DE102022133634A1 - Method for operating a heating device, computer program, control device, heating device and use of a throttle device - Google Patents

Abstract

A method is proposed for operating a heater (1) having a burner (3), to which a mixture of fuel gas and combustion air is supplied via a mixture channel (11) by means of a conveyor device (2), and a controllable throttle device (12) arranged in a combustion air supply (4), a mixture channel (11) and/or in an exhaust gas path (9, 10) of the heater, and a flow sensor (21) which is used to regulate the heater (1), wherein the heater (1) is set up for modulation and the throttle device (12) is partially closed at modulation points below a first limit value. In addition, a heater (1) and regulating and control device (7), a computer program and the use of a throttle device (12) are proposed.

Description

The invention relates to a method for operating a heating device, a computer program, a regulating and control device, a heating device and a use of a throttle device.

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.

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. A flashback is the spread of a flame from the burner in the direction of a mixture feed of the heater, causing considerable noise pollution and can also lead to damage to the heater, for example to a conveyor device (a fan).

To prevent flashbacks, flame arresters can be used, which 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 used, for example, in the DE10 2020 125 351 A1 The disadvantage of using a flame arrester is that it is expensive, especially since flame arresters that become clogged regularly have to be replaced.

Based on this, the object of the invention is to propose a method for operating a heating device which at least partially overcomes the problems of the prior art described. In particular, robust operation of a heating device should be enabled and flashbacks should be reliably prevented.

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.

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 reasonable manner and define further embodiments of the invention. In addition, the features specified in the patent claims are specified and explained in more detail in the description, with further preferred embodiments of the invention being presented.

A method for operating a heater contributes to this, wherein the heater has at least the following components: A burner, to which a mixture of fuel gas and combustion air can be or is supplied via a mixture channel by means of a conveyor device. A controllable throttle device, which is arranged in a combustion air supply, a mixture channel and/or in an exhaust gas path of the heater. A flow sensor, which can be or is used to regulate the heater. The heater is set up for modulation, wherein the throttle device is at least partially closed when the heater is operated at at least one modulation point below a first limit value.

The method can be carried out continuously while a heating device is in operation. The method is used in particular to ensure safe operation of a heating device and in particular to prevent flashbacks.

The heating device is in particular a gas heating device that is designed to burn a fuel gas, such as natural gas or in particular hydrogen, with the supply of ambient air (combustion air) and to generate thermal energy, for example to heat a heat carrier of a heating circuit or to provide a hot water supply. In particular, the heating device can be a condensing boiler. The heating device usually has a conveyor device or a fan that can feed a mixture of fuel and combustion air to a burner arranged in a combustion chamber via a mixture channel (mixture gas channel, mixture feed). The combustion products can then be fed to an exhaust system through an exhaust channel of the heating device. The entirety of the exhaust channel and the exhaust system can also be referred to as the exhaust path.

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

The burner can comprise at least one flat perforated plate or a perforated plate in cylindrical form, which is 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 from the perforated plate and be burned there. In the area of the perforated plate, an ignition device can also be arranged, 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 opening that can connect the mixture channel of the heater to the burner cavity. A burner in cylindrical form can have a flange for fastening to the burner door, which can be connected to the burner door, for example by means of a screw connection. A seal, for example a high-temperature-stable graphite seal, is usually arranged between the burner and the burner door.

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 the case of a burner designed in a cylindrical shape, the flame arrester can also be designed in a cylindrical shape with a largely constant distance from the perforated plate. In the case of a flat (level) perforated plate, the flame arrester can also be designed flat and level and arranged at a distance from the perforated plate in the burner cavity.

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

In particular, the heater can adapt the burner output to the requirement, also known as modulation. The modulation range of a heater describes the output range in which the device can modulate. Through modulation, the burner output of the heater is automatically and preferably continuously adapted to the actual requirement. This enables a longer running time, which reduces the cycling of the heat generator and the load on the components. In addition, the operational reliability and energy efficiency of the device are increased. The larger the modulation range of a heater, the more flexible the heat output. Gas condensing boilers can work with a modulation range of 30 to 100% of the nominal output.

For this purpose, 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 and regulation device of the heater can adjust the output of the heater's fan 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 avoid flashbacks in low power ranges, the combustion air ratio is often adjusted, in particular the proportion of combustion air is increased.

