United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-92/058 May 1992
EPA Project Summary
Controlling Odorous
Emissions from Iron
Foundries
Gerhard Gschwandtner and Susan Fairchild
The main process sources of odors
in an iron foundry are (1) mold and
core making, (2) casting, and (3) sand
shakeout. The odors are usually caused
by chemicals, which may be presenlt
as binders and other additives to thei
molding sand, or as breakdown prod-
ucts when these chemicals are sub-
jected to molten iron as it is poured
into molds. There are many binder for-
mulations; typical formulations arei
based on using some form of an oil,,
urethane, formaldehyde, phenol, or fu
ran. Common additives include coal;)
cereals and starches, clays, and refrac-
tory minerals such as silica. A great
many possible compounds can bei
formed when these chemicals are ex-
posed to molten iron. Common parr
ticulate removal technologies may alsoj
reduce odors, although the odors are>
probably caused by vapor-phase com-
pounds that are not well controlled by
cyclones and bag filters. Carbon ad-
sorption may be effective but might
also be very expensive. Wet scrubbers
with special additives in the water may
be more effective but have drawbacks!
such as generating a waste water treat-
ment requirement and the potential for
corrosion. Another technology report-
edly used in Europe is biofiltration.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Tri-
angle Park, NC, to announce key find-
ings of the research project that is fully
documented In a separate report of the
same title (see Project Report ordering'
Information at back.
Introduction
The control of industrial odor can be
difficult. The choice of a control method
depends on many technical and economic
considerations. The chemical characteris-
tics of the odorous pollutant, the volume
of emissions to be treated, and the manu-
facturing process are only a few consider-
ations. There are many types of odor con-
trol, including masking, various removal
techniques, and process modifications.
This report describes several removal tech-
niques including wet chemical scrubbing,
biofiltration, adsorption, and new emerg-
ing techniques. The adaptation of these
controls to a particular process can be
complicated and requires careful planning.
Many pollutants have low odor thresh-
olds and require the removal of extremely
small concentrations from large volumes
of air. This is technically difficult and may
require huge amounts of energy, capital
investment, and large control devices de-
pending on the options selected. Further-
more, odor may not be completely con-
trolled, arid some level of odor may per-
sist despite the addition of controls.
Once the decision is made to control
odor, the course of action may be deter-
mined by the availability of water, energy,
and waste water treatment facilities. Most
control methods employ water sprays,
tanks,-and mists to trap water-soluble
chemicals and particulate. In the absence
of sufficient quantities of water, it may be
necessary to consider using other meth-
ods such as carbon adsorption or
biofiltration.
Printed on Recycled Paper
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Discussion
Sources of Odorous Emissions
in Iron Foundries
In an earlier report, the U.S. EPA iden-
tified major sources of air toxic pollutant
emissions in iron foundries. Of these pol-
lutants, organic compounds are the most
odorous, although metals and dust may
also be sources of odor. The main sources
of organic emissions in iron foundries are
mold and core making operations, casting
operations, and sand shakeout.
Mold and core making may be subdi-
vided according to resin sand operations,
commonly referred to as shell molding,
green sand operations, and stack mold-
ing. In general, these processes have the
greatest potential to release odors because
of the relatively high concentrations of or-
ganics in the uncontrolled emissions.
Most organic emissions originate from
the casting process when molten metal is
poured into a mold. During this process,
chemical reactions involving various binder
ingredients are driven by the intense heat
of the molten metal. The resulting gas-
eous emissions may be the products of
numerous reactions of the initial binder
ingredients, the products of decomposi-
tion, and the reactions among the prod-
ucts of decomposition. In addition, fine
particulate matter is released during cast-
ing. PMt? emission factors range from
2,500 to 4.2 x 10* mg/Mg of metal poured.
Foundry dust typically contains inorganic
emissions such as nickel, lead, boron, and
chromium, depending on the composition
of the poured metal and its impurities.
The uncontrolled removal of castings
from sand molds during the sand shakeout
process releases moisture, dust, resin and
binder fumes, and products of thermal de-
composition. Information on volatile organic
compound (VOC) emission factors is rare,
but some information is available for par-
ticulate, matter that suggests a wide range
of PM)0 emissions from 85 x 103 to 9 x 106
mg/Mg of iron castings.
Most odorous emissions originate from
mold and core making operations and from
casting operations. These emissions re-
sult from the use of chemical binders and
resin and sand additives.
Odor Thresholds
The threshold concentration for odor de-
tection and recognition varies from person
to person and from compound to com-
pound. Many articles have been written
on odor evaluations and threshold values.
Odor detection varies depending on the
compound being evaluated and on the
presence of other compounds that may
mask or enhance the odor. Some com-
pounds may be offensive even in low con-
centrations, especially certain sulfur com-
pounds, while others, such as certain es-
ters, may be less objectionable.
