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ANTHRACITE FILTER MEDIA
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Lower Backwash Rates with CEI Anthracite
DUAL-MEDIA
Dual-Media filters (anthracite on top of sand) must include a fluidizing backwash rate at
some time before the end of the water backwash. This ensures that the two layers are
restratified into their normal layers of anthracite on top and sand below.
The advantages of CEI Anthracite for dual-media filters is that the ratio of the coarser
grain size of the anthracite to the effective size (e.g. d90/d10), is lower, and therefore
the required backwash rate for fluidization is considerably lower than for other high
uniformity coefficient anthracites. Consider the following example which assumes a typical
log-normal size distribution.
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Media
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E.S. (mm)
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U.C.
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d90 (mm)
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Vmf* gpm/sq.ft.
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CEI Anthracite
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1.0
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1.3
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1.54
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9.2
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Generic Coal
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1.0
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1.6
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2.2
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16.4
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*Approximate minimum fluidization velocity based on water at 10° C
(50° F) with anthracite density = 1.65 g/cm3.
Furthermore, with CEI Anthracite, there is less stratification of the smaller sized grains
on top of a layer and larger sized grains at the bottom. There is more tendency for the
carious-sized grains to mix, rather than to stratify. This is particularly evident if the
d90/d10 ration is 1.3 or less for the anthracite.
TRI-MEDIA
CEI Anthracite would provide similar advantages in lower backwash rates for tri-media beds
using low uniformity coefficient CEI Anthracite. This is a particular advantage for
those designers who prefer to minimize the extent of mixing between adjacent layers in
tri-media filters.
MONO-MEDIA
CEI Anthracite also benefits mono-media filters with coarse grain size that are usually
backwashed with air and water simultaneously below fluidization velocity. During this
sub-fluidized backwash, the media migrates slowly from top to bottom and from bottom to
top assisting in the release of solids from the bed. Such migration of media is encouraged
by provision of low uniformity coefficient media.
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All Products Exceed AWWA Standards. NSF Approved. |
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