Boiler Performance Improvement Due to Intelligent Sootblowing

Technical Paper
Boiler Performance Improvement Due to Intelligent
Sootblowing Utilizing Real-Time Boiler Modeling on
UP® Boilers
S. J. Piboontum, S. M. S wift, and R. S. Conrad
The Babcock & Wilcox Company
Barberton, Ohio, U.S.A.
Presented to:
Electric Power 2005
April 5-7, 2005
Chicago, IL, U.S.A
BR-1766
Boiler Performance Improvement Due to Intelligent
Sootblowing Utilizing Real-Time Boiler Modeling on
UP® Boilers
S. J. Piboontum
The Babcock & Wilcox Company
Barberton, Ohio, U.S.A.
S. M. Swift
The Babcock & Wilcox Company
Barberton, Ohio, U.S.A.
R. S. Conrad
The Babcock & Wilcox Company
Barberton, Ohio, U.S.A.
BR-1766
Presented to
Electric Power 2005
April 5 - 7, 2005
Chicago, Illinois, U.S.A.
Abstract
To achieve optimum boiler operation and performance it is necessary to control the cleanliness and limit the fouling and slagging of
the heat transfer surfaces. Historically, the heating surfaces were
cleaned by air-blowing, steam-blowing, or water-blowing
sootblowers on a scheduled time-based interval. With the advent of
fuel switching strategies such as changing from bituminous to Powder River Basin (PRB) subbituminous coals to reduce emissions,
the control of heating surface cleanliness has become more problematic for many steam generator owners. A scheduled cleaning
approach does not easily address changes in operation. Also, as
power plant operators push to achieve greater efficiency and performance from their boilers, the ability to more effectively optimize cleaning cycles has become increasingly important.
Sootblowing only when and where it is required to maintain unit
performance can reduce unnecessary blowing, save on blowing
medium utilization, and reduce tube erosion and wear.
The Babcock & Wilcox Company’s (B&W’s) core technology
for boiler design is based on modeling of boiler heating surfaces to
establish heating surface requirements and performance. The modeling process also must consider fuel types and the combustion
requirements. This same technology is used to model the expected
performance of existing units. By establishing the boiler model it is
possible to accurately determine when and where heating surfaces
are experiencing diminished performance due to ash buildup and
fouling.
The ability to model the heating surface and determine real-time
cleanliness indexes is important in developing a system that can
more accurately initiate the cleaning cycle of the boiler heating surfaces. The performance of the individual convection pass banks is
interrelated; consequently, determining the best sootblowing program must not only rely on the cleanliness of the specific bank to
initiate or trigger blowing. By coupling the real-time cleanliness
index data with the measured operating parameters of the boiler it is
possible to establish strategies to drive sootblower operation.
Presented in this paper is the approach taken by B&W in developing the Powerclean™ system, a sootblowing optimization system. Also presented are the performance improvements made with
the Powerclean system at two utilities in the United States (U.S.) –
one utility located in the southern states and AEP Rockport Unit 2.
It should be noted that these units are supercritical, B&W Universal Pressure® (UP) boilers which are operated differently from
subcritical natural circulation drum boilers. UP boilers often behave and are controlled differently when they slag and foul; thus,
the control of slagging and fouling is often more difficult and complicated.
Power generation from coal
More than 50% of the power generated in the U.S. is from coalfired power plants. Coal will continue to be a dominant fuel source
for fossil-fuel steam generation into the foreseeable future. Pressure to reduce the emissions of sulfur dioxide (SO2), nitrogen oxides (NOx), mercury (Hg) and carbon dioxide (CO2) make it imperative for owners to seek cost effective strategies to meet the
regulations. One option being used by an increasing number of
utilities is low sulfur western fuels such as PRB coals, which produce less SO2 emissions and reduce the need to install high cost wet
or dry scrubbers. However, this western fuel also contains greater
amounts of moisture with less heating value on a per pound asreceived basis. Western fuels can also have lower ash softening
temperatures. The result of the fuel switching is greater ash loading, with greater fouling and slagging of the boiler surfaces. This
places a premium on effective use of sootblowers to control the
buildup of ash deposits. The addition of sootblowers or improved
blower designs may be part of the strategy when switching to a
western fuel; however, improved use of the blowers by better
determination of where and when to clean heating surfaces is also
important. Historically, a program of monitoring the unit is implemented to develop a set of “best practices” for use of the blowers
based on load, fuel source, etc. Currently, improved control systems are available to allow “intelligent” cleaning of heating surfaces.
