Control valves

Desuperheaters

4.8.21

Detailed example 2

Steam is required at 5 bar g (saturated) for use in a Shell & Tube Heat Exchanger. The Client has steam available at 5 bar g, 350 °C.

Minimum steam flow is 8 500 kg / h, maximum is 25 000 kg / h. Boiler feedwater at 20 °C is available as the cooling medium.

B

Steam supply

Desuperheater

2

3

Cooling water

Method

Non return

valve

Temperature

controller

Temperature regulating

control valve

4

As the turndown is approximately 3:1 we can select

any type of Desuperheater. There are 3 options:

SAD - Steam atomising desuperheater

This would require atomising steam at 7.5 bar g

(min).

VTD - Venturi type desuperheater

This could be selected, however, this desuperheater

is not part of a pressure reducing station,

consequently if we select a VTD venturi type

desuperheater, the discharge steam pressure will

be reduced by the pressure drop across the unit.

The steam could be desuperheated to Tsat+3 °C.

STD - Spray type desuperheater

The unit is capable of handling the turndown with

no steam-side pressure drop and can desuperheat

to Tsat+5 °C.

In this case the client states that Tsat+5 °C is

acceptable so we will select an STD.

The Spirax Sarco Online Spray Type Desuperheater

Sizing Program would be completed as shown

opposite:

This section

does not

need to be

completed

Page 10 of 12

TI-P475-06 CH Issue 3