United States
Environmental Protection
Industrial Environmental Research
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
  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).
  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.
  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

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
  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.

  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.

   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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