Technical and economical aspects of solar desalination with particular emphasis on solar pond powered distillation plants

Desalination remains an important and interesting application for the use of solar radiation as a source of undepletable energy. After almost a decade of research and development including the installation and testing of various smaller pilot systems, our solar desalination technology - among others - is now becoming available on a commercial level.The paper discusses the evolution of the technology both of the desalination and the collector-subsystems as a result of the technical and economical constraints associated with the utilization of solar energy, a highly fluctuating energy source of low surface density.Performance data is presented in particular for the coupling of a selfregulating MSF unit with a solar pond energy collection and storage system, both inhouse developments.The performance and layout data was obtained both from computer simulation and experimental results with a small sized solar pond and desalination subsystem in Switzerland. The economy assessment, which is presented for Middle East climate conditions, clearly demonstrates that solar desalination already becomes competitive for medium sized installation at remote locations. Potential further cost reductions also through upscaling may lead to the use of desalinated water for agricultural applications one day.     

Distillation vs. membrane filtration: overview of process evolutions in seawater desalination

The worldwide need for fresh water requires more and more plants for the treatment of non-conventional water sources. During the last decades, seawater has become an important source of fresh water in many arid regions. The traditional desalination processes [reverse osmosis (RO), multi stage flash (MSF), multi effect distillation (MED), electrodialysis (ED)] have evoluated to reliable and established processes; current research focuses on process improvements in view of a lower cost and a more environmentally friendly operation. This paper provides an overview of recent process improvements in seawater desalination using RO, MSF, MED and ED. Important topics that are discussed include the use of alternative energy sources (wind energy, solar energy, nuclear energy) for RO or distillation processes, and the impact of the different desalination process on the environment; the implementation of hybrid processes in seawater desalination; pretreatment of desalination plants by pressure driven membrane processes (microfiltration, ultrafiltration and nanofiltration) compared to chemical pretreatment; new materials to prevent corrosion in distillation processes; and the prevention of fouling in reverse osmosis units. These improvements contribute to the cost effectiveness of the desalination process, and ensure a sustainable production of drinking water on long terms in regions with limited reserves of fresh water.     

Applicability of flashing desalination technique for small scale needs using a novel integrated system coupled with nanofluid-based solar collector

The present study introduces an attempt for the application of flash desalination technique for small scale needs. An integrated system uses a flashing desalination technique coupled with nano-fluid-based solar collector as a heat source has been made to investigate both the effect of different operating modes and that of the variation of functioning parameters and weather conditions on the fresh water production. The flashing unit is performed by similar construction design technique of commercial multi-stage flashing (MSF) plant. The thermal properties of working fluid in the solar collector have been improved by using different concentrated nano-particles. Cu nano-particle is used in the modeling to determine the proper nano-fluid volume fraction that gives higher fresh water productivity. An economic analysis was conducted, since it affects the final cost of produced water, to determine the cost of fresh water production. Although a system may be technically very efficient, it may not be economical. The effect of different feed water and inlet cooling water temperatures on the system performance was studied. The mathematical model is developed to calculate the productivity of the system under different operating conditions. The proposed system gives a reasonable production of fresh water up to 7.7 l/m²/day under the operation conditions. Based on the cost of energy in Egypt, the estimated cost of the generated potable water was 11.68 US$/m³. The efficiency of the system is measured by the gained output ratio (GOR) with day time. The gained output ratio (GOR) of the system reaches 1.058. The current study showed that the solar water heater collecting area is considered a significant factor for reducing the water production cost. Also, the produced water costs decrease with increasing the collecting area of the solar water heater. The volume fractions of nano-particle in solar collector working fluid have a significant impact on increasing the fresh water production and decreasing cost.     

