RU2187053C1 - Method of continuous sublimation drying of thermolabile materials - Google Patents

Abstract

FIELD: drying technique; sublimation drying of thermolabile materials, for example drugs, medical preparations and food-stuff. SUBSTANCE: method of continuous sublimation drying consists in forming granules and freezing granules of capillary porous material in vacuum, additional drying of material in field of infra-red radiation; granules with partially dried outer surfaces form layer of granules moving downwards which are subjected to continuous radiation in upper portion of layer by microwave field; layer of material being dried is blown by inert gas flow, for example, argon; residual pressure above upper surface of layer is maintained according to saturation temperature of sublimable vapors equal to minimum freezing temperature; in layer of one third of height from upper surface does not exceed cryoscopic temperature of product; temperature on lower surface of layer of material being dried is set in flow of inert gas not above temperature reducing its biological activity by performance at residual pressure of water vapor corresponding to cryostatic temperature of material freezing; when granules are moving inlayer, difference in change of pressure of water vapor between upper and lower surfaces of layer is maintained constant in the course of continuous drying of material. EFFECT: intensification of continuous sublimation drying process in vacuum at retained high quality of final product. 2 dwg

Description

 The invention relates to a drying technique, in particular to a freeze-drying technique of heat-sensitive materials, for example, medicines, medicines and food products.

 Closest to the proposed is a method of continuous freeze drying, implemented in a dryer [1], including spraying the product, self-freezing its granules in vacuum and simultaneous sublimation under the influence of infrared radiation to form a dried crust on the surface of the granules. A.S. 848932 USSR. Installation of continuous operation for freeze-drying of heat-sensitive materials B.I. 27, 1981. Subsequently, the dried granules in free fall fall on vibrating electrically heated shelves, where they are dried to a moisture equilibrium.

 The disadvantage of the method implemented in the dryer is the use of conductive energy supply and vibration to the granulated product frozen in vacuum with a crust dried on the surface. The conductive energy supply during vibration of the granular product can only reduce the external hydrodynamic resistance, which affects the outflow of sublimated steam, but does not activate the supply of heat in each granule directly to the sublimation zone through the dried outer layer.

 The task of the invention is to intensify the process of continuous sublimation dehydration of the material in vacuum while maintaining the high quality of the final product.

 The solution of this problem is carried out by organizing a microwave energy supply directly into the sublimation zone of the frozen granular material and by removing sublimated steam in a preformed capillary-porous structure of a granular continuously moving dried material layer.

 The technical result is achieved by the fact that in the method of continuous freeze drying, including the formation of granules and freezing of granules of a capillary-porous material in vacuum, drying it in the field of infrared radiation until a dry crust forms on the surface of the granules and moving them from granules with a dried outer surface, create a layer with granules continuously moving in it from top to bottom, which are constantly irradiated in the upper part of the layer with a microwave field and purged below this layer of the dried material with an inert gas stream, for example argon measures, while the residual pressure above the upper surface of the layer is maintained corresponding to the saturation temperature of sublimating vapors equal to the minimum freezing temperature, the temperature in the layer at one third of the height from the upper surface does not exceed the cryoscopic temperature of the product, the temperature on the lower surface of the dried material layer is set in an inert stream gas is not higher than the temperature, which reduces its biological activity by the characteristic parameter at the residual pressure of water Vapor corresponding cryoscopic freezing temperature of the material, and moving the granules in the layer of the pressure difference measurement of water vapor between the upper layer and the lower surface is left constant during the continuous drying material.

 In FIG. 1 shows a continuous freeze drying scheme. Figure 2 shows the installation that implements this method.

Figure 1 presents a diagram illustrating a method of continuous freeze drying (below the triple point) in the microwave field and the inert gas stream. In the tank 1, FIG. 1, dried to form a dry crust from the surface, the frozen granules of the product form a layer H. In the upper part of layer H, a freezing temperature T _{3 is} maintained on its surface by observing the corresponding residual pressure P ₃ in chamber 1 and cooling its walls. A microwave energy supply is brought to the upper part of the layer to the level H = N / 3. At the level of H = N / 3 from the upper surface of the temperature is maintained close to cryoscopic, T _to . Accordingly, the pressure of saturated water vapor at this level is supported by P _to = f (T _to ). From the bottom of layer H, a stream of inert gas, such as argon, heated to a temperature T _p , is fed. In the microwave field in a vacuum, free residual crystalline moisture is removed. In an inert gas stream, bound moisture is removed from the granules. The driving force of the filtration transfer is the pressure difference ΔP = P _to -P ₃ . The granules in the layer H are moved from top to bottom when it is continuously filled from above with frozen granules and the bottom of the layer dried up to the specified moisture content of granules.

