Reverse osmosis method and apparatus

• US 4,187,173 A
• Filed: 03/14/1978
• Issued: 02/05/1980
• Est. Priority Date: 03/28/1977
• Status: Expired

• Current Assignee: Recovery Engineering, Incorporated (The Procter & Gamble Company)
• Original Assignee: Bowie G. Keefer
• Inventors: Keefer, Bowie G.
• Primary Examiner(s): Spear, Jr., Frank A.
• Application Number:
  US05/886,429
• Time in Patent Office: 693 Days
• Field of Search: 210/321 R, 210/136, 210/416 M, 210/23 H, 210/433 M, 417/374, 417/225, 417/241, 417/392
• US Class Current: 210/652
• CPC Class Codes: B01D 2313/18 Specific valves
• CPC Class Codes: B01D 2313/246 Energy recovery means
• CPC Class Codes: B01D 61/06 Energy recovery
• CPC Class Codes: F03D 15/15 Changing or adjusting stroke
• CPC Class Codes: F03D 9/28 the apparatus being a pump or a compressor
• CPC Class Codes: F04B 1/02 having two cylinders in V-arrangement F04B1/04
• CPC Class Codes: F04B 11/0083 the pistons having different cross-sections
• CPC Class Codes: F04B 5/02 with double-acting pistons
• CPC Class Codes: F04B 53/143 Sealing provided on the piston
• CPC Class Codes: F04B 7/0053 for reciprocating distribution members
• CPC Class Codes: F05B 2220/62 for desalination
• CPC Class Codes: Y02A 20/131 Reverse-osmosis
• CPC Class Codes: Y02A 20/141 Wind power
• CPC Class Codes: Y02E 10/72 Wind turbines with rotation axis in wind direction
• CPC Class Codes: Y02P 80/10 Efficient use of energy, e.g. using compressed air or pressurized fluid as energy carrier

Abstract

Reverse osmosis, particularly for water desalination, is achieved using semipermeable membranes which selectively permeate purified water from a feed solution pressurized by reciprocating piston or diaphragm pump. Pump action is assisted by returning pressurized concentrate fluid acting on reverse side of the pump piston or diaphragm. Directional valves controlling alternating admission and venting of concentrate fluid to and from pump cylinder are actuated mechanically by reversal of force applied to the piston rod. Mechanical dwell is provided in the piston or diaphragm motion during directional valve actuation. Pump may be operated by a manual lever or by a crank mechanism on a low speed rotary shaft. An optional differential surge absorber provides continuity of feed solution circulation past membrane surfaces during the return pump stroke, thus minimizing detrimental salt concentration build-up on the membranes.

Claims

1. A method of membrane separation of a feed fluid into permeate fluid and concentrate fluid fractions which respectively are permeated and rejected by selective membrane means, the membrane means being exposed to pressurized feed fluid supplied by a reciprocating pump means having a cylinder and piston means and cooperating with valve means in conduit means, the piston means dividing the cylinder into a pumping chamber in which feed fluid is pressurized and an expansion chamber in which the concentrate fluid is depressurized;

the method being characterized by steps of;

(a) inducting feed fluid into the pumping chamber by an induction stroke of the piston and simultaneously exhausting concentrate fluid from the expansion chamber,

(b) reversing direction of force applied to the pump means and simultaneously hydraulically biasing the piston means against movement due to reversal of force so that reaction to reversal of force is transmitted to the valve means causing the valve means to shift in preference to relative piston means movement so as to mechanically shift the valve means to direct fluid flow between the pump means and the membrane means, the transfer of reaction forces causing a dwell period so that the valve means shifts across a closed intermediate position thereof during an interval of substantially zero fluid transfer in the expansion chamber thus incurring timely valve shifting,

(c) pressurizing the feed fluid in the pumping chamber by a compression stroke of the piston means which forces pressurized feed fluid to the membranes, and admitting the concentrate fluid fraction from the membrane means into the expansion chamber to supplement energy supplied to the piston in the compression stroke by using pressure of the concentrate fluid,

(d) separating the feed fluid into a permeate fluid fraction which passes through the membranes, and a concentrate fluid fraction which is returned from the membranes to the expansion chamber to recover some fluid pressure for pressurizing the feed fluid.

2. A method as claimed in claim 1 in which the feed fluid is pressurized by external means to provide additional energy to supplement energy provided by the mechanical power means.

3. A method as claimed in claim 1 further characterized by:

(a) storing a volume of feed fluid under a pressure sufficient to maintain adequate flow over the membrane means during reversal of the stroke of the piston means,

so as to maintain essentially uniform feed fluid pressure and flow across the membranes to reduce concentrate polarization effects.

