United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-84-038 Apr. 1984
Project Summary
Characterization of
Emissions from a
Fluidized-Bed Wood-Chip
Home Heating Furnace
Robert S. Truesdale
Emissions from a residential wood-
chip combustor, operated in both a
fluidized-bed and a cyclone-fired mode,
were measured and are compared to
emissions from a conventional wood-
stove and industrial wood-fired boilers.
In general, the combustion efficiency of
the fluidized-bed and cyclone-fired wood-
chip burner is higher than that of
conventional woodstoves. Concomi-
tant with this increase in efficiency is a
decrease in most emissions. For the
fluidized-bed tests, significant reduc-
tions of total hydrocarbons and CO
were observed, compared to woodstove
emissions. The cyclone test showed ,
PAH levels far below those of conven-
tional woodstoves, approaching levels
measured in industrial wood-fired boil-
ers. A baghouse, installed during two
fluidized-bed tests, was extremely effec-
tive in reducing both particulate and
PAH emissions. Method 5 samples
from above the fluid bed suggest that
appreciable PAH is formed in the upper
region of the furnace or in the watertube
heat exchangers. In general, the cyclone-
fired mode was more effective in reduc-
ing emissions from residential wood
combustion than the fluidized-bed
mode.
This Project Summary was developed
by EPA's Industrial Environmental Re-
search Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
Funded by the U.S. Department of
Energy (DOE), ETS, Inc. of Roanoke, VA,
has designed and constructed a novel
home heating unit that is fired on wood
chips instead of the cord wood that is
normally used in wood stoves. The device
was developed for three reasons: (1) by
increasing combustion efficiency, the
device can significantly reduce air pollu-
tion from wood combustion; (2) using
wood chips enables the design and
construction of automated fuel handling
facilities, greatly increasing the potential
convenience of heating with wood chips
instead of cord wood in fireplaces and
wood stoves; and (3) wood chips are
cheaper than cord wood and promise
more efficient use of timber resources,
because the entire tree, rather than just
the main wood portions, can be chipped
and used for fuel. This study was under-
taken to measure the atmospheric emis-
sions from this novel residential wood
Chip combustor and to compare these
emissions with those from both a resi-
dential wood stove and industrial wood-
fired boilers.
Procedure
The wood-chip-fired furnace used dur-
ing this study consists of five basic
components: (1) a wood feed conveyor,
for feeding wood into the unit; (2) a
furnace with a 36 cm (14 in.) diameter
bed, a gas/water heat exchanger, and a
forced-draft fan (interchangeable burner
assemblies for the lower portion of the
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furnace enable it to operate as a f luidized-
bed combustion unit or a cyclone-fired
combustor); (3) a fabric filter using a 13
cm (5 in.(diameter inside-outflow shaker-
cleaned filter bag, removable ash con-
tainer, and induced draft fan; (4) a hot
water heater to supply domestic hot
water to the house; and (5) an auxiliary
heater for supplying space heat to the
house when the wood system is not
operating.
During fluidized-bed operation, wood is
fed through a tube in the center of the bed
and dropped onto particles of the fluidized
bed where combustion takes place. In the
cyclone mode, wood is fed through a
forced-draft fan and blown into the cy-
clone burner where it is combusted.
Fuel used in these tests was chipped
pine; chips were about 0.6 cm (1 /4-in.) to
1.3 cm (1 /2-in.) long. Fuel characteristics
include an average moisture content of
11.2 percent, a bulk density of 0.24
g/cm3 (15 Ib/ft3), and a heating value of
17.7 J/kg (8,500 Btu/lb) on a dry basis.
During this study, emissions were
measured during four sets of duplicate
test runs of the experimental furnace.
Gaseous emissions measured during
these test runs included nitrogen oxides
(NOX), measured continuously using a
photoluminescent detector, and CO, C02,
and light organics measured using dis-
crete gas samples and gas chromatog-
raphy. A modified Method 5 sampling
train was used to sample particulate and
organic emissions during each duplicate
test run. Total particulates and water
were measured using standard Method 5
procedures. Glass capillary gas chroma-
tography was used to measure the con-
centration of polycyclic aromatic hydro-
carbons (PAHs) in modified Method 5
sample extracts. Gas chromatography
and gravimetric analysis was used to
measure total organics collected by the
modified Method 5 sampling train.
