SE449448B - PROCESS AND LAUNCH COLUMN TO Separate Ice Crystals In A Slurry Of Ice Crystals In A Water Discharge From Said Water Discharge - Google Patents

Description

10 449 448 2 at said shielded opening to maximize the speed of with which the particles can be removed at the column output end.

When operating this type of device, the two remain significant difficulties in freezing the screen, which causes disruption of operations, as well as losses, which occur by mixing the aqueous solution between ice crystals and the washing liquid. These losses are increased by channel the phenomenon. This phenomenon gives rise to formation of "channels" in the bed of ice crystals, through which the washing liquid passes. When, for example, liquid food substances are concentrated, the concentration is partially destroyed and when it comes to seawater desalination, the fresh water goes lost as it mixes with the concentration treated brine, which is dispensed with. In addition, the washing liquid, which reaches the screen, the tendency to cause clumping. The washing liquid has a higher freezing point than the concentrated solution. The screen cools down of this concentrated solution and the washing liquid, which comes in contact with the screen, will freeze and to, as mentioned, cause clumping, whereby possibly the process will be halted.

The difficulties associated with freezing of the screen, has been well described in the two American U.S. Patent Nos. 3,885,399 and 3,992,900. see column 1, lines 23-57 of the latter patent.

To avoid this clogging have in these patents a two-step process has been proposed, using two washing columns, as described in the foregoing U.S. Patent No. 3,587,859. The two U.S. patents No 3 885 399 and No 3 992 900 show evidence of the that there has been no solution so far. problem to avoid washing liquid reaching the screen, which, among other things, is reduced to the problem of sering in the packed bed.

The serious difficulties, which occur through channeling and freezing of the screen, it also appears except as clear from a recent Gerson survey Grossmann (AICHE Journal, vol. 22 no. 6, November, 1976 449 448 3 sid. 1033-1042). To get a clear picture of these problems and their meaning is referred to in particular pages 1033 and 1034 at the top.

By practicing the present invention, anyone can these difficulties are reduced and in special cases forms are completely eliminated, which means a procedure and an apparatus is utilized, whereby freezing and channeling can be effectively avoided and operation, which carries mainly zero loss, is ensured. In order to the principle of the invention must be clearly stated, it is with the following discussion of the Probstein washing column which is mentioned above in U.S. Pat 3,587,859.

Particular attention is paid to Figure 1 i the said U.S. patent and against Figures 1 and 2 of the Grossmann the publication.

The washing device usually consists of a vertical one column, which is provided with a screen at the middle part of the column wall. According to U.S. Pat 3,587,859 (column 1, line 41; column 4, lines 17-18) the ice particles form a plug.

The water concentrate is said to flow up through it lower leg of this plug and out through the screen. The pressure of the water concentrate itself is used to provide the force for moving the ice particles upwards (see U.S. Patent No. 3,587,859, column 1, lines 44-45), which means that the concentration of the concentrate on the plug causes the latter to move up towards the friction on the walls and the limiting forces at the upper part. These limiting forces at it the upper part derives, for example, from the traction of the bed against the washing liquid and the scraper device used to dissolve the plugs and discharge them through the solution formed the particles.

According to what is ideal should be in procedures according to this prior art only a small amount of liquid flows down through the upper leg of the ice plug and out through the screen (which is temporary in itself 449 448 4 would tend to clog the screen) but the balance is disturbed as soon as the channeling occurs.

The situation, as it appears in the American Patent No. 3,587,859 and in the Grossmann publication, illustrates a "brine crown", which in fact constitutes the washing front or in other words the interface between the concentrate and the washing liquid - which is strongly curved, wherein in addition flow lines of the concentrate are heavily curved. This is unavoidable at the event according to the prior art. The curvature of the washing the front and of the flow lines in its vicinity in gear ratio with differences in density (porosity) of the packed bed (when viewed in a cross section perpendicular to the axis line).

