JP2519177B2 - Continuous crystallization method for sugar production - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous crystallization method for sugar production when sugar is obtained from sugar cane or beet as a raw material. Therefore, it mainly relates to a crystallization method in the crude sugar stage.

[0002]

BACKGROUND ART As is well known, sugar is often obtained from sugar cane or beet as a raw material. The outline of the process is to use sugar cane or beet as a raw material and recover sugar by a compression method or a diffusion method. Then, after clarification, it was concentrated in a multi-effect can to obtain concentrated syrup,
Further, it is heated and crystallized in a crystal can, and the obtained crystal slurry (under white) is purified and commercialized.

In this case, the crystallization from the concentrated syrup has traditionally been carried out in a batch system, and seed crystals (seed or seed magma) having a uniform particle size distribution are added to the concentrated syrup, and the evaporation rate is increased. While adjusting the syrup supply rate, the crystal is grown as quickly and uniformly as possible.

[0004]

In the sugar factory, the crystallization process occupies most of the energy consumed. Moreover, since the crystallization process is a batch process, the use of steam for crystallization is intermittent, which causes a fluctuation in the steam load of the entire factory and is not economically effective.

Therefore, an object of the present invention is to reduce energy consumption by performing continuous crystallization.

[0006]

[Means for Solving the Problems] The above problem is to provide a plurality of crystal cans, connect the final crystal can to a centrifuge, and supply syrup to the first crystal can to obtain a concentrated crystal slurry. It is supplied to the subsequent crystal can, and the crystal slurry from the final crystal can is supplied to the centrifuge as it is, and in this centrifuge, separation into heavy liquid and light liquid is continuously performed, and the centrifuge is used. It is possible to solve the problem by setting the gravitational acceleration at 50 to 250 G and commercializing the heavy liquid, and using the light liquid as a seed or re-dissolving it into a syrup.

[0007]

In the present invention, crystallization is continuous. Therefore, the amount of steam used for the crystallization can be made uniform over time, and the amount of steam used in the sugar factory can be stabilized, resulting in economical operation.

It is believed that the main reason why the crystallization has not been continuous in sugar mills has been the belief that traditionally, batch processing can obtain a crystal slurry having a good particle size distribution. In fact, as will be shown in Examples described later, even if the crystal cans are simply made into series, the particle size distribution of the obtained crystal slurry varies as compared with the case of the batch type, and the uniform coefficient (uniform number) becomes worse.

[0009] However, as in the conventional case, the crystal slurry (white bottom) from the continuous crystallization process is once introduced into the holding tank and slowly mixed so that the crystals do not deposit, and then the batch type centrifugal separator. Instead of obtaining the decoction, the crystal slurry is directly subjected to a centrifuge to separate it into a heavy liquid with a relatively large crystal grain size and a light liquid with a relatively small crystal grain size. It was found that when the gravitational acceleration at 50 is set to a low value of 50 to 250 G, the mechanical crushing action received during the centrifugal separation operation is suppressed, and the spread of the particle size distribution can be suppressed. In fact, as shown in the examples below, the uniform number of heavy liquids obtained from the centrifuge is practically comparable to that of the batch type.

It has been considered that the sugar liquid is difficult to be classified because of its high viscosity of several hundred to several thousand cP and the small difference in specific gravity between the sugar liquid and sugar crystals. However, under low gravitational acceleration, it is considered that the thickness of the slurry inside the centrifuge and the size of the gap created by the crystals with a large particle size aggregated by the centrifugal force become appropriate. On the other hand, as a centrifuge, a centrifuge having a low gravitational acceleration is sufficient, and therefore an expensive one is unnecessary.

On the other hand, the heavy liquid classified by the centrifugal separator is
The raw sugar is introduced into the sugar production process and finally commercialized.
The light liquid is supplied to the first crystal can by using the light liquid as a seed, or syrup is added and heated and stirred to be dissolved into a raw syrup. Of course, both modes can be used together.

Conventionally, seeds are batch-produced,
This is also an obstacle to continuity. However, when the light liquid is used as the seed, the seed can be obtained in the continuous process, and it is not necessary to separately produce the seed, which is particularly effective.

[0013]

The present invention will be described in more detail by way of examples with reference to the drawings. FIG. 1 is a schematic diagram of equipment for carrying out the method of the present invention, in which the concentrated syrup 1 obtained in the previous step is used.
Are sequentially supplied to a plurality of, in the illustrated example, two crystal cans 2A and 2B, and the crystal slurry from the final crystal can 2B (bottom white).
Is directly supplied to the centrifugal separator and the centrifugal decanter 3 by the extraction pump 3P. The heavy liquid 4H classified by the centrifugal decanter 3 is supplied to the heavy liquid tank 5A, guided to a separator (not shown) by the heavy liquid pump 6A, and finally made into crude sugar.

On the other hand, the light liquid 4L is supplied to the light liquid tank 5B, part of which is supplied by the light liquid pump 6B through the path 7 to the first crystal can 2A together with the seed magma 8 and The rest is supplied to the syrup tank 10 through the path 9, heated and redissolved, and then supplied to the first crystal can 2A by the pump 11 together with the supplemental syrup.

The crystal cans 2A and 2B may be of any suitable type, but in the embodiment, calandria of double stirring blade type (so-called DP type) (having a heating tube group of forced circulation type vertically). The system was used. The crystal slurry from the first crystal can 2 </ b> A is supplied to the second crystal can 2 </ b> B through the transition passage 12 by a free fall method. A pump transfer is also possible.

