Deaerator and Blowdown Systems

A deaerator heats boiler feedwater and mechanically removes dissolved oxygen, free carbon dioxide, and other non-condensable gases before the water enters the boiler.Removing these corrosive gases helps prevent oxygen pitting and corrosion damage in boilers, economizers, boiler feed water piping, and condensate systems. Corrosion caused by dissolved gases can lead to leaks, equipment failure, and disintegration of metal components. Maintaining low oxygen content in the feedwater is crucial to extending boiler lifespan and minimizing maintenance needs.

A deaerator also preheats the feedwater to its saturation temperature using low pressure steam, which improves overall boiler room efficiency, reduces thermal shock, and minimizes heat loss. This preheating supports stable pressure control in steam generating boiler systems and enhances steam quality by removing dissolved gases. Typical deaerators operate at 5-7 psi pressure and 225-227 degrees Fahrenheit to optimize the solubility of gases and facilitate effective deaeration. The deaerated boiler feedwater, with traces of oxygen reduced to 7 ppb or less, is then supplied to the boiler to ensure reliable steam generation and protect the water system from corrosion.

It depends on the size and operating conditions of your steam plant. Smaller, low-pressure heating plants with high condensate return rates may operate with an atmospheric feedwater tank and proper chemical treatment.

Larger boiler plants, higher-pressure systems, process steam applications, and facilities with significant makeup water often benefit from a pressurized deaerator. Tri-Tech Sales can help evaluate the boiler capacity, condensate return, makeup water, and water chemistry to determine the right approach.

Both designs remove dissolved gases, but they use different methods.

Spray-type deaerators atomize incoming water through spray nozzles into a steam atmosphere inside a horizontal vessel, where low-pressure steam enters to strip dissolved gases. They are commonly used in smaller and mid-sized plants.

Tray-type deaerators distribute water over a tray stack in a vertical domed deaeration section mounted on a horizontal storage vessel. Low-pressure deaeration steam flows upward counter to the water flowing downward, providing greater contact and scrubbing of the water. This design is often used in larger plants or applications with high makeup water rates and changing loads, and is commonly built to Heat Exchange Institute (HEI) performance standards.

In many cases, yes. Upgrading to a pressurized deaerator can improve dissolved-gas removal, stabilize feedwater temperature, reduce oxygen-scavenger chemical usage, and provide better protection for the boiler and feedwater system.

The new unit must be properly sized for the plant's steam load, condensate return, makeup water, storage requirements, and available boiler room space.

A deaerator removes dissolved gases like oxygen and carbon dioxide from boiler feedwater by using two key principles: gas solubility decreases as water temperature rises, and dissolved gases escape most effectively when water is dispersed thinly and scrubbed with steam. Boiler feedwater enters the deaerator through a feedwater spray nozzle or cascades over perforated trays, coming into direct contact with low-pressure steam rising from below. This steam heats the water to near its saturation temperature, at which point the water can no longer hold dissolved oxygen and carbon dioxide, causing these gases to be stripped out.

The steam heats the boiler feedwater, facilitating the removal of gases which then separate from the water. These gases are carried upward by the rising steam and exit through a vent valve at the top of the deaerator, often creating a small visible plume of steam. The deaerated, heated water then commonly falls into a horizontal cylindrical vessel where it is stored as hot water, ready to be pumped into the steam generating boiler system. Low pressure steam obtained from the plant is introduced via a sparger pipe to keep the stored boiler feedwater warm and maintain water quality.

A well-maintained deaerator typically lasts 20 to 30 years or more. Its lifespan depends heavily on water chemistry, operating practices, and how consistently the control system maintains proper pressure and temperature. Signs that replacement is needed include pitting of the vessel, damaged spray valves or trays, failing level controls, and rising dissolved oxygen levels.

If your boiler shows oxygen pitting or oxygen scavenger chemical usage increases, it often indicates deaerator issues. Many large industrial facilities rely on deaerators to remove oxygen and carbon dioxide to prevent corrosion, which can cause 10-15 g of iron loss per m3 of water and lead to disintegration of metal piping and equipment. Vacuum deaerators, which operate under low pressure, can reduce oxygen content to less than 7 ppb (0.007 mg/L), significantly lowering corrosion risk.

Including a deaerator as part of your steam generating systems ensures that boiler feedwater enters the boiler with minimal dissolved gases, improving steam quality, stabilizing boiler pressure, and extending boiler lifespan by preventing corrosion and thermal shock. Both the deaeration section and storage section work together to provide just enough steam to remove oxygen and other gases, ensuring efficient and reliable boiler operation.