oEPA
United States
Environmental Protection
Agency
Industrial Environmental Research EPA-600/7-78-177b
Laboratory December 1978
Research Triangle Park NC 27711
University of Washington
Electrostatic Scrubber
Tests at a Coal-fired
Power Plant
Interagency
Energy/Environment
R&D Program Report
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tems. The goal of the Program is to assure the rapid development of domestic
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EPA-600/7-78-177b
December 1978
University of Washington
Electrostatic Scrubber Tests
at a Coal-fired Power Plant
by
M.J. Pilat and G.A. Raemhild
University of Washington
Department of Civil Engineering
Seattle, Washington 98195
Grant No. R804393
Program Element No. EHE624A
EPA Project Officer: Dale L. Harmon
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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Abstract
A 1000 acfin University of Washington Electrostatic Spray Scrubber pilot
plant was tested on the coal fired boiler unit no. 2 at Centralia Power
Plant to demonstrate its effectiveness for controlling the emissions of
fine particles. The multiple pass, portable, pilot plant operates by
combining oppositely charged aerosol particles and water droplets in
two spray towers. Aerosol charging sections at a negative polarity pre-
cede each spray tower. The pilot plant was operated at gas flows beyond
its rated capacity. Inlet gas flow as high as 1600 acfm were recorded.
Tests to determine the effect of reducing the size of the unit were
performed. The scrubber was operated and tested in two operating modes.
The two stage mode included two active particle charging corona sections
and two spray towers. The one stage mode utilized only one corona
section:and one spray tower.
Simultaneous inlet and outlet source tests utilizing University of
Washington Cascade Impactors and in-stack filters provided both size-
dependent and overall mass basis particle collection efficiency informa-
tion. Measured overall particle collection efficiencies ranged from
99.30 to 99.99% depending upon scrubber operating conditions and the
inlet particle size distribution and mass concentration. Particle mass
concentrations measured at the scrubber outlet ranged from ,00018 grains/
sdcf to .00116 grains/sdcf. The average overall particle collection
efficiency for all tests performed in the two stage mode was 99.93%
while the one stage average efficiency was 99.825%. An integrating
nephelometer was utilized at the scrubber outlet because of low outlet
mass concentrations and subsequent low sample weights. The light
scattering coefficient was measured as a relative indication of outlet
mass concentration for different operating parameters. Tabular and
graphical data is presented to illustrate the size dependent and overall
collection efficiencies for all tests performed.
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Contents
Page
Abstract til
Contents iv
List of Figures vi
List of Tables viii
Acknowledgements ix
Abbreviations and Symbols Used x
I. SUMMARY AND CONCLUSIONS 1
II. RECOMMENDATIONS 2
III. RESEARCH OBJECTIVES 3
IV. DESCRIPTION OF SOURCE 4
V. DESCRIPTION OF UW ELECTROSTATIC SCRUBBER APPARATUS 7
A. Review of Previous Work 7
B. Description of Overall System 7
C. Cooling Tower 9
D. Particle Charging Corona Section 9
E. Water Spray Towers 12
F. Mist Eliminator 14
G. Tests Ducts 14
H. Fan 14
I. High Voltage Power Supplies 16
J. Water Supply System 16
K. Purge Air Heating System 17
VI. EXPERIMENTAL PROCEDURES AND TEST EQUIPMENT 20
VII. PARTICULATE COLLECTION EFFICIENCY RESULTS 23
A. General Test Description 23
B. Particulate Collection Efficiency (Two Stage Mode) 23
1. Cascade Impactor Measurements 23
2. In-stack Filter Measurements 26
TV
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Contents (cont.)
Page
C. Participate Collection Efficiency (One Stage Mode) 32
1, General System Description 32
2. In-Stack Filter Measurements 32
3. Cascade Impactor Measurements 38
4. Integrating Nephelometer Measurements 41
VIII. REFERENCES 43
APPENDIX A 44
Detatls on Sampling Techniques 45
APPENDIX B 46
Converting Units of Measure 47
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List of Figures
Page
IV-1 Photograph of UW Electrostatic Spray Scrubber Located
at Boiler Unit No. 2, Centralia Power Plant 5
IV-2 Schematic of Ducting Arrangement to UW Electrostatic
Spray Scrubber Pilot Plant at Centralia Power Station 6
V-l General Layout of Electrostatic Scrubber Pilot Plant 8
V-2 Cooling Tower Schematic 10
V-3 Particle Charging Corona Section 11
V-4 Collection Plate Flushing System 13
V-5 Spray Header and Nozzle Arrangement Typical to Spray
Towers #1 and #2 15
V-6 Charged Liquor Recycle System 18
V-7 Heated Purge Air System 19
VI-1 UW Cascade Impactor Sampling Train 22
VII-1 Particle Collection Efficiency and Penetration vs.
Particle Size for Impactor Tests 3-8 (Two Stage System) 25
VII-2 Particle Mass Concentration for Particles Less Than
Stated Diameter for Impactor Tests 3-5 26
VII-3 Particle Mass Concentration for Particles Less Than
Stated Diameter for Impactor Tests 6-8 27
VII-4 Inlet and Outlet Particle Size Distributions for
Cascade Impactor Tests 3-5 (Log-Normal Approximation) 29
VII-5 Inlet and Outlet Particle Size Distributions for
Cascade Impactor Tests 6-8 (Log^Normal Approximation) 30
VII-6 Particle Collection Efficiency and Penetration vs.
Particle Size for Impactor Tests 12-18 (One Stage System) 35
VII-7 Particle Mass Concentration for Particles Less Than
Stated Diameter for Impactor Tests 12-15 36
VII-8 Particle Mass Concentration for Particles Less Than
Stated Diameter for Impactor Tests 16-18 37
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VII-9 Inlet and Outlet Particle Size Distributions for
Cascade Impactor Tests 12-15 (Log-Normal Approximation) 39
VII-10 Inlet and Outlet Particle Size Distributions for
Cascade Impactor Tests 16-18 (Log-Normal Approximation) 40
VII-11 Light Scattering Coefficient, Bscat, Measured at the
Outlet of the UW Electrostatic Spray Scrubber for Various 42
Spray Voltages (All Other Parameters Held Constant)
VTT
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List of Tables
Page
V-l High Voltage Power Supply Units. 16
VI-1 Participate Source Test Parameters and Measurement
Techniques. 20
VII-1 Results of Cascade Impactor Tests 3 Through 8 at
Centralia Power Plant (Two Stage System). 24
VII-2 Results of Simultaneous In-stack Filter Tests 1-F
Through 8-F at Centralia Power Plant (Two Stage
System). 31
VII-3 Results of Simultaneous In-stack Filter Tests 9-F
Through 16-F at Centralia Power Plant (One Stage
System). 33
VII-4 Results of Simultaneous Impactor Tests 12-18,
Centralia Power Plant (One Pass System). 34
VII-5 Comparison of Incremental Particle Collection
Efficiencies Between the Two Stage and One Stage
System. 41
vn
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ACKNOWLEDGEMENTS
The authors wtsh to express their appreciation for the assistance
and cooperation of the Project Officer, Mr. Dale Harmon, Chemical
Engineer in the Particle Technology Branch of the Environmental
Protection Agency. The cooperation of Bob Werner, Gary Slanina,
Ted Phillips, and Tom White of Pacific Power and Light Co. is also
greatly appreciated.
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ABBREVIATIONS AND SYMBOLS USED
SCA Specific collection area (ft2/scfm)
L/G Liquid to gas ratio (gallons/1000 scfm)
dj-Q Aerodynamic cut diameter of cascade
impactor stages (microns)
y Gas viscosity (gm/cm-sec)
D. Jet diameter (cm)
J
I|VQ . Inertial impaction parameter at 50% col-
lection efficiency for particles of dia-
meter d5Q
C Cunningham correction factor
V. Gas velocity in the jet (m/sec)
-1
B . Light scattering coefficient (m )
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Section 1
SUMMARY AND CONCLUSIONS
The University of Washington Electrostatic Spray Scrubber portable pilot
plant was tested at the Pacific Power and Light Power Plant in Centralia,
WA on coal fired boiler unit no. 2 to demonstrate its effectiveness in
controlling the fine particle emissions. The pilot plant consists of a
cool.ing tower, two corona sections which charge the particles to a nega-
tive polarity, two spray towers into which positively charged water
droplets are sprayed and on electrostatic mist eliminator.
