EP4015904A1 - Method and device for protecting a heater during the ignition of a mixture of air and hydrogen-containing fuel gas - Google Patents

Abstract

The invention relates to a method and a corresponding device for igniting a combustion process in a combustion chamber (13) of a heating device (1), which is operated with hydrogen or a fuel gas containing hydrogen, and a flame monitor (11) for detecting a flame with a response time (x) after the beginning of the supply of an ignitable mixture of air and combustible gas to the combustion chamber (13), an ignition process is triggered for a maximum of the duration of a predeterminable ignition time interval (z), which is shorter than a safety time interval (y), after the end of which the supply of an ignitable mixture is terminated if no flame has been detected up to this point. The present invention increases safety when starting a heating device operated with hydrogen or a fuel gas containing hydrogen and enables particularly gentle and safe ignition processes.

Description

The invention relates to a method and a device for protecting a heating device when a mixture of air and fuel gas containing hydrogen is ignited, in particular for preventing damage caused by pressure pulses.

Modern heating systems are often operated with premix burners, in which air and fuel gas are mixed in a suitable ratio and then the ignitable mixture is fed by a blower through openings in a burner body into a combustion chamber where the mixture is ignited and burned. A great deal of attention has always been paid to the ignition process, since a temporal malfunction of the ignition can lead to the accumulation of an explosive mixture in the combustion chamber or other components of the system, which can lead to uncontrolled deflagration (so-called misfires or hard ignitions) in the event of later ignition.

When using hydrogen as a fuel gas or a fuel gas with a high hydrogen content of z. B. more than 50%, especially more than 97%, it must also be considered that such deflagration can be much more violent than with conventional combustible gases (e.g. natural gas), since high flame speeds and large pressure increase gradients occur when hydrogen and air are burned and hydrogen flames can flash back into the torch body through very small openings.

According to the state of the art, when the heater is started, the blower is first switched on, then a suitable quantity of fuel gas is added to form an ignitable mixture, and after a suitable time interval (empirical value, e.g. depending on the length of the paths in the premixing system), the actual ignition process started. Here and in the following it is assumed that the ignition process is accomplished by electronically generated ignition sparks using an ignition electrode, ie an arc or a rapid sequence of ignition sparks is started and then remains switched on. According to the state of the art, for safety reasons there is always a flame monitor in or on the combustion chamber, which detects whether a flame is burning in the combustion chamber or not. Its signal is also used to end the ignition process (but not the supply of mixture) as soon as a flame is detected. According to the prior art, if no flame is detected, the ignition process and at least the fuel gas supply are terminated after a safety time interval has elapsed. With conventional combustible gases, standard flame monitors (e.g. ionization measuring devices or optical sensors) respond very quickly, so that ignition of the mixture can be detected almost immediately. If no flame is detected within the safety time, the ignition process is aborted because otherwise too much ignitable mixture could accumulate in the combustion chamber. Flushing with air and a repetition of the entire starting process can then follow and/or a fault message or shutdown of the system can take place.

However, when using hydrogen as fuel gas or fuel gases containing hydrogen, the situation is different for two reasons. On the one hand, as explained above, there is a higher potential for damage in the event of a deflagration, and on the other hand, flame monitors for such combustible gases are based on other measuring principles and take much longer to detect the presence of a flame. So you have a typical design Response time, which means that an ignited flame can only be detected with a delay. This response time can B. in the range of 0.1 to 5 s [seconds]. The response time can depend on the intensity of the flame to be detected, with safety considerations always assuming a maximum possible response time for a weak flame.

The object of the present invention is to take into account the problems described with reference to the prior art in an ignition process in a heater and in particular to achieve the safest possible course of ignition processes in heaters operated with hydrogen or hydrogen-containing fuel gas.

A method and a device as well as a computer program product according to the independent claims serve to solve this task. Advantageous refinements and developments of the invention are specified in the respective dependent claims. The description, in particular in connection with the drawing, illustrates the invention and specifies further exemplary embodiments.