In this context, attention is drawn to "American Reissue 23,810" (especially Figure 1 and column 2 lines 47-50). Packed ice crystals are pushed through a zone (c), where liquid is removed, a "transition zone" (b) and a water-ice zone (a). At this event is it in the transition zone (b), as the curved wash front can be assumed to be formed (if a correct "front" overhead formed). To stabilize a curved wash front has however, proved to be difficult. To avoid these have difficulty in U.S. Patent No. 2,854,494 proposed to force a pulsating return current of washing liquid through the packed bed of ice crystals.

It is assumed that a "shaking" of the transition zone would contribute to counteracting difficulties, such as channeling, as discussed above.

According to the present invention, a sharp is made possible and stable washing front only if such measures are taken, that the washing front (the interface between the concentrate and the washing liquid) lies in an even plane perpendicular to the direction in which the packed bed moves.

According to the invention, a process is thus achieved for separating the ice crystals present in a slurry of an aqueous solution and ice crystals, from the aqueous solution and for washing the ice crystals É449 448 with a washing liquid, whereby a packed bed of ice numbers are provided, which is subjected to a continuous movement, while creating a wash front in the bed of washing crystals between said aqueous solution and the washing liquid, the process being characterized in that the aqueous solution and the water-washing liquid adjacent to said wash front is essentially stagnant and of a ' stable washing front is created, which lies in an even plane perpendicular to the movement of the packed In the bed of ice crystals.

In general, this will involve a process for separating the ice crystals in a slurry of ice crystals in an aqueous solution from said aqueous solution washing of said ice crystals with an aqueous washing liquid, the process in series comprising * the following steps: a) to continuously introduce said slurry in a first cylindrical zone; b) being in said first cylindrical zone continuously remove some of the aqueous solution from the slurry to provide a packed bed of ice crystals; Q c) to move the packed bed continuously through a second cylindrical zone, which contains a substantially stagnant layer of water solution in a first section and a substantially stagnant standing layers of washing liquid in a second section, which is adjacent to the first section, thus a wash front is created between said first and second sec ~ ensuring that the packed bed is obtained a homogeneous structure before it reaches the wash front; and d) to continuously disintegrate it continuously forward passing washed packed bed and to discharge the product of this decomposition. over the washing front there will be a "jump" in temperature, since the aqueous solution between ice pallets, which are more concentrated than the washing liquid, will have a lower temperature than this washing liquid.

'G1 449 448 6 In the normal case, the washing liquid being water, the temperature will of course be 0 ° C, so that the ice crystals in the aqueous solution will have a temperature below 0 ° C. Then the washing liquid comes into contact with the aqueous solution comes a part of it, which fits between the ice crystals, to freeze, whereby these crystals will generally be bound together.

At the washing front, a solid porous is formed in this way ice plug, First, therefore, a thickened slurry must achieved, measures must be taken to allow a homogeneous structure of the thickened slurry to a packed bed and measures must also be taken to impart a moving motion to the bed. The most important is that ice crystals, before reaching the wash front, has been brought to distribute evenly over the packed total cross-section of the bed. In principle, it may be possible it is possible to use the drawing of the flowing water-soluble to move the packed bed and still ensure a homogeneous construction of this bed, which reaches the interface between the aqueous solution and the washing liquid (washing front). Towing or towing may result transport of the ice crystals in the zone in which the water the solution is removed. The ice crystals that are collected there, can shoot at others. At the washing front, homo- is achieved if this washing front is located sufficiently far from the place at which the washing solution has been removed, despite the fact that from the beginning a non-homogeneous structure of the thickened slurry obtained at the site of removal of water solution, ie when it comes to a wall filter. This thickened and initially non-homogeneous slurry must however, be able to or be made to homogenize sera. It must be homogeneous across its cross section, then it arrives at the washing front. This is necessary to avoid radial differences in resistance to fluid flow. If these differences occur, it will the washing front not to be flat but curved on one or * another way. 449 448 7 Another possible arrangement is the following. Slam- is inserted at the bottom of a vertical cylinder. Bottom is provided with a screen or screen, through which water solution is removed. A stirrer-scraper device, which is connected to a shaft through the bottom of the cylinder and which affected by a motor, keeps the screen clean and homogeneous ser the thickened slurry. The slurry can inserted laterally or through the agitator-scraper device (hollow) shaft. The screen through which the aqueous solution removed, does not necessarily have to be at the bottom but can, for example, occur in the wall of the cylinder near the bottom. The ice crystals, which are collected in the lower the part of the cylinder pushes other crystals upwards, whereby a packed bed is formed. The liquid in the lower part of the cylinder is aqueous solution and the liquid in the upper part washing liquid. The interface between the aqueous solution and the the liquid consists of the washing front, which is kept at approx. constant level by adjusting the pressure of the incoming slurry and the pressure of the washing the liquid. This can be achieved in the way that more closely in detail described below.

