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Tuesday, 17 October 2017

Geothermal Energy (Earth-Science)


EARTH SCIENCE I        


TOPIC: GEOTHERMAL ENERGY


INTRODUCTION

Geothermal energy systems use heat from the interior of the earth as a source of power. The word geothermal comes from Greek words geo (earth) and therme (heat). The center of our planet is extremely hot, reaching temperatures of 7,000 to12,000 degrees Fahrenheit. This heat is primarily the result of the slow radioactive decay of heavy elements at the earth’s core. Only the very surface of our planet has cooled enough to form the crust we live on. This crust is typically anywhere from three to 35 miles thick and below the crust exists the mantle, made of partially molten magma (melted rock) and reaching temperatures of 1000-2000 degrees Fahrenheit. This heat becomes available near the surface at areas where thermal conduction and intrusion of molten magna into unusually thin sections of the earth’s crust occurs. Such geothermal zones often give rise to naturally occurring surface features such as hot springs, geysers and volcanoes. High temperature geothermal zones offer a ready source of heat that can be used to generate electricity. Lower temperature geothermal resources can be used for various applications such as heating buildings, drying crops, year-round greenhouses or heating water for fish-farming activities.

CHARACTERISTICS OF GEOTHERMAL ENERGY
Geothermal electrical power is an extremely reliable source of energy. Power plants driven by geothermal power have historically much better online records than other electrical power sources. Geothermal energy systems represent a renewable, long-term source of power. These systems are combustion-free producing very low emission levels and avoiding the problems of acid rain, greenhouse gas emissions and other pollutants associated with fossil fuel based systems.
More than 27 countries use geothermal power systems. The development of geothermal power systems is growing by 9 percent every year. Even in locations where hydrothermal activity is not available, geothermal heat pumps are still applicable.

USES OF GEOTHERMAL ENERGY
Some applications of geothermal energy use the earth's temperatures near the surface, while others require drilling miles into the earth. The three main uses of geothermal energy are:
1.) Direct Use and District Heating Systems which use hot water from springs or reservoirs near the surface.

2.) Electricity generation in a power plant requires water or steam at very high temperature (300 to 700 degrees Fahrenheit). Geothermal power plants are generally built where geothermal reservoirs are located within a mile or two of the surface.

3.) Geothermal heat pumps use stable ground or water temperatures near the earth's surface to control building temperatures above ground.

TYPES OF GEOTHERMAL POWER PLANTS
Dry steam plants use steam directly from a geothermal reservoir to turn generator turbines. The first geothermal power plant was built in 1904 in Tuscany, Italy, where natural steam erupted from the earth.

Flash steam plants take high-pressure hot water from deep inside the earth and convert it to steam to drive generator turbines. When the steam cools, it condenses to water and is injected back into the ground to be used again. Most geothermal power plants are flash steam plants.

Binary cycle power plants transfer the heat from geothermal hot water to another liquid. The heat causes the second liquid to turn to steam, which is used to drive a generator turbine.







Reference: Energy for Missouri: Today and Tomorrow - Educator's Guide PDF














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