Uprating Through Condenser Reconstruction - Balcke-Dürr ...

Uprating Through Condenser Reconstruction
Uprating Through Condenser Reconstruction
J. Scheurlen, R. Scharf and W. Schulz
Abstract
Uprating Through
Condenser Reconstruction
Due to necessary modifications to the feed
water chemistry at Stade nuclear power plant,
the turbine condensers fitted with brass tubes
have been converted to use austenitic cooling
water tubes. At the same time, a completely
new design of tube bundle and air
cooling system has been installed. A significant
improvement in heat transfer and considerably
more effective air extraction and also
increased net output by up to 4 MW have
been attained using the new condenser.
Kurzfassung
Authors
Leistungserhöhung durch
Kondensatorumbau
Durch die notwendige Änderung der Speisewasserchemie
im Kernkraftwerk Stade wurden
die mit Messingrohren ausgerüsteten
Turbinenkondensatoren auf austenitische
Kühlwasserrohre umgerüstet. Zugleich wurde
eine völlig neue Konstruktion der Rohrbündel
und des Luftkühlersystems eingesetzt. Mit
dem neuen Kondensator wird eine deutlich
bessere Wärmeübertragung und eine erheblich
wirkungsvollere Luftabsaugung sowie eine
um bis zu 4 MW gesteigerte Nettoleistung
erreicht.
Dipl.-Ing. J. Scheurlen
Dr.-Ing. R. Scharf
PreussenElektra AG
Hanover/Germany
Dipl.-Ing. W. Schulz
Balcke-Dürr AG
Ratingen/Germany
In 1987, the operator of the Stade nuclear
power plant (KKS) faced the task of adjusting
the feedwater chemistry to higher ammonia
(NH3) contents in order to create more favourable
conditions for steam generator operation.
This adjustment made it necessary to replace
all the cupriferous materials in the steam circuit
as it is a well-known fact that copper and
ammonia are not compatible. The most extensive
individual measure in connection with
this material change involved the turbine condensers
which have a total of 43,000 brass
tubes (total length 570 km) and yellow metal
tubesheets. Difficulties with ammonia corrosion
occurred even with the relatively low
NH3 contents of the previous mode of operation
and this led to repairs having to be carried
out. So-called air pockets, in which the
non-condensable gases including an increased
concentration of NH3 occurred, formed due to
the unfavourable design of the tube fields.
Various proposals were investigated as a preliminary
step to the required reconstruction
measures. The comparison in Ta b l e 1 shows
that the concept involving completely prefabricated
bundle modules (variant 6) could be
implemented within an extremely short period,
thus offering decisive cost advantages.
The reconstruction times required for all variants
involving retubing on the jobsite were
considerably longer than the time required for
manufacture in the workshop. Moreover, the
poorer conductivity of the copper-free tube
material would have meant a definite reduction
in the turbo generator output if the tube
layout remained unchanged. Operating experience
with turbo generators which have been
reconstructed in this way confirmed this [1].
It is possible to avoid such undesirable loss of
output when carrying out the reconstruction
on the jobsite using a more up-to-date tube
Table 1. Concepts for the reconstruction of the condenser in the KKS.
layout, but only at the expense of significantly
longer inspection times. The concept involving
condensers completely prefabricated in
the workshop (variant 5) also proved to be uneconomic.
Design
The thermodynamic design data were determined
after checking how the turbo generator
is used:
Cooling water inlet temperature 9.8 °C
Cooling water mass flow 4 x 7,425 kg/s
Heat flow to be discharged 1,214 MW
The external dimensions of the bundle modules
were to a great extent determined by the
existing condenser shell. A height limitation
due to the concrete crossbeam of the power
house made the situation more difficult.
The optimum was found to be a cooling surface
area of 37,820 m2 for the entire condenser
with a tube outer diameter of 22 mm, a
condenser pressure of 34.7 mbar thus being
guaranteed.
Titanium and stainless steel were considered
as tube material.
The advantages of titanium are:
− somewhat better thermal conductivity
− unsusceptibility to standstill corrosion
The advantages of stainless steel are:
− greater admissible spacing of the supporting
walls,
− lower price
As no corrosion had occurred on the stainless
steel tubes (material no 1.4439) used for re-
1 2 3 4 5 6
Measure Retubing and new tubesheets Prefabricated
condensers
(Condenser
modules)
Tube layout Unchanged Modernised
Manufacture Jobsite Workshop
Prefabricated
tube
internals
(Bundle
modules)
Outages x calendar days 2 x 81 1 x 97 2 x 100 1 x 122 2 x 50 1 x 39
Turboset output Decrease Increase
Cost factor 5.4 4.1 7.0 5.1 3.8 1
3