Material for one of the biggest Biogas Plants

The first units are due to start operation in August. The 13-hectare biogas park is being built by WELtec BioPower in the town of Könnern, population 8,000, near Halle. The special feature of this eco-friendly project is an innovative treatment process that allows the biogas to be fed directly into the natural gas grid. The heart of a biogas plant is the so-called digester, in which the biological reactions take place. As the very aggressive gas attacks many materials, WELtec BioPower is using stainless steel for tanks and internal components. The material for the core elements of the plant, the 16 digesters, was supplied by ThyssenKrupp Nirosta.

Nature meets technology: After full commissioning in 2009, the new biogas park will process around 120,000 tons of liquid manure and maize delivered to the site by 30 local farmers. It will use special bacteria to produce around 30 million cubic meters of raw biogas per year. This will be turned into approx. 15 million cubic meters of biomethane by an innovative process and then fed into the natural gas grid, providing enough energy to heat roughly 10,000 homes for a year. The energy stored in the methane will thus be optimally utilized. Biomethane production is also CO2-neutral, an additional benefit for the environment. The remaining part of the biogas will be converted into electricity.

The central elements of the plant are the 16 digesters, huge tanks 6.30 meters tall and 25 meters in diameter. During biogas production, undesirable components such as sulfur and ammonia are also formed. “These components are very corrosive, placing high demands on the material for the digesters. That’s why we use stainless steel exclusively for our plants,” explains Hajo Schierhold, head of sales and marketing at WELtec BioPower. “Comparable solutions using concrete or enameled steel are either too prone to corrosion or much more expensive.”

WELtec BioPower’s sole supplier of stainless steel is ThyssenKrupp Nirosta. In the past two years the company has supplied a total of 1,500 tons of material for various projects carried out by the Vechta-based plant builder. Depending on the loading, different stainless steel grades are used, e.g. for the tank walls in contact with the liquid or gas. “The majority of our deliveries have been our standard sheet steel Nirosta 4301,” reports Martin Stöckl from the ThyssenKrupp Nirosta sales team. “What’s particularly important for WELtec BioPower is the cold-worked condition, 2H. This means that thinner steel can be used to build the digesters without any loss of strength and stability. It also means a significant cost saving.” Another advantage is the extremely smooth surface. “The dense surface of Nirosta 4301 2H gives aggressive substances no opportunity to attack the material,” says WELtec BioPower sales chief Schierhold. “Bacteria have no chance to take hold, so corrosion is nipped in the bud, which is an important factor for longevity and efficiency.”

Following the amendments to the Renewable Energies Law that came into force on January 1, 2009, the number of eco-friendly biogas plants is set to increase further. The biogas trade association (Fachverband Biogas) forecasts that a further 780 biogas plants with an installed electrical capacity of at least 200 megawatts will be built this year, taking the total number of plants in operation by the end of 2009 to 4,780, capable of supplying electricity around the clock to over three million homes.

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