Feasibility of geothermal energy in the Belgian deep railway tunnels: case of the Liefkenshoek tunnel

Abstract

The energy sector is undergoing a major transition aimed at reducing or eliminating fossil fuels in favour of renewable sources such as solar, biomass, wind and geothermal energy. In the case of geothermal energy, the use of geostructures is expanding due to the possibility of thermally activating them by integrating heat exchangers; thermally activated tunnels (energy tunnels) are a representative application. Thermal activation of tunnels offers strong potential owing to their large contact area with the ground, an essential advantage underpinning this feasibility study. This work assesses the technical and economic fea- sibility of thermally activating the Liefkenshoek railway tunnel (Belgium) by evaluating both the exploitable geothermal potential and the project’s profitability. To this end, an analytical heat transfer model was developed and tested under different conditions. The analysis also accounts for variations in several key parameters: the inlet temperature of the heat transfer fluid, its flow rate through the exchanger, and the air temperature inside the tunnel. The results indicate that water saturated sand yields the highest geothermal potential, and under specific conditions, an exploitable potential of 27W/m² was identi- fied. Finally, the economic assessment indicates that, under suitable operating conditions, the project is economically viable, with the heat production cost remaining significantly lower than the typical selling price observed on district heating networks. This work, therefore, contributes to the valorisation of existing infrastructure within the energy tran- sition and recommends the systematic integration of thermal activation in future tunnel construction projects.