The need for life-supporting water worldwide is growing much faster than the ability to supply it. We need to find ways to tap seawater supplies cheaply and quickly to meet the demand. Thispaper outlines a proposal for doing so. It is not traditional or existing technology, and parts of itwill be achievable well before others, but we can't wait to have everything in place before westart. If some of the steps in this proposal seem impossible or uneconomical, consider poweredspace flight and what has been done with that, and by way of contrast think of what is at stakehere.
As the fresh water dries up, we also face grave deficits in clean energy supplies, coupled with theinexorable conversion of vast land areas into desert or arid waste. We also suffer from heavily-polluted sources of water now, and lack the means to replenish them. We can't afford to usemassive amounts of non-renewable energy and polluting energy to make this project happen. Atthe outset we may be forced to use what we have, but our goal is to reduce that dependence alongthe way to the minimum possible. By the time we are supplying the world with its freshwaterneeds, we should be doing it with completely renewable solar energy.
Scope
There are deserts everywhere in the hotter regions of the world, even in those regions termedtemperate. These deserts receive overabundant sunshine. Currently it simply goes to waste. Every country on the planet can benefit from the purification and pumping of fresh water usingthe currently-wasted energy.
We have thousands, even millions, of fine minds and hands available to meet the challenges ofproviding fresh water and energy to the world's population. If we start now, we can explore thepossibilities, find the best of them, and build and improve our methods of delivery of the neededwater. Everything proposed here should be seen as a first step among many other attempts, but inthe end we will be doing these things everywhere, not just for our survival, but also for ourprosperity and health. Although the startup costs are significant and the false starts likely to bemany, the end result will transcend expectations, and transform the planet from a tragic waste intoan abundant garden.
Vision
Here's the way it should all appear when it is finished. Starting at the ocean shorelines andleading into desert areas, lines of distillation units many meters tall dot the sand. Between the
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distillation units, pipelines run from the top of each seaward unit to the foot of each unit tolandward, carrying water that at each stage is successively purer. The height difference betweenthe top of one distillation unit and the foot of the next allows the generation of a head of waterpressure to accommodate rising land as we move away from the seashore.
Fig.1
Desalination Unit
In one possible design, each distillation unit is a two-part structure made up of a boiler and acondenser tower. See Fig. 1. The boiler is a hollow cylindrical vessel lying nearly on its side, itsaxis aligned north to south. One end of the vessel is raised so as to make the cylinder's axisperpendicular to the equinoctial sun angle at midday, maximizing its exposure to solar radiation. The upper half-surface of the cylinder is transparent glass that transmits infrared and lightradiation. The lower half of the cylinder has a mirrored surface to concentrate the radiation in theregion of the cylinder axis. Water is fed into the lower end of a pipe running the length of the
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cylinder axis. The mirrored surfaces focuses sunlight on the pipe at the axis, bringing it aboveboiling point and driving the resulting steam upward along the pipe.
The pipe turns to a vertical run upward within a tower supporting a large spheroidal cooling andcondensation chamber at its top. The cooling chamber is shielded and insulated from the sun to adegree that allows condensation of the water vapor. The condensate is collected in the bottom ofthe cooling chamber, and funneled down one or more separate conduits into an outgoing pipeline. The daily heating/cooling cycle of the deserts may be used to evaporate the saline water during theday and condense the purified water at night. Variations of the design draw off some of the solarenergy to generate electricity, which may be used in removing the waste minerals and supplyingelectric power to meet nearby demand.
A long series of such distillation units serves as a passive water delivery system across entireregions, using few or no mechanical pumping devices, with electricity as a by-product. In normaloperation, the system consumes only solar energy, and requires only cleaning out theaccumulations of salts and other waste from the sea.
Getting to the Vision
This project should be seen as a step in an evolutionary process that continually improves,concentrates, and enriches the technologies needed to make it work as well as possible. It must beunderstood that the earliest stages will be done more crudely and with less-advanced capabilitieswithin our immediate reach, and that later stages will propagate new methods, efficiencies,components, and systems throughout the whole world as they unfold from our gainedunderstanding of what we're doing.
Basis in Principles
The essential ideas are quite simple. Use solar heat to evaporate water to vapor, collect and storethe vapor, cool the vapor, collect the condensate, and repeat, as in a still. In the evaporation step,use the heat of expansion to raise the vapor higher than the source water, making a pump toelevate the condensate without the use of anything except solar energy. Concatenate a series ofsuch stills to purify the incoming water and pump it to higher elevations for distribution anddelivery.
These steps must operate across the boiling temperature range of water, in both less-pure andpurer forms. It is preferable that the steps operate in as narrow a temperature range as possible inorder to reduce the cost of raising and lowering the temperatures of water and water vapor acrossthe boiling temperature range.
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Ideally this is an entirely passive system, with no moving parts or labor except for those requiredfor removal of salts and minerals from the evaporative components of the stills. Clearly a set offactors exist which prevent ideal operation, e.g., sandstorms that abrade the glass components ofthe stills and reduce the light transmission efficiency, heavy deposits of salts requiring frequentremoval, and breaks in the pipelines that move the solar-pumped water from one distillation unitto the next across country.
Efficiency of the initial systems is expected to be low. This outline doesn't address the broadrange of possible engineering improvements to the basic idea that would yield greater efficiencywith smaller units and less effort and material requirements. Such improvements are expected tobe made as the project progresses, and retrofitted whenever and wherever appropriate.
Building: An Example
There are many ways to attempt this project, and what follows is a speculative presentation. Thesuccess of any actual attempt will hinge on the application of detailed engineering principles andpractices to all aspects of the basic idea.
