Adsorption plant operation is very sensitive to the temperature of the incoming gas. Generally, the adsorption efficiency decreases as the temperature increases.
The temperature of the regeneration gas that commingles with the incoming wet gas ahead of the dehydrators is also important. If the temperature of these two gas streams differs more than 15°F to 20°F, liquid water and hydrocarbons will condense as the hotter gas stream cools. The condensed liquids can shorten the solid desiccant life.
The temperature of the hot gas entering and leaving a desiccant tower during the heating cycle affects both the plant efficiency and the desiccant life. To assure good removal of the water and other contaminants from the bed, a high regeneration gas temperature is needed. The maximum hot gas temperature depends on the type of contaminants and the “holding power” or affinity of the dessicant for the contaminants, A temperature of 450°F to 60G°F is normally used.
The desiccant bed temperature attained during the cooling cycle is important. If wet gas is used to cool the desiccant, the cooling cycle should be terminated when the desiccant bed reaches a temperature of
approximately 215°F. Additional cooling may cause water to be adsorbed from the wet gas stream and presaturate or preload the desiccant bed before the next adsorption cycle begins. If dry gas is used for cooling, the desiccant bed should be cooled within 10°F~20°F of the incoming gas temperature during the adsorption cycle, thereby maximizing the adsorption capacity of the bed.
The temperature of the regeneration gas in the regeneration gas scrubber should be low enough to condense and remove the water and hydrocarbons from the regeneration gas without causing hydrate problems.
