Method for detecting presence of flame in premixed hydrogen burner

Abstract

The object of the invention is a control method for verifying the presence of flames in the combustion chamber (41) of a premixed gas burner (1) through which air and a gas mixture mainly and / or essentially containing hydrogen H2 are fed. The method is based on the use of at least one temperature sensor (6), sending its values to a control device (8), the control device (8) using these values to calculate a derivative T'of temperature T over time, comparing it with appropriate feedback thresholds (Tau1, Tau2; Tau3, Tau4) to determine the occurrence of ignition, the failure of ignition or the extinguishment of the flame.

Description

Technical Field

[0001] The following describes a method for controlling the presence of a flame in a premixed gas burner, in particular a premixed gas burner with adjustable power and adjustable excess air coefficient λ.

[0002] Also described is a premixed gas burner, in particular a premixed gas burner with adjustable power and adjustable excess air coefficient λ, equipped with means for controlling the presence of a flame.

[0003] The control method described below is suitable for verifying the presence of a flame in the premixed gas burner during both the ignition step and the steady - state operation step.

[0004] The control method is particularly suitable for premixed burners fed with pure hydrogen or a gas with a high hydrogen content (e.g., a hydrogen volume content equal to or greater than 98%).

[0005] The method and burner briefly described are particularly intended for a condensing boiler fed with hydrogen H2 and intended for the production of domestic hot water. Background Art

[0006] It is well known that it is appealing to pre - mix the fuel gas with combustion air to suppress the emissions of nitrogen oxides (NOx), and to supply an amount of air greater than the stoichiometric air, i.e., to operate with an excess air coefficient λ.

[0007] It is also well known that the excess air coefficient λ is changed according to the operating power of the burner, so as to have a more stable flame (reducing the risk of flashback at low power or flame lift - off at high power).

[0008] It is also well known that during the ignition step, the excess air coefficient λ is increased, thus reducing the risk of flashback and the risk of explosion due to delayed ignition. Compared with the combustion of gaseous hydrocarbons, the combustion of hydrogen has some characteristics that should be considered both in the design and operation management of the burner.

[0009] For example, the risk of flashback in hydrogen combustion is greater than that encountered in the combustion of traditional gaseous hydrocarbons (such as methane, butane, ethane, and propane). This risk of flashback, which is more likely to occur when the burner is ignited or at low heat power, can be avoided, for example, by increasing the excess air coefficient λ.

[0010] In addition, the flame of hydrogen is not an ionized flame. If not at the highest power level: in the case of hydrogen combustion, it is therefore impossible to monitor the presence of the flame by resorting to traditional ionization sensors (as typically occurs in traditional methane or other light - hydrocarbon burners), but other solutions must be resorted to for monitoring the presence of the flame.

[0011] In addition, air-hydrogen mixtures are particularly prone to explosion; therefore, in the absence of combustion, accumulation of the mixture in the combustion chamber should be avoided (especially the accumulation that may occur during the burner ignition step instant and the accidental extinction step).

[0012] Therefore, when a premixed burner is fed with hydrogen, special attention should be paid to minimizing the ignition time of the flame and the time between accidental extinction of the flame and restart or deactivation of the burner.

[0013] Obviously, the flame detection system should have a short enough response time to minimize these transients.

[0014] Some solutions are known for monitoring the presence of a flame during hydrogen combustion in a premixed burner.

[0015] A known technique monitors the presence of a flame resulting from hydrogen combustion by an optical device that monitors ultraviolet emission (e.g., in a frequency range corresponding to the presence of the hydroxyl radical OH).

[0016] When the burner operates at low power or at a high air / gas ratio (a situation that occurs during both the ignition step and the low-power operation step), the time constant of the ultraviolet sensor is very low, but there is a problem of low sensitivity.

[0017] In other words, when the ultraviolet emission intensity of the flame is very low, the reliability of the ultraviolet sensor is poor.

[0018] Therefore, when the burner operates at low power or in any situation where the burner operates at a high air / gas ratio, since this may occur, for example, during low-power operation or during the ignition step of the burner, proper management of the burner is very complex.

