Posted on 04/05/2002 9:52:14 AM PST by Willie Green
Website excerpts:
For education and discussion only. Not for commercial use.
Water Supply & Demand
Seventy percent of the planet is covered with water, but only 2.5% of that is fresh water. Nearly 70% of this fresh water is frozen in the icecaps of Antarctica and Greenland. Most of the rest is in the form of soil moisture or in deep inaccessible aquifers or falls at the wrong time and place – in monsoons and floods. Less than 0.08% of the world´s water is thus readily accessible for direct human use, and even that is very unevenly distributed. Currently an estimated 1.1 billion people lack safe water. The resulting human toll is roughly 3.3 billion cases of illness and 2 million deaths per year. Moreover, even as the world´s population grows, the limited easily accessible freshwater resources in rivers, lakes and shallow groundwater aquifers are dwindling as a result of over-exploitation and water quality degradation. According to “business-as-usual” forecasts, about two thirds of the world´s population will face shortages of clean freshwater by 2025.
Better water conservation, water management, pollution control and water reclamation are all part of the solution to projected water stress. So too are new sources of fresh water, including the desalination of seawater. Desalination technologies have been well established since the mid-20th century and widely deployed in the Middle East and North Africa. The contracted capacity of desalination plants was 20 Million m3/d worldwide as of 1995 (IDA statistics) and has since been increasing by an annual average of 1 Million m3/d.
Desalination Processes
Large-scale commercially available desalination processes can generally be classified into two categories:
Distillation processes that require mainly heat plus some electricity for ancillary equipment. The two major processes in use are :
Multi-Stage Flash (MSF) Distillation:
This process produces vapor by heating the seawater close to its boiling temperature and passing it to a series of stages under successively decreasing pressures to induce flashing. The vapor produced is then condensed and cooled as distillate.
Multi-Effect Distillation (MED)
In this process, vapor produced by an external heating steam source is multiplied by placing several evaporators (effects) in series under successively lower pressures, and using the vapor produced in each effect as a heat source for the next.
Reverse Osmosis (RO) processes
In this process, pure water is forced to pass under pressure through special semi-permeable membranes, while salt is rejected. The pressure differential must be high enough to overcome the natural tendency of water to move from the low salt concentration side of a membrane to the high concentration side, as defined by osmotic pressure.
Nuclear Desalination
Nuclear desalination is defined to be the production of potable water from seawater in a facility in which a nuclear reactor is used as the source of energy (electrical and/or thermal) for the desalination process. The facility may be dedicated solely to the production of potable water, or may be used for the generation of electricity and the production of potable water, in which case only a portion of the total energy output of the reactor is used for water production. In either case, the notion of nuclear desalination is taken to mean an integrated facility in which both the reactor and the desalination system are located on a common site and energy is produced on-site for use in the desalination system. It also involves at least some degree of common or shared facilities, services, staff, operating strategies, outage planning, and possibly control facilities and seawater intake and outfall structures.
Role of Small & Medium Reactors (SMRs):
Small and medium reactors are important for desalination because the countries most in need of freshwater often have limited industrial infrastructures and electricity grids. The size of the grid limits the possibilities for integrating a co-generating nuclear power plant into the grid to supply the electricity market, in addition to meeting the energy requirements of a desalination plant. The largest power unit that can be integrated into an electricity grid is about 10-20 % of the grid capacity. Thus existing large reactor designs developed principally for North America, Western Europe, the former Soviet Union, or Japan are less compatible with electricity grids in many developing countries. Smaller reactors are also more appropriate for remote areas that are not suitable for connections to the grid. For both cases – i.e., remote areas and limited grids – progress on new smaller reactor designs should make nuclear power an increasingly attractive potential energy source for desalination.
