GB1601519A

GB1601519A - Reverse osmosis method and apparatus

Info

Publication number: GB1601519A
Application number: GB30531/80A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-03-28
Filing date: 1978-03-20
Publication date: 1981-10-28
Also published as: AU513613B2; DE2812761A1; JPS53144472A; FR2385427A1; IL54291A0; DE2812761C2; EG13490A; JPS641667B2; IL54291A; AU3429978A; FR2385427B1; GB1601518A; CA1118365A

Description

0

)o CD 4 PATENT SPECIFICATION ( 21) Application No 30531/80 ( 22) Filed 20 March 1978 ( 62) Divided out of No 1601518 ( 31) Convention Application No 782540 ( 32) Filed 28 March 1977 in ( 33) United States of America (US) ( 44) Complete Specification published 28 Oct 1981 ( 51) INT CL 3 B Ol D 13/00 CO 2 F 1/44 F 04 B 19/04 ( 52) Index at acceptance Bl X 6 A 1 6 B 3 6 F 1 FIW 100 203 220 CM ( 54) REVERSE OSMOSIS METHOD APPARATUS ( 71) I, BOWIE GORDON KEEFER, a Canadian Citizen, of 4324 West 11 Avenue, Vancouver, British Columbia, Canada V 6 R 2 M 1, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the

following statement:-

The invention relates generally to reverse osmosis and ultrafiltration fluid separation processes, and is applicable particularly to water desalination and purification by reverse osmosis.

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 ( 11) 1 601 519 AND almost full working pressure, but before the concentrate stream is exhausted from the apparatus, it must be depressurised In common reverse osmosis apparatus the concentrate stream is depressurised 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, lifeboats, etc would be almost unpracticable.

Similarly, using wind power for desalination is.discouraged by high energy consumption.

Furthermore, for high recovery concentration polarisation must be controlled Concentration polarisation 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 polarisation 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 polarisation 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 2 1,601,519 2 polarisation 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 severe concentration polarisation.

Operation at low ratios of product flow to concentrate flow is also generally favourable to the reduction of concentration polarisation effects, but of course increases the feed pumping energy expenditure for given product flow delivery.

According to the present invention there is provided 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 apparatus including: reciprocating pump means having a cylinder, a movable piston means and a piston rod means, the piston means dividing the cylinder into a pumping chamber for the feed fluid and an expansion chamber for the concentrate fluid fraction, the piston rod means extending through the expansion chamber, the cylinder and piston rod means having relative diameters which define cylinder/piston rod proportions to determine in part recovery ratio of permeate fluid fraction to total feed fluid flow; inlet conduit means to admit feed fluid into the pumping chamber; outfeed conduit means to conduct feed fluid from the pumping chamber to the membrane means; return conduit means to conduct the concentrate fluid fraction from the membrane means to the expansion chamber; surge reducing means communicating with the outfeed and return conduit means to reduce fluctuations in pressure and feed fluid flow across the membrane means; first valve means communicating with the expansion chamber and having a closed intermediate position between first and second positions, and non-return second valve means communicating with the pumping chamber, the first valve means co-operating with the conduit means to direct fluid flow to and from the expansion chamber of the pump; rotatable drive means activating the piston rod means and the first valve means whilst maintaining a phase angle difference between the piston means stroke and first valve means actuation so that pressurised feed fluid is fed from the pumping chamber to the membranes through the second valve means while pressurised concentrate fluid is discharged through a port of the first valve means into the expansion chamber and is depressurised therein to assist in pressurising the feed fluid, followed by exhausting depressurised concentrate fluid from the expansion chamber through a port 70 of the first valve means while feed fluid is inducted into the pumping chamber through the second valve means; wherein the apparatus incorporates dwell means associated with the pump means and the 75 drive means to ensure that there is dwell interval between the piston means movement and valve actuation so that the first valve means is shifted across the closed intermediate position in which said ports 80 are closed during an interval of essentially zero fluid transfer from the cylinder by the piston means after initiation of each stroke of the piston rod means, the dwell means being constructed and arranged to permit 85 variation of fluid volume relationship between the pumping and expansion chambers whereby to permit approximate equalisation of pressure between the pumping and expansion chambers following 90 reversal of piston rod means movement, so that initial movement of the piston rod means causes approximate equalisation of the pressures across that port of the first valve means which is about to be opened 95 prior to opening of said port.

