POWER September 2010 - 38

TOP PLANTS
ponents: two SGT5-4000F gas turbines, two
SST5-5000 steam turbines, two hydrogencooled
generators, and the entire electrical
and SPPA-T3000 instrumentation and control
equipment.
The facility also uses once-through Benson-type
boilers. The advantages of this type
of boiler are many: its design minimizes limitations
due to thermal stresses, it facilitates
very high cycling, it reduces start-up time;
and it is proven technology for coal-fired
power plants, and recently was adapted for
use with combine-cycle gas turbines.
Natural gas burned in the gas turbine results
in very low NOx
and CO2
emissions,
and the exhaust gas is then passed through a
boiler. In the boiler, the heat of the exhaust
gas causes steam to be produced. This steam
is then led through a steam turbine. Together,
the gas and steam turbines drive the
generator. This very effective use of residual
heat from the gas turbine's exhaust makes
Sloe Centrale a highly efficient combinedcycle
plant.
Steam from the steam turbine exhaust is
cooled by seawater in the condenser. Finally,
the electricity is transmitted through an underground
transmission cable to a distribution
plant.
The plant uses natural gas transported
and supplied by Gasunie Transport Service
and Fluxys, which is based in Belgium.
These companies obtain their natural gas
from diverse sources: the Netherlands, Norway,
the United Kingdom, Russia, and the
1. All lined up. This interior view of the Sloe
Centrale combined-cycle plant shows the gas
turbine, generator, and steam turbine arranged
on a single shaft. Courtesy: Siemens Energy
Siemens' fast-cycling concept allows a fully
automated start-up and shutdown.
liquefied natural gas-producing countries
(primarily Qatar).
During construction, the plant provided
work for an estimated 700 workers. Since
the plant was put into operation, approximately
40 people keep it running. Siemens'
fast-cycling concept allows a fully automated
start-up and shutdown, which reduces the
time and operator workload required during
these evolutions.
The construction and maintenance contract
totaled €550 million. Siemens Netherlands
was contracted for maintenance of the
facility.
Providing Balance to Fluctuating
Renewables
The design team had three key design drivers
for the facility: flexibility, reliability, and
efficiency. For example, one of important
purposes of this plant is to provide electricity
during periods when renewable sources such
as solar and wind power produce intermittent
amounts of electricity due to changing
weather conditions.
" Renewable and discontinuous power
generation technologies such as wind and
solar power are increasingly penetrating the
European electric power market, " Balling
said. " Renewable resources certainly are
leading the way to reduced CO2
emissions
in Europe; however, on the other hand, their
limited availability and predictability pose a
considerable challenge to grid stability. "
Periods of low generation from renewable
sources due to weather conditions (low
winds, overcast skies, and day/night cycles)
have to be covered by other types of power
generation such as fossil-fired power plants,
explained Balling. As a result, the requirements
related to operational flexibility and
rapid load response of the existing and newbuilt
fossil fleet, as formulated in grid codes
and customer specifications, are constantly
increasing. These grid code and customer
specification changes drive modern power
plant design to place a strong focus on operational
flexibility and grid support operation.
Fast Cycling: The Need for Speed
In recent years, the demand for quicker startups
at CCPPs soon followed the demand for
more frequent start-ups, Balling explained.
This market demand finally resulted in the
launch of a development project by Siemens
that combined all the initial engineering ideas
38
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into a single integrated plant concept called
FACY (derived from FAst CYcling). The aim
of the subsequently initiated research and development
program was to design a plant for
an increased number of starts and to reduce
start-up times. If possible, no limits were to
be placed on the gas turbine by other power
plant components, such as the heat-recovery
steam generator or steam turbine, during hot
and warm starts.
During the course of the project, potential
areas came to light in which further optimization
could be achieved, although these had
to wait for a second development generation
to be implemented. The major improvement
offered by this second generation involved
the start-up procedure, according to Balling.
" Hold points, " which are stages at which
plant personnel had to wait until certain
steam parameters had been reached before
the start-up process could begin, were eliminated
as part of the shortened " start on the
fly " start-up procedure. With second-generation
FACY plants, the steam turbine is started
up in parallel with the gas turbine using the
first steam that becomes available after a hot
start. Whereas the first-generation FACY
plants reduced start-up times for a hot start
from 100 to 55 minutes, second-generation
FACY plants succeeded in pushing start-up
times down below the 40-minute mark for an
output of 850 MW.
" The Sloe Centrale plant was one of the
first plants in commercial operation that incorporated
the advantages of both the first and
second generations of the FACY concept, "
Balling said. " During its acceptance tests
that achieved more than 59% net efficiency,
the Sloe Centrale plant recorded impressive
30-minute start-up times. Equally good results
have been exhibited by other reference plants.
This means that the expectations placed on
the second generation of FACY have been far
surpassed in a number of cases. "
Winning Combination
The Sloe Centrale Power Plant promises to
provide an abundant, reliable source of electricity
with low emissions to the citizens of
Zeeland Province well into the future.
" The new power plant impressively shows
how security of supply, cost-effectiveness,
and environmental compatibility can be harmonized, "
Balling said. ■
-Angela Neville, JD, is POWER's
senior editor.
POWER | September 2010
http://www.powermag.com
POWER September 2010

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