JP4293525B2 - Method and apparatus for continuous crystallization in sugar production - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus capable of continuously crystallizing a large particle size sugar having a particle size of about 1000 μm or more.
[0002]
[Prior art]
Crystal cans used in sugar factories are batch-type sucrose cans (eg, Non-Patent Document 1) that have been used for a long time. Usually, multiple crystal cans are installed to collect various products and crystals for recovery. It was divided. This form does not change even in the current sugar factory, especially in the domestic refined sugar factory, a large number of sugar types are assembled according to the order of the end user, and the sucrose plan is divided and distributed to multiple crystal cans. .
[Non-Patent Document 1]
“3.13 Sugar Production” by Kaoru Kamota, <Factory Operation Series> Revised and Crystallized, Chemical Industry Co., Ltd., February 1, 1974, first edition, P172-173
[0003]
[Problems to be solved by the invention]
When using batch type crystal cans with special sugars such as dinosaccharides (especially medium disaccharides) and low-yield sugar seeds, usually 2 to 4 times of sucrose / separation to grow to the specified particle size・ Since it is necessary to repeat a series of operations such as drying, the efficiency of the equipment is low and the energy efficiency is low with respect to the production volume. On the other hand, large-scale raw sugar (cane sugar) factories overseas have already begun using continuous crystal cans 30 years ago and are actually operating in many factories. However, most of the continuous crystal cans are C sugar (recovered sugar) and the crystal grain size is as small as 250μ. Therefore, when the currently adopted method is applied as it is to the production of sugar crystals with a large particle size, such as dime sugar, sufficient under-white circulation in the can cannot be secured, resulting in crystal sedimentation / deposition. Problems such as an increase in the amount of pseudo crystals generated, a decrease in crystal growth rate, and blockage of piping are expected. In addition, compared with the batch method, the particle size distribution is inevitably widened in the continuous method, and the problem of yield reduction remains.
[0004]
Therefore, the main problem of the present invention is to enable continuous production and to prevent the expansion of the size distribution of sugar crystals due to the continuous process while improving the production efficiency and energy efficiency, and to maintain the yield.
[0005]
[Means for Solving the Problems]
The present invention that has solved the above problems is as follows.
<Invention of Claim 1>
A continuous crystallization method in which a plurality of crystal cans are used, and a crystal slurry comprising a seed crystal and a supersaturated sucrose solution is transferred from an upstream crystal can to a downstream crystal can, and crystals are grown in each crystal can. ,
After supplying the crystal slurry to a propeller type crystal can having one or more propellers that form a circulating flow of crystal slurry in the can and performing the first crystal growth,
The crystal slurry is supplied to a horizontal multistage crystal can having three or more compartments, and the crystal slurry is sequentially transferred from the upstream compartment to the downstream compartment according to the degree of crystal growth, and Grow crystals in the room,
Fine crystals are extracted from the crystal slurry by particle size classification in the propeller type crystal can and downstream thereof,
A seed crystal having an average particle size of 450 μm is grown to an average particle size of 1500 μm or more by initial crystal growth using the propeller-type crystal can, and is grown to an average particle size of 2300 μm or more by crystal growth using the horizontal multistage crystal can. A continuous crystallization method in sugar production.
[0006]
(Function and effect)
Usually, when producing dime sugar, crystals of 450 to 550 μm are used as seed crystals. In order to perform an operation for growing from this particle size to a product of 2300 μm crystals with a single crystal can, a considerably large crystal can is required, and new problems such as non-uniformity of liquid circulation occur. In this case, as disclosed in, for example, Japanese Patent Application Laid-Open No. 5-277000, the problem due to an excessive crystal can can be avoided by performing the crystallization operation stepwise with a plurality of crystal cans.
[0007]
However, they can avoid the problem caused by the size of the crystal can, but cannot improve the quality further, and there is room for improvement regarding the problem caused by the generation of pseudo crystals. That is, the generated pseudo crystals are difficult to separate and remove, and this point remains as a problem to be improved.
[0008]
With respect to this problem, the present invention dares to perform at least initial crystal growth using a propeller-type crystal can. Propeller-type crystal cans are fully mixed crystal cans, which can make the stirring intensity uniform in the cans, so that the crystal grain size distribution can be made uniform, and the generation of pseudo crystals can be suppressed very effectively. In the present invention, this is intentionally used for the first crystal growth to suppress the generation of pseudo crystals as much as possible, to make the particle size distribution uniform and prevent the yield from being lowered.
