vyEPA
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 2771 1
EPA-600/7-78-193
October 1978
Particle Collection
by a Venturi
Scrubber Downstream
from an Electrostatic
Precipitator
Interagency
Energy/Environment
R&D Program Report
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
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9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from, adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
systems; and integrated assessments of a wide range of energy-related environ-
mental issues.
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This report has been reviewed by the participating Federal Agencies, and approved
for publication. Mention of trade names or commercial products does not con
stitute endorsement or recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/7-78-193
October 1978
Particle Collection by a Venturi
Scrubber Downstream from an
Electrostatic Precipitator
by
L E. Sparks, G. H. Ramsey, and B. E. Daniel
Environmental Protection Agency
Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, North Carolina 27711
Program Element No. EHE624
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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ABSTRACT
The results of pilot plant experiments of participate collection by
a venturi scrubber downstream from an electrostatic precipitator (ESP)
are presented. The data, which cover a range of scrubber operating
conditions and ESP efficiencies, show that particle collection by the
venturi scrubber is not affected by the upstream ESP; i.e., for a given
scrubber pressure drop, particle collection efficiency as a function of
particle diameter is the same for both ESP on and ESP off. The experi-
mental results are in excellent agreement with theoretical predictions.
Order of magnitude cost estimates indicate that particle collection by
ESP scrubber systems is economically attractive when scrubbers must be
used for SO control.
A
ii
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TABLE OF CONTENTS
Page
Abstract i i
List of Figures iv
List of Tables iv
Nomenclature v
Introduction 1
Conclusions 2
Recommendations 2
Experimental Equipment 3
Test Program 5
Experimental Results 5
ESP Scrubber System Performance 11
Theoretical Analysis of Combined ESP Scrubber Systems 11
Discussion 16
Cost Analysis 19
Plume Opacity 24
References 28
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FIGURES
Number Page
1 Scrubber system added to ESP outlet 4
2 Graded penetration curves for venturi scrubber
- phase 1 experiments 8
3 Graded penetration curves for venturi scrubber
- phase 2 experiments 9
4 Average graded penetration curves for venturi scrubber
- phase 2 experiments 10
5 Graded penetration curves for ESP scrubber system 12
6 Graded penetration curves for ESP scrubber system 13
7 Graded efficiency curve for ESP with penetration
of 0.0771 17
8 Penetration versus particle diameter for scrubber with
pressure drop = 23 cm HLO, density - 2.4 g/cc 18
9 Graded penetration curve for ESP scrubber system
- ESP penetration = 0.0771; scrubber pressure drop =
23 cm H20 20
10 Parameter K as a function of the log-normal size
distribution parameters for a white aerosol 25
TABLES
Number ' Page
1 Experimental Conditions for ESP Scrubber Experiments 6
2 Summary of Calculated Results for ESP Scrubber System 15
3 Estimated Light Transmission and In-Stack Plume Opacity
for ESP Scrubber Systems 26
IV
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NOMENCLATURE
AC - Annualized cost, $
C - Cunningham correction factor
CC - Capital cost, $
CCESp - Capital cost of ESP, $
CC
scrubber - Capital cost of scrubber, $
d - Particle diameter, ym
d. - Aerodynamic particle diameter, ymA
E - Fan efficiency
H - Number of operating hours per year
I - Intensity of light transmitted through aerosol
I - Intensity of light source
32
K - Light scattering parameter, cm /m
K - Cost of electric power, $/kW-hr
L - Optical path length
L/G - Liquid to gas flow rate ratio, m /m
PtESP " Overa11 penetration through ESP
Ptrrnq - Overall penetration through ESP scrubber
Pt(d)ESp - Penetration of particles with diameter d through ESP
pt(d)ESps _ penetration of particles with diameter d through ESP scrubber
Pt(d) - Penetration of particles with diameter d through scrubber
s 3
Q - Flow rate, m /hr
r - Geometric mass mean particle radius
gw 23
SCA - Specific collector area, m /Am /s
23
SCAmin - Minimum specific collector area, m /Am /s
W - Mass concentration of particles
AP - Pressure drop, cm of water
p - Density, g/cc
a - Geometric standard deviation
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INTRODUCTION
There is considerable interest in using electrostatic precipitator
(ESP) scrubber systems for particulate collection in coal fired utility
boilers. At least one utility plans to use a moderately efficient ESP
followed by a scrubber to meet emission standards for a new boiler. The
recent amendments to the Clean Air Act which require SO removal for
/\
most plants are likely to increase interest in ESP scrubber systems.
