June 2008 -- The company E.ON Westfalen Weser Energie-Service GmbH, Kirchlengern, had the task of building a biogas plant in the lower Saxon region of Hessisch Oldendorf in Germany for a town with approximately 20,000 inhabitants on the Weser River. The plant will produce 11 million kilowatt hours of power annually; 13,000 t of corn and 3,000 t crop, as well as liquid manure, lopping and kitchen waste are required each year.
The waste heat caused by the power production is intended to be fed into a long distance heating network. The warmed up water will reach the end consumer at a temperature of approximately 70°C and flows back to the biogas plant at approximately 40°C. Powerful pumps keep the water circuit flowing. On the way to the end consumer, any heat loss must be avoided. Therefore insulation and a network control are decisive factors for the pipe system to be installed.
Bonded outer pipes from the manufacturer Isoplus from Rosenheim were installed for the forward and reverse flow. Inside the 280 mm PE outer pipes the 168 mm OD medium pipes, made of steel, were bedded inside a hard foam layer to provide heat insulation. Control veins were integrated inside the insulation, which react to any leakages. The long distance heating pipes are suitable for operating temperatures of up to 155°C and an operating pressure of up to 25 bar.
About 2 km of the total 2.5 km bore length have already been installed from the biogas plant to the town with the open trench method. In compact areas it is virtually impossible to use this method.