Abstract:
A fast cycle system for transport of particulate material in dense phase has a feeder assembly dispensing material into a pulse pod assembly. The latter is connected to a pressurized pipeline and the pod of material is sent into the pipeline upon receipt of a pressure drop signal. Boosters spaced along the pipeline selectively vent and pressurize the pipeline driving the pod through to a receiver. The system including a receiving hopper and discharge valve in the receiving hopper for imparting, when actuated, peristaltic motion to the particulate material moving in the pipeline.

Description:
BACKGROUND OF THE INVENTION 
     1. Cross Reference to Related Patent Application 
     The present application is a continuation-in-part of my earlier patent application Ser. No. 07/881,628 filed May 12, 1992 now abandoned. 
    
    
     2. The Field of the Invention 
     The present invention pertains to a method and system for transporting particulate material in dense phase over substantial distances and with fast cycling. 
     3. The Prior Art 
     It is well known that pneumatic conveying systems are particularly useful for transporting particulate materials, such as pellets of plastics materials. However, the existing pneumatic conveying techniques tend to be rather inefficient in that the ratio of energy consumption per pound of particulate material, which is transported, is quite high. In order to obtain any degree of efficiency, the system must be capable of moving large quantities of bulk solids from point A to point B through a pipeline with compressed air while, at the same time, maintaining the mixture in turbulent flow and preventing it from plugging the pipe. When particulate material is conveyed in this fashion and there is a high ratio of air to product, then this is referred to as operating in the &#34;dilute phase&#34; and requires high pick-up air velocity. The dilute phase technique achieves a substantially continuous transport of particulate material. A second technique involves filling a portion of the pipe with sufficient particulate material to substantially plug the pipe. Then enough pressurized air must be provided in a burst to push this plug of particulate material through the pipeline without converting it into dilute phase. This technique is called &#34;dense phase&#34; and, clearly, is a batch or discontinuous type of operation. 
     Both of the above described approaches to pneumatic conveying of particulate material are quantified by their respective ratios of solids to air, in pounds. For example, dilute phase is generally considered to be in the range of 0 to 10 pounds of solid material per pound of air while dense phase is generally considered in the higher range of 10 to 50 pounds of solid material per pound of air. 
     There are three distinct disadvantages associated with dense phase conveying, namely: 
     1. Complex and expensive equipment is required to feed the particulate material into the conveying line. 
     2. The expansion of the conveying air from the initial high pressure, at the feed end, to substantially atmospheric pressure, at the discharge end, can result in extremely high velocities being imparted to the particulate material at the point of discharge. 
     3. High in-feed pressures prevent continuous loading of the system so that the vast majority of all dense phase systems are discontinuous or batch type operations. 
     The particulate material conveying industry has a definite preference for dilute phase systems because of their relative structural and operational simplicity and ease of maintenance, not to mention that these systems cost up to 50% less than dense phase systems. However, dilute phase systems are not without their own disadvantages. 
     The disadvantages of dilute phase pneumatic conveying are: 
     1. High velocities are imparted to the particulate material at pick-up and this velocity can cause severe damage to the particulate material, during transport, as it impacts on the surface of the pipeline in addition to the pipeline suffering erosion, particularly when the particulate material being conveyed is abrasive in nature. 
     2. Frequent maintenance is required for the rotary airlock, required for feeding material into the system, and the other system components. 
     3. Air pollution prevention means, such as expensive dust collectors, are required due to the large volumes of air required for dilute phase transport. 
     A common disadvantage in both of the above described systems is the limited distance over which the particulate material can be conveyed, regardless of the phase. This distance can be increased by the addition of air to the system at spaced intervals. However, there are many problems associated with adding air along the transport pipe, such as the timing of the added air impulse and insuring that the added air will not adversely affect the phase of the flowing material, for example diluting dense phase transport into dilute phase. 
     Another related problem is dispensing of the particulate material into the feed hopper. There are many well known screw feeding devices, but all of these have the disadvantage of substantial length so that they require a significant amount of space for installation, mounting, and maintenance. 
