In high-pressure steam generation facilities, mechanical spray-tray deaerators eliminate dissolved non-condensable gases from feedwater before it enters the boiler economizer. Cold makeup water is atomized through spray valves into a pressurized steam environment, raising the liquid to its saturation temperature and liberating the majority of entrained oxygen. The water then trickles down through a series of perforated stainless steel trays, where counter-flowing low-pressure steam scrubs out residual carbon dioxide. By stripping these corrosive elements, the system prevents oxygen-induced pitting and carbonic acid formation in downstream piping. To guarantee complete thermal degassing, operators must maintain the deaerator vessel at a constant positive internal pressure, typically five to seven pounds per square inch above atmospheric levels.
According to the passage, how is leftover carbon dioxide extracted from the boiler feedwater?
- ABy atomizing cold makeup water through spray valves directly inside the boiler economizer
- BBy generating carbonic acid to chemically bind and liberate entrained oxygen from piping
- By passing descending liquid across tiers of slotted metal plates against an opposing vapor currentCevap
- DBy reducing the interior chamber pressure five to seven pounds per square inch below atmospheric levels