Liquid nitrogen freezing and nitrogen filling packaging system and using method

Abstract

The invention discloses a liquid nitrogen freezing and nitrogen-filled packaging system and a use method, relates to the technical field of quick freezing of foods, and aims to solve the problems that the existing liquid nitrogen freezing equipment cannot fully utilize the cooling capacity after liquid nitrogen vaporization and cannot recycle nitrogen. Comprising a belt conveyor and a quick-freezing box, the belt conveyor penetrates through the quick-freezing box, a spraying device is arranged on the upper portion of an inner cavity of the quick-freezing box, the spraying device is connected with a liquid nitrogen storage tank through a pipeline, the belt conveyor penetrates through the pre-cooling box, a pre-cooling air nozzle is arranged in the pre-cooling box, and the pre-cooling air nozzle is connected with the pre-cooling nitrogen storage tank through a pipeline. The pre-cooling air nozzle is connected with a pre-cooling nitrogen storage tank through a pipeline; the lower part of the inner cavity of the quick-freezing box is provided with a balancing air tap, and the precooling nitrogen storage tank is also connected with the quick-freezing box through a pipeline. According to the quick-freezing device, food quick-freezing is achieved, and meanwhile cold energy utilization after liquid nitrogen vaporization can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of quick freezing of food, in particular to a liquid nitrogen freezing and nitrogen filling packaging system and a use method thereof. Background Art

[0002] Quick freezing is one of the important technologies for preserving fresh food. It can preserve the flavor and nutrition of food to the greatest extent and is conducive to extending the storage period. There are many factors that affect the quality of quick-frozen food, such as raw material quality, pre-treatment process, freezing rate, etc. These factors are interrelated, and the freezing rate is the decisive factor. Freezing equipment can be divided into slow freezing (0-1cm / h), medium freezing (1-5cm / h) and fast freezing (5-20cm / h) according to the freezing rate. Different freezing speeds make the size, shape and distribution of ice crystals inside the food different after freezing, which greatly affects the quality of frozen food.

[0003] Slow freezing speed leads to loss of food nutrients. For some expensive foods, liquid nitrogen freezing is a good way to freeze quickly. Liquid nitrogen is a low-temperature liquid, non-toxic, with a boiling point of -196°C. It can freeze quickly and complete the freezing process in a short time, maximizing the freshness of food; reducing water loss and maintaining a good taste; not destroying the cell tissue of food, and not causing nutrient loss, which is the so-called instant freshness preservation, and extreme freezing locks in nutritional value. In addition, the gas produced by liquid nitrogen freezing technology is inert nitrogen. Liquid nitrogen isolates the air during the vaporization process and plays a role in protecting food. The ultra-low temperature quick freezing method of liquid nitrogen freezing can also play an effective role in disinfection and sterilization, and there is no need to worry about the growth of bacteria attached to the food and destroying the quality of the food.

[0004] Chinese patent 2015104381948 discloses a jacketed liquid nitrogen spraying refrigeration box, in which a jacket layer is separated from the top of the box by a partition, and a plurality of air outlet holes are arranged on the partition; a liquid nitrogen spraying device is arranged in the jacket layer, and the liquid nitrogen spraying device is connected to the liquid storage tank through a liquid inlet pipeline. The refrigeration box adopts a jacketed spraying air supply method, and the temperature field is more uniform. The setting of the partition prevents liquid nitrogen from dripping on fruits and vegetables, causing frostbite.

[0005] Chinese Patent 2016201960582 discloses a large-scale quick-freezing room structure for pastries, including a fan, a circular conveyor belt, a quick-freezing room body and a liquid nitrogen spray pipe. The quick-freezing room body is divided into a residual cold collection chamber and a nitrogen quick-freezing chamber by a heat-insulating partition. A circular conveyor belt is arranged inside the quick-freezing room body, and one end of the circular conveyor belt is arranged outside the quick-freezing room body; a liquid nitrogen spray pipe is installed in the nitrogen quick-freezing chamber, and a plurality of nozzles are arranged on the liquid nitrogen spray pipe, and a plurality of fans are installed under the circular conveyor belt; the quick-freezing room structure effectively extends the quick-freezing distance of pastries, reduces the length and volume of the quick-freezing room body, effectively avoids cold leakage, and has a good cooling effect, thereby improving the quick-freezing efficiency. The quick-freezing room structure conveys pastries into the quick-freezing room body through a circular conveyor belt, and after quick-freezing, the pastries are conveyed outside the quick-freezing room body by the circular conveyor belt.

