EPA-650/2-74-129-Q
June 1975 Environmental Protection Technology Series
OF CENTRIFIELD SCRUBBER
U.S. Environmental Protection Agency
Office of Research and De
Washington, 0. C. 20460
-------
EPA-650/2-74-129-0
EVALUATION
OF CENTRIFIELD SCRUBBER
by
Joseph D. McCain
Southern Research Institute
2000 Ninth Avenue South
Birmingham, Alabama 35205
Contract No. 68-02-1480
ROAP No. 21ADL-004
Program Element No. LAB012
EPA Project Officer: Dale L. Harmon
Control Systems Laboratory
National Environmental Research Center
Research Triangle Park, N. C. 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
WASHINGTON, D.C. 20460
June 1975
-------
EPA REVIEW NOTICE
This report has been reviewed by the National Environmental Research
Center - Research Triangle Park, Office of Research and Development.
EPA, and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the Environmental
Protection Agency, nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environ-
mental Protection Agency, have been grouped into series. These broad
categories were established to facilitate further development and applica-
tion of environmental technology. Elimination of traditional grouping was
consciously planned to foster technology transfer and maximum interface
in related fields. These series are:
1. ENVIRONMENTAL HEALTH EFFECTS RESEARCH
2. ENVIRONMENTAL PROTECTION TECHNOLOGY
3. ECOLOGICAL RESEARCH
4. ENVIRONMENTAL MONITORING
5. SOC1OECONOMIC ENVIRONMENTAL STUDIES
6. SCIENTIFIC AND TECHNICAL ASSESSMENT REPORTS
9. MISCELLANEOUS
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to
develop and demonstrate instrumentation, equipment and methodology
to repair or prevent environmental degradation from point and non-
point sources of pollution. This work provides the new or improved
technology required for the control and treatment of pollution sources
to meet environmental quality standards.
This document is available to the public for sale through the National
Technical Information Service, Springfield, Virginia 22161.
Publication No. EPA-650/2-74-129-a
11
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ABSTRACT
This report presents the results of fractional and
overall mass efficiency tests of an Entoleter, Inc.,
Centrifield Scrubber. The tests were performed on a
full scale scrubber used for controlling particulate
emissions from an asphalt plant. Total flue gas particu-
late mass concentrations were determined at the inlet
and outlet of the scrubber by conventional (Method 5)
techniques. Inlet and outlet particulate concentrations
as functions of size were determined on a mass basis
using cascade impactors for sizes from about 0.3 ym to
5 Mm, and on a number basis for sizes smaller than about
1 urn using optical, diffusional, and electrical methods.
The text of this report includes brief 'descriptions
of the asphalt batching process, the Centrifield Scrubber,
the measurement methods, inlet and outlet size distribution
data, and fractional efficiencies.
This report was submitted in partial fulfillment of
Contract Number 68-02-1480 to Southern Research Institute
under the sponsorship of the Environmental Protection
Agency. The work reported here was completed January 31,
1975.
