SEPA
United States Industrial Environmental Research EPA-600/7-78-093
Environmental Protection Laboratory June 1978
Agency Research Triangle Park NC 27711
Evaluations of
Novel Particulate
Control Devices
Interagency
Energy/Environment
R&D Program Report
-------
Research reports of the Office of Research and Development, U.S. Environmental Protec-
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EPA-600/7-78-093
June 1978
Evaluations
of
Novel Particulate Control Devices
by
Joseph D. McCain
Southern Research Institute
2000 Ninth Avenue, South
Birmingham, Alabama 35205
Contract No. 68-02-1480
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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TABLE OF CONTENTS
Page No.
SECTION I - CONCLUSIONS 1
SECTION II - INTRODUCTION 2
SECTION III - MEASUREMENT TECHNIQUES 4
SECTION IV - ARONETICS SCRUBBER 7
Manufacturer's Description 7
Test. Results. . 12
SECTION V - CENTRIFIELD SCRUBBER 21
Manufacturer's Description 21
Test Results 22
SECTION VI - GRAVEL BED FILTER 33
Manufacturer's Description 33
Test Results 37
SECTION VII - VARIABLE THROAT VENTURI SCRUBBER 63
Manufacturer's Description 63
Test Results 69
SECTION VIII - SUMMARY 88
BIBLIOGRAPHY 92
11
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ABSTRACT
This report presents the results of fractional and overall
mass efficiency tests of four novel particulate control devices.
Three of the four devices were wet scrubbers; these were an Aronetics
(Chemico) Two Phase Jet scrubber, an Entoleter Centrifield scrubber,
and a CEA Variable Throat Venturi scrubber. The fourth
device tested was a Rexnord Gravel Bed Filter. The devices,
in the order listed, were used for controlling emissions from
a submerged arc ferro-alloy furnace, an asphalt batching plant,
a pulverized coal fired utility boiler, and a Portland cement
clinker cooler.
Total flue gas particulate mass concentrations and emission
rates were determined at the inlets and outlets of these devices
by conventional techniques. Inlet and outlet emission rates
as functions of particle size were determined on a mass basis
using cascade impactors for sizes from about 0.5 ym to 5 ym and
on a number basis for sizes smaller than 1 ym using optical, and
diffusional and/or electrical mobility methods.
The text of this report includes brief descriptions of the
control devices and the process on which each was utilized, the
measurement methods, inlet and outlet size distributions, and overall
and fractional efficiencies.
This report was submitted in fulfillment of contract number
68-02-1480 to Southern Research Institute under the sponsorship
of the Environmental Protection Agency.
111
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SECTION I
CONCLUSIONS
These evaluations were conducted as a part of a series of
studies being conducted by the Industrial Environmental Research
Laboratory of the Environmental Protection Agency. The studies
have as their goal the identification and testing of novel devices
which are capable of high efficiency collection of fine particu-
lates. The test methods used may not have been consistent with
compliance type methods, but were state-of-the-art techniques
for measuring mass and fractional efficiencies. The techniques
used included standard mass train, inertial, optical, diffusional,
and.electrical mobility methods.
Not all of the devices tested performed at 90% or greater
efficiency in collecting particles smaller than 3 ym, an approxi-
mate criterion for high efficiency collection of fine particles.
Three of the four devices were related to the class of control
devices known as wet (spray) scrubbers. One of the four utilized
waste process heat to provide most of the energy required to
drive the scrubber and transport the flue gases.
In comparing the devices with each other and with more con-
ventional gas cleaning systems consideration should be given
to the efficiency needed, the efficiency which each can attain,
and to the operating expenses and capital costs.
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SECTION II
INTRODUCTION
This report presents synopses of the results of tests con-
ducted by Southern Research Institute to determine the capabilities
of four novel particulate control devices in controlling fine par-
ticle emissions. The four devices tested were full scale devices
in commercial service. The goals of the tests were to determine
overall mass efficiencies and fractional efficiencies of the
devices under normal operating conditions; and, when possible,
to determine what effect changes in operating conditions produced
in the gas cleaning efficiencies.
The devices tested are presented in alphabetical order,
by the name usually associated with them. The principal features
of each device and the manufacturers are listed below.
• Aronetics Scrubber - uses waste heat to drive a two phase
jet which produces a high energy spray that cleans and
moves the gas. (Chemico Air Pollution Control Co., NY.,
NY.)
• Centrifield Scrubber - creates counter current vortex
flow to improve the collection efficiency of its spray.
(Entoleter, Inc.; New Haven, Conn.)
• Gravel Bed Filter - Dry Filtration using a fixed bed of
fine gravel (Rexnord, Inc.; Louisville, Ken.)
• Variable Throat Venturi Scrubber - utilizes a variable
cross-section venturi throat to provide control of scrubber
energy usage. (Combustion Equipment Associates, Inc.;
NY, NY)
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The following sections provide brief descriptions of the
measurement techniques used in the test programs, descriptions
of collectors that were tested and summaries of the test results,
More detailed information on each test can be obtained from the
individual test reports which are listed in the bibliography.
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SECTION III
MEASUREMENT TECHNIQUES
A total of five measurement techniques were used during
the tests. These were: (1) diffusional techniques using con-
densation nuclei counters and diffusion batteries for determining
concentration and size distribution on a number basis for par-
ticles 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) inertia! 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 deter-
mining total inlet and outlet mass loadings.
The rnrisg train measurements either utilized instack filters
in a manner like that of the current EPA Method 17, or were made
using Method 5. When Method 5 was not used it was because of
the possibility of forming particulates by condensation of vapor
phase components of the gas system (for instance H2S04) which
would interfere with the objectives of this study.
Diffusional and electrical mobility methods were not used
in conjunction on all the tests. Rather, in most instances, one
or the other was used as deemed most appropriate.
The useful concentration ranges of the optical counter,
electrical aerosol analyzer (Thermosystems Model 3030 Electrical
Aerosol Analyzer), and the condensation nuclei counters are such
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that extensive dilution of the gas streams being sampled was re-
quired. Dilution factors ranging from about 10:1 to 2000:1 were
used as required by the particular circumstances. In order to
insure that condensation effects were minimal, and that the par-
ticles 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 electrical/diffusional
sizing equipment was available, it was not possible to obtain
.simultaneous inlet and outlet data with these methods. The system
would first be installed at the inlet sampling location, and
all the inlet data would be obtained. Subsequently, the equipment
would be moved to the outlet and the necessary outlet data would
be obtained. For the purposes of calculating the efficiency
of the control device, the assumption was made that the process
was sufficiently repetitive that the inlet data, as obtained
above, were valid representations of those which would have been
obtained during the times the outlet measurements were made.
Accuracy in the measurements were often limited by process varia-
tions 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 reported fractions
of the influent material penetrating the control devices 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 ob-
tained 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.
Inertial sizing was usually accomplished using Brink Cascade
Impactors for inlet measurements and Andersen or University of
Washington Impactors for outlet measurements. Sampling was done
at or near isokinetic rates. Errors due to deviations from
5
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isokinetic sampling should be of little consequence for particles
having aerodynamic diameters smaller than 5 vim. In those cases
in which liquid droplets were present or in which the flue gas
was at a temperature near a dewpoint, the impactors were heated
to temperatures about 20°C above the flue gas temperature. This
would tend to insure that the particles were dry when collected
and sized.
Because of the wide disparities in the inlet and outlet
mass loadings, complete simultaneity in inlet and outlet sampling
was not possible. Outlet samples were generally of about one
to eight hours duration while inlet samples were of about five
to forty-five minutes duration. Because the inlet sampling could
not correspond directly with the outlet sampling, an average
inlet mass loading was synthesized for each size interval covered
by the inlet impaction stages as appropriate for each outlet
sample.
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 measured or assumed true
particle densities. If the true particle densities are lower
than the value used, 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/cm .
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SECTION IV
ARONETICS SCRUBBER
MANUFACTURER'S DESCRIPTION
A pressurized, heated, liquid when passed through a properly
designed nozzle will produce a two-phase mixture of vapor and
liquid droplets that is an excellent cleaning medium. The drop-
lets can be accelerated to extremely high velocity as a result
of the expansion force created by a portion of the liquid being
converted to vapor. The general configuration of this type of
scrubber is shown in Figures la and Ib. The proper arrangement
of components allows a draft to be induced which eliminates or
drastically reduces fan power requirements. The two-phase jet
scrubber produces water droplet velocities which vary with the
temperature of the scrubbing fluid as shown in Figure 2. It
is Aronetic's experience that jet velocities in the range of
1000 feet per second are quite satisfactory for particulate re-
moval in the size range down to 0.10 microns. The velocity in
the region immediately downstream of the nozzle is probably sub-
stantially supersonic since there is considerable evidence that
sonic velocity in a two-phase mixture may be as low as 350 feet
per second. However, Aronetic's believes that inertial impaction
is the controlling mechanism in cleaning and that the existence,
or absence, of shock phenomena associated with supersonic flow
is not an advantage in the cleaning effectiveness. Thus, the
velocity in feet per second is the controlling parameter rather
than the Mach Number, or relationship of velocity to the local
speed of sound. The device operates at a very low noise level.
The sound frequency and level is similar to that generated by
a garden hose nozzle.
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Figure la. Generalized Two Phase Jet Scrubber Nozzle.
TWO-PHASE
JET NOZZLE
•HEAT EXCHANGER
HOT GAS
.MIXING
SECTION
SEPARATOR -
MAKE-UP^,
WATER
nsr.
STACK
PUMP
WASTE WATER
TREATMENT
Figure lb. Generalized Two Phase Jet Scrubber System.
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450
400
u_
e
^
tu
tr
£ 350
300
250
NOZZLE EFFICIENCY 90 PER CENT
200
400 600 800
WATER JET VELOCITY, ft/sec
1000
1200
I4OO
Figure 2. Variation of water droplet velocity from
Two Phase Jet Nozzle with water temperature,
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With respect to the draft producing capacity of this type
of scrubber system, it should be evident that this is a pure
momentum transfer mechanism; therefore, the amount of draft is
a function of the amount of fluid passed through the nozzle and
the degree to which this fluid is accelerated. The velocity
is a function of initial water temperature, as shown in the pre-
vious figure. The effect of water flow rate on system pressure
rise is shown in Figure 3 for water at a temperature of 400°F.
