Burner

Details Burner Burner

2000-03-15

2001-06-26

Lazarus, Ira S. (Department: 3743)

Combustion

Mixer and flame holder

C431S353000, C431S346000, C431S076000, C431S264000

Reexamination Certificate

active

06250913

ABSTRACT:

The present invention relates to a gas burner suitable for use in incinerators, boilers, space heating appliances and ovens, furnaces or high temperature reactors used in industry, for example. A burner incorporating the flame holder is also highly suitable for use in a flare stack.
The gas to be used as fuel can be any of the combustible gases commonly used in gas burners. For example, the gas can be butane, propane, natural gas and hydrocarbon product gases produced by gasification of organic materials, such as commercial or general domestic waste.
The burner disclosed hereinafter has been devised to secure complete mixing of the fuel and air or oxygen, and to admit them to a mixing chamber in the burner only in the correct stoichiometric ratio required by the fuel for its complete combustion whilst providing a stable flame over a turn-down ratio of up to 60:1, at least.
A preferred burner for combusting gaseous fuel, comprises a burner tube open at one end and closed at its other end with a flame holder at which fuel is burnt adjacent the open end, the flame holder being traversed by passages for fuel and air to be consumed, the burner having inlets adjacent the closed end respectively for air, or oxygen, and fuel, the inlets being furnished with metering nozzles for separately delivering air and fuel substantially radially into the tube which forms a mixing zone between the inlets and the flame holder, the metering nozzles having orifices with flow cross-sectional areas correlating to the stoichiometric ratio of air-to-fuel for which the fuel is substantially completely burnt.
A burner of the present invention beneficially tolerates widely-varying air/fuel flow rates, i.e. it has a high turn-down ratio. Conventional burners have turn-down ratios of the order of 4 or 5 to 1. Thus, the supply rates of air and fuel can be reduced to one quarter or one fifth of the maximum capacity of such burners. Further reduction results in flame instability; ultimately the flame fails and is extinguished.
The present invention seeks to provide a burner with a much larger turn down ratio. Accordingly, it provides a burner for combusting gaseous mixture of gaseous fuel with a combustion supporting gas, such as oxygen or air, comprising a burner tube open at one end and closed at its other end with a flame holder at which fuel is burnt adjacent the open end, the flame holder being traversed by passageways for the gaseous mixture, the burner having inlets adjacent the closed end connected to combustion supporting gas and gaseous fuel supply lines, one of said lines having a control valve operable for controlling the size of the flame, the said one line having a pressure or flow transducer and the other line having a variable booster or restricter responsive to the transducer, for balancing air and fuel supplied to the burner to ensure the gaseous mixture remains stoichiometric irrespective of the size of the flame and such that the lowest gaseous fuel mixture flow rate is at least as low as {fraction (1/60)}
th
the highest flow rate of the gaseous fuel mixture each passageway having a flared exit at the end nearer the open end of the burner each passageway being dimensioned such that at the highest obtainable flow rate of gaseous fuel mixture the flames do not lift off from the flamer holder, at the lowest flow rate the velocity of the gaseous fuel mixture at some point within the passageway is sufficient to prevent flame back through the flame holder.
The burner of the present invention represents a marked departure from prior art burners in that the burner can provide a stable flame at the flame holder at low flow rates yet can provide a 60 fold increase in gaseous mixture flow rate by providing sources of gaseous fuel and combustion supporting gas which can provide sufficiently high pressures to provide, at the high flow rate, a sufficient pressure drop over the flame holder passageways to obtain the required flow rate.
The burner of the present invention holder of the can provide a turn-down ratio of the order of 60:1, and thus a stable flame is retained even when the supply of air and fuel is reduced to one sixtieth of the maximum capacity.
Such a high turn-down ratio is highly advantageous, since heat output can be controlled over a wide range. Moreover, such a burner is ideal for use in situations where the gas supply is variable, such as may occur in the case of flare stacks.
The inlets may be furnished with metering nozzles for separately delivering air and fuel non-axially, e.g. substantially radially into the tube which forms a mixing zone between the inlets and the flame holder the metering nozzles having orifices with flow cross-sectional areas correlating to the stoichiometric ratio of air-to-fuel for which the fuel is substantially completely burnt. Preferably the inlets are disposed in the tube for delivering air and fuel in directions which impinge, to create turbulence and mixing inside the tube, for example by locating the inlets diametrically opposite one another in the tube.
Conveniently, the flame holder provides a mounting for an igniter and associated ground electrode, and, optionally, further provides a mounting for an ionization probe.
Preferably the burner includes a monitor and control system coupled to the probe, for interrupting the fuel supply should the unburnt carbon exceed a predetermined level.
In such an embodiment, there may be a valve in the air supply line and a booster or restricter in the fuel line, or there may be a valve in the fuel line and a variable speed fan provided in the air line.
The flame holder may comprise two or more radially nested tubes each pair of adjacent tubes defining therebetween one of said passageways of the flame holder for the gaseous fuel, but other ways of defining the passageways may be employed, for example, a plurality of holes in a disc.
The tubes (
30
a
,
30
b
,
30
c
) may be held in position relative to each other by one or more transverse pins (
33
) and include a central bore with a flared exit.
Each flared exit may have its terminal portion defined by inner and outer cylindrical walls which are parallel to the longitudinal axis of the flame holder.


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patent: 4752213 (1988-06-01), Grochowski et al.
patent: 4875850 (1989-10-01), Cagnon et al.
patent: 5447427 (1995-09-01), Susuki
patent: 5547372 (1996-08-01), Smith
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patent: 1004647 (1998-06-01), None
patent: 0002289 (1927-08-01), None
patent: 2138733 (1999-09-01), None

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