Download - Geothermal Energy Power Generation
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Geothermal EnergyPower Generation
San Jose State University
FX RongèreMarch 2009
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Geothermal Power Generation in the World
Located along the main plate boundaries
1995 2000 2003(MWe) (MWe) (MWe)
Argentina 1 - -Australia 0 0 0Austria - - 1China 29 29 28Costa Rica 55 143 163El Salvador 105 161 161Ethiopia - 7 7France 4 4 15Germany - - 0Guatemala - 33 29Iceland 50 170 200Indonesia 310 590 807Italy 632 785 791J apan 414 547 561Kenya 45 45 121Mexico 753 755 953New Zealand 286 437 421Nicaragua 70 70 78Papua New Guinea - - 6Philippines 1,227 1,909 1,931Portugal 5 16 16Russia 11 23 73Thailand 0 0 0Turkey 20 20 20USA 2,817 2,228 2,020Total 6,833 7,973 8,402
Country
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Hydrothermal Sites
Source: Boyle, Renewable Energy, 2nd edition, 2004
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The Geysers (CA)
Power generation: 1,400 MWe
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The Geysers Geology
The Geysers
Caenozoic: Sedimentary non marine Sedimentary marine VolcanicMezozoic
Paleozoic
Intrusive Igneous Rocks Granite Ultramafic
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Geologic Time
A
B
C
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The Geysers Geology
Typical Porosities of ground materialUnconsolidated Sediments Porosity (%)
Clay 45-60Silt 40-50San, Volcano ash 30-40Gravel 25-35
Consolidated sedimentary rocksMudrock 5-15Sandstone 5-30Limestone 0.1-30
Crystalline RocksSolidified lava .001-1Granite .0001-1Slate .001-1
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Geysers Geothermal resource
A steam reservoir is located about 2,000 meters under the surface
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Geothermal resource at the Geysers
Average temperature gradient in the crust
0
500
1000
1500
2000
2500
3000
0 50 100 150 200 250
Temperature (C)
Depth
(m
)
The Geysers
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Dry Steam Cycle
At Geysers, the steam is dry (250oC – 30 bars). It is directly used to drive steam turbines
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Steam Cycle
It is an open Rankine Cycle (the ground is the Steam Generator)
0 1 2 3 4 5 6 7 8 90
50
100
150
200
250
300
350
400
s [kJ/kg-K]
T [
C]
30 bar
0.056 bar
SteamNBS
CondensorQ
turbineW
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Power by the turbine
turbineW
).( AAAA
AA
AA
AOpen
khmWQdt
dE
12. hhmW Turbine
AA
AA A
A
Open
smT
Q
dt
dS.
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h-s Diagram
Enthalpy variation may directly be read on the diagram
0 1 2 3 4 5 6 7 8 90
500
1000
1500
2000
2500
3000
3500
4000
s [kJ/kg-K]
h [
kJ
/kg
]
30 bar
0.056 bar
SteamNBS
CondensorQ
turbineW
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Generated Power
Computations of the power by the turbine Isentropic (Perfect) Turbine
Actual Turbine
1
2
12
,22
1,2,2
,2
.1
.
85.
.
skgm
m
Whh
WW
hhmW
h
isT
T
isis
is
Intersection of vertical from and P=0.056 bars
Enthalpy Entropy Temperature Pressure Quality
kJ /kg KJ /kg.K oC bar -Inlet 1 2,855 6.29 250 30 100%
2_is 1,928 6.29 35 0.056 74%2 2,067 6.74 35 0.056 79%
TurbineOutlet
kW kW kW kW kW/ K W/ K W/ K W/ KIsentropic Turbine - -927 0 927 0 0 0 0Actual Turbine - -788 0 788 0 0 -0.45 0.45
WQ AAA
A
khm
dt
dE
dt
dSA
A
sm.
A A
A
T
Q
Steam turbines cannot resist to more than 12% of water drops in low pressure steamMulti-stage steam turbine are used
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Heat rejected at the Condenser
Energy balance on the condenser
).( AAAA
AA
AA
AOpen
khmWQdt
dE
CondensorQ
23. hhmQCondenser
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Rejected Heat Computation of the heat rejected at the condenser
mLv
Qm
QW
W
condEvap
cond
System
.79.
%29
Enthalpy Entropy Temperature Pressure Quality
kJ /kg KJ /kg.K oC bar -Inlet 1 2,855 6.29 140 30 100%OutletInletOutlet 3 147 0.51 35 0.056 0%
2 2,067 6.74 51 0.056 79%Turbine
Condenser
kW kW kW kW kW/ K kW/ K kW/ K kW/ KTurbine 0 -788 0 788 0 0 -0.45 0.45Condenser 0 0 -1,920 1,920 0
W
Q AAAA
khm
dt
dEdt
dSA
A
sm.
