United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-01/011 March 2001
Emissions of Air Toxics from a
Simulated Charcoal Kiln
Equipped with an Afterburner
Paul M. Lemieux
A laboratory-scale charcoal kiln simu-
lator was constructed and tested to de-
termine if it could be used to produce
charcoal that was similar to that pro-
duced in Missouri-type charcoal kilns.
An afterburner was added later to study
conditions for oxidizing the volatile or-
ganic compounds contained in the com-
bustion gases that are produced when
wood is converted to charcoal. Five
burns were conducted to shake down
the operation of the afterburner. Then
four full burns were completed to mea-
sure the effectiveness of the after-
burner. Based on these simplified
studies on the effect of an afterburner
on emissions from Missouri-type char-
coal kilns, it appears that, while the af-
terburner can offer significant benefits
under some conditions, the operation
of the afterburner is not a trivial matter.
A system, such as a charcoal kiln, that
relies on natural draft for operation may
be upset by adding an afterburner due
to pressure changes in the stack that
influence the natural draft. Optimizing
the process, both in the sense of good
charcoal quality and good afterburner per-
formance, may be difficult without the
benefit of continuous emission monitors.
This Project Summary was developed
by the National Risk Management Re-
search Laboratory's Air Pollution Pre-
vention and Control Division, Research
Triangle 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
A Missouri-type charcoal kiln is a small
building (usually about 40 ft wide, 60 ft long,
and 16 ft high), often constructed with brick,
cement, or metal, that is used to burn wood
in a limited supply of air to produce char-
coal. The U.S. Environmental Protection
Agency, National Risk Management Re-
search Laboratory, Air Pollution Preven-
tion and Control Division (APPCD) agreed
to provide EPA Region 7 Air, RCRA (Re-
source Conservation and Recovery Act),
and Toxics Division with chemical and
physical information to characterize the
plumes from Missouri-type charcoal kilns.
That work was completed as planned and
resulted in several important conclusions,
including:
•[Charcoal could be produced in the
laboratory-scale kiln simulator. The
charcoal produced in the simulator
was identical to that produced in
Missouri-type kilns according to char-
acteristic measurements performed
on the two charcoals.
•D"he simulated charcoal kiln produced
combustion gases containing signifi-
cant amounts of volatile and
semivolatile organic compounds.
Benzene was found in the combus-
tion gases at concentrations ap-
proaching 2000 ppmv.
•CMany oxygenated organic com-
pounds were found in the combus-
tion gases from the simulated
charcoal kiln.
•[Several polycyclic aromatic hydrocar-
bons (PAHs) were found in the simu-
lated charcoal kiln combustion gases.
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As the earlier experiments were being
conducted, Region 7 requested that an
additional research study be conducted
by APPCD during fiscal year 1998 to ob-
tain information on the effectiveness of
adding afterburners to these kinds of char-
coal kilns.
The objectives of this work were:
•CTo install an afterburner on the simu-
lator used in the earlier experiments.
• [Jo produce charcoal that was repre-
sentative of that produced in
Missouri-type charcoal kilns while
using the afterburner.
•CTo install a larger dilution tunnel ca-
pable of greater dilution ratios and
more representative samples of con-
densable organic matter and particu-
late.
• [Jo improve the seals in the kiln simu-
lator to minimize unknown sources
of air in-leakage.
•CTo determine the concentrations of
several pollutants that were not mea-
sured in the earlier tests in the com-
bustion gases generated as the wood
was converted into charcoal.
•CTo determine if any of those pollut-
ants could be destroyed by passing
them through an afterburner inserted
into the exit duct from the simulated
charcoal kiln.
Variables that were measured on a
continuous basis included the weight of
the kiln, the temperature at various places
inside the simulator, and the concentra-
tions of carbon monoxide (CO), carbon
dioxide (CO2), nitric oxide (NO), total hy-
drocarbon compounds (THCs), and oxy-
gen (O2) in the combustion gases as the
gases exited the afterburner. This set of
variables is referred to collectively in this
document as the "continuous measure-
ment variables." Nine experiments were
performed altogether. Five experiments
(Runs A through E) were performed to
optimize the operating conditions of the
kiln and the afterburner. Four additional
experiments (Runs 1 through 4) were
performed while additional data were ob-
tained by analyzing extractive samples
for volatile organic compounds (VOCs),
semivolatile organic compounds (SVOCs),
aldehydes, and particulate matter (PM):
two of the four runs were performed with
the afterburner switched off, and two were
made with the afterburner switched on.
An additional blank experiment was per-
formed to assess system contamination.