The unit was operated and tested in two operational modes. The two
stage mode utilized both particle charging corona sections and both
charged droplet spray towers while the one stage mode utilized only
one corona section and one spray tower. Overall particle collection
efficiencies measured for the two stage mode ranged from 99.30% to
99.99% at corona section specific collection areas (SCA) of 0.050 to
0.068 ft2/scfm. Overall particle collection efficiencies for one stage
operation ranged from 99.50% to 99.89% at an SCA range of .024 to .037
ft2/scfm. The UW Electrostatic Scrubber SCA range from about 0.024 to
0.068 ftVscfm is significantly less in magnitude than the corresponding
efficiency electrostatic precipitator with an SCA range of 0.3 to 0.8
ft2/scfm.
In conclusion it is apparent that the UW Electrostatic Spray Scrubber is
effective in the collection of particulate emissions from a coal fired
boiler. A 37% reduction in active length of the scrubber resulted in
particle collection efficiencies still in excess of 99%. The effect of
this size reduction, from a full scale design point of view, results in
a decrease in both capital and operating costs of the unit while main-
taining high overall particle collection efficiencies.
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Section II
RECOMMENDATIONS
To better evaluate the UW Electrostatic Spray Scrubber performance on a
coal fired boiler, it is recommended that additional fan capacity be added
to the system to provide a greater volumetric gas flow rate. This would
result in an even shorter gas residence time and greater particle mass
concentrations at the scrubber outlet sampling port. An increased mass
concentration at the outlet would result in greater sample weights and
consequently greater statistical reliability in the data. The process
changes and system perturbations apparent in the Centralia tests would
also have less of a relative effect upon the results.
We also recommend that the pilot plant be used to demonstrate its effec-
tiveness for simultaneous control of particulate and S02 emissions from
coal fired boilers. To accomplish this, it is felt that the installation
of continuous S02 monitoring equipment would expedite the study as well
as increase the accuracy of the measurements.
Design and construction of a larger, improved liquor recycle system is
also recommended. This would be particularly appropriate for an S02
study.
Future considerations should be given to design and installations of a
larger scale (10,000 acfm) pilot plant or demonstration unit with a self
contained liquor recycle system.
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Section III
RESEARCH OBJECTIVES
The primary objective of the field tests at Pacific Power and Light's
Centralia Power Plant was to determine the effectiveness of the UW
Electrostatic Spray Scrubber in controlling fine particle emissions from
a coal fired power boiler. Simultaneous inlet/outlet particulate collec-
tion measurements provided the basis for this study.
The effect of a variation in certain scrubber operating parameters (gas
residence time, SCA, L/G, and applied voltages) on particle collection
efficiency was also an objective of this research. This information would
then be used in the design and economic analysis of a full scale retrofit
system for a coal fired boiler.
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Section IV
DESCRIPTION OF THE SOURCE
The Centralia Steam-Electric Project located near Centralia, Washington is
a coal fired electric power generating station owned by eight Northwest
utilities and operated by Pacific Power and Light Company personnel. The
plant contains two units which have a combined generating capacity of
1,330,000 kilowatts of electricity (665,000 kilowatts per unit). The two
boilers, manufactured by Combustion Engineering, are pulverized coal fired
type, each with a designed steam rate of 5,200,000 pounds per hour at
2400 psig at the turbine inlet. The two turbine generators were manufactured
by Westinghouse Electric Corporation, each with a guaranteed rating of
664,898 kilowatts. The primary fuel is sub-bituminous C coal which comes
from a strip mine adjacent to the plant. The coal is low in sulfur content
(0.5 - 0.75%) and has a design heating value of 8100 BTU's per pound. Fly ash
particulate emission is controlled by two electrostatic precipitators.
In October, 1977, the U of W Electrostatic Spray Scrubber was transported
to the Centralia Power Plant. The sample gas stream (approximately 1500 acfm)
was tapped from the outlet of boiler unit number 2. A 12 inch sampling
scoop was installed (facing upstream) at the center point of the transition
duct between the air preheater and the precipitator. Ten inch diameter
aluminum ducting connects the sampling scoop to the scrubber which is located
approximately 60 feet below on the ground level. Due to the high negative
static pressure in the main duct, a Dayton centrifugal blower was installed
at the scrubber inlet to boost the air flow capabilities. Figure IV-1 shows
the location of the scrubber trailer (on the right) and the laboratory
trailer (on the left). A schematic of the ducting arrangement showing the
lengths of duct from the sampling scoop to the inlet of the pilot plant is
shown in Fig. IV-2.
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en
Fig. IV-1. Photograph of UW Electrostatic Spray Scrubber Located
at Boiler Unit No. 2, Centralia Power Plant
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.Air Preheater
Precipitator
59'
Sampling
Port
Scrubber
Ducting Arrangement to UW Electrostatic Spray Scrubber
MATERIAL:
10" Dia. Aluminum
Ducting
TOLERANCE:
.X ±
.XX ±
.XXX ±
UNIVERSITY OF WASHINGTON
DEPARTMENT OF CIVIL ENGINEERING
DRAWING NO.
DRAWING BY:
APPROVED BY:
SCALE:
DATE:
6/27/78
DATE:
Fig. IV-2. Schematic of Ducting Arrangement to UW Electrostatic Spray
Scrubber Pilot Plant at Centralia Power Station
6
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Section V
DESCRIPTION OF UW ELECTROSTATIC SCRUBBER APPARATUS
A. Review of Previous Work
Penney (1944) patented an electrified liquid spray test precipitator
involving particle charging, by corona discharge and droplet charging
by either ion impaction or induction. Penney1s system consisted of
a spray scrubber with electrostatically charged water droplets col-
lecting aerosol particles charged to the opposite polarity. Kraemer
and Johnstone (1955) reported theoretically calculated single droplet
(50 micron diameter droplet charged negatively to 5,000 volts) col-
lection efficiencies of 332,000% for 0.05 micron diameter particles
(4 electron unit positive charges per particle). Pilat, Jaasund, and
Sparks (1974) reported on theoretical calculation results and labora-
tory tests with an electrostatic spray scrubber apparatus. Pilat
(1975) reported on field testing during 1973-74 with a 1,000 acfm UW
Electrostatic Scrubber (Mark IP model) funded by the Northwest Pulp
and Paper Association. Pilat and Meyer (1976) reported on the design
and testing of a newer 1,000 acfm UW Electrostatic Scrubber (Mark 2P
model) portable pilot plant. Pilat, Raemhild, and Prem (1978) reported
on tests of the UW Electrostatic Scrubber at a steel plant. The UW
Electrostatic Scrubber (Patent Pending) has been licensed to the Pollu-
tion Control Systems Corporation (of Renton and Seattle, Washington)
for production and sales.
3. Description of Overall System
The major components of the pilot plant include a gas cooling tower,
an inlet and outlet test duct, two particle charging corona sections,
two charged water droplet spray towers, and a mist eliminator. Aux-
iliary equipment includes transition ductwork between major components
and a fan. The pilot plant is housed in a 40 ft. long trailer and can
be easily transported to different emission sources.
The general layout of the pilot plant is shown in Figure V-l. Incoming
gases enter the top of the trailer to be treated in the vertical gas
cooling tower and then turn vertically upward to enter the inlet test
duct. After moving down through the inlet test duct, the gases enter
the first of three horizontal passes.
The first pass contains both particle charging corona sections and the
first of two water spray towers. The two coronas are at either end of
this pass and are separated by spray tower #1. Spray tower #2 comprises
the entire second horizontal pass and the last (third) pass contains the
mist eliminator.
At the outlet of the third horizontal pass, the gases enter the top of
the outlet test duct and are then directed to the fan before being
exhausted through the trailer roof.
