Tunnels, a new potential for sensible heat storage in rock: 3D numerical modelling of a reversible exchanger within tunnel

Transcription

1 Tunnels, a new potential for sensible heat storage in rock: 3D numerical modelling of a reversible exchanger within tunnel Chaima SOUSSI, Olivier FOUCHÉ, Gonzague BRACQ, Sophie MINEC soussichaima@gmail.com 1

2 2 Outline Introduction and context Principle and feedback 3D Numerical modelling Results and discussion Conclusion

3 Introduction and context Increasing the contribution of geothermal energy in the energy mix by developing geothermal heat pumps The National Project «Ville D Ville d idées» Improving the contribution of the underground resources in the urban development Geothermal structures New technique, Future opportunity : Geothermal tunnel Grand Paris Express 205 km of metro lines Piles Duration: 4 to 5 years from January 2013 Budget: 5 million. Partners: Diaphragm 30 organizations walls 3

4 Principle of this new technology 4 Prefabricated segment Pipes Soil/Concret : extrados Conduction Heat Pump Ring Air/Concret: intrados Convection

5 Feedback Traditional method First project used activated prefabricated segment Production of heat for a building Activated length of tunnel : 54 m 5

6 3D Numerical modelling Physics Heat transfer in solid Concrete Heat transfer in porous medium Non isothermal fluid in pipes 6

7 Equations Heat transfer in solid Coupled physical phenomena Non isothermal fluid in pipes Transfer in porous medium Heat transfer in porous medium Continuity equation Darcy s law Heat equation Non isothermal fluid in pipes Heat transfer in solid with 7

8 8 3D Model Outer diameter of the tunnel =9.5 m Thickness of the concrete ring =40 cm Width of a ring = 1.8 m Inner pipe diameter 21mm. Mesh Defined by user Linear elements for pipes Tetrahedrons for concrete and rock Model without water table Model with water table

9 Temperature ( C) Temperature ( C) Initial / boundary conditions Rock temperature T roche Convective flow Inlet fluid temperature T in Fluid flow rate Fluid outflow pressure Groundwater velocity Temperature of the tunnel s air RATP data line 8 11Juill-31 Déc Août-29 Novemb Sep Août Janv-12 Mars 2011 Convective flow Temperature used in modelling Time (month) 9

10 Simulations Parametric Comparative Parameters of fluids Thermal properties of the rock Non-activated tunnel Thermal activated tunnel 12 months of heat extraction for 8 years 7 months heating + 1 month break + 3 months cooling + 1 month break 8 mois heating + 3 mois cooling + 1 mois break Superposition of geological layers with groundwater

11 Φ from a ring (W/m²) Fluid parameters Results and discussion C 3 C 4 C 5 C Flow (l/s) A wide range of heat flux of 15 W / m to 40 W / m² Heat extraction and hydraulic loss increase with fluid flow Finding an equilibrium between the thermic and hydraulic problems Fixed parameters T in in winter: 4 C and flow rate: 0.1 l / s Hydraulic Thermic 11

12 Annual energy exchanged with the rock (MWh) Annual energy exchanged with the rock (MWh) Thermal properties of the rock Thermal conductivity Temperature déstockée extracted stockée stored déstockée extracted stockée stored 0.0 1,6 W/(m.K) 2 W/(m.K) 2,4 W/(m.K) Energy exchanged increases with the thermal conductivity: Extracted 2 MWh / year / ring Injected 2.5 MWh / year / ring C 13 C 14 C Stored energy decreases with temperature Extracted energy increases with temperature Decrease of the difference 12

13 Rock temperature ( C) Anual energy by ring (MWh) Φ by ring (W/m²) Φ by ring (W/m²) Time (d) Non activated tunnel φintrados φextrados Time (d) φintrados φextrados Tair Textrados Temperature ( C) Heat exchange between the tunnel and the rock in both directions Warming of the rock Temps (j) à l'extrados à 3m à 6m à m From march to mid-september, the heat diffuses from the tunnel to the rock and in the opposite direction in the rest of the year stockée déstockée Quantity of heat stored > extracted 13

14 Annual energy (MWh) Rock temperature ( C) Anual enrgy by ring (MWh) Annual energy by ring (MWh) intrados extrados Heating 3 4 Cycle (years) Total annual energy exchanged with the rock by a ring storage Time (year) destorage Equilibrium after 4 years of operation, with an excess of heat storage about 0.2 MWh / year 6 7 Thermal activated tunnel The air in the tunnel is responsible for 2/3 of the production of heat in winter; All the heat is distributed in the rock in summer extrados intrados 1er cycle 2éme cycle 3ème cycle 4ème cycle Cycle (years) Time (d) Cooling 5ème cycle à l'extrados à 6m Warming of the rock Negligible changes from the 4th cycle 6ème cycle 7ème cycle à 3m à m 14

15 Rock temperature ( C) Rock temperature ( C) Comparison between thermal activated and non-activated tunnel The temperature distribution around the tunnel The temperature profile in the rock 15 At 6m from the tunnel sans échangeur 7 H+3 C H+ 3 C 12 months of heat extraction Time(d) Radial shape around non-activated tunnel Snail shape around activated tunnel At m from the tunnel The exchanger system reduces thermal disturbance of the rock without exchanger 7 H+ 3 C 8 H + 3 C months of heat extraction Time (d) 15

16 Effect of groundwater flow Behavior of the water table around the tunnel Clay λ= 2,4 W/(m.K) C p = 2000 J/(kg.K) ρ = 1700 kg/m 3 Marles λ= 1,7 W/(m.K) C p = 2000 J/(kg.K) ρ = 2600 kg/m 3 Superposition of two geological layers Groundwater level is 2m below the interface 16

17 Effect of the groundwater on the thermal equilibrium of the rock Velocity m/s Velocity m/s The Fast velocity thermal of regeneration the groundwater has a great Slower influence thermal on regeneration the thermal equilibrium of rock and thus the heat exchange 17

18 Response to heating needs, case of new offices Heating needs Scenario adopted 8 months H 1 month B 3 months C Annual needs : 140 MWh Heating production 8.5 MWh/ year/ ring 4.7 MWh/ year/ ml 30 meters linear of the tunnel = 17 rings must be activated 18

19 Conclusion Ecological benefits: reducing consumption of fossil energy and thermal disturbances of the rock, Stable and sustainable system, In the case of absence of groundwater flow, the fluid properties have more remarkable effect than that of the thermal properties of the rock, Velocity of the groundwater has a great influence on the behavior of the system: rapid flow allows the thermal regeneration but not the heat storage in the rock. 19

20 20 For more information: Poster will be presented today at 16:00-18:00