that is, of the flow rate of mixture. By non-return valve is meant a valve configured to allow a fluid to flow in one direction only and to prevent the fluid from flowing back in the opposite direction in the event of counterpressure.

[0091] In an embodiment, the regulator comprises at least two partializing valves. In an embodiment, one partializing valve is configured to vary its position in a working range different from that of the other partializing valve.

[0092] The device 1 comprises a control unit 5. The control unit 5 is configured to control the speed of rotation v of the fan 9 between a first rotation speed, corresponding to a minimum flow rate of oxidizer, and a second rotation speed, corresponding to a maximum flow rate of oxidizer.

[0093] The control unit 5 is configured to generate drive signals 501 used to control the fan 9 and the gas regulating valve 7. The drive signals 501 represent a rotation speed of the fan 9.

[0094] In an embodiment, the control unit 5 is configured to control opening of the gas regulating valve 7. Thus, in an example embodiment, the drive signals 501 represent opening the gas regulating valve 7, hence a flow of gas delivered to the mixing zone.

[0095] In an embodiment, the device 1 comprises a user interface 50, configured to allow a user to enter configuration data. The configuration data comprise data that represent working parameters of the device 1 such as, for example, temperature of the fluid heated by the burner, pressure of the fluid in the burner, flow rate.

[0096] In an embodiment, the control unit 5 is configured to receive configuration signals 500′, representing the configuration data, and to generate the drive signal 501 as a function of the configuration signals 500′.

[0097] The device 1 comprises a first monitoring device 41 (that is, a first flame sensor 41). The first flame sensor 41 is configured to generate a first control signal 401 (or first flame signal 401). In an embodiment, the first flame signal 401 represents a state of combustion in the burner 100 due to the combustion of a first type of fuel. Preferably, the first type of fuel is hydrogen. The first flame sensor 41 is located in a combustion head TC of the burner 100.

[0098] The first flame signal 401 is a signal representing a physical parameter which the respective sensor is configured to detect in order to assess combustion. For example, in the case of hydrogen, the first flame signal 401 is preferably a signal representing the detection of ultraviolet—UV—rays.

[0099] In a particularly advantageous embodiment, the device 1 comprises a second monitoring device 42 (that is, a second flame sensor 42). The second flame sensor 42 is configured to generate a second control signal 402 (or second flame signal 402). In an embodiment, the second flame signal 402 represents a state of combustion in the burner 100 due to the combustion of a second type of fuel. Preferably, the second type of fuel comprises methane, LPG or, more in general, a mixture of hydrocarbons. The second flame sensor 42 is located in a combustion head TC of the burner 100.

[0100] The second flame signal 402 is a signal representing a physical parameter which the respective sensor is configured to detect in order to assess combustion of the second type of fuel. For example, in the case of the hydrocarbons, the second flame signal 402 is preferably a signal representing the entity of a current due to the ionization, or alternatively to the impedance measured by an electrode immersed in the flame and supplied with voltage.

[0101] In an embodiment, the processor receives fuel data 403, representing the fact that the fuel used belongs to the first type, to the second type or is a mixture of the first and the second type.

[0102] In an example, the fuel data 403 are sent via the user interface 50, for example, as part of the configuration data entered manually by the user.

[0103] In a preferred embodiment, the first and the second flame signal 401, 402 are sent to (are received in) the processor. In other embodiments, the processor receives only one between the first and the second flame signal 401, 402, based on the fuel that is being used, that is to say, based on the fuel data 403.

[0104] In an embodiment, the device comprises a memory unit containing first regulation data R1 representing regulation data of the burner in the presence of fuel of the first type, and second regulation data R2 representing regulation data of the burner in the presence of fuel of the second type. More generally speaking, the memory unit includes a plurality of regulation data groups R, each of which is associated with a respective type (composition) of the fuel being used.

[0105] The processor is programmed to select the first or the second regulation data R1, R2 based on the fuel data 403.

[0106] The processor is programmed to generate the drive signals 501 based on the regulation data selected and based on the first and/or the second flame signal 401, 402.

