United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 2771
Research and Development
EPA/600/S7-87/012 May 1987
x>EPA Project Summary
Environmental Assessment of a
Wood-Waste-Fired Industrial
Watertube Boiler
C. Castaldini and L. R. Waterland
This report describes emission results
from field tests of a wood-waste-fired
industrial watertube boiler. Two series
of tests were performed: one firing dry
wood waste (11% moisture), and the
other firing green wood waste (34%
moisture). Emission measurements in-
cluded: 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 pol-
lutants, and flue gas concentrations of
73 trace elements; Method 5 sampling
for particulate; controlled condensation
system sampling for SO2 and SO3; and
grab sampling of boiler mechanical col-
lector hopper ash for inorganic and
organic composition determinations.
Flue gas CO emissions from the boiler
were quite high, averaging about 10,000
ppm (dry at 3% O2) firing dry wood and
about 2,000 ppm firing green wood.
These high emissions were attributed
to the high excess air levels at which
the unit operated: approaching 400%
while firing dry wood and about 200%
while firing green wood. NO, emissions
were comparable, with both fuels in the
175 - 200 ppm (3% O2) range. SO2 and
SO3 emissions levels were less than 10
ppm, in keeping with the low sulfur
content of both fuels. Total organic
emissions from the boiler decreased
from 60 - 135 mg/dscm firing dry
wood to 2 - 65 mg/dscm firing green
wood, in parallel with corresponding
boiler CO emissions. The more volatile
organics (boiling point less than 100°C)
accounted for most of the total organic
emissions measured. Emissions of 11
polycyclic organic matter (POM) species
and phenol were quantitated for one or
both tests. Again, emission levels were
higher for the dry wood test.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that Is fully docu-
mented 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 for space heating in the
commercial and residential sector. As an
indirect consequence, emissions from
wood combustion and associated air
quality impacts have received attention
since recent studies have suggested that
wood combustion can produce significant
emissions of potentially hazardous or-
ganic pollutants. The report describes the
results of comprehensive emissions test-
ing of an industrial watertube'boiler
converted to burn wood waste from a
furniture manufacturing plant. The unit
was tested firing both a dry wood waste
and a green wood waste. The flue gas
was analyzed for criteria pollutants as
well as total organic and several organic
and inorganic species.
The tests were conducted in conjunc-
tion with an independent test program by
the North Carolina Department of Natural
Resources and Community Development
-------
(DNR)to measure POM species emissions
from this boiler and other wood-fired
boilers located in North Carolina.
The tests were performed on a balanced
draft Wickes stoker-fired industrial boiler
modified to burn wood waste (a mixture
of chips, shavings, and saw dust from
oak and pine woods). The boiler was
originally rated at 6.3 kg/s (50,000. Ib/hr)
of 1.7 MPa (250 psig), 338°C (640°F)
superheated steam when burning bitu-
minous coal. However, modifications to
allow 100% wood burning resulted in a
decrease in steam capacity to about 3.2
kg/s (25,000 Ib/hr), with lower super-
heater steam pressure and temperature.
The unit was equipped with a mechanical
collector (cyclone) for paniculate control.
Summary and Conclusions
Boiler Operation
The test program for this unit called for
emissions evaluation while firing dry
wood (Test 1) and green wood (Test 2).
Table 1 summarizes boiler operating
characteristics and ultimate analyses of
wood fuel for both tests. As indicated.
boiler operation was not held constant
during either test. Changing steam re-
quirements by the plant caused fluctua-
tions in boiler steam load and wood feed
rate. Because of the extremely high
excess air levels (almost 400% for Test 1
and over 200% for Test 2), boiler effici-
encies were a modest 55 and 61% for
Tests 1 ,and 2, respectively, based on the
standard ASME heat loss calculation
method.
