POWER October 2011 - 24

8. Bank of condensers. This group of
air-cooled condensers is used to condense
the organic turbine exhaust vapor from a
series of small geothermal power systems.
APR was used to track down the location of
several tube leaks in only two days. Source:
AcousticEye
9. Clean pipes first. The presence of
a leak was considered highly irregular given
that the condenser bank was only three
years old. To facilitate inspection, some of
the condenser tubes were removed, revealing
large amounts of corrosion and debris.
Source: AcousticEye
Geothermal Plant Case Study
The multiple condensers in a geothermal
plant were recently inspected by APR
techniques. There are multiple condensers
because multiple, small, standard-size
geothermal modules are used. At this
plant, multiple condensers are grouped
into banks or " units, " each condenser having
284 finned tubes of about 18 meters in
length. The units are placed in long rows,
several feet above ground (Figure 8).
A leak of organic gas was found in one
mated by observing the highest threshold
crossed by the corresponding peak in the
signal.
For example, 20 APR measurements are
shown in Figure 6. Clearly, most of the signals
fluctuate close to the horizontal axis,
though some of them exhibit large peaks,
which probably represent faults. Adding
positive and negative noise thresholds
(the red line) helps distinguish random
fluctuations from faults.
Finally, observing one of the measurements
along with the blockage thresholds
(Figure 7) shows there is a blockage at
15.3 meters, blocking about 23% of the
cross section.
of the condensers. In this case the leak
was large enough that the pressure differential
caused the leaking gas to freeze
into visible clumps at the bottom of the
condenser. Further analysis revealed a loss
of approximately 70 kilograms of gas per
day. The failed unit was shut down and
the faulty condenser bank was taken out
of service. The unit was put back online a
day later, excluding the faulty condenser
(Figure 9).
Metallurgical analysis confirmed what
was visually apparent: The leaks were
caused by advanced corrosion. Such corrosion
does not normally occur in these
tubes because, in operation, they are
filled with a noncorrosive organic fluid.
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POWER October 2011

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