Experimental Study And Optimization Of Compressed Air Drying System Using Liquid Desiccant Driven By Waste Heat Recycled From Air Compressor

Compared with the traditional cooling dehumidification and solid adsorption dehumidification,the compressed air-drying system using liquid desiccant has the advantages of small volume,easy operation and recycling waste heat from the air compressor to drive solution regeneration.Based on reducing energy consumption,it can effectively replace the traditional cooling dehumidification,realize reliable control of dew point and cover the market blank area with dew point of-20~10?.The experimental and theoretical study on the dehumidification performance of the compressed air-drying method using liquid desiccant was carried out in our previous paper.To further verify the feasibility of using waste heat recycled from the air compressor to drive solution regeneration,a complete compressed air-drying system will be established in this paper,including dehumidifier,regenerator,waste heat recovery module of the air compressor.The combination of theory and experiment is used to explore system performance and optimize the process of the system.Firstly,working procedure of the compressed air-drying system is introduced,and experimental bench is established.The main components in the experimental bench,such as the air compressor,packed towers(dehumidifier and regenerator),solution pumps,measuring devices,etc.,are introduced.In addition,the error analysis of the experimental data is carried out.The analysis results show that the maximum relative error of the main parameters is within 9%,indicating that the experimental data has certain reliability.Secondly,the system performance was explored from experimental and theoretical dimensions based on the established test bench.The experimental results show that the dew point at 0.8MPa can reach below 0?(the minimum value is-7.7?),indicating that the compressed air-drying system using liquid desiccant can replace the traditional cooling dehumidification and broaden the drying range.Besides,the average regeneration temperature of the solution can reach 70? and the ratio of regeneration heat consumption to theoretical waste heat amount is between 30%and 35%,indicating using waste heat from the air compressor to drive solution regeneration is completely feasible.Moreover,effect of different key parameters,including solution flowrate,solution temperature and ambient conditions on system performance is analyzed by mathematical model.It can be concluded that relative higher solution flow rate,lower inlet solution temperature of dehumidifier and higher inlet solution temperature of regenerator can get a lower humidity ratio.Considering the stability of the system to prevent crystallization of the solution,the inlet solution temperatures of regenerator selected are 70?(summer),39?(winter),60?(transitional season)respectively.The heat and mass transfer characteristics in the dehumidification process are explored from two aspects based on established system mathematical model.The two aspects are the comparison of heat and mass transfer of LiCl and LiBr in the dehumidification process under high pressure,and the heat and mass transfer of LiCl solution in the dehumidification process under high pressure and normal pressure.For LiCl and LiBr solution,effect of different key parameters,including air pressure,air flow rate,inlet solution concentration of dehumidifier,inlet solution temperature of dehumidifier,inlet solution flow rate of dehumidifier,on the trend of heat and mass transfer in the dehumidification process is same.The flow rate of compressed air has a great influence on the mass transfer coefficient during dehumidification.The increase of flow rate can significantly enhance the mass transfer capacity during dehumidification under high pressure.Comparing and analyzing the heat and mass transfer characteristics of LiCl solution in the dehumidification process under high pressure and normal pressure,it is found that for atmospheric dehumidification,the increase of air flow rate does not significantly enhance the mass transfer.The experimental data were selected using LiCl solution as liquid desiccant,coupled to obtain the heat and mass transfer correlation in the dehumidification process under high pressure,and verified.The experimentally measured data is compared with the values calculated by mathematical model,the results show that the deviation of the outlet humidity ratio is within±10%,the outlet temperature of compressed air and solution is within±5%.The deviation is within the acceptable range indicating that the model is reliable.Then,the dehumidification range of the compressed air-drying system using liquid desiccant is theoretically analyzed based on the established system mathematical model.In the theoretical analysis,LiCl solution is selected as the desiccant,and the pressure of the compressed air is 0.8 MPa.The compressed air-drying system using liquid desiccant can dry the compressed air to dew point of 0? at normal temperature,indicating that it can replace the traditional cooling dehumidification technology at normal temperature.For areas where the degree of dryness is higher,an additional source of cooling is needed to enhance the dehumidification capacity.For dry places where the dew point is required to be higher than-10?,choose to combine with the chiller.For the dry place where the dew point is required to be-20? to-10?,choose the refrigeration system to combine,which can provide a cold source below 0?.Finally,a compressed air-drying system with a gas volume of 10 Nm~3/min is designed by the steady state model of the system,and the system process is optimized from the theoretical level.After the system is added to the self-circulation,the drying performance is basically unchanged compared with the system without self-circulation.However,the regeneration heat consumption and the cooling load of the solution cooler are greatly reduced,and the corresponding percentage reductions are 53.5%and 43.7%,respectively.In addition,the compression power consumption of wet air is greater than that of dry air.It is necessary to install a pre-dehumidification module in the southern part of China,followed by the eastern and central parts of China,and no need to set up in the north and west.On the choice of month,the pre-dehumidification module is set from April to September in the southern part of China and set from June to August in the eastern and central parts of China.After adding the pre-dehumidification module,the percentage of energy savings is around 2%.