Particulate Emissions from Biomass Combustion in IEA Countries (2008)

Biomass combustion, especially in small-scale applications, is related to high emissions of particulate matter (PM) smaller than 10 microns (PM10). Since PM10 is regarded as a major indicator for the health relevance of ambient air pollution, a further propagation of biomass combustion is hindered by the disadvantage of high PM emissions. The present study gives a survey on emission factors as reported from the member countries of the IEA Task 32. To collect information, a detailed questionnaire was sent to all member countries. A total of 17 institutions from seven countries, i.e., Austria, Denmark, Germany, Norway, The Netherlands, Sweden, and Switzerland, participated in the survey. Valuable data are available for residential wood combustion, whereas data from automatic combustion plants are strongly related to particle removal equipment and national or local emission limits. Hence the results refer mainly to residential wood combustion and show that huge ranges are found for manual wood combustion devices. For existing stoves and boilers, ideal operation is regarded as a major target to reduce PM emissions. Furthermore, the method of ignition is important for the PM emissions of wood stoves and boilers. For typical wood stoves, ignition from the top of the batch of wood logs instead of ignition from the bottom can often avoid visible smoke during start-up and reduce the total PM emissions by more than 50%. For log wood boilers, beside optimised ignition and start-up, the implementation of a heat storage tank is essential, as thanks to a heat storage, part-load operation related to high PM emissions can be avoided. With respect to the measurement of PM emissions, the mass on solid particles in the hot flue gas (as collected on filters) and the additional mass of condensables need to be distinguished. Under poor combustion conditions, the mass of condensables can exceed the mass of solid particles and hence should be considered in future immission inventories.

IEA Bioenergy Task 32 "Biomass Combustion and Co-firing"
IEA Implementing Agreement "Bioenergy"