Bedrock-hosted diffusive hot storage for large-scale thermo-electric energy storage by thermal doublet Paper ID #274
D.
a, Nguyen *,
E.G.
b Macchi ,
C.
b Colin ,
Modeling individual geothermal HX • •
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Paper addresses mechanical and thermal behavior for the ground diffusive hot storage a.k.a. geostock For thermodynamic of CO2 transcritical Rankine cycle, efficiency of electricity storage concept and project experimental setup: see others SeleCO2 project publications, e.g., ORC 2015, HEFAT 2016, HPC 2017, etc.
Ground diffusive hot storage into crystalline bedrock •
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T.
d Tartière
(a) BRGM Languedoc-Roussillon, 1039 rue de Pinville, 34000 Montpellier, France – (b) IMFT, Université de Toulouse, 2 Allée du Professeur Camille Soula, 31400 Toulouse, France – (c) CEA, LITEN DTBH/SBRT/LS2T, 17 rue des Martyrs, 38054 Grenoble, France – (d) Enertime, 1 rue du Moulin des Bruyères, 92400 Courbevoie, France
Large-scale electricity storage by {Ground storage + Ice storage} thermal doublet & CO2 as working fluid
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N.
c Tauveron ,
Several hundred of geothermal heatexchangers (HX) within “optimal” R=h cylindrical global volume. Typically: 2160 HX, 12m long, 200mm diameter and 50cm apart on hexagonal lay-out HX set up on serial/parallel configuration into unfractured dry crystalline bedrock (e.g., granite): 48 lines of 45 HX in series Thermal energy transferred from/to the working fluid (sCO2) circulating the closedloop coaxial exchangers, to/from the encasing bedrock, during storage charge/discharge resp. Flow direction of working fluid is from central to peripheral HX during thermal charge of the geostock, and the opposite during thermal discharge Input temperature of working fluid (sCO2) in the first HX in the line: 138°C at thermal charge, 30°C at thermal discharge
Very high Reynolds number for sCO2 fluid dynamic inside the geothermal HX (Re between 105 and 106) discards unsteady conjugate heat transfer CFD for modeling individual geothermal HX Axisymmetric simplification resorting to an unsteady 1D computational model for the fluid, coupled with an unsteady 2D axisymmetric computational model for the heat transfer inside the rock, with heat transfer coefficient using correlations from Kirillov for heating and cooling of supercritical fluids in mixed convection, (1D model), still too computationally intensive for modeling the complete geostock i.e., 48 lines of 45 HX in series Model of HX based on solution of global mass and energy balances for each HX, Kirillov correlations for heat transfer coefficient, and a supplementary hypothesis on the outlet enthalpy for each HX in the line, was developed by the research project (0D model) 0D model and 1D model simulation results are comparable. 0D model computes fast and makes feasible thermal simulation for the geostock
Thermal simulation for the geostock • • • •
Input temperature of working fluid (sCO2) in the first HX in the line: 138°C at thermal charge, 30°C at discharge. Pressure: 120bar (no pressure drop). Mass flow sCO2: 2kg/s per HX line Thermal cycling: 6h thermal charge followed by 6h thermal discharge, 0h stand-by in-between At start of the thermal cycling (thermal cycle #1): 20°C in geostock & environment Illustrations below show geostock thermal situation at the end of #10 charge (#10C) and #10 discharge (#10D), and some results for the simulated case
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High-temperature high-pressure geothermal HX •
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Silicone rubber material for the walls of the 200mm diam. coaxial HX Top part of HX in contact with the ambient atmospheric pressure hold in place by a self-locking harness made of aramid straps HX design solves the technological issue of thermal coupling with bedrock for T>100°C HX design eases the containment of working fluid inside pressure (120bar sCO2)
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Mechanical simulation for the geostock • • •
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Average flux of all 2160 HX to the geostock (i.e., the geostock thermal power): 14.4MW Thermal losses to the environment below 1% of geostock thermal power In some situations environment can return heat back to the geostock (negative values of flux in figure)
Thermal losses lowering along with operation Asymptotic value for 12h losses (r1=12m; r2>>r1): 726kWh
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Exergy efficiency ηex to evaluate the decrease in “quality” of the thermal energy between charge and discharge in the geostock
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Exergy efficiency: 58% for the simulated case
The authors acknowledge the support of the French National Research Agency (ANR) under grant ANR-13-SEED-0004 (SeleCO2 project). Project partners are ENGIE, BRGM, CEA, ENERTIME, IMFT.
http://seleco2.free.fr/
Working fluid (sCO2) pressure inside geothermal HX: 120bar Maximum displacement in bedrock: 1.7mm Von Mises stress between 12 and 18MPa within elastic range, well below the elastic limit of granite Experimental uniaxial compression strength and thermal conductivity of Sénones granite samples (50mm diam. - 150mm height) do not appear to change significantly after several hundred of thermal cycles between 30°C and 140°C
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Almost no change for working fluid temperatures going from thermal cycle #4 to thermal cycle #5 Charge/Discharge thermal cycling rapidly reaches a “dynamically stable” situation
