Biomass as energy source

Austrian law (ÖNORM M 7101) defines "biomass" as follows: "The term biomass denotes all organic substances that are biogenic, not fossil, in nature. It includes all matter that lives and grows in nature, as well as associated waste products (deriving from either live or dead organisms)."

Put differently, biomass is chemically bonded solar energy. In the process of photosynthesis, plants use solar energy and carbon dioxide (CO2) to create organic matter. When wood, plants, and organic waste (or products derived from it) are combusted, the same amount of energy is released back into the atmosphere. In other words, the combustion process produces exactly as much CO2 as the plant has absorbed over the course of its lifespan. Biomass combustion is carbon-neutral.

Raw materials

Biomass can be solid, liquid, or gaseous. In Austria, wood is the primary source for biomass. Wood-based materials make up almost 70% of the domestic consumption of renewable energy sources (hydropower excluded). Among these materials are cord firewood, wood chips, industry residual timber, and wood pellets.

Other excellent energy sources include straw, grains, and other energy plants, as well as organic waste products (biowaste).

Chief among the liquid sources for biomass are vegetable oils (canola and sunflower) and products refined out of them (biodiesel). Biodiesel can also be produced from cooking oil and fat waste, which are collected from restaurants and private households.

Plants that are rich in starches and sugars -- such as grains or sugar beets -- can be used to produce alcohol fuels (bioethanol), which can replace fossil fuels.

Increasingly, biogas is being utilized as a viable energy source, often produced in agricultural biogas facilities. Such facilities employ anaerobic fermentation to create biogas out of wet organic waste.

Depending on the source materials, biogas comprises primarily methane (CH4) -- between 50 and 75% -- and carbon dioxide (CO2) -- between 20 and 50%. It can further contain small amounts of oxygen, nitrogen, and trace gases (e.g. hydrogen sulfide).

In addition, biogas can also be generated in sewage plants (sewage gas) and landfills (landfill gas). Even wood can be gasified at very high temperatures, thus serving as a source material for biogas production.

Energy-related applications

The solar energy stored in biomass can be deployed in many ways: to generate heat, to produce biofuels, or to create electricity.

At present, about 10% of Austria's gross energy consumption is covered by biomass technology, with heat use being the main application. Wood-fired heating systems are very popular in Austria, ranging from single ovens, small-scale furnaces (pellets, wood chips, cord firewood), and tiled stoves to large heating plants that supply heat for single buildings, or even entire district heating networks. More than two thirds of the total amount of biomass are utilized within this low-temperature sector, i.e., for the purpose of indoor heating.

However, the heat resulting from biomass combustion can also be used to produce steam that drives a turbine that generates electricity. Apart from this method, there are several other procedures to create electricity from biomass (ORC process, Stirling engine, wood gasification). All these technologies utilize a combined heat and power cycle (CHP) to produce heat and electricity.

The most cost-effective method of biomass-based electricity production is the so-called cofiring, i.e., to add the combustion of biomass to an existing power plant. This method is cost-effective mainly because it is based on the assumption that an often decades-old coal power plant can be utilized free of charge.

A significant portion of biomass is being used to produce process heat -- especially in the paper and pulp industries, as well as in the woodworking industry. The waste lye generated in the paper and pulp industries can also be deployed as a renewable energy source. In addition to bark, this type of lye (mainly consisting of lignin) is typically combusted in fluidized bed incinerators, in order to supply the facility with electricity, heat, and especially process heat.

Biogas, too, is often used to generate electricity. This allows the agricultural sector to include thousands of hectares of agricultural land in the process of energy production. Another use for biogas is fuel production. Once agricultural crude gas is refined to natural gas grade, it can be used to fuel all modern gas-powered vehicles. Currently, this eco-friendly alternative is being explored primarily in urban areas. Furthermore, refined biogas can also be fed into the natural gas network, which turns biogas into as versatile and mobile an energy source as its fossil counterpart.

The category of biofuels includes still more types: cold-pressed vegetable oils, biodiesel (fatty acid methyl ester), and ethanol fuels. While the primary sources for diesel production are canola and sunflower oils, the production of alcohol is mostly based on grains or sugar beets.

(Source: Austrian Biomass Association)