FILTRATION APPARATUS AND METHOD

• US 3,679,052 A
• Filed: 03/27/1970
• Issued: 07/25/1972
• Est. Priority Date: 03/27/1969
• Status: Expired due to Term

• Current Assignee: Jean-Jacques Asper
• Original Assignee: Jean-Jacques Asper
• Inventors: Asper, Jean-Jacques
• Primary Examiner(s): Adee, John
• Application Number:
  US05/025,169
• Time in Patent Office: 851 Days
• Field of Search: 210/75,193,67,82,195,295,411
• US Class Current: 210/777
• CPC Class Codes: B01D 21/0012 Settling tanks making use of filters, e.g. by floating layers of particulate material
• CPC Class Codes: B01D 21/02 Settling tanks with single outlets for the separated liquid
• CPC Class Codes: B01D 21/30 Control equipment
• CPC Class Codes: B01D 21/34 Controlling the feed distribution; Controlling the liquid level ; Control of process parameters
• CPC Class Codes: B01D 2201/287 Filtering elements with a vertical or inclined rotation or symmetry axis
• CPC Class Codes: B01D 29/15 arranged for inward flow filtration
• CPC Class Codes: B01D 29/605 by level measuring
• CPC Class Codes: B01D 29/6484 with a translatory movement with respect to the filtering element
• CPC Class Codes: B01D 29/661 by using gas-bumps
• CPC Class Codes: B01D 29/668 with valves, e.g. rotating valves for coaxially placed filtering elements
• CPC Class Codes: B01D 37/00 Processes of filtration processes specially adapted for filtering gases B01D46/00
• CPC Class Codes: B01D 37/02 Precoating the filter medium; Addition of filter aids to the liquid being filtered devices for feeding reagents C02F1/685 and sub-groups; filter aids
• CPC Class Codes: B01D 37/04 Controlling the filtration

Abstract

A pressure filter and a method of filtering of the type employing a particulate filter aid may be operated substantially continuously through an operating cycle composed of a cleaning stage of short duration, say on the order of 4 or 5 seconds, in which the filter aid layer and accumulated filter cake are purged from an open-work, supporting filter element, a coating stage in which a new layer of filter aid is formed on the filter element and involving a time of about 10 seconds, and a filtering stage. A rapid coating of the element with a layer of filter aid is facilitated by using a filter aid having a mean particle size approximately equal to the size of the openings in the support. The filter aid purged from the filter chamber during each cleaning cycle is recovered by conducting the mixture of filter aid, impurities, and raw liquid from the filter, upon cleaning, to a holding tank and then recycling, over a period of time or continuously, the mixture from the holding tank through a separator. The filter aid fraction is separated and conducted into a filter aid storage tank for use during the next cycle, make-up filter aid and filtrate being added to the filter aid storage tank as required. The level in the holding tank is reduced just before each cleaning to the extent required to provide a capacity sufficient to receive the mixture purged from the filter during cleaning. Continuous filtrate output may be achieved by accumulating filtrate in a storage reservoir during the filtering stage (for delivery) during the cleaning and filter aid coating stages.

Claims

2. A pressure filter according to claim 1 and further comprising a receptacle for storing the filter aid in suspension in a liquid, means for selectively supplying filter aid from the storage receptacle to the inlet of the filter chamber, a holding tank, means for conducting material from the cleaning outlet of the filter chamber to the holding tank, means for separating a mixture of filter aid liquid and the impurities extracted upon filtering, such mixture constituting the aforesaid material, into a first fraction containing predominantly filter aid and a second fraction containing predominantly impurities, means for supplying the material from the holding tank to the separating means, means for supplying the first fraction from the separating means to the filter aid storage receptacle, and means for supplying the second fraction from the separating means to the holding tank.

3. A pressure filter according to claim 1 wherein the means for controlling the discharge valve provides a partial open position in which the pressures on either side of the open-work partition are substantially balanced.

4. A pressure filter according to claim 2 wherein the separating means includes a dynamic separator.

5. A pressure filter according to claim 4 wherein the dynamic separator is a cyclone separator.

6. A pressure filter according to claim 2 and further comprising means for supplying makeup filter aid from a source thereof to the filter aid storage tank.

7. A pressure filter according to claim 2 and further comprising means for selectively supplying filtrate from the outlet of the filter chamber to the filter aid storage tank.

8. A pressure filter according to claim 2 and further comprising conduit means coupled to the filter chamber filtrate outlet for selectively discharging effluent from the outlet section of the chamber to waste.

