EP2594848B1 - Method for controlling a firing device and firing device - Google Patents

Description

The invention relates to a method for controlling a firing device, in particular a gas burner, and a firing device, in particular a gas burner, which comprises a gas valve for adjusting the fuel supply to the firing device.

In the household gas burners, for example, as a water heater, for the preparation of hot water in a boiler, to provide heating and the like. Ä. Used. In the respective operating conditions, different requirements are placed on the device. This concerns in particular the output of the burner.

The power output is essentially determined by the setting of the supply of Fuel gas and air and determined by the set mixing ratio between gas and air. The temperature generated by the flame is also a function of the mixing ratio between gas and air. The mixing ratio can be specified, for example, as the ratio of the mass flows or the volume flows of the air and the gas. However, other parameters, such as the fuel composition, have an influence on the sizes mentioned.

In addition, for any given air mass flow or gas mass flow, a mixing ratio can be determined which maximizes the effectiveness of the combustion, i. where the fuel burns as completely and clean as possible.

For this reason, it has proven to be useful to regulate the mass flows of gas and air and always set so that in each case an optimal combustion is achieved under changing requirements and boundary conditions. A regulation can take place continuously or at regular intervals. In particular, a control in a change of the operating state, but for example also due to changes in the fuel composition in continuous operation is required.

To provide the air / gas mixture through which the burner flame is fed, known gas burners are usually equipped with a radial fan, which sucks the mixture of air and gas during operation. The adjustment of the mass flows of air and gas can be done for example by changing the speed and thus the suction of the impeller of the radial fan. In addition, valves can be provided in the gas and / or air supply line, which can be actuated to set the individual mass flows or their ratio. To measure individual parameters, various sensors can be arranged at suitable locations. Thus, appropriate measuring devices can be provided for measuring the mass flow and / or the volume flow of the gas and / or the air and / or the mixture. Likewise, state variables such as the temperature of the air, pressures, etc., can be measured at appropriate locations, evaluated and used for the control.

The regulation of the mixing ratio is done today by default, especially for gas burners used in the household, by pneumatic control of a gas valve in dependence on the volume flow of the supplied air quantity (principle of pneumatic composite). In pneumatic control, pressures or pressure differences on orifices, in constrictions, or in venturi nozzles are used as control variables for a pneumatic gas control valve that adjusts the gas supply to the airflow. A disadvantage of the pneumatic control, however, is in particular that mechanical components must be used which are subject to hysteresis effects due to the friction. Especially at low working pressures, inaccuracies in the control, so that the blower must always produce a certain minimum pressure to achieve a sufficiently precise control, which inversely leads. But to over-dimensioning of the blower for the maximum performance. 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. To be able to make desired adjustments to the gas supply nevertheless, additional equipment, such as actuators, must be prepared and adjusted, which means considerable additional expense in the installation or maintenance of a gas heater.

For these reasons, one goes to equip gas burner with an electronic composite. With electronic control easily controllable valves, such as pulse width modulated coils or stepper motors, can be used. The electronic composite operates by detecting at least one combustion characterizing signal which is fed back to a feedback control loop.

However, the use of the electronic interconnect also presents situations that can not be adequately addressed, such as a change in sensitivity of the sensors due to contamination. In addition, there is a risk that changes in the load or the operating state or immediately after the start of operation of the gas burner, that the scheme due to the inertia of the sensors delayed in time, resulting in an imperfect combustion and in extreme cases to extinguish the burner flame.

The DE 100 45 270 C2 discloses a firing device and method for controlling the firing device with fluctuating fuel quality. In particular, when the gas quality changes, the fuel-air ratio becomes corresponding changed. In this case, the mixture composition is adjusted for each suitable type of fuel until the desired flame core temperature is reached. In addition, maps are used for different fuels, from which a new, suitable fuel-air ratio is read out whenever the performance requirements change.

The procedure of DE 196 27 857 C2 should avoid large deviations in the control circuit of the gas burner. For this purpose, a derivative component for the control signal of the gas valve is derived from the speed change of the air blower. Since the power control signal characteristic is known and stored in an evaluation circuit, the derivative part can be determined. When changing the reference signal J ', ie a change in the power requirement, the speed of the fan is changed. This change in the speed determines via an adder a positive or negative derivative part, by which the control signal is adjusted. The resulting control signal changes accordingly the position of the gas valve.

The EP 1 293 727 A1 further discloses a burner control apparatus using an ionization electrode and a calibration unit.

In the GB 2 270 748 A a control system for a gas burner is shown. The regulation takes place here using a temperature measured at the burner surface. Since the surface temperature depends on the flow rate of the air-gas mixture, falling below a certain temperature, the speed of the fan motor is lowered, whereby the air flow and thus the air-gas ratio is lowered.

