vvEPA
              United States
              Environmental Protection
              Agency
              Industrial Environmental Research
              Laboratory
              Research Triangle Park NC 27711
              Technology Transfer
Summary Report

Sulfur Oxides  Control
Technology  Series:
Flue Gas Desulfurization

Spray Dry0r Process
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Technology Transfer
EPA 625/8-82-009
Summary Report

Sulfur Oxides  Control
Technology  Series:
Flue Gas  Desulfurization

Spray Dryer Process
September 1982
This report was developed by the
Industrial Environmental Research Laboratory
Research Triangle Park NC 27711

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This summary report was prepared jointly by the Radian Corporation of
Austin TX and the Centec Corporation of Reston VA. E. D. Gibson, M. A.
Palazzolo, and M.; E. Kelly of Radian are the principal contributors. T. G. Brna
is the EPA Project Officer. Photographs taken at Argonne National
Laboratory are by Al Meyers and Ron Skidmore of the Argonne Graphic
Arts Division.    ;

Comments on or ^questions  about this report or requests for information
regarding EPA flue gas desulfurization programs should be addressed to:

Emissions/Effluent Technology Branch
Utilities and Industrial Processes Division
IERL, USEPA (MD-61)
Research Triangle Park NC 27711
This report has been reviewed by the Industrial Environmental Research
Laboratory, U.S. Environmental Protection Agency, Research Triangle
Park NC, and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the U.S. Environmental
Protection Agency, nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
COVER PHOTOGRAPH: Argonne National Laboratory power plant,
500,000-lb/h steam capacity

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Introduction
The Environmental Protection
Agency (EPA) is studying spray dryer
flue gas desulfurization  (FGD) as
part of an extensive program of FGD
technology development. In this
throwaway process (Figure 1),
sulfur dioxide (SO2) is removed from
the flue gas by an atomized lime
slurry [Ca(OH)2] or a solution
of sodium carbonate (Na2CO3). The
hot flue gas dries the droplets to
form a dry waste product while the
absorbent reacts with sulfur
dioxide in the fliie gas.  Dry waste
solids—consisting of sulfite (SO3)
and sulfate (S04) salts, unreacted ab-
sorbent,  and fly ash—are col-
lected in a fabric filter (baghouse) or
electrostatic precipitator (ESP) and
are typically disposed of by landfill.

By mid-1 981, a total of 12 utility and
11 industrial spray dryer systems had
been sold in the. United States.
All but three of these systems will use
lime as a reagent. One 100-MW
utility demonstration (at North-
ern States Power Company's River-
side Station, Minneapolis,
Minnesota) and two industrial sys-
tems (atStrathmore Paper, Woronco,
Massachusetts; and Celanese
Fibers Company's Amcelle Plant,
Cumberland, Maryland) were
operational as of mid-1981.1

The EPA has been active in sponsor-
ing the demonstration and test-
ing of spray dryer FGD: From
December 1979 to July 1980, pilot
tests were performed with various
absorbents on a unit treating
20,000 actual ft3/min (570 actual
m3/min) at the City of Colorado
Springs' Martin Drake Station.2 From
May 1980 to December 1980,
additional pilot testing was con-
ducted on a  unit treating 10,000 ac-
tual ft3/min (285 actual m3/min)
at Public Service of Colorado's
                                       Key
        H^H  Flue gas/off-gas

        H^Bll  Cleaned flue gas

        1HHJI  Absorption feed

        [P-'-~- '\  Air pollutants

        H^^H  Other systems
                                                                                         Cleaned
                                                                                         flue gas
                                                                Lime or sodium
                                                                carbonate
                                                        Flue
                                                        gas
                                                                   Disposal
                                    Figure 1.       ;

                                    Major Components of Spray Dryer FGD Process

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Comanche Station.3 These tests pro-
vided data on key process vari-
ables that affect SO2 removal.

Emission testing funded by EPA was
carried out at Celanese Fibers'
Amcelle Plant from May 1980 to
December 1980. The Amcelle testing
included 23 days of continuous
SC>2 monitoring in support of the New
Source Performance Standards
(NSPS) being developed for indus-
trial boilers.4

Spray dryer FGD is currently the only
commercially applied dry FGD
process. Other dry  FGD processes
under development include
dry injection and combustion of coal-
alkali fuel mixtures. Several fac-
tors, including mandated and
voluntary increases in coal use and
the 1979 NSPS for utility boilers, have
promoted increased research
and development and commercial
application of the dry FGD
technology.

Interest in spray dryer FGD has been
spurred primarily by the poten-
tial cost savings dry FGD offers over
conventional wet FGD, particu-
larly for low-sulfur-coal (less than 1.5
percent) applications. Advantages
of spray dryer FGD over wet
FGD systems include dry waste pro-
duction, lower initial capital
investment,  lower projected operat-
ing costs for fuels of moderate
sulfur content (up to 3 percent), and
less  process complexity, which
may  lead to greater system
reliability.

Higher absorbent cost is the major
disadvantage of spray dryer
FGD relative to wet FGD systems.
This higher  cost results from the
higher priced absorbent (lime versus
limestone) and the higher
Spray dryer exit. Coyote Electric Generating Station, Beulah, North Dakota
stoichiometric ratios necessary.
Current limits on the applicability of
spray dryer FGD stem from a lack
of data on installations firing high-
sulfur coal, although vendors report
high SO2 removal capabilities.
This summary report provides a basic
description of the spray dryer
FGD process. Both sodium carbonate
and lime spray drying are dis-
cussed, although lime is emphasized
because of the higher reagent
costs  and waste disposal problems
associated with sodium carbon-
ate and the greater commercial
acceptance of lime for  dry FGD.

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Process Description
Spray dryer FGD consists of four
major steps:

• Absorbent preparation
• Absorption and drying
• Solids collection
• Solids disposal

Solids disposal is not an integral part
of the process but is associated
with spray dryer FGD. Figure 2 illus-
trates the process flow for a
typical spray dryer FGD system.

Flue gas exiting the combustion air
preheater comes in contact
with an alkaline solution or slurry in a
spray dryer. The flue gas passes
through a contact chamber,  and the
solution or slurry is sprayed  into
the chamber with a rotary or nozzle
atomizer. The heat of the flue
gas dries the atomized droplets while
the droplets absorb sulfur dioxide
from the flue gas. The sulfur
dioxide reacts with the alkaline re-
agent to form solid phase sul-
fite and sulfate salts.

Most of the solids (and any fly ash
present) are carried out of the
dryer in the exiting flue gas. The rest
fall to a hopper at the bottom of
the dryer. With spray drying, in con-
trast to wet FGD, the flue gas is
not saturated with moisture after the
absorption step. The gas approaches
20° F to 50° F (11 ° C to 28° C) of
the saturation temperature.
                                    The solution or slurry sprayed into
                                    the dryer is pumped from
                                    an absorbent holding tank. Fresh
                                    absorbent and dilution water are
                                    added to the tank and the con-
                                    tents  are stirred as needed. In some
                                    systems, dilution  water is also
                                    added to the absorbent feed just up-
                                    stream of the spray dryer to
                                    improve control of the outlet flue gas
                                    temperature. When  lime  is the
                                    absorbent,  recycle solids from the
                                    spray dryer hopper or downstream
                                    solids collection equipment contain
                                    unreacted absorbent and are  often
                                    used  to supplement the fresh
                                    absorbent feed. Either recycle
                                    solids are slurried separately  and
                                    added to the absorbent feed just up-
stream of the spray dryer, or they
are added directly to the fresh
absorbent in the;holding tank.

Flue gas may be reheated after it
leaves the spray dryer to prevent con-
densation in downstream solids
collection equipment. To accomplish
reheat, the flue gas from the
spray dryer is mixed either with hot
flue gas from upstream of the
combustion air preheater or with
warm flue gas from upstream of the
spray dryer. The reheated flue
gas then flows to the solids collec-
tion device where the dry solids
(reaction products, unreacted
absorbent, and fly ash) are collected.
A fabric filter (baghouse) is the
most  common solids collection de-
vice, but ESP's are also  used.
When a baghouse is used, significant
absorption of sulfur dioxide
may occur during solids collection.5
Absorbent in the solids  collected
on the surface of the bags reacts with
sulfur dioxide remaining  in the
flue gas.

The cleaned flue gas leaves the
collection device and is exhausted
to the atmosphere through a stack.
Dry waste solids collected  in the
spray dryer and the collection device
are typically disposed of by landfill.


Absorbent Preparation

Absorbent solutions or slurries are
prepared on site for spray dryer
processes. Lime is the most popular
reagent, although  sodium car-
bonate may be used. Other sodium-
based reagents, such as  nahcolite
and trona ore, have also  been
shown to be effective absorbents for
spray drying.2

Sodium carbonate absorbent is pre-
pared as a concentrated  solution
and stirred in a tank. Sodium carbon-
ate is more soluble and  more reac-
tive than lime; however,  the
leachability of sodium reaction prod-
ucts can result in waste disposal
problems.

