JPS5913882B2 - Continuous packed bed washing column - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates generally to a continuous process and apparatus for separating ice crystals contained in a slurry of an aqueous solution and ice crystals from an aqueous solution and washing the ice crystals with an aqueous washing liquid.

Typically, this aqueous cleaning liquid is water, but multi-stage processing is possible so that the cleaning liquid for a particular stage is an aqueous solution drawn from the next stage.

Slurries of this type are produced in industrial processing methods whereby an aqueous solution is recovered as a product and the ice crystals are separated, or conversely, the ice crystals are recovered as a product and the aqueous solution is discarded.

The first method in the food industry is the freeze concentration of aqueous liquids such as fruit, sugar, beer, wine and coffee extracts.

The second method is to create pure water by freezing and concentrating seawater, which involves discarding the salt water and collecting and melting the ice crystals.

A continuous packed bed washing column is described in U.S. Pat. No. 3,587,859.
[Probstein], and specifically describes the production of pure water from seawater.

A porous bed of particle ice crystals is formed in this wash column, and the liquid brine is allowed to flow out of the column through a screened opening (located midway between its ends).

A wash liquid is introduced at one end of the column and displaces liquid medium from the interstices between the particles as the porous bed moves continuously through the column.

Control means are provided to control the relationship between the liquid pressure at the end of the porous bed and the liquid pressure at such screened openings, thereby minimizing the rate at which particles may be removed at the outlet end of the column. do.

The two main difficulties in operating this type of equipment are:
Losses caused by freezing of the screen and mixing of the aqueous solution between the ice crystals and the wash solution cause operational breakdown.

These losses are exacerbated by channeling phenomena.

This phenomenon involves the formation of "channels" in the bed of ice crystals through which liquid escapes.

For example, when concentrating liquid foods, some of the concentration does not take place, and when desalting seawater, pure water is lost because it mixes with the concentrated brine that is discarded.

Additionally, cleaning fluid that reaches the screen tends to clog it.

The wash solution has a higher freezing point than the concentrated solution.

The screen is cooled by this concentrated solution, and the cleaning liquid in contact with the screen freezes, thereby causing clogging.
Eventually, the process comes to a halt.

The difficulties associated with freezing the screen are discussed in U.S. Patent No. 38.
No. 85399 and No. 3992900 (assigned to Campbell Avco).

In particular, column 1, lines 23-57 (U.S. Patent No. 39929
No. 50).

To avoid this clogging (chloragging), a two-stage process using two wash columns was proposed in these patents and is described in the aforementioned US Pat. No. 3,587,859.

U.S. Patent Nos. 3,885,399 and 3,992,900 are
It proves that there is no solution to the problem that avoids cleaning fluid reaching the screen.

Therein, among other things, the problem of preventing channeling in packed beds is summarized.

Serious difficulties with channeling and freezing screens, Gershon Grosman
(AICHE Journal 22)
Vol. 6, November 1976, pp. 1033-1042).

See especially pages 1033 and 1034 thereof for a thorough examination of these issues and their relationship.

By practicing the present invention, all of these difficulties have been alleviated, and in particular embodiments completely eliminated, as the present invention effectively avoids freezing and channeling and provides nearly zero-loss operation. It can be said that we provide a method and apparatus for obtaining the same.

In order to clearly understand the idea of the present invention, the discussion in Section F regarding Probstein's wash column above is appropriate.

In particular, note FIG. 1 of US Pat. No. 3,587,859 and FIGS. 1 and 2 of the Grossman publication.

Backwashing usually consists of a vertical column with a screen in the middle part of the wall.

According to US Pat. No. 3,587,85 (column 1, page 41, column 4, pages 17-18), ice crystals form a blockage.

The aqueous concentrate flows up through the bottom of this closure and out through the screen.

The pressure of this aqueous concentrate itself is utilized to provide the driving force to move the ice crystals upward (US Pat. No. 358
7859, column 1, lines 44-45).

That is, the traction of the aqueous concentrate on the closure will cause the ice crystals to move upwards against the friction with the walls and the restraining forces at the top.

