JP4909145B2 - Forward freeze concentration method - Google Patents

Description

  The present invention relates to a forward freeze concentration method. As a method of concentrating liquids to be concentrated such as foods and pharmaceuticals, a freeze concentration method capable of obtaining a concentrate of excellent quality has attracted attention. Among the freeze concentration methods, the suspension crystallization method and the forward freeze concentration method are known. Of these, the present invention relates to the forward freeze concentration method, and more particularly to the concentrated solution and the refrigerant while circulating the concentrated solution and the refrigerant. It is related with improvement of the method of forward freeze concentration.

  Conventionally, as a forward freeze concentration method, the refrigerant is circulated through the refrigerant flow path of the freeze concentrator while the liquid to be concentrated is circulated through the refrigerant flow path of the freeze concentrator. A method of freeze-concentrating the liquid to be concentrated by sequentially forming and growing ice crystals is known (see, for example, Non-Patent Documents 1 and 2 and Patent Document 1).

  In such a forward freeze concentration method, two factors, the flow rate of the concentrated solution at the freezing interface and the growth rate of ice crystals, have a great influence on efficiently concentrating the concentrated solution. For example, if the flow rate of the concentrated liquid at the freezing interface is slow, the solute uptake rate into the ice crystals increases accordingly. The load on the device increases. Further, for example, if the growth rate of ice crystals is fast, the solute uptake rate into the ice crystals increases accordingly, and conversely, if the growth rate of ice crystals is slow, the freeze concentration time increases accordingly. In the above-described forward freeze concentration method, the flow rate of the concentrated solution at the freezing interface during freeze concentration, in other words, the flow rate of the concentrated solution in the concentrated solution flow path of the freeze concentrator and the growth rate of ice crystals are optimized. Although it is important to control the value, it is necessary to grow ice crystals with a uniform thickness as much as possible over the entire wall surface of the concentrate flow path of the freeze concentrator. . If the thickness of the ice crystals growing on the wall surface varies depending on the location of the concentrated liquid flow path of the freeze concentrator, the flow rate of the concentrated liquid also varies depending on the location, and the pressure loss increases due to the thick portion of the ice crystals. As a result, the pulsation of the pump for circulating the liquid to be concentrated increases, and the flow rate of the liquid to be concentrated becomes unstable.

However, in general, in the case of forward freeze concentration of the liquid to be concentrated, the liquid to be concentrated is circulated in a certain direction through the liquid to be concentrated in the freeze concentrator by a pump for circulating the liquid to be concentrated, and the refrigerant is circulated in the refrigerant. Circulates in the refrigerant flow path of the freeze concentrator in a certain direction by the pump for the concentrated liquid, the downstream side of the concentrated liquid circulating pump has a more concentrated liquid flow path than other parts, for example, the upstream side. The ice crystals that grow on the wall surface are thinner, and the ice that grows on the wall surface of the concentrated liquid flow path in the co-current area where the liquid to be concentrated and the refrigerant flow in the same direction than the countercurrent area in which both flow in the opposite direction. There is a problem that the crystal becomes thin. In the conventional method of Patent Document 1 described above, the volume expansion amount detecting means of the concentrated liquid is connected to the concentrated liquid flow path, and the wall surface of the concentrated liquid flow path is determined from the volume expansion detected by the volume expansion detecting means. The thickness of the ice crystals grown on the surface is obtained, and the flow rate of the concentrated liquid and the growth rate of the ice crystals in the flow path of the concentrated liquid are controlled to be set values through a predetermined operation based on the thickness. As described above, if the thickness of ice crystals growing on the wall surface varies depending on the location of the concentrated liquid flow path of the freeze concentrator, it is difficult to perform such control with high accuracy. It becomes more difficult to perform such control accurately in the second half of the freeze concentration in which the concentration becomes higher and the influence becomes larger.
Food and Technology (December 1997, Vol. 318, 1-8) Abstracts of the 1st Annual Meeting of the Japan Food Engineering Society (FY2000) (page 85) JP 2005-81215 A

  A first problem to be solved by the present invention is to circulate a refrigerant in the refrigerant flow path of the freeze concentrator while circulating the liquid to be concentrated in the liquid concentrate flow path of the freeze concentrator. In forward freeze concentration, in which ice crystals are successively formed and grown on the wall surface of the flow path to freeze and concentrate the concentrated liquid, ice having a uniform thickness over the entire wall surface of the concentrated liquid flow path of the freeze concentrator The second problem is to provide a method capable of growing crystals, and the second problem is to overcome the first problem and to have a great influence on efficiently freezing and concentrating the liquid to be concentrated. The present invention is to provide a method capable of accurately controlling one factor, that is, the flow rate of the liquid to be concentrated at the freezing interface and the growth rate of ice crystals during freeze concentration to the optimum values, in other words, the set values.

