Combustion – Mixer and flame holder
Reexamination Certificate
2001-06-04
2004-05-04
Cocks, Josiah (Department: 3749)
Combustion
Mixer and flame holder
C431S177000, C431S278000, C239S418000, C137S602000, C137S599030
Reexamination Certificate
active
06729874
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to venturis which induce the flow of a fluid when an inducing flow of another fluid is passed therethrough. The invention further relates to industrial burners, and in particular to burners which utilize venturis to induce the flow of one or more of the components of a combustible mixture and thereby create such mixture for introduction into a combustion zone. The invention also relates to burner devices capable of creating and handling oxygen rich combustible mixtures.
2. The State of the Prior Art
Venturi devices for inducing the flow of one fluid (the induced fluid) by flow of another fluid (the inducing fluid) are known. These devices generally consist of a tube which has an inlet end, a throat area and an outlet end. Generally speaking, the throat has a smaller flow area than the inlet end whereby to provide a low pressure area at the throat. The inducing fluid flows through the tube from the inlet end of the venturi to the outlet end, and a source of the induced fluid is in fluid communication with the low pressure area created in the throat of the device by the flow of the inducing fluid. Thus, the induced fluid is drawn into the throat and mixes with the inducing fluid.
Venturi devices are particularly useful in burners where a flow of fluid fuel is used to induce a flow of air to thereby create a mixture of the fuel and the air in the venturi. Sometimes, however, it is useful to use the combustion air to induce a flow of the fuel. Alternatively, a flow of air or fuel through the venturi may be used to induce a flow of recirculated flue gas or other diluent to control flame temperature and thus influence NO
x
production.
In spite of their wide spread use, venturis still have certain limitations. In the first place, the capacity of the venturi for inducing a flow of induced fluid is limited by the available pressure of the inducing fluid and the quantity of the latter needed for a given application. In addition, the length of an efficient venturi typically is directly related to the diameter of the throat. The physical dimensions of the work environment thus may have a limiting influence on the capacity of the venturi.
In a more general sense, the reduction and/or abatement of NO
x
in industrial burners has always been a desirable aim. Some NO
x
abatement has been achieved in the past by using a fuel lean primary combustible fuel/air mixture coupled with staging of a portion of the gaseous fuel. Fuel lean primary mixtures are potentially desirable in some applications because the excess air provides a load to reduce flame temperatures whereby to reduce NO
x
. Staged gas may then be introduced into the combustion zone either from gas tips arranged around the periphery of the burner or from a center gas tip which protrudes through the center of the downstream end of the burner nozzle. The secondary fuel is combusted with the excess air in an environment where flue gases are available as a diluent. These arrangements have not always been successful in reducing NO
x
to desirable levels.
In some instances, a fuel lean primary mixture is introduced into the combustion zone at a relatively high velocity due to the extra mass provided by the excess air. Such velocity may sometimes be so high that the flame speed is exceeded providing an unstable flame environment.
SUMMARY OF THE INVENTION
In accordance with the principles and concepts of the invention, the same provides, in one important aspect, a compound venturi structure which includes a venturi cluster made up of a plurality of venturis. Thus, by definition, in accordance with this aspect of the invention, the compound venturi structure has at least two venturis. Desirably, the structure may have at least three, often will have at least six, and in some instances, depending upon the exigencies of a particular application, may have even more than six venturis. An important purpose of the present invention is to provide practical solutions for problems that are extant in the burner field today, in particular those that involve the production of excessive NO
x
levels. Thus, the invention provides structure and methodology directed to addressing and alleviating the problems which have been mentioned above. Moreover, the invention solves problems that relate to venturis generally. Because of the increased surface area provided by the multiplicity of venturis, a given volume of the inducing fluid may educe a greater flow of the induced material. Moreover, for a given flow of inducing fluid, the throats of the venturis in a bundle have smaller throats and therefore may be smaller in length.
Each of the venturis of the cluster may have an inlet, a throat and an outlet, and each may be arranged and adapted for causing the flow of an induced material by passage of an inducing fluid therethrough. This action creates, in each venturi, a respective mixture of induced material and inducing fluid, which mixture may then be discharged from the outlets of the respective venturis. The structure also may desirably include a collector having an inlet end which is connected to and arranged in fluid communication with the outlets of the venturis. Thus, the respective mixtures of inducing fluid and induced material discharged from the outlets may be collected and intermixed to present a single mixed stream for discharge from an outlet end of the collector. The induced material most often may be a fluid material; however, in accordance with the broader aspects and contemplations of the invention, the induced material may be a solid flowable material, such as, for example, a powder or a flake material.
The venturis of the compound venturi structure of the invention may desirably, but not necessarily, be in the form of elongated, essentially straight tubes. Preferably, but not necessarily, the tubes may be arranged in essential parallelism relative to one another. The venturis may also have essentially the same physical capacity; however, this also is not a necessary or critical feature of the invention, and in fact, there are many applications where it may be desirable for at least one of the venturis of a given cluster to have a different physical capacity than another of the venturis of that same cluster.
In another important aspect of the invention, the compound venturi structure may be a component of a novel burner assembly. In accordance with this aspect of the invention, in addition to the venturi cluster and the collector, the burner assembly may include a burner tip that is attached to and in fluid communication with an outlet end of the collector. Thus, the tip may be arranged for receiving the single mixed stream of fluids from the collector and directing the same into a combustion zone.
In one important embodiment of the invention, the tip may be elongated and adapted and arranged for directing the single mixed stream out of the tip and into the combustion zone in a generally radial direction relative to a longitudinal axis of the tip. Such a tip may desirably be configured so as to create a round flat flame which surrounds the tip.
In another important embodiment of the invention, the tip may be elongated and adapted and arranged for directing the single mixed stream out of tip and into the combustion zone in a generally axial direction relative to a longitudinal axis of the tip. This tip may desirably be configured so as to create a cylindrical flame which extends along the axis.
In a general sense, either a gaseous fuel or air may be the inducing fluid; however, desirably, at least one of the venturis may be adapted and arranged for operation with a gaseous fuel as the inducing fluid. When a gaseous fuel is used as the inducing fluid, either air or recirculated flue gas may be the induced fluid. Desirably, at least one of the venturis may be adapted and arranged to operate with air as the induced fluid. Thus, when a gaseous fuel is used as the inducing fluid and air is the induced fluid, the single mixed stream created in the collector may compri
Bussman Wesley Ryan
Chung I-Ping
Hayes Ralph Robert
Jayakaran Jaiwant D.
Jones Andrew
Cocks Josiah
John Zink Company LLC
Marsh, Jr. James H.
Stinson Morrison Hecker LLC
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