Patent Publication Number: US-4257334-A

Title: Apparatus and method for regulating the distribution of granulate

Description:
TECHNICAL FIELD 
     This invention relates to the distribution of airborne granular material such as pulverized coal to a plurality of points of consumption such as to multiple furnace burners. More specifically, this invention relates to the independently regulated distribution of airborne granular material to each of such plural points. 
     BACKGROUND ART 
     Various systems for the distribution of granular material such as pulverized coal for the feeding of a plurality of furnace burners are known but all offer certain disadvantages in their use. One such known system utilizes a circular housing having a plurality of openings therein. A granular material air mixture is distributed through these openings by centrifugal force. A particular difficulty with this type of system is that the quantity of airborne granular material distributed through each opening cannot be individually regulated. Equal quantities of granular material are fed through all openings. 
     Another known airborne granular material distribution system includes a knee-shape distributor pipe in an annular housing. An outside ring is turned such that the end of the distributor pipe through which granulate flows is stopped for variable and controllable lengths of time at each of a plurality of apertures in sequence. By controlling the time during which the end of the distributor pipe is aligned with a specific opening, the amount of granulate flowing through each opening is controlled. The major disadvantage of such an arrangement is that individual points of consumption are fed only intermittantly and any change of the tarry time at a particular opening automatically results in variation in the relative feed time of another point of consumption. 
     In another prior art granulate distribution system, the granulate is distributed to a plurality of points of consumption by means of pulses of controllable length. A disadvantage of this type of system is the intermittent delivery and consequent effects on the operation of the various points of consumption. Certain types of consumers must be fed continuously while the rate of feed is regulated within a predetermined range. 
     Other airborne granular material distributing systems control the flow rate of the granulate by changing various parameters relating to the airflow at distributor outlets. However, the distribution in such systems is highly dependent upon the condition of the granulate itself. For example, changes in moisture, particle size, and particle friction result in changes in the feed rate thereby making such system somewhat unreliable under certain conditions. 
     DISCLOSURE OF INVENTION 
     In accordance with the present invention, there is provided a granulate distribution apparatus and method for distributing granulate to a plurality of points of consumption overcoming these difficulties inherent in the operation of currently available systems. The apparatus and method of the present invention provides for the independent regulation of the flow rate of granular material to each point of a plurality of points of consumption, while allowing for continuous feed of the granular material to all such points of consumption, or as many points of consumption as desired. 
     The apparatus and method according to the present invention provide a means for mechanically feeding a solid fuel such as pulverized coal to a burner or plurality of burners in such a manner that temperature control is as accurate as with the burning of gases or liquid fuels. 
     Either one burner or a plurality of burners can be supplied with pulverized coal from one storage container. If multiple burners are being used, each burner is individually controllable. It is now possible, utilizing the present invention to maintain a multiple burner coal furnace system with individual burner control and centrally located metering and feeding adjustment. 
     An exemplary apparatus for the independently regulated distribution of granular material to a plurality of points of consumption includes: 
     a container having a plurality of ports; 
     slides for controlling the size of these ports; 
     a rotatable shaft positioned laterally along these ports and positioned close enough to these ports so as to convey granular material flowing through these ports; and 
     troughs corresponding to each port positioned so as to gather granular material conveyed by the rotating shaft from the corresponding port and a plurality of air injectors, one such injector associated with each trough for entraining the granular material conveyed over the shaft into an air stream for distribution to points of consumption. 
     The rotatable shaft in this exemplary embodiment extends parallel to the bottom longitudinal edge of the container and is rotated such that the apex of the shaft rotates away from the container. Granular material appearing at the ports by gravity feed is stopped by the presence of the shaft when the shaft is not rotating and is conveyed by the shaft when it is rotating by the action of friction between the particles of granulate and the surface of the shaft. The rate of granular material flow is determined by the speed of rotation of the shaft and the size of the individual container ports. By adjusting the slides associated with each container port, the relative granular material flow rates to individual points of consumption can be controlled. 
     An exemplary method for the independently regulated distribution of granular material to a plurality of points of consumption is also disclosed and includes the following steps: 
     storing granular material to be distributed within a container having a plurality of ports therein, the size of these ports being controllable; 
     rotating a shaft in the vicinity of these ports; 
     conveying granular material along the surface of the shaft; 
     receiving the granular material conveyed over the surface of the shaft into a plurality of troughs corresponding to the plurality of container ports; and 
     conducting the granular material at each such trough through an air injection mechanism to a distribution pipe for conduction to a plurality of points of consumption. 
