L'ATTIVITÀ DI ENEL NEL CAMPO DELLE RISORSE GEOTERMICHE A BASSA ENTALPIAGEOTERMICHE A BASSA ENTALPIA
Marco PaciENEL Engineering & Innovation – Research Technical Area
Giovanni PasquiENEL Green Power – Engineering & Construction
Ferrara, September 2010
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Geothermal energy: a big potential
• Hydrothermal systems – situated at relatively shallow depths from the earth’s surface.steam-dominated systems – steam is the continuous phase that controls the reservoir pressure and stem only (+NCG) is produced by the wells.water-dominated systems - water is the continuous phase that controls the reservoir pressure; the wells produce water, or more often a mixture of water and steam + NCG at high temperature (100÷370°C) and pressure.Hot water reservoirs with temperature ranging from 30°C
GeoThermoExpo 2010 – Ferrara, Settembre 2010 2
Hot water reservoirs with temperature ranging from 30°C to 85°C can be typically used for district or green house heating.Hot dry rocks – rocky masses situated at a considerable depth beneath the earth’s crust and characterized by high temperature and total absence of circulation fluids.
• Geo-pressurized reservoirs – made up of water at high temperature (200°C) and a pressure level near to th e lithostatic one (depths >4000 m).
• Magmatic systems – magma bodies relatively close to the earth’s surface.
With wind and solar energy we look at the sky, but there is a lot of energy under our feet . (J. Tester, MIT)
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Main geothermal fields worldwide
Salton SeaSalton SeaSalton SeaSalton SeaSalton SeaSalton SeaSalton SeaSalton Sea
336 336 336 336 336 336 336 336 MWMWMWMWMWMWMWMW
(California)(California)(California)(California)(California)(California)(California)(California)
The GeysersThe GeysersThe GeysersThe GeysersThe GeysersThe GeysersThe GeysersThe Geysers
1421 1421 1421 1421 1421 1421 1421 1421 MWMWMWMWMWMWMWMW
(California)(California)(California)(California)(California)(California)(California)(California)
CosoCosoCosoCosoCosoCosoCosoCoso
OtakeOtakeOtakeOtakeOtakeOtakeOtakeOtake
153 153 153 153 153 153 153 153 MWMWMWMWMWMWMWMW
(Japan)(Japan)(Japan)(Japan)(Japan)(Japan)(Japan)(Japan)
Installed capacity ~10.000 MWe Potential capacity >100.000 MWe
GeoThermoExpo 2010 – Ferrara, Settembre 2010 3
Cerro PrietoCerro PrietoCerro PrietoCerro PrietoCerro PrietoCerro PrietoCerro PrietoCerro Prieto
720 720 720 720 720 720 720 720 MWMWMWMWMWMWMWMW
(Mexico)(Mexico)(Mexico)(Mexico)(Mexico)(Mexico)(Mexico)(Mexico)
TongonanTongonanTongonanTongonanTongonanTongonanTongonanTongonan
723 723 723 723 723 723 723 723 MWMWMWMWMWMWMWMW
(Philippines)(Philippines)(Philippines)(Philippines)(Philippines)(Philippines)(Philippines)(Philippines)
(California)(California)(California)(California)(California)(California)(California)(California)
LarderelloLarderelloLarderelloLarderelloLarderelloLarderelloLarderelloLarderello
810 810 810 810 810 810 810 810 MWMWMWMWMWMWMWMW
(Italy)(Italy)(Italy)(Italy)(Italy)(Italy)(Italy)(Italy)
Los AzufresLos AzufresLos AzufresLos AzufresLos AzufresLos AzufresLos AzufresLos Azufres
188 188 188 188 188 188 188 188 MWMWMWMWMWMWMWMW
(Mexico)(Mexico)(Mexico)(Mexico)(Mexico)(Mexico)(Mexico)(Mexico)
MiravallesMiravallesMiravallesMiravallesMiravallesMiravallesMiravallesMiravalles
163 163 163 163 163 163 163 163 MWMWMWMWMWMWMWMW
(Costa Rica)(Costa Rica)(Costa Rica)(Costa Rica)(Costa Rica)(Costa Rica)(Costa Rica)(Costa Rica)
CosoCosoCosoCosoCosoCosoCosoCoso
274 274 274 274 274 274 274 274 MWMWMWMWMWMWMWMW
(California)(California)(California)(California)(California)(California)(California)(California)
