Combustion – Process of combustion or burner operation – Controlling or proportioning feed
Patent
1998-09-24
2000-09-05
Price, Carl D.
Combustion
Process of combustion or burner operation
Controlling or proportioning feed
431 18, 431 75, 431 79, 431 89, F23N 308, F23N 504, F23N 508, F23N 512
Patent
active
061133841
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to gaseous fuel combustion systems and in particular to a method and apparatuses in accomplishment of same, for controlling the combustion to obtain: flame stability, low emissions, in the most wide field of burner capacity modulation required in practice, even in feeding conditions with limit gases, in a so simple and practical way to be used also for apparatus with capacity of only few KW.
The gas combustion system is the assembly of the burner with, the combustion chamber, the heat exchanger, the means for the circulation of air and exhausts, if existing, as well as the control apparatus with its sensors; more elements of the assembly can form a sole body therefore a distinction only possible for functions.
The gas combustion systems are the main functional assembly of domestic and industrial appliances as central heating boilers, water heaters, of two main types: istantaneous and storage water heater, room heater and furnaces, gas cookers etc..
For burner it is understood the fictional assembly of the parts which create the mixture of air and fuel-gas and make possible the outflowing of them in the combustion chamber through the flame openings.
The invention applies in particular to fuel-gas combustion systems, where the mixture, formed by air, said primary air, and fuel gas (hereafter simply said mixture) is by approx. stoichiometric to strongly hyperstoichiometric (0.95<.lambda.<1.6, where .lambda. is the ratio between air actually present in the mixture and the air existing in the stoichiometric mixture of the same gas in the same conditions); flow in combustion chamber, out from the flame openings of the burners with substantially laminar flow, having an out flow velocity between 0.2 and 4.0 meter per second, and generates a lamellar flame, means of big surface and minimum thickness (magnitude order of a millimetre), this means that the ratio surface thickness is well over a value of ten, substantially detached from the area occupied by the flame openings; the flame front, that is the surface where the combustion starts, coincides with the flame itself being the combustion monostadium for the presence of all the necessary oxygen since the ignition and is from laminar to wrinkled. The invention applies to combustion systems with gas atmospheric burners but also with forced burners, where the air gas mixture is obtained, in the wanted flow and composition, with the help of auxiliary means (for example fans, or compressors) both types operate either with the presence of secondary air (called partially pre-mixed burners) or with only primary air (called totally pre-mixed burners). In all types of burners the mixture outflows from the flame openings with a velocity fairly higher to the flame speed so as to avoid that the flame adheres to the opening itself (flame substantially detached).
In the combustion chamber the mixture ignited, at least initially, by suitable ignition devices, forms the flame which is kept in stability conditions from a sort of anchorage system, acting at least in some points. Opening configurations, in particular slots obtained in thin thickness sheet, so close to create an almost homogeneous sole jet of mixture are considered single flame opening. The front of flame is recognisable because it emits in the visible, even if the specific maximum emission due to OH and CH ions is respectively in the wavelength between 305 and 320 mm and around 431.5 and 438 mm.
BACKGROUND OF THE INVENTION
A problem arises when instead of the standard fuel-gas for which the apparatus is set, a fuel-gas from the same family as said standard fuel-gas but prone on flame blow-off or prone to flash back are fed. Specifically, the burner flame openings surface may attain critical temperature value, and in some other occasion, the flame may become unstable, resulting in poor combustion of fuel-gas.
A method, applicable to highly premixed but only atmospheric burners, to maintain stable the temperature of the flame openings and reduce the harmful
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