Patent ID: 12257588

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A centrifugal separator10for separating solids from a liquid stream is shown, generally identified by reference numeral10, will now be described with reference toFIGS.1and6.

Referring toFIG.1, the centrifugal separator10will be described in terms of tailings that carry suspended solids, which may be present, for example, in a tailings pond. It will be understood that the teachings herein may be applicable to other situations where suspended solids are carried in a liquid, typically water, and other sources of tailings other than a tailings pond44as depicted inFIG.1. The term suspended solids is generally used to refer to fine particles that have a specific gravity sufficiently close to that of water that the fine particles do not tend to separate from water either by gravity or in a centrifuge, or that are otherwise suspended within the water. The size of what may be considered fine tailings may vary depending on the source, but may be particles that are sized at around 50 microns or less. In the depicted example, the water is sourced from tailings pond44, where a dredging apparatus46removes water and material from the bottom of the body of water, and delivers the slurry through a line48. The slurry may pass through an initial separator50that removes debris and larger particles that can be more easily removed from the slurry, and which are removed from the process as an output stream52. The remaining liquid stream12is then delivered to centrifugal separator10. Centrifugal separator10creates a solids output stream54and a liquid output stream56. In other situations, the water containing suspended solids may be obtained from different sources, and transported using other known or conventional transportation equipment. If required initial separator50may be used to remove particles or solids greater than a certain size, such as an initial separator50may be a filter screen, a centrifugal separator, a gravity separator, or other known type of separator that is able to remove heavier solids from water. Initial separator50may include more than one stage, and more than one type of equipment, depending on what is being removed from the slurry. Initial separator50may also include the use of flocculants, which may be used to flocculate the suspended particles and increase the size of particles, making it easier to remove the particles. This may be done prior to or during processing in initial separator50, or prior to being injected into centrifugal separator10. Initial separator50will preferably remove most or all of the larger components that may be found in the fluid stream, such that centrifugal separator10deals primarily with the fine tailings that remain in the slurry.

As noted above, the specific gravity of fine tailings are similar to that of water, making it difficult to separate the particles using gravity or centrifugal force. In addition, the fine tailings may have electrical charges or may be polar molecules that interact with the water molecules that also prevent them from separating by gravity or centrifugal force. As will be described in more detail below, the presently described separator and method of separation uses a filtering screen carried by an outer drum that captures very small particles, while allowing water particles to exit the drum. The drum is rotated at very high speeds, and in particular, on the order of typical centrifuges that may be used in industry, to apply centrifugal forces that will draw the water out of the slurry that enters the drum. Typically, a centrifuge is used to separate components with different specific gravities into layers. As this is not an effective separation strategy for a slurry based on tailings, the separator provides apertures that allow water to exit the drum. In addition, in order to prevent the filtering screen from becoming clogged or blocked with solids, an auger-type structure is provided that rotates at a different speed than the rotating drum in order to scrape or wipe the inner surface of solids, while also continually conveying solids toward the outlet. At the same time, a stream of pressurized cleaning fluid, such as air, nitrogen, water, cleaning solution, etc. impinges on the outer surface of the drum to clear the apertures in the screen of solids. Generally, the stream of pressurize fluid will be in a fixed position relative to the rotating drum, such that the apertures are cleared for each rotation of the drum, or partial rotation, if more than one stream of pressurized fluid is provided around the drum. This design is intended to allow for a design that allows for continual separation, rather than batch separation, and in large volumes that may be required in processing tailings from ponds.

Referring toFIG.2toFIG.6, different embodiments of centrifugal separator10are shown. Referring now toFIG.2, centrifugal separator10for separating solids from a liquid stream12is shown. Centrifugal separator10has a rotating drum14with a perforated outer wall16, an inlet18at a first end20for receiving liquid stream12to be separated, and a solids outlet22at a second end24of rotating drum14. Centrifugal separator10may also have a housing42that surrounds perforated outer wall16to capture liquids exiting rotating drum14. Perforated outer wall16may be made from titanium or other material that has sufficient structural strength to withstand the forces to be applied, while maintaining the structural integrity and size of the perforations. The perforations may be laser cut into the material. As shown inFIG.4, it may be necessary to provide a reinforcing outer shell17for perforated outer wall16to provide additional structural support. This reinforcing outer shell may, for example, be a metal mesh placed along the exterior of perforated outer wall16, or other design that reinforces outer wall16.

