Water spray cyclone scrubber

A wet cyclonic scrubber is a cyclone collector with centrally located, coarse water sprays. These water sprays are usually directed radially outward,... 

Venturi and orifice scrubbers are simple forms of wet scrubbers. The turbulence created by the venturi or orifice is used to atomise water sprays and promote contact between the liquid droplets and dust particles. The agglomerated particles of dust and liquid are then collected in a centrifugal separator, usually a cyclone. 

Almost all particle-separating devices can be converted into wet scrubbers by adding liquid spraying systems. Three types of commonly used scrubbers are the spray chamber, cyclonic scrubber, and venturi scrubber. Figure 7.18 shows a simple spray chamber in which water is sprayed through a series of nozzles into a settling chamber. The dust-laden gas is fed from the bottom of the chamber and exits from the upper portion of the chamber. 

The collection of particles is achieved in a countercurrent flow between the water droplets and the particulates. In a cyclonic scrubber, water is injected into the cyclone chamber from sprayers located along the central axis, as shown in Fig. 7.19. The water droplets capture particles mainly in the cross-flow motion and are thrown to the wall by centrifugal force, forming a layer of slurry flow moving downward to the outlet at the bottom of the cyclone. Another type of scrubber employs a venturi, as shown in Fig. 7.20. The velocity of the gas-solid suspension flow is accelerated to a maximum value at the venturi throat. The inlet of the water spray is located just before the venturi throat so that the maximum difference in velocity between droplets and particles is obtained to achieve higher collection efficiency by inertial impaction. A venturi scrubber is usually operated with a particle collector such as a settling chamber or cyclone for slurry collection. 

Venturi scrubber, (Fig. 5.7) the gas is accelerated by passage through a narrow throat into which water sprays are injected. As a result of the high relative velocity of the gas and water droplets and the high turbulence in the exit of the throat, efficiency is high, but the pressure drop is also considerable giving rise to relatively high operational costs. Residual water spray is removed by a cyclone separator (Fig. 5.7). 

Methods of dust removal depend mainly on the particle size of the dust and the temperature and moisture content of the gas. The methods used are broadly divided into dry methods and wet methods. The dry methods involve the use of gravity and baffle chambers, cyclones, filters, and electrostatic precipitators, while the wet methods involve the use of spray towers and venturi scrubbers. In principle, wet cleaning is preferred to dry cleaning because of the excessive wear associated with and the difficulty in handling the fine dusty material removed in the dry methods. The wet methods, however, must be followed by such operations as filtration, drying of filter cakes, and recycling of water. 

In a single-stage spray dryer the process is finished when most of the moisture in the pore space has dried. The agglomerates accumulate in the lower part of the spray-drying chamber and are removed by the suction of a fan driving a dust-collection system. The agglomerates are collected in a cyclone while dust is collected in a wet scrubber. Material-laden scrubber water may be recirculated and mixed with the liquid feed. 

Wet spinner scrubbers. Wet spinner scrubbers operate on the basis of the same principle as dry vortex separators, however, they are equipped with jets to spray water. The jets form a continuous film of water on the walls of the cyclone, thus making possible a removal of captured solid particles to the outlet neck of the scrubber. The gas temperature must not exceed 150° C. Types with an tangential inlet of the gas as weU as those with an axial inlet (with the use of a spinner) are used. The specific water consumption is between 0.1 and 0.41 m, in the case of wet scrubber with the spinner, the separation limit is below 1.5 /xm. The maximal input dust... 

Venturi scrubbers Water is sprayed into the gases as they pass through a venturi. The acceleration of the gas flow in the venturi throat causes an intensive mixing of both media. The dust particles are damped, making them heavier, so that they can be separated in a cyclone or other system placed downstream. If the gas flow drops, the venturi throat is adjusted to maintain the collection efficiency... 

---