Atmospheric water generator
An Atmospheric water generator (AWG), is a device that extracts water from humid ambient air.
Condensation of the air moisture to water is possible by three main processes:
- Cooling below the dew point;
- Adsorption using desiccants
- Pressure.
Two techniques are being used nowadays:
The first acts in a similar way to air conditioning systems by reduction of air temperature, which reduces the water capacity of the air, resulting in the liquification of the water vapors; this is the most common technology (cooling condensation) to condense air humidity.
The second uses desiccants, such as silica gel or zeolite, and additional few using liquid desiccants, such as LiCl or LiBr. Liquid desiccants have better adsorption capacity, but gas-liquid interface makes the use of liquid desiccants technically problematic and the liquid desiccants themselves are very toxic. Moreover, upon air desiccation, liquid desiccants are being polluted by air contaminants, while solid desiccant almost unaffected by pollution. The currently prevailing desicant based technique involves solid desiccant combined with pressure condensation. Cost effective adsorption of atmospheric moisture and low dependency on ambient relative humidity and temperature are its main advantages.
Applied Technologies
Many AWG's operate in a manner very similar to that of a dehumidifier: air is passed over a cooled coil, causing water to condense. The rate of water production depends on the ambient temperature, humidity, the volume of air passing over the coil, and the machine's capacity to cool the coil. An AWG is very useful for locations where pure drinking water is difficult to obtain or impossible to have, as there is almost always a small amount of water in the air. It is estimated that 12,900 cubic kilometers (or 0.04%) of the earth's total supply of fresh water is contained in the atmosphere, mostly as water vapor.[1]
An alternative technology for AWG is described in patent WO/2008/018071[2]. The technology was implemented to yield reliable products for water supply, incorporating a novel breakthrough and cost effective processes to supply remarkable quantities of water from the atmosphere. Instead of the traditional condensation concept described above, the new technology utilizes a multi-stage, dry, chemically based concept that is unaffected by air pollution and suits most climatic conditions. It also breaks the cost barriers of equivalent technologies thanks to sophisticated heat exchange and energy management, to the point of enabling the obtention of carbon credits.
History
Collecting water from the air has been a practice for some 2,000 years, in the form of air wells in Middle Eastern deserts, and later in Europe. Around the 1400s, history records water-collecting dew ponds, and later fog fences. [3] [4]
Principle of operation - Cooling Condensation technology
A Cooling Condensation based AWG is essentially a conventional dehumidifier that condenses water from air. A compressor circulates refrigerant through a condenser coil. A controlled-speed fan pushes filtered air over the coil which creates an artificial dew point causing water to condense. This water is then passed into a holding tank with purification and filtration system to keep the water pure. AWG features vary depending on the manufacturer. In order to meet stringent FDA standards and NSF, most systems are coupled to one or more advanced filter systems.[5]
The rate at which water can be produced depends on relative humidity and ambient air temperature and size of the compressor. AWGs become more effective as relative humidity and air temperature increase. As a rule of thumb, Cooling Condensation AWGs do not work efficiently when the temperature falls below (65°F), the relative humidity drops below 30%. The cost-effectiveness of an atmospheric water generator depends on the capacity of the machine, local humidity and temperature conditions and the cost to power the unit.
Principle of operation - Dry Desiccation with Pressure Condensation (DPC) technology
A typical machine made according to this technology incorporates three identical units, each unit producing fresh liquid water through the following process.
- Stage 1 – Door opens, air blow through and released dry.
- Stage 2 – Door closes, lower blower turns off, heat exchanger valve opens and the chamber is heated to 85c, filling with steam
- Stage 3 – Steam valve opens and the steam is sucked out by a piston and pressed into the condensation container.
- Stage 4 – Steam is condensed in the condensation container and pumped out as water.
- Stage 5 – Latent and pressure heat is returned to the heat storage tank.
- Stage 6 – Heating and steam valves are closed, followed by door opening.
AWG's using DPC technology are effective from as little as 20% of relative humidity and in temperatures ranging from 4°c to 45°c. A key advantage of dry desiccation is that no air filtration is required and micro-organisms or air pollutants cannot contaminate the produced water - so no filtering or purification of the water is needed (since the water is pure H2O, trace amounts of calcium and magnesium have to be added to make the water drinkable). Most of the energy involved is thermal, electricity being needed only to operate the air blowers and some auxiliary motors. The DPC technology has a positive energy balance that allows to recover about 90% of the latent heat involved in the water production process and enables to integrate solar heat as a complementary heat source. Energy is needed mainly to blow the air through the desiccation filters, while the condensation process utilizes the latent heat released upon adsorption, and the heat formed by applying pressure is recovered and returned to the process. The system reuses energy through heat transfers and storage in a heat reservoir, so incremental therma energy can be provided by almost any heat source (such as residual heat from power generators, cooling towers, waste incineration, or solar thermal panels). In biomass terms, it takes about 5kg of biomass (or 5 litres of diesel fuel) to produce 1,000 litres of fresh water. The energetic efficiency increases upon scaling up to higher capacity models, reducing the cost to $0.50 per 1,000 litres of water at the efficient end[6].
External links
- Template:Dmoz - lists commercial sites
References
- ^ Gleick, P. H., 1996: Water resources. In Encyclopedia of Climate and Weather, ed. by S. H. Schneider, Oxford University Press, New York, vol. 2, pp.817-823
- ^ (WO/2008/018071) METHOD AND APPARATUS FOR EXTRACTING WATER FROM ATMOSPHERIC AIR
- ^ Pugsley, Alfred J (1939). Dewponds in Fable and Fact. London: Country Life Ltd.
{{cite book}}: Cite has empty unknown parameter:|coauthors=(help) - ^ Oxford English Dictionary: dew-pond
- ^ http://everestwater.com/purification.htm
- ^ The Water - Vegetation - Waste - Energy Cycle in rural areas http://www.ewa-tech.net/about/ewas_agri_cycle.htm