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Anthracite Building

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. 

Media E.S. (mm) U.C. d90 (mm) Vmf* gpm/sq.ft.
CEI Anthracite 1.0 1.3 1.54 9.2
Generic Coal 1.0 1.6 2.2 16.4

*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. 

All Products Exceed AWWA Standards. NSF Approved.

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