US3849313A

US3849313A - Belt for a vacuum filter

Info

Publication number: US3849313A
Application number: US00310996A
Authority: US
Inventors: E Lopker
Original assignee: Pullman Inc
Current assignee: Pullman Inc
Priority date: 1972-11-30
Filing date: 1972-11-30
Publication date: 1974-11-19
Anticipated expiration: 1991-11-19

Abstract

A belt for a vacuum filter has a series of transverse drainage channels formed by ribs running from the outer edges of the belt towards perforations positioned along the longitudinal center line of the belt. The floors of the drainage channels are sloped downwardly from the outer edges of the belt towards the center line perforations. The top surfaces of the ribs forming the channels are notched to minimize diversion of wash liquid by the top surfaces.

Description

United States Patent 1191 Lopker 1451 Nov. 19, 1974 1 BELT FOR A VACUUM FILTER 3,245,518 4/1966 Reibel et a1 198/198 3,477,583 11/1969 Krynski et a]... 210/401 [75] Inventor- Ef Lopkeri Laudeirdale 3,677,411 7/1972 lshigaki 210/401 x [73] Assignee: Pullman incorporated, Houston, Primary Examiner-ROY Lake Tex., Assistant Examiner-J. W. Davie [22] Filed: Nov. 30, 1972 ABSTRACT [2]] Appl' 310996 A belt for a vacuum filter has a series of transverse drainage channels formed by ribs running from the 52 U.S. c1. 210/400, 210/489 outer edges of the belt towards perforations Positioned 51 1111. C1 B0ld 33/04 along the longitudinal center line of the The [58] Field of Search 210/400, 401, 405, 489; floors of the drainage channels are Sloped downwardly 198/198 from the outer edges of the belt towards the center line perforations. The top surfaces of the ribs forming [56] References Cited the channels are notched to minimize diversion of UNITED STATES PATENTS wash liquid by the top surfaces. 3,104,223 8/1963 Kasuya 210/400 24 Claims, 5 Drawing Figures 32 30 I6 27 25 26 32 l4 l5 f D -"J'* 4 1 I ISTFP 31 1 f t- '9 un a v o 7. "Z 24 '8 I IT I Pmmmr m m 3.849.313

SHEEI 10$ 2 mgmg :xrusnsm I 1, SHE 2m: 2 3 849 313 32 3O l6 2T 25 FIG. 2.

FIG. 3

UNWASHED AREAS FIG. 5.

(PRIO ART) FIG. '4.

BELT FOR A VACUUM FILTER The present invention pertains to the art of filtration, and more particularly pertains to an improved belt for a continuous belt vacuum filter.

Continuous belt vacuum filters are commonly used to separate the liquid and solid portions of a slurry. Such filters generally comprise an endless belt, usually made of rubber or other elastomeric material, which belt is carried on two horizontally positioned drums, one of which is driven to provide for continuous travel of the belt around the drums. The belt surface contains a series of ribs positioned transversely to the length of the belt, the ribs forming a series of transverse drainage channels running from near the edges of the belt towards the center line thereof. A series of perforations are positioned along the center line of the belt in liquid fiow communication with the drainage channel.

The belt outer surface is covered by a porous filter cloth, the cloth being supported over the drainage channels by the top surfaces of the ribs. The filter cloth is sufficiently taut so that it bridges the drainage channels to form a porous roof over each such channel.

Normally, the axes of rotation of the two end drums are positioned in the same horizontal plane so that the continuous belt comprises an upper (filtration) portion and a lower (return) portion, both of which are positioned horizontally. A vacuum box is positioned between the two end drums just beneath and in contact with the bottom surface of the belt upper segment. The vacuum box normally extends for substantially the entire distance between the end drums, only sufficient clearance for rotation of the end drums being provided on either end of the vacuum box. The vacuum box is in sliding, sealing engagement with the bottom surface of the upper, filtration portion of the belt.

The surface of the vacuum box in contact with the filtration portion of the belt is provided with a longitudinally extending opening or series of openings which are in flow communication with the belt perforations, as the belt passes over the vacuum box.

The vacuum box is provided with vacuum connections through which a vacuum is imposed on the box and liquid filtrate, air and gases pulled into the box are withdrawn.

A series of liquid sprays to distribute wash liquid over the filter cake which accumulates on the filtration portion of the belt may also be employed.

