United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-85/005 Apr. 1985
Project Summary
Flue Gas Conditioning
S-C. Yung, R. G. Patterson, B. L. Hancock, and S. Calvert
The particle collection efficiency of
an electrostatic precipitator (ESP) for
coal-fired power-plant flue-gas cleaning
depends on the electrical properties of
the fly ash, among other things. Flue
gas conditioning refers to the addition
of chemicals to the flue gas for modifi-
cation of fly ash properties and/or
electrical conditions in the ESP to
improve the collection efficiency of
ESPs. It is usually used for upgrading
existing ESPs.
Many existing chemicals have been
used as conditioning agents in power
plants or have been studied in the
laboratory as potential agents. This
report gives results of a survey of
available agents and user experience.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
Electrostatic precipitators (ESPs) have
proved reliable, economic, and effective
at controlling particle emissions from
coal-fired utility boilers. Sometimes their
performance has been unsatisfactory
because of: (2) coal composition change;
(2) more stringent particle emission regu-
lations; (3) unstable electrical conditions;
(4) changes in boiler and associated
equipment operating conditions; (5) in-
sufficient collection area; or (6) poor
maintenance.
There are several methods for upgrad-
ing ESP performance: (1) adding collector
plate area to the existi ng ESP to overcome
poor performance; (2) using a wet ESP; (3)
increasing or lowering the gas tempera-
ture in the ESP; and (4) adding chemicals
to modify the fly ash or the electrical
conditions in the ESP.
For older ESPs, flue gas conditioning is
often the most cost effective way to
upgrade performance. Several chemicals
are available or have been proposed as
conditioning agents. This report gives
results of a survey on available flue gas
conditioning agents and user experience.
Flue Gas Conditioning
Flue gas conditioning refers to the
addition of chemicals to the flue gas in a
coal-fired power plant in order to modify
fly ash properties and/or improve elec-
trical conditions in the ESP and thus
improve the collection efficiency of ESPs.
It is usually used to retrofit existing ESPs
whose performance has deteriorated, or
which are operating below design effi-
ciency.
Collecting fly ash in an ESP involves the
precipitation of the ash followed by its
successful removal: first from the collec-
tion plates; then from the hoppers. For an
ESP of given size and operating under
fixed conditions, the collection efficiency
of the ESP is affected by: (1) the electric
field strength and ion density in the
precipitation zone; (2) the adhesive and
cohesive properties of the fly ash; and (3)
the average particle size and size distri-
bution.
A conditioning agent may affect some
or all of these factors. The ash resistivity
is important because it can affect both (1)
and (2) above.
Conditioning Mechanisms
A conditioning agent may influence the
ESP collection efficiency through one or
more of the following mechanisms: (1)
adsorbing on the surface of fly ash to
reduce surface resistivity; (2) adsorbing
on the fly ash to change the adhesion and
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cohesion properties of the ash; (3) increas-
ing ultrafine particle concentrations for
space charge enhancement; (4) increas-
ing the electrical breakdown strength of
the flue gas, (5) increasing the mean
particle size; and (6) changing the acid
dew point in the flue gas.
The effects of these mechanisms on
ESP performance are described in Table
1.
Flue Gas Conditioning Agents
Many chemicals have been used as
conditioning agents in power plants or
have been studied in the laboratory as
potential conditioning agents. Table 2
lists these chemicals and their principal
conditioning mechanisms.
Sulfur Trioxide
Sulfur trioxide (SO3) is the most widely
used conditioning agent in the U.S. It is a
natural component of flue gas from fossil
fuel combustion. It is hygroscopic and
readily becomes sulfuric acid when water
is present. When injected in flue gas it
may easily be adsorbed to form a layer of
conductive solution on the ash surface,
thereby reducing the ash resistivity.
