Proceedings World Geothermal Congress 2005
Antalya, Turkey, 24-29 April 2005
Improving Geothermal Power Plant Performance by Repowering with Bottoming Cycles
Uri Kaplan and Daniel N. Schochet
ORMAT Nevada, Inc., Sparks, Nevada
ukaplan@ormat.com and dshochet@ormat.com
Keywords: Power Plants, Topping Cycles, Bottoming
Cycles
3. CASE HISTORIES
ORMAT® Energy Converter (OEC) units are specifically
designed to match the resource conditions. OEC units may
be located near the heat source, away from the space
constraints of the main plants. Since the OECs are designed
for automatic operation and remote monitoring, they may
be operated either as part of the main plant or as free
standing power plant units.
ABSTRACT
Additional generating capacity may be obtained in a cost
effective manner by re-powering of existing geothermal
power plants utilizing otherwise untapped geothermal
energy, without drilling new wells. Often this re-powering
also provides additional environmental benefits. The ability
to increase power production, by modest amounts can lead
to significant increase in profitability for operating plants.
The case histories in this presentation, which include
projects of different sizes and ownership structure, have
been selected to illustrate the technical, economic and
environmental benefits of re-powering existing geothermal
power plants, as well as the applications of bottoming
cycles.
This presentation looks at the case histories of several
geothermal re-powering applications, including the 5MW
brine recovery binary power plant at the Brady power plant
in Nevada installed in August of 2002, the 10 MW brine
recovery binary power plant at Momotombo in Nicaragua
installed in early 2003. and the 20 MW Miravalles V brine
recovery plant installed by ICE Costa Rica. With
geothermal power plant owners and operators concerned
with costs and competition, increasing plant output by repowering, with its incremental advantages, is a highly
desirable and cost effective option.
3.1 The Svartsengi Geothermal Project, Reykjanes
Peninsula, Iceland1
The Svartsengi Geothermal Power Plant is owned and
operated by the Sudurnes Regional Heating Corporation
(Sudurnes), which supplies geothermal heat and electricity
to the Reykjanes Peninsula in southwestern Iceland. At
Svartsengi shallow wells produced dry steam from a boiling
zone and deeper wells have produced geothermal fluids
with temperatures over 290oC. The original power plants
built in 1978 and 1980 utilized three backpressure steam
turbines to generate 8 MW to the local grid. Exhaust steam
from these turbines was used to heat water for district
heating with a portion discharged into the atmosphere.
2. INTRODUCTION
Fossil fuels are delivered to a power plant at a per-unit price
while geothermal energy, which fuels the power plant for
the life of the project, is obtained during project execution,
usually at a high up-front cost. Therefore the extraction of
the heat from geothermal fluids must be maximized. With
sustainability demand growing and competitive pressures
increasing, the incentives for optimizing existing facilities
are clear. Re-powering of existing plants by using otherwise
wasted brine, is viewed very favorably by investors and
governmental agencies, since it conserves energy while
often reducing environmental impacts. Geothermal power
project conversion technologies employed are sensitive to
resource conditions, which vary over time. This often offers
unique opportunities for re-powering. Specifically the use
of the bottoming cycles results in increased power
generation from otherwise untapped recovered energy,
including:
•
Non Condensing Geothermal Steam Turbines, which
release exhaust steam into the atmosphere at
temperatures above 100oC. This wastes heat energy
and has a serious negative environmental impact, and
•
Geothermal Brine, where the steam flow from
steam/brine separators is usually 10 to 30 percent of
the total flow, resulting in large amounts of brine
injected into the reservoir or surface discharged. This
brine, at temperatures of 110 to 180oC, contains a
significant percentage of untapped or otherwise wasted
energy.
Sudurnes installed three 1.3 MW water-cooled OEC binary
modules, generating 3.6 MW, in 1989, as the first repowering phase. These OECs use steam turbine exhaust as
the heat source. In 1993 four more 1.3 MW air cooled OEC
binary modules, generating 4.8 MW were added, bringing
the total OEC capacity to 9.1 MW and the total power
station production capacity to 16.4 MW. The re-powered
plant is operated with essentially the same staff since the
new equipment was integrated into the existing facility.
Shown in Figure 1 is a photograph of the first re-powering
phase.
Figure 1: Sudurnes OEC Bottoming Unit
1
Kaplan and Schochet.
After 10 years of continuous operation the OEC units were
operating at over 97% availability, and the waste steam was
utilized to produce an additional 8.4 MW of power, more
than doubling the installed power of the Sudurnes power
plant from 8 to 16.4 MW.
environmental problem of the surface discharge of
potentially hazardous geothermal brine.
