Performance study of RO systems in Saudi Arabia

Desalination of water is one of the most important engineering tasks facing Saudi Arabia today. Lacking unlimited supplies of potable Water, the Kingdom must depend upon the desalination process of brackish well water or sea water to satisfy the ever increasing demands. These demands are expected to reach the 430 MGD figure in 1980 and 700 MGD in 1985.

Abstract

until quite recently, the reverse osmosis played a rather modest role in the country's desalination program and was almost exclusively limited to brackish water applications and plants not exceeding a capacity of 1 MGD. Within the last year, significant changes took place in favor of these processes. The estimated total output of RO units to be commissioned this year will be about 70 MGD. This figure includes the 3.2 MGD plant for desalting the sea water in Jeddah and the 55 MGD plant in Riyahd from brackish well water.

This paper deals primarily with the performance of RO systems, their cost of operation/maintenance and the factors affecting the cost. These factors may be divided into three groups as related to feed water, system design and system operation. The quality of feed water and good pretreatment plays an extremely important role in performance of a RO system. This study pays special attention to these parameters in expectation that more cost effectiveness will evolve in the future either through a better understanding of the processes or an improved process design match to materials employed.     

Desalination costs in Australia: A survey of operating plants

A survey of desalination costs in Australia was conducted using data obtained from plant operators, and is reported in second quarter 1986 A$. Unit water costs range from $0.76/kL (for a precursor to deionisation for boiler feed) to $14/kL (for emergency supplies for an island resort).

However, an average figure for desalination of brackish water is $3–$4/kL, and for seawater, $5–10/kL in medium-sized installations.

Capital costs for brackish water plants have been correlated with plant design capacity ranging from 10 to 3400 kL/d.

There is insufficient information to allow a proper comparison between reverse osmosis and electrodialysis for brackish water desalination.     

Hybrid systems in seawater desalination—practical design aspects, present status and development perspectives

Ever since seawater desalination has been applied on an industrial scale, and particular in the countries of the Arabian Gulf, the application of desalination processes in dual-purpose facilities—water and power—as a hybrid configuration has been discussed in many feasibility investigations and also planning concepts. It is above all the combination of reverse osmosis with thermal processes that has found increasing interest with the aim of ensuring, as economically as possible, uniform water supplies under the specific, greatly varying load conditions in the Gulf countries. Such design concepts for hybrid configurations encompass straightforward structures with a low degree of coupling between membrane and thermal desalination processes, but range up to very complex configurations with strong interconnections on both the water side and thermally, as well as with several desalination processes connected in series or in parallel. Classical hybrid concepts in which the permeate from an RO desalination component is mixed with distillate from thermal desalination have already been implemented in Saudi Arabian dual-purpose plants, like Jeddah and Yanbu-Medina. Although hybrid systems of greater complexity have been addressed in many design studies and publications, up to now none has been brought to fruition. Coming into consideration asthe design basis for determining the capacity shares of the various desalination processes operated in a hybrid configuration are: arrangement of thermal cycle of the power plant component; water/power ratio of the dual-purpose seawater desalination and power plant; provision of undiminished water production of the desalination plant as electricity generation varies; provision of a specified drinking water quality with regard to composition and salt content; combination of all these aspects. Also gaining in importance are concerns of environmental pollution and sustainable development when selecting seawater desalination and power plant configurations, as well as their optimization when considering desalination and electricity generation as a whole. In the practical design of hybrid membrane and thermal systems, aspects come to light, though, that restrict linking of the two systems and joint utilization of facilities, as conceived in studies and conceptual design investigations. This applies both for common utilization of intakes and the use of heated up cooling water from thermal processes as a feed stream for the RO part of the desalination process. Additionally, requirements of drinking water composition, particularly chloride content, TDS and compliance with a specific residual content of boron, influence specifically the design of the membrane process part and its share in the total desalination capacity. Such practical aspects have greatly influenced the design and configuration of the Fujairah hybrid plant for which, from a total desalination capacity of 100 MIGD (454,600 m³/d), the share of 37.5 MIGD (170,500 m³/d) makes its seawater RO plant the biggest currently being constructed anywhere in the world. From the findings of the engineering of this plant and the idea that, by increasing interconnection between the two processes on the water side, it is possible to advance a hybrid configuration of this type with regard to cost optimization in the membrane installation, but also by joint utilization of the intake equipment, perspectives result for applied research efforts over the near and long terms, for example: long-term behavior of membranes at elevated temperatures; tendency for biofouling in membrane process with common utilization of cooling water and brine; influences of such interconnections on the overall availability of the facility. But also for the operation and maintenance organization of such large facilities, consequences can be foreseen for the future development of hybrid plants, particularly for operation management and organisation of the interplay of the different power plant and desalination systems, monitoring of SWRO membrane replacement and cleaning, as well as controlling water quality.     

