Researchers at the Fraunhofer Institute for Environmental, Energy and Safety Technology have developed a "biobattery" in the form of a highly efficient biogas plant that can turn raw materials like straw, scrap wood and sludge into a variety of useful energy sources including electricity, purified gas and engine oil. The new plant design, currently being put to the test in a prototype plant in Germany, is said to be highly modular and economically viable even at the small scale.
The production of biogas – gas created by the breakdown of organic matter, by fermentation or through the action of anaerobic bacteria – is an interesting complement to other sources of renewable energy since it can not only generate electricity at little cost to the environment, but also create biofuel, fertilizer and engine oil. One issue, however, is that these plants only accept few organic substances as raw materials.
A new biogas plant developed at the Fraunhofer Institute could solve this problem by taking a number of materials that would normally have to be disposed of at great cost (like industrial biomass waste, sewage sludge, straw, scrap wood or manure) and process them with high efficiency into a more useful output, all through a highly modular, flexible design.
The raw materials pass through a sluice in an airless environment and into a continuously rotating screw. There the material is heated and broken down into biochar and volatile gases. The gases are in part purified and collected, and in part condensed into a liquid containing a mixture of water and high-quality oil.
The end products can be used in various ways: the oil can be turned into fuel for ships or airplanes; the gases are used to produce electricity in a combined heat and power plant; and the biochar can be used as fertilizer.
Besides the flexibility that comes from accepting multiple raw materials and producing multiple outputs, another crucial advantage to the biobattery is that, according to the scientists’ financial analysis, even a small-scale plant requiring a small investment would be financially profitable. Because of the built-in modularity, the plant could then be gradually upgraded to process more materials with higher efficiency.
The technology is being demonstrated in a pilot plant that can process 30 kg (66 lbs) of biomass per hour, and plans are being made for larger installations.
Source: Fraunhofer Institute
