CN113280583A

CN113280583A - Freeze drying method and apparatus

Info

Publication number: CN113280583A
Application number: CN202110648469.6A
Authority: CN
Inventors: 王兆霖; 钱骅; 王启军
Original assignee: Nanjing Zhiyikaiwu Technology Co ltd
Current assignee: Nanjing Zhiyikaiwu Technology Co ltd
Priority date: 2021-06-10
Filing date: 2021-06-10
Publication date: 2021-08-20

Abstract

The invention relates to a freeze drying apparatus comprising: a circulating air duct; the temperature control device, the water catching device, the sample freeze drying tower and the negative pressure source are positioned on the circulating air duct; and an external air source for supplying air to the circulating air duct. In the invention, as the moisture of the frozen material is taken away by the high-speed convection drying cold air under the normal pressure state, the moisture in the convection cold air is filtered by the evaporator of the capture water-cooling trap and the dewatering filtering column and then circulates through the freeze drying tower, so that the cold air passing through the sample at each time is dried, the speed of dewatering is obviously improved by diffusion sublimation compared with the traditional vacuum freeze drying, the drying efficiency is high, and the speed of freeze drying the sample is improved. Compared with the traditional vacuum freeze drying, the freeze drying process of the invention basically operates under normal pressure, and has greater energy-saving advantage.

Description

Freeze drying method and apparatus

Technical Field

The invention relates to a freeze drying method and equipment, and belongs to the technical field of freeze drying.

Background

The freeze drying is a method for removing the water content from the solid material and drying the solid material under the condition of low temperature by freezing the water-containing material at low temperature in advance and continuously transferring the water content from the surface of the solid material to the environment by utilizing the water vapor partial pressure difference after ice sublimation on the surface of the solid material at low temperature.

Vacuum freeze drying: a low-temperature freeze drying method for thermosensitive medicines and fresh-keeping foods. The method is that firstly the water-containing material to be dried is frozen at low temperature in advance, then in order to improve the partial pressure of sublimed water vapor on the surface of the frozen material and increase the mass transfer driving force between the frozen material and the environment, the frozen material is kept under a certain vacuum environment, so that the water on the surface of the solid material is removed at a higher transfer speed, and the purpose of quickly drying the water-containing material is achieved.

The traditional vacuum freeze drying technology is widely applied to the manufacturing of thermosensitive drugs and biological products and the drying processing of high-quality food, and has the remarkable characteristics that the biological activity, food nutrient components and quality (flavor, form, rehydration and other properties) of the thermosensitive drugs and the biological products can be furthest preserved in the drying process, but the drying process removes water from materials in a way of heating to sublimate ice by vacuumizing under the freezing condition, usually requires dozens of hours or several days, and has long time consumption, large energy consumption and very low drying speed, thereby belonging to a typical high-energy-consumption and low-efficiency process.

China is the first major fruit and vegetable producing country in the world, and according to the data of the State statistical administration, the total yield of fruits and vegetables in 2019 is 9.7 hundred million tons, wherein 2.7 hundred million tons of fruits and 7.0 hundred million tons of vegetables are produced. However, the fruits and vegetables contain a large amount of water, are easy to damage and are not storage-resistant, and the fruits and vegetables are produced in China with many places and inconvenient traffic, low processing level, and unsound industrial chain, supply chain and value chain, so that the fruit and vegetable loss rate is up to 30% and the fruit and vegetable loss is over billions of yuan every year in China. The freeze-drying processing has important significance for reducing the loss of fresh fruits and vegetables and maintaining the nutrition of the fruits and vegetables, the fruits and vegetables are products very suitable for freeze-drying processing, fast and energy-saving freeze-drying equipment and technology are developed, the production cost is reduced, the urgent needs of people on freeze-dried fruit and vegetable products are met, and the market prospect is wide.

Disclosure of Invention

The invention aims to provide a freeze-drying method and freeze-drying equipment, which overcome the technical defects of high equipment manufacturing cost, long process time, high energy consumption, high production cost and the like of the conventional vacuum freezing technology, and simultaneously solve the practical contradiction between large demand of the freeze-dried fruit and vegetable market and the lack of energy-saving and efficient freeze-drying technology and equipment. The invention adopts circulating high-speed convection drying cold air to dry the frozen material, and realizes the rapid removal of the water in the frozen material based on the principle that the mass transfer rate of the water in the convection process is far greater than that of the traditional vacuum freezing sublimation process.

