Synthesis and characterization of new nitrate salt mixtures to - - PowerPoint PPT Presentation

Synthesis and characterization of new nitrate salt mixtures to molten salt storage Thomas Bauer, Alexander Bonk, Antje Wörner, EERA Conference

• Nov. 25, 2016 – Birmingham

DLR.de • Slide 1

• Thermal energy storage (TES) and the “Energiewende” in Germany
• High-temperature TES technologies and applications
• Material challenges in TES development
• Molten salt TES
• Systems and applications
• Material aspects
• Summary and Conclusions

Contents

DLR.de • Slide 2

Scenario of Electricity Generation in Germany

DLR.de • Slide 3

• Excess renewable electricity requires coupling of sectors (Power-to-X)
• Volatile power from PV & wind requires flexibility & storage

Installed power [GWel] Power production [TWhel]

Source: Energiereferenzprognose 2014, Zielszenario, Bilder von IER, Stuttgart Hr. Hufendiek

Options in the Energy System for Storage, Flexibility and Power-to-X

DLR.de • Slide 4

Conventional Power plants

Higher flexibility, hybrid fuel/ electricity

• peration, decoupling heat and

electricity in CHP, …

Transportation

E-mobility, Battery, thermal management, …

Industry

Demand Side Management, Power-to-Heat, Thermal storage, Power-to-Product/Chemical, Hybrid gas-electricity operation,…

Renewable Energy

Shut-down of plants Concentrating solar power plants (CSP), Demand orientated biomass, Geothermal with storage,…

Domestic

Demand Side Management, Power-to-Heat + thermal storage, Heat pump + thermal storage, …

Electrical Storage

Battery, Pumped hydro, Pumped thermal energy storage, Adiabatic compressed air storage, Liquid air

Electrical Grid Electricity generation End-use Chemical Storage

Power-to-gas/ gas network Electrolysis, Power-to-Liquid/Fuel, …

Storage  Thermal energy storage as inexpensive cross-sectoral

technology in all fields (electricity generation, storage, end-use)

Gases/Fuels

Institute of Engineering Thermodynamics

• Prof. André Thess, Director

Jörg Piskurek, Vice Director

Thermal Process Technology

• Dr. A. Seitz

Electrochemical Energy Technology

• Prof. A. Friedrich

Systems Analysis and Technology Assessment

• Dr. Ch. Schillings / C.

Hoyer-Klick

~ 190 staff in Stuttgart, Köln, Hamburg, and Ulm ~ 20 Mio. EUR annual budget with 50% third party funding „We are the scientific pathfinder for the energy storage industry“

Energy System Integration

• Prof. A. Thess
• Prof. J. Kallo

Computational Electrochemistry

• Prof. A. Latz

DLR.de • Slide 5

Locations and employees

DLR:

• Approx. 8000 employees across

33 institutes and facilities at 16 sites. Offices in Brussels, Paris, Tokyo and Washington. Thermal energy storage group:

• Stuttgart
• Cologne

 Cologne  Oberpfaffenhofen

Braunschweig 

 Goettingen

Berlin 

 Bonn  Neustrelitz

Weilheim  Bremen 

 Trauen

Lampoldshausen  Stuttgart  Stade  Augsburg 

 Hamburg

Juelich 

DLR.de • Slide 6

Department of Thermal Process Technology

• Dr. Antje Seitz

Thermal Power Plant Components

• Dr. Stefan Zunft

Regenerator and solid media storage High temperature heat exchangers

Thermal Systems for Fluids

• Dr. Thomas Bauer

Molten salt storage

Thermal Systems with Phase Change

• Dr. Dan Bauer

Latent heat storage

Thermo- chemical Systems

• Dr. Marc Linder

Thermochemical Storage Thermal Upgrade H2-Storage

Alternative Fuels

• Dr. Uwe Dietrich

Regenerative power in liquid hydrocarbons Technoeconomic evaluation

DLR.de • Slide 7

~ 50 staff in Stuttgart and Köln Focus on high-temperature thermal energy storage technologies

