Search

© 2018 Desalination Publications. All rights reserved. A dual stage PRO process has been proposed for power generation from a salinity gradient across a semi-permeable membrane. Both closed-loop and open-loop dual stage PRO system were evaluated using 2 M NaCl and Dead Sea as draw solutions, whereas the feed solution was either fresh water or seawater. The impact of feed salinity gradient resource and feed pressure on the net power generation and water flux were evaluated. The results showed that power density in stage one reached a maximum amount at ΔP = p/2, but the maximum net power generation occurred at ΔP = p/2. This result was mainly attributed to the variation of net driving pressure in stage one and two of the PRO process. The dual stage PRO process was found to perform better at high osmotic pressure gradient across the PRO membrane, for example when Dead Sea brine or highly concentrated NaCl was the draw solution. Total power generation in the dual stage PRO process was up to 40% higher than that in the conventional PRO process. This outcome was achieved through harvesting the rest of the energy remaining in the diluted draw solution. Therefore, a dual stage PRO process has the potential of maximizing power generation from a salinity gradient resource.

The feasibility of pressure-retarded osmosis (PRO) for power generation was evaluated with consideration of the energy inputs and losses in the process. The effects of the concentration polarization, reverse salt diffusion, and external resistance at the membrane porous layer were quantified, for the first time, along the membrane module to determine their contributions to the energy loss in the PRO process. Concentration polarization was responsible for up to 40% of the energy loss during the PRO process. However, increasing the PRO membrane modules from 1 to 4 resulted in a variable increase of the energy output depending on the salinity gradient. The energy requirements for draw and feed solution pretreatment were estimated to be over 38% of the total energy inputs. Results showed that coupling seawater (SW) with river water (RW) was unable to generate sufficient energy to compensate for the energy inputs and losses during the PRO process. With 0.39 kwh/m 3 maximum specific energy in the PRO process, the energy yield of reverse osmosis brine (ROB)-wastewater (WW) salinity gradient was slightly greater than the total energy inputs, although using Dead Sea-SW/ROB salinity gradient was more promising. Overall, the primary current limitation is the lack of suitable PRO membranes that can withstand a high hydraulic pressure.

In this paper, a commercial spiral wound PGMD module was modeled and optimized for seawater desalination using Response Surface Methodology (RSM). Permeate flux (P flux ) and specific thermal energy consumption (STEC) were the main performance parameters to optimize, while evaporator inlet temperature (T evap ), condenser inlet temperature (T cond ) and feed flow rate (F) were the three operating parameters chosen. Analysis of variance (ANOVA) was used to evaluate statistically the response surface models. According to the study, T evap had the strongest effect on P flux and STEC, increasing the former and decreasing the latter, F increased both responses, and T cond had a weak effect on P flux and practically none on STEC. The models were validated with further experimental data and a good correlation between experimental and predicted values of the responses was obtained for P flux and STEC respectively. An optimization was performed to determine the operating conditions that produce a maximum value of P flux and a minimum value of STEC simultaneously. The result of the multiple responses optimization using desirability function was a maximum P flux of 2.66 l/h·m 2 and a minimum STEC of 255.8 kWh/m 3 .

© 2017 Elsevier Ltd This work proposes an analysis of conventional (single stage) and dual stage Closed-Loop Pressure Retarded Osmosis (CLPRO) for power generation from a salinity gradient resource. Model calculations were performed taking into account the influence of operating parameters such as the draw solution concentration, membrane area, and draw solution pressure on the performance of the CLPRO process. Modeling results showed that the dual stage CLPRO process outperformed the conventional CLPRO process and power generation increased 18% by adding a second stage of PRO membrane. Multi-Effect Distillation (MED) was selected for the regeneration of the draw solution taking advantage of an available source of waste heat energy. The performance of MED process has been assessed by investigating two key parameters: the specific thermal consumption and the specific heat transfer area. The model calculations showed that the power generation by the single and dual stage CLPRO was higher than the electrical power consumption by the MED plant. In the case of the power generation obtained by the dual stage CLPRO, it was 95% higher than the electrical power consumption by the MED plant, proving the possibility of using low-grade heat for producing electricity from a salinity gradient resource.

A stand-alone small-scale renewable heat powered polygeneration system to provide cold for space cooling, electricity, and seawater desalination was proposed and numerically modelled. The system is based on Permeate/Conductive-gap MD modules (P/CGMD) and an ammonia/water absorption power-refrigeration system driven by heat from an evacuated flat plate solar collector field with a biomass-fired backup boiler. Energy and exergy performance of the system was analysed using climate conditions of a typical location well-endowed with solar irradiation and characterized by a potential shortage of freshwater supply and high cooling demand. In the base-case, the system provided 130 kW of cooling capacity at 11 °C, 6.4 kW of net electrical power, and 41.4 m3/day of desalinated water based on annual average weather conditions of Almeria (Spain). The overall system's resource utilization efficiency and exergy efficiency were estimated at 44.2% and 6.9% respectively. The use of CGMD reduced the required specific membrane surface area by 53% compared to the PGMD. The results of this study show that a thermally coupled absorption refrigeration system and MD process can be implemented (i) to increase the efficiency of the entire thermal energy conversion process and (ii) to cost-effectively utilize the solar thermal installation, particularly in regions where desalination is a necessity.

