Deaerator temperature

[bethw]

Our plant has a DA that is maintained at 5 lbs. It is supplied by steam from a prv. The steam pressure before the prv is 85 lbs. If I remember my basic thermo right, because this steam comes through a prv, it is superheated when it is reduced to the 5 lbs. Using what I remember about the adiabatic throttling process, the temperature of this steam after the prv should be around 290 degF, in a perfect world. So the steam entering the DA should be at about the same temp, right? So why is the temp of the DA and the condensate leaving it only at the saturation temp of 5 lbs (about 230F)? Has the "extra" enthalpy gone into the water requiring less steam usage?

 

[rmw]

Yes. You are right on.

rmw

 

[bethw]

This must be because there is no such thing as superheated water. Any "extra" entalpy above the saturation temp. would be used to heat the condensate up to saturation? Sounds like an extra effiecent way to deaerate. Bethw

 

[djack77494]

bethw,
You are most unlikely to have fully saturated water entering the deaerator (though it may be very close). A little extra enthalpy in the steam is no problem. It can be absorbed into slightly subcooled water or it can even go towards vaporizing a small amount of saturated water to reduce the steam requirement. My suggestion is to not worry about it.

 

[MJCronin]

To all

Addtionally, DAs typically have a vent for non-condensibles.

Energy is unavoidably lost in the removal of air...etc

_MJC