Abstract:
A pneumatic fuel distributor for solid fuel boilers is described incorporating in various embodiments one or more of the following features: a converging nozzle section, a converging adjustable orifice section and an integral trajectory plate. The nozzle, orifice and trajectory plate are preferably all interconnected and rotate together about a common axis. The orifice damper is, in one embodiment, a rotating convergent section and independently adjustable. The unit preferably incorporates a viewing glass and access port and the rotating components are preferably removable for maintenance. The unit is preferably reversible for left or right hand installation and the trajectory plate is easily replaceable.

Description:
This application claims priority from U.S. Provisional Patent Application No. 61/037,169, which is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to fuel distributors for solid fuel boilers. 
     BACKGROUND OF THE INVENTION 
     Pneumatic solid fuel distributors are well known in the operation of boilers to improve the distribution of fuel in the boiler. They typically feed bark, “hog fuel” (mixtures of bark and cardboard, sludge, or other waste materials), coal, and/or other solid fuels, separately or combined. They are also referred to as “bark distributors” or “wind swept spouts”. Common designs incorporate a nozzle section (fixed or pivoting) and a pivoting trajectory plate to adjust the angle at which the solid fuel is injected into the boiler. The trajectory plate pivots about a horizontal axis thereby controlling the vertical angle at which the fuel is injected. A more recent design incorporates a flexible trajectory plate and a means for spreading the fuel in a broader horizontal pattern. 
     Solid fuel boilers are typically constructed as large boxes (up to 100 m 2  or more floor area) with heavy steel tubing forming the walls of the box, typically referred to as the front, sides, and rear walls. The tubing is typically 63.5 mm or 76.2 mm outside diameter, arrayed in parallel relationship forming flat panels with the tubes running vertically. The tubes are typically spaced apart about 10-12 mm with a steel membrane or fin bridging the gap. The whole assembly is seal welded together forming an air tight structure. The boiler walls, or tube panels, run vertically to the top of the boiler, up to 30 m or more tall. The walls are fed re-circulating water by headers at their lower extremity. Typically the front wall tubes are bent over more or less horizontally to form the roof of the boiler and the side walls end in relieving headers feeding back to a steam drum. The rear wall either ends in a header or feeds directly into the steam drum. In order to feed fuel and combustion air into the boiler, and for other purposes, the boiler tubes are bent apart to form openings in the tube panel. 
     The bottom of the boiler may be arranged as a grate type boiler, fluidized bed boiler, or other arrangement. Grate type boilers include traveling grates, vibrating grates, tilting grates, and hydro-grates. Typically the grates cover the bottom of the boiler and are made of heavy cast iron components with slots for combustion air to rise through the grate from a plenum below. The solid fuel lands on the grate and burns there. The ash is dumped off of the grate as the grate moves (rotates like a tank tread), vibrates, or tilts (in sections). Fluidized bed boilers generally have a mass of sand or other media through which a stream of air or boiler flue gas is percolated to fluidize the bed. The fluidized bed acts as a heat sink, turbulent fuel/air mixing system, fuel distribution system, and means for separating fuel and ash in the boiler. Additional combustion air ports, typically called “over fired air” (OFA) are arranged to blow air in above the grate or fluidized bed to help complete the combustion. In all of these arrangements if the fuel is not properly distributed on the grate or fluidized bed, poor combustion can result leading to poor operational efficiencies and high environmental emissions. 
     In current practice the solid fuel is fed by gravity through large chutes, steeply mounted and about 500 mm square, from a hopper and/or conveyor system above, to the lower portion of the boiler just above the grate or fluidized bed. There are typically multiple chutes penetrating a wall or walls of the boiler. The solid fuel distributor is often integral with and at the bottom of the chute right at the interface with the boiler wall. Mechanical distributors and pneumatic distributors are commonly used. Grate type boilers generally require some type of fuel distribution whereas fluidized bed boilers can be run without them as the fluidized bed can distribute the fuel, albeit inefficiently. In the case of the pneumatic fuel distributor, the solid fuel slides down the chute, passes across the pneumatic orifice and hits the trajectory plate where it is blown off and into the boiler by the pneumatic media. A recent variation attempts to develop a boundary layer of pneumatic media along the top of the trajectory plate such that the solid fuel does not contact the plate. In any case it is the flowing pneumatic media that propels the solid fuel into the boiler. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an improved pneumatic fuel distributor for a solid fuel furnace. 
