EP2447609A1

EP2447609A1 - Method for operating a fan assisted, atmospheric gas burner

Info

Publication number: EP2447609A1
Application number: EP10014183A
Authority: EP
Inventors: Umberto Corti; Mauro Sesana; Costantino Sabbatinelli; Gerwin Langius
Original assignee: Honeywell Technologies SARL
Current assignee: Garrett Motion SARL
Priority date: 2010-11-02
Filing date: 2010-11-02
Publication date: 2012-05-02
Anticipated expiration: 2030-11-02
Also published as: EP2447609B1

Abstract

Method for operating a fan assisted, atmospheric gas burner (10), said gas burner comprising a burner chamber (11) in which a gas/air mixture can be burned, said gas burner (10) further comprising a heat exchanger (12) for heating water by burning said gas/air mixture, said gas burner (10) further comprising an air pipe (15) for providing the air of the gas/air mixture and an exhaust pipe through which exhaust flowing out of said burner chamber can emerge into the ambient of the gas burner, said gas burner further comprising a fan (19) being assigned to the exhaust pipe (17) or to the air pipe, whereby a measurement signal of a temperature sensor (20) measuring the exhaust temperature is used to determine the opening and/or closing status of said exhaust pipe (17) and/or air pipe.

Description

The invention relates to a method for operating a fan assisted, atmospheric gas burner as defined in the preamble of claim 1.
Fan assisted, atmospheric gas burners comprise a burner chamber. A gas/air mixture can be burned within said burner chamber when the gas burner is ignited. Fan assisted, atmospheric gas burners further comprise a heat exchanger for heating water by burning said gas/air mixture within said burner chamber. The water entering into the heat exchanger is often called return-flow water and the water exiting the heat exchanger is often called forward-flow water. Fan assisted, atmospheric gas burners further comprise an air pipe or air duct for providing the air of the gas/air mixture, a gas pipe or gas duct for providing the gas of the gas/air mixture and an exhaust pipe or exhaust duct through which exhaust flowing out of the burner chamber can emerge into the ambient of the gas burner. In addition, fan assisted, atmospheric gas burners comprise a fan being assigned to the exhaust pipe or the air pipe.
For a safe operation of such a fan assisted, atmospheric gas burner it is important to know if the exhaust pipe and/or air pipe is opened or closed. According to the prior art, an air pressure switch is used to detect the flow through the exhaust pipe and/or air pipe and thereby to check or determine the opening and/or closing status of the exhaust pipe and/or air pipe. However, air pressure switches can fail especially at low temperatures because at temperatures around or below the freezing point (0°C) dynamical parts of air pressure switches like membranes and or springs may become blocked.
Against this background, a novel method for operating a fan assisted, atmospheric gas burner, namely a method for checking the opening and/or closing status of the exhaust pipe of the gas burner and/or air pipe, is provided.
The new method provides a reliable way to determine the opening and/or closing status of the exhaust pipe and/or air pipe even at low temperatures around or below the freezing point. The novel method makes use of a measurement signal provided by an exhaust temperature sensor to determine the opening and/or closing status of the exhaust pipe and/or air-pipe.
Preferably the measurement signal of said exhaust temperature sensor in combination with a measurement signal of an ionisation sensor is used to determine the opening and/or closing status of said exhaust pipe and/or air pipe.
According to a preferred embodiment of the invention, at a burner start up when the gas burner becomes ignited the fan is operated at maximum fan speed and a first exhaust temperature value is measured by said exhaust temperature sensor and a first ionization current value is measured by said ionisation sensor, whereby after a defined time period the fan is operated at a lower fan speed and a second exhaust temperature value is measured by said exhaust temperature sensor and a second ionization current value is measured by said ionisation sensor, whereby when a difference between said first exhaust temperature value and said second exhaust temperature value and a difference between said first ionization current value and said second ionization current value are both relatively big or high, the exhaust pipe and/or air pipe is in a opened status, preferably in a fully opened status.
When during burner start up the difference between said first exhaust temperature value and said second exhaust temperature value and the difference between said first ionization current value and said second ionization current value are both relatively small or low, the exhaust pipe and/or air pipe is in a closed status, preferably in a partially closed status.
When during burner start up the difference between said first exhaust temperature value and said second exhaust temperature value is relatively big or high and the difference between said first ionization current value and said second ionization current value is relatively small or low, the exhaust pipe and/or air pipe is in a closed status, preferably in a partially closed status.
According to another preferred embodiment of the invention, when the burner is in a running mode in which the same is ignited and burns a gas/air mixture within the burner chamber, the actual value of the exhaust temperature measured by said temperature sensor is compared with a set point of the same. The exhaust pipe and/or air pipe is in a opened status when the actual value of the exhaust temperature differs from the set point by not more than a defined offset value, whereby the exhaust pipe and/or air pipe is in a closed status when the actual value of the exhaust temperature differs from the set point by more than a defined offset value.
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 drawing of a fan assisted, atmospheric gas burner;
Figure 2: shows a diagram showing the determination of a set point for the exhaust temperature value a function of the outlet water temperature of said heat exchanger and as a function of the burner load;
Figure 3: shows a diagram showing the measures exhaust tempera- ture of a burner being in a running mode; and
Figure 4: shows a schematic drawing of another fan assisted, atmos- pheric gas burner

