EP3841326A1 - Heating device and method for regulating a fan-operated gas burner - Google Patents

Abstract

A method for regulating a gas burner, wherein the gas burner has a combustion air supply fan whose rotational speed can be set variably, has the following steps: – operating the fan and detecting a fan rotational speed (nVBL); – changing the fan rotational speed; – measuring an ionization voltage (UION) which correlates with an ionization flow in a flame region of the gas burner; – finding a minimum of a gradient of the measured ionization voltage at the current fan rotational speed; – determining an operating point by measuring the current ionization voltage and storing as an operating point; – while the burner is operating, continuously measuring the current ionization voltage; – determining a deviation between the currently measured ionization voltage and the operating point; – checking whether the deviation (Delta UION) is within a predefined limit (UY) and carrying out a case differentiation: + if the deviation is within the predefined limit (UY), continuing the continuous measurement of the current ionization voltage; + if the deviation is not within the predefined limit (UY), repeating the method from the above change in the fan rotational speed.

Description

 Heater and

Method of controlling a blower gas burner

The invention relates to a method for regulating a gas burner, the gas burner having a fan for supplying combustion air, the speed of which can be variably adjusted. Furthermore, the invention relates to a Heizvorrich device with a correspondingly adjustable gas burner.

Various possibilities are known for monitoring the presence of a flame in a gas burner, which are based in particular on thermal, optical or electrical principles. Ionization flame detection, in which the ionization effect of a flame is used to detect whether the burner is generating a flame or not, is particularly reliable.

Examples of such devices are described, for example, in EP 2 357 410 A2 and DE 10 2005 012 388 A1.

In flame ionization detection, an alternating voltage is applied in the area of the flame, usually with the aid of an ionization electrode and a ground electrode. When the flame burns, it causes a rectifying effect on the AC voltage, which causes current to flow from the ground to the ionization electrode. This current flow is evaluated or worked up by measuring electronics and can be provided in the form of an ionization voltage. The ionization voltage provided as the measurement result at the output of the measuring electronics thus correlates with the ionization current.

If the measuring electronics output an ionization voltage that exceeds a certain limit, this is recognized as the presence of a flame. On the other hand, falling below a corresponding limit value can be interpreted as meaning that no flame is burning.

Gas burners, in particular fan-operated gas burners, are frequently exposed to changing environmental conditions, which can lead to changing combustion behavior. Such environmental parameters are, for example, air pressure, temperature of the combustion supply air, gas pressure (pressure at which the fuel gas is supplied), type of gas and also the energy value of the gas. It should be borne in mind that the composition of the fuel gas can often vary. To the For example, the composition of typical gas mixtures such as LPG (liquefied petroleum gas - LPG) or typical propane / butane mixtures can be changed. Depending on the gas supply, it is possible for pure propane, pure butane or an undefined propane / butane mixture to be supplied.

Due to the changing environmental parameters, there is a possibility that the gas burner will not be operated at the optimal operating point at which the fuel is optimally burned and the pollutant emissions are minimal. This state is often identified with l = 1, in which the fuel gas and oxygen are in a stoichiometrically determined ratio.

DE 10 2017 204 012 A1 describes a method for regulating a gas burner.

From DE 10 2008 027 010 Al a method for checking an ionization signal of a burner is known.

DE 10 2015 1 16 458 A1 describes a method for distinguishing two combustion gases with different energy levels provided for a combustion process.

Another method for regulating a gas burner is described in US Pat. No. 5,971,745.

DE 199 47 181 A1 discloses a method for determining a signal representative of the current air ratio.

Finally, DE 198 31 648 A1 is concerned with a method for the functional adaptation of control electronics to a gas appliance.

The invention has for its object to provide a method for controlling a gas burner with which a defined operating point for a burner operation can be ensured. The operating point should then be close to the op timum for burner operation.