A 72 m3/d pilot low-temperature multi-effect distillation plant located at the Plataforma Solar de Almeria has been experimentally characterized at steady state to study the influence of the variation in certain parameters that control the process (the hot water inlet temperature as external thermal energy source and the last effect vapor temperature) on the distillate production, the thermal consumption, and the thermal energy efficiency of the plant. Results allowed characterizing the increase in the water production and the thermal consumption with the increase in the hot water inlet temperature and with the decrease in the last effect vapor temperature. The performance ratio reached its maximum when the last effect vapor temperature ranged from 25 to 35°C, since the temperature difference between effects was lower. The preliminary characterization of this plant provides useful experimental information for design criteria and for the analysis of control strategies of other large-scale MED plant...

© 2016 Balaban Desalination Publications. All rights reserved. Novel desalination approaches are required to provide both drinking and agricultural water as there is ever increasing stress upon precious freshwater resources. It was our hypothesis that a modified Forward Osmosis (FO) process had the potential for production of irrigation water comprising of appropriate concentrations of fertilizers from a seawater feed. Four agents, KNO3, Na2SO4, CaNO3, and MgCl2, plus 35 g/L seawater were used as the draw and feed solutions of the FO process. Net Driving Pressure in the FO process was manipulated either by increasing the concentration of draw solution (FO process) or by increasing feed pressure (Pressure Assisted FO (PAFO) process). A series of nanofiltration (NF) and reverse osmosis (RO) membranes were used for the regeneration of draw solution. The results suggested that a PAFO process was more energy efficient than simple FO, provided the energy relating to the brine flow from the NF/RO membrane for pressurizing the feed solution of PAFO process was used. Furthermore, this study suggested using a mixture of a primary draw solution, MgCl2, and a secondary draw solution, KNO3, for NO3 supply into the irrigation water was preferable. As such, MgCl2 provided the driving force for fresh water extraction while KNO3 was the source of fertilizer in the irrigation water. Results showed that water quality provided by application of a MgCl2 + KNO3 draw solution was better than that from KNO3 or Ca(NO3)2. The concentrations of NO3 and SO4 in irrigation water were within recommended levels when the diluted draw solution was regenerated by a dual stage low-pressure RO process.

Forward Osmosis (FO) has been proposed as an alternative method for seawater desalination, wherein Reverse Osmosis (RO) membrane technology is used for regeneration of the draw solution. Previous studies have indicated that a standalone Reverse Osmosis unit is more energy efficient than a Forward Osmosis-Reverse Osmosis system and as such it was recommended that an FO-RO system was best employed only for the desalination of high salinity seawaters. This study examined FO-RO applicability in more detail by examining the impact of seawater salinity, impact of an Energy Recovery Device (ERD), and the effect of membrane fouling. For comparison purposes, the performance of the FO process was improved to minimize the impact of concentration polarization and optimize the concentration of draw solution. Model calculations revealed that FO-RO was more energy efficient than RO when no Energy Recovery Device was employed. However, results showed there was no significant difference in the power consumption between the FO-RO system and the RO unit at high seawater salinities, particularly when a high efficiency ERD was installed. Moreover, the FO-RO system required more membrane area than conventional a RO unit which may further compromise the FO-RO desalination cost.

Experiments were conducted with a commercial membrane distillation module, which has an air-gap membrane distillation (AGMD) and spiral-wound configuration. Tests were performed simulating the salinity and temperature of the water using as a case study the Albian aquifer in Algeria. Solar thermal energy from a field of stationary flat-plate solar collectors was supplied to the module. The total productivity of the AGMD system was analyzed for different operational conditions and compared with that from the RO system. The effect of brackish water temperature on the energy consumption was scrutinized, and the energy requirements assessed toward the design of a pilot unit for decentralized autonomous solar desalination. Results showed that for producing a higher volume of distillate, module with less surface area is better. Also, it was found that recovery ratio increases linearly with the temperature difference in both modules. The maximum value was 6% for the highest feed flow rate operated in modu...