B&W boiler modeling technology and
intelligent sootblowing
B&W has been modeling boilers and the combustion process for
many decades. A common misconception about B&W’s technology is that it only applies to B&W designed boilers. In fact, B&W
has modeled and improved on the designs of many other boiler
manufacturers.
B&W’s technology is based on the principles of heat transfer,
fluid flow and combustion. Much of what makes B&W’s modeling
technology effective has been the application of this technology to
operating units in which actual measured field data were used to
empirically update the modeling for accurate prediction of performance. Commercial PC-based versions of the B&W performance
modeling programs have been deployed on operating units since
the early 1980s. The first systems were offered to allow plant
engineers and operators to track the real time performance of the
unit.
Even in those early days, plant engineers used the performance
and cleanliness data provided by the systems to optimize the
sootblowing process. These users found that an accurate firstprinciples model of the boiler provided repeatable cleanliness factors that they could use to make changes to better optimize
sootblowing. One of the drawbacks of these early systems was
that they were advisory, such that a plant engineer needed to use
the data to track and manually alter the sootblowing schedules.
Today, B&W’s commercial version of the boiler modeling system is
the Heat Transfer Manager™ (HTM) performance program.
Heat Transfer Manager™ performance modeling
The Heat Transfer Manager (HTM) program is the core of the
Powerclean sootblower optimization system. The HTM program
is applicable to boilers manufactured by B&W as well as other
manufacturers. The HTM program is based on heat transfer analysis methods that B&W has developed over many years of designing
and upgrading boilers. The heat transfer analysis begins with combustion and efficiency calculations that HTM calculates in accordance with ASME Performance Test Code 4 procedures. Input
data are obtained from the plant historian, DCS or data acquisition
system.
In a typical installation for a reheat utility boiler, the HTM
model consists of the following components: furnace, economizer,
primary superheater, furnace platens, secondary superheater, and
reheater. Fuel input is calculated from measured boiler output and
efficiency. Flue gas weight is calculated stoichiometrically from
fuel input and excess air which is determined from measured oxygen in the flue gas.
HTM includes a detailed computer model in which the furnace
as well as the convection surfaces are configured. The furnace
portion of the model divides the furnace into volumes whereby the
location and input of burners and changes in furnace shape, such as
2
the furnace arch, are described. The furnace model calculates the
expected furnace exit gas temperature (FEGT) for comparison to
the FEGT value determined analytically.
The convection portion of the boiler model consists of tube
banks, flue gas cavities between the tube banks, and the steam/
water cooled enclosure surface surrounding the banks and cavities.
Tube banks are modeled in detail and include parameters such as
tube diameter, tube side and back spacing, heating surface, gas free
flow area, steam/water flow per tube, etc. Starting at the air heater
gas inlet (economizer gas outlet), the gas temperature entering each
component is calculated by heat balance based on calculated gas
weight and measured absorption of each boiler component. For
units with parallel gas paths for reheat steam temperature control,
it is also possible to calculate gas splits between the reheater and
superheater gas paths, provided the gas temperature leaving each
path is measured.
Utilizing the measured steam/water temperature entering and
leaving each component and the calculated gas temperatures, the
actual as well as expected overall heat transfer coefficient is determined for each boiler component. The relative measure of the
actual versus expected heat transfer coefficient provides the cleanliness index that is critical to intelligent sootblowing decisions.
Since the HTM program is based on the technology used by B&W
for boiler design and performance evaluation, there is extensive
empirical data and validation of the accuracy of the program for
predicting heat absorption within tube banks. This is true for
boilers originally supplied by B&W as well as units designed by
other manufacturers.
In configuring the boiler model, B&W reviews the complete
Input/Output (I/O) list of plant data available from the data acquisition system (DAS), DCS or historian to select the points needed
for HTM analysis and for use in setting sootblowing strategy. In
general, all the critical data used by the HTM model are part of the
normal measured operating data for the boiler controls. Once the
boiler model is established, the system is installed at the site and
interfaced with both the sootblower controls and the plant DAS,
DCS or historian. The HTM model provides the critical boiler
performance and heating surface data that is used by the Powerclean
module when setting up strategies that guide sootblowing. HTM
model results are displayed on the Powerclean graphical interface
in a boiler sideview for a comprehensive view of cleanliness by
boiler region (Figure 1).