The invention also provides a method of membrane separation of a feed fluid into permeate fluid and concentrate fluid fractions which respectively are permeated 100 and rejected by selective membrane means, the membrane means being exposed to pressurised feed fluid supplied by a reciprocating pump means having a cylinder and piston means connected to the 105 membrane means by valve means and conduit means, the piston means dividing the cylinder into a pumping chamber in which feed fluid is pressurised and an expansion chamber in which the 110 concentrate fluid is depressurised; said pressurised feed fluid being supplied via conduit means connected to surge reducing means; the method including the steps of:

rotating rotary drive means to cause the 115 piston means to move alternately through inducting and pumping strokes to actuate the valve means, so that in each inducting stroke a port of the valve means is opened to exhaust depressurised concentrate fluid 120 from the expansion chamber as the piston inducts feed fluid into the pumping chamber, and in each pumping stroke a port of the valve means is opened to admit pressurised concentrate fluid into the 125 expansion chamber to supplement energy supplied to the piston in the pumping stroke as the piston pressurises the feed fluid in the pumping chamber; the method being characterised by: during initiation of the 130 1,601,519 1,601,519 pumping stroke and of the induction stroke, simultaneously (a) shifting the valve means across a closed intermediate position in which said ports of the valve means are closed; and (b) varying the fluid volume interrelationship of the pumping and expansion chambers and approximately equalising the pressures across that port of the valve means that is about to be opened, prior to opening of said port.

The invention enables reverse osmosis to be achieved with low energy consumption; and enables operation at a low ratio of product flow to concentrate flow without excessive energy consumption normally associated with large feed flows because of the recovery of fluid pressure energy from the concentrate stream Concentration polarization effects are reduced by the surge reducing means to maintain the continuity of feed flow circulating past the membranes The dwell means increases tolerance to valve actuation, thus simplifying manufacture and servicing.

The term "piston means" is used herein as a general term for a piston or diaphragm, and in one embodiment the piston means comprises a diaphragm.

The invention will be described further, by way of example, with reference to the accompanying drawings, wherein:Figure 1 is a simplified section through embodiment of reverse osmosis apparatus according to the invention; Figure 2 is a simplified elevation, partially in section, of the piston means shown in Figure 1, which shows also dwell means and drive means of the apparatus, Figure 3 is a timing diagram showing relative angular positions of piston and valve means shown in Figure 2; Figure 4 is a fragmented section of an alternative valve means for the apparatus; Figure 5 is a fragmented section of a second form of piston means for use in the apparatus:

Figure 6 is a detailed fragmented section of an alternative differential surge absorber for use in the Figure 1 embodiment; and Figure 7 is a simplified fragmented section of a further form of a piston means with dwell means incorporated therein.

The directions "upwards" and "downwards" refer to the figures as drawn, but clearly the apparatus could be in other orientations.

Referring to Figures 1, 2 and 3 the apparatus includes a reciprocating pump means 12, valve means 13, a drive means 14 (Figure 2) mechanically connected to the pump means and valve means (as shown in Figure 2), and a differential surge absorber 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 70 respectively permeated and rejected by the membrane means.

The reciprocating pump means 12 generally comprises a pump cylinder 24 and a movable piston means 25, the piston 75 means dividing the cylinder into a pumping chamber 27 in which the feed fluid is pressurised, and an expansion chamber 28 in which the concentrate fluid is depressurised The piston means co 80 operates with a piston rod means 32 extending through the expansion chamber, and sealing means 163 (described hereinafter with reference to Figure 2) prevents leakage of fluid Inlet conduit 85 means 36 admits feed fluid 21 to the ,pumping chamber 27 from a conduit portion 35 immersed in feed fluid, via a nonreturn check valve 37 and the filter 18, which valve 37 prevents return flow from 90 the chamber into the conduit portion 35.

Outfeed conduit means 39 connects the pumping chamber with the membrane means 17 via the differential surge absorber and filter 19 to conduct pressurised feed 95 fluid from the pumping chamber to the membrane means, a non-return check valve preventing return flow of fluid into the pumping chamber.

The outfeed conduit means 39 consists of 100 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 105 portion 43 extending from the filter 19 to the membrane vessel means A return conduit means 44 connects the membrane means with the expansion chamber 28 to conduct the concentrate fluid fraction from 110 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 115 46 extending between the directional valve means 13 and the differential surge absorber The valve means 13 has a vent conduit 47 to conduct the concentrate fluid fraction 23, usually to waste, and a connecting 120 conduit 48 communicating with the expansion chamber 28.