As described above, in the present invention, the initial crystal growth is performed by the propeller type crystal can, so that the generation of pseudo crystals at the initial stage can be effectively suppressed. However, if the crystal grows to a certain extent by this, nucleation due to the crushing of the crystal is likely to occur, and it is difficult to obtain a uniform particle size distribution due to the large growth of the uncrushed crystal. However, when a crystal can other than the propeller type is used, circulation under white becomes insufficient, and it becomes difficult to obtain a uniform particle size distribution due to an increase in the amount of pseudo crystals generated.
[0009]
On the other hand, a crystal grown to a certain degree in the first stage is grown using a horizontal multistage crystal can having three or more compartments. Using horizontal multistage crystal cans, the residence time of crystals in the can can be made uniform, and crystallization conditions can be optimized for each compartment. . Therefore, the first crystal growth is efficiently performed with the propeller type crystal can while suppressing the generation of pseudo crystals, and the subsequent crystal growth is performed while suppressing the generation of pseudo crystals and crystal crushing as much as possible. Large crystals with a distribution can be obtained.
[0010]
In the present invention, as described above, the generation and increase of pseudo crystals can be suppressed by deliberately using the first crystal can as a propeller type crystal can. However, as described in claim 4, the crystal slurry can be obtained at an appropriate stage. By performing the operation of extracting fine crystals such as pseudo crystals from the crystallization system out of the crystallization system, it is possible to more effectively suppress the increase in the amount of pseudo crystals while ensuring the continuity of the crystallization operation.
[0011]
<Invention of Claim 2 >
The withdrawn fine crystals, after complete dissolution the sugar content adjusted by mixing a supersaturated sucrose solution and hot water, the solution performs the withdrawn position or the upstream side or back downstream operate, according to claim 1, wherein Continuous crystallization method in sugar production.
[0012]
(Function and effect)
In this way, by pulling out the fine crystal out of the crystallization path, re-dissolving it and returning it into the crystallization path, while ensuring the continuity of the crystallization operation, more effectively, such as pseudo crystals It is possible to suppress problems such as suppression of increase, prevention of decrease in crystal growth rate, and blockage of piping, and reduction of yield due to extraction of fine crystals.
[0013]
<Invention of Claim 3 >
By measuring the viscosity and sugar content of the crystal slurry in the propeller type crystal can and downstream thereof, depending on the measurement result, by adding warm water to the crystal slurry at the measurement position or upstream or downstream thereof The continuous crystallization method in sugar production according to claim 1 or 2 , wherein fine crystals in the crystal slurry are dissolved.
[0014]
(Function and effect)
In the present invention, as described above, the generation and increase of pseudo crystals can be suppressed by darely using the first crystal can as a propeller type crystal can. However, as described in claim 6, the viscosity and sugar content of the crystal slurry can be suppressed. By dissolving the fine crystals in the crystal slurry according to the on-line measurement results, it is possible to further suppress the increase of pseudo crystals and the problems associated therewith while ensuring the continuity of the crystallization operation.
[0015]
<Invention of Claim 4 >
Continuous crystallization with multiple crystal cans, configured to grow crystals in each crystal can while transferring the crystal slurry consisting of seed crystals and supersaturated sucrose solution from the upstream crystal can to the downstream crystal can A device,
The crystal can for initial crystal growth is a propeller type crystal can having one or more propellers that form a circulating flow of crystal slurry in the can.
The crystal slurry obtained from the propeller-type crystal can is a horizontal multi-stage crystal can having three or more compartments,
According to the degree of crystal growth, while the crystal slurry is sequentially transferred from the upstream compartment to the downstream compartment, crystals are grown in each compartment,
Fine crystals are extracted from the crystal slurry by particle size classification in the propeller type crystal can and downstream thereof,
A seed crystal having an average particle size of 450 μm is grown to an average particle size of 1500 μm or more by initial crystal growth using the propeller type crystal can, and is grown to an average particle size of 2300 μm or more by crystal growth using the horizontal multistage crystal can. and it has a continuous crystallizer in a sugar, characterized in that.