[0019] In addition, the use of an optical sensor also brings further problems: for example, specific glass is required to obtain an optical connection to the combustion chamber, which increases the risk of fogging of the glass in the instantaneous operating state of the burner, resulting in incorrect sensor readings.

[0020] A second known technique monitors the presence of a flame resulting from hydrogen combustion by a temperature sensor that measures the temperature inside the combustion chamber.

[0021] This prior art compares the detected temperature with a lower consensus threshold to identify the occurrence of extinction, and compares the detected temperature with an upper consensus threshold to identify the occurrence of ignition.

[0022] However, the response time of currently known temperature sensors for detecting the occurrence of ignition or extinction is too long, so the risk of too high a concentration of the air / hydrogen mixture in the combustion chamber is very high, resulting in an explosion risk. Patent application EP3933267 is an example of the prior art just mentioned, which describes a method for controlling the presence of a flame in a premixed burner for hydrogen feeding during a flame ignition step and during stable operation, wherein the measured temperature value is compared with an expected value, i.e., with a previously stored reference value.

[0023] The comparison between the measured value and the expected value allows to understand whether ignition occurs correctly and whether there is a flame.

[0024] However, for the reasons mentioned above, the solution described in EP3933267 is not reliable.

[0025] In fact, measuring the temperature when the burner is ignited takes too long to detect the presence of a flame; similarly, when the burner is accidentally extinguished, it takes a long time to reach the reference value representing the absence of a flame, which is not compatible with the risk of excessive accumulation of the air / hydrogen mixture in the combustion chamber.

[0026] Another solution similar to the one described in EP3933267 is described in application DE19903305. However, this application relates to a device and an associated method for controlling the start of combustion in a vehicle engine.

[0027] Patent application DE102021102740 presents another prior art, which relates to a method for monitoring the presence of a flame in a premixed burner, and the burner body is made of two different metal materials forming a thermocouple.

[0028] By monitoring the thermoelectric voltage generated by the thermocouple and comparing it with a reference value, DE102021102740 can identify whether a flame is ignited.

[0029] Therefore, the prior art DE102021102740 overcomes some problems of the prior art. However, it is necessary to use a burner body with two different metal materials; in addition, in the case of external interference of electromagnetic nature, the voltage signal generated by using the thermocouple may lead to incorrect readings. Summary of the Invention

[0030] The object of the present invention is to solve at least partially the problems of the prior art, in particular the above-mentioned problems.

[0031] In particular, the object of the present invention is to propose a reliable solution for monitoring the presence of a flame in a premixed gas burner fed with hydrogen, in particular a premixed gas burner with adjustable power and adjustable excess air coefficient λ.

[0032] Another object of the present invention is to propose a solution for monitoring the flame of a premixed burner burning hydrogen, in particular under low thermal power conditions and / or in the case of a high value of the air / gas ratio. Description of the Drawings

[0033] Some possible embodiments of a flame control method and related devices using such a method are described below with reference to the accompanying drawings, wherein: Figure 1 is a schematic diagram of a control and regulation device for a premixed burner with hydrogen feed; Figure 2.A is a qualitative graph showing the temperature trend in the space where the burner flame forms during the ignition step of the burner; Figure 2.B is a qualitative graph showing the trend of the temperature derivative over time in the space where the burner flame forms during the ignition step of the burner; Figure 3 is Figure 2.B a detailed schematic diagram as shown, depicting the trend of the temperature derivative over time in the case where the burner flame is correctly ignited; Figure 4 is a qualitative graph showing the trend of the temperature derivative over time in the space where the burner flame forms during the ignition step of the burner in the case of an error signal or subsequent flame extinction; Figure 5.A is a qualitative graph showing the temperature trend in the space where the burner flame forms during the stable operation step of the burner in the case of flame extinction; Figure 5.B is a qualitative graph showing the trend of the temperature derivative over time in the space where the burner flame forms during the stable operation step of the burner in the case of flame extinction; Figure 6 is a qualitative graph showing the trend of the temperature derivative over time in the space where the burner flame forms during the stable operation step of the burner in the case of actual flame extinction; Figure 7 is a qualitative graph showing the trend of the temperature derivative over time in the space where the burner flame forms during the stable operation step of the burner in the case of a false flame extinction signal; Figure 8 Schematically shows a block diagram summarizing the steps of a method for controlling the presence of a flame during the ignition step of a burner according to Figure 3 and Figure 4 as shown; Figure 9 Schematically shows a block diagram summarizing the steps of a method for controlling the presence of a flame during the stable operation step of a burner according to Figure 6 and Figure 7 as shown.