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                                                                                           Flue gas/off-gas

                                                                                           Cleaned flue gas

                                                                                           Absorption feed

                                                                                           Air pollutants

                                                                                           Other systems
                                                                                           To disposal
Figure 2.

Spray Dryer FGD Process
Sodium carbonate dissolves in water
to produce sodium ions:
Na2C03 Za 2Na+ + COg2         (1)

In lime systems,  pebble  lime (CaO)
must be slaked to produce  a
reactive lime slurry (Figure 3a). The
slaking reaction can be repre-
sented as:
              Ca(OH)2
(2)
 Slaked lime dissolves in waterto pro-
 duce calcium ions:
 Ca(OH)2 ^ Ca+2 + 20H~
(3)
Absorbent utilization can often be
improved by recycle of the waste
solids, particularly in lime systems,
where the unreacted absorbent
remaining in the waste solids can
be used. Waste solids recycle
may not be advantageous for
sodium-based systems, however,
because the more reactive sodium-
based reagent is usually com-
pletely consumed during the first
pass through the  spray dryer.


Absorption and Drying

Gaseous sulfur dioxide is absorbed
from the flue gas  in the spray
dryer (Figure 3b).  As flue gas enters
the dryer,  it disperses and imme-
diately mixes with atomized
solution or slurry. Gas phase sulfur
dioxide  rapidly dissolves into
the liquid  phase of the droplets and
reacts with the absorbent to form
solid phase salts; simulta-
neously, the solid particles are
dried by the heat of the flue gas. Flue
gas carrying solid particles exits
the spray dryer and flows to a solids
collection device. Some S02 absorp-
tion also takes place downstream
of the spray dryer.6

During absorption, the flue gas in the
spray dryer is adiabatically
humidified by water evaporated from
the solution or slurry. The amount
of water injected into the spray
atomizer with the absorbent solution
or slurry therefore controls the gas
temperature approach to the
adiabatic saturation temperature.

Process variables that affect SO2
removal in the spray dryer include ap-
proach to adiabatic saturation
temperature, the flue gas residence
time in the spray dryer, and the
absorbent stoichiometry. These vari-

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                                                                                           Flue gas/off-gas

                                                                                           Cleaned flue gas

                                                                                           Absorption feed

                                                                                           Air pollutants

                                                                                           Other systems
                                                      »\\ \
                                              / '   i   i«»
                                              ii'1,   '    \
                                                Spray dryer
         Fresh
         absorbent
         holding
         tank
   (a)
                                                               (d)
                                                                                                f
                                                                                             To landfill
Figure 3.                                           '.

Lime Spray Dryer FGD with Baghouse: (a) Absorbent Preparation, (b) Absorption and Drying, (c) Solids Collection, and
(d) Solids Disposal
ables are discussed in the Design
Considerations section.

The overall SO2 absorption reactions
for lime spray drying can be repre-
sented as:
Ca(OH)2(s)
  CaSO3 •
        S02(g) +.H2O(I) ^
              + %H2O(I)
   • 1/2H2O(s)
 3/2H2O(l) ^±
2H20(s)
                               (4)
                               (5)
                                For the sodium carbonate process,
                                the overall SO2 absorption reac-
                                tions are:
Na2C03{s) + S02,(g) J±
  Na2SO3(s) + CQ2(g)

Na2S03(s)+1/202(g)^±
  Na2SO4(s)
(6)


(7)
                                    Reaction mechanisms and mathe-
                                    matical models have  been pos-
                                    tulated for the lime spray dryer
                                    process.7-8 Equations 8 through 1 3
                                    show the series of reactions that
                                    lead to the overall reactions of
slaked lime and sulfur dioxide
(Equations 4 and 5).8

The sulfur dioxide is absorbed in
water and reacts with water to form
sulfurous acid (H2SO3) before disso-
ciating to form sulfite ions, accord-
ing to the following sequence
of reactions:
     S02(g) ;± S02(aq)

     SO2(aq) + H2O i± H2SO3

     H2S03 i± H+ + HS0  J±
                                                                                 S03-2
                                                                   (8)

                                                                   (9)


                                                                  (10)

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Argonne fly ash hopper system
Dissolved lime (see Equation 3) and
other alkaline species from re-
cycled solids orfly ash neutralize the
absorbed sulfur dioxide and
thereby drive the reactions in Equa-
tions 8, 9, and 10 to completion.

Some of the sulfite ions are oxidized
by flue gas oxygen to form sul-
fate ions:
SOT2 + 1/202
(11]
The sulfite and sulfate ions then pre-
cipitate as calcium salts:
Qa+2 -(. SCT2 + M-t-UO ^
  CaSO3-VaHzCHs)             (12)

Ca+2 + SO"2 + 2H20 j±
  CaS04 • 2H20(s)             (13)

The quantity of calcium ions avail-
able in the liquid phase of the
slurry to form the calcium salts is lim-
ited by the solubility of slaked
lime in water. Theicalcium ions react
in the liquid phase of the slurry
droplet, and they are replaced with
fresh ions from the dissolution
of additional solid phase slaked lime
(Equation 3).

The reactions leading to  the overall
reactions of sodium carbonate
and sulfur dioxide (Equations 6 and 7)
are the same as those given for
the overall reactions of slaked lime

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and sulfur dioxide (Equations 4
and 5). The sulfite and sulfate  ions
precipitate as sodium salts:
2Na+ + SO"2

2Na+ + SO"2
              : Na2S03(s)

               Na2SO4(s)
               (14)

               (15)
In lime spray dryers, carbon dioxide
(CO2) absorbed from the flue gas
can react with the slurry to form cal-
cium carbonate (CaCO3), thus
reducing the availability of  calcium
ions.
C02(g) J± C02(aq)
CO2(aq) + H2O J± H2CO3

H2C03
  2H+
Ca+2
         C032

       C032 ±;
: CaCO3(s)
(16)

(17)


(18)

(19)
The importance of carbon dioxide
absorption in lime spray drying
has not been fully investigated. Pilot
plant tests have indicated,
however, that the absorbent lost to
reaction with carbon dioxide may
be recovered by solids product
recycle.2       ;


Solids Collection

Solid particles in flue gas exiting the
spray dryer are collected by a
baghouse or ESP  (Figure 3c). The
solid particles consist of reac-
tion  products, unreacted absorbent,
and fly ash. The cleaned flue gas
leaves the collection device and is
exhausted through a stack.

When  baghouses are used, SO2 ab-
sorption continues during  the
solids collection step as unreacted
absorbent in the solid waste
reacts with the sulfur dioxide remain-
ing in the flue gas.6 This additional
SO2 absorption! can  only occur
when residual rrioisture remains in
the solid particles.9
Solids Disposal

Disposal methods for solids collected
from spray dryer processes vary
with the type of absorbent used.
Spray dryer FGD has an advantage
over conventional wet FGD in
that sludge handling equipment
(such as clarifiers, thickeners,
vacuum filters, and centrifuges) is not
required. Waste solids from spray
dryer processes have handling
properties  similar to dry fly ash and
are usually conveyed pneumatic-
ally to storage bins and then trucked
to landfill sites for disposal
(Figure 3d).


Integrated System

The foregoing steps are part of the
integrated system. Figure  3
shows how the four steps—absorb-
ent preparation, absorption and
drying, solids collection, and solids
disposal—relate to form a com-
plete lime spray dryer FGD process.

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  Design Considerations
 Several design elements must be
 considered in the selection
 and operation of a spray dryer FGD
 system:

 • Absorbent selection and
   preparation
 • Spray dryer design and operation
 • Solids collection
 • Solids recycle


 Absorbent Selection and Preparation

 The selection of an absorbent de-
 pends mainly on  reagent cost
 and availability, ease  of waste dis-
 posal, and SO2 removal require-
 ments. Most spray dryers use lime in-
 stead of sodium-based reagents
 for three primary  reasons:

 • Lime is generally the less expen-
   sive reagent.
 • Lime is the more readily available
   in most  areas.
 • Lime spray dryer wastes can  be
   disposed of more easily in an
   environmentally acceptable
   manner.

 Sodium carbonate is quite soluble in
 water. In the spray dryer environ-
 ment it is highly reactive,  which
 leads to good material utili-
 zation. The high solubility of the
 resultant sodium salts, however, cre-
 ates a waste disposal problem
 because of the potential for leaching.

 Lime, on the other hand, has a rela-
tively low solubility and is less
 reactive in  the spray dryer. Material
 utilization is lower :as a result,
 particularly when  high SO2 removal
 is required. Low utilization can
be partly overcome by modifications
in the process design; for exam-
ple, solids recycle can be used. Lime
has an advantage in that the
wastes produced can usually be dis-
posed of in landfills without
special treatment.
 Absorbent preparation techniques
 are particularly important in lime sys-
 tems. Slaking water used to pro-
 duce lime slurries for spray drying
 must be of good quality.2 Low-
 solids water produces small,
 highly porous, reactive particles.
 High-solids wastewater, such as
 cooling tower blowdown, produces
 large slurry particles that are less
 reactive and decrease lime
 utilization.