The heater can have a gas valve to control the mass flow of fuel gas, which can generally 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 mass flow of fuel gas. The safety valve is intended to prevent unburned fuel gas from escaping and is only released when the heater is started, for example, after the conveyor device has been started up to a starting power suitable for the start-up process.

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

The flame monitoring can be used to determine the presence of a flame as well as to control a lambda value (combustion air ratio, air number) of the combustion. In this way, a (current) lambda value can be assigned to a flame monitoring signal (UV or temperature sensor) using reference values or a reference characteristic map (lambda control curve). The heater's lambda is often controlled using a flame monitoring signal as 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 a conclusion to be drawn about the combustion air flow rate, the flame monitoring signal and a reference context.

In the flow path of combustion air, gas mixture and/or exhaust gas of the heater, (at least) one throttle device is arranged, which is designed to reduce the flow cross-section and thus increase the flow resistance. The throttle device can in particular be controlled by a motor and can be designed as a throttle valve, for example. The flow path can in particular comprise a combustion air supply, a mixture channel or an exhaust channel of the heater.

Modern heaters often have a large modulation range, for example 3.5 kW [kilowatts] to more than 20 kW. The advantage of these heaters is that they can be used flexibly and frequent switching on and off can be avoided. The large modulation range in conjunction with the desire for fast modulation leads to high modulation speeds, i.e. operating points with considerable differences in performance that can be reached within a short period of time.

It was found that when the heater is operated at (particularly) low modulation points (i.e. at operating points of the heater with a low output, or below a determined or predeterminable modulation point), a disturbance, for example due to a gust of wind at an outlet of the exhaust system, can have a significant impact on the (low) volume flow of combustion air delivered and resulting fluctuations in the combustion air flow rate (for a short period of time until the lambda value control intervenes) can lead to an undershoot of the lambda value and thus to too high a proportion of fuel gas in the combustion mixture. The period in which the lambda value is too low can represent a critical operating state, since, for example, the risk of a flashback increases significantly with a low lambda value. The drop in the combustion air flow rate can be recognized by the flame monitoring system as a drop in the lambda value and the controller then reduces the added mass flow of fuel gas in order to regulate to the specified target lambda. At the same time, the flow sensor can detect the combustion air flow rate reduced by the disturbance and increase the performance of the conveying device in order to regulate the combustion air flow rate back to a combustion air mass or volume flow rate specified for the current modulation point.

The modulation range below the first limit value can indicate a power range of the heater in which the flow rate delivered is significantly susceptible to faults and/or a critical state of the heater (e.g. flashback) can occur in connection with a fault with sufficient or a predetermined probability. Other factors such as an installation location (and associated information on climate or weather data, geodetic altitude, etc.) can also be taken into account in determining the first limit value. The first limit value can, for example, be determined in advance in (laboratory) tests on a reference heater. The first limit value will often be in a range from 15 KW [kilowatts] to 5 KW or from 50% [percent] to 15% of the nominal power of the heater.

An undershoot of the lambda value here means a briefly significantly reduced lambda value until the control system detects this based on the flame monitoring signal and can correct it by acting on the gas valve. A connection here can be seen in a delayed reaction of the gas valve to a reduced mass flow of combustion air. Such an undershoot can also occur due to faults, for example a temporarily reduced volume flow of combustion air 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 fed to the burner, which can lead to critical conditions in the heater, for example a flashback (backfire).

For example, partially closing the throttle device and the associated increase in flow resistance and the subsequent increase in the performance of the conveyor can cause a shift in the operating point in the fan characteristic curve of the conveyor, where pressure surges have a lesser effect. Since the conveyor is also operated at low power in low performance ranges of the heater, an increase in its performance can be easily implemented using a method proposed here.

When the throttle device is partially closed, an increase in the flow resistance corresponding to an adjustable opening width can be achieved, in particular the conveying device can easily convey the mass flow of combustion air to be set for the modulation point. In addition, the opening width to be set should cause a sufficient shift of the operating point in the fan characteristic curve so that possible disturbances or pressure surges cannot have a relevant effect on the conveyed mass flow of combustion air, whereby an undershoot of the lambda value of the combustion can be prevented or at least significantly dampened.

According to one embodiment, the opening width of the throttle device to be set can depend on the modulation point (the current output) of the heater. In particular, the flow resistance can be increased as the output of the heater decreases.

