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.
The bore path was placed behind the houses on a 3 to 4 m wide public strip with a water guiding mill trench. A distance of 2 m is kept between both long distance heating pipes for the forward and reverse flow.
The head of this project Lutz Homeier comments: "An advantage of the new Grundodrill 15 N is the fact hand written logging of the bore data is no longer necessary. This is automatically stored in a data logger. The detailed evaluation can be processed after the bore process on a computer back at the office."
The bore path was chosen to allow for a flat entry and exit angle, in order not to overstrain the bending stiffness of the heating cables too much. This provided a total bore length of 228 m. The effective bore length was 180 m.
Initially the bore had to be expanded in 2 working processes to 385 mm and 485 mm diameter and cleaned, to ensure a faultless pipe installation. The pulling in process was carried out without any problems. After the installation of the first 96 m length there was a short interruption, so that the second pipe length could be welded on. After 4 hours, which were required for the welding, x-raying and subsequent insulation of the connection seams, the rest of the pipe was then pulled in. The total pipe weight was guessed at 7 t, but the maximal pulling force was only 3 t. The complete project, including the parallel bore and the other section with 2 bores each over 100 m each were completed after 12 working days.
First of all the long distance heating will be provided to the town hall, the school and the hospital, but many private consumers are already showing interest. The next step will be to connect public access outlets. The supply of long distance heating is available from April 2008 onwards.