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Geothermal energy
LOW ENTHALPY LOW ENTHALPY APPLICATIONAPPLICATION OF OF
GEOTHERMAL ENERGYGEOTHERMAL ENERGYPART IPART I
Ruggero BertaniRuggero Bertani
Enel – InternationalEnel – International
Rome – ItalyRome – Italy
ruggero.bertani@enel.itruggero.bertani@enel.it
Rome, 2007 10Rome, 2007 10thth May May
Geothermal energy
Contents1° PART1° PART
1. Introduction
2. Geothermal energy basic concepts
3. Electricity generation
4. Binary plants
• Case studies
2° PART
1. Low Enthalpy applications
• Introduction
2. Direct Uses
• SPA
• Heating
• Geothermal Heat Pumps
• Agriculture
• Aquaculture
• Industrial applications
3. Conclusion and case studies
Geothermal energy
Enel 2006 Results
Power plants MW
Hydro (616 pp)18,151
Thermal (53 pp)28,857
Wind (46 pp)591
Geothermal (31 pp)671
Other Renewables (6 pp)46
Nuclear (2 pp) 2,460
Total production (TWh)131,4
Domestic103.9
International27.5
Net installed capacity (MW)50,776
Domestic40,475
International10,301
Electricity Distribution & Sales
Enel distribution (TWh)267.6
Domestic255.0
International12.6
Enel sales (TWh) 159.9
Domestic142.7
International17.2
Customers (millions)32.5
Domestic30.4
International2.1
Netz (km/thousands)1,179.3
Gas Distribution & Sales
Enel Sales (bcm)
4.5Customers (millions)
2.3Gas Pipeline (km/thousand)
31.1
Geothermal energy
Canada 22 MWHydro, biomass
USA 380 MWHydro, wind
Guatemala 69 MW - Hydro
Costa Rica55 MW - Hydro, wind
Chile100 MW - Hydro
Italy 15,358 MW Hydro, geothermal, wind, solar
Spain900 MW
Hydro, wind, cogeneration
Slovakia 2.329 MW
Hydro
Brazil97 MW - HydroPanama
300 MW - Hydro
Over 19.000 MW
of renewable energy
El Salvador
44 MW geo
Geothermal energy
Northern Pool
SouthEastern EU
Central EU +Centrel + Italy
Iberia
NorthAmerica
LatinAmerica
A solid international playerA solid international player
• Growth in all technologies & upstream gas in Europe and Russia
• Growth in Renewables worldwide
• Growth in all technologies & upstream gas in Europe and Russia
• Growth in Renewables worldwide
Geothermal energy
Contents1° PART1° PART
1. Introduction
2. Geothermal energy basic concepts
3. Electricity generation
4. Binary plants
• Case studies
2° PART
1. Low Enthalpy applications
• Introduction
2. Direct Uses
• SPA
• Heating
• Geothermal Heat Pumps
• Agriculture
• Aquaculture
• Industrial applications
3. Conclusion and case studies
Geothermal energy
Geothermal system
Heat source
Depth 5-10 km
T > 600- 700 ° C
Meteoric water
Hot fluid
Production wells
CaprockThickness 500 – 1500 m
Impervious rocks
Utilization of geothermal energy has been limited to areas in which geological conditions permit a carrier (water in the liquid phase or
steam) to 'transfer' the heat from deep hot zones to or near the surface, thus giving rise to geothermal system
ReservoirPorous – fractured
rocksTickness 500 – 1500 m
T = 150 – 300 °C
Reinjection well
Power plant
Steam gathering
system Drilling rig
Geothermal energy
Geothermal systems
Geothermal energy
400oF (200oC)
300oF (150oC)
200oF (95oC)
100oF (40oC)
0oF (-20oC)
Temperature use for direct use applications
Geothermal energy
Utilization of geothermal energy as a
function of the resource
temperature
Geothermal energy
Energy saving & pollution avoidedGEOTHERMAL ENERGY FOR ELECTRICITY GENERATION
56875 GWh in 2004
2%
44%
37%
12% 5% AFRICA
AMERICAS
ASIA
EUROPE
OCEANIA
Electric use
•Energy saving of fuel oil per year 96,6 million barrels or 14, 5 millions tonnes
•Carbon pollution avoided (millions tonnes year) 3 (natural gas) or 13 (oil) or 15 (coal)
Total energy saving of fuel oil per year over 220 million barrels
Total carbon pollution avoided per year over 29 (oil) million tonnes