At the upper part of the cylinder can be a scraper device arranged to disintegrate the washed packed bed * and discharge the product of this decomposition. This will also be described in more detail below. The disintegration can also be achieved by melting.

At an alternative and preferred arrangement the zone in which the aqueous solution is removed from slurry, including hollow perforated (shielded) centrifuge blades, which are attached to a rotatable shaft, whereby the aqueous solution is removed. These leaves can be attached to the shaft in such a way that they are free rotatable about small axis lines perpendicular to the axis, which means that they can take on a certain slope, depending on the current factors at hand, eg the rotational speed of the shaft and the traction of the aqueous solution removed through these cavities leaf. In this case, the blades do not provide the energy to shoot 449 448 8 the crystals forward without the displacing force present in the draw of the aqueous solution being removed. The in crystals, which are collected by the removal of aqueous solution, pushing other crystals forward. About the shaft, to which the shielded hollow blades are attached and freely movable, not caused to rotate, so will the leaves to assume a position parallel to the axis of the washing column, pointing to the discharge end, especially if the leaves are shielded at both ends. It is, however advantageous to turn the shaft. This is coming to a great extent to help counteract any tendency to formation of inhomogeneities through the passage of the thickened the slurry along the screen.

Another preferred measure according to the invention involves the use of mechanical means to assist bring the thickened slurry of ice crystals a moving movement, whereby a continuous sliding packed bed of these crystals simultaneously created. This can be achieved, for example, by using inclined blades, which are attached to a rotatable shaft, in such a way that the blades have a fixed inclination ning. Again, the screen for removing water the solution be located in these leaves, if they are hollow.

By using mechanical means for removal of the packed bed, this movement is made in large extent independent of the pressure of the incoming the aqueous solution, the outgoing aqueous solution and the washing liquid and the respective differences. Through rotation of the fixed inclined blades, the filtration the layer next to the filter to be continuously renewed on in such a way as to ensure homogeneity.

To facilitate a homogeneous construction of the packed bed in the radial direction (which, as " already mentioned, is especially important when the bed reaches front) may be an annular structure of said bed recommended, especially when the washing column has large diameters and when the removal of aqueous solution from the slurry is accomplished via a screen, which is located l0 449 448 9 in the direction of movement of the packed bed (eg a filter in the wall of the cylinder). You must then use a device, which consists of a cylinder, which is arranged coaxially inside another cylinder of larger diameter. The difference in diameter and the distance between the screen and the washing front must be selected in such a way that the packed bed under working conditions has a homogeneous structure at the washing front.

This generally means that when the aqueous solution removed via the screen in the wall of either of or at both the cylinders, which together delimit the ring shaped space in which the packed bed is provided, this annular space must be relatively narrow, for example 2-5 cm. It should be obvious that the aqueous solution via a screen in the wall of the column will tend to favor the formation of inhomogeneities in the packed bed. This tendency is better counteracted the narrower the annular ring is (associated with In the foregoing, we refer to the Swedish patent application No. 7800273-O).

In the event that the aqueous solution is removed via a screen which is more or less perpendicular to the movement the movement of the packed bed (as already mentioned written), the ring can be considerably wider. When we utilizes slanted blades and the outer cylinder inner diameter is 10 cm, the ring may, for example, have one width of 20 cm. The tendency to an inhomogeneous structure of the packed bed is much smaller.