A A
A
T
Q
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Water Re-injection In 1997 and 2003 a re-injection system was built to
offset the depletion of the Geysers steam reservoir. It provides 19 M Gallons per day (=832 kg.s-1).
This re-injection should covered a power generation of 830 MW
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Casa Diablo Located by the Mammoth Mountain on the
East side of the Sierra Nevada
About 40MW by three power plants
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Long Valley Caldera
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Bishop Tuff
Porosity: 48% to 65%
Source: J. Roberge Permeability study of pumice samples from the Bishop Tuff, Long Valley Caldera, CA
American Geophysical Union, Spring Meeting 2004, abstract #V21A-07
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Caldera Formation
The caldera was formed 760,000 years ago by the explosion of a volcano
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Alimentation of the Hydrothermal Reservoir
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Hydrology Water flow starts in the west by the
Mammoth Mountain and continues to the southeast toward Crowley Lake.
Reservoir temperatures decline from 230°C near the Inyo Craters to 50°C near Crowley Lake
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Geothermal resource at Casa Diablo
Average temperature gradient in the crust
0
500
1000
1500
2000
2500
3000
0 50 100 150 200 250
Temperature (C)
Depth
(m
)
The Geysers
Casa Diablo
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Water Extraction Because of the low temperature and no impermeable
cap, there is no steam and the system is not pressurized
Hot water is pumped from the reservoir to run the Power Plant
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Binary Cycle Power Plant
At Casa Diablo, the thermal water temperature is only 170oC. The Power Plant uses a Binary Cycle with Isobutane as the working fluid
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Why the iso-butane?
0.0 0.5 1.0 1.5 2.0 2.5 3.0-100
-50
0
50
100
150
200
s [kJ/kg-K]
T [
C]
20 bar
10 bar
5 bar
1 bar
n-Butane
Evaporation temperature is lower than for steam Higher pressure at the turbine -> Cheaper turbine
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0.5 1.0 1.5 2.0150
250
350
450
550
650
s [kJ/kg-K]
h [
kJ
/kg
] 31 bar
10 bar
3 bar
n-Butane
Enthalpy-Entropy Diagram
evaporatorQ
turbineW
pumpW
comdensorQ
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Summary
Fluid state at each connection point:
Enthalpy Entropy Temperature Pressure Quality
kJ /kg KJ /kg.K oC bar -Inlet 1 638.6 1.861 140 31.14 100%OutletInletOutletInletOutletInletOutlet 1 638.6 1.861 140 31.14 100%
36.72 31.14 0%
Turbine
Condenser
Pump
Evaporator186.7
3
4 0.6686
3.312 100%
177.3 0.6544 35 3.312 0%
2 554.2 1.875 50.72
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Power delivered by the turbine
turbineW
12. hhmW Turbine
1.50 1.60 1.70 1.80 1.90 2.00460
480
500
520
540
560
580
600
620
640
s [kJ/kg-K]
h [
kJ
/kg
]
31 bar
10 bar
3 bar
n-Butane
1./4.84
skgkWW Turbine
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Heat transferred at the Condenser
Energy balance on the condenser
CondensorQ
23. hhmQCondenser
1./377
skgkWQCondenser
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Water Branch of the Condenser
We can assess the flow of water required to cool the condenser
inwoutwwCondenser hhmQ
.
CondensorQ
Tw-in is imposed by the weather
conditions, sizing for the hottest day: 30oC (dry Aero-Condenser)
Tw-out is limited by the temperature
in the condenser
skgmw /20
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Graph Enthalpy-Temperature
The two lines cannot intersect because heat goes naturally from the hotter to the colder fluid (Second law of Thermodynamics)
150 200 250 300 350 400 450 500 550 60020
25
30
35
40
45
50
55
h[i]
T[i
]
Tw[i
]
n-butane
waterin
out
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Effect of dry Aero-Condensor
Air dew point defines the evaporation Wet-bulb temperature defines the lowest temperature for
water evaporating in an air stream
-10 0 10 20 30 400.000
0.010
0.020
0.030
0.040
0.050
T [C]
Hu
mid
ity
Ra
tio
Pressure = 1.0 [bar]
0.2
0.4
0.6
0.8
0 C
10 C
20 C
30 C
AirH2O
Wet-bulb Temperature
Dew Point
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Effect of dry Aero-Condensor
With evaporative cooling towers the temperature of water entering the condenser would have been 15oC
This would allow a condenser temperature of 20oC rather than 35oC leading to a gain of 2 points in conversion rate
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Pump
The pump brings the n-butane back to high pressure
Its power is much lower than the Turbine power because the fluid is liquid
34. hhmW Pump
1./4.9
skgkWW Pump
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Evaporator
Energy balance on the evaporator
EvaporatorQ
12. hhmQEvaporator
1./452
skgkWQEvaporator
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Water Branch of the Evaporator
We can assess the flow of water required to cool the evaporator
inaoutaaEvaporator hhmQ
.
