United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-87/010 May 1987
Project Summary
Environmental Assessment of a
Wood-Waste-Fired Industrial
Firetube Boiler
R. DeRosier and L R. Waterland
This report gives emission results
from field tests of a wood-waste-fired
industrial firetube boiler. Emission
measurements included: continuous
monitoring of flue gas emissions;
source assessment sampling system
(SASS) sampling of the flue gas with
subsequent laboratory analysis of
samples to give total flue gas organics
in two boiling point ranges, compound
category information within these
ranges, specific quantitation of the
semivolatile organic priority pollutants,
and flue gas concentrations of 65 trace
elements; Method 5 sampling for
particulates; controlled condensation
system (CCS) sampling for SO2 and
SOa; and grab sampling of boiler
bottom ash for trace element content
determinations.
Flue gas CO emissions were quite
variable during the tests, and often
quite high. Emissions ranged from
about 100 to almost 10,000 ppm (dry,
3% O2). The high emission levels were
attributed to the high excess air level
at which the unit operated, approxi-
mately 160%. NOX emissions, at about
300 ppm (3%, O2), were relatively high
for a wood-fired boiler, although the
fuel nitrogen content (0.18%) was
relatively high for a wood fuel. SO2 and
SOs emissions were less than 10 ppm,
in keeping with the low sulfur content
of the wood-waste fuel. Total organic
emissionsf rom the boiler were 5.7 mg/
dscm (3.4 ng/J heat input or 65 mg/
kg fuel); about 90% of these consisted
of volatile (boiling point less than
100°C) compounds. Emission levels of
five polycyclic organic matter (POM)
species and phenol were quantitated.
Except for naphthalene, all species
were emitted at concentrations less
than 0.4 pg/dscm; naphthalene
emissions were 3.3 /jg/dscm.
Trace element composition data
show selective concentration of several
elements in emitted coarse fraction (>3
pm) particulate over boiler bottom ash.
However, further concentration to fine
fraction «3 yum) particulate did not
seem evident.
This Project Summary was devel-
oped by EPA's Air and Energy Engi-
neering Research Laboratory, Research
Triangle Park. NC. to announce key
findings of the research project that is
fully documented in two separate
volumes of the same title (see Project
Report ordering information at back).
Introduction
In recent years wood has experienced
a revival as a primary or alternate source
of energy for steam raising in industrial
boilers as well as space heating in the
commercial and residential sectors. As
an indirect consequence, emissionsfrom
wood combustion and associated air
quality impacts have become of interest
since recent studies have suggested that
wood combustion can produce signifi-
cant emissions of potentially hazardous
organic pollutants. The report describes
the results of comprehensive emissions
testing of an industrial firetube boiler
designed to burn wood waste from a
furniture manufacturing plant. The flue
gas was analyzed for criteria pollutants
as well as total organic and several
organic and inorganic species. The tests
were conducted in conjunction with an
independent test program by the North
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Carolina Department of Natural Resour-
ces and Community Development (DNR)
to measure POM species emissions from
this boiler and other wood-fired boilers
in North Carolina.
The tests were performed on a McBur-
ney horizontal return tube, firetube boiler
designed to fire wood waste. The boiler
has a three-pass design with flyash
reinjection. Rated capacity is 3.15 kg/
s saturated steam (25,000 Ib/hr) at 1.0
MPa (150 psig). The unit normally burns
a mixture of pine, oak, hickory, glue, and
ground masonite blown in by a pair of
wood-feeder blowers. After combustion,
the flue gas proceeds through three heat
exchanger passes. Before entering the
stack, the flue gas passes through a
cyclone which separates the larger flyash
particles for reinjection.
Summary and Conclusions
Boiler Operation
Table 1 summarizes the operating
conditions for the tests performed. The
fuel analysis is given in Table 2. The tests
were conducted over a 6-hr period with
no unusual operating difficulties. How-
ever, because of the relatively high
average excess air level over the test
period (160%), boiler efficiency was a
modest 64.5%, based on the ASME heat
loss calculation method. The wood waste
flowrate noted in Table 1 is not a
measured value: it was calculated based
on measured stack gas flowrate (Method
5) and O2 level, and the fuel analysis.
This value should be treated with cau-
tion. If the expected steam flowrate is
calculated based on the fuel flowrate and
heating value and the boiler efficiency
noted in Table 1, a value of 2.4 kg/s
(19,400 Ib/hr) results. This contrasts
with the control panel steam meter
reading of 1.7 kg/s (13,600 Ib/hr). The
calculated value is more likely to be
nearly correct.
