Method for vacuum sublimation drying with convective input of thermal energy and vacuum sublimation drying installation

FIELD: food industry.

SUBSTANCE: invention relates to food industry. In accordance with the method proposed evaporation of a liquid hydrophobic working medium is performed. The working medium vapours, moving as a result of differential pressure, are heated and passed through a layer of frozen product being dried. This process is performed one or several times, passing heated working medium vapours through, accordingly, one or several layers of frozen product being dried. The produced mixture of water vapours and working medium vapours is passed through one or more desublimators/absorbers where desublimation/absorption of water vapours from the mixture is performed. One performs condensation of working medium vapours and liquid working medium return to the process beginning. The working medium is represented by a low-boiling liquid or an easily liquefied gas. Proposed is a device for the method implementation.

EFFECT: usage of this group of inventions enables drying time reduction and prevention of contact of the product being dried with atmospheric oxygen.

10 cl, 1 dwg

 

The invention relates to the field of food, microbiological and chemical industry and can be used for freeze-drying of frozen solutions or suspensions, freeze-drying the frozen food.

The known method of atmospheric freeze-drying, in which a layer frozen moisture-containing product blow hot air with a low partial pressure of water vapor. Passing through the layer of product, the air gives up heat energy to the frozen product, which is spent on sublimation evaporation of moisture from the product. Exiting product cooled air with a high content of water vapor fed to the evaporator of the refrigeration unit (desublimator), the surface of which is desublimate airborne moisture. The cooled and dehumidified air is heated and again served in the layer of frozen product. The air supply is carried out by natural circulation (free convection) or by using an air blower (forced convection).

The disadvantage of this method is a significant drying time and reduce the quality of dried product due to long-term contact of the dried product with oxygen.

(See Semenov, G.V., Kasyanov GI "raw material Drying: m is co, fish, vegetables, fruits, milk" study and practice guide. Series "Technology of food production". Rostov n/D: publishing center "March", 2002, s-87).

The technical result achieved by the invention is the reduction of the drying time and prevent contact drying of the product with oxygen.

The technical result is achieved by a method of vacuum freeze-drying with the convective supply of thermal energy to the dried product is that the system vacuumized cameras in terms of dilution:

a) carry out the evaporation of the hydrophobic liquid working fluid;

b) moving under the action of pressure difference of the pair of the working fluid is heated using the heater and passed through a layer of frozen dried product, this process is carried out once or several times, passing the heated vapors of the working fluid respectively through one or more layers of frozen dried product;

c) the resulting mixture of water vapor and vapor of the working fluid is passed through one or more desublimation/absorbers, which are desublimation/absorption of water vapor from the mixture;

d) are dehydrated condensation of vapors of the working fluid;

e) returns the liquid working fluid for the process "a"; the TP is t working fluid in the evaporation zone by gravity or by means of a pump.

As the working fluid used low-boiling liquid or legositigames gas, insoluble or slightly soluble in water, such as butane, pentane, hexane and its isomers.

The partial pressure of water vapor in all areas of the system vacuumized cameras support at a level not exceeding the equilibrium partial pressure of water vapor over the frozen dried product.

To heat the vapor of the working fluid in the coils use high-grade thermal energy source or use a heat pump that uses as a source of low-grade thermal energy heat of desublimation/absorption of water vapor in desublimator/absorbers.

Evaporation of the working fluid is preferably carried out due to the energy of condensation of the vapor of the working fluid, the heat capacity of which increases by the heat pump.

The temperature of desublimation/absorbers, Desublimers/absorbing water vapor from the stream of vapor of the working fluid, is maintained at the level at which there is no condensation of vapor of the working fluid on the surfaces of desublimator/absorber, i.e. at a level higher than the temperature of the condensing vapor of the working fluid at an operating pressure in desublimator/absorber.

The absorption of water vapor from the vapor mixture is performed chilled antifreeze RA is tworoom electrolyte, for example, a solution of calcium chloride, chloride or lithium bromide.

The technical result is achieved in that the vacuum freeze-drying with convection heat supply to the product contains the evaporator, the working fluid, multiple heaters to heat the vapor of the working fluid, several vacuumized drying chambers (vessels), which is frozen dried product, one or more desublimation/absorbers for selective desublimate/absorption of water vapor from the stream of vapor of the working fluid, and a condenser for the working fluid, forming a total sealed system, and the vacuum pump is enabled in the system depression; as a working body of the setup used boiling hydrophobic agent, such as butane, pentane, hexane and their isomers.

