Environmental Engineering Reference
In-Depth Information
Open-Loop System
This type of system uses well or surface body water as the heat-exchange fluid that
circulates directly through the GHP system. Once it has circulated through the sys-
tem, the water returns to the ground through the well, a recharge well, or surface
discharge. This option is obviously practical only where there is an adequate supply
of relatively clean water and all local codes and regulations regarding groundwater
discharge are met.
ENVIRONMENTAL IMPACTS OF
GEOTHERMAL POWER DEVELOPMENT *
There are several potential environmental impacts from any geothermal power
development:
Gaseous emissions —Gaseous emissions result from the discharge of non-
condensable gases (NCGs) that are carried in the source stream to the
power plant. For hydrothermal installations, the most common NCGs are
carbon dioxide (CO 2 ) and hydrogen sulfide (H 2 S), although species such as
methane, hydrogen, sulfur dioxide, and ammonia are often encountered in
lower concentrations.
Water pollution —Liquid streams from well drilling, stimulation, and pro-
duction may contain a variety of dissolved minerals, especially for high-
temperature reservoirs (>230°C). The amount of dissolved solids increases
significantly with temperature. Some of these dissolved minerals (e.g.,
boron and arsenic) could poison surface or ground waters and also harm
local vegetation. Liquid streams may enter the environment through surface
runoff or through breaks in the well casing.
Solids emissions —There is practically no chance for contamination of sur-
face facilities or the surrounding area by the discharge of solids per se from
the geofluid. The only conceivable situation would be an accident associ-
ated with a fluid treatment or minerals recovery system that somehow failed
in a catastrophic manner and spewed removed solids onto the area.
Noise pollution —Noise pollution from geothermal operations is typical
of many industrial activities (DiPippo, 1991). The highest noise levels are
usually produced during the well drilling, stimulation, and testing phases
when noise levels ranging from about 80 to 115 decibels A-weighted (dBA)
may occur at the plant fence boundary. During normal operations of a geo-
thermal power plant, noise levels are in the range of 71 to 83 decibels at a
distance of 900 m (DiPippo, 2005).
* Adapted from MIT, The Future of Geothermal Energy , Massachusetts Institute of Technology,
Cambridge, MA, 2006 ( https://www1.eere.energy.gov/geothermal/pdfs/egs_chapter_8.pdf); Tribal
Energy and Environmental Information Clearinghouse, http://teeic.anl.gov/er/biomass/impact/con-
struct/index.cfm.
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