The object is achieved according to the invention by a method having the features of claim 1. Advantageous refinements are specified in the dependent claims. A method for regulating a gas burner is specified, the gas burner having a blower for supplying combustion air, the speed of which can be variably adjusted. The method has the following steps in particular:

 Operating the blower and sensing a blower speed;

 Changing the fan speed;

 Measuring an ionization voltage that correlates to an ionization current in a flame region of the gas burner;

 Finding a minimum of a gradient of the measured ionization voltage to the current fan speed;

 Determining an operating point by measuring the current ionization voltage and storing it as an operating point;

 continuous measurement of the current ionization voltage during burner operation;

 Determining a deviation between the currently measured ionization voltage and the operating point;

 Check whether the deviation is within a predefined limit and carry out a case distinction: if the deviation is within the predefined limit, continue the continuous measurement of the current ionization voltage; if, on the other hand, the deviation is not within the predetermined limit, repeat the process from the above step "changing the fan speed".

The process is usually carried out by a processing and control unit, which processes the process steps and communicates with the corresponding components (flame detector or ionization voltage sensor, fan motor, etc.).

With the aid of the method, the fan of the gas burner is thus operated in order to supply combustion air. The fan speed is recorded in a suitable manner, for example by one or more Hall sensors or by determining the so-called commutation harmonics of the rotor and stator packets on the supply voltage of the rotor. Correspondingly, for example, pulses can be generated per minute by a measuring device and made available to a processing and control unit. Other methods for detecting the speed are also known which are suitable for the control described here. The processing and control unit is able to change the fan speed, ie to reduce or increase it. To do this, it can control the blower motor accordingly.

According to the method, an ionization voltage is measured which correlates to an ionization current in a flame area of the gas burner. The voltage value is generated by a rectified frequency signal from the burner flame and made available to the processing and control unit via a so-called shunt resistor and by means of an analog / digital conversion.

As stated above, when a flame is present, there is a current flow (ionization current) due to the rectifying effect of the flame on the AC voltage applied. This ionization current is converted into a representative voltage (ionization voltage) with the aid of an evaluation circuit with differential amplifier, so that the further evaluation can be carried out voltage-based or - after the analog / digital conversion - digitally. The voltage values can thus be digitized and further processed.

According to the method, while the fan speed is being changed, an attempt is made to find a minimum of a gradient of the measured ionization voltage to the current fan speed. The fan speed is thus specifically changed, i.e. decreased or increased. At the same time, the ionization voltage is determined. As long as the ionization voltage changes more than the fan speed, the fan speed will continue to vary. Only when the optimum in the form of the minimum of the gradient has been found is there no further change in speed.

The specified gradient describes the ionization voltage change measured in the flame in relation to the speed change of the combustion air blower. The gradient minimum is exactly the point that serves as a distinguishing feature or boundary between a rich or a lean operation of the gas burner. At a lower speed, the so-called “rich area” begins, in which the combustion air supplied by the combustion air blower is not sufficient to completely burn the fuel gas. At a higher speed, the so-called “lean area” exists, in which more combustion air is supplied than is necessary. This decision criterion cannot be determined with absolute values alone, since it always has to take into account the changes that belong together.

The gradient thus describes the reaction of the burner (in the form of the ionization voltage) to the change in speed.

Based on the operating state thus found, i.e. an operating point for the ionization voltage is determined and stored, the current ionization voltage and the corresponding fan speed. For this purpose, the parameters (fan speed or the correspondingly changing ionization voltage) can also be changed in advance, as will be explained later.

This state is considered to be optimal in which the gas burner is to be operated on the basis of the environmental parameters given at this point in time.

Subsequently, the measurement of the current ionization voltage is carried out continuously or continuously, that is to say, for example, at certain time intervals. The currently measured ionization voltage is compared with the operating point or the previously stored ionization voltage at the operating point. A deviation is determined.

In the following it is checked whether the deviation thus determined is within a predetermined limit. As long as the deviation lies within the specified limit, the current ionization voltage is continuously measured.

On the other hand, if the deviation is not within the predetermined limit and is therefore too large, the above-described method for determining a new operating point is repeated. In this case, it is recognized that the environmental parameters have changed such that the burner can no longer be operated in the optimum state, which necessitates a readjustment by determining a new operating point.

To start the method, it is possible to operate the blower at a predetermined output speed and then to reduce the blower speed before measuring the ionization voltage. Only then does the measurement of the ionization voltage begin and the subsequent finding of the gradient minimum. The measurement and further processing of the ionization Voltage in the manner described above only makes sense if a flame is also generated by the burner, i.e. a flame has been ignited.