In operation, an end drum is driven by a suitable motor so that the belt travels continuously around the end drums. A slurry to be filtered is applied to one end of the upper, filtration portion of the traveling belt so that the slurry travels with the beltalong the length of the filtration surface. A vacuum is imposed upon thevacuum box and this causes the liquid portion of the slurry, i.e., the filtrate, to be drawn through the filter cloth, into the drainage channels, and through the perforations in the belt, thence into the vacuum box, leaving the solids behind as a filter cake on the filter cloth. The vacuum acts from the vacuum source through the vacuum connections to the vacuum box, through the slot opening in the vacuum box and the perforations in the belt.

A wash liquid, usually water, may be applied to the filter cake which accumulates on the filter cloth. The wash liquid displaces filtrate remaining in the filter cake and passes through the cake and cloth into the vacuum box under the influence of the vacuum, in the same manner as the liquid filtrate.

When the liquid filtrate is a valuable product, and/or when the filter cake must contain not more than a given amount of residual filtrate, it is necessary to carefully control the washing to insure that the required degree of filtrate removal from the filter cake is attained. Prior artfilter belts suffer from several shortcomings in this regard.

One of the problems is that the top surfaces of the ribs, which top surfaces serve to support the filter cloth, act as baffles which divert wash liquid applied to the filter cake around the portion of the cake directly above the rib top surfaces. As the filter cake increases in thickness upon the filter cloth, this diversion of the wash liquid results in areas of the filter cake above the ribs not being thoroughly washed. Since, in a typical filter belt construction, the width of the rib is equal to the width of the drainage channel, one-half of the total filter cloth area is blocked by the underlying rib top surfaces, and the totality of wash water is diverted through the remaining one-half of the filter cloth area.

Another difficulty with the prior art belts is that since the filtration surface of the belt is positioned horizontally, the floors of the drainage channels are also positioned horizontally, and there is no static liquid head to assist in flowing the liquid along the length of the channel into the belt perforations.

Prior art attempts to overcome this shortcoming, which tends to hold up liquid in the drainage channels, has been to raise the belt supports at a slight angle so that the outer edges of the belt are raised relative to the center portion of the belt, resulting in a broad, shallow U-shaped cross-section of the belt filtration area. This results in the filter cake being thicker along the belt center line than at the edges, with consequent disadvantages including the occurrence of slower filtration rates at the center of the belt than at the edges of the belt.

In accordance with the present invention, there is provided an improved belt for a continuous belt vacuum filter which overcomes the aforesaid shortcomings of the prior art, and which provides an improved, efficient belt design.

In accordance with the present invention, there is provided a belt for a continuous belt vacuum filter containing drainage channels which are formed by horizontal ribs (horizontal ribs" meaning that the top surfaces of the ribs are horizontal) which increase in depth in a direction (usually from the outer edges towards the center line of the belt) such that the floor of the drainage channel is downwardly sloped towards the belt perforations contained therein.

In accordance with another aspect of the invention, the tops of the ribs forming the drainage channels are notched along substantially the entire length thereof which is in contact with the filter cloth.

Understanding of the invention will be facilitated by considering the following detailed description and drawings illustrating the specific embodiments of the invention wherein:

FIG. 1 shows a schematic perspective view of the basic components of a typical continuous belt vacuum FIG. 2 is a partial section view taken transversely.

across the filter belt along lines 22 in FIG. 1;

FIG. 3 is a partial plan view of a filter belt in accordance with the invention;

FIG. 4 is a section view taken along line 44 of FIG.

FIG. 5 is a view corresponding to that of FIG. 4 but showing a prior art filter belt.

Referring now to FIG. 1, the major components of a vacuum belt filter comprise a pair of end drums l0 and 12 over which is mounted a filter belt 14. The belt is driven by a motor and drive means (not shown) which rotates one of the end drums so that filter belt 14 and end drums l0 and 12 travel in the directions shown by the arrows in FIG. 1. The belt, drive motor, end drums and other components are supported on a suitable structural frame 8. Filter cloth 16 overlies filter belt 14 and travels with it.

A vacuum box 18 is positioned beneath the upper segment of filter belt 14 and extends for substantially the entire distance between end drums and -12, the length of vacuum box 18 occupying the entire distance between

end drums

10 and 12 except for so much as is required to permit adequate clearance between the ends of vacuum box 18 and the rotating end drums l0 and 12.

