• Energy Research

Solar thermal conversion systems can be used for driving a Multi-Effect Distillation (MED) unit, namely: parabolic trough collectors, compound parabolic concentrators, evacuated tube collectors, flat plate collectors and salinity-gradient solar ponds. This paper deals with an experimental test campaign of a Multi-Effect Distillation (MED) unit installed at the Plataforma Solar Almería (PSA-CIEMAT) operated out of its nominal working conditions in order to provide experimental information required for design criteria and for the analysis of control strategies in solar MED plants. The MED plant (SOL-14) assessed is a conventional forward-feed unit with preheaters, 14 effects and nominal capacity of 3 m3/h. The experimental test campaign of the SOL14 plant conducted at the PSA proves that the PR exhibits low deviations within the range of working conditions analysed. The SOL-14 unit makes an efficient use of the energy consumption even when it is operated out of the nominal working conditions. The effects of part load operation are higher on distillate production than in PR. On the contrary, at working conditions over nominal, the PR suffers from higher deviation than distillate production, which remains unchanged within the range analysed.

Abstract Process simulation has become an accepted tool for the performance, design, and optimization calculations of solar desalination process units. Solving the mathematical models representing these units and systems is a tedious and repetitive problem. Nested iterative procedures are usually needed to solve these models. Also, the process configurations are characterized by existence of a number of recycle streams. To tackle these problems, several researchers have developed different methods, techniques, and computer programs for the simulation of a very wide range of variety of solar desalination process units and systems. It is of interest in this work to show and demonstrate a new program working under Matlab/SimuLink environments for solar desalination processes calculation and modeling. Using these environments a visual design and simulation for different types and configurations of standalone (common) and solar desalination processes can be performed. Embedded user block programming with SimuLink is implemented to construct a flexible reliable and friendly user-interface package. The solar heating systems and desalination plant components (named here as blocks), such as heat exchangers, flash chambers, evaporators, pumps, steam ejector, compressor, reverse osmosis membrane, pipes, etc., are stored as icons in a visual library. This library enables the user to construct different configurations by just clicking the mouse over the required units (blocks). The interface aids designers, and operators to perform different analyses and calculations such as energy, exergy, and thermoeconomics. Typical desalination processes such as multi stage flash, and reverse osmosis are presented to show the wide scope and the validity, reliability, and capability of the developed package.

This paper deals with seawater desalination systems driven by renewable energies. A review of pilot plants and perspectives of development is presented. There are many reasons why the use of renewable energies in seawater desalination is suitable, especially for remote areas where conventional energy supply and skilled workers are not usually available. Nevertheless, desalination systems driven by renewable energies are scarce and they tend to have a limited capacity.

Abstract The lack of access to electricity grid and fresh water strongly limits the development and the quality of life to many rural locations. The distributed solar power generation can be applied to many basic needs, not only electricity generation, but also desalination, cooling, heating, etc. For this reason it provides opportunity of social and economic development and therefore promoting employment. This paper is focused on the analysis of distributed solarpowered generation systems for driving a reverse osmosis desalination process based on solar-heated Rankine cycles. Three different top temperature ranges are considered in order to consider medium to low temperature solar thermal collectors. Results presented in this paper points out that desalination systems coupled to solar-powered organic Rankine cycles exhibit lower specific consumption of solar energy than solar distillation and solar photovoltaic reverse osmosis systems. Therefore, there are interesting prospects for developing cost-effective solar desalination systems based on such a technology although intensive experimental research is still needed.

Abstract Exergy analysis is a powerful tool to determine how inefficiencies of the processes influence system performance. The exergy analysis of a seawater reverse osmosis desalination plant with 21,000 m3/d of nominal capacity located in Tenerife (Canary Islands, Spain) was studied. Once defined, the flow chart of the process, the exergy rate and exergy cost of flows were determined as well as the exergy destruction rate in equipment. The main results indicate that 80% of the exergy destruction is placed on core processes (high pressure pumping and valve regulation, reverse osmosis separation and energy recovery), 29% extra exergy is necessary to obtain the unit of feed exergy from previous stages (seawater pumping and pretreatment) and extra exergy of 1.06 kJ is needed to generate 1 kJ of final product exergy (exergy performance about 50%). In addition, the moderate fluctuations of seawater environmental conditions in the Santa Cruz de Tenerife metropolitan area (and Canary Islands as a whole) establish that environmental parameters present a less important influence on exergy analysis.