Dual stage PRO process has been proposed for power generation from a salinity gradient across a semi-permeable membrane. Closed-loop and open-loop dual stage PRO system were evaluated using 2 M NaCl and Dead Sea as draw solutions whereas the feed solution was either fresh water or seawater. The impact of feed salinity gradient resource and feed pressure on the net power generation and water flux was evaluated. The results showed that power density in stage one reached a maximum amount atΔP = π/2 but the maximum net power generation occurred atΔP < π/2. This was mainly attributed to the variation of net driving pressure in stage one and two of the PRO process. The dual stage PRO process was found to perform better at high osmotic pressure gradient across the PRO membrane, for example when Dead Sea brine or highly concentrated NaCl is the draw solution. Total power generation in the dual stage PRO process is up to 40% higher than that in the conventional PRO process. This was achieved through harvesting the rest of energy remaining in the diluted draw solution. Therefore, dual stage PRO process has the potential of maximizing power generation from a salinity gradient resource.

The combination of desalination with concentrated solar power (CSP) plants (CSP + D) is considered as the most realistic opportunity for the development of large-scale desalination with solar energy. The availability of solar power and waste heat in CSP plants offers possibilities for both reverse osmosis (RO) and thermal desalination systems. In the case of RO the combination can be done directly by transporting the electricity. In the case of thermal desalination technologies there are different alternatives for coupling with CSP plants which can offer advantages with respect to the CSP + RO combination such as the reduction of the cooling needs of the power cycle. A techno-economic analysis of different schemes of multi-effect distillation (MED) systems coupled with CSP plants is presented here and compared to the CSP + RO option. The study is done using validated models of MED plants and considering the three conventional cooling methods available in CSP plants: dry cooling, once-through and wet cooling. The analysis is performed using operating conditions of real plants. The comparisons are done for the two main regions where the cogeneration of electricity and fresh water using CSP + D is proposed: the Mediterranean basin and the Arabian Gulf.

The aim of this work is to analyse whether the integration of Multi-Effect Distillation (MED) process into Concentrating Solar Power (CSP) plants can be more competitive, under certain conditions, than the independent freshwater and power production by connecting a Reverse Osmosis (RO) system to a CSP plant. For this purpose, different CSP + MED configurations using the steam from the turbine as the thermal energy source of the desalination process have been evaluated and compared to the simple combination of a CSP plant connected to a RO plant. A sensitivity analysis has been carried out varying different parameters of the whole system (the specific electric consumption and the exhaust steam temperature) and calculating in each case the overall thermodynamic efficiency of the combined system for the same net production of electricity and desalinated water. This analysis has been performed for the three types of cooling methods usually employed in power plants (dry cooling, once-through and evaporative water cooling) and the results have been discussed in detail.

A dual stage pressure retarded osmosis (PRO) process was investigated for power generation using different types of membranes. Polyamide (PA) and cellulose triacetate (CTA) membranes were used in the first and second stage of the PRO process to improve the process performance due to the high water permeability of PA membranes. A comparison between dual stage PA–CTA and CTA–CTA membrane systems were carried out using seawater as a draw solution, while fresh water and wastewater effluent were the feed solution in the first and second stage of the process. The impact of draw solution flow rate on the process performance was evaluated. The performance of first and second stage of the PRO process increased by 11.5 and 28.6%, respectively, when the draw solution flow rate increased by a factor of 2.5. In return, there was a negligible increase in the total specific power consumption of the PRO process. In general, power consumption of the dual stage PRO process was as low as 0.3 kWh/m3. Furthermore, the...

Two-stage forward osmosis (FO)–reverse osmosis (RO)/BWRO and conventional RO/BWRO processes were evaluated for saline water treatment. Three different salts, NaCl, MgCl2 and MgSO4, were used as a draw solution. The performance of FO, RO and BWRO regeneration processes was simulated using predeveloped software. The simulation results showed that the water and solute flux across the FO membrane decreased with increasing the FO recovery rate. The highest water flux was in case of 1.2 mol NaCl draw solution for seawater desalination. The total power consumption for seawater desalination was lower in the RO process than in the FO–RO process. However, as the RO recovery rate increased, the difference in total power consumption between the conventional RO process and 0.65 mol MgCl2 FO–RO processes was insignificant. In case of brackish water desalination, the lowest specific power consumption and permeate TDS were in case of the conventional BWRO process and then followed by 0.32 mol MgSO4, 0.22 mol MgCl...

The agri-food chain consumes about one third of the world’s energy production with about 12% of it for crop production and nearly 80% for processing, distribution, retail, preparation and cooking. The agri-food chain also accounts for 80-90% of total global freshwater use where 70% alone is for irrigation. Additionally, on a global scale, freshwater production consumes nearly 15% of the entire energy production. It can therefore be argued that making agriculture and the agri-food supply chain independent from fossil fuel use has a huge potential to contribute to global food security and climate protection not only for the next decades but also for the coming century. Provision of secure, accessible and environmentally sustainable supplies of water, energy and food must thus be a priority. One of the major objectives of the world’s scientists, farmers, decisions makers and industrialists is to overcome the present dependence on fossil fuels in the agro-food sector. This dependency increases the volatility of food prices and affects economic access to sustenance. This book provides a critical review of recent developments in solar, wind and geothermal energy applications in agriculture and the agro-food sector such as processing, distribution, retail, preparation and cooking.

