EP0833106B1 - Method and device for operation optimisation of a gas burner - Google Patents

Description

In order on the one hand to make the best possible use of the fuel and on the other hand to largely reduce the emission of harmful combustion products into the environment, attempts are made to supply gas burners with such a gas / air mixture that this burns optimally and completely. In the case of conventional gas / air controllers, a predetermined Wobbe index of the fuel gas is assumed and the mixing ratio is accordingly kept constant. However, the gas supply does not in any way supply fuel gas with the same or constant Wobbe index, so that, in particular in the case of premixed gas burners and atmospheric burners with low NO _x emissions, sometimes not with the conventional gas / air control devices which comply with a predetermined gas / air ratio a really optimal combustion can be achieved in all cases. An additional oxygen sensor has therefore been provided in the flue gas outlet, which, depending on the oxygen content of the flue gases, changes the gas / air mixture ratio via a regulator that acts on the gas or air supply in the direction of optimal combustion with a small excess of air, for example 4%. Such an additional oxygen or NO _x sensor increases the costs of the control device and, since it is arranged in the flue gas outlet, is subject to considerable contamination. It must therefore be regularly serviced and cleaned or replaced.

Various methods are known in the prior art, the gas / air ratio without Monitor or regulate the oxygen sensor in the flue gas outlet. So describes DE 41 12 449 A1 describes a method for regulating a surface burner, in which the air supply in Depending on the temperature in the area of the burner is regulated. For this is in the Burner plate a temperature sensor arranged. Raises the flame if it is too high Excess air from the burner plate reduces its temperature and the temperature sensor gives the fan a control signal that reduces its speed. That way Disturbances such as changing gas quality, fluctuations in the supply voltage of the Blower motor or changes in air temperature automatically compensated. You get one Type lambda control without the disadvantages of a lambda probe in the flue gas outlet.

DE-39 37 290 A1 describes a method for controlling the one to be fed to a burner Gas / air mixture, the electrical conductivity of the flame region, i.e. the size the ionization current of a flame rod immersed in the flame as a parameter for the mixture composition serves. The conductivity of the flame area is measured and compared with an empirically determined target value. The deviation of the actual value from Setpoint value delivers a signal that changes the mixture composition, for example the blower motor, which changes the mixture composition until the Flame rod signals that the conductivity setpoint in the flame area has been reached. On in this way, even with varying gas quality and changing air conditions constant combustion quality can be achieved. Also DE 44 33 425 A1 and DE 195 02 901 A1 use the ionization current of a flame sensor to control the mixture.

Furthermore, a burner is known from DE-22 52 618 A1, in which the position of the flame in is visually monitored with respect to the burner plate, including a flame to glow brought platinum wire and a photo element. Strikes the flame on the burner back, the platinum wire located near the burner plate is heated and that Radiation of the platinum wire is applied to the photoelement. This turns into the speed of the fan increasing signal derived. On the other hand, the flame travels from the burner gone, the platinum wire is no longer heated and the photo element receives from this no more radiation. The resulting signal lowers the fan speed.

Finally, CH 389 539 describes a safety device on gas burners with a thermoelectric sensor, if the gas / air mixture is properly composed just touched the perimeter of the blue core of the flame. The changes Composition, the sensor protrudes into a cooler part of the flame, causing the sensor cools down and the gas valve closes.

The invention proposes a method and a device for operating a gas burner which do not require an additional oxygen or NO _x sensor in the flue gas outlet and nevertheless lead to an at least approximately optimal combustion even when using different types of gas with a different Wobbe number.

The method and the device according to the invention are in the independent Characterized claims. Advantageous configurations result from the Dependent claims. The invention uses the anyway to monitor the burner flame existing flame sensor additionally in the course of a calibration of the burner system, the optimal gas / air ratio depending on the type of gas determine. The invention takes advantage of the fact that on the one hand with sufficient Excess gas ignites the flame with certainty and on the other hand the flame in dependence the size and position of the burner in relation to the amount of air changed. At high Air content increases the outflow speed of the gas / air mixture from the burner than the rate of combustion. This causes the flame to rise from the burner. If one arranges the flame sensor in such a way that it detaches the flame from the Burner can determine, this lifting of the flame can be evaluated that it as a sign of an excessively high proportion of air, i.e. for a non-optimal gas / air ratio is exploited. During the flame sensor in normal operation when the flame goes out it delivers a signal to stop the burner during the calibration despite the burning Flame will also give off a signal indicating the absence of a flame, if removed the flame from the flame sensor. With a single flame sensor you can on the one hand the presence of the flame in normal operation and on the other hand the position of the Monitor flame during calibration. Of course, you could go for the two processes also use separate flame sensors. It may be one in the flame immersed thermal flame sensor, e.g. a flame rod or one act optical flame sensor, which is sufficiently focused to raise the flame to be able to recognize.