[0016]
(Function and effect)
The same effect as that of the first aspect of the invention can be achieved.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an example of equipment for carrying out the continuous crystallization method according to the present invention. Reference numeral 1 denotes a crystal slurry supply unit, which is mainly composed of a storage tank 2 and a mixing tank 3 for the sucrose solution FL in this example. A necessary amount of the sucrose solution FL supplied and temporarily stored in the storage tank 2 is extracted by a pumping device P1 such as a pump and continuously supplied to the mixing tank 3. A predetermined amount of seed crystals is continuously supplied to the sucrose solution FL supplied into the mixing tank 3 and is stirred by the stirring device 3s to continuously generate crystal slurry having a predetermined mixing ratio. In this invention, the production | generation method of another crystal slurry can also be taken.
[0018]
The obtained crystal slurry is then extracted from the mixing tank 3 by a pumping device P2 such as a pump and supplied to the propeller type crystal can 10. Along with the supply of the crystal slurry, the sucrose solution FL stored in the storage tank 2 is extracted by the pressure feeding device P 1 and supplied to the propeller-type crystal can 10. The propeller type crystal can 10 used in the present invention is not particularly limited as long as it has one or a plurality of propellers 11 that form a circulating flow of crystal slurry in the can. For example, DP (double double) developed by the present applicant is used. As in the case of a propeller type crystallizer, it is preferable to use a plurality of propellers 11A and 11B to make the slurry concentration in the can more uniform and to reduce or substantially eliminate dead space. This DP type crystallizer 10 is shown in FIG. 1 and FIG. 2, a portion above the liquid surface of the crystal can 10 is an evaporation chamber 12, and a suction port 12 x communicates with the evaporation chamber 12. While configured to be capable of vacuum evaporation by vacuum suction in the evaporation chamber 12 via the suction port 12x, a cylindrical indirect heat exchanger 13 is supported along the vertical direction below the liquid level. An inner propeller 11A located inside the cylinder and an outer propeller 11B located outside the cylinder are provided in the middle portion in the longitudinal direction of the cylindrical heat exchanger 13, and these are integrally attached to the outside of the can. The rotary drive source 10M is configured to be rotationally driven. When the crystal slurry supplied from the slurry inlet 14 at the bottom of the crystal can 10 rises in the cylindrical heat exchanger 13 as indicated by an arrow in the figure and is discharged from the upper end opening of the cylindrical heat exchanger 13, for example, This time, after wrapping outside the cylindrical heat exchanger 13 and descending to the lower end opening of the cylindrical heat exchanger 13, it is returned to the cylindrical heat exchanger 13, and as a result, a circulating flow is formed through the entire crystal can 10. The On the other hand, a heating medium such as steam is supplied to the heat exchanger 13, and the slurry in the crystal can 10 is heated in the circulation process, and the crystal slurry is concentrated by boiling evaporation. Thus, after a supersaturated region is formed and crystal growth is achieved, it is taken out by the pump P3 through the slurry outlet 15.
[0019]
The DP type crystallizer 10 has (a) uniform slurry concentration in the can, (b) low pseudosaturation because it can reduce supersaturation, and (c) uniform circulation concentration allows uniform circulation crystals. (D) The boiling point is the central part in the can, so there is little crystal adhesion to the inner wall surface. (E) Crystals are present in the supersaturated part, and crystal growth occurs immediately at that part. Since it is performed and is not kept in a supersaturated state for a long time, pseudo crystals are unlikely to occur, (f) propellers can be rotated at low speed, crystal crushing is unlikely to occur, and extra nuclei are unlikely to be generated. In other words, a crystal having a large particle size and a uniform particle size can be obtained, which is suitable for the first crystal growth of the present invention.
[0020]
In this example, the crystal slurry having undergone crystal growth by the propeller type crystallizer 10 is supplied to a horizontal multistage crystal can 20 having three or more compartments 21A to 21C. In the present invention, other types of crystal cans that do not have compartments, for example, the above-described DP type crystallizers may be connected in series, and as described above, the horizontal multistage crystal can 20 is suitable. is there. As the horizontal multi-stage crystal can 20, known ones such as those described in Japanese Patent Publication No. 58-20278 and Japanese Patent Publication No. 58-20279 can be used, and are particularly shown in FIG. 1, FIG. 3 and FIG. Those are preferred.
