United States
Environmental Protection
Agency
Air and Energy Engineering Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-84-025 Mar. 1985
Project Summary
Economic Evaluation of
Advanced Limestone, Davy
S-H, and Dowa Gypsum-
Producing FGD Processes
R. L. Dotson, J. D. Maxwell, andT. A. Burnett
The economics of three gypsum-
producing flue gas desulfurization proc-
esses were evaluated: advanced lime-
stone (in-loop forced oxidation with
adipic acid additive), Davy S-H (lime,
and Dowa (aluminum sulfate, lime-
stone). For a 500-MW power unit
burning 3.5% sulfur coal and meeting
the 1979 New Source Performance
Standards, capital investments in 1982
costs are $93 million ($186/kW) for
the advanced limestone process, $116
million ($23l/kW) for the Davy S-H
process, and $121 million ($243/kW)
for the Dowa process. First-year annual
revenue requirements in 1984 costs for
these processes are $26, $33, and $32
million (9.4,11.9, and 11.7 mills/kWh),
respectively. The lower capital invest-
ment and annual revenue requirements
of the advanced limestone process are
due in part to the use of adipic acid,
which allows partial scrubbing at 95%
removal. The Davy S-H process has
slightly higher annual revenue require-
ments than the Dowa process because
lime is used instead of limestone. Chang-
es in power unit size and coal sulfur
content affect the costs of all three
processes similarly. The Davy S-H proc-
ess is more sensitive to raw material
costs because lime is used. Landfill
waste disposal is a minor cost element
in all three processes.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
Since 1967, the Tennessee Valley
Authority (TVA) has been evaluating the
economics of flue gas desulfurization
(FGD) processes and related technology
of electric utility power plants. Many of
these evaluations have been sponsored
by the U.S. Environmental Protection
Agency (EPA) as part of its FGD research
and development program. The major
objective of each evaluation is to prepare
economic analyses that are represent-
ative of current U.S. utility power plant
conditions on a consistent basis that
allows equitable process comparisons.
This study for EPA is the fifth in a series
begun in 1977 to evaluate the economics
of advanced FGD processes that have
promise of commercial development.
Three gypsum-producing FGD processes
with landfill disposal are evaluated in this
study: a limestone scrubbing process
with adipic acid addition and forced
oxidation (the advanced limestone proc-
ess), the Davy S-H (Saarberg-Holter)
process, and the Dowa process.
Although the technology is not new,
production of gypsum (rather than calc-
ium sulf ite sludge) in limestone scrubbing
is an emerging FGD technology which
has only recently attracted wide com-
mercial interest in the U.S. In Japan,
many limestone and lime FGD systems
produce gypsum by the forced-oxidation
method since there are few natural
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gypsum deposits and the byproduct FGD
gypsum can be sold to the wallboard and
cement industries. In the U.S., the major
emphasis has not been on producing
gypsum for sale, but to solve the waste
problems associated with disposal of
calcium sulfite sludge. Calcium sulfite
sludge forms an unstable semiliquid
when disposed of in a pond, is difficult to
dewater, and must be stabilized to be
disposed of by landfill. Gypsum slurries
are easier to dewater, can be disposed of
in a landfill without stabilization, and can
be dewatered to 80% to 85% solids with a
conventional vacuum filter. The filter
cake, resembling a moist soil, is easily
handled by conventional solids-handling
equipment. Although some byproduct
FGD gypsum can probably be sold to U.S.
wallboard and cement manufacturers,
this evaluation assumes that all waste
gypsum is landfilled.