[0006] Both of the above prior arts propose to freeze food by spraying liquid nitrogen. However, liquid nitrogen vaporizes into nitrogen after heat exchange with food. On the one hand, nitrogen carries a certain amount of cold that is not utilized, and on the other hand, there is a lack of collection and reuse of nitrogen. Summary of the invention

[0007] The object of the present invention is to provide a liquid nitrogen freezing and nitrogen filling packaging system and a use method, which are used to solve the problems of the existing liquid nitrogen freezing equipment that the cold capacity after liquid nitrogen vaporization cannot be fully utilized and the nitrogen recovery and reuse is lacking.

[0008] The technical solution adopted by the present invention to solve its technical problems is: a liquid nitrogen freezing and nitrogen filling packaging system, comprising a belt conveyor and a quick freezing box, the belt conveyor runs through the quick freezing box, the upper part of the inner cavity of the quick freezing box is provided with a spray device, the spray device is connected to the liquid nitrogen storage tank through a pipeline, and also comprises a precooling box, a precooling nitrogen storage tank and a packaging nitrogen storage tank, the belt conveyor runs through the precooling box, and the precooling box and the quick freezing box are arranged front and back along the conveying direction of the belt conveyor, the precooling box is provided with a precooling air nozzle, and the precooling air nozzle is connected to the precooling nitrogen storage tank through a pipeline; the lower part of the inner cavity of the quick freezing box is provided with a balancing air nozzle, and the balancing air nozzle is connected to the air outlet of the quick freezing box. The blower is connected to the quick-freezing box, the air inlet of the blower is connected to the inner cavity of the quick-freezing box, the air outlet of the balancing air nozzle faces the belt conveyor, the pre-cooling nitrogen storage tank is also connected to the quick-freezing box through a pipeline, and the packaged nitrogen storage tank is connected to the pre-cooling box through a pipeline; when working, the liquid nitrogen in the liquid nitrogen storage tank is sprayed on the food on the belt conveyor through the spray device, and the pre-cooling nitrogen carrying cold energy after the liquid nitrogen is vaporized flows in the quick-freezing box under the action of the balancing air nozzle, and enters the pre-cooling nitrogen storage tank for storage, the pre-cooling nitrogen in the pre-cooling nitrogen storage tank enters the pre-cooling box through the pre-cooling air nozzle to pre-cool the food, and the pre-cooling nitrogen exchanges heat with the food in the pre-cooling box and then enters the packaged nitrogen storage tank.

[0009] Furthermore, a precooling box inlet is provided on one side wall of the precooling box, and a precooling box outlet is provided on the other side wall opposite to the precooling box; a quick freezing box inlet is provided on one side wall of the quick freezing box, and a quick freezing box outlet is provided on the other side wall opposite to the quick freezing box; the belt conveyor passes through the precooling box inlet, the precooling box outlet, the quick freezing box inlet and the quick freezing box outlet in sequence; the lower edges of the precooling box inlet, the precooling box outlet, the quick freezing box inlet and the quick freezing box outlet have sealing pads in contact with the upper conveyor belt of the belt conveyor.

[0010] Furthermore, the pre-cooling box inlet and the quick-freezing box outlet are both provided with a sealing assembly, and the sealing assembly includes two rows of symmetrically arranged baffles, one end of the baffle is hingedly connected to the corresponding pre-cooling box side wall and the quick-freezing box side wall, and a pre-tightening member is provided between the baffle and the corresponding pre-cooling box and the quick-freezing box. When the pre-tightening member is subjected to the minimum force, the other ends of the two rows of baffles of the sealing assembly are in contact and the two adjacent baffles in the same row remain in contact, thereby achieving sealing of the pre-cooling box inlet and the quick-freezing box outlet.

[0011] Furthermore, the pre-cooling box and the quick-freezing box are provided with rollers, and the rollers are in contact with the upper conveyor belt of the belt conveyor.

[0012] Furthermore, the spray device comprises an upper nozzle, a side nozzle and a lower nozzle, the upper nozzle is located above the upper conveyor belt, the side nozzles are located on both sides of the upper conveyor belt, and the lower nozzle is located below the upper conveyor belt.

