Travelling Band Screens
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Travelling Band screens
Travelling Band Screens (TBS) are used where large volumes
of water must be screened to remove floating and suspended material, which
might damage downstream pumps and equipment.
The screen mesh is attached to basket frames arranged in an endless link
chain system. As the water flows through the baskets, debris is retained
within the baskets, allowing the clean water to flow through the screens.
The trapped screenings are carried over to the top by the revolving band
screen where jets of water discharge the debris into a refuse trench for
disposal. The spray header pipe is fitted with highly efficient spray nozzles
to effectively backwash the screening baskets. The spray header pipe can
also be fitted with an internal cleaning device for cleaning the spray nozzles.
Macmet designs and supplies Revolving travelling
band with sealed drive unit and automatic basket cleaning operation with
mesh sizes 100 micron. Three types of TBS with different flow patterns are
available for removal of solids from water.
Through-Flow Band Screen: Designed
for water flow through the screens and discharging retained solids into
a refuse trench. 50% effective submerged mesh area. Mesh sizes from 4 to
10 mm.
Dual-Flow Band Screen: Designed for
water flow from outside to inside of the screens and discharging retained
solids into a refuse trench. 100% effective submerged mesh area. Mesh sizes
from 4 to 10 mm.
Centre-Flow Band Screen: Designed for
water flow from inside to outside of the scrfeens and discharging retained
solids into an internal collecting trough. 150% effective submerged mesh
area due to basket configuration. Mesh sizes from 0.1 to 10 mm.
The flow pattern across the screen in case of Dual
flow and Centre-flow TBS eliminates any possibility of carrying over of
collected trash to the downstream side.
When compared to Through-flow type TBS, the Dual-flow and Centre-flow
TBS provides an increase in screening capacity by approximately 50% and
100% respectively. The Centre-flow type TBS with its unique semi-circular
basket design provides much higher trash removal capacity compared to flat
basket design in other two types of TBS. The semi-circular baskets are equipped
with a retaining plate, which provides bucket elevator type characteristics
to carry bulky debris without any fallout. Also, as the debris is discharged
by gravity, less wash water is required for back-washing the screens. The
mesh size is selected to obtain the quality of water required for individual
applications. Fine mesh openings are most effective for removal of tiny
particles and jelly fish. Common sizes of mesh opening for power utilities
and desalination stations are 1 mm to 2 mm. This guarantees high quality
water and eliminates the requirement of further downstream filtration equipment
particularly at condenser inlet.
C entre-flow type TBS can be designed for flow rates up to 100,000 m3/hr
with optimum debris removal because of its high screening capacity. One
of the most important features of a Centre-flow TBS is the reduced civil
construction on account of the possible higher sump level. Compared to Centre-flow
screens, the civil structures for Dual-flow and Through-flow screens are
higher by 30% and 50% respectively.
Macmet has supplied the largest Water Intake System in India consisting
of 6 channels of 55000 cu.m per hour and 2 channels of 8000cu.m per hour
for Nuclear Power Corporation.
The first Centre flow Band Screen operating in India has also been supplied
to Nirma Ltd. for a capacity of 25,000 cu.m per hour with 2 mm screen opening.
In Europe and other developed nations, Centre flow type Travelling Band
Screens are most commonly used when compared to the other two type of screens
because of the efficiency and ease of operation of the center flow TBS.
