The present patent application relates to a method for operating a gas burner.
EP 0 833 106 B1 discloses a method for operating a gas burner. According to this prior art document, during burner-on phases of the gas burner a defined gas/air mixture having a defined mixing ratio of gas and air is provided to a burner chamber of the gas burner. The defined gas/air mixture is provided by mixing an air flow provided by an air duct with a gas flow provided by a gas duct. The quantity of the air flow is adjusted by a fan. The defined mixing ratio of the gas/air mixture is controlled by a controller.
It is further known from EP 0 833 106 B1 that the defined gas/air mixture has to be calibarted to the quality of the gas in order to ensure an optimum and complete combustion of the gas. The quality of the gas is defined by the so-called "Wobbe-Index". EP 0 833 106 B1 disclosed a method to calibrate the defined gas/air mixture to different gas qualities depending on a signal provided by an ionization sensor.
EP 0 962 703 B1 discloses that the calibration of the defined gas/air mixture to different gas qualities on basis of a signal provided by an ionization sensor shall only be performed in a range close to full-load operation of the gas burner, whereby the range close to full full-load operation lies between 60% and 100% of full full-load operation of the gas burner.
EP 1 309 821 B1 discloses that the calibration of the defined gas/air mixture to different gas qualities on basis of a signal provided by an ionization sensor shall be only performed at selected times, namely immediately after installation of the sensor and/or immediately after restart of the gas burner and/or immediately after a reset.
DE 10 2010 026 389 A1 discloses a method to control a so-called "λ-value" of the defined gas/air mixture on basis of a dead time between a change of the gas/air mixture and a signal change of sensor positioned downstream of a mixing device used to mix the air flow with the gas flow. DE 10 2010 026 389 A1 relates to a method to control the air flow and/or the gas flow depending on said dead time.
Against this background, novel methods for operating a gas burner are provided.
A method for operating a gas burner according to a first aspect of the present application is defined in the claim 1. Before the calibration of the defined gas/air mixture is started, the gas/air mixture is changed and a dead time between the change of the gas/air mixture and a corresponding signal change of a sensor positioned downstream of the mixing device is determined. The dead time is compared with a reference value, whereby the defined gas/air mixture is calibrated to different gas qualities only if the determined dead time is equal or smaller than the reference value.
The method according to the first aspect of the present application is directed to the calibration of the defined gas/air mixture to different gas qualities. The calibration is only performed if the dead time is equal or smaller than the reference value. The dead time is an indication of the burner load. The dead time and thereby the indication of the burner load can be determined using sensors being present in the gas burner application. No additional sensors are required. The method is easy, reliable and cost effective.
According to a preferred embodiment of the invention, only the decision if the calibration of the defined gas/air mixture is performed or if the calibration of the gas/air mixture is not performed depends on the determined dead time. The calibration of the gas/air mixture as such is independent from the determined dead time.
Another method for operating a gas burner is defined in the claim 7. The gas/air mixture is changed and a dead time between the change gas/air mixture and a corresponding signal change of sensor positioned downstream of the mixing device is determined. The dead time is compared with a reference value depending on the speed of a fan adjusting the quantity of the air flow, whereby a blocked flue is determined when the dead time is equal or larger than the reference value.
The method according to the second aspect of the present application is directed to the diction of a blocked flue. No additional sensors are required. The method is easy, reliable and cost effective.
Preferably, both methods are used in combination with each other.
The present application further relates to a controller of a gas burner having means for performing the method according to the first aspect of the present application and/or means for performing the method according to the second aspect of the present application.
Preferred developments of the invention are provided by the dependent claims and the description which follows. Exemplary embodiments are explained in more detail on the basis of the drawing, in which:
- Figure 1
- shows a schematic view of a gas burner; and
- Figure 2
- shows diagram used in connection with one aspect of the present invention.
Figure 1 shows a schematic view of a gas burner 10. The gas burner comprises a burner chamber 11 in which combustion of a defined gas/air mixture having a defined mixing ratio of gas and air takes place during burner-on phases of the gas burner 10. The combustion of the gas/air mixture results into flames 12 monitored by e.g. an ionization sensor 13.
The defined gas/air mixture is provided to the burner chamber 11 of the gas burner 10 by mixing an air flow with a gas flow. A fan 14 sucks in air flowing through an air duct 15 and gas flowing though a gas duct 16. A gas valve 17 for adjusting the gas flow through the gas duct 16 and safety valves 18, 19 are assigned to the gas duct 16.
The defined gas/air mixture having the defined mixing ratio of gas and air is provided to the burner chamber 11 of the gas burner 10. The defined gas/air mixture is provided by mixing the air flow provided by an air duct 15 with a gas flow provided by a gas duct 16. The air flow and the gas flow become preferably mixed by a mixing device 23. Such a mixing device can be designed as a so-called Venturi nozzle.
The quantity of the air flow and thereby the quantity of the gas/air mixture flow is adjusted by the fan 14, namely by the speed of the fan 14. The fan speed can be adjusted by an actuator 22 of the fan 14.
The defined mixing ratio of the defined gas/air mixture is controlled by a controller 20. The controller 20 generates a control variable for the gas valve 17, namely for an actuator 21 of the gas valve 17. The gas valve position of the gas valve 17 is adjusted by the actuator 21 of the same on basis of this control variable in order to provide the defined mixing ratio of gas and air in the defined gas/air mixture.
