United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-81-018  July 1981
Project  Summary

Second  Survey  of  Dry  SO2
Control  Systems
Mary E. Kel y and S. A. Shareef
  This repor: is an update of the first
survey report on the status of dry flue
gas desulfurization(FGD) processes in
the  United   States  published  in
February  I960.  This  updated
assessment of dry  FGD  systems is
based  on review  of  current and
recently completed research, develop-
ment, and commercial activities. Dry
FGD systems covered include spray
dryers with a fabric filter or an electro-
static precip tator (ESP), dry injection
of alkaline material into flue gas
combustion of a pulverized coal/alkali
in an  ESP or a fabric  filter, and
combustion  of  coal/alkali  fuel
mixtures.
  Almost all new systems use a lime
sorbent and include a fabric filter for
particulate  collection. Removal
guarantees for SOz range between 62
and 85 percent,  depending on coal
sulfur content. Two full-scale indus-
trial spray diying systems are current-
ly in operation, with the first  large
utility system scheduled for start-up in
the Spring of  1981.
  A number of pilot-scale demonstra-
tion  programs funded  by  vendors
and/or utilities have been completed
in the past year.  The Environmental
Protection Agency (EPA) is currently
funding  three demonstration  pro-
grams (two spray drying and one dry
injection). The Agency is also funding
development  of  two  combustion
processes for SO2 control: combus-
tion of coal/limestone fuel pellets and
combustion of a pulzerized coal/alkali
fuel  mixture  in a low-NOx  burner.
Favored sorbents for continuing pilot
test programs of dry injection include
nahcolite, trona, and upgraded trona
(90 percent NaHCOs).
  This Project Summary was develop-
ed by EPA's Industrial Environmental
Research Laboratory, Research  Tri-
angle 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).


Introduction
  This report is a semi-annual updateon
dry  flue gas  desulfurization  (FGD)
processes in the United States for both
utility and industrial applications. Forthe
purposes of the report,  dry FGD is
defined as any process which involves
contacting a sulfur-containing flue gas
with an alkaline material and which
results in a  dry  waste product for dis-
posal. This includes (1) systems which
use spray dryers for a contractor with
subsequent  baghouse or electrostatic
precipitator  (ESP) collection of waste
products; (2) systems which involve dry
injection of alkaline material intotheflue
gas with subsequent baghouse or ESP
collection;  and  (3) other varied  dry
systems which are primarily concepts
that involve addition of alkaline material
to a fuel prior to combustion. Also since
the open loop, spray  dryer contractor
portion of the Rockwell  process had been
adapted for  a "throwaway" system, it
has been included here.
  The report discusses the commercial
and developmental activities for each
type of process (spray drying, dry irtjec-

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tion, and -combustion of a  coal/lime-
stone fuel mixture); an assessment of
the state-of-the-art for each type of
process;  a  brief comparison  of the
advantages  and  disadvantages  of dry
and wet  FGD systems; and, areas for
further research.
Recent Developments

  Spray drying continues to be the only
commercially applied dry FGD process.
Since the last survey was conducted in
the Fall of 1979, eight new utility andtwo
new industrial  spray drying systems
have been sold, bringing the total to ten
utility and  four industrial  commercial
systems (Table 1). All but one of the new
systems  use a lime sorbent and  all
include a  fabric filter for particulate
collection. (One industrial system uses a
sodium carbonate  solution in a spray
dryer-based system designed to remove
SOz  and HCI  from high temperature
gases.)  Removal guarantees  for S02
range between 60 and 90 percent on the
systemssoldtodate.Thefull-scale utility
systems are designed for relatively low
sulfur coals (0.5 to 1.3 percent sulfur),
while higher sulfur  coals (1.5 to 2.5
percent sulfur) are burned at two indus-
trial systems.
  Systems designs are  similar, except
for variations  between spray  dryer
designs, atomization and slaking (lime
preparation) techniques, and the use of
gas bypass or solids recycle. The major
spray dryer system  vendors offer a basic
system design with recycle  or gas
bypass.
  Ongoing bench-scale studies aim at
better understanding the mechanisms
of the reaction occurring in the  spray
dryer.
  Sodium-based sorbents are favored
for dry injection; nahcolite, trona, and
upgraded  trona appear to  be the most
viable choices. Sorbent availability and
waste disposal, as well as high stoichio-
metric  requirements and  somewhat
limited S02 removal capability (about 80
percent maximum in  tests to  date),
continue  to restrict  the  commercial
application of dry injection.
  Development of coal/limestone
pellets and combustion of a coal/alkali
fuel  mixture in a  low  NO, burner  are
continuing,  under  EPA-funding,  on
development- and  pilot-scales, respec-
tively. The minimal equipment require-
ments of these techniques make them
particularly attractive,  but large-scale
demonstrations and  full characteriza-
tion of the effects on boiler design and
operation, as well as particulate control,
remain.