     According to this method, the rate of delivery of the granular material is determined by the position of the shaft with respect to the container ports, its rate of rotation and the absolute and relative sizes of the container ports themselves. 
     By utilizing apparatus and method according to the present invention, the rate of delivery of granulate to each of a plurality of points of consumption can be controlled. The overall magnitude of granular material flow can be determined by controlling the rate of rotation of the shaft and the relative rates of granular material flow can be adjusted by altering the relative sizes of the ports in the container. Large or small quantities delivered to the various points of consumption being accurately controlled. Delivery of granular material can be either continuous or intermittent by controlling the rotation of the shaft, i.e. the rotation of the shaft can be completely stopped at desired intervals. Another feature of the present invention is that the influence of the condition of the granular material (its moisture content, etc.) is minimal on the distribution rates of the granular material to the various points of consumption. 
     The apparatus and method according to the present invention are particularly well suited for the mechanical, controlled metering and feeding of pulverized coal into an air stream transporting the coal to a burner designed to operate at a controlled or evenly maintained temperature. 
     Using this method for precisely regulating the amount of coal induced into the air stream, burner temperature can be controlled. The availability of the system and method providing the temperature controlled burning of airborne granular material, such as coal, allows burners previously operating on gases or liquid fuels to be operated on pulverized coal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Many of the attendant advantages of the present invention will be readily apparent as the invention becomes better understood by reference to following detailed description and the appended claims, when considered in conjunction with the accompanying drawings, wherein: 
     The FIGURE is a cutaway perspective view of the airborne granular material distribution apparatus according to the present invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Referring to the FIGURE wherein like reference numerals designate like or corresponding parts throughout, there is a cutaway perspective view of the granular material distribution apparatus according to the present invention. There is shown a container 1 which is, in essence, a storage bin partially filled with granular material 10 to be distributed. Located near the bottom of container 1 are a plurality of container ports 4. A slide 5 is mounted to container 1 at each container port 4 so that the size of each port is individually controllable by the action of its associated slide. Container 1 is oriented such that gravity forces granular material 10 within the container to accumulate at container ports 4 and to flow therethrough unless blocked. Of course, for granular material to flow, container 1 must be filled to a level above the position of apertures 4. 
     A shaft 2, rotatably mounted, is longitudinally positioned adjacent to container 1 and parallel to container ports 4 and acts as a metering roller. The placement of shaft 2 with respect to container ports 4 is chosen such that the point of intersection of the angle of repose of granular material 10 appearing at container aperture 4 and the periphery (surface) of shaft 2 is situated such that no granular material 10 flows over the apex of the shaft when it is stationary. In other words, the maximum angle of respose for the granular material always intersects the shaft below its apex (i.e. topmost center). Shaft 2 may, if desired, include a roughened or serrated surface at its periphery so that when rotated, greater friction develops between the shaft and granular material 10 when conveying the granular material appearing at ports 4 over the surface of the shaft. A drive 3 controls the rotational rate of shaft 2 so that it can be rotated at any desired rotational rate including intermittant rotation. For a given slide 5 position, the rotational rate of shaft 2 determines the overall rate at which granular material 10 is delivered to the points of consumption. 
     Opposite each container port 4, on the other side of shaft 2 is a trough 6 for receiving granular material 10 conveyed over the surface of the shaft during its rotation, one such trough for each container port. Granular material 10 flowing into a trough 6 is collected into one of a plurality of feed tubes 7, one such supply pipe associated with each trough. Each feed tube 7 is coupled into an air injector 8 receiving an air flow from an air manifold 9 coupled to an air source. Air injectors 8 are positioned below feed tubes 8 and troughs 6 so that granular material 10 feeds by the action of gravity into the air injectors. Granulate 10 collected in a trough 6 flows by the action of gravity through a supply pipe 7 and into an air injector 8 where it is entrained in an air stream supplied by air manifold 9. By regulating the air pressure within manifold 9, the air-granulate mixture developed within air injector 8 is controlled. The output of each air injector 8 is coupled via a pipe 11 to a point of consumption, usually the burner of a furnace. 
     The overall rate of delivery of granular material 10 is determined by the speed of rotation of shaft 2. Thus, the rate of delivery of granular material 10 to the various points of consumption is controlled by varying the speed of rotation of shaft 2. The relative rates of delivery to the various points of consumption are controlled by adjustment of the respective cross-sectional areas of container ports 4 by operation of slides 5. In this manner, the rate of delivery of granular material to any particular point of consumption can be controlled independently from the rate of delivery of granular material to any other particular point of consumption. 
