Research progress in the application of CO2 refrigeration technology to agricultural product cold chain logistics preservation

Abstract: Energy-efficient, green, and environment-friendly refrigeration technology can be developed for agricultural products, particularly under the "double carbon" goal in the world. Carbon dioxide (CO2/R744) can be expected to serve as one of the ideal substitutes for traditional refrigerants, due to the colorless, tasteless, non-toxic, non-flammable natural refrigerant, and excellent thermal stability. A high per-unit refrigerating capacity of swept volume can be obtained with a low greenhouse effect. The characteristics of CO2 have drawn much attention in environmental protection and efficient refrigeration after the early action and the middle silent period. Therefore, CO2 has been relaunched as a natural refrigerant in various industries. The current CO2 refrigeration technology has been used in the cold chain logistics of agricultural products, ice-making, and air conditioning. The refrigeration effect is better than that of the traditional. However, the high energy expenditure can be the general issue in cold chain logistics. Therefore, it is a high demand for energy-saving and green refrigeration to reduce the large post-production loss in modern agriculture. In this study, the characteristics and development history of CO2 refrigeration were reviewed to compare the critical temperature, critical pressure, ODP, GWP, and per-unit refrigerating capacity of swept volume between different refrigerants. The CO2 refrigeration facilities and devices were also introduced in terms of refrigeration systems, equipment, and accessories, such as compressors, heat exchangers, and throttling devices. The application of CO2 refrigeration was summarized in the storage and transportation of agricultural products. The future direction was also proposed for the use of CO2 refrigeration technology in the cold chain logistics preservation of agricultural products, according to the actual agricultural products and requirements. The current difficulties were determined to improve the matching degree of equipment under different working conditions, and the efficiency of CO2 compression and liquefaction under low-temperature environments. Some recommendation was also addressed to accelerate the CO2 refrigeration facilities and equipment, such as CO2 mobile refrigerant storage, and three-dimensional intelligent refrigerant storage suitable for the preservation of agricultural products in cold chain logistics. CO2 refrigeration can be expected to integrate with the cold chain logistics of agricultural products. The reliability and stability of CO2 refrigeration equipment and system should be improved to fully meet the strong demand in different industries of cold chain logistics. The finding can provide technical support to reduce the post-production losses of agricultural products in China. The product quality during storage and transportation can be improved for the energy saving of cold storage, in order to promote the cold chain logistics towards the green, low-carbon, and recyclable direction.