Ro, MSF and VTE/VC desalination: a comparative evaluation

The two main processes currently in vogue, for sea -water desalination 3?-- multistage flash. (MSF) and reverse osmosis (R.O.) -- are compared, on the basis of cost economics. Cost data are reported for unit sizes up to 10 million (U.S.) gallons per day. Both single-pass and double-pass systems are considered for the R. 0. unit, while the cost of water from MSF plants is calculated for different performance ratios. Controlling factors such. as fuel prices, pretreatment costs, membrane life, energy recovery and terms of financing, are discussed.On the basis of present technology, notwithstanding new developments, it is concluded that R. 0. is the more economical of the two for small unit sizes and regions of high fuel costs. There is a break-even point, depending on these two parameters, beyond which the MSF process yields lower water costs.Attention is focussed on a third process —- Vertical Tube Evaporation/Vapor Compression (VTE/VC), a self-contained, low-energy consuming system which is particularly suitable for barge-mounted or land-based single- purpose (water only) installations. The process, -which, is in an advanced stage of development under Envirogenics Systems Company's R and D program, is potentially competitive with R.O , even for small unit sizes. Future improvements and operational experience could make this the process of choice for single-purpose sea water desalination plants.     

Implications of desalination for water resources in China — an economic perspective

China is a country with severe water shortages. Water is becoming scarcer due to population growth, industrialization and urbanization. Recent studies show that by the next 50 years water resources per capita will go down to around 1700 m³, which is the threshold of severe water scarcity. Especially in North China, water shortage has become a critical constraint factor for socioeconomic development in the long run. To solve or eliminate water shortage problems, seawater desalination draws more and more attention as an alternative water supply source. The objective of the study is to assess the potential of desalination as a viable alternate water source for China through analysis of the costs of desalination, the water demand and supply situation as well as water pricing practices in China. Based on the investment costs and estimated operation and maintenance costs, an economic appraisal for the costs of desalination for two main processes, MSF and RO, has been conducted. The study shows that there is a decline of unit cost of desalination over time and the average unit cost of the RO process was lower than that of the MSF process. A unit cost of 0.6 $/m³ for desalting brackish water and 1.0 $/m³ for seawater are suggested to be appropriate for the potential application of desalination in China. Future trends and challenges associated with water shortages and water prices are discussed, leading to conclusions and recommendations regarding the role of desalination as a feasible source of water for the future.     

Solar thermal desalination technologies

The use of solar energy in thermal desalination processes is one of the most promising applications of the renewable energies. Solar desalination can either be direct; use solar energy to produce distillate directly in the solar collector, or indirect; combining conventional desalination techniques, such as multistage flash desalination (MSF), vapor compression (VC), reverse osmosis (RO), membrane distillation (MD) and electrodialysis, with solar collectors for heat generation. Direct solar desalination compared with the indirect technologies requires large land areas and has a relatively low productivity. It is however competitive to the indirect desalination plants in small-scale production due to its relatively low cost and simplicity. This paper describes several desalination technologies in commercial and pilot stages of development. The primary focus is on those technologies suitable for use in remote areas, especially those which could be integrated into solar thermal energy systems.     

降膜蒸发内回热型太阳能海水淡化装置的实验研究

对一台利用太阳能驱动的横管降膜蒸发内回热型海水淡化装置进行了实际天气条件下的动态测试。系统采用了多效内回热措施,在蒸发及冷凝过程中,大部分水蒸汽的凝结潜热被重复利用于海水的预热及蒸发过程,在相同的天气条件下,该装置的产水率比单级盘式太阳能蒸馏器提高了2～3倍。太阳辐射越强,产水率越大;启动温度越高,产水量越大。对影响淡水产量的其他因素也进行了分析讨论。     

Section seven - new energy sources : An introduction to new energy sources for desalination

The papers presented in the section “New Energy Sources for Desalination” illustrate that a variety of new energy sources are being utilized to provide power for desalination. However, aside from solar stills there is only limited experience with pilot scale facilities using these new sources. The future of desalination with new energy sources depends on reducing the costs of producing reliable energy conversion devices and increasing the efficiency of the desalination units.     

Efficient thermal desalination technologies with renewable energy systems: A state-of-the-art review

Due to the current fossil fuel crisis and associated adverse environmental impacts, renewable energy sources (RES) have drawn interest as alternatives to fossil fuels for powering water desalination systems. Over the last few decades the utility of renewable energy sources such as solar, geothermal, and wind to run desalination processes has been explored. However, the expansion of these technologies to larger scales is hampered by techno-economic and thermo-economic challenges. This paper reviews the state-of-the-art in the field of renewable energy-powered thermal desalination systems (RE-PTD) to compare their productivity and efficiency through thermodynamic, economic, and environmental analyses. We performed a comparative study using published data to classify RE-PTD systems technologies on the basis of the energy collection systems that they use. Among RE-PTD systems, solar energy powered-thermal desalination systems demonstrate high thermo-environ-economic efficiency to produce fresh water to meet various scales of demand.     

