Geothermal energy
LOW ENTHALPY APPLICATION
OF GEOTHERMAL ENERGY
PART I
Ruggero Bertani
Enel – International
Rome – Italy
ruggero.bertani@enel.it
Rome, 2007 10th May
Geothermal energy
Contents
1° PART
1.
Introduction
2.
Geothermal energy basic concepts
3.
Electricity generation
4.
Binary plants
•
Case studies
2° PART
1.
Low Enthalpy applications
•
2.
3.
Introduction
Direct Uses
•
SPA
•
Heating
•
Geothermal Heat Pumps
•
Agriculture
•
Aquaculture
•
Industrial applications
Conclusion and case studies
Geothermal energy
Enel 2006 Results
Net installed capacity (MW)
Domestic
International
Power plants
50,776
40,475
10,301
MW
Hydro (616
Thermal (53
Wind (46
Geothermal (31
Other Renewables (6
Nuclear (2
pp)
pp)
pp)
pp)
pp)
pp)
Total production (TWh)
Domestic
International
18,151
28,857
591
671
46
2,460
Electricity Distribution & Sales
Enel distribution (TWh)
Domestic
International
267.6
255.0
12.6
Enel sales (TWh)
Domestic
International
159.9
142.7
17.2
Customers (millions)
Domestic
International
32.5
30.4
2.1
Netz (km/thousands)
131,4
Gas Distribution & Sales
103.9
27.5
Enel Sales (bcm)
Customers (millions)
Gas Pipeline (km/thousand)
1,179.3
4.5
2.3
31.1
Geothermal energy
Canada 22 MW
Hydro, biomass
Italy 15,358 MW Hydro,
geothermal, wind, solar
USA 380 MW
Hydro, wind
Guatemala
69 MW - Hydro
Slovakia
2.329 MW
Hydro
El Salvador
44 MW geo
Costa Rica
55 MW - Hydro, wind
Panama
300 MW - Hydro
Brazil
97 MW - Hydro
Chile
100 MW - Hydro
Over 19.000 MW
of renewable energy
Spain
900 MW
Hydro, wind,
cogeneration
Geothermal energy
Northern Pool
South
Eastern EU
North
America
Iberia
Latin
America
Central EU +
Centrel + Italy
• Growth in all technologies &
upstream gas in Europe and Russia
• Growth in Renewables worldwide
A solid international player
Geothermal energy
Contents
1° PART
1.
Introduction
2.
Geothermal energy basic concepts
3.
Electricity generation
4.
Binary plants
•
Case studies
2° PART
1.
Low Enthalpy applications
•
2.
3.
Introduction
Direct Uses
•
SPA
•
Heating
•
Geothermal Heat Pumps
•
Agriculture
•
Aquaculture
•
Industrial applications
Conclusion and case studies
Geothermal energy
Geothermal system
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
Power plant
Steam
gathering
system
Production
wells
Meteoric water
Drilling rig
Reinjection
well
Caprock
Thickness 500 – 1500 m
Impervious rocks
Reservoir
Porous – fractured rocks
Tickness 500 – 1500 m
T = 150 – 300 °C
Heat source
Depth 5-10 km
Hot fluid
T > 600- 700 ° C
Geothermal energy
Geothermal systems
Geothermal energy
400oF (200oC)
300oF (150oC)
200oF (95oC)
100oF (40oC)
0oF (-20 oC)
Temperature use for direct use applications
Geothermal energy
Utilization of
geothermal energy
as a function of the
resource
temperature
Geothermal energy
Energy saving & pollution avoided
GEOTHERMAL ENERGY FOR
ELECTRICITY GENERATION
56875 GWh in 2004
12%
AFRICA
5%2%
44%
37%
Electric use
AMERICAS
ASIA
EUROPE
•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)
OCEANIA
GEOTHERMAL ENERGY FOR
DIRECT USE OF HEAT
72632 GWh
Direct uses
•Energy saving of fuel oil per year
123,4 million barrels or 18,5 millions tonnes
•Carbon pollution avoided (millions tonnes year)
4 (natural gas) or 16 (oil) or 18 (coal)
AFRICA
2%
1%
32%
44%
AMERICAS
ASIA
21%
EUROPE
OCEANIA
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
Contents
1° PART
1.