 Two types of slakers can be used to
 prepare lime slurries: ball mill slak-
 ers and paste slakers.10 Ball  mill
 slakers are more popular because
 they generally produce a more
 finely ground absorbent and contrib-
 ute to a more reactive slurry. Paste
 slakers offer a potential benefit,
 however, in that the resulting slurry is
 somewhat less abrasive than the
 slurry from ball mills and may
 reduce wear on pipes and pumps.
 Slaking temperature, amount of
 water, and lime purity also affect the
 quality of the slaked lime slurry.2


 Spray Dryer Design and Operation

 Primary considerations in spray dryer
 design  and  operation include  the
 quantity of flue gas to  be cleaned,
 the inlet flue gas temperature
 and moisture content, the flue gas
 SO2 content, and the desired SO2
 removal efficiency. These fac-
 tors determine the physical size
 of the dryer and the amount of
 absorbent required. Thus, they affect
 capital and operating costs
 significantly.

 The design of the spray dryer contact
 chamber, the flue gas disperser,
 and the solution or slurry atomizers
 is important to efficient removal
 of sulfur dioxide. Contact chamber
 volume must provide a flue
 gas residence time that maximizes
 SO2 removal and permits ade-
 quate drying of the absorbent
 particles. Most lime spray dryers
 have a flue gas residence time of 10
to 12s.
8

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The flue gas disperser and the spray
atomizer should provide for inti-
mate mixing of the flue gas and the
atomized droplets. Complete
mixing aids the mass transfer of sul-
fur dioxide to the droplets. There-
fore, the flue gas disperser should
ensure that the gas flow pat-
terns within the contact chamber
bring all the flue gas in contact with
the atomized spray. The atomizer
should also  produce small
droplets  to maximize the droplet
surface area available for SO2 absorp-
tion. If the droplets are too small,
however, they may dry out
before sufficient S02 absorption
has occurred.

Atomizer types used in spray dryer
FGD processes include rotary
atomizers and two-fluid nozzles.
Each type has its advantages and
disadvantages, although most
vendors  prefer rotary atomizers.1
Rotary atomizers use a rapidly spin-
ning disk (up to 20,000 r/min) to
produce a fine droplet mist in
the spray dryer. The size of the drop-
lets .varies, with the velocity and
diameter of the rotating disk and is
reasonably independent of the
liquid feed rate to the atomizer. Thus,
rotary atomizers have one  impor-
tant advantage  in that  droplet size
can be kept the same regardless
of the feed rate of absorbent solution
or slurry. This advantage is impor-
tant because the required absorbent
feed rate varies with fluctuations
in the flue gas flow rate and the
 inlet SO2 concentration. The pri-
 mary disadvantage is that rotary
 atomizers are mechanically complex
 compared with nozzles. A second,
 potential disadvantage is plugging of
 the atomizer orifices; many ven-
 dors minimize this problem through
 improved disk design.11

 Two-fluid nozzles use high-pressure
 air (or steam) to break up the  ab-
 sorbent solution or slurry  into a fine
 mist of small droplets. These
 nozzles have two main advantages:
they have no moving parts, and
large passages for liquid can be used
to minimize plugging. Their pri-
mary disadvantage is that the change
in absorbent liquid feed rate al-
ters the droplet size, which varies the
SO2 removal efficiency. This
problem  is somewhat alleviated by
multiple  nozzles; but more operat-
ing problems seem to  occur
with nozzle atomizers  than with
rotary atomizers;11

Further commercial experience with
spray dryer FGD systems is
needed for a full assessment of the
drawbacks and benefits unique to
each type of atomizer.

Design variations in the placement of
flue gas  discharge points  in the
spray dryer, the type of gas disperser,
and the  numberof atomizers are
based on vendor experience or
preference. Because commercial
experience with these varia-
tions is lacking,itechnical compari-
son is difficult. For example, flue
gas discharge points are usually near
either trie.top or the bottom of the.
spray dryer hopper. Placing the
gas discharge point near the top may
be advantageous because plugging
of the spray dryer hopper would
not interfere with gas  flow unless
the hopper were to become com-
pletely filled. More operating experi-
ence is needed  at full-scale utility
FGD units to determine the
likelihood of hopper plugging.

Several important process or operat-
ing variables affect the design
and performance of the spray dryer,
including: flue gas  approach to
saturation temperature at the  dryer
outlet, absorbent stoichiometry,
and inlet SO2 concentration.The out-
let flue gas temperature is con-
trolled by the amount of water
injected into the spray atomizer
with the absorbent solution or slurry.
As this temperature approaches
the adiabatic saturation temperature,
the residual moisture  level in the
spray-dried solids increases. The
 residual  moisture aids the mass trans-
fer of unreacted absorbent from
the center of the particle toward the
surface, where it.can react with
the absorbed sulfur dioxide. Absorb-
ent is utilized more readily at the
particle's surface because of
the greater area available for SO2 ab-
sorption. Thus,  SO2 removal rates
and absorbent utilization increase as
the approach to saturation is
narrowed. Most spray dryers are
operated with an approach between
20° F and 50° F (11 ° C and 28° C)
above the adiabatic saturation
temperature.1

The closeness of the approach to sat-
uration is restricted by the need to
avoid condensation in downstream
solids collection equipment. The
restriction can be overcome in part if
warm or hot gas is bypassed
around the spray, dryer to reheat the
dryer outlet gas, but the amount of
untreated gas used for this purpose
may limit removal  of sulfur di-
oxide in  the spray dryer process.
Also, an energy penalty is associated
with the use of hot gas from up-
stream of the combustion air pre-
heater because less energy is
available for air preheat.

Absorbent stoichiometry directly
affects SO2  removal in the spray
dryer. Stoichiometry for dry scrub-
bing has been  defined as moles of
fresh sorbent introduced to the
system divided by moles theoretically
required for complete reaction
with all the sulfur dioxide entering
the system, whether or not all
the sulfur dioxide  is removed. This
definition results in a lower
stoichiometric ratio than does the
conventional definition for wet
scrubbing, which is based on moles
of sulfur dioxide removed by the
system. For example, a reported stoi-
chiometric ratio of 1.2 for a dry sys-
tem achieving 80  percent SO2
removal  would  be equivalent to
1.5 for a wet scrubbing system.

The absorbent stoichiometry may be
raised by an increase in the
amount of absorbent fed to the
spray dryer. A higher absorbent stoi-
chiometry enhances removal of

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  Coyote soda ash holding tank (left) and control panel (right)
  sulfur dioxide. This method is limited
  by two factors, however. First,
  absorbent utilization decreases with
  increased stoichiometry, raising
  absorbent and disposal costs.
  Second, an upper limit is reached on
  the solubility of the absorbent or
  on the percent by weight of absorb-
  ent solids  in the slurry. Decreased
  absorbent utilization can be
  partly overcome by operation of the
  spray dryer at a  closer approach to
  the saturation temperature and
  by recycle of the collected
  solids. Preliminary tests at the
  Northern States  Riverside demon-
  stration system have shown
  that overall S02  removals of 80 per-
  cent can be achieved (spray dryer
  and baghouse) with an absorb-
  ent stoichiometry of less than 1.2 at
  an inlet S02 concentration of
  about 900 ppm.12
The effect of inlet SO2 concentration
on  spray dryer performance has
not been fully investigated; however,
over the range of concentrations
studied (500-1,500 ppm), increases
in concentration only moderately
decrease SO2 removal.2'5 The range
studied corresponds to the
concentrations of sulfur dioxide in
flue gas from boilers using low-
to moderate-sulfur coals (gen-
erally less than 3 percent sulfur by
weight). Additional information on
the effects of higher SOZ con-
centrations will soon be available
from testing at one Utility demonstra-
tion (Northern States' Riverside
Station) and at three industrial sys-
tems [Department of Energy's
(DOE) Argonne National Laboratory,
Argonne, Illinois; Strathmore
Paper; and General Motors' Buick
Division, Flint, Michigan].