     The present invention provides an improved fuel distributor for a solid fuel boiler. A preferred fuel distributor includes several novel aspects, not all of which need be present in all embodiments. Some embodiments of the invention use a converging nozzle section that provides improved fluid flow to distribute fuel more evenly. Some embodiments of the invention include an adjustable orifice that efficiently controls the flow at the exit of the nozzle, rather than upstream of the nozzle. Some embodiments include nozzle surfaces that converge toward the orifice to efficiently guide the pneumatic flow to and through the orifice. Some embodiments of the invention include an integral trajectory plate in which the nozzle, orifice and trajectory plate are all interconnected, preferably by a frame, and rotate together about a common axis. Some embodiments of the invention allow for easy removal of the distributor from the boiler. Some embodiments of the invention provide an access port that can be used to clean the unit in case it gets plugged and a viewing port that allows an operator to see into the distributor. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more through understanding of the present invention, and advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a sectional side view elevation of a typical fuel chute, boiler tube wall, and a preferred embodiment of a fuel distributor of the present invention; 
         FIG. 2  is an isometric view of the preferred embodiment of  FIG. 1  shown from inside the boiler; 
         FIG. 3  is an isometric view of the preferred embodiment of  FIG. 1  shown from outside the boiler; 
         FIG. 4  is a sectional side view elevation of preferred embodiment of  FIG. 1  showing the orifice damper fully open; and 
         FIG. 5  is a sectional side view elevation of preferred embodiment of  FIG. 1  showing the orifice damper partially closed. 
     
    
    
     The accompanying drawings are intended to aid in understanding the present invention and, unless otherwise indicated, are not drawn to scale. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Although pneumatic solid fuel distributors have been in service for many years, applicants have found that the current state of the art suffers from significant deficiencies, including poor control of the fluid media; poor nozzle design; poor alignment of the pneumatic nozzle, orifice, and trajectory plate; poor serviceability and maintenance access; and poor observational access. 
     Although prior art mechanical and pneumatic fuel distributors improve the operation of the boiler, Applicants have found that current pneumatic distributors have several deficiencies. First, current designs have a poor orifice that does not efficiently control the flow of the pneumatic media. They either have a fixed orifice opening with an upstream damper to control the flow or an adjustable orifice poorly designed fluid dynamically. This results in high flow losses, high pressures required upstream, and/or higher flows required. Second, current designs generally have poorly designed nozzles or plenum boxes that impair the flow of the pneumatic media through the device. When a plenum is used, the transition from the plenum to the orifice is often not smooth resulting in high turbulence and high pressure drop into the orifice. When a smoothly transitioned nozzle is used, the nozzle portion is too small resulting in very high velocities that again require high pressures to overcome. Third, the angle of the trajectory plate on current designs is generally adjusted independently of the nozzle angle and in some cases the nozzle angle is fixed. This results in the jet of pneumatic media impinging on the trajectory plate at a poor angle, resulting again in flow losses, reduced functionality, and the requirement of higher flow and/or pressure. Fourth, current designs are generally integral with the solid fuel chutes and therefore not easily removable from the boiler for maintenance and service. They also suffer from lack of access in case they get plugged or otherwise have a problem. Fifth, current designs generally do not allow the boiler operators to observe the function of the device because there is no way to look through the orifice. 
     Various embodiments of the present invention solve one or more of the problems described above. Some embodiments incorporate a converging adjustable orifice that controls the flow of the pneumatic media independently of the pressure and is designed to maintain the momentum of the pneumatic media as it passes through the orifice. This reduces the pressure and kinetic energy losses upstream, reducing the pressure and flow rates required to evenly distribute fuel. Some embodiments of the present invention incorporate a fixed angle between the nozzle, orifice, and trajectory plate to maximize the efficiency of the device. The pneumatic media then always impinges on the trajectory plate at a preferred angle, reducing the flow rate and pressure required to evenly distribute the fuel. Some embodiments of the present invention incorporate a viewing window that is aligned with the orifice and allows the operators to observe the operations of the distributor. Some embodiments of the present invention incorporate a cleaning port that permits an operator to clean out the distributor without disassembling it and removing it from the boiler. Some embodiments of the present invention are not integral with the sold fuel chutes and can be readily removed from the boiler for maintenance. 
     Referring to  FIG. 1 , which shows a preferred embodiment of a solid fuel distributor of the present invention, a fuel chute  1  is rigidly attached to a boiler  33  and passes through a tube wall  2 . A fuel distributor  3  is rigidly attached by means of a mounting frame  11  to both the fuel chute  1  and the boiler  33 . Fuel enters the chute at the top  4 , passes down the chute and exits at the bottom  5 . Pneumatic media  6 , either air or re-circulated flue gas or both, enters through the side of a nozzle  32  and passes through a converging section  7 , then through a converging orifice damper  8 . The solid fuel lands on a plate  9  and is blown off, as shown by the arrow, into the boiler  10 . 
     Referring to  FIG. 2  and  FIG. 3 , the preferred embodiment includes a mounting frame  11  incorporating two pivot blocks  12 , an angle locking bracket  13 , and an angle locking bolt  16 . An orifice chamber  19  is cylindrical in form, pivotally mounted through the pivot blocks  12 , and rigidly connected to a converging nozzle section  27  and a trajectory plate  21 . Converging nozzle section  27  has a cross section that tapers, that is, gets narrower, in the direction of the boiler. To adjust the angle of the nozzle-orifice-trajectory plate assembly, the locking bolt  16  is loosened and moved through the slot in the angle locking bracket  13  by means of a handle  17 . When the desired angle is reached the locking bolt  16  is tightened. An orifice opening  22  is adjusted by loosening locking bolt  14 , and then adjusting handle  15  is moved to the desired location and locking bolt  14  is retightened. 