As mentioned above, the defined mixing ratio of the defined gas/air mixture is controlled by a controller 20. The control of the defined mixing ratio of the gas/air mixture is preferably based on a signal provided by the ionization sensor 13. The controller 20 compares an actual value of the signal provided by the ionization sensor 13 with a corresponding nominal value, whereby a control deviation between said actual value and said nominal value is used by the controller to determine a control variable for the actuator 21 of the gas valve 17 in such a way that the actual value follows the nominal value. In this way the defined mixing ratio of the defined gas/air mixture is kept constant. This control of the gas flow by the control variable for the actuator 21 of the gas valve 17 is also often called modulation of gas flow.
As also mentioned above, the quantity of the air flow and thereby the quantity of the gas/air mixture flow is adjusted by the fan 14, whereby the controller 20 provides a control variable for the actuator 22 of the fan 14 for adjusting the quantity of air flow and thereby the quantity of gas/air mixture flow. By changing the speed of the fan 14 the load of the gas burner 10 can be adjusted. Over the entire load range of the gas burner 10 the defined mixing ratio of the defined gas/air mixture is kept constant. This control of the fan speed of the fan 14 is also often called modulation of air flow or modulation of the burner load.
Exhaust gas resulting form the combustion of the defined gas/air mixture within the burner chamber 11 during burner-on phases of the gas burner 10 is leaving the burner chamber 11 through an exhaust flue 25 of the burner chamber 11 of the gas burner 10. An exhaust gas temperature sensor 24 may be assigned to the exhaust flue 25.
As described above, the controller 20 comprises means for controlling the defined mixing ratio of the defined gas/air mixture by modulating the gas flow and means for controlling the burner load by modulating the speed of the fan 14. Further on, the controller 20 comprises means for calibrating the defined mixing ratio of the defined gas/air mixture to different gas qualities on basis of a signal provided by a sensor positioned downstream of the mixing device 23.
The calibration of the defined mixing ratio of gas and air of the defined gas/air mixture to different gas qualities as such is known to the person skilled, e.g. from EP 0 833 106 B1. The calibration as such is preferably performed on basis a signal provided by the ionization sensor 13 positioned downstream the mixing device 23.
According to the first aspect of the present application, before the calibration of the defined gas/air mixture as such is started by the controller 20, the controller 20 changes the gas/air mixture and determines a dead time between the change of the gas/air mixture and a corresponding signal change of sensor positioned downstream of the mixing device 23.
The sensor which is used to determine the above dead time and the sensor which is used for performing the calibration of the defined gas/air mixture to different gas qualities as such can be the same. In this case, e.g. the ionization sensor 13 is used to determine the dead time and is further used to perform the calibration as such.
Alternatively, the sensor which is used to determine the above dead time and the sensor which is used for performing the calibration of the defined gas/air mixture to different gas qualities as such can be different sensors. In this case, e.g. the exhaust gas temperature sensor 24 is used to determine the dead time and the ionization sensor 13 is used to perform the calibration as such.
Other sensors can be used to determine the above dead time, e.g. CO sensor or O2 sensor detecting the CO or O2 content in the exhaust gas.
The controller 20 compares the above dead with a reference value stored in the controller 20.
The defined mixing ratio of the defined gas/air mixture is calibrated to different gas qualities only if the determined dead time is equal or smaller than the reference value. The defined mixing ratio of the defined gas/air mixture is not calibrated to different gas qualities if the determined dead time is greater than the reference value.
Accordingly, only the decision if the calibration of the defined gas/air mixture to different gas qualities is performed or if this calibration of the gas/air mixture is not performed depends on the above dead time. The calibration of the defined gas/air mixture to different gas qualities as such is independent from the determined dead time. Further on, the control of the defined mixing ratio of the defined gas/air mixture by modulating the gas flow and the control of the burner load by modulating the speed of the fan 14 are both independent from the determined dead time.
According to the second aspect of the present application, which is preferably used in combination with the first aspect of the present application, the dead time is compared with a reference value depending on the speed of the fan 14. A blocked exhaust flue 25 is determined when the dead time is equal or larger than the reference value.
The reference value which is used in the first aspect of the present application does not depend on the speed of the fan 14. The reference value which is used in the second aspect of the present application depends on the speed of the fan 14. Figure 2 shows a curve in which the relationship of reference value for the dead time Δt and the speed n of the fan 14 are shown. The controller 20 knows the actual speed n of the fan 14 and can determine from this fan speed n the reference value for the dead time Δt. If the dead time is equal or larger than this reference value, the controller 20 detects a blocked exhaust flue 25.
Preferably, the dead time is compared with a first reference value and a second reference value both depending on the speed of the fan 14. A warning signal is generated when the dead time is equal or larger than the first reference value. The burner 10 is turned off when the dead time is equal or larger than the second reference value. The second reference value is larger than the first reference value.
List of reference signs
- 10
- gas burner
- 11
- burner chamber
- 12
- flame
- 13
- ionization sensor
- 14
- fan
- 15
- air duct
- 16
- gas duct
- 17
- regulating valve
- 18
- safety valve
- 19
- safety valve
- 20
- controller
- 21
- actuator
- 22
- actuator
- 23
- mixing device
- 24
- exhaust gas temperature sensor
- 25
- exhaust flue