Present Trends in Geothermal Resources Development in India
Posted June 13, 2008on:
The geothermal resources in India are mostly aligned along the sub-Himalayan belt, Son Narmada lineament and the West Coast. As many of these hot springs are intermediate enthalpy resources, the activity at present is confined to utilizing them for direct uses or their chemical content. Because of the ready availability of coal resources for generating thermal power and the low priority assigned by the State to geothermal power generation, the development of geothermal energy in India continues to take a back seat after practically three decades of geoscientific studies. The latter led the Geological Survey of India to select prospects for pilot-scale power generation from proven shallow geothermal reservoirs.
The geothermal waters are a storehouse of many rare elements. Metals such as Cs, As, Cd, Rb and Li are expensive and have wide applications in electronics, space research and chemical technology. The on-going research projects are mainly directed at the exploitation of these rare elements.
At Puga, the most promising geothermal field in India, the shallow reservoir has an estimated electricity generation potential of 1.7 MWe using binary cycle power plants. A project is currently under way in this field for the cascade use of the effluent water from the proposed plant and to design equipment for greenhouse and space heating. The hot water from the Puga springs has the following metal contents: Rb ~1 ppm, Li ~ 7 ppm and Cs ~ 9 ppm, (i.e., Cs > Li). The thermal water is enriched in cesium because of the rather high volatility of this element compared to lithium. The concentration of rare alkalies in thermal waters may be attributed to the absorption of the vapors from the magmatic source by circulating geothermal fluids.
Studies are also being conducted at Puga on extracting the rare alkalies from the thermal discharge and soils. Laboratory experiments have been carried out on extracting cesium from the thermal water by “ammonium 12 molybdophosphate” within the pH range of 6 – 7, using Al+3 as a catalyst. Recovery of seventy percent cesium, from the initial content of 10 µg/ml, is possible by this method At Chuza, in the Spiti Valley area, the Geological Survey of India, in collaboration with the National Metallurgical Laboratory, is studying the economic exploitation of cesium, using the high rate of evaporation of cesium and an eutectic process. A study of rare element content, directed at an eventual utilization of cesium, rubidium and lithium, is now underway in the Sohna Valley area, Rajasthan. In the Parbati Valley area, an attempt is being made to define the relationship between geothermal activity and mineral deposition.
Geochemical surveys are still being carried out around hot springs and drill-sites to assess elements, such as arsenic, that are pathfinders to gold mineralization. The arsenic content is of considerable importance as this element is an indicator of gold-bearing epithermal systems. Chemical analysis of deposits formed near Ramshila, Kulu, has shown the following metal content: arsenic ~ 1500 ppm, Hg ~ 810 ppb, Pb ~ 100 ppm, besides the base metal minerals.
The base metal content from thermal water in the Beas Valley area and at Kasol in the Parbati Valley area, suggests that base metal mineralization might be present at deeper levels. Monitoring of thermal water from wells planned for use in direct heat applications, including irrigation, is continuing in Pittorgarh area and at Tapoban, Uttar Pradesh. The Geological Survey of India has taken on a project to study the feasibility of bottling thermal waters (29 – 36°C) from wells at Gaziabad.
The Himalayan foothills are a major earthquake-prone belt. Geothermal studies in the earthquake-affected areas have revealed the influence of seismicity on geothermal parameters. Monitoring of physical and chemical changes in the post-earthquake period in the Bhagirathi Valley area has revealed a drying-up and an emergence of hot springs, which may be attributed to changes in fracture patterns resulting from seismic activity.
As a further follow-up to the proposed 300 kWe binary cycle pilot power plant at Tatapani, Surguja district, technical and economic feasibility studies, including an MT survey to establish the configuration of the high temperature deeper reservoir, well testing to measure temperature and pressure gradients and monitoring of water quality, are being pursued to realize the goal of a full scale (18 MWe) power generation project.
Hot springs are a major tourist attraction. A major impulse is being given to the development of hot spring areas as tourist attractions, in the West Coast area. The main activity in the West Coast area consists of a survey of the heat requirements of a number of industrial units in this region and the preparation of a project document on the commercial utilization of hot springs.