[0107] In the embodiment in which the processor receives both the first and the second flame signal 401, 402, the processor is programmed to automatically receive the fuel data 403.

[0108] More specifically, in an embodiment, the intensity of the first flame signal (that is, the intensity of the UV signal) is associated with the quantity of hydrogen used in the combustion head TC. Further, the intensity of the second flame signal (that is, the intensity of the continuous ionization signal) is associated with the quantity of fossil fuels used in the combustion head TC.

[0109] This allows distinguishing the type of fuel used so that the burner can be monitored, run and maintained more safely and efficiently.

[0110] The processor, therefore, is programmed to derive a presence of the first and/or the second type of fuel (to define the fuel data 403) based on the intensity of the first and/or the second flame signal 401, 402. Preferably, the processor is programmed to derive a quantity of the first type of fuel and/or a quantity of the second type of fuel (to define the fuel data 403) based on the intensity of the first and/or the second flame signal 401, 402.

[0111] Based on the first and/or the second flame signal 401, 402, the processor may also determine a flow rate (a quantity) of fuel of the first type and/or of the second type in the combustion head.

[0112] In an embodiment, the monitoring device 4 comprises a flow or flow rate sensor 43 (or a sensor for measuring differential pressure between one side of a diaphragm or Venturi and the other). The flow sensor 43 is located on the intake duct 2 or on the injection duct 3 and is configured to detect a flow rate signal 431 representing a flow of fuel-oxidizer mixture delivered to the combustion head TC or a flow of fuel injected into the mixing zone. In an embodiment, there may be more than one flow sensor 43 to form a plurality of flow sensors 43. The flow sensors 43 may be pressure sensors or flow meters. In an embodiment, one flow sensor 43′ is located in the gas injection duct 3 and another flow sensor 43″ is located on the intake duct 2. In another embodiment, the flow sensor 43″ is located on the intake duct upstream of the fan to provide data relating only to the flow rate of oxidizer.

[0113] The processor receives the flow rate signal 431 from the flow sensor 43.

[0114] In an embodiment, the flow sensor 43 is configurable on the basis of the fuel data 403. More specifically, the flow sensor 43 is configurable in such a way as to select a working curve that is more suitable for the fuel to be measured. In an embodiment, the sensor 43 located in the duct 2 may be a mixture composition sensor.

[0115] It is specified that the device of this disclosure can work independently of the presence of the flow sensors 43, 43′ and 43″, although the presence of these sensors can provide additional information for controlling the mixture or for cross checking the measurements.

[0116] The processor is programmed to compare the flow rate calculated with the flow sensor 43 with the flow rate calculated from the first and/or the second flame signal 401, 402. Based on this comparison, the processor calculates a real (measured) ratio between fuel and oxidizer. The processor compares the real (measured) ratio between fuel and oxidizer with an ideal ratio and accordingly generates an adjustment signal. The processor processes the adjustment signal and generates the drive signals 501 based also on the adjustment signal to set the real (measured) ratio between fuel and oxidizer as close as possible to the ideal ratio again.

[0117] It should be noted that in an embodiment, comparing the flow rate calculated with the flow sensor 43 with the fuel flow rate calculated from the first and/or the second flame signal 401, 402 makes it possible to derive information regarding the correct operation of the flow sensor 43, which is an essential condition for the safety measurements of the control device.

[0118] In an embodiment, the monitoring device 4 comprises a temperature sensor 44. The temperature sensor 44 is located in the combustion head TC. This temperature may, for example, be measured both in contact with, or in proximity to, the inside surface of the burner (not on the side where the flame is formed) or on the outside, in the combustion chamber, (on the side where the flame is) with a similar result.

[0119] The temperature sensor 44 is configured to detect a temperature signal 441, representing a temperature inside the combustion head TC. In an embodiment, there may be more than one temperature sensor 44 to form a plurality of temperature sensors 44.