WairakeiWairakeiWairakeiWairakeiWairakeiWairakeiWairakeiWairakei
220 220 220 220 220 220 220 220 MWMWMWMWMWMWMWMW
(New Zealand))(New Zealand))(New Zealand))(New Zealand))(New Zealand))(New Zealand))(New Zealand))(New Zealand))
KamojangKamojangKamojangKamojangKamojangKamojangKamojangKamojang
140 140 140 140 140 140 140 140 MWMWMWMWMWMWMWMW
(Indonesia)(Indonesia)(Indonesia)(Indonesia)(Indonesia)(Indonesia)(Indonesia)(Indonesia)
SalakSalakSalakSalakSalakSalakSalakSalak
330 330 330 330 330 330 330 330 MWMWMWMWMWMWMWMW
(Indonesia)(Indonesia)(Indonesia)(Indonesia)(Indonesia)(Indonesia)(Indonesia)(Indonesia)
DarajatDarajatDarajatDarajatDarajatDarajatDarajatDarajat
135 135 135 135 135 135 135 135 MWMWMWMWMWMWMWMW
(Indonesia)(Indonesia)(Indonesia)(Indonesia)(Indonesia)(Indonesia)(Indonesia)(Indonesia)
MakMakMakMakMakMakMakMak--------BanBanBanBanBanBanBanBan
426 426 426 426 426 426 426 426 MWMWMWMWMWMWMWMW
(Philippines)(Philippines)(Philippines)(Philippines)(Philippines)(Philippines)(Philippines)(Philippines)
PalinpinonPalinpinonPalinpinonPalinpinonPalinpinonPalinpinonPalinpinonPalinpinon
192 192 192 192 192 192 192 192 MWMWMWMWMWMWMWMW
(Philippines)(Philippines)(Philippines)(Philippines)(Philippines)(Philippines)(Philippines)(Philippines)
TiwiTiwiTiwiTiwiTiwiTiwiTiwiTiwi
330 330 330 330 330 330 330 330 MWMWMWMWMWMWMWMW
(Philippines)(Philippines)(Philippines)(Philippines)(Philippines)(Philippines)(Philippines)(Philippines)
100 100 100 100 ÷÷÷÷ 400 400 400 400 MWMWMWMW
50 50 50 50 ÷÷÷÷ 100 100 100 100 MWMWMWMW
< < < < 50 50 50 50 MWMWMWMW
400 400 400 400 ÷÷÷÷ 1500 1500 1500 1500 MWMWMWMW
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Low enthalpy geothermal resources
Ring of fireRing of fire
High temperature geothermal resources naturally occur in geologically active
areas
GeoThermoExpo 2010 – Ferrara, Settembre 2010 4
Medium/low temperature hydrothermal reservoirs are abundantly available and
have by far the biggest electricity generation potential throughout Europe and
worldwide
ORC technology represents the best way to generate electricity fromlow-enthalpy geothermal resources
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Binary cycles for low enthalpy geo-resources
GeoThermoExpo 2010 – Ferrara, Settembre 2010 5
� For water-dominated resources with temperature lower than 180°C , the binary cycle technology is the most efficient.
� The geo-fluid energy is transferred through a heat exchanger to a secondary fluid that works in a closed ORC cycle.
� The binary power plants have the least environmental impact due to the “confinement” of the geo-fluid.
Conventional working fluid: -Isobutane-Isopentane-Butane-Pentane
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ENEL’s interest in low enthalpy geothermal resources
LATERA Geothermal Power Plant:
1st ENEL attempt (1999) to use binary technology based on ORC, as bottoming cycle.
•Installed capacity: 5 MW
•OEM : ORMAT
•Units : 2 (2500 kW net each)
GeoThermoExpo 2010 – Ferrara, Settembre 2010 6
•Working fluid : N-Pentane 394 t/h
•Cold Source : Geothermal Steam Condensate from Wet Cooling Towers 4000 t/h @ 25°-35°C
•Hot Source : Geothermal Brine – 1250 t/h @ 130°C
•Plant has been shut down (2002) due to public acceptance problems.
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ENEL’s interest in low enthalpy geothermal resources
• In early 2007 Enel North America acquired the rights to develop 4 geothermal fields in California, Nevada and Utah.
• Approximately 65 MWe from low enthalpy geo-resources are now in operation (Stillwater and Salt Wells power plants).