电渗析苦咸水淡化技术研究进展

电渗析苦咸水淡化技术具有脱盐效果好、成本较低、绿色环保等优点,但存在制膜工艺繁琐、传质模型不够精确、能效有待提升等问题。本文首先分析了苦咸水电渗析用离子交换膜的制备及改性方法,对膜材料存在的问题进行了探讨。综述对比了苦咸水电渗析在简化模型、理论模型、半经验模型方面的原理及最新进展,系统总结了常规苦咸水电渗析过程的运行方式和工艺优化策略,并进一步介绍了以新型电去离子、冲击电渗析、可再生能源驱动电渗析为代表的新型电渗析过程在苦咸水淡化方面的原理及应用。在此基础上,提出了今后的研究方向集中于降低制膜成本、优化传质模型、探究集成膜法淡化工艺以及新型电渗析过程等方面。     

Sustainable fuel cell integrated membrane desalination systems

According to the United Nations, between two and seven billion people will face water shortages by the year 2050. Further, it is estimated that the amount of water available per person will shrink by a third during the next two decades. Inadequate supply of good-quality water coupled with higher water demand due to rapid population growth and industrialisation in developing countries are among the major reasons for the worsening water situation. Current shortages of potable water around the world and looming water scarcity especially in the developing countries is the driving force behind the implementation of membrane technologies for seawater and brackish water desalination. Typical energy consumption in seawater reverse osmosis (RO) plants operating at 40–45% product water recovery and with energy recovery from the high pressure reject stream currently is about 3–4 kWh/m³. The near-term goal of the industry is to reduce energy consumption to less than 2 kWh/m³ by using a combination of energy efficient RO pumps, more efficient energy recovery devices, high performance low energy RO membranes, hybrid membrane systems, advanced pretreatment technologies and alternate energy integrated membrane systems. The beneficial aspects of using alternate energy systems such as on-site distributed fuel cell systems integrated with membrane desalination units in remote locations are discussed.     

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.     

Reverse osmosis desalination plants — marine environmentalist regulator point of view

The environmental characteristics of the brine and its impacts on the marine environment were always the “backyard” and the less concern while planning and operating RO desalination plants. The lack of drinking water in Israel made desalination a national goal. The first huge RO plant was initially operated in Israel on 2005 — 100 Mm³/y and by the end of 2010 305 Mm³/y potable water expected to be produced. Construction and installation of desalination plants requires applying suitable environmental solutions for protecting and preserving the marine and coastal environment from ruin or deterioration.

The Israeli environmental legislation is described including the marine environmental policy and regulations as well as the acquired operational experience during the last two years. Results from the first year of operation and monitoring are shown along with the new appearance of the red phenomenon discharge of VID desalination plant in Ashkelon.

The environmental policy based on the precautionary principle is performed and includes environmental requirements and guidelines for pretreatment, discharge composition, planning marine outfall, background and compliance marine monitoring program and discharge quality standards.     