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IV
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TABLE OF CONTENTS
Page
ABSTRACT iii
CONCLUSIONS 1
INTRODUCTION 2
DISCUSSION 5
APPENDICES 22
A - MANUFACTURER'S DESCRIPTION OF THE
SCRUBBER OPERATIONS 22
B - PLANT PRODUCTION DATA 25
FIGURES
1 - Schematic diagram of the asphalt plant and
scrubber layout and the locations of the sam-
pling points used in the tests 3
2 - Typical inlet data segment obtained with
optical and diffusional methods 7
3 - Typical outlet data segment as obtained with
optical and dif f usional methods 8
4 - Inlet and outlet size distributions as
obtained with optical, diffusional, and elec-
trical techniques 10
5 - Fractional efficiencies as determined by the
four methods used in the test program. The
particle sizes shown for the impactor data
are Stoke's Diameters based on a particle
density of 2.5 grams/cm3 11
6 - Entoleter Scrubber inlet and outlet size
distributions on a cumulative percentage by
weight basis. Data obtained with Cascade
Impactors 15
-------
TABLE OF CONTENTS
(Continued)
FIGURES (Cont'd.) Page
7 - Entoleter Scrubber inlet and outlet size
distributions on a cumulative mass
loading basis 16
8 - Fractional efficiencies of the Entoleter
Centrifield Scrubber as determined from
cascade impactor data 18
9 - Representative cut diameters as a function
of pressure drop (power per unit flow) for
several scrubber types, after Calvert, (1974)
J. APCA, 24:929. The performance of the
Entoleter Centrifield scrubber during
these tests is represented by the cross (+).. 21
Al - Centripetal vortex balances gas velocity
against centrifugal force 23
TABLES
I - Inlet Mass Loadings By Size Interval From
Brink Impactor Data 13
II - Outlet Mass Loadings By Size Interval From
Andersen Impactor Data 14
III - Method Five Results 19
VI
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SECTION I
CONCLUSIONS
This evaluation was one of a series of such
evaluations being conducted by the Control Systems
Laboratory of the Environmental Protection Agency to
identify and test novel devices which are capable of
high efficiency collection of fine particulates. The test
methods used may not be consistent with compliance-type
methods, but were state-of-the-art techniques for measuring
mass and fractional efficiency using the standard mass
train and inertial, electrical, optical and diffusional
techniques.
The collection efficiency of the Entoleter Inc. ,
Centrifield Scrubber determined by conventional (Method 5)
techniques on a source producing particulate having a
mass mean diameter of about 100 yM was 99.50 and 99.73
for two days of testing. Measured fractional efficiencies
were about 90% at 0.03 ym, about 50% at 0.05 ym, 20%
at 0.1 ym, 50% at 0.5 ym, 90% at 1 ym, and 99.7% at 5 ym.
The scrubber energy usage during the tests was approximately
3 JOULES/1000 SCM (80 BTU/1000 SCF) at a pressure drop
of 17 cm (6.7 inches) w.c. The Centrifield Scrubber was not
found to be substantially different in efficiency from the
class of scrubbers known as conventional scrubbers. As
shown in Figure 9 of this report, the power consumption
for the Centrifield was somewhat lower but not substantially
different from that for a well-designed venturi scrubber
giving the same particulate collection efficiency.
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SECTION II
INTRODUCTION
This report presents results of tests conducted by
Southern Research to determine the capability of the
Entoleter, Inc., Centrifield Scrubber to collect fine
particulates. The goals of the tests were to determine
the overall mass efficiency and the fractional efficiency
of the scrubber while operating under normal conditions
at an asphalt batching plant. Figure 1 is a schematic
of the basic asphalt plant and scrubber system showing
the inlet and outlet sampling locations. (The scrubber
normally operates without a stack and the ducting shown
beyond the scrubber exit was added specifically for these
tests).
The tests were conducted on a 4 ton Simplicity 200
asphalt plant equipped with a 250 ton/hr capacity H & B
dryer, burning No. 2 fuel oil. The plant was operated
on an intermittent basis during the test period producing
approximately 300 tons of hot mix per day at rates of
approximately 150 to 175 tons per hour. The plant used
crushed, screened slag obtained from a local steel plant
as aggregate. In the batching process, appropriate
quantities of roughly sized aggregate are surface dried
in the rotary kiln in order to insure that the asphalt will
adhere to the aggregate (asphalt will not adhere to a
moist surface). After drying, the screened aggregate is
weighed in sequence and discharged from hot bins to the
weigh hopper in approximately one minute. It is then dis-
charged to the mixer, with the addition of hot asphalt
requiring an additional one half minute and then immediately
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EXHAUST DUCT ADDED
FOR TEST , PROGRAM
FLOW
STRAIGHTENERS
OUTLET TEST POINTS
VENT LINE AIR
ROTARY
DRYER
SCRUBBER
SECONDARY
COLLECTOR
INLET TEST
POINTS
Figure 1. Schematic diagram of the asphalt plant and scrubber
layout and the locations of the sampling points used
in the tests.