It should be emphasized that this is a rise in pressure across
the scrubber and should not be confused with the pressure drop
which is associated with the venturi type scrubber. In most
applications, the pressure rise produced by the two-phase jet
is sufficient to overcome the pressure drop in other components
of a complete system.
The most direct application of the two-phase scrubbing sys-
tem is in the control of emissions from processes which generate
high temperature gases, laden with submicron particulate. Typi-
cal examples are the various metallurgical furnaces and processes.
Figure Ib shows schematically the general arrangement of the
components as tested. An economizer type of heat exchanger is
used to transfer thermal energy from the high temperature pro-
cess exhaust gas to pressurized hot water which is delivered
to the heat exchanger by a pump. Water exiting the heat exchanger
is delivered directly to the nozzle in its liquid state. For
most applications, the water temperature is approximately 400°F
and the water pressure is approximately 350 psi, or high enough
to ensure that the fluid remains in the liquid state until it
has passed the nozzle throat. A properly dimensioned mixing
section must be provided for intimate contact between the accele-
rated water droplets and the particle laden gas. The final com-
ponent in the scrubbing system train is a separator which will
remove the dirty water droplets and allow the clean gas to be
discharged. Water drained from the separator is passed to water
10 .
-------
8
cf 5
I
co 4
o
£ 3
o
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WATER TEMPERATURE-
I . I
-400°F
I
8
12
16
20
PRESSURE RISE, inches of water
Figure 3. System pressure rise as a function of water
flowrate.
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treatment equipment which may be used to remove substances scrub-
bed from the gas and to prepare the scrubbing liquid for recycling.
In the present instance, the water is used for approximately
three passes through the system before final discharge.
If the process off-gas is at a temperature level above 1200 F,
an additional option becomes available in the selection of compo-
nents. The economizer type of heat exchanger may still be used
to deliver heated water directly to the nozzle, or a steam boiler
may be used as an intermediate step in the heating of water.
If sufficient energy is contained in the gas, it is possible
that a quantity of steam may be produced which is greater than
the demands of the scrubber. This steam is then available for
other possible plant applications. Other elements of the system
remain essentially the same with the exception of the addition
of a method to transfer thermal energy from steam to water.
The choice between the steam boiler and the economizer type of
system for the very high temperature gases is dictated by local
conditions at the site in question.
TEST RESULTS
The tests were conducted on a 7.5 MW submerged arc ferro-
alloy furnace at Chromasco, Inc.'s Memphis, Tennessee facility.
The furnace was operating continuously 24 hours per day, producing
approximately 31 metric tons/day of ferrochrome. The furnace
was tapped at approximate 2 hour intervals with several charging
and stoking operatoins taking place at irregular intervals between
each consecutive tap. The actual timing for any one furnace
cycle varied somewhat from the nominal 120 minute tap cycle.
The operations for any one batch were: (1) charging of the fur-
nace with ore, coke, remelt, and gravel requiring about 10% of
the time for one tap cycle; (2) stoking, requiring about 8% of
the time over one tap cycle, and (3) tapping, requiring about
12% of the cycle. The highest particulate emission rates occur
during the tapping portion of the operation, with the actual
12
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emission rate and size distribution of the particulate being
quite variable throughout the cycle. This variability caused
some difficulty in both measurement and interpretation of data.
Figure 4 is a schematic of the basic furnace and scrubber
system showing the inlet and outlet sampling locations. The
waste process gases, at temperatures of about 920°K (1200°F)
from the furnace, are carried through a duct to a heat exchanger
which supplies approximately 480°K (400°F) high pressure water
to drive the scrubber and provide the necessary system draft.
The gas temperature leaving the heat exchanger is about 380°K
(220°F). The draft for the entire furnace and scrubber system
is provided by the two phase jet in the scrubber module. During
operation, the scrubber produces a net pressure rise from inlet
to outlet of 31.8 cm water gauge (12.5 in. H20) at a gas flow of
227 kg/min (500 Ibs/min) and 40.6 cm water gauge (16 in. H20) at
a gas flow of 250 kg/min (550 Ibs/min). Typical volumetric gas
flow rates were about 197 M3/min (6944 SCFM) during these tests.
Figure 5 shows typical averaged inlet and outlet size distributions
as obtained by optical and diffusional methods over approximately
one furnace cycle. Figure 8 shows the fractional efficiencies
calculated from these data together with results from the impactor
measurements. (In Figure 8, the impactor data are presented using
particle diameters based on particle densities of 4.5 grams/cm3.)
Figure 6 shows the averaged inlet mass size distribution on a
cumulative percentage basis for both aerodynamic and physical
sizes. The fractional efficiencies as calculated from the impactor
data are shown in Figure 7 on an aerodynamic diameter basis and in
Figure 8 on a physical basis.
The results of the total particulate measurements are shown
in Table 1. The overall efficiencies, by mass, based on these
results are included in Table 1. Typical scrubber operating con-
ditions are shown in Table 2.
13
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EMERGENCY
VENT
SCRUBBER
INLET DUCT SAMPL
PORTS .METHOD 5
AND IMPACTORS.
SCRUBBER
EXHAUST SAMPLE
PORTS,METHOD 5
AND IMPACTORS^.
SCRUBBER EXHAUST
SAMPLING POINT
OPTICAL / Dl FFUSIONAL-
HEAT
EXCHANGER
SCRUBBER
SYSTEM
RECYCLED
WATER ,-(0)
NOZZLE
DEMISTER
GROUND LEVEL
INLET SAMPLING POINT,
OPTICAL/DIFFUSIONAL
Figure 4. General layout of furnace and scrubber system
showing sampling locations.
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PARTICLE DIAMETER,
10.0
Figure 5. Average inlet and outlet size distributions
on a cumulative concentration basis.
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PARTICLE SIZE, AERODYNAMIC DIAMETER
Figure 7. Fractional efficiency of the Aronetics Wet Scrubber
calculated from the weighted averages of 30 inlet
(Brink) and 6 outlet (Andersen Mark II) Impactor
tests. Particle sizes are given as aerodynamic
diameters (density = 1 gm/cm3).
-------
00
I
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D OPTICAL
O DIFFUSIONAL
O.I
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PARTICLE DIAMETER ,
Figure 8.
Fractional efficiency of the Aronetics Scrubber
based on optical, diffusional, and impactor data,
10.0
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TABLE 1
MASS TRAIN (METHOD 5) RESULTS
Position
Date
Test No.
Time Start
Duration, min.
Avg. Gas Temp, °K
R
Moisture, Vol. %
Avg. Gas Velocity, M/sec
Sample Vol. at Stack
Conditions, M3
Sample Vol. at Dry
Std. Conditions, M3
Grams/ACM
Grams/DSCM
Grains/DSCF
Efficiency
Inlet
6-26-74
1
1045
180
894
1610
4.18
20.59
7.01
2.21
.117
.366
.160
Inlet
6-26-74
2
1504
180
894
1610
3.39
20.56
7.03
2.24
.181
.570
.249
Inlet
6-27-74
3
0915
180
894
1610
5.33
18.68
8.33
2.60
.174
.554
.242
Inlet
6-27-74
4
1302
180
894
1610
3.41
21.01
8.39
2.67
.130
.410
.179
Outlet
6-26-74
5
1047
•360
334
601
22.87
5.05
10.06
6.88
.016
.023
.010
95.1
Outlet
6-27-74
6
0915
360
337
607
20.42
3.36
9.00
6.29
.011
.016
.007
96.7
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TABLE 2. TYPICAL SCRUBBER OPERATING CONDITIONS
Water Flow 170 1pm
Water Inlet Temperature 315 °K
Water Outlet Temperature 500 °K
Air Inlet Temperature 865 °K
Air Outlet Temperature 380 °K
Air Flow 250 Kg/min.
Water Pressure 24 Atmos.
2Q
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SECTION V
CENTRIFIELD SCRUBBER
MANUFACTURER'S DESCRIPTION
Modern, high-efficiency wet scrubbers for the removal of
entrained particulates from industrial exhaust gases depend,
almost without exception, on spray contact for particle intercep-
tion. The atomization and acceleration of the scrubbing liquid
into contacting zone can be performed by a wide variety of mech-
anical arrangements. A new high-performance contactor, the '
centripetal vortex contactor, is now available.
The centripetal vortex principle is illustrated in Figure 9.
For any point on radius rc and tangential gas velocity v-t, 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 configuration, the vortex selectively develops a
specific droplet diameter distribution within the rotating field,
as determined by rc, v^ and 4>. 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. Drop-
let diameter is one of the basic parameters of spray contactor
efficiency.
Gas scrubber performance is most conveniently described by
the relationship: Nt = aPy, where N. = loge [I/(1-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.
21
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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 contactors, in single or
multiple stage arrangements, are often the only feasible mass
transfer device, especially in applications where insoluble par-
ticulate 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 the L/G ratio and specific droplet
surface area. Since specific surface area varies inversely with
droplet diameter, it is reasonable to expect that the centri-
petal vortex, with its unusually small equilibrium droplet diameter,
would exhibit superior mass transfer capabilities.
TEST RESULTS
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 approximate 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 quanti-
ties of roughly sized aggregate are surface dried in the rotary
kiln in order to insure that the asphalt will adhere to the aggre-
gate (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 discharged to the mixer, with the addition of hot asphalt
requiring an additional one half minute and then immediately dis-
charged 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 por-
tions of the batch operations. Figure 10 is a schematic of the
basic asphalt plant and scrubber system showing the inlet and out-
let sampling locations. (The scrubber normally operates without
a stack and the ducting shown beyond the scrubber exit was added
specifically for these tests.)
22
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CENTRAL RISER
STATIONARY
VANE CAGE
DROPLET
FORMATION
INLET VELOCITY
VECTORS
INLET VANES
LIQUID INLET
A-A
Figure 9. Centripetal vortex balances gas
velocity against centrifugal force,
23
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VENT LINE AIR
ROTARY
DRYER
EXHAUST DUCT ADDED
FOR TEST , PROGRAM
FLOW
STRAIGHTENERS.
\
OUTLET TEST POINTS
SCRUBBER
SECONDARY
COLLECTOR
INLET TEST
POINTS
Figure 10. Schematic diagram of the asphalt plant and scrubber
layout and the locations of the sampling points used
in the tests.
