The two main types of boiler deaerators

The two main types of boiler deaerators

Tray-type deaerator   A tray-type deaerator typically has a deaeration section mounted above a horizontal feedwater storage vessel. Water enters the deaeration section into a stainless-steel enclosure through stainless steel spray valves mounted to a horizontal header pipe.  During the 1st stage of deaeration, the water is dispersed in a fine film or droplets above a section of trays.  The water is deaerated in a 2nd stage, as it cascades downward through openings in the trays. Low-pressure steam enters the enclosure below the trays and flows upward counterflow to the water. The combined action of the 1st and 2nd stages of deaeration guarantees very high performance, as it allows for longer contact time between steam and water.  The steam strips the dissolved gases from the boiler feedwater and exits via the vent connection at the top of the vessel. It is critical for proper operation that the vent line be opened sufficiently, or the deaerator will not work properly, causing high oxygen content in the feedwater going to the boilers. The vent line usually includes a valve that allows just enough steam to escape with the vented gases to provide a small visible telltale plume of steam.  The deaerated feedwater flows down into the horizontal storage vessel from where it is pumped to the boiler.

Spray-type deaerator   A spray-type deaerator is typically a single horizontal vessel which has a preheating section and a deaeration section. The boiler feedwater is sprayed into the preheating section where it is preheated by the saturated environment of the deaerator. The feedwater is heated to its saturation temperature to facilitate the stripping of the dissolved gases in the deaeration section.  The preheated feedwater then flows into the deaeration section, where it meets the steam entering the system. The non-condensable gases are stripped out of the water and exit via the vent at the top of the vessel.  The deaerated feedwater is pumped from the bottom of the vessel to the boiler.

Spray Unit vs. Tray Unit comparison

DescriptionSprayTray
Typical Oxygen Guarantee7 ppb7 ppb
Pressure Vessel Wall Protected from Oxygen AttackNoYes
All Non-Condensable Contained in a Stainless EnclosureNoYes
Meet HEI RequirementsNoYes
Turndown3 to 120 to 1
Typical Life Span5-15 years30 + years
Typical ConfigurationSingle VesselVaries per application
Overall Design FlexibilityLimitedExtensive
Initial CostLowerMarginally higher

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