After over 10 years of continuous operation the OEC
Kawerau Geothermal Power Plants are operating at over
98% availability with very low incremental operations and
maintenance expenses.
The re-powering was implemented in two steps, reducing
investment risk while increasing the efficiency of the plant
and decreasing power costs. Environmental damage, caused
by acid rain from the exhaust steam droplets has been
eliminated and the non-condensable gases in the steam,
mostly CO2, are now available for beneficial industrial use
in making dry ice and liquid CO2..
3.3 The Leyte Geothermal Optimization Project, The
Philippines2
In March 1995, the Philippine National Oil Company –
Energy Development Corp. (PNOC-EDC), solicited
competitive proposals for converting otherwise untapped
geothermal energy into electricity at four (4) major
operating geothermal projects on Leyte. ORMAT won the
50 MW Leyte Geothermal Optimization Project award,
which has the form of a ten-year energy conversion
agreement between ORMAT and PNOC-EDC. PNOCEDC, as owner, made the decision to use the otherwise
untapped geothermal energy produced by existing
capitalized facilities. The overall optimization generated
49 MW, adding almost 10% in cost effective power. The
Project consists of 4 individual power plant units, including
the Malitbog bottoming cycle unit.
3.2 Bay of Plenty, Geothermal Power Plants, Kawerau,
North Island, New Zealand1
The Bay of Plenty Electric Power Board services a wide
variety of domestic, farming, commercial and industrial
installations, including some of New Zealand’s major
manufacturers. This area encompasses the Kawerau
geothermal field, which is one of the most explored and
proven geothermal fields in the world. With a total tested
capacity of 200 MWe, the Kawerau field has 31 drilled
wells, with a maximum depth of 1611 meters and a
maximum bottom hole temperature of 310oC.
The main Malitbog Power Plants have a capacity of
231 MW (77 MWx3), utilizing steam at 5.85 bara. The well
field facility produces 109 tons/hr of second flash steam,
which is used by an ORMAT constructed condensing steam
turbine Bottoming Cycle to generate 13.35 MW net. The
bottoming plant utilizing water-cooled condensers, with a
cooling tower, is shown in Figure 3.
Since the early 1960s, the New Zealand Ministry of Energy
through its Gas and Geothermal Trading unit was selling
geothermal process steam to Tasman Pulp and Paper. The
process was surface discharging the separated brine at
174oC, both as steam into the atmosphere and brine into the
Tarawera River. Bay of Plenty Electric obtained the rights
to this partially spent geothermal fluid and installed two
1.3 MW air cooled modular binary OEC units in 1989 and
one 3.8 MW air cooled modular binary OEC in 1993, for a
total of 6.4 MW of installed capacity. Figure 2 is a
photograph of the second phase power plant unit.
Figure 3: Malitbog Steam Bottoming Unit
3.4 Brady Nevada OEC Bottoming Cycle Unit
The Brady Power Plant Project, located approximately 60
miles east of Reno, Nevada, is fed by geothermal fluid from
pumped wells, with a dual flash configuration utilizing two
high pressure turbines and one low pressure turbine. In
1992, the Brady power plant was commissioned with the
well field producing at an approximate rate of 10,000 gpm,
at a plant inlet temperature of about 182.2ºC. Temperatures
in the production wells declined rapidly reaching 162ºC by
mid-1993. and by mid-1995 the temperature to the plant
was 168ºC and trending downward.
Figure 2: Kawerau OEC Bottoming Unit
These OEC units utilize the 174oC brine, cooling it to
110oC, in the first two 1.3 MW units, and to 80oC in the
3.5 MW unit. The total electricity generated from a total
flow of some 550 tons/hr of geothermal fluid, is 7.1 MW.
The technical, economic and environmental benefits from
this project include providing the local electricity supplier,
Bay of Plenty Electric, with reliable, clean electricity for
the local communities. The OEC modular binary power
plants operate efficiently, have proven to be very cost
effective and were installed in less than 15 months from
purchase awards. In addition the air-cooled plants, which
have near zero environmental impact, have also solved the
In early 2000 remote injection was put into use with
approximately 60% of the flow was diverted to the remote
injection area. In April 2001, supply conditions to the plant
were then 7,800 gpm at157ºC and power output from the
Brady Power Plant was 13.5 MW gross, 8.8 MW net.
2
Kaplan and Schochet
Following the acquisition of the Brady Geothermal Power
Project by ORMAT in July 2001, a detailed review of the
total process of the project was performed and three issues
were evaluated:
1. Is each component in the plant and field operating at its
historical efficiency level?
