NL8104086A - Soln. concentrating appts. in continuous process - comprising vessel to recrystallise solvent and units combining crystal sepn. and wash-out - Google Patents

Abstract

Appts. comprises a closed re-crystallisation vessel which is fed via a cooled and scraped pre-crystallisation unit and contains a stirrer. The vessel has one or more outlets on the top leading to crystal separators each comprising a vertical cylinder contg. a movable sieve element which compacts the crystals against the underside of the column of crystals being formed in the cylinder. This column is thereby moved upwards towards a rotatably driven scraper in the closed upper end of the cylinder where the crystals at the top of the column are successively removed via an outlet by washing-out liq. admitted via an inlet. Concentrating soln. by crystallising the solvent and removing crystals in separators with wash-out liq. supply. The arrangement combines sepn. with wash-out and permits continuous operation by using a number of, possibly standard-size, separators on one vessel.

Description

s 4 ..- Λ N.O. 29,697

Combined crystallizer wash column for aqueous suspensions.

The invention relates to a device for crystallizing a solvent and a solution, consisting of a closed (re-) crystallizer vessel, a scraped heat exchanger with a supply for the solution 5 and a discharge to a directly connected thereto, from a stirrer provided recrystallizer, with an outlet to at least one separator of the crystals from the concentrated solution.

An apparatus of this kind is known from Dutch patent 148.242. This patent describes a crystallizer of the solvent from a solution, which, viewed in the flow direction, ends with a separator of the crystals from the concentrated solution. The crystals, although separated, are still surrounded by such a large amount of concentrated solution that in practice the device described in the publication is followed by a so-called washing device. All known washing machines, which also work well, are of the non-continuously operating type. The crystallizer, however, operates continuously and therefore optimally if its yield could also be continuously discharged. The latter is often not the case for the reason described above. The recirculation of part of the concentrated solution described in the Dutch patent already requires a well-functioning control system per se, because the method is already sensitive per se through recrystallisation, but this control is additionally made more difficult by the non-continuous discharge of the crystal flow.

The object of the invention is now to avoid these complications and also to make a part of the device superfluous.

The device described in the preamble according to the invention is now characterized in that each separating device comprises a cylinder which is placed in open connection with and on the (pe) crystallizer vessel, which has a movable sieve member in the cylinder with little clearance. with which the sieved crystal 8104086

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all can be homogeneously compacted and the crystal column thus formed is movable to the other, closed end of the cylinder, that a take-off member (such as a rotary scraper) is placed near this closed end and that a connection there for the supply of a washing liquid and a connection for the discharge of the removed crystals mixed with washing liquid, this is such that the separating device also functions as a washing device.

As described above, the separator in accordance with the aforementioned Netherlands patent, including its control means, has been canceled and replaced by only separators placed directly on the recrystallizer vessel 15 in the form of a combined screen compactor, combined with a washing device. The latter is known from Dutch patent application 7106457.

Apart from the simplification by omitting a separate separator with the associated control means, a further advantageous effect is that several of the described sieve wash columns can be placed on a recrystallizer vessel. By now having these cylinders which do not operate continuously per se cyclically operate consecutively, their joint operation approaches a continuous process more and more. No solution is extracted from the system and therefore does not need to be supplemented. This works favorably on the production of the recrystallizer. In addition, the size and yield of the crystallizer can be easily adapted to the wishes of the user. However, the critical screen-wash column cylinder is much less flexible in scale enlargement. By adapting the number of cylinders on a crystallizer vessel, adaptation to the capacity of the whole can take place using or at most a small number of types and sizes of standardized and tested sieve wash columns.

