Cleaning of filters

• US 4,935,143 A
• Filed: 03/10/1988
• Issued: 06/19/1990
• Est. Priority Date: 07/11/1986
• Status: Expired due to Fees

• Current Assignee: Memtec Ltd. (Danaher Corporation)
• Original Assignee: Memtec Ltd. (Danaher Corporation)
• Inventors: Fabig, Marcus J., Wyatt, Kerrie, Kopp, Clinton V., Streeton, Robert J. W.
• Primary Examiner(s): Spear, Frank
• Application Number:
  US07/191,164
• Time in Patent Office: 831 Days
• Field of Search: 210/500.23, 210/636, 210/321.69, 210/410, 210/412
• US Class Current: 210/636
• CPC Class Codes: B01D 2313/48 Mechanisms for switching between regular separation operations and washing
• CPC Class Codes: B01D 2321/04 Backflushing
• CPC Class Codes: B01D 2321/18 Use of gases
• CPC Class Codes: B01D 63/02 Hollow fibre modules
• CPC Class Codes: B01D 65/02 Membrane cleaning or sterilisation ; Membrane regeneration

Abstract

A filter (10) has a shell (11) within which there is a bundle of microporous fibres (12). Pressurized feed suspension is introduced through inlet (15) and passes over the external walls of the fibers (12) with the clarified liquid being drawn from the lumens of the fibres (12) through outlet port (16) and the concentrated ffee being discharged through outlet (17). The solids retained within the shell are removed by a gaseous backwash cycle in which pressurized gas is introduced through the lumens and passes through the wall of the fibres (12) to dislodge solids retained on or in the fibre walls. The gaseous cleaning step is enhanced by varying the pressure within the housing (11) of the filter (10) while the gas is being introduced into the filter.

Claims

1. A method of operating a filter having elastic, microporous, hollow fibers within a shell or housing having a feed inlet thereto and a feed outlet therefrom comprising the steps of:

(i) introducing a liquid suspension feedstock through the feed inlet to the shell or housing and directing said feedstock to the outer surface of the fibers including;

(a) passing some of said feedstock through the walls of the fibers so as to be drawn from the fiber lumens as a filtrate or permeate,

(b) retaining some of the solids in said feedstock on or in the pores of the fibers, and discharging the non-retained solids through a feed outlet from the shell or housing with a remainder of said feedstock,

(ii) periodically cleaning away the retained solids by;

(a) introducing a pressurized gas into the fiber lumens which passes through the walls of the fibers to dislodge the retained solids, and,

(b) varying the pressure within the shell while the gas is being introduced into the lumens.

3. A method according to claim 1 or claim 2 wherein the pressure within the shell is varied during cleaning by increasing the pressure within the shell above the normal gaseous cleaning pressure and then returning the pressure to the normal gaseous cleaning pressure.

4. A method according to claim 3 wherein the feed flow is maintained during the backwash and the pressure increase is achieved by stopping the outflow of feed and the return to the normal gaseous cleaning pressure is achieved by recommencing flow of feed in the reverse direction.

5. A method according to claim 4 wherein the reversal of feed flow is repeated during gaseous cleaning.

6. A method according to claim 3 wherein the feed flow is maintained during the backwash and the pressure increase is achieved by terminating the outflow of feed and the return to normal gaseous cleaning pressure is achieved by resuming outflow of feed.

7. A method according to claim 6 wherein the termination and resumption of feed outflow is repeated during gaseous cleaning.

8. A method according to claim 3 wherein the pressure variation cycle is repeated during gaseous cleaning.

9. A method according to claim 3 wherein the inflow of feed is terminated before commencing the gaseous backwash.

10. A method according to claim 9 wherein the shell outlet is closed and further including the steps of:

(a) introducing a second gas into the shell side of the fibers at a pressure substantially the same as the pressure of the lumen cleaning gas,

(b) terminating the flow of the second gas,

(c) opening one of the feed inlet and the feed outlet to release the gas pressure on the shell side of the fibers and to allow the lumen gas to escape substantially uniformly through the fiber walls.