[0013] Furthermore, the pre-cooling box and the quick-freezing box are arranged closely front and back.

[0014] Furthermore, the pre-cooling air nozzle is located on a side close to the outlet of the pre-cooling box.

[0015] Furthermore, the balancing air nozzle is located on a side close to the outlet of the quick-freezing box, and the spraying device is located on a side close to the inlet of the quick-freezing box.

[0016] The present invention also provides a method for using the liquid nitrogen freezing and nitrogen filling packaging system, comprising the following steps: S1, starting the belt conveyor, placing the food to be quick-frozen on the belt conveyor, and the belt conveyor conveys the food into the pre-cooling box; S2, delivering the precooling nitrogen in the precooling nitrogen storage tank to the precooling nozzle to precool the food in the precooling box, and the precooled food enters the quick freezing box; S3, transporting the liquid nitrogen in the liquid nitrogen storage tank to the spraying device, spraying the liquid nitrogen onto the food through the spraying device to achieve quick freezing; starting the fan to circulate the air flow in the quick freezing box to make the temperature in the quick freezing box balanced; S4, collecting the precooling nitrogen in the quick freezing box into a precooling nitrogen storage tank for precooling food; S5. Collecting the nitrogen in the pre-cooling box into a packaging nitrogen storage tank for food packaging.

[0017] The beneficial effects of the present invention are as follows: the present invention sprays liquid nitrogen to food through a spray device, thereby realizing quick freezing of food; the setting of a balanced bellows in the quick freezing box allows airflow in the quick freezing box, thereby balancing the temperature in the quick freezing box, thereby ensuring the consistency of quick freezing degree of food; the quick freezing box is filled with inert nitrogen, realizing effective disinfection and sterilization at ultra-low temperature; the pre-cooling nitrogen in the quick freezing box is collected, and the pre-cooling nitrogen is used to pre-cool the food before quick freezing of the food to reduce the consumption of liquid nitrogen; the nitrogen in the pre-cooling box is collected for inflatable packaging of food. The present invention uses liquid nitrogen to quick freeze food, and the liquid nitrogen is used to balance the temperature of the quick freezing box after vaporization to ensure the consistency of quick freezing degree, and the liquid nitrogen is used to pre-cool the food after vaporization, and the nitrogen is collected after pre-cooling contact for food packaging, and the whole process is connected. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a system structure diagram of the present invention; Figure 2 It is the main view assembly drawing of the belt conveyor, pre-cooling box and quick-freezing box; Figure 3 It is the sectional assembly drawing of the precooler and quick freezer; Figure 4 This is the internal structure diagram of the quick freezer; Figure 5 This is the internal structure diagram of the pre-cooling box; Figure 6 This is a right side view of the quick freezing box; Figure 7 for Figure 4 A local enlarged view of point A in FIG. Figure 8 A side view of a spraying device spraying food; Fig. 9 It is a schematic diagram of air flow in the quick freezing box; Fig.10 It is a schematic diagram of air flow in the pre-cooling box; Fig.11 It is a schematic diagram of food transportation, liquid nitrogen flow direction, and nitrogen flow direction of the present invention; In the figure: 1 belt conveyor, 11 conveyor belt, 2 precooling box, 21 precooling box inlet, 22 precooling box outlet, 23 baffle, 24 roller, 25 sealing pad, 26 precooling air nozzle, 27 packaging nitrogen outlet, 3 quick freezing box, 31 quick freezing box inlet, 32 quick freezing box outlet, 33 upper nozzle, 34 side nozzle, 35 lower nozzle, 36 balancing air nozzle, 37 precooling nitrogen outlet, 4 liquid nitrogen storage tank, 5 precooling nitrogen storage tank, 6 packaging nitrogen storage tank, 7 food. DETAILED DESCRIPTION

[0019] like Figures 1 to 11 As shown, the liquid nitrogen freezing and nitrogen filling packaging system of the present invention comprises a belt conveyor 1, a precooling box 2, a quick freezing box 3, a liquid nitrogen storage tank 4, a precooling nitrogen storage tank 5 and a packaging nitrogen storage tank 6. The structure, working principle and use method of the present invention are described in detail below in conjunction with the accompanying drawings.

