Performance Study On The Cooling And Liquid Desiccant Dehumidifier With Multi-stage Matrix Structure

Industrial gas is called the "blood" of modern industry,and has been widely used in steel,coal chemical,semi-conductor,aerospace and other fields.Large scale low temperature air separation technology is one of the main methods to obtain oxygen,nitrogen,argon and other industrial gases.The energy consumption of large-scale cryogenic air separation system is huge,and the energy consumption of compressor system accounts for more than 70% of the total energy consumption,which has great potential for energy saving.The inlet air cooling and dehumidification is an effective method to reduce compression work.It has been applied in the field of energy saving of small compressors,but there is less research on dehumidification pretreatment for air compressors in the large-scale cryogenic air separation system.This is because the air intake dehumidification of air separation compressor has the characteristics of large air flow,deep dehumidification,simultaneous dehumidification and cooling.It is difficult for traditional dehumidification methods to meet the above requirements.Therefore,the following research work has been carried out in this paper:1)A multi-stage cooling and solution integrated dehumidification system is proposed,including a dew-point cooling dehumifier with a multi-stage matrix structure(MCD)and an internally cooled liquid desiccant dehumidifier with a multi-stage internal circulation structure(MICLDD).A multi-stage cooling and solution integrated dehumidification system is proposed,including a dew-point cooling dehumifier with a multi-stage matrix structure(MCD)and an internally cooled liquid desiccant dehumidifier with a multi-stage internal circulation structure(MICLDD).The process air is pre-cooled and pre-dehumidified by a dew-point cooling dehumifier,and then dehumidified further by an internally cooled liquid desiccant dehumidifier.The MCD is a packing tower where packing modules are arranged in a multi-stage matrix structure.Using the external and internal drainage devices,the cooling capacity is evenly distributed to different areas inside the packing modules.Therefore,the overall cooling and dehumidification efficiency is improved.In the MICLDD,there are three stages in the direction of air flow and eleven layers in the direction of solution flow.The solution is cooled by the coolers before flowing through each layer of packing and can maintain low temperature and high dehumidification potential.In addition,the solution concentration and flow rate can be evenly distributed according to the air humidity distribution along the dehumidification process due to the internal circulation structure.Therefore,it can expand the handling capacity and improve the dehumidification efficiency.2)Performance of the integrated dehumidifier is investigated.The advantages of the multi-stage matrix structure dehumidifier compared to the traditional single-stage cross flow structure dehumidifier are compared;furthermore,the advantages of the integrated dehumidifier compared to the single dehumidifier are analyzed.Firstly,performance study of the MCD and the MICLDD is carried out based on the numerical model.It is found that compared with the traditional cooling dehumidifier with single stage cross flow structure,the cooling water can be distributed evenly in the MCD,which will strengthen the heat and mass transfer process between the cooling water and process air.Therefore,the dehumidification performance of the MCD will be improved.In addition,performance comprison between the MICLDD and the PTCT proposed by Bansal et al.[41] is investigated.The results show that the MICLDD improves the heat transfer performance between the cooling water and the desiccant solution,thereby improving the dehumidification efficiency.Furthermore,the dehumidification performance of the cooling and solution integrated dehumidifier is simulated.Compared with the single MCD and MICLDD,the integrated dehumidificer can integrate the advantages of solution dehumidification(strong dehumidification capacity)and cooling dehumidification(low outlet temperature,relatively high COP),and achieve the cold and dry air with a relatively high COP.Compared with the single MICLDD,the COP of the integrated dehumidifier can be increased by 6%-8%.3)The dehumidification performance of the cooling dehumidifier is initially tested.The effects of air flow and cooling water temperature on the overall dehumidification rate,dehumidification efficiency,and heat exchange capacity of the dew-point cooling dehumidifier are analyzed.The dehumidification performance of the cooling dehumidifier is experimentally tested.The effects of air flow and cooling water temperature on the overall dehumidification rate,dehumidification efficiency,and heat exchange capacity of the dew-point cooling dehumidifier are analyzed.The calculation formulas for the heat and mass transfer coefficients of the cooling and dehumidification process are summarized based on the experimental results.The experimental results are compared with the simulation results to verify the reliability of the model.The results show that the average errors of moisture content and temperature at the outlet of dehumidifier are 8.6% and 2.1%,respectively and the model shows good accuracy.An energy-saving scheme of air separation system compressor based on cooling and solution dehumidification device is proposed.The influence of different operation parameters on the performance of the dehumidification device is studied by simulation,and the enhanced dehumidification mechanism of the device is analyzed.The results provide theoretical support for the optimal design of dehumidifier and industrial application.