U.S. patent number RE32,144 [Application Number 06/346,364] was granted by the patent office on 1986-05-13 for reverse osmosis method and apparatus.
Invention is credited to Bowie G. Keefer.
United States Patent |
RE32,144 |
Keefer |
May 13, 1986 |
Reverse osmosis method and apparatus
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.
Inventors: |
Keefer; Bowie G. (Vancouver,
B.C., CA) |
Family
ID: |
26994817 |
Appl.
No.: |
06/346,364 |
Filed: |
February 5, 1982 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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782540 |
Mar 28, 1977 |
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Reissue of: |
886429 |
Mar 14, 1978 |
04187173 |
Feb 5, 1980 |
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Current U.S.
Class: |
210/637;
210/321.66; 417/374; 210/136; 210/416.1; 210/652 |
Current CPC
Class: |
F03D
9/28 (20160501); F04B 11/0083 (20130101); F04B
1/02 (20130101); F04B 7/0053 (20130101); F04B
53/143 (20130101); F03D 15/15 (20160501); B01D
61/06 (20130101); F04B 5/02 (20130101); Y02E
10/722 (20130101); B01D 2313/246 (20130101); Y02A
20/131 (20180101); F05B 2220/62 (20130101); B01D
2313/18 (20130101); Y02A 20/141 (20180101); Y02E
10/72 (20130101) |
Current International
Class: |
F04B
11/00 (20060101); F04B 1/00 (20060101); F04B
1/02 (20060101); F04B 53/14 (20060101); F04B
53/00 (20060101); F04B 5/00 (20060101); F04B
5/02 (20060101); F04B 7/00 (20060101); F03D
9/00 (20060101); B01D 013/00 () |
Field of
Search: |
;417/374,323,517,541
;210/416.1,637,652,433.2,321.1,134,136,137 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2442741 |
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Mar 1976 |
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DE |
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2444740 |
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Apr 1976 |
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DE |
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2717297 |
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Oct 1978 |
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DE |
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2850650 |
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Jun 1980 |
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DE |
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1355682 |
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Feb 1963 |
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FR |
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1497712 |
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Oct 1966 |
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FR |
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54-101778 |
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Aug 1978 |
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JP |
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Primary Examiner: Spear; Frank
Attorney, Agent or Firm: Rogers, Bereskin & Parr
Parent Case Text
CROSS REFERENCES TO OTHER APPLICATIONS
This is .Iadd.a re-issue of my patent No. 4,187,173 which was
.Iaddend.a Continuation-in-Part of my application Ser. No. 782,540
filed 28 Mar. 1977 entitled REVERSE OSMOSIS APPARATUS AND METHOD
WITH ENERGY RECOVERY RECIPROCATING PUMP now abandoned.
Claims
I claim:
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.]. .Iadd.recovering energy from
.Iaddend.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 .Iadd.means .Iaddend.and
simultaneously exhausting .[.concentrate.]. fluid from the
expansion chamber .Iadd.through the valve means.Iaddend.,
.[.(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).]. (.Iadd.b) .Iaddend.pressurizing the .[.feed.]. fluid in
the pumping chamber by a compression stroke of the piston means
which forces pressurized .[.feed.]. fluid to .[.the membranes,.].
.Iadd.a load .Iaddend.and admitting .[.the concentrate.]. fluid
.[.fraction.]. from the .[.membrane means.]. .Iadd.load
.Iaddend.into the expansion chamber .Iadd.through the valve means
.Iaddend.to supplement energy supplied to the piston in the
compression stroke by using pressure of the .[.concentrate.].
fluid, .Iadd.and
(c) preventing relative movement between the piston means and the
cylinder by means of the fluid in the pump means during a dwell
period between the induction and compression strokes of the pump
means, whereby substantially no fluid is displaced from the
cylinder by the piston means during the dwell period to facilitate
timely shifting of the valve means during said dwell period.
.Iaddend.
.[.(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.].
.Iadd.wherein the load is a reverse osmosis system which includes
membrane means comprising a sealed vessel and semi-permeable
membranes contained in the vessel for separating pressurized feed
fluid into permeate fluid and concentrate fluid fractions, wherein
the piston means comprises a piston and piston rod means attached
to the piston, and wherein the method includes the additional steps
of 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 and
wherein the fluid is substantially incompressible.Iaddend..
4. A method as claimed in claim 1 .Iadd.or 3 .Iaddend.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 .Iadd.or 3 .Iaddend.further
characterized by:
(a) upon reversal of the .[.reciprocating.]. force .Iadd.applied to
the reciprocating pump means.Iaddend., 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 fraction, which respectively are permeated and rejected by
selective membrane means, the pumping apparatus being characterized
by.]. .Iadd.comprising.Iaddend.:
(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.]. .Iadd.the pump means having an induction stroke
during which fluid is inducted into the pumping chamber and
simultaneously fluid is exhausted from the expansion chamber, and a
compression stroke during which the fluid in the pumping chamber is
pressurized and fluid which has been discharged under pressure from
a load is admitted to the expansion chamber during the compression
stroke to supplement energy supplied to the piston
means.Iaddend.,
(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.]. .Iadd.load .Iaddend.so as to
conduct pressurized feed fluid from the pumping chamber to the
.[.membranes.]. .Iadd.load.Iaddend.,
(d) return conduit means adapted to communicate the .[.membranes.].
.Iadd.load .Iaddend.with the expansion chamber so as to conduct the
concentrate fluid fraction from the .[.membranes.]. .Iadd.load
.Iaddend.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).]. .Iadd.(e) .Iaddend.first and second valve means, the
first valve means communicating with the expansion chamber and
having .[.a closed.]. .Iadd.an .Iaddend.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.]. .Iadd.load.Iaddend.,
.[.(g).]. (.Iadd.f) .Iaddend.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.]. .Iadd.applied to .Iaddend.the first valve means such
that reversal of force reverses the valve means,
.[.(h).]. (.Iadd.g) .Iaddend..[.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.]. .Iadd.means for connecting the
first valve means, drive means and piston means such that when the
pump means is changing between its induction and compression
strokes the first valve means moves from either of its first or
second positions through its intermediate position before the
piston means reverses its direction of travel and the first valve
means passes through its intermediate position during a dwell
period during which the piston means is held against movement by
the fluid in the pump means, whereby substantially no fluid is
displaced from the cylinder by the piston means during the dwell
period to facilitate timely shifting of the first valve means
during the dwell period, so that during the compression stroke of
the pump means, pressurized fluid from the pumping chamber is fed
to the load when the first valve means is in its first position and
simultaneously fluid is returned to the expansion chamber through
the first valve means and the return conduit means, and during the
induction stroke of the pump means depressurized fluid in the
expansion chamber is exhausted from the expansion chamber through
the first valve means and simultaneously fluid is inducted into the
pumping chamber.