  The present invention for solving the above-mentioned problems is to circulate the refrigerant to the refrigerant flow path of the freeze concentrator while circulating the liquid to be concentrated to the liquid concentrate flow path of the freeze concentrator. In forward freeze concentration in which the concentrated liquid is frozen and concentrated by sequentially forming and growing ice crystals on the wall surface, during the freeze concentration of the concentrated liquid, the circulation direction of the concentrated liquid in the concentrated liquid channel is changed. The present invention relates to a forward freeze concentration method characterized by changing.

  The forward freeze concentration method according to the present invention (hereinafter simply referred to as the method of the present invention) circulates the refrigerant to the refrigerant flow path of the freeze concentrator while circulating the liquid to be concentrated to the liquid concentrate flow path of the freeze concentrator. In the forward freeze concentration in which the concentrated liquid is freeze-concentrated by sequentially forming and growing ice crystals on the wall surface of the concentrated liquid flow path, the entire area of the wall surface of the concentrated liquid flow path of the freeze concentrator is This is a method for growing ice crystals having a uniform thickness over the entire area.

  As the freeze concentrator, various types of freeze concentrators can be used. However, it is preferable to use one composed of two or more multi-tubular tubes, and two or more such multi-tubular tubes are provided. More preferably, the concentrated liquid flow paths of the multiple cylindrical tubes are connected in series as a whole, and the refrigerant flow paths of the multiple cylindrical tubes are connected in parallel as a whole. Is a double cylindrical tube, in which a concentrated liquid flow path is formed inside each double cylindrical pipe, and a refrigerant flow path is formed outside. Here, for example, the freeze concentrator includes a total of 10 double cylindrical tubes, the concentrated liquid flow paths formed inside each double cylindrical tube are connected in series as a whole, and each double cylindrical tube The refrigerant flow paths formed on the outside are connected in parallel as a whole because all the concentrated liquid flow paths of the double cylindrical tubes are connected in series, and the refrigerant of each double cylindrical tube In addition to the case where all of the flow paths are connected in parallel, two pairs of adjacent double cylindrical tubes are combined to form a total of 5 sets, and the concentrated liquid flow paths are parallel in each set. However, the liquid flow paths to be concentrated are connected in series between each of the total of 5 sets, and conversely, the refrigerant flow paths are connected in series in each set. It means that the refrigerant flow paths are connected in parallel between the groups.

  In the method of the present invention, when the concentrated solution is forward freeze-concentrated using the freeze concentrator as described above, the circulation direction of the concentrated solution in the concentrated solution flow path is changed during freeze concentration of the concentrated solution. . As in the conventional method described above, during freeze concentration, the refrigerant is always circulated through the refrigerant flow path of the freeze concentrator in a fixed direction by a refrigerant circulation pump, and the concentrated liquid is also circulated by the concentrated liquid circulation pump. Instead of always circulating in the concentrating liquid flow path of the freeze concentrator in a constant direction, the circulation direction is changed.

  As a means for changing the circulation direction of the concentrated liquid in the concentrated liquid flow path of the freeze concentrator, it can be performed by a valve operation, but the pump for circulating the concentrated liquid is reversed from normal rotation to normal rotation from reverse rotation. Preferably. In addition, the period for changing the circulation direction of the concentrate to be concentrated is usually done periodically, but the freeze concentration time required to obtain the freeze concentrate with the target concentration can be calculated approximately. It is preferable to change the circulation direction of the liquid to be concentrated at such a time, and in this sense, it is more preferable to change the circulation direction of the liquid to be concentrated once or an odd number of times. For example, when the freeze concentration time is 60 minutes, the circulation direction of the liquid to be concentrated is changed only once every 30 minutes from the start of freeze concentration, or three times in total, 15 minutes, 30 minutes and 45 minutes from the start of freeze concentration. .

  In the method of the present invention, during the freeze concentration of the liquid to be concentrated, as described above, the circulation direction of the liquid to be concentrated in the flow path to be concentrated of the freeze concentrator is usually periodically changed, whereby a pump for circulating the liquid to be concentrated is obtained. The wall of the concentrated liquid flow path of the freeze concentrator in the same way as the upstream side of the freezing concentrator, and also in the cocurrent flow area where the liquid to be concentrated and the refrigerant flow in the same direction, as in the countercurrent area where both flow in the opposite direction. The above-mentioned two factors that need to be controlled in order to efficiently freeze and circulate the liquid to be concentrated, that is, freeze concentration during freeze concentration, grow ice crystals of uniform thickness over the entire area. It is preferable to control two factors, the flow rate of the concentrated liquid in the concentrated liquid flow path of the vessel and the growth rate of ice crystals, to the optimum values.

