Design and classification of extraction equipment (extraction towers)

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The design and classification of extraction equipment (extraction towers) mainly involve determining the diameter of the tower and the height of its working section. First, divide the liquid flow rate by the operating speed to obtain the tower cross-section, and then calculate the tower diameter. Then, based on the characteristics of the tower, as well as the properties of the material stream and the separation requirements, the height of each mass transfer unit and the number of such units are determined; multiplying these two values gives the operating height of the tower. There are also methods that calculate the working section height based on the equivalent height and theoretical series. Compared to extraction towers, centrifugal extractors can use centrifugal force to accelerate the sedimentation and stratification of droplets, thereby allowing for intensified stirring to break down the droplets and enhance the extraction process. Centrifugal extractors are of two types: staged contact and differential contact. The former incorporates a stirring device inside the centrifuge, resulting in single-stage or multi-stage centrifugal extractors. Centrifugal extractors are particularly suitable for systems with a small density difference between the two phases or those prone to emulsification. Since the residence time of the material inside the extractor is very short, they are also suitable for the extraction of substances with unstable chemical and physical properties. Common designs and classifications of extraction towers include: ① Rotary disk extraction tower: In the working section, a set of ring plates is installed at equal intervals, dividing the working section into a series of small chambers; each chamber has a rotating disk at its center that serves as an agitator. These disks are mounted on a main shaft located at the center of the tower, and are rotated by mechanical devices outside the tower. The rotary drum tower has a simple structure, high processing capacity, and considerable separation efficiency, and is widely used in the petroleum refining industry and petrochemical sector. ②Pulsating extractor: In the working section, groups of sieve plates (without overflow pipes) or packing are installed. The pulsating liquid flow generated by the pulsation device is introduced into the bottom of the tower through pipes, causing the liquid within the entire tower to undergo reciprocating pulsations. The pulsating fluid flow moves at high speed relative to one another between the sieve plates or packing, generating vortices that help to break down and distribute the liquid droplets evenly. Pulsating columns can achieve higher separation efficiency, but have a lower processing capacity; they are commonly used in nuclear fuel and rare elements plants. ③Vibrating plate extractor: The sieve plates are connected in a series and driven by a mechanical device located above the top of the tower to move back and forth vertically, thereby stirring the liquid flow and serving a function similar to that of stirring in a pulsating tower.