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us patent for spiral separator patent (patent # 4,476,980 issued october 16, 1984) - justia patents search

us patent for spiral separator patent (patent # 4,476,980 issued october 16, 1984) - justia patents search

The invention provides a spiral separator of the type for use in separating a pulp of water and minerals into mineral fractions of differing densities and having a helical trough (30) supported with its axis upright. The shape of the trough working surface profile (30) varies (FIGS. 2A-2D) from place to place along the trough. The profile has a point of maximum displacement (32A, 32B, 32C, 32D) at which profile (30) is at a maximum spacing below a notional straight line (40) joining the inner end (31) and outer end (22) of the trough working surface profile (30). The distance of the point of maximum displacement (32A, 32B, 32C, 32D) from one end (31 or 22) of the profile varies along the trough. A method for manufacture of troughs according to the invention is also described and claimed.

Each trough has a floor situated between an outer trough wall and an inner trough wall. As herein used, the expression "Working surface" means that portion of the trough floor which in use supports pulp or solids. The expression "working surface profile" means any profile of the working surface viewed in a cross section taken in a vertical plane extending radially from the helix axis. The trough working surface profile generally inclines upwardly and outwardly, from the radially inner wall or column towards the radially outer wall. In some separators the column may be, or may be a part of, the inner trough wall. It will be understood that the trough floor at, or adjacent to, the radially innermost end of the working surface profile may curve inwardly upwards to blend with the inner wall or column. Likewise at or adjacent to the radially outermost end of the working surface profile, the floor may curve upwardly to blend with the outer wall. The radially inner and outer walls serve to retain materials but generally play no role in the separation process.

In operation of such separators, a "pulp" of slurry of the materials to be separated and water is introduced to the upper end of a trough at a predetermined rate and as the pulp descends the helix, centrifugal forces act on less dense particles in a radially outwards direction while denser particles segregate to the bottom of the flow and after slowing through close approach to the working surface gravitate towards the column. The streams are separated at intervals by adjustable splitters, the mineral fractions to be recovered being carried away through take off openings associated with the splitters.

In the most usual form of spiral separator a number of adjustable splitters are employed along the length of each helix with the section of trough between each splitter and the next being essentially identical with the section of trough between any other splitter and the next. Some of the heavier mineral is separated in each trough section and removed by the subsequent splitter. To assist the removal of low specific gravity particles from the underlying high specific gravity particles it is often necessary to supply from a separate system a small amount of water flowing radially outwards. This is normally referred to as wash water. Both the splitters and wash water systems may require periodic adjustment. Commonly two or three helices are supported by the column each with a number of splitters and each helix is mounted so that the starts are equiangularly spaced about the column and as close as practicable to coplanar to facilitate the simultaneous feed of pulp to all three.

Preferred embodiments of the present invention permit the segregation and separation of the heavier particles of a pulp and their separation from lighter particles to proceed with a reduced need for periodical removal of heavy particles via a splitter. The number of splitters required per trough is thus greatly reduced. In addition, preferred embodiments permit thin films of the water originally present in the pulp to flow with a radially outwards component in the areas in which light particles overlie heavy particles to achieve the function of the wash water separately supplied in prior art spiral separators.

Preferred embodiments of the present invention enable the production of a concentrate of mineral sands almost free of low specific gravity particles, and where multiple types of high specific gravity particles are present in the feed, enable preferential extraction of various types at various levels. Moreover this may be achieved with greater efficiency and less frequent adjustment than has been necessary with prior art separators.

Accordingly to a first aspect the present invention has a spiral separator of the type comprising a helical trough supported with its helical axis upright and adapted to separate a pulp of water and minerals flowing theredown into mineral fractions of differing mineral density, said separator being characterised in that the shape of the working surface profile varies from place to place along the trough and in that the distance of the point of maximum displacement (as herein defined) from one end of the profile also varies from place to place along the trough.

As herein used the expression "Point of Maximum Displacement" means, in relation to a trough working surface profile, the point or zone at which the profile is at a maximum spacing below a notional straight line joining the radially inner end and the radially outer end of said working surface profile.

For preference, prior to a splitter, the point of maximum displacement moves progressively radially outwards across a working surface a constant inside and outside diameter but in other embodiments the same relative effect is achieved by variation of the profile inside diameter or the outside diameter and the point of maximum displacement as the helix is descended.

Also, for preference, the profile comprises an inner zone between the point of maximum displacement and the radially inner end of the profile which is rectilinear and an outer zone between the point of maximum displacement and the radially outer end of the profile which is rectilinear. The rectilinear inner and rectilinear outer zones lie at an angle having the point of maximum displacement as an apex. In other embodiments the working surface profile is dished so as to extend curvilinearly between the inner end and outer end thereof. In that event the point of maximum displacement is also preferably the point of maximum curvature of the profile.

With reference to FIG. 1 there is shown an upright column 1 supporting a hellical trough 2. Conventional means (not shown in FIG. 1) are provided for admitting a slurry to the trough at a predetermined rate to or adjacent the top and for splitting the descending slurry stream into fractions and recovering certain desired fractions.

The trough in cross-section comprises an upright inner wall 10, a support web 11 whereby the lip of inner wall 10 is connected with column 1, an upright outer wall 20 terminating in a lip 21 and a trough floor 30 extending between the inner wall and the outer wall.

Trough floor 30 has a working surface which extends outwardly and upwardly with respect to the helix radial direction from a lowermost point 31. In the example illustrated the working surface profile inner end is at lowermost point 31 of floor 30 and the outer end is at the heel 22 of outer wall 20. In other embodiments the working surface profile inner end need not be the lowermost point thereof and the outer end of the working surface need not be at the heel, if any, of the outer wall but it will be apparent to those skilled in the art where the inner and outer ends of the working surface lie.

The point of maximum displacement 32 is spaced apart from and below a notional line 40 (shown as a broken line in FIGS. 2A to 2D) which extends between the radially inner end 31 and the radially outer end 22 of the working surface profile. The point of maximum displacement is the point on the working surface profile which is at a maximum displacement below line 40.

In the present example the trough working surface comprises an inner zone 33 which lies substantially in a straight line inclined to the horizontal and sloping upwardly from the lowermost point 31 to a point of maximum displacement 32 situated radially outwardly of lowermost point 31. The trough working surface profile further comprises an outer zone 34 which also lies substantially in a straight line but which is inclined at a greater angle to the helix radial direction and thus slopes more steeply upwardly and outwardly from the point of maximum displacement 32 towards outer wall 20.

In the example illustrated the point of maximum displacement 32 is also the apex of an obtuse angle formed at the intersection of the line on which the inner zone 33 and the line on which outer zone 34 of the trough floor lie.

Inner wall 10 curves at 12 to blend smoothly with trough floor 30 at lowermost point 31. As herein defined curve 12 is not a part of the trough working surface and is regarded as a part of inner wall 10 by virtue that in use that part of the trough does not support pulp or minerals.

As is most apparent from FIG. 3, the shape of the working surface profile varies from place to place along the trough and the point of maximum displacement 32 is situated at distance from the inner end 31 which becomes greater as the helix is descended. It should be noted that the profiles shown in FIGS. 2A to 2D are at progressively lower altitudes of the helix and in FIG. 3 the cross-section marked A is in fact at a higher altitude of the helix than the cross-section marked D.

In the embodiment being described the inner end of each trough working surface profile is at a substantially uniform radial distance from the helix axis, the point of maximum displacement moves radially outwardly, and the inner zone extends over a progressively greater distance as the helix is descended.

Also, in the embodiment illustrated, outer wall 20 is at a substantially uniform distance from the spiral axis and the outer zone is progressively shortened with respect to the radial direction as the inner zone lengthens with descent of the helix.

Furthermore in the embodiment illustrated the slope of the inner zone is maintained at a constant angle to the helix radial direction as the helix is descended and the slope of the outer zone is maintained at a second constant angle to the helix radial direction.

In the embodiment illustrated the upper lip of inner wall 10 and of outer wall 20 are maintained at a constant pitch and the depth from the inner wall lip to the lowermost point of the trough becomes more shallow as the helix is descended.

By virtue that the radially outer zone of the trough working surface slopes more steeply, high specific gravity (and slower) particles are assisted to migrate inwards while the flatter sloped inner zone of the bottom assists low specific gravity (fast) particles to migrate outwards.

Furthermore, in preferred embodiments of the invention wherein the inner zone of lesser slope extends radially outwards over a greater distance as the helix is descended then, as the separation proceeds the high specific gravity particles become stabilized in a low speed layer adjacent the surface of the inner portion.

These particles may therefore be spread to a greater radius without loss due to centrifical force while increasing the possibility of rejecting low specific gravity particles to the radially outer areas due to the greater centrifugal forces acting on these higher speed particles.

The change in the profile of the working portion of the bottom of the trough also controls the radial distribution of the water in the slurry in that the mass of water is permitted to move radially outwards as the centre of curvature of the bottom of the trough moves radially outwards. This in turn causes thinning of the water layer towards the inner edge until a point is reached at which waves inevitably form in the film. The wave fronts tend to move tangentially to the helical flow and therefore have a component of movement radially outwards. If the profile is correctly designed these waves can be generated in the area in which light particles overlie heavy particles and the wave action in the thin film effectively performs the same function as the wash water separately supplied in earlier forms of spiral separators.

(b) middlings which include particles which may fall in specific gravity between those in the concentrate and those in the tailings, or a mixture of high and low specific gravity particles which the device has not succeeded in separating into concentrate or tailings.

(d) tailings-water fraction which includes (i) water not required for handling granular tailings (ii) some granular tailings (iii) small, high specific gravity particles, which can become trapped in the high velocity water stream but may be recovered by separate treatment of the water stream.

The more nearly horizontal slope of the inner zone at all levels enables the provision of efficient splitting and draw-off means at upper levels of the helix than is obtainable with helixes having a steeply sloped or radiused bottom at upper levels.

In another embodiment (not illustrated) the trough cross-section does not alter continuously in cross-section from that shown in FIG. 2A to that shown successively in FIGS. 2B, 2C and 2D. Instead the spiral is constructed from helix portions each of a constant cross-section, respectively as shown in FIGS. 2A to 2D and transition are provided between each helix portion. For preference the transition occurs over less than one turn of the helix, for example half a turn.

It is not essential that the working portion of the trough bottom in cross-section be composed of two straight lines. The bottom may be curved between the lowermost point and the point of maximum displacement, and/or between the point of maximum displacement and the outer wall.

It is not essential but highly desirable that the point of maximum displacement moves radially outwards as the helix is descended to a splitter. It will be understood that in embodiments not illustrated the trough working surface profile may alter from place to place along the trough so that the point of maximum displacement remains at a uniform radial distance from the helix axis but moves nearer an end of the profile by virtue that the end moves radially inwards or outwards from the axis. It will be understood that when an intermediate splitter is employed the point of maximum displacement may be moved radially inwards immediately after the splitter before recommencing radially outwards movement.

