JPH0773519B2 - Crystal growth control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to improvement of a crystal growth control method for obtaining crystals of a target substance from a solution or suspension containing the target substance, and particularly to organic compounds such as glutamic acid. It can be effectively applied to the control of crystal growth of acids and the like.

<Prior Art> The outline of an automatic crystallizer for a crystal can is described with reference to FIG. 1 is a crystal can, 2 is a heating part provided under the crystal can,
S is heating steam supplied to the heating unit 2, 3 is a hardness meter for measuring the hardness of the crystallization slurry in the can, 5 is a level meter for measuring the level of the crystallization slurry, 6 is a stirring blade, 7 Is an electric motor for driving stirring, and 8 is a liquid supply valve for the solution F to be supplied into the can.

Reference numeral 9 is a sequence control device, which controls the opening and closing of the liquid supply valve 8 based on the measurement signals e _M and e _L from the hardness meter 4 and the level meter 5. Although not shown, a differential water supply control valve for controlling differential water into the can is also provided, and the sequence controller also controls the opening and closing of the differential water supply control valve.

The crystallization method in the crystallization process based on the measured value of the hardness meter is
Each time the measured value of hardness reaches the programmed set value, differential water or a solution is supplied, and once the hardness of the slurry is loosened, concentrated crystallization is continued, and the hardness is a constant value than the previous set value. When the set value reaches a very high value, the operation of loosening the hardness of the slurry by supplying the water difference or the solution again is intermittently executed, and when the level in the can reaches a constant value, the concentration is finished. Generally, liquid crystal deposition is performed in the crystal growing process.

The mechanism of crystal growth is extremely complicated and has not been clarified in the past.However, according to the applicant's research, an intermediate substance having both liquid and solid properties called spore germination is found in the solution as it is concentrated. To exist and surround the crystals to form a blast zone surrounding the blast, and to grow these buds and blast zones by concentrating, and to carry out the control to collapse them at a certain stage of growth. Thus, it was confirmed that the conversion from the blast zone to crystals can be promoted.

In this case, the measured value e _M of the hardness meter is measured as a physical quantity including the three parameters of the dissolved mass, the amount of spores (the amount of spores + the amount of spore zones), and the amount of crystals. The so-called intermittent control, in which a solution is supplied each time the measured value of hardness reaches a constant value, carries out an operation to disintegrate the spore volume, that is, the volume of spores and the volume of spore zone each time they reach a certain amount. You are doing it.

FIG. 3 shows a comparison of the program control of the hardness of sugar and glutamic acid in the concentration and crystallization stage, and the glutamic acid shown by the solid line shows the hardness M ₁ in the initial period of crystal growth T ₁ .
It is necessary to gradually raise the hardness in the relatively soft region of ~ M ₂ , and the measured value of the hardness meter becomes almost flat. This is smaller than that in the case of blast production, and the measured value e _M
This is because the degree of influence on

On the other hand, if sugar shown by the dotted line, the hardness M ₃ ~ in period T ₁
Since the operation of increasing the hardness with a fairly steep gradient in the relatively hard region of M ₄ is performed, the amount of blast and the amount of blast zone can be grasped from the measurement value of the hardness meter from the beginning.

FIG. 4 is an enlarged view of program control of crystallization of sugar solution or crystallization of glutamic acid in the middle to late stages of crystallization (period T ₂ in FIG. ₂ ), and as shown in FIG. At time t ₁ when the measured value e _M of M reaches the set value of M ₃ , as shown in (B), the liquid supply valve 8 is opened for a certain period of time to supply the solution, and once the hardness is loosened, the concentrated crystallization is performed. , And at time t ₂ , the previous hardness setting value
The solution was fed again fixed time is reached that is higher set value M ₄ .DELTA.M than M _3, and the same operation is repeated hereinafter.

<Problems to be solved by the invention> As described above, even in the case of sugar or glutamic acid, the set gradient of the hardness is considerably large in the crystallization period in which the increase in the spore volume and the spore zone can be measured by the hardness meter. Since it can be made suddenly, the value of ΔM can be made sufficiently large compared to the fluctuation of the set value e _M due to disturbance.
Therefore, controlling the opening and closing of the liquid supply valve 8 based only on the level change of e _M causes no problem.

However, in crystallization of amino acids and the like, it is necessary to control the liquid supply valve in the period T _{1 in} which the change in the measured value of hardness is small as described above, and it is necessary to make ΔM extremely small. If noise such as is superposed on e _M there is a risk that the erroneous operation. Further, the hardness meter has a structure in which the blade is rotated in the can and the hardness is measured by the reaction force thereof, and when a lump of crystals hits the blade due to the flow of slurry inside the can by a stirrer, the hardness is temporarily measured. The measured value e _M fluctuates. Even if this fluctuation exceeds ΔM, it causes an erroneous operation, which makes the operation extremely unstable, and there is a problem that it is difficult to realize program control based on hardness.

An object of the present invention is to provide a crystal growth control method capable of solving such a problem.

