[Haichuan Illustrated Chemical Equipment] Series Posts – Rotary Extractor Tower

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Get to know equipment, understand it, and make good use of it. [Haichuan’s Illustrated Guide to Chemical Equipment] series posts: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=5719196. Everyone is welcome to participate in the discussions. ----------------------------------------------------------- The Rotating Disc Contactor (RDC) is a very classic and efficient liquid-liquid extraction device used in the chemical industry. 01 Core Principle: What is liquid-liquid extraction? In simple terms, liquid-liquid extraction is a process that utilizes the difference in solubility of a substance in two immiscible (or slightly soluble) solvents to transfer the target substance from one solvent to another. Imagine you have a cup of saltwater mixed with sand, and you want to extract the salt. Liquid-liquid extraction is like adding a magical liquid (an extractant) that does not mix with water, but salts really like it and flock to this magical liquid. Finally, by separating these two liquids, you obtain pure salt. 02 The “internal components” of the rotary extractor Tower. Based on the visual images above, the rotary extractor tower is primarily composed of the following key components: Column Body: The vertical enclosure of the entire device; it is usually quite tall to ensure that the liquid has sufficient time to stay and come into contact with other elements. Rotor Discs: A series of smooth discs mounted on a central rotating shaft. They are the “heart” of the tower, driven by motors at the top to rotate at high speed. Stator Rings/Fixed Rings: Ring-shaped baffles fixed to the tower wall. They divide the tall towers into separate, vertically connected “small rooms” (extraction stages). Phase inlet/outlet: Heavy Phase: A liquid with high density that enters at the top of the tower, flows downward due to gravity, and exits from the bottom of the tower. Light Phase: A liquid with low density that enters at the bottom of the tower, rises upward due to buoyancy, and exits at the top of the tower. 03 How does it wield its “magic”? (Workflow) Counter-current encounter: The heavy-phase liquid moves downward, while the light-phase liquid rises upward; the two come into counter-current contact within the tower. This counterflow design maximizes extraction efficiency. High shear force (action of the rotating disk): As the liquid flows past a rapidly rotating disk, the disk acts like invisible knives that \"break\" one of the liquid phases (usually the dispersed phase) into countless tiny droplets. Efficient mass transfer: The smaller the droplets, the larger the contact area between the two liquids! The target substance (solute) is on the surfaces of these thousands of tiny droplets, rapidly transferring from one phase to another. In chemical engineering, this is called “mass transfer”. Constraint of the stationary disk: Without a stationary disk, the liquid would rotate together with the rotating disk (forming a unified swirl), resulting in mixing between the upper and lower layers and reducing efficiency. The function of the stationary disk is to break this swirl, guide the liquid to flow upward and downward, and create localized intense turbulence within each \"small chamber\", thereby further promoting mixing. Clarification zones at both ends: At the very top and bottom of the tower, there are no rotating or stationary disks; these are areas of relative calm (clarification zones). The mixed liquid is left to stand here, where the small droplets recombine into larger droplets, ultimately leading to a complete separation of the two phases.