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Particles and gaseous emissions from realistic operation of residential wood pellet heating systems
Dalarna University. (MERO)ORCID iD: 0000-0002-4308-3980
Dalarna University.
Dalarna University.
2012 (English)In: Atmospheric Environment, ISSN 1352-2310, Vol. 59, 320-327 p.Article in journal (Refereed) Published
Abstract [en]

Gaseous and particulate emissions from six residential wood pellet heating systems are determined at a realistic six day operation sequence. The study aims to investigate the total emissions from a realistic operation of the heating systems including start-up and stop phases. Five combined solar and pellet heating systems and one reference boiler without solar system with an integrated DHW preparation was tested in a laboratory at realistic operation conditions. The investigated emissions comprised carbon monoxide (CO), nitrogen oxide (NO), total organic carbon (TOC) and particulate matter (PM2.5). In this study, the emissions are presented as accumulated total emissions from the whole six days period and the emissions from start-up and stop phases are also presented separately to evaluate the influence of the emissions from these phases on the total emissions. Emission factors of the measured systems from the six day period are between 192 and 547 mg MJ -1 for the CO emissions, between 61 and 95 mg MJ -1 for the NO, between 6 and 45 mg MJ -1 for the TOC, between 31 and 116 mg MJ -1 for the particulate matter and between 2.1 × 10 13 and 4 × 10 13 for the number of particles. The emissions from the start-up and stop phases are significantly high for the CO (63-95 %) and the TOC (48-93 %). NO and particles emissions are shown to dominate during stationary operation. However, 30-40 % of the particle emissions arise from the start and stop periods. It is also shown that the average emissions of CO, TOC and particles under the realistic annual conditions were higher than the limit values of two eco labels.

Place, publisher, year, edition, pages
2012. Vol. 59, 320-327 p.
Keyword [en]
Combustion; Emissions; Pellet boiler; Pellet stove; Start-up phase; Stop phase; Wood pellet
National Category
Energy Systems
Research subject
Energy- and Environmental Engineering
Identifiers
URN: urn:nbn:se:mdh:diva-29574DOI: 10.1016/j.atmosenv.2012.05.016Scopus ID: 2-s2.0-84863482378OAI: oai:DiVA.org:mdh-29574DiVA: diva2:872361
Note

Export Date: 18 November 2015

Available from: 2015-11-18 Created: 2015-11-18 Last updated: 2015-11-19Bibliographically approved
In thesis
1. Emissions from realistic operation of residential wood pellets heating systems
Open this publication in new window or tab >>Emissions from realistic operation of residential wood pellets heating systems
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Emissions from residential combustion appliances vary significantly depending on the firing behaviours and combustion conditions, in addition to combustion technologies and fuel quality. Although wood pellet combustion in residential heating boilers is efficient, the combustion conditions during start-up and stop phases are not optimal and produce significantly high emissions such as carbon monoxide and hydrocarbon from incomplete combustion. The emissions from the start-up and stop phases of the pellet boilers are not fully taken into account in test methods for ecolabels which primarily focus on emissions during operation on full load and part load.

 The objective of the thesis is to investigate the emission characteristics during realistic operation of residential wood pellet boilers in order to identify when the major part of the annual emissions occur. Emissions from four residential wood pellet boilers were measured and characterized for three operating phases (start-up, steady and stop). Emissions from realistic operation of combined solar and wood pellet heating systems was continuously measured to investigate the influence of start-up and stop phases on total annual emissions. Measured emission data from the pellet devices were used to build an emission model to predict the annual emission factors from the dynamic operation of the heating system using the simulation software TRNSYS.

 Start-up emissions are found to vary with ignition type, supply of air and fuel, and time to complete the phase. Stop emissions are influenced by fan operation characteristics and the cleaning routine. Start-up and stop phases under realistic operation conditions contribute 80 – 95% of annual carbon monoxide (CO) emission, 60 – 90% total hydrocarbon (TOC), 10 – 20% of nitrogen oxides (NO), and 30 – 40% particles emissions. Annual emission factors from realistic operation of tested residential heating system with a top fed wood pelt boiler can be between 190 and 400 mg/MJ for the CO emissions, between 60 and 95 mg/MJ for the NO, between 6 and 25 mg/MJ for the TOC, between 30 and 116 mg/MJ for the particulate matter and between 2x1013 and 4x1013 /MJ for the number of particles. If the boiler has the cleaning sequence with compressed air such as in boiler B2, annual CO emission factor can be up to 550 mg/MJ. Average CO, TOC and particles emissions under realistic annual condition were greater than the limits values of two eco labels. These results highlight the importance of start-up and stop phases in annual emission factors (especially CO and TOC). Since a large or dominating part of the annual emissions in real operation arise from the start-up and stop sequences, test methods required by the ecolabels should take these emissions into account. In this way it will encourage the boiler manufacturers to minimize annual emissions.

 The annual emissions of residential pellet heating system can be reduced by optimizing the number of start-ups of the pellet boiler. It is possible to reduce up to 85% of the number of start-ups by optimizing the system design and its controller such as switching of the boiler pump after it stops, using two temperature sensors for boiler ON/OFF control, optimizing of the positions of the connections to the storage tank, increasing the mixing valve temperature in the boiler circuit and decreasing the pump flow rate. For 85 % reduction of start-ups, 75 % of CO and TOC emission factors were reduced while 13% increase in NO and 15 % increase in particle emissions was observed.

Place, publisher, year, edition, pages
Västerås: Mälardalen University, 2015
Series
Mälardalen University Press Dissertations, ISSN 1651-4238 ; 195
Keyword
Wood pellet, Heating, Combustion, boiler, stove, emissions, particulate matter
National Category
Energy Systems
Research subject
Energy- and Environmental Engineering
Identifiers
urn:nbn:se:mdh:diva-29582 (URN)978-91-7485-246-2 (ISBN)
Public defence
2015-12-14, rum Clas Ohlson, Högskolan Dalarna, Borlänge, 10:15 (English)
Opponent
Supervisors
Available from: 2015-11-18 Created: 2015-11-18 Last updated: 2015-11-25Bibliographically approved

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Win, Kaung Myat

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Citation style
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