 The method is implemented in the installation, figure 2, comprising a vacuum chamber 1, a capacitor 2, a vacuum pump 3 and a device 4 dispersion / granulation / material. A microwave generator 5 is connected to the side of the camera 1.

 In the area of the microwave generator 5 around the perimeter of the chamber 1, the cooling tube 6 of the dryer from the condenser 2 is spirally located. Above the device 4 is an infrared heater 7 for organizing the drying of the dispersible material.

 At the base of the chamber 1 there is a screw 8, an intermediate chamber 9, a collection chamber 10 of the finished material. The chamber 1 is connected to the vacuum pump 3 by valves 11, 12. The condenser 2 is connected to the cooling tube 6 by the valve 13. At the end of the screw 8, the chamber 1 is connected to the chamber 9 and 10 by valves 14, 15, 16. At the base, the chamber 1 has porous inserts 17 for the input of gas, such as argon, through the control valve 18 from the cylinder 19. The inert gas is heated by an electric heater 20.

In the quasi-stationary mode of continuous freeze drying and the formation in the chamber 1 of a layer H of material control:
- residual pressure above the layer H of frozen product by the sensor 21,
- residual pressure P ₂ over the screw 7 by the sensor 22,
- pressure P ₃ near the vacuum pump with a vacuum gauge 23,
- temperature T _{1 by the} sensor 24 at a height of H = 1 / 3H from the upper level of the product layer H with registration by the registrar 25,
- temperature T _{2 by the} sensor 26 at the base of the chamber 1 above the screw 7 with registration by the registrar 27.

 The sensors 21 and 22 are connected through the registrars 28, 29 to the first output of the differentiator 30, the comparison unit 31, the converter 32 and the microwave generator 5. The output from the registrar 25 and the output from the registrar 27 are connected to the differentiator 33, the last with the comparison unit 34. Blocks 31 and 34 are connected by their outputs to the setters 35 and 36. The sensor 27 is connected through a block 33 with a comparison unit 34, an actuator 37 and a heater 20. The temperature at a height of H = 1 / 3H is recorded by a recorder 25 through a sensor 24. Camera 10 is connected to camera 1 valve 38.

 The method of continuous freeze-drying of thermolabile preparations in the installation, figure 2, is implemented as follows.

 When the vacuum pump 3 and the cooled condenser 2 are turned on with the valves 11, 12 open, the set vacuum is reached in the dryer 1, which is recorded by the registrars 23, 28, 29.

When the valve 13 is open through the tube 6, the housing of the chamber 1 is cooled in the zone of the microwave field. The infrared emitter 6 is turned on. When a stable vacuum is established in the chamber 1, the dispersible / granular / product is introduced by the device 4. The chamber 1 is filled with a granulated product with a dried crust under the action of an infrared emitter 6 to a height H. The microwave generator 5 of the heater 20 is turned on and the valve 18 is opened, warm inert gas is introduced from the cylinder 19. The following are introduced into the setters 35, 36:
to the setter 35:
ΔP = P ₂ (T _e ) -P ₁ (T ₃ ), (1)
where the value of P ₂ (T _e ) is the vapor pressure at a minimum eutectic temperature T _{e the} dried material;
P ₁ (T ₃ ) is the pressure of saturated water vapor at a temperature of T ₃ complete freezing of the material:
T ₃ = T _e -10, (2)
those. when the percentage of unfrozen moisture in the product in this case is minimal / at T _e this value is from 88 to 96% /.

Differentiator 36 determines the temperature difference in the layer at a height of H = 1 / 3H:
ΔT = T ₁ -T _k , (3)
i.e., T _c is the cryoscopic freezing temperature of the dried material,
T ₁ - the temperature of the material, preserving its high commercial biological quality in the final dried form / for juices, vegetable purees, vaccines ~ 25 ^o C /.

 The value ΔT according to the ratio / 3 / for a particular product to be dried is introduced into the unit 36. Upon exposure to a microwave energy supply and an inert gas stream in layer H, a free / frozen / and bound moisture zone is formed, FIG. 1. The screw 8 is turned on, the valve 14 opens. When filling the chamber 9, the valve 15 opens and the product enters the chamber 10. After filling the chamber 10, the valve 15 closes, the valve 16 opens and the dry product is removed from the chamber 10. After the product is removed, the valve 16 closes and valve 38 opens to evacuate chamber 10. After reaching a predetermined vacuum, valve 38 closes and the cycle of filling and emptying chambers 9, 10 with a dry product is repeated.

When carrying out continuous freeze-drying of blackcurrant juice in a layer H = 600 mm in the ratio / 1 /:
ΔP = P ₂ (T _e ) -P ₁ (T ₃ ) = 100-30 = 70 Pa.