The invention adopts the following technical scheme:

a freeze drying apparatus comprising: a circulating air duct; a temperature control device, a water catching device, a sample freeze drying tower 8 with a weight sensor, a circulating fan and a negative pressure source which are positioned on the circulating air duct; and an external air source for supplying air to the circulating air duct.

Preferably, the sample freeze-drying tower 8 comprises a motor 86, an output shaft of the motor 86 is fixedly connected with the rotating shaft 82, and a plurality of groups of rotatable sample hanging trays 84 are fixed on the rotating shaft 82.

Further, part of the structure of the sample freeze drying tower 8 faces the circulating air duct, and part of the structure extends out of the circulating air duct laterally, and each sample hanging platform 84 sequentially faces the air flow of the circulating air duct along with the rotation of the rotating shaft 82, so that the movement direction of the sample hanging platform 84 is opposite to the direction of the air flow.

Preferably, the sample freeze-drying tower 8 is cylindrical and has an air inlet 810 and an air outlet 820; at least one layer of air flow distribution plate 830 for bearing the sample to be dried; the sample freeze-drying tower 8 is divided into a plurality of cavities by an air flow distribution plate 830, and each cavity has a feed opening 850 with controllable opening and closing at the upper part and a discharge opening 860 with controllable opening and closing at the lower part.

Further, the pore diameters and the distribution of the air holes of the air flow distribution plate 830 are uniformly distributed 831 or centripetally graded non-uniform distribution 832, and an airtight gasket is arranged between the air flow distribution plate and the inner wall of the freeze drying tower 8.

Optionally, a group of rails 101 is axially arranged on the inner wall of the sample freeze-drying tower 8, a support frame 108 capable of moving along the rails 101 is arranged in the rails 101, and a group of sample racks 103 for containing or suspending frozen samples are sequentially fixed on the support frame 108; an inner tube 105 which can move axially under the driving of external power is arranged in the middle of the support frame 108, an outer tube 104 is sleeved outside the inner tube 105, the outer tube 104 has a side wall with a porous structure, and the tail end of the inner tube 105 is open or has a porous structure; the outer tube 104 is fixed on the support bracket 108; the initial end of the inner tube 105 is connected with the negative pressure source.

Further, the end of the inner tube 105 is in the shape of a porous ball 107.

Preferably, the temperature control device and the water capture device are integrated in the evaporator and water capture trap system 2, the evaporator and water capture trap system 2 comprises an evaporator 21, an air inlet 22 and an air outlet 23, the evaporator 21 is externally connected with the compressor 1, and the air inlet 22 is communicated with the outlet end of the negative pressure source.

Further, still be equipped with airflow dewatering module 4, airflow purification module 5, airflow temperature regulation module 6 on the circulation wind channel in proper order, airflow

direction fan system

7, 8 entry ends of sample freeze-drying tower with direction fan system 7 is connected, the exit end with negative pressure source intercommunication.

Furthermore, the external air source is arranged between the negative pressure source and the water trap system 2.

Still further, the external gas source includes a gas supplement module 9, and the gas supplement module 9 includes a compressed gas storage tank or cylinder 91 and a valve 92.

A freeze drying method adopts the freeze drying equipment; the method comprises the following steps:

s1, after the material to be freeze-dried is placed in the sample freeze-drying tower 8, the material to be freeze-dried is gradually cooled from the normal temperature to the temperature below the freezing point of the material by adjusting the temperature control device and adopting circulating drying airflow with proper temperature to enter the freeze-drying tower 8;

s2, high-speed cold air drying is carried out on the completely frozen material by adopting high-speed cold air drying at the temperature which is equal to or slightly lower than the temperature of the ice crystal point of the material to be frozen and dried, until the residual water content reaches the set value;

and S3, adjusting the temperature of the circulating air flow to gradually raise the temperature of the dried goods to the normal temperature state so as to take out the finished products from the freeze drying tower 8 for collection.

The invention has the beneficial effects that:

1) the freeze drying efficiency is high: because the dry cold air that is taken away through high-speed convection current under the ordinary pressure state by freezing material moisture, the moisture circulates through the freeze drying tower after being filtered by the evaporimeter of water-cooling trap and dewatering filter column in the convection current cold air to make the cold wind that passes through the sample at every turn dry, it is showing through diffusion sublimation dewatering speed and improves to make traditional vacuum freeze drying, thereby improved the speed of freeze drying sample.