The valve means 13 is a three-way directional control valve, and has a sliding valve spool 49 for opening and closing ports 125 of the valve assembly The spool is shown in the upper limit of travel in which a port 50 is open which connects the conduit portion 46 with the connecting conduit 48 to conduct the concentrate fluid fraction from the 130 1,601,519 membranes to the expansion chamber In a lower limit of travel, not shown, a port 51 is open so that 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 minimise leakage and prevent spool seizure.

Thus, the valve assembly 13 is a twoposition, centre-closed, three-way valve having a movable spool, the spool having travel between two positions through a closed intermediate position in which the ports 50, 51 are closed to interchange conduit connections The valve means 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 co-operate 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 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 co-operates with a piston rod means 69 extending through the concentrate surge absorber chamber 66, and comprises a piston having sealing means 70 to engage the cylinider to prevent mixing of fluid Sealing means 71 is provided to prevent leakage of fluid from the cylinder For smooth operation of the surge absorber the seals of the sealing means are selected for low friction characeteristics 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 co-operates 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 pressurised 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 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 70 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 75 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 80 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 It should be noted that 85 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 90 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 95 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 100 container vessel is designed to ensure sufficient forced convection of the feed fluid to prevent excessive concentration polarisation effects If the feed fluid flow velocity is dropped too low, concentration 105 polarisation effects can become severe.

The general arrangement of the apparatus is such that, during a downwards pumping stroke of the piston means, the valve spool 49 is held in its uppermost 110 position to close the vent conduit 47 and to connect the conduit portion 46 with the connecting conduit 48 so as to pass the pressurised concentrate fluid fraction from the membrane vessel 16, through the 115 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 120 28 augments the force applied to the piston means by the drive means in direction of arrow 74 to pressurise feed fluid in the chamber 27 The check valve 37 is held closed by the feed fluid pressure and the 125 check valve 40 is open to transmit pressurised feed fluid from the pumping chamber 27 through the conduit portion 41 into the feed surge absorber chamber 67 of the differential surge absorber 15 130 1,601,519 Pressurised 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 in to 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 utilised, 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, the drive means has to supply only a fraction of the power that would have been required without energy recovery.

As explained hereinafter with reference to Figure 3, during each upwards induction stroke of the piston means the valve spool 49 is held in a down position in which the conduit portion 46 is closed, thus isolating the chamber 28 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 The check valve 37 is opened by the upwards movement of the piston means to induct feed fluid into the pumping chamber 27 and the check valve 40 is closed to prevent return flow of fluid from the differential surge absorber 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 polarisation 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 70 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 75 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 80 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 85 uniform feed fluid flow across the membranes.

The piston means and the drive means are arranged to provide dwell means to permit actuation of the first valve means during an 90 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 (which arises when the 95 first valve means is closed) without destructive shocks.

As shown in Figure 2 the drive means 14 includes a powered crank shaft 138 mounted in journals, not shown, for rotation 100 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 105 at top dead centre Connecting rods 143 and 144 connect the throws 140 and 141 to the piston rod means 32 and the valve spool 49 respectively, and the spool travel is limited by the crank shaft rotation and the throw of 110 the crank 141.

The piston rod means 32 has a pair of spaced stops 159 and 160 fitted with oppositely facing resilient pads 158 The piston means 25 includes a piston disc 161 115 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 120 when the disc 161 contacts the stops.

Sealing means, in the form of 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 125 Spacing 164 between the pads 158 of the stops and thickness of the disc are such that the piston rod means 32 can move axially through the disc 161 with negligible movement of the disc between 130 1,601,519 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 32 The ratio of permeate flow to feed flow is only partially determined by the simple ratio of piston rod section area to piston area, because the strokes of piston rod and piston are inequal.

Upon reversal of piston rod movement there is relative movement, i e axial sliding, between the disc 161 and the piston rod means 32 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.