Compared to the known washing column described in Dutch patent application 7106457, a further advantageous one is described. The effect is achieved by the fact that the piston with the sieve effect according to 8104086 έ * - 3 - this patent application is no longer loaded on the S4n side by the liquid pressure in the system. The screener according to the invention experiences only a slight spring position when the concentrated solution flows through the screen openings, but further the same liquid pressure prevails on both sides at approx. Therefore, the drive device need only be sized for the forces required to compact the sieved crystals and advance the compressed crystal bed in the direction of the take-off member. The driving device of the screen member is also simplified, because it now takes place from the closed end of the cylinder and no more flexible supply and discharge lines to the piston are required, as required by the device according to the said patent application. In a non-continuous operation, the above-described screen device washing column according to a preferred embodiment is characterized in that the movable screen member is formed by a piston-shaped filter disc, built up of two concentric parts, and by a central piston rod, the outer annular part is fixedly attached to the central piston rod and the middle part is freely movable between stops along the rod and can thus open and close the round opening in the piston, that the piston rod extends concentrically through the cylinder beyond the closed end of the cylinder and there is coupled to a reciprocating driving device, that the piston rod is surrounded over almost its entire length by a stationary heat-insulating pipe or sleeve fixed to the closed end of the cylinder, within which the rod is movable with little play, that the take-off member is attached to a hollow shaft, which is rotatable in the closed end of the cylinder can be received and which rotatably surrounds the insulating pipe, the hollow shaft being provided with rotatable seals both internally and externally.

However, it is possible to also implement the device according to the invention in a continuous operation and for this purpose the device is characterized in that the movable screen-40 member is formed by a piston-shaped filter disc with 8104086 *. Spherical peripheral surface, and by a central rotating drive shaft, at the end of which a swash disk is fixedly mounted, the filter disk being concentrically mounted on the swash disk and held against rotation, the cylinder being rotated The location of the filter disc is designed to be correspondingly spherical, such that over the outer part of the tumbling stroke the space above the filter disc has an open connection with the (re) crystallizer vessel and cooperates sealingly with the inner part of the tumbling stroke. the circumference of the filter disc, that the drive shaft extends concentrically through the cylinder beyond the closed end of the cylinder and is mounted there and coupled to a rotary drive device, the drive shaft extending along its entire length by a stationary, a heat-insulating pipe or sleeve fixedly secured to the closed end of the cylinder is surrounded, within which the shaft is movable with little play, that the take-off member is mounted on a hollow shaft, which can be rotatably received in the closed end of the cylinder and which rotatably surrounds the insulating pipe, the hollow shaft being provided with rotatable seals both internally and externally.

In both embodiments, the compacting screen member is driven from the closed end of the cylinder, in the non-continuously operating case via a reciprocating rod, in the continuously operating device using a continuously rotating drive shaft.

Reciprocating sieves, which are combined with a crystallizer, are known from the two US patents 2,613,136 and 2,615,794. The recrystallization section is lacking in the crystallization process described, while sieve valves operating per se are known from the latter US patent. However, the concentric sieve valve according to the invention guarantees a much more homogeneous construction of the ice crystal bed in the cylinder of the washing column than would ever be possible with the devices according to the two American publications.

It is sufficiently known to the skilled person in this connection how difficult it is to obtain a homogeneous and symmetrical structure of the crystal bed.

8104086 i * - 5 -

In a similar manner as described in Dutch patent application 7106457, stabilization of the washing front in the washing column takes place by regulating the pressure of the washing liquid in connection with the liquid pressure in the entire recrystallizer vessel.

It will be appreciated that in particular the crystallizer of the recrystallizer vessel may be of any other type without affecting the essence of the present invention as long as it is capable of containing reasonably small crystals of uniform size. to make.

Dutch patent application 7904919 discloses a continuously operating washing column with a rotating scraper device at the end of the column, where the washing liquid is supplied and discharged. The construction of the crystal bed, however, takes place with a rotating screen plate, which "smears" the sieved crystals against the crystal bed. The proper functioning of this is questionable, in contrast to the continuously operating embodiment according to the invention, where the screen plate rolls the crystals down against the crystal bed. Moreover, the device according to this publication is complicated by the two-sided drive of the scraper and the sieve compacting device, respectively. Placement on a (re-) crystallizer vessel is therefore absolutely not possible.