24
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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 (24,72Q ACFM). The
scrubber water flowrate was approximately 0.53 £/M3 (4 gal/
1000 CF).
Figure 11 shows typical averaged inlet and outlet size dis-
tributions as obtained by optical, electrical, and diffusional
methods over approximately one batch. Figure 12 shows the frac-
tional efficiencies calculated from these data together with
results from the impactor measurements. In Figure 12, the im-
pactor 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 scrub-
ber. 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 fractional
efficiencies indicate, to some extent, the uncertainties intro-
duced by process variations.
Figure 13 shows averaged inlet and outlet mass size distri-
butions obtained using cascade impactors on a cumulative percentage
by mass basis. Figure 14 shows the same distributions on a
cumulative mass concentration basis. The fractional efficiencies
as. calculted from these data are shown in Figure 15 on an aero-
dynamic diameter basis and were shown in Figure 12 on a physical
basis.
The results of the total particulate measurements are shown
in Table 3. The overall efficiencies, by mass, based on these
results are also included in Table 3.
25
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10'
INLET OUTLET
• O - ELECTRICAL
4 0 ~ DIFFUSIONAL
A A - OPTICAL
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Figure 11.
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PARTICLE DIAMETER,/am
10
Inlet and outlet size distributions as obtained
with optical, diffusional, and electrical techniques
26
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—
O
99.99
99.9
99.8
99
98
95
90
80
>
1 60
40
t 20}
UJ
10
5
2
I
O.I
0.01
0.01
Figure 12.
I I I I I I I
o -ELECTRICAL
O-DIFFUSIONAL
A-OPTICAL
o-INERTIAL
I I I I
T I I
I I r
T IT
o
A,
I I
I i ml
o.i
i.o
PARTICLE DIAMETER ,
i i 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
-------
to
GO
0.5
AERODYNAMIC DIAMETER
Figure 13. Entoleter Scrubber inlet and outlet size distributions
on a cumulative percentage by weight basis. Data obtained
with Cascade Impactors.
-------
I04
2
o
o>
E
•» •
» I03
o
3
V)
UJ
>
§ I02
o
10'
I I I I I I I I
I Mill
I I I I I I I
O.I
I I I I I I II
I I I I I I IT
Figure 14.
1.0 10
AERODYNAMIC PARTICLE DIAMETER,ftm
Entoleter Scrubber inlet and outlet
size distributions on a cumulative mass
loading basis.
100
29
-------
99.99
99.9
99.8
v? 99
98
o
3 95
UJ
90
g 80
O
UJ
8 60
40
20
10
- O
I I I T I I I
I
I
I I I I I I
0.5
1.0 . 10
AERODYNAMIC PARTICLE DIAMETER.Mm
Figure 15 . Fractional efficiencies of the
Entoleter Centrifield Scrubber as determined
from cascade impactor data.
30
-------
TABLE 3
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
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
31
-------
In addition to measuring particulate collection efficiencies,
SOX collection efficiencies were determined by using HaOa in the
impingers following the mass train to react with any SOa present
to form HaSOii. Subsequent HzSOi, concentration determinations were
made on the impinger water samples from which the SO collection
X
efficiencies were calculated. These were 84%, 68%, and 88% for
the three test runs for which such data were obtained.
32
-------
SECTION VI
GRAVEL BED FILTER
MANUFACTURER'S DESCRIPTION
The gravel bed filter system is a system comprised of par-
ticulate filter beds used in conjunction with mechanical or
other particulate separators in different configurations and
combinations for the purpose of collecting dry particulates from
dust-laden gas streams. The gravel bed filter system process
consists basically of pre-separating large coarse particles from
the dust-laden gas stream by means of mechanical collectors, al-
though other means can be employed. The mechanical collector
is usually the least expensive method for achieving this pre-
cleaning operation. The mechanical collectors can be in series
with the filter beds, an integral part of each module, or they
can be separate pieces of equipment connected in different ar-
rangements by ductwork.
The multichamber cyclone-gravel bed filter combination con-
sists of several units of equal size, connected by common raw
gas and clean gas ducts. The operation of the system is illustrated
in Figure 16. The raw gas is led into the filter via a parallel-
connected raw gas plenum (1). An immediate separation of very
coarse materials, by settling, takes place in this plenum chamber.
From there, the gas enters the cyclone type preliminary separator
(2), where the entrained medium and coarse dust is separated and
removed via the discharge airlock (3) at the outlet. The pre-
cleaned raw gas now rises from the cyclone through the vortex
tube (4) and enters the filter chambers (5). It passes from the
top of the horizontal filter beds to the bottom, so that the re-
maining fine dust is deposited on the quartz grains and in the
interstices of this bed (6). The cleaned gas now flows through
the clean gas collection chamber (8), and passes via the 3-way
33
-------
OPERATING PHASE
BACKFLUSH PHASE
14
12
BACKFLUSH
AIR
1. INLET CHAMBER
2. PRIMARY COLLECTOR (CYCLONE)
3. DOUBLE TIPPING GATE (DUST DISCHARGE)
4. VORTEX TUBE
5. FILTER CHAMBER
6. GRAVEL BED
7. SCREEN SUPPORT FOR BED
8. CLEAN GAS COLLECTION CHAMBER
9. EXHAUST PORT
10. BACKWASH CONTROL VALVE
11. BACKWASH AIR INLET
12. VALVE CYLINDER
13. STIRRING RAKE
14. STIRRING RAKE MOTOR/REDUCERS
Figure 16. Operation of gravel bed filter,
34
-------
valve (10) into the clean gas duct (9). Cleaning of a filter unit
can be initiated by means of a preset sequencer or by a pressure
differential across the filter bed. During the cleaning cycle,
the unit is isolated from the gas stream by the 3-way valve.
Then, backwash air is admitted to the filter chamber in a reverse
flow direction. It is either forced in by using a backwash air
blower, or sucked in by negative pressure (11). The backwash air
loosens the filter bed. During the cleaning process the rake-
shaped double arm stirring device (13) is rotated by the geared
motor (14). Thus the dust is thoroughly removed from the gravel
and entrained by the backwash air, and the fluidized filter gravel
is again settled after the cleaning operation. The large agglom-
erated dust particles are carried by the backwash air via the
vortex tube (4) into the preseparator (2), where the velocity is
reduced and the gas stream deflected so that a large percentage
of the dust is settled out. The backwash air, containing the re-
maining dust, mixes with the dust-laden air in the raw gas duct
and is then subjected to cleaning in the remaining units of the
filter. The filter, as has been described, consists of the filter
top section, containing the filter bed, and the upstream cyclone
located underneath. The flow rate of the filter bed is, of course,
important to the dimensioning of the cyclone, which generally has
a smaller diameter than the filter section proper. Attainment of
optimum flow rate for both filter bed and cyclone would result in
a very large filter bed relative to the cyclone.
To efficiently use the space required for the overall unit,
it is desirable to increase the bed area without increasing the
bed diameter to a value much greater than that of the cyclone.
As can be seen from Figure C2, this objective was obtained by
placing two parallel-connected filter beds one on top of the other.
The cyclone-gravel bed filter combination is automatically
controlled via a program transmitter. Following the signals of
this continuously operating program transmitter, the clean gas
port for a chamber to be cleaned is shut and the backwash air port
35
-------
opened. The drive of the raking device is started after a time
lag. The adjustment of the duration of the cleaning process and
of the intervals presents no difficulty. When the cleaning pro-
cess is over, the raking device is stopped first. Then, after
another time lag, the clean gas port is opened; and, at the
same time, the backwash air flow is stopped so that filtering
can be resumed in this chamber.
The design of the double bed filter element and its stirring
(leveling) 'device and drive is also simple.
The rake-shaped double arm of the raking device is firmly
connected to the vertically arranged geared motor via a rigid
coupling. This coupling is provided with an asbestos washer
serving as a thermal insulation. The bearing of the geared motor
is reinforced so that the forces, which result when the rake is
rotating, can be absorbed without any further intermediate bear-
ing. The filter bed is spread on a woven supporting screen made
of spring or stainless steel. Thanks to the special method applied
for dust removal, this supporting screen is not subject to signifi-
cant wear.
As has already been mentioned, the gases enter the cyclone at
relatively low velocities, so that generally no significant wear
occurs in the cylindrical section. The outlet cone of the presepara-
tor is protected against wear by means of a ceramic lining. A
weighted double-acting valve assembly (tipping valves) is arranged
beneath the outlet cones, where it serves as a dust discharge device
and as an air seal. In many cases, this valve assembly is mechan-
ically actuated. All moving parts required for the cleaning process
will be in operation during that period only. Normally, the dura-
tion of the cleaning phase is about three to five minutes.
Once the large dense particulates have been removed in the
first pass of the raw gas through the precleaning stages of the
system, the gas containing the residual fines passes through the
36
-------
packed solids filter beds. In this passage, the impingement of
the small particulates on the discrete filter media causes an
agglomeration to take place in which the fine particles are
joined with other fine particles to form larger agglomerates.
Periodically that particular filter is taken out of the system
and back-washed by reversing a gas flow upwardly through the
bed while it is being mechanically stirred by a rake. The bed
is both mechanically and pneumatically disturbed and this re-
sults in a semifluidized state in which the agglomerates (which
are lighter than the filter media and have a greater surface
area/weight ratio) are blown backwards from the bed and are
then collected in the common precleaning cyclones or recollected
in the remaining gravel bed.
TEST RESULTS:
The tests were conducted on a gravel bed filter system con-
trolling the emissions from clinker coolers on two 500-tons/day
Portland cement kilns. Both kilns were operating at full capacity
during the majority of the tests. In the process a slurry of water
and powdered raw materials is introduced to a kiln in which they
are calcined, forming clinker which drops onto a moving bed
clinker cooler. A series of fans beneath the moving bed blow
cool, ambient air through it to reduce the temperature of the
product. The bulk of the air from the clinker cooler is used as
combustion and secondary air for the kiln. Scavenge air from the
system (that air not required by the kiln) is drawn off through
the gravel bed filter. Because the air to the gravel bed is
scavenge air, the airflow through the filter is subject to con-
siderable variation in both temperature and volumetric flow rate.
Inlet gas temperatures ranged from 77°C (170°F) to 230°C (450°F).
Outlet temperatures ranged from 71°C (160°F) to 129°C (265°F).