Emission Measurements and
Results
The sampling and analysis procedures
used in this test program conformed to
a modified EPA Level 1 protocol. The flue
gas measurements included:
• Continuous monitors for Oz, CO, and
NO,
• SASS
• CCS for S02and SO3
• EPA Method 5 for paniculate
• Grab sample for onsite Ci-C6 hydro-
carbon analysis
Table 1. Boiler Operating Conditions
Steam flow, kg/s
(103 Ib/hr)
Drum pressure,
MPa Ipsig)
Feed water pressure,
MPa (psig)
Furnace outlet pressure,
kPa (in. H,O)
Collector pressure,
kPa (in. H20)
Stack temperature,
°C(°F)
Ambient air, °C (°F)
Wood flowrate kg/s
(Ib/hr)'
Excess air, percent"
Boiler efficiency,
percent*
1.71 (13.6)
0.841 (122)
1.09(158)
0.25 (1.0)
0.54(2.10)
343 (650)
25 (77)
0.514(4,070)
160
64.5
"As fired, calculated from stack gas flow.
and fuel analysis.
^Calculated from the Oj measurement and
fuel analysis.
"Based on heat loss method.
Table 2. Ultimate fuel Analysis (Percent
by Weight)*
Carbon, C
Hydrogen, H
Nitrogen, N
Sulfur, S
Oxygen. O
(by difference)
Ash
Moisture"
47.60
5.75
0.18
0.04
45.93
0.50
5.66
Higher heating value,
kJ/kg(Btu/lb) 20,060(8,630)
"Dry basis, except as noted.
"As received.
In addition, samples of the boiler bottom
ash and the wood fuel fired were col-
lected for analysis.
The analysis protocol included:
• Analyzing the fuel, SASS train sam-
ples, and the mechanical collector
hopper ash for 65 trace elements
using spark source mass spectrometry
(SSMS), supplemented by atomic
absorption spectrometry (AAS)
• Analyzing SASS train samples for
total organic content in two boiling
point ranges: 100°C to 300°C by total
chromatographable organics (TCO)
analysis and >300°C by gravimetry
(GRAV)
• Analyzing the SASS train sorbent
module extract for 58 semivolatile
organic species including many of the
POM compounds
• Infrared (IR) spectrometry analysis of
organic sample extracts
• Determining the alpha and beta
radiometric activity of particulate and
mechanical collector hopper ash
samples
• Performing several mutagenicity and
toxicity health effects bioassays and
several aquatic toxicity ecological
effects bioassays of SASS samples
and the bottom ash
Table 3 summarizes exhaust gas
emissions measured in the test program.
Emissions are presented both as nano-
grams per Joule (ng/J) of heat input and
micrograms per dry standard cubic meter
(/jg/dscm) of flue gas. CO emissions are
presented as a range because CO con-
centrations exhibited too large a variation
to allow defining a meaningful average.
As a measure of the relative potentia
significance of the emissions, an occu-
pational exposure guideline for each
species is also noted in Table 3. Tht
guideline noted is the time-weightec
average Threshold Limit Value (TLV)
These are noted only to aid in rankinj
the potential significance of pollutan
species emissions. Conclusions regard
ing the absolute risk associated witl
emission levels ocmpared to occupa
tional exposure guidelines are not, am
should not be, drawn. With respect t
ranking, however, species emitted a
levels several orders of magnitude highe
than their occupational exposure guide
lines might warrant further considers
tion. Species emitted at levels signifi
cantly lower than their occupation*
exposure guidelines could be considere
of little potential concern. Only specie
emitted at levels exceeding 100% of the
occupational exposure guidelines ar
noted in the table.
Table 3 shows that several trac
elements were emitted at levels betwee
0.1 and 2 times their respective guid<
lines. For comparison, CO emissior
ranged up to almost 50 times its occi
pational exposure guideline; average N(
emissions (as NO2> were over 40 tirm
its guideline.
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Table 3. Summary of Flue Gas Emissions
Criteria Pollutants and
Other Vapor Species
CO
NO, fas NOt)
Particulate
SASS
Method 5; solid
MethodS: condensible
DNR Method 5": solid
Total gravimetric organics (GRA V)
Total chromatographable organics
Total volatile organics ^Ci to CeJ
Trace Elements
Nickel, Ni
Phosphorus, P
Barium, Ba
Lead, Pb
Chromium, Cr
Potassium, K
Silver, Ag
Copper, Cu
Iron. Fe
ng/J Heat Input
26 to 1.580
154
114
108
1.1
127
0.42
<0.006
3.0
0.11
XX072
X>.77
0.027
0.0090
XJ.24
0.0077
0.079
X3.084
Emissions
ug/dscm
4.4 x 10*102.53x10"
2.56x70*
7. 90 x 70s
7.80x7 0s
1,900
2.00x705
700
<70
5,000
790
>720
>790
45
15
>400
1.9
32
>140
Occupational
Exposure
Guideline'
(ug/m3)
55,000
6,000
—
—
—
—
—
—
—
100
100
500
150
SO
2,000
10
200
1,000
'Threshold Limit Value.