The invention is further elucidated on the basis of exemplary embodiments shown in the drawings.

Pig. 1 shows a recrystallizer vessel with a separator of crystals from the concentrated solution according to the invention, equipped with a reciprocating sieve.

Pig. 2 and FIG. 3 show enlarged cross-sectional and top plan details of the screen device of FIG. 1, respectively.

Fig. 4 shows an alternative separator 35 for continuous operation with rotary drive and swashplate driven screener.

In Fig. 1, 1 denotes the recrystallizer vessel in its entirety. On this vessel are placed one or more combined sieve washers 2, 2 as screeding devices. A vessel 3 is shown schematically, in which 8104086 X '* - β - the recrystallization takes place, which vessel is closed by a lid 4 via a circumferential flange 5. The separating devices 2 are arranged on this cover 4. 6 denotes the heat exchanger as a whole, which is placed according to Fig. 1 within the crystallizer vessel 1. It will be clear that this arrangement is not necessary for operation and that this heat exchanger could also be located outside the vessel. The crystallizer / heat exchanger consists of a cylindrical pipe 7, which is surrounded by a cooling jacket 8. A coolant with a lower temperature than the crystallization temperature of the solution to be processed is passed through the cooling jacket 8 via an inlet pipe 15 and a discharge pipe 14. . Within the cylinder 7 of the heat exchanger there is a rotating scraping device 9, which is driven by a schematically shown motor 10. The solution supplied via lines 11 and 12 and to be concentrated in a more detailed manner is introduced into the heat exchanger pipe 7. The solvent, mostly water, will mainly settle as a pure crystal form on the inside of the cylinder 7 at the location of the cooling jacket 8. The crystals continuously depositing thereby are mechanically removed by the scraper 9 and together with the more concentrated solution thereby discharged via conduit 13 to the interior 17 of the recrystalizer vessel 1. In order to prevent heat transfer to the outside of the heat exchanger 8, it can be externally heat-insulating, as indicated schematically at 16. All the cold power supplied with the coolant 15 is thus transferred to the solvent via the internal surface of the crystallizer cylinder 7.

The entire recrystallizer vessel 1 is filled with concentrated solution and crystals. The scraped crystals enter via the outlet 13 into the vessel in which there is a stirrer 18, which regularly and intensively mixes the entire contents. The stirrer is driven via a shaft feed-through 19 by a motor 20. Recrystallization takes place in the recrystallizer, the small crystals entering the recrystallizer via the outlet 13 being converted into a smaller number of large crystals. For this purpose, among other things, the light in the crystallizer as well as in the recrystallizer is of great importance, as is known, inter alia, from Dutch patent 148,242.

The residues in the crystallizer can be influenced by recirculating part of the concentrated solution and running the crystallization and recrystallization cycle again with fresh solution 11. For this purpose, schematically indicated, a crystal screen 21 is provided, which screen delivers concentrated solution via a vessel 22 and a line 23 to the suction of a pump 24. This pushes the concentrated solution back via the line 25 to the supply line 11, 12. Concentrated solution can be withdrawn from the circuit as desired via a line 26. The blow-off valve 27 is schematically shown for draining or draining the recrystallizer vessel.

As already mentioned above, the interior 17 of the recrystallizer vessel 1 is completely filled with a homogeneous mixture of concentrated solution and crystals of the solvent. These are conveyed via two or more standpipes 28 placed on the lid 4 to the combined sieve washing device 2. In Fig. 1 an embodiment is shown diagrammatically for the combined sieve washing device 2, which operates continuously. A continuously operating device is discussed later in Figure 4.

