In the US we take our bountiful supply of food for granted - except once a year, perhaps, as the Thanksgiving season approaches. My somewhat-shifting social consciousness must be responsible for slipping this vision of a better world, with food for all, into a dream last night.
Many readers of this forum have also dreamt (fantasized) about a future in which very large, mega-scale engineering projects - which are just beyond our present technological grasp, become feasible; such as sky-tethers, sea-level canals across Mexico, OTEC etc. The following is some food for thought about another oft-mentioned project � one which might become feasible in the near future. With rising populations, arable land will be a problem soon, which can be mitigated by turning well-chosen desert-areas of earth (there are a few good candidate areas in Africa and Australia which meet the criteria) into arable land using water which is desalinated and pumped into those areas at extremely low net energy cost. But how can one desalinate the equivalent of a large river for little net expenditure of energy? It all depends on finding the proper site (and proper <pi> cites), and perhaps being able to build underground tunnels cheaply using robotics and lasers. However, Mother-nature herself can provide most of the desalination energy and most of the pumping for free ! At least that is the speculation involved here, based solely on a dream. I apologize if this is common knowledge � I couldn't�t find any reference to it on the web. There is a lot of information about the �water-density� anomaly � which is the increase in density of water, which starts at 4 degrees C. and then suddenly reverses once ice crystals form - as ice is less dense. This factor intertwines with salt content at the ocean depths. First, let me describe an enabling technology, which might make this work. It would be the ability to cut and remove large amounts of stone cheaply. Most of us are familiar with the high cost of the boring the �Chunnel� between France and England using essentially what are gigantic drills which must pulverize 100% of the mass of material in their path. But imagine how much cheaper a much large diameter tunnel � a deep underground river, in effect, could have been built � if instead of essentially grinding massive amounts of soft rock and hard mud into a pump-able slurry, we had the luxury of choosing a special kind of geology where a tunnel through much stronger rock could be built � �if only.� The �if only� part involves developing a laser cutting technology for hard rock and then the accompanied robotics � especially the 24/7 robotics necessary to remove the rock in large (marketable) pieces. Since the energy cost could be reduced greatly (and with energy and labor reductions being probably 75% of the cost) and with a market for the stone itself, it is possible that an underground river of perhaps a hundred miles in length could be built some 6000 feet below sea level using robotics � sometime in a future 40-50 years removed, where these things and especially the robotics have been perfected. Humans cannot operate at that depth for very long but robotic machines can operate continuously. With the progress in computers continuing - these robotics should be on the near-term horizon. Outside of factory and farm automation, this may be the best application for robotics imaginable on earth. Now what about that �free� desalinization and pumping. For water, of course, decreasing temperature leads to freezing. Unlike most solids - ice is LESS dense than water and floats. Maximum density is at ~4 degrees C, then ice lattices start to form and the ice will become buoyant and separate from salt on its own. Consider this in regard to: A. Freezing Temperature of Seawater Sunlight cannot penetrate below a depth of about 600 feet, around the start of what's known as the bathyal zone (it ends where the water temperature drops to 4 degrees Celsius - at about 6000 feet). Salts lower the freezing temperature- and interfere with the orderly arrangement of H2O molecules in ice. Seawater freezes at ~ -2 �C Ice crystals are �pure water,� leaving concentrated more dense salt water behind. It is true that some small amount of salt may and does get incorporated into sea ice as a result of too-rapid freezing, but that can be easily controlled. B. Salinity and Density Salts have a greater atomic mass that pure H2O. Density increases with increasing salinity. Densest waters = cold and salty � all the better for desalination IF it can occur at the depth of a mile of more. At depth of one mile, the water is already "almost cold enough" to freeze, once we remove some of the pressure. Once the salt water freezes by removal of the extra heat, nature will separate out the ice by it lower density and solidity. Once the pure water ice slurry has been separated from the saltier water in a submarine factory, the �coldness� is removed from the newly formed ice with heat pumps to provide that few degrees necessary to get 4 degree pure water frozen. IOW most of the energy needed is returned and recycled. Heat pumps are fairly efficient in this situation. Compared to osmosis or flash desalinization, this may be 20-50 times less energy intensive. C. Deep water oceans near desert? There are good candidates but we must locate the ones with the proper geology- strong enough rock and deep ocean trenches near shore - so that the tunnel can be laser cut and removed in large pieces: thereby lowering the mass of the material which must be mechanically altered by a factor about 100 billion to one (laser cuts are very thin). D. Strong undersea factory This is really not problem other than cost. Our nuclear submarine program has taken care of the bulk of the technology. Once such a factory is constructed and lowered into place in a deep ocean trench and connected to the underground �river� which has been robotically constructed, then fresh water can be produced using some nuclear energy but mostly by using mother-natures bag-of-tricks - and then the fresh water channeled to irrigate the desert (or large citries) with little pumping cost as there is a strong and recoverable pressure differential involved between the ocean at a mile deep. Has anyone seen this exact suggestion before (freeze-desalinization at great depth)? It seems obvious, but I may be missing something. After all - it was just a dream not 8 hours old ... now, I just wish that I hadn't misplaced my raggedy copy of "Aunt Sally's Policy Players Dream Book" as the Lotto jackpot is climbing up there once again ... but I'm not even sure that Aunt Sally's oraculum has a number equivalent for "freeze-desalinization".... Jones