Determining Acceptable Levels
of Odors
Due to the subjective nature of odors, it
is difficult to establish an acceptable level
of exposure, especially when many com-
pounds and emission sources are involved.
Ideally, the concentration of an odorous
compound should be below the odor
threshold. While emission controls help
reduce the odor, some pollutants such as
thiols (mercaptans) require virtual elimina-
tion before they are undetectable.
Objective evaluation of an odor should
be the first step in controlling it. ft is im-
portant to know which compound or com-
binations of compounds is causing the
odor. Usually, an independent, third-party
assessment of unwanted odor is neces-
sary to form an objective conclusion. Both
on-s'rte and community surveys can pro-
vide important information for identifying
sources of the odor, establishing condi-
tions that elicit complaints in the affected
community, and confirming odor levels pre-
dicted by source sampling, analysis, and
atmospheric dispersion estimation tech-
niques.
Selecting a Control Efficiency
Not all odorous compounds may be suf-
ficiently controlled with the same control
device. For example, one compound may
require only 99% control efficiency while
another may require 99.999% control effi-
ciency to reduce the concentration below
its odor threshold value. In this case, two
different control devices may be needed
to solve the odor problem.
Rather than attempting to reduce all
odorous emissions simultaneously, reason-
able available control technology should
be applied first to reduce total emissions,
including particulate matter and organic
compounds. In addition, the dispersion and
dilution of the emissions should be en-
hanced to the maximum extent possible.
A comprehensive approach to controlling
foundry emissions is better than control-
ling each odorous pollutant individually.
Selecting the Best Control
Option
Several methods are available for con-
trolling odor from iron foundries. Aside
from reducing overall emissions and good
operating practices, emission control tech-
nologies that are applicable to iron foundry
processes include:
• Fabric filtration
• Adsorption (activated charcoal)
• Wet scrubbers with chemical additives
• Biofiltration
• Photocatalytics and oxidization
There are several basic considerations
when selecting one of these control tech-
niques for an iron foundry. The ideal tech-
nology would be one that does not require
water, energy, or maintenance, costs little,
effectively removes many different odor-
ous compounds, and produces no solid or
hazardous waste. The ideal technology
would also not interfere with existing pro-
cess operations and conditions.
Fabric filtration is essential to remove
sand and other fine particulate matter and
should be used first before controlling or-
ganic compounds by other means. The
control efficiency of various types of wet
scrubbers can be enhanced by using vari-
ous chemical additives. The ideal additive
is one that creates harmless waste in small
quantities, does not affect process equip-
ment, and does not require special treat-
ment, conditioning, or monitoring.
Selection of a chemical additive requires
judgment and knowledge about the chemi-
cal reactions with the targeted pollutants.
Many companies can recommend and sup-
ply chemical additives usually in conjunc-
tion with a particular type of scrubber. The
particular requirements should be care-
fully analyzed beforehand, and all aspects
of the wet scrubber (including waste dis-
posal, supply requirements, and system
operation and maintenance requirements)
should be considered.
Incineration, thermal oxidation, and cata-
lytic oxidation are generally not suitable to
iron foundries because of the large air
flow rates. Odor masking, a technique
where a stronger pleasant odor is added
to the exhaust stream, generally has not
provided consistent and satisfactory re-
sults.
Deciding What Is Feasible and
Reasonable
Many environmental regulations use the
words "feasible" and "reasonable" when
describing control requirements. In the
case of odor control, specific requirements
are often unclear and left to interpretation.
Since the ideal control technology does
not exist, iron foundry operators wishing
to control odorous emissions must accept
some level of inconvenience or expense.
This report provides basic information that
can be used in comparing and selecting a
control technology.
Whether a technology is feasible or rea-
sonable depends on the circumstances of
the foundry. For example, shortage of wa-
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ter would eliminate many of the traditional elude the use of certain chemical adcli- advantages over older, traditional systems
wet scrubbers described in this report. tives in wet scrubbers. and should be considered. These new
The need to reduce maintenance costs, As technology changes, better and methods have been tried and proven at
for example, might preclude the use of proven systems may become available. many different industries here and abroad
carbon adsorption, while the lack of on- Currently, atomized mist scrubbers, and can be adapted to the major sources
site waste disposal facilities might pre- biofiltration, and photocatalytics offer many of odor at iron foundries.
•&V.S. .GOVERNMENT PRINTING OFFICE: 1992 - 648-080/40253
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Gerhard Gschwandtner and Susan Fairchild are with E. H. Pechan and Associates,
Durham, NC 27707.
Robert a McCrlllls is the EPA Project Officer (see below).
The complete report, entitled "Controlling Odorous Emissions from Iron Foundries,"
(OrderNo. PB92-166 925/AS; Cost: $17.00, subject to change) will be available
only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
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Penalty for Private Use $300
EPA/600/SR-92/058
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