EPA-340/1-77-004
March 1976
PRELIMINARY EVALUATION
OF AIR POLLUTION ASPECTS
1 OF THE
DRUM-MIX PROCESS
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Enforcement
Office of General Enforcement
Washington, D.C. 20460
-------
EPA-340/1-77-004
PRELIMINARY EVALUATION
OF AIR POLLUTION ASPECTS
OF THE
DRUM-MIX PROCESS
Prepared by
JACA Corp.
506 Bethlehem Pike
Fort Washington, Pennsylvania 19034
in partial fulfillment of Task 8
Contract No. 68-02-1356
EPA Project Officer: Kirk Foster
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Enforcement
Office of General Enforcement
Washington, O.C. 20460
March 1976
-------
This report was furnished to the U.S. Environmental Protection
Agency by JACA Corp., Fort Washington, Pennsylvania, in partial fulfill-
ment of Contract No. 68-02-1356, Task No. 8. The opinions, findings, and
conclusions expressed are those of the contractor and not necessarily
those of the Environmental Protection Agency. Any mention of products
or organizations does not constitute endorsement by the U.S. Environmen-
tal Protection Agency.
11
-------
Table of Contents
Section Page
ACKNOWLEDGMENTS i:Li
LIST OF EXHIBITS iv
1 INTRODUCTION 1
2 THE DRUM-MIX PROCESS 3
3 EMISSIONS 16
4 EMISSION CONTROL TECHNIQUES 20
5 EMISSION DATA ANALYSIS 29
6 EMISSION FACTORS 40
7 SOURCE TESTING 43
8 FINDINGS AND RECOMMENDATIONS 46
REFERENCES 49
APPENDIX A Manufacturers of Drum-Mix Plants A-l
APPENDIX B Sampling Train Modification A-2
111
-------
ACKNOWLEDGMENTS
The assistance obtained from many individuals from EPA and sev-
eral State air pollution control agencies during the conduct of this evaluation
is gratefully acknowledged. JACA Corp. wishes to especially thank Mr.
Kirk Foster of EPA for his supervision and coordination with the various
regional offices of the agency. We also wish to express our appreciation
for information provided by a number of manufacturers of the drum-mix pro-
cess contacted by us during this study.
IV
-------
LIST OF EXHIBITS
Figure Page
1 Schematic of Shearer Type Drum-Mix Plant 6
2 Drum-Mix Plant With Separate Asphalt Injection 8
3 Typical Drum-Mix Moisture Content and Aggregate Mix
Temperature Profiles 9
4 Venturi Scrubber 25
5 Efficiency vs. Size for Typical Venturi ' 27
6 Uncontrolled Emissions from Drum-Mix Process 32
7 Emissions With Dry Mechanical Collectors 34
8 Emissions With Wet Scrubber Controls 35
9 Emissions With Venturi Scrubber 37
10 Typical Drum-Mix Exhaust Flow Rates 41
11 Relationship Between Condensibles and Type of Control 45
Table
1 Number of Drum-Mix Plants By Site 15
2 Composition of Asphalt Hot-Mix Emissions from Truck
Loading of Product 18
3 Particle Size. Distribution Before and After
Primary Collection 23
4 Emission Factors for the Drum-Mix Process 42
-------
Section 1
INTRODUCTION
New Source Performance Standards for the asphalt concrete industry
were published on March 8, 1974 (39 FR 9308), pursuant to Section 111 of
the Clean Air Act (42 USC 1857 et. seq.). These standards are applicable
to sources whose construction or modification commenced after June 11, 1973.
There has been a new process development of significance in asphalt
concrete production technology since the promulgation of the standards. A
new production process called the "drum-mix" process (also known as "drum
dryer", "turbulent mass") has gained increased commercial acceptability in
the industry and now constitutes an important portion of new asphalt con-
crete plants. It is estimated that 30% of new asphalt concrete plant con-
struction over the past 3 years is of the drum-mix type.
Although various versions of the drum-mix process have been in exis-
tence for a number of years, its significant use in the production of asphalt
concrete is a recent phenomenon. There are at least eight manufacturers of
such plantr (See Appendix A). Based on information gathered during this
evaluation, it is estimated that there are at present approximately 130
to 150 asphalt concrete plants in the U.S. using the drum-mix process. New
Source Performance Standards are applicable to between 50 and 70 percent of
these plants. It was the intent of this preliminary evaluation to rely on
existing data rather than develop new data through extensive plant inspec-
tions and emission testing. Although this approach would be susceptible to
data inadequacies since there was no control over the source test reporting,
it was felt that such an approach was commensurate with the modest time and
funds available for the task.
-------
EPA regional offices, state air pollution control agencies and
manufacturers of drum-mix plants were therefore the chief sources of data.
Seventy emission tests were obtained and screened for methodology, calcu-
lations, isokinetic conditions, etc. Sixty-three tests were found accep-
table for inclusion in the analysis contained in Section 5. Even these
tests, however, often inadequately described process materials, control
equipment operating parameters, and process operating conditions. One
drum-mix plant was tested by the contractor using EPA Method 5 with some
equipment changes.
-------
Section 2
THE DRUM-MIX PROCESS
There are approximately 4000 asphalt concrete plants in the United
States of the familiar "conventional" type described in several publica-
345
tions. ' ' The salient features of the newer drum-mix process can best
be described by comparing it with the way in which asphalt concrete is
produced in these "conventional" asphalt plants.
The conventional process begins with the conveying of a pre-determined
mixture of different sized cold aggregates from separate storage bins into
an inclined rotary drum which drys the aggregate by counter-current flow
interaction with combustion gases from a burner mounted at one end of the
drum. The dried, heated aggregate is then transported by a hot elevator
to a set of vibrating screens located over storage bins where it is sized
and stored. Pre-designed quantities of the sized}dried aggregate are
weighed and fed into a pugmill where it is mechanically mixed with heated
asphalt to produce the desired finished product. The mixing of the aggre-
gate with "he asphalt is accomplished by either a batch or continuous pro-
cess. Thus the drying and heating of the aggregate, and its mixing with
aj.phnlt are carried out in separate stages in the conventional asphalt plant.
A majority of the emissions are from the drying and heating stage in the form
of entrained particles, the remainder coming from vents from the mixing
tower which is nearly totally enclosed.
In the drum-mix process, the aggregate is dried, heated and mixed
with asphalt in the same vessel -- a specially designed rotary drum dryer.
This obviates the need for a separate mixing tower with screens, weigh
hopper and pugmill, thereby reducing plant capital costs and improving
-------
portability. These are two of the advantages cited by drum-mix process
manufacturers in selling their equipment.