For conditioning, SOa is produced by
one of the following processes: (1) vapor-
ization of a sulfuric acid solution; (2)
vaporization of liquid SOi (3) vaporization
of liquid S02 and oxidation to S03 over a
vanadium pentoxide catalyst; and (4)
burning liquid sulfur in air to produce SOz
and then oxidation to SO3.
Ammonia
Ammonia is a vapor at room conditions,
and its critical temperature is 132°C.
Above this temperature, ammonia exists
as a single phase and cannot boil or
condense. Therefore, condensation on
the fly ash would not be expected with
ammonia above 132°C, although adsorp-
tion might.
Because of the high volatility of am-
monia, it is injected in the vapor form
under its own vapor pressure. In Australia,
ammonia is also injected in aqueous
solution form.
Ammonium Compounds
Conditioning with ammonium com-
pounds offers a more convenient way of
injecting ammonia. The commonly used
ammonium compounds are sulfamic acid,
ammonium sulfate, and ammonium bisul-
fate. When injected upstream of the air
preheater, these compounds could de-
compose to ammonia and sulfuric acid
and, therefore, may provide a combination
of the effects of ammonia and sulfuric
acid conditioning.
Organic Amines
Organic amines have been studied in
the laboratory and pilot scale ESPs as
possible flue gas conditioning agents.
Currently, there are no commercial users.
Of all the amines, triethylamine has
received the most attention. It is an
organic nitrogen compound and is highly
soluble in water. It behaves similarly to
ammonia, but is a substantially stronger
base. The melting and boiling points of
triethylamine are -115°C and 90°C,
respectively. It decomposes extensively
to ammonia, hydrogen cyanide, nitrogen
dioxide, and nitric oxide at temperatures
above 340°C(650°F).
Dry Alkali
Ash resistivity is indirectly related to
the alkali content in the ash, and reduction
of ash resistivity by increasing the alkali
concentration has been tried. Of the many
alkali salts, sodium salts are the most
commonly used conditioning agents be-
cause of their availability and relatively
low cost. The widely used sodium com-
pounds are sodium carbonate and sodium
sulfate. Sodium chloride has been tried in
the laboratory and found to be effective.
However, it is not used because it can
lead to corrosion of metal equipment.
The mechanism for sodium condition-
ing depends on how the sodium is applied.
If a sodium compound is injected into the
boiler along with coal, it will decompose
and the sodium is bound in the ash. The
sodium will increase the conductivity and
lower the ash resistivity the same way as
natural sodium.
If the sodium compound is co-precipi-
tated with the ash, the compound trapped
in the space between the particles on the
dust layer offers an additional conductive
path for charge dissipation.
Alkali earth compounds have also been
studied, including dry limestone and
magnesia. It is thought that these com-
pounds react with excess sulfuric acid to
enhance the space charge effect.
Proprietary Formulations
Most of the proprietary chemicals are
ammonium compounds with minor addi-
tives, such as surface active agents.
Preparations such as this would perform
similarly to ammonium compounds.
Miscellaneous Compounds
Several metal oxides, such as iron and
vanadium oxides, have been investigated
as possible conditioning agents. Iron an
vanadium oxides are claimed to catalyz
the reaction of S02 to S03 and thu
increase the quantity of S03 present i
the flue gas. This claim has not bee
substantiated in the literature.
Results
Table 3 lists past and present flue ga
conditioning users in the U.S. Summarie
of user experiences follow.
Sulfur Trioxide
SO3 conditioning is limited to cold-side
ESPs. The most common injection loca
tion is between the air preheater and the
ESP inlet. The temperature at the point o
injection and in the precipitation shoulc
be above the sulfuric acid dew point of the
gas after addition.
The dosage for SOa injection normally
is in the range of 5 to 30 ppmv, but can be
as high as 70 ppmv. The required dosage
will depend on the composition of the ash
surface; i.e., if it is acidic, neutral, or
basic. If the ash has a large amount of
alkaline compounds, a higher dosage of
S03 is needed because the alkaline
compounds will react with, or neutralize,
the adsorbed sulfuric acid.
