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Extraction of Water from the Air


One of the basic problems that mankind confronts is the issue of clear fresh water. Reserves of this water are enormous; nevertheless, they are concentrated in regions that are difficult to access. Only 3% of fresh water on Earth is contained in rivers, lakes and soil. This is the water that serves as the source of water supplies. Large amount of water is circulating in the atmosphere. Thus. 1 km3 of atmospheric boundary level in warm, dry and desert regions of Earth contain up to 20000 tons of water vapors. Still, weather and climatic conditions in these regions prevent water vapors from reaching saturated condition and fallout in form of atmospheric condensation. Thus, in dry and desert areas on Earth the process of moisture cycle is incomplete.

To the most problematic areas, from the point of view of biogeography classification, desert climate with non-regular atmospheric condensation may be referred: equatorial climates (Peru coastal area), tropical (South-Western Africa, Southern Arabia), with distinct condensation periods (Sahara, Northern California, Eastern Turkestan). Climates of extra-desert regions: inter-tropical, with or without dry season, extra-tropical continental and Mediterranean (with numerous versions), sub-polar and polar.

In this context, more and more sea water in the world is freshened. Distilled water is mostly used in various therapeutic programs with the purpose of excretion, but regular consumption of this water may lead to washout of useful minor elements: calcium, magnesium, potassium. First of all, this is dangerous for the bones, as their strength depends on presence of calcium and minor elements securing regular performance of human organism. For example, in the regions where water is soft, i.e., with reduced content of mineral admixtures, scientists notice increase of cardiovascular disease cases. Where water is harder, situation with heart diseases is better - such cases are seldom registered. Moreover, water hardness influences the level of caries cases - the more mineral substances are found in water, the less often doctor calls occur.

It was also established that due to low mineralization level distilled water has unsatisfactory organoleptic properties and has adverse impact on water-salt metabolism and functional condition of pituitary and adrenaline system regulating major metabolic processes in organism.

In the course of constant consumption of distilled drinking water the patients show series of changes in electrolyte metabolism - increased concentration of chlorides, potassium and sodium in blood and their increased excretion from the organism with urine. In this connection, the need for consideration of additional criterion for drinking water - physiological soundness - is scientifically justified. This criterion provides standardization of required optimal levels of total water mineralization and content of series of biological macro- and microelements along with maximal allowable concentrations (MAC) for chemical substances and elements.

Filter "Reverse Osmosis" makes water practically sterile. But the experts of Drinking Water Center call this water dead and do not advise to drink it every daily!

Yuriy Gonchar, Director of Check and Test Center gave following comments:

"We do not recommend such water for food purposes as, according to the experiments that were held with tiny fish, it was obvious that, over a generation the fish contained in such water was becoming almost sterile, and root system of plants irrigated with such water is depressed significantly if compared with irrigation with normal water".

That is why regular consumption of distilled water shall be avoided in order to prevent harm to organism and development of serious diseases. It shall be remembered that mineral contents of distilled water does not comply with natural contents (this especially concerns absence of calcium, magnesium and potassium ions). Low-mineralized waters, apart from their poor tastiness, do not allay thirst sufficiently and have inferior salt composition.

Atmospheric moisture is a different matter, as, apart from transfer of water and heat, performs other, functions of the same importance, but the studies of their essence and significance has just started. It occurs that water contained in atmosphere actively participates in transfer of solid particles masses. Wind lifts soil particles to the air, takes away the foam from sea waves, bringing away small drops of salty water. Apart from that, salts may get to the air in molecular and dispersed form due to so-called physical evaporation from ocean surface. That is why the ocean may be considered to be the main supplier of chlorine, boron and iodine for the atmosphere, rain and river waters.

Thus, rain moisture, while in the cloud, already contains certain volume of salts. In the course of powerful circulating processes occurring in cloud mass, water and salts, soil, dust particles, in the process of their interaction, form solutions with various contents. According to academician V.I. Vernadskyi, average salt content of a cloud may reach up to 34 mg/l.

Raindrops contain dozens chemical elements and various organic compounds. When leaving the cloud, each drop contains 9, 3*10-12 mg of salts at the average. On the way to the Earth, while getting in touch with atmospheric air, it absorbs new portions of salts and dust. Regular raindrop with the weight of 50 mg, in the process of falling from the height of 1 km "washes" 16 liters of air, and 1 liter of rain water absorbs admixtures from 300 thousand liters of air. As the result, each liter of rain water brings up to 100 mg of admixtures to the Earth. In total volume of dissolved solids taken from the mainlands to the oceans by the rivers almost half returns back with atmospheric condensation. At that, each square kilometer of earth surface receives up to 700 kg of nitrogen compounds (in terms of plain nitrogen), and this is a notable fertilization for the plants.

Particularly large amount of salts is contained in condensations in sea regions. For example, in England storm event with chloride concentration of up to 200 mg/l was registered, and in Holland rainfall with chlorine concentration of up to 300 mg/l was registered.

