Supplemental Cooling: An Application of Thermal Energy Storage in the Power Industry
Energy Storage in the Electric Network WorkshopInstituto Nacional de Electricidad y Energias Limpias
November 14-16; Cuernava, Mexico
Joshua Charles, Sudhakar Neti, Chunjian Pan, Carlos E. Romero, ArunachalamSubramanian, Xingchao Wang, He Yun, et al.
Energy Research Center
Lehigh University
Typical Coal-Fired Power Plant
Thermal efficiency severely limited by temperature difference between hot and cold
reservoirs of the thermodynamic cycle.
2
Thermal water discharge rates are limited for once-
through cooled plants.
Cooling LimitationsThere is a strong interest in greatly reduce
water withdraw and consumption from fossil power plants.
Air cooled condensers can be severely limited when
ambient temperatures rise.
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For this plant, a temperature rise from
72°F to 92°F on average reduces
generator output by 25%.
Impact of Air Cooled Condensers
To meet grid demand, this lost generation must come
from other generation sources. Fossil generation has a 1:1 relationship with
emissions.
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The
Proposed
Solution
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Air Cooled Condensers with Thermal Energy Storage
Warm Cooling
Fluid In
Cooled Cooling
Fluid Out
Fans
Thermosyphon with Internal Switch
Phase Change Material
Self-Agitated Fins
Research on a novel dry cooling
technology for application in power
plants (part of ARPA-e’s Advanced
Research in Dry Cooling (ARID) Program).
Project participants include ACT, Inc.,
Univ. of Missouri, Evapco, Inc. and
Lehigh University.
ARPA-e’s target for LCOE of
supplemental cooling is <$150/kWth.
Cool storage system involves heat pipes,
phase change materials (PCMs) and self-
agitated fins.
Salt hydrate PCMs are inexpensive and
their melting point can be tuned to
optimize the system efficiency for
different seasons and time of the day.
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AIR COOLED CONDERSERS WITH THERMAL ENERGY STORAGE
1. Initial screening of PCM candidates by their storage capacity (latent heat), using Differential Scanning Calorimetry (DSC). Target storage capacity = 170 J/g.
2. Drop calorimeter designed and calibrated to measure storage capacity of encapsulated PCMs. Target degradation of storage capacity <10%.
3. Cycling apparatus designed and fabricated to provide short-term and long-term thermal cycling performance evaluation (300 and 2,000 cycles, with ~2 hours - heating/cooling).
4. Supercooling and phase instability issues studied with programmable water bath, Thermogravimetric Analyzer (TGA).
5. Static and cycling corrosion testing of encapsulated materials (ASTM-G1). Target performance indicated by < 2 mils/year, < 12% increase in thermal resistance, ease of fabrication.
6. CFD simulations of heat transfer and melting process to guide and optimize design, and perform scale-up analysis.
7. Design and testing of 0.06, 1.0 and 200 kWh prototype systems.
8. Thermo-economic analysis.
Work Plan
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8
Lehigh University - PCM and System Development
PCM Development Corrosion Testing System Modeling
DSC
Testing
PCM
Cycling
Drop
Calorimeter
Test
Method
Verificatio
n & Metal
Selection
Isothermal
Testing
Cycle
Testing
One Unit
Cell Model
1kWh
System
Model
Full-Scale System
Model
0 10 20 30 40 500
0.2
0.4
0.6
0.8
1
Time (mins)
Tota
l avera
ge L
iquid
Fra
ction
dT=7C convection
dT=7C conduction
dT=10C convection
dT=10C conduction
Tm [°C] Hf [kJ/kg] $/kg $/MJ
Hydrated Salts
KF · 4H2O 18.5 231 1 4
CaCl2 ∙ 6H2O 29.0 180 0.3 1.5
Na2SO4 ∙ 10H2O 32.5 250 0.1 0.5
Hydrated Salt Mixtures
CaCl2 · 6H2O (93%) + KNO3 (7%) 25 120 0.3 2
CaCl2 ∙ 6H2O (66%) + MgCl2 ∙ 6H2O (33%) 25 127 0.1 0.7
Tm [°C] Hf [kJ/kg] $/kg $/MJ
Hydrated Salts
KF · 4H2O 18.5 231 1 4
CaCl2 ∙ 6H2O 29.0 180 0.3 1.5
Na2SO4 ∙ 10H2O 32.5 250 0.1 0.5
Hydrated Salt Mixtures
25 120 0.3 2
25 127 0.1 0.7
The Phase Change Materials
Correct Phase Change Temp. (15-30°C)
High Latent Heat
No Health Hazards
Long-Term Stability/Performance
Low Cost
Selection
Criteria
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DSC of CaCl2·6H2O + MgCl2·6H2O
Tm ~ 25°C
Hf as found in literature.
