The information on this page was prepared by:
| Frances Li | francesl@usc.edu | Undeclared Engineering |
Geothermal: Environmental Impact
Geothermal energy is a clean resource that doesn’t emits little or no greenhouse gases. Only excess water vapor is emitted from steam and flash plants. No emissions are discharged by a binary geothermal plant because they run on a closed-loop system. Geothermal fields produce about one-sixth of the carbon dioxide that a considerably cleaner burning fossil fuel, natural gas, produces. Nitrous oxide emission is little or nil. Geothermal energy is always reliable because the heat is contained in the earth, aside from natural disasters that are surface level. A geothermal system has a average availability of 95%. The energy is available 24/7 and plants can run even in case of natural disaster. Geothermal energy is available at home. It does not need to be imported from another country. Therefore the revenues that are collected from this source of energy stays in home territory. If the heat from the earth can be tapped efficiently, there would be less dependence on foreign oil. The United States can develop the means of tapping earth’s heat efficiently and sell their ideas to other countries.
Hot water taken from the reservoirs can be re-injected and reused. Salts and dissolved minerals contained in geothermal fluids are injected back into the reservoir a depth well below ground water aquifers. The water is recycled and used over and over again through the cycle of producing steam that liquefies, replenishing the reservoir. In Santa Rosa. California, waste water from the city is piped up to the Geyser powers plants to be used for re-injection fluid. The reservoirs lasts longer as the wastewater is recycled.
Some geothermal plants do produce solid materials and sludge’s that are disposed of safely. Some of these materials and siphoned and extracted for sale, such as sulfur and zinc. The Geysers power plants in California uses geothermal fluid that contains hydrogen sulfide. The sulfur, about 1.5 kg per Mwh is separated, de-watered and recycled for sulfuric acid production. Technologies are being developed for more efficient use of the emissions. At most geothermal plants with extremely high temperatures, the concentration of hydrogen sulfide is relatively low that is does not need to special controls to comply with environmental regulations. Water has to be re-injected into the ground to maintain reservoir pressure.
The three different technological uses to tap earth’s heat are geothermal pumps, direct-use applications, and power plants.
Just below the Earth’s surface, the temperature remains on an average of 50 to 60 degrees Fahrenheit, within 50 feet of the earth. A geothermal heat pump system consists of pipes buried in the ground near the building, heat exchanger, and duct-work in the building. Even during the winter, the heat from the ground is unaffected and is pumped into homes through the heat exchanger. In the summer, the hot air from the house is pulled through the heat exchanger into the cooler ground. The heat removed from the air in the summer can be used to heat water at no cost. For each 1000 houses using geothermal pumps, two to five less megawatts of utilities have to be installed.
Direct use of hot water warms greenhouses and melts sidewalk snow.
In the United States, most geothermal reservoirs are located in the western states, Alaska, and Hawaii. But it can be tapped from anywhere in the work with geothermal heat pumps and direct-use applications. Reservoirs range from 70 F to 300 F are used directly. Hot water near the Earth’s surface can be piped directly into buildings and facilities to heat buildings, grow plants in greenhouses, dehydrate onions and garlic, heat water for fish farming, and pasteurize milk. Cities pipe the heated water under roads and sidewalks to melt the snow. Different district heating applications are used to pipe hot water to heat buildings or whole communities.
District heating systems and geothermal plants are easily integrated into communities. Power plants use relatively small acreages of land, without the need for storage, transportation, or combustion of fuels.