DE102021124643A1 - Method for detecting flame extinction of a burner - Google Patents

Abstract

Method for detecting the extinction of a flame (1) on a burner surface (2) of a burner (3) for burning gas, temperature changes in the flame (1) being 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), extinguishing of the flame (1) being detected when both temperature sensors (4, 5 ) a decreasing temperature change (6) is measured and/or a deviation of the temperature changes (6) measured with the first temperature sensor (4) and the second temperature sensor (5) reaches a limit value.

Description

According to legal requirements, gas-fired heaters must have a device for flame detection that ensures that no unburned combustible gas-air mixture is supplied to the combustion chamber of the heater for longer than the maximum permissible time.

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.

Ionization-based flame detection is based on the availability of a certain amount of freely available charge carriers. This proportion varies depending on the carrier gas. at z. B. pure hydrogen combustion, the number of available charge carriers can be too small. Reliable flame detection based on the electrical conductivity of the flame using hydrogen or gas mixtures with a high proportion of hydrogen can therefore not be realized.

Against this background, new methods for flame detection are desirable, especially for heaters and burners that are operated for the combustion of gas mixtures with high levels of hydrogen or even pure hydrogen.

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 with the invention according to the features of the independent patent claims. Further advantageous configurations are specified in the dependently formulated patent claims and in the description and in particular also in the description of the figures. It should be pointed out that a person skilled in the art can combine the individual features with one another in a technologically sensible manner and thus arrive at further configurations of the invention.

Such a new method, a burner set up accordingly for the method, a control device and a computer program product are to be described below.

A method for detecting the extinction of a flame on a burner surface of a burner for burning gas is described here, temperature changes in the flame being measured at least with a first temperature sensor and a second temperature sensor, the first temperature sensor and the second temperature sensor being at a different distance from each other are arranged on the surface of the burner, extinguishing of the flame being detected when a decreasing temperature change is measured with both temperature sensors and/or a deviation of the temperature changes measured with the first temperature sensor and the second temperature sensor exceeds a limit value.

The burner preferably designates a burner body, from which the fuel gas flows outwards through a plurality of openings into a combustion chamber which surrounds the burner and in which there are preferably lines which then dissipate the heat generated by the burner. The torch body is preferably cylindrical and made of a metal material. The outer (facing the combustion chamber) surface of the burner body is referred to herein as the burner surface, from which the flames extend into the combustion chamber.

A distance between the temperature sensors and the burner surface means here, in particular, a distance measured perpendicularly (or normal, or perpendicularly) to the burner surface. The so-called flame height depends on the output of the burner, which is set by the quantity or pressure of the mixture that is made available to the burner for combustion. The temperature sensors can be thermocouples, for example. In principle, however, other types of temperature sensors are also possible. The temperature sensors are preferably suitable for the temperatures occurring at their respective installation site during the operation of the burner. The temperature sensors are usually set up to withstand temperatures of up to, for example, 1,300°C. However, the temperature sensors are particularly preferably 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.

First temperature sensors are preferably arranged at a distance from the burner surface which is smaller than the distance at which the greatest temperatures of the flame occur. Second temperature sensors are preferably arranged at a distance from the burner surface which is greater than the distance at which the greatest temperatures of the flame occur.

It has been found that flame detection based on a (single) temperature sensor positioned on the burner surface or in the flame does not respond to changes in performance due to thermal mass the legally prescribed time between the two scenarios of a power reduction and the extinguishing of the flame. In both cases, the difference would only become apparent later via the change in slope and an associated approach to a target temperature.

At least two sensors, positioned at different points in relation to the flame height, have an opposing temperature behavior in the case of modulation (i.e. when there is a change in the output of the burner), so that at least one sensor always measures a rising temperature profile. This applies in particular if the difference in the distance between the first temperature sensor and the second temperature sensor is suitably selected. If the flame were to go out, on the other hand, both temperature sensors would measure a falling temperature profile within the legally specified time. In preferred embodiment variants, more than two temperature sensors can also 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 method described, in which the temperature changes measured with the individual temperature sensors are evaluated and it can then be determined whether the different temperature behavior, which is measured with the individual temperature sensors, indicates that the flame allows.

In principle, when there is a change in output, there is not only a change in the combustion output. In addition, the position of the flame relative to the burner surface usually changes as well. In particular, the point of maximum temperature of the flame migrates in the direction of distance away from the burner surface or towards the burner surface. This displacement of the flame relative to the burner surface when there is a change in output means that an opposite temperature behavior usually occurs if (only) there is a change in output and the flame does not go out. The change in the position of the flame relative to the burner surface is due, for example, to the fact that the flame becomes larger overall when power is increased and smaller when power is reduced. In addition, the flow of mixture out of the burner normally pushes the flame farther away from the burner surface as power is increased, and the flame moves closer to the burner surface again as power is reduced.