The major equipment differences can be shown in table form as follows:
Conventional Plant
Cold Storage bins § hoppers
usually with vibratory feeds
Load cells sometimes used
Dryer with less sophisticated
flight design $ counter cur-
rent flow - no asphalt injec-
tion
Hot elevator
Hot screens
Weigh Hopper
Pug Mill
Storage silo and conveyor
optional but usually found
in continuous process
Drum-Mix Plant
Same
Load cell nearly always
used
Dryer with sophisticated
flight design, parallel flow
and asphalt injection
Not required
Not required
Not required
Not required
Storage silo § conveyor re-
quired
The different versions of the drum-mix process can be classified
in two ways: the manner in which the material flows with respect to the
flow of gases, and the point at which asphalt is introduced into the drum.
The majority of the designs currently marketed in the U.S. utilize
a parallel - flow dryer, where the flow of material and hot gases is in
the same direction. The hottest flame and gases exist at the charging
end of the drum, where the aggregate is at its coldest temperature. It
is felt that in this manner, asphalt is best protected from oxidation
by moisture. Another characteristic of the parallel-flow dryer is that
lower aggregate discharge temperatures result.
4
-------
In the counter-flow dryer design, the aggregate and asphalt are com-
bined at the inlet end of the drum, and the drying-mixing process proceeds
toward the burner end of the drum, where the mixture is discharged before it
comes into direct contact with the flame. It is estimated that the counter
flow dryer design accounts for only 5-10% of the drum dryer market, and
plants using this design are generally lower in capacity than the parallel-
flow dryer. Typical capacities of a counter-flow dryer are 40-50 tons per
hour, whereas those of the parallel-flow dryer range from 100 to 600 tons
per hour.
Parallel-flow dryers which comprise 90% of known drum-mix plants
can be divided into two general types based on the point of introduction
of the asphalt.
In the Shearer process, the aggregate and asphalt arrive in the mixer
at the same time, alongside a stainless steel firebox which shields the
mixture from direct contact with the burner flame. A chute then discharges
the mixture into the next section of the drum where the flight design pro-
duces a mixing action without developing a full curtain of material through
the flame. In the following section of ^ he drum, the flight design causes
a full curtain of material to develop, where mixing action takes place in
?n atmosphere of steam and hot gases. The finished mix is discharged at
the end of the drum mixer onto a conveyor where it is transferred into a
heated storage silo for delivery into trucks. This process is shown sche-
matically in Figure 1.
Another version of the Parallel-flow design introduces the aggre-
gate separately into the dryer drum. Drying of the aggregate begins imme-
diately in direct contact with the burner flame. A full curtain of ag-
gregate is developed in the first section of the dryer drum: In the next
section of the drum, out of direct contact with the flame, adjustable
5
-------
Heated
Storage
Silo
Conveyor
To Exhaust Fan
t i
Lħ
ITU
Finished Product
to Trucks
Asphalt
Pump
Rotary Drum
Asphalt
Storage
Tank
Aggregate Storage Bins
Burner and
Turbo-Compressor
able Speed
Conveyor Belts
Figure 1
SCHEMATIC OF SHEARER TYPE DRUM-MIX PLANT
-------
spray bars coat the aggregate with hot asphalt. Mixing is completed fur-
ther along in the drum and the mixture is discharged as described previously.
This process (shown in Figure 2) can be further described by the moisture
content and mix temperature changes in the dryer as shown in Figure 3. This
shows that the bulk of the moisture is removed during Phase 1 where the ag-
gregate is in the burning zone. Asphalt is generally introduced during
Phase 2 where it is assumed* that moisture trapped deeper into the aggregate
surface begins to vaporize. The escape of this moisture through partial
coating of the asphalt, in Phase 3, produces violent foaming, which is said
to increase the uniformity of the asphalt layer coat on the stone particles.
Phase 4, at the far end of the drum, sees a rapid increase in the mix tem-
perature after the moisture has escaped from it.
The extent to which these drum-mix plants will be found in new asphalt
concrete plant construction depends on the resolution of a number of questions
concerning product quality, efficiencies of operations, and the nature of
emissions from the drum-mix system as opposed to what has been called the
"conventional system." The nature of drum-mix system emissions is discussed
in subseq. ;nt sections of the report, while the product and efficiency
questions will be briefly covered here. It is not the intention of this
trif.f discussion to present an authoritative, quantifiable analysis of the
two systems since that was not the primary purpose of the project. Jleadily
available data was used which was not verified in all cases although some
effort was expended to resolve obvious ambiguities. Information frequently
advanced by manufacturers, users, and state personnel which may have a
bearing on the growth of the market and hence the amount of effort EPA should
devote to enforcement related activity in this area is presented in reportorial
fashion with limited analysis of the information advanced by the various
sources.
-------
Aggregate Storage Bins
Asphalt
Storage
Tank
Adjustable
Spray Bars
Finished Product
to Trucks
Burner and
Turbo-Compressor
Variable Speed
Conveyor Belts
Figure 2
Drum Mix Plant with Separate Asphalt Injection
-------
280
260
240
220
J2 200
180
160
140
PHASE 1
DRUM MIXER LABORATORY SIMULATION
DENSE GRADED LIMESTONE MIX:
MOISTURE AND TEMPERATURE
PROFILES
PHASE_2 PHASE 3 PHASE 4
-i-REMOVE FREE WATER
-=-DEVELOP INTERNAL
VAPOR PRESSURE
-T VIOLENT FOAMING
~ RAPID TEMP. RISE
u
£
o
o
I
H
CO
M
TIME THROUGH DRUM, (MINUTES)
Figure 3
TYPICAL DRUM-MIX MOISTURE CONTENT AND AGGREGATE MIX TEMPERATURE PROFILES
Source: Reference 1
-------
Feed
Since the drum-mix process does not use hot screens to control the
aggregate blend, more careful control of cold aggregate gradation is neces-
sary. Usually three or four cold aggregate storage bins are employed with
variable speed conveyor belts from each bin, sometimes coupled with variable
gates that feed the aggregate onto a main conveyor belt, where the aggre-
gate weight is monitored by means of a load cell. Some plants monitor the
aggregate weight on each belt conveyor being fed by the storage bins.
The rate of asphalt feed is controlled either manually or automatically
to maintain the proper ratio of asphalt to aggregate. The trend in asphalt
plants of both the conventional and drum-mix type is to make greater use of
automatic control. Where automatic control is used a frequent technique
employed is to feed the signal from the aggregate load cell(s) back through
a control loop which actuates a pump to feed the heated asphalt into the
dryer drum.
The combination of aggregate feed rate and size control, and asphalt
injection rate, allows the operator to change both the production rate and
product mix throughout the cycle.
Asphalt
Penetration grade asphalts are used in the drum-mix process, often
in conjunction with proprietary chemicals to insure proper coating and
adhesion.
Product
Asphalt concrete top mixes can be produced at a temperature of 210
to 220 F, compared to 300 to 325 F in the conventional process. At these
discharge temperatures, the mixture contains from 1 to 3% moisture,
10
-------
compared to 1/4% or less in conventional mixtures. Manufacturers of drum-
mix plants claim that this higher moisture assists in laying the product;in
that during the field compacting operation, it acts as a lubricant. Moisture
equilibrium of the layed product from a drum-mix plant is attained by a
loss of moisture while the layed product from a conventional plant reaches
moisture equilibrium by a gain in moisture from the surroundings.
