The Deaeration Principle

Using Henry's law of partial pressures, the principle behind deaeration can be explained as follows: The quantity of a gas dissolved in a given quantity of liquid is directly proportional to its partial pressure surrounding the liquid. Therefore, by reducing the partial pressure of the unwanted gasses in the surrounding atmosphere, the gasses are diminished. These partial pressures are reduced by spraying the liquid into a countercurrent flow of steam. The steam, which is free of non-condensable gasses, is the liquid's new atmosphere and Henry's law prevails. Using steam is advantageous in that the solubility of a gas in a liquid decreases with an increase in the temperature of that liquid. The liquid is sprayed in thin films in order to increase the surface area of the liquid in contact with the steam, which, in turn, provides more rapid oxygen removal and lower gas concentrations.

Deaerator Operation - Stage One

The prime element in our vent condenser zone is the self-adjusting spray valve that allows incoming water, which is to be deaerated, to discharge as a thin-walled, hollow cone spray. Because steam flows countercurrent, intimate water to steam contact occurs with consequent latent heat transfer. As the falling water reaches the tray stack (tray type deaerator), or the collection basin (spray type deaerator), its temperature is within 2°F (1ºC) of the counter-flowing saturated steam temperature. Most of the dissolved oxygen and free carbon dioxide have been removed at this point. Since nearly all of the steam has been condensed, the non-condensable gasses and the small amount of "transport" steam exits through the vent piping.

Deaerator Operation - Stage Two

Tray Type Deaerator

The partially deaerated water enters the tray stack at saturation temperature. The heated water flows down over the trays, through counterflow steam. This arrangement provides additional retention time to allow a final oxygen strip by the purest steam. The two-stage tray deaeration technique is the most reliable method for meeting critical performance over a complete load range.

Spray Type Deaerator

Water from the collection basin flows down the vertical downcomer and into the scrubber section where it comes in contact with upcoming steam. Through carefully sized orifices, the steam and water violently mix, heating and removing the remaining gasses from the water. The mixture moves to the top of the scrubber housing and there the steam separates from the water and gasses and continues to flow up into the spray area and the vent condensing zone (Stage One of our deaerator).

Critical Components

Spray Nozzles

Our quality Spray Valves are investment cast of type 316 S.S., hydraulically balanced and pro-vided with Teflon stem guides for extended life and quiet operation. These rugged valves are designed to handle flow fluctuations from 0% to 200% of design.

Trays

Our Trays are stamped and riveted as recommended by the HEI Standard. Our 16 ga., 430 S.S. trays are the most rugged available in the industry and have been utilized successfully by central station utilities for over 30 years. Our tray locking tabs and com-pression tray hold-down system will resist deaerator transient loads and reduce tray damage under upset conditions.

 Reliability As The Basis Of Design

In response to the demand for a more reliable deaerator, Kansas City Deaerator Co. has devel-oped an innovative Header Design. This new design provides greater durability and extended life with improved operational features and ease of maintenance. In addition, this new design uti-lizes an improved fabrication process which allows for stricter quality control and ensures that our deaerators will be in service long after others have been replaced.

Cost and Justification

 Cost

 There is no additional energy cost associated with operating a Deaerator, and the maximum of steam exported to the plant is the same with or without the Deaerator, because the steam used to increase the feed water temperature comes from the higher boiler output.

Justification

 The principle reasons for selecting a Deaerator are

• To reduce oxygen levels to a minimum without the use of chemicals. This will eliminate corrosion in the boiler feed system.
• A cost saving can be achieved with respect to chemicals.
• Chemicals added to control the oxygen content of the boiler water will themselves require blowing down. Therefore by reducing / eliminating the addition of chemicals, the blow down rate will be reduced with associated cost savings.
• Since the water is at saturation temperature converting it in to steam will require less amount of fuel in Boiler, thereby increasing efficiency of system.

Assuring Quality, Safety At Every Turn

Kansas City Deaerator Co. relies on the latest technology to provide quality design, fabri-cation and document control. With sophisti-cated computer programs for vessel calcula-tions, nozzle load calculations, heat balances, ratings and CAD drawings, we’ll take you

from conception to start-up — error free —consistently. Likewise, when specified, our work is per-formed, in strict accordance with ASME codes, NACE and HEI standards to assure not only quality, but long-term safety and reliability. To assure quality upon completion, our units are typically inspected by three to five inspectors prior to shipment.