The temperature drop between the inlet and outlet results primarily
from the addition of approximately 283 M3/min (100,000 CFM) of
ambient air which is used to periodically clean the gravel beds.
During these tests, the gravel bed system pressure drop was
approximately 12 cm water column -.(4.7 in). The system flow
37
-------
rate ranged from about 600 to 1000 DNM3/nun at the inlet. (The
latter figures exclude the backflush air). Testing took place
during the months of August and November 1975. The second series
of tests were done as a result of a determination by the manufacturer
that the system was not operating under optimal conditions during
the August test. The results of the November tests did show sub-
stantial improvement in system performance as compared with the
August data.
Figure 17 is a schematic of the basic Portland cement kiln,
clinker cooler, and gravel bed systems showing the inlet and out-
let sampling locations.
The gravel bed filter is constructed on a modular basis, with
eight modules making up the system in this instance. Each module
consists of a cyclonic inlet section followed by two gravel beds
operating in parallel.
At any one time, during normal operations, seven (7) of the
eight (8) modules are on line in the forward flow direction with
one being cleaned and renewed by backflushing with heated ambient
air. In the installation tested, the modules were cleaned in
sequence with a backflush time of 6 to 20 minutes. During the
first 45 seconds of the backflush period, a mechanical raking
system is actuated to stir up the dirty gravel. The particulate
laden air from the module being backflushed is exhausted into
the inlet plenum of the remaining modules. This backflush and
raking operation and the frequency with which it takes place has
a very pronounced influence on the collection efficiency achieved
by the system as will be discussed later in this report. The
tests of this unit were done under long term steady-state conditions
with backwash periods of 12 and 6 minutes. In addition, limited
short term tests under transient conditions were made using 6 and
20 minute backwash intervals during a period when the system was
normally being operated with a 12-minute backwash interval.
Design values for the system tested are given in Table 4.
38
-------
Burner
Clinker Cooler
Product
Discharge
Figure 17a . Portland cement kiln and clinker cooler layout.
Arrows indicate directions of air flow.
Inlet sampling
points
j a a a
Outlet sampling
points
X.
F""
h"_^
Gravel Bed Filter
System
Stack
Figure 17b. Gravel bed filter system layout and sampling locations.
39
-------
Table 4
Design Specifications Of The System As Tested
Inlet Volume Flow: 2266 ACM/min at 204°C
(80,000 ACFM at 400°F)
Backflush Volume Flow: 317 ACM/min at 66°C
(11,200 ACFM at 150°F)
Pressure Drop: 25.3 cm w.c. (10 inches w.c.)
Gravel Size: 4 mm (5/32 inch) x No. 6 mesh
Bed Depth: 11.4 cm (4% inch)
Bed Area: 3.72 m2/Bed (40 ft2/Bed)
2 2
(For a total of 59.5 m of bed area with 52 m actively
filtering in normal operation.)
40
-------
The data obtained by Method 5 technique is summarized in
Tables 5 and 6. The overall collection efficiency for each of
these tests is also given in Table 6, together with the gas flow
per module (at flue conditions). It would appear from these data
that the collection efficiency of the system is sensitive to the
gas flow per module and improved markedly with decreasing gas
flow over the range of values that were obtained during this
series of tests. The differences in the inlet and outlet gas flows
in Tables 5 and 6 are due to the addition of the backflush air.
During these tests, the backwash duration was 12 minutes.
On a service-inspection trip by Rexnord personnel subsequent
to this test series, it was found that the rakes were being acti-
vated a fraction of a second to a few seconds before the backwash
valves were actuated, which would tend to reduce the average col-
lection efficiency of the device. In addition, accumulated exper-
ience with the gravel bed system in this application indicated
that the beds were not being adequately cleaned with the 84 min-
ute forward-flow/12 minutes backwash cycle, which results in a
buildup of dust within the beds. This increases the energy require-
ments and decreases the collection efficiency of the system. Re-
setting the rake.timers and changing the backwash intervals to
provide a 42-minute forward flow/6 minute backwash cycle resulted
in a substantial improvement in performance as reported by plant
personnel. Consequently, a second series of tests were run during
the month of November, 1975. Method 5 measurements were not made
during the retests. The outlet impactor data during the second
test series indicated a reduction in the outlet particulate load-
ing by approximately a factor of 3.5 as compared to the impactor
outlet data obtained during the first test series, while inlet
data from cascade impactors indicated no disceirnable differences
in loading and size distribution between the two test series.
Thus, in steady state operation under a more nearly optimum operat-
ing cycle, the overall efficiency in this application is estimated
to be approximately 99.5%.
41
-------
Table 5
Mass Emission Tests - Method 5
Inlet
Run #
Date
Time
%, Moisture
Velocity, m/s (f/s)
ACM/min (ACFM)
SDCM/min (SDCFM)
Grams/ACM (Grains/ACF)
Grams/SDCM (Grains/SDCF) 3.192(1.395)
Kg/hr. (Lbs/hr.) 179.46(395.65)
8-25-75
1350
2.33
10.44(34.24)
1467.3 (51812)
937.1(33089)
2.039(0.891)
8-26-75
1015
1.65
9.70(31.48)
1364.5(48140)
1088.4 (38431)
1.144(0.500)
1.435(0.627)
93.68(206.54)
8-26-75
1435
2.60
7.42(24.35)
1043.5(36847)
761.6(26891)
1.602(0.700)
2.197(0.960)
100.37(221.27)
8-27-75
1050
1.54
8.50(27.89)
1195.2(42203)
875.3(30906)
2.130(0.931)
2.911(1.272)
152.84 (336.96)
8-27-75
1515
1.80
7.97(26.15)
1120.6(39570)
739.9(26128)
2.078(0.908)
3.146(1.375
139.68(307.94)
-------
Table 6
Mass Emission Tests - Method 5
Outlet
Run #
Date
Time
Velocity, m/s(f/s)
%, Moisture
ACM/min(ACFM)
SDCM/min(SCDFM)
Grams/ACM(Grains/ACF)
Grams/SDCM(Grains/SDCF)
Kg/hr.(Lbs/hr.)
No. of Active
Modules
Average Flow per
Active Module
in ACM/min(ACFM)*
Efficiency
8-25-75
1400
8.82(28.94)
2.29
1631.7(57619)
1239.3(43759)
0.094(0.041)
0.121(0.053)
9.02(19.88)
7
233.1(8230)
95.00
8-26-75
1015
8.76(28.73)
1.83
1619.9(57201)
1326.4(46837)
0.030(0.013)
0.037(0.016)
2.91(6.42)
7
231.4(8170)
96.9
8-26-75
1445
6.79(22.29)
1.86
1256.8(44379)
1017.5(35927)
0.064(0.028)
0.080(0.035)
4.89(10.78)
4
8-27-75
1100
7.98(26.18)
1.64
1476.2 (52124)
1174.2(41461)
0.043(0.019)
0.055(0.024)
3.87 (8.53)
7
314.2(11095) 210.8(7445)
95.1
97.5
8-27-75
1515
7.26(23.81)
1.38
1342.5(47405)
1049.7(37067)
0.034 (0.015)
0.043(0.019)
2.74(6.04)
7
191.7 (6770)
98.0
*Includes backflush air.
-------
The impactor data are summarized in Figures 18 and 19.
Figure 18 shows averaged inlet and outlet mass size distributions
on a cumulative percentage versus aerodynamic diameter basis.
Figure 19 shows the same size distributions on a cumulative mass
concentration basis. Inlet sampling times of three hours produced
catches of substantially less than one milligram on all stages
collecting particles smaller than 3 ym with the Brink impactors.
These catches were considered too low to give reliable loadings
so only the Andersen inlet data were used for fractional efficiency
calculations.
The high concentrations of large particles in the gas streams
coupled with the non-ideal particle separation and collection
characteristics of the impactors tend to make the impactor filter
catches difficult to interpret. In sampling particulate having
the properties and size distribution of the type encountered here
the impactor back-up filter catches can be dominated by oversized
particles, a small fraction of which are not retained by the stages
which should collect them. As a result, no fractional efficiencies
were based on the impactor back-up filters and the size distribu-
tions obtained with the impactors as shown in Figures 18 and 19
are given both with and without the back-up filter catches.
The fractional efficiencies as calculated from the impactor
data are given in Table 7 together with the gravel bed operating
pressure loss and are shown in Figures 20 and 21. Also shown in
.Figures 20 and 21 are fractional efficiency curves derived from
overall averages of the respective data obtained during the two
test series. Because the outlet loadings appear to be decoupled
from the inlet insofar as short term behavior is concerned, these
overall averages may better illustrate the system performance
than do the individual tests. The negative efficiencies shown for
some particle sizes are discussed later.
Data on the concentration and size distribution of ultra-
fine particulates were determined during the first test series
44
-------
I
O
•H
0)
N
a
-p
en
•H
I
-U
s
o
M
t Outlets
Ti-ttH-l
Andersen with filter;
0 Andersen less filter
• Brink with filter
O Brink less filter
August with filter
V August less filter
November with filter
November less filter
5 10 20
Aerodynamic Diameter,
Figure 18. Inlet and outlet size distributions on a cumulative
percentage by weight basis.
-------
1000
^
0)
N
w 100
0)
4J
(0
U
•H
•s
I
EH
in
en
CP
(0
3
en
in
£
0)
-p
nj
rH
3
u
Asymptotic to 2700 mg/DSCM :
August outlet with I
V August outlet less filter
November outlet with filter
A November outlet less filter
^Average inlet with filter (Andersen data)
Average inlet less filter (Andersen data)
Average inlet (Brink data)
100
Aerodynamic Diameter, yM
Figure 19. Inlet and outlet size distributions on a mass basis.
46
-------
Table 7
Gravel Bed Filter Fractional Efficiencies As
Measured With Andersen Impactors
Date
8/27
8/28
8/28
8/29
8/29
11/4
11/5
Inlet
Gas Flow
DSCM/min.
739
917
606
1039
682
732
856
Inlet
Temp.
°C
149
181
227
193
149
166
152
Typical
Bed Pres.
Drop
cm/H2 0
11.0
13.6
10.2
13.26
9.75
6.4
9.1
System
Pres.
Drop
cm/H20
12.39
17.3
12.8
17. 5&
11.58
9.6
14.0
Backf lush
Period
12 min.
12 min.
