Patent Application
20060029895
The present invention relates to fuel injectors for use in connection with a furnace. More particularly, the present invention relates to a fuel injector and a furnace where pulverized coal or other solid fuel is transferred with a carrier gas and efficiently burned within a combustion chamber of the furnace so that the formation of Nitrogen Oxides (NOx) and other undesirable by-products associated with unburned fuel are reduced.
Low NOx pulverized coal burners consist of a fuel injector and secondary air register controls that have two or more passageways through which secondary air flows. The pulverized coal is carried by one or more gasses, generally air, and passes through the fuel injector into the furnace. The carrier gas is considered the primary air. However, the primary air carrying the coal typically represents no more than 25% of the total combustion air required for combustion. The remaining combustion air enters the furnace through secondary air registers. In many additional cases some of the secondary air is directed to separate staging ports such as overfire air ports, to make combustion of the coal more efficient.
Coal burners, particular low NOx pulverized coal burners, must develop a strong stable flame well rooted in the throat of the burners. Among the design problems typical of these types of burners are maintaining their high reliability of the fuel injector while creating a distribution of pulverized coal and carrier (primary) air that minimizes the generation of NOx, and creating a near zone aerodynamic stabilization pattern of the secondary combustion air that enters the burner around the fuel injector.
Many older designs use flame stabilizers, impellers or collecting ports in the coal stream to attempt create an optimal ratio of fuel/air distributed into the burner. However, these arrangements are subject to rapid wear of the parts, potential overheating and coking (undesired build-up) of the coal on the parts and the resultant reduction in service life. Further, as the parts wear their geometry changes and causes the combustion to degrade.
In typical low NOx burners the secondary air enters the burner through two or more concentric passageways to create an “air staging” effect. Generally these designs include an inner and an outer secondary air zone with adjustable swirl generators in each zone. Consequently, balancing and optimizing the air between the inner and outer zone independently of swirl is not attainable. These designs do not have independent means of optimizing the flow quantity and swirl in the inner versus outer secondary air zones.
Low NOx burner designs separate the functions of fuel injection and secondary air flow control into essentially independent functions, but integrate the two assemblies into one burner. The fuel injector from one type of burner is generally not transferable into a register assembly from another burner design system.
The present invention solves problems associated with known low NOx burner designs by providing a fuel injector with an uninterrupted passageway through which pulverized fuel and its carrier gas flow. External flame stabilizers are arranged to provide excellent stability of the flame within the burner. A fixed vane swirler and an air control damper are also arranged on the fuel injector to further control the flame produced upon combustion of the pulverized fuel. The present fuel injector resolves the operational and reliability problems discussed above. Further, such fuel injector can be utilized in virtually any burner configuration: Circular burner arrangements as well as the vertically stacked linear burners typical of “corner” or “tangential” firing.
As used herein, the term “fuel injector” is intended to cover devices used to transport pulverized fuel and a carrier gas to be burned within an associated furnace. It should be appreciated that the term “pulverized fuel” is intended to cover various types of fuel such pulverized coal or the like. While the term “pulverized coal” is used for convenience to describe a preferred embodiment, it is also intended to encompass various types of pulverized fuels other than coal. Further, the term “carrier gas” covers gasses other than those present in air. However, since air is used to transport the pulverized coal in accordance with a preferred embodiment of the present invention, the term “primary air” will often be used herein and is intended to encompass various types of carrier gasses other than air.
The design of the fuel injector of the present invention has been developed to enhance the performance and reliability of low NOx burners. Thus, the design features of the present invention are applicable to various types of low NOx burner systems.
In accordance with a preferred embodiment of the present invention, a fuel injector is provided for use in a furnace. The fuel injector comprises an inner barrel having inlet and outlet ends, and a passageway extending between inlet and outlet ends through which a fuel stream including a carrier gas and fuel particles are permitted to flow. The inner barrel is preferably free of obstructions between the inlet and outlet ends such that the carrier gas and fuel particles can flow without interruption into an associated furnace. The fuel injector preferably comprises an outer barrel surrounding at least a portion of the inner barrel, and an outer passageway therebetween through which secondary air is permitted to flow. A plurality of stabilizer vanes are preferably arranged within the outer passageway near the outlet end of the inner barrel. The secondary air flowing through the outer passageway will impact the stabilizer vanes and will help maintain combustion of the fuel streams near the outlet end of the inner barrel. A plurality of axial vanes are also preferably arranged within the outer passageway between the inner and outer barrels. Each of the axial vanes are arranged between a corresponding pair of the stabilizer vanes, and function in concert with the stabilizer vanes to create desired flow of the secondary air with respect to the fuel stream flowing from the outlet end. A fixed vane swirler is also preferably arranged within the outer passageway between the inner and outer barrels. The fixed vane swirler includes a structure sufficient to impact the secondary air and create a rotational flow thereof around the stabilizer and axial vanes.