The inner zone or the outer zone of the bottom portion cross-section are not essentially of constant slope throughout the descent and the diameter of the inner wall and the outer wall of the trough while preferably constant throughout the helix are not essentially so.

In the manufacture of apparatus for use in the method it has been found desirable to manufacture a plurality of helical portions or modules having a predetermined cross-section according to the invention, some modules differing in cross-sections from others.

These portions are then linked together to form an extended helix via transition pieces. For example, an assembly may be made in which two helical modules having a cross-section as in FIG. 2A, may be linked with each other and may be linked by a transition portion with 3 interlinked modules having a cross-section as in FIG. 2B and so on.

A continuous casting (for example in glass reinforced plastic) may then be taken from the assembly of modules, with this casting then becoming a mould for the making of continuous helices of the same shape as the original assembly of modules.

As will be apparent to those skilled in the art the above described method of manufacture of helices is also applicable to helical separators other than those described herein when a change in radial cross-section is desired between the upper and lower end of the helix.

A particular advantage of preferred embodiments of the present invention is that splitters may be located on more or less flat trough areas at all altitudes. Splitters, which may be set in recesses of the trough bottom, have been found to work more efficiently when the adjacent surrounds are flat.

1. A spiral separator having at least a portion comprising a helical trough supported with its helical axis upright for separating a pulp of water and minerals flowing theredown into mineral fractions of differing mineral density, said helical trough having an upwardly facing working surface, which, when viewed in vertical cross-section, is non-linear and is defined by a radial inner end, a radial outer end at a higher vertical location than said radial inner end and a point of maximum displacement between said ends, said point being located on said surface at a maximum spacing below a notional straight line joining said inner and outer ends;

4. Apparatus according to claim 1 wherein a profile of the trough working surface comprises a portion which is substantially linear and is between the point of maximum displacement and the inner end of the profile.

5. Apparatus according to claim 1 wherein a profile of the trough working surface comprises a portion which is substantially linear and is between the point of maximum displacement and the outer end of the profile.

6. Apparatus according to claim 1 wherein a profile of the trough working surface comprises an inner zone which is substantially rectilinear and is between the point of maximum displacement and the inner end of the profile and an outer zone which is substantially rectilinear and is between the point of maximum displacement and the outer end of the profile, said inner and outer zones lying at an angle to each other, the increase in distance from the inner end to the point of maximum displacement comprising the apex of the angle moving radially outwards as at least one portion of the helix is descended.

us patent for spiral separator with improved separation surface patent (patent # 5,184,731 issued february 9, 1993) - justia patents search

us patent for spiral separator with improved separation surface patent (patent # 5,184,731 issued february 9, 1993) - justia patents search

A spiral trough separator for treating a slurry of ore particles in water to separate heavier fines from other particles includes a helical trough making a plurality of revolutions around a vertical axis and having the surface of the trough modified with protuberances to agitate the ore particles to allow entrapped impurities to be liberated and grooves to provide enhanced flow of the finer heavier ore fines closer to such axis to increase the efficiency of the recovery.

Vertical helical or spiral ore separators have been known for the use of concentrating heavy mineral particles and separating them from lighter rock particles. Typical of such separators are those shown in U.S. Pat. Nos. 629,595, 840,354 and 4,597,861; and in South African Patent Application No. 842,673 filed Nov. 4, 1984. None of these provides a high quality separation due principally to the failure to agitate the slurry and its particles sufficiently to cause good lateral movement across the width of the slurry conduit perpendicular to the direction of travel of the slurry.

It is an object of this invention to provide an improved helical ore separator. It is another object of this invention to provide an improved helical ore separator having a modified flow surface. Still other objects will become apparent from the more detailed description which follows.

This invention relates to a vertical axis helical trough separator having 3-10 revolutions about said axis, a feed end at the top of said separator and a discharge end at the bottom of the separator, the trough having an internal concave surface adapted to direct the flow of a slurry of solid particles in a liquid medium in a downward helical path, the surface containing a plurality of upwardly projecting spaced protuberances to agitate the ore particles thus permitting entrapped impurities interspersed with the heavier fines to be released. Preferably a plurality of downwardly projecting spaced grooves at selected locations between the feed end and the discharge end spacedly follows the protuberances.

In preferred embodiments of the invention the helical trough has 4-8 revolutions in its length with the middle revolutions being provided with a plurality of protuberances and spiral grooves in the flow path of the slurry, and the upper and lower revolutions having a smooth surface in the flow path of the slurry.

The novel features believed to be characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

The separator as seen in FIGS. 1-2 is a vertical helical trough 10 symmetrical about vertical axis 11 and including 4-8 revolutions around vertical axis 11 from the upper feed end 14 to the lower discharge end 15. In general this is used to concentrate the higher specific gravity mineral particles in an aqueous slurry of ore particles introduced at feed end 14 and allowed to flow downwardly by gravity to discharge end 15 where the heavier particles will concentrate closer to axis 11 and lighter particles will concentrate farther away from axis 11. Thus the product can be represented by a first stream at arrow 20 representing the heavier mineral particles and a second stream at arrow 21 representing the lighter weight gauge particles that may be discarded or recirculated. A splitter means 28 may also be employed to direct the streams to different outlets, as is common in the art.

The helical trough 10 may be supported in any manner appropriate for the purpose, such as that shown here of a column 12 and/or a plurality of supporting arms 13 extending radially outward from column 12 and attached at their distal ends to trough 10. Trough may be made in any size which will handle the separations required. Generally a size of between 4 and 12 feet vertical length and 2-3 feet in trough diameter with 4-8 revolutions in the total length is sufficient for most purposes.

The principal features of this invention lie in the surface modifications of the flow path of trough 10. The concave internal surface 27 of trough 10 which serves as the conduit for the slurry may be modified by a plurality of small upwardly projecting protuberances 23, such as hemispheres of 1/4 to 1/2 inch in diameter or by a plurality of spiral grooves 24 projecting downwardly in the internal surface 27, e.g., 0.01 to 0.05 inch wide and deep. Generally, the protuberances 23 extend laterally across the flow path of the slurry (radially with respect to axis 11), and if they are small, separate protuberances, are spaced apart in checkerboard arrangement (diamond formation) so as to prevent any unobstructed spiral channels in the direction of flow as indicated by arrow 22. Grooves 24 are arranged in a spiral direction so as to direct the flow of the slurry and its ore particles toward axis 11. Thus, the flow tends to be directed away from outer edge 25 of trough 10 and towards inner edge 26 of trough 10. The direction of grooves 24 is not parallel to outer edge 25 but is in a spiral cutting across flow direction 22 toward the inner edge 26. The surface modification of projecting protuberances tends to improve separation by agitating the ore particles and allowing entrapped impurities to be further liberated and the spiral grooves influence the flow of the finer heavier particles closer to vertical axis 11 improving recovery.

The vertical pattern of surface modifications can also be varied to suit particular conditions. Thus, a preferred arrangement is for upper portion 16 to be 1-3 revolutions of the helical trough 10, middle portion 17 to be 1-3 revolutions of the helical trough 10 and the lower portion 18 to be 1-3 revolutions of helical trough 10. Preferably, in middle portion 17 the surface modifications are protuberances 23 and grooves 24, with the upper portion 16 and lower portion 18 being smooth and free of any modifications.

In certain circumstances, it may be desirable, depending on many factors including the density of the slurry and the materials to be separated, also to provide protuberances and/or grooves in some parts of upper portion 16 and some parts of lower portion 18. For example, protuberances and/or grooves may be positioned in the lower parts of upper portion 16 and/or the upper parts of the lower portion 18 to obtain more efficient separation. In any event there always should be a beginning part of upper portion 16 and an ending part of lower portion 18 that is smooth and free of protuberances and/or grooves, In certain circumstances in any part of the spiral trough separator where protuberances and grooves are both used, the protuberances should be upstream and the grooves downstream, respectively, of each other. This can be maintained whether there is only one section of protuberances followed by a section of grooves, or whether there is a series of such protuberances followed by grooves; the section farthest downstream being grooves.

While the invention has been described with respect to certain specific embodiments, it will be appreciated that many modifications and changes may be made by those skilled in the art without departing from the spirit of the invention. It is intended, therefore, by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.

1. A vertical axis spiral trough separator having 3-10 revolutions about said axis, a feed end at the top of said separator and a discharge end at the bottom of said separator, said trough having an internal concave surface adapted to direct the flow of a slurry of solid particles in a liquid medium in a downward helical path, said surface containing a plurality of upwardly projecting and spaced protuberances at selected locations between said feed end and said discharge end, said separator having an upper portion, a middle portion, and a lower portion, said middle portion including about 1-6 revolutions of said trough wherein said internal concave surface contains said protuberances, and said upper and lower portions each include about 1-2 revolutions of said trough in which said internal concave surface is smooth and free of any said protuberances.

9. A vertical axis spiral trough separator adapted to receive and conduct by gravity in a downward helical path a slurry of water and particles of an ore and to recover a stream of said slurry containing concentration of heavy said particles and another stream of said slurry containing lighter said particles, said separator comprising a trough arranged in a helix about a vertical axis with 3-10 revolutions in said helix, said separator having a feed end at the upper extremity of said helix and a discharge end at the lower extremity of said helix, said helical trough including an upper portion having about 1-2 said revolutions adjacent said feed end, a lower portion having about 1-2 said revolutions adjacent said discharge end; and a middle portion located between said upper portion and said lower portion and including about 1-6 said revolutions, said trough having an internal concave surface for conducting said slurry in said helical downward path, said surface being modified at selected locations along said path with a plurality of small protuberances projecting upwardly from the surface and arranged laterally across said path to agitate said particles, and said discharge end including splitter means to direct said stream and said another stream to different outlets.

10. The separator of claim 9 wherein said middle portion includes said internal concave surface modified with said protuberances, and said upper and lower portions include said internal concave surface which is smooth and free of said protuberances.

13. The separator of claim 9 further comprising a plurality of downwardly projecting shallow grooves at other selected locations in said surface of said trough arranged in a spiral direction to direct flow of said slurry generally toward said axis.

18. A vertical axis spiral trough separator adapted to receive and conduct by gravity in a downward helical path a slurry of water and particles of an ore and to recover a stream of said slurry containing a concentration of heavy said particles and another stream of said slurry containing lighter said particles, said separator comprising a trough arranged in a helix about a vertical axis with 3-10 revolutions in said helix; said separator having a feed end portion of 1-2 revolutions at the upper extremity of said helix and a discharge end portion of 1-2 revolutions at the lower extremity of said helix, said trough having a middle portion located between said feed end and discharge end portions, said trough further having an internal smooth concave surface for conducting said slurry in said helical downward path, said surface being modified at selected spaced locations along said path only in said middle portion with a plurality of small separate protuberances projecting upwardly from the surface and spacedly arranged laterally across and along said path to agitate said particles, and said discharge end portion including splitter means to direct said stream and said another stream to different outlets.

us patent for spiral separators patent (patent # 4,277,330 issued july 7, 1981) - justia patents search

us patent for spiral separators patent (patent # 4,277,330 issued july 7, 1981) - justia patents search

A spiral separator for the wet gravity separation of solids of different specific gravities has a number of helical sluices or spirals mounted about a vertical column, the bottom of each spiral being substantially straight in cross-section and inclining upwards from inside to outside of the spiral, the pitch of the outside of the spiral being substantially uniform, but the angle of the spiral bottom to horizontal, and therefore the pitch of the inside part of the spiral, varying, this angle and the inside pitch of the spiral being greater in the upper part of the spiral than in the lower part.

