19-08-2014, 10:18 AM
Mixer settlers are commonly used for liquid-liquid contacting with various objectives such as mass transfer, chemical reaction, separation and purification of metals etc. It has wide spread applications in the nuclear industry. A mixer in which the pumping action of the impeller is utilized for the flow of the phases is called as Pump-Mix mixer. When the impeller rotates, a low pressure region is developed in the vicinity of the impeller. This low pressure region causes suction of the phases into the mixer. Pump-mix mixer avoids the need for interstage liquid pumping. Hydrodynamics of pump mix mixer have been studied over wide range of system geometry and operating conditions. The optimum location of the impeller has been found just above the suction box. Head and flow developed just above the suction box is higher than other locations.
Mixer settlers are commonly used for liquid-liquid contacting with various objectives such as mass transfer, chemical reaction, separation and purification of metals etc. It has wide spread applications in the nuclear industry. A mixer in which the pumping action of the impeller is utilized for the flow of the phases is called as Pump-Mix mixer. When the impeller rotates, a low pressure region is developed in the vicinity of the impeller. This low pressure region causes suction of the phases into the mixer. Pump-mix mixer avoids the need for interstage liquid pumping. Hydrodynamics of pump mix mixer have been studied over wide range of system geometry and operating conditions. The optimum location of the impeller has been found just above the suction box. Head and flow developed just above the suction box is higher than other locations.
Different impellers have been compared at this location based on equal power consumption basis. It has been observed that pitch blade turbine upflow type impeller gives better head and flow compared to other impellers. To reduce recirculation of the liquid in mixer, stator rotor system has been used. It has been found that head and flow developed in presence of the stator is higher compared to without stator system.
To utilize low pressure region of higher intensity created at the tip of the impeller blade, annulus orifice configuration has been used. It has been observed that head and flow developed in case of annulus orifice is higher compared to simple orifice. In two phase study, it has been observed that as speed increases, drop size reduces due to increased shear rate. It has been found that drop size formed by pitch blade turbine upflow impeller and disc turbine impeller is found to be same at equal P/V. It has been found that as flowrate increases drop size also increases due to increased coalescing rate. It has been observed that as speed increases, dispersion band thickness in the settler increases due to formation of the fine drops in the mixer. Effect of the speed on dispersion band thickness has been compared for different type of the impeller at given power consumption. Batch settling experiments has also been carried out.