1) Spray-Type deaerators
In this type the feedwater enters the heater through nozzles that spray it into the extraction-steam-filled heater space. The water is heated and scrubbed to release the noncondensables gases. A second agitation of the now-heated feedwater by another steam flow is provided by an internal baffling system.
2) Tray-Type deaerators.
Here the feedwater is directed onto a series of cascading horizontal trays. It falls in sheets or tubes from tray to tray and comes into contact with rising extraction steam admitted from the bottom of the tray system. As scrubbing occurs and noncondensables gases and some steam rise, they come into contact with colder water, resulting in a reduced volume of high concentration of noncondensables to vent into the atmosphere.
3) Combination spray-tray deaerator
In this type, the feedwater is first sprayed into a steam-filled space, then made to cascade down trays. This combination type with horizontal stainless steel trays is currently preferred by utilities.
You noticed that just below the heater, is a relatively large feedwater tank (Storage Tank) which allows sufficient water for rapid load variations.