The present invention relates to a method for operating a fan assisted, atmospheric gas burner.
Figures 1 and 4 show both a schematic drawing of a fan assisted, atmospheric gas burner 10. Said gas burner 10 comprises a burner chamber 11 in which a gas/air mixture can be burned. Said gas burner 10 further comprises a heat exchanger 12 for heating water by burning said gas/air mixture. Water 13 entering into the heat exchanger 12 is often called return-flow water 13 and water 14 exiting the heat exchanger 12 is often called forward-flow water 14.
Said gas burner 10 further comprises an air pipe 15 or air duct for providing the air of the gas/air mixture, a gas pipe 16 or gas duct for providing the gas of the gas/air mixture and an exhaust pipe 17 or exhaust duct through which exhaust flowing out of said burner chamber 11 can emerge into the ambient of the gas burner 10. A gas valve 18 is assigned the gas pipe 16 for adjusting the gas flow through the gas pipe 16. Said gas burner 10 further comprises a fan 19. In Figure 1 said fan 19 is assigned to the exhaust pipe 17. In Figure 4 said fan 19 is assigned to the air pipe 15.
The present invention relates to a method for checking the opening and/or closing status of the exhaust pipe 17 and/or air pipe 15 without using an air pressure switch. For a safe operation of the gas burner 10 both the exhaust pipe 17 and the air pipe 15 have to be fully opened. In case the exhaust pipe 17 and/or air pipe 15 is closed, the burning of the gas/air mixture is preferably stopped.
According to the present invention a measurement signal of an exhaust temperature sensor 20 measuring the exhaust temperature is used to determine the opening and/or closing status of said exhaust pipe 17 and/or air pipe 15. Figure 1 and 4 both show such an exhaust temperature sensor 20 being positioned in the region of an exhaust outlet 21 of the burner chamber 11.
Preferably a measurement signal of an exhaust temperature sensor 20 being positioned at a roof wall 22 of the burner chamber 21, namely at a flange or hook 23 of said roof wall 22 at which said exhaust pipe 17 and preferably said fan 19 are mounted to said burner chamber 11, is used to determine the opening and/or closing status of said exhaust pipe 17 and/or air pipe 15.
According to a preferred embodiment of the invention, the measurement signal of said exhaust temperature sensor 20 in combination with a measurement signal of an ionisation sensor 24 is used to determine the opening and/or closing status of said exhaust pipe 17 and/or air pipe 15. The ionisation sensor 24 is positioned in the region of flames 25 originating when burning the gas/air mixture. The ionisation sensor 24 provides as measurement signal an electrical ionisation current which depends on the burner load and thereby on the gas pressure or gas flow.
At a burner start up, e.g. at each start up or at selected burner start ups, when the gas burner 10 becomes ignited the fan 19 is operated at maximum fan speed and a first exhaust temperature value is measured by said exhaust temperature sensor 20 and a first ionization current value is measured by said ionisation sensor 14.
After a defined time period the fan 19 is operated at a lower fan speed and a second exhaust temperature value is measured by said exhaust temperature sensor 20 and a second ionization current value is measured by said ionisation sensor 24.
When a difference between said first exhaust temperature value and said second exhaust temperature value and a difference between said first ionization current value and said second ionization current value are both relatively big or high, the exhaust pipe 17 and/or air pipe 15 is in a opened status, preferably in a fully opened status. The precise values of said differences are quantified on real application of the gas burner.
However, when the difference between said first exhaust temperature value and said second exhaust temperature value and the difference between said first ionization current value and said second ionization current value are both relatively small or low, or when the difference between said first exhaust temperature value and said second exhaust temperature value is relatively big or high and the difference between said first ionization current value and said second ionization current value is relatively small or low, the exhaust pipe 17 and/or air pipe 15 is in a closed status, preferably in a partially closed status. The precise values of said differences are quantified on real application of the gas burner.
When the difference between said first exhaust temperature value and said second exhaust temperature value and/or the difference between said first ionization current value and said second ionization current value are both close to zero, the must be failure in the exhaust temperature sensor 20 and/or the ionisation sensor 24 because the change of the fan speed of the fan 19 must cause a change in the combustion of the gas/air mixture.
After said defined time period the fan 19 is reduced to a minimum fan speed at which a defined amount of CO within the exhaust is not exceeded. This CO limit depends on the country in which the gas burner is to be operated. In an example the fan speed is reduced to a minimum fan speed at which 2000 ppm (parts per million) of CO (carbon monoxide) within the exhaust is not exceeded.
When during burner start up the fan 19 is operated at maximum fan speed, the gas burner is preferably operated at maximum load with a completely opened gas valve 16. In order to check if the gas burner 10 is operated with the correct burner load, the position of a gas valve 18 being assigned to a gas pipe 16 is determined, preferably from the measurement signal, namely electrical ionisation current, provided by the ionisation sensor 24.
It is also possible to determine the thermal capacity of the gas burner 10 from the position of a gas valve 18.
This method can be used for a hot ignition burner start up and a cold ignition burner start up.
When the method is used for a hot ignition burner start up and when a drop of the exhaust temperature is detected just before ignition, this drop of the exhaust temperature can be used to detect an air flow though the air pipe due to the running fan 19.
When the method is used for a cold ignition burner start up, there must be just after ignition an increase for the exhaust temperature. With a partially blocked or closed exhaust pipe and/or air pipe this increase will be slower.
When the gas burner 10 is in a running mode in which the same is ignited and burns a gas/air mixture within the burner chamber 11, the actual value of the exhaust temperature measured by said temperature sensor 20 is compared with a set point of the same. The exhaust pipe 17 and/or air pipe 15 is in a opened status when the actual value of the exhaust temperature differs from the set point by not more than a defined offset value, whereby the exhaust pipe 17 and/or air pipe 15 is in a closed status when the actual value of the exhaust temperature differs from the set point by more than a defined offset value.
Said set point for the exhaust temperature is preferably determined as a function of the forward-flow water temperature of said heat exchanger 12 and/or as a function of the gas burner load.
Figure 2 illustrates the dependency of the set point T_SET for the exhaust temperature from the forward-flow water temperature T_w and the gas burner load BL. The gas burner load BL can be determined from the ionisation current I_oc measured by the ionisation sensor 24 or from a gas pressure p_GAS or from the amount of gas flowing through the das valve 18 which can be determined from the position of the gas valve 18 or the position of a gas valve operator (not shown).
With increasing forward-flow water temperature T_W the set point T_SET for the exhaust temperature increases. With increasing gas burner load BL or increasing ionisation current I_OC or increasing gas pressure p_GAS the set point T_SET for the exhaust temperature also increases.
Figure 3 illustrates the method of the present invention for a gas burner 10 being in a running mode. The actual value of the exhaust temperature T_EXH measured by said temperature sensor 20 is compared with the set point T_SET of the same. The set point is determined as described in connection with Figure 2.
At the time t1 the actual value of the exhaust temperature T_EXH drops and differs from the set point T_SET by more than a defined offset value AT. So, beginning with the time t1 a closed status of the exhaust pipe 17 and/or air pipe 15 is detected.
At the time t2 the actual value of the exhaust temperature T_EXH rises and differs from the set point T_SET by not more than the defined offset value ΔT. So, beginning with the time t2 an opened status of the exhaust pipe 17 and/or air pipe 15 is detected.
According to a preferred embodiment of the invention, the exhaust pipe 17 and/or air pipe 15 is in a fully opened status when the actual value T_EXH of the exhaust temperature differs from the set point T_SET by not more than a defined first offset value ΔT1, whereby the exhaust pipe 17 and/or air pipe 15 is in a partially closed status when the actual value T_EXH of the exhaust temperature differs from the set point T_SET by not more than a defined second offset value ΔT2, whereby the first offset value ΔT1 and the second offset value ΔT2 are identical or differ from each other.
List of reference signs

