JPH0627624B2 - Freeze dryer for liquid substances - Google Patents

Description

TECHNICAL FIELD The present invention relates to an apparatus for freeze-drying a liquid substance having a high added value such as foods, pharmaceuticals, industrial chemicals, ceramics and magnetic materials, and particularly freeze-drying is the same. It is characterized in that it is performed under reduced pressure.

(Prior Art) A continuous freeze-drying device comprises a freezing device and a vacuum drying device, in which a liquid substance is first frozen and then transferred to a vacuum drying device for drying.

Since this apparatus can efficiently dry the material without degrading the material, it is suitable for drying a high value-added liquid material such as foods, pharmaceuticals, industrial chemicals, ceramics and magnetic materials.

(Problems of the conventional technique) On the other hand, in the conventional device, the freezing device operates at normal pressure and there is a large pressure difference from the drying device. Therefore, an airlock device is provided between the freezing device and the drying device. Therefore, it is necessary to install a supply device for the frozen material from the freezing device to the airlock device and a supply hopper from the airlock device to the vacuum drying device, which makes the device complicated and increases the equipment cost. there were.

The above-mentioned conventional continuous freezing device is a rotating drum type freezing device or a belt conveyor type freezing device.However, in this device, the cooling of the liquid substance is performed by heat conduction between the liquid substance and the rotating drum or the conveyor belt, so the freezing capacity is 25 It is as small as ~ 60kg / m ² · hr, and it requires heat removal of about 115kcal / kgH ₂ O to cool water at room temperature (20 ° C) to -30 ° C, which increases cooling cost. It will be.

Needless to say, a reduced-pressure freezing device such as a spray-drying freezing device has also been used in the past. However, this device does not require a cooling device, but the liquid material is limited to those that can be sprayed, and it is suitable for dusting processing and self-freezing. The size of the device becomes large in order to keep the required time.

In addition, in the conventional continuous freeze-drying device, either the radiant heating method or the conduction heating method was adopted as the heating method for the vacuum drying apparatus.However, in the case of the radiant heating method, the heating temperature is increased to increase the drying capacity. If the temperature is raised, the surface portion of the material to be dried will be deteriorated or burned, leading to deterioration of the product, so that the temperature cannot be raised above a certain level. Especially in the latter half of drying (decrease rate drying period), the temperature of the heating plate must be lowered to about 80-100 ° C.
The drying speed will be extremely reduced. In addition, in the case of the conduction heating method, if the temperature of the heating plate is raised to raise the initial temperature, the part in contact with the heating surface may deteriorate the product or adhere to the belt etc. depending on the material. Therefore, it is difficult to raise the temperature of the heating section to the permissible quality temperature.

(Means for Solving Problems) The present invention has been made in view of the above points, and is one in which a liquid material is frozen in a freezing chamber having the same degree of vacuum as a vacuum dryer, for example, rotary cylinder cooling. The drum is installed in the freezing chamber, and the liquid material is supplied and applied on the surface of the drum to freeze the liquid by self-evaporation and conduction cooling. The frozen material is scraped off with a scraper on the drum surface,
Flake-shaped frozen particles are obtained. However, in addition to increasing the freezing efficiency of the liquid material, the freezing device is directly connected to the vacuum drying device to form the airlock device and the supply hopper attached to it, simplifying the device and reducing equipment costs and operating costs. In addition, the vacuum drying device uses both the conduction heating method and the radiant heating method, and the conveyor belt is equipped with a stirring mechanism to enable efficient drying at high temperatures.

(Example) In the figure, reference numeral 1 is a freezing device, and 2 is a vacuum drying device. The freezing device 1 uses both conduction cooling and self-evaporation, and the freezing chamber 3 is provided with a cooling drum 4 and a vacuum pump.
14 are connected. The liquid material is conductively cooled by the cooling drum 4, and the refrigerator 5 is connected to the cooling drum 4. The brine liquid is fed into the cooling drum 4 to lower the surface temperature thereof to about -30 ° C. In addition, a liquid injection nozzle 6 is attached to the upper portion of the drum 4, and the liquid material fed by the liquid feed pump 7 is evenly poured and applied onto the surface of the cooling drum 4. It is supposed to do. Also a vacuum pump
Reference numeral 14 is designed to reduce the pressure in the freezing chamber 3 to about 0.1 to 1 torr to promote evaporation of water in the liquid material poured onto the cooling drum 4.