Spiral separators are used extensively for the wet gravity separation of solids according to their specific gravities, for example in separating various kinds of mineral sands from silica sand, or in cleaning crushed coal by the removal of ash and other impurities.

A spiral separator consists usually of a vertical column about which there are supported a number, commonly two, of helical troughs or sluices, generally known as "spirals." The spirals are of constant or uniform pitch, corresponding parts of the spirals of a two-start spiral separator being diametrically opposed at the same level. A "pulp" or slurry of the materials to be separated and water, is fed at a predetermined rate into the upper ends of the spirals, and as the fluid mixture passes down through them it tends to form bands or strata of minerals of different specific gravities. These strata are separated at intervals by adjustable splitters, the mineral fractions which are required to be recovered, and which are thus separated, being carried away through take-off openings, wash water being introduced at intervals to the inside parts of the spirals to correct the pulp density and prevent "sand-barring" or the formation of stationary deposits of the material of lesser specific gravity on the bottom of the spirals.

A separator of this type is of fairly complex character, with its numerous adjustable splitters, which may require re-adjustment from time to time, and with the hoses connected to and leading down from the take-offs, and the hoses feeding wash water at intervals to each spiral, any of which hoses may become blocked by fibrous particles and require to be cleared. The separator, then, is expensive to manufacture, and requires fairly constant attention at a number of points to achieve acceptable results.

Normally, spiral separators of this type are used to separate the required materials by a number of successive and interrelated treatments. Thus, in the first pass, the material is divided into a heavy fraction or concentrate and a light fraction or tailings; the heavy fraction is re-treated to produce a concentrate and a tailing, which is combined for re-treatment with a heavier fraction split from the tailing of the first pass, and so on. At each stage, the volume of tailing which is thrown, or discarded, as containing only an insignificant amount of the mineral to be recovered, is not substantial. The repeated re-treatment of much of the pulp is, of course, slow and expensive.

The present invention has been devised with the general object of providing a spiral separator which, as well as being simple and ecomonical to manufacture and operate, may be used to produce a rich concentrate and throw a very substantial final tailing on a single pass of material through the apparatus, a middling cut being taken for re-treatment.

With the foregoing and other objects in view, the invention resides broadly in a spiral separator of the type having a helical sluice or spiral supported with its axis substantially vertical, capable of receiving at its upper end a pulp of water and minerals to be separated and having dividing means for dividing strata of different densities from the flow and for withdrawing these separately, wherein the bottom of the spiral is, in cross-section, substantially straight and at an angle to horizontal, inclining upwardly from inside to outside, the pitch of the outside part of the spiral is substantially uniform, the pitch of the inside of the spiral varying, the angle of the spiral bottom to horizontal being greater in the upper part of the spiral than in the lower part. Other features of the invention will become apparent from the following description.

The separator shown in the drawings includes a central vertical tubular column 10. Three identical helical sluices or spirals 11, each of five complete turns, are mounted coaxially on the central column 10. Each of the spirals may be moulded as an integral unit, of fiberglass for example. Each spiral has a bottom 12 of which the greater part, in cross-section, is substantially straight, inclining upwards from the inside to the outside of the spiral at an angle A, as indicated in FIGS. 2, 3, 4 and 5. The inside part of the bottom, nearest the axis of the spiral, has a fairly short upward curve to meet the column 10, and the outside part of the bottom leads up through a small-radius curve to the nearly vertical outside wall 13 of the spiral. The outside wall 13 is formed, at the top, with an outwardly projecting rim 14, over which there is fitted closely and secured an extruded flexible cover strip 15 made of a suitable plastics material.

The pitch of the outside part of the spiral is uniform, but the cross-sectional angle A of the spiral bottom 12 to horizontal, and consequently the pitch of the inside part of the spiral, is varied. In the first two complete turns of each spiral, this angle A, as shown in FIG. 2, is about 21.degree.. Below these two upper turns, the angle A of the spiral bottom to horizontal is reduced to about 15.degree. in the third turn as shown in FIG. 3; is further reduced to about 12.degree. in the fourth turn, as shown in FIG. 4, and is further reduced again to about 9.degree. for the fifth and final turn of the spiral, as shown in FIG. 5. In each case, the reduction of the angle A is not abrupt but the change is made gradually, through about a third of a turn of the spiral.

The uppermost part of each of the spirals 11 is covered by a top plate 16, through which a tubular pulp inlet 17 leads to the top part of the spiral. The three spirals are so mounted on the central column 10 that the pulp inlets 17 are about as close as is practical, to facilitate the simultaneous feed of pulp to all three.

In the lowermost part of each of the spirals (FIG. 6) two splitter blades 18 and 19 are mounted on a pair of pins 20 secured to and extending upwardly from the spiral bottom 12. Each of these splitter blades may suitably be moulded of a plastics material, and in plan view is substantially of arrowhead form, with a sharp upright edge directed up-stream, the down-stream part of the splitter blade being apertured for a friction fit on its pin 20, so that the blade will remain in the position to which it is turned. The splitter blades 18 and 19 have their lower parts within adjacent substantially sector-shaped recesses 21 and 22 formed in the spiral bottom 12, the sharp up-stream edge of the blades 18 and 19 closely approaching the arcuate up-stream edges of the recesses. Down-stream of the splitter blades 18 and 19 the spiral bottom is shaped to form a concentrates channel 23, a middlings channel 24 and a tailings channel 25, the splitter blade 18 being arranged between the entries to the concentrates channel 23 and middlings channel 24, the splitter blade being arranged between the entries to the middlings channel 24 and the tailings channel 25. The three channels 23, 24 and 25 develop into tubular passages to which are connected, respectively, a concentrates hose 26, a middlings hose 27 and a tailings hose 28, each leading down to an appropriate receptacle (not shown).

In use, a pulp of water and solids to be separated into, for example, mineral sands and silica sands, is fed simultaneously into the pulp inlets 17 of the three spirals 11. Within the uppermost turns of the spirals, the mineral sands, of fairly high specific gravity, tend to move down across the steeply sloping bottom 12 of each of the spirals towards the central column 10, where the angle of descent is very steep, and at the same time, the less dense silica sands tend to move centrifugally outwards towards the outer wall 13 of the spiral. The reduction of the spiral bottom angle A, in the third turn of each spiral, exercises a braking effect on the flow of the material particularly on flow of the material near to the inside of the spiral, where the change in pitch and of the gradient of descent of the material is most pronounced. Consequently there is a spreading of the innermost stratum of the pulp which appears to facilitate the separation cut from this stratum of fine silica particles which otherwise are likely to remain locked into the flow of concentrated mineral sands. Between the innermost stratum of fairly concentrated mineral sands and the outer stratum mainly of silica sands there becomes apparent a zone which we call a "flick zone," indicated at Z in FIGS. 3, 4 and 5, and characterized by rapidly recurring outward surges of sand, more or less tangential to the innermost stratum of mainly high density mineral sand. It appears that a substantial amount of separation of the mineral and silica sands occurs in this flick zone, which with many materials is more shallow than the concentrate stratum inwardly of it, or the tailings stratum outwardly of it, the silica sand separating centrifugally outwards and generally above the inwardly moving denser mineral sands.

The flow of the pulp is further braked in the fourth turn of the spiral, with the reduction in the pitch of its inner part consequent in the further reduction of the angle A. The flick zone remains pronounced in appearance, but it moves outwardly, relative to the position it occupies in the third turn of the spiral, and the rapidly occurring outward surges are somewhat diminished in strength. With the further reduction in the pitch of the inside part of the spiral, which occurs in the fifth and final turn, and the resultant further deceleration of the innermost stratum of the material, the width of the space between the innermost stratum of concentrated mineral sands and the outermost stratum mainly of silica sands becomes wider, the distance of this zone from the axis of the spiral is further increased, and the apparent strength of the outward surges therein is further decreased.

The splitter blades are adjusted manually to make the required cuts in the still rapidly flowing pulp, to direct the concentrate stratum, containing mainly heavy minerals, to the concentrates channel 21 and hose 24, the middlings stratum, containing mainly silica sand but including also a significant proportion of the heavier mineral sands, into the middlings channel 22 and middlings hose 25, and the tailings stratum, containing no more than an insignificant quantity of the minerals sought to be recovered, into the tailings channel 23 and tailings hose 26.

It has been found that the setting of the splitter blades 18 and 19, on the bottoms of the recesses 21 and 22 with the lower parts of their sharpened up-stream edges close to the upstream edges of these recesses, greatly increases the efficiency of the splitters. If a splitter blade is, instead, set on a plain or un-recessed spiral bottom, and adjusted at an angle to the direction of flow of the pulp, then the pulp does not divide cleanly at the sharp edge of the blade, but divides instead at a main impact position some distance from the sharp edge, a proportion of the pulp reversing direction to flow back and around this edge. In the arrangement illustrated, however, the pulp divides against the sharpened edges of the splitter blades as it flows down into the recesses 21 and 22, and thus clean and accurate cuts are made by the splitter blades.

The long and uninterrupted flow of the pulp through each spiral undisturbed by splitters and take-offs and by any introduction of wash water, is found to be very conducive to the efficient gravity separation of the constituents of the pulp. The flat-bottomed configuration of each spiral and the reduction in the angle of the spiral bottom and the consequent development of the flick zone wherein the separation of denser and less dense materials is accelerated, are further very material contributions to the efficient mineral separation, with the overall result that the tailings, normally by far the major fraction of the pulp, will contain no significant proportion of the minerals required to be recovered, and may straightway be discarded; and the concentrate will be very rich in the denser minerals. The middlings only, then, are normally reserved for re-treatment.

The elimination from the spirals of hoses for the introduction at intervals of wash water, which is found to be unnecessary in spirals of the configuration according to the invention, and also the elimination of the series of splitters and take-offs hitherto normally provided at close intervals throughout the length of each spiral enables three spirals to be mounted about a central column instead of the two spirals of conventional separators. The floor area of a treatment plant using separators according to the invention may therefore be very materially reduced, and as fewer separators will be required for a given through-put of material, the roof height of the plant may also be reduced, since the length of gravity feed conduits from the separators may be greatly reduced.

Any adjustment which may from time to time be required to be made to the splitter blades of a separator according to the invention may be easily and quickly carried out, whereas the adjustment of series of splitters in conventional separators is difficult and time-consuming.

With certain materials which are very difficult to separate efficiently with conventional plant, spirals according to the invention may be modified to achieve optimum results, particularly by changing the bottom angles of the spiral. For example, the final or lowermost one, or two, reductions of the bottom angle A of the spiral may be eliminated, the angle A remaining constant in the lowermost two or three turns of the spirals.

