Important Terms from A to Z
BtL Fuel (Biomass-to-Liquid-Fuel)
BtL fuels (biomass-to-liquid fuels) are synthetic fuels made from biomass – generally from solid biomass such as firewood, organic waste and animal meal. They belong to the second-generation biofuels. These fuels are currently not yet available on the mass market.
As a synthesis product (therefore sometimes called SynFuel) BtL fuels have the great advantage that their properties can be precisely adjusted during production and optimally adapted to modern engine designs. This allows complete combustion and therefore correspondingly lower exhaust emissions. According to currently valid fuel standards, DIN EN 228 for gasoline and DIN EN 590 for diesel fuel, these may contain BtL fuels.
One advantage of BtL fuels in relation to the first-generation biofuels is that rather than just part of the plant being used (like only vegetable oil in biodiesel, for example), the total biomass is used. As a result, the energy yields per hectare are higher than with first-generation biofuels. According to estimates by the Agency for Renewable Resources (FNR e.V.) the equivalent of around 3,900 liters of diesel fuel can be produced from the raw materials of one hectare of arable land. Thus, the yield would be more than twice as much as that of vegetable oil and biodiesel. It is estimated that up to 3.5 million hectares can be made available for the cultivation of energy crops in Germany by 2020.
As woody components can also be processed, there is a broad spectrum of raw materials that can be used as a base for BtL fuels. For example, interesting cultures include short rotation coppice (e.g. planted with willow or poplar trees) that can be machine-harvested. According to calculations by the German Energy Agency (dena), sufficient biomass could be made available in Germany to meet up to 20% of fuel demands with BtL fuels.
However, the production of BtL fuels is costlier than the production of fuels based on vegetable oils, because in BtL synthesis the biomass must first be heated to temperatures of between 200°C and 1,000°C in a gasification reactor (pyrolysis) and converted into a synthesis gas under pressure. The resulting gas mainly consists of hydrogen and carbon monoxide, but also contains carbon dioxide. This gas is then treated and liquefied, usually based on the Fischer-Tropsch synthesis principle, which was developed back in the 1920s. This complex manufacturing process is a drawback of BtL fuels and means that decentralized generation is not economical due to high investment costs for the production. Operating large plants in turn results in higher costs for transporting the biomass. The relatively high demand for process energy also has hampered the economic production of BtL fuels.
Beyond this, competition for raw materials is on the increase: Wood prices have risen sharply in recent years, which also makes it difficult to produce BtL fuels economically.
As a result, the euphoria over an imminent use of BtL fuels that was triggered by research projects after 2002 has since evaporated.