11. A method according to claim 9 and including the step of introducing a second gas through the shell inlet and wherein the pressure increase is achieved by stopping the outflow of the second gas and the return to the normal gaseous cleaning pressure is achieved by recommencing the flow of the second gas in the reverse direction.

12. A method according to claim 11 wherein termination and reversal of the second gas flow is repeated during gaseous cleaning.

13. A method according to claim 12 wherein the second gas is a high pressure gas.

14. A method according to claim 11 wherein the second gas is a high pressure gas.

15. A method according to claim 14 wherein the second gas is a low pressure gas.

16. A method according to claim 11 wherein the second gas is a low pressure gas.

17. A method according to claim 9 and including the step of introducing a second gas through the shell inlet and wherein the pressure increase is achieved by terminating the outflow of the second gas and the return to normal gaseous cleaning pressure is achieved by resuming the outflow of the second gas.

18. A method according to claim 17 wherein the termination and resumption of second gas outflow is repeated during gaseous cleaning.

19. A method according to claim 18 wherein the second gas is a high pressure gas.

20. A method according to claim 18 wherein the second gas is a low pressure gas.

21. A method according to claim 17 wherein the second gas is a high pressure gas.

22. A method according to claim 17 wherein the second gas is a low pressure gas.

23. A method according to claim 22 and including the step of introducing a second gas through the shell inlet and wherein the pressure reduction is achieved by terminating the inflow of the second gas and the return to normal gaseous cleaning pressure is achieved by recommencing the flow of the second gas in the reverse direction.

24. A method according to claim 23, wherein the termination and reversal of the second gas flow is repeated during gaseous cleaning.

25. A method according to claim 24 wherein the second gas is a high pressure gas.

26. A method according to claim 24 wherein the second gas is a low pressure gas.

27. A method according to claim 23 wherein the second gas is a high pressure gas.

28. A method according to claim 23 wherein the second gas is a low pressure gas.

29. A method according to claim 1 or claim 2 wherein the pressure within the shell is varied during cleaning by decreasing the pressure within the shell below the normal gaseous cleaning pressure and then returning the pressure to the normal gaseous cleaning pressure.

30. A method according to claim 29 wherein the feed flow is maintained during the backwash and the pressure reduction is achieved by terminating the inflow of feed and the return to normal gaseous cleaning pressure is achieved by resuming inflow of feed.

31. A method according to claim 30, wherein the termination and resumption of feed inflow is repeated during gaseous cleaning.

32. A method according to claim 24 wherein the pressure variation cycle is repeated during gaseous cleaning.

33. A method according to claim 29 wherein the feed flow is maintained during the backwash and the pressure reduction is achieved by terminating the inflow of feed and the return to normal gaseous cleaning pressure is achieved by recommencing flow of feed in the reverse direction.

34. A method according to claim 33 wherein the termination and resumption of feed is repeated during gaseous cleaning.

35. A method according to claim 29 wherein the inflow of feed is terminated before commencing the gaseous backwash.

36. A method according to claim 35 and including the step of introducing a second gas through the shell inlet and wherein the pressure reduction is achieved by terminating the inflow of the second gas and the return to normal gaseous cleaning pressure is achieved by recommencing flow of the second gas.

37. A method according to claim 36 wherein the second gas is a high pressure gas.

38. A method according to claim 36 wherein the termination and resumption of outflow is repeated during gaseous cleaning.

39. A method according to claim 38 wherein the second gas is a low pressure gas.

40. A method according to claim 38 wherein the second gas is a high pressure gas.

41. A method according to claim 38 wherein the second gas is a low pressure gas.

42. A method according to claim 35 wherein the shell outlet is closed and further including the steps of:

(a) introducing a second gas into the shell side of the fibers at a pressure substantially the same as the pressure of the lumen cleaning gas,

(b) terminating the flow of the second gas,

(c) opening one of the feed inlet and the feed outlet to release the gas on the shell side of the fibers and to allow the lumen gas to escape substantially uniformly through the fiber walls.