The first crystal can 2A and the second crystal can 2B are operated under vacuum by a vacuum pump 13, and the generated vapor is a vapor vapor condenser 14, for example, a vertical falling liquid film type shell and tube heat exchanger. The low pressure refrigerant in the refrigerant circulation path 17 passing through the screw compression heat pump 15 and the evaporation generator 16 is evaporated, and condensed as drain 18 itself. Reference numeral 19 is a variable flow rate ejector functioning as an expansion valve, and 20 is a drive motor.

On the other hand, the hot water returned from the crystal cans 2A, 2B is supplied to a steam generator 16, for example, a vertical falling liquid film type shell-and-tube heat exchanger, and a high-pressure refrigerant whose pressure is increased by a screw compression heat pump 15. The condensation latent heat of the gas is removed to evaporate, and the heaters 2h of the crystal cans 2A and 2B,
It is supplied for 2 hours and is used as a heat source for heating and evaporating the sugar solution.

In the prior art, the concentrated syrup was heated and evaporated to supersaturation by the boiler steam, and the evaporation vapor was discharged from the upper part of the crystal can and cooled and condensed with seawater by the barometric condenser. According to this, it was found that the required energy is about 1/6. In addition, there are cases where bagasse is used as fuel for the boiler, but there is also an advantage that it can be used for other purposes.

The white bottom from the final crystal can 2B is classified into a heavy liquid and a light liquid by the centrifugal decanter 3. As the operation condition, the gravitational acceleration is set to 50 to 250 G, and more preferably 100 to 200 G. Residence time is 10
20 seconds is preferred. Residence time exceeds 20 seconds, especially 30
If it exceeds the second, the crushing rate of the crystal increases, and the particle size distribution is broadened. Also, light liquid crocodile has an average particle size of 100
It is suitable to classify crystals having a size of about 300 μm and operate so as to raise the uniform number of heavy liquid waft by about 0.5 from the stage under the white line. Therefore, it is preferable that the centrifugal decanter 3 can freely change the rotation speed by an inverter or the like.

In the present invention, the number of crystal cans can be further increased. Three to four cans are preferable. An agitator in the crystal can is not essential, but it is desirable to provide a stirring means at least in the final crystal can in order to ensure circulation and uniformity of the sugar solution. The centrifuge is not limited to the decanter type.

(Experimental Example) The effect of the present invention will be described below with reference to an experimental example. Crude sugar was obtained under the system configuration of FIG. The structure of the equipment is as follows: 1st and 2nd crystal can: Calandria type crystal can, effective capacity 2m ³ , heat transfer area 24m ² , extraction pump / heavy liquid pump / light liquid pump: positive displacement pump, centrifugal decanter: rotor diameter 250mmφ , Heavy liquid tank: ribbon mixer type, light liquid tank: with heating coil and stirrer.

The operating conditions are as follows. Heating steam pressure (mmHg) 400-420 (saturated steam temperature conversion 83-84 ° C) Steam vapor pressure (mmHg) 85-90 (saturated steam temperature conversion 48-49 ° C) Syrup (Bx) 60 Under-white concentration (Bx) 88 -92 seeds (Bx) 80-90 seed ratio (wt%) 15-30 retention time in can (hr) 3-4 crystal production amount (kg / hr) 800-900 Under these conditions, each stage of Table 1 When the average particle diameter and the uniform number in were examined, the results shown in the same table were obtained.
Here, the average particle size is the 50 wt% particle size in the RR diagram for particle size distribution analysis, and the uniform number is the slope (tangent) of the distribution line on the same line graph, and the numerical value of the particle size distribution is large. It shows that the width is narrow (the particle diameters are uniform). In the table, F is decanter feed, H is decanter heavy liquid, L
Indicates decanter light solution. Further, RT in the remarks column indicates the residence time of the crystal can.

[0023]

[Table 1]

As can be seen from the results, the uniform number in the bottom of white is not good as compared with the case of batch processing, but the uniform number of heavy liquid from the decanter is improved and there is no practical problem. Is. Further, the self-seeding operation using the light liquid as the seed does not substantially differ from the seed supply operation in which the seed is obtained from the outside.

[0025]

As described above, according to the present invention, continuous crystallization brings advantages such as reduction of energy consumption.

[Brief description of drawings]

FIG. 1 is a schematic view of equipment for carrying out the method of the present invention.

[Explanation of symbols]

1 ... (concentration) syrup, 2A, 2B ... Crystal can, 2h ... Heater, 3 ... Centrifugal decanter, 3P ... Extraction pump, 4
H ... heavy liquid, 4L ... light liquid, 5A ... heavy liquid tank, 5B ... light liquid tank,
8 ... Seed (magma), 12 ... Transition path, 13 ... Vacuum pump, 14 ... Steam vapor condenser, 15 ... Heat pump,
16 ... Evaporation generator, 17 ... Refrigerant circulation path 17, 20 ... Drive motor.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Masao Hino Inventor Masao Hino 2-17-15 Tsukushima Machinery, Chuo-ku, Tokyo (72) Inventor Yasuhiko Kamijo 2-17-15 Tsukushima, Chuo-ku, Tokyo Tsukishima Machinery Co., Ltd.

Claims (1)

(57) [Claims] 1. A plurality of crystal cans are provided, a final crystal can and a centrifuge are connected, syrup is supplied to a first crystal can, and a crystal slurry having a high concentration is supplied to a subsequent crystal can, The crystal slurry from the final crystal can is supplied to the centrifuge as it is, and the centrifuge continuously separates the heavy liquid and the light liquid, and the gravity acceleration in the centrifuge is 50 to 250 G. And the light liquid is used as a seed, or the light liquid is used as a seed, or redissolved into a syrup to provide a continuous crystallization method for sugar production.