Method for detecting a flame flash back in a heater, control and control device, heater and computer program

Abstract

A method for detecting a flame flashback (20) in a heating appliance (1) is proposed, comprising a conveying device (2) for conveying a combustion mixture of fuel gas and combustion air to a burner (3), wherein a flame flashback (20) is inferred if the following conditions are detected simultaneously or in rapid succession: a) a loss of flame at the burner (3), and b) a predetermined signal change (21) of a signal (27) that allows conclusions to be drawn about the mass flow of combustion air, fuel gas, or combustion mixture supplied to the burner (3). Furthermore, a heating appliance (1), a control and regulating device (7), and a computer program are specified.

Description

[0001] The invention relates to a method for detecting a flame flashback in a heating appliance; a control and regulating device, a heating appliance and a computer program.

[0002] During the operation of a gas burner, the start-up process in particular can trigger critical conditions. Examples of such critical conditions include a hard ignition, a deflagration, or a flame flashback, i.e., flame propagation from the burner into the fuel gas / combustion air supply during a start-up or ignition process. These operating conditions lead to reduced user comfort due to noise emissions and can also cause critical damage to the heating appliance, resulting in its failure. When using hydrogen as the fuel gas, such critical conditions are more likely because hydrogen's significantly higher flame speed, volatility, and low density result in considerably less reliable start-up behavior, coupled with a greater influence from environmental factors such as wind gusts affecting the exhaust system or air intake.The initial start of a cold heating appliance (cold start) can usually be particularly difficult.

[0003] To avoid such critical conditions, EP 3 992 529 A1 proposes using a pilot flame with its own fuel supply to ignite a main burner, the function of which can be monitored by a sensor and which is also arranged in such a way that the pilot flame cannot be extinguished by air escaping from the main burner. However, such a design is associated with considerable effort.

[0004] To enable more reliable ignition of a heating appliance, DE 10 2019 121 973 A1 proposes arranging a catalyst material within the heating appliance, specifically within the gas-air mixture flow. Due to its properties, the catalyst material can provide the necessary activation energy to initiate combustion without additional thermal energy, such as a spark or pilot flame. This solution, however, is also associated with considerable effort and expense.

[0005] AT 510 002 A4 describes a method in which a pressure difference between the gas and air supply of a premixing gas burner is measured and the dispersion of the measured values ​​is determined. If a reference value is exceeded by a threshold, the minimum speed of the gas burner's blower can be increased to prevent flame flashbacks.

[0006] The aforementioned prior art solutions can reduce the probability of flame flashbacks occurring, but cannot detect their occurrence itself.

[0007] To detect a flame flashback, EP 4 043 793 A1 proposes observing a thermal and an optical effect of the flame flashback inside a premixing burner.

[0008] EP 3 919 817 A1 discloses a method for detecting ignition faults in a burner, in which the rotational speed of a blower and the position of the gas valve are monitored during the ignition process. If characteristic changes are detected, an ignition fault can be assumed.

[0009] Based on this, the object of the invention is to propose a method for detecting a flame flashback in a heating appliance; a control and regulating device, a heating appliance, and a computer program that at least partially overcome the problems of the prior art described above. In particular, the invention is intended to enable the detection of a flame flashback in a heating appliance.

[0010] Furthermore, the invention should be suitable for being carried out at least partially automatically and should require as few structural changes as possible compared to a heating device according to the prior art.

[0011] These problems are solved by the features of the independent claims. Further advantageous embodiments of the solution proposed here are specified in the independent claims. It should be noted that the features listed in the dependent claims can be combined with one another in any technologically meaningful way and define further embodiments of the invention. Furthermore, the features specified in the claims are further specified and explained in the description, which also presents further preferred embodiments of the invention.

[0012] This includes a method for detecting a flame flashback in a heating appliance, wherein the heating appliance comprises a conveying device for conveying a combustion mixture of fuel gas and combustion air to a burner, and a flame flashback is detected by simultaneously or in rapid succession detecting the following (operating) states: a) loss of flame at the burner, and b) a predetermined signal change, in particular signal termination, of a signal that allows a conclusion to be drawn about the mass flow of combustion air, fuel gas or combustion mixture supplied to the burner.

