Combustion – Process of combustion or burner operation
Reexamination Certificate
2001-06-01
2004-02-10
Bennett, Henry (Department: 3743)
Combustion
Process of combustion or burner operation
C431S239000
Reexamination Certificate
active
06688876
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to combustion systems using liquid fuel and oxidizer containing from around 20% to 100% by volume of oxygen (air, oxygen-enriched air, industrially pure oxygen). In this type of burner, the stability of the flame is a condition sine qua non of operation. The present invention makes it possible to define the geometry of the burners of this type so as to ensure the stability of the flame as well as correct positioning of the flame generated by the burner.
2. Brief Description of the Related Art
Numerous high-temperature processes (glass furnace, reheat furnace, incineration furnace, etc.) use combustion and in particular combustion with the aid of liquid fuels. One of the key steps in the combustion of liquid fuel is atomization: the liquid jet must firstly be transformed into drops which are vaporized and then burned. Several means are available for making these drops. A first example is mechanical atomization in ambient air, consisting essentially of impacting the liquid onto a gas at rest. Another example consists in using the intervention of a moving atomization gas, such as air, oxygen, steam, or any other available gas. For further details regarding the various categories of atomizer, reference may be made to the work by A. Lefebvre entitled: “Atomization and Sprays”, 1989, published by Taylor & Francis, p. 136 et seq.
The atomizer is generally placed in a glory hole (typically made of a refractory material) into which an oxidizer gas flows. Although in theory there is nothing to prevent the atomizer being positioned set back from the exit plane of the glory hole, nobody has hitherto been able to demonstrate any relationship whatsoever between the stability of the flame and the positioning of this injector in the glory hole.
The expression stable flame should be understood to mean, according to the present invention, a flame for which the average position of its root does not vary substantially over time. This position will typically be tagged with respect to the injector.
In gaseous combustion, the stability of the flame is governed by the recirculation structures formed at the boundary of the gaseous jet (see the article by J E Broadwell, W J A Dahm and M G Mungal, “Blowout of turbulent diffusion flames” published in the 20
th
Symposium (International) on Combustion, by The Combustion Institute, pp 303-310, 1984). The combustion which takes place at the core of these recirculation zones will provide the energy necessary for the stabilization of the flame.
It has been found that the problem of stability is trickier in the case of a liquid-fuel flame than in the case of a gas-fuel flame. Specifically, the vaporization of the drops will consume energy. This energy will no longer be available to sustain the combustion and stabilize the flame. It has therefore been demonstrated that it was necessary to take into account, for this type of flame, an additional factor for stability: the small-sized drops. Specifically, the latter meet two criteria. Firstly, they have the capacity to follow the gaseous flow. It is then possible to trap them in the recirculation zones. Thereafter, they evaporate rapidly and can therefore feed these recirculation zones with gaseous fuel and thus allow the flame to be held according to the same mechanisms as for gas flames.
One means of ensuring the stability of a flame is to create extra recirculation zones (different from the recirculation zones created “naturally” along the jet). In gaseous combustion, it is known from U.S. Pat. No. 5,645,413 to create internal recirculation, whereas it is known from U.S. Pat. No. 4,536,152 and U.S. Pat. No. 5,791,893 to supplement the burner with a flame holder.
Liquid-fuel atomizers furnished with a flame holder (or stabilizer) are described for example in U.S. Pat. No. 4203719 (“disc-shaped baffle”) and U.S. Pat. No. 4836772 (“stabilizing ring”).
However, the use of flame-holder fittings in enriched-air or pure oxygen flames is generally impossible since the temperature withstand of this type of fitting in this type of flame would be greatly compromised.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, a process for combustion with the aid of a liquid fuel and a gaseous oxidizer containing from 20% to 100% volume of oxygen comprises the steps of injecting the fuel with an injector having an internal height d placed inside a glory hole having an internal height D at its end corresponding to the ejection of the gaseous mixture towards the zone of heating of a charge; maintaining the coefficient S defined by the relation:
S
=
a
1
V
equivalent
-
a
2
L
a
3
d
(
2
-
e
-
L
/
10
D
)
with
a
1
=2.5·10
−11
, seconds
a
2
=1·10
−9
, dimensionless
a
3
=(0.875&ggr;+0.525)·10
−6
, dimensionless
at a value less than or equal to 1 for substantially the entire duration of combustion, wherein L is defined as the distance between the end of the liquid fuel injection and a downstream end in the fluid flow direction of the glory hole, V
equivalent
is defined either as the equivalent velocity representative of the average velocity of the spray of drops of liquid fuel in the case of mechanical atomizers and being equal to 2.4 M/(&rgr;&pgr;d
2
), or a velocity equal to 0.5 times V
atomization
, and &ggr; is defined as the overall (volume) percentage of oxygen in the gases at the exit of the glory hole.
Still other objects, features, and attendant advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description of embodiments constructed in accordance therewith, taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 3836315 (1974-09-01), Shular
patent: 3861858 (1975-01-01), Hemsath et al.
patent: 4683541 (1987-07-01), David
patent: 4851722 (1989-07-01), Zauderer
patent: 5199866 (1993-04-01), Joshi et al.
patent: 5449286 (1995-09-01), Snyder et al.
patent: 5490775 (1996-02-01), Joshi et al.
patent: 5617997 (1997-04-01), Kobayashi et al.
patent: 5620316 (1997-04-01), Duboudin et al.
patent: 6123542 (2000-09-01), Joshi et al.
patent: 0 614 044 (1994-09-01), None
patent: 97/06386 (1997-02-01), None
Broadwell, Dahm, Mungal; “Blowout of Turbulent Diffusion Flames”, 1984.
Bodelin Pierre
Delabroy Olivier
Joshi Mahendra
Labegore Bernard
Lacas François
Bennett Henry
Burns Doane Swecker & Mathis L.L.P.
Dagostino Sabrina
L'Air Liquide Societe Anonyme a Directoire et Conseil de Su
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