Advances in green technology
Biomass is a source of renewable energy, resulting from organic matter such as wood, plants, residues from agriculture or forestry or even municipal and industrial waste. Although biomass produces about the same amount carbon dioxide as fossil fuels, it is environmentally friendly because it is reduced, recycled and then reused. This is mainly due to the fact that the plants providing biomass are continuously replenished. Biomass can be efficiently utilised for decentralised energy production, with suitable site selection and appropriate conversion technology. In the context of BIO-STIRLING project a pilot small-scale Combined Heat and Power (CHP) plant was erected, based on a newly designed and developed 8-cylinder Stirling engine. Stirling engines are based on a closed cycle, where the working gas is alternately compressed in a cold cylinder volume and expanded in a hot cylinder volume. The heat transfer from the combustion of the fuel into the working gas is performed through a set of hot heat exchangers at high temperature. The resulting power output and efficiency is dependant on the temperature in the hot heat exchanger and for high electric efficiency the temperature should be as high as possible. The designed Stirling engine has eight cylinders arranged in two separated squares and at each cylinder corresponds one heat exchanger. The engine has been designed as a hermetically sealed unit with helium used as working gas, making it the first 8-cylinder, largest hermetically sealed, Stirling engine ever made. The Stirling engine has been running successfully, fuelled only by wood chips and wood pellets with an electrical power of 75kW. This is a major step forward for small-scale CHP plants. The engine is now going to be marketed as the best provider of power using biofuels of its kind.
