Method for starting a gas burner

Abstract

The invention relates to a method for starting a gas burner, in which: the gas burner is supplied with air and, from a first time point, also with a fuel gas; from the first time point at the latest, a fuel gas mixture formed from the air and the fuel gas is exposed to ignition sparks in a combustion chamber for a first predetermined time interval (z); and a supply of the fuel gas is interrupted if there is no flame after a second predetermined time interval (y), which is greater than the first time interval (z), has elapsed. According to the invention, the supply of fuel gas to the air is increased at least from a first actual supply amount to a second actual supply amount within the second predetermined time interval (y) until a flame is detected.

Description

[0001] Procedure for starting a gas burner

[0002] The invention relates to a method for starting a gas burner according to the preamble of patent claim 1.

[0003] A method for starting a gas burner of the type mentioned at the beginning is known from document EP 4 015 904 A1. In this method, air is supplied to the gas burner on the one hand and, from a first point in time, a fuel gas is also supplied to the burner. Furthermore, from the first point in time at the latest, a fuel gas mixture formed from the air and the fuel gas is exposed to ignition sparks in a combustion chamber for a first predetermined time interval. Furthermore, if there is no flame, the supply of fuel gas is interrupted after a second predetermined time interval, which is longer than the first time interval. In this solution, a fuel gas valve which determines the supply of fuel gas is optionally open or closed.

[0004] For the sake of completeness , it is also pointed out that 20 both in the above - mentioned prior art and in the solution according to the invention explained below , the second time interval , just like the first time interval , starts with the said first point in time .

[0005] 25

[0006] The invention is based on the object of improving a method of the type mentioned at the outset. In particular, an even more reliable method for starting a gas burner is to be created, especially a gas burner in which the fuel gas consists at least partially of hydrogen. 30 This object is achieved by a method for starting a gas burner having the features listed in the characterizing part of patent claim 1.

[0007] According to the invention it is therefore provided that the supply of 5 fuel gas to the air is increased at least from a first actual supply quantity to a second actual supply quantity within the second predetermined time interval until a flame is detected.

[0008] 10

[0009] In other words, the method according to the invention is characterized in that the supply of fuel gas to the air within the second predetermined time interval is no longer simply switched on, as in the aforementioned prior art, meaning that only one (single) actual supply quantity is present, because no supply is not a supply quantity, but rather that the quantity of supplied fuel gas is increased in at least two steps until a flame is detected. This brings with it the considerable advantage, particularly if the increase occurs continuously, as is preferred, that the flame is ignited practically only with the minimum required quantity of fuel gas and a possible pressure increase in the combustion chamber or combustion space due to sudden ignition during ignition can be reduced to a minimum. 25

[0010] The requirement "in at least two steps" represents, in a sense, a lower linguistic limit to the aforementioned prior art, whereby, as already explained, a successive, possibly multi-stage increase in the supply of fuel gas is particularly preferably provided during the second predetermined time interval. A further advantageous development of the method according to the invention, which will be discussed in more detail below, further consists in the fact that, in order to prevent unwanted late ignition, an oxygen content in the combustion chamber is recorded with a measuring device at least during the first time interval.

[0011] Other advantageous developments of the method according to the invention emerge from the dependent patent claims. 10

[0012] The method according to the invention, including its advantageous developments according to the dependent patent claims, is explained in more detail below with reference to the drawing of a preferred embodiment and with reference to three diagrams 15.

[0013] It shows

[0014] Figure 1 schematically shows a gas burner; 20

[0015] Figure 2 as a diagram with three different starting phases;

[0016] Figure 3 as a diagram of the oxygen content in the combustion chamber indicated by the measuring device during proper ignition; and 25

[0017] Figure 4 is a diagram showing the oxygen content in the combustion chamber indicated by the measuring device when ignition retardation is imminent.

[0018] In the method according to the invention for starting a gas burner, air is first supplied to the gas burner in a known manner, and from a first point in time, a fuel gas is also supplied. Furthermore, from the first point in time at the latest, a fuel gas mixture formed from the air and the fuel gas is exposed to ignition sparks in a combustion chamber for a first predetermined time interval z. Furthermore, if there is no flame, the supply of fuel gas is interrupted after the expiration of a second predetermined time interval y, which is longer than the first time interval z.

[0019] Preferably, the detection of a flame is carried out using a flame sensor. An optical sensor (for example, a UV probe) or an electrical sensor (for example, an ionization electrode) is particularly preferably used as the flame sensor 3.