Solids Collection

The choice of the paniculate collec-
tion device is influenced by SO2
removal during particulate collection
and by vendoror customer pref-
erence. Fabric filters (or baghouses)
are the  most widely used collec-
tion devices in commercial
spray dryer systems sold as of mid-
1 981. Of 23  utility and industrial
systems sold, only 1 specifies
an ESP. The primary advantage of,
baghouses over ESP's is that
unreacted alkalinity in the  solids
10


-------
collected on the bag surface can re-
act with sulfur dioxide in the
flue gas. Studies have shown that
baghouses can account for 10  per-
cent of the total sulfur dioxide
removed by a system.2 Baghouses
also may be more economical
and effective in  collecting highly
resistive fly ash; they can achieve
high particulate  removal efficiencies
regardless  of the type of coal
burned, whereas the highly resistive
fly ash from low-sulfur western
coals may be more difficult and costly
to collect using  ESP's.11

The ESP's  have  a  potential advan-
tage over baghouses because
they are less sensitive to condensa-
tion and, therefore, the spray
dryer can be operated closer to the
saturation temperature, which
results in higher S02 removals across
the spray dryer.  The primary dis-
advantage of ESP's is that they may
not be able to meet stringent
particulate emission regulations if
the inlet particulate concentrations
become too high.13 Future testing
of full-scale systems  should pro-
vide more  information on the
maximum inlet concentrations  that
can be expected.
Baghouses collecting spray drying
solids usually use fiberglass
filter bags with pulse-jet cleaning
mechanisms in industrial applica-
tions and reverse-air cleaning
mechanisms in utility applications.1
Solids Recycle \

Recycling waste solids to the spray
dryer reduces raw material re-
quirements because unreacted
absorbent is  consumed during
recycle. Moreover, if the fly ash is
high in available alkalinity, the
available alkaline species may aid SO2
absorption by reacting with sulfur
dioxide in the flue gas.9'11 The
amount of alkalinity available in the
fly ash depends; primarily on the
type of coal fired.

The type of absorbent and the
amount of alkalinity available in the
fly ash are important in determin-
ing the benefits and economics of
solids recycle for  a particular
spray dryer application. Solids re-
cycle is particularly beneficial
for lime systems because utilization
is low for once-through absorb-
ent. Solids recycle can increase SO2
removal in 1ime:spray dryers as
much as 10  percent at a given
absorbent stoichiometry.4 Thus
solids recycle can achieve a required
SO2 removal with less raw material.
As a rule, solids recycle is not bene-
ficial in sodium  carbonate sys-
tems because utilization is relatively
high for once-through  absorbent.
The potential reduction in raw mate-
rial requirements may  not justify
the cost of a waste solids re-
cycle system.

Maximum benefit from available fly
ash alkalinity is pbtained by slurrying
the waste recycle solids separately
from the fresh absorbent feed.
The recycle slurry is then mixed with
the fresh absorbent at the point of
injection into the spray dryer.
If the recycle solids are slurried sep-
arately, the alkaline species
dissolve more readily and may then
react with sulfur dioxide in the
flue gas to reduce absorbent
requirements.2

As a further benefit, the fly ash in the
waste  solids recycle may also
act as  a surface catalyst for absorb-
ent utilization by providing an
alternative site for precipitation of
the absorption reaction products,2'6
thereby decreasing the solid
deposits on the absorbent parti-
cles. Absorbent utilization is improved
because more absorbent sur-
face area is available for reaction
with sulfur dioxide.
                                                                                                          11

-------
  Environmental
  Considerations
 Important environmental considera-
 tions in spray dryer FGD include
 SO2 and particulate removal capabil-
 ities and dry waste product dis-
 posal properties. In both pilot-  and
 demonstration-scale  testing
 with low-sulfur fuels, the spray dryer
 FGD process has consistently
 shown the ability to meet the NSPS
 for removal of sulfur dioxide from flue
 gas exiting coal-fired boilers.
 Most available data are from  pilot-
 scale applications of-the process
 because only one utility-size
 demonstration system  and two
 industrial-size commercial systems
 are operational.

 The EPA funded pilot-scale testing at
 Colorado'Springs' Martin Drake
 station. These tests [20,000 actual
 ft3/min (570 actual m3/min)]
 showed overall SO2 removal effi-
 ciencies above 75 percent for a lime
 stoichiometry of less than 1.6 mol
 lime permol inletsulfurdioxide.2The
 tests were conducted at inlet SO2
 concentrations of 1,500 ppm,
 without solids recycle,  and at an ap-
 proach to saturation temperature
 of 20° F (11 ° C). In other tests,
 fly ash from high-sulfur eastern coals
 was added to the flue  gas along
 with sulfur dioxide to simulate high-
 sulfur (about 4 percent) coal appli-
 cation; SO2 removals greater
 than 90 percent were measured
 with a lime stoichiometry of 1.6 mol
 lime per mol inlet sulfur dioxide.14
 These tests were conducted at
 inlet SO2 concentrations of
 4,000 ppm, with 50 percent solids
 recycle, and at an approach to satur-
 ation temperature  of  20° F (11 ° C).

 Preliminary tests oh the lime utility-
 scale (100-MW) demonstration
 system at Northern States' Riverside
 Station showed an overall S02 re-
 moval efficiency of 94 percent at an
 absorbent stoichiometry of less
than 1.4. These tests were
 conducted at an inlet S02 con-
 centration of about 840 ppm, at an
approach to saturation  temper-
ature of 18° F (10° C), and with solids
 recycle.12          ;
Test results are also available from
two commercial lime spray
dryer installations. Compliance
test results from the Strathmore
Paper system, which treated flue gas
produced by combustion of
moderate-sulfur coal, show an aver-
age S02 removal  efficiency of
92 percent.15 With  coal averaging
2 percent sulfur,4 an average
S02 removal of 70  percent was
achieved at the Celanese Fibers sys-
stem, based  on 23  days of accept-
able continuous SO2 monitoring
data obtained over  a 33-day
test period. These tests were con-
ducted without solids recycle.

Further operating experience will be
required to reach optimal S02
removal efficiencies in full-scale
spray dryer systems. The available
test results, however, have provided
data sufficient for the design  and
sale of 12 utility and 11 indus-
trial spray dryer systems.

All the spray dryer systems sold to
utilities specify low-sulfur west-
ern coals or lignite  (average
sulfur content of 1.5 percent or less).
The SO2  removals guaranteed for
these systems range from 61  to
87 percent, depending on the coal
sulfur content.1

So far, for fuels with more than
1.5 percent sulfur, spray dryer FGD
applications  have  been for industrial
boilers. The overall cost effect of
the extra absorbent needed for high-
sulfur coal application is less
severe in these smaller systems than
in utilities, which  must treat larger
quantities of flue gas. Many of
the planned and operating industrial
spray dryer systems are applied to
higher sulfur (up to 3.5 percent)
eastern coals. These systems  have
SO2 removal guarantees from
70 to 90 percent.3
12

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High participate removal efficiencies
(99 percent or greater) can usually
be obtained by ESP's or fabric
filter baghouses !n coal-fired applica-
tions. In spray dryer systems, both
ESP's and baghouses should be
capable of achieving high par-
ticulate removal. The baghouse may
be advantageous, however, in
locations where environmental con-
siderations require low outlet par-
ticulate concentrations, such as
0.01 gr/ft3 (0.02 g/m3). Inlet dust
loadings as  high as 25 gr/ft3
(57 g/m3) require an ESP efficiency
of 99.96 percent—a value that
may be difficult to achieve  consist-
ently with an ESP in a power plant.13
Properly designed  baghouses,
on the other hand, should be able to
meet an outlet emission of 0.01 gr/ft3
(0.02 g/m3), regardless of inlet
loading. In addition, the baghouse
will usually  be more reliable in
achieving  low opacity.9

Spray dryer  FGD systems collect the
fly ash together with the FGD
reaction products.  The composi-
tion of the waste solids varies
depending on the coal type and the
operating  conditions of the proc-
ess. Waste product from a  spray
dryer system applied to a boilerfiring
low-sulfur coal consists of approx-
imately 75 percent fly ash, 1 5 to
20 percent calcium sulfite and sul-
fate salts, 5 percent moisture,
and less than 5 percent unreacted
sorbent.16

Waste solids from  spray dryer sys-
tems have handling properties
similar to  fly ash, and are therefore
more  easily  disposed of than
wastes from conventional wet FGD
systems. The dry waste from lime
spray drying exhibits physical
properties suitable for on-site land-
fill disposal. The waste solids
are nonhazardous under current EPA
Resource Conservation and
Recovery Act guidelines—their
leaching characteristics have been
determined andlare well within
the guidelines set by EPA for
definition of a nonhazardous
waste.16-17

Fly ash from low-sulfur western coal
exhibits cementltious (pozzo-
lanic) properties;.  Fixation reactions
associated with|these properties
have been studied to determine the
landfill characteristics of wastes
from spray dryer systems applied  to
boilers firing low-sulfur west-
ern coals. The addition of about 20
percent water is:reported to give the
most desirable  landfill disposal
properties for solid wastes contain-
ing fly ash from low-sulfur western
coals.16'17

Another method for disposing of lime
spray drying wastes  has been de-
veloped  by Niro, Atomizer, Inc.
(patent pending). The dry waste
product is combined with 10
to 20 percent water  and pelletized
to between 2.5 and  3 times its
bulk density. The resulting syn-
thetic gravel (Nirok) is reported to
have a cured density of about
120 Ib/ft3 (1,900 kg/m3) and a
compressive strength of over 10,000
Ib/in2 (69,000 kPa). It can be  used
in concrete mixes, cement founda-
tions, and roadbase compositions.16

Solids from sodium-based spray
dryer systems are not consid-
ered suitable for disposal by conven-
tional landfill methods. The
sodium  salts produced by the  proc-
ess are  highly Water  soluble, and
a lined landfill is  necessary to
prevent them from leaching into the
ground water.11-18 The Sinterna®
Process has been developed to
stabilize these wastes by converting
the untreated waste material to
pellets with reduced leaching poten-
tial, but the process.does not
appear to be economically desir-
able.17 Wastes from lime-based
systems are economically and envi-
ronmentally preferable, therefore,
because they can be landfilled
without special treatment.