[0120] It is noted that in calculating the real (measured) ratio between fuel and oxidizer, the processor receives the temperature signal and calculates the flow rate (the quantity) of the fuel of the first type and/or of the second type in the combustion head (that is, the real ratio between fuel and oxidizer) based on the temperature signal 441. The correlation between the fuel-oxidizer ratio and a process sensor (for example, the temperature sensor which detects the temperature signal 441) may be used as additional information to assess the correctness of the measurement given by the two sensors in the sensor unit. For example, if the temperature exceeds a first limit value (or a multiplicity of first limit values to build a curve), determined as a function of the power burn and corresponding to the ideal/chosen combustion for a given fuel (that is to say, in the presence of a combustion richer in fuel or in the absence of air), the control performs one or both of the following steps: compensating the reading of the air sensor, allowing the system to bring the quantity of air back to the correct value (increasing it) by controlling the fan, and/or compensating the reading of the fuel sensor to reduce the quantity of fuel by controlling the gas regulating valve. Similarly, it is possible for action to be taken if the temperature is below a second limit value (or a multiplicity of second limit values to build a curve), determined as a function of the power burn (that is to say, should combustion be poor in fuel or excessively rich in air). In this case, the control performs one or both of the following steps: compensating the reading of the air sensor, allowing the system to bring the quantity of air back to the correct value (decreasing it) by controlling the fan, and/or compensating the reading of the fuel sensor to increase the quantity of fuel by controlling the gas regulating valve.

[0121] In an embodiment, the device comprises a gas detection sensor, configured to measure the presence and/or the quantity of gas (preferably hydrogen) present inside the burner or in an outside space adjacent thereto.

[0122] In an embodiment, the processor has access to experimental data including, amongst other things, the ignition flow rate ranges for the first type of fuel and the second type of fuel (or a mixture thereof) and, for each ignition flow rate range, a respective expected flame signal (first flame signal 401 or second flame signal 402) and expected fuel flow rate.

[0123] In the step of igniting the burner, the method comprises supplying a progressive flow of fuel and interrupting the progression once the presence of the flame is detected (via the first flame signal 401 or the second flame signal 402).

[0124] Once ignition has been ascertained, the method comprises determining the type of gas being supplied, based on the level of the ionization signal and/or on the intensity of the UV radiation and/or on the fuel flow.

[0125] When the type of gas being supplied has been identified, the flow sensor 43 can be reconfigured in such a way as to select a working curve more suitable for the fluid to be measured (typically, in this specific case, for the oxidizer), hence keeping accuracy and resolution at the maximum allowed by the instrument, for improved adjustment quality and working/modulation range (defined as the ratio between the maximum and the minimum flow rate of the appliance). The configurability of the flow sensor 43 might not be automatic (via a self-learning boiler control) but determined by factory setting or set during installation. The configurability of the sensor may occur via data communications (for example, serial communication or remote communication).

[0126] Another drawback overcome by this invention regards cases where the gas supply pressure is low or where the supply is cut off altogether.

[0127] In the prior art, for example, in systems comprising only flow/pressure sensors or even mixture composition sensors, the management of low pressure or absence of gas is not safe. In effect, if the sensor does not detect the necessary quantity of fuel flow, the control systems might adjust the mixture by reducing the quantity of air but without direct feedback from combustion (in the case of a faulty sensor or a reading corrupted for some other reason), with possible dangerous consequences such as, for example, an increased risk of flashback or explosion.

[0128] Detecting the first flame signal 401 (that is, the intensity of UV radiation) allows confirming whether the presumed reduction in the availability of fuel is real and thus allows the quantity of air to be reduced and the appliance to operate correctly in complete safety, albeit with a reduced range.

[0129] Another function useful for safety is, at the ignition stage, checking whether the presence of the flame is detected via the first and/or the second flame signal 401, 402 even in the cases where the detected gas flow rate is not within a range considered minimal for ignition. In effect, in such a case, it is more than likely that the problem lies in a fault or malfunction of the flow sensor 43.

