High Temperature Thermal Energy Storage Development at DLR ECI - - PowerPoint PPT Presentation

High Temperature Thermal Energy Storage Development at DLR

ECI – Massive Energy Storage Conference, Newport Beach, June 23-26 2013

• M. Eck, D. Laing, W.-D. Steinmann, S. Zunft

German Aerospace Center Institute of Technical Thermodynamics

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Outline

• Introduction / Motivation
• Phase change media (PCM) storages
• Compressed air energy storages (CAES)
• Cell-Flux storage concept
• Conclusions / Outlook

Source: Solar Millennium

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Introduction / Motivation

Technical options for thermal energy storages in CSP plants storage system ONE single storage technology will not meet the unique requirements of different solar power plants

Heat Transfer Fluid Collector System Pressure Temperature synthetic oil trough/Fresnel 15 bar 400°C saturated steam tower/Fresnel 40 bar 260°C superhaeted steam trough/Fresnel 50-120 bar 400-500°C molten salt tower/trough 1 bar 500-600°C air tower 1 bar 700-1000°C air tower 15 bar 800-900°C new concepts Heat Engine ORC steam turbine gas turbine Stirling engine

• thers

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• Sensible heat storages
• Molten Salt
• Concrete
• Regenerator Storages
• Latent Heat Storages
• Phase Change Media
• Thermochemical Storages
• Limestone

Introduction / Motivation

Thermal energy storages under Development at DLR

Nitrate Salts Compressed Air Energy Storages CellFlux Concept

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Evaporation 65% Preheating 16% Super- heating 19%

Parabolic solar field Fresnel solar field Solar tower

Solar Receiver

260°C – 400°C 107 bar

Phase change media (PCM) storages

Fundamentals

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Phase change media (PCM) storages

Fundamentals

100 200 300 400 500 600 700 800 900 1000

• 100

100 200 300 400 500 600 700 800 900 1000 Temperatur [°C] Schmelzenthalpie [J/g]

Wasser Fluoride Carbonate und Chloride Hydroxide Nitrate Salz- hydrate Salz- Wasser Paraffine

Heat of Fusion [J/g] Temperature [°C]

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Nitrate salt represent possible PCMs for applications beyond 100 °C Important PCM criteria: thermal conductivity, melting enthalpy, thermal stability, material cost, corrosion, hygroscopy

50 100 150 200 250 300 350 400 100 150 200 250 300 350 Temperature [°C] Enthalpy [J/g] KNO3 NaNO3 NaNO2 KNO3-NaNO3 LiNO3-NaNO3 KNO3-LiNO3 KNO3-NaNO2-NaNO3 LiNO3 50 100 150 200 250 300 350 400 100 150 200 250 300 350 Temperature [°C] Enthalpy [J/g] KNO3 NaNO3 NaNO2 KNO3-NaNO3 LiNO3-NaNO3 KNO3-LiNO3 KNO3-NaNO2-NaNO3 LiNO3

Phase change media (PCM) storages

Current Materials

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solid liquid Fluid solid liquid Fluid

Heat transfer coefficient is dominated by the thermal conductivity of the solid PCM → Low thermal conductivity is bottleneck for PCM

Heat carrier: water/steam Phase Change Material (PCM) Tube Fins

schematic PCM-storage concept

Finned Tube Design effective λ > 10 W/mK

Source: DLR

Phase change media (PCM) storages

Challenges

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Phase change media

Demonstrated at DLR: NaNO3 - KNO3 - NaNO2 142°C LiNO3 - NaNO3 194°C NaNO3 - KNO3 222°C NaNO3 306°C

Experimental validation

5 test modules with 140 – 2000 kg PCM Worlds largest high temperature latent heat storage with 14 tons of NaNO3 (700 kWh) operating 2010-11

Phase change media (PCM) storages

Development of Prototypes

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PCM-Evaporator module:

• Capacity ~ 700 kWh
• PCM: NaNO3
• Melting point: 306°C
• Salt volume: 8.4 m³
• Total height 7.5 m
• Inventory ~ 14 t

Phase change media (PCM) storages

Latest Demonstrator

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• Cost-effective production and assembly
• Free flow path in vertical direction

=> no risk with volume change during phase change

• Controlled distribution of heat in the

storage

• Concept optimized by FEM analysis
• Successful demonstration in lab-scale
• Major cost reduction expected

Enhanced heat transfer by extruded longitudinal fins

Source: DLR

Phase change media (PCM) storages

Current Developments at DLR

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Compressed Air Energy Storages (CAES)

Fundamentals

Objectives:

• Peak load/Reserve power 300 MWel, 4-8 turbine full load hrs.
• > supports grid integration of RE
• Highly efficient due to storage-based heat management
• > ~70% storage round-trip efficiency
• TES technology: Direct contact solid media storage („regenerator storage“)
• Specifications: ~600 ˚C @60 bar
• Design aspects:

best heat transfer, fast start-up, efficient solutions for HT-insulation, solutions for pressurised containment, durability of materials in hot & humid atmosphere

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Compressed Air Energy Storages (CAES)

Chosen Concept

• Direct contact between HTF and storage medium
• High temperature applications, simple setup
• Broad choice of applicable inventory materials
• Typical setup: stacked bricks, packed beds allow cost reduction
• Challenges: Thermo-mechanical aspects (packed beds), fluid-

dynamic aspects, durability/erosion, containment

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Compressed Air Energy Storages (CAES)

Current Development at DLR

• Develop tools and design solutions for
• ptimized thermal design
• Tools and design solutions considering the

thermally induced mechanical loads in large-scale packed storage (particle- discrete simulation)

• Develop design solutions for the fluid

dynamic aspects (flow distribution, pressure loss)

• Reduce lifetime uncertainty of materials

through extensive material testing

• Validate TES design solutions through

pilot-scale testing

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Liquid Storage Media (Molten Salt) Solid Storage Media (Concrete) Molten Salt 49% Heat Exchanger 57% Structure of capital costs

Limited potential for further cost reductions due to physical constraints  New Basis Concept required

CellFlux Storage Concept

Motivation

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CellFlux Storage Concept

Innovative approach

• Large heat transfer surfaces

(short path length for heat conduction within solid storage material)

• Direct contact between storage medium and working fluid

(no expensive piping / coating)

• Storage volume at atmospheric pressure

(no expensive pressure vessels)

solid state storage media

cost effective no freezing

Requirements

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CellFlux Storage Concept

Innovative approach

Problem: Low volume specific energy density of air

• large pressure losses
• part load operation difficult

Storage volume closed air cycle Heat exchanger Fan from solar field to solar field

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CellFlux Storage Concept

Innovative approach

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5 10 15 280 300 320 340 360 380 400 Start and End Temperature Profile with 2°C Maximum Rise of ExitTemperature Flow Length of Storage [m] Storage Material Temperature [°C] Initial Temperature Profile End Temperature Profile Usage of Storage 2°C Exit Temperature Rise

CellFlux Storage Concept

Current Development at DLR

• Theoretical and experimental investigation of

sub-system behavior

• Design and construction of demonstration

plant

• Development of design and sizing tools

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• Different technical approaches for different process requirements available
• Phase change media (PCM) storages
• Demonstration level (700 kWh)
• Operating Temperature 300°C
• Focus on system optimization and cost reduction
• Compressed Air Energy Storages (CAES)
• State of the art in commercial operation
• Optimization by use of thermal energy
• Thermo Mechanical investigation
• CellFlux Concept
• Proof of concept
• Design and Optimization of components
• System optimization

Conclusions