EPA
TECHNOLOGY
TRANSFER
62362-77
FABRIC FILTER
PARTICULAR CONTROL
ON COAL-FIRED
UTILITY BOILERS:
NUCLA CO.
AND SUNBURY PA.
U.S. ENVIRONMENTAL
PROTECTION AGENCY
'. ENVIRONMENTAL
. RESEARCH
INFORMATION
CENTER
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EPA
TECHNOLOGY
TRANSFER
FABRIC FILTER
PARTICUATE CONTROL
ON COAL-FIRED
UTILITY BOILERS:
NUOLA, CO.
AND SUNBURY, PA.
U.S. ENVIRONMENTAL
PROTECTION AGENCY
ENVIRONMENTAL
. RESEARCH
INFORMATION
CENTER
EPA-625/2-77-013
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Sunbury plant profile
.:-,: ;,,7:_ _
-S :=-n:-!kLi;::'r!!?j«?~-r,E.T--ss«-r;;».j
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Fabric filters are one of the oldest means of
controlling aerosol particles. Since the 1950's, they
have been used widely as air cleaning devices in
asphalt plants, cement manufacturing, carbon black
plants, glass furnaces, and a variety of ferrous and
nonferrous foundry operations. To date their use in
the electric utility industry has been limited, primarily
because of reservations about the durability of the
filter bags under harsh stack gas conditions. The use
of new glass fabrics and the development of high-
temperature lubricants to enhance bag life, however,
has rekindled electric utility interest in fabric filters
as a means of controlling particulate emissions. As
shown in Table 1, four utilities currently use fabric
filters, and eleven more are under construction.
Table 1. Status of Fabric Filter Installations in the Electric Utility Industry
Unit
^Pennsylvania
Power and Light Co.
=r~ Pennsylvania
"Power and Light Co.
5- Colorado Ute
- Electric Association
^Public Service Co.
_of Colorado
Southwestern Public
^ Service Co.
g.r , " - ' ..
~-- Texas Utilities
- Service Inc.
I^Board of Public Utilities
" Location
. * fc_ -
PP--
Sunbury, Pa.
s Mr
rHoItwood, Pa.
. Nucla, Colo.
Cameo, Colo.
I?***'
plAmarillo, Texas
Mount Pleasant,
jexas
nsas City,
Kansas
of Colorado Springs f Colorado Springs,
r' " " ' jpcoio.
i, .: .: : -. ".. .- I m -
'- Colorado Ute , |^Meatrose, Colo.
£ Electric Assn.
i^Crisp County Power Co.
_
bituminous coal
estern coal
ybbituminous
.ignite
}1 Minnesota Power
f^& Light Co.
Nebraska Public Power
Public Service of
: Colorado
^ Texas Utilities
Tbrdele, Ga.
"tohasset, Minn.
Jellevue, Nebr.
palisade, Colo.
Bpbertson City,
xas
Note: N/A = Information not available.
Combination of
etroleum coke
hd anthracite
Combination of
etroleum coke
anthracite, ,
. ,p^ Operational
J FT since 1973
1
-,_;J
1
^Operational
if* <;inrf> Innp '
te
;since June, 1975
Operational
' 1974
N/A
^Startup: Mid-1977
Startup:
jjune 1978
" Startup:
March 1978
Startup: 1979
^Startup: 1980
-j-
Startup: 1977
Startup: 1975
Startup: 1978
Startup: 1977
-i.^
Startup: 1977
/ Startup: 1980
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Electrostatic precipitators are by far the pre-
ferred control devices for participates in the electric
power industry. Their low maintenance requirements
and high control efficiencies have resulted in their
widespread acceptance. Recently, however, a num-
ber of circumstances have enabled fabric filters to
compete with electrostatic precipitators. The increase
in demand for solid fuels has caused many utilities
to depend upon variable coal supplies, which in turn
results in a varying chemical composition of the
fuels. The abundant low-sulfur fuel in the Western
states may soon replace some dwindling supplies in
the Eastern coal fields. With dwindling fuel supplies,
increased attention is being paid to the use of mixed
fuels; Pennsylvania Power and Light Company, for
example, uses anthracite waste and petroleum coke
at its Sunbury Station. Each of these circumstances
can affect the performance of electrostatic precipi-
tators. Variations in fuel composition, for instance,
alter the ash surface chemistry which affects the
electrical resistivity of the particulates. Electrostatic
precipitator efficiency is a direct function of particle
resistivity. Fabric filter efficiencies, on the other
hand, are much less dependent upon ash surface
chemistry. For high sulfur fuels, the condensation
and oxidation of sulfur oxides on paniculate surfaces
decreases particle resistivity and hence enhances
precipitator efficiency. Thus, the trend toward lower
sulfur fuels could adversely affect electrostatic pre-
cipitator performance. Fabric filters, on the other
hand, are well suited for low-sulfur fuels. In fact,
lower sulfur content aids bag filter operation, since
high concentrations of sulfur trioxide can accelerate
fabric deterioration. Table 2 summarizes the per-
formance characteristics of fabric filters and electro-
static precipitators with respect to selected power
plant operating conditions and fuel properties.