Although Membrane Distillation (MD) has been extensively studied for desalination, it has other applications like removing all kinds of solutes from water and concentrating non-volatile substances. MD offers the possibility of producing a clean stream while concentrating valuable compounds from waste streams towards their recovery, or emerging contaminants and pathogens present in wastewater in order to facilitate their chemical elimination. This paper analyses the elimination of bacterial spores from contaminated water with MD and the role of MD in the subsequent treatment of the concentrate with photo-Fenton process. The experiments were performed at Plataforma Solar de Almeria (PSA) using a plate and frame bench module with a Permeate Gap Membrane Distillation (PGMD) configuration. Tests were done for two different kinds of spores in two different water matrixes: distilled water with 3.5wt% of sea salts contaminated with spores of Bacillus subtilis (B. subtilis) and wastewater after a secondary treatment and still contaminated with Clostridium sp. spores. An analysis of the permeate was performed in all cases to determine its purity, as well as the concentrated stream and its further treatment in order to assess the benefits of using MD. Results showed a permeate free of spores in all the cases, demonstrating the viability of MD to treat biological contaminated wastewater for further use in agriculture. Moreover, the results obtained after treating the concentrate with photo-Fenton showed a shorter treatment time for the reduction of the spore concentration in the water than that when only photo-Fenton was used.

Power generation by means of Pressure Retarded Osmosis (PRO) has been proposed for harvesting the energy of a salinity gradient. Energy recovery by the PRO process decreases along the membrane module due to depleting of the chemical potential across the membrane and concentration polarization effects. A dual stage PRO (DSPRO) design can be used to rejuvenate the chemical potential difference and reduce the concentration polarization on feed solution. Several design configurations were suggested for the membrane module arrangements in the first and second stage of the PRO process. PRO performance was evaluated for a number of salinity gradients proposed by coupling Dead Sea water or Reverse Osmosis (RO) brine with seawater or wastewater effluent. Maximum specific energy of inlet and outlet feeds was calculated using a developed computer model to identify the amount of recovered and remaining energy. Initially, specific power generation by the PRO process increased by increasing the number of modules of the first stage. Maximum specific energy is calculated along the PRO module to understand the degradation of the maximum specific energy in each module before introducing a second stage PRO process. Adding a second stage PRO process resulted in a sharp increase of the chemical potential difference and the specific energy yield of the process. Between 10% and 13% increase of the specific power generation was achieved by the DSPRO process for the Dead Sea-seawater salinity gradient depending on the dual stage design configuration. For Dead Sea-RO brine, 12–16% increase of the specific power generation was achieved by the dual stage PRO process. For Dead Sea-wastewater and RO brine-wastewater, a neutral and sometimes negative impact occurred when a second stage PRO process was introduced. We concluded that, for a given draw solution concentration, dual stage performs better than the conventional PRO process at high feed salinities, yet requires lower hydraulic pressure.

© 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.

The demand of freshwater has surpassed the renewable limit and new water sources are associated with an intensive use of energy. Coincidence between scarcity of water and availability of solar radiation makes solar energy the most suitable option to mitigate the water deficit. This paper analyzes the use of energy for decentralized water production using membrane desalination systems fed with solar energy. An analysis is performed based on experimental results from the most advanced commercial prototypes of different technologies of membrane distillation using various configurations, i.e., air-gap, permeate-gap and vacuum; with flat-plate and spiral-wound membranes. The systems operate with thermal energy, although there is some electrical consumption for pumping and in some cases for sustaining vacuum. The thermal energy requirements per unit volume of water produced are assessed in each case, considering the effect of different operational conditions like the temperature regime and the salinity of the input water.

The use of solar energy to feed the MD desalination process is being evaluated at Plataforma Solar de Almeria, the largest European facility for solar energy research, located in SE Spain. A test bed for the evaluation of membrane distillation modules is under operation coupled to a field of static solar collectors. Different commercial modules and real-scale prototypes are tested in continuous operation and coupled with a solar thermal source, in order to obtain data in conditions closer to real applications than the tests performed at laboratory scale. This particular study shows an evaluation of two different modules using spiral-wound membranes, one with a liquid-gap configuration (built by Solar Spring) and the other with an air-gap configuration (built by Aquastill). An assessment of the influence of the operational parameters in the performance was done within the allowed ranges of operation of each prototype, with special attention to the temperatures and the feed flow rate. Also, the infl...