7. Pumping apparatus as claimed in claim 6.Iadd., 20 or 23
.Iaddend.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.]. .Iadd.having .Iaddend.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 means .Iadd.means .Iaddend.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 claims 6.Iadd., 20 or 23
.Iaddend.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.]. .Iadd.20 or 23
.Iaddend.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 charge 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.]. .Iadd.20
.Iaddend..[.in which the.]. .Iadd.including .Iaddend.means to
provide uniform fluid flow across the membranes .[.includes.].
.Iadd.comprising.Iaddend.:
(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 .Iadd.or 23
.Iaddend.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 permeat 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 .Iadd.or 23
.Iaddend.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 .Iadd.or 20 .Iaddend.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.Iadd., 12, 20 or 23
.Iaddend.in which the reciprocable drive means .[.and dwell means
are.]. .Iadd.is .Iaddend.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
.Iadd.means .Iaddend.serving as a fulcrum for the lever .Iadd.when
it is held against movement.Iaddend..
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.
.Iadd.
20. A pumping apparatus as claimed in claim 6 wherein the load is a
reverse osmosis system which includes membrane means comprising a
sealed vessel and semi-permeable membranes contained therein for
separating a pressurized feed fluid into permeate fluid and
concentrate fluid fractions and wherein the fluid is substantially
incompressible. .Iaddend. .Iadd.21. A pumping apparatus as claimed
in claim 20 wherein the ratio of permeate fluid flow to feed fluid
flow is proportional to the ratio of the respective volumes of the
pumping chamber and the expansion chamber. .Iaddend. .Iadd.22. A
method as claimed in claim 1 or 3 wherein the valve
means is closed in its intermediate position. .Iaddend. 23. A
pumping apparatus as claimed in claim 6 wherein said first valve
means is closed in its intermediate position. .Iadd.24. A method as
claimed in claim 3 including the step of 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 concentration polarization
effects. .Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to reverse osmosis and
ultrafiltration fluid separation processes, and is applicable
particularly to water desalination and purification by reverse
osmosis.
2. Prior Art
Desalination by reverse osmosis is achieved by pumping a feed
stream of saline water at an elevated working pressure into a
pressure resistant vessel containing an array of semipermeable
membranes. Purified product water of greatly reduced salinity
permeates across the membranes into low pressure collection
channels if the working pressure exceeds feed stream osmotic
pressure. Considerable excess working pressure above the feed
stream osmotic pressure is required to produce sufficient product
water flux across membranes of reasonable surface area, and also to
ensure sufficient dilution of the small but finite salt diffusion
through the membrane which always exists when there is a
concentration gradient across such membranes. For sea water whose
osmotic pressure is about 25 Kg/sq. cm, typical working pressure
for single stage reverse osmosis is in the order of 70 Kg/sq.
cm.
While some of the feed stream permeates through the membranes, the
balance becomes increasingly concentrated with salt rejected by the
membranes. In a continuous reverse osmosis process, a concentrate
stream must be exhausted from the vessel to prevent excessive salt
accumulation. In sea water desalination, this concentrate stream
may be typically 70% and sometimes as much as 90% of the feed
stream. The concentrate stream leaves the vessel at almost full
working pressure, but before the concentrate stream is exhausted
from the apparatus, it must be depressurized. In common reverse
osmosis apparatus the concentrate stream is depressurized by
throttling over a suitable back pressure valve, for example a
restrictor valve, which regulates the working pressure while
dissipating all the pressure energy of the concentrate stream. It
is known to recover some of the concentrate stream pressure energy
using recovery turbine devices, however such energy recovery
devices have mostly seemed practicable only for large stationary
plants where efficiency and economy advantages of scale would
apply.
Without energy recovery devices, small scale manually operated
reverse osmosis desalinators for use in households, life-boats,
etc. would be almost unpracticable. Similarly, using wind power for
desalination is discouraged by high energy consumption.
Furthermore, for high recovery concentration polarization must be
controlled. Concentration polarization in the feed stream is the
tendency for a concentration gradient to develop in the feed stream
with high salt concentration on the membrane face during reverse
osmosis. This tendency results from the bulk transport of saline
feed water toward the membrane face and the accumulation of salt in
the boundary layer as less saline water permeates through the
membrane, balanced by diffusion of salt back out of the boundary
layer. Concentration polarization is detrimental especially with
feed solutions of high osmotic pressure such as sea water, because
the membrane sees a higher concentration which raises the effective
osmotic pressure. When concentration polarization occurs, working
pressure for given product flux must be increased, product salinity
will be increased, and membrane life may be impaired.
Reverse osmosis systems are typically designed to reduce
concentration polarization effects by forced convection through the
membrane array. Forced convection may be provided by circulating a
low ratio of product flow to concentrate flow through suitably
configured feed channels between the membrane faces, or by
auxiliary recirculation or mechanical stirring devices. It is
essential that continuous feed circulation be maintained through
the membrane array, because even momentary stagnation of flow may
cause severse concentration polarization.
Operation at low ratios of product flow to concentrate flow is also
generally favourable to the reduction of concentration polarization
effects, but of course increases the feed pumping energy
expenditure for given product flow delivery.
SUMMARY OF THE INVENTION
The invention achieves reverse osmosis with low energy consumption,
particularly for manually operated or wind driven desalination
devices. Concentration polarization effects are reduced by
providing means to maintain the continuity of feed flow circulating
past the membranes, and by enabling operation at a low ratio of
product flow to concentrate flow without excessive energy
consumption normally associated with large feed flows. The device
has a simple and effective means to control directional valve
timing which enables the recovery of fluid pressure energy from the
concentrate stream. All embodiments described have dwell means to
increase tolerance to valve actuation, thus simplifying manufacture
and servicing.
Membrane separation apparatus according to the invention separates
the feed fluid into a permeate fluid fraction and a concentrate
fluid fraction which respectively are permeated and rejected by
semipermeable membrane means. The apparatus is characterized by a
reciprocating pump means, a drive means, inlet, outfeed and return
conduit means, means communicating with the membrane means to
provide essentially uniform pressure and feed fluid flow across the
membranes, first and second valve means for directing fluid to and
from the membranes, and a dwell means to ensure timely valve
actuation. The reciprocating pump means has a cylinder and movable
piston 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 piston means
also separates the pumping and expansion chambers and cooperates
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 have relative diameters which
define the cylinder/piston rod proportions such that ratio of swept
volume of piston rod means to swept volume of piston means
determines the recovery ratio of permeate fluid fraction to total
feed fluid flow. The drive means is reciprocable and is
mechanically connected to the pump means to apply a reciprocating
action to the pump means. The inlet conduit means communicates the
pumping chamber with a feed fluid source to admit feed fluid into
the pumping chamber, and the outfeed conduit means communicates the
pumping chamber with the membrane means to conduct pressurized feed
fluid from the pumping chamber to the membrane means. The return
conduit means communicates the membrane means with the expansion
chamber to conduct the concentrate fluid fraction from the membrane
means to the expansion chamber. The first valve means communicates
with the expansion chamber and mechanically cooperates with the
pump means so as to be shifted between first and second positions
upon reversal of the reciprocating action applied to the pump
means. The first valve means has a closed intermediate position
between the first and second positions. The second valve means is a
non-return valve means communicating with the pumping chamber. The
first and second valve means cooperate with the conduit means so as
to direct fluid from the fluid source and to and from the membrane
means. 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. The dwell means is 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 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
the pumping action. The dwell means is associated with the pump
means to ensure that the first valve means is shifted during an
interval of zero fluid transfer in the expansion chamber of the
pump means. Thus, 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 the feed fluid. In
a second position of the first valve means, depressurized
concentrate fluid is vented from the expansion chamber through the
first valve means while feed fluid is inducted into the pumping
chamber through the second valve means.
