Concentrated Solar Power on Demand-CSPond - MIT
Concentrated Solar Power on Demand CSPond: Solar Harvesting and Storage Charles Forsberg Department of Nuclear Science and Engineering (NSE) Massachusetts Institute of Technology 77 Massachusetts Ave; Bld. 42-207a; Cambridge, MA 02139 Tel: (617) 324-4010; Email: [email protected] November, 2011
CSPond Faculty: Alexander Slocum (ME), Jacopo Buongiorno (NSE), Charles Forsberg (NSE), Thomas McKrell (NSE), Alexander Mitsos (ME), Jean-Christophe Nave (ME) CSPond Students: Daniel Codd (ME), Amin Ghobeity (ME), Corey J. Noone (ME), Stefano Passerini (NSE), Jennifer Rees (ME), Folkers Rojas (ME)
2
Joint Mechanical and Nuclear Science and Engineering Project Solar beam
Shared Liquid-Salt Technology Base Aperture (closes at night or in bad weather) Ground
L D
Fluoride-Salt HighTemperature Reactor (FHR)
Z
Graphite
Molten Salt Pond
Insulation
Salt to/from salt in loop at steam generator
Concentrated Solar Power on Demand (CSPonD)
3
Outline Existing solar systems CSPond Base Case Design Experimental Validation Alternative Design Options Path Forward A. Slocum, J. Buongiorno, C. W. Forsberg, T. McKrell, A. Mitsos, J. Nave, D. Codd, A. Ghobeity, C. J. Noone, S. Passerini, F. Rojas, “Concentrated Solar Power on Demand,” J. Solar Energy
4
Existing Solar Power Towers Mirrors reflect sunlight to boiler Boiler tubes on top of tall tower absorb light Heat water and convert to steam Steam turbine produces electricity Poor economics
High capital cost Low thermal efficiency PS-10, 11MWe peak, image courtesy of N. Hanumara
5
The Challenge is Cost Low efficiency system
In theory: high efficiency In practice
Low steam temperatures to avoid boiler-tube thermal fatigue from variable light
Wind and sunlight always changing energy fluxes
High heat loses from exposed boiler tubes
High costs
Mirrors
Largest cost component Incentives for efficient light to electricity system
Tall tower
PS-10, Spain, 11MWe peak, image courtesy of N. Hanumara
6
CSPond Base-Case Design
7
CSPond Characteristics Combining Many Technologies in a New Way Concentrated solar thermal power system Built-in thermal storage Heliostat field similar to solar power tower Radically different light receiver to:
Boost light-to-electricity efficiency Provide thermal heat storage
Unique features:
Light volumetrically absorbed in liquid salt bath Salt bath could operate to 1000°C
8
CSPond Description Figure Next Page
Mirrors shine sunlight to receiver Receiver is a high-temperature liquid salt bath inside insulated structure with open window for focused light
Small window minimizes heat losses but very high power density of sunlight through open window
Light volumetrically absorbed through several meters of liquid salt Building minimizes heat losses by receiver Enables salt temperatures to 900 C
Power density would destroy conventional boiler-tube collector Light absorbed volumetrically in several meters in salt
Requires high-temperature (semi-transparent) salt— Similar salt requirements as for FHR heat transfer loop
9
Two Component System Non-Imaging Refractor Lid
Lid Heat Extraction Hot Salt to HX
Cold Salt from HX Light Reflected From Hillside Heliostat rows to CSPonD System
(Not to scale!)
