When the number of absorber trays and lean glycol concentration are fixed, the dew-point depression of a saturated gas is a function of the glycol circulation rate. The more glycol that comes in contact with the gas, the more water vapor is stripped out of the gas. Whereas the glycol concentration mainly affects the dew point of the dry gas, the glycol rate controls the total amount of water that can be removed. The minimum circulation rate to assure good glycol-gas contact is about two gallons of glycol for each pound of water to be removed. Seven gallons of glycol per pound of water removed is about the maximum rate. Most standard dehydrators are designed for approximately three gallons of glycol per pound of water removed.
An excessive circulation rate may overload the reboiler and prevent good glycol regeneration. The heat required by the reboiler is directly proportional to the circulation rate. Thus, an increase in circulation rate may decrease reboiler temperature, decreasing lean glycol concentration, and actually decrease the amount of water that is removed by the glycol from the gas. Only if the reboiler temperature remains constant will an increase in circulation rate lower the dew point of the gas.