United States
 Environmental Protection
 Industrial Environmental Research
 Research Triangle Park NC 2771.1
 Research and Development
 EPA-600/S7-81 -091  Dec. 1981
 Project  Summary
 Control  of  Emissions  from
 Residential Wood  Burning  by
 Combustion  Modification
 John M. Allen and Marcus W. Cooke
 An exploratory study is described of
 factors contributing to atmospheric
 emissions from residential wood-fired
 combustion equipment.  Three com-
 mercial appliances were operated
 with both normal and modified de-
 signs, providing different burning
 modes: up-draft with a grate, up-draft
 with a hearth, cross-draft, down-
 draft, and a high-turbulence mode
 utilizing a forced-draft blower. Fuels
 were naturally dried commercial oak
 cordwood, commercial  green pine
 cordwood, oven-dried fir  brands, and
 naturally dried oak cut into reproduc-
 ible triangles. Continuous measure-
 ments  of stack gases included Oa,
 CO2, CO, NO, SOa, and total hydro-
 carbons (FID) as an  indication of the
 total organic species in the stack gases
 during batchtype operation. Several
 combustion modification  techniques
 were identified which have an appre-
 ciable effect on emission factors and,
 therefore, can be developed and applied
 to reduce emissions in consumer use.
 The more promising design modifi-
 cations include: preventing heating of
 the wood inventory within the stove,
 focusing the air supply into the primary
 burning area with high turbulence,
 and increasing the temperatures in the
 secondary burning regions of the

  This Project Summary was developed
by EPA's Industrial Environmental
Research Laboratory, Research  Tri-
 angle Park, NC, to announce key
 findings of the research project that is
 fully documented in a separate report
 of the same title (see Project Report
 ordering information at back).

   The study reported in this document
 was initiated to explore the combustion
 modification techniques that might be
 applied beneficially to wood stoves, and
 more specifically to identify those tech-
 niques which show promise of providing
 a significant improvement in emissions
 when adequately developed and applied.
 The focus of the  effort  is on naturally
 drafted, hand-fired radiant stoves, as
 these constitute the majority of units
 used extensively for residential heating.
  The combustion in wood stoves, and
 the resulting emissions, can be modified
 in many ways. In this experimental
 program several modifications were
 made in stove operation in attempts to
 correlate specific changes in emissions
 with each of several specific combustion
 modifications. Synergistic effects of
 several simultaneous modifications
 were not specifically sought. However,
 each set of tests conducted to demon-
 strate the effects of a specific modifi-
 cation necessarily depends on the other
 design and operating conditions in use
 at  the time. The  effects of a specific
 modification under different design and
 operating  conditions can only be as-
sumed, and the  synergistic  effects
determined by inference.

Table 1.    Summary of Wood Combustion Research Reviewed

                  Performing Laboratory
                                       Project Focus
  Monsanto Research Corporation

  California Air Resources Board

  Bowdoin College

  Canadian Combustion Research Laboratory

  Auburn University

  Argonne National Laboratory

  Tennessee Valley A uthority

  Virginia Polytechnic Institute

  National Bureau of Standards

  Thermocore, Inc.

  New York University (Plattsburgh)

  Vermont Environmental Control Agency

  Institute of Man and Resources
  U.S. EPA. Industrial Environmental Research
  Laboratory (RTF), Combustion Research

  Del Green Associates
  OMNI Environmental
                   Extensive analysis of residential wood stove emissions

                   Residential and laboratory tests on free standing stoves

                   Measured paniculate emissions at low burn rates using
                   a dilution tunnel

                   Continuous monitoring of gas emissions including
                   efficiency measurements of different stove designs
                   and fireplaces at low rates of burning

                   Measured stove performance and safety, focusing
                   on efficiency measurements

                   Measuring emission factors for residential
                   wood stoves

                   Evaluation of several wood stoves including
                   particulate and gas  emission and efficiency

                   Studies of catalytic-bed after-burners and
                   staged combustion

                   Basic study of detailed characterization of
                   emissions and their formation

                   Measurement of air supply configuration effects
                   in stove design

                   Studies on thermostatic control development
                   and stove design focused on particulates

                   Ambient emission studies focusing on particulates
                   in the atmosphere

                   Paniculate and limited gas measurements
                   for 10 central systems using wood for
                   residential heating

                   Continuous measurement of gas emissions and
                   comparison of stack sampling and dilution
                   tunnel sampling during several phases of burning
                   cordwood and pellets used as fuels

                   Just starting an emission measurement program
                   using six stoves to determine reasonable standards
                   for emissions, to develop a simplified testing
                   procedure, and to evaluate the effects of fuel moisture

                   An emission evaluation to establish baseline data on
                   several new, commercially available stove designs  	
  The modifications conducted  in this
laboratory program were of three types:
stove design, fuel properties, and oper-
ator techniques. The uses of non-wood
fuel and combustion additives were not
considered. The use of processed wood,
such as pellets, was also not considered,
as this fuel can most effectively be
burned in equipment  specifically de-
signed for its use.

