Patent Application
20210008596
This invention relates generally to the field of transport, handling and sieving of materials.
An embodiment of the invention may therefore comprise a screw auger conveyor, the screw auger conveyor comprising a conveyor pipe having a first axial length section of an outer wall of the conveyor pipe comprising a first fixed grid-size screen which allows particles of a first predetermined size to pass through the screen, at least one helical conveying screw auger inside the conveyor pipe, a first vessel that collects the first predetermined size particles that pass through the first fixed grid-size screen.
An embodiment of the invention may further comprise a method of conveying and separating feedstock in a selected gravity environment, the method comprising introducing a feedstock into a cylindrical conveying pipe of a screw auger conveyor, conveying the feedstock along the screw auger conveyor via a helical conveying screw auger, collecting a first predetermined size particles in a first vessel wherein the first predetermined size particles pass through a first fixed grid size screen in an outer wall of the conveying pipe.
The present invention describes a system and method for transporting, handling and sieving materials. The materials may be dry granular solids. The system and method of the invention both convey and size-separates the sieving materials. Unique size-separated configurations of the sieving materials are a result. Such size-separated materials may be useful in various industries, e.g. feedstock industries.
Different methods and systems can be used to move or sift materials. A screw conveyor, or rotating screw auger, may convey granular solids and may operate in one of two different modes. A screw auger may operate in a slow rotation mode, similar to an Archimedes screw with material sliding down the face of a horizontal, or slightly inclined, screw auger with minimal effects from centrifugal acceleration. A screw auger may also operate in a rapid rotation mode where the centrifugal acceleration of the material inside the conveyor exceeds the acceleration of gravity. Vertical, near vertical, or otherwise steeply inclined upward conveying screw augers generally cannot convey material if the screw rotates in a slower mode. Those skilled in the art will understand the necessary speed of rotation in consideration of an inclined upward angle in order to convey material. As such, in order to convey material up an incline, or a steep incline, a screw conveyor generally operates in a mode where the material is following a swirling vortex path of the opposite “hand” from that of the conveying screw. In other words, a left-hand vortex motion of the material in a screw conveyor with a right hand screw thread, and vice versa, generally results. As a person skilled in the art will understand, once the rotation rate of the conveying screw is at a fast enough spin rate for centrifugal acceleration at the periphery of the screw to exceed the acceleration of gravity, the mode of flow inside of the conveyor becomes a rapid swirling vortex flow mode which is also the mode of flow inside of a typical vertical screw conveyor. It has been shown experimentally that the material inside of such rapidly rotating screw conveyors (horizontal, vertical or inclined) exhibits a swirling vortex flow mode of motion similar to that utilized in vertical screw conveyors.
Sieves and sifters may also be used for separation of fine material from course material. Dry granular solids exhibit size segregation when they experience various kinds of dynamic motion in a gravity field or in an environment with a body force that resembles gravity. For example, dry granular materials exhibit size segregation, usually with the larger particles rising to the top and smaller particles migrating toward the bottom if the container holding the material is vibrated. Dry granular materials undergoing shear deformation during flow in an environment with a body force such as gravity, or centrifugal acceleration in a rotating reference frame, also exhibit size segregation somewhat similar to the segregation occurring when a bed of granular material is vibrated. Under shearing flow, smaller particles generally migrate toward the bottom, or outer region, and larger particles rise toward the top, or inner surface, of the material undergoing shear deformation in a body force environment.
Vibration or shearing flow form the physical basis for the processes that occur in most sieving, sifting, mechanical size segregation, or size classifications. Standard laboratory vibrational sieve columns consist of a vertical stack of horizontal screens attached to the bottom of pans or trays. A fixed grid size screen forms the bottom surface of each tray or pan in the vertical stack of multiple pans. The largest screen opening is on the top pan, and each successive pan below has a smaller grid size screen. When a granular material is placed in the top pan and the entire stack is strapped onto a vibration inducing drive mechanism, the granular material of various sizes slowly flows down through each of the screens for which it is small enough to pass. This results in different size fractions remaining on the different size screens in the stack. The largest particles remain in the top pan, the next size fraction is in the pan just below the top pan and so forth.
A similar screen separation or sieving method (generally termed “sifting”) depends on shearing flow instead of vibration to achieve movement of material through screens. This is generally applied to only a single screen layer since each screen requires a separate moving blade or scraper to shear the material over the screen. A means of achieving the shearing flow across a horizontally oriented screen surface is by moving a blade laterally across the screen surface, or just above the screen surface. A wire, brush or other means to mechanically move the material sitting on a horizontal screen, laterally back and forth across the screen accomplishes the same function of shearing the material sitting on the screen and induces the particles smaller than the screen openings to pass through the screen. This type of system may be referred to as a sifter.