[0020] like Figures 1 to 11 As shown, a liquid nitrogen freezing and nitrogen filling packaging system includes a belt conveyor 1 and a quick freezing box 3. Figure 1 , Figure 2 As shown, the belt conveyor 1 passes through the quick freezing box 3, and the upper part of the inner cavity of the quick freezing box 3 is provided with a spraying device, which is connected to the liquid nitrogen storage tank 4 through a pipeline. The belt conveyor 1 is used to transport the food to be quick-frozen into the quick freezing box 3, and a pump is provided on the pipeline between the liquid nitrogen storage tank 4 and the spraying device. The pump transports the liquid nitrogen in the liquid nitrogen storage tank 4 to the spraying device, and the liquid nitrogen is sprayed on the food in the form of atomization or water droplets through the spraying device to achieve quick freezing of the food.

[0021] As an innovative point of the present invention, the present invention is further provided with a precooling box 2, a precooling nitrogen storage tank 5 and a packaging nitrogen storage tank 6, and the belt conveyor 1 also runs through the precooling box 2. Along the conveying direction of the belt conveyor 1, the precooling box 2 and the quick freezing box 3 are arranged in front and behind. That is, the food on the belt conveyor 1 first enters the precooling box 2 and then enters the quick freezing box 3. The food is precooled in the precooling box 2. For this purpose, Figure 3 , Figure 5 As shown, the precooling box 2 has a precooling nozzle 26, the air outlet of the precooling nozzle 26 faces the belt conveyor 1, and the precooling nozzle 26 is connected to the precooling nitrogen storage tank 5 through a pipeline. In order to prevent the precooling nitrogen from flowing out of the precooling box 2 in large quantities, as shown in FIG. Figure 5 As shown, the pre-cooling nozzle 26 is located on a side close to the pre-cooling box outlet 22, and the side wall of the pre-cooling box 2 has a packaged nitrogen outlet 27, which is located on a side close to the pre-cooling box inlet 21. The pre-cooling nitrogen storage tank 5 is also connected to the quick freezing box 3 through a pipeline, and the packaged nitrogen storage tank 6 is connected to the pre-cooling box 2 through a pipeline. The nitrogen in the pre-cooling box 2 enters the pipeline through the packaged nitrogen outlet 27 and finally enters the packaged nitrogen storage tank 6. Fig.10As shown, the precooling nitrogen in the precooling nitrogen storage tank 5 enters the precooling box 2 through the precooling nozzle 26 and blows directly onto the food to precool the food; and the nitrogen gas circulates in the precooling box 2. When the nitrogen in the precooling box 2 circulates to the position of the precooling box inlet 21, it moves out of the precooling box 2 through the packaging nitrogen outlet 27.

[0022] To achieve a balanced temperature in the quick-freezing box 3, Figure 3 , Figure 4 As shown, the lower part of the inner cavity of the quick freezing box 3 is provided with a balancing air nozzle 36, which is connected to the fan located outside the quick freezing box 3, the air inlet of the fan is connected to the inner cavity of the quick freezing box 3, and the air outlet of the balancing air nozzle 36 faces the belt conveyor 1. After the fan is started, the precooled nitrogen in the quick freezing box 3 enters the balancing air nozzle 36, as shown in FIG. Fig. 9 As shown, the nitrogen is then sprayed back into the quick-freezing box 3 through the balancing air nozzle 36, thereby realizing the circulation of the pre-cooling nitrogen in the quick-freezing box 3. Through the continuous air circulation, the temperature in the quick-freezing box 3 gradually tends to be balanced.

[0023] When working, Fig.11 As shown, the belt conveyor 1 conveys food so that the food enters the precooling box 2 and the quick freezing box 3 in sequence. The liquid nitrogen in the liquid nitrogen storage tank 4 is sprayed on the food on the belt conveyor 1 through the spray device. The precooling nitrogen carrying the cold amount after the liquid nitrogen is vaporized flows in the quick freezing box 3 under the action of the equalizing air nozzle 36, and enters the precooling nitrogen storage tank 5 for storage to be used for precooling food. The precooling nitrogen in the precooling nitrogen storage tank 5 enters the precooling box 2 through the precooling air nozzle 26 to precool the food. The precooling nitrogen exchanges heat with the food in the precooling box 2 and enters the packaging nitrogen storage tank 5 to be used for inflating and packaging food.

