POWER July 2013 - 49

PLANT DESIGN
Table 4. Case Study 3: Cyclone-fired boiler FDS upgrades benefits and
costs. The investment breakeven point was approximately 18 months. Source: The Fuel Delivery
Subcommittee of the ASME Research Committee on Energy, Environment, and Waste
Component
Cyclone modernization
Upgrade
Feeder/crusher island New feeders and
instrumentation
Cyclone upgrades
and new " split " air
damper
Boiler control system Update boiler control
system
Project management &
engineering services
Total
25%
Cost ($ x 1,000)
Savings ($ x 1,000/year)
$1,200 Combine with cyclone modernization.
$2,880 Seven days' full-load operation due to elimination
of downtime caused by slagging:
$3,360.
$400 Efficiency improvements, $298; fan energy
savings, $157.
$1,120 NA
$5,600 $3,815
Table 5. Impact of capacity factor on plant retrofit economics. Note the
simple payback for each case study remains less than two years for a capacity factor down to
60%. Source: The Fuel Delivery Subcommittee of the ASME Research Committee on Energy,
Environment, and Waste
Case study & boiler type
1: Opposed wall
2: Tangential
3: Cyclone
Results
60%
Savings ($ x 1,000)
Payback (months)
Savings ($ x 1,000)
Payback (months)
Savings ($ x 1,000)
Payback (months)
Notes: NA = not applicable, SOFA = secondary overfire air.
Fuel Preparation System. The feedercrusher
" island " was included in the FDS
boundary, because this equipment is a vital
part of coal sizing necessary for good combustion.
It was generally agreed that some
modification would have been made to
the feeder-crusher island when switching
to PRB coal, which would have included
dust control and other safety-related issues.
The same would have been included in all
the coal conveyors, but the coal conveyors
from the feeder-crusher island to the cyclone
are not part of the FDS.
As part of the FDS upgrade, some upgrades
will be made to the feeder-crusher
island to improve coal grind at a given or
increased throughput, and these costs were
estimated. In discussing the cyclone modification,
it was agreed that the 12 cyclones,
feeders, and burners would have been previously
modified, but that the upgrades to
reduce UBC, which is in some cases 20%
to 30%, would be required. Upgrades include
a new posimetric feeder, fine grind
cage crusher, and motor upgrades at
$1,200,000.
Cyclone Modernization. Cyclones
were upgraded with new split secondary
July 2013 | POWER
air dampers and damper actuators. Benefits
include reduced NOx
and UBC by improving
combustion (allowing low excess
air operation); more even flue gas distribution
in the furnace convection sections,
SCR, and air heater; and reduced slagging.
Upgrades were estimated at $2,800,000.
The benefits were reduced operation at
lower loads with individual cyclones
forced out of service due to cyclone slag
buildups and downtime for boiler deslagging.
Longer time is usually required to
cool cyclone furnaces for deslagging and
maintenance work.
The savings estimates are based on an
additional seven full days of operation in
a year by reducing forced outages for cyclone
cleaning. Modification costs were
calculated at $3,360,000.
It was noted that if the cyclones themselves
were nearing the end of their useful
life and were to be replaced, there are
numerous upgrades that should be incorporated
in the replacement cyclones to
further enhance PRB coal firing. However,
if the cyclones were not to be replaced,
these pressure part upgrades would not be
made just to improve PRB coal firing. For
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$8,295
20
$7,973
18
$2,861
23
Capacity factor
70%
$9,096
18
$9,301
15
$3
20
80%
$10,925
15
$10,630
13
$3,815
18
this reason the costs of new cyclones or
cyclone pressure part upgrades were not
addressed by this study. Also not included
was the use of iron oxide additives for improved
slag flow.
Boiler Control System. Only an upgrade
to the BCS was required-no BCS
and neural network additions. This upgrade
provided savings similar to those shown for
Case Study 1, except there was no significant
NH3
to efficiency ($298,000) and fan operation
($157,000), for a total of $455,000.
Project Management and Engineering
Services. A consistent 25% of
the upgrade costs was included, which is
$1,120,000.
The total upgrade cost is estimated as
$5,600,000, total savings as $3,815,000,
and the breakeven at 18 months, as shown
in Table 4. Again, note that 88% of the cost
savings are attributable to potential recovery
of lost generation due to derates or
forced outages caused by convective pass
slagging.
The Effect of Capacity Factor
The case study estimates are all based on
a capacity factor of 80%, as noted earlier.
While the study was under way, the
increased use of natural gas reduced coal
plant average capacity factor during 2012
in many regions of the U.S. Rising natural
gas prices have pushed some utilities
to increase coal-fired generation as the
least cost option in early 2013. Table 5 illustrates
the analysis results for a range of
capacity factors, assuming the investment
cost remains constant. Even with capacity
factors in the range of 60%, the breakeven
point for each project is less than two
years.
The subcommittee solicits comments on
the results of the analysis and suggestions
for additional study. Please forward your
comments and suggestions to Subcommittee
Chair Robert Sommerlad. ■
-Robert E. Sommerlad (rsommerl@aol
.com) is a consultant and Subcommittee
Chair. Donald B. Pearson is secretary
of the PRB Coal Users' Group.
Grant E. Grothen is principal, Burns &
McDonnell. Steven McCaffrey is with
Greenbank Energy Solutions Inc. Other
members of the Subcommittee were
Robert Chase, Terrasource Global;
Blaz Jurko, Gebr. Pfeiffer Inc.; David J.
Stopek, Consultant, Sargent & Lundy
LLC; Melanie Green, CPS Energy; Richard
Himes, EPRI; Tony Licata, Licata
Engineering Consulting and Chair RC
EEW; and Todd Melick, Vice President,
Promecon USA.
49
savings. The savings again related

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POWER July 2013

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