ARRANGEMENT OF AN OPTICAL SENSOR ON A WINDOW OR WALL TO A COMBUSTION CHAMBER OF A HEATING DEVICE

Description

[0001] The invention relates to an arrangement of an optical sensor on a window (sight glass) or a wall of a combustion chamber of a heating device, in particular for the combustion of hydrogen-containing fuel gas, preferably with a hydrogen content greater than 10%, in particular greater than 50%, and most preferably greater than 97%. Hydrogen as a fuel gas or as an additive to fuel gases is becoming increasingly important, and great efforts are being made to upgrade new or existing heating devices for operation with it.

[0002] This applies not only to large systems, but also to wall-mounted water heating units and, more generally, to heating appliances for heating buildings and / or providing hot water. Hydrogen differs from previously used fuel gases in several respects when it is burned (with ambient air). In particular, a hydrogen flame is almost invisible to the human eye, radiates less heat than flames generated with carbon-containing fuels, and hydrogen flames require different measuring systems for monitoring than other fuels. In particular, ionization measurements do not always provide reliable signals when the fuel gas contains high proportions of hydrogen. The present invention is therefore particularly, but not exclusively, applicable to heating appliances operated with pure hydrogen or with fuel gas containing hydrogen.

[0003] The use of optical sensors (for the visible, but especially also the ultraviolet range of light) for flame monitoring and combustion control using optical filters is already known for applications in heaters 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, and DE 19 509 704 A1 also deal extensively with optical measurement systems for flame monitoring. Such optical sensors can also be used in the infrared range.

[0004] The structural connection of an optical sensor can be designed in different ways. In particular, it is aligned with the flame in the combustion chamber using a holder so that the optical sensor can measure this flame. The holder must meet certain structural requirements. In addition, the light must be able to escape from the combustion chamber in order to be optically detected. A window is incorporated into a housing of the combustion chamber, particularly in a burner door next to a burner, for this purpose. This allows the optical sensor to detect the light of the combustion. When detecting infrared radiation (i.e. thermal radiation), the wall of a combustion chamber can also be observed without a window, at least in suitably designed locations.

[0005] It was recognized that the optical evaluation of hydrogen combustion is subject to a conflict. The closer the sensor is to the flame and the combustion chamber, the clearer the resulting flame signal. However, this also means greater exposure to the heat of combustion. Depending on the sensor's sensitivity, the distance to the flame can be increased. If sufficient sensitivity is not available for a distance sufficient to limit the temperature, the optical sensor must be positioned very close to or directly on a wall or window of the combustion chamber. However, this leads to high temperatures during operation, which optical sensors cannot tolerate.

[0006] Such an arrangement of an optical sensor is described in US 2017 / 003 8251 A1, in which an optical sensor is proposed in a housing. The housing has a window and can be connected to a combustion system. However, when used in conjunction with a combustion chamber of a heating device, the sensor in the proposed design can reach excessively high temperatures.

[0007] EP 3 872 462 A1 also discloses an optical sensor unit for measuring the optical emissions from the combustion chamber caused by combustion through a sight glass. To protect the sensor unit, it is cooled by a fluid line. The disadvantages of this arrangement are complex and there is a risk of leakage at the connection to the fluid line.

[0008] The object of the present invention is to at least partially solve the problems mentioned with reference to the prior art. In particular, an arrangement with an optical sensor for observing flames in a combustion chamber is to be created that largely prevents overheating of the optical sensor. The arrangement is to be designed to be cost-effective and robust for everyday use.

[0009] This object is achieved by an arrangement according to the independent claim. Advantageous embodiments and further developments of the invention are specified in the dependent claims. The description, particularly in conjunction with the drawings, illustrates the invention and provides further exemplary embodiments.

[0010] To achieve the object, an arrangement of (at least) one optical sensor on the outside of a window or a wall to a combustion chamber of a heating device contributes, wherein the optical sensor is arranged less than 2 cm [centimeters], preferably less than 1 cm, in particular without any distance, from the window or the wall, but is (largely) thermally decoupled from it.

[0011] A (large) thermal decoupling can be achieved by transferring as little heat as possible to the optical sensor and / or by dissipating heat transferred to the optical sensor as quickly as possible, so that the optical sensor is kept within a permissible operating temperature range.

[0012] The heater is particularly designed for stationary installation or setup, e.g., in or on a building. The combustion chamber comprises a burner through which a fuel-air mixture is introduced into the combustion chamber and, after entering the combustion chamber, ignited and burned. The at least one sensor is positioned at a distance from a control unit of the heater, with the signals or data acquired by the sensor preferably being transmitted via cable to the control unit positioned in a significantly cooler area. The at least one sensor is particularly designed to detect visible light, in particular (also) the ultraviolet range, or to detect infrared radiation. If a distance is provided, this describes the "free path" from the sensor to the window or wall where the radiation to be detected leaves the combustion chamber.The at least one sensor is arranged outside the combustion chamber.

[0013] The window or wall has thermally insulating properties. Sensors sensitive to infrared light do not require a window that is transparent to the human eye. Such measurements can also be performed behind a wall, but thermally insulating properties, e.g., a two-layer wall with an insulating filling, have a negative impact on the quality and speed of the measurements because temperature changes can only take effect slowly and are integrated over a certain time (i.e., performed as if with a type of low-pass filter). For measurements in the ultraviolet range, a window that is permeable to such radiation is required. However, this window can be designed with a double wall and an insulating filling, making it less permeable to thermal radiation (infrared radiation).In this way, heat can be effectively kept away from an optical sensor for ultraviolet light despite good quality and speed of the measurements.

[0014] The window or wall is constructed of at least two layers separated by an insulating filling, preferably gas, especially air. Double glazing and multi-layer walls are used with great success in other technical fields for thermal insulation.