• 1. Increased efficiency of energy-intense industrial

processes by utilization of waste heat streams

• 2. Additional operational flexibility in power plants and

industrial processes

• 3. Increased share of renewable energies
• a. Dispatchability of solarthermal power plants
• b. Power-to-heat for industrial processes

Thermal Energy Storage as a Cross-Sectoral Technology Applications

DLR.de • Slide 8

Thermal Energy Storage as a Cross-Sectoral Technology Integration of TES in systems

DLR.de • Slide 9

Key Performance Indicators

• Storage density (system)
• System cost (CAPEX, OPEX)
• Space needed
• CO2-mitigation potential
• Operation characteristics …

Storage Technology

Thermo- chemical Latent Heat Sensible Heat

Application

Storage Requirements

• Temperature level
• Heat transfer fluid
• (Dis-) Charging characteristics
• Storage capacity
• Power density

• Cowper-Storage (regenerator storage)
• Gaseous heat transfer fluids in direct contact
• High temperatures above 1000 ºC

 Steel industry (hot blase for furnaces)

• Molten Salt Storage
• Thermal oil or molten salt as heat transfer fluid
• Temperatures up to 560 ºC

 Concentrated solar power plants

• Ruths-Storage (steam accumulator)
• Steam as heat transfer fluid
• Floating pressure, typically up to 250 °C

 Steam supply in industry, etc.

Established TES Technologies

DLR.de • Slide 10

Importance of Material Research for TES Development Steps for Storage Systems

DLR.de • Slide 11

System integration Lab-scale tests Material screening Thermal properties of storage materials and fluids Stability, compatibility Heat exchanger / heat transfer enhancement Thermophysical properties Thermo-mechanical design Technical material quality Containment, corrosion

Importance of Material Research for TES Materials and Sub-Components

TES requires more than research on the storage material itself

Storage material Container Heat exchanger Heat transfer fluid Additional components: pumps, valves, connection pipes, insolation, foundation, instrumentation and control devices Water, natural rocks, ceramics, concrete salts, metal oxides Pressurized vessels, packed bed designs, corrosive media Finned tubes, shell-and-tube heat exchanger Air, flue gas, water/steam, molten salt, thermal oil

DLR.de • Slide 12

Sensible heat storage in MOLTEN SALTS Commercial two-tank technology

Direct storage system Indirect storage system for solar tower systems for parabolic trough systems (Storage medium = HTF) (Storage medium ≠ receiver HTF)

DLR.de • Slide 13

Sensible heat storage in MOLTEN SALTS Commercial status of two-tank indirect storage technology

Source: Solar Millennium Source: Abengoa

• Andasol systems in Spain
• 50 Mwel
• Storage capacity: 1,000 MWh (8h)
• 28,000 t of nitrate salts
• 2 tanks: 34 m Ø, 14 m high
• Largest System in USA

(Solana, Abengoa):

• 280 Mwel
• Storage capacity: 6h
• 12 tanks: 37 m Ø, 15 m high

DLR.de • Slide 14

Impact of TES:

• Extended operation hours
• Reduction of part-load operation
• Dispatchable power

Example: Crescent Dunes plant 110 MWel

• Commercial operation up to 24/7
• Molten salt as heat transfer fluid

and TES medium

• 10 h direct two-tank Solar Salt storage
• ΔT = 565 °C - 290 °C = 275 K
• Thermal storage efficiency 99 %

TES potential:

• Cost savings with thermocline/filler concept
• Technology transfer to other sectors

Sensible heat storage in MOLTEN SALTS Commercial status of direct storage technology

Source: SolarReserve Source: SolarReserve

DLR.de • Slide 15

Sensible heat storage in MOLTEN SALTS Installed global capacity for grid-connected storage

Source: https://www.iea.org/newsroomandevents/graphics/2015-06-30-installed-global-capacity-for-grid-connected-storage.html

• CSP grid-connected molten salt storage power > 1500 MWel in 2015
• CSP grid-connected molten salt storage capacity > 30 GWhth in 2015

DLR.de • Slide 16

Sensible heat storage in MOLTEN SALTS Focus of the DLR group

System aspects

Components

Process technology Material (Upscaling) aspects

DLR.de • Slide 17

Sensible heat storage in MOLTEN SALTS TESIS:com - component test-bench

DLR.de • Slide 18

Sensible heat storage in MOLTEN SALTS TESIS:com - component test-bench

Aim:

• Test and qualification of molten salt

components for research and industry (e.g. valves, receiver tubes, measurement & control)

• Examine operational molten salt aspects

(e.g. freezing events) Operating Parameters:

• Temperature of 150 - 560 °C with

NaNO2,NaNO3,Ca(NO3)2,KNO3,LiNO3

• max. thermal gradient 50 K/s
• max. mass flow of 8 kg/s
• max. heating power 420 kW
• max. cooling power 420 kW

DLR.de • Slide 19

Sensible heat storage in MOLTEN SALTS TESIS:store - Storage Test Section

DLR.de • Slide 20

Sensible heat storage in MOLTEN SALTS TESIS:store - Storage Test Section

Aim:

• Demonstration of single-tank thermocline concept with filler

Operating Parameters:

• Operation temperature 150 - 560 °C

with NaNO2, NaNO3, Ca(NO3)2, KNO3, LiNO3 salt mixtures

• Storage capacity (ΔT=250K):

200 kWh/m³ with 20 m³ and 4 kg/s Research topics:

• Heat / mass transfer, thermomechanics
• Material compatibility
• Operational aspects, scaling issues
• System integration

Potential

• Previous examination at Sandia

estimate 20 -37 % cost reduction

DLR.de • Slide 21

Sensible heat storage in MOLTEN SALTS Material aspects

• Development of alternative salt mixtures
• Reduced melting temperature < 140 ºC
• Thermal stability up to 700 ºC
• Investigation of the decomposition

mechanisms of nitrate salts

• Interactions of molten salts with
• metals / corrosion
• natural stone / filler materials
• Thermal properties determination and

post-analysis of composition

DLR.de • Slide 22

Sensible heat storage in MOLTEN SALTS Material characteristics

DLR.de • Slide 23

• Liquid state over large temperature range
• Ability to dissolve a relatively

large amount of compounds (corrosion may occur)

• Low vapor pressure and high stability
• Low viscosity
• High heat capacity per unit volume
• Several salts are inexpensive/available
• Often nontoxic, nonflammable and

no explosive phases Model of molten Sodium Chloride

Source: Baudis (2001) Technologie der Salzschmelzen

Nitrate salt in a glass beaker Solid Liquid

www.DLR.de • Slide 24

Sensible heat storage in MOLTEN SALTS Ideal chemistry of molten nitrate salts

Steel N2 O2 NO3

• Cation

Anion K+ Na+

www.DLR.de • Slide 25

Steel

Sensible heat storage in MOLTEN SALTS Chemistry of molten nitrate salts with side reactions

N2 O2 CO3

2-

NO2

• CO2

O2- NO2 NO3

• Cation

Anion OH- H2O CrO4

2-

K+ Na+ NO

Sources: Federsel, K., Wortmann, J., Ladenberger, M. (2015) Energy Procedia, 69, pp. 618-625. Nissen, D.A., Meeker, D.E. (1983), Inorganic Chemistry, 22, pp. 716-721 Bradshaw, R.W., Dawson, D.B., De La Rosa, W., et al. (2002) Report SAND2002-0120. Bauer, T., Pfleger, N., Laing, D., et al. (2013) Chapter 20 in "Molten Salt Chemistry: from Lab to Applications"

www.DLR.de • Slide 26

Sensible heat storage in MOLTEN SALTS Thermal stability in air - methodology

• Materials:
• Solar Salt ~1kg
• Experimental conditions
• Tilting furnace
• Air atmosphere (no gas purging)
• 560 °C
• Sampling over 4000 h and post analysis of salt
• Differential scanning calorimeter
• Titration
• Ion chromatography
• UV-VIS spectroscopy

www.DLR.de • Slide 27

 Agreement of nitrite (NO2

• ) results with UV-VIS and ion chromatography

 Relatively stable nitrite (NO2

• ) and oxide (O2-) levels

 Significant carbonate (CO3

2-) formation from atmospheric CO2

Sensible heat storage in MOLTEN SALTS Thermal stability in air – results of carbonate formation