SOaConditioning is effective in reducing
ash resistivity and improving ESP per-
formance if it is applied properly, but only
where high particle resistivity is the
limiting factor in ESP performance. For
highly resistive ashes, an addition rate of
20 ppmv can lower the resistivity by two
orders of magnitude (from about 109 to
10'° ohm-cm to 107 to 108 ohm-cm).
There are cases of non-effectiveness
where SOs conditioning has not been
effective for one or more of the following
reasons: (1) the conditioner supply mal-
functioned; (2) the ESP performance is
limited by phenomena other than ash
resistivity; (3) the ash resistivity may
already be satisfactory; (4) the tempera-
ture may be so low that acid condenses at
the injection point before the SO3 is
mixed with the flue gas; and (5) the
temperature is much higher than the acid
dew point.
Even though S03 conditioning can
improve the particle collection efficiency
of the ESP, it can increase the emissions
of sulfuric acid mist and particulate sulfate
compounds. The emission rate of added
S03 is higher for acidic ashes and high
gas temperatures existing in ESPs.
Due to increased particle collection by
the ESP, plume opacity is usually lower
with conditioning. However, an "acid
plume" could be formed if the S03dosage
and gas temperature are too high. (
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Table. 1. Mechanisms by Which a Conditioning Agent May Affect Precipitability
Effect of
Conditioning Agent
Electrical Result
Mechanical Result
Effect on
Efficiency*
Comments
Adsorbs on surface of fly ash
and reduces surface resistivity
Increases the magnitude of
the precipitation field: Reduces
the voltage drop in the dust
layer; Delays the onset
of black corona; Increases the
sparkover voltage
S/£ Useful for high resistivity dusts:
Increases charging and
precipitation field strength;
Reduces electrical adhesion on
the wall and thus improves the
effectiveness of rapping.
Reduces the electrical
adhesion effect on the wall
IE Beneficial for high resistivity
or dusts. If used with low or medium
DE resistivity dusts, further lowering
of adhesion forces could lead to
reentrainment losses.
Adsorbs on fly ash and
changes cohesiveness or
"stickiness"
Aids agglomeration and
increases mean particle size
IE Size enhancement may occur
independently of resistivity
change and thus improve
migration velocity.
Dust layer on wall becomes
more cohesive
IE Larger size fraction also aids
removal by rapping;
Cohesive dust layer tends to
shear off collecting plate with
less reentrainment losses.
Dust layer has stronger
adhesion to wall
IE Stronger adhesion is an
or advantage for low resistivity
DE dusts; Could be a disadvantage
for high resistivity dusts.
Increases particle concentra-
tion due to presence of fines
(i.e., paniculate reaction
products)
Reduces ion density (and thus
current) due to space charge
suppression
IE The current reduction could
or reduce charging effectiveness.
DE On the other hand, the lower
current density will alleviate
field reduction problems caused
by the voltage drop through a
high resistance dust layer.
Increases collection field
strength due to space charge
enhancement
IE Space charge increases the
field strength near the collecting
electrode.
Increases sparkover voltage
IE A slight increase in sparkover
voltage usually results from
increased space charge.
Increases electrical breakdown
strength of flue gas
Increases the magnitude of the
precipitator field: Increases
sparkover voltage; Delays
onset of back corona
SIE The breakdown characteristics of
flue gases are very sensitive to
minor concentrations of electro-
negative species and to surface
conditions of the dust layer. This
can be independent of fly ash
resistivity.
Neutralizes acid in flue gas
Decreases acid dew point. This
reduces surface "tracking" on
high voltage insulators, allowing
higher voltages to be applied.
SIE With some high sulfur coals, the
sulfuric acid concentration in
the flue gas is so high that the
acid dew point may be above the
flue gas temperature. This may
result in acid condensation
on support insulators.
"S/F = strong tendency to increase efficiency.