Process Description
The advanced limestone process is
similar to the basic limestone slurry
process except that: (1) adipic acid is
added to the scrubbing liquid to enhance
S02 removal and increase limestone
utilization, and (2) forced oxidation by air-
sparging is incorporated to produce gyp-
sum. The design and operating conditions
are based in part on data from EPA-
sponsored tests at TVA's Shawnee test
facility. The process uses a counter-cur-
rent spray tower with a presaturator and
a chevron-type mist eliminator. The pre-
saturator cools the entering gas from
300°F to 124°F.* The absorbent liquid is
an 8% solids slurry of finely ground (90%
minus 325 mesh) limestone prepared
onsite by crushing and ball milling. A
stoichiometry of 1.07 mols CaCO3/mol
(SO2 + 2HCI) absorbed is used. The liquid-
to-gas (L/G) ratio is 4 gal./1000 acf for
the presaturator and 80 gal./1000 acf for
the absorber. An adipic acid concentration
of 1,500 ppm is maintained in the absorp-
tion loop by metering adipic acid into the
makeup limestone slurry tank. Air, at a
stoichiometry of 2.5 Ib atoms 0/lb mol
S02 absorbed, is injected into the absorb-
er effluent tank to oxidize the sulfite. A
bleedstream is pumped to a thickener and
rotary vacuum filter for dewatering. The
dewatered gypsum is trucked to a landfill
1 mile from the FGD facility.
The Davy S-H process is a lime-based
process using a clear alkaline absorbent
*Nonmetric units are used in this report for con-
venience. Readers more familiar with metric units
may use the conversion factors at the end of this
Summary.
liquid buffered with formic acid. The SC>2
is removed in a Rotopart absorber (a
patented modular-design cocurrent spray
column with an integral gas/liquid sepa-
rator). Each module consists of two
absorption tubes containing liquid-shed-
ding rings (venturi throats) connected to a
single gas/liquid separator (Rotopart)
section. The buffering action of formic
acid acts to slow and control the pH drop
to 4.5 to 5.0, ensuring formation of
bisulfite. The concentrations of both the
formic acid and a ferric chloride catalyst
and the absorber L/G ratio are proprietary
information. The lime stoichiometric ratio
is 1.02 mols (CaO/mol (S02 + 2HCI)
absorbed. The absorber effluent is oxi-
dized by air-sparging in an oxidizer vessel
at a stoichiometry of 5 Ib atoms 0/lb mol
SO2 absorbed. The gypsum slurry over-
flows from the oxidizer to the thickener
through a mixing trough. Lime slurry and
makeup formic acid are added to this
trough. The thickened slurry is dewatered
in a rotary vacuum filter. The dewatered
gypsum is trucked 1 mile to a landfill.
The Dowa process is a double-alkali
process that uses a basic aluminum
sulfate—AlzlSOuJa—solution to absorb
S02 and limestone to precipitate gypsum
and regenerate the scrubbing solution. A
packed-bed countercurrent absorber
with a fresh-water wash on the wall at
the gas/liquid interface is used for SOa
removal. The absorber is packed with
Ecodyne Poly-Grid packing. An L/G ratio
of 45 gal./1000 acf is used. The absorber
effluent is oxidized by air-sparging in an
oxidizer vessel in the absorber liquid loop
at an air stoichiometry of 4 Ib atoms 0/lb
mol S02 absorbed. A chloride purge
prevents an excessive buildup of chlorides
in the system. A bleedstream from the
oxidation tank is neutralized with lime-
stone to regenerate the basic AI^SOVs
solution and precipitate gypsum. A stoich-
iometry of 1.03 molsCaCOa/mol of (SO2 +
2HCI) absorbed is used. The gypsum
slurry is dewatered in a thickener and a
rotary vacuum filter, and the gypsum is
trucked 1 mile to a landfill for disposal.
Design and Economic
Premises
The economic evaluations are based on
a conceptual design developed from the
design premises and engineering data
such as flow diagrams, material balances,
and equipment costs. The Davy S-H and
Dowa processes are based on vendor-
supplied data; the limestone process is a
generic design. A base-case, new 500-
MW power unit burning a 3.5% sulfur.
16% ash (both are dry basis) bituminous ^
coal, and complying with the 1979 New fl
Source Performance Standards(NSPS) is
used as the primary basis of comparison.
Design Premises
The coals used are three eastern bitu-
minous coals containing 5.0%, 3.5%, and
2.0% sulfur (dry basis). The coals have a
heating value of 11,700 Btu/lb as fired.
