JPS61157303A - Method and apparatus for distillatory crystallization - Google Patents

Abstract

PURPOSE:To continuously perform distillatory crystallization for a long time without adhering a crystal, by allowing distilled vapor to rise through a distillation tower having a large number of a mesh trays or slit shelf stages in such a state that said trays or stages are wetted with a solution or slurry. CONSTITUTION:In a distillation tower having a large number of mesh trays or slit shelf stages, for example, shelf stages 2a comprising 20 stages of mesh trays, distillation/crystallization operation is performed in such a state that each shelf stage 2a is wetted with the solution or slurry present thereon, pref., the solution or slurry substantially fills the whole of the distillation tower 2. By directly blowing raw steam 7 into the tower from the bottom thereof, the lower part of the tower is heated and distillation operation is performed and distilled vapor is allowed to rise through the tower through the solution or slurry. By this operation, the solution or slurry is well dispersed under stirring by rising vapor and, therefore, the adhesion of a crystal ready to precipitate to each shelf stage part is prevented. As a result, distillation to each shelf stage part is prevented. As a result, distillatory crystallization can be continuously performed for a long time without adhesion.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides basic ammonium zinc carbonate [Zn(NHx
) 41 Basic zinc carbonate [2ZnC
;(h ・3Zn(OH)z *ril*ZnC01@
The present invention relates to a distillation crystallization method and an apparatus for crystallizing 3Zn(OH)ze H20] by a distillation method.

[Conventional Technology J In steel works, waste zinc is discharged from Zn plating equipment, etc. However, since Zn has a wide range of uses, such as being used as a pigment and a vulcanization accelerator in the form of ZnO, it is necessary to treat the waste summer lead to remove impurities such as heavy metals derived from the production process. It is a good idea to collect it.

Therefore, the present inventors disclosed a method for recovering zinc carbonate from a Zn-containing material in Japanese Patent Laid-Open No. 59-88319.

When recovering zinc carbonate from a Zn-containing material, at least NH40)1 and (NH)
It is preferable to dissolve the Zn-containing material in a liquid containing 4C(h) and then crystallize zinc carbonate.On the other hand, as mentioned above, since the initial waste zinc raw material contains heavy metals, By removing it, it is possible to widen the range of uses for higher quality products.

According to research conducted by the present inventors, it has been found that the process of dissolution → ion exchange → crystallization is optimal in terms of removing impurities as much as possible. The reaction is as follows.

O dissolution process Zn+ (NH4)2 GOx + 2NH40)1+
[ZN(NHi)4]coff+H2↑+2
H20, (1) O ion exchange step Me2+ + Zn-+ Me↓+Zn2+
,,,, (2) O crystallization step・5[Zn(NHt)4] CCh +382
042ZnCOx ・3Zn(OH)z ↓+3CO□
↑+2ONHx ↑,,,, (3A) ・NZn (NHI)4 ] C(h +4H20
+ZnGOz ・3211(OH)2 ・Hz O↓+
3C02↑+ 113NHgo↑ ,,,, (3B) In this case, the reaction of 3B accounts for 80 to 90%, and the reaction of 3A is considered to be small.

[Problems to be Solved by the Invention] When carrying out the above-mentioned crystallization step, according to common technical knowledge, one or more crystallization tanks should be provided.

By the way, in the crystallization process, when the conventional technology is adopted as it is and the crystallization process is carried out in a crystallization tank, it is advantageous to operate multiple crystallization tanks in a multi-effect manner. The generated steam is guided to the next pot one after another,
In order to achieve an ammonia concentration of, for example, 1000 ppts or less by evaporative distillation of ammonia, it is necessary to arrange a considerable number of crystallization tanks and a large amount of steam is required. Moreover, since the operation is similar to simple distillation,
Since it is a batch system, 1M integrated operation is not possible.

In contrast, the present inventors have discovered that the reaction in the crystallization step described above can be carried out in a distillation column. This is completely outside the common sense of chemical engineers.

