Continuous Percolation through Granular Carbon

In a continuous percolation system, the raw liquid is passed through a bed of carbon of sufficient depth to provide a finished liquid of the desired purity.6,9,13 The flow will range from 1 to 3 GPM per square foot of the cross section of the bed area the depth 

Minimum recommended height-to-diameter ratio of a column is 2 to 1, but ratios greater than 2 to 1 will improve the performance. 

Columns of granular carbon are designed for economical and convenient working pressure. Actual operating pressure seldom rises above one pound per foot of bed depth even with a liquid of 10 centipoise viscosity. Good design allows for some excess pressure. 

A moving bed incorporates an effective countercurrent operation within a single column.6,9 These systems are especially applicable 

In a moving bed column the flow of liquid is up through the bed of carbon, while the carbon advances periodically down through the column.9 This permits frequent removal of small amounts of spent carbon from the bottom of the column and corresponding additions of fresh carbon to the top. The withdrawal of spent carbon is controlled by a valve below the cone-shaped bottom. The fresh carbon should be immersed in water or in the liquid being treated to facilitate its entry at the top of the column.9 

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Bone char and granular carbon are generally used in fixed beds or in cylindrical columns 20 to 25 feet high and about 10 feet in diameter. Some recent systems percolate liquor upward or downward through a stationary bed of adsorbent or by counter-current flow of liquor and adsorbent (CAP or continuous adsorption process). (See below. Fig. 9.17.)... 

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