From the AT 411 189.B a method for controlling a gas burner is known in which the CO concentration in the exhaust gases of the burner flame is detected with an exhaust gas sensor. A certain CO value corresponds to a certain gas-air ratio. Starting from a known, for example experimentally determined, gas-air ratio at a certain CO value, a desired gas-air ratio can be set.

The EP 770 824 B1 shows a control of the gas-air ratio in the fuel-air mixture by measuring a Ionisationsstrorns, which depends on the excess air in the exhaust gases of the burner flame. In stoichiometric combustion is known a maximum of the ionization current is measured. Depending on this value, the mixture composition can be optimized.

A disadvantage of the last-mentioned method, however, is that the feedback signal can only be detected when the flame is burning and fed back to the control loop. In addition, the inertia of the sensors limits accurate readjustment. In addition, the sensors used are subject to contamination, so that the combustion is suboptimal regulated over time and thus increase the pollutant levels. In particular, during the starting process, in which there is no combustion signal, or load changes in which significant changes in operating parameters are required in a short time, it can cause difficulties and in extreme cases to extinguish the flame Frequently, for these reasons, resort to pneumatic regulator which, however, increases the complexity of the plant as well as the costs.

Based on this, it is an object of the present invention to provide a control system to a firing device, which reliably ensures a gas-independent fuel supply during fast load changes and in the starting phase without delay, on the other hand even under greatly changed conditions, in particular with regard to the fuel composition or a change the measurement characteristics of the sensors or the settings of the system parameters without malfunctioning failures works.

The inventive method for controlling a firing device, in particular a gas burner, is characterized by the combination of features according to claim 1.

With the help of this method, stable conditions can be achieved with fast load changes, but especially during the starting process. A readjustment of the gas valve, which takes a great deal of time with large fluctuations in the operating parameters and is imperfect due to the inertia of the sensors, can thus be dispensed with. The control is replaced by a controller that specifies a setpoint value for a new setting as a function of the target value of the first parameter. Only in the following step is realignment carried out using real measured variables. With the method, regardless of the inertia of the sensors used for the control, a fast and reliable adjustment of the gas valve being found. The real opening of the gas valve is between an upper and a lower limit. For rapid setpoint changes, the actuators, such as the fan or a gas control valve, after a certain period of time, which depends on the inertia of the sensors, be readjusted. It thus takes place in the execution of the method according to the invention, a transition from a pure control to a control.

The parameter corresponding to the burner load is the mass flow of the air to be supplied to the firing device. The opening values of the gas valve can therefore be represented in this embodiment as a function of the mass of the air. The characteristic of this characteristic is determined inter alia by the properties of the gas valve.

The burner load is substantially proportional to the amount of air supplied to the gas burner per unit time. Thus, it is clear that the representation of the opening of the gas valve as a function of mass flow of the air is equivalent to a representation of the opening of the gas valve in response to a load on the burner.

The change of the opening of the gas valve may be performed by the modulation of a pulse width, by the variation of a voltage or a current of a valve spool, or by the operation of a stepping motor of a valve. Exceeding the upper or lower limit of the opening of the gas valve can be detected in the process. While after the control process, the opening of the gas valve is between the upper and lower limit, after the control step, the gas opening may be above or below the upper or lower limit. This can occur, in particular, if the setpoint values for the opening of the gas valve that are defined when the characteristic curve is generated deviate greatly from the optimally adjusted values. This can be due to changes in the fuel composition, changes in the measurement characteristics of the sensors or the settings of the system parameters.

The characteristic resulting from the opening values of the gas valve as a function of the parameter corresponding to the burner load is recalibrated based on the control unit operating parameters set by the controller. Falls after the regulation, the value of the opening of the gas valve from the through the upper and lower limits limited range, so a recalibration of the characteristic can be performed. For example, during this recalibration, the setpoints may be shifted so that the new setpoint line passes through the adjusted value for the opening of the gas valve. In the same way, the upper and lower limits can be shifted, so that the new setpoint curve is surrounded by a tolerance corridor, as in the previously valid characteristic curve.

Exceeding the upper or falling below the lower limit can, in particular after the expiry of a predetermined period of time, lead to switching off the firing device. This measure can be based on both safety concerns and economic considerations. Control to a range outside the desired margin indicated by the limits may, for example, indicate an undesirable change in the default settings of the gas burner, so that it may operate in an unsafe or ineffective operating range. The device would have to be checked and maintained below.