Fuel
The burners are usually fired with fuel oil although liquid propane
can also be used when available.
Since the asphalt concrete produced by drum-mix plants is at a lower
temperature, fuel savings are claimed from the process. A conventional
plant uses an average of 2 gallons of fuel oil to produce one ton of mix.
A drum-mix plant under the same conditions of aggregate moisture and ambient
temperature is reported to require an average of 1 1/2 gallons of fuel oil
per ton of mix.
Process/Product Considerations
Major commercial advantages of the drum-mix process over the con-
ventional process as cited by drum-mix manufacturers are overall lower
capital costs and increased portability due to the elimination of the mixing
tower. This portability advantage is reflected in the high number of por-
table plants. It is estimated that more than 70% of the drum-mix plants
currently in operation are portable. This portability poses secondary
control problems when wet collection systems are employed. Each new site
must have an appropriate water supply available, and must have a proper
water disposal facility to assure that applicable water pollution control
11
-------
regulations are being met. From an enforcement viewpoint the ability to
move the plant could increase record keeping and inspection problems es-
pecially when different state jurisdictions are involved.
Lower operating costs arising from fuel economy, and lower maintenance
costs due to generally fewer system components are also cited. On the other
hand, process controls to ensure desired product quality are more complex
with the drum-mix process, and the ability of the process to detect changes
in product quality and to correct for it is limited because the proportioning
of different sized aggregates and asphalt is carried out prior to their
entry in the drum. In a conventional plant, the aggregate is monitored
at the point of introduction into the dryer and before entering the mixer
from hot bins which store the dry aggregate according to size. In conventional
batch plants finer control is accomplished because each individual batch can
be mixed after preweighing all the ingredients for that individual batch.
The amount of fine material (frequently classified as aggregate passing a
200 mesh screen) in the product is also similarly capable of better control
in a conventional plant where the fines can be metered back into either the
hot elevator or the hot bin from the dry collector (cyclone and/or fabric
filter).
The major market for asphalt concrete is highway construction, where
local, state and federal highway departments exercise careful product quality
control. Highway specifications for asphalt concrete include sizing of
aggregate, proportions of asphalt to aggregate, coating of asphalt, tem-
perature and final moisture content of the product depending upon the grade
(e.g. sub-base, base, top, curbing), or use of the product. Each asphalt
concrete plant doing business with the highway department is approved,
based on the product quality and the ability to control it. The product
12
-------
quality control capability of the drum-mix process is being carefully in-
vestigated by state transportation agencies with varying degrees of accep-
tance. Many Eastern States have given only conditional acceptance as for
example in Pennsylvania,.where approval of a drum-mix plant for highway
work is conditional, and determined on a case-by-case basis.
Two other limitations of the drum-mix process from a production
point of view were often encountered. The drum mix process design lends
itself to long, continuous production runs with the same mix. Consequently,
it is less suited for applications where the demand for different types
of mix is random, even on a given day, as in the case of many plants loca-
ted near urban areas, especially in the East. The dwell time of the mix
in the dryer is on the order of 5-7 minutes, and by the time a change is affec-
ted at the input proportions of the aggregate, as much as a half hour may be
required before a new steady state is reached for the production of a dif-
ferent mix. In the conventional plant, on the other hand, a product change
can be accomplished within a matter of minutes by simply changing the pro-
portion of different sized, dried aggregates in the pugmill mixer, prior
to making a change in the dryer input gradation.
Many plants buy aggregate from different sources depending upon need
and price. The size specification generally covers a range, and within the
designated range there is considerable variability in size characteristics
of aggregate occurring between sources, depending upon type of rock, crush-
ing and screening sequence, etc. Such variations in the source of aggre-
gate cannot be easily accommodated with a drum-mix plant, because a new
setting of dryer input controls is required to produce the same product.
In areas West of the Mississippi, with less population and highway
concentration, the ability of a plant to move from one construction site to
another, an advantage of the drum-mix, apparently outweighs the above limi-
13
-------
tations. The majority of drum-mixer plants thus exist in the Western half
of the United States as can be seen from Table 1 which shows known plant
location by state. It should be noted that the plants can be moved so that
locations shown are subject to change.
14
-------
Table 1
NUMBER OF DRUM-MIX PLANTS BY STATE
Arizona 5
California 1
Colorado 5
Georgia 2
Illinois 1
Indiana 4
Iowa 4
Kansas 9
Louisiana 2
Maryland 1
Michigan 2
Minnesota 7
Mississippi 2
Montana 1
Nebraska 1
Nevada 3
North Dakota 11
Ohio 1
Oklahoma 4
Oregon 10
Pennsylvania 4
South Dakota 4
Texas 12
Utah 5
Virginia 1
Washington 3
Wisconsin 3
Wyoming 3
15
-------
Section 3
EMISSIONS
Sources of air pollution from the drum-mix process include both fu-
gitive and stack emissions. In both instances, the source, nature and mag-
nitude of the emissions are considerably different from their counterparts
in the conventional process. This difference is attributable to the marked
difference in the processing techniques.
The sources of emissions of the conventional and drum-mix plant
are shown in the following table:
Conventional
c
Fugitive emissions from stockpiles, cold
feed bins and conveyors
Fugitive emissions from finished product
discharge to trucks, or to storage
Stack emission from scavenger ductwork
to hot elevators, hot screens, bins,
weight hopper, mixer
Stack emissions from dryer
Drum-Mix
Same
Finished product conveyor to silo
None
Stack emissions frm drum-mix
Fugitive emissions from stockpiles, cold feed bins and the conveying
machinery prior to the introduction of the aggregates into the drum-mix,
are, as in the case of the conventional process, dependent of the moisture
content, size of aggregate and ambient conditions. The conveying of finished
product from the drum-mix to the storage silo produces fugitive emissions
similar to those in conventional plants with continuous processes which
are generally equipped with storage silos.
16
-------
Stack emitted dust from scavenger ductwork connected to emission
sources such as the hot elevator, screens, bins and mixer are eliminated
in the drum-mix process. Any fugitive emissions from these sources are
also eliminated in the case of drum-mix plants.
Fugitive emissions from the finished product in discharge to trucks
or storage from conventional plants have been characterized in a study done
by the Asphalt Institute and the Exxon Research and Engineering Company,
and are summarized in Table 2. These data identify the various components
in the fugitive emissions from the handling of the finished product.
As in the conventional plant, stack emissions are the major air pol-
lution source in the drum-mix plant. The new source performance standards
apply to the stack emissions in the form of emission concentration and
opacity. The opacity standard, however, also applies to the entire process
subsequent to the introduction of the aggregate in the drum, and therefore
covers fugitive emissions from that point on.
