Residence time model for respirator sorbent beds.

An experimental bed residence time model has been developed to characterize the performance of sorbent beds in removing gaseous contaminants. This model is applicable to both adsorption and chemisorption processes. The fundamental characteristics produced can be used to predict the performance of respirator cartridges and canisters over a wide range of operating conditions. A family of performance curves can be constructed for a specific product type for application in determining minimum service life and renewal frequency. This model is described in terms of a dynamic sorption concept, and is demonstrated using ASC I carbon and sulfur dioxide in air at concentrations of 500 ppm, 1000 ppm and 5000 ppm. Adsorption data is also provided for carbon tetrachloride. The effects of bed depth and superficial velocity reduce to a unique relationship between breakthrough time and bed residence time. The influences of moisture, concentration and heat transfer at the walls of the sorbent containment have all been investigated in this study. The dynamic sulfur dioxide capacity of ASC I carbon was found to increase significantly at increasing levels of adsorbed moisture for decreasing sulfur dioxide concentrations. The interrelation of moisture and concentration of sulfur dioxide produces a secondary removal mechanism for which the chemistry is briefly described.