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discharged to a truck. The complete sequence including
drying requires a total time of about 30 minutes. The
particulate emissions from the process are dominated by
the drying, screening and mixing portions of the batch
operations. Because the test program was carried out
during a normally slack season for the industry, some dry
runs (runs made without the introduction of the asphalt)
of the plant were required in order to obtain sufficient
plant operating time for making all the required measure-
ments. Subsequent to the tests, it appeared that the
aggregate temperatures were not as closely controlled
during the dry runs as during actual operations and that
the inlet dust loading to the scrubber was higher during
the dry runs than during the normal runs. However, these
factors probably had only a small influence on the results
of the tests.
The exhaust gases from the plant pass through a coarse
cyclone to the fan at a temperature of about 55°C (130°F) and
from the fan are forced through the scrubber, emerging at
a temperature of about 46°C (115°F). During these tests,
the scrubber pressure drop was about 17 cm w.c. (6.7" w.c.)
and the system flowrate was about 11.67 M3/sec (24,720 ACFM).
The scrubber water flowrate was approximately 0.53 liters/M3
(4 gal/1000 CF). A description of the operation of the
scrubber is given in Appendix A.
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SECTION III
DISCUSSION
A total of five measurement techniques were used during
the tests. These were: (1) diffusional techniques using
condensation nuclei counters and diffusion batteries for
determining concentration and size distribution on a number
basis for particles having diameters less than approximately
0.2 ym, (2) optical techniques to determine concentrations
and size distribution for particles having diameters between
approximately 0.3 ym and 1.5 ym, <3) electrical methods to
determine concentrations and size distribution on a number
basis over the size range from 0.01 ym to 1 ym, (4) inertial
techniques using cascade impactors for determining concentrations
and size distributions on a mass basis for particles having
diameters between approximately 0.25 ym and 5 ym, and
(5) standard mass train measurements for determining total
inlet and outlet mass loadings.
The useful concentration ranges of the optical counter,
electrical counter (Thermosystems Model 3030 Electrical
Aerosol Analyzer), and the condensation nuclei counters
are such that extensive dilution of the gas streams being
sampled was required. Dilution factors of about 50:1
were used for both inlet and outlet measurements. In order
to insure that condensation effects were minimal, and that
the particles were dry as measured, the diluent air was
dried and filtered, and diffusional driers were utilized in
the lines carrying the diluted samples to the various
instruments.
Because only one set of optical and diffusional sizing
equipment was available, it was not possible to obtain
simultaneous inlet and outlet data with these methods. The
-------
system was first installed at the inlet sampling location,
and all the inlet data were obtained. Subsequently,
the equipment was moved to the outlet and the necessary
outlet data were obtained. For the purposes of calculating
the efficiency of the scrubber, the assumption was made
that the process was sufficiently repetitive that the
inlet data, as obtained above, were a valid representation
of that which would have been obtained during the time the
outlet measurements were made. Accuracy in the measurements
was limited by process variations and the efficiencies derived
from these data are somewhat uncertain. However, the trends
in the fractional efficiencies derived from the data are
probably real and the fractions of the influent material that
penetrate the scrubber are believed to be generally correct
to within a factor of two.
The optical data are presented on the basis of equivalent
polystyrene latex sizes and the indicated sizes can differ
from the true sizes by factors as large as two to three.
Data obtained using this method were primarily intended
as a means of real time monitoring of process changes, but
also serve as rough checks on the data obtained with the
cascade impactors.
The tests took place on the dates of October 14 through
October 23, with October 14 and 15th primarily used for
instrumentation setup, checkout, and preliminary measure-
ments. Because of difficulties in erecting the outlet
ducting, no outlet data was obtained until October 21.
The scrubber conditions were checked by a representative of
the manufacturer prior to the start of the tests.
Figures 2 and 3 show records made at the scrubber inlet
and outlet using the optical and diffusional systems. Figure 2
shows inlet data obtained during a dry run on October 18,
while Figure 3 shows outlet data obtained during an actual
batching operation.
-------
1,000,000
u
o
i
<"
750,000
O
in
g 500,000
250,000 —
1 ' 1
0 DIFFUSIONAL DATA PARTICLE
A
/ \ A OPTICAL DATA PARTICLE DIA.
y—
-------
00
2,500,000
2,000,000
u
o
c 1,500,000
I
o
z
o
en
=
U.
IJ-
O
1,000,000—
500,000
\
ODIFFUSIONAL DATA PARTICLE DIA >Q.O\nm
A OPTICAL DATA PARTICLE DIA. 0.35-0.6/im
\
I
10,000
7,500 §
5,000
1
Q.
O
2,500
10
20
30 40
TIME , minutes
50
60
70
Figure 3. Typical outlet data segment as obtained with optical and diffusional methods,
-------
It is evident from Figures 2 and 3 that large variations
in the particulate concentration and size distribution
occurred. The major swings in the condensation nuclei counter
(diffusional) data appear to result from variations in
the fuel feed rate caused by the servo system used to
control the surface temperature of the dried aggregate.
Records of the kiln exit gas temperature show swings having
patterns like those shown in the condensation nuclei counter
data. The variations in the optical counter data probably
result for the most part from variations in the aggregate
feed rate to the kiln. The accuracy of the fractional
efficiency results were thus limited by the degree to which
appropriate inlet and outlet time averages could be obtained.
Figure 4 shows typical averaged inlet and outlet size
distributions as obtained by optical, electrical, and
diffusional methods over approximately one batch. Figure 5
shows the fractional efficiencies calculated from these
data together with results from the impactor measurements.
In Figure 5, the impactor data is presented using particle
diameters based on particle densities of 2.5 g/cm3. Because
the diffusional and electrical data sets were not usually
obtained simultaneously, the averages of the data sets
obtained with each method were not the same. The difference
was especially large at the outlet of the scrubber. Thus,
the fractional efficiencies calculated from the two data
sets do not precisely agree although both show the same
general trends. The differences in the calculated frac-
tional efficiencies indicate, to some extent, the uncertain-
ties introduced by process variations.
Inertial sizing was accomplished using Brink Cascade
Impactors for inlet measurements and Andersen Impactors for
outlet measurements. Sampling was done at near isokinetic
rates. Errors due to deviations from isokinetic sampling
should be of little consequence for particles having
aerodynamic diameters smaller than 5 ym. The outlet impactor
-------
10'
INLET OUTLET
• O - ELECTRICAL
4 0 - DIFFUSIONAL
A A - OPTICAL
I06
u
8 105
a
u
o: +—
o
I01
•
O
o
A
I
001
Figure 4.
O.I 1.0
PARTICLE DIAMETER,//m
10
Inlet and outlet size distributions as obtained
with optical, diffusional, and electrical techniques
10
-------
u
UJ
o
.
UJ
99.99
99.9
99.8
99
98
95
90
80
i
. 60
40
20
10
5
2
I
O.I
0.01
0.01
Figure 5.
o - ELECTRICAL
O-DIFFUSIONAL
A-OPTICAL
o-INERTIAL
I I I I I I I I
T 1 | I I I I I
I I I I I I I I
O.I
1.0
PARTICLE DIAMETER,
I I I I I I
10
Fractional efficiencies as determined by the four methods used in
the test program. The particle sizes shown for the impactor data
are Stoke's Diameters based on a particle density of 2.5 grams/cm3
-------
samples were obtained with the impactors heated to about
22°C (40°F) above flue gas temperature to insure that no
condensation took place within the impactor. Such con-
densation might cause operational difficulties or lead to
incorrect sizing. Liquid droplets, mist and fog were
present in the outlet duct and insufficient drying time
was available in the inlet nozzles of the impactors for
complete evaporation of large droplets, resulting in
substantial losses of large droplets in the inlet nozzles.
Material contained in these droplets was not included in
the impactor data reported here.