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INCOMING
GASES
CO
INLET TEST DUCT
SPRAY TOWER NO. 2
CORONA NO. I
EXHAUST
CASES
SECTION A-A
CROSS SECTIONAL VIEW OF
THREE WSS HORIZONTAL SECTION
OUTLET TEST DUCT
MIST
ELIMINATOR
SPRAY TOWER NO, I
ELEVATION VIEW
. SPWAY TOWER NO. 2
FAN
Fig. V-l. General Layout of Electrostatic Scrubber Pilot Plant
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C. Cooling Tower
The cooling tower is designed to lower the gas temperature to below
250°F in order to maintain structural integrity of the system
which is constructed of steel and fiberglass reinforced plastic. The
cooling tower, as shown in Figure V-2 is 1 ft. 2 in. in diameter x
9 ft. 8 in. in height and is constructed of 21 gage T. 304 stainless
steel. Cooling water is introduced through four ports spaced at 2 ft.
intervals on one side of the tower and is sprayed vertically upward
from the tower's center!ine. Four Bete Model W 10080 F full cone
stainless steel nozzles used for spraying are capable of delivering
up to 3.0 gpm at 50 psig. A funnel built into the bottom of they
spray tower extends through the trailer floor for cooling water re-
moval .
D.. Particle Charging Corona Sections
Particle charging corona sections are located at either end of the
first horizontal gas passage. The corona shells are constructed from
3/16 in. wall thickness fiberglass reinforced plastic (FRP) with in-
terior dimensions of 2 ft. wide x 3 ft. 6 in. high x 5 ft. long in
the direction of gas flow. Access to a corona interior is through
removable 2/16 in. FRP end plates which are normally bolted to 2 in.
full perimeter face flanges on either end of a corona.
The coronas are designed to operate in either a single or double lane
gas passage mode. Switching from one to another requires rearrangement
of the adjustable collection plates and discharge frame(s). The width
of individual gas lane(s) for either mode is maintained at 1 ft. and
the discharge frame to collection plate spacing is therefore 6 in. Fig-
ure V-3 shows a cutaway schematic of a corona set up for single lane
operation. The testing at Centralia Power Plant was performed with
single lane corona section. u
The overall dimensions of the discharge frame shown in Figure V-3 are
27-1/2 in. high x 3 ft. 9 in. long. The frame is constructed of 1/4 in.
x 3/4 in. T. 304 stainless steel rectangular bar stock members. Prior
to the Centralia test program these frames were modified by welding
1/8 in. diameter stainless steel rods in 1-3/4 in. lengths perpendicular
to the vertical members of each discharge frame. The spikes have
sharp points on both ends and are welded at 2 in. intervals. This
modification has decreased the plate to frame spacing by 1/4 in.
The collection plates shown in Figure V-3 are 41-1/4 in. high x 59 in.
long and are constructed from 11 gage T. 316 stainless steel. The
plates serve as full chamber baffles to keep the gases within the con-
fines of the single lane passage.
A negative corona is used to charge the particles negatively. This is
accomplished by maintaining the discharge frame(s) at a high negative
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REMOVABLE GROUND PLATE (S.S.)
FOR ONE LANE OPERATION
HIGH VOLTAGE
FEEDER CABLE
HIGH
VOLTAGE INSULATOR
DISCHARGE FRAME
SUSPENSION ROD
HIGH VOLTAGE
DISCHARGE FRAME
GAS INLET
AND OUTLET OPENING
PURGE AIR DUCT
FRP WALLS
S.S. GROUND PLATE (OUTER)
FOR TWO LANE OPERATION
Stainless Steel- Discharge Spikes
GROUND PLATE ALIGNMENT
AND SUPPORT BARS
Fig. V-3. Particle Charging Corona Section
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potential and the collection plates at a neutral or ground potential.
Field strengths generated in corona #1 and corona #2 are 13.65 KV/in.
and 15.61 KV/in. respectively. Corona power supplies are discussed
in a later section. The discharge frame is electrically isolated
from all other components inside the corona. This isolation is pro-
vided by suspending the frame on two 1 in. diameter T. 303 stainless
steel rods which are connected to porcelain insulators. The Cerama-
seal Model 902B1353-6 insulators are housed in 1 ft. diameter x 2 ft.
long x 1/4 in. wall thickness plexiglass tubes which are centered
3 ft. 6 in. apart and are located on top of the corona shells. Two
1 ft. to 1 ft. 2 in. x 3 in. FRP reducing flanges are used to join
the plexiglass tubes to the corona top.
The insulators are continually flushed with a supply of heated purge
air. The temperature of the purge air is maintained at about 120°F
and an even flow across a plexiglass tube section is obtained by
introducing the purge air through a distribution plate having approxi-
mately 10% hole area. The flushing face velocity of the purge air
is set at about 0.6 ft/sec. This same purge air distribution flange
discharge frame(s), is bolted directly to it. The high voltage lead-
in to the discharge frame is through one of the two feed-through type
insulators.
The collection plate and discharge frame flush system is shown sche-
matically in Figure V-4. A continuous wall wash is supplied to the
collection plates through 1 in. FRP square tube which had 1/8 in.
diameter holes drilled diagonally into the corner adjacent the
collection plate. The discharge frame flush is an intermittent spray
supplied by two Bete 80° fan nozzles. Both corona section and the
mist eliminator are equipped with this flushing system.
At the nominal gas flow rate of 1,000 acfm, the gas velocity in the
corona is 4.76 ft/sec for single lane operation and 2.38 ft/sec for
double lane operation. The corresponding gas residence times are
1.05 and 2.10 seconds. By varying the volume of air flow through
the system, however, the gas residence time can range from 0.70 sec-
onds (single lane operation at 1,500 acfm to 4.20 seconds (double
lane operation at 500 acfm).
E. Water Spray Towers
The first of two spray towers used in the pilot plant is situated in
the middle of the first horizontal gas passage (between the two coronas)
while the second spray tower comprises the entire horizontal gas pas-
sage. Both spray towers are 3 ft. in diameter x 3/16 in wall thick-
ness and are constructed from FRP. The lengths of the two spray
towers are 10 ft. and 24 ft. for tower #1 and #2 respectively. Gas
velocity in the spray towers at a nominal gas flow of 1000 acfm is
2.36 ft/sec. Corresponding gas residence times are 4.24 and 10.17
seconds for towers #1 and #2 respectively.
12
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Collection Plate Flush
COLLECTION PLATES
(SINGLE LANE OPERATION)
PURSE AIR AND HIGH
VOLTAGE ENTRY (PURGE
AIR DUCTS, INSULATORS,
SUSPENSION RODS AND
DISCHARGE FRAME) OMITTED
FOR CLARITY
Discharge Frame Sprays
CORONA SHELL
Fig, V-4, Collection Plate Flushing System
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Utilizing a single spray header in each tower, a maximum of 21 nozzles
can be used in the two towers. The total number of nozzles used can
vary depending on the type of nozzle, the total water flow rate and
the pressure head desired. All nozzles spray in the direction of gas
flow (co-currently). A maximum of 6 nozzles can be used in spray
tower #1 although only the 3 nozzles located farthest upstream were
used to avoid flooding of corona section #2 with spray droplets. A
single spray header in spray tower #2 can accommodate a maximum of
16 nozzles. A total of 5 to 12 nozzles were used in the Centralia
tests depending on the desired flow rate. Bete L-80 spiral fog nox-
zle/header arrangement typical for both spray towers #1 and #2 is
shown schematically in Figure V-5.
A positive charge is imparted to the water droplets by maintaining
the nozzles at a positive potential (direct charging). The nozzles
are electrically isolated from the spray tower walls by introducing
heated purge air through 3 in. diameter x 4 in. long polyvinyl
chloride (PVC) entry caps which are situated on top of the two
spray towers (see Figure V-5). Both the water and the high voltage
lead-in cable enter through a 1/4 in. diameter street tee fitting
connected to the middle of each entry cap.
F. Mist Eliminator
The mist eliminator is situated in the middle of the third and last
horizontal pass and is used to remove entrained water droplets from
the airstream. The mist eliminator is identical to the corona sec-
tions with the exception of the discharge frame being maintained at a
positive potential and the total height being 2 in. shorter (neces-
sitating an equivalent shortening of the discharge frame and collec-
tion plates).
