Geothermal EnergyPower Generation

San Jose State University

FX RongèreMarch 2009

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

Hydrothermal Sites

Source: Boyle, Renewable Energy, 2nd edition, 2004

The Geysers (CA)

Power generation: 1,400 MWe

The Geysers Geology

The Geysers

Caenozoic: Sedimentary non marine Sedimentary marine VolcanicMezozoic

Paleozoic

Intrusive Igneous Rocks Granite Ultramafic

Geologic Time

A

B

C

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

Geysers Geothermal resource

A steam reservoir is located about 2,000 meters under the surface

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

Dry Steam Cycle

At Geysers, the steam is dry (250oC – 30 bars). It is directly used to drive steam turbines

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

Power by the turbine

turbineW

).( AAAA

AA

AA

AOpen

khmWQdt

dE

12. hhmW Turbine

AA

AA A

A

Open

smT

Q

dt

dS.

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

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

Heat rejected at the Condenser

Energy balance on the condenser

).( AAAA

AA

AA

AOpen

khmWQdt

dE

CondensorQ

23. hhmQCondenser

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

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

Casa Diablo Located by the Mammoth Mountain on the

East side of the Sierra Nevada

About 40MW by three power plants

Long Valley Caldera

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

Caldera Formation

The caldera was formed 760,000 years ago by the explosion of a volcano

Alimentation of the Hydrothermal Reservoir

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

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

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

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

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

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

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

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

Heat transferred at the Condenser

Energy balance on the condenser

CondensorQ

23. hhmQCondenser

1./377

skgkWQCondenser

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

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

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

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

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

Evaporator

Energy balance on the evaporator

EvaporatorQ

12. hhmQEvaporator

1./452

skgkWQEvaporator

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

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

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

Imperial Valley

Located between Salten Sea and the Gulf of California

570 MW by 15 power plantsSalten Sea units 3 and 4

Imperial Valley GeologyAbout 300oC at -1,000 m

Geology

Cenozoic: Sedimentary non marine Sedimentary marine VolcanicMezozoic

Paleozoic

Intrusive Igneous Rocks Granite Ultramafic

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

Steam Flash Cycle

Simple flash cycle: 30bars – 230oC

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

Steam Flash Cycle

Double flash cycle

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

Geothermal Power in California

In Operation:2,400 MWe

Total Potential:4,900 MWe

Source: California Geothermal Energy Collaborative/GeothermEx, 2006

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

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

Example: Soultz (Fr)

Soultz Power Plant project

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

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

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