The vacuum drying device 2 is a belt conveyor type drying device that uses both conductive heating and radiant heating. A belt conveyor 9 is provided in the drying chamber 8 and a belt is provided below the transfer surface of the belt conveyor 9 so as to contact the belt. A conduction heating plate 10 is attached to heat the belt to about -20 to 120 ° C., and a radiant heating plate 11 is attached to the upper part of the conveyor toward the transfer surface. The material to be dried is irradiated with heat rays of about 100 to 200 ° C.

This is a 12-rotation bar type agitator. This one makes it possible to raise the heating temperature by stirring the material to be dried placed on the belt conveyor 9 to eliminate heating unevenness, and to suppress the possibility of product deterioration due to overheating and adhesion to the belt. , To improve the heating efficiency.

By the way, the freezing chamber 3 is directly attached to the upper surface of the starting end portion of the vacuum drying chamber 8, and the two chambers communicate with each other. Therefore, the internal pressures of both chambers are the same, and the liquid material fed into the freezing chamber 3 is frozen here and then dropped directly onto the vacuum drying chamber 9 as the material to be dried.

(Operation) Bringing the brine liquid into the cooling drum 4 to reduce the surface temperature thereof-
Cooling to about 30 ° C. and operating the vacuum pump 14 to reduce the pressure in the freezing chamber 3 and the vacuum drying chamber 8 to 1 torr or less, and then operate the liquid feed pump 7 to direct the liquid nozzle 6 toward the cooling drum 4. Pour the prescribed amount of liquid material evenly.
Then, the liquid material is deprived of heat by the cooling drum 4 to lower the temperature. At the same time, the water content in the material evaporates,
The heat of evaporation further lowers the temperature, and eventually freezing. Then, this is scraped off by the scraper 13 and put on the belt conveyor 9 of the vacuum drying device 2 as a flake-like freeze-drying material.

In the vacuum drying apparatus 2, the material to be dried is agitated by the agitator 12 and heated by conduction heating from the conveyor belt and radiant heating from the radiant heating plate 11 and gradually dried to be a dried product and taken out of the system. Is done.

(Experimental example) In a freezing device, a rotating cylindrical drum was cooled to -30 ° C, and 0.4 to 0.
Place in a vacuum of 5 torr, water, dextrin 15%, 30%,
A 40% aqueous solution, a 45% aqueous ferrite solution, and a 15% lactose aqueous solution were supplied, and all of them could produce a freezing capacity of 400 kg / m ² · hr. When operated under atmospheric pressure with the same device,
It has a freezing capacity of kg / m ² · hr, and it was possible to obtain a capacity almost 16 times by operating under vacuum.

In a vacuum dryer, when a 15% aqueous lactose solution was frozen in the freezer and conductively dried, the conductive heating plate was heated to 40 ° C or higher to cause adhesion, and the drying capacity during the constant rate period was 1 kg. H ₂ O / m ² · hr
It will be about. When this material is radiantly heated at 180 ° C, the drying capacity during the constant rate period is 2.2 kg · H ₂ O / m ² · hr. Approximately 3 kg by using conduction and radiation together
・ It was possible to maintain the drying capacity of H ₂ O / m ² · hr. In addition, as a result of a dry test of a frozen substance using a dextrin 15% aqueous solution using the same freezing device (in the case of dextrin, adhesion does not occur even if the temperature of the conduction heating plate is raised to about 100 ° C from the beginning), conduction heating At 100 ° C,
The drying capacity (evaporation capacity) was 2.6 kg · H ₂ O / m ² · hr in the constant rate drying period, but the combined use of radiant heating at 100 ° C resulted in a drying capacity of 3.5%. We were able to raise to kg · H ₂ O / m ² · hr.

Also, during the rate-decreasing drying period, a 15% aqueous solution of dextrin was frozen in the same freezer at 100 ° C for conduction heating only, and for both conduction and radiation heating at 100 ° C. As a result of comparison, the average drying capacity during the reduction period was 1.9 kg · H ₂ O / m ² · hr, and there was almost no difference. By the way, in the case of only radiant heating at 100 ° C, the average drying capacity during the reduction period was 0.8 kg · H ₂ O / m ² · hr, which was extremely small.

If a 15% aqueous solution of dextrin is frozen in the same freezing device by conducting conduction heating at 100 ° C and drying is not performed, the constant rate drying period is 56.7% D.I. B to water 20
0% D. However, when stirring is performed, 80 to 100% D.I.
B, and the average drying capacity during constant rate period (up to 100% DB) can be increased from 1.8kg ・ H ₂ O / m ²・ hr to 2.6kg ・ H ₂ O / m ²・ hr. It was Also, the average drying capacity during the rate reduction period (100% DB or less) is from 0.6 kg ・ H ₂ O / m ²・ hr to 1.9 kg ・
I was able to raise it to H ₂ O / m ² · hr. In addition, the effect of stirring not only increases the drying capacity, but also has the effect of uniformly heating, which results in improvement in quality by suppressing unevenness in water content. The effect of using radiant heating and conduction heating together in a constant rate period is that, in addition to the above-mentioned effect, even if the particle size distribution of frozen particles is wider than in the case of only conduction heating, uniform heating is possible,
Even in actual experiments, some lumps (about 5 mm) in the material
Even with this, it was possible to suppress unevenness in water content.

