Empa develops a particle separator for small wood-burning fires

Combating unhealthy smoke from the fireplace

Sep 29, 2004 | MARTINA PETER
Fireplaces and heating ovens are becoming ever more popular in Swiss homes. However, the smoke from small wood-burning fires contains soot particles which are damaging to human health. This fine particulate matter can be greatly reduced by the use of a particle separator developed at Empa. Recently the device was presented to representatives of public environmental authorities.
Heating houses with a cosy wood fire is both economic and a sustainable use of resources. The locally produced raw material is replaced by regrowth, is available in plenty and is CO2 neutral. When wood is burned, only as much carbon dioxide is generated as was extracted from the air by the tree during its lifetime. A wood fire not only warms the sitting room and the cockles of one’s heart, it also soothes one’s conscience! This year there were about 600,000 small wood burning fires in Swiss households, principally fireplaces and tiled heating stoves. The trend is upwards, but it is easy to forget that the popular and exemplary energy converter also has a «dirty» side. Wood smoke contains soot particles which are only about 100 nanometres (or one ten thousandth of a millimetre) in diameter and which penetrate very deeply into the lungs when inhaled. High concentrations of this so-called PM10 fine particulate causes bronchial and circulatory illnesses in humans.


False assumptions

The emission of fine particulate matter from various sources has been the subject of study at Empa for several years. In the perception of the general public, diesel motors have been the biggest culprits to date. But while they have been subject to concentration limits for a long time now, and even tighter controls are already in the pipeline, there are no such limits applied to emissions from fireplaces and other wood burning ovens. New data shows, however, that today in certain locations a major part of the fine particulate matter in the air is due not to diesel exhaust but to emissions from small wood burning fires. In residential areas and during the winter months this proportion is particularly high.


Electrically charged soot particles

A technical solution has been developed at the Empa with support from the Federal Office of Energy and Swiss Agency for the Environment, Forests and Landscape (SAEFL). The particle scrubber removes soot from the smoke using the principle of electrostatic separation. A high voltage is applied to a thin wire placed in the chimney, which charges the soot particles in the ascending smoke. They are then attracted to the inner surface of the metal chimney tube where they remain stuck, in much the same way that dust sticks to a computer monitor screen. The use of this method enables about two thirds of the soot to be removed from the smoke.
Recently the Empa Academy, in collaboration with SAEFL, organized an information day on the reduction of fine particulate emission by wood burning ovens to which representatives of the local, cantonal and federal environmental authorities were invited. The Empa introduced the prototype version of the new particle separator, which it intends to further develop into a cheap mass-produced item within the next two years.


For more technical information:

Christian Bach, Combustion Engines Internal Laboratory, Tel. +41 44 823 41 37,


Matthias Kündig, Logistics, Controlling, Marketing Tel. + 41 44 823 43 96,
Remigius Nideröst, Logistics, Controlling, Marketing , Tel. +41 44 823 45 98, remigius.nideroest@empa.ch