[0130] In an embodiment, the device 1 comprises a sensor unit 10. The device 1 preferably also comprises a mixer 6, which is associated with the intake duct 2 and with the injection duct 3. More specifically, the mixer 6 at least partly defines the mixing zone 202, allowing the fuel and the oxidizer to be mixed together. The sensor unit 10 is configured to detect a first differential pressure P1, between a first detecting section A1, located in the intake duct 2 upstream of the mixing zone 202 in the direction of inflow V and a second detecting section A2, located in the intake duct 2 downstream of the mixing zone 202 in the direction of inflow. The sensor unit 10 is configured to detect a second differential pressure P2, between the first detecting section A1 and a third detecting section G1, located in the injection duct 3 between the gas regulating valve 7 and the mixing zone 202.

[0131] In a purely exemplary embodiment, the sensor unit 10 comprises a first sensor 101. The sensor unit comprises a second sensor 102. The first sensor 101 is configured to detect the first differential pressure P1. The second sensor 102 is configured to detect the second differential pressure P2.

[0132] In an example embodiment, the mixer 6 comprises a receiving slot 61. The mixer 6 comprises a first cavity 62. The mixer 6 comprises a second cavity 63. The mixer 6 comprises a third cavity 64. In an example embodiment, the mixer 6 comprises a fourth cavity 65.

[0133] The mixer 6 comprises an outside wall 601. In an example embodiment, the outside wall 601 comprises an outside surface 601′ having a profile which is defined by a first portion 601C′, preferably cylindrical, and a second portion 601P′, preferably prismatic, which extends from the first, cylindrical portion 601C′.

[0134] The second, prismatic portion 601P′ defines the receiving slot 61.

[0135] The second, prismatic portion 601P′ defines at least one connecting surface SC. In an embodiment, the second, prismatic portion 601P′ defines a first connecting surface SC1 and a second connecting surface SC2. The first connecting surface SC1 is opposite the second connecting surface SC2. In effect, in such a case, the prismatic portion 601P′ extends from the cylindrical portion 601C′ in two opposite directions, which in practice define, with respect to the cylindrical portion 601C′, two protrusions which define the first connecting surface SC1 and the second connecting surface SC2.

[0136] In an embodiment, the first and the second sensor 101, 102 are both connected to the at least one connecting surface SC. In other embodiments, on the other hand, comprising the first connecting surface SC1 and the second connecting surface SC2, the first sensor 101 is connected to the first connecting surface SC1 and the second sensor 102 is connected to the second connecting surface SC2.

[0137] The outside wall 601 comprises an inside surface 601″, preferably cylindrical.

[0138] The mixer 6 comprises an inside wall 602. Preferably, the inside wall 602 is a cylindrical wall, coaxial with the outside wall 601.

[0139] The inside wall 602 and the outside wall 601 define an annular groove CA, comprising an annular space and interposed between the outside wall 601 and the inside wall 602.

[0140] The outside wall 601 comprises an injection orifice 601A. The injection orifice 601A is connected to the injection duct 3. Thus, the gas reaches the annular groove from the injection duct 3.

[0141] The mixer 6 comprises a connecting flange 603, connected to the portion of the intake duct 2 that is connected to the combustion cell TC. The connecting flange 603 is connected to the outside wall 601. The portion of the intake duct 2 that is connected to the combustion cell TC is connected to the connecting flange 603.

[0142] In an embodiment, the annular groove CA is open, at one end of it, onto the intake duct 2, downstream of the injection duct 3 in the direction of inflow V. In other embodiments, the inside wall 602 comprises a plurality of slits, through which the gas can mix with the air flowing in the inside wall 602.

[0143] In an embodiment, the mixer 6 comprises a connecting duct 604, which is open onto the intake duct 2, downstream of the injection duct 3 in the direction of inflow V (downstream of the mixer itself).

[0144] The connecting duct 604 is a blind duct. In other words, the connecting duct 604 has a first end which is open onto the intake duct 2 in a zone where the gas and the oxidizer are already mixed, and a second end which is closed. This allows the pressure in the connecting duct 604 to be equal to the pressure downstream of the mixing zone (downstream of the Venturi) in the direction of inflow V.