GEOTHERMAL ENERGY FOR DIRECT USE OF HEAT
72632 GWh
1%32%
21%
44%
2% AFRICA
AMERICAS
ASIA
EUROPE
OCEANIA
Direct uses
•Energy saving of fuel oil per year123,4 million barrels or 18,5 millions tonnes
•Carbon pollution avoided (millions tonnes year) 4 (natural gas) or 16 (oil) or 18 (coal)
Geothermal energy
Contents1° PART1° PART
1. Introduction
2. Geothermal energy basic concepts
3. Electricity generation
4. Binary plants
• Case studies
2° PART
1. Low Enthalpy applications
• Introduction
2. Direct Uses
• SPA
• Heating
• Geothermal Heat Pumps
• Agriculture
• Aquaculture
• Industrial applications
3. Conclusion and case studies
Geothermal energy
Geothermal system
Geothermal energy
Japan
535 MW
Russia 79
MW
Philippines 1970
MW
Indonesia 992 MW
New Zealand 472 MW
USA 2687 MW
Costa Rica
163 MWKenya 129 MW
Iceland421 MW
Italy 811 MW Turkey
38 MW
Portugal 23 MW
Ethiopia 7 MW
France 15 MW
China 28 MW
Mexico 953 MW
Australia 0,2 MW
Austria 1 MW
Germany 8 MW
El Salvador204 MW
Guatemala
53 MWNicaragua
87 MW
PapuaNew
Guinea 56 MW
Thailand
0,3 MW
GEOTHERMAL ELECTRICIT WORLDWIDE TOTAL INSTALLED CAPACITY 9,7 GW
Geothermal energy
Contents1° PART1° PART
1. Introduction
2. Geothermal energy basic concepts
3. Electricity generation
4. Binary plants
• Case studies
2° PART
1. Low Enthalpy applications
• Introduction
2. Direct Uses
• SPA
• Heating
• Geothermal Heat Pumps
• Agriculture
• Aquaculture
• Industrial applications
3. Conclusion and case studies
Geothermal energy
Generating electricity from low-to-medium temperature geothermal fluids and from the waste hot waters coming from the separators in
water - dominated geothermal fields has made considerable progress since improvements were made in binary fluid technology.
The binary plants utilize a secondary working fluid, usually an organic fluid
that has a low boiling point and high vapour pressure at low temperatures when compared to steam.
The secondary fluid is operated through a conventional Rankine cycle: the geothermal fluid yields heat to the secondary fluid through heat exchangers, in which this fluid is heated and vaporizes; the vapour
produced drives a normal axial flow turbine, is then cooled and condensed, and the cycle begins again.
Geothermal energy
By selecting suitable secondary fluids, binary systems can be designed to utilize geothermal fluids in the temperature range 85-
175°C.
The upper limit depends on the thermal stability of the organic binary fluid, and the lower limit on technical-economic factors: below this temperature the size of the heat exchangers required would render
the project uneconomical.
Apart from low-to-medium temperature geothermal fluids and waste fluids, binary systems can also be utilized where flashing of the geothermal fluids should preferably be avoided (for example, to
prevent well sealing).
In this case, downhole pumps can be used to keep the fluids in a pressurized liquid state, and the energy can be extracted from
the circulating fluid by means of binary units.
Geothermal energy
Geothermal energy
After long trial and error, binary plant technology is emerging as a very cost-effective and reliable means of converting into electricity the energy available from water-dominated geothermal fields (below
175°C).
A new binary cycle system has been developed recently, called the Kalina cycle.
The Kalina cycle uses an ammonia-water mixture as the working fluid and takes advantage of regenerative heating.
The ammonia-water mixture has a low boiling point, so that the excess heat coming from the turbine’s exhaust can be used to vaporize a substantial portion of the working fluid.
This plant is estimated to be up to 40% more efficient than existing geothermal binary power plants.