Light Collected Inside Insulated Building With Open Window
10
Advantages of Hillside Heliostat Field
Eliminate tower-based receiver—heavy equipment on ground Avoid remote storage and high pressure pumps Downward focused light Potentially lower land costs
11
CSPond Light Receiver
Efficient light-to-heat collection
Non-Imaging Refractor Lid
Hot Salt to HX
Concentrate light Focus light through small open window Minimize heat losses
Challenge Light energy per unit area very high Will vaporize solid collectors
Lid Heat Extraction
Cold Salt from HX
Light Volumetrically Absorbed in Liquid Salt Bath
12
Light Focused On “Transparent” Salt Light volumetrically absorbed through several meters of salt Molten salt experience Metal heat treating baths (right bottom) Molten salt nuclear reactor Advantages No light-flux limit No thermal fatigue Can go to extreme temperatures Molten Chloride Salt Bath (1100°C)
12
13
Salt Vapor Condenses On Ceiling Cooled ceiling: Lid Heat Extraction Salt buildup until “liquid” salt layer with flow back to salt bath Self-protecting, self-healing ceiling Highly reflective
Non-Imaging Refractor Lid
Lid Heat Extraction Hot Salt to HX
Cold Salt from HX
14
Capture Efficiency: Energy Balance
Heat to lid:
Qin
Qrad, pond-lid
Qconv, pond-lid Qvaporization Qreflected
System Losses: Qrad, lid-aperture Qconv, lid-aperture Qrad, pond-aperture
Qsalt
Qtank
ηcapture =
Qsystem Qin
=
Qin – Qlosses Qin
=
Qin – (Qrad, l-a + Qconv, l-a + Qrad, p-a + Qtank) Qin
15
Two Classes Of Molten Salts
Near-term: Nitrates
Appearance of molten NaCl-KCl salt at 850°C
Used in some concentrated thermal energy solar systems Off the shelf Temperature limit of ~550°C (Degradation)
Longer-term: Chlorides and Carbonates
Thermodynamically stable Peak temperatures > 1000°C
16
System Design Enables Efficient Light Collection and High Temperatures 1.0
fraction of incident energy at aperture
0.9
NREL Solar II: salt 565C
0.8 0.7 0.6
Chloride Salt: 950C lid temp 660C
NREL Solar I: steam 500C
0.5
Compares favorably with measured values for CSP Power Tower Systems
Nitrate Salt: 550C lid temp 240C
Peak & average values
0.4 0.3
Aperture to Illuminated Pond Area ratio
0.2
system output (MWe):
4
nominal pond size
0.1
diameter (m):
0.0 0
500
1000
1500
2000
2500
Peak Concentration (kW/m^2, 'suns')
3000
3500
depth (m):
avg beam down angle (deg): Nitrate Salt, Lid peak temp (C): Chloride Salt, Lid peak temp (C): NREL (2003)
25.0 5.0 21.4 550/240 950/660 16/29
17
CSPond Integral Heat Storage
Divider plate (moves down)
Salt tank has insulated separator plate Plate functions
Daytime
Separates hot and cold salt Bottom light absorber
Storage role
If excess heat input, plate sinks to provide hot salt storage volume If power demand high, plate raised with cold salt storage under plate
Nighttime
Divider plate (moves up)
18
Virtual Two-Tank Concept 4 MWe System Sizing: 2500 m3 salt 40 hours storage
Hot salt
Divider plate (moves down)
5m ∅28m
Daytime = charging
24/7 “hot salt” as the average temperature of the tank decreases when the sun is not shining
Nighttime
Cold salt Divider plate (moves up)
19
System Performance Uses for lid heat:
Chloride (950/660)
Overall System Useful Energy
Nitrate (550/240) Salt Useful Energy
Low temp (Nitrate) •Power cycle pre/reheat •RO feedwater heat •MED feedwater heat High temp (Chloride) •Power cycle primary heat system output (MWe):
4
nominal pond size Lid Useful Energy
diameter (m):
25.0
depth (m):
5.0
avg beam down angle (deg):
21.4
Nitrate Salt, Lid peak temp (C):
550/240
Chloride Salt, Lid peak temp (C):
950/660
Lid αvis /εir
0.44
Low-temp heat rejection (C):
25
20
CSPond Experimental Testing and Analysis
21
Molten Salt Optical Characterization Solar Irradiance Attenuation of NaClKCl (50-50wt%) salt at 850°C NaNO3-KNO 3 (60-40wt%)
NaCl-KCl (50-50wt%)
(l) Variable optical path length transmission apparatus (r) Appearance of molten NaCl-KCl salt at 850°C
Experimental Range
Stefano Passerini, Dr. Tom McKrell, Prof. Jacopo Buongiorno, MIT
22
60-Sun Solar Simulator 7x 1500 W metal halide lights MIT CSP Simulator
Spectral Intensity (arbitrary units)
Terrestrial solar spectrum
300
60 kW/m2 peak
∅38 cm aperture
Adjustable:
400
500
700
800
900
1000
height (0-1 m)
ε n = α solar = 0.11
70
Calculated Optical Power (kW/m 2)
600
wavelength (nm)
80
MIT CSP Solar Simulator
Commercial Xenon Solar Simulator
60
50
angle (0-90° tilt)
ε n = 0.05 α solar = 0.11