2. What will be the added benefits (and cost) of replacing
original components with new ones designed to operate at
existing conditions?
3. What will be the contribution of adding equipment to the
power plant or well field, and at what payback? For
example, what will the benefits be for drilling wells, adding
cooling tower cells, etc.
In the first two cases replacing equipment and adjusting
well field management strategy increased the power output
by 1.5 MW. Focus was then shifted to improving the power
plant, to optimize the utilization of the available resource.
The Addition of a binary OEC bottoming unit was selected
as having no impact on performance of existing plants, with
subsequent cooling of the brine to 82ºC.
Figure 5: Miravalles V OEC Bottoming System
The advantage of ORMAT’s binary technology is twofold.
First, ORMAT’s technology efficiently utilized brine that
otherwise would be wasted for electricity generation.
Second, ORMAT’s technology re-injects 100% of the brine
back into the aquifer, thereby assuring that the resource is
not depleted. The Miravalles V Project is one more step in
the development of renewable power generation in Costa
Rica and in Latin America.
The OEC modular binary unit was constructed in 95 days
and was on-line by August of this 2002. Its net generation
with 236o F brine is 5.0 MW annual average, increasing the
overall project power output to approximately 20 MW, its
contractual requirement. Figure 4 is a photograph of the
OEC unit.
3.6 Momotombo, Nicaraugua3
At the time ORMAT signed a 15-year concession and
Power Purchase Agreement with ENEL for the
rehabilitation and operation of the Momotombo Geothermal
power plant in Nicaragua, the project constructed in 1990
was producing only 8 MW. After an investment of 35
Million Dollars in well drilling and rehabilitation as well as
new generation equipment, the power output has been
increased to 35 MW.
ORMAT rehabilitated the existing steam plant, drilled new
wells and installed an ORMAT® Energy Converter, (OEC)
which produces approximately 5 MW of additional power
from the heat contained in geothermal brine which
previously was disposed of into Lake Momotombo. This
brine is now is fully re-injected back into the ground for
better reservoir management and also avoiding any
pollution of an important water resource.
Figure 4: Brady OEC Bottoming Unit
At the OEC dedication ceremony on February 19, 2003,
President of Nicaragua, Ing. Enrique Bolaños Geyer stated
that “…We are very enthusiastic and optimistic today at the
inauguration of the new ORMAT® Energy Converter Plant,
which produces clean energy using the steam arising from
the depths of the volcano. This has even a higher value
today, as it is accentuated by the uncertainty in oil prices,
since 70% of Nicaragua’s electricity is based on oil.” The
rehabilitated and re-powered Momotombo plant provides
the country’s lowest cost electricity at 4.79 US cents a
kWh, saves Nicaragua the import of 90 000 tons of fuel per
year, and avoids a yearly emission of 120 000 tons of CO2
and the pollution of Momotombo Lake.
3
3.5 Miravalles V, Costa Rica
Miravalles V is part of the Electric Development Program
III, financed by the International Development Bank.
ORMAT was selected by ICE (Instituto Costarricense de
Electricidad), as a result of an international tender to supply
the power plant as well as construction materials and
engineering services.
The Miravalles V plant consists of two binary cycle watercooled non-polluting and fuel-free OECs that convert into
electric power the presently unexploited energy contained
in the hot brine discharged from the existing Miravalles
plants. The ORMAT® Energy Converters actually exceed
their design purchase specification of 15.5 MW and add
19.5 MW to the power output from the existing Miravalles
geothermal field, without increasing the overall steam
consumption or necessitating the drilling of new wells. The
Project is now in full operation. See Figure 5.
3
Kaplan and Schochet.
projects enjoy the benefits of re-powering and OEC
modular bottoming cycle units which have been field
proven as reliable and easily maintained power plants.
OEC re-powering bottoming units have been purchased
directly by facility owners as well as financed as
independent power projects. Re-powering has been proven
as the most cost-effective way to generate additional
geothermal power.
REFERENCES
1. Elovic, A., Repowering Geothermal Power Plants, RC
Resources Bulletin (1992).
2. Hennagir, T., Philippines Fast Track, Independent
Energy (1997).
3. Schochet, D., Ormat in Latin America, 35 Years of
Collaboration, GRC Bulletin (2003).
Figure 6: Momotombo OEC Bottoming Unit
4. CONCLUSIONS
Re-powering of existing geothermal power plants has
proven to be technologically viable as well as economically
and environmentally beneficial. Both large and small
4