Carbon Neutral Solution for Desalination: Harnessing Geothermal Sources

Water shortages are hard on some parts of the world, and as global temperatures rise, more and more regions may experience drought conditions.

Countries such as Saudi Arabia use desalination plants to provide drinking water to their residents and produce 5 million cubic meters of desalinated water a day. The method requires a large amount of energy, which can limit the use of the process in many parts of the world.

Researchers have been working on the use of renewable energy sources such as solar and wind to power desalination plants, and have reduced the need for traditional methods using fossil fuels. New research now presents an untapped resource for desalination: geothermal energy.

"We are currently looking for better methods, low-carbon methods, to create energy," said Thomas Missimer of Florida Gulf Coast University. "We want electricity generated at the base, in other words, 24 hours a day, without interruption Geothermal energy is one of those energies."

Missimer says that geothermal energy provides energy in two ways: a wet stone and a dry stone. Wetlands, like Iceland, use hot water from the depths of the earth to provide the energy needed to move the turbines and to produce energy. But this type of geothermal heat is rare.

On the other hand, the geothermal potential of dry rocks is more widespread on a global scale. Missimer suggests using these areas, such as Southern California, North Africa and the Red Sea, to heat water that can be used to produce energy.

Geothermal methods of dry rock are currently used in some parts of the world for energy production, but according to Missimer, heat can be used more efficiently, especially with desalination. Details of new research on the construction of a "geothermal-water campus" will be presented Monday at the 2018 annual meeting of the Geological Society of America, in Indianapolis, Indiana.

Usually, the ground-heated geothermal water is converted to steam, this steam feeding a turbine to produce electricity, then the heated water is discharged into the atmosphere while it is still hot – always above 100 degrees Celsius. Instead of purging, the team wants to use this steam in their desalination process.

The first desalination process is multi-effect distillation (MED), which requires hot water (above 100 degrees Celsius), but the second process, adsorption desalination (AD), can be run on cooler water, says Missimer. As the steam passes through the system and cools, it is still effective in fueling desalination. "You now have an efficient system in which you have kept the latent heat captured in the soil through three processes: power generation by turbine, MED and AD."

At the end of the desalination process, Missimer indicates that the distilled water and chilled water (from the AD process) are the final products. Although distilled water can be consumed, even chilled water is reused. Fresh water can be recycled through the factory to help with air conditioning.

Finally, researchers propose storing excess water in aquifers for later use, which, according to Missimer, will save energy in the future. "By storing some of this excess water, you can use this water seasonally when you need more water and somehow balance the demands of the system."

The benefits of such a system are vast: there is no carbon dioxide produced at the factory because it is fully self-sufficient and powered by geothermal rather than fossil fuels. It also has an economic advantage. "If you consider the benefit like Saudi Arabia, saving 6 million barrels of oil a day, at $ 100 a barrel, it's a helluva fortune," Missimer said.

Missimer says that this solution is even more effective than a solar power plant because it can run 24 hours a day, instead of hours of daylight. He adds that the benefits really derive from the efficiency of the operations. "In an installation like this, if it works properly, you do not consume resources," says Missimer, adding that the heat continues to circulate and that it is renewable.

For the moment, the idea is theoretical and has not been put into practice. But Missimer adds that different parts of the plant and technology have been around for a while – they just have not been combined into one plant. "We have learned that sometimes you do not need a new technology to make progress," he said. "Sometimes it is a matter of constructively rebuilding old technology to improve the efficiency of operations." He and his colleagues hope to realize their CO2-free desalination ideas in the near future.

Explore further:
Researchers test a system using electrodialysis to produce safe drinking water

More information:
Linking geothermal power generation to multiple processes of desalination and storage and recovery of aquifers: a method to reduce the use of fossil fuels and the carbon footprint of many parts of the world. Geological Society of America Abstracts with programs. Flight. 50, No. 6

DOI: 10.1130 / abs / 2018AM-320494, https://gsa.confex.com/gsa/2018AM/webprogram/Session45325.html