The effective design of any ZLD
system is therefore dependent on the
correct analysis of the water/waste
stream, making it essential to have
an accurate analysis of composition,
flow rates, chemistry, etc. Without
this, any designed solution will fail to
deliver the required results, if it works
at all.
Energy-efficient evaporation
Vapour compression evaporation is
a common method used in ZLD as
evaporation can recover up to 95
per cent wastewater as distillate.
Any remaining concentrate is further
treated physically or chemically to
produce solid residues (such as
crystals) and water. By running the
evaporators at lower pressures,
the boiling point of the liquid being
treated is reduced. This means
that multi-effect evaporation can
be made possible; that is, steam
from a previous evaporation stage is
used as thermal energy in the next
stage which works at a lower boiling
point. This way, multiple evaporation
stages are combined, generating
significant energy savings. For many
components, crystal precipitation
is favoured at lower temperatures,
therefore lowering evaporation
temperatures helps to increase the
solids yield.
The role of heat exchangers
ZLD is certainly not the only waste
treatment solution available: it will
not be suitable for all situations and
it is not a panacea for the treatment
of hazardous wastes. However, in
the right situation it can play a key
role in reducing waste volumes or
preparing waste streams for final,
safer, disposal. In the case of India’s
textile industry, ZLD has helped to
clean up the area around the city of
Tirupur and the Noyyal River, saving
the area’s textile industry at the same
time.
In Europe HRS Heat Exchangers
have installed a ZLD system for an
industrial client, which uses proven
technology. Heat exchangers
play a crucial role in reducing the
running costs of a ZLD system by
utilising heat from process water
and other existing sources, and also
recapturing heat at the end of the
process and reusing it to boost the
energy efficiency of the overall ZLD
system. Where there is a hazardous
liquid waste stream to deal with,
then the potential to utilise ZLD
techniques as part of the overall
treatment solution should definitely
be investigated.
SERVICES, PRODUCTS, SOLUTIONS
HRS Unicus Series scraped-surface evaporators are used
to maintain thermal efficiency and remove fouling during
evaporation in ZLD installations
HRS provide a range of heat exchangers, modules and
complete processing systems that help you to optimise
production, make the most of raw materials, whilst reducing
energy consumption, waste and emissions.
info@au.hrs-he.com www.hrs-heatexchangers.com/nz
NZ: +64 9 889 6045 AU: +61 3 9489 1866
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