Forward Osmosis (FO) has many applications in water and wastewater treatment and seawater desalination. In this paper, the FO was suggested for seawater pretreatment to the thermal desalination processes such as Multi Stage Flashing (MSF). The integrated FO–MSF hybrid system was designed to reduce the cost of desalination in which the brine reject from MSF was recycled and reused as a draw solution in the FO process. A simple model was suggested here to estimate water flux and power consumption in the FO process and compared with Nanofiltration (NF) process which was previously used in seawater softening. The simulation results showed that for feed salinities between 32,000 mg/L and 50,000 mg/L the recovery rate in the NF was higher than that in the FO. It is also found that the water permeability and specific power consumption was higher in the NF than that in the FO. However, power consumption in the FO wasn't affected by the feed salinity while it increased with feed salinity in NF. Therefore, the FO process has the potential to replace the NF seawater pretreatment for thermal desalination.

A steady-state mathematical model of a vertically stacked forward feed multi-effect distillation (MED) plant has been carried out using a number of simplifying assumptions. The model has been developed taking into consideration the same design and operational characteristics as the pilot MED plant at Plataforma Solar de Almeria (PSA), in the southeast of Spain. It is a forward feed MED plant with preheaters, which uses low steam temperature coming from a parabolic-trough solar collector field as the thermal energy source. The pilot plant has a special distillate distribution for increased energy recovery which has also been taken into account in the model. This model is simple to implement and suitable for its use in optimization of water production in power and water cogeneration systems. The results of the model have been compared with the experimental data of the pilot plant showing a maximum prediction error of 9%.

The combination of Forward Osmosis (FO) and Reverse Osmosis (RO) was evaluated for seawater desalination. RO process was suggested for the draw solution regeneration because of its high efficiency and applicability for a wide range of ionic solution treatments. Two different salts, NaCl and MgCl2, were used as a draw solution. The performance of FO and RO regeneration processes was simulated using pre-developed software. A comparison between the RO and FO-RO processes was carried out. The simulation results showed that the total power consumption in the RO was lower than that in the FO-RO process. But, the difference in total power consumption between the RO and 0.65mol MgCl2 FO-RO processes was insignificant. The results also showed that the power consumption in the FO process was only 2%-4% of the total power consumption in the FO-RO process. However, the difference in total power consumption between the RO process and the FO-RO process decreased with a higher seawater salinity. In the FO-RO process, the results showed that the permeate TDS was increased with increasing the concentration of draw solution. The lowest permeate TDS was achieved in the 0.65mol MgCl2 FO-RO process and it was attributed to the high rejection rate of MgCl2 by the RO regeneration unit. © 2014 Elsevier B.V.

Different alternatives for the effective integration of desalination technologies in the cooling of concentrating solar power (CSP) plants in the Mediterranean area are discussed and evaluated. Two cases are considered where a low temperature multi-effect distillation (LT-MED) plant is integrated into a CSP plant replacing the condenser of the power cycle. In one case, a LT-MED plant is fed by steam at the outlet of the turbine expanded to 70 °C. In the other case a LT-MED is fed by the steam obtained from a thermal vapour compressor (TVC) which uses the exhaust steam of the CSP plant (at 37 °C, 0.063 bar) together with some from the high pressure turbine extraction (17 bar). The two cases are compared with that of a reverse osmosis (RO) unit powered by the electricity produced by the CSP plant. In this case, two different wet cooling technologies, once-through and evaporative water cooling, and a dry air cooling are considered for the CSP plant. Thermodynamic simulations are presented for all cases, together with an economic analysis.

The development of society is strongly dependent on water and electricity. There is an increasing water and energy demand driven by population growth and rising industrial and agricultural production. The combination of concentrated solar power (CSP) and desalination processes has a huge potential for producing both energy and water in arid regions suffering from fresh water scarcity and facing the current energy challenge. One of the regions is Middle East and North Africa (MENA), where plans are currently under discussion to make possible large CSP plants developments. The integration of desalination (CSP+D) into solar power plants could make CSP technology even more attractive in such regions. The focus of this study is thermodynamic characterization and an economic evaluation of different configurations for coupling parabolic trough solar power plants and desalination facilities at a MENA location in Egypt chosen as reference for its Southern coast (Port Safaga). The desalination technologies...

