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CONSTRUCTION
Environmental Safety of Construction
D0l.org/10.5281/zenodo.897011
Mironov V., Ivanyushin A., Yakimova I.
VICTOR MIRONOV, Doctor of Engineering Sciences, Professor of the Department, e-mail: vvmironov@list.ru
YURIY IVANYUSHIN, Candidate of Engineering Sciences, Associate Professor,
e-mail: ivanyushin_yuriy@mail.ru
Department of Water Supply and Sewerage
Industrial University of Tyumen
38 Volodarskogo St., Tyumen, Russia, 625000
IRINA YAKIMOVA, Candidate of Engineering Sciences, e-mail: coalabee@mail.ru LLC ELECTRORAM
33/1 Przewalskogo St., Tyumen, Russia, 625023
Using energy of sea waves to get fresh water out of the air
Abstract: The paper presents a new engineering solution aimed to extract fresh water from humid sea air in the coastal regions of the planet, where water resources are scare. The extraction of fresh water is carried out through condensing moisture from compressed atmospheric air. The actuator of the plant to extract fresh water from air is made with the use of the renewable energy of sea waves. The calculations carried out in accordance with the method developed by the authors and the results enable one to speak of the technology of fresh water extraction from the compressed humid sea air without any extra costs of external energy as a promising one.
Key words: energy of wave, condensation, fresh water, water-yielding capacity, water stress, pneumatic energy.
Introduction
Although 71 percent of the planet is water, but reserves of fresh water, which suitable for human life, is not limitless. Only small share of percent is available for use from the total water on the planet [8, 17]. Now the total amount of such surface water sources as freshwater lakes, rivers and reservoirs is only 90 thousand km . Thus the volume of such main sources of water, which are directed on household and industrial needs of humanity, as rivers are only about 2 thousand km [8]. Renewability of these resources is linked to the hydrological cycle. They are computed on the basis of this water cycle. Today it's not enough to ensure the needs of humanity in all corners of the planet by water. Besides that factors such as anthropogenic pollution of water bodies (for example China's rivers have a high level of pollution [8], about 90 percent), non-uniformity location of water resources and population contribute to the growing water scarcity in many regions of the world [2, 5]. But the quality of drinking-water is a powerful environmental, which determinant for health. In these regard water is not only a necessary resource but also a valuable commodity. In the UAE the price of drinking waters one and a half-time more than the price of gasoline [6]. At present the profit of world companies in the supply of bottled water reaches 1 trillion USD per year, approximately it's about 40 percent of the profit of oil companies [7]. There are instances of strained relations and military conflicts over access to water resources between countries in the world [17].
© Mironov V., Ivanyushin A., Yakimova I., 2017
About the article: Received: 05.03.2017; Financing: the micrograin of the Skolkovo Foundation.
The problem of providing the population with water resources
Water consumption against to population growth over the last century has increased three-fold (water consumption in 10 times, population in 3 times). Considering different scenarios by 2050 the world's population will reach 9-11 billion, about 30-40 percent higher than today. In turn, this will lead to increasing of household consumption, and also to increasing of the total water intensity of production and growth of water's volumes for irrigation for farmland. The world structure of water consumption has the form: 70 percent for agriculture, 10 percent for various industries, and 20 percent for household needs and other. According to projections of World Resources Institute [21] extremely high water stress will exist in more than 30 world countries in 2040 (fig. 1).
WORLD RESOURCES INSTITUTE Fig. 1. Water stress in countries - 2040 [21].
In this regard, there is problem of wastewater treatment and reuse in industry and everyday life. In Russia Federation only 12 percent of water bodies can be classified as relatively clean, while 56 percent are contaminated. It's not surprising that maximal level of pollution is observed in areas where two-thirds of Russian population lives. Already today there is a shortage of fresh water and people have learned to obtain her with using various technologies. As a rule, these technologies associated with desalination of sea water or fresh water production from atmospheric air by condensation. Water can be desalinated by chemical (chemical precipitation, ion exchange), physical (distillation, osmotic methods, electrodialysis and freezing) and biological methods, which are based on the ability of certain algae to absorb salt from sea water. Besides alternative methods which involve the use of ultrasound, acoustic and shock waves and electromagnetic fields are under development [9]. From all volume of desalinated water overwhelming amount produced by distillation plants - 96 percent, the share of electrodialysis installations is 2.9 percent, by reverse osmosis - 1 percent and 0.1 percent by other methods [10]. They all have one disadvantage. In desalination process of sea water formed a highly concentrated aqueous solution of salt (brine), which in large quantities are dangerous for the environment. Also note that energy costs account for up to 60% of the total costs for desalination of sea water.
