AIR PARTICLE EMISSION BY SCRUBBERS

Scrubbers or wet collectors are designed to increase the particle size by using water or slurry droplets because it is easy to collect the larger particles. 

Wet Scrubber

There are various types of scrubbers but two types are discussed here:

• Conventional Scrubbers
• Venturi Scrubbers

There are several modes of particle collection in scrubbers. In the upper part of scrubber the falling water droplets collide and collect the particles from the upward moving dity gas. In packed section special shapes are used to increase the area of contact between liquid and aerosols. The plugging is a problem faced in packed section despite the specific shapes used. Below the packed section there exists a flooded perforated disc. that supports many centimeters of water and allowed the contact between liquid and water bubbles containing particles. The liquid passes through perforations and fall in another falling drop collection section. 

The particles collection is not achieved in all the droplets and particles collision due to surface tension of droplets and particles wettability properties. Chemicals are added to reduce the surface tension of droplets and to improve their abilities to absorb the gases and particles. 

Venturi Scrubber

The liquid containing particles are moved to the bottom of tower and shifted to settling basin or filtering device for the removal of particles. The water is recirculated with or without treatment to result zero discharge system. 

The demistor the exit point of scrubber is a particles collector. It is designed to remove the drops of liquid from gas stream. 

The size of water drops is critical in determining the performance of scrubber. If the water drops are large than particles then drag forces displace the particles out of the path of falling drops and collision number decreases. 

The pressure loss from conventional scrubbers is 15 to 40 cm of water. Collector efficiency increase with the pressure loss and it may be as high as 95 %.

Scrubbers are designed to operate at high temperature and avoid corrosion. Operating cost is high for pressure loss scrubbers but the capital cost is comparatively low from other collectors.