A deaerator is a device with two primary functions. Its main function is to remove all non-condensable gases from the condensate, primarily oxygen. The other function is to initially heat the feedwater (along with preheaters) to minimize energy wastage in the reactor for heating, directing most of it into evaporation.
In order to remove gases, water must be heated to its boiling point since the possibility of gas dissolution is minimal at that temperature. Therefore, the deaerator water should be heated to approximately 108 degrees Celsius, which is slightly above the atmospheric pressure boiling point within the deaerator. The pressure should be maintained between 1.1 and 1.6 bars.
The deaerator has two primary controls for the steam section (the water section is controlled on the cooling panel). The inlet valve regulates the amount of steam entering the deaerator, while the outlet valve controls the amount of air discharged outside. The outlet valve should always be set to a minimum of 50% to ensure proper degasification, while the inlet valve should be used to maintain the proper pressure and temperature close to the ideal point of 108 degrees.
The deaerator water temperature will primarily depend on the amount of steam injected but will also be influenced by the reactor temperature, as it is initially preheated. The deaerator pressure will be determined by the amount of steam, the outflow valve, and the water level.
Deaerator in U2 has also a breakable rupture disk. In case the pressure grows too high (this might be caused by overfilling deaerator too quickly) a rupture disk will break requiring manual replacement. In order to replace the disk:
- put deaerator inlet at 0 with switch at neutral
- tag the inlet switch
- go to the deaerator in turbine hall
- manually close two valves
- click on the pipe assembly to move it to the ground
- click on two clips on the assembly
- click on the upper part of the assembly
- click on the disk to remove it
- dispose of the disk in airlock area and pick a new one
- install the disk and repeat the whole procedure in reverse (upper part, clips, assembly, valves, remove tag)