Experimental Study On Liquid Desiccant-based Dehydration Under Low-temperature Wet Flue Gas

The flue gas emitted from coal-fired power plant contains a large amount of water vapor.The water vapor content entrained by flue gas is approximately 80g/kg(dry gas),which makes one of the main consumption of water resource in power plant,and takes huge of low-temperature waste heat with the form of latent heat.Simultaneously,water vapor in flue gas causes a serious of problems such as stack corrosion,liquid discharge and plume downwash.With the intensive study of water and heat extraction from flue gas,the technology of wet flue gas dehumidification is attracting more and more attention.The technology of liquid desiccant dehumidification,based on the difference between partial pressure of desiccant solution and wet gas,achieves water absorption from humid air.It can be potentially used in the field of wet flue gas dehumidification.Desiccant selection is one of the key factors for system performance and economy.Considered of the application environment,desiccant property,price and other factors,Calcium Chloride was chosen as the desiccant for testing.Firstly,numerical approaches for counter-flow tube falling film gas dehumidifier were applied to preliminarily study the system performance and features.With the governing equations describing the physical problem,the finite difference method is applied to study the heat and mass exchange in the dehumidifier.The effect of solution temperature,concentration,Reynolds number,mass transfer area and gas inlet temperature on dehumidification efficient are investigated,the variation of gas side and liquid side are predicted.The numerical calculation confirms the feasibility of this technology.Water recovery efficiency could be more than 50%.This process adapted in a wide range of saturated gas temperature.Solution temperature raise is the main factor for performance reduction.The heat and mass transfer resistance is mainly in the gas side.This simulation contributes to the understanding of dehumidification and provides reference for further test.Secondly,a laboratory scale adiabatic tube falling film dehumidifier was designed and established,with CaCl2 solution as liquid desiccant,the performance of this technology and the effect of influence factors such as solution temperature,concentration,mass transfer area was tested.Moreover,a comparison between condensation and liquid desiccant-based dehumidification was carried out.The research results show that this technology can satisfy the requirement of gas dehumidification with a maximum efficient more than 70%.The influence of each factor has a relative consistent trend with the simulation results.Solution concentration and temperature are the key factors influence humidification efficiency;the solution concentration should be less than 45%.Lower solution temperature would improve the efficiency,but the solution crystallization temperature and system economy should be taken into account.A fully consideration of measures of solution temperature monitor and control is necessary in the process of application.Comparing with condensation,which achieves efficiency of 16.9%-33.9%,the water recovery efficiency is about 40%?55%under the same operating parameters,moreover,the relative humidity of gas outlet is approximate 60%,which indicates the potential for preventing stack corrosion.In the end,the mass transfer coefficient has been yielded,it was in the range of 0.009m/s?0.040m/s.The dehumidification efficiency correlation was derived from the experimental results as ?=467.24Tain0.4805Xin0.841T-aolin1.843?lg0.074A0.432.These results are helpful for further research in pilot scale.