[0013] The proposed method can be repeated continuously and / or in short succession (fractions of a second). The method enables the detection of a flame flashback on a heating appliance and can be performed, in particular, on the control unit of a heating appliance.

[0014] The heating appliance in question is, in particular, a gas-fired heating appliance designed to burn a fuel gas, such as natural gas or, more specifically, hydrogen, with the addition of ambient air, and to generate heat energy, for example, to heat a heat transfer fluid in a heating circuit or to provide hot water. Specifically, the heating appliance may be a condensing boiler and designed to burn hydrogen or a hydrogen-containing mixture. The heating appliance typically has a combustion chamber and a conveying device or fan that can supply a mixture of fuel and combustion air via a mixture channel into a combustion chamber containing a burner. The combustion products can then be discharged through an exhaust duct of the heating appliance into an exhaust system.

[0015] The heating appliance can, in particular, adjust (modulate) the burner output to the demand. To this end, upon detecting a change in heat demand, for example, by taking into account the flow and return temperatures of a heating circuit connected to the appliance, a control unit within the appliance can adjust the fan output and thus the combustion air mass flow rate to the heat demand. Simultaneously, a control system adjusts the fuel mass flow rate to the changing combustion air mass flow rate.

[0016] The burner can comprise at least one perforated plate connected to a burner cavity. The burner cavity is connected to the mixture channel, allowing the combustion mixture to flow through the cavity and perforated plate, where it is combusted. An ignition device can also be arranged in the area of ​​the perforated plate, configured to ignite a mass flow of combustion mixture exiting through the perforated plate. The burner cavity, also referred to as the burner body, can be designed, in particular, as a cylinder (a right circular cylinder), with one of the cylinder's base surfaces connected to the mixture channel. Alternatively, the burner cavity can also be cuboidal, with the perforated plate forming the upper boundary. A flame arrestor can also be arranged in the burner cavity to prevent the flame from propagating towards the mixture channel.However, the flame arrestor may, especially after prolonged use, have a defect that allows a flame to penetrate and thus a flame flashback.

[0017] The burner can be located in the combustion chamber of the heating appliance, within a burner door. For this purpose, an opening in the burner door can connect the burner cavity to the mixture channel, and the burner can be attached to the burner door. Additionally, a flame monitor can also be attached to or integrated with the burner door.

[0018] The heating appliance may also include a flame monitoring device that can detect the presence of a flame at the burner and interrupt the gas supply if the flame goes out. A signal from the flame monitoring device can be used to regulate and control the heating appliance, in particular to determine and regulate the combustion air-fuel ratio of the gas mixture. The flame monitoring device may include an optical sensor, for example, to detect UV (ultraviolet) radiation emitted by the flame, a device for measuring the flame's ionization current, such as an ionization electrode, and / or a temperature sensor for detecting the flame temperature.For heating appliances that use hydrogen or a hydrogen-containing mixture as fuel, robust and reliable flame monitoring using ionization current measurement is often not possible because the combustion of hydrogen does not produce a sufficient number of free charge carriers. Therefore, heating appliances designed for hydrogen combustion employ the other methods mentioned above, or a combination thereof.

[0019] A flame flashback is characterized by the flame spreading from the burner of the heating appliance (backwards, i.e., against the usual flow direction) towards the mixture channel. This can cause, for example, an area of ​​the surface of the perforated plate to heat up so intensely from the flame at the burner that the combustion mixture in the burner cavity ignites. The resulting deflagrations or pressure surges in the flow path of the heating appliance can damage the flow path or connected components, such as the conveying mechanism. This damage can also lead to a leak in the flow path to the surrounding environment, which can allow (unburned) fuel gas to escape. Continuing to operate the heating appliance in the event of a leak could therefore pose a significant safety risk.The occurrence of a flame flashback is significantly more likely when using hydrogen or a hydrogen-containing mixture as a fuel gas due to the physical properties, especially the flame speed and the volatility, of hydrogen.

