United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-87/028 Feb. 1988
&EPA Project Summary
Conceptual Designs and Cost
Estimates for E-SOX Retrofits to
Coal-Fired Utility Power Plants
D. F. Becker and J. L. DuBard
A conceptual design and cost esti-
mate, based on information available
at the beginning of 1987, was done for
six cases of a retrofit of the E-SOX
process to a utility. The annualized cost
ranged from $301 to $378 per ton of
SO2 removed. The generic cost basis,
used for other cost estimates, was used
in this study and applied to a 500 MWe
utility burning eastern medium sulfur
(2.5%) bituminous coal. Capital costs
compare very favorably with other
retrofit SO2 removal technologies.
Sorbent or reagent cost is the largest
single component of the costs.
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
ordering information at back).
Background
E-SOx technology has been proposed
as a feasible way to lower SO, emissions
from power plants upon retrofit to an
existing electrostatic precipitator (ESP).
In a conceptual study to evaluate various
retrofit situations, applicable bases were
kept identical with those of a similar
study in 1983 on Limestone Injection
Multistage Burner (LIMB) systems.
The conceptual designsdiscussed here
are based on a generic power plant. All
subsystems necessary for a complete E-
S0« system are included in the costs.
Equipment and systems were optimized
on a limited basis, because this is not
a site-specific study. Thus, costs will vary
from those presented here, as specific
locations are considered. The study
provides a point of reference for compar-
ison purposes, and shows where future
research and development efforts should
be concentrated.
Scope and Approach
After the LIMB study, plant size was
selected as 500 MW, with existing
particulate control equipment designed
to meet the 1971 New Source Perfor-
mance Standards for particulate matter.
The process designs were based on lime
stoichiometries and approach tempera-
tures necessary to achieve 50% sulfur
reduction for a typical eastern, medium
sulfur (2.5%) bituminous coal. Two
process conditions were selected using
hydrated lime as a reagent, and one using
quicklime. For one of the lime hydrate
process conditions, four ESP upgrade
conf igurations were evaluated. Six E-SOx
cases were investigated:
Case /—Hydrated lime reagent, Ca/S =
1.3, approach temperature 4°C,
original 218 SCA ESP, retrofit-
ted with precharger and large
diameter electrodes.
Case 2—As Case 1, except no pre-
charger, weighted wires instead
of large diameter discharge
electrodes, and 0.5 m longer
collecting plates in each field.
Case 3—As Case 1, except original 150
SCA ESP, plate height increased
by 0.9 m, and collecting plates
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in each field increased in length
by 0.5 m.
Case 4—As Case 3, except no pre-
charger, weighted wires instead
of large diameter discharge
electrodes, and an additional
short third active field.
Case 5—As Case 1, except a Ca/S ratio
of 1.5 and an approach temper-
ature of 10°C.
Case 6—As Case 1, except pebble
quicklime is used as a reagent.
The study consisted of the conceptual
equipment selection, equipment arran-
gement, and capital and first year
operating and maintenance cost esti-
mates for the E-SOx system and all
supporting equipment for the above six
cases.
Findings
The mechanical equipment used as a
basis for these designs is predominantly
commercial. Lime receiving and storage
and slurry preparation are state-of-the-
art for many existing scrubbers, both wet
and dry. On the other hand, the two-fluid
nozzle arrangement, because of its
requirement for a relatively flat and fine
droplet size distribution (40-50 fim),
requires some developmental work. Also
some of the chosen ESP modifications,
which use advanced technology to
achieve the required particulate removal
(e.g., the precharger and large-diameter
electrodes), require developmental work.
Hence, there is more uncertainty in the
ESP performance of Cases 1, 3, 5, and
6 than in Cases 2 and 4, which are more
conventional ESP upgrades. Because
limited laboratory scale process data are
available, process uncertainties are
associated with reagent stoichiometry,
approach temperature, and residence
time. Residence time also raises the
question of whether adequate spray
drying can occur without wetting the
ESP.
Concerning ESP performance for the
E-SOx process, computed ESP collection
efficiency and particulate mass emis-
sions are tabulated for each case in Table
1. ESP performance was assessed using
Southern Research Institute's ESP
Mathematical Model. A comparison of
Cases 1 and 2 shows that a modest
increase in plate length will achieve the
same ESP performance improvement as
the installation of novel electrodes. With
low-resistivity fly ash and reasonable
plate area after an E-SO, retrofit (SCA
of 173 ft2/1000 acfm [571 m2/1000 m3/
min] prior to ESP modifications), the
precharger offers little performance
advantage. It quickly charges the dust
particles that otherwise would be
charged within 0.6 or 0.9 m of travel
along a conventional gas passage. The
large-diameter discharge electrodes, on
the other hand, pffer a performance
advantage due to the increased intere-
lectrode electric field. In Cases 3 and 4,
with a much lower plate area after an
E-SO, retrofit (SCA of 118 ft2/1000 acfm
[391 mVlOOO mVmin] prior to ESP
modifications), a substantial rebuild of
the ESP is required to limit particulate
emissions to 0.1 lb/108 Btu (0.04342 kg/
GJ).
