Energy Fuels 2011, 25, 307–314 Published on Web 01/05/2011
: DOI:10.1021/ef100774x
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Stove Performance and Emission Characteristics in Residential Wood Log and Pellet Combustion, Part 1: Pellet Stoves Christoffer Boman,*,† Esbj€ orn Pettersson,‡,§ Roger Westerholm, Dan Bostr€ om,† and Anders Nordin†
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† Energy Technology and Thermal Process Chemistry, Umea˚ University, SE-901 87 Umea˚, Sweden, ‡Energy Technology Centre, Box 726, SE-941 28 Pitea˚, Sweden, §Division of Energy Engineering, Lulea˚ Technical University, SE-987 78 Lulea˚, Sweden, and Department of Analytical Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden
Received June 20, 2010. Revised Manuscript Received December 5, 2010
Stove performance, characteristics, and quantities of gaseous and particulate emissions were determined for two different pellet stoves, varying fuel load, pellet diameter, and chimney draft. This approach aimed at covering variations in emissions from stoves in use today. The extensive measurement campaign included CO, NOx, organic gaseous carbon, volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), total particulate matter (PMtot) as well as particle mass and number concentrations, size distributions, and inorganic composition. At high load, most emissions were similar. For stove B, operating at high residual oxygen and solely with primary air, the emissions of PMtot and particle numbers were higher while the particles were smaller. Lowering the fuel load, the emissions of CO and hydrocarbons increased dramatically for stove A, which operated continuously also at lower fuel loads. On the other hand for stove B, which had intermittent operation at lower fuel loads, the emissions of hydrocarbons increased only slightly lowering the fuel load, while CO emissions increased sharply, due to high emissions at the end of the combustion cycle. Beside methane, dominating VOCs were ethene, acetylene, and benzene and the emissions of VOC varied in the range 1.1-42 mg/MJfuel. PAH emissions (2-340 μg/MJfuel) were generally dominated by phenanthrene, fluoranthene and pyrene. The PMtot values (15-45 mg/MJfuel) were in all cases dominated by fine particles with mass median diameters in the range 100-200 nm, peak mobility diameters of 50-85 nm, and number concentrations in the range 4 1013 to 3 1014 particles/MJfuel. During high load conditions, the particulate matter was totally dominated by inorganic particles at 15-25 mg/MJfuel consisting of potassium, sodium, sulfur, and chlorine, in the form of K2SO4, K3Na(SO4)2, and KCl. The study shows that differences in operation and modulation principles for the tested pellet stoves, relevant for appliances in use today, will affect the performance and emissions significantly, although with lower scattering in the present study compared to compiled literature data. and there are design improvements promising still lower emissions.6 It has been shown that particulate matter (PM) from well working pellet stoves are dominated by particles around 0.1 μm and contains mostly inorganic salts.7-9 There is today a strong consistency that particulate air pollution is detrimental to health, mainly based on a vast number of epidemiological studies.10 Still, no differentiation regarding noncarcinogenic toxicological potential is available concerning wood smoke particles of different chemical properties, e.g., particles containing large amounts of organic material, soot, or pure inorganic salts. It has been demonstrated that the carcinogenic effects of biomass combustion particles are very much larger if the particles contains larger proportions of organic constituents compared with particles containing mostly inorganic salts.11 Health effects other than the carcinogenic effect may also depend on the specific constituents in the wood smoke particles, although poorly studied so far.12
1. Introduction Residential wood combustion (RWC) has been identified as an important source of ambient air pollution in many urban areas.1 Wood logs are the most common fuel for current RWC appliances. Only a small but steadily growing portion of the fuel is pellets, e.g., in Sweden about 20% of fired biomass fuels in residential houses are pellets.2 All wood firing, especially in old wood log appliances, can suffer from nonoptimal conditions, resulting in considerable emissions of products of incomplete combustion (PIC), e.g., CO, hydrocarbons, and carbonaceous soot particles, giving concerns about health effects.3,4 However, modern appliances using pellets show substantial lower emissions than old wood log appliances5 *To whom correspondence should be addressed. Telephone þ46 90 7866750. E-mail
[email protected]. (1) Krecl, P. Dissertation, Stockholm University, Stockholm, Sweden, 2008. (2) Swedish Energy Agency. Report ES 2009:07, 2009. (3) Boman, C.; Forsberg, B.; Sandstr€ om, T. Eur. Respir. J. 2006, 27, 446–447. (4) Gustafson, P. Dissertation, Institute of Medicine at Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden, 2009. (5) Johansson, L. S.; Leckner, B.; Gustavsson, L.; Cooper, D.; Tullin, C.; Potter, A. Atmos. Environ. 2004, 38, 4183–4195. (6) Brunner, T.; Obernberger, I.; Scharler, R. In Proceedings of 17th European Biomass Conference, Hamburg, Germany, 2009; De Santi, G. F., Dallemand, J. F., Ossenbrink, H., Grassi, A., Helm, P., Eds.; ETA-Florence Renewable Energies: Florence, Italy, 2009; pp 1319-1328. r 2011 American Chemical Society
€ (7) Wieser, U.; Gaegauf, C.; Macquat, T. Okozentrum Langenbruck, Switzerland, 2001; http://www.bfe.admin.ch/dokumentation/energieforschung/ index.html?lang=en&publication=7221. (8) Johansson, L. Licentiate Thesis, Chalmers University of Technology, Gothenburg, Sweden, 2002. (9) Boman, C. Dissertation, Umea˚ University, Umea˚, Sweden, 2005. (10) Dockery, D. Ann. Epidemiol. 2009, 19, 257–263. (11) Klippel, N.; Nussbaumer, T. In Proceedings of 15th European Biomass Conference, Berlin, Germany, 2007; ETA-Florence Renewable Energies: Florence, Italy, 2007; paper W1612.
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Energy Fuels 2011, 25, 307–314
: DOI:10.1021/ef100774x
Boman et al.
Table 1. Characteristics of the Used Pellet Fuels
effective heating value moisture volatile matter ash C H O N Cl K2O Na2O S
unit
pellet fuel 1 (diameter 6 mm) unknown mixture of pine and spruce
pellet fuel 2 (diameter 8 mm) >90% pine and the rest spruce
MJ/kg dry weight (d wt) % % d wt % d wt % d wt % d wt % d wt % d wt % d wt % d wt % d wt mg/kg d wt
19.2 8.2 84.6 0.4 50.9 6.3 42.4
