International seminar on 


Friday, March 18, 2005

Graz, Austria


Combustion of solid biomass offers the highest short-term potential for significant CO2-reduction in energy production of all renewable energy technologies in a cost-effectve manner. Comprehensive R&D work carried out during the last decades has already led to a state-of-the-art which allows a highly efficient combustion of a wide range of solid biomass fuels at high plant availabilities as well as low gaseous emissions. 

However, several problems related to the formation of fine particulates during combustion, so called aerosols, are still unsolved. These problems affect both, the plant operation itself due to the formation of deposits and ash mixtures with comparably low melting temperatures as well as particulate emissions. Therefore, a considerable number of research projects has been initiated to find solutions for these technological problems. Aerosol immissions as well as their impact on the human health are nowadays intensively investigated and discussed. 

Against this background and to present and discuss on-going research, IEA Bioenergy, Task 32, "Biomass Combustion and Co-firing" in co-operation with the Austrian Bioenergy Centre and the Graz University of Technology have organised an international seminar "Aerosols in Biomass Combustion". The seminar presented, discussed and assessed the actual state-of-science in this field and provided information about non-technical issues especially related to legislative regulations, aerosol immissions and health effects of fine particulate immissions. Approximately 70 researchers, furnace and boiler manufacturers, filter manufacturers as well as utilities, plant operators, energy agencies and public authorities participated in the workshop.


One should clearly distinguish between old and new biomass combustion devices. This is of special importance if small-scale units are considered because new biomass furnaces achieve an almost complete burn-out, which substantially reduces the amount of organic aerosols formed.

Due to the fact that old small-scale biomass combustion plants emit significantly larger amounts of aerosols (due to incomplete combustion) than new systems, aerosol emissions from biomass combustion could be substantially reduced by replacing old with new automatically operated small-scale biomass combustion devices or at least by improving the operation of old systems (e.g. by the installation of storage tanks).

Inventories concerning aerosol emissions and immissions need actual and secured data. New data con­cerning aerosol emissions from biomass combustion (based on measurements per­formed within ongoing R&D projects) should therefore be supplied for new as well as old combustion devices as well as concerning the actual ratio between old and new systems installed in a certain country. These data are of great relevance in order to achieve correct calculations and evaluations regarding the influence of aerosols from biomass combustion on the overall emission and immission situation.

Regarding health effects of aerosols from biomass combustion, first studies are ongoing but there is still a long way to go in order to understand which influencing variables are of rele­vance (e.g. particle size, chemical composition). Besides cell tests also inhalation tests will be necessary to evaluate health effects properly.

First sets of release data, describing the amount of aerosol forming species released to the gas phase during combustion, are available for pulverised biomass fuels as well as for grate com­bustion systems and will also be further investigated. These data are of great relevance for aerosol formation as well as for subsequent deposit formation modelling.

Aerosol formation models for biomass combustion systems have already achieved a high level of development and will be further improved within the next years. These models are of great relevance to understand aerosol formation pathways as well as relevant influencing variables.

Moreover, relevant investigations regarding the influence of aerosols on deposit formation have been performed and have shown that aerosols can strongly influence the ash melting behaviour of deposits due to the formation of salt mixtures with low melting points.

New small-scale aerosol precipitation devices are under development. Tests with prototypes have started but these technologies are not yet commercially available.

Medium and large-scale biomass combustion plants (nominal boiler capacity > 500 kWth) can precipitate aerosols well if appro­priate filters are installed. An efficient aerosol precipi­tation can be achieved by electrostatic precipitators as well as by baghouse filters.



The proceedings of the Aerosol Workshop have been published as a separate book (Volume 6) in the Thermal Biomass Utilization book series of BIOS Bioenergy Systeme. Orders can be directly made through BIOS.



Most of the presentations held at this workshop can be downloaded below. 




Welcome address

I. Obernberger, Graz University of Technology (A)

S. van Loo, IEA Bioenergy, Task 32 (NL)

E. Fercher, Austrian Bioenergy Centre (A)


Fly ash and aerosol formation in biomass combustion processes – an introduction

I. Obernberger, Graz University of Technology (A)

Session 1: PM immissions and health effects 

Chairman: S. van Loo, IEA Bioenergy Task 32 (NL)


Co-ordinated international activities to abate European PM emissions

W. Winiwarter, ARC systems research (A)


PM imissions in Austria – 2000 to 2004

J. Schneider, Department of Air Quality Control (A)


Coffee break


Health effects of ambient aerosols

H. Hauck, Austrian Academy of Sciences (A)


Health relevance of aerosols from biomass combustion in comparison to diesel soot

N. Kippel, Verenum Zürich (CH)



SESSION 2:Aerosol formation and behaviour in biomass combustion processes 

Chairman:C. Tullin, SP (S)


Release of aerosol forming species during combustion in pulverised fuel systems

R. Korbee, ECN - Energy Research Centre of the Netherlands (NL)


Release of aerosol forming species in fixed-bed systems

Flemming Frandsen, Technical University of Denmark (DK)


Modelling of aerosol formation

M. Joeller, Graz University of Technology (A)


Aerosol and particle transport in furnaces

H.P. van Kemenade, Technical University Eindhoven (NL)


The influence of aerosol particles on the melting behaviour of ash deposits in biomass fired boilers

R. Backman, Umea University (S)


Coffee break

SESSION 3:Aerosol emissions and emission control 

Chairman: I. Obernberger, Graz University of Technology (A)


Automated analyses of aerosols formed during biomass combustion by SEM/EDX

S. Mitsche, Graz University of Technology (A)


Particle Emissions from residential biofuel boilers and stoves

C. Tullin, Swedish National Testing and Research Institute (S)


Fine particle emissions from fluidised bed combustion of peat and wood

V. Linna, VTT Processes (FIN)


Exhaust gas cleaning for small wood fired appliances – recent progress and field test results

V. Schmatloch, Swiss Federal Institute for Materials and Testing (CH)


Particle precipitation in medium- and large-scale biomass combustion plants

T.Brunner, BIOS Bioenergysysteme GmbH (A), M. Lixl, Scheuch GmbH (A)


Summary and Conclusions


This workshop was organised by Prof. Dr. Ingwald Obernberger on behalf of


Institute for Resource Efficient and Sustainable Systems

„Thermal Biomass Utilisation"

Graz University of Technology

EU-Project SES6-CT-2003-502679 - BIOASH