Òåõíè÷åñêèå íàóêè/5. ýíåðãåòèêà

Kirpichnikova I. M.,

Rakhmatulin I. R.

South Ural State University, Russia

Desalination using wind and solar energy                          

In drinking water every day need billions of people and millions of other living creatures that inhabit our planet. The Earth's surface is covered by seas and oceans, but the water is undrinkable.

Of the total volume of water in the world supply of fresh make up only 2.5%, of which 74% is frozen in glaciers, 25.7% are under the ground or in the soil and only 0.3% are available for use on the surface in the form of fresh water.

Each year, the sources of fresh water on Earth is getting smaller, and as a result, 40% of the worlds population already faced with serious water shortages.

For Russia and neighboring countries today a large scale shortage of fresh water is not observed. But there is a disadvantage in Kalmykia, the Crimea, Kazakhstan, Turkmenistan, Uzbekistan, North Caucasus and in areas such as Kurgan, Kursk, etc.

However, in each region there are sufficient supplies of water, not suitable for use without its pre-treatment. Water purification or desalination is economically justified, if we apply such methods with which to clean water solutions at a lower cost than its transport from the nearby regions.

Therefore, many countries are looking for different opportunities and ways to get fresh water.

In some cases, water must be cleaned of impurities, in others - to desalinate. And in either case requires energy expenditure, which in turn depend on the proximity and access to the source of water salinity and quality, the specifics of the process of desalination, etc.

The cost of electricity for the desalination process can range from 30% to 60% of operating costs, so that small changes in electricity tariffs have a direct impact on the cost of treated water.

There are two main desalination technology, widely used in the world: a method based on the change of the phase state of matter (thermal method) and the membrane that can be achieved by several methods.

By phase change technology include:

- 

Multi-stage flash distillation (MSF);

-

  Multi- effect (MED)

- Vapor compression (VC)—thermal (TVC) and mechanical (MVC);

      - Other processes, including distillation (SD), humidification, dehumidification (PP) with solar installations.

     Membrane technology, in addition to membrane distillation (MD), includes two main processes: reverse osmosis (RO) and electrodialysis (ED). These two technologies for removing salt from water using a membrane (Fig. 1):

Figure 1 - membranes to remove salts

 

Both processes require more energy to overcome the existing osmotic pressure between fresh and salt water. ED technology is generally used only for the brackish water in which salt water is drawn from the stream and pass through the membranes are under the influence of electric current (Fig. 2).

Figure 2 - The process of removing salt in reverse osmosis and    electrodialysis [1]

Reverse osmosis technology is applicable for desalination of saline or sea water. In this case, the water at high pressure passes through a membrane made ​​of cellulose acetate or aromatic polyamide, free from salt.

There are three process based on membrane technology, not used in desalination processes, but are used to improve the quality of drinking water. These include microfiltration (MF), ultrafiltration (UF) and nanofiltration (NF).

Thermal processes also require large amounts of energy on them, so that such equipment is usually installed near the thermal power, which they use the exhaust steam heat.

One solution to the energy supply of desalination processes is the use of renewable energy sources (RES), which provides many advantages and benefits, most of which are acceptable wind and sun.

Solar energy is the most used type of other renewable energy sources, and its use may be in the form of electrical energy (solar photovoltaic cells - SPC), and in the form of heat (solar thermal power plants - SPP).

In Fig. 3 shows the possible combinations of renewable energy technology and the basic methods of water desalination.

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 3 - Possible combinations of the major renewable energy technologies and methods of water desalination

The use of these sources is determined by the capacity to solar or wind energy areas. Figure 4. shows the distribution of renewable energy sources currently used in the processes of purification and desalination.

One option for the effective use of renewable energy is solar desalination plant, built on the basis of reverse osmosis - the separation of molecules and ions in solution, passing under pressure through a semipermeable membrane. The cleaning process begins at the moment the sun's rays on the solar module. In this case the pump, which delivers high pressure water into the vessel. The water passing the membrane of a polymer material, gives her salts and minerals.

Êàðòèíêà 20 èç 109

            Figure 5 - Diagram desalination plant with solar modules [2]

Such installations are equipped with control system which makes optimum use of solar energy. With the weakening of solar radiation is proportional to the device reduces the power of the pump and other energy consumers. On a clear sunny day the system is faster and produces more water.

Windmills (wind turbines) recently began to be used to obtain high-quality water, but there is a tendency in this direction and development. Hybrid systems are usually a combination of wind turbines and solar installations, sometimes supplemented by a diesel generator.

Currently the most used method is the method of water purification reverse osmosis, but thanks to the use of renewable energy, distillation plant can exceed its technical indicators [4].

One of the most important indicators of clean water is a qualitative result, and one of the methods that can guarantee this is the method of distillation, which provides a high level of purification.

Consider installing a distillation scheme of instant boiling (Fig. 6) The higher the temperature of sea water at the entrance to the evaporation chamber, the less need to expend energy to bring the temperature of sea water to a boil.

        

             Figure 6 - Scheme of instant boiling distillation setup [3]

 Consider a variant of the plant, when to preheat the water before it is fed to the evaporation chamber using solar collectors (Fig. 7).

            Figure 7 - Scheme of distillation plants using solar collectors

Obviously, depending on the number of solar collectors will change the performance setting. To install an instant boiling distillation with a capacity of 15 / d, we obtain the following values ​​to increase distillate yield with increasing temperature (Table 1)

Table 1 - Dependence of the increase in productivity distillation set to the number of solar collectors.

The increase in temperature, ΔT

The number of solar collector tubes

Increased productivity of distillate

10

103

0,5

20

207

1,36

30

314

2,3

40

418

3

 

For the Urals when working in conjunction with the desalination plant should be used tubular solar collectors, because they have higher efficiency compared to flat plate collectors, and their work is almost independent of the position of the sun.

In addition to collectors for electric energy needed to operate the elements of the installation, you can use a small wind power capacity.

This decision will allow for the process of desalination of water in its location, including in remote areas and not electrified.

Installations based on renewable sources of energy can be applied when creating new systems for water treatment and to improve the performance of existing desalination plants.

References:

1.      L. García-Rodríguez, V. Romero-Ternero, C. Gómez-Camacho. Economic analysis of wind-powered desalination, Desalination, 137 (2001) 259–265

2.      Información adicional sobre las nuevas tecnologías en España: www.technologyreview.com/spain/solar

3.      Îïðåñíèòåëüíûå óñòàíîâêè. – Âëàäèâîñòîê: ÄÂÃÌÀ, 1999. – 244 ñ, èë.

4.       Êèðïè÷íèêîâà, È.Ì. Îïðåñíåíèå âîäû ñ èñïîëüçîâàíèåì ýíåðãèé âåòðà è ñîëíöà/ È.Ì.Êèðïè÷íèêîâà// Âåñòíèê ÞÓðÃÓ, ñåðèÿ «Ýíåðãåòèêà», 2012. 16 (275),  âûï. 17, ñòð. 78 – 81.