Salinity gradient power is proposed as a source of renewable energy when two solutions of different salinity are mixed. In particular, Pressure Retarded Osmosis (PRO) coupled with a Reverse Osmosis process (RO) has been previously suggested for power generation, using RO brine as the draw solution. However, integration of PRO with RO may have further value for increasing the extent of water recovery in a desalination process. Consequently, this study was designed to model the impact of various system parameters to better understand how to design and operate practical PRO-RO units. The impact of feed salinity and recovery rate for the RO process on the concentration of draw solution, feed pressure, and membrane area of the PRO process was evaluated. The PRO system was designed to operate at maximum power density of Δ P = Δ π 2 . Model results showed that the PRO power density generated intensified with increasing seawater salinity and RO recovery rate. For an RO process operating at 52% recovery rate and 35 g/L feed salinity, a maximum power density of 24 W/m2 was achieved using 4.5 M NaCl draw solution. When seawater salinity increased to 45 g/L and the RO recovery rate was 46%, the PRO power density increased to 28 W/m2 using 5 M NaCl draw solution. The PRO system was able to increase the recovery rate of the RO by up to 18% depending on seawater salinity and RO recovery rate. This result suggested a potential advantage of coupling PRO process with RO system to increase the recovery rate of the desalination process and reduce brine discharge.

Integrated power and desalination plants (IPDP) may provide a key solution for the pressing freshwater deficit and energy problems in many regions of the world. The current study investigates the potential of low-temperature multi-effect distillation (LT-MED) and thermal vapor compression multi-effect distillation (TVC-MED) coupled with a concentrating solar power (CSP) plant, taking also into account a reverse osmosis (RO) unit connected to the same power plant. The thermodynamic performance of the proposed schemes of IPDP has been evaluated by the assessment of the net output thermal capacity and the net power cycle efficiency of the different configurations, together with the estimation of the size of the solar field required to provide the corresponding thermal capacity. The results show that the combination with LT-MED is more efficient thermodynamically than with TVC-MED. Also, the CSP plant coupled with TVC-MED is more cost-effective than the independent processes because it requires a smaller solar field. The integration of a MED plant reduces the cooling requirements of a CSP power plant but the CSP + RO combination has a better thermodynamic efficiency. However, the difference with respect to CSP + LT-MED is small, so the latter can be more convenient in some cases.

A solar desalination system based on membrane distillation (MD) is presented and evaluated. In the context of a European project, the MEDESOL project, a pilot plant was built to evaluate the system, which consists of three commercial MD modules coupled with a static solar collector's field. The MD modules employed have been developed and manufactured by the Swedish company Scarab AB. They have a flat sheet air gap membrane distillation (AGMD) configuration with a total membrane surface area per module of 2.8 m2. The MD system is intended to be technically simple to operate, robust and able to cover water demands of small settlements. It also contemplates the use of a multi-stage layout to minimize energy consumption. Experiments were run during solar hours (the layout didn’t include heat storage) and addressed to characterize the performance of the system (i.e. distillate production and quality, thermal efficiency and recovery ratio) as a function of operation variables and salt concentration, as well as to identify the operating capacities and the potential improvements of the MD technology. Aqueous NaCl solutions of 1 and 35 g/l concentration were used as feed. Temperatures up to 85 °C in the feed and up to 75 °C in the refrigeration were employed. Maximum specific distillate flux values registered were in the range of 7 l/h m2. Multi-stage layouts were tested in order to evaluate the improvement of the system's thermal efficiency and recovery ratio. The MD technology assessed proved to be suitable for coupling with transient solar thermal energy but inefficiencies inherent to scaling-up compared to laboratory experiences reported in literature were also identified, namely affecting specific distillate production and thermal consumption. The results of the characterization, performance assessment and operational issues description of the pilot plant are shown.

The combination of desalination technology into concentrating solar power (CSP) plants needs to be considered for the planned installation of CSP plants in arid regions. There are interesting synergies between the two technologies, like the possibility of substituting the condenser of the power cycle for a thermal desalination unit. This paper presents a thermodynamic evaluation of different configurations for coupling parabolic-trough (PT) solar power plants and desalination facilities in a dry location representing the Middle East and North Africa (MENA) region. The integration of a low-temperature multi-effect distillation (LT-MED) plant fed by the steam at the outlet of the turbine replacing the condenser of the power cycle has been simulated and compared with the combination of CSP with a reverse osmosis (RO) plant. Furthermore, an additional novel concept of concentrating solar power and desalination (CSP+D) has been evaluated: a LT-MED powered by the steam obtained from a thermal vapour compressor (TVC) using the exhaust steam of the CSP plant as entrained vapour and steam extracted from the turbine as the motive vapour of the ejector. This new concept (LT-MED-TVC) has been analyzed and compared with the others, evaluating its optimization for the integration into a CSP plant by considering different extractions of the turbine.

Watergy project is funded by the European Community’s Vth Framework in its Energy, Environment and Sustainable Development programme. It consists of the development of a humid air solar collector system that follows the principle of a closed two phase thermosyphon. A combination of evaporation and condensation allows to use solar thermal energy in a much more efficient way. The main advantage is not only the reduction of costs in space cooling and heating, but the possibility of water purification, as the system can be fed with low quality water to obtain distilled water. The decentralization of heat and water supply opens the possibility of residential areas where greenhouses fed with low quality water (grey water and brackish water) could be used to produce distilled water as well as heat and fruits. The project contemplates the development of two prototypes: one application for arid climates in Southern Europe with an emphasis on water production in the context of greenhouse horticulture, and another for temperate Central European climate focused on heat and water production for sustainable architecture.