  The flow rate of the concentrated liquid in the concentrated liquid flow path of the freeze concentrator is controlled by adjusting the circulation amount of the concentrated liquid in the concentrated liquid flow path of the frozen concentrator. The ice crystal growth rate is controlled by adjusting the temperature and / or circulation rate of the refrigerant in the refrigerant flow path of the freeze concentrator, and a method for controlling these to the optimum value, that is, the set value during freeze concentration. As such, various methods can be applied.

  One such method predicts the flow rate of the concentrate and the growth rate of ice crystals in the concentrate flow path of the freeze concentrator during freeze concentration, and in accordance with such prediction, the concentration is increased as time passes for freeze concentration. In this method, the number of rotations of the pump for circulating the concentrate is sequentially decreased, and the temperature of the refrigerant is sequentially decreased. However, according to this method, in fact, the flow rate of the concentrate and the growth rate of ice crystals may greatly vary.

  Another method is the method described in Patent Document 1 described above. In this method, first, a volume expansion amount detecting means of the liquid to be concentrated is connected to the liquid concentrate flow path of the freeze concentrator, and ice crystals in the liquid concentrate flow path are detected from the volume expansion amount detected by the volume expansion amount detecting means. Find the thickness. As freeze concentration of the liquid to be concentrated proceeds, ice crystals are sequentially formed on the wall surface of the liquid to be concentrated and grow as time passes. The growth of ice crystals causes volume expansion, and apparently the amount of liquid to be concentrated increases by the volume expansion. The resulting increase amount of the liquid to be concentrated, that is, the volume expansion amount of the liquid to be concentrated is detected by the volume expansion amount detecting means connected to the liquid channel to be concentrated. Since the shape and size of the concentrated liquid channel, for example, the diameter and length are known, the ice crystal thickness in the concentrated liquid channel is calculated from the detected volume expansion. Next, in this method, the following operations A and B are performed based on the ice crystal thickness in the concentrated liquid flow path obtained as described above, and the flow rate of the concentrated liquid and the ice crystals in the concentrated liquid flow path are performed. To control the growth rate to be a set value. In operation A, the inner diameter of the ice crystal in the concentrated liquid channel is calculated from the ice crystal thickness, and the flow rate of the concentrated liquid in the concentrated liquid channel is determined from the inner diameter and the set value of the flow rate of the concentrated liquid in the concentrated liquid channel. The required flow rate of the liquid to be concentrated is calculated, and the circulation amount of the liquid to be concentrated is adjusted so that the actual flow rate of the liquid to be concentrated in the flow path of the concentrated liquid becomes the required flow rate. In operation B, the ice crystal growth rate in the concentrated liquid flow path is calculated from the ice crystal thickness, and the refrigerant temperature and / or circulation rate is adjusted so that the growth rate becomes a set value. According to this method, the flow rate of the liquid to be concentrated and the growth rate of ice crystals can be controlled stably correspondingly to the optimum value, that is, the set value, but it is necessary to separately provide a means for detecting the volume expansion amount of the liquid to be concentrated. There is.

  For these two methods, the circulation amount of the concentrated liquid in the concentrated liquid flow path of the freeze concentrator is adjusted according to the following operation M, and the temperature of the refrigerant in the refrigerant flow path of the frozen concentrated condenser and / or Alternatively, if the amount of circulation is adjusted according to the following operation N, it is not necessary to separately provide a means for detecting the volume expansion amount of the liquid to be concentrated, and the flow rate of the liquid to be concentrated and the growth rate of ice crystals become optimum values, that is, set values. So that it can be controlled stably.

Operation M: The measured Brix value B ₀ before concentration of the concentrated liquid, the measured Brix value B _n during freeze concentration, and the ice crystals of the concentrated liquid flow path determined in advance according to the measured Brix value B _n determine the ice crystals amount and a ratio a _n of the solute in該被concentrate flow path, calculates the inner diameter of the ice crystals from the ice crystal volume, the flow rate of該被concentrate in said inner and該被concentrate passage To calculate the required flow rate of the liquid to be concentrated in the flow path of the concentrated liquid from the set value of Operation to adjust the circulation rate.
Operation N: The ice crystal thickness is calculated from the ice crystal amount in operation M, the ice crystal growth rate in the concentrated liquid flow path is calculated from the ice crystal thickness, and the refrigerant is set so that the growth rate becomes a set value. To adjust the temperature and / or the circulation rate.