Ta-in is imposed by the water
temperature of the Geothermal resource
Ta-out is limited by the temperature
in the evaporator
skgma /10
EvaporatorQ
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100 200 300 400 500 600 70030
49
68
86
105
124
143
161
180
He[i]
Te[i
]
Graph Enthalpy-Temperature
The two lines cannot intersect because heat goes naturally from the hotter to the colder fluid (Second law of Thermodynamics)
n-butane
waterin
out
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Summary
Balance of Energy and Entropy on each component
Conversion rate:
W W W W W/ K W/ K W/ K W/ KTurbine 0 -84 0 84 0 0 -0.014 0.014Condenser 0 0 -377 377 0 -1.22 1.22 0Pump 0 9.4 0 -9.4 0 0 -0.014 0.014Evaporator 0 0 452 -452 0 1.19 -1.19 0
-75 75 0 -0.028 0 0.028
W
Q AAAA
khm
dt
dEdt
dSA
A
sm.
A A
A
T
Q
%17
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Imperial Valley
Located between Salten Sea and the Gulf of California
570 MW by 15 power plantsSalten Sea units 3 and 4
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Imperial Valley GeologyAbout 300oC at -1,000 m
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Geology
Cenozoic: Sedimentary non marine Sedimentary marine VolcanicMezozoic
Paleozoic
Intrusive Igneous Rocks Granite Ultramafic
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Geothermal resource at Casa Diablo
Average temperature gradient in the crust
0
500
1000
1500
2000
2500
3000
0 50 100 150 200 250
Temperature (C)
Depth
(m
)
The Geysers
Casa Diablo
Salten Sea
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Steam Flash Cycle
Simple flash cycle: 30bars – 230oC
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Simple Steam Flash
0 1 2 3 4 5 6 7 8 90
500
1000
1500
2000
2500
3000
3500
4000
s [kJ/kg-K]
h [
kJ
/kg
]
30 bar
0.056 bar
SteamNBS
Liq
Vap
turbineW
50 bars, 300oC230oC
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Steam Flash Cycle
Double flash cycle
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Double Steam Flash
0 1 2 3 4 5 6 7 8 90
500
1000
1500
2000
2500
3000
3500
4000
s [kJ/kg-K]
h [
kJ
/kg
]
30 bar
0.056 bar
SteamNBS
Liq
Vap 10 bar
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Geothermal Power in California
In Operation:2,400 MWe
Total Potential:4,900 MWe
Source: California Geothermal Energy Collaborative/GeothermEx, 2006
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Hot Dry Rock (HDR)
Injection of water in a dry hot rock
Source: http://www.geothermal-resources.com.au/exploration.html
A Hot Rock Source: Granite that is generating abnormally high internal heat from the natural radioactive decay of minerals An insulating blanket of sediments, that effectively entraps the heat generated from the buried granite. Adequate fracturing of the hot dry rock source that allows circulation of a horizontal fluid flow regime
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Geology Soultz
Radioactive granite under a layer of low thermal conductivity sedimentary rocks
Cenozoic Non marine Sedimentary Rocks
Late Mezosoic Shelf and slope Sedimentary Rocks
Granitic rocks
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Example: Soultz (Fr)
Soultz Power Plant project
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Average temperature gradient in the crust
0
1000
2000
3000
4000
5000
0 50 100 150 200 250
Temperature (C)
Depth
(m
)
Geothermal resource at Soultz
The Geysers
Casa Diablo
Soultz
Salten Sea
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Other Experiments
Project Country Started Closed
Fenton Hill USA-NM 1974 1992
Folkenberg Germany 1976 1985
Rosemanowes UK 1976 1991
Urach I Germany 1977 1980
Le Mayet France 1977 Cont.
Ogachi Japan 1981 2004
Fjallbacka Sweden 1986 Cont.
Soulz France 1986 Cont.
Hijori Japan 1987 2001
Urach II Germany 1990 Cont.
Hunter Valley Australia 1999 Cont.
Coso EGS USA-CA 2003 Cont.
Desert Peak EGS USA 2003 Cont.
Cooper Basin Australia 2003 Cont.Source: MIT
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Companies to follow Calpine www.calpine.com Geothermal Energy Association www.geo-energy.org Great Basin Geothermal
www.greatbasingeothermal.com ENEX www.enex.is Western GeoPower Corp. www.geopower.ca Geo-Heat Center http://geoheat.oit.edu Fuji Electric www.fujielectric.com Electratherm www.electratherm.com Ormat www.ormat.com CalEnergy www.calenergy.com
Leathers Geothermal Plant in Imperial Valley