CA1042358A

CA1042358A - Filtration methods and apparatus

Info

Publication number: CA1042358A
Application number: CA205,268A
Authority: CA
Inventors: Michael J. Bykowski; Lloyd Ewing
Original assignee: Water Pollution Control Corp
Current assignee: Water Pollution Control Corp
Priority date: 1974-07-22
Filing date: 1974-07-22
Publication date: 1978-11-14

Abstract

FILTRATION METHODS AND APPARATUS
ABSTRACT OF THE DISCLOSURE
Filtration in an internal rotary filter system is improved by externally impacting the filter screen as it rotates with a programmed spray of liquid that is varied from a relatively low to a relatively high pressure. In certain instances, this programmed spray is controlled by an electric timer circuit so arranged that the high pressure spray is on for a period of time which does not too unduly burden the system with fluid, but which is sufficient period of time to prevent slime formation on the screen. This can for instance keep the screen free of slime when no germicidal agent (e.g. Cl2) is employed.

Claims

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. In the process of separating a liquid from solids in an admixture of the two by using an internal rotary filter system comprised of a rotatable hollow drum defining therewithin a filter zone, said filter zone com-municating with a liquid collection zone external to the drum through a filter medium located on the drum, and wherein separation is accomplished by presenting the admix-ture in the filter zone, rotating the drum, causing solids to adhere to the internal portion of the filter medium and causing liquid to flow through the filter medium and to said liquid collection zone, and wherein the separated solids are collected by contacting the filter medium with a fluid to dislodge the solids from the medium and cause them to collect in a solids collection zone separate from said liquid collection zone, the improvement comprising contact-ing the filter medium with the fluid cycled at at least two different finite pressures including high pressure in the range of about 60 to about 200 psig and low pressure in the range of about 15 to about 60 psig, the duration of the high pressure segment of each cycle being equal to at least about the time required for one complete revolution of said drum, and representing from about 0.5% to about 33% of the total time in each cycle whereby the combination of time, pressures and interval of each within the cycle removes substantially all solids from the filter medium without overburdening the system with fluid.

2. A process according to claim 1 wherein said admixture is contaminated with filter-fouling ingredients and said combination of pressures and time interval are sufficient to prevent any substantial amount of fouling of said filter medium.

3. A process according to claim 1 wherein said fluid is obtained from the liquid collection zone.

4. A process according to claim 3 wherein said fluid is sprayed through nozzles external of the drum and directed at an unsubmerged portion of the exterior of the drum, wherein said solids collecting zone includes collec-ting means located within the drum, below the said nozzles but above the level of liquid in said filter zone.

5. A process according to claim 4 wherein the admixture is sewage containing solids in a concentration sufficiently dilute for removal by microscreen treatment and the liquid collected in said collection zone contains less than 10 ppm solids.

6. A process according to claim 4 wherein the drum is rotated at a peripheral speed of at least about 30 feet per minute.

7. A process for separating a liquid and a solid from an admixture of the two which includes filter-fouling materials, by using apparatus including an inlet means for transmitting said admixture to a filter zone, a hollow rotatable drum means defining a filter zone therewithin, a liquid collection zone external to the drum means and com-municating with the filter zone through a filter medium located on the drum, means for rotating the drum to thereby cause solids to adhere to the internal portion of the filter medium and to cause liquid to flow through the filter medium and to said liquid collection zone, shower means for apply-ing fluid to the outer surface of said filter medium for backflushing said filter medium at a sufficient volumetric flow rate to dislodge the solids therefrom, supply means including a motor and pump means having an inlet connected with a source of filtered liquid and an outlet connected with said shower means, and solids collection means separated from said filter zone and said liquid collecting zone for collecting the dislodged solids, the improved-process which comprises: applying the fluid -in repeated cycles, which cycles include segments of operation at at least two different finite pressures, including high pressure in the range of about 60 to about 200 psig and low pressure in the range of about 15 to 60 psig, said high pressure averaging at least about 1.5 times said low pressure; and apportioning said high and low pressure segments of each cycle for providing high pressure segments which are individually equal to at least about the time required for one complete revolution of said drum and which represent from about 0.5% to about 33% of the total time in each cycle; whereby the combination of time, pressures and interval of each within the repeated cycles effectively removes solids from the filter medium over extended periods of operation without overburdening the system with fluid.

8. A process according to claim 7 wherein said filter medium is filter cloth of interwoven strands or filaments defining apertures therebetween.

9. A process according to claim 7, wherein said apparatus includes means for rotating said drum at a periph-eral speed of at least about 30 feet per minute.

10. A process according to claim 7, wherein said source of filtered liquid is said liquid collection zone.

11. A process according to claim 7 wherein the high and low pressure segments are apportioned to provide oper-ation cycles in the range of about 30 minutes to about one day.

12. A process according to claim 7 which includes applying high pressure averaging at least about 2 times said low pressure.

13. A process according to claim 7 including provi-ding high pressure segments which are individually equal to at least about the time required for three complete revolutions of said drum.

14. A process according to claim 7 including provi-ding high pressure segments which represent from about 0.5% to about 25% of the total time in each cycle.

15. A process according to claim 7 including oper-ating said motor at at least two different speeds by high speed and low speed windings in said motor which can be electrically switched to change speeds.

16. A process according to claim 15 which includes energizing the high speed and low speed windings of said motor by timer means.

