How are Nitrogen Generators Used for Sweep Gas?
Contactors, or Membrane contactors, are devices that allow a gaseous phase and a liquid phase to come into direct contact with each other, for the purpose of mass transfer between the phases, without dispersing one phase into the other. A typical use for these devices is the removal of oxygen within water. For removal of oxygen within the water stream, membrane contactors are operated with the liquid water on one side of the hydrophobic membrane, and a nitrogen sweep gas and vacuum applied to the other side of the membrane. Since the membrane is hydrophobic, the membrane will not allow the liquid water to pass through the pores into the gas side of the membrane.
By adjusting the partial pressure of the nitrogen, oxygen can be removed from the water side of the contactor. This is accomplished in accordance with the Young-Laplace equation, which is also known as the breakthrough pressure equation. The design of the membrane contactor allows for a breakthrough pressure exceeding 150 pounds per square inch.
With the use of nitrogen as the sweep gas, and lower pressure present within a vacuum, oxygen from the water stream migrates through the hollow fibers as it is attracted to the lower pressure side of the contactor. Along with the breakthrough pressure, the quality of the sweep gas is also very important to the process.
Depending on the final process for which the degasified water is used, different levels of nitrogen purity are acceptable as the sweep gas. For most sweep gas nitrogen applications, purity levels over the 99.99% level are used. This allows for the sweep gas to accept larger ratios of oxygen during degasification.
The water is introduced into the contactor on the outside (shell-side) while the vacuum or sweep gas flows through the inside of the hollow fiber (lumen-side) of the contactor. This process is performed with the water, and the vacuum or sweep gas, running in opposite directions within the contactors. The nitrogen sweep is pulling the oxygen away from the water and venting outside of the process. The end result is water that is now devoid of the free flowing oxygen molecule that can be used in a wide range of applications from corrosion protection to food and beverage processes.
A PSA Nitrogen gas generator from South-Tek Systems conveniently produces the N2 needed at the site, through a simple and safe mechanical air separation process. Learn more about the convenience and cost-effectiveness of our Nitrogen Generators at www.southteksystems.com. For more information regarding Membrane contactors, visit Liqui-Cel at www.liquicel.com