In operation M, the measured Brix value B ₀ before freeze concentration of the liquid to be concentrated, the measured Brix value B _n during freeze concentration, and the ice crystals in the flow path of the liquid to be concentrated predetermined according to the measured Brix value B _n and a ratio a _n of the solute to be incorporated in, obtaining the ice crystal amount in該被concentrate flow path. Since the shape and size of the concentrated liquid channel, for example, the diameter and length are known, the inner diameter of the ice crystal in the concentrated liquid channel is calculated from the obtained amount of ice crystals, and the inner diameter and the concentrated liquid are calculated. The required flow rate of the concentrated liquid in the concentrated liquid channel is calculated from the set value of the flow rate of the concentrated liquid in the flow channel, and the actual flow rate of the concentrated liquid in the concentrated liquid channel is calculated as the required flow rate. The circulation amount of the liquid to be concentrated is adjusted so that the flow rate is adjusted. In the operation N, the ice crystal thickness is calculated from the ice crystal amount in the operation M, the ice crystal growth rate in the concentrated liquid flow path is calculated from the ice crystal thickness, and the growth rate is a set value. The refrigerant temperature and / or circulation rate is adjusted so that

In the operation M, the ratio of the solute A _n taken into the ice crystals in the liquid channel to be concentrated can be determined in advance by the following method according to the measured Brix value B _n during freeze concentration. One method is to conduct preliminary freeze-concentration experiments in advance and measure the Brix value C ₁ of ice crystals when freeze-concentrated from the measured Brix value B ₀ to B _{1, and} then at C ₁ / B ₁ The ratio A _{1 of} the solute taken into the ice crystals is determined. Similarly, A when frozen concentrated from _{B 1 B A} 2 when frozen concentrated to _{2, B 2} from _{B 3 A} 3 when frozen concentrated to, to ... from the end _{B n-1} to _{B n Find n} . When actually freeze-concentrating, the measured Brix values B ₀ to B ₁ are A ₁ , B ₁ to B ₂ are A ₂ , B ₂ to B ₃ are A ₃ , and B _{n- 1} to _{B n} is a method of using the _{a n.} Other one way, from the data of _A 1 to A _n for said _B 1 .about.B _n, obtains an approximate expression for the variable _{B n} for calculating _{A n,} for example, _A n = a × _{B n} obtains an approximate expression such as -b, from such approximate expression determines the _{a n} in accordance with the measured Brix value _{B n} in freeze concentration.

  As the means for adjusting the circulation amount of the liquid to be concentrated in the operation M, various types of means can be used. However, a pump for circulating the liquid to be concentrated in the liquid channel to be concentrated, that is, the liquid to be concentrated It is preferable to control the rotation speed by controlling the frequency of the circulation pump. Further, as the means for adjusting the temperature of the refrigerant in the operation B, it is possible to use various types of means per se, but it is preferable to control the operation of a cooler for cooling the refrigerant, A refrigerant supplied from a refrigerant tank connected to a cooler for cooling the refrigerant to an inlet of the refrigerant channel, and the refrigerant channel discharged from the outlet of the refrigerant channel without passing through the refrigerant tank It is more preferable to control the flow rate of the refrigerant returned to the inlet. Further, as a means for adjusting the circulation amount of the refrigerant in the operation B, various methods can be used as such, but a pump for circulating the refrigerant in the refrigerant flow path, that is, a refrigerant circulation pump is used. It is preferable to control the rotation speed by controlling the frequency.

  According to the present invention, the refrigerant is circulated through the refrigerant flow path of the freeze concentrator while the liquid to be concentrated is circulated in the liquid concentrate flow path of the freeze concentrator, and ice crystals are formed on the wall surface of the liquid concentrate. By forming and growing sequentially, in the forward freeze concentration in which the concentrated solution is freeze-concentrated, ice crystals with a uniform thickness can be grown across the entire wall surface of the concentrated solution flow path of the freeze concentrator, This makes it possible to control the concentration rate of the concentrate at the freezing interface and the growth rate of ice crystals according to the set values. it can.

  FIG. 1 is a system diagram schematically illustrating an embodiment of the method of the present invention. A total of 20 double cylindrical tubes 11, 12,... 30 with the concentrated liquid passages 11a, 12a,... 30a formed on the inner side and the refrigerant flow paths 11b, 12b,. The concentrated liquid flow paths 11a, 12a,... 30a are connected in series to form one circulation flow path 11c. A supply container 41 for the liquid to be concentrated is disposed above the double cylindrical tubes 11 and 12, and the supply container 41 is connected to the circulation channel 11c. The refrigerant flow paths 11b, 12b,... 30b are connected in parallel with each other at the upper and lower parts thereof, and the refrigerant inlet is provided at the lower part and the refrigerant outlet is provided at the upper part. The inlet and outlet are connected to the cooler 51.

