POWER August 2010 - 18

expander provides more uniform expansion
and superior contact of the sleeve outside
diameter with the ID of the parent tube.
Additionally, the sleeves were strengthwelded
to the parent tubes at the face of
the outlet tubesheet.
Grimes adds that with projects that utilize
the advanced tube testing and sleeving
technologies, there are benefits that
are somewhat immeasurable. " In most
cases, sleeving can be performed with the
heater isolated while the unit remains online,
which allows the utility to continue
to generate electricity. "
Grimes notes that APS recommended installing
the sleeves because plugging such
a large percentage of tubes would have
led to reduced thermal performance and
increased feedwater velocity in the inlet
of the unplugged tubes. Additionally, the
plant may have had to cut a bypass orifice
in the pass partition plate in order to
prevent higher tube inlet velocities that
would have led to further heat transfer
degradation.
" I would say that, using this technology,
our customers can realize savings of
over 80% of the cost of a new heat exchanger
if they elect to install sleeves
rather than replace their problem heat exchangers, "
says Grimes. After the sleeving
project at Tanner's Creek unit was finished,
Jay King was surprised to see that heater
performance was substantially maintained
(Figure 4).
" We would have expected to see a
slight performance decay, since you
have the sleeves in place in the desuperheating
zone, because it's now a
heavier-walled tube, " he says. " But that
4. Weld the tube ends. The hydraulic
expander provides more uniform expansion
and superior contact of the sleeve outside diameter
with the inside diameter of the parent
tube. Additionally, the sleeves were welded
to the parent tubes at the face of the outlet
tubesheet for added strength. Courtesy:
American Power Services
didn't happen. We maintained the same
performance levels. The TTD [terminal
temperature difference] and the saturation
temperature of the heater (based
on the pressure) versus the feedwater
outlet, have not decayed at all. " Quite
possibly that resulted from the selective,
limited use of sleeving.
" The thing I liked best about going
this route is that we didn't have to abandon
the heaters, " adds King. " That would
have presented us with a very difficult
situation on how we would start and shut
down the unit without some serious pipe
modifications and major changes in operating
procedures. These heaters are used
during start-up and are equipped with
alternate drains that drain back to the
condenser that must be utilized during
start-up. The piping modifications would
have meant a large added O&M expense
and time lost for engineering to assess
needed operational changes. The installation
of the sleeves allowed us to maintain
efficiency and return the unit to
service maintaining a design basis. "
-Contributed by American Power Services.
Local Warming:
Helsingin Energia Uses
CHP to Heat a City
Power plant operators, especially those
located in countries with enforceable carbon
emissions standards, are concerned
about their CO2
emissions. But for Helsingin
Energia-which provides power,
heating, and cooling for Helsinki, Finland's
300,000 residents-the main concern
is local warming, not global warming.
In Helsinki, temperatures on midsummer
afternoons only reach an average 21C, and
for half the year daytime temperatures are
below 10C.
Unlike other parts of the world, where
the norm is to site huge power plants
away from population centers, Finland
has adopted the strategy of maximizing
plant energy efficiency by placing electric
generators near cities and capturing the
excess energy to provide building heat.
" Helsinki is quite cold, and in the wintertime
we need to warm up the houses, "
says Taneli Lampinen, an engineer for
Helsingin Energia. " Since 1952, Helsinki
has been using combined heat and power.
It is now all over the city, with 92% of the
heating being done by district heating. "
But although combined heat and
power (CHP) is extremely efficient in
the winter, when there is a demand for
the waste heat, summers are a different
story. To boost its year-round efficiency,
Helsingin Energia has installed
18
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dual mode equipment at its Vuosaari
Power Plant: In the winter, steam is
used to heat homes and buildings, but
in the summer that heat is used to drive
a steam turbine generator. To boost
efficiency even further, the company
generates and stores heat overnight in
the form of hot water, making it readily
available for use during peak morning
hours and making the turbines available
for generating electricity during the
day, when demand is higher.
" This combined power and heat
production is the cornerstone of our
operations, providing efficiency and
environmental benefits as well as economic
ones, " says Lampinen. " Our overall
annual efficiency, depending on the
weather and the price of electricity, averages
80%, but in 2009 it was close
to 90%. "
This efficiency led the European Parliament
in November 2008 to award Helsingin
Energia with a European Regional Champion
Award in the Energy Champion category,
stating that " Helsingin Energia possesses
unique capabilities and know-how, which
make it the world leader in cogeneration
and energy efficiency. "
A Long Tradition of Power Production
The first local power plant was built in
1884, and by 1900 there were 30 separate
producers providing electricity, mainly for
lighting. In 1907, the city built its own
steam plant, and two years later all the
independent producers were merged into
the city utility. In 1957, with the opening
of the coal-fired Salmisaari A plant,
it also began offering district heating for
buildings in the city.
Several other plants were added over
the years, the most recent being the Vuosaari
Plant, which began operations in
1991. Unlike the earlier facilities, Vuosaari
was designed to run on natural gas from
Russia. With this addition, the majority of
the city's power now comes from natural
gas, and more than 90% of the buildings
receive district heat. " It is also possible to
run oil as a reserve fuel, " says Lampinen,
" But we have a 10-year deal for the gas,
so its prices don't change as often as oil
or coal prices. "
The Vuosaari plant is based on two
combined-cycle units. Vuosaari A has
two Siemens V64.3 gas turbines (now
called SGT-1000F). Those units are ISO
rated at 53 MW each, but in Helsinki's
cold winters, that rises to 63 MW each.
The 500C flue gas boils water to drive a
40-MW single-cylinder backpressure extraction
turbine from MAN-GHH coupled
POWER | August 2010
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POWER August 2010

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