Filter belt 14 is supported along its upper, filtration portion by vacuum box 18 and support beams 21. The center line portion of belt 14 is provided with a wear strip 23 which bears upon the flange portion of vacuum box 18 in sliding, sealing engagement.

As filter belt 14 and filter cloth 16 travel around discharge end drum l2, belt support rollers 11 support the lower, return run portion of filter belt 14, and rollers 11A space filter cloth 16 from filter belt 14 along the return run, as is known in the art, in order to facilitate cleaning of filter cloth 16. Such cleaning is generally accomplished by spraying the cloth with water or other wash liquid in order to remove any residual solids from the cloth. A drip pan 7 extends underneath the return run portion of filter cloth 16 to catch the water or other wash liquid used to wash the filter cloth.

A longitudinally disposed opening 20 is provided along the top surface of vacuum box 18 for substantially the entire length thereof. The portion of filter belt 14 above vacuum box 18 is the filtration portion of the filter belt.

Filter belt 14 is provided with a series of perforations 22 positioned along the longitudinal center line thereof, and with a series of transversely positioned drainage channels 24 formed between-ribs 26 along the entire length of filter belt 14. The drainage channels run from near either edge 15 of belt 14 to each of the apertures 22. The edges 15 of belt 14 are of raised construction to contain liquid slurry upon the belt.

As best seen with reference jointly to FIGS. 2, 3 and 4, the floor 25 of drainage channel 24 slopes downwardly from the edge 15 of belt 14 towards the belt perforations 22. Only a slight slope is required to provide a small hydrostatic head to the liquid which passes through filter cloth l6 and into drainage channel 24, to flow the liquid along the floor 25 of drainage channel 24 and into apertures 22. A typical slope of the floor 25, would be A inch per foot, which is adequate for most operations, and about /a inch to about 3/4 per foot is preferred.

The top 27 of ribs 26 are horizontal and provide a substantially horizontal flat surface (as best seen in FIGS. 2 and 4) which serves to support filter cloth l6 which, as best seen in FIG. 4, is stretched tautly enough over the tops 27 of ribs 26 to provide a substantially horizontal support for the filter cake 30 which accumulates thereon. As may be seen with reference to FIG. 1, the substantially flat and horizontal support provided by the tops 27 of ribs 26 is provided along the upper (filtration) portion of the belt.

In operation, a slurry to be filtered is introduced onto filter belt 14 via slurry conduit 13. A vacuum is applied to vacuum box 18 via vacuum connections 19 and the liquid portion of the slurry is pulled by the force of the vacuum (cooperating with atmospheric pressure above the belt) through filter cloth 16 into drainage channels thence through longitudinal opening 20 into vacuum box 18. The flow of liquid through drainage channel 24 (as shown by the arrows A in FIG. 2) is aided by the slope of floor 25. The liquid filtrate, and air and gases pulled in by the vacuum, enter vacuum box 18 and are withdrawn therefrom via vacuum connections 19. The solids contained in the slurry accumulate upon filter cloth 16 to form filter cake 30, which travels towards the discharge end (at end drum 12) of the belt, from which it is dropped into a suitable receptacle (not shown).

In order to displace residual filtrate from filter cake 30 before its removal from the belt, a wash liquid, usually water, may be applied through wash liquid conduits 17 and spray headers 17A. Wash liquid, together with the filtrate it displaces from filter cake 30, passes through filter cake 30 and filter cloth 16 into drainage channels 24 and through apertures 22 and longitudinal opening 20 into vacuum box 18.

Successive applications of wash liquid provide progressively weaker solutions of mother liquor (the original liquid component of the slurry) in wash liquid.

Vacuum box 18 may be divided into a series of compartments in order that the filtrates withdrawn through the separate vacuum connections 19 at various stages of the filtration and washing may be maintained separate, one from the other.

As shown in FIG. 5, one difficulty with prior art filter belts is that a portion of the wash liquid is diverted by the top surfaces 27 of ribs 26, which results in leaving unwashed that portion of filter cake 30 immediately above the rib top surfaces 27. Since, in a typical filter belt design, the ribs 26 are as wide as the drainage channels 24, one-half of the surface of filter cake 30 is subject to the incomplete washing. The problem becomes progressively worse as the thickness of filter cake 30 increases, leaving behind unwashed areas of the filter cake roughly triangular in cross-section as shown in FIG. 5. The path of wash water through the filter cake and filter cloth is shown by the arrows in FIG. 5.

