Combustion – Process of combustion or burner operation – Controlling or proportioning feed
Reexamination Certificate
1999-11-05
2001-10-09
Yeung, James C. (Department: 3743)
Combustion
Process of combustion or burner operation
Controlling or proportioning feed
C431S025000, C431S075000, C431S078000
Reexamination Certificate
active
06299433
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to the control of burners, particularly gaseous fuel burners. More particularly, the invention relates to methods and apparatus for the control of such burners based on flame intensity.
Burners wherein a gaseous fuel such as natural gas, methane, propane, butane, ethane or the like, for example, is burned with a combustion oxidant gas such as oxygen, oxygen-enriched air or air, for example, are well known. For example, such gas burners find application in various residential, commercial and industrial combustion or heating assemblies such as those that include furnaces, water heaters, boilers, and the like.
In general, proper or desired operation of such burner apparatus involves responsive controlled operation beyond the mere supplying of fuel and oxidant at fixed flow rates. Unfortunately, such responsive control has to date proven relatively difficult and/or costly to achieve in a manner practical and economical for desired broader based applications.
It has long been recognized that flame intensity associated with the burning of such fuel and oxidant combustion mixtures is influenced by a variety of parameters, such as including firing rate, oxidant to fuel (also sometime referred to herein as “O/F” or, more specifically air to fuel ratio, when referring to systems wherein air is employed as the oxidant source), exact oxidant and fuel compositions, and the thermal environment of the flame, for example. It has also been long recognized that means to measure flame intensity are relatively simple and readily commercially available. In fact, flame intensity is routinely measured in many devices as a means of assuring the occurrence of combustion.
Numerous attempts have been made to apply simple flame intensity sensors to the control of oxidant to fuel ratio. Such a control method would significantly reduce the cost of oxidant to fuel ratio control, which is currently primarily achieved with rather expensive sensors that measure the concentration of oxygen in the exhaust. The simplicity and reduction in cost could open up considerable markets for oxidant to fuel ratio control for which it is currently unaffordable. In addition, since the measurement of flame intensity can be made at an individual burner, it would be possible to control the oxidant to fuel ratio from individual burners. In view thereof, potential applications include residential (e.g., air heating or water heating), commercial (e.g., air heating and boilers), industrial (e.g., furnaces and boilers), and power generation (e.g., boilers and gas turbines), for example. Thus, an invention that would enable such a control system could have considerable economic potential and impact.
Unfortunately, because of the dependency of flame intensity on parameters other than the oxidant to fuel ratio (such as parameters such as firing rate, fuel composition, and thermal environment, for example) it has been generally impossible to achieve oxidant to fuel ratio measurement with these sensors without knowing such other parameters as well.
It has also been recognized that the peak in the curve of flame intensity versus oxidant to fuel ratio generally occurs at the same oxidant to fuel ratio as long as the fuel composition is kept reasonably constant, for example, different compositions of natural gas are generally acceptable. Several measurement and control mechanisms based on this principle have been proposed. Unfortunately, the peak in the curve of flame intensity versus oxidant to fuel ratio typically or generally occurs at slightly or even significantly fuel rich conditions. For most combustion systems, operation under such fuel rich conditions is not desirable and for many combustion systems such operation is unacceptable. Consequently, various control schemes have been proposed that require only occasional operation at such fuel rich conditions, in order to calibrate the system. Unfortunately, application of such control schemes results in the control system not being a closed loop control system, but rather an open loop system with periodic calibrations. Furthermore, for some systems even periodic operation under such fuel rich conditions is unacceptable.
Thus, there is a need and a demand for a method and an apparatus for controlling such burner apparatus which more readily permits the use of relatively simple flame intensity sensors, such as known in the art.
In particular, there is a need and a demand for a relatively simple method and apparatus for the closed loop control of such burner apparatus. In addition, there is a need and a demand for burner apparatus control methods and apparatus which avoid or do not require undesired fuel rich condition operation.
SUMMARY OF THE INVENTION
A general object of the invention is to provide improved burner control.
A more specific objective of the invention is to overcome one or more of the problems described above.
The general object of the invention can be attained, at least in part, through a method for controlling operation of a burner apparatus in which a combustion reaction mixture of a combustion oxidant and a fuel gas are burned. For this burner apparatus, flame intensity values are mathematically transformable to create a parameter R. A plot of R versus oxidant to fuel ratio has a slope M which is independent of the burner apparatus firing rate and which varies relative to oxidant to fuel ratio in a known relationship such that each oxidant to fuel ratio is uniquely associated with a particular M value. In accordance with one preferred embodiment of the invention such method includes burning a first combustion reaction mixture wherein the combustion oxidant and the fuel gas are at a first oxidant to fuel ratio, with a first flame intensity being measured for the first combustion reaction mixture. Such method further includes burning a second combustion reaction mixture wherein the combustion oxidant and the fuel gas are at a second oxidant to fuel ratio and wherein the second oxidant to fuel ratio and the first oxidant to fuel ratio differ in a known relative proportion, with a second flame intensity being measured for the second combustion reaction mixture. The measured first and second flame intensities are mathematically transformed to corresponding parameter values R
1
and R
2
, respectively. Then, using the parameter values R
1
and R
2
, the known relative proportion difference of the first and second oxidant to fuel ratios, and the known relationship by which the parameter R varies relative to oxidant to fuel ratio for the burner apparatus, the second oxidant to fuel ratio associated with the second flame intensity is determined.
In one particular embodiment, such a method additionally includes the step of adjusting the combustion oxidant to fuel gas ratio of the combustion reaction mixture to a desired oxidant to fuel ratio.
In another particular embodiment of the invention, such a method additionally comprises comparing the second oxidant to fuel ratio with a target range of oxidant to fuel ratios and, where the second oxidant to fuel ratio is not within the target range, shutting off the burner apparatus or setting off an alarm.
The prior art has generally failed to provide responsive burner control which is as simple and as inexpensive to practice as has been desired. In particular, the prior art has generally failed to provide burner control that more freely permits application of simple flame intensity sensors to the control of oxidant to fuel ratio in such burner apparatus. Thus, the prior art has generally failed to provide a burner control method and apparatus of desired simplicity and reduced cost and such as may find as wide as desired potential application.
In accordance with one particularly preferred embodiment, the invention further comprehends a method for controlling operation of a premixed gas burner apparatus. In one specific form, such a method includes:
burning a combustion reactant mixture comprising a fuel gas and a combustion oxidant;
monitoring a first degree of ionization (I
Benson Charles Edward
Gauba Gautam
Macadam Scott
Schmidt Stephan Erwin
Thijssen Johannes H. J.
Gas Research Institute
Pauley Petersen Kinne & Fejer
Yeung James C.
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