Spray Towers

The spray towers or spray chambers are a form of pollution control technology. They consist of steel or plastic empty cylindrical vessels and the nozzles that are used to spray liquid into the vessels. When the liquid is sprayed downwards from one or more levels, the inlet gas stream usually enters the bottom of the tower and moves upward. The flow of inlet gas and liquid in the opposite direction is called countercurrent flow.

Countercurrent flow

These countercurrent flows always use to exposes the outlet gas with the lowest concentration of the freshest scrubbing liquid. At different level of heights lot number of nozzles are placed across the tower to spray all of the gas as it travels through the tower. Why should many towers are used, the reason behind is to increase the number of fine droplets impacting the pollutant particles and also it provides a large surface area for absorbing gas. The higher collection of efficiency is achieved for both gaseous and particulate pollutants, if the smaller droplets are formed. So the liquid droplet should not be smaller to not to be carried out by the scrubbed outlet gas stream. For this reason the spray towers are used. The spray towers make use of the nozzle to produce the larger droplets that are ranging from 500 to 1000µm in diameter. You can be doubtful they are small in size, but when compared with the venturi scrubbers these droplets will be larger. The venturi scrubbers ranging from 10 to 50µm in size, but their gas velocity is kept low from 0.3 to 1.2 m/s,  this  is to prevent the excess droplets from being carried out of the tower.

Collections of particles

Spray towers is called as low energy scrubbers. When it is compared with the venture scrubbers the contacting power is lower and pressure drops are generally less than 2.5 cm of water. Due to the higher liquid pressures at the nozzle, smaller droplets can be formed. Though the smaller droplets have the small settling velocities, so the droplet size for the scrubbers is optimum range that work by this mechanism. The very high pressure of water is injected ranging from 2,070 to 3,100 kPa which creates a fog of very fine droplets. The higher particle collection efficiencies can be achieved in such cases until the collection mechanism other than inertial impaction occurs. The more power will be used by these spray nozzles to form droplets that would a venture operating at the same collection efficiency.

Questions:

• Explain spray tower?
• What is mean by Countercurrent flows?