Reverse osmosis with free rotor booster pump

• US 4,973,408 A
• Filed: 02/23/1989
• Issued: 11/27/1990
• Est. Priority Date: 04/13/1987
• Status: Expired due to Term

• Current Assignee: Keefer, Bowie G.
• Original Assignee: Keefer, Bowie G.
• Inventors: Keefer, Bowie G.
• Primary Examiner(s): SPEAR JR, FRANK
• Application Number:
  US07/314,192
• Time in Patent Office: 642 Days
• Field of Search: 210/416.1, 210/652, 210/321.66, 210/137, 241/46.17, 417/245, 366/296
• US Class Current: 210/652
• CPC Class Codes: B01D 61/06 Energy recovery
• CPC Class Codes: B01D 61/10 Accessories; Auxiliary operations
• CPC Class Codes: F04C 2/3446 the inner and outer member being in contact along more than one line or surface
• CPC Class Codes: F04D 1/08 the stages being situated concentrically
• CPC Class Codes: F04D 1/12 Pumps with scoops or like paring members protruding in the fluid circulating in a bowl
• CPC Class Codes: F04D 13/043 the pump wheel carrying the fluid driving means

Abstract

Apparatus and process for reverse osmosis or other pressure-driven membrane fluid separations, with a free rotor booster pump to increase the pressure of a feed fluid from an initial feed pressure to a working pressure at which perm-selective membranes separate the feed fluid into permeate and concentrate fluid fractions. The free rotor booster pump is powered solely by expansion of the concentrate fluid, thus recovering pressure energy from the concentrate fluid to amplify the pressure of the feed fluid. The free rotor booster pump is self-starting, provides desirable self-regulating characteristics to the apparatus, and simplifies the process since auxiliary valves that were required with prior art energy recovery turbines for starting procedures and running adjustments may be eliminated.

Claims

1. Apparatus for separation of a feed fluid into permeate and concentrate fluid fractions by subjecting the feed fluid to a working pressure over selective membrane means, the membrane means permeating the permeate fluid and rejecting the concentrate fluid to define a ratio of permeate fluid flow to feed fluid flow, the apparatus comprising:

(a) the membrane means contacting a membrane feed channel within a pressure vessel, the membrane feed channel having a feed channel inlet for the feed fluid and a feed channel outlet for the concentrate fluid,

(b) free rotor booster pump assembly comprising pump means and expander means, the pump means having a pump rotor and the expander means having an expander rotor, and the pump rotor and expander rotor being mechanically coupled to each other, so that said expander means is the sole source of power for said pump means,

(c) said pump means being adapted to receive and pump the feed fluid to attain the working pressure, and having an inlet to receive the feed fluid from a feed fluid supply means at an initial feed pressure, and also having an outlet in fluid communication with the feed channel inlet to provide feed fluid at substantially the working pressure to the inlet of the membrane feed channel,

(d) said expander means having an inlet in fluid communication with the feed channel outlet, and being adapted to expand and exhaust the concentrate fluid, so as to recover energy from the concentrate fluid to drive the said pump means in order to boost the feed fluid pressure from the initial feed pressure to the working pressure, the ratio of the initial feed pressure to the working pressure being sufficiently greater than the ratio of the permeate flow to the feed fluid flow so as to overcome efficiency losses,

and the free rotor booster pump has the characteristic of decreasing the ratio of permeate fluid flow to feed fluid flow as the working pressure developed by the free rotor booster pump rises in response to increased resistance of the membrane means to the permeate flow.

2. The apparatus of claim 1, in which the pump rotor and turbine rotor are directly coupled to rotate about the same axis at the same speed.

3. The apparatus of claim 1, in which the rotary pump means is a centrifugal pump.

4. The apparatus of claim 3, in which the expander means is a radial inflow turbine.

5. The apparatus of claim 4, in which the pump rotor is a centrifugal pump impeller, the expander rotor is a turbine runner, and said impeller and said runner are integral with a single combined rotor for reducing disc friction losses.

6. The apparatus of claim 5, in which the impeller and runner are mounted back-to-back on the rotor.

7. The apparatus of claim 6, with an inlet nozzle to convert a portion of the initial feed pressure at the inlet of the pump to velocity head, the inlet nozzle also injecting the feed fluid to the impeller at a sufficient radial distance from the axis of rotation so as to reduce axial thrust due to pressure imbalance across the rotor, and also to reduce leakage at the edge of the rotor between the pump means and the turbine means at the rim of the rotor.

