Tuesday, June 15, 2010

Fresh Water from the Sea: Cheap, Clean, Abundant

The surface of Earth is 70% seawater. There would be a lot more seacoast available for human settlement if only more freshwater for drinking and plant cultivation were available. Desalination is the sensible answer, but desalination requires a lot of energy. New approaches to cheaper desalination promise to open up a lot more of the oceans and seacoasts to human settlement.

Brian Wang provides a look at a new desalination technology from Saltwork Technologies that promises to reduce the energy costs of desalination by up to 80%.

Canadian scientists from Saltworks Technologies have recently discovered a new technology for water desalination. The process reduces the electrical energy consumption needed by the process by 70%. Saltworks Technologies reported that they can produce 1 cubic meter of fresh water using just 1kWh compared to 3.7kWh per cubic meter achievable using reverse osmosis.
But how does the actual technology really work? Simple: solar heat or waste heat is used to evaporate water and concentrate salt water. As a fact, solar energy is converted into osmotic energy and the resulted osmotic energy is used to desalinate water. The concentrated salt water is exposed to two separate solutions of regular salt water via two different ‘bridges’, one which is porous to chloride ion and the other which is porous to sodium ions.

Sodium and chloride ion are able to migrated across the bridges into the salt water solution. The two elements have the role to equalize the difference in ion concentration between the two solutions. In this way the two solutions get charged positively with the sodium ions and negatively with the chloride ion. To continue the process, the resulted solutions are exposed across two similar bridges to the water to be desalinated.
Sodium ions are attracted into the chloride solution and chloride ions into the sodium solution (different changes attract themselves) resulting desalination. The 1kWh energy used in the process for 1 cubic meter of water, comes mainly from pumping fluids around the pipework. To reduce costs, plastic pipes can be used instead of steel pipes as the system in not working under high pressure. _GreenOptimist_via_BrianWang

More approaches to cheaper desalination from NextBigFuture:
Dais Analytic
Dais Analytic’s “new generation of desalination technology” concentrates on desalination by molecular diffusion. This low-cost, pressure desalination process uses commercialized nanotechnology, and employs a solid polymer membrane to reject dissolved solids by size, polarity and diffusion concentration, leaving fewer than 100 PPM TDS. The Dais “MD” membrane does not foul or need regeneration, nor does it scale or support marine growth, making it a viable option where environmental concerns are uppermost. It can be used in applications with capacities of up to 10,000m3/d.
NanoH20 has developed a membrane that attracts water molecules and repels other types of molecules, thus speeding up the desalination process. A membrane that uses nanotechnology to separate pure water from seawater at a lower energy cost than existing reverse osmosis membranes. NanoH2O’s next generation reverse osmosis membranes are thin-film composite membranes that contain nano-structured material. Their enhanced permeability should enable dramatic improvements to be made in the process economics of seawater reverse osmosis. NanoH2O claims that their thin-film nanocomposite membranes will allow 10-15% to be shaved off the cost of producing potable grade water. The company aims to have its first commercial product available within 18-24 months. Research into the application of the technology in brackish water and fresh water scenarios is planned to follow from 2009, making the product suitable for a variety of desalination and water reuse applications.
Clathrate Desalination (Mouchel and Water Science)
A joint venture between Mouchel and Water Science has come up with a new approach to separating fresh water from seawater based on trapping water molecules in carbon dioxide molecules as clathrates. Carbon dioxide forms a clathrate with water spontaneously at more than 30 bar pressure and less than 80 degrees Celcius temperature. The new multipass solution developed by the team for separating and cleaning the clathrate crystals holds the key to the concept’s main attraction – ultra-low energy use. The breakthrough system is predicted to reduce energy consumption to below 1.3 kWh/m3, with the thermodynamics of salt solutions providing the simple explanation behind the baseline economics. The goal is to apply the technology in large-scale industrial desalination plants, remote desalination facilities using renewable energy, and in the oil & gas sector, for the treatment of waste well water.



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