Concentration of Evaporator Concentrates - NUKEM Technologies

The vapours leaving the evaporator
tank flow through a droplet separator
first where the entrained aerosols are
separated. The collected liquid flows
back to the evaporator tank via a
siphon. The vapours leaving the
droplet separator are condensed in a
water-cooled condenser. The
resulting distillate flows into the
distillate collection tank. The distillate
is transferred in batches to the
wastewater treatment tanks.
The required vacuum during the
evaporation is produced by means of
a liquid ring pump. The circulating
water of the liquid ring pump is
cleaned from the entrained gas in a
water separator where the water is
cooled before being re-circulated to
the vacuum pump. Excess
condensed water overflows to the
water drainage system.
The off-gas from the water separator
is collected in the vessel and
directed to the off-gas treatment
system of the nuclear facility.
The evaporation of the concentrate is
continued until the remaining
water content in the viscous superconcentrate
or granular product
reaches the required concentration.
The residual water content will
depend on the final form of the final
end product.
At the end of processing a batch, the
vacuum and the heating systems are
interrupted. A valve at the bottom of
the evaporator is opened and the
product flows past the special
shaped agitator into the collection
container.
Ion exchange resins and/or filter residues
can be concentrated together
with evaporator concentrates
containing enough borates. The salts
from the evaporator concentrates
form a matrix for the ion exchange
resins and filter residues. The end
product is a homogeneous mixture of
the three different kinds of waste.
Other than operating the evaporator
in the batch mode as described
above, it is also possible to operate it
in the semi-continuous mode. In this
case, the level of the product in the
evaporator tank is maintained
constant by the continuous feed of
evaporator concentrate and the
simultaneous removal of the distillate
until the desirable product
characteristics are reached. This
mode of operation doubles the
capacity in comparison batch
processing.
RDA
(From the German Rotationsdünnschichtverdampfer
- Anlage i.e.
rotating thin-film evaporator facility)
-see also simplified process
flowsheet on Fig. 3 –
The evaporator concentrate is
transferred from the feed tank to the
rotating thin-film evaporator by
means of a dosing pump. This
transfer occurs continuously. The
solution is evaporated in the steamheated
evaporator to a highly
viscous state. The rotating blades in
the vertical evaporator ensure a
regular film distribution and prevent
scale build-up of the evaporator
surfaces and loss of heat transfer to
the concentrate.
The concentrate leaves the
evaporator at its discharge port flows
into a storage container set in a
transport container. This transfer
occurs via a special filling device.
The highly concentrated salt mixture
forms a solid salt block containing no
free water as it cools to room
temperature.
4
NUKEM Technologies GmbH
2007