Fuel analysis
HTM requires an analysis for the typical fuel being used. It is
commonly thought that a different fuel analysis is required for all
variations of fuel used in a boiler. However, when using a reliable
first-principles model such as HTM, different fuel analyses are
only required when major changes are made to the fuel source. As
an example, one representative fuel analysis is needed for firing
many different coals of the same rank such as bituminous coal from
more than one source. However, significant changes in coal from
one rank to another, such as the use of a subbituminous coal
instead of bituminous, will require that a different fuel analyses be
used to ensure accurate performance modeling results. Since B&W
uses the modeling behind Heat Transfer Manager for boiler design,
the company has extensive data on coal types and their impact on
boiler performance. When determining the coal analyses for use in
HTM, all coals used by the plant are considered. The program can
The Babcock & Wilcox Company
Fig. 1 HTM boiler sideview.
be configured so that a different fuel analysis is substituted when a
significant fuel switch (e.g. change of coal rank) is made.
Furnace exit gas temperatures
As noted above, the HTM program calculates upper furnace
exit gas temperatures for use by the Powerclean system in optimizing sootblowing. This is an important feature of the B&W system
since it eliminates the need for installing field instrumentation for
this purpose. Upper furnace temperature measuring devices such
as optical pyrometers or acoustic pyrometers can be costly to
install and difficult to maintain in reliable operation. Field installed
devices are also dependant on the installation location and field of
view such that determining an expected temperature for making
cleaning decisions is best done by a period of operation and learning in the specific unit. By contrast, HTM calculates a thermodynamic average FEGT in a specific plane of the boiler which is
consistent with FEGT values used by B&W for design. This allows use of an FEGT value that can be compared to an expected
value based on historical empirical data. Not only does this calculated FEGT provide important information to aid in optimizing
performance but it also allows calculation of a furnace cleanliness
factor that is used to help determine when best to clean the furnace
walls.
The Powerclean intelligent sootblowing system has been installed on boilers with instrumentation for measuring furnace gas
temperatures. Figure 2 shows a comparison of the platen inlet gas
temperature (PIGT) and FEGT as determined by HTM versus the
upper furnace temperature as measured by two optical furnace
The Babcock & Wilcox Company
pyrometers. The furnace pyrometers were installed on the east
and west sides of the boiler in the upper furnace. Note that the
temperatures behave similarly in response to actual furnace conditions. The values are not in exact agreement since the HTM values
are thermodynamic average temperatures in a specific plane of the
boiler while the pyrometers detect the average peak temperature
based on their physical location with a heavier weighting toward
the near field in its field of view.
The Powerclean™ sootblowing optimization
program
Because boiler heating surface performance may not be the only
reason to clean or not clean an area of the boiler, B&W combines the
performance diagnostic capabilities of HTM with an expert system to capture and implement strategies for cleaning the unit. The
Powerclean™ sootblowing optimization system is the name given
to this combination of expert rules module with the HTM software.
When developing the Powerclean system, B&W realized that
other parameters, in addition to how dirty tube surfaces have become, must be considered when deciding to clean a given region of
the boiler. As an example, a plant may want to set a lower limit on
cleanliness (i.e., let the surface get dirtier) for the secondary superheater (SSH) outlet sections if the unit is operating below a threshold for reheat outlet temperature. This may be necessary as increased absorption in the SSH would further reduce attainable reheat temperature.
In general, the goal in creating Powerclean was to give the sys-
3
HTM Furnace Gas Temperatures vs Measured Furnace Gas Temperatures
HTM PIGT
HTM FEGT
Measured FEGT West
Measured FEGT East
2750
2700
2650
Temperature (F)
2600
2550
2500
2450
2400
2350
Time
Fig. 2 HTM furnace gas temperatures versus measured furnace gas temperatures.
tem enough flexibility such that the observations of the plant engineer, operator or a B&W service engineer could be incorporated
into cleaning strategies as needed. With the rule-based expert system designed to capture and implement unit-specific knowledge
about sootblowing, the Powerclean approach provides the engineer
or operator with significant flexibility to set different strategies for
cleaning the unit under different conditions. For instance, separate
strategies can be developed for multiple operating load ranges. The
Powerclean system also serves as a useful tool to evolve cleaning
strategies and practices over time. The user can update and modify
the expert system as needed when changes occur. One example is a
significant change in fuel source.
Powerclean system experience on a Universal Pressure boiler
In this paper, two applications of Powerclean on a Universal
Pressure (UP) boiler are presented. The first application involves
the installation of the Powerclean intelligent sootblowing system
on a B&W supercritical, UP boiler that was originally designed
with a maximum continuous rating (MCR) steam capacity of
5,525,000 lbs/hr at 3,850 psi, 1010F at the superheater (SH) outlet.
