Residential Heating

Informations on residential heating

1. Current Problem

To reduce the anthropogenic greenhouse effect, which is caused by human beings’, the European Union and their member states focus on renewable energies and increase the efficiency of the use of energy. For that reason the energetic utilization of biomass took on greater significance during the last years. The combustion of chemical untreated wood in small-scale furnaces’ contributes the provision of warmth and hot water all over Europe.

Currently there is seen use in different biomass small-scale furnaces’, such as pellet-, wood chips- and logs stoves as well as different fireplace- and tiles stoves. There still dominate old plants, such as logs-stoves, which are fuelled by logs. Compared with new plants, which fulfil the latest state-of-the-art, old biomass small scale-furnaces’ emit a considerably increased amount of gas and particles. The big amount of these old plants contributes to the fact, that the emission of biomass small-scale furnaces’ beside traffic is one of the main polluter of fine dust in most European regions.

2. Advantages of regenerative energies, such as Wood.

Amongst all renewable sources of energy (excepted hydropower), biomass currently and prospectively possesses the biggest using potential for the generation of warmth and electricity. Wooden biomass is very important to that because it’s the only renewable energy source, which can absorb carbon dioxide from the atmosphere and convert it in the course of photosynthesis. For that reason biomass also contributes enormously to the world wide reduction of carbon dioxide emissions.

Biomass is also attractive to agriculture and forestry polics of European countries, because farmers can develop a market through producing combustible. Therefore he can also use withered farm land and corn fields and cultivate wood for energy instead. Based on the small energy density of biomass (compared to fossil energy sources) the regional exploitation is in the fore. Hence power generation of biomass covers the national energy requirement (small dependence on imports) contributes to a commercial reinforcement of rural areas through employment creation.

3. Physical and chemical characteristics of wood.

Wood consists of a variety of single cells. The cell wall material actually is what we name wood. The main constituents are Cellulose and Lignin. Furthermore wood contains extracts, such as gum, fats, farina, tannins as well as minerals. Hollows within the xylem often contain aqueous water solutions and gas mixtures. Generally speaking dry (water free) wood .consists of about 50% carbon, 43% oxygen, 6% hydrogen and also 1% ash forming minerals (calcium, potassium, magnesium, phosphorous, manganese, ferric, sulphuric abd so on.). The water content of wood, which is used as a fuel in biomass small-scale furnances, amounts between about 10wt% (pellets, briquettes, dry firewood) and 25 wt% (woodchips).

4. Wood Combustion

During the combustion of wood, carbon converts into carbon dioxide and hydrogen converts into water vapour. The mineral parts form the ash. A part of the contained azotic converts into gaseous nitrogen oxide emissions (NO and NO2). Inavoidable are also emissions of anorganic fine dust (predominantly potassium salts). Up to a certain extend avoidable are, by contrast, emissions, which are a result of an insufficient gas phase combustion. In this connection are carbon monoxide, organic hydrocarbons and polycyclic aromatic hydrocarbons (PAH) as well as organic fine dust and carbon black. For the maximum effect of the combustion, the smoke gases have to be well mixed with the air of the combustion and to place a long time with high temperatures at the disposal.

Modern biomass small-scale furnace’s satisfy these criteria because they are technically good developed, whereas old technologies, which are still often in use, don’t fulfill any criteria. That leads to an increasing of gaseous fine dust emission. Concerning fine dust emissions it’s important to mention, that modern small-scale furnace’s not only emit less fine dust, but also emit healthier because of the right combustion. The emission mainly consists of potassium salts and they show only a small amount of organic connections or black carbon)

5. Overview of small-scale furnaces’

Biomass small-scale furnaces’ basically fall into the following categories:

Hand charged small-scale furnaces’ and pellet stoves: small-scale furnaces’ (fireplace, chimney, storage stoves, heating stove, cooking stoves)

Advanced small-scale furnaces (central heating stoves, advanced tiled stoves or chimney stoves)

Central heating stoves: Pellet bowl, wood chips bowl und firewood bowl

The market advertises a variety of products from different producers, whereby also the technological achievements diversify strongly. Modern small-scale furnaces’ distinguish oneself through a high utilisation-comfort, a good effectiveness and low emissions

6. Summary/ Perspective of Wood combustion

Rising prices for fossile energy sources as well as national and international efforts to reduce CO2 emissions, resulted in an enhanced Use of biomass small-scale furnaces’ to warmth rooms. Compared to old furnances modern small-scale furnaces’ distinguish oneself through a high utilization-comfort, a good effectiveness and low emissions. The technical advance, which was attained in the last years, documentate a strong reduction of fine dust emissions. So one of the most important measures to reduce fine dust is to exchange old small-scale furnaces’ for new biomass heating systems.

Sources:

  • Winiwarter, Wilfried/ Schmidt-Stejskal, Hermann/ Windsperger Andreas (Hrsg.): Aktualisierung und methodische Verbesserung der österreichischen Luftschadstoffinventur für Schwebstaub. Endbericht, Wien, 2007.
  • Holzabsatzfonds. Absatzförderungsfonds der deutschen Forst- und Holzwirtschaft (Hrsg.): Moderne Holzfeuerungsanlagen, Bonn, 2004.
  • Umweltbundesamt (Hrsg.): Schwebestaub in Österreich. Fachgrundlagen für eine kohärente österreichische Strategie zur Verminderung der Schwebestaubbelastung. (Bericht BE-277, Juni 2005), Wien, 2005.
  • Brunner Thomas, 2006: Aerosols and coarse fly ashes in fixed-bed biomass combustion. PhD-thesis, book series “Thermal Biomass Utilization”, Volume 6, Graz University of Technoloy. ISBN 3-9501980-2-4
  • Obernberger Ingwald, 1997: Nutzung fester Biomasse in Verbrennungsanlagen unter besonderer Berücksichtigung des Verhaltens aschebildender Elemente, Schriftenreihe "Thermische Biomassenutzung", Band 1, ISBN 3-7041-0241-5, dbv-Verlag der Technischen Universität Graz, Graz, Österreich