Natural Vacuum Distillation

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The majority of currently used water desalination methods require a large amount of energy input in the form of heat or electricity. Use of renewable energy sources such as wind, solar, geothermal and biomasses will result in a cleaner environment and sustainable energy production. Different desalination methods can take advantage of a number of these renewable energy sources. Among these methods is a relatively new procedure which aims to mimic the natural hydrological cycle of water, known as natural vacuum distillation [33-35]. This system is composed of a large inverted U-shaped tube, which holds 10.33 m of water vertically, consequently creating vacuum. Note, due to its density, thermodynamic properties and surrounding atmospheric pressure, seawater cannot elevate in a vacuum higher than * 10.33 m before evaporating. In order to create this vacuum, natural means (gravity, changing tides, and atmospheric pressures) can be used. As a result of the vacuum condition, water can evaporate at a reduced temperature. Heat can be provided by solar radiation, which was sufficiently available in the country where one of the first studies of this method was performed [16]. The pressure drop as a result of the natural vacuum can reach as low as 4 kPa (the National Institute of

Natural Vacuum

Fig. 19.10 Schematic of a natural vacuum distillation system [16]

Distilled Water Tank Fresh Water Tank

Fig. 19.10 Schematic of a natural vacuum distillation system [16]

Standards and Technology (NIST) regards 101.325 kPa, or 1 atm, standard atmospheric pressure) [36]. A schematic diagram of the NVD process is shown in Fig. 19.10:

This natural evaporation system consists of an evaporation column, vapor tank, and condensation column. A fan and a vacuum pump can be also added to the system to improve efficiency. Additionally, an electric heat battery for an increased evaporation rate and a coolant battery to aid condensation could be employed. The procedure of the NVD method is as follows:

1. A water column (Fig. 19.10: right) is formed due to the vacuum and is heated by solar radiation.

2. Vacuum condition holds elevated water levels within the vapor tank.

3. Due to relatively low pressure and raised temperature, some water evaporates at the surface and flows toward the condensation column (left, often aided by a fan).

4. Distilled water is then collected in the condensation column and transported to the outlet.

Under Vacuum Distillation
Fig. 19.11 A more detailed representation of the NVD system used by [16]

In these systems, the vacuum condition in the upper tank gives rise to a much lower pressure and therefore boiling temperature. Water elevated at such levels (* 10.33 m) evaporates at a saturation temperature around 55°C. The schematic diagram of the marine NVD system used in [16] (Fig. 19.11).

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Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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