Results And Conclusions
Based on these simplified studies on
the effect of an afterburner on emissions
from Missouri-type charcoal kilns, it ap-
pears that, while the afterburner can offer
significant benefits under some conditions,
the operation of the afterburner is not a
trivial matter. A system, such as a char-
coal kiln, that relies on natural draft for
operation may be upset by adding an
afterburner due to pressure changes in
the stack that influence the natural draft.
Optimizing the process, both in the sense
of good charcoal quality and good after-
burner performance, may be difficult with-
out the benefit of continuous emission
monitors.
When pyrolysis is used to manufacture
charcoal from wood, many different or-
ganic compounds are released into the
air, depending on the specific pyrolysis
or burn conditions. Table 1 lists com-
pounds found in the smoke of every burn
tested to date. Other compounds found in
the combustion gases of most burns in-
cluded the low molecular weight alde-
hydes, alcohols, acids and diacids, and
several low molecular weight halogenated
aliphatic and aromatic compounds.
Compounds found in most samples
along with an approximate upper con-
centration range are shown in Table 1.
In addition to specific organic com-
pounds, the concentration of THCs was
usually above 5000 ppm, and the con-
centration of total PM was often above
20,000 g/m3 of air.
Additional Conclusions from
the Current Study
•CThe afterburner attached to the labo-
ratory charcoal kiln simulator was dif-
ficult to operate in such a way as to
successfully create charcoal. The
back pressure that the afterburner
exerted on the system affected the
natural draft of the kiln, impacting its
ability to make charcoal. It is not
known whether this conclusion will
hold for a full-scale operation, but it
is a concern.
• [Other pollutants, such as aldehydes,
were produced during the charcoal
manufacturing process. Emissions of
aldehydes were somewhat less than
those of VOCs and on the same or-
der of magnitude as those of PAHs.
• [During a typical burn, the tempera-
ture increased for approximately 1
hour to about 700 °C where it peaked
and then slowly decreased after the
supply of O2 was switched off.
•DDuring a burn, the consumption of
oxygen preceded the rise in tempera-
ture by 15-20 minutes. As the con-
centration of oxygen decreased, the
concentration of all other combustion
gases including CO, CO2, NO, and
THCs increased. Typical concentra-
tions at the time of the maximum kiln
temperature were: O2, 6%; CO2,13%;
CO, 4%; NO, 100 ppm; and THCs,
over 5000 ppm.
•[Even under laboratory conditions, the
temperature readings throughout the
kiln simulator were very uneven dur-
ing most runs with the afterburner on,
indicating that the process was not
under control as well as hoped for. It
may be difficult to control the process
in the field as a retrofit to existing
charcoal kilns, which may affect the
quality of the charcoal produced.
• H)n average, 3.95 g of benzene is emit-
ted for every 1 kg of wood fed into
the simulator. On this basis, therefore,
633 Ib of benzene would be released
by 80 tons of wood.
Table LnApproximate Upper Concentration
Ranges for Compounds as Measured
in the Dilution Tunnel
Compound
Aldehydes & Ketones
Methanol
Formaldehyde
Acetaldehyde
Propanal
PAHs
Napthalene
Acenaphthalene
Phenanthrene
2-Methylnaphthalene
Dibenzofuran
Fluoranthene
Pyrene
Fluorene
Anthracene
Acenapthene
Benz[a]anthracene
Chrysene
Benz[a]fluorene
VOCs
Benzene
Toluene
Xylenes
Acetophenone
Styrene
Ethylbenzene
SVOCs
Phenol
4-Methylphenol
2-Methylphenol
2,4-Dimethylphenol
Upper
Concentration
(g/rrP
2500
100
10
1
7500
2000
1800
1200
720
700
700
500
300
200
200
150
100
17,000
2000
1800
400
200
100
12,000
4000
3000
3000
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Paul M. Lemieux is also the EPA Project Officer (see below).
The complete report, entitled "Emissions of Air Toxics from a Simulated Charcoal Kiln
Equipped with an Afterburner," (Order No. PB2001-102799; Cost $25.50, subject
to change) will be available only from:
National Technical Information ServiceO
5285 Port Royal RoadO
Springfield, VA 221610
Telephone: (703) 605-60000
(800) 553-6847 (U.S. only)
The EPA Project Officer can be contacted at:
Air Pollution Prevention and Control Division
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711-0001
United StatesD
Environmental Protection Agency D
CenterforEnvironmental Research InformationD
Cincinnati, OH 45268D
PRESORTED STANDARDD
POSTAGES FEES PAIDD
EPAD
PERMIT No. G-35D
Official Business
Penalty for Private Use
$300
EPA/600/SR-01/011
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