The compositions of the coals are shown
below. The 3.5% sulfur coal is the base-
case coal.
Sulfur, %
Heat
Ash, Moisture, content,
% % Btu/lb
Coal
Dry
basis
As-fired basis
Eastern
bituminous 50 4.80 15.10 40 11,700
Eastern
bituminous 35 3.361514 40 11,700
Eastern
bituminous 20 1.9215.08 40 11,700
The power plant site is assumed to be in
the north-central region of the U.S. The
base-case power unit is a new, single
500-MW, balanced-draft, horizontally
fired, dry-bottom boiler burning pulver-
ized coal. Power unit size variations
consist of similar 200- and 1,000-MW
units. The power units have a 30-year life
a nd operate at full load for 5,500 hr/yr for
a total lifetime operation of 165,000
hours. Existing power units with 20years
of remaining life at 5,500 hr/yr of full-
load operation are also evaluated. This
operating schedule is equivalent to a total
remaining lifetime operation of 110,000
hours.
Flue gas compositions are based on a
total air rate equivalent to 139% of the
stoichiometric requirement, including
19% air leakage. It is assumed that 80% of
the ash in the coal is emitted as fly ash
and 92% of the sulfur is emitted as SO,.
Three percent of the sulfur emitted as SO,
is SOs, and the remainder is SO2. Cold-
side electrostatic precipitators (ESPs),
sized to meet the 0.03 lb/106 Btu 1979
NSPS, are assumed for paniculate con-
trol. Costs for ash collection and disposal
are not included in the economic evalua-
tion.
S02 emissions from new coal-fired
utility plants are regulated by the revised
1979 NSPS. SO2 emissions from existing
units are based on a representative state
implementation plan (SIP) emission stand-
ard of 0.6 Ib S02/106 Btu. The controlled
outlet SO2 emission and S02 removal
-------
efficiencies for new plants for each of the
coals are shown below.
Equivalent
Equivalent Overall SO2
SO: equivalent removal Controlled
content S02 required outlet
of coal, reduction in FGD emission,
lbS02/ required, system, lbSO2/
Coal 10'Btu % % 10"Btu
Eastern
bit.,
5.0% S 8.21
Eastern
bit.
3.5% S 5.74
Eastern
bit.
2.0% S 3.28
90.0 89.1 0.82
89.6 88.7 0.60
81.7 80.1 0.60
The FGD systems are coupled to the
power unit by a plenum into which the
power plant ID fans discharge. Separate
ID fans are provided for the FGD system.
FGD costs include ductwork and asso-
ciated equipment between the power
plant ID fans and the stack plenum. Costs
for the stack plenum and the stack are
excluded. Absorption trains are sized for a
maximum of 125 MW of flue gas(513,000
scf/min). Spare trains are provided for a
minimum of 25% redundancy, and pro-
vision for emergency bypass of 50% of the
scrubbed gas is included. For all of the
advanced limestone cases, partial scrub-
bing of the flue gas at an SOZ removal
efficiency of 95% S02 is used. Partial
scrubbing of 89% of the flue gas at 90%
SO2 removal is used for the 2.0% sulfur
coal cases for the Davy S-H and the Dowa
processes. This corresponds to the quan-
tity of gas bypassed shown below. Indirect
steam reheat to 175°F is provided as
necessary. The dewatered gypsum cake
is disposed of in a landfill, 1 mile from the
FGD facilities. The gypsum disposal area
includes loading, trucking, spreading,
and compaction operations, and general
landfill maintenance and reclamation.
Flue gas bypass, %
Coal
Advanced
limestone
Davy S-H Dowa
Eastern
bit.,
5.0% S
Eastern
bit.,
3.5% S
Eastern
bit.,
2.0% S
6.2
6.7
15.7
11.0
11.0
Economic Premises
A 3-year construction period, from
early 1981 to late 1983, is used for both
new and existing units. Mid-1982 costs
are used for capital investment. Mid-
1984 costs are used for annual revenue
requirements.