[0024] The structures of the precooling box 2 and the quick freezing box 3 are described below: Figure 5 As shown, a precooling box inlet 21 is provided on one side wall of the precooling box 2, and a precooling box outlet 22 is provided on the other side wall opposite to the precooling box 2. Figure 4 As shown, a quick-freezing box inlet 31 is provided on one side wall of the quick-freezing box 3, and a quick-freezing box outlet 32 ​​is provided on the other side wall opposite to the quick-freezing box 3. The belt conveyor 1 passes through the precooling box inlet 21, the precooling box outlet 22, the quick-freezing box inlet 31 and the quick-freezing box outlet 32 ​​in sequence, and the upper conveyor belt 11 of the belt conveyor 1 passes through the precooling box 2 and the quick-freezing box 3, and the lower conveyor belt 11 of the belt conveyor 1 is located outside the precooling box 2 and the quick-freezing box 3, and is located below the precooling box 2 and the quick-freezing box 3. The precooling box inlet 21, the precooling box outlet 22, the quick-freezing box inlet 31 and the quick-freezing box outlet 32 ​​are located at the same height, as shown in FIG. Figure 7As shown, the lower edges of the precooling box inlet 21, the precooling box outlet 22, the quick freezing box inlet 31 and the quick freezing box outlet 32 ​​are provided with a sealing gasket 25 in contact with the upper conveyor belt 11 of the belt conveyor 1. The sealing gasket 25 has a smooth surface and has little friction with the conveyor belt 11. The side wall of the quick freezing box 3 is provided with a precooling nitrogen outlet 37, and the precooling nitrogen outlet 37 is connected to the precooling nitrogen storage tank 5 through a pipeline.

[0025] The precooling box inlet 21 and the quick freezing box outlet 32 ​​are sealed to reduce the loss of nitrogen and cold capacity in the precooling box 2 and the loss of precooling nitrogen and cold capacity in the quick freezing box 3. Figure 3 As shown, the pre-cooling box inlet 21 and the quick-freezing box outlet 32 ​​both have sealing components, such as Figure 6 As shown, the sealing assembly includes two rows of symmetrically arranged baffles 23. On the precooling box 2, one end of the baffle 23 is hingedly connected to the side wall of the precooling box 2, and a pre-tightening member is provided between the baffle 23 and the precooling box 2. On the quick freezing box 3, one end of the baffle 23 is hingedly connected to the side wall of the quick freezing box 3, and a pre-tightening member is also provided between the baffle 23 and the quick freezing box 3. When the pre-tightening member is subjected to the minimum force, the other ends of the two rows of baffles 23 of the sealing assembly are in contact and the two adjacent baffles 23 in the same row remain in contact, thereby achieving the sealing of the precooling box inlet 21 and the quick freezing box outlet 32. When the belt conveyor 1 drives the food into the precooling box 2, after the food contacts the baffle 23 at the precooling box entrance 21, the food squeezes the baffle 23 so that the baffle 23 swings around the hinge point until the food enters the precooling box 2 and separates from the baffle 23, and the pre-tightening member returns to its original state, and the baffle 23 is reset under the action of the pre-tightening member to achieve re-blocking / sealing of the precooling box entrance 21. When the belt conveyor 1 drives the food out of the quick-freezing box 3, after the food contacts the baffle 23 at the quick-freezing box exit 32, the food squeezes the baffle 23 so that the baffle 23 swings around the hinge point until the food moves out of the quick-freezing box 3 and separates from the baffle 23, and the pre-tightening member returns to its original state, and the baffle 23 is reset under the action of the pre-tightening member to achieve re-blocking / sealing of the quick-freezing box exit 32.

[0026] To lift food, such as Figure 3 As shown, the pre-cooling box 2 and the quick-freezing box 3 are provided with rollers 24 , and the rollers 24 are in contact with the upper conveyor belt 11 of the belt conveyor 1 .

[0027] To improve the quick freezing efficiency, Figure 8 As shown, the spraying device includes an upper nozzle 33, a side nozzle 34 and a lower nozzle 35. The upper nozzle 33 is located above the upper conveyor belt 11, the side nozzles 34 are located on both sides of the upper conveyor belt 11, and the lower nozzle 35 is located below the upper conveyor belt 11. The upper nozzle 33 sprays the food from above, the side nozzle 34 sprays the food from the side, and the lower nozzle 35 sprays the food from below. By spraying the food from different directions, the quick freezing efficiency can be ensured.