Wood feed rates listed in Table 1 are
not measured values: they were cal-
culated based on the stack conditions
(volumetric gas flowrate and 02 level)
and the fuel analysis. These wood feed
rates should thus be considered approxi-
mate. In addition, the steam flowrates
shown in Table 1, which were taken from
the control room steam meter (deemed
unreliable by plant personnel), should
also be viewed with caution. If the boiler
steam flowrate is calculated based on the
heat input (wood flowrate x heating value),
boiler efficiency (ASME: heat loss), and
steam conditions, the resulting steam
flows would be 1.1 and 1.6 kg/s (8,400
and 13,000 Ib/hr) for Tests 1 and 2,
respectively. This is quite different from
what the control room steam meter
indicated.
Emission Measurements
and Results
The sampling and analysis procedures
used in this test program conformed to £
modified EPA Level 1 protocol. The flut
gas measurements included:
• Continuous monitoring for 02, CO
and NOX
• SASS train sampling
• Controlled condensation systen
(CCS) for SO2 and SO3
• EPA Method 5 for particulate
• Grab sample for onsite analysis o
C, to C6 hydrocarbons by GC
In addition, samples of the mechanica
collector hopper ash and the fuel fired fo
each test were collected for analysis.
The analysis protocol included:
• Analyzing the fuels, SASS trail
samples, and the mechanical col
lector hopper ash for 73 trac
elements using spark source mas
spectrometry (SSMS), supplemente
Tabto 1. Summary of Boiler Operation and Fuel
Test parameter
Test 1
(dry wood)
Test 2
(green wood)
Boiler operation:
Steam load, kg/s (103 Ib/hr)
Superheater steam temp., °C (°F)
Superheater steam press., MPa (psig)
Economizer inlet water temp., °C (°F)
Economizer outlet water temp., °C (°F)
Stack temperature after collect., °C (°F)
Bridgewall temperature, °C f°F)
Silo A (dry wood) feed, rpm
Silo B (wet wood) feed, rpm
Furnace draft. Pa (in. H2O)
Underfire air. Pa (in. H2O)
Overfire air, kPa (in. H2O)
Pressure before collector. Pa (in. H2O)
Pressure after collector, kPa (in. H2O)
Wood feed rate3, kg/s (Ib/hr)
Excess air, percent
Boiler efficiency^, percent
Wood fuel ultimate analysis
(percent by weight as fired):
Carbon
Hydrogen
Sulfur
Nitrogen
Oxygen
Ash
Moisture
Higher heating value kj/kg (Btu/lb)
Bulk density kg/m3 (Ib/ft3)
1.8-2.2
227-274
1.OO-1.17
63-69
121-133
216-238
354-483
390-700
(14-17)
(440-525)
(145-170)
(145-155)
(250-270)
(420-460)
(740-90OJ
Oto-100
75-200
5.5-5.6
450-600
0.5-7.0
0.25
387
(0 to-0.4)
(0.3-0.8)
(22.0-22.5)
(1.8-2.4)
(2.0-4.0)
(2.270)
55.3
45.27
5.44
0.04
0.12
37.78
0.33
11.02
0.88-1.4
271-296
1.13-1.30
66-69
113-121
216-233
538-594
(7-11)
(520-565)
(165-190)
(15O-155)
(235-250)
(420-450)
(1.OOO-1.10C
500-620
-25 to-50
125-175
5.5-5.6
320-500
0.55-0.75
0.54
f-0. 1 to-0.2)
(0.5-0.7)
(22.0-22.5)
(1.3-2.0)
(2.2-3.0)
(4.310)
213
61.3
17,900
233
(7.719)
(14.52)
13.3OO
192
35.07
3.60
0.02
0.10
26.06
1.29
33.85
(5.738)
(11.95)
aAs-fired (wet) basis (a calculated value)
b Based on heat loss method
-------
by atomic absorption spectrometry
(AAS)
> Analyzing SASS train samples and
the mechanical collector hopper ash
for total organic content in two
boiling point ranges: 100° to 300°C
by total chromatographable organics
(TCO) analysis, and greater than
300°C by gravimetry (GRAV)
1 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
Liquid chromatrography (LC) separa-
tion of selected sample extracts with
subsequent TCO, GRAV, and IR
analysis of LC functions
Direct inspection probe and batch
inlet low-resolution mass spectro-
metry (LRMS) of selected sample
extracts
Obtaining aqueous leachates of the
mechanical collector hopper ash and
analyzing the leachate for 73 trace
elements and 9 teachable anions
Determining the alpha and beta
radiometric activity of paniculate and
mechanical collector hopper ash
samples
• Performing several mutagenicity and
toxicity health effects bioassays and
several toxicity ecological effects
bioassays of SA6S samples and the
mechanical collector hopper ash
Table 2 summarizes emissions mea-
sured in the stack gas from the boiler.