Current Status of Dry FGD
Processes

Spray Drying
  Two  commercial  industrial   spray
drying systems are operational  at this
time. The Rockwell/Wheelabrator-Frye
system at Celanese  Fibers Company's
Amcelle  plant passed Maryland State
S02 compliance tests in February 1980.
The  Mikropul system  at  Strathmore
Paper has been in operation since July
1979. Although there were some initial
problems with atomization, availability
during the past 11 months of about 90
percent based on boiler demand has
been reported.
  Both  of  the  operational  industrial
systems  burn medium sulfur eastern
coals (1.5 to  3 percent sulfur) and are
designed for 70 to 85  percent S02
removal  with   lime  sorbents.  Both
designs include a spray dryer followed
by a fabric filter. The Mikropul system
uses  four  two-fluid  nozzles for
atomization and a pulse-jet fabric filter.
A single rotary atomizer and a pulse-jet
fabric  filter   are  included   in  the
Rockwell/ Wheelabrator-Frye system.
  The first large scale commercial utility
system start-up is scheduled for the
Rockwell/Wheelabrator-Frye system at
Otter  Tail  Power Company's Coyote
Station. The 110-MW Joy/Niro retrofit
system at  Northern States Power  is
scheduled to  begin operation in the Fall
of 1980,  but will be operated initially as
a demonstration unit. Testing at about
half the maximum  gas  flow  rate  is
scheduled to  begin this fall. Arvexisting
ESP will be  used until the  baghouse
portion of the system is completed in
early 1981.
  The  utility systems  guarantee S02
removals from 61 to 87 percent. Almost
all  of  the  utility systems use  a lime
sorbent and  include a  fabric filter for
collection  of  fly ash  and  the dried
product  solids.   Exceptions  are the
Coyote system which will use a sodium-
based sorbent (initially commercial soda
ash) and a  Babcock & Wilcox system .at
Laramie  River that will use four ESPs
rather than a fabric filter. Some designs
include hot or warm gas bypass and/or
recycle of spent solids mixture.
  The  differences  between  system
design include the use of nozzle or rotary
atomizers and the atomizer configura-
tion in the spray dryer. However, several
vendors claim that there are more plug-
gage or erosion problems with nozzles,
especially for lime slurries.  Nozzles,
however, generally have lower  capital
and operating costs. Some vendors offer
a "multiple atomizers per dryer" design.
This allows the  absorber to remain
operational  even  when  a  particular
atomizer has to be taken out of service.
The use of multiple atomizers in non-
FGD applications, however, is not very
common.
  Other basic system design differences
include:

  1.  use of an ESP instead of a fabric
     filter  for particufate  collection
     (most use fabric filters),

  2.  variations in size and shape of
     spray dryer  (top,  side, or bottom
     gas entry; single-  or two-point
     discharge;   horizontal  dryer   or
     cylindrical  tower with  conical
     bottom, concurrent, or  counter-
     current flow), and

  3.  reagent  preparation techniques
     for lime (less costly paste slakers
     with  grit removal  or  ball  mill I
     slakers that produce more finely ™
     ground product).

  In addition to developing a capacity for
supplying a commercial  spray  drying
system, many firms, as well as EPA,  are
involved in large scale  demonstrations
and fundamental research on the finer
points of the technology.
  There  are six major demonstration
programs that have been recently com-
pleted or are underway (Table 2). These
systems range in sjze from  8500 to
120,000 acfm. Many of the studies are
investigating various  portions  of  the
spray-dryer-based process including:

  1.  fabric filter vs. ESP collection with
     regard to collection efficiency and
     effect on SOz removal,

  2.  atomization technique,

  3.  reagent preparation techniques,

  4.  reactivity of various sodium- and
     calcium-based sorbents, and

  5.  waste solids disposal.

Key process parameters that are varied  I
to characterize and optimize the process

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 Table 1.    Key Features of Commercial Spray Drying Systems Sold to Date
 System
 (Vendor)
       Coal/SOz Removal
          Guarantees
            System
           Description
           Status
 Otter Tail Power, Coyote
 Station, Unit 1. 410 MW.
 (Rockwell/ Wheelabrator-
 Frye)
 Basin Electric Power
 Coop, Antelope Valley
 Station,  Unit 1. 440 MW.
 (Joy/Niro)
 Basin Electric Power
 Coop, Laramie River
 Station, Unit 3, 500 MW.
 (Babcock  & WHcox)
 Northern States Power,
 Riverside Station, Units
 6 & 7, 110 MW. Retrofit.
 (Joy/Niro)
 Tucson Electric, Springer-
 ville Station, Units 1 & 2
 350 MW each. {Joy/Niro)

 United Power Association,
 Stanton Station, 65 MW.
 (Research-Cottrell)
Plan River Power Author-
ity, Rawhide Station, Unit
 1, 250 MW. (Joy/Niro)

Colorado Ute Association,
Craig Station, Unit 3, 450
MW. (Babcock & WHcox)
 North Dakota lignite, 0.78%
 S average, 7050 Btu/lb,  7%
 ash, 70% SOi removal for
 all fuels.
 North Dakota lignite, 0.68%
 S average, 1.22% S maxi-
 mum. 62% SOs removal for
 average coal, 78% for
 maximum S  coal.
 Wyoming subbituminous,
 0.54% S average, 0.81% S
 maximum, 8140 Btu/lb, 8%
 ash. 82% SOz removal for
 average S coal, 90% for
 maximum S coal.

 1% S Montana Coal, 3.0 to
 3.5% S Illinois coal. SO2
 removal varying between
 70 and 90% during demon-
 stration tests.
New Mexico coal, 0.69% S.
61% SOz removal.
Low and intermediate sulfur
Montana subbituminous
coal.
 Western subbituminous-
 coal. 1.3% S 80% SOt J/.
 removal.

0.70% S, 8950 Btu/lb, 14%
ash design coal; 0.40% S,
 10250 Btu/lb, 8% ash per-
formance coal. 87% SOa
removal for design coal.
 Four parallel spray dryers
 with 3 centrifugal atomizers
 each, followed by fabric filter
 with Dacron bags. Will initially
 use commercial soda ash.
 Sorbent utilization guarantee
 of 80%.

 Five parallel spray dryers
 (one spare), single rotary
 atomizer per dryer, followed
 by fabric filter with Teflon-
 coated fiberglass bags. Lime
 sorbent with partial recycle
 of solids. Ball mill slaker.

 Four parallel reactors (one
 spare) with 12 fluid nozzles
 each. Each reactor followed
 by as ESP. Lime sorbent, no
 solids recycle.
 One spray dryer with rotary
 atomizer.  Will initially be
 demonstrated at 300,000
 acfm with ESP. Full flow
 with fabric filter. Ball mill
 and attrition slaker for lime
 sorbent.

 Spray dryer/fabric filter
 design. Lime sorbent.
 Rotary atomization.

 Spray dryer/fabric filter
 rotary atomizers, possibly
 multiple atomizers per dryer.
 Lime sorbent.

 Spray dryer/fabric filter
 design. Rotary atomizers
 Lime  sorbent.

Horizontal spray dryers with
nozzle atomizers, followed
by fabric filter. Solids recycle.
Ball mill slaker for lime
sorbent.
 Start-up scheduled for mid-
 1981.
 Start-up scheduled for April
 1982.
 Start-up scheduled for
 Spring 1982.
 Testing with existing ESP
 scheduled to start Fall 1980.
 Fabric filter on-line in early
 1981.
Unit 1 scheduled to start up
in late 1984; Unit 2 in 1986.
Start-up scheduled for 1981.
Start-up scheduled for 1983.
Initial operation in November
1982. Commercial operation
in April 1983.
Sunflower Electric Coop.
 'olcombe Station, Unit 1,
'31O MW. (Joy/Niro)
Western subbituminous
coal 80% SOi removal.
Spray dryer/fabric filter.
Rotary atomization. Lime
sorbent.
Start-up scheduled for 1983.

