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Johndec Engineering Plastics Pty Ltd manufactures a complete
range of high efficiency fume scrubbers that are essential fittings
on fume cupboards or corrosive exhaust systems. Their installation
may be desirable or mandatory where highly corrosive substances
are in use, or where there are problems with safe discharge or
gaseous effluent.
Services available include:
- Engineered design to suit all airflow requirements and treatment
of all types of gaseous contaminants.
- Manufacture
- Maintenance and repairs
- Testing
Contaminated air enters the unit and passes through a packed
bed then through the liquid spray section, a mist eliminator and
then into the exhaust system for release outside the building.
The scrubbing liquor is recirculated from the sump and back to
the top of the system using a pump. The air and the scrubbing
liquor pass in a counter current fashion for efficient gas/liquid
contact. Water-soluble gases, vapours and aerosols are dissolved
into the scrubbing liquor. Removal efficiencies for most water
soluble acid and base laden airstreams is 95-99.9%.
The scrubbing liquor is usually water and contains dissolved
contaminants from the airstream, other dissolved minerals from
the makeup water which are concentrated as the water evaporates
into the airstream, and optionally, some neutralizing solution
which is usually a weak acid or base depending on the contaminant
to be neutralized.
Maintaining the scrubbing liquor involves three controllers.
As the system operates, the air entering the scrubber absorbs
water from the liquid stream and becomes saturated. The water
consumed in this process needs to be replaced or the scrubber
will run dry. This is accomplished using a level controller that
opens and closes a water valve to maintain the liquid level in
the scrubber.
As mentioned earlier, as water evaporates from the system, minerals
from the makeup water stream are concentrated. Acid/Base neutralization
reactions also produce salts that become concentrated in the scrubbing
liquor. The concentration of these minerals and salts are called
Total Dissolved Solids or TDS. Most TDS compounds are strongly
ionic and can be measured using a conductivity meter of Td controller.
To control TDS, scrubbing liquor is drained from the system using
a blowdown with fresh water thereby maintaining a stable liquid
and TDS level.
The liquor pH may also be controlled in a similar way using blowdown
or be using a neutralizing chemical feed. For example, if the
airstream contains acid, a base may be used, the amount of basic
solution fed into the system is controlled be a pH controller.
Fume scrubber will effectively reduce concentrations of certain
water-soluble acids, base and organic contaminants exhausted from
a gaseous exhaust system. If you are concerned about corrosion,
hazardous stack emissions or other environmental factors, you
may want to consider a scrubber.
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