Method for operating a heating device, computer program, control device, and heating device

Abstract

A method is proposed for operating a heating device (1) which has at least one burner (3), to which a mixture of fuel gas and combustion air is supplied via a mixture channel (11) by means of a conveying device (2), and a gas valve (5) designed to control a fuel gas flow rate. In the method, when a drop in the combustion air flow rate with a gradient below a predetermined limit value is detected, the supplied fuel gas mass flow is reduced for a stabilization period. Furthermore, a computer program, a regulating and control device (7), and a heating device (1) are specified.

Description

[0001] The invention relates to a method for operating a heating device, a computer program, a control and regulating device and a heating device.

[0002] A large number of heating devices are known which burn a mixture of a fuel, in particular gas or hydrogen, and ambient air in a combustion chamber in order to generate heat to supply a building or to provide hot water.

[0003] The increasing use of hydrogen as a fuel increases the risk of flashbacks in such heaters. One reason for this is the significantly higher flame speed of hydrogen compared to other fuels. Flashback refers to the propagation of a flame from the burner toward the heater's mixture feed. This causes significant noise pollution and can also lead to damage to the heater, for example, to a conveying device (a fan).

[0004] To prevent flashbacks, flame arresters can be used. These often cover the available flow cross-section, especially in the area between the burner and the mixture supply, and cannot be penetrated by a flame. A heater with such a flame arrester is presented, for example, in DE10 2020 125 351 A1. The disadvantage of using a flame arrester is that it is complex, especially since the flame arresters become clogged and must be replaced regularly.

[0005] Based on this, the object of the invention is to propose a method for operating a heater that at least partially overcomes the described problems of the prior art. In particular, it is intended to enable robust operation of a heater and reliably prevent flashbacks.

[0006] In addition, the invention should at least not significantly increase the complexity of a heating device and require no or only minor structural changes to a heating device.

[0007] These objects are achieved by the features of the independent patent claims. Further advantageous embodiments of the solution proposed here are specified in the independent patent claims. It is pointed out that the features listed in the dependent patent claims can be combined with one another in any technologically expedient manner and define further embodiments of the invention. Furthermore, the features specified in the patent claims are further specified and explained in the description, with further preferred embodiments of the invention being presented.

[0008] A method for operating a heating device contributes to this, wherein the heating device has at least the following: a burner, to which a mixture of fuel gas and combustion air is supplied via a mixture channel by means of a conveying device, and a gas valve configured to control a fuel gas flow rate. The method comprises reducing the supplied fuel gas mass flow for a (specified) stabilization period upon detection of a drop in the combustion air flow rate with a (currently determined) gradient below a predefined limit value.

[0009] This procedure or test can be performed or activated continuously during the operation of a heater. The procedure serves to ensure the safe operation of a heater and, in particular, to prevent flashbacks.

[0010] The heater is, in particular, a gas heater designed to burn a fuel gas, such as natural gas or, in particular, hydrogen, with the addition of ambient air (combustion air) and to generate thermal energy, for example, to heat a heat transfer medium in a heating circuit or to provide hot water. In particular, the heater can be a condensing boiler. The heater typically has a conveying device or fan that can feed a mixture of fuel and combustion air to a burner arranged in a combustion chamber via a mixture duct (mixture gas duct, mixture feed). The combustion products can then be fed to an exhaust system through an exhaust duct of the heater.

[0011] The conveying device can have a controller, for example a speed controller of a conveying device designed as a fan, which controls a predetermined speed of the fan by means of a control signal, often a pulse width modulated (PWM) signal.

[0012] The burner can comprise at least one flat perforated plate or a cylindrical perforated plate arranged between a burner cavity and the combustion chamber. The burner cavity can be connected to the mixture channel in such a way that combustion mixture can flow from the mixture channel through the burner cavity, exit the perforated plate, and be combusted there. An ignition device can also be arranged in the region of the perforated plate, designed to ignite a mass flow of combustion mixture exiting through the perforated plate. The burner can be arranged on a burner door of a combustion chamber of the heater. The burner door can have a flow-through opening that can connect the mixture channel of the heater to the burner cavity. A cylindrical burner can have a flange for attachment to the burner door, which can be connected to the burner door, for example, by means of a screw connection.There is usually a seal between the burner and the burner door, for example a high-temperature stable graphite seal.