Table 2. Performance Characteristics of Fabric Filters and Electrostatic Precipitators
c
1 Power Plant Variable
: Maximum Collection
; Efficiency
i, Fuel S Concentrations
, Ash Metallic Qxi.de
; Concentration
Paniculate Loading
Flow Rate
Temperature
Hot Side
ESP
"It
Fabric Filter
Cold Side
99.0 to 99.8 * F ' 99.0 to>99.T*W
I I P- " -- " ~
s -S
f-
Minor
^Dependence
r Very Important
i - I. . r
'- No Dependence ' Very Important
o Dependence3
«. ' ^
%^ v f, , l «i*
3^1ov Dependence
" Loading Swings Decrease Collec- _ . Ip'et Loading Does Not Signifi-
f tion Efficiency Significantly L cantly Affect Efficiency. All
i- i ' " i ^1 |2?riatioris fn Outfet tConcentra- ^ ^
In. - . ,.,-,,", ,.,.T ,| are^ampened Considerably
J t- > .' i,r »-> J ^S**"1 -«r»»iiic^ ass (,*"jf.'vj - ^ r^s, Mt
t Nonuniform Velocity Distribution _ ^Wide Velocity Range Does Not
i Causes Decreased Collection , SiSn'^'cant'y Affect Performance
' '
ffiq
1 ..... UN '
I Non
. ^ ».. .. » .
onuniform Flue Gas Temperature ^.No Temperature Dependence for
, f. Causes Decreased Collection m Collection Efficiencyb
^.Efficiency
-s
_J
aHigh SOX concentration in gas streams causes high deterioration rates in many fabrics.
Multiple temperature excursions through the acid dew point will increase fabric deterioration rates.
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As previously mentioned, two coal-fired stations
have been using fabric filters since 1973 the Nucla
Plant of the Colorado Ute Electric Station and the
Sunbury Station of the Pennsylvania Power and Light
Company. Each of these operations is described in
Table 3.
The Nucla fabric filtration facility was designed
to control the entire particulate load from the three j
stoker-fired boilers of the 39 MW facility. This instal-'
lation, shown on the cover, has been able to meet !
the Colorado air pollution regulations with ease. j
Every boiler has its own baghouse which consists of
six independent compartments, each containing 112
bags for a total of 672 bags per baghouse. The
design gas flow through each baghouse is 86,240
acfm at 360°F. Bag cleaning is accomplished by a
combination of reverse air and gentle shaking. The
Table 3. Description of the Nucla and Sunbury Fabr
air used to clean the bags is cleaned flue gas recycled
from the baghouse discharge. Cleaning all six com-
partments requires about 30 minutes, with the
cleaning cycles initiated automatically by preset
limits for baghouse pressure drop.
The Sunbury powerplant operated for 2 years
using the original bags with only slight problems
and without appreciable bag failures. Tests per-
formed on samples of the two year old fabric and
new fabric indicated the used fabric to be nearly as
strong as the new material. At Nucla, changes in the
baghouse thimble plate improved bag wear. One
baghouse containing over 600 fiberglass bags, oper-
ated 6 months without a bag failure.
c Filtration Facilities
SiLocation
^Total MW Capacity
fiCombustion Units
=rInstallation Date
jiCoal Type
_.... , _...... ........ ,
^Manufacturer
H . , , --
tCJeaning Technique
Fabric Type
:Number of Baghouses
ENumber of Bags Per
^Baghouse
HBag Size
LAir/cloth ratio (net)
Pressure Drop at Full Load
ucla, Colorado
MW
15^ ^ mj ^ u ^ ^* ~ 1
r Three Spreader Stokers
'-":- - -"1
)ecember 1973
Bituminous,
f(0.6 to 1.8% S)
^A/heelabrator-Frye (Baghouse)
|W,W. Crisweil Co. (Bags)
Combination of shaking and
'"'everse air flow
|,Graphite/silicone coated fiberglass
r3
;2 ft. long x 8 in. diameter
K, ,; .