Abstract This paper presents a preliminary design for a solar thermal-powered reverse osmosis desalination system. The high pressure pump in the seawater reverse osmosis unit requires a 95-kW input, while the reject energy is recovered by way of pressure exchangers. The unit's specific energy consumption is 6.48 MJ/m3 (1.8 kWh/m3) for a recovery rate close to 50% and a feed pressure of 5.53 MPa. The unit was coupled to a solar power cycle based on a Rankine cycle with toluene, hexamethyldisiloxane (MM) and octamethylcyclotetrasiloxane (D4) as working fluids and two different models of parabolic trough collectors. In addition, configurations using both direct vapor generation as well as a heat transfer fluid are proposed. The coupling was done assuming all the mechanical energy produced by the cycle was consumed by the high pressure pump in the reverse osmosis unit. A subsequent assumption was that all the cycle's rejected thermal energy went to preheat the seawater feed flow. This latter aspect does not result in a significant increase in the desalinated water output. The results obtained indicate that with the system proposed it is possible to produce, for a solar direct irradiance of 850 W/m2, 0.11 m3/h with toluene as the working fluid in the cycle and 0.088–0.094 m3/h with D4 or MM of desalinated water per square meter of LS3s parabolic trough collector aperture area. Likewise, for the IND300 collector, it is possible to obtain 0.078–0.085 m3/h with toluene and 0.07–0.077 m3/h with D4 or MM.

Abstract Thermo-economy is a useful and powerful tool that combines thermodynamics and economics. It can evaluate how irreversibility and costs of any process affect the exergoeconomic cost of the product. In this work, a number of comparisons for solar thermal-powered different recovery units for reverse osmosis desalination system are performed using thermo-economic analysis. Three different configurations are used for this comparison (Basic, Pelton Wheel Turbine, and the Pressure Exchanger) with Sharm El-Shiekh RO desalination plant for a total productivity about 145.8 m 3 /h (40.5 kg/s). As a result of this analysis, the unit product cost of Pelton Wheel Turbine (PWT) and Pressure Exchanger (PEX) configurations are 24% and 24.2% respectively less than that of the basic configuration. Thermo-economic analysis shows that the minimum investment and operating & maintenance costs are obtained by PEX configuration. Also, it achieves minimum exergy destruction against the two other configurations (Pelton Wheel and Basic systems). Therefore, the final conclusion of this work is that the PEX configuration is more economical than either stand alone or PWT configurations.

Experience in combining solar thermal and seawater or brackish water reverse osmosis (RO) desalination technologies is very limited. Two SOFRETES systems were in operation in the early 1980s for brackish water desalination. Only such two implementations involving a single design can be cited, along with a reduced number of theoretical analyses and design proposals. Nevertheless, since RO is the most cost-effective desalination technology and its energy requirements are low, solar thermal-driven reverse osmosis desalination is promising in comparison to other desalination processes driven by solar energy. In addition the research conducted in other renewable energy-driven RO technologies would be profitable for developing RO technology based on solar thermal systems as special designs of energy recovery systems, direct coupling of wind and photovoltaic systems without batteries or assessment of membranes damage due to change of operational parameters in stand-alone systems.

Abstract This paper deals with the design recommendations for solar reverse osmosis (RO) desalination based on solar organic Rankine cycles (SORC). This technology can be the most energy-efficient technology for seawater and brackish water desalination within the small to medium power output range (up to 500 kW) of the power cycle if the system is properly designed. However, theoretical studies, design proposals and experimental works are very scarce and only very few solar reverse osmosis systems driven by ORC has been either implemented or analysed in the past. In this paper, those systems are outlined and general design recommendations from previous detailed analysis already publish are given for future RO desalination system to be designed based on SORC. Useful information is given about the selection of the working fluid and boundary conditions of the ORC, operation temperature and configuration of the solar field, suited solar collector and thermal energy storage technology, etc. Recommendations are exemplified with well selected numerical cases based on recommended working fluids and solar cycle configuration with proper values of design point parameters. Recommendations given in this paper could be helpful in future initiatives regarding the research and development of this promising solar desalination technology.