Energy geothermal

Geothermal energy in total can be estimated to about 2 10 J, very roughly assuming mean temperatures, densities, and heat capacities (Table 2.17). 

Geothermal energy is the heat generated in the Earth s interior. The heat can be used to run geothermal power plants that include steam generator, turbine, condenser, and electrical generator. 

Underground heat in the form of steam, hot water, or hot rock used to produce steam has been employed as an energy resource for about a century and can be regarded as largely renewable. This energy was first harnessed for the generation of electricity at LardereUo, Italy, in 1904, and has since been developed in Japan, Russia, New Zealand, the Philippines, and at the Geysers in northern California. 

Underground dry steam is relatively rare, but it is the most desirable from the standpoint of power generation. More commonly, energy reaches the surface as supeiheated water and steam. In some cases, the water is so pure that it can be used for irrigation and livestock in others, it is loaded with corrosive, scale-forming salts. Utilization of the heat from contaminated geothermal water generally requires that the water be reinjected into the hot formation after heat removal to prevent contamination of surface water. 

The utilization of hot dry rocks for energy requires fracturing of the hot formation, followed by injection of water and withdrawal of steam. This technology is still in the experimental state but promises approximately 10 times as much energy production as steam and hot water sources. 

Land subsidence and seismic effects, such as the mini-earthquakes that occur when water is pumped under extreme pressure into hot rock formations that fracture as a consequence, are environmental factors that may hinder the development of geothermal power. However, this energy source holds considerable promise, and its development continues. 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

The total world consumption of energy in all forms is only about 300 EJ (300 quads) thus the earth s heat has the potential to supply all energy needs for the foreseeable future (5). Economic considerations, however, may preclude the utilisation of all but a small part of this potential resource. Only a miniscule fraction of this energy supply has been tapped. 

Temperatures of hydrothermal reservoirs vary widely, from aquifers that are only slightly warmer than the ambient surface temperature to those that are 300°C and hotter. The lower temperature resources are much more common. The value of a resource for thermal appHcations increases directiy with its temperature, and in regions having hotter water more extensive use of geothermal resources has been implemented. Resources in remote areas often go unused unless hot enough to be employed in generating electricity. 

In instances where test bores have been completed, it may sometimes be possible to predict the general locations of productive fractures. When these are encountered by surprise, however, the appropriate adjustments in the drilling strategy must be implemented rapidly, slowing the progress of the drilling operation and increasing the costs. 

The temperature in the core of the Earth—due to the decay of radioactive isotopes—is on the order of 4,000°C, the temperature of the lava of volcanoes is about 1,200°C, and the temperature of thermal springs can reach 350°C. If the groundwater temperature exceeds 150°C, flash steam power plants can be built, and if it is between 100 and 150°C, binary cycle power plants can be operated. 

Post-Oil Energy Technology After the Age of Fossil Fuels 

In all three cases (flash steam, binary cycle, and GHP installations), after the heat content of the geothermal water is utilized, the spent fluid is reinjected into the underground water reservoir. 

In the case of enhanced geothermal systems (EGS), thermal energy is obtained by pumping water onto hot rocks in the ground rather than harvesting hot water already there. 

Fuel cells generate electricity, heat, and distilled water by reacting H2 with oxygen (air). This process emits no C02, no carbon monoxide, no sulfur dioxide, no volatile organic compounds, and no fine particles. The only byproduct of the oxidation of H2 is distilled water. There are some 1,035 firms that are active in the field of fuel cell development and manufacturing (http //www. fuelcells.org/directory). This field of technology is fast advancing, the delivery of new units increased by 75% to approximately 100,000 units in 2007. 

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