In the method according to the invention for igniting a combustion process in a combustion chamber of a heater, which is operated with hydrogen or a hydrogen-containing fuel gas and has a flame monitor for detecting a flame with a response time, after the start of the supply of an ignitable mixture of air and fuel gas to the combustion chamber an ignition process is triggered for a maximum of the duration of a predeterminable ignition time interval, which is shorter than a safety time interval, after the end of which the supply of ignitable mixture is ended if no flame could be detected up to that point.

As explained, an ignitable mixture with hydrogen as a component has a higher damage potential than other ignitable mixtures, which is why, for safety reasons, such a mixture should only be ignited in the combustion chamber as long as the maximum quantity is limited. After that, ignition should no longer be possible, even if the mixture is still flowing. This means that the ignition process (ignition spark) may only last until the maximum amount is reached. This can be a relatively short ignition time interval of, for example, 1 to 5 s, in particular 2 to 3 s. The safety time interval, on the other hand, must be longer, in particular because the flame monitor needs at least the response time to recognize whether the ignition process was successful. According to the invention, therefore, the ignition time interval and the safety time interval are specified independently of one another according to the properties of a heating device and the safety requirements to be met. Under favorable conditions, it can still be the case that the flame monitor detects a flame during the ignition time interval and ends the ignition process (prematurely), but the ignition time interval can also be shorter than the response time of the flame monitor, which means that the ignition process ends before the flame is detected becomes.

In a particular embodiment, measures to intensify combustion can be taken during and/or after the ignition time interval has elapsed within the safety time interval. Since a flame cannot initially be detected due to the response time and ignition is no longer to be feared at least after the end of the ignition time interval, the supply of mixture can be increased or the composition (lambda value - ratio of air to fuel gas compared to a stoichiometric mixture) can be changed. This takes place on the assumption that ignition has been successful and has simply not yet been detected. If the assumption is correct, the combustion becomes more intense and the detection of the flame easier possible. This reduces the probability that a successfully ignited flame will not be detected by the end of the safety time interval (and the desired output of the heater will be reached more quickly). If the ignition was actually unsuccessful or if no flame was detected by the end of the safety time interval, the starting process is ended without the change in the supply of mixture being able to cause any damage.

Increasing the speed of a fan and/or changing the position of a fuel gas valve are particularly suitable and preferred measures. Increasing the speed increases the combustion performance and, in the case of a pneumatic combustible gas/air combination, reduces the lambda value. Changing the position of a fuel gas valve also affects performance and/or the lambda value.

In a typical embodiment of the invention, at least the supply of fuel gas is terminated at the end of the safety time interval. As a result, no further ignitable mixture gets into the combustion chamber. If the blower continues to run, the mixture in the combustion chamber is even diluted by air and flushed out, so that a new starting process has the original starting conditions again.

The method described is particularly preferably repeated automatically, with the combustion chamber being purged with air before it is repeated. A failure to start a heater is not uncommon and does not have to be immediately classified as a fault. If ignition is successful on a second or more attempts, no further consequences are generally required.

In order to increase the chances of a successful ignition, other parameters for the formation of the ignitable mixture are preferably set automatically each time the method is repeated, specifically parameters changed in the direction that ignition becomes more likely. Although an attempt is initially made to start the heater at the lowest possible output to protect the heater, the probability is higher with higher output, possibly also with a lower lambda value, which is used here.

In a particular embodiment of the invention, the ignition time interval is at most as long as the safety time interval minus the response time of the flame monitor. This is based on the consideration that ignition shortly before the end of the safety time interval would not be of any use if the flame detector does not have enough time to detect a developing flame due to its (long) response time, so that the starting process is aborted despite the flame being ignited would. This can be taken into account when specifying a maximum length of the ignition time interval.