Because of the wide disparity in the inlet and outlet
mass loadings (inlet ^ 20,000-69,000 mg/DSCM (9-30 grains/
DSCF)) and outlet ^ 110-230 mg/DSCM (.05-.! grains/DSCF),
complete simultaneity in the inlet and outlet sampling was
not possible. Outlet samples were generally of about 45
minutes duration while inlet samples were of about 5 minutes
duration. Because the inlet sampling could not correspond
directly with the outlet sampling, an average inlet mass
loading for one batch was synthesized for each size
interval covered by the inlet impaction stages from a total
of 14 runs.
The sizes reported here for the inertial data are given
in two forms, "aerodynamic" and "physical", or Stoke's,
diameters. The "physical" diameters are based on an assumed
particle density of 2.5 g/cm3. If the true particle
densities are lower than this value, the sizes as given
should be increased by a factor equal to the square root of
ratio of the assumed density to true density. Aerodynamic
diameters are diameters based on a particle density of
1 g/cm3. The impactor data are summarized in Tables I and II,
Figure 6 shows averaged inlet and outlet mass size distri-
butions on a cumulative percentage versus aerodynamic
diameter basis. Figure 7 shows the same size distributions
12
-------
U)
TABLE I
Inlet Mass Loadings By Size Interval From Brink Impactor
Loading (mg/DSCM)
Data
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Date
10/15
10/15
10/16
10/16
10/17
10/18
10/21
10/21
10/22
10/22
10/23
10/23
10/23
10/23
Start
3:30
9:40
10:30
11:45
3:40
11:30
2:00
9:12
9:20
12:30
12:40
uui.ai.j.uii
(Mm.)
3.0
3.0
3.0
1.5
3.0
3.0
3.5
3.3
3.0
3.0
3.0
3.0
3.0
3.0
p = 2.3 >9.4
28800
55800
34300
15800
47300
68700
58100
95400
65900
43000
117000
17600
1890
49800
Dia., ym >14.2
p = 1.0
6.7-9.4
634
2720
2680
430
2240
535
970
3060
1790
1330
2930
2140
1250
2240
10.1-14.2
3.80-6.7
396
1940
2300
219
1560
1670
1220
2660
1410
1980
4110
2180
1050
2970
5.8-10
2.25-3.80
211
908
750
106
635
1530
717
1280
1160
1130
2740
1190
695
1170
3.4-5.8
1.57-2.25
96.3
307
342
30.2
177
428
525
404
279
2150
692
507
228
460
2.4-3.4
.83-1.57
81.5
222
223
15.1
97.8
210
337
261
185
181
369
306
177
240
1.3-2.4
.60-. 83
37.0
55.6
66.9
22.6
22.6
1440
84.2
78.6
66.8
55.0
145
74.7
55.0
62.9
.94-1.3
.34-. 60
25.9
25.9
3.71
22.6
18.8
40.6
47.1
64.3
31.4
31.4
130
82.5
43.2
31.4
.56-. 94
<.34
37.0
81.5
29.7
98.0
7.52
48.0
90.9
60.7
70.7
102
122
134
35.4
11.8
<.56
-------
TABLE II
Outlet Mass Loadings By Size Interval From Andersen Impactor Data
Loading (mg/DSCM)
1
2
3
4
5
6
7
8
9
10
11
Date
10/21
10/21
10/21
10/22
10/22
10/22
10/22
10/23
10/23
10/23
10/23
Start
11:33
11:40
3:28
10:13
11:25
1:22
3:43
9:12
9:12
12:36
12:38
UU1.CIUJ.UI1
(Mm.)