[0145] This structure allows the different detecting sections to be aligned along a radial direction R, perpendicular to the direction of flow of the fluid in the intake duct 2. In other words, in a particularly advantageous embodiment, the first detecting section A1, the second detecting section A2 and the third detecting section G1 are aligned along the radial direction R.

[0146] In effect, the space in the inside wall 602 defines the first detecting section A1, the annular groove CA defines the third detecting section G1 and the connecting duct 604 defines the second detecting section A2.

[0147] Preferably, the receiving slot 61 is aligned radially with the connecting duct 604. This allows the sensor to be vertically aligned with the connecting duct 604.

[0148] Thus, the first cavity 62 and/or the fourth cavity 65 are open onto the space in the inside wall 602. The second cavity 63, on the other hand, is open onto the connecting duct 604. Lastly, the third cavity 64 is open onto the annular groove CA. The first, second, third and fourth slots 62, 63, 64, 65 are open towards the outside of the mixer, at the receiving slot 61, so as to be able to receive the respective connectors provided in the first sensor 101 and/or in the second sensor 102.

[0149] The first sensor and/or the second sensor 101, 102 are housed in the receiving slot 61.

[0150] The first sensor 101 comprises a first, air pressure connection 101A and a second, mixture pressure connection 101B. The second sensor 102 comprises a second, air pressure connection 102A and a respective, gas pressure connection 102B.

[0151] It is noted that the first pressure connection of this disclosure corresponds to the first, air pressure connection 101A or to the second, air pressure connection 102A. In effect, as described above, in some cases, the air pressure connection may be shared between the two sensors 101, 102.

[0152] In an embodiment, the first, air pressure connection 101A is located inside the first cavity 62. In an embodiment, the second, air pressure connection 102A is located inside the fourth cavity 65. In an embodiment, the mixture pressure connection 101B is located inside the second cavity 63. In an embodiment, the gas pressure connection 102B is located inside the third cavity 64.

[0153] The first and the second sensor 101, 102 are connected to the control unit to send signals representing the first differential pressure P1 and the second differential pressure P2.

[0154] Preferably, the mixer 6 comprises a narrowing member 66. The mixer comprises a plurality of supporting elements 67. The narrowing member is located inside the intake duct 2 (that is, inside the space in the inside wall 602). More specifically, the narrowing member 66 is kept at a uniform distance from the inside wall 602 by the supporting elements 67. The narrowing member 66 comprises walls which are inclined with respect to the flow of oxidizer, so as to reduce the section area through which the fluid in the intake duct 2 flows in the direction of inflow V. The reduction in the section area causes the fluid to accelerate and produces a negative pressure, making gas suction (injection) and its subsequent mixing with the oxidizer more efficient.

[0155] According to an aspect of it, this disclosure provides a method for controlling a premix gas burner.

[0156] In particular, the method of this disclosure, comprises a step of runtime checking for the purpose of controlling the burner during its operation, and a step of performing a diagnostic test to check and control the sensors and other components of the control device.

[0157] Thus, during the step of runtime checking, the control unit receives control signals, such as, for example, but not only, the first flame signal 401, the second flame signal 402, the flow rate signal 431 and/or the temperature signal 441. Based on the control signals, the control unit generates the drive signals to operate the gas regulating valve 7 or vary the rotation speed of the fan 9. For this purpose, the control unit 5 has access to regulation data (for example, the first regulation data R1 or the second regulation data R2), defining working curves of the burner 100.

[0158] In the step of performing a diagnostic test on the sensors, on the other hand, the control unit 5 is intended to identify any malfunctions connected with the sensors, specifically malfunctions caused by sensor faults or drift giving rise to incorrect readings that could have a negative impact on sensor operation.

[0159] More specifically, the step of performing a diagnostic test can be carried out in two different configurations of the device (and of the burner): a configuration with the burner off and a configuration with the burner in operation.

