METHOD AND ARRANGEMENT FOR ENSURING THE PRESENCE OF FLAMES IN A COMBUSTION ROOM DURING MODULATION OF A HEATING APPLIANCE

Description

[0001] The invention relates to a method and an arrangement for ensuring the presence of flames in a combustion chamber during the modulation of a gas-fired heating appliance, in particular a heating appliance that can be operated with hydrogen and / or a hydrogen-containing fuel gas. This applies not only to large systems, but also to wall-mounted units for heating water and, more generally, to heating appliances for heating buildings and / or providing hot water. Modern heating appliances are not simply switched on and off, but can be operated at different power levels, allowing for precise adaptation to various demand situations. In particular, the power output of such heating appliances can be changed during operation, i.e., while a combustion process is underway; this is also known as modulation.For safe and environmentally friendly operation, such modulation requires stable flames in the combustion chamber before, during, and after changes in power output. Therefore, gas-fired heating appliances must, in many countries even due to legal requirements, be equipped with a flame detection device (also called a flame monitor) that ensures that unburned air-fuel gas mixture is not supplied to the combustion chamber of the heating appliance for longer than a maximum permissible time.

[0002] Heating appliances generally employ simple and robust sensors for temperature, light or heat radiation, pressure, volume flow, and the like to regulate the appliances and ensure their safe operation. An important function of such sensors is to detect the presence of a stable flame (a so-called flame detector); another is to adjust the combustion air-to-fuel gas ratio (lambda value) to ensure stable and environmentally friendly combustion.

[0003] If the flames ignite properly, this is detected by at least one sensor in or on the combustion chamber, as is any (unexpected) extinguishing of the flames. Ionization meters, temperature sensors, or optical sensors, e.g., for UV radiation, are used as sensors. The flame detector ensures that combustion always occurs when fuel gas is supplied, or that the system shuts down if the flames fail to ignite or extinguish.

[0004] For cost reasons and to keep the complexity of a heating appliance low, such flame detectors are very reliable, but usually only a single unit, so that checking their function or implementing redundancy in measurement systems is not always feasible. Particularly when the output of a heating appliance is modulated, it can be difficult to reliably evaluate the signals from existing measurement systems within a short time and correctly classify them as (a) "flame present" or (b) "flame not present". Ionization measurements, in particular, are not always reliably interpretable at low outputs, especially with high hydrogen content in the fuel gas. Thermal sensors can also deliver incorrect or time-delayed signals when the output changes.

[0005] EP 0 225 655 A1 describes a method for starting a burner. During burner start-up, the air / fuel gas mixture is reduced until ignition occurs. As the mixture composition is reduced, the fan speed is decreased. This results in a mixture with a higher fuel gas content, which can facilitate flame ignition.

[0006] The object of the present invention is to at least partially solve the problems described with reference to the prior art and, in particular, to avoid unnecessary shutdowns due to false reports of flame extinguishment and a critical supply of air-fuel gas mixture despite flame extinguishment not being (immediately) detected, without additional expenditure on measuring instruments or other devices.

[0007] To solve this problem, a method, a heating device, and a computer program product according to the independent claims are provided. Advantageous embodiments and further developments of the invention are specified in the respective dependent claims. The description, particularly in conjunction with the drawing, illustrates the invention and provides further exemplary embodiments.

[0008] A method for operating a heating appliance with a combustion chamber and an ignition device and for ensuring the presence of flames in the combustion chamber during modulation of the heating appliance contributes to solving the problem, comprising the following steps: Modulating the power output of the heating appliance by changing the air and / or fuel gas supply; activating the ignition device in the combustion chamber during modulation, including a reduction in power output.

[0009] Every heating appliance has an ignition device to ignite combustion at the start of a combustion process. It is generally used only for this purpose and typically consists of an ignition electrode supplied with high voltage by ignition electronics, capable of generating an electric arc. By activating the ignition device during modulation of the heating appliance's output—that is, a change in the air and / or fuel gas supply—even a brief extinguishing of the flames would not pose a problem, because the ignition device would immediately reignite the subsequently supplied air-fuel gas mixture (unless a non-ignitable mixture is supplied, which is practically impossible during modulation). An (immediate) shutdown is not necessary, even if the extinguishing of the flames were detected by a flame sensor.Conversely, no (immediate) shutdown is required if a flame detector (briefly) erroneously reports that the flames have gone out, as extinguishing the flames and then reigniting poses no problem. Even extinguishing the flames undetected by the flame detector therefore has no consequences for operational safety. Because ignition conditions are created here, the permissible time for flame detection is available, which is longer than the permissible time for detecting a loss of flame. At the latest after the maximum permissible time for the supply of unburned air-fuel mixture has elapsed, a reliable signal from the flame detector must be present again.