In one variant, after the step of “finding a minimum of a gradient of the measured ionization voltage relative to the current fan speed” and before the step “determining an operating point”, the additional step is carried out that the fan speed is increased by an offset value.

The offset value is burner-dependent or device-specific and thus represents the device-specific distance from the minimum speed at which the burner works as optimally as possible with regard to exhaust gas values and / or output.

As stated above, the method aims to find a minimum of the gradient of the ionization voltage to the fan speed so that the burner can be operated in the optimal operating state. From practice, however, it is known that in typical burners, even small deviations, for example in relation to the environmental parameters, can result in the burner's combustion behavior changing drastically at this speed minimum. It has therefore proven to be expedient that the burner should not be operated at this minimum, but just above it. This leads to a "good-natured" burner behavior.

The offset value is determined in such a way that the legal limit values are observed even when operating with extreme values of the operating parameters. For example, in practice there are cases where e.g. (Fuel) gas supplied from a gas bottle contains more butane than is the case with a generally customary propane / butane mixture. There is therefore a risk that CO emissions will increase. For this extreme case, the offset is set in such a way that even with operation with a higher butane content in the fuel gas, the legally maximum permissible limit value is not exceeded. In other words: The offset is chosen so that you are as far away from the sensitive minimum value as possible, but not so far that you can change special, but actually existing and therefore known or predictable effect changes outside of the legal. Norms lies.

The determination of the offset value follows from the measurement of the burner type and is therefore also dependent on how far the manufacturer should be allowed to move away from the minimum (optimum). Typically can such an offset value is in the range from 50 rpm to 1,000 rpm, although other values can also be useful.

The following steps can be carried out for the step of "finding a minimum of a gradient of the measured ionization voltage at the current fan speed":

 Reducing fan speed;

 Measuring the current ionization voltage;

 Determining the gradient of the measured ionization voltage to the current fan speed;

 To make a case distinction:

 If the gradient is less than zero (0), decrease the fan speed and repeat the above steps of measuring the current ionization voltage and finding the gradient. If the gradient is greater than zero, increase the fan speed and repeat the above steps of measuring the current ionization voltage and finding the gradient. If the gradient is zero, determine the gradient as the minimum and continue the procedure.

The criterion that the gradient can be "zero" does not have to mean that it must be exactly "0". Rather, it is sufficient here if the gradient is below a predetermined threshold, that is to say also just above zero or below zero.

With the help of the steps described here, it is possible to find the gradient minimum by varying the fan speed, so that this minimum can subsequently be determined as the operating point, if necessary after adjustment by an offset value, as already explained above.

The output speed of the fan when starting the process should sensibly be set to a high value. For example, the output speed of the fan can be set to a value in the upper third of the speed range of the fan, particularly in the upper quarter, in the upper fifth or in the upper 10% of the speed range. It is also possible to select the maximum speed of the fan as the output speed and then to reduce the speed in order to find the minimum gradient.

Fan-assisted gas burners are known in which the so-called first ignition point when the burner is started by means of a so-called ramp start. is determined table. With a fixed gas flow rate and a permanently running ignition device, the speed of the combustion air blower is continuously reduced from a very high speed until the gas / air mixture has the best possible composition and ignites automatically. The speed measured here is then the output speed for the further regulation according to the method described above.

Alternatively, it is possible to set the output speed of the blower to a previously known ignition speed. A known ignition speed (depending on the barometric air pressure, the temperature of the combustion air and the gas flow) can also be selected as the starting point.

A typical starting speed can be, for example, 4,000 rpm.

The ionization voltage can be determined based on the ionization current such that the ionization current is determined as the current flow that occurs when rectification of an AC voltage caused by the presence of a flame is applied to an ionization electrode arranged in the flame region, the ionization current being passed through an evaluation circuit is converted into a corresponding ionization voltage.

A heating device has at least one gas burner which has a combustion air blower driven by a motor, in particular by a speed-controllable motor, and a flame ionization voltage measuring device for detecting an ionization voltage which is dependent on a flame generated by the gas burner. A processing and control unit is also provided, which is coupled to the motor and the flame ionization voltage measuring device. The processing and control unit can be designed to carry out the method described above and regulate the speed of the motor of the combustion air blower in particular on the basis of an evaluation of the ionization voltage.