^North Carolina Department of Natural Resources and Community Development.
Emissions of sulfur oxides (SO2 and
SO3) were sampled but not detected
above a detection limit of 10 ppm in the
flue gas. This is not entirely surprising
since total conversion of the sulfur in the
wood to SOz would have resulted in, at
most, 26 ppm stack emissions.
Table 4 shows the emitted particle size
distribution as determined by the SASS
train. The preponderance of less than 1
yum paniculate (51% by weight) agrees
with expectations. Flyash reinjection
should cause emitted particulate to be
relatively fine.
Table 5 summarizes the organic emis-
sion results for this test. Most of the
organics (88%) consist of species in the
nominal Ci-C8 boiling point range. No
organics were present above the protocol
detection limits in the nominal
Table 4.
Particulate Size Distributions
Emissions
Particle Size Cut
>70 fjm (10 urn cyclone plus probe wash)
3 to 10 um (3 um cyclone)
1 to 3 um (1 um cyclone)
<1 um (filter)
Total
ng/J
26
18
12
58
114
mg/dscm
44
29
20
97
190
Percent
of Total
Particulate
23.1
15.5
10.5
50.9
100.0
boiling point range of 100°-300°C. The
remaining 12% of the organics were in
the nominal Ci6+ boiling point range of
greater than 300°C. The semivolatile
analysis result (nominally CT-CIS organ-
ics with boiling points in the 100°-300°C
range) is compromised somewhat
because the XAD-2 sorbent resin used
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Table 5. Summary of Total Organic Emissions
mg/dscm
Volatile organic gases analyzed in the
field by gas chromatography:
C,
C2
C3
C5
C6
Total Ci-
1.2
0.5
2.8
0.5
ND
ND
5.0
Nonvolatile organics analyzed by
gravimetry:
Probe wash
JO + 3 fjm cyclones
Filter + J fjm cyclone
XAD-2 cartridge
Organic module condensate
<0.2
<0.2
0.4
0.3
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Table 6. POM and Other Organic Species Emission Summary
This Study
DNR 1*
DNR2"
Compound
Acenaphthylene
Fluoranthene
Naphthalene
Phenanthrene
Pyrene
Phenol
Detection limit
fig/dscm
0.30
0.08
3.3
0.30
0.20
0.38C
0.04
fjg/kg tuef
3.4
0.9
37.5
3.4
2.3
4.3
0.5
/jg/dscm
NA
ND
6.34
ND
ND
NA
0.12
ug/kg fuef"
NA
ND
83.2
ND
ND
NA
1.6
ug/dscm
NA
ND
0.85
ND
0.30
NA
0.08
ug/kg fuef
NA
ND
12.1
ND
4.3
NA
1.2
NA—Compound not analyzed.
ND—Compound not detected above detection limit.
"North Carolina Department of Natural Resources and Community Development.
"Dry basis.
C60 percent of phenol noted detected in the organic module condensate; all other results from XAD-2 extract only.
Table 7. Health Effects Bioassay Results
Bioassay
Sample Ames" CHOb
Bottom ash ND NP
Composite paniculate ND NP
XAD-2 extract M M
RAM* \NAf
L/ND ND
L NP
NP NP
ND—Nondetectable
L — Low.
M — Moderate.
NP — Assay not performed.
"Mutagenicity test.
0 Toxicity test.
Table 8.
Algae
Ecological Effects Bioassay
Results for the Boiler Bottom
Ash
Daphnia
Freshwater
Fish
UNO
ND
L—Low toxicity.
ND—Nondetectable toxicity.
R. DeRosier and L. R. Water/and are with Acurex Corporation. Mountain View
CA 94039.
Robert E. Hall is the EPA Project Officer (see below).
The complete report consists of two volumes, entitled "Environmental
Assessment of a Wood-Waste-Fired Industrial Firetube Boiler:
"Volume I. Technical Results," (Order No. PB 87-176 285/AS; Cost: $13.95)
"Volume II. Data Supplement," (Order No. PB 87-176 293/AS; Cost: $18.95)
The above reports will be available only from: (costs subject to change}
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
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use S300
EPA/600/S7-87/010
0000329 PS
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