(Effects) As described in detail above, according to the present invention, the freezing chamber 3 of the freezing device 1 is decompressed so that the liquid material is frozen by the combined use of conduction cooling and self-evaporation. The freezing capacity is increased to 5 to 10 times as compared with the cooling drum type freezing device, and the vacuum drying device 2 uses both conduction heating and radiant heating, and a stirrer 12 is attached to prevent local heating of the material to be dried. The heating efficiency can be increased by increasing the heating temperature, and the freezing chamber 3 is directly connected to the vacuum drying chamber 8 by making the freezing chamber 3 and the vacuum drying chamber 8 have the same pressure. By connecting, eliminating the air lock device and other intermediate devices, greatly simplifying the entire device,
The equipment cost is reduced and the operating rate of the equipment is increased.

That is, in the freezing device, by reducing the pressure in the freezing chamber 3 to 1 torr or less, the moisture in the material evaporates and self-freezes, so that the cooling capacity per unit area of the cooling drum 4 is 200 to 4
It will be 00 kg / m ² · hr. Moreover, in most liquid materials, 80 to 90% of the removal heat amount required for freezing is due to self-freezing, so the capacity of the refrigerator 5 can be made significantly smaller than in the case of the normal pressure type, and especially the material that is easily frozen. Since conduction cooling can also be omitted, the device is further simplified and the consumption of cooling energy is reduced.
In the figure, the freezing device 1 and the vacuum pump 14 are connected to a collector 15
An example in which the liquid material is attached is shown. However, since the liquid material is poured into the cooling drum 4, there is no dust scattering unlike the conventional spray freezing device. It is possible to supply high materials and materials with high solid content concentration, and the range of application of materials is widened.

In addition, the vacuum drying device has 10 materials to be dried.
Since the water content of ~ 20% is reduced during the freezing process, the equipment can be made smaller, and radiation and conduction heating are sampled during the constant rate drying period, and the conduction heating method is used during the rate drying period. Therefore, in the constant rate drying period, even if the material that easily adheres to the belt is operated by lowering the temperature of the conduction heating plate (-20 ℃ to 40 ℃), the drying capacity is maintained by the radiant heating from the top. It is possible to evaporate 3 to 4 kg · H ₂ O / m ² · hr with the addition of drying by conduction heating without extremely increasing the radiant heating temperature. Also, in the rate-decreasing period, radiation heating reduces the emissivity of the material,
Also, in order to avoid quality deterioration of the material, the drying capacity is drastically reduced due to the reduction of the heat dose by lowering the radiant heating temperature, but the conduction heating method is adopted and the conduction mechanism is provided by the stirring mechanism or the rocking mechanism. The heating temperature can be raised to around 100 ° C (the particle surface is dry during the rate-decreasing drying period, and the belt does not adhere), and the drying capacity can be maintained nearly twice that of radiant heating.

Incidentally, the reason why radiant heating is not adopted in the rate-decreasing drying period is that the contribution to drying is smaller than that of conduction as described above,
By avoiding the complexity of the device.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention, and FIG. 2 is a system diagram showing the main part of the same. 1; Freezing device, 2; Vacuum drying device 3; Freezing chamber, 4; Cooling drum 5; Freezer, 6; Injection nozzle 7; Liquid feed pump, 8; Drying chamber 9; Belt conveyor, 10; Conductive heating plate 11 Radiant heating plate, 12; stirrer 13; scraper, 14; vacuum pump 15; collector

Claims (1)

[Claims] 1. A vacuum pump is connected to a freezing chamber and a rotary cooling drum is provided in the freezing chamber. A liquid material is applied to the surface of the cooling drum, the liquid material is frozen by conduction cooling and self-evaporation, and scraped by a scraper. The freezing chamber of the above freezing device is directly connected to the drying chamber of the vacuum drying device which has a radiant heating plate and a conduction heating plate and has a stirrer for the material to be dried, and the freezing chamber and the drying chamber are 1 torr or less. A freeze-drying device for liquid substances, characterized in that the same pressure is applied.