United States
Environmental
Protection Agency
Industrial
Environmental
Research Laboratory-RTP
Particulate
Technology
Branch
Controlling
Emissions
of Participates
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Introduction
Every year, millions of tons of particulates
get into the air we breathe. Some come
from natural sources like forest fires, dust
storms, and volcanoes. But a growing
percentage is produced by manmade
sources like factories and power plants,
metal processing, stone crushing, and
construction projects. Even the tires on
our cars release particles of rubber as we
drive.
Some of these particles, like dust and dirt,
are nontoxic. But others, especially those
from fossil fuel combustion and industrial
processes, can be very dangerous to
human health. Particles containing beryl-
lium, lead, asbestos, and certain hydro-
carbons are suspected causes of cancer.
And particles of sulfate, nitrate, and other
chemical substances can cause respira-
!Pplilงงse, especially in children andY;,,,^,
older pe?opl%
Because of these dangers, particulates are
orje of the six atr pollutants thus far
identified by the Environmental
Agency (EPA) as having "potential for
widespread adverse effects on human
health and welfare." Acting on the
authority of the Clean Air Act Amendments
of 1970, EPA has set a primary National
Ambient Air Quality Standard for total
suspended particulates in our air of 75
micrograms per cubic meter (annual
average). Since 1970, air quality has
been substantially improved in many areas.
Yet today, particulate concentrations mea-
sured by half the air pollution monitoring
sites in our country still exceed the
standard set by EPA to protect our health.
What's more, with an increasing number of
industries and power plants scheduled to
be built in the coming decades, particulate
pollution could get worse unless we take
steps to control it.
That's exactly what's happening at the
Industrial Environmentฎ.Research Labora-
tory (IERL), part of EPJVs Office of
Research and DeyeSYtirf/iit jn Research
Triangle Parker.;!!; ^myxSjjt- There, t
Particulate Technology Sfarjch (PATB)
working to find more effective and
econom|?a:l, 'ซ;?ys of reducing particulat|
Like other branches of IERL-RTP, PATB
supports EPA's Office of Air Quality
Planning and Standards by providing
technical information for setting realistic,
attainable standards for particulates emit-
ted by power plants and industries all over
the country.
But that's only part of the job. To help
industry meet air quality standards, PATB
has programs underway to improve the
efficiency and cost-effectiveness of par-
ticulate collection devices in use today.
New control technology is also being
developed to solve the problem of
particulates from advanced combustion
equipment that will be used to produce
our nation's energy in the future.
EPA has already made a significant
contribution to improving the quality of our
nation's air. Since 1970, the national
average concentration of particulates in
the atmosphere has dropped by almost 20
rcent, and this downward trend is
itinuing. But a great deal of work
ains to be done before we reach our
itional goal of safe, clean air for
ourselves and our children.
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The Problem of
Particulates
Particulate matter comes in all shapes and
a wide range of sizes from particles as
large as grains of sand to tiny particles
visible only under an electron microscope.
Most manmade fine particulates about
3.5 million tons a year come from the
industries that produce our nation's power,
products, and materials. Dust from stone
crushing and fumes from metallurgical
operations are both major contributors.
But the largest source of particulate
pollution is the flyash given off when coal
is burned. And with coal consumption in
our country predicted to double in the next
15 years, the concentration of particulate
in our air could get worse without more
effective controls.
Most airborne particles the kind that
can do widespread damage to humans,
animals, and vegetation are smaller
than 100 micrometers, about the diameter
of a human hair. Particles under 3 micro-
meters fine particulates can be
especially dangerous. Once in the air,
these particles can stay suspended for
days and may be spread by winds for
miles, contributing to smog and even
altering the weather. And, because fine
particles are so small, they can pass
FINE COARSE
through the natural filters in our nasal
passages and damage our lungs.
Today's particulate control devices do a
good job of trapping larger particles. In
many cases, those devices capture more
than 99 percent (by weight) of the
particulate before it reaches the air.
But fine particulate is a different story.
Current equipment is far less effective at
trapping fine particles than large ones.
