Abstract
Flooded mines constitute groundwater reservoirs that can be exploited with geothermal heat pump systems. Modelling such a reservoir is challenging because groundwater flow and heat transport equations need to be solved within the complex geometry of mine workings. To address this challenge, we developed a tridimensional numerical model to estimate the geothermal heat pump and underground energy storage potential, using the Con Mine near Yellowknife, Northwest Territories, Canada as an example. We used the finite element method to simulate the transient 3D temperature field within the water and in the rock mass. The shafts and tunnels of the mine are represented with 1D elements embedded in a tridimensional matrix. Hydraulic and thermal properties were evaluated at the mine site and in the laboratory with samples from outcrops and cores. The numerical model was calibrated to reproduce hydraulic head and temperature measured while pumping one of the shafts. Then, the long-term temperature of the water under different cases of geothermal heat pump operation was simulated for 25 years. The total energy delivered to buildings per year for a flow rate of 0.06 m3 s−1 was 953 MWh vs. 18,048 MWh when the pump depth was 0.3 vs 1 km. We also simulated heat production using solar thermal collectors to provide additional energy storage. The results suggest that it would be easier to increase energy production by augmenting the flow rate or by placing the pump at a greater depth than by adding solar collectors.
摘要
摘要: 水淹矿井形成了可被地热泵系统开采利用的地下水水库。对这种地下水水库进行建模是很有挑战性的, 因为需要在矿井复杂的几何结构中求解地下水流和热传递方程。为了解决这个难题, 以加拿大西北地区的Yellowknife附近的地下矿井为例, 本文提出了一种估算地热热泵和地下储能潜力的三维数值模型。本文采取有限元方法模拟了水体和岩石内的瞬时三维温度场, 该矿井的竖井和巷道用嵌入三维矩阵的一维元素表示, 并且在矿场和实验室对露头和岩芯的样品进行了水力和热力性能的评估。模型在校准后可用于模拟某一竖井在抽水时的水头和温度, 之后对在不同的地热泵运行方案下的25年内的水体温度进行了模拟。若以0.06 m3/s的速率开采, 每年向建筑物输送的总热量为953 MWh; 与泵深度为1 km时相比, 泵深度在0.3 km时每年可输送的总热量为18048 MWh。本文还计算了太阳能集热器提供的额外热能储量。研究结果表明, 通过增加流量或将泵放置在更大的深度, 将比通过增加太阳能集热器来增加热能产量更容易。
Zusammenfassung
Geflutete Bergwerke sind Grundwasserreservoire, die mit geothermischen Wärmepumpensystemen genutzt werden können. Die Modellierung eines solchen Reservoirs ist eine Herausforderung, da die Gleichungen für die Grundwasserströmung und für den Wärmetransport die komplexe Geometrie der Grubenbaue abbilden müssen. Um diese Herausforderung zu bewältigen, wurde ein dreidimensionales numerisches Modell entwickelt, um das Potenzial von Erdwärmepumpen und unterirdischen Energiespeichern am Beispiel der Con-Mine in der Nähe von Yellowknife (Northwest Territories, Kanada) abzuschätzen. Das instationäre 3D-Temperaturfeld im Wasser und im Gestein wurde mit der Finite-Elemente-Methode simuliert. Die Schächte und Stollen des Bergwerks werden durch 1D-Elemente dargestellt, die in eine dreidimensionale Matrix eingebettet sind. Die hydraulischen und thermischen Eigenschaften wurden am Standort des Bergwerks und im Labor anhand von Aufschluss- und Bohrkernproben untersucht. Das numerische Modell wurde kalibriert, um die hydraulische Förderhöhe und die Temperatur zu reproduzieren, die beim Abpumpen eines der Schächte gemessen wurden. Anschließend wurde die Langzeittemperatur des Wassers unter verschiedenen Betriebsbedingungen der geothermischen Wärmepumpe für 25 Jahre simuliert. Die Gesamtenergie, die pro Jahr an die Gebäude geliefert wurde, betrug bei einer Durchflussrate von 0,06 m3/s 1.953 MWh bei einer Einbautiefe der Pumpe von 300 Meter und 18.048 MWh bei einer Einbautiefe der Pumpe von 1.000 Meter. Zusätzlich wurde die Wärmeerzeugung mit solarthermischen Kollektoren für eine zusätzliche Energiespeicherung simuliert. Die Ergebnisse zeigen, dass es einfacher ist, die Energieproduktion durch eine Erhöhung des Durchflusses oder eine größere Pumpentiefe zu steigern als durch den Einsatz von solarthermischen Kollektoren