The drying chamber is connected in series to each other along the vapor of the working fluid before each drying chamber is at least one of the heater.

The condenser the working fluid preferably connected by a heat pump with an evaporator working fluid is further cooled by the refrigeration unit.

The use of the claimed invention would eliminate the contact of the dried product with oxygen. Will provide high speed and uniformity of dive torches etc who and thermal energy for drying the product through the use of forced convective heat energy is transferred to the product by using the vapor of the working fluid. Provide a high speed exhaust released from the product of water vapor due to the high volumetric flow rate of dilute vapor of the working fluid. High volume flow rate of the vapor of the working fluid is provided a low density vapor of the working fluid and a significant pressure difference between the evaporation zone and the condensation zone of the working fluid. High (dwuhtsepochechny) the differential pressure is provided by a small (10-15C) temperature difference between the evaporation zone and the condensation zone of a working body that will allow you to return the condensation heat of the vapor of the working fluid in the evaporation zone by means of a heat pump. High volumetric flow rate will increase the coefficient of heat transfer from the coil pairs of the working fluid and the heat transfer coefficient from the vapor of the working fluid to the granules (particles) drying of the product.

The invention is illustrated by the drawing, which shows a variant of vacuum freeze-drying with convection heat supply to the product.

The installation contains a group of drying chambers 1 with frozen dried product and the heaters 2, the low-temperature heater 3, the absorbers 4 and 5 with a cooled coils 6 and 7, the capacitor 8 with a cooled coil 9, the evaporator 10 with the heating coil 11 and a cooling coil 12, the pump 13 to 15, the compressor 16, vacuumn the second pump 17, throttle valves 18 and 19, control valves 20 and 21, the hydraulic lock 22, refrigeration units 23 and 24. As the working fluid applied pentane. In the absorbers 4 and 5 are served antifreeze water solution 25 and 27, which are in the form of dilute solutions 26 and 28 are discharged installation.

The installation is carried out as follows.

Liquid pentane is withdrawn from the lower portion of the evaporator 10 and the pump 15 through a distribution device is returned to the inside of the evaporator 10, moistening the surface of the heating coil 11 of the evaporator. On the surface of the coil 11 of the evaporator is boiling pentane, the resulting pentane vapor passes through the cooling coil 12 of the evaporator, which is part of the pentane vapor condenses and flows down to the lower area of the evaporator 10. Passed through the coil 12 pairs of pentane heated in the low temperature heater 3, and then heated in high temperature heater 2 and pass through the frozen layer drying of the product in the drying chamber 1. In the chamber 1 is heated pair of pentane partially cooled, transferring warmth to the frozen moisture in the product. Under the action of the obtained heat part of the frozen moisture sublimates. The resulting mixture of pentane vapor and water vapor is again heated in the following in the course of the heater and again p is uhodit through the camera with frozen dried product. This process is repeated N times, after which the mixture pentane vapor and water vapor is supplied to the absorber 4, the cooling coil 6 which is continuously wetted by a weak antifreeze water solution of lithium chloride (widely used in air conditioning systems) or calcium chloride. Continuously cooled solution absorbs the main part of the water vapor from flowing through the coil 6 steam mixture. The circulation of the solution is ensured by the pump 13, which also provides continuous removal of a portion of the circulating solution 26 on regeneration - removing the absorbed moisture. The regenerated solution 25 is returned to the absorber 4.

Released from the absorber 4 steam mixture with a low content of water vapor enters the combined group of devices - absorber 5 and the capacitor 8, which is fully separate the absorption of water vapor and the condensation of the vapors of pentane. Non-condensable gases trapped in the steam mixture from the dried product and through leaks in the vacuum system installation, are removed together with a small amount of water vapor and vapor of pentane vacuum pump 17 into the atmosphere (through the treatment system).

