Podbielniak Extractor
The Podbielniak contactor is a horizontally mounted centrifuge. The Pod has perforated, concentric cylindrical bands that fit into grooves on the rotor at one end and the endplate at the other. As seen in Figure 3, the rigid inner shaft supports the rotor, and also provides the ports that serve as process liquid inlets and outlets. The shaft is drilled almost to the center from each side, but not through. There is a central channel and an annular channel on both the sides. This provides the four channels needed for process liquid flow.
Feed tubes are provided inside the rotor for each inlet and outlet that connect to the shaft. These tubes extend to the rim and are drilled into the rotor for added stability. These tubes are cross-drilled at the appropriate radius to provide an inlet or outlet for a liquid.
The heavy liquid (HLI) is introduced near the shaft, and the light liquid (LLI) is introduced near the rim of the rotor. As a result of the centrifugal force and density difference, the heavy liquid is forced out to the rim. As the heavy liquid propagates through the perforations, it displaces an equal volume of light liquid towards the shaft. The two liquids flowing countercurrently are forced to pass each other through the perforations on each band, leading to intense contact. The light liquid is collected at the shaft (LLO), and the heavy liquid is collected at the rim (HLO). This countercurrent series of dispersion and coalescence allows multi-stage extraction.
The internal volume of the Pod is divided into three cylindrical zones based on the radial position of the two liquid inlets. The countercurrent contact zone is the volume enclosed between the two inlet radii. In this zone, the two liquids are forced countercurrently through the perforations leading to intimate contact and maximum surface area generation for mass transfer.
Inboard of the contact zone is light liquid clarification zone, where the light liquid is settled and entrained heavy liquid is removed. Similarly, the heavy liquid clarification zone, which is outboard of the contacting zone, clarifies the heavy liquid before it exits the Pod.