As an alternative or additional criterion to a parallel falling temperature change, which is measured with the two temperature sensors, and which is used to determine that the flame has gone out, a deviation between the temperature change, which was measured with the two temperature sensors, can also be used as a criterion for the Flame extinguishing detection can be used. In principle, this is possible by comparing the deviation with at least one limit value, with either falling below or exceeding a limit value being able to be used to detect extinction.

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

Increasing temperature changes will not normally appear at any of the temperature sensors when the burner goes out. An increasing temperature change on at least one of the temperature sensors is usually a clear indication of a change in performance of the burner.

It is also advantageous if a temperature is also measured with at least one of the temperature sensors and the limit value is set as a function of the measured temperature.

The temperature is often also a measure of the performance of the burner. In embodiment variants, the weighted temperatures of several of the temperature sensors can also be used to determine the limit value.

It is also advantageous if the first temperature sensor is arranged directly on the burner surface and is set up to measure a temperature change on the burner surface.

It is also advantageous if the first temperature sensor is arranged on an underside of the burner surface and is set up to measure a change in temperature of the burner surface.

At the positions proposed here for the first temperature sensors, there is normally a relatively sluggish reaction of the temperature to changes in output, because the thermal mass of the burner reduces the measurability of temperature changes. In addition, the temperatures that occur in these places are usually relatively low, or low compared to the highest in temperatures occurring during the flame. For this reason, the first temperature sensors here are usually not exposed to such high temperatures.

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.

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

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

A proportion of 50% or more hydrogen results in a fuel gas whose properties are already essentially dominated by hydrogen. A gas with 97% or more hydrogen can be considered approximately as pure hydrogen.

It is also advantageous if an air mass flow sensor is also evaluated to measure an air mass flow supplied to the burner and is used together with measurement signals from the first temperature sensor and/or the second temperature sensor to regulate a gas/air mixture.

A limit value for comparing temperature changes measured with the various temperature sensors as a function of the signal from an air mass flow sensor is also preferably set.

Even signals from the first temperature sensor and the second temperature sensor are preferably used to regulate the gas-air mixture. In particular, by using both temperature sensors, statements can also be made about the temperature distribution in the flame along the distance, which is very helpful for controlling a gas-air mixture.

With at least two temperature sensors, a very dynamic gas/air mixture control, which is suitable for process water applications, can also be implemented, since the temperature in or on the flame can be assigned to a defined gas/air mixture ratio when the air mass flow is known. The lambda value of the mixture can therefore be inferred from the temperature measured with the temperature sensors. This applies in particular when using two temperature sensors, because then a profile of the temperature of the flame over the flame height can be estimated.

A burner for the combustion of gas with a burner surface is also to be described here, having at least a first temperature sensor and a second temperature sensor, which are arranged at a different distance from the burner surface, the burner being set up in particular to carry out the method described.

A control device set up to evaluate signals from at least two temperature sensors of a burner according to the described method is also to be described.

Also to be described is a computer program comprising instructions that cause the burner described to perform the method steps described.

The invention and the technical context of the invention are explained in more detail below with reference to the figures. The figures show preferred exemplary embodiments to which the invention is not limited. It should be pointed out in particular that the figures and in particular the proportions shown in the figures are only schematic.

• 1: eine erste Ausführungsvariante eines beschriebenen Brenners,
• 2: eine zweite Ausführungsvariante eines beschriebenen Brenners,
• 3: ein erstes Temperaturverlaufsdiagramm der Signale der Temperatursensoren,
• 4: ein zweites Temperaturverlaufsdiagramm der Signale der Temperatursensoren,
• 5: ein erstes Leistungsdiagramm eines Brenners, und
• 6: ein zweites Leistungsdiagramm eines Brenners.

They represent:

• 1 : a first embodiment variant of a described burner,
• 2 : a second embodiment variant of a described burner,
• 3 : a first temperature curve diagram of the signals from the temperature sensors,
• 4 : a second temperature curve diagram of the signals from the temperature sensors,
• 5 : a first performance diagram of a burner, and
• 6 : a second performance diagram of a burner.