Crown Copyright © 2014 Published by Elsevier B.V. All rights reserved. PRO and FO coupling with an RO membrane process is proposed to reduce the cost of seawater desalination and the potential for power generation. Three conceptual design configurations, PRO-RO, FO-RO and RO-PRO were evaluated here using standard seawater concentration and impaired water as the draw and the feed solutions respectively. The PRO-RO and RO-PRO designs were evaluated for power generation and seawater desalination while the FO-RO design was proposed for seawater desalination only. The impact of the draw and feed solutions' flow rate and the impaired water TDS on the performance of each design was estimated using pre-developed software. The simulation results showed that the performance of all designs was more sensitive to the increase in the flow rate of draw solution than to the flow rate of feed solution. Furthermore, all designs showed a decrease in membrane flux and recovery rate with increasing the TDS of feed water from 0.2 g/L to 10 g/L as a result of decreasing the net driving force across the membrane and the concentration polarization phenomenon. The FO-RO design produced the lowest RO permeate concentration followed by the PRO-RO and RO-PRO designs respectively. In terms of power generation, the RO-PRO design was more efficient than the PRO-RO design. The FO-RO design exhibited the lowest desalination power consumption followed by the PRO-RO and RO-PRO designs respectively. At 10 g/L feed concentration, the net power consumption in the FO-RO was 9.4% less than that in the PRO-RO which was in turn 5.3% less than that in the RO-PRO design. The estimated cost of the FO/PRO module in the PRO-RO design was 2.2 and 4.3 times higher than that in the FO-RO and RO-PRO designs respectively.

This paper describes the basic operation of a new type of closed greenhouse for solar thermal energy storage, water recycling, water desalination and advanced horticultural use. A system of constant air humidification enables the transfer of large amounts of energy via latent heat from the greenhouse to a thermal storage. To accomplish this, only little air velocity is required and can be provided by a buoyancy driven air circulation system. It is realised by a combination of a cooling tower and a secondary heat collector. In this heat collector the air is humidified to the maximum level before the process of heat exchange. INTRODUCTION Greenhouse production is a highly profitable technology for food production in Central and Southern Europe, but is facing growing challenges caused by increasing energy prices (for heating, transport) and limited water resources (for irrigation). Desalination is a technology used to supply future growing demands for water, but common technologies have a large demand for primary energy. A widely discussed technological solution for these challenges is the idea of heat and water recovery from greenhouse exhaust air, or from the inside of closed greenhouses, aided by heat exchangers and heat accumulation systems (Warshall, 1996). The major challenges of such endeavours can be described as follows: Usually, a large amount of electric energy is needed for ventilation to reach a sufficient transport of hot air to a heat exchanger. The primary energy needed for this transport is close to the primary energy of the heat that can be captured. Because of this, such a system is only marginally effective. (Mackroth, 1982) Air has little heat capacity. Therefore, any transfer of heat from air to water or to any other storage media is little effective. Greenhouse temperatures are limited due to crop tolerances, a situation that leads to very low supply temperatures and therefore low efficiencies of heat exchangers and thermal storage systems. Placement of heat exchangers in the roof zone, representing the hottest area of a greenhouse, originates unwanted shading of the plants. Additionally, the heat transfer between the rising hot air and the falling cooled air from the roof zone results in insufficient cooling in the lower plant zone. NEW GREENHOUSE ELEMENTS The Watergy system (Buchholz, 2000) contains two innovative elements: a greenhouse cooling tower and a secondary collector element. These elements aim at working against the challenges mentioned above: The cooling tower is used to overcome the need for electric fans by creating free, buoyancy driven ventilation. It consists of an air duct that drives heated air from the greenhouse to the top of the tower and an internal cooling duct with a large air-to-water heat exchanger made of plastic, which is connected to a heat accumulator. The air passes, driven by the buoyancy force, from the greenhouse into the chimney. After being cooled Proc. IC on Greensys Eds.: G. van Straten et al. Acta Hort. 691, ISHS 2005 510 by the heat exchanger, the air falls back ground level. Vapour from the greenhouse condenses, releasing thermal energy and producing distilled water. The resulting cool dry air can circulate within the system. The cycling process can be used for greenhouse cooling, air dehumidification and energy transport to the heat exchanger. Using such a cooling duct, the produced cool air can be directed to the lower volume of the vegetation area without being mixed with the hotter air, which rises inside the greenhouse. The constant process of cooling and condensation along the whole duct also constitutes an effective means of dehumidification of the greenhouse air. A secondary collector aims at further heating and humidification of the greenhouse air while on its way to the cooling tower, resulting in a higher efficiency of the heat transfer and –storage processes. Higher temperatures result in higher heat exchanger supply temperatures and in a higher loading capacity of the storage system. A higher absolute humidity means a larger amount of thermal energy available, while it is transported with the same amount of air movement. In other words, less total air flow is needed for the transfer of solar energy from the secondary collector to the heat exchanger. Additionally, the higher humidity also results in a larger amount of energy that is released directly at the heat exchanger surface during the condensation process without thermal barriers of laminar air zones at the surface, and thus resulting in a higher total transfer rate of the heat exchanger. Since the secondary collector is separated from the vegetation area, salty water can be used to feed the evaporation process of the secondary collector for desalination purposes. Through working with large amplitudes of salinity between the storage loading and de-loading phase, also endothermic and exothermic effects within the brine can be used as a part of the energy storing process. PLACEMENT OF THE SECONDARY COLLECTOR The placement of the secondary collector is dependent on the amount of irradiation. In areas with high irradiation, the collector can be placed above the vegetation zone and can be operated like a flexible shading system: Components of the greenhouse roof like a plastic layer and a water film can already filter a relevant part of the incoming radiation. If needed, additional shading can be provided by conventional shade curtains underneath the plastic film, or by mixing shading additives into the water film that can be added/removed mechanically in a controlled way. Both methods aim at using the solar radiation to heat up the water film for a consistent proportion of air heating and air humidification. The secondary collector is limited to the basal surface and to a certain capacity, because of its position above the crop area and the need for as much radiation as possible for plant growth. On the other hand, the advantage of an installation above the plants is the possibility of having large, continuous greenhouse surfaces. For areas with limited irradiation conditions (e.g., Central Europe), light is most of the time already a limiting factor for plant growth. Therefore, the secondary collector surface has to be placed outside the greenhouse. The resulting flexibility in the size of this collector surface allows for it to be sized in relation to the crop production area and to the desired crop production temperatures. Since this area without plants is required in such a configuration, it is useful to think about an additional use of such a surface. A logical application can be integrating building facades and –roofs in combination with greenhouses within an urban context. In the Watergy project, both versions will be tested within two different prototypes. The first one is a single greenhouse for which the main focus is thermal control and water production. The thermal energy, that is stored during the day will be utilised for greenhouse heating at night during wintertime and for further water evaporation/condensation at night during summer, in particular evaporation of salty water for desalination purposes on the heat exchanger and condensation on the greenhouse cover. By unloading the storage at night, coolant for the next day is made available in both cases. (Saitoh, 2000)

