United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-85/016 July 1985
Project Summary
Economics of Retrofitting
Big Rivers Electric Corporation's
Lime-Based FGD System to
Organic-Acid-Enhanced
Limestone Operations
Dennis Laslo, Norman Ostroff, Richard Foley, and Donald G. Schreyer
In 1982-83, Peabody Process Sys-
tems, Inc. (PPSI) conducted pilot plant
tests at the R.D. Green Station of Big
Rivers Electric Corporation (BREC).
PPSI's final report of the pilot testing
included comparisons of the operating
costs of a lime-based full-sized
absorber, to a retrofit limestone system
enhanced with dibasic acid (DBA) or
adipic acid. The site specific changes
required for BREC to converttheir
existing lime FGD system to a lime-
stone system enhanced by DBA or
adipic acid, and the costs of making
such a change are described in this
paper. Results of this analysis indicated
that an annual cost savings of $2.6 mil-
lion could be achieved by converting
the existing BREC lime system to an
adipic-acid-enhanced limestone sys-
tem, and an annual savings of $3.1 mil-
lion could be achieved by converting to
a DBA-enhanced system.
This Project Summary was devel-
oped by EPA's Air and Energy Engi-
neering Research Laboratory, Research
Triangle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report of
the same title (see Project Report order-
ing information at back).
Introduction
In 1982-83, Peabody Process Systems,
Inc. (PPSI) conducted pilot plant tests at
the R.D. Green Station of Big Rivers
Electric Corporation (BREC). PPSI's final
report of the pilot testing included com-
parisons of the operating costs of a lime-
based full-sized absorber, toa retrofit
limestone system enhanced with dibasic
acid (DBA) or adipic acid. The economics
did not include the cost of new equipment
required to make the conversion. A
second project was funded by the EPA to
define the capital requirements neces-
sary for the retrofit, thereby completing
the economic comparison.
The existing R.D. Green Station has
two 240 MW boilers that use an Ameri-
can Air Filter (AAF) flue gas desulfuriza-
tion (FGD) system employing a spray
tower absorber and dolomitic lime as a
reagent. Dolomitic lime enhances SO2
removal efficiency by accumulating dis-
solved alkalinity (MgSO3), allowing a rel-
atively low liquid-to-gas ratio (L/G) to be
used for the system. Adipic acid and DBA
enhance the performance of limestone
scrubbing systems such that a mixture of
limestone and DBA or adipic acid may be
substituted for lime with minor changes
to an existing FGD system.
This report addresses the site specific
changes required for BREC to convert
their existing lime FGD system to a lime-
stone system enhanced by DBA or adipic
acid, and the costs of making such a
change. Results of this analysis, which
was based on site specific capital and raw
material costs, indicated that an annual
cost savings of $2.6 million could be
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achieved by converting the existing lime
system to an adipic acid enhanced lime-
stone system, and an annual savings of
$3.1 million could be achieved by con-
verting to a DBA-enhanced system.
Required Process Modifications
Prediction of Full-Scale SO2
Removal Efficiencies with
Limestone/Organic Acid
The BREC pilot plant test results could
not be used to predict SO2 removal effi-
ciencies for the full-scale spray tower
because wall effects reduced the spray
zone mass transfer effectiveness for the
pilot plant operations. An attempt was
made to compare the existing BREC spray
tower performance to that of the 10 MW
Shawnee spray tower. Typically, larger
diameter spray towers are more efficient
than the 10 MW Shawnee spray tower;
consequently, use of the 10 MW data for
predicting full-scale performance should
be conservative.
However, a direct comparison of the
operation of the full-scale BREC spray
tower to the Shawnee operations could
not be made since much of the required
process data (Mgt+concentration, pH,
L/G, inlet S02 concentration, and tem-
perature) were not available. For this rea-
son, semi-empirical equations (devel-
oped by Bechtel for limestone scrubbing
with adipic acid) were used to estimate
full-scale liquid pumping requirements
for achieving 90 percent S02 removal as
a function of inlet S02 concentration.
