Patel et al, International Journal of Advanced Engineering Research and Studies

E-ISSN2249–8974

Review Article REVIEW OF SOLAR DISTILLATION METHODS Hiren Patel1, Mrs. Pragna Patel2, Mr. Jatin Patel3

1

Address for Correspondence

Master of Engineering Student, Mechanical Engineering, L.D.R.P. Institute of Technology & Research, Gandhinagar-Gujarat. 2 Asst. Prof., L.D.R.P. Institute of Technology & Research, Gandhinagar-Gujarat. 3 Lecture, School of Technology, Pandit Deendayal Petroleum University, Gandhinagar-Gujarat ABSTRACT The availability of drinking water is the prime requirement for all. Plenty of water sources are available on the earth but very few of them can be used for drinking water purpose. The various methods are developed by the researchers to distil the brackish water and sea water. The effort has been made to review all the existing technology for water distillation with their potential in this article. It is found form the critical literature survey that, the hybrid technology is to be developed for the water distillation which is acceptable and convinced to the society. KEYWORDS- Solar stills, Humidification dehumidification (HDH), multi-stage flash (MSF), multiple effect distillation (MED), reverse osmosis (RO), electro dialysis (ED).

wherein the seawater, for example, can be preheated. The module for solar collection can be optimized almost independently of the humidification or condensation component. The HDH process, thus, promises higher productivity due to the separation of the basic processes M.Zamen et al [1] Author evaluates multistage technique to improve the efficiency of the solar HD process through mathematical programming method. Also it is concluded that according to modelling results and construction cost, 2-stage process is the most suitable choice for fresh water production. This unit could be designed as a combined system for simultaneously fresh water and hot water production. Lixi Zhang et al [2] they was introduced a solar desalination process using air humidification and dehumidification. In order to increase the output of freshwater, multi-technologies are adopted; the double-pass solar air heater and tubular solar collector are used to heat the air and seawater respectively. The air is humidified by bubbling in the seawater pool, and dehumidified in the inorganic heat pipe condenser M. Abd Elkader [3] found the principle of desalination in every stage is based on evaporation to and condensation from a closed natural convection air loop in a thermal insulation box. A three stage multieffect humidification (MEH)-dehumidification process Fig. 1 Rain cycle A. Humidification dehumidification (HDH) with energy storage system The experimental test results showed that, the increase of seawater mass desalination technology Nature uses solar energy to desalinate ocean water by flow rate through the system from 0.1 liter/s to 0.13 means of the rain cycle (Figure 1). In the rain cycle, liter/s increases the productivity of the system by 10 %. sea water gets heated (by solar irradiation) and It can be seen from the results also that the use of humidifies the air which acts as a carrier gas. Then the energy storage increases the productivity by 13.5%. humidified air rises and forms clouds. Eventually, the Shaobo Hou et al [4] the solar evacuated tube clouds ‘dehumidify’ as rain. The man-made version of collector is employed in the desalination system, humidification dehumidification this cycle is called the humidification- multi-effect desalination (HDD) process is plotted, and then the dehumidification desalination (HDH) cycle. water rejected from multi-effect HDD process is The main drawback of the solar still is that the various functional processes (solar absorption, evaporation, reused to desalinate in a basin-type unit further. condensation, and heat recovery) all occur within a Javier Leon et al [5] solar seawater desalination single component. By separating these functions into using parabolic trough solar collectors coupled with distinct components, thermal inefficiencies may be conventional Multi-Effect Desalination plants. reduced and overall performance improves. This However, and besides significant achievements in the separation of functions is the essential characteristic of process energy efficiency, by the development and the HDH system. For example, the recovery of the implementation of a double-effect absorption heat latent heat of condensation, in the HDH process, is pump, the technology cannot yet compete in cost affected in a separate heat exchanger (the dehumidifier) reduction with conventional thermal distillation. I. INTRODUCTION Solar distillation is a relatively simple treatment of brackish (i.e. contain dissolved salts) water to convert fresh water. Distillation is one of many processes that can be used for water purification and can use any heating source. Solar energy is a one best option. In this process, water is evaporated; using the energy of the sun then the vapour condenses as pure water. There are classified in two group the phase-change or thermal processes and membrane process. In phase change process further classified multi-stage flash (MSF) distillation, multiple effect distillation (MED), vapour compression (VC), and thermal process is further classified as reverse osmosis (RO), electro dialysis (ED). II. REVIEW

IJAERS/Vol. II/ Issue I/Oct.-Dec.,2012/157-161

Patel et al, International Journal of Advanced Engineering Research and Studies

B. Solar stills Solar still is a device to desalinate impure water like brackish or saline water. It is a simple device to get fresh distilled water from impure water, using solar energy as fuel, for its various applications in domestic and industrial sectors. The basic concept of using solar energy to obtain drinkable fresh water from salty, brackish or contaminated water is really quite simple. Water left in an open container in an open area will evaporate into the air. The purpose of a solar still is to capture this evaporated (or distilled) water by condensing it onto a cool surface.