G. Test Ducts
The inlet and outlet test ducts are located immediately before the
first corona and immediately after the mist elinimator respectively
(see Figure V-l). Both test ducts are constructed from 3/16 in. wall
thickness FRP and are 12 in. in diameter x 4 ft. long. Vertical gas
flow in a downward direction is employed because it allows the most
convenient positioning of the particle sizing source test equipment
used and described in Section VI, "Particulate Sampling Apparatus."
The particle sizing source test equipment also dictated the size of
the test ports which are 6 in. wide x 1 ft. 6 in. high. The test
ports are located three duct diameters downstream and one duct dia-
meter upstream from flow disturbances.
H. Fan
The fan used to induce the air flow (i.e., clean side) through the
pilot plant is a New York Blower Model RFE-12. The straight-bladed
14
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WATER HIGH
VOLTAGE AND
PURGE AIR ENTRY
CAP
Fig. V-5. Spray Header and Nozzle Arrangement Typical
to Spray Towers #1 and #2.
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fanwheel and housing are constructed from FRP. The fan is driven
through a split pulley belt drive by a Westinghouse 5 H.P., 208 volt,
3-phase motor .turning at 1,800 rpm and is capable of delivering up to
1,500 acf.m at 8 in. water column (WC) static pressure. The fan has a
horizontal inlet and vertical outlet. A 3/16 in. FRP wall thickness x
1 ft. diameter exhaust duct containing an adjustable damper extends
up through the trailer roof.
As previously mentioned, a Dayton centrifugal blower was installed
at the scrubber inlet to increase the air flow capabilities at the
Centralia Power Plant.
I. High Voltage Power Supplies
Four high voltage power supply units used in the pilot plant serve the
coronas, mist eliminator, and water droplet charging. All four units
operate off a 110 volt, 50 Hz, 1 0 supply and are equipped with multi-
range voltage and current meters on the high voltage output side. The
units are also equipped with overvoltage and overcurrent surge protection.
The power supplies used for the two corona sections are equipped with
spark rate controllers. The Universal Voltronics unit which energizes
corona #1 has a L.L. Little P-30 automatic voltage control and the NWL
unit for corona #2 has an integrated NWL spark rate controller. The
four power supplies are described in the following table.
Table V-l. High Voltage Power Supply Units.
Source
Corona #1
Corona #2
Mist Eliminator
Droplet Charging
Model
Universal Voltronics
NWL
Hipotronics #860-16
Hipotronics #825-40
Polarity
Negative
Negative
Positive
Positive
Rated Peak
Output
KV
40
90
60
25
mA
25
30
16
40
0. Water Supply System
The water supply system for the scrubber is controlled with a single
control panel situated,near the inlet sampling port. Two different
sources supply water to the control panel: charged.water (either
recycled or fresh) and uncharged fresh water. The charged water is
used as scrubbing liquor in spray towers #1 and #2 and the uncharged
water is used for the corona flushing systems and the cooling tower.
16
-------
A schematic of the charged scrubbing liquor system is shown in Figure
V-6. The arrangement illustrated in Figure V-6 is for recycled liquor
with fresh water make up. The Centralia Power Plant tests were per-
formed with fresh (not recycled) water. The 3 in. drain to the set-
tling tank (#3) was disconnected and ducted to the power plant water
treatment system. Fresh water was then supplied to the settling tank
at the same consumption rate as supplied to spray towers #1 and #2
combined.
A Goulds centrifugal pump model 3196 ST provides the necessary liquor
flow requirements of 95 psig and a total flow rate of 17 gpm. A
maximum flow of 5 gpm is provided to spray tower #1 while a maximum
of 12 gpm is supplied to spray tower #2.
The water in the settling tank (either recycled or fresh) is trans-
ferred into the sump tank by a 1 $ Deming centrifugal pump through the
recycle sump sprays.
The fresh water supply is used in the gas cooling tower (approximately
3 gpm) and the corona section flush systems (flow rate is unmonitored).
K. Purge Air Heating System
The new purge air heating system is schematically illustrated in Figure
V-7. The system consists of both commercially available and custom
built components. The fan is a Barry Blower model BUF-90 Junior Fan
employing a 1/3 HP motor with a maximum capacity of 500 cubic feet per
minute. The discharge air then passes through a custom design Nelco
Duct Heater. It is a 9 Kw heating unit with 4 stages to regulate the
degree of heating required. The duct heater operated on 208V, 3 power
with a 110V control source which is external of the heater. A custom
designed distribution plenum follows the heater and provides an adjus-
table purge air supply to the high voltage access points on the two
corona sections, the mist eliminator section and the recycle sump tank.
The basic design criterion for the purge air system is to provide 150°F
purge air at a range of up to 500 acfm (total).
17
-------
LIQUOR FLOW- RATE
CONTROL BOARD
FRESH
WATER
MAKE-
ELECTRICAL
VALVE
LEVEL
CONTROL
oo
PURGE AIR
4 VENT
..
"-PURGE AIR ["[{"[--PURGE AIR[iT]*- PURGE AIR
ii ii
, ,- ^
I ^ '':
AIR FL6wy* ;;^
>
P--1!- -,t --,r -
-------
FRESH WATER
MAKE-UP
SPRAY
RECYCLE SUMP
MIST
ELIMINATOR
DISTRIBUTION PLENUM.
FILTER
CORONA N0.2
DUCT
HEATER
PURGE AIR
INLET
ELEVATION VIEW
MIST ELIMINATOR
"PLAN VIEW"
Fig. V-7. Heated Purge Air System
-------
Section VI
EXPERIMENTAL PROCEDURES AND TEST EQUIPMENT
The following table indicates the source test equipment used to measure
various parameters. Further information concerning the UW Cascade
Impa'ctor is given below.
Table VI-1. Particulate Source Test Parameters and Measurement Techniques.
Parameter
Equipment
1. Air
a. Velocity and volume
b. Temperature
c. Moisture
2. Water Spray Towers
a. Water flow
3. Aerosol
a. Mass concentration
b. Size distribution
S-type pitot tube with draft
gauge
Thermometer
Wet and dry bulb thermometer
and checked by volume of
condensate
Rotometers
UW Mark III and Mark V Cascade
Impactors
UW Mark III and Mark V Cascade
Impactors
The Mark III and Mark V Cascade Impactors were used to measure both
particle size distribution and mass concentration at both the inlet and
outlet test ducts respectively. The impactors provide this information
by segregating the aerosol sample into discrete size intervals (seven
collection plates plus one final filter for Mark III and eleven col-
lection plates plus one final filter for Mark V). The aerosol
20
-------
weight on each plate provides size distribution information and the
total weight is used to determine the mass concentration. The basic
components of a sampling train utilizing a UW Cascade Impactor are
shown schematically in Figure VI-1. The impingers are used to collect
water vapor tn the sample air stream and provide a basis for calculat-
ing the moisture content of gas stream which may be checked against
the wet and dry bulb determination. The dry gas meter is used to
determine isokinetic sampling conditions as well as the total sample
volume.
By conducting simultaneous particle size distribution tests at both
the inlet and outlet test ducts, the size-dependent collection effi-
ciency curve of the pilot plant may be measured.
Overall efficiency measurements were also performed using in-stack
filters simultaneously at the inlet and outlet of the scrubber.
These measurements were performed per EPA Method 17 using a 3.54 in.
filter at the scrubber inlet and a 1.85 in. filter at the scrubber
outlet. Reeve Angel pre-washed glass fiber filters were used to
minimize any SCL reaction with the filter material.
21
-------
GAS I
FLOW
TEST DUCT
IMPACTOR
1/2 f> STEEL
PIPE PROBE
COURSE ADJUST
VALVE
VACUUM
HOSES
VACUUM
GAUGE
*
0
0
/
f^
-
X
r
4
" .
3.
