High pressure steam frequently passes through pressure reduction stations resulting in superheated steam at the point of use. Steam may also be superheated before reticulation.
In both cases it is economical to reduce the temperature of the superheated steam to close to saturation.
Spray type Desuperheater
This requires a cooling water pressure of usually 1500 kPa above the steam pressure. Maximum turndown ratios are 3:1
Steam Atomising Type Desuperheater
These units utilise high pressure steam to atomise the cooling water. This action also allows a very large turndown ratio of up to 30:1 – especially with recycling of excess spray water.
The atomising steam pressure must be approximately twice that of main stream pressure.