Windmill With A Twist Can Provide Fresh Water From Seawater Directly

The first prototype has been built and is already working at a location near the A13 motorway near Delft. This prototype is to be dismantled and transported to Curaçao the first week of March. There the concept will be tested on seawater. (Credit: Image courtesy of Delft University of Technology)

ScienceDaily (Mar. 3, 2008) — A traditional windmill which drives a pump: that is the simple concept behind the combination of windmill/reverse osmosis developed by the Delft University of Technology (TU Delft) in The Netherlands. In this case, it involves a high-pressure pump which pushes water through a membrane using approximately 60 bar. This reverse osmosis membrane produces fresh water from seawater directly.

The windmill is suited for use by, for instance, small villages in isolated, dry coastal areas.

The combination of windmills and desalination installations is already commercially available. These windmills produce electricity from wind power, the electricity is stored and subsequently used to drive the high-pressure pump for the reverse osmosis installation. The storage of electricity in particular is very expensive. Energy is also lost during conversion.

In the TU Delft installation, the high-pressure pump is driven directly by wind power. Water storage can be used to overcome calm periods. The storage of water is after all a great deal cheaper than that of electricity.

The chosen windmill is normally used for irrigation purposes. These windmills turn relatively slowly and are also very robust. On the basis of the windmill’s capacity at varying wind speeds, it is estimated that it will produce 5 to 10 m3 of fresh water per day: enough drinking water for a small village of 500 inhabitants. A water reservoir will have to ensure that enough water is available for a calm period lasting up to five days.

Three safeguards (in the event of the installation running dry, a low number of revolutions or a high number of revolutions) are also performed mechanically so that no electricity is needed.

A traditional windmill which drives a pump…In this case, it involves a high-pressure pump which pushes water through a membrane using approximately 60 bar. This reverse osmosis membrane produces fresh water from seawater directly.

It is a nice idea but fraught with problems that the author neglects to mention.

Let’s start with the High Pressure Pump. 60 bar (about 870 psi) not really high pressure but high enough. These pumps can be well built but still will need maintenance. A village that does not have electricity is not likely to have the necessary skilled personnel or tools to perform maintenance on a complex multistage high pressure pump.

Next the Reverse Osmosis unit. The article says that the unit can Provide Fresh Water From Seawater Directly while this is true it is a simplification. In reality to work efficiently and reliably long term the unit will have to have a fairly sizable settling pond to draw sea water from or a backwashable filter to remove suspended solids before passing the water through the RO) unit. Fine suspended solids will clog the membranes and if permitted to remain in the RO membranes permanently damage them.
The RO membrane also needs to be periodically backwashed to remove bacteria and fine suspended solids. The membranes also need to be flushed periodically with proprietary chemicals to remove minerals from the membrane’s pores.
More technical maintenance that a village wit out electricity is not likely to be equipped to perform.

A simple windmill one would think should not be a problem for a reasonably intelligent person with some mechanical aptitude. But this regardless of what the author says is not your typical windmill pump water from a well to a watering trough.
This is a windmill attached to a high pressure pump. In order to drive this pump the in between the windmill and the pump there must be a gear box to change torque (a torque converter) in to the necessary revolutions per minute to generate the required pressure. This torque converter must be able to regulate the number of revolutions per minute to what is required to produce the required pressure. To much seed and to much pressure is produced and the RO membrane is damaged. To little pressure and little fresh water is produced.
This high tech device is the lynch pin of the whole system it will need maintenance and will be the most complex of the mechanical equipment.

Lastly keeping fresh water safe to drink is not a simple task. In the US people responsible for potable water plants must pass test and are licensed. Water can not be stored for long periods as the article suggest. A water reservoir mentioned by the article usually means one open to the sky, available to water fowl and other creatures likely to defecate in the water. A better solution is a cistern below ground and covered. But even a cistern requires that the water be turned over (water cycled in and out) and periodically cleaned.

All of the above means that to make use of even this type of technology requires trained knowledgeable personnel with the appropriate skills and tools to manage the system. Things that you are not likely to find where this article suggest that they intend to place this technology.

I believe the system that they have designed can produce water of excellent quality. But without the people trained to maintain and operate it will not work properly for long.

Rural Aussies have already solved the water tank problem. Pollie tanks as the Aussies say, or polyethylene tanks. There are more brands of water tanks than you can poke a stick at- Nylex (ARI) Plastank and Nylex Pura Tank, Bushman, Clarks, Aquasource, Rainmaster, Tankmasta, Team Poly, Duraplas, Rainhaven, Poly Water Tanks and a host of others around the country. The proliferation of brands is a product of the cost of trucking the tanks long distances.

Personally I don’t see this as a solution to Third World water shortages, but rather a solution for 7 star resort islands to appeal to their super rich and eco-trendy clientele. hence they are testing in Curacao.

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