Commercial centrifugal sifters may utilize a horizontal cylindrical screen with several very slightly tilted paddle blades rapidly rotating around a horizontal shaft. The shearing motion of the paddle blades drives particles that are small enough through the surrounding cylindrical screen and the slight tilt of the paddles slowly moves the remaining material axially along the cylinder to the axial exit for the course fraction of the material. The rapid rotating motion of the paddle blades also induces air flow radially throughout the surrounding screen which may enhance the movement of fine particles through the screen.
Embodiments of the invention may comprise a screw conveyor configuration for dry granular solids with either an open coil or a central shaft mounted helical conveying screw auger with a stationary cylindrical pipe outer wall. In some embodiments the configuration may be oriented with the conveying axis in a horizontal or upwardly sloping direction. Embodiments of the invention may further comprise a mechanism or means for feeding material into the screw augur conveyor, a mechanism or means to provide rotational torque to drive the conveying screw at rotations rates high enough that the centrifugal acceleration at the periphery of the screw is greater than the local effective gravitational acceleration, a set of one or more fixed grid size curved screens replacing selected sections of a conveying pipe wall, at different axial positions along the conveying axis to allow material of a size smaller than each screen grid to pass through that screen into separate collections vessels located at each screen section and at the end of the conveyor. With appropriate selection and positioning of the screen sections, the collection vessels separately collect material of different sizes, with the smallest size screen in the first location after the entrance and successive screens having larger grid sizes. The screens separate the material into size segregated output streams which are deposited into separate collection vessels. The size classification system of embodiments of the invention may operate independent of gravity when the rotation rate is sufficient. The size classification system of embodiments of the invention may also not depend on air flow to assist movement of finer materials through screens. Accordingly, embodiments of the invention may be suitable for use under vacuum conditions. Embodiments of the invention may operate under ambient terrestrial, lunar, or asteroid surface environments. Feeding and removing material under microgravity conditions may require special material handling equipment. Those skilled in the art will understand such special material handling equipment such as microgravity storage vessels and conveying line feeders for cohesive regolith.
Different processes and ISRU (In-Situ Resource Utilization) operations that use regolith may require feedstock material in specific size ranges and may require delivery to a movable or relocatable end-point. Some processes may need material in fixed quantity batches. Other processes may require material supplied at a steady continuous rate. Embodiments of the invention provide new and improved systems and methods to accomplish these functions independent of the prevailing gravity level. Systems and methods of the invention may also operate without any gas-solid separation steps and advances the technology readiness levels of the technologies involved.
The inclination of the segregating conveying tube 130 and some of specifics, such as the geometry of the collection vessels) are suitable to design choice based on the choices of someone skilled in the art. Different variables that may influence this may include whether the size segregation is taking place under a reduced gravity situation, similar to what one may find on earth's moon or on another planet such as Mars, or on whether the separation is being performed under very low gravity conditions as may occur on a moon of Mars or a small airless NEO (near earth object).
The pitch of the central screw auger 110 may be as small as one quarter of the diameter of the cylindrical tube 130 or as large as two diameters of the cylindrical tube. The central screw auger 110 and cylindrical tube 130 may be horizontal, or angled up at any angle, even vertical. Preferred embodiments for terrestrial-gravity implementation would generally be angled up at angles exceeding 25 degrees above horizontal. The central screw auger may be a helical open-coil screw auger that both delivers the torque and conveys material along the cylindrical tube 130. The central screw auger may have varying pitches at the different slotted sections 140a-c. Three may be different diameters of the central screw auger 110 and the surrounding conveying pipe in the successive slotted sections 140a-c. There may also be an abrupt or tapered diameter adjustment section between the different slotted sections with different diameters of the central screw auger 110 and the cylindrical tube 130.
