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Control systems Desuperheaters
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. 5. Cooling water pressure. 2. Turndown. 6. Auxiliary higher pressure steam available for atomising. 3. Accuracy of final temperature. 7. Cost. 4. Available pressure drop. 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
5:1
7:1
10:1 20:1 50:1
Approach to saturation
Spray type desuperheater (STD) Spray nozzle type desuperheater (SND)
T sat +5 °C (+41 °F)
T sat +5 °C (+41 °F)
T sat +7 °C (+44.6 °F)
'Cost effective option for turndown duties' Minimum water pressure: Steam +0.6 bar (8 psi)
Max. W.P:
Max. W.P:
Max. W.P: Steam +4.5 bar (+65 psi)
4.8 6
Steam
Steam +12.5 bar (+180 psi)
+8 bar (+115 psi)
Vertical installations only
Venturi type desuperheater (VTD)
T sat +3 °C (+5 °F
T sat +5 °C (+41 °F)
T sat +7 °C (+44.6 °F)
T sat +3 °C (+5 °F
'Our most popular desuperheater, ideal for most duties'
Max. W.P: Steam +0.9 bar (+15 psi)
Max. W.P: Steam +2.5 bar (+35 psi)
Max. W.P:
Max. W.P:
Minimum water pressure: Steam +0.1 bar (+1.5 psi)
Steam +4.9 bar
Steam +10 bar (+145 psi)
(+70 psi)
Steam atomising type desuperheater (SAD)
SAD (with recycle)
T sat +3 °C (+37.4 °F)
T sat +3 °C (+37.4 °F)
Atomising steam required at 1.5 x Desuperheater inlet steam pressure or 3 bar g (45 psi) minimum
'Special desuperheater for high turndown duties' Required water pressure: Same as steam pressure
Note: For VTD’s, turndowns above 7:1 must not be offered until design checks have been made by Spirax Sarco.
TI-P475-01 TES Issue 5
Page 6 of 9
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