Collection of particles smaller than 3
micrometers can be improved with larger
control devices or ones that use more
energy, but only at great or even
prohibitive expense. As a result, the
particles that pose the greatest threat to
human health are the ones that escape in
greatest numbers to our atmosphere.
There's only one way to prevent this kind
of pollution: trap particles at their sources,
before they get into the air. With more
than 20,000 major stationary sources of
pollution in the United States, that's a big
order. But it's a job that must be done to
protect the quality ot our air.
Particles from power plant
Particle chains
METALLURGICAL DUST & FUMES
0,01 0.1 1 10 100 1000
SIZES OF TYPICAL PARTICLES MICROMETERS
KRAFT PULP MILLS
OIL & GAS COMBUSTION
CEMENT PLANTS
ASPHALT PLANTS
MAJOR SOURCES OF
FINE PARTICULATES
THOUSANDS OF TONS/YEAR
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The Role of PATB
To support both a healthy environment
and a healthy economy, the Particulate
Technology Branch of IERL-RTP is work-
ing with industry to find cheaper and more
effective ways to reduce particulate
emissions from many different kinds of
pollution sources. Since fine particles are
the most serious problem today, the focus
of much of PATB's work is on increasing
the efficiency of devices used to control
fine particulate .emissions.
Because utilities and industries in the
United States already have billions of
dollars invested in particulate collection
equipment, one of PATB's main aims is to
improve the devices in use today. At the
same time, PATB is looking ahead to the
particulate problems that will be caused by
fuels and combustion processes of the
future.
PATB's work begins with fundamental
research into the basic physical and
chemical mechanisms involved in particle
formation and collection. These theoretical
studies are helping us understand why
particles behave the way they do, and
how they can be collected more
effectively.
Another component of PATB's work is
pilot-scale testing. Here, many different
particulate collection techniques are being
PARTICULATE RESEARCH BRANCH: PROGRAMS
TODAY'S
ENERGY
NEEDS
TOMORROW'S
ENERGY
NEEDS
tried out under controlled conditions in the
laboratory to determine whether they offer
significant advantages in both cost and
efficiency over today's equipment.
Once a technique has passed the hurdle
of pilot-scale testing, it is evaluated on
full-scale equipment in the field to make
sure it can do the job under actual
working conditions. In these tests, the
effect of the control technique on fuel
economy or equipment life is also studied.
The result is reliable particulate collection
technology that utilities and industry can
depend on.
As part of both pilot-scale testing and field
demonstrations, PATB operates four mobile
particulate collection vans. Each van is
outfitted with a specific type of particulate
control device. The vans are used in the
field to find the best particulate control
IMPROVE CURRENT EQUIPMENT TO
COLLECT FINE PARTICULATES
MODIFY COLLECTION EQUIPMENT
TO MEET CURRENT NEEDS OF
LOW-SULFUR COAL COMBUSTION
COST-EFFECTIVE
PARTICULATE CONTROL
TECHNOLOGY
TECHNOLOGY
TRANSFER
DEVELOP NEW DEVICES FOR
ADVANCED ENERGY PROCESSES
DEVELOP NEW CONCEPTS AND
DEVICES FOR COST-EFFECTIVE
PARTICULATE COLLECTION
technique for specific types of pollution
sources and to test the effectiveness of a
particulate control device on a pollution
source before money is spent for a full-
scale installation.
At PATB, projects are underway in every
major area of particulate collection tech-
nology. To share the knowledge gained in
these projects, PATB publishes articles
and reports and sponsors symposia and
seminars that bring industry and govern-
ment together to discuss and solve the
problems of particulate pollution. This
technology transfer brings advances in
particulate collection techniques out of the
laboratory and into the field where they
can make a difference.
PATB's budget for programs like these
was $4.7 million in 1976. That sounds like
a lot of money. But in the same year,
particulate control devices cost industry
nearly $800 million. Furthermore, in the
next 5 years it is expected that industry
will spend an additional $7 billion for
collection equipment.
In other words, the amount spent by PATB
is a small fraction of the money that goes
into particulate control in the United States
every year. And because PATB is
working to lower the cost of collection
equipment and improve efficiency, its
research dollars will save utilities and
industries many millions of dollars in years
to come, while helping to keep our air
clean in the years ahead.