[0013] The burner can comprise (at least) one flame arrester, which is designed and arranged in the burner cavity in such a way that combustion mixture flowing to the perforated plate must penetrate the flame arrester. In other words, the flame arrester can cover the entire existing flow cross-section in the burner cavity, so that combustion mixture flowing to the perforated plate must penetrate the flame arrester. For example, in a cylindrical burner, the flame arrester can also be cylindrical with a largely constant distance from the perforated plate. In a flat (planar) perforated plate, the flame arrester can also be flat and planar and arranged at a distance from the perforated plate in the burner cavity.

[0014] According to one embodiment, the burner and flame arrester can be formed as a unit. The burner can be connected to the burner door via a seal made of graphite or a similar material.

[0015] In particular, the heater can adjust the burner output to meet demand, also known as modulation. The modulation range of a heater refers to the output range within which the heater can modulate. Through modulation, the heater's burner output is automatically and preferably continuously adjusted to the actual demand. This allows for longer running times, which reduces the heat generator's cycling and the strain on its components. In addition, the operational reliability and energy efficiency of the heater are increased. The larger the modulation range of a heater, the more flexible the heat output. Gas condensing boilers can operate with a modulation range of 30 to 100% of the nominal output.

[0016] To this end, when a change in heat demand is detected, for example, taking into account the flow and return temperatures of a heating circuit connected to the heater, a control unit of the heater can adjust the heater fan output and thus the combustion air mass flow to the heat demand. At the same time, a control system adjusts the fuel mass flow to the changing combustion air mass flow. To prevent flashbacks in low power ranges, the combustion air ratio is often adjusted, particularly by increasing the combustion air ratio.

[0017] To control the fuel gas mass flow, the heater can have a gas valve, which can typically include a gas safety valve and a gas control valve. The gas control valve can, in particular, be a stepper motor valve that can set a defined fuel gas mass flow. The safety valve is intended to prevent the escape of unburned fuel gas and is released, for example, during a heater start-up process, only after the delivery system has reached a starting power suitable for the start-up process.

[0018] The heater can also have a flame monitor. Various methods are known for this; in particular, reliable flame monitoring can be provided by detecting the ionization current of the flame. However, due to the lack of sufficient free charge carriers during hydrogen combustion, this method cannot be used robustly for hydrogen-powered heaters. Other methods are used for flame monitoring in hydrogen-powered heaters, for example, detecting the temperature of the flame and / or the UV (ultraviolet) radiation emitted by the flame.

[0019] Flame monitoring can be used to detect the presence of a flame or to control a lambda value (combustion air ratio, air number) of the combustion. This way, a (current) lambda value can be assigned to a flame monitoring signal (UV or temperature sensor) by incorporating reference values ​​or a reference map (lambda control curve). The heater's lambda is often controlled using a flame monitoring signal as the controlled variable. For this purpose, a flame monitoring signal value corresponding to the target lambda can be determined and adjusted using a parameter that allows conclusions to be drawn about the combustion air flow rate, the flame monitoring signal, and a reference relationship.

[0020] Modern heaters often have a wide modulation range, for example, from 3.5 kW [kilowatts] to more than 20 kW. These heaters are advantageous for flexible use, and frequent switching on and off can be avoided. The wide modulation range, combined with the desire for rapid modulation to ensure high user comfort, leads to high modulation speeds, i.e., operating points with significant performance differences that must be reached within a short period of time.

[0021] It has been found that, particularly at high modulation speeds, a reduction in power can lead to an undershoot of the lambda value. In this case, an undershoot means a briefly significantly reduced lambda value until the control system detects this based on the flame monitoring signal and can correct it by influencing the gas valve. A connection here can be seen in a delayed reaction of the gas valve to a reduced combustion air mass flow. Such an undershoot can also occur due to disturbances, for example a temporarily reduced combustion air volume flow triggered by a gust of wind acting on the exhaust system. The undershoot of the lambda value means a (temporarily) increased proportion of fuel gas in the combustion mixture supplied to the burner, which can lead to critical conditions in the heater, for example a flashback (backfire).

[0022] One idea of ​​the invention is to ensure operational safety during operation of a heater by preventing such undershoots of the lambda value. For this purpose, a gradient of the combustion air flow rate can be determined. If the combustion air flow rate drops (decreases) with a gradient below a predetermined limit, the supplied fuel gas mass flow can be reduced for a stabilization period. To reduce the fuel gas mass flow, for example, the opening width of the gas control valve can be reduced.