There are numerous undocumented reports that a scrubber downstream
from an ESP works better than expected. Theoretical and experimental
studies of particle collection by drops indicate that there is no reason
to expect a scrubber downstream from an ESP to have different performance
characteristics than a scrubber alone. But data on ESP scrubber combinations
are insufficient to allow one to determine if the results from drop
collection theory apply to scrubbers.
The experimental study discussed in this report was undertaken to
provide the necessary data. Also a theoretical study was conducted to
determine what ESP scrubber configurations are capable of meeting the
possible particulate New Source Performance Standard for utility boilers
of 13 ng/J (0.03 lb/106 Btu). Order of magnitude cost estimates
were also made.
The objectives of the program were to:
1. Determine the effect of an ESP on the particle penetration
(1 minus efficiency) of a venturi scrubber as a function of
particle diameter characteristics.
2. Determine the overall mass penetration and particle
penetration as a function of particle diameter
for the ESP scrubber system.
3. Determine, with the aid of mathematical models, the ESP
scrubber configurations capable of meeting an emission
standard for fly ash of 13 ng/J.
-------
4. Estimate order of magnitude costs for the systems in 3 above.
CONCLUSIONS
The results of the experimental and theoretical studies support the
following conclusions:
1. The performance of a venturi scrubber is not affected
by the ESP; i.e., the particle penetration versus particle
diameter characteristics of the scrubber are the
same whether the ESP is on or off.
2. The performance of the scrubber is adequately modeled
by the SR-52 programmable calculator model described
2
by Sparks.
3. An ESP scrubber system can achieve an emission of
13 ng/J.
4. Annualized costs of an ESP scrubber system are attractive
when compared to costs for an ESP alone for many cases.
5. Plume opacity from an ESP scrubber system may be much
higher for a given mass emission than the plume
opacity from an ESP alone.
RECOMMENDATIONS
1. Detailed cost studies of ESP scrubber sytems should be
conducted to determine their economics.
2. Experimental and theoretical studies of plume opacity
from ESP scrubber systems should be undertaken.
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EXPERIMENTAL EQUIPMENT
The scrubber system tested in conjunction with the ESP system
consisted of a venturi scrubber, an entrainment separator, and a blower
and motor. The venturi scrubber had a round cross section with a throat
length of 25.4 cm. The throat section could be removed so various
throat diameters could be tested. The ESP scrubber tests involved only
two throat diameters: 7.62 and 10.16 cm. Larger diameters could not be
installed due to the limiting size of the opening at the throat bottom
flange. The water was added tangentially at two points at the top of
the scrubber. The water flow rate could be varied up to a maximum of
-2 3
6.43 X 10 m /min. The scrubbing water was not recirculated. Maximum
gas flow was about 28 m /min.
Following the venturi scrubber, the gas stream entered a cyclonic
entrainment separator. The separator had a diameter of 50.8 cm and was
1.22 m in height. The gas entered the separator at the bottom and
exited tangentially near the top. The gas was moved through the system
by a blower powered by a 15 hp motor.
The installation of the scrubber to the outlet of the ESP involved
removing a 3 m section of duct from the ESP system and rerouting the gas
stream through the scrubber system and back to the original ESP system
duct, as shown in Figure 1. A transition section was added to the ESP
duct to reduce the duct diameter from 30.48 to 15.24 cm to accommodate
the scrubber. Flexible duct was used to connect the transition section
to the scrubber. The gas was exhausted from the entrainment separator
through a 15.24 cm duct to the fan and through a flexible duct (30.48 cm
diameter) to connect the fan to the original ESP exhaust system.
Pressure taps were added to the duct at the entrance to the scrubber,
between the scrubber and separator, and at the exit of the separator.
The pressure taps allowed for measurement of pressure drop over the
scrubber and separator.
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ORIGINAL ESP
EXHAUST DUCT
ROTA-
METER
TRANSITION DUCT
(30.48 cm DIAMETER TO 15.24 cm DIAMETER)
ORIGINAL
ESP EXHAUST
DUCT
\
15.24 cm FLEXIBLE DUCT
20.32cm SQUARE
SECTION
Figure 1. Scrubber system added to ESP outlet.