新型太阳能海水淡化技术研究进展

总结了微纳尺度下毛细驱动的局域热法太阳能海水淡化的相关机制,包括毛细驱动水分传输、太阳能热量传递机理。叙述了界面太阳能局域热法光蒸汽系统最近发展,并归纳了在1个太阳辐照下突破单级产水量理论极限的新型研究思路,指出了太阳能局域热法海水淡化的当前挑战,包含盐分结晶和蒸汽冷凝效率低等问题。认为界面太阳能局域热法海水淡化技术在效率和成本上都具有极大的优势,系统材料制备简单、结构紧凑、系统创新明显,特别适用于偏远山区和海岛地区电力缺乏的家庭生活淡水制备。随着研究者更多地转向保证蒸汽高效凝结和收集、水蒸汽潜热回收利用,预计这种新型海水淡化技术的未来应用范围将不断扩大。     

海水淡化的现状与未来

本文介绍了近来主要海水淡化方法－ＳＷＲＯ、ＭＳＦ、ＭＥＤ的某些新进展。海水淡化市场的激烈竞争和海水淡化技术进步,尤其是ＳＷＲＯ的进展,使淡化的能耗下降了近一半,产水的出厂价也几乎下降了一半。     

Computer code for optimizing MSF desalination plant

Egypt faces the prospect of population growth pressing on available agricultural land resources. A very large areas of coastal desert could be helpful in population density redistribution and of great economical interest, with the installation of a suitable water supply.Of the many desalination processes, the Multi-Stage Flash (MSF) desalination process is still the most developed and reliable technology for large scale conversion of sea water to fresh water.In this paper, a computer code was developed for optimizing a large scale MSF plant. This code can calculate the optimum design for the plant, and the minimum cost of product fresh water, as a function of both design and operating variables.Sample results obtained using this code for the Egyptian conditions are presented. The effect of energy and material costs, the chemical treatment type, and the feed water salinity on the optimum performance ratio and the minimum fresh water cost are drawn.     

MSF Desalination plants. Availability,reliability and safety analysis

While good MSF desalination plant performance exerts a positive influence on plant economics, as part of water supply systems in isolated regions, the availability of the desalination system becomes a major design criteria. Reliability problems have historically been a major cause of poor performance for desalination plants. The emphasis of this paper is on the importance of availability modeling methodology to MSF desalination plant reliability problems by providing a context in which the effect of unit unavailability can be quantified.An assessment is made of failures and outages which impact the availability of MSF desalination plants. Limited fault tree logic for system failures is developed and reliability data from the literature is incorporated, where possible. The impact of other water supply system failures on the reliability requirements of the desalination plant is quantified as are the effects of increased average water system demands.The single largest influence on the effective capacity of a water supply system based on MSF desalination of sea water is found to be the availability and maintainability of the desalination plant. Forced outages as a result of equipment failure are significant, but other dominant contributions to unit unavailability include externally caused problems, such as silting. The design configuration of the desalination plant is also found to have an impact on the acceptability of water supply system performance.     

Parametric analysis to improve the performance of a solar desalination unit with humidification and dehumidification

A solar desalination unit with humidification and dehumidification, characterized by reusing some of somewhat concentrated saline water after evaporation, recovering condensation heat, and forced air flow, was expected to produce more fresh water. A mathematical model of the unit is presented. The model was experimentally validated for numerical simulation. Parametric analysis was conducted in order to optimize the unit performance. The effect of some of the operating conditions such as flow rates, temperatures of feed water, air and cooling water, etc., was studied in detail. The daily solar productivity corresponding to unit square meter of collector area is about 6 kg/m²/d with 20 MJ solar energy input a day under given conditions. The unit has proven to be an efficient device to utilize solar energy for obtaining fresh water from saline water.     

