Reverse osmosis system

• US 5,207,916 A
• Filed: 05/20/1992
• Issued: 05/04/1993
• Est. Priority Date: 05/20/1992
• Status: Expired due to Fees

• Current Assignee: MESCO, Inc. (Mitsui Mining and Smelting Company Limited)
• Original Assignee: MESCO, Inc. (Mitsui Mining and Smelting Company Limited)
• Inventors: Goheen, Duane F., Nethercot, David C.
• Primary Examiner(s): Sever, Frank
• Application Number:
  US07/886,527
• Time in Patent Office: 349 Days
• Field of Search: 210/634, 210/637, 210/641, 210/644, 210/649-652, 210/97, 210/130-133, 210/195.2, 210/257.2, 210/321.65, 210/321.72
• US Class Current: 210/637
• CPC Class Codes: B01D 61/026 comprising multiple reverse osmosis steps
• CPC Class Codes: B01D 61/06 Energy recovery

Abstract

A single, reverse osmosis membrane system having a double-pass, product-staged design using first and second banks of membranes in series, with excessive pressure supplied by the pump to the feed to the first bank so that the concentrate flow from the first bank will be at sufficient elevated pressure to drive a turbocharger for increasing the low pressure product flow sufficiently to pass through the second bank of membranes, the excess pressure on the first bank being balanced by increased osmotic pressure from feedback of concentrate flow from at least one of the banks to the feed supply. Preferably, part of the concentrate flow from the first bank is dried on a double drum dryer or a single drum flaker for recycle use or disposal. The membranes for the first set are high rejection, high pressure membranes. The membranes for the second set are low rejection, low pressure membranes.

Claims

1. A reverse osmosis separation system operable to separate a feed liquid having dissolved solids into a purified liquid and concentrate, through a single unit, double-pass, reverse osmosis unit with successive banks of reverse osmosis membranes in series while using only one high pressure pump, comprising:

a first bank of cross flow reverse osmosis membranes;

a high pressure pump arranged to apply excessive high pressure to feed liquid having solids therein to said first bank of reverse osmosis membranes;

a feed supply including a feed inlet to said pump;

said first bank of membranes having a product flow outlet for liquid that has passed through said first bank of membranes with loss of pressure, and a concentrate flow outlet for liquid that has not passed through said first bank of membranes and remains at high pressure;

means for providing an alterative to a second pump, including;

said high pressure pump;

a dual chamber turbocharger downstream of said first bank of membranes and having a product flow outlet and a concentrate flow outlet, said turbo charger having a concentrate flow inlet for receiving from said first bank of membranes concentrate flow under high pressure as the dynamic liquid and discharging it out said concentrate flow outlet, and having a product flow inlet for receiving product flow under low pressure as the passive liquid and thereby elevating the pressure of said product flow to an elevated pressure when discharged from said turbocharger product flow outlet;

a second bank of cross flow reverse osmosis membranes downstream of said turbocharger product flow outlet and having a product flow inlet for receiving said elevated pressure product flow from said turbocharger product flow outlet, said second bank having a product flow outlet and a concentrate flow outlet; and

said concentrate flow outlet from at least one of said first and second banks of membranes being connected back to said feed supply for supplying a controlled amount of concentrate flow back to said feed inlet to thereby increase the natural osmotic pressure across said first set of membranes a controlled amount for balancing excess pressure of said feed liquid on said first bank of membranes sufficient to control net drive force and maintain proper flux rates at said first bank of membranes in a manner to avoid excess pressure causing overproduction at said first set of membranes.

2. The reverse osmosis separation system in claim 1 wherein part of said concentrate flow from said first bank is connected back to said feed supply.

3. The reverse osmosis separation system in claim 1 wherein said concentrate flow from said second bank is connected back to said feed supply and part of said concentrate flow from said first bank is connected back to said feed supply.

4. The reverse osmosis separation system in claim 3 including an evaporator, the other part of said concentrate flow from said first bank being connected to said evaporator.

5. The reverse osmosis separation system in claim 4 wherein said evaporator is a double drum dryer.

6. The reverse osmosis system in claim 4 wherein said evaporator is a single drum flaker.

7. The reverse osmosis separation system in claim 1 including a retention bank connected to said product outlet from said second bank of membranes and arranged to allow product flow back to said membranes when said high pressure pump and said turbocharger are not operative, whereby flow through said membranes by natural osmotic pressure at least partially cleans said membranes of solids thereon.

8. The system in claim 1 wherein said first bank of membranes comprises high rejection, high pressure membranes.

9. The system in claim 8 wherein said second bank of membranes comprises low rejection, low pressure membranes.

10. A method for reverse osmosis separation of dissolved and/or suspended solids from a carrier liquid in a feed solution comprising the steps of:

pumping at excess elevated pressure the feed solution to a first bank of reverse osmosis semipermeable membranes, said excess pressure tending to cause overproduction at said first set of membranes, to produce a low pressure product flow of liquid through said membranes and an elevated pressure concentrate flow of liquid and solids not passing through the membranes;

providing an alternative to a second pump for a second bank of reverse osmosis membrane, comprising;

providing downstream of said first bank of membranes a turbocharger having a dynamic turbine part and a passive pump part;

introducing said elevated pressure concentrate flow from said first bank of membranes to the dynamic turbine part of the turbocharger while introducing said low pressure product flow from said first bank of membranes to the pump part of the turbocharger to elevate the pressure of said product flow to a value greater than the natural osmotic pressure on said product flow across a second bank of reverse osmosis, semipermeable membranes;

passing the elevated pressure product flow from said first bank through the second bank of reverse osmosis semipermeable membranes to produce a purified product flow and a concentrate flow; and

increasing the osmotic pressure at said first bank of membranes by returning at least a portion of the concentrate flow from at least one of said first bank and said second bank back to said feed solution.

11. The method in claim 10 including returning part of the concentrate flow from said first set back to said pumping step, and returning the concentrate from said second set back to said pumping step.

12. The method in claim 10 including the step of evaporating the carrier liquid from the other part of the concentrate flow.

13. The method in claim 12 wherein said evaporating step is conducted on at least one of a double drum dryer and a single drum flaker.

14. The method in claim 10 including providing high rejection, high pressure, reverse osmosis, semipermeable membranes for said first bank.

15. The method in claim 14 including providing low rejection, low pressure, reverse osmosis, semipermeable membranes for said second bank.

16. The method in claim 10 including the step of conducting the purified product flow from said second bank to a storage vessel, and allowing the purified product flow to return out of the storage vessel when said pumping step and said turbocharging step are ceased, to result in purified product flow through membranes in a return direction to clean solids off the membranes.