Wet Scruber Mist Eliminator Working Principle

In wet scrubbing processes, liquid or solid particles are removed from a gas stream by transferring them to a liquid. The liquid most commonly used is water.Wet scrubbers can also be used to remove acid gas.

There are three energy usage levels for wet scrubbers.

 A low energy wet scrubber utilizes pressure drops less than 5 inches of water column and are capable of efficiently removing particles greater than about 5-10 microns in diameter. 

A medium energy scrubber has a pressure drop from 5 to 25 inches of water column and is capable of removing micron particles, but is not very efficient on sub-micrometer particles. 

A high energy scrubber expends the most energy and has a pressure drop of 25 to over 100 inches of water column, which is necessary to remove sub-micrometer particles.

A spray tower scrubber is a low energy scrubber and is the simplest wet scrubber used for particulate control. It consists of an open vessel with one or more sets of spray nozzles to distribute the scrubbing liquid. Typically, the gas stream enters at the bottom and passes upward through the sprays. The particles are collected when they impact the droplets.  

The most common high energy wet scrubber is the venturi, although it can also be operated as a medium energy scrubber. In a fixed-throat venturi, the gas stream enters a converging section where it is accelerated toward the throat section. In the throat section, the high-velocity gas stream strikes liquid streams that are injected at right angles to the gas flow, shattering the liquid into small drops. The particles are collected when they impact the slower moving drops. 

All wet scrubber designs incorporate mist eliminators or entrainment separators to remove entrained droplets. The process of contacting the gas and liquid streams results in entrained droplets, which contain the contaminants or particulate matter. The most common mist eliminators are chevrons, mesh pads, and cyclones. 

Chevrons mist eliminators is  cause the gas stream to turn several times as it passes through the mist eliminator. The liquid droplets are collected on the blades of the chevron and drain back into the scrubber.

 Mesh pads are made from interlaced fibers that serve as the collection area.

 A cyclone is typically used for the small droplets generated in a venturi scrubber. The gas stream exiting the venturi enters the bottom of a vertical cylinder tangentially. The droplets are removed by centrifugal force as the gas stream spirals upward to the outlet.