88 POWER PLANT ENGINEERING
However, largest geothermal energy reserve of petro-geothermal type and are called Hot Dry
Rock type that is without underground water. HDR deposits have largest geothermal energy potential
in the world.
Extraction of geothermal energy through these hot dry rocks requires injection of water into
artificially created fractured rock cavities in hot dry rock and extraction of hot water and steam by
means of production wells. Cold water is injected into the well by means of injection wells and hot
water and steam is extracted by the production wells. Water injected into the well acts as a heat collect-
ing and heat transporting medium. Cavity in hot dry rock acts like a boiler steam generator. Cold water
is injected and hot water/steam is obtained.
2.20.3 Site Selection
India has about 150 known geothermal sites having geothermal fluid of moderate and low tem-
perature (< 160°C). The geothermal fields in India are in the form of hot water springs (40 to 98°C) and
shallow water reservoir temperatures are less than 160°C.
The important hydro-geothermal resource locations are
Puga Hydro-Geothermal Field, Jammu and Kashmir.
West-Coast Hydro-Geothermal Field, Maharashtra, Gujarat.
Tattapani-Hydro-Geothermal Field, Madhya Pradesh.
Due to moderate and low temperatures of geothermal fluids, the prospects of geothermally elec-
trical power plants in India are very low. However, Geothermal Hydrothermal Energy is likely to have
several applications in the temperature range of 30°C to 190°C.
For site selection of geothermal energy, the following factor may be considered.
(1) Borax deposits present
(2) Some locations with water at 120°C at 200 to 500 m depths
(3) Na-Ca-Cl-SO 4 contents
(4) Some shallow depth reservoir with water at 80 to 110°C.2.20.4 Geothermal Power Plants
The first mechanical conversion was in 1897 when the steam of the field at Larderello, Italy, was
used to heat a boiler producing steam which drove a small steam engine. The first attempt to produce
electricity also took place at Larderello in 1904 with an electric generator that powered four light bulbs
Fig. 2.31. First Geothermal Power Plant, 1904 Fig. 2.32. Modern Geothermal Power Plant.
Lardarello, Italy.