An auger26is positioned within rotating drum14. The helical flight28of auger26has an outer edge30that is immediately adjacent to an inner surface of outer wall16. A driver32rotates rotating drum14and auger26about axis of rotation34. Driver32rotates rotating drum14at a first rotational speed to apply a centrifugal force to fluids within the rotating drum14, while auger26is rotated at a second rotational speed that is different than the first rotational speed. During operation, the rotation causes liquids and the solids to move toward perforated outer wall16, such that liquids exit rotating drum14via perforated outer wall16, while solids are pressed against perforated outer wall16. As solids are pressed against perforated outer wall16, outer edge30of auger26engages the solids against the inside of perforated outer wall16such that outer edge30scrapes or wipes outer wall16of any solids, which are then conveyed toward solid outlet22. Centrifugal separator is intended to be operated at speeds that generate forces commonly found in centrifuges. The speed of rotation will depending on the size of rotating drum14. In some circumstances, the force may be achieved, for example, at speeds of around 800 rpm, 1000 rpm, or more.

Driver32may be any suitable driver that is able to drive rotating drum14and auger26at different speeds. This may include two separate motors, or may be a single motor that is geared differently for each rotational component. Driver32may be direct drive motors, or may be connected by gears, belts, pulleys, chains, etc. to a suitable drive shaft or gear. Preferably, the actual and/or relative rotational speed of rotating drum14and auger26are controllable and adjustable to allow a user to optimize the operation of auger press10. Auger26may rotate in the same direction as drum14, but at a different speed, such that, in relative terms, auger26moves relative to drum14. Auger26may be rotated faster or slower than drum14. This may depend, for example, on the direction in which helical flight28turns around shaft40in order to convey solids toward solids outlet22during operation. Drum14may have liquid overflow openings15located near first end20to allow for excess fluid12to leave drum14, as shown inFIG.3.

Referring toFIG.3, inlet18may be connected to an inner cavity41of shaft40such that fluid12passes first into inner cavity41and then into rotating drum14. Inner cavity may have a plurality of discharge ports43through which fluid12enters rotating drum14and a spreader45that helps to direct fluid12through discharge ports43.

Outer edge30of auger26may be a wiper edge that engages the inner surface of outer wall16. The wiper edge may act to clear the solids collected against the inner surface of outer wall16to allow auger26to convey those solids towards solids outlet22. In one example, to control the moisture content of the solids exiting rotating drum14, solids outlet22may use a variable back pressure surface38, which opens when a certain pressure is applied as the solids are compressed against variable back pressure surface38. Other outlet designs may also be used.

In order to account for the decreasing volume as water exits rotating drum14and to apply additional compression of the solids in order to remove additional water, the volume between the flights of auger26may decrease as the solids progress toward solids outlet22relative to adjacent to inlet18. Referring toFIG.6, this may be achieved by providing helical flight28with a pitch that changes along the length of auger26. As shown, the pitch of helical flight28adjacent to inlet18is greater than the pitch of helical flight28adjacent to solids outlet22, such that the turns are more closely spaced toward solids outlet22. The pitch of helical flight28may decrease continually along the length of auger26as shown, or the change in pitch may occur at discrete transition points or steps. Alternatively or in addition, referring toFIG.2, auger26may include a shaft40that has a diameter that increases toward solids outlet22. As with the pitch of helical flight28, the change may be gradual, or occur at discrete locations or in discrete sections. These features may be combined to provide a decreasing volume due to both the decreased pitch and the increased diameter in proximity to solids outlet22.

As drum14and auger26are rotated and solids are compressed, water exits rotating drum14via the perforations in perforated outer wall16, and may be captured, for example, by an outer housing42and exits via outlet56. The sizes of the perforations will be selected based on the size of the particles being separated, and in the case of tailings, will preferably be less than 60 microns, such that they are on the scale of the suspended solids being removed. In one example, the size of the perforations may be around 30 microns, and will generally be greater than 1 micron. Referring toFIG.3, as these perforations may become clogged or blocked and may not be cleaned by outer edge30of auger26, centrifugal separator10may be provided with a high pressure fluid source36outside drum14, and may be immediately adjacent to an outer surface of perforated outer wall16such that it extends parallel to axis of rotation34along some or all of drum14. High pressure fluid source36applies a pressure differential across perforated outer wall16to clear perforations of obstructions, and will generally be close enough that sufficient pressure is applied to outer wall16. High pressure fluid source36may comprise a gas or liquid. For example, high pressure fluid source36may use air, nitrogen, etc., or may use water or another appropriate wash fluid. High pressure source36may, for example, be fixed to outer housing42and direct fluid towards rotating drum14, or a discrete chamber sealed against the exterior of outer wall16may be provided along axis of rotation34. High pressure fluid source36may also be provided by a movable nozzle or other means of directing high pressure fluid onto a surface as are known in the art. As shown, high pressure source36is positioned at a particular rotational position on the outside of drum14. High pressure source36is preferably operated continuously such that the perforations in outer wall16are cleared at each rotation of drum14.