Figure 3 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 centre 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 centre, which is immediately prior to a piston induction stroke, is designated B. Dwell D is the inverval 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 Figure 2, 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 13 connects conduits 48 and 47 to vent concentrate fluid from the expansion chamber, while conduit 46 is closed Fluid pressure in chambers 27 and 28 is low and shortly after A, at G the conduits 48 and 47 are disconnected or closed with the conduit 46 remaining closed Piston rod means 32 is now moving downwards into the chamber 28 whilst the piston disc 161 remains stationary so as to vary the fluid volume relationship of the pumping and expansion chambers, the rod means acting as a pump plunger compressing feed fluid in the chamber 28 As pressure in the chamber 28 increases, slightly before E and H the check valve 40 (see Figure 1) begins to open to deliver feed fluid into the differential surge absorbers 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 equalised 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 49 reaches top dead centreposition of its stroke at I and then starts to descend At bottom dead centre 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 first valve means 13 closes the conduits 48 and 46, with the conduit 47 remaining closed The piston rod means again passes through the piston disc 161 and acts as a pump plunger to withdrawn from the chamber 28 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 28 through the conduit 36 Shortly afterwards, at M the valve means 13 connects the conduits 48 and 47 at which stage the pressure in the conduits 48 and 47 has been approximately equalised 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 centre position at N and then reverses The piston rod means 32 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; and J and E (and the 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 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 ( 90-D/2) degrees lagging the throw 140 and thus, 1,601,519 valve top centre I follows piston top dead centre A by a phase shift angle of ( 90-D/2).

Similarly, N precedes A by a phase shift angle of ( 90-D/2) degrees.

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 ( 90-D/2) 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 equalisation of pressures across the ports of the first valve means about to be opened or closed.

Approximate pressure equalisation across said ports 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 equalisation of pressure differences across ports 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 The apparatus 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 centre positions at ends of piston stroke in the pump cylinder It can be seen that both the piston rod means 32 and the valve spool 49 of Figure 2 have smooth quasi-harmonic reciprocating motion, and the desired amount of dwell is afforded 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 centre 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 quasiharmonic 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 70 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 75 long to enable valve actuation at acceptable speeds and also to enable full pressure equalisation across the first valve.

Excessively long dwell periods are undesirable in most applications because the 80 piston rod would have acquired considerable velocity at the end of the dwell interval.

The first valve means is shown displaced laterally relative to the piston means, 85 however, other relative positions can be devised to be within the scope of the invention, and alternative first valve means can be substituted.

An alternative first valve means 81 is for 90 use with the embodiment 10 of Figure 1 and equivalents is shown in Figure 4, and a three-way valve having a spool or sliding cam 82 The cam 82 actuates two two-way poppet valves 85 and 86, having 95 complementary seats 87 and 88 in ports, which valves are connected to conduits as follows A return conduit portion 89 connects valve 85 with the differential surge absorber, not shown, a connecting conduit 100 connects both valves with the expansion chamber of the pump means, not shown, and a vent conduit 91 connects the valve 86 with a concentrate fluid outlet, not shown.

The valves 85 and 86 have respective springs 105 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, 110 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 to keep one of the ports 115 closed 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 120 the link 144 of Figure 2, and the means 81 can be directly substituted for the valve means 13 and functions similarly.

In operation, the valve is shown in a fully raised position, in which position the cam 82 125 lifts the valve 85 off the seat 87 to open the port of fluid flow so that conduits 89 and 90 are connected to admit pressurised concentrate fluid from the membrane means into the expansion chamber The 130 1,601,519 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 to open the port to fluid flow 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.

Figure 5 shows alternative pump means which includes an alternative pump cylinder to which with the inlet conduit 36, the outfeed conduit 39 and the connecting conduit 48 are connected as previously described with reference to Figure 1 The pump cylinder 105 has an alternative piston rod means 106 which co-operates with piston means comprising 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 substitute for the piston means 25.

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 163 of the piston means 25 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 to permit a variation in the fluid volume interrelationship of the pumping and expansion chambers Thus, it can be seen that resilience of the diaphragm provides dwell to permit substantial equalisation of the pressure differences across the diaphragm during valve shifting.

An alternative differential surge absorber 65 118 is shown in Figure 6 for the differential surge absorber 15 of Figure 1 The absorber 118 has an alternative cylinder 119 communicating with conduit portions 41 and 42 of the outfeed conduit means 39, and 70 with conduit portions 45 and 46 of the return conduit means 44 The surge absorber 118 has an alternative piston rod means 121 which co-operates with a flexible diaphragm or bellows 123 which is secured 75 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 80 surge absorber chamber 130 A coil spring 131 encircles the piston rod means 121 and functions similarly to the spring 72 of Figure 1 Consideration relating to the substitution of the piston means 25 of, 85 Figure 1 by the alternative piston means comprising the diaphragm 108 of Figure 5, apply also to the structure of Figure 6.