1. A spiral separator supported with its axis substantially vertical which is adapted to receive at an upper end thereof a pulp of water and minerals to be separated, said spiral separator including:

2. A spiral separator as claimed in claim 1 wherein each helical turn of the separator also includes an inner portion located inwardly of the straight portion and in which said heavy particles flow throughout the length of the spiral separator, there also being provided dividing means for dividing the heavy particles from the intermediate size particles and means for withdrawing said heavy particles and intermediate size particles separately.

3. A spiral separator as claimed in claim 1 or claim 2 wherein the starting point of the straight portion of each helical turn shifts progressively inwardly toward the longitudinal axis of the spiral separator from top to bottom throughout at least the major part of the length of the spiral separator.

us patent for spiral-wound electrodialysis module patent (patent # 10,926,224 issued february 23, 2021) - justia patents search

us patent for spiral-wound electrodialysis module patent (patent # 10,926,224 issued february 23, 2021) - justia patents search

A spiral-wound electrodialysis module includes an inner electrode positioned about a central axis and an outer electrode surrounding the inner electrode. Ion exchange membranes are arranged in a stack, and each membrane extends in a spiral outward from an inner position proximate the inner electrode to an outer position proximate the outer electrode. The spirals expand outward at a greater-than-linear rate as a function of angle along a length of the spiral from the inner positions to the outer positions.

While improvements have been made to individual components, the basic architecture of commercial electrodialysis (ED) stacks has not significantly changed since the concept of a multi-compartment ED cell having alternating cation and anion exchange membranes was first proposed by Meyer and Strauss in 1940 [Meyer and Strauss, La permeabilite des membranes. VI. Sur le passage du courant electrique a travers des membranes selectives, 23 Helv. Chim. Actra. 795-800 (1940)]. Commercial ED stacks manufactured, for example, by GE Power and Water and Hangzhou Iontech have a similar architecture in which flat, rectangular membranes are sandwiched between two or more electrodes.

For any given ED stack having a set membrane area, the desalination rate is maximized when the applied current density (the amount of electric current per unit cross-sectional area of membrane) is maximized. However, this applied current density must lie below the limiting current density (LCD), the current density that results in a zero ion concentration at the membrane surface in the diluate channel. The LCD is governed by diluate stream velocity, salt concentration, and channel spacer geometry. Studies that investigate the cost-optimal design of flat stack architectures reveal that if membrane costs are dominant over pumping costs (both capital and energetic), then operating close to the LCD at all points in the flow path within an ED stack is preferred [Hong-Joo Lee, et al., Designing of an electrodialysis desalination plant, 142 Desalination 267-286 (2002), and Sahil R. Shah, Natasha C. Wright, Patrick A. Nepsky, and Amos G. Winter, Cost-optimal design of a batch electrodialysis system for domestic desalination of brackish groundwater, 443 Desalination 198-211 (2018)].

Commercial ED systems typically run in continuous mode, where the flow path is designed to achieve the desired concentration reduction in a single pass through the system. In order to operate close to the LCD throughout the process, individual ED stacks are staged in series with decreasing applied voltage over each successive stage. As a result of this staging, the applied current density decreases as the diluate solution concentration and LCD also decrease. While it is possible to apply the voltages in the system such that the applied and adjusted limiting current densities (adjusted down from the limiting current to provide a margin of safety) match at the outlet of each stack in the series, the applied current density will be lower than the LCD at all other locations in the stacks due to the non-linear relationship between salt concentration and electrical resistance. Thus, conventional ED stacks operating under constant voltage cannot maintain matching applied current density and LCD at all locations along the flow path.

In a spiral-wound ED module, the diluate and concentrate streams flow in parallel from a perforated inner electrode to an outer electrode along a spiral path. FIG. 1 shows how the feed water enters the alternating CEMs 16 and AEMs 18 and separates into alternating diluate and concentrate streams 24 and 22. A voltage applied across the anode 12 and cathode 14 (in other embodiments, the cathode 14 can be perforated and at the center with the anode 12 being at the perimeter) drives a current, I, that separates the feed 20 into the diluate and concentrate streams 24 and 22. Both the limiting and applied current densities (ilim and i, respectively) decrease as the diluate concentration, Cd, decreases.

This stack configuration is of interest because the applied current density decreases with each successive revolution of the spiral by nature of the increasing effective membrane area through which the current must pass. The applied current density thus decreases as the concentration in the diluate stream and associated LCD decreases. By matching the applied current density as closely as possible to the LCD at any given location in a stack, the required amount of membrane area is minimized.

Arden and Solt first patented the concept of a spiral-wound ED module in 1953 [GB 759275 A]. Solt went on to analytically model both parallel and crossflow configurations with Wen and Sun in the early 1990s [G. S. Solt, et al., Modeling the spirally wound electrodialysis process: Single start, parallel flow, 127 Institution of Chemical Engineers Symposium Series 11-22 (1992), and T. Wen, et al., Modeling the cross flow spirally wound electrodialysis SpED process, 103 Desalination 165-176 (1995)]. Wen, et al., also tested a parallel flow spiral-wound ED stack experimentally [T. Wen, et al., Spirally wound electrodialysis SpED modules, 101 Desalination 79-91 (1995)]; however, the performance was not compared to the analytical model and disclosure was lacking as to design of the spiral. Previous work has focused on the Archimedean spiral (which is the locus of points corresponding to the locations over time of a point moving away from a fixed point with a constant speed along a line that rotates with constant angular velocity or, when defined in polar coordinates (r, ), the spiral can be described by r=a+b, where a and b are real numbers).

A spiral-wound electrodialysis module and methods for electrodialysis are described herein, where various embodiments of the apparatus and methods may include some or all of the elements, features and steps described below.

A spiral-wound electrodialysis module includes an inner electrode positioned about a central axis and an outer electrode surrounding the inner electrode. Ion exchange membranes are arranged in a stack, and each membrane extends in a spiral outward from an inner position proximate the inner electrode to an outer position proximate the outer electrode. The spirals expand outward at a greater-than-linear rate as a function of angle along a length of the spiral from the inner positions to the outer positions (in a non-Archimedean spiral) and/or expand outward at a linear rate over less than five revolutions (e.g., with no more than 1, 2, 3, or 4 revolutions) from the inner to the outer positions (e.g., in the form of an Archimedean spiral).

r ( ) = r 0 1 - ( 1 - CR - 1 f ) , where r() represents local spiral radius as a function of angle, r0 represents a radius of the inner electrode, represents local spiral angle, CR represents concentration ratio (i.e., the concentration of the feed water divided by the concentration of the diluate/product water), and f represents angle at an outer end of the spiral.

In additional embodiments, the spirals are shaped so as to generate an applied current density that is within 60%, within 40%, within 30%, within 20%, within 10%, or even within 5% of limiting current density at each location in the stack.

The ion exchange membranes can comprise a plurality of cation exchange membranes and a plurality of anion exchange membranes, wherein the cation exchange membranes alternate in sequence with the anion exchange membranes. Channels configured for fluid flow can be defined between adjacent membranes, wherein the channels include diluate channels and concentrate channels that alternate in sequence. Moreover, fluid pumps can be configured to pump both a diluate stream and a concentrate stream in parallel flow along the spiral pathways from the inner to outer electrodes or to pump the diluate stream to flow from the inner electrode to the outer electrode along a spiral pathway and to pump the concentrate stream to flow in a cross-flow orientation (parallel to the central axis) or in a counter-flow orientation relative to the diluate stream.

In a method for performing electrodialysis using the spiral-wound electrodialysis module, feed liquid is flowed from a central channel through an inner electrode to a plurality of channels, including alternating diluate channels and concentrate channels, defined between the ion exchange membranes. A voltage potential is applied across the inner and outer electrode. Ions are drawn by the charges of the electrodes to selectively flow through the ion exchange membranes from the diluate channels into the concentrate channels. A concentrate solution is then extracted from the concentrate channels; and a diluate solution is extracted from the diluate channels, wherein the concentrate solution has a greater salinity than the diluate solution.

Spiral-wound electrodialysis (ED) modules are of interest because, when the diluate and stream flows from the inner electrode to the outer electrode along a spiral path, the applied current density decreases as the concentration in the diluate stream and associated limiting current density (LCD) decrease. By matching the applied current density as closely as possible to the LCD at any given location in a stack (e.g., within 5, 10, 20%, 30%, 40%, or 60%), the required amount of membrane area is minimized, reducing capital cost. Presented herein is an analytical model for a spiral-wound ED module and experimental validation of that model using a prototype stack with two cell pairs and four revolutions. A constant voltage was applied, and the total current and stream conductivities at mid-stack and at the output were recorded. Experimental results agreed with the model for all parameters to within 15%. The model was used to explore the most cost-effective spiral stack designs for desalting brackish groundwater, examining both a standard Archimedean spiral (as is common for spiral-wound RO modules) and an ideal non-Archimedean spiral. The ideal spiral shape was found to reduce total cost by 21% and capital cost by 39% with respect to an Archimedean spiral.

The analytical model for a parallel flow, spiral-wound electrodialysis (ED) module presented herein builds upon existing work by accounting for channel properties (such as spacer geometry) and LCD. Given a set membrane and spacer type, the shape of the Archimedean spiral that allows for matching applied and limiting current densities at both the inner and outer electrode is a function of the feed and product water concentrations, the number of revolutions of the spiral, the number of cell pairs, and linear flow velocity, alone.

Forms of electrodialysis in which the ED modules and methods, described herein, can be used include electrodionization (EDI), which is electrodialysis performed with a resin in the channels between the membranes.

FIG. 1 shows a spiral-wound ED module 10 in which feed water 20 entering through a perforated center electrode 12 flows between alternating anion and cation exchange membranes 18 and 16, which have been wound in a spiral around the center electrode 12.

FIG. 3 is a chart plotting the adjusted current density (0.7ilim) as a function of diluate concentration for an ED module with the stack in the form of an Archimedean spiral for a particular initial-feed saline concentration, wherein applied current density for the Archimedean spiral is shown via the lower dashed line, while the limiting current density is shown via the solid line, and where these current densities are seen to match at the beginning and end of the stack but not elsewhere. The applied current density of an ideal spiral shape is shown via the upper dashed line, which continuously substantially matches the limiting current density.

FIG. 6 provides representations of a cost-minimized design of a spiral stack module for a particular feed concentration with an Archimedean spiral of the cation and anion exchange membranes 16 and 18 on the left and an ideal spiral of the cation and anion exchange membranes 16 and 18 on the right.

FIG. 8 is a representation of a cost-minimized three-stage ideal spiral pattern for a particular feed concentration, shown on the same grid as the single-stage Archimedean and the ideal spiral shape representations from FIG. 6.

In the accompanying drawings, like reference characters refer to the same or similar parts throughout the different views. The drawings are not necessarily to scale; instead, an emphasis is placed upon illustrating particular principles in the exemplifications discussed below. For any drawings that include text (words, reference characters, and/or numbers), alternative versions of the drawings without the text are to be understood as being part of this disclosure; and formal replacement drawings without such text may be substituted therefor.

