Adaptive filter concentrate flow control system and method

• US 4,879,040 A
• Filed: 12/22/1988
• Issued: 11/07/1989
• Est. Priority Date: 11/15/1984
• Status: Expired due to Term

• Current Assignee: Baxter International Inc.
• Original Assignee: Baxter International Inc.
• Inventors: Clark, Ronald L., Schoendorfer, Donald W., Prince, Paul R., Ford, Michael G.
• Primary Examiner(s): Spear, Frank
• Application Number:
  US07/291,413
• Time in Patent Office: 320 Days
• Field of Search: 210/651, 210/433.2, 210/90, 210/85, 210/929, 210/637, 210/87, 604/4, 604/5, 604/6
• US Class Current: 210/637
• CPC Class Codes: A61M 1/262 rotating
• CPC Class Codes: A61M 1/34 Filtering material out of the blood by passing it through a membrane, i.e. hemofiltration or diafiltration
• CPC Class Codes: A61M 1/3403 Regulation parameters
• CPC Class Codes: A61M 1/341 by measuring the filtrate rate or volume
• CPC Class Codes: A61M 2205/3331 Pressure; Flow
• CPC Class Codes: A61M 2205/3334 Measuring or controlling the flow rate
• CPC Class Codes: B01D 2313/243 Pumps
• CPC Class Codes: B01D 2313/90 Additional auxiliary systems integrated with the module or apparatus
• CPC Class Codes: B01D 2313/903 Integrated control or detection device
• CPC Class Codes: B01D 2315/02 Rotation or turning
• CPC Class Codes: B01D 61/22 Controlling or regulating
• CPC Class Codes: B01D 63/16 Rotary, reciprocated or vibrated modules

Abstract

An adaptive filter concentrate flow control system and method includes a filter system, a pumping system driving feed fluid, concentrate and filtrate flowing through the filter system and a flow control system controlling the pumping system to maintain optimum filtrate flow rates along a control curve in a transmembrane pressure--feed fluid rate--filtrate flow rate three dimensional space. Actual sensed operating point data is used to locate the control curve so as to assure an optimized filtrate flow rate at which reversible blocking of the membrane has begun to occur without irreversible plugging. The system is advantageously employed to control and maximize the flow of plasma in a plasmapheresis system.

Claims

1. A fluid flow control system for controlling a flow of filtrate through a filter system having a filter membrane with a predictable transmembrane pressure-filtrate flow rate relationship when the filter system is operated under nonobstructing operating conditions, the control system comprising:

a flow regulating system coupled to control flows of feed fluid, concentrate fluid and filtrate fluid in the filter system in response to at least one control signal;

a pressure sensor disposed to sense and generate indications of transmembrane pressure in the filter system; and

a fluid flow control system coupled to receive an indication of transmembrane pressure from the pressure sensor and generate the at least one control signal to control the flow regulating system in response thereto maintain the transmembrane pressure at an intersection with a particular curve having a shape conforming to the predictable transmembrane pressure-filtrate flow rate relationship and a pressure offset from the received pressure indication by a predetermined positive pressure difference.

2. The fluid flow control system according to claim 1 above, wherein the predictable transmembrane pressure-filtrate flow rate relationship is a substantially linear relationship in which pressure increases with filtrate flow rate.

3. The fluid flow control system according to claim 1 above, wherein the fluid flow control system is operable to collect data defining an actual nonobstructing transmembrane pressure-filtrate flow rate operating point during each filtration cycle and to determine the particular control curve in response to the collected actual operating point data.

4. The fluid flow control system according to claim 2 above, wherein the fluid flow control system is operable to determine an actual nonobstructing transmembrane pressure-filtrate flow rate operating point during each filtration cycle and to determine the predictable transmembrane pressure-filtrate flow rate relationship as a straight line passing through the determined actual operating point with a predetermined slope.

5. The fluid flow control system according to claim 1 above, wherein the fluid flow control system is operable to determine a plurality of actual nonobstructing transmembrane pressure-filtrate flow rate operating points dependent upon actual feed fluid, fluid pumping system, and filter membrane characteristics encountered during each filtration cycle and to determine the particular control curve in response to the determined actual operating points.

6. The fluid flow control system according to claim 2 above, wherein the fluid flow control system is operable to determine a plurality of actual nonobstructing transmembrane pressure-filtrate flow rate operating points dependent upon actual feed fluid, fluid pumping system, and filter membrane characteristics encountered during each filtration cycle and determine the predictable transmembrane pressure-filtrate flow relationship as a straight line passing through the determined actual operating points.