2) The drying uniformity is good: the design of the air flow distribution plate, the guide fan system and the sample rotation (embodiment I) ensures the uniformity of material drying.

3) The special design of the sample freeze drying tower: part structure just to the circulation wind channel, part structure side direction stretches out the circulation wind channel, along with the rotation of pivot each sample hangs the platform and just right with the air current in circulation wind channel in proper order, and makes the direction of motion of sample hanging the platform and the direction of air current are in the same direction and are right (embodiment one), has controlled the air current flow, has promoted the air current velocity of flow, makes the air current and the sample move the direction in the same direction and right, has promoted dry effect and the efficiency of sample simultaneously.

4) Energy conservation: the system is operated at normal pressure, the gas is recycled inside and the design of a heat insulation pipeline ensures that the technology has the advantages of energy conservation, consumption reduction and environmental protection.

5) The air flow velocity and the air flow temperature in the air flow pipeline of the equipment are controllable, so that materials with different ice crystal points can be frozen and dried by adopting cold air with different temperatures, and the effects of high efficiency, energy conservation and good freezing quality of frozen products are achieved.

6) Each module of the equipment has the characteristics of detachability and replaceability, and the equipment is convenient to update or maintain.

7) The sample drying in the freeze drying tower flows through the feed opening and the discharge opening by adjusting the direction of the circulating drying gas in the drying cavity, so that the dried sample is quickly heated, quickly fed and quickly discharged, and the freeze drying tower has the beneficial characteristics of energy conservation and simplicity and convenience in operation (embodiment II).

Drawings

FIG. 1 is a schematic view of the overall construction of a freeze-drying apparatus of the present invention;

FIG. 2 is a schematic view of an upright sample hanging disc of a freeze drying apparatus according to a first embodiment of the present invention;

FIG. 3 is a schematic longitudinal sectional view of a freeze-drying tower according to a second embodiment of the present invention.

FIG. 4 is a plan view of two kinds of flow distribution plates (uniform distribution and centripetal gradient type non-uniform distribution) according to the second embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view of a freeze-drying tower of a freeze-drying apparatus according to a third embodiment of the present invention;

FIG. 6 is a schematic view of the gas flow conduit of the freeze-drying tower of the freeze-drying apparatus according to the third embodiment of the present invention;

reference numbers for parts in the drawings: 1. a compressor; 11. a compressor base; 2. an evaporator and a water trap system; 21. an evaporator; 22. an air inlet; 23. an air outlet; 24. a thermal insulation material; 25. a tapping port; 3. an airflow circulation conduit; 4. an airflow dewatering module; 5. an airflow purification module; 6. an airflow temperature adjustment module; 61. a temperature display screen; 7. an airflow directional fan system; 8. a sample freeze drying tower; 81. a material inlet and a material outlet; 82. a rotating shaft; 83. a bearing; 84. a rotatable sample basket hanging turntable; 85. a sample drying basket; 86. a motor; 9. a gas replenishment module; 91. a compressed gas storage tank or cylinder; 92. a valve; 93. a pressure gauge; 10. a freeze drying tower; 101. an I-shaped rail; 102. a metal pulley; 103. a sample holder; 104. an outer tube; 105. an inner tube; 106. a vent hole; 107. a porous ball; 810. an air inlet; 820. an air outlet; 830. an air flow distribution plate; 840. bracket 850, feed inlet 860, discharge outlet 870, sample to be dried 831, even distribution 832, gradual non-uniform distribution.

Description of the drawings: the "main line exhaust valve" is not shown in the drawing and may be installed in the vicinity of the pressure gauge 93. In addition, the detachable screw structure of each module of the device is not shown for simplifying the figure.

Detailed Description

The invention is further described with reference to the following figures and specific examples.

The first embodiment is as follows:

referring to fig. 1 and 2, the equipment is a closed loop circulating cold air freeze drying device which is composed of a compressed air source, a compressor refrigeration and cold trap water catching module 2, a circulating air flow dewatering module 4, an air flow purification module 5, an air flow temperature adjusting module 6, a freeze drying tower module 8, an air flow circulation pipeline, an air flow guide fan module 7 and a support (or a base) or a part of the modules, wherein the modules are detachably and hermetically connected through pipelines, and a freeze protection is attached.