[0023] In this context, it should be noted that a flow rate (combustion air, fuel, or a mixture of both) can also be understood as a mass or volume flow. Thus, a mass flow can easily be converted into a volume flow, and vice versa, given knowledge of the density and temperature of the medium.

[0024] The specified limit value can be selected so that a critical condition of the heater (e.g., a flashback) occurs with sufficient or a predetermined probability. The limit value can, for example, be determined on a reference heater using (laboratory) tests. As a rule, the limit value will be in a range from 1 kilowatt per second [kW / s] to 10 kW / s or (specified as a relative change in power) from 3 percent [%] of the heater's rated power per second [P / (P rated xt] / to 30 percent of the heater's rated power per second.

[0025] According to one embodiment, the combustion air flow rate can be measured using a flow sensor. The flow sensor can, in particular, be a mass flow or volume flow sensor.

[0026] According to one embodiment, a flow sensor can be used that has a short measurement delay, i.e., requires only a very short period of time from a change in the flow rate to a corresponding change in the sensor signal. The flow sensor can be a calorimetric flow sensor that outputs a signal for the differential pressure of the flow rate at a high frequency, for example, every 5 ms [milliseconds]. This signal can then be converted into a mass flow.

[0027] According to one embodiment, the flow rate and thus also the flow rate gradient can also be determined based on operating data of the heater. This operating data can be, for example, a speed, power consumption, or a control signal from a controller of the conveying device. Alternatively, the combustion air flow rate can be determined during a modulation process based on knowledge of the old and new modulation points, a gradient of the combustion air flow rate.

[0028] According to one embodiment, if a drop in the combustion air flow rate with a gradient below a limit value is detected, the fuel gas mass flow can be reduced by 0% to 50%, based on the fuel gas mass flow during normal operation. The specific reduction required depends on the specific heater and the current modulation process or the intensity of any disturbances that occur, and can vary considerably. The reduction required to compensate for an undershoot of the lambda value can also be determined in advance using laboratory tests. The reduction in the fuel gas mass flow can cause a shift in the lambda value towards lean combustion between 0 and 1.

[0029] According to one embodiment, the reduction in the fuel gas mass flow can be achieved depending on the gradient of the decrease in the combustion air flow rate. In other words, the reduction can be increased as the gradient of the decrease in the combustion air flow rate decreases.

[0030] According to one embodiment, the stabilization period can be in a range of 5 to 60 seconds. It has been shown that, within this range, undershoot due to modulation or disturbances can be compensated until the control system can correct the undershoot.

[0031] According to one embodiment, the stabilization time can be determined depending on the gradient of the decrease in the combustion air flow rate. For example, with a very small decrease gradient, a longer stabilization time can be selected to compensate for a stronger undershoot.

[0032] According to a further aspect, a control and regulating device for a heating device is also proposed, configured to carry out a method proposed here. For this purpose, the control and regulating device can, for example, have and / or be equipped with a processor. In this context, the processor can, for example, execute the method stored in a memory (of the control and regulating device). For this purpose, the control and regulating device can, in particular, be electrically connected to a conveying device and / or a flow sensor. In addition, data acquired or required within the scope of carrying out a method proposed here can be stored in a memory of the control and regulating device, for example limit values ​​for the gradient of the combustion air flow rate.

[0033] According to a further aspect, a heating device is also proposed, configured to combust a combustion mixture of combustion air and fuel gas. The heating device can be a gas heater, in particular a hydrogen-powered gas heater. The gas heater can have a burner and a conveying device with which a mixture of fuel (hydrogen) and combustion air can be supplied to the burner via a mixture channel. The heating device can have a flame monitor, a signal from which can be used to regulate the lambda value of the combustion. The heating device can also have further means adapted to carry out the steps of the method disclosed here. The means can comprise a regulating and control device.

[0034] According to one embodiment, the heater may include a flow sensor in a combustion air supply for detecting the combustion air flow rate. In particular, the flow sensor may be a particularly fast-measuring flow sensor capable of outputting a measurement signal at a measurement rate of approximately 5 ms (milliseconds) to 10 ms.