12 min.
12 min.
12 min.
6 min.
6 min.
.72
-37
-146
4
13
-229
-104
-31
Collection Efficiencies At
Indicated Aerodynamic Diameters (un
1.09 2.04 3.70 5.45 8.26
-68
-56
-32
-43
-56
-29
0
32
2
-42
11
25
66
78
60
34
19
37
67
93
94.1
91 97.7
>71
>40
>67
>57
98.1
96.3
-------
<*>
u
c
0)
•rH
o
•H
14-1
14-1
W
C
O
o
u
PRES. DROP
(cm w.c.)
Typical
Bed System
8/27
8/28
8/28
8/29
8/29
Average
m
-180
Aerodynamic Diameter, yM
Figure 20. Fractional efficiencies as determined using Cascade
impactors. August data.
48
-------
<*>
0
s
•H
O
-H
4-1
4-1
W
c
O
•rH
-P
O
0)
^H
H
O
u
Typical
Date Bed System Symbol
11/4
11/5
-4- Average
Aerodynamic Diameter, yM
Figure 21. Fractional collection efficiencies as determined using
Cascade impactors. November data.
49
-------
using diffusional sizing techniques with General Electric Con-
densation nuclei counters for determining the various ultrafine
particulate concentrations. Attempts were made to use a Thermo-
systems Model 3030 Electrical Aerosol Analyzer; however, rapid,
random fluctuations in particulate concentrations and size dis-
tribution in this size range rendered.the data from this method
almost totally uninterpretable. In addition, a Gardner small
particle detector (a manually operated CNC) was used throughout
the tests as a crude monitor of the exit concentration and size
distribution (using a variable supersaturation method) of ultra-
fine particles. Some inlet data were also obtained with the var-
iable supersaturation method during the November tests. This
instrument was used without dilution and much of the time the par-
ticulate concentration exceeded its range; however, it showed
qualitative agreement with the data obtained using the more elab-
orate system in those instances during which they were at a common
location. During the second (November) tests series, only the
Gardner small particle detector was used to obtain data on ultra-
fine particulates. Accuracy in the measurements was limited by
the rapid and frequent concentration variations and the efficiencies
derived from these data are uncertain. However, the trends in
the fractional efficiencies derived from the data are probably
real and the fractions of the influent materials that penetrate
the scrubber are believed to be generally correct to within a
factor of two. The data obtained during the August test series
are summarized in Table 8. The fractional efficiencies derived from
the August data are shown in Figure 22. Also shown in Figure 22
are fractional efficiencies obtained from simultaneous measurements
with the small particle optical counter and cascade impactors. The
limited comparison data obtained during the November tests are given
in Table 9. The efficiency for the +0.2 ym diameter particles in
the November data appears to be substantially higher than was the
case in August. It is unlikely that the collection efficiency in
the 0.02 to 0.20 range was increased to a value as high as 80 to
90%; however, values of about 50% cannot be excluded.
50
-------
Table 8
Ultrafine Particulate Data—August Test
Cumulative Concentration Larger Than Indicated Size
Diffusional Method
Date:
Dia. , ijm
.01
.02
.063
.10
.20
Inlet
8/26
3.
2.
5.
2.
5xl06
OxlO6
5xl05
9xl05
7x10"
Inlet
8/27
2.3xl06
l.SxlO6
4xl05
2xl05
3x10"
Variable Supersaturation Method
Outlet
8/28
4.
1.
9.
4.
1.
2xl06
7xl06
6xl05
4xl05
4xl05
Outlet Outlet Outlet
8/26 8/27 8/28
1.3xl06 2.5xl06 >2.8xl06
7.9xl05 2xl06 >2.8xl06
6. 9x10* 2.1xl05 2.2xl05
Date:
Dia., ym
.01
.02
.20
Table 9
Ultrafine Particulate Data—November Test
Cumulative Concentration Larger Than Indicated Size*
Inlet Outlet
11/4
11/5
>2.8xl06 >2.8xl06
>2.8xl06 >2.8xl06
2.1xl05 3.0xl05
11/4
H/5
>2.8xl06 >2.8xl06
>2.8xl06 >2.8xlO"
l.SxlO5 3.5xl05
*A11 by variable supersaturation method.
51
-------
100
80
60
40
20
O Diffusional Method
O Optical Method _
Impactors (Aerodynamic Diameters)-^
G1 -20
c
0)
•H
3 -40
-60
l.i
u
0)
r-\
i-l
O
o
-80
-100
ffi
I I
dtttE
1-H
ffi
fta
i i
-120
-140
-160
i+httt
-180
i i
U.Oi
0.02
0.05 0.5
Particle Diameter, yM
Figure 22. Fractional efficiencies as determined using diffusional,
optical and inertial (Cascade impactor) methods. August
data.
-------
Two optical particle counters (Royco Model 225) were used
during these tests. The first was used in conjunction with the
ultrafine measurement system to obtain data on fractional effi-
ciencies over the size range from 0.35 ym to 2.0 ym. The second
was used only at the outlet of the gravel bed for obtaining real
time information on relative changes in concentration of par-
ticles over the size range from 0.6 to 50 ym.
Inlet and outlet data with the small particle unit (0.35 to
2 ym) were obtained at the same times as were the ultrafine data.
These data are thus not simultaneous sets and are subject to some
of the same uncertainties as were the diffusional data. The in-
let concentrations of particles in this size range were much more
stable than the ultrafine concentrations, although still subject
to large swings, and were probably dominated by entrained partic-
ulate from the clinker cooler and relatively unaffected by the
ambient airborne particulate. The results of the measurements
are given in Table 10. Fractional efficiencies determined from
the optical data were shown in Figure 22, from which it can be
seen that the negative fine particle collection efficiencies which
were found from the impactor data were verified by the particle
counter data.
The outlet data from both the small particle (0.3 to 2 ym)
and large particle (0.6 to 50 ym) systems showed pronounced effects
from the backflush cycle on emission rates. Typical examples of
the time variations in the outlet particulate concentrations are
shown in Figure 23, which represents an approximate 30-minute data
segment obtained with the continuous monitoring large particle
system during the August tests. A large "puff" followed by a
slow decline in concentration occurs each time a clean module is
put back on line (once every 12 minutes in this case). During
the August test series, this 12-minute interval was varied for
two special one-hour duration tests (one with 6-minute intervals,
the other at 20-minute intervals) in order to allow some estimate
53
-------
Table 10
Summary of Small Particle Optical Data
Concentration In Size Range (number/cc)
Inlet
Date:
Averaging Time
Dia. Range, ym*
.35-. 43
.43-. 58
.58-1.2
1.2-1.4
1.4-2.0
8/26
(2.5 hrs)
S.OxlO2
3.4xl02
2.4xl02
1.4xl02
3.1xl02
8/27
(6 hrs)
7.46xl02
4.7xl02
3.1xl02
l.SxlO2
4.1xl02
Outlet
8/28 8/29
(0.75 hrs) (5 hrs)
14.3xl02 9.0xl02
14.0xl02 13.0xl02
9.6xl02
5.2xl02
7.9xl02
3.6xl02
6.0xl02 3.9xl02
*Polystyrene equivalent diameter
54
-------
Ul
U1
c
03
0)
N
•M
U)
T)
0)
u -p
•rH -H
'd c
C D
C !-<
•H (0
C --H
O XJ
•H V-l
-p <
-P
C
oj
u
c
O
O
•H
4J
(0
i-H
QJ
05
3.6-7.2 ym diameter
1.8-3.6 urn diameter
•12 min,
,6-1.8 ym diameter
Figure 23.
Temporal variations of particulate concentrations in three size bands at the outlet
of the gravel bed filter system. Concentration units are arbitrary and not to the same
scale for the three size bands.
-------
to be made of the sensitivity of the gravel bed system to changes
in operating conditions. The results of these tests are given in
Table 11. During these one hour tests the system did not have
time to come to a steady state condition, thus the results obtained
during them may not well represent what might be obtained under
steady-state conditions.
The November tests, which were made with the gravel bed system
operating in a steady state condition with a 6-minute backflush
time, showed a substantial improvement in performance as evidenced
by the impactor data, in contrast to the rather small perform-
ance change observed during the one hour of operation with a
6-minute backflush cycle during the August tests.
The combined particle counter and cascade impactor data suggest
that a large portion of the outlet fine particle emissions result
from the breaking up of agglomerated fine particles during the
raking operations in the cleaning of the off-line beds. The nature
of the clinker cooler process is such that a substantial portion of
the particulates lofted from the clinker bed by the cooling air
could be agglomerates. A limited number of tests were run in Nov-
ember in order to explore the hypothesis that the negative effi-
ciencies resulted from the breakup of agglomerates. These tests
were made using only the realtime large particle system for monitor-
ing the particulate concentrations in the gravel bed effluent gas
stream. During these tests, clean beds were put on line without
simultaneously backflushing another bed and dirty beds were back-
flushed with and without raking, with no clean bed being put on
line.
The effects of these operations are illustrated in Figure 24
which shows strip chart recordings of the particle counter out-
put during these tests. Events marked as "N" are the puffs nor-
mally observed when a new bed is placed in the backflush mode at
which time a clean bed is simultaneously placed on line. Events
marked "C" are the result of placing a clean bed on line without
56
-------
Table 11
Effect of Backflush Interval On Particulate Emission Rate
Clean Module Insertion Relative Particulate Emission Rate In Size
Interval (Minutes) Bands Indicated (Arbitrary Units, 1 Hr. Avg.)
.6-1.8 ym dia. 1.8-3.6 ym dia. 3.6-7.2 ym dia.
6 36 42.5 37
12 31 39.2 40
20 25 38.5 52
57
-------
t
MOpiiTliijiil]
iiijjji'iiiij-nih-iiijHiF
iliih j^iiinU;t^i-
w ;0i/i7jyj!iiiil>T iFffrnf
0.6-1.8
ILi :i:U'.
Time
Figure 24.
Relative emission rates in three particle size intervals during explorations
of the effects of backwash operations on emissions. For explanation of sym-
bols see text.
-------
initiating a backflush cycle on another module. Events marked
"R" are the result of raking a dirty bed which is being back-
flushed without simultaneously placing a clean bed on line. The
event marked "B" resulted from backflushing a bed without raking
it and without simultaneously placing a clean bed on line.