43. A method according to claim 1 and including the step of pressurizing the fibers after the completion of the backwash and the releasing the pressure to remove trapped air from the pores of the fibers.

44. A method according to claim 43 wherein the step of pressurizing the fibers is carried out while lumen flow is blocked.

45. A method according to claim 44 wherein the lumen flow is blocked in a pulsing fashion.

46. A method according to claim 45 wherein the step of pressurizing the fibers is carried by applying a hydraulic pressure to the feed side of the fibers.

47. A method according to claim 45 wherein the step of pressurizing the fibers is carried out by applying a hydraulic pressure to the feed side of the fibers.

48. A method according to claim 43 wherein the step of pressurizing the fibers is carried out by applying a hydraulic pressure to the feed side of the fibers.

49. A method according to claim 43 wherein the step of pressurizing the fibers is carried out by applying a hydraulic pressure to the feed side of the fibers.

50. A method according to claim 1 wherein the fiber lumens are drained before commencement of the gaseous backwash.

51. A method according to claim 1 wherein the shell is drained before commencement of backwash.

52. A method according to claim 1 wherein the introduction of the pressurized gas includes the steps of:

(a) initially applying the gas at a pressure below the bubble point of the walls of the fibers so as to displace any liquid from the fiber lumens,

(b) closing the feed inlet to and the feed outlet from the shell,

(c) increasing the pressure of the gas above the bubble point of the walls of the fibers, and,

(d) opening the feed inlet and outlet to allow the gas to escape substantially the uniformly through the fiber walls.

53. A method according to claim 1 wherein the filter is a cross-flow filter.

54. A method according to claim 1 wherein the filter is operated in a dead-end filtering mode with no outflow of feed and solids from the shell during the dead-end filtration.

55. A method according to claim 1 wherein during the pressure variation step, feed is introduced into the shell between the shell inlet and outlet and is discharged through both the shell inlet and shell outlet to an external collection point.

2. A method of operating a filter having a plurality of elastic, microporous hollow fibers with a shell or housing having a feed inlet thereto and a feed outlet therefrom, comprising the steps of:

(i) introducing a liquid suspension feedstock into the shell or housing and applying said feedstock to the outer surface of the fibers including;

(a) passing some of said feedstock through the walls of the fibers so as to be drawn from the fiber lumens as a filtrate or permeate,

(b) retaining some of the solids in said feedstock on or in the pores of the fibers, and removing the non-retained solids from the shell with a remainder of said feedstock,

(ii) cleaning away the retained solids by;

(a) applying to the fiber lumens a gas at a pressure sufficient to stretch substantially all of the pores, followed by,

(b) maintaining the flow of gas through the lumens for a time period sufficient to drive the liquid from the pores having a bubble point below the pressure of the gas so as to wash out any solids in those pores and to dislodge any solids retained on the outer surface of the fibers such that the washed and dislodged solids are removed from the shell to an external collection point, and,

(c) varying the pressure within the shell whilst the pressurized gas is being introduced into the lumens.

56. A filter system comprising:

(a) a shell or housing,

(b) a plurality of elastic, microporous hollow fibers within the shell,

(c) a feed inlet to the shell,

(d) a feed outlet from the shell,

(e) a filtrate outlet from the shell,

(f) valve means for introducing a liquid suspension feedstock through the feed inlet to the shell and for directing said feedstock to the outer surface of the fibers such that;

(i) some of said feedstock passes through the walls of the fibers to be drawn from the fiber lumens as a filtrate or permeate and to be discharged through the filtrate outlet,

(ii) some of the solids in said feedstock are retained on or in the pores of the fibers, with the non-retained solids being discharged through the feed outlet from the shell or housing with the remainder of said feedstock,

(g) valve means for controlling the outflow through the shell outlet,

(h) valve means for introducing a pressurized gas into the fiber lumens which passes through the walls of the fibers to dislodge the retained solids, and,

(i) control means for varying the pressure within the shell while the gas is being introduced into the lumens.