The compressed gas source comprises a compressed gas storage tank or a compressed steel cylinder, the compressed gas comprises air, nitrogen and carbon dioxide, the compressed gas is stored in the compressed storage tank or the compressed gas steel cylinder and is communicated with a main pipeline of the refrigeration equipment through a metal pipeline with a control valve, and the compressed gas source can provide gas for the circulating cold air refrigeration equipment and assist in adjusting the pressure in the pipeline of the equipment.

The compression refrigeration system comprises a refrigeration compressor 1, an evaporator, a water trap system 2 and a condenser, wherein the compressor 1 is arranged outside a main circulation pipeline and is connected with the evaporator through a pipeline. The evaporator and water trap system 2 is arranged on the main circulation channel through an air inlet 22, an air outlet 23 and a heat-preservation jacket; the evaporator is arranged in the cold trap; the airflow dewatering module 4 is a dewatering filter column with good air permeability and arranged in an airflow pipeline at a proper position behind the water-catching-cooling trap; the gas flow purification module 5 is a gas impurity removal filter column with good gas permeability which is arranged in a gas flow pipeline at a proper position behind the water removal material filter column; the gas flow temperature adjusting module 6 comprises a digital display temperature control heat exchange unit arranged at a proper position of a closed-loop gas channel; the sample freeze-drying tower 8 is a special (expanded) part of a closed-loop gas channel, the tower structure is designed according to the difference of the output size and the product property difference, and the freeze-drying tower is a place for taking and placing freeze-drying samples and comprises a movable sample basket or a sample frame for auxiliary design; depending on the nature of the articles being dried and the purpose of drying, different gas flow guides may be employed and designed within the drying tower, including gas flow guides and blowers mounted at one or more suitable locations within the closed-loop gas path.

The drying gas mainly adopts inert gas or air, can be single or combined compressed gas, and comprises air and nitrogen, and can also select other non-inert gases such as carbon dioxide and the like according to special needs.

In this embodiment, the compressed gas storage tank or cylinder is installed before the water trap in the direction of gas flow.

In this embodiment, the refrigerating temperature range of the compression refrigerator is-70 to 10 ℃,

in this embodiment, the cold trap gas inlet passes through the upper surface of the evaporator at its lower end, opening toward the evaporator.

In this embodiment, the upper surface of the evaporator is seamlessly sealed from the periphery of the cold trap, and only the distal gas inlet end has a gas escape port, preferably made of cold resistant plastic tubing.

In this embodiment, the cold trap gas outlet is provided at an upper position of the cold trap.

In this embodiment, the airflow secondary dewatering material filter column is composed of a plurality of semicircular plastic grooves, strong hygroscopic filling materials such as magnesium chloride are filled in the grooves, and the hygroscopic materials are wrapped in the air-permeable paper tube.

In this embodiment, the airflow purification material filter column is composed of a plurality of semicircular plastic grooves, adsorbent fillers such as activated carbon are filled in the grooves, and the adsorbent materials are wrapped in the air-permeable paper cylinder.

In the embodiment, the temperature control range of the digital display air flow temperature control heating calandria is-30 ℃, the temperature precision is +/-2 ℃, a T-shaped thermocouple temperature probe is arranged in the center of the front air flow and the rear air flow of the temperature control calandria, and the measured temperature can be digitally displayed on a temperature display screen;

in this embodiment, the sample freeze-drying tower is mounted behind the airflow temperature control module through an airflow pipeline;

in this example, the sample freeze-drying tower consists of 2 equal part incubation chamber shells, 2 chamber shells can be tightly combined into one chamber by screws. The sample basket hanging turntable is mounted at the center of a cavity shell through a rotatable bearing, and a rotating motor is mounted outside the cavity shell and can control the rotation of the sample basket hanging turntable, as shown in fig. 2.

It should be noted that (not shown in fig. 2), part of the structure of the sample freeze-drying tower 8 faces the circulating air duct, and part of the structure extends out of the circulating air duct, and each sample hanging platform 84 sequentially faces the air flow of the circulating air duct along with the rotation of the rotating shaft 82, and the movement direction of the sample hanging platform 84 is opposite to the direction of the air flow, so it is not difficult to imagine that the part of the air circulating channel located in the sample freeze-drying tower 8 is designed into a special-shaped structure, which can realize the above functions and achieve the desired effect.

In this embodiment, the sample freeze-drying tower cavity has a circular opening at the front and rear ends thereof, and can be closely connected with the gas flow pipe.