     SUMMARY OF THE INVENTION 
     The present invention concerns a method and system for fast cycle dense phase transport of particulate material over substantial distances. A quantity of the particulate material is dispensed into a pulse pod assembly and then is moved through the pipeline as a substantially solid mass, or pod, by pressurizing the pipeline in such a manner as to cause a controlled low velocity movement of the mass or pod through the pipeline. A feed assembly assures a properly mixed, loosely compacted delivery of particulate material to the pulse pod assembly. Pressurized air is added at spaced intervals to sequentially advance the mass or pod of particulate material through the system. The pulse pod assembly has a three step operational sequence, namely loading or creation of a mass or pod of particulate material; transport of the mass or pod into the pipeline; and purging in preparation for loading the next mass or pod. A plurality of boosters are spaced along the pipeline to periodically and sequentially supplement the driving air to keep the mass or pod in constant movement through the system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings in which: 
     FIG. 1 is a schematic diagram of a typical prior art dilute phase system; 
     FIG. 2 is a schematic diagram of a typical prior art dense phase system; 
     FIG. 3 is a diagrammatic view of the system of the present invention: 
     FIG. 4 is a side elevation, partially in section, of the pulse pod assembly of the subject invention in a loading mode; 
     FIG. 5 is a side elevation, similar to FIG. 4, showing the pulse pod assembly of the subject invention in a transport mode; 
     FIG. 6 is a partial vertical section through one embodiment of one of the air pressure booster assemblies of the present invention; 
     FIG. 7 is a top plan view of the feeder assembly of the present invention; 
     FIG. 8 is a vertical suction through the feeder assembly of FIG. 7; 
     FIG. 9 is a vertical section through a discharge valve assembly for the subject invention, shown in the closed condition; and 
     FIG. 10 is a similar vertical section showing the discharge valve of FIG. 9 in the open condition. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning first to the prior art, FIG. 1 shows a typical dilute phase system 10 in which particulate material is loaded into hopper 12 and continuously fed through an air lock 14 to a pipe system 16 where pressurized air from source 18 causes the material to be conveyed to hopper 20 where it arrives at substantially atmospheric pressure. The dense phase system 22 of FIG. 2 has a single hopper 24 feeding a pair of charging hoppers 26, 28 which alternately discharge a plug of material into the feed line 30 where pressurized air from source 32 drives the plug of material to the receiving hopper 34. It is easy to make a comparison of the above discussed advantages and disadvantages of the two types of systems from these two figures. 
     The system of the present invention is shown in diagrammatic form in FIG. 3. The subject invention 36 has a feeder assembly 38 connected for discharging particulate material directly into an inlet of pulse pod assembly 40. The outlet of pulse pod assembly 40 is connected to the inlet of a conveying or transport pipeline 42, the outlet of which is connected to the inlet of receiving hopper 44. A plurality of air pressure boosters 46, 48, 50, 52 are connected into and spaced along delivery pipeline 42. An air source tank 54 is connected to the pulse pod assembly 40 and boosters 46, 48, 50, 52 by means of control pipe 56. 
     The rapidly cycling pulse pod assembly 40 of the present invention is shown in detail in FIGS. 4 and 5 and includes a preferably cylindrical housing 58 defining a chamber 60 and having an inlet opening 62 connected to the particulate material feeder assembly (see FIG. 3) by inlet pipe 64. A discharge opening 66 is connected to conveying or transport pipeline 42. 
     A poppet valve assembly 68 is mounted substantially centrally of the chamber 60 and includes an inner cylindrical member 70 mounted substantially coaxially within the chamber 60. An air feed pipe 72 has one end entering into the inner member 70 adjacent a first closed or bottom end 74 and its opposite end connected to the air source 54. A plurality of apertures 76 are formed in spaced array about the periphery of and intermediate the ends of inner member 70. The upper end 78 of inner member 70 is open. The inner member 70 is fixedly mounted in the housing 58 by known means, such as first deflector plate 80 and air feed pipe 72. An outer cylindrical member 82 is loosely and slidably mounted on the inner cylinder member 70 and carries on its upper free end 84 a shaped valve member 86 which is adapted to engage annular seal 88 surrounding the inlet opening 62. 