  A circulation channel 11c on the upstream side of the concentrated liquid channel 11a is provided with a pump 61 for circulating the concentrated liquid, and a refrigerant is interposed between the refrigerant inlet to the refrigerant channel 30b and the cooler 51. A circulation pump 62 is interposed. In addition, a sugar flow meter 71 and a flow meter 72 are interposed in the circulation flow path 11c on the downstream side of the liquid concentrate flow path 30a until reaching the pump 61, and the refrigerant to the pump 62 and the refrigerant flow path 30b. A thermometer 73 is interposed between the inlet and the inlet. The sugar content meter 71, the flow meter 72, and the thermometer 73 are connected to the calculation control device 81, and the calculation control device 81 is connected to the cooler 51 and the pump 61.

  In the system diagram schematically shown in FIG. 1, the liquid to be concentrated is fully poured from the supply container 41 into the circulation flow path 11c including the liquid flow paths 11a, 12a,. The pump 61 is operated to circulate the liquid to be concentrated in the circulation flow path 11c including the liquid concentrate flow paths 11a, 12a,... 30a by turning right, and the cooling machine 51 and the pump 62 are operated to cool the liquid. The refrigerant cooled by the machine 51 is circulated to the refrigerant flow paths 11b, 12b,. Ice crystals are sequentially formed and grow on the wall surfaces of the concentrated liquid flow paths 11a, 12a,... 30a, that is, the inner wall surfaces of the cylindrical tubes inside the double cylindrical tubes 11, 12,. Although it is concentrated, during such freeze concentration, the pump 61 is periodically reversed from normal rotation by a signal issued from the arithmetic and control unit 81, and if necessary, further reversed from normal rotation and then reversed from normal rotation again. . By the inversion of the pump 61, the liquid to be concentrated circulates in the left turn in the circulation channel 11c including the liquid channels 11a, 12a,.

First, in the system diagram of Figure 1 performs a preliminary freeze concentration experiments as described above, from the data of _A 1 to A _n for the resulting _B 1 .about.B _n, the approximation of _A n = a × _B n -b An expression is obtained (where _An is the ratio of the solute taken into the ice crystals during freeze concentration, B _n is the Brix value of the liquid to be concentrated during freeze concentration), and this approximate expression is input to the arithmetic and control unit 81. deep. During freeze concentration, the Brix value _{Bn of the} liquid to be concentrated is sequentially detected by the saccharimeter 71, and the signal is sequentially input to the arithmetic and control unit 81. The arithmetic and control unit 81, and the measured Brix value _{B 0} before freeze concentration of the concentrated liquid, and the measured Brix value _{B n} in freeze concentration, that when it is determined from the approximate expression in accordance with the measured Brix value _{B n} and a ratio a _n of the solute to be incorporated into the ice crystals, sequentially calculates the ice crystal volume.

  The set values of the flow rate of the liquid to be concentrated and the growth rate of ice crystals in the liquid channels to be concentrated 11a, 12a,... 30a are input in advance to the arithmetic and control unit 81. In the system diagram of FIG. .. 30a is calculated from the amount of ice crystals of the liquid and the concentration of the flow rate of the liquid to be concentrated in the liquid channels 11a, 12a,. The required flow rate of the liquid to be concentrated in the concentrated liquid channels 11a, 12a,... 30a is calculated, and the actual flow rate of the liquid to be concentrated in the concentrated liquid channels 11a, 12a,. The frequency of the pump 61 is controlled by a signal generated from the arithmetic and control unit 81 so as to obtain a flow rate, and the number of rotations is controlled to adjust the circulation amount of the liquid to be concentrated. At the same time, the ice crystal thickness in the concentrated liquid flow channels 11a, 12a,... 30a is calculated from the ice crystal amount, and the ice crystal growth rate is calculated from the thickness. Thus, the operation of the cooler 51 is controlled by a signal generated from the arithmetic and control unit 81, and the temperature of the refrigerant detected by the thermometer 73 is adjusted.