[0034] In all the above qualitative graphs, the derivative T' of the temperature T (or the temperature T if otherwise specified) is on the vertical axis, and the time t is on the horizontal axis. Detailed implementation mode Reference Figure 1 , the reference numeral 1 represents a premixed gas burner including a combustion control and regulation device 8.

[0035] The burner 1 includes a first duct 11 (or combustion air flow duct), a second duct 12 (or gaseous fuel flow duct, specifically mainly and / or substantially composed of hydrogen H2), and a variable-speed fan 2 having a suction port 21 and a delivery port 22 connected to the first duct 11.

[0036] The speed of the fan 2 can vary according to the required thermal power and the required excess air coefficient λ.

[0037] The mixing of the air from the first duct 11 and the gaseous fuel from the second duct 12 can be carried out through a Venturi tube 3, and the Venturi tube 3 can be located, for example, upstream of the fan 2.

[0038] The second duct 12 communicates with the narrow part of the Venturi tube 3, thereby sucking in the gaseous fuel.

[0039] An electric valve 7 is provided to regulate the flow rate of the gaseous fuel passing through the second duct 12.

[0040] A first duct 13 or an outflow duct for the air and gaseous fuel mixture is provided, located downstream of the Venturi tube 3 that supplies the burner body 4.

[0041] The burner body 4 can be a conventional burner body of the perforated surface type and is inserted into the combustion chamber 41.

[0042] An ignition device 5 is provided to ignite the air and gaseous fuel mixture that escapes from the Venturi tube 3 and reaches the burner body 4.

[0043] The flame ignition device 5 can be of the discharge type.

[0044] There is at least one temperature sensor 6 in the combustion chamber 41, adapted to detect the presence of a flame.

[0045] For the sake of simplicity of description, hereinafter, reference will be made to a variant of the present invention in which there is a single temperature sensor 6, without prejudice to the possibility of a second temperature sensor, which could be used as a redundant sensor to determine the correct operation of the first temperature sensor.

[0046] In the illustrated embodiment, the temperature sensor 6 does not contact the burner body 4 but is positioned so as to be hit by the flame escaping from the opening of the burner body 4.

[0047] The temperature sensor 6 must be able to withstand the temperature generated in the combustion chamber 41.

[0048] In this regard, it should be noted that in the case of hydrogen combustion, the temperature of the flame can vary from approximately 800 °C to approximately 1200 °C, depending on the value of the excess air coefficient λ and the operating power of the burner 1.

[0049] In a possible embodiment, the temperature sensor 6 can be of the thermocouple type.

[0050] In another embodiment, the temperature sensor 6 can be a thermistor, in particular a positive temperature coefficient thermistor (so-called PTC).

[0051] In the said embodiment, the temperature sensor 6 comprises an outer coating of ceramic material (such as SiC or Si3N4) to protect the sensor from the strong oxidizing atmosphere generated in the combustion chamber 41 during the combustion process.

[0052] The electronic control and regulation device 8 receives the input signal ST from the temperature sensor 6 and a control signal SC indicating the required thermal power (for example from a user interface not shown in the figure).

[0053] Then, the device 8 provides an ignition output signal SA to the ignition device 5, a signal SV for regulating the speed of the fan 2, and a signal SG for regulating the opening degree of the electric valve 7. According to the invention, the device 8 is capable of using the signal ST received from the temperature sensor 6 to check whether there is a flame in the combustion chamber 41.

[0054] In particular, the device 8 is capable of verifying whether the ignition step of the burner 1 is carried out regularly and whether there is any accidental flame extinction during the stable operation step.

[0055] For this purpose, as described below, the device 8 uses the signal ST received from the temperature sensor 6 to calculate the derivative of the temperature with respect to time and compares it with a suitable feedback threshold to determine ignition occurrence, ignition failure, or flame extinction.

