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Particulate and gaseous emissions from residential biomass combustion
Umeå University, Faculty of Science and Technology, Applied Physics and Electronics.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Biomass is considered to be a sustainable energy source with significant potentials for replacing electricity and fossil fuels, not at least in the residential sector. However, present wood combustion is a major source of ambient concentrations of hydrocarbons (e.g. VOC and PAH) and particulate matter (PM) and exposure to these pollutants have been associated with adverse health effects. Increased focus on combustion related particulate emissions has been seen concerning the formation, characteristics and implications to human health. Upgraded biomass fuels (e.g. pellets) provide possibilities of more controlled and optimized combustion with less emission of products of incomplete combustion (PIC´s). For air quality and health impact assessments, regulatory standards and evaluations concerning residential biomass combustion, there is still a need for detailed emission characterization and quantification when using different fuels and combustion techniques.

This thesis summarizes the results from seven different papers. The overall objective was to carefully and systematically study the emissions from residential biomass combustion with respect to: i) experimental characterization and quantification, ii) influences of fuel, appliance and operational variables and iii) aspects of ash and trace element transformations and aerosol formation. Special concern in the work was on sampling, quantification and characterization of particulate emissions using different appliances, fuels and operating procedures.

An initial review of health effects showed epidemiological evidence of potential adverse effect from wood smoke exposure. A robust whole flow dilution sampling set-up for residential biomass appliances was then designed, constructed and evaluated, and subsequently used in the following emission studies. Extensive quantifications and characterizations of particulate and gases emissions were performed for residential wood and pellet appliances. Emission factor ranges for different stoves were determined with variations in fuel, appliance and operational properties. The emissions of PIC´s as well as PMtot from wood combustion were in general shown to be considerably higher compared to pellets combustion. PAHtot emissions were determined in the range of 1300-220000 µg/MJ for wood stoves and 2-300 µg/MJ for pellet stoves with phenantrene, fluoranthene and pyrene generally found as major PAH´s. The PM emissions from present residential appliances was found to consist of significant but varying fractions of PIC´s, with emissions in the range 35-350 mg/MJ for wood stoves compared to 15-45 mg/MJ for pellet stoves. Accordingly, the use of up-graded biomass fuels, combusted under continuous and controlled conditions give advantageous combustion conditions compared to traditional batch wise firing of wood logs. The importance of high temperature in well mixed isothermal conditions was further illustrated during pellets combustion to obtain complete combustion with almost a total depletion of PIC´s. Fine (100-300 nm) particles dominated in all studied cases the PM with 80-95% as PM1. Beside varying fractions of carbonaceous material, the fine PM consisted of inorganic volatilized ash elements, mainly found as KCl, K3Na(SO4)2 and K2SO4 with mass concentrations at 15-20 mg/MJ during complete combustion. The importance of the behavior of alkali elements for the ash transformation and fine particle formation processes was further shown, since the stability, distributions and compositions also directly control the degree of volatilization. In addition to the alkali metals, zinc was found as an important element in fine particles from residential biomass combustion. Finally, the behaviour of volatile trace elements, e.g. Zn and Cd, during pellets production and combustion were studied. A significant enrichment in the pellet fuel during the drying process was determined. The magnitude and importance of the enrichment was, however, relative small and some alternative measures for prevention were also suggested.

Place, publisher, year, edition, pages
Umeå: Tillämpad fysik och elektronik , 2005. , 45 p.
Series
ETPC Report, ISSN 1653-0551 ; 05-03
Keyword [en]
Chemistry, aerosols, air pollution, emissions, fuel pellets, residential biomass combustion, inorganic characterization, incomplete combustion, particulate matter, polycyclic aromatic hydrocarbons, trace elements
Keyword [sv]
Kemi
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:umu:diva-501ISBN: 91-7305-871-8 (print)OAI: oai:DiVA.org:umu-501DiVA: diva2:143635
Public defence
2005-04-29, KB3B1, KBC-huset, Umeå universitet, Umeå, 10:00
Opponent
Supervisors
Available from: 2005-04-18 Created: 2005-04-18Bibliographically approved
List of papers
1. Adverse health effects from ambient air pollution in relation to residential wood combustion
Open this publication in new window or tab >>Adverse health effects from ambient air pollution in relation to residential wood combustion
2003 In: Scandinavian Journal of Work, Environment and Health, Vol. 29, no 4, 251-260 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-4499 (URN)
Available from: 2005-04-18 Created: 2005-04-18Bibliographically approved
2. Evaluation of a constant volume sampling set-up for residential biomass fired appliances: influence of dilution conditions on particulate and PAH emissions
Open this publication in new window or tab >>Evaluation of a constant volume sampling set-up for residential biomass fired appliances: influence of dilution conditions on particulate and PAH emissions
2005 (English)In: Biomass and Bioenergy, ISSN 0961-9534, E-ISSN 1873-2909, Vol. 29, no 4, 258-268 p.Article in journal (Refereed) Published
Abstract [en]