This restraining force on the top arises, for example, from a traction force against the filter scraper used to break up the cleaning liquid and the closure, discharging the particles produced by the break-up.

In prior art methods, ideally only a small amount of cleaning fluid flows down through the top of the ice block and out through the screen (i.e., it has a tendency to clog the screen), but when channeling occurs, the equilibrium is upset. .

The situation described in US Pat. No. 3,587,859 and the Grossman reference represents a "frain crown."

The salt water crown is in fact the washing front, in other words the interface between the concentrate and the washing liquid.

This is highly curved and is also a highly curved concentrate flow path.

This is unavoidable in the prior art approach in question.

The whitening of the wash front itself and the whitening of the flow lines in its vicinity is correlated with differences in the density (porosity) of the packed bed (when viewed in a section perpendicular to the axis).

In this connection, US reissue 23810 (particularly FIG. 1 and column 2, lines 47-50) should be noted.

The packed ice crystals are forced through the "transition zone" b and the water-water zone a, through zone C, where liquid is withdrawn.

In this manner, if a curved cleaning front is retained and formed (if a proper "front" is formed),
It is inside the transition area.

However, stabilization of curved wash fronts has proven difficult.

To circumvent this difficulty, U.S. Patent No. 2,864,494
No. 2, it is proposed to pass a pulsating circulating flow of cleaning fluid through a packed bed of ice crystals.

Perhaps reordering due to shocks applied to the transition region, such as channeling, will help alleviate the above-mentioned difficulties.

A sharp and stable washing front according to the invention is only possible if measures are taken such that this washing front (interface between concentrate and washing liquid) lies in a flat plane, perpendicular to the direction of movement of the packed bed.

Therefore, according to the present invention, the ice crystals contained in a slurry of aqueous solution and ice crystals are separated from the aqueous solution, the ice crystals are washed with an aqueous washing solution, thereby creating a packed bed of ice crystals, which is continuously moved, while A wash front is created in the ice crystal bed between the aqueous solution and the aqueous wash liquid, the aqueous solution and the aqueous wash liquid adjacent to the wash front are substantially stationary, and a stable wash front is caused by the moving motion of the ice crystal packed bed. A method is provided, characterized in that the object is made lying on a straight plane perpendicular to the object.

Generally, this is a method of separating ice crystals contained in a slurry of aqueous solution and ice crystals from the aqueous solution and washing the ice crystals with an aqueous washing solution, which basically includes the following steps.

(a) continuously introducing the slurry into a first cylindrical space; (b) continuously removing a portion of the aqueous solution from the slurry in the first cylindrical space; (c) moving the packed bed continuously through a second cylindrical space, in which a stationary layer of aqueous solution is provided on the first cross-section; and a substantially stationary layer of cleaning fluid on a second cross section adjacent to the first cross section, creating a cleaning front between the first and second cross sections; (d) continuously advancing packed beds; Crush and extract the crushed product.

As the aqueous solution between the ice crystals becomes more concentrated than the wash liquid, it is at a lower temperature than the wash liquid, so there is a temperature "jump" across the wash front.

When the cleaning liquid is water, the temperature is, of course, 0°C, and the temperature of ice crystals in the aqueous solution is 0°C or lower.

Freezes in the cleaning solution between the cleaning solution and the ice crystals, and
When this freezing occurs, the crystals generally bond together.

In this way, a solid porous ice blockage is formed at the cleaning front.

Therefore, first of all a concentrated slurry must be created, provision must be made to build up the concentrated slurry homogeneously into a packed bed, and provision must be made to provide it with a moving movement.

Most importantly, the ice crystals are distributed evenly over the packed bed before reaching the cleaning front.

In principle, it is possible to move the packed bed using the traction force of the flowing aqueous solution, and it is possible to uniformly create this bed that has reached the interface between the aqueous solution and the cleaning liquid (cleaning front).

The traction force can move ice crystals into the area where the aqueous solution is being pulled.

Ice crystals that accumulate there can push others forward.

