RU2276313C2 - Device for liquid concentration and sublimation drying - Google Patents

Abstract

FIELD: food, microbiological and chemical industries, applicable for sublimation concentration and drying of frozen aqueous solutions or suspensions, sublimation drying of frozen food products, as well as for concentration or drying of liquid solutions and suspensions.

SUBSTANCE: dehydration of the product under drying is accomplished by its engagement with a liquid drying agent with high depression characteristics by a free mass transfer through a vapor phase in the conditions of a high rarefaction, for evaporation of moisture from the product being dried use is made of the heat of moisture absorption by the liquid drying agent transferred through the heat-conducting walls separating the product under drying from the drying agent.

EFFECT: reduced power consumption.

6 cl, 2 dwg

Description

The invention relates to the field of food, microbiological and chemical industries and can be used for freeze-drying and drying of frozen aqueous solutions or suspensions, freeze-drying of frozen food products, as well as for concentration or drying of liquid solutions and suspensions.

A freeze-drying device is known, comprising a vacuum chamber in which open containers with a frozen, dried product are located; heating elements that transfer heat to the dried product for evaporation (sublimation) of moisture from it; a desublimator in which condensation (desublimation) of evaporated moisture occurs; and a vacuum pump supporting vacuum in the vacuum chamber and desublimator. This device can also be used for liquid concentration. The operation of this device is as follows: the heat required to evaporate moisture from a frozen product is transferred to the product from an external source, after which the evaporated moisture is forcibly (with energy costs) condensed in a desublimator. The maximum concentration or drying rate is achieved when the gas phase consists only of water vapor, so the process is carried out under conditions of high vacuum.

The disadvantages of this device are: significant energy consumption for evaporation of moisture from the dried product, the difficulty of uniform distribution of heat supplied throughout the volume of the product located in the vacuum chamber, as well as significant energy consumption and the complexity of equipment for condensation of evaporated moisture.

(See. Kamovnikov. "Vacuum-freeze-drying food" M., 1985)

The aim of the invention is the elimination of energy consumption for evaporation and condensation of moisture during the drying process and the simplification of the design of the installation.

The goal is achieved in that in a device for liquid concentration and freeze-drying containing a vacuum chamber, in which open containers with a dried product are located, according to the invention, the dried product is dehydrated by its interaction with a liquid drying agent located in open containers located in a vacuum chamber , by free mass transfer through the gas phase and heat transfer through solid partitions separating the product to be dried and the drying agent, under conditions low vacuum, and for the evaporation of moisture from the dried product, the heat of moisture absorption by the liquid drying agent is used, transmitted through the heat-conducting walls separating the dried product from the drying agent.

As a drying agent, preferably, a salt-water solution with a degree of temperature depression exceeding the degree of temperature depression of the product to be dried, for example, a concentrated solution of calcium chloride or lithium bromide, can be used. A high degree of temperature depression of the drying agent means that at the same temperature the equilibrium pressure of the water vapor above the drying agent is lower than the equilibrium pressure of the water vapor above the drying product.

Recovery of the depression characteristics of the spent drying agent (regeneration) is preferably carried out by boiling it in a closed boiler (steam generator), and the steam released is used as a conditioned product with high heat content.

Vacuum in the vacuum chamber can be created by a vacuum pump, and in the chamber a continuous change of spent drying agent to a fresh one can be performed.

The process temperature can be controlled by vacuum in the vacuum chamber using a vacuum pump, or by the temperature of the supplied drying agent.

The use of the claimed invention allows to simplify the design of the freeze-drying device, to increase reliability and reduce irreversible energy costs for its operation.

The invention is illustrated by drawings, where in Fig.1 shows the operation of the device on the example of a unit tank with a drained product located in a vacuum chamber; figure 2 shows the General technological scheme of a variant of a device for liquid concentration and freeze-drying.

The device comprises a vacuum chamber 1, a block of pallets 2 with tanks 3, a liquid pump 4, a heat exchanger 5, a boiler 6, a throttle valve 7, a distribution manifold 8 and a vacuum pump 9.

The operation of the device is as follows.

Drained product 10 is distributed among containers 3 (trough-shaped), which are installed in pallets 2. Pallets 2 are folded into a block and placed in a vacuum chamber 1, from which air is removed by a vacuum pump 9. The drying agent 11 through the throttle valve 7 and the distribution manifold 8 is fed into the pallets 2, flows by gravity to the other edge of the pallets and flows to the lower part of the vacuum chamber 1. As the pallets 2 flow through, the drying agent absorbs water vapor contained in the vacuum chamber, very warming up. The heat of absorption of moisture is transferred to the drained product 10, where it is expended on the evaporation of moisture from the product. Heat is transferred either through the walls of the tank 3, or indirectly: from the drying agent 11 to the walls and bottom of the pan 2, through them to the bottom and walls of the tank 3, and then to the dried product 10. The moisture evaporated from the product is again absorbed by the drying agent, completing the cycle. As moisture is saturated, the depressive characteristics of the drying agent decrease and it needs regeneration.

A drying agent with reduced depression characteristics from the lower part of the vacuum chamber 1 is pumped through a heat exchanger 5 to a boiler (steam generator) 6 through a heat exchanger 5, in which part of the water is removed from it and, accordingly, its depression characteristics are restored. The heat spent on the regeneration of the drying agent is almost completely transferred to the conditioned product - steam and is used to solve other technological problems. The regenerated drying agent through the heat exchanger 5, the throttle valve 7 and the distribution manifold 8 is returned to the vacuum chamber on the trays 2.

The temperature of the processes in the vacuum chamber is controlled by the temperature of the supplied drying agent or by adjusting the water vapor pressure by the operation of the vacuum pump.

To carry out the freeze-drying process, the drained product 10 is pre-frozen. Freezing is carried out either by pumping water vapor from the vacuum chamber with a vacuum pump 9, or by using a liquid drying agent 11 cooled to sub-zero temperatures, supplied to the trays.

Claims (6)

1. A device for liquid concentration and freeze-drying, containing a vacuum chamber in which open containers with a drained product are located, characterized in that the dehydrated product is dehydrated by its interaction with a liquid drying agent located in open containers located in a vacuum chamber by mass transfer through gas phase and heat transfer through solid partitions separating the product to be dried and the drying agent. 2. The device according to claim 1, characterized in that a water-salt solution with a degree of temperature depression exceeding the degree of temperature depression of the drained product is used as a drying agent. 3. The device according to claim 1, characterized in that the vacuum in the vacuum chamber is created using a vacuum pump. 4. The device according to claim 1, characterized in that in the vacuum chamber there is a constant change of the spent drying agent to a fresh one. 5. The device according to claim 1, characterized in that the regeneration of the drying agent is carried out by boiling it in a closed boiler (steam generator), and the released steam is used as a conditioned product with high heat content. 6. The device according to claim 1, characterized in that the process temperature is controlled by vacuum in the vacuum chamber using a vacuum pump or the temperature of the supplied drying agent.

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