Decomposition reactions: 𝑂𝑃3

− → 𝑂𝑃2 − → 𝑃2− 𝐷𝑃2 𝐷𝑃3 2−

DLR.de • Slide 28

Oven test Supplier, Type, form, purity DSC Tm

in ºC

DSC ∆H

in J/g Merck, min. 99,99%, crystalline 304.6 175 Merck, min. 99,0%, crystalline See photo left BASF, typ. 99,2%, crystalline (without anti-caking agent) 303.9 171 BASF, typ. 99,2%, crystalline (with anti-caking agent) 303.1 167 SQM, typ. 99,6%, prills, refined grade (SSR) 302.6 165 SQM, min 98% Industrial grade, prills (SSI) 291.3 130

Sensible heat storage in MOLTEN SALTS Technical salt quality

Sensible heat storage in MOLTEN SALTS Thermophysical Properties – Heat Capacity

DLR.de • Slide 29

0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 50 100 150 200 250 300 350 400 450 500 Temperature [°C] Heat capacity [J/(g.K)]

KNO3 Gmelin (31) KNO3 Janz 1979 (2) KNO3 Nguyen-Duy 1980 (29) KNO3 Takahashi 1988 (93) KNO3 Carling 1983 (53) KNO3 Rogers 1982 (149) KNO3 Tufeu 1985 (122) KNO3 Gustafsson (117) KNO3 Barin 1995 (199) KNO3 Börnstein (153) KNO3 Chem. Kal. (184) KNO3 Kobayasi (160) KNO3 Perry (268) KNO3 Touloukian (102) NaNO3 Janz 1979 (2) NaNO3 Takahashi 1988 (93) NaNO3 Nguyen-Duy 1980 (29) NaNO3 Carling 1983 (53) NaNO3 Gmelin (31) NaNO3 Tufeu 1985 (122) NaNO3 Buckstegge (119) NaNO3 Rogers 1982 (149) NaNO3 Gustafsson (117) NaNO3 Barin 1995 (199) NaNO3 Chem. Kal. (184) NaNO3 Kobayasi (160) NaNO3 Perry (268) NaNO3 Touloukian (102) Hitec Janz 1981 (3) Hitec Voskresenskaya 1948 (23) Hitec Coastal Chem. (72) Hitec Janz 1983 (85) Hitec Buckstegge (119) Hitec Tufeu 1985 (122) Hitec Durferrit (130) Hitec Wagner (147) Hitec Kobayasi (160)

Heat flux type Differential Scanning Calorimeter (DSC)

Sensible heat storage in MOLTEN SALTS Thermophysical Properties – Thermal Diffusivity

DLR.de • Slide 30

• Equipment (Netzsch LFA457)
• Pulse heating: Nd-Glass laser
• Temperature measurement: InSb, N2 cooled
• 3-Layer aluminum or platinum crucible
• NaNO3 und Pt, Al: cp(T), a(T), ρ = const.
• Model: Netzsch (based on Hartmann et al.,

includes heat losses and pulse correction)

• Water reference measurements

Pt - layer 1 Laser beam SiC lid with thread Pt lid with expansion holes Solid or liquid salt sample Pt crucible SiC holding plate Optics and IR-detector (liquid N2 cooled) Graphite coating Graphite coating Salt - layer 2 l1 l2 l3 Pt - layer 3 0.31 mm 0.66 mm 0.30 mm Platinum lid with solid salt

• ca. 8 mm
• ca. 8 mm

Sensible heat storage in MOLTEN SALTS Metallic corrosion

DLR.de • Slide 31

• Major structural alloys:
• Low alloyed carbon steel (≤ 400°C)
• Cr-Mo steel (≤ 500°C)

(Cr-content up to about 9 wt%)

• Stainless Cr-Ni steel (≤ 570°C)

(with/without Mo, Nb, Ti alloying)

• Ni-alloys (≤ 650°C) (i.e. Alloy 800)
• Corrosion aspects:
• Solubility of metals from steel (e.g., Cr)
• Nitrate salt impurities (e.g., Cl)
• Nitrate salt decomposition products
• Stress corrosion cracking (SCC)

