METHOD AND ARRANGEMENT FOR DETECTING CONTAMINATION IN THE LIGHT PATHWAY OF AN OPTICAL SENSOR FOR OBSERVING A FLAME IN A COMBUSTION ROOM AND COMPUTER PROGRAM PRODUCT

Description

[0001] The invention relates to a method and an arrangement for detecting and / or compensating for contamination in the light path of an optical sensor on a window (sight glass) to a combustion chamber of a heating appliance, in particular for the combustion of hydrogen-containing fuel gas, preferably with a hydrogen content greater than 10%, particularly greater than 50%, most preferably greater than 97%, as well as a corresponding computer program. Hydrogen as a fuel gas or as an additive to fuel gases is becoming increasingly important, and considerable efforts are being made to adapt new or existing heating appliances for operation with it.

[0002] This concerns not only large systems, but also wall-mounted units for heating water and, more generally, heating appliances for building heating and / or hot water supply. Hydrogen differs from previously used fuel gases in several respects during its combustion (with ambient air). In particular, a hydrogen flame is almost invisible to the human eye, radiates less heat than flames generated with carbon-based fuels, and hydrogen flames require different measuring systems for monitoring than those used with other fuels. Ionization measurements, in particular, do not provide reliable signals at high hydrogen concentrations in the fuel gas. The present invention is therefore particularly, but not exclusively, applicable to heating appliances that operate with pure hydrogen or with fuel gas containing hydrogen.

[0003] The use of optical sensors (for the visible, but especially also for the ultraviolet range of light) for flame monitoring and combustion control using optical filters is already known for applications in heating appliances that are operated with hydrogen-containing fuel gas, for example from DE 10 2019 101 329 A1. EP 2 223 016 B1, US 5 829 962 A, DE 41 21 987 A1 and DE 19 509 704 A1 also deal extensively with optical measuring systems for flame monitoring.

[0004] The optical sensor can be mounted in various ways. A bracket positions the sensor so that it is aligned with the flame in the combustion chamber, enabling it to measure the flame. This bracket must meet certain design requirements. Furthermore, light must be able to escape from the combustion chamber to be optically detected. A window is incorporated into the combustion chamber housing, particularly in a burner door next to a burner, to allow the optical sensor to capture the combustion light.

[0005] However, contamination can occur at various points along the path that light travels from the flame in the combustion chamber to the optical sensor. In particular, contamination or alterations (which impair light transmission) can occur on both sides of a sight glass or optics of the optical sensor, as well as within the optical sensor itself. Contamination and other such alterations are collectively referred to as "contamination" in the following. For example, dust particles can accumulate on the optics, reducing the light signal. Contamination can also be deposited on the sight glass due to air cooling of the optical sensor. Finally, alterations can result from excessive heat transfer to the sensor and its components.

[0006] DE 41 21 987 A1 describes a method and a device for controlling the fuel-air ratio in the fuel gas supply of a radiant burner. For this purpose, a sensor is provided for detecting the radiation emitted by the flame, which transmits the radiation from a window of the combustion chamber via a first optical fiber cable. In addition, a calibration radiation source is provided, the emitted radiation of which is guided to the sensor via both a second optical fiber cable and the first optical fiber cable. A cover plate can block the radiation path from the flame to the sensor, thus enabling system calibration even when the burner is lit.

[0007] German patent DE 20 2006 021 270 U1 proposes the use of an electromagnetic radiation source, hereinafter referred to as a light source or luminaire, to check the cleanliness of the light path. Radiation emitted by the electromagnetic radiation source can be sent through the window (whose cleanliness is to be checked) onto an external reflector and from there reflected back to the sensor. The luminaire can generate a pulsed output signal to distinguish the signal from the background radiation.

[0008] US patent 2017 / 003 8251 A1 describes a system very similar to DE 20 2006 021 270 U1, comprising a flame sensor for a combustion device and an electromagnetic radiation source. The radiation source can emit radiation through an observation window of the flame sensor, and a dirty observation window can be detected when the radiation is reflected from the window.

[0009] The aforementioned state of the art has in common that an additional radiation source is necessary to detect contamination in the light path. This is complex and significantly increases the overall complexity.

[0010] The object of the present invention is to at least partially solve the problems mentioned with reference to the prior art. In particular, a method and an arrangement for detecting and / or compensating for contamination in the light path when observing flames in a combustion chamber by means of a sensor are to be provided.

[0011] To solve this problem, a method, an arrangement, and a computer program product according to the independent claim 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.

[0012] A method for detecting contamination in a light path from a flame in a combustion chamber to an optical sensor contributes to solving the problem, wherein measured values ​​from the optical sensor are compared with a stored measured value for this flame state at at least one defined state and, if there is a deviation above a predefinable difference, a conclusion is drawn that there is contamination in the light path.