The foregoing and other features and advantages of various aspects of the invention(s) will be apparent from the following, more-particular description of various concepts and specific embodiments within the broader bounds of the invention(s). Various aspects of the subject matter introduced above and discussed in greater detail below may be implemented in any of numerous ways, as the subject matter is not limited to any particular manner of implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes.

Unless otherwise herein defined, used or characterized, terms that are used herein (including technical and scientific terms) are to be interpreted as having a meaning that is consistent with their accepted meaning in the context of the relevant art and are not to be interpreted in an idealized or overly formal sense unless expressly so defined herein. For example, if a particular composition is referenced, the composition may be substantially (though not perfectly) pure, as practical and imperfect realities may apply; e.g., the potential presence of at least trace impurities (e.g., at less than 1 or 2%) can be understood as being within the scope of the description. Likewise, if a particular shape is referenced, the shape is intended to include imperfect variations from ideal shapes, e.g., due to manufacturing tolerances. Percentages or concentrations expressed herein can be in terms of weight or volume. Processes, procedures and phenomena described below can occur at ambient pressure (e.g., about 50-120 kPafor example, about 90-110 kPa) and temperature (e.g., 20 to 50 C.for example, about 10-35 C.) unless otherwise specified.

Although the terms, first, second, third, etc., may be used herein to describe various elements, these elements are not to be limited by these terms. These terms are simply used to distinguish one element from another. Thus, a first element, discussed below, could be termed a second element without departing from the teachings of the exemplary embodiments.

Spatially relative terms, such as above, below, left, right, in front, behind, and the like, may be used herein for ease of description to describe the relationship of one element to another element, as illustrated in the figures. It will be understood that the spatially relative terms, as well as the illustrated configurations, are intended to encompass different orientations of the apparatus in use or operation in addition to the orientations described herein and depicted in the figures. For example, if the apparatus in the figures is turned over, elements described as below or beneath other elements or features would then be oriented above the other elements or features. Thus, the exemplary term, above, may encompass both an orientation of above and below. The apparatus may be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. The term, about, can mean within 10% of the value recited. In addition, where a range of values is provided, each subrange and each individual value between the upper and lower ends of the range is contemplated and therefore disclosed.

Further still, in this disclosure, when an element is referred to as being on, connected to, coupled to, in contact with, etc., another element, it may be directly on, connected to, coupled to, or in contact with the other element or intervening elements may be present unless otherwise specified.

The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting of exemplary embodiments. As used herein, singular forms, such as those introduced with the articles, a and an, are intended to include the plural forms as well, unless the context indicates otherwise. Additionally, the terms, includes, including, comprises and comprising, specify the presence of the stated elements or steps but do not preclude the presence or addition of one or more other elements or steps.

Additionally, the various components identified herein can be provided in an assembled and finished form; or some or all of the components can be packaged together and marketed as a kit with instructions (e.g., in written, video or audio form) for assembly and/or modification by a customer to produce a finished product.

The discussion that follows expands on the previous literature by incorporating calculations of the limiting current density (LCD), electrical resistance in the fluid boundary layer, and the effects of spacer geometry into the analytical model. Incorporation of the LCD provides an important advantage, as the proposed benefit of a spiral stack is to maintain current density near limiting at all points along the spiral. In ideal spiral configurations described herein, the radius varies along the length of the spiral to ensure that the applied current density and LCD not only decrease with each successive revolution, but match in value along the entire length of the spirala condition that is not possible to achieve with a standard Archimedean spiral.

The analytical model presented herein can be based on an existing model for standard flat stack configurations developed and experimentally validated by the authors [Natasha C. Wright, Sahil R. Shah, Susan E. Amrose, Amos G. Winter V Robust model of brackish water electrodialysis desalination with experimental comparison at different size scales, 443 Desalination 27-43 (2018)]. Modifications to that model that are implemented to represent the spiral architecture will be discussed here.

The model describes a spiral design with a known inner electrode radius, r0; a number of cell pairs, N; and a total number of revolutions, S, and calculates the desalination rate, membrane and electrode area, and energy consumption. Further below, we discuss the inverse problem of determining the optimal number of cell pairs, the number of revolutions, the inner electrode radius, and the applied voltage such that matching between LCD and applied current density occurs at the beginning and end of the spiral (using an Archimedean spiral shape) and then along the length of the entire spiral (using an ideal non-Archimedean spiral shape).

An Archimedean spiral (also called an arithmetic spiral) is a spiral in which the radius increases by a constant value with each successive revolution of the spiral (i.e., the radius increases linearly moving outward along the length of the spiral). The Archimedean spiral thus defines the shape that would be achieved if standard ED cell pairs were wrapped around a center electrode since the thickness of the cell pairs remains constant. This shape is also employed by spiral-wound RO modules. The local radius of an ED stack wrapped as an Archimedean spiral is defined in polar coordinates as follows:

r ( ) = r 0 + Nt cp 2 , ( 1 ) where r0 is the radius of the center electrode; is the angle around the spiral; and tcp is the thickness of a single cell pair, given as the sum of channel heights, h, and the AEM/CEM membrane thicknesses (la and lc, respectively) such that tcp=2h+la+lc. FIG. 2 shows a two-cell pair (N=2), two-revolution (S=2) Archimedean spiral, where the radius, r, increases at a constant rate equal to the cell pair thickness, tcp, with each successive revolution. The Archimedean spiral ends at a final angle of =2S. The bulk concentration of the diluate 24 at the end of any given revolution, s, is denoted as Cd,sb.

L = 0 f r ( ) + dr d d , ( 2 ) where the integral is evaluated from 0 to f=2S, the angle at the end of the spiral. The total volumetric flow rate of the diluate, Qd(m3/s), is: Qd=NWhuch,(3) where W is the width of a single membrane (m), h is the channel height (m), uch is the spacer-filled channel velocity (m/s), and is the void fraction. The total membrane area, Atotal, in the spiral is then given by the following equation: Atotal=2NLW,(4) while the projected area for any given membrane segment, j, covering less than 2 radians, Aj, can be approximated by the following equation: Aj=(21)r(1)W,(5) where r is evaluated at 1. As (1-2) goes to zero, the stack is segmented into smaller paths for the current to flow, and the discrete analysis approaches the continuous solution.

We begin by neglecting the contribution of back-diffusion due to the ionic concentration gradient between the concentrate and diluate channels. Doing so allows us to solve the set of equations in this section without the use of an iterative solver. The effect that this assumption has on predicted salt removal rates is discussed, further below. The quantity of salt removed in a single pass through the spiral is then a result of migration due to the applied current, I, alone and is calculated by the following equation:

( C d , 0 c - C d , S b ) = I S N zFQ d , ( 6 ) where Cd,0b is the feed water salinity in the bulk solution (mol/m3) at the center electrode; Cd,Sb, is the final diluate salinity in the bulk solution (mol/m3) as it leaves the stack at the final revolution; S, is the current leakage factor; z is the ion charge number; and F is Faraday's constant (C/mol).

Because the same amount of current must pass through each successive revolution of the spiral, the change in concentration must also be the same (Cd,0bCd,1b=Cd,1bCd,2b). Equation 6 thus leads to the equation for the diluate concentration, Cd,sb, in any given revolution of the spiral,

i lim = I lim A A = C d b zFk t mem - t + , - = C d b zFD aq 0.29 Re d 0.5 Sc 0.33 d h ( t mem - t + , - ) , ( 8 ) where definitions of the area porosity, A, Reynold's number, Re, Schmidt number, Sc, mass transfer coefficient, k, hydraulic diameter, dh, diffusion coefficient of the aqueous solution, Daq, and the transport numbers, tmem, and t+, are as defined in Natasha C. Wright, Sahil R. Shah, Susan E. Amrose, and Amos G. Winter, A robust model of brackish water electrodialysis desalination with experimental comparison at different size scales, 443 Desalination 27-43 (2018). Introducing a desired current ratio (=I/Ilim) and setting the applied current, I, in Eq. 6 equal to the adjusted limiting current, Ilim, we can solve for the inner electrode radius that would facilitate the desired current to be applied at the beginning of the flow path when Cd,0b=Cd,0b, as follows:

= h 3 / 2 3 / 2 1 / 6 ( t mem - t + , - ) 0.29 ( 2 + 8 ( 1 - ) ) 1 / 2 1 / 6 D aq 2 / 3 A , and where CR=Cd,0b/Cd,Sb, the ratio of feed to product water concentration. Note that if a certain membrane and spacer type is assumed (properties of which are used to calculate ), the full spiral shape (Eq. 1) can be defined using only CR, the channel velocity, uch, the number of revolutions, S, and the number of cell pairs, N.

Just as with standard flat-stack ED architectures, the spiral ED stack is modeled as an analogous DC circuit. However, the spiral is distinct in that the current passes through the same solution S times, and the area of each successive flow channel/membrane increases as you move from the inner to outer electrode. The voltage at the electrodes, Etotal, is related to the current by the following equation:

E total = E el + 1 A j - 1 J ( R d , j b + R d , j BL + R mem A d , j + R c , j b + R c , j BL + R mem A c , j ) + j = 1 J E mem , j . ( 10 ) Here, j indicates the channel location such that j=1 is the diluate and concentrate channel closest to the inner electrode, and that a total of J=NS diluate channels and J=NS concentrate channels exist between the inner and outer electrode. The area resistances, Rd,jb, Rd,jBL, Rc,jb, and Rc,jBL are associated with the bulk and boundary layer fluid in the diluate and concentrate streams, respectively (Q m2). The average area resistance of the AEM and CEM is given by Rmem (m2). Ad,j and Ac,j are the projected areas of the diluate and concentrate channel (m2) such that both increase as j increases, in accordance with Eq. 5. Emem is the potential across each membrane pair and is a function of the concentration at the membrane wall and, thus, also changes based on channel location, j. Finally, Eel is electrode potential difference. Given a known bulk concentration and effective area for each channel location, each of the terms in Eq. 10 can be calculated as presented in Natasha C. Wright, Sahil R. Shah, Susan E. Amrose, and Amos G. Winter, A robust model of brackish water electrodialysis desalination with experimental comparison at different size scales, 442 Desalination 27-43 (2018).

total = IE total Q d + 2 P pump , ( 11 ) where P is the pressure drop over the stack (Pa), and where pump is the efficiency of the pump. It is assumed that the volumetric flow rate and pressure drop is the same in the concentrate and diluate streams. The pressure drop in the spiral is modeled using the correlation developed by Ponzio, et al., Experimental and computational investigation of heat transfer in channels filled by woven spacers, 104 International Journal of Heat and Mass Transfer 163-177 (2017), which was found to be the best match to an existing commercial ED system in [Natasha C. Wright, et al., A robust model of brackish water electrodialysis desalination with experimental comparison at different size scales, 442 Desalination 27-43 (2018)].