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Improving Today's
Control Devices
Cyclones whirl particulate-laden gas
streams inside a large funnel,
throwing particles outward. The
particles strike the walls of the
cyclone, fall to the bottom and are
removed.
Gas streams enter the baghouse
and are passed through a series of
porous, flexible bags that collect the
particulate. Particles are removed
by shaking or flexing the fabric.
Current particulate collection devices
cyclones, baghouses, wet scrubbers, and
electrostatic precipitators are large and
expensive pieces of equipment that often
use tremendous amounts of energy.
Baghouses, for example, can stand as
high as 25 meters and cost millions of
dollars to purchase and install. Scrubbers
for a 1000-megawatt power plant can
consume as much as 5 megawatts of
electricity, enough power for over 2000
homes. This makes operating costs very
high. PATB is working to reduce these
costs, and to improve the efficiency of
control devices at the same time.
Among the least expensive particulate
collectors are cyclones. These are widely
used to clean up industrial operations like
grinding and polishing metals, crushing
stone and gravel, and woodworking.
Though cyclones are very efficient for
large particles, they are only about 40-
percent efficient for fine particles. The
efficiency of cyclones can be improved by
increasing the velocity of the airflow but
only at the cost of substantially more
energy. As a result, cyclones work best
on sources that do not emit many fine
particles.
Fabric filter baghouses are more effective
in controlling fine particulates. Today,
baghouses are used mainly to treat
process gases from operations like primary
metal smelting and chemical and fertilizer
production. Field tests conducted by
PATB have shown that baghouses can
operate with efficiencies over 99 percent,
providing the filter fabric is compatible with
the chemicals, temperature, and moisture
of the gas stream.
Although baghouses are currently one of
the most expensive control devices, they
are potentially the least expensive to
operate. In one of PATB's recent
programs, a full-scale demonstration bag-
house with a modified design was
constructed for use on a coal-fired
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industrial boiler. Its new design will allow
it to operate with airflow velocities 3 to 4
times those of conventional baghouses.
This should increase collection efficiency
at greatly reduced cost.
Wet scrubbers have been used as
particulate collection devices since the
early 1920's. Although they're inexpensive
to install compared to large baghouses or
electrostatic precipitators, scrubbers are
costly to operate. They require large
amounts of water and electricity, and
create a sludge that must be disposed of.
However, newer scrubbers have proved to
be effective in collecting fine particles.
The most promising of recent designs are
flux force/condensation scrubbers. PATB
is evaluating these new scrubbers in
several pilot demonstration programs, in-
cluding some that are cutting costs by
using industrial waste heat.
Electrostatic precipitators (ESPs) are more
than 99-percent efficient for large particles,
and only slightly less for some kinds of
fine particulate. They cost more to install
than scrubbers or fabric filters, but they're
less expensive to operate. The main
drawback to current ESPs is their inability
to trap certain types of fine particles. To
solve that problem, PATB is testing
conditioning agents to reduce the re-
sistivity of particles to electrical charge,
and studying the potential of ESPs that
use water to help capture particles. In
another program, a computer model of
electrostatic precipitation has been de-
veloped to study the effects of design
changes on ESP performance.
All of PATB's programs to improve current
particulate control devices are helping
utilities and industries find efficient ways to
meet our national air quality standard for
particulates. And by finding more
economical ways of controlling particulates
from coal combustion, PATB is making an
important contribution to conserving our
nation's supplies of oil and gas.
Scrubbers spray small droplets of
water into particle-laden gas
streams. Particulates collect on the
water droplets and are removed with
the water.
Electrostatic precipitators charge
particles in the gas stream, collect
the particles on a grounded metal
plate, and remove them by flushing
or vibrating the plate.
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New Concepts,
Novel Devices
There are two main ways to improve
substantially the collection efficiency of
conventional control devices, especially for
fine particulates. One is to increase the
collector area, and the other is to increase
the power supplied to the device. In
either case, costs rise enormously.
To cut costs, brand new approaches to
particulate collection are needed. That's
why one of PATB's most important jobs is
to seek out ideas for new collection
mechanisms, evaluate them, and support
development of those that offer promise of
better and more economical particulate
control.