[0056] In this specification, the term "derivative" refers to the absolute value of the instantaneous change of the temperature T of the flame with time, and also includes the discrete derivative obtained by sampling the temperature signal T with a sufficiently small sampling step (for example, every 0.1 second).

[0057] Figure 3 The method according to the invention during the ignition step of the burner 1 is shown. The ignition step starts with introducing an air flow and fuel gas into the burner body 4 and generating a discharge in the combustion chamber 41 for a first time interval Δt1.

[0058] For this purpose, the fan 2 must be started and the electric valve 7 must be opened to ensure that the air and fuel gas mixture flows into the burner body 4 and flows out through the openings on the burner surface.

[0059] During a first time interval Δt1, the sensor 6 detects the temperature T of a point P of the combustion chamber 41 near the outer surface of the burner body 4.

[0060] The electronic device 8 receives the temperature value detected by the sensor 6 and calculates the derivative T’ of the temperature T with respect to time at the point P of the combustion chamber 41 during the first time interval Δt1.

[0061] If, during the first time interval Δt1, the derivative T’ never exceeds a first threshold Tau1, it can be reasonably assumed that the ignition of the flame has not occurred or has occurred irregularly in any case.

[0062] In this case, at the end of the first time interval Δt1, the device 8 interrupts the ignition cycle by driving the ignition device 5 to stop and the electric valve 7 to close, so as to avoid the undesired accumulation of gas in the combustion chamber 41.

[0063] Preferably, the fan 2 remains running for a period of time to allow the complete cleaning of the combustion chamber 41, thereby removing any accumulation of hydrogen therein: this extended operation of the fan 2 can be defined as a post-ventilation step, a term that will be used in the following description.

[0064] This can avoid any explosion phenomenon during the next ignition attempt of the burner 1.

[0065] On the contrary, if the derivative T’ of the temperature T at the point P during the first time interval Δt1 exceeds a first preset threshold Tau1, it can be considered that the flame has been ignited, and the air and gas flows can be maintained for the next flame stabilization cycle.

[0066] In this case, the device 8 drives the ignition device 5 to stop and immediately stops generating the discharge: it should be noted that the first time interval Δt1 is very short only to avoid the excessive accumulation of the air and hydrogen mixture in the combustion chamber 41, thereby avoiding the risk of a loud and dangerous explosion during a possible delayed flame ignition, i.e., at the last moment of ignition, for the integrity of the burner 1.

[0067] However, it is impossible to rule out that reaching the first preset threshold Tau1 is not a false positive, for example, caused by a temporary external interference of electromagnetic nature. In addition, although ignited during the first time interval Δt1, it is impossible to rule out that the flame is unstable for any reason.

[0068] To ensure that the flame is indeed ignited and remains lit, the method proposed by the inventor continues to calculate the derivative T’ of the temperature T during a second time interval Δt2 (after Δt1), where Δt2 > Δt1.

[0069] If, during the second time interval Δt2, the derivative T’ always remains above a second preset threshold Tau2 (where |Tau2| < Tau1), then it is confirmed that the flame remains lit (see again Figure 3 ).

[0070] It can be inferred that the ignition step of burner 1 was successful and the flame is stable: Therefore, it is possible to continue supplying the air and gas mixture to the burner body 4 for the transition to the stable operation step of burner 1.

[0071] Otherwise, i.e., in the case where the derivative T’ drops below the second threshold Tau2 during the second time interval Δt2, the device 8 closes the electric valve 7 and keeps the fan 2 on for a period of time in order to completely purge the combustion chamber 41 through a post-ventilation step.

[0072] Figure 4 The situation of flame extinction during the ignition cycle of burner 1 is shown, where an instantaneous decrease of the derivative T’ of the temperature T below the threshold Tau2 during the second time interval Δt2 is shown.

[0073] In the case of combustion of hydrogen or a gas with a high hydrogen content, the first threshold Tau1 may be between approximately 20 °C / s and 70 °C / s, while the second threshold Tau2 may be between approximately 5 °C / s and 30 °C / s, it being understood that generally |Tau2| < Tau1.

