Reduction of the Measuring Gas Dew Point - Concentration Changes and Washing Out of Noxious Gases and Odorous Compounds

Abstract

Gas cooling devices are used as a means of conditioning humid measur- ing gas flows. In these devices, the dew point is lowered. This causes the surplus quantity of water to condense. Two resulting effects influence the concentration of noxious gases and odorous compounds. The condensa- tion part of the humidity reduces the total gas flow. Therefore, the con- centrations of the other gas components rise. Water-soluble components, however, cause additional washing-out due to absorption in the conden- sate. The concentration of these components diminishes. Both effects are influenced by the degree of dew point reduction and the temperature in the cooler. At low temperatures, gas solubility and the quantity of con- densing water increase. Therefore, the largest washing out effect occurs here. In the case of odorous compounds, the washing-out effect must be taken into special consideration. In order to pass the mucous membrane which covers the olfactory receptors in the nose, odorous molecules must be water-soluble. Depending upon the degree of water solubility, different concentration shifts occur. The resulting odour impression may therefore alter significantly due to the change in relative composition. The alter- native dilution of the measuring gas with dry air for dew point reduction results in a considerable reduction of the concentrations. In this contribution, the fundamental procedures and methods for the calculation of these effects are presented.