If the cleaning front is sufficiently far away from where the aqueous solution is being drawn, it may be possible to create a heterogeneous concentrated slurry, as opposed to what can occur in the case of filters, for example, where the aqueous solution is being drawn. Homogenized at the washing front.

This concentrated, originally heterogeneous slurry should have the opportunity to homogenize.

When the washing front is reached, homogenization must take place over its cross section.

To do this, it is necessary to avoid differences in radial resistance to liquid flow.

If this difference exists, the wash front will be uneven;
In some cases, it ends up being curved.

Other possible methods are as follows.

The slurry is introduced into the bottom of the vertical cylinder.

It has a screen at the bottom to take out the aqueous solution.

An agitator-scraper connected to the shaft through the bottom of the cylinder and driven by a motor cleans the screen and homogenizes the concentrated slurry.

The slurry can be poured from the side or from the stirrer-scraper (
cavity) is introduced through the shaft.

There is no need for a screen at the bottom from which the aqueous solution is drawn off.

However, it may also be on the cylindrical wall, for example near the bottom.

Ice crystals that accumulate at the bottom of the cylinder push others upwards, forming a packed bed.

The liquid at the bottom of the cylinder is an aqueous solution, and the liquid at the top is a cleaning liquid.

The interface between the aqueous solution and the cleaning liquid is the cleaning front, which is held at approximately constant level by adjusting the incoming slurry pressure and the cleaning liquid pressure.

This is done in the manner described below.

There is a scraper at the top of the cylindrical part that crushes the washed packed bed and extracts the crushed product.

This is explained further below.

Crushing can also be done by melting.

In yet another preferred arrangement, the area for withdrawing the aqueous solution from the slurry has a hollow perforated (screen) blade connected to a rotating shaft.

Aqueous solution is extracted through the shaft.

These vanes are connected to a shaft, are free to rotate about a small axle perpendicular to the shaft, and are free to tilt depending on process factors, such as the rotational speed of the shaft, the traction of the aqueous solution being extracted through the hollow vanes, etc. It is something that can be changed.

In this case, the wings do not provide energy to push the crystal upwards, but the force of movement lies in the traction of the aqueous solution being removed.

The crystals that accumulate as the aqueous solution is withdrawn are pushed forward.

When the free-moving shaft, fitted with hollow wings with screens, is not rotated, it assumes a position parallel to the axis of the washing column and, in particular, when the wings have screens on both sides, towards the withdrawal end.

However, it is advantageous to rotate the shaft.

This greatly helps to reduce the tendency for inhomogeneities created by passing the concentrated slurry along the screen.

Another preferred strategy according to the invention is to use mechanical means to impart movement to the concentrated slurry of ice crystals;
By doing so, the packed bed of ice crystals can be reliably advanced.

This can be achieved, for example, by using a tilted wing coupled to a rotating shaft with a fixed tilt.

Screens for removing aqueous solutions may also be located in the wings if they are hollow.

By moving the packed bed using mechanical means, the movement of the packed bed becomes largely independent of the pressures of the incoming aqueous solution, the outgoing aqueous solution, the cleaning liquid, and the differences thereof.

By rotating the blades with a fixed inclination, the lachrymal membrane and the adjacent filtration layer are continuously refreshed to ensure homogeneity.

The annular structure of this bed is particularly important when the washing column has a large diameter and It may be advisable if the removal of the aqueous solution from the slurry is carried out through a screen (for example a cylindrical wall filter) placed in the direction of movement of the packed bed.

Therefore, a device must be used consisting of a cylindrical part coaxially arranged within another cylindrical part with a larger diameter.

The difference in diameter and the distance between the screen and the cleaning front is
During operation, the packed bed must be selected in such a way that it is homogeneous at the washing front.

This is because when the aqueous solution is withdrawn through a screen in one or both walls of the cylinder defining the cylindrical space in which the packed bed is formed, this cylindrical space is generally narrow (e.g. 2-5 cIrl). It means there is a need.

Removing the aqueous solution through a screen in the column wall tends to make the packed bed heterogeneous.

