بهره برداری از انرژی خورشیدی جمع آوری شده توسط تصاویر ثابت خورشیدی برای آب شیرین کن بوسیله تقطیر غشایی

The aim of this work was to evaluate the technical feasibility of producing potable water from simulated seawater by integrating a membrane distillation module with a solar still. The relatively hot brine in the solar still was used as a feed to the membrane module. The synergistic action of the solar still and the membrane module in the production of potable water was quantified. For this purpose, two types of experiment were conducted, indoor experiments and outdoor experiments. The sensitivity of the permeate flux to the brine temperature, flow rate, salt concentration and solar irradiation were all investigated. Overall, the flux of water from the solar still was no more than 20% of the total flux. The brine temperature significantly affected the flux of both the solar still and the membrane module, while the effect of salt concentration was marginal. The effect of these process parameters was more noticeable in the membrane module than in the solar still.

The demand for good-quality drinking water is increasing steadily world-wide. Increasing population, with the desire to improve standards of living, contribute to the increased demand. The severity of the problem is more pronounced in the Middle East region, especially in countries such as Jordan, which suffers from a shortage of running surface water, scanty rainfall and rapid population growth. Although over two-thirds of the planet is covered with water, 99.3% of the total water is either too salty (seawater) or inaccessible (ice caps). Since water is potable if it contains less than 500 ppm of salt, much research has gone into finding efficient methods of removing salt from seawater and brackish water. These are called desalination processes [1]. Process technologies for the treatment of saline water are consequently increasing in importance and developing at a rapid pace. Desalination processes can broadly be divided into two categories: processes with a phase change such as distillation and freezing, and processes without a phase change such as reverse osmosis (RO) and electrodialysis (ED). Membrane distillation (MD) is a hybrid of thermal distillation and membrane processes. The concept of MD was first described in the technical literature in 1967 [2]. Numerous research groups around the world have contributed to the understanding of the process. Its technical feasibility has been shown in such applications as the desalination of seawater [3], [4], [5] and [6], the removal of alcohols from aqueous streams [7], and the concentration of juices [8], bovine blood [9] and mineral acids, such as hydrochloric [10] and sulfuric [11] acids. The number of commercial applications of membrane distillation is small but growing. Desalination plants were built in Florida and the Cayman Islands but are no longer operated [12]. Recently, a Swedish company began marketing the process for water purification in nuclear plants. Membrane distillation can best be described as trans-membrane evaporation. It is a thermally driven process in which a hydrophobic membrane is in contact with a hot or warm feed solution. Vapor evolved from the feed solution passes through the pores of the membrane and is collected on the other side. Methods for collecting the vapor permeate include immediate condensation within a colder liquid flowing on the second side of the membrane [Fig. 1(a)], or condensation on a cold surface located at some distance from the membrane [Fig. 1(b)]. In the latter situation, vacuum can be applied to draw more vapor through the membrane. Full-size image (12 K) Fig. 1. Configurations of membrane distillation modules: (a) direct-contact membrane distillation; (b) air-gap membrane distillation. Figure options Membrane distillation differs from most other membrane processes (reverse osmosis, nano-, ultra- and micro-filtration) in that the transport across the membrane takes place in the vapor phase. Pervaporation also produces a vapor permeate but the vapor molecules move through an impermeable membrane by dissolution within the membrane material rather than by diffusion through open pores. The materials used most commonly to produce hydrophobic membranes suitable for membrane distillation are polypropylene (PP), polytetrafluoroethylene (PTFE) and poly(vinylidene fluoride) (PVDF). Membrane distillation is a relatively new process that can be adapted effectively for water desalination. It is technically viable, requiring moderate temperatures to produce the thermal driving force across the membrane. Economically it could be competitive in situations where renewable energy resources are available year-round such as solar energy. Solar energy can be used as an alternative energy source to run most types of desalination process. It can be used either as thermal energy to heat the brines in the distillation process or converted to electricity through photovoltiacs to run the compressors in the reverse osmosis and electrodialysis processes. On the other hand, solar energy can be used directly to desalinate seawater as in solar stills. The objective of the present work was to investigate the feasibility of coupling a solar still with a membrane distillation module to produce distillate water from simulated seawater. Use of a solar still to collect solar energy benefits in both heating the seawater that will be pumped at moderate feed temperature to the membrane module and in direct production of pure water through its own mechanism. Thus, pure water is produced simultaneously from the solar still and the membrane module. The effect of process parameters on the production rate of pure water from both the solar still and the membrane module was also investigated. For this purpose, indoor experiments and outdoor experiments were conducted. The indoor experiments were necessary in order to study the effect of process parameters under steady-state conditions.

The production of potable water using solar-powered membrane distillation has been investigated. The solar still was used for both brine heating and potable water production. The effects of temperature, brine flow rate, salt concentration and solar irradiation on the desalination process were tested. Interestingly, it was found that the contribution of the solar still in the distillate production was no more than 20% of the total flux in the outdoor experiments and less than 10% in the indoor experiments. The brine flow rate significantly affected the flux of the membrane module. The flux increased rapidly when the flow rate was switched from laminar flow to turbulent flow. The fluxes of the membrane module and solar still were exponentially dependent on the feed temperature. The effect of salt concentration on the flux of the membrane module and the solar still was marginal. However, the effect of salt concentration on water production rate was more pronounced in the membrane module than in the solar still. As solar intensity increased, brine temperature increased and consequently more flux was achieved. Fluxes of water from both the solar still and the membrane module reached their maximum values 2–3 h after the solar irradiation peak.