Increased concerns about particulate matter (PM) and polycyclic aromatic hydrocarbons (PAH) emissions from residentialbiomass combustion and their potential health effects, motivates detailed emission measurements under controlled conditions. Traditional sampling in raw flue gases can suffer from drawbacks mainly related to transient flows and the condensable nature of organic compounds. Whole flow dilution with constantvolumesampling (CVS) is an alternative method but different samplingconditions may, however, influence the emission characteristics. The objective was to design a CVS system for emission measurements in residentialbiomassfiredappliances and determine the influence of dilutionsamplingconditions on the characteristics and distributions of PM and PAH. Softwood pellets were combusted in a pellet stove with variations in; dilution ratio (3–7x), sampling temperature (45–75 °C), dilution tunnel residence time (2–4 s) and fuel load (2.3 and 4.8 kW) according to a statistical experimental design. The samplingconditions did not influence either the emission concentrations of PM, CO and NO or the particle size distribution. Variations in residence time had no significant effect on any studied emission parameter. However, increased concentrations of organic gaseous carbon (OGC) and PAH were observed with increased dilution ratio. The distribution between particulate and semivolatile phase was influenced for 12 of the 37 analyzed PAH compounds, mainly by increased fractions of semivolatile material at higher sampling temperature. No influence of sampling temperature was observed for the concentrations of PAHtot or the dominating PAH compounds, i.e. phenanthrene, fluoranthene and pyrene. The results together with practical considerations also suggest sampling at 50±5 °C and 3–4 times dilution as robust and applicable conditions in the presently designed setup.

Place, publisher, year, edition, pages
Elsevier, 2005
Keyword
Pellets, Emissions, Dilution, Particulates, PAH
National Category
Engineering and Technology
Identifiers
urn:nbn:se:umu:diva-4500 (URN)10.1016/j.biombioe.2005.03.003 (DOI)
Available from: 2005-04-18 Created: 2005-04-18 Last updated: 2017-12-14Bibliographically approved
3. Characterization of inorganic particulate matter from residential combustion of pelletized biomass fuels
Open this publication in new window or tab >>Characterization of inorganic particulate matter from residential combustion of pelletized biomass fuels
2004 (English)In: Energy and Fuels, ISSN 0887-0624, Vol. 18, no 2, 338-348 p.Article in journal (Refereed) Published
Abstract [en]

The increased focus on potential adverse health effects associated with exposure to ambient particulate matter (PM) motivates a careful characterization of particle emissions from different sources. Combustion is a major anthropogenic source of fine PM, and, in urban areas, traditional residential wood combustion can be a major contributor. New and upgraded biomass fuels have become more common, and fuel pellets are especially well-suited for the residential market. The objective of the present work was to determine the mass size distributions, elemental distributions, and inorganic-phase distributions of PM from different residential combustion appliances and pelletized biomass fuels. In addition, chemical equilibrium model calculations of the combustion process were used to interpret the experimental findings. Six different typical pellet fuels were combusted in three different commercial pellet burners (10−15 kW). The experiments were performed in a newly designed experimental setup that enables constant-volume sampling. Total-PM mass concentrations were measured using conventional filters, and the fractions of products of incomplete combustion and inorganic material were thermally determined. Particle mass size distributions were determined using a 13-step low-pressure cascade impactor with a precyclone. The PM was analyzed for morphology (using environmental scanning electron microscopy, ESEM), elemental composition (using energy-dispersive spectroscopy, EDS), and crystalline phases (using X-ray diffractometry, XRD). For complementary chemical structural characterization, time-of-flight secondary ion mass spectrometry (TOF−SIMS), X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) spectroscopy were also used. The emitted particles were mainly found in the fine (<1 μm) mode with mass median aerodynamic diameters of 0.20−0.39 μm and an average PM1 of 89.5% ± 7.4% of total PM. Minor coarse-mode fractions (>1 μm) were present primarily in the experiments with bark and logging residues. Relatively large and varying amounts (28%−92%) were determined to be products of incomplete combustion. The inorganic elemental compositions of the fine particles were dominated by potassium, chlorine, and sulfur, with minor amounts of sodium and zinc. The dominating alkali phase was KCl, with minor but varying amounts of K3Na(SO4)2 and, in some cases, also K2SO4. The results showed that zinc is almost fully volatilized, subsequently and presumably forming a more complex solid phase than that previously suggested (ZnO). However, the formation mechanism and exact phase identification remain to be elucidated. With some constrains, the results also showed that the amounts and speciation of the inorganic PM seemed to be quite similar to that predicted by chemical equilibrium calculations.

