DEAERATOR OPERATING PRINCIPLE
Guaranteed oxygen levels (<5 ppb) without use of oxygen scavenger
The operating principle of the Stork spray type deaerator is based on physical deaeration which takes place in two steps:
- Pre-deaeration in which water is sprayed in to a part of the steam space;
- Final-deaeration in the water tank where steam is brought in to close contact with the water to be deaerated. The pre-deaeration is achieved by the Stork spraying device. Under all kinds of operating conditions, the sprayer assures heating up of the condensate to saturation temperature and provides for a very large area for mass transfer. As the solubility of oxygen in water at saturation conditions is practically zero, oxygen transfers from the water droplets to the surrounding steam. As the steam condenses on the water droplets, the concentration of oxygen in the direct vicinity of the sprayer is increased making it possible to vent a small amount of steam with a relatively high oxygen concentration.
Final deaeration in the water tank is achieved by injection of steam in to the water tank. Depending on the conditions, steam, pressurized hot water, or steam/water mixture can be used for deaeration.
A properly designed steam device, taking into account the hydro-dynamics in the water tank, will result in good contact between water and steam, allowing the oxygen to move from the water to the steam in accordance with Henry’s law.
For detailed information see: The principle of physical deaeration.
Start up: Deaerated water available already
Instead of heating up the entire water bulk in the vessel during initial filling, only a small volume of water in the vessel is heated up to operating temperature. Once this small volume is heated (and thus also deaerated) the deaerator can be filled to normal operating level. As this occurs water already deaerated will be routed through the boiler.
Starting up the deaerator by heating up a small volume of water will not only result in the availability of deaerated water during start-up, but will also eliminate the chance of water hammer.
The Stork spray type deaerator design already provides deaerated water available during start-up. This heating process contributes to safe and reliable operation.