It appears that when a clean bed is placed on line, some
residual particulate which has been loosened by the backwash
operation is carried out directly to the stack causing a short
duration, low amplitude puff. The valving operations also appear
to produce a very short duration, concentration spike designated
"V" in Figure 24. The initial burst of backflush air to a bed that
is entering the cleaning cycle appears to create a puff of lesser
amplitude. The raking process during the backwash process produces
moderate to large amplitude concentration increases which last
slightly longer than the time period during which the rakes are
activated. The puffs labeled "B" and "R" result from particulate
.that was entrained in the backwash air and passed in the normal,
forward flow direction through the on line, active, modules. It
was therefore concluded that the backwash and raking cycle does
in fact result in a large amount of deagglomeration of the particulate
which has been collected by a bed, and that in some aerodynamic
size ranges, the emissions resulting from the portion of this re-
entrained material that is not recollected by the active beds ex-
ceeds the rate at which particulate in those size ranges is car-
ried into the system from the clinker cooler. Estimates of the
percentages of total emissions in several size intervals resulting
from the puffs were made from the data obtained with realtime moni-
tors. These estimates are presented in Table 12 for the August
and November tests.
/
Estimates of the fundamental collection efficiencies of the
gravel beds were made by subtraction of relative contributions
due to the puffs from the cascade impactor outlet data and re-
calculating fractional efficiencies based on the revised data.
The results of these calculations are given in Table 13, together
with the efficiencies calculated from the original data. These
estimates indicate that the collection efficiency of the gravel
59
-------
Table 12
Percentage of Emissions In Puffs
Monitor #1
Monitor #2
.35-. 6
29
N.A.
.6-1.2
51
N.A.
.6-1.8
55
(29)
1.8-3.6
70
67
3.6-7.2
62
(41)
Date: Size Interval:
August (12 min Backwash)
November (6 min Backwash)
N.A.: Not Available - Monitor #1 not used during November tests.
Values in parentheses are uncertain.
60
-------
Table 13
Fractional Efficiencies From August and November
Data With and Without Contribution From Cleaning Cycle
Collection Efficiencies
Date
8/27
8/28
8/28
8/29
8/29
11/4
11/5
with
-37
-146
4.4
13
-229
-104
-116
72 pm
w/o
42
-3
71
63
-38
(-53)-
(-62)
with
-68
-56
-32
-43
-56
-29
15.5
At Indicated Aerodynamic Diameters
1.09
w/o
13
19
31
26
19
(33)
(55)
2.04
with
32.1
2.2
-42
11
24.5
66.2
73.8
w/o
69
56
36
60
66
90
92
3.
with
60
33.8
19
37.2
67
93
94.8
7
w/o
72
54
43
56
77
97
98
Value in parentheses uncertain.
61
-------
bed under the conditions of these tests was low for particles
smaller than about 2 ym even without the effect of the puffs.
The difference between the August results and the November
results is attributed primarily to the more frequent backwash-
ing, which reduced the pluggage of the beds and resulted
in lower operating pressure drops for the same gas flows. At
the same time, as a result of the better cleaning of the beds,
the residual dust concentration in the beds is lowered which in
turn reduces the loading surge to the active beds when a bed is
backwashed. The lower bed loadings also reduce the available
dust which can be carried directly out to the stack when a bed
is put back on line. It is also possible that with the beds
in the highly plugged condition that existed during the August
tests they may have become partially fluidized during the back-
wash cycle. - This would enhance the deagglomeration process and
perhaps result in the production of particulate from coarser
particles'by mechanical actions.
62
-------
SECTION VII
VARIABLE THROAT VENTURI SCRUBBER
MANUFACTURER'S DESCRIPTION:*
The flue gas cleaning system (Figure 1) now in operation on
the two Colstrip 360 MW units is unique in that a wet scrubbing
system is used for both particulate and S02 control and captured
ash provides the alkalinity for the S02 removal.
The system currently installed on the two 360 MW units 1
and 2 is illustrated in Figures 25 and 26. The hot flue gas
leaving the boiler is cooled in the heat recovery air heater and
enters the flue gas scrubbing system at about 300°F. Each scrub-
ber module, as shown in simplified drawing in Figure 26, consists
of a downflow venturi scrubber centered within an upflow spray
tower contactor. The venturi is equipped with a variable throat
to maintain constant pressure drop at variable loads. In the
venturi the scrubbing liquid is finely dispersed by the high
velocity flue gas and serves to efficiently wet and trap the par-
ticulate fly ash. In the spray tower the gas contacts a recycle
spray of absorption slurry. The slurry from the venturi and the
spray contactor is collected and held in the base of the scrubber
and recirculated at an L/G rate of 15 for venturi and 18 for the
absorber spray. An agitator in the scrubber base serves to main-
tain suspension of the fly ash and solid reaction products.
Slurry is bled from the recycle to maintain a 12% suspended
solids concentration. Slaked quick lime is added as lime slurry
*Taken from a paper by C. Grimm, J. Z. Abrams, W. W. Leffmann,
I. A. Raben, and C. Lamatia. Presented at the 1977 National
Meeting of the AIChE.
63'
-------
THE MONTANA POWER CO. PUGET SOUND POWER & LIGHT
2 - 360 MW COLSTRIP UNITS 1 & 2
MERGENCY WATER
LUMB BOB
^-CLEAN FLUE GAS
MAKE-UP
«—M. WATER
*»-»•
WASH TRAY POND
FLYASH POND
Figure 25
The Montana Power Co.-Puget Sound and Light
Colstrip Units 1 and 2- (360 MW Each) Flue Gas
Cleaning System.
-------
RECYCLE HOLD-UP TANK
8 MINUTES TURNOVER
Figure 26. Colstrip Scrubber Module
65
-------
only if needed to augment the fly ash alkali and maintain the
desired slurry pH.
Each scrubber module is designed to clean 120 MW of equiva-
lent gas flow under normal conditions and 144 MW under emergency
conditions. (i.e., when one module is down, the two in operation
will clean the amount of flue gas generated at 80% of boiler
design load.)
The treated gas leaving the spray section passes through the
water wash tray which serves to trap and dilute the entrainment.
The gas leaving the washtray passes through a chevron demister
followed by a mesh pad demister and leaves the absorption section
water-saturated and cooled to the saturation temperature of about
120°F.
To preclude condensation in the fan and stack, and improve
the gas buoyancy, the cooled gas from the scrubber is reheated to
50-75°F by a steam-heated exchanger. The warmed gas then passes
through the dry induced draft fans and is discharged to the atmos-
phere from the top of a 500 foot stack.
As shown in Figure 25 the slurry discharged from the ab-
sorption loop is passed to an intermediate retention pond where
the solids settle and from which the clarified water is returned
to the absorption system. At intermittent intervals (currently
only during the warm summer months), a floating dredge is used
to reclaim the settled solids from the intermediate settling pond
and transport them as a 30% slurry by pipeline to the remotely
located permanent disposal pond. Decanted water (supernate) from
the disposal pond is returned, also intermittently, through the
same slurry pipeline to the intermediate pond for recycle to the
absorption system. No stabilization of the sludge is required
and a closed water loop is maintained.
Fresh water is added to the absorption system in an amount
equivalent to that evaporated into the warm gas stream plus that
66
-------
retained in the waste sludge. This fresh makeup water is introduced
to the system as dilution water for minimizing the calcium satura-
tion level in the mist eliminator washwater. This washwater is
trapped by and withdrawn from the washtray and circulated to a
small pond where entrained solids are separated. A portion of
the water from this pond is returned and used to wash the under-
surface of the washtray. Another portion of the flow is diluted
with the fresh makeup water, and used for bottom wash of the mist
eliminator.
The scrubber has been free of scale while the pH of the re-
cycle liquid remains in the expected range. Corrosion problems
in the reheater and demister plugging have not been experienced
with the installation.
A detailed chemical analysis of the fly ash (see Table 14)
revealed that it contained alkali metal oxides in an amount the-
oretically sufficient to react with and absorb the sulfur dioxide
produced by the coal combustion. Laboratory experiments simulating
absorption conditions revealed that this alkalinity was only us-
able under low pH absorption conditions (<5.6). It also revealed
that absorption under these low pH conditions would result in
extensive oxidation of the absorbed SO2 producing calcium sulfate
rather than calcium sulfite as the predominant reaction product.
Laboratory tests were conducted by Bechtel to determine the
process conditions under which the alkalinity of the fly ash
could be utilized while at the same time accommodating the scaling
potential of the calcium sulfate. The conditions selected were a
pH of. 5 to 5.6, low enough for alkali utilization and high enough
for adequate SOa absorption capability. The other, and perhaps
the key operating factor, was the use of a high level of suspended
solids in the absorption slurry (12 to 15% by weight, of which
some 3-4% is calcium sulfate formed in the absorption). This
provided a high concentration of calcium sulfate seed crystals
67
-------
Table 14
Fuel And Ash As Described
In Specifications
COAL: Average, As Received
Moisture 23.87%
Volatile Matter 28.59%
Fixed Carbon 38.96%
Ash 8.59% (Max. 12.58%, Min. 6.1%)
Heating Value 8843 Btu/lb. (Min. 8162 Btu/lb.)
Sulfur .777% (Max. 1.0% Min. 0.4%)
ASH: (Estimated composition, sulfur trioxide-free basis)
Si02 41.60%
A1203 22.42%
Ti02 0.79%
Fe203 5.44%
CaO 21.90%
MgO 4.95%
Na20 0.31%
K20 0.13%
P205 0.41%
(balance unidentified)
Later fly ash data varies slightly from above as follows:
LEACHED IN H20 (1% Fly Ash)
pH 11.8
Conductivity 4.150
Total Dissolved Solids 930 ppm
Calcium 396 ppm
Magnesium 0 ppm
Chloride 15 ppm
Sulfate (50., = ) 30 ppm
LEACHED IN HC1
% Acid insolubles (Si02) 57.59
% Calcium as CaO 22.00
% Magnesium as MgO 1.27
% Aluminum As A1203 15.59
% Iron as Fe203 4.97
% Sulfate as SO,, 0.71
% Carbonate as C03 0.70
68
-------
to promote desupersaturation. A long residence time for the re-
cycle slurry in a stirred tank external to the scrubber was also
proposed to ensure alkali utilization and to provide crystalliza-
tion of calcium sulfate under controlled and non-scaling conditions.