To guide the development of new
concepts, PATB conducts fundamental
research to improve our understanding of
basic particulate collection techniques.
Though we know, for example, that
electrostatic forces can be used to trap
particulates in exhaust streams, much
remains to be discovered about how those
forces actually work. As research
increases our knowledge of electrostatic
and other forces, better ways will be found
to harness them for more effective
particulate control.
In evaluating new concepts and devices,
PATB uses a number of methods. One of
the most productive is mathematical
modeling that simulates basic particulate
collection mechanisms. These models
can be used to predict the performance of
innovative devices, and save time and
money by eliminating concepts that are
technically or economically unsound.
Once theoretical studies have shown that
an idea has promise, pilot-scale versions
of new devices are built and thoroughly
evaluated before being demonstrated in
the field on full-scale pollution sources.
PATB is studying and testing several new
particulate collection concepts with poten-
tial for cutting costs and improving
efficiency, including charged droplet scrub-
bers, ceramic membrane filters, magnetic
filter beds, and a number of new types of
fiber filters.
Work in advanced fiber filters is especially
important today, because research and
pilot-scale testing have shown that fabric,
felt, or fiber bed filters can trap fine
particles with very high efficiency. In
addition, novel filters may also be able to
reduce the size of collection equipment.
Controls using cartridge filters, for ex-
ample, may be 10 times smaller than
current equipment. Devices using mag-
netic fiber beds could be 100 times
smaller.
PATB is also exploring how particles
behave in many different kinds of filters.
It's been found that particles chain
together in these filters larger particles,
in effect, acting as traps for smaller ones.
Experiments are underway to find methods
of taking advantage of this phenomenon to
increase collection efficiency.
PATB has already reviewed over 50 new
ideas for particulate control, and has
identified the most promising of them. As
efficient new particulate collection devices
are developed from these ideas, PATB's
research into innovative control techniques
will help save money and reduce par-
ticulate pollution as well.
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Controls For Low-
Sulfur Coal
Today, power plants and industries in the
United States burn about 700 million tons
of coal a year. It has been estimated
that, in the next 15 years, coal consump-
tion will increase dramatically because of
dwindling supplies of oil and natural gas.
By 1990, our country is expected to be
using close to 1.3 billion tons of coal
annually almost twice the current rate.
Most coal burned today is eastern coal
mined in Pennsylvania, Illinois, West
Virginia, and Kentucky. But, over the next
two decades, many power plants and
industries especially west of the Rocky
Mountains will be switching to western
coals mined in Montana, Wyoming, and
Colorado. Part of the reason is that this
coal will be used to satisfy the growing
energy needs of the West. But equally
important is the fact that western coal has
a much lower sulfur content less than
1 percent compared to 2 to 3 percent for
eastern coal. This means that when
western coals are burned, they emit much
less sulfur oxides into the air. And since
sulfur oxides are a dangerous pollutant,
this makes western coal environmentally
attractive at first glance.
But, paradoxically, the flyash from coals
with low sulfur content is much more
resistant to an electrical charge than
flyash from high-sulfur coals. As a result,
electrostatic precipitators the most
widely used particulate control devices for
power plants are far less effective with
low-sulfur coals. In fact, burning low-sulfur
coal can increase particulate emissions by
as much as a factor of 10 from sources
equipped with conventional ESPs.
PATB is working to solve the problem of
particulate emissions from low-sulfur coals
in a number of different ways.
To improve our understanding of the basic
physical and chemical mechanisms in-
volved, PATB is conducting theoretical
studies of the relationship between the
sulfur content of coal and the resistance
of flyash to an electrical charge. A
comprehensive computer model of this
relationship has been developed and is
being used by EPA and industry to
improve the design of today's electrostatic
precipitators.
Building on these theoretical studies, PATB
is exploring ways of modifying conven-
tional ESPs to make them more efficient in
collecting the high-resistivity flyash from
low-sulfur coal. A special particulate
charging device has been designed and
tested in laboratory-scale experiments.
