METHOD FOR DETECTING THE EXTINGUISHMENT OF A BURNER FLAME

Description

[0001] In accordance with legal requirements, a flame detection device must be implemented in gas-fired heaters to ensure that no unburned fuel gas-air mixture is fed into the combustion chamber of the heater for longer than the maximum permissible time.

[0002] Gas-fired heaters that are fired with fossil fuel gases use the ionization current for reliable flame detection, based on freely available charge carriers in the flame and at least one electrode in the flame.

[0003] DE 29612 014 U1 relates to a gas burner for atmospheric, premixed operation, in which combustion is controlled by a flame detection device and adjusted to changing gas qualities. This device has a flame detection device on the burner surface with at least two flame detection elements. These are mounted at different distances from the burner surface and control combustion with their signals via a controller. With an increased number of thermocouples or ionization electrodes, the resolution can be increased accordingly.

[0004] DE 103 48 159 A1 discloses a burner arrangement, in particular for heating a furnace chamber of an industrial furnace with a diffusion burner, in which it is possible to regulate or maintain constant the fuel / combustion air ratio and the thermal power introduced into the furnace chamber when the type or quality of the fuel changes and / or under different operating conditions. For this purpose, a sensor is assigned to the burner surface of an auxiliary burner designed as a fully premixed surface burner, to which a fuel and a combustion air partial flow are supplied, with an oscillation being imposed on the combustion air partial flow. Two temperature sensors for detecting the flame temperature can be arranged at a defined distance from one another above the burner surface of the auxiliary burner.In this way, the temperature level or a gradient can be determined, which allows conclusions to be drawn about the energy input into the furnace chamber and the flame speed. The temperature measurements can be compared with setpoints in the evaluation / control unit. Depending on the difference between the setpoint and actual values, a control signal for the fuel and / or combustion air flow to the burner can be generated.

[0005] Ionization-based flame detection relies on the availability of a certain amount of freely available charge carriers. This proportion varies depending on the carrier gas. For example, in pure hydrogen combustion, the number of available charge carriers may be too low. Thus, reliable flame detection based on the electrical conductivity of the flame may not be feasible using hydrogen or gas mixtures with a high hydrogen content.

[0006] Against this background, novel methods for flame detection are desirable, particularly for heaters and burners that are operated for the combustion of gas mixtures with high hydrogen or even pure hydrogen.

[0007] The subsequently published EP 4 063 732 A1 describes a method and arrangement for monitoring flames in a heater that can be operated with hydrogen and / or a hydrogen-containing fuel gas. In this heater, this function of a flame monitor is performed by two temperature sensors that are differently designed and / or positioned. They are connected to the evaluation unit via measuring lines. A temperature change (or ignition or extinguishing) of the flames thus affects the two temperature sensors differently. A sensor that is thermally more inert and / or further away from a changing heat source (e.g., flames 7) follows a temperature change later and more slowly than a sensor that is less inert or closer. In this way, modulations of the heater and other events that lead to temperature changes can be distinguished from the ignition and extinguishing of the flames, thus avoiding unnecessary shutdowns.

[0008] The object of the present invention is to at least partially solve the problems described with reference to the prior art. This object is achieved by the invention according to the features of the independent patent claims. Further advantageous embodiments are specified in the dependent claims as well as in the description and, in particular, in the description of the figures. It should be noted that the person skilled in the art can combine the individual features in a technologically expedient manner and thus arrive at further embodiments of the invention.

[0009] Such a novel process, a burner configured accordingly for the process, a control unit and a computer program product are described below.

[0010] Described here is a method for detecting the extinguishing of a flame on a burner surface of a burner for combustion of gas, wherein temperature changes of the flame are measured at least with a first temperature sensor and a second temperature sensor, wherein the first temperature sensor and the second temperature sensor are arranged at a different distance from the burner surface, wherein an extinguishing of the flame is detected when a deviation of the temperature changes measured with the first temperature sensor and the second temperature sensor exceeds a limit value.

[0011] Flame extinguishing can also be detected if both temperature sensors measure a decreasing temperature change.

[0012] The burner preferably refers to a burner body, from which the fuel gas flows outward through a plurality of openings into a combustion chamber surrounding the burner and preferably containing ducts that then dissipate the heat generated by the burner. The burner body is preferably cylindrical and made of a metal material. The outer surface of the burner body (facing the combustion chamber) is referred to herein as the burner surface, from which the flames extend into the combustion chamber.