Introduction
2.
Geothermal energy basic concepts
3.
Electricity generation
4.
Binary plants
•
Case studies
2° PART
1.
Low Enthalpy applications
•
2.
3.
Introduction
Direct Uses
•
SPA
•
Heating
•
Geothermal Heat Pumps
•
Agriculture
•
Aquaculture
•
Industrial applications
Conclusion and case studies
Geothermal energy
Geothermal system
Geothermal energy
Germany
Austria
1 MW
8 MW
France
15 MW
USA
2687
MW
Italy
811
MW
Turke
y
38 MW
Iceland
421
MW
El
Salvador
204 MW
Japan
535 MW
Philippine
s 1970
MW
Ethiopia
Guatemal
a
53 MW
Thailand
0,3 MW
Russi
a 79
MW
Portugal
23 MW
Mexico
953
MW
China
28 MW
7 MW
Costa
Rica
163 MW
Nicaragua
87 MW
Kenya
129
MW
Indonesia
992 MW
GEOTHERMAL ELECTRICIT WORLDWIDE
TOTAL INSTALLED CAPACITY 9,7 GW
Australia
0,2 MW
Papua
New
Guinea
56 MW
New
Zealand
472 MW
Geothermal energy
Contents
1° PART
1.
Introduction
2.
Geothermal energy basic concepts
3.
Electricity generation
4.
Binary plants
•
Case studies
2° PART
1.
Low Enthalpy applications
•
2.
3.
Introduction
Direct Uses
•
SPA
•
Heating
•
Geothermal Heat Pumps
•
Agriculture
•
Aquaculture
•
Industrial applications
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 costeffective 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
Reservoir fluid
Steam
Dominated
Electricity
Production
High Enthalpy
BOTTOM CYCLE
BINARY PLANT
Water
Dominated
Utilization
Energy Content
Low Enthalpy
BINARY
PLANT
Direct uses
of the Heat
Geothermal energy
BINARY PLANTS FOR OPTIMIZATION
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
Plant
Capacity
(MW)
Iceland
Svartsenegi
8
Mexico
Los Azufres
3
New Zealand
Kawerau
6
New Zealand
Mokai
27
New Zealand
Rotokawa
13
New Zealand
Wairakei
14
Nicaragua
Momotombo
7
Philippines
Mak-Ban
16
Philippines
Tongonang
19
Philippines
Mahandong
19
Philippines
Mahiaio
5
Philippines
Malitbog
12
TOTAL
150
Geothermal energy
chimney
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
Non condensable
gas
Gas extractor
Two phase mixture
from reservoir
turbine
~
generator
separator
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)
Cooling tower
condenser
Liquid phase
for the reinjection
at 170°C
Cold reinjection
(20°)
Discarded water
Steam and non condensable gas
Typical Flash plant from high enthalpy Liquid Reservoir
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.
Temperature
°C
Injection
Temperature
°C
Flow
Rate
t/h
Gross
Capacity
MW
Efficient
Capacity
Still Water II
NEVADA
154
79
3,200
49
31
Salt Wells
NEVADA
135
77
2,000
21
13
Cove Fort I
UTAH
152
77
1,500
25
19
Cove Fort II
UTAH
152
77
2,700
44
33
Surprise Valley
CALIFORNIA
165
85
2,700
46
32
185
128
Field
TOTAL
MW
Geothermal energy
CONCLUSION
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
Geothermal energy
Thanks for your attention
For any further information please contact me
at the following e-mail address:
ruggero.bertani@enel.it