Both particulate as well as gaseous components are present in the
stack emissions from a drum-mix operation. The particulate emissions gen-
erally include mineral, hydrocarbon and carbonaceous matter. Aggregate
dust entrained during the drying-mixing action in the drum is the source
of the mineral matter, while the hydrocarbon and carbonaceous matter results
primarily from the exposure of asphalt to various degrees of oxidation in
the drum. This, as well as the combustion of the fuel, also accounts for
the gaseous emissions in the stack. Section 5 includes data on emission
tests of plants with varying production capacity and different degrees
of control.
The test data indicate that uncontrolled stack emissions from drum-
mixers .are significantly less than those from the conventional plant, by
almost an order of magnitude. The simultaneous drying and mixing of the
17
-------
Table 2
COMPOSITION OF ASPHALT HOT-MIX EMISSIONS FROM TRUCK LOADING OF PRODUCT
(Conventional Plants)
Sample Location .
Number of Samples
Edison, N. J.
Greensboro, N. C.
2
Non-Visible Components (ppm)
Carbon monoxide (CO) 4-6 3-4
Nitrogen dioxide (N02) <0.1 .05-.08
Sulfur dioxide (S02) <2 <0.5
Hydrogen sulfide (H2S) <0.2-1.5 <0.2
Carbonyl sulfide (COS) <0.2 <0.2
Mercaptan (RSH) <0.2 <0.2
Aldehydes (ECHO) <0.1 0.3-0.4
Phenol (00H) <1 <1
Ozone (0^) <0.1
Methane (CH^) 2-3 2-3
Non-methane Hydrocarbons (C2-Cg) (NMH) <1 <1
Volatile organic compounds (Cy-C-^) (VOC) . 0.5-1.5 0.5-1.0
Particulates (mg/m^)
Total particulates 2.6-7.2 0.5-5.7
Benzene solubles 0.3-2.8 0.2-5.4
Polynuclear aromatics (total), max. 0.00034 0.00016
Nickel (Ni), max. 0.000005 0.00004
Vanadium (V), max. 0.00008 <0.0001
Cadmium (Cd) <0.00005
Lead (Pb) <0.00005
NOTE; Where the less than (<) values are indicated, the numbers represent the
sensitivity of the sampling or testing procedure used. If the component
is present at all, it is below the value shown.
Source: Reference 2
18
-------
aggregate with asphalt in the drum tends to trap a large portion of air-
entrained mineral particles in the asphalt spray resulting in "balls" which
further breakdown, coating the surface of the aggregate. Manufacturers
claim that this considerably reduces the amount of mineral dust carried
over by the exhaust gases, and promotional literature from manufacturers
prominantly advertises this attribute. However, a reduction in the uncon-
trolled emissions does not generally make it any easier for a drum-mixer
to meet the new source performance standards as will be discussed in Section 5.
An increase in the asphalt-related emissions is generally found in the
drum-mix exhaust, as compared to the exhaust from a conventional plant.
In a conventional plant, this type of emission is vented into the exhaust
from the enclosed mixer, accounting for approximately 5 to 10 percent of
the total exhaust flow rate directed to the control device. The genera-
tion as well as entrainment of asphaltic emissions is therefore limited.
In the drum-mixer, on the other hand, the asphalt is exposed to the total
exhaust in a turbulent fashion, thereby tending to increase the entrain-
ment of asphaltic products.
While the uncontrolled mineral dust is generally less in a drum-mix
plant, and the asphalt-related emissions greater, than a conventional
plant, the amounts are a function of process design and operating variables
of a facility.
19
-------
Section 4
EMISSION CONTROL TECHNIQUES
Control techniques applied to existing drum-mix process plants have
varied from state to state because of the varying stringency of regulations
for existing plants which are included in the State Implementation Plans.
In the case of plants that should fall under the New Source Perfor-
mance Standards, another preliminary study for EPA' has indicated that
reporting of such new plants may suffer appreciable omissions so that it
can be expected that some plants, that should be classified as new, and hence
under federal regulations, may be classified under SIP. Such plants will
then be frequently operating at levels that meet the SIP, but which may not
meet the NSPS.
Controls at the 63 plants reported in the various test records reviewed
included the following:
Type of Control No. of Plants Percent of Plants Reported
None (May have knockout boxes 14 22
as an integral part of
the output ducting)
Cyclones or multicyclones 7 11
Low energy wet scrubbers 24 38
Venturi scrubbers 18 29
Baghouses 0 0
Electrostatic precipitators 0 0
An important word of caution concerning the above table and the
description of control devices that follow: This preliminary evaluation
20
-------
of air pollution aspects of the drum-mix process did not involve develop-
ment of primary data. Instead, it is based on information available in
stack test reports that were available to us, sometimes only after they
were several times removed from the actual testing organization. In almost
all cases the stack test reports gave no or only meager data on the type
of control system being used. For example, in the case of wet systems the
liquor flow rate and pressure drop was not usually presented. Details
of stack sprays insofar as their location, type and number of nozzles and
liquor flow rate was not stated. It was therefore necessary to ascribe
pressure drops and some operating characteristics to some of the vague
descriptions given in the reports based on experience with conventional
reports.
Fourteen reports indicated no controls used. We believe that in
these cases there may have been a knock-out box which was never mentioned
in the report. Such boxes operate on the principal of abruptly changing
the direction of the gas stream so that inertial force of the heavier par-
ticles overcame the entrainment forces of the gas stream and they are
essentially "knocked out" of the stream. This phenomenon is an undesirable
effect where it inadvertently occurs in poor duct design causing duct wear
and pile-up of material. The technique has only low efficiency, operating
best when the size distribution of particles is heavily toward larger and/
or more dense particles.
Primary cyclones of the type generally used with conventional plants
are more efficient that the knock-out boxes in that they remove between
50 and 70% by weight of the entrained dust from conventional asphalt batching
plants. Such cyclones operate on the centrifugal force principle. Practical
limitations on their use usually involve re-entrainment problems and unworkable
21
-------
high pressure drops. The overall efficiency of the cyclone depends on
particle size, geometric design of the cyclone and pressure drop. In most
practical situations involving mineral dust, pressure drops are on the
order of 2 to 4 inches of water. Table 3 shows the particle size distri-
bution before and after entering a cyclone collector on a conventional
asphalt plant.
Stack sprays were mentioned in the reports, but as previously stated
there was no detail on the type nozzles, location, and liquor rates. The
techniqe however is to inject water droplets into the exit stack relying
on impaction and agglomeration of the dust particles to produce particles
either heavy enough to overcome the upward force of the gas stream so that
they settle to a collection sump, or of sufficient mass to be removed by
baffle plates upon which particles can impinge, or by centrifugal forces
applied by mechanical means subsequent to the introduction of the spray.
Another type of wet collector frequently encountered in conventional
plants and what we think the testers generally meant when they referred to
"wet scrubber" in their test reports on the drum-mix plants used in this
preliminary 'investigation was a dynamic scrubber which incorporates a wet
fan as an integral part of the unit. A spray of water is either directed
toward an impeller type fan or is fed axially in the case of paddle-wheel
fans. The mechanism is mainly one of impingement of dust particles on the
wetted rotating blades. The purpose of the sprays is to keep the fan blades
wet and to flush away the collected dust. This technique also relieves
the abrasion and condensation buildup which would otherwise accumulate on
the blades. Our experience with these devices on conventional plants indicates
that they usually operate at 5" to 10" water gauge.