The experimental furnace was operated
and sampled in four test modes, the first
three of which involved sampling at the
flue gas outlet of the baghouse: (1) with
the fluidized-bed burner and fabric filter
bag in place; (2) with the fluidized-bed
burner in place and no fabric filter bag; (3)
with the cyclone burner in place; and (4)
with the fluidized-bed burner in place, but
with samples taken just above the fluid
bed in the furnace chamber. Duplicate
runs were conducted at each test point,
resulting in eight test runs. NO, measure-
ments were continuous during each test
run, and one or two discrete gas samples
were taken during each test. The modified
Method 5 sampling commenced as soon
as steady-state conditions were reached
during each test run, and continued until
over 2 m3 (70 ft3) had been sampled or
until particulate loading on the filter
reduced the gas flow through the system
so that no more sample could be taken.
Results and Discussions
In general, the residential wood-chip
combustor tested in this study was suc-
cessful in reaching its goals of higher
efficiency and lower emissions than
conventional wood-fired heating appli-
ances. Efficiencies ranged from 62 to 77
percent during the tests. Consumption of
the chipped pine fuel ranged from 3.0 to
5.6 kg/h.
The following observations are based
on emission data from the wood-chip-
fired furnace:
1. Both the fluidized-bed and cyclone-
fired combustion units produced
lower emissions of particulate, total
hydrocarbons, and CO than those
from a conventional residential
wood stove.
2. PAH emission factors for the cy-
clone-fired combustion test were
significantly lower than those for
conventional wood stoves. How-
ever, PAH emission factors for the
fluidized-bed combustion tests
were similar to those from wood
stoves for the lighter PAHs, and
were higher than residential wood-
stoves for the heavier PAHs. Lower
total hydrocarbon emission factors
for fluidized-bed combustion tests,
compared to those for wood stoves,
imply that a larger fraction of the
total hydrocarbons from fluidized-
bed combustor are being converted
to PAHs.
3. The baghouse on this fluidized-bed
combustion unit proved extremely
effective in reducing total sus-
pended particulate emissions from
the unit. In addition, collection of
partially burnt carbonaceous wood
particles in the baghouse resulted
in significantly lower emission fac-
tors for heavier PAHs during the
fluidized-bed combustion tests.
4. Hydrocarbon emission sampling
just above the bed for the fluidized-
combustion mode indicates that
most of the significant formation of
heavier PAH compounds is occur-
ring above the bed at the inlet of the
watertube heat exchanger or in the
watertube heat exchanger itself.
5. Overall the cyclone combustor is
superior to the fluidized-bed com-
bustor in reducing all emissions
except NO,. NOX emissions are only
slightly higher for the cyclone com-
bustor than for the fluidized-bed
combustor. From an emission stand-
point, therefore, the cyclone-fired
wood-chip combustor appears to be
superior to the fluidized-bed wood-
chip combustor. This is especially
true for PAH emission factors: the
cyclone combustor emission factors
for PAH compounds were almost as
low as those measured from in-
dustrial wood-fired boilers. This is a
result of very low levels of total
hydrocarbon emissions from the
cyclone furnace which precludes
significant PAH formation.
Conclusions
Compared to woodstove emissions,
emissions from the residential fluidized-
bed combustion unit were significantly
reduced with respect to particulate, total
hydrocarbons, and CO. PAH emission
factors were similar to those of wood
stoves for lighter PAHs, but higher by
approximately an order of magnitude for
the heavier PAHs. Thus, significant PAH
formation is occurring in the furnace
above the fluid bed. Using a filter bag for
particulate control reduced the air emis-
sions of heavier PAHs for the fluidized-
bed tests. Except for NO,, the cyclone-
fired tests showed significant reductions
in all emissions measured, over those
from a residential wood stove. Cyclone
furnace emissions were also lower than
those measured in industrial wood-fired
boilers. Cyclone-firing thus appears to be
superior to fluidized-bed firing, as pres-
ently designed, in reducing emissions
from the combustion of wood in resi-
dential home heating units. However,
although not tested for, introducing the
wood chips into the fluid bed rather than
on top of it may cause more complete
combustion and hence lower emissions
in the fluidized-bed mode.
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Robert S. Truesdale is with Research Triangle Institute, Research Triangle Park,
NC 27709.
Michael C. Osborne is the EPA Project Officer (see below).
The complete report, entitled "Characterization of Emissions from a Fluidized-bed
Wood-chip Home Heating Furnace," /Order No. PB84-179 878; Cost: $10.00,
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:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati. OH 45268
ft U S GOVERNMENT PRINTING OFFICE. 1984 — 759-015/7686
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Environmental Protection
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