JPH0542279B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to an improvement in a method for supplying a solution in a continuous crystallizer (crystallizer).

(Prior Art) The concept of a general type continuous crystal can will be explained with reference to FIG. 1 is a crystal can having a calandria-type heater 2, 3 is a supply pipe for steam S, 4 is a supply pipe for solution A, 5 is an exhaust pipe for reducing the pressure inside the can, and 6 is a stirring of the solution in the can. 7 indicates the drive motor of the stirrer.

Solution A is heated in a can to evaporate the solvent (water, etc.) contained in the solution, bring the solute concentration to a supersaturated state, and precipitate the solute as crystals in the solution.
It is continuously extracted as magma B from the bottom of the can into a crystal collector 8.

The extracted magma B is led to a slurry tank 9, and is further separated into crystals C and sifted F by a separator 10.
separated into

In a continuous crystallization tank, the vacuum pressure inside the tank, the temperature of the solution, and the stirring speed are usually determined, and the solution A with a constant solute concentration is continuously supplied at a constant flow rate as shown in Figure 4. It is operated to extract a commensurate constant flow rate of magma B.

(Problems to be Solved by the Invention) Such an operating method has the following problems in terms of the crystal growth rate in the solution.

The most important point in precipitating or growing crystals in a solution is the crystal growth rate. This is due to restrictions on the range of motion of the molecules that make up the solute.
depends on the number and size of Moreover, this number and size are related to the degree of supersaturation of the solution in the crystallization can, the stirring speed, the flow rate of the solution supplied to the crystallization can, and the like.

Spores accumulate in micro finals (seeds) that are born in the solution, and are a reserve army for growing crystals, but their number and size depend on the timing of the solution supply and the magnitude of its flow rate. In some cases, the result is that the spores end up collapsing.

Therefore, the solute-specific crystallization rate is greatly affected by the way the solution is supplied, and if the solution is not supplied appropriately, the growth rate will be greatly inhibited. If K ₁ is the crystallization rate coefficient obtained by proper supersaturation and solution circulation, the influence of inhibition will range from 0.8K ₁ to 0.33K ₁ , which will significantly reduce the efficiency of the operation.

An object of the present invention is to provide a solution supply method that can solve these problems and stably realize an operation close to the ideal crystal growth rate.

(Means for Solving the Problems) The first feature of the method of the present invention is that when the degree of supersaturation of the solution reaches the corresponding degree of seed generation supersaturation at the time when seeds are generated or just before the generation of seeds, a solution supply step of starting the supply of the solution and stopping the supply of the solution when a species division supersaturation level corresponding to a state in which spores of a certain size in the solution divide and collapse; After the supply is stopped, when the spores grow and the supersaturation degree of the solution reaches the seed generation supersaturation degree, the solution stop step is repeated and executed intermittently. be.

The second feature of the method of the present invention is that when the growth time of spores changes, the period of the solution stop step is changed.

(Function) According to the present invention, the supply of the solution is stopped during the period during which the growth of the spores is captured, and the solution is supplied at the time when seeds are generated or just before the generation of the seeds,
By regularly generating seeds through periodic intermittent supply, operation with maximum crystal growth rate is achieved.

(Example) Fig _. 2 shows _an example of supplying a solution when the method of the present invention is carried out _. Open the on-off valve 11 inserted into the pipe line 4 to release the solution A.
is supplied into the can.

The solution supply time t ₁ is determined by the time when the spores of a certain size (the size that will transform into a new one when it has a certain surface area) in the solution in the can are in a state of division and collapse, and t ₁ and With a period T such that the relationship of t ₂ is approximately 2.5t ₁ =t ₂ for a certain sugar type, the crystal growth rate can be maintained at the maximum and stable operation can be expected.

The method for determining t ₂ is based on determining the initial value by measuring the growth amount and number of spores, but for example, the solution is mechanically stirred and the crystal ratio + solution concentration + spore amount is measured. .

Specifically, the amount of spore growth is best measured as the degree of supersaturation of the solution as described above.
Set the seed generation supersaturation level that corresponds to the time when seeds in the solution are generated or just before they occur, and the species division supersaturation level that corresponds to the state in which spores of a certain size in the solution divide and collapse. The solution is supplied and stopped depending on the supersaturation value. That is, the operation of starting the supply of the solution into the can when the supersaturation degree of the solution reaches the species generation supersaturation degree and stopping the solution supply when the degree of species division supersaturation is reached is repeated.

The degree of supersaturation is detected as the fluidity or concentration of the solution obtained by a sensor installed inside the crystallizer, but it may vary depending on various factors such as the size of the crystallizer, the heating conditions of the solution, and the stirring conditions. Because of the differences, it is necessary to thoroughly test and set the equipment before operating it.

Figure 3 shows that when the time for spore growth is extended due to a change in the purity of the solution in the middle of the operation, the period of the stop step is set to _t3 , which is longer than _t2 , and the solution is stopped at a new intermittent cycle. Here is an example of executing the supply of .

(Effects) As explained above, according to the method of the present invention, the following effects can be expected.

(1) Crystallization is possible at the crystallization rate specific to the solution,
Crystal yield per unit time is improved.

(2) Crystal quality (color value, crystal purity, average grain size and grain size distribution) is improved compared to conventional methods.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of a continuous crystallizer, FIGS. 2 and 3 are explanatory diagrams showing an example of solution supply according to the method of the present invention, and FIG. 4 is an explanatory diagram showing a conventional solution supply method. DESCRIPTION OF SYMBOLS 1... Crystal can, 2... Heating section, 3... Steam supply pipe, 4... Solution supply pipe, 5... Exhaust pipe, 6
... Stirrer, 8 ... Crystal collector, 9 ... Slurry tank, 10 ... Separator.

Claims (1)

[Claims] 1. In a continuous crystallization can, the supply of the solution into the can is started when the degree of supersaturation of the solution reaches the corresponding degree of seed generation supersaturation at the time when seeds are generated or just before the generation of seeds. a solution supply step of stopping the supply of the solution when a species division supersaturation degree corresponding to a state in which spores of a certain size in the solution divide and collapse;
After the supply of the solution is stopped, when the spores grow and the supersaturation degree of the solution reaches the seed generation supersaturation degree, the solution stop step is repeated and executed intermittently. A method for supplying a solution to a continuous crystallizer, characterized in that: 2. In a continuous crystallization can, when the degree of supersaturation of the solution reaches the corresponding degree of seed generation supersaturation at the time when seeds are generated or just before the generation of seeds, supply of the solution into the can is started and a certain size in the solution is started. A solution supplying step of stopping the supply of the solution when a species division supersaturation level corresponding to a state in which the sac buds divide and collapse;
After the supply of the solution is stopped, when the spores grow and the supersaturation degree of the solution reaches the seed generation supersaturation degree, the solution stop step is repeated and executed intermittently. Additionally, a method for supplying a solution to a continuous crystallizer, characterized in that when the growth time of the spores changes, the period of the solution stop step is changed.