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Wet and dry (sometimes called semi-wet) scrubbers are very complicated from a flow modeling standpoint, and it
can sometimes be difficult to sort out just what model is right for your application. Besides the typical
decision between a physical scale model or a CFD model, there are a host of decisions to be made with either
one.
Three basic scopes exist for flow models of wet or semi-wet scrubbers:
- Inlet duct model only. This type of model can be used to ensure that the gas
flow into the unit is not stratified. Particularly in the case of wet
scrubbers, this type of model can also be used to ensure that gas flow near the floor is sufficient to prevent slurry
back-up into the inlet duct, since this can cause corrosion of the ductwork.
- Model of gas-only flow through the scrubber. Using this type of model, the resistance
added by the spray is sometimes added as a perforated plate or a distributed resistance.
This can often be used to ensure reasonable bulk behavior, such as overall flow
uniformity, but cannot be used to predict mixing between the untreated gas
and other injected gases or evaporating liquids.
- Model including spray injection and possibly evaporation. For most
scrubbers, quench liquid injection will have significant effects on
the flow field. The bulk effect can be simulated using a distributed
resistance, but the detailed local effects of the injection and
subsequent gas cooling are often of interest. Evaporation of these
particles can be included if a CFD model is employed. Since the actual
quench liquid injection is modeled, all effects including temperature change,
gas momentum, and turbulence levels are naturally
included.
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Detailed models of parts of a scrubber, such as a mist eliminator, can also help to deal with specific challenges.