The water supply problem of deficient districts is so actuate, that the last decades of the hotly debates about projects for interregional water transfer including using of main water pipelines and transporting by tankers, involvement of the flow of northern rivers of Western Siberia (Ob and Irtysh) at water sector of the southern regions [8]. Scientists simulate the transportation projects of the Arctic icebergs [16, 17]. Periodically fading and reappearing with mixed success such projects continue own life.
Another direction receiving fresh water is the condensation of water vapor from atmospheric air. At a time the Earth atmosphere contains about 14 thousand km of vapor in absolute values. Annually from surface of continents and oceans evaporates 577 thousand km of water, which later falls as atmospheric precipitation [14]. The lower atmospheric air is to the earth's surface, the more moisture it contains. Technologies for extracting moisture from the air become extremely relevant for waterless districts in which traditional sources of water supply are completely absent or in short supply. Possible quality of fresh water obtained thus is quite high for most regions of the planet: practically no heavy metals and their salts, and also pathogens. Condensation of water vapor can be carried out with natural and forced air circulation.
All these technologies require power inputs [1], which usually is produced by burning hydrocarbon fuels. But their reserves are not limitless too. We separately note quality of life impact on world water consumption along with number of population. The higher the degree of improvement, the greater the amount of water a person spends on sanitary needs [15]. In advanced Nations the norm of water consumption can reach 400 liters or more on person per day while in developing countries these values are ten times lower. Therefore, in addition to the development and implementation of new technologies for producing fresh water, especially in developed countries, officially are conducted programs of water saving. Energy and water-saving devices appear in everyday life.
Using renewable energy for producing fresh water, in particular energy of sea waves, together with the known technologies of water saving will reduce the cost of production of fresh water and to avoid losses of precious resource.
Wave hydropower is one of cleanest and safest sources of renewable energy [3, 4]. As a rule, wave power is used to generate electricity [13, 19]. This resource is used very little compared to other alternative sources, though efficiency factor such technologies can reach 85 percent [4]. The start of active widespread and practical implementation of such technologies begins in the XXI century. There are many districts around the world, where WHPP (Wave Hydro Power Plants) is really efficiency. In Russian Federation wave power relevant to the Barents and the Black sea, and Pacific coasts. The coastal strip of the Atlantic Ocean (from North Africa to Scandinavia), the West coast of Canada and the East Coast of USA, West Coast of Chile, South Africa, and the Australian region have the highest energy potential [3]. In some cases, areas of higher wave energy density (kW/m of coastline) coincide with the predicted regions of water stress. Precisely in these regions the use of wave energy for obtaining fresh water would be most effective. In addition, a set of generating units is a manmade resistance for motion of the wave. This point is also an advantage because it allows suppressing «excessive elemental force».
Sea air has a relative humidity close to 100% particularly in countries with a hot climate. A well-known the effect of increasing the temperature of the dew point when the air pressure is increased. Using this effect, method of obtaining fresh water from humid sea air was developed. We propose to use the renewable energy of sea waves to compress the moist sea air for increasing the temperature of the dew point and condensation of moisture.
Formulation of the problem
Objective is to create a technology for converting the pneumatic energy into the useful power needed to produce fresh water by condensation.
The main task is to maximize the use of renewable energy sources because modern technologies for obtaining water by condensation require energy costs, which is usually produced by burning hydrocarbon fuels.
Description of the technical solution
Technological scheme of fresh water production from the humid sea air is presented in figure 2.
Fig. 2. Technological scheme of fresh water production [12]
1 - generator of compressed air; 2 - condenser; 3 - rope; 4 - air receiver; 5 - discharge line;
6 - suction line; 7 - rod; 8 - reverse suction and discharge valves; 9 - flexible joint (rope);
10 - deferent pipe; 11 - float valve; 12 - perforated part of pipe for output dehumidified air;
13 - output valve; 14 - air intake; 15 - main deferent pipe; 16 - mechanical or gas spring in compressor; 17 - cargo with negative floating.