A firing device according to the invention, in particular a gas burner, comprises: a gas valve for adjusting the fuel supply to the firing device; a memory for storing set values that depend on a parameter corresponding to the burner load and upper and lower limits; a device for controlling the opening of the gas valve, which, in the event of a change of the parameter corresponding to the burner load from a starting value to a target value, adapts the opening of the gas valve from a first to a second opening value according to a stored nominal value, the second opening value between a stored upper and a lower limit, and wherein during the transition of the opening of the gas valve from the first to the second opening value, no control of the fuel supply is performed; Means for controlling, after reaching the target value of the parameter corresponding to the burner load, operating parameters of the firing device and means for recalibration a characteristic resulting from the set values for the opening (w) of the gas valve in dependence on the parameter (m _L ), based on the operating parameters set by a controller following the control, when the valve opening (w) is above an upper limit curve (K ₁ ) or below a lower limit curve (K ₂ ).

The gas valve may be an actuator, in particular a stepper motor, a pulse width modulated or a coil controlled by an electrical variable.

The firing device has at least one mass flow sensor for measuring the amount of air supplied to the firing device per unit time. The firing device may further comprise a mass flow sensor for measuring the amount of fuel medium supplied to the firing device per unit time and / or the amount of the supplied mixture of air and fuel medium.

In particular, the firing device in the region of the burner flame may have a device for measuring a temperature generated by the firing device.

The temperature sensor may be arranged, for example, in the region of the flame, but also on the burner in the vicinity of the flame. For example, a thermocouple can be used as a temperature sensor.

Fig. 1

eine Feuerungseinrichtung;

Fig. 2

eine Kennlinie, wie sie zur Durchführung des erfindungsgemäßen Verfahrens verwendet wird.

Further features and advantages of the subject of the invention will become apparent from the following description of specific embodiments. Show it:

Fig. 1

a firing device;

Fig. 2

a characteristic curve, as used for carrying out 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, is sucked through the combustion air L. A mass flow sensor 2 measures the mass flow of the air L sucked in by a blower 9. 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 arranged in a bypass (not shown) and using a laminar element.

In the air supply section 1, a valve 3 may be arranged for the combustion air. However, however, usually a regulated fan with air mass flow sensor will be used, so that the valve can be omitted.

For the gas supply, a gas supply section 4 is provided, which is connected to a gas supply line. The gas flows through the section 4, during operation of the gas burner. Through a valve 6, which may be an electronically controlled valve, the gas flows through a conduit 7 into the mixing region 8. In the mixing region 8, a mixing of the gas G with the air L takes place. The fan of the fan 9 is driven at an adjustable speed to suck in both the air L and the gas G.

The valve 6 is adjusted so that, taking into account the other operating parameters, such as the speed of the fan, a predetermined air-gas ratio enters the mixing area 8. The air-gas ratio should be chosen so that the most clean and effective 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 controlling or controlling the gas burner. 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 the mass flow sensor 2 and outputs control signals to the valve 6 and 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 as well as a corresponding data processing unit which is set up to carry out the corresponding methods.

In FIG. 2 is a dependence of the opening w of the gas valve 6, which determines the fuel supply, shown in dependence on the mass flow m _L of the burner supplied air. In this case, the mean curve K3 corresponds to a desired value curve which indicates the predetermined opening values w _{soll of} a gas valve 6 as a function of a corresponding air mass flow m _L.

When the prescribed burner load Q changes, for example when the operating state changes or when the system is started, the air mass flow m _{L is changed} from an initial value m _L1 to a second value m _L2 and adapted to the new load Q ₂ .

Since a control of the gas supply would be greatly delayed in time at the relatively short transition from m _L1 to m _L2 due to the inertia of the sensors, the control is switched off and the opening value w of the gas valve from previously set value w _{1 changed} to a new target opening value w ₂ , The value w ₂ is on the target opening curve K3.

The adjusting opening of the gas valve is in any case between an upper limit curve K1 and a lower limit curve K2, which indicate a tolerance range for the opening of the gas valve. The upper limit curve K1 corresponds to a maximum allowable opening of the gas valve, the lower limit curve K2 a minimum allowable opening of the gas valve. 6

Thereafter, a regulatory action shoots. In the control process, the operating parameters of the firing device, in particular the setting of the valve 6 and the speed of the fan of the fan 9 are adjusted so that the combustion process is optimized. The scheme can be done in any way. In the present example it is done by measuring a generated by the burner flame 13 in its sphere of temperature T _is 12 by a temperature sensor The control can for example take place as in the method described above.

It is useful to use pulse width modulated valves, electronically controlled valves or valves with a stepper motor actuated actuator.

The control signal for adjusting the opening of the gas valve can accordingly trigger, for example, the operation of a stepping motor, or change the pulse width, the voltage or the current of a coil. The air mass flows m _L and gas mass flows m _G are measured by mass flow sensors 2 and 5.

If a valve opening w, which lies above the upper limit curve K1 or below the lower limit curve K2, is now set in one phase of the method before or after the control process has been carried out, appropriate consequences can be drawn. According to the invention, leaving the tolerance corridor lying between K1 and K2 can lead to a calibration process. During calibration, the conditions set after the control could be stored in a memory of the controller and used for the next start. The setpoint curve K3, like the limit curves K1 and K2, can be shifted so that a uniform tolerance corridor for the opening of the gas valve 6 around the setpoint curve K3 also results in the new curve.