Wood Combust/on
  The combustion of wood is generally
recognized as involving three processes
or  phases:   moisture   evaporation,
pyrolysis with subsequent space burning,
and surface char burning. These
processes occur successively at any
local particle of wood, but in real com-
bustion systems there  is appreciable
overlap resulting in all three processes
occurring simultaneously within a
combustion chamber loaded with wood.
This overlap is especially significant
when a reservoir of fuel is supplied
within the combustion  space for pro-
longed burning, as often occurs in
Types of Wood Combustors
  Several  options of air flow and fuel
patterns within the stove have been
adopted in commercialized designs.
This study investigated up-draft airflow
using a  grate, up-draft  using an
impervious  hearth, cross-draft,  and
down-draft through a grate. Also studied
was a novel residential combustor
design using forced-draft, highly
turbulent  combustion  with  additional
design characteristics promoting low

 Fuel Characteristics
   Several types of wood were burned
 including commercially available air-
 dried oak cordwood, commercially
 available green pine, oven dried fir, and
 air-dried oak cut into reproducible
 triangles. The effects of piece size and
 dryness on emissions were found to be
 significant: extremely dry wood and
 small pieces resulted in high emissions
 of CO and hydrocarbons.

 Operator Techniques
   Stove operation at high burning rates
 was shown  to result  in reduced
 emissions of CO and organics as
 compared to  low burning  rates, and
 large inventories of wood in the com-
 bustion chamber reservoir also increase
 these emissions.

 Current Research Summaries
   This study i ncl uded a review of current
 research programs  related to wood
 stove emissions. Table 1  summarizes
 the programs and organizations
 performing wood combustion research
 including the emission  measurements
 discussed  in this study. There may be
 other studies unknown to the authors.

   This laboratory program included an
 investigation of the effects  of several
 independent variables on the atmo-
 spheric emissions averaged  over com-
 plete burning cycles. Emissions were
 measured for CO and a total of organic
 species as indicated by total hydrocarbons
 (THC) measured by flame ionization
 detection. For a few tests, emissions of
 polycyclic aromatic hydrocarbons (PAH)
 and benzo(a)pyrene  (BaP) were also
 measured by integrated gas chromatog-
 raphy and mass spectroscopy.
  When  burning air-dried  oak at mod-
 erate rates, >4.5 kg/hr (>10 Ib/hr),
 small differences were observed between
 up-draft burning with a grate and side
 draft burning modes in Table  2. The up-
 draft mode burning on a hearth resulted
 in  lower emissions. When the side-draft
stove was converted to the down-draft
 burning  mode, the emissions  were
appreciably lower. Emissions from the
 novel high-turbulence wood burner
were lower than those of conventional
radiant wood stoves.
  In the few tests involving  measure-
ments of specific PAH compounds from
five different conditions of burning, the
total PAH emissions varied from 11 x
10 3g/kg wood for high-turbulence
 Table 2.   Atmospheric Emissions as Measured by Flame Ionization Detection

                                 g emitted per kg wood as fired*
Burning Mode
Up-Draft on Hearth
Up-Draft with a Grate
High - Turbulence
33 to 37
200 to 400
34 to 210
4 to 110
8 to 19
32 to 42
24 to 220
5 to 56
Table 3.    Summary of Emission Control Techniques

         Factors Adversely
        Affecting Emissions
                 Approaches for
              Possible Improvements
to Existing
 Premature Pyrolysis in Wood
 Magazine Within Stove
 Pyrolysis Rate in Primary
 Combustion Area Exceeds
 Local Air Supply Preventing
 Complete Combustion
 Control of Emissions in
 Primary Burning Area
 Control of Emissions in
 Secondary Combustion Zone
 Add-on Systems Affecting
 Emissions Reduction
1.  Preventing heating of wood inventory
2.  Feed wood frequently in small amounts
3.  Use large wood pieces,  low surface-to-
   volume ratio
4.  Burn moderate moisture content wood to
   retard pyrolysis
5.  Burn devolatilized wood, charcoal

1.  Maintain high rate of primary air supply,
   with ensuing high burning rates
2.  Focus air supply into limited burning
   area to prevent widespread burning
3.  Maintain high turbulence in active
   combustion re'gion
4.  Limit quantity of fuel in active burning
   area; i.e. approach fuel-controlled
5.  Maintain high temperatures in active
   burning area
6.  Avoid sharp and/or frequent reductions
   in air supply rate

1.  Provide high level of turbulence in
   burning area to promote mixing
2.  Maintain high temperatures in burning area
3.  Provide long gas residence time at the
   high temperatures
4.  Duct pyrolysis products from magazine
   into burning area
5.  Provide down-draft combustion, with bed
   area reduction to accomodate low burning

1.  Maintain high temperatures
2.  Use heated secondary air
3.  Increase combustible content of primary
   combustion products
4.  Provide anxilliary combustion using an
   ignition source and/or supplementary fuel

1.  Use catalytic afterburner
2.  Use separately fueled afterburner
3.  Add heat storage capacity to the system,
   permitting other modifications to be
   acceptable for consumer utilization    	




























John M. Allen and Marcus W. Cooke are with Battelle-Columbus Laboratories,
  505 King Avenue. Columbus, OH 43201.
Robert E. Hall is the EPA Project Officer (see below).
The complete report, entitled "Control of Emissions from Residential Wood
  Burning by Combustion Modification,"(Order No. PBS 1-217 655; Cost: $9.50,
  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
        Research Triangle Park, NC 27711
                                                              . S. GOVERNMENT PRINTING OFFICE: 1982/559-092/3370

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