Vibration may also be utilized to assist for the finest feedstock size 220 which will fall through the smallest slots 240a. For near zero-gravity conditions, the unit may be at any orientation. Further the slots 240a-c can be around the entire circumference of the conveying tube 230 in near zero gravity situations. The collection vessels 140a-c as shown in
The central conveying auger 110, 210 as shown in
While inefficient conveying may provide desirable characteristics for the central auger 110, 210 in the separations units shown in
Typically, in terrestrial gravity situations, in vertical or steeply inclined screw conveying, increasing the gap size improves robustness by reducing or preventing jamming. However, large gaps can decrease conveying efficiency. Accordingly, trade-offs must be made between robustness and conveying efficiency. Similarly, open-core helical screws may be more robust, but less efficient than standard central shaft augers for vertical or steeply inclined conveying. DEM simulations may be used to determine relationships between gap spacing and robustness and conveying efficiency. Such simulations may also examine conveying behavior with open coil helix screws. It may be determined how much the relations change as the gravity level is reduced in those simulations. Those skilled in the art will understand the nature and efficacy of such DEM simulations.
The articulated views shown in
Fine particulates behave in a more cohesive manner than larger particles. For granular materials with a large size distribution, the bulk cohesion is most strongly influenced by the smallest size fraction in the distribution, for instance, the particles in the smallest 20% by mass. Also, as gravity level decreases, the bulk cohesive behavior of granular materials change toward the behavior normally exhibited by smaller more cohesive powders under terrestrial conditions. Measured and predicted behavior of lunar regolith simulants can provide some insight into how significant those changes in build behavior might be in going from terrestrial to lunar gravity levels.
Lunar material may not flow through centimeter scale openings under its own weight on the moon. Circular openings from conical hoppers may be sized to ensure flow, and a slot hopper may need to be also sized accordingly to ensure reliable flow under typical industrial conditions under terrestrial gravity. For instance, conical hoppers may be sized from 5 cm to 6c, in diameter and slot hoppers may be about 3 cm wide. For reliable gravity flow from a circular opening under a conical hopper, one may need to have an opening of from 30 cm to 36 cm in diameter. For a slot hopper the dimensions are somewhat smaller and only require widths of 18 cm for reliable flow under lunar gravity.
Figure S shows a swirl action utilized for centrifugal ejection of regolith (SAUCER) storage unit/dynamic feeder for conveying under microgravity conditions. The embodiment shown effectively deals with cohesive material in very low gravity environments. This centrifugal pump like storage and dispensing vessel overcomes flow problems with cohesive materials by using centrifugal acceleration to produce the motive force to move regolith out of a storage vessel and into a conveying line. There is an effective slot-hopper (based on the converging angles of the “top” to “bottom” conical section of the vessel). There is an exit slot 530 around the periphery of the SAUCER vessel 510. When the vessel 510 spins around its axis, centrifugal forces exceed the cohesive arch strength of any regolith inside and some material will be ejected through the peripheral exit slot 530 into a surrounding stationary ring 540. There may be one or more exit slots 530. An exit slot 530 may be a circular hole in the stationary ring 540 allowing the swirling material to pass through the outer ring wall and into an attaches screw conveyor 550. The material entering the conveyor 550 is then conveyed by the rotating auger/screw conveyor 550. Because the opening in the outer ring is circular, there is no preferred orientation for the attached screw conveyor 550. In some embodiments it may be preferred that the opening lie in a tangent plane to the outer circumference of the ring 540. The ring 540 and the screw conveyor 550 remain in a fixed orientation while the two conical shells of the SAUCER vessel 510 are connected together and rotate about their common axis to produce a centrifugal force enabling the material inside the SAUCER vessel 510 to be ejected through the outer slot 530 into the dispensing ring 540. An auger 560 and conveyor tube 570 is used to transfer material into the SAUCER vessel 510 along the center axis of the SAUCER vessel 510.
Terrestrial mining operations invariably involve ultimate creation or selection of size appropriate feedstock for the processes that will utilize the material extracted. The final operation in most processes that involve terrestrial movement of dry granular solids is gravity flow out of one container into another vessel or processing unit. For some specialized pressurized fluid bed processes or combustion processes, more complex transfer approaches are required. Gravity flow is by far the most common method of transfer into the final process or container. Under milli-gravity or micro-gravity the small gravity driving forces that exist are very unlikely to overcome particle-particle cohesion. Accordingly, so other method and system is needed to move material into and out of containers.
This Non-Provisional patent application claims the benefit of the U.S. Provisional Patent Application No. 62/828,666, entitled “SYSTEM AND METHOD FOR SIZE SEPARATING CONVEYOR,” which was filed with the U.S. Patent & Trademark Office on Apr. 3, 2019, which is specifically incorporated herein by reference for all that it discloses and teaches.
| Number | Date | Country | |
|---|---|---|---|
| 62828666 | Apr 2019 | US |