22
-------
Table 3
PARTICLE SIZE DISTRIBUTION
BEFORE AND AFTER PRIMARY COLLECTION
FROM DRYER AND VENT
Size/C % Less Than
FROM PRIMARY COLLECTOR
Size/* % Less Than
5
10
15
20
25
30
55
40
45
19.5
30.5
38.2
45.1
50.1
55.5
60.0
64.0
67.5
5
10
15
20
25
30
35
40
45
78.00
96.40
97.50
97.80
97.90
98.03
98.20
98.28
98.40
Source: Air Pollution Control Technology and Costs In Nine Selected
Areas, Industrial Gas Cleaning Institute
23
-------
Those installations which exhibited the best degree of control were
venturi scrubbers. Again, the reports did not adequately describe them
nor note the pressure drop or liquor flow rate. Such venturi scrubbers
could fall into several categories as shown in Figure 4, but their operating
principles are essentially similar.
These scrubbers, with pressure drops in the range of 20 inches of
water, or greater, generally are capable of reducing emissions of conven-
tional plants to below the required NSPS of 90 mg/scm (0.04 gr./dscf).
The venturi scrubber is a high efficiency wet collector that operates
by impinging particulates on atomized water droplets. The effective mass
of the particle thus increased, cyclonic separation is then possible.
As the particle laden gas enters the device, a constriction reduces
the cross-sectional area of the gas stream, thereby increasing the stream
velocity. This correspondingly increases the velocity of the particles
relative to the formerly stationary water droplets that were introduced at
the apex of the constriction. Increasing the relative speeds heightens the
probability that a particle will impinge upon the water droplet. As the
dust-laden water droplets leave the venturi constriction, they further
agglomerate due to deceleration. The gas stream then passes through a cyclonic
separator, which removes the larger, heavier particles formed during the
agglomeration phase.
Venturi scrubbers can achieve collection efficiencies in excess of
99%. Variables affecting efficiency include pressure drop, water injection
rates, venturi design, and particle concentration and size. Collection
efficiencies improve with higher pressure drop, attainable by increasing
the throat velocity by constricting the throat and to a lesser extent by
increasing the water injection rate. Pressure drops will probably be 20"
24
-------
Figure 4
VENTURI SCRUBBER
Venturi scrubber may feed liquid through jets (a)
over a weir (b), or swirl them on a shelf (c).
Source:
Control Techniques for Particulate Air Pollutants. USDHEW 1969
25
-------
or more for most venturies while water injection rates normally encountered
will nominally be 6 and 10 gallons of water per minute per 1000 acf of gas.
Efficiencies fall rapidly at injection rates below this range; rates in
excess of 10 gallons of water per minute 1000 acf of gas produce lesser
increases in collection efficiencies.
Greater particle concentration also improves collection efficiency.
Assuming the number of water droplets formed in the system is constant,
the frequency of particle collisions is increased when more particles are
introduced into the system. Figure 5 shows a nominal collection efficiency
and particle size relationship for a typical venturi scrubber. Note that
the efficiency is greater than 97% for particles larger than 1.5 microns;
note too that the efficiency falls sharply for particles less than 1 micron
for a fixed set of conditions.
Disadvantages of venturi scrubbers include high operation costs
associated with producing high pressure drops, and also the need for large
quantities of water which entails elaborate recycling of alkaline, acidic
or adoriferous water. This would require the use of settling basins which
also present a problem of solid waste disposal when they must be dredged.
Advantages of venturi scrubbers include their relatively low initial
cost, and their ability tİ partially control $be hydrocarbon emissions
from the drum-mix operation.
No drum-mix plants using fabric filter controls were encountered
in this preliminary investigation. The asphaltic emissions from the drum-
mix process as well as mineral particles coated with asphalt are difficult
to control with fabric filters because of sticking and blinding of the filter
medium. Two sources have reported that they were experiencing plugging
even using cyclones from these emissions.
-------
Figure 5
EFFICIENCY vs. SIZE FOR TYPICAL VENTURI
IS)
-------
Electrostatic precipitators were also not encountered. The low gas
volumes associated with conventional asphalt concrete plants and the high
fixed costs for the portion of the precipitator that develops the high
voltages needed generally renders such devices economically less attractive
than other solutions. They can however attain collection efficiencies of
over 99% in conventional plants with proper gas conditioning.* Wet electro-
static precipitators that do not require rapping, but remove the captured
particles by a film of water on the collector wall might reduce some of the
sticking problems. Even with the somewhat higher gas volumes found in the
drum-mix plants, however, they may not be economically attractive, and they
may impose some plant portability restrictions.
Important trends are discernable in the development of this relatively
young process technology. One manufacturer has reported to us that they
are trying to affect certain changes in the process variables (such as
flight design through sections of the drum, rotational speed, slope, and
the point at which the asphalt is sprayed in the drum) whereby asphaltic
emissions could be reduced, even at the cost of increasing the mineral
particulate emissions, so that a fabric filter could be used for the control
of process emissions.
Stack Test performed by JACA Corp. for compliance with Pennsylvania
Regulations
28
-------
Section 5
EMISSION DATA ANALYSIS
.. The preceding sections provide general background of the drum-mix
process, and control techniques employed. Quantitative information about
the emissions from the drum-mix process, collected during this study, is
presented here.
It is important for the reader to keep in mind the sources and
limitations of the data which are described below. The analysis is based
on information obtained from regional EPA offices, state air pollution
control agencies, independent stack testing companies and drum-mix manu-
facturers. One counter flow drum mix plant was tested using Method 5 with
slightly modified equipment.
The test information was obtained in various forms. While most of the
information analyzed here is based on actual emission test reports; in
other cases, it was necessary to utilize aggregated summaries of test results
in others. In one instance only the combined results of 31 tests were made
available to us by a drum-mix manufacturer.
Thorough analysis and comparison of data contained in information
gathered from such diverse sources is hampered by two limitations: (1)
the various modifications of the basic EPA sampling train used and approved
in various parts of the country does not permit full comparison of data
results from all tests and, (2) adequate information on source conditions
and description of control equipment and parameters was usually unavailable.
For example, some tests report particulate concentrations based on the front
half catch, some of the 'total' catch, and some do not report the 'condensible'
fraction. None of the reports give important details of control equipment
29
-------
configuration and only a few specified production rates, liquor rates and
pressure drops on wet scrubbers.
Another limitation is that the source test data had to be judged
as to its acceptability on the basis of broad yardsticks such as isokineticity,
thoroughness in reporting the various stack-test related variables, although
a majority of the tests were conducted for compliance purposes and were
presumably accepted by the relevant government agency.