Emissions are presented as both nano-
grams per Joule (ng/J) heating input and
micrograms per dry standard cubic meter
Oug/dscm) of flue gas. As a measure of
the relative potential significance of the
emissions, an occupational exposure
guideline concentration for each species
is also noted in the table. The guideline
noted is the time-weighted-average
Threshold Limit Value (TLV). These are
noted only to aid in ranking the potential
significance of pollutant species emis-
sions. Conclusions regarding the absolute
risk associated with emission levels
compared to occupational exposure
guidelines are not, and should not be,
drawn. With respect to ranking, however,
species emitted at levels several orders
of magnitude higher than their occupa-
tional exposure guidelines might warrant
further consideration. Species emitted at
levels significantly lower than their oc-
cupational exposure guidelines could be
considered of little potential concern. Only
species emitted at levels exceeding 10%
of their occupational exposure guidelines
are noted in Table 2.
CO was emitted during both tests in
concentrations well over an order of
magnitude higher than its occupational
exposure guidelines. During the dry wood
test, CO was measured in concentrations
ranging from about 1,000 - 3,400 ppm at
stack conditions averaging 9,800 ppm
corrected to 3% O2 (3.0 g/dscm). During
the green wood test, CO emissions were
measured in the range of about 280 -
2,300 ppm at stack conditions averaging
2,810 ppm corrected to 3% 02 (1.3
g/dscm). CO emissions varied with the
amount of 02 in the flue gas, increasing
substantially with increasing O2.
NOX was emitted at levels over an
order of magnitude higher than its oc-
cupational exposure guidelines. NOX
emissions averaged 175 and 194 ppm for
Tests 1 and 2, respectively, both corrected
to 3% 02. In contrast to CO emissions,
NOX levels were found to be relatively
Table 2. Summary of Flue Gas Emissions
Species
Criteria pollutant and
total organic emissions
CO
NOX las N02)
Solid paniculate
Condensible paniculate
Total volatile
organics (C, to Cg)
Total chromatographable
organics (C7 to C16)
Total GRAV
oragnics (C,6J
Trace elements
Silver. Ag
Nickel, Ni
Phosphorous, P
Barium, Ba
Potassium, K
Iron, Fe
Sodium, Na
Chromium, Cr
Copper, Cu
Lead, Pb
Cobalt, Co
ng/J
3,690
108
204
16
58 to 150
7.7
12
0.98
0.15
>0.20
>0.20
>0.37
>0.24
>0.87
0.010
0.014
0.007
0.007
Test 1 (dry wood)
emissions3
pg/dscm
2.77 x 1O6
0.87 x JO5
1.64x 1O5
0.1 3 x 10s
(4.7 to 12)x 104
6,200
9.500
790
120
>160
>160
>300
>190
>720
8.2
11
5.2
5.6
g/kg fuel
66.0
1.93
3.64
0.29
1.0 to 2.7
0.14
021
0.017
0.0026
>O.OO35
X5.0035
>O.O066
>O.OO42
>0.016
1.8x 104
2.4 x 1O4
1.1 xi a4
1.2xW4
ng/J
1.080
123
267
4
2.8 to 63
0.60
1.2
0.012
0.24
>0.23
>0.27
>1.1
>0.39
>0.31
0.014
0.049
0.015
0.0007
Test 2 (green wood)
emissions3
ng/dscm
1 31 x 106
1.49x 10s
3.24 x 1O5
0.05x1 0s
(0.34 to 7.6) x 104
730
1.400
14
290
>280
>330
>1.3OO
>470
>370
17
59
18
0.79
g/kg fuel
14.4
1.63
355
0.05
0037 to 0.84
0.008
0.015
1.6 xlO4
0.0032