<Means for Solving Problems> A feature of the method of the present invention is that a solution is supplied into the can each time the hardness of the crystallization slurry in the crystal can reaches a certain value to temporarily loosen the hardness. In the crystal growth control method in which the operation is repeated, during the period when the measured value of the hardness becomes almost flat, the next solution supply is performed based on the measured value of the supersaturation degree and the measured value of the level of the crystallization slurry in the can. In point.

<Operation> According to the present invention, during the period in which the measured hardness value is substantially flat, the next solution supply is performed based on the measured supersaturation value and the measured crystallization slurry level in the can. .

<Embodiment> An embodiment of the method of the present invention will be described with reference to a functional block diagram in the control device 9 in FIG. First, the program control (period T _{2 in} the case of glutamic acid) by a hardness meter that is constantly executed will be described.

91 is a hardness setter that programmatically supplies a set value e _MS that is higher than the previous set value by ΔM, and 92 compares the set value e _MS with the measured hardness value e _M, and if e _M ≧ e _MS When the comparator 93 outputs the output e _M0 , 93 is the supply signal that outputs the operation signal e _V0 for opening the liquid supply valve 8 for a certain time and supplying the solution into the can when the comparison output e _M0 is transmitted during the period T ₂ . It is a liquid valve control means.

Reference numeral 94 is a peak determination means for realizing the characteristic part of the present invention, in which the measured value e _SS of the supersaturation meter 10 provided in the can and the slurry level measured value e _L are input, and the upper limit peak of e _SS and e Judgment output e _S0 is transmitted at a timing near the lower limit of _L peak.

The liquid supply valve control means 93 _{causes the} determination output e _S0 during the period T ₁ .
When is transmitted, the liquid supply valve 8 is opened for a certain time as in the case of e _M0 , and an operation signal e _V0 for supplying the solution into the can is transmitted.

Next, the principle and operation of the control method of the present invention will be described with reference to FIG. (A) is the measured value of supersaturation e _SS in period T ₁ , (B) is the measured value of slurry level e _L , (C)
Shows the supply state of the solution F by opening and closing the liquid supply valve 8.

In (A), the period T ₁ is the period T in which the crystal is very small.
₁₁ , period T ₁₂ when the crystals became large to some extent, period when the crystals became larger and the crystallization rate exceeded the concentration rate
When subdivided into T ₁₃ , in period T ₁₁ , the supersaturation degree e _SS is temporarily decreased as a result of the previous solution supply and rises due to concentration, and reaches the peak points P ₁ and P ₂ Timing t ₁ and t ₂ are spores It coincides with the peak of the amount, and in the periods T ₁₂ and T ₁₃ , the peak of the sprouting amount is reached slightly after the peaks P _{3 to} P ₆ . Further, in any of the periods, the peak of the spore volume corresponds to the lower limit peaks l ₁ , l ₂ ... l ₆ of the slurry level.

Therefore, if the solution is supplied at a timing near both the peak of the supersaturation degree e _SS and the lower limit peak of the slurry level, intermittent control of growth and disintegration of the blast and blast zone can be performed by measuring the hardness value. It can be executed without using it.

The peak of supersaturation has a value specific to the solution, but the lower limit of the slurry level can be set in the program. That is, when the value of the lower limit peak (l ₁ ) at the slurry level is a _i and the value of the subsequent upper limit peak is b _i , the value a _{i + 1} of the next lower limit peak (l ₂ ) is 1> When α> 0, it can be determined by a _{i + 1} = (b _i −a _i ) · α.

Therefore, the tamming reaching the lower limit set value is regarded as the lower limit peak, and the beak determining means 94 determines the determination output e _S0 by the logical product with the peak of the measured value of the supersaturation degree.
Call.

<Effects of the Invention> As described above, according to the control method of the present invention, in the initial period of crystal growth, the crystallization rate is slower than the concentration rate,
Crystallization of solutes such as glutamic acid, for which it is difficult to detect buds and blast zone growth with a hardness meter, can be controlled by the method of bud growth and decay control by intermittent solution supply based on accurate timing determination. Therefore, the efficiency of crystal growth control can be significantly improved as compared with the estimated solution supply method.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a crystal can control apparatus to which the method of the present invention is applied, FIG. 2 is an explanatory diagram of program control by hardness, FIG. 3 is an operation explanatory diagram of the method of the present invention, and FIG. The figure is an explanatory diagram of the operation of a general hardness program control method. 1 ... Crystal can, 2 ... Heating part, 3 ... Crystallization slurry, 4
…… Hardness meter, 5 …… Level meter, 6 …… Stirring blade, 7 ……
Electric motor, 8 ... Liquid supply valve, 9 ... Sequence control device, 10
...... Supersaturation meter

Claims (1)

[Claims] 1. A method for controlling crystal growth in which a method of supplying a solution into the can to temporarily loosen the hardness each time the hardness of the crystallization slurry in the crystal can reaches a certain value is repeated. During the period when the measured value of is almost flat, the next solution supply is performed based on the measured value of the supersaturation degree and the measured value of the level of the crystallization slurry in the can.