As a result of the data gathering phase, emission tests results
were obtained from 70 different plant tests (not including 31 test runs
from plants where only the aggregate data were made available to us by a
manufacturer). Of these 70 different plant tests we decided to exclude a
total of seven tests, 2 because the tests were run outside the isokinetic
range, 3 due to a paucity of information available (including the only two
counter current plants) and 2 because they were repeat runs on the same
plants included in the analysis.
Of the 63 tests found to be acceptable for inclusion in the analysis,
14 were on uncontrolled plants, 7 were on plants with dry mechanical con-
trols such as cyclones and multicyclones, 24 were from plants with scrubbers
of the spray, impingement or wet fan type, and 18 were on plants with ven-
turi scrubbers of varying pressure drops.
The 63 tests gave a total of 158 independent runs for analysis, of
which 108 reported only "front-half" results, 7 reported only the "total"
particulate matter, and 43 reported both front-half as well as total par-
ticulate concentrations.
The emission concentrations obtained from the above tests are reported
below, in order of increasing level of controls, for parallel flow plants
which account for more than 90% of known drum-mix plants.(the one counter
30
-------
current flow plant is plant D of Figure 6). Due to the large variability
associated with these results, they have been plotted, in Figures 6, 7, 8
and 9, on a logarithmic scale. Plants identified with letters are on the
horizontal axis, and information regarding control device, production rate
and capacity, where available, is indicated below each plant. Where
available, maximum, minimum and arithmetic average concentrations are shown
for each plant tested. The percentages shown above the test results for
some plants are percentage opacity readings reported in the test records.
The opacity data suffers from many of the problems encountered in
the test reports. There was no data sheet showing number of readings,
specific time, position of the observer, atmospheric conditions, etc.
Information on opacity in those reports where it was mentioned was almost
parenthetical, a brief statement that the opacity was a particular percentage.
Figure 6 shows the range of particulate emission concentrations for
uncontrolled plants. (Figures 6 through 9 include results from parallel-
flow plants except for plant D of Figure 6).
The combined results from 31 tests on 9 uncontrolled plants (Figure 6)
with capacities varying from 300 to 350 tons per hour, at maximum moisture
removal rates, shows an extremely wide range of particulate concentration,
a maximum grain loading of 40.5 gr./scfd, a minimum of 0.14 gr./scfd, a
mean of 6.19 gr./scfd with a standard deviation of 8.2 gr./scfd! The other
five plants all have much lower average readings and the ranges of plant
B § F are more like those encountered in conventional plants. Of the three
plant reports with opacity data only plant E was outside of NSPS.
The significant variation in uncontrolled emissions from plant to
plant suggests that process variables might be one of the principal causes.
Plant D for example was known to be a counter current flow plant as described
31
-------
4-1
ii
CTJ
C
o
4-1
4-1
(J
1/1
-a
I/I
c
H
nJ
f-i
CJ3
50
1C
1.0
0.5
0.1
.05
.04
.01
Plant
Figure 6
UNCONTROLLED EMISSIONS FROM DRUM-MIX PROCESS
I
Maximum
^Average
Minimum
T
%=opacity
T
I
10%
30-35%
I I
Federal Standard =0.04
Avg.
Production
Rate, tph
200
175
Capacity,
tph
60
100
166
200
95
200
Combined
Data from
31 tests,, 9 plants
300-350
300-350
32
-------
on page 5 while all others are parallel flow plants. The other plants are
made by a variety of vendors and plants have a considerable range of process
settings - much more so than do conventional plants. Some vendor companies
indicated that they were conducting research on product characteristics
and emissions as a function of several process variables including:
Point of injection of asphalt
Flight design
Aggregate mix
Moisture content
Temperature gradient through the dryer
Drum rotational speed
Rate of production
Temperature of mix
Type of Asphalt
The analysis of the effect of these parameters was not attempted in
this work, and would entail quite a large study because of the number of
different suppliers and the present state of design flux.
Emission concentrations from seven plants controlled with dry mechanical
collectors are shown in Figure 7. The results fall between a high of 3.0
to a low of 0.03 grains/scfd. Plant L for example just met the NSPS stan-
dard of 0.04 gr./scfd. The mean of all the results was 0.853 gr./scfd, with
a standard deviation of 1.16! Of the three plants reporting opacity readings
only one was within NSPS.
Results of emission tests from 24 plants controlled with wet scrubbers
as described in Section 4 are shown in Figure 8. Seven out of twenty-four
plants were within NSPS. Excluding plants N and T for which only the total
33
-------
Figure 7
EMISSIONS WITH DRY MECHANICAL COLLECTORS
5.0
(4-1
iI
n)
X
o
o
I/)
tn
C
rt
1.0
0.5
0.1
.05
.04
.01
Maximum
Average %
Minimum
I
= Opacity
Federal Standard = 0.04
1
30%
ğħ
ħH
15%
30-40%
HE
3H
Plant
Average
Production
Rate,tph
Capacity
tph
G
Cyclone
380
450
H
Cyclone
250
450
Multi-
Cyclone
500
500
J
Cyclone
360
500
K
Multi-
Cyclone
170
200
L
Multi-
Cyclone
250
450
M
Cyclone
160
-------
l/J
en
Figure 8
EMISSIONS WITH WET SCRUBBER CONTROLS
1 .0
.04
1 1 I 1
1 |
. j I |
| |
Maximum
Average
Minimum
= Opacity
' '
1 LJ '
10°;
a - Scrub.-'
b - IV ct !' i
c - Stack
* Include;
i b 1 es
10°,,
15-20%
10%
Federal Standard = 0.04
0-10%
1 1 1 1 1 1 1 1 1
1 1 1 1
Plant N* 0 p . Q !< S T* U V W AA BB CG DD BE FF OG ;1H II JJ '.-' '.I, MM NN
Controls b,ab aaaaa a a a b aaaaaa a a a a a a
c
Average
i'rou. 210 5S5 425 ? 215 350 400 250 225 ? 450 110 225 278 392 336 200 528 400 350 400 125 240 540
Kate,tph
Capaci t v
toh dOO 600 TOO V 400 400 700 600 600 ? 600
? 400 400 400 ? 600 400 400 430 ' 400 600
-------
catch results were available, the values range from 0.394 to 0.017, with a
mean of .094 gr./scfd, with a standard deviation of 0.089 gr./scfd. Of the
twelve plants reporting opacity readings, two were greater than 20 percent.
Figure 9 shows the results of emission tests on 18 plants with ven-
turi scrubber controls. The pressure drops across the venturi scrubber
axe only known for three plants. These are shown in inches water gauge
in the lower right of the data plot. The emission values vary from a
maxium of 0.191 to a low of 0.005 grains/dscf. The mean of these values
is 0.0557 and the standard deviation is 0.052. Of the eight plants reporting
opacity readings, all were within NSPS.
The data (excluding the one countercurrent flow plant) shows that
the percentage^plants passing NSPS was:
Uncontrolled 0%
Dry Mechanical (Multicyclone) 14%
Wet Scrubber (Per the broad description in Section 4) 29%
Venturi Scrubber (Pressure drop known in only 3 instances) 50%
Attempts to relate emissions concentrations with production rates,
or production rate as a fraction of the plamt capacity for each of the
four sets of data presented abow failed to show any consistent pattern.
