IM-P537-01
EMM Issue 1
31
Pressurised Thermophysical deaerator with operator manual for the control unit
5.1 Operation
The PDA deaerator unit consists of a complete, safe and functional package system able to eliminate the
gases dissolved in the feedwater of steam generators.
The deaeration system operates as follows:
-
The condensate and make-up water are fed into the upper part of the deaerator head, are mixed and fall
on a series of plates with which the turret has been sized. The amount of make-up water is regulated by
an actuated valve (pneumatic or electric), depending on the level set point.
-
The steam fed into the system is divided into two circuits:
-
stripping steam fed into the lower part of the deaerator head
-
tempering steam introduced through an injection pipe into the main body of the deaerator
A pressure reduction valve is installed on the steam circuit inlet line, which allows the pressure and
relative temperature to be maintained in the conditions defined in the design phase based on system data.
-
The thermophysical deaerator includes a series of safety devices, such as:
-
safety valves
-
check valves with vacuum breaker function
-
automatic overflow drain cock
-
assembly with discharger for mechanical leakage
-
safety pressure switch for high pressure
-
level transmitter with limit switch for high and low level contacts
-
The venting of the non-condensable gases is done through the vent valve located on top of the deaerator
turret
For a good thermophysical deaeration it is necessary:
1.
Heat the water to a temperature close to the saturation temperature. However, the saturation temperature
alone does not ensure complete gas removal.
2.
It is important to spray the water as wide as possible to increase the surface area so that it exceeds the
surface tension and viscosity that retains dissolved gases.
3.
Reduce the distance the dissolved gases have to travel within the water, while also intensifying the
heating process.
4.
Ensure that the time allotted to the first three activities is sufficient for deaeration.
5.
Ensure that the released gases have a chance to escape the cycle throughout the entire deaeration
process.
6.
Maintain a balanced dynamic process. The deaeration process must maintain a constant vapour
pressure in the system in order to be effective. Large load fluctuations can adversely affect the water
deaeration process.
The unit is fully automatic and equipped with a control panel.
The main controls of the unit are the pressure, temperature and water level inside the deaerator tank. These
controls are interlocked by always active (both in automatic and manual adjustment mode) electromechanical
protections on the unit panel, according to the regulations in force.
5. Operation