A method of membrane separation according to the invention uses an
apparatus as generally described above and is characterized as
follows. The feed fluid is inducted into the pumping chamber by an
induction stroke of the piston means and simultaneously the
concentrate fluid is exhausted from the expansion chamber. The
direction of force applied to the pump means is reversed and the
piston means is biased hydraulically against movement due to
reversal of force. Thus reaction of force is transmitted to the
first valve means causing the valve means to shift in preference to
relative piston means movement so as to mechanically shift the
first valve means to direct fluid flow between the pump means and
the membrane means. The transmission of reaction forces produces a
dwell which causes the valve means to shift across a closed
intermediate position thereof during an interval of zero fluid
transfer in the expansion chamber thus incurring timely valve
shifting. The feed fluid is then pressurized in the pumping chamber
by a compression stroke of the piston means which forces
pressurized feed fluid to the membrane means, and the concentrate
fluid fraction from the membrane means is admitted into the
expansion chamber to supplement energy supplied to the piston in
the compression stroke by using pressure of the concentrate fluid.
The feed fluid is separated into a permeate fluid fraction which
passes through the membrane means, 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.
A detailed disclosure following, related to the drawings, describes
a preferred method and apparatus according to the invention which
are capable of expression in method and apparatus other than that
particularly described and illustrated.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified section through a manually powered
embodiment of a lever actuated reverse osmosis apparatus according
to the invention,
FIG. 2 is a fragmented section of an alternative valve means of the
invention,
FIG. 3 is a fragmented section of a second embodiment of a piston
means for use in the FIG. 1 embodiment,
FIG. 4 is a detailed fragmented section of an alternative
differential surge absorber for use in the FIG. 1 embodiment,
FIG. 5 is a simplified elevation, partially in section, of an
alternative crank shaft actuated apparatus according to the
invention showing a third embodiment of a piston means with dwell
means incorporated therein,
FIG. 6 is a timing diagram showing relative angular positions of
piston and valve means of the FIG. 5 embodiment,
FIG. 7 is a simplified fragmented section of a fourth embodiment of
a piston means with dwell means incorporated therein,
FIG. 8 is a simplified elevation, show partially in section, of a
wind powered embodiment of the apparatus of FIG. 1,
FIG. 9 is a schematic of a lever actuated apparatus of the
invention having two cylinders.
The directions "upwards" and "downwards" refer to the figures as
drawn, but clearly the apparatus could be in other
orientations.
DETAILED DISCLOSURE
FIG. 1
A first embodiment 10 of a lever actuated membrane separation
apparatus according to the invention includes a reciprocating pump
means 12, a directional three-way valve assembly 13, a drive means
14 mechanically connected to the pump means and valve assembly, and
a differential surge absorber 15. The apparatus further includes a
membrane vessel 16 containing semipermeable membrane means 17, and
optional low and high pressure filters 18 and 19. Feed fluid 21 is
separated into a permeate fluid fraction 22 and a concentrate fluid
fraction 23 which are respectively permeated and rejected by the
membrane means.
The reciprocating pump means 12 has a pump cylinder 24 and a
movable piston means 25, the piston means dividing the cylinder
into a pumping chamber 27 in which the feed fluid is pressurized,
and an expansion chamber 28 in which the concentrate fluid is
depressurized. The piston means cooperates with a piston rod means
32 extending through the expansion chamber, and sealing means 30
and 33 prevent mixing and leakage of fluid. The cylinder 24 and
thus the piston means 25, and the piston rod means 32 have relative
diameters which define piston rod/cylinder proportions such that a
ratio of the swept volume of piston rod means to swept volume of
the piston means determines recovery ratio of the permeate fluid
fraction to the total fluid fraction. Alternatively, the recovery
ratio can be defined in terms of displacement ratio of the piston
rod means to the piston means. Inlet conduit means 36 communicate
with the pumping chamber 27 to admit feed fluid 21 from a conduit
portion 35 immersed in feed fluid, a non-return check valve 37
admitting the feed fluid through the filter 18 and conduit portion
35 whilst preventing return flow from the chamber into the conduit
36. Outfeed conduit means 39 communicate the pumping chamber with
the membrane means 17 via the differential surge absorber 15 and
filter 19 to conduct pressurized feed fluid from the pumping
chamber to the membrane means, a non-return check valve 40
preventing return flow of fluid into the pumping chamber.
The outfeed conduit 39 consists of a conduit portion 41 extending
between the differential surge absorber 15 and the pumping chamber,
a conduit portion 42 extending between the differential surge
absorber and the filter 19, and a conduit portion 43 extending from
the filter 19 to the membrane vessel means. A return conduit means
44 communicates the membrane means with the expansion chamber 28 to
conduct the concentrate fluid fraction from the membrane means to
the expansion chamber 28. The means 44 has a conduit portion 45
extending between the differential surge absorber 15 and the
membrane vessel 16, and a conduit portion 46 extending between the
directional valve assembly 13 and the differential surge absorber
15. The valve assembly 13 has a vent conduit 47 to conduct the
concentrate fluid fraction 23, usually to waste, and a connecting
conduit 48 communicating with the expansion chamber 28.
The valve assembly 13 is a three-way directional control valve and
has a sliding valve spool 49 having linear travel limited by lower
and upper stops 50 and 51 which determine upper and lower limits of
travel of the spool respectively, the spool being shown in the
upper limit of travel in which the conduit portion 46 is connected
with the connecting conduit 48 to conduct the concentrate fluid
fraction from the membranes to the expansion chamber. In a lower
limit of travel, not shown, the connecting conduit 48 is connected
to the vent conduit 47 as will be described. Because water has low
viscosity and lubricity, the spool 49 is fitted with dynamic
sealing rings 52 of suitable composition, for example glass-filled
fluorocarbon polymeric compounds to minimize leakage and prevent
spool seizure. Thus, the valve assembly 13 is a two-position,
center-closed, three-way valve having a movable spool, the spool
having travel between two positions through a closed intermediate
position to interchange conduit connections, the travel being
limited by stops. The valve assembly 13 directs fluid to or from
particular conduits communicating with the expansion chamber 28,
and is termed a first valve means. The non-return valves 37 and 40
control flow in conduits communicating with the pumping chamber 27
and are termed second valve means. As will be described, the first
and second valve means cooperate with the conduit means so as to
direct fluid flow from the fluid source and to and from the
membrane means, and clearly alternative first and second valve
means can be substituted.
