Research on the performance of compressed air system with the freeze dryer used for suction air pretreatment

Suction air pretreatment is an effective method to enhance the energy efficiency of air compressors especially under conditions of high ambient temperature. To address the issues of low annual utilization rates and extra placement space of the suction air pretreatment unit, a novel compressed air system that uses the freeze dryer for suction air cooling is proposed in this paper. It enables the precise control over the temperature and humidity of suction air by simply adding a high-temperature evaporator. Thermodynamic and economic models are established and solved based on the summer climatic data of Nanjing. System specific power, overall system efficiency, energy-saving ratio and payback period are defined as the performance indexes. Performance comparisons are carried out between the novel system and conventional systems without or with an independent refrigeration unit for suction air pretreatment. The results indicate that: optimal balance among the cooling load, system specific power and overall system efficiency is achieved with a suction air temperature around 26°C. Compared to the system without suction air pretreatment, the novel system exhibits a 15.5% average reduction in system specific power, a 2.15% increase in overall system efficiency. Besides, compared to the system using an independent pretreatment unit, the novel system also shows superior economic benefits. For an air compressor with a volume flow rate of 10 m 3 /min, an annual energy saving can be amounted to 435.68 kWh and payback period of the modified freeze dryer for suction air pretreatment is only about 23 days.