Fig. 2 Simple solar stills Increasing water temperature and the area of water in contact with the air can accelerate the rate of evaporation. A wide, shallow black painted pan makes an ideal vessel for the water. It should probably be baked in the sun for a while before it is used in order to free the paint of any volatile toxicants, which might otherwise evaporate and condense along with the drinking water. The pan is painted black (or some other dark color) to maximize the amount of solar energy absorbed. It should also be wide and shallow to increase the surface area, assuming the availability of a substance with good solar absorbing properties and durability in heated salt water. To capture and condense the evaporated water, we need some kind of surface close to the heated salt water, which is several degrees cooler than the water. The evaporating pan is usually covered by a sheet of clear glass or translucent plastic (to allow sunlight to reach the water) which is tilted to a slight angle to let the fresh water that condenses on its underside trickle down to a collecting trough. The glass creates a cavity and also holds the heat inside. Figure 2 combines all these components in a simple solar still design. Murase et al. [6] have analyzed a specific problem associated with the feeding system of a roof type solar still and they have also analyzed a specific problem associated with the metallic materials i.e. metallic materials would not be suitable for the construction of solar stills with low productivity. Copper Nickel alloys have been widely used for the tube material Toyama et al. [7] have developed a technology for trouble free operation of this type of still, i.e. to form a stable liquid film flow below the surface of wick. Therefore, a sophisticated idea was provided, i.e. the heat penetrating plate is bended at the centre line and has a channel for liquid flow below the crease of bending. A laboratory test apparatus of two effects having 500 mm _ 500 mm heat penetrating area was designed and made mainly from polyethylene film. The upper surface was illuminated by infrared lamps in the intensity range between 240 and 650 W/m2. The water to power ratio is of the order of 5 m3/kWh, which was several hundred times that of conventional dual purpose systems. Concentration of salt water was 1% NaCl (by wt.) to trace bypassing and leakage, and IJAERS/Vol. II/ Issue I/Oct.-Dec.,2012/157-161

E-ISSN2249–8974

feed rate varies from 0.7 to 1.0 g/m2s. The upper plate of the test still was heated by infrared lamps through two sheets of frosted glass to attain uniform irradiation. Mousa et al. [8] have focus in achieving high efficiency with respect to temperature difference between the water in basin and glass cover. Several improvements have been proposed such as the use of forced convection, a dye, and external condensers. Authors found drawbacks, i.e. the need for a controllable air supply, the effect of dye on distillate quality and the need for an electric power supply. C. Multi-Stage flash (MSF) Flashing phenomena take place when a liquid’s temperature exceeds a certain degree of superheat. In other words, flashing is the phenomenon observed when the surrounding liquid conditions suddenly change and become lower than its saturated conditions. At such a variation as a sudden pressure drop, the liquid, initially at equilibrium, becomes superheated, and the whole energy cannot be contained in the liquid as sensible heat, and the surplus heat is converted into latent heat of vaporization. The temperature of the liquid decreases quickly towards the equilibrium value, so the degree of superheat can be defined as ∆Tsup = Tin – Tsat. The phenomena can be manifested in the chemical and process plants where liquid superheat is essential. Flashing is a process which gives rise to a vaporization flow rate more significant than that obtained during simple evaporation. It is very quick phenomena caused by abrupt pressure drop which transforms the initially sub cooled liquid into superheated. Soteris Kalogirou [9] present that desalination methods are analysed with respect to their primary energy consumption, sea-water treatment requirement and equipment cost From this analysis, the multipleeffect boiling evaporator is concluded to be the most suitable method for stimulation by solar energy. The parabolic-trough solar-collector is selected mainly due to its ability to function at high temperatures with high efficiency. System modeling is used to predict the rate of fresh water produced by four sizes of systems, varying from small 10m2 to large 2160m2 collectorarea applications.

Fig:3 The steam flash steam-generation concept

Fig: 4 The Direct Steam- Generation Concept

Patel et al, International Journal of Advanced Engineering Research and Studies

An easy way to comply with the conference paper formatting requirements is to use this document as a template A diagram of a steam flash system is shown in Fig. 1. Water, pressurized to pre-vent boiling, is circulated through the collector and then flashed across a throttling valve into a flash vessel. Treated-feed water input maintains the level in the flash vessel and the sub cooled liquid is recirculated through the collector. The direct or in-situ boiling concept, shown in Fig. 2, uses a similar system configuration without a flash valve. Sub cooled water is heated to boiling and steam forms directly in the receiver tube. Andrea Cipollina et al [10] present that multi-stage flash technology has been carried out to provide better insight on flashing phenomena in MSF chambers conducted by performing an experimental investigation on a laboratory scale MSF unit, allowing the phenomenological study of flashing and its dependences on operating parameters. The effects of nucleation and turbulence promoters on flashing efficiency were analysed. Efficiency enhancements due to nucleation promoters (i.e. metallic net and abrasive paper) only arose when these counteracted the effect of high brine levels responsible for inhibiting bubble formation and growth. On the contrary, efficiency enhancements due to turbulence a promoter (i.e. Raschig rings) has been strongly observed in all the experimental runs conducted. H.S. Fath et al [11] Gives an experimental coverage of the flashing process through a superheat liquid jet using tap water at low pressures. The spray nozzles of diameters