The term geothermal comes from the Greek geo meaning earth and
therme meaning heat thus geothermal energy is energy derived from
the natural heat of the earth..
The earth’s temperature varies widely, and geothermal energy is
usable for a wide range of temperatures from room temperature to well
over 300° F. For commercial use, a geothermal reservoir capable of
providing hydrothermal (hot water and steam) resources is necessary.
Geothermal reservoirs are generally classified as being either low
temperature (<150° C) or high temperature (>150° C).
Generally speaking, the high temperature reservoirs are the ones
suitable for, commercial production of electricity. Geothermal
reservoirs are found in “geothermal systems” which are regionally
localized geologic settings where the earth’s naturally occurring heat
flow is near enough to the earth’s surface to bring steam or hot water
to the surface

Power plants using dry
steam systems were the
first type of geothermal
power generation plants
built. They use the steam
from the geothermal
reservoir as it comes
from wells, and route it
directly through
turbine/generator units
to produce electricity. An
example of a dry steam
generation operation is
at the Geysers in
northern California

Hot water geothermal
reservoirs are the most
common type. In a liquiddominated reservoir, the hot
water has not vaporized into
steam because the reservoir is
saturated with water and is
under pressure. To generate
electricity, the hot water is
piped from geothermal wells
to one or more separators
where the pressure is lowered
and the water flashes into
steam. The steam then propels
a turbine generator to
produce electricity.
Based on Juli 2004 data:
40 % total geothermal on the word.
Range capacity: 3 MW – 90 MW
On the same geothermal fluid condition
15 – 20% more power output.

A binary cycle power
plant is used when the
water in a hot water
reservoir is not hot enough
to flash into steam. Instead,
the lower-temperature hot
water is used to heat a fluid
that expands when
warmed. The turbine is
powered from the
expanded, pressurized
fluid. Afterwards, the fluid
is cooled and recycled to
be heated over and over
again.
Fluid
Formula
Mollar mass
Relative Exit Area
Ammonia
NH3
17.03
1.0
Propane
C3H8
44.09
1.9
i-Butane
i-C4H10
58.12
4.9
n-Butane
C4H10
58.12
6.3
i-Pentane
i-C5H12
72.15
12.2
n-Pentane
C5H12
72.15
14.6
Condition: Turbine inlet temperature 400 K
Condensing Temp: 320 K
Geothermal energy is a renewable energy source that does little damage to the
environment.
Geothermal steam and hot water do contain naturally occurring traces of
hydrogen sulfide (a gas that smells like rotten eggs) and other gases and
chemicals that can be harmful in high concentrations. Geothermal power plants
use "scrubber" systems to clean the air of hydrogen sulfide and the other gases.
Sometimes the gases are converted into marketable products, such as liquid
fertilizer. Newer geothermal power plants can even inject these gases back into
the geothermal wells.
Geothermal power plants do not burn fuels to generate electricity as do fossil
fuel plants. Geothermal power plants release less than one to four percent of the
amount of carbon dioxide (C02) emitted by coal plants.
Emissions of sulfur compounds from motor vehicles and fossil fuel plants are also
major contributors to acid rain. Geothermal power plants, on the other hand,
emit only about one to three percent of the sulfur compounds that coal and oilfired power plants do. Well-designed binary cycle power plants have no
emissions at all.
Geothermal power plants are compatible with many environments. They have
been built in deserts, in the middle of crops, and in mountain forests.
GEOTHERMAL

Relatively smaller unit size
(Max. 110MW) makes unit
construction cost high
(because of (1) availability
of geothermal steam; (2)
difficulty of transportation
to geothermal power plant
located in mountainous
area; (3) limitation of
turbine last blade length.).
CONVENTIONAL STEAM
POWER PLANT

The size can be decided
depending on power
demand, availability of fuel,
etc. Plant size and unit size
are big (600 to 1,000MW)
makes unit construction
cost low.
CONVENTIONAL STEAM
POWER PLANT
GEOTHERMAL


Because steam pressure is
relatively low (Usually 6
to10 bara, Max. 19 bara),
size of the turbine is bigger
compared to thermal power
plants of the same capacity
All stainless steel (316L) or
stainless clad steel because
of NCGs.


High steam pressure (about
90 bara) makes size of
steam turbine small
Depend on available main
cooling water.
GEOTHERMAL

Because geothermal power
plants are usually located
in mountainous area where
sufficient cooling water is
not available, cooling tower
is mandatory.
CONVENTIONAL STEAM
POWER PLANT

N/A: Because most of
thermal power plants are
located at sea side for fuel
transportation and cooling
(sea) water, cooling tower
is not necessary
STEAM
POWER
PLANT
Reference
Data
Steam Flow (ton/Hr)
Output (kW) at 145t/h
P1 (bara)
Turbine Inlet
Steam
Condition
Turbine Outlet
Steam
Condition
Theoretical
heat drop
145
34,179
145 (= 40.28 kg/s)
20,000 1.71 times
87.3
8
T1 (deg C)
510
170
h1 (kJ/kg)
3,415
2,767
s1 (J/kg K)
6,709
6,660
0.09
0.11
T2 (deg C)
44
48
s2 (J/kg K)
6,709
6,660
0.80
0.80
h2 (kJ/kg)
2,112
2,120
Δh (kJ/kg)
1,302
647
52,457
26,067
P2 (bara)
Theorotical
Calculation
GEO
THERMAL
X2
Theoretical output (kW)
at 145t/h
2.01 times
Equipment / System
Thermal
Geothermal
Fuel System
Yes
N/A
Boiler
Yes
N/A
Turbine
Yes
Yes
Condenser
Yes
Yes
Boiler Feed Water System
Yes
N/A
Cooling Tower
N/A
Yes
Small
Big
Yes
N/A
Yes (1)
N/A
Gas Extraction System
Feed Water Treatment System
Flue Gas De-sulferization
Equipment
(2) Depend on Environmental Regulation
The main cooling system of the main condenser
comprises :
 the two main circulating pumps 50 %,
 the cooling tower,
 the piping and valves.
The cooling system of the geothermal plant comprises a cooling
tower of natural draught or forced draught type whose function
is to discharge to atmosphere the waste heat rejected at the
condenser.
Considering the flow range of water to be cooled (average 6,500
m3/h for 20 MW unit / 15,900 m3/h for 55 MW unit) a forced
draught tower with air directed through the tower by means of a
fan, is the most suitable type for this application.
The auxiliairy cooling water system shall comprise
 The primary auxiliary cooling water system,
 The secondary auxiliary cooling water system.
Primary auxiliary cooling water system
The primary auxiliary cooling water system is
derived from the cooled water of the cooling tower
and shall be designed :
 To ensure steam condensation inside the two
ejectors condensers,
 To ensure the heat dissipation of the secondary
auxiliary cooling system.
The secondary auxiliary cooling water system is a closed circuit
fed from the treated fresh water system ensuring cooling of the
turbo-generator coolers through the two water/water
exchangers.
This system shall mainly include :
 The two secondary auxiliary cooling pumps,
 The two water/water exchangers,
 A make up tank.
 The turbo-generator air-coolers,
 The generator air-coolers,
 The air compressors coolers (if compressed air system water
cooled),
 Various small coolers,