Hybrid RO/PRO system

A method for operating one system, at alternate times, either to produce high quality water from saline water that is supplied in an RO mode or to produce power from two aqueous streams of different salt concentrations that are supplied in a PRO mode, which method comprises the steps of:

• providing a semipermeable membrane separation element capable of operating in either an RO or a PRO mode, which element has two subchambers that are separated by a semipermeable membrane, and a pair of ports connected respectively to each said subchamber;
• and
• either in the PRO mode:
• supplying an inlet liquid stream of a high salt concentration aqueous solution under a pressure which is not greater than about 90% of the osmotic pressure difference between said two aqueous streams to a first chamber of said subchambers,
• supplying an inlet liquid stream of a low salt concentration aqueous solution to a second subchamber under low pressure so that water passes through the membrane to dilute the high salt concentration stream in said first subchamber, and
• delivering at least some of a dilute liquid stream of amplified volume exiting said first subchamber to a hydroturbine power generator;
• or in the RO mode:
• halting the supply of any inlet aqueous stream of low salt concentration,
• supplying a continuous liquid stream of high salt concentration aqueous solution under a pressure of at least about 700 psig to the second subchamber of said semipermeable membrane element,
• withdrawing a continuous stream of aqueous permeate from the first subchamber of said semipermeable membrane element,
• withdrawing a continuous stream of brine from the second subchamber equal to a volume of at least about 40% of the inlet stream volume thereto, and
• (a) directing said withdrawn stream of brine to the hydroturbine, and/or
• (b) transferring the pressure of the withdrawn brine stream to raise the pressure of said high salt concentration liquid being supplied to the second subchamber.

A method for operating one system, at alternate times, to either produce high quality water from saline water that is supplied in an RO mode or to produce power from two aqueous streams of different salt concentrations that are supplied in a PRO mode, which method comprises the steps of:

• providing a semipermeable membrane separation element capable of operating in either an RO or a PRO mode, which element has first and second liquid subchambers that are separated by semipermeable membrane, and pairs of ports connected respectively to each said subchamber;
• providing a rotary liquid pressure transfer device having a high pressure inlet port, a low pressure inlet port, a high pressure outlet port and a low pressure outlet port;
• supplying a continuous incoming liquid stream of high salt concentration aqueous solution to said low pressure inlet port of said pressure transfer device;
• and either in the PRO mode:
• supplying a liquid feedstream of high salt concentration aqueous solution under a pressure which is not greater than about 90% of the osmotic pressure difference between said two aqueous streams to said first subchamber through a first port thereof,
• supplying a continuous liquid stream of low salt concentration aqueous solution to the second subchamber of said element through a first port thereto under low pressure so that water passes through the membrane to dilute the high salt concentration stream in said first subchamber,
• delivering a dilute stream of amplified volume exiting from a second port of the first subchamber partly to a hydroturbine power generator and partly to the high pressure inlet port of the rotary liquid pressure transfer device, and regulating the flow being delivered so that a volume of dilute liquid about equal to the volume that flows across the semipermeable membrane is directed to said hydroturbine which operates to generate power, with the remainder of said volume being directed to said high pressure inlet port, and
• delivering the pressurized stream of high salt concentration aqueous solution from said high pressure outlet port of said rotary pressure exchange device to said first subchamber as said incoming supply;
• or in the RO mode:
• halting the supply of any inlet aqueous stream of low salt concentration,
• supplying a continuous liquid stream of high salt concentration aqueous solution under a pressure of at least about 700 psig to said second subchamber;
• withdrawing a continuous stream of aqueous permeate from said first subchamber,
• withdrawing a continuous stream of brine from said second subchamber equal to a volume of at least about 40% of the inlet stream volume thereto,
• directing said withdrawn stream of brine to the high pressure inlet port of the rotary pressure transfer device where it raises the pressure of said incoming stream of high salt concentration aqueous solution, and
• boosting the pressure of said stream exiting the high pressure outlet port of the rotary pressure transfer device and combining same with a makeup stream of high salt concentration aqueous solution to constitute said supply of high concentration aqueous solution to said second subchamber,
• whereby water permeates through the semipermeable membrane in the same direction in both the RO and PRO modes, so that in an RO mode high quality water is efficiently provided, and in a PRO mode power is generated.