More than just an adsorbent fabric, RP18's special design
qualities make it a good filter too. The construction of
RP18 is such that there is a large amount of free space
which allows water to pass through whilst retaining the
This has been illustrated also in 'A
method for Cleaning Foreshores' case study.
This fabric is useful where water flows
are high and the amount of oil retained is low. If the fabric
is used as a full flow filter care must be taken in the
design of unit to ensure that flow through the fabric is
not enough to cause captured oil to migrate through the
filter element. A large area with very low flow is ideal
and the thickness of the element will determine the time
between renewals. Because the fabric is white the captured
oil causes a brown stain as it percolates through the fabric,
it is therefore easy to see when the element is fully loaded
with oil requires replacement.
This picture shows
RP18 as a filter in a drainage outlet alongside a
locomotive works. Tests showed that the oil discharged
into the freshwater streams was reduced from 50 ppm
to less than 10 ppm using this method of oil pollution
The RP18 fabric was changed every 10 days depending
on flow rates. Fabric on final weir was replaced every
4 weeks - used purely as a final polish.
- At 1 cm head - 0.141cc/sq.cm/sec
- At 10cm head - 0.550cc/sq.cm/sec
Fabric loaded with oil at 0.55cc/sq.cm
- At 1 cm head - 0.027cc/sq.cm/sec
- At 10cm head - 0.186cc/sq.cm/sec
In order to prevent carry over of retained
oil it is best not to exceed a flow density with a head
of 10 cm of 330 litres/min/sq.m.
When the quantity of oil retained reaches
0.8cc/sq.cm the flow rate should not exceed 100 litres/min/sq.m.
The above parameters refer to a single
thickness of 9mm nominal, the number of layers do not significantly
affect the overall performance.
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