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The aim of the present work is to evaluate the effect of tube bundle arrangement and the seawater feed distribution on the dry zone and scale formation in the large sized Multiple Effect Distillation (MED) evaporator. A mathematical model of the seawater feed distribution is developed and validated for a triangular pitch tube bundle of MED evaporator. The developed model includes CaCO 3 scale formation and CO 2 release. The simulation results showed that the dripping seawater flow rate on the column based on the 2nd row is lower than that of the 1st row. Consequently, the wetting rate of the tubes in the column based on the 2nd row is less than that based on the 1st row. This explains why the tubes based on the 2nd row experience more CaCO 3 scale deposit than that based on the 1st row. The simulation results showed that increasing the feed seawater to twice that of the original flow will reduce the scale thickness by 15%. Increasing the tube pitch by twice the diameter will reduce the scale thickness by 30%. The combined effect of modified feed flow and increase in the tube pitch would significantly reduce the scale precipitation thickness.

© 2014 Elsevier B.V. The current study highlights the advancement in Pressure Retarded Osmosis (PRO) process and covers most recent development in the process applications. The first application of PRO process goes back to 1973 by Sidney Loeb who suggested using the concept of osmotic energy for power generation. In principle, two solutions of different concentrations are separated by semipermeable membrane of, relatively, high water permeability and solute rejection rate. The high-concentration solution is usually known as the draw solution while the low-concentration solution is called the feed solution. The draw solution is pressurized before entering the membrane. Due to the osmotic pressure gradient across the membrane, fresh water transports in the direction of the osmotic pressure gradients resulting in the dilution of the high-concentration solution. After leaving the membrane, the diluted draw solution is depressurized in a turbine system for power generation. Different types of membrane materials and solute gradient resources were proposed and their impact on the performance of PRO process was investigated. In addition to power generation, the hybridization of PRO process with membrane and thermal processes for power generation and seawater desalination is not unusual nowadays. The current study provides a critical review about the recent advancements in the PRO process and research outcomes.

© 2014 . A dual stage PRO process is proposed here for power generation using osmotic energy. The process is able to handle a wide range of feed water salinities with different pretreatment requirements in order to reduce the membrane fouling problems. In the current study, the salinity gradient resource consisted of seawater at standard TDS, 35. g/L, while the first stage feed water was brackish water or fresh water and the second stage feed water was wastewater effluent. The diluted seawater from the first stage of PRO process was the draw solution in the second stage of PRO process. The performance of dual stage PRO process was evaluated for a number of brackish water salinities ranged from 1. g/L to 5. g/L. The TDS of wastewater and freshwater was assumed 0.2. g/L. The results showed that a better PRO performance was achieved when the brackish water and the wastewater were introduced in the first stage and the second stage respectively. In case when wastewater and brackish water were introduced in the first and second stage respectively there was about 28% decrease in the second stage permeate flow. The results also showed a decrease in the first stage permeate flow with increasing the feed salinity but the second stage permeate flow increased with increasing the feed salinity. Furthermore the results showed that the first stage maximum power density was achieved at δP=. δπ/2 while the second stage maximum power density was achieved at δP=. δπ/1.5. Unlike the conventional PRO process, it has been found that the impact of feed salinity increase on the performance of dual stage PRO process was insignificant. Finally, the power generation in the dual stage PRO process was higher than that in the conventional PRO process. The difference was equal to the entire amount of power generated in the second stage of PRO process.

In this study, a methodology is developed to assess the feasibility of a reverse osmosis (RO) desalination system powered by a stand-alone salinity driven pressure retarded osmosis (PRO) technology. First, the proposed hybrid RO–PRO system is analysed as a thermodynamic cycle and its feasibility is mathematically interpreted using a feasible condition (FC) number, several dimensionless operational variables and a number of constraints to represent the objective of zero brine discharge. Then, a study of the stand-alone feasibility of a hybrid seawater RO–PRO system is carried out. The results show that lower RO water recovery and higher dimensionless flow rate improve the stand-alone feasibility of the system. A subsystem, a look inside the PRO, is developed to study the applied pressure and the required membrane area to achieve the operations with optimum FC numbers. It is found that the optimum applied hydraulic pressure is inversely proportional to the dimensionless flow rate in the feasible range of stand-alone operations and more area of membrane is required by a larger FC number. Finally, a case study of a selected operation is presented based on its energy performance, and two influencing factors, the inefficiency of the components and the salinity concentration of the feed water.

A tilted wick-type solar still was designed and constructed. Its practical aspects and performance are presented. Charcoal cloth was used as an absorber/evaporator material and for saline water transport. The distillation system consists of five main parts: (1) the still, (2) main reservoir, (3) constant head device, (4) distillate bottle, and (5) brine reservoir. Indoor and outdoor experimental testings were carried out to investigate the effect of input water flow rate and salinity on the still productivity together with the variation of the solar still efficiency with absorber temperature. The representative daily efficiency of the still was about 53% on clear days in summer. It has been concluded that, the charcoal cloth is a good material for use as an absorber/evaporator and also as a water transport medium. Increase of the input water mass flow rate leads to a reduction in the efficiency of the wick-type solar still. The still efficiency decreased linearly with increase of salinity of the input saline water e.g. it decreased, by indoor testing, from 37.7% to 20% as the NaCl salt concentration increased from 0% to 10% by weight.

A new semi-empirical model for the pure water permeability in polymeric membranes for pressure-driven membrane separation processes is presented. The proposed new model is based on a combination of two well-known models, the solution diffusion (SD) and the pore flow (PF). The new model, the SDPF, assumes that water transfer across the membrane is jointly carried out by diffusion and pore flow mechanisms. This model may be useful to explain the effects of membrane micro-structural parameters and water physical properties on the permeability. This model further incorporates two empirical correlations for the operational conditions of the trans-membrane hydraulic pressure difference and the temperature. The SDPF model permeability function is to be regarded as the upper reference limit for the membrane permeability when using aqueous solutions as feed, as described in Part II of this work.