Comparison Of Macro-Mixing And Mass Transfer Characteristics Of A Stirred Tank With Different Impellers

Stirred tanks are widely used in chemical industrial process,such as metallurgy,pharmaceutical processes,paper and energy.Impeller is the core component of the stirred tanks,and its configuration and operation conditions are important factors affecting the performance of the stirred reactor.A preliminary study found that the invented centripetal impeller has excellent performance,however,it has not been systematically studied.In order to enrich the data of centripetal impeller performance,the macro-mixing characteristics and gas-liquid mass transfer characteristics of stirred tanks installed with centripetal impeller,Rushton impeller,three pitched blade impeller and punched blade impeller were systematically studied.The influence of impeller speed,impeller off-bottom clearance,impeller type on mixing time,power,mixing efficiency and gas-liquid mass transfer efficiency of the stirred tank was investigated.It will provide fundamentally theoretical basis for the industrial enlargement and application of the centripetal impeller.Chapter ?,introduction.The development of impeller type,especially radial impeller,axial flow impeller,concentric slurry and combined slurry,was described in detail,and the research results of macro-mixing time and mass transfer coefficient,the internal relations and conclusions,and the research methods were expounded.In particular,the gas-liquid mass transfer coefficient reflects the key parameters of the stirred tank characteristics.The mass transfer process is the reaction of the control steps,and the role of the design of the reactor was described.Chapter ?,the experimental methods of gas-liquid mass transfer coefficient,macroscopic mixing time and power measurement are described.In the course of studying the mixing characteristics,the conductivity method was used to measure the macroscopic mixing time of the single-layer impeller mixing tank,and the torque method was used to measure the power of the impeller,while in the study process of gas-liquid mass transfer characteristics,the gas-liquid mass transfer coefficient in the monolayer mixing tank was measured by adding sodium sulfite method.Chapter III,the macro-mixing characteristics of stirred tanks were studied through conductometry method.The results show that the mixing time of the four impellers are all decreased with increasing impeller speed,and the power are all increased.At the same impeller speed,the power of the Rushton impeller is the highest,and the three pitched blade impeller is the lowest.The power of centripetal impeller is only a little higher than that of the three pitched blade impeller.However,the macro-mixing time of the four impellers shows different trends with increasing the impeller off-bottom clearance.The importance of the factor affecting the macro-mixing efficiency is impeller speed>impeller type>impeller off-bottom clearance.Among the four impellers,the overall evaluation of the macro-mixing efficiency of the centripetal impeller is the highest.Chapter IV,the gas-liquid mass transfer efficiency of stirred tanks installed with different type impellers were compared.The results show that the gas-liquid mass transfer coefficient of the four impellers are all increased with increasing impeller speed.However,the gas-liquid mass transfer coefficient of the four impellers shows different trends with increasing the impeller off-bottom clearance.By comparing the gas-liquid mass transfer coefficient under the same power consumption,it is found that the gas-liquid mass transfer coefficient of the centripetal paddle is the highest under high power consumption,and it shows good gas-liquid mass transfer performance.