Method And Heating Unit For Flame Monitoring During Gas Combustion

Abstract

A method of monitoring a flame during gas combustion in a combustion chamber (10). A heating unit (1) has an evaluation unit, an extraction line (11) and a sensor (12). The sensor (12) is arranged in the extraction line (11) to detect thermal substance properties of the gas. Thus, it is determined if it is ambient air (B), a non-combusted fuel-air mixture (C) or particularly the hydrogen-air mixture, or a waste gas (A) generated during combustion. The sensor (12) transmits a recorded measured value to the evaluation unit. The evaluation unit uses the measured value to determine whether ambient air (B), the non-combusted fuel-air mixture (C), or waste gas (A) is flowing through the extraction line (11) and thereby determines whether the flame is burning or extinguished.

Claims

1. A method for monitoring a flame during gas combustion in a combustion chamber of a heating unit operated with gaseous fuel having an evaluation unit, an extraction line, through which waste gas flows during combustion, and a sensor arranged in the extraction line for detecting thermal substance properties of a gas flowing through the extraction line, comprising: monitoring the gas flowing through the extraction line; determining if the gas flow is ambient air from an environment adjoining the heating unit, a non-combusted fuel-air mixture, or a waste gas generated during combustion, transmitting a recorded measured value to the evaluation unit; determining, via the evaluation unit, using the measured value, whether ambient air, the non-combusted fuel-air mixture, or waste gas is flowing through the extraction line; and determining whether the flame is burning or extinguished.

2. The method according to claim 1, wherein a primary fraction of the fuel is hydrogen and the fuel is particularly a pure hydrogen gas or wherein the fuel is a mixture of hydrogen and a gas of the second family of gases as well as air and propane, wherein the fraction of air and propane together in the mixture has a volume fraction of less than 40%.

3. The method according to claim 1, wherein the sensor detects a thermal conductivity k and/or a thermal diffusivity a of the gas flowing through the extraction line.

4. The method according to claim 1, wherein the heating unit has several sensors arranged in the extraction line in order to detect thermal substance properties of the gas flowing through the extraction line that respectively detect the same or different thermal substance properties.

5. The method according to claim 1, wherein the heating unit has at least one auxiliary sensor arranged in the extraction line in order to detect boundary conditions prevailing in the extraction line, wherein the at least one auxiliary sensor transmits the detected boundary conditions to the evaluation unit, as measured values, and the evaluation unit normalizes the detected thermal substance properties via the sensor based on the boundary conditions detected by the at least one auxiliary sensor.

6. The method according to claim 1, further comprising cooling the gas flowing through the extraction line by a cooling device, arranged along the flow path from the combustion chamber, through the extraction line, to the sensor before that sensor.

7. The method according to claim 1, further comprising controlling a volumetric flow of the gas flowing through the extraction line by a throttling element, arranged along the flow path from the combustion chamber, through the extraction line, to the sensor after or before that sensor.

8. The method according to claim 1, wherein the extraction line in the combustion chamber has an inlet, arranged in a direct vicinity of the flame or a burner generating the flame such that the waste gas resulting during combustion flows directly into the extraction line through the inlet and is routed through the extraction line to the sensor

9. The method according to claim 1, wherein the heating unit has a primary waste gas line and a first partial stream of the waste gas generated during combustion flows through the extraction line and a second partial stream of the waste gas generated during combustion flows through the primary waste gas line during combustion.

10. The method according to claim 1, further comprising flushing the combustion chamber and the extraction line with ambient air before a start of combustion, and the substance properties of the ambient air are measured by the sensor during the flushing.

11. The method according to claim 1, wherein the evaluation unit compares the measured value with a predetermined threshold value or at least a value range and determines from the comparison of the measured value whether ambient air, the non-combusted fuel-air mixture, or waste gas is flowing through the extraction line.

12. The method according to claim 1, wherein the evaluation unit determines a rate of change of the measured value from two or more sequentially determined measured values; and wherein the rate of change is used to determine whether ambient air, the non-combusted fuel-air mixture, or waste gas is flowing through the extraction line.

13. A heating unit comprising: a combustion chamber; an evaluation unit, and an extraction line, it being possible for waste gas resulting during gas combustion of a gaseous fuel in the combustion chamber to flow through the extraction line; a sensor arranged in the extraction line, the sensor detecting a thermal substance property of a gas flowing through the extraction line by recording a measured value, the sensor is connected to the evaluation unit in order to transmit the measured value, and the evaluation unit uses the measured value to determine whether ambient air, a non-combusted fuel-air mixture, or waste gas is flowing through the extraction line and determines whether a flame in the combustion chamber is burning or extinguished.

14. The heating unit according to claim 13, wherein the heating unit implements the method according to claim 1.

Description

DRAWINGS

[0045] Other advantageous further developments of the disclosure are identified in the dependent claims or presented below together with the description of the preferred embodiment of the disclosure with reference to the figure.

[0046] FIG. 1 is a schematic view of a first variant of a heating unit.

[0047] FIG. 2 is a schematic view of a second variant of a heating unit.

[0048] FIG. 3 is a schematic view of a third variant of a heating unit.

[0049] FIG. 4 is a schematic view of thermal substance properties of various gases.

DETAILED DESCRIPTION

[0050] The figures are schematic examples. The same reference numerals in the figures indicate equivalent functional and/or structural features.

[0051] FIG. 1 shows a first variant of a heating unit 1 according to the disclosure, with which the method according to the disclosure can be implemented.

