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Emissions Characterisation of residential pellet boilers during start-up and stop periods
Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.ORCID iD: 0000-0002-4308-3980
Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
2010 (English)In: 3rd International Scientific Conference on “Energy systems with IT”, Älvsjö, Stockholm, Sweden, 2010Conference paper, (Refereed)
Abstract [en]

In this study, gaseous emissions and particles are measured during start-up and stop periods for an over-fed boiler and an under-fed boiler. Both gaseous and particulate matter emissions are continuously measured in the laboratory. The measurement of gaseous emissions includes oxygen (O2), carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxide and (NO). The emissions rates are calculated from measured emissions concentrations and flue gas flow. The behaviours of the boilers during start-up and stop periods are analysed and the emissions are characterised in terms of CO, NO, TOC and particles (PM2.5 mass and number). The duration of the characterised periods vary between two boilers due to the difference in type of ignition and combustion control. The under-fed boiler B produces higher emissions during start-up periods than the over-fed boiler A. More hydrocarbon and particles are emitted by the under-fed boiler during stop periods. Accumulated mass of CO and TOC during start-up and stop periods contribute a major portion of the total mass emitted during whole operation. However, accumulated mass of NO and PM during start-up and stop periods are not significant as the duration of emission peak is relatively short.

Place, publisher, year, edition, pages
Älvsjö, Stockholm, Sweden, 2010.
Keyword [en]
Emissions, pellets, boilers, combustion, start-up, stop period, burn-out, ignition
Research subject
Energi, skog och byggd miljö, SWX-Energi, Integrerade system för sol och biobränsle
Identifiers
URN: urn:nbn:se:du-4866OAI: oai:dalea.du.se:4866DiVA: diva2:522151
Conference
3rd International Scientific Conference on “Energy systems with IT” , Älvsjö, Stockholm, Sweden, 16-17 March, 2010
Available from: 2010-06-29 Created: 2010-06-29 Last updated: 2015-12-21Bibliographically 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 2x10-13 /MJ and 4x10-13 /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
Bioenergy
Research subject
Energy, Forests and Built Environments, SWX-Energi, Integrerade system för sol och biobränsle
Identifiers
urn:nbn:se:du-20462 (URN)978-91-7485-246-2 (ISBN)
Public defence
2015-12-14, Clas Ohlson, Borlänge, 13:55 (English)
Opponent
Supervisors
Available from: 2015-12-21 Created: 2015-12-18 Last updated: 2016-03-16Bibliographically approved

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