Evaluating The Merits Of Carbon Adsorption

Where activated carbon is a potential treatment technology, the first evaluation step is generally to run simple isotherms to determine feasibility. Isotherms are based on batch treatment where impurities reach equilibrium on available carbon surface. While such tests provide an indication of the maximum amount of impurity a GAC can adsorb, it cannot give definite scale up data for a GAC operation due to several factors:

• In a GAC column, dynamic adsorption occurs along an adsorption wave front where the impurity concentration changes.

• GAC rarely becomes totally exhausted in a column.

• Ground GAC exhibits a significantly greater rate of adsorption than a normal GAC.

• Effects of recycling with regeneration cannot be studied.

Because of these factors, pilot column tests should be conducted using the most promising carbons as indicated by the isotherms in order to give an accurate comparison of the carbons. In addition to this, by utilizing reliable scaling-up calculations, pilot tests can be used for system sizing. Pilot column tests can be operated with columns arranged in parallel or in series. The choice of arrangement of the columns is dependent on the scope of the test; such as (1) comparison of GAC grades and/or the effect of regeneration, or (2) scale up to full plant design. In the first case, the columns should be arranged in parallel. In the secind case, the columns arranged in series loaded with one GAC grade. Mobile pilot column systems can be leased from some vendors or assembled using guidelines described below. The columns are mounted vertically and arranged as shown in Figure 18 for the example of scale up tests and downflow operation. It is often good practice to operate columns in upflow as this reduces the opportunity for channeling.

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