Bavaria has the largest number of biogas plants in the whole of Germany. The eco-power share at the Haag power stations in Upper Bavaria is around 20 %, which is almost double the German national average. The farmers in this region have been converting renewable raw materials into gas from the mid-1990s and generating energy from maize, abattoir waste or liquid manure using on-farm combined thermal power stations. A waste product from the electricity generating process is heat. Using powerful plate heat exchangers this thermal energy can be put to use to heat nearby dwellings and production buildings.
One of the pioneers using these combined thermal power stations was the "Niedermeier Bayern BHKW GmbH" based in Wasentegernbach/Dorfen, in the Erding District. This family-run company has been in the regenerative power generation business since 1921 and reliable quality in all plant components has always been an essential factor. Every year this 10-man operation builds 20 combined thermal power stations – biogas and plant oil systems with an output of between 100 and 1000 kW, with customers being increasingly interested in the thermal utilization of the waste heat. "Bayern BHKW" uses high-performance plate heat exchangers by Kelvion to guarantee optimum utilization of the thermal energy. "We install only plate heat exchangers made by Kelvion. The quality is excellent, and they are excellent value for money. But even more important for us is the service and the short delivery times. And Kelvion can offer all of that. And the plate heat exchangers are also really compact in height despite their high efficiency. This allows us a certain degree of flexibility when we have to install a combined thermal power station where space is at a premium," says Max Niedermeier, Managing Director of Bayern BHKW. "A biogas plant is really nothing but a gigantic cow", says Alexander Niedermeier, responsible for the production processes. At the front end for example, maize is put in as a high-energy, renewable raw material that ferments and generates energy in the fermenters where liquid manure is added. And what comes out at the other end is used as fertiliser on the fields for the next harvest. An ecologically sound and economically profitable cycle. For years good money could be made with this type of practical environmental protection. Thanks to subsidies and the legally guaranteed price paid for power fed to the grid under the German EEG, the "Renewable Energies Act". And even if the Erding District is an idyllic spot where Bavaria is still typically Bavarian, these German biogas farmers are certainly not idealists, but business professionals operating under economic considerations. A biogas plant has to guarantee a profit to make farmers invest. For every kW installed (electric) a biogas plant, depending on the farmer's own investment, costs up to 4000 euros. The most popular plant size in Bavaria is around 200 kW electric. The electricity is fed into the public grid, and the power generating companies reimburse this bio-power with up to 17.5 cents per kW in line with the Renewable Energies Act. The investment has generally amortized after seven to eight years. At least this was true until 2006. But then the prices for raw materials suddenly exploded.
Supply and demand on the world market drove prices spiralling upwards. Legislators reacted with an amendment to the EEG Act to increase the guaranteed price paid for the electricity to 21.67 cents per kW/electric. The aim of the law is to encourage that the electric and thermal energy in cogeneration leads to the best possible overall efficiency. A further 3 cents are paid for every sensibly used thermal kilowatt. The law is expected to come into force at the beginning of 2009. The geostructural reality in Upper Bavaria makes it almost impossible to efficiently use thermal energy. Isolated farms, and all around nothing but countryside. And this is why a large part of the heat was simply blown off as waste air. However the aim is to utilize the heat, for example by establishing local and district heating networks. And here lies the future of combined thermal power stations.
The farmer fills the maize via a hopper into the fermenter, a kind of enclosed liquid manure trough, where the mash decomposes under the influence of natural and highly sensitive bacterial strains. Methane gas is released during this process. This gas flows through a gas drier installed downstream of the fermenter, is desulphurized and finally ends up in the combustion chamber of a powerful MAN engine. "Our drive unit of choice" says Alexander Niedermeier. The engine cooling water heated to 85 C° is pumped in counterflow through the VT 10 CDH-10 plate heat exchanger from Kelvion. Cold industrial water flows in on the other side of the plate heat exchanger. As it flows through the plates the industrial water adopts the temperature and at the same time cools the process water. Heated in this way, the industrial water flows back into the heating water circuit. The heat exchanger surface area of the 59 plates is 6.56 m2 and generates a heat output of 185 kW. This heat exchanging process is absolutely necessary to cool the engine constantly. If the heat is not dissipated, the unit would overheat and be destroyed. Farmer Anton Obermeier, whose family has been one of the biogas pioneers since 1995, operates a 125 kW plant from "Bayern BHKW" at his farm. 100 % of the electricity is fed into the public grid, and the farmer takes back 15 to 20 kW "to meet the demand for the whole farm complex", says Mr. Obermeier. He can only use 30 percent of the heat to keep the house and the farm at a cosy temperature and to keep the fermenter at a constant 40 C°, the ideal temperature for the fermentation process. Mr. Obermeier's upgraded system has been running without any problems since the end of 2006. In this period 1,277,055 kW of electricity were generated by the unit.
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