[0013] The distance between the temperature sensors and the burner surface refers in particular to a distance measured perpendicular (or normal, or perpendicular) to the burner surface. The so-called flame height depends on the burner's output, which is adjusted by the quantity or pressure of the mixture supplied to the burner for combustion. The temperature sensors can be thermocouples, for example. However, other types of temperature sensors are also possible. The temperature sensors are preferably suitable for the temperatures occurring at their respective installation location during burner operation. The temperature sensors are typically designed to withstand temperatures up to, for example, 1,300 °C.However, it is particularly preferred that the temperature sensors are positioned in such a way that, on the one hand, they enable good monitoring of temperature changes and temperatures of the flame, but, on the other hand, they are not arranged in the area in which the flames have the highest temperatures.

[0014] Preferably, first temperature sensors are arranged at a distance from the burner surface that is smaller than the distance at which the highest flame temperatures occur. Preferably, second temperature sensors are arranged at a distance from the burner surface that is greater than the distance at which the highest flame temperatures occur.

[0015] It has been found that flame detection based on a (single) temperature sensor positioned on the burner surface or in the flame cannot distinguish between the two scenarios of a power reduction and flame extinguishment within the legally specified timeframe when the power changes due to the thermal mass. In both cases, the difference would only become apparent later, through a change in the gradient and the associated approach to a target temperature.

[0016] At least two sensors, positioned at different locations relative to the flame height, exhibit opposing temperature behavior during modulation (i.e., when the burner's output changes), so that at least one sensor always measures an increasing temperature curve. This is especially true if the difference in the distance between the first temperature sensor and the second temperature sensor is appropriately selected. If the flame were to extinguish, however, both temperature sensors would measure a decreasing temperature curve within the legally specified time. In preferred embodiments, more than two temperature sensors can be arranged at different distances from the burner surface (e.g., three temperature sensors at three different distances from the burner surface).The three temperature sensors can then be subjected to an evaluation using the described method, in which the temperature changes measured with the individual temperature sensors are evaluated and it can then be determined whether the different temperature behavior measured with the individual temperature sensors allows a conclusion to be drawn about the extinguishing of the flame.

[0017] In principle, a change in output not only results in a change in the combustion output. In addition, the position of the flame relative to the burner surface usually also changes. In particular, the point of greatest temperature of the flame moves in the direction of the distance away from the burner surface or towards the burner surface. This shift of the flame relative to the burner surface when the output changes means that an opposite temperature behavior usually occurs when (only) a change in output occurs and the flame does not extinguish. The change in the position of the flame relative to the burner surface is due, for example, to the fact that the flame overall becomes larger when output increases and smaller when output decreases.In addition, the flow of the mixture out of the burner normally pushes the flame further away from the burner surface when power is increased and the flame moves closer to the burner surface again when power is reduced.

[0018] According to the invention, a deviation between the temperature change measured by the two temperature sensors can be used as a criterion for detecting flame extinguishing. This is generally possible by comparing the deviation with at least one limit value, whereby either the undershoot or the exceedance of a limit value can be used to detect flame extinguishing.

[0019] As an additional criterion, the extinguishing of the flame can be determined based on a synchronously decreasing temperature change, which is measured with the two temperature sensors.

[0020] It is particularly advantageous if a change in the burner's output is detected when an increasing temperature change is measured with one of the temperature sensors.

[0021] Increasing temperature changes do not usually occur at any of the temperature sensors when the burner goes out. An increasing temperature change at at least one of the temperature sensors is usually a clear indication of a change in burner performance.

[0022] It is also advantageous if at least one of the temperature sensors also measures a temperature and the limit value is set depending on the measured temperature.

[0023] Temperature is often also a measure of the burner's performance. In some versions, the temperatures of several temperature sensors can be weighted to determine the limit value.

[0024] Furthermore, it is advantageous if the first temperature sensor is arranged directly on the burner surface and is designed to measure a temperature change of the burner surface.

[0025] It is also advantageous if the first temperature sensor is arranged on an underside of the burner surface and is designed to measure a temperature change of the burner surface.

[0026] At the positions suggested here for initial temperature sensors, the temperature response to power changes is typically relatively slow because the thermal mass of the burner reduces the measurability of temperature changes. Furthermore, the temperatures occurring at these locations are typically relatively low, or low compared to the highest temperatures occurring in the flame. For this reason, initial temperature sensors are typically not exposed to such high temperatures.