When using an annular structure for it packed bed can the mechanical means (eg, inclined leaf), which was used to impart the packed bed a advancing movement in the direction of the cylindrical the chin line of the washing column, as well as the scraper means used to disintegrate the packed bed after that it 'has passed through the washing front, be fastened at the inner cylinder. In this case, the interior must the cylinder rotates. 449 448 It is also possible to let the inner cylinder be stationary. In this case, they must be mechanical the means for feeding the packed bed and the scraping the organs (if used) are affected separately. This is coming to be described in more detail in an example below.

However, the inner cylinder may also be attached to same shaft as the mechanical means for feeding it packed the bed. An optimal opportunity for process control can, depending on the circumstances, be obtained by the inner cylinder, the mechanical feed means and the scraper means are provided with separate actuating mechanisms, so that their respective rotational speeds can be varied according to wish.

When using the inclined blades as mechanical means for propelling the packed bed it may also be advantageous to provide for the blade is adjustable. This increases the possibility of control of the process depending on what is dictated of the prevailing circumstances.

Decomposition of the packed bed of ice crystals after the washing front has been passed can be achieved by melting. However, it has particularly good results obtained by using scrapers. Scrap devices for this purpose are known per se. Reference is made, for example, to U.S. Pat 3,872,009 and in the following example comes a slightly modified construction to be described. As already mentioned comes the limiting force, which counteracts the movement of the bed of ice crystals, to pack the bed so firmly that the ice crystals, under the influence of the temperature jump at the washing front will bond together, creating a solid porous ice plug. It has been proven in several cases that this ice plug will consist of about two-thirds of solid ice and about a third of interconnected pores but this ratio may vary according to the ratio dena. While the washing front actually stands still then it moves relative to the packed bed through these 449 448 ll porer. In this way, the bed is washed "inside". Laundry- the position of the front in the washing column can be kept mainly fixed by a sensing device with feedback to the mode of achieved by two adjacent tem- this washing front. This can, for example temperature sensors at different sides of the wash front. This will be described in more detail in the following.

The invention also comprises an apparatus for carrying out of the process described above. According to the invention an apparatus is thus provided for separating the ice crystal in a slurry of ice crystals in an aqueous solution from said solution and washing said ice crystals at a washing front with a water wash liquid, the appliance The rate includes the following operationally cooperating bodies: a) an enclosed cylindrical space with an input and an output side; b) feeding means for feeding a slurry of ice crystals to the feed side of the cylindrical the space c) discharge means for removing the decomposition products from the discharge side of the space; d) washing means for supplying washing liquid to the discharge side of the cylindrical space; e) means at the feed side of the cylindrical the space to remove solution from the slurry while the ice crystals, which provide a thickened slurry, maintained; f) mechanical means arranged in the cylindrical the space to bring the thickened slurry to move continuously in the form of a packed bed of ice crystals in the axial direction towards the discharge the side of the cylindrical space; g) means at the discharge side of the space for disassemble the washed, packed bed, leaving the appliance characterized in that the mechanical means, which are mentioned under f) consists of slanted leaves attached to a rotatable shaft coaxial with the cylindrical shaft ._., ._____..........__..____....___.__. > 449 448 12 space, which cooperate with sensing devices and control means for sensing and controlling the position of the washing front, so that during the operation of the washing column the washing front motorized between the sensing devices in an area of the cylindrical space which lacks elements, which could interfere with the homogenization of the washing front.

The most preferred embodiments of the invention the ring comprises those, whereby an annular structure of the washing column is combined with rotating hollow blades with a fixed inclination, through which water-soluble is removed from the slurry, thereby scraping the organs on one side and the oblique leaves on the other hand, are provided with separate body. In general, this will mean that the scraper means will obtain a higher rotational speed. hot than the slanted leaves.

The invention will now be described in more detail below in the form of a preferred embodiment with reference to to the accompanying drawing.

Figure 1 shows the different process functions from which the process according to the invention is complex.

Figure 2 shows the preferred embodiments of the invention.

Figure 3 shows a top view of the cross section along the line III-III in figure 2.

Figure 4 shows a cross section of a hollow blade along the line IV-IV in figure 3.