In this embodiment, 1 airflow guide fan is installed at the pipeline between the refrigeration evaporator and the airflow secondary dehydration module; 1 airflow guide fans are arranged at a pipeline between the airflow temperature control module and the sample freeze drying cavity; 1 airflow guide fans are arranged on a pipeline between the sample freeze drying cavity and the refrigeration evaporator;

in this embodiment, the modules are connected by pipes, and the modules can be flexibly disassembled and assembled, so that the modules can be conveniently updated and maintained.

The technical process implementation mode of the freeze drying of the equipment is that after materials with proper size and cut blocks or original size to be freeze-dried are placed in a sample drying tower, a freeze circulation system is adjusted, circulating drying air flow with proper temperature is adopted to enter the drying tower, the materials to be dried are gradually cooled to the temperature below the freezing point of the materials from normal temperature, and high-speed drying cold air with the temperature equal to or slightly lower than the ice crystal point temperature is adopted to carry out high-efficiency cold air drying on the completely frozen materials until the water content of the materials to be dried reaches the specified requirement. And then adjusting the temperature of the circulating air flow to gradually raise the temperature of the dried articles to the normal temperature state so as to take out the finished products from the drying tower for collection.

Example two:

the difference between the present embodiment and the first embodiment is that the specific structural part of the sample freeze-drying tower 8, as shown in fig. 3, the sample freeze-drying tower 8 is cylindrical and has an air inlet 810 and an air outlet 820; at least one layer of air flow distribution plate 830 for bearing the sample to be dried; the sample freeze-drying tower 8 is divided into a plurality of cavities by an air flow distribution plate 830, and each cavity has a feed opening 850 with controllable opening and closing at the upper part and a discharge opening 860 with controllable opening and closing at the lower part.

In this embodiment, referring to fig. 4, the pore diameter and distribution of the air flow distribution plate 830 are uniformly distributed 831 or centripetally graded non-uniform distribution 832, and an airtight gasket is installed between the air flow distribution plate and the inner wall of the freeze-drying tower 8.

It should be noted that, in this embodiment, the direction of the circulating drying gas in the freeze-drying tower can be adjusted, for example, after the sample to be dried is fed into the freeze-drying tower 8 from the feeding port 850, as shown in fig. 3, the circulating drying gas is fed into the freeze-drying tower from bottom to top, the dried sample fed onto the distribution plate is fluidized and loosened to achieve uniform material thickness accumulation, and then the direction of the circulating drying gas is switched (from top to bottom) to enter the subsequent conventional drying process. Therefore, the embodiment has the beneficial characteristics of energy conservation and simple and convenient operation.

Example three:

the difference between this embodiment and the first embodiment lies in the specific structural part of the sample freeze-drying tower 8, as shown in fig. 5, the inner wall of the sample freeze-drying tower 8 is provided with a set of tracks 101 along the axial direction, such as a pair of tracks 180 ° apart as shown in fig. 5; a support frame 108 capable of moving along the rail 101 is disposed in the rail 101, and in this embodiment, the support frame 108 is in a flat plate shape; a group of sample holders 103 for holding or suspending the frozen samples are sequentially fixed on the support frame 108.

An inner tube 105 which can move axially under the driving of external power is arranged in the middle of the support frame 108, an outer tube 104 is sleeved outside the inner tube 105, the outer tube 104 has a side wall with a porous structure, and the tail end of the inner tube 105 is in the shape of a porous ball 107;

the outer tube 104 is fixed on the support bracket 108; the initial end of the inner tube 105 is connected with the negative pressure source.

During actual work, the inner pipe is communicated with the negative pressure source, and only the end part of the inner pipe is provided with the opening, so that the air flow speed can be effectively improved, the electric power requirement of the negative pressure source is reduced, and the drying efficiency and effect are improved; meanwhile, the inner pipe 105 can move axially relative to the outer pipe 104, and the gas flowing position on the outer pipe 104 can be changed, so that the drying uniformity is improved; the porous ball 107 makes the air flow suction surface convex outwards, which can improve the suction area of the air flow inner pipe and improve the stability and uniformity of the air flow.

The following description is continued by way of example:

1) and (5) freeze-drying the litchi by using freeze-drying equipment.