[0027] It is also advantageous if the second temperature sensor is arranged at a distance of at least 0.5 cm [centimeters] from the burner surface.

[0028] This distance is greater than the distance at which the highest temperatures of the flame normally occur.

[0029] It is also advantageous if the gas burned with the flame contains at least 50%, preferably even 97%, hydrogen.

[0030] A hydrogen content of 50% or more results in a fuel gas whose properties are already largely dominated by hydrogen. A gas with 97% or more hydrogen can be considered almost like pure hydrogen.

[0031] Furthermore, it is advantageous if an air mass flow sensor is additionally evaluated for measuring an air mass flow supplied to the burner and is used together with measurement signals from the first temperature sensor and / or with the second temperature sensor for controlling a gas-air mixture.

[0032] Preferably, a limit value is also set for comparing temperature changes measured with the various temperature sensors as a function of the signal from an air mass flow sensor.

[0033] Preferably, signals from the first temperature sensor and the second temperature sensor are used to control the gas-air mixture. In particular, the use of both temperature sensors also allows for information about the temperature distribution in the flame along the distance, which is very helpful for controlling a gas-air mixture.

[0034] With at least two temperature sensors, highly dynamic gas-air mixture control can be achieved, making it suitable for domestic hot water applications. This is because the temperature in or at the flame can be assigned to a defined gas-air mixture ratio with a known air mass flow. Therefore, the temperature measured by the temperature sensors can be used to determine the lambda value of the mixture. This is especially true when using two temperature sensors, as this allows a flame temperature profile to be estimated across the flame height.

[0035] Also to be described here is a burner for the combustion of gas with a burner surface, comprising at least a first temperature sensor and a second temperature sensor, which are arranged at a different distance from the burner surface, wherein the burner is designed in particular to carry out the described method.

[0036] Also to be described is a control device configured to evaluate signals from at least two temperature sensors of a burner according to the described method.

[0037] A computer program is also to be described, comprising instructions which cause the described burner to carry out the described process steps.

[0038] The invention and the technical context of the invention are explained in more detail below with reference to the figures. The figures show preferred embodiments to which the invention is not limited. It should be noted in particular that the figures, and in particular the proportions depicted in the figures, are only schematic.

[0039] They represent: Fig. 1 : a first embodiment of a burner described, Fig. 2 : a second variant of a burner described, Fig. 3 : a first temperature curve diagram of the signals from the temperature sensors, Fig. 4 : a second temperature curve diagram of the signals from the temperature sensors, Fig. 5 : a first performance diagram of a burner, and Fig. 6 : a second performance diagram of a burner.

[0040] In Fig. 1 and in Fig. 2Two different embodiments of a burner 3 are shown. The burner 3 is preferably designed as a hollow body with a plurality of openings. The mixture to be burned flows through a supply line 14 into the interior 15 of the burner 3 and then passes through the openings (not shown individually here) into the combustion chamber 13. The flames 1 of the combustion are located on an outer burner surface 2 of the burner 3. Depending on the set power, the flames 1 are larger or smaller. In both Figures 1 and 2Different power levels of burner 3 are shown schematically. On the left, a power level "L" with a lower burner power is shown. On the right, a power level "H" with a higher burner power is shown. It should be noted that the representation of the two power levels in an illustration of burner 3 is only schematic. Normally, a burner 3 has the same power level throughout one operating stage (across the entire burner surface 2). This means that the flames are the same size across the entire burner surface 2. It can be seen that the flames 1 at power level H are larger and further away from the burner surface 2 than at power level L. The burners 3 each have a first temperature sensor 4 and a second temperature sensor 5, which are arranged at different distances 7 from the burner surface 2. In the embodiment according to Fig. 1Both temperature sensors 4, 5 are arranged above the burner surface 2 in the combustion chamber 13. In the variant according to Fig. 2The first temperature sensor 4 is arranged in an interior space 15 of the burner 3 on an underside of the burner surface 2 and thus measures the temperature or temperature changes on the burner surface 2. The signals from the first temperature sensor 4 and the second temperature sensor 5 are preferably made available to a control unit 12, which evaluates the signals from the temperature sensors 4, 5 and carries out the described method. Preferably, a fan 19 for supplying the burner 3 with the mixture, as well as an air inlet 18 and a gas inlet 17, are provided on the supply line 14 for the mixture of gas and air. Preferably, there is also an air mass flow sensor 9, with which an air mass flow through the air inlet 18 into the supply line 14 and into the burner 3 can be monitored.The air mass flow sensor 9 is preferably also connected to the control unit 12 so that the control unit 12 can also process signals from the air mass flow sensor 9.