  FIG. 2 is a system diagram schematically illustrating another embodiment of the method of the present invention. Concentrated liquid flow paths 31a, 32a,... 40a are formed on the inner side and refrigerant flow paths 31b, 32b,. A total of ten double cylindrical tubes 31, 32,... 40 are formed as a pair, and a total of five sets are formed. In each set, the concentrated liquid flow paths of the double cylindrical tubes are connected in parallel. For example, in the double cylindrical pipes 31 and 32 forming one set, the concentrated liquid flow paths 31a and 32a are connected in parallel. However, the concentrated liquid passages are connected in series between the sets, and the concentrated liquid passages 31a, 32a,... 40a form one circulation passage 31c. . A supply container 42 for the liquid to be concentrated is disposed above the double cylindrical tubes 31 and 32, and the supply container 42 is connected to the circulation channel 31c. The refrigerant flow paths 31b, 32b,... 40b are connected in parallel and communicated at the upper and lower parts thereof, and the refrigerant inlet is provided at the lower part and the refrigerant outlet is provided at the upper part. Are connected to a refrigerant tank 53, and the refrigerant tank 53 is connected to a cooler 52.

  A circulation channel 31c on the upstream side of the liquid concentrate flow path 31a is provided with a pump 63 for circulating the liquid concentrate, and a refrigerant is interposed between the refrigerant inlet to the refrigerant flow path 40b and the refrigerant tank 53. A circulation pump 64 is interposed. Further, a sugar flow meter 74 and a flow meter 75 are interposed in the circulation flow path 31c on the downstream side of the concentrated liquid flow path 40a until reaching the pump 63, and the refrigerant to the pump 64 and the refrigerant flow path 40b. A thermometer 76 is interposed between the inlet and the inlet. A three-way valve 65 is interposed between the refrigerant outlet from the refrigerant flow path 40b and the refrigerant tank 53, and a bypass is passed from the three-way valve 65 to a connecting pipe connecting the refrigerant tank 53 and the pump 64. ing. The sugar meter 74, the flow meter 75, and the thermometer 76 are connected to the calculation control device 82, and the calculation control device 82 is connected to the pump 63 and the three-way valve 65.

  In the system diagram schematically shown in FIG. 2, the liquid to be concentrated is filled from the supply container 42 into the circulation flow path 31c including the liquid flow paths 31a, 32a,. The pump 63 is operated to circulate the liquid to be concentrated in the circulation flow path 31c including the liquid concentrate flow paths 31a, 32a,... 40a by turning right, and the cooling machine 52 and the pump 64 are operated to cool the liquid. The refrigerant cooled by the machine 52 is circulated through the refrigerant tank 53 to the refrigerant flow paths 31b, 32b,. Ice crystals are sequentially formed and grow on the wall surfaces of the concentrated liquid flow paths 31a, 32a,... 40a, that is, the inner wall surfaces of the cylindrical tubes inside the double cylindrical tubes 31, 32,. Although it is concentrated, during such freeze concentration, the pump 63 is periodically reversed from normal rotation by a signal issued from the arithmetic and control unit 82, and if necessary, it is further reversed from normal rotation and reversed from normal rotation again. . Due to the inversion of the pump 63, the liquid to be concentrated circulates in a counterclockwise direction in the circulation channel 31c including the liquid channels 31a, 32a,.

First, in the system diagram of FIG. 2 performs a preliminary freeze concentration experiments as described above, from the data of _A 1 to A _n for the resulting _B 1 .about.B _n, the approximation of _A n = a × _B n -b An expression is obtained (where _An is the ratio of the solute taken into the ice crystals during freeze concentration, B _n is the Brix value of the liquid to be concentrated during freeze concentration), and this approximate expression is input to the arithmetic and control unit 82. deep. During freeze concentration, the Brix value _{Bn of the} liquid to be concentrated is sequentially detected by the saccharimeter 74, and the signal is sequentially input to the arithmetic and control unit 82. The arithmetic and control unit 82, and the measured Brix value _{B 0} before freeze concentration of the concentrated liquid, and the measured Brix value _{B n} in freeze concentration, that when it is determined from the approximate expression in accordance with the measured Brix value _{B n} and a ratio a _n of the solute to be incorporated into the ice crystals, sequentially calculates the ice crystal volume.

  The preset values of the flow rate of the liquid to be concentrated and the growth rate of ice crystals in the liquid channels 31a, 32a,... 40a to be concentrated are previously input to the arithmetic and control unit 82. In the system diagram of FIG. The inner diameter of the ice crystals in the concentrated flow channels 31a, 32a,... 40a is calculated from the amount of ice crystals of the concentrated liquid crystal, and the flow rate of the concentrated liquid in the concentrated liquid channels 31a, 32a,. The required flow rate of the liquid to be concentrated in the concentrated liquid channels 31a, 32a,... 40a is calculated, and the actual flow rate of the liquid to be concentrated in the concentrated liquid channels 31a, 32a,. The frequency of the pump 63 is controlled by a signal generated from the arithmetic and control unit 82 so as to obtain a flow rate, thereby controlling the rotational speed and adjusting the circulation amount of the liquid to be concentrated. At the same time, the thickness of ice crystals in the concentrated liquid flow paths 31a, 32a,... 40a is calculated from the amount of ice crystals, and the growth rate of ice crystals is calculated from this thickness. In such a manner, the opening degree of the three-way valve 65 is adjusted by a signal issued from the arithmetic and control unit 82, and the flow rate of the refrigerant supplied from the refrigerant tank 53 to the inlet of the refrigerant passage 40b and the outlet of the refrigerant passage 40b are discharged. The temperature of the refrigerant detected by the thermometer 76 is adjusted by controlling the flow rate of the refrigerant returned to the inlet of the refrigerant flow path 40b via the three-way valve 65 and the bypass without reaching the refrigerant tank 53. To do.

