Combustion – Separately supplied or controlled – physically related flame... – Coaxial
Patent
1995-05-15
1998-06-23
Price, Carl D.
Combustion
Separately supplied or controlled, physically related flame...
Coaxial
431 8, 431187, 431278, F23D 2300
Patent
active
057696241
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a burner configuration and in preferred embodiments to a variable flame burner configuration. The invention has particular though certainly not exclusive application to a variable flame burner fuelled by natural gas and is applicable to kilns such as rotary cement kilns, furnaces and other process heating arrangements. The invention also relates to a method of generating a burner flame.
BACKGROUND ART
The present applicant's international patent publication WO88/08104 (PCT/AU88/00114) and the associated U.S. Pat. No. 5,060,867 disclose a fluid mixing nozzle in which a primary flow of a first fluid separates from the internal wall structure and reattaches itself asymmetrically to the wall upstream of the nozzle outlet. A flow of a second fluid induced through the outlet swirls in the chamber between the flow separation and reattachment and induces precession of the separated reattached flow, which exits the nozzle asymmetrically. This nozzle has come to be termed a precessing jet nozzle and such terminology is adopted herein. By the optional addition of a centre-body within the chamber, part of the primary flow can be caused to recirculate within the chamber and induce the precession.
When the precessing jet nozzle is operated as a burner, using eg natural gas as the fuel and primary flow, it has been observed that, in comparison with a simple turbulent jet burner, the precessing jet nozzle generates a more bulbous flame whose stand-off distance is reduced by an order of magnitude and whose blow-off velocity is increased by a factor of four. These features have been found to enhance the stability and radiation characteristics of the flame in furnaces and boilers and to enhance the performance of kilns such as rotary cement kilns employed to produce cement clinker. Both the quality of the clinker produced in such kilns and the energy required to produce it, are significantly influenced by the "heat release profile" of the flame generated by the burner and by the proportion of the energy which is radiated, as opposed to being convected, to the product. The heat release profile of the flame is the proportion of the total energy which is released in each part of the kiln, and it will thus be appreciated that the precessing jet burner, with its closer bulbous flame and higher blow-off velocity, is well suited in principle to kiln application.
Preliminary trials of the precessing jet nozzle burner in a cement kiln have demonstrated a reduction in NO.sub.X emissions by up to 75% relative to a more conventional turbulent jet burner and have shown potential to benefit the clinkering process. However, the flame has been found to release too much heat at the front of the kiln during some phases of the kiln operation, which adversely affects the life of the refractory bricks. Similar constraints may be anticipated in some applications of the precessing jet nozzle burner to other direct process heating in, for example, the metals, glass and chemical industries.
SUMMARY OF THE INVENTION
In accordance with the invention, it has been realised that the aforementioned problem can be overcome, and perhaps other advantages obtained, by providing a burner configuration including at least one precessing jet nozzle and at least one further burner nozzle having mixing characteristics different from the precessing jet nozzle.
Most generally, the invention provides a burner configuration comprising a set of fuel nozzles including at least one precessing jet nozzle and at least one further nozzle having mixing characteristics which are different from the precessing jet nozzle.
Preferably, the burner configuration further includes means to set or control the proportions of fuel flow to the nozzles, wherein the nozzles of the set are in sufficient proximity that the combined flame of the burner configuration can be determined or controlled by setting or varying the relative flows of fuel to the nozzles of the set.
The further nozzle(s) may be a simple turbulent jet nozzle, eg a st
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Luxton Russell Estcourt
Nathan Graham Jerrold
Luminis Pty. Ltd
Price Carl D.
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