[0020] According to a method proposed here, a flame flashback can be detected by the (almost) simultaneous or immediately successive occurrence of two operating states, namely a) a loss (failure to capture) of the flame and b) a predetermined (significant) signal change, in particular a drop or fall, of a (monitoring) signal that allows a conclusion to be drawn about the mass flow of combustion air, fuel gas or combustion mixture supplied to the burner.

[0021] A flame flashback typically results in flame loss, meaning the flame goes out at the burner. Flame loss alone can have a variety of other causes, such as faults in the gas supply, a partially blocked exhaust path, or similar issues.

[0022] According to one embodiment, the loss of flame (state a)) can be detected by means of the flame monitoring of the heating device, in particular by a signal change - interruption or jump of a determined sensor value of the flame monitoring.

[0023] State b), namely a significant signal change or even a complete signal loss that allows conclusions to be drawn about the mass flow of combustion air, fuel gas, or combustion mixture supplied to the burner, can be determined by acquiring signals from appropriate sensors or components. When a signal change is considered "significant" can be determined through tests and / or observations of the heating appliance and, if necessary, stored in a data storage device as a reference. In the case of a conveying device designed as a blower, this could be, in particular, the blower speed. This information is often already available for the heating appliance's control processes. A control signal from a controller of the conveying device can also be used. The controller could, for example, be a speed controller, and the control signal a pulse-width modulated (PWM) signal.

[0024] Alternatively or cumulatively, signals from a mass flow sensor in the mixture channel, a combustion air supply, and / or a gas supply can also be used to detect state b). In this context, it should be noted that a volumetric flow rate can also be used and, given the density of the respective medium and the temperature, can easily be converted into a mass flow rate.

[0025] A predetermined signal change or signal termination refers to a sudden change in the signal, i.e., a sudden increase or decrease in the signal. In this context, a sudden change can be defined as a signal change of at least 10%, or in particular at least 20%, 30%, or 40%. The signal change can occur within a short period, for example, within one second, but especially within half a second or a quarter of a second.

[0026] With a signal indicating the speed of the conveying device, a sudden drop in signal can occur due to the pressure surge on the pressure side of the conveying device caused by a flame flashback. A similar behavior is to be expected with a signal from a mass flow sensor in the mixture channel, a combustion air supply, and / or a gas supply. With a control signal from the conveying device, a sudden increase in signal is to be expected due to a flame flashback, since a speed control system will increase the control signal to counteract a drop in speed (due to the flame flashback).

[0027] Condition b) can also occur in a heating appliance due to other circumstances, for example, a pressure surge caused by strong wind in the exhaust system outlet or in the combustion air intake (supply). However, the simultaneous occurrence of condition b) in conjunction with a loss of flame (condition a)) can be a reliable indication of a flame flashback.

[0028] According to one design, if a flame flashback is detected, the heating appliance can be taken out of service to avoid associated safety risks. Furthermore, the heating appliance can be put into a fault state that can only be cleared by a qualified person, such as a service technician. This advantageously ensures that the heating appliance can be inspected for damage caused by the flame flashback before being put back into operation.

[0029] According to a further embodiment, information about a detected flame flashback can be displayed via a display device and / or made available for retrieval via a network, particularly the internet, and / or sent as a message. For example, the information can be made available for retrieval on an appliance interface of the heating device or on network storage (cloud). Advantageously, this allows, for example, a user / operator of the heating device and / or a specialist company to be informed about a fault during the implementation of a procedure proposed here, and the specialist company can then schedule and carry out an appointment for maintenance and / or repair accordingly. In particular, this can lead to a rapid resolution of a fault condition of the heating device.

[0030] In addition, a control unit for a heating appliance is proposed, designed to carry out a procedure proposed herein. This control unit may, for example, include a processor. In this context, the processor can, for instance, execute the procedure stored in the control unit's memory. The control unit may, in particular, be electrically connected to a conveying system and a flame monitoring system.