-------
The ESP used for the experiment is a one lane wire duct ESP and is
fully described by Lawless et al.
The aerosol generator consisted of two sand blast guns which were
fed fly ash by a vibrating screw feeder. Preliminary experiments were
conducted with fly ash fed directly to the sand blast guns. These
experiments showed that significant fly ash settled in the inlet duct. A
cyclone was placed in the line between the feeder and the sand blast
guns, to prevent dust fallout in the inlet duct. Previous experience
showed that this aerosol generator was stable. Additional information
can be found in Lawless et al. The particle size distribution was
approximately log-normal with a geometric mass mean diameter of about
5.5 ymA and geometric standard deviation of 2.3 when the cyclone was
used.
All size distribution measurements were made with Meteorology
Research, Inc. (MRI) cascade impactors with greased substrates. The
impactors were calibrated by personnel of EPA Industrial Environmental
Research Laboratory's Particulate Technology Branch (PATB), using the
4
procedure described by Calvert et al.
TEST PROGRAM
The experimental program was divided into two phases: Phase 1 was
a preliminary study, and Phase 2 was a systematic study with replication.
The variables studied in the Phase 2 experiments were:
ESP on or off
ESP penetration 1 to 0.037 (efficiency 0 to 96.3%)
Liquid/gas ratio 6.65 x 10"4 to 2.66 x 10~3 m3/Am3
The experimental conditions for all tests are shown in Table 1.
EXPERIMENTAL RESULTS
The overall penetrations for the ESP, the scrubber and the ESP
scrubber system are shown in Table 1. Since the particle size distribution
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Table 1. EXPERIMENTAL CONDITIONS FOR ESP SCRUBBER EXPERIMENTS
Date
12/17/77
12/18/77
12/19/77
1/16/78
1/17/78
1/19/78
1/23/78
1/24/78
1/25/78
1/26/78
1/27/78
2/3/78
2/6/78
2/7/78
2/6/78
2/14/78
2/16/78
2/21/78
2/23/78
ESP
Penetration
0.05
ESP off
0.034
0.382
0.34
ESP off
ESP off
ESP off
ESP off
0.328
0.516
ESP off
ESP off
0.257
0.256
ESP off
ESP off
0.733
0.0375
Scrubber Parameters
Throat
Diameter, cm
10.16
10.16
10.16
10.16
10.16
10.16
10.16
10.16
10.16
10.16
10.16
7.62
7.62
7.62
7.62
10.16
10.16
10.16
10.16
L/G, m3/m3
1 X 10"3
1 X 10"3
1 X 10"3
1.2 X 10"3
1.2 X 10"3
1.2 X 10"3
1.2 X 10"3
2.3 X 10"3
2.3 X 10"3
2.3 X 10"3
2.3 X 10"3
1.2 X 10"3
1.2 X 10"3
1.2 X 10~3
1.2 X 10~3
5.32 X 10"4
5.32 X 10"4
5.32 X 10"4
-4
5.32 X 10
AP,cm H20
31.1
31.1
31.1
39.6
39.6
39.6
39.6
68.3
68.3
68.3
68.3
62.2
62.2
62.2
62.2
26.7
26.7
26.7
26.7
Penetration
0.0226
0.022
0.024
0.0129
0.0165
0.0106
0.010
0.0022
0.0020
0.0034
0.004
0.0041
0.0048
0.0072
0.0079
0.0235
0.019
0.0138
0.0911
Overall
Penetration
for System
0.00113
0.022
0.000816
0.0049
0.0056
0.0106
0.010
0.0022
0.0020
0.0011
0.0021
0.0041
0.0048
0.0018
0.0020
0.0235
0.019
0.010
0.0034
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into the scrubber depends on the penetration through the ESP, the overall
penetration results shown in Table 1 must not be used to determine the
effect of the ESP on scrubber performance. Instead, the particle penetration
as a function of particle diameter (the graded penetration) curves for
the scrubber must be used to determine the effect of the ESP. (The
graded penetration curve for a scrubber is independent of the inlet
particle size distribution.)
The graded penetration curves for Phase 1 are shown in Figure 2 as
a plot of penetration versus aerodynamic particle diameter, dA. (dA = d
/P C where d is the physical particle diameter, p is the density of the
particle, and C is the Cunningham correction factor.) The predicted
graded penetration curve is also shown in Figure 2.
