International Geologiical Congress - Oslo 2008

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GET-05 Geothermal utilization - direct use, electrical production, heat pumps, industry and leisure

 

Geothermal energy for desalination of sea water

 

Gerardo Hiriart, National University of Mexico (Mexico)
 

 

The National University of Mexico begun two years ago a multidisciplinary program to find practical ways to desalinate sea water with renewable energy. The selected site for the program was the Baja California Peninsula where there is an increasing water demand in a place with no water but with abundant alternative energies.
Among the natural resources found on site, the most important one is the abundance o geothermal heated sea water. Over 84°C have been measured at a meter depth in the beach of Los Cabos, and more than a hundred hot springs have been identified, some of them a few meters into the sea and some others several miles into the land. A brief study of the zone has shown a real possibility of finding hot sea water at temperatures than can reach up to 160 °C when drilling small wells of some 50 meters deep. In the project, several ways to use the hot water for desalination have been found: Generating electricity with a binary plant (1 MW is enough to operate a reverse osmosis plant that produces 6 000 cubic meters per day, enough for 30 000 peoples). This one is the best when one has sea water at 120°C or more. When less temperature, the direct use of the heat in a modified Multi-Effect thermal desalinating plant has been studied. Also the hot sea water can be used to preheat the intake of the reverse osmosis plant, gaining 3% efficiency for every °C of increase in water inlet temperature. We also found that many problems, caused by the chemistry of the hot water, must be solved before practical applications can be reached.
Among others sources of energy, the use of the heat from deep hydrothermal vents is under study with good possibilities to install soon a test plant at shallow depth. Also wind energy has been studied, to save energy from the grid, in a reverse osmosis desalinating plant, located close to a large salt producer in Gerrero Negro, where the rejected brine can be used as concentrated sea water supply for the evaporating lagoons of the process. The possibility to generate electricity using tidal energy has been also evaluated and found to be on the order of several thousands of MW in the upper part of the Gulf of California where the tide amplitude is 6 meters.
The research program is lead by the Institute of Engineering in collaboration with other five Research Institute of the National University. It has shown to be an excellent way to organize a broad scope research around a very interesting, scientific and applied problem, which will eventually solve an important problem of the country, i.e. "Desalinate sea water with renewable energy".
During year 2008, the geothermal exploration to understand and to evaluate the shallow geothermal aquifers will be intensified. Also, several prototypes will be deployed to determine their real behavior.

 

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