For this purpose, exceeding the limit curves K1 or K2 upwards or downwards after a certain period of time or in case of repeated overshoot or undershoot can cause the device to be switched off. It may happen that certain gas burner settings change over time or certain boundary conditions have changed so that a safety hazard occurs or the gas burner operates in a non-effective operating state. A deviation of the opening of the gas valve from the permitted corridor can be triggered for example by a deviation of the gas pressure from the permissible inlet pressure range or by a malfunction of the sensors. The shutdown can thus be interpreted as an indication that a review and maintenance of the device is required.

By means of the method described, it can be ensured that, until an effective control of the gas supply can start, a plausible opening w _{2 of} the gas valve is set by the control, be it during a load change of the gas burner or in the starting phase. In this way it can be prevented that, for example, the flame goes out during the load change.

By the method is ensured at the start of the burner, that in a wide range, adapted to the predetermined burner load, can be ignited. During load changes, a quick adaptation of the gas supply to the new load takes place, before the fine adjustment is found by a subsequent regulation.

Claims (9)

1. A method for controlling a firing device having a subsequent regulation, wherein
   when a parameter (m_L) which is a mass flow of air provided to the firing device and which corresponds to the burner load (Q) is changed from a start value (Q1) to a target value (Q2), the supply of fuel to the firing device is adapted by a change to the opening of the gas valve (6) from a first (w₁) to a second opening value (w₂) specifying a desired value which is dependent upon the parameter (m_L) received by a measurement of the air mass flow, the second opening value (w₂) lying between an upper and a lower limit value, and during the transition of the opening of the gas valve from the first (w₁) to the second opening value (w₂), no regulation of the supply of fuel being implemented, and after the target value of the parameter (m_L), which corresponds to the burner load (Q), has been reached, regulation of the operating parameters of the firing device being implemented, wherein a characteristic which is produced from the desired values for the opening (w) of the gas valve dependent upon the parameter (mL) which corresponds to the burner loading (Q), is re-calibrated upon the basis of the operating parameters of the firing device set by the regulation when the valve opening (w) is above an upper limiting line (K1) or below a lower limiting line (K2).
2. The method according to claim 1, wherein the burner load (Q) is substantially in proportion to the quantity of air supplied to the gas burner per unit of time (m_L).
3. The method according to claim 1 or 2, wherein the change to the opening of the gas valve is implemented by modulating a pulse width, by varying a voltage or a current of a valve coil, or by actuating a stepper motor of a valve.
4. The method according to one of the claims 1 to 3, wherein passing the upper or lower limit value of the opening is registered.
5. The method according to one of the claims 1 to 4, wherein passing over the upper or passing below the lower limit value, after a pre-determined period of time has passed, leads to the firing device shutting down.
6. Firing device for conducting the method according to one of the claims 1 to 5 comprising:

   a gas valve (6) for setting the supply of fuel to the firing device;

   a storage unit for storing desired values which are dependent upon a parameter (m_L) which corresponds to the burner load (Q) and upon upper and lower limit values;

   at least one air mass sensor (2, 5) for measuring the mass flow of air (mL) supplied to the firing device per unit of time which is used as the parameter;

   a device for controlling the opening of the gas valve which, when a parameter (m_L), which corresponds to the burner load (Q), is changed from a start value to a target value, adapts the opening of the gas valve from a first (w₁) to a second opening value (w₂) according to a stored desired value, the second opening value (w₂) lying between a stored upper and a lower limit value, and during the transition of the opening of the gas valve from the first (w₁) to the second opening value (w₂) no regulation of the fuel supply being implemented; and

   regulating means which, after reaching the target value of the parameter, which corresponds to the burner load (Q), regulate the operating parameters of the firing device, and

   means for re-calibrating of a characteristic which is produced from the desired values for the opening (w) of the gas valve dependent upon the parameter (m_L) which corresponds to the burner loading (Q), upon the basis of the operating parameters of the firing device set by the regulation following a controlling when the valve opening (w) is above an upper limiting line (K1) or below a lower limiting line (K2).
7. The firing device according to claim 6, wherein the gas valve (6) comprises a correcting element, in particular a stepper motor, a pulse width modulated coil or a coil controlled by an electrical value.
8. The firing device according to claim 8, wherein the firing device has at least one mass flow sensor (2, 5) for measuring the quantity of fuel medium (m_G) supplied per unit of time and/or the quantity of the mix (m_M) of air and fuel medium supplied.
9. The firing device according to one of the claims 6 to 8, wherein in the region of the burner flame (13), the firing device has a device (12) for measuring a temperature (T_ist) produced by the firing device.

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