Special Publication from Nuclear Europe Worldscan ... - Balcke-Dürr

Special Publication from Nuclear Europe Worldscan
No.9-1 0/1999 / Page 44 to 45
UPRATING BY INSTALLING
HIGH-PERFORMANCE TUBE BUNDLES
IN TURBINE CONDENSERS
Winfried Schulz and Jörg Stahlhut
ENGINEERING
Merger of Balcke-Dürr Energietechnik and Thermal Engineering International

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In 1998 the operator of the Gef111an 2 X
1350-MW nuclear power plant Gundremmingen
(BWR) was faced with the task of
refurbishing the four turbine surface condensers
ofpower generating units B and C
because ofthe erosion and corrosion damage
to the cooling tubes made ofbrass. The
condensers belonging to the boiling water
systems which have been in operation for
about 14 years are fitted with a total of approximately
4 X 43000 tubes and have a
heat exchange surface area of about 4 X
38300 m2.
Refurbishment concepts
There was a choice between three refurbishment
concepts which were subject of
a preliminary study:
(I) retubing on jobsite using the previous
tube material brass and previous tube field
geometry;
(II) retubing onjobsite using the new tube
material stainless steel and previous tube
field geometry;
(III) installing of tube bundle modules
completely prefabricated at works and
made of the new tube material stainless
steel with improved tube field geometry
according to Balcke- Dürr TEPEE-design.
Nuclear Eurape Warldscan 9-10/1999
The comparison of the results obtained
from the study and set out in the table below
shows that concept III involving the
installation of new prefabricated tube bundles
(variants 5 and 6) can be applied in
comparatively short reconstruction time
and also leads to an increase in the output
ofthe turboset, i.e. it is the most economic
and best technical solution.
Both variants which entail retubing on the
jobsite (concepts I and II) require significantly
longer outages for reconstruction.
A further disadvantage of concept I is that
the wet steam erosion resistance of the
cooling tubes is not adequately improved
by continuing to use brass as the tube material.
This improvement is achieved by concept
II through the use of stainless steel tubes
but at the cost of a reduced turboset output.
In view ofthe considerably lowerthermal
conductivity of stainless steel compared
to brass, the retention ofthe existing
tube field geometry means a reduction in
the heat transition coefficient and consequently
a rise in the condenser pressure as
well as a decrease in output. The tube field
geometry must therefore be changed in
order to avoid these undesirabte forfeits in
performance.
Cross-section through a condenser (four TEPEE tube bundles)
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TEPEE bundle modules
For the aforementioned reasons the decision
was taken to completely replace the
existing tube bundle with a modem TE-
PEE bundle1 as a modular construction.
This proven bundle design, whose thermohydraulically
optimized form is reminiscent
of an Indian tent (Tepee ), allows
the steam-side pressure drop in the condenser
to be kept to a minimum, the noncondensable
gases to be extracted specif -
ically and the undesirable condensate subcooling
to be virtually avoided.
An increase in the electrical turboset output
of more than 20 MW is achieved at
rated load point using the thin-walled (0.5
and 0.7 mm) cooling tubes made of stainless
steel (DIN Mat. No. 1.4439). For this
particular application, the high efficiency
and capacity of the TEPEE bundle even
permits the condensers to be provided
with a heat exchange surface around 9%
smaller than that required for the thermohydraulic
design in accord with the HEl
standard.
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Refurbishment concepts
Concept
Variant
II III
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