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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