Rotary disc filtration process having means to prevent settlement of solids

• US 5,849,202 A
• Filed: 08/27/1997
• Issued: 12/15/1998
• Est. Priority Date: 11/06/1992
• Status: Expired due to Fees

• Current Assignee: Andritz-Patentverwaltungs-Gesellschaft m.b.H.
• Original Assignee: Andritz-Patentverwaltungs-Gesellschaft m.b.H.
• Inventors: Riemer, Hubert, Koch, Manfred
• Primary Examiner(s): Popovics, Robert J.
• Application Number:
  US08/917,737
• Time in Patent Office: 475 Days
• Field of Search: 210/780, 210/784, 210/791, 210/805, 210/806, 210/808, 210/330, 210/331, 210/332, 210/391, 210/396, 210/398, 210/406, 210/407, 210/248, 210/196, 210/197, 210/456, 210/383, 210/408, 210/413, 210/219, 210/319
• US Class Current: 210/780
• CPC Class Codes: B01D 2201/282 Filtering elements with a horizontal rotation or symmetry axis
• CPC Class Codes: B01D 2201/48 Overflow systems
• CPC Class Codes: B01D 29/01 with flat filtering elements B01D29/39 takes precedence
• CPC Class Codes: B01D 29/114 arranged for inward flow filtration B01D29/15, B01D29/33 take precedence
• CPC Class Codes: B01D 29/52 in parallel connection
• CPC Class Codes: B01D 29/86 Retarding cake deposition on the filter during the filtration period, e.g. using stirrers B01D29/908 takes precedence
• CPC Class Codes: B01D 29/885 with internal recirculation through the filtering element B01D37/02 takes precedence
• CPC Class Codes: B01D 29/90 for feeding
• CPC Class Codes: B01D 33/073 arranged for inward flow filtration
• CPC Class Codes: B01D 33/21 with hollow filtering discs transversely mounted on a hollow rotary shaft
• CPC Class Codes: B01D 33/466 scrapers
• CPC Class Codes: B01D 33/68 Retarding cake deposition on the filter during the filtration period, e.g. using stirrers
• CPC Class Codes: B01D 33/705 with internal recirculation through the filter
• CPC Class Codes: B01D 33/72 for feeding
• CPC Class Codes: B01D 33/722 containing fixed liquid displacement elements or cores

Abstract

A process and device for the filtration of solid-liquid mixtures, in particular, solid-liquid suspensions with readily sedimenting substances, uses a filtration device such as a rotary filter optionally operating at an overpressure and in a pressure vessel. The process primarily comprises producing a movement in addition to the natural or usual filtration movement of the or in the mixture. Conveniently, a filtration device and, in particular, with rotary filters in a pressure vessel, includes a partly open feeding device, in particular, a feeding pipe for the supply of mixture or suspension, and a device for additionally influencing the natural or usual filtration movement of or in the mixture or suspension for generating an additional flow of the mixture.

Claims

1. A process for filtering solid-liquid mixtures comprising:

feeding a first solid-liquid mixture from a supply into a filtration device, said filtration device having a trough for containing said mixture and a rotating filter surface for rotating through said mixture in said trough, said feeding being directed from above or in proximity to a surface of said mixture in said trough,

providing a guiding plate spaced from a sidewall of said trough and spaced from and substantially parallel to said filter surface above or below said surface of said mixture in said trough,

directing said feed of said first mixture along said guiding plate substantially parallel to said filter surface and in a downward direction into said mixture in said trough to produce a first downward flow stream in said mixture in said trough,

producing a second flow movement stream in said mixture in said trough directed against said first mixture flow stream and against a direction of settlement of solid particles in said mixture to maintain solids in suspension and resist settlement from said mixture in said filtration means, and

rotating said filter through said mixture and filtering said mixture on said rotating filter surface.

2. The process of claim 1, wherein said guiding plate comprises a pair of spaced-apart plate members, each of said plate members being spaced from and substantially parallel to said sidewall of said trough and spaced from said filter surface, said process comprising feeding said first mixture between said plate members downwardly into said mixture contained in the trough to produce the first flow stream.

3. The process of claim 2, wherein said plate members extend below said surface of the mixture contained in said trough, and said process comprises feeding said first mixture between said plate members to prevent disturbing said surface of the mixture contained in said trough.

