Variable Area Type Desuperheaters
This is again a non-integral type desuperheater which requires separate spray water control valve. The spray nozzle is loaded with a calibrated spring that helps to maintain a constant pressure inside, as a function of differential pressure between water & steam pressure.
Under this type, we have 6 variants depending upon the water quantity & DSH Kv. The nozzle designed is such that the before the water is actually injected, it is rotated around the control plug. The design of plug & the nozzle body is such that it creates a maximum velocity at the point of injection of water. The high velocity at the point of injection guarantees the fine mist which provides fast evaporation of cooling water.
The control characteristics of the nozzle compensates for any load variation in external spray control valve by changing orifice section of nozzle, assuring the optimum aromatisation of water.