In another preferred embodiment, an air controlled damper may be arranged within the outer passageway form between the inner and outer barrels. The air control damper may be structured and arranged to control the quantity of the secondary air flowing through the fixed vane swirler.
The stabilizer and axial vanes may be attached to the inner barrel, and the fixed vane swirler may be attached to the outer barrel. However, the specific arrangement of these features are optional and represent one preferred embodiment.
The air control damper may comprise a perforated plate and an axially movable sleeve to permit selective control of the quantity of air permitted to flow through the fixed vane swirler.
In another preferred embodiment, a furnace system is provided. The furnace may comprise a housing, a combustion zone arranged within the housing, and one or more fuel injectors having the features discussed above.
Low NOx burner designs separate the functions of fuel injection and secondary air flow control into essentially independent functions, but integrate the two assemblies into one burner. The fuel injector from one type of burner system cannot typically be integrated into a register assembly of another burner design system design.
The present invention is a stand-alone fuel injector that includes its own integral stabilization air flow controls and devices. Consequently, the present fuel injector can be inserted into various types of register assemblies. The present fuel injector provides for improved flame stability, lower NOx output and better control of carbon monoxide and unburned carbon.
Accordingly, it is an object of the present invention to provide an improved fuel injector, and optionally an entire furnace, which provides a low NOx output. It is another object to provide a fuel injector, and optionally a furnace system, having enhanced flame stabilization. These and other objects and advantages of the present invention will be more readily understood when considered in conjunction with the accompanying drawings and a detailed description of the preferred embodiments which follows.
Referring to
A preferred embodiment of the fuel injector 10 of the present invention is illustrated in
An air control damper 28 is also arranged in the passageway between the inner barrel 12 and outer barrel 20. The air control damper assembly includes a perforated plate 30 and an axially movable sleeve 32. A control arm 34 is connected to the movable sleeve for permitting an operator to axially adjust it so that a desired amount of secondary air can flow into and around the fixed vane swirler 26.
As also shown in
Low NOx flame stabilization nozzle 15 is an important element for obtaining excellent flame stability and minimum NOx output.
Stabilizer and axial vanes 22 and 24 act in combination to create a complex flow of secondary air from the inner zone over and around the fuel streams leaving the nozzle 15. The effect is to create an initial stabilization zone close to the fuel injector nozzle 15.
Flame stabilizers function as previously described in U.S. Pat. No. 5,762,007, the disclosure of which is incorporated herein by reference. In general,
The fixed vane swirler 26 is attached to the outer barrel 20 of the fuel injector 10. The position of the swirler 26 is constant and no adjustments are required. It provides rotation to the air that flows over the flame stabilizers 22 and enhances their effect in controlling the root of the flame formed by the coal leaving the nozzle 15.
Air control damper 28 includes perforated plate 30 surrounded by an axially movable sleeve 32. The damper is operable to control the quantity of air flowing through the fixed vane swirler 26 and over the flame stabilizers 22 surrounding the nozzle 15. The axially movable sleeve 32 is connected to a control arm 34, which permits control of the quantity of air flow and allows for the optimization of the flame position and internal stoichiometry in the region close to the burner of the furnace 38.
The fuel injector assembly 10 with its own air flow controls represents an independent assembly that is no longer required to be installed as an integral part of one specific burner geometry. Thus it can be used in conjunction with a relatively simple single register assembly which, when combined with the presently disclosed fuel injector assembly, completes the two stage secondary air aerodynamics typical of low NOx burners.
The fixed vane swirler 26 is attached to the outer barrel 20 of the fuel injector 10. The position of the swirler is fixed and no adjustments are required.
An alternate type of combustion system is shown in
In the corner-fired arrangement a secondary air flow divider is integrally installed around the present enhanced flame stabilization fuel injector 10 to direct the secondary air over the integral fixed van swirler 26. An air blocking plate is attached to the flow divider to prevent secondary air from bypassing around the outside of the flow divider and, thereby, not passing through the fixed vane swirler 26 that is inside the flow divider and between it and the coal nozzle 15.
The present enhanced flame stabilization fuel injector 10 discloses a fuel injector assembly that can be incorporated into a wide variety of pulverized coal burner types while maintaining the conditions for optimal aerodynamics and fuel flow to assure minimal NOx generation without compromising combustion performance.
It should be appreciated that various modifications to the configuration and size of the present fuel injector 10 and associated furnace system may be made to the preferred embodiment of the present invention without departing from the scope thereof as defined in the claims set forth below.
This application claims benefit of U.S. Provisional Patent Application 60/551,143, filed Mar. 8, 2004, the disclosure of which is incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 60551143 | Mar 2004 | US |