[0031] Another aspect proposed is a heating appliance, including a control and regulation device as suggested here. This heating appliance can be a gas-fired appliance, specifically a hydrogen-powered gas-fired appliance. The gas-fired appliance can include a burner and a delivery system for supplying a mixture of fuel (hydrogen) and combustion air to the burner. The heating appliance can also include a flame monitoring system that can detect a loss of flame at the burner.

[0032] In addition, a computer program is proposed that is designed to (at least partially) execute one of the procedures presented here. In other words, this specifically concerns a computer program (product) comprising commands that, when executed by a computer, cause it to carry out the procedure proposed here. The computer program can, in particular, be executed on a control unit of the heating device.

[0033] Another aspect that is proposed is a machine-readable storage medium on which the computer program is stored.

[0034] The machine-readable storage medium is usually a computer-readable data carrier.

[0035] The details, features, and advantageous configurations discussed in connection with the process can also occur in the computer program, control unit, and heating device presented here, and vice versa. In this respect, full reference is made to the explanations provided therein for a more detailed characterization of the features.

[0036] This document presents a method for detecting flame flashback in a heating appliance, a control and monitoring device, a heating appliance, and a computer program, which at least partially solve the problems described with reference to the prior art. In particular, the method for operating the heating appliance, the computer program, the control and monitoring device, the heating appliance, and its use contribute, at least in part, to the unambiguous detection of flame flashback in a heating appliance and, if necessary, to the initiation of appropriate measures. Furthermore, the method proposed here is advantageously fully computer-implemented and generally requires no structural modifications compared to a heating appliance built according to the prior art.

[0037] The invention and its technical context are explained in more detail below with reference to the accompanying figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the situations described in the figures and combine them with other components and findings from the present description. It should be emphasized that the figures, and especially the depicted dimensions, are only schematic. They show: Fig. 1 : a heating device suggested here, and Fig. 2 : a burner during the occurrence of a flame flashback, and Fig. 3 : a parameter profile that may occur when carrying out a procedure proposed here.

[0038] Fig. 1 Figure 1 shows an exemplary and schematic representation of a heating device 1 proposed here. This device can include a burner 3 arranged in a combustion chamber 8. Combustion air can be drawn in via a combustion air supply 4, in which a mass flow sensor 12 may be arranged, by a conveying device 2, in particular designed as a blower. The conveying device 2 can be connected to a speed controller 6, which can regulate the speed n of the conveying device by means of a pulse-width modulated (PWM) signal. A gas valve 5 can add fuel gas from a gas supply 14 to the drawn-in mass air flow of combustion air and includes a safety valve and a gas control valve for controlling the mass flow of fuel gas to be added. The generated mixture of fuel gas and combustion air can flow to the burner 3 via a mixture channel 11.The burner 3 can have a cylindrical shape, which can be attached to a burner door 15 at its base in such a way that the combustion mixture can flow from the mixture channel into the burner 3. After combustion, the combustion products can be discharged to the outside via an exhaust pipe 9 of the heating appliance and an exhaust system 10.

[0039] The heating device 1 proposed here can be configured specifically for the combustion of hydrogen. Furthermore, the heating device 1 can have a flame monitoring device 13 on / in the burner door 15, which can be designed as a sensor for UV (ultraviolet) radiation emitted by the flame.

[0040] A control and regulating unit 7 can be set up to regulate the heating device 1. For this purpose, it can be electrically connected, for example, to the speed controller 6, the conveying device 2, the gas valve 5, the flame monitoring device 13 and a network 16 (Internet).

[0041] Fig. 2 Figure 1 shows a cross-sectional view of a burner 3 during the occurrence of a flashback. The burner 3 can have a cylindrical shape with an externally arranged perforated plate 23 and a burner cavity 22, in which a flame arrestor 17 can be arranged. This flame arrestor is intended to prevent a regular flame from passing from outside the perforated plate 23 into the burner cavity 22 and further into the mixture channel 11. However, particularly after prolonged use, the flame arrestor 11 may develop a defect 19 through which flame passage is possible.

