Reference Manual

7−8
Figure 7-9. The TBX utilizes an external
spraywater manifold with multiple nozzles for
moderate to large volume applications.
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Steam conditioning valve designs can vary
considerably, as do the applications they are
required to handle. Each has particular
characteristics or options that yield efficient
operation over a wide range of conditions and
customer specified requirements.
The TBX steam-conditioning valve (figure 7-9)
combines pressure and temperature control in a
single valve. Finite element analysis (FEA) and
computational fluid dynamic (CFD) tools were
used in its development to optimize the valve’s
operating performance and overall reliability. The
rugged design of the TBX proves capable of
handling full mainstream pressure drops, while its
flow-up configuration, in conjunction with Whisper
Trim technology, prevents the generation of
excessive noise and vibration.
The simplified trim configuration used in the TBX
accommodates rapid changes in temperature as
experienced during a turbine trip. The cage is
casehardened for maximum life and is allowed to
expand during thermally induced excursions. The
valve plug is continuously guided and utilizes
cobalt-based overlays both as guide bands and to
provide tight, metal-to-metal shutoff against the
seat.
Figure 7-10. Detail of AF Spray Nozzle.
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The TBX incorporates a spraywater manifold
downstream of its pressure reduction stage. The
manifold features variable geometry, backpressure
activated AF nozzles that maximize mixing and
quick vaporization of the spraywater.
The AF nozzle (figure 7-10) was developed
originally for condenser dump systems in which
the downstream steam pressure can fall below the
saturation level. In these instances, the
spraywater may flash and significantly change the
flow characteristic and capacity of the associated
nozzle at a critical point in the operation.
Spring loading of the valve plug within the AF
nozzle prevents any such changes by forcing the
plug to close when flashing occurs. With flashing,
the compressibility of the fluid changes, and the
nozzle spring will force closure and
re-pressurization of the fluid leg. Once this is
done, the fluid will regain its liquid properties and
reestablish flow to the condenser.
The TBX injects the spray water towards the
center of the pipeline and away from the pipe wall.
The number of injection points varies by
application. With high differentials in steam
pressure, the outlet size of the valve increases
drastically to accommodate the larger specific
volumes. Correspondingly, an increased number
of nozzles are arranged around the circumference
of the outlet making for a more even and complete
distribution of the spray water (figure 7-11).
The simplified trim arrangement in the TBX
permits extending its use to higher pressure
classes (through ANSI Class 2500) and operating
temperatures. Its balanced plug configuration