ε n = 0.06 α solar = 0.14
40
30
x
20
10
0
10.5 kWe
0
2
4
6
X = radial offset from aperture center (cm)
8
10
23
Volumetric Light Absorption 1
0.9
2.8 h
t=0 0.8
8.3 h
Height (x/L)
0.7
0.6
Increasing Increasing time time
0.5
0.4
0 h salt 0 h tank
0.3
2.8 h salt 0.2
2.8 h tank 8.3 h salt
0.1
8.3 h tank 0 200
220
240
260
280
300
320
340
Temperature (°C)
Temperature distribution of NaNO3KNO3 (60-40wt%) heated optically
360
24
Virtual Two-Tank System Testing Salt tank @ 300°C with nitrate salt
Ceramic (high temp) insulation
Fiberglass insulation
Inside Solar Simulator
25
Divided Thermocline Storage UP
DOWN
Temperature distribution of NaNO3-KNO3 (60-40wt%) heated optically Enables 24/7 power
25
26
Tank Wall Design
Flexible alloy liner Reduces thermal shock in refractory lining “Internal” firebrick insulation allows for mild steel tank shell
Flexible protective liner made of AISI 321H stainless steel
from Kolb (1993) and Gabbrielli (2009)
27
Solar Flux Distribution Modeling Incident Beam-down angle =
ϕ
Reflected θi
θr
θt
Transmitted
θ i = 90° − φ θr = θi n salt sin θ t = n air sin θ i
sin(θ t − θ i ) Rs = sin(θ t + θ i )
2
tan(θ t − θ i ) Rp = tan(θ t + θ i ) R = (Rs + R p ) / 2
2
CSPonD beam-down systems are in this range
1 Reflected intensity
0 0
45 Beam-down angle
90
Flux distribution in receiver from a single central heliostat
28
CSPond Alternative Design Options
29
Heliostat Field Placement Options Mirrors to Hilltop Collector
Tower Reflects Light Downward
Hillside Mirrors to Collector
30
Multiple Power Cycle Options Salt Temperature: 500°C, 700°C, and 700+°C
Steam power cycles--Today Supercritical carbon dioxide power cycle
High efficiency Very compact and potentially low cost Advanced technology
Air Brayton power cycle
Existing technology No cooling water options Requires 700 C salt temperatures
31
Carbon Dioxide Properties Result in Very Small Equipment Main compressor wheel: 85kW
Manufactured by Barber & Nichols for SNL
32
50-MWe Power Conversion Unit
Small Units Shop Fabricated
33
Air-Brayton Power Cycles Air Brayton power cycles have low cooling requirements relative to other power cycles Viable at salt peak temperatures of ~700 C
Significant efficiency penalties at lower temperatures
Several different options
34
Open-Air Recuperated Brayton Liquid-Salt Power Conversion Cycle
Stack
Air Inlet Recuperator
Heater
Reheater
salt
salt
Liquid Salt Air
Generator Compressor
Turbines
35
Open-Air Brayton Liquid-Salt Combined Cycle Power Cycle
Stack
Heat Recovery Steam Generator
Air Inlet
High Temperature Salt Air Water or Steam
Heater
Reheater
Reheater
salt
salt
salt
Generator Compressor
Turbines
36
Comparison of Brayton Power Cycles 700 C1 Salt; 100 MW(t) Plant Cycle
Air Brayton
Combined Cycle
Efficiency
40%
44%
Condenser Heat Rejection*
None (No water requirement)
28 MW(t)
1Efficiency
drops rapidly with peak temperature 2Traditional closed power cycles (Steam, Carbon Dioxide, Helium) with 50% efficiency reject 50 MW(t) to Condenser
37
CSPond Status Patents Pending
38
Two Parallel or Sequential Paths Forward Small 100 kw systems integration test using nitrate salts Uses proven existing solar salt Rapid testing possible
Develop higher-temperature chloride or carbonate CSPond Higher efficiency with potentially lower costs Robust against salt degradation Follow-on integration test with different salts
39
Next Step: 100 kWt Research System salt loop to/from HX
Overall receiver size: ~ 4m dia x 3m (w/o lid)
Lid geometry T.B.D. for 1-bounce down
Hot salt
Salt Tank: •2m dia x 2m depth •6.2 m3 salt capacity (11.2 metric tons) •Nitrate salt (550C/275C) •15 h storage (1.5 MWh) •2.4 MWh daily solar input required for continuous operation
Cold salt
Not shown: aperture cover, concentration “booster”, lid heat rejection system and divider plate actuator
40
Next Step: Alternative Salts Insufficient Data for Non-Nitrate Systems NaNO Solar Irradiance Attenuation of NaCl3-KNO3 (60-40wt%) KCl (50-50wt%) salt at 850°C
NaCl-KCl (50-50wt%) Higher temperature salts more robust (no possibility of thermal decomposition) Higher efficiency with open air Brayton power cycles and no water requirements
Experimental Range
Stefano Passerini, Dr. Tom McKrell, Prof. Jacopo Buongiorno, MIT
41
Conclusions Analysis and experiments indicate significantly better economics than existing concentrated solar power-tower systems (Higher efficiency) Significant uncertainties (Path forward)
