EP1761728B1 - Method for adjusting the excess air coefficient on a firing apparatus, and firing apparatus - Google Patents

Description

Method for setting operating parameters on a firing device, in particular on a gas burner with blower, wherein the temperature (T _ist ) generated by the firing device depends on the value of the air ratio (λ) and at the value λ ₁ = 1 a maximum (T _max ) having. Moreover, the invention relates to a firing device, in particular a gas burner, which is adapted to carry out the method.

In the household gas burners are used for example as a water heater for the preparation of hot water in a boiler or to provide heating. In the respective operating conditions, different requirements are placed on the device. This relates in particular to the output of the burner, commonly referred to as the burner load, and the temperature generated by the burner flame.

The burner load is essentially determined by the adjustment of the amount of combustion air and the mixing ratio between gas and air. The Adjustment of the mixing ratio takes place, in particular for gas burners used in the household, by a pneumatic gas control valve (principle of the pneumatic composite). In pneumatic control, pressures or pressure differences are measured at orifices, in constrictions or in venturi nozzles. These quantities are used as control variables for the gas control valve. A disadvantage of the pneumatic control, however, is in particular that sensitive mechanical components must be used, which are subject to hysteresis effects due to the friction. Therefore, especially at low working pressures it comes to inaccuracies. In addition, the expense of manufacturing the diaphragm-equipped pneumatic gas control valves is remarkable because of the high precision requirements. In addition, in the pneumatic network it is not possible to respond flexibly to changes in the gas type and quality. In order to be able to make desired adjustments to the gas supply nevertheless, additional devices, eg nozzles and orifices, must be provided depending on the gas type, which means additional expense.

In an electronic control, however, an easily controllable gas control valve, such as pulse width modulated coil or stepper motor, can be used to set in conjunction with a variable speed fan the desired amount of air and the desired gas-air mixing ratio (electronic composite). It is possible to respond flexibly to changes in gas quality.

For a given amount of air, the mixing ratio between gas and air must be adjusted so that the gas burns as completely and cleanly as possible. The air ratio λ is typically used to characterize the mixing ratio between gas and air. It is defined as the ratio of the actual amount of air supplied to the amount of air theoretically required for optimal stoichiometric combustion. To optimize the exhaust gas values (CO, CO ₂ ), gas burners are typically operated with excess air. The setpoint for the air ratio λ _s is 1.3 for hygienically optimal combustion. When operating a gas burner with an electronic composite, it must be ensured that the air ratio λ at the different burner loads is always as close as possible to the setpoint λ _s . In addition, it should be noted that the operating conditions may change after commissioning the device and then the parameters of the combustion control must be adjusted accordingly.

In the EP 770 824 B1 a method is described in which by means of an ionization electrode, a calibration cycle for adjusting the electrical setpoint of the ionization electrode is going through. This should be compensated for changes in the thermal coupling between the ionization and the gas burner, which arise for example due to wear, bending and due to contamination.

With this method, which solely relies on the signal of the ionization electrode, it is possible to determine the ionization signal for λ = 1 exactly. However, the setpoint for the air ratio can not then be set precisely, since, for example, the system characteristic is ignored.

US 5971745 also describes a method for setting operating parameters on a firing device by means of an ionization electrode.

It is therefore an object of the invention to provide a method by which the parameters of the combustion can be adjusted to required burner loads easily and reliably. It is also an object of the invention to provide a corresponding device with which the method can be performed.

The object is achieved by a method according to the main claim and by a device according to claim 6.

• Einsteuern eines vorgegebenen Luft-Massenstroms (m_L);
• Ermitteln des für die Temperatur (T_max) zugehörigen Gasmassenstroms (m_GTmax).
• Festlegen eines Sollwerts der Luftzahl(λ_hy) für eine gewünschte hygienische Verbrennung;
• Einsteuern der gewünschten hygienischen Verbrennung durch Erhöhen des Luft-Massenstroms (m_L) um den Faktor (λ_hy) bei konstanter Zufuhr des Gasmassenstroms (m_GTmax)_·

In the method for setting operating parameters on a firing device, in particular on a gas burner with blower, with an air mass measurement, wherein the temperature generated by the firing device (T _ist ) depends on the value of the air ratio (λ) and at the value λ ₁ = 1 has a maximum (T _max ), the following steps are performed:

• Controlling a given air mass flow (m _L );
• Determining the gas mass _flow associated with the temperature (T _max ) (m _GTmax ).
• Setting a desired value of the air ratio (λ _hy ) for a desired hygienic combustion;
• Controlled supply of the desired hygienic combustion by increasing the air mass flow (m _L) by a factor (λ _{h y)} at a constant supply of the gas mass flow (m _GTm ax) _·

The resulting actual temperature is registered.