From the ratio / 2 / freezing temperature T ₃ :
ΔT ₃ = T _e + 10 = 250-10 = 240 K,
where T _e - the eutectic temperature of blackcurrant juice (t _e = -23 ^o C).

In the ratio / 3 /:
ΔТ = Т ₁ -Т _к = 298-267 = 31 ^o С,
where T ₁ is the temperature of the argon introduced into the chamber ~ 25 C ^o ,
T _to - cryoscopic temperature - 267 ^o C for blackcurrant juice.

 With these parameters, the continuous process of freeze-drying of blackcurrant juice in chamber 1 is carried out to a final moisture content of ~ 3.4%, while maintaining vitamin C in the final product of at least 96%. The microwave energy supply level was selected no more ...

The change in the operating parameters ΔP, ΔT ₃ , ΔT in the chamber 1 during continuous freeze-drying can be associated with the following reasons: increase / decrease / consumption of the granular product with increasing / decreasing / its humidity in the dispersion device 4;
- the work of the screw 7, which does not provide a rational mode of output from the chamber 1 of the dried product;
- increase in residual pressure in the chamber 1 due to the freezing of the material when it is dispersed in vacuum;
- increase / cast / residual pressure in the evacuation chamber 10 of the collection of the finished product;
- cyclic operation of the capacitor 2 / desublimator / in the process of regeneration of the working surfaces.

All the indicated possible parameter changes are continuously recorded:
- sensors 21, 22 control the residual pressure and the vacuum gauge 23;
- temperature sensors 25, 26.

 Consider a possible case of increasing the residual pressure in the chamber 1 over the granular product layer H, which is detected by the sensor 21 in the recorder 28. In this case, the temperature at the boundary of the free and bound moisture removal zone increases, the temperature recorded by the sensor 24 in the recorder 25. The signal from the recorder 28 to the input of the differentiator 30, then to the comparison unit 31 and compared in the setter 35 with the value and the desired value goes to the converter 32, where it reduces the level of microwave heating, thereby reducing intensively the freezing of free moisture in the layer N. At the same time, the temperature of the product at the junction of the granular product with frozen and bound moisture increases by the signal of the sensor 24, it is registered by the recorder 25, the differentiator 33 is transmitted, and through the comparison unit 34 it is compared with the sensor 36, from where the signal through the actuator 37 through the rheostat changes the voltage at the heater 20. Thereby, the temperature of the inert gas at the inlet through the porous inserts 17 into the base of the chamber 1 changes.

 In the case of an increase in the final humidity of the product, it is possible to increase the pressure recorded by the sensor 22, or lower the temperature detected by the sensor 26. When the pressure of the signal from the sensor 22 increases, it is registered by the recorder 29, from where it is supplied to the differentiator 30, where it is compared with the signal recorded by the sensor 21. The signal difference gets into the comparison unit 21, is compared with the sensor 35 and gets into the converter 32, where the level of microwave energy supply increases.

 The temperature decrease recorded by the sensor 26 is supplied to the differentiator 23, introduced into the block 34, compared with the signal of the sensor 36, and the difference in the signals is supplied to the actuator 37, which increases the voltage on the heater 20 and increases the heating of the inert gas supplied through the porous inserts 17 to the chamber 1 .

Thus, the complex of sensors 21, 22, 24, 26 and the control system maintains the parameters ΔP, ΔT _e , ΔT at a given level and allow you to get the final product of high quality and a given humidity from any feedstock that can be granulated in vacuum. Previously found experimentally or known from the reference data, the values of T _e , T ₃ , T _k , T ₁ and the dependences / 1 / ÷ / 3 / allow you to implement the method of continuous freeze drying with the power of the installation, figure 2, for any product.

Claims (1)

 The method of continuous freeze-drying, including the formation of granules and freezing of granules of a capillary-porous material in vacuum, drying it in the field of infrared radiation to form a dry crust on the surface of the granules and moving them, characterized in that a layer is continuously created from granules with a dried outer surface granules moving in it from top to bottom, which are constantly irradiated in the upper part of the layer with a microwave field, and blow down this layer of the material to be dried with a stream of inert gas, for example, argon, while the pressure at the top surface of the layer is maintained at the corresponding saturation temperature of sublimated vapors equal to the minimum freezing temperature, the temperature in the layer at one third of the height from the upper surface does not exceed the cryoscopic temperature of the product, the temperature on the lower surface of the dried material layer is set in an inert gas stream not higher than the temperature, reducing its biological activity in the characteristic parameter at a residual pressure of water vapor, correspondingly cryoscopic at freezing temperature of the material, and moving the granules in the layer of the pressure difference measurement of water vapor between the upper layer and the lower surface is left constant during the continuous drying material.

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