[0013] Since heating systems are operated over long periods and often with only annual or even less frequent maintenance, a great deal of experience exists regarding their long-term behavior. It has been shown that certain (defined) states (with consistently identical operating conditions) occur frequently, and the same measured values ​​are consistently obtained from various sensors, provided they are functioning correctly. This also applies, in principle, to light emitted by the flame and received by an optical sensor. This can be used to detect soiling by measuring the readings under one or more defined operating states (e.g.,...).Under specific load conditions (characterized by a fan speed and a fuel gas valve position, possibly also taking ambient temperature and humidity into account), the measured values ​​of the optical sensor are recorded and stored in a memory as a reference when the system is new. If at least one such defined condition is later reached or deliberately set (this does not necessarily have to happen every time, but can occur at predefined time intervals), the current measured value of the optical sensor can be compared with the stored value. If the difference is zero or very small (for example, less than 1% of the stored measured value), the optical sensor is functioning correctly and the light path is free of relevant contamination. However, if the deviation exceeds a predefined difference, e.g.,If the measured value exceeds 1%, and especially 5%, of the stored value, then contamination of the optical path and / or aging of the optical sensor must be assumed. Since the aging behavior of sensors is usually well known, contamination of the optical path can thus be detected.

[0014] The method may include detecting the presence of a defined or predetermined flame state in the combustion chamber or heating appliance and then initiating the procedure for detecting contamination in the light path. Alternatively or cumulatively, the method may include setting a defined or predetermined flame state in the combustion chamber or heating appliance, defined by the heating appliance or its control unit, before and / or at the beginning of the procedure for detecting contamination in the light path. Means and / or processes may be provided to verify and evaluate whether the defined or predetermined flame state actually exists in the combustion chamber or heating appliance. Means and / or processes may be provided to maintain the defined or predetermined state for a specified period of time, for example, by blocking modulation.It is possible that, within the process for detecting contamination in the light path, several defined or predetermined states are activated and / or traversed before a decision is made regarding the degree of contamination. It is possible that deviations from several (temporally reported and / or different) states are determined and then compared separately, cumulatively, and / or on average with the predetermined difference. The stored measured values ​​can be provided as concrete data, curves, characteristic maps, or the like. A comparator for the current and stored measured values ​​can be provided, which, for example, can be part of a control unit (of the sensor and / or the heating device).The conclusion that contamination has occurred includes, in particular, the (automatic) creation, transmission, provision in a processable format and / or display of information that characterizes the increased degree of contamination.

[0015] The method proposed here offers the particular advantage that a check for contamination in the light path can be carried out simultaneously with the observation of (controlled) flames in a combustion chamber using the (same) sensor. It is not necessary to interrupt flame observation or to make separate adjustments to the light path and / or radiation sources. Rather, it is possible to perform the check in parallel with the proper operation of the heating appliance.

[0016] It should be noted that instead of using data stored in the initial state, a calibration light source can also be switched on in the combustion chamber (without a flame) as a defined operating state. The light from this light source is received by the optical sensor and results in a current measurement, which can be compared with a value stored in the initial state. This eliminates the need to wait until a defined operating state occurs or can be set to measure the contamination; instead, the calibration light source can be switched on at regular intervals. However, it must be ensured that the calibration light source itself cannot become contaminated.

[0017] If the optical sensor is used solely as a flame detector (determining whether a flame has ignited, is burning, or has extinguished), a decrease in the measured value over time due to contamination is not a safety issue, as long as the deviation does not exceed a safety threshold, which could be, for example, 30 or 50% of the stored measured value. The function of a flame detector can continue to be reliably fulfilled for a long time even with decreasing measured values, since contamination does not appear or increase suddenly, but rather develops over extended periods of weeks, months, or even years.

[0018] This method is preferably used in heating systems that are operated with pure hydrogen or a hydrogen-containing fuel gas, where the flame is generated by the combustion of this hydrogen-containing fuel gas and the sensor is sensitive to ultraviolet and / or infrared light. In such cases, other measuring systems such as ionization meters cannot always operate reliably.

[0019] To increase the reliability and redundancy of the analyses, measurements are taken at at least two different defined flame states and compared with stored measurements for these states before a decision is made regarding fouling. This enables a reliable assessment of fouling and its impact on measurements at different states.

[0020] In a specific configuration, if a deviation exceeding a predefined threshold is detected, a message is issued and / or the flame is shut off. In most cases, a shutdown will not be necessary; it will only be triggered if the deviation exceeds a predetermined safety threshold. However, a warning message (display on the unit, message to remote maintenance, etc.) is almost always advisable so that the fouling can be removed during the next maintenance or even brought forward. If necessary, heating mode or (temporarily) burner operation can also be activated to reduce fouling.