Adipic acid and liquid pumping require-
ments for the retrofit were calculated for
several inlet SO, conditions. Increased
L/G rates would be obtained by increas-
ing the rpm of the existing recycle pumps
to the capacity of the existing motors.
Calculation results showed that, even at
the highest sulfur coal, there is sufficient
pumping capacity for meeting com-
pliance when 3,000 ppm of adipic acid is
used.
Basis for Retrofit Equipment
Design
The ultimate coal analysis typical of
coal burned at BREC was used as a basis
for combustion calculations, which
assumed an excess air rate of 50 percent
and a coal feed rate of 277,000 Ib/hr*
which were consistent with operating
conditions measured in a series of test to
evaluate the performance of BREC's ESP.
Combustion calculation results were also
consistent with measured values and
were thus used as the basis for perform-
ing material balance calculations to
establish required equipment sizes.
Retrofit Equipment Required
The existing lime system would be con-
verted by utilizing as much existing
equipment as possible. Only a ball mill
and organic acid feed system will be
added. No changes to the absorption por-
tion of the system were required.
An existing equipment list of the BREC
FGD system was prepared jointly by PPSI
and BREC. A site visit was made by PPSI
engineers to determine possible use of
existing equipment in the limestone ret-
rofit and to locate sites for new equip-
ment construction.
Existing lime silos will be used to store
coarse limestone; however, the lime
slakers will not be operated. Three 50
ton/hr* ball mills (one spare) will be
housed in an electrically heated building
near the existing silos. DBA or adipic acid
storage and handling facilities will also
be in the ball mill area. Conveyors have
been priced to transport the crushed
limestone from the storage silos to any of
the three ball mill feeds. Supernate,
tapped from a nearby 6 in.* line, will be
used to slurry the limestone, and the
organic acid will also be added to the ball
mill. A crane was priced for new ball addi-
tion to the ball mill.
Tanks, pumps, and agitators for the
limestone/organic acid feed system
*1 ton = 907 2 kg, 1 in = 2.54 cm..
were sized and priced based on maxi-
mum coal feed rate and maximum sulfur
coal. Note that costs for an electrical sub-
station to provide power for the ball mills
were not included: BREC felt that suffi-
cient electrical capacity was available
from existing equipment. If this substa-
tion were included, it would raise the
capital costs by $52,000.
Process Conversion Costs
To provide cost comparisons of various
full-scale process alternatives, a base
case of BREC was calculated, using the
parameters of Table I. The typical operat-
ing load of 75 percent was obtained using
BREC-projected load demands through
1995.
Potential process alternatives consid-
ered in this evaluation are:
- Limestone - with adipic acid addition.
- Limestone - with DBA addition.
Direct and indirect capital requirements
for new equipment are summarized in
Table 2. Capital requirements are based
on equipment sizing for 100 percent load
and maximum sulfur. The ball mills are
very conservative since the limestone
work index supplied by BREC for a typical
quarry was 12. Other quarries were not
surveyed but finding a work index of 10 or
lower should not be difficult.
Operating costs shown in Table 3 were
calculated based on typical conditions,
since an unfair advantage for lime-
stone/organic acid would result at maxi-
mum boiler load and coal sulfur. By using
a fixed capital recovery factor of 20 per-
cent, the annualized costs of a lime-
stone/organic acid retrofit and the
Table 1.
Parameters Assumed for Base Case Calculations
BREC's Green Station Unit No. 2
Plant Load
Module Gas Flow
Inlet SO2 Concentration
Lime Stoichiometry"
Lime Consumption
SO2 Removal Required
L/G (max.)