Capital investment consists of direct
investment, indirect investment, and oth-
er capital investment. Direct investment
consists of the installed costs of all
process equipment, including provisions
for services, utilities, and miscellaneous,
and costs associated with the landfill.
Indirect capital investment consists of
fees for engineering design and super-
vision, architect and engineering contrac-
tor, construction expense, contractor
fees, and contingency. An allowance for
start-up, modifications, and interest dur-
ing construction is included. No royalty
charges are included for the advanced
limestone and Dowa processes. Royalty
charges for the Davy S-H process were
obtained from the process vendor. Proc-
ess and waste disposal area land is
charged at $5,000 per acre.
For existing plants, a capital invest-
ment retrofit factor of 1.3 is assigned to
cover the additional investment required
for fitting the equipment into the available
space. Each area investment (e.g., mate-
rial handling) is multiplied by the retrofit
factor. The remaining investment costs
are calculated in the same manner as for
new units.
Annual revenue requirements consist
of various direct and indirect operating
and maintenance costs and capital charg-
es. Both first-year and levelized annual
revenue requirements are reported. Level-
ized capital charges are used in both first-
year and levelized annual revenue re-
quirements. Levelized operating and mainte-
nance costs are determined by multiply-
ing the first-year operating and mainte-
nance costs by a 30-year levelizing factor
of 1.886, representing an annual inflation
rate of 6% and a discount rate of 10%.
Systems Estimated
All three processes are divided into
materials handling, feed preparation, gas
handling, SOz absorption, reheat, oxida-
tion, solids separation, and disposal ar-
eas. In the Dowa process two additional
areas, neutralization and chloride purge,
are included. There are no equivalent
areas in the other processes. The mate-
rials handling and feed preparation areas
consist of equipment to receive, store,
and prepare absorbent slurry. Limestone
is crushed and wet ball milled. Lime is
slaked and slurried. For processes that
use additives, supplemental equipment is
included in the preparation area for
addition. The gas handling area consists
of a feed plenum that distributes the flue
gas to the individual absorber trains,
ductwork, and one ID fan per absorber
train. Two emergency bypass ducts are
included to handle 50% of the scrubbed
gas and to serve as bypass ducts if some
of the flue gas is normally bypassed. The
absorption area consists of the absorbers
and the absorbent liquid recirculation
system. All FGD systems are designed for
a flue gas temperature of 175°F at the
entrance to the stack. Reheat is provided
by indirect, inline steam reheat with
provisions to account for compression by
the ID fans and heating by bypassed flue
gas. The oxidation area consists of air
compressors, the oxidation tank, a sparg-
ing ring, and an agitator. The neutraliza-
tion and chloride purge areas in the Dowa
process include tanks, agitators, pumps,
and limestone addition equipment to
precipitate gypsum and aluminum hydrox-
ide. The solids separation area consists of
thickeners and rotary vaccum filters to
generate an 85% solids gypsum waste.
Trucks are used to transport the filter
cake to the landfill.
Results
The economics developed consist of
capital investments and first-year and
levelized annual revenue requirements
for the three processes, based on the
design and economic premises and the
specific process designs.
Capital Investment
Capital investments for each process
are summarized in Table 1. The advanced
limestone process has the lowest capital
investment, followed by the Davy S-H
process (25% higher in the base case) and
the Dowa process (31 % higher in the base
case).