Example According to the system diagram described above with reference to FIG. 1, the liquid to be concentrated was frozen and concentrated under the following conditions.
Concentrated liquid: water, isomerized sugar aqueous solution adjusted to Brix 3.0, and isomerized sugar aqueous solution adjusted to Brix 10.0 Refrigerant: Mixed liquid mainly composed of propylene glycol NFP) 83% aqueous solution Set value of flow rate of concentrated liquid in concentrated liquid flow path: 2.0 m / s
Set value of ice crystal growth rate in the concentrated liquid flow path: 8.0 mm / h
Freeze concentration Time: 30 minutes pump 61 in the forward and the approximate using a total of 60 minutes of 30 minutes inversion formula: the concentrate _A n = 0 in the case of water, the isomerized sugar aqueous solution adjusted to Brix3.0 _a n = 0.0096 × _B n -0.043 _{if, a n = 0.0108 × B n} -0.053 (a n in the case of isomerized sugar aqueous solution adjusted to Brix10.0 during freeze concentration The ratio of the solute taken into the ice crystals, _Bn is the Brix of the liquid to be concentrated during freeze concentration)
Note that the above approximate expression is obtained by subjecting the aqueous isomerized sugar solution adjusted to Brix 3.0 or 10.0 to the same preliminary freeze concentration experiment, and in the case of the aqueous isomerized sugar solution adjusted to Brix 3.0, the first time Obtained from Brix 3.0 to Brix 4.5, the second time from the results of Table 1 below when freeze-concentrated from Brix 4.5 to Brix 6.8, and in the case of an isomerized sugar aqueous solution adjusted to Brix 10.0, the first time Was obtained from the results in Table 1 below when freeze-concentrated from Brix10.0 to Brix14.7 and secondly from Brix14.7 to Brix22.6.

Comparative Example As a whole, as in the example, except that the pump 61 was not inverted during freeze concentration, and the liquid to be concentrated was frozen and concentrated while maintaining normal rotation.

  After freeze concentration, the thickness of ice crystals formed on the wall surfaces of the concentrated liquid passages 11a, 12a,... 30a of a total of 20 double cylindrical tubes 11, 12,. It was shown to.

  FIG. 3 is a graph showing the results during freeze concentration when the aqueous isomerized sugar solution adjusted to Brix 10.0 in the above-described Examples was freeze concentrated. The horizontal axis shows the freeze concentration time (min), the left vertical axis shows the calculated ice crystal growth rate (mm / h) in the concentrated liquid flow path, and the right vertical axis shows the pump 61. The discharge pressure (MPa) is graduated. A line A connecting the white circles in the figure indicates the calculated ice crystal growth rate (mm / h), and a line B connecting the black circles indicates the discharge pressure (MPa) of the pump 61. The broken line C indicates the set value of the ice crystal growth rate (mm / h).

  Table 3 shows the result of freeze concentration when the isomerized sugar aqueous solution adjusted to Brix 10.0 in the above-described Examples and Comparative Examples was freeze concentrated. The partition coefficient in Table 3 is a value determined by Brix (%) of ice crystals / [{Brix (%) of the concentrate before freeze concentration + Brix (%) of the concentrate after freeze concentration} / 2]. The higher this value is, the higher the solute uptake rate into ice crystals, and the lower this value is, the lower the solute uptake rate into ice crystals is. This means that freeze concentration has not progressed at all.

  From the results of Table 2, FIG. 3 and Table 3, according to the present invention, ice crystals having a uniform thickness can be grown over the entire wall surface of the liquid flow path of the concentrate to be frozen. It can be understood that the flow rate of the liquid to be concentrated at the freezing interface and the growth rate of ice crystals at the freezing interface can be controlled as set values, so that the liquid to be concentrated can be freeze-concentrated efficiently.