[0021]
That is, the illustrated horizontal multi-stage crystal can 20 includes a horizontally long crystal can main body and partition walls 23 and 23 that divide the lower part of the can into three compartments 21A to 21C in the longitudinal direction. Are provided with stirring blades 24, 24..., And indirect (or non-contact type) heat exchangers 25, 25... Such as calandria are disposed so as to surround the stirring blades 24, 24. It is what. A heating medium such as steam is supplied to the indirect heat exchangers 25, 25... Via the heating medium supply path N6.
[0022]
The upper portion of the partition wall 23 in the crystal can 20 is not partitioned, and is an evaporation chamber 26 that communicates with all the compartments 21A to 21C, and a suction port N11 is communicated with the evaporation chamber 26 portion. It is configured such that vacuum evaporation is possible by vacuum suction in the evaporation chamber 26 via the suction port N11.
[0023]
Reference numeral N1 indicates a slurry supply path for supplying the slurry to the upper side of the stirring blades 24 in each of the compartments 21A to 21C, and reference numeral N2 indicates a slurry discharge path provided at the bottom of each of the compartments. The crystal slurry that has been grown in the crystal can 10 and discharged from the slurry outlet 15 is supplied into the horizontal multi-stage crystal can 20 through the slurry supply passage N1 in the upstream compartment 21A. The crystal slurry supplied into the upstream compartment 21A is stirred by the stirring blade 24 and is supersaturated by heating with the heat exchanger 25 in the process of circulating in the compartment 21A, so that crystals grow. A large amount of crystals that have grown to a certain degree are present in the lower part of the compartment 21A, and this is extracted as crystal slurry by the pump P4 through the slurry discharge passage N2, and in the intermediate compartment 21B in the illustrated example in the next stage. On the other hand, it is supplied via the slurry supply path N1. Thereafter, similarly to the case of the upstream compartment 21A, the crystal growth is sequentially performed in the middle compartment 21B and the downstream compartment 21C. Thus, the crystals are sequentially grown in each of the compartments 21A to 21C while the crystal slurry is sequentially transferred from the upstream compartment 21A to the downstream compartment 21C according to the degree of crystal growth, and grown to a predetermined grain size. A crystal slurry containing the prepared crystals is produced.
[0024]
By the way, although the above method can sufficiently avoid the adverse effects caused by the generation of pseudo crystals and the crushing of crystals, the adoption of the following method makes it possible to produce crystals with a more uniform particle size distribution.
[0025]
That is, the first method is to extract fine crystals such as pseudo crystals and crushed crystals from the crystal slurry by particle size classification in the propeller type crystal can 10 and downstream thereof. As a technique for extracting fine crystals by particle size classification in the crystal cans 10 and 20, a method is proposed in which lightweight fine crystals are extracted together with the slurry through outlets 10X and 20X that open near the liquid surface. In the application example to the horizontal multistage crystal can 20, as shown in FIG. 3, the outlet 20 </ b> X opens near the liquid surface in each of the compartments 21 </ b> A to 21 </ b> C. The number of outlets 20X can be appropriately determined according to the size and type of the crystal can. However, when a stirring device 24 such as a propeller is provided to circulate the crystal slurry, the liquid level is rippled and the classification accuracy is lowered. Therefore, as shown in the figure, a retaining wall 27 extending from above the liquid surface to a certain depth in the liquid is provided so as to surround the outlet 20X, so that the slurry flows from the lower side of the retaining wall 27. It is preferable that the liquid 27 in the wall 27 can be drawn out while preventing the liquid surface from undulating. The same configuration can be adopted in the propeller type crystal can 10. In the propeller type crystal can 10 shown in FIGS. 1 and 2, a cylindrical retaining wall 16 is provided coaxially on the outside of the heat exchanger, and an outlet 10X is provided on the inner wall surface of the can corresponding to the cylindrical retaining wall. In this case, the fine crystal slurry extracted by the pumping device P6 such as a pump is supplied to the reservoir 2 of the supersaturated sucrose solution.
[0026]
In addition, a particle size classifier such as a liquid cyclone, a thickener, a decanter or the like is interposed in an appropriate path, for example, an outlet side flow path of the crystal cans 10 and 20 (for example, a crystal slurry supply path from the propeller type crystal can 10 to the horizontal type crystal can 20). Even so, it is possible to extract fine crystals.