>0.0031
>0.0037
>0.014
>0.0052
>0.004J
1.9x 104
6.5 xW4
2.0 x 10-4
8.8 x 10 6
Occupational
exposure
guideline1'
(ng/m3)
5.5 x 104
6.000
I.Ox 104
—
—
—
—
10
. 100
100
500
2,000
1,000
2,000
50
200
150
SO
'Average flue gas 02 at the stack was 16.4 and 13.9% for Tests 1 and 2, respectively
b Threshold Limit Value
-------
insensitive to 02 levels. Higher wood
moisture during Test 2 did not result in a
net decrease in NOX emissions as might
have been anticipated. Any combustion
temperature reducing effect of the higher
water content in the fuel was most likely
insignificant compared to the expected
low combustion temperature associated
with the high excess air levels fired. The
nitrogen content of both fuels were
comparable and low (see Table 1). Sulfur
oxides (S02 and S03) emissions were
measured, but not detected in the flue
gas above a detection limit of 10 ppm for
either test. This is not entirely surprising
since total conversion of sulfur in the
wood to SO2 would have resulted in, at
most, about 12 ppm at stack conditions
for both tests.
Other pollutants emitted at levels ex-
ceeding their occupational exposure
guidelines were Ag, Ni, and P for both
tests.
Tables 3 and 4 summarize organic
emission results for the dry wood and
green wood tests, respectively. The top
portion of each table summarizes the
semivolatile TCO organic content and the
nonvolatile GRAV organic content of the
XAD-2 sorbent extract, as eluted (by polar
character) into the seven LC fractions,
and the TCO and GRAV of the OMC. The
bottom portion of the tables summarizes
organic compound categories identified
by LRMS of the LC fractions and the
OMC, supplemented by IR spectra.
Total organic emissions during Test 1
(dry wood) were significantly greater than
those from Test 2 (green wood). This
result is consistent with the higher CO
emissions measured. Organics trapped
in the XAD-2 sorbent accounted for over
95% of the nominal >C7 organics with
boiling points >100°C (212°F). The in-
ferences from IR and LRMS data are that
the XAD-2 extracts contained primarily
aliphatic hydrocarbons, aldehydes, and
carboxylic acids for both tests. Phenols,
aromatic hydrocarbons, and heterocyclic
oxygen compounds were additional sig-
nificant components in the dry wood test
extracts. The POM compounos detected
at highest levels in the XAD-2 organic
extracts were, naphthalene, phenan-
threne, and acenaphthylene in concen-
trations corresponding to emissions in
the 5-7 pig/dscm range, as shown in
Table 5.
The TCO results shown in Tables 3 and
4 are compromised somewhat because
the XAD-2 sorbent resin used in these
tests had been inadvertently contaminated
with acetone prior to field use. This
resulted in high TCO values in both the
4
sample extracts and the field blank. Gas
chromatography/mass spectrometry
(GC/MS) analyses were performed to
identify and quantitate specific con-
taminant species, thereby allowing cor-
rected sample and blank TCO values to
be obtained. The resulting data are
defensible, though still compromised to
some degree.