     To remove the nozzle-orifice-trajectory plate assembly from the boiler, an access plate  20  and pivot block caps  24  are removed, and the assembly can be withdrawn. To seal the removable portion against the escape of boiler gas the pivot blocks  12  and the pivot block caps  24  contain o-rings (not shown) riding against the outside surface of the orifice chamber  19 . In a preferred embodiment, the trajectory plate  21  is removable from the nozzle-orifice assembly  27 ,  19  to facilitate replacement. The trajectory plate is subject to erosion from the solid fuel and heat of the boiler and will require periodic replacement. Another feature of some embodiments of the invention is that an inlet pipe  23  and adjusting means  13 ,  14 ,  15 ,  16 , and  17 , are reversible from one side to the other to accommodate the desired side to feed the pneumatic media to the fuel distributor. To accomplish this, adjusting handle  17  incorporates a cover plate  18  to seal the hole in the unused side of nozzle  27 . 
     Additional features of some embodiments of the invention include a viewing glass  25  and an access port  26 , both mounted on the face of the nozzle  27 . Because the pneumatic media is fed from the side, the face of the nozzle is clear of obstructions providing room for the viewing glass and access port. Furthermore, because the nozzle-orifice-trajectory plate are all pivotally interconnected, the viewing glass and access port are always aligned with the orifice and trajectory plate thereby ensuring the proper angle to view the function of the distributor. 
     Now referring to  FIG. 4  and  FIG. 5 , the nozzle-orifice-trajectory plate assembly  27 ,  19 ,  21  can rotate through an angle  30  of approximately plus or minus 30 degrees. Within the orifice chamber  19  resides the damper  28  which is semi-cylindrical on top and flat on the bottom such that the semi-cylindrical top part is concentric with and immediately adjacent to the inside radius of the orifice chamber  19 . The damper  28  is rotatably mounted within the orifice chamber  19  and connected to the adjusting handle  15  ( FIG. 2 ) by means of the tie rods  29 . The damper  28  provides non-parallel surfaces that form between them a region which tapers in the direction of the orifice opening into the boiler, the size of the orifice opening being adjustable by changing the relative position or orientation of the surfaces, which are configured to guide the pneumatic media toward the orifice. In the embodiment described, the lower surface of the nozzle is fixed, while the upper surface of the damper rotates to reduce the size of the opening. In other embodiments, the lower surface or both surfaces may be rotated or translated to change the size of the opening. 
       FIG. 4  shows the damper  28  in the full open position and  FIG. 5  shows the damper  28  in a partially closed position. The pneumatic media exits at the end of the damper. The combination of nozzle  32  and damper  28  provides a converging path toward the orifice  22 . The damper forms part of a converging adjustable orifice. As shown in  FIG. 4 , the converging nozzle section transitions smoothly into the converging adjustable orifice defined in part by the damper. As shown in  FIG. 5 , the transition may be less smooth depending on the adjustment of the damper, and the passage may widen somewhat between the converging nozzle and the converging adjustable orifice. 
     Prior art pneumatic solid fuel distributors use dampers that are typically parallel plates that throttle the flow of the pneumatic media into a plenum upstream of the nozzle, which reduces the kinetic energy of the pneumatic media and therefore more pneumatic media at higher pressure is required to distribute the fuel from the trajectory plate. The embodiment described above essentially uses a damper positioned at the end of the nozzle as an adjustable orifice that not only controls the size of the orifice, but also provides a converging cross section to guide the flow of the pneumatic media. The pneumatic media in the embodiment described above is directed smoothly along the path with reduced pressure loss and energy loss, when compared to fluid opening into a plenum and then exiting through an orifice. By using a nozzle and damper that provide a converging path that funnels, rather than blocks, the pneumatic media, the kinetic energy of the pneumatic media exiting the orifice is greater than in the prior art designs, and less media is required to distribute the fuel. This is a great advantage in application in which the pneumatic media, such as flue gases, have limited availability. 
     When the damper  28  is partially or fully closed, the semi-cylindrical top portion of the damper covers the unused portion of the orifice  31 . This prevents solid fuel particles from entering the orifice chamber when the nozzle-orifice-trajectory plate assembly is tilted with the trajectory plate pointing upward by preventing solid fuel from sliding down the fuel chute and entering the orifice chamber on top of the damper plate, which could block the plate from rotating. To seal the cylindrical surfaces of the orifice chamber  19  against escaping boiler gas, adjustable seal bars  34  ride against the orifice chamber  19 . The bars are machined with a groove to accept o-ring strips along their lengths. 
     The present invention includes several novel aspects that provide various advantages, and not all embodiments of the invention will use all aspects. Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.