No small pilot plant under realistic conditions Limited review (Wider review underway now that patent filings complete) Large incentives for higher-temperature salt than nitrate (more robust system and dry cooling) but limited experimental data
Large incentives to determine commercial viability of CSPond
42
Questions
42
43
Biography: Charles Forsberg Dr. Charles Forsberg is the Executive Director of the Massachusetts Institute of Technology Nuclear Fuel Cycle Study, Director and principle investigator of the HighTemperature Salt-Cooled Reactor Project, and University Lead for Idaho National Laboratory Institute for Nuclear Energy and Science (INEST) Nuclear Hybrid Energy Systems program. Before joining MIT, he was a Corporate Fellow at Oak Ridge National Laboratory. He is a Fellow of the American Nuclear Society, a Fellow of the American Association for the Advancement of Science, and recipient of the 2005 Robert E. Wilson Award from the American Institute of Chemical Engineers for outstanding chemical engineering contributions to nuclear energy, including his work in hydrogen production and nuclear-renewable energy futures. He received the American Nuclear Society special award for innovative nuclear reactor design on salt-cooled reactors. Dr. Forsberg earned his bachelor's degree in chemical engineering from the University of Minnesota and his doctorate in Nuclear Engineering from MIT. He has been awarded 11 patents and has published over 200 papers.
CSPond Faculty: Alexander Slocum (ME), Jacopo Buongiorno (NSE), Charles Forsberg (NSE), Thomas McKrell (NSE), Alexander Mitsos (ME), Jean-Christophe Nave (ME) CSPond Students: Daniel Codd (ME), Amin Ghobeity (ME), Corey J. Noone (ME), Stefano Passerini (NSE), Jennifer Rees (ME), Folkers Rojas (ME)
2
Joint Mechanical and Nuclear Science and Engineering Project Solar beam
Shared Liquid-Salt Technology Base Aperture (closes at night or in bad weather) Ground
L D
Fluoride-Salt HighTemperature Reactor (FHR)
Z
Graphite
Molten Salt Pond
Insulation
Salt to/from salt in loop at steam generator
Concentrated Solar Power on Demand (CSPonD)
3
Outline Existing solar systems CSPond Base Case Design Experimental Validation Alternative Design Options Path Forward A. Slocum, J. Buongiorno, C. W. Forsberg, T. McKrell, A. Mitsos, J. Nave, D. Codd, A. Ghobeity, C. J. Noone, S. Passerini, F. Rojas, “Concentrated Solar Power on Demand,” J. Solar Energy
4
Existing Solar Power Towers Mirrors reflect sunlight to boiler Boiler tubes on top of tall tower absorb light Heat water and convert to steam Steam turbine produces electricity Poor economics
High capital cost Low thermal efficiency PS-10, 11MWe peak, image courtesy of N. Hanumara
5
The Challenge is Cost Low efficiency system
In theory: high efficiency In practice
Low steam temperatures to avoid boiler-tube thermal fatigue from variable light
Wind and sunlight always changing energy fluxes
High heat loses from exposed boiler tubes
High costs
Mirrors
Largest cost component Incentives for efficient light to electricity system
Tall tower
PS-10, Spain, 11MWe peak, image courtesy of N. Hanumara
6
CSPond Base-Case Design
7
CSPond Characteristics Combining Many Technologies in a New Way Concentrated solar thermal power system Built-in thermal storage Heliostat field similar to solar power tower Radically different light receiver to:
Boost light-to-electricity efficiency Provide thermal heat storage
Unique features:
Light volumetrically absorbed in liquid salt bath Salt bath could operate to 1000°C
8
CSPond Description Figure Next Page
Mirrors shine sunlight to receiver Receiver is a high-temperature liquid salt bath inside insulated structure with open window for focused light
Small window minimizes heat losses but very high power density of sunlight through open window
Light volumetrically absorbed through several meters of liquid salt Building minimizes heat losses by receiver Enables salt temperatures to 900 C
Power density would destroy conventional boiler-tube collector Light absorbed volumetrically in several meters in salt
Requires high-temperature (semi-transparent) salt— Similar salt requirements as for FHR heat transfer loop
9
Two Component System Non-Imaging Refractor Lid
Lid Heat Extraction Hot Salt to HX
Cold Salt from HX Light Reflected From Hillside Heliostat rows to CSPonD System
(Not to scale!)