40
40
30
20
21
15
20
20
20
20
20
p = 2.5 >9.6
1.50
4.12
2.41
2.82
2.14
2.54
3.78
7.69
6.48
7.25
6.55
6.7-9.6
2.23
3.30
2.57
2.03
1.68
2.77
4.11
4.30
5.96
3.29
3.28
4.2-6.7
1.67
1.50
4.59
2.47
1.34
2.89
17.7
5.99
7.30
5.51
4.52
2.9-4.2
1.88
2.72
3.50
2.56
0.50
2.42
18.7
5.88
5.96
3.19
4.41
1.9-2.9
1.31
3.25
5.75
5.91
2.18
3.93
11.5
15.8
13.3
6.19
5.31
.88-1.9
12.2
15.1
22.1
23.7
4.20
14.3
12.7
18.2
20.7
12.8
11.7
.53-. 88
17.1
21.3
38.3
31.9
7.98
23.9
9.31
33.7
30.0
21.1
19.2
.38-. 53
11.1
14.9
31.3
19.0
3.28
11.3
8.14
25.1
21.4
11.9
12.8
<.38
6.42
11.90
27.9
10.8
1.26
4.96
4.45
10.7
10.8
8.22
5.99
Dia., vim
p = 1.0 >14.5 10.2-14.5 6.3-10.2 4.4-6.3
2.9-4.4 1.37-2.9 .84-1.37 .62-.84
<.62
-------
CO
<
tr
en
LU
o
o
£E
Ul
Q.
UJ
>
o
99
98
95
90
80
60
40
10
I I I I
I I
I I I I I I I
100
AERODYNAMIC DIAMETER,urn
Figure 6. Entoleter Scrubber inlet and outlet size distributions
on a cumulative percentage by weight basis. Data obtained
with Cascade Impactors.
-------
O.I
10 10
AERODYNAMIC PARTICLE DIAMETER, urn
Figure 7. Entoleter Scrubber inlet and outlet
size distributions on a cumulative mass
loading basis.
16
-------
on a cumulative mass concentration basis. The fractional
efficiencies as calculated from these data are shown in
Figure 8 on an aerodynamic diameter basis and were shown
in Figure 5 on a physical basis.
Mass train measurements were obtained by Guardian
Systems, Inc., Anniston, Alabama, under subcontract to
Southern Research Institute on October 21 and 22, and the
results of these measurements are shown in Table III.
The overall efficiencies, by mass, based on these results
are included in Table III. Runs 1, and 3 were dry runs
of the asphalt plant that were made solely to permit
sampling to take place while runs 2, and 4 were actual
batching operations. From the differences in inlet
particulate loadings under the two conditions, it would
appear that the dry runs may not well represent typical
plant operations, although they were deemed to be satisfactory
for the purposes of characterizing the performance of the
scrubber. Records of the aggregate temperatures leaving
the rotary dryer also showed pronounced differences between
the dry runs and the actual runs. Both the inlet and
outlet particulate loadings during all these tests were
substantially higher than they were during previous tests
on the same scrubber performed by another group. This
may have been due in part or wholly to the fact that subsequent
to the previous tests an American Air Filter Multiclone
that had preceded the Entoleter Scrubber was removed from
the system.
In addition to measuring particulate collection effi-
ciencies, SOx collection efficiencies were determined by
using Had2 in the impingers following the mass train to
react with any SO2 present to form HaSOi*. Subsequent
H2 SO it concentration determinations were made on the impinger
water samples from which the SOX collection efficiencies
17
-------
99.99
7 ill
99.9
99.6
99
> 98
o
1 M
uj 90
p 80
o
u
8 60
- O
40
20
10
0.5
I I
I
1.0 10
AERODYNAMIC PARTICLE DIAMETER.
Figure 8. Fractional efficiencies of the
Entoleter Centrifield Scrubber as determined
from cascade impactor data.
18
-------
TABLE III
METHOD FIVE RESULTS
Inlet
Run Number
Date
Duration (Min.)
Temperature R
Temperature K
Grains/DSCF
Grams/DSCM
Outlet
Run Number
Date
Duration (Min.)
Temperature °R
Temperature K
Grains/DSCF
Grams/DSCM
Collection
1
10/21
52
602
334
8.88
20.3
1
J»
10/21
100
575
319
.052
.119
99.41
2
10/21
15
601
334
25.82
59.2
2
10/21
50
583
324
.120
.275
99.54
3
10/22
40
582
323
14.66
33.6
3
10/22
90
576
320
.071
.163
99.52
4
10/22
40
579
321
28.53
65.3
4
10/22
90
574
318
.045
.103
99.84
Efficiency
19
-------
were calculated. These were 84%, 68%, and 88% for the three
tests runs for which such data were obtained.
