Investigation On Drying Performance And Heat And Mass Transfer Characteristic Of A Novel Compressed Air Drying System Using Pressurized Liquid Desiccant

Considering disadvantages exist in traditional compressed air cooling dehumidification such as the compressed air drying systems consume huge electricity power and refrigerant leakage of the refrigeration system leads to a series of environmental problems, a novel compressed air drying method based on pressurized liquid desiccant dehumidifier is proposed in this paper. Compared with cooling dehumidification, it consumes less electricity, and is friendly to environment. Besides, it is smaller in size and easier to operate. Moreover, the regeneration process can be driven by the low-grade heat with the temperature approximately 60-80℃ such as the waste heat generated in air compressor, reducing the energy consumption of compressed air drying process. This paper mainly presents theoretical and experimental study on the performance of the novel compressed air drying system.The relevant background of traditional compressed air drying systems and liquid desiccant system performance under atmospheric pressure condition have been reviewed, including the disadvantages and advantages of various drying systems and the related theoretical and experimental research.The operating principle of the novel compressed air drying method based on pressurized liquid desiccant dehumidifier is expounded. An experimental setup for counter-flow dehumidifier using LiCl solution as liquid desiccant is established, and the shape and dimension of the main dehumidifying device such as air compressor, pressurized dehumidifier structured packing and solution pump are introduced in detail. The errors under the typical experimental conditions data are analyzed, and the result indicates that the maximum average relative error of the main performance parameters is within 5%. So the experimental data has high accuracy and reliability.The humidity ratio of outlet compressed air, vapor removal of processed compressed air, moisture removal rate, and dehumidification efficiency are selected as the pressurized dehumidifier performance indices. Calculated results demonstrate that the minimum possible humidity ratio of outlet compressed air could reach 0.11 g/kg under 0.80MPa and different inlet solution parameters. In addition, the influence of the inlet compressed air and aqueous solution parameters such as air pressure, compressed air velocity, solution flow rate, temperature as well as concentration on these performance indices has been experimentally studied based on the established test-bed. Furthermore, the optimum ratio of liquid to compressed air flow rate is recommended to keep around 1.5 under different experimental pressures. Theoretical analysis and experimental result are useful to verify the feasibility of the proposed method in industrial application and it also provides some reference for the optimized operation of the novel drying system.A theoretical model based on finite volume method is firstly developed and validated by reliable experiments. The impacts of inlet parameters on heat and mass transfer coefficients are obtained using calculated program based on experimental data and mathematical model. In addition, the empirical correlations of heat and mass transfer coefficients are obtained through the experimental data, and then validated through the comparisons of calculated results with experimental data. Result indicates that the discrepancies of the temperature and humidity ratio of outlet compressed air and the outlet temperature of solution between simulation and experimental results are within±1.5℃, ±0.3g/kg and ±0.5℃ respectively. Reliable and important data of heat and mass transfer coefficients are provided for optimum design of dehumidifier, which is also meaningful for understanding the heat and mass transfer behavior between compressed air and liquid desiccant. Theoretical analysis shows that the optimum ratio of liquid to compressed air flow rate is in the range of 1.3-1.6.The energy consumption level of the proposed method and cooling dehumidification under summer dehumidification conditions in Nanjing are discussed theoretically. In addition, the feasibility of regenerating though the waste heat from the air compressor in the proposed compressed air drying system is verified. Results indicates that the electricity consumption of pressurized liquid desiccant system is 16.0% lower than the conventional compressed air cooling dehumidification and the difference of electricity consumption for per gram water removal between them can reach 1.42 kJ/g when reaching the same humidity ratio under 0.30MPa. Considering compressed air drying using pressurized liquid desiccant can reach under lower pressure (0.65MPa) than cooling dehumidification (0.80MPa), the electricity consumption is 17.9% lower than cooling dehumidification and the difference of electricity consumption for per gram water removal between them can reach 2.94kJ/g.Furthermore, the waste heat of air compressor can satisfy the heat consumption of regeneration process under different dehumidification conditions. Hence, the novel compressed air drying method based on pressurized liquid desiccant is expected to replace the conventional compressed air cooling dehumidification in the practical industrial application.