Starting from a random or last set mixing ratio between air and fuel, the amount of fuel supplied per unit time is changed continuously or stepwise at a constant rate of air supplied per unit time. By determining and recording the measured in the range of the burner flame Temperature, the amount of fuel supplied per unit time is adjusted so that the measured temperature assumes a maximum. Subsequently, the amount of air supplied per unit time is increased while maintaining the previously set amount of fuel using the air mass flow sensor by the factor λ _hy . In this way, for any desired burner load at different gas qualities, but also when changing settings or when changing the characteristics of the sensors arranged on the gas burner, the setpoint of the air ratio for hygienically optimal combustion can be set accurately, safely and reliably.

For design reasons, it may be possible that with the increase in the amount of air inevitably accompanied by an increase in the amount of gas. In such a case, a structurally suitable blending geometry can reduce the increase of the amount of gas to a negligible value.

By using mass flow sensors in the gas mass flow, however, a control _{device can} reset the gas mass flow to the value m _Gtmax found at T _max by means of a corresponding admission of the gas valve without constructive adaptation.

Finally, it is also possible to calculate the increased gas mass flow and set the air ratio λ _hy correspondingly higher. Also, it can be thought to reduce the amount of gas by the calculated value, but this requires a highly accurate valve.

In particular, with variations in the quality of the combustion gas, a readjustment of the air ratio should be made to ensure the hygienically optimal combustion. An adjustment of the air ratio can be carried out, for example, at periodic intervals, during a load change, at the start of operation, or during maintenance of the device.

The firing device according to the invention, in particular a gas burner, is adapted to carry out one of the above-mentioned methods.

In particular, the firing device has a temperature sensor in the area of action of the burner flame of the firing device. The temperature sensor can be arranged in the flame kernel, at the base of the flame, at the tip of the flame, but also at some distance from the flame, for example at the burner plate itself.

In addition, the firing device preferably has a gas valve with an actuator, in particular with a stepper motor, a pulse-width-modulated coil or with a coil controlled by an electrical variable. Since the method is particularly suitable for the electronic composite, said valves, which are simple and precise operable, can be used.

According to the invention, the firing device has a mass flow sensor for measuring the amount of air supplied to the firing device per unit time.

Further features and advantages of the subject matter of the invention will become apparent from the following description of particular embodiments of the invention.

Fig. 1

eine Feuerungseinrichtung gemäß der Erfindung;

Fig. 2

eine Kennlinie zur Verdeutlichung des erfindungsgemäßen Verfahrens;

Fig. 3

eine weitere Kennlinie zur Verdeutlichung des erfindungsgemäßen Verfahrens.

Show it:

Fig. 1

a firing device according to the invention;

Fig. 2

a characteristic curve to illustrate the method according to the invention;

Fig. 3

a further characteristic for clarification of the method according to the invention.

FIG. 1 shows a gas burner in which a mixture of air L and gas G is premixed and burned.

The gas burner has an air supply section 1, via which combustion air L is drawn in by a variable-speed fan 9. A mass flow sensor 2 measures the mass flow of the intake air L. The mass flow sensor 2 is arranged so that as laminar a flow as possible is generated in its environment in order to avoid measurement errors. In particular, the mass flow sensor could be placed in a bypass (not shown) and using a flow straightener. With the aid of the mass flow sensor and the variable-speed blower 9, the air supply into the mixing region 8 can be precisely controlled.

For the gas supply, a gas supply section 4 is provided, which is connected to a gas supply line. The gas supply section may be provided with a mass flow sensor of suitable design. By means of a valve 6, for example a pulse-width-modulated or electronically controlled valve, which is equipped, for example, with an actuator with a stepping motor, the inflow of gas through a line 7 into the mixing region 8 is controlled. In the mixing region 8, a mixing of the gas G with the air L takes place. The fan of the fan 9 is equipped with an adjustable Speed driven to suck in both the air L and the gas G.

At vogegebenem air mass flow, the valve 6 is opened so far that the air-gas mixture passes with the desired mixing ratio in the mixing region 8. The air ratio λ is set so that a hygienically optimal combustion takes place.

Via a line 10, the air-gas mixture flows from the blower 9 to the burner part 11. There it exits and feeds the burner flame 13, which is to deliver a predetermined heat output.

On the burner part 11, a temperature sensor 12, for example a thermocouple, is arranged. With the aid of this thermocouple an actual temperature is measured, which is used in carrying out the method described below for setting the setpoint λ _{h of} the air ratio. In the present example, the temperature sensor 12 is arranged on a surface of the burner part 11. However, it is also conceivable to arrange the sensor elsewhere in the area of action of the flame 13. The reference temperature of the thermocouple is measured at a position outside the effective range of the flame 13, for example in the air supply line 1.

A device, not shown, for controlling or regulating the air and / or gas flow receives input data from the temperature sensor 12 and from the mass flow sensor 2 and outputs control signals to the valve 6 as well as to the drive of the blower 9. The opening of the valve 6 and the speed of the fan of the fan 9 are adjusted so that the desired air and gas supply results.

The control is carried out by performing the method described below. In particular, the control device has a memory for storing characteristic curves or nominal values and a corresponding data processing unit which is set up to carry out the method.