' /
I
««
» *
*
\j
/
=^
» *
-
e
9
[
a «
o a
/ /
Y^
3
*
0
1
; O
r
' /'
I
*
400*
0 °
u
/
^
1
''
t
f
7
IMPINGER
KNOCK
OUT
FINE ADJUST THERMOMETERS
VALVE
AIR TIGHT
PUMP
DRY GAS
METER
ICE BOTTLE BATH
Fig. VI-1. UW Cascade Impactor Sampling Train
-------
Section VII
PARTICIPATE COLLECTION EFFICIENCY RESULTS
A. General Test Description
Participate collection efficiency measurements on the U of W Electro-
static Spray Scrubber were performed with the unit in two basMc
operating modes. In the first mode (two stage), two particl^ charg-
ing corona sections and two spray towers were used. The components
were connected in series (corona #1, spray tower #1, corona #2, spray
tower #2) followed by an electrostatic mist eliminator. In the
second mode (one stage), only one corona section and one spray tower
were on. Water flow and high voltage power to corona #1 and spray
tower #1 were turned off and they were utilized as ducting only.
Scrubber operating parameters (SCA, L/G, gas residence time, no. of
components, etc.) were subsequently reduced. Simultaneous cascade
impactor measurements and in-stack filter tests, described in Section
VI, were performed on the scrubber in both operating modes.
B. Particulate Collection Efficiency (Two Stage Mode)
1. Cascade Impactor Measurements
Initial cascade impactor tests were performed with the scrubber
in the two stage mode. Results of simultaneous inlet/outlet
impactor tests 3-8 are shown in Table VII-1. Scrubber operating
parameters (corona voltage, mist eliminator voltage, and liquor
flow rate) were held constant for all tests with a variation in
spray voltage from 0 to 10 KV. A significant variation in inlet
gas flow from 919 scfm (1179 acfm) to 1244 scfm (1515 acfm) was
noted. This variation was unavoidable. With both the scrubber
I.D, fan and the booster fan operating at full capacity, a
variation in the negative static pressure at the outlet of the
air preheater (due to varying boiler conditions) resulted in
subsequent variations in inlet gas flow. This created changes
in the parameters L/G, SCA, and gas residence time. The levels
of these parameters for impactor tests 3-8 are shown in page 2
of Table VIM. A variation in inlet gas temperature (measured
downstream of the cooling tower) from 133°F to 154°F was also
noted. Overall particle collection efficiency for these tests
ranged from 99.30% to 99.89% (0.11% to 0.70% penetration). The
particle collection efficiency and penetration as a function of
particle size (aerodynamic cut diameter of cascade impactor
stages, d5g) for tests 3-8 are shown in Figure VII-1, The aero-
dynamic cut diameter of the impactor stages is defined as the
diameter of the particle of unit density collected with 50%
efficiency and is calculated by
23
-------
Table VII-1. Results of Cascade Impactor Tests 3 Through 8 at Centralia Power Plant
(Two Stage System).
Test No./
Date
3
11/30/77
4
11/30/77
5
12/1/77
6
12/1/77
7
12/8/77
8
12/14/77
Inlet Gas
Flow
(SCFM)
1031
1055
1071
1244
919
1076
Particle Hass Cone.
(grains sdcf)
Inlet
0.25924
0.20721
0.37242
0.31301
0.53698
0.37494
Outlet
.00052
.00099
.00056
. 00068
.00039
.00029
Overall
Coll. Eff.
(*)
99.73
99.30
99.77
99.70
99.88
99.89
Penetration
(*)
0.27
0.70
0.23
0.30
0.12
0.11
Total Lfquor
Flow Rate
(gpm)
15.5
15.5
15.5
15.5
16.0
15.5
Corona Voltage
(KV)
41
68
68
68
68
68
68
*2
80
80
80
80
80
80
Spray Voltage
(KV)
11
0
0
2
2
10
0
n
0
0
2
2
10
0
SCA
(ftVscfm)
0.061
0.059
0.058
0.050
0.068
0.058
L/G
(Gal/1000 scf)
15.0
14.7
14.5
12.7
17.4
14.4
Gas Residence Time (sec.)
Corona
Section
1.82
1.78
1.76
1.51
2.05
1.75
Spray
Tower
13.99
13.67
13.46
11.59
15.69
13.40
Mist
El fminator
0.86
0.84
0.83
0.72
0.97
n.83
-------
89.89
T T i r
98.9
89.0
80.0
0.0
UW Electrostatic Scrubber
Centralia Power Plant
Nov.-Dec. 1977
Units
Overall Efficiency (%)
Overall Penetration (%)
SCA (ft2/scfm)
L/G (gal/1000 scf)
/
Symbol
CD
A
+
X
t
Test
No.
3
4
5
6
7
8
Overall
Eff.
99.73
99.30
99.77
99.70
99.88
99.89
Pen.
0.27
0.70
0.23
0.30
0.12
0.11
SCA
.061
.059
.058
.050
.068
.058
L/G
15.03
14.69
14.47
12.66
17.41
14.40
10-2
4 £
0
6 85
O-
f) *- -^
IOP
O
cr
ILJ
10"1 2 4 8 8 10° 2 4 6 8 ID1
PflRTICLE flERODYNflMIC DIflMETER, D50(MICRONS)
6
8
02
22.50
Fig. VII-1. Particle Collection Efficiency and Penetration vs. Particle
Size for Impactor Tests' 3-8 (Two Stage System)
25
-------
= r
L
18y D
5o CY:
where y is the gas viscosity, Dj the jet diameter, ^50 the
inertia! impaction parameter at 50% collection efficiency for
particles of diameter d5Q, C the Cunningham correction factor,
and Vj the gas velocity in the jet diameter. The collection
of particles of diameter less than 1.0 micron ranged from about
90% to 99. 5% (1.5 to 10% penetration). The particle mass con-
centrations (grains/sdcf) less than the stated particle aero-
dynamic diameter, den (microns), for these tests are shown in
Figures VII-2 and VII-3. The curves in these graphs illustrate
the reduction in the particle mass concentration for a particular
particle size range on going from the scrubber inlet to the
outlet.
The cumulative particle size distributions (log-normal approxi-
mation) measured at the scrubber inlet and outlet are shown in
Figures VII-4 and VII^5. The particle mass mean diameter
(particle diameter at which 50% of the particle mass is greater
than this diameter, and at which 50% is less than this diameter)
was in the 11.5 to 29.4 micron diameter range at the scrubber
inlet and in the 0.27 to 1.07 micron dtameter range at the outlet.
A good correlation existed between the actual particle size
(as measured with the cascade impactors) and the straight line
(log-normal) approximation, this analysis uses the log-normal
approximation to the particle size distribution.
Particle mass concentrations measured at the scrubber outlet
ranged from .00029 gratns/sdcf to .0099 grains/sdcf. Sample
weights on the outlet impactor substrates were consequently
quite low (,01 to .15 mg). The difference between the parti cu-
late grain loading at the scrubber inlet and outlet prevented
simultaneous sampling. Despite outlet sampling times as high
as 1 hour, low weights were recorded. Details on the sampling
techniques (sampling rates, nozzle sizes, types of substrates
used, etc,) for both the impactor tests and the in-stack filter
tests are listed in Appendix A.
2. In-stack Filter Measurements
Overall particulate collection efficiency measurements using in-
stack filters were also performed with the scrubber in the two
stage mode. The results of tests 1-F through 8-F are shown in
Table VII-2. The isokinetic sampling rate for the outlet filter
was increased to collect a larger sample (80 to 100 acf). All
scrubber operating parameters were held constant with the
exception of spray voltage which was varied between 0 and 10 KV.
Inlet conditions (mass concentration, gas flow, etc.) did not
vary as significantly as for impactor tests 3-8. Overall parti-
culate collection efficiencies ranged from 99.77% (.23% penetra-
26
-------
1.0
1.0
10.0 20 30
100.0
o
T3
(O.
o>
Oi
0)
r
O
-------
0.1 1.0 10.0 20 30 100.0
^^
.0
T3
CO
' .
CO
c
^*
i.
Cl
t. 0. 1
OJ
1 }
re
Q
(D
u
4->
i-
O. '
T3
O)
4-J
re
to .01
c
re
_£H
1
co
0)
1
§
U
r*
£
c
CD
U
C
3 .001
CO
CO
CD
U
4J
i.
re
Q.
