POWER August 2012 - 61

ENVIRONMENTAL
Table 2. Plant improvement and potential increase in plant efficiency.
Source: Reducing CO2 Emissions by Improving the Efficiency of the Existing Coal-fired Power
Plant Fleet, NETL, 2008.
Plant improvements
Air heater surface increase
Coal drying
Combustion control improvement
Condenser optimization
Feedwater heater improvement
Reduction of slag and furnace fouling
Sootblower optimization
Steam leak reduction
gy Company and Detroit Edison Company)-
this one involving Detroit Edison's Monroe
Station-led to still more requirements for
power plant operators. That utility made efficiency
improvements to a steam turbine, but
because it was a non-routine modification, it
had to prove for five years after the changes
were made that actual emissions from the
combustion turbine did not increase above
PSD thresholds.
The result is that if efficiency improvements
enable a unit to be run more often,
PSD may be tripped. On the one hand, this
discourages many efficiency improvement
projects that could help reduce overall emissions.
On the other hand, it encourages the
seemingly perverse decision to maximize
emissions as much as possible in the years
before an efficiency improvement project.
By doing so, the operator improves the likelihood
that its future emissions will be no
worse after the efficiency improvements than
they were before.
The bottom line is that since practically
nothing is considered by the EPA to be " routine
maintenance, " almost any change at
a plant is potentially subject to PSD. This
makes operators justifiably wary of making
efficiency improvements. Environmental
groups benefit from the confusion because
the vague definition of " routine " and accompanying
standards provides them with a
substantial stick to wield against a utility. So
although the EPA's GHG rules view efficiency
improvements as BACT for compliance,
the longstanding record of often ambiguous
and sometimes hostile precedent works
counter to those goals.
Efficiency Improvement Gains
Table 2 lists some common improvement
projects along with typical efficiency gains.
For the hot gas path, increased sootblowing
or online furnace cleaning to minimize slag
formation will work toward this goal. Reducing
slag and furnace fouling also can be
62
Potential plant efficiency increase
2.10%
0.1% to 1.7%
0.15% to 0.84%
0.7% to 2.4%
0.2% to 2.0%
0.4%
0.10% to 0.65%
1.1%
achieved by magnesium hydroxide injection.
Maximum reductions in slagging and fouling
can increase plant performance by 0.4%.
A regenerative air heater with better seals
or new baskets will reduce air leakage and increase
heat transfer, resulting in better combustion
performance. Removal of excessive
ash buildup in the air heater also will increase
heat transfer while reducing the pressure
loss and saving on auxiliary power (Figure
2). The increase in effective surface area of
the air heater can lead to plant efficiency improvements
up to 2.1%.
Increased heat transfer efficiency for
steam condensers, feedwater heaters, cooling
towers, and closed cooling water systems
all support increased plant efficiency. Optimizing
an existing condenser can increase
plant efficiency from 0.7% to 2.4% while improvements
to the feedwater heating system
can add an additional 0.2% to 2.0% to plant
efficiency. Ensuring that rotating equipment
is operating at its best efficiency point and
that material-handling systems are optimized
help to reduce auxiliary plant loading. Energy
losses through electrical equipment such
as transformers also should be evaluated to
minimize plant losses.
Reducing the amount of steam and energy
lost through boiler tube leakage is another
critical plant improvement. Replacing
defective tubes can increase overall plant
performance by 1.1%. Analyzing combustion
performance and upgrading control systems
to better measure and control fuel also
will result in increased plant performance.
Increases in plant performance of between
0.15% and 0.84% can be experienced by
this upgrade. Additionally, better combustion
controls can have the added benefit of reducing
the formation of nitrogen oxides and carbon
monoxide.
In case a more stringent plant maintenance
program is unacceptable as BACT, additional
measures may be taken to ensure a minimum
heat rate is achieved. These may include the
www.powermag.com
addition of heat transfer area in the economizer
section, additional sootblowers to reduce
slag formations, or fuel switching to
a lower-moisture-content fuel, resulting in
better boiler efficiency. The addition of sootblowers
or optimized sootblowing techniques
has the potential to add another 0.1% to
0.65% to plant efficiency. If possible, waste
heat from various sources could be utilized
to " dry " a fuel source to achieve better combustion
performance. Such fuel drying has
the potential to add another 0.1% to 1.7% to
plant efficiency.
In all these cases, however, maximum efficiency
and best heat rate is typically achieved
at full-load operation. During startup and
shutdown, provisions will be needed to exceed
accepted plant efficiency. Upset conditions
that require the plant to operate at partial
load also will be problematic for achieving
maximum plant efficiency. It is quite undesirable
and inefficient for large coal plants to be
required to shut down due to heat rates not
being met at part-load operation.
Under Pressure
Already under a substantial amount of
pressure from the EPA's recently finalized
Mercury and Air Toxics Standard and the
litigated Cross-State Air Pollution Rule,
coal power has increasingly been the subject
of much environmental scrutiny. With
another round of proposed environmental
regulations designed to implement CCS and
limit the release of CO2
, the likelihood of a
new coal power plant being constructed in
the U.S. would appear to be minimal. The
GHG Tailoring Rule remains active and
ambiguous as to what BACT will be for
greenhouse gases. Combined, these regulations
leave coal-fired generation in a much
less attractive position than natural gas combined
cycle plants. ■
-Brandon Bell, PE (brandon.bell@kbr
.com) is a principal mechanical engineer
with KBR Power and Industrial, Chicago.
POWER | August 2012
2. Plugged solid. Excessive ash buildup in a
regenerative air heater can severely reduce the
boiler combustion efficiency. Courtesy: KBR
http://www.powermag.com

POWER August 2012

Table of Contents for the Digital Edition of POWER August 2012

Contents
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