IE = tendency to increase efficiency.
DE = tendency to decrease efficiency.
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Table. 2. Flue Gas Conditioning Agents and Mechanisms
Conditioning Agent Conditioning Mechanisms
SOa (HgSO^ Resistivity modification
NH3 Adhesion and cohesion
Space charge enhancement
Ammonium Compounds Space charge enhancement
(SO2QH)NH3 (sulfamic acid) Resistivity modification
NHtHS04
(NH^CO
Organic Amines
(CH3CHi)3N (Triethylamine)
(CH 'a/a/V (Trimethylamine)
(Cyclohexylamine)
Alkali Compounds
Na2SOt
Na2C03
Proprietary Compounds
Apollo LPA-30
Apollo LPA -40
Apollo LPA -50
Koppers "K"
Resistivity modification
Resistivity modification
Resistivity modification
Space charge enhancement
Operating Problems—Interviews of
several users of SO3conditioning revealed
the following operating difficulties: (1)
corrosion of injection lines; (2) deactiva-
tion of catalysts in the 862 to SOa
converter; and (3) over-conditioning (re-
sistivity lowered too much).
Economics—The estimated capital and
operating costs of a S03 flue gas condi-
tioning installation as of December 1982
are $5.15/kW and 0.105 mills/kWh,
respectively.
Ammonia
Ammonia is injected either before or
after the air preheater in vapor or liquid
form. Most of the users inject it down-
stream of the air preheater to avoid
plugging the preheater with deposits of
ammonia reaction products.
The ammonia injection dosage is about
15 to 20 ppmv. In most situations, am-
monia can improve the ESP performance.
However, the way in which ammonia
affects the performance of ESPs is not
completely understood. It seems that in
different applications, it affects ESP per-
formance through different mechanisms.
It is not effective with all ashes, and its
behavior in each case appears to depend
mainly upon the initial ash resistivity, flue
gas composition, and temperature.
The ability of ammonia to alter resistiv-
ity is not clear. Ammonia-conditioned
resistivities can be less than, the same as,
or greater than the unconditioned values.
The temperature of the ESP has great
effect on resistivity modification by am-
monia. Since the critical temperature for
ammonia is 132°C, physical adsorption
or condensation of ammonia is not ex-
pected to occur above this temperature.
Therefore, ammonia injection will not
change the ash resistivity above this
temperature unless it is sorbed as a
reaction product as NH5S04.
The improvement in ESP performance
when ammonia is injected is more likely
due to space charge enhancement and
improvement in cohesive force between
the ash particles. The injected ammonia
reacts with the existing sulfuric acid
vapor, forming a fume of fine salt particles
of ammonium bisulfate and sulfate. This
fume creates a large surface area for
collecting electrons. These charge car-
riers have a lower mobility than electrons,
allowing for a more stable corona, higher
electrical field strength without break-
down, and higher specific power.
Ammonia is sometimes injected along
with S03. Sulfuric acid condensation in
the presence of ammonium bisulfate and
sulfate leads to the adsorption of acid and
salts to water on the surface. These
surface deposits are viscous and cohesive,
which reduces particle reentrainment
from the collection plates.
The emissions caused by ammonia
injection are minimal. A significant part
of the ammonia is reacted with nitrogen
oxides to form elemental nitrogen. Re-
action between ammonia and S03 alsi
decreases the S03 emission.
Operating Problems—Ammonia condi
tioning could have the following operatinj
and maintenance problems: (1) plugging
of injection nozzles; (2) leakage anc
freezing of injection lines; and (3) dus
buildup on discharge electrodes.
Economics—The capital and operating
costs of ammonia conditioning, in De-
cember 1982 U.S. dollars, are $0.21 /kV\i
and 0.022 mills/kWh, respectively.
