Impingement Plate Fume Scrubbers
Pressure drop is a prime factor in determining the choice of scrubber and it is in this respect that plate type scrubbers compare most favourably with other methods of gas cleaning.
Depending upon the type of plate specified the pressure drop across each impingement plate stage will vary between 500 Pa - 750 Pa. In order to obtain total pressure drop, therefore, this must be multiplied by the number of stages and additions made for inlet /outlet and mist eliminator losses. The number and types of stages in plate scrubbers are specially designed according to the conditions; further stages can be added should these conditions change.
A great advantage of plate type scrubbers is their flexibility in operating conditions in which the flow rates vary, because under such conditions the dust cleaning and absorption efficiencies of the system are minimally affected.
The chemical absorption of noxious contaminants gases such as sulphur dioxide, hydrochloric acid, chlorine, hydrogen sulphide etc, can be achieved by contact of the air stream with suitable chemicals on the plates.
The impingement plates in the APMG units operate on the proven impingement principle, whereby the gas is passed vertically through fine perforations in a plate and is impinged on targets and contacted with water or other liquid flowing horizontally across the plate.
The gas and liquid flow velocities are such as to create high turbulence and intimate mixing and as a result dust removal, absorption and gas cooling take place.
Wet scrubber systems operate on a recirculatory or single pass basis. The scrubbing liquid is either recirculated to the scrubber from a holding tank, or is passed to a drain (or back to process) after passing once through the scrubber. Care is taken in the design of the internal layout to ensure satisfactory hydraulic flow and to gain maximum efficiency of cleaning.
Although plate type scrubbers are regarded as constant volume units there is considerable latitude in the definition of the volume that can be handled in such units.
It is generally recognised that variations from the design volume of ±20% can be accommodated with little effect on the dust removal and gas absorption efficiencies. Outside these limits impingement plate scrubbers can be operated in many cases down to 50% of design volume.