Current and planned disposal
methods for spray drying wastes
parallel established practices for wet
FGD systems. Wastes from the
only commercial  systems in opera-
tion, at Celanese Fibers' Amcelle
Plant and Strathmore Paper, are
being trucked to  landfill, as are the
wastes from the demonstration
at Northern States' Riverside
Station. Tentative waste dispo-
sal plans of utilities with con-
tracts for commercial systems range
from dry landfill to clay-lined
ponds for wetted solids. Eight util-
ities have reported disposal plans as
follows:1

•  Natural clay-lined landfill
•  Landfill lined with PVCa
•  Landfill with fixation
•  Wetted transport to landfills  (two
   utilities)
•  Wetted transport to clay-lined
   pond
•  Unspecified landfills (two utilities)

Studies by EPA,  DOE, the Electric
Power Research Institute (EPRI), and
many vendors are being con-
ducted to characterize further the
physical and chemical properties of
the dry waste. As more commer-
cial systems begin operation, these
efforts should gain momentum
and result in a broader data base.
                                                                        aPolyvinyl chloride.
                                                                                                        13

-------
 Status of Development
The application of spray drying to
FGD developed from earlier commer-
cial uses of spray dryers. These
devices had been used for many
years in a wide range of drying, reac-
tion, and purification processes
in the chemical industry. Most FGD
spray dryer designs are direct
adaptations of the standard designs
used in other industries, such as
the food processing  industry.11

Spray dryer FGD also evolved in part
from early dry injection FGD
studies initiated in the 1 960's. In
the systems studied, dry absorbents
were injected into the flue gas,
and the reaction products were col-
lected  in fabric filter baghouses
or ESP's. Results from many of these
early studies were disappointing,
but interest in the technology
continued because of the potential
benefits of such uncomplicated
approaches to FGD.

Unlike efforts in the development of
wet FGD, where the Government
has predominated, early efforts in
spray dryer FGD were supported pri-
marily by industry.^Several com-
mercial dry scrubbing systems had
been sold  before the Govern-
ment started to support research
and development in this area.18 Early
test work included that of Atomics
International with its aqueous
carbonate  process at Southern
California Edison's Mohave Station,
Laughlin, Nevada, in 1972; testing
involved a pilot-scale demonstration
of the spray dryer for S02 removal.
In 1 974, Niro Atomizer initiated tests
of spray drying for FGD applica-
tion at its Copenhagen facility, inves-
tigating various alkaline sorbents
such as lime, limestone, and sodium
carbonate.

A major impetus to the development
of spray dryer FGD occurred in
 1977 when the Basin Electric Power
Cooperative expanded dry injection
studies at its Leland Olds Station
to include spray drying. Basin Elec-
tric requested bids' for new plants to
 be fueled with western coal and
 lignite. Several vendors built and
operated small pilot units to prequal-
ify as bidders. Test units were
operated at Basin Electric's Neal
and Leland Olds Stations in
North Dakota and at Otter Tail Power
Company's Hoot Lake Station in
Minnesota. These were the first U.S.
applications of the spray dryer for
a nonregenerable FGD system,
and three contracts were awarded in
1 978 on the  basis of the tests.
The recipients were Babcock  &
Wilcox and two joint ventures: Joy
Manufacturing Company and Niro
Atomizer (Joy-Niro), and Rock-
well International and Wheelabrator-
Frye, Inc. (Rockwell-WF).

In  the past few years several com-
panies and consortia have become
active in dry FGD. Thirteen
firms currently offer commercial
spray dryer systems, and several
have contracted to build commercial
units. All the utility units are for
lignite or low-sulfur western coal
applications,  where removal
efficiencies and absorbent consump-
tion are usually lower than with
high-sulfur coals and, in some cases,
the alkalinity of the fly ash can
supplement the absorbent.11

As of mid-1981, 12 utility systems
(totaling over 3,800 MW)  and
11 industrial systems had been sold
(Tables 1 and 2).1 These systems
are mostly lime spray dryer and bag-
house combinations. Only two
commercial systems, both applied to
industrial boilers, were fully oper-
ational: the Rockwell-WF system
at Celanese Fibers' Amcelle
Plant and  Mikropul Corporation's
system at Strathmore  Paper. The
first utility system to become opera-
tional will likely be another
Rockwell-WF system, this one at
Otter Tail  Power's Coyote  Station,
Beulah, North Dakota.  Startup
procedures at Coyote  were initiated
in January 1 981.1 Two of the
most recent industrial systems sold
will be applied to boilers firing high-
sulfur coal. At least five utilities
have specified dry FGD only or are
considering either dry or wet FGD for
14

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Table 1.
Commercial Utility Spray Dryer FGD

Process, utility, and station

Lime:
Basin Electric Power Coop.:
Antelope Valley, Beulah ND:
Unit 1 	
Unit 2 	
Laramie River, Wheatland WY:
Unit 3 	
Colorado Ute Electric Association: Craig
Station, Craig CO Unit 3
Marquette Board of Light & Power: Shiras
Station, Marquette Ml, Unit 3 	
Platte River Power Authority: Rawhide
Station, Fort Collins CO, Unit 1
Sierra Pacific Power & Light: North Valmy
Station, Valmy NV 	
Sunflower Electric Coop.: Holcombe Sta-
tion, Hays KS Unit 1
Tucson Electric: Springerville Station,
Tucson AZ:
Unit 1 	
Unit 2 	
United Power Association: Stanton Sta-
tion, Stanton ND 	
Sodium carbonate:
Otter Tail Power: Coyote Station, Beulah,
ND Unit 1

Systems Sold as of
FGD units ;
Spray dryers;
(MW) Atomizers
per dryer
430 5° 1 rotary
430 5C 1 rotary'
500 4° 1 2 nozzles
450 NA Nozzlesd
44 1 1 rotary
250 NA Rotaryd :
270 3 3 rotary
310 NA Rotaryd
350 NA Rotaryd
350 NA Rotaryd
65 NA Rotaryd •
41 0 4 3 rotary •

Mid-1981
Gas
treated
actual
ft3/min)
2 200
• 2 200
2 810
NA
226
NA
1,200
NA
NA
NA
NA
1 890


Coal

Type % Sa



subbitu-
minous
nous
Western 0 5
subbitu-
minous
Western 1 .3
subbitu-
minous
Subbitumi- 04-1 0
nous
Western 1 3
subbitu-
minous
subbitu-
minous
subbitu-
minous
Lignite (a)




% SO2 Solids
removal collection .
u • • i -i • b date
(design) device
62 FF 1 982
62 FF 1 985
82 ESP 1 982
87 FF 1983
80 FF 1 982
80 | FF 1983
76 FF 1984
80 FF 1 983
61 FF 1 984
61 ' FF 1984
NA FF 1 981
70 FF 1 981

8Average.                                                         '                                     '        !
bFF = fabric filter; ESP = electrostatic precipitator.                    :
clncludes 1 spare.
dNumber not available.                                            i
eLow to medium.              . .            .                       :                                 •
Note.—NA = Data not available.                                     i                                             ;
SOURCES: Kelly, M. E., and S. A. Shareef, Third Survey of Dry SO 2Contrbl Systems, EPA 600/7-81-097, NTIS No. PB 81-21 8976, June 1981.Gehri,
Dennis, Rockwell International, personal communication, Sept. 25, 1981.
                                                                                                                                   15

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 Table 2.
 Commercial Industrial Spray Dryer FGD Systems Sold as of Mid-1981
FGD units
Process, company, and station
Limo:
Argonne National Laboratory, Argonne II 	
ColaneSQ Fibers: Amcelle Plant, Cumber-
land MD 	

Fairchild Air Force Base, Spokane WA:
Unit 1 	
Unit 2 	
Unit 3 	
General Motors: Buick Division, Flint,
Ml 	

