POWER November 2014 - 47

EMISSIONS
spray flow), and a dirty reheater, which
can cause plugging and excessive fan
horsepower. Managing this balance with
sequences and manual intervention at Hawthorn
proved to be problematic.
Platen Superheater Slagging. Platens
are the most prone to slagging, and platen
sootblowers are the most frequently blown
sootblowers. Slag rate is heavily influenced
by coal type and combustion parameters in
the furnace. Sequence controls are unable to
respond to these changes, leading to overblowing
during low-slag conditions and under-blowing
during high-slag conditions.
Over-Blowing at Low Load. Although
Hawthorn was designed as a baseload unit
and intended to cruise near full load, in
2012 there were more than 3,000 operating
hours between 350 MW and 550 MW. At
these reduced loads, sootblowing needs are
significantly lower than at full load, but the
sequence-based controls were programmed
for full load-resulting in significant overblowing
during these periods.
Carbon Emissions Reduction. Another
wrinkle was that in 2007, the Sierra Club
and KCP&L agreed on a set of initiatives
to offset the utility's carbon dioxide (CO2
)
and other emissions by adding wind power
and taking steps to conserve energy on a
large scale. KCP&L employed an engineering
consultant to conduct a study of the best
technologies to employ fleetwide to meet a
portion of its CO2
reduction goals via plant
efficiency improvements. The first tier of
proposed projects focused on improved performance
monitoring and manual optimization.
The second tier focused on advanced
optimization using closed-loop products,
such as combustion and sootblowing optimizers.
After completing the first tier,
KCP&L reviewed a fleetwide proposal for
combustion and optimized sootblowing.
Finding the Best Solution
Generally, operators want a sootblowing
optimizer to clean the boiler using minimal
blowing media and without damaging tubes
or cleaning certain sections too heavily relative
to others. They want to reduce the total
number of blowing operations while maintaining
other key process parameters.
Sootblowing is also only a piece of the optimization
process. It's important to consider
a comprehensive program that includes the
ability to optimize other processes such as
combustion. Taking a holistic approach ensures
that all of the subparts work together to
maximize the impact of each.
For KCP&L, the key process parameters
to optimize/minimize were:
■ Reheat and superheat steam temperature
November 2014 | POWER
variations and excursions
■ Reheat and superheat attemperation spray
flows
■ Flue gas exit temperature
■ Load derates
■ Auxiliary power usage
■ Unplanned outages
Looking to improve those parameters, increase
their process and boiler optimization at
Hawthorn Unit 5, and meet their CO2
emissions
goal, KCP&L chose the Siemens SPPAP3000
sootblowing optimization solution.
An important differentiator for the team
when choosing the SPPA-P3000 optimizer
was its adaptive technology. KCP&L wanted
a flexible platform that would support both
combustion and sootblowing optimization
and allow for future alterations. For sootblowing,
individual blower activation was
important. Sootblowing a group of sootblowers
in a given section was known to upset
boiler operation, and the team knew most
plants had little operational margin for upsets
when operating at full load.
The SPPA-P3000 offers a customized
solution that determines the need for sootblowing
based on dynamic plant operating
conditions, equipment availability, and plant
operational drivers. The system then generates
individual sootblower activation signals
for propagation to the existing sootblower
control system in a closed-loop manner at
optimal times. With sootblowing optimization,
new equipment and sensors are not required.
The SPPA-P3000 interfaces with an
existing control system, takes a current set of
plant parameters that are available, and works
with those. Unit-specific customizations can
be viewed and modified by the end user-
making it flexible, reliable, and extensible-
which results in sustained benefits.
The SPPA-P3000 is able to work alongside
a foreign distributed control system.
This technology allows plants to keep their
current control system while gaining the
benefits from the sootblowing optimizer
(Figure 2).
Putting Optimization to Work
With the new system in place, KCP&L and
Siemens engineers could attack individual
plant-specific problems by fine-tuning sootblowing
individually for each blower. To
achieve successful results, however, engineers
found a balanced approach was necessary.
The optimizer was configured to make
blowing decisions based primarily on EEGT.
The measured results of previous blowing
operations allowed the optimizer to automatically
select the best blower to improve
EEGT. Because of this, some areas were
blown more frequently.
www.powermag.com
There were also sensitive areas that
needed extra controls to prevent temperature
and spray flow excursions. The reheat
section, in particular, was configured to
prevent any consecutive or near-consecutive
blowing operations.
By the end of the initial tuning process,
it appeared that the sootblowing optimizer
was going to be a success. The next step was
to release to plant operations staff for continuous
operation. Despite a few hurdles,
operators generally embraced the optimizer
after it proved to reduce sootblowing-related
problems. Operators had the ability to enable
and disable the optimizer at any time,
but its in-service rate during the first year
was over 95%.
When the system was up and running, plant
operators helped identify an opportunity for
additional sootblowing optimization. During
soft market conditions, Hawthorn was operating
in evening hours at minimum load and
significant daytime hours at low load. Generally,
there are very few sootblowing needs at
low load and not much time spent there, so
it was Hawthorn's previous practice to suspend
automatic blowing and blow manually
only as needed. The optimizer was initially
set up to match this protocol. Operators saw
the opportunity for the optimizer to handle
this low-load blowing, and the optimizer was
easily updated with logic that allowed for
minimal blowing at low loads.
After commissioning, another configuration
change was related to process stability.
47
2. Easy implementation. The P3000
sootblowing optimization system can be
installed alongside an existing distributed
control system. Courtesy: Alistair Tutton Photography
http://www.powermag.com
POWER November 2014

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