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Table 1.    (continued)
 System
 (Vendor)
Coal/SOz Removal
   Guarantees
  System
 Description
 Status
 Industrial
Celanese Fibers Com.,
Amcelle Plant, 65000
acfm. (Rockwell/Wheela-
brator-Frye)
Strathmore Paper,
Woronco, MA, 40000
acfm. (Mikropuf)
University of Minnesota,
2 units at 120,000 acfm
each. (Kennecott-
Development Co., Environ-
mental Products Division)

Calgon, KY, 57000 acfm.
(Joy/Niro)
   1.5 to 2.0% S eastern coals.
   SOZ removal. 70% for 1.0%
   S coal and 87% for 2% S
   coal.
   2.3 to 3% S eastern coal.
   75% SOz removal.
   Subbituminous coal, 0.6 to
   0.7% S. 70% S02 removal.
   6000-8000 ppm SOa 8000
   ppm halides. 75% S02
   removal, 90% HCI removal.
Spray dryer with single
rotary atomizer followed by
fabric filter with felt/fiber-
glass bags. Paste slaker for
lime sorbent. No solids
recycle.

Spray dryer with four two-
fluid nozzles, followed by
fabric filter with specially
finished acrylic bags.

Spray dryer with single
rotary atomizer followed by
fabric filter with fiberglass
bags. Lime sorbent.
Spray dryer/fabric filter.
Rotary atomizer. Soda ash
sorbent. Removing SOi HCI
from 1700°F gases. Solids
recycle.
Operational. Passed
Maryland State compliance
tests in February 1980.
Has achieved guaranteed
removal.
Operational. Now achieving
removal guarantee.
Commercial operation in
Fall 1981.
Under construction.
Table 2.    Major Spray Drying Demonstration Activities
  Vendor
    Location
                                                    Size
                                                     Comments
Babcock & Wilcox
Buell Envjrotech/
Anhydro

Combustion Engineering
Combustion Engineering
Ecolaire Systems, Inc.
Research-Cottrell
(Cottrell Environmental
Sciences)
   Pacific Power & Light
   Jim Bridget Station

   Colorado Springs-Martin
   Drake Station

   Northern States Power
   Sherburne County Unit #1

   Alabama Power-Gadsden
   Station (under construction}
   Nebraska Power - Gerald
   Gentlemen Station

   Public Service of Colorado
   Comanche Station
  120,000 acfm    Testing in progress.
    8,500 acfm    Also EPA-funded dry injection
                  program at same location.

  20,000 acfm    Testing complete.
  100,000 acfm    Testing to start in September
                  1980 soon after construction
                  is completed.

   10,000 cfm     Testing in progress.
mobile pilot plant

   10,000 acfm    EPA-funded, test in progress

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 Include SOz inlet concentration, sorbent
'stoichiometry,  flue  gas  temperature
 drop over the spray dryer, gas residence
 time in dryer, approach  to saturation,
 atomizer disc speed  (rotary atomizers),
 sorbent slurry or solution concentration,
 and source (spray dryer  fallout or col-
 lected  solids) and  amount  of  solids
 recycle. An additional  objective  of the
 programs is todemonstratethe system's
 capability to achieve the desired SOz
 removal on a sustained basis.
   Objectives of smaller scale  funda-
 mental research also being conducted
 include obtaining a better understand-
 ing  of  the  reaction  mechanisms and
 definition of the  most important vari-
 ables affecting the rate and degree of
 completion, characterizing the effects of
 atomized droplet size,  sorbent particle
 size, and fly ash alkalinity, and charac-
 terizing  the chemical  and physical
 stability properties  of  sodium- and
 calcium-based  waste  solids.   These
 activities are geared toward increasing
 the  applicability of spray drying to high
 sulfur coal-fired units.