58. A filter system according to claim 56 or claim 57 wherein the control means is adapted to actuate the valve means to increase the pressure within the shell above the normal gaseous cleaning pressure and to return the pressure to the normal gaseous cleaning pressure.

59. A filter system according to claim 58 wherein the control means is adapted to actuate the shell outlet valve means to close the shell outlet and then to open the shell outlet.

60. A filter system according to claim 59 wherein the control means is adapted to actuate the shell outlet valve means to close the shell outlet and wherein the system further includes valve means for reversing the flow of feed through the shell and the control means is adapted to actuate the reversing valve means to re-establish reverse flow of feed through the shell.

61. A filter system according to claim 59 wherein the control means is adapted to actuate the shell inlet valve means to close the shell inlet and wherein the system further includes valve means for reversing the flow of feed through the shell and the control means is adapted to actuate the reversing valve means to reestablish reverse flow of feed through the shell.

62. A filter system according to claim 56 or claim 57 wherein the control means is adapted to actuate the valve means to decrease the pressure within the shell below the normal gaseous cleaning pressure and to return the pressure to the normal gaseous cleaning pressure.

63. A filter system according to claim 62 wherein the control means is adapted to actuate the shell inlet valve means to close the shell inlet valve and to open the shell inlet.

64. A filter system as claimed in either claim 56 or claim 57 and including valve means for introducing a second gas through the shell inlet.

65. A filter system according to claim 64 wherein the control means is adapted to close the shell outlet to effect a pressure increase in the shell and to open the shell outlet to re-establish outflow through the shell outlet.

66. A filter system, according to claim 65 and further including valve means for reversing the flow of the second gas through the shell and wherein the control means is adapted to operate the reversing valve means.

67. A filter system according to claim 66 and further including valve means for reversing the flow of the second gas through the shell and wherein the control means is adapted to operate the reversing valve means.

69. A filter system according to claim 64 wherein the control means is adapted to close the shell inlet to effect a pressure decrease in the shell and to open the shell inlet to re-establish inflow of the second gas.

70. A filter system according to claim 64 and including means for closing off the filtrate flow.

57. A filter system comprising:

(a) a shell or housing,

(b) a plurality of elastic, microporous hollow fibers within the shell,

(c) a feed inlet to the shell,

(d) a feed outlet from the shell,

(e) a filtrate outlet from the shell,

(f) valve means for introducing a liquid suspension feedstock through the feed inlet to the shell and for applying said feedstock to the outer surface of the fibers such that;

(i) some of said feedstock passes through the walls of the fibers to be drawn from the fiber lumens as a filtrate or permeate and to be discharged through the filtrate outlet,

(ii) some of the solids in said feedstock are retained on or in the pores of the fibers, with the non-retained solids being removed from the shell with the remainder of said feedstock,

(g) valve means for controlling the outflow through the shell outlet,

(h) valve means for introducing a pressurized gas through the fiber lumens which passes through the walls of the fibers to wash out at least some of the retained solids and then,

(i) valve means for introducing through the fiber lumens a pressurized gas which passes through the walls of the fibers and stretches elastically at least some of the pores to dislodge any solids retained in those pores and which washes the external walls of the fibers, the gas being applied at a pressure which is sufficient to overcome the resistance to gas flow of the surface tension of the continuous phase of the control filtrate within the pores of the membrane, and,

(j) means for varying the pressure within the shell whilst the pressurized gas is being introduced into the lumens.

68. A filter system according to 66 and including means for closing off the filtrate flow.