Saturday, March 22, 2008

Geothermal energy - Use and working principle

Geothermal energy is energy that is gained thanks to an intensive heat that continuously flows outward from deep within the Earth. Word “geothermal” has its roots in two Greek words, “gheo” which means Earth and “thermal” which means heat. This energy is mainly generated from Earth's core since temperature of Earth's center is reaching temperatures above 6000 degrees Celsius which is even hot enough to melt a rock. Lesser part of this energy is gained from the crust, the planet's outer layer by decay of radioactive elements which are present in all the rocks. In nature this energy is usually shown in the form of the volcanoes, hot water springs and geysers, which are all areas on which heat is concentrated near the earth’s surface.

Geothermal energy was for centuries used in some countries in the form of hot springs that provided recreational and medical bathing, not to mention that positive therapeutic effects of hot springs were known in ancient times by many nations like ancient Romans. However, progress in science didn't stop only in exploring healing effects of geothermal energy and has pushed use of geothermal energy in many different ways of which two take special place, namely its use in generating the electricity and its use in heating of households and industrial facilities. Uses of geothermal energy for central heating of the buildings and for generating electricity are the main ways of its exploration, but not the only ones.

One of many geysers on Iceland. Click on picture for full size.

Geothermal energy can be also used in many other ways and it's used for pasteurizing milk, paper manufacturing, in swimming pools, drying timber and wool, animal husbandry etc. Main advantage of geothermal energy lies in the fact that this is renewable energy source since heat of Earth's core is constantly radiating from within, and the main flaw is the fact that the best geothermal resources are located in areas where volcanic activity is increased which means that this energy source is not widely distributed. Geothermal power plants have almost negligible negative effect on environment and they can be successfully implemented in different environmental surroundings, from farms, sensible desert environments and forest recreation centers.

It's also important to mention that use of geothermal energy isn't expensive and has significantly smaller operational costs than many other energy sources and geothermal water is source of many minerals and other chemical elements which have healing effects on many skin diseases. First geothermal power station was built more than hundred years ago, at Landarello, Italy in 1904, and second one was built in Wairekei in New Zealand. Largest geothermal system that is used for central heating is located in Iceland's capital Reykjavik, city in which almost all buildings use geothermal energy heat and 89 % of all households in Iceland are heated this way.

Geothermal energy – Working principle

Through this article I will present geothermal energy working principle used for building heating and generating electricity (simplified version). First step needed is to extract the geothermal energy from steam, hot water and hot rocks from Earth's crust. The success of this process depends on how hot the water gets, and water temperature depends on how hot were rocks to start with, and how much water is pumped down to these rocks. The water is pumped down through an „injection well“, it passes through the cracks in these rocks and then comes back up again through a „recovery well“ towards the surface, and because of the great pressure water is transformed into a steam when getting to the surface.

Geothermal energy working principle used for generating electricity. Click on picture for full size.

This created steam then needs to be separated from brine what is usually done in central separation chamber. After this process of separation is over, complete steam is transferred to heat exchangers which are located inside the power plant. After steam is transferred to heat exchangers it’s possible to transfer it even further to the steam turbines where it can be generated into electricity, and in the same time through the exhaust pipes unused energy is being released.

In heat exchangers steam is being cooled under the pressure in condensate and after that heat is transferred into cold water in condensate heat exchangers. This cold water that is gained on this way gets pumped from wells to storage tanks from which is transferred to heat exchangers where water's temperature gets increased and then passes through deaerators where it boils and where released oxygen and other gases that could cause corrosion (when being heated) are removed by final water cooling.

Speaking in simple term it's all in the process of water heating and its transfer to steam which can be then used to drive a turbo-generator that generates electricity or this steam passes through heat exchangers and heats water creating necessary heat for central heating of households and industrial facilities.

Location of geothermal power plants around the world. Click on picture for full size.

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