US Geothermal Provinces
GeoThermoExpo 2010 – Ferrara, Settembre 2010 7
Salt Wells Stillwater Surprise Valley Cove Fort II
Brine mass flow [kg/s] 504 ÷ 560 877 756 756
Brine Temperature [°C] 135 154 165 152
Temperature > 100°CTemperature < 100°CAreas suitable for geothermal heat pumps
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Stillwater PlantPFD at Design point
Air Cooled Condensers
Turboexpander 1-1
~Hot Brine
7255 kph
310 °F
STILLWATER PLANT2 Units in parallelTotal Power @ des. point:- GROSS 47.2 MW- NET 33.6 MW
To Unit 2
Turboexpander 1-2
~
Unit 1
Hot Air(84 °F)
261 °F ; 455 psia
261 °F ; 455 psia
1556 kph
1556 kph
Cool Air (53.7 °F)
Hot Air(84 °F)
GeoThermoExpo 2010 – Ferrara, Settembre 2010 8
Isobutane feed pumps
Vaporizer
Hot Brine
Pre-Heater 2
Production Wells
Pre-Heater 1
Injection Wells
From Unit 2
7255 kph
157.5 °F
Accumulator
Cool Air (53.7 °F)
Cold Brine
3113 kph ; 88 °F ; 495 psia
Demister
84 °F ; 61,5 psia
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Innovation in binary cycle technology
ENHANCED PERFORMANCESENHANCED PERFORMANCES & & OPERATIONAL FLEXIBILITYOPERATIONAL FLEXIBILITY
• To upgrade geothermal
BYNARY PLANTBYNARY PLANTCAPITAL COSTCAPITAL COST
1200 ÷1600 €/KW(1 ÷ 5 MWe unit )
2300 €/kW(400 ÷ 500 kWe unit)
ORC CYCLE ORC CYCLE EFFECTIVENESSEFFECTIVENESS
7% ÷ 12%
INNOVATION INNOVATION MAINSTAYSMAINSTAYS
GeoThermoExpo 2010 – Ferrara, Settembre 2010 11
• To upgrade geothermal resources exploitation (electric generation more profitable)
• To better match the intrinsic characteristics of geothermal reservoirs
• To avoid performance decline due to the natural resources depletion and temperature drop
ORC power production from low temperature resources has a low thermal efficiency
(400 ÷ 500 kWe unit)
Low efficiency requires increased power plant
equipment size that can become cost prohibitive
STATE OF THE ARTSTATE OF THE ART
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PHASE 1 - Development of an innovative supercritical pilot binary plant ( 500 kWe)
PHASE 2 - Development of a prototipal Hybrid PlantDetection of the configuration that optimizes the efficiency and the productivity of binary plants
Effi
cien
cy
15%
18%
Project “Geotermia Innovativa”
GeoThermoExpo 2010 – Ferrara, Settembre 2010 12
State of art
• 1-5 MWe subcritical binary ORC
• Net specific work 35÷40 kJ/kg brine
plant ( 500 kWe)
•Optimization of the cycle’s configuration to aim at the maximum flexibility
•Detection of the best working fluidEffi
cien
cy
12%
15%
Time1 year 3-4 year
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Project “Geotermia Innovativa” - Objectives
• To develop an advanced, supercritical, ORC technology in order to improve ENEL’s geothermal production from low enthalpy geothermal resources worldwide (with a specific focus to USA).
- Net specific work > 44 kJ/kg brine (~ +30% compared to actual technology).
- High operation flexibility (capability to work with high performances in a wide range of brine temperatures).
- Reduced investment cost.
GeoThermoExpo 2010 – Ferrara, Settembre 2010 13
• To demonstrate an advanced ORC at the pilot scale (500kWe).
- Cycle thermodynamic performance.
- Operating flexibility.
- Component design and scale-up criteria (with a particular focus on turbo - expander).
- Component reliability during long term operation (some thousands hours).
• To evaluate the feasibility to increase the productivity of ENEL’s ORC geothermal plants in the USA by means of integration with solar energy.
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Project “Geotermia Innovativa” - Overview
Project time schedule
GeoThermoExpo 2010 – Ferrara, Settembre 2010 14
Short -Middle Term
Activities
• TD cycle and working fluid have been selected.
• Basic design of pilot plant SC ORC (Apr. '10).
• Permitting procedure start-up (Dec. '09).
• Construction works at ENEL’s Leghorn experimental area (Sep. '11).
• Pre-feasibility study completion for geo-solar hybrid cycles (Sep. ‘10).
• An agreement has been signed with Turboden and Milan Polytechnic for an advanced ORC development, pilot plant EPC and ORC testing (Phase 1) on April the 24th of 2009.
• A cooperation has been activated with MIT in order to evaluate the feasibility of geo-solar integration in USA geothermal fields.