[0028] To reduce the loss of cold, the precooling box 2 and the quick freezing box 3 are arranged closely front and back to avoid the cold in the quick freezing box 3 directly exchanging heat with the air. At this time, the cold in the quick freezing box 3 exchanges heat with the precooling box 2 to ensure the precooling effect of the food in the precooling box 2.

[0029] After quick freezing of food, the temperature of the food should be balanced, such as Figure 4 As shown, the balancing air nozzle 36 is located on a side close to the quick freezing box outlet 32, and the spray device is located on a side close to the quick freezing box inlet 31. The spray device is close to the quick freezing box inlet 31, so that part of the pre-cooling nitrogen after the liquid nitrogen is vaporized will directly enter the pre-cooling box 2 through the quick freezing box inlet 31 and the pre-cooling box outlet 22. The balancing air nozzle 36 is located on a side close to the quick freezing box outlet 32, which can ensure that the quick freezing degree of the food removed from the quick freezing box outlet 32 ​​is consistent.

[0030] A method for using a liquid nitrogen freezing and nitrogen filling packaging system of the present invention comprises the following steps: S1, start the belt conveyor 1, place the food 7 to be quick-frozen on the belt conveyor 1, and the belt conveyor 1 conveys the food 7 to the pre-cooling box 2; S2, the precooling nitrogen in the precooling nitrogen storage tank 5 is transported to the precooling nozzle 26 to precool the food in the precooling box 2, and the precooled food enters the quick freezing box 3; S3, the liquid nitrogen in the liquid nitrogen storage tank 4 is transported to the spraying device, and the liquid nitrogen is sprayed onto the food 7 through the spraying device to achieve quick freezing; the fan is started to circulate the air flow in the quick freezing box 3, so that the temperature in the quick freezing box 3 is balanced; S4, collecting the precooling nitrogen in the quick freezing box 3 into the precooling nitrogen storage tank 5 for precooling food; S5. Collect the nitrogen in the precooling box 2 into the packaging nitrogen storage tank 6 for food packaging.

[0031] The present invention sprays liquid nitrogen to food through a spray device, thereby realizing quick freezing of food; the setting of the equalizing bellows 36 in the quick freezing box 3 enables airflow in the quick freezing box 3, thereby balancing the temperature in the quick freezing box 3, thereby ensuring the consistency of quick freezing degree of food; the quick freezing box 3 is filled with inert nitrogen, realizing effective disinfection and sterilization at ultra-low temperature; the precooling nitrogen in the quick freezing box 3 is collected, and the precooling nitrogen is used to precool the food before quick freezing of the food to reduce the consumption of liquid nitrogen; the nitrogen in the precooling box 2 is collected for gas packaging of food. The present invention uses liquid nitrogen to quick freeze food, and the liquid nitrogen is used to balance the temperature of the quick freezing box 3 after vaporization to ensure the consistency of quick freezing degree, and the liquid nitrogen is used to precool the food after vaporization, and the nitrogen is collected after precooling contact for food packaging, and the whole process is connected.

Claims

1. A liquid nitrogen freezing and nitrogen filling packaging system, comprising a belt conveyor and a quick freezing box, wherein the belt conveyor runs through the quick freezing box, and the upper part of the inner cavity of the quick freezing box is provided with a spray device, and the spray device is connected to a liquid nitrogen storage tank through a pipeline. It is characterized in that It also includes a precooling box, a precooling nitrogen storage tank and a packaged nitrogen storage tank. The belt conveyor runs through the precooling box, and the precooling box and the quick-freezing box are arranged front and back along the conveying direction of the belt conveyor. The precooling box is provided with a precooling air nozzle, and the precooling air nozzle is connected to the precooling nitrogen storage tank through a pipeline; the lower part of the inner cavity of the quick-freezing box is provided with a balancing air nozzle, and the balancing air nozzle is connected to the fan located outside the quick-freezing box. The air inlet of the fan is communicated with the inner cavity of the quick-freezing box, and the air outlet of the balancing air nozzle faces the belt conveyor. The precooling nitrogen storage tank is also connected to the quick-freezing box through a pipeline. The quick freezing box is connected, and the packaged nitrogen storage tank is connected to the precooling box through a pipeline; when working, the liquid nitrogen in the liquid nitrogen storage tank is sprayed on the food on the belt conveyor through the spray device, and the liquid nitrogen is vaporized to become precooling nitrogen carrying cold energy, and the precooling nitrogen circulates in the quick freezing box under the action of the balancing air nozzle, and enters the precooling nitrogen storage tank for storage, the precooling nitrogen in the precooling nitrogen storage tank enters the precooling box through the precooling air nozzle to precool the food, and the precooling nitrogen exchanges heat with the food in the precooling box and then enters the packaged nitrogen storage tank.

