Geothermal Energy and Geothermal Power Plants

Geothermal Power Production:

There are two ways of electric power production from geothermal energy 

1. Heat energy is transferred to a working fluid which operates the power cycle. this may be particularly useful at places of fresh volcanic activity where the molten interior mass of earth vents to the surface through fissures and substantially high temperatures such as between 450 to 550 degree centigrade can be found. 

2. The hot geothermal water and/or steam is used to operate the turbines directly from the wellhead the steam is transmitted by pipelines up to 1 meter in diameter over distances up to about 3 km to the power station. water separators are usually employed to separate moisture and solid particles from steam.

Geothermal plants are of following types

1. Vapour dominated (or) dry steam fields

Steam extracted from the well is cleaned in centrifugal separator which removes solid matters. The cleaned steam is then supplied directly into the steam turbine and the exhaust steam from the steam turbine is wet steam (i.e a mixture of water and steam) which passes through the condenser. The condenser condenses wet steam into water (through a cooling tower)

2. Liquid dominated high temperature systems 

     a) the flash steam open system

     b) the binary cycle system

In flash steam open system hot brine from the reservoir reaches the wellhead at lower pressure by throttling process. the flash chambers brine separators which improves the quality of mixture. now steam is separated as a dry saturated steam and supplied to the steam turbine which produces electric power through a generator.

In binary cycle system the steam turbine is isolated from corrosive or non corrosive material and/or to accommodate higher concentration of non condensable gases. this is basically a rankine cycle with an organic working fluid.

3. Total flow concept system

in such a system both kinetic energy and heat energy of the steam fluid mixture, produced by flashing the geothermal brine are utilized. the overall efficiency for conversion in to electrical energy should be greater than other methods in which only the heat content of the brine is utilized. the hot brine from geothermal well is throttled where it becomes a two phase mixture of low quality. the two phases at this point are not separated and the full flow is expanded in the mixed phase expander which is coupled to the generator. the mixture from this expander/turbine is discharged in to condenser, then the brine condensate is re injected in to the well.

Geothermal Energy Advantages,Disadvantages

Advantages of geothermal energy over other energy forms:

1) Geothermal energy is quite cheaper which means the cost of geothermal power is constant over the lifetime of the facility since no fuel is purchased and facility costs are largely fixed 

2) It is least polluting as compared to other conventional energy sources 

3) Geothermal energy is amenable for multiple uses from a single source 

4) Geothermal power plants have highest annual load factors of 85% to 90% compared to 45%-50% for fossil fuel plants. 

5) It is versatile in it's use 

6) It delivers greater amount of net energy from it's system as compared to other alternative or conventional systems. 

7) Geothermal energy from the earth's interior is almost as inexhaustible as solar or wind energy, so long as it's sources are actively sought and economically tapped. 

Disadvantages: 

1) The efficiency of power generation is less about 15% compared to 35%-40% for fossil fuel plants.

2) Noisy operation due to drilling 

3) Large area is required for the geothermal power generation 

4) The withdrawal of large amounts of steam or water from a hydrothermal reservoir may result in surface subsidence or settlement. 

5) Some geothermal plants do produce toxic solid materials, or sludges, that require disposal in approved sites.

Geothermal Energy and the power from the earth

Geothermal Energy: Power from the earth

•Geothermal energy is the energy produced by heat within the Earth.

•In some areas, deposits of water in the Earth’s crust are heated by geothermal energy.

•The United States is the world’s largest producer of geothermal energy.Although geothermal energy is considered a renewable resource, the water that is used must be aged carefully so that it is not depleted. 

•Geothermal power plants generate electricity using the following steps.

1)Steam rises through a well as in the figure the red arrow indicates the flow of steam rising.

2)The raised steam drives turbines which generates electricity and left over liquid is pumped back in to the hot rock as shown in the diagram by blue arrow.

3)The left over liquid water is returned to earth's crust because it can be reheated by geothermal energy and used again.