+* ^ * 4
5 in. of water
Sunbury
1
-SJOsimokin Dam, Pennsylvania
S^ ^v, _ T" j- * *, H^ *
;>s MW " J*
iFpur pulverized fuel boilers
Sfebruary 1973
^Anthracite and Petroleum Coke
(1.2 to 3.2% S)
, Western Precipitation (Baghouse)
f^Menardi-Southern Co. (Bags)
Reverse air flow
1 Teflon coated fiberglass
I
j
30 ft. long x 12 in. diameter
^3 in. of water on 2 year old bags
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The pressure drop across the Sunbury baghouse
at full load was a nearly constant 2.5 in.h^O. During
the two years of operation, baghouse increase in
pressure drop was less than 1.0 in.H2O. The average
pressure drop across the Nucla bags was approxi-
mately 4.5 in. H2O.
The Sunbury steam electric station, shown on the
inside cover, replaced an electrosatic precipitator
collection system which was unable to meet the
particle control efficiency required by state regula-
tions. The fuel, a combination of low sulfur anthracite
and high sulfur petroleum coke in proportions of
15 to 35 percent coke by weight, produced a high
resistivity in the ash which led to decreased precipi-
tator efficiency. The replacement bag filter system
has met the Pennsylvania regulations since its initial
operation in 1973. Each Sunbury baghouse handles
222,000 acfm at temperatures on the order of 325°F.
Individual baghouses contain 1260 bags which are
divided equally among 14 compartments. Every 30
minutes, the entire system is cleaned by a sequential
cleansing of each individual compartment.
The bag filtration system installed at these
utilities is depicted schematically in Figure 1. The
only major differences in the designs of these instal-
lations is the variation in the fabric cleaning method
employed by these facilities and the coarse particle
removal system installed upstream from the fabric
filter. The Nucla facility employs a combination of
gentle shaking and reverse air flow for cleaning,
while the Sunbury system uses only reverse air flow
as depicted in Figure 2. The Sunbury facility also
differs in the application of a mechanical collector
which removes the larger particulate matter in the
flue gas (about 70 percent) prior to bag filtration. At
Nucla, a single deflection baffle is used to remove
the coarser particles from the filter influent
Figure 1. Schematic Diagram of a Flue Gas Cleaning
System Incorporating a Fabric Filter Baghouse
Figure 2. Gas Flow Through Baghouse Compart-
ments During Normal Operation and Cleaning
MECHANICAL
COLLECTOR
1-GAS INLET DAMPER-OPEN
2-CAS INLET DAMPER-CLOSED
3-BAC COLLAPSING DAMPER-OPEN
4-BAC COLLAPSING DAMPER-CLOSED
5-OUTLET DAMPER-OPEN
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Nucla plant profile
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Sunbuiy - view of upper walkway, bag tension springs and bag caps
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The U.S. EPA Industrial Environmental Research
Laboratory in Research Triangle Park, North Carolina
sponsored field sampling programs at both the Nucla
and Sunbury facilities. Emission testing and analysis
was performed by CCA/Technology Division,
Bedford, Massachusetts. A major objective of the
project was to characterize the performance of fab-
ric filter systems used to remove particulates from
boiler flue gases.* Total mass emission rates were
measured using the standard EPA Method 5 techni-
ques. Isokinetic sampling of both the inlet and outlet
ducts, which provided accurate determination of
particulate mass concentrations, allowed for precise
measurement of bag filter efficiencies. Thirty-one
tests were run at the Sunbury facility. The average
mass emission rate of 0.0&46 pounds of particulates
per 106 Btu of coal fired Corresponded to an average
weight collection efficiency of 99.91 percent. Twenty-
two runs at the Nucla Plant indicated an average
mass emission rate of 0.01 pounds per 106 Btu input
to the boiler and a collection efficiency of 99.84
percent.