9. A pressure filter according to claim 2 and further comprising means for conducting overflow from the filter aid storage tank to the holding tank, thereby to retain any excess of the suspension of filter aid in the tank in the system.

10. A pressure filter according to claim 2 and further comprising means for selectively drawing down the level in the holding tank to a point such that it has the capacity to receive a given quantity of the mixture from the cleaning outlet of the filter chamber.

11. A pressure filter according to claim 2 and further comprising a filtrate storage reservoir connected by a branch conduit to a conduit connected to the filtrate outlet of the filter chamber, valve means upstream, relative to the direction of flow of filtrate frOm the filter, from the branch conduit for selectively cutting of flow from the filter to the reservoir, and valve means downstream from the branch conduit for restricting the flow of filtrate from the reservoir.

12. A method of filtering liquids under pressure through a filter layer composed of particulate filter aid material in a pressure filter having a filter chamber enclosing an open-work partition having openings of given size and having an inlet and an outlet separated by said partition;

means defining a gauged throttling passage associated with said inlet for connection thereof to a source of the liquid to be filtered under pressure while restricting the rate of inflow of said liquid to said chamber;

means defining a filtrate reservoir in communication with said outlet, for receiving filtrate and maintaining it at a given pressure;

a cleaning outlet in communication with the filter chamber on the inlet side thereof;

a discharge valve associated with the cleaning outlet; and

means for successively operating the valve to provide a rapid cyclic operation thereof including a closed stage for filtering and an opened stage for producing a sudden pressure drop in the liquid on the inlet side of the chamber to a value below said given pressure in the filtrate reservoir effective to cause an abrupt reversal of the pressure gradient across the partition and a removal of the layer of filter aid and impurities from the partition;

said method comprising the steps of;

(a) forming said filter layer during a brief period at the beginning of said closed stage of the discharge valve by choosing said filter aid material so that the mean particle size thereof is substantially equal to the size of the openings of said partition and by rapidly injecting into a stream of liquid flowing from said inlet to said outlet a given amount of said material corresponding to a filter layer of given thickness, such that substantially all the injected filter aid particles are carried by said stream to said partition and are retained thereby to form said layer, while the liquid stream substantially free of filter aid particles flows to said outlet;

(b) thereafter filtering said liquid under pressure through said filter layer during said closed stage of the discharge valve while conducting the filtrate from said outlet partially to said reservoir;

(c) after using said layer for filtering, providing sudden removal thereof from the partition during said opened stage of the discharge valve and rapid discharge of the material of the used layer through said cleaning outlet; and

(d) cyclically repeating steps (a), (b) and (c) during the whole operation of said pressure filter, such as to provide substantially continuous filtrate delivery, with prolonged filtration during each step (b) and brief interruptions thereof during steps (c) and (a) for providing rapid renewal of the filter layer.

13. A method of filtering according to claim 12 and further comprising the step of supplying make-up filter aid from a source thereof to the filter aid storage tank.

14. A method of filtering according to claim 12 and further comprising the step of selectively supplying filtrate from the outlet of the filter chamber to the filter aid storage tank at some time during the normal filtering step of an operating cycle.

15. A method of filtering according to claim 12 wherein the outflow from the outlet section of the filter chamber is discharged during step (a) of an operating cycle to a place separate from the place to which the filtrate is normally discharged.

16. A method of filtering according to claim 12 wherein the overflow from the filter aid storage tank is conducted to the holding tank, thereby to retain any excess of the filter aid therein in the system.

17. A method of filtering according to claim 12 and further comprising the step of drawing down prior to step (c) in each cycle the level in the holding tank to a point such that it has the capacity to receive the quantity of the filter aid layer, liquid and imPurities discharged from the cleaning outlet of the filter chamber.

18. A method of filtering according to claim 12 and further comprising the step of accumulating a quantity of filtrate in a filtrate storage reservoir at some time during step (b) of a cycle, and releasing at least a part of the accumulated filtrate from the reservoir during step (c) of each cycle.

19. A method of filtering according to claim 20 wherein a portion of the filtrate accumulated in the storage reservoir is released during step (a) of each cycle.

20. A method of filtering according to claim 19 wherein the rate of filtrate flow from the reservoir during step (a) is controlled to a value less than the rate of filtrate flow during step (b).

21. A method according to claim 12 and further comprising the steps of conducting the material removed through the cleaning outlet during step (c) to a holding tank, separating the filter aid from the impurities by rapidly circulating the contents of the holding tank through a separator during at least a portion of the time that step (b) is carried out, and storing the separated filter aid in a storage tank for reuse in a subsequent cycle.