A method of producing water from air [12] includes energy generators compressed air (1), cooling of the compressed air stream after generators in condensers (2) with sedimentation and next moisture extraction. Feed the atmospheric moist air produced in the vicinity of the surface of the sea, where it humidity is maximum. Generators of compressed air are performed as piston compressors. They are under the sea level and fixed with the help of ropes (3) and (or) rock bolts (17) with surface of sea bottom. The moving part of the compressor is connected to the air receivers (4) with positive flotation. Discharge lines (5) of the compressors are connected with the condensers of air moisture (2). Condensers made in the form of a spiral pipe, which attached to the air receiver.
As the main material, recommended to use of elements made of polymers (e.g. polyethylene or polypropylene).
The technology is based on the principle of the oscillating body [4, 22], which in this case is the float receiver, which use sea wave energy. The generators of the potential energy of compressed air are driven with the use of the Archimedes force which required for the reciprocating motion of the floating receivers connected to the movable bodies of the compressors.
Sedimentation of moisture from air occurs at the inner surface of walls of the condensers. The higher the excess pressure in the capacitor, the greater the amount of moisture is released from sea air, as the temperature rises to the dew point. In addition, the condenser is under sea level where temperature is below the temperature of atmospheric air (in summer). It's also contributes to the sedimentation of atmospheric moisture from the sea air on the inner surface of the underwater part of the capacitors.
The precipitated moisture delivered by pipeline (10) and (15) to consumers using energy in the form of excess air pressure in condensers. The dehumidified air is discharged into air receiver (4) to create a permanent overpressure in order to saving of positive flotation. Depleted and dehumidified air is discharged into the atmosphere. If necessary, the received condensate is subjected to additional water treatment (including mineralization) in order to bring it to the required quality, before it feed to the consumer.
Consider the process of obtaining fresh water from the humid sea air, using the above technology.
Theoretical dependencies
The receiver and air condenser have positive flotation. The piston stroke of the compressor (pos. 1 of figure 2) corresponds to wave height, which varies widely depending on the region of the world. So, output per hour by air in case fixed parameters of piston compressor will be, nm /hour:
Qair = 3600'
D o
4 t
y
(1)
where Dp - inside diameter of piston camera of compressor, m; hw - wave height, m; n - coefficient which takes into account the presence of harmful space in the cavity of compression camera; t - wave period, s.
As can be seen from formula (1), on the performance of generator of compressed gas will influence not only the height of the waves but also their periodicity.
Quantity of produced condensate depends from water vapor content in atmospheric air and water-yielding capacity:
Qaqua Qair q (2)
where q - water-yielding capacity of water vapor, kg/m (figure 3), according to [11, 20]:
Pat
q = WC1 - C2
V p + Pat y
(3)
3
where C1 - maximum possibility of transferring water vapor by air at outdoor temperature T1, kg/m ; C2 -
3.
maximum possibility of transferring water vapor by air temperature of sea water T2, kg/m ; W - relative air humidity at the location; p - gauge pressure in discharge line, Pa; pat - atmosphere pressure, Pa.
Using data on average monthly temperatures of the seawater and air of atmosphere were calculated parameters of water-yielding capacity for the Black sea region (table 1). The temperature of the outside air and its moisture content is adopted at [18], temperature of sea water, as an average over the last five years. As can be seen from the table 1, we obtain a condensing effect which is noticeable when the dew point is shifted under pressure.
Table 1
The water-yielding capacity of the atmospheric air in the Black sea (district of Yalta) with relative humidity W = 70% and degree of compression of the dried air s = 4
Month I II III IV V VI VII VIII IX X XI XII
Ti, 0C 4,1 4,2 6 10,6 15,7 19,8 23,6 23,2 19 13,6 9,5 6,1
T2, 0C 9,4 8,8 8,8 10,4 16,4 21,4 24,0 24,8 21,8 18,0 14,0 11,4
q, g/m3 2,22 2,34 2,91 4,43 5,73 7,28 9,47 8,88 6,62 4,22 3,36 1,92
Note that the data given are the averages, during each day will be a certain unevenness of condensation, expressed as the deviation from the mean.
Next, also needed to test work capacity of installations which place in the waters of the sea. The main forces are gravity force and the Archimedes force, which act on the elements of the technological scheme.
