Abstract:
A system for pneumatically conveying metered amounts of a bulk particulate material comprising a first conduit formed of a gas permeable material having a material inlet and outlet, a second conduit formed of a gas impermeable material encompassing and spaced from said first conduit, and means for intermittently supplying a fluidizing gas under pressure to the plenum between the first and second conduits.

Description:
[0001]    This invention relates to the pneumatic conveying of bulk particulate materials and more particularly to a system and method of stabilized metering of such pneumatically conveyed material at low flow rates. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the prior art, there has been developed a system and method for pneumatically conveying bulk particulate materials including cohesive and sluggish granular and powder materials which are illustrated and described in U.S. Pat. Nos. 6,179,500 and 6,764,253 assigned to The Young Industries, Inc., of Muncy, Pa., and are incorporated herein by reference. In the use of such systems to not only convey but meter the feed rate of such material, some adjustment of the feed rate has been found to be possible by controlling the flow rate of the gas supply. It further has been found that there is a minimum feed rate that can be achieved by controlling the flow rate of the gas. Decreasing the flow rate of the gas has been found to reach a point at which material flow will become erratic or even discontinued. Such lower limit point often is greater than the desired flow rate for accurate, consistent and reliable metering of material. Accordingly, it is the principle object of the present invention to provide a system and method of the type described which will accurately, consistently and reliably meter the feed rate of bulk particulate materials over a greater range of feed rate and particularly at a lower feed rate that is available in prior art systems and methods. 
       SUMMARY OF THE INVENTION 
       [0003]    The principal object of the present invention is achieved by providing a system for pneumatically conveying metered amounts of a bulk particulate material generally consisting of a first conduit formed of a permeable material having a material inlet and outlet, a second conduit formed of a gas impermeable material encompassing and spaced from the first conduit, and means for intermittently supplying a fluidizing gas under pressure to the plenum between the first and second conduits. Preferably, in such a system, the gas supply means is operable to supply gas for an interval in the range of 0.05 seconds to 10 seconds and then discontinue the supply of gas for an interval in the range of 0.05 seconds to 20 seconds per cycle. In another embodiment of the invention, a hopper is provided for feeding material into such first conduit, which hopper includes a first peripheral wall section formed of a gas permeable material, having an outlet communicating with the inlet of the first mentioned conduit for feeding a material therethrough and a second peripheral wall section spaced from an encompassing the first peripheral wall section formed of a gas impermeable material, to provide a peripheral chamber therebetween, and means for intermittingly supplying a fluidizing gas under pressure to such peripheral chamber. In such embodiment, the means for supplying gas to the peripheral chamber is operable to cycle differently from the cycle of the first mentioned means for supplying gas to the plenum between the first and second conduits. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is a side elevational view of an embodiment of the invention; and 
           [0005]      FIG. 2  is a schematic of the embodiment shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0006]    Referring to the drawings, there is illustrated a system for metering a bulk particulate material embodying the present invention which generally includes a material transport line  10 , a material holding hopper  11  operatively connected to the transport line for gravity feeding material thereto, a gas supply system  12  connected to the transport line and hopper and a control system  13  operatively connected to the gas supply system. As best shown in  FIG. 2 , transport line  10  consists of a first, inner conduit  14  consisting of a gas permeable material and a second, outer conduit  15  formed of an impermeable material encompassing and spaced from inner conduit  14  to provide an annular chamber  16 . As shown, annular chamber  16  may be provided with longitudinally spaced annular partitions  17  to further provide a plurality of annular chambers encompassing inner conduit  14 . Hopper  11  includes an inner, peripheral section  18  formed of a gas permeable material and a spaced, outer wall section  19  spaced from and encompassing inner wall  18 , formed of a gas impermeable material to provide a peripheral chamber  20 . The lower end of the hopper is provided with a passageway  21  through which material in the hopper may be gravity fed into an inlet of inner conduit  14 . To the extent that such passageway does not merely form an outlet communicating directly with an inlet of conduit  14 , such passageway is defined by a similar inner conduit formed of a gas permeable material and an outer, spaced conduit encompassing such inner conduit and formed of a gas impermeable material to form an annular chamber therebetween as shown in  FIG. 2 . 
