TRAVELLING BAND SCREENS
CENTRE-FLOW FROM INSIDE TO OUTSIDE

PURPOSE AND APPLICATION

Travelling screens are used to arrest the small debris contained in the water so that the downstream users remain unobstructed and clean (condensers, exchanges, spray-water circuits, membranes etc). Debris can be of all types including fish, shrimps, jellyfish, grass, man-made refuse, plastics, seaweed, etc. They are especially suited to deep pits.

They are used in thermal and nuclear power plants, LNG terminals, desalination or fertilizer plants, drinking water, sewage and irrigation plants.

DESCRIPTION

Installed in a channel in which the water to be cleaned flows, the screen consists of a set of rectangular screening mesh panels carried by two endless chains. The panels travel up and down again between an upstream partition set across the channel, with an inlet central aperture and a downstream wall set across the channel. The water enters through the aperture in the upstream partition, flows through the upstream face of the panels on each side, where the debris are arrested. The water flows out through the apertures on both sides of the downstream wall-plate.

The debris-laden panels travel up above deck level, around the top and down again. One or two spray pipes with fantail jet nozzles set on the down stream side of the panels within the screen’s head structure, back-wash the panels, remove the debris which are projected into a collection trough. They travel in a deck flume to the debris disposal system (basket, separator, etc.)

The screens are normally stopped and are washed periodically when obstructed by debris. Permanent rotation can be provided.

Center-flow Travelling Band Screen Hydraulics

ADVANTAGES

Large debris-handling capacity
Compact civil structure
Fully automatic
Capable of high-speed rotation
Fish-friendly option
Reduced maintenance
Cost effective
No debris carry-over
Easy access to external debris trough
No internal debris interference

NECESSARY ANCILLARIES

Spray-water supply circuit
Head-loss monitoring system
Electrical control cabinet
Upstream bar rack (25 to 75 mm spacing (1 to 3”)
Pit dewatering stoplogs
Trash collecting system (basket, etc).

SIZES AND DATA

Mesh aperture
From 1x1 to 10x10 mm (0.04 to 3/8”)
Flow rates
Up to 70000 m3/h (300000 gpm)
Tidal variation
No practical limit
Panel frame useful width
0.6 to 4 m (2 to 13 ft)
Wider machines on special order

OPTIONAL FEATURES

Two or three-speed operation
Seismic qualification
Special high travel speed design for handling heavy debris loads
Jellyfish lifting trays
Screening medium resistant to fiber build-up
Screening medium preventing jellyfish adherence
Low pressure water-life protection system
Atex compliance
“Scoop-a-fishTM” total fish survival system
Wall-mounted chain guides on full carrying structure
By-pass valves

MATERIALS

Main structure, panels, frames, guide rails
For fresh-water applications: painted carbon steel or AISI 304L stainless steel
For seawater applications: AISI 316L stainless stee, duplex or super-duplex stainless steel
Head-shaft, sprockets, chain links and pins, tensioning capstan screws
For fresh-water applications: High-tensile steel
For seawater applications: Duplex or super-duplex stainless steel
Bolts, nuts, washers
For fresh-water applications: A2 or A4 stainless steel
For seawater application: A4, duplex or super-duplex stainless steel
Small fittings, spray-water pipes
For fresh-water applications: AISI 304L stainless steel
For seawater applications: AISI 316L, duplex or super-duplex stainless steel
Screening mesh frames, sprocket teeth
In all cases: composite materials
Covers
GRP or stainless steel on special request
Anodes
None required for fresh-water applications
For seawater applications: required for use with AISI 316L stainless steel and sometimes for duplex stainless steel.