The Water Deaeration is necessary for boilers and steam generators to eliminate the dissolved oxygen and preventing the boilers from corrosion. The usual required duty is 5 ppb as residual oxygen content.
The Thermal deaeration process involves the reaching of the saturation condition of the water to reduce the partial pressure of the dissolved gases: under this condition the gas content in a saturated liquid is zero, the gases tendency is therefore leaving the liquid phase, crossing the liquid-vapor interface and migrate to the vapor phase.
Saturated conditions may be realized either in pressure or under vacuum. On this basis the deaerators can be divided into the following process families:
- Thermal deaerators operating at the saturated conditions either atmospheric or under pressure with steam inlet
- Vacuum deaerators, operating under vacuum without steam inlet
The process kinetics is then an important factor since the resident time must be set adequate to let the time to gases for disengaging from the liquid phase.
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