The better this tendency can be alleviated, the narrower the annular ring (related to the above, Japanese Patent Application No. 1606 of 1973)
(see issue).

In the direction of movement of the aqueous solution (as already explained) in the packed bed,
If extracted through a more or less vertical screen, the annulus can be considerably wider.

That is, for example, when using a sloped wing, the inner diameter of the outer cylinder can be 100 Crn and the width of the ring rt20α.

The tendency of heterogeneous formation of packed beds becomes even smaller.

When using an annular structure in the packed bed (such as slanted blades)
Mechanical means may be attached to the inner cylindrical portion, such as a scraper means used to impart a moving motion to the packed bed in the axial direction of the cylindrical wash column and to break up the packed bed by forcing it past the wash float.

In this case, the inner cylindrical part must be coaxial.

It is also possible for the inner cylinder to be stationary.

In this case, the mechanical means for advancing the packed bed and the scraper means (if applicable) must be driven separately.

This is explained in more detail in the example below.

However, the inner cylinder can be coupled to the same shaft as the mechanical means for delivering the packed bed.

Optimized process control can be obtained by providing separate drive means for the inner cylinder, the mechanical feed means and the scraper means, so that the rotational speed of each can be varied at will.

When using inclined wings as the mechanical means for advancing the packed bed, it is advantageous to be able to adjust the inclination of those wings.

This increases the possibility of controlling the treatment method according to special circumstances.

This can be achieved by melting into a packed bed of ice crystals, which are crushed after passing through a washing front.

However, particularly good results were obtained with the use of a scraper.

Scrapers for this purpose are known. US Patent No. 38
72009, several different configurations will be described in the following examples.

As already mentioned, the restraining forces that impede the movement of the ice crystal bed generally cause it to pack very tightly and, under the influence of temperature jumps at the washing front, cause the ice crystals to harden together and form solid porous water. Creates a blockage.

This ice blockage has occurred several times so far with about 273 solid water and about 1
/3, but it has been found that this relationship can vary depending on the 14 conditions.

Although virtually stationary, the cleaning freon) [moves through its holes relative to the packed bed.

In this way, the packed bed is "internally washed."

The position of the wash front in the wash column may remain substantially fixed in position by a sensing device with feedback.

This is achieved, for example, by temperature sensors placed on different sides of the cleaning front with two σ intervals.

This will be explained in more detail below.

The invention also includes an apparatus for carrying out the above treatment method.

The present invention provides an apparatus for separating ice crystals contained in a slurry of an aqueous solution and ice crystals from the aqueous solution and washing the ice crystals with a cleaning front aqueous cleaning liquid, which has the following configuration.

(a) Enclosing wall means defining a first cylindrical space; (b)
(c) means for providing the slurry into the cylindrical space;
means for removing a solution from the slurry in the cylindrical space while leaving behind the ice crystals, thereby creating a concentrated slurry; (Φ enclosure means defining a second cylindrical space: (e)
means for moving the concentrated slurry from the first cylindrical space into the second cylindrical space; (f) means for continuously moving the concentrated slurry through the second cylindrical space to the outlet side; (g) in the second cylindrical space;
means for retaining a stationary layer of aqueous solution on its outlet side; (i) means for continuously fracturing the packed bed of ice crystals and discharging the shattered product at the outlet end of the second cylindrical space;

A most preferred embodiment of the invention combines the annular structure of the wash column with a rotating cavity having a fixed inclination, through which the aqueous solution is drawn from the slurry and is removed by a scraper at one end. Wings with one end and a cant at the other end are provided with separate drive means.

Generally, this means that the scraper means is given a higher rotational speed than the canted blade.

The invention will be further explained in more detail by reference to the following examples and the accompanying drawings.

In FIG. 1, a slurry of ice crystals is supplied at 1 and 2
The withdrawal of the V'i aqueous solution is shown, which is discharged through line 3 leaving behind a concentrated slurry.

The homogenization function is shown in 4 and the packed bed formation function is shown in 5.

The movement of the packed bed through the static layer of aqueous solution is shown at 6 and reaches the cleaning surface 7.

