Scraper Bridges Installed
Quickly And Safely
At London Tideway
T
he company was
be built as flat bottomed, with the tank
One of the most notable advantages of
commissioned to design,
walls prefabricated off site in sections.
suction abstraction is that the level of
build and install twelve 40
This reduced the on-site construction
suction can be adjusted at each tube from
metre diameter rotating
requirements - and its inherent risks - while
the bridge deck, so that the operation of
full-bridge suction lift scrapers on the final
compressing the construction schedule
each is optimised.
settlement tanks at the Crossness Sewage
and lowering the overall cost of the tanks.
Tr eatment Works near Woolwich in South
East London as a turnkey contract and part
of the Tideway project.
The bridges were built off site and
included all mechanical and electrical
equipment so that installation required
minimal extra work on site. The contract
requirements also included full CFD
(computational fluid dynamics) analysis
of the tanks in order to verify that
the EDI (Energy Dissipating Inlet) had
been optimised for the prevailing flow
conditions. The decision to use rotating
full-bridge suction lift scrapers was
made so that the treatment tanks could
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PECM Issue 22
A&J Fabtech is able to offer a range
of suction-lift scrapers, including
customised and bespoke designs as
an alternative to traditional
rotating scrapers. While
conventional scrapers work by
moving sludge to a central hopper
for abstraction, suction-lift
scrapers collect the sludge within
the chevron- pattern scraper blades
as the machine travels around the
tank. The sludge is then abstracted
directly by suction tubes from these
points.
Another major benefit of suction lift
scrapers is the lack of need for either
a central sludge collection hopper or
sloped tank floor, thereby simplifying
civil construction and its associated cost
greatly. This can also allow a deeper side
wall depth, which improves the settlement
flow patterns within the tank, thus
improving performance.
Abstraction-at-source also reduces sludge
age within the tank and allows the outside
of the sludge blanket to be removed
preferentially. This reduces movement of
suspended solids plumes over the weirs.