Combustion – Fuel disperser installed in furnace – Plural feed means extending to common wall opening of furnace
Reexamination Certificate
2000-05-08
2001-11-13
Clarke, Sara (Department: 3743)
Combustion
Fuel disperser installed in furnace
Plural feed means extending to common wall opening of furnace
C239S424000, C239S424500, C239S400000, C239S406000
Reexamination Certificate
active
06315551
ABSTRACT:
The present invention is an improvement to burners having at least three air feed ducts, including an axial air duct and a rotary air duct concentric with at least one fuel feed, and a central stabilizer.
The technical field of the invention is making a burner capable of using one or more fuels, simultaneously or otherwise, with particular arrangements of the gas feed ducts, which gas can be air or a fuel gas.
BACKGROUND OF THE INVENTION
The main application of the invention is for use in burners for a rotary tubular furnace in which at least 80% of primary combustion air is delivered via at least two concentric ducts disposed around any fuel feed duct and via a third, central feed duct into which the remaining not more than 20% of the primary air is injected.
In a preferred embodiment, of said two concentric annular ducts feeding said burners with at least 80% of their primary air, one of them feeds the air in the form of a swirling current of air having peripheral flow components, and the other feeds air in the form of an axial flow having flow components that are substantially axial; said two primary air flow ducts are thus disposed radially outside any fuel duct, and in particular at least one annular duct for feeding pulverized coal; the central duct inside which at least one fuel feed pipe is slid, at least for starting purposes, is partially obstructed by a flame stabilizer in the form of a flange surrounding the central opening into which said pipe opens out, and has openings for passing a portion of the primary combustion air, i.e. said not more than 20%, and even in fact not more than 10% of the primary air, in such a manner that in the central zone situated downstream from said stabilizer no significant combustion of the fuel takes place, such that said central zone can be said to be “dead”; such a burner is described and claimed in European patent 421 903 published on Apr. 10, 1991 and filed by the same Applicant as for the present invention.
The present invention can be considered as being an improvement applied to such burners and more generally to any burner that can be considered as being a “modern” burner, having fuel and combustion air feed ducts in the above-defined main application, which ducts form a nozzle assembly for mounting on an-orifice provided for that purpose in the wall of an enclosure forming the hearth of the furnace or combustion chamber, and around which secondary air is delivered.
OBJECTS AND SUMMARY OF THE INVENTION
The object of the present invention is to avoid having a central zone at the outlet from said central primary air feed duct that is too reducing for the fuel because only 20% at most or even only 10% of the primary air is injected into said zone; this small proportion of the air (which proportion is adjustable) makes it possible, as described in the above-referenced prior patent, to obtain a wider range over which the operating rate of the burner can be adjusted by moving the beginning of combustion and the flame to a greater distance ahead of the center of the burner nozzle compared with methods and burners known prior to patent EP 421 903.
In the invention, the above object is obtained by enriching the air and fuel mixture in the central zone of such burners having at least four substantially concentric fuel and primary combustion air feed ducts, while nevertheless ensuring that less than 20% or even less than 10% of the primary air is injected into said central zone; the other at least 80% of the primary air is injected as axial air and as rotary air via the openings of ducts located outside any fuel outlet opening, and said burner has a central stabilizer placed at the outlet of a -central primary air delivery duct, which air opens out through orifices of said stabilizer; said stabilizer projects radially relative to the opening of any tube placed in said central primary air duct and within which fuel can be injected, said central zone being the zone situated ahead of said central stabilizer relative to the nozzle of the burner; according to the invention, the burner has at least one additional gas feed opening out into said stabilizer around said opening at any diameter lying between any tube into which fuel can be injected through the stabilizer and the outer tube defining the central primary air delivery duct.
In a particular embodiment, said additional gas feed is a fourth primary air feed making it possible to favor the mixing of air and fuel in said central zone, the air and fuel mixture in said zone being below the stoichiometric ratio.
In another particular embodiment, said gas feed is an additional fuel gas feed, e.g. natural gas or gas having low calorific power.
When said gas feed is a fourth primary air feed, it can be implemented via an opening placed in said central stabilizer and fed by the central primary air delivery duct without having a specific feed duct proper separate from that for feeding said central primary air.
In a particular embodiment, said fourth primary air feed can be implemented by a peripheral opening disposed around the outer edge of said stabilizer, which opening can either be directly implemented in said central stabilizer without a special duct as mentioned above, and as shown in accompanying
FIG. 6
, or else it can be defined by the outer tube surrounding said stabilizer and a concentric inner tube; together said two tubes then constitute a feed duct independent of the other primary air feeds.
In other embodiments, adapted either to feeding additional fuel gas or a fourth primary air feed, said additional gas feed is implemented independently of any other gas feed via a concentric tube outside the tube via which any fuel can be injected into the central zone: this is the embodiment which is shown by way of example in most of the accompanying figures.
The result thus makes it possible to obtain an improvement to burners having at least three air feed ducts, including an axial air duct and a rotary air duct disposed concentrically with at least one fuel feed, and a central stabilizer, making it possible to achieve the above-explained object, i.e. enriching the air/fuel mixture more quickly in the central zone of the burner downstream from the stabilizer, either by diminishing the reducing nature of the air/fuel mixture in said zone, or by improving said mixture, or both, while nevertheless conserving the adjustment and operating advantages of the burners to which this improvement is applied, and thus improving the specific qualities thereof.
REFERENCES:
patent: 3147795 (1964-09-01), Livingston et al.
patent: 4208180 (1980-06-01), Nakayasu et al.
patent: 4679512 (1987-07-01), Skoog
patent: 5090339 (1992-02-01), Oikura et al.
patent: 5178533 (1993-01-01), Collenbusch
patent: 5878676 (1999-03-01), Jochem et al.
patent: 6116171 (2000-09-01), Oota et al.
patent: 3823599 (1990-01-01), None
patent: 0421903 (1991-04-01), None
patent: 1537037 (1978-12-01), None
patent: WO9840668 (1998-09-01), None
Endres Gerhard
Guiot Roland
Salzsieder Patrick
Bachman & LaPointe P.C.
Clarke Sara
Entreprise Generale de Chauffage Industriel Pillard
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