The results of all the Phase 2 tests are shown in Figure 3. The
average graded penetration curves for each of the Phase 2 tests are
shown in Figure 4.
It is obvious from the data shown in Figures 2 and 4 that scrubber
performance is dominated by the pressure drop across the scrubber and
that the ESP has no effect on the performance of the scrubber. It is
also clear from Figure 2 that the predicted graded penetration curve is
in excellent agreement with the experimental data.
Statistical analysis of the data showed that:
1. There was no effect on scrubber performance due
to the ESP.
2. Particle collection in the venturi was dominated
by pressure drop.
3. Changes in throat diameter (i.e., changes in gas
velocity in the throat) had more effect than changes
in L/G.
4. The estimated standard deviation in the experimental
graded penetration curves was about 20%.
-------
1.0
1 I I
T I I I I I
1 I I
I I t I I
o
H
0.10
01
O MEASURED • ESP ON 12/17/77
ESP PENETRATION = 0.05
SCRUBBER Ap = 31.1 cm H20
D SCRUBBER PENETRATION-PREDICTED
SCRUBBER Ap= 31.1 cm H20
A ESP OFF -MEASURED 12/20/77
Ap=31.1cmH20
• ESP ON-12/19/77
ESP PENETRATION = 0.034
SCRUBBER Ap = 3i.ic
I 1 1
L 1 I I I I I
0.1 1.0
AERODYNAMIC PARTICLE DIAMETER, micrometers
Figure 2. Graded penetration curves for venturi scrubber - phase 1 experiments.
10
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0.10 —
o
t-
oc
21 6/78
21 7/78
21 8/78
2/14/78
2/15/78
2/21/78
2/23/78
0.010
0.001
1.0 10
AERODYNAMIC PARTICLE DIAMETER, micrometers
Figure 3. Graded penetration curves for venturi scrubber - phase 2 experiments.
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1.0
F 0.10
0.01
1 I r
i I r
I I I IT
O ESP ON
D ESP OFF
• ESP ON
ESP OFF
ESP OFF
ESP ON
I
I I I
10.16 cm THRO AT
- SCRUBBER AP = 39.6cmH20
• SCRUBBER AP = 39.6 cm H20
- SCRUBBER AP = 68.3 cm H20
- SCRUBBER AP = 68.3cmH20
7.62 cm THROAT
- SCRUBBER AP = 62.2cmH20
- SCRUBBER AP = 62.2 cm H20
I I I I I I I
III I I I I I I
0.1 1.0 10
AERODYNAMIC PARTICLE DIAMETER, micrometers
Figure 4. Average graded penetration curves for venturi scrubber - phase 2 experiments.
10
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ESP Scrubber System Performance
The overall mass penetration of the ESP scrubber system for each
run is summarized in Table 1. Note that in all cases the overall mass
penetration is quite low; i.e., the overall mass collection efficiency
is quite high.
Typical graded penetration curves for the ESP scrubber system are
shown in Figures 5 and 6. These curves indicate that the ESP scrubber
system is capable of meeting the proposed revised New Source Performance
Standard. In other words, a particle collection system operating with
the characteristics shown in Figures 5 and 6 can collect fly ash with a
typical size distribution with penetrations less than 0.003 (efficiencies
greater than 99.7%).
THEORETICAL ANALYSIS OF COMBINED ESP SCRUBBER SYSTEMS
The data presented in previous sections clearly show that particle
collection by a scrubber is adequately modeled by Calvert's venturi
scrubber model. ESP particle collection data show that the EPA/SoRI ESP
5
model adequately predicts ESP performance. Therefore, the performance
of a combined ESP scrubber system should be adequately predicted by a
combination of the two models.
The predictions of the two models were combined to obtain order of
magnitude estimates of the performance and economics of using an ESP
scrubber system as opposed to either an ESP or a scrubber alone. In
essence such a system represents a tradeoff between scrubber pressure
drop and ESP plate area.
Two cases were examined:
A low current density case which corresponds to a
fly ash with high electrical resistivity (^ 5 x 10
ohm cm) such as produced by low sulfur coal (<1% S).
11
-------
0.10
I I I
0.010
tu
z
tu
0.001
0.1
I I I I I
IIII\I I I l_
DATE OF RUN
O 1/26/78
n 1/27/78
A 2/23/78
III I I I I I I I
1.0
AERODYNAMIC PARTICLE DIAMETER, micrometers
Figure 5. Graded penetration curves for the ESP scrubber system.
