A deaerator is an essential auxiliary component of a reliable feedwater system and are available in a number of configurations. The selection criteria for a particular model includes boiler-plant design, capacity, and system pressure rating. Deaerators serve a multitude of functions in a healthy steam-plant:
- Collection tank for process condensate return.
- Mix hot return condensate and cold makeup water.
- Provide preheated feedwater to improve boiler efficiency.
- Remove oxygen and carbon dioxide from feedwater to mitigate corrosion.
- Hold treated hot water in reserve for load change(13 to 15 minutes).
- Ideal location for feeding and blending chemicals and testing protocol.
- Feed a constant, pressurized supply of water to boiler feed pumps.
- Convenient location for instrument controls and feedwater test data.
- Help to ensure precise drum water level and pressure inside of a boiler.
One of the critical functions performed by a deaerator is the removal of dissolved oxygen and carbon dioxide, which are highly corrosive to boilers and boiler system components. If the free oxygen is not contained or eliminated from the feedwater, a new boiler can completely fail in a matter of a few months.
How Do Deaerators work?
Most deaerators operate at 5 to 15 psig by utilizing a low-pressure steam supply and maintaining a water temperature of 225°F, which is the minimum temperature required to remove dissolved oxygen and carbon dioxide from feedwater. Oxygen is 10 times more corrosive than carbon dioxide and carbon dioxide is 40 percent more corrosive when working in conjunction with oxygen. Carbon dioxide forms in the boiler’s feed tank when the water is heated. The amount of carbon dioxide formation depends upon the amount of carbonates in the feedwater, especially bicarbonate. Carbon dioxide can be completely removed from the system by applying heat in conjunction with maintaining a pH in the boiler water between 9 and 12.5.
At t 225°F , feedwater pumps, piping, and economizers are subject to severe O2 corrosion attacks even though only a minute level of O2 is dissolved in the water. An attack on a boiler’s waterside surface is often evident in the form of blisters. Beneath these blisters are small holes that penetrate the tube metal until it fails and leaks. A properly operating deaerator should scrub oxygen levels to 5 to 10 ppb residual.
Deaeration begins by reducing the surface tension through a system that either sprays or films (spreads out) the water for eventual gas bubble release. The water is then heated, which causes the gasses to lose their solubility and form the bubbles. Next is a mechanical agitation or scrubbing process that liberates the gasses, allowing them to flow into the atmosphere.
Deaeration is part of a complete water treatment program including filtration, softening, dealkalization and chemical treatment.
Why Work with Blake?
Blake Equipment is the only distributor AND manufacturers rep of water AND thermal energy equipment, supplies and services in the Northeast providing solutions to the full spectrum of applications. We understand boilers and the water they require to operate at peak efficiency over a long lifetime of service. We are experts at all facets of water conditioning. Blake brings these two critical areas of expertise together to bring customers solutions that work.
Evaluating Deaerator Operation; System analyses reveal savings opportunities; Jan 1, 2010 By GARY WAMSLEY, PE, CEM; JoGar Energy Services; Alpharetta, Ga. | HPAC Engineering