Resumen
Las minas inundadas constituyen reservorios de agua subterránea que pueden ser aprovechados con sistemas de bombas de calor geotérmicas. Modelar dicho reservorio es un desafío debido a la necesidad de resolver las ecuaciones de flujo de agua subterránea y transporte de calor dentro de una compleja geometría de las operaciones mineras. Para abordar este desafío, un modelo numérico tridimensional fue desarrollado para estimar el potencial de la bomba de calor geotérmica y almacenamiento de energía subterránea, utilizando la mina Con cerca de Yellowknife (Territorios del Noroeste, Canadá), como ejemplo. Utilizamos el método de elementos finitos para simular el campo de temperatura tridimensional transitoria dentro del agua y en la masa rocosa. Los pozos y galerías de la mina se representan con elementos unidimensionales incrustados en una matriz tridimensional. Las propiedades hidráulicas y térmicas se evaluaron tanto en la mina como en el laboratorio con muestras de afloramientos y testigos. El modelo numérico se calibró para reproducir la carga hidráulica y la temperatura medida mientras se bombeaba uno de los pozos. Luego, se simuló la temperatura a largo plazo del agua bajo diferentes casos de operación de la bomba de calor geotérmica durante 25 años. La energía total suministrada a los edificios por año para una tasa de flujo de 0.06 m3/s fue de 953 MWh frente a 18,048 MWh cuando la profundidad de la bomba era de 0.3 frente a 1 km. También se simuló la producción de calor utilizando colectores solares térmicos para proporcionar almacenamiento de energía adicional. Los resultados sugieren que sería más fácil aumentar la producción de energía aumentando la tasa de flujo o colocando la bomba a una mayor profundidad que mediante la adición de colectores solares
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Abbreviations
- A :
-
[m2] Area
- c [MJ m− 3 K− 1]:
-
Volumetric heat capacity
- g [m2/s]:
-
Gravitational acceleration
- h [m]:
-
Hydraulic head
- K [m s− 1]:
-
Hydraulic conductivity
- Q [W m− 3]:
-
Heat exchange rate
- Q’ [m3 s− 1]:
-
Water exchange or flow rate
- q [W m− 2]:
-
Conductive heat flux
- SP [W]:
-
Solar production
- STP [W m− 2]:
-
Solar thermal production per area
- S [m− 1]:
-
Specific storage
- s [Pa− 1]:
-
Compressibility of the host rock
- T [K]:
-
Temperature
- t [s]:
-
Time
- u [m s− 1]:
-
Velocity field
- \(\beta\) [4.4⨯10– 10 Pa− 1]:
-
Compressibility of water
- \(\in\) [-]:
-
Solar collector efficiency
- \(\theta\) [-]:
-
Porosity
- λ [W m− 1 K− 1]:
-
Thermal conductivity
- ρ [kg m− 3]:
-
Density
- amb:
-
Ambient
- c:
-
Injected in the mine water during cooling season
- cooling:
-
Cooling of the buildings
- eff:
-
Effective
- g:
-
Ground
- h:
-
Extracted from the mine water during eating season
- heating:
-
Heating of the buildings
- i :
-
Denoting the direction with subscripts x, y, and z
- inj:
-
Injection
- prod:
-
Production
- r:
-
Host rock
- s:
-
Solar thermal collector
- w:
-
Water
- COP :
-
Coefficient of performance
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Acknowledgements
The support of the Northwest Territories Geological Survey, the Geological Survey of Canada, Newmont Mining Corp, and the funding of the Northern Geothermal Potential Research Chair by the Institut nordique du Québec is acknowledged.
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Mandemvo, D.D.N., Comeau, FA., Raymond, J. et al. Numerical Assessment of the Geothermal and Thermal Energy Storage Potential of the Underground Con Mine (Northwest Territories, Canada). Mine Water Environ 43, 148–167 (2024). https://doi.org/10.1007/s10230-024-00976-4
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DOI: https://doi.org/10.1007/s10230-024-00976-4