Trace element analyses were performed
on the two fuels fired, the emitted par-
ticulate, and the mechanical paniculate
collector hopper ash. The trace element
compositions of the two fuels (dry and
green wood) were very similar. In addition,
the trace element compositions of the
coarse particulate emitted in the flue gas
(10 /^m + 3 Mm cyclone catches ) and the
Tab/0 3. Organic Extract Summary — Test 1 (Dry Wood) XAD-2 and OMC Extracts
XAD-2 extract liquid
chromatography fraction0
LCI
LC2 + 3 LC4 + 5 LC6 + 7
OMC
Total
Total organics, mg
TCO, mg
GRAV. mg
4.5
1.2
3.3
17
12
5
32
16
16
132
16
116
13
4.9
8.0
200
SO
150
Assigned intensity —
Category
Aliphatic
hydrocarbons
LCI
100—0.21
LC2 + 3
LC4 + 5
mg/dscm
LC6 + 7
Total,
mg/dscr
(mg/kg
OMC fuel)
0.2 1
(4.6)
Carboxylic
acids
Polynuclear
aromatic
hydrocarbons,
MW>216
Aldehydes
Ethers
Nitriles
Amines
Heterocyclic
sulfur
compounds
Halogenated
aliphatics
Aromatic
hydrocarbons
Phenols
Heterocyclic
oxygen
compounds
Ketones
Heterocyclic
nitrogen
compounds
10—0.70
1—0.07
100—0.091 0.79
(17)
1—0.001
0.0071
(0.16)
100—1.2 10—0.5
10—0.009 1.8
(40)
100-O.091 0.091
(2.0)
100—0.091 O.O91
(2.0)
10Q—O.O91 0.091
.12.0)
100—0.091 0.091
(2.0)
10—0.1 10—0.5
10—0.1 100—4.7
10—0.1 10—0.5
10—O.009 0.009
(0.2)
10—O.O09 0.61
(13)
100—0.091 4.8
(110)
100—0.009 0.61
(13)
10—O.O09 0.009
. (0.2)
10—0.009 O.OO9
(0.2)
"Fractionation by polarity: LCI is nonpolar, LC7 is higher polar
-------
mechanical collector hopper ash for the
dry wood test were similar to respective
discharges for the green wood test.
Furthermore, for both tests, the coarse
paniculate trace element composition
was similar to that of the mechanical
collector hopper ash, but somewhat dif-
ferent from that of the fine paniculate (1
^m + filter catches) in th flue gas. This is
consistent with the mechanical collector
being more efficient in collecting coarse
particulate.
The organic content of the mechanical
collector hopper ash was similar for both
tests (about 0.70 mg/kg). These high
levels are consistent with the relatively
inefficient boiler operation during both
tests.
An aqueous leachateof the mechanical
collector hopper ash from the dry wood
test contained levels of Ba, Cr, Pb, and Ni
which exceeded respective water quality
criteria by factors of 1.5 - 10. However,
these were the only elements with
leachate concentrations exceeding water
quality criteria.
Radionuclide emissions were indirectly
measured by analysis of the alpha and
beta activities of the particulate and
mechanical collector hopper ash samples.
The alpha plus beta activities of the
particulate samples, converted to emission
rates, correspond to 770 and 760 pCi/kg
wood for Tests 1 and 2, respectively.
These are similar to emission rates from
controlled model coal-fired powerplants.
TaWe 4. Organic Extract Summary — Test 2 (Green Wood) XAD-2 and OMC Extracts
XAD-2 extract liquid
chromatography fractiorf
LCI
LC2+3 LC4+5 LC6+7
OMC
Total
Total organics, mg
TCO, mg
5.4
0.53
1.8
<0.04
2.5
<0.04
13
1.7
0.2
0.2
23
2.3
GfiAV. mg
4.9
1.8
2.5
11.2
<3.0
20.4
Category1'
Aliphatic
hydrocarbons
LCI
100—0.20
Assigned intensity
LC2 + 3 + 4 + 5
— mg/dscm
+ 6+7
Total.
