Reference Manual

7−7
Figure 7-7. The DSA desuperheater utilizes two external control valves: a spraywater unit and an atomizing steam valve.
DSA DESUPERHEATER
C0817 / IL
Figure 7-8. TBX-T Cooler
W8786-1
comes to actual performance comparisons. Since
a desuperheater is not a final control element its
performance is linked directly to its system
environment; thus, the actual turndown is more a
function of system parameters rather than based
on the equipment’s empirical flow variations. Once
this is understood, it is obvious that even a good
desuperheater cannot overcome the limitations of
a poorly designed system. They must be
evaluated on their own merits and weighed
accordingly.
A final design parameter for all insertion type
desuperheaters is its ability to withstand high
levels of thermal cycling. Due to the nature of
operation of today’s plants, desuperheaters should
be designed with the intent to operate under daily
cycling environments. Exposure to frequent daily
cycling can lead to thermal fatigue and
desuperheater failure if the unit is not designed for
the operation. Design upgrades for this application
consist of thermal liners to reduce thermal loads
and structural optimization to reduce induced
vibration at stress sensitive welds.
To summarize the requirements to correctly size a
desuperheater, the following system and operating
information is required:
D Minimum and Maximum Steam Flow
D Steam Pressure and Temperatures
D Cooling Water Pressure and Temperature
D Required System Turndown Ratio
D Pipe Size and System Layout
D Planned Mode of Operating
Steam Conditioning Valves
Steam conditioning valves represent
state-of-the-art control of steam pressure and
temperature by integrally combining both functions
within one control element unit. These valves
address the need for better control of steam
conditions brought on by increased energy costs
and more rigorous plant operation. Steam
conditioning valves also provide better
temperature control, improved noise abatement,
and require fewer piping and installation
restrictions than the equivalent desuperheater and
pressure reduction station.