Degassing, also known as degasification,  is the removal of dissolved gases from liquids, especially water or aqueous solutions. There are numerous possible methods for such removal of gases from solids. Gases are removed for various reasons. Chemists remove gases from solvents when the compounds they are working on are possibly air- or oxygen-sensitive, or when bubble formation at solid-liquid interfaces becomes a problem. The formation of gas bubbles when a liquid is frozen can also be undesirable, necessitating degassing. There are numerous methods for removing gases from liquids, like Thermal degassing , Membrane degassing and Chemical degassing. Drug production, Production of paint and adhesives are some applications of Degassed water.

1. DEGASSING

2. INTRODUCTION
Degassing, also known as degasification, is the removal of dissolved gases from liquids, especially water or
aqueous solutions. There are numerous possible methods for such removal of gases from solids. Gases are
removed for various reasons. Chemists remove gases from solvents when the compounds they are working
on are possibly air- or oxygen-sensitive, or when bubble formation at solid-liquid interfaces becomes a
problem. The formation of gas bubbles when a liquid is frozen can also be undesirable, necessitating
degassing. There are numerous methods for removing gases from liquids, like Thermal degassing ,
Membrane degassing and Chemical degassing. Drug production, Production of paint and adhesives are some
applications of Degassed water.

3. MEMBRANE DEGASSIFICATION
Membrane Degassing systems effectively use a membrane barrier and vacuum on the other side of the membrane to
remove the dissolved gas. Membrane Degassing requiring no consumption or disposal of dosing chemicals to remove
gases from solution. The technique uses a device known as a Membrane Contactor, or Membrane Degassing Unit
(MDU). It employs a gas-permeable membrane, normally in combination with either a vacuum, or a flow of gas such as
nitrogen, to remove the unwanted gases in the supply stream.
A membrane degassing system basically consists of:
Membrane contactors
Prefilter with 3 µm filter fineness for stripping gas
Prefilter with 5 µm filter fineness for the liquid being degassed
Measuring instruments and valves
Frame and piping
Components for the stripping gas
Vacuum pumps / fan
Pipelines

4. How Water Degasifier Membrane Contactors Work
 Membrane Degassing systemsuse Liqui-Cel Membrane Contactors with a microporous hollow fiber
membrane to remove gases from liquids.
 The hollow fiber is knitted into an array and wrapped around a center tube inside of the contacter housing.
 During typical operation, liquid flows over the shellside (outside) of the hollow fibers while a vacuum is
applied to the lumenside (inside) of the fibers.

5.  Because the membrane is hydrophobic it acts as an inert support that allows direct contact
between a gas and liquid phase without dispersion.
 Applying a higher pressure to the liquid stream relative to the gas stream creates the driving force
for dissolved gas in the liquid to pass through the membrane pores.
 The gas is carried away by the vacuum pump.

6. Operating conditions
The water flowing in should at least be decarbonised (partially desalinated) or softened, since during degassing
hardeners precipitate and the membrane fibres can block up (scaling) due to the shift in the lime-carbonic acid
equilibrium. As many undissolved substances as possible must also be removed by filtration, otherwise they will
also cause blockages (fouling).
For striping gas operation (with CO2 removal), the media temperature should be 30 °C maximum. Higher
operating temperatures (up to 60 °C) are possible when nitrogen is used as the stripping gas (for O2 removal).

7. THERMAL DEGASSIFICATION
 Thermal degassing (TD) is a physical process that consists of removing the dissolved gases in
demineralized water by taking advantage of their insolubility at a temperature of 104ºC
 The only alternative treatment capable of reaching the O2 and CO2 levels obtained with TD would
be chemical treatment with hydrazine (N2H4), amines or Na2SO3, but they have a higher
operating cost and, in many cases, these reagents are toxic and unstable.
 The TD process in water is based on three fundamental laws that govern the solubility of gases.
 Henry’s Law => p = H·x
 There are two type thermal degasifiers , Tray degassing and Spray degassing
 The most widespread technology is spray TD because of its construction simplicity and high
efficiency.
 There is a mixed technique (sprays – trays), which reaches values even lower than this (< 3 ppb),
but the equipment is more complex and expensive and is applicable for very demanding uses
only.

8. EQUIPMENT DESCRIPTION
A spray type degasifier consists of two main parts:
DOME, composed of:
A chamber containing the demineralized water diffuser sprays and a heater which receives the water spray, and first comes
into contact with the ascending vapor from the storage tank. The pre-degassed water is bubbled into a scrubber that
overflows into the storage tank. This provides greater water-steam contact; thereby promoting the removal of gases in
solution to the required limits (< 0.02 ppm for HP boilers, according to the UNE-EN 12952-12:2004 standard).
STORAGE TANK
This tank must be elevated on a metal structure in such a way that it can be connected to suitable pump inlets, which have
a very low required NPSH (1-2 mwc), and thus prevent the negative effect of cavitation.
The tank may be horizontal or vertical, depending on its capacity; usually its independent operating range is 10-30 minutes.
If it is horizontal, which usually occurs for degassed water flows > 15 m3/h, support cradles will be available, with one of
them being mobile to release the tension due to expansion.
Inside the tank a heating coil with steam is housed to start the equipment.