Reheat (RH) capacity is 4,793,000 lbs/hr steam flow at 652 psi
reheater outlet pressure and 1005F. The unit was designed to
produce MCR steam flow and generate approximately 775MWe
while burning 100% western lignite fuel.
The convection pass heating surfaces are arranged with three
vertical platen superheater banks followed by the pendant secondary superheater (SSH) banks and pendant reheat superheater banks
4
in the upper horizontal pass (Figure 3). The economizer is located
in the vertical down pass of the unit. Steam temperature from the
superheater and reheater is controlled by spray attemperation. To
control slagging and fouling of the furnace and convection pass tube
surfaces, the unit employs Diamond Power IR wall blowers and IK
retractable sootblowers. The blowing medium is air which is supplied by dedicated compressors. The furnace waterwalls have 43
wall blowers. The convection pass surfaces are cleaned by 32
retractable air sootblowers covering the superheater platens, pendant SH and pendant RH. Eight blowers are in the vertical down
pass to clean the economizer horizontal tube banks.
Operating history
For most of its life the unit has burned 100% western lignite
fuel. In recent years a blend of lignite and subbituminous coal has
been fired. The preference is to burn as much subbituminous coal
as possible without hurting the operation of the unit. Heavy slagging
and fouling can occur with resulting pluggage if cleaning is not
closely monitored and controlled.
In general, the unit has had an excellent operating history with
good availability. Normal preventive maintenance has been performed over the years to address component wear and deterioration as required including the burners, pulverizers and sootblowers.
With the current setup, the sootblowing system has a finite capacity which limits the number and combination of sootblowers that
can be run at one time. This requires good coordination and management of the sootblowers to ensure that the system pressure
does not drop to the point of tripping the compressors.
The Babcock & Wilcox Company
Fig. 3 Universal Pressure boiler.
Powerclean was installed on this unit to manage the sootblowing
process with the goal of improving unit operation while firing a
blend of lignite and subbituminous coal.
Powerclean system installation and operation
Powerclean was installed with a communications link to the
Honeywell PHD historian that interfaces with the DCS. Closed
loop control for furnace and convection pass cleaning was implemented through a communications link from the Powerclean PC to
the Diamond Power BOS® for Windows® system PLC.
Once communications were established and the I/O points were
The Babcock & Wilcox Company
imported into Powerclean, the system was configured for the components, regions and blower sequences specific to this unit. As is
typical of Powerclean installations, the initial configuration of
Powerclean utilized B&W’s experience on similar unit types and
fuels. During the configuration of regions, the initial blowing strategies were also developed.
The Powerclean system design includes remote access such that
B&W engineers can monitor, collect data, and modify the system
from their offices during initial startup and commissioning. During
this period, plant data was evaluated to determine where surfaces
were dirtiest, the rate of degradation of heat transfer, and the effec-
5
Fig. 4 Powerclean™ results screen.
tiveness of specific blower sequences.
Based on initial testing and setup, furnace sootblowing was
divided into four different regions. The east wall required two
separate regions for the upper and lower furnace. This breakdown
of the east wall was the result of observation and feedback from
plant operations that the east wall of the furnace tended to slag
more rapidly requiring more cleaning than the rest of the furnace
walls. Blowers for the north, south and west walls of the unit were
split between the other two furnace regions. This illustrates the
use of experience and operating knowledge in implementing a cleaning strategy that targets specific areas where greater cleaning is
needed while reducing blower cycles in areas that do not slag as
heavily.
Similarly, the secondary superheater pendants were originally
divided into the inlet and outlet banks. They were reconfigured to
three regions – SSH inlet lower, SSH outlet lower and SSH upper.
Since most of the slagging on these banks occurs on the lower
portion of the inlet and outlet pendants, the sequences were modified to allow more blowing on the lower sections to achieve optimal
cleaning in that region and reduce sootblower erosion on the upper
areas of the SSH pendants.
Results
The Powerclean system has had a very positive impact on the
operation and maintenance of the unit. Powerclean continues to
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monitor unit operation, operate in closed loop, and initiate
sootblowing sequences in the furnace and convection pass.
Operational improvements
Operations personnel have found the system to be very helpful
since it manages the task of scheduling sootblowing so that the
operators do not have to focus on this activity. In the past, operations personnel had to manually initiate sequences from the
sootblowing control system. Blowing areas of the boiler at the
appropriate times has also reduced boiler exit gas temperature concerns, which often resulted in overblowing already clean areas.