[0021] A warning message is therefore preferably triggered without a shutdown, as long as the deviation does not exceed a predetermined or specifiable safety threshold.

[0022] It is possible to correct a detected deviation below a safety threshold by applying a correction factor to the measured values. This is particularly useful when the optical sensor is used not only as a flame detector but also to control the combustion process. A reading that is too low due to contamination would distort the control, so correcting it to the expected reading when the sensor is new improves the accuracy of the control. If information about contamination is collected under several defined operating conditions, even non-linear effects can be corrected. In most cases, however, a simple correction factor by which the current reading is multiplied will suffice.

[0023] A device for detecting contamination in a light path from a flame in a combustion chamber to an optical sensor also contributes to solving the problem. The optical sensor is connected via measuring leads to evaluation electronics configured to compare measured values ​​at a defined flame state with stored values ​​for that state. If a deviation exceeds a predefined difference, the electronics trigger a warning and / or flame shutdown. Most systems, especially heating systems, have a central control unit (typically with at least one microprocessor and storage space for calibration data, programs, and other data) into which the evaluation electronics can be integrated.

[0024] Preferably, especially in heating systems operated with hydrogen or hydrogen-containing fuel gas, the optical sensor is sensitive to ultraviolet and / or infrared light. Such light is emitted particularly by a hydrogen flame.

[0025] In a typical design, the optical sensor is located outside the combustion chamber behind a window into the combustion chamber. This window can, for example, be incorporated into a so-called burner door, to which a burner projecting into the combustion chamber is also attached.

[0026] The evaluation electronics store measured values ​​for two or more defined operating states of the flame. These values ​​can either be recorded when the system is new or predefined based on empirical data for a specific system type. Preferably, during commissioning, values ​​for various defined states that occur repeatedly in a particular system are stored when the system is new.

[0027] The evaluation electronics can also be configured to calculate a correction and apply it to current measured values ​​if the comparison of the current measured values ​​with a stored measured value under a defined flame condition reveals a deviation above a predefined difference but below a safety threshold. In this way, a virtually new state of the system can be simulated, allowing the measured values ​​to be used for control as if the system were new, even though there is (increasing) soiling of the light path.

[0028] Another aspect concerns a computer program product, comprising commands that cause the described arrangement to execute the described procedure. The evaluation electronics, for example, require a program and data to perform the desired function, such as flame monitoring or control, and both must be updated occasionally.

[0029] 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.

[0030] A schematic embodiment of the invention, to which it is not limited, will now be explained in more detail with reference to the drawing. It illustrates: Fig. 1: schematically a combustion chamber of a heating device with external optical sensor and evaluation electronics.

[0031] Fig. 1 Figure 1 schematically shows a combustion chamber 2 of a heating appliance 1, which is surrounded by a housing 3. A burner door 4 (or flap) is located in the housing 3, to which a burner 5 is attached, projecting into the combustion chamber 2. This burner 5 is supplied with a mixture of air and hydrogen or hydrogen-containing fuel gas via a mixture supply line 6.

[0032] During the combustion of this mixture, which exits from the burner 5 into the combustion chamber 2 when the heating appliance 1 is in operation, a flame 7 is produced that is almost invisible to the human eye, at least when pure hydrogen is used as the fuel gas. Nevertheless, this flame 7 emits optical radiation, particularly in the ultraviolet spectral range, which can be observed by means of an optical sensor 9. Due to the high temperatures in a combustion chamber 2, the optical sensor 9 is usually located on the outside in front of a window 8 (sight glass), which is transparent to the optical radiation to be observed. Since the window 8 and its surroundings can also be at very high temperatures, the optical sensor 9 is often positioned at a certain distance, e.g., 2 cm to 20 cm, preferably 5 to 15 cm, from the window 8. The further the optical sensor 9 is from the flame 7, the more sensitive it must be to function, e.g.,to function as a flame detector or to regulate combustion, since the optical radiation arriving at the optical sensor 9 decreases with distance. Because the sensitivity cannot be increased arbitrarily, small distances of a few centimeters to the window 8 are usually required. Therefore, the optical sensor 9 is often cooled with a cooling airflow 11 (indicated by arrows), especially with air that is drawn in to form the mixture to be burned.

[0033] The optical sensor 9 can therefore be located in or near an air intake duct (not shown here) so that it remains within a permissible temperature range, e.g., below 70°C. Contaminants 18 can form over time both on the inside (in the combustion chamber 2) of the window 8 and on its outside, as well as on the sensor 9 and any associated optics. Generally, contaminants 18 can form at various points and for various reasons along the light path 17 between the flame 7 and the optical sensor 9, increasingly reducing the current measured values ​​compared to a new state over time.