The drive means 14 includes a manually operated lever 54 having an
inner end hinged on a hinge pin 55 which is carried at an outer end
of the piston rod means 32. A link 57 is pinned at one end with a
pin 58 to the lever 54 and at an opposite end with a pin 59 to an
outer end of the spool 49. It can be seen that reciprocation action
applied to the lever 54 is an arc shown by a double headed arrow 61
results in corresponding linear movement of the piston rod means 32
and the spool 49, relative shifting of the spool and piston rod
being dependent on leverage and resistance to motion of the piston
means and the spool. The position of the spool 49 determines a
hydraulic bias effect on the piston means 25 such that the spool 49
must shift before the piston can reverse. The hydraulic bias
inhibits piston movement in one direction and permits the piston
means to move relatively easily in an opposite direction, the
direction being determined by the spool 49 as follows. When the
conduits 46 and 48 are connected, upwards movement of the piston
means is resisted by concentrate fluid in the chamber 28 which
pressure assists in downwards movement of the piston. When the
conduits 47 and 48 are connected, downwards movement of the piston
is resisted by the check valves 37 and 40, whereas upwards movement
is relatively easy due to vent pressure in the chamber 28. Thus,
when the spool is in the upper position as shown in FIG. 1,
swinging the lever 54 downwards shifts the spool to the lower
position before the piston moves within the cylinder, and vice
versa for opposite swinging of the lever. The hydraulic bias causes
the piston to serve as a temporary fulcrum for the lever which
provides dwell and is of major importance to operation of the
invention because the valve spool must shift between its two limits
when the piston is stationary because the fluid is essentially
incompressible and damage would likely result if the piston shifted
before the spool had interchanged connections.
The differential surge absorber 15 has a cylinder 65 and a piston
means 64, the piston means dividing the cylinder 65 into a
concentrate surge absorber chamber 66 and a feed surge absorber
chamber 67. The piston means cooperates with a piston rod means 69
extending through the concentrate surge absorber chamber 66 and has
sealing means 70 and 71 to prevent mixing and leakage of fluid. For
smooth operation of the surge absorber the seals are selected for
low friction characteristics. A compression coil spring 72 encloses
the piston rod means and extends between the piston means 64 and
the chamber so that the piston means is effectively spring-loaded
and double-acting and reciprocable within the cylinder. Thus, the
spring means cooperates with the piston means to force the piston
means in a direction to exhaust the feed surge absorber chamber.
The feed surge absorber chamber 67 is exposed to pressurized feed
fluid in the portion 41 of the outfeed conduit 39 and also
communicates with the membrane vessel 16 through the conduit
portions 42 and 43. The concentrate surge absorber chamber 66 is
exposed to the concentrate fluid fraction in the conduit portion 45
of the return conduit means 44 and also communicates with the valve
assembly 13 through the portion 46.
The piston rod means 69 and the cylinder 65 of the surge absorber
15 have relative diameters similar to the piston rod/cylinder
proportions of the pump means, but have a displacement several
times greater and thus can accommodate the recovery ratio of the
permeate fluid fraction to the total fluid fraction. The key
feature of the differential surge absorber is rigid coupling of the
concentrate and feed surge absorber chambers 66 and 67 with a ratio
similar to that of the pump means 12, i.e. a similar displacement
ratio so as to serve as a load leveller for the pump means. The
spring 72 is relatively small and the piston rod means 69 is of
relatively small area when compared with the piston means 64, and
the differential surge absorber is charged to full effectiveness
within a few pump strokes when starting up as will be described. It
should be noted that extension of the piston rod means 69 from the
surge absorber provides a visual indication of hydrostatic pressure
of the system by its position at any instant. Piston rod/cylinder
area proportions or displacement volumes can be within the range of
1:10 and 1:2 for practical recovery ratios.
The membrane means 17 are housed in the membrane vessel 16 in
suitable arrays known in the art and a low pressure product channel
76 receives product water from the membranes which is discharged
through product conduit 77. The geometry of the membrane arrays in
the membrane container vessel is designed to ensure sufficient
forced convection of the feed fluid to prevent excessive
concentration polarization effects. If the feed fluid flow velocity
is dropped too low, concentration polarization effects can become
severe.
OPERATION
Referring to FIG. 1, as the lever 54 is swung manually upwards
about the hinge pin 55, the valve spool 49 is held in its uppermost
position against the lower stop 50, closing the vent conduit 47 and
connecting the conduit portion 46 with the connecting conduit 48 so
as to pass the pressurized concentrate fluid fraction from the
membrane vessel 16, through the chamber 66 of the differential
surge absorber, through the valve assembly 13 into the expansion
chamber 28 to act on a rear face of the piston means 25. The force
from the concentrate fluid in the chamber 28 augments force from
the lever 54 and the piston means simultaneously travels downwards
in the pump cylinder 24 in direction of arrow 74 to pressurize feed
fluid in the chamber 27. The check valve 37 is held closed by the
feed fluid pressure and the check valve 40 is open to transmit
pressurized feed fluid from the pumping chamber 27 through the
conduit portion 41 into the feed surge absorber chamber 67 of the
differential surge absorber 15. Pressurized feed fluid from the
chamber 67 passes through the conduit portion 42, through the high
pressure filter 19 and the conduit portion 43 into the membrane
vessel 16. The permeate fluid fraction is permeated by the membrane
means and passes into the low pressure product channels 76 to be
collected from the product conduit 77. The concentrate fluid
fraction is rejected by the membrane means and passes through the
conduit portion 45 into the concentrate surge absorber chamber 66,
through the conduit portion 46 and the valve assembly 13 into the
expansion chamber 28. The concentrate fluid pressure acts on the
rear face of the piston means 25 and hydrostatic pressure energy of
the concentrate fluid can be utilized, permitting recovery of a
substantial portion of the energy in the feed fluid. Pressure of
the concentrate fluid in the expansion chamber 28 is only slightly
less than pressure of feed fluid in the pumping chamber 27 and
thus, taking into consideration the reduced area of the rear face
of the piston upon which pressure of the concentrate fluid acts, an
operator has to supply only a fraction of the power that would have
been required without energy recovery.
Reversing the reciprocation action manually applied to the lever
54, that is pushing the lever downwards, swings the lever about the
hinge pin 55 which acts at the actual fulcrum and the hydraulic
bias on the piston means prevents initial upwards movement of the
piston means and initially causes the valve spool 49 to move
downwards until the downwards movement is limited by the stop 51.
In this position, the conduit portion 46 is closed, thus isolating
the valve from the surge absorber 15, and the vent conduit 47 is
open and communicates with the connecting conduit 48, and is thus
exposed to fluid in the expansion chamber 28. When the spool stops,
the hydraulic bias is now reversed and the piston means 25 can move
upwards on a return stroke, that is opposite to direction of the
arrow 74, and the check valve 37 opens to induct feed fluid into
the pumping chamber 27 and the check valve 40 closes preventing
return flow of fluid from the differential surge absorber. It can
be seen that the first valve means is responsive to force applying
the reciprocation action to the pump means in such a manner that
the reciprocating force transmitted to the pump means is reacted in
part by the first valve means. Upwards movement of the piston means
also forces concentrate fluid from the expansion chamber through
the valve assembly and the vent conduit 47, usually to waste.
