For critical applications all dissolved gases have to be removed from the water.  A forced draft degasifier will remove gases like carbon dioxide, hydrogen sulfide, and volatile organics.  However, it will saturate the water with oxygen.  A vacuum degasifier is used where all gases, including oxygen, need to be removed from the water for high purity or corrosion protection purposes.

Vacuum Degasifier with platforms during assembly for Orlando Utilities.

This is accomplished using a tower design with packing similar to the forced draft degasifier.  However, the tower is a pressure vessel rather than an atmospheric tank.  Construction is rubber lined steel with an ASME code stamp.  The principal of operation is the same as a forced draft unit.  The inlet water is sprayed over tower packing.  The water forms a film over the packing.  A vacuum is drawn on the tank, and the dissolved gases are released from the water and sucked out of the vessel.

Design considerations include the temperature, analysis of the raw water including oxygen and carbon dioxide, and the treated water quality desired. Different style vacuum pumps, tower construction, and type, depth, and size of the packing used can all be varied to meet the performance requirements. Towers can be designed with single, two, or three stages.  Vacuum pumps can be a water seal design, and eductors can be used to improve performance.