Figur 1

schematisch einen Hauptbrenner mit austretenden Flammen und zwar im Normalbetrieb (A) mit optimaler Flammenhöhe, bei etwas zu hohem Luftüberschuß (B) sowie bei starkem Luftüberschuß und abgehobener Flamme (C);

Figur 2

eine Gas/Luft-Regeleinrichtung mit einem in Abhängigkeit vom Wärmebedarf ein- und abschaltenden Gasventil; sowie

Figur 3

eine ähnliche Regeleinrichtung mit in Abhängigkeit vom Wärmebedarf modulierendem Brennstoffventil.

The invention is explained below with reference to exemplary embodiments shown in the drawings. It shows:

Figure 1

schematically a main burner with escaping flames, namely in normal operation (A) with an optimum flame height, with excess air excess (B) and with excessive air excess and flame (C);

Figure 2

a gas / air control device with a gas valve that switches on and off depending on the heat requirement; such as

Figure 3

a similar control device with modulating fuel valve depending on the heat requirement.

In all three operating states A, B and C shown in FIG. 1, several flames 1 occur from corresponding openings of the burner 2 and are in by a flame sensor Form of a flame rod 3 monitored. In the optimal operating state A, the flame begins directly at the outlet opening of the burner 2 and has a size such that the Flame rod 3 into the flame tip, i.e. the flame area with the highest temperature protrudes. So here is an optimal gas / air mixture, which is almost complete Combustion and thus the lowest possible unburned content in the flue gas guaranteed.

In operating mode B, the gas / air mixture supplied to burner 2 contains too much air, which increases the flame. Here the flame sensor 3 no longer protrudes into the Area of the flame tips, but into the middle flame area, the opposite the tip of the flame has a lower temperature. Nevertheless, the recognizes Flame sensor 3 the presence of the flames 1.

In operating mode C, the gas / air mixture has a very high excess of air. The flames 1 are still present, but so far from the burner 2 that the Flame rod 3 is no longer immersed in the flame 1 itself. The flame sensor 3 can do not recognize the presence of the flames 1, but reports to a connected one Monitoring circuit a flame failure, although the flames 1 in reality available. This lifting of the flames 1 from the burner 2 is according to the invention used to calibrate the gas / air ratio when the burner contains gases different Wobbe index should burn optimally.

For this purpose, a test copy of the burner is operated with an optimal gas / air mixture and at the same time measured the oxygen content in the exhaust gas. The purpose of this measurement is that Actually optimally adjust gas / air mixture. The operating mode is A. Then increase the excess air until finally the flames 1 according to operating mode C. as far as are lifted from the burner 2 that the flame sensor 3 the presence of the No longer detects flames, but reports a flame failure. At the same time, by what percentage of excess air compared to optimized operating mode A. Has. This percentage increase in excess air until the flame is lifted from Flame rod 3 is a characteristic parameter of the burner, which is used only once for the relevant burner type must be determined.

When installing a burner and then at regular intervals, for example once or twice a day, the burner is calibrated as follows:
The burner is started with sufficient gas excess so that it ignites in any case and the flames are created. The excess gas depends on the gas with the lowest calorific calorific value to be burned in the installation in question. The setting of the corresponding control elements for gas and air supply is known. After the flame has been ignited, the gas / air ratio is changed in the direction of excess air by appropriate adjustment of the actuators determining the gas / air ratio, for example by means of a gas / air controller. As soon as the excess air has reached a value at which the flames 1 lift off the flame rod 3, the flame sensor 3 switches off the burner. This is a characteristic and repeatable operating point of the burner in cooperation with the flame sensor. From this operating point, the gas / air ratio is changed by the aforementioned percentage, once determined, in the direction of a reduction in the excess air and thus achieves the optimum gas / air ratio in accordance with operating mode A. Now the burner is in view of the Wobbe number of the gas just burned is calibrated and can be operated optimally by keeping this gas / air ratio constant. The maintenance of the gas / air ratio is predetermined by the setting of the relevant actuators or can be ensured by a gas / air controller known per se.