Geothermal energy
BOTTOM CYCLE BINARY PLANT• In many cases, additional generating capacity may be obtained in a cost-
effective manner by repowering existing geothermal power plant utilizing otherwise untapped geothermal energy, without additional wells;
• For cost effective power generation, the extraction of heat from geothermal fluid must be maximized;
• Often this repowering also provides concomitants environmental benefits, since it conserves energy while reducing environmental hazardous waste;
• These plant retrofit additions can be designed at any stage of the life of each generation facility, they are modular and can be realized in different steps;
• The typical cost is two million USD for MW and the timing for the realization of the entire phases of the project can be very short (one year);
• Approximately 150 MW are installed worldwide.
LOW TEMPERATURE BINARY PLANT• In many cases where it is present a low temperature resource, binary plant
technology is the only one feasible for electricity generation from geothermal fluid;• There are about 600 MW of binary plants installed worldwide.
Geothermal energy
• The utilization of geothermal energy for the electricity production reached the value of 9,000 MW in 24 countries;
• The economics of electricity production is influenced by the drilling costs and resource development;
• The productivity of electricity per well is a function of reservoir fluid thermodynamic characteristics (phase and temperature);
• The higher the energy content of the reservoir fluid, the lesser is the number of required wells and as a consequence the reservoir CAPEX quota is reduced:
Utilization of low temperature resource can be achieved only
with binary plant.
Binary plant can be an efficient way for recovery the energy content of the reservoir fluid after its primary utilization in standard flash plant,
achieving a better energy efficiency of the overall system.
Geothermal energy
Steam Dominated
Water Dominated
Reservoir fluid
Energy Content
Utilization
High Enthalpy
Low Enthalpy
Electricity Productio
n
Direct uses of
the Heat
BINARY PLANT
BOTTOM CYCLE BINARY PLANT
Geothermal energy
OPTIMIZATION• Bottoming cycle technique is widely used
worldwide, as shown in the attached table;• This electricity is produced using the waste water
from the separated brine: it can be considered as an un-expensive and rich of value by-product of the primary flash power plant.
LOW TEMPERATURE• For temperature below 150°C, the conventional
flash is not able to reach satisfactory efficiency: at this temperature, only 10% of steam can be produced at about 1 bar of separation pressure; the steam will have a very low efficiency, due to its low pressure and temperature, for producing 20 MW it will be necessary to mine up to 3,000 t/h of fluid (to be compared with 500 t/h from 300°C liquid reservoir);
• The UNIQUE way to exploit the geothermal energy for producing electricity is the use of a binary plant on the pressurized fluid, which will be handled through a closed loop from production and reinjection.
• It is a zero emission cycle. The total installed capacity of such binary plants is about 600 MW worldwide.
Country PlantCapacit
y (MW)
IcelandSvartseneg
i8
MexicoLos
Azufres3
New Zealand
Kawerau 6
New Zealand
Mokai 27
New Zealand
Rotokawa 13
New Zealand
Wairakei 14
NicaraguaMomotom
bo7
Philippines Mak-Ban 16
Philippines Tongonang 19
PhilippinesMahandon
g19
Philippines Mahiaio 5
Philippines Malitbog 12
TOTAL 150
BINARY PLANTS FOR OPTIMIZATION
Geothermal energy
Typical Flash plant from high enthalpy Liquid Reservoir
~turbine generatorGas extractor
Non condensable gas
condenser
Discarded water
separatorTwo phase mixture
from reservoir
Liquid phase for the reinjection
at 170°C
Steam and non condensable gas
chimney
Cooling tower
Cold reinjection (20°)
Average value for 20 MW plant (Res. Temp. 300°C)•Fluid extraction 470 t/h•Steam in 140 t/h Fluid (30% of the fluid)•Flash: temperature 170°C and pressure 8 bar•Gas out 4 t/h•Cold Reinjection 40 t/h•Hot reinjection 330 t/h•Cooling tower evaporation 96 t/h (75% of steam)
The hot reinjection fluid at 170°C is approximately 2-3 times the steam fraction, accordingly to the initial fluid temperature; this energy can be utilized using a BOTTOM CYCLE BINARY PLANT
Geothermal energy
In El Salvador, our local partner LaGeo installed a new bottom cycle
binary plant at the existing old power station of Berlin (2x28 MW,
completed in 1999), using the separated water from four wells; it is
utilized in two heat exchanger for boiling an organic fluid (Isopentane), which has a low temperature boiling point; the isopentane steam expands
into a 9,5 Gross MW turbine, generating 7,8 MW net of electricity, without any
additional expenditure from the reservoir development, and
achieving a better utilization of the overall energy content of the
geothermal fluid.