These and other advantages and features of the invention are explained in more detail below using examples with the aid of the accompanying figures. Show it:

Fig. 1 is a schematic block diagram for a control system for

Regulating a gas burner; and Fig. 2 is a flowchart with a control method for a ge-powered gas burner.

Fig. 1 shows a very rough representation of the basic structure of a Regelsys system, on which the inventive method for regulating a blower-operated gas burner can be carried out.

The control system has a processing and control unit 1. Furthermore, a sensor 2 is provided with which the ionization current is measured in the area of a flame generated by the burner and converted into an ionization voltage U _ION using a suitable evaluation circuit. The ionization voltage U _ION is output as a measured value and passed to the processing and control unit 1.

In a practical application, the ionization voltage U _ION at the output of the measuring circuit in the presence of a flame can, for example, be in the range between 0.3 V to 3.3 V depending on the quality of the combustion. If the voltage is less than 0.3 V, the flame is recognized as extinguished. In order to increase the robustness of the detection, a hysteresis window of, for example, 0.3 V to 0.7 V is provided. This means that when the flame is detected for the first time, it is only recognized as existing when the ionization voltage reaches at least 0.7 V. In contrast, the flame is only recognized as extinguished when the voltage drops below 0.3 V.

The processing and control unit 1 is also connected to a motor 3 of a combustion air blower, not shown. In particular, the processing and control unit 1 can control the speed of the motor 3 and thus the combustion air blower. Conversely, it is necessary for the processing and control unit 1 to receive information about the speed n _{VBL of} the engine 3 and thus of the combustion air blower. The speed information can be determined in a suitable manner. So it is possible that the processing and control unit 1 itself also specifies the speed by a corresponding control of the motor 3. Likewise, 3 sensors (for example one or more Hall sensors) can be provided on the motor in order to determine the speed of the motor 3. Various options are known for this, which need not be deepened here.

The control of the rotational speed of the motor 3 and thus the speed of the combustion air blower can be achieved, for example, by a pulse width Modulation can be specified in a range from 0% to 100% of the rotational speed. Alternatively, the drive voltage of the motor 3 or the drive current of the motor for speed control can also be set directly.

FIG. 2 shows a flow diagram with a method for regulating a blown gas burner.

At the start of the method, the combustion air blower is operated at an output speed which should correspond to a relatively high speed at a starting point SO. Starting from this speed, the speed n _{VBL is} reduced in a step S 10. In a step S20, the ionization voltage U _ION is measured in the manner described above.

In a step S30, a gradient of the ionization voltage U _ION to the speed n _{VBL is subsequently} determined. If the gradient is less than 0, the method goes to step S 10, so that the speed n _{VBL is} further reduced.

On the other hand, if the gradient in step S30 is greater than 0, the speed is increased in step S40. Subsequently, the ionization voltage U _{ION is} measured again in a step S50 and the gradient is determined in a step S60.

If the gradient is then still greater than 0, the rotational speed is increased further in step S40 and a gradient is determined again in step S60.

If it was recognized in steps S30 or S60 that the gradient is 0 or very close to 0, this is recognized as the minimum of the gradient (based on the amount) and thus as the optimum. At the same time, this point also corresponds to a minimum speed for the fan speed.

The "minimum of the gradient" is to be understood as the absolute value. The minimum of the gradient is therefore found at the value 0, while values greater or less than 0 lie above the minimum.

This operating point thus recognized means that the ratio between the air supply (determined by the combustion air blower) and the fuel gas supply is optimal for the burner, so that the energy content of the fuel gas can be optimally utilized, with at the same time minimal pollutant emissions. The burner is therefore operated in an optimal operating state. A further reduction in the fan speed would result in too little combustion air being supplied, so that the mixture to be burned would be set too rich. This would result in unnecessarily high fuel gas consumption.

In step S70, the speed is changed using an offset speed n _x . This change in step S70 is optional and does not necessarily have to be carried out. However, it has been found that, in the case of conventional burners, even small deviations, for example in relation to the environmental parameters, can result in the combustion behavior of the burner changing significantly when operating in the speed minimum described above. In order to allow a greater tolerance and thus a more good-natured behavior here, the minimum value for the rotational speed just found in steps S30 and S60 is increased by the offset value n _x . The n _x value follows from measurements of the type of burner used and can be determined by the manufacturer depending on the design goal.