 Dry Injection
   Dry injection is a very attractive alter-
 native for combined removal of SOz and
 'ly  ash  with  minimized  equipment
 requirements.  But   the  commercial
 development of thistechnology has been
 constrained due to the lack of the pre-
 ferred sorbent (nahcolite) and accept-
 able disposal practices for the sodium-
 based waste solids.
   Studies have shown that dry injection
 of nahcolite intothedirtyfluegasstream
 and collection of the solids in a fabric
 filter results in 60 to 80 percent SOz
 removal at moderate gas temperatures
 (300 to 350 °F) and inlet SOzConcentra-
 tions «2000 ppm). Nahcolite utilization
 is generally less than 80 percent but it is
 not available in the quantities required
 for  large scale commercial operations.
 Trona is less reactive than nahcolite and
 thus  higher   stoichiometries  are
 required to achieve the  same SO2 re-
 moval.  Lime and  limestone achieve
 significant SOz removal only at much
 higher gas temperatures (<600°F).
   Despite these constraints, several dry
 injection development studies are being
 conducted (Table 3). Objectives of these
 programs   include  improvement  of
 sorbent reactivity (utilization), particu-
 larly for the more available sorbents and
 characterization of the waste solids for
>acceptable  disposal  techniques.  The
 following  process  parameters  were
varied during the te
method (continuous
combination of thos
ing cycle time, inje
sorbent particle size
tration, and sorb
Sorbents being inve
lite, trona, upgradec
sodium bicarbonate
bonate.
Combustion of
Fuel Mixtures
Variations of comb
include test work or
coal/limestone pe
stokers, which is b
Battelle Laboratorie;
3.5:1 Ca:S (mole
scheduled to begin ir
a 60,000 Ib steam/I
Motors' Indianapoli
scale tests havesho
retention of the avail
the 3.5:1 Ca:S pellet
Energy and Em/in
Inc., (EERC) is alsov
tion of a pulverize
mixture in a low-NO,
Btu/hr scale. Limes
both been tested, wi
ing higher sulfur r
percent retention i
ratio of 2 to 3). The
been demonstrated
cant SOa removal. F
be carried out on the
Btu/hr scales.
Research and dev
with both processes
characterizing effec
operation, and maim
strating the degre<
achievable, and (3
effects of the resulti
ulate loading.
State-of-the-Ar
Dry FGD isanattr
st: sorbent feeding
batch, precoat, or a
3 methods), clean-
;tion temperature,
S02 inlet concen-
nt stoichiometry.
itigated are nahco-
trona, commercial
, and sodium car-

?oal/Alkali

ustion modification
the combustion of
lets in spreader
3ing conducted by
i. A 1 4-day test of a
ratio) pellet was
November 1980on
ir boiler at General
j plant. Laboratory
wn 50 to 75 percent
ablefuel sulfur with

inmental Research
orkingoncombus-
d coal/alkali fuel
burner on a 70,000
one and trona have
h limestone show-
stention (50 to 70
t a stoichiometric
technique has also
to achieve signifi-
jture test work will
1,10, and 50x106

elopment activities
are focused on (1)
s on boiler design.
enance, (2)demon-
of SOz removal
determining the
g increased partic-

Assessment
ctive alternative to
conventional wet scrubbing because it
produces a dry,  easy-to-handle waste
rather than a wet-sludge. There are also
potential capital and operating  costs
savings resulting  from  reduced
equipment requirements, lower energy
and water requirements, and relative
process simplicity.

Advantages/Disadvantages of
Dry FGD vs Conventional
Wet Scrubbing
  The advantages and disadvantages of
the three technologies discussed here
are based on  pilot plant data, limited
reported operating  experience,  and
conceptual studies.
  Technically, spray drying and wet FGD
can be compared in four areas: reagent
requirements,   energy  requirements,
operation and maintenance  require-
ments, and waste disposal requirements.
  Dry systems require a  higher stoichi-
ometric ratio of sorbent on the basis of
moles  of sorbent required per mole of
SOz removed.  Stoichiometric ratios for
dry systems, are  based on moles of
sorbent required per mole of SOz in the
inlet flue gas. Thus, a reported stoichio-
metric ratio (SR) of 1.22 for a dry system
achieving 80   percent  SOz removal
would  translate into a SR of 1.5 under
the conventional   definition for  wet
systems. Dry systems also require an
increased SR  to achieve a given SOz
removal at  increased  inlet  SOz
concentrations. This factor may pose a
technical limit to  application of  spray
drying  to high sulfur  coals, since the
amount  of   liquid   (and  therefore,
sorbent) that can be sprayed into the gas
is  limited by  the  available flue gas
temperature drop over the spray dryer.
This temperature drop  is  in turn fixed by
the inlet gas temperature, the margin of
safety  (in terms of degrees above the-
adiabatic saturation temperature) that
must be maintained, and the overall SOz
removal  efficiency  required  (which
limits  warm or hot gas bypass). The
maximum attainable solution concen-
tration or weight percent solids  in the
sorbent slurry also limits the amount of
sorbent that can be added per unit time.
  The  energy  consumption of the  dry
system should be  less than for the wet
scrubbing because of lower pumping
requirements (lower L/G) and reduction
or elimination  of the need for flue gas
reheat.
  Several vendors claim that the spray-
dryer-based systems  will have  lower
maintenance requirements and  more
operational flexibility than .comparable
wet  systems.  Spray  dryer  system
designs do not include sludge handling
equipment or large slurry recirculation
equipment.  There  is   no wet/dry
interface in the spray dryer system other
than that in the gas suspension, making
the process operation more flexible with
respect to variations in boiler load and
inlet SOz concentration.
  Economics appear to  be one  of the
major driving forces behind selection of
spray  drying  over conventional wet
systems for low sulfur coal applications.
Basin Electric evaluated the cost of a dry

