502-348-9647 P.O. BOX 354, BARDSTOWN, KY 40004 FAX 502-331-0873

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Deaerator Performance

Introduction:

A deaerator preheats the boiler feedwater and assists in the removal of non-condensable

gases, such as oxygen and carbon dioxide. These gases are undesirable because they

promote corrosion in the feedwater system. Deaerators are generally of three basic

designs: (1) the spray type, (2) the tray type, and (3) the spray-tray type. There are some

vacuum deaerators in use today but they are not very common, and they are not as

efficient. These common types mentioned above use-saturated steam to raise the

temperature of the feedwater and to provide a scrubbing action for release of the

dissolved, non-condensable grease. The trays and sprays are for the purpose of breaking

the water up into small droplets and/or mist, thereby exposing more surface area and

making the scrubbing action of the steam more efficient.

Proper Operation

When a deaerator is working properly, the water exiting the unit should be with 1 deg (F)

of the saturated steam at its use pressure, the oxygen content should meet the

specifications of the deaerator manufacturer (usually 5 to 7 ppb) and there should be no

evidence of corrosion in the feedwater system. A continuous 18-inch plume of escaping

steam above the deaerator vent line is recommended. Adjusting the air outlet valve on

the vent system can control this plume. Caution should be exercised so as to avoid

throttling the valve too much, because air and non-condensable gases will accumulate in

the deaerator. This will result in decreased heating and incomplete deaeration. This

condition is known as air blanketing and can contribute to a wide variation between the

saturated steam temperature and the deaerated water temperature. Before chemicals can

economically complete the oxygen removal requirement, the deaerator must be operating

properly.

Troubleshooting

Troubleshooting is important in keeping the deaerator functioning efficiently. Therefore,

six of the more common problems will be discussed below:

1. Insufficient Heat – This condition is said to exist when the difference between

the saturated steam temperature at use pressure and the outlet water

temperature is in excess of 3 deg (F). When this condition exists, the first

priority should be to make sure the pressure and temperature gauges are

working properly. Having satisfied this requirement, the following causes and

remedies should be investigated:

a. Insufficient venting – Increase the vent rate by opening the manually

operated air vent valve.

502-348-9647 P.O. BOX 354, BARDSTOWN, KY 40004 FAX 502-331-0873

www.gowatersense.com

b. Steam pressure – Reducing valve operating improperly – Check to see that

the valve operates freely, lubricate if necessary – make sure all instrument

lines to the valve controller are connected properly.

c. Improper spray from nozzle – Check nozzle for partial pluggage from

sediment – check for deposits on the seat – check for broken spring.

d. Excessive air in the deaerator – Check stuffing boxes for leaks on pumps

upstream of the deaerator – repair leaks or seal with water.

2. High or Low Water Level – Improper operation of the inlet water control valve –

adjust as required.

3. High Pressure – Check the operation of the steam pressure-reducing valve –

check the pressure relief valves on the deaerator and in the main steam supply

system, for proper operation.

4. Low Pressure – Check the operation of the steam pressure-reducing valve and

adjust as necessary – check the steam pressure of the main supply system.

5. Excessive Steam Pressure Losses Through The Deaerator – Check the trays for

sediment and deposits – remove and clean if necessary.

6. Vent Plume Disappears Periodically – This could be creating a vacuum each time

the plume disappears, thereby pulling outside air into the deaerator – check to

see if large amounts of cold makeup water is entering the unit during the time

the plume disappears – this kills the steam, reduces the temperature and

contributes to inefficient deaeration – the cause could be a periodic loss of

condensate, an erratic steam demand, a malfunctioning steam reducing valve or

a sticking water level control valve.

Deaerators perform a vital function in the efficient product of steam. However,

knowledge of how they work, how they should be operated, how they should be

maintained, and how to troubleshoot problems, is necessary if they are to perform

efficiently.