POWER March 2016 - 45

HEAT RECOVERY STEAM GENERATORS
1. Steam or water? This graph shows activity inside the secondary superheater (SH2)
drain pipe during a hot startup from 575 psig. The ultrasonic flowmeter equipment was monitoring
but not controlling during this test. Source: FLEXIM Americas
130
120
110
100
90
80
70
60
50
40
30
20
10
188
184
180
176
172
168
164
160
156
152
148
144
Water in SH2
Drain pipe
temperature
Water returns when
purge begins here
intermittently siphons
from SH2 to SH1 when
SH1 drain opens
SCNR ≈ 15 indicates
water in pipe
SCNR ≈ 5
indicates no
water in pipe
Water exits SH2 at GT
lightoff when SH2 drain
valve opens here
mounting procedure that greatly reduces installation
time and increases accuracy. The
biggest challenge would be the combination
of high-temperature and small-diameter,
thick-wall pipes. Flow knew they would need
to have a clear and accurate distinction between
the signal produced by water and that
produced by steam.
EPRI Testing
Concluding that an ultrasonic flowmeter had
good potential for detecting the transition
from water to steam, EPRI initiated a research
project to look into this new approach
to condensate monitoring.
" The object was to find some kind of sen07:26
07:33 07:40 07:48 07:55 08:02 08:09 08:16 08:24 08:31 08:38 08:45 08:52 09:00 09:07 09:14 09:21
Frank if ultrasonics could tell the difference
between steam and water inside the pipe. He
told me that through signal and sound speed
diagnostics it would be easy to identify the
differences between water and steam. I determined
to try it out at my first chance. "
But Anderson was also concerned about
the high temperatures of the steam pipes and
whether or not the meters could stand up
to them. Flow assured him that FLEXIM's
system could withstand a very broad range
of temperatures. He noted that the standard
meter is capable of accurate measurements
in conditions up to 400F, and if temperatures
are higher that that, the company's patented
WaveInjector mounting fixture (Figure 2)
greatly increases the meter's range.
The WaveInjector attaches to the pipe and
thermally separates the meter's transducers
from the pipe, enabling it to accurately
measure temperatures from -260F to 750F.
The company also recently developed a new
sor that could tell us whether there was water
or steam in the pipe, " said Anderson. " Their
funding allows them to sponsor or perform
research that otherwise wouldn't be done.
That's how this project is funded. "
After successful initial testing to prove
the concept, EPRI purchased a couple of
the ultrasonic meters for further analysis.
The management team at Oglethorpe Power
Corp.'s 1,250-MW Thomas A. Smith Energy
Facility near Dalton, Ga., agreed to use the
meters on one of their HRSG systems.
" We put one meter on each of two drains
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March 2016 | POWER
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45
Noise rate (dB)
Temperature (C)

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POWER March 2016

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