[0027]
In addition, the fine crystals extracted by these first methods may be extracted out of the crystallization system and used for seed crystal raw materials or other applications, or may be discarded in some cases, but in order to improve the yield. Further, after mixing with a supersaturated sucrose solution and warm water and completely dissolving by adjusting the sugar content, it is desirable to carry out an operation of returning the solution to the extraction position or its upstream side or downstream side. Therefore, in the embodiment shown in FIG. 1, a dissolution tank 30 is provided, and a slurry containing fine crystals extracted from the horizontal multistage crystal can 20 is supplied to the dissolution tank 30, and a supersaturated sucrose solution FL and hot water are supplied. After the fine crystals are completely dissolved and the sugar content is adjusted, the fine crystals are returned and supplied to the horizontal multi-stage crystal can 20 at the extraction position by a pumping device P7 such as a pump. In addition, in the dissolution tank 30 shown in the figure, a stirring device 31 for promoting dissolution is provided, and an indirect heat exchanger 32 such as a heating jacket is provided for temperature adjustment, and a heating medium such as hot water is supplied thereto. It is configured.
[0028]
On the other hand, the first method is to extract fine crystals from the main path of the crystal slurry. As the second method, a predetermined position of the main path, for example, in the propeller type crystal can 10 and the horizontal multistage crystal can 20 is used. The viscosity and sugar content of the crystal slurry are measured by the measuring device m, and in the propeller-type crystal can 10 and the horizontal multi-stage crystal can 20 which are measurement positions, or in the main path on the upstream side or the downstream side according to the measurement result Also proposed is a method of dissolving fine crystals in the crystal slurry by adding warm water to the crystal through an addition path. In this second method, since crystals other than the fine crystals are slightly dissolved, it is not suitable for producing a large crystal as much as possible. However, the fine crystal is not extracted in the main path without extracting the fine crystal. Therefore, there is an advantage that ancillary facilities such as the dissolution tank 30 as shown in the figure are small.
[0029]
(Other)
(A) Although the present invention is basically not limited to the grain size of crystal grains, a seed crystal having an average grain diameter of 450 μm is grown to an average grain diameter of 1500 μm or more by initial crystal growth using a propeller-type crystal can. It is preferable to grow to an average particle size of 2300 μm or more by crystal growth using a multistage crystal can because crystals with a very uniform particle size distribution can be obtained.
[0030]
(B) The movement of the crystal slurry between the compartments 21A to 21C in the horizontal multi-stage crystal can example 20 is performed via the outside of the can using the pumping devices P4 and P5 such as a pump, but the pumping device is used. Alternatively, an overflow form in which the slurry moves beyond the partition wall 23 may be employed, or a form in which the slurry is transferred via the inside of the can may be employed.
[0031]
【Example】
(Preliminary experiment 1)
A continuous crystallization experiment using only the DP type crystallizer was performed in the form shown in FIG. A seed crystal having an average particle diameter of 450 μm was added to the sucrose solution so as to be 30 wt% to prepare a seed crystal slurry. This seed crystal slurry and a sucrose solution having a solid content concentration of 67 wt% were supplied to a DP-type crystallizer, and vacuum evaporation was performed to concentrate to a solid content concentration of 74 wt%. After setting the degree of vacuum to 100 to 150 mmHg, supply of seed crystal slurry and sugar solution, extraction of fine crystals, and discharge of crystal slurry were started. The operating time was 18 consecutive hours. During this time, the temperature in the DP was 60 to 65 ° C., and the sugar content Bx was 74.0 to 76.0. The crystals at the outlet had an average particle size of 1500 μm, a CV value of 0.30, and a slurry concentration of 30 wt%. In this experiment, the residence time of the crystals was 6 hours.
[0032]
(Preliminary experiment 2)
A continuous crystallization experiment using only a horizontal multistage crystal can was performed in the form shown in FIG. A seed crystal slurry was prepared by adding a seed crystal having an average crystal grain size of 1500 μm to 30 wt% to a saturated liquid prepared at a solid content concentration of 73.8 wt% and a temperature of 58 ° C. The seed crystal slurry and a sucrose solution having a solid content concentration of 67 wt% were supplied to a horizontal multi-stage crystal can and vacuum evaporated to concentrate to a solid content concentration of 74 wt%. After the degree of vacuum was set to 100 to 150 mmHg, supply of the seed crystal slurry and the sugar solution to each chamber, transfer between the compartments, and extraction of fine crystals were started. The operating time was 18 consecutive hours. The horizontal multi-stage crystal can has a structure in which the inside of the liquid can be visually observed from the outside. When pseudo-crystal generation was confirmed, water was dissolved at any time during the operation time and dissolved. During this time, the temperature in the horizontal multistage crystal can was 60 to 65 ° C., and Bx was 74.0 to 76.0. The crystal at the outlet had an average particle size of 2350 μm, a CV value of 0.32, and a slurry concentration of 30 wt%.
