Vacuum
Evaporators
continued...
Forced
air evaporators often employ a packed tower and air
blown in the opposite direction to the flow of liquid
to reduce energy requirements and improve evaporation
efficiency. However, energy reduction is limited and
there is still often the potential for release of
hazardous emissions to atmosphere.
Vacuum
evaporators boil off liquids in an enclosed vessel
or “kettle” which is operated under low
negative pressure (30-80 mbar). By operating under
vacuum the vapour pressure of the liquid within the
kettle is reduced, allowing the liquid to boil at
lower temperature.
For
example, in a typical vacuum evaporator water will
boil at 40 deg. C rather than 100 deg. C when at atmospheric
pressure. As a result, energy requirement is dramatically
reduced.
At
atmospheric pressure, approximately 0.62 kW of energy
are required to transform 1 litre of water into steam
(this does not account for any inefficiency in the
boiling process). In our vacuum evaporators this energy
requirement is reduced to around 0.15 kW per litre,
a significant reduction.
By
boiling off liquids in an enclosed vessel and operating
a dedicated condenser the potential for hazardous
emissions is also removed.
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