JPS62176502A - Crystallization method and device therefor - Google Patents

Abstract

PURPOSE:To control the average particle diameter of crystals prepared by a crystallization device and minimize the range of diameter variation to stabilize the particle diameter by supplying micro crystals to work as seeds of controlled quantity in mother liquor. CONSTITUTION:A screening device 10 to classify fine crystals to be used as seeds out of crystals dried by a dryer 5 and a metering means 11 to measure crystals to be used as seeds coming out of said device 10 and send a required quantity to a mother liquor tank 6 are provided. By putting a controlled quantity of crystals for seeding into mother liquor returning to a crystallization can 1, the number of crystals remaining in the crystallization can 1 and a surface area of crystallization are maintained within a fixed range, and average particle diameters of crystals produced by a crystallization device are controlled to minimize the range of variation and stabilize particle diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a crystallization apparatus for crystallizing caustic soda, sugar, etc.

<Prior Art> Crystallization equipment for concentrating and crystallizing caustic soda, sugar, etc. is widely used in the food industry and the like.

FIG. 2 is a flow sheet of such a crystallization apparatus.

In Figure 7J12, 1 is the crystallizer, 2 is the heater, and 3 is the centrifuge i! Iff machine, 4 is a conveyor, 5 is a dryer, 6 is a mother liquor tank, and γ is a circulation pump. The raw material liquid is introduced into a circulation system between the crystallizer 1 and the heater 2. The liquid in the crystal can and the raw material liquid are sent together to the heater 2 by a pump 9. The heater 2 is a steam heating type heat exchanger, and the liquid is heated by steam and returned to the crystal can 1. The crystal can 1 is called a DTB type in this example, and the inside of the can is divided into a wave phase and a gas phase, and the liquid phase part is equipped with a draft tube 1a, a baffle plate lb, and an agitator 1C. is circulated between the draft tube and baffle plate as shown in the figure. The vapor evaporated in the evaporator 1 is discharged from the upper part of the evaporator and is sucked and condensed by a condenser (not shown).

One method involves concentrating in a can to precipitate crystals. The precipitated crystals settle in a cone-shaped portion at the bottom of the can, and the mother liquor containing the crystals is sent in slurry form from the classification leg 1e to the centrifuge 3 via the pump 8.

In the centrifugal valve 11if1 machine 3, the liquid is classified into mother liquor and wet crystals. The wet crystals are sent by a conveyor 4 to a dryer 5, where they are dried, and the dry crystals are discharged outside as a product. On the other hand, the mother liquor separated in the centrifugal part 11 [1 Iso 3 flows down to the mother liquor tank 6, where it is temporarily stored, and then the circulation pump 7
As a result, it is returned to the circulation system between the crystal can 1 and the heater 2.

<Problems to be Solved by the Invention> In such a crystallization apparatus, the average grain size of the crystals precipitated in the crystallizer periodically increases or decreases with the passage of time, as shown in FIG. is repeated. This is because when a certain number of crystals exist in the mother liquor, very few fine crystals that become new seeds are generated and the crystals grow actively, but the grown crystals are separated by the separator 3 and added to the mother liquor. When the number decreases, the surface area of the crystals inside the can becomes insufficient, and many fine crystals that serve as seeds are generated at once, and they begin to grow again. Since such a phenomenon is repeated, it is thought that periodic fluctuations in the average crystal grain size occur as mentioned above.

Generally, the grain size of crystals as a product needs to be controlled within a certain range, but conventionally the crystal grain size from the crystallization equipment is random, and it is sieved and separated into different grain size ranges. The product was obtained, and by sieving, coarse crystals that were found to be out of specification were crushed, and fine crystals were redissolved.

As a result, there are problems such as deterioration of product yield, increase in operating costs, and increase in energy loss.In addition, it is difficult to control particle size when particularly high yields of products in a certain particle size range are desired. there were.

<Objective of the Invention> The present invention was devised in view of the problems of the prior art, and it is possible to improve the crystallization rate obtained by a crystallization apparatus by supplying fine crystals that serve as controlled seeds into the mother liquor. It is an object of the present invention to provide a crystallization method and apparatus in which the average particle size is controlled, its fluctuation is small, and the particle size is stable.

<Means for Solving the Problems> In order to achieve the above object, the crystallization method of the present invention separates the mother liquor containing crystals discharged from the crystallizer into crystals and mother liquor, and returns the mother liquor to the crystallizer for circulation. The crystallization method is characterized in that seed crystals are metered into the mother liquor which is returned to the crystallizer.

Further, the crystallization apparatus of the present invention receives a crystallization can and a mother liquor containing crystals discharged from the crystallization can, and divides one part into crystals and mother liquor.
! 181, a dryer for receiving and drying the wet crystals separated by the separator, a mother liquor tank for receiving and storing the mother liquor separated by the separator, and a circulation means for returning the mother liquor in the mother liquor tank to the crystal can. In a crystallization device equipped with a sieving device that classifies thin crystals for seeds from the crystals dried in a dryer, and a sieving device that weighs the seed crystals from the sieving device and sends the required amount to a mother liquor tank. It is characterized by being equipped with a sieving device.

However, by putting a controlled amount of seed crystals into the mother liquor that returns to the crystallizer, the number of crystals remaining in the crystallizer and the surface area of the crystals are kept within a certain range, and the crystals are grown. This method controls the average grain size of the crystals obtained from the crystallization apparatus, reduces its fluctuation, and stabilizes the grain size.

Practical example An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the flow chart 1 of the crystallization apparatus of the present invention.

