| Abstract |
Development of a research probe for geothermal boreholes Project ZWERG in prototyping phase Benedict Holbein Karlsruhe Institute of Technology KIT, Institute for Applied Computer Science, IAI, 76344 Eggenstein-Leopoldshafen, Herrmann-von-Helmholtz-Platz-1, Germany, E-Mail: benedict.holbein@kit.edu +49(0)721/608-25765, Web: www.iai.kit.edu/geothermie The project ZWERG contains the development and testing of a modular probe for geothermal boreholes. The main target is to quickly realize new monitoring probes which allow the investigation of boreholes within their complete life-cycle. Modules to take water samples and save them under their current conditions and cameras, to name a few examples, will be usable with the probe. At the moment components and modules of ZWERG are in development and in the testing phase. Surrounding pressures of 600bar, corrosive media and temperatures around 200°C are the main difficulties for the usage of the probe in depths up to 5km. The geometrical restrictions for the usage in boreholes make the construction more difficult. Therefore a specific material search and a good working heat-management are needed. To handle the heat problem an active coolant system with a reliable insulation or the integration of high temperature components, are the both ways being followed simultaneously. First test results show that a vacuum insulation can reduce the heat input strongly. A vacuum generated in the double wall of the probe body, increased the time until reaching 70°C from 44 minutes to 13h and 21 minutes. The body was heated at 200°C from outside and the vacuum amounted 5E-4 mbar. To cope with the measuring and controlling functions a high temperature embedded system HiTES was developed. The system is based on high temperature electronic components which are working at ambient temperature up to 200°C. A first application is a BLDC servo regulator for a Maxon EC 22 HD motor. For this task the HiTES is extended by a high temperature power electronic. For the implementation of the active coolant system to conduct the heat from the inside, every component is being engineered and tested. The cooling capacity of an evaporator which has been manufactured specially is getting verified in the laboratory at the moment with acetone as refrigerant. Currently some technical details for the manufacture of the outer heat exchanger, which result from the special construction and materials, have to be clarified. It shall be integrated in the experiment next spring. A special compressor is in development phase, too. During next year, if all components are ready, the full cooling circuit shall be installed and simulated. A probe camera to take pictures in the borehole and a module for sampling geothermal water just as other modules to do measurements will be ready to use in the finished probe. With its help it will be possible to receive extensive data out of boreholes with minimal expense. This would mark a big step forward for geothermal energy supply. |