The present study evaluated the performance of pressure retarded osmosis–reverse osmosis (PRO–RO) process for power generation and seawater desalination. Two pre-developed software were used separately to estimate the performance of forward osmosis (FO) and RO process. The draw and feed solutions in the FO process were seawater and low-quality water; i.e. wastewater effluent and brackish water. The simulation results showed that the FO performance increased with increasing seawater salinity and decreased with increasing feed water TDS. Increasing the feed and draw solution flow rate resulted in an increase in the FO performance especially when brackish water was used as a feed solution in the FO process. Power generation from the PRO process was found to increase with increasing the TDS of seawater and the flow rate of feed and draw solutions. The simulation results, however, showed that the PRO process was more sensitive to the increase in the seawater TDS than the flow rate of feed and draw solutions. For fresh water supply, the diluted seawater from the FO process was treated by RO membrane system. Up to 31% decrease in the desalination power consumption can be achieved by the PRO–RO process. It was also found that the increase in the draw solution flow rate resulted in an increase of the permeate concentration and power consumption. This issue should be considered in the operation of the PRO–RO system in order to reduce the overall treatment cost.

In warm climates, high temperature can limit growth and development of greenhouse crops and their product quality. Therefore greenhouse cooling has a high-priority to reduce these adverse effects. Together with natural ventilation, shade produced by whitewashing the greenhouse roof is the most usual cooling method in the whole of the Mediterranean area. However, this technique is not homogeneous; it is not selective and not adjustable. This inconvenience can be overcome by the use of other techniques such as shading with folding or rolling screens and/or evaporative cooling. This work evaluates three cooling techniques in parral greenhouses using a sweet pepper crop: whitening, shading with a mobile internal screen and cooling with a low pressure fog system. The latter gave the highest reduction in air temperature in the greenhouse in warm periods. However, final water consumption in the fog system was 319 mm, whereas irrigation water consumption was 520 mm. The evaporative cooling system, with 6.5 kg m -2 of marketable production and the use of interior shade screens (with 6.7 kg m -2 ), did not increase the yield obtained by means of traditional whitening (7.1 kg m -2 ) used by growers in the area.