[0035] According to one embodiment, the heater can have a flow sensor in a combustion air supply, and a method proposed here can be implemented in a combustion lambda control system. An evaluation unit for the flow sensor signal includes a differential element (differentiator) that determines a gradient of the combustion air flow rate. If the gradient falls below the limit value, this influences the target (opening) position of the gas valve, for example, via an integrator, and can cause it to drop (close) disproportionately. For example, an integrator of the I component of the controller can be used here.

[0036] According to a further aspect, a computer program is also proposed, which is configured to (at least partially) carry out a method presented here on a heating device proposed here. In other words, this relates in particular to a computer program (product) comprising instructions which, when executed by a computer, cause the computer to carry out a method proposed here. The computer program can in particular be executed on a control and regulating device of a heating device proposed here.

[0037] According to a further aspect, a machine-readable storage medium on which the computer program is stored is also proposed. The machine-readable storage medium is usually a computer-readable data carrier.

[0038] Thus, a method for operating a heater, a computer program, a control device, and a heater are provided, which at least partially solve the problems described with reference to the prior art. In particular, the method for operating a heater, the computer program, the control device, and the heater at least contribute to compensating for an undershoot of the combustion lambda value due to rapid modulations of the heater or (external) disturbances, thus significantly increasing the operational reliability of a heater by effectively preventing flashbacks.

[0039] In addition, the invention can be implemented with no or only minor structural changes to a heater.

[0040] The invention and the technical environment 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 cited. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and combine them with other components and findings from the present description. In particular, it should be noted that the figures and, in particular, the illustrated proportions are only schematic. They show: Fig. 1: a heating device proposed here, Fig. 2: parameter curves that can occur when carrying out a method proposed here, and Fig. 3: a control system for carrying out a method proposed here.

[0041] Fig. 1 shows, by way of example and schematically, a heating device 1 proposed here. This can comprise a burner 3 arranged in a combustion chamber 8. The burner 3 can have the shape of a hollow cylinder, wherein a burner cavity can be formed inside. In the burner cavity, a flame arrester 12 can be aligned parallel to the surface of the burner 3 or concentrically to it and can cover the entire flow cross-section available in the burner cavity.

[0042] Combustion air can be sucked in via a combustion air supply 4 by a conveying device 2, in particular designed as a fan. A flow sensor 21 can be arranged in the combustion air supply 4. The conveying device 2 can be connected to a speed controller 6, which can regulate a speed n of the conveying device 2 by means of a pulse width modulated (PWM) signal. A gas valve 5 can add fuel gas from a gas supply 14 to the sucked-in air mass flow of combustion air and can comprise a safety valve and a gas control valve for controlling the mass flow of fuel gas to be added. The generated combustion mixture of fuel gas and combustion air can flow via a mixture channel 11 to the burner 3 and be ignited there by the ignition device.The burner 3 can have a cylindrical shape, which can be attached by a base surface to a burner door 15 such that combustion mixture can flow from the mixture channel into the burner 3. Heat generated during combustion can be transferred via a heat exchanger 20 to a heating circuit 19, via whose heating flow 17 heat transfer medium of the heating circuit 19 can be supplied and returned to the heater 1 via a heating return 18. After combustion, the combustion products can be discharged to the outside via an exhaust pipe 9 of the heater 1 and an exhaust system 10 connected to the heater 1.

[0043] The heater 1 proposed here can be configured, in particular, for the combustion of hydrogen. Furthermore, the heater 1 can have a flame monitoring device 13 on or in the burner door 15, which in the example is designed as a sensor for UV (ultraviolet) radiation emitted by the flame.

[0044] A control and regulation device 7 can be configured to regulate the heating device 1. For this purpose, it can be electrically connected, for example, to the speed controller 6, the conveyor device 2, the gas valve 5, the flame monitor 13, and a network 16 (Internet). The control and regulation device 7 can be configured to implement a method proposed here.

[0045] Fig. 2 a) und b) show two curves of a lambda of the combustion of the combustion mixture supplied to the burner over time t after the effect of a disturbance 26. A target lambda 22 corresponding to the modulation point and a limit lambda 23 are specified, below which a significant risk of flashback can occur. Fig. 2 a) The curve of the lambda λ combustion air is shown without including a method proposed here. Following the disturbance 26, the first curve 24 drops below the limit lambda 23 and thus a significant risk of flashback occurs. In contrast, in Fig. 2 b) In the second course 25, by including a procedure proposed here following the disturbance 26, the course can be kept above the limit lambda 23, the risk of flashback can be significantly reduced.

