The Effect of Weathering on Charcoal Filter Performance: I. The Adsorption and Desorption Behavior of Contaminants

Abstract

Triethylenediamine (TEDA) impregnated charcoals, used in nuclear reactors to safeguard against the release of airborne radioiodine, show high efficiency under various reactor operation and accident conditions when they are new. However, during normal operation, charcoal filters are continuously degraded (or weathered) due to the adsorption of moisture and other air contaminants. The effect of weathering on the efficiency of charcoal for removing radioiodine is of great interest. The results of a study on the adsorption behavior of various contaminants {NO₂, SO₂, 2-butanone [methyl-ethyl ketone (MEK)], and NH₃} on TEDA charcoal are presented. This study is an attempt to characterize and quantify the weathering process of TEDA charcoal by these contaminants. The adsorption and desorption of characteristics of these contaminants range from completely irreversible (NO₂) to completely reversible (NH₃). The effect of adsorbed water (or humidity) on adsorption is different for each contaminant. Adsorbed water increases the adsorption rate and capacity of TEDA charcoal for NO₂, while it does not significantly change those for SO₂. However, it appears that SO₂ is adsorbed as H₂SO₄ on the wet charcoal. Adsorbed water slightly reduces the adsorption capacity of the charcoal for MEK, but does not affect the adsorption of NH₃.