Podbielniak® Centrifuge Video
B&P Littleford, manufacturers of Baker Perkins and Littleford Day machinery, is one of the world's largest suppliers of process equipment for the food and chemical processing industries. And has provided high quality equipment with proven reliability ranging from customized individual machines to totally automated production lines. For more than 50 years, B&P's pod contactor has served the chemical processing industries need for liquid-liquid processing. More than 1,500 units are currently in service worldwide on five continents in a number of major processing applications. Ranging from acid treating to vanadium recovery, from essential fragrance oil separation to water pollution monitoring.
POD Liquid-Liquid Processes
The pod contactor is generally used for liquid-liquid processes including extraction, reaction, separation, and washing. To better understand how this versatile machine can handle such a wide range of processes, let's look at the unit in more detail. Using this scale model, we can see that the pod contactor is a simple rotating device that employs centrifugal force to contact and separate phases of different specific gravities in liquid-liquid systems. The spinning rotor contains a series of concentric perforated sheet-metal cylinders called elements. The elements provide coalescing surfaces. And as liquids flow through the perforations, intimate contact is assured. Generating up to 3,000 times the force of gravity, the pod is capable of separating liquids with specific gravity differentials as low as 0.01 and handling the continuous flow equivalent of a gravity sieve column with thousands of times its volume.
The pod rotor and shaft assembly is supported by a massive base and covered by a hinged enclosure. The precision balance rotor and shaft turn with rugged bearings. A static conducting poly V-belt drive is used to spin the rotor and shaft assembly. In this cutaway of the rotor we can see the series of concentric elements each with perforations. Liquids flow into and out of the rotor through distribution tubes. These rows of tubes extend radially from the rotor shaft like the spokes on a wheel. The tubes in this row are Asko tubes. They are removable and permit access to the rotor for periodic cleaning. Each row of tubes distributes one of the feed liquids or collects an affluent. In this stylised schematic of a typical rotor, the heavy liquid out or HLO, the light liquid in or LLI, and the heavy liquid in or HLI, tubes are attached to the shaft.
At the rotor rim, they are sealed by Asko plugs. The removable Asko tubes are positioned over the light liquid out passageway and are not attached to the shaft. Holes are drilled in the distribution tubes. The position of the holes is determined by what liquid the tubes will convey. The drilled holes permit liquid to flow from the distribution tubes to the rotor. To understand how the pod contactor operates, let us now introduce a liquid into the machine. The arrangement of inlets and outlets shown in this example, is typical of many extraction installations. However, the pod can be modified to fit specific applications. The blue color represents the flow of the heavy liquid. In this example, the blue heavy liquid feed flows into the right side of the contactor. Through the small seal and down the center shaft channel. The heavy liquid feed then flows into the distribution tubes which intersect the right central shaft channel.
The heavy liquid in or HLI distribution tubes have holes drilled in them at a distance of about 25% to 35% of the distance to the rim of the rotor. The location of these holes is precisely selected for each specific application. The heavy liquid feed flows out through the holes in the distribution tubes and is fed into the proper processing volume in the rotor. As the heavy liquid is centrifuged outward toward the rotors rim, it flows through the perforations in the concentric elements. The perforations in these elements are also custom tailored to each specific process need. The heavy liquid collects at the rotor rim where it flows into a set of heavy liquid out, or HLO return tubes, with holes drilled just at the inside surface of the rotor rim. These tubes root the flow of heavy liquid back to the annular channel on the left side of the shaft. Where then flows past the large seal and out of the pod contactor.
Next, let's introduce some light liquid feed into the pod and trace entries its path. The red light liquid is fed into the left side of the pod contactor through the small seal and flows down the central shaft channel. The light liquid feed then flows from the shaft into distribution tubes which intersect the left central shaft channel. The light liquid in, or LLI distribution tubes, have holes drilled in them at a distance of about 80% to 90% of the distance to the rim of the rotor. The light liquid in feed tubes assure that the light liquid inlet is evenly distributed around the circumference of the rotor at the precise radius selected for any given process. The light liquid feed next flows out through the holes in the distribution tubes and is fed into the rotor. The light liquid is displaced inward toward the rotor shaft where it flows through the perforations in the concentric rotor elements. As the light liquid reaches the shaft it flows directly into the annular channel on the right side of the shaft, where it then flows past the large seal and out of the pod contactor.
In a real process, when both heavy liquids and light liquids are flowing simultaneously through the pod contactor, the blue heavy liquid is centrifuged out toward the rim of the rotor while the red light liquid is displaced inward toward the shaft by the heavy liquid. The two liquids are flowing in opposite directions countercurrent to each other. Since both phases must flow through the perforations in the rotor elements, a series of intimate contacts results. These contacts provide the multistage capability of the pod for extraction, reaction, and washing. Here is a simplified view of a two-phased countercurrent process to illustrate how the liquids flow through the feed distribution tubes and into the shaft channels.
As the blue heavy liquid enters, it flows outward. The red light liquid flows inward. The location of the holes in the light liquid in and the heavy liquid in feed tubes divides the rotor volume into three functional zones. In Board of the heavy liquid inlet is the light liquid clarification zone. No heavy phase flows through the zone. This volume is where the light liquid is progressively clarified as it moves toward the shaft. Outboard of the light liquid inlet is the heavy liquid clarification zone. In this zone, the coalescing element surfaces help remove the last traces of light liquid from the heavy liquid effluent as this phase moves toward the rim. Between the two inlets is the two-phase contact zone where both the heavy and light liquids are present flowing in opposite directions through the perforations in the bands.
Separation Application Example
Now, let us briefly turn our attention to a simple separation application. Where no contacting is required, the mix is evenly distributed throughout the rotor, and the entire rotor volume is used to clarify the two liquids. In addition to this simple separation system, the pod also features counter-current capabilities for processes such as separation and washing applications. To illustrate, in this washing application, wash water is introduced into the large seal and pumped through the pod to wash the light liquid. Pod contactors truly are exceptional and versatile machines. They are built in five standard sizes ranging in capacity from 0.40 to 600 gallons per minute. Each basic model can be specifically configured to your exact requirements.
For more than 50 years, B&P has dealt successfully with a variety of liquid-liquid processing problems. Why not let us with that experience and expertise to work for you. Whether you need a machine or a complete system. Our experienced process engineers are available to assist in design, installation or start-up, or for any future modifications in your process. The Pod contactor and B&P, the possibilities are endless.