WHY IS A PERMEATION DRIER SUPERIOR TO ANY CONDENSING SYSTEM?
Nitrogen dioxide and sulfur dioxide gases react with water, but not with water vapor. Even in the most carefully designed condensing type of water removal system, some of the gas will come into contact with the condensing water and this will cause partial removal of NO2 and SO2 from the sample stream resulting in incorrect measurement of their concentrations. In a permeation drier the water is removed while it is still in its vapor state and before it begins to condense. Thus, there is virtually no loss of NO2 and SO2 from the sample stream. For NO2 measurements, see figures 3&4 on Technical Paper #2. For SO2 measurements, see figures 3&4 on Technical Paper #1.
