Chemical Engineering

Podbielniak Centrifugal Extractor

August 27, 2020

Podbielniak Centrifugal Extractor:– Extraction is a process in which the components of interest in a liquid mixture are separated by contacting the feed liquid mixture with another liquid called solvent and mixing both the liquids thoroughly. The components of the feed liquid mixture will redistribute themselves between the feed itself and the solvent.

The purpose of extraction can be either to remove impurities from the feed liquid mixture or to separate the valuable components from the feed liquid mixture.

The centrifugal extractors are type of extractors which contain provisions for rotating the liquids around fixed axis. Podbielniak Extractor is the oldest type of extractor which is still in use in industries. The Podbielniak extractors are also called as ‘Pods’.

The Structure of Podbielniak Extractor

The equipment is mounted by an outer casing and consists of a shaft mounted centrally. Various thin concentric cylindrical shells are placed one above the other. These cylindrical shells are perforated throughout their lengths and circumference and the axis of these thin perforated cylindrical shells align with the axis of the shaft. The shaft is hollow from inside. Feed tubes are placed inside the rotor, the shaft supports the rotor and also provides port which serve as liquid inlets and outlets. The rotating drum is provided by a drive pulley. Proper sealing arrangements are made at the contact between stationary and rotating parts.

Working of Podbielniak Extractor

The heavy liquid and the light liquid are introduced into the shaft but they are introduced from the opposite ends of the shaft.

The heavy liquid is let out from the center of the shaft and it spreads throughout the equipment from that point. The light liquid is channeled to the periphery of the rotating drum. It means initially when the operation has just begun, the heavy liquid is concentrated at the axis of the rotating drum and the light liquid is concentrated at the outer portion, near the periphery of the rotating drum.

Due to the rotation effect and due to the density of the heavy liquid, the heavy liquid moves outwards away from the shaft towards the periphery of the rotating drum. While doing so, the heavy liquid displaces an equal volume of light liquid. It means the light liquid moves inwards towards the shaft.

As the movement of both the liquids happen in diametrically opposite way, they come in to contact and mass transport of the component or components of interest takes place between the heavy liquid and the light liquid.

The extractor is designed in a manner that the contact takes place for only a few seconds.

The heavy liquid which reaches the periphery moves through the channel and gets out of the equipment through the shaft. The light liquid which reaches the centre of the shaft moves in and gets out through the shaft from the opposite direction of the heavy liquid. In this way a continuous operation is maintained.