Although results and the impact of the system will vary from unit
to unit, the data from this plant have shown improvements in both
reduced sootblower usage and improved unit heat rate.
Data was available from the Powerclean historian which had
been collecting raw plant data since the communications link was
established. Results reflect initial closed loop control in August
through the end of December, 2004. Full load unit operational data
were used, providing relevant analysis for determination of maximum benefits achieved from the Powerclean system.
The unit experienced an improvement in net unit heat rate with
Powerclean in closed loop operation. Based on data from Heat
Transfer Manager and the plant’s net unit heat rate calculation,
progressive gains have been made. Increased cleanliness in the
furnace and the convection pass (Figure 5) improved heat absorption and allowed for more generating capacity with the same amount
The Babcock & Wilcox Company
Unit Cleanliness Values
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
Avg Aug
Avg Sep
Avg Oct
Avg Nov
Avg Dec
Furn CF
0.617066423
0.669491775
0.697019292
0.699484186
0.78263597
PSH CF
0.755037775
0.784412424
0.794458307
0.796641141
0.8317416
Econ CF
0.880659173
0.859193364
0.86692551
0.893692957
0.864293847
RH CF
0.718104539
0.815865848
0.821156326
0.860018035
0.844048661
SSH In CF
0.662848609
0.723698586
0.723897274
0.740415168
0.727664841
SSH Out CF
0.81410336
0.898544737
0.893089871
0.915783018
0.934219999
Fig. 5 Unit cleanliness from August through December.
of heat input.
From August through December, there was approximately a
110 Btu/kWh reduction in heat rate as indicated in the plant heat
rate calculation. This translates into almost a 0.9% improvement
to the unit. During this time generation increased an average of 21
MW or 2.5% in output.
Furnace exit gas temperature
Furnace exit gas temperatures progressively declined from initial closed loop operation to an optimal unit cleanliness range in
December. FEGT dropped 62F from August to December, indicating that Powerclean was effective in lowering the FEGT values by
keeping the furnace walls much cleaner for improved heat absorption.
There is a significant correlation between improvements in unit
heat rate and back end temperature reductions. From a combustion
standpoint, this is often achieved by reducing O2 (i.e., excess air).
In this case, the unit’s heat rate improved in spite of an increase in
excess air and gas weight from August to December.
Economizer exit gas temperature
Economizer exit gas temperature decreased from 751F in August to 746F in December. This reduction was a result of increased
furnace and the convection pass cleanliness. Powerclean’s Heat
Transfer Manager provides cleanliness values for the furnace, primary superheater, reheater, economizer, and the secondary super-
The Babcock & Wilcox Company
heat inlet and outlet pendants. These calculations indicated that
the unit realized a general trend of improved cleanliness from August through December with the exception of the economizer. (Figure 5.) The economizer had previously run with a high cleanliness
and the cleanliness values remained high and stable.
Overall unit improvements
The most significant results from Powerclean sootblowing optimization were improvements made to the furnace waterwalls, the
reheater, and the secondary superheater outlet pendants. Cleanliness values for these three regions improved with no negative impact on RH spray flow and temperatures. The RH temperatures
were maintained due to a cleaner RH surface. Furnace absorption
improved resulting in a lower FEGT. The RH temperature set
point of 1000F was maintained and spray flow was reduced. The
reduction in spray flow contributed to the improved unit heat rate.
From August to December, the combination of lowered RH
spray and reduced economizer outlet gas temperature had a positive impact on unit efficiency and heat rate.
Sootblowing frequencies
With the improvements in the furnace, the conditions entering
the convection pass changed slightly since the furnace exit gas
temperature has been reduced since installing the Powerclean system. Most of the regions of the convection pass are blowing less
frequently while the cleanliness factors for each component remain
similar or improved (Figure 5).
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Daily Sootblowing Frequency
120.0
July 2004
Aug 2004-Jan 2005
% Change
Average Number of Blows Per Day
110.0
IK
85.2
78.5
-7.9%
IR
95.9
99.2
+3.5%
100.0
90.0
80.0
70.0
60.0
50.0
Jul-04
Aug-04
Sep-04
IK
IR
Oct-04
Linear (IR)
Nov-04
Dec-04
Jan-05
Linear (IK)
Fig. 6 Daily sootblowing average frequency.