The equipment comprises the following components: compressed air is adopted as compressed air, a 10P refrigeration compressor is selected, 404A fluorine-free refrigerant is adopted, the refrigeration temperature can reach minus 50 ℃, the inner diameter of a stainless steel metal pipeline is 16CM, modules are connected in a screw closed manner, the inner diameter of a barrel-shaped cold trap is 36CM, a finned evaporator is adopted for 23X 10CM, an air-permeable airflow dewatering filter column 16X20CM, an air-permeable airflow purifying filter column 16X20CM is adopted for the airflow temperature adjusting module, an 800W intelligent water bath temperature control system is selected for the airflow temperature adjusting module, a sample freeze drying tower adopts a barrel cavity body with one door opening at one end and about 1.5 cubic meters (2M length X1M inner diameter), an I-shaped rail is respectively arranged at the upper part and the lower part in the freeze drying cavity, 6 layers of cylindrical metal sample racks (the size is about 1.8M length X0.9M outer diameter) are matched with the barrel-shaped freeze drying cavity, metal pulleys 102 matched with the I-shaped rails 101 are arranged at the upper end and the lower end of the sample racks, a double-layer hollow metal tube is arranged in the middle of the sample holder, the length of the outer tube is 1.8M, the diameter of the outer tube is 10CM, and the tube body is provided with uniform vent holes 106; the tail end of the inner pipe 105 is a spherical and porous airtight hose with a compressible pipe body, the inner pipe is communicated with the air flow pipeline through the porous ball at the tail end, when the air-catching water-cooling trap works, the porous ball 107 at the tail end of the inner pipe does uniform telescopic motion in the outer pipe 104, and air flow is pumped out by a guide fan arranged on the main air flow pipeline through the porous ball 107 at the tail end of the inner pipe and enters the water-catching cold trap through the main air flow pipeline; the door of the drying chamber is connected with the drying chamber through a hinge, and is closed and opened through a wrench structure and the drying chamber, two ends of the drying chamber are provided with openings with the inner diameter of 16CM, the openings are in butt joint with the gas circulation pipeline in a closed mode through screw and nut structures, and 3 guide fans of 50W are selected and installed at proper positions of the gas circulation pipeline. The outside of the whole airflow pipeline is wrapped by an insulating layer material with the thickness of 8 CM.

Freeze drying litchi: slowing down a metal sample rack 103, pushing 100 kilograms of fresh lychees with shells into a sample drying tower, hermetically connecting all modules, opening a compressed air valve, properly putting a proper amount of compressed air into the sample drying tower to ensure that the air pressure in a pipeline is 1.02 atmospheric pressure, then setting the temperature of a compression refrigerator to-40 ℃, starting a guide fan to ensure that the guide fan operates at a low speed, driving the air in an airflow pipeline to circularly flow, keeping an airflow temperature control module in a closed state at the moment, gradually reducing the pressure along with the cooling of the air, continuously putting a proper amount of compressed air into the airflow temperature control module, always keeping the pressure between 1.0 and 1.02, when the temperature of the airflow from a freeze drying cavity reaches-15 ℃, enabling the guide fan to operate at a medium speed, and when the temperature of the airflow from the freeze drying cavity reaches-20 ℃, enabling the guide fan to operate at a high speed, and (2) closing the refrigeration compressor, opening the air flow heating module, simultaneously opening the pressure control exhaust valve, closing the air flow heating module, closing the guide fan, opening the drying cavity, taking out the dried air, reloading the air to be dried and carrying out cold air freeze drying when the temperature of the air flow is increased to be consistent with the external temperature, wherein the air flow heating module is closed, the guide fan is closed, the drying cavity is opened, and the air flow is dried until the temperature of the air flow entering the two ends of the freeze dryer is not different from the temperature of the air flow exiting the freeze dryer (such as-25 ℃) and the weight sensor of the sample senses that the weight of the sample meets the drying requirement (29-30 kilograms).

The freeze-dried litchi produced by the technology has dark red shell color, white pulp color, less nutrient loss and less water content of the pulp; compared with vacuum freeze drying, the time and the total energy consumption required by drying are respectively saved by 30 percent and 50 percent, the time consumption is 10 to 15 hours, and the quality of freeze drying is almost the same as that of vacuum freeze drying.

2) And (5) freeze-drying with a freeze-drying device.