Ammonium Compounds
Ammonium compound injection rates
are in the range of 0.25 to 1 .Og/kg of coal
burned. They are injected in solution form
either upstream or downstream of the air
preheater. Upstream is preferred because
it offers long residence time and high
temperature to vaporize or decompose
the agent. However, upstream injection
could cause plugging of the air preheater.
Since ammonium compounds currently
used for conditioning decompose to am-
monia and sulfuric acid, they improve the
ESP performance through the mecha-
nisms of resistivity modification and
space charge effect. They are not as
effective as SO3 in lowering the ash
resistivity. Results show that they can
lower the ash resistivity by about half an
order of magnitude.
The injection of compounds decompos-
ing to ammonia and SO3 may cause
increased sulfate and ammonia emis-
sions. Sulfate emission rates of about 20
and 1,500 £tg/m3 were measured in a
field study, without and with conditioning,
respectively.
Problems—The most common
operating problem with ammonium
compound conditioning agents has been
plugging of the air preheater by deposits
of combustion products when the agent is
injected upstream of the air preheater.
Economics—There is no information
on capital costs for ammonium
compound conditioning systems. The
operating costs range from 0.024 to
0.052 mills/kWh (December 1982 U.S.
dollars).
Organic Amines
Even though triethylamine is less vola-
tile than ammonia, it can be injected in
the vapor phase as well as in the solution
form. Because it decomposes at high
temperature, it is injected downstream of
the air preheater.
The mechanism of triethylamine is not
fully understood. The most likely mecha-
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Table. 3. Past and Present Flue Gas Conditioning Users
Company Name Plant Name
Alabama Power Co.
AEPSCO Appalachian Power
AEPSCO Appalachian Power
AEPSCO Columbus & Southern Ohio Electric
Arizona Public Service Co.
Baltimore Gas & Electric
Central Illinois Light
Central Illinois Light
Central Illinois Light
Cincinnati Gas & Electric Co.
City of Colorado Springs DPU
Cleveland Electric Illuminating Co.
Cleveland Electric Illuminating Co.
Cleveland Electric Illuminating Co.
Cleveland Electric Illuminating Co.
Colorado-Ute Electric Assoc.
Commonwealth Edison
Commonwealth Edison
Commonwealth Edison
Commonwealth Edison
Commonwealth Edison
Commonwealth Edison
Commonwealth Edison
Commonwealth Edison/Indiana
Commonwealth Edison/ Indiana
Commonwealth Edison/Indiana
Consumers Power Co.
Consumers Power Co.
Detroit Edison
Detroit Edison
Detroit Edison
Detroit Edison
Detroit Edison
Detroit Edison
Duke Power
Duke Power
East Kentucky Rural Electric Power Coop.
Florida Power
Georgia Power
Gulf Power Co.
Iowa Public Service Co.
Lansing Board of Water & Electric Light
Montana Power Co.
New England Power Co.
New England Power Co.
New Jersey Gas & Electric
New York State Electric & Gas
New York State Electric & Gas
Northern Indiana Public Service Co.
Northern Indiana Public Service Co.
Ohio Edison Co.
Ohio Edison Co.
Ohio Edison Co.
Ohio Edison Co.
Pacific Power & Light
Pacific Power & Light
Barry
Cabin Creek
Kanawha Ftiver
Conesville
Four Corners
H. A. Wagner
Duck Creek
E. D. Edwards
Ft. S. Wallace
W. C. Beckjord
Martin Drake
Ashtabula
A von Lake
Eastlake
Lake Shore
Hayden
Crawford
Fisk
Joliet
Joliet
Powerton
Waukegan
Will County
State Line
State Line
State Line
B. C. Cobb
J. C. Weadock
Conners Creek
Harbor Beach
Monroe
Pennsalt
Port Huron
Trenton Channel
Belews Creek
Marshall
W. C. Dale
Crystal Ftiver
Harllee Branch
Scholz
G. W. Neat
Erickson
J. E. Corette
Salem Harbour
Brayton Point
Mercer
Goudey
Greenidge
D. H. Mitchell
D. H. Mitchell
Edgewater
Gorge
W. H. Sammis
W. H. Sammis
Bridger
Central/a
Boiler No.
