JPS5818122B2 - Shoseki Hannousouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crystallization reaction apparatus for continuously producing and separating desired coarse crystals, and is particularly preferably applied to, for example, obtaining gypsum by a neutralization reaction between dilute sulfuric acid and limestone. It relates to a crystallization reaction apparatus for obtaining.

In normal crystallization operations, the generation of new crystal nuclei and the growth of crystals proceed at the same time, and it is not easy to always ensure that the crystals grow to the desired coarse crystal size. This leads to the appearance of undesirable shapes such as crystals.

Attempts to avoid this difficulty include adding seed crystals separately to the crystallization reactor and adjusting the rate of addition to control the crystal particle size distribution, or evaporating the crystal solvent at a predetermined rate. Alternatively, methods of controlling crystal growth by methods such as cooling have been used.

However, in reactive crystallization operations that involve chemical reactions, the reaction rate between chemically reactive components is generally high, and for this reason, unlike ordinary simple crystallization operations that do not involve chemical reactions, it is extremely difficult to control the supersaturation degree of the crystallization system. However, it is not easy to continuously generate crystal nuclei at a desired rate and grow them to a desired grain size.

. The conditions required of the crystallization reaction apparatus 1 in order to obtain crystals with a desired particle size are: (1) not to generate excessive crystal nuclei in the crystallization system;
1) Maintaining a high slurry concentration of crystallization reaction system crystals
(ND) Separating the fine crystals to be grown from the coarse crystals and circulating and suspending them in the crystallization reaction system can be mentioned.

To further explain the above three points, first of all, in order to prevent the generation of excessive crystal nuclei, the degree of supersaturation of the reaction product can be relatively reduced by diluting the chemical reaction components with the mother liquor and reacting. Need to keep it low.

Further, in crystallization accompanied by a reaction, uniform stirring is required because there is a risk that crystal nuclei will be generated excessively due to localized non-uniform stirring.

Keeping the second slurry concentration high is an essential operation from the viewpoint of reducing the degree of supersaturation of the crystallization system, preventing the generation of excessive seed crystals, and promoting crystal growth.

There is also a concentration method, such as the existing glue, T, and B (draft tube baffle) type crystallizers, which is equipped with a baffle on the outside of the draft tube and extracts the mother liquor obtained by solid-liquid separation in the settling region. In crystallization operations that involve gas generation, such as the production of gypsum by neutralizing limestone with limestone, gas (
As such, the T and B methods are not suitable for concentrating slurry in a crystallization reaction system that involves gas generation because the rising air flow reduces the solid-liquid separation effect in the cell-IJing region.

Appropriate means are therefore required to keep the slurry concentration high.

Thirdly, since a simple complete mixing tank type crystallizer will widen the particle size distribution of the resulting product, a separate classification device will be installed to selectively take out only coarse crystals, and fine crystals will always be circulated to the crystallization reaction system. There is a need to.

The present invention provides a device designed to satisfy the above three conditions.

This equipment consists of three zones: the center (crystallization zone), the bottom (classification zone), and the top (clarification zone). It is equipped with a tube for supplying substances and a stirrer to stir and suspend the crystal slurry produced by the crystallization reaction. (2) The lower part (classification zone) is designed to classify the crystals produced in the crystallization zone. Equipped with an outlet for extracting the obtained coarse crystals to the outside of the crystallization reactor.

A mother liquor supply pipe is provided to supply the clarified mother liquor to the classification zone in order to return the classified fine crystals to the crystallization zone. A prevention plate is provided at the boundary between the crystallization zone and the classification zone or at the top of the classification zone.

(3) The upper part, or clarification zone, is designed to clarify the dilute slurry fed from the center (crystallization zone) and allow the resulting mother liquor to overflow. Even if gas is generated from the crystallization zone or is separately introduced into the crystallization zone, this gas will not entrain the crystals in the crystallization zone to the clarification zone. This is a crystallization reaction apparatus characterized by being equipped with a gas venting pipe for preventing the above.

More specifically, the apparatus of the present invention has a clarification zone in the upper part, a crystallization zone in the center, and a classification zone in the lower part. prevent reaching excessive supersaturation.

Among the reaction products generated in the crystallization zone, the dilute slurry is separated into a clarified mother liquor and a thick slurry in the clarification zone due to the difference in specific gravity, and by overflowing the clarified mother liquor and returning the thick slurry to the crystallization zone, the natural In particular, the slurry concentration in the crystallization zone is increased.

In order to prevent the clarification action of the clarification zone from being disturbed by stirring in the crystallization zone, the clarification zone and the crystallization zone are separated by a funnel-shaped partition plate with an open bottom end.

The crystallization zone is also equipped with a gas vent pipe for preventing the crystals in the crystallization zone from being entrained into the clarification zone by the gas generated or the gas introduced there as needed.