An alternative piston means 168 is shown in the pumping cylinder 24 of Figures 1 and 90 2 and co-operates 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 95 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 100 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 105 The disc is fitted between the supports and is thus deformed into a saucer-like shape by the cylinder The disc is sufficiently flexaible so that as the piston rod reverses its axial motion, inner portions of the disc 110 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 115 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 by a relatively small 120 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 125 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 1.601,519 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 negligible piston disc movement and thus can provide dwell to permit timely valve shifting as previously described, so that the first valve means opens or closes conduits only when pressure across the disc has been approximately equalised, 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 Figure 7, the floating piston disc 161 of Figure 2 and the diaphragm 108 of Figure 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 co-operate with piston means and can be used with alternative drive means.

Claims

WHAT I CLAIM IS:-

1 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 apparatus including: reciprocating pump means having a cylinder, a movable piston means and a piston rod means, the piston means dividing the cylinder into a pumping chamber for the feed fluid and an expansion chamber for the concentrate fluid fraction, the piston rod means extending through the expansion chamber, the cylinder and piston rod means having relative diameters which define cylinder/piston rod proportions to determine in part recovery ratio of permeate fluid fraction to total feed fluid flow, inlet conduit means to admit feed fluid into the pumping chamber; outfeed conduit means to conduct feed fluid from the pumping chamber to the membrane means; return conduit means to conduct the concentrate fluid fraction from the membrane means to the expansion chamber; surge reducing means communicating with the outfeed and return conduit means to reduce fluctuations in pressure and feed fluid flow across the 65 membranes means; first valve means communicating with the expansion chamber and having a closed intermediate position between first and second positions, and non-return second valve means 70 communicating with the pumping chamber, the first valve means co-operating with the conduit means to direct fluid flow to and from the expansion chamber of the pump; rotatable drive means activating the piston 75 rod means and the first valve means whilst maintaining a phase angle difference between the piston means stroke and first valve means actuation so that pressurised feed fluid is fed from the pumping chamber 80 to the membranes through the second valve means while pressurised concentrate fluid is discharged through a port of the first valve means into the expansion chamber and is depressurised therein to assist in 85 pressurising the feed fluid, followed by exhausting depressurised concentrate fluid from the expansion chamber through a port of the first valve means while feed fluid is inducted into the pumping chamber 90 through the second valve means; wherein the apparatus incorporates dwell means associated with the pump means and the drive means to ensure that there is dwell interval between the piston means 95 movement and valve actuation so that the first valve means is shifted across the closed intermediate position in which said ports are closed during an interval of essentially zero fluid transfer from the cylinder by the 100 piston means after initiation of each stroke of the piston rod means, the dwell means being constructed and arranged to permit variation of fluid volume relationship between the pumping and expansion 105 chambers whereby to permit approximate equalisation of pressure between the pumping and expansion chambers following reversal of piston rod means movement, so that initial movement of the piston rod 110 means causes approximate equalisation of the pressures across that port of the first valve means which is about to be opened prior to opening of said port.

2 Apparatus as claimed in claim 1 in 115 which the dwell means incorporates 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 120 means in response to reversal of the piston means stroke.

3 Apparatus as claimed in claim 2 in which the yieldable means comprises a pair of spaced stops provided on the piston rod 125 means, and a disc of the piston means, said disc having a bore accepted as a sliding fit on the piston rod means, the disc being interposed between the stops, wherein the 1,601,519 spacing between the stops and thickness of the disc permit relative axial sliding between the disc and the piston rod limited by the stops so that piston stroke is less than piston rod stroke.

4 Apparatus as claimed in claim 2 in which the piston means comprises a flexible diaphragm attached to said piston rod means and separating the pump chamber from expansion chamber, wherein said diaphragm serves as the yieldable means so that resilience of the diaphragm permits the piston rod means to move without fluid transfer in the expansion chamber so as to essentially equalise fluid pressures across conduits to be connected prior to shifting of the first valve means.

Apparatus as claimed in claim 2 in which the piston means comprises a flexible disc mounted on the piston rod means having a periphery in sliding sealing contact with the pump cylinder, wherein the flexible disc serves as the yieldable means, the flexibility of the disc 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.

6 Apparatus as claimed in any preceding claim in which the surge reducing means comprises a differential surge absorber 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 substantially uniform feed fluid flow.

7 Apparatus as claimed in claim 6, wherein the differential surge absorber comprises a cylinder and a piston means which is spring-loaded and double-acting and reciprocable with the cylinder, the piston means of the differential surge absorber having a displacement several times greater than that of the piston means of the pump means.