[0010] To avoid unnecessary measures, the ignition device is preferably activated only during modulation where faulty signals from a flame detector are expected. This depends on the type of flame detector and the power ranges within which modulation occurs. As a rule, lower power levels and rapid power changes and reductions are more critical than, for example, slow increases at high load. In particular, thermal flame detectors can mistakenly interpret an intended power reduction as an unintended extinguishing of the flame, so the invention offers significant advantages precisely for such modulations.

[0011] Preferably, the ignition device is activated at least from the beginning of the modulation until its end. This prevents events at the beginning and end of a power change from extinguishing the flames without reignition.

[0012] If prolonged, continuous activation of the ignition device is undesirable or detrimental to it, the ignition device can, in a special embodiment, be switched on at intervals during modulation, with the time between two intervals being shorter than the maximum permissible time for the flow of air-fuel mixture without flames. This prevents overloads, excessive wear, or damage to the ignition device.

[0013] A particularly advantageous feature is that an evaluation unit checks during modulation whether the supply of fuel gas and air meets at least one condition, and ideally all conditions, for generating an ignitable mixture in the combustion chamber. In typical heating appliances, the position of a fuel gas valve and the speed of a fan are always available in a control unit, often along with other parameters such as the temperature of the air-fuel gas mixture, the humidity of the air, etc., so that an evaluation of this data provides a reliable result as to whether a supplied air-fuel gas mixture is ignitable. If this is the case, then with the ignition device activated, the flames will not extinguish without immediate reignition (within the maximum permissible time without flames).

[0014] When the procedure is implemented as described so far, the signals of a flame detector can be (briefly) ignored during modulation (at least for triggering measures), thus avoiding unnecessary shutdowns.

[0015] The invention is preferably used when an ionization measuring device and / or at least one thermal sensor are employed as flame detectors during the operation of the heating appliance, the signals of which are (briefly) ignored during a modulation phase. This is particularly advantageous when using fuel gas with a high hydrogen content. It is obvious that these signals cannot and should not be permanently ignored. Rather, this is a brief process phase required for a verification procedure. These sensor data are taken into account again after the start of this process phase, at the latest when the maximum permissible operating time of the heating appliance with gas supply but without flame has been reached.

[0016] Consequently, it is advantageous that the heating device can be operated with hydrogen as fuel gas or a hydrogen-containing fuel gas.

[0017] A heating device also contributes to solving the problem, comprising an arrangement for ensuring the presence of flames in a combustion chamber during modulation of a heating device, wherein the heating device has an ignition device and a control and regulation unit as well as an evaluation unit which are configured to activate the ignition device during modulation of the heating device.

[0018] Preferably, the evaluation unit is configured to detect whether an ignitable mixture is being supplied to the combustion chamber. If this is the case and the ignition device is activated, the maximum permissible time without flames is maintained to ensure a reliable reading from the flame detector. Therefore, signals from flame detectors can be temporarily ignored or evaluated with a delay during the modulation period without creating an increased risk. Unnecessary shutdowns are also avoided.

[0019] Another aspect concerns a computer program product comprising commands that cause the described heating device to execute the described procedure. The evaluation electronics, for example, require a program and data to perform the desired function as a replacement for a flame sensor during modulation, and both must be updated occasionally.

[0020] The explanations of the procedure can be used to further characterize the arrangement, and vice versa. The arrangement can also be set up in such a way that the procedure is carried out using it.

[0021] A schematic embodiment of the invention, to which it is not limited, and the functioning of the method will now be explained in more detail with reference to the drawing. The drawing shows: Fig. 1: a heating device with blower and control and regulating unit and Fig. 2: a diagram to illustrate the processes according to the invention when the power of a heating device is modulated.

[0022] Fig. 1 Figure 1 schematically shows a heating appliance 1 designed specifically for operation with hydrogen as fuel gas or with hydrogen-containing fuel gas. However, it is also applicable to other fuel gases. The heating appliance 1 has a blower 2 which supplies a burner 3 with air from an air supply 4. Fuel gas from a fuel gas supply 6 is mixed with the air via a fuel gas valve 5. A control unit 7 is connected to the blower 2 and the fuel gas valve 5 via data lines 13, so that a mixture suitable for ignition and / or continuous operation can be generated and the settings made for this purpose (e.g., speed of the blower 2 and opening of the fuel gas valve 5) can be reported back. When this mixture is burned in a combustion chamber 15, flames 16 are produced, the effect of which (and thus their presence) is observed by at least one sensor 10 at a measuring point 19.Sensor 10 serves as a flame sensor and can be used to regulate the air-fuel ratio. An ionization meter, a UV sensor, a temperature sensor, or another measuring system can be used, depending on the requirements of the respective heating appliance 1. Sensor 10 is also connected to the control unit 7 via a data line 13. The combustion chamber 15 is surrounded by a housing 8, which contains only indicated heat exchanger surfaces. Combustion gases are discharged to the environment via an exhaust system 9. An ignition electrode 17 is located in the combustion chamber 15 to ignite the combustion; this electrode is connected to an ignition control unit 12 via an ignition line 14. A display 18 (which may be located elsewhere for remote maintenance) provides information about the status of the heating appliance 1.In the present invention, an evaluation electronics unit 11 (which can be integrated into the control unit 7) evaluates, for example, the speed of the blower 2 or a corresponding parameter and a position of the fuel gas valve 5 in order to check whether an ignitable mixture is supplied to the combustion chamber 15.