         [0007]    Gas supply system  12  includes a main line  30  connected to a source of gas under pressure, a first branch line  31  interconnecting such main line and peripheral chamber  20  of the hopper, a second branch line  32  interconnecting main line  30  and annular chamber  15  and a branch line  33  interconnecting the main line and annular chamber  16 . An additional branch line  32   a  interconnects branch line  32  and the annular chamber surrounding passageway  21 . Disposed in main gas line  30  between its connections with branch lines  31  and  32  is an electrically actuated solenoid valve  34 , and disposed in branch line  31  between the branch line and peripheral chamber  20  of the hopper is an electrically actuated solenoid valve  35 . In addition, branch line  31  is provided with a manually operated valve  36 , branch line  33  is provided with a manually operated valve  37 , branch line  32  is provided with a manually operated valve  38  and branch  32   a  is provided with a manually operated valve  39 . Such manually operated valves may be used to adjust the flow rate to the annular chambers when valves  34  and  35  are open. 
         [0008]    Control system  13  essentially consists of a controller  40  operatively connected to electrically actuated solenoid valves  34  and  35 . It may consists of an electromechanical, repeat-cycle time delayed relay, a programmable logic controller or a computer, operable or programmed to intermittently open and close solenoid valves  34  and  35  to permit a pulsating flow of gas under pressure to either or both of the annular or peripheral chambers of the transport line and/or hopper. In practice, it has been found that sequentially opening valve  34  for 0.05 to 10 seconds and closing such valve for an interval in the range of serial 0.05 seconds to 20 seconds is sufficient to provide a pulsating gas flow to the transport line to convey material at a low feed rate. It further has been found that to operate solenoid valve  36  to sequentially open for an interval in the range of 0.05 seconds to 10 seconds and close for an interval in the range of 0.05 seconds to 60 seconds per duty cycle, will enhance a steady and reliable feed rate of the material being dispensed. 
         [0009]    In the use if the system as described, with valves  34  and  35  closed and controller  40  properly programmed, material to be metered is loaded in hopper  11  and controller  40  is operated to open valve  34 . Under such conditions, a pulsating flow of fluidizing gas will be fed to the transport line to convey material gravity fed into the transport line from hopper  11  at a controlled flow rate. To enhance such flow rate controller  40  further may be operated to sequentially or concurrently open valve  35  to further assure a continuous and controlled flow rate of material from hopper  11  to conduit  10 . The desired feed rate of the material being metered in the system may be adjusted simply by adjusting the duty cycle of the gas supplied to the transport line and the duty cycles of the gas supplied to both the hopper and the transport line. 
         [0010]    The transport line may be positioned horizontally and may be disposed at a small downward angle to facilitate the flow of material. The gas pressure may be of any suitable amount although a pressure of 5 psig has been found to be suitable for most purposes. 
         [0011]    Adjustment of fluidizing gas pulse length and frequency results in reliable and consistent flow of solids when the solenoid valve is turned on and consistent shutoff of solid flow when the solenoid valve is turned off. When operating in the pulse flow mode, it is neither necessary nor desirable to adjust the manual flow control valves away from their optimum settings for use in continuous-mode feeding and conveying. In pulse flow mode, feed rate is easily adjusted by changing the length of time the solenoid actuated compressed gas valve is on and the length of time it is off. 
         [0012]    Experience with operating the system as described has shown that when handling certain particularly cohesive and sluggish powder materials, it is desirable also to provide a periodic, brief fluidizing gas pulse to the supply hopper above the inlet to the conveyor to ensure reliable flow of powder with the conveyor. 
         [0013]    From the foregoing detailed description, it will be evident that there are a number of changes, adaptations and modifications of the present invention, which come within the province of those persons having ordinary skill in the art to which the aforementioned invention pertains. However, it is intended that all such variations not departing from the spirit of the invention be considered as within the scope thereof as limited solely by the appended claims.