Geothermal Energy

GEOTHERMAL ENERGY GEOTHERMAL comes from the Greek Words GEO (Earth) and THERME (Heat). It means heat of the Earth It is the thermal energy trapped beneath and within the solid crust of the Earth. This Energy exists in the form of steam, hot water, and/or hot and molten rock.

HOW DOES GEOTHERMAL HEAT GET UP TO EARTH‘S SURFACE ? Conduction:- Heat from the Earth’s interior flows outward. It is transferred to the outer layer of rock or the crust. Convection:- In some regions, the mantle beneath the crust may be hot enough to partly melt and create magma. Magma rising upward out of the mantle can bring intense shallow heat into the crust

HOW HAVE PEOPLE USED GEOTHERMAL ENERGY IN THE PAST ? Bathing: Ancient civilizations used hot springs for bathing Medical Therapy: Early Romans used geothermal water to treat eye and skin disease Cooking: Native Americans and others used geothermal water for cooking Heating: Early Romans used geothermal water to heat their homes

Different Geothermal Energy Sources  Hot Water Reservoirs: As the name implies these are reservoirs of hot underground water. There is a large amount of them in the US, but they are more suited for space heating than for electricity production.  Natural Stem Reservoirs: In this case a hole dug into the ground can cause steam to come to the surface. This type of resource is rare in the US.  Geopressured Reservoirs: In this type of reserve, brine completely saturated with natural gas in stored under pressure from the weight of overlying rock. This type of resource can be used for both heat and for natural gas.

Geothermal Gradient The geothermal gradient is the rate at which the Earth's temperature increases with depth, indicating heat flowing from the Earth's warm interior to its cooler surface.

 Normal Geothermal Gradient: At any place on the planet, there is a normal temperature gradient of C per km dug into the earth. Therefore, if one digs 20,000 feet the temperature will be about C above the surface temperature. This difference will be enough to produce electricity. However, no useful and economical technology has been developed to extracted this large source of energy.  Hot Dry Rock: This type of condition exists in 5% of the US. It is similar to Normal Geothermal Gradient, but the gradient is 40 0 C/km dug underground.  Molten Magma: No technology exists to tap into the heat reserves stored in magma. The best sources for this in the US are in Alaska and Hawaii.

Direct uses of geothermal energy is appropriate for sources below C space heating air conditioning industrial processes drying Greenhouses Aquacultures hot water resorts and pools melting snow Timber Seasoning

BASIC BLOCK DIAGRAM OF BLOCK GEOTHERMAL POWER PLANT

How Direct Uses Work Direct Sources function by sending water down a well to be heated by the Earth’s warmth. Then a heat pump is used to take the heat from the underground water to the substance that heats the house. Then after the water it is cooled is injected back into the Earth.

Types of Geothermal Resources 1.Hydrothermal 2.Hot Dry Rock (HDR) 3.Geopressurised 4.Magma Out of these only Hydrothermal Energy is being presently utilized since the technology for commercial utilization of other is not available

Types of Hydrothermal Resources Hydrothermal Resources Dry Steam Fields Wet steam Fields Binary Cycle

Dry Steam They use steam from the geothermal reservoir as it comes from wells and route it directly through turbine/generator units to produce electricity. An example of a dry steam generation operation is at the Geysers Region in northern California.

Flash Steam Plants These are the most common type of geothermal power generation plants in operation today They use water at temperatures greater than 360°F (182°C) that is pumped under high pressure to the generation equipment at the surface Upon reaching the generation equipment, the pressure is suddenly reduced, allowing some of the hot water to convert or “flash” into steam This steam is then used to power the turbine/generator units to produce electricity The water condensed from the steam, is generally pumped back into the reservoir. An example of an area using the flash steam operation is the CalEnergy Navy I flash geothermal power plant at the Coso geothermal field.

Binary Cycles

Binary cycle geothermal power generation plants differ from dry steam and flash steam systems because the water or steam from the geothermal reservoir never comes in contact with the turbine/generator units. In the binary system, the water from the geothermal reservoir is used to heat another “working fluid,” which is vaporized and used to turn the turbine/generator units The geothermal water and the “working fluid” are each confined in separate circulating systems or “closed loops” and never come in contact with each other The advantage of the binary cycle plant is that they can operate with lower temperature waters (225°F to 360°F) by using working fluids that have an even lower boiling point than water An example of an area using a binary cycle power generation system is the Mammoth Pacific binary geothermal power plants at the Casa Diablo geothermal field.

Hot Dry Rocks It Receives heat from magma The simplest models have one injection well and two production wells. Pressurized cold water is sent down the injection well where the hot rocks heat the water up. Then pressurized water of temperatures greater than F is brought to the surface and passed near a liquid with a lower boiling temperature, such as an organic liquid like butane. The ensuing steam turns the turbines. Then, the cool water is again injected to be heated. This system does not produce any emissions. US geothermal industries are making plans to commercialize this new technology.

Advantages of Geothermal Energy Reliable source of energy and available continuously throughout the year Independent of weather condition No thermal Energy storage facility is required Capital and generation cost is low as compared to conventional thermal power plant No Solid pollutants Needs very small land area 400m 2 can produce a gigawatt of energy over 30 years. Flash and Dry Steam Power Plants emit 1000x to 2000x less carbon dioxide than fossil fuel plants, no nitrogen oxides and little SO 2. Binary and Hot Dry Rock plants have no gaseous emission at all. Geothermal power plants can have modular designs, with additional units installed in increments when needed to fit growing demand for electricity

Disadvantages of Geothermal Energy Parts of plant may corrode due to presence of salt Geothermal fluids also bring in dissolved gases like CO 2, NH 3 and other solutes which causes air pollution and land pollution Life of the plant is low compared to conventional power plants due to corrosive and abrasive geothermal fluids Continuous extraction of fluid may cause settlement of land Cause Noise pollution due to exhaust, centrifugal separators blow down etc. Thus silencers are required on some equipments