Desalination Progress

Desalination is slowly advancing and is becoming cheaper.  These two reports catches us up on it all. 

I have already posted on Saltworks in an earlier posting. What I find most promising there is that we are substantially modifying conventional ideas for making seaside salt into a much more efficient full desalination system using ambient solar energy and low cost fluid transfer.

None of the hardware should be costly as pressure and heat is not involved at all.  With the pilot plant, operational costs should sort themselves out as well as actual productivity.  It is really a way to farm the seaside for salt and potable water.  I think it is a great plan and may well be deliverable in small units.

The second item is the work on clathrates.  This looks promising because it may allow us to do something really neat.  The cost comes in accommodating the necessary pressure.  Conventionally we would use a pressure chamber(s).  An alternative is it to use the high pressure of the ocean at depth.

A working chamber open to the sea needs to be placed on the sea bed at an appropriate depth.  CO2 can be injected and encouraged to form the clathrates and in the process separating the water out of the sea water.  If this could even work then it might be possible to produce a continuous cycle between the CO2 supply and the clathrates and a release mechanism such as to produce fresh water continuously.  It may be necessary to pump the clathrates somewhat up the pressure gradient to achieve release.

I think it is worth the attempt to engineer a solution in the lab to see if it could be made to work.  Done right it should even produce sustaining energy.

The payoff could be simple subsea devices pumping fresh water onshore.

JUNE 14, 2010

Saltworks' patent pending technology employs an innovative Thermo-Ionic™ energy conversion system that uses up to 80 per cent less electrical/mechanical energy relative to leading desalination technologies. The energy reduction is achieved by harnessing low temperature heat and atmospheric dryness to overcome the desalination energy barrier.

Saltwater is evaporated to produce a concentrated solution. This solution, which has concentration gradient energy, is fed into Saltworks' proprietary desalting device to desalinate either seawater or brackish water. Some electrical energy is used to circulate fluids at a low pressure, yet the bulk of the energy input is obtained through the evaporation of saltwater.

The minimum energy barrier is often characterized as 0.75 kWh of energy to produce 1,000 litres of fresh water from seawater.

Reverse Osmosis (RO)

Electrodialysis (ED) and Electrodionization (EDI) involve forcing ions from saltwater through ion exchange membranes under an electrical field.

Multi Stage Flash (MSF) involves introducing heated saltwater into a lower pressure container. 

Multiple Effect Distillation (MED) consists of several consecutive cells (effects) at decreasing pressure and temperature. 

Vapour Compression (VC) is another thermal process that uses the same principles of reduced boiling points with lower pressure.

Chemical Processes - This category includes processes such liquid-liquid extraction, gas hydrate, and other precipitation schemes. While not commercially widespread, these technologies are used in speciality applications such as specific feed water contamination. 

Next Generation Water Companies

Desalination technology costs have fallen by as much as 80% over the past few years. Meanwhile, the total global desalination capacity growth of more than 47% over the past five years, according to a recent Credit Suisse investment report, and all of a sudden, desalination looks a bit more attractive. 

The reverse osmosis process, which separates out salt with a membrane, costs about 50 cents per cubic meter of water. Reverse osmosis systems also have to be monitored so that the membrane doesn’t get fouled or clogged

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.

Most of the world’s desalination plants today separate salt by distilling seawater, but this requires an immense amount of energy. 
Newer desalination plants typically use a process called reverse osmosis. This is when the seawater is forced against a membrane that filters out the salt and other minerals. The approach is less energy-intensive than distillation, but the big pumps that push the water through the membrane still require lots of electricity. 
Saltworks thermoionic process can cut the energy demands of a desalination plant by more than half, and in some cases by as much as 80 per cent.
Saltworks has a small pilot plant is already operating in Vancouver that can process 1 cubic metre of ocean water a day.
There are many companies working on nanomembranes and modification of reverse osmosis for greater energy efficiency.
A commercial Saltworkplant that could handle 50,000 cubic metres a day would require an evaporation tower 80 metres in diameter. 
Seawater desalination is about two-thirds of the desalination market. Another 20 percent is for desalination of brackish water and the remainder is for desalination of waste water streams.

NanoH2O’s membranes can expect up to a 20 percent reduction in energy consumption, or a 70 percent increase in water production, or a 40 percent smaller plant footprint.

The goal now is to scale-up manufacturing. The firm has 26,000 square feet of manufacturing infrastructure in the Los Angles area and looks to come to market with a commercial product in mid-2010.
NanoH2O chief executive Jeff Green said the membranes are a true composite membrane – not a coating – where porous, inorganic and hydrophilic nanoparticles are encapsulated within a polyamide membrane film. “We have shown we can get a salt rejection greater than 99.7 percent while operating our nanocomposite membranes at a flux of at least 30 gfd [50 Lmh].

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