Info

Liquid Out

Cocurrent Spray

Liquid In

Ejector Venturi

Entrainment Separator

Liquid Out

Cocurrent Spray

Liquid In

Ejector Venturi

SPRAY COLLECTORS—TYPE I

With spray-type units, particles are collected on liquid droplets within the scrubbing unit. The liquid droplets are formed either by atomization, where the flow rate of the scrubbing liquid and pressure in the atomizing nozzle control the droplet size and number, or by the moving gas stream, which atomizes and accelerates the resulting droplets.

Preformed Spray

With a preformed spray, droplets are formed by a nozzle and are then sprayed through the dust-laden air (see Figure 5.18.4). Removal of the dust is primarily by impaction, although diffusion and diffusiophoresis can also contribute to particle collection. Spray scrubbers, taking advantage of gravitational settling, achieve cut diameters around 2 /m, with high-velocity sprays capable of reducing this lower limit to about 0.7 /m (aerodynamic diameter) (Calvert et al. 1972).

Gas-Atomized Spray

With a gas-atomized spray, high-velocity, particle-laden gas atomizes liquid into drops, and the resulting turbulence and velocity difference between droplets and particles enhances particle-droplet collisions and hence particle removal (see Figure 5.18.5). Typical gas velocities range from 60 to 120 m/sec (200-400 f/sec), and the pressure drop in these units is relatively high. A typical example of this type of unit is the venturi scrubber. Venturi scrubbers have achieved cut diameters down to 0.2 /m (Calvert 1977).

Centrifugal Scrubbers

With centrifugal scrubbers, the scrubbing liquid is sprayed into the gas stream at the same time the unit is imparting a spinning motion to the mixture of particles and droplets (see Figure 5.18.6). The result is a centrifugal deposition of the particle-droplet mixture on the outer walls of the scrubber. Depending on the amount of scrubbing liquid used, the collection efficiency is good for particles down to about 1 to 2 /m diameter (aerodynamic) (Calvert et al. 1972). The tangential velocities in these units should not

Gas Plus Dust In

Liquid Gas Plus Dust In Liquid

Liquid Gas Plus Dust In Liquid

Spray Annular Orifice

Liquid

Liquid

Spray Annular Orifice

Spray Venturi

FIG. 5.18.5 Examples of gas-atomized spray unit.

Gas Out

Cleaned Gas Out t

Cleaned Gas Out t

Liquid Out

FIG. 5.18.6 Centrifugal scrubbers.

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