POWER March 2016 - 46

HEAT RECOVERY STEAM GENERATORS
2. Innovative mounting feature. The WaveInjector fixture holds the ultrasonic flowmeter's
transducers up to 4 inches off the pipe's surface, increasing the meter's operating
temperature range to -260F to 750F. Courtesy: FLEXIM Americas
3. Smaller does not mean easier.
Engineers got creative and used noise levels
to determine whether water or steam was
passing through the 2-inch drain pipe. Courtesy:
FLEXIM Americas
of the HRSG superheater so the meter could
identify the presence of water and initiate the
draining of condensate during a startup, " said
Anderson. " If the water is not drained quickly
enough, it finds its way into the tubes. The
water quenches the hot tubes, causing high
stresses at tube-to-header attachment welds,
especially tubes with bends, so it's critical to
make sure all of the water is drained. "
When tubes require repair, it can be very
expensive. Any cracked welds have to be redone,
and all repairs must pass quality conSEE
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trol inspections. It can take a huge amount of
time, and the HRSG system has to be down
during the whole procedure.
" Initially, one of the two meters was working
great, but the other did not work as well
as we wanted. We found that a portion of the
drain pipe was running slightly uphill to where
the meter was mounted, so it didn't fill with
water when the valve remained closed, " Anderson
said. " We moved the meter to a lower
part of the pipe, so when water formed in the
superheater, the meter could see the water in
the pipe and then open the drain valve. "
Size Matters
Another problem occurred on the 2-inch pipe.
The walls have to be thick enough to handle
the intense pressure, but with the small diameter
it was difficult for the meter to distinguish
between water and steam. However,
FLEXIM's engineering team developed a
rather novel solution.
Because the flow rate was not important
in detecting the presence of water, the engineers
came up with the idea of modifying the
meter's firmware to use the signal-to-correlated-noise
ratio in decibels (dB) to measure
the water versus steam signal difference with
better distinction. A low dB level indicated
an empty pipe, and a high dB level indicated
the presence of water (Figure 3).
" The new firmware makes liquid detection
the best way to bolt!
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46
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in 2-inch pipe possible, " said Anderson. " It
also provides a wider, more consistent range
between empty-pipe values and full-pipe
values in all size pipes. So we finally have
an economic solution for HRSG condensate
removal. " ■
-Jack Sine (jacksine@verizon.net) is
a freelance writer specializing in the
petrochemical, heating, ventilation, air
conditioning, and refrigeration industries.
POWER | March 2016
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POWER March 2016

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