Patent Application
20100014926
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.
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.
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.
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
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 32a 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 32a 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.
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.
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.
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.
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.
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.
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.