In a device according to the invention for igniting combustion in a combustion chamber of a heater, the heater can be operated with a mixture of air and hydrogen or a fuel gas containing hydrogen, and a flame detector for detecting the presence of a flame in the combustion chamber with a response time is arranged on or in the combustion chamber , wherein the heater has an automatic ignition system that is set up to trigger an ignition process for the duration of a definable ignition time interval after the start of a supply of ignitable mixture to the combustion chamber, which is shorter than a safety time interval, after which the supply of ignitable mixture is ended if no flame detected became. In general, the automatic ignition is part of a control and regulation unit for the entire operation of a heater.

The automatic ignition system is preferably set up to initiate measures to intensify the combustion during and/or after the ignition time interval up to the end of the safety interval at most. This increases the probability that a successfully ignited flame can be detected by the end of the safety time interval. More intensive combustion shortens the response time of the flame monitor and/or increases its measurement signal.

In a typical embodiment of the invention, the automatic ignition is set up to trigger a flushing process of the combustion chamber after an ignition process has been aborted and then to repeat the ignition process of the heater.

In this case, the automatic ignition system is particularly preferably set up in such a way that, with each repetition of the ignition process, other parameters for the supply of ignitable mixture are set, namely parameters changed in the direction that ignition becomes more likely.

For gentle operation of a heater, the automatic ignition system is set up in particular to carry out the ignition process on a first ignition attempt with the smallest possible volume flow of mixture and to increase the speed of a fan and/or the supply of fuel gas with each repetition.

A further aspect of the invention relates to a computer program product, comprising instructions which cause the device described to carry out the method described executes An electronic unit with automatic ignition requires a program and data for controlling the heater and evaluating the signals from the flame monitor, both of which must or can be updated occasionally, for which purpose a computer program product can be used.

The explanations of the method can be used for a more detailed characterization of the device, and vice versa. The device can also be set up in such a way that the method is carried out with it.

Fig. 1:

schematisch ein erfindungsgemäßes Heizgerät mit Zündautomatik und Flammensensor und

Fig. 2:

ein Diagramm zur Veranschaulichung der erfindungsgemäßen zeitlichen Abläufe beim Start eines Heizgerätes.

A schematic embodiment of the invention, to which it is not limited, and the mode of operation of the method will now be explained in more detail with reference to the drawing. They represent:

Figure 1:

schematically a heater according to the invention with automatic ignition and flame sensor and

Figure 2:

a diagram to illustrate the time sequences according to the invention when starting a heater.

1 shows a schematic of a heater 1 according to the invention, in which air is sucked in by a blower 2 from an air inlet 4 and conveyed to a burner 3 . Hydrogen or a hydrogen-containing fuel gas from a fuel gas supply 8 is added to the air via a fuel gas valve 5 . The combustible gas/air mixture produced is ignited and burned in a combustion chamber 13 by means of an ignition electrode 12 . Exhaust gases that are produced give off most of their heat to a heat exchanger 14 and are then discharged into the environment through an exhaust system 10 . One Automatic ignition 6, usually integrated into a control and regulation unit 7, controls every start of the heater and the actual ignition process that takes place (the generation of ignition sparks). A flame detector 11, which is specially designed for the detection of hydrogen flames, is arranged on or in the combustion chamber 13. Such a flame monitor has a response time before it can reliably detect a flame after it has developed. The control and regulation unit 7 is equipped with a display 9, which can display the status of the system and/or warning signals.

2 illustrates the invention using an example of the time sequences for repeated ignition processes with changing parameters. The time (t) in seconds is given on the x-axis of the diagram. Curve A shows the course of the speed of the blower 2 over time. It can be seen that the speed increases step by step with each starting process and in between there are brief times with additional increases. In curve B, the opening of the fuel gas valve 5 is indicated. The respective opening time for a start attempt corresponds to the safety time interval y. There are 5 attempts to start, the last of which is successful. Curve C shows the times during which the actual ignition process (ignition spark active) takes place. 5 starting attempts are shown, each with an ignition time interval z, z being smaller than y according to the invention. Curve D shows the times when a flame is present. A flame actually erupted during three attempts to start, but this could not be detected twice, which is why the relevant starting processes were aborted despite the flames. As curve E shows, during the last attempt to start, a flame that had developed was also detected, so that the combustion process was continued. The time delay between the occurrence of the flame in curve D and the time of detection corresponds to the response time x of the flame monitor 11. If no flame had been detected again, the starting processes would have ended completely and the combustion chamber would have been flushed 13 is done with air. Curve A also shows that more air was supplied with each start attempt and that after the end of the respective ignition time interval z the speed of fan 2 was increased in order to intensify combustion (if ignition should have taken place). In addition, the blower 2 continues to run after the fuel gas valve has been switched off in order to flush the combustion chamber 13 . At the end, the speed is increased to the desired output of the heater.