[0046] Fig. 3shows a control system for implementing a method proposed here. For this purpose, an evaluation unit 29 is integrated into a combustion control system 27 of the heater 1. The combustion control system 27 has a resistor 31 of a flame monitor 13 (for example, a hot surface ignitor (HSI) thereof) and a combustion air mass flow 32, which can be detected by the flow sensor 21, as an input signal. For clarification, it should be noted that the flame monitor can also include a UV (ultraviolet) sensor, the signal of which could also be an input signal of the combustion control system 27. An output signal of the combustion control system 27 can be a gas valve position 28, which can be transmitted to the gas valve 5. The evaluation unit 29 can have the detected combustion air mass flow 32 as an input signal and can include a D element (also referred to as a differentiator) that forms a gradient of the detected combustion air mass flow 32.In addition, the signal can be filtered in the evaluation unit 29 and subjected to an influencing factor before the signal is transferred to a control unit 30, in which, if the gradient is below a predetermined limit value, the signal influences the gas valve position 28, which can correspond to a reduction in the opening width of the gas valve 5. The influencing factor can be used to adjust the effect of the signal from the evaluation unit 29 on the gas valve position 28 to be set.

[0047] As a precaution, it should be noted that the numerals used here ("first", "second",...) primarily serve (only) to distinguish between several similar objects, quantities, or processes, and therefore do not necessarily prescribe any interdependence and / or sequence of these objects, quantities, or processes. Should a dependence and / or sequence be required, this is explicitly stated here or will be obvious to the person skilled in the art upon studying the specifically described embodiment. To the extent that a component can occur multiple times ("at least one"), the description of one of these components can apply equally to all or part of the majority of these components, but this is not mandatory. List of reference symbols

[0048] 1 Heater 2 Conveyor system 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 duct 12 Flame arrester 13 Flame monitoring 14 Gas supply 15 Burner door 16 Network 17 Heating flow 18 Heating return 19 Heating circuit 20 Heat exchanger 21 Flow sensor 22 Target lambda 23 Limit lambda 24 First curve 25 Second curve 26 Fault 27 Combustion control 28 Gas valve position signal 29 Evaluation unit 30 Control unit 31 Flame monitoring resistor 32 Combustion air mass flow

Claims

1. A method for operating a heating device (1), comprising at least one burner (3) to which a mixture of fuel gas and combustion air is supplied via a mixture channel (11) by means of a conveying device (2), and a gas valve (5) configured to control a flow rate of fuel gas, wherein upon detection of a drop in the flow rate of combustion air with a gradient below a predetermined limit value, the supplied mass flow of fuel gas is reduced for a stabilization period.

2. Method according to claim 1, wherein a combustion air flow rate is detected by means of a flow sensor (21).

3. Method according to claim 1, wherein the flow rate is determined based on operating data of the heater (1). ​4. Method according to one of the preceding claims, wherein the mass flow of fuel gas is reduced from 0% [percent] to 50%, based on the mass flow of fuel gas provided during normal operation.

5. Method according to one of claims 1 to 3, wherein the reduction of the mass flow of fuel gas takes place as a function of the gradient of the decrease in the flow rate of combustion air.

6. Method according to one of the preceding claims, wherein the stabilization period is from 5 to 60 seconds.

7. Method according to one of claims 1 to 5, wherein the stabilization time is determined as a function of the gradient of the decrease in the combustion air flow rate.

8. Heating device (1), comprising a burner (3), a conveyor device (2), a gas valve (5), control of a combustion lambda by means of a flame monitor (13) and means for carrying out a method according to one of the preceding claims.

9. Heating device (1) according to claim 8, wherein the heating device (1) has a flow sensor (21) in a combustion air supply (4), and a method according to one of claims 1 to 8 is implemented in a control of the combustion lambda, wherein an evaluation unit (29) of the signal of the flow sensor (21) comprises a D-element (differentiator) that determines a gradient of the combustion air flow rate.

10. Regulating and control device (7) configured to carry out a method according to one of claims 1 to 7.

11. A computer program comprising instructions which cause a heating device (1) according to claim 8 or 9 to carry out a method according to any one of claims 1 to 7.​

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