Which one of the following devices is not used for both the absorption as well as the liquid-liquid extraction processes ?

ANS:D - Wetted wall columns

Wetted wall columns are a type of chemical processing equipment used for gas-liquid contact operations, particularly gas absorption or scrubbing. They are designed to facilitate the transfer of a gaseous component into a liquid phase by creating intimate contact between the gas and a thin liquid film flowing down the interior walls of the column. Here's a breakdown of the key components and operation of wetted wall columns:

1. Column Design: Wetted wall columns typically consist of a vertical cylindrical vessel or column with a smooth interior surface. The column is often packed with inert material to enhance the wetting of the walls and to provide support for the liquid film.
2. Liquid Distribution System: A liquid distribution system is installed at the top of the column to evenly distribute the liquid across the interior walls. This system may include spray nozzles, perforated pipes, or distributors designed to ensure uniform coverage of the wall surface.
3. Wetted Wall Surface: The interior walls of the column are wetted with the liquid being used for absorption. The liquid flows down the walls as a thin film, creating a large interfacial area for contact with the gas flowing through the column.
4. Gas Flow: The gas to be absorbed enters the column from the bottom or the top, depending on the design. As the gas flows upward through the column, it comes into contact with the thin liquid film flowing down the wetted wall surface.
5. Mass Transfer: Mass transfer occurs at the interface between the gas and liquid phases. The gas component to be absorbed dissolves into the liquid film due to the concentration gradient between the two phases. The intimate contact between the gas and liquid maximizes the mass transfer rate, allowing for efficient absorption of the desired component.
6. Separation: Once the gas has passed through the column and undergone absorption, it exits the column either at the top or the bottom, depending on the configuration. The absorbed component is now dissolved in the liquid and can be separated from the liquid phase using further downstream processes if necessary.

Wetted wall columns are commonly used in various industries for gas-liquid absorption processes, such as removing pollutants from industrial exhaust gases, recovering valuable chemicals from gas streams, and controlling emissions in environmental applications. Their simple design, efficient mass transfer, and scalability make them suitable for a wide range of absorption applications.