[0074] Both thresholds Tau1 and Tau2 are preset and stored values in the device 8, defined experimentally or by similar empirical methods in the laboratory.

[0075] In the case of combustion of hydrogen or a gas with a high hydrogen content, the first time interval Δt1 is suitably less than or equal to approximately 2 seconds, while the second time interval Δt2 is generally less than or equal to approximately 4 seconds.

[0076] As expected, the above-mentioned burner 1 is also able to monitor the presence of the flame after the ignition step, thus verifying any accidental extinction phenomenon during the stable operation step.

[0077] To this end, the temperature T at point P of the combustion chamber 41 is monitored and the derivative T’ of the temperature T with respect to time is continuously calculated during the first time interval Δt3.

[0078] Since during the stable operation step of a hydrogen burner the temperature T of the flame is indicatively between 800 °C and 1200 °C, in the case of accidental extinction, the derivative T’ of the temperature T shows an instantaneous downward trend and can be immediately verified by comparing its value with a preset feedback threshold Tau3.

[0079] If the derivative T’ of the temperature T does not drop below a first preset threshold Tau3 within a first time interval Δt3 (which has a very short duration, preferably equal to the minimum sampling step, e.g., 0.1 seconds, precisely because of the continuous monitoring of the derivative’s variation over time), it can be assumed that the flame is lit and the stable operation of the burner 1 can continue correctly.

[0080] Conversely, if the derivative T’ of the temperature T drops below the first preset threshold Tau3 within the first time interval Δt3, it can be reasonably assumed that an accidental extinction of the flame has actually occurred.

[0081] To confirm that the flame has actually gone out and that the derivative T’ of the temperature T reaching the first threshold Tau3 is not a false positive caused by, for example, a temporary external interference of an electromagnetic nature, the proposed method continues to calculate the derivative T’ of the temperature T in a second time interval Δt4 (immediately following Δt3), where Δt4 > Δt3.

[0082] During the second time interval Δt4, the air and gas flows remain in operation.

[0083] If, during the second time interval Δt4, the derivative T’ continues to always remain below the above-mentioned second preset threshold Tau4 (where in absolute value Tau4 < Tau3), it is confirmed that the flame has actually gone out.

[0084] At this point, the device 8 interrupts the gas flow by acting on the electric valve 7 and performs a post-ventilation step to clean the combustion chamber 41, thus preparing the burner for a new ignition step.

[0085] Figure 6 The situation of flame extinction during the operating cycle of the burner 1 is shown, where it is shown that the derivative T’ of the temperature T suddenly drops by more than the threshold Tau3 and then fails to reach the second threshold Tau4 during the second time interval Δt4, proving that the flame has actually gone out.

[0086] Conversely, if the flame is actually still lit during the second time interval Δt4 (the derivative T’ reaching the threshold Tau3 during the first time interval Δt3 being configured as a false positive), the trend of the derivative T’ will undergo an instantaneous reversal and will exceed the second preset threshold Tau4: in this case, the device 8 continues to supply the air and gas mixture to the burner body 4 for continuing the normal stable operation step of the burner 1.

[0087] Figure 7 The situation of a false flame extinction during the operating cycle of the burner 1 is depicted, where it can be seen that the derivative T’ of the temperature T exceeds the threshold Tau4 within the second time interval Δt4, proving that the flame is actually lit or re-lit during the second time interval Δt4.

[0088] Like the thresholds Tau1 and Tau2, the thresholds Tau3 and Tau4 are preset values stored in device 8 and defined in the laboratory by experimental or similar empirical methods.

[0089] In the case of combustion of hydrogen or a fuel gas with a high hydrogen content, the first threshold Tau3 may be between approximately 20 °C / second and 70 °C / second, while the second threshold Tau4 may be between approximately 5 °C / second and 30 °C / second, it being understood that generally |Tau4| < |Tau3|.

[0090] As described above, the duration of the first time interval Δt3 is very short, e.g., 0.1 second, because during the stable operation step of burner 1, the control of the derivative over time must be continuous.

