May 28, 2024
Source: Energy & Management Powernews
Researchers at Fraunhofer IEG are testing a new micro-borehole turbine in Switzerland. This should make it possible to create heat storage facilities at more locations.
In future, the underground should store waste heat from commercial operations in summer so that it can be used to heat homes in winter. The regional Swiss energy supplier "Energie Wasser Bern ewb" is developing the "Geospeicher" pilot project at its Forsthaus energy center. It is intended to store surplus heat and use it in the winter months. Researchers from the Fraunhofer Research Institution for Energy Infrastructures and Geothermal Energy IEG are also on board. This is because the development of underground heat storage requires new drilling technology.
By using the innovative "Micro Turbine Drilling - MTD" drilling method, the Fraunhofer IEG was able to successfully create pathways for water in rock layers up to 500 meters deep, the institute announced on 27 May. The drilling activity was part of an ongoing development under the Swiss capital Bern, which is to be expanded into a heat storage facility in future project phases.
The turbine can be used from conventional boreholes to drill radial side arms. In this way, it increases the inner surface of the borehole system in a controlled and reliable manner and specifically increases the permeability for the working medium water.
Further information on the topic of heat storage:
Cluster-Treff Wärmespeicherung für Industrie und Stadtwerke - Technologien und Anwendung
Storing heat for the winter
At the Forsthaus energy center, ewb operates a waste recycling plant, a wood-fired power plant and a gas and steam combined-cycle power plant. These plants generate electricity and heat. The heat produced is fed into the district heating network. In summer in particular, the heat from waste incineration cannot be fully utilized. In winter, however, this heat would be in high demand.
This is where the "geothermal storage" pilot project comes in. In summer, the storage rock at a depth of up to 500 meters is to be heated with excess waste heat from the energy plants. The sandstone underground would be heated with water at 90 degrees, like a tiled stove. In the winter months, the energy stored in the rock could then be recovered using water as a working medium at around 60 degrees Celsius and fed back into the district heating network. In this way, the project partners hope that the energy supplier could build up a seasonal energy supply of 12 to 15 gigawatt hours of heat in the future.
Drilling to provide important findings
Three main boreholes have now been drilled to a depth of 500 meters, according to the Fraunhofer Institute. At this depth, the project has discovered the coveted sandstone in several layers. However, the rock layers are more compact than hoped and the achievable circulation of water is therefore not high enough. This is where the new turbine comes into play.
In order to improve circulation, the Fraunhofer IEG team has now drilled further pathways for the water using its new MTD technology. A compact micro-drilling turbine equipped with a special drill bit is used for this. With dimensions of just 3.6 centimetres in diameter and 5 centimetres in length, the device is extremely small. The micro drilling turbine is attached to a hose, through which it is powered by up to 150 liters of water per minute at an inlet pressure of around 150 bar to set the bit in rotation. The water that drives the microturbine also serves as a cooling system to prevent the drill bit from overheating and as a flushing system to remove the drilling dust. In the "Geospeicher" project, the Fraunhofer IEG team has now drilled more than 20 side arms with an average length of 5 meters at a depth of around 500 meters. Energie Wasser Bern is now carrying out further hydraulic tests, which will provide the necessary data for the next expansion phases.
Author: Heidi Roider
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