However, when performing a crystallization operation in a distillation column, if a solution with a Zn concentration of 10% by weight or more (hereinafter % is by weight) is distilled and crystallized, the solid content concentration in the product slurry will be 20% or more. becomes. The upper several stages of the distillation column are a region where the volatility of ammonia is high and the amount of evaporation is large due to the distillation characteristics of ammonia, so a large amount of zinc carbonate is crystallized. As a result, crystals adhere to the internal walls and trays of the distillation column, and after only a few days of operation, the bubble bell etc. become clogged, requiring the operation to be stopped and cleaning to be performed.

For example, in the case of a perforated plate, as shown in the upper part of FIG. 3, and in the case of a bubble bell tower, as shown in the upper part of FIG. 4, crystals X are deposited.

The present inventors attempted to prevent the deposition of crystals by variously changing the material and shape of the distillation column, but found that this could not provide a fundamental solution. In addition, in the course of investigating various measures to prevent crystal adhesion, we found that crystallization occurs when the distillation column alone is used because the concentration of the stock solution is high. It was concluded that it would be effective to provide a crystallization tank and perform a certain proportion of the crystallization operation in the first stage to lower the concentration of the liquid supplied to the distillation column to form a crystal slurry.

However, the operation of a general distillation column is such that each tray is brought into contact with vapor as it descends in sequence. However, in such an operation, the amount of liquid retained in each tray is small, and if crystallization occurs in this state, adhesion of crystals on the tray portion is unavoidable.

Therefore, the main object of the present invention is to provide a distillation crystallization method and an apparatus therefor that can be operated continuously for a long time without crystal adhesion.

[Means for Solving the Problems] The method of the present invention for solving the above problems involves supplying a raw solution to a distillation column having a plurality of perforated plates or slit trays, heating the lower part of the distillation column, and dissolving the solution. - The distillation vapor is raised in the distillation column while the slurry is present on at least each of the trays and wets the trays.

In addition, the device of the present invention has a hole diameter or width of 8 to 20 m.
The column is characterized by having a plurality of perforated plates or slit trays having a large number of perforated plates or slits, and having means for heating the solution/slurry at the lower part of the tower.

[Function] In the method of the present invention, distillation and crystallization are performed using a distillation column, so not only continuous operation is possible, but even if the crystallization tank is placed in front of the distillation column, the A very small number of tanks is sufficient.

In addition, when using a distillation column, 1. Usually a bubble column is considered, but in this type, no matter what means are added, it is essentially impossible to prevent the adhesion of crystals. If a slit plate is used, by appropriately selecting the hole diameter, crystal adhesion can be prevented and stable continuous operation for a long period of time is possible.

However, if the solution/slurry is present on each shelf and is not kept wet, crystals will adhere to it. This state can be easily maintained by appropriately selecting the supply amount of the stock solution. More preferably, the distillation and crystallization operations are performed in a state where the solution/slurry substantially fills the entire distillation column. Then, when the lower part of the column is heated and a distillation operation is performed, the distilled vapor passes through the solution/slurry and rises inside the column.The solution/slurry is well agitated and dispersed by the rising vapor, so that it is deposited on the trays. This prevents crystals from attaching to each other. Moreover, if we look at a certain shelf, it means that it holds the liquid in the entire area up to the shelf above it, so compared to the case where there is only a small amount of liquid held on a normal shelf, the liquid is The amount of liquid retained is much larger, and therefore crystallization occurs in a large amount of liquid retained, so crystal adhesion is also prevented on this surface.

Furthermore, when crystallization occurs, in order for the crystal particles to grow, the crystal particles must be suspended in a supersaturated liquid in the metastable region, and the slurry containing the crystal particles must be suspended in the supersaturated liquid. The amount of crystallization per 1 m of supersaturated liquid is determined, and the degree of supersaturation is balanced and maintained in equilibrium. Therefore, as the crystal slurry volume increases, crystal growth occurs in a liquid with a lower degree of supersaturation, and the distillation column The degree of supersaturation differs depending on the specific properties of a certain substance, but if it is lower than a certain value, the amount of supersaturation attached to the wall column and the growth of crystals at that point will be extremely small. , continuous operation becomes possible.In this point, as in an example of the present invention, the entire interior of the distillation column is filled with the solution slurry,
It is effective to lower the degree of supersaturation. In addition, it is effective to stir the solution-slurry with a distillation vapor to prevent uneven distribution of concentration, and to discharge crystals that tend to adhere to the perforated plate of the shelf or the transparent part of the slit plate to prevent clogging. .