University of Minnesota: Unit 1 , Minneap-
olis MM 	

Size
(1 ,000
Ib/h
steam)
170
110
170
110
11O
110
450
85
NA
Spray dryers
No.
1
1
1
1
1
1
1
1
2
Atomizers
per dryer
1 rotary^
rotary,
rotary
rotary '
rotary'
rotary,
1 rotary
4 nozzles
1 single
nozzle.
Gas
volume
treated
(1 ,000
actual
ft3/min)
75
65
NA
46.5
46.5
46.5
167
40
120
Coal
Type
Illinois
bitu-
minous
Eastern
NA
NA
NA
NA
Indiana
bitu-
minous
Eastern
Subbitu-
minous
%sa
3.5
1.5-2.5
1.0
1.0
1.0
1.0
1 .0-3.0
2.0-3.0
0.6-0.7
%S02
removal
(design)
79
70-85
NA
85
85
85
70-90
75
70
Solids
collection
device6
FF
FF
FF
FF
FF
FF
FF
FF
FF
Startup
date
1981
1980
1981
1983
1983
1983
1982
1979
1981
 Sodium carbonate:
    Calgon, Catlettsburg KY	     NA
    University of Minnesota: Unit 2, Minneap-
      olis MN	     NA
                                                    1 multi-
                                                    ple
                                                    nozzle
        1   1 rotary,     57

        1   1 rotary     120
                              NA
Subbitu-
  minous
          1.0-2.0

          0.6-0.7
75

75
FF

FF
1981

1981
 'Average.
 bFF - fabric filter.
 Now.—NA = not available.                                  !
 SOURCES: Kelly, M. E.,and S. A. Shareef, Third Survey of Dry SO2 Control Systems, EPA 600/7-81-097, NTIS No. PB 81-218976, June 1 981. Steele,
 Gone, Niro Atomizer, personal communication, July 1 6, 1981.
 new units that will go on line
 before the end of the decade.1 There
 are also two important full-scale
 (100-MW) utility demonstrations:
 theJoy-Niro lime system at Northern
 States' Riverside Station (now
 operational) and the Flakt, Inc.,
 lime system adapted for lime or
 sodium carbonate at  Pacific Power
 and Light Company's Jim Bridger
 Station, Rock Springs, Wyoming
 (planned for startup in 1982).
Current research and development
efforts are examining process
variables affecting SO2 removal, as
well as application of the tech-
nology to high-sulfur coal. Studies by
EPA, DOE, EPRI, vendors, and
others include assessments of the
following:7

• Importance of lime stoichiometry
• Effect of flue gas approach to
  saturation temperature
• Effect of waste solids recycle from
  the spray dryer and baghouse
        • Refinements of atomization and
          sorbent preparation techniques
        • Role of alkalinity in fly ash removal
        • Need for reheat

       The technical and economic feasibil-
       ity of the vendors' approach to
       design features such as type
       of atomizer, degree of approach to
       saturation, particulate collection
       method, and waste recycle remain to
       be demonstrated. Current trends
16

-------
suggest that many new systems will
use a lime slurry with rotary atom-
izers, partial flue gas bypass
for reheat, and fabric filter collection.
Most of these spray dryer FGD
units will  likely be limited to low-
sulfur-coal conditions, because the
cost of lime spray drying relative
to wet limestone scrubbing for high-
sulfur-coal applications  is still
uncertain.
The rapid growth of spray dryer FGD
results partly frorn its potential
technical and economic benefits
and from the increased use of west-
ern coals by utilities, for which
spray drying is especially  suited.
Also important has been the broad
base of spray dryer and particu-
late collection technology from
which spray dryer FGD directly
evolved. The April 1981 Dis-
trict Court decision upholding the
NSPS for utility boilers has been a
recent impetus to the technology.
The NSPS include a variable
percentage SO2 removal provi-
sion that requires at least 70 percent
S02 removal for boilers firing coal.
Spray drying provides a potentially
lower cost alternative to wet FGD
for low-sulfur-coal applications.
                                                                                                        17

-------
                                        Raw Materials and Utilities          • Electric energy for auxiliary equip-
                                                                                  ment such as agitators/ con.
                                        The raw material requirements of        veyors, and feed preparation
                                        spray dryer FGD processes are           equipment
                                        for lime or sodium  carbonate re-      prQcess wgter     irements  include
                                        agent, and the ut.lity needs are       dj|ution wgter for absorbent  prep.
                                        for energy and process water. Energy   ^.^ and for sprgy dryer Qut|et f|(je
                                        requirements include:                 ggs temperature control. In lime
                                        • Pumping energy to move absorb-   spray dryer systems, slaking
                                          ent solution or slurry to the        water accounts  for 10 to  30 per-
                                          spray dryer atomizer                cent of the total process water
                                        • Electric energy forflue gas booster   requirements.
                                          blowers  (forced- or induced-
                                          draft fans)                          Table 3 gives the estimated annual
                                        • Electric energy to rotate the        raw material and utility requirements
                                          atomizers (if rotary type)           of sodium carbonate and  lime
                                        Table 3.          !

                                        Estimated Annual Raw Material and Utility Requirements for Lime and
                                        Sodium Carbonate Spray Dryer FGD Processes: New 500-MW Coal-Fired
                                        Power-Generating  Unit

                                                          ,         Component                              Requirement

                                        Low-sulfur coal:     ;
                                            Lime spray dryer system:a'b
                                                Raw materials (lime, 1,000 tons)	       1 °->
                                                Utilities:    '.
                                                    Fuel (1,000 gal)	••      1 63'8
                                                    Process water (106 gal)	• •       82-2
                                                    Electricity (106 kWh)	• •,• •       39-6
                                            Sodium carbonate  spray dryer systern:b'°
                                                Raw materials (sodium carbonate, 1,000 tons)	       18.4
                                                Utilities:
                                                    Fuel (1,000 gal)	      1 65-7
                                                    Process Water (10s gal)	       70-2
                                                    Electricity (106 kWh)	• •       41 -2

                                        High-sulfur coal: Lime spray dryer system:d
                                            Raw materials (lime, 1,000 tons)	• •      112.4
                                            Utilities:
                                                Fuel (1.000 gal).   	      ^
                                                Process water (106 gal)	      143-6
                                                Electricity (1Q6 kWh)	       42'7
                                                Energy for reheat  (106 Btu)	      137-4

                                        "Warm gas bypass reheat. Stoichiometry of 1.2 mol lime per mol S02 absorbed. Landfill disposal
                                         1 mi from FGD facilities.
                                        bCoal with  0.7% S. Meets emission regulation of 1.2 Ib S02/106 Btu with 70% S02 removal.

                                        °No gas bypass. Stoichiometry of 1 mol sodium carbonate per mol SO2 absorbed. Lined-
                                         pond-disposal 1 mi from FGD facilities.
                                        dHot gas bypass reheat. Coal  with 3.5% S. Stoichiometry of 1.8 mol lime per mol SO2 absorbed.
                                         Includes electrical requirements of fabric filter baghouse. Meets emission regulation of
                                         1.2 Ib S02/106 Btu with 90% S02 removal. Landfill disposal 1 mi from FGD facilities.

                                         Notes.—Midwest plant operating 5,500 h/yr.
                                         SOURCE- Burnett T X., and K. D.Anderson, Technical Review of Dry FGD Systems and Economic
                                         Evaluation of Spray Dryer FGD Systems, EPA 600/7-81-014, TVA EDT-1 27, NTIS No. PB 81 -
                                         206476, Feb. 1981.
18

-------
spray dryer processes for a new
500-MW power-generating unit
firing low-sulfur coal.11  System de-
sign and operating conditions
affect the requirements and must
be considered for each specific
installation. Absorbent needs vary
with the desired SO2 removal, the
coal sulfur  content, the use of
recycle, and (if recycle is used) the
available alkalinity in the fly  ash.
Fuel requirements given are  for
trucking dry waste solids to  the
landfill site. The table includes elec-
trical needs of the fabric filter
baghouse.

Spray dryer systems  using hot  gas
bypass  (from upstream of the
combustion air preheater) to reheat
the flue gas incur an energy  penalty
because of the decrease in energy
available to heat air in the preheater.
Hot gas bypass will usually be
necessary only when high SO2 re-
movals  (approaching 90 percent) are
required, as in higher sulfur  coal
applications. Hot gas bypass min-
imizes the  amount of untreated
gas that must be bypassed around
the spray dryer and thus increases
the SO2 removal that can be
obtained with a  given spray  dryer
system.

Table 3 also gives the estimated raw
material and utility requirements of
a lime spray dryer process for a
new 500-MW boiler firing high-
sulfur coal,11 and includes the
estimated energy penalty associated
with hot gas bypass for this sys-
tem. Because data are lacking  for
full-size spray dryer systems applied
to boilers firing high-sulfur coal,
these estimates may change
considerably after ongoing
demonstration-scale studies are
completed.1

Reagent requirements are the major
cost component of the annual
material and utility needs of the spray
dryer FGD  process. Comparison by
weight of the raw material require-
ments of lime and sodium carbon-
ate spray dryer systems can be
somewhat misleading because the
molecular weight of sodium car-
bonate (106) is nearly twice that
of lime (56.1). In molar terms, lime
systems usually require more reagent
than do sodium carbonate sys-
tems because lime is less reactive
and therefore has lower material
utilization. In terms of weight, how-
ever, sodium carbonate sys-
tems require more raw material, and
the higher cost per unit weight
of sodium carbonate usually
makes these systems more expen-
sive to operate. ;Substituting other
sodium compounds for sodium  car-
bonate may make sodium sys-
tems more  competitive with lime
systems. In particular, trona ore
appears to  be an attractive alter-
native in Western States where it is
readily available.19 No commercial
spray dryer systems sold as of
mid-1981,  however,  plan to use
trona ore as an absorbent.