If the burner is switched between two calibration cycles as a result of an excessive change in the If the gas quality does not ignite, the calibration process can be repeated automatically. Each the more often such a calibration is carried out, the lower the risk that the Burner between two calibrations with a non-optimal gas / air ratio is operated. The invention is for both burners with a switching and with a modulating gas valve.

With the help of FIG. 2, the method of operation when using a switching is first described On / off gas valve explained. Gas is the combustion chamber or the burner 2 from a Gas line G forth supplied via such an on / off gas valve 4 and a gas injector 5. At the same time, a blower 6 generates a stream of combustion air, which is passed through an air nozzle 7 Burner 2 arrives. As long as only one type of gas is burned, the blower 6 could with one operated by the desired gas / air ratio predetermined speed. The However, the invention provides an adaptation of this speed to the gas type in question to set an optimal gas / air mixture by means of the calibration mentioned. To do this the system started with a low speed of the blower 6, so that with certainty Burner ignites and the flame sensor 3 reports the presence of flames. Then the controller 8 increases the speed of the fan 6 until as a result of the increased Excess air, the flames are lifted from the flame sensor in accordance with operating mode C. have and this consequently delivers a flame failure signal to the controller 8. The preferred controller 8 equipped with a microprocessor and memory does not switch over here individual shown but known signal connections from the system and saves at the same time the speed value given when the flames go out. The controller then reduces 8 is the target value of the fan speed by the above-mentioned predetermined percentage, that from the shutdown operating point according to operating mode C, the excess air on the optimal mode of operation A is reduced. Now the system is optimized with this Gas / air ratio or excess air released for operation. For example, once a room to be heated or a hot water tapping point the supply of heat and thus requests the burner to be switched on, the controller 8 puts the system into operation by the Gas valve 4 opened and the blower 6 at the now optimized speed is operated until there is no longer any need for heat. With only rarely switched on systems Such a calibration process can be preceded by every activation. For plants, which switch on and off more often is usually sufficient if the calibration is done once or takes place two times a day. The Wobbe index of the supplied gas changes frequently Security not.

The calibration process can also be carried out without interrupting burner operation be when the controller 8 when switching on the system and when the Flame failure signal due to the flame lifting off the burner the fan speed reduced by the specified percentage without reducing the gas supply and thus the Interrupt the burning process.

Figure 3 shows in simplified form a burner system with modulating operation, i.e. Gas and Air supply changes depending on the respective heat requirement. The fuel gas G arrives again via an injector 5 and the combustion air L via an air nozzle 7 to the burner 2. A modulating gas valve 14 and the speed-controlled blower 6 are from one Gas / air controller 15 in the sense of maintaining a predetermined optimal gas / air ratio controlled. Examples of this are from EP 0 390 964 B1 (72400679) or EP 0 644 377 A (72200796) is known. Is between the gas valve 14 and the gas injector 5 a gas throttle 16 is switched on, which is controlled by the controller 8.

In a known manner, the speed of the fan 6 is dependent on the heat requirement changed. About the gas / air regulator 15, the gas supply through the gas valve 14 in Controlled to maintain a given gas / air ratio. Such a Gas / air regulator 15 has a predetermined modulation range over which it is automatic Adjustment of gas and air supply is effective. The gas injector 5 is designed so that it with throttle 16 fully open and using a gas with the lowest too expected heat content achieved the desired gas / air ratio.

The system is started with throttle 16 fully open. As soon as the flame ignites The controller 8 slowly changes the flow cross section of the throttle 16. When the flame from the flame sensor 3, the controller 8 switches, as in the above embodiment, the Plant from. When you switch on again, the flow cross section of the throttle 16 is around predefined percentage between withdrawal value (operating mode C) and optimal operation (Operating mode A) increased, for example using a servomotor, which at constant Speed is in operation for a predetermined duration corresponding to the percentage mentioned.

This sets the gas / air ratio to the desired optimal value. The system is then released for normal operation. Here, too Setting the optimal gas flow in relation to the air flow using the throttle 16 and the controller 8 during the first switch-on of the system without interrupting the Burner operation take place.

