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Adsorption with dry regeneration |
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Polaris
has recently developed a new technique for the adsorption/desorption
with activated carbons (or other adsorbent materials) of volatile
organic compounds from gaseous emissions, for which it is on
course the procedure for national and international patent (PCT),
and which has already been used successfully in some industrial
applications. The adsorption
phase proceeds as usual, but with a pretreatment of the emission
in order to minimise the water humidity present in the effluent.
The relevant innovation is related
to the regeneration phase of the adsorption bed, and consists
of a procedure of heating the bed with hot nitrogen in closed
circuit, and desorption under vacuum, in order to realise
a quantitative removal of the adsorbed compounds, associated
to the simultaneous use of cryogenic energy of evaporated
liquid nitrogen which is recovered as gas and used in the
regeneration circuit to keep an inert atmosphere.
Only a very little nitrogen flow, but enriched and saturated
with the desorbed compounds, is sent to a cryogenic condenser,
where such compounds are quantitatively separated from the
stream and recovered, using the above mentioned cryogenic
energy, eventually integrated by lower cost utilities (cooling
tower or chilled water). |
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Methylene chloride and
acetone recovery plant - size 10.000 m3/h
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With
the above described technique all the cryogenic energy of liquid
nitrogen is recovered, as well as the resulting gas nitrogen.
The regeneration costs are reduced, thanks to a rational and
efficient use of energy, avoiding the competitive heating/cooling
of the huge regeneration stream made of nitrogen and desorbed
compounds, which is typical of conventional nitrogen regeneration
systems.
Thanks to the features of this new system, the effectiveness
of regeneration is complete. All streams of the treatment unit,
the main cleaned effluent as well as the minor streams produced
during regeneration, are released to atmosphere absolutely free
from contaminants. The use of hot nitrogen instead of steam
avoids the formation of huge quantities of waste water to be
managed/treated. The overall environmental impact is thus minimised
or nullified. |
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With
the above described technique all the cryogenic energy of liquid
nitrogen is recovered, as well as the resulting gas nitrogen.
The regeneration costs are reduced, thanks to a rational and
efficient use of energy, avoiding the competitive heating/cooling
of the huge regeneration stream made of nitrogen and desorbed
compounds, which is typical of conventional nitrogen regeneration
systems.
Thanks to the features of this new system, the effectiveness
of regeneration is complete. All streams of the treatment unit,
the main cleaned effluent as well as the minor streams produced
during regeneration, are released to atmosphere absolutely free
from contaminants. The use of hot nitrogen instead of steam
avoids the formation of huge quantities of waste water to be
managed/treated. The overall environmental impact is thus minimised
or nullified.
The presence of oxygen or water in phase of regeneration is
avoided in phase of heating of the adsorbent and adsorbed materials,
so that the duration of adsorbent life is increased and the
possible oxidation/hydrolysis of the adsorbed compounds is avoided.
The desorbed and recovered products, not contaminated by addition
of more substances nor water, has thus better quality.
The new technique is suitable not only for activated carbons,
but also for all adsorbent materials, in particular it allows
an easier use of macroporous resins, which are sensitive to
high regeneration temperatures, in particular in presence of
oxygen, as the method avoids such conditions. Definitively
the principal benefits of this technology are listed here
below:
- "dry" regeneration,
in inert circuit
- maximum safety, even in presence of highly flammable compounds
- compatibility with compounds that present hydrolysis problems
- reduction of waste water treatment costs
- easier recovery of the separated organic compounds
- compared to other regeneration techniques with inert circuit,
the operating costs are lower
- compliance with emission limits indicated by the more strict
norms
- the process is suitable for practically all substances,
also to the more volatile ones (even gases), for which the
other conventional regeneration techniques are not effective |
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Methylene chloride recovery
unit 2000 m3/h
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| ©
Polaris Srl - R1.0 - June 2005 |
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