The role of desalination in bridging the water gap in Jordan

The water resources of Jordan have always been scarce. The demand for water in the country exceeds the available resources and the gap between the water supply and demand is continuously increasing. Furthermore, the quality of water resources has dramatically deteriorated in recent years, which prevented the utilization of some resources. To secure the economic sustainability of the country, it is important at this stage to consider non-conventional water resources, such as sea and brackish water desalination. This study examines the water resources of Jordan, projected water demand, and the gap between the demand and supply based on two scenarios. The possibility of closing this gap by water desalination was investigated. Both sea and brackish water desalination were considered. The analysis revealed that seawater desalination process is economically infeasible for domestic water uses at this stage. This is attributed to that Jordan is not an oil producing country and the location of sea shoreline in Aqaba is on the Red Sea, away from the consumption centers. However, seawater desalination may be a viable option for tourist and industrial enterprises that will be established as a result of the new Law of Aqaba Free Zone. The most convenient and realistic option for Jordan in the short term, is the desalination of brackish water by reverse osmosis (RO). The brackish water with total dissolved solids between 2000-10000 mg/l is available from many aquifers and springs of the country. The study concluded that Jordan is facing a severe water crisis. Until recently, the water planners have not given the water desalination the required attention as a potential source of water supply. Taking into account the progress that is being achieved in the field of desalination technology, Jordan has to consider the desalination option more seriously and to start building a national capacity in the field of water desalination. It was emphasized that desalination is not a substitute to traditional water resources, it is rather a supplementary source that can contribute in bridging the water gap of the country.     

考虑不同水质输入的水电联产优化设计

结合已有的反渗透/多级闪蒸混产系统和发电-多级闪蒸联产系统,设计了一个新的包括热力发电系统、反渗透海水淡化系统和多级闪蒸海水淡化系统的水电联产超结构,对以不同盐度苦咸水、海水为原水的水电联产系统进行了优化设计,通过求解系统以年费用最小为目标函数的非线性数学模型,得到不同盐度下联产系统优化的生产结构. 结果表明,在低盐度(≤25000 mg/L)下采用冷凝式发电和一级反渗透产水,高盐度下采用抽汽冷凝式发电和热膜混合产水,可降低联产系统的年费用,获得较低成本的淡化水. 在本工作所定的生产规模下,优化联产方案的年费用可降低23%~36%.     

A small solar desalination plant for the production of drinking water in remote arid areas of southern Algeria

The common methods of desalination salt water for production of fresh water by distillation, reverse osmosis and electrodialysis are intensive energy techniques. However, in remote arid areas, the desalination needs not exceed a few cubic meters per day. This decentralised demand favours local water production by developing other desalination processes, especially those using renewable or recovered energy (solar, geothermal, etc.). Solar desalination process is one of these methods used to resolve the scarcity of fresh water. Several reviews have been published by different authors. Small production systems as solar stills can be used if fresh water demand is low and the land is available at low cost. To supply the population of remote arid lands of South Algeria with drinkable water, solar distillation of brackish waters is recommended. It satisfies some of theses demands. Solar stills are used to produce fresh water from brackish water by directly utilising sunshine. These stills represent the best technical solution to supply remote villages or settlements in South Algeria with fresh water without depending on high-tech and skills. The production capacity indicates a possible daily production of far more than 15 l/m²d. Therefore, the still has a place in the upper range of known comparable products with regards to production output. This depends on the material used and the price of the solar stills and their accessories. The best working temperature solves most problems. Small, modular high-performance stills with features like the possibility of decentralised use, less maintenance and robust construction can help to reduce fresh water scarcity. The recent development of stills based on new concepts and heat recovery has been successful. The technical optimization is still in process today, it aims to improvement of the efficiency of these distillers. In our research work, a plant for brackish water distillation by directly sunshine and heat recovery was constructed and investigated experimentally and theoretically in South Algeria. This study aims the improvement of the performance of this solar distillation plant, conducted under the actual insulation, for brackish underground geothermal water desalination.     