Sootblowing frequency data was available from the plant
sootblowing control system from July 2004 to January 2005. Data
from the month of July is indicative of sootblowing frequency
prior to Powerclean. August through January data exhibited some
reduction in IK blower usage and a slight increase in the blowing
frequency of the IR blowers. (Figure 6.) Specifically, the IK blowers used in the back pass experienced a 7.9% reduction in sootblowing
frequency. The improved management of the furnace has been a
large contributor to the reduction in convection pass blowing.
Overall, the unit is cleaner which has improved heating surface
absorption and reduced the cost of operation.
Conclusion
The use of the Powerclean intelligent sootblowing system has
been successful in providing better control of heating surface cleanliness and improving overall unit performance. It has also proven
to be a valuable tool for plant personnel.
Powerclean™ system experience: American Electric Power – Rockport Unit 2
American Electric Power Rockport Unit 2 is a 1350 MW, universal pressure coal-fired boiler supplied by The Babcock & Wilcox
Company. Unit 2 is a forced draft, opposed-wall fired unit equipped
with fourteen (14) B&W-89 Roll Wheel™ Pulverizers. The unit is
designed for MCR main steam flow of 9,775,000 lb/hr at 3846 psig
8
and 1010F. Reheat steam flow is 7,956,000 lb/hr at 635 psig and
1000F. The unit fires an 85/15 blend of PRB and Eastern Bituminous coal to achieve maximum load, and 100% PRB during the
nonpeak season.
The convection pass heating surfaces are arranged with furnace
wingwalls, followed by the pendant secondary superheater (SSH)
banks and pendant reheat superheater outlet bank in the upper
horizontal pass. The vertical pass consists of the horizontal primary superheater (PSH) followed by the horizontal reheater bank
and the economizer. Superheater and reheater steam temperature
are controlled by spray attemperation (Figure 7).
The furnace is equipped with four Diamond Power HydroJet®
systems in the lower furnace and 29 waterlances in the upper
furnace. The horizontal backpass includes 30 IK blowers to clean
the SSH and RH sections with an additional 32 IK blowers in the
vertical convection pass to clean the PSH, RH and economizer
sections. Powerclean controls the convection pass retractable steam
sootblowers to prevent fouling and slagging. Also, the system
monitors furnace operation and provides a comparison of actual
furnace performance to design expected performance throughout
the load range. This provides feedback on the overall furnace cleaning operations to assess whether it is being overcleaned or
undercleaned.
The Babcock & Wilcox Company
Fig. 7 American Electric Power – Rockport Unit 2.
Rockport 2 – operating history
Historically, Rockport Unit 2 experienced issues with slagging
of the SSH outlet pendants. The unit burns a low sulphur western
coal from the Powder River Basin. This unit was intended to run
base loaded and continuously at around 1300MW. As a result,
slagging increased considerably above 1000MW.
The slag buildup generally occurs within the first 15 pendants
from each sidewall with all other pendants remaining relatively
clean. Slagging on the left side of the SSH is heavy with bridging of
the pendants, while slagging on the right side of the pendants is
moderate with no bridging. Combustion tuning with backend O2
grids has been performed to maintain O2 balance across the unit and
reduce the amount of slagging from side to side.
There have been instances of tube leaks resulting from slag falls
that have pinched lower slope tubes, in turn causing an overheat
condition. Slag falls have also directly ruptured lower slope tubing
and damaged support structures and casings.
The Babcock & Wilcox Company
Rockport 2 – Powerclean installation and operation
American Electric Power upgraded the core sootblowing controls while installing the Powerclean sootblowing optimization
system. Applied Synergistics, Inc. (ASI), a subsidiary of Diamond
Power International, Inc., was contracted to provide this upgrade.
The system supplied by Diamond-ASI for HydroJet and sootblower
control is the Boiler Cleaning Management System (BCMS). Since
both the ASI sootblowing control system and the Powerclean optimization system required a personal computer interface, both systems were installed on the same Windows based workstation. By
installing the Powerclean system with the sootblowing controls on
the same workstation, integration problems were minimized and
space was conserved in the control room. The entire system required no additional real estate as it replaced the previous
sootblowing control system.
The Powerclean system was delivered and installed during Fall
2003, concurrently with the plant’s upgrade to Diamond Power’s
HydroJet system. The system was interfaced, via an OPC connection, to the plant PI system for the data necessary to drive the
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Fig. 8 Powerclean results screen.
boiler and combustion modeling. Powerclean was running in advisory mode while the HydroJets and BCMS were placed into operation. After the fundamental HydroJet and BCMS startup control was complete, Powerclean was placed into closed loop operation.