Referring now to FIGS. 3 and 4, the filter belt of the invention is seen to contain a series of notches 32 formed along the top surfaces 27 of ribs 26. The notches shown are rectangular in plan view and are cut at approximately a 45 angle down into ribs 26 to form a series of drainage paths through which the wash water may pass as shown by the arrows in FIG. 4.

Notches 32 are arranged in a staggered pattern so that diversion of the wash liquid around any given area of filter cloth 16 (and consequently filter cake 30) is minimized. Washing of substantially the entire area of the filter cake is attained, even when the cake is a thick one.

It will be apparent that the particular configuration of notches shown is only one of many that can be used. The notches may be cut in a circular or semi-circular design or in any other desired design, and may form a drainage path at any desired angle down through ribs 26. It suffices so long as a sufficiently good distribution of notches 32 along the top surfaces 27 is provided, so that drainage paths for the wash liquid are provided substantially all along the length of top surfaces 27. The particular embodiment illustrated in FIGS. 3 and 4 has about 40 percent of the total surface area of top surfaces 27 cut away to provide liquid drainage paths. Naturally, other designs in accordance with the invention may have the same or a lesser or greater proportion (about 25 percent to about 75 percent is preferred) of the top surface area of the ribs cut away to form the drainage paths.

The improved filter belt of the present invention is therefore seen to comprise a filter belt wherein the drainage channel floors are provided with a slope running downwardly towards the apertures in the belt, and the ribs of which have a portion of their top surfaces (those which support the filter cloth) cut away to provide drainage for liquid passing therethrough.

These design features may be employed independently, a belt may have the sloped drainage channel floor but not the notches, or vice-versa, but it is preferred, for maximum efficiency, that both inventive features be incorporated in the belt.

The inventive features may be employed with any type of filter belt, with or without raised edge portions. E.g., the raised edges of the preferred embodiment may be done away with, and longitudinal weirs be provided on the filter adjacent both edges of the belt to contain the liquid slurry therebetween.

While the invention has been described in some detail with reference to specific embodiments thereof it will be appreciated that, as exemplified above, many variations on the specific design disclosed can be made which variations nonetheless fall within the spirit of the invention. It is intended to include all such variations within the scope of the appended claims.

I claim: floor,

l. A filter belt for a continuous belt vacuum filter, said belt having a series of ribs having horizontal top surfaces which provide a substantially horizontal, fiat surface on the filtration portion of said belt, said ribs being positioned along the surface of said belt and spaced one from the other to define therebetween a series of drainage channels having a floor a series of perforations through said belt, said perforations being in liquid flow communication with the floor of said drainage channels, and

the floor of said drainage channels being sloped downwardly from said horizontal top surfaces towards said perforations.

2. The filter belt of claim 1 wherein said perforations are positioned along the longitudinal center line of said belt, and said drainage channel floors are sloped downwardly from the outer edges of said belt towards the center line thereof.

3. The filter belt of claim 1 wherein the edges of said belt are of raised construction.

4. The filter belt of claim 1 wherein said drainage channel floor is sloped between about one-eighth inch per foot to about three-fourths inch per foot.

5. The filter belt of claim 4 wherein said floor is sloped at about one-fourth inch per foot.

6. The filter belt of claim 1 wherein said ribs and the drainage channels formed therebetween are positioned substantially transversely to the longitudinal length of the belt.

7. The filter belt of claim 1 further including a filter cloth overlying said belt and supported on said top surfaces of said ribs.

8. The filter belt of claim 7 wherein said drainage channel floor is sloped between about one-eighth inch per foot to about threefourths inch per foot.

9. A filter belt for a continuous belt vacuum filter, said belt having a series of ribs having top surfaces, said ribs being positioned along the belt surface and spaced one from the other to define therebetween a series of drainage channels having a floor,

a series of perforations through said belt, said perforations being in liquid flow communication with the fioor of said drainage channels, and

a series of notches formed in said top surfaces of said ribs to form a series of liquid drainage paths through said ribs.

10. The filter belt of claim 9 wherein about 20 to about percent of the total surface area of said top surfaces is cut away to form said notches.

