Imagine having two beers in front of you—one cold and the other warm. If you were to pour both of these beers from the can into two separate glasses, the warm one will inevitably foam over. This happens because, as a liquid warms up, its ability to hold onto dissolved gases decreases. This is the first principle in how a deaerator (DA) works: warming water drives off dissolved gases.
Now imagine you have two beers in front of you again. This time you take one of the beer and shake it up. You pour both beers into two separate glasses and the shaken beer will inevitably foam over. (If it doesn’t explode in your face first). This is because agitation helps release the dissolved gases in liquid. This is the second principle of how a deaerator works: agitating water drives off dissolved gases.
Warming Up Water: The Boiling Point and Pressure Dynamics
A deaerator works by warming up water to drive off dissolved gases. This is done by injecting steam to heat up the feed water and condensate returns. We heat the water to near its boiling point to drive off as much dissolved gas as we can. Under normal conditions this would be 212°F, but deaerators operate under pressure. They typically sit between 5 and 10 PSI depending on the manufacturer. At 5 PSI the boiling point of water is 227°F, so that is what we look for when the DA is in operation to ensure effective deaeration.
Agitation and Its Role in Deaeration
Spray Type DA
Next up lets talk agitation. In a DA, we achieve this agitation through various methods. The 3 most common types of DAs are Spray Type, Tray Type and Packed Column.
The Spray Type
A spray type deaerator is similar to your sprinkler head at home. Your sprinkler atomizes water into fine droplets as it shoots it across your lawn. Similarly, a spray type deaerator agitates water by atomizing it into fine droplets and sprays them into the DA. These sprayed droplets are exposed to steam, heating them to the boiling point before they collect in the storage section. Proper atomization is crucial in these units. If the flow is too low, water doesn’t atomize well. Think of just barley cracking the valve to your sprinkler, how a low flowing stream of water just drains out. Just barley cracking the valve on a DA doesn’t allow the water to heat up properly, resulting in ineffective deaeration.
Tray Type DA
Tray Type DA:
In this type of DA the water is sprayed above a tray section. The water is then allowed to drip through trays, agitating it. The trays also provide additional surface area for steam contact, ensuring thorough heating and agitation.
Packed Column DA:
In this type of DA, water drips through packing material. These are similar to tray types, but with different structural elements for promoting gas release.
Monitoring Your DA
To ensure your DA is functioning correctly, compare the temperature in the storage section with the pressure in the steam dome. For instance, at 5 PSI, the storage section should be around 227°F. Discrepancies can indicate issues like improper atomization, inaccurate instrumentation, or static head effects on the pressure reading.
Getting Professional Help
If you’re unsure about your DA’s performance, consult with your chemical treatment provider. They can perform dissolved oxygen testing to evaluate the DA’s efficiency and provide insights into potential issues, like excessive oxygen levels or incorrect chemical dosages.