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Table 3.     Current Dry Injection Programs
          Vendor
         Location
   Size
            Comments
EPA/Buell-Envirotech
Colorado Springs -
Martin Drake Station
DOE/Grand Forks Energy   GFETC Labs
Technology Center
DOE/Pittsburgh Energy
Technology Center

EPRI/KVB
PETC Labs
Public Service Company
of Colorado - Cameo Station
 4500 acfm      Testing completed in May 1980,
                EPA funded.

  200 acfm      Testing complete. Report expected
                in Fall 1980.

500 Ib coal/hr   Testing in progress.
furnace
    20MWe
Testing in progress.
system to be 15 to 25 percent less over a
35-year plant life than a wet system for
Laramie  River and  Antelope Valley,
respectively.  The  Tennessee  Valley.
Authority (TVA) found the cost of a lime-
based spray drying  system to be con-
siderably less than for a wet system. The
basis for this estimate was a new 500-
MV plant burning a  low sulfur western
coal with a 70 percent S02 removal
requirement. The higher  reagent  re-
quirements and the reagent cost differ-
ential between lime  and limestone may
result in a significant economic disad-
vantage for spray drying for high sulfur
applications.
  The same advantages with respect to
energy, and operation and maintenance
requirements  should  apply for a  dry
injection system. The equipment  re-
quirements for dry injection are lessthan
for conventional wet scrubbing or spray
drying.  However,  the  dry injection
system has a distinct disadvantage with
regard  to  reagent  utilization  and
reagent-related operating costs. Nahco-
lite utilization has been relatively low in
tests conducted to date (60 to SOpercent),
leading to fairly high  reagent require-
ments to achieve high 862 removal.
Also, sodium-based  sorbents are much
more reactive than lime or limestonebut
are considerably more expensive. The
present dry  injection technique would
then be limited to relatively low sulfur
coals.  Sodium-based  wastes,  being
readily soluble in water, also entail high
disposal  costs relative to the stabilized
lime and limestone-based wastes.
  The  combustion of coal/alkali  fuel
mixtures to control  SO2 has obvious
economic potential because of minimal
              equipment requirements and the fact
              that significant S02 removal has been
              demonstrated with limestone. However,
              both  processes  (combustion  of  coal/
              limestone pellets and firing a pulverized
              coal/limestone mixture in  a low-NO*
              burner) are still  in the early stages of
              development, and the effects on boiler
              design, operation,  and  maintenance
              have yet to be fully characterized. Also,
              these technologies are currently limited
              to specific boiler types; i.e., spreader
              stokers for the pellets  and  dry bottom
              pulverized coal boilers for thecoal/lime-
              stone fuel mixture. Fuel sulfur content
              may be limited by the sheer volume of
              reagent  required  for  higher  sulfur
              applications and the resulting effects on
              boiler  and  particulate control device
              operation.

              Areas for Further Research
                There  are several  areas requiring
              further research if dry FGDtechnology is
              to become a widely applicable alterna-
              tive   to  conventional  SO2  control
              techniques.
                Concerning spray  drying, research
              effort in the following areas could serve
              to  increase  process  applicability  for
              units firing high sulfur coal:

                1.  Improved  understanding of  the
                    absorber and downstream SO2/
                    sorbent reaction mechanisms,

                2.  improved  reagent  preparation
                    techniques,

                3.  improved understanding of fly ash
                    alkalinity utilization and investiga-
                         4.
             tion  of  various  sorbent  recycle
             schemes, and

             development of a limestone spray
             drying process.
                          In addition to research in areas (1)
                        through (3)  above, dry injection work
                        may also need to focus on improving the
                        reactivity of  sorbents that are  more
                        readily available than nahcolite and do
                        not pose the same waste disposal prob-
                        lems as those with sodium compounds.
                          Research in combustion of coal/alkali
                        fuel mixtures will  need to define the
                        important process variables, suchasbed
                        temperature, and their effect on SOz
                        retention; and further evaluate the long-
                        term effects of firingfuel/alkali mixtures
                        on boiler operation.
                                                                                       4 U.S GOVERNMENT PRINTINO OFFICE. 1801-757.012/7166

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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
          PS   0000329

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