A method of separating solids from liquid stream12will now be described. Liquid stream12is introduced into rotating drum14at a first end20, and rotating drum14is rotated about axis of rotation34at a first rotational speed to apply a centrifugal force to fluids within the rotating drum. Liquid is then permitted to exit rotating drum14through perforated outer wall16. Auger26is rotated about axis of rotation34at a second rotational speed that is different than the first rotational speed to cause auger26to convey solids in rotating drum14toward solids outlet22. For example, rotating drum14may be rotated at 1000 rpm or more, but generally not less than 800 rpm, while auger26is rotated at a speed that is faster or slower than rotating drum, depending on the direction of the flights in auger26. The actual speeds will depend on the preferences of the user and the conditions of use that may be determined during optimization of the process. This results in relative movement of auger26to rotating drum14, which will cause outer edge30to dislodge solids that build up on the inner surface of perforated outer wall16due to the centrifugal force applied to the fluids. Generally speaking, it is desired to have the relative speeds set such that auger26pushes solids toward solids outlet22. As liquid is able to exit rotating drum14through perforated outer wall16, while solid particulates are generally prevented from exiting through the perforations due to the small size of the perforations, solids will build up against outer wall16to be conveyed towards solids outlet22by auger26. It will be understood that this will result in the liquid content being highest near first end20, and the density of solids will increase as the solids are conveyed towards second end24, as the liquid is removed while the solids continue to travel within outer wall16and encounter other solids. The relative rotational speeds may be controlled in order to control a discharge rate from solids outlet22, as well as a liquid content in solids discharged from solids outlet22.

The method may also include the step of applying a pressure differential across perforated outer wall16to clear perforations of obstructions. Outer edge30of auger26may not clear all of the solid particulate from perforated outer wall16, or particulate may become fixed in the perforations and not be dislodged by outer edge30. In order to ensure that liquid is able to exit through outer wall16, the perforations may be cleaned using high pressure fluid source36. This cleaning may be done intermittently, or continuously along a portion of perforated outer wall16that extends parallel to axis of rotation34, as shown inFIG.1. Auger26may be designed to compress the solids as they move towards solids outlet22, and this may be achieved by decreasing the volume available as the solids move towards solids outlet22, either by decreasing the pitch of helical flight28, increasing the diameter of shaft40, or a combination thereof, as described above. In order to further decrease the liquid content of the solids, the pressure in proximity to solids outlet22may also be controlled by applying a variable back pressure using a variable back pressure surface38. For example, variable back pressure surface38may be used to prevent solids that have not yet been compressed to a selected pressure from exiting through solids outlet22, providing the opportunity for further liquid to be compressed out of the solids through perforated outer wall16. Liquid that has exited perforated outer wall16may be captured by an outer housing42as shown inFIG.1, and directed to liquids outlet56.

Depending on the application of the centrifugal separator10and the method of separating solids from liquid stream12, it may be desired to calibrate the system to allow for different throughputs. For example, the liquid output56may be recycled back to become part of liquid stream12, passing through centrifugal separator10more than once and allowing for additional separation of solids. The calibration may be for high throughput, achieved for example by selecting a perforated outer wall16having larger perforations, and allowing liquid to be separated more quickly, or the calibration may be for higher separation, such as by selecting a perforated outer wall16having smaller perforations, and thereby preventing more of the solids from passing through outer wall16.

The initial separation50may provide a number of separation stages and treatments to the fluid from line48. For example, large particulate may be separated by filtration or settling, or other conventional separation techniques. The fluid may also be treated with a flocculate prior to entering centrifugal separator10. Perforated outer wall16of rotating drum14as shown inFIG.1is a thin metal screen having very fine perforations formed therein. The material is preferably selected in order to allow for the preferred perforation size to be formed therein. It has been found that titanium may be a suitable material. Solids may be discharged from solids outlet22onto a screw or belt conveyor for disposal, or may undergo other treatments after exiting centrifugal separator10. As an example, the solids may be transmitted to conventional dry-stack tailings facilities.

Centrifugal separator10may be provided with a number of sensors (not shown) and configured inputs that provide parameters such as fluid input flow and velocity, liquid output flow and velocity, conductivity of the input and outputs, rotation rates of rotating drum14and auger26and their relative rotation, densities in and out of centrifugal separator10, air pressures, temperature, the volume of flocculant injected (if any), retention time of the flocculant, the size of the perforations in perforated outer wall16, the injection pressure applied by high pressure fluid source36, and the frequency with which fluid is applied through high pressure fluid source36. These parameters may be provided to a processor, which may then be configured to vary certain parameters to optimize the performance of centrifugal separator10. In particular, it may be desired to ensure that a particular liquid content is achieved in the solids that exit solids outlet22, and the liquid content of these solids may be measured and used to optimize the operation of centrifugal separator10to ensure the desired liquid content is achieved. The processor may employ a learning algorithm to determine optimal operating conditions given a number of input parameters.

In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there be one and only one of the elements.

The scope of the following claims should not be limited by the preferred embodiments set forth in the examples above and in the drawings, but should be given the broadest interpretation consistent with the description as a whole.