Direct capital investments by process
area for the base-case processes are
shown in Table 2. The Davy S-H process
has the highest gas handling area cost
(due to the limited but costly use of 316
stainless steel ducting) and oxidation
cost (due to a unique sparger constructed
with 316 stainless steel). The Davy S-H
process has the lowest feed preparation
area cost (due to the use of lime) and SO2
absorption area cost (due to the modular
Rotopart). However, the high cost areas of
the Davy S-H process are not offset by the
lower cost areas and, therefore, result in
the Davy S-H process having the second
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Table 1. Capital Investment Summary
Advanced
limestone
Davy S-H
Dow a
$106
S/kW
S106
$/kW
$10*
$/kW
New Units'
200 MW. 3.5% S
500 MW, 2.0% S
500 MW, 3.5% S
500 MW, 5.0% S
1,000 MW, 3.5% S
Existing Units*
54.4
79.1
92.8
97.9
155.5
272
158
186
196
156
63.0
99.8
115.5
121.4
206.7
315
200
231
243
207
66.4
102.6
121.3
130.3
216.1
332
205
243
261
216
200 MW, 3.5% S
500 MW, 3.5% S
1,000 MW, 3.5% S
59.8
118.5
211.7
299
237
212
80.6
148.1
268.1
403
296
268
85.4
156.2
281.3
427
312
281
"New FGD facilities are constructed simultaneously with the power plant and have a 30-year
remaining life.
^Existing FGD facilities are retrofit installations on existing power plant facilities and have a
20-year remaining life.
highest capital investment. The Dowa
process has only two major areas (S02
absorption and solids separation) that are
lower in cost than the advanced limestone
process; and they are only marginally
lower in cost. The higher costs in the
other processing areas result in the Dowa
process having the highest capital invest-
ment for the base case.
Case Variations
As shown in Table 1, the capital
investment ranking remains the same for
all case variations as that of the base
cases. The capital investment approxi-
mately doubles as the power unit size
increases from 200 to 500 MW and
triples as the size increases from 200 to
1,000 MW. For existing units, the cost
relationships are essentially the same as
for new units. The capital investment
increases 15% to 18% as the coal sulfur
increases from 2.0% to 3.5%. The in-
crease is 22% to 27% as the coal sulfur
increases from 2.0% to 5.0%.
The 200-MW units have a 50% spare
capacity because only two operating
absorption trains (arbitrarily used as the
minimum) are required, while the 500-
and 1,000-MW units have only 25%
spare capacity. The additional capital
required for the 200-MW unit increases
the cost (in dollars per kilowatt), resulting
in an exaggerated economy of scale as
the power unit size increases from 200 to
500 MW. Partial scrubbing is used in all
processes for the 2% sulfur coal. For
advanced limestone, the SC>2 absorption
and gas handling equipment are sized to
handle 84.3% of the total gas; the re-
maining 15.7% is bypassed. For Davy S-H
and Dowa processes, the SOz absorption
equipment and gas handling equipment
are sized to handle 89% of the total gas;
the remaining 11% is bypassed. The
reduction in equipment size and materials
because of the bypassfurther reduces the
capital investment for the 2.0% sulfur
coal, compared with the 3.5% and 5.0%
sulfur coal for the Davy S-H and the Dowa
processes. For the advanced limestone
process, where partial scrubbing is used
in all cases, the corresponding reductions
are not as significant.
Annual Revenue Requirements
As shown in Table 3, the advanced
limestone process also has the lowest
annual revenue requirements, but there
is little difference between the Davy S-H
and Dowa processes. Although the Dowa
process has a higher capital investment,
it has marginally lower annual revenue
requirements because it uses limestone
(at $8.50/ton) whereas the Davy S-H
uses lime at $75/ton. The Davy S-H
process lime cost is 4.0 and 3.3 times
higher than the limestone costs of the
advanced limestone and Dowa processes.
Other raw material costs (adipic acid,
formic acid, and aluminum sulfate) are
minor.
The largest component of the first-year
annual revenue requirements (as shown
in Table 4 for the base-case application)
for all processes is capital charges, which
are over 50% of the total. Except for raw
material cost, all processes have the
same order of major cost components:
levelized capital charges, maintenance,
plant and administrative overheads, and
electricity, in order of decreasing impor-
tance. Raw material cost, however, is the
second highest component of annual
revenue requirements for the Davy S-H
process; whereas, it is the fifth highest
component for the advanced limestone
and Dowa processes.
Table 2.
