Edition 03/2017

Until 2020 Denmark wants to reduce its gross energy consumption - regardless of the aspired economic growth - by 12% compared with 2006. Another goal: Until 2050 the own power and heat requirements shall exclusively be served by renewable energies, thus, becoming independent from fossil fuels in the long run. The kingdom is right out in front in Europe, with more than 80 biogas plants. In Germany, they are still discussing about “using up” the cultivated silage, whereas, in Denmark the bacteria satisfy their hunger with manure from pigs and cattle. Slaughterhouse waste and fish waste, transported by ships from Norway, is being fermented after pasteurisation in a just recently expanded plant at Herning.650 tons of manure is conveyed daily into four fermentation towers at Herning Bioenergi A/S. These towers with volumes of 2 x 3,500 m³ and 2 x 8,000 m³ produce biogas. The gas consists of 70% methane, the residual is carbon dioxide. Unlike many German biogas plants, in Herning there is no power generation by block-type thermal power stations. The biogas is not separately purified to be fed into the gas grid. Rather, Herning Bioenergi has two big direct customers who belong to Arla Foods, one global, cooperative-owned dairy company counting more than 13,500 dairy farmers from Sweden, Denmark, Germany, Great Britain, Belgium, Luxembourg and the Netherlands.The biogas plant in Herning is connect-ed with the first plant in Naviro via a 21 km long gas piping. From there, another 6 km-piping leads to the production site in Videbæk. Three block-type thermal power stations burn biogas on these two production sites. The electricity generated is used for the base load supply on site just like the heat. All three block-type thermal power stations reach a rating of approx. 3 megawatts with their combined heat and power generation (CHB). The demand of the two milk processing establishments is much higher. “As the base load is high and we have only a small part in it, we can be sure that the biogas is really needed,” explains Olav Hald, Production Manager of the biogas plants in Herning. This delivery certainty forms the basis for a continuous operation with optimum biological processes. “The produced biogas is primarily used up and fossil fuels, such as natural gas, can be procured on production basis,” says Edvin Andersen, Technical Manager of Messrs. Bigadan & Herning Bioenergi.

The biogas from Herning is conveyed by blowers made by AERZEN. In order to convey for the current application, three Delta Blowers, type GM35 S (maximum data, each 1,900 m³/h at 1,000 mbar with 90 kW drive), are needed with a medium differential pressure. “With the installed piping diameter, the biogas conveying can even be increased in future if needed. This would mean a pressure increase of up to 1,000 mbar,” explains Jörg Brockmann, Project Manager Bigadan Deutschland. The AERZEN Delta Blowers are designed for these pressure ranges. “In Herning we have to withstand a higher pressure, so that the biogas reaches at the end of the piping the gas storage facilities of the block-type thermal power stations with the required minimum overpressure. If the overpressure is too low, the block-type thermal power stations switch off.” The twelve assemblies made by AERZEN are divided in four groups of three. The first trio conveys the biogas, produced in Herning, from an interim storage facility into the piping. At the first station, the second trio takes over the supply of the block-type thermal power stations. A third stage acts as pressure increasing station for the further transport of the remaining gas to Arinco, final destination. Three AERZEN Delta Blowers are installed in a machine housing and provide the two block-type thermal power stations with the appropriate pressure.Due to the optimum provision of spare parts, Herning Bioenergi and plant manufacturer Bigadan use Delta Blowers GM35 S, despite different gas volume flows and differential pressures, for all three locations. The assemblies have been adapted to the rating required thanks to corresponding motor designs and accessories. The base configuration is identical. Thus, the local Danish biogas network does not need to be served with complete stand-by assemblies, but rather with a few stand-by stages. “These stand-by stages can be combined with all motor types. We take care of the maximum availability, without investing too much money into standy-by machines,” explains Wolfgang Ohlau, Sales Engineer AERZEN Deutschland.The demands on the availability are high. Depending on the process, the biogas plant produces around the clock. The interim storage facilities have only a limited volume. Apart from the fact that biological processes can hardly be stopped, it would mean the breakdown of the gas conveyance in the Arla factories and consequently loss of earnings for the biogas company. Herning Bioenergi relies on this income, as in Denmark exists no law which can be compared with the German Renewable Energies Act (EEG). “It is mandatory for us as plant operator to act economically,” emphasises Edvin Andersen. AERZEN ensures a high availability with long service life, as the Delta Blowers are ATEX approved and adapted to the conveyance of biogas. “The blower in biogas design consists of a housing made of special nodular iron, a ChemCoat conveying chamber coating and particularly coated rotors,” explains Wolfgang Ohlau. Prior to transport the biogas is cooled and drained in Herning. However, the biogas still contains small amounts of residual moisture and hydrogen sulphide. In case of longer standstills, the residual moisture condenses, leading to permanent damage of the blower when a special coating is not provided. “Humidity and hydrogen sulphide as acid producers is a difficult subject in this matter, but, thanks to AERZEN solution no longer a problem,” summarises Ohlau.This is why blower technology made by AERZEN is applied in Denmark. In addition, the Delta Blowers fit perfectly for the application thanks to their performance capability. “What we need is a differential pressure of one bar. We have not found a supplier besides AERZEN who can do this with a single stage. Less pressure is not sufficient for us and a multi-stage design is bad for the energy efficiency. Looking at our plants, running 24 hours a day for 365 days a year, it is essential that the blowers run efficiently,” emphasises Edvin Andersen.