Absorption of water vapor is a strong antifreeze water solution of lithium chloride (or bromide, lithium), the wetting power is the capacity of the cooling coil 7 of the absorber 5. Continuously cooled solution absorbs water vapor, providing them with the residual pressure in the group of units 5 and 8 at the level at which there is desublimate of water vapor on the surface of the cooled coil 9 of the condenser 8. The circulation of the solution is provided by the pump 14, which also provides continuous removal of a portion of the circulating solution 28 on regeneration - removing the absorbed moisture. The regenerated solution 27 is returned to the absorber 5.

A pair of pentane from entering the combined group of devices 5 and 8 steam mixture are condensed on the surface of the cooled coil 9 of the condenser 8. The temperature of the cooled coil 9 is supported at a lower level than the temperature of the cooling coil 7, to prevent condensation of vapor pentane on the surface of the cooling coil 7, but the temperature difference should not be significant to prevent desublimation of water vapor on the surface of the cooling coil 9.

The condensed vapors pentane gravity flow through the water seal 22 is returned from the condenser 8 to the evaporator 10.

The cooling coils 7 and 9 through the heat pump, the condenser is the coil 11 of the evaporator 10. The heat pump works as follows. Refrigerant gas, which is the working body is a black pump, compressed by the compressor 16 and served inside of the coil 11, in which it condenses, transferring heat of condensation liquid pentane, wetting the outer surface of the coil. The condensed refrigerant pipeline through the throttle valves 18 and 19 is supplied to the coils 7 and 9, in which at reduced pressure and temperature evaporates (boils), by removing heat from absorbed water vapor and condensable vapors pentane, respectively. The vapors of the refrigerant sucked by the compressor 16, closing the loop.

The removal of excess heat from the evaporator 10 is refrigerating unit 24, the cooling coil 6 of the absorber 4 is a refrigerating unit 23. Part of the heat energy, exhaust units 23 or 24, is transmitted in the low-temperature heater 3 for heating cold pentane vapor leaving the evaporator 10.

1. Method of vacuum freeze-drying, characterized in that the system vacuumized cameras in terms of dilution:
a) carry out the evaporation of the hydrophobic liquid working fluid;
b) moving under the action of pressure difference of the pair of the working fluid is heated and passed through a layer of frozen dried product, this process is carried out once or several times, passing the heated vapors of the working fluid respectively through one or more layers C is ice cream dried product;
c) the resulting mixture of water vapor and vapor of the working fluid is passed through one or more desublimation/absorbers, which are desublimation/absorption of water vapor from the mixture;
d) carry out the condensation of the vapor of the working fluid;
e) returns the liquid working medium for the process.

2. The method according to claim 1, characterized in that the working medium is applied hydrophobic low-boiling liquid or liquefied gas, for example butane, pentane, hexane and its isomers.

3. The method according to claim 1, characterized in that the partial pressure of water vapor in all areas of the system vacuumized cameras support at a level not exceeding the equilibrium partial pressure of water vapor over the frozen dried product.

4. The method according to claim 1, characterized in that the temperature of desublimation/absorbers, Desublimers/absorbing water vapor from the stream of vapor of the working fluid, is supported at a level higher than the temperature of the condensing vapor of the working fluid at an operating pressure in desublimator/absorber.

5. The method according to claim 1, characterized in that the heating of the vapor of the working fluid in the coils use high-grade thermal energy source or use a heat pump that uses as a source of low-grade thermal energy heat of desublimation/p is the absorption of water vapor in desublimator/absorbers.

6. The method according to claim 1, characterized in that the evaporation of the working fluid carried out by the energy of condensation of the working fluid, the heat capacity of which increases by the heat pump.

7. The vacuum freeze-drying, characterized in that it contains the evaporator, the working fluid, multiple heaters to heat the vapor of the working fluid, several vacuumized drying chambers, which is frozen dried product, one or more desublimation/absorbers for selective desublimate/absorption of water vapor from the stream of vapor of the working fluid, and a condenser for the working fluid, forming a total sealed system, and the vacuum pump is enabled in the system depression; as a working body installation applied hydrophobic low-boiling liquid or liquefied gas.

8. Installation according to claim 7, characterized in that the drying chamber is connected in series to each other along the vapor of the working fluid before each drying chamber is at least one of the heater.

9. Installation according to claim 7, characterized in that the working medium is installed applied pentane.

10. Installation according to claim 7, characterized in that the condenser the working fluid is connected by a heat pump with an evaporator working fluid is further cooled by the refrigeration AGR is Gata.



 

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