4. A method as claimed in claim 1 further characterized by:

(a) permitting yielding between the piston means and the piston rod means so that there is relative movement therebetween to provide the dwell interval between valve shift and reversal of pumping action.

5. A method as claimed in claim 1 further characterized by:

(a) upon reversal of the reciprocating force, using a first portion of a following reciprocating stroke to shift the valve means, and a remaining portion of the stroke to cause relative piston means movement.

6. A pumping apparatus for a membrane separation apparatus for separation of a feed fluid into permeate fluid and concentrate fluid fractions which respectively are permeated and rejected by selective membrane means, the pumping apparatus being characterized by:

(a) a reciprocating pump means having a cylinder and moveable piston means, the piston means dividing the cylinder into a pumping chamber in which the feed fluid is pressurized and an expansion chamber in which the concentrate fluid fraction is depressurized, the piston means cooperating with piston rod means extending through the expansion chamber with sealing means to prevent leakage of fluid from the cylinder, the cylinder and piston rod means having relative diameters which define cylinder/piston rod proportions such that ratio of swept volume of piston rod means to swept volume of the piston means determines recovery ratio of permeate fluid fraction to total feed fluid flow,

(b) inlet conduit means communicating with the pumping chamber to admit feed fluid into the pumping chamber,

(c) outfeed conduit means adapted to communicate the pumping chamber with the membranes so as to conduct pressurized feed fluid from the pumping chamber to the membranes,

(d) return conduit means adapted to communicate the membranes with the expansion chamber so as to conduct the concentrate fluid fraction from the membranes to the expansion chamber,

(e) means communicating with the outlet and return conduit means to reduce fluctuations in pressure and feed fluid flow across the membrane means,

(f) first and second valve means, the first valve means communicating with the expansion chamber and having a closed intermediate position between first and second positions, the second valve means being non-return valve means communicating with the pumping chamber, the first and second valve means cooperating with the conduit means so as to direct fluid flow from a feed fluid source and to and from the membrane means,

(g) reciprocable mechanical drive means mechanically connected to the pump means and the first valve means so that the first valve means is responsive to force applying the reciprocation action to the pump means in such a manner that reciprocating force transmitted to the pump means is reacted in part by the first valve means such that reversal of force reverses the valve means,

(h) dwell means associated with the pump means to ensure that the first valve means is shifted during an interval of substantially zero fluid transfer in the expansion chamber, the dwell means being characterized by a hydraulic bias effect acting on the piston means to inhibit relative motion of the piston means in one direction as determined by the position of the first valve means and to permit relative piston motion in the opposite direction, such that following reversal of force applied to the pump means, the first valve means shifts between the first and second positions thereof prior to reversal of pumping action,

so that in a first position of the first valve means pressurized feed fluid from the pumping chamber is fed to the membranes through the second valve means while concentrate fluid is discharged into the expansion chamber through the first valve means, so that depressurization of the concentrate fluid returning from the membrane means assists in pressurizing of the feed fluid, and in a second position of the first valve means depressurized concentrate fluid is exhausted from the expansion chamber through the first valve means while feed fluid is inducted into the pumping chamber through the second valve means.

7. Pumping apparatus as claimed in claim 6 in which the dwell means is further characterized by:

(a) yieldable means associated with the piston means and the piston rod means to permit, upon reversal of pump action, relative axial movement between a portion of the piston means and the piston rod means permitting the piston rod means to commence a stroke prior to displacement of fluid from the expansion chamber by the piston means,

so that fluid pressures across the conduits of the first valve means that are about to be connected are approximately equalized prior to actuation of the first valve means.

8. Pumping apparatus as claimed in claim 7 in which the yieldable means is characterized by:

(a) the piston rod means having a pair of spaced stops,

(b) the piston means have a disc with a bore accepted as a sliding fit on the piston rod means, the disc being interposed between the stop means, spacing between the stops and thickness of the disc permitting relative axial sliding between the disc and the piston rod limited by the stop means so that piston stroke is less than piston rod stroke.

9. Pumping apparatus as claimed in claim 7 in which the yieldable means is characterized by:

(a) a resilient piston means mounted on the piston rod means having a periphery in sliding sealing contact with the pump cylinder, the resilience permitting, upon reversal of piston means stroke, movement of the rod relative to the piston means with negligible movement of the periphery relative to the cylinder.