In the following, the ionization voltage is measured for the "optimal" speed thus established in step S80 and stored as the operating point U _B. The burner can be operated optimally at this operating point, provided that the environmental parameters do not change or only change slightly.

In the subsequent operation, the ionization voltage is continuously measured in step S90 and the quality of the flame is thus detected. The ionization voltage can be measured continuously or at regular or widely specified intervals.

In step S 100, a difference between the ionization voltage U _ION measured in step S90 and the ionization voltage U _B determined as the operating point in step S80 is determined in the form of the value delta U _ION . This deviation of the ionization voltage values is then compared with a value U _Y , which represents a decision criterion for the permissible change in the ionization voltage.

If it is determined in step S 100 that the deviation of the current ionization voltage U _ION from the ionization voltage U _B specified for the operating point is less than or equal to the value U _Y , the measurement is continued in step S90 and the burner operates kept unchanged. However, if it is determined in step S 100 that the deviation is too large, the method determines that a readjustment of the operating point is necessary. One reason for this can be a change in one or more environmental parameters, for example, which means that the burner can no longer be operated at the optimum operating point at this point in time.

The method is then carried out again, by reducing the speed in step S 10. Before that, it is sensible to raise the speed to a higher value (output speed) in order to be able to change the speed over a larger range.

Claims

claims 1 . Method for regulating a gas burner, the gas burner having a fan for supplying combustion air, the speed of which can be set variably, with the steps Operating the blower and sensing a blower speed (n _VBL );  Changing the fan speed;  Measuring an ionization voltage (UION). which correlates to an ionization current in a flame area of the gas burner;  Finding a minimum of a gradient of the measured ionization voltage to the current fan speed;  Determining an operating point by measuring the current ionization voltage and storing it as an operating point;  continuous measurement of the current ionization voltage during burner operation;  Determining a deviation between the currently measured ionization voltage and the operating point; Check whether the deviation (Delta U _ION ) is within a specified limit (U _Y ) and carry out a case distinction: + if the deviation is within the predetermined limit (U _Y ), continuing to measure the current ionization voltage continuously; + if the deviation is not within the specified limit (U _Y ), repeat the procedure from the above changing the fan speed. 2. The method according to claim 1, wherein to start the method, the following steps are carried out before measuring the ionization voltage:  Operating the blower at an output speed;  Reduce the fan speed. 3. The method of claim 1 or 2, wherein after the step "Finding a minimum of a gradient of the measured ionization voltage to the current fan speed" and before the step "Determining an operating point", the additional step is carried out: Increase the fan speed by an offset value (n _x ). 4. The method according to any one of the preceding claims, wherein for the step "Finding a minimum of a gradient of the measured ionization voltage at the current fan speed", the following steps are carried out: Reducing fan speed;  Measuring the current ionization voltage;  Determining the gradient of the measured ionization voltage to the current fan speed;  To make a case distinction:  + if the gradient is less than zero, reduce the fan speed and repeat the above steps of measuring the current ionization voltage and finding the gradient;  + if the gradient is greater than zero, increase the fan speed and repeat the above steps of measuring the current ionization voltage and finding the gradient;  + if the gradient is zero, determine the gradient as a minimum and continue the method. 5. The method according to any one of the preceding claims, wherein the output speed of the blower is set to a value in the upper third of the speed range of the blower. 6. The method according to any one of the preceding claims, wherein the output speed of the fan is set to a known ignition speed. 7. The method according to any one of the preceding claims, wherein the ionization voltage (UION) is determined on the basis of the ionization current, such that  the ionization current is determined as the current flow which occurs in the rectification of an AC voltage caused by the presence of a flame, which is applied to an ionization electrode arranged in the flame region; and that  the ionization current is converted into a corresponding ionization voltage by an evaluation circuit. 8. Heater, with  at least one gas burner having a combustion air blower driven by a motor (3);  a flame ionization voltage measuring device (2) for detecting an ionization voltage (UION). which is dependent on a flame generated by the gas burner; and with a processing and control unit (1), which is coupled to the motor (3) and the flame ionization voltage measuring device (2); in which  the processing and control unit (1) is designed to carry out the method according to one of the preceding claims.