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Solids, like biological waste and green waste will be transported to a bunker for material in a reception hall. From there the solids will reach the main fermenter by walking floor and screw conveyors. Tank cars deliver liquid material, e.g. liquid manure and dairy products, to a collection tank. Feeding pumps pump the liquid material into the main fermenter. |
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The main fermenter is a cylindrical, monolithic reinforced concrete tank, which is heated by coiled pipes and covered by a double membrane roof. The double membrane roof is used for storage as well as sealing off the inside of the fermenter from outside air.
Two submersed motors and one long shaft big wing stirrer are located in the main fermenter. The agitators mix the tank capacity, with a dry matter content of approximately 12%. The heating coils heat the tank capacity up to 38 – 40 °C. The bacteria of the substrate mixture cause a transformation of carbohydrates, fats and proteins to biogas which consists of 50-60% methane and 40-50% CO2. The feeding of solid substrates happens continuously. After a retention time of 20 – 30 days the mixture of substrates arrives to the post fermenter by an overflow.
The second fermenter has the same characteristics as the main fermenter. In this fermenter, a further transformation of carbohydrates, fats and proteins to biogas takes place. After a retention time of 40 – 70 days the mixture of substrates leaves the fermenters. The mixture has then to be stored for a legal compulsory time in order for the spreading of the material on the fields to be allowed. The end substrates are a high-quality fertilisers and nearly odourless.
The biogas stored in the double membrane gas storage will be transpoted to a Combined Heat and Power system (CHP) to generate electrical power and heat in a gas-otto-motor. For interruption time and maintenance work, an emergency flare is installed which burns the biogas. The cooling water with about 95°C serves for heating the fermenters and could be used if possible in a district heating network. Engine exhaust gases with about 400°C could be transformed to steam heat up, thermal oil or even hot water. On customer’s request end substrates can be separated into liquid and solid share by a centrifuge. The solids can be composted, the liquids can be evaporated and after vapour condensation recovered as distilled water. Likewise processing with ultrafiltration and reverse osmosis is possible.
The control system of the Brückner Biotec biogas plant requires special mention:
It is a platform of communication with the plant. In time the control system informs the operators about all important changes of the operating status and supports the operator by automatic control functions. The control system records all important process sequences and facilitates a safe and optimal course of the fermentation process. |
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