Synthesis and characterization of new nitrate salt ... · PDF fileSynthesis and...

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

Insta

lled

po

wer

[GW

el]

Po

wer

pro

du

cti

on

[T

Wh

el]

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 operation, 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

o Storage density (system)

o System cost (CAPEX, OPEX)

o Space needed

o CO2-mitigation potential

o Operation characteristics …

Storage Technology

Thermo-

chemical

Latent

Heat

Sensible

Heat

Application Storage Requirements

o Temperature level

o Heat transfer fluid

o (Dis-) Charging characteristics

o Storage capacity

o 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


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


Commercial status of direct storage technology

Source: SolarReserve

Source: SolarReserve

DLR.de • Slide 15


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

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





















Focus of the DLR group

System aspects

Components

Process technology

Material (Upscaling)

aspects

DLR.de • Slide 17


TESIS:com - component test-bench

DLR.de • Slide 18


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


TESIS:store - Storage Test Section

DLR.de • Slide 20


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


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


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


Ideal chemistry of molten nitrate salts

S

teel

N2 O2

NO3-

Cation Anion

K+ Na+


S

teel


Chemistry of molten nitrate salts with side reactions

N2 O2

CO32-

NO2-

CO2

O2-

NO2

NO3-

Cation Anion

OH-

H2O

CrO42- 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"



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


Agreement of nitrite (NO2-) results with UV-VIS and ion chromatography

Relatively stable nitrite (NO2-) and oxide (O2-) levels

Significant carbonate (CO32-) formation from atmospheric CO2


Thermal stability in air – results of carbonate formation

Decomposition reactions:

𝑁𝑂3− → 𝑁𝑂2

− → 𝑂2−𝐶𝑂2

𝐶𝑂32−

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


Technical salt quality


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

0 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)


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


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


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)


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


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


Multicomponent mixtures – DLR innovative approach

DLR.de • Slide 35

FilterFilter

AB

A

B B

A

BA

BAB

A AB

A

B B

A

BA

BAB

A

Valve 1Container 1SensorHeaterFilter

DrainValve 2

Container 2Vacuum pump

S

2.)Slow heating of pellet in apparatusT < Tsolidus

AB

A

B BA

BA

BAB

A

3.)Liquid phase formation, detection, opening of valves and extraction by suctionT ≥ Tsolidus

S

4.)Follow-up examinations of new salt mixture:1.) Thermal analysis (DSC, TG)2.) Chemical composition with regard to anions and cations

New salt mixtureNew salt mixture

1.)Preparation of a compressed salt pellet with constituent A and B

DLR.de • Slide 36


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

[email protected]

+ 49 2203 601 4094

Cologne, Germany

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