Plotting the limiting current density, ilim (solid line), and the applied current density, i (lower dashed line), as a function of the local concentration in the spiral (FIG. 3) reveals that, although an Archimedean spiral could allow for matching applied and limiting current densities at the inlet and outlet of the stack, there remains a significant amount of wasted membrane capacity in the middle revolutions, where the applied and limiting current densities do not match. A new ideal spiral shape is required to allow for continuous matching (top dashed line).

The Archimedean spiral shape provides for a linearly decreasing diluate concentration with each successive revolution (Eq. 7), resulting in a linearly decreasing limiting current density (LCD) (ilimCdb, Eq. 8). However, the radius, and thus the effective area, increases linearly with each revolution of the spiral. As a result, the applied current density (which scales as I/A) will not decrease linearly as desired, rather it will decrease inversely with each successive revolution.

Combining Eqs. 7-9 and setting I (Eq. 7) equal to him (Eq. 8) for all Cd, we can solve for the equation of a spiral that would allow the local applied and adjusted limiting current densities to match along the entire length of the spiral. This spiral is described in polar coordinates as follows:

A prototype stack was assembled in three stages, and a schematic illustration of the stack is shown in FIG. 4. The prototype used for model validation was constructed by rolling two membrane/spacer cell pairs 32 (two adjacent membranes separated by a permeable spacer) around a perforated titanium inner electrode 12 to produce a spiral shape. The spiral was sealed by compressing the outer electrodes 14 against the membrane surface using clamps made out of high-density polyethylene (HDPE) and using epoxy resin to seal and cap the ends. The stack also includes a feed water inlet 26; a pair of brine outlets 30; a pair of diluate outlets 28; clear half-tubes 34 for collecting water; gasket seals 36 between the outer membrane surfaces and half-tubes 34; and clamps 38 holding the outer electrode 14, gasket seals 36, and half-tubes 34 tightly against the outer-most membrane area. The final resin seal is not shown.

Membrane Properties Supplier Suez AEM model AR204SZRA CEM model CR67HMR AEM resistance ( cm2) 7 CEM resistance ( cm2) 10 AEM thickness (mm) 0.5 CEM thickness (mm) 0.6 Spacer Properties Supplier Conwed Plastics Model X0B354 Filament pitch (mm) 2.9 0.1 Filament diameter (mm) 0.53 0.03 Spacer thickness (mm) 0.76 0.01 Spacer area porosity 0.67 0.02 Spiral Properties Flow path width (cm) 17.5 Flow path length (cm) 91.4 Number of cell pairs 2 Number of revolutions 4 Inner electrode radius (cm) 2.54 Channel height (mm) 0.82 0.02 Calculated void fraction 0.83 0.03 Electrode coverage 0.79 Combined View-Factor 0.53

The inner electrode 12 was made from a grade-2 titanium tube with a 50.8-mm outer diameter and a 0.89-mm wall thickness; 6.35-mm diameter holes were added to allow water to enter the flow channels between the membranes 16 and 18. Two cell pairs (20.5-cm membrane width, 91.4-cm individual membrane length) allowed four full revolutions before reaching the outer electrode 14, which was made from 0.13-mm thick 316SS (stainless steel) foil. Anion exchange membranes (model AR204SZRA from (Suez Water Technologies & Solutions) and cation exchange membranes (model CR67HMR from (Suez Water Technologies & Solutions), both homogeneous, were used. The mesh spacer was made from Conwed Plastics' 31-mil RO spacer material.

Clear polyvinyl chloride (PVC) pipe (inner diameter 15.8 mm) cut in half lengthwise was used to collect water as it exited the stack. 316SS (stainless steel) tubing was inserted into the spiral one-third and two-thirds of the way along the membrane length and used to collect mid-stack water conductivity. Clamps were designed out of high-density polyethylene (HDPE) sheet to compress the half-tubes and their gaskets to the membranes. Finally, West System 105 and 207 epoxy resin and hardener was used to seal the ends of the stack. The epoxy serves as a replacement for the gasket material that lines the perimeter of traditional flat-stack spacer designs and ensures that the solution flows from the inner electrode to the outer electrode without coming out the ends of the spiral. Prior testing showed that the epoxy rose 1.5 cm into the flow channels. As a result, the effective membrane width decreased to 17.5 cm; W is set equal to this value in the model comparisons.

The diluate and concentrate streams 24 and 22 were run in continuous mode, flowing in a parallel configuration from the inner electrode tube 12 to the outer collection tubes 34. The feed solution 20 was prepared using deionized water and the appropriate amount of reagent grade NaCl. A Shuro 4008-101-E65 pump was used to provide feed solution to the stack 20; flow rate was controlled manually using a butterfly valve and measured using a Blue-White Industries F-1000-RB paddle wheel flowmeter (0.2 L/min). It is assumed that the flow divides equally between the concentrate and diluate channels providing 50% recovery. A Dr. Meter HY3005F-3 power supply was used to apply a constant voltage (0.1 V) across the electrodes and measure current (0.01 A). The mid-stack and final water stream conductivities were recorded manually over a period of 10 minutes for each test. Conductivity (1% of reading) and temperature (0.1 C.) measurements were taken using a Myron 4PII meter. Experimental error bars in the following tables and figures are reported as the quadrature of the sensor accuracy (given in this paragraph) and the 95% confidence interval over 5 measurements taken over the course of each experiment.

Table 1 lists the prototype stack parameters required for comparison with the analytical model. Note that while a spacer thickness of 0.76 mm was measured prior to rolling the spacer, we were not able to roll the spiral tightly enough to ensure that the channel height was equal to the spacer thickness at all points in the stack. This divergence was confirmed when measurements taken of the outside diameter of the spiral revealed its diameter to be 94.8 mm, whereas the calculated diameter with a spacer thickness of 0.76 mm should be 92.7 mm. Instead, the average channel height was back-calculated (h=0.82 mm), and the void fraction calculation was correspondingly updated from that found in Natasha C. Wright, et al., A robust model of brackish water electrodialysis desalination with experimental comparison at different size scales, 442 Desalination 27-43 (2018) to Eq. 13, where df is the filament diameter (mm) and If is the filament pitch (mm). This resulted in an estimated void fraction of =0.83, derived as follows:

Additionally, the fractional membrane area available for ion transport, which is typically set to the area porosity of the mesh spacer in the flow channels (A=0.67), needs to be adjusted. The outer electrode sheets covered only 79% of the outermost membrane area in order to leave space for the water collection half-tubes. It is assumed that this coverage affects the area available for ion transport in the same way as the spacer area porosity. A combined view-factor representing the combined effects of the spacer porosity and electrode coverage is applied, where VF=(0.79)(0.67)=0.53.

Tables 2-6 (representing tests 1-5), below, present the time-averaged results from the experiment alongside the model prediction of the same parameters for all five tests on the prototype Archimedean spiral ED stack, each of which had different feed water concentration and applied voltages. Note that the experimentally measured applied current, feed water conductivity, and flow rate served as inputs to the model; voltage potential, specific energy, and product, brine, and mid-stack conductivities were model outputs. Measurements matched the model within 1-15% (average 7%) for the voltage potential and specific energy, and within 1-11% (average 5%) for the conductivities.

TABLE 2 (test 1): Parameter Experimental Model Voltage [V] 7.5 0.1 7.6 Current [A] 0.95 0.30 0.95 Flow rate [L/min] 2.07 0.22 2.07 Feed conductivity [S/cm] 1436 16 1436 Product conductivity [S/cm] 971 11 943 Brine conductivity [S/cm] 1882 21 1921 Mid-stack diluate 1 conductivity [S/cm] 1240 14 1191 Mid-stack diluate 2 conductivity [S/cm] 1079 12 1067 Specific energy [kWh/m3] 0.06 0.02 0.06

TABLE 3 (test 2): Parameter Experimental Model Voltage [V] 8.0 0.1 8.0 Current [A] 1.44 0.02 1.44 Flow rate [L/min] 2.03 0.20 2.03 Feed conductivity [S/cm] 2149 23 2149 Product conductivity [S/cm] 1495 24 1402 Brine conductivity [S/cm] 2882 35 2883 Mid-stack diluate 1 conductivity [S/cm] 1880 29 1778 Mid-stack diluate 2 conductivity [S/cm] 1638 40 1591 Specific energy [kWh/m3] 0.09 0.01 0.09

TABLE 4 (test 3): Parameter Experimental Model Voltage [V] 10.0 0.1 11.0 Current [A] 2.53 0.03 2.53 Flow rate [L/min] 1.98 0.20 1.98 Feed conductivity [S/cm] 3022 31 3022 Product conductivity [S/cm] 1903 22 1697 Brine conductivity [S/cm] 4231 50 4312 Mid-stack diluate 1 conductivity [S/cm] 2567 28 2365 Mid-stack diluate 2 conductivity [S/cm] 2191 38 2033 Specific energy [kWh/m3] 0.21 0.02 0.23

TABLE 5 (test 4): Parameter Experimental Model Voltage [V] 14.0 0.1 12.8 Current [A] 2.30 0.05 2.30 Flow rate [L/min] 2.46 0.22 2.46 Feed conductivity [S/cm] 1983 42 1983 Product conductivity [S/cm] 940 45 988 Brine conductivity [S/cm] 2881 67 2950 Mid-stack diluate 1 conductivity [S/cm] 1524 34 1490 Mid-stack diluate 2 conductivity [S/cm] 1246 33 1240 Specific energy [kWh/m3] 0.22 0.02 0.20

TABLE 6 (test 5): Parameter Experimental Model Voltage [V] 10.0 0.1 8.5 Current [A] 2.94 0.06 2.94 Flow rate [L/min] 2.65 0.36 2.65 Feed conductivity [S/cm] 4503 46 4503 Product conductivity [S/cm] 3471 112 3389 Brine conductivity [S/cm] 5380 78 5597 Mid-stack diluate 1 conductivity [S/cm] 4077 42 3948 Mid-stack diluate 2 conductivity [S/cm] 3774 44 3669 Specific energy [kWh/m3] 0.18 0.03 0.16

The conductivity results for test 1 are shown as a bar graph in FIG. 5 in order to better visualize the trend in the data. We note, for example, that the model slightly under-predicts the experimental values in the diluate stream, while over-predicting the experimental values in the brine stream. This trend was present for all tests, except test 4. This difference is expected given the decision to neglect back diffusion in the model, allowing the set of equations presented, above, to be solved directly without iteration.

There are a number of design changes that can be incorporated in additional prototype stacks to help determine the source of any additional error between the model and the experiments, as well as to improve its overall performance and life. First, the small tubes inserted in two locations in the stack to probe for concentration can be added to every revolution and in both the diluate and concentrate streams 24 and 22, allowing for better accounting of propagated error. In these tests, the first membrane layer 16/18 did not lie perfectly flat on the inner electrode 12, resulting in a fluid layer between the two surfaces and increased electrical resistance. Better assembly of the spiral would provide for a flush fit along the center electrode 12. Additionally, the stainless-steel outer electrode 14 and titanium inner electrode 12 can be replaced with coated titanium to avoid development of pitting and rust. Alternatively, the electrodes 12 and 14 can be formed of any of a variety of other materials.

