Sand filter configuration

Where sand filters are installed to remove suspended matter in recirculating cooling water, it is usually sufficient to provide capacity based on 1 to 5% of the pumped flow rate. Smaller systems with highly rated cooling towers or evaporative condensers, or systems with high cycles of concentration, will tend to need filters installed in a bypass configuration at 4 to 5% of... 

In the second type of filtration, depth or deep-bed filtration, the particles penetrate into the pores of the filter medium, where impacts between the particles and the surface of the medium are largely responsible for their removal and retention. This configuration is commonly used for the removal of fine particles from very dilute suspensions, where the recovery of the particles is not of primary importance. Typical examples here include air and water filtration. The filter bed gradually becomes clogged with particles, and its resistance to flow eventually reaches an unacceptably high level. For continued operation, it is therefore necessary to remove the accumulated solids, and it is important that this can be readily achieved. For this reason, the filter commonly consists of a bed of particulate solids, such as sand, which can be cleaned by back-flushing, often accompanied by... 

In the early 1960 s, however, it was found that the use of three materials, each of different density and with carefully controlled sizes, could approach quite closely the ideal configuration. The three materials generally used are coal with a specific gravity (S.G.) of 1.55 silica sand, 2.6 S.G. and garnet or ilmenite, 4 + S.G. Sizes vary from ]. 0 mm for coal down to 0.15 mm for the high-density materials. Typically, a mixed-media filter is composed of 10- to 15-percent garnet or ilmenite, 25- to 30-percent sand, and 55-to 60-percent anthracite coal. There is no layer effect. The coarser, low-density coal forms the upper portion of the filter bed the intermediate density and size sand forms the middle portion and the finely sized, high-density material forms the bottom. 

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