On the basis of in the FIG. 2 the characteristic shown is the method of the invention will be described. In this figure, the measured temperature is shown as a function of the air ratio λ

At the beginning of the process is set by the speed of the blower and the opening of the gas valve, a certain air ratio λ ₀ , which corresponds for example to the last set value. In the present case, λ _{0 is} above the value λ ₁ , at which the temperature maximum T _max results. By increasing the supplied mass flow λ is reduced to fuel gas at a constant air mass flow m _L1 . The change in the gas mass flow can be carried out stepwise, for example, by varying the steps of the stepping motor of the gas valve. At each step, the actual temperature T _ist determined with the temperature sensor 12, which is arranged in the region of the burner flame. With suitable iteration method, the opening of the gas valve is then varied until the temperature maximum T _{max is} established.

In the second method step, while maintaining the opening of the gas valve, the air mass flow m _{L1 is} increased by the desired value λ _{hy of} the air ratio. The result is the new air mass flow m _hy = λ _hy m _L1 . The air ratio is thus set exactly to the desired setpoint λ _hy , and the combustion is hygienically optimal. After setting the desired air ratio λ _hy , the associated temperature T _{soll is} measured.

In a load change, that is, in a required change in the burner load, the process is usually carried out again. The process can also be performed after switching on the gas burner or repeated at periodic intervals. In this way it is ensured that the gas burner is always operated in an optimal range.

In order to prevent the process from having to be carried out again at each load change, a second characteristic, as in FIG. 3 shown to be determined. In FIG. 3 is the set temperature T _soll , which is like in FIG. 2 has been determined, depending on the air mass flow m _L1 , which is directly proportional to the burner load, shown. The setpoint of the air ratio λ _hy arises at a certain burner load exactly when the measured in the range of action of the burner flame temperature T _is from the FIG. 3 read target temperature T _soll corresponds. A regulation of the actual temperature T _{is set} to the predetermined target value T _soll automatically leads to a setting of the optimum air ratio at a given burner load.

By using the second in FIG. 3 shown characteristic curve can be operated over a certain period of time, in which preferably the boundary conditions are not crucial, the system without re-implementation of the method with changing burner loads, ie in different operating conditions. However, here too, at regular intervals or on certain occasions, for example during maintenance of the device, the characteristic curve should be redetermined in order to adapt to the available gas quality or instabilities in the system Reach system.

In FIG. 3 is the Sölltemperatur T _soll in dependence on the mass flow of air m _L , which corresponds to a certain burner load, represented. If the load is switched from an operating state 1 to an operating state 2, corresponding to the air mass flows m _L1 or m _L2 , then the temperature of the gas burner is controlled so that the temperature T _soll2 sets. For this purpose, the air-gas mixture is emaciated or greased by adjusting the gas valve 6.

Instead of a complete redetermination of the second characteristic according to FIG. 3 If required, individual values for specific services can also be recorded and replace the corresponding values previously contained in the characteristic curve. It is also conceivable to shift the characteristic in accordance with a currently measured value for a given load in total.

The implementation of the method leads to an operating mode in which a hygienically optimal combustion is achieved.

Claims (8)

1. A method for setting operating parameters on a firing device, in particular on a gas burner with a fan, with a air mass measurement, wherein the temperature (T_actual) produced by the firing device being dependent upon the value of the air ratio (λ) and having a maximum (T_max) at the value A₁=1, comprising the steps:

   · controlling a pre-determined air mass flow (m_L);

   · establishing the gas mass flow (m_GTmax) corresponding to the temperature (T_max);

   · defining a desired value for the air ratio (λ_hy) for a desired hygienic combustion;

   · controlling the desired hygienic combustion by increasing the air mass flow (m_L) by the factor (λ_hy) with a constant supply of gas mass flow (m_GTmax).
2. The method according to Claim 1, characterised in that the air mass flow (m_Lhy) corresponding to the hygienic desired value (λ_hy) for the air ratio is controlled by changing the ventilator speed of the fan.
3. The method according to either of the preceding claims, characterised in that the air mass flow (m_L) and the gas mass flow (m_G) are measured respectively by a mass flow sensor.
4. The method according to any of the preceding claims, characterised in that the gas mass flow (m_GTmax) corresponding to the temperature maximum (T_max) is established by iterative approximation of the value of the gas mass flow (m_G) to the value (m_GTmax) corresponding to the temperature maximum.
5. The method according to any of the preceding claims, characterised in that the desired value (λ_hy) for the air ratio is approximately 1.3.
6. A firing device, in particular a gas burner, characterised in that the firing device has a temperature sensor (12) in the effective region of the burner flame (13) of the firing device and at least one mass flow sensor (2, 5) for measuring the quantity of air supplied to the firing device per unit of time, so that the firing device is adapted to implement said method according to any of the preceding claims.
7. The firing device according to claim 6, characterised in that the firing device has a valve (6) with a correcting element for setting the gas mass flow (m_G), in particular with a stepper motor, a pulse width modulated coil or a coil controlled by an electrical value.
8. The firing device according to any of the preceding Claims 6 to 7, characterised in that the firing device has at least one mass flow sensor (2, 5) for measuring the quantity of gas supplied per unit of time and/or the quantity of mixture of air and gas supplied.

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