Control valves

Desuperheaters

4.8.15

Desuperheater selection chart

Turndown

1:1

2:1

Spray type desuperheater (STD)

3:1

4:1

5:1

7:1

10:1

20:1

50:1

Spray nozzle type desuperheater (SND)

'Cost effective option for turndown duties'

Minimum water pressure: Steam +0.5 bar

Venturi type desuperheater (VTD)

Approach to

saturation

Tsat +5 °C

Tsat +5 °C

Tsat +7 °C

Max. W.P:

Max. W.P:

Steam +4.5 bar

Max. W.P:

Steam +8 bar

St +12.5 bar

Tsat +3 °C

'Our most popular desuperheater, ideal for most duties'

Minimum water pressure: Steam +0.1 bar

Tsat +3 °C

Max. W.P:

Steam +0.9 bar

Steam atomising type desuperheater (SAD)

'Special desuperheater for high turndown duties'

Required water pressure: Same as steam pressure

Other considerations

Desuperheater orientation

Vertical

installations

only

Tsat +5 °C Tsat +7 °C

Max. W.P:

Steam +2.5 bar

Max. W.P:

Max. W.P:

St +4.9 bar

St +10 bar

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

Desuperheaters may be installed either horizontally or vertically (with the steam flowing upwards). In a vertical installation, increased

turndown can be achieved; as the steam and water are countered by gravity, the water is less likely to fall out of suspension. Spirax

Sarco strongly advises against installations in which the steam flow is vertically downwards, as the opposite would occur.

In the case of a horizontal installation the cooling water connection (and the atomising steam connection on a SAD (steam atomising

desuperheater) should ideally point downwards, as this gives the best orientation for drainage of fluids in a shutdown situation. Other

orientations are acceptable for satisfactory operation, but drainage is not as effective.

In a vertical installation we recommend that, the cooling water pipework (and atomising steam pipework, if applicable) should be brought

to the desuperheater from below the corresponding connections on the desuperheater. This will provide the best layout for drainage of

fluids on shutdown.

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TI-P475-06 CH Issue 3