4. The process according to claim 1, comprising withdrawing a portion of said first mixture through an overflow outlet or through a discharge outlet below said surface of said first mixture in said filtration means to produce said second movement stream.

5. The process according to claim 4, comprising recycling a portion of the first mixture from the overflow outlet or through said discharge outlet to said supply.

6. The process according to claim 4, comprising providing said trough with said discharge outlet at a lowest point and withdrawing a portion of the mixture from said lowest point of said trough through said discharge outlet.

7. The process according to claim 1, wherein said filtration device includes an impeller in said trough, and wherein said process comprises actuating said impeller to produce said second movement stream of the mixture.

8. The process of claim 7, wherein said filtration device includes a disc filter and a guide plate positioned between said impeller and an outer circumference of said disc filter, said guide plate having sidewalls extending substantially parallel to opposite sides of said disc filter, and said process comprising producing said second flow movement stream between said trough and said guide plate.

9. The process according to claim 1, wherein said filtration device includes an injection nozzle positioned below the surface of the mixture in said trough, and wherein said process comprises injecting a second solid-liquid mixture into said mixture in said trough to produce said second movement stream.

10. The process according to claim 9, wherein said injection nozzle is positioned below said guiding plate, and said process comprises injecting said second mixture to produce said second movement stream upwardly toward said guiding plate.

11. The process of claim 1, comprising applying a pressure above atmospheric pressure to a surface of said mixture in said filtration device and to said filter surface, and filtering said mixture at an elevated pressure difference.

12. The process of claim 1 wherein said rotating filter surface is selected from the group consisting of drum filters and disc filters.

13. A process for filtering a solid-liquid mixture, comprising the steps of:

providing a filtration device containing a solid-liquid mixture, said filtration device having sidewalls defining a filter trough, a rotating filter disc having filter surfaces spaced from and substantially parallel to said sidewalls, and a feed device positioned at a surface of said mixture, said feed device having a feed pipe with an elongated opening extending parallel to said surface of the mixture, and a pair of guiding plates adjacent said opening in said pipe and extending parallel to and spaced from said filter surface, and spaced from said sidewalls of said trough,

feeding a solid-liquid mixture through said feed pipe and downwardly between said guiding plates into said mixture contained in the trough and producing a first downward flow stream in the mixture in the trough and in a direction substantially parallel to the filter surfaces,

producing a second upward flow stream in the mixture and directing the second flow stream against the first flow stream and substantially parallel to the filter surface to resist settlement of solids in the trough, and

rotating said filter disc whereby said filter surfaces rotate substantially parallel to said first and second flow steams to filter said mixture.

14. The process of claim 13, wherein said filtration device comprises a plurality of parallel rotating filter discs, and a plurality of said feed pipes and guiding plates, one of said feed pipes and guiding plates being positioned adjacent each filter surface of each filter disc, wherein said process comprises,

feeding said first mixture through each of said feed pipes and between said guiding plates and producing a first flow stream substantially parallel to and adjacent each filter surface of said filter discs, and

producing a plurality of said second flow streams directed upwardly against said first flow streams.

15. The process of claim 13, wherein said filtration device comprises a pair of said feed devices, a first of said feed devices being positioned adjacent a first side of said filter disc and a said second of said feed devices positioned adjacent a second side of said filter disc.

16. The process of claim 15, wherein said filtration device includes an injection nozzle positioned on each side of said filter disc below the surface of said mixture in the trough, wherein said process comprises injecting said mixture through said injection nozzles into said trough to produce a second upward flow stream on each side of said filter disc.

17. The process according to claim 13, comprising diverting said second flow stream of said mixture in said trough into at least two flow streams directed upwardly against the first flow movement stream.

18. The process of claim 13, comprising directing said second flow stream toward said guiding plates.

19. The process of claim 13, comprising providing a flow pipe and guide means in said trough and producing said second flow stream through said flow pipe and against said guide means for redirecting said second flow stream toward said filter disc and said first flow stream.

20. The process of claim 13, wherein said filtration device includes an injection nozzle positioned below the surface of said mixture in said trough, wherein said process further comprises directing said injection nozzle toward said feed device and injecting said mixture into said trough to produce said second flow stream.

21. The process of claim 20, wherein said injection nozzle includes an outlet opening having a length extending substantially parallel to said feed device, for producing said second flow stream substantially along a length of said feed device.