Posted by Lathrop Trotter & filed under Boilers.

Deaerators are often used in conjunction with steam-generating boilers for the removal of oxygen and other dissolved gases from the boiler’s feedwater. Deaerators are typically designed to remove oxygen down to levels of 7 ppb by weight (0.005 cm³/L) or less, while virtually eliminating carbon dioxide.

The removal of these contaminants is important due to the serious damage untreated feedwater can do boiler systems. Contaminants in the water attach to the walls of piping and other metal equipment to form oxides, or rust. Dissolved carbon dioxide combines with water to form carbonic acid, which is responsible for further corrosion. Removal of oxygen and carbon dioxide are not the only advantages of using a deaerator with a boiler system.

Deaerators Enhance Operation

Using steam as a scrubbing gas, the deaerator effectively heats the boiler feedwater as it is treated. Introducing hot feedwater into a boiler system greatly lessens the likelihood of thermal shock due to expansion and contraction of heating surfaces.

Some systems have on-off pumping cycles, which require the flow rate of the pump to be significantly higher to maintain steam requirements. Even when a deaerator is used, on-off cycles in some boiler designs disturb thermal circulation by flooding the boiler with a surplus of water, which collapses the active steam bubbles. The resulting unstable water levels and firing rates mean the system puts an erratic load on the deaerator. Deaerators in this type of system should have an integrated centrifugal pump designed for modulating service, and boilers should have fully modulating feedwater regulators. Water should be put into the boiler at the same rate it in which it leaves as steam.

Heat Transfer is Improved with a Deaerator

Since air acts as an insulator, it significantly impairs heat transfer when it concentrates in process equipment. It is important to rid systems of unwanted non-condensable gases. A deaerator prevents them from entering the system in the first place.

Deaerators Provide Energy Savings

High-pressure steam that otherwise would be lost to atmosphere can be captured and directly returned to a deaerator to be used as the scrubbing gas. The flash steam recovered by a deaerator typically amounts to a significant percentage of the fuel required for process heat. Continuous blowdown heat recovery can be incorporated into a deaerator cycle at minimal cost and without having to shut down the boiler system.

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