Corrosion system Source: Materials Testing Institute (MPA), University of Stuttgart

Metallic corrosion in molten salt flow

Sensible heat storage in MOLTEN SALTS Multicomponent mixtures with reduced melting temperature

DLR.de • Slide 32

Ion No. System Classification Example System with Tm 2 Single salt NaNO3 306 °C; KNO3 334 °C 3 Binary system, common anion K,Na//NO3 222 °C (“Solar Salt” system) 3 Binary system, common cation Na//NO2,NO3 230 °C 4 Ternary additive, common anion Ca,K,Na//NO3 ~130 °C (HitecXL) 4 Ternary additive, common anion K,Li,Na//NO3 ~120 °C (LiNaK) 4 Ternary reciprocal K,Na//NO2,NO3 142 °C (Hitec) 5 Quaternary additive, com. Anion Ca,K,Li,Na//NO3 90-110 °C 5 Quaternary reciprocal Li,Na,K//NO2,NO3 80 °C 6 Quinary reciprocal Ca,Li,Na,K//NO2,NO3 ~70 °C (DLR)

Sensible heat storage in MOLTEN SALTS Multicomponent mixtures – phase diagrams

DLR.de • Slide 33

Three-dimensional graphical representation of the quaternary reciprocal phase diagram A,B,C//Y,Z

• 6 vertices (single salts)
• 9 edges (binary systems)
• 6 common anion
• 3 common cation
• 5 faces (ternary systems)
• 2 ternary additive
• 3 ternary reciprocal

Source: Bauer, T. et al., Chapter 20 in "Molten Salt Chemistry: from Lab to Applications, " edited by Lantelme, F. and Groult, H., Elsevier

Sensible heat storage in MOLTEN SALTS Multicomponent mixtures – Existing methods for identification

DLR.de • Slide 34

• Present work focuses on high-throughput-screening methods
• Advantage:
• Applicable to all conceivable salt mixtures
• Disadvantage:
• For more complex systems numerous sub-systems exist
• For every system numerous salt compositions have to be analyzed

Sensible heat storage in MOLTEN SALTS Multicomponent mixtures – DLR innovative approach

DLR.de • Slide 35

Filter Filter A B A B B A B A B A B A A B A B B A B A B A B A Valve 1 Container 1 Sensor Heater Filter Drain Valve 2 Container 2 Vacuum pump S

2.)

Slow heating of pellet in apparatus T < Tsolidus A B A B B A B A B A B A

3.)

Liquid phase formation, detection,

• pening of valves and

extraction by suction T ≥ Tsolidus S

4.)

Follow-up examinations

• f new salt mixture:

1.) Thermal analysis (DSC, TG) 2.) Chemical composition with regard to anions and cations New salt mixture New salt mixture

1.)

Preparation of a compressed salt pellet with constituent A and B

DLR.de • Slide 36

Sensible heat storage in MOLTEN SALTS Multicomponent mixtures – results of identified salt

• Quinary reciprocal mixture with 4 cations and 2 anions
• LiNO3-Ca(NO3)2-NaNO2-KNO2 (24.6 - 13.6 - 16.8 - 45.0 wt%)
• Liquidus temperature: ~70 °C
• Long-term thermal stability: 400 °C in N2

(~70 K lower than Solar Salt by thermogravimetry)

• Heat capacity: 1.65 J/gK

DSC-measurement TG-measurement

• Thermal energy storage (TES) as a cross-sectoral technology for
• Increased flexibility to integrate volatile renewable energy
• Higher efficiency of industrial and power plant processes
• TES solutions from a broad technological basis for specific application
• TES material challenges are not only directed towards improved storage materials,

but also to material aspects in other components (e.g. vessel, heat exchangers…)

• Development of TES system includes several material aspects:
• Thermal and thermophysical properties
• Thermomechanical stability
• Metallic corrosion and material compatibility
• Decomposition processes and reaction kinetics
• Phase diagrams, melting and solidification processes (e.g. new mixtures)

Summary and Conclusions

DLR.de • Slide 37

Discussion

• Dr. Thomas Bauer

thomas.bauer@dlr.de + 49 2203 601 4094 Cologne, Germany