The cost for this unit is 16,5 MUSD, with a very positive
return of the investment
Total utilized geothermal fluid 1,000 t/h at 180°C; isopentane
flow rate 700 t/h, working between 160°C and 44°CC;
wet cooling tower; GE turbine, ABB generator; Mexican heat Exchanger; Enex (ICELAND) design and EPC contractor.
Geothermal energy
Heat Exchanger
Turbine
Power Plant Housing
Geothermal energy
Chena Hot Springs is located approximately 100 km northeast of Fairbanks, Alaska, in the interior of the state. In August 2006 a low temperature power plant was commissioned to provide power for the isolated resort. The 200 kW plant, a binary or organic Rankine cycle unit built by United Technology Corporation, is the first geothermal power plant in Alaska, and uses the lowest temperature geothermal resource in the world at 74°C for power generation.
The secondary fluid in the plant is R-134a, which has a lower boiling point than water and is heated by geothermal water at 32 l/s through a heat exchanger at 74°C. Cooling water from a shallow well or infiltration gallery is around 4°C, providing a large temperature difference which improves the efficiency of the system. As the resort is isolated from the electric grid, it has used diesel generators in the past, costing around 30 cents/kWh with a daily average cost of $1,000. The new power plant will provide electricity at 7 cents/kWh, a major saving for the resort. Maintenance is estimated to be $50,000 per year.
The total unit cost around $1,300 per installed kW. Plans are to add another 200 kW unit, and then shortly to reach one MW.
Geothermal energy
TURKEY: Salavatli geothermal field is located in one of the most promising geothermal regions, namely on the northern flank of Menderes graben.
The Salavatli-Sultanhisar geothermal system was delimited after a resistivity survey. Two wells were drilled in 1987 and 1988 to 1500m and 962m, and temperatures of 170°C were
recorded. In the past two years, two more wells were also drilled to the depths 1300m and 1430m
for reinjection and stand by production, and both have struck similar temperatures.
The geothermal fluid contains an average of 1% of CO2 by weight, which is similar to that of other geothermal fields in the region.
An air cooled binary power plant with 7 MWe gross power is being installed.
Specific consumption of plant is 500 t/h of water at 156°C, discharged at 76°C, producing 8 MW in winter and 5,3 MW in summer; 600 kW parasitic load of fan cooling.
Geothermal energy
USA: Enel has finalized the acquisition of four geothermal field in USA; these reservoirs should be exploited through binary plants. The relevant data are collected in the attached table.
As working fluid has been selected the isobutane, for achieving better performances in such range of temperatures.
The use of isobutane will requires higher operating pressure which could result in slight increase in equipment cost, and it implies an increase of risks concerning safety aspects due to higher operating pressures
(near supercritical conditions) and its higher volatility respect to isopentane.
All plants will be air cooled, while the Cove Fort units I and II will be water cooled, due to availability of water source.
FieldTemperature
°C
InjectionTemperatur
e°C
Flow Ratet/h
GrossCapacity
MW
Efficient
Capacity
MW
Still Water II NEVADA
154 79 3,200 49 31
Salt Wells NEVADA
135 77 2,000 21 13
Cove Fort IUTAH
152 77 1,500 25 19
Cove Fort IIUTAH
152 77 2,700 44 33
Surprise Valley
CALIFORNIA165 85 2,700 46 32
TOTAL 185 128
Geothermal energy
The most abundant geothermal resource in the world is given by hot pressurized water.
Whereas in the dry steam reservoir (Larderello-Italy, The Geyser-USA) the exploited energy of the fluid can be fully utilized, in all the other
situation the majority of the thermal energy from the extracted fluid is lost, being reinjected at high temperature and practically not-used and wasted.
The binary plants on the reinjection stream could be a very effective way of producing cheap energy, because
there will not be any additional mining costs associated with this extra production
The binary plants technology represents an unique way of producing geothermal electricity for medium/low temperature geothermal system,
Increasing the overall exploitable potential worldwide
CONCLUSIONCONCLUSION
Geothermal energy
Thanks for your attention
For any further information please contact me at the following e-mail address:
ruggero.bertani@enel.it
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