The packed bed is moved through a substantially stationary bed of wash liquid 8, thereby consolidating into a solid porous block of water, which is then subjected to crushing at 9, ejecting the crushed product at 10, and removing at 11.

The functions of 2, 4, 5, and 6 are simultaneously performed in certain embodiments of the invention (as described above, for example, when using a device having an annularly spaced cavity with a fixed slope for extracting an aqueous solution, 2 , 4.50 functions are performed virtually simultaneously.

Most generally, it is important that when the concentrated slurry reaches the wash front, it is packed homogeneously, thereby forming a flat, uncurved wash front perpendicular to the axis of the wash column. That's true.

In FIG. 2, the outer shell of the device is cut lengthwise to show the inside.

17 is a cylindrical outer shell having a bottom plate 18 and a covering plate 19.

The inner cylindrical portion 20 is shown.

A shaft 21 is connected to this cylindrical part, and the opposite end contacts a strip 22, which is bolted to a cover plate 19.

The other cylindrical part contacts the shaft 24 at 23 and has a toothed wheel 25.

This wheel 25ri is engaged with a gear 26, and a motor 27
driven by.

It has a cylindrical section 23&-j hollow sloped wing 28 and an upper surface provided with a screen 29.

The wings are shown in a simplified manner and are shown in detail in Figures 3 and 4.
Please refer to the figure.

The interior of the cavity 28 communicates with the duct 2g, through which liquid can be drained.

The cylinder 23 has a pin 30, while the outer shell 17 has wings 31.

A disk 32 with a knife 33 and a slot 34 acts as a scraper.

The disc 32 is in contact with the cylinder 35 and in contact with the gear 37 which meshes with the gear 38 .

A gear 38 is driven by a motor 39.

The slurry enters the slurry from the slurry population 40 and is well stirred by the pin 30 cooperating with the blade 31 to prevent settling of crystals.

The aqueous solution is passed through the screen 29 and taken out, and the hollow tool 28
and exit through duct 29' and screen 29
leaving a concentrated slurry on the surface of the

A cylindrical body 23 filled with this concentrated slurry and having wings 28
It is pushed through the annular space 41 by zero rotation.

The dotted line 42ri shows the cleaning surface, and the annular space 41 (
It is the surface that separates the space 36 (in which is an aqueous solution) and the space 36 (in which is a cleaning solution (usually water)).

Temperature sensing device 57.58 [keeps the wash front within narrow limits.

These record the constant temperature difference that exists between the aqueous solution and the cleaning solution.

As the cleaning front rises and falls, this temperature difference disappears, and an electrical impulse from control unit 59 moves valve 60, causing
Close or open depending on the situation.

The space 36 is most often filled with a plug of porous solid water, which is broken up by the rotation of the disk 320 with the knife 33.

The particles produced by this crushing are passed through the slot 34,
Enter Space 43.

The cleaning liquid is circulated by a pump 44.

Then, the cleaning liquid enters the space 43 with a volume 45, and ice particles are discharged from the ice particle outlet 46.

Ice particles are melted by a melter. When the wash front remains in place, the amount of water leaving the device through valve 60 is the same as the amount of ice removed by scraper 32.

As the wash front is lowered, valve 6"0 is opened somewhat further, allowing more water to drain, thus restoring equilibrium.

In FIG. 3 29 indicates one screen of the hollow canted wing, shown at 28 at its end.

Space 48 for slurry to pass between two inclined wings
There is.

The wing is connected to a cylindrical body 23 in which there is an annular groove 49.

Inside the hollow sloped wing, a channel 50 communicates with the annular groove 49 .

The cylindrical body 23 is connected to the shaft 51 by a convex ridge 52 .

A duct 2g is provided on the shaft and connected to the annular groove 49 by a channel 53.

In FIG. 4, the bottom 54 of the wing is provided with longitudinal ridges 55 to support the screen 29.

The ridges 55 are provided with holes 56 for passage of an aqueous solution.