Beari ng in mind the nearly total lack of process and control setting
data, the t< ;sts reported shows:
1. Emissions associated with drum-mixers show a very large
variability. Process factors discussed previously may be
responsible for these differences.
36
-------
Figure 9
EMISSIONS WITH VENTURI SCRUBBER
04
~. .005
.00!
1'iaiu 00
Control -
Average i:5
ProJ.
Rate, tph
Capacityjoo
tph
Maximum
\voraye
Mi n imuin
= ilp;ic i ty
1 0°,,
' = 25-30 ''K.I'.
ta'idai\! =
iI A P= 11 :.<;.
QQ
UU
VV WW
Vonturi
Bl
PI
160 230 300 275
200 250 500 500 500
400 dOO 174 500
500 600 200 600
380 300 210 450 230 300 400 200
400 220 600 400 400 400 250
-------
2. No uncontrolled parallel flow plant met NSPS
3. The single countercurrent flow uncontrolled plant marginally
met NSPS, but we are advised that such designs have inherent
limitations in production capability, and are not expected to
be a significant part of the market
4. All but one of the mechanical collector controlled plants failed
NSPS on grain loading as did two out of three of these plants
reporting opacity readings
5. All eight plants reporting opacities which were controlled by
venturi scrubbers were within NSPS opacity limits.
Although an extensive hydrocarbon emission analysis was not under-
taken as a part of this study, several of the particulate emission tests
contained various hydrocarbon analysis. The results are described below:
Analysis of the particulate catch from a test performed on
Plant K, controlled by a multicyclone, showed that 21% of the
filterable particulate was hydrocarbon. The test lab assumed
this material was asphalt.
Total hydrocarbon (THC) analysis were run on Plant II controlled
by a venturi scrubber. Tests were performed by chromotography
and the results for the three test runs were 163 ppm, 501 ppm
and 112 ppm.
A more extensive hydrocarbon analysis was performed on samples
from Plant U controlled by a wet scrubber:
38
-------
THC = (methane equivalent) - 41.5ppm
methane - .6 pprn
ethane - 25.6 ppm
x - 16.4 ppm
propane - .6 ppm
propylene - 1.0 ppm
THC = measured on two other dates on the same plant were
as follows, but no explanation was given for the large differences from
the other dates:
2/75 - 7830 ppm
4/75 - 1187 ppm
Plant R controlled by wet scrubber showed THC as 13.5 lbs./hr.,
90% of which was methane and 5% ethane. The test lab stated
that no reactive hydrocarbons were found in measurable quan-
tities.
This aspect of the emissions will also require further testing and
analysis, once an acceptable method of hydrocarbon analysis is developed.
39
-------
Section 6
EMISSION FACTORS
The large variation in emission concentrations from drum-mix plants
with varying degrees of control shown in Section 5 makes the task of assigning
an emission factor for a given degree of control difficult. The emission
factor estimates developed here, therfore, should be used with this limitation
in mind. For purposes of assigning emission rate values to a plant in air
quality studies, NEDS applications, etc., however these factors are reasonably
appropriate.
Figure 10 shows the typical range of flow rates as a function of
drum-mix production rates. They were developed from theoretical calculations
based on a 5 percent moisture remove, 70°F inlet air, 350°F aggregate mix
and exhaust temperatures. The higher limit of the range for a given pro-
duction rate is associated with a lean burning condition (ratio of flow
to stoichiometric flow = 2.5) and the lower limit with a richer burning
condition (ratio of flow to stoichiometric flow = 1.5). This range of
conditions are typically found in drum-mix plants. This analysis yields
a value of 7000 to 4000 dscf air requirement per ton, respectively. (Analysis
of available test data essentially confirms this range).
The emission concentration (mean values) found fres Section 5 for
each degree of control, when multiplied by the air requirement determined
above yields a range of emission factors shown in Table 4.
40
-------
Figure 10
TYPICAL DRUM-MIX EXHAUST FLOW RATES
140,000
rt
ai
o
x
tu
120
100
80
60
40
20,000
1
acfm range
at 350°F
dscfm range
100 200 300
Production Rate, tph
400
500
600
41
-------
Table 4
EMISSION FACTORS FOR
THE DRUM-MIX PROCESS*
Degree of Control
Uncontrolled
Cyclone or Multi-cyclone
Wet Scrubber (Stack spray, wet fan,
dynamic scrubber)
Venturi Scrubber
Particulate
Emission Factor,
Ibs/ton of product
3.6 - 6.2
.49 - .85
.05 - .09
.03 - .06
The reader must bear in mind that there are different process designs
and that control parameters such as pressure drop, liquor flow, etc.
were generally not included in reports from which these data were taken.
42
-------
Section 7
SOURCE TESTING
Difficulties in source testing drum-mix exhausts by means of the
EPA train have been reported. The chief reason for this is the clogging
of the filter in the front half of the test train with asphaltic emissions,
which prevent isokinetic flow rates through the train because of high pressure
drop created at the filter.
Source testing personnel who have had experience with drum-mixers
were contacted during this study, and the conclusion is that clogging of
the filter diminishes as the degree of control increases. Tests on plants
with no controls or with dry mechanical controls asphaltic emissions appear
to be the cause of filter blinding since plants with wet controls were
reportedly not as difficult to test in this regard.
Based on JACA's test experience on an uncontrolled drum-mixer, and
the experience of EPA's Emission Measurement Branch on the source testing
of asphalt roofing plant exhausts, the following techniques are suggested
to minimize the clogging problem and to reduce the need to frequently change
the filter during a run.
A loosely packed portion of glass wool, inserted into the top
half of the filter holder causes the sticky, asphaltic material
to adhere to it, without causing excessive pressure drops through
the train (See Appendix B).
A cyclone and flask inserted in the hot box between the probe
tube and the filter holder retains bigger particles, thereby
reducing the build up on the filter medium.
43
-------
Methylene chloride is the preferred solvent for use in the
sample recovery operations.
Another potential area of concern was whether, due to the presence
of asphaltic matter in various stages of oxidation, the process emissions
contain large amounts of matter which escapes the filter but gets caught
in the impingers as "condensibles" matter.
This aspect was studied by analyzing the ratio of "condensible" to
"front-half" catch for a total of 43 runs for which such data was available.
Figure 10 shows how this ratio varies with degree of control. For uncon-
trolled plants, the condensible catch is on an average 35% of the front
half catch, but as the degree of control increases, this ratio decreases.
For drum-mix plants where the test reports cited venturi control devices,
this ratio reduces to 10%, although one anomalous result was found here with
a ratio of 83%.
