Principle of the Scrubbers
Scrubbers are used to remove solid particles or liquid droplets from gases. These utilize water to scrub the particles (droplets) by countercurrent contact. The principles of inertial impact and absorption are responsible for the separation.
The construction of a water scrubber is shown in Figure 1. It consists of a cylindrical shell with a conical bottom. It has the provision to allow the gas to enter tangentially. Provisions are made to introduce water at the top and a water outlet at the bottom. A series of deflectors are mounted on the top of the stationary vanes, which are in turn supported by annular shelves. An air outlet is provided at the top.
The gas carrying the suspended particles enters tangentially at the bottom and passes upwards. At the same time, curtains of the waterfall from the deflector cones. The gas passes through the sheets of liquid (towards the center of the tower). The gas changes the direction: and passes through the vanes. Thus, several contacts permit the higher entrainment of droplets. The water moves out from the top of the separator. This equipment combines the action of the cyclone (entrainment separator) for the separation of entrained droplets of water. Finally, the gas leaves the dust washer.
A Venturi scrubber is a variant in which a venturi tube is placed in the line. The gas flows through the tube at high velocity. From the upstream of the venturi throat, the scrubbing liquid is introduced at low pressure.
The gas collides with the liquid so that the sheet of liquid is disrupted and liquid particles are rapidly formed. The velocity of gas decreases at the diverging section, and small particles (in the gas) are wetted by the finely divided liquid droplets. Then, particles coalesce. The discharge of the scrubber goes to a cyclone separator where coalesced particles are removed from the gas stream.
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