Did you ever notice the difference when opening a hot or cold carbonated drink? The hot drink will make a loud whish as lots of bubbles rise to the top and are released when the pressure changes, leaving you with a flat drink with little dissolved gas. The cold drink will make a softer whish and retain its dissolved gasses even when the pressure drops. This is deaeration in action.
Deaerators are designed to remove oxygen and other dissolved gasses from feedwater to protect boilers, piping and equipment from corrosion. Deaerators rely on pressure and temperature to function properly. Henry's Law states that the mass of a gas which will dissolve into a solution is directly proportional to the partial pressure of that gas above the solution. In its simplest form, the high temperature in a dearator reduces the solubility of dissolved gasses such as carbon dioxide and oxygen and allows them to escape the liquid (water) and be vented to the atmosphere. In order to accelerate this process, deaerators use either a tray type or spray type feed system that drastically increases the surface area of the water and allows the steam that is injected into the deaerator to heat the water more rapidly. A proper operating deaerator should be able to get the total concentration of oxygen down to 5 ppb.
5 common deaerator problems and ways to ensure high-quality feedwater.
- Poor venting from the deaerator vent. You should see a 2-4 foot plume of steam coming out of the stack, anything less and you could have a venting or temperature issue, anything more and you could be adding too much steam or you have a trap leak in your plant. Confirm both by monitoring the pressure and temperature of the Deareator.
- High variation between steam and water temperatures. Your deaerator should have separate thermometers for the steam and water inlet lines. The water temperature should be no more than 2° below the steam temperature.
- Inaccuracy of temperature sensing devices. Periodically verify and calibrate thermometers and temperature transmitters to help ensure temperatures remain at the target value. Accurate temperature sensors help make sure the DA is hot enough to properly deaerate the water.
- Poor steam pressure. Steam pressure readings need to be maintained between 3-10 PSI and steady. Variations in deaearator operating pressure or pressure that is too low can result in poor deaeration of the water.
- The DA tank should never be rumbling or vibrating excessively. Check the internals for clogged spray nozzles or cracked condenser tubes.
How a deaerator works:
Video credit: ConvergenceTraining.com
If you detect mechanical deaerator problems with your system, contact Watertech for assistance in treating your boiler water to get rid of free oxygen. Watertech also offers FreedomPlus Pretreatment Services to provide routine service and maintenance for all your pretreatment equipment. If you would like more information reach out to us at firstname.lastname@example.org or 414-425-3339.