.0001
i i i ? i i i i | i i i i i i i i | i i i i i i i i__
'. UW Electrostatic Scrubber
Centrali a Power Plant
Dec. 1977
A
A
* X "
A ^-Q
..o
A X
i A ^' ' '-
X'
,'" \j
AO/X
-
A /
/- . 7
// X'
/
& /
"/y ' *^
/'/ ///
/d /
/ '' ' \ '
' &d / G Test 6 -
A7 ' x A Test 7
/ X Test 8" - ' -
/Tnlrv't" Tn ** t **
i II 1 c L 1 cb Lb . : -
x ... ._ Outlet Tests ' . ;
!
- -
_
^v-.- e
.... -;:--A ' ":°:r
A^
A- ' '
A x---x
x-- " "
X
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
0.1 l".0 10.0 20 30 100.0
Particle Aerodynamic Diameter, C^ (microns)
Fig. VII-3. Particle Mass Concentration for Particles Less Than
Stated Diameter for Cascade Impactor Tests 6-8.
28
-------
100.0
80.0
60.0
50.0
40.0
30.0
20.0
10.0
8.0
1 6<0
& 5.0
i4.0
S 3.0
tit
I 2.0
u
.8
.6
.5
.4
.3
.2
0.1
I I
UW Electrostatic Scrubber
Centralia Power Plant
Nov.-Dec. 1977
Inlet Size
Distribution
'
/
// /
///
/
-------
100.'0
80.0
60.0
50.0
40.0
30.0
20.0
10.0
8.0
I 6'°
& 5.0
I 4.0
S 3.0
e-
tal
2
§2.0
bl
U
.8
.6
.5
.4
.3
.2
0.1
i r
r i
UW Electrostatic Scrubber
Centralia Power Plant
Nov.-Dec. 1977
Inlet Size
Distribution
/'
/' '
/' /
/ 7
/
8
/ Outlet Size
/ Distribution
1 1 I L
OCX
0.1 0.2 Q5 I 2 3 10 20 30 40 50 60 70 80 90 95
99 99B 99.9 99.99
% of MASS LESS THAN STATED DIAMETER
Figure VII-5. Inlet and Outlet Particle Size Distribution for
Cascade Impactor Tests 6-8 (Log-Normal Approximation)
30
-------
Table VII-2. Results of Simultaneous In-stack Filter Tests 1-F Through 8-F at Centralia Power Plant
(Two Stage System).
Test No./
Date
1-F
1/24/78
2-F
1/24/78
3-F
1/24/78
4-F
1/24/78
-5-F
1/24/78
6-F
1/24/78
7-F
2/1/78
8-F
2/1/78
Inlet Gas
Flow
(scfm)
1072
1091
1061
1108
1146
1192
1182
1142
Particle Mass Cone.
(grains/sdcf )
Inlet
0.40634
0.39347
0.31080
0.37958
0.39473
0.45178
0.83886
0.63517
Outlet
.00052
.00067
.00030
. 00022
.00021
.00015
.00018
.00029
Overall
Coll. Eff.
(%)
99.85
99.77
99.88
99.99
99.94
99.96
99.96
99.93
Penetration
(«)
0.15
.23
.12
.01
.06
.04
.04
.07
Total Liquor
Flow Rate
(gpm)
17.5
18.5
17.5
17.5
17.5
16.1
17.0
17.0
Corona Voltage
(KV)
#1
68
68
68
68
68
68
68
68
12
80
80
80
80
80
80
80
80
Spray Voltage
(KV)
#1
0
0
0
5
5
10
0
10
#2
0
0
0
5
5
10
0
10
SCA
(ft2/ scfm)
.058
.057
.059
.056
.055
.052
.053
.055
L/G
(Gal/1000 scf)
16.32
16.96
16.49
15.79
15.70
13.51
14.38
14.98
Gas Residence Tine (sec.)
Corona
Section
1.75
1.72
1.77
1.70
1.64
1.58
1.59
1.65
Spray
Tower
13.45
13.22
13.59
13.01
12.58
12.10
12.20
12.63
Mist
Eliminator
0.83
0.82
0.84
0.80
0.78
0.75
0.75
0.78
-------
tion) with no charge on the sprays to 99.99% (.01 penetration)
with 5 KV(+) charge on the sprays. A direct correlation between
particle collection efficiency and spray voltage was not apparent
although the 3 tests exhibiting the highest overall participate
collection efficiencies were either a 5 KV(+) or 10 KV(+) charge
on the sprays. The outlet particle mass concentrations measured
ranged from 0.00018 to 0.00067 grains/sdcf. Simultaneous sampling
at the inlet and outlet of the scrubber was not possible for
either the in-stack filter tests or the impactor tests due to
the extreme difference between inlet and outlet mass concentra-
tions in this operating mode.
C. Particulate Collection Efficiency (One Stage Mode)
1. General System Description
Operation of the scrubber in the one stage mode involves utiliza-
tion of corona #2 and spray tower #2 only. With corona #1 and
spray tower #1 inactive, the active length (in the direction of
gas flow), of particle charging section and spray tower section
is reduced 50% and 29% respectively. Gas residence time in the
combined active sections is subsequently reduced 32%. The gas
cooling tower and the electrostatic mist eliminator were used
in both the one and two stage modes. Inlet volumetric gas flow
rate remained approximately the same as measured for the two
stage tests. Total liquor flow to the spray sections was reduced
to approximately 12.0 gpm resulting in a reduction in liquor to
gas flow rate ratio of about 27%.
2, In-stack Filter Measurements
Overall particle collection efficiency measurements (in-stack
filter tests) were initially performed on the one stage system.
The results of tests 9-F through 16-F are shown in Table VII-3.
Overall collection efficiency ranged from 99.77% to 99.89%
(0.23% to 0.11% penetration). Particle mass concentration
measured at the scrubber inlet ranged from 0.6774 to 1.1390
grains/sdcf while outlet particle mass concentrations varied
from 0,00077 to 0.00116 grains/sdcf. Despite the reduction in
the operating parameters previously described, outlet particle
mass concentrations remained low, resulting in extended sampling
time and low outlet sample weights. No direct correlation
between spray voltage and particle collection efficiency was
noted. Such a correlation is difficult to establish when the
low outlet sample weights introduced a significant probable
error associated with weighing. In addition to weighing related
errors, there are other probable errors inherent in the sampling
process. The difference in inlet and outlet sampling times
necessitated by the difference in mass concentration also had
a possible effect upon the results. During the outlet testing
period (up to 60 min.), system upsets and perturbations could
affect the outlet sample and not be accounted for by the inlet
(10 minute) sample.
32
-------
Table VII-3. Results of Simultaneous In-stack Filter Tests 9-F Through 16-F at Centralia Power Plant
(One Stage System).
Test No./
Date
9-F
2/2/78
10-F
2/2/78
11-F
2/2/78
12-F
2/2/78
13-F
2/2/78
14-F
2/3/78
15-F
2/3/78
16-F
2/3/78
Inlet Gas
Flow
(scfm)
1279
1122
1179
1253
1210
1141
1190
1173
Particle Mass Cone.
(grains/sdcf)
Inlet
1.1390
0.8584
0.6774
0.6920
0.7530
0.7650
0.7110
0.7030
Outlet
.00095
.00116
.00077
.00088
.00101
.00115
.00085
.00113
Overall
Coll. Eff.
(X)
99.89
99.80
99.84
99.82
99.82
99.79
99.83
99.77
Penetration
(%)
.11
.20
.16
.18-
.18
.21
.17
.23
Total Liquor
Flow Rate
(gpm)
12.5
12.5
12.0
12.0
12.0
12.5
12.5
12.0
Corona Voltage
(KV)
#1
..
.-
__
--
._
--
#2
80
80
80
80
80
80
80
80
Spray Voltage
(KV)
#1
..
..
__
__
.-
..
--
12
0
2
5
10
0
5
2
10
§W
(ftz/scfm)
.024
.028
.027
.025
.026
.027
.026
.027
L/G
(Gal/1000 scf)
9.77
11.14
10.18
9.58
9.92
10.96
10.50
10.23
Gas Residence Time (sec.)
Corona
Section
0.74
0.84
0.80
0.75
0.73
0.82
0.79
0.80
Spray
Tower
7.96
9.07
8.63
8.12
8.41
8.92
8.55
8.68
Hist
Eliminator
0.70
0.79
0.75
0.71
0.74
0.78
0.75
0.76
CO
CO
-------
Table VII-4. Results of Simultaneous Impactor Tests 12-18, Centralia Power Plant
(One Pass System).