     Booster 46, which is representative of all the boosters, is shown in detail in FIG. 6 and includes an outer housing pipe 90 and a porous inner pipe 92. The inner pipe 92 preferably has the same inner diameter as the transport pipeline 42 while the outer pipe 90 is somewhat larger to define an annular chamber 94 therebetween. The outer pipe 90 is provided with mounting flanges 96, 98 to engage with similar flanges 100, 102 on the transport pipeline 42 with appropriate known sealing means (not shown) therebetween. A control assembly 104 is mounted on each booster 46 in communication with the annular chamber 94. Each control assembly 104 includes a T-shaped pipe junction 106 with two identical control members 108, 110 mounted on the opposing arms of junction 106. Each control member 108, 110 has a housing 112 defining a chamber 114, an axial inlet 116 leading to the chamber 114 and forming a valve seat 118, and a radial inlet 120 opening into the chamber 114. A flexible diaphragm 122 is mounted for movement relative to the valve seat 118 to selectively open and close communication between the two inlets 116, 120. Gasket 124 is carried by the diaphragm aligned to engage the valve seat 118. Pilot signal means (not shown) are connected to the housing 112 through coupling 126 to control movement of the diaphragm 122. One of the control members 108 is connected to the junction 106 by its axial inlet 116 while its radial inlet 120 is connected to a source of pressurized air 54 (see FIG. 3) by line 56. The other control member 110 has its radial inlet 120 connected to the junction 106 while its axial inlet 116 is open to atmosphere. 
     FIGS. 7 and 8 show an embodiment 128 of feeder assembly 38 which is particularly useful in close quarter conditions. It includes an upper hopper 130, a transversely directed helical screw assembly 132 and a lower hopper 134. The upper and lower hoppers have substantially axially aligned vertical axes, as shown, to reduce the overall length of this feeder embodiment. The upper hopper 130 has an inclined inlet plate 136 which is axially offset along the length of the screw assembly 132. The screw assembly 132 has an elongated cylindrical tunnel 138 with a helical screw 140 rotatably mounted therein. The screw assembly includes screw drive means 142 outside of the tunnel and hoppers. The tunnel 138 has an upwardly directed inlet opening 144 and a downwardly directed outlet opening 146, with the openings being axially offset along the screw to be out of vertical alignment. The screw 140 receives particulate material from the upper hopper 130 through inlet opening 144, moves the particulate material axially to over the outlet opening 146 to drop through the lower hopper 134. Thus the screw 140 does not extend beyond the hopper and affords a compact design. 
     Operation of the pulse pod assembly of the present invention is rather simple. The automatic sequencing of the present invention is initiated by pneumatic control means (not shown). In the initial at rest or fill condition, as shown in FIG. 4, the pulse pod internal pressure is removed (supply air valves are closed) and the inlet poppet valve 68 is opened by gravity. The particulate material is allowed to fill the transport chamber for a preset period. A timer (not shown) holds the unit in the fill condition for an adjustable time cycle, usually from 1 to 7 seconds. At the end of this time period, a control means signals a conveying valve to open venting a diaphragm pilot (not shown) thereby pressurizing the chamber 60 which closes the poppet valve 68 and initiates the conveying cycle. The incoming air fluidizes the solids which are directed by deflector plate 80 and driven out of the chamber 60 through exit port 66 to transport pipe 42. The pressure continues to rise causing the product to flow smoothly through the transport line to the receiving hopper. The unit remains in the conveying mode until the pressure falls (indicating that the product has been delivered) to the empty line setting, which closes the conveying valve and initiates a subsequent fill cycle. A pressure sensor 75 monitors the source tank 54 and will hold the unit in the fill cycle until the tank has regained sufficient pressure for the next conveying cycle. This will insure that an adequate air supply is ready for the next pulse. The entire transport cycle will vary in relation to the conveying distance, but will range from 5 to 15 seconds, transporting 10 to 20 lbs of product in each pulse. 
     Thus the operation of the subject system is rather straight forward. In the fill or charge condition, FIG. 4, the inlet or poppet valve 68 has outer cylindrical member 82 resting against the open end 78 of the inner cylindrical member 70. This uncovers the inlet port 62 to allow the material to flow under the influence of gravity through input pipe 64 to at least partially fill the transport chamber 60. Feeding pressurized air axially into the poppet valve 68 drives the outer member 82 vertically up to engage the seal 88 allowing further pressurization of the chamber 60 and conveying of product in the chamber. The unit remains in the conveying mode until the pressure falls to an empty line setting which closes the conveying valve and initiates another fill cycle by the member 82 dropping, under the force of gravity, from the position shown in FIG. 5 to the position shown in FIG. 4. 
     A pressure sensor 75 monitors the surge tank 54 and will hold the poppet valve assembly 68 in the fill condition until the tank 54 has regained sufficient pressure for the next cycle. This will insure that an adequate air supply is ready for the next pulse. The entire transport cycle will vary in relation to the conveying distance but will range from 5 to 15 seconds transporting 10 to 20 pounds of product per pulse. 