FIG. 2 is a system diagram schematically showing an embodiment of the method of the present invention. FIG. 3 is a system diagram schematically illustrating another embodiment of the method of the present invention. The graph which illustrates the result during freeze concentration in the method of the present invention.

Explanation of symbols

11-40 Double cylindrical tube 11a-40a Concentrated liquid flow path 11b-40b Refrigerant flow path 11c, 31c Circulation flow path 41, 42 Supply container 51, 52 Cooling machine 53 Refrigerant tank 61-64 Pump 65 Three-way valve 71, 74 Sugar meter 72,75 Flow meter 73,76 Thermometer 81,82 Arithmetic control device

Claims (11)

  While circulating the concentrate to the concentrate flow path of the freeze concentrator, the refrigerant is circulated through the refrigerant flow path of the freeze concentrator, and ice crystals are sequentially formed on the wall of the concentrate to grow. In the forward freeze concentration in which the concentrated solution is freeze-concentrated, the forward freeze concentration method is characterized by changing the circulation direction of the concentrated solution in the concentrated solution flow path during the freeze concentration of the concentrated solution. .   2. The forward freeze concentration method according to claim 1, wherein a circulation direction of the concentrated liquid in the concentrated liquid flow path is periodically changed during freeze concentration of the concentrated liquid.   3. The forward freeze concentration method according to claim 1 or 2, wherein a circulation direction of the concentrated liquid in the concentrated liquid flow path is changed one or more odd times during freeze concentration of the concentrated liquid.   The freeze concentrator is equipped with two or more multiple cylindrical tubes, the concentrated liquid flow paths of the multiple cylindrical tubes are connected in series as a whole, and the refrigerant flow paths of the multiple cylindrical tubes are connected in parallel as a whole The forward freeze concentration method according to any one of claims 1 to 3, wherein the method is a forward freeze concentration method.   5. The forward freeze concentration according to claim 4, wherein the multi-tubular tube is a double cylindrical tube, and each double cylindrical tube has a concentrated liquid flow path formed inside and a refrigerant flow path formed outside. Method.   The flow rate of the concentrated liquid in the concentrated liquid flow path is controlled by adjusting the circulation amount of the concentrated liquid in the concentrated liquid flow path of the freeze concentrator, and the refrigerant flow rate in the refrigerant flow path of the frozen concentrated condenser is controlled. The forward freeze concentration method according to any one of claims 1 to 5, wherein a growth rate of ice crystals in the concentrated liquid flow path is controlled by adjusting a temperature and / or a circulation amount. The circulation amount of the liquid to be concentrated in the concentrated liquid passage of the freeze concentrator is adjusted according to the following operation M, and the temperature and / or circulation amount of the refrigerant in the refrigerant flow path of the freeze concentrator is adjusted as follows. The forward freeze concentration method according to claim 6, which is performed according to operation N.
Operation M: The measured Brix value B ₀ before concentration of the concentrated liquid, the measured Brix value B _n during freeze concentration, and the ice crystals of the concentrated liquid flow path determined in advance according to the measured Brix value B _n determine the ice crystals amount and a ratio a _n of the solute in該被concentrate flow path, calculates the inner diameter of the ice crystals from the ice crystal volume, the flow rate of該被concentrate in said inner and該被concentrate passage To calculate the required flow rate of the liquid to be concentrated in the flow path of the concentrated liquid from the set value of Operation to adjust the circulation rate.
Operation N: The ice crystal thickness is calculated from the ice crystal amount in operation M, the ice crystal growth rate in the concentrated liquid flow path is calculated from the ice crystal thickness, and the refrigerant is set so that the growth rate becomes a set value. To adjust the temperature and / or the circulation rate.   The forward freezing and concentration method according to claim 7, wherein the adjustment of the circulation amount of the liquid to be concentrated in the operation M is based on a rotational speed control by a frequency control of a pump for circulating the liquid to be concentrated in the liquid channel to be concentrated.   The forward freeze concentration method according to claim 7 or 8, wherein the adjustment of the temperature of the refrigerant in the operation N is based on operation control of a cooler for cooling the refrigerant.   The adjustment of the temperature of the refrigerant in the operation N includes the refrigerant supplied from the refrigerant tank connected to the cooler to the inlet of the refrigerant flow path, and the refrigerant discharged from the outlet of the refrigerant flow path without passing through the refrigerant tank. The forward freezing and concentrating method according to claim 7 or 8, which is based on flow rate control with the refrigerant returned to the inlet of the refrigerant flow path.   The forward freeze concentration according to any one of claims 7 to 10, wherein the adjustment of the circulation amount of the refrigerant in the operation N is based on a rotational speed control by a frequency control of a pump for circulating the refrigerant in the refrigerant flow path. Method.

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