Base-Case Capital Investment Summary by Processing Areas"
$10e
Advanced
limestone
Davy S-H
Dowa
Materials handling
Feed preparation
Gas handling
SOi absorption
Reheat
Oxidation
Neutralization
Chloride purge
Solids separation
Total process
capital
Total direct
investment
Total capital
investment
2.6
4.3
10.5
17.7
2.3
3.2
-
-
3.5
44.1
51.0
92.8
3.5
1.2
18.6
14.7
4.2
5.0
—
—
. 2.6
49.8
57.0
115.5
2.9
5.3
14.3
17.6
4.0
4.7
0.6
0.8
2.7
52.9
60.3
121.3
"500 MW. new power unit, 3.5% sulfur coal, 1982 dollars.
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Table 3. Annual Revenue Requirement Summary
Dowa
First year Level/zed
JTfJ*mills/kWh JTU*mills/kWh 573*mills/kWh TTG1 mills/kWh $10* mills/kWh S/0S mills/kWh
Advanced limestone Davy S-H
First year Levelled First year Level/zed
New Units"
200MW, 3.5%S 15.3 13.95 21.9 19.86 17.7 16.06 25.1 22.83 18.0 16.33 25.2 22.94
500MW.2.0%S 21.6 7.86 30.4 11.07 26.7 9.69 37.3 13.55 26.8 9.76 37.2 13.54
500MW,3.5%S 25.8 9.38 36.6 13.31 32.7 11.88 46.5 16.93 32.3 11.74 45.1 16.39
500MW,5.0%S 27.7 10.07 39.5 14.36 35.9 13.08 52.0 18.90 34.8 12.65 48.6 17.68
1.000 MW. 3.5% S 42.8 7.78 60.4 10.99 57.4 10.44 81.4 14.80 56.1 10.21 77.7 14.13
Existing Units"
200 MW, 3.5% S 17.1 15.53 22.0 20.04 21.9 19.87 27.8 25.28 22.7 20.66 28.7 26.14
500 MW, 3.5% S 32.5 11.83 41.5 15.10 40.2 14.63 51.2 18.62 40.9 14.86 51.4 18.71
1,000 MW, 3.5% S 56.9 10.34 72.1 13.12 71.6 13.02 90.6 16.48 71.9 13.08 90.0 16.36
'New FGD facilities constructed simultaneously with the power plant and have a 30-year remaining life.
"Existing FGD facilities are retrofit installations on existing power plant facilities and have a 20-year remaining life.
Table 4. Major Cost Components for Base-Case Annual Revenue Requirements
Major operating cost components
(% of first-year annual revenue requirements)
Process 123'
Advanced
limestone
Davy S-H
Dowa
Levelized
capital charges
52.7
Levelized
capital charges
52.0
Levelized
capital charges
55.3
Maintenance
14.7
Raw materials
14.1
Maintenance
14.3
Plant and
adm. overheads
12.0
Maintenance
10.1
Plant and
adm. overheads
10.9
Electricity
6.6
Plant and
adm. overheads
8.3
Electricity
6.2
Raw materials
4.3
Electricity
6.7
Raw materials
4.3
Capital investments play a major role in
the ranking of the annual revenue require-
ments because levelized capital charges
are a direct function of total capital
investment and maintenance costs are a
function of direct investment. In addition,
overheads are a function of maintenance
costs.
Case Variations
As shown in Table 3, the levelized
annual revenue requirements for new
units increase 70% to 85% as the power
unit size increases from 200 to 500 MW,
and 175% to 225% as the power unit size
increases from 200 to 1,000 MW. For
existing units, the costs increase 80% to
90% for the 200- to 500-MW power unit
size increase, and 215% to 230% for the
200- to 1,000-MW range.
Although the Davy S-H process has the
highest base-case levelized annual reve-
nue requirements, this relationship is not
true of all power unit sizes. At the 200-
MW size, the levelized annual revenue
requirements for the Dowa process are
slightly higher than those of the Davy S-H
process. As the power unit size increases,
the levelized annual revenue require-
ments for the Davy S-H process increase
more rapidly than those of the Dowa
process. This is due to the relationship
between the variable raw material costs
and the fixed-percentage capital-related
costs (maintenance and levelized capital
charges). Since the Dowa process has the
highest total capital investment in every
case, its maintenance cost and capital
charges are also highest; but the Davy
S-H process has the highest raw material
cost for all cases. As the power unit size
increases, the effect of raw material cost
surpasses the effects of maintenance
cost and capital charges.
