aquatherm delivers the right solution for an European pilot project
On 15th June 2005, the Arnsberg (North Rhine-Westphalia/Germany) municipal utilities already started with the ambitious project engineering of a geothermal deep drilling. At the time of planning, the deepest drilling throughout Germany should bring in a maximum return of energy by using energy-efficient components, thus letting Arnsberg appear as a lighthouse of municipal energy economy. It was and is the aim of the drilling to produce 2.1 million kWh per year, which was to cover a large part of the heat load of the local “Nass” pleasure swimming pool. The functional principle is relatively simple: Cold water is transported into a big depth in a closed system by the consumer (here: the pleasure swimming pool). On the way down, the medium absorbs the ambient heat of the rocks. Geologists assume an increase of temperature of approx 3°K per 100 m. 83°C were measured at the bottom of the 2,835 m deep drilling in Arnsberg. The heated water is then to be returned to the surface without any heat loss. The heat is there extracted from the water by the consumer which is then conveyed into the depth in a cooled condition again. After having provided and started the drilling, this form of energy production is not only economical and climate-friendly, but also covers basic loads by the continuous operation, contrary to solar or wind energy. The deep geothermal drilling planned in Arnsberg was already realized in March 2008. However, the efforts of a high energy-efficient extraction failed because of the deep geothermal inliner (return pipe) made of glass fiber reinforced duroplastic (GFK) planned at that time. The GFK double wall pipes intended by the project engineer did not resist the loads, therefore alternatives and innovations were looked for all over the world. For this plan which can be considered to be a prestige project, a deep geothermal probe had to be developed that can be proved to resist the static loads occurring during the installation in a 2,835 m deep drilling and to show optimal thermal properties during later operation.
In a comparable project, the “Super C” deep drilling of RWTH Aachen / Germany (technical university with very high, international reputation), pilot tests with a polypropylene pipe were carried out some years ago. At that time, the tests failed because of the extremely high tensile and pressure forces occurring during installation, which could not be absorbed by the PP used. Despite of the highly scientific competence, the deep drilling is not in the planned condition of operation to this day. We became aware of the problem in Arnsberg by the media and directly got in touch with the local authority and the drilling firm Daldrup & Söhne (Westphalia), always being convinced to find a solution with our experience and technical thinking. After the result of development, an absolute world first, had positively passed various tests at the institute for crude oil and natural gas technology of the Clausthal technical college, the composite pipe was presented to the Arnsberg municipal authorities. The composite pipe consists of a steel pipe (outer pipe) and an aquatherm PP inliner. By that it will be ensured that both mechanical and energetic requirements will be met. Exemplarily, the PP pipe’s behavior was tested in an autoclave (pressure-temperature chamber) at a temperature of 95°C and a pressure of 320 bar. These are real conditions at the bottom of a deep drilling. The project team now assumes that the installation works will still be finished this year and then deliver heat energy for the “Nass” pleasure swimming pool nearby. The project is pioneering for deep geothermics. Numerous other projects will profit from the findings that are gained in Arnsberg; and that not only in Germany, but worldwide.