Once - through boilers operate at
Option (A)
subcritical pressure
Option (B)
supercritical pressure
subcritical as well as supercritical pressure
critical pressure only
Correct Option:
Question Solution:
The once-through boiler or monotube boiler as the name implies has only one tube almost 2 km long and there is no steam drum. It is only type suited to super critical pressure operation i.e. above 221.2 bar as there is no latent heat of vepourization involved , and water on being heated at constant pressure (theoretically) suddenly flashes into vapour and steam is further heated to desired temperature in super heater. Water is fed to the boiler by boiler feed pumpat inlet through a number of parallel paths and come out at outlet as superheated steam.