According to one embodiment, if a drop in the combustion air flow rate is detected with a gradient below a second limit value, the throttle device can be opened at least partially. A fault could thus cause a drop in the combustion air flow rate, and by at least partially opening the throttle device, an undershoot of the lambda value caused by a delayed intervention of the control can be prevented or dampened. The second limit value can here indicate a gradient of the drop in the combustion air flow rate, below which an undershoot caused by the control is sufficiently likely. The second limit value can also be determined in tests on a reference heater.

According to one embodiment, a flow sensor can be used which has a short delay in a measuring process, i.e. only requires a very short period of time from a change in the flow rate to a corresponding change in the sensor signal. This can be particularly helpful for determining the gradient of the combustion air flow rate. The flow sensor can in particular be a calorimetric flow meter which outputs a signal for the differential pressure of the flow rate at high frequency, for example at intervals of 5 ms [milliseconds], which can then be converted into a mass flow.

According to a further aspect, a control device for a heater is also proposed, set up to carry out a method proposed here. For this purpose, the control device can, for example, have a processor and/or have one. In this context, the processor can, for example, carry out the method stored in a memory (of the control device). For this purpose, the control device can be electrically connected in particular to a conveyor device, a throttle device, a gas valve and/or a flow sensor. In addition, data recorded or required as part of the implementation of a method proposed here can be stored in a memory of the control device, for example a first and/or second limit value.

According to a further aspect, a heating device is also proposed, designed to burn a combustion mixture of combustion air and fuel gas. The heating device can be a gas heating device, in particular a hydrogen-operated gas heating device. The gas heating device can have a burner and a conveyor 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. In addition, the heating device can comprise a throttle device, suitable for increasing the flow resistance by reducing the flow cross-section in the flow path. The heating device can also comprise further means which are adapted to carry out the steps of the method disclosed here. The means can comprise a regulating and control device.

According to one embodiment, the heater can have a flow sensor in a combustion air supply for detecting the combustion air flow rate.

According to a further aspect, a computer program is also proposed which is set up 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 commands which, when the program is executed by a computer, cause the computer to carry out a method proposed here. The computer program can in particular be carried out on a control device of a heating device proposed here.

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

According to a further aspect, the use of a throttle device in a flow path of the heater is also proposed to compensate for an undershoot of the lambda value of the heater. The use can be carried out in particular at low modulation points or in low power ranges of the heater, in particular below a first limit value, wherein the throttle device can be partially closed.

The details, features and advantageous embodiments discussed in connection with the method can also occur in the computer program, the control device, the heater and the use presented here and vice versa. In this respect, reference is made in full to the explanations there for a more detailed characterization of the features.

A method for operating a heater, a computer program, a control and regulating device and a heater are therefore specified here, 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 and regulating device and the heater at least help to compensate for an undershoot of the lambda value of the combustion due to rapid modulations of the heater or (external) disturbances and thus significantly increase the operational reliability of a heater by effectively preventing flashbacks.

In addition, the invention can be implemented with no or only minor structural changes to a heating device.

• 1: ein hier vorgeschlagenes Heizgerät,
• 2: Parameterverläufe, die sich bei Durchführung eines hier vorgeschlagenen Verfahrens einstellen können.

The invention and the technical environment are explained in more detail below with reference to the attached figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments given. 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 size relationships shown are only schematic. They show:

• 1 : a heater proposed here,
• 2 : Parameter curves that can occur when carrying out a procedure proposed here.

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 can be aligned parallel to the surface of the burner or concentrically to it and cover the entire flow cross-section available in the burner cavity.

Combustion air can be sucked in via a combustion air supply 4 through a conveyor device 2, in particular designed as a fan. A flow sensor 21 can be arranged in the combustion air supply 4. The conveyor device 2 can be connected to a speed controller 6, which can regulate a speed n of the conveyor 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 mixture of fuel gas and combustion air produced 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 with a base to a burner door 15 in such a way 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 carrier 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. A throttle device 12 can be arranged in the exhaust pipe 9, which is designed to increase the flow resistance in the flow path of the heater 1 by reducing the flow cross section.

The heating device 1 proposed here can be designed in particular for the combustion of hydrogen. In addition, the heating device 1 can have a (device for) flame monitoring 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.