[0091] Conversely, the second time interval Δt4 is generally less than or equal to approximately 4 seconds to avoid the risk of a loud and dangerous explosion due to the excessive accumulation of the air and hydrogen mixture in combustion chamber 41 and the resulting ignition discharge delay for the integrity of burner 1, especially in the case where the flame is actually extinguished within the second time interval Δt4.

[0092] The above-described flame presence control method is particularly effective in the management of a premixed burner burning hydrogen, thus eliminating the problems caused by the use of a temperature sensor to monitor the flame in the prior art.

[0093] Relative to the corresponding consensus thresholds Ta and Tau representing the occurrence of flame ignition, Figure 2.A and 2.B the qualitative diagrams compare the temperature trend of the burner ( Figure 2.A ) and the trend of the derivative of temperature with respect to time ( Figure 2.B ) during the ignition step of the burner.

[0094] It can be clearly seen from the comparison that, compared with the methods of monitoring the flame using a temperature sensor known to date, the main advantage of the control method just described is the ability to detect the achievement of the consensus threshold for flame ignition more quickly: in fact, compared with having to confirm the achievement of the Figure 2.A feedback threshold Ta of temperature T in Figure 2.B the definition of the feedback threshold Tau of the derivative T' of temperature T in

[0095] allows an almost instantaneous or significantly shorter achievement. The exact same situation occurs when considering the feedback threshold of temperature T (according to the known method) and the derivative T' of temperature T (according to the method proposed by the present invention) during the flame extinction step, as shown respectively in Figure 5.A and 5.BAs shown: Using the value of the derivative T’ enables confirmation of the absence of a flame in a significantly shorter time, which is beneficial for the safety of burner 1, in terms of reducing the risk of a loud and dangerous explosion, a risk to the integrity of the burner.

[0096] The above control method can be schematically shown in the block diagrams of Figure 8 and Figure 9 respectively, relative to the ignition step and the subsequent stable operation step of the burner.

[0097] As described above, also with the help of Figure 3 and Figure 4 in the ignition step of the burner, the steps of the method are as follows: a1) Introduce the air and gas mixture into the burner body 4 and generate a discharge through the ignition device 5 for a first time interval Δt1; b) Measure the temperature T at point P in the combustion chamber 41; c) Calculate the derivative T’ of the temperature T in the first time interval Δt1; d) Compare the derivative T’ with a first preset threshold Tau1; If the derivative T’ never exceeds the first preset threshold Tau1 during the first time interval Δt1, then: e1) Determine that the flame is not ignited, and further: e11) Drive the ignition device 5 to stop, e12) Close the gas valve 7 to interrupt the gas flow into the burner body 4, e13) Preferably carry out a post-ventilation step, keep the fan 2 running for a period of time to allow air to flow into the burner body (4); Otherwise, if the derivative T’ exceeds the first preset threshold Tau1 during the first time interval Δt1, then: f1) Determine that the flame is ignited, and further: f11) Drive the ignition device 5 to stop, f12) Keep the air and gas mixture flowing into the burner body 4; g) Calculate the derivative T’ of the temperature T in a second time interval Δt2 to compare it with a second preset threshold Tau2, where the second time interval Δt2 is greater than the first time interval Δt1, and the second threshold Tau2 is lower than the first threshold Tau1 in absolute value, If the derivative T’ does not exceed the second threshold Tau2 during the second time interval Δt2, then: h1) Determine that the flame is not ignited or has extinguished, and further: h11) Close the gas valve 7 to interrupt the gas flow into the burner body 4. h12) Keep the fan 2 running for a period of time to allow an air flow to enter the burner body 4 for a post-ventilation step. Otherwise, if the derivative T’ exceeds the second threshold Tau2 during the second time interval Δt2, then: i1) Confirm that the flame is lit, and further: i11) Keep the air and gas mixture flowing into the burner body 4 to switch to the stable operation step of the burner 1.