Place, publisher, year, edition, pages
ACS publications, 2004
Identifiers
urn:nbn:se:umu:diva-4501 (URN)10.1021/ef034028i (DOI)
Available from: 2005-04-18 Created: 2005-04-18 Last updated: 2011-01-27Bibliographically approved
4. Slagging tendencies of wood pellet ash during combustion in residential pellet burners
Open this publication in new window or tab >>Slagging tendencies of wood pellet ash during combustion in residential pellet burners
Show others...
2004 (English)In: Biomass and Bioenergy, ISSN 0961-9534, E-ISSN 1873-2909, Vol. 27, no 6, 585-596 p.Article in journal (Refereed) Published
Abstract [en]

Ash related problems have more than occasionally been observed in pellet burners during the last years. These problems can lead to reduced accessibility of the combustion systems as well as bad publicity for the market. The objectives of the present work were to; (i) evaluate how different raw materials for pellets affect the accessibility of the existing burner equipment, (ii) determine which of the ash forming element(s) that could be responsible for the deposit/slagg formation and, (iii) estimate the critical slagging temperature for the different raw materials. Stored and fresh materials from sawdust, logging residues and bark were used as raw material in three different pellet burners. The results showed that the slagging properties were relatively sensitive to the variations in total ash content and ash forming elements of the fuel. It is therefore recommended that ash rich fuels like bark and logging residues should not be used in the existing residential pellet burners. Both fuel and burner type affected the amounts of ash deposit produced. The degree of sintering (i.e. the strength of the deposits) was mostly affected by the fuel composition. Subsequent controlled sintering test of the produced deposits/slags showed critical slagging temperatures of about 850–900 °C for stored bark and about 1000 °C for fresh bark and stored and fresh materials from sawdust and logging residues. The results further indicated that the Si-content in the fuel correlated (relatively) well to the sintering tendencies in the burners. Chemical equilibrium models were used to interpret the experimental findings, and good quantitative agreements between modelling and experimental results were generally obtained.

Place, publisher, year, edition, pages
Oxford: Pergamon Press, 2004
Keyword
Deposit, Slag, Fuel pellets, Pellet burners, Combustion
Identifiers
urn:nbn:se:umu:diva-4502 (URN)10.1016/j.biombioe.2003.08.016 (DOI)
Available from: 2005-04-18 Created: 2005-04-18 Last updated: 2017-12-14Bibliographically approved
5. Gaseous and particulate emissions from combustion in residential wood log and pellet stoves-experimental characterization and quantification
Open this publication in new window or tab >>Gaseous and particulate emissions from combustion in residential wood log and pellet stoves-experimental characterization and quantification
Show others...
Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-4503 (URN)
Available from: 2005-04-18 Created: 2005-04-18 Last updated: 2010-01-13Bibliographically approved
6. Effects of temperature and residence time on emission characterstics during fixed-bed combustion of conifer stem-wood pellets.
Open this publication in new window or tab >>Effects of temperature and residence time on emission characterstics during fixed-bed combustion of conifer stem-wood pellets.
Show others...
Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-4504 (URN)
Available from: 2005-04-18 Created: 2005-04-18 Last updated: 2010-01-13Bibliographically approved
7. Trace element enrichment and behavior in wood pellet production and combustion processes.
Open this publication in new window or tab >>Trace element enrichment and behavior in wood pellet production and combustion processes.
(English)Manuscript (Other academic)
National Category
Other Natural Sciences
Identifiers
urn:nbn:se:umu:diva-4505 (URN)
Available from: 2005-04-18 Created: 2005-04-18 Last updated: 2013-04-10

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