Stripping
Stripping , stripping or stripping is a physical separation process in which substances are transferred from a liquid phase to the gas phase by desorption processes (using Henry's law ). For this purpose, the liquid phase is brought into contact with a gas using the countercurrent principle .
execution
Technically, the stripping is usually carried out in packed columns. The pumped liquid is finely distributed at the top of the column via a nozzle so that it trickles over the packing in the column into the bottom. The stripping gas (e.g. air) is conveyed through the column in countercurrent. The packing is used to finely distribute the liquid and thus to maximize the phase interface. The cleaning performance is also determined by the gas / liquid ratio, with the transition of the contamination from the liquid to the gas being described by the Henry's constant of each substance. The stripping is usually followed by cleaning the exhaust gas, for example by adsorption , cooling or decomposition.
The process can be adapted to the requirements within wide limits, so that the desired exit concentration is obtained for a given entry concentration of impurity in the liquid phase.
Several stripping towers are also implemented in a multi-stage system in order to achieve the desired cleaning performance. Theoretically, this procedure corresponds to an increase in the height of the packing.
The variables that determine the effectiveness of the stripping are:
- Diameter of the column
- Packing height
- Packing type
- temperature
- pressure
- Gas and liquid pollution
An optimal column diameter can be calculated for the amount of liquid to be cleaned. A minimal countercurrent flow means that the column has an infinite number of transition units. The determination of the countercurrent flow is an optimization process between column height and countercurrent flow.
application
Stripping is used in petroleum processing to remove lighter components from the product drawn off from the side of a column, for example kerosene from the lower-boiling gasoline.
In wastewater treatment, it can remove ammonia , hydrogen sulfide , mercaptans , phenols , organic halogen compounds and hydrocarbons .
In certain applications, sludge from precipitation reactions ( iron , manganese ) can clog the packing and reduce the cleaning performance of the process. In these cases, prior iron removal is necessary.