The spiral configuration of the spiral ED stack can be designed to minimize or reduce the 10-year total cost and the capital cost of the system and its operation. The calculation of capital cost includes the cost of the diluate and concentrate pumps and the stack cost (assuming $1200/m2 electrode area, $40/m2 membrane area, $10/m2 spacer area). The total 10-year cost assumes 10,000 L/day total production and includes the capital cost, 10% interest over 5 years, $0.10/kWh for both pumping and desalination energy, and pump replacement in the fifth year.

For Archimedean spiral designs, we can ensure that the applied current density is equal to the adjusted LCD (=0.7) at the beginning and end of the spiral. For ideal spiral designs, the applied current density is equal to the adjusted LCD (=0.7) at all points along the spiral. In both cases, the spiral completes a minimum of one full revolution of (f2). The design variables and associated bounds investigated for both cases are the channel height (0.3 mm

Example calculation steps used to determine the two cost objectives for the Archimedean spiral are provided, below. 1. Calculate the minimum total number of revolutions, S, required to achieve the desired concentration change, given the design variables h, uch, and N, where this methodology is likely to produce an S of less than five revolutions, and where it is advantageous to use the minim number of revolutions to remove a given amount of salt:

S = [ ( u ch 1 / 2 t cp N ) ( C d , 0 2 - C d , J 2 C d , 0 C d , J - 2 ) ] 1 / 2 . ( 16 ) 2. Calculate the radius of the inner electrode, r0, such that i=ilim at the beginning of the spiral (Eq. 9). Calculate the concentration reduction in each revolution (Eq. 7). 3. Calculate the maximum number of cell pairs that can start from the inner electrode (Eq. 14). If N

A representation of the overall spiral stack module (top) and pattern (bottom) for a cost-minimized Archimedean spiral (at left) and an ideal non-Archimedean spiral (at right) are provided in FIG. 6. In both cases, a design in which equal importance is placed on total cost and capital cost is presented. A single membrane 16 is shown in bold and 1/15th of the total cell pairs are included for visual clarity. Membrane width, W, is shown for the 1000 L/hr case and would scale linearly with production rate.

The relationship between the spiral angle, , and the local spiral radius r() for various ideal spirals having different numbers of total revolutions, S, and concentration ratios, CR, is shown in FIG. 7. Since stacks designed for the same CR and having the same number of revolutions have the same capital cost, and lower CR stacks have smaller inner and outer electrode radii (FIG. 7), it is prudent to consider the effect of staging multiple smaller CR stacks in series, where the output of the first stage is used as the input to the second stage, and where the output of the second stage is used as the input of the third stage. For example, a single stack with a CR=8 would have the same concentration reduction as three stacks in series, each with CR=2, as long as all stacks had the same number of revolutions. The reduced electrode area in a staged system could make the stack easier to manufacture.

A representation is provided in FIG. 8 of a cost-minimized three-stage ideal spiral pattern, shown on the same grid as the single-stage Archimedean and ideal spiral shape representations from FIG. 8. Note that the inner and outer diameter of each three-stage spiral is substantially smaller than the single-stage designs capable of achieving the same concentration reduction.

Herein, we have thus far discussed a parallel-flow configuration where the feed water divides equally into diluate and concentrate from the center electrode. This configuration becomes difficult to implement as the number of cell pairs (and thus collection tubes at the outer electrode) increases. Additionally, achieving a recovery greater than 50% would require a complicated division of flow at the center electrode, such that the concentrate stream could be recirculated.

A cross-flow spiral configuration avoids both of these concerns by allowing the diluate stream 24 to flow from the inner electrode 12 to outer electrode 14 in a spiral fashion while the concentrate stream flows axially (the direction into the page in FIG. 1). In this configuration, the diluate stream concentration, LCD, and applied current density would still decrease with each successive revolution, as desired. Since the electrical resistance and LCD of the diluate stream 24 is dominant over that of the concentrate, a cross-flow configuration is expected to have minimal effect on the predicted desalination rate and energy consumption. With the two streams hydraulically separated, it would be easier to increase the number of cell pairs and recovery ratio of the system.

In describing embodiments of the invention, specific terminology is used for the sake of clarity. For the purpose of description, specific terms are intended to at least include technical and functional equivalents that operate in a similar manner to accomplish a similar result. Additionally, in some instances where a particular embodiment of the invention includes a plurality of system elements or method steps, those elements or steps may be replaced with a single element or step. Likewise, a single element or step may be replaced with a plurality of elements or steps that serve the same purpose. Further, where parameters for various properties or other values are specified herein for embodiments of the invention, those parameters or values can be adjusted up or down by 1/100th, 1/50th, 1/20th, 1/10th, th, rd, , rd, th, th, 9/10th, 19/20th, 49/50th, 99/100th, etc. (or up by a factor of 1, 2, 3, 4, 5, 6, 8, 10, 20, 50, 100, etc.), or by rounded-off approximations thereof, unless otherwise specified. Moreover, while this invention has been shown and described with references to particular embodiments thereof, those skilled in the art will understand that various substitutions and alterations in form and details may be made therein without departing from the scope of the invention. Further still, other aspects, functions, and advantages are also within the scope of the invention; and all embodiments of the invention need not necessarily achieve all of the advantages or possess all of the characteristics described above. Additionally, steps, elements and features discussed herein in connection with one embodiment can likewise be used in conjunction with other embodiments. The contents of references, including reference texts, journal articles, patents, patent applications, etc., cited throughout the text are hereby incorporated by reference in their entirety for all purposes; and all appropriate combinations of embodiments, features, characterizations, and methods from these references and the present disclosure may be included in embodiments of this invention. Still further, the components and steps identified in the Background section are integral to this disclosure and can be used in conjunction with or substituted for components and steps described elsewhere in the disclosure within the scope of the invention. In method claims (or where methods are elsewhere recited), where stages are recited in a particular orderwith or without sequenced prefacing characters added for ease of referencethe stages are not to be interpreted as being temporally limited to the order in which they are recited unless otherwise specified or implied by the terms and phrasing.

2. The spiral-wound electrodialysis module of claim 1, wherein the spiral has a shape that substantially matches the following function: r ( ) = r 0 1 - ( 1 - CR f ), where r() represents local spiral radius as a function of the angle, ; r0 represents a radius of the inner electrode; CR represents concentration ratio; and f represents angle at an outer end of the spiral.

3. The spiral-wound electrodialysis module of claim 1, wherein the spirals are shaped so as to generate an applied current density that is in a range from 40% of a local limiting current density to the local limiting current density at each location in the stack.

4. The spiral-wound electrodialysis module of claim 1, wherein the spirals are shaped so as to generate an applied current density that is in a range from 60% of a local limiting current density to the local limiting current density at each location in the stack.

5. The spiral-wound electrodialysis module of claim 1, wherein the spirals are shaped so as to generate an applied current density that is in a range from 80% of a local limiting current density to the local limiting current density at each location in the stack.

6. The spiral-wound electrodialysis module of claim 1, wherein the ion exchange membranes comprise a plurality of cation exchange membranes and a plurality of anion exchange membranes, wherein the cation exchange membranes alternate in sequence with the anion exchange membranes.

7. The spiral-wound electrodialysis module of claim 6, wherein channels configured for fluid flow are defined between adjacent membranes, wherein the channels include diluate channels and concentrate channels that alternate in sequence.

8. The spiral-wound electrodialysis module of claim 7, including at least one fluid pump configured to pump a diluate stream to flow from the inner electrode to the outer electrode along a spiral pathway.

9. The spiral-wound electrodialysis module of claim 1, wherein the spirals can be characterized by outward expansion at a greater-than-linear rate as a function of angle, , along a length of the spiral from the inner positions to the outer positions.

12. The method of claim 11, wherein the spiral has a shape that substantially matches the following function: r ( ) = r 0 1 - ( 1 - CR f ), where r() represents local spiral radius as a function of the angle, ; r0 represents a radius of the inner electrode; CR represents concentration ratio; and f represents angle at an outer end of the spiral.

13. The method of claim 11, wherein the electrodes generate an applied current density that is in a range from 40% of a local limiting current density to the local limiting current density at each location in the stack.

14. The method of claim 11, wherein the electrodes generate an applied current density that is in a range from 60% of a local limiting current density to the local limiting current density at each location in the stack.

15. The method of claim 11, wherein the electrodes generate an applied current density that is in a range from 80% of a local limiting current density to the local limiting current density at each location in the stack.

16. The method of claim 11, wherein the ion exchange membranes comprise a plurality of cation exchange membranes and a plurality of anion exchange membranes, wherein the cation exchange membranes alternate in sequence with the anion exchange membranes.

17. The method of claim 16, wherein channels configured for fluid flow are defined between adjacent membranes, wherein the channels include diluate channels and concentrate channels that alternate in sequence.

18. The method of claim 17, including at least one fluid pump configured to pump a diluate stream to flow from the inner electrode to the outer electrode along a spiral pathway and to pump a concentrate stream to flow in a cross-flow orientation to the diluate stream.

19. The method of claim 11, wherein the spirals can be characterized by outward expansion at a greater-than-linear rate as a function of angle, , along a length of the spiral from the inner positions to the outer positions.

us patent for method to fabricate a three dimensional battery with a porous dielectric separator patent (patent # 8,663,730 issued march 4, 2014) - justia patents search

us patent for method to fabricate a three dimensional battery with a porous dielectric separator patent (patent # 8,663,730 issued march 4, 2014) - justia patents search

Methods to manufacture a three-dimensional battery are disclosed and claimed. A structural layer may be provided. A plurality of electrodes may be fabricated, each electrode protruding from the structural layer. A porous dielectric material may be deposited on the plurality of electrodes.

This application claims priority under 35 U.S.C. section 119(e) to U.S. Provisional Application No. 60/884,846, entitled Three-Dimensional Lithium Battery Separator Architectures, filed on Jan. 12, 2007, and to U.S. Provisional Application No. 60/884,828, entitled Three-Dimensional Batteries and Methods of Manufacturing Using Backbone Structure, filed on Jan. 12, 2007, both of which are hereby incorporated by reference herein in their entirety.

Lithium batteries are the preferred energy source in various applications due to their energy density, power, and shelf life characteristics. Examples of lithium batteries include non-aqueous batteries such as lithium-ion and lithium polymer batteries.

A separator between positive and negative electrodes of a conventional lithium battery constitutes an important component of the battery. Separators for conventional, planar lithium-ion batteries are typically solid micro-porous polyolefin films that are assembled in a sheet form and rolled in the form of a cathode/separator/anode/separator stack. This stack is rolled tightly and inserted into a can, filled with electrolyte, and then sealed. For example, reference to P. Arora and Z. Zhang, Battery separators, Chem. Rev., 2004, 104, 4419-4462, may help to illustrate the state of the art in battery separators, and is therefore incorporated by reference as non-essential subject matter herein.