[0034] Such contamination 18 is to be detected using the described method or arrangement and, if necessary, compensated for by a correction. For this purpose, the optical sensor 9 is connected to an evaluation unit 12 via a measuring line 10. This unit contains a comparator 13, in which a current measured value under a defined operating condition is compared with a measured value stored in a reference data memory 14 when the heating device 1 was new (or cleaned). The current measured value is then forwarded from the comparator 13 to a correction module 15, together with information about the deviation of the current measured value from the stored measured value. If the deviation exceeds a predefined difference, the correction module 15 activates a warning / signaling device 16, which generates a warning message (acoustic, visual, or electronic).If the deviation exceeds a safety threshold, the flame 7 is (additionally) shut off for safety reasons, thus terminating the fuel gas supply. The safety threshold is set such that the optical sensor 9 can function reliably as a flame detector until it is reached. The correction module 15 can determine a correction (usually a correction factor) from the deviation of the current measured values ​​from the measured values ​​stored when new (i.e., expected with a clean light path 17) and correct the current measured values ​​by this factor so that they then correspond to the expected measured values ​​and can be routed via a relay 19 to their intended purpose.This forwarding (possibly with correction) takes place throughout the entire operation, so that the evaluation electronics 12 only become active when a defined state is reached (or set) in which the described comparison can provide new information about contamination 18. By analyzing changes in contamination 18 per unit of time, information about the expected remaining operating time of the heating device 1 (until maintenance or shutdown becomes necessary) can also be obtained.

[0035] The present invention enables the detection of contaminants 18 in the light path 17 from the flame 7 to the optical sensor 9 and an estimation of the remaining trouble-free operating time of a heating device, as well as the compensation of contaminants 18 by correcting current measured values. This allows for increased safety, particularly in heating devices operated with hydrogen or hydrogen-containing fuel gas, and enables the early detection of necessary maintenance measures. Reference symbol list

[0036] 1 Heater 2 Combustion chamber 3 Housing 4 Burner door 5 Burner 6 Mixture supply line 7 Flame 8 Window / sight glass 9 Optical sensor 10 Measuring line 11 Cooling air flow 12 Evaluation electronics 13 Comparator 14 Reference data storage 15 Correction module 16 Warning / signaling device 17 Light path 18 Contamination 19 Transmission of the (corrected) measured value

Claims

1. Method for detecting contamination (18) in a light path (17) from a flame (7) in a combustion chamber (2) to an optical sensor (9), wherein measured values measured by the optical sensor (9) in at least one defined state of the flame (7) are compared with a stored measured value for this defined state of the flame (7), characterised in that, in the event of a deviation above a predeterminable difference, contamination (18) in the light path (17) is concluded.

2. Method according to claim 1, wherein the flame (7) is generated by combustion of a hydrogen-containing fuel gas, and the optical sensor (9) is sensitive to ultraviolet and / or infrared light.

3. Method according to claim 1 or 2, wherein measured values are measured at at least two different defined states of the flame (7) and compared with stored measured values for these states.

4. Method according to one of the preceding claims, wherein, upon detection of a deviation above the preset difference, a message is issued and / or the flame (7) is switched off.

5. Method according to claim 4, wherein a warning message is triggered without switching off as long as the deviation does not exceed a safety threshold.

6. Method according to one of the preceding claims, wherein a detected deviation below a safety threshold is corrected by applying a correction to measured values.

7. Arrangement for detecting contamination (18) in a light path (17) from a flame (7) in a combustion chamber (2) to an optical sensor (9), comprising the optical sensor (9), a measuring line (10) and an evaluation electronics unit (12), wherein the optical sensor (9) is connected via the measuring line (10) to the evaluation electronics unit (12), which is designed to compare measured values at a defined state of the flame (7) with measured values stored for this state, characterised in that, in the event of a deviation above a predeterminable difference, a message and / or a shutdown of the flame (7) is triggered.

8. Arrangement according to claim 7, wherein the optical sensor (9) is sensitive to ultraviolet and / or infrared light.

9. Arrangement according to claim 7 or 8, wherein the optical sensor (9) is arranged outside the combustion chamber (2) behind a window (8) to the combustion chamber (2).

10. Arrangement according to one of claims 7 to 9, wherein measured values for two or more defined states of the flame (7) are stored in the evaluation electronics (12).

11. Arrangement according to one of claims 7 to 10, wherein the evaluation electronics (12) are designed to calculate a correction and apply it to current measured values if the comparison of the current measured values with a stored measured value for a defined state of the flame (7) results in a deviation above a predeterminable difference but below a safety threshold.

12. Computer program product comprising instructions that cause the arrangement according to one of claims 7 to 11 to execute the method according to one of claims 1 to 6.