Table 2 summarizes the capital and
operating and maintenance (O&M) costs
for the six E-SO, cases. The capital costs
compare very favorably with other retrofit
S02 removal technologies. This is attrib-
uted to the maximum use of existing
equipment and minimal new equipment
requirements. First year O&M costs are
largely influenced by lime consumption
and delivered cost.
As a way to compare overall costs of
the systems. Table 3 presents total first
year costs on an annualized basis, as well
as costs per ton of SOz removed. The
costs per ton of S02 removed indicate
that E-SOxtechnology, if it can be suc-
cessfully commercialized, should com-
pete very favorably with other retrofit SOz
removal technologies.
In summary, the following conclusions
can be drawn:
• The mechanical system design for the
most part utilizes commercially avail-
able equipment. The only items that
pose developmental problems are the
two-fluid nozzle spray system, the ESP
precharger, and the ESP large diame-
ter electrodes.
• From an operating point of view, the
greatest concern is adequate spray
drying in the (gutted) first field of the
ESP to minimize tenacious deposits in
subsequent ESP fields.
• ESP performance on this type of
particulate needs to be verified. In
particular, the mass loadings and size
distribution of the particulate at the
end of the spray section, the ESP
electrical properties (secondary vol-
tages and currents), and gas distribu-
tion device requirements need to be
established.
• The capability of a vacuum type fly ash
handling system to continuously
remove hopper material needs to be
demonstrated. Additional equipment
requirements(for example a delumper
to prevent oversize material) need to
be defined.
• Retrofit capital costs will be very site
specific, particularly if conventional
ESP modifications (taller plates or an
outlet field) are required.
• The largest single component affect-
ing the operating cost is reagent
consumption. Therefore, process
stoichiometry is critical to cost. Also,
pebble lime shows a distinct economic
advantage over lime hydrate.
• Future research efforts should be
concentrated on optimizing the pro-
cess parameters, in particular, slurry
droplet size, Ca/S ratio, approach
temperature, and residence time
requirements.
• Because of the performance advan-
tages indicated by the precharger and
large diameter electrodes, these
technologies should be further dem-
onstrated at an appropriate equipment
scale.
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Table 1. Precipitator Performance
Case No.
SCA. ff/IOOOacfm*
Outlet Emissions, lt>/10eBtu>>
Co/lection Efficiency, %
1
173
0.08
99.59
2
201
0.08
99.56
3
163
0.08
99.57
4
148
0.07
99.62
5
171
0.08
99.57
6
172
0.08
99.58
*1 ftV/000 acfm = 3.32 m*/m3/min
"1 /b/W6Btu = 0.4342 kg/GJ
Table 2. Cost Summary
(January 1987 Dollars)
First Year Operating and
Capital Cost
Case No.
1
2
3
4
5
6
stooo
19.100
23,700
22,700
19,400
19.100
15.900
$/kW
38
47
45
39
38
32
Maintenance Cost
SlOOO/yr
6,800
6,980
6.940
6.890
7,480
6.070
Mills/kWh
2.39
2.45
2.44
2.42
2.62
2.13
Table 3. First Year Annual/zed Costs (January 1987 $1000/yr)
Case No.
Annual/zed Capital Cost
First Year O&M Cost
Total First Year
Annual/zed Cost
$/ton SOi Removed
1
3.440
6.800
10.240
345
2
4.260
6,980
11.240
378
3
4.090
6.940
11.030
371
4
3.500
6.890
10.390
350
5
3.440
7,480
10,920
368
6
2.870
6,070
8,940
301
D. Becker is with Gilbert/Commonwealth, Inc., Reading, PA 19603; and J.
DuBard is with Southern Research Institute, Birmingham, AL 35255.
Samuel L. Rakes is the EPA Project Officer (see below}.
The complete report, entitled "Conceptual Designs and Cost Estimates for E-
SO, Retrofits to Coal-Fired Utility Power Plants," fOrder No. PB 88-143 995/
AS; Cost: $14.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, V'A 22161
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
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