[0098] Regarding the method in the stable operation step of the burner (also described above with the aid of Figure 6 and Figure 7 ), the block diagram in Figure 9 shows the following steps: a2) Keep the air and gas mixture flowing into the burner body 4 to maintain the flame ignition. b) Measure the temperature T at point P in the combustion chamber 41. c) Calculate the derivative T’ of the temperature T in the first time interval Δt3. d) Compare the derivative T’ with the first preset threshold Tau3. If the derivative T’ never exceeds the first preset threshold Tau3 during the first time interval Δt3, then: e2) Determine that the flame continues to burn, and further: e21) Keep the air and gas mixture flowing into the burner body 4 to continue the stable operation step of the burner 1. Otherwise, if the derivative T’ exceeds the first preset threshold Tau3 during the first time interval Δt3, then: f2) Determine that the flame is extinguished, and further: f21) Keep the air and gas mixture flowing into the burner body 4 for a second time interval Δt4. g) Calculate the derivative T’ of the temperature T in the second time interval Δt4 to compare it with the second preset threshold Tau4, where the second time interval Δt4 following the first time interval Δt3 is greater than the first time interval Δt3, and the second threshold Tau4 is less than the first threshold Tau3 in absolute value. If the derivative T’ does not exceed the second threshold Tau4 during the second time interval Δt4, then: h2) Confirm that the flame is extinguished, and further: h21) Close the gas valve 7 to interrupt the gas flow into the burner body 4. h22) Keep the fan 2 running for a period of time to allow an air flow to enter the burner body 4 for a post-ventilation step. If the derivative T’ exceeds the second threshold Tau4 during the second time interval Δt4, then: i2) Determine that the flame is ignited, and further: i21) Keep the air and gas mixture flowing into the burner body 4 to continue the stable operation step of the burner 1.

Claims

1. A method for controlling the presence of a flame in a combustion chamber (41) of a premixed gas burner (1) for feeding an air and gas mixture mainly and / or essentially containing hydrogen gas H2, wherein the burner (1) includes a burner body (4) inserted into the combustion chamber (41), the presence of the flame is controlled by at least one temperature sensor (6), and a signal (ST) representing the temperature T measured at a point (P) in the combustion chamber (41) by the temperature sensor is sent to a control device (8), and the control device (8) uses the signal to perform at least the following steps during the ignition and stable operation steps of the burner (1): a1) In the ignition step, introducing the air and gas mixture into the burner body (4) and generating a discharge by an ignition device (5); a2) In the stable operation step, maintaining the flow of the air and gas mixture into the burner body (4) to keep the flame ignited; b) Measuring the temperature T at the point (P) in the combustion chamber (41); c) Calculating the derivative T' of the temperature T in a first time interval (Δt1, Δt3); d) Comparing the derivative T' with a first preset threshold (Tau1, Tau3); If the derivative T' never exceeds the first preset threshold (Tau1, Tau3) in the first time interval (Δt1, Δt3), then: e1) In the ignition step, determining that the flame is not ignited, e2) In the stable operation step, determining that the flame continues to be ignited; Otherwise, if the derivative T' exceeds the first preset threshold (Tau1, Tau3) in the first time interval (Δt1, Δt3), then: f1) In the ignition step, determining that the flame is ignited, f2) In the stable operation step, determining that the flame is extinguished; g) Calculating the derivative T' of the temperature T in a second time interval (Δt2, Δt4) to compare it with a second preset threshold (Tau2, Tau4); If the derivative T' does not exceed the second threshold (Tau2, Tau4) in the second time interval (Δt1, Δt4), then: h1) During the ignition step, determining that the flame is not ignited or is extinguished, f2) In the stable operation step, confirming that the flame is extinguished; Otherwise, if the derivative T' exceeds the second threshold (Tau2, Tau4) in the second time interval (Δt2, Δt4), then: i1) In the ignition step, confirming that the flame is ignited, i2) In the stable operation step, determining that the flame is ignited.

2. The control method according to claim 1, It is characterized in that wherein the ignition step of the burner (1) includes the following steps: If the derivative T' never exceeds the first threshold (Tau1) in the first time interval (Δt1), then after step e1), the method further includes the following steps: e11) Driving the ignition device (5) to stop, e12) Closing the gas valve (7) to interrupt the gas flow into the burner body (4). Otherwise, if the derivative T’ exceeds the first threshold (Tau1) during the first time interval (Δt1), then after step f1), the method further comprises the following steps: f11) Drive the ignition device (5) to stop, f12) Keep the air and gas mixture flowing into the burner body (4); And perform step g), wherein the second time interval (Δt2) is greater than the first time interval (△t1), and the second threshold (Tau2) is lower than the first threshold (Tau1) in absolute value.