[0020] Furthermore, it is preferably provided in a manner known per se that the ignition sparks are generated with an ignition electrode 4. In addition, the supply of fuel gas to the air is preferably regulated with a controllable valve or a control valve 1.

[0021] What is essential for the method according to the invention is - and in this regard, particular reference is made to Figure 2 - that the supply of fuel gas to the air is increased at least from a first actual supply quantity to a second actual supply quantity within the second predetermined time interval y until a flame is detected. In Figure 2, the upper curve shows the ignition, which is either on or off (plotted over time); the lower curve shows, also plotted over time, the degree of opening of the control valve 1, the lowest position corresponding to a closed control valve

[0022] 1 corresponds to . 30 In all of this, it is particularly preferred, as already mentioned at the beginning, that the supply of fuel gas to the air is continuously increased within the second predetermined time interval y until a flame is detected. As explained in Wikipedia (see https : / / de . wikipedia . org / w / index . php?title=Stetige_ 5 Funktion&oldid=232205358 ), the term "continuous" ultimately means a function which, in clear terms, is characterized by the fact that its graph in a Cartesian coordinate system is a connected curve within its domain of definition, i.e. the graph does not have any jumps and can be drawn without lifting the pen.

[0023] In the left-hand, i.e. first example in Figure 2, no flame is detected, i.e. at the end of the second time interval y15 the control valve 1 is closed. In the middle example in Figure 2, a flame is only detected after the end of the first time interval z, but still within the second time interval y, and from this point on the actual supply quantity of fuel gas is no longer increased or is kept constant. In the right-hand, i.e. last example in Figure 2, a flame is already detected within the first time interval z, and from this point on the actual supply quantity of fuel gas is no longer increased or is kept constant. As can be seen, after flame detection 25 the burner in the right-hand example is operated with a smaller quantity of fuel gas than in the middle example.

[0024] Looking at all of this in more detail, it is preferably provided that the first time interval z, also called the ignition time, ends after a maximum of 4 seconds, preferably after a maximum of 2.5 seconds, particularly preferably after a maximum of 1.5 seconds. Furthermore, it is preferably provided that the second time interval y, also called the safety time for flame detection, ends after a maximum of 10 seconds, preferably after a maximum of 7.5 seconds, particularly preferably after a maximum of 5 seconds. As already mentioned at the beginning, it is also true, as also shown in Figure 5, that the first and second time intervals y, z begin at the same time.

[0025] Furthermore, as also already mentioned at the beginning, it is particularly preferred that a gas mixture containing at least 70-vol% hydrogen, preferably at least 90-vol% hydrogen, is used as the fuel gas.

[0026] A further special feature of the method according to the invention is that, at least during the first time interval z (preferably during the entire time interval y, i.e., during the entire safety time), the oxygen content in the combustion chamber is measured with a measuring device 5 in order to prevent unwanted delayed ignition of the fuel gas mixture. It is preferably provided that an oxygen probe, preferably a (so-called) broadband lambda probe (see https: / / de.wikipedia.org / w / index.php?title=Lambdasonde&oldid=228167358 and therein in particular "broadband lambda probe"), is used as the measuring device. The broadband lambda probe preferably has a probe head with 25 cell membranes made of zirconium dioxide.

[0027] Looking at this in more detail (see Figures 3 and 4), it is preferably provided that, at least in the first time interval z (preferably during the entire time interval y, i.e., during the entire safety time), a curve of the oxygen content in the combustion chamber is searched for extreme values, because such a (mathematical) extreme value (see also https: / / de.wikipedia.org / w / index.php?title=Extrem-wert&oldid=230203628) is an indication that, from this moment onward, the oxygen content in the combustion chamber is no longer increasing, but decreasing, or vice versa. This effect 5 is attributable to a particular cross-sensitivity of the broadband lambda sensor with unburned hydrogen, which is ultimately based on the consumption of the oxidizer due to a locally heterogeneously catalyzed hydrogen reaction. 10

[0028] Furthermore, it is particularly preferably provided that, when (such) extreme values ​​are present, an amount of a difference value and / or an increase in the oxygen content between a first and a second extreme value is optionally determined. This amount provides an indication of the strength of the above-described change in the oxygen content.