Results show that the approach is
technically feasible, and demonstrations of
full-scale ESPs are planned for the near
future.
PATB is also investigating ways of making
flyash from low-sulfur coal better able to
conduct an electrical charge by adding a
conditioning agent to the exhaust of coal-
fired boilers and furnaces before it
reaches the ESP. A successful demon-
stration on a full-scale utility boiler has
shown that sodium carbonate can lower
the resistivity of low-sulfur coal flyash.
Sulfur trioxide, ammonia, hydrogen chlor-
ide, and phosphoric acid have also been
tested as conditioning agents. Since most
of these substances are toxic, further
research is needed before flyash condi-
tioning can be considered an environ-
mentally sound way to reduce particulate
emissions from low-sulfur coal.
PARTICULATE EMISSIONS
FROM LOW-SULFUR COAL
LOW MODERATE HIGH
COAL SULFUR CONTENT %
COAL CONSUMPTION
MILLIONS OF TONS/YEAR
1275
965 1970 1975 1980 1985 1990
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At the same time, PATB is conducting
detailed evaluations of both fabric filters
and scrubbers as alternatives to ESPs for
low-sulfur coal. In one project, a fabric-
filtration baghouse is being constructed for
a 350-megawatt utility boiler that burns
low-sulfur western coal. After completion
in 1978, this baghouse will be operated for
a year to collect data on performance,
operating life, and cost-effectiveness. Full-
scale demonstrations of scrubbers on
utility and industrial boilers firing low-sulfur
coal are also planned.
All of this research will help make low-
sulfur coal an environmentally sound fuel
that can help satisfy our country's demand
for energy in the decades ahead.
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Controls For High-
Temperature, High-
Pressure Processes
Coal conversion is one of the most
promising new technologies for meeting
our country's energy requirements in the
decades ahead. One of the main kinds of
conversion processes is coal gasification.
In this process, coal is converted to
synthetic gas under carefully controlled
conditions at high temperature and pres-
sure temperatures as high as 1800ฐC
at 1 atmosphere and pressures up to 100
atmospheres at 900ฐC. Much of the
energy in the coal is retained by the
synthetic gas, and can be burned in gas
turbines, boilers, furnaces, kilns, or heaters.
As supplies of natural gas run out, it may
be possible to pump synthetic gas
produced by coal conversion through
pipelines to industries and homes all over
the country eliminating the need to
replace gas-burning equipment now in use.
Another important coal conversion process
is pressurized fluidized bed combustion.
Here, coal is burned under pressure in a
bed of limestone or similar material. The
sulfur in the coal is removed by the
limestone before it can be emitted as
sulfur oxides to the atmosphere. The
burning process generates both heat,
which produces steam for electric power
or industrial uses, and hot pressurized
gases, which can be used to drive gas
turbines.
EFFECTS OF HIGH-TEMPERATURE,
HIGH-PRESSURE
Successful development of coal gasifi-
cation and pressurized fluidized bed
combustion will require solving a number
of problems. Both processes produce a
high-temperature gas stream full of par-
ticulates that have to be removed before
the gas can be used in turbines or other
combustion equipment. But, today's
particulate collection devices can't take
the high temperatures and pressures in
gasifiers and fluidized bed combustors.
Moreover, theoretical studies show that
conventional designs would not work
efficiently at high temperature and pres-
sure. So it's not just a matter of building
scrubbers or fabric filters or electrostatic
precipitators that can withstand tremen-
dous heat and pressure. Altogether new
devices need to be developed for high-
temperature, high-pressure particulate
control.
To help make advanced coal-conversion
processes environmentally sound, PATB is
exploring high-temperature, high-pressure
particulate control technology. Close
coordination is being maintained with the
Department of Energy's advanced energy
processes program.
Since coal conversion is still in the
experimental stage, there is very little
information today on the physical, chemi-
cal, or kinetic mechanisms of particulates
at high temperature and pressure. There
is also very little reliable data on the
degree of particulate control that will be
needed for gasifiers and fluidized bed
combustors. To collect this basic
information, PATB has a 2-year study
underway to define the problem of
particulates at high temperature and
pressure, and to describe the state of the
art in high-temperature, high-pressure
particulate collection.