Light Collected Inside Insulated Building With Open Window
10
Advantages of Hillside Heliostat Field
Eliminate tower-based receiver—heavy equipment on ground Avoid remote storage and high pressure pumps Downward focused light Potentially lower land costs
11
CSPond Light Receiver
Efficient light-to-heat collection
Non-Imaging Refractor Lid
Hot Salt to HX
Concentrate light Focus light through small open window Minimize heat losses
Challenge Light energy per unit area very high Will vaporize solid collectors
Lid Heat Extraction
Cold Salt from HX
Light Volumetrically Absorbed in Liquid Salt Bath
12
Light Focused On “Transparent” Salt Light volumetrically absorbed through several meters of salt Molten salt experience Metal heat treating baths (right bottom) Molten salt nuclear reactor Advantages No light-flux limit No thermal fatigue Can go to extreme temperatures Molten Chloride Salt Bath (1100°C)
12
13
Salt Vapor Condenses On Ceiling Cooled ceiling: Lid Heat Extraction Salt buildup until “liquid” salt layer with flow back to salt bath Self-protecting, self-healing ceiling Highly reflective
Non-Imaging Refractor Lid
Lid Heat Extraction Hot Salt to HX
Cold Salt from HX
14
Capture Efficiency: Energy Balance
Heat to lid:
Qin
Qrad, pond-lid
Qconv, pond-lid Qvaporization Qreflected
System Losses: Qrad, lid-aperture Qconv, lid-aperture Qrad, pond-aperture
Qsalt
Qtank
ηcapture =
Qsystem Qin
=
Qin – Qlosses Qin
=
Qin – (Qrad, l-a + Qconv, l-a + Qrad, p-a + Qtank) Qin
15
Two Classes Of Molten Salts
Near-term: Nitrates
Appearance of molten NaCl-KCl salt at 850°C
Used in some concentrated thermal energy solar systems Off the shelf Temperature limit of ~550°C (Degradation)
Longer-term: Chlorides and Carbonates
Thermodynamically stable Peak temperatures > 1000°C
16
System Design Enables Efficient Light Collection and High Temperatures 1.0
fraction of incident energy at aperture
0.9
NREL Solar II: salt 565C
0.8 0.7 0.6
Chloride Salt: 950C lid temp 660C
NREL Solar I: steam 500C
0.5
Compares favorably with measured values for CSP Power Tower Systems
Nitrate Salt: 550C lid temp 240C
Peak & average values
0.4 0.3
Aperture to Illuminated Pond Area ratio
0.2
system output (MWe):
4
nominal pond size
0.1
diameter (m):
0.0 0
500
1000
1500
2000
2500
Peak Concentration (kW/m^2, 'suns')
3000
3500
depth (m):
avg beam down angle (deg): Nitrate Salt, Lid peak temp (C): Chloride Salt, Lid peak temp (C): NREL (2003)
25.0 5.0 21.4 550/240 950/660 16/29
17
CSPond Integral Heat Storage
Divider plate (moves down)
Salt tank has insulated separator plate Plate functions
Daytime
Separates hot and cold salt Bottom light absorber
Storage role
If excess heat input, plate sinks to provide hot salt storage volume If power demand high, plate raised with cold salt storage under plate
Nighttime
Divider plate (moves up)
18
Virtual Two-Tank Concept 4 MWe System Sizing: 2500 m3 salt 40 hours storage
Hot salt
Divider plate (moves down)
5m ∅28m
Daytime = charging
24/7 “hot salt” as the average temperature of the tank decreases when the sun is not shining
Nighttime
Cold salt Divider plate (moves up)
19
System Performance Uses for lid heat:
Chloride (950/660)
Overall System Useful Energy
Nitrate (550/240) Salt Useful Energy
Low temp (Nitrate) •Power cycle pre/reheat •RO feedwater heat •MED feedwater heat High temp (Chloride) •Power cycle primary heat system output (MWe):
4
nominal pond size Lid Useful Energy
diameter (m):
25.0