Electrodialysis desalination designed for off-grid wind energy

An electrodialysis desalination plant has been set up and tested to treat brackish water while driven from an off grid wind energy system. The tests were carried out in the framework of a wider scope project, located on Gran Canaria Island (Spain). The main goal of this project was to test and identify the most suitable desalination systems for connection to the above-mentioned medium-scale off grid wind farm. After having previously analysed the behaviour of the system on-grid, the following stage was to develop an operational envelope for the electrodialysis reversal (EDR) unit while operating off grid, i.e., only coupled to the wind farm. The unit included power converters for the membrane stacks (DC-drivers) and variable frequency drivers (VFD) for the feed pumps. The tests were carried out to establish the power intervals for the EDR unit depending on the product flow rate specified as well as water quality. Product flow rate between 3 and 8.5 m³/h, power requirements between 4 and 19 kW, while product water conductivity ranged between 200 and 500 μS/cm were recorded. The desalination unit showed good flexibility, adapting smoothly to variations in wind power, even when sudden drops or rises occurred. The control system, slightly modified from a standard design, can cope with such sudden variations. Good agreement between performance predicted with software and the actual operating performance was observed. The presence of harmonics in the electric system due to DC drivers and VFD became harmful for the control and electric system, and care must be taken through appropriate mitigating measures.     

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.     

Membrane processes for water supply and reuse - a question of energy consumption and cost

This paper is limited primarily to reverse osmosis which is the dominating membrane process in commercial plants. Desalination of brackish water and seawater with reverse osmosis, with special emphasis on costs and energy consumption, is the primary subject discussed in the paper. Some aspects of and development trends in industrial and domestic applications of membrane processes are also taken up, particularly with regard to by-product recovery and water reuse in connection with advanced wastewater treatment.The first RO plant to be brought into operation in Riyadh, Saudi Arabia, is located at Salbukh. The investment and total operation costs for this plant have been calculated in the paper. The water cost is at least twice as high as in a continental U.S. location. The main reason for this is the very high cost of civil and local works in Saudi Arabia. A similar calculation has been made for RO seawater desalination.Increased energy costs during the last decade have directed research and development work for all desalination methods towards reducing energy consumption. It is shown in the paper that energy recovery in connection with RO seawater desalination is particularly feasible. Different methods for energy recovery have been investigated and reported, the preferred methods depending on the size of the RO plant. A large underground RO plant for energy recovery, based on utilization of the static pressure instead of high pressure pumps, has also been studied.Another possible energy-saving, but also water quality improving method has been proposed, viz . a combined MSF-RO dual purpose plant. Excess power for reverse osmosis seems to be more and more available in Saudi Arabia due to the high power/water ratio in MSF dual purpose plants compared to the real demand for power and water.     

RO membrane autopsy of Zarzis brackish water desalination plant

Tunisia, located in a semi-arid zone, has limited water resources. The shortage of good water quality in particular at the south regions required a brackish water desalination to supply these regions with potable water. Zarzis desalination plant, working since 1999, has revealed difficulties related to the loss of membrane performances. In the aim to determine the reason of membrane fouling, foulant layer were analysed. The membrane autopsy has achieved by different methods, such as TOC (total organic carbon) measurement, SEM (scanning electron microscopy), AFM (atomic force microscopy), FTIR (fourier transform infrared spectroscopy) analysis, diffraction by X-ray. Results show that the foulant layer composed mostly of SiO₂, clay, organic matter (polysaccharide, protein), CaSiO₃, Fe₃O₄, AlPO₄, and CaSO₄. The characteristics bonds obtained by IR indicate the presence of polysaccharides and proteins that constitute a source for further microbiological growth; this is the problem of biofouling. The metallic elements results of corroded stainless steel and internal coating of cartridges filter that are damaged by the silica particle rejected by sand filters. The scale of CaSO₄ and CaSiO₃ deposition is owing to the bad antiscaling efficiency. The results are presented and discussed in the light of new trends in material.     

Operating experiences of a 15,000 cubic meter per day municipal desalting plant at Corfu, Greece

The initial eighteen month period of operation of the 15,000 m³/day municipal plant on the Island of Corfu, Greece, is described.

The 15,000 m³/day desalting plant employing the electrodialysis reversal process (EDR) produces potable water (500 ppm) from a blend of brackish sources with salinities up to 2000 ppm TDS. The paper describes the plant and integration of the plant into the municipal system. The unique system employed to segregate the treatment of the different brackish waters employing only the highest salinity water for blowdown water is also described.

The plant was started up in the fall of 1977 and provided water to the municipal system during the 1978 season.

The paper presents operating cost data for this period and compares these costs with projected costs which form part of the contractual agreement, with the Municipality.     