Referring to Figure 1, at 1 slurry the formation of ice crystals, 2 representing the removal of the aqueous solution discharged at 3 below leaving a thickened slurry. Homogenization the function is represented by 4 and the function for formation of a packed bed with 5. The movement of the packed the bed through a stationary layer of aqueous solution represented at 6 and arrival at the laundry front at 7. The bed then moves through the essential the stationary layer of washing liquid 8, whereby it is normally consolidated into a solid porous ice block, _ ... _, ..... ......... _ _ _ ... _... ._-.__..._-. - .._.._. _ .. m -, .-., ........ '10 449 448 13 after which decomposition takes place at 9, while decomposition the division product is transported away at 10 and discharged at ll. Some of the functions 2, 4, 5 and 6 can be performed simultaneously in particular embodiments of the invention, which have been described above. When using an appliance with an annular space and hollow leaves with fixed slope, through which leaves the aqueous solution is removed, For example, functions 2, 4 and 5 can be done practically taken at the same time.

In general, however, it is significant that the thickened slurry, when it arrives to the wash front, is homogeneously packed to form a smooth, non-curved wash front perpendicular to the wash column axis line.

As can be seen from Figure 2, the body of the apparatus is cut lengthwise to illustrate the inside in side view.

At 17, a cylindrical housing with a bottom is illustrated. plate 18 and a cover plate l9. An inner cylindrical body illustrated at 20. This body is attached to a shaft 21, which in turn is attached to it at the cover plate 19 bolted band 22. Another cylindrical body is shown at 23 and is attached to the shaft 24, which carries the gear 25.

This wheel 25 cooperates with the gear 26, which is actuated of the motor 27. The body 23 carries the hollow inclined ones the blades 28, which at the upper surface are provided with the screen 29.

The leaves are represented here more or less simplified and otherwise reference is made to Figures 3 and 4.

The inside of the hollow blades 28 are in communication connecting connection with the line 29 ', through which liquid can be removed. The body 23 also has pins 30 while the housing 17 has vertical blades 31.

A disc 32, which is provided with knives 33 and wear- sar 34, acts as a scraper device. Disc 32 is attached at the cylindrical body 35, which is attached to gear 37, which cooperates with gear 38. Engine 39 affects the gear 38.

The slurry passes at 40 and is well maintained stirred by the pins 30, which cooperate with the blades 31, 449 448 14 to prevent the crystals from depositing. Aqueous solution removed through the screen 29 and exits through the i- hollow blades 28 and conduit 29 ', one thickened slurry is left at the surface of the screen 29. This thickened slurry is packed and pushed through the ring shaped space 41 by rotating the body 23 with sheets 28. The dashed line 42 represents the washing the front, which is the dividing plane between the space 41, in which the liquid consists of an aqueous solution, and space 36, in which the liquid is washing liquid (normally water). Temperature sensing devices 57 and 58 keeps the movement of the washing front within fine limits. These devices will record a certain temperature difference, which may occur between the aqueous solution and the washing liquid. If the washing front moves up or down then this temperature difference will disappear and an electrical pulse from the controller 59 will affect valve 60, which is further opened or closed depending on the conditions.

The space 36 will in most cases be filled of a porous solid ice plug, which will disintegrate by turning the disc 32 with the knives 33. They through the decomposition effected the particles, which pass through the slots 34, will fit into the space 43.

Washing fluid will be pumped around by the pump 44. It will fit in space 43 at 45 and flush the ice particles at 46. The ice particles were melted by the device 47. When the washing front remains at a fixed place comes the amount of water, which leaves the system via valve 60, to be equal to the amount of ice which discharged by the scraper 32. If the washing front touches downwards, the valve 60 opens slightly further so that additional water is removed, and vice versa. On this way the balance is maintained.

Figure 3 shows at 29 the screen of one of the hollow, oblique leaves, the edge of which is shown at 28. Between two oblique leaves, the space 48 can be detected, by which the slurry passes. The leaves are attached to it 449 448 annular cylindrical body 23, in which a cylindrical ~ risk track 49 exists. Inside of the hollow, oblique the blades are connected to the circular through channels 50 the groove 49. The annular cylindrical body 23 is attached to the shaft 51 through the projecting edge 52.