10
12
-------
0.10
I I I I I 1 I
I I
I I I I I L
F 0.010
0.001
DATE OF RUN
O 2/7/78
Q 2/8/78
I 111 I I I I I I I | I LJ I I I I I I
1.0 10
0.1
AERODYNAMIC PARTICLE DIAMETER, micrometers
Figure 6. Graded penetration curves for the ESP scrubber system.
13
-------
A moderate current density case which corresponds
to a fly ash with moderate electrical resistivity
(^3 x 10 ohm cm) such as produced by moderate
sulfur coals (^1.5-2% S).
The following assumptions were made:
1. The fly ash size distribution was log-normal with
mass mean diameter of 20 ym and geometric standard
deviation of 4.5.
2. Fly ash density was 2.4 g/cc.
3. Gas flow distribution in the ESP was characterized
by a normalized standard deviation of 0.25.
4. The factor for sneakage and nonrapping reentrainment
in the ESP was 0.1.
5
5. Rapping losses were typical as described by McDonald.
The results of the calculations are summarized in Table 2.
The results summarized in Table 2 show that the scrubber pressure
drop, AP, is a function of the penetration through the ESP, T^fpcp*
and is essentially independent of the current density. The pressure
drop to PtpSp relationship is:
AP = 85~PtESp (1)
where AP is in cm water and H is a fraction.
Because the specific collector area, SCA, required to give a given
PtESP *s a funct^on °f tne current density, the relationship between AP
and SCA is different for the two current densities:
14
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Table 2. SUMMARY OF CALCULATED RESULTS FOR ESP SCRUBBER SYSTEM
Configuration
ID Number
ESP Parameters
SCA
m2/Am3/s Ft Resistivity
ScrubDer Parameters
P
cm water Pt
Overall
Penetration
1
2
3
4
5
6
7
8
9
10
11
156.1
78.04
33.93
16.43
8.214
74.32
35.47
15.30
7.094
3.393
0
0.0024 high
0.0165
0.0771
0.187
0.330
0.002 moderate
0.0164
0.0762
0.186
0.331
_ _
-
9.1
24.0
34
43
-
8
24
34
43
67
-
0.182
0.0389
0.016
0.009
-
0.183
0.0394
0.016
0.0091
0.0029
0.0024
0.003
0.003
0.003
0.003
0.002
0.003
0.003
0.003
0.003
0.003
15
-------
For the high current density case,
AP = exp (3.94 - 0.0536 SCA) (2)
For the low current density case,
AP = exp (3.90 - 0.0220 SCA) (3)
2 3
For both, P is in cm water and SCA is in m /Am /s.
The calculated results show that the SCA can be reduced by about a
factor of 2 for both moderate and high resistivity cases, for a scrubber
AP of about 10 cm water.
DISCUSSION
The initial reaction to the calculated and experimental results is
one of disbelief. It does not appear reasonable to expect a fairly
inefficient ESP and a moderate to low pressure drop scrubber to perform
as well as both the experimental data and the calculated results
show. An examination of the particle penetration versus particle diameter
curves (the graded penetration curve) for both devices acting alone and
the combined graded penetration curve can explain the results.
The calculated graded penetration curve for an ESP with a penetration
of 0.0771 is shown in Figure 7. Note that the ESP curve has a broad
peak from about 0.4 to 1 ym and then drops fairly rapidly on both sides
of the peak. On the other hand the graded penetration curve, Figure 8,
for a scrubber needed to produce an emission of 13 ng/J in combination
with the ESP drops rapidly from essentially 1.0 at 0.1 ym to less than
0.01 at 3 ym. The scrubber is seen to be efficient in particle diameter
regions where the ESP is inefficient and the ESP is efficient in particle
diameter regions where the scrubber is inefficient. The two devices
complement each other.
The graded penetration of the ESP scrubber system can be obtained
by multiplying the two separate graded penetration curves; i.e,.
16
-------
10
1—I I I I 11
i r~i—i—i iiiu
oc 0.10
0.01
I I I I I I I
I
I i I
I I I I I I
0.1
1.0
PHYSICAL PARTICLE DIAMETER, micrometers
Figure 7. Graded efficiency curve for ESP with penetration of 0.0771.
