POWER October 2012 - 50

TOP PLANTS
a result of scale formation and consequent
overheating. The tubes would overheat when
scale came off the inner walls and accumulated
at the bends, disturbing fluid flow.
In order to address this problem, the tube
design for Units 3 and 4 was changed to incorporate
TP347 stainless steel, which has
better strength at high temperatures. In addition,
temperature monitoring was greatly
expanded. The original design had thermocouples
installed at only 46 points; the upgraded
design incorporated monitoring of all
1,157 boiler tubes. The additional monitoring
allowed overheating to be detected early and
addressed by unclogging the blocked areas
with steam blowing using the high-pressure
turbine bypass valve.
Unit 3 entered commercial operation in
2009 and has an 870-MW supercritical twopass,
once-through boiler. The net plant thermal
efficiency is 43.4%.
Major contributors to the project included:
■ KOPEC: architecture and engineering
■ Hyundai Construction, SK Construction, and
Samboo Construction: plant construction
■ Doosan Heavy Industries: boiler island
and air quality control equipment
■ Hitachi: steam turbine generator
■ Emerson Process Management: integrated
control and monitoring system, including
Ovation expert control system
Fuel Challenges
As originally designed, all of the Yeongheung
plant units were built to burn bituminous and
high-quality subbituminous coal with an optimum
calorific value of around 6,000 kcal/
kg. However, increased demand, especially
in Asia, has decreased the availability and
increased the costs of high-quality coal. As a
result, the plant has been forced to switch to
lower-quality subbituminous and brown coal
of around 5,400 kcal/kg.
Though fuel costs have been reduced, the
use of highly moist and low-calorific value
coal carries other problems with it. It increases
the volume of flue gases and thus increases
the load on the draft system. It also results
in more slagging, as well as increasing the
volume of sulfur- and nitrogen oxide (NOx)
emissions, which leads to increased costs for
emissions controls.
To ensure that the cost savings from the
cheaper coal were not offset by higher operating
costs, a task force was created to study
the changes necessary to handle the different
fuel. Among other adjustments, operators
at Unit 3 lowered the pulverizer outlet
temperature. In addition, in order to address
the increased volume of flue gases, the plant
increased the draft flow by 12% through alteration
of the fans.
50
Such advanced monitoring and controls, and
a commitment to efficient operation, enabled
Unit 3 to achieve an almost 100% capacity factor
in 2011, with zero forced outages. The plant
uses an integrated control room for all four units,
enabling operators to monitor conditions across
the entire facility (Figure 1).
Emissions Restrictions
Because of its close proximity to the capital,
Yeongheung Unit 3 is subject to strict environmental
restrictions. The plant employs selective
catalytic reduction (SCR) for NOx removal and
a wet electrostatic precipitator for particulate
control. A high-efficiency flue gas desulfurization
facility is used to remove sulfur oxides
(SOx). The plant was designed to emit very low
concentrations of pollutants: SOx-25 ppm,
NOx-15 ppm, and particulates-5 mg/Sm3.
In practice, it has exceeded expectations and
has been able to achieve levels of 22 ppm, 13.5
ppm, and 2.9 mg/Sm3 respectively.
The environmental controls are especially
important because the local municipality,
Incheon, is preparing to host the 2014 Asian
Games. The need to provide an attractive,
healthy environment for the games places a
higher standard on environmental controls.
The Yeongheung plant is upgrading its desulfurizing
and denitrifying equipment to cut
emissions even further, to 14 ppm, 12 ppm,
2.5 mg/Sm3 respectively.
The strict controls have necessitated some
creative operational adjustments, however.
The SCR suffered from heavy ammonium
bisulfate (ABS) buildup because of higher
volumes of ammonia being used, which led
to fouling of the air preheater. Normally, the
whole unit needs to be shut down to remove
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ABS buildup, but the cost and loss of generating
capacity led Unit 3 operators to experiment
with washing only one chain of the draft
system without shutting down the whole plant.
Though this proved to be very difficult, the results
were satisfactory, and the Yeongheung
plant is now planning to introduce the techniques
developed to enable washing under
normal operation in the future.
Unit 3 is a zero-liquid discharge facility.
Wastewater is treated in accordance with Korean
government regulations via catchment,
neutralization, cohesion, precipitation, filtering,
and absorption. Wastewater is reused as
feedwater for the desulfurizer, and wastewater
from the desulfurizer is reused again as
feedwater for treatment of fly ash. More than
5 billion tons of wastewater were reused in
2010, and almost $300,000 were saved by
not buying industrial water.
Poised for the Future
The addition of Yeongheung Units 3 and 4 to
the generation base has resulted in a substantial
decrease in transmission losses and increased
grid stability, which is critical to the
ever-growing South Korean economy. Unit
3 has demonstrated an impressive reliability
record over the past year.
The Yeongheung site is theoretically large
enough to incorporate 12 coal-fired plants
similar to Units 1-4. Units 5 and 6, currently
under construction, are scheduled for completion
by December 2014. This will allow
the plant to serve up to 30% of the capital
area's demand. Two more units, Units 7 and
8, are planned. ■
-Thomas W. Overton, JD is POWER's gas
technology editor.
POWER | October 2012
1. Bringing it all together. The Yeongheung facility uses an integrated control room to
monitor conditions and operation across all four generating units. Courtesy: Korea Southwest
Power Co.

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POWER October 2012

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