In the present example, the project entails four stages of building: fabricating the building blocksand elements, assembling the blocks and elements into the mechanisms, combining themechanisms to make the desalination plants, and putting the plants to work turning seawater intofresh water. At first, some of these steps must be done with what we have already, using perhapsfossil and nuclear and other fuels to bootstrap the more-efficient and cleaner solar-energysolutions into place.
Fabrication
The first stage of the project is diagrammed in Fig. 2. Sand is our basic building material. It issilicon dioxide, and we currently make a wide variety of glasses and ceramic structural elementsfrom it. The abundance of solar energy in the deserts may be tapped to focus sunlight ontocrucibles and systems that melt, refine, and temper the sands to fabricate blocks, pipes, valves,and mirrors for cylindrical boilers. Waste glass from the fabrication process may be recycled asinput alongside the sand, improving efficiency and reducing waste.
The crucibles and systems could make up a mobile ceramic foundry, which crawls from onedistillation unit site to the next, taking in sand, solar energy, some metals, and reclaimed wasteglass to produce the pipes, blocks, mirrors, and glass required for the distillation units. In analternative system, ceramic foundries can be set permanently in locations where the best-qualitysand is found, and transportation of the products can be done from these locations.
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Fig. 2Project Phase 1 Diagram
The fabricated blocks take various forms: an opaque insulating form and a transparent energy-conducting form. Some blocks are formed as transparent glass sectors for the light-admitting partof the boiler vessel. Some blocks are used as the backing and support for the mirrored parts of theboiler vessel. Some blocks are cast, cut, or shaped into a sector of a circle as is a large brick for achimney. The circle has the radius of the whole condensation tower. Some blocks are cast, cut,or shaped into different sectors of a spheroid to form the coooling and condensation chamber andits insulating outer layers.
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The second stage of the project is diagrammed in Fig. 3. The distillation unit is built from theblocks described, by transporters and constructors that carry and assemble the blocks into the unit. In regions with abundant solar energy, these transporters and constructors may be fully or partiallypowered by that energy.
Fig. 3Project Phase 2 Diagram
The working length of the boiler's pipe depends on the pressure head on the incoming water. Atthe seaside, there is no pressure head without separate pumping facilities, so the water must beraised using either an evaporation pan with a collector above the pan, or else a mechanical pump.
See Project Phase 3 Diagram. Distillation units are connected in series over long distances, toprovide multiple distillation stages and movement of the water to its desired destiantions. Distillation units may also be stacked vertically in overlapping fashion to provide added elevation
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to the final output of one distillation site. The final output is then sent down a descending opaqueglass pipe to the next site.
Fig. 4Project Phase 3 Diagram
Valves fabricated for these units allow inflow of water to the bottom of each unit but prevent thepressure of the heated water and water vapor from blocking the influx of further intake water. Given a small head of pressure in the incoming water, a ball valve can be used; manyimprovements on such a design are possible.
See Project Phase 4 Diagram. When the desalination system is in operation, it uses solar energyand sea water in large quantities, and a small amount of metals and other materials in smallquantities, to deliver both fresh water and electric power to communities at great distances fromthe sea water source point. In addition, some minerals and metals may be reclaimed from the saltsand other impurities left behind as solids in the distillation process.
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Fig. 4Project Phase 3 Diagram
Assembly and Combination
The assembly process should contain as many automated steps as possible due to the harshenvironmental conditions that would make manual labor difficult or impossible. This automationshould encompass everything from fabrication to the actual bricklaying and pipefitting of eachtower. The constructor equipment that automates the process must also be mobile enough tomove along the route of the pipeline so that it can be reused for each tower and lay the pipesbetween towers as it goes. The powering of the constructors can be done at least partially throughsolar energy in some form, even by something as simple as steam created from the water producedalong the pipeline and heated by reflectors.
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One significant advantage of this kind of design is the reusability of its lessons in extraterrestrialsettings, such as lunar, asteroidal, or other-planetary.
Thanks to the pervasive availability of solar energy all along the route of the pipelines, suchenergy may also be used to support 'welding' of the ceramic pipe segments produced in fabricationfrom the sands. Fabrication of glasses and ceramics is an art that offers a wide range of propertiesin the products, including higher or lower melting temperatures, differing fusing characteristics,different hardnesses and toughnesses, and much more.
At the seaside, the proposed system serves primarily to remove salts, minerals, and otherimpurities from the sea water. As the pipeline carries the water to towers further and furtherinland, the role of the units shifts along the way from purification to pumping, all driven solely bysunlight.
An added opportunity presents itself: the possibleuse of energy-capture technologies now indevelopment to produce electricity directly fromthe bricks being fabricated for the desalinationprocess. Such electricity could be used to powermonitoring and management systems for thepipelines, and even supply electricity tocommunities along the path of the pipelines.
Furthermore, the constructors may also be fitted toproduce low-efficiency solar cell arrays that itdistributes along its route, wiring them togetherwith conventional electrical-power distribution
components. These arrays provide two things: power from the sun, and shelter beneath theirpanels. Coupled with a small supply of water from the adjacent pipeline, the result might behabitable space where some crops might be grown, given the availability of fertilizers and othersoil-development components.
Desalination
In the end, we get pure water, delivered to regions of the world that have not seen water of anykind for periods ranging from decades to millennia. We can also get some added energy fed intothe power grids of areas that have never seen such things. The systems that produce all this havefew if any moving parts, and little or no fuel costs. The result will be the transformation of entirenations from abject submission to the extremes of heat and drought to productive, stable, healthy,and prosperous existence, in harmony with each other and their planet.