11. The filter belt of claim 10 wherein about 40 percent of the total top surface area is so cut away.

12. The filter belt of claim 9 further including a filter cloth overlying said belt and supported on said top surfaces of said ribs.

13. The filter belt of claim 8 wherein about 20 to about 75 percent of the total surface area of said top surfaces is cut away to form said notches.

14. The belt of claim 7 wherein said ribs and said drainage channels formed therebetween are positioned transversely to the longitudinally extending length of the belt.

15. A filter belt for a continuous belt vaccum filter, said belt having a series of ribshaving horizontal top surfaces which provide a substantially horizontal, flat surface on the filtration portion of said belt, said ribs being positioned along the surface of said belt and spaced one from the other to define therebetween a series of drainage channels having a floor,

a series of perforations through said belt, said perforations being in liquid flow communiation with the floor of said drainage channels,

the floor of said drainage channels being sloped downwardly from said horizontal top surfaces towards said perforations, and

16. The filter belt of claim 13 wherein said perforations are positioned along the longitudinal center line of said belt, and said drainage channel floors are sloped downwardly from the outer edges of said belt towards the centerline thereof.

17. The filter belt of claim 13 wherein said drainage channel floor is sloped between about one-eighth inch per foot to about three-fourths inch per foot.

18. The filter belt of claim 17 wherein said floor is sloped at about one-fourth inch per foot per foot to about three-fourths inch per foot.

23. The filter belt of claim 19 wherein about 20 per cent to about percent of the total surface area of said top surfaces is cut away to form said notches.

24. The filter belt of claim 13 wherein said ribs and said drainage channels formed therebetween are positioned substantially transversely to the longitudinally extending length of the belt.

Claims

1. A filter belt for a continuous belt vacuum filter, said belt having a series of ribs having horizontal top surfaces which provide a substantially horizontal, flat surface on the filtration portion of said belt, said ribs being positioned along the surface of said belt and spaced one from the other to define therebetween a series of drainage channels having a floor a series of perforations through said belt, said perforations being in liquid flow communication with the floor of said drainage channels, and the floor of said drainage channels being sloped downwardly from said horizontal top surfaces towards said perforations.

8. The filter belt of claim 7 wherein said drainage channel floor is sloped between about one-eighth inch per foot to about three-fourths inch per foot.

9. A filter belt for a continuous belt vacuum filter, said belt having a series of ribs having top surfaces, said ribs being positioned along the belt surface and spaced one from the other to define therebetween a series of drainage channels having a floor, a series of perforations through said belt, said perforations being in liquid flow communication with the floor of said drainage channels, and a series of notches formed in said top surfaces of said ribs to form a series of liquid drainage paths through said ribs.

10. The filter belt of claim 9 wherein about 20 to about 75 percent of the total surface area of said top surfaces is cut away to form said notches.

13. The filter belt of claim 8 wherein about 20 to about 75 percent of the total surface area of said top surfaces is cut away to form said notches. 14. The belt of claim 7 wherein said ribs and said drainage channels formed therebetween are positioned transversely to the longitudinally extending length of the belt.

15. A filter belt for a continuous belt vaccum filter, said belt having a series of ribs having horizontal Top surfaces which provide a substantially horizontal, flat surface on the filtration portion of said belt, said ribs being positioned along the surface of said belt and spaced one from the other to define therebetween a series of drainage channels having a floor, a series of perforations through said belt, said perforations being in liquid flow communiation with the floor of said drainage channels, the floor of said drainage channels being sloped downwardly from said horizontal top surfaces towards said perforations, and a series of notches formed in said top surfaces of said ribs to form a series of liquid drainage paths through said ribs.

18. The filter belt of claim 17 wherein said floor is sloped at about one-fourth inch per foot

19. The filter belt of claim 13 wherein about 20 percent to about 75 percent of the total surface area of said top surfaces is cut away to form said notches.

20. The filter belt of claim 19 wherein about 40 percent of said total surface area is so cut away.

21. The filter belt of claim 13 further including a filter cloth overlying said belt and supported on said top surfaces of said ribs.

22. The filter belt of claim 14 wherein said drainage channel floor is sloped between about one-eighth inch per foot to about three-fourths inch per foot.

23. The filter belt of claim 19 wherein about 20 percent to about 75 percent of the total surface area of said top surfaces is cut away to form said notches.