An interesting thing to note is that the function of rain as carrier of mineral compounds and fertilizing substances cannot be reduced to plain calculation like 'certain volume of brought in fertilizers is equal to certain harvest increased. V.Е. Kabaev had been studying direct connection between cotton harvest volumes and amount of water in the condensations for many years. In 1970 he made an interesting conclusion: stimulating effect of the rain on the crops is obviously resulting from presence of hydrogen peroxide. Regular volume of H2O2 in atmospheric condensation (7...8 mg/l) is sufficient for atmospheric hydrogen to enter into combination fertilizing the plants, improving of elements mobility in soil (first of all, this refers to phosphorus), activation of photosynthesis. Having established this function of rain, the scientist found it possible to bring hydrogen peroxide to the plants artificially, by adding it to the water in the process of spray treatment.

On of the low budget variants for water extraction from the atmosphere is the method of streamer discharges for ionization of air molecules with following process of electrostatic water vapor deposition.

Major advantages of the method:

- moderate power intake and low resistance to gas stream;
- effective capture of smallest particles in submicrometer range;
- degree of treatment depends on period during which the particles remain in the electric filter

Advantages of electric filtration process:

- treatment efficiency reaches 99,9% in wide range of concentration (from several mg to 200 g/m3) and degree of particles dispersion (to deciles of micron) and low electric power consumption (about 0,1…0,5 kW-h per 1000 m3 of gases);
- electric filter is capable of removing dust from wet and severe gas medium with the temperature up to 500°С;
- capacity of electric filters reaches hundreds thousands m3/h of treated gas.

Disadvantages of electric filters:

- high responsiveness to keeping treatments parameters,
- high specific content of metal and large dimensions,
- high requirements to the quality of installation and maintenance.

As the basic circuit of low voltage pulse converter (НВИП) and high-voltage high-frequency converter, the IGBT-module-based transistor circuit of impulse generator was selected.

Brush-type tip electrodes should be used as electrodes system.

Switched power supply sources for technological gas treatment systems shall have following properties:

Um пп = 60 / 100 kW,
Um оп = 20 / 40 kW,
tпп = 50 / 100 Mx,
tоп = 100 / 200 Mx,
tф < 100 ns
fсл = 1 / 10 kHz,
Uпит = 380 W,
Pист. = 12 / 15 kW

Crown may be lit and kept stable at voltage pulse amplitude up to 60 kW. Established time values for voltage pulse: duration of positive half-wave - 50 - 100 Mx at the front less than 100 ns, duration of negative half-wave is twice as much as of the negative, i.e. 100 - 200 Mx with the amplitude that is thrice as little as of the positive half-wave.

Optimal pulse-recurrence rate - 1,3 kHz.

In order to form the air stream it is proposed to construct draft tower with ventilating effect based on the difference of temperatures and pipe height.

Hot air density is lesser than density of cold air, therefore, gas column pressure (?gh) of hot air is lesser. This fact conditions occurrence of difference of pressures inside and outside of the pipe. If the pipe is not sealed, then, due to pressure differential at the bottom of the tower the air flow directed inwards occurs. At that, hot air is expulsed upwards and leaves through the openings in the top of the construction, while cold air penetrates inwards through the openings in the bottom of the construction. Thus, natural air ventilation occurs.

This effect is increased simultaneously with increase of temperatures differential and pipe height. In our case, streamer discharge heats incoming air to the temperature in the range of 150-200 °C, increasing draft in the pipe significantly.

With tower height of 100 m, base diameter of 20 m, air velocity at the pipe inlet V = 20 m/s, and absolute air humidity of 30 g/m?, it is possible to obtain 81388 m? of water daily. Electric power consumption per 1 m? of Н2O vary from 16,67 kW/hour to 3,34 kW/hour. With the cost of electric power for companies in Ukraine 1 kW - 0,01 $, the cost of extraction of 1 m? of Н2O from the air makes 1,67 - 0,34 $. With such electric power consumption the water has high prime cost. We propose using aerodynamic energy of air stream by installing turbine generator with capacity of 11 mW; thus, obtained water will have zero prime cost. Basic costs of construction of the unit for water extraction from atmosphere and 11 mW power plant at the amount of 56 million USD will be repaid in 2 years, on condition of sales of fresh water to the consumers at 1 $ per 1 m? of water. Daily water output makes 81388 m?, annual - 29 million 706 thousand 620 m?. Term of designing - 1 year, term of construction - 1 year. Design operating life of the power plant - 100 years.

Proposed plasma-and-vacuum plant is designed for provision of reliable supply of fresh potable water to small towns and villages, as well as for replacement of costly equipment for desalination of sea water. Important factor determining project feasibility is the quality of water manufactured by the plant. Water is decontaminated by removing harmful bacteria and viruses, contains dissolved minerals and 7-8 mg/l of hydrogen peroxide (H2O2) that fortifies plants fertilization, improves elements mobility in soil (first of all this refers to phosphorus), activates photosynthesis, increases agricultural crops yield by 50%. At that, distilled water has depressing impact on organisms of plants and animals.