With a view to the operation of the combined screen-25 washing device, reference is made to Dutch patent application 7106457. This device consists of a cylindrical column 30, which is placed via a flange 29 on the short stand pipe 28. In the middle part of its length there is a compacted ice crystal bed 30 in column 30. Via a reciprocating screen member 32, which will be explained in more detail below in FIGS. 2 and 3, crystals with concentrated solution allowed above the sieve 324, 325 (Fig. 2, 3). During the upstroke, the crystals are retained by the sieve 35, while the concentrate can flow back through the sieve slits to the standpig 28. In the upstroke of the sieve member 32, the crystals are compressed into a homogeneous skew against the bottom of the crystal. talbed 31a. The concentrated solution between the crystals is then taken out and pushed back through the 8104086-8 screen slits. If the new disc of crystals is sufficiently compacted with the continuing upward stroke of the screen member 32, then, with continued upward stroke, the entire crystal bed 31 will be pushed upwards through the interior of the column 30. Via the piston rod 33 and the driving device 34 the reciprocating movement of the screen member 32 is controlled and operated. As soon as the described compaction pressure in the crystals is sufficiently high, the rotating mechanical scraper 35 is set in motion via transmission 38 by the motor 37. The scraper 35 is thereby fixedly mounted via a hollow shaft 3β in the closed end cover of the column. 30. At the same time, washing liquid, usually the same solvent, is introduced under pressure into the upper part of the washing column 30 under pressure and mixes there with the scraped-off crystals. The scraped-off crystals are discharged together with the washing liquid via an opposite pipe 62. By discharging the mixture under counter-pressure, the pressure of the washing liquid at the top of the washing column 30 can be maintained at a high level relative to the pressure in the recrystallizer vessel, so that through the apertures regularly provided in the scraper 35 an over the the entire cross-section, evenly distributed relative velocity of the washing liquid with respect to the crystals in the crystal bed is maintained. At the same time, the concentrated solution located between the crystals in the crystal bed 31 is displaced relative to the crystals. Dashed line 63 schematically denotes the washing front to which the washing liquid may penetrate between the crystals in the crystal bed, thereby expelling the concentrated solution against the upward movement of the crystal bed. To this end, the column 30 can be made of transparent material, so that by means of, for example, photo-optical means, the location of the wash front 63 can be effectively observed and can be maintained in that control by / of the difference between the pressure of the washing liquid and the prevailing liquid pressure in the interior 17 of the crystallizer 1.

The stroke of the sieve device 32 is limited such that with each ascending stroke a certain layer is first added to the bottom of the crystal bed, then over a second part or the compression part of the stroke of the sieve, the layer is crystals compacted. During the first and second parts of the stroke, the scraper device 35 is stationary, in order to be able to press the new plates or crystals in homogeneous form against the bottom of the present crystal bed 31, then during a third part of the upstroke, a disc of crystals 31 of the same height scraped from the top of the crystal bed 31 pressed forward. Despite the reciprocating action, a crystal bed 31 will therefore always be present, with an average height which exceeds the height of the crystal disc supplemented or scraped off per stroke many times. This makes it possible to maintain a constant washing front 63.