7. The fluid flow control system according to claim 1 above, wherein the flow regulating system includes a concentrate pump coupled to pump concentrate fluid from the filter system and the at least one control signal from the fluid flow control system controls the pumping system by controlling the flow rate of the concentrate pump.

8. The fluid flow control system according to claim 1 above, wherein the flow regulating system includes a feed fluid pump operating to pump feed fluid to the filter system and a concentrate pump coupled to pump concentrate fluid from the filter system and wherein the at least one control signal from the fluid flow control system controls the pumping system by controlling the flow rate of the concentrate pump relative to the flow rate of the feed fluid pump.

9. The fluid flow control system according to claim 1 above, wherein the flow regulating system includes a feed fluid pump operating to pump feed fluid to the filter system and a filtrate pump coupled to pump filtrate fluid from the filter system and wherein the at least one control signal from the fluid flow control system controls the pumping system by controlling the flow rate of the filtrate pump relative to the flow rate of the feed fluid pump.

23. A fluid flow control system according to claim 1 wherein the particular curve has a substantially equal pressure offset at each of a plurality of different filtrate flow rates from a prediction curve which passes through a pressure point indicated by the received pressure indication.

24. A fluid flow control system according to claim 1 wherein the particular curve has substantially no rotation relative to a prediction curve representing the predictable transmembrane pressure-filtrate flow rate relationship.

25. A fluid flow control system according to claim 1 wherein the particular curve is rotated relative to a prediction curve representing the predictable transmembrane pressure-filtrate flow rate relationship.

27. A fluid flow control system according to claim 1 wherein the predetermined pressure difference is substantially equal at each of a plurality of different filtrate flow rates.

10. A fluid flow control system comprising:

a filter system having a filter membrane with a predictable transmembrane pressure-filtrate flow rate relationship when the filter system is operated under nonobstructing operating conditions;

a flow regulating system coupled to control flows of feed fluid, concentrate fluid and filtrate fluid in the filter system;

a pressure sensor disposed to sense and generate indications of transmembrane pressure in the filter system; and

a fluid flow control system coupled to receive an indication of transmembrane pressure and control the flow regulating system in response thereto to maintain the transmembrane pressure at an intersection with a particular control curve having a shape conforming to the predictable transmembrane pressure-filtrate flow rate relationship and a pressure offset from the indicated transmembrane pressure by a predetermined pressure difference.

28. A fluid flow control system according to claim 10 wherein the particular control curve is rotated relative to a curve representing the predictable transmembrane pressure-filtrate flow rate relationship.

11. A filter fluid flow control system comprising:

means for filtering coupled to receive and filter a feed fluid, the filtering means including a porous separator separating filtrate fluid from the feed fluid to produce concentrate fluid, the flow of filtrate fluid through the membrane having a predictable pressure curve characteristic for nonobstructing filtering conditions;

means for pumping disposed to control the flow of feed fluid, concentrate fluid and filtrate fluid in the filtering means;

means for sensing and indicating pressure differential across the separator; and

means for controlling fluid flow coupled to receive pressure indications from the pressure sensing and indicating means, the fluid flow controlling means being operable to control the pumping means to maintain the pressure across the separator and filtrate fluid flow rate at a point of intersection with a flow control curve having a shape conforming to the predictable pressure curve characteristic and a predetermined pressure offset relative to at least one nonobstructing filter condition actual system operating point.

12. The filter fluid control system according to claim 11 above, wherein the feed fluid is blood, the concentrate is packed cells, and the filtrate is plasma.

13. The filter fluid control system according to claim 11 above, wherein the porous separator is a rotating membrane and the filtrate has a centripetal flow direction through the rotating membrane.

14. A method of optimizing a flow of filtrate through a filter comprising the steps of:

determining a flow rate control curve in a flow rate versus transmembrane pressure coordinate system, the control curve having a shape conforming to a sensed nonobstructing concentrate flow rate versus transmembrane pressure characteristic and a predetermined pressure offset and rotation relative to the sensed nonobstructing concentrate flow rate transmembrane pressure characteristic; and

automatically controlling the filter operating point to produce filter operation at a point which intersects the flow rate control curve.