L/G (current)
CURRENT
Recycle, Module A
Recycle, Module B
Operation
Cake Solids
205 MW
1,525.000 Ib/hr/tower
or 383.000 acfm/modu/e '
2,550 ppm wet
1.02
12 tons/hr
90%
57
41
14,900 gpmc
16,500 gpm
7,560 hr/yr
42.0%
•1 lb = 0454kg.
1ft3 = 28.3 L
Moles Ca per mole S02 absorbed.
C1 gal. =3.79 L.
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Table 2. Cost Estimate Summary, BREC Limestone/Organic Acid Retrofit
(1982 Cost Basis/
Direct Investment ($ 1.000s)
Limestone/Adipic Acid
Limestone/DBA
Description
Foundations,
Site Preparation
Buildings
Structural Steel
Tank Heater
Process Tanks
Limestone Preparation
Pumps & Drives
Machinery
Insulation
Piping & Valves
Instrumentation
Electrical
Painting
Freight
Material
50
170
94
4
2,145
18
30
105
115
173
1
25
Labor
50
77
56
2
736
4
12
65
30
108
4
Total
100
247
150
6
2,281
22
42
170
145
281
5
25
Material
50
170
94
1
24
2.125
18
30
6
105
115
173
1
25
Labor
50
77
56
1
8
126
4
12
6
65
30
108
4
Total
100
247
150
2
32
2.251
22
42
12
170
145
28 1
5
25
Total Direct Costs
2,930 544 3.474 2,937 547
Indirect Investment ($ 1,000s)
existing lime system were compared. The
results shown in Table 4 indicate a yearly
savings of $2,642,000 for limestone with
adipic acid and $3,153,000 for limestone
with DBA. These results would be differ-
ent for other locations due primarily to
variation in the cost differential between
lime and limestone.
3,484
Start-up Expenses
Field Expenses
Vendor Salary
Vendor Expenses
Vendor Overhead
Contingency
Vendor Profit @ 15%
Total Indirect Costs
Total Cost
100
20
100
117
337
10
20
20
20
22
92
10
20
120
20
120
139
585
1.014
4.488
100
20
100
117
337
10
20
20
20
22
92
10
20
120
20
120
139
587
1.016
4,500
Table 3.
Operating Cost Summary - Typical Operating Conditions3BREC Limestone/Or-
ganic Acid Retrofit
(1982 Cost Basis)
First Year Cost ($ 1,000s)
Lime Limestone/Adipic
Limestone/DBA
Alkali
Lime @ $60/ton 5,856
Limestone @ $6.50/ton
Additive
Utilities
Electricity @ $0.01369/kWh 215
1.222
931
378
1.222
418
378
Total
6.071
2,531
2,018
Savings Compared to
Lime System
3,540
4,053
" Typical Operating Conditions:
Firing Rate - 100 tons/hr per boiler
3.0% sulfur coal
Lime Stoichiometry = 1.O2 mole CaO/mole S02 removed
Limestone Stoichiometry = 1.05 mole CaCO3/mole S02 removed
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Table 4. BREC Limestone/Organic Acid Retrofit Projected First Year Cost Differential for
Conversion from Lime
(1982 Cost Basis)
Limestone/A dipic Limestone/DBA
New Investment
Annual Charge @ 20% ($ 1.000s)
New Annual
Operating Costs ($ 1.000s)
Total
Annual Savings
SI, OOOs
mills/ kWh
898
-3.540
2.642
0.927
900
-4.053
3.153
1.106
D. Laslo. N. Ostroff, R. Foley, andD. Schreyerare with Peabody Process Systems,
Norwalk, CT 06851.
J. David Mobley is the EPA Project Officer (see below).
The complete report, entitled "Economics of Retrofitting Big Rivers Electric
Corporation's Lime-Based FGD System to Organic-Acid-Enhanced Limestone
Operations," (Order No. PB 85-191 146/AS; Cost: $8.50, subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S7-85/016
OOOC329 PS
U S ENVIR PROTECTION AGENCY
REGION 5 LIERA
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STREET
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