As pressure in the feed surge absorber chamber 67 drops slightly as
a result of continuing permeation of product water through the
membrane means 17, the spring 72 forces the differential surge
absorber piston means 64 downwards towards the conduit portions 41
and 42. Force from the spring 72 is augmented by pressure of
concentrate fluid from the membrane means flowing into the
concentrate surge absorber chamber 66 and acting on the rear face
of the piston means 64. Downward movement of the piston means 64 of
the differential surge absorber maintains a flow of feed fluid into
the membrane vessel and across the membrane means, thus tending to
reduce concentration polarization effects that would otherwise
occur. Thus, stagnant flow conditions on the concentrate fluid side
of the membrane means during the return stroke of the pump means
are reduced and there is sufficient displacement of the piston
means 64 to maintain adequate flow through the membrane vessel
throughout the return stroke. It can be seen that the differential
surge absorber 15 serves as a means communicating with the membrane
means to provide essentially uniform pressure and feed fluid flow
across the membranes during operation of the apparatus. The
differential surge absorber communicates with the outfeed and
return conduit means and is interposed between the membrane means
and the first and second valve means to absorb pressure
fluctuations while providing essentially uniform feed fluid flow
across the membranes.
Upon reversal of the reciprocation action again, the valve assembly
shifts before the piston means changes direction and the operation
as previously described will be repeated. Note that the piston
means 25 of the pump chamber does not have to travel full stroke of
the pump cylinder 24 prior to reversal of piston action, i.e.
reversal of pump stroke can occur anywhere in the cylinder 24.
Thus, the operator may reverse the lever stroke at any point in its
arc of travel as the apparatus is insensitive to the positional
limits of lever travel. Because the valve means 13 shift as a
direct result of reversal of reciprocating action applied to the
lever, and it always shifts before reversal of pump action because
of hydraulic bias which causes the spool 49 to be moved more easily
in a particular direction than the piston means 25, the first valve
means always shifts in a period when the piston rod means is
stationary and there is therefore zero displacement of fluid from
the expansion chamber. This is essential for operation of the
device as premature displacement of fluid from the expansion
chamber before the valve spool has shifted completely would likely
result in damage to the apparatus. Thus, it can be seen that as the
direction of reciprocation action applied to the lever means is
reversed, the piston rod means serves as a fulcrum for the lever to
shift the first valve means initially between the two positions
thereof. When stopped in either of the two positions, the first
valve means then provides a fulcrum for the lever means. In the
FIG. 1 embodiment, the three-way valve assembly 13 has a closed
center or intermediate position in which all first valve conduits
are closed to provide a temporary hydraulic lock for the piston
means between the two valve positions. Thus, the lever 54 and the
link 57 serve as mechanical linkage means cooperating with the
first valve means and the pump means so that reversal of
reciprocation action applied to the pump means shifts the first
valve means between the first and second positions thereof.
There is thus a time delay or dwell between actuation of the first
valve means and transfer of fluid relative to the expansion
chamber, and this is attained by interposing a dwell means between
the pump means and the first valve means. In the FIG. 1 embodiment,
the dwell means is the linkage means and selection of force
difference required to shift the valve spool before movement of the
piston rod means. Alternative dwell means can be substituted so as
to be, in effect, interposed between the pump means and the first
valve means. The dwell means determines that reversal of force
applying reciprocating action to the pump means shifts the valve
means between the first and second positions thereof prior to
reversal of pump action in the expansion chamber, i.e. displacement
or transfer of fluid. Alternative dwell means are to be described
with reference to FIGS. 3 or 5 through 7 and all such dwell means
permit actuation of the first valve means during an interval of
zero fluid transfer in the expansion chamber which follows
completion of a piston stroke. The dwell means accommodates the
hydraulic lock of the piston means without destructive shocks.
Thus, in summary, the method is characterized by steps as follows.
The feed fluid is inducted into the pumping chamber 27 by the
induction stroke of the piston means 25, and simultaneously
concentrate fluid is exhausted from the expansion chamber 28.
Direction of force applied to the pump means is reversed and the
piston is hydraulically biased against movement so that reaction to
reversal of force is transmitted to that valve means. This
mechanically shifts the first valve means to direct fluid flow
between the pump means and the membrane means, dwell means causing
the valve means to shift in preference to relative piston movement
across a closed intermediate position thereof during an interval of
zero fluid transfer in the expansion chamber, thus incurring timely
valve shifting. The feed fluid in the pumping chamber is
pressurized by a compression stroke of the piston means which
forces pressurized feed fluid to the membrane means and
simultaneously admits 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. The feed fluid is separated by the
membrane means into a permeate fluid which passes through the
membrane means and a concentrate fluid fraction which is returned
from the membrane means to the expansion chamber to recover some
pressure energy for pressurizing the feed fluid.
ALTERNATIVES AND EQUIVALENTS
The first valve means is shown displaced laterally relative to the
piston means, however other relative positions can be devised to be
within the scope of the invention. If desired, alternative first
valve means can be substituted, however an intermediate closed
position between the two valve positions is required to
hydraulically lock the piston means for a finite period between the
two valve positions.
FIG. 2
An alternative first valve means 81 is for use with the embodiment
10 of FIG. 1 and equivalents, and is a three-way valve having a
spool or sliding cam 82 having spaced stops 83 and 84 limiting
movement of the spool. The cam 82 actuates two two-way poppet
valves 85 and 86 having complementary seats 87 and 88 communicating
with conduits as follows. A return conduit portion 89 communicates
with the differential surge absorber, not shown, a connecting
conduit 90 communicates with the expansion chamber of the pump
means, not shown, and a vent conduit 91 communicates with a
concentrate fluid outlet, not shown. The valves 85 and 86 have
respective springs 93 and 94 which initiate closure of the valve
with fluid pressure differences augmenting sealing of the valve.
Seals 96 and 97 mounted in stem guides prevents fluid leakage past
the stems of the poppet valves, and hardened steel balls 98 and 99
protect the stems against lateral forces. It is mandatory that
profile of sliding cam 82 be such that at least one of the poppet
valves will remain seated at all times. If both poppet valves were
lifted at once, even momentarily, the conduits 89 and 90 would be
connected to vent pressure and the apparatus would be inoperative.
The spool 82 is connected to the link 57 of FIG. 1, and the means
81 can be directly substituted for the valve assembly 13 and
functions similarly.
In operation, the valve is shown in a fully raised position limited
by the stop 84, in which position the cam 82 lifts the valve 85 off
the seat 87 so that conduits 89 and 90 are connected to admit
pressurized concentrate fluid from the membrane means into the
expansion chamber. The valve 86 is seated by the spring 94 and
unbalanced hydrostatic pressure. On the pump return stroke, the
valve 86 is lifted off the seat 88 so as to vent the expansion
chamber into the vent conduit 91, and the valve 85 is closed by the
spring 93 and hydrostatic pressure, thus preventing concentrate
fluid flow from the membrane means.