mg/dscm
(mg/kg
OMC fuel)
0.20
(2.21
Aldehydes
Carboxylic
acids
100—0.32
100—0.32
100—0.003 0.32
(3.5)
100—0.003 0.32
(3.5)
aFractional/on by polarity: LCI is nonpolar, LC7 is highly polar
* Summary of organic emissions are based on IR results primarily since LRMS did not show any
organic groups
Table S. POM and Other Organic Species Emission Summary — Total Flue Gas
Test 1 (dry wood)
Test 2 (green wood)
Compound
ng/dscm pg/kg fuel" yg/dscm ttg/kg fueP
Acenaphthene
A cenaphthylene
Anthracene
Benzo/j+k/fluoranthenes
Chrysene
Fluoranthene
Fluorene
Naphthalene
Phenanthrene
Phenol
Pyrene
Other polynuclears
_b
0.5
—
0. 10
—
—
0.65
4.5
7.0
4.7
0.30
<0.05
//
—
2.2
—
—
14
100
160
100
6.7
<1.1
0.1
5.2
0.2
—
0.04
0.3
—
—
2.0
0.36
0.2
<0.04
1.1
57
2.2
—
0.4
3.3
—
—
22
//
2.2
<0.44
"kg fuel on wet basis
* Dashes indicate compound was not found to have concentration above the detection limits of
0.05 pg/dscm for Test 1 results and 0.04 ng/dscm for Test 2 results (more flue gas was sampled
in the Test 2 SASS run resulting in a lower detection limit)
Bioassay tests were performed on the
organic sorbent (XAD-2) extracts, flue
gas particulate, and the mechanical col-
lector hopper ash. Both health and
ecological effects tests were performed.
The bioassay tests performed on the
XAD-2 extracts were health effects tests
only. These were the Ames mutagenicity
assay and the CHO cytotoxicity assay. In
addition to the Ames test, health effects
bioassay tests performed on mechanical
collector hopper ash and the particulate
catch were the rabbit alveolar macro-
phage (RAM) cytotoxicity assay and the
whole animal acute toxicity (WAT) test in
live rodents.
Table 6 summarizes the results of the
Ames, CHO, RAM, and WAT assays.
Overall, the results suggest that all
samples except the XAD-2 extracts were
of nondetectable to low toxicity and
mutagenicity. The XAD-2 extracts showed
high toxicity and mutagenicity. Flyash
samples from the mechanical collector
hopper were also tested for acute toxicity
to freshwater invertebrates (Daphnia
magna), freshwater fish (fathead minnow,
Pimephales promelas), and freshwater
algae (Selenastrum capricornutum). Table
7 summarizes the results of these assays,
which suggest that samples are of non-
detectable to low toxicity.
Conclusions
Emission tests of a wood-waste-fired
industrial boiler suggest that emissions
of potential concern can arise from in-
efficient (very high excess air) operation
of the unit. In the tests, CO emissions
were very high and varied with the excess
air level fired, decreasing as excess air
was decreased. Total organic emission
levels (the volatile, boiling point less than
100°C, organics predominated) and POM
emission levels paralleled CO emission
levels; they were higher in the test with
the higher average CO emissions. Dif-
ferences in relative emission rates of the
pollutants analyzed between firing a dry
wood fuel and a wet wood fuel were not
discernable. Major differences noted
between the tests were best ascribed to
the different excess air levels' fired for
each fuel.
-------
Table 6. Health Effects Bioassay Results
Bioassay
Test Sample Ames" CHO" RAM" WAT"
1 Combined paniculate NO — — —
(Dry wood) (cyclones and filter catches)
XAD-2 sorbent extract H/M H — —
Flyash ND — L/ND NO
2 10tim+3nm ND — L/ND
(Green wood) cyclone catches
1 pm cyclone and filter catches ND — M —
XAD-2 sorbent extract H H — —
Flyash /VD — ND ND
a Mutagenicity test
* Toxicity test
ND — Nondetectable
L — Low
M — Moderate
H -High
— Assay not performed
Table 7. Ecological Effects Bioassay Results
Test Sample
1 Flyash
Invertebrate3
ND/L
Aquatic organisms
Freshwater fishP Freshwater algaef
ND L
(Dry wood)
2
(Green wood) Flyash
aDaphnia magna
b Pimephales promelas
c Selenastrum capricornutum
ND — Nondetectable toxicity
L — Low toxicity
— Assay not performed
C. Castaldini and L. ft. 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 Watertube Boiler:"
"Volume I. Technical Results," lOrder No. PB 87-177 523/AS; Cost: $18.95)
"Volume II. Data Supplement." (Order No. PB 87-177531 /AS; Cost: $36.95)
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
-------
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S7-87/012
OC00329 PS
'"""
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