On the other hand, if a perforated plate or a slit plate is used as the shelf and the hole diameter is in the range of 8 to 20 mm (in the case of slits, the diameter may be within this range and the length may exceed 20 mm), It is not necessarily necessary to adopt the filling mode of the solution/slurry as described above, and the adhesion of crystals can be sufficiently prevented.

[Specific Examples of the Invention] The present invention will be explained below using a specific example of crystallization of zinc carbonate shown in the drawings.

First, the entire crystallization process will be explained with reference to FIG. 2, and then details of an example of the present invention will be described with reference to FIG. .

The stock solution 3 that has undergone the steps of dissolution, ion exchange, and precision filtration according to formulas (1) and (2) above is led to the first crystallization tank IA via the supply liquid pipe 8A. Each crystallization tank IA-10 is
It has the same structure and has a draft tube 4, a stirring blade 5, and a cracker vibro inside.

From the first tank IA to the final fourth tank ID, the liquid that has been crystallized by the heat of the live steam 7 directly blown into the 7A distillation column 2 is sequentially passed through the feed liquid pipes 8B to 8D to the previous tank. It is designed to be supplied as a feed liquid. Final 4th crystal tank ID
A low Zn feed liquid having a Zn concentration of approximately 2 to 3% is extracted from the bottom of the distillation column 2 by a pump 9 and supplied to the top of the distillation column 2 via a feed liquid pipe 8E.

The distillation column 2 includes, for example, 20 trays 2 a of perforated plates.
, 2 a, ·φ·, and live steam 7 is directly blown into the bottom of the column. 10 is a stirring blade.

Also in the distillation column 2, the reaction of the above-mentioned formula (3A) or (3B) occurs, a crystallization operation is performed, and the product basic zinc carbonate slurry is extracted from the bottom of the column by the slurry pump 11, followed by filtration.・Move on to the drying process. The steam generated in distillation column 2 is:

It rises inside the tower, passes through the steam supply v12A from the top of the tower, is led to the final cracker vibro of the fourth crystallization tank ID, and is used as a crystallization heat source in the fourth crystallization tank ID.

Subsequently, the steam generated in the fourth crystallization tank ID is transferred to the steam supply pipe 12.
B is introduced into the third crystallization tank tC.

In this way, the steam supply pipe 12C is sequentially connected to the previous crystallization tank.
, 120, and finally the generated steam from the first crystallization tank is transferred to the solution preparation step.

In this way, in the example of the present invention, the supply liquid and the generated steam flow in countercurrent flow.

In the above example, four crystallization tanks were provided, but the number of crystallization tanks may be one or another number. Depending on the target liquid, a crystallization tank may not be necessary. In any case, the Zn5% transferred from the final crystallization tank to the distillation column 2 is 1 to 5%, especially 2 to 3%.
．． Since Zn concentration of the stock solution is preferably about 5% (normally 1
0%), it is necessary for each crystallization tank to bear that amount. In addition, the crystallization rate of each crystallization tank is 330-
1O01t/m3 is preferable.Furthermore, in the case of four crystallization tanks, the ammonia concentration is approximately 3
%, 4%, 6%, 58%.

Now, referring to the m1 diagram, in a preferred embodiment of the present invention, the amount of basic ammonium zinc carbonate solution supplied to the distillation column 2 and the amount of slurry withdrawn from the bottom of the column are controlled to control the amount of liquid e in the column. The slurry level L is preferably located above the top shelf.

To fill the inside of the tower with liquid slurry, a liquid level gauge 13 that can cover the entire height of the tower is provided, and a slurry withdrawal amount control valve ``15'' is adjusted by a level mr1 total 14.