In addition to the necessary conditions which enable the above-described operation of the washing column 30, it is the case that the crystal-solution mixture drawn in with each stroke is homogeneously admitted, that is to say, it is symmetrically as good as possible. through and on the screen. This is shown on an enlarged scale in Figures 2 and 3. Figures 2 and 3 show the non-continuously operating reciprocating screen member 32 of Figure 1 on an enlarged scale. At 30 the cylinder of the wash column is again shown, at 31 the crystal bed 25 with the flat bottom 31 * as this bio is deposited in the compacted form the last upstroke of the screen. The crystal bed is located between the outside of the insulating sleeve 39 and the inside of the column cylinder 30. The piston rod 33 has just started its downward stroke in FIG. 2, in which the sieve surfaces 324 and 325 have come loose from the bottom. 311 of the crystal bed. Due to the liquid pressure in the space 17 of the crystallizer, the central annular screen portion 323 remains so that, according to arrow T, a mixture of crystals with concentrated solution can flow into the expanding space between the crystal bed and the screen surface. The sieves 324 and 325 are sized to retain the crystals but allow the concentrated solution to flow through them with little resistance? after the piston 321 reverses the direction of movement with the piston rod 33 in the bottom point of the 8104086 - 10 - stroke and moves wear upwards. The inner part 323 of the screen member then sinks into the recess of the outer part 321 of the screen member intended for this purpose. This part is fixed with a number of spokes, for example with screw thread 322, to the end of the rod 33. With continued upward stroke, the sieve surfaces 324 and 325 form a continuous surface on which the crystals deposit and with further upward stroke the face 31 * get hit and get compacted against it. The concentrated solution which was between the crystals, meanwhile, can flow back between the crystals and through the opening of the sieve to the standpipe 28. The central part 323 of the sieve 32 can only perform a limited stroke between the 15 stops 326 on the top and 327 in the form of the spokes of the annular screen member. The total stroke of the rod 33 with the outer annular screen member 321 is, of course, longer than the limited stroke between its stops of the disc-shaped central portion 323 of the screen member. The outer circumference of the annular portion 321 of the screen member 32 fits like a piston sealingly but slidingly into the column cylinder 30.

Fig. 4 shows an alternative embodiment for the screen member with compacting properties, wherein the operation is continuous. In this embodiment, the column cylinder 30 is placed on the lid 4 of the (re-) crystallizer with the aid of the flange 29, the short position pipe 28 being missing. Instead of the short standpipe 28, an extension 40 of the column cylinder 30 projects down into the space 17 of the recrystallizer. The bottom edge has a number of openings 42 circumferentially through which concentrated solution with crystals can flow. There, the internal diameter of the cylindrical part 40 is greater than that of the actual wash column cylinder 30. The transition 41 is spherical. At the center point of the spherical surface is a ball 46 mounted rotatably and in fixed height position on a rotary driven shaft 33. This shaft is the same as that shown in Fig. 1, but the bearing and drive are 40 such that the shaft 33 rotates continuously in vasteη fixed height - 8104086> - 11 - position. The shaft 33 is also surrounded here by an insulating stationary sleeve or pipe 39. Here too, the compacted ice bed is located between the outside of the sleeve 39 and the inside of the washing column cylinder 30 and the top 3 cylindrical part of the downwardly extended cylinder 40. The bottom of the compacted ice bed is again indicated by 31 *. An inclined wobble disc 48 is fixed to the ball 46, which tumbles when the shaft 33 is rotated. With the aid of diagrammatically illustrated bearings 49 ', a non-rotating sieve member 32 is mounted on the tumbler disc, which sieve member 32 makes a tumbling - non-rotating movement when the shaft 33 and the tumbler disk 48 rotate. The tumbling movement of the screen member 32 takes place about the center of the inner spherical surface 41 of the cylinder 40. The outer surface of the screen member 32 is therefore also correspondingly spherical from the same center, so as to cooperate slidingly and sealingly with the surface 41. The top of the sieve member 32 consists of a conical sieve construction with sieve bars or sieve plates 53, including a flow space $ 4 for the concentrated solution. The space 54 under the sieve 53 communicates with the space 17 of the crystallizer vessel via bores 55, a ring channel 56 and discharge openings 57. The extended stub shaft 45 of the shaft 33 is received in a support bearing 44, which is fastened to the lower edge of the extension cylinder 40 by means of a number of spokes 43.

