Application of Liquid Nitrogen Quick Freezing Technology in Poultry Food
2020-12-30 09:34:32
Characteristics of liquid nitrogen
The liquefied nitrogen-liquid nitrogen, is a colorless, transparent and low-viscosity liquid with stable chemical properties. The boiling point of liquid nitrogen at atmospheric pressure is 77.35K. It does not chemically react with poultry food ingredients and meets the requirements of food hygiene. It is an ideal freezing preservative. The content of nitrogen in the air is about 78%, so in the atmosphere surrounding the earth, it can be said that there is inexhaustible nitrogen.
The Mechanism of Liquid Nitrogen Quick Freezing and Keeping Fresh
Under atmospheric pressure, when the liquefied nitrogen changes into a gaseous state from a liquid state, the average latent heat of evaporation per kilogram of liquefied nitrogen is 199.29 kJ, and the heat absorbed when it rises from 77.35K to 273K is 202 kJ . Liquid nitrogen quick freezing is to use this ultra-low temperature and heat absorption characteristics to directly spray it on the required bird body. At this time, the temperature difference is as high as 200K or more. It can carry out strong heat exchange and make the bird body freeze instantaneously, usually in 20 minutes. The entire freezing process can be completed around, 30 times faster than the ordinary freezing method. Because the freezing time is short, the ice crystals produced are very small, and the freezing speed is greater than the vapor penetration rate inside and outside the cell. Ice crystals are produced inside and outside the cell at the same time, which has no destructive effect on the cell. Therefore, the original color, fragrance, taste and freshness can be maintained after thawing. State is the best product of all countries in the world today.
Liquid nitrogen quick freezing process and equipment
The liquid nitrogen quick-freezing device suitable for quick-freezing poultry is shaped like a tunnel with a stainless steel wire mesh conveyor belt in the middle. The poultry body to be frozen is placed on the belt and passes through the pre-cooling zone, the freezing zone and the uniform temperature zone as it moves. After the freezing is completed The liquid nitrogen tank is sent out from the other end and placed outside the box. It is introduced into the freezing zone through a pipe system at a pressure of 4.9×104N/m2 for spray freezing. The temperature of the superheated nitrogen after endothermic vaporization is still very low, generally 258K At this time, the nitrogen gas is sent to the inlet by the fan to make contact with the poultry body that has just entered the tunnel for heat exchange and pre-cooling. After the poultry body enters the freezing zone, it comes into contact with the 83K atomized liquid nitrogen sprayed from the spray pipe It is frozen instantaneously and then enters the uniform temperature zone, so that the temperature of the surface and the center of the bird's body tends to be consistent, achieving the purpose of freezing through. It can be seen that the process of completing the entire process is to achieve quick freezing and preservation by consuming liquid nitrogen. As far as the refrigeration system is concerned, it can be called an open cycle.
The liquid nitrogen tank is placed outside the freezing box, the internal structure is a metal vacuum sandwich, and the outside is also covered with polyurethane heat insulation material for heat preservation. The pressure in the tank is generally within the range of 13.7%×104N/m2. If the pressure is too low, it will affect Normal spraying, too high liquid supply will affect safety, so there is a safety valve to ensure that the pressure in the system does not exceed the specified value. The amount of liquid nitrogen stored in the tank can be indicated by the liquid level indicator, and the filling valve can be used after use The tank is filled with liquid nitrogen, and the spray pipe system is welded by stainless steel pipes. In addition, there are 6 axial fans for stirring and conveying nitrogen.
Characteristics of liquid nitrogen quick-freezing and fresh-keeping device
1. High freezing quality:
The main factor that affects the freezing quality of poultry food is the size of the ice crystals formed in the cells. The color, aroma, and taste are directly related to the amount of cell destruction in the poultry body during the freezing process. The old ordinary freezing method takes a long time to form. The large ice particles will cause cell deformation and damage, while the freezing time of liquid nitrogen spray is short, and it has quick-freezing properties. This can be completely avoided. The ice crystals formed are very small, so it can maintain the original freshness, color and fragrance Its nutritional value, and does not explode, burn or rot during low temperature storage, and can be stored for a long time; the structure is simple, safe and reliable. The analysis shows that the moving parts of the whole set of equipment are only the moving mechanism of the conveyor belt and the simple axial flow fan. It is not as complicated as the ordinary refrigeration system, and there are many mechanical moving parts, which reduces the possibility of failure, and the system has low working pressure. No high-voltage equipment; simple operation. It can be seen that the device is a conveyor belt, continuous operation in a straight line. The operator only needs to operate simple buttons outside the box and pick up and drop frozen products outside the inlet and outlet; it consumes less power. This device relies on liquid nitrogen phase change refrigeration and the transformation of internal energy to achieve the purpose of quick freezing and preservation. Unlike ordinary refrigeration systems, which require a large amount of electricity to drive refrigeration machinery during freezing, so from the principle of refrigeration, it is It does not need to consume electricity directly; it is sanitary and clean and has no environmental pollution. The freezer box is composed of assembled heat-insulating panels, and the inner and outer guard plates are made of stainless steel, which is easy to disassemble and easy to clean, and it is quick to reinstall. The conveyor belt directly in contact with the bird body is also of stainless steel structure, which is more convenient to clean.
Since this freezing process does not require the CFC refrigerant in the ordinary freezing system, it has no destructive effect on the atmospheric ozone layer and is a trend of vigorous development in the future. In addition, it has the characteristics of small footprint and low noise.
2. Economic benefit analysis
We know that the cost of the device includes one-time investment and economic expenses during use. The former is mainly used to purchase a complete set of equipment. The amount is determined by the scale of production. The frequent expenses during use include the cost of liquid nitrogen, equipment depreciation, Labor costs, a small amount of electricity costs. If in the future, liquid nitrogen quick-freezing is used for fresh-keeping of poultry, shrimp and foods with high nutritional value, the demand for liquid nitrogen will be very huge.
Nuoruida (Tianjin) science and Technology Co., Ltd. is committed to research, development, and sales of liquid nitrogen freezer. Using European technology, we provide a variety of equipment. The main equipment is liquid nitrogen cryogenic freezer, liquid nitrogen cabinet freezer, liquid nitrogen tunnel freezer,sub-zero processing equipment, cryogenic freezing equipment, and so on.