Further, a clarified mother liquor is supplied to the bottom of the classification zone, and the mother liquor is allowed to flow upward to classify the crystals, extracting coarse crystals of a desired particle size from the bottom and returning fine crystals to the crystallization zone.

Further, in order to prevent the classification efficiency of the classification zone from decreasing due to stirring in the crystallization zone, a vortex prevention plate is provided between the crystallization zone and the classification zone or above the classification zone.

With the crystallization reaction apparatus of the present invention that takes such considerations into account, the three conditions mentioned above can be satisfied for the first time, and the desired crystallization reaction operation can be easily carried out.

An example of the device of the invention is shown in the accompanying drawing.

However, the present invention is not limited to this embodiment.

Reference numeral 1 denotes a crystallization reaction apparatus similar to a cylindrical vertical stirring tank, in which reaction components are supplied to the crystallization zone 3 through reactant supply pipes 7 and 8 and stirred.

The crystallization zone 3 is separated from the clarification zone 2 by funnel-shaped partition plates 5a and 5b with open bottom ends, and particle suspension by the stirrer 9 does not reach the clarification zone 2.

Further, by designing the inclination angle α of the funnel-shaped partition plate 5a to be greater than the angle of repose of the crystals, consideration is given to returning the crystals that have settled in the clarification region to the crystallization region.

Furthermore, the opening and inclination angle of the funnel-shaped partition plate 5b may be determined so as to exhibit the following functions in cooperation with the partition plate 5a.

In other words, the gas generated by the reaction, such as carbon dioxide gas generated when dilute sulfuric acid is neutralized with limestone, or the gas sent to the crystallization zone as needed, destroys the crystals in the crystallization zone when it floats to the surface. The funnel-shaped partition plates 5a and sb also perform shielding and gas collection to prevent the gas from being entrained into the clearing area.

The funnel-shaped partition plate is provided with gas vent pipes 6a and 6b at the upper part of the funnel-shaped partition plate for discharging the collected gas to the outside of the crystallization reaction system.

In addition, in the classification zone 4, in order to return the fine crystals to the crystallization zone 3, the mother liquor is sent from the clarification zone 2 to the bottom of the classification zone using the circulation pump 12 through the mother liquor circulation feed pipe 11 and the mother liquor supply pipe 13. The crystals are classified by the upward flow of the mother liquor, and the remaining coarse crystals are extracted from the crystal outlet 10 to the outside.

In this case, in order to prevent the vortex generated by the stirrer 9 from reducing the crystal classification effect in the classification zone, it is desirable to install one or more vortex prevention plates 14.

In this embodiment, an overflow liquid outlet 16 is provided for overflow, and a gas outlet 15 is provided for discharging gas mixed into the clarification area or gas accumulated in the upper part of the clarification area via a gas vent pipe.

As is clear from the above, the apparatus of the present invention prevents excessive generation of crystal nuclei while performing various operations such as concentration, stirring, clarification, and classification necessary to promote crystal growth, and produces desired coarse crystals. This is a crystallization reactor with a simple structure for producing .

[Brief explanation of drawings]

The figure is a longitudinal sectional view showing an embodiment of the present invention. 1... Crystallization reactor main body, 2... Clarification zone, 3... Crystallization zone, 4... Classification zone, 5
a, sb... funnel-shaped partition plate, 6a16b
... Gas venting pipe, 7 ... °°°° reactant supply pipe, 8 ... Reactant supply pipe, 9 ... Stirrer,
10...Crystal extraction port, 11...Mother liquid circulation feed, No. 12...Pump, 13...
... Mother liquor supply pipe, 14 ... Vortex prevention plate,
15...Gas outlet, 16...Overflow liquid outlet, α...Inclination angle.

Claims (1)

[Scope of Claims] 1. A crystallization reaction device for continuously producing and separating desired coarse crystals, wherein a crystallization reaction tower constituting the main body of the device has a crystallization zone in the center and a classification zone in the lower part. (1) The crystallization zone includes a tube for introducing the reaction components to be crystallized into the crystallization zone, and a stirring means for stirring and suspending the formed crystal slurry. (2) The classification zone includes an outlet for extracting the desired coarse crystals generated in the crystallization zone out of the crystallization reactor, and a supply port for supplying the clarified mother liquor to the classification zone in order to return the classified fine crystals to the crystallization zone. and a vortex prevention plate to prevent a drop in classification efficiency due to agitation in the crystallization zone; A tube for overflowing the obtained clarified mother liquor, a tube for circulating the clarified mother liquor to the classification zone as necessary, and a tube for preventing a decrease in clarification efficiency due to stirring in the crystallization zone and for preventing the reaction from occurring in the crystallization zone. In order to prevent the gas generated or sent from the outside to the crystallization zone from entraining the crystals in the crystallization zone to the clarification zone, preventive means such as a funnel-shaped partition plate with an open bottom end equipped with a gas vent pipe are provided. The crystallization reaction apparatus characterized in that it comprises: