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Wood energy utilization - a case study

In the past few years, considerable progress has been made in the development of small- and medium-scale wood-based energy plants in Austria. The demand for wood originating from thinning operations has been shrinking over the last decades owing to a steady decrease in the number of households using wood energy and also to low prices for this wood. This has encouraged research institutes, agencies and individuals to focus on improvement of technology in wood-based energy production. The focus has been on the development of small- and medium-scale energy plants, rather than on the smallest plants heating a single house, because of the high investment involved and in order to make the use of wood energy as cost-effective and reliable as that of fossil fuels such as oil and gas.

FAO, therefore, intends to carry out a case study in cooperation with a private enterprise in Austria in order to collect data and analyse the technical, economic, environmental and socio-economic aspects and issues of the whole process of fuelwood production, harvesting and utilization of a typical geographical area where wood is used as a source of energy; this could serve as an example for Eastern European and developing countries of the wise use of renewable energy sources. (Contributed by: Norbert Winkler, Consultant on Environmental Impact Assessment, Forest Harvesting, Trade and Marketing Branch (FOPH), Forest Products Division, FAO.)

For more information please contact: Mr Rudolf Heinrich, Chief, Forest Harvesting, Trade and Marketing Branch (FOPH), Forest Products Division, FAO, Viale delle Terme di Caracalla, 00100 Rome, Italy.
Fax: +39 06 5225 5618;
e-mail: Forest-Harvesting@fao.org

[More information on this case study will be given in the next issue of Forest Energy Forum.]


Domestic heating

Owing to the nature of its landscape, Austria has always been a land of forests, which still cover 40 percent of its area. This is the result of a foresighted policy which introduced legislation ensuring a sustainable use of Austrian forests at the turn of this century.

Since the mid-1970s, a remarkable revival of wood as an energy source has taken place. Within 15 years, its contribution rose to about 12 percent of national primary energy use. Together with the use of hydropower, Austria is able to derive a quarter of its energy demand from renewable resources.

The most significant contribution to renewable energy use in Austria comes from domestic heating with logwood. Since 1990, a marked decline in wood use for domestic heating can be observed as a result of the replacement of wood stoves and old wood boilers with central heating systems based on natural gas and oil.

The reversal of this trend towards the increasing use of modern wood boilers is the greatest challenge for Austria's renewable energy policies at present. It is particularly difficult as the switch to other energy carriers is partly due to the decline of traditional lifestyles that involved producing fuelwood privately in the forest. Thus the effects of lifestyle changes must be offset by new strategies and services that make heating with wood attractive to young people who give comfort a high priority in the choice of heating systems.

Financial incentives have been established in a number of provinces in order to stimulate the installation of modern wood boilers. Complementary actions will be necessary to enhance fuel supply services, distribution networks and maintenance services.

The most convenient option for domestic heating with wood is district heating. More than 350 small-scale biomass district heating plants have been established for this purpose, mostly in rural areas. (Source: Energy from Biomass - Research and Development in Austria, a brochure prepared by the Austrian Federal Ministry of Science and Transport.)

For more information, please contact: Dipl. Ing. Brigitte Weiss, Bundesministerium für Wissenschaft und Verkehr, Minoritenplatz 5, A1014 Vienna, Austria.
Fax: +43 531 20 6480;
e-mail: brigitte.weiss@bmwf.gv.at


Decentralized biomass combined heat and power plant technologies

Potential applications, technological and economic evaluation

Scientific studies and the successful implementation of electricity generation projects in the low power range realized during the past years, as well as changing economic conditions for decentralized combined heat and power plants using biomass, have greatly improved the situation of electricity generation from biomass.

Decentralized thermal use of biomass is of great importance in Austria. In addition to small- and large-scale plants in the paper making and cellulose industries, as well as in wood processing plants, biomass district heating installations with a rated output of 0.5 to 10 MWth constitute an important factor in the supply of energy. During the past ten years, the biomass district heating systems' sector experienced annual increases of more than 10 percent. By the end of 1997, 359 plants were already in operation.

However, at present, electricity from biomass is generated at only about ten locations in Austria in major plants operated by the paper making and cellulose industries (with bark and waste lye as fuel) and in about ten small and medium-sized plants of the wood processing industry.

Biomass district heating plants currently only produce heat. On account of the abundance of forest in Austria and a highly decentralized demography, energy supply concepts based on decentralized biomass combined heat and power (CHP) plants seem to be particularly advantageous.

Some of the reasons for the slow implementation of such concepts are:

Over the past few years, there has been an emphasis on the development and further improvement of technologies for electricity generation in the 2 MWel power range, which seems to be promising for the use of biomass in CHP plants. Plants of this type should be operated predominantly on a thermal basis in order to achieve a high total rate of efficiency. As potential operators of such plants usually have only limited financial and personnel resources, these projects should fulfil the requirements of robustness, flawless operation, and controllability or automation, respectively.

The study, Decentralized Biomass CHP Technologies, which was commissioned by the Austrian Federal Ministry of Science and Transport and carried out by Ingenieurbüro BIOS Obernberger & Narodoslawsky OEG, Graz, in cooperation with the Energieverwertungsagentur Wien, evaluated and compared such concepts from a technological point of view (operation, control technology, maintenance, ecological aspects, state of development). In addition, a detailed economic evaluation of technologies, which are either already standard practice or will soon be marketable, has been conducted.

At present, there are two marketable technologies for electricity generation from solid biomass: the steam turbine and the steam piston process. Three other technologies, i.e. the steam screw engine, the Stirling engine process and the ORC-process, have already reached a high state of development and are on the verge of marketability. Solid-bed and fluidized-bed combustion with gas engine or gas turbine can also reach this state of development as soon as the problem of process gas purification is solved efficiently on the basis of practicable concepts. In addition, two other innovative technologies are being developed: the direct (inverse) gas turbine process and the indirect gas turbine process (hot air turbine process).

All the technologies that have been evaluated still show a great potential for economic and technological development. Therefore, the concepts involved also incorporate a certain potential as to the increase in efficiency and a reduction of costs. (Source: Home Page of Forschungsforum, Energy Environment Transport, Division of Energy and Environmental Technologies, Austria; www.bmwf.gv.at/6extern/forschungsforum/titel_e.htm)


Solar energy and biomass - a good combination

Much research has been dedicated to the possibility of storing solar energy in the summer for use for residential heating in the winter. In a way, biomass is also a seasonal store of solar energy; however, its heat storage density is about 50 times higher than that of water storage. Thus solar energy and biomass are a good combination as they offer the most economical way to realize 100 percent of renewable energy supply for domestic heating and hot water.

The most economical and effective system to achieve a full solar heating system for single family houses at present is the combination of a logwood boiler, a water tank (2-3 m3) and thermal solar collectors. In the summer, the solar system provides hot water and stores it in the tank; in the autumn and spring, the solar system can also provide heating (depending on its size), whereas in the winter the biomass boiler uses the heat store, which allows full power operation of the boiler and continuous heat retrieval at any required load.

The most advanced project of low-energy, full solar housing is the Sundays project in Gleisdorf. This combines a number of innovative achievements at a total construction cost of about ECU 1 300/m2 of living area. Owing to high installation standards and passive solar energy features, the total energy consumption in one year is 32 kW/m2 (a typical value for a new single family house is 100 kW/m2). This energy is provided by a combined solar energy and biomass system. The Sundays project is constructed of innovative solid wood panels and even the insulation is made of a new, wood-derived product. Thus the household does not produce any net CO2 for heating and acts as a carbon sink. It will be available on the market as a standard prefabricated house at a competitive price. (Source: Energy from Biomass - Research and Development in Austria, a brochure prepared by the Austrian Federal Ministry of Science and Transport.)

For more information, please contact: Arge Erneuerbare Energie, Feldgasse 19, A-8200 Gleisdorf, Austria.
Fax: +43 3112 5886 0;
e-mail: office@aee.at


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