A slurry holdup of 8-10 hours was selected based on bleed rate.
The above two conditions, i.e., low slurry pH and long contact
with the oxygen-containing flue gas, provided substantially com-
plete oxidation. This high oxidation was shown to improve the dis-
posal characteristics of the waste sludge produced.
TEST RESULTS:
The tests were conducted on one of the three identical scrub-
ber modules which are operated in parallel to control SOa and par-
ticulate emissions from the power boiler. The three modules are
independently controlled with respect to liquor flows and venturi
pressure drop. Pressure drops across the Venturis are regulated
by adjusting the position of the "plumb bob" shown in Figure 27,
thereby increasing or decreasing the cross sectional area of the
venturi throat. Throughout these tests, with the exception of
one brief period, the pressure drop across the venturi on the module
being tested was held at 46 ± 2 cm w.c. Gas temperatures at the
scrubber inlet ranged from 129°C to 137°C. The scrubber exit gas
temperatures ranged from 57°C to 60°C and temperatures at the out-
let test plane ranged from 94°C to 99°C. The temperature rise
between the scrubber exit and the outlet mass sampling location
results from a flue gas reheat system and the action of the fan,
both of which are located between the scrubber outlet and the
sampling plane. The gas flow handled by the scrubber throughout
the tests was approximately 130 DNCM/sec (280,000 DSCFM). The
venturi sections have a designed pressure drop range of 30.5 cm
(12 in.) to 50.8 cm (20 in.) w.c. with a nominal operating pres-
sure drop of 43 cm (17 in.) w.c. Design L/G rates are 2.0 H/m3
(15 gal/1000 CF) in the venturi section and 2.41 SL/m3 (18 gal/
1000 CF) in the absorber section.
69
-------
INLET
TEST
PLANE
BUTTERFLY ISOLATION DAMPER.
11-
'PLUMB BOB DRIVE
STACK
FLUE GAS
FROM AIR
PREHEATER Q
AND BOILER '
FROM PLANT FIRE WATER SYSTEM
EMERGENCY COOLING SPRAY
PLUMB BOB
FROM SEAL WATER SUPPLY
MIST ELIMINATOR UNDERSPRAY
* r—*
(GUILLOTINE
SHUT-OFF
Z I- INDUCED
8 O DRAFT FAN
EFFLUENT
TANK
RECYCLE PUMPS
SCRUBBER VESSEL SEAL POT C WASH TRAY
0 RECYCLE TANK
[CV
\
WASH TRAY
RECYCLE PUMP
AND SPARE
WASH TRAY
POND
OUTLET
TEST PLANE
WASH TRAY
POND RETURN PUMP
AND SPARE
NOTE: VALVES SHOWN ARE MAJOR CONTROL. BLOCK VALVES IN SYSTEM
EFFLUENT PUMP ^^-^.- f\-=_ — -4
AND SPARE
FLYASH POND
ASH POND PUMP
AND SPARE
Figure 27. Simplified scrubber flo w diagram.
-------
High alkali metal oxides content in the fly ash permitted
the scrubber to be designed to use a recirculating slurry of
flyash for S02 removal. The system operates with a slurry hav-
ing a pH of 5.0 to 5.6 containing 12 percent solids by weight.
The pH is controlled by the addition of small amounts of lime
as required. The scrubber design parameters are given in Table
15.
The data obtained by Method 17 testing are summarized in
Tables 16 and 17. The overall collection efficiencies for each
of the pairs of tests are given in Table 18.
The impactor data are summarized in Figures 28 through 31.
Figures 28 and 29 present averaged inlet and outlet size distri-
butions, respectively, on a cumulative percentage (by mass)
basis versus aerodynamic particle diameter, while Figures 30 and
31 show the same data on a cumulative mass concentration basis.
Figure 32 shows the fractional efficiency curve as a function of
aerodynamic particle diameter as derived from the inlet and out-
let data that were presented in the previous figures. The
fractional efficiency curve is shown later in Figure 35 on a
Stoke1s diameter basis (p = 2.30) together with the efficiency
curves derived from the ultafine particulate data. The scrubber
was operating at a venturi pressure drop of about 48 cm w.c.
throughout the impactor test periods.
Inlet size distributions obtained using optical and electrical
mobility, methods are shown, in. Figure • 33. Outlet size distributions
on a similar basis are shown in Figure 34 for the normal scrubber
operating conditon (48 cm w.c. venturi pressure drop). Figure 35
shows the fractional efficiencies for ultrafine particles. Also
shown in Figure 35 are the fractional efficiencies as a function
of Stoke's diameter, obtained from the impactor data.
The scrubber was operated at venturi pressure drops of 31,
36, 41, 47, and 51 cm w.c. for a brief period at each condition
71
-------
Table 15
Design Parameters For The CEA Variable Throat Venturi Scrubber
(Colstrip Application)
Venturi Pressure Drop
Venturi L/G
Absorption Spray L/G
% suspended solids in
recirculating slurry, by weight
Residence time in the recycle tank
Gas velocity in mist eliminator zone
Wash tray pressure drop
Mist eliminator pressure drop
Reheat pressure drop
Total system pressure drop
(including reheat)
Total scrubber pressure drop
(less reheat)
43.2 cm w.c. (17 in.)
2 H/m (15 gal/1000 ACF,
saturated)
2.41 5,/m (18 gal/1000 ACF,
saturated)
12%
8 minutes
2.65 m/sec (8.7 ft/sec)
9.65 cm w.c. (3.8 in.)
(1 in.)
(2.2 in.)
2.5 cm w.c.
5.6 cm w.c
64.8 cm w.c
55.4 cm w.c.
(25.5 in.)
(21.8 in.)
72
-------
Table 16
CEA Variable Throat Venturi Test
Inlet Mass Data
Run
Number
Date
Time
Moisture, %
Gas Tempera-
ture, °C
Volumetric
Flow, m3/sec
ACFM
Volumetric
Flow, DNCM/s
DSCFM
Concentration,
grams/ACM
Concentration,
grams/DNCM
Isokinetic, %
1
5-16-77
1715
10.30
134
274
208.6
442,000
116.5
247,700
2
5-17-77
1455
11.62
132
269
201.3
426,500
110.3
233,600
3
5-18-77
1235
10.25
129
265
233.9
495,500
131.9
279,500
4
5-18-77
1545
10.87
129
264
236.9
502,000
132.9
281,500
5
5-19-77
0825
11.86
137
278
238.8
506,000
130.1
275,600
6
5-19-77
1245
12.26
133
272
227.6
482,300
124.4
263,500
2.0184 2.8325
3.6145
107.62
5.1701
105.85
*
3.3097 3.4820 3.5145 3.5829
5.8663 6.2079 6.4512 6.5546
104.23 108.62 103.79 103.56
**
* Used points for 10 ft. stack
**Test cut short by 3 points (6 minutes) due to boiler shutdown.
73
-------
TABLE 17
CEA Variable Throat .Venturi
Outlet Mass Train Data
Run
Number 123456
Data 5-16-77 5-17-77 5-18-77 5-18-77 5 19-77 5-19-77
Time 1700 1315 1500 830 1300
Moisture, % 14.01 19.45 17.37 16.53 18.70 18.15
Gas Temp.
°C
op
99.4 94.4 96.1 96.1 96.1 96.1
211 202 205 205 205 205
Volumetric
Flow,M3/s 194.9 224.8 238.9 273.8 237.8 239.3
ACFM 413,000 476,200 506,200 579,300 503,800 507,000
Volumetric
Flow, DNM3/S 118.4 128.4 140.0 162.1 137.3 139.3
DSCFM 250,800 171,100 196,700 343,500 290,900 295,200
Concentration,
mg/ACM 26.09 25.86 19.66 21.52 24.23 19.23
Concentration,
mg/DNCM 42.79 45.31 33.58 36.28 41.90 33.04
Isokinetic, % 105.71 113.99 106.40 106.76 103.91 104.66
74
-------
TABLE 18
CEA Variable Throat Venturi Scrubber Efficiences
From Mass Train Data
Date Efficiency (%)
5-18-77 99.43
5-18-77 99.42
5-19-77 99.35
5-19-77 99.50
75
-------
CD
a
01
Ld
ID1,:
10
'1
++
10° 101
AERODYNAMIC DIAMETER (MICROMETERS)
u
CD
a
a
.01
,<
Figure 28. Average inlet particle size distribution on a
cumulative mass concentration basis from cascade
impactor data.
76
-------
99.99T
99.5
99
H
M
95
90
80
70
BO
50
40
30
Sir
±\\
0.5^
O.O1
10
rl
H—I I I HH| 1—I I I Mll| 1—I I I HIM
icP
101
103
AERODYNAMIC DIAMETER (MICROMETERS)
Figure 29. Average inlet particle size distribution from
cascade impactor data on a cumulative percent by
mass basis.
77
-------
103,:
CD
a
a
en
101,:
10
,-t
-10
fa
<
,-l!
a
--in-sai
-ID
i ii i mil —i i M mil 1—i i i MII|
10'
10P
ID1
102
. AERODYNAMIC DIAMETER (MICROMETERS)
Figure 30. Average outlet particle size distribution on a
cumulative mass concentration basis from cascade
impactor data.
78
-------
1
ffi
LJ
M
j
a
99.99-
99.5^
99^
9BJ
95:
90^
70 \
BOi
50i
401
EO
^i
E-
1-
0.5-
O.E-
o n-i
.
-
IH
•
[
*
•
r
:
i i i i i ml 1 1 1 1 1 IIH 1 — 1 1 1 Mill
10
1-1
icf
AERODYNAMIC DIAMETER (MICROMETERS)
Figure 31. Average outlet particle size distribution from
cascade impactor data on a cumulative percent
by mass.
79
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FE1SETRATIDN-EFFICIENIY
101::
10'H
or O.O
::90.0
1
-33.3
10~CH 1—i ' i HM| 1—i > i mil 1—i M INI
10'1 10° 101 1
AERODYNAMIC DIAMETER (MICROMETERS)
Figure 32. Fractional efficiency curve on an aerodynamic
particle diameter basis for the CEA variable
throat venturi scrubber operating at a venturi
pressure drop of 48 cm (19 in.) w.c..
.99
80
-------
10
14
10
13
CO
Z
Q
6
O
O
O
U
a.