Both facilities easily satisfied the local particulate
emission regulations that the previously installed I
Sunbury electrostatic precipitators and the Nucla
mechanical collectors had been unable to meet.
Note that the emissions form both facilities are also
considerably less than the New Source Performance
Standards of 0.1 pounds per 106 Btu input for fossil
fuel-fired steam generators. Filter efficiency as a
function of particle diameter was also determined
using inertial impactors. Daily isokinetic impactor
sampling combined with condensation nuclei
counter and diffusion denuder data on submicron
particle concentrations provided accurate determi-
nation of the mass mean diameter, defined to be the
diameter at which 50 percent of the mass emitted is
composed of particles with larger diameters. The
mass median diameters at the outlets of the bag-
houses from Sunbury and Nucla were 3.9 and 8.3
microns, respectively.
The test programs measured emission rates for a
variety of fuel compositions and boiler and bag filter
operating conditions. No significant deviations from
the average emission rates were noted for variations
in firing rate, fuel sulfur content, or ash content of
the coal-coke mixture.
Only the condition of the filter bags was found
to affect the mass mean diameter measurements.
Measurements when new bags were in use indicated
a slightly lower (about 10 percent) mass median
diameter for the effluent particulate matter than did
the results of tests on used bags. No other test
caused any significant degradation of the fabric
filter performance.
The Industrial Environmental Research Laboratory's Utilities and jndustrial Power Division has issued reports on the Nucla and
Sunbury Plants. More detailed information is available in the follbwing reports:
EPA 600/2-76-077a: Fractional Efficiency of a Utility Boiler Baghpuse
Sunbury Steam-Electric Station. March 1976.
EPA 600/2-75-013a: Fractional Efficiency of a Utility Boiler Baghjause
Nucla Generating Plant. August 1975.
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Sunbury - view of exterior walkways to baghouse and exhaust ducts
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Available information on the capital investments
required for the fabric filter installations at Nucla j
and Sunbury are summarized in Tables 4 and 5.
Because both Nucla and Sunbury were retrofit con-
structions replacing original mechanical and electro-
static precipitator equipment, a direct cost comparison
between the two facilities is difficult. The Sunbury
construction costs, for example, include the installa-
tion of an ash slurry pumping and piping facility for
a settling pond more than two miles away from the
plant. The data in Tables 4 and 5, however, do
provide a useful frame of reference for judging
some of the costs encountered in fabric filter
installation.
Table 4. Sunbury Steam Electric Station Bag Filter In
Item
"I
Capital investments for ESP are comparable to
baghouse costs. Figure 3 presents the estimated
range of fly ash precipitator costs for both hot and
cold side ESPs designed to remove high resistivity
particulates. Cost data for a typical ESP installation at
the TVA Gallatin Steam Plant is presented in Table 6.
This ESP controls the particulate emissions from one
300 MW unit at a design efficiency of 95 percent.
Annual operating costs of the Nucla and
Sunbury baghouses are summarized in Tables 7
and 8. For 1977, the Nucla and Sunbury facilities had
estimated annual operating costs of $1.15 per acfm
and $0.82 per acfm, respectively. Using an electro-
static precipitator operating at 92 to 95 percent, the
TVA Gallatin Steam Plant operating costs were
estimated to be $0.61 acfm.
stallation Cost Breakdown (1972 $)
aterial Cost
PFour baghouses
sJQesJgn and Engineering
£ Vacuum cleaning system
% Platforms and ladders
: Supplements and contingencies
Upland.and land rights
-. Foundation and site preparation
Ash slurry pump house
KAsh removal system-baghouse
sh slurry system
^Additions and improvements
Electrical equipment
^Overhead
~ Total capital expenditure
ST.: Total capital expenditure
fe (1977 estimate)3
aSca!e factor from Chemical Engineering M & S equipment cost index 1972 - 4th quarter
1,266,985
30,415
95,105
39,800
90,800
241,500
343,000
v3"5a
55,400
35,600
Total Cost
2,286,985" "
563,140
74T22.5
116,310
161,030
" 1,500
192,500
179'60°
414,700
221,100
' r
72,000
662,800'
,500,100'
\
1976.