In Figure 1, 1 is a crystallizer, 2 is a heater, 3 is a centrifuge, 4 is a conveyor, 5 is a dryer, 6 is a mother liquor tank, and 7
is the circulation pump, and 8 is the centrifugal part from crystal can 1! 9 is a pump that circulates the liquid between the crystal can 1 and the heater 2, 10 is a sieving device, 11 is a measuring means,
In this example, the on-off valve is controlled by a timer, and 12 is a conveyor. The crystallization apparatus of the present invention is a conventional crystallization apparatus in which a sieving device and an 11-quantity means are added, so the same parts as in the conventional example shown in FIG. do.

The sieving device 10 and the measuring means 11 will be mainly explained below.

The sieving device 10 is a vibrating screen having an upper screen with a large mesh and a lower screen with a small mesh, and receives the crystals from the drying device 5 and separates the coarse crystals remaining on the upper screen into a product A1, an upper screen bath, and a lower screen. The remaining product B is a medium-grain crystal product, and the product C is a fine crystal product in the lower screen pass.

In this embodiment, the measuring means 11 is an on-off valve controlled by a timer, and is always closed, and is opened for a short time at intervals set by a timer (not shown) to remove the crystals remaining above the valve into the mother liquor tank. Drop it to 6.

Next, the action will be explained. The crystals dried in the dryer 5 are sent to a sieving device 10 by a conveyor 12.

The sent crystals are put into the raw material 10d of the sieving device 10. The crystals first pass onto the upper screen, where they are classified into coarse particles remaining on the upper screen and fine particles in the bath.The coarse particles are discharged from the outlet 10a and collected as product A, and in the pass, the fine particles are separated. It rides on the lower screen, where it is classified into medium-sized crystals remaining on the lower screen and fine particles in the pass, and the medium particles are discharged from the outlet 10b and collected as product B, and the fine particles in the bath are is discharged from the outlet 10C.

Fine particles discharged from outlet 10C pass through duct 13 to Y
This leads to the joint 14. The fine particles are separated by the Y joint 14 into a duct 15 leading to the mother liquor tank 6 and a duct 16 leading to a route where they are recovered as a product C. The duct 15 has an on-off valve 11
is provided, and this valve is normally closed, so Y
The fine particles stay in the duct portion 15a between the joint 14 and the valve 11, and after the duct portion 15a is filled, all the fine particles flow into the duct 16. The on-off valve 11 opens for a short time every time set by a timer, and all fine particles staying in the duct portion 15a fall into the mother liquor tank 6. Now, assuming that the volume of the duct portion 15a is Vcm3 and the set time of the timer is t seconds, the apparent volume Wcm3 of fine grained crystals supplied to the mother liquor tank 6 per minute is given by W = 60V.

Note that the measuring means may not have an open structure as described above, but may be a more precise one using a scale.

By metering and supplying fine seed crystals into the mother liquor tank 6 as described above, the crystals are placed in the crystal can. 1) The number of crystals retained and the crystal surface area are maintained within a certain controlled range, and the average grain size obtained from the crystallization apparatus becomes smaller during fluctuations as shown in FIG. Also, if the number of seed crystals ff1 supplied to the mother liquor tank 6 is large, the average particle size will become smaller, and vice versa, it will become larger, so by adjusting the amount of seed crystals supplied to the mother liquor tank, The average particle size obtained in the crystallizer can be controlled.

The evaporator is not limited to the DTB type, and the evaporator may not be of the centrifugal type.

<Effects of the Invention> As described above, the crystallization method and apparatus of the present invention have the following effects.

(1) Since the seed crystals are weighed and supplied to the mother liquor that is returned to the crystal can, the number of crystals retained in the crystal can is reduced.
The crystal surface area is maintained within a certain range, and the temporal change in the average grain size of the resulting crystals is reduced and stabilized.

(2) Since the average particle size obtained can be controlled by controlling the amount of seed crystals supplied to the mother liquor, the yield of products with the desired particle size is improved.

[Brief explanation of drawings]

Fig. 1 is a flow sheet of the crystallization apparatus of the present invention, Fig. 2 is a flow sheet of a conventional crystallization apparatus, Fig. 3 is a graph of the change in average particle size over time of the conventional crystallization apparatus, and Fig. 4 is a graph of the change in average particle size over time of the crystallization device of the present invention. 1... Crystal can 2... Heater 3... Centrifugal separator 5... Dryer 6... Mother liquor tank 7 ...Circulation pump 10...Sieving device 17...Metering means Fig. 3 Fig. 4 Time

Claims (2)

[Claims] (1) In a crystallization method in which the mother liquor containing crystals discharged from the crystallizer is separated into crystals and the mother liquor, and the mother liquor is returned to the crystallizer and circulated, a fine grain for seeds is weighed in the mother liquor that is returned to the crystallizer. A crystallization method characterized by supplying crystals. (2) A crystal can, a separator that receives the mother liquor containing crystals discharged from the crystal can and separates it into crystals and mother liquor, a dryer that receives and dries the wet crystals separated by the separator, and a separator. a mother liquor tank that receives and stores the mother liquor separated by the
A crystallization apparatus equipped with circulation means for returning mother liquor in a mother liquor tank to a crystallization can, a sieving apparatus for classifying thin crystals for seeds from crystals dried in a dryer, and a sieving apparatus for classifying thin crystals for use as seeds from crystals dried in a dryer, and seeds from the sieving apparatus. 1. A crystallization apparatus comprising: measuring means for weighing crystals for use and sending the required amount to a mother liquor tank.