10: gas burner
11: burner chamber
12: heat exchanger
13: water / return-flow water
14: water / forward-flow water
15: air pipe / air duct
16: gas pipe / gas duct
17: exhaust pipe / exhaust duct
18: gas valve
19: fan
20: exhaust temperature sensor
21: exhaust outlet
22: roof wall
23: flange / hook
24: ionisation sensor
25: flame

Claims

Method for operating a fan assisted, atmospheric gas burner, said gas burner comprising a burner chamber in which a gas/air mixture can be burned, said gas burner further comprising a heat exchanger for heating water by burning said gas/air mixture, said gas burner further comprising an air pipe or air duct for providing the air of the gas/air mixture and an exhaust pipe or exhaust duct through which exhaust flowing out of said burner chamber can emerge into the ambient of the gas burner, said gas burner further comprising a fan being assigned to the exhaust pipe or to the air pipe, namely a method for checking the opening and/or closing status of the exhaust pipe and/or air pipe, characterized in that a measurement signal of a temperature sensor measuring the exhaust temperature is used to determine the opening and/or closing status of said exhaust pipe and/or air pipe.
Method according to claim 1, characterized in that a measurement signal of an exhaust temperature sensor being positioned in the region of an exhaust outlet of the burner chamber is used to determine the opening and/or closing status of said exhaust pipe and/or air pipe.
Method according to claim 1 or 2, characterized in that a measurement signal of an exhaust temperature sensor being positioned at a roof wall of the burner chamber, namely at a flange of said roof wall at which said fan and said exhaust pipe are mounted, is used to determine the opening and/or closing status of said exhaust pipe and/or air pipe.
Method according to any of claims 1 to 3, characterized in that a measurement signal of said temperature sensor in combination with a measurement signal of an ionisation sensor is used to determine the opening and/or closing status of said exhaust pipe and/or air pipe.
Method according to claim 4, characterized in that at a burner start up when the gas burner becomes ignited the fan is operated at maximum fan speed and a first exhaust temperature value is measured by said exhaust temperature sensor and a first ionization current value is measured by said ionisation sensor, that after a defined time period the fan is operated at a lower fan speed and a second exhaust temperature value is measured by said exhaust temperature sensor and a second ionization current value is measured by said ionisation sensor, whereby when a difference between said first exhaust temperature value and said second exhaust temperature value and a difference between said first ionization current value and said second ionization current value are both relatively big or high, the exhaust pipe and/or air pipe is in a opened status, preferably in a fully opened status.
Method according to claim 5, characterized in that when the difference between said first exhaust temperature value and said second exhaust temperature value and the difference between said first ionization current value and said second ionization current value are both relatively small or low, the exhaust pipe and/or air pipe is in a closed status, preferably in a partially closed status.
Method according to claim 5 or 6, characterized in that when the difference between said first exhaust temperature value and said second exhaust temperature value is relatively big or high and the difference between said first ionization current value and said second ionization current value is relatively small or low, the exhaust pipe and/or air pipe is in a closed status, preferably in a partially closed status.
Method according to any of claims 5 to 7, characterized in that when the gas burner is ignited and the fan is operated at maximum fan speed the burner is operated with maximum load and the position of a gas valve assigned to a gas pipe or gas duct providing the gas is determined.
Method according to any of claims 5 to 8, characterized in that after said defined time period the fan speed is reduced to a minimum fan speed at which a defined amount of CO within the exhaust is not exceeded.
Method according to any of claims 1 to 9, characterized in that a set point for the exhaust temperature value is determined as a function of the forward-flow water temperature of said heat exchanger and/or as a function of the burner load.
Method according to claims 10, characterized in that said set point for the exhaust temperature is determined as a function of the forward-flow water temperature of said heat exchanger and/or as a function of the gas pressure measured by a gas pressure sensor being assigned to a gas pipe or gas duct proving the gas to the burner chamber.
Method according to claims 10, characterized in that said set point for the exhaust temperature is determined as a function of the forward-flow water temperature of said heat exchanger and/or as a function of the ionisation current measured by an ionisation sensor being assigned to the burner chamber.
Method according to any of claims 1 to 12, characterized in that when the burner is in a running mode in which the same is ignited and burns a gas/air mixture within the burner chamber, the actual value of the exhaust temperature measured by said temperature sensor is compared with a set point of the same, whereby the exhaust pipe and/or air pipe is in a opened status when the actual value of the exhaust temperature differs from the set point by not more than a defined offset value, and whereby the exhaust pipe and/or air pipe is in a closed status when the actual value of the exhaust temperature differs from the set point by more than a defined offset value.
Method according to claim 13, characterized in that the exhaust pipe and/or air pipe is in a fully opened status when the actual value of the exhaust temperature differs from the set point by not more than a defined first offset value, and that the exhaust pipe and/or air pipe is in a partially closed status when the actual value of the exhaust temperature differs from the set point by not more than a defined second offset value, whereby the first offset value and the second offset value are identical or differ from each other.