15. A method of optimizing a flow of filtrate through a filter comprising the steps of:

determining a flow rate control curve in a flow rate versus transmembrane pressure coordinate system, the control curve having a shape conforming to a sensed nonobstructing concentrate flow rate transmembrane pressure characteristic and a predetermined pressure offset and rotation relative to the sensed nonobstructing concentrate flow rate transmembrane pressure characteristic, the control curve being determined by detecting at least one nonobstructing actual filter operating point and using as the known nonobstructing concentrate flow rate pressure characteristic a prediction curve passing through the detected at least one nonobstructing actual filter operating point; and

automatically controlling the filter operating point to produce filter operation at a point which intersects the flow rate control curve.

16. The method according to claim 15 above, wherein the prediction curve is a straight line, on a linear coordinate system.

17. The method according the claim 15 above, wherein the detecting step detects exactly one nonobstructing actual filter operating point and the prediction curve is linear and has a predetermined slope.

18. The method according to claim 15 above, wherein the detecting step detects exactly two nonobstructing actual filter operating points and the prediction curve is linear and passes through the two detected nonobstructing actual filter operating points.

19. An adaptive flow filter system comprising:

a filter receiving a flow of feed fluid and separating the received feed fluid to produce separate flows of concentrate fluid and filtrate fluid;

a pumping system coupled to cause the feed fluid, concentrate fluid and filtrate fluid to flow at controlled flow rates;

a pressure sensor coupled to sense and indicate any pressure differential between the received feed fluid and filtrate fluid; and

a fluid flow control system coupled to receive pressure indications from the pressure sensor and control the pumping system in response thereto, the fluid flow control system being operable in a three dimensional pressure verses feed fluid flow rate verses filtrate flow rate coordinate system to determine at least one filter system actual operating point and to determine from the at least one actual operating point a control curve having a pressure offset relative to a locus of anticipated nonblocking actual operating points, the fluid control system being operable to control the pumping system in response to a pressure difference between an actual sensed pressure indicated by the pressure sensor and a pressure at a corresponding point on the control curve to tend to reduce the pressure difference, these relationships being scaled linearly with feed fluid flow rates.

20. The filter system according to claim 19 above wherein the fluid flow control system operates to integrate the pressure difference and control the pumping system in response to the integral of the pressure difference.

21. The filter system according to claim 20 above, wherein the pumping system includes a feed fluid pump pumping the feed fluid and wherein the fluid flow control system operates to command operation of the feed fluid pump at a commanded feed fluid velocity and to further control the operation of the pumping system to tend to reduce the pressure difference in response to a product of the integral of the pressure difference and the commanded feed fluid velocity.

22. The filter system according to claim 21 above, wherein the pumping system includes a flow rate efficiency correction to further maximize the safe operating filtrate flow rate.

26. A fluid flow control system according to claim wherein the particular curve is rotated about a point thereon at flow rate of 20 milliliters per minute to reduce a slope thereof relative to a prediction curve representing the predictable transmembrane pressure-filtrate flow rate relationship.

29. A fluid flow control system comprising:

a filter system having a filter membrane with a transmembrane pressure-filtrate flow rate relationship which conforms in shape and orientation to a predictable prediction curve when the filter system is operated under nonobstructing operating conditions;

a flow regulating system coupled to control flows of feed fluid, concentrate fluid and filtrate fluid in the filter system;

a pressure sensor disposed to sense and generate indications of transmembrane pressure in the filter system; and

a fluid flow control system coupled system coupled to receive an indication of transmembrane pressure at a given filtrate fluid flow rate and control the flow regulating system in response thereto to maintain the transmembrane pressure at an intersection with a particular control curve having a shape and orientation conforming to the shape and orientation of the prediction curve and a pressure offset from the indicated transmembrane pressure by a predetermined pressure difference at the given filtrate flow rate.

30. A fluid flow control system comprising:

a filter system having a filter membrane with a transmembrane pressure-filtrate flow rate relationship which conforms in shape and orientation to a predictable prediction curve when the filter system is operated under nonobstructing operating conditions;

a flow regulating system coupled to control flows of feed fluid, concentrate fluid and filtrate fluid in the filter system;

a pressure sensor disposed to sense and generate indications of transmembrane pressure in the filter system; and

a fluid flow control system coupled to receive an indication of transmembrane pressure at a given filtrate fluid flow rate and control the flow regulating system in response thereto maintain the transmembrane pressure at an intersection with a particular control curve having a shape conforming to the shape of the prediction curve and an orientation that is rotated about a given point relative to the orientation of the prediction curve.

31. A flow control system according to claim 30 wherein the control curve has a predetermined pressure offset relative to the prediction curve at a given filtrate flow rate.