[0041] Fig. 3 and Fig. 4each show temperature curves 8, which are measured with the first temperature sensor 4 and the second temperature sensor 5, plotted over time 11. Various operating phases are shown in which the burner output changes. Phases (a), (c) and (d) each show cases in which the burner output increases. Then the temperature measured with the first temperature sensor 4 (located closer to the burner surface) drops, so that a decreasing temperature change occurs here. At the same time, the temperature measured with the second temperature sensor 5 (located further away from the burner surface) rises, so that a rising temperature change occurs. This effect arises because the flame moves further outwards (away from the burner surface) when the output increases. Conversely, phases (b) and (e) show the situation in which the burner output decreases.Here, in particular, the temperature measured by the first temperature sensor 4 increases because the flame moves closer to the burner surface, while the temperature measured by the second temperature sensor 5 decreases. In phase (f), both temperatures (the temperature measured by the first temperature sensor 4 and the temperature measured by the second temperature sensor 5) decrease. This allows the identification of a flame extinguishing point 16.

[0042] The Figures 5 and 6 show the performance 10 of the burner in the individual phases, which are also already in the Figs. 3 and 4 are shown. List of reference symbols

[0043] 1 Flame 2 Burner surface 3 Burner 4 First temperature sensor 5 Second temperature sensor 6 Temperature change 7 Distance 8 Temperature 9 Air mass flow sensor 10 Power 11 Time 12 Control unit 13 Combustion chamber 14 Supply line 15 Interior 16 Extinction point 17 Gas inlet 18 Air inlet 19 Fan

Claims

1. Method for detecting the extinguishing of a flame (1) on a burner surface (2) of a burner (3) for burning gas, wherein temperature changes of the flame (1) are measured at least with a first temperature sensor (4) and a second temperature sensor (5), wherein the first temperature sensor (4) and the second temperature sensor (5) are arranged at a different distance (7) from the burner surface (2), characterised in that an extinguishing of the flame (1) is detected when a deviation in the temperature changes (6) measured with the first temperature sensor (4) and the second temperature sensor (5) reaches a threshold.

2. Method according to claim 1, wherein extinguishing of the flame (1) is detected when a decreasing temperature change (6) is measured with both temperature sensors (4, 5).

3. Method according to any one of the preceding claims, wherein a change in the power of the burner (3) is detected when an increasing temperature change (6) is measured with one of the temperature sensors (4, 5).

4. Method according to any one of the preceding claims, wherein a temperature (8) is also measured with at least one of the temperature sensors (4,5) and the threshold is set as a function of the measured temperature (8).

5. Method according to any one of the preceding claims, wherein the first temperature sensor (4) is arranged directly on the burner surface (2) and is designed to measure a temperature change (6) of the burner surface (2).

6. Method according to any one of the preceding claims, wherein the first temperature sensor is arranged on an underside of the burner surface and is designed to measure a temperature change (6) of the burner surface (2).

7. Method according to any one of the preceding claims, wherein the second temperature sensor (5) is arranged at a distance (7) of at least 0.5 cm [centimeters] from the burner surface (2).

8. Method according to any one of the preceding claims, wherein the gas burned by the flame (1) contains at least 50 %, preferably even 97 %, hydrogen.

9. Method according to any one of the preceding claims, wherein an air mass flow sensor (9) for measuring an air mass flow supplied to the burner (3) is also evaluated, and together with measuring signals for the first temperature sensor (4) and / or with the second temperature sensor (5), is used to control a gas-air mixture.

10. Controller (12), designed to evaluate signals from at least two temperature sensors (4, 5) of a burner (3) according to the method according to any one of claims 1 to 9.

11. Burner (3) for burning gas with a burner surface (2), having at least a first temperature sensor (4) and a second temperature sensor (5), which are arranged at a different distance (7) from the burner surface (2), wherein the burner (3) has a controller (12) according to claim 10.

12. Computer program, comprising commands, which instruct the controller (12) of a burner (3) according to claim 11 to perform the method steps according to any one of claims 1 to 9.