The present invention increases safety when starting a heating device operated with hydrogen or a fuel gas containing hydrogen and enables particularly gentle and safe ignition processes.

Reference List

1

heater

2

fan

3

burner

4

air intake

5

fuel gas valve

6

automatic ignition

7

control and regulation unit

8th

fuel gas supply

9

advertisement

10

exhaust system

11

Flame Warden

12

ignition electrode

13

combustion chamber

14

heat exchanger

A

Fan speed curve

B

Curve position fuel gas valve

C

Ignition spark curve

D

curve flame

E

Flame detection curve

x

response time

y

safety time interval

e.g

ignition timing interval

Claims (13)

Method for igniting a combustion process in a combustion chamber (13) of a heating device (1), which is operated with hydrogen or a fuel gas containing hydrogen and has a flame detector (11) for detecting a flame with a response time (x), wherein after the start of the supply of a ignitable mixture of air and combustible gas to the combustion chamber (13), an ignition process is triggered for a maximum of the duration of a predeterminable ignition time interval (z), which is shorter than a safety time interval (y), after which the supply of ignitable mixture is terminated if to until then no flame could be detected. Method according to claim 1, wherein during and/or after the ignition time interval (z) has elapsed within the safety time interval (y) measures are taken to intensify combustion. Method according to Claim 2, in which the measures include increasing the speed of a fan (2) and/or changing a position of a fuel gas valve (5). Method according to one of Claims 1 to 3, in which at least the supply of fuel gas is terminated at the end of the safety time interval (y). A method according to any one of the preceding claims, wherein the method is repeated automatically, with the combustion chamber (13) being flushed with air before a repetition. Method according to Claim 5, in which, with each repetition of the method, different parameters for the formation of the ignitable mixture are automatically set, parameters changed in the direction that ignition becomes more likely. Method according to one of the preceding claims, in which the ignition time interval is at most as long as the safety time interval (y) minus the response time (x) of the flame monitor (11). Device for igniting combustion in a combustion chamber (13) of a heater (1), the heater (1) being operable with a mixture of air and hydrogen or a fuel gas containing hydrogen and a flame monitor (11) on or in the combustion chamber (13) arranged to detect the presence of a flame in the combustion chamber (13) with a response time (x) and wherein the heater (1) has an automatic ignition system (6) which is set up to initiate an ignition process for the Trigger duration of a predetermined ignition time interval (z), which is shorter than a safety time interval (y), after which the supply of ignitable mixture is terminated if no flame was detected. Device according to Claim 8, in which the automatic ignition system (6) is set up to initiate measures for intensifying the combustion during and/or after the ignition time interval (z) up to at most the end of the safety interval (y). Device according to claim 8 or 9, wherein the automatic ignition system (6) is set up to trigger a flushing process of the combustion chamber (13) after an ignition process has been aborted and then to repeat the ignition process of the heater (1). Device according to Claim 10, in which the automatic ignition system (6) is set up to set different parameters for the supply of ignitable mixture each time the ignition process is repeated, namely parameters changed in the direction that ignition becomes more likely. Device according to claim 11, wherein the automatic ignition system (6) is set up to carry out the ignition process in a first ignition attempt with the smallest possible volume flow of mixture and to increase the speed of a fan (2) and/or the supply of fuel gas with each repetition. A computer program product comprising instructions that cause the apparatus of any one of claims 8 to 12 to carry out the method of any one of claims 1 to 7.

Images