10
17
-------
1JJ
F0.10
OKI
n — i i i i i
rn — i i i i i u
J 1 I
I I
I I I I
0.1
1.0
PHYSICAL PARTICLE DIAMETER, micrometer*
10
Figures. Penetration versus particle diameter for scrubber with pressure drop = 23 cm
density - 2.4 g/cc.
18
-------
Pt(d)ESps = Pt(d)ESp x Pt(d)s (4)
where
Pt(d)ESps, Pt(d)ESp and Pt(d)s are the penetrations of
particles with diameter d for the ESP scrubber system, the ESP alone,
and the scrubber alone, respectively. The resulting graded penetration
curve is shown in Figure 9. Note the curve has a sharp peak at about
0.3 ym and drops rapidly on both sides. This sharp peak is characteristic
of the ESP scrubber system and, as is discussed in the section on plume
opacity, may cause problems with respect to plume opacity limits. (Note
that the curves in Figures 7, 8, and 9 are for penetration versus physical
particle diameter, not aerodynamic particle diameter as in Figures 2, 3,
4, 5, and 6.)
The experimental graded penetration curves for the ESP scrubber
system do not show the peak in penetration because data for particle
diameters less than about 0.7 micrometers are not available.
COST ANALYSIS
A detailed cost analysis is necessary to determine if the trade off
between pressure drop and SCA is justified.
The order of magnitude cost analysis involves the following assumptions:
1. The total turnkey capital cost of a cold-side ESP is
$30/m2 plate area. (A rough range of total turnkey
cost is $270 to $370 per m .)
2. There is no capital cost of the scrubber because it is
needed for SO control.
A
3. Fan efficiency is 60%.
4. Electricity cost is $0.03/kW hr.
19
-------
1.0
0.10
0.01
T—i—n—i—rr
T—i—n—\—i i i i L
j i « i i
J i i i i L
0.1
io!
PHYSICAL PARTICLE DIAMETER, micrometers
Figure 9. Graded penetration curve for ESP scrubber system - ESP penetration = 0.0771 scrubber
pressure drop = 23 cm fO.
20
-------
5. Annualized capital charges are 15% of total turnkey
capital cost.
6. Plant operates 6100 hrs per year (<\70% capacity).
7. ESP operating and maintenance costs are insignificant
compared with capital costs of ESP and can be
neglected.
a. Scrubber maintenance and liquid loop costs are not
included because they are needed for the SO system.
A
9. Costs are for 1 MW which produces 5440 Am /hr of
flue gas.
With these assumptions the total annualized cost per MW is given by:
AC = Q [4.38 x 10"3 HK Af_ ] +0.15 CC (5)
15.8E
where AC is the annualized cost
Q is the flow rate in Am /hr,
H is the number of operating hours per year
K is the cost of electric power in $ per kW hr
AP is the scrubber pressure drop in cm ^0
E is the fan efficiency
CC is the capital cost in $
4.38 x 10 and 15.8 are unit conversion constants
For a 1 MW plant:
Q = 5440 Am3/hr
H = 6100
Ke = $0.03
E = 0.60
CC = 320 x SCA x Q
3600
21
-------
2 3
where SCA is the specific collector area in m /Am /sec, and 3600 is
3 3
necessary to convert Am /hr to Am /sec.
For the moderate resistivity case
AP = exp (3.94 - 0.0536 SCA)
and for the high resistivity case
AP = exp (3.90 - 0.022 SCA)
The cost equation for the moderate resistivity case is:
AC = 5440 {[ 4.38 x 10"4 x 6100 x 0.03 exp (3.94 - 0.0536)] (6)
15.8 x 0.6
+ 0.15 x 320 SCA}
3600
The SCA for minimum cost can be obtained from dAC/dSCA = 0. For the
moderate resistivity case:
_dAC = 5440 [8.46 x 10"3 exp (3.94-0.0536 SCA) x - 0.0536 + 1.33 x 10"2]
dSCA
= 4.53 x 10"4 exp (3.94 - 0.0536 SCA) + 1.33 x 10"2 = 0 (7)
4.53 X 10"4 exp (3.94 - 0.0536 SCA) = 1.33 x 10"2 . (8)
3.94 - 0.0536 SCA^ - In frg * ftf (9)
SCA. = 3.94 - In 29 (10)
^"n 0.0536
=10.7 m2/Am3/sec
For the high resistivity case the only change is in the exponential term
and
= 3.90 - In 71.4 = - 0.37 m2/Am3/sec (11)
22
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In other words the scrubber alone is the minimum cost option. The cost
for the moderate resistivity case is:
$2.1 x 103/year/MU
The cost for the high resistivity case is
$2.3 x 103/year/MW
The maximum cost for the high resistivity case is for the ESP alone and
2
is $11 x 10 /year/MW. The maximum cost for the moderate resistivity
case is also for the ESP alone and is $5 x 103/year/MW.