8. The apparatus of claim 6, with a feed pump impeller driven to generate the total initial feed pressure as partly static head and partly velocity head, the feed pump impeller rotating coaxially with the pump means so that feed fluid discharged by the feed pump impeller is admitted substantially directly to the inlet of the centrifugal pump impeller.

9. The apparatus of claim 8, in which the static head and the velocity head are substantially equal portions of the total initial feed pressure at the inlet of the centrifugal pump impeller.

10. The apparatus of claim 3, in which the expander means is an impulse turbine.

11. The apparatus of claim 10, in which the impulse turbine is a Pelton turbine.

12. The apparatus of claim 1, in which the pump means is a rotary fixed displacement pump and the expander means is a rotary fixed displacement expander, and the ratio of the respective displacements of the pump means and the expander means are approximately equal to the ratio of the feed fluid flow to the concentrate fluid flow.

13. The apparatus of claim 12, in which the pump means is a gear pump and the expander means is a gear motor.

14. The apparatus of claim 12, in which the pump means is a vane pump and the expander means is a vane motor.

15. The apparatus of claim 14, wherein said vane pump and vane motor are integrated, and have a common vane rotor carrying a plurality of vanes within an asymmmetric double-lobed housing, said rotor revolving within said housing to define swept volume of said vanes, said housing having a larger lobe and a smaller lobe with respect to the swept volume of said vanes, said larger lobe of the housing serving as the pump means and said smaller lobe of the housing serving as the expander means, so that each vane pumps feed fluid as it sweeps through said larger lobe and expands concentrate fluid as it sweeps through said smaller lobe.

16. The apparatus of claim 1, with means to provide a portion of the total initial feed pressure at the inlet of the pump means as velocity head.

17. A process for separating a feed fluid into permeate and concentrate fractions, comprising the steps of:

(a) providing a free rotor booster pump assembly comprising pump means coupled to expander means, with the pump means and expander means each having an inlet and an outlet, and the expander means being the sole source of mechanically coupled power to the pump means,

(b) providing selective membrane means for separating at a working pressure the feed fluid into permeate and concentrate fractions, the membrane means having a feed channel inlet in fluid communication with the pump means outlet and a feed channel outlet in fluid communication with the expander means inlet,

(c) admitting to the inlet of the pump means fluid pressurized to an initial feed pressure less than the working pressure,

(d) conveying feed fluid from the outlet of the pump means to the feed channel inlet of the membrane means,

(e) admitting to the inlet of the expander pressurized concentrate fluid from the feed channel outlet of the membrane means,

(f) depressurizing the concentrate fluid by permitting free rotation of the expander means and thereby achieving pressurization of the feed fluid at the pump means outlet to the working pressure by causing simultaneous rotation of the pump means, with the ratio of the initial feed pressure to the working pressure being greater than the ratio of the permeate fluid flow to the feed fluid flow so that the expander means can drive the pump means while overcoming efficiency losses,

the process further providing that the ratio of the permeate fluid flow to the feed fluid flow decreases while the working pressure increases, in response to increased resistance of the membrane means to the permeate flow.

18. The process of claim 17, in which the ratio of the permeate fluid flow to the feed fluid flow decreases with increase of working pressure, and increases with decrease of working pressure.

19. The process of claim 18, in which the process is self-regulating under changes in effective membrane permeability, so as to avoid large independent changes in working pressure or the ratio of permeate fluid flow to feed fluid flow.

20. The process of claim 19, in which self-regulation is achieved through torque balance of the free rotor booster pump so as to compensate changes in effective membrane permeability by passively changing the speed of rotation.

21. The process of claim 18, including the steps of:

(a) providing the pump means as a centrifugal pump and the expander means as a radial inflow turbine, and

(b) mechanically coupling the centrifugal pump to the turbine.

22. The process of claim 18, including the steps of:

(a) providing the pump means as a centrifugal pump and the expander means as an impulse turbine, and

(b) mechanically coupling the centrifugal pump to the turbine.

23. The process of claim 22, in which the impulse turbine is a Pelton turbine, and self-regulation against changes in effective membrane permeability is achieved without adjustment of the Pelton turbine nozzle.

24. The process of claim 17, including the step of:

(a) pressurizing the feed fluid to the initial feed pressure with a hydrostatic head prior to admitting the feed fluid to the pump means.

25. The process of claim 17, in which up to approximately half of the total initial feed pressure at the inlet of the pump means is provided as velocity head.