cooling options for geothermal and concentrating solar...
TRANSCRIPT
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Chuck KutscherNational Renewable Energy Laboratory
Cooling Options for Geothermal and Concentrating Solar Power Plants
EPRI Workshop on Advanced Cooling Technologies
July 9, 2008
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Geothermal
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Relevance• Air-cooled geothermal plants especially susceptible to
high ambient temperature
• Plant power decreases ~1% of rated power for every 1ºF rise in condenser temperature
• Output of air-cooled plant can drop > 50% in summer, when electricity is highly valued
Unit 200 Performance Data
-
500
1,000
1,500
2,000
2,500
3,000
40 45 50 55 60 65 70 75 80 85Ambient Temperature °F (@weather station)
Net
Out
put -
kW
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Water-Saving OptionsApproach Pros Cons
ACC + WCC in Series - ACC can handle desuperheating load
- Cost of dual equipment- Condensate temp. very
limited ACC + WCC in Parallel - Simple design
- Improves approach to dry bulb
- Condensate temp. limited by dry bulb
ACC w/ Evap Media - Can achieve good approach to wet bulb on inlet air
- Cost of media- Pressure drop lowers
flow rate and LMTDACC w/ Spray Nozzles - Simple, low cost of
nozzles- Low pressure drop
- Overspray and water waste
- Cost of water treatment or mist eliminator
- Nozzle maintenance- Potential damage to
finned tubesDeluge of ACC - Highest enhancement - Water treatment or
protective coating needed
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Spreadsheet Model of Evaporative Enhancements to Existing Air-Cooled Plants
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System 1 - Spray Cooling
• Low cost, low air pressure drop• High water pressure• Over-spray and carryover or cost of mist
eliminator• Nozzle clogging
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System 2 - Munters Cooling
• High efficiency, minimum carryover• High air pressure drop (reduces air flow
rate and decreases LMTD)• High cost
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System 3 – Hybrid Cooling
• Inexpensive and simple, used in poultry industry
• Over-spray, carryover, and nozzle cleaning
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System 4 – Deluge Cooling
• Excellent performance• Danger of scaling and deposition without
pure water
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Example Analysis: Net Power Produced
Total Kilowatt-hours Produced
500,000
600,000
700,000
800,000
900,000
Kilo
wat
t-hou
rs
No EnhancementSpray CoolingMunters CoolingDeluge CoolingHybrid Cooling
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
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Example Cost Results
5.2
6.4
7.67.2
8.5
9.9
5.7
7.2
8.7
3.54.2
4.9
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0C
ents
/kW
h
System 1 - SprayCooling
System 2 -Munters Cooling
System 3 -Hybrid Cooling
System 4 -Deluge Cooling
Incremental Cost of Added ElectricityDiscount Rate = 10%, Plant Life = 25 years
$0/kgal$0.5/kgal$1/kgal
Note: Value of electricity will be affected by time-of-day ratesand capacity payments.
Note: Value of electricity will be affected by time-of-day ratesand capacity payments.
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Geothermal Analysis Conclusions
• Deluge most attractive if scaling/corrosion issues can be addressed
• Systems 1 to 3 obtain ~40 kWh/kgal of water; deluge can produce an average of ~60 kWh/kgal
• Results very sensitive to water costs, electric rate structure, installation costs
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Coated Fin Test ResultsCoated Fin Test Results
OMP-coated fin unaffected by salt spray
Plain fin pitted
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Measurements at Mammoth
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Measurements at Mammoth Binary-Cycle Geothermal Power
PlantMunters system
Hybrid spray/Munters system
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Mammoth Measurement Results: 2001
• Field instrumentation: Type T thermocouples, optical dew point (chilled mirror) hygrometer, handheld anemometer
• Munters had 79% saturation efficiency; hybrid was 50%
• Flow rate with Munters dropped 22-28%
• Munters increased net power 62% (800 kW to 1,300 kW) at 78ºF ambient
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Munters Performance at Mammoth
Unit 200 Performance Data
-
500
1,000
1,500
2,000
2,500
3,000
40 45 50 55 60 65 70 75 80 85Ambient Temperature °F (@weather station)
Net
Out
put -
kW
after Munters
before Munters
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Mammoth Measurement Results: 2002
• Munters system modified, brine used for cooling water. Munters efficiency dropped from 79% to 66%
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Geothermal Conclusions• All operators of air-cooled plants interested in evaporative
enhancement
• Costs at existing plants are site-specific and negotiable; $0.50 to $2.00 per thousand gallons
• Reclaimed water becoming more widely available
• Two-Phase Engineering showed successful use of nozzles with brine
• Can reduce average cost of electricity by about 0.3¢/kWh, depending on cost of water
• Capacity payments can be as high as 30 ¢/kWh and lower average cost of electricity by 2–3 ¢/kWh
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Tabbed Fin Concept
Tabbed Plate FinTabbed Plate Fin Tabbed Plate Fin Heat ExchangerTabbed Plate Fin Heat Exchanger
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Individual Fins
GEA fins w/spacersGEA fins w/spacers NREL tabbed circular finNREL tabbed circular fin
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Detailed CFD Model Isometric Views:
Heat Flux and Total Pressure
Surface Heat FluxSurface Heat Flux Total PressureTotal Pressure
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CSP: The Other Solar Energy
Parabolic trough
Linear Fresnel
Power towerDish-Stirling
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354 MW Luz Solar Electric Generating Systems (SEGS)1984 - 1991
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New 64 MW Acciona Solar Parabolic Trough Plant
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CSP Power Plant with Thermal Storage
HX
HotTank
ColdTank
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Study of Evaporative Pre-Cooling for Trough Plants
• Air-Cooled• Water-Cooled• Air-Cooled with Spray Enhancement
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0
2000
4000
6000
8000
10000
12000
0 1 2 3 4 5 6 7 8 9 10 11 12 13Month Number
Ele
ctric
ity P
rodu
ced
[MW
e-hr
]
Water CooledEvaporatively Pre-cooledAir Cooled
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Effect of Purchase Price of Electricity on Yearly Revenue(Water Cost = $2/kgal)
-4.0%
-2.0%
0.0%
2.0%
4.0%
6.0%
0.00 0.04 0.08 0.12 0.16 0.20 0.24
Price of Electricity [$/kWh]
Perc
ent I
ncre
ase
in Y
early
Rev
enue
(C
ompa
red
to A
ir-C
oole
d)
Water CooledEvaporatively Pre-cooled
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Report on Reducing CSP Water Usage
• Hybrid air/water cooling systems can reduce water use 80% with modest performance and cost penalties
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0.94
0.95
0.96
0.97
0.98
0.99
1.00
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Fraction of wet cooling tower water consumption
Frac
tion
of w
et c
oolin
g to
wer
net
pla
nt o
utpu
t
Dry
8 in. HgA
6 in. HgA
4 in. HgA
2.5 in. HgA
Wet
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CSP Cooling Conclusions
• Water cooling most economic • Water-cooled trough plant uses about 800
gal/MWh of which 20 is for mirror washing; power towers use less, linear Fresnel uses more; dish/engine air-cooled
• Air cooling eliminates 90% of water use but increases LEC by 2 to 10%
• Hybrid (parallel air/water) reduces cost penalty while still saving about 80% of the water