17. A process according to claim 16 which includes shutting off the pump means for an incremental period of time during the cycle by said timer means and employing as the shower means self-purging nozzle means which are located externally of the drum and which are capable of purging themselves of solids when said pump means are shut off.

18. A process according to claim 17 wherein said source of filtered liquid is said liquid collection zone.

19. A process in accordance with claim 7 wherein said pump means is maintained in operation with said shower means spraying during at least 95% of each cycle.

20. In an apparatus for separating a liquid and a solid from an admixture of the two which includes an inlet means for transmitting said admixture to a filter zone, a hollow rotatable drum means defining a filter zone there-within, a liquid collection zone external to the drum means and communicating with the filter zone through a filter medium located on the drum, means for rotating the drum to thereby cause solids to adhere to the internal portion of the filter medium and to cause liquid to flow through the filter medium and to said liquid collection zone, means for applying a fluid to said filter medium to dislodge the solids therefrom, and solid collection means separated from said filter zone and said liquid collection zone for collecting the dislodged solids, the improvement including pressure controlling means for applying the fluid in cycles at at least two different finite pressures, and, during each high pressure segment of a cycle, for maintaining the higher of said pressures for at least one complete revolution of said drum.

21. An apparatus according to claim 20 wherein said pressure controlling means includes pump means having at least two different speeds for varying the pressure at which said fluid is applied.

22. An apparatus according to claim 21 wherein said pressure controlling means also includes timer means for controlling the speed at which said pump means operates.

23. An apparatus according to claim 22 wherein said timer means includes means for shutting off the pump means for an incremental period of time during the cycle and said means for applying said fluid are self-purging nozzle means which are located externally of the drum and which are capable of purging themselves of solids when said pump means are shut off.

24. An apparatus according to claim 23 wherein the inlet of said pump means is connected to the liquid collec-ting means.

25. An apparatus according to claim 20 wherein the inlet means includes an inlet tank connected to a conduit which communicates with the filter zone, an overflow tank not in flow communication with said filter zone and an overflow weir means connecting said inlet tank with said overflow tank such that if the admixture admitted to said inlet tank reaches a preselected level, any excess there-over will flow via said overflow weir and into said over-flow tank, thereby by-passing the filter zone.

26. An apparatus according to claim 25 wherein the height of the overflow weir is sufficiently low such that the admixture in the filter zone is prevented from over-flowing into the solids collection means.

27. In an apparatus for separating a liquid and a solid from an admixture of the two which includes filter-fouling materials, said apparatus including an inlet means for transmitting said admixture to a filter zone, a hollow rotatable drum means defining a filter zone therewithin, a liquid collection zone external to the drum means and com-municating with the filter zone through a filter medium located on the drum, means for rotating the drum to thereby cause solids to adhere to the internal portion of the filter medium and to cause liquid to flow through the filter medium and to said liquid collection zone, shower means for applying fluid to the outer surface of said filter medium for backflushing said filter medium at a sufficient volumetric flow rate to dislodge the solids therefrom, supply means including a motor and pump means having an inlet connected with a source of filtered liquid and an outlet connected with said shower means, and solids collection means separated from said filter zone and said liquid collecting zone for collecting the dislodged solids, the improvement characterized in that: said motor is provided with means for operating said motor at at least two different speeds for applying the fluid in repeated cycles, which cycles include at least two different finite pressures, including high pressure in the range of about 60 to about 200 psig and low pressure in the range of about 15 to about 60 psig, said high pressure averaging at least about 1.5 times said low pressure; and said apparatus includes means for appor-tioning the high and low pressure segments of each cycle for providing high pressure segments which are individually equal to at least about the time required for one completa revolution of said drum and which represent from about 0.5%
to about 33% of the total time in each cycle; whereby the combination of time, pressures and interval of each within the repeated cycles effectively removes solids from the filter medium over extended periord of operation without overburdening the system with fluid.

28. Apparatus according to claim 27 wherein said filter medium is filter cloth of interwoven strands or fila-ments defining apertures therebetween.

29. Apparatus according to claim 27, including means for rotating said drum at a peripheral speed of at least about 30 feet per minute.

30. Apparatus according to claim 27 wherein said source of filtered liquid is said liquid collection zone.

31. Apparatus according to claim 27 wherein said means for apportioning the high and low pressure segments provides operating cycles in the range of about 30 minutes to about 1 day.

32. Apparatus according to claim 27 wherein said means for operating said motor at at least two different speeds provides high pressure averaging at least about 2 times said low pressure.

33. Apparatus according to claim 27 wherein said means for apportioning provides high pressure segments which are individually equal to at least about the time required for three complete revolutions of said drum.

34. Apparatus according to claim 27 wherein said means for apportioning provides high pressure segments which represent from about 0.5% to about 25% of the total time in each cycle.

35. Apparatus according to claim 27 wherein said means for operating said motor at at least two different speeds includes high speed and low speed windings in said motor-which can be electrically switched to change speeds.

36. Apparatus according to claim 35 which includes timer means for energizing the high speed and low speed windings of said motor.

37. Apparatus according to claim 36 in which the timer includes means for shutting off the pump means for an incremental period of time during the cycle and said shower means are self-purging nozzle means which are located externally of the drum and which are capable of purging themselves of solids when said pump means are shut off.

38. Apparatus according to claim 37 wherein said source of filtered liquid is said liquid collection zone.

39. Apparatus according to claim 27 wherein said apportioning means is adapted for maintaining said pump means in operation with said shower means spraying during at least 95% of each cycle.