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Image of an area suffering from salination problems. Image of Shakespeare quote

A Few Suggested Designs

The core principle is to pump seawater inland in such a way that distillation occurs during movement of the water. As the seawater becomes concentrated it returns to the sea or to a mineral processing plant, flow rates being regulated to maintain salt concentration below 17 g % in the system to prevent the accumulation of precipitated minerals.

A fundamental difficulty of solar powered distillation systems is that a large surface area is required to trap sufficient solar energy. The primary answer to this is to arrange for distillation to occur during movement of seawater inland and back to the sea, thus using the large area of the distribution system itself to provide an adequate area for the absorption of solar energy. When a litre of water evaporates, 2.44 kJ of heat is absorbed from the water. This heat may be derived from a structure containing the water or immersed in it, such as black stones or a black bitumen floor in a channel. Whatever the immediate source the effect of evaporation is to cool the water. In a solar powered system the heat must be replaced by the sun's rays, which can provide around 4000 kJ/ m2 on an average day. By absorbing the heat in a black pipe, the energy can be used to increase water temperature without the energy cost of evaporation. The heat can then be retained and used for evaporation at a separate site. In this way evaporation can continue in the absence of sunlight at night. This consideration is an indication of the many alternatives to be considered in arriving at practical designs. Another is that the same amount of heat as is required for evaporation is liberated as water vapour condenses to liberate pure water. Some designs are recorded in the literature which aim to recover this heat to assist in evaporation. This may be possible, for example by preheating air as it flows over the walls of a condenser chamber, then directing that air through water to be evaporated. The focus here however must be practical and simple, since the aim is to provide concepts which can be applied to large geographical areas. Such systems must be simple and easy to construct. A selection of the very large number of design concepts which I have considered are described in this brochure. It is my hope that from these concepts a range of designs will emerge which are of practical value. In considering these concepts it is of the utmost importance to recognise that the design chosen must be fitted to the particular topology of the region to be supplied with water and so may vary greatly from one part of the system to another.

MAXWATER basic concept. Seawater is moved inland through ducts (double blue lines) under transparent cover and evaporates. Evaporation areas may be expanded where conditions permit, as shown. Water vapour is condensed in ambient temperature thin metal walled condenser ducts (black lines) and distributed to storage tanks and areas of need. Concentrated seawater returns to sea or to a mineral processing plant.

Distillation occurs during movement of the water inland. As the seawater becomes concentrated it returns to the sea or, where appropriate, to a mineral processing plant Distillation continues on the return journey to the sea and flow rate is regulated such that the concentration of salt and other minerals is below that which would result in precipitation. In practice this is estimated to require that the seawater to reach the sea after giving up no more than about 80% of it's water to the system

As an example, the U shaped channel might run 200 Km inland, 50 Km parallel to the coast, and 100 Km returning to the sea. The output of pure water from such an installation would be approximately 8 megalitres per hour. This calls for the flow of 10 megalitres of seawater inland per hour and the return of 2 megalitres of concentrated seawater per hour to the sea. To maintain the required slow flow rate a gradient of 1% to 1.5% is expected to be necessary. The energy required to achieve this could be provided by a large number of small wind turbines distributed along the 250 Km length of the system. acting as pumps (without the necessity of conversion to electricity)

Figure 1 shows a schematic aerial view of the general arrangement of a large scale system for inland irrigation. This may be called a Type I system.


Figure 2: Suggested arrangement along coastline where topography is suitable. Multiple evaporating channels (green lines) and pure water ducts (blue lines) run in parallel. Concentrated seawater returns to sea or mineral processing pond (black lines). Seawater may be preheated in black pipes during initial part of inland flow.