Along with this study, PATB is conducting
research on advanced particulate removal
devices that look promising for coal-
conversion processes. These include
ceramic fiber filters, ceramic membrane
filters, granular bed filters, and high-
temperature, high-pressure electrostatic
precipitators. An initial theoretical investi-
gation of the effect of high temperature
and pressure on all these collection
devices has already been completed.
Results are being used to design and
evaluate particulate cleanup equipment.
At present, tests of advanced particulate
collection devices are being carried out on
laboratory or pilot-scale facilities. In
coming years, PATB will evaluate promis-
ing high-temperature, high-pressure clean-
up devices on full-scale equipment in the
field to find the most effective technology
for coal conversion processes. The result
will be reliable, economically feasible
control equipment that users and manu-
facturers of gasifiers and fluidized bed
combustors can depend on.
Advanced energy processes for coal and
other fuels are essential to our country's
future. PATB's work will ensure that we
will not have to sacrifice our environment
to satisfy our energy needs.
PARTICLE DIAMETER
13
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Looking Ahead
Over the next few years, one of our most
critical problems in the control of par-
ticulate pollution will be control of flyash,
as industries and utilities switch to coal to
meet the immediate need for plentiful fuel.
PATB's programs to improve electrostatic
precipitators and other devices for trapping
particulate from coal combustion will help
us take advantage of our nation's valuable
reserves of coal. At the same time, PATB
will be working to solve the problem of
particulates from synthetic fuels and high-
temperature, high-pressure energy sys-
tems technologies that can answer our
longer-term energy requirements.
PATB will also be focusing attention on
pollution problems that haven't been
addressed before like fugitive emissions
from hard-to-control sources such as
mining sites, conveyors, and storage piles
of coal and other materials.
Charged-fog spray devices may be one
possible solution to controlling particulates
from these kinds of sources. Installed on
solids-handling equipment, like hoppers or
conveyors, or at strategic points in
warehouses or storage yards, charged-fog
sprayers could eliminate many major
sources of fugitive emissions. PATB, in
cooperation with the University of Arizona,
has already begun to study the feasibility
of this promising approach to controlling
fugitive emissions.
In all of this work, a great deal of new
information will be generated on better,
more economical ways to control par-
ticulates. And to make sure this
information reaches the industrial com-
munity, PATB will be stepping up its
technology-transfer program in the years
ahead. Through a variety of symposia,
conferences, and publications, PATB will
spread knowledge of the latest develop-
ments in particulate control technology to
owners and operators of factories and
power plants, as well as thousands of
people in government and universities all
across the country.
One of the most important effects of
PATB's work in coming years will be
improved standards for the quality of our
nation's air. By law, emissions limits must
be backed up by technology that's proven
to be efficient and economical. As PATB
develops and tests new and more effective
particulate control devices, air quality
standards can be improved, making our air
cleaner and healthier to breathe.
PATB's goal for the next 5 years is to
increase the effectiveness of particulate
control devices by 10 times compared to
today's equipment. And, to make it
practical for industry to install those
devices, PATB is aiming to cut costs by ฃ
factor of 10. That's an ambitious goal.
But, to provide the energy we need
without damaging the air we breathe
it's a goal that must be achieved.
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This report has been reviewed by the U.S.
Environmental Protection Agency, and
approved for publication. Mention of trade
names of commercial products does not
constitute endorsement or recommendation
for use.
Prepared by Aerotherm Division of Acurex
Corporation under EPA Contract 68-02-
2611. Photos courtesy of Aerotherm
Division of Acurex Corporation; U.S.
Environmental Protection Agency, Par-
ticulate Technology Branch; U.S. En-
vironmental Protection Agency, Project
Documerica; U.S. Department of Energy,
Grand Forks Energy Research Center;
Roger J. Cheng, State University of New
York at Albany; Buell Emissions Control
Division, Envirotech Corporation; Pacific
Gas and Electric Company; Aerospace
Corporation, Materials Sciences Lab;
Donaldson Company, Inc.; Meteorology
Research, Inc.; University of Arizona,
Department of Electrical Engineering.
15
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