BACKGROUND OF THE INVENTION

The present invention relates to a pan filter.

A pan filter is a continuous vacuum filter designed for filtration of granular, fibrous, and coarse fast-settling solids. The filter pan or table of a pan filter provides a circular filtration surface that rotates in a generally horizontal plane about a generally vertical axis. The pan may be divided into sectors each equipped with respective fixed filter media. Cake drying may be implemented by vacuum and steam or hot air. Cake washing may also be provided.

A pan filter also allows for cake washing in counter current mode thereby achieving an optimal cake washing efficiency at reduced wash media consumption. Cake moisture is effectively reduced by gravity and/or means of an applied vacuum and/or additional methods, if required, before the cake is removed from the filter surface via a discharge scroll conveyor.

The filter media may be any of a wide range of textiles and metals and include advanced cloth-fixing methods including cassette designs.

Filter pans of current pan filters have upper surface areas that are generally no larger than

71 m . This size is not competitive with other filtration methods for large projects owing to the large number of pan filters that would be required.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide an improved pan filter.

A more specific object of the present invention is to provide a pan filter that has a filter pan surface area substantially greater than 71 m .

Another object of the present invention is to provide such a pan filter that has a significantly higher throughput than conventional pan filters. These and other objects of the present invention will be apparent from the drawings and description herein. Although every object of the invention is believed to be attained by at least one embodiment of the invention, there is not necessarily any one embodiment of the invention that achieves all of the objects of the invention.

SUMMARY OF THE INVENTION

The present invention aims to provide a pan filter of larger size, thereby enabling the economically feasible use of pan filters for large projects such as mine tailings filtration and for the larger product throughput requirements of modern beneficiation plants.

The present invention recognizes that increased pan size leads to increased tangential velocities of the pan at the periphery. The increased velocities may cause the cake at the edges of the filter surface to slide off of the pan, and other discharge problems and/or limitations. The increased velocities may also cause the complete discharge of the filtrate from each sector to be delayed, with subsequent negative effect relating to such issues as filter cake washing, especially in cases of counter current washing. These are just some of the reasons for the conventional limitation in pan size. Although the speed of pan rotation may be reduced in order to prevent radial cake slippage and/or cake washing problems, the result is inefficient in that the cake residence time is increased while not resulting in significantly drier cake. Thus, simply increasing the pan size does not necessarily result in increased throughput. Furthermore, while the pan may be provided with circumferential barriers to hold the cake against slippage, this makes effective cake removal problematic.

The present invention solves the problem by providing multiple feeds and multiple discharge scrolls with multiple discharge points. This will allow the pan filter to operate at a lower rotational speed while keeping the filtration cycle as short as the characteristics of the product dictate in order to achieve the highest possible throughput. Accordingly, a rotary pan filter in accordance with the present invention comprises a support platform or base, a filter pan or table rotatably supported on the platform or base for rotation about a substantially vertical axis, a plurality of radially extending feed distribution mechanisms such as pipes, open channels, and/or chutes, generally disposed above the filter pan or table at locations angularly spaced from each other, and a plurality of radially extending scroll conveyors also disposed generally above the filter pan or table at locations angularly spaced from each other. Furthermore, besides the feed devices mentioned, the feed distribution mechanisms could also include various pressure fed devices, for example various pumps, and their accompanying controls and piping. In addition, other filter cake removal devices besides scroll conveyors, such as various plows and/or scrapers, can be used to remove the resulting filter cake.

Pursuant to another feature of the present invention, the scroll conveyors each have a pair of oppositely inclined spiral conveyor blades including a radially inner blade configured to move solids in a radially inward direction along the filter pan or table and a radially outer blade configured to move solids in a radially outward direction along the filter pan or table.

Pursuant to a further feature of the present invention, the pan filter has at least one center discharge chute located at a center of the filter pan or table for receiving solids moved to the center by the radially inner blades of the scroll conveyors. The pan filter also generally includes at least one perimeter, generally peripheral, discharge chute, sometimes equal in number to the scroll conveyors and then located at angularly spaced locations about a periphery or outer edge of the filter pan or table for receiving solids moved outwardly by the radially outer blades of respective ones of the scroll conveyors.

In a preferred embodiment of the invention, the feed distribution mechanisms are two in number and the scroll conveyors are two in number. Preferably, the feed distribution

mechanisms are collinearly disposed or aligned, i.e., are disposed at 180° relative to one another. Similarly, the scroll conveyors are collinear and disposed on diametrically opposed sides of the pan filter. Thus, the scroll conveyors are oriented at a common angular angle with respect to respective ones of the feed distribution mechanisms. This pertains even if there are more than two sets of infeed mechanisms and discharge scrolls.

Pursuant to an additional feature of the present invention, the pan filter further comprises a circular pan support rail disposed between the platform or base and the filter pan or table for rotatably supporting the filter pan or table on the platform or base. The rail's central axis is generally at least parallel, and may be concentric or coaxial, to or with the central axis of the center discharge chute.