The cost picture is changed somewhat if a scrubber has to be purchased
for particulate removal. In this case Equation 6 becomes
AC = 5440 [ 8.46 x 10"3 exp (3.94 - 0.0536 SCA) + 1.33 x 10"2 SCA] (12)
+ °'15 CCscrubber
for the moderate resistivity case and
AC = 5440 L 8.46 x 10"3 exp (3.90 - 0.022 SCA) + 1.33 x 10"2 SCA] (13)
+ °'15 CCscrubber
for the high resistivity case. ccscruDber is tne capital cost of a
scrubber. Ensor et al. reported that the turnkey capital cost of a
particulate scrubber system is $50/kW or $50,000/MW. The annualized
cost of the scrubber is 0.15 x $50,000 = $7,500 which must be added to
the minimum costs calculated earlier. The annualized cost for the
moderate resistivity cases becomes $9,600 per MW per year, which
exceeds the cost of ESP alone. The annualized cost for the high resistivity
case becomes $9,800/MW/year which is still less than the cost of
the ESP alone.
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It must be noted that the cost calculations above are based on
general cost data which have a great deal of uncertainty in them.
However, the cost calculations do show that once the decision to install
scrubbers for SO control is made, the particulate collection job should
A
be shared by the ESP and the scrubber.
PLUME OPACITY
Theoretical calculations of in-stack light transmittance (1 minus
the plume opacity) as measured by a transmissometer are inexact due to
lack of data on particle refractive index and other parameters, especially
the particle size distribution. However, useful estimates can be made
based on the work of Ensor.
The in-stack plume opacity is a function of the particle size
distribution, the refractive index of the particles, the particle concen-
tration, and the optical path length. Ensor has shown that the in-stack
light transmittance is given by
In (I/I ) = WL (14)
KP
where I is the intensity of the light transmitted through the aerosol
I is the intensity of the light source (I/IQ is the transmittance)
W is the mass concentration of particles
L is the optical path length which is usually the stack diameter
K is a parameter which depends on the particle size distribution,
the particle refractive index, and the wavelength of light
p is the particle density
A plot of K for a log-normal particle size distribution versus
geometric mass mean radius with geometric standard deviation as a parameter
for wavelength of light = 550 run and a refractive index = 1.50 is shown
in Figure 10.
The graded penetration curves for the ESP, scrubber, and ESP scrubber
system can be used to estimate the log-normal parameters for various system
24
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I I I I I III)
REFRACTIVE INDEX = 1.50
WAVE LENGTH OF LIGHT = 550 nm
I'll ""I 1 I I I II
GEOMETRIC MASS MEAN RADIUS, rgw (microns)
Figure 10. Parameter K as a function of the log-normal size distribution
parameters for a white aerosol.
(§} D.S. ENSOR USED BY PERMISSION OF COPYRIGHT OWNER
25
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Table 3. ESTIMATED LIGHT TRANSMISSION AND IN-STACK PLUME OPACITY
FOR ESP SCRUBBER SYSTEMS
Configuration*
ID Number
1
2
3
4
5
11
System
ESP alone
ESP & Scrubber
ESP & Scrubber
ESP & Scrubber
ESP & Scrubber
Scrubber alone
Transmission
'"o
0.85
0.63
0.70
0.73
0.76
0.80
Opacity
1-I/I0
0.15
0.37
0.30
0.27
0.24
0.20 ^
Configuration ID number refers to Table 2.
All systems produce outlet emission of 13 ng/J.
26
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configurations that meet the 13 ng/J emission limit. These log-normal
parameters can then be used to estimate K from Figure 10. The light
transmittance can then be calculated from
I/I0 = exp (-WL/Kp) (is)
We will assume W = 0.02 g/Am3 (roughly equivalent to 13 ng/J)
L = 10 m
P = 2.4 g/cc
The estimated light transmittance for each of the system configurations
in Table 2 is shown in Table 3. Because the particle size distributions
of the ESP scrubber system are essentially the same for both the moderate
and high resistivity cases when the ESP penetration is constant, only
results for the high resistivity cases are shown in Table 3.