The equipment comprises the following components: compressed gas adopts compressed nitrogen, a 10P refrigeration compressor is selected, 404A fluorine-free refrigerant is adopted, the refrigeration temperature can reach-50 ℃, the inner diameter of a stainless steel metal pipeline is 16CM, modules are connected in a screw closed manner, the inner diameter of a barrel-shaped cold trap is 36CM, a finned evaporator is 23 multiplied by 10CM, a permeable airflow dewatering filter column 16 multiplied by 20CM, a permeable airflow purifying filter column 16 multiplied by 20CM, and an airflow temperature adjusting module adopts a 300W intelligent water bath temperature control system;

the sample freeze drying cavity adopts a cylindrical cavity body with one end opened with a door, the length of the cylindrical cavity body is 1.05 cubic meters (1.2M multiplied by 0.6M inner diameter), an I-shaped track is respectively arranged at the upper part and the lower part in the freeze drying cavity, a cylindrical 6-layer metal sample rack (the size is about 1.0M multiplied by 0.5M outer diameter) is matched with the cylindrical freeze drying cavity, and metal pulleys matched with the I-shaped track are arranged at the upper end and the lower end of the sample rack; a double-layer hollow metal tube is arranged in the middle of the sample holder, the length of the outer tube is 1.0M, the diameter of the outer tube is 8CM, and the tube body is provided with uniform ventilation circular holes; the tail end of the inner pipe is a spherical and porous airtight hose with a compressible pipe body, the inner pipe is communicated with the air flow pipeline through the porous ball at the tail end, when the air-catching water-cooling trap works, the porous ball 107 at the tail end of the inner pipe does uniform telescopic motion in the outer pipe, air flow is pumped out by a guide fan arranged on the main air flow pipeline through the porous small ball at the tail end of the inner pipe, and enters the water-catching cold trap through the main air flow pipeline; the door of the drying chamber is connected with the drying chamber through a hinge, and is closed and opened through a wrench structure and the drying chamber, two ends of the drying chamber are provided with openings with the inner diameter of 16CM, the drying chamber is in butt joint with a gas circulation pipeline in a closed mode through a screw and nut structure, and 3 guide fans of 20W are selected and installed at proper positions of the gas circulation pipeline. The outside of the whole airflow pipeline is wrapped by an insulating layer material with the thickness of 8 CM.

And (3) freeze-drying mango: cutting about 20 kg of fresh ripe mangoes into slices, subpackaging the slices in a metal sample frame, pushing the slices into a sample drying tower, hermetically connecting each module, firstly opening an exhaust valve of an airflow channel, then opening a compressed nitrogen valve, slowly introducing nitrogen, so as to slowly discharge air in a pipeline, after most of air is discharged, closing the exhaust valve of a main airflow channel, continuously introducing nitrogen, so that the air pressure in the pipeline is about 1.03 atmosphere, then setting the temperature of a compression refrigerator to-30 ℃, starting a guide fan, so that the guide fan operates at a low speed, driving the air in the airflow channel to circularly flow, wherein the airflow temperature control module is in a closed state, the pressure is gradually reduced along with the cooling of the nitrogen, then continuously introducing a proper amount of compressed nitrogen, and always maintaining the pressure between 1.01 and 1.03, when the temperature of airflow from a freeze drying cavity reaches-10 ℃, and (2) operating the guide fan at a medium speed, operating the guide fan at a high speed after the temperature of the airflow from the freeze drying cavity reaches-18 ℃, and closing the refrigeration compressor, opening the airflow heating module and simultaneously opening the pressure control exhaust valve when the temperature of the airflow at two ends of the freeze drying cavity does not differ from the temperature of the airflow at the outlet, and the sample weight sensor senses that the weight of the sample reaches the drying requirement (3.9-4.0 kilograms), closing the guide fan, opening the drying cavity, taking out the freeze-dried mango, and packaging. And then reloading the mixture to be dried, and carrying out cold air freeze drying.

The dried mango produced by the technology has golden color, high polyphenol content and less nutrient loss, and the moisture content of the dried mango is lower than 6%; compared with vacuum freeze drying, the time and the total energy consumption required by drying are respectively saved by 40 percent and 60 percent, the time is consumed by 3 to 5 hours, and the quality of freeze drying is almost the same as that of vacuum freeze drying.

The above two are preferred embodiments of the present invention, and those skilled in the art can make various changes or modifications based on the above embodiments without departing from the general concept of the present invention, and such changes or modifications should fall within the scope of the present invention as claimed.

