Development Trend of Heat Pump Drying

- May 07, 2019 -

<> At present, the development of heat pump drying is mainly manifested in the following aspects:

(1) The research and development of high-pressure refrigeration compressor using compound refrigerant to improve the condensation temperature and meet the higher drying temperature requirements.

(2) A new type of heat pump with multi-stage evaporation was applied to meet the temperature requirements of different materials or the same materials in different drying periods. K. J. Chua and others from the Department of Mechanical Engineering, National University of Singapore have carried out two-stage evaporative heat pump drying experiments. The results show that the two-stage evaporative heat pump drying system can change the temperature and relative humidity of the drying system in a large range, and can improve the operating coefficient (COP) of the system and save energy consumption.

(3) Heat pump combined drying system. In order to further shorten the drying time and improve the drying efficiency, many foreign scholars have studied the combined drying system of heat pump and solar energy, as well as the combined drying system of heat pump with infrared or microwave heating. The combined drying equipment of heat pump and solar energy overcomes the shortcomings of large dispersibility, low calorific value, low temperature rise, low drying speed, limited by climatic conditions and unstable drying process. At the same time, it reduces the high cost of heat pump drying, which is suitable for high quality, green and low energy consumption drying of agricultural products (aquatic products) in southern China.

(4) Research and development of new heat pump technology. Based on the development of heat pump dryer with absorption refrigeration cycle, the absorption refrigeratory uses the characteristic that the solution can precipitate the vapor of low boiling point component under certain conditions, and can absorb the vapor of low boiling point component strongly under another condition to complete the refrigeration cycle. It realizes refrigeration by consuming heat energy as compensation. It has the characteristics of large refrigeration and heating capacity and wide fuel range, and is very suitable for the dry heat pump. Drying this kind of application object with high evaporation temperature. Chemical heat pump refers to a heat pump system driven by reversible heat absorption and exothermic chemical reaction. Compared with compression heat pump, chemical heat pump has the advantages of no power consumption, high temperature rise (heating temperature can reach more than 200 C), less operating components, low noise, and more conducive to environmental protection.

(5) Application of automatic control technology. Drying process is a complex and changeable process. According to material dehydration and environmental conditions, timely control of drying process parameters is conducive to improving energy efficiency and product quality. Heat pump drying system can adjust air humidity and air temperature in both directions. Therefore, the combination of modern detection, sensing and control technology in heat pump drying process can easily realize full automatic artificial intelligence control of drying process, thus reducing operation cost and improving product quality. In recent years, with the maturity of heat pump drying, its excellent energy-saving effect has been proved by various experimental studies. In addition to people's attention to environmental issues, heat pump drying has shown broad application prospects. Heat pump drying has begun to be applied to the drying of food, biological products, seeds and other heat-sensitive materials. New environmentally friendly refrigerants reduce the adverse effects of environmental problems on the application of heat pump drying. The application of multi-stage evaporative heat pump cycle system, combined heat pump drying equipment, multi-purpose heat pump combination system and automatic control technology will be the main development direction of heat pump drying technology.

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