depth (m):
5.0
avg beam down angle (deg):
21.4
Nitrate Salt, Lid peak temp (C):
550/240
Chloride Salt, Lid peak temp (C):
950/660
Lid αvis /εir
0.44
Low-temp heat rejection (C):
25
20
CSPond Experimental Testing and Analysis
21
Molten Salt Optical Characterization Solar Irradiance Attenuation of NaClKCl (50-50wt%) salt at 850°C NaNO3-KNO 3 (60-40wt%)
NaCl-KCl (50-50wt%)
(l) Variable optical path length transmission apparatus (r) Appearance of molten NaCl-KCl salt at 850°C
Experimental Range
Stefano Passerini, Dr. Tom McKrell, Prof. Jacopo Buongiorno, MIT
22
60-Sun Solar Simulator 7x 1500 W metal halide lights MIT CSP Simulator
Spectral Intensity (arbitrary units)
Terrestrial solar spectrum
300
60 kW/m2 peak
∅38 cm aperture
Adjustable:
400
500
700
800
900
1000
height (0-1 m)
ε n = α solar = 0.11
70
Calculated Optical Power (kW/m 2)
600
wavelength (nm)
80
MIT CSP Solar Simulator
Commercial Xenon Solar Simulator
60
50
angle (0-90° tilt)
ε n = 0.05 α solar = 0.11
ε n = 0.06 α solar = 0.14
40
30
x
20
10
0
10.5 kWe
0
2
4
6
X = radial offset from aperture center (cm)
8
10
23
Volumetric Light Absorption 1
0.9
2.8 h
t=0 0.8
8.3 h
Height (x/L)
0.7
0.6
Increasing Increasing time time
0.5
0.4
0 h salt 0 h tank
0.3
2.8 h salt 0.2
2.8 h tank 8.3 h salt
0.1
8.3 h tank 0 200
220
240
260
280
300
320
340
Temperature (°C)
Temperature distribution of NaNO3KNO3 (60-40wt%) heated optically
360
24
Virtual Two-Tank System Testing Salt tank @ 300°C with nitrate salt
Ceramic (high temp) insulation
Fiberglass insulation
Inside Solar Simulator
25
Divided Thermocline Storage UP
DOWN
Temperature distribution of NaNO3-KNO3 (60-40wt%) heated optically Enables 24/7 power
25
26
Tank Wall Design
Flexible alloy liner Reduces thermal shock in refractory lining “Internal” firebrick insulation allows for mild steel tank shell
Flexible protective liner made of AISI 321H stainless steel
from Kolb (1993) and Gabbrielli (2009)
27
Solar Flux Distribution Modeling Incident Beam-down angle =
ϕ
Reflected θi
θr
θt
Transmitted
θ i = 90° − φ θr = θi n salt sin θ t = n air sin θ i
sin(θ t − θ i ) Rs = sin(θ t + θ i )
2
tan(θ t − θ i ) Rp = tan(θ t + θ i ) R = (Rs + R p ) / 2
2
CSPonD beam-down systems are in this range
1 Reflected intensity
0 0
45 Beam-down angle
90
Flux distribution in receiver from a single central heliostat
28
CSPond Alternative Design Options
29
Heliostat Field Placement Options Mirrors to Hilltop Collector
Tower Reflects Light Downward
Hillside Mirrors to Collector
30
Multiple Power Cycle Options Salt Temperature: 500°C, 700°C, and 700+°C
Steam power cycles--Today Supercritical carbon dioxide power cycle
High efficiency Very compact and potentially low cost Advanced technology
Air Brayton power cycle
Existing technology No cooling water options Requires 700 C salt temperatures
31
Carbon Dioxide Properties Result in Very Small Equipment Main compressor wheel: 85kW
Manufactured by Barber & Nichols for SNL
32
50-MWe Power Conversion Unit
Small Units Shop Fabricated
33
Air-Brayton Power Cycles Air Brayton power cycles have low cooling requirements relative to other power cycles Viable at salt peak temperatures of ~700 C
Significant efficiency penalties at lower temperatures
Several different options
34
Open-Air Recuperated Brayton Liquid-Salt Power Conversion Cycle
Stack
Air Inlet Recuperator
Heater
Reheater
salt
salt
Liquid Salt Air
Generator Compressor
Turbines
35
Open-Air Brayton Liquid-Salt Combined Cycle Power Cycle
