POWER March 2014 - 12

and tear on auxiliary equipment used during
cycling, and corrosion caused by oxygen
entering the system and condensation
from cooling steam. " Those consequences
of cycling can take several years to show
up as damage or forced outages.
Several physical modifications were
made to the boilers, pulverizers, turbines,
rotors, and condensers at the plant, but
once the physical changes were in place,
" 90% of future savings in costs came
from adjustments to operating procedures, "
the report reveals. For example,
establishing procedures and training to
control boiler ramp rates has been especially
effective, as have been high-energy
piping inspections.
The report echoes several conclusions
reached by a number of prominent analytical
entities, and it likewise suggests
that if modified to be more flexible, older
coal units can still serve a purpose in an
increasingly low-carbon energy system.
Most coal power plants are " capable of
some dynamic operation and are designed
to be able to cycle with moderate ramp rates
and potentially even handle two-shift operation
(where the plant is started up and shut
down daily), " observes the International Energy
Agency's Coal Industry Advisory Board
(CIAB) in a 2013 report titled " 21st Century
Coal: Advanced Technology and Global Energy
Solution. " However, the increased need
for flexibility " will impact costs, maintenance,
and reliability, " the CIAB also concludes.
" Most
notably, higher cycling will increase
wear and tear while the number of
operating hours decreases, resulting in an
increase of specific maintenance costs/
MW-hr over time. Moreover, as coal power
plants add more complex environmental
control systems such as [carbon capture
and storage] in the future, their ability to
operate dynamically may be reduced, " the
CIAB says.
Yet, as illustrated by some countries
with a high share of intermittent renewables,
if a portfolio of strategies involving
both technical and operational improvements
is implemented, the flexibility
of current and future coal plants can be
achieved, the CIAB suggests.
One prominent example is Germany,
which is moving to produce 80% of its
power with renewables by 2050. A tenfold
increase in wind and solar photovoltaic capacity
in Germany since 2000 has resulted
in a second " feed in " load fluctuation in
addition to the traditional consumer demand
fluctuation.
Meanwhile, in a much-cited paradox for
the country that is promoting a massive
shift to renewables with billions of euros
in subsidies, Germany's production of
coal-fired power rose in 2013 to its highest
level since 1990 as natural gas prices
soared. Last November, Steag opened its
2. Hard but flexible coal. The 750-MW Lünen hard coal-fired power plant owned by Trianel
Kohlkraftwerk Lünen came online in December 2013 in northwest Germany and is predicted
to run 7,000 full-load operating hours in 2014. Siemens Energy and IHI Corp., which built the turnkey
plant, say it has an efficiency of almost 46%. The plant's Siemens SST5-6000 steam turbine
is designed to enable highly responsive ramping, which is crucial to meeting load adjustments
posed by intermittent renewable generation. Courtesy: Siemens Energy
725-MW Walsum-10 unit near the western
city of Dortmund, and Trianel started
commercial operation of a 750-MW Lünen
plant (Figure 2) in North Rhine-Westphalia
in December. Meanwhile, eight hard coal
power plants are scheduled to begin operation
in the next two years, including
Vattenfall's 1.5-GW Moorburg plant near
Hamburg and RWE's Hamm facility in the
Dortmund area.
According to the CIAB, Germany's existing
power plants are optimized " to
cater to flexible operation, " even if they
were built before expansion targets for
wind and photovoltaic plants had been
adopted. " In many plants, measures to
allow greater flexibility have been implemented
subsequently, so that power
plants can meet increased requirements
for market load adjustments. As a result,
there are very few baseload plants that
do not allow for flexible operation, it
notes. At the same time, new coal-fired
power plants are specifically designed
for flexible operation. " Pure baseload
power plants are no longer being built. "
The CIAB notes, however, that Germany
also suffers higher electricity prices
than most developed countries. That
means the impact of increased costs due
to the fluctuating operation of conventional
power plants is " somewhat less
significant, " it says.
MHI, Southern Co.
Complete Demonstration
Phase of CCS Test
Mitsubishi Heavy Industries Ltd. (MHI) and
Southern Co. have completed the initial
demonstration phase of a carbon capture
and storage (CCS) test at the Plant Barry
power station in Mobile, Ala.
The companies built a 25-MW carbon
capture demonstration plant, consisting
of a flue gas scrubber, flue gas carbon dioxide
(CO2
) capture/regeneration system,
CO2 compression machinery, and electrical
components, adjacent to the seven-unit
James M. Barry Plant owned by Southern
subsidiary Alabama Power (Figure 3).
Notably, the facility employs the KM CDR
Process, which uses a proprietary KS-1
high-performance solvent for CO2
absorption
and desorption that was jointly developed
by MHI and Japanese utility Kansai
Electric Power Co. and is said to use less
energy than comparable systems.
Testing of the facility's carbon capture
capabilities, which the developers say is a
" globally unprecedented " 500 metric tons
per day (mtpd), began in June 2011. Inte12
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POWER March 2014

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