Vacuum Deaerator or degasifier are designed to effectively remove select non-condensable gases from the liquid stream. A vacuum is pulled on a stream of water, and the vacuum draws the dissolved gas out of solution, removing it from water.
There are two basic systems available:
Vacuum Deaerator
A vacuum deaerator is typically used as part of a demineralizer system to remove entrained gasses like CO2 and oxygen from boiler-feed water for high-pressure boilers.
Liquid is sprayed into a vessel onto selected packing material through fine nozzles to increase the water/gas transfer surface. The vacuum causes the gas to be released, and it is extracted from the system by the suction.
To enable the most efficient removal, the size of the transfer surface and the contact time are optimized. Vacuum deaerator is utilized to remove O2, CO2 and N2 and is capable of producing water with part-per-billion levels of these dissolved gasses.
In a vacuum deaerator, water flows by gravity down through a tower filled with packing as a vacuum is drawn on the tower. The packing in the tower has a very high surface area, disperses the water very effectively, thereby enhancing the removal of O2, CO2 and N2.
Performance is further enhanced by using atomizing nozzles as the water enters the tower. Since the vessel has to bear full vacuum, a steel ASME code vessel with a rubber lining is used.
Polypropylene tower packing is utilized in the same fashion as forced draft degasifiers. A vacuum pump with or without an ejector typically is used on the vessel.
Membrane Deaerator
A Membrane Deaerator is an equipment where liquid flows across one side of a membrane surface while a vacuum is drawn on the other side. Jet eductors or liquid ring pumps are used to generate the vacuum required.
Gas-Liquid Separation membranes allow gas but not liquid to pass through. Flowing a solution inside a gas-liquid separation membrane makes the dissolved gas go out through the membrane with the used of the vacuum.
This method has the advantage of being able to prevent redissolution of the gas, so it is used to produce very pure solvents.