FIG. 3
An alternative pump cylinder 105 communicates with the inlet
conduit 36, the outfeed conduit 39 and the connecting conduit 48,
as previously described with reference to FIG. 1. The pump cylinder
105 has an alternative piston rod means 106 which cooperates with a
flexible diaphragm or bellows 108 which is secured to the pump
cylinder 105 by a static seal 110 at one end thereof and at an
opposite end thereof to the piston rod means. The diaphragm thus
divides the pumping cylinder into a pumping chamber 109 on one side
of the diaphragm and an expansion chamber 111 on an opposite side
of the diaphragm and thus separates feed and concentrate fluid
fractions and serves as substitution for the piston means of the
FIG. 1 embodiment. The flexible diaphragm is feasible because only
small differences in hydrostatic pressure normally exist between
the pump chamber 109 and the expansion chamber 111. The flexible
diaphragm or bellows eliminates the friction losses of the sealing
means 30 of the piston means 25 of FIG. 1 and also may simplify
manufacturing since tolerances may be less critical. Preferably the
diaphragm should be elastically relatively stiff to prevent
collapse under pressure differences, because if collapse occurs,
its displacement will be reduced and it will not function
satisfactorily. Alternatively, the feed fluid can be supplied to
the inlet conduit 36 at a boost pressure exceeding exhaust pressure
in connecting conduit 48. The diaphragm does not provide rigid
boundaries between the feed and concentrate fluids and it can be
seen that motion of the piston rod means can cause fluid
displacement in the pumping chamber 109 with zero fluid
displacement in the expansion chamber 111. Thus the diaphragm is
yieldable to fluid pressure as a result of piston rod motion and
thus is compliant upon reversal of reciprocation action applied to
the lever means. Thus, it can be seen that resilience of the
diaphragm provides a means to attain dwell to permit timely valve
shifting without fluid transfer in the expansion chamber, and thus
serves as an alternative dwell means which can be substituted for,
or used in combination with, the dwell means associated with force
differences in shifting the valve assembly.
FIG. 4
An alternative differential surge absorber 118 can be a direct
substitution for the differential surge absorber 15 of FIG. 1. The
absorber 118 has an alternative cylinder 119 communicating with
conduit portions 41 and 42 of the outfeed conduit means 39, and
with conduit portions 45 and 46 of the return conduit means 44. The
surge absorber 118 has an alternative piston rod means 121 which
cooperates with a flexible diaphragm or bellows 123 which is
secured to the cylinder by a static seal 125 at one end thereof,
and at an opposite end thereof to the piston rod means. The
diaphragm divides the cylinder 119 into a concentrate surge
absorber chamber 129 and a feed surge absorber chamber 130. A coil
spring 131 encircles the piston rod means 121 and functions
similarly to the spring 72 of FIG. 1. Consideration relating to the
substitution of the rigid piston means 25 of FIG. 1 for the
diaphragm means 108 of FIG. 3, apply also to the structure of FIG.
4.
FIGS. 5 and 6
A second embodiment 136 of a pump means has an alternative drive
means 137 which includes a powered crank shaft 138 mounted in
journals, not shown, for rotation about an axis 139. The shaft 138
has a pair of crank pins or throws 140 and 141 spaced at a suitable
phase angle, as will be described, the throw 140 being shown at
approximately mid-stroke and the throw 141 being shown at top dead
center. Connecting rods 143 and 144 connect the throws 140 and 141
to an alternative piston rod means 146 and an alternative valve
spool 148 respectively of the pump means 136. The piston rod 146
reciprocates within a pump cylinder 150 which is generally similar
to the cylinder 24 of FIG. 1 having inlet and outfeed conduits 36
and 39, and the valve spool 148 cooperates with conduit portions 45
and 46 and connecting conduit 48 of a three-way valve assembly or
first valve means 152 which is generally similar to the valve
assembly 13 of FIG. 1. Stops on the spool 148, equivalent to the
stops 50 and 51 on the spool 49 of FIG. 1 are eliminated in the
FIG. 5 embodiment, as spool travel is limited by the crank shaft
rotation.
The pump means 136 has an alternative piston means 154 mounted on
the rod means 146, the means 154 dividing the pump cylinder into an
expansion chamber 156 and a pumping chamber 157. The piston rod
means 146 has a pair of spaced stops 159 and 160 fitted with
oppositely facing resilient pads 158. The alternative piston means
154 includes a piston disc 161 with a bore 162 accepted as a
sliding fit on the piston rod means, the disc being interposed
between the pads 158 of the spaced stops and being free to slide
between the stops, the pads reducing shock loads when the disc 161
contacts the stops. A dynamic seal 163 surrounds an outer periphery
of the piston disc to prevent leakage of fluid past the outer
periphery and the cylinder wall. Spacing 164 between the pads 158
of the stops and thickness of the disc are such that the piston rod
means 146 can move axially through the disc 161 with negligible
movement of the disc between approximately 10 and 20 percent of
total piston stroke. Hence the piston disc 161 floats on the piston
rod means and the reciprocating stroke of the piston disc 161 will
be less than that of the piston rod means 146. Unlike the first
embodiment, the ratio of permeate flow to feed flow is no longer
given by the simple ratio of piston rod section area to piston
area, because the strokes of piston rod and piston are inequal.
Operation of the second embodiment 136 follows closely that of the
first, but it is noted that upon reversal of piston rod movement
there is relative movement, ie. axial sliding, between the disc 161
and the piston rod means 146 which results in lost motion or dwell
of the piston disc following piston rod reversal. In the
description following, the piston disc is described as
reciprocating between stops on the piston rod means, whereas in
fact it reciprocates between the pads 158 on the stops.
FIG. 6 shows piston and valve relative positions and sequences for
a complete clockwise revolution of the crank shaft 138, angular
spacing being exaggerated for clarity. Top dead center of the throw
140 of the piston rod means is taken as crank shaft datum and is
designated A which is immediately prior to a piston compression
stroke, and corresponding bottom dead center, which is immediately
prior to a piston induction stroke, is designated B. Dwell D is the
interval of zero fluid transfer in the expansion chamber following
reversal of reciprocating action applied to the drive means and, in
this embodiment dwell can be defined as the interval, expressed as
angular spacing or phase angle, between commencement of piston rod
compression stroke at A and commencement of piston means
compression stroke designated E. The same definition applies for a
piston rod induction stroke and is angular spacing between B and F.
The sequence of operation is as follows. The throws 140 and 141 are
indicated in broken outline on the diagram spaced at a phase angle
C compatible with FIG. 5, but are shown in different positions
relative to the crank shaft datum.