     The boosters 46, 48, 50, 52 work in response to receipt of a pilot signal at coupling 126. The pneumatic lines for conveying this signal have not been shown for sake of clarity of the drawings. However, this is well known and could also be accomplished by a plurality of electrically operated valves connected to line 56 and tapping a small amount of pressure therefrom. This signal causes control member 108 to open and control member 110 to close so that pressurized air from the source tank 54 flows through member 108 and junction 106 into annular chamber 94, through the porous pipe 92 to add driving force to the air in the transport pipe 42. 
     The receiver is an important part of the present invention as it controls the flow of the system. The pulse pod assembly feeding the pipeline is balanced by the controlled exit at the discharge valve 148 in the receiver. This discharge valve is shown in FIGS. 9 and 10 in the closed and opened positions, respectively. The discharge valve is similar in both structure and operation to half a booster control. The discharge control valve 148 has a housing 150 defining a chamber 152, an axial inlet 154 leading to the chamber 152 and forming a valve seat 156, and a radial inlet 158 opening into the chamber 152. A flexible diaphragm 160 is mounted for movement relative to the valve seat 156 to selectively open and close communication between the two inlets 154, 158. Gasket 162 is carried by the diaphragm 160 aligned to engage the valve seat 156. Pilot signal means (not shown) are connected to the housing 150 through coupling 164 to control movement of the diaphragm 160. 
     Fundamentally the subject system operates by moving a section of mass of pod of particulate material over a measured distance from one booster to the next by pressurizing the entire pipeline and selectively venting the next section which is to receive the mass or pod. The entire conveying pipeline is under pressure and operates by venting the pressurized air downstream of the mass or pod in a pattern which stimulates peristaltic motion beginning at the discharge receiver and rapidly moving in an upstream direction. It is expected that the cycle will travel at speeds up to 25 ft/sec or higher. 
     Opening and closing vents, thereby controlling pressure, will cause the mass or pod in the pipeline to move downstream in a rippling motion. The venting control will be rapid by sensing the downstream pressure and opening, very briefly, to maintain flow. 
     Important to smooth flow is the receiver, which controls the mass or pod discharge by periodically opening the discharge valve in timed sequence with the peristaltic control valve. 
     A unique feature of the subject system is the continuous pressurization of the pipeline. Material is caused to flow toward the low pressure zones which are produced by selective sequential control of the venting valves. The continuous pressure is maintained by valve means in the receiver which opens at the appropriate time to release material into the receiver from the conveying pipeline. 
     Once filed with product, the subject system actually starts by opening a discharge valve in the receiver, thereby creating a void in the pipeline which is filled by consecutively opening and closing peristaltic valves back to the pulse pod assembly. As described previously, the pulse pod assembly is filled by the momentary release of pressure during the fill cycle. The cycle then begins again by opening the discharge valve in the receiver. 
     Conveying distances can be enormous and the only limitation would be the ability to provide substantially uniform pressure throughout the length of the system. As an example, it would be possible to transport materially horizontally and vertically many thousands of feet. 
     Potentially it would be possible to move solids coast to coast in a pipeline, just as liquids and gases are now moved. Another advantage is that the pipeline will be completely filled with solids making this far more efficient than any other system which could contain some voids. 
     Existing systems can be converted to the subject system quite easily by installing peristaltic valves, a receiver, and a pulse pod assembly into an existing pipeline. The advantage would be an immediate increase in solids flow rates and reduction in operating horsepower. Each system would be evaluated for its individual advantages and cost savings. 
     A traditional dense phase system operating at +/-5 lbs of product per lb of air requires approximately 8 psig to transport a distance of 150&#39; with 50&#39; of vertical and four (4) 90° degree elbows. A 4&#34; diameter pipe system will deliver 16,000 lbs/hr requiring 50 HP. The air volume would be approximately 550 SCFM. With the subject peristaltic system, the same requirements would be 10% or less of the standard dilute system. The peristalsis method will take the same system and increase the rate to as high as 40,000 lbs/hr using 69 to 148 SCFM at 60 psig. 
     The present invention may be subject to many modifications and changes without departing from the spirit or essential characteristics thereof. The present embodiment should therefor be considered in all respects as being illustrative and not restrictive of the scope of the invention as defined by the appended claims.