Test No./
Date
12
2/8/78
13
2/8/78
14
2/8/78
15
2/8/78
16
2/9/78
17
2/9/78
18
2/9/78
Inlet Gas
Flow
(scfm)
1026
1066
982
970
1025
855
1142
Particle Mass Cone.
(grains/sdcf)
Inlet
.33605
.57211
.26609
.20468
.22907
.42355
.48158
Outlet
.00060
.00071
.00088
.00045
.00047
.00042
.00081
Overall
Coll. Eff.
W
99.73
99.83
99.50
99.65
99.70
99.84
99.77
Penetration
(%)
.27
.17
.50
.35
.30
.16
.23
Total Liquor
Flow Rate
(9pm)
12.5
12.0
12.0
12.5
12.0
12.0
12.0
Corona Voltage
(KV)
11
--
--
--
--
--
--
--
n
80
80
80
80
80
80
80
Spray Voltage
(KV)
*1
--
--
--
--
--
--
--
#2
0
2
2
0
0
0
10
SCA
(ftVscfm)
.030
.029
.032
.032
.031
.037
.027
L/G
(Gal /1 000 scf)
12.18
11.26
12.22
12.89
11.71
14.04
10.51
Gas Residence Time (sec.)
Corona
Section
0.92
0.88
0.96
0.97
0.92
1.10
0.82
Spray
Tower
9.92
9.55
10.37
10.49
9.93
11.91
8.91
Hist
Eliminator
0.87
0.83
0.91
0.92
0.87
1.04
0.78
OJ
-------
99.99
£ 99.9
UJ
UJ
Q.
^-f
UJ
O
»I
UJ 99.0
O
8
UJ
d
90.0
UW Electrostatic Scrubber
Centralia Power Plant
Feb. 1978
Units
Overall Efficiency (%)
Overall Penetration (%)
SCA (ft2/scfm)
L/G (gal/1000 scf)
0.0 L_
10-1
/
Symbol
O
A
4-
X
<1>
*
X
Test
No.
12
13
14
15
16
17
18
Overall
Eff .
99.73
99.83
99.50
99.65
99.70
99.84
99.77
Pen,
0.27
0.17
0.50
0.35
0.30
0.16
0.23
SCA
.030
.029
.032
.032
.031
.037
.027
L/G
12.18
11.26
12.22
12.89
11.71
14.04
10.51
10
.-2
4 LJ
6 UJ
8
z
o
cc
a:
UJ
UJ
o_
2 4 6 8 10° 2 4 6 8 Id1
PRRTICLE RERODYNflMIC DIRMETER, D50(MICRONS)
2 2
6
8
102
50
Fig. VII-6. Particle Collection Efficiency and Penetration vs.
Particle Size for Impactor Tests 12-18 (One Stage System)
35
-------
1.0
c
o
o
i.
O)
-t->
a;
IO
r-
Q
O)
O
(O
a.
a
a;
c
(O
QJ
C
o
c
(U
o
on
I/)
(O
(U
O
0.1
.01
.001 -
,0001
I III
"T
IIII1Ti
UW Electrostatic Scrubber
Centralia Power Plant
Feb. 1978
Inlet
Tests
Q Test 12
-I- Test 13
Test 14
X Test 15
-£>
Outlet
Tests
i i
ji i
0.1
1.0 10.0
Particle Aerodynamic Diameter, d50 (microns)
100.0
Fig. VII-7. Particle'Mass Concentration for Particles Less Than
Stated Diameter for Cascade Impactor Tests 12-15.
36
-------
1.0
0
o
(A
1
I/I
c
i-
0)
!->
0)
Q
Ol
O
fO
0.
c
OJ
u
o
o
ai
o
r-
4->
S-
a.
0.1
.01
.001 -
.0001
UW Electrostatic Scrubber
Centralia Power Plant
Feb. 1978
Inlet
Tests
O Test 16
4- Test 17
X Test 18
Outlet
Tests
i i i
j _ i
0.1
1.0 10.0 20.0 30.0
Particle Aerodynamic Diameter,
-------
Comparing the composite results of the two stage and one stage
systems, the decrease in certain operating parameters as previously
discussed has only a slight affect on the overall particle collec-
tion efficiency of the system. The average overall particle col-
lection efficiency of the two stage system (tests 1-F through 8-F)
is 99.93% (0.07 penetration). The results of tests 9-F through
15-F (one stage system) show an average overall particle collec-
tion efficiency of 99.825% (0.18% penetration).
3. Cascade Impactor Measurements
Particle collection efficiency measurements using cascade impactors
were also performed with the scrubber operating in the one stage
mode. The results of these tests are shown in Table VII-4. Over-
all particle collection efficiency ranged from 99.50% to 99.84%
(0.16% to 0.50% penetration). Particle mass concentration measured
at the scrubber inlet varied from 0.30458 to 0.57211 grains/sdcf
while outlet concentrations ranged from 0.00042 to 0.00088 grains/
sdcf. Particle collection efficiency as a function of particle
size for these tests is illustrated in Figure VII-6. The collec-
tion efficiency for particles smaller than 1.0 micron in diameter
ranged from about 83% to 99%. Figures VII-7 and VII-8 illustrate
the particle mass concentration (grains/sdcf) less than stated
particle diameter (microns) for the cascade impactor tests on the
one stage system. Relative particulate concentrations (grains/
sdcf) measured at the scrubber inlet and outlet for a particular
size range can be directly obtained from these curves. The cumu-
lative particle size distributions (log-normal approximations)
measured at the scrubber inlet and outlet for impactor tests 12-18
are shown in Figures VII-9 and VII-10. Mass mean diameter (dso)
ranged from 23.13 to 76.5 microns at scrubber inlet and from
0.0324 to 1.032 microns at the scrubber outlet.
A comparison of the particle collection efficiency as a function of
particle size between the two stage and one stage system is shown in
Table VII-5. The incremental particle collection efficiencies are shown
in the mean values for all the cascade impactor tests performed in either
the one stage or two stage modes. The particle diameter is repre-
sented by the midpoint of the increment. The reduction of certain
operating parameters (SCA, L/G, gas residence time) on changing from
the two stage to one stage mode resulted in an increase, in the
particle penetration from 3.35% to 7.29% at 0.4 microns diameter and
from 0.76 to 1.4% at 1.2 microns diameter. In general the particle
penetration for these submicron particle sizes doubled on going from
two stage to one stage operation.
38
-------
100.0
80.0
60.0
50.0
40.0
30.0
20.0
10.0
8.0
I 6-°
§ 5.0
I 4.0
£ 3.0
s 2.0
I
.8
.6
.5
.4
.3
.2
UW Electrostatic Scrubber
Centralia Power Plant
Feb. 1978
Inlet Size
Distributions
14 15
12
I
I
/ y
/ '
/ '
/
// //
/ / /Outlet Size
/ / V Distributions
, if i
/ / /
/ i
'I I
15
0.1
00*
O.I 0.2 09 I 2
10 20 30 40 50 60 70 80 90 95
99 99B 99.9 99.99
% Of MASS LESS THAN STATED DIAMETER
Figure VII-9. Inlet and Outlet Particle Size Distributions for Cascade
Impactor Tests 12-15 (Log-Normal Approximation)
39
-------
100.0
80.0
60.0
50.0
40.0
30.0
20.0
10.0
8.0
| 6.0
I 5.0
I 4.0
5 3.0
>-
Ul
I 2.0
u
_!
U
.8
.6
.5
.4
.3
.2
0.1
i r
I I I
UW Electrostatic Scrubber
Centralia Power Plant
Feb. 1978
Inlet Size
Distributions,
18 16 17
J I
I i i
/ x/
- / // Outlet Size
/ // Distributions
/
18
I/
16
0.01 0.1 0.2 Q5 I 2
10
20 30 40 50 60 70 80 90 95
99 99B 99.9 9999
% Of MASS LESS THAN STATED DIAMETER
Figure VII-10. Inlet and Outlet Particle Size Distributions for
Cascade Impactor Tests 16-18 (Log-Normal Approximation)
40
-------
Table VII-5 Comparison of Particle Collection Efficiencies
Between the Two Stage and One Stage System
Particle
Diameter
(microns)
0.4
0.5
0.6
0.75
0.95
1.20
Two Stage
Coll. Eff.