10. Pumping apparatus as claimed in claim 6 in which the piston means and dwell means are further characterized by:

(a) flexible diaphragm means attached to said piston rod means and separating the pump chamber from expansion chamber,

so that resilience of the diaphragm permits the piston rod means to move without fluid transfer in the expansion chamber so as to essentially equalize fluid pressures across conduits to be connected prior to shifting of the first valve means.

11. A pumping apparatus as claimed in claim 6 further including:

(a) a second pump means having a respective cylinder, piston rod means and first valve means, the respective cylinders and first valve means of the first and second pump means cooperating with each other to provide approximately uniform feed fluid flow,

(b) a piston rod connecting means connecting the piston rod means of the first and second pump means,

(c) a valve actuator connecting means connecting valve actuators of the first valve means of the first and second pump means,

and the drive means is characterized by;

(d) a lever means hinged to the piston rod connecting means and to the valve actuator connecting means,

so that reciprocation of the lever means simultaneously actuates the piston rods of both the pump means so as to actuate the pump means in reverse phase to each other, and the respective first valve means of each pump are actuated essentially simultaneously shortly after reversal of piston rod means stroke so that a pumping chamber and expansion chamber of the first pump means feed fluid to the membrane means and receives fluid from the membrane means respectively, whilst the pumping chamber and expansion chamber of the second pump means admits feed fluid from the fluid source and discharges concentrate fluid respectively so as to reduce fluid flow variations across the membranes, thus serving as means to provide essentially uniform pressure and feed fluid flow across the membrane means.

12. A pumping apparatus as claimed in claim 6 in which the means to provide uniform fluid flow across the membranes includes:

(a) a differential surge absorber means communicating with the outfeed and return conduit means and interposed between the membrane means and the first and second valve means to absorb pressure fluctuations thus providing essentially uniform feed fluid flow.

13. A pumping apparatus as claimed in claim 12 in which:

(a) the cylinder and piston rod means of the pump means have relative diameters which define cylinder/piston rod proportions such that ratio of swept volume of piston rod means to swept volume of the piston means determines recovery ratio of permeate fluid fraction to total feed fluid flow,

(b) and the differential surge absorber is a cylinder and a piston means, the piston means being spring-loaded and double-acting and reciprocable with the cylinder, the cylinder and piston means of the differential surge absorber being of similar proportions to the cylinder and piston rod means of the pump means but having a displacement several times greater.

14. Pumping apparatus as claimed in claim 12 in which the differential surge absorber is characterized by:

(a) a cylinder and a piston means, the piston means dividing the cylinder into a concentrate surge absorber chamber and a feed surge absorber chamber, the feed surge absorber chamber being exposed to pressurized feed fluid in the outfeed conduit and the concentrate surge absorber chamber being exposed to the concentrate fluid fraction in the return conduit means,

(b) the piston means cooperates with a piston rod means extending through the concentrate surge absorber chamber with sealing means to seal the surge absorber against leakage,

(c) spring means cooperating with the piston means to force the piston in a direction to exhaust the feed surge absorber chamber.

15. Pumping apparatus as claimed in claim 14 in which the piston means of the differential surge absorber is characterized by:

(a) a flexible diaphragm means attached to the piston rod means and separating the feed surge absorber chamber from the concentrate surge absorber chamber.

16. Pumping apparatus as claimed in claim 6 in which:

(a) the first valve means is a two-position, centre-closed, three-way valve having a movable spool, the spool having travel between the two positions limited by stops.

17. Pumping apparatus as claimed in claim 16 in which the first valve means is further characterized by:

(a) the spool serving as a cam means,

(b) a pair of normally-closed, two-way poppet valves to close respective conduit means, the poppet valves being unseated and opened by the cam means, the cam means being adapted to unseat and open one poppet valve whilst leaving the remaining poppet valve seated and closed,

so that both poppet valves are never open simultaneously.

18. A pumping apparatus as claimed in claim 6 in which the reciprocable drive means and dwell means are characterized by:

(a) a lever means connecting the piston rod means to the first valve means,

so that the first valve means shifts between the first and second positions thereof as direction of reciprocating action of the lever means is reversed, the hydraulically biased piston serving as a fulcrum for the lever.

19. A pumping apparatus as claimed in claim 18 further characterized by:

(a) the first valve means having a spool means reciprocable between the first and second positions,

(b) a link connecting the lever means to the spool means,

(c) the lever means being hinged to the piston rod means,

so that as the direction of the reciprocating action applied to the lever means is reversed, the piston rod means provides a fulcrum for the lever means to shift the first valve means initially between the two positions thereof, and when stopped in either of the two positions thereof, the first valve means provides a fulcrum for the lever means to apply a reversed force to the pump means.