44
-------
Figure 11
RELATIONSHIP BETWEEN CONDENSIBLES AND TYPE CF CONTROL
in
Type of Control
No Control
Mechanical
Wet Scrubber
Venturi Scrubber
10
20
30
40
Percentage Ratio: Condensible
Front Half
-------
Section 8
FINDINGS 5 RECOMMENDATIONS
Drum-mix asphalt concrete plants are likely to constitute an impor-
tant fraction of new asphalt concrete plant construction, falling within
the New Source Performance Standards. There are at present approximately
150 drum-mix plants occuring in 27 states in the United States of which
it is estimated that 50-70% fall under the provisions of NSPS. At least
eight companies are engaged in the manufacture of drum-mix plants.
Some product use restrictions imposed by state departments of trans-
portation at present inhibit the market acceptance of the process, but
further product test evaluations and experience by highway officials may
reduce this barrier. The fact that eight manufacturers including four
prominent in conventional plants have entered the field indicates an ex-
panded use of the drum-mix process.
This source can be typified as a growing one with relatively young
process and control experience.
Although uncontrolled emissions are less than those from a conven-
tional plant of comparable production capacity, they clearly exceed NSPS.*
These uncontrolled plant emissions also generally exceed 100 tons per year.
Furthermore, this potential of exceeding 100 tons per year is enhanced
because the production capacities of drum-mix plants often exceed those of
conventional plants.
An analysis of 63 stack tests which included 158 test runs showed
high variability of emissions at each level of control which may be related
One Teported countercurrent flow plant met NSPS emissions.
46
-------
to a variety of process designs marketed by different manufacturers and
continuing refinements in design, in addition to the normal causes of such
variations such as raw material, and condition of a given type of control.
Control results improved from mechanical (14% meeting NSPS) through wet
scrubber (29%) to venturi scrubbers (50%). Baghouse and precipitator con-
trols were not encountered in this study.
The ratio of "condensibles" to the "front half" catch averaged
35% for uncontrolled plants and decreased to 10% for venturi scrubbers.
This means that a considerable amount of emissions are not measured by
Method 5 under the NSPS since the back half of the measurement train that
reports condensibles is not used. Secondly it may mean that water pollution
problems could be encountered in a drum-mix plant using wet collection
techniques unless appropriate ponds or closed loop recycling is used.
Recommendations
Better primary data are needed if firm, accurate information on
emissions and control efficiency on drum-mix plants is desired. This pre-
liminary study pointed out the shortcomings of relying on published test
reports. To provide meaningful primary data it is necessary that future
reports include more data on the model and type of drum-mix plant, details
on the control device(s) including as a minimum design feature, pressure
drops, and liquor flow. Information in the test reports as to the type
of raw material and the size gradation should also be included.
We would recommend a two-pronged approach in developing these data:
47
-------
1. New drum-mix plants being tested by either the federal govern-
ment or the states should be provided with data sheets or asked
to report the data noted above. If convenient, federal rep-
resentatives should witness the tests
2. An effort should be launched to develop better data from the
tests already reported. While it is difficult if not impossible
.to identify some factors that held during the test such as
pressure drop, liquor rate, and raw material gradation, it may
be possible to obtain better information on the type drum-mix
and a better description of the controls, and the design parameters
of the control system.
There is significant current R§D effort by manufacturers in improving
the product and air'pollution characteristics of the drum-mix process.
(One goal is to make fabric filters feasible). This indicates the need for .
continuing attention by EPA as these R§D efforts are reflected in equipment
and emission changes.
Method 5 testing of drum-mix asphalt concrete plant emissions is
feasible with minor modifications to the sampling train.
48
-------
REFERENCES
Number
R. W. Beaty and B. M. Bunnel "The Manufacture of Asphalt
Concrete Mixtures in the Dryer Drum" presented at the annual
meeting, Canadian Technical Asphalt Association, November 1973.
"Asphalt Hot-Mix Emission Study". The Asphalt Institute,
Research Report 75-1, March 1975.
"Background Information For New Source Performance Standards".
EPA, 450/2-74-003 (APTD-1352C) February 1974.
"Inspection Manual For Enforcement of New Source Performance
Standards: Asphalt Concrete Plants", Contract 68-02-1356,
Task 2, JACA Corp., June 1975.
"Air Pollution Engineering Manual". EPA, AP 40, 2nd Edition,
May 1973
"Group Buying to Reduce Air Pollution Costs for Small Plants",
JACA Corp. for Conservation Foundation, August 1972.
"Study of Selected Potential Problem Areas in the NSPS Sur-
veillance of the Asphalt Concrete Industry", JACA Corp., for
EPA, March 1976.
49
-------
Appendix A
MANUFACTURERS OF DRUM-MIX PLANTS
Aedco, Inc.
13333 U.S. Highway 24 West
Fort Wayne, Indiana 46804
Astec Industries, Inc.
P.O. Box 2787
Chattanooga, Tennessee 37407
Barber-Greene Company
Aurora, Illinois 60507
Boeing Construction Equipment Co.
P.O. Box 3707
Seattle, Washington
CMI Corporation
P.O. Box 1985
Oklahoma City, Oklahoma 73101
Iowa Manufacturing Company
Cedar Rapids, Iowa 52401
Stansteel Corporation
5001 S. Boyle Avenue
Los Angeles, California 900.58
Portec, Inc.
Minneapolis, Minnesota 55414
Type of Flow
Counter
Parallel
Parallel
Parallel
Parallel
Parallel
Parallel
Parallel
A-l
-------
Appendix B
SAMPLING TRAIN MODIFICATION
Desiccate a quantity of Pyrex glass wool for 48 hours. Using large
tongs, loosely pack the top of the glass filter holder with the glass wool.
Remove and weigh the wool to a constant weight. Repack the glass wool into
the filter holder top and assemble the filter holder.
During the sample recovery procedures in the laboratory, remove the
glass wool from the filter holder and place it on clean, tared pyrex dish.
Desiccate the glass wool for 48 hours and re-weigh it to a constant weight.
Include the net weight gain in calculating the particulate emission rate.
If any tarry residue is trapped on the filter holder top, rinse it
with methylene chloride and include the washings with the probe and nozzle
washes.
A-2
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-340/1-77-004
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Preliminary Evaluation of Air Pollution Aspects of the
Drum-Mix Process
5. REPORT DATE
Issue: March 1976
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
JACA Corp.
506 Bethlehem Pike
Fort Washington, PA 19034
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-02-1356
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Protection Agency
Division of Stationary Source Enforcement
Washington, DC 20460
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report focuses on the air pollution aspects of a process of recent practical
application in the asphalt concrete industry, called the Drum-Mix process. In-
cluded in this report is a description of the drum-mix process, factors affecting
its use in new asphalt concrete plant construction, its air emission potential,
and applicable emission control techniques. Data from emission tests on uncon-
trolled and controlled drum-mix plants are analyzed, and emission factors for
various levels of control are reported. Also included in this report is a dis-
cussion on the ways to overcome sampling problems particular to the drum-mix
exhaust.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COS AT I Field/Group
Asphalt Concrete Plants
Air Pollution Control
Emission Factors
Emission Testing
Drum-Mix Process
13. DISTRIBUTION STATEMENT
Release unlimited
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
55
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
B-l
------- |