Deaerators are a key component to many boiler systems that require regular maintenance to ensure long and efficient equipment life. Their primary purpose is to remove dissolved gases (such as oxygen and CO2) from the water going into the system. This helps prevent oxygen pitting inside the piping and boiler. Before we discuss how to prevent common deaerator problems lets take a closer look at why they are necessary.
As mentioned above, a deaerator helps prevent corrosion. Corrosion occurs when oxygen in the water reacts with iron in the system. If you do nothing to remove the oxygen, the iron in the system will! The metal will react chemically & disintegrate, forming rust.
The chemical process starts when iron interacts with water to form Ferrous Hydroxide.
Fe + 2H2O = Fe(OH)2 + 2H+ Iron + Water = Ferrous Hydroxide + Hydrogen
(the top layer of Ferous Hydroxide protects the remaining iron)
If dissolved oxygen is present, it combines with the ferrous hydroxide to form an insoluble compound, ferric hydroxide, which is rust.
4Fe (OH)2 + O2 + H2O = 4Fe(OH)3
Ferrous Hydroxide + Oxygen = Ferric Hydroxide (Rust)
If the system continuously cycles dissolved oxygen, the ferrous hydroxide will be continuously removed from the system until the metal has been totally dissolved.
What Needs To Happen For Deareration To Occur?
1. Temperature – Water cannot absorb gasses when it is heated to saturation temperature. Water also only releases gasses when it reaches saturation temperature.
2. Turbulence – This helps to break the surface tension of water and aids in the release of gases.
3. Time – You need to have enough time for the release of gases to occur.
4. Venting – The gases that are released in the steps above need to be able to escape.
5. Steady State Conditions – without steady state conditions, the deaeration process can not occur!
- A constant flow of water through spray nozzles or trays insures adequate turbulence.
- Stead flow of feed water, with only gradual temperature changes, allows pressure controllers to satisfy demands for steam.
- Steady flows of feed water also assures that the deaerator will operate with the capacity for which it was designed.
8 Steps To Prevent Common Problems:
1. Prevent Corrosion on the Tank.
Address corrosion early to reduce the risk of more significant problems. Leaking pipe outside the tank cause corrosion issues on the exterior of the tank. This can become a serious issue if neglected and should be addressed as soon as a leak is spotted. Be sure to inspect your system on a regular basis and fix leaks as they appear.
2. Clean the Components.
The water and steam that pass through the tank are normally of high purity. This means the necessity for cleaning should be infrequent. On the other hand, inspect spray or tray assemblies at least annually for any evidence of corrosion, scaling or other damage.
Be sure to check the spray valve nuts are tight with no evidence of leakage under the gasket. If you start to experience new or unusual noise, the spray valve is a good place to start looking. If the spring breaks within this nozzle the valve can remain open, which will cause water hammer when the supply valve comes on.
3. Test Water Hardness.
Test water hardness regularly to ensure the water going into the deaerator isn’t bringing in unwanted minerals. If you are unsure what your makeup water hardness should be, contact your boiler water chemistry provider.
Important Note: If oxygen scavenger usage increases over time or there is a marked decrease in performance, you may have larger problems. This could indicate issues with the way the deaerator is being operated, or it could indicate something internally is damaged.
4. Flush Strainers.
Strainers are frequently installed on the pump inlet to protect the pump from debris. These should be flushed regularly (if a valve is present) and should be cleaned and inspected on an annual basis. This will prevent blockages from reducing the flow of water to the pump, causing flashing and severe pump damage.
5. Perform Chemical Pump Maintenance.
You will want to verify daily that the pumps feeding chemicals into the system are working properly. It is also imperative to use the appropriate chemical treatment while operating your steam system. If either of these items is neglected it can result in corrosion or scale damage inside the boiler system.
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6. Test Float Switch.
It is important to take the time to occasionally check the float level control operation to confirm that the float is moving freely. It is also important to blown down float operated controls routinely. You should also ensure the level controls are filling to the appropriate level and will turn off the pumps for low water.
7. Clean Gauge Glass.
It is important to keep this component clean to allow for a proper visual inspection. You will want to look for etching, thinning or damage while the unit is cool. If any damage is present or you are not able to easily identify the water level, replace the gauge immediately.
8. Install A Surge Tank
If the deaerator is having trouble sometime it calls for additional equipment. As we mentioned earlier, steady state condition are required to operate effectively. When temperature or feed water flow fluctuate drastically it can wreak havoc on the system.
A surge tank helps “averages out” the flow and steam loads so a steady state can be provided. Surge tanks will also receive make-up water and mix it with returns, as well as collect gravity returns.
Here are 3 rules of thumb to know if you should use a surge tank.
1. A single tank spray deaerator needs a surge tank when the returns exceed 30% of the capacity.
2. A single tank spray deaerator needs a surge tank if the loads vary during operation. (A spray-tray needs one if loads vary widely)
3. A spray-tray deaerator needs a surge tank when the returns exceed 50% of the capacity.
Deaerator Problems Got You Stumped?
Be sure to follow the manufacturers recommendations for maintenance to ensure your boiler system runs as efficiently as possible. If you’re experiencing deaerator problems that have you stumped, reach out for a free estimate, call us at 1-800-237-3141 or chat with an agent. Our team is here to help!