Claims

1. A freeze drying apparatus, comprising:

a circulating air duct;

the temperature control device, the water catching device, the sample freeze drying tower (8) and the negative pressure source are positioned on the circulating air duct;

and an external air source for supplying air to the circulating air duct.

2. A freeze drying apparatus as claimed in claim 1, wherein: the sample freeze-drying tower (8) comprises a motor (86), an output shaft of the motor (86) is fixedly connected with a rotating shaft (82), and a plurality of groups of rotatable sample hanging trays (84) are fixed on the rotating shaft (82).

3. A freeze drying apparatus as claimed in claim 2, wherein: the sample freeze drying tower (8) is partially opposite to the circulating air duct, partially laterally extends out of the circulating air duct, and each sample hanging plate (84) is sequentially opposite to the air flow of the circulating air duct along with the rotation of the rotating shaft (82), so that the movement direction of the sample hanging plate (84) is opposite to the direction of the air flow.

4. A freeze drying apparatus as claimed in claim 1, wherein:

the sample freeze-drying tower (8) is cylindrical and is provided with an air inlet (810) and an air outlet (820); at least one layer of air flow distribution plate (830) is arranged in the drying device and is used for bearing the sample to be dried;

the sample freeze drying tower (8) is divided into a plurality of cavities by an air flow distribution plate (830), the upper part of each cavity is provided with a feed opening (850) which can be controlled to open and close, and the lower part of each cavity is provided with a discharge opening (860) which can be controlled to open and close.

5. The freeze drying apparatus of claim 4, wherein: the pore diameter and the distribution of the air holes of the air flow distribution plate (830) are uniformly distributed (831) or are distributed in a centripetal gradual-change type non-uniform mode (832), and an air-tight gasket is arranged between the air flow distribution plate and the inner wall of the freeze drying tower (8).

6. A freeze drying apparatus as claimed in claim 1, wherein:

a group of rails (101) are axially arranged on the inner wall of the sample freeze drying tower (8), a supporting frame (108) capable of moving along the rails is arranged in each rail (101), and a group of sample racks (103) for containing or suspending frozen samples are sequentially fixed on each supporting frame (108);

an inner pipe (105) which can move axially under the driving of external power is arranged in the middle of the support frame (108), an outer pipe (104) is sleeved outside the inner pipe (105), the outer pipe (104) is provided with a side wall with a porous structure, and the tail end of the inner pipe (105) is opened or is also provided with a porous structure;

the outer tube (104) is fixed on the support frame (108);

the starting end of the inner tube (105) is connected with the negative pressure source.

7. The freeze drying apparatus of claim 6, wherein: the end of the inner tube (105) is in the shape of a porous sphere (107).

8. A freeze drying apparatus as claimed in claim 1, wherein: the temperature control device and the water catching device are integrated in the evaporator and the water catching trap system (2), the evaporator and the water catching trap system (2) comprise an evaporator (21), an air inlet (22) and an air outlet (23), the evaporator (21) is externally connected with a compressor (1), and the air inlet (22) is communicated with the outlet end of the negative pressure source.

9. A freeze drying apparatus as claimed in claim 8, wherein: the sample freeze drying device is characterized in that an air flow dewatering module (4), an air flow purification module (5), an air flow temperature adjusting module (6) and an air flow guiding fan system (7) are sequentially arranged on the circulating air duct, the inlet end of the sample freeze drying tower (8) is connected with the guiding fan system (7), and the outlet end of the sample freeze drying tower is communicated with the negative pressure source.

10. A freeze drying apparatus as claimed in claim 9, wherein: the external air source is arranged between the negative pressure source and the water-catching trap system (2).

11. A freeze drying apparatus as claimed in claim 10, wherein: the external gas source comprises a gas supplement module (9), and the gas supplement module (9) comprises a compressed gas storage tank or a steel cylinder (91) and a valve (92).

12. A freeze-drying method characterized by:

using a freeze-drying apparatus according to any one of claims 1 to 11; the method comprises the following steps:

s1, after the material to be freeze-dried is placed in a sample freeze-drying tower (8), circulating drying air flow with proper temperature is adopted to enter the freeze-drying tower (8) by adjusting a temperature control device, and the material to be freeze-dried is gradually cooled from normal temperature to below the freezing point temperature of the material;

s3, adjusting the temperature of the circulating air flow to gradually raise the temperature of the dried goods to the normal temperature state so as to take out the finished products from the freeze drying tower (8) for collection.