Experience with nuclear desalination:
Japan: Over 100 reactor-years of nuclear powered desalination
Kazakhstan: About 30 reactor-years with the Aktau fast reactor (Shutdown in 1999 at end of reactor life)
India: A 6,300 m3/d MSF-RO unit at the Kalpakkam nuclear power plant
Experience in nuclear desalination has been obtained in Kazakhstan and Japan. The fast breeder reactor BN-350 in Kazakhstan had for many years been used partly for desalination. Several nuclear power units in Japan are equipped with seawater desalination facilities to get fresh water for make-up of the plant water system and in-plant household use. The experience has proven technical feasibility of nuclear seawater desalination over the 100 reactor-years of successful operation. Relevant technical experience has been also accumulated in Russia, Eastern European countries and Canada in utilizing nuclear heat for district heating and other process heat use. Successful operating experience exceeds 1000 reactor-years.
For more information, please visit the International Atomic Energy Agency -- Nuclear Desalination website.
Another application would be irrigation for farming. A lot of land that's now desert could become fertile, thereby reducing malnutrition.
Nuke-powered desalinators are a win-win idea.
Freshwater from the Seas
by L. Wedekind, Chief Editor,
IAEA Division of Public Information
IAEA, 6 August 2001Tapping the world's seas to produce freshwater for cities and towns takes energy, and countries are looking at nuclear electricity plants to provide it. India is among countries looking to couple a nuclear power plant to a desalination facility, working through international cooperative projects supported by the IAEA.
The technology of desalination -- or desalting seawater -- is not new. Over the past fifty years, its use has grown, particularly in the Middle East and North Africa, where freshwater is scarce. The facilities are energy intensive, and usually draw the steam or electricity they need from conventional fossil-fueled plants. But as environmental concerns grow over greenhouse gas emissions, other cleaner sources of energy are being sought.
The technology of coupling nuclear energy and desalination plants already has taken hold in Japan and Kazakhstan, where commercial facilities have been operating since the 1970s. India is seeking to expand the base of national and international experience through a demonstration plant it is building at Kalpakkam in the southeast of the country. Other countries involved in nuclear desalination projects include the Republic of Korea, Russian Federation, Pakistan, Iran, Egypt, Saudi Arabia, Indonesia, Morocco, Tunisia, Argentina, Canada, France, and China.
In 2002, the IAEA is planning an international symposium to review and update the global status of nuclear desalination. As more experience is gained and shared, the technology's use could help more countries meet rising demands for electricity and for freshwater. About two-thirds of the world's population is projected to face shortages of clean freshwater over the coming decades.
For more information, see "Freshwater from the Seas", a feature by T. Konishi and B.M. Misra in the latest edition of the IAEA Bulletin.
Another interesting invention that has never been implemented on a large scale was designed in 1931 by M. Achille Knapen. He succeeded in condensing and extracting water from warm air to irrigate fields and vineyards in southern France with what he called, an "air well" (See U.S. patent no. 1,816,592). Looking like a 40-foot concrete beehive, it was possible to produce as much as 6,000 gallons of water daily for every 1,000 square feet of condensing surface. An airwell can be built on practically any scale, and the wall materials can be concrete blocks, bricks or concentric hollow shells filled with sand or earth. A small airwell 12 feet high and 12 feet across with walls 2 feet thick can supply a generous output of daily water. It can be fitted with top and bottom air pipes, and a multitude of condensing plates on the inside. Warm air circulates and gives up moisture on the cool inside condensing plates angled downward toward a catch basin at the bottom were it is collected. Using scrap and local materials, makeshift air wells could help solve many water problems in drought ridden areas of the world, especially in Third World countries. """
What's great about these is that water vapor is one of the greatest "global warming" gasses. What could be better than to extract water vapor so that is usable by humans. Take it easy.
I am a little late to the thread but it is most interesting!
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Desalination, Nuclear Power, Mass Transportation: they're all big $$$ infrastructure with plenty of dogmatic naysayers. But they're also complimentary technologies that are available NOW to address some of the major challenges facing Kalifornia: power & water shortages, air-traffic and highway congestion.
It's a tough battle. But IMHO, these technologies make too much sense to be postponed.
I've read that something similiar is done in the Andes Mountains, only it is called "fog farming." Sheets of plastic are staked and the fog passing through every morning condenses underneath.
Cool, huh ?
I had heard they did this sort of thing in the Andes but I didn't know they called it "fog farming". I like it! I'll do a search on it later. Thanks for the ping.
The walls of Babylon may have been air wells.
Been reading also of water shortages in the desert US--
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