Carcamo-Medel Mauricio, Narsilio Guillermo, Fuentes Raul
Department of Infrastructure Engineering, The University of Melbourne, Parkville, 3010, Australia.
Institute of Geomechanics and Underground Technology, RWTH Aachen University, 52074, Aachen, Germany.
Sci Rep. 2024 Aug 19;14(1):19191. doi: 10.1038/s41598-024-69225-6.
The addition of ground heat exchangers (GHEs) to a pit lake's basin has the potential for abundant, clean and renewable geothermal energy extraction using shallow geothermal systems. Basin-embedded GHEs avoid direct interaction with mine water, which has been shown to impact efficiency and longevity in mine open-loop geothermal systems negatively. The now accelerated closure of open-pit coal mines presents itself as an opportunity to use this technology. However, no guidelines currently exist for designing or operating GHEs embedded in the sediment of water bodies. Furthermore, the two-way coupling between the complex annual thermal fluid dynamics that lakes are naturally subjected to and heat fluxes on the sediments and the GHE system has not been explored. In this study, we develop and validate finite element models to assess the relevance of lake thermal stratification in the performance of a geothermal system embedded in water bodies basins, e.g., on open-pit mine closures, under temperate residential thermal loads. The results show that the pit lake's role as a thermal sink improves significantly when the lake's thermal dynamics are accounted for, with an increase of up to 292% in the lake's available energy budget. A minor variation in energy budget (~8%) was found whether the lake is modelled explicitly or simplified as a transient Dirichlet temperature boundary condition. This small difference vanishes if horizontal circulation along the lake is considered, highlighting the lake's thermal energy potential. Finally, the impact on the GHE Coefficient of Performance (COP) is evaluated, with a maximum of ~15% difference among all cases.
在矿坑湖的盆地中添加地源热交换器（GHEs），利用浅层地热系统有潜力提取丰富、清洁且可再生的地热能。嵌入盆地的地源热交换器避免了与矿井水的直接相互作用，而矿井水已被证明会对矿山开环地热系统的效率和寿命产生负面影响。目前露天煤矿加速关闭，这为利用这项技术提供了契机。然而，目前尚无关于设计或运行水体沉积物中嵌入的地源热交换器的指导方针。此外，湖泊自然经历的复杂年度热流体动力学与沉积物和地源热交换器系统上的热通量之间的双向耦合尚未得到研究。在本研究中，我们开发并验证了有限元模型，以评估湖泊热分层在水体盆地中嵌入的地热系统性能中的相关性，例如在温带住宅热负荷下露天矿关闭的情况下。结果表明，考虑湖泊的热动力学时，矿坑湖作为热汇的作用显著改善，湖泊可用能量预算增加高达292%。无论湖泊是明确建模还是简化为瞬态狄利克雷温度边界条件，能量预算都有微小变化（约8%）。如果考虑沿湖的水平环流，这种小差异就会消失，突出了湖泊的热能潜力。最后，评估了对GHE性能系数（COP）的影响，所有情况之间的最大差异约为15%。
