Fine particulate filters for small combustion systems: Glass wool makes chimneys clean

Small combustion systems such as stoves as well as pellet and woodchip burners are a valuable contribution to climate protection, because they replace fossil fuels used for space heating. However, these systems also come with a big disadvantage: They blow up to 25,000 tonnes of particulate matter into the air every year and are a danger to both the environment and to health. Researchers under the Technology of Fuels Unit (TEER) at RWTH Aachen University have developed a filter made of glass wool, which allows chimneys to work cleanly.

In Germany alone, there are an estimated 10-15 million stoves and 600,000 pellet and woodchip burners. Some 20 per cent of private households are heated using wood. Since the 1st of January 2015, a new legal limit has been set in order to limit the PM (particulate matter) emissions from these systems.

Up until now, the crude gas contained between 50 and 150 milligrams per cubic metre (m3), depending on the type of combustion system. The values for hand-fed combustion systems are even higher in part. According to the new law, only 20 mg (boilers) or 40 mg (stoves) are permitted. Time is of the essence: because the law is already in force, existing systems have to be converted quickly. The team led by Prof. Peter Quicker from the TEER unit at RWTH Aachen has now developed a filter that can reduce PM pollution in crude gas by up to 99 per cent.

Engine for progress:

  • contribution to clean combustion of renewable raw materials
  • filtration efficiencies of up to 99% for particulate matter
  • cheap, easily retrofitted, low-maintenance
  • improve air quality through PM reduction
  • the product should reach market maturity by 2016
  • savings of 2,000 tonnes of CO2 per year

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Photo: TEER

Many different natural fibres have been tested as possible materials for the PM filter.

Glass wool as an ideal material

Cotton, hemp, linen, merino wool – Quicker's team examined many natural fibres in order to find the best material. But these fibres could not withstand the harsh conditions in thermal tests at up to 230°C. The newly developed PM filter is made of glass wool. "Glass wool has the advantage of being heat resistant, cheap and moisture-resistant," explains Quicker. Furthermore, the fibre structure is designed so that the few micrometres (0.1 - 10 micrometres) of particulate matter particles are very well absorbed. "We can achieve a filtration efficiency of 99 per cent, which means that less than one milligram of PM per cubic metre remains in the waste gas," explains Quicker. Whereas, in the case of other filtering systems the filtration efficiency can vary greatly, very consistent and therefore reliable values can be achieved with the glass wool filter.

Long-term test examines suitability in practice

The research team have now developed a chimney attachment with glass wool. Retrofitting is easy and maintenance is uncomplicated. The filter does not have to be cleaned. Instead, it can simply be replaced as soon as it is "full". Ideally, this should happen at most once a year. "This is exactly what we wish to examine now in a pilot test," says Quicker. Soon, ten test systems are to be installed on Aachen chimneys and are expected to confirm the positive lab results in the long term.

Photo: Prof. Peter Quicker

"Small biomass combustion systems are now the main sources of particulate matter emissions. The particularly small particle size is problematic and represents a considerable risk potential. In order not to counteract the benefits of bio-energy for climate and resource protection, efficient and economically feasible filtration solutions are essential!"

Prof. Peter Quicker, Field of Teaching and Research: Technology of Fuels (TEER), RWTH Aachen

Partners and sponsors

  • RWTH Aachen, Lehr- und Forschungsgebiet Technologie der Energierohstoffe (TEER)
  • Dezentec ingenieurgesellschaft mbH
  • Oberland Mangold
  • Bundesministerium für Ernährung und Landwirtschaft (BMEL)