[0023] It has become apparent how in Fig. 2This illustrates that it can be advantageous, at least during critical modulations of the output of a heating device 1, particularly when reducing output in an already low power range, to activate the ignition device 12, 14, 17 during modulation. This would ensure that even if the flames 16 were to go out, for example due to an irregularity in the supply of the air-fuel mixture, ignition would occur very quickly, thus eliminating the need for a warning or shutdown. Furthermore, the signals from a sensor 10 serving as a flame detector could even be temporarily ignored or evaluated with a time delay. The diagram shows, as an example, the rotational speed n of the fan 2 (Y-axis) as a function of time t (x-axis) before, during, and after a modulation of the output of the heating device 1.Furthermore, the activity z of the ignition device 12, 14, 17 is shown, whereby it can be seen that the ignition device 12, 14, 17 is not active before and after the modulation, but is active during the modulation.

[0024] The present invention increases the safety and availability of a heating device 1 during power modulation, thereby avoiding unnecessary shutdowns due to faulty or time-delayed signals from a flame detector and ensuring safe and rapid reignition if the flames go out during the modulation process. Reference symbol list

[0025] 1 Heater 2 Blower 3 Burner 4 Air supply 5 Fuel gas valve 6 Fuel gas supply 7 Control and regulation unit 8 Housing 9 Exhaust system 10 Sensor (flame monitor) 11 Evaluation electronics 12 Ignition control 13 Data lines 14 Ignition lead 15 Combustion chamber 16 Flames 17 Ignition electrode 18 Display 19 Measuring point

Claims

1. Method for operating a heating appliance (1) with a combustion chamber (15) and an ignition device (12, 14, 17) and for ensuring the presence of flames (16) in the combustion chamber (15) during modulation of the heating appliance (1), comprising the following steps: - modulating the output of the heating appliance by changing the air and / or fuel gas supply; - activating the ignition device (12, 14, 17) in the combustion chamber (15) during modulation, including a reduction in power.

2. Method according to claim 1, wherein the ignition device (12, 14, 17) is activated from the start of the modulation until its end.

3. Method according to claim 1, wherein the ignition device (12, 14, 17) is switched on at intervals during modulation, wherein the time between two intervals is less than a maximum permissible time for the flow of air-fuel mixture without flames (16).

4. Method according to claim 1, 2 or 3, wherein an evaluation electronics (11) checks during modulation whether the supply of fuel gas and air fulfils at least one condition for producing an ignitable mixture in the combustion chamber (15).

5. Method according to one of the preceding claims, wherein the signals from a flame detector are ignored during modulation.

6. Method according to one of the preceding claims, wherein an ionisation measuring device and / or at least one thermal sensor are used as flame detectors (10) during operation of the heating appliance (1), the signals of which are ignored during modulation.

7. Method according to one of the preceding claims, wherein the ignition device (12, 14, 17) is only activated during modulation in which faulty and / or delayed signals from a flame detector (10) are to be expected.

8. Method according to one of the preceding claims, wherein the heating appliance (1) is operated with hydrogen as fuel gas or a hydrogen-containing fuel gas.

9. Heating appliance (1) with an arrangement for ensuring the presence of flames (16) in a combustion chamber (15) during modulation of the heating appliance (1), wherein the heating appliance (1) has an ignition device (12, 14, 17), a combustion chamber (15), a control and regulation unit (7) and an evaluation unit (11) which are designed to activate the ignition device (12, 14, 17) during modulation of the heating appliance (1) in accordance with a method according to one of claims 1 to 8.

10. Arrangement according to claim 9, wherein the evaluation unit (11) is designed to detect whether an ignitable mixture is being supplied to the combustion chamber (15).

11. Computer program product comprising instructions that cause the heating appliance (1) to execute the method according to one of claims 1 to 8 according to one of claims 9 or 10.