Combustion – Process of combustion or burner operation – Controlling or proportioning feed
Reexamination Certificate
2001-05-07
2003-03-25
Yeung, James C. (Department: 3743)
Combustion
Process of combustion or burner operation
Controlling or proportioning feed
C431S025000, C431S075000, C431S078000
Reexamination Certificate
active
06537059
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a regulating device for a burner and includes an ionization electrode arranged in the flame region of the burner, and a setting member which influences the fuel flow or the air flow depending on a setting signal.
2. Description of the Prior Art
Ionization electrodes for flame monitoring purposes in burners have long been in use. In general, however, the ratio of the amount of air to the amount of fuel, often referred to as lambda, is mutually matched in regard to any output demand either by a control system (i.e. without feed-back or the like) or by a regulating system (i.e. with feed-back or the like) and sensors. In general lambda at each output demand should be slightly above the stoichiometric value of 1, for example 1.3.
Unlike controlled burners, air ratio-regulated burners react to external influences which alter combustion. They therefore have a higher degree of effectiveness and thus a higher level of efficiency as well as lower pollutant emissions and thus a lower level of environmental pollution. The sensors required for that purpose, often gas sensors, in particular oxygen sensors, or temperature sensors, are however expensive, unreliable, require maintenance and/or involve a short operating life.
For that reason, for many years now burner manufacturers and regulating device manufacturers have endeavored to use the ionization electrode which is already present, not just for flame monitoring but also as a sensor for burner regulation purposes. German Patent DE-A1-39 37 290 describes a test structure for regulating the gas-air ratio, in which the ionization electrode is supplied with a dc voltage. That principle is not very suited to mass production. Monitoring the flame with the same ionization electrode is not possible as for that purpose only the rectifier property of the flame may be used.
Italian Patent IT-95U000566 and European Patent EP-A1-909 922 which describe regulating devices for gas burners appeared some years ago. In a simplified illustration, those specifications describe how the setting member is controlled on the basis of a stored characteristic in the event of dynamically rapid changes in the gas or air volume flow. In contrast, in the event of slow changes in the gas or air volume flow, a fine setting occurs on the basis of a regulation with the ionization signal as a measurement parameter.
Rapid changes in the fuel flow or the air flow typically occur due to sudden changes in the output demand. In addition, changes in air ratio and thus changes in the fuel or air volume flow can be caused by a change in the fuel composition, a change in the air pressure, changes in the gas pressure, temperature changes, fouling and wear of mechanical burner components, and so forth.
The stored characteristic in the regulating devices disclosed in the Italian Patent IT-95U000566 and the European Patent EP-A1-909 922 establishes at each air pressure of the blower, and thus at each demanded level of power, a setting signal which corresponds to an approximately desired status of the setting member for the gas valve. Also described is an alternative regulating device in accordance with which the air volume flow is adapted to the gas volume flow and the stored characteristic approximately establishes the desired blower speed depending on the setting parameter of the gas valve.
A burner-specific characteristic is obtained by the burner being operated under a respective different loading with changing setting member statuses, in which case emission values and a level of efficiency are measured with additional sensors and the desired setting parameters are determined in that way.
Air ratio-regulated burners have advantages over apparatuses which are controlled by means of characteristics. With a constant output, changes in temperature, fuel pressure, air pressure, fuel composition, wear and fouling of mechanical components etc. allow the set working point to drift away.
For that reason, the regulating devices disclosed in the Italian Patent IT-95U000566 and the European Patent EP-A1-909 922 admittedly implement control on the basis of the stored characteristic when rapid changes in output occur, but compensate for the incompleteness thereof insofar as they initially displace the last status of the setting signal a constant distance along the stored characteristic to a new value.
Approximately at the same time the proprietor of the European Patent EP-A2-806 601 developed regulating devices which also have a characteristic stored for the setting signal. The characteristic also basically serves to provide for preliminary control of the setting member in the event of rapid changes in output.
The last-mentioned regulating devices include an ionization evaluating device which is connected downstream of the ionization electrode and which produces an ionization signal, a control unit in which characteristic data for determining a first mode of behavior of the setting member are stored, which at least at times produces a first control signal, and a regulator which produces the above-mentioned setting signal at least at times depending on the ionization signal and at least at times depending on the first control signal.
The above-indicated regulating devices known from the state of the art have disadvantages. More specifically, some use additional sensors and/or do not hold the air-gas ratio very stable upon dynamic variations in output. Market acceptance is correspondingly low.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a regulating device for a burner
comprising an ionization electrode arranged in a flame region of the burner, and
a setting member which influences a fuel flow or an air flow depending on a setting signal, and is
equipped with an ionization evaluating device which is connected downstream of the ionization electrode and which produces an ionization signal;
a control unit in which characteristic data for determining a first mode of behavior of the setting member are stored and which at least at times produces a first control signal;
a regulator which produces the setting signal at least at times depending on the ionization signal and at least at times depending on the first control signal; and
wherein also stored in the control unit are characteristic data for determining a second mode of behavior of the setting member,
the control unit produces at least at times a second control signal, and
the regulator produces the setting signal at least at times depending on the second control signal.
It has been found that a substantial improvement in terms of regulating a burner by way of the ionization electrode lies in the features of the invention that characteristic data for determining a second mode of behavior of the setting member are stored in the control unit, the control unit at least at times produces a second control signal, and the regulator produces the setting signal at least at times depending on the second control signal.
The structure of a regulating device according to the invention requires few resources such as electronic components and computing capacity of a microprocessor. For a one-off initial setting of a regulating device to a certain type of burner, instead of previously one, now two or more burner-specific characteristics have to be established.
Practice has shown that the second control signal makes an above-average contribution to making control of the setting signal more precise.
The regulating device moreover can be so designed that, upon the detection of suitable conditions, it itself implements a setting method for the detection of new characteristic data.
Thus, occasional or regular re-calibration takes place, in order to compensate for any incremental changes in the regulating system, for example wear or fouling of the ionization electrode. Another possible option provides that the control characteristics are determined automatically, even for gases having characteristics that are not covered by the pre-set char
Greer Burns & Crain Ltd.
Siemens Building Technologies AG
Yeung James C.
LandOfFree
Regulating device for a burner does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Regulating device for a burner, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Regulating device for a burner will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3072475