3. The method according to claim 2, Among them, If the derivative T’ exceeds the first threshold (Tau2) during the first time interval (Δt1), then after step i1), the method further comprises the following steps: i11) Keep the air and gas mixture flowing into the burner body (4) to transition to the stable operation step of the burner (1); Otherwise, after step h1), the method further comprises the following steps: h11) Close the gas valve (7) to interrupt the gas flow into the burner body (4), h12) Keep the fan (2) running for a period of time to allow air flow into the burner body (4) for post-ventilation step.

4. The method according to claim 2, Among them, After step e1), the method further comprises the following steps: e13) Keep the fan (2) running for a period of time to allow air flow into the burner body (4) for post-ventilation step.

5. The method according to any one of claims 2 to 4, Wherein the first time interval (Δt1) is less than or equal to 2 seconds.

6. The method according to any one of claims 2 to 5, Wherein the second time interval (Δt2) is greater than the first time interval (△t1) and less than or equal to 4 seconds.

7. The method according to any one of claims 2 to 6, Wherein the first threshold (Tau1) is between 20 °C / second and 70 °C / second, and the second threshold (Tau2) is lower than the first threshold (Tau1) in absolute value and between 5 °C / second and 30 °C / second.

8. The control method according to claim 1, It is characterized in that The stable operation step of the burner (1) comprises the following steps: If the derivative T’ never exceeds the first threshold (Tau3) during the first time interval (Δt3), then after step e2), the method further comprises the following steps: e21) Keep the air and gas mixture flowing into the burner body (4) to continue the stable operation step of the burner (1); Otherwise, if the derivative T’ exceeds the first threshold (Tau3) during the first time interval (Δt3), then after step f2), the method further comprises the following steps: f21) Keep the air and gas mixture flowing into the burner body (4); and performing step g), where the second time interval (Δt4) is greater than the first time interval (△t3), and the second threshold (Tau4) is lower than the first threshold (Tau3) in absolute value.

9. The method according to claim 8, Among them, if the derivative T’ exceeds the first threshold (Tau4) during the second time interval (Δt4), then after step i2), the method further comprises the following steps: i21) maintaining the air and gas mixture flow into the burner body (4) to continue the stable operation step of the burner (1); otherwise, after step h2), the method further comprises the following steps: h21) closing the gas valve (7) to interrupt the gas flow into the burner body (4), h22) keeping the fan (2) running for a period of time to allow the air flow to enter the burner body (4) for post-ventilation.

10. The method according to claim 8 or 9, where the first time interval (Δt3) is about 0.1 second.

11. The method according to any one of claims 8 to 10, where the second time interval (Δt4) is greater than the first time interval (△t3) and less than or equal to 4 seconds.

12. The method according to any one of claims 8 to 11, where the first threshold (Tau3) is between 20 °C / second and 70 °C / second, and the second threshold (Tau4) is lower than the first threshold (Tau3) in absolute value and between 5 °C / second and 30 °C / second.

13. The control method according to any one of the preceding claims, where the first threshold (Tau1, Tau3) and the second threshold (Tau2, Tau4) are preset and stored values in the control device (8).

14. A premixed gas burner (1), mainly and / or substantially fed with hydrogen H2, comprising at least: - a burner body (4) inserted into a combustion chamber (41) and in communication with an outlet duct (13) for the air and gas mixture, - an ignition device (5) for igniting the air and gas mixture, - at least one temperature sensor (6) adapted to measure the temperature value T at a point (P) in the combustion chamber (41), characterized in that: it further comprises a combustion control and regulation device (8) adapted to receive an input signal (ST) from the at least one temperature sensor (6) to implement the method according to claims 1 to 13.

15. The burner (1) according to claim 14, It is characterized in that where the at least one temperature sensor (6) is a thermocouple or a thermistor.

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