[0033]
(This experiment)
A continuous crystallization experiment was performed in an example of equipment shown in FIG. 1 in which the seed crystal slurry was supplied to a DP crystal can and the slurry extracted from the DP crystal can was supplied to a horizontal multistage crystal can. The conditions for each crystal can were the same as in Examples 1 and 2. The crystals at the outlet had an average particle size of 2200 μm, a CV value of 0.35, and a slurry concentration of 30 wt.
[0034]
【The invention's effect】
As described above, according to the present invention, production by continuous operation is possible, and while improving production efficiency and energy efficiency, it is possible to prevent an increase in the size distribution of sugar crystals due to continuation and to maintain a yield. As you can.
[Brief description of the drawings]
FIG. 1 is a flow diagram showing an example of a continuous crystallization facility according to the present invention.
FIG. 2 is a perspective view showing an example of a propeller type crystal can.
FIG. 3 is a longitudinal sectional view of a horizontal multi-stage crystal can.
FIG. 4 is a cross-sectional view of a horizontal multistage crystal can.
[Explanation of symbols]
10 ... propeller type crystal cans, 20 ... horizontal multi-stage crystal cans.

Claims (4)

A continuous crystallization method in which a plurality of crystal cans are used, and a crystal slurry comprising a seed crystal and a supersaturated sucrose solution is transferred from an upstream crystal can to a downstream crystal can, and crystals are grown in each crystal can. ,
After supplying the crystal slurry to a propeller type crystal can having one or more propellers that form a circulating flow of crystal slurry in the can and performing the first crystal growth,
The crystal slurry is supplied to a horizontal multistage crystal can having three or more compartments, and the crystal slurry is sequentially transferred from the upstream compartment to the downstream compartment according to the degree of crystal growth, and Grow crystals in the room,
Fine crystals are extracted from the crystal slurry by particle size classification in the propeller type crystal can and downstream thereof,
A seed crystal having an average particle size of 450 μm is grown to an average particle size of 1500 μm or more by initial crystal growth using the propeller-type crystal can, and is grown to an average particle size of 2300 μm or more by crystal growth using the horizontal multistage crystal can. A continuous crystallization method in sugar production. The withdrawn fine crystals, after complete dissolution the sugar content adjusted by mixing a supersaturated sucrose solution and hot water, the solution performs the withdrawn position or the upstream side or back downstream operate, according to claim 1, wherein Continuous crystallization method in sugar production. By measuring the viscosity and sugar content of the crystal slurry in the propeller type crystal can and downstream thereof, depending on the measurement result, by adding warm water to the crystal slurry at the measurement position or upstream or downstream thereof The continuous crystallization method in sugar production according to claim 1 or 2 , wherein fine crystals in the crystal slurry are dissolved. Continuous crystallization with multiple crystal cans, configured to grow crystals in each crystal can while transferring the crystal slurry consisting of seed crystals and supersaturated sucrose solution from the upstream crystal can to the downstream crystal can A device,
The crystal can for initial crystal growth is a propeller type crystal can having one or more propellers that form a circulating flow of crystal slurry in the can.
The crystal slurry obtained from the propeller-type crystal can is a horizontal multi-stage crystal can having three or more compartments,
According to the degree of crystal growth, while the crystal slurry is sequentially transferred from the upstream compartment to the downstream compartment, crystals are grown in each compartment,
Fine crystals are extracted from the crystal slurry by particle size classification in the propeller type crystal can and downstream thereof,
A seed crystal having an average particle size of 450 μm is grown to an average particle size of 1500 μm or more by initial crystal growth using the propeller type crystal can, and is grown to an average particle size of 2300 μm or more by crystal growth using the horizontal multistage crystal can. and it has a continuous crystallizer in a sugar, characterized in that.

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