8 Apparatus as claimed in claim 6 in which the differential surge absorber comprises a cylinder and a 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 pressirised feed fluid in the outfeed conduit means and the concentrate surge absorber chamber being exposed to the concentrate fluid fraction in the return conduit means; wherein the piston means co-operates with a piston rod extending through the concentrate surge absorber chamber, there being sealing means to seal the surge absorber against leakage; and wherein spring means cooperates with the piston means to force the piston means in a direction to exhaust the feed surge absorber chamber.

9 Apparatus as claimed in claim 8 in which the piston means of the differential surge absorber comprises a flexible diaphragm attached to piston rod means and separating the feed surge absorber chamber from the concentrate surge absorber chamber.

Apparatus as claimed in claim 8 in which the piston means of the differential surge absorber comprises a piston provided with a seal to engage the cylinder to prevent mixing of fluid in the cylinder.

11 Apparatus as claimed in any preceding claim, wherein 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 the drive means.

12 Apparatus as claimed in claim 11, wherein the spool serves as a cam means; and wherein said first valve means comprises a pair of normally-closed twoway poppet valves to close said ports, the poppet valves being unseated to open the ports 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.

13 Apparatus as claimed in claim 11, wherein said spool serves to open and close said ports and is provided with sealing means to prevent leakage from the valve.

14 Apparatus as claimed in any 100 preceding claim, wherein the rotational drive means is arranged so that the first valve means closes a few degrees of rotation of the drive means after the piston rod means has reached the limit of each stroke 105 Apparatus as claimed in claim 14, wherein the dwell means provides dwell through a rotational angle D of the drive means which angle commences as the piston rod reaches the limit of each stroke, 110 and wherein the first valve means is actuated to open one of said ports a few degrees before the end of said dwell.

16 Apparatus as claimed in claim 15, wherein the dwell angle D lies in the range 115 of 100 to 30 .

17 Apparatus as claimed in claim 15 or 16, wherein said rotational drive means is a crankshaft having a first throw for the piston rod means, and a second throw for 120 the first valve means, and wherein said second throw lags the first throw by an angle of ninety degrees less half of the dwell angle D.

18 Membrane separation apparatus 125 substantially as hereinbefore described with reference to Figures 1 to 3, or Figures 1 to 3 as modified by Figures 4, 5, 6 or 7 of the accompanying drawings.

1,601,519 19 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 pressurised feed fluid supplied by a reciprocating pump means having a cylinder and piston means connected to the membrane means by valve means and conduit means, the piston means dividing the cylinder into a pumping chamber in which feed fluid is pressurised and an expansion chamber in which the concentrate fluid is depressurised; said pressurised feed fluid being supplied via conduit means connected to surge reducing means; the method including the steps of:

rotating rotary drive means to cause the piston means to move alternately through inducting and pumping strokes to actuate the valve means, so that in each inducting stroke a port of the valve means is opened to exhaust depressurised concentrate fluid from the expansion chamber as the piston inducts feed fluid into the pumping chamber, and in each pumping stroke a port of the valve means is opened to admit pressurised concentrate fluid into the expansion chamber to supplement energy supplied to the piston in the pumping stroke as the piston pressurises the feed fluid in the pumping chamber; the method being characterised by: during initiation of the pumping stroke and of the induction stroke, simultaneously (a) shifting the valve means across a closed intermediate position in which said ports of the valve means are closed; and (b) varying the fluid volume interrelationship of the pumping and expansion chambers and approximately equalising the pressures across that port of the valve means that is about to be opened, prior to opening of said port.

A method as claimed in claim 19 in which the piston means is moved by piston rod means connected to the drive means, wherein the varying of the fluid volume interrelationship is performed by permitting yielding between portions of the piston means and the piston rod means so that there is relative movement therebetween.

21 A method as claimed in claim 20, wherein the shifting of the valve means across the closed position is completed before said relative movement ends.

22 A method of membrane separation of a feed fluid into permeate and concentrate fluid fractions substantially as hereinbefore described with reference to the accompanying drawings.

H N & W S SKERRETT, Chartered Patent Agents, Rutland House, 148, Edmund Street, Birmingham, B 3, 2 LQ.

Agents for the Applicant.

Printed for Her Majesty's Stationery Office, by the Courier Press, Leamington Spa, 1981 Published by The Patent Office, 25 Southampton Buildings, London, WC 2 A IAY, from which copies may be obtained.

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