Within the scope of the invention, numerous modifications of the design of the device are possible possible. The throttle 16 can thus be part of the modulating gas valve 14. The setting the gas / air ratio during calibration can not only in the gas flow path, but instead be carried out in the flow path of the air L when one appropriate adjustment device between the fan 6 and air nozzle 7 provides. However, this is less cheap, because in this case the use of different gas types Heat output of the burner would change. Instead of a thermal flame sensor, e.g. a flame rod 3 can also be a sufficiently focused optical or other Flame sensor are used, which not only the presence of the flame 1 but also detects their lifting from the burner 2. The combustion air supply can also be through a throttle valve arranged in the air flow can be regulated. The one used for calibration Regulator 8 and a combined gas / air regulator 15 can be made into a single regulator sum up.

Claims (9)

1. Method of operating a gas burner with a calibrated controller, the controller controlling the gas supply and/or air supply of the gas burner monitored by a flame sensor, having the following measures:

   a) a burner test piece, in order to calibrate the controller, is operated at rated load with an optimum gas/air mixture, the maintenance of which is monitored by an oxygen measurement in the exhaust-gas passage; the excess air is then increased until the flame sensor indicates that the flames have lifted off from the burner test piece; the percentage by which the excess air was increased between the operation with optimum gas/air mixture and the lifting-off of the flame from the burner test piece is subsequently determined, and this percentage is stored in the controller;

   b) a gas/air mixture with excess gas is fed to the gas burner, and the gas burner is ignited;

   c) the excess gas is reduced until excess air appears;

   d) as soon as the flame lifts off from the flame sensor with preset excess air, the flame sensor delivers a flame-failure signal;

   e) from the gas/air mixture ratio which is present when the flame-failure signal appears, the gas/air mixture is changed towards a higher proportion of gas by the percentage stored according to measure a);

   f) the gas burner is operated with this optimum gas/air mixture ratio until the next optimization.
2. Method according to Claim 1, characterized in that the optimized gas/air mixture has about 4% excess air.
3. Apparatus for operating a gas burner, having:

   a) a calibrated controller, a burner test piece, in order to calibrate the controller, being operated at rated load with an optimum gas/air mixture, the maintenance of which is monitored by an oxygen measurement in the exhaust-gas passage; the excess air then being increased until the flame sensor indicates that the flames have lifted off from the burner test piece; the percentage by which the excess air was increased between the operation with optimum gas/air mixture and the lifting-off of the flame from the burner test piece subsequently being determined, and this percentage being stored in the controller;

   b) a gas burner (2) supplied with a gas/air mixture;

   c) a flame sensor (3) assigned to the gas burner;

   d) a gas valve (4, 14) and a combustion-air blower (6); and

   e) a controller (8) which is connected to the flame sensor and which, in the event of flame failure, interrupts the gas supply or gas/air supply to the gas burner and, in order to influence the gas/air ratio, acts on an actuator (6, 16) controlling the gas supply or air supply;
   characterized in that the controller (8)

   f) supplies a control signal to the actuator when the gas burner (2) is switched on, this control signal producing excess gas sufficient for the reliable ignition of the gas burner;

   g) after the appearance of a flame signal, indicating the ignition of the flame, from the flame sensor (3), changes the control signal towards excess air until the flame signal disappears;

   h) has a memory for the percentage determined during the calibration;

   i) contains a device for changing the actuating signal by the preset percentage towards an increase in the proportion of gas in the gas/air mixture; and

   j) maintains this optimized value of the gas/air ratio in the subsequent operating phase of the gas burner.
4. Apparatus according to Claim 3, characterized in that an output of the controller (8) is connected to a speed-control input of a blower (6) for the combustion-air supply.
5. Apparatus according to Claim 4, characterized in that the gas valve is an on/off valve (4) controlled by the heat requirement.
6. Apparatus according to Claim 3 or 4, characterized in that the gas valve is a modulating valve (14) controlled by the heat requirement.
7. Apparatus according to Claim 6, characterized in that an output of the controller (8) is connected to the actuator (16) in the flow path (14, 16, 5) of the gas.
8. Apparatus according to Claim 6 or 7, characterized in that a combined gas/air controller (15) is connected on the input side to a heat-requirement sensor and acts on the output side, on the one hand, on a speed-control circuit for the blower (6) and, on the other hand, on the gas valve (14).
9. Apparatus according to Claim 8, characterized in that the memory for the percentage determined during the calibration is part of the combined gas/air controller (15), preferably a microprocessor controller.

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