Control valves

Desuperheaters

4.8.7

Sizing and selection

There are a number of factors which must be considered in determining the best type of desuperheater for each application. Such

factors are:-

1. Residual superheat.

2. Turndown.

3. Accuracy of final temperature.

4. Available pressure drop.

5. Cooling water pressure.

6. Auxiliary higher pressure steam available for atomising.

7. Cost.

With so many factors, it is not an easy task to develop a decision tree to aid selection, but the charts below have been developed to

assist engineers in desuperheater selection.

Please read this first chart in conjunction with the note at the bottom of the page.

Desuperheater selection chart

Turndown

1:1

2:1

3:1

4:1

Tsat +5 °C

5:1

7:1

10:1

20:1

50:1

Approach

to

Spray nozzle type desuperheater (SND) saturation

Spray type desuperheater (STD)

'Cost effective option for turndown duties'

Minimum water pressure: Steam +0.5 bar

Venturi type desuperheater (VTD)

Max. W.P:

Steam +4.5 bar

Tsat +3°C

Max. W.P:

Steam +0.9 bar

Tsat +5 °C

Tsat +7 °C

Max. W.P:

Max. W.P:

Steam +8 bar

St +12.5 bar

Tsat +3°C

Max. W.P:

Steam +2.5 bar

'Our most popular desuperheater, ideal for most duties'

Minimum water pressure: Steam +0.1 bar

Tsat +5°C

Max. W.P:

St +4.9 bar

Vertical

installations

only

Tsat +7°C

Max. W.P:

St +10 bar

Steam atomising type desuperheater (SAD)

'Special desuperheater for high turndown duties'

Required water pressure: Same as steam pressure

Atomising steam required at 1.5 x

Desuperheater inlet steam pressure or 3 bar g minimum

Tsat +3 °C

SAD

(with recycle)

Tsat +3 °C

Note: For VTD’s, turndowns above 7:1 must not be offered until design checks have been made by Spirax Sarco.

Page 6 of 9

TI-P475-01 CH Issue 3

Direct Contact Desuperheaters