Myth and reality of the hybrid desalination process

The paper discusses some misconceptions that have contributed to the continued use of thermal desalination processes and promotion of the hybrid desalination process for new plants being built or considered at Middle East locations. The misconceptions are examined both on the basis of fundamental thermodynamic principles and in terms of practical engineering parameters. The analysis shows that there is no economic or performance advantage in the installation of greenfield hybrid power/thermal desalination/ seawater reverse osmosis (SWRO) plants in preference to power/SWRO plants, because the latter would produce water more cheaply under all conditions and at all fuel costs, and would provide more operational flexibility than the former. The paper identifies situations where the hybrid desalination process can be fully justified: in existing power/desalination plants, where aging boilers and multistage flash (MSF) units need to be repaired or replaced, through retrofitting and repowering. In such situations, abandonment of the MSF process would result in a reduction in the power output of the plant. The paper refers to previous work which showed that the repowering of a typical existing power/desalination station with refurbishment/replacement of the MSF units, together with the addition of SWRO units, would result in a several-fold increase in the water and power output and a dramatic improvement in the fuel efficiency, without any additions to the existing seawater intake system. The paper emphasizes the importance of test stations/demonstration plants at existing power/desalination stations in the Middle East in order to obtain data and make improvements in the technology of higher temperature SWRO, with the feed obtained from the cooling water returning from the power plant condenser and the thermal desalination plant. The paper shows that the potential benefits would easily justify the investment in research and development required to validate this concept.     

Entsalzung von Umkehrosmosekonzentraten mittels elektrisch getriebenen Membranverfahren zur Maximierung der Permeatausbeute einer Prozesswasseraufbereitungsanlage

Worldwide present water stress situations lead to the necessity to use alternative water sources like brackish water or wastewater. To enable this, new desalination technologies like electrically driven membrane processes have to be implemented. These technologies were used to desalinate the reverse osmosis concentrate of a process water treatment plant up to a certain point, at which the resulting diluate could be used as feed water for the reverse osmosis. As a result, the concentrate volume to be discharged was halved and the permeate yield of the overall plant was increased. A focus was set on the required energy consumption for the additional treatment step.     

Integrating hybrid systems with existing thermal desalinationplants

In Gulf countries, most power plants are co-generation power desalting plants (CPDP) that generate electric energy and also produce fresh water through the desalination of seawater. This paper provides detailed technical and economical analyses to evaluate a new generation of dual purpose technology that includes the integration of reverse osmosis (RO) processes with existing thermal desalination processes and power generation (triple hybrid system) at Layyah plant, Sharjah, UAE. Hybridization of sweater reverse osmosis (SWRO) and the multi-stage flash (MSF) technology was considered to improve the performance of latter and reduce the cost of the produced water. Moreover, “idle” power in winter (seasonal surplus of unused power) was mainly utilized by RO to further reduce the cost of the hybrid system for six months of the year. Spinning reserve was also used to further reduce the cost of the proposed hybrid system. Integration ofthe three processes of MSF, MED, and RO desalination technologies could be made at different levels through which the resulting of water cost will depend on the selected configuration and the cost of materials of construction, equipment, membrane, energy, etc. Thus, the capital and annual operating costs were calculated for all potential alternatives for various plant capacities. It was found that for all plant capacities, integrated hybrid systems resulted in most cost effective solution. For example, at a capacity of 50 MIGD, the present worth of the cost was calculated to be 588.7, 443.2, and 380 million US$ for MSF, MED, and hybrid RO systems, respectively.     

LTE desalination utilizing waste heat from a nuclear research reactor

Nuclear reactors produce significant amounts of low-quality waste heat which can be utilized for producing high-quality water from seawater by coupling a low-temperature evaporation (LTE) desalination unit. Salient features of the desalination plant, the nuclear research reactor and the waste heat utilization from the reactor are discussed. The scheme of integrating desalination plants with the nuclear research reactors is also presented. This LTE desalination plant utilizing waste heat from a nuclear research reactor will be the first of its kind while demonstrating the safety and economics of nuclear desalination technology as a viable alternative to producing demineralised water from seawater.