Rotary shaft driven reverse osmosis method and apparatus

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 feed pump means having a feed cylinder, a feed displacer and a feed displacer rod, the feed displacer dividing the feed 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 displacer cooperating with the displacer rod extending through the expansion chamber with sealing means to prevent leakage of fluid from the cylinder, the cylinder and displacer rod having relative diameters which define cylinder/displacer rod proportions such that ratio of swept volume of displacer rod to swept volume of the displacer determines in part 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 outfeed and return conduit means to reduce fluctuations in pressure and 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, and to exhaust depressurized concentrate fluid fraction from the expansion chamber,
• (g) rotatable drive means activating the feed displacer rod and the first valve means whilst maintaining a phase angle difference between the feed displacer stroke and first valve means actuation,
• (h) dwell means associated with the pump means and the drive means to ensure that the first valve means is shifted across the closed intermediate position thereof during an interval of essentially zero fluid transfer from the cylinder by the displacer after the beginning of each stroke of the displacer rod, the dwell means being characterized by a yieldable means associated with the feed displacer and the displacer rod to permit relative axial movement between a portion of the feed displacer and the feed displacer rod in response to reversal of pump action, and cooperation between the feed displacer and drive means being such that there is a dwell interval between valve actuation and displacer movement sufficient to approximately equalize pressure differences across ports of the first valve means that are about to be opened prior to opening of such ports,
• 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 pressurized 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.