Combustion – Porous – capillary – particulate or sievelike flame holder,...
Patent
1992-12-28
1995-01-31
Jones, Larry
Combustion
Porous, capillary, particulate or sievelike flame holder,...
431 8, 431354, 239559, F23D 340, F23C 500
Patent
active
053854675
DESCRIPTION:
BRIEF SUMMARY
SUMMARY OF THE INVENTION
The invention relates to a method of bringing about the combustion of gases while controlling harmful emissions, and to the relative burner and system, that is, a new procedure by which to obtain thermal energy from gases such as methane, butane, propane or others, and blends thereof, whether by supplying the gas-air mixture to the burner partly premixed, i.e. with an aeration rate (the ratio between the effective quantity of air present in a given volume of the mixture and the quantity required to bring about stoichiometric combustion in the same volume) less than or equal to 1, or by supplying a mixture totally premixed, that is, with an aeration rate higher than 1, in such a way that harmful emissions (principally NOx and CO) are either eliminated completely or reduced to negligible levels; such a method is implemented by means of a burner and variable power fuel feed system also constituting subject matter of the disclosure. The prior art embraces a method of bringing about gas combustion at low NOx and CO emission levels as disclosed in application for international patent number PCT/IT 87/00079 filed Mar. 8, 1987 by the same applicant, which comprises the steps of:
aspirating a quantity of primary air equal to at least 80% of the quantity stoichiometrically required;
directing a quantity of secondary air to the single flames, from the start of combustion, in excess of 100% of the stoichiometric value;
bringing combustion to completion internally of a thin flame of lamellar configuration, evidence of which, in the case of natural gas, is the emission of a violet colour of wavelength less than 0.42 nm.
For the implementation of such a method, the above application discloses exclusively an atmospheric burner, that is, a burner connected into a circuit through which fuel and air circulate naturally, in association with a horizontally disposed tubular diffuser affording groups of slots for the passage of the fuel and primary air mixture, distributed over the surface of the diffuser in successive sets extending transversely to its axis, which are set apart one from the next by an amount equal to nd/2, where d is the axial length of the group and n is the number of groups in each set, or the number of groups in two successive sets in the case of a chequered distribution pattern; the distance which separates the groups of slots of one set in the transverse direction is equivalent to at least 65% of the length of the longest slot of one group.
Each group generates a lamellar flame appearing as a pair of divergent wings, butterfly-like in form, of which the axis of symmetry coincides with the longitudinal median plane of each group.
Whilst reflecting notable progress in the control of emissions, particularly NOx and CO, the method set forth in the aforementioned PCT application in effect neither envisages nor permits of feeding the diffuser with mixtures containing percentages of oxygen close to or exceeding stoichiometric values; neither can combustion be sustained in the presence of post-combustion gases, due to the instability of the flame and consequent impossibility of operation in these particular conditions, a fact attributable to the limitations of the method and of the design of the burner, both separately and in combination.
With regard to the control of output variations and feed, the prior art embraces devices as in patents DE 3010014 and DE 3018752, both filed in 1980.
The former discloses regulation of the combustion assisting air by governing pressure upstream and downstream of the combustion chamber, which can be achieved by the installation of a diaphragm, in conjunction with control over the pressure of the gas supplied to the burner nozzles. The latter discloses a nozzle with two chambers in series, of which the outlet sections are controlled by respective obturators associated with a single stem, in conjunction with means by which to control both the flow of primary air and the flow of the fuel-air mixture.
In both devices, there is the disadvantage that a high rat
REFERENCES:
patent: 3445175 (1969-05-01), Krieger
patent: 3936003 (1976-02-01), Hapgood et al.
patent: 4169430 (1979-10-01), Cheetham
Fogliani Giuseppe
Sebastiani Enrico
Jones Larry
Smith Albert C.
Worgas Bruciatori S.r.l.
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