[0029] For the purpose of detecting an unwanted late ignition, it is furthermore particularly preferred that a local minimum is considered as the first 20 extreme value and a local maximum of the oxygen content is considered as the second extreme value, because it is characteristic of a late ignition, as corresponding laboratory tests have shown, in the combustion of hydrogen that the oxygen content drops according to the measuring device up to the first extreme value 25, but then rises up to a second extreme value and then falls again.

[0030] Since the said effect or the inherently undesirable late ignition is, however, entirely tolerable within a certain range, it is further preferably provided that a signal is generated (only) when the amount of either the difference value and / or the gradient is greater than a predefined limit value.

[0031] Finally, in order to ensure consistent implementation of the information obtained, it is preferably provided that the signal is used to close a safety valve 2 acting on the fuel gas supply and to lock the gas burner, before the unwanted and dangerous late ignition occurs.

[0032] 10 Again, from a slightly different perspective, the following physical boundary conditions must be taken into account when burning hydrogen:

[0033] The pressure increase over time (so-called KG value) is at least 10 times greater for fuel gas-air mixtures with 100% hydrogen than for methane or natural gas, assuming the same combustion air ratios are used. With increasing hydrogen content, both the ignition limits and the combustion speed increase, while the ignition delay time decreases, so that a lean ignition with a low pressure increase over time in the combustion chamber is desired. However, lean ignition conflicts with flame detection, since this is only ensured in near stoichiometry (air ratio less than 2 [power-dependent]) with sufficient flame intensity. Taking various fault scenarios into account, only short ignition times can be permitted for the combustion of hydrogen.For example, delayed ignition leads to a significant temporal increase in pressure in the combustion chamber with corresponding effects (destruction!) 30 on the chimney system and noise emissions in the area surrounding the device. For this reason, the start-up process is adapted according to the invention when hydrogen is used so that direct ignition is only active for a limited time during the safety time. In the first phase of the safety time with activated ignition, the physical initialization or ignition of the flame in the combustion chamber takes place in all tolerance positions. This is ensured by the movement of the control valve (gas ramp according to the characteristic curve). In the second phase of the safety time, the gas ramp is continued according to the characteristic curve without ignition. 10 The gas ramp stops at the end of the safety time at the latest or when the flame is detected.If the flame signal disappears after initial flame detection or after the safety time has elapsed, a fault lockout is initiated with closure of safety valve 2. 15.

[0034] List of reference symbols z first time interval y second time interval

[0035] 1 control valve

[0036] 2 safety valve

[0037] 3 flame sensor

[0038] 4 ignition electrode

[0039] 5 Measuring device

Claims

Patent claims 1. Method for starting a gas burner, in which on the one hand air and on the other hand from a first time also a fuel gas is supplied to the gas burner, in which at the latest from the first time a fuel gas mixture formed from the air and the fuel gas is exposed to ignition sparks in a combustion chamber for a first predetermined time interval (z), and in which a supply of the fuel gas is interrupted in the absence of a flame after the expiry of a second predetermined time interval (y) which is longer than the first time interval (z), characterized in that the supply of fuel gas to the air is increased at least from a first actual supply quantity to a second actual supply quantity within the second predetermined time interval (y) until a flame is detected.

2. Method according to claim 1, characterized in that the supply of fuel gas to the air is continuously increased within the second predetermined time interval (y) until a flame is detected.

3. A process according to claim 1 or 2, characterized in that a gas mixture containing at least 70% by volume of hydrogen is used as the fuel gas.

4. Method according to one of claims 1 to 3, characterized in that at least during the first time interval (z) an oxygen content in the combustion chamber is detected by a measuring device.

5. Method according to claim 4, characterized in that an oxygen probe, preferably a broadband lambda probe, is used as the measuring device.

6. Method according to claim 4 or 5, characterized in that at least in the first time interval (z) a profile of the oxygen content in the combustion chamber is searched for extreme values.

7. Method according to claim 6, characterized in that when extreme values ​​are present, an amount of a difference value and / or a gradient of the oxygen content between a first and a second extreme value is determined.

8. Method according to claim 7, characterized in that a local minimum is considered as the first extreme value and a local maximum of the oxygen content is considered as the second extreme value.

9. Method according to claim 7 or 8, characterized in that a signal is generated when the amount of either the difference value and / or the gradient is greater than a predefined limit value.

10. Method according to claim 9, characterized in that the signal is used to close a safety valve acting on the fuel gas supply and to lock the gas burner.

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