A dual-feed dual-discharge pan filter in accordance with the present invention may have a filter surface area of up to or even more than 250 m while minimizing cake residence time and rotation speed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of a pan filter in accordance with the present invention. FIG. 2 is a side elevational view, partially broken away and on a larger scale, of the pan filter of FIG. 1.

FIG. 3 is a top plan view of the pan filter of FIGS. 1 and 2.

FIG. 4 is a top plan view, similar to FIG. 3, showing the pan filter of FIGS. 1-3 with a walkway removed.

FIG. 5 is a cross-sectional view taken along line V-V in FIG. 3.

FIG. 6 is a cross-sectional view taken along line VI- VI in FIG. 3.

DETAILED DESCRIPTION

A rotary pan filter generally comprises a superstructure 10 including a primary support platform or base 12 and a secondary platform or base 14 coextensive with and parallel to one another. A generally horizontal filter pan or table 16 comprising a plurality of interconnected sectors 18 is rotatably supported on platform or base 12 for rotation about a generally vertical axis 20 (FIGS. 2, 5, 6). A flat upper surface 22 of filter pan 16 receives filter media (not separately shown).

Two collinear and radially extending horizontal feed distribution mechanisms such as pipes 24 and 26 are disposed above filter pan or table 16. Pipes 24 and 26 are angularly spaced 180° from one another. Two radially extending and horizontally oriented scroll conveyors 28 and 30 are disposed above filter pan or table 16 at 180° from one another. Scroll conveyor 28 has a pair of oppositely inclined spiral conveyor blades (FIGS. 2 and 6) including a radially inner blade 32 configured to move solids in a radially inward direction along filter pan or table upper surface 22 and a radially outer blade 34 configured to move solids in a radially outward direction along filter pan or table surface 22. Similarly, scroll conveyor 30 has a pair of oppositely inclined spiral conveyor blades including a radially inner blade 36 configured to move solids in a radially inward direction along filter pan or table upper surface 22 and a radially outer blade 38 configured to move solids in a radially outward direction along filter pan or table surface 22.

A center discharge chute 40 (FIGS. 1, 2, 5 and 6) is located at a center of the filter pan or table 16 for receiving solids moved to the center by the radially inner blades 32 and 36 of scroll conveyors 28 and 30. Two perimeter discharge chutes 42 and 44 are provided at diametrically opposed locations about a periphery or outer edge 46 of filter pan or table 16 for receiving solids moved outwardly by the radially outer blades 34 and 38 of scroll conveyors 28 and 30.

Filter pan or table 16 is provided on a lower side with one or more plenum or vacuum chambers 48 (FIGS. 2, 5, 6). Pan 16 is rotatably supported on primary platform 12 by wheels or bearings (not shown) rollingly engaging a circular pan support rail 50 sandwiched between plenum or vacuum chambers 48 on an upper side and platform or base 12 on a lower side. Rail 50 is concentric or coaxial with center discharge chute 40.

Pan filter 16 together with plenum or vacuum chambers 48 is further supported via a circular bearing 52 on a hollow cylindrical pillar or post 56 resting on lower platform 14 and coaxial with center discharge chute 40. A valve 54 is provided for the removal of liquid effluent from plenum or vacuum chambers 48.

A truss-work walkway bridge 58 is mounted via truss-work supports 60 and 62 on platform 12 and extends over scroll conveyors 28 and 30.

In manufacturing a rotary pan filter as described herein, one fabricates filter pan or table 16 to have a predetermined radius significantly larger than the radii of conventional pan filter tables. One determines a maximum permissible rotational velocity for filter pan or table 16 in accordance with the sliding friction values of expected slurries to be dried and the predetermined radius. One further determines a travel angle of filter pan or table 16 for which residence time of a wet slurry on the filter pan or table as driven at the maximum permissible rotational velocity will be effective to dry the wet slurry to an acceptable dryness. One provides a plurality of feed distribution mechanisms such as pipes 24, 26 and a plurality of filter cake removal devices such as scroll conveyors 28, 30 each equal in number to 360° divided by the travel angle. One installs the feed distribution mechanisms such as pipes 24, 26 in a horizontal plane above filter pan or table 16, with the pipes angularly spaced by the calculated travel angle. Similarly, one disposes the filter cake removal devices such as scroll conveyors 28, 30 above filter pan or table 16, with the scrolls angularly spaced by the calculated travel angle.

Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. For instance, a pan filter assembly pursuant to the invention may incorporate three or more feed mechanisms such as pipes and three or more dual discharging scrolls. In the triplicate or tripartite case, the feed mechanisms or feed pipes would generally be disposed at 120° relative to each other. Likewise, the discharging scrolls would generally be disposed at 120° relative to each other.

A dual discharging scroll conveyor with oppositely inclined blades as disclosed herein may be useful in the smaller conventional pan filters having only one feed pipe and discharge scroll.

Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.