2. A liquid nitrogen freezing and nitrogen filling packaging system according to claim 1, It is characterized in that A precooling box inlet is provided on one side wall of the precooling box, and a precooling box outlet is provided on the other side wall opposite to the precooling box; a quick freezing box inlet is provided on one side wall of the quick freezing box, and a quick freezing box outlet is provided on the other side wall opposite to the quick freezing box; the belt conveyor passes through the precooling box inlet, the precooling box outlet, the quick freezing box inlet and the quick freezing box outlet in sequence; the lower edges of the precooling box inlet, the precooling box outlet, the quick freezing box inlet and the quick freezing box outlet are provided with sealing pads in contact with the upper conveyor belt of the belt conveyor.

3. A liquid nitrogen freezing and nitrogen filling packaging system according to claim 2, It is characterized in that The inlet of the precooling box and the outlet of the quick-freezing box are both provided with a sealing assembly, and the sealing assembly includes two rows of symmetrically arranged baffles, one end of the baffle is hingedly connected to the corresponding side wall of the precooling box and the side wall of the quick-freezing box, and a pre-tightening member is provided between the baffle and the corresponding precooling box and the quick-freezing box. When the pre-tightening member is subjected to the minimum force, the other ends of the two rows of baffles of the sealing assembly are in contact and the two adjacent baffles in the same row remain in contact, thereby achieving sealing of the inlet of the precooling box and the outlet of the quick-freezing box.

4. A liquid nitrogen freezing and nitrogen filling packaging system according to claim 1, It is characterized in that The precooling box and the quick freezing box are provided with rollers, and the rollers are kept in contact with the upper conveyor belt of the belt conveyor.

5. A liquid nitrogen freezing and nitrogen filling packaging system according to claim 1, It is characterized in that The spray device comprises an upper nozzle, a side nozzle and a lower nozzle, wherein the upper nozzle is located above the upper conveyor belt, the side nozzles are located on both sides of the upper conveyor belt, and the lower nozzle is located below the upper conveyor belt.

6. A liquid nitrogen freezing and nitrogen filling packaging system according to claim 1, It is characterized in that The precooling box and the quick freezing box are arranged closely front and back.

7. A liquid nitrogen freezing and nitrogen filling packaging system according to claim 1, It is characterized in that The pre-cooling air nozzle is located at a side close to the outlet of the pre-cooling box.

8. A liquid nitrogen freezing and nitrogen filling packaging system according to claim 7, It is characterized in that The balancing air nozzle is located on a side close to the outlet of the quick-freezing box, and the spraying device is located on a side close to the inlet of the quick-freezing box.

9. A method for using a liquid nitrogen freezing and nitrogen filling packaging system according to any one of claims 1 to 8, It is characterized in that The following steps are involved: S1, starting the belt conveyor, placing the food to be quick-frozen on the belt conveyor, and the belt conveyor conveys the food into the pre-cooling box; S2, delivering the precooling nitrogen in the precooling nitrogen storage tank to the precooling nozzle to precool the food in the precooling box, and the precooled food enters the quick freezing box; S3, transporting the liquid nitrogen in the liquid nitrogen storage tank to the spraying device, spraying the liquid nitrogen onto the food through the spraying device to achieve quick freezing; starting the fan to circulate the air flow in the quick freezing box to make the temperature in the quick freezing box balanced; S4, collecting the precooling nitrogen in the quick freezing box into a precooling nitrogen storage tank for precooling food; S5. Collecting the nitrogen in the pre-cooling box into a packaging nitrogen storage tank for food packaging.

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