New Liquid Desiccants For Different Humidity Requirements Physical Properties Measurement And Performance Study

The requirements of humidity in indoor and industrial environments can be meted better by liquid desiccants technology and the waste heat、waste heat、solar energy and other low-grade energy can be used to achieve regeneration,which is an low-carbon dehumidification method.The existing liquid desiccants in humid environment dehumidification/regeneration performance to be improved,expensive,corrosive.In addition,when dehumidifying in low humidity environment,there is a risk of solution crystallization due to the limitation of solubility,which limits dehumidification capacity and thus cannot dehumidify safely and efficiently.In response to the above problems,this paper has carried out a study on the physical properties and performance of new liquid desiccants for high and low humidity environments respectively,and has also conducted a comparative analysis with conventional liquid desiccants:Firstly,a model framework for screening desiccants in humid environmentwas constructed and its reliability was verified based on the gas-liquid phase equilibrium theory.The model obtained the values of pressure drop indicators for 6 anions,9 cations and 54solutions,respectively.At the same time,with reference to the numerical index of pressure drop of different solutions in the model,the Ca Br₂liquid desiccants was selected to create indoor building comfort heat and humidity environment requirements for high humidity environment.Then,the solution saturation vapor pressure measurement test bench was designed and built,through which the saturation vapor pressure data gaps of high concentration Ca Br₂solution in the field of dehumidification were filled.Apart from that,the specific heat capacity,viscosity and density of Ca Br₂liquid desiccants were measured systematically,and a nonlinear fit of the relevant physical properties of the Ca Br₂solution was also performed based on the experimental data,which enriched the basic thermal property data of Ca Br₂solution in the field of liquid desiccants.By collecting the relevant research data about the physical properties of Li Br solution,Li Cl solution and Ca Cl₂solution,the differences in the changes of saturation vapor pressure,specific heat capacity,viscosity and density of different solutions under the above four equivalent concentrations were compared and analyzed.Among them,the specific heat of Li Cl solution is the largest at equivalent concentration,the viscosity of Ca Cl₂solution is the largest,and the density of Ca Br₂solution is the largest,which enriches the basic thermal physical property data of Ca Br₂solution in the field of dehumidification;the physical property data provide relevant theoretical basis for the experimental results.Secondly,the experimental concentrations of Ca Br₂solution and Li Br and Li Cl solutions was determined based on the above saturated vapor pressure test results.The dehumidification/regeneration performance of the three dehumidification solutions under high humidity environment was studied,and the dehumidification/regeneration performance under different air speed,solution flow rate,solution temperature and air temperature were explored,and the economy and corrosiveness of the three solutions were compared and analyzed,and finally the comprehensive performance of the three solutions was evaluated based on the dehumidification/regeneration performance,economy,corrosiveness and energy consumption of transmission and distribution,and the following conclusions were drawn:the dehumidification performance of the three solutions at equivalent concentrations is comparable,and the difference in dehumidification capacity between the three solutions is within 7%.but the regeneration of Ca Br₂solution is about 14.2%higher than that of Li Cl solution and about 17.1%higher than that of Li Br solution on average,which is mainly due to the large value of pressure drop index of Ca Br₂solution and the high mass transfer driving potential of the solution in the regeneration process;because Ca Br₂solution is significantly stronger than the traditional dehumidification solutions Li Cl and Li Br in terms of regeneration performance and price,while the difference between dehumidification performance and transmission and distribution energy consumption is not significant,so Ca Br₂has the best overall performance.Then,to meet the dehumidification needs of low humidity environment,low vapor pressure,low corrosiveness,low crystallization temperature of imidazole type ionic liquids was chosen..Through the analysis of the thermal properties of ionic liquids found:the ionic liquid P-T curve has a lower saturated vapor pressure at low temperatures,high saturated vapor pressure at high temperatures of the characteristics.In addition,the specific heat and thermal conductivity of the ionic liquid is more sensitive to concentration performance and not sensitive to temperature performance,the same temperature,the thermal conductivity of ionic liquids than water thermal conductivity is lower 38%-61%,when the concentration of ionic liquids greater than 50%,viscosity is more sensitive to temperature and concentration,when the concentration of ionic liquids less than 50%,viscosity is more sensitive to concentration.Finally,the differences in dehumidification/regeneration performance of ionic liquids and near-saturated Li Br solutions at different wind speeds and different solution flow rates were compared and analyzed in a low humidity environment,and the experimental results showed that:Low wind speed ionic liquid and Li Br solution dehumidification volume difference within 10%,because the ionic liquid viscosity is larger,in the same flow rate of ionic liquid cloth liquid effect is not as good as Li Br solution thus resulting in dehumidification volume difference.In addition,in the dehumidification interval,the difference in solution viscosity makes the difference in the degree of gas-liquid interface disturbance increases with the increase in the inlet wind speed,so the difference in dehumidification capacity of the two solutions appears to increase with the increase in wind speed.However,the difference in moisture content between ionic liquid and Li Br solution is always less than 0.2g/kg,while ionic liquid does not crystallize and has low corrosiveness.the regeneration performance of the ionic liquid is significantly stronger than that of the Li Br solution,and the difference in regeneration amount can be up to 48%.The experimental results are consistent with the physical property analysis,indicating that the imidazole-based ionic liquid has good combined dehumidification/regeneration performance in low humidity environment.