热膜耦合海水淡化系统的优化设计

采用混合节点和分配节点的概念,建立了多级闪蒸(MSF)和反渗透(RO)海水淡化集成系统的超结构模型,以年度总费用最小为目标,引入产水比的概念,并将该参数作为集成系统的一个优化变量,采用改进的遗传算法进行求解,获得了集成系统的最优结构及相应的操作条件。实例结果表明:集成海水淡化系统的淡水成本比独立运行的RO和MSF低,产水比为0.45时集成系统的费用最小,流程结构为MSF-RO。     

Theoretical study on multi-effect solar distillation system driven by tidal energy

Based on an analysis of the characteristics of solar and tidal energy, an innovative, multi-effect solar distillation unit for seawater desalination utilizing solar and tidal energy has been developed. The uniqueness of the system is that without being transferred to electricity, tidal energy is utilized to supply power for water supply and drainage, and vacuum extraction instead of pumps powered by electricity. So the cost can be greatly reduced. The system is based on multi-effect evaporation-condensation processes and operates under vacuum condition, so low grade solar heat can be used with a high thermal efficiency. Hydrodynamic and thermal analysis is carried out for the water supply and drainage system driven by tidal energy. The operating mechanism of the vacuum extraction system driven by tidal energy is presented. A parametric study of the behavior of the solar desalination unit has been performed.     

Development of a Membrane Distillation module for solar energy seawater desalination

Membrane Distillation (MD) processes are gaining growing interest among novel desalination technologies, in particular for small scale applications also coupled with non-conventional energy sources. In the present work an original laboratory scale planar geometry Membrane Distillation unit was designed, built and tested for future coupling with solar energy. Though conceptually simple, the original geometry was developed in order to allow for multi-stage arrangement, compactness, internal heat recovery and possible integration with a polymeric heat exchanger for final brine heating by means of solar energy or waste heat. The laboratory scale unit was tested in order to investigate the effect of operating conditions, i.e. hot feed temperature and flow rate, on the process performance, with particular attention paid to parameters relevant to the design of the system coupled with solar energy. Also the effect of different airgap configurations was investigated, namely (i) free airgap, (ii) permeate-gap and (iii) partial vacuum airgap arrangements.     

Conceptual design of a novel hybrid fuel cell/desalination system

A novel concept for integrating fuel cells with desalination systems is proposed and investigated in this work. Two unique case studies are discussed — the first involving a hybrid system with a reverse osmosis (RO) unit and the second — integrating with a thermal desalination process such as multi-stage flash (MSF). The underlying motivation for this system integration is that the exhaust gas from a hybrid power plant (fuel cell/turbine system) contains considerable amount of thermal energy, which may be utilized for desalination units. This exhaust heat can be suitably used for preheating the feed in desalination processes such as reverse osmosis which not only increases the potable water production, but also decreases the relative energy consumption by approximately 8% when there is an increase of just 8°C rise in temperature. Additionally, an attractive hybrid system application which combines power generation at 70%+ system efficiency with efficient waste heat utilization is thermal desalination. In this work, it is shown that the system efficiency can be raised appreciably when a high-temperature fuel cell co-generates DC power in-situ with waste heat suitable for MSF. Results indicate that such hybrid system could show a 5.6% increase in global efficiency. Such combined hybrid systems have overall system efficiencies (second-law base) exceeding those of either fuel-cell power plants or traditional desalination plants.     

A hybrid solar desalination process of the multi-effect humidification dehumidification and basin-type unit

This paper presents a hybrid solar desalination process of the multi-effect humidification dehumidification and the basin-type unit. The sketch of the hybrid solar desalination process is given. The solar vacuated tube collector is employed in the desalination system, multi-effect humidification dehumidification desalination (HDD) process is plotted according to pinch technology, and then the water rejected from multi-effect HDD process is reused to desalinate in a basin-type unit further. The gain output ratio (GOR) of this system will rise by 2–3 at least through reusing the rejected water. The research proves that the multi-effect HDD has much room to be improved. A hybrid solar desalination process of the multi-effect humidification dehumidification and the basin-type unit should be noticed.