HI
GO
2
D
UJ
O
10
12
10"
10
10
• EAA
D ROYCO
10-1
LOWER SIZE LIMIT, micrometers
10°
Figure 33.
Scrubber inlet particle size distribution from
electrical aerosol analyser data.
81
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101V
I
z
Q
~ 1013
o
1
+•*
O
u
-------
POSETRATIOSH
§
y
LJ
CL
LJ
U
o:
LJ
Cl-
TA A A
lO1::
100,:
icrH
10
"E
A A
IT 0.0
::30.0
A EAA
O IMPACTORS
s
I I I III!
I I I II
I Mill
I I I II
10"c 10"1 10° 1O1
PARTICLE DIAMETER (MICROMETERS)
::33.
S
M
U
M
L.
LJ
U
LJ
Q_
- - ^5^5 ^-l
wf-33.
10s
93
Figure 35.
Fractional efficiencies based on electrical mobility
and optical methods shown on a "physical" diameter
basis. Also shown are fractional efficiencies from
the cascade impactor data on a basis of Stoke's dia-
meters.
83
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on May 21, during which time the outlet concentrations were
monitored with the EAA and the optical counter. No significant
concentration changes were noted .in the EAA data over this range
of pressure drops; however, the optical counter data did show
significant changes. In the 2 ym to 4 ym size interval, a 50%
reduction in concentration was ofcn ained by increasing the venturi
pressure drop from 31 to 51 cm w.c. and a 35% reduction in con-
centration occurred in the 0.6 ym to 2.0 ym particle diameter
range. These relative concentration changes are shown in Fig-
ure 36.
Table 19 summarizes the scrubber operating conditions through-
out the test period. The liquid to gas ratio in the venturi
portion of the scrubber during the. tests was typically about
3.3 VDNCM.
S02 concentrations and collection efficiencies were also
measured during the test program. Results of these measurements
are given in Table 20, from which it can be seen that typically
the SOa collection efficiency is about 80%.
84
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UJ
o
o
o
14
12
10
25
9CH 1 x 100 (0.55 - 1.8 (Jim)
*CH2 x W (1.8-4.1
30
35
40
45
VENTURI PRESSURE DROP, CM. \N.C.
50
Figure 36. Relative outlet particulate concentrations in two
size ranges as functions of venturi pressure drop.
85
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Table 20
Colstrip Power Plant
Scrubber SC>2 Removal Efficiency
Date Inlet S02 Reheater Outlet S02 Removal
Concentration S02 Concentration Efficiency
(ppm) (ppm) (%)
5-17-77 658 130 80.2
5-18-77 525 103 80.4
5-19-77 553 130 76.5
5-20-77 625 90 85.6
86
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SECTION VIII
SUMMARY
The performance obtained by the devices described in this
report can be compared with the expected performance figures for
other types of scrubbers using the "cut diameter" method des-
cribed 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%). Typical performance
figures for the devices tested are shown in Figure 37 ', which 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. Line 1 is for a sieve plate type scrub-
ber with froth density F = 0.4 and hole diameter d, = 0.3.
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 dia-
meter. 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.
87
-------
10
4
2
u 1
5
I- 0.4
o
y 0.2
<
0.25 0.50 1.0
POWER, hp/1000 acfm
2.5 5.0 10.0 25 50 100 250 500
u
Q.
Q
of
LU
Q
O
DC
LU
0.1
0.04
0.02
0.01
1 SIEVE PLATE
2a, 2b VENTURI
3 IMPINGEMENT PLATE
4 PACKED BED
• ARONETICS
• CEA
A CENTRIFIELD
• REXNORD
I
1.0 2.0 4.0 10 20 40 100 200 400 1000 2000 4000 10000
EQUIVALENT PRESSURE DROP, cm H2O
Figure 37. Representative cut diameters as a function
of pressure drop for several scrubber types,
after Calvert (1974), J. APCA 24:929.
88
-------
The collection efficiency of the Aronetics Two Phase Scrub-
ber determined by conventional total mass techniques on a source
producing particulate having a mass mean diameter of about 3 ym
was 95.1 and 96.7% for two days of testing. Measured fractional
efficiencies were about 70% at 0.01 ym, about 35% at 0.05 ym,
35% at 0.1 ym, 99% at 0.5 ym, 99% at 1 ym, and 99.4% at 5 ym.
The scrubber energy usage during the tests was approximately
633000 JOULES/SCM (17000 BTU/1000 SCF) at a net pressure rise
of 12 1/2 to 16 in. H20. This energy usage was a result of using
all the process waste heat available and may have been in excess
of the minimum amount required to achieve the efficiencies ob-
tained during these tests.
The collection efficiency of the Entoleter Inc., Centri-
field Scrubber determined by conventional total particulate tech-
niques on a source producing particulate having a mass mean dia-
meter of about 100 ym was 99.50 and 99.73 for two days of test-
ing. 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 2980 JOULES/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 37, the power consumption for the Centrifield was some-
what lower but not substantially different from that for a well-
designed venturi scrubber giving the same particulate collection
efficiency.
The collection efficiency of the Rexnord gravel bed filter,
determined by conventional (method 5) techniques on a source
89
-------
.producing particulate having a mass median diameter of about 200
ym ranged from 95% to 98% during three days of testing throughout
which the collector was not operating in an optimum mode. Over-
all efficiencies determined from cascade impactor data during a
second two-day test series were found to be 99.3% and 99.7%.
The system pressure drop in the first test series ranged from
11.6 to 17.6 cm w.c. while during the second test series the
system pressure drop ranged from 9.6 to 14 cm w.c. Measured
fractional efficiencies were about 50% at 0.04 ym, zero or nega-
tive over the size interval from about 0.08 ym to 1.0 ym,
approximately zero at 1 ym, 30% at 2 ym, and about 97.5% at 5 ym.
The system energy usage during the tests was approximately 1780
JOULES/SCM (47.7 BTU/1000 SCF) at a pressure drop of 11.8 cm
(4.7 inches) w.c.
Most of the devices tested to date under the novel device
test program have been scrubbers. For this reason it has been
convenient to compare their performance to a conventional venturi
scrubber. The Rexnord gravel bed, while not a scrubber, has also
been compared on the same basis as shown in Figure 37. It was
determined that the power consumption of the Rexnord unit was
somewhat higher but not substantially different from that of a
well-designed venturi scrubber giving the same particulate col-
lection efficiency.
The overall collection efficiency of the CEA variable throat
venturi scrubber, determined by conventional (Method 17) techni-
ques on a pulverized coal fired power boiler producing particulate
having a mass median diameter of about 20 ym ranged from 99.12
to 99.50 during three days of testing. The venturi pressure
drop ranged from 44.5 cm w.c. to 48.3 cm w.c. Measured
fractional efficiencies were about 5% at 0.06 ym, 25% at 0.1 ym,
40% at 0.20 ym, 50% at 0.5 ym, 98.4% at 1.0 ym, and 99.99% at
2 ym. The system energy usage during the tests was approximately
90
-------
7200 JOULES/DNCM (193 BTU/1000 SCF). S02 collection efficiency
ranged from 76.5% to 85.6%.
A comparison of the performance of the CEA scrubber with
that of conventional scrubbers of various types is shown in
Figure 37.
The results of this comparison indicate that the scrubber
tested performed somewhat better than a well designed conven-
tional venturi scrubber operating at the same pressure drop;
however, the difference may well be within the uncertainty in
the measured performance.
91
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BIBLIOGRAPHY
1. McCain, Joseph D., "Evaluation Of Aronetics Two-Phase
Jet Scrubber." EPA-650/2-74-129, Contract Number 68-02-
1480, December, 1974.
2. McCain, Joseph D., "Evaluation Of Centrifield Scrubber."
EPA-650/2-74-129-a, Contract Number 68-02-1480, June, 1975,
3. McCain, Joseph D., "Evaluation Of Rexnord Gravel Bed
Filter." EPA-600/2-76-164, Contract Number 68-02-1480,
June, 1976.
4. McCain, Joseph D., "Evaluation Of CEA Variable Throat
Venturi Scrubber." SORI-EAS-77-650, Contract Number
68-02-1480, November 16, 1977.
92
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-78-093
3. RECIPIENT'S ACCESSION NO.
4. TITLE ANDSUBTITLE
Evaluations of Novel Particulate Control Devices
5. REPORT DATE
June 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Joseph D. McCain
8. PERFORMING ORGANIZATION REPORT NO.
SORI-EAS-78-347
3344F
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Southern Research Institute
2000 Ninth Avenue, South
Birmingham, Alabama 35205
10. PROGRAM ELEMENT NO.
E HE 62 4 A
11. CONTRACT/GRANT NO.
68-02-1480
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 ANC
Final; 6/74-1/78
NO PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA/600/13
is SUPPLEMENTARY NOTES IERL-RTP project officer is Dale L. Harmon, Mail Drop 61, 919/
541-2925.
16. ABSTRACT
The report gives results of fractional and overall mass efficiency tests of
four novel particulate control devices. Three were wet scrubbers: an Aronetics
(Chemico) Two-Phase Jet Scrubber, an Entoleter Centrifield Scrubber, and a CEA
Variable-Throat Centuri Scrubber. The fourth was a Rexnord Gravel-Bed Filter.
The devices were used for controlling emissions from a submerged-arc ferroalloy
furnace, an asphalt batching plant, a pulverized-coal-fired utility boiler, and a
Portland cement clinker cooler, respectively. Total flue gas particulate mass con-
centrations and emission rates were determined at device inlets and outlets by con-
ventional techniques. Inlet and outlet emission rates as functions of particle size
were determined on a mass basis using cascade impactors for sizes from about 0. 5
to 5 micrometers, and on a number basis for sizes smaller than 1 micrometer
using optical and diffusional and/or electrical mobility methods. The report includes
brief descriptions of the control devices and the process on which each was utilized,
the measurement methods, inlet and outlet size distributions, and overall and frac-
tional efficiencies.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI r-'icId/Group
Pollution
Dust Control
Gas Scrubbing
Scrubbers
Gas Filters
Ferroalloys
Furnaces
Asphalt Plants
Portland Cements
Coal
Boilers
Measurement
Pollution Control
Stationary Sources
13 B
07A,13H
131
13K
11F
13A
11B
21D
14B
13. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
96
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
93
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