Stack
Heat Recovery Steam Generator
Air Inlet
High Temperature Salt Air Water or Steam
Heater
Reheater
Reheater
salt
salt
salt
Generator Compressor
Turbines
36
Comparison of Brayton Power Cycles 700 C1 Salt; 100 MW(t) Plant Cycle
Air Brayton
Combined Cycle
Efficiency
40%
44%
Condenser Heat Rejection*
None (No water requirement)
28 MW(t)
1Efficiency
drops rapidly with peak temperature 2Traditional closed power cycles (Steam, Carbon Dioxide, Helium) with 50% efficiency reject 50 MW(t) to Condenser
37
CSPond Status Patents Pending
38
Two Parallel or Sequential Paths Forward Small 100 kw systems integration test using nitrate salts Uses proven existing solar salt Rapid testing possible
Develop higher-temperature chloride or carbonate CSPond Higher efficiency with potentially lower costs Robust against salt degradation Follow-on integration test with different salts
39
Next Step: 100 kWt Research System salt loop to/from HX
Overall receiver size: ~ 4m dia x 3m (w/o lid)
Lid geometry T.B.D. for 1-bounce down
Hot salt
Salt Tank: •2m dia x 2m depth •6.2 m3 salt capacity (11.2 metric tons) •Nitrate salt (550C/275C) •15 h storage (1.5 MWh) •2.4 MWh daily solar input required for continuous operation
Cold salt
Not shown: aperture cover, concentration “booster”, lid heat rejection system and divider plate actuator
40
Next Step: Alternative Salts Insufficient Data for Non-Nitrate Systems NaNO Solar Irradiance Attenuation of NaCl3-KNO3 (60-40wt%) KCl (50-50wt%) salt at 850°C
NaCl-KCl (50-50wt%) Higher temperature salts more robust (no possibility of thermal decomposition) Higher efficiency with open air Brayton power cycles and no water requirements
Experimental Range
Stefano Passerini, Dr. Tom McKrell, Prof. Jacopo Buongiorno, MIT
41
Conclusions Analysis and experiments indicate significantly better economics than existing concentrated solar power-tower systems (Higher efficiency) Significant uncertainties (Path forward)
No small pilot plant under realistic conditions Limited review (Wider review underway now that patent filings complete) Large incentives for higher-temperature salt than nitrate (more robust system and dry cooling) but limited experimental data
Large incentives to determine commercial viability of CSPond
42
Questions
42
43
Biography: Charles Forsberg Dr. Charles Forsberg is the Executive Director of the Massachusetts Institute of Technology Nuclear Fuel Cycle Study, Director and principle investigator of the HighTemperature Salt-Cooled Reactor Project, and University Lead for Idaho National Laboratory Institute for Nuclear Energy and Science (INEST) Nuclear Hybrid Energy Systems program. Before joining MIT, he was a Corporate Fellow at Oak Ridge National Laboratory. He is a Fellow of the American Nuclear Society, a Fellow of the American Association for the Advancement of Science, and recipient of the 2005 Robert E. Wilson Award from the American Institute of Chemical Engineers for outstanding chemical engineering contributions to nuclear energy, including his work in hydrogen production and nuclear-renewable energy futures. He received the American Nuclear Society special award for innovative nuclear reactor design on salt-cooled reactors. Dr. Forsberg earned his bachelor's degree in chemical engineering from the University of Minnesota and his doctorate in Nuclear Engineering from MIT. He has been awarded 11 patents and has published over 200 papers.
