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Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility Christian Odenthal, Freerk Klasing and Thomas Bauer German Aerospace Center (DLR) Institute of Engineering Thermodynamics (ITT) Stuttgart / Cologne
Advantages of Molten Salt
> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 2
Unpressurized (low vapor pressure)
High heat transfer rates Low viscosity Operation temperature up
to 560 °C Most common HTF in solar
tower plants Trend for future parabolic
trough plants
Molten Salt as Heat Transfer Fluid (HTF)
Molten Salt as Storage Material
Unpressurized Less expensive than
synthetic oil No heat exchanger to HTF
molten salt Nontoxic, nonflammable
and no explosive phases Spec. heat capacity (liquid
phase): about 1.5 kJ/(kgK)
2-Tank (state of the art)
Overview of molten salt storage technology
> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 3
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cold tank hot tank
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Thermocline
single tank
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Thermocline with filler
single tank
Test section for molten salt energy storage – TESIS:store Flexible test section for alternative
thermal energy storage concepts Long-term / permanent testing
possible
Research at DLR – TESIS Facility Test facility for Thermal Energy Storage In Molten Salts
> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 4
Supply tank coldSupply
tank coldSupply
tank hotSupply
tank hot
Indoor
Outdoor
Test moduleTest module
Supply tank hotSupply
tank hotSupply
tank coldSupply
tank coldStorage
test facilityComponent test facility
PumpPump
MixerMixer Component test section
SaltFillerSalt
FillerValveValve
PumpPump
ValvesValves
Test section for molten salt components – TESIS:com Flexible set-up for various
components (e.g. valves, receiver tubes or instruments)
Critical conditions possible
Research at DLR – TESIS Storage Test Section TESIS:store
> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 5
Molten salt medium Nitrate - Nitrite salt mixtures
Min. operation temperature 150 °C
Max. operation temperature 560 °C
Max. mass flow rate 4 kg/s
Max. mass of filler material 45 t
Max. empty tank volume 22 m³
Behavior of storage system, model validation / refinement, molten salt chemistry on large scale
Photo of the TESIS Plant
> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 6
Foundation(15 %)
-42 %Storage Tank
(13 %)
-25 %
Storage Material (52 %)
-72 %
Piping & Pumps (10 %)
- 22%
Other Costs(10 %)
-55 %
Cost Reduction Potential for Thermocline Storage
Potential for Cost-Reduction of Molten Salt Systems
> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 7
Limited operational experience
Potential #1:
Understanding of molten salt degradation / small ∆T
Understanding of corrosion mechanisms
Source: 100 MWe power plant, DLR inhouse cost calculations
Potential #2:
General potential:
Energy Source: (Solar field)
Example for Cost-Reduction: Exergy
> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 8
Scenario: Tout = 560 °C
Tin = 290 °C
• 12 hours charging time
• 2.82 GWh thermal energy
Nominal Exergy:
~1.59 GWh
Regained Exergy:
< 1.59 GWh Parametric study: Adapt length of storage volume for
• 12 hours charge time and • permitted drop of exit temperature
10000
10500
11000
11500
12000
12500
13000
99 99,2 99,4 99,6 99,8 100
Flui
d m
ass /
t
Exergy regain / %
Necessary Fluid Mass (Size of Storage),depending on Exergy Regain
• 100s of possible storage configurations • Every configuration fits into the scenario • Difference: Regained exergy vs. molten salt holdup (storage size)
Result of Parametric study
> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 9
Pareto Optimum
Selected Results of the Parametric Study
> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 10
System Thermocline, 𝜀𝜀 = 𝟒𝟒𝟒𝟒% 2-Tank -
Permitted change in exit temperature (𝚫𝚫𝑻𝑻𝐞𝐞) 10 30 50 70 0 K
Exergy regain (Ξ) 99.8 99.8 99.7 99.6 100 % Storage volume (𝑉𝑉stor) 16.7 14.9 14.6 14.4 13.7 10³m³
Fluid mass (𝑚𝑚f) 12.2 10.9 10.7 10.5 25.1 kt Solid mass (𝑚𝑚s) 30.0 26.8 26.2 25.8 0.0 kt
Cross-sectional area (𝐴𝐴0) 400 400 400 400 400 m² Particle diameter (𝑑𝑑part) 2 2 2 2 - mm
Storage length (𝐿𝐿stor) 41.8 37.4 36.5 35.9 34.2 m LD storage (𝐿𝐿stor/𝐷𝐷stor) 1.85 1.66 1.62 1.59 1.51 -
Pressure loss (Δ𝑝𝑝f) 118 106 103 102 - mbar
Summary
> IRES 2017 > Christian Odenthal • Demonstrating Cost Effective Thermal Energy Storage in Molten Salts: DLR’s TESIS Test Facility > 15.03.2017 DLR.de • Chart 11
Molten salt thermal energy storage is proven technology with large cost reduction potential
DLR has built two test facilities TESIS:store and TESIS:com, which help
understanding storage behavior, salt chemistry and testing components for faster market application
Example based on exergy has shown that thermocline storage with filler can achieve
high exergetic efficiency and significant reduction of salt inventory (investment cost)
Thank you for your attention Christian Odenthal German Aerospace Center (DLR) Institute of Engineering Thermodynamics (ITT) [email protected] www.dlr.de/tt/en