Spray tower

The inlet gas stream usually enters at the bottom of the tower and moves upward, while the liquid is sprayed downward from one or more levels.

Countercurrent flow exposes the outlet gas with the lowest pollutant concentration to the freshest scrubbing liquid.

The reason for using many nozzles is to maximize the number of fine droplets impacting the pollutant particles and to provide a large surface area for absorbing gas.

Theoretically, the smaller the droplets formed, the higher the collection efficiency achieved for both gaseous and particulate pollutants.

In crosscurrent-flow spray towers, also called horizontal-spray scrubbers, the gas and liquid flow in directions perpendicular to each other.

Contacting power is much lower than in venturi scrubbers, and the pressure drops across such systems are generally less than 2.5 cm (1 in) of water.

For example, spray towers are used to remove HCl gas from the tail-gas exhaust in manufacturing hydrochloric acid.

Spray towers are also used for odor removal in bone meal and tallow manufacturing industries by scrubbing the exhaust gases with a solution of KMnO4.

Because of their ability to handle large gas volumes in corrosive atmospheres, spray towers are also used in a number of flue-gas desulfurization systems as the first or second stage in the pollutant removal process.

To reduce these problems, a settling or filtration system is used to remove abrasive particles from the recycled scrubbing liquid before pumping it back into the nozzles.

Many scrubbing systems use sprays either prior to or in the bottom of the primary scrubber to remove large particles that could plug it.