Wet scrubbers pull a gas stream through a vessel where there is a liquid spraying or trickling down over packing material. The idea is to produce surface area on the liquid to enhance an exchange between the gas and liquid. Wet scrubbers are common in power plants with FGD systems, but smaller versions are found in many chemical processing industries as well.

To keep the liquid in the vessel, designers of wet scrubbers place a device called a mist eliminator (ME) at the top of the vessel. Without an ME pad, droplets become airborne and are carried out of the vessel by the moving gas stream, which causes problems because liquid ends-up where it is not meant to go. ME's are also referred to as droplet separators or moisture separators.

An ME usually consists of a series of plastic slats called chevrons (most of the time having curved profiles) that lay on edge next to each other to form a small labyrinth that the gas has to pass through. Since the droplets cannot zig and zag as fast as the gas, they hit and stick to the surface of the chevrons, eventually dripping back into the vessel. The illustration to the left shows a typical SO_x scrubber with the ME labeled "Moisture Separator."

ME's normally have wash systems that consist of headers of full cone nozzles which spray directly onto the chevrons. This system keeps the chevrons clean which in-turn helps the liquid drip back into the scrubber, preventing deposits from building up on the surface. The spray nozzles are usually operated on a timed cycle and then shut off rather then spraying continuously. A large tower can have several hundred nozzles spread over one, two or three levels, depending on whether there are multiple ME levels.

ME wash nozzles should have the following attributes: