When a gas and liquid are in contact with each other, some of the gas dissolves in the liquid and some of the liquid dissolves in the gas. This phenomenon, known as mass transfer, is dependent on the relative concentrations of the gas in liquid and liquid in gas and the temperature of the liquid. Therefore, to reduce the amount of gas that is dissolved in a liquid, the temperature of the liquid is increased and/or the gas concentration in contact with the liquid is reduced. A gas stripper uses the principle of reduction of the gas concentration in contact with the liquid by using another gas other than the gas desired to be removed.
In a gas stripping system, water and gas are introduced into a vessel to reduce the oxygen in the water by creating an oxygen concentration gradient between the gas and water. Effective mass transfer from the liquid to the gas is accomplished by creating intimate surface area contact between the two fluids. Under this condition, oxygen transfers from the water to the gas and is removed from the vessel with the gas.
The degree of removal is determined by the amount of contact surface area created, the amount of gas available for use and the oxygen concentration difference between the gas and water. Because the last traces of dissolved oxygen are the most difficult to remove, 50 parts per billion is the lowest practical level that can be achieved with gas stripping. To reduce the oxygen concentration further requires addition of an oxygen scavenger chemical.