[0042] Thus, a local overheating 18 of the perforated plate 23 can ignite the mixture of fuel gas and combustion air between the perforated plate 23 and the flame arrestor 17, and the flame can penetrate further through the defect 19 into the burner cavity 22 and the mixture channel 11, leading to a flame flashback 20 there.

[0043] Fig. 3Figure 27 shows an exemplary and schematic parameter profile of the rotational speed n of the conveying device 2 as signal 27, which allows conclusions to be drawn about the mass flow of combustion air, fuel gas, or combustion mixture supplied to the burner 3 as a function of time t. If, during the execution of a procedure proposed here, a flame loss (i.e., extinguishing of the regular flame at the burner 3) is detected by the flame monitoring 13, and thus state a) is recorded, state b) can be detected, for example, by signal 27 of the rotational speed n of the conveying device 2. Upon a change in signal 21, the rotational speed n can drop from a first speed 24, which may correspond to the current operating point of the heating device 1, to a second speed 26 within a short period 25 of a quarter of a second. Subsequently, the rotational speed n can rise again to the first speed 24.It should be noted as a precaution that the numerical terms used here ("first", "second", etc.) primarily serve (only) to distinguish between several similar objects, quantities, or processes, and thus do not necessarily dictate any dependency and / or sequence between these objects, quantities, or processes. Should a dependency and / or sequence be required, this is explicitly stated here, or it will be obvious to a person skilled in the art upon studying the specific configuration described. Where a component can occur multiple times ("at least one"), the description of one of these components may apply equally to all or some of the multiple components, but this is not mandatory. Reference symbol list

[0044] 1 Heating unit 2 Conveyor 3 Burner 4 Combustion air supply 5 Gas valve 6 Speed ​​controller 7 Control unit 8 Combustion chamber 9 Exhaust pipe 10 Exhaust system 11 Mixture channel 12 Mass flow sensor 13 Flame monitoring 14 Gas supply 15 Burner door 16 Network 17 Flame arrestor 18 Overheating 19 Fault 20 Flame backfire 21 Signal change 22 Burner cavity 23 Perforated plate 24 First speed 25 Time period 26 Second speed 27 Signal

Claims

1. Method for detecting a flame flashback (20) in a heating appliance (1), comprising a conveying device (2) for conveying a combustion mixture of fuel gas and combustion air to a burner (3), wherein a flame flashback (20) is inferred if the following conditions are detected simultaneously or in quick succession: a) a loss of flame at the burner (3), and b) a predetermined signal change (21) of a signal (27) which allows a conclusion to be drawn about the mass flow of combustion air, fuel gas or combustion mixture supplied to the burner (3).

2. Method according to claim 1, wherein the condition b) is selected on the basis of a signal (27) from the heating appliance (1) selected from: - rotational speed n of a conveying device (2) designed as a fan; - control signal of the conveying device (2); - signal from a mass flow sensor in a combustion air supply, fuel gas supply or a mixture channel of the heating appliance (1), is detected.

3. Method according to one of the preceding claims, wherein state a) is determined by means of a flame monitoring device (13) of the heating appliance (1).

4. Method according to claim 3, wherein the flame monitoring device (13) comprises an optical sensor, a device for measuring an ionisation current of the flame and / or a thermal sensor.

5. Method according to one of the preceding claims, wherein, upon detection of a flame failure (20), the heating appliance (1) is taken out of operation and / or the heating appliance (1) is placed in a fault state in which the heating appliance (1) can only be put into operation by a qualified person.

6. Method according to one of the preceding claims, wherein, upon detection of a flame failure (20), information thereon is made available for retrieval on a display device and / or via a network (16) or is sent as a message.

7. Control and regulating device (7) of a heating appliance (1) designed to carry out a method according to one of claims 1 to 6.

8. Heating appliance (1) comprising a conveying device (2), a flame monitor (13), a burner (3) and a regulating and control device (7) according to claim 7.

9. Computer program comprising commands which cause a heating appliance (1) according to claim 8 to carry out the method steps according to one of claims 1 to 6.

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