Sensitivity testing for initial setup
As part of the implementation process, each sootblower was
run and its cleanliness factor response was evaluated to determine
its effectiveness. The sootblowers were also run in various sequences to test their response and interaction. Knowing the effectiveness and location of each blower, the unit was divided into unit
specific regions. Some of the regions represented entire boiler
components like the primary superheater. Other regions represented portions of components or particularly effective blower
groupings. The regions configured for Rockport Unit 2 are displayed in the Powerclean Sootblowing and Performance Results
overview. (Figure 8.)
During testing, Rockport plant operations and engineering personnel were consulted to document past cleaning practices. This
experience is valuable and is an important part of formulating
sootblowing strategies that are implemented in the Powerclean system. The objective is to integrate past best practices, prevent bad
practices, and optimize blowing and unit performance.
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Driving cleaning strategies with performance
The Heat Transfer Manager program provided information critical to the evaluation and control of furnace cleanliness. The HTM
calculation of FEGT and furnace cleanliness factor were important
considerations in evaluating overall sootblowing. Convection pass
cleanliness factors, their rate of change and the sootblowing equipment cleaning effectiveness depend in large part on the cleanliness
of the furnace. Since HTM compares actual furnace operation to
expected furnace operation, it provided key information for setting
up the operation of the furnace watercleaning operations. HTM
provides an important measure - from a boiler performance perspective – of when the furnace is being undercleaned and overcleaned.
The HTM boiler sideview (Figure 9) displays temperatures and
cleanliness factors in their respective boiler locations, along with
other critical boiler performance statistics. As a quick reference
during data evaluation, a data trend for a temperature or cleanliness
factor can be selected and displayed.
Results
The Powerclean system has had a positive impact on the operation of American Electric Power Rockport Unit 2. Sootblowing
strategies have been developed based on reliable technical data and
analysis, and Powerclean allowed the strategies to be implemented
The Babcock & Wilcox Company
Fig. 9 Powerclean display – boiler sideview.
in a consistent manner. Plant personnel have found that Powerclean
allows them to study and evaluate the effectiveness of sootblowing.
To assess the impact of the system on Unit 2, data were collected from the Powerclean historian for analysis. Baseline data,
which represent how the unit was operating prior to the implementation of Powerclean, were retrieved for the time period of March
8, 2004 to March 18, 2004. Data from November 12, 2004 to
November 29, 2004 were chosen to represent unit operation after
the Powerclean system was operating in closed loop. For consistent and meaningful analysis, data at or above 1300MW were used.
Reheater cleanliness and temperature control
Powerclean boiler cleanliness evaluations and sootblowing patterns resulted in significant reheater cleanliness and temperature
control. Reheat (RH) sprays were running higher at 299 klb/hr
during the March operation of the unit as opposed to the November time period of 284 klb/hr when the Powerclean system was
fully installed and running in closed loop. This was a reduction of
19 klb/hr in the average spray flow which contributes to a lower
heat rate.
The RH temperature set point for Rockport Unit 2 at full load
operation is 1000F. As Rockport experienced, side-to-side temperature imbalances in the reheat section of the convection pass can
be address by targeted cleaning of specific areas of the pendant
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tube banks. (Figure 10.) In this case, the B side RH outlet temperature shows a steady balance from before to after Powerclean installation with an average temperature of 1003F. RH outlet temperature on the A side of the unit shows that it was running much lower
with an average temperature of 997F. The A side of the RH pendants may have been insufficiently cleaned, resulting in a lower
outlet temperature. With Powerclean’s targeted cleaning, the system was able to sufficiently maintain a more uniformly clean RH
section, allowing for better heat absorption into the A side. In turn,
this helped to raise RH outlet temperature from a side-to-side
average of 1000F to 1002.5F. A RH temperature gain will also
contribute to improved unit heat rate.
Unit heat rate
The improvement in overall unit efficiency was consistent with
the improvement anticipated by lowering the RH sprays and raising the RH outlet temperature by almost 3F. As shown in Figure
11, a heat rate improvement of around 0.26% was achievable from
March to November. Heat rate declined from 9113 Btu/kWh in
March to 9089 Btu/kWh in November. A lower unit heat rate
contributes to lower fuel consumption for the same output, and in
the long term, reduces unit operating costs.