[0052] The sensor 12 measures the thermal substance properties of the waste gas resulting during combustion in the combustion chamber 10. The waste gas is routed from the combustion chamber 10 to the environment 2 through the extraction line 11. In this case, the flow through the extraction line 11 is a partial flow. A flue is provided as the primary waste gas line 16. Due to the flue, waste gas likewise flows from the combustion chamber 10 into the environment 2 during combustion. The sensor 12 is exposed to the partial flow of waste gas removed from the combustion chamber 10. Thus, the sensor 12 can detect the thermal substance properties of the gas or gas mixture flowing by it.

[0053] The waste gas is removed in the direct vicinity of the burner 15. Thus, the waste gases generated during combustion flow directly into the extraction line 11. It can also be characterized as the extraction line.

[0054] In this case, a pressure higher than that in the environment 2 prevails in the interior of the combustion chamber 10. Thus, the waste gases are conveyed due to the pressure difference from the combustion chamber 10.

[0055] Furthermore, a throttling element 14 is provided to regulate and control the flow of waste gas or the partial flow of waste gas through the extraction line 11.

[0056] An optional cooling device 13 is further provided with the variant shown in FIG. 1. The cooling device cools the gas flowing through the extraction line 11 before it reaches the sensor 12. The cooling of the gas means that the gas flowing to the sensor 12 has a preferably constant temperature. Thus, the thermal substance properties measured in the various gases are comparable.

[0057] In the embodiment according to FIG. 1, the heating unit further has a heat exchanger 17. The heat generated by the burner 15 or from the combustion chamber 10 during combustion can be discharged and rendered usable with heat exchanger 17.

[0058] In addition, a condensate drain 18 discharges condensate occurring in the combustion chamber 10 from the combustion chamber 10.

[0059] The variant of the heating unit 1 shown in FIG. 2, which is preferably formed as a gas boiler, has two sensors 12′, 12′, in addition to the components described in relation to FIG. 1. The sensors detect further properties of the gas flowing through the waste gas line 11. These additional sensors would be a temperature sensor 12′ and a pressure sensor 12″. In the variant shown by example, the measured values determined from the three sensors 12, 12′, 12″ are each transmitted to the evaluation unit. The evaluation unit determines whether the flame is extinguished or not based on all measured values. To this end, values recorded, for example, by the sensor 12 can be normalized based on a respective temperature determined by the temperature sensor 12′ and part of the value and a likewise corresponding pressure detected by the pressure sensor 12″. Thus, the various values recorded by the sensor 12 are comparable and can optionally be collated with a table or with characteristic values stored in the evaluation unit. Thus, a determination can reliably be made as to whether the gas in the extraction line is waste gas, ambient air, or the non-combusted fuel-air mixture or whether the flame is extinguished or present.

[0060] With the variant as it is shown in FIG. 1 as well as with the variant as it is shown in FIG. 2, the throttling element 14 may alternatively be arranged upstream of the optional cooling device 13. In the event there is no cooling device 13, it is arranged upstream of the sensor 12 or sensors 12, 12′, 12″, as it relates to the flow direction.

[0061] FIG. 3 shows a variant of the heating unit 1. Similar to the variant according to FIG. 2, three sensors 12, 12′, 12″ are provided along the extraction line 11, which, however, is integrated into the primary waste gas line 16 or into the flue 16 in this case. Thus, there is no separate extraction line 11 or separate primary waste gas line 16. Nevertheless, a separate region can be provided in the primary waste gas line 16, wherein which only a part of the gas flows through the region and where the sensors 12, 12″, 12″ are arranged and a measurement is taken. Furthermore, the embodiment according to FIG. 3 does not have a cooling device 13. Thus, a temperature fluctuation in the gases can be considered using a measurement of the temperature of the temperature sensor 12′.

[0062] FIG. 4 shows a comparison of the thermal conductivity k or the thermal diffusivity a of the media flowing past the sensor 12, i.e. of ambient air B from an environment 2 adjoining the heating unit 1, a non-combusted fuel-air mixture C, or a waste gas A generated during combustion. The functional principle of flame monitoring of the evaluation unit should be clarified.

[0063] Due to the application of the thermal substance properties of the various gases at a constant temperature in FIG. 4, it is clear that the thermal properties of the three substantially different gases, that can flow past the sensor 12, deviate significantly from one another at the same temperature and preferably same pressure or air pressure. Thus, the gases can be differentiated from one another by the detected substance property. The thermal substance properties of the waste gas A are less than those of the ambient air B. If the flame goes out during operation, the flame is extinguished, the non-combusted hydrogen-air mixture or fuel-air mixture C passes the sensor 12. Thus, the threshold value X shown as an example is exceeded. When the measured value exceeds the threshold value X, it can thus be detected, for example, when the flame is extinguished, and the supply of fuel will be stopped.

[0064] In addition to the thermal substance properties of the waste gas A and of the non-combusted fuel-air mixture C, the substance properties of the ambient air B are also shown. The substance properties are detectable as a reference value, for example, during flushing of the extraction line 11 with ambient air B before the ignition of combustion. In addition, the correspondingly selected threshold values can be used to determine whether flushing of the combustion chamber before the start of combustion, before ignition, or after the flame is extinguished was successful.

[0065] If the measured values fall below or exceed the correspondingly selected limit or threshold values, respective gas A, B, or C can be detected, and conclusions can be drawn about the presence of the flame.

[0066] The disclosure is not limited in its design to the aforementioned preferred exemplary embodiments. Rather, a number of variants is conceivable, which would make use of the solution shown even with essentially different designs.

[0067] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.