POWER July 2013 - 48

PLANT DESIGN
burner management (such as new scanners
and cabinets) for a total of $5,400,000. The
only direct benefit was some NOx
reduction
that reduced annual NH3 usage by $210,000.
The other benefits for improved combustion
were improved boiler performance, shown
in the next section.
Boiler Control System. In a detailed
analysis by a Burns & McDonnell team,
all the various upgrades were examined
and critiqued with a review and modification
of the cost when merited. In the original
consideration of upgrades to the BCS it
was felt a new BCS would provide benefits
as well as a neural net system. As it turned
out, the Burns & McDonnell team revised
the BCS upgrade to only a neural network
at a cost of $300,000. This applied to pulverized
coal-fired boilers (Case Studies 1
and 2) and provided unexpected benefits.
Two good rules of thumb were useful
in this analysis. First, " 10% excess air =
0.5% boiler efficiency " and " 10% excess
air = 22% fan power. " Using these rules of
thumb, the difference is (22.8% - 16.1%)
= 6.7% change in excess air, which results
in approximately 0.34% improvement in
boiler efficiency and 15% improvement
(decrease) in fan power.
The savings due to boiler efficiency improvements
can be estimated as 500 MW
x $0.05/kWh x 7,008 hours/year x 0.0034
= approx. $600,000/year of cost savings.
Assuming 2 x 4,000 horsepower (hp)
fans, 8,000 hp x 0.7457 kW/hp x $0.05/
kWh x 7,008 hours/year x 0.15 = approx.
$314,000/year savings in fan power.
Improving NOx
from 0.17 lb NOx
Btu to 0.15 lb NOx
/106
/106 Btu will decrease
the amount of ammonia consumed. Assuming
10,500 Btu/kWh heat rate, $400/
ton anhydrous ammonia, SCR outlet NOx
of 0.04 lb/106
tor, the reagent savings are approximately
$85,000/year.
Project Management and Engineering
Services. Engineering services,
including commissioning costs, were estimated
as about 15% plus an additional
10% for project management costs, which
amounted to $2,725,000.
Thus, the total installed cost is estimated
as $13,625,000 and the total savings are estimated
as $10,925,000-a simple payback
of 15 months, as shown in Table 2. It is important
to note that 83% of the cost savings
were the recovery of a presumed 5% unit
derate taken when the unit was converted
from eastern bituminous coal to a western
subbituminous PRB coal.
Case Study 2:
Tangential-Fired Boiler
The 500-MW tangential-fired boiler used
in the analysis is a single furnace with five
levels of burners and five pulverizers, 100
MW per pulverizer. Many boilers of this
size and age do not have SCRs, but they
often have lower NOx
and UBC than other
boiler designs. The subcommittee consensus
was that burner modifications would be
appropriate regardless of whether or not an
SCR was added.
The first improvement was separating
the burner levels to further reduce NOx
emissions. The benefits of DCs with regard
to recovery of lost capacity apply, but the
need to improve slagging and fouling may
not be as great. Burner modifications would
involve changing buckets and adding separate
overfire air (SOFA). NOx
be less, but NOx
reduction may
emissions are likely to be
Table 3. Case Study 2: Tangential-fired boiler FDS upgrades benefits and
costs. The investment breakeven point was approximately 13 months. Source: The Fuel Delivery
Subcommittee of the ASME Research Committee on Energy, Environment, and Waste
Component
Feeder
Pulverizer
Coal pipes
Upgrade
New feeders
Dynamic classifiers
Coal-air flow
Burner modernization New burners SOFA,
pressure part mods,
ducts, and dampers
Boiler control system Neural network
Project management &
engineering services
Total
Notes: NA = not applicable, SOFA = secondary overfire air.
48
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25%
Cost ($ x 1,000)
Savings ($ x 1,000/year)
$750 Combine with dynamic classifiers.
$3,000 5% performance recovery savings, $8,760;
two days' operation, $960.
$584 Combine with boiler control system.
$4,800 Some NOx reduction, but no significant savings:
$0.
$300 Efficiency improvements, $596; fan energy
savings, $314.
$2,359 NA
$11,793 $10,630
Btu at 80% capacity faclow.
Neural networks would provide similar
improvements. Several of the suggested upgrades
are described below and summarized
in Table 3.
Feeders. The upgrades were much the
same as in Case Study 1 but with five new
feeders, costing $750,000 installed. The cost
benefits were included with DCs.
Pulverizers. The cost of the upgrade
follows the calculations presented in Case
Study 1, or $3,000,000. The calculation of
benefits likewise followed the methods used
in Case Study 1. Savings from the 5% capacity
" recovery " were $8,760,000 and two
days of full load was $960,000, for a total
savings of $9,368,000.
Coal Pipes. As in Case Study 1, unit
upgrades chosen were coal pipe flow and
primary airflow measurement at a total of
$584,000.
Burner Modernization. The modernizations
comprise some bucket replacement
and the addition of SOFA ports,
which would require some boiler pressure
part modifications. SOFA was estimated at
$4,800,000. Benefits were some claimed
NOx
and UBC reductions, but no significant
savings were estimated.
Boiler Control System. The same upgrade
of a neural network with no new BCS
is estimated to cost $300,000 with the similar
savings forecasted in Case Study 1: boiler efficiency,
$600,000, and fan reduced power
costs of $314,000. There are no NH3
savings
because there is no SCR. Thus, the total estimated
savings are $914,000.
Project Management and Engineering
Services. A consistent 25% of the upgrade
costs was included, which amounts to
$2,359,000.
Total cost of the upgrades is $11,793,000,
with a total savings of $10,630,000. The
breakeven point for the investment is approximately
13 months, as shown in Table 3.
As before, 82% of the savings are attributable
to recapturing 5% of the unit capacity lost as
part of the initial fuel switch from an eastern
bituminous coal to a lower heat content subbituminous
PRB coal.
Case Study 3: Cyclone-Fired Boiler
The cyclone boiler investigated for this
case study was originally designed (in the
late 1960s) to fire Illinois Basin bituminous
coal, but it now burns PRB coal (since the
late 1980s). It has been retrofitted with OFA
(1990s), SCR, dry flue gas scrubber, fabric
filter, induced draft fans (converted from
pressurized to balanced draft), various boiler
and turbine modifications, and new O2
analyzers (2000s). Several of the suggested
upgrades are described below and summarized
in Table 4.
POWER | July 2013

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POWER July 2013

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