The performance obtained with the Centrifield scrubber
during these tests can be compared with the expected perfor-
mance figures for other types of scrubbers using the "cut
diameter" method described by Calvert (1974) J APCA, 24:929.
This method is based on the idea that the most significant
single parameter to define both the difficulty of separating
particles from gas and the performance of a scrubber is the
particle diameter for which the collection efficiency is 0.5
(50%) . Figure 9 is adapted from one presented by Calvert
(op cit). It shows control device aerodynamic cut diameter
graphed against power per unit flow rate (hp/1000 acfm).
Also shown is the equivalent air pressure drop if all the
power went into moving the volume of air through a flow
resistance. The lines shown are theoretical and not experimental.
Lines la and Ib are for sieve plate type scrubbers with froth
density F=0.4, hole diameters dh=0.5 and 0.3 cm respectively.
Line 3 is for impingement plates and line 4 is for a packed
column from 1 to 3 M high and packing of nominal 2.5 cm
diameter. Line 2a for venturi scrubbers (f=0.25) represents
the performance of venturi scrubbers in collecting hydrophobic
particles while line 2b (f=0.5) represents the same class of
scrubbers in collecting hydrophyllic particles. From the
Centrifield scrubber operating conditions given in Section II
of this report and the measured performance data as given in
Section III the Centrifield scrubber during these tests
operated a power of 1.68 KW/CM/sec (1.16 H.P./1000 ACFM)
and produced an aerodynamic cut diameter of about 0.7 ym. The
location of these performance figures is shown as a cross (+)
in Figure 9.
Appendices are included which contain summaries of
the plant operation and production data and a manufacturer's
description of the scrubber operating principles.
20
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ro
u
a.
4.0
3.0
2.0
1.0
u 0.8
5 °'6
0 0.5
o
i 0.4
<
z
I 0.3
IT
UJ
0.2
O.I
Figure 9,
I 5
0.25
PRESSURE DROP, inches H20
5 6 7 8 9 10 15 20
30 40 50 60 80 100
I I
T
Sieve plate scrubbers-
Venturi scrubbers
Impingement plate
Packed columns
i
I
I
0.5
0.8 1.0 2.0
POWER, hp/IOOOocfm
I i i
3.0
5.0
I i I
8.0 10
6 7 8 9 10
20 30 50
PRESSURE DROP , cm H20
70 90 100
20O
300
Representative cut diameters as a function of pressure drop (power per unit
flow) for several scrubber types, after Calvert, (1974) J. APCA, 24:929.
The performance of the Entoleter Centrifield scrubber during these tests is
represented by the cross (+) .
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APPENDIX A
MANUFACTURER'S DESCRIPTION OF THE SCRUBBER OPERATIONS
Modern, high-efficiency wet scrubbers for the removal
of entrained particulates from industrial exhaust gases
depend, almost without exception, on spray contact for
particle interception. The atomization and acceleration
of the scrubbing liquid into contacting zone can be
performed by a wide variety of mechanical arrangements.
A new high-performance contactor, the centripetal vortex
contactor, is now available.
The centripetal vortex principle is illustrated in
Figure Al. For any point on radius rc and tangential gas
velocity v^/ a particle may exist whose terminal velocity
toward the vortex periphery exactly equals radial gas
velocity vr. If the particles consist of liquid droplets,
and the peripheral inlet vanes are of the proper configu-
ration, the vortex selectively develops a specific droplet
diameter distribution within the rotating field, as deter-
mined by rc, vi, and . The average droplet diameter
created by a field of this type is substantially smaller than
that created by a conventional spray contactor at the same
energy level. Droplet diameter is one of the basic para-
meters of spray contactor efficiency.
Gas scrubber performance is most conveniently described
by the relationship: Nt = apY, where Nt = loge [l/(l-collection
efficiency)] and P = energy input per unit of gas treated.
For a given dispersoid, an improvement in gas scrubber
design results in an increase in a. The centripetal vortex
principle should theoretically increase a by approximately
20% over a conventional contactor.