Sootblowing steam consumption and blowing
frequencies
A Powerclean implementation often results in reduced
11
Reheat Superheat Outlet Temperature
1020
1015
1010
Deg F
1005
1000
995
990
Baseline Data 3/8 to 3/18 @ 997F RH Tmp A
@ 1003F RH Tmp B
RH Temperature Side to Side Avg is 1000F
985
Test Data 11/12 to 11/19 @ 1002F RH Tmp A
@ 1003F RH Tmp B
RH Temperature Side to Side Avg is 1002.5F
980
0
2000
4000
6000
8000
10000
12000
14000
16000
Time
RH Tmp A
RH Tmp B
Fig. 10 Reheater outlet temperature.
Heat Rate
9400
Avg Heat Rate 3/11 - 3/18 @ 9113
9350
Avg Heat Rate 11/12 - 11/29 @ 9089
9300
Heatrate (btu/kwh)
9250
9200
9150
9100
9050
9000
8950
8900
0
1000
2000
Heat Rate Before
3000
Heat Rate After
4000
5000
Linear (Heat Rate Before)
6000
7000
8000
Linear (Heat Rate After)
Fig. 11 HTM heat rate.
12
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AEP Rockport Unit 2
Daily Sootblowing Frequency for IK Blowers
375.0
Before
After
% Change
341.4
321.2
-5.9%
Average Number of Blows Per Day
350.0
325.0
300.0
275.0
250.0
Jun, '04 Oct, '04
Jul, '04 Nov, '04
Aug, '04 Dec, '04
Before Powerclean Installation
Sep, '04 Jan, '05
After Powerclean Installation
Fig. 12 Daily sootblowing frequencies for June 2004 to January 2005.
sootblowing frequency, correcting for previous overcleaning where
it was not required. While the unit operating conditions have remained similar, and the flue gas conditions entering the convection
pass have not changed, there is a considerable improvement in how
the convection pass is now being cleaned. Most of the regions in
the back pass have maintained or improved cleanliness factors, but
the blowing frequency of the IK blowers has been reduced substantially (Figure 12). From June to September, leading up to the
installation of the Powerclean system, there was an average of 341
individual sootblower cycles per day. From October to January
2005, after Powerclean was in closed loop control of the convection pass, the required number of sootblowers in operation dropped
almost 6% to an average of 321 individual sootblower cycles per
day.
The reduced amount of blowing translates into steam savings.
On average (Table 1), the amount of sootblowing cycles was reduced by 20 blows per day, translating to a steam consumption
savings of approximately 28,980 lb of steam per day. The estimate
is based on IK blowers running at 200 psig with a flow of 161 lb/
min through each blower, with an average cycle time of 9 minutes.
Rockport conclusions
Based on the results to date, the Powerclean system has proven
to be a valuable addition to Unit 2 at the AEP Rockport plant.
Using the system, it is possible to establish strategies that anticipate and react to the behavior of the unit. The overall cleanliness of
the convection pass has improved while sootblowing has decreased.
Experience to date has illustrated that cleaning in the right places at
the right frequency can improve operation of the boiler even while
reducing the overall use of sootblowing.
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Table 1
Rockport Unit 2 Sootblower Steam Savings
Assume
Flow
Cycles
Blows Per Day
Days
200
161
9
20
28,980
350
10,143,000
psig
lb/min
min per blowing cycle
reduced blowing amount
lbs steam/day
days/year
lbs steam/year
The Powerclean system with the HTM model continues to
provide critical data for unit performance and cleanliness. Rockport
Unit 2 is able to derive multiple benefits from the use of the
Powerclean system. It continuously evaluates furnace operation
and performance which contributes to the proper operation of the
furnace watercleaning equipment. Powerclean also optimizes the
convection pass blowing with improvements including reduced
sootblowing steam consumption, improvements in net unit heat
rate, the balancing of RH outlet temperatures on the A and the B
side, the increase in overall RH outlet temperature, and the reduction in RH spray flows. All of these improvements contribute to
the more efficient operation of Rockport Unit 2. In the longer
term, Powerclean will contribute to a reduced rate of tube erosion
in the convection pass, limit the number of forced outages, and
yield long term maintenance costs savings.
Acknowledgments
The authors would like to extend a special thanks to Denis
Hutchinson from American Electric Power for his help and
cooperation in providing information and feedback for this
technical paper.
13
Copyright© 2005 by The Babcock & Wilcox Company
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retrieval system, without the written permission of the copyright holder. Permission requests should be addressed to: Market Communications, The Babcock & Wilcox Company, P.O. Box 351, Barberton, Ohio, U.S.A. 44203-0351.
Powerclean™ and Heat Transfer Manager™ are trademarks of the Babcock & Wilcox Company. Diamond Power® and Selective
Pattern® are registered trademarks of Diamond Power International, Inc.
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14
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