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The Podbielniak Contactor, popularly known as the "Pod," is a liquid-liquid centrifugal extractor and separator providing differential countercurrent extraction in a compact hermetic rotor.
The Pod operates on two principles: separation and extraction. Separation effectiveness is a function of the density difference, separation force, and the residence time at that separation force. In a centrifuge like the Pod, the centrifugal force creates a separation force many times normal gravity.
Liquids are forced countercurrently through the perforations, leading to intense contact between the two liquids and generation of interfacial surface area for mass transfer.
The Podbielniak extractor is analogous to a sieve plate column that is rotated about the top. The Podbielniak contactor has perforated cylindrical bands that serve the same purpose as the horizontal plates in the sieve plate tower.
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. 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 Pod is flooded with the process liquids during operation. The Pod is equipped with mechanical seals in order to facilitate hermetic operation. As the Pod is flooded with process liquids at all times, internal volume usage is maximized. Podbielniak contactors are automated by the use of a variable frequency drive. The only mechanical monitoring required is for speed, lubrication flow for the bearings and product flow for wetting of the mechanical seals. Once the Pod is up and running, it requires minimal supervision.
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 criteria for process feasibility in a Pod are that the two liquids are at least partially immiscible and have a density difference. If the two liquids are totally miscible, they cannot be physically separated.
Robust mechanical features along with distinctive process design make the Pod a unique contactor for extraction and separation. The Pod is a differential countercurrent centrifugal extractor, (opposed to the batch-wise countercurrent configuration in mixer-settlers and most centrifuges) which increases extraction efficiency at a given flow rate ratio. Internal clarification zones allow handling of easily emulsified systems resulting in both effluent streams that are free of entrainment in most cases. The unique design of the Pod reduces solvent usage and operating costs while producing better product at higher yields in a safer environment.
The Pod has worked well in applications where an organic product stream is purified by reacting the impurities out using an acid or a caustic wash. The Pod has been used for many applications like acrylics, aromatics, fumaric acid, plasticizer refining, polycarbonate washing, insecticide and herbicide manufacturing, acid and caustic treating of lube oil, etc.
S/N 58332
Liquid SP GR 1.0
Baker Perkins
Model B10P
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