The droplet formation within a spray contactor is
inherently in co-current flow in respect to the gas stream,
which limits its gas absorption efficiency to a maximum
of one theoretical plate per stage. Nevertheless, spray
22
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CENTRAL RISER
STATIONARY
VANE CAGE
DROPLET
FORMATION
A-A
Vt INLET VELOCITY
VECTORS
Vr
INLET VANES
LIQUID INLET
Figure Al. Centripetal vortex balances gas
velocity against centrifugal force,
23
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contactors, in single or multiple stage arrangements,
are often the only feasible mass transfer device,
expecially in applications where insoluble particulate is
present, or where the product of the absorption process
tends to foul conventional packing and sieve plates. Mass
transfer efficiency in a spray contactor is, as would be
expected, a function of L/G ratio and specific droplet
surface area. Since specific surface area varies inversely
with droplet diameter, it is reasonable to expect that the
centripetal vortex, with its unusually small equilibrium
droplet diameter, would exhibit superior mass transfer
capabilities.
24
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APPENDIX B
PLANT PRODUCTION DATA
Base Aggregate Diameters <^ 1 inch
Top Aggregate Diameters <_ h inch
Sheet Aggregate Diameters <_ 1/8 inch
PLANT PRODUCTIONS IN TONS
to
m
10-16 10-17 10-18 10-21 10-22 10-23
Base 57 13 133 366 75
Top 134 140 112 10 464 127
Sheet 0 0 0 0 29
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TECHNICAL REPORT DATA
(Please read luu/vciiviis on the reverse before completing)
1 REPORT NO
EPA-650/2-74-129-a
3 RECIPItNT S ACCESSION-NO
A TITLE AND SUBTITLE
Evaluation of Centrifield Scrubber
5 REPORT DATE
June 1975
6 PERFORMING ORGANIZATION CODE
7 AUTHOR(S)
Joseph D. McCain
8 PERFORMING ORGANIZATION REPORT NO
SORI-EAS-75-334
9 PERFORMING ORGANIZATION NAME AND ADDRESS
Southern Research Institute
2000 Ninth Avenue, South
Birmingham, Alabama 35205
1O PROGRAM ELEMENT NO.
1AB012; ROAP 21ADL-004
11 CONTRACT/GRANT NO
68-02-1480
12 SPONSORING AGENCV NAME AND ADDRESS
EPA, Office of Research and Development
NERC-RTP, Control Systems Laboratory
Research Triangle Park, NC 27711
13 TYPE OF REPORT AND PERIOD COVE RED
Task Final; Through 1/31/75
14 SPONSORING AGENCY CODE
5 SUPPLEMENTARY NOTES
6 ABSTRACT
The report gives results of fractional and overall mass efficiency tests of a Centri-
field Scrubber (Entoleter, Inc.). The tests were performed on a full scale scrubber
used for controlling particulate emissions from an asphalt plant. Total flue gas
particulate mass concentrations were determined at the inlet and outlet of the scrub-
r by conventional (Method 5) techniques. Inlet and outlet particulate concentrations
as functions of size were determined on a mass basis using cascade impactors for
sizes from about 0. 3 to 5 jum, and on a number basis for sizes smaller than about
1 jum using optical, diffusional, and electrical methods. The report includes brief
descriptions of the asphalt batching process, the Centrifield Scrubber, measurement
methods for determining fractional efficiency, inlet and outlet size distribution data,
and fractional efficiencies.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c COSATI Field/Group
Air Pollution
Scrubbers
Evaluation
Tests
Asphalt Plants
3atching
Measurement
Flue Gases
Air Pollution Control
Stationary Sources
Centrifield Scrubber
Mass Efficiency
Particulate
13 B
07A
14 B
13H
20F
21B
8 DISTRIBUTION STATEMENT
Unlimited
19 SECURITY CLASS (This Report)
Unclassified
21 NO OF PAGES
32
20 SECURITY CLASS (Thispage)
Unclassified
22 PRICE:
EPA form 2220-1 (9-73)
26
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