     Thus, exemplary apparatus for the independently regulated distribution of granular material 10 to a plurality of points of consumption is disclosed including: 
     a container 1 having a plurality of container ports 4; 
     slides 5 for controlling the size of these container ports; 
     a rotatable shaft 2 positioned laterally along these container ports and positioned close enough to these ports so as to convey by friction granular material flowing through these ports; and 
     troughs 6 corresponding to each container port positioned so as to gather granular material conveyed by the rotating shaft from the corresponding container aperture and a plurality of air injectors 8, one such injector associated with each trough for entraining the granular material conveyed over the shaft into an air stream for distribution to points of consumption. 
     The rotatable shaft 2 extends parallel to the bottom longitudinal edge of container 1 and is rotated such that the apex of the shaft rotates away from the container. Granular material 10 appearing at ports 4 by the action of gravity feed is stopped by the presence of shaft 2 when the shaft is not rotating and is conveyed by the shaft when it is rotating by the action of friction between the particles of granulate and the surface of the shaft. The rate of granular material flow is determined by the speed of rotation of the shaft and the size of the individual container ports. By adjusting slides 5 associated with each container port 4, the relative granular material flow rates to individual points of consumption can be controlled. 
     In addition, an exemplary method for the independently regulated distribution of granulate 10 to a plurality of points of consumption is disclosed, the method including the steps of: 
     storing granular material to be distributed within a container having a plurality of ports therein, the size of these ports being controllable; 
     rotating a shaft in the vicinity of these ports; 
     conveying granular material along the surface of the shaft; 
     receiving the granular material conveyed over the surface of the shaft into a plurality of troughs corresponding to the plurality of container ports; and 
     conducting the granular material at each such trough through an air injector mechanism to a distribution pipe for conduction to a plurality of points of consumption. 
     According to this method, the rate of delivery of granular material 10 is determined by the position of the shaft 2 with respect to container ports 4, its rate of rotation and the absolute and relative sizes of the container ports themselves. 
     By way of a specific, non-limitative but typical example, in an apparatus and according to the method of the present invention, coal granulate is the granular material being distributed to a plurality of coal burning furnaces. The diameter of shaft 2 is two (2) inches and the rate of rotation of the shaft is 0-100 RPM. For a maximum flow of 20 lbs. of coal per hour per burner, all conduits (feed tubes 7, pipes 11) are at least 3/4 inch in diameter. The opening size of ports 4 is determined by capacity, type of coal granulate and the angle of repose of the coal granulate at the ports. 
     As an additional non-limitative example, when the apparatus according to the present invention is used for granulate coal distribution to a tunnel kiln, the rotational rate of shaft 2 is 0-60 RPM. Air pressure to air injectors 8 is 10-16 oz. The rate of coal delivery is from 0-20 lbs. per burner per hour for coal granulate particle sizes up to 1/8 inch in diameter. Feed rate, controlled by the rotational rate of shaft 2 is dependent upon the temperature desired within the kiln. 
     When the present invention is applied to the delivery of granular coal to a coal burner furnace, there is defined a method for the temperature regulation of the furnace including the steps of: 
     storing granular coal within a container having at least one port therein, the size of said port being adjustable; 
     rotating a metering roller in the vicinity of said port outside of said container so as to convey granular coal over the surface of the roller; 
     entraining the granular coal conveyed over the surface of the roller into an air stream creating a coal/air mixture; and 
     conducting the coal/air mixture to a burner, whereby the temperature of the furnace is controlled by the size of the ports and the rate of rotation of the roller. 
     Therefore, it is apparent that there has been provided an apparatus and a method for the delivery of granular material to a plurality of points of consumption and that this delivery is independently regulated such that the amount of granular material delivered to a particular point of consumption is not dependent on the amount of granular material delivered to any other point of consumption. By controlling the speed of rotation of shaft 2 the overall rate of granular material flow is determined and by controlling the relative positions of slides 5, the relative rates of flow to the various points of consumption are controlled. 
     The apparatus and method disclosed are not limited to the distribution of granulate coal to a plurality of furnaces but rather are applicable to the regulated distribution of any granular material. Other embodiments and modifications of the present invention will be apparent to those of ordinary skill in the art having the benefit of the teachings presented in the foregoing description and drawings. 
     For example, other gases could be substituted for air in distribution pipe 9. The surface of shaft 2 could be modified to convey more or less granular material as desired by creating an array of detents or scoops. It is, therefore, to be understood that this invention is not to be unduly limited and that such modificcations are intended to be included within the scope of the appended claims.