Three-dimensional battery architectures (e.g., interdigitated electrode arrays) have been proposed in the literature to provide higher electrode surface area, higher energy and power density, improved battery capacity, and improved active material utilization compared with two-dimensional architectures (e.g., flat and spiral laminates). For example, reference to Long et. al., Three-dimensional battery architectures, Chemical Reviews, 2004, 104, 4463-4492, may help to illustrate the state of the art in proposed three-dimensional battery architectures, and is therefore incorporated by reference as non-essential subject matter herein. FIG. 1 shows a schematic representation of a cross-section of one example of a three-dimensional battery that has been proposed in the literature. The battery includes a cathode current collector 10 from which cathodes 11 extend into a height direction at various points. A similar structure is made with an anode current collector 14 and anodes 13. The regions between the cathodes 11 and the anodes 13 (and some areas of the current collectors 10 and 14) include electrolyte 12.

The cathodes 11 and anodes 13 may be assembled in various three-dimensional configurations. This can include, for example, inter-digitated pillars or plates where the anodes 13 and the cathodes 11 are in proximity to each other in more than one direction. For example, in FIG. 1, each anode 13 is in close proximity to two cathodes 11, one on either side. In structures such as pillars, each electrode could be in proximity to surfaces from more than 2 counter electrodes. The anode and cathode current collectors 10 and 14 can be separate (top and bottom connection as shown in FIG. 1) or co-planar.

Methods to manufacture a three-dimensional battery are disclosed and claimed. A structural layer may be provided. A plurality of electrodes may be fabricated, each electrode protruding from the structural layer. A porous dielectric material may be deposited on the plurality of electrodes. Other aspects and advantages of the present invention can be seen upon review of the figures, the detailed description, and the claims that follow.

FIG. 3 is a representation of a process for incorporating a separator in a three-dimensional battery using a solid film sub-ambient pressure/suction process, according to an embodiment of the invention.

FIG. 7 illustrates a bi-layer deposition method to incorporate a separator in a three-dimensional battery, first using chemical vapor deposition and then using a dip coating, according to an embodiment of the invention.

Existing energy storage devices, such as batteries, fuel cells, and electrochemical capacitors, typically have two-dimensional laminar architectures (e.g., planar or spiral-wound laminates) with a surface area of each laminate being roughly equal to its geometrical footprint (ignoring porosity and surface roughness). A three-dimensional energy storage device can be one in which an anode, a cathode, and/or a separator are non-laminar in nature. For example, if electrodes protrude sufficiently from a backplane to form a non-laminar active battery component, then the surface area for such a non-laminar component may be greater than twice the geometrical footprint of its backplane. In some instances, given mutually orthogonal X, Y, Z directions, a separation between two constant-Z backplanes should be at least greater than a spacing between electrodes in an X-Y plane, divided by the square root of two.

Some examples of three-dimensional architectures that are capable of use with certain embodiments of the present invention, and that have cathodes and anodes protruding from the same backplane, are shown in FIGS. 2A-D. FIG. 2A shows a three-dimensional interdigitated array of lithium ion insertion electrodes in the shape of pillars, FIG. 2B shows a three dimensional assembly with cathodes and anodes in the shape of plates (e.g., a plurality of fins protruding at least 50 microns from a structural layer), FIG. 2C shows a three-dimensional assembly with cathodes and anodes in the shape of concentric circles, and FIG. 2D shows a three-dimensional assembly with cathodes and anodes in the shape of waves. Other configurations, such as honeycomb structures and spirals might also be used with certain embodiments of the present invention. In FIGS. 2A-D, cathodes 20 and anodes 21 protrude from the same backplane and are alternating in a periodic fashion. However, in other embodiments the cathodes 20 may protrude from a different backplane than anodes 21.

The three-dimensional architecture may be fabricated by depositing a conductive material on to an inactive backbone structure, for example in the shape of a plurality of fins, and electrophoretic deposition of electrode material on to the conductive material to create a plurality of anodes and/or cathodes. The backbone structure may be optionally removed as part of or at the conclusion of the fabrication process, for example by etching. Alternatively, or in conjunction with this technique, a structural layer may be provided and then a plurality of protrusions can be formed that protrude from the structural layer. Each of the protrusions may include or may be provided with an electrically conductive surface, and an electrode layer may be deposited on the plurality of protrusions.

FIG. 3 shows an example of a method for adding a separator 31 to a three-dimensional architecture. In this case, a current collector 32, which either serves as a structural layer itself or which is deposited upon a structural layer that is not shown, has a plurality of anodes 30 fabricated upon it, for example by photolithographic patterning followed by vacuum deposition, so that the anodes 30 protrude from the current collector 32. A sheet of the separator 31 comprising a porous dielectric material is laid on top of the anodes 30, and this assembly is placed or kept in a sub-ambient pressure chamber. A pressure level within the chamber is then reduced sufficiently below ambient pressure to cause the separator 31 to conformally coat the anodes 30. At this point, this assembly can be removed from the sub-ambient pressure chamber, and cathodes 33 can be assembled or deposited on top in order to make a three-dimensional battery. In another embodiment, various components can all be loaded after mechanical alignment into the sub-ambient pressure chamber in order to assemble the battery.

Materials that can be used as the porous dielectric material for a separator in a three-dimensional architecture according to an embodiment of the present invention may include, without limitation, organic materials such as polypropylenes, polyethylenes, polyamides, polytetraflouroethylenes, polyvinylidine fluorides, polyvinylchlorides, polyimides, polycarbonates, and cellulosics, and inorganic materials such as aluminum oxide, titanium dioxide, silicon dioxide, and zirconium dioxide. The materials that may be used as separators for aqueous and non-aqueous energy storage systems may include spin-on dielectrics. For example, a spin-on glass dielectric can be used as porous barriers between a cathode and an anode in a battery. Some examples are phosphosilicates, MSQ (Methyl-Silsesquioxane), SiLK, and the like. Many of these materials can be spun on and subsequently cured to form a consistent porous film.

FIG. 4 shows an example of processing a spin-on dielectric on a three-dimensional battery. A substrate 40 has anode current collectors 41 and cathode current collectors 42, on top of which anodes 43 and cathodes 44 sit, respectively. This assembly is then subjected to spin coating of a spin-on glass dielectric 45 and is at least partially planarized by spinning at a suitable rate to provide planar films. Further planarization may be accomplished by a suitable method such as chemical-mechanical polishing (CMP). A resulting porosity can then be obtained on the dielectric 45 by thermal or light-assisted curing. Alternatively, or in conjunction, a spin-on glass can be initially molded into a desired shape and pitch using a sacrificial mold. After setting the spin-on glass, the mold can be removed using a standard mold removal technique. The anodes 43 and the cathodes 44 can subsequently be assembled into a grid of the resulting separator. The separator resulting from this method may have reduced mechanical stress relative to other methods, potentially leading to a more reliable battery.

Another method that can be used for forming separators is electrophoretic deposition of separator materials. Electrophoretic deposition is typically a potential-driven phenomenon, where particles of non-conducting or poorly conducting materials are driven to either a cathode or an anode by an applied voltage. Thick films can be deposited by this technique. Also, the films can be tailored to different porosities by adding different amounts of sacrificial binders that can be co-deposited electrophoretically and subsequently driven off by temperature. Due to surface effects, the deposition is typically self-limiting. Therefore, a thickness and an available separator spacing can be optimized in order to get full coverage between the cathode and the anode. This process is schematically shown in FIG. 5. In particular, a substrate 50 has anode current collectors 51 and cathode current collectors 52, on top of which anodes 53 and cathodes 54 sit, respectively. This assembly is then immersed in an electrophoretic deposition bath that has a separator material and a desired concentration of a binder for providing porosity. The electrophoretic deposition is carried out by changing the potential of the anodes and/or cathodes using high-voltage DC power supply with a voltage preferably in the range of 1-1500 V, and most preferably in the range of about 10-150 V. The separator resulting from this method may have reduced mechanical stress relative to other methods, potentially leading to a more reliable battery.

Yet another way to deposit separator materials is to use a liquid solution of polyolefins or any other separator material of interest that can be made into a liquefied form in temperatures less than about 100 C. An assembly including electrodes can be immersed into a solution containing the liquefied separator material and a solvent, and a sub-ambient pressure atmosphere can be established around the assembly (e.g., via evacuation from the top of a chamber) in order to fill up crevices with the liquefied material. Once the sub-ambient pressure has been sufficiently established, the solution can wick into the crevices and can displace air in the crevices. In addition, when ambient pressure is restored, any residual bubbles that are present can expand sufficiently so that they will be forced out to be displaced by the liquefied material. The solvent is evaporated or allowed to evaporate with the dielectric material remaining on the plurality of electrodes. An exemplary schematic of this process is shown in FIG. 6. In particular, a substrate 60 has anode current collectors 61 and cathode current collectors 62, on top of which anodes 63 and cathodes 64 sit, respectively. This assembly is then immersed in a solution 65 containing a liquefied material and the solvent, as depicted in the bottom portion of FIG. 6. The separator resulting from this method may have reduced mechanical stress relative to other methods, potentially leading to a more reliable battery.

FIG. 7 shows a two-operation process for deposition of a separator material. In particular, a substrate 70 has anode current collectors 71 and cathode current collectors 72, on top of which anodes 73 and cathodes 74 sit, respectively. The first operation, as shown in the middle portion of FIG. 7, is a chemical vapor deposition process, which adds thin layers of a porous material 75 around the exposed electrodes 73 and 74. This material 75 is then solidified by drying, and the assembly then gets a second coating of the same or a different material 76 by spin-on methods or one of the other methods of deposition described herein, as shown in the bottom portion of FIG. 7. Thus, more than one layer of porous dielectric material may be deposited to fabricate the separator in a three-dimensional architecture.

Likewise, a sheet separator incorporated into a three-dimensional battery according to an embodiment of the present invention need not be formed from a single sheet of material. When the separator is formed from a single sheet of material that is mechanically compressed in order to make a battery, a defect may be magnified during mechanical compression. On the other hand, in three-dimensional structures as shown in FIGS. 4-7, two coincident defects would have to be substantially proximate in the deposited separator in order to have electrical shorts. This feature reduces a probability of separator-related shorting defects in a battery. Similarly, for the exemplary separator shown in FIG. 7, more than two (e.g., three or four) defects would have to be substantially proximate for electrical shorts to occur, which reduces the probability even further.

While the invention has been described with reference to the specific exemplary embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention as defined by the appended claims. It is contemplated that various features and aspects of the invention may be used individually or jointly and possibly in a different environment or application. The specification and drawings are, accordingly, to be regarded as illustrative and exemplary rather than restrictive. Comprising, including, and having, are intended to be open-ended terms.

8. The method of claim 1 wherein the method further comprises thermally treating the electrophoretically co-deposited material to drive-off the binder to tailor the porosity of the porous separator material.

11. The method of claim 1 wherein the porous dielectric material is selected from the group of organic materials consisting of polypropylenes, polyethylenes, polyamides, polytetrafluoroethylenes, polyvinylidine fluorides, polyvinylchlorides, polyimides, polycarbonates, and cellulosics.

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