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Table 5. Nucla Steam Electric Station Bag
Filter Installation Cost Breakdown (1974 $)
h I Item :
I Three baghouses
; Ash conveyor system
aiiiRetrpfit items
k Overhead
tT Engineering and fee
,.. P P 3
i Total capital expenditure
F Total capital expenditure
j: (1977 estimate)3
*Tptal Cost
B 1,740,000
250,000
210,000
, 120,000
300,000
Sz
2,620,000
3,188,000
t
-, f
1
I
1
i
i
i
i
aScale factor from Chemical Engineering, M & S
equipment cost index 1972 - 4th quarter 1976.
Figure 3. Estimated range of fly,ash precipitator
costs hot and "enlarged" (cold). (From JAPCA
September 1974 article by N. W. Frisch and
D. W. Coy of Research-Cottrell, Inc.)
20
o 15.
1000 MW plant
subbituminous coal
99.5% efficiency
10'
Cold precipitator operating resistivity, ohm-cm
Table 6. Average Costs of ESP Operation at the Gallatin Steam Plant
j: Capital Cost ~
* i '*
i , i i
t ESP
& ! , ' t
* ' i f
s Direct Operating Costs
1 !, :.. , , !
I;; ; : I
| Utilities
1 ESP maintenance
*' Ash handling fuel consumption
2 Ash handling maintenance labor
1 and material
j Indirect Operating Costs
! Total Annual Operating Cost
7 Total Annual Operating Cost (1977 Estimate)3
-
IT-
HI
IS
1-
P"
r
L
".fi~
" 1" ' " "^ "1,324,000
~* f. ^ I^R tf3^ a, ai^, p
(Annual average 1969-1971
"" »IS-St"lSSEttll^--fW1P 1?
"* 7,835
"* " ' - ; ' "%5iD8( ""
2,200
58,980
r . i "2 a'j
164,100
235,215
343,470
, J
f- s| r»« "f
figures)
rfSMSftS s*
1
t
f
_,
1
: 1
""-> I
sfTtST hi
i i
I
i
i
s
aSca!e factor from Chemical Engineering, M & S equipment cost index 1972 - 4th quarter 1976.
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1
Nucla - view of rappers located on top of baghouse
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Sunbury - view of hoppers capturing flyash
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Table 7. 1976 Nucla Bag Filter Installation
Operating Cost Estimate
K & iSi-^.---* ... . _
/year ^Percent j
ia£^....r^.:^ Sft^'n', w>*w^T-i
aScale factor from Chemical Engineering, M & S
equipment cost index 1972 - 4th quarter 1976.
Table 8. Average Annual Operating Costs at Sunbur^ S.E.S. Bag Filter Installation (1973, 1974, 1975)
Direct Costs
Operation and maintenance labor
Maintenance material
^Utilities
|. Ash handling
Tndirect Costs
l^pepreciation 4.9%
t 3.4%
^Insurance 0.1 %
s,TTaxes
tjotal Annual Operating Cost
, 1977 estimate3
aScale factor from Chemical Engineering, M & S equi
Percent
^'"^"1
^?,337
JASPS.
complete baghouse
Placement each year)
jment cost index 1972 - 4th quarter 1976.
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The successful application of fabric filtration to
the coal-fired utility boilers at Nucla and Sunbury
Indicate their potential for further electric utility
installation. Bag filters should be considered for all
new and retrofit particulate control systems when
the following conditions are present:
control efficiencies exceeding 95 percent
are required
effluent gas flow rate varies widely due to
frequent load changes or regular cycling
fuel composition is variable resulting in
changing chemical concentration on the fly
ash surfaces
high ash resistivity causing inefficient particle
collection by electrostatic precipitators.
In some cases, high-volume systems using ESPs
could benefit from the installation of a baghouse in
parallel to the ESP to reduce the volume flow and
increase its efficiency.
New fabric materials have eliminated the excess
maintenance requirements of the original baghouse
designs, resulting in operating costs comparable to
electrostatic precipitators. Initial capital investments
are also similar and lower in situations where collec-
tion efficiency requirements are greater than 99
percent. Therefore, as new, more restrictive regula-
tions are promulgated and the use of low-sulfur,
Western coals increases, the fabric filter will become
the first choice for many utility boiler operations
firing solid fuels.
Sunbury - filter bag support frames and tension adjusting device
This capsule report has been prepared jointly by Technology Transfer and the Utilities and Industrial
Power Division, Industrial Environmental Reasearch Laboratory. For further information write to:
Particulate Technology Branch
Utilities and Industrial Power Division, IERL
Research Triangle Park, N.C. 27711
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