4
4
4
3
1.2.3
7. 8. 9, 10
1,2.4
1.5
5
9
5
18
1.2
7.8
19
3. 4. 5. 6
71, 72, 81, 82
51.52
15. 16. 17.8
4
1-1. 1-2. 1-3
1-4. 1-5. 1-6
2-1, 2-2. 2-3. 3. 4
1. 2. 3. 4. 5
7.8
15, 16
1
1,2
5
7. 8. 9 A
1,2
3.4
2
3. 4
2.4
1
1
11, 12
4.5.6
4. 5.6,11
1. 2, 3. 4. 5. 6. 7
1.2
PGC Licensor
Wahlco
Apollo
Apollo
Apollo
Wahlco
Wahlco
Wahlco
Research- Cottrell
Wahlco
Wahlco
Wahlco
Wahlco
Apollo
Wahlco
Wahlco
Wahlco
Wahlco
Wahlco
Wahlco
Wahlco
Wahlco
Wahlco
Wahlco
Wahlco
Wahlco
UOP
Wahlco
Wahlco
Research- Cottrell
Wahlco
Apollo, Nalco
Apollo
Wahlco
Wahlco
Apollo
Nalco
Nalco
Apollo
Wahlco
Wahlco
Wahlco
Apollo
Dusco
Dusco
Wahlco
Apollo
FGC Agent
Sulfur trioxide
LPA-445
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
LPA-40
LPA-40
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Ammonia
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Table. 3. (Continued).
Company Name
Pennsylvania Electric Co.
Pennsylvania Electric Co.
Pennsylvania Power & Light Co.
Pennsylvania Power & Light Co.
Pennsylvania Power & Light Co.
Pennsylvania Power & Light Co.
Public Service Co. of Colorado
Public Service Co. of Colorado
Public Service Co. of Colorado
Public Service Co. of Colorado
Public Service Co. of Colorado
Public Service Electric & Gas, New Jersey
Public Service Electric & Gas. New Jersey
Salt River Project
South Carolina Public Service Authority
Tampa Electric Co.
Tampa Electric Co.
Tennessee Valley Authority
Tennessee Valley Authority
Tennessee Valley Authority
Tennessee Valley Authority
Tennessee Valley Authority
TUGCO Dallas Power & Light
TUGCO Dallas Power & Light
Toledo Edison
UGI Corp. Luzerne Electric
Upper Peninsula Generating Corp.
Upper Peninsula Generating Corp.
Utah Power & Light
Virginia Electric & Power
Wisconsin Electric Power Co.
Wisconsin Power & Light
Plant Name
Front Street
Keystone
Brunner Island
Montour
Montour
Sunbury
Arapahoe
Cameo
Cherokee
Comanche
Valmont
Hudson
Mercer
Hayden
Jefferies
Big Bend
F. J. Gannon
Bull Run
Gallatin
Kingston
Shawnee
Widows Creek "B"
Big Brown
Monticello
Bayshore
Hunlock Creek
Presque Isle
Presque Isle
Naughton
Yorktown
Pleasant Prairie
Columbia
Boiler No.
9, 10
1,2
1,3
1,2
3.4
1, 2. 3. 4
2
1. 2. 3. 4
1.2
5
2
3.4
5.6
1
4
5
10
7,8
1,2
1. 2, 3. 4. 5, 6
1. 2, 3. 4, 5, 6
3
1.2
1
PGC Licensor
Wahlco
Wahlco
Wahlco
Apollo
Wahlco
Wahlco
Lodge-Cottrell
Nalco
Apollo
Apollo
Apollo
Apollo
Apollo
Apollo
Nalco
UOP
Apollo
Wahlco
Wahlco
Apollo
Wahlco
FGC Agent
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
LPA-402A
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
LPA-40
LPA-40
LPA-40
Ammonia
Ammonia
Ammonia
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
Sulfur trioxide
nism is ash resistivity reduction. One pilot
plant study showed that resistivity de-
creased from 3 x 10" ohm-cm (without
conditioning) to 5 x 107 ohm-cm (with a
triethylamine dosage of 60 ppm). Another
pilot plant study showed similar results.
