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Control systems Desuperheaters
Desuperheater selection chart
Turndown 1:1
2:1
3:1
4:1
5:1
7:1
10:1
20:1
50:1
Approach to saturation T sat +9 °F (+5 °C)
Spray type desuperheater (STD) Spray nozzle type desuperheater (SND) 'Cost effective option for turndown duties' Minimum water pressure: Steam +8 psi (+0.6 bar)
T sat +12 °F(+7 °C)
T sat +9 °F (+5 °C) Max. W.P: Steam
Max. W.P: Steam + 180 psi (+12.4 bar)
Max. W.P: Steam +65 psi (+4.5 bar)
+115psi (+7.9 bar)
Vertical installations only T sat + 12 °F (+7 °C) Max. W.P:
Venturi type desuperheater (VND) 'Our most popular desuperheater, ideal for most duties' Minimum water pressure: Steam +1.5 psi (+0.1 bar)
T sat + 5 °F (+3 °C) Max. W.P: Steam +15 psi (+1 bar)
T sat + 5 °F (+3 °C) Max. W.P: Steam +35 psi (+2.4 bar)
T sat +9 °F (+5 °C) Max. W.P:
Steam + 70 psi (+4.8 bar)
Steam +145 psi (+10 bar)
4.8 14
Steam atomizing type desuperheater (SAD) 'Special desuperheater for high turndown duties' Required water pressure: Same as steam pressure
Atomizing steam required at 1.5 x Desuperheater inlet steam pressure or 45 psi (3.1 bar g) minimum
T sat + 5 °F (+3 °C)
T sat + 5 °F (+3 °C)
SAD (with recycle)
Other considerations Desuperheater orientation
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 advizes 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 atomizing steam connection on a SAD (steam atomizing 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 atomizing 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.
TI-P475-06 CTLS Issue 4
Page 4 of 12
Desuperheater Online Program Sizing Guidance
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