The shaft 51 is provided with a central channel 29 ', which is connected to the circular groove 49 via the channel 53.

Figure 4 shows that the bottom 54 of the blade is provided with longitudinally extending chambers 55, which serves to support the screen 29. The chambers 55 are seen with holes 56 for passage of the aqueous solution. The magazine is attached to the cylindrical body 23, which is provided with the channel 50 and the groove 49 where all the leaf fluid collected. The axis on which the cylindrical body 23 is attached, is shown at 51 and includes the central channel 29 ' for removal of the aqueous solution.

It will be appreciated that the described apparatus and other related embodiments, which include i- hollow blades can serve as a continuous sludge thickener. when the disintegration device is omitted.

Claims (5)

10 15 20 25 30 35 449 448 1 6 PATENT CLAIMS A process for separating the ice crystals in a slurry of ice crystals in an aqueous solution from said aqueous solution and washing the ice crystals with a water-washing liquid, thereby creating a packed bed of ice crystals, which is subjected to a continuous movement, while a washing front ( 42) is created in the packed bed of ice crystals between the aqueous solution and the water-washing liquid, characterized in that the aqueous solution and the water-washing liquid next to said washing front are kept substantially stationary, and that when it reaches the washing front, the packed bed is homogeneous over the entire cross section a stable wash front is created in an even plane perpendicular to the movement of the packed bed of ice crystals. Process according to claim 1, characterized in that it successively comprises the following steps: a) continuously introducing the slurry into a first cylindrical zone (41); b) in said first cylindrical zone, continuously removing a portion of the aqueous solution from the slurry to provide a packed bed of ice crystals; In c) causing the packed bed to move continuously through a second cylindrical zone (36), which contains a substantially stationary layer of aqueous solution in a first section and a substantially stationary layer of washing liquid in a second section, adjacent the first section, to create a washing front (42) between said first and second sections, ensuring that the packed bed obtains a homogeneous structure before it reaches the washing front; and d) continuously disintegrating the continuously passing washed packed bed, and discharging the product obtained by the disintegration. f, * r lO 15 20 25 30 35 449 448 17 A washing column for separating the ice crystals in a slurry of ice crystals in an aqueous solution from said aqueous solution and washing the ice crystals with a water washing liquid, thereby creating a packed bed of ice crystals, which is subjected to a continuous movement, while a washing front 42) is created in the packed bed of ice crystals between the aqueous solution and the water-washing liquid comprising: a) a closed cylindrical space (36.4l), with an inlet and an outlet side; b) feeding means (40) for feeding a slurry of ice crystals to the feeding side of the cylindrical space (36,41); c) discharge means (46) for removing decomposition products from the discharge side of the space (36,4l); d) supply means (45) for supplying washing liquid to the discharge side of the cylindrical space; e) means (29) at the inlet side of the cylindrical space for removing solution from the slurry while maintaining the ice crystals, which cause a thickened slurry; f) mechanical means (28) arranged in the cylindrical space to cause the thickened slurry to move continuously in the form of a packed bed of ice crystals in the axial direction towards the discharge side of the cylindrical space; g) means (32,33) at the discharge side of the space for disintegrating the washed, packed bed, characterized in that the mechanical means mentioned under f) consist of inclined blades (28) attached to a rotatable shaft (24), which is coaxial with the cylindrical space, which cooperates with sensing devices (57,58) and control means (59,60) for sensing and controlling the position of the washing front (42), so that, during the operation of the washing column, the washing front (42) is stabilized between the sensing devices (57,58) in an area of the cylindrical space which lacks elements which could interfere with the homogenization of the washing front. 10 449 448 18 Washing column according to claim 3, characterized in that the blades (28) are hollow and provided with an inner space and perforated surface, and that the inner space is connected to a conduit (29 ') in the rotatable shaft ( 24) in such a way that solution can be removed from the slurry of ice crystals and can be discharged. Washing column according to claim 3, characterized in that said means, mentioned under e), comprise a screen (29) arranged above each of the inclined blades (28). W