The total utility needs of lime spray
dryer systems are generally lower
than those  of limestone wet
scrubbing systems.11 These needs
vary, however, with system de-
sign and the type of coal burned,
which determine the absorbent feed
rate requirements and the amount
of solids to be disposed  of.

In low-sulfur-coal applications,  lime
spray dryer systems have slightly
lower energy requirements
than wet limestone systems because
less energy is needed for pumping.
Considerably less solution or slurry
must be moved through spray
dryer systems. A large part of the
associated  energy savings, however,
is lost to the energy needed for
atomizing the solution or slurry.

In high-sulfur-cpal applications, the
total energy requirements for lime
spray dryer systems are much
lower than  for wet systems because
pumping energy needs are re-
duced and  less ;energy is needed
for flue gas reheat.11 Although spray
dryer systems on boilers firing
high-sulfur coal incur an energy
penalty for hot gas bypass, the pen-
alty is much less than the energy
needed to reheat exit gases from wet
scrubbing systems.


Installation Space and Land

Installation space and total  land
requirements for spray dryer FGD
systems vary depending on the  plant
size, the spray dryer design, and the
type of absorbent used. Installa-
tion  space requirements for a lime
spray dryer system have been
estimated from recent Tennessee
Valley Authority (TVA) and EPA
studies.11-20

The total estimated installation
space requirement for a  500-MW
lime spray dryer FGD system is about
2.3 acres  (0.9 ha), including space
for a recycle waste solids slurry
system and a process control area
(Figure 4). The total area  needed  for
process control, solids recycle, and
absorbent preparation and stor-
age is estimated at 0.3 acre (0.1 ha).

Total installation space requirements
for a 500-MW sodium carbonate
spray dryer system should not
differ significantly from those of
the lime system shown in Figure 4.
Space requirements for the
spray dryer and solids collection
equipment would be similar for both
systems. Absorbent preparation
would require less space in the
sodium carbonate system, and space
would probably hot be needed for
solids recycle storage. Absorb-
ent storage, however, would
require more  space; sodium car-
bonate reagent is stored as a
saturated aqueous solution, and
would need approximately twice the
storage space needed for the lime
system feed.11

A large additional area is  needed  for
waste solids disposal, on or off
site. Assuming a 30-yr lifetime (or
165,000 h of operation), a lifetime
                                                                                                      19

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                                                                                 Key
  260ft
                                                       Flue gas/off-gas

                                                       Cleaned flue gas

                                                       Absorption feed

                                                       Air pollutants

                                                       Other "systems
                                                             ID fan
                                                                                    Recycle
                                                                                    storage
                                                                                    bins
        Fabric filter
        baghouse
                                                                                                     125ft
                                                                             product
                                                                             tanks
                                      ' 340ft
                                                                                    i 110ft i
 Figure 4.

 Lime Spray Dryer Installation Space Requirements
 landfill for a 500-MW lime spray
 dryer system applied to low-sulfur
 coal (0.7 percent sulfur) would
 require an area of about 154 acres
 (62 ha) with an initial depth of 30 ft
 (9.1 m). A sodium carbonate
 system would require a clay-lined
 pond 30 ft (9.1 m) deep with an
 area of 195 acres (79 ha). These dis-
 posal area requirements include
 space for fly ash  disposal as well as
waste FGD solids. The sodium
carbonate system requires more
solids disposal area than does the
lime system because a greater total
volume of waste is; produced.

Spray dryer systems need a  larger
total area for waste disposal  than do
wet scrubbing systems. For  exam-
ple, a 500-MW wet limestone
scrubbing system would need about
134 acres (54 ha) of disposal land
with an initial depth .of 30 ft (9.1 m).11
Spray dryer systems produce more
waste because their raw material
utilizations are lower. Any disadvan-
tages and costs associated with the
greater volume of waste are
usually outweighed by the advan-
tage of a dry waste product, which
eliminates the need for  dewater-
ing equipment and may allow earlier
reclamation of land used for FGD
waste disposal.
20

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Costs
Reasonably accurate cost estimates
for spray dryer systems can be
based on vendor-supplied capital
cost information and on operating
data from pilot- and demonstration-
scale studies. Capital and oper-
ating cost estimates for lime and
sodium carbonate spray dryer FGD
systems have been prepared by TVA
for comparison with wet lime-
stone scrubbing FGD systems.11 The
actual costs of commercial-size
spray dryer systems may vary
widely from  these estimates, de-
pending on design and operating
developments resulting from full-
scale operation  in the near future.

Tables 4 and  5 give specific compo-
nents of annual operating costs
                                   Argonne spray dryer, 75,000 actual ft3/min
                                                                                                     21

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  Table 4.
  Annual Operating Costs for Lime Spray Dryer FGD System on  a  New 500-MW Coal-Fired Power-Generating Unit
                                                                                                   Costs
                            Component
                                                                    Annual quantity
                                                                                        Unit ($)
                                                            Annual
                                                           operating
                                                           ($1,000)
                             Mills/kWh
  Direct costs, first yean
      Conversion costs:                                        '
          Operating labor and supervision:                         i
             Flue gas desulfurization	;...    25,400 man-hours   15.00/man-hour       381      0.14
             Solids disposal	;...    28,152 man-hours   21.00/man-hour       591      0.21
          Utilities:                                            !
             Fuel	    163,750 gal        1.60/gal             262      0.10
             Process water	;...    82.2 X106 gal      0.14/1,000 gal         12      0.004
             Electricity	i...    39.6 X 106 kWh     0.037/kWh         1,464      0.53
          Maintenance, labor and materials	                                       2,136      0.78
          Analyses	    4,191 man-hours    21.00/man-hour        88      0.03

       Total conversion costs	j...                                       4,934      1.794

      Delivered raw materials (lime)	'....    10,100 tons        102.00/ton         1,030      0.37

       Total direct costs	J...                                       5,964      2.164

  Indirect costs: Overhead, first year, plant, and administrative	.'...                                       1,717      0.62

       Total first-year operating and maintenance costs	'-....                                       7,681      2.784

  Lovehzod capital charges (14.7% of total capital investment)	:...                                      11,336      4.12

       Total first-year revenue requirements	                                      19,017      6.904


  Lovclizod operating and maintenance costs (1.886 X first-year operating;and
   maintenance)	;...                                      14,486      5.27
  Levelized capital charges (14.7% of total capital investment)	'...                                      11,336      4.12

       Total levelized annual operating  costs	',...                                      25,822      9.39
  Notes.—Upper Midwest plant operating 5,500 h/yr. 1984 revenue requirements. 30-yr plant life. 1,346,700 tons/yr western coal burned, 9,500
  Btu/kWh. 0.7% sulfur. Warm gas bypass reheat and waste solids recycle. Stoichiometry of 1.2 mol lime per mol S02 absorbed. Meets emission
  regulation of 1.2 Ib S02/106 Btu with 70%S02 removal. Maintenance costs estimated at 6% of nonlandfill capital investment plus 3% of landfill invest-
  ment. Landfill disposal 1 mi from plant. Includes investment and revenue requirements for fly ash removal and disposal. Total direct investment,
  $38,587,000; total fixed investment, $59,369,000; total capital investment, $77,113,000.

  SOURCE: Burnett, T. A., and K. D. Anderson, Technical Review of Dry FGD Systems and Economic Evaluation of Spray Dryer FGD Systems, EPA 600/
  7-81-014. TVA EDT-127, NTIS No. PB 81-206476, Feb. 1981.
  and capital charges for a lime and
  a sodium carbonate spray dryer FGD
  system. The tabulations assume
  installation on a new 500-MW
  power-generating unit burning low-
  sulfur coal (0.7 percent sulfur). Both
  FGD systems are designed for 70
  percent SC"2 removal. The lime sys-
  tem, however, uses both untreated
  warm gas reheat and waste solids
recycle, and the sodium carbonate
system uses neither. Because all the
flue gas must be treated in the
sodium carbonate system, this
system requires four operating spray
dryers. The lime system operates
with three spray dryers because by-
pass reheating reduces the flow of
flue gas to be treated.

The annual operating costs for the
sodium carbonate system are about
9 percent higher than those for the
lime system, primarily because raw
material costs and total capital
investment are higher for the sodium
carbonate system. The higher cap-
ital investment results mainly
from the costs associated with con-
structing an environmentally safe
pond for sodium waste  disposal.
22

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Table 5.