Proposed system for obtaining water from air by electrostatic deposition of water vapors from the air by preliminary ionization of air molecules includes high-voltage equipment for the systems of excitation and maintenance of stable streamer discharges in the units and electrostatic deposition of particles, tower that is equipped with deflector in the upper section - for use of wind power. Outer surface of the tower is made of heat insulating materials. Tower shaft and built-in aerodynamic appliances for vacuum formation are made in form of Venturi pipes, at that, the smaller one is connected to turbine generator on the narrow end, that is located in the sound-insulated room in the base section of the station.

Fig. General view of the tower and water reservoir



The project has no analogs, but the principle of stable draft formation in the pipe is described below.

Distinctive feature is that hot air rising in the tower by means of known aerodynamic appliances is accelerated in the bottleneck of the pipe at the generator turbine to the speed of V =150...280 m/s.

Calculation was made for the City of Nikolaev considering:

- energy conservation law;
- principle of trickle continuity in the air stream;
- Bernoulli law.

Air stream power may be calculated using kinetic energy equation for the body with weight m, moving with speed v:

By replacing weight m in this equation with the weight of air stream passing through the cross section per one second (unit mass mo), output N of the air stream will be obtained:

where p - плотность воздушного потока - 1,29 кг/м3; F - площадь поперечного сечения трубы у генератора, м2.

Then we insert equation [3] to equation (2):

In order to create vacuum Venturi pipes were used (В). Venturi pipe consists of two hollow truncated cones connected on smaller bases. When the air passes through the pipe with such section, its velocity will be greater in the areas with smaller area of cross section. According to Bernoulli law, in the area where air velocity is greater, its static pressure is lower. Ratio of squares of diameters determines by how many times the velocity in smaller section is greater than velocity on pipe inlet:

where D - diameter of Venturi pipe inlet; d - smaller section diameter.

Ориентировочный расчет solar and vacuum power plant was carried out on the basis of following assumptions:

1. Air velocity in the pipe near generator turbine shall not exceed speed of sound V < 300 m/s.
2. Velocity of air in narrow section of Ventury pipes shall not exceed average velocity in the pipe by 5-6 times, i.e., n < 5-6.
3. Air velocity in Venturi pipe is a variable value. In the beginning of the pipe V н is equal to air flow velocity in tower section, at the level of inlet to this Venturi pipe, and in the end of the pipe V к is equal to the flow velocity in the narrow section of Venturi pipe where it is inserted.

On the basis of these conditions average velocity in each of Venturi pipes will make:

and velocity in each narrow section of Venturi pipe will make:

Let's assume that:

- tower height is equal to 100 m;
- base diameter 1/5 0,20 20,00 m;
- air velocity at the inlet to the tower V н 4 m/s;
- increase of velocity in narrow section of each pipe, n = 5 times.

Solution

Then we determine the diameter of Venturi pipe at the generator and capacity of air stream on the basis of (8):

- velocity in narrow section of the tower Vу = 20 m/sec;
- velocity in narrow section of internal pipe Vувн = 60 m/s;
- velocity in narrow section of generator pipe Vуг = 160 m/s; < 300 m/s;
- total velocity increase in the systems - by 40 times.

Then, on the basis of formula (6), diameter of narrow section of Venturi pipe at the generator shall make:

and the area of cross section F = 7,5 m2 (4).

Most probably, diameter of pipes near turbine generators shall be reduced by their number, at least, by 4. Air flow power N = 20272 kW (5).

With coefficient of efficiency of the turbine and the generator of 0,73, aerodynamic losses caused мические потери от турбулентности 0,7.

Capacity of solar vacuum power plants may be equal to 10359 (about 10,5 mW).



The figure shows principal scheme of water extraction from the air by means of electrostatic deposition, with preliminary ionization of air molecules with streamer volume discharge. The system is accompanied with 11 mW turbine generator.


1 - tower bearing walls in form of wall supports and heat resistant roofing d=200 m;
2 - pipe is made in form of truncated cone, lower d= 50 m, upper = 20 m, h=100 m;
3 - air streams inside the tower and point of connection of Venturi pipes;
4 - 11 mW power generator;
5 - pipes for spiral water drainage to the reservoir;
6 - location of truncate Venturi pipe d of the lover point = 3,1 m, скорость воздушного потока за счет вакуума составляет 150-280 м/с.
7 - air deflector;
8 - direct pipe from the tower to reservoir;
9 - water storage reservoir;
10 - electrostatic collectors of charged air molecules (+/-);
11 - high-frequency electric equipment for the systems of exciting and maintenance of stable streaming discharges;
12 - soundproof chamber.