Cleaver-Brooks - Complete Boiler Room Solutions

Deaerators Help Prevent Boiler Deterioration

Tip Sheet: July 2017

Key Facts

  • Deaeration is one of the best ways to remove oxygen and carbon dioxide from boiler feedwater
  • A deaerator also holds hot condensate returning from the system, which reduces the fuel spend
  • Select a deaerator based on head room, floor-loading limits, capacity and system requirements

Deaeration is one of the best ways to remove oxygen and carbon dioxide from boiler feedwater. When water and steel are combined, the resulting chemical reaction begins to dissolve the steel. Dissolved or soluble oxygen contained within a boiler’s water accelerates the vessel’s rate of corrosion.

Corrosion is generally seen in the form of blisters on a boiler’s waterside surface. Beneath these blisters are small holes that penetrate the tube metal until it fails and leaks. This process happens quickly. If the free oxygen is not contained or eliminated from the boiler water, a new boiler can fail within its first few months of operation.

Water inherently has a high degree of surface tension that holds everything in place unless a surfactant is applied or some other means is imposed on the water to reduce the tension, which is how deaeration works.

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 simultaneously heated, which causes the gases to lose their solubility and form the bubbles. Next is a mechanical agitation or scrubbing process that liberates the gases, enabling them to flow into the atmosphere.

There are several different types of deaerators available:

• Spray type. The normal capacity ranges from 7,000 to 280,000 pounds of steam per hour. This type requires far less head room compared to the others. Its assembly consists of several moving parts, which may require more mechanical field maintenance throughout the life of the equipment, thereby affecting routine operating cost and reliability.

Packed-column type. The typical capacity of this type is 1,500 to 135,000 pounds ofsteam per hour. Unlike in the spray type, a packed-column deaerator has two separate vessels: one for the deaerating column and one for holding the deaerated feedwater (storage tank).  Like the spray type, a packaged-column deaerator comes fully assembled with the stand, pumps and controls.

Tray type. These deaerators can be quite large, not only in capacity, but also in physical size. A tray deaerator typically supports large, industrial watertube boilers, and is similar to the column type in that it has a separate column or tank where deaeration occurs. Unlike the column, which has stainless steel rings for reducing surface tension and providing a means of contact for the (heating) steam, the tray has stainless steel separators that serve the same purpose.

Each of these deaerators eliminates oxygen to 0.005 CC/liter (7 PPB), so selection should be made based on head room, floor-loading limits, capacity and system requirements, as well as budget.

Another key benefit of deaerators is their ability to hold hot condensate returning from the system. This significantly reduces the fuel spend. For every 10 degrees of improvement, there is a one percent gain in boiler system efficiency.

Deaeration is recommended to achieve a highly efficient and long-lasting boiler system. To learn more about deaerators, watch the Basic Deaerator Science Revealed webinar or contact your local Cleaver-Brooks representative.