In 1 and in 2 two different variants of a described burner 3 are shown. The burner 3 is preferably designed as a hollow body with a large number 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) into the combustion chamber 13. The flames 1 of combustion are on an outer burner surface 2 of the burner 3. Depending on the power set, the flames 1 are larger or smaller. In both 1 and 2 are each different power levels of the burner 3 shown schematically. A power level "L" with a lower burner power is shown on the left. A power level "H" with a higher burner output is shown on the right. It should be noted that the representation of the two power levels in a figure of the burner 3 is only schematic. Normally, the same power level is present uniformly (on the entire burner surface 2) on a burner 3 in one operating stage. This means that the flames are of the same size over the entire burner surface 2 . It can be seen that the flames 1 at 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 at different distances 7 from the burner surface 2 are arranged. In the variant according to 1 Both temperature sensors 4, 5 are arranged above the burner surface 2 in the combustion chamber 13. In the variant according to 2 the first temperature sensor 4 is arranged in an interior 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 of the first temperature sensor 4 and the second temperature sensor 5 are preferably available to a control unit 12 provided, which carries out an evaluation of the signals from the temperature sensors 4, 5 and carries out the method described. Preferably, there is a fan 19 on the supply line 14 for the mixture of gas and air for supplying the burner 3 with the mixture, as well as an air inlet 18 and a gas inlet 17. There is also preferably an air mass flow sensor 9, with which an air mass flow through the air inlet 18 in 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 .

3 and 4 each show temperature curves 8, which are measured with the first temperature sensor 4 and the second temperature sensor 5, plotted over time 11. Different operating phases are shown, in which the output of the burner changes. The phases (a), (c) and (d) each show cases where the output of the burner increases. Then the temperature measured by the first temperature sensor 4 arranged (closer to the burner surface) falls, so that there is a falling temperature change here. At the same time, the temperature measured by the second temperature sensor 5 (further away from the burner surface) increases, so that there is an increasing temperature change. This effect occurs because the flame travels further outward (away from the burner surface) as the power increases. Conversely, phases (b) and (e) show the situation that the output of the burner decreases. In particular, the temperature measured with the first temperature sensor 4 increases here because the flame moves closer to the burner surface, while the temperature measured with the second temperature sensor 5 decreases. In phase (f) both temperatures drop (the temperature measured with the first temperature sensor 4 and the temperature measured with the second temperature sensor 5). This can be used to identify an extinction point in time 16 at which the flame is extinguished.

The 5 and 6 show the performance 10 of the burner in the individual phases, which are also already in the 3 and 4 are shown.

reference list

1

flame

2

burner surface

3

burner

4

first temperature sensor

5

second temperature sensor

6

temperature change

7

Distance

8th

temperature

9

air mass flow sensor

10

Performance

11

Time

12

control unit

13

combustion chamber

14

supply line

15

inner space

16

Expiration Time

17

gas inlet

18

air intake

19

fan

Claims (11)

Method for detecting the extinction of a flame (1) on a burner surface (2) of a burner (3) for burning gas, temperature changes in the flame (1) being detected at least with a first temperature sensor (4) and a second temperature sensor (5) are measured, the first temperature sensor (4) and the second temperature sensor (5) is arranged at a different distance (7) from the burner surface (2), extinguishing of the flame (1) being detected when a falling temperature change (6) is measured with both temperature sensors (4, 5). and/or a deviation in the temperature changes (6) measured with the first temperature sensor (4) and the second temperature sensor (5) reaches a limit value. procedure after claim 1 , wherein a change in output of the burner (3) is detected when an increasing temperature change (6) is measured with one of the temperature sensors (4, 5). Method according to one of the preceding claims, wherein a temperature (8) is also measured with at least one of the temperature sensors (4, 5) and the limit value is set as a function of the measured temperature (8). Method according to one of the preceding claims, wherein the first temperature sensor (4) is arranged directly on the burner surface (2) and is set up to measure a temperature change (6) of the burner surface (2). Method according to one of the preceding claims, wherein the first temperature sensor is arranged on an underside of the burner surface and is set up to measure a temperature change (6) of the burner surface (2). Method according to one of the preceding claims, in which the second temperature sensor (5) is arranged at a distance (7) of at least 0.5 cm [centimeters] from the burner surface (2). Method according to one of the preceding claims, in which the gas combusted with the flame (1) contains at least 50%, preferably even 97%, hydrogen. Method according to one of the preceding claims, in which an air mass flow sensor (9) is additionally evaluated to measure an air mass flow supplied to the burner (3), and together with measurement signals from the first temperature sensor (4) and/or from the second temperature sensor (5) to control a Gas-air mixture is used. 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), the Burner (3), in particular for carrying out the method according to one of Claims 1 until 8th is set up. Control unit (12), set up to evaluate signals from at least two temperature sensors (4, 5) of a burner (3) according to the method according to one of Claims 1 until 8th . Computer program comprising instructions that cause the burner (3) of the claim 9 the method steps according to one of Claims 1 until 8th executes

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