A control and regulating device 7 can be set up to regulate the heating device 1. For this purpose, it can be connected, for example, to the speed controller 6, the conveyor device 2, the gas valve 5, the Flame monitoring 13, the throttle device 12 and a network 16 (Internet) can be electrically connected. The regulating and control device 7 can be set up to carry out a method proposed here.

2 shows, by way of example and schematically, a fan characteristic curve for the conveying device 2 of the heater 1, which indicates the conveyed volume flow 7 as a function of the pressure drop ΔP caused. A first curve 22 shows the conveyed volume flow 7 as a function of the pressure drop ΔP caused with the throttle device 12 open. A second curve 23 shows the course under the influence of a disturbance that causes a pressure drop 24. From the intersection points of the first curve 22 and the second curve 23 with a first fan characteristic curve 26, a drop in the volume flow 25 resulting from the disturbance and the corresponding pressure drop 24 without the influence of the throttle device 12 can be determined.

A third curve 27 shows the volume flow V delivered as a function of the pressure drop ΔP 24 caused with the throttle device 12 partially closed. This can be partially closed as part of a method proposed here, since the heater 1 is operated at a modulation point (with a power) below a first limit value. The fourth curve 28 shows the course of the third curve 27 when a fault occurs that causes the same pressure drop 24 as in the first curve 22 and second curve 23. The resulting drop in the volume flow 30 with the throttle device 12 partially closed can be determined from the intersection points with a second fan characteristic curve 29. The drop in the volume flow 30 with the throttle device 12 partially closed is advantageously significantly lower than the drop in the volume flow 25 with the throttle device 12 open.

3 a) and b) show two curves of a mass flow ṁ _air conveyed by the conveying device 2 over time t after the effect of a disturbance 31. A target mass flow 32 corresponding to the modulation point and a limit mass flow 33 are specified, below which there may be a considerable risk of flashback. In 3 a) the course of the mass flow ṁ _air combustion air is shown without including a method proposed here. Following the disturbance 31, the course 34 falls below the limit mass flow 33 and thus there is a significant risk of a flashback. In contrast, in the second course 35, by including a method proposed here following the disturbance 31, the course can be kept above the limit mass flow 33 and the risk of a flashback can be significantly reduced.

As a precaution, it should be noted that the numerals used here ("first", "second", ...) primarily serve (only) to distinguish between several similar objects, sizes or processes, and in particular do not necessarily specify a dependency and/or sequence of these objects, sizes or processes. If a dependency and/or sequence is required, this is explicitly stated here or it is obvious to the person skilled in the art when studying the specifically described design. If 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

1

heater

2

Conveyor system

3

burner

4

Combustion air supply

5

Gas valve

6

Speed controller

7

Control and regulation device

8th

Combustion chamber

9

Exhaust pipe

10

Exhaust system

11

Mixture channel

12

Throttle device

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

first curve

23

second curve

24

Pressure drop

25

Waste volume flow with open throttle device

26

first fan characteristic curve

27

third curve

28

fourth curve

29

second fan characteristic curve

30

Waste volume flow with partially closed throttle device

31

Disturbance

32

Target mass flow

33

Limit mass flow

34

first course

35

second course

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• DE 102020125351 A1 [0004]

Claims (7)

Method for operating a heater (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 controllable throttle device (12) arranged in a combustion air supply (4), a mixture channel (11) and/or in an exhaust gas path (9, 10) of the heater (1), and a flow sensor (21) which is used to regulate the heater (1), wherein the heater (1) is set up for modulation and at modulation points below a first limit value the throttle device (12) is partially closed. Procedure according to Claim 1 , wherein at a modulation point below the limit value, an opening width of the throttle device (12) is adjusted depending on the modulation point. Procedure according to Claim 1 , wherein when a drop in the combustion air flow rate with a gradient below a second limit value is detected, the throttle device (12) is at least partially opened. Heating device (1), comprising a burner (3), a conveyor device (2), a gas valve (5), a control of a lambda of the combustion by means of a flame monitor (13), a flow sensor (21), a supply of combustion air (4), a throttle device (12), a mixture channel (11) and an exhaust gas path (9,10) and means adapted for carrying out a method according to one of the preceding claims. Control device (7) designed to carry out a method according to one of the Claims 1 until 3 . Computer program comprising commands which control a heating device (1) according to Claim 4 to initiate proceedings under one of the Claims 1 until 3 to execute. Use of a throttle device (12) in a flow path of the heater (1) to compensate for an undershoot of the lambda value of the heater (1).

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