[0160] In the configuration with the burner off, the control unit 5 is programmed to check whether the sensors of the control device 1 are reliable. For this purpose, the control unit 5 is reprogrammed to generate drive signals 501 representing a predetermined rotation speed of the fan 9 (or representing a predetermined pressure signal P1 or by feedback control of a predefined pressure/pressure difference signal P1) corresponding to a predetermined flow rate. The sensor unit 10 is also configured to detect the first differential pressure P1 and the second differential pressure P2 and to send these values to the control unit 5.

[0161] The control unit 5 compares the first differential pressure P1 and the second differential pressure P2 with reference data representing a correlation between a first predetermined differential pressure and a second predetermined differential pressure, associated with the specific flow rate set by the control unit 5.

[0162] The control unit 5 assesses the operation of the first and/or the second sensor 101, 102 based on the comparison of the first differential pressure P1 and the second differential pressure P2 with the reference data. If the first differential pressure P1 and the second differential pressure P2 do not match the reference correlation, the control unit 5 generates a notification of a possible fault of at least one between the first sensor 101 and the second sensor 102.

[0163] More specifically, the control unit 5 can detect the following cases: [0164] (a) the correlation between the two measurements does not match the reference correlation; [0165] (b) the correlation between the two measurements matches the reference correlation but the first and the second differential pressure P1, P2 are too low (in absolute terms) compared to the predetermined values, as might be the case, for example, if an occlusion downstream of the sensors causes a reduction in the flow rate.

[0166] In the case of point (a) above, the control unit is programmed to compare the first and the second differential pressure P1, P2 with the respective first and second predetermined differential pressure, respectively, so as to determine which of the two sensors is faulty or has drifted. After determining this, the control unit 5 performs one or both of the following steps: [0167] stopping the burner 100 or placing it in secure mode; [0168] determining the drift (deviation) between the first and the second differential pressure P1, P2 and the corresponding first or second predetermined differential pressure; [0169] automatically correcting the measurement of the first sensor 101 or of the second sensor 102, based on the drift calculated.

[0170] In the case of point (b) above, the control unit is programmed to alert the user to the possible presence of a potential occlusion and/or of increased load losses along the intake duct 2 or on the exhaust of the appliance or downstream of the combustion chamber (for example, clogging of the exchanger).

[0171] It is noted that the configuration with the burner off also includes one of the following configurations: [0172] the burner is switched off after a period of operation in order to perform a further check on the congruency of the measurements of the sensor unit; [0173] the burner is switched off periodically in order to perform further checks on the congruency of the measurements of the sensor unit.

[0174] In these two cases, the control unit 5 performs the same checks as those set out above with reference to the configuration with the burner off.

[0175] In the configuration with the burner in operation, on the other hand, the control unit 5 is programmed to generate drive signals 501 that represent a predetermined variation in the rotation speed of the fan 9 or a predetermined movement of the gas regulating valve, corresponding to a variation in the flow rate. The sensor unit 10 is also configured to detect a variation in the first differential pressure P1 (first variation) and/or a variation in the second differential pressure P2 (second variation) and to send the first and the second variation to the control unit 5.

[0176] The control unit 5 compares the first variation and the second variation with the reference data representing a predetermined variation in the first differential pressure and a predetermined variation in the second differential pressure, due to the predetermined flow rate variation set by the control unit 5.

[0177] The control unit 5 assesses the operation of the first and/or the second sensor 101, 102 based on the comparison of the first variation and the second variation with the reference data. More specifically, the control unit 5 checks that: [0178] (c) the first variation corresponds (within a certain tolerance range) to the predetermined variation in the first differential pressure; [0179] (d) the second variation corresponds (within a certain tolerance range) to the predetermined variation in the second differential pressure; [0180] (e) the first variation and the second variation are the same in sign, that is that both of the sensors detect, at the second section A2 and at the third section G1, the same pressure reduction or increase resulting from the variation in the flow rate.

[0181] If at least one of the points (c), (d) or (e) is not true, the control unit is programmed generate a notification of a fault of the first sensor 101 and/or of the second sensor 102 or, where possible, to compensate the reading of the sensor.