Environmental Engineering Reference
In-Depth Information
ENERGY CONVERSION
The conversion of heat to electricity is common to most power plants. This is the
case whether the energy source is coal, gas, nuclear power, wind power, solar power,
water power, or geothermal power. Powering the nontransportation section of our
economy is important, of course, so converting any fuel source to electrical power
for industrial use is a prime objective in our constant and insatiable appetite for
energy. It is tempting to think that we should focus solely on the production of elec-
tricity to power not only our industries and homes but also everything else—one
genie in one bottle to accomplish everything. Liquid fuels are the fuels of choice
right now because they are accessible, available, and relatively inexpensive. Thus,
although our ongoing research for other energy sources persists, we still do not have
that absolute pressing need to come up with a liquid fuel replacement—at least not
yet. Anyway, when our energy-needs focus shifts due to necessity, absolute or oth-
erwise, geothermal energy will be available, and we need to continue our research
in this important area. Energy conversion occurs routinely today, with a variety of
types of energy, and geothermal conversion is nothing new; only the procedures and
methodology differ.
Geothermal energy conversion refers to the power-plant technology that converts
the hot geothermal fluids into electric power. Even though geothermal power plants
have much in common with traditional power-generating stations—turbines, genera-
tors, heat exchangers, and other standard power-generating equipment—there are
important differences between geothermal and other power-generating technologies.
Each geothermal site, for example, has its own unique set of characteristics and
operating conditions that must be taken into account. The fluid produced from a
geothermal well can be steam, brine, or a mixture or the two, and the temperature
and pressure of the resource can vary substantially from site to site. The chemical
composition of the resource can contain dissolved minerals, gases, and other sub-
stances that are difficult to manage. Because these site-specific conditions can have
a profound affect on efficiency, productivity, and economic viability, engineers strive
to fine tune geothermal conversion technology, precisely matching plant design to
the site-specific conditions.
GEOTHERMAL POWER PLANT TECHNOLOGIES
Geothermal power plants fall into one of three conversion categories:
dry steam
,
flash
, or
binary cycle
. The type of conversion used depends on the state of the fluid
(whether steam or water) and its temperature. The first geothermal power generation
plant built was a dry steam power plant; this type of plant uses the steam from the
geothermal reservoir as it comes from wells and routes it directly through turbine/
generator units to produce electricity. Flash steam plants, the most common type of
geothermal power generation plants in operation today, pump water at temperatures
greater than 360°F (182°C) and under high pressure to generation equipment at the
surface. Binary cycle geothermal power generation plants differ from dry steam and
flash steam systems in that the water or steam from the geothermal reservoir never
comes in contact with the turbine/generator units.