[0015] Alternatively or additionally, the optical sensor is equipped with active or passive cooling. Passive cooling occurs through heat radiation, heat conduction, and / or convection, essentially without the influence of moving parts or gas flow. Active cooling involves actively passing a cooling medium, particularly air or a fuel gas mixture or cooled exhaust gas, over the optical sensor.

[0016] Particularly preferably, the optical sensor is mounted on a heat sink with cooling fins or an otherwise enlarged surface. This improves and evens out heat dissipation.

[0017] In a special embodiment, the sensor is cooled by means of at least one heat pipe. A heat pipe is a tube partially filled with a liquid that boils and condenses within a desired temperature range and is closed at its ends. This tube can very effectively transport heat from a hot end to a cold end within this temperature range. The cold end can thus be arranged in an area of ​​the heating system where a low temperature prevails, for example in the air stream of incoming combustion air or incoming fuel gas, but also in an exhaust gas stream after it has cooled in a heat exchanger. The hot end is connected to the optical sensor and dissipates heat from it. This allows for very effective, cost-effective, and less susceptible to failure cooling of the optical sensor.

[0018] Schematic embodiments of the invention, to which the invention is not limited, will now be explained in more detail with reference to the drawings, in which like parts are provided with like reference numerals throughout the figures. They show: Fig. 1: schematically shows a combustion chamber of a heater with an external optical sensor, Fig. 2: schematically and enlarged a longitudinal section through a double-walled window and Fig. 3: schematically shows the arrangement of a sensor with heat sink and cooling fins.

[0019] Fig. 1 schematically shows a combustion chamber 2 of a heater 1, which is surrounded by walls 3 forming a housing. Located in the housing is a burner door 4 (or flap), 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.

[0020] During the combustion of this mixture, which exits from the burner 5 into the combustion chamber 2 during operation of the heater 1, flames 7 are created that are almost invisible to the human eye, at least when pure hydrogen is used as the fuel gas. Nevertheless, these flames 7 emit optical radiation, particularly in the ultraviolet (or infrared) spectral range, which can be observed by means of an optical sensor 9 connected to a control and regulation unit (not shown) via a measuring line 10.

[0021] Due to the high temperatures in a combustion chamber 2, the sensor 9 is usually arranged outside in front of a window 8 (sight glass), which is transparent to the optical radiation to be observed. In the case of infrared sensors, this can also be a suitable section of the wall 3. Since the window 8 and its surroundings can also be at very high temperatures, the optical sensor 9, which serves, for example, as a flame detector or to regulate combustion, is arranged close to the window 8, since the optical radiation arriving at the optical sensor 9 decreases with the distance from the window 8. Since the sensitivity cannot be increased indefinitely, small distances of less than 2 cm, preferably less than 1 cm, from the window 8 are usually required.

[0022] Cooling 16 may be required. Such targeted cooling can particularly preferably be achieved, for example, by a so-called heat pipe 17, whose hot end 18 is in contact with the optical sensor 9 and whose cold end 19 is located in a cooler area, particularly around which incoming air, fuel gas, or mixture flows. Thus, no energy is lost from the heater 1, since the heat extracted at the optical sensor 9 is fed back into the process.

[0023] Fig. 2 illustrates an alternative or additional possibility for protecting the optical sensor 9 from overheating. For this purpose, the window 8 is designed as a double-walled structure with a first layer 11 and a second layer 12, between which there is an insulating filling 13, which can in particular be air or a thermally well-insulating gas. Such a structure is also possible for a location where infrared radiation is to be measured behind the wall 3. Such a location is also understood here under the term "window" 8. However, a thermally insulating structure always delays the effects of infrared radiation, so the described measure cannot always be used for an optical sensor 9 in the infrared range. However, with ultraviolet radiation, (UV-permeable) double glazing is very useful against overheating of the optical sensor 9.

[0024] Fig 3shows an embodiment of an optical sensor 9 with a heat sink 14, which in turn has cooling fins 15. With such a heat sink 14, a simple cooling 16 (indicated by arrows) can be realized, in particular by passing a portion of the supplied ambient air or fuel gas (or a mixture thereof) over the heat sink 14.

[0025] The present invention allows the attachment of an optical sensor 9 directly or close to a window 8 or a wall 3 to a combustion chamber 2 while simultaneously maintaining a permissible temperature range of the optical sensor 9. In this way, combustion processes operated with hydrogen-containing fuel gas can also be reliably monitored. List of reference symbols

[0026] 1 Heater 2 Combustion chamber 3 Wall (housing) 4 Burner door 5 Burner 6 Mixture supply line 7 Flames 8 Window / sight glass 9 (optical) sensor 10 Measuring line 11 First layer 12 Second layer 13 Insulation filling (gas / air) 14 Heat sink 15 Cooling fins 16 Cooling 17 Heat pipe 18 Hot end 19 Cold end

Claims

1. Arrangement of an optical sensor (9) on the outside of a window (8) or on a wall (3) to a combustion chamber (2) of a heating appliance (1), wherein the sensor (9) is arranged at a distance of less than 2 cm from the window (8) or the wall (3), but is thermally decoupled therefrom, characterised in that the window (8) or the wall (3) is constructed from at least two layers (11, 12) separated from one another by an insulating filling (13).

2. Arrangement according to claim 1, wherein the window (8) or the wall (3) has heat-insulating properties.

3. Arrangement according to one of the preceding claims, wherein the optical sensor (9) is provided with active or passive cooling (16).

4. Arrangement according to claim 3, wherein the optical sensor (9) is arranged on a heat sink (14) with cooling fins (15)5. Arrangement according to one of the preceding claims, wherein the optical sensor (9) is cooled by means of at least one heat pipe (17).