A cylindrical body 23 is connected to the wing, all of which are provided with channels 50 and grooves 49 for collecting fluid from the wing.

The shaft 1d51 with which the cylindrical body 23 is connected is shown and is provided with a duct 29' for discharging the aqueous solution.

The devices described above and other related embodiments with hollow blades, when the crushing device is removed, can serve as continuous slurry concentrators.

2 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the various processing functions of which the processing method according to the invention is comprised.

FIG. 2 illustrates one preferred embodiment of the invention.

FIG. 3 is a plan view of a cross section taken along line 11-11 of FIG. 2.

14 is a cross-sectional view of the hollow airfoil along line IV-IV in FIG. 3; FIG.

Claims (1)

[Scope of Claims] 1. A method for separating ice crystals contained in a slurry of an aqueous solution and ice crystals from the aqueous solution and washing the ice crystals with an aqueous washing solution, the packed bed of ice crystals being subjected to continuous moving motion. is formed in the ice crystal packed bed between the aqueous solution and the aqueous cleaning solution, while the aqueous solution and the aqueous cleaning solution adjacent to the cleaning front are substantially stationary and stable. A method according to claim 1, characterized in that the cleaning front is formed in a flat plane perpendicular to the moving movement of the packed bed of ice crystals. 2 (a) continuously introducing the slurry into a first cylindrical space; (b) continuously removing a portion of the aqueous solution from the slurry within the first cylindrical space to form ice crystals; (c) moving the packed bed continuously through a second cylindrical space; the space includes a stationary layer of the aqueous solution at a cross-section of the first space and a substantially stationary layer of cleaning liquid at a second cross-section adjacent the first cross-section, thereby (d) continuously fracturing the continuously advancing packed bed;
The method according to claim 1, characterized by the steps of: extracting the crushed product; 3. A method as claimed in claim 2, characterized in that the packed bed is moved through the second cylindrical space by means of inclined vanes attached to a shaft coaxial with the cylindrical space. 4. The method of claim 3, wherein the aqueous solution is removed from the slurry by holes in the surface of the sloped blade. 5. The method according to any one of claims 2 to 4, wherein the first and second cylindrical spaces have an annular structure. 6. A method according to any one of claims 2 to 5, characterized in that said crushing is achieved by scraping said packed bed with a rotating disk provided with slots and knives. 7. An apparatus for separating ice crystals contained in a slurry of an aqueous solution and ice crystals from the solution and washing the ice crystals with an aqueous cleaning solution, comprising: (a) enclosure means defining a first cylindrical space; (b)
means for providing the slurry into the first cylindrical space; (e) means for removing a solution from the slurry in the cylindrical space while leaving behind the ice crystals, thereby creating a concentrated slurry; Gi) a second Enclosing wall means defining a cylindrical space; (e)
means for moving the concentrated slurry from the first cylindrical space into the second cylindrical space; (f) means for continuously moving the concentrated slurry through the second cylindrical space to the outlet side; (g)
means for retaining a stationary layer of aqueous solution in said second cylindrical space on its outlet side; (h) causing said concentrated slurry to be homogenized in its cross section before reaching the washing front; means for producing a uniform packed bed of ice crystals; (i) means for continuously crushing the packed bed of ice crystals at the outlet end of the second cylindrical space and delivering the crushed product; The device characterized in: 8(f), the means for continuously moving the concentrated slurry through the second cylindrical space to the outlet side is an inclined vane connected to a rotating shaft coaxial with the cylindrical space. The device according to claim 7, characterized in that: 9. Each of the wings is hollow and has an inner space and a hole in the surface, the inner space being coupled with a duct in the rotating shaft to remove and drain the solution from the slurry of ice crystals. 9. A device according to claim 8, characterized in that it makes it possible to: 10. The device according to any one of claims 7 to 9, wherein the cylindrical space described in claim 7 has an annular structure. 11 It is noted that the means for continuously crushing the packed bed of ice crystals mentioned under clause (i) in claim 7 is a scraping means consisting of a rotating disk equipped with slots and knives. A device according to any one of claims 7 to 10 characterized by: