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Technology
20
high calcium content is another
challenge to be met in effluent
treatment technology: it can
seriously affect performance
due to scaling in the anaerobic
reactor
Scaling due to high calcium content
means that with large effluent quantities,
tons of lime mixed with biomass
are deposited in the anaerobic
reactor every day. Furthermore, the
spherical anaerobic biomass sludge
pellets form around a limestone core
up to 2 mm in diameter and can also
have a limestone shell, known as the
“eggshell” effect. The results are only
too well known:
c Non-uniform fluidization of the
pellet bed
c Undesirable deposits causing
so-called “cold points”
c Formation of preferential flow
channels
c Serious overload symptoms
despite theoretically adequate biomass
content in the system.
Lime scaling on
sludge pellets
As a consequence, the anaerobic reactor
performance declines so rapidly
that it generally has to be shut down
and cleaned out. Not only does this
involve a production outage, but also
the reactor has to be refilled with new
active biomass.
The R2S reactor has no scaling
problems
The new R2S reactor solves the
problem of scaling that cannot be
avoided by taking process technology
and design measures.
It does this thanks to the inflow mode
in the reaction zone, internal flow
streaming, and systematic dwell
zones. Lime sludge and pellets deactivated
by scaling can be removed
without problem during operation.
By preventing deposits, the R2S
reactor’s newly designed flow path
ensures uniform processing over the
entire reactor cross-section. Floating
sludge layers are systematically
removed separately from the system.
Design measures have been taken
to prevent air pocket formation at
critical transition points, thus reducing
lime precipitation potential.
The R2S reactor stays free of
deposits and blockages
It is not possible in practice to entirely
avoid problems due to erroneous
drainage of surface-active substances
into effluent, such as oil, retention
agents and caustic soda. These problems
include weir blockage at the
reactor head due to uncontrolled pellet
buoyancy. The necessary cleaning
work at heights up to 30 m is not
easy – particularly a challenge for the
personnel during the winter months.
By taking systematic design measures
at bottleneck points with a high
throughput of gas, water and sludge,
or by using water flushing to assist
sludge throughput, scaling and blockages
in the R2S reactor are prevented
and the circulating sludge is reactivated
in good time.
The R2S reactor is flow-
optimized for maximum space
utilization
Another important feature of the
R2S reactor is its innovative clog-free
charging system. This distributes
incoming effluent uniformly over the
entire reactor cross-section area.
24 I 2007 I Voith Paper I twogether