5-Cycle test showed good
stability.
CaCl2 · 6H2OPhase Change Temp: 29°C
Latent Heat: 180 J/g
The GoodLow Cost (it’s Road Salt)
Safe
Well-researched
The BadSupercooling
Corrosive
Long-term Phase Instability
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No Supercooling
Supercooling
Must lower temperature below freezing temperature before freezing begins
Supercooling
Freezing Temp.
What did we do? CaCl2 · 6H2O + 3% SrCl2 · 6H2O
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Long-Term Stability200g PCM samples were prepared along with a drop calorimeter to
measure their latent heat
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Cycling
Over 20 of these samples were cycled
with 1 heating or cooling period lasting 75
minutes.
Each sample was calorimetry tested
before and after cycling to note any change in
the latent heat.
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Hot and cold water is cycled between two PCM tanks.
Heating and cooling systems maintain water temperature.
A pump circulates water to the top tank.
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Cycling Results
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Solving Separation
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Appears to have some separation over several thousand cycles.
Appears to have no
meaningful separation
even after 2000 cycles.
Corrosion Testing5 Metals were Corrosion Tested in all 3 PCM’s
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Corrosion
Testing
Carbon steel had good long-term corrosion performance
while in contact with all 3 PCMs
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20
Copper Low Carbon Steel
Al 5086 Al 6061
PCM: CaCl₂⋅6H₂O
Long-term Corrosion Testing of PCM/Metal Pairs
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CaCl2·6H2O
All metals perform well at
isothermal conditions
Al 5086 fails under cycling
Long-term Corrosion Testing of PCM/Metal Pairs
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CaCl2·6H2O
+
7% KNO3
CaCl2·6H2O +
18%
MgCl2·6H2O
System Development
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PCM System Modeling
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Unit-Cell PCM Module Model 1 kWh System Model
Showed potential for modeling PCM-heat
pipe system by looking at a single unit cell.
0 10 20 30 40 500
0.2
0.4
0.6
0.8
1
Time (mins)T
ota
l avera
ge L
iquid
Fra
ction
dT=7C convection
dT=7C conduction
dT=10C convection
dT=10C conduction
Applied results from unit-cell model to model of 1 kWh system (a stack of unit
cells)
2D PCM Model
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Optimization Studies of Prototype System
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Qf/V is always greater for radial plate fins than for base fins,
which implies that fewer trays with more radial fins is optimal
Is it better to have more trays (more base fins)
or more radial plate fins?
Analy
tical R
esu
lts
Full-Size System Modeling
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Overview of Proposed PCM Cold Storage System
Have proposed a Layered Thermal Resistance (LTR)
model to further simplify the model of the 800 MWh
system.
Full-Size System Modeling
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Mismatch between
energy flux and ambient
temperature curves
A system for optimal usage
of the PCM is being
developed
Equations and parameters
governing the control of this
system are under development.
Testing of A Carbon Steel Heat Pipe
Time (Second)
Tem
per
atu
re (
Cel
siu
s)
Tem
per
atu
re V
aria
tio
n (
Cel
sius)
Tem
per
atu
re V
aria
tio
n (
Cel
siu
s)
Tem
per
atu
re (
Cel
siu
s)
29
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Accomplishments
• Modeling results to date demonstrate
cost benefit below $140/kWth.
• Accelerated heat pipe life test has
determined potential envelope/working
fluid choices.
• Fin agitator has demonstrated 60%
improvement in HTC.
• No appreciable change in PCM latent
heat of fusion through 2,000 thermal
cycles, solving supercooling and
separation issues.
• Less than 2 mil/year corrosion rate for
salt hydrates on metal materials.
Prototypes
• 1 kWh integrated test system
• 200 kWh full scale system (in progress)
Current Research Effort
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Technology to Market
• Value Proposition
• Reduce water consumption/peak
power demand
• Low cost, fast payback
• Easy to retrofit
• Long-term Target Market
• Power Plant Dry Cooling
• Value Proposition
• TEA shows lowered power plant
LCOE and improved efficiency
• Tunable PCM maximizes the
benefit of cool storage
• Self-Agitated Fin reduces the
power consumption during PCM
regeneration
• Analysis of Full-Scale Plant Data
• NREL
• Covanta
• Dominion Energy
For More Information, Contact:
Dr. Carlos E. Romero
Director
Lehigh University
Energy Research Center
117 ATLSS Drive
Bethlehem, PA 18015-4729
Telephone: (610) 758-4092
Fax: (610) 758-5959
Internet: [email protected]
www.lehigh.edu/energy
Questions???