With an injected concentration of 25 ppm
of triethylamine, resistivity decreased one
to two orders of magnitude in the tem-
perature range of 100°C to 150°C. It is
more effective the lower the temperature,
the less basic the ash composition, and
the greater the concentration of the
agent.
Triethylamine has only been studied in
the laboratory and in pilot plants. There
are no commercial users, so no user
experience or economic data are avail-
able.
Dry Alkali
Sodium conditioning, unlike with other
conditioning agents, is not limited to cold-
side ESPs. It can be added to the boiler
6
along with coal or into the flue gas just
ahead of the ESP. It can be applied either
in solution or dry powder form. The most
important parameter which affects its
effectiveness is the mixing of the sodium
salt and the fly ash. To be effective, the
sodium must be either incorporated into
all the ash particles or co-precipitated
with the ash on the ESP plates so it yields
well-mixed deposits.
When sodium is applied in dry powder
form for co-precipitation, there may be
difficulties in obtaining well-mixed de-
posits. Some researchers applied the
sodium in solution form and claimed that
a uniform coating of sodium salts was
obtained on ash particles. When the agent
is injected for co-precipitation with the
ash, the dosage is 2 to 5 percent of the
solids as NazO. The co-precipitated
sodium compound should have a particle
size distribution comparable to that for
the ash.
Sodium is effective in reducing the fly
ash resistivity if the sodium is mixed well
with the ash. In situ resistivity measure
ments of co-precipitated ash showed tha
resistivity decreased from 2.1 x 1010 ohm
cm (without conditioning) to 3.7 x 10
ohm-cm (when conditioned with a 1.0 ti
1.5 percent concentration of sodiurt
carbonate as sodium oxide). A reductioi
of resistivity from 1 x1010to1 x108ohm
cm was measured by another researche
when the sodium oxide content of the ast
was increased to 2.5 percent from the
inherent 0.3 percent.
Problems—Commercial users have onl^
limited experience with sodium condi-
tioning; therefore, operational problems
are not well documented. However, one
potential problem associated with adding
sodium compound to the coal is slagging
and boiler fouling if the system is not
operated properly.
Economics—The capital costs for a
liquid solution conditioning system are
about $1.55 to $3.10 per installed kilo-
watt. The operating costs, excluding
depreciation, are about 0.03 mills/kWh.
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Conclusions
Of the many agents available, S03 is
the most commonly used. SO3 is effective
in reducing ash resistivity and will im-
prove the ESP performance if particle
resistivity is the limiting factor. The
conditioning mechanisms of ammonia,
ammonium compounds, and organic
amines are not fully understood, and the
effectiveness of these compounds is not
consistent.
Flue gas conditioning appears to be an
acceptable (and the least expensive)
option for upgrading ESP performance for
collecting high resistivity fly ash. How-
ever, before deciding on flue gas condi-
tioning, the reasons for poor ESP per-
formance should be determined. The poor
performance could be due to factors other
than high resistivity. Once conditioning
has been chosen, the conditioning system
should be designed and operated with
extreme care to avoid harmful emissions
due to conditioning agents.
S-C. Yung, R. G. Patterson, B. L Hancock, and S. Calvert are with Air Pollution
Technology, Inc., San Diego, CA 92109.
Leslie C. Sparks is the EPA Project Officer (see below).
The complete report, entitled "Flue Gas Conditioning," (Order No. PB 85-173
912/AS; Cost: $13.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
4USGPO: 1985 — 559-111/10810
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
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