MA C H I N E R Y
When treating
Evaporate at low temp? Sure...
wastewater, sludge
and digestate, it
can be beneficial
to reduce the volume of material
or increase the solids content.
Mechanical dewatering via a
centrifuge or belt press to separate
solids and liquids is standard for
the water treatment and anaerobic
digestion sectors – but what if you
want to further reduce the water
content of the remaining liquid
fraction?
The two main reasons to remove or
reduce water from effluent and waste
are either to reduce the volume of
material in order to cut storage,
handling and disposal costs; or
to produce materials with distinct
properties (such as liquid and solid
fractions of digestate), which can
then be stored and used in the most
appropriate way. Traditionally, there
have been two ways to achieve
this: drying and evaporation. Drying
usually requires large quantities
of heat and energy, is costly and
inefficient, and is unsuitable for
materials with high water content.
Conventional evaporation techniques
require temperatures in excess of
100 deg. C, which is usually provided
by boiling water or steam.
However, due to the low
temperatures used in wastewater
treatment and aerobic digestion,
such energy is not usually available
without additional fuel inputs, making
evaporation a high-energy option.
However, for many types of effluent,
low temperature evaporation can
be a very energy efficient method
of water removal. Where process
temperatures are 85-90 deg. C, low
temperature evaporation combines
the use of a vacuum to reduce
the boiling point of the liquid to be
removed, together with traditional
high temperature evaporators, based
on heat exchanger technology.
Where the temperature of the
effluent or digestate falls below the
necessary temperature, it can often
be increased via heat exchangers,
utilising surplus heat from heaters
and CHP engines.
Heat exchangers from HRS are
capable of recovering heat from
other sources, such as the heat
left from the CHP engine or from
pasteurisation, and using this as
the basis for an evaporation system
can further improve overall process
efficiency. Additionally, using a
vacuum in the system to reduce the
boiling point reduces the amount of
energy required even further.
Combining systems into a multipleeffect
quantities of water to be removed
for the same initial heat input.
Each evaporator is held at a lower
pressure than the previous one:
because the boiling temperature
of water decreases as pressure
decreases, the vapour boiled off in
one vessel can be used to heat the
next – only the first vessel requires
an external source of heat, which
can be taken from another process
elsewhere or generated specifically
for the purpose.
The type of heat exchanger used
will depend on the nature of the
products being treated. For materials
with low or medium viscosities,
Avoid messy situations
with NHP’s Eldon
HDW enclosures
The Eldon HDW wall mount hygienic enclosure range from NHP is
designed to protect valuable electrical equipment while meeting
the unique requirements and strict hygiene standards of the food,
beverage and pharmaceutical industries.
Available in eight standard sizes to accommodate most common
applications, the Eldon HDW enclosures from NHP are the ideal
solution for hygienically clean environments.
For more information,
visit nhp.com.au/more/hdw
evaporator allows larger
1300 NHP NHP
0800 NHP NHP
such as wastewater and effluent
with low concentrations of organic
solids, using the HRS K Series as
an evaporator module provides
high heat transfer rates with good
resistance to fouling. For more
challenging and viscous materials,
such as thicker effluents, digestate
and solids with higher dry matter
concentrations, the HRS Unicus
Series contains a self-cleaning
scraper mechanism which reduces
fouling and maintains heat transfer
rates (and therefore operational
efficiency).
nhp.com.au
AUS
NZ nhp-nz.com
NHP18177 10/19
60 NOVE1M81B7E7_RM 2a0rk1e9tplace_HDW Enclosures_HP_AD.indd 1 10/10/2019 10:27:25 AM
/hdw
/nhp.com.au
/nhp-nz.com