As the piston means is approaching the end of the induction stroke
at A, the valve means 152 connects conduits 48 and 45 to vent
concentrate fluid from the expansion chamber, while conduit 46 is
closed. Fluid pressure in chambers 156 and 157 is low and shortly
after A, at G the conduits 48 and 45 are disconnected or closed
with the conduit 46 remaining closed. Piston rod means 146 is now
moving downwards into the chamber 157, whilst the piston disc 161
remains stationary, the rod means acting as a pump plunger
compressing feed fluid in the chamber 157. As pressure in the
chamber 157 increases, slightly before E at H the check valve 40
(see FIG. 1) begins to open to deliver feed fluid into the
differential surge absorber 15 through the conduit portion 41.
Between H and E, at J the first valve means re-opens to connect the
conduit portions 48 and 46 at which time pressure in these two
conduit portions has already been approximately equalized by the
plunger action of the piston rod means, and shortly thereafter at E
the stop 159 contacts the piston disc 161 so that the piston disc
now moves with the piston rod means, thus terminating the dwell
interval D.
Further rotation of the crank shaft 138 completes the piston rod
stroke, whilst the valve spool 148 reaches top dead center position
of its stroke at I and then starts to descend. At bottom dead
center B the piston disc reaches its lower limit in the cylinder,
commencing the dwell interval and the check valve 40 closes.
Shortly thereafter at K the valve 152 closes the conduits 48 and
46, with the conduit 45 remaining closed. The piston rod means
again passes through the stationary piston disc 161 and acts as a
pump plunger to withdraw from the chamber 157. When the pressure is
fully reduced shortly before F, the check valve 37 opens at L and
feed fluid begins to enter the pumping chamber 157 through the
conduit 36. Shortly afterwards, at M the valve 152 connects the
conduits 48 and 45 at which stage the pressure in the conduits 48
and 45 has been approximately equalized. Shortly thereafter at F,
the stop 160 contacts the piston disc 161 terminating the piston
dwell period and the piston now commences an induction stroke. The
piston disc completes the induction stroke while the valve passes
its bottom dead center position at N and then reverses. The piston
rod means 146 returns to the top dead center position A, completing
the cycle which is then repeated. Angular separation between points
A and G, H and J, J and E and corresponding positions on the
diametrically opposite side are shown exaggerated and typically
might be between 2 and 5 degrees depending on manufacturing
tolerances, fluid compressibility and volume changes of the
cylinder, etc. due to pressure variations. Dwell D might be between
10 degrees and 30 degrees. Projections P and R from the diagram
represent piston rod stroke and piston disc stroke
respectively.
To retain the above sequence of valve actuation relative to piston
means position, the throw 141 of the valve means must be spaced 90
degrees from a mid-point S of the dwell interval D. Thus, as drawn,
the throw 141 is spaced at a phase shift of ##EQU1## degrees
lagging the throw 140 and thus, valve top center I follows piston
top dead center A by a phase shift angle of ##EQU2## Similarly, N
preceeds A by a phase shift angle of ##EQU3## degrees. The same
results may be achieved alternatively by spacing the throw 141 with
the phase shift of ##EQU4## degrees leading throw 140.
Thus the provision of dwell using a floating piston requires a
crank shaft having throws for actuation of the piston and
respective valve means to be spaced apart or phased apart at angle
other than 90 degrees to accommodate this dwell, at a phase angle
of ##EQU5## degrees. This enables the first valve means to be fully
closed during the dwell period, that is the valve closure angle V
of the first valve means is overlapped at both ends by the dwell
angle D which permits equalization of pressures across conduits of
the first valve means about to be opened or closed. Approximate
pressure equalization across related conduits increases life of
critical valve seals and seats without severe erosion and wear
usually experienced with high pressure fluids of low viscosity, low
compressibility and low lubricity. Approximate equalization of
pressure differences across conduits about to be opened also
reduces the forces that must be applied to actuate the valve means,
thus extending life and reliability of valve actuation mechanism.
In contrast with the embodiment of FIG. 1 where motion of piston
means 25 and the three-way valve 13 is intermittent because of
spool travel between the stops of the valve spool, the embodiment
136 of FIG. 5 relies essentially on the position of the piston
means as determined by the linkage to interchange smoothly the
three-way valve assembly 152 as the piston means reaches its dead
center positions at ends of piston stroke in the pump cylinder. It
can be seen that both the piston rod means 146 and the valve spool
148 of FIG. 5 have smooth quasi-harmonic reciprocating motion which
contrasts with the intermittent motion of the piston means 25 and
the spool 49 of FIG. 1. The intermittent motion of the embodiment
of FIG. 1 is appropriate for small or low speed units, but the
embodiment of FIG. 5 is more appropriate for larger units or higher
shaft speeds where discontinuous motion would be unacceptable, and
the desired amount of dwell is then provided by floating the
piston. With large apparatus where flow momentum effects are
material, increasing dwell above the minimum required for valve
sequencing further reduces hydraulic shock which might otherwise
occur. Clearly, in view of the incompressible character of sea
water, the crank shaft actuated apparatus could not function
without positive dwell provided by the floating piston means or
equivalents. Relatively slow actuation of directional valves
conveying a harsh liquid is desirable and this is attained by the
quasi-harmonic valve actuation and dwell means. Valve closure angle
V can be increased by slowing valve speed or extending closed
center portion of the valve spool, but dwell D must overlap V at
both ends.
Alternative crank mechanisms equivalent to the simple two throw
crank shaft can be substituted to provide separate quasi-harmonic
motion of the piston rod means, a piston dwell interval after each
reversal of the piston rod means and a 90 degree phase difference
from the mid-point of the dwell interval for actuation of the
three-way valve. Alternative mechanisms includes for example swash
plate drives, scotch yoke drives, axial and radial roller cam
drives and others. Clearly, particularly with cam drives, a wide
range of piston rod and valve spool accelerations and velocities
are possible, and a wide range of dwell separations and periods can
be attained by suitable cam design.
The dwell interval should be sufficiently long to enable valve
actuation at acceptable speeds and also to enable full pressure
equalization across the first valve. Excessively long dwell periods
are undesirable in most applications because the piston rod would
have acquired considerable velocity at the end of the dwell
interval.
FIG. 7
An alternative piston means 168 is shown in the pumping cylinder
150 of FIG. 5 and cooperates with an alternative piston rod means
169 as follows. The piston rod means has a pair of spaced supports
171 and 172 having partially spherical surfaces 173 and 174
disposed oppositely to each other. A flexible disc 176 has a
central bore to accept the rod means 169 and has shallowly,
convexly curved opposite faces 177 and 178 when in an undeformed
state, not shown, and has an outer periphery 179 of slightly larger
diameter than bore of the cylinder. The periphery carries a hard
wearing, low friction sealing ring 180 which projects from the
periphery sufficiently to be in sliding and sealing engagement with
cylinder walls. The disc is fitted between the supports and is thus
deformed into a saucer-like shape by the cylinder. The disc is
sufficiently flexible so that as the piston rod reverses its axial
motion, inner portions of the disc flex to follow the rod movement
whilst outer portions of the disc remain in static contact with the
cylinder walls until limit of deformation of the disc is reached,
at which time the periphery of piston disc slides on the cylinder
walls. The piston is thus sufficiently compliant to permit, upon
reversal of piston rod movement, movement of the piston rod means
and adjacent portions of the disc a relatively small amount,
typically between about 10 and 20 percent of total piston rod
stroke, with negligible sliding of the sealing ring on the cylinder
wall. It can be seen that the piston disc deforms from an upwardly
convex shape as shown when the piston travels downwards to a
downwardly convex shape, shown in broken outline at 176.1, upon
reversal of piston rod movement. This deformation of the disc
occurs with negligible slippage of the disc relative to the walls.
