Methyl iodide penetration of charcoal beds: variation with relative humidity and face velocity

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Australian Atomic Energy Commission
The retention of methyl iodide in charcoal beds was found to vary with the distance from the leading edges of the beds. Near the leading edges, retention was less than in the deeper regions, probably due to the chemi-sorption of competing vapours in the airstream drawn through the beds. One of the poisoning agents was identified as di-methyl sulphate vapour. The penetration of methyl iodide fell exponentially with distance in the deeper regions of the beds. The slope of the penetration curves in these deeper regions was dependent on the relative humidity and the face velocity in a more complex manner than the simple relationship assumed in the 'Stay Time" concept. An empirical formula, which gave the slope of the penetration curve within a standard deviation of 7 per cent, was derived to correlate the parameters over the range of practical interest, i.e. 30-99 per cent relative humidity and from 1.1 m s-1 down to at least 0.16 m s-1, and probably much lower. The uncertainty in the results could have been caused by variations within the batches of charcoal. A formula was derived to translate the results of an in situ test at a measured flowrate and humidity into an expected performance at high humidity and any other flowrate. The expression is independent of the slope of the penetration curve and the thicknesses of both the poisoned and unpoisoned regions of the bed, which suggests that it may be valid even for heavily poisoned beds.
Air filters, Charcoal, Chemisorption, Humidity, Velocity, Methyl iodide
May, F. G., & Polson, H. J. (1974). Methyl iodide penetration of charcoal beds: variation with relative humidity and face velocity. (AAEC/E322). Lucas Heights, NSW: Australian Atomic Energy Commission.