As the coal sulfur increases from 2.0%
to 3.5%, the levelized annual revenue
requirements increase 20% for the ad-
vanced limestone and Dowa processes
and 25% for the Davy S-H process. As the
coal sulfur increases from 2.0% to 5.0%,
the increases are 30% and 40%. The
levelized annual revenue requirements of
the Davy S-H process are equivalent to
-------
the Dowa process for 2.0% sulfur coal,
but they are higher for 3.5% and 5.0%
sulfur coal. As in the power unit size
variation, this trend is due to the relation-
ship of raw material costs and capital-
related costs.
The sensitivity of the Dowa process
economics to changes in the absorber
L/G ratio was evaluated since the base-
case costs were calculated using an L/G
ratio of 45 gal./1000 acf; whereas,
recent tests indicate that an L/G ratio of
about 80 gal./1000 acf is required for
90% S02 removal. The higher L/G ratio
increases the capital investment 4%,
primarily because larger pumps and
piping were required, and increased the
levelized annual revenue requirements
about 5% because of the higher electricity
cost and the higher levelized capital
charges. The levelized annual revenue
requirements for the Dowa process be-
came slightly higher than those of the
Davy S-H process, but the cost differences
between the two processes remain small.
Conclusions
The capital investment relationships
among the processes remain the same
for all power unit sizes and coal sulfur
contents. Landfill capital investment is a
minor element of capital investment and
is similar for all processes.
The capital investment and annual
revenue requirements of the advanced
limestone process are substantially lower
(about 25% and 10%, respectively) than
those of the Davy S-H and Dowa process-
es. This is largely the result of more
extensive use of partial bypass for the
advanced limestone process, which is
possible because using adipic acid allows
scrubbing at 9% removal, compared with
90% for the other processes. The capital
investment and annual revenue require-
ments of the Davy S-H and Dowa proc-
esses do not differ appreciably: the Davy
S-H process is slightly lower in capital
investment and slightly higher in annual
revenue requirements. The cost relation-
ships of the three processes hold true for
different power unit sizes and coal sulfur
contents, except that the Davy S-H proc-
ess annual revenue requirements in-
crease slightly more rapidly with increas-
ing power unit size and coal sulfur
content.
The Davy S-H process is most sensitive
to raw material cost changes because
lime is used as the ultimate absorbent.
The processes using limestone have
absorbent costs three to four times lower.
Other raw material costs (adipic acid.
formic acid, and aluminum sulfate) are
insignificant.
Approximately doubling the L/G ratio
(from 45 to 90 gal./1000 acf) increases
the capital investment and annual reve-
nue requirements of the Dowa process
4% to 5%, which has no large effect on
the cost relationships of the processes.
Using a chloride purge in the Dowa
process, which is not used in the other
processes, has no material effect on the
costs.
Landfill is a minor element of the
capital investment and annual revenue
requirements of all processes.
Conversion Factors
Readers more familiar with metric
units may use the following factors to
convert from the nonmetric units used in
this report.
Nonmetric Multiplied by Yields metric
acre
Btu
°F
ft3
gal.
Ib
mi
ton
4047
1.055
5/9(°F-32)
0.283
3.785
0.454
1.609
907.2
m2
kJ
°C
m3
1
kg
km
kg
R. L. Dotson. J. D. Maxwell, and T. A. Burnett are with TVA's Office of Power,
Muscle Shoals, AL 35660.
Norman Kaplan is the EPA Project Officer (see below).
The complete report, entitled "Economic Evaluation of Advanced Limestone, Davy
S-H, and Dowa Gypsum-Producing FGD Processes," (Order No. PB 85-143 253;
Cost: $ 17.SO, 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
U. S. GOVERNMENT PRINTING OFFICE: 1985/559 111 /10801
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