Thus, it can be seen that such a piston disc 176 serves in effect
as a resilient, essentially plane diaphragm means carried on the
piston rod means and has sufficient resilience to permit piston rod
movement with negigible piston disc movement and thus can provide
dwell to permit timely valve shifting as previously described.
A resilient piston disc as above described, when used with a crank
shaft similar to the crank shaft 138 of FIG. 5, has the important
advantage over a rigidly secured piston similar to the sliding
piston disc of FIG. 5 in that the first valve means opens or closes
conduits only when pressure across the disc has been approximately
equalized, thus reducing pressure differences and corresponding
flow velocities with resultant erosion. Reducing pressure
differences also reduces forces for valve actuation and this
correspondingly reduces valve wear.
It can be seen that the flexible piston disc 176 of FIG. 7, the
floating piston disc 161 of FIG. 5 and the diaphragm 108 of FIG. 3
are generally equivalent and can be defined as yieldable means
associated with the piston means and the piston rod means to permit
relative axial movement between a portion of the piston means and
the piston rod means in response to reversal of pump action. The
yieldable means provide a positive dwell which can be selected for
a desired value and is particularly important when the apparatus is
used for desalination of brine which has harsh properties of low
viscosity, poor lubricity and corrosiveness. Other yieldable means
can be substituted to cooperate with piston means and can be used
with alternative drive means, a further example of which is
described as follows.
FIG. 8
A third embodiment 181 of the invention is adapted for wind power
and has a supporting frame 183 and a mechanical drive means 182
which utilizes power from a horizontal axis wind turbine 184 which
drives a crank shaft 185. The shaft 185 has a connecting rod 186
and is journalled in a yoke 188 which is journalled for rotation
about a vertical axis 189 relative to the frame 183 to permit the
turbine to operate in all wind directions. Aligned shafts 191 and
192 are carried in bushings 193 and 194 mounted in the frame 183,
and a swivel coupling 196 connects the shafts to permit relative
rotation therebetween with negligible axial relative movement. The
shaft 191 is hinged to the connecting rod 186 and the shaft 192 is
hinged to a link 198. The link 198 is hinged to a coupling 199
secured to the lever 54 of the first embodiment 10 of the
apparatus. The lever 54 cooperates with the piston rod means 32 and
the valve spool 49 as previously described, and it can be seen that
the coupling 199 can be shifted axially along the lever 54 and thus
adjust pump stroke with a corresponding change in average torque
requirement for the crank shaft 185. When used with a wind turbine,
axial adjustment of the coupling can be useful to adjust pump
delivery to prevailing wind speed and also to unload the wind
turbine for easier starting.
Clearly, the mechanical drive means 182 of FIG. 8 can be applied to
drive the lever 54 from any low speed rotating shaft powered by any
prime motor. If the orientation of the shaft is fixed in such
applications, the swivel 196 and the aligned shafts 191 and 192 can
be eliminated and a single connecting shaft substituted. It may be
convenient in some installations to connect the connecting rod 186
directly to the coupling 199 without intervening linkage.
FIG. 9
An alternative multi-cylinder embodiment 201 of the invention has a
first pump means and first valve means 203 and 204 having piston
rod means and valve actuating means 205 and 206 respectively. The
valve actuator can be an outer portion of the valve spool or
equivalent means to shift the three-way directional valve. The
embodiment 201 has a similar second pump means 208 with respective
first valve means 209, piston rod means 210 and valve actuating
means 211, the pump cylinders and first valve means being directly
opposed to each other to minimize side loads on the piston rod
means and the valve actuators. A piston rod connecting means 213
aligns and connects the piston rod means 205 and 210 of the first
and second pump means, and an articulated valve actuator connecting
means 214 connects the valve actuators 206 and 211 of the first
valve means of the first and second pump means. A lever means 216
serving as a drive means for both pumps is hinged to the piston rod
connector means and the valve actuator connecting means of both the
first and second pump means, so that reciprocation of the lever
means simultaneously actuates the piston means of both pump means
so as to actuate the pump means in reverse phase to each other.
Respective first valve means of each pump means are actuated
essentially simultaneously shortly after reversal of the piston
stroke.
A feed fluid source 218 communicates with inlet conduits 219 and
220 of the first and second pump means, and a conventional
independent surge absorber 222 communicates with outfeed conduit
means 223 and 224 extending from the first and second pump means.
An independent conventional concentrate surge absorber 226
communicates with return conduit means 227 and 228 communicating
with the first valve means 204 and 209 of the first and second pump
means respectively. Vent conduits 230 and 231 extend from the first
valve means 204 and 209 to dump concentrate fluid fractions and a
membrane vessel 234 and high pressure filter 235 in conduit 236
communicates with the return conduit means 228 and the outfeed
conduit means as shown. When two or more pump cylinders are
provided phased equally apart, feed flow fluctuations across the
membrane means are reduced thus permitting reduction of
differential surge absorber displacement, or use of conventional
accumulators as disclosed above.
In operation, it can be seen that pumping chamber and expansion
chamber of the first pump means, not shown, feed fluid to the
membrane means and receive 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, the two cylinder arrangement with the conventional
accumulators serves as means to provide essentially uniform
pressure and feed fluid flow across the membranes. Thus, multiple
pump means in combination with accumulators can be considered
equivalent to the differential surge absorber of FIG. 1. The surge
absorbers can be spring-loaded pistons or diaphragms as shown for
the differential surge absorbers, or alternatively other types of
surge absorbers known in the art, including pneumatic bladder
accumulators or weight-loaded piston accumulators can be used.
Clearly, one of the first valve means can be eliminated by
combining in one valve assembly a spool which has a function of a
four-way valve to open respective chambers of one pump means whilst
closing chambers of the remaining pump means. Other variations are
envisaged, such as providing mechanical actuation of the non-return
check valves in the inlet and outfeed conduits.
A further variation in the method of operating the invention is
applicable when two or more pumps phased equally apart are used.
Some or all of the energy required to power the pump may be
provided by pressurizing the feed fluid by a relatively low powered
external feed pump means to a pressure below the membrane working
pressure. A feed pump 238 is shown in broken outline in the inlet
conduit extending from the feed fluid source 218, so as to
pressurize the inlet conduits 219 and 220. If the feed fluid has a
sufficiently high pressure prior to entry into pump means, no
further mechanical energy need be supplied to drive the system by
either lever or crank mechanism. The lever 216 of FIG. 9 would then
provide only a valve timing function.
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