The estimates of transmittance show that the ESP scrubber system
can have considerably lower transmittance (higher opacity) than either
the ESP-only system or the scrubber-only system.
It must be noted that these calculations of transmittance are subject
to large uncertainties; e.g., the calculated outlet size distributions
are not exactly log-normal. The ESP computer model predictions of graded
penetration curves are not well confirmed with experimental data. Slight
changes in the non-ideal factors in the ESP model can have a large effect
on the predicted outlet size distribution, which will affect the calculated
transmittance.
In spite of the uncertainties in the calculations, the fact that ESP
and scrubbers operate on the particle size distribution differently will
tend to make the outlet particle size distribution finer and more monodisperse.
This tendency to make a fine monodisperse outlet particle size distribution
should cause higher opacities for a given mass emission.
27
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REFERENCES
1. Sparks, L. E., "The Effect of Scrubber Operating and Design
Parameters on the Collection of Particulate Air Pollutants." Ph.D.
Dissertation, University of Washington, 1971.
2. Sparks, L. E., "SR-52 Programmable Calculator Programs for
Venturi Scrubbers and Electrostatic Precipitators," EPA-600/7-78-026
(NTIS PB 277-672/AS), March 1978.
3. Lawless, P., G. Ramsey, and B. Daniel, "Characterization of
the IERL/RTP Pilot Scale Electrostatic Precipitator." EPA report in
press, 1978.
4. Calvert, S., C. Lake, and R. Parker, "Cascade Impactor Calibration
Guidelines," EPA-600/2-76-118 (NTIS PB 252-656/AS), April 1976.
5. McDonald, J. R., "Modeling and Programming the Electrostatic
Precipitation Process." EPA report in press, 1978.
6. Ensor, D. S., B. S. Jackson, S. Calvert, C. Lake, D. V. Wallon,
R. E. Nilan, K. S. Campbell, T. A. Cahill, and R. G. Flocchini, "Evaluation
of a Particulate Scrubber on a Coal-Fired Utility Boiler." EPA-600/2-
75-074 (NTIS PB 249-562/AS), November 1975.
7. Ensor, D. C., "Smoke Plume Opacity Related to the Properties
of Air Pollutant Aerosols." Ph.D. Dissertation, University of Washington,
1972.
28
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TECHNICAL REPORT DATA
(Please read Instructions on t/ie reverse before completing)
. REPORT NO.
EPA-600/7-78-193
2.
3. RECIPIENT'S ACCESSION NO.
. TITLE AND SUBTITLE
Particle Collection by a Venturi Scrubber Downstream
from an Electrostatic Precipitator
5. REPORT DATE
October 1978
6. PERFORMING ORGANIZATION CODE
AUTHOR(S)
j.E.Sparks, G.H.Ramsey, andB.E. Daniel
8. PERFORMING ORGANIZATION REPORT NO.
IERL-RTP-612
. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
EHE624
See block 10
11. CONTRACT/GRANT NO.
NA (Inhouse report)
2. 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; 12/77 - 2/78
14. SPONSORING AGENCY CODE
EPA/600/13
15.SUPPLEMENTARY NOTES Coauthor Sparks' mail drop is 61; his phone is 919/541-2925.
repOrt gjves results of pilot plant experiments of particulate collection
a venturi scrubber downstream from an electrostatic precipitator (ESP). The data,
covering a range of scrubber operating conditions and ESP efficiencies, show that
particle collection by a venturi scrubber is not affected by the upstream ESP; i. e. ,
for a given scrubber pressure drop, particle collection efficiency (as a function of
particle diameter) is the same whether the ESP is on or off. The experimental results
are in excellent agreement with theoretical predictions. Order of magniture cost
estimates indicate that particle collection by ESP scrubber systems is economically
attractive when scrubbers must be used for SOx control.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COS AT I Field/Group
Air Pollution
Dust
Scrubbers
Venturi Tubes
Electrostatic Precipitators
Sulfur Oxides
Air Pollution Control
Stationary Sources
Particulate
Venturi Scrubbers
13B
11G
07A,13I
14B
07B
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGE?
34
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
29
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