(«).
96.65
97.60
98.13
98.60
98.97
99.24
Penetration
(o/\
\h]
3.35
2.40
1.87
1.40
1.03
0.76
One Stage
Coll. Eff.
(%)
92.71
94.76
96.02
97.17
98.04
98.60
Penetration
(%)
7.29
5.24
3.98
2.83
1.96
1.40
4. Integrating Nephelometer Measurements
An integrating nephelometer was used to measure the light scat-
tering coefficient at the scrubber outlet where the particle mass
concentration was typically 0.0004 to 0.0015 grains/sdcf. A sample
gas volume was extracted from the outlet test port through a heated
probe (to prevent condensation) and into the nephelometer. The
single wavelength (530 nm) nephelometer is an .instrument which meas-
ures the scattering portion of the extinction coefficient due to
particles in the sample gas. It provides an instantaneous, continu-
ous readout of the coefficient Bscat (M-l) which is a direct indi-
cation of particle concentration, particularly in the 0.1 to 1.0
micron size range. The nephelometer was originally designed for
atmospheric measurements and is consequently sensitive to extremely
low particle concentrations. Since no means of monitoring the inlet
particle mass concentrations was available, the results of this test
provide only a relative measurement of particle mass concentration
at the scrubber outlet with variations in spray voltage.
For this test the scrubber was operated in the one stage mode with
the voltage to corona #2 at 80 KV(-), mist eliminator voltage at
60 KV (+) and liquor flow rate at 12 gpm. The voltage to the liquor
sprays was held at 0, 2, 5, 10, 15, and 20 KV with 5 minute time
intervals for each voltage setting. During this time period the
light scattering coefficient, Bscat> was measured using the inte-
grating nephelometer. The light scattering measurement results
of this test are presented in Figure VII-11.
41
-------
2.24 -
2.0
1.75 -
cscat
(M'1)
ro
1.50-
1.25 -
1.0
(Spray Voltage)
(20 KV) ' (0 KV)
(0 KV) (2 KV) , (5 KV)
Figure VII-11.
Time (min.)
Light Scattering Coefficient, Bsca^, Measured at the Outlet of the UW
Electrostatic Spray Scrubber for Various Spray Voltages (All Other
Parameters Held Constant)
-------
Section VIII
REFERENCES
1. Kraemer, H. F. and H. F. Johnstone (1955) "Collection of aerosol
particles in the presence of electric fields," Ind. Engr.
Chem. 47_ 2426.
2. Penney, G. W. (1944) "Electrified liquid spray dust precipitatpr,"
U.S. Patent No. 2,357,354.
3. Pilat, M. J., S. A. Jaasund, and L. E. Sparks (1974) "Collection
of aerosol particles by electrostatic droplet spray scrubbers,"
Envir. Sci. & Tech. 8_ 340-348.
4. Pilat, M. J. (1975) "Collection of aerosol particles by electro-
static droplet spray scrubber," APCA Journal 25_ 176-178.
5. Pilat, M. J. and D. F. Meyer (1976) "University of Washington
electrostatic spray scrubber evaluation" Final Report on
Grant No. R-803278, EPA Report No. EPA-600/2-76-100 (NTIS
No. PB 252653/AS).
6. Pilat, M. J., G. A. Raemhild, and A. Prem (1978) "University of
Washington electrostatic scrubber tests at a steel plant,"
EPA Report No. EPA-600/7-78-177a.
43
-------
APPENDIX A
Details on Sampling Techniques
44
-------
Sampling Details
Test Sequence
Type of Test
Collector Used
Type of
Substrate
Sampling
Nozzle Dia.
Samp! ing
Time
Gas Volume
Sampled
(acf)
Inlet
Outlet
Inlet
Outlet
Inlet
Outlet
Inlet
Outlet
Inlet
Outlet
3-8
Simultaneous
Cascade Impactor
11 stage MK5
Cascade Impactor
7 stage MK3
Cascade Impactor
Ungreased, s.s.
Impaction Insert
Ungreased, s.s.
Impaction Insert
3/16 in.
1/4 in.
8-15 min.
18-60 min.
2.8-3.5
13.4-66.4
IF - 8F
Simultaneous
In-Stack Filter
90 mm
Filter
47 mm
Filter
Reeve Angel
934AH Filter
Reeve Angel
934AH Filter
3/16 in.
1/4 in.
10 min.
40 min.
1.8-3.0
60.5-113.5
9F - 16F
Simultaneous
In-Stack Filter
90 mm
Filter
47 mm
Filter
Reeve Angel
934 AH" Filter
Reeve Angel
934AH Filter
3/16 in.
1/4 in.
10 min.
40 min.
2.8-3.5
88.3-111.3
12 - 18
Simultaneous
Cascade Impactor
11 Stage MK5
Cascade Impactor
7 stage MK3
Cascade Impactor
Ungreased, s.s.
Impaction Insert
Ungreased, s.s.
Impaction Insert
3/16 in.
1/4 in.
20 min.
60 min.
5.0-7.16
80.5-95.4
-------
APPENDIX B
Converting Units of Measure
46
-------
Appendix B
CONVERTING UNITS OF MEASURE
Environmental Portection Agency policy is to express all measure-
ments in Agency documents in metric units. In this report, however,
to avoid undue costs or lack of clarity, English units are used
throughout. Conversion factors from English to metric units are
given below.
\
To convert from
pounds
To
Multiply by
f
feet
inches
BTU
BTU/lb
acfm
gpm
grains/sdcf
f2scfm
Kg
dynes /cm2
n,2
m3
meters
meters
joules
joules/gm
acm/hr
1/m
gm/sdcm
2
m scm/hr
°C
0.45359
+14.7 x 68947.6
0.0929
0.028317
0.3048
0.0254
1054.35
2.235
1.699
3.79
2.29
0.0547
5/9
47
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing}
1. REPORT NO.
EPA-600/7-78-177b
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
University of Washington Electrostatic Scrubber Tests
at a Coal-fired Power Plant
5. REPORT DATE
December 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
M.J. PilatandG.A. Raemhild
9. PERFORMING ORGANIZATION NAME AND ADDRESS
University of Washington
Department of Civil Engineering
Seattle, Washington 98195
10. PROGRAM ELEMENT NO.
E HE 62 4 A
11. CONTRACT/GRANT NO.
Grant R804393
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final; 6/77 - 10/78
14. SPONSORING AGENCY CODE
EPA/600/13
IB. SUPPLEMENTARY NOTES T£RL-RTP project officer is Dale L.
541-2925.
Harmon, Mail Drop 61, 919/
16. ABSTRACT
The report gives results of tests of a 1700 cu m/hr University of Washing-
ton Electrostatic Spray Scrubber pilot plant on a coal-fired boiler to demonstrate
its effectiveness for controlling fine particle emissions. The multiple-pass, portable
pilot plant combines oppositely charged aerosol particles and water droplets in two
water spray towers. Aerosol negative-charging sections precede each,spray tower.
The scrubber was tested in two modes: two-stage, including two active; particle
charging corona sections and two spray towers; and single-stage, including only one
corona section and one spray tower. Simultaneous inlet and outlet source tests pro-
vided both size-dependent and overall mass basis particle collection efficiency in-
formation. Measured overall particle collection efficiencies ranged from 99. 30 to
99.99%, depending on scrubber operating conditions , inlet particle size distribution,
and mass concentration. Particle mass concentrations measured at the scrubber
outlet ranged from 0.00041 to 0.0027 g/cu m. The average overall particle collection
efficiency for all tests performed in the two-stage mode was 99. 93%; single-stage
average efficiency was 99. 83%.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS C. COS AT I Field/Group
Pollution
Gas Scrubbing
Scrubbers
Electrostatics
Coal
Combustion
Dust
Aerosols
Pollution Control
Stationary Sources
Particulate
University of Washing-
ton Scrubber
13B
07A,13H
131
20C
2 ID
21B
11G
07D
I. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
58
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
48
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