The sum of gravity forces of air receiver and condenser:
G = (ml + m2 )■ g, (4)
• • 2 • • • where g - acceleration of gravity, m/s ; m1 & m2 - masses of air receiver and condenser with fixed
sizes, which equal to
mi =Ppec D ■H ■S; (5)
m2 =PKanDK ■ LK ■S, (6)
whereppec & pKOH - the density of material of air receiver's and condenser's walls, kg/m ; D and DK- outside diameters of pipes of which is made receiver and condenser, m; H - total height of the air receiver, m; LK - length tube of the condensing coil, m.
Given that the core winding in this case is air receiver, the length of the condensing coiled pipe is defined as:
Lk = n(D + DK )■ nK, (7)
where nk - number of turns of the condenser, which is determined from conditions of the location of entire spiral in working area of air receiver (below sea level).
Total the Archimedes force, acting on the receiver F1 and condenser F2, in case the installation is completely below sea level:
Fa = Fi + F2 = p^ g ■(Vi + V2), (8)
3
where p - the density of environment (sea water), kg/m ; V1 & V2 - volumes of receiver and condenser, m3:
Vi = nD2H; (9)
n- D2
V2 =n-f^■ LK. (10)
Total the Archimedes force FA balanced by gravity force G and heft of cargo with negative floating. Weight of cargo with negative floating (pos. 17 of figure 2), which required for fixing air receiver in vertical plane, is determined by the formula:
, Fa - G
m , = k^-, (11)
g
where k - safety coefficient, increase the weight of cargo by 20-30%.
On the piston of compressor must act force Fp, which is equal to the Archimedes force FA at a given pressure p:
F, = P (12)
Results
Figure 3 shows the water-yielding capacity of sea air at different degrees of compression, temperatures of suction and condensation.
The calculation was carried out for hypothetical production of fresh water from the humid sea air on the basis of the above presented dependencies. The calculation results are presented in table 2. For the original data taken of the diameter of the receiver D = 0.8 m, height H = 3 m. Spiral condenser DK= 0.10 m, the number of turns of the condenser nc = 20pieces. The wall thickness is the receiver and condenser S = 0.01 m. The working pressure is excess of a piston compressor p = 3 bar. The diameter of the compression chamber of the piston is equal to Dp = 0.25 m, the piston stroke depends on the height of waves was in the range of - 0.1-0.4 m, the ratio of harmful extent of the piston compressor /n = 0.9. The basic elements of material - polyethylene (ppec & pKOH accepted 941 kg/m ). The wave peri-
od adopted t = 1 s, atmospheric humidity W = 98%, the ambient temperature equal 30oC (303 K) and the temperature of the water is 25oC (298 K). The number of objects located in the waters of the sea n = 400 pieces.
6g ci
28,0 26,0 24,0 22,0 20,0 18,0 16,0 14,0 12,0
■ 30/25
---28/23
--25/20
-----23/18
--- 20/15
2
4
6
8 10 Degree of air compression e
Fig. 3. Theoretical water-yielding capacity of atmospheric air q when varying degrees of compression in a piston compressor s depending on the ratio of temperatures of the intake of atmospheric air and environment of condensation when the relative humidity W = 98%.
Table 2
The productivity of one condensing unit
Parameter Different wave height hw, m
0,10 0,20 0,30 0,40
Required mass cargo with negative floating mp, kg-103 (with 20% amendment) 2,057
Output per hour by air: - by volume Qair, nm3/hour - by mass M, kg/hour
15,90 31,81 47,71 63,62
18,60 37,19 55,78 74,38
Water-yielding capacity q, kg/m3 0,024
Quantity of produced fresh water for n units Qaqua, m3/day (24 hour) 3,69 7,37 11,06 14,74
Conclusion
Calculations showed that if the number of units located in the sea area is 400, the total water productivity can reach over 14 m /day on the wave height of 0.4 meters. In addition, when the modules are operating, their performance is influenced in a greater degree by the temperature difference. The ratio of the input and output pressures is affected significantly less.
For regions with low humidity of atmospheric air, it is required to provide devices for forced preliminary saturation of air with moisture.
In general, the results of calculations of the proposed technical solution show us, that using this technology will allow obtaining a sufficient quantity of fresh water for settlements located on the coastline of the seas. The method of obtaining fresh water by condensation is workable even with a slight agitation of the sea surface, which is observed for most of the year practically in every part of the World Ocean.
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