Annual Operating Costs for Sodium  Carbonate Spray Dryer FGD System on a
Generating Unit
                                          New 500-MW Coal-Fired  Power-
                                                                                                  Costs
                          Component
                                                                  Annual quantity
                                                                                      Unit ($)
                                                          '. Annual
                                                          operating
                                                          ($1,000)
                                                                                                             Mills/kWh
Direct costs, first year:
    Conversion costs:             •                           ;
        Operating labor and supervision:                        ]
            Flue gas desulfurization	;.....   16,640 man-hours   15.00/man-hour      250       0.09
            Solids disposal		   28,362 man-hours   21.00/man-hour      596       0.22
        Utilities:                                            :                                   •      :
            Fuel	   165,700 gal        1.60/gal             265       0.10
            Process water	!....   70.2 X106 gal      0.14/1,000 gal    '     10       0.004
            Electricity	   41.15 X106kWh    0.037/kWh         1,523       0.55
        Maintenance, labor and materials	,....                                     ;  1,863       0.70
        Analyses	;• • • •   4,191  man-hours    21.00/man-hour        88       0.03

      Total conversion costs	I	                                     :  4.595	1.694

    Delivered raw materials (sodium.carbonate)	;	   1 8,350 tons        145.00/ton         2,661       0.97

      Total direct costs	:	                                     I  7,256	2.664

Indirect costs: Overhead, first year, plant, and administrative	j. . . .                          :           :  1,475       0.54

      Total first-year operating and maintenance costs	;....                                       8,731       3.204

 Levelized capital charges (14.7% of total capital investment)	I. . . .                                      11,679       4.25

      Total first-year revenue  requirements	.!....                                     ; 20,410       7.454


 Levelized operating and  maintenance costs (1.886 X first-year operating and
   maintenance)	.;.-..                                      16,467       5.98
 Levelized capital charges (14.7% of total capital investment)	                                      11,679       4.25

      Total levelized annual operating costs	i....                                     , 28,146      10.23
 Notes.—Upper Midwest plant operating 5,500 h/yr. 1984 revenue requirements. 30-yr plant life. 1,346,700 tons/yr western coal burned, 9,500
 Btu/kWh, 0.7% sulfur. No gas bypass, no waste solids recycle. Stoichiometry of 1.0 mol sodium carbonate per mol SO2 absorbed. Meets emission
 regulation of 1.2 Ib SO2/106 Btu with 70% S02 removal. Maintenance costs estimated at 5% of nonlandfill capital investment plus 3% of pond invest-
 ment. Pond disposal 1 mi from plant. Total direct investment, $40,941,000; total fixed investment, $61,408,000; total capital investment,
 $79,448,000.

 SOURCE: Burnett, T. A., and K. D.Anderson, Technical Review of Dry FGD Systems and Economic Evaluation of Spray Dryer FGD Systems. EPA 600/
 7-81-014, TVA EDT-127, NTIS No. PB 81-206476, Feb. 1981.
 Table 6 gives estimated capital and
 annual operating costs of 500-MW
 lime spray dryer systems for four
 different coals. The costs depend on
 a number of site-specific factors.
 Any specific situation should
 be evaluated for availability and
 cost of raw materials, utilities, and
 area for waste disposal. Annual oper-
 ating costs for spray dryer systems
 will be most sensitive to the costs of
 raw materials and electricity.
The cost estimates given for lime
spray dryer systems were compared
with cost estimates for wet lime-
stone  scrubbing systems.11  For
all three low-sulfur-coal applications,
the comparison showed that both
the capital and operating costs
of lime spray dryer systems are lower
than those for limestone scrub-
bing systems.
In the high-sulfur-coal applications,
the capital and operating costs for
the spray dryer and limestone scrub-
bing systems were essentially
the same within  the  accuracy of the
cost estimates.11  Further study of
spray dryer processes on boilers
firing high-sulfur coal should provide
data for improved estimates of the
relative costs of  the  two  FGD
systems in high-sulfur-coal applica-
tions.
                                                                                                                     23

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Table 6. j
Estimated Capital and Operating Costs for Lime Spray Dryer FGD Process on a New 500-MW
Generating Unit
„. . . . Total capital
System characteristics . b
investment
C°altyP9° %S _,,- Absorbent n .
in %S% stoichi- Operating 6
coal removal ometry* varlables
Lignite 	 07 70 12 Warm gas 826 165
! bypass
reheat,
i waste
solids
recycle
Western 	 07 70 12 Warm gas 771 1 54
; bypass
reheat,
waste
solids
recycle
Eastern 	 , 	 07 70 1 3 Warm gas 75 3 151
', bypass
; reheat,
| no waste
solids
recycle
i pass
! reheat,
waste
i solids
; recycle ,
Coal-Fired Power-
Annual
operating costs0
/ $106 Mills/kWh
28 7 1043
25 8 9 39
25 2 918
47 1 1713

  'Coal heating values: lignite = 6,600 Btu/lb; western = 9,700 Btu/lb; eastern = 11,700 Btu/lb.
   Project beginning early 1981, ending late 1983. Average cost for sea ling, mid-1 982. Minimum in-process storage, redundant spray-drying train, pumps
   are spared. FGD process investment begins at boiler heat exit. Excludes stack plenum and stack; includes only nominal construction overtime.
  C1984 revenue requirements.                                       ''
  dMoets emission regulation of 1.2 Ib S02/106 Btu.                    :
  *mol S02 absorbed.                                                ;
  Notes,—Midwest plant operating 5,500 h/yr. 30-yr plant life. Landfill disposal 1 mi from plant. Includes investment and revenue requirements for fly ash
  removal and disposal.
  SOURCE: Burnett, T. A., and K. D. Anderson, Technical Review of Dry FGD Systems and Economic Evaluation of Spray Dryer FGD Systems, EPA 600/7-
  81-014. TVA EDT-127. NTIS No. PB 81-206476, Feb. 1981.           ;
24

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References
1 Kelly, M. E., and S. A. Shareef.
 Third Survey of Dry SO2 Control
 Systems. EPA 600/7-81 -097,
 NTIS No. PB 81-218976.
 June 1981.

2Parsons, Edward L, L. F. Hemen-
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 R. L. Ostop. "S02 Removal by
 Dry FGD."  In Proceedings: Sympo-
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 Houston,  Texas, October 1980.
 Vol. II. EPA 600/9-81-01 9b, NTIS
 No. PB 81-243-164. Pp. 801-852.
 Apr. 1981.   !

3Stevens, N. J., G. B. Manavizadeh,
 G. W. Taylor, and  M. J. Widico.
 "Dry Scrubbing S02 and Particulate
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 U.S. EPA's Third Symposium on
 the Transfer and Utilization of
 Particulate Control Technology,
 Orlando FL, Mar. 1981.

4Kezerle, J. A., S. W. Mulligan, D. P.
 Dayton, and P. J. Terry. Perform-
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 Spray Dryer for SO2 Control.
 EPA 600/7-81-H 43. Aug. 1981.

 5Stevens, N. J. "Dry S02 Scrubbing
 Pilot Test Results." In  Proceed-
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 October 1980. Vol. II.  EPA
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 6Hurst, T. B., and G. T.  Bielawski.
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 81-243-164. Pp. 853-869.
 Apr. 1981.   '

 7Downs, W., W. J. Sanders, and
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 9Meyler, J. A. "Dry Flue Gas Scrub-
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 1980's." Paper presented at the
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 Phoenix AZ, Sept. 1 980.

10Kelly, M. E., and S. A. Shareef,
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 NTIS  No. PB 81-157919.
 Oct. 1980.     ;

"Burnett, T. A., and K. D. Anderson.
 Technical Review of Dry FGD
 Systems and Economic Evaluation
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 EPA 600/7-81 -014, TVA EDT-127,
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 Feb. 1981.

12Brown, B., M. Fitzpatrick,
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13The Mcllvaine Company. The Elec-
 trostatic Precipitation Manual.
  Vol. III. Ch. IX. Northbrook  IL,
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14Gibson, E. D., ed. "Dry FGD Pilot
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  Report, 5:2, Aug. 1981.

15Surman, J. S., Jr. A Paniculate and
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  Platt Associates, May 1 981.
                                                                                                   25

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 ieRasmussen, E. L, J. C. Buschmann,
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 "Parsons, E. L, V. Boscak, T. G.
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  Mar. 1981.
18Brna, T. G. "Dry Flue Gas Desul-
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 Paper presented at Third
 E.C.E. Conference on Desulfuri-
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 Triangle Park NC)
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  presented at 89th National AlChE
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20Drabkin, M., and E. Robinson.
  "Spray Dryer FGD Capital and Oper-
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  October 1980. Vol. II. EPA 600/9-
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  164.  Pp. 731-760. Apr. 1981.
26

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