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• Working fluid screening criteria
- 6 Hydrocarbons tested
Cycle optimization and working fluid selection
• Cycle modelling
- Sub-critical cycles (saturated, superheated)
- Super-critical cycles
GeoThermoExpo 2010 – Ferrara, Settembre 2010 15
- 4 Refrigerants tested
•Low boiling point and high vapor pressure fluids related to operating T and P
•Heavy fluid, characterized by small enthalpy drop; hence, the turbo-machinery stress is reduced
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Calculation Hypotheses
Constraints of the model and cycle optimization criteria
in
netth Q
Wη =
in
netu E
Wη =
PERFORMANCE INDICATORS• Utilization
efficiency
• Thermal efficiency
OPTIMIZATION VARIABLES
• Working fluid mass flow rate• Working fluid turbine inlet pressure • Working fluid condensing pressure
GeoThermoExpo 2010 – Ferrara, Settembre 2010 16
MAIN INPUT DATA
Brine inlet temperature: 100°C ÷ 200°CBrine reinjection temperature: ≥70°CCooling water: NOT AVAILABLEGeothermal fluid mass flow: 100 kg/sDead-state temperature (Air ambient temperature): 20°CTurbine isentropic efficiency:
85% for fully-vapor expansions<85% when liquid is present (calculated from the Baumann equation)
Turbine exit vapor quality: 90%Pump efficiency: 80%
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Subcritical vs. Supercritical Cycles
Subcritical cycle Supercritical cycle
GeoThermoExpo 2010 – Ferrara, Settembre 2010 17
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30
40
50
60U
tiliz
atio
n E
ffici
ency
(%
)
SupercriticalCyclesH-1
H-2R-1R-2R-3
Simulation results 1/2
GeoThermoExpo 2010 – Ferrara, Settembre 2010 18
0
10
20
30
100 110 120 130 140 150 160 170 180 190 200
Geo-fluid Temperature (°C)
Util
izat
ion
Effi
cien
cy (
%)
SubcriticalCycles
Supercritical cycles provide higher utilization efficiency for the whole geo-fluid temperature range, resulting in 23% max. increase in net power.
Temperature range of interest
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4
6
8
10
12
Pow
er (
MW
e)
Gross Turbine Power
Net Power
6
7
8
9
10
Pow
er (
MW
e)
Gross Turbine Power
Simulation results 2/2
Subcritical cycle
Supercritical cycle
GeoThermoExpo 2010 – Ferrara, Settembre 2010 19
Power, MW H-1 @ 100°C H-2 @ 150°C H-1 @ 200°C
Gross 1.03 4.37 9.12
Parasitic losses 40% 31% 22%
Net 0.62 3.00 7.07
0
2
100 110 120 130 140 150 160 170 180 190 200
Geofluid Temperature ( oC)
CP Power
ACC Fan Power
0
1
2
3
4
5
100 110 120 130 140 150 160 170 180 190 200
Geofluid Temperature ( oC)
Pow
er (
MW
CP Power
ACC Fan Power
Net Power
Power, MW R-1 @ 100°C R-2 @ 150°C R-3 @ 200°C
Gross 1.41 5.43 11.23
Parasitic losses 53% 34% 26%
Net 0.66 3.56 8.30
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ORC Turbine coupled with
500kWe
generator
Primary Heat Exchangers
Air cooled condenserIntermediate
Heat Exchanger
Advanced 500 KWe ORC pilot plant PFD
GeoThermoExpo 2010 – Ferrara, Settembre 2010 20
Boiler
(2,8kg/s steam 30bar/a sat.)
Circulation pump
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CASPER
EFCC
Auxiliary boiler already available 5,6 MW (8,5 t/h, 250°C)
Livorno
Advanced 500 KWe ORC pilot plant
GeoThermoExpo 2010 – Ferrara, Settembre 2010 21
CASPER
EFCC
EFCC
200 m2 foundation platform for pilot plant installation
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Hybrid-cycles – First resultsPhase 2: Preliminary results for the old Stillwater Plant
Stillwater, NV, USA
GeoThermoExpo 2010 – Ferrara, Settembre 2010 22
Hybrid
Geothermal only
Incremental energy
0
100
200
300
400
500
600
700
800
900
Janu
ary
Febr
uary
Mar
ch
April
May
June
July
Augus
t
Septe
mbe
r
Oct
ober
Novem
ber
Decem
ber
Energ
y (
MW
h)
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Concluding remarks
• Within the temperature range investigated and for the design specifications assumed, supercritical binary cycles are more efficient than subcritical cycles, producing up to23% more net power, despite the fact that parasitic pumping losses are 2-3 times higher in the supercritical cases than in subcritical ones.
• Refrigerants performed very well as working fluids, especially for supercritical cycles.
• In a supercritical cycle the possibility of operating outside the fluid saturation diagram during the heat adduction phase guarantees a greater operational flexibility with respect to subcritical cycles.
•
GeoThermoExpo 2010 – Ferrara, Settembre 2010 23
• Based on the positive results of the work undertaken, ENEL has signed a cooperation agreement with Turboden and Milan Polytechnic aimed at designing and constructing a 500 kWe pilot plant in its experimental area in Leghorn in order to assess TD performance, component reliability and costs of the new technology.
• In the meantime, the techno-economical feasibility of geo-solar integration for ENEL’s binary plant in the USA is under evaluation in cooperation with Massachusetts Institute of Technology, aiming at increasing production, reducing risks and increasing flexibility.
• ENEL Green Power geothermal development relies heavily on ORC technology, foreseeing more investments in the USA as well as in Southern Europe and in the Mediterranean countries.