When live steam 7 is blown in this state, ´-0 becomes bubbles.
At the same time, the Nlh gas and COt gas generated by the heat of the live steam 7 become bubbles and rise. In the process of passing through the slit holes in the perforated plate of the shelf, these bubbles become finer or aggregate, rise, and are dispersed into the liquid/slurry.

As a result, the liquid/slurry is disturbed by air bubbles,
Crystal particles are dispersed 6 Therefore, even if the crystal particles try to adhere to the perforated plate, the slit holes of the perforated plate, or the inner wall of the tower, they are dispersed and cannot adhere.Thus, the adhesion of crystals within the tower is prevented.

By the way, in the above example, direct injection of live steam was used,
Even with normal indirect heating, MHz gas and COz are generated.
Since the gas becomes bubbles, they are functionally the same. If only one indirect heating is used, crystals will adhere to the heating surface, and the amount of bubbles will be too large and the disturbance effect will be small, so the preferred example of the present invention is the former direct injection of live steam.

On the other hand, if it is desired to further prevent the adhesion of crystals, as shown in FIG. A pump 17 is provided, and pump 1 is used for liquid/slurry.
It is preferable to perform alternate suction and discharge operations in step 7 to fluidize the liquid/slurry.

The trays in the present invention include a bubble bell type 20 shown in FIG. 4 as a tray type used in general distillation columns, a perforated plate plate 21 shown in FIGS. 3 and 6, or a perforated plate plate 21 shown in FIG. 7. The slit plate 22 has a greater crystal adhesion prevention effect.
Look at the slit hole diameter of the perforated plate, l+, the end is 8 to 20
m5 is preferred.

If it is less than 8 cm, crystals will adhere to it, and if it exceeds 20 cm, there will be no clogging, but the dispersibility of air bubbles will be poor and crystals will adhere to the inner wall of the tower, etc. Slit length 11 is 20+m
Although it may exceed 100%, it is preferable that the maximum length be about 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000%

Note that although the above example is an example of crystallization of zinc carbonate, it can of course be applied to crystallization of other substances.

FIG. 8 shows an example in which a perforated plate plate 21 and a slit plate 22 are used to prevent crystal adhesion only by controlling the amount of liquid on each shelf without filling the plate with solution/slurry. 2
3 indicates a droplet, and 24 indicates a bubble. If a perforated plate or slit plate is used, the air bubbles will pass directly upward through the holes with a large momentum, so the holes will always be in a state of being cleaned, and it is thought that the adhesion of crystals will be prevented. When the air bubbles 24 are injected into the slurry, the slurry is stirred and the shelf plate is vibrated, which also peels off the growing crystals, which also shows the effect of preventing crystal adhesion. This is thought to be the cause.

[Effects of the Invention] As described above, the present invention provides advantages such as being able to prevent crystals from adhering to portions such as trays and enabling long-term operation.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the implementation apparatus according to the method of the present invention, Fig. 2 is a schematic diagram of the entire crystallization process, Fig. 3 is an example of the state of crystal adhesion to the tray of the perforated plate, and Fig. 4 is the bubble Figure 5 is a schematic view of another example of the method of the present invention, Figures 6 and 7 are plan views of the shelves, and Figure 8 is a diagram of another specific example. It is a schematic diagram. IA-10, ..., crystallization tank 2, ..., distillation column 2a
,,,Shelf 7,,,Live steam 21,,
,, Perforated plate plate 22 ,,, Slit plate Patent applicant Tsukishima Kikai Co., Ltd. Sumitomo Metal Industries, Ltd. Figure 4 Figure 3 Figure 5

Claims (3)

[Claims] (1) The raw solution is supplied to a distillation column having a plurality of perforated plates or slit trays, the lower part of the distillation column is heated, and the solution/slurry is present on at least each of the trays and wets the trays. A distillation crystallization method characterized by causing distilled vapor to rise inside a distillation column while (2) The distillation crystallization method according to claim 1, wherein the solution/slurry substantially fills the entire distillation column. (3) It is characterized by having a plurality of perforated plates or slit trays each having a large number of perforated plates or slits each having a hole diameter or width of 8 to 20 mm, and having means for heating the solution/slurry at the bottom of the column. Distillation crystallizer.