When the shaft 33 is rotated with the swash plate 48, a radius of the sieve surface 53 is at all times located at the highest point and this is indicated by 53 *. In the diagonally opposite area of the sieve surface 53 (left in Fig. 4), concentrated solution with crystals can flow through one or more of the openings 42 in the triangular space between the bottom 31 * of the crystal. 35 bed, the top of the screen member 53 and the spherical inner surface 41 of the cylinder 40. This inflow is schematically indicated by an arrow T. Now if the swash disk rotates further, the top edge of the screen member 32 closes the opening 42 and compacts the crystals in the said triangular space. Since there is initially still concentrated 8104036 -J * · · ν - 12 - solution, the crystals with this solution will homogeneously fill the triangular space, with concentrate gradually being squeezed out through the sieve slits 53, the space 54 and the channels 53, 56 and 57. At a given moment, the crystals 5 can no longer escape from the narrowing space and push the ice bed 31 upwards. Finally, the situation is reached as shown in Fig. 4 on the right, where the sieve bars 53 * have fully crystallized the crystals and pushed them upwards sufficiently against the bottom of the crystal bed 31. The crystal bed 31 is slowly but continuously scraped by the top scraper.

In the same manner as described in Figs. 1, 2 and 3, a washing front 63 is maintained using supply and discharge lines for washing liquid 61 and 62, not shown in Fig. 15.

Although the screen compactor shown in Figure 4 and discussed herein operates continuously, several may be placed on the lid 4 of the single crystallizer in order to be able to provide total condensers with stepwise different flow rates using standardized units.

8104086

Claims (3)

1. Apparatus for crystallizing a solvent from a solution, consisting of a closed (re-) crystallizer vessel, a scraped heat exchanger with a supply for the solution and a discharge to a directly connected recrystallized stirrer. sator, with an exit to at least one separating inlet of the crystals from the concentrated solution, characterized in that each separating device comprises a cylinder which is placed in open communication with and on the (re) crystallizer vessel, which is placed in the cylinder with a slight clearance is placed a movable screen member, with which the sieved crystals can also be homogeneously compacted and the crystal column thus formed can be moved to the other, closed end of the cylinder, which has a take-off member (such as such a rotating scraping device) is placed in the cylinder and that there is a connection for the supply of a washing liquid and a connection The expression for the removal of the removed crystals mixed with washing liquid is such that the separating device also functions as a washing column. 2. Device according to claim 1, characterized in that the movable screen member is formed by a piston-shaped filter disc, built up from two concentric parts, and by a central piston rod, the outer annular part being fixedly attached to the central piston rod and the middle part is movable freely along the rod between stops and can thus open and close the round opening 30 in the piston, that the piston rod extends concentrically through the cylinder beyond the closed end of the cylinder and is coupled there to a reciprocating drive device. the piston rod is enclosed for almost its entire length by a stationary heat-insulating pipe or sleeve fixed to the closed end of the cylinder, within which the rod is movable with little play, that the take-off member is attached to a hollow shaft which can be rotatably mounted in the closed end of the cylinder 8104086-14 and which rotates the insulating pipe surrounding the hollow shaft with rotatable seals both internally and externally. 5 3. Device as claimed in claim 1, characterized in that the movable screen member is formed by a piston-shaped filter disc with spherical peripheral surface, and by a central rotating drive shaft, at the end of which a tumbler disc is fixed, the filters being concentrically arranged. is mounted on the swash plate and is held against rotation, the cylinder at the location of the filter disc being of correspondingly spherical shape that over the outer part of the tumbling stroke the space above the filter disc 15 has an open connection with the (re- crystallizer vessel and sealingly engages over the inner part of the tumbler stroke with the periphery of the filter disc, the drive shaft extending concentrically through the cylinder beyond the closed end of the cylinder and supported thereon and rotating rotary device coupled, that the drive shaft along its entire length through